WorldWideScience

Sample records for nanocrystalline grain size

  1. Simulation of grain size effects in nanocrystalline shape memory alloys

    Science.gov (United States)

    Ahluwalia, Rajeev; Quek, Siu Sin; Wu, David T.

    2015-06-01

    Recently, it has been demonstrated that martensitic transformation in nanocrystalline shape memory alloys can be suppressed for small grain sizes. Motivated by these results, we study the grain size dependence of martensitic transformations and stress-strain response of nanocrystalline shape memory alloys within the framework of the Ginzburg-Landau (GL) theory. A GL model for a square to rectangle transformation in polycrystals is extended to account for grain boundary effects. We propose that an inhibition of the transformation in grain boundary regions can occur, if the grain boundary energy of the martensite is higher than that of the austenite phase. We show that this inhibition of transformation in grain boundary regions has a strong influence on domain patterns inside grains. Although the transformation is inhibited only at the grain boundaries, it leads to a suppression of the transformation even inside the grains as grain size is decreased. In fact, below a critical grain size, the transformation can be completely suppressed. We explain these results in terms of the extra strain gradient cost associated with grain boundaries, when the transformation is inhibited at grain boundaries. On the other hand, no significant size effects are observed when transformation is not inhibited at grain boundaries. We also study the grain size dependence of the stress strain curve. It is found that when the transformation is inhibited at grain boundaries, a significant reduction in the hysteresis associated with stress-strain curves during the loading-unloading cycles is observed. The hysteresis for this situation reduces even further as the grain size is reduced, which is consistent with recent experiments. The simulations also demonstrate that the mechanical behavior is influenced by inter-granular interactions and the local microstructural neighbourhood of a grain has a stronger influence than the orientation of the grain itself.

  2. Relative importance of grain boundaries and size effects in thermal conductivity of nanocrystalline materials.

    Science.gov (United States)

    Dong, Huicong; Wen, Bin; Melnik, Roderick

    2014-11-13

    A theoretical model for describing effective thermal conductivity (ETC) of nanocrystalline materials has been proposed, so that the ETC can be easily obtained from its grain size, single crystal thermal conductivity, single crystal phonon mean free path (PMFP), and the Kaptiza thermal resistance. In addition, the relative importance between grain boundaries (GBs) and size effects on the ETC of nanocrystalline diamond at 300 K has been studied. It has been demonstrated that with increasing grain size, both GBs and size effects become weaker, while size effects become stronger on thermal conductivity than GBs effects.

  3. Specimen- and grain-size dependence of compression deformation behavior in nanocrystalline copper

    OpenAIRE

    Okamoto, Norihiko L.; Kashioka, Daisuke; Hirato, Tetsuji; Inui, Haruyuki

    2014-01-01

    The compression deformation behavior of electrodeposited nanocrystalline copper pillars with average grain sizes (d) of 360, 100, and 34 nm has been investigated as a function of specimen size (D). The yield stress for nanocrystalline pillars with d = 360 and 100 nm does not depend on specimen size, exhibiting essentially the bulk yield stress until the specimen size is reduced down to the critical values ((D/d)∗ = 35 and 85), below which the yield stress decreases with the decrease in specim...

  4. Grain size stabilization of nanocrystalline copper at high temperatures by alloying with tantalum

    Energy Technology Data Exchange (ETDEWEB)

    Darling, K.A., E-mail: kristopher.darling.civ@mail.mil [U.S. Army Research Laboratory, Weapons and Materials Research Directorate, Aberdeen Proving Ground, MD 21005-5069 (United States); Roberts, A.J. [ORISE Program, U.S. Army Research Laboratory, Aberdeen Proving Ground, MD 21005-5069 (United States); Mishin, Y. [George Mason University, Dept of Physics and Astronomy, Fairfax, VA 22030 (United States); Mathaudhu, S.N. [U.S. Army Research Laboratory, Army Research Office, Research Triangle Park, NC 27709-2211 (United States); Kecskes, L.J. [U.S. Army Research Laboratory, Weapons and Materials Research Directorate, Aberdeen Proving Ground, MD 21005-5069 (United States)

    2013-10-05

    Highlights: •A mean grain size of 167 nm is retained after annealing at 97% of the melting point. •Hardness surpasses conventional pure nanocrystalline Cu by 2.5 GPa. •Extreme stability is attributed to both thermodynamic and kinetic stabilization. -- Abstract: Nanocrystalline Cu–Ta alloys belong to an emerging class of immiscible materials with potential for high-temperature applications. Differential scanning calorimetry (DSC), Vickers microhardness, transmission and scanning electron microscopy (TEM/SEM), and atomistic simulations have been applied to study the structural evolution in high-energy cryogenically alloyed nanocrystalline Cu–10 at.%Ta. The thermally induced coarsening of the as-milled microstructure was investigated and it was found that the onset of grain growth occurs at temperatures higher than that for pure nanocrystalline Cu. The total heat release associated with grain growth was 0.553 kJ/mol. Interestingly, nanocrystalline Cu–10 at.%Ta maintains a mean grain size (GS) of 167 nm after annealing at 97% of its melting point. The increased microstructural stability is attributed to a combination of thermodynamic and kinetic stabilization effects which, in turn, appear to be controlled by segregation and diffusion of Ta solute atoms along grain boundaries (GBs). The as-milled nanocrystalline Cu–10 at.%Ta exhibits Vickers microhardness values near 5 GPa surpassing the microhardness of conventional pure nanocrystalline Cu by ∼2.5 GPa.

  5. Effect of grain size on the elastic properties of nanocrystalline {alpha}-iron

    Energy Technology Data Exchange (ETDEWEB)

    Latapie, A.; Farkas, D

    2003-03-03

    The effect of grain size on the elastic properties of nanocrystalline {alpha}-iron is reported using atomistic simulations. A softening of the elastic properties is observed for grain sizes ranging from 12 nm down to 6 nm. The decrease in the Young's and shear moduli with decreasing grain size is in agreement with experimental data and matches an analytical model based on the rule of mixtures for composite materials.

  6. NANOCRYSTALLINE GROWTH AND GRAIN-SIZE EFFECTS IN AU-CU ELECTRODEPOSITS

    Energy Technology Data Exchange (ETDEWEB)

    Jankowski, A F; Saw, C K; Harper, J F; Vallier, R F; Ferreira, J L; Hayes, J P

    2005-02-25

    The processing-structure-property relationship is investigated for electrodeposited foils of the gold-copper alloy system. A model is presented that relates the deposition process parameters to the nanocrystalline grain size. An activation energy of 1.52 eV {center_dot} atom{sup -1} for growth is determined for a long pulse (>10 msec) mode, and is 0.16 eV {center_dot} atom{sup -1} for short pulses (<5 msec). The affect of nanocrystalline grain size on the mechanical properties is assessed using indentation measurements. A Hall-Petch type variation of the Vickers microhardness with nanocrystalline grain size (>6 nm) is observed for Au-Cu samples with 1-12 wt.% Cu as tested in cross-section. The hardness increases three-fold from a rule-of-mixtures value <1 GPa to a maximum of 2.9 GPa.

  7. Modeling the dependence of strength on grain sizes in nanocrystalline materials.

    Science.gov (United States)

    He, Wei; Bhole, Sanjeev D; Chen, DaoLun

    2008-01-01

    A model was developed to describe the grain size dependence of hardness (or strength) in nanocrystalline materials by combining the Hall-Petch relationship for larger grains with a coherent polycrystal model for nanoscale grains and introducing a log-normal distribution of grain sizes. The transition from the Hall-Petch relationship to the coherent polycrystal mechanism was shown to be a gradual process. The hardness in the nanoscale regime was observed to increase with decreasing grain boundary affected zone (or effective grain boundary thickness, Δ) in the form of Δ(-1/2). The critical grain size increased linearly with increasing Δ. The variation of the calculated hardness value with the grain size was observed to be in agreement with the experimental data reported in the literature.

  8. High-temperature grain size stabilization of nanocrystalline Fe–Cr alloys with Hf additions

    Energy Technology Data Exchange (ETDEWEB)

    Li, Lulu, E-mail: lli18@ncsu.edu; Saber, Mostafa; Xu, Weizong; Zhu, Yuntian; Koch, Carl C.; Scattergood, Ronald O.

    2014-09-08

    The influence of 1–4 at% Hf additions on the thermal stability of mechanically alloyed nanocrystalline Fe–14Cr alloys was studied in this work. XRD-calculated grain size and microhardness results were reported versus isochronal annealing treatments up to 1100 °C. Microstructural evolution was investigated using channeling contrast FIB imaging and TEM. Grain size of samples with 4 at% Hf was found to be maintained in the nanoscale range at temperatures up to 1000 °C. Zener pinning was considered as a major source of high temperature grain size stabilization. By comparing the Orowan strengthening contribution to the total hardness, the deviation of grain size predictions from the actual grain size in Fe–14Cr–4Hf suggests the presence of thermodynamic stabilization by the solute segregation to grain boundaries (GBs). A predictive thermodynamic model indicates that the thermodynamic stabilization can be expected.

  9. Grain-size effect on the electrical properties of nanocrystalline indium tin oxide thin films

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Jong Hoon [Korea Research Institute of Standards and Science, 267 Gajeong-Ro, Yuseong-Gu, Daejeon 305-340 (Korea, Republic of); Kim, Young Heon, E-mail: young.h.kim@kriss.re.kr [Korea Research Institute of Standards and Science, 267 Gajeong-Ro, Yuseong-Gu, Daejeon 305-340 (Korea, Republic of); University of Science & Technology, 217 Gajeong-Ro, Yuseong-Gu, Daejeon 305-350 (Korea, Republic of); Ahn, Sang Jung [Korea Research Institute of Standards and Science, 267 Gajeong-Ro, Yuseong-Gu, Daejeon 305-340 (Korea, Republic of); University of Science & Technology, 217 Gajeong-Ro, Yuseong-Gu, Daejeon 305-350 (Korea, Republic of); Ha, Tae Hwan [University of Science & Technology, 217 Gajeong-Ro, Yuseong-Gu, Daejeon 305-350 (Korea, Republic of); Future Biotechnology Research Division, Korea Research Institute of Bioscience and Biotechnology (KRIBB), 125 Gwahak-ro, Yuseong-Gu, Daejeon 305-806 (Korea, Republic of); Kim, Hong Seung [Department of Nano Semiconductor Engineering, Korea Maritime and Ocean University, 727 Taejong-Ro, Busan 606-791 (Korea, Republic of)

    2015-09-15

    Highlights: • Nanometer-sized small grains were observed in the ITO thin films. • The grain size increased as the post-thermal annealing temperature increased. • The mobility of ITO thin films increased with increasing grain size. • The ITO film annealed at 300 °C was an amorphous phase, while the others were polycrystalline structure. - Abstract: In this paper, we demonstrate the electrical properties, depending on grain size, of nanocrystalline indium tin oxide (ITO) thin films prepared with a solution process. The size distributions of nanometer-sized ITO film grains increased as the post-annealing temperature increased after deposition; the grain sizes were comparable with the calculated electron mean free path. The mobility of ITO thin films increased with increasing grain size; this phenomenon was explained by adopting the charge-trapping model for grain boundary scattering. These findings suggest that it is possible to improve mobility by reducing the number of trapping sites at the grain boundary.

  10. EXAFS study of structural characteristics of nanocrystalline selenium with different grain sizes

    Institute of Scientific and Technical Information of China (English)

    1999-01-01

    Extended x-ray-absorption fine-structure measurements(EXAFS) were performed on nanocrystalline (nc) elemental Se samples with grain sizes ranging from 13 to 60 nm.Accompanied with the previous study,we concluded that,with the refinement in nc.Se.the intrachain structure (the bond length,the coordination number)is unchanged while the interchain spacing is enlarged.The grain boundary in the nc Se is found to be in a low-energy configuration that is different from the disordered gaslike grain boundary structure.

  11. Effect of texture and grain size on the residual stress of nanocrystalline thin films

    Science.gov (United States)

    Cao, Lei; Sengupta, Arkaprabha; Pantuso, Daniel; Koslowski, Marisol

    2017-10-01

    Residual stresses develop in thin film interconnects mainly as a result of deposition conditions and multiple thermal loading cycles during the manufacturing flow. Understanding the relation between the distribution of residual stress and the interconnect microstructure is of key importance to manage the nucleation and growth of defects that can lead to failure under reliability testing and use conditions. Dislocation dynamics simulations are performed in nanocrystalline copper subjected to cyclic loading to quantify the distribution of residual stresses as a function of grain misorientation and grain size distribution. The outcomes of this work help to evaluate the effect of microstructure in thin films failure by identifying potential voiding sites. Furthermore, the simulations show how dislocation structures are influenced by texture and grain size distribution that affect the residual stress. For example, when dislocation loops reach the opposite grain boundary during loading, these dislocations remain locked during unloading.

  12. Incorporating gold into nanocrystalline silver dressings reduces grain boundary size and maintains suitable antimicrobial properties.

    Science.gov (United States)

    Unrau, Kevin R; Cavanagh, Marion H; Cheng, On Kwan; Wang, Shiman; Burrell, Robert E

    2013-12-01

    Nanocrystalline silver dressings are widely known to be potent antimicrobial and anti-inflammatory agents and have long been used to treat topical wounds. Gold is known to be a strong anti-inflammatory agent and has been used in the treatment of rheumatoid arthritis for >70 years. The purpose of this work was to study the effect of incorporating gold into nanocrystalline silver dressings from antimicrobial and anti-inflammatory perspectives. Gold and silver dressing alloys were created by direct current magnetron sputtering and compared with pure silver nanocrystalline dressings using conventional biological (log reduction and corrected zone of inhibition) and physical (X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, atomic absorption spectroscopy, atomic force microscopy and scanning electron microscopy) characterisation techniques. While the gold/silver dressings were slightly weaker antimicrobials than the pure silver nanocrystalline structures, the addition of gold to the nanostructure reduces the minimum crystallite size from 17 to 4 nm. This difference increases the number of grain boundary atoms from 12% to 40% which could augment the anti-inflammatory properties of the dressings. The formation of gold oxide (Au2O3) was thought to be responsible for the observed decrease in crystallite size.

  13. Effects of grain size distribution on remanence and coercivity of Pr2Fe14B nanocrystalline magnet

    Institute of Scientific and Technical Information of China (English)

    He Shu-Li; Zhang Hong-Wei; Rong Chuan-Bing; Chen Ren-Jie; Shen Bao-Gen

    2005-01-01

    The demagnetization curves of Pr2Fe14B nanocrystalline magnets are calculated using micromagnetic finiteelement method. Samples with three different distributions of grain size are simulated. We find that the remanence enhancement does not depend on grain size distribution but on the mean diameter of grains, and the influence of grain size distribution on coercivity is affected by the strength of intergrain exchange coupling.

  14. Grain size refinement in nanocrystalline Hitperm-type glass-coated microwires

    Energy Technology Data Exchange (ETDEWEB)

    Talaat, A. [Departamento de Física de Materiales, UPV/EHU, 20018 San Sebastián (Spain); Departamento de Física Aplicada, EUPDS, UPV/EHU, 20018 San Sebastián (Spain); Val, J.J. del [Departamento de Física de Materiales, UPV/EHU, 20018 San Sebastián (Spain); Zhukova, V. [Departamento de Física de Materiales, UPV/EHU, 20018 San Sebastián (Spain); Departamento de Física Aplicada, EUPDS, UPV/EHU, 20018 San Sebastián (Spain); Ipatov, M. [Departamento de Física de Materiales, UPV/EHU, 20018 San Sebastián (Spain); Klein, P.; Varga, R. [Institute of Physics, Faculty of Science, University of Pavol Jozef Safarik, Park Angelinum 9, 04154 Kosice (Slovakia); González, J. [Departamento de Física de Materiales, UPV/EHU, 20018 San Sebastián (Spain); Churyukanova, M. [National University of Science and Technology “MISIS”, Moscow 119049 (Russian Federation); Zhukov, A., E-mail: arkadi.joukov@ehu.es [Departamento de Física de Materiales, UPV/EHU, 20018 San Sebastián (Spain); Departamento de Física Aplicada, EUPDS, UPV/EHU, 20018 San Sebastián (Spain); IKERBASQUE, Basque Foundation for Science, 48011 Bilbao (Spain)

    2016-05-15

    We present a new-Fe{sub 38.5}Co{sub 38.5}B{sub 18}Mo{sub 4}Cu{sub 1} Hitperm glass-coated microwires obtained by Taylor-Ulitovsky technique with nanocrystalline structure consisting of about 23 nm of BCC α-FeCo and an amorphous precursors in as-prepared samples. Annealing resulted in a considerable decrease of such nano-grains down to (11 nm). Obtained results are discussed in terms of the stress diffusion of limited crystalline growth and the chemical composition. Rectangular hysteresis loops have been observed on all annealed samples that are necessary conditions to obtain fast domain wall propagation. An enhancement of the domain wall velocity as well as mobility after annealing has been obtained due to the structural relaxation of such grains with positive magnetostriction. These structure benefits found in the nanocrystalline Hitperm glass-coated microwires are promising for developing optimal magnetic properties. - Highlights: • Grains size refinement upon annealing. • Enhancement of the domain wall velocity as well as mobility after annealing. • Nanocrystalline structure in as-prepared microwires.

  15. Dependence of Effective Anisotropy on Grain Size in Nanocrystalline Nd2Fe14B Hard Magnetic Material

    Institute of Scientific and Technical Information of China (English)

    Feng Weicun; Gao Ruwei; Han Guangbing; Zhu Minggang; Li Wei; Sun Guangfei

    2005-01-01

    Taking nanocrystalline Nd2Fe14B as a typical sample, based on Herzer′s random anisotropy theory and the cubic grain model, the partial exchange-coupling interaction model was established and the dependence of effective anisotropy constant Keff on grain size was investigated. Calculation results reveal that the exchange-coupling interaction enhances and the effective anisotropy of material Keff decreases with the reduction of grain size. The variation of Keff is basically the same as that of coercivity. The decrease of effective anisotropy is the main reason of the reduction of coercivity for nanocrystalline Nd2Fe14B permanent magnetic material.

  16. Grain size effects on stability of nonlinear vibration with nanocrystalline NiTi shape memory alloy

    Science.gov (United States)

    Xia, Minglu; Sun, Qingping

    2017-10-01

    Grain size effects on stability of thermomechanical responses for a nonlinear torsional vibration system with nanocrystalline superelastic NiTi bar are investigated in the frequency and amplitude domains. NiTi bars with average grain size from 10 nm to 100 nm are fabricated through cold-rolling and subsequent annealing. Thermomechanical responses of the NiTi bar as a softening nonlinear damping spring in the torsional vibration system are obtained by synchronised acquisition of rotational angle and temperature under external sinusoidal excitation. It is shown that nonlinearity and damping capacity of the NiTi bar decrease as average grain size of the material is reduced below 100 nm. Therefore jump phenomena of thermomechanical responses become less significant or even vanish and the vibration system becomes more stable. The work in this paper provides a solid experimental base for manipulating the undesired jump phenomena of thermomechanical responses and stabilising the mechanical vibration system through grain refinement of NiTi SMA.

  17. Grain size control and phase transformations in nanocrystalline ZrO(2)-Al(2)O(3)

    Science.gov (United States)

    Smyser, Bridget Maureen

    1998-12-01

    An effort has been made to develop nanocrystalline ZrOsb2-Alsb2Osb3 powders that exhibit grain size and phase stability during one thermal cycle from room temperature to 1100-1200sp°C for potential use as thermal barrier coating materials. For this use, the tetragonal phase of ZrOsb2 must be maintained. Tetragonal ZrOsb2 can be prevented from transforming to the monoclinic form by maintaining the grain size below a critical value. Alsb2Osb3 was intended to provide this grain size control due to its immiscibility with ZrOsb2. Several sol-gel and precipitation methods of producing the powders were compared, along with two different forms of high energy mixing. The powders were subsequently calcined and heat treated in order to assess their ability to maintain the desired phase distribution during thermal cycling. The powders were characterized by x-ray diffraction and transmission electron microscopy. The method producing the greatest fraction of tetragonal ZrOsb2 with the least amount of added Alsb2Osb3 was that in which a commercial colloidal solution of ZrOsb2 was mixed with an aluminum nitrate solution. The critical grain size of ZrOsb2 in this system was 30 nm. The grain size was controlled not by a pinning mechanism as is often seen in conventional, high Alsb2Osb3,\\ Alsb2Osb3-ZrOsb2 ceramics, but instead by mutual constraint of surrounding grains aided by sluggish grain boundary diffusion. The grain growth kinetics in all the phases tended to be slower than in micron sized materials, and a range of grain growth exponents from n = 1 to n = 30 were determined for the various phases. Transformation kinetics in ZrOsb2 followed classic Avrami behavior. Alsb2Osb3 phase transformation kinetics were not specifically determined, however, gamma-Alsb2Osb3 was identified at temperatures well beyond its usual stability, which is possibly a grain size effect.

  18. Grain size effect on the Neel temperature and magnetic properties of nanocrystalline $NiFe{_2}O{_4}$ spinel

    OpenAIRE

    Chinnasamy, CN; Narayanasamy, A.; Ponpandian, N; Joseyphus, RJ; Jeyadevan, B.; Tohji, K.; Chattopadhyay, K.

    2002-01-01

    Nanocrystalline NiFe2O4 spinel ferrites with various grain sizes have been synthesized by ball milling the bulk NiFe2O4. The average grain sizes were estimated from the X-ray line broadening of the (3 1 1) reflection. The Neel temperatures of NiFe2O4 for various grain sizes were determined by magneto thermogravimetric method. The magnetic behaviour has been explained by combining the effects of changes in cation distribution on milling and finite size scaling. The shift in B-H loops has been ...

  19. THE INFLUENCE OF GRAIN SIZE AND TEMPERATURE ON THE MECHANICAL DEFORMATION OF NANOCRYSTALLINE MATERIALS:MOLECULAR DYNAMICS SIMULATION

    Institute of Scientific and Technical Information of China (English)

    WEN YU-HUA; ZHOU FU-XIN; LIU YUE-WU

    2001-01-01

    Nanocrystalline (nc) materials are characterized by a typical grain size of 1-100nm. The uniaxial tensile deformation of computer-generated nc samples, with several average grain sizes ranging from 5.38 to 1.79nm, is simulated by using molecular dynamics with the Finnis-Sinclair potential. The influence of grain size and temperature on the mechanical deformation is studied in this paper. The simulated nc samples show a reverse Hall-Petch effect. Grain boundary sliding and motion, as well as grain rotation are mainly responsible for the plastic deformation. At low temperatures, partial dislocation activities play a minor role during the deformation. This role begins to occur at the strain of 5%, and is progressively remarkable with increasing average grain size. However, at elevated temperatures no dislocation activity is detected, and the diffusion of grain boundaries may come into play.

  20. Combined grain size, strain rate and loading condition effects on mechanical behavior of nanocrystalline Cu under high strain rates

    Institute of Scientific and Technical Information of China (English)

    Lu-Ming Shen

    2012-01-01

    Molecular dynamics simulations of nanocrystalline Cu with average grain sizes of 3.1 nm,6.2 nm,12.4 nm and 18.6 nm under uniaxial strain and stress tension at strain rates of 108 s-1,109 s-1 and 1010 s-1 are performed to study the combined grain size,strain rate and loading condition effects on mechanical properties. It is found that the strength of nanocrystalline Cu increases as grain size increases regardless of loading condition.Both the strength and ductility of nanocrystalline Cu increase with strain rate except that there is no monotonic relation between the strength and strain rate for specimens under uniaxial strain loading.Moreover,the strength and ductility of specimens under uniaxial strain loading are lower than those under uniaxial stress loading.The nucleation of voids at grain boundaries and their subsequent growth characterize the failure of specimens under uniaxial strain loading,while grain boundary sliding and necking dominate the failure of specimens under uniaxial stress loading.The rate dependent strength is mainly caused by the dynamic wave effect that limits dislocation motion,while combined twinning and slipping mechanism makes the material more ductile at higher strain rates.

  1. Grain size effect on magnetic and electric properties of LuMnO3 nanocrystalline materials

    Science.gov (United States)

    Han, Tai-Chun; Chen, Jia-Wern; Liu, Yuan-Hsun; Hu, Yu-Min

    2013-05-01

    Magnetic and electric properties are investigated for the nanosized LuMnO3 samples with different grain sizes (30 nm to 500 nm) synthesized by a modified Pechini method. It shows that magnetic and electric properties are strongly dependent on the grain size. The magnetic characterization indicates that with increasing grain size, the antiferromagnetic (AFM) transition temperature increases from 72 to 89 K. The temperature-dependent dielectric measurements show an anomaly in the dielectric constant at temperatures close to the AFM ordering temperature for all samples. A corresponding shift of the peak-positions of dielectric anomaly and magnetic ordering indicates a strong correlation between the magnetic ordering and the electric polarization. Further analysis suggests that the rising of AFM transition temperature with increasing grain size should be from the structural origin, in which the strength of AFM interaction as well as the electrical polarization is dependent on the in-plane lattice parameters.

  2. Grain size stability and hardness in nanocrystalline Cu–Al–Zr and Cu–Al–Y alloys

    Energy Technology Data Exchange (ETDEWEB)

    Roy, D., E-mail: droy2k6@gmail.com [Material Science and Engineering Department, North Carolina State University, Raleigh, NC 27606 (United States); Materials and Metallurgical Engineering Department, NIFFT, Ranchi 834003 (India); Mahesh, B.V. [Department of Mechanical and Aerospace Engineering, Monash University (Australia); Atwater, M.A. [U.S. Army Research Laboratory, Weapons and Materials Research Directorate, RDRL-WMM-F, Aberdeen Proving Ground, MD 21005-5069 (United States); Chan, T.E.; Scattergood, R.O.; Koch, C.C. [Material Science and Engineering Department, North Carolina State University, Raleigh, NC 27606 (United States)

    2014-03-01

    Cryogenic high energy ball milling has been used to synthesize nanocrystalline Cu–14Al, Cu–12Al–2Zr and Cu–12Al–2Y alloys by mechanical alloying. The alloys were studied with the aim of comparing the effect of substituting Y and Zr in place of Al, in Cu–Al alloys, on the grain size stability at elevated temperatures. The as-milled alloys were subjected to annealing at various temperatures between 200 and 900 °C and the resulting grain morphology has been studied using X-ray diffraction and transmission electron microscopy. The addition of Y results in significantly reduced susceptibility to grain growth whereas in case of CuAl and CuAlZr alloys, the susceptibility to grain growth was much higher. The hardness is substantially increased due to Zr and Y addition in the as-milled CuAl powders. However, the hardness of Cu–12Al–2Zr gradually decreases and approaches that of Cu–14Al alloy after the annealing treatment whereas in case of Cu–12Al–2Y alloy, the relative drop in the hardness is much lower after annealing. Accordingly, the efficacy of grain size stabilization by Y addition at high homologous temperatures has been explained on the basis of a recent thermodynamic stabilization models.

  3. Solvothermal synthesis of grain size controlled nanocrystalline SnO2

    Institute of Scientific and Technical Information of China (English)

    XU Gang; XU Sheng-ming; CHEN Song-zhe; WU Fang; LI Lin-yan

    2006-01-01

    Uniform nanocrystalline SnO2 with different particle sizes was prepared by a solvothermal method using SnCl4(5H2O as the starting material and ethanol as the solvent in the presence of different concentrations of HCl or KOH. The as-prepared powders were characterized by X-ray diffraction(XRD), transmission electron microscopy(TEM), thermo-gravimetry and differential thermal analysis(TG-DTA), and nitrogen BET measurements. With increasing alkalinity of the precursor solution, the crystallite size of the as-prepared SnO2 nanocrystals decreases from 7.1 nm to 3.2 nm, while the specific surface area of the as-prepared powders increases from 101 m2/g to 195 m2/g. When calcined at 500 ℃ for 2 h in air, the crystallite size of the as-calcined powders increases slightly (12-5.9 nm) and the specific surface area of the as-calcined powders is 42-63 m2/g.

  4. Effects of grain size on the quasi-static mechanical properties of ultrafine-grained and nanocrystalline tantalum

    Science.gov (United States)

    Ligda, Jonathan Paul

    The increase in strength due to the Hall-Petch effect, reduced strain hardening capacity, a reduced ductility, and changes in deformation mechanisms are all effects of reducing grain size (d) into the ultrafine-grained (UFG, 100 replacement for depleted uranium in kinetic energy penetrators. However, an ideal replacement material must also plastically deform in tension under quasi-static rates to survive initial launch conditions. This raises the question: if the material forms ASBs at dynamic rates, will it also form shear bands at quasi-static isothermal rates? As well as, is there a specific grain size for a material that will plastically deform in tension at quasi-static rates but form adiabatic shear bands at dynamic rates? Using high pressure torsion, a polycrystalline bulk tantalum disk was refined into the UFG/NC regime. Using microscale mechanical testing techniques, such as nanoindentation, microcompression, and microtension, it is possible to isolate locations with a homogeneous grain size within the disk. Pillars are compressed using a nanoindenter with a flat punch tip, while "dog-bone" specimens were pulled in tension using a custom built in-situ tension stage within a scanning electron microscope (SEM). The observed mechanical behavior is related to the microstructure by using transmission electron microscopy (TEM) on the as-processed material and tested specimens. Synchrotron X-ray based texture analysis was also conducted on the disk to determine if any changes in the deformation texture occur during HPT processing. Nanoindentation data shows a trend of increasing hardness with radial position that saturates at 4.5 GPa near the edge, and decreasing strain rate sensitivity. The micromechanical tests show two distinct regions on a processed circular disk, a non-shearing region and a shearing region. Microcompression/tension tests in the region of 1.0 5.3 mm show a drastic switch to localized plastic deformation in the form of shear bands, with

  5. Novel aspect in grain size control of nanocrystalline diamond film for thin film waveguide mode resonance sensor application.

    Science.gov (United States)

    Lee, Hak-Joo; Lee, Kyeong-Seok; Cho, Jung-Min; Lee, Taek-Sung; Kim, Inho; Jeong, Doo Seok; Lee, Wook-Seong

    2013-11-27

    Nanocrystalline diamond (NCD) thin film growth was systematically investigated for application for the thin film waveguide mode resonance sensor. The NCD thin film was grown on the Si wafer or on the SiO2-coated sapphire substrate using the hot filament chemical vapor deposition (HFCVD). The structural/optical properties of the samples were characterized by the high-resolution scanning electron microscopy (HRSEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDS), near edge X-ray absorption fine structure (NEXAFS), X-ray diffraction (XRD), and ultraviolet-visible (UV-vis) spectroscopy. The waveguide modes of the NCD layer were studied by prism coupler technique using laser (wavelength: 632.8 nm) with varying incident angle. A novel aspect was disclosed in the grain size dependence on the growth temperature at the relatively low methane concentration in the precursor gas, which was important for optical property: the grain size increased with decreasing growth temperature, which was contrary to the conventional knowledge prevailing in the microcrystalline diamond (MCD) domain. We have provided discussions to reconcile such observation. An optical waveguide mode resonance was demonstrated in the visible region using the microstructure-controlled transparent NCD thin film waveguide, which provided a strong potential for the waveguide mode resonance sensor applications.

  6. Linear grain growth kinetics and rotation in nanocrystalline Ni

    OpenAIRE

    Farkas, Diana; Mohanty, S.; Monk, J.

    2007-01-01

    We report three-dimensional atomistic molecular dynamics studies of grain growth kinetics in nanocrystalline Ni. The results show the grain size increasing linearly with time, contrary to the square root of the time kinetics observed in coarse-grained structures. The average grain boundary energy per unit area decreases simultaneously with the decrease in total grain boundary area associated with grain growth. The average mobility of the boundaries increases as the grain size increases. The r...

  7. Nanocrystalline and ultrafine grain copper obtained by mechanical attrition

    Directory of Open Access Journals (Sweden)

    Rodolfo Rodríguez Baracaldo

    2011-03-01

    Full Text Available This article presents a method for the sample preparation and characterisation of bulk copper having grain size lower than 1 μm (ultra-fine grain and lower than 100 nm grain size (nanocrystalline. Copper is initially manufactured by a milling/alloying me- chanical method thereby obtaining a powder having a nanocrystalline structure which is then consolidated through a process of warm compaction at high pressure. Microstructural characterisation of bulk copper samples showed the evolution of grain size during all stages involved in obtaining it. The results led to determining the necessary conditions for achieving a wide range of grain sizes. Mechanical characterisation indicated an increase in microhardness to values of around 3.40 GPa for unconsolida- ted nanocrystalline powder. Compressivee strength was increased by reducing the grain size, thereby obtaining an elastic limit of 650 MPa for consolidated copper having a ~ 62 nm grain size.

  8. Grain boundary and triple junction diffusion in nanocrystalline copper

    Energy Technology Data Exchange (ETDEWEB)

    Wegner, M., E-mail: m.wegner@uni-muenster.de; Leuthold, J.; Peterlechner, M.; Divinski, S. V., E-mail: divin@uni-muenster.de [Institut für Materialphysik, Universität Münster, Wilhelm-Klemm-Straße 10, D-48149, Münster (Germany); Song, X., E-mail: xysong@bjut.edu.cn [College of Materials Science and Engineering, Beijing University of Technology, 100124 Beijing (China); Wilde, G. [Institut für Materialphysik, Universität Münster, Wilhelm-Klemm-Straße 10, D-48149, Münster (Germany); Institute of Nanochemistry and Nanobiology, School of Environmental and Chemical Engineering, Shanghai University, 200444 Shanghai (China)

    2014-09-07

    Grain boundary and triple junction diffusion in nanocrystalline Cu samples with grain sizes, 〈d〉, of ∼35 and ∼44 nm produced by spark plasma sintering were investigated by the radiotracer method using the {sup 63}Ni isotope. The measured diffusivities, D{sub eff}, are comparable with those determined previously for Ni grain boundary diffusion in well-annealed, high purity, coarse grained, polycrystalline copper, substantiating the absence of a grain size effect on the kinetic properties of grain boundaries in a nanocrystalline material at grain sizes d ≥ 35 nm. Simultaneously, the analysis predicts that if triple junction diffusion of Ni in Cu is enhanced with respect to the corresponding grain boundary diffusion rate, it is still less than 500⋅D{sub gb} within the temperature interval from 420 K to 470 K.

  9. Kinetic constants of abnormal grain growth in nanocrystalline nickel

    Science.gov (United States)

    Aleshin, A. N.

    2016-02-01

    The grain growth in nanocrystalline nickel with a purity of 99.5 at % during non-isothermal annealing was experimentally investigated using differential scanning calorimetry and transmission electron microscopy. Nanocrystalline nickel was prepared by electrodeposition and had an average grain size of approximately 20 nm. It was shown that, at a temperature corresponding to the calorimetric signal peak, abnormal grain growth occurs with the formation of a bimodal grain microstructure. Calorimeters signals were processed within the Johnson-Mehl-Avrami formalism. This made it possible to determine the exponent of the corresponding equation, the frequency factor, and the activation energy of the grain growth, which was found to be equal to the activation energy of the vacancy migration. The reasons for the abnormal grain growth in nanocrystalline nickel were discussed.

  10. Enhancing the High Temperature Capability of Nanocrystalline Alloys: Utilizing Thermodynamic Stability Maps to Mitigate Grain Growth Through Solute Selection

    Science.gov (United States)

    2013-12-01

    nanocrystalline alloys. nanocrystalline materials , grain growth, grain boundary energy, grain boundary segregation 46 Mark A. Tschopp 410-306...grant DMR-1005677. vi 1. Introduction For nanocrystalline materials to be useful, they must be sufficiently resistant to grain growth at elevated...temperatures to retain their nanoscale grain size (d < 100 nm). One strategy for stabilizing nanocrystalline materials is to add segregating solutes to

  11. Novel analytical model for the determination of grain size distributions in nanocrystalline materials with low lattice microstrains by X-ray diffractometry

    Energy Technology Data Exchange (ETDEWEB)

    Sanchez-Bajo, F. [Departamento de Electronica e Ingenieria Electromecanica, Escuela de Ingenierias Industriales, Universidad de Extremadura, Avda. de Elvas S/N, Badajoz 06071 (Spain); Ortiz, A.L. [Departamento de Electronica e Ingenieria Electromecanica, Escuela de Ingenierias Industriales, Universidad de Extremadura, Avda. de Elvas S/N, Badajoz 06071 (Spain)]. E-mail: alortiz@unex.es; Cumbrera, F.L. [Departamento de Fisica, Facultad de Ciencias, Universidad de Extremadura, Badajoz 06071 (Spain)

    2006-01-15

    We have developed a novel, analytical model for the determination of grain size distributions in nanocrystalline (nc) materials with low internal stresses by X-ray diffractometry (XRD). The model assumes explicitly that the XRD peaks are pseudo-Voigtian and that the grain size distributions are lognormal, both of which are assumptions amply supported by the experimental evidence. It was found analytically that the grain size dispersion depends on the shape of the XRD peaks only, whereas the grain size median depends on both the shape and width of the XRD peaks. In addition, the theoretical predictions resulting from the model were validated using standard XRD peaks obtained by computer simulation from first principles. Particular emphasis is given to the discussion of the validity limits of the model, and to the analysis of the influence of the characteristics of the grain size distributions on the nature of the XRD peaks. We then show how to calculate the average and apparent grain sizes from the grain size distribution determined with the model, and how this compares with the Scherrer method. Implications for the characterization of (undistorted and distorted) nc-materials are indicated, and a case study of an nc-powder of cubic ZrO{sub 2} is presented. The application of the model itself is simple, involving only the fit of a pseudo-Voigt function to a single XRD peak followed by the use of two equations. This suggests that the model may have an important role to play in the characterization of nc-materials.

  12. Highly oriented NdFeB nanocrystalline magnets from partially recombined compacts with ultrafine grain size by reactive deformation under low pressure

    Institute of Scientific and Technical Information of China (English)

    余云萍; 李军; 刘颖; 王仁全; 郑青; 连利仙

    2015-01-01

    The partially recombined compacts with ultrafine grain size were taken advantage of preparing anisotropic nanocrystalline magnets with full density and homogenous microstructure and texture by reactive deformation under low pressure. Because of the ul-trafine grain size of the precursors, the partially recombined phases could quickly achieve recombination. The results suggested that the newly recombined Nd2Fe14B grains with fine grain size could undergo deformation immediately during the desorp-tion-recombination reaction, and then an obvious anisotropy and uniform alignment would be obtained. The magnetic properties, (BH)max=214 kJ/m3,Br= 1.26 T,Hcj=463 kA/m, were obtained after being treated for 5 min at 820 ºC in high vacuum under low pres-sure less than 26 MPa. Microstructures of the magnets were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) respectively. Magnetic measurements were carried out using a vibrating sample magnetometer (VSM) with the maximum field of 2.88 T. Accurate phase contents were measured by a Mossbauer spectrometer.

  13. A constitutive model of nanocrystalline metals based on competing grain boundary and grain interior deformation mechanisms

    KAUST Repository

    Gurses, Ercan

    2011-12-01

    In this work, a viscoplastic constitutive model for nanocrystalline metals is presented. The model is based on competing grain boundary and grain interior deformation mechanisms. In particular, inelastic deformations caused by grain boundary diffusion, grain boundary sliding and dislocation activities are considered. Effects of pressure on the grain boundary diffusion and sliding mechanisms are taken into account. Furthermore, the influence of grain size distribution on macroscopic response is studied. The model is shown to capture the fundamental mechanical characteristics of nanocrystalline metals. These include grain size dependence of the strength, i.e., both the traditional and the inverse Hall-Petch effects, the tension-compression asymmetry and the enhanced rate sensitivity. © 2011 Elsevier B.V. All rights reserved.

  14. Weakened Flexural Strength of Nanocrystalline Nanoporous Gold by Grain Refinement.

    Science.gov (United States)

    Gwak, Eun-Ji; Kim, Ju-Young

    2016-04-13

    High density of grain boundaries in solid materials generally leads to high strength because grain boundaries act as strong obstacles to dislocation activity. We find that the flexural strength of nanoporous gold of grain size 206 nm is 33.6% lower than that of grain size 238 μm. We prepared three gold-silver precursor alloys, well-annealed, prestrained, and high-energy ball-milled, from which nanoporous gold samples were obtained by the same free-corrosion dealloying process. Ligaments of the same size are formed regardless of precursor alloys, and microstructural aspects of precursor alloys such as crystallographic orientation and grain size is preserved in the dealloying process. While the nanoindentation hardness of three nanoporous golds is independent of microstructural variation, flexural strength of nanocrystalline nanoporous gold is significantly lower than that of nanoporous golds with much larger grain size. We investigate weakening mechanisms of grain boundaries in nanocrystalline nanoporous gold, leading to weakening of flexural strength.

  15. Grain rotation mediated by grain boundary dislocations in nanocrystalline platinum

    Science.gov (United States)

    Wang, Lihua; Teng, Jiao; Liu, Pan; Hirata, Akihiko; Ma, En; Zhang, Ze; Chen, Mingwei; Han, Xiaodong

    2014-01-01

    Grain rotation is a well-known phenomenon during high (homologous) temperature deformation and recrystallization of polycrystalline materials. In recent years, grain rotation has also been proposed as a plasticity mechanism at low temperatures (for example, room temperature for metals), especially for nanocrystalline grains with diameter d less than ~15 nm. Here, in tensile-loaded Pt thin films under a high-resolution transmission electron microscope, we show that the plasticity mechanism transitions from cross-grain dislocation glide in larger grains (d>6 nm) to a mode of coordinated rotation of multiple grains for grains with d<6 nm. The mechanism underlying the grain rotation is dislocation climb at the grain boundary, rather than grain boundary sliding or diffusional creep. Our atomic-scale images demonstrate directly that the evolution of the misorientation angle between neighbouring grains can be quantitatively accounted for by the change of the Frank–Bilby dislocation content in the grain boundary. PMID:25030380

  16. Predicting Grain Growth in Nanocrystalline Materials: A Thermodynamic and Kinetic-Based Model Informed by High Temperature X-ray Diffraction Experiments

    Science.gov (United States)

    2014-10-01

    Predicting grain growth in nanocrystalline materials requires modeling approaches that incorporate grain boundary thermodynamics and kinetics. In...growth in nanocrystalline materials and this extended model can be applied to understanding how grain size evolves with temperature in other nanocrystalline systems....this work, a thermokinetic model for grain growth was applied to experimental X-ray diffraction measurements from nanocrystalline Fe Zr in an effort 1

  17. Size-dependent deformation behavior of nanocrystalline graphene sheets

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Zhi [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, Shaanxi (China); Huang, Yuhong [College of Physics and Information Technology, Shaanxi Normal University, Xi’an 710062, Shaanxi (China); Ma, Fei, E-mail: mafei@mail.xjtu.edu.cn [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, Shaanxi (China); Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China); Sun, Yunjin [Faculty of Food Science and Engineering, Beijing University of Agriculture, Beijing Key Laboratory of Agricultural Product Detection and Control of Spoilage Organisms and Pesticide Residue, Beijing Laboratory of Food Quality and Safety, Beijing 102206 (China); Xu, Kewei, E-mail: kwxu@mail.xjtu.edu.cn [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, Shaanxi (China); Department of Physics and Opt-electronic Engineering, Xi’an University of Arts and Science, Xi’an 710065, Shaanxi (China); Chu, Paul K., E-mail: paul.chu@cityu.edu.hk [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China)

    2015-08-15

    Highlights: • MD simulation is conducted to study the deformation of nanocrystalline graphene. • Unexpectedly, the elastic modulus decreases with the grain size considerably. • But the fracture stress and strain are nearly insensitive to the grain size. • A composite model with grain domains and GBs as two components is suggested. - Abstract: Molecular dynamics (MD) simulation is conducted to study the deformation behavior of nanocrystalline graphene sheets. It is found that the graphene sheets have almost constant fracture stress and strain, but decreased elastic modulus with grain size. The results are different from the size-dependent strength observed in nanocrystalline metals. Structurally, the grain boundaries (GBs) become a principal component in two-dimensional materials with nano-grains and the bond length in GBs tends to be homogeneously distributed. This is almost the same for all the samples. Hence, the fracture stress and strain are almost size independent. As a low-elastic-modulus component, the GBs increase with reducing grain size and the elastic modulus decreases accordingly. A composite model is proposed to elucidate the deformation behavior.

  18. Science at the interface : grain boundaries in nanocrystalline metals.

    Energy Technology Data Exchange (ETDEWEB)

    Rodriguez, Mark Andrew; Follstaedt, David Martin; Knapp, James Arthur; Brewer, Luke N.; Holm, Elizabeth Ann; Foiles, Stephen Martin; Hattar, Khalid M.; Clark, Blythe B.; Olmsted, David L.; Medlin, Douglas L.

    2009-09-01

    Interfaces are a critical determinant of the full range of materials properties, especially at the nanoscale. Computational and experimental methods developed a comprehensive understanding of nanograin evolution based on a fundamental understanding of internal interfaces in nanocrystalline nickel. It has recently been shown that nanocrystals with a bi-modal grain-size distribution possess a unique combination of high-strength, ductility and wear-resistance. We performed a combined experimental and theoretical investigation of the structure and motion of internal interfaces in nanograined metal and the resulting grain evolution. The properties of grain boundaries are computed for an unprecedented range of boundaries. The presence of roughening transitions in grain boundaries is explored and related to dramatic changes in boundary mobility. Experimental observations show that abnormal grain growth in nanograined materials is unlike conventional scale material in both the level of defects and the formation of unfavored phases. Molecular dynamics simulations address the origins of some of these phenomena.

  19. Simulation of grain growth in nanocrystalline nickel induced by ion irradiation

    CERN Document Server

    Voegeli, W; Hahn, H

    2003-01-01

    Molecular dynamics simulations of 5 keV cascades in nanocrystalline nickel with grain sizes of 5 and 10 nm are presented. If the spike volume is exceeding the grain size or overlapping the grain boundary (GB) area we observe ion-beam induced grain growth for both grain sizes. In contrast cascades located in the grain volume lead to the formation of vacancies and interstitials, where the latter are mostly accommodated by the GBs upon annealing. Finally, we show that ion-beam induced grain growth is a direct result of recrystallisation of the thermal spike and therefore inherently different to grain growth observed in long time thermal annealing simulations.

  20. Electronic structure studies of nanocrystalline diamond grain boundaries

    Energy Technology Data Exchange (ETDEWEB)

    Zapol, P.; Sternberg, M.; Frauenheim, T.; Gruen, D. M.; Curtiss, L. A.

    1999-11-29

    Diamond growth from hydrogen-poor plasmas results in diamond structures that are profoundly different from conventionally CVD-grown diamond. High concentration of carbon dimers in the microwave plasma results in a high rate of heterogeneous renucleation leading to formation of nanocrystalline diamond with a typical grain size of 3--10 nm. Therefore, up to 10% of carbon atoms are located in the grain boundaries. In this paper the authors report on density-functional based tight-binding molecular dynamics calculations of the structure of a {Sigma}13 twist (100) grain boundary in diamond. Beginning with a coincidence site lattice model, simulated annealing of the initial structure was performed at 1,500 K followed by relaxation toward lower temperatures. About one-half of the carbons in the grain boundary are found to be three-coordinated. Coordination numbers, bond length and bond angle distributions are analyzed and compared to those obtained in previous studies.

  1. The effect of electronic energy loss on irradiation-induced grain growth in nanocrystalline oxides.

    Science.gov (United States)

    Zhang, Yanwen; Aidhy, Dilpuneet S; Varga, Tamas; Moll, Sandra; Edmondson, Philip D; Namavar, Fereydoon; Jin, Ke; Ostrouchov, Christopher N; Weber, William J

    2014-05-07

    Grain growth of nanocrystalline materials is generally thermally activated, but can also be driven by irradiation at much lower temperature. In nanocrystalline ceria and zirconia, energetic ions deposit their energy to both atomic nuclei and electrons. Our experimental results have shown that irradiation-induced grain growth is dependent on the total energy deposited, where electronic energy loss and elastic collisions between atomic nuclei both contribute to the production of disorder and grain growth. Our atomistic simulations reveal that a high density of disorder near grain boundaries leads to locally rapid grain movement. The additive effect from both electronic excitation and atomic collision cascades on grain growth demonstrated in this work opens up new possibilities for controlling grain sizes to improve functionality of nanocrystalline materials.

  2. The Effect Of Electronic Energy Loss On Irradiation-induced Grain Growth In Nanocrystalline Oxides

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yanwen; Aidhy, Dilpuneet S.; Varga, Tamas; Moll, Sandra; Edmondson, Philip D.; Namavar, Fereydoon; Jin, Ke; Ostrouchov, Christopher N.; Weber, William J.

    2014-03-03

    Grain growth of nanocrystalline materials is generally thermally activated, but can also be driven by irradiation at much lower temperature. In nanocrystalline ceria and zirconia, energetic ions deposit their energy to both atomic nuclei and electrons. Our experimental results have shown that irradiationinduced grain growth is dependent on the total energy deposited, where electronic energy loss and elastic collisions between atomic nuclei both contribute to the production of disorder and grain growth. Our atomistic simulations reveal that a high density of disorder near grain boundaries leads to locally rapid grain movement. The additive effect from both electronic excitation and atomic collision cascades on grain growth demonstrated in this work opens up new possibilities for controlling grain sizes to improve functionality of nanocrystalline materials.

  3. Chemistry of grain boundary environments in nanocrystalline Al 7075

    Energy Technology Data Exchange (ETDEWEB)

    Ferragut, Rafael, E-mail: rafael.ferragut@polimi.i [Physics Department, LNESS and CNISM, Politecnico di Milano, via Anzani 42, I-22100 Como (Italy); Liddicoat, Peter V. [Australian Key Centre for Microscopy and Microanalysis and ARC Centre of Excellence for Design in Light Metals, University of Sydney, NSW 2006 (Australia); Liao Xiaozhou [School of Aerospace, Mechanical and Mechatronic Engineering, University of Sydney, NSW 2006 (Australia); Zhao, Yong-Hao; Lavernia, Enrique J. [Department of Chemical Engineering and Materials Science, University of California, Davis, CA 95616 (United States); Valiev, Ruslan Z. [Institute of Physics of Advanced Materials, Ufa State Aviation Technical University, K. Marksa 12, Ufa 450000 (Russian Federation); Dupasquier, Alfredo [Physics Department, LNESS and CNISM, Politecnico di Milano, via Anzani 42, I-22100 Como (Italy); Ringer, Simon P. [Australian Key Centre for Microscopy and Microanalysis and ARC Centre of Excellence for Design in Light Metals, University of Sydney, NSW 2006 (Australia)

    2010-04-16

    Positron annihilation spectroscopy in two variants (coincidence Doppler-broadening CDB and lifetime spectroscopy LT) was used for the characterisation of severely deformed nanocrystalline 7075 Al alloy, with specific attention to the distribution of solute in the proximity of grain boundaries. The 7075 samples were deformed via the high pressure torsion (HPT) technique after solution treatment and quenching. The grain size at the end of the deformation was sub 100 nm. The deformed samples have undergone 3 months of natural ageing post-processing. CDB and LT measurements consistently indicate that the fraction of trapped positrons in these samples is near to 90%. The analysis of CDB data shows that the environment of the positron traps is enriched with solute up to 50 at.%, nearly evenly divided between Mg and transition metals (Zn and Cu). The CDB results indicate an enhancement of solute concentration at grain boundaries associated with HPT deformation.

  4. Distortion Regions near the Grain Boundary and Their Effects on Nanocrystalline Materials

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The distortion regions near grain boundaries in α-Fe-C solid solution were studied by use of internal friction method. It was found that the total thickness of these regions is quite large though the thickness of real grain boundaries is usually very thin. It was also found that the smaller the grain size, the thicker the total distortion region. A model for the structure of distortion regions near grain boundaries is proposed. Their effects on nanocrystalline materials are discussed.

  5. Molecular Dynamic Simulation of Lattice Distortion Region Produced by Rounded Grain Boundary in Nanocrystalline Materials

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The distortion structure in nanocrystalline NiAl is studied using molecular dynamics simulation. The rounded grain boundaries in these nanograins are a direct source for the observed lattice distortion. The change of grain size affects directly the volume fraction of the distorted lattice in the nanograin.

  6. Linking stress-driven microstructural evolution in nanocrystalline aluminium with grain boundary doping of oxygen.

    Science.gov (United States)

    He, Mo-Rigen; Samudrala, Saritha K; Kim, Gyuseok; Felfer, Peter J; Breen, Andrew J; Cairney, Julie M; Gianola, Daniel S

    2016-04-13

    The large fraction of material residing at grain boundaries in nanocrystalline metals and alloys is responsible for their ultrahigh strength, but also undesirable microstructural instability under thermal and mechanical loads. However, the underlying mechanism of stress-driven microstructural evolution is still poorly understood and precludes rational alloy design. Here we combine quantitative in situ electron microscopy with three-dimensional atom-probe tomography to directly link the mechanics and kinetics of grain boundary migration in nanocrystalline Al films with the excess of O atoms at the boundaries. Site-specific nanoindentation leads to grain growth that is retarded by impurities, and enables quantification of the critical stress for the onset of grain boundary migration. Our results show that a critical excess of impurities is required to stabilize interfaces in nanocrystalline materials against mechanical driving forces, providing new insights to guide control of deformation mechanisms and tailoring of mechanical properties apart from grain size alone.

  7. Microstructure Evolution and Grain Growth Kinetics in Annealed Nanocrystalline Chromium

    Energy Technology Data Exchange (ETDEWEB)

    Chojnowski, Grzegorz [Warsaw University; Przenioslo, Radoslaw [Warsaw University; Sosnowska, Izabela [Warsaw University; Bukowski, Mirko [University of Saarbrucken, Saarbrucken, Germany; Natter, Harald [University of Saarbrucken, Saarbrucken, Germany; Hempelmann, Rolf [University of Saarbrucken, Saarbrucken, Germany; Fitch, Andrew [European Synchrotron Radiation Facility (ESRF); Urban, Volker S [ORNL

    2007-01-01

    The kinetics of thermal evolution of the microstructure of nanocrystalline chromium (nano-Cr) has been studied by time-resolved synchrotron radiation techniques: high-resolution powder diffraction and small-angle X-ray scattering (SAXS). The as-prepared electrodeposited nano-Cr with average grain size of 27 nm shows the same bcc structure as {alpha}-Cr. The nano-Cr cubic lattice parameter thermal expansion is the same as that of reference polycrystalline {alpha}-Cr. Annealing of nano-Cr at temperatures above 400 C leads to a grain growth process with the final grain size not exceeding 125 nm even at a temperature of 700 C. The single power-law behavior is observed by SAXS in as-prepared nano-Cr changes during annealing above 400 C. In nano-Cr samples annealed at temperatures between 400 and 700 C, the low-q part of the SAXS signal shows a Porod-type behavior while the high-q part shows a power-law Q-{alpha} with the exponent {alpha} < 4. This effect is probably due to changes of the grain surface roughness during grain growth.

  8. A new approach to grain boundary engineering for nanocrystalline materials

    Directory of Open Access Journals (Sweden)

    Shigeaki Kobayashi

    2016-11-01

    Full Text Available A new approach to grain boundary engineering (GBE for high performance nanocrystalline materials, especially those produced by electrodeposition and sputtering, is discussed on the basis of some important findings from recently available results on GBE for nanocrystalline materials. In order to optimize their utility, the beneficial effects of grain boundary microstructures have been seriously considered according to the almost established approach to GBE. This approach has been increasingly recognized for the development of high performance nanocrystalline materials with an extremely high density of grain boundaries and triple junctions. The effectiveness of precisely controlled grain boundary microstructures (quantitatively characterized by the grain boundary character distribution (GBCD and grain boundary connectivity associated with triple junctions has been revealed for recent achievements in the enhancement of grain boundary strengthening, hardness, and the control of segregation-induced intergranular brittleness and intergranular fatigue fracture in electrodeposited nickel and nickel alloys with initial submicrometer-grained structure. A new approach to GBE based on fractal analysis of grain boundary connectivity is proposed to produce high performance nanocrystalline or submicrometer-grained materials with desirable mechanical properties such as enhanced fracture resistance. Finally, the potential power of GBE is demonstrated for high performance functional materials like gold thin films through precise control of electrical resistance based on the fractal analysis of the grain boundary microstructure.

  9. A new approach to grain boundary engineering for nanocrystalline materials.

    Science.gov (United States)

    Kobayashi, Shigeaki; Tsurekawa, Sadahiro; Watanabe, Tadao

    2016-01-01

    A new approach to grain boundary engineering (GBE) for high performance nanocrystalline materials, especially those produced by electrodeposition and sputtering, is discussed on the basis of some important findings from recently available results on GBE for nanocrystalline materials. In order to optimize their utility, the beneficial effects of grain boundary microstructures have been seriously considered according to the almost established approach to GBE. This approach has been increasingly recognized for the development of high performance nanocrystalline materials with an extremely high density of grain boundaries and triple junctions. The effectiveness of precisely controlled grain boundary microstructures (quantitatively characterized by the grain boundary character distribution (GBCD) and grain boundary connectivity associated with triple junctions) has been revealed for recent achievements in the enhancement of grain boundary strengthening, hardness, and the control of segregation-induced intergranular brittleness and intergranular fatigue fracture in electrodeposited nickel and nickel alloys with initial submicrometer-grained structure. A new approach to GBE based on fractal analysis of grain boundary connectivity is proposed to produce high performance nanocrystalline or submicrometer-grained materials with desirable mechanical properties such as enhanced fracture resistance. Finally, the potential power of GBE is demonstrated for high performance functional materials like gold thin films through precise control of electrical resistance based on the fractal analysis of the grain boundary microstructure.

  10. Influence of inhomogeneity of grain-boundary region of nanocrystalline materials on elastic properties

    Institute of Scientific and Technical Information of China (English)

    Stepanov; Y.; N.; Alymov; M.; I.

    2005-01-01

    Experimental data indicate that Young's modulus of materials decreases with the decreasing of the grain size. Obviously, the primary factor of this decrease is presence of grain-boundary region, which Young's modulus other than in the bulk of crystallites. There is a set of various expressions for calculation of Young's modulus of polycrystals, obtained under the assumption, that it is possible to consider a polycrystal as a composite consisting of a crystalline matrix and a intercrystalline layers (grain-boundary region). Calculations showed incorrectness of application of a majority of these expressions and a large error in the calculations for the nanocrystalline materials. By us, on the basis of the same assumptions, is also obtained analytical expression for calculating Young's modulus of materials with grain size more than 30 nm, which is more exact, than all others.It is necessary to consider under the calculation of effective Young's modulus nanocrystalline materials with grain size of less than 30nm, that grain-boundary region itself is not uniform. It is reliably established,that the triple joints of grain boundaries have a structure and properties, different from the structure and the properties of grain boundaries, which these joints connect. For nanocrystalline materials the volume fraction of the triple joints in the grain-boundary region can reach 50% and even more. Therefore assumption was made, that the nanocrystalline materials should be represented as consisting of three phases (triple joints,grain boundary between the triple joints and crystallite). On the basis of this idea is obtained analytical expression for calculating of Young's modulus nanocrystalline materials. The analysis shows that Young's modulus calculated by this analytical expression coordinated with the theory and the experiment.

  11. Micromechanical modelling of nanocrystalline and ultrafine grained metals: A short overview

    DEFF Research Database (Denmark)

    Mishnaevsky, Leon; Levashov, Evgeny

    2015-01-01

    An overview of micromechanical models of strength and deformation behaviour of nanostructured and ultrafine grained metallic materials is presented. Composite models of nanomaterials, polycrystal plasticity based models, grain boundary sliding, the effect of non-equilibrium grain boundaries...... and nanoscale properties are discussed and compared. The examples of incorporation of peculiar nanocrystalline effects (like large content of amorphous or semi-amorphous grain boundary phase, partial dislocation GB emission/glide/GB absorption based deformation mechanism, diffusion deformation, etc.......) into the continuum mechanical approach are given. The possibilities of using micromechanical models to explore the ways of the improving the properties of nanocrystalline materials by modifying their structures (e.g., dispersion strengthening, creating non-equilibrium grain boundaries, varying the grain size...

  12. Constitutive modeling of stress-driven grain growth in nanocrystalline metals

    KAUST Repository

    Gürses, Ercan

    2013-02-08

    In this work, we present a variational multiscale model for grain growth in face-centered cubic nanocrystalline (nc) metals. In particular, grain-growth-induced stress softening and the resulting relaxation phenomena are addressed. The behavior of the polycrystal is described by a conventional Taylor-type averaging scheme in which the grains are treated as two-phase composites consisting of a grain interior phase and a grain boundary-affected zone. Furthermore, a grain-growth law that captures the experimentally observed characteristics of the grain coarsening phenomena is proposed. To this end, the grain size is not taken as constant and varies according to the proposed stress-driven growth law. Several parametric studies are conducted to emphasize the influence of the grain-growth rule on the overall macroscopic response. Finally, the model is shown to provide a good description of the experimentally observed grain-growth-induced relaxation in nc-copper. © 2013 IOP Publishing Ltd.

  13. In-situ TEM observation of the response of ultrafine- and nanocrystalline-grained tungsten to extreme irradiation environments.

    Science.gov (United States)

    El-Atwani, O; Hinks, J A; Greaves, G; Gonderman, S; Qiu, T; Efe, M; Allain, J P

    2014-05-06

    The accumulation of defects, and in particular He bubbles, can have significant implications for the performance of materials exposed to the plasma in magnetic-confinement nuclear fusion reactors. Some of the most promising candidates for deployment into such environments are nanocrystalline materials as the engineering of grain boundary density offers the possibility of tailoring their radiation resistance properties. In order to investigate the microstructural evolution of ultrafine- and nanocrystalline-grained tungsten under conditions similar to those in a reactor, a transmission electron microscopy study with in situ 2 keV He(+) ion irradiation at 950 °C has been completed. A dynamic and complex evolution in the microstructure was observed including the formation of defect clusters, dislocations and bubbles. Nanocrystalline grains with dimensions less than around 60 nm demonstrated lower bubble density and greater bubble size than larger nanocrystalline (60-100 nm) and ultrafine (100-500 nm) grains. In grains over 100 nm, uniform distributions of bubbles and defects were formed. At higher fluences, large faceted bubbles were observed on the grain boundaries, especially on those of nanocrystalline grains, indicating the important role grain boundaries can play in trapping He and thus in giving rise to the enhanced radiation tolerance of nanocrystalline materials.

  14. In-situ TEM observation of the response of ultrafine- and nanocrystalline-grained tungsten to extreme irradiation environments

    Science.gov (United States)

    El-Atwani, O.; Hinks, J. A.; Greaves, G.; Gonderman, S.; Qiu, T.; Efe, M.; Allain, J. P.

    2014-05-01

    The accumulation of defects, and in particular He bubbles, can have significant implications for the performance of materials exposed to the plasma in magnetic-confinement nuclear fusion reactors. Some of the most promising candidates for deployment into such environments are nanocrystalline materials as the engineering of grain boundary density offers the possibility of tailoring their radiation resistance properties. In order to investigate the microstructural evolution of ultrafine- and nanocrystalline-grained tungsten under conditions similar to those in a reactor, a transmission electron microscopy study with in situ 2 keV He+ ion irradiation at 950°C has been completed. A dynamic and complex evolution in the microstructure was observed including the formation of defect clusters, dislocations and bubbles. Nanocrystalline grains with dimensions less than around 60 nm demonstrated lower bubble density and greater bubble size than larger nanocrystalline (60-100 nm) and ultrafine (100-500 nm) grains. In grains over 100 nm, uniform distributions of bubbles and defects were formed. At higher fluences, large faceted bubbles were observed on the grain boundaries, especially on those of nanocrystalline grains, indicating the important role grain boundaries can play in trapping He and thus in giving rise to the enhanced radiation tolerance of nanocrystalline materials.

  15. Characterization of bulk ultrafine grained and nanocrystalline materials

    Science.gov (United States)

    Chauhan, Manish

    Thermal stability in bulk ultra fine grained (UFG) 5083 Al that exhibited initial grain size of 305 nm, and that was processed by gas atomization followed by cryomilling, consolidation and extrusion, and in bulk nanocrystalline (nc) Ni, initial grain size of 15 and 20 nm, prepared by electrodeposition was investigated. In both the materials, two grain growth regimes were identified: a low temperature region and a high temperature region. In the low temperature regime, relatively low activation energy was found: 25 +/- 5 kJ/mol for UFG 5083 Al and 11 +/- 3 kJ/mol for nc-Ni. It is suggested that this low activation energy represents the energy for the reordering of thermodynamically non-equilibrium grain boundaries in the UFG and nc-materials. In the high temperature regime the value of activation energy for UFG 5083 Al (124 +/- 5 kJ/mol) lies in between that for grain boundary diffusion and lattice diffusion of polycrystalline Al. For nc-Ni an approximate activation energy of 105 +/- 3 kJ/mol, which is close to the activation energy for grain boundary diffusion in polycrystalline Ni, was measured. The value of the grain growth exponent, n, for both the materials (deduced from the grain growth data) were higher than the value of 2 predicted from elementary grain growth theories. The discrepancy was attributed to the operation of strong pinning forces on boundaries during the annealing treatment. An examination of the microstructure suggests that the origin of the pinning forces is most likely related to the presence of impurities and dispersion-particles on the grain boundaries. Creep and ductility behavior of UFG 5083 Al were also studied in the temperature range of 523 K-648 K in the present investigation. The curve of ductility as a function of strain rate shows the presence of a maximum that shifts to higher strain rates with increasing temperature. An analysis of the experimental data indicates that the true stress exponent is about 2, and that the ductility

  16. Grain growth in nanocrystalline Ni-20%Fe alloy

    Energy Technology Data Exchange (ETDEWEB)

    Park, Y.B.; Park, J.; Kim, S.S. [Dept. of Materials Science and Metallurgical Engineering, Sunchon National Univ., Sunchon (Korea); Yim, T.H. [Materials Process Technology R and D Center, Korea Inst. of Industrial Technology, Chonan (Korea)

    2001-07-01

    Grain growth was investigated in a nanocrystalline Ni-20wt-%Fe alloy fabricated by an electrodeposition method, and its effect on the texture evolution was examined. The as-deposited specimens revealed a strong {l_brace}100{r_brace} and a weak {l_brace}111{r_brace} fibre-type textures. Grain growth in the material occurred on annealing beyond 370 C and resulted in the texture change that the {l_brace}111{r_brace} fibre strongly developed at the expense of the {l_brace}100{r_brace} fibre. It was observed using orientation imaging microscopy (OIM) that the {l_brace}111{r_brace} grains are much coarser than other oriented grains in the early stages of grain growth. The relationship between the texture evolution and the microstructural change accompanied by grain growth is interpreted and discussed in terms of the orientation dependency of grain growth. (orig.)

  17. Textures and grain growth in nanocrystalline Fe-Ni alloys

    Energy Technology Data Exchange (ETDEWEB)

    Seo, J.H.; Kim, J.K.; Park, Y.B. [Dept. of Materials Science and Metallurgical Engineering, Nanomaterials Research Center, Sunchon National Univ. (Korea); Yim, T.H. [Production Technology Center, Korea Inst. of Industrial Technology, Chonan (Korea)

    2005-07-01

    The texture evolution due to grain growth that takes place during annealing was investigated in nanocrystalline Fe-Ni alloys fabricated by using a continuous electroforming method. In the current materials, grain growth occurred during annealing at much lower temperatures than in conventional coarse-grained counterparts. With regard to the macrotextures, the as-deposited textures were of fibre-type characterized by strong <100>//ND and weak <111>//ND components, and the occurrence of grain growth resulted in the strong development of the <111>//ND fibre texture with the minor <100>//ND components. It was clarified using orientation imaging microscopy that abnormal growth of the <111>//ND grains in the early stages of grain growth plays an important role on the texture evolution. The origin of the abnormal grain growth has been discussed in terms of the orientation dependence of energy density. (orig.)

  18. Magnetic anisotropy of grain boundaries in nanocrystalline Ni

    Science.gov (United States)

    Bian, Q.; Niewczas, M.

    2017-01-01

    Temperature-dependent magnetic anisotropy due to grain boundaries in nanocrystalline Ni has been studied by simulating experimental magnetization data with the stochastic Landau-Lifshitz-Gilbert theory. In the model the grain boundary magnetic anisotropy energy is expressed as the sum of the uniaxial anisotropy and the cubic anisotropy, characterized by Kua and Kca anisotropy constants. By comparing the calculated magnetization with the experimental magnetization measurements at finite temperatures, the values of Kua and Kca can be determined. For nanocrystalline Ni it is found that with increasing temperature Kua decreases and Kca increases. At low temperatures Kua dominates the grain boundary anisotropy energy, whereas Kca is very small and it can be neglected. At room temperature Kua and Kca are of the same order with the corresponding ratio Kua /Kca ≈ 1.9 , both coefficients are much larger than the magnetocrystalline anisotropy constant.

  19. Effect of electrodeposition temperature on grain orientation and corrosion resistance of nanocrystalline pure nickel

    Science.gov (United States)

    Jinlong, Lv; Tongxiang, Liang; Chen, Wang

    2016-08-01

    The nanocrystalline pure nickels with different grain orientations were fabricated by direct current electrodeposition process. The grain size slightly decreased with the increasing of electrodeposition solution temperature. However, grain orientation was affected significantly. Comparing with samples obtained at 50 °C and 80 °C, sample obtained at 20 °C had the strongest (111) orientation plane which increased electrochemical corrosion resistance of this sample. At the same time, the lowest (111) orientation plane deteriorated electrochemical corrosion resistance of sample obtained at 50 °C.

  20. Nano-analysis of grain boundary and triple junction transport in nanocrystalline Ni/Cu.

    Science.gov (United States)

    Reda Chellali, Mohammed; Balogh, Zoltan; Schmitz, Guido

    2013-09-01

    Nanocrystalline materials are distinguished by a high density of structural defects and grain boundaries. Due to the small grain size, a particular defect of the grain boundary topology, the so-called triple junction takes a dominant role for grain growth and atomic transport. We demonstrate by atom probe tomography that triple junctions in nanocrystalline Cu have 100-300 times higher diffusivity of Ni than standard high angle grain boundaries. Also, a previously unexpected systematic variation of the grain boundary width with temperature is detected. The impurity segregation layer at the grain boundaries grows from the 0.7 nm at 563 K to 2.5 nm at 643 K. This variation is clearly not controlled by simple bulk diffusion. Taking this effect into consideration, the activation energies for Ni diffusion in triple junctions and grain boundaries in Cu can be determined to be (83 ± 10) and (120 ± 15) kJ/mol, respectively. Thus, triple junctions are distinguished by considerably lower activation energy with respect to grain boundaries.

  1. Strain-induced grain growth of cryomilled nanocrystalline Al in trimodal composites during forging

    Energy Technology Data Exchange (ETDEWEB)

    Yao, B. [Advanced Materials Processing and Analysis Center, and Department of Mechanical, Materials, and Aerospace Engineering, University of Central Florida, Orlando, FL 32816 (United States); Simkin, B.; Majumdar, B. [Materials and Metallurgical Engineering Department, New Mexico Institute of Mining and Technology, Socorro, NM 87801 (United States); Smith, C.; Bergh, M. van den [DWA Aluminum Composites, Chatsworth, CA 91311 (United States); Cho, K. [Weapons and Materials Research Directorate, U.S. Army Research Laboratory, Aberdeen Proving Ground, MD 21005 (United States); Sohn, Y.H., E-mail: Yongho.Sohn@ucf.edu [Advanced Materials Processing and Analysis Center, and Department of Mechanical, Materials, and Aerospace Engineering, University of Central Florida, Orlando, FL 32816 (United States)

    2012-02-28

    Highlights: Black-Right-Pointing-Pointer Grain growth of cryomilled nanocrystalline aluminum during hot forging. Black-Right-Pointing-Pointer Use of hollow cone dark field imaging technique in TEM for grain size measurement. Black-Right-Pointing-Pointer Grain growth model of strain, strain rate and temperature for forging optimization. - Abstract: Grain growth of nanocrystalline aluminum ({sup nc}Al) in trimodal Al metal-matrix-composites (MMCs) during hot forging was investigated. The {sup nc}Al phase formed through cryomilling of inert gas-atomized powders in liquid nitrogen has an average grain size down to 21 nm, exhibits excellent thermal stability. However, substantial grain growth of {sup nc}Al up to 63 nm was observed when the Al MMCs were thermo-mechanically processed even at relatively low temperatures. Grain growth of the cryomilled {sup nc}Al phase in trimodal Al MMCs after hot forging was documented with respect to temperature ranging from 175 Degree-Sign C to 287 Degree-Sign C, true strain ranging from 0.4 to 1.35 and strain rate ranging from 0.1 to 0.5 s{sup -1}. Hollow cone dark field imaging technique was employed to provide statistically confident measurements of {sup nc}Al grain size that ranged from 21 to 63 nm. An increase in forging temperature and an increase in true strain were correlated with an increase in grain size of {sup nc}Al. Results were correlated to devise a phenomenological grain growth model for forging that takes strain, strain rate and temperature into consideration. Activation energy for the grain growth during thermo-mechanical hot-forging was determined to be 35 kJ/mol, approximately a quarter of activation energy for bulk diffusion of Al and a half of activation energy for static recrystallization.

  2. Mechanically Driven Grain Boundary Relaxation: A Mechanism for Cyclic Hardening in Nanocrystalline Ni

    Science.gov (United States)

    2012-01-01

    are of significant scientific and technological interest, but have been primarily studied with a focus on the impact of grain size (d). The suppression...addition to being of scientific interest, the possibility that applied stresses can relax GBs in nanocrystalline materials may dramatically impact wear...more microplastic activity that can restructure GBs. Somewhat less intuitive is the result that hydrostatic expansions do not seem to cause significant

  3. Constitutive modeling of strain rate effects in nanocrystalline and ultrafine grained polycrystals

    KAUST Repository

    Gurses, Ercan

    2011-05-01

    We present a variational two-phase constitutive model capable of capturing the enhanced rate sensitivity in nanocrystalline (nc) and ultrafine-grained (ufg) fcc metals. The nc/ufg-material consists of a grain interior phase and a grain boundary affected zone (GBAZ). The behavior of the GBAZ is described by a rate-dependent isotropic porous plasticity model, whereas a rate-independent crystal-plasticity model which accounts for the transition from partial dislocation to full dislocation mediated plasticity is employed for the grain interior. The scale bridging from a single grain to a polycrystal is done by a Taylor-type homogenization. It is shown that the enhanced rate sensitivity caused by the grain size refinement is successfully captured by the proposed model. © 2011 Elsevier Ltd. All rights reserved.

  4. Microstructure and nanoindentation of the CLAM steel with nanocrystalline grains under Xe irradiation

    Science.gov (United States)

    Chang, Yongqin; Zhang, Jing; Li, Xiaolin; Guo, Qiang; Wan, Farong; Long, Yi

    2014-12-01

    This work presents an early look at irradiation effects on China low activation martensitic (CLAM) steel with nanocrystalline grains (NC-CLAM steels) under 500 keV Xe-ion bombardment at room temperature to doses up to 5.3 displacements per atom (dpa). The microstructure in the topmost region of the steel is composed of nanocrystalline grains with an average diameter of 13 nm. As the samples were implanted at low dose, the nanocrystalline grains had martensite lath structure, and many dislocations and high density bubbles were introduced into the NC-CLAM steels. As the irradiation dose up to 5.3 dpa, a tangled dislocation network exists in the lath region, and the size of the bubbles increases. X-ray diffraction results show that the crystal quality decreases after irradiation, although the nanocrystals obviously coarsen. Grain growth under irradiation may be ascribed to the direct impact of the thermal spike on grain boundaries in the NC-CLAM steels. In irradiated samples, a compressive stress exists in the surface layer because of grain growth and irradiation-introduced defects, while the irradiation introduced grain-size coarsening and defects gradients from the surface to matrix result in a tensile stress in the irradiated NC-CLAM steels. Nanoindentation was used to estimate changes in mechanical properties during irradiation, and the results show that the hardness of the NC-CLAM steels increases with increasing irradiation dose, which was ascribed to the competition between the grain boundaries and the irradiation-introduced defects.

  5. Grain-growth kinetics of nanocrystalline iron studied in situ by synchrotron real-time X-ray diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Natter, H.; Schmelzer, M.; Loeffler, M.S.; Krill, C.E.; Fitch, A.; Hempelmann, R.

    2000-03-23

    Pulsed electrodeposition (PED) is used to prepare nanocrystalline iron with an average grain size of 19 nm and thermal stability up to 550 K. At 663 K {le} T {le} 783 K the kinetics of grain growth, with respect to size and size distribution, is studied in situ by means of real-time synchrotron X-ray diffraction. The Bragg peak line shapes of the large number of diffractograms are analyzed using a Warren/Averback procedure improved with respect to reliability and efficiency. The authors observe two regimes of grain growth: at less elevated temperatures grain growth is smooth and moderate up to limiting size values between 50 and 100 nm, depending on temperature. The initially rather narrow width of the size distribution increases slightly, and the activation energy of grain growth, about 100 kJ/mol, corresponds to the literature value for grain boundary self-diffusion in nanocrystalline Fe. At higher temperatures the grains grow first rapidly and then slowly up to limiting values between 200 and 400 nm, depending on temperature. The size distribution becomes rather broad, and the activation energy for grain growth, about 175 kJ/mol, corresponds to the literature value for grain boundary self-diffusion in coarse-grained polycrystalline Fe. The authors do not find evidence of a change of the type of distribution which indicates normal grain growth. The quality of the diffraction data allows a critical evaluation of different kinetic models of grain growth.

  6. Irradiation-induced grain growth and defect evolution in nanocrystalline zirconia with doped grain boundaries.

    Science.gov (United States)

    Dey, Sanchita; Mardinly, John; Wang, Yongqiang; Valdez, James A; Holesinger, Terry G; Uberuaga, Blas P; Ditto, Jeff J; Drazin, John W; Castro, Ricardo H R

    2016-06-22

    Grain boundaries are effective sinks for radiation-induced defects, ultimately impacting the radiation tolerance of nanocrystalline materials (dense materials with nanosized grains) against net defect accumulation. However, irradiation-induced grain growth leads to grain boundary area decrease, shortening potential benefits of nanostructures. A possible approach to mitigate this is the introduction of dopants to target a decrease in grain boundary mobility or a reduction in grain boundary energy to eliminate driving forces for grain growth (using similar strategies as to control thermal growth). Here we tested this concept in nanocrystalline zirconia doped with lanthanum. Although the dopant is observed to segregate to the grain boundaries, causing grain boundary energy decrease and promoting dragging forces for thermally activated boundary movement, irradiation induced grain growth could not be avoided under heavy ion irradiation, suggesting a different growth mechanism as compared to thermal growth. Furthermore, it is apparent that reducing the grain boundary energy reduced the effectiveness of the grain boundary as sinks, and the number of defects in the doped material is higher than in undoped (La-free) YSZ.

  7. Investigation of grain boundary activity in nanocrystalline Al under an indenter by using a multiscale method

    Institute of Scientific and Technical Information of China (English)

    Shao Yu-Fei; Yang Xin; Zhao Xing; Wang Shao-Qing

    2012-01-01

    Grain boundary activity in nanocrystalline Al under an indenter is studied by using a multiscale method.It is found that grain boundaries and twin boundaries can be transformed into each other by emitting and absorbing dislocations.The transition processes might result in grain coarsening and refinement events.Dislocation reflection generated by a piece of stable grain boundary is also observed,because of the complex local atomic structure within the nanocrystalline Al.This implies that nanocrystalline metals might improve their internal structural stability with the help of some special local grain boundaries.

  8. Effect of Second Phase Particles on Grain Growth for Nanocrystalline AZ31 Mg Alloy by Phase Field Methods

    Directory of Open Access Journals (Sweden)

    Wu Yan

    2015-01-01

    Full Text Available The grain growth of nanocrystalline AZ31 magnesium alloy containing spherical particles with different sizes is simulated by phase field methods. It is shown that the role of pinning effect of the second phase particles during grain growth is interesting. There is a critical particle size to affect the grain growth in nanostructure. If the size of particles is lower than the critical value, the effect of pinning for grain growth will be increased with further decreasing the size. If the size is larger than the critical value, the particles nearly have no pinning effects. The critical value is 200 nm when the content of particles is 10%. It is found that the grain growth exponents in kinetic equation decrease when the sizes of particles increase in nanostructure with the same volume fraction of the particles, and the pinning effect of particles on the grain growth is decreased as well.

  9. Magnetic Properties of Grain Boundaries of Nanocrystalline Ni and of Ni Precipitates in Nanocrystalline NiCu Alloys

    Science.gov (United States)

    Wolf, H.; Guan, Z.; Li, X.; Wichert, Th.

    2001-11-01

    Perturbed γγ-angular correlation spectroscopy (PAC) was used to investigate nanocrystalline Ni and NiCu alloys, which are prepared by pulsed electrodeposition (PED). Using diffusion for doping nanocrystalline Ni with 111In four different ordered grain boundary structures are observed, which are characterized by unique electric field gradients. The incorporation of 111In on substitutional bulk sites of Ni is caused by moving grain boundaries below 1000 K and by volume diffusion above 1000 K. The nanocrystalline NiCu alloys prepared by PED are microscopically inhomogeneous as observed by PAC. In contrast, this inhomogeneity cannot be detected by X-ray diffraction. The influence of the temperature of the electrolyte, the current density during deposition, and the optional addition of saccharin to the electrolyte on the homogeneity of nanocrystalline NiCu alloys was investigated.

  10. Nanocrystalline ceramic materials

    Science.gov (United States)

    Siegel, Richard W.; Nieman, G. William; Weertman, Julia R.

    1994-01-01

    A method for preparing a treated nanocrystalline metallic material. The method of preparation includes providing a starting nanocrystalline metallic material with a grain size less than about 35 nm, compacting the starting nanocrystalline metallic material in an inert atmosphere and annealing the compacted metallic material at a temperature less than about one-half the melting point of the metallic material.

  11. The role of grain size in He bubble formation: Implications for swelling resistance

    Science.gov (United States)

    El-Atwani, O.; Nathaniel, J. E.; Leff, A. C.; Muntifering, B. R.; Baldwin, J. K.; Hattar, K.; Taheri, M. L.

    2017-02-01

    Nanocrystalline metals are postulated as radiation resistant materials due to their high defect and particle (e.g. Helium) sink density. Here, the performance of nanocrystalline iron films is investigated in-situ in a transmission electron microscope (TEM) using He irradiation at 700 K. Automated crystal orientation mapping is used in concert with in-situ TEM to explore the role of grain orientation and grain boundary character on bubble density trends. Bubble density as a function of three key grain size regimes is demonstrated. While the overall trend revealed an increase in bubble density up to a saturation value, grains with areas ranging from 3000 to 7500 nm2 show a scattered distribution. An extrapolated swelling resistance based on bubble size and areal density indicated that grains with sizes less than 2000 nm2 possess the greatest apparent resistance. Moreover, denuded zones are found to be independent of grain size, grain orientation, and grain boundary misorientation angle.

  12. A quantum mechanical study of the stability of SnO sub 2 nanocrystalline grains

    CERN Document Server

    Mazzone, A M

    2002-01-01

    The purpose of this study is to gain insight into the instability which is observed, under operative conditions, in SnO sub 2 nanocrystalline materials. To this end, the binding and fragmentation energies of SnO sub 2 crystalline grains have been evaluated quantum mechanically at the semi-empirical level using the extended Debye-Hueckel approximation. The size and shape of the grains, whose lattice has a rutile structure, are variable and a parametric search has been carried out on both quantities. The main result of this study is that the oxygen content, which depends on the grain structure, has a critical effect on its stability. This finding is supported by calculations for small homonuclear clusters formed by oxygen and tin.

  13. Grain growth of nanocrystalline 3C-SiC under Au ion irradiation at elevated temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Limin; Jiang, Weilin; Dissanayake, Amila C.; Varga, Tamas; Zhang, Jiandong; Zhu, Zihua; Hu, Dehong; Wang, Haiyan; Henager, Charles H.; Wang, Tieshan

    2016-01-09

    Nanocrystalline silicon carbide (SiC) represents an excellent model system for a fundamental study of interfacial (grain boundary) processes under nuclear radiation, which are critical to the understanding of the response of nanostructured materials to high-dose irradiation. This study reports on a comparison of irradiation effects in cubic phase SiC (3C-SiC) grains of a few nanometers in size and single-crystal 3C-SiC films under identical Au ion irradiation to a range of doses at 700 K. In contrast to the latter, in which lattice disorder is accumulated to a saturation level without full amorphization, the average grain size of the former increases with dose following a power-law trend. In addition to coalescence, the grain grows through atomic jumps and mass transport, where irradiation induced vacancies at grain boundaries assist the processes. It is found that a higher irradiation temperature leads to slower grain growth and a faster approach to a saturation size of SiC nanograins. The results could potentially have a positive impact on structural components of advanced nuclear energy systems.

  14. Size-dependent resistivity and thermopower of nanocrystalline copper

    Science.gov (United States)

    Okram, Gunadhor S.; Kaurav, Netram

    2011-07-01

    Nanocrystalline copper (NC-Cu) of average particle size (D) ranging from 29 to 55 nm was prepared using the polyol method. The compacted pellets of these nanoparticles were investigated using electrical resistivity (ρn) and thermopower (Sn) measurements in the temperature range from 5 to 300 K. The observed electrical resistivity and thermopower data for all the samples are typical of a good metal and the ρn(T) data are analyzed in the framework of the Bloch-Grüneisen theory. Our analysis indicates systematic departure from the bulk property for NC-Cu samples, decreasing effective Debye temperature, exponential decay of both the residual resistivity ratio (RRR) and the temperature coefficient of resistivity [α = (1/ρ)dρ/dT] as D decreases, yet the Boltzmann theory of electron transport still holds true (kFl ≫ 1). Further, the validity of the Nordheim-Gorter rule is also discussed. The temperature dependence of Sn is found to be quite sensitive as compared to bulk thermopower SBulk behavior, revealing the evolution of Sn and exhibiting a significant enhancement of the phonon drag peak as D decreases. The present findings overall suggest the significant influence of the grain boundaries, surface atoms, and phonon confinement.

  15. Studies of methods to restrict the grain growth of nanocrystalline metal oxides

    CERN Document Server

    Al-Angari, Y

    2002-01-01

    There is considerable interest in nanocrystalline materials. This thesis is concerned with nanocrystalline oxides and the development of methods to prevent their grain growth on heating. This growth, which is evident at temperatures as low as 400 deg C, presents a serious problem in the study and applications of nanocrystalline oxides. The systems that were studied were nanocrystalline magnesium oxide, zirconium oxide, cerium oxide and tin oxide. The methods of preventing grain growth included the encapsulation of the oxide in the pores of porous silica, mixing with nanocrystals of alumina and treating the surface with a silanising agent, hexamethyldisilazane. All the methods employed showed some effect on reducing the grain growth. Encapsulation in the pores of silica was effective, however it proved difficult to get large amounts of the oxides into the pores. A more efficient method of preparing large samples was the incorporation of alumina, which was achieved by a sol-gel process. An alkoxide of the targe...

  16. Shear-Coupled Grain Growth and Texture Development in a Nanocrystalline Ni-Fe Alloy during Cold Rolling

    Science.gov (United States)

    Li, Li; Ungár, Tamás; Toth, Laszlo S.; Skrotzki, Werner; Wang, Yan Dong; Ren, Yang; Choo, Hahn; Fogarassy, Zsolt; Zhou, X. T.; Liaw, Peter K.

    2016-12-01

    The evolution of texture, grain size, grain shape, dislocation, and twin density has been determined by synchrotron X-ray diffraction and line profile analysis in a nanocrystalline Ni-Fe alloy after cold rolling along different directions related to the initial fiber and the long axis of grains. The texture evolution has been simulated by the Taylor-type relaxed-constraints viscoplastic polycrystal model. The simulations were based on the activity of partial dislocations in correlation with the experimental results of dislocation density determination. The concept of stress-induced shear coupling is supported and strengthened by both the texture simulations and the experimentally determined evolution of the microstructure parameters. Grain growth and texture evolution are shown to proceed by the shear coupling mechanism supported by dislocation activity as long as the grain size is not smaller than about 20 nm.

  17. Grain boundary resistance to amorphization of nanocrystalline silicon carbide

    Science.gov (United States)

    Chen, Dong; Gao, Fei; Liu, Bo

    2015-11-01

    Under the C displacement condition, we have used molecular dynamics simulation to examine the effects of grain boundaries (GBs) on the amorphization of nanocrystalline silicon carbide (nc-SiC) by point defect accumulation. The results show that the interstitials are preferentially absorbed and accumulated at GBs that provide the sinks for defect annihilation at low doses, but also driving force to initiate amorphization in the nc-SiC at higher doses. The majority of surviving defects are C interstitials, as either C-Si or C-C dumbbells. The concentration of defect clusters increases with increasing dose, and their distributions are mainly observed along the GBs. Especially these small clusters can subsequently coalesce and form amorphous domains at the GBs during the accumulation of carbon defects. A comparison between displacement amorphized nc-SiC and melt-quenched single crystal SiC shows the similar topological features. At a dose of 0.55 displacements per atom (dpa), the pair correlation function lacks long range order, demonstrating that the nc-SiC is fully amorphilized.

  18. Micromechanical modelling of nanocrystalline and ultrafine grained metals: A short overview

    DEFF Research Database (Denmark)

    Mishnaevsky, Leon; Levashov, Evgeny

    2015-01-01

    An overview of micromechanical models of strength and deformation behaviour of nanostructured and ultrafine grained metallic materials is presented. Composite models of nanomaterials, polycrystal plasticity based models, grain boundary sliding, the effect of non-equilibrium grain boundaries...... and nanoscale properties are discussed and compared. The examples of incorporation of peculiar nanocrystalline effects (like large content of amorphous or semi-amorphous grain boundary phase, partial dislocation GB emission/glide/GB absorption based deformation mechanism, diffusion deformation, etc...

  19. The Effect of Eectronic Energy Loss on Irradiation-Induced Grain Growth in Nanocrystalline Oxides

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yanwen; Aidhy, Dilpuneet S.; Varga, Tamas; Moll, Sandra; Edmondson, P. D.; Namavar, Fereydoon; Jin, Ke; Ostrouchov, Christopher N.; Weber, William J.

    2014-01-01

    Grain growth of nanocrystalline materials is generally thermally activated, but can also be driven by irradiation at much lower temperature. In nanocrystalline ceria and zirconia, contributions from both displacement damage and ionization to the grain growth are identified. Our atomistic simulations have revealed fast grain boundary (GB) movements due to the high density of disorder near GBs. Our experimental results have shown that irradiation-induced grain growth is a function of total energy deposited, where the excitation of target electrons and displacement of lattice atoms both contribute to the overall disorder and both play important roles in grain growth. The coupling of energy deposition to the electronic and lattice structures should both be taken into consideration when engineering nanostructural materials.

  20. Nanocrystalline ceramic materials

    Science.gov (United States)

    Siegel, R.W.; Nieman, G.W.; Weertman, J.R.

    1994-06-14

    A method is disclosed for preparing a treated nanocrystalline metallic material. The method of preparation includes providing a starting nanocrystalline metallic material with a grain size less than about 35 nm, compacting the starting nanocrystalline metallic material in an inert atmosphere and annealing the compacted metallic material at a temperature less than about one-half the melting point of the metallic material. 19 figs.

  1. Improvement of NiTi shape memory actuator performance through ultra-fine grained and nanocrystalline microstructures

    Energy Technology Data Exchange (ETDEWEB)

    Frenzel, Jan; Burow, Juri A.; Payton, Eric J.; Rezanka, Stefan; Eggeler, Gunther [Institut fuer Werkstoffe, Ruhr-Universitaet Bochum, Universitaetsstr. 150, 44801 Bochum (Germany)

    2011-04-15

    Ultra-fine grain sizes have been shown to enhance some key mechanical and functional properties of engineering materials, including shape memory alloys. While the effect of ultra-fine and nanocrystalline grain sizes on pseudoelastic shape memory materials is well-appreciated in medical device engineering, the effect of such microstructures on actuators has not been sufficiently characterized. In the present work, it is demonstrated that NiTi spring actuators with ultra-fine grained microstructures can be obtained by conventional wire drawing in combination with heat treatments and that the final grain size can be controlled by varying the final annealing temperature. Annealing at 400 C for 600 s allows for the evolution of microstructures with median grain sizes of about 34 nm, while annealing at 600 C for the same length of time results in median grain sizes of about 5 {mu}m. It is observed that the grain size strongly affects the elementary processes of the martensitic phase transformation. Small austenite grain sizes inhibit twinning accommodation of transformation strains, such that a higher driving force is required to nucleate martensite. This increase in the martensite nucleation barrier decreases the martensite transformation temperatures such that only partial transformation to martensite is possible upon cooling to room temperature. The incomplete martensitic transformation reduces the exploitable actuator stroke; however, a reduction in grain size is shown to improve the functional stability of the material during thermal and thermomechanical cycling by reducing the irreversible effects of dislocation plasticity. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  2. The vibrational spectrum of the atoms in the grain boundaries of nanocrystalline Pd

    Energy Technology Data Exchange (ETDEWEB)

    Stuhr, U. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Wipf, H.; Hahn, H. [Technische Hochschule Darmstadt (Germany); Natter, H.; Hemperlmann, R. [Universitaet des Saarlandes, Saarbruecken (Germany); Andersen, K. [Institut Max von Laue - Paul Langevin (ILL), 38 - Grenoble (France)

    1997-09-01

    The vibrational excitations of the atoms in nanocrystalline Pd was investigated by neutron-time-of-flight spectroscopy. Hydrogen was used as a probe for the vibrations in the grain boundaries. The separation between the H and Pd vibrations was done by spin analysis. The results show that in the grain boundary the density of states of low energy excitations ({<=}5 meV) is drastically increased. (author) 3 figs., 3 refs.

  3. The influence of temperature and grain boundary volume on the resistivity of nanocrystalline nickel

    Energy Technology Data Exchange (ETDEWEB)

    Darnbrough, J. E., E-mail: J.E.Darnbrough@bristol.ac.uk; Flewitt, P. E. J. [Interface Analysis Centre, School of Physics, University of Bristol, H. H. Wills Physics Laboratory, Tyndall Avenue, Bristol, BS8 1TL (United Kingdom); Roebuck, B. [National Physical Laboratory, Hampton Rd, Teddington, Middlesex, TW11 0LW (United Kingdom)

    2015-11-14

    The thermal stability and modes of recrystallisation of nanocrystalline nickel has been observed through a conduction-based non-destructive test. Resistivity measurements have been utilised to quantify grain boundary volume fraction and microstructure. This observation makes clear the distinction of the factors that contribute to resistivity and demonstrates that these contributions are related to microstructure, either directly or in-directly. In static systems, the contribution of ordered grains and low-order grain boundary atomic arrangements in small grained material has been measured and correlated with resistivity. Measurements of in-situ resistivity conducted at high temperature gives changes with time which are related to grain growth, during heat treatment. This shows that resistivity can be used as a technique for observing the microstructure and grain growth of small grained material.

  4. Influence of grain growth on the structural properties of the nanocrystalline Gd2Ti2O7

    Science.gov (United States)

    Kulriya, P. K.; Yao, Tiankai; Scott, Spencer Michael; Nanda, Sonal; Lian, Jie

    2017-04-01

    The microstructural evolution and grain growth kinetics of the nanocrystalline Gd2Ti2O7 drastically affect its properties and functionalities as thermal barrier coatings and nuclear waste forms for actinide incorporation. Here, we report the synthesis of the dense nano-sized Gd2Ti2O7 by high energy ball milling (HEBM), and spark plasma sintering (SPS), and also investigated the isothermally annealing induced grain coarsening and structural properties variations. As-prepared nano powder (D∼60 nm) by HEBM exhibited an amorphous nature, which was consolidated to a dense single phase crystalline pyrochlore nano-ceramic (D∼120 ± 10 nm) by SPS sintering at 1200 °C. Isothermal annealing was performed at different temperatures (1300 °C - 1500 °C) with holding time varying from 0.5 to 8 h, and the pyrochlore phase is stable with no indication of a transformation into a defect fluorite structure. A rapid initial grain growth was observed which increased with temperature and annealing durations due to the large driving force of the curvature-driven grain coarsening of the nano-ceramics, and grain growth saturates at longer durations. The calculated value of the time constant and activation energy for the nanocrystalline Gd2Ti2O7 were 0.52 ± 0.02 and 240 ± 20 kJ/mol (∼2.48 eV), respectively. The enhanced grain growth kinetics with a lower value of activation energy can be explained by the effect of fast diffusion across the grain boundaries for dense nanoceramics.

  5. INTER-GRAIN EXCHANGE INTERACTION FOR SINGLE-PHASE NANOCRYSTALLINE Nd-Fe-B MAGNETS

    Institute of Scientific and Technical Information of China (English)

    WANG XUE-FENG; JIN HAN-MIN; ZHAO SU-FEN; YAN YU

    2001-01-01

    The demagnetization curve as a function of intensity of the inter-grain exchange interaction was calculated for single-phase nanocrystalline Nd-Fe-B magnets by use of the finite-element technique of micromagnetics. Also,the strength of the exchange interaction was estimated as a function of the Nd content x for the nanocrystalline NdxFe94-xB6 magnets by comparing the above result with the experimental relation between iHc and x for the magnets. We found that the inter-grain exchange interaction decreases with the increase of x, are≈70% and≈60% of the inter-grain exchange interaction for x=15.5(p0 iHc ≈2.0T) and x=19(p0 iHc ≈2.3T), respectively.

  6. The NGDC Seafloor Sediment Grain Size Database

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The NGDC (now NCEI) Seafloor Sediment Grain Size Database contains particle size data for over 17,000 seafloor samples worldwide. The file was begun by NGDC in 1976...

  7. Effect of stress-induced grain growth during room temperature tensile deformation on ductility in nanocrystalline metals

    Indian Academy of Sciences (India)

    Weichang Xu; Pinqiang Dai; Xiaolei Wu

    2010-10-01

    In the present study defect-free nanocrystalline (nc) Ni–Co alloys with the Co content ranging from 2.4–59.3% (wt.%) were prepared by pulse electrodeposition. X-ray diffraction analysis shows that only a single face-centred cubic solid solution is formed for each alloy and that the grain size reduces monotonically with increasing Co content, which is consistent with transmission electron microscopy (TEM) observations. In the nc Ni–Co alloys, both the ultimate tensile strength and the elongation to failure increase as the Co content increases. The TEM observations reveal that stress-induced grain growth during tensile deformation is significantly suppressed for the nc Ni–Co alloys rich in Co in sharp contrast to those poor in Co. We believe that sufficient solutes could effectively pin grain boundaries making grain boundary motions (e.g. grain boundary migration and/or grain rotation) during deformation more difficult. Thus, stress-induced grain growth is greatly suppressed. At the same time, shear banding plasticity instability is correspondingly delayed leading to the enhanced ductility.

  8. Grain-size effects on thermal properties of BaTiO3 ceramics

    Indian Academy of Sciences (India)

    C J Xiao; Z X Li; X R Deng

    2011-07-01

    Dense nanocrystalline BaTiO3 ceramics are successfully prepared by the high pressure assisted sintering. Microstructures are observed by scanning electronic microscopes. The grain sizes are estimated to be about 30 and 150 nm. In comparison, BaTiO3 ceramics with the grain size of 600 nm and 1.5 m are fabricated by conventional pressure-less sintering. The thermal properties of BaTiO3 ceramics with different grain sizes are investigated by differential scanning calorimetry and thermal expansion. The results suggest that the enthalpy values for the tetragonal-cubic transition decreased and the thermal expansion values increased with decreasing grain size. Furthermore, the Curie temperature shifts to lower temperature with decreasing grain size.

  9. Modelling of grain boundary effects in nanocrystalline/multicrystalline silicon heterojunction solar cells

    Science.gov (United States)

    Farrokh-Baroughi, Mahdi; Sivoththaman, Siva

    2006-07-01

    Heterojunction solar cells formed by nanocrystalline silicon films on fine-grained multicrystalline silicon substrates are simulated in the presence of grain boundaries. The effects of grain boundaries on the dark and illuminated current-voltage (I-V) characteristics and spectral response (SR) of heterojunction (HJ) solar cells are assessed using 1D and 2D device simulations. The grain boundary in fine-grained multicrystalline silicon is modelled in two ways: as a defective surface with continuous defect distribution throughout the bandgap, and as a hypothetical sheet with a certain recombination velocity for electrons and holes. The SR and I-V characteristics of HJs are exploited to characterize grain boundary effects on the photovoltaic properties of the solar cells and photodetectors. Simulation results show noticeable differences on the dark I-V and SR of on- and off-grain boundary HJs. Grain boundary effects become important when fine-grained multicrystalline substrates are used. Measurement results of tiny test structures fabricated on the grain boundary show consistently inferior dark I-V and SR characteristics compared to those fabricated away from the grain and allow us to quantify the recombination at the grain boundary.

  10. SEGMENTATION AND GRAIN SIZE OF CERAMICS

    Directory of Open Access Journals (Sweden)

    Xavier Arnould

    2011-05-01

    Full Text Available This paper presents some methods to automatically extract the grain boundaries of materials in order to develop an automatic method to determine the grain size and morphological parameters of ceramic materials. Results are presented in the case of sintered cerine (CeO2 materials.

  11. Deformation in nanocrystalline metals

    OpenAIRE

    Helena Van Swygenhoven; Julia R. Weertman

    2006-01-01

    It is now possible to synthesize polycrystalline metals made up of grains that average less than 100 nm in size. Such nanocrystalline metals contain a significant volume fraction of interfacial regions separated by nearly perfect crystals. The small sizes involved limit the conventional operation of dislocation sources and thus a fundamental question arises: how do these materials deform plastically? We review the current views on deformation mechanisms in nanocrystalline, face-centered cubic...

  12. On tension-compression asymmetry in ultrafine-grained and nanocrystalline metals

    KAUST Repository

    Gurses, Ercan

    2010-12-01

    We present a physically motivated computational study explaining the tension/compression (T/C) asymmetry phenomenon in nanocrystalline (nc) and ultrafine-grained (ufg) face centered cubic (fcc) metals utilizing a variational constitutive model where the nc-metal is modeled as a two-phase material consisting of a grain interior phase and a grain boundary affected zone (GBAZ). We show that the existence of voids and their growth in GBAZ renders the material pressure sensitivity due to porous plasticity and that the utilized model provides a physically sound mechanism to capture the experimentally observed T/C asymmetry in nc- and ufg-metals. © 2010 Elsevier B.V. All rights reserved.

  13. Phenomenological description of grain growth stagnation for nanocrystalline films and powders

    Energy Technology Data Exchange (ETDEWEB)

    Dannenberg, R.; Stach, E.A.; Groza, J.R.

    2000-08-24

    At fixed hold temperatures, grain growth usually stagnates indefinitely after sufficiently long hold times. The change in the growth behavior can be very abrupt, resulting in a sudden plateau in plots of grain size versus time at fixed temperature. Standard grain growth laws do not formally predict the rapid onset of growth stagnation, merely a slow down of grain growth to imperceptible rates. Therefore, the grain size in the plateau regions for long hold times is typically not in agreement with that predicted with kinetic variables derived from the size versus time curves for short hold times where there is pronounced curvature. Standard laws lead to endpoint grain sizes with strong dependences on the hold times. The experimental observation in many cases is a nearly linear temperature dependence that is independent of the hold times after a sufficient duration. Additionally, the growth process may restart from a stagnated state with sufficient temperature increases, where again, the stagnated grain size temperature dependence is linear. For growth laws including size dependent opposing forces, endpoint grain sizes are predicted to be either independent of temperature, or exponentially temperature dependent with thermodynamic reversibility, the latter an impossibility. We derive, heuristically, a stagnation force, phenomenologically incorporating these observations: a near linear temperature dependence of endpoint grain sizes, and irreversible growth. This description reduces to standard laws commonly used for data fitting, and leads to a normal grain size distribution. Other laws are discussed and compared. Fits to size versus time data are successfully made.

  14. Dislocation Dynamics in Nanocrystalline Nickel

    OpenAIRE

    Shan, Z. W.; Wiezorek, J. M. K.; Stach, E. A.; Follstaedt, D. M.; Knapp, J. A.; Mao, S. X.

    2007-01-01

    It is believed that the dynamics of dislocation processes during the deformation of nanocrystalline materials can only be visualized by computational simulations. Here we demonstrate that observations of dislocation processes during the deformation of nanocrystalline Ni with grain sizes as small as 10 nm can be achieved by using a combination of in situ tensile straining and high-resolution transmission electron microscopy. Trapped unit lattice dislocations are observed in strained grains...

  15. Deformation of nanocrystalline binary aluminum alloys with segregation of Mg, Co and Ti at grain boundaries

    Science.gov (United States)

    Zinovev, A. V.; Bapanina, M. G.; Babicheva, R. I.; Enikeev, N. A.; Dmitriev, S. V.; Zhou, K.

    2017-01-01

    The influence of the temperature and sort of alloying element on the deformation of the nanocrystalline (NC) binary Al alloys with segregation of 10.2 at % Ti, Co, or Mg over grain boundaries has been studied using the molecular dynamics. The deformation behavior of the materials has been studied in detail by the simulation of the shear deformation of various Al bicrystals with the grain-boundary segregation of impurity atoms, namely, Ti, Co, or Mg. The deformation of bicrystals with different grain orientation has been studied. It has been found that Co introduction into grain boundaries of NC Al has a strengthening effect due to the deceleration of the grain-boundary migration (GBM) and difficulty in the grain-boundary sliding (GBS). The Mg segregation at the boundaries greatly impedes the GBM, but stimulates the development of the GBS. In the NC alloy of Al-Ti, the GBM occurs actively, and the flow-stress values are close to the values characteristic of pure Al.

  16. The effect of temperature and stress on creep behavior of ultrafine grained nanocrystalline Ni-3 at% Zr alloy

    Science.gov (United States)

    Meraj, Md.; Pal, Snehanshu

    2017-02-01

    In this paper, molecular dynamics (MD) simulation based study of creep behavior for nanocrystalline (NC) Ni-3 at% Zr alloy having grain size 6 nm has been performed using embedded atom method (EAM) potential to study the influence of variation of temperature (1220-1450 K) as well as change in stress (0.5-1.5 GPa) on creep behavior. All the simulated creep curves for this ultra-fine grained NC Ni-Zr alloy has extensive tertiary creep regime. Primary creep regime is very short and steady state creep part is almost absent. The effect of temperatures and stress is prominent on the nature of the simulated creep curves and corresponding atomic configurations. Additionally, mean square displacement calculation has been performed at 1220 K, 1250 K, 1350 K, and 1450 K temperatures to correlate the activation energy of atomic diffusion and creep. The activation energy of creep process found to be less compared to activation energies of self-diffusion for Ni and Zr in NC Ni-3 at% Zr alloy. Formation of martensite is identified during creep process by common neighbour analysis. Presence of dislocations is observed only in primary regime of creep curve up till 20 ps, as evident from calculated dislocation density through MD simulations. Coble creep is found to be main operative mechanism for creep deformation of ultrafine grained NC Ni-3 at% Zr alloy.

  17. Intergranular fracture in nanocrystalline metals

    Science.gov (United States)

    Farkas, D.; van Swygenhoven, H.; Derlet, P. M.

    2002-08-01

    Crack propagation studies in nanocrystalline Ni samples with mean grain sizes ranging from 5 to 12 nm are reported using atomistic simulations. For all grain sizes pure intergranular fracture is observed. Intergranular fracture is shown to proceed by the coalescence of microvoids formed at the grain boundaries ahead of the crack. The energy released during propagation is higher than the Griffith value, indicating an additional grain-boundary accommodation mechanism.

  18. Structural and magnetic properties of bulk nanocrystalline Erbium metal

    Directory of Open Access Journals (Sweden)

    Ming Yue

    2011-06-01

    Full Text Available Bulk nanocrystalline Erbium metals were prepared via Spark Plasma Sintering (SPS and subsequent annealing process. The nanocrystalline Er metals have the same hexagonal close packed structure as that of coarse-grained sample. Decrease in grain size results in remarkable changes in the three magnetic ordering temperatures of the nanocrystalline Er metal. At 5 K, the magnetization drops by 10.9%, while the coercivity increases by 4 times for nanocrystalline Er compared with those of coarse-grained sample. These results indicate the remarkable influence of the nanostructure on the magnetism of Er due to finite size effect.

  19. The Effect Of Grain Size On The Mechanical Properties Of Aluminum

    Directory of Open Access Journals (Sweden)

    Jeong G.

    2015-06-01

    Full Text Available Although many studies have focused on the unique plastic deformation behavior of nanocrystalline aluminum (e.g., the positive deviation from Hall-Petch relation, the unusual yield-drop phenomenon in tensile mode, etc., the data reported by different research groups are inconsistent with each other, possibly because of different fabrication processes. In this study, aluminum samples with a wide grain-size spectrum – from a few micrometers down to 100 nanometers – are manufactured by powder metallurgy. The grain size was measured by X-ray diffraction analysis and transmission electron microscope observation. Furthermore, the tensile behavior, which varied according to a grain size, is discussed with a comparison of the theoretical models.

  20. Grain size dependent mechanical properties in nanophase materials

    Energy Technology Data Exchange (ETDEWEB)

    Siegel, R.W. [Argonne National Lab., IL (United States); Fougere, G.E. [Northwestern Univ., Evanston, IL (United States). Dept. of Materials Science and Engineering

    1995-02-01

    It has become possible in recent years to synthesize metals and ceramics under well controlled conditions with constituent grain structures on a manometer size scale (below 100 nm). These new materials have mechanical properties that are strongly grain-size dependent and often significantly different than those of their coarser grained counterparts. Nanophase metals tend to become stronger and ceramics are more easily deformed as grain size is reduced. The observed mechanical property changes appear to be related primarily to grain size limitations and the large percentage of atoms in grain boundary environments. A brief overview of our present knowledge about the grain-size dependent mechanical properties of nanophase materials is presented.

  1. Molecular dynamics simulation of thermal stability of nanocrystalline vanadium

    Institute of Scientific and Technical Information of China (English)

    WEI; Mingzhi; XIAO; Shifang; YUAN; Xiaojian; HU; Wangyu

    2006-01-01

    The microstructure and thermal stability of nanocrystalline vanadium with an average grain size ranging from 2.86 to 7.50 nm are calculated by means of the analytic embedded-atom method and molecular dynamics. The grain boundary and nanocrystalline grain atoms are differentiated by the common neighbor analysis method. The results indicate that the fraction of grain boundary increases with the grain size decreasing, and the mean energy of atoms is higher than that of coarse crystals. The thermal-stable temperatures of nanocrystalline vanadium are determined from the evolution of atomic energy, fraction of grain boundary and radial distribution function. It is shown that the stable temperature decreases obviously with the grain size decreasing. In addition the reasons which cause the grain growth of nanocrystalline vanadium are discussed.

  2. Deformation Twinning During Nanoindentation of Nanocrystalline Ta

    OpenAIRE

    Wang, Y. M.; Hodge, A. M.; Biener, J.; Hamza, A.V.; Barnes, D E; Liu, Kai; Nieh, T. G.

    2005-01-01

    The deformation mechanism of body-centered cubic (bcc) nanocrystalline tantalum with grain sizes of 10–30 nm is investigated by nanoindentation, scanning electron microscopy and high-resolution transmission electron microscopy. In a deviation from molecular dynamics simulations and existing experimental observations on other bcc nanocrystalline metals, the plastic deformation of nanocrystalline Ta during nanoindentation is controlled by deformation twinning. The observation of multiple twin i...

  3. Superplasticity and cooperative grain boundary sliding in nanocrystalline Ni{sub 3}Al

    Energy Technology Data Exchange (ETDEWEB)

    Mara, N.A. [Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)], E-mail: namara@lanl.gov; Sergueeva, A.V.; Mara, T.D. [Materials Science Division, University of California, Davis, One Shields Avenue, Davis, CA 95616 (United States); McFadden, S.X. [Sandia Laboratories, Livermore, CA 94550 (United States); Mukherjee, A.K. [Materials Science Division, University of California, Davis, One Shields Avenue, Davis, CA 95616 (United States)

    2007-08-15

    Cooperative grain boundary sliding (CGBS) has been shown to account for the majority of macroscopic strain seen in microcrystalline metallic systems undergoing superplastic deformation. While CGBS has been observed on the surface of microcrystalline samples deforming superplastically through the shifting of diamond scribe lines, there have been few transmission electron microscopy results showing such occurrences in the bulk of the material, or the details behind the micromechanism of CGBS. In this work, nanocrystalline Ni{sub 3}Al produced via high-pressure torsion is deformed superplastically in the electron microscope. High-temperature ({approx}700 deg. C) in situ tensile testing shows the nature of CGBS at the nanoscale through direct observation of this phenomenon.

  4. Molecular dynamics investigation of the grain boundary migration hysteresis of nanocrystalline Ni under cyclic shear loading

    Science.gov (United States)

    Wang, Peng; Yang, Xinhua; Peng, Di

    2017-02-01

    The deformation behavior and grain boundary (GB) response of nanocrystalline Ni under cyclic shear loading are investigated by molecular dynamics simulations. The GB migration hysteresis phenomenon, in which the GB migration displacement lags behind the change in nominal shear strain, is observed in the symmetric tilt GBs for the first time. The elementary structure transformation occurring at the two end segments of the observed GB during GB migration produces a disordered and irreversible state, while the transformation in the middle segment is reversible. Both dislocation retraction and nucleation occur during unloading. Relatively large cyclic strain amplitudes lead to disordered GB segments of greater length, such that the residual GB migration displacement increases with increasing cyclic amplitude. GB migration hysteresis vanishes after the GB becomes immobile owing to a cyclic shear induced transition to a disordered state along its entire length.

  5. [Methods for grain size analysis of nanomedicines].

    Science.gov (United States)

    Geng, Zhi-Wang; He, Lan; Zhang, Qi-Ming; Yang, Yong-Jian

    2012-07-01

    As nanomedicines are developing fast in both academic and market areas, building up suitable methods for nanomedicine analysis with proper techniques is an important subject, requiring further research. The techniques, which could be employed for grain size analysis of nanomedicines, were reviewed. Several key techniques were discussed with their principles, scope of applications, advantages and defects. Their applications to nanomedine analysis were discussed according to the properties of different nanomedicines, with the purpose of providing some suggestions for the control and administration of nanomedicines.

  6. Paleowattmeters: A scaling relation for dynamically recrystallized grain size

    Science.gov (United States)

    Austin, Nicholas J.; Evans, Brian

    2007-04-01

    During dislocation creep, mineral grains often evolve to a stable size, dictated by the deformation conditions. We suggest that grain-size evolution during deformation is determined by the rate of mechanical work. Provided that other elements of microstructure have achieved steady state and that the dissipation rate is roughly constant, then changes in internal energy will be proportional to changes in grain-boundary area. If normal grain-growth and dynamic grain-size reduction occur simultaneously, then the steady-state grain size is determined by the balance of those rates. A scaling model using these assumptions and published grain-growth and mechanical relations matches stress grain-size relations for quartz and olivine rocks with no fitting. For marbles, the model also explains scatter not rationalized by assuming that recrystallized grain size is a function of stress alone. When extrapolated to conditions typical for natural mylonites, the model is consistent with field constraints on stresses and strain rates.

  7. Grain-size sorting and slope failure in experimental subaqueous grain flows

    NARCIS (Netherlands)

    Kleinhans, M.G.; Asch, Th.W.J. van

    2005-01-01

    Grain-size sorting in subaqueous grain flows of a continuous range of grain sizes is studied experimentally with three mixtures. The observed pattern is a combination of stratification and gradual segregation. The stratification is caused by kinematic sieving in the grain flow. The segregation is

  8. Grain-size sorting and slope failure in experimental subaqueous grain flows

    NARCIS (Netherlands)

    Kleinhans, M.G.; Asch, Th.W.J. van

    2005-01-01

    Grain-size sorting in subaqueous grain flows of a continuous range of grain sizes is studied experimentally with three mixtures. The observed pattern is a combination of stratification and gradual segregation. The stratification is caused by kinematic sieving in the grain flow. The segregation is ca

  9. Structure and thermal stability of nanocrystalline materials

    Indian Academy of Sciences (India)

    B S Murty; M K Datta; S K Pabi

    2003-02-01

    Nanocrystalline materials, which are expected to play a key role in the next generation of human civilization, are assembled with nanometre-sized “building blocks” consisting of the crystalline and large volume fractions of intercrystalline components. In order to predict the unique properties of nanocrystalline materials, which are a combination of the properties of the crystalline and intercrystalline regions, it is essential to understand precisely how the structures of crystalline and intercrystalline regions vary with decrease in crystallite size. In addition, study of the thermal stability of nanocrystalline materials against significant grain growth is both scientific and technological interest. A sharp increase in grain size (to micron levels) during consolidation of nanocrystalline powders to obtain fully dense materials may consequently result in the loss of some unique properties of nanocrystalline materials. Therefore, extensive interest has been generated in exploring the size effects on the structure of crystalline and intercrystalline region of nanocrystalline materials, and the thermal stability of nanocrystalline materials against significant grain growth. The present article is aimed at understanding the structure and stability of nanocrystalline materials.

  10. Deformation in nanocrystalline metals

    Directory of Open Access Journals (Sweden)

    Helena Van Swygenhoven

    2006-05-01

    Full Text Available It is now possible to synthesize polycrystalline metals made up of grains that average less than 100 nm in size. Such nanocrystalline metals contain a significant volume fraction of interfacial regions separated by nearly perfect crystals. The small sizes involved limit the conventional operation of dislocation sources and thus a fundamental question arises: how do these materials deform plastically? We review the current views on deformation mechanisms in nanocrystalline, face-centered cubic metals based on insights gained by atomistic computer simulations. These insights are discussed with reference to recent striking experimental observations that can be compared with predictions made by the simulations.

  11. Size-induced enhancement of bulk modulus and transition pressure of nanocrystalline Ge

    DEFF Research Database (Denmark)

    Wang, Hua; Liu, J.F.; He, Yongqi;

    2007-01-01

    In situ energy dispersive X-ray diffraction measurements with synchrotron radiation source have been performed on nanocrystalline Ge with particle sizes 13, 49 and 100 nm by using diamond anvil cell. Whereas the percentage volume collapse at the transition is almost constant, the values of the bulk...

  12. An Investigation on Hall-Petch Relationship in Electrodeposited Nanocrystalline Cu-Ni-P Alloys

    Institute of Scientific and Technical Information of China (English)

    Haiqing Sun; Yinong Shi

    2009-01-01

    Nanocrystalline Cu-Ni-P alloys with average grain sizes of 7, 10 and 24 nm were synthesized by means of electrodeposition.The grain size dependences of tensile strength and hardness of the nanocrystalline Cu alloys were investigated.The breakdown of Hall-Perch relation was exhibited in both tensile strength and hardness.

  13. A maximum in the strength of nanocrystalline copper

    DEFF Research Database (Denmark)

    Schiøtz, Jakob; Jacobsen, Karsten Wedel

    2003-01-01

    We used molecular dynamics simulations with system sizes up to 100 million atoms to simulate plastic deformation of nanocrystalline copper. By varying the grain size between 5 and 50 nanometers, we show that the flow stress and thus the strength exhibit a maximum at a grain size of 10 to 15...... nanometers. This maximum is because of a shift in the microscopic deformation mechanism from dislocation-mediated plasticity in the coarse-grained material to grain boundary sliding in the nanocrystalline region. The simulations allow us to observe the mechanisms behind the grain-size dependence...

  14. Complete grain boundaries from incomplete EBSD maps: the influence of segmentation on grain size determinations

    Science.gov (United States)

    Heilbronner, Renée; Kilian, Ruediger

    2017-04-01

    Grain size analyses are carried out for a number of reasons, for example, the dynamically recrystallized grain size of quartz is used to assess the flow stresses during deformation. Typically a thin section or polished surface is used. If the expected grain size is large enough (10 µm or larger), the images can be obtained on a light microscope, if the grain size is smaller, the SEM is used. The grain boundaries are traced (the process is called segmentation and can be done manually or via image processing) and the size of the cross sectional areas (segments) is determined. From the resulting size distributions, 'the grain size' or 'average grain size', usually a mean diameter or similar, is derived. When carrying out such grain size analyses, a number of aspects are critical for the reproducibility of the result: the resolution of the imaging equipment (light microscope or SEM), the type of images that are used for segmentation (cross polarized, partial or full orientation images, CIP versus EBSD), the segmentation procedure (algorithm) itself, the quality of the segmentation and the mathematical definition and calculation of 'the average grain size'. The quality of the segmentation depends very strongly on the criteria that are used for identifying grain boundaries (for example, angles of misorientation versus shape considerations), on pre- and post-processing (filtering) and on the quality of the recorded images (most notably on the indexing ratio). In this contribution, we consider experimentally deformed Black Hills quartzite with dynamically re-crystallized grain sizes in the range of 2 - 15 µm. We compare two basic methods of segmentations of EBSD maps (orientation based versus shape based) and explore how the choice of methods influences the result of the grain size analysis. We also compare different measures for grain size (mean versus mode versus RMS, and 2D versus 3D) in order to determine which of the definitions of 'average grain size yields the

  15. Formation of nanocrystalline during flash welding of 0Cr16Ni22Mo2Ti steel

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A nanocrystalline layer was fabricated in bond area of 0Cr16Ni22Mo2Ti austenite steel using flash welding. The mean grain size near bond line is about 20 nm, and the farther the distance from bond line, the larger the size of the nanocrystalline. The thickness of the nanocrystalline layer is about 50 mm. The formation mechanism of the nanocry- stalline may be that the metal in semisolid state is deformed severely and its solid grains are fragmented.

  16. Nanocrystalline, ultra-degradation-resistant zirconia: its grain boundary nanostructure and nanochemistry.

    Science.gov (United States)

    Matsui, Koji; Yoshida, Hidehiro; Ikuhara, Yuichi

    2014-04-23

    Y2O3-stabilized tetragonal ZrO2 polycrystal (Y-TZP) has been known to be an excellent structural material with high strength and toughness since the pioneering study by Garvie et al. in 1975. However, Y-TZP is not considered an environmental or biomedical material because it undergoes an inherent tetragonal-to-monoclinic (T → M) phase transformation in humid or aqueous environment, which leads to premature failure, so-called low-temperature degradation (LTD). In this study, we demonstrate for the first time that this fatal shortcoming of Y-TZP can be resolved by controlling the grain boundary nanostructure and chemical composition distribution in Y-TZP. Nanocrystalline Y-TZP doped with Al(3+) and Ge(4+) ions exhibits no LTD for more than 4 years in hot water at 140 °C, whereas 70% of the tetragonal phase in conventional TZP transforms to the monoclinic phase within only 15 h. This innovative Y-TZP can be fabricated by pressureless sintering at 1200 °C; far below the sintering temperature for conventional Y-TZP. The developed TZP ceramics will be useful in numerous environmental-proofing applications, particularly in the biomedical engineering field.

  17. Nanocrystalline, Ultra-Degradation-Resistant Zirconia: Its Grain Boundary Nanostructure and Nanochemistry

    Science.gov (United States)

    Matsui, Koji; Yoshida, Hidehiro; Ikuhara, Yuichi

    2014-04-01

    Y2O3-stabilized tetragonal ZrO2 polycrystal (Y-TZP) has been known to be an excellent structural material with high strength and toughness since the pioneering study by Garvie et al. in 1975. However, Y-TZP is not considered an environmental or biomedical material because it undergoes an inherent tetragonal-to-monoclinic (T-->M) phase transformation in humid or aqueous environment, which leads to premature failure, so-called low-temperature degradation (LTD). In this study, we demonstrate for the first time that this fatal shortcoming of Y-TZP can be resolved by controlling the grain boundary nanostructure and chemical composition distribution in Y-TZP. Nanocrystalline Y-TZP doped with Al3+ and Ge4+ ions exhibits no LTD for more than 4 years in hot water at 140°C, whereas 70% of the tetragonal phase in conventional TZP transforms to the monoclinic phase within only 15 h. This innovative Y-TZP can be fabricated by pressureless sintering at 1200°C far below the sintering temperature for conventional Y-TZP. The developed TZP ceramics will be useful in numerous environmental-proofing applications, particularly in the biomedical engineering field.

  18. Nanocrystalline, Ultra-Degradation-Resistant Zirconia: Its Grain Boundary Nanostructure and Nanochemistry

    Science.gov (United States)

    Matsui, Koji; Yoshida, Hidehiro; Ikuhara, Yuichi

    2014-01-01

    Y2O3-stabilized tetragonal ZrO2 polycrystal (Y-TZP) has been known to be an excellent structural material with high strength and toughness since the pioneering study by Garvie et al. in 1975. However, Y-TZP is not considered an environmental or biomedical material because it undergoes an inherent tetragonal-to-monoclinic (T→M) phase transformation in humid or aqueous environment, which leads to premature failure, so-called low-temperature degradation (LTD). In this study, we demonstrate for the first time that this fatal shortcoming of Y-TZP can be resolved by controlling the grain boundary nanostructure and chemical composition distribution in Y-TZP. Nanocrystalline Y-TZP doped with Al3+ and Ge4+ ions exhibits no LTD for more than 4 years in hot water at 140°C, whereas 70% of the tetragonal phase in conventional TZP transforms to the monoclinic phase within only 15 h. This innovative Y-TZP can be fabricated by pressureless sintering at 1200°C; far below the sintering temperature for conventional Y-TZP. The developed TZP ceramics will be useful in numerous environmental-proofing applications, particularly in the biomedical engineering field. PMID:24755733

  19. Evolution of the microstructure in nanocrystalline copper electrodeposits during room temperature storage

    DEFF Research Database (Denmark)

    Pantleon, Karen; Somers, Marcel A. J.

    2007-01-01

    and continued with an unprecedented time resolution until stationary values of the recorded data were obtained. Independent of the copper layer thickness, the as-deposited microstructure consisted of nanocrystalline grains with orientation dependent crystallite sizes. Orientation dependent grain growth...

  20. Molecular Dynamics Simulation of Microstructure of Nanocrystalline Copper

    Institute of Scientific and Technical Information of China (English)

    WEN Yu-Hua; ZHOU Fu-Xin; LIU Yue-Wu

    2001-01-01

    The microstructure of computer generated nanocrystalline coppers is simulated by using molecular dynamics with the Finnis-Sinclair potential, analysed by means of radial distribution functions, coordination number, atomic energy and local crystalline order. The influence of the grain size on the nanocrystalline structure is studied.The results reveal that as the grain size is reduced, the grain boundary shows no significant structural difference,but the grain interior becomes more disordered, and their structural difference diminishes gradually; however,the density and the atomic average energy of the grain boundary present different tendencies from those of the grain interior.

  1. Prediction of HAZ grain size in welding of ultra fine grained steel with different parameters

    Institute of Scientific and Technical Information of China (English)

    Zhao Hongyun; Zhang Hongtao; Li Dongqing; Wang Guodong

    2010-01-01

    The temperature field and thermal cycling curve in the heat-affected zone during welding 400 MPa ultra fine grained steel by plasma arc were simulated using finite element method.The principle of grain growth kinetics was used to predict the grain size in the heat-affected zone under different welding parameters.The simulation results show that the growing tendency of HAZ grain could be controlled by adjusting the welding parameters,but the growth of HAZ grain could not be eliminated at all.The HAZ grain size became small with increasing of the cooling rate and added with increasing of welding current,arc voltage and welding speed.

  2. Size modification of recent pollen grains under different treatments

    NARCIS (Netherlands)

    Reitsma, Tj.

    1969-01-01

    The effect of various chemicals on the size of recent pollen grains of Corylus avellana L. and Quercus robur L. was studied. The size of acetolysed grains was affected by the treatment prior to acetolysis and moreover by the duration of acetolysis. Preparation methods, which produce comparable sizes

  3. Size modification of recent pollen grains under different treatments

    NARCIS (Netherlands)

    Reitsma, Tj.

    1969-01-01

    The effect of various chemicals on the size of recent pollen grains of Corylus avellana L. and Quercus robur L. was studied. The size of acetolysed grains was affected by the treatment prior to acetolysis and moreover by the duration of acetolysis. Preparation methods, which produce comparable sizes

  4. Surface structures of cerium oxide nanocrystalline particles from the size dependence of the lattice parameters

    Science.gov (United States)

    Tsunekawa, S.; Ito, S.; Kawazoe, Y.

    2004-10-01

    Cerium oxide nanocrystalline particles are synthesized and monodispersed in the size range from 2 to 8nm in diameter. The dependence of the lattice parameters on particle size is obtained by x-ray and electron diffraction analyses. The size dependence well coincides with the estimation based on the assumption that the surface is composed of one layer of Ce2O3 and the inside consists of CeO2. The effect of particle size on lattice parameters is discussed from the differences in the fabrication method and the surface structure.

  5. Corrosion resistance of nanocrystalline nickel prepared by pulse electrodeposition%脉冲电沉积纳米晶体镍的耐蚀性能

    Institute of Scientific and Technical Information of China (English)

    巴志新; 陈永安; 何征字; 钱小立; 王章忠

    2012-01-01

    Nanocrystalline nickels with different grain size were prepared by pulse electrodeposition, and corrosion behavior of coarsed- grained nickel and nanocrystalline nickel in 10% HC1 solution and 20% NaOH solution was studied respectively by soak method and electrochemical polarization method. The results show that the corrosion resistance of nanocrystalline nickel is worse than that of coarse- grained Ni in HC1 solutions, and with grain size decreasing the corrosion rate of nanocrystalline nickel increases. The active dissolution of Ni is the main corrosion mechanism. In NaOH solution, nanocrystalline nickel present the better corrosion resistance than coarsed-grained nickel, and with grain size decreasing the corrosion rate of nanocrystalline nickel decreases. The existing passivation film is the main reason to improve the corrosion resistance of nanoerystalline nickel.

  6. MODELING NANOCRYSTALLINE GRAIN GROWTH DURING THE PULSED ELECTRODEPOSITION OF GOLD-COPPER

    Energy Technology Data Exchange (ETDEWEB)

    Jankowski, A F

    2005-10-27

    The process parameters of current density, pulse duration, and cell potential affect both the structure and composition of electrodeposits. The mechanism for nucleation and growth as determined from current transients yield relationships for nucleus density and nucleation rate. To develop an understanding of the role of the process parameters on grain size, as a design structural parameter to control strength for example, a formulation is presented to model the affects of the deposition energy on grain size and morphology. An activation energy for the deposition process is modeled that reveals different growth mechanisms, wherein nucleation and diffusion effects are each dominant as dependent upon pulse duration. A diffusion coefficient common for each of the pulsed growth modes demarcates an observed transition in growth from smooth to rough surfaces.

  7. Surface Energy in Nanocrystalline Carbon Thin Films: Effect of Size Dependence and Atmospheric Exposure.

    Science.gov (United States)

    Kumar, Manish; Javid, Amjed; Han, Jeon Geon

    2017-03-14

    Surface energy (SE) is the most sensitive and fundamental parameter for governing the interfacial interactions in nanoscale carbon materials. However, on account of the complexities involved of hybridization states and surface bonds, achieved SE values are often less in comparison with their theoretical counterparts and strongly influenced by stability aspects. Here, an advanced facing-target pulsed dc unbalanced magnetron-sputtering process is presented for the synthesis of undoped and H/N-doped nanocrystalline carbon thin films. The time-dependent surface properties of the undoped and H/N-doped nanocrystalline carbon thin films are systematically studied. The advanced plasma process induced the dominant deposition of high-energy neutral carbon species, consequently controlling the intercolumnar spacing of nanodomain morphology and surface anisotropy of electron density. As a result, significantly higher SE values (maximum = 79.24 mJ/m(2)) are achieved, with a possible window of 79.24-66.5 mJ/m(2) by controlling the experimental conditions. The intrinsic (size effects and functionality) and extrinsic factors (atmospheric exposure) are resolved and explained on the basis of size-dependent cohesive energy model and long-range van der Waals interactions between hydrocarbon molecules and the carbon surface. The findings anticipate the enhanced functionality of nanocrystalline carbon thin films in terms of selectivity, sensitivity, and stability.

  8. Self-healing properties of nanocrystalline materials: a first-principles analysis of the role of grain boundaries.

    Science.gov (United States)

    Xu, Jian; Liu, Jian-Bo; Li, Shun-Ning; Liu, Bai-Xin; Jiang, Yong

    2016-07-21

    Understanding the self-healing mechanisms of defects in nanocrystalline materials is of particular importance for developing structural materials that can support the extended lifetime of components under extremely hostile conditions in nuclear reactors. Since grain boundaries are prevalent in nanocrystalline materials, they must affect, to some extent, the overall self-healing properties and the resultant mechanical responses. In the present work, first principles calculations are carried out to investigate the energetic landscape of point defects (i.e. self-interstitials, He-interstitials, and vacancies) induced by the irradiation damage and the kinetics of the self-healing process in the vicinity of grain boundaries (GBs) in copper, focusing on six symmetric tilt grain boundaries that vary in their energies. Our results indicate that the interaction of vacancies with the self-interstitial- and He-interstitial-loaded GBs is very sensitive to the GB character. Low-energy GBs are generally accompanied by a higher propensity for self-healing behavior, in which the inter-granular interstitials and intra-granular vacancies recombine with each other. The recombination process is proved to be regulated by two mechanisms: the interstitial emission mechanism and the vacancy mediated mechanism. For low-energy GBs, the former mechanism demonstrates its efficiency in describing the atomic motion, while for the high-energy ones, the latter turns out to be superior. With the aid of these mechanisms, we conclude that low-energy GBs are comparatively more radiation-resistant than the high-energy counterparts, which may shed light on the rational design of high-performance structural materials based on nanocrystalline alloys.

  9. Austenite and ferrite grain size evolution in plain carbon steel

    Energy Technology Data Exchange (ETDEWEB)

    Militzer, M.; Giumelli, A.; Hawbolt, E.B.; Meadowcroft, T.R. [British Columbia Univ., Vancouver, BC (Canada)

    1995-01-01

    Grain size evolution in a 0.17%C, 0.74%Mn plain carbon steel is investigated using a Gleeble 1500 thermomechanical simulator. Austenite grain growth measurements in the temperature range from 900 to 1150{degrees}C have been used to validate the Abbruzzese and Luecke model, which is recommended for simulating grain growth during reheating. For run-out table conditions, the ferrite grain size decreases from 1l{mu}m to 4{mu}m when the cooling rate from the austenite is increased from 1 to 80{degrees}C/s.

  10. Grain dissection as a grain size reducing mechanism during ice microdynamics

    Science.gov (United States)

    Steinbach, Florian; Kuiper, Ernst N.; Eichler, Jan; Bons, Paul D.; Drury, Martin R.; Griera, Albert; Pennock, Gill M.; Weikusat, Ilka

    2017-04-01

    Ice sheets are valuable paleo-climate archives, but can lose their integrity by ice flow. An understanding of the microdynamic mechanisms controlling the flow of ice is essential when assessing climatic and environmental developments related to ice sheets and glaciers. For instance, the development of a consistent mechanistic grain size law would support larger scale ice flow models. Recent research made significant progress in numerically modelling deformation and recrystallisation mechanisms in the polycrystalline ice and ice-air aggregate (Llorens et al., 2016a,b; Steinbach et al., 2016). The numerical setup assumed grain size reduction is achieved by the progressive transformation of subgrain boundaries into new high angle grain boundaries splitting an existing grain. This mechanism is usually termed polygonisation. Analogue experiments suggested, that strain induced grain boundary migration can cause bulges to migrate through the whole of a grain separating one region of the grain from another (Jessell, 1986; Urai, 1987). This mechanism of grain dissection could provide an alternative grain size reducing mechanism, but has not yet been observed during ice microdynamics. In this contribution, we present results using an updated numerical approach allowing for grain dissection. The approach is based on coupling the full field theory crystal visco-plasticity code (VPFFT) of Lebensohn (2001) to the multi-process modelling platform Elle (Bons et al., 2008). VPFFT predicts the mechanical fields resulting from short strain increments, dynamic recrystallisation process are implemented in Elle. The novel approach includes improvements to allow for grain dissection, which was topologically impossible during earlier simulations. The simulations are supported by microstructural observations from NEEM (North Greenland Eemian Ice Drilling) ice core. Mappings of c-axis orientations using the automatic fabric analyser and full crystallographic orientations using electron

  11. The effects of the size of nanocrystalline materials on their thermodynamic and mechanical properties.

    Science.gov (United States)

    Yu, Xiaohua; Zhan, Zhaolin

    2014-01-01

    This work has considered the intrinsic influence of bond energy on the macroscopic, thermodynamic, and mechanical properties of crystalline materials. A general criterion is proposed to evaluate the properties of nanocrystalline materials. The interrelation between the thermodynamic and mechanical properties of nanomaterials is presented and the relationship between the variation of these properties and the size of the nanomaterials is explained. The results of our work agree well with thermodynamics, molecular dynamics simulations, and experimental results. This method is of significance in investigating the size effects of nanomaterials and provides a new approach for studying their thermodynamic and mechanical properties.

  12. The effect of nanocrystalline magnetite size on arsenic removal

    Directory of Open Access Journals (Sweden)

    J.T. Mayo et al

    2007-01-01

    Full Text Available Higher environmental standards have made the removal of arsenic from water an important problem for environmental engineering. Iron oxide is a particularly interesting sorbent to consider for this application. Its magnetic properties allow relatively routine dispersal and recovery of the adsorbent into and from groundwater or industrial processing facilities; in addition, iron oxide has strong and specific interactions with both As(III and As(V. Finally, this material can be produced with nanoscale dimensions, which enhance both its capacity and removal. The objective of this study is to evaluate the potential arsenic adsorption by nanoscale iron oxides, specifically magnetite (Fe3O4 nanoparticles. We focus on the effect of Fe3O4 particle size on the adsorption and desorption behavior of As(III and As(V. The results show that the nanoparticle size has a dramatic effect on the adsorption and desorption of arsenic. As particle size is decreased from 300 to 12 nm the adsorption capacities for both As(III and As(V increase nearly 200 times. Interestingly, such an increase is more than expected from simple considerations of surface area and suggests that nanoscale iron oxide materials sorb arsenic through different means than bulk systems. The desorption process, however, exhibits some hysteresis with the effect becoming more pronounced with small nanoparticles. This hysteresis most likely results from a higher arsenic affinity for Fe3O4 nanoparticles. This work suggests that Fe3O4 nanocrystals and magnetic separations offer a promising method for arsenic removal.

  13. Tensile behavior of nanocrystalline copper

    Energy Technology Data Exchange (ETDEWEB)

    Sanders, P.G.; Weertman, J.R. [Northwestern Univ., Evanston, IL (United States). Dept. of Materials Science and Engineering; Eastman, J.A. [Northwestern Univ., Evanston, IL (United States). Dept. of Materials Science and Engineering]|[Argonne National Lab., IL (United States). Materials Science Div.

    1995-11-01

    High density nanocrystalline copper produced by inert gas condensation was tested in tension. Displacements were measured using foil strain gauges, which greatly improved the accuracy of the strain data. The Young`s modulus of nanocrystalline copper was found to be consistent with that of coarse-grained copper. Total elongations of {approx} 1% were observed in samples with grain sizes less than 50 nm, while a sample with a grain size of 110 nm exhibited more than 10% elongation, perhaps signifying a change to a dislocation-based deformation mechanism in the larger-grained material. In addition, tensile tests were performed as a function of strain rate, with a possible trend of decreased strength and increased elongation as the strain rate was decreased.

  14. Nano-Sized Grain Refinement Using Friction Stir Processing

    Science.gov (United States)

    2013-03-01

    friction stir weld is a very fine grain microstructure produced as a result of dynamic recrystallization. The friction stir ... Friction Stir Processing, Magnesium, Nano-size grains Abstract A key characteristic of a friction stir weld is a very fine grain microstructure...state process developed on the basis of the friction stir welding (FSW) technique invented by The Welding Institute (TWI) in 1991 [2]. During

  15. GRAIN SIZE CONSTRAINTS ON HL TAU WITH POLARIZATION SIGNATURE

    Energy Technology Data Exchange (ETDEWEB)

    Kataoka, Akimasa; Dullemond, Cornelis P [Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, D-69120 Heidelberg (Germany); Muto, Takayuki [Division of Liberal Arts, Kogakuin University, 1-24-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo 163-8677 (Japan); Momose, Munetake; Tsukagoshi, Takashi, E-mail: kataoka@uni-heidelberg.de [College of Science, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512 (Japan)

    2016-03-20

    The millimeter-wave polarization of the protoplanetary disk around HL Tau has been interpreted as the emission from elongated dust grains aligned with the magnetic field in the disk. However, the self-scattering of thermal dust emission may also explain the observed millimeter-wave polarization. In this paper, we report a modeling of the millimeter-wave polarization of the HL Tau disk with the self-polarization. Dust grains are assumed to be spherical and to have a power-law size distribution. We change the maximum grain size with a fixed dust composition in a fixed disk model to find the grain size to reproduce the observed signature. We find that the direction of the polarization vectors and the polarization degree can be explained with the self-scattering. Moreover, the polarization degree can be explained only if the maximum grain size is ∼150 μm. The obtained grain size from the polarization is different from that which has been previously expected from the spectral index of the dust opacity coefficient (a millimeter or larger) if the emission is optically thin. We discuss that porous dust aggregates may solve the inconsistency of the maximum grain size between the two constraints.

  16. Hard-core thinnings of germ-grain models with power-law grain sizes

    CERN Document Server

    Kuronen, Mikko

    2012-01-01

    Random sets with long-range dependence can be generated using a Boolean model with power-law grain sizes. We study thinnings of such Boolean models which have the hard-core property that no grains overlap in the resulting germ-grain model. A fundamental question is whether long-range dependence is preserved under such thinnings. To answer this question we study four natural thinnings of a Poisson germ-grain model where the grains are spheres with a regularly varying size distribution. We show that a thinning which favors large grains preserves the slow correlation decay of the original model, whereas a thinning which favors small grains does not. Our most interesting finding concerns the case where only disjoint grains are retained, which corresponds to the well-known Mat\\'ern type I thinning. In the resulting germ-grain model, typical grains have exponentially small sizes, but rather surprisingly, the long-range dependence property is still present. As a byproduct, we obtain new mechanisms for generating hom...

  17. Grain size effects on He bubbles distribution and evolution

    Energy Technology Data Exchange (ETDEWEB)

    Wang, J. [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); School of Physical Science and Technology, Lanzhou University, Lanzhou 730000 (China); Gao, X.; Gao, N. [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); Wang, Z.G., E-mail: zhgwang@impcas.ac.cn [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); Cui, M.H.; Wei, K.F.; Yao, C.F.; Sun, J.R.; Li, B.S.; Zhu, Y.B.; Pang, L.L. [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); Li, Y.F. [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); School of Physical Science and Technology, Lanzhou University, Lanzhou 730000 (China); Wang, D. [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Xie, E.Q. [School of Physical Science and Technology, Lanzhou University, Lanzhou 730000 (China)

    2015-02-15

    Highlights: • SMAT treated T91 and conventional T91 were implanted by 200 keV He{sup 2+} to 1 × 10{sup 21} He m{sup −2} at room temperature and annealed at 450 °C for 3.5 h. • He bubbles in nanometer-size-grained T91 are smaller in as-implanted case. • The bubbles in the matrix of nanograins were hard to detect and those along the nanograin boundaries coalesced and filled with the grain boundaries after annealing. • Brownian motion and coalescence and Ostwald ripening process might lead to bubbles morphology presented in the nanometer-size-grained T91 after annealing. - Abstract: Grain boundary and grain size effects on He bubble distribution and evolution were investigated by He implantation into nanometer-size-grained T91 obtained by Surface Mechanical Attrition Treatment (SMAT) and the conventional coarse-grained T91. It was found that bubbles in the nanometer-size-grained T91 were smaller than those in the conventional coarse-grained T91 in as-implanted case, and bubbles in the matrix of nanograins were undetectable while those at nanograin boundaries (GBs) coalesced and filled in GBs after heat treatment. These results suggested that the grain size of structural material should be larger than the mean free path of bubble’s Brownian motion and/or denuded zone around GBs in order to prevent bubbles accumulation at GBs, and multiple instead of one type of defects should be introduced into structural materials to effectively reduce the susceptibility of materials to He embrittlement and improve the irradiation tolerance of structural materials.

  18. Study of 44Ti grain boundary self-diffusion in thin nanocrystalline TiO2 films

    Energy Technology Data Exchange (ETDEWEB)

    Straumal, Petr [Institut fuer Materialphysik, Universitaet Muenster, D-48149 Muenster (Germany); National University of Science and Technology, MISIS, 119049 Moscow (Russian Federation); Divinski, Sergiy; Wilde, Gerhard [Institut fuer Materialphysik, Universitaet Muenster, D-48149 Muenster (Germany)

    2011-07-01

    Titanium dioxide is known for its photo-catalytic properties and enhanced corrosion resistance in aqueous environments. Due to these properties TiO2 is very attractive material for light-induced self-cleaning glass, water-cleaning and producing hydrogen from water applications. Numerous works are dedicated to the diffusion of various dopants like niobium or chromium in TiO2 but so far, none studied the self-diffusion of titanium in nanocrystalline TiO2. The grain boundary self-diffusion in thin nanocrystalline TiO2 films is investigated. The oxide films are produced using a novel deposition method from metal-organic precursors at relatively low (400-500 C) temperatures. A relaxation annealing at 800 C was performed. The diffusion was measured in temperature interval between 200 C and 600 C by means of the radiotracer technique applying the 44Ti isotope and utilizing ion beam sputtering for sectioning. The diffusion was measured at different oxygen pressures. In addition, the microstructure and its possible evaluation during diffusion annealing was investigated using TEM. The results are discussed with respect of the relationship between grain boundary self-diffusion and the synthesis pathway, the oxygen pressure and resulting microstructure of the nanoscale functional oxide films.

  19. The MAFLA (Mississippi, Alabama, Florida) Study, Grain Size Analyses

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The MAFLA (Mississippi, Alabama, Florida) Study was funded by NOAA as part of the Outer Continental Shelf Program. Dr. L.J. Doyle produced grain size analyses in the...

  20. The optimum grain size for minimizing energy losses in iron

    Energy Technology Data Exchange (ETDEWEB)

    Campos, M.F. de [Escola de Engenharia Industrial Metalurgica de Volta Redonda/Universidade Federal Fluminense Av. dos Trabalhadores 420, Vila Santa Cecilia, 27255-125, Volta Redonda, RJ (Brazil)]. E-mail: mcampos@metal.eeimvr.uff.br; Teixeira, J.C. [Instituto de Pesquisas Tecnologicas do Estado de Sao Paulo, Av. Prof. Almeida Prado 532, 05508-901, Sao Paulo, SP (Brazil); Landgraf, F.J.G. [Instituto de Pesquisas Tecnologicas do Estado de Sao Paulo, Av. Prof. Almeida Prado 532, 05508-901, Sao Paulo, SP (Brazil)]. E-mail: landgraf@ipt.br

    2006-06-15

    A model able to predict the optimum grain size for textured electrical steels used in motors or transformers is presented. The model is based on the Pry and Bean model for the anomalous losses. The validity of the model is restricted to the frequency range of 1-1000 Hz. The model predicts that the optimum grain size decreases as: resistivity decreases or frequency increases or thickness of steel sheet increases. The predictions of the model are compared with experimental results.

  1. Activation of Big Grain1 significantly improves grain size by regulating auxin transport in rice.

    Science.gov (United States)

    Liu, Linchuan; Tong, Hongning; Xiao, Yunhua; Che, Ronghui; Xu, Fan; Hu, Bin; Liang, Chengzhen; Chu, Jinfang; Li, Jiayang; Chu, Chengcai

    2015-09-01

    Grain size is one of the key factors determining grain yield. However, it remains largely unknown how grain size is regulated by developmental signals. Here, we report the identification and characterization of a dominant mutant big grain1 (Bg1-D) that shows an extra-large grain phenotype from our rice T-DNA insertion population. Overexpression of BG1 leads to significantly increased grain size, and the severe lines exhibit obviously perturbed gravitropism. In addition, the mutant has increased sensitivities to both auxin and N-1-naphthylphthalamic acid, an auxin transport inhibitor, whereas knockdown of BG1 results in decreased sensitivities and smaller grains. Moreover, BG1 is specifically induced by auxin treatment, preferentially expresses in the vascular tissue of culms and young panicles, and encodes a novel membrane-localized protein, strongly suggesting its role in regulating auxin transport. Consistent with this finding, the mutant has increased auxin basipetal transport and altered auxin distribution, whereas the knockdown plants have decreased auxin transport. Manipulation of BG1 in both rice and Arabidopsis can enhance plant biomass, seed weight, and yield. Taking these data together, we identify a novel positive regulator of auxin response and transport in a crop plant and demonstrate its role in regulating grain size, thus illuminating a new strategy to improve plant productivity.

  2. On the maximum grain size entrained by photoevaporative winds

    CERN Document Server

    Hutchison, Mark A; Maddison, Sarah T

    2016-01-01

    We model the behaviour of dust grains entrained by photoevaporation-driven winds from protoplanetary discs assuming a non-rotating, plane-parallel disc. We obtain an analytic expression for the maximum entrainable grain size in extreme-UV radiation-driven winds, which we demonstrate to be proportional to the mass loss rate of the disc. When compared with our hydrodynamic simulations, the model reproduces almost all of the wind properties for the gas and dust. In typical turbulent discs, the entrained grain sizes in the wind are smaller than the theoretical maximum everywhere but the inner disc due to dust settling.

  3. Size Effect in Tension Perpendicular to Grain

    DEFF Research Database (Denmark)

    Astrup, Thomas; Clorius, Christian Odin; Hoffmeyer, Preben;

    2004-01-01

    The strength of wood is reduced when the stressed volume is increased. The phenomenon is termed size effect and is often explained as being stochastic in the sense that the probability of weak locations occurring in the wood increases with increased volume. This paper presents a hypothesis where ...

  4. Nanoscale size effects on the mechanical properties of platinum thin films and cross-sectional grain morphology

    KAUST Repository

    Abbas, K

    2015-12-10

    © 2016 IOP Publishing Ltd. The mechanical behavior of polycrystalline Pt thin films is reported for thicknesses of 75 nm, 100 nm, 250 nm, and 400 nm. These thicknesses correspond to transitions between nanocrystalline grain morphology types as found in TEM studies. Thinner samples display a brittle behavior, but as thickness increases the grain morphology evolves, leading to a ductile behavior. During evolution of the morphology, dramatic differences in elastic moduli (105-160 GPa) and strengths (560-1700 MPa) are recorded and explained by the variable morphology. This work suggests that in addition to the in-plane grain size of thin films, the transitions in cross-sectional morphologies of the Pt films significantly affect their mechanical behavior.

  5. Radiation pressure on fluffy submicron-sized grains

    CERN Document Server

    Silsbee, Kedron

    2015-01-01

    We investigate the claim that the ratio {\\beta} of radiation pressure force to gravitational force on a dust grain in our solar system can substantially exceed unity for some grain sizes, provided that grain porosity is high enough. For model grains consisting of random aggregates of silicate spherules, we find that the maximum value of {\\beta} is almost independent of grain porosity, but for small (<0.3 {\\mu}m) grains, {\\beta} actually decreases with increasing porosity. These results affect the interpretation of the grain trajectories estimated from the Stardust mission, which were modeled assuming {\\beta} values exceeding one. We find that radiation pressure effects are not large enough for particles Orion and Hylabrook captured by Stardust to be of interstellar origin given their reported impact velocities. We also investigate the effect of metallic iron inclusions in the dust grains, and find that metallic iron will increase {\\beta}, but at least half the grain (by mass) must be iron in order to raise...

  6. Novel ultrafine grain size processing of soft magnetic materials.

    Energy Technology Data Exchange (ETDEWEB)

    Michael, Joseph Richard; Robino, Charles Victor

    2009-01-01

    High performance soft magnetic alloys are used in solenoids in a wide variety of applications. These designs are currently being driven to provide more margin, reliability, and functionality through component size reductions; thereby providing greater power to drive ratio margins as well as decreases in volume and power requirements. In an effort to produce soft magnetic materials with improved properties, we have conducted an initial examination of one potential route for producing ultrafine grain sizes in the 49Fe-49Co-2V alloy. The approach was based on a known method for the production of very fine grain sizes in steels, and consisted of repeated, rapid phase transformation cycling through the ferrite to austenite transformation temperature range. The results of this initial attempt to produce highly refined grain sizes in 49Fe-49Co-2V were successful in that appreciable reductions in grain size were realized. The as-received grain size was 15 {micro}m with a standard deviation of 9.5 {micro}m. For the temperature cycling conditions examined, grain refinement appears to saturate after approximately ten cycles at a grain size of 6 {micro}m with standard deviation of 4 {micro}m. The process also reduces the range of grain sizes present in these samples as the largest grain noted in the as received and treated conditions were 64 and 26 {micro}m, respectively. The results were, however, complicated by the formation of an unexpected secondary ferritic constituent and considerable effort was directed at characterizing this phase. The analysis indicates that the phase is a V-rich ferrite, known as {alpha}{sub 2}, that forms due to an imbalance in the partitioning of vanadium during the heating and cooling portions of the thermal cycle. Considerable but unsuccessful effort was also directed at understanding the conditions under which this phase forms, since it is conceivable that this phase restricts the degree to which the grains can be refined. Due to this difficulty

  7. Microstructure and Performances of Nanocrystalline Zinc-nickel Alloy Coatings

    Institute of Scientific and Technical Information of China (English)

    LI Guang-yu; LIAN Jian-she; NIU Li-yuan; JIANG Zhong-hao

    2004-01-01

    Nanocrystalline zinc-nickel alloy coatings were deposited from an alkaline zincate bath contained an organic additive that can reduce polarization and a complexing agent. SEM and TEM observations and XRD analysis were performed to examine the microstructure and phase composition of the coatings. The nickel content in deposits is 12.0~14.7% and the coating is consisted of single nanocrystalline γ-phase structure (Ni5Zn21), with grain average grain size about 15nm. The nanocrystalline zinc-nickel alloy coatings have better corrosion resistance, less brittleness and higher microhardness than the conventional zinc coatings.

  8. Exceptional high fatigue strength in Cu-15at.%Al alloy with moderate grain size

    Science.gov (United States)

    Liu, Rui; Tian, Yanzhong; Zhang, Zhenjun; An, Xianghai; Zhang, Peng; Zhang, Zhefeng

    2016-06-01

    It is commonly proposed that the fatigue strength can be enhanced by increasing the tensile strength, but this conclusion needs to be reconsidered according to our study. Here a recrystallized α-Cu-15at.%Al alloy with moderate grain size of 0.62 μm was fabricated by cold rolling and annealing, and this alloy achieved exceptional high fatigue strength of 280 MPa at 107 cycles. This value is much higher than the fatigue strength of 200 MPa for the nano-crystalline counterpart (0.04 μm in grain size) despite its higher tensile strength. The remarkable improvement of fatigue strength should be mainly attributed to the microstructure optimization, which helps achieve the reduction of initial damage and the dispersion of accumulated damage. A new strategy of “damage reduction” was then proposed for fatigue strength improvement, to supplement the former strengthening principle. The methods and strategies summarized in this work offer a general pathway for further improvement of fatigue strength, in order to ensure the long-term safety of structural materials.

  9. A Model for Evaluation of Grain Sizes of Aluminum Alloys with Grain Refinement Additions

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Based on the assumption that the nucleation substrates are activated by constitutional undercooling generated by an adjacent grain growth and solute distribution during the initial solidification, a model for calculation of the grain size of aluminum alloys with the grain refinement is developed, where the nucleation is dominated by two parameters, I.e. Growth restriction factor Q and the undercooling parameter P. The growth restriction factor Q is proportional to the initial rate of constitutional undercooling development and can be used directly as a criterion of the grain refinement in the alloys with strong potential nucleation particles. The undercooling parameter P can be regarded as the maximum of constitutional undercooling △TC. For weak potential nucleation particles, the use of RGS would be more accurate. The experimental data of the grain refinement of pure aluminum and AISi7 alloys are coincident predicted results with the model.

  10. Effects of grain size evolution on mantle dynamics

    Science.gov (United States)

    Schulz, Falko; Tosi, Nicola; Plesa, Ana-Catalina; Breuer, Doris

    2016-04-01

    The rheology of planetary mantle materials is strongly dependent on temperature, pressure, strain-rate, and grain size. In particular, the rheology of olivine, the most abundant mineral of the Earth's upper mantle, has been extensively studied in the laboratory (e.g., Karato and Wu, 1993; Hirth and Kohlstedt, 2003). Two main mechanisms control olivine's deformation: dislocation and diffusion creep. While the former implies a power-law dependence of the viscosity on the strain-rate that leads to a non-Newtonian behaviour, the latter is sensitively dependent on the grain size. The dynamics of planetary interiors is locally controlled by the deformation mechanism that delivers the lowest viscosity. Models of the dynamics and evolution of planetary mantles should thus be capable to self-consistently distinguish which of the two mechanisms dominates at given conditions of temperature, pressure, strain-rate and grain size. As the grain size can affect the viscosity associated with diffusion creep by several orders of magnitude, it can strongly influence the dominant deformation mechanism. The vast majority of numerical, global-scale models of mantle convection, however, are based on the use of a linear diffusion-creep rheology with constant grain-size. Nevertheless, in recent studies, a new equation has been proposed to properly model the time-dependent evolution of the grain size (Austin and Evens, 2007; Rozel et al., 2010). We implemented this equation in our mantle convection code Gaia (Hüttig et al., 2013). In the framework of simple models of stagnant lid convection, we compared simulations based on the fully time-dependent equation of grain-size evolution with simulations based on its steady-state version. In addition, we tested a number of different parameters in order to identify those that affects the grain size to the first order and, in turn, control the conditions at which mantle deformation is dominated by diffusion or dislocation creep. References Austin

  11. Universal scaling of grain size distributions during dislocation creep

    Science.gov (United States)

    Aupart, Claire; Dunkel, Kristina G.; Angheluta, Luiza; Austrheim, Håkon; Ildefonse, Benoît; Malthe-Sørenssen, Anders; Jamtveit, Bjørn

    2017-04-01

    Grain size distributions are major sources of information about the mechanisms involved in ductile deformation processes and are often used as paleopiezometers (stress gauges). Several factors have been claimed to influence the stress vs grain size relation, including the water content (Jung & Karato 2001), the temperature (De Bresser et al., 2001), the crystal orientation (Linckens et al., 2016), the presence of second phase particles (Doherty et al. 1997; Cross et al., 2015), and heterogeneous stress distributions (Platt & Behr 2011). However, most of the studies of paleopiezometers have been done in the laboratory under conditions different from those in natural systems. It is therefore essential to complement these studies with observations of naturally deformed rocks. We have measured olivine grain sizes in ultramafic rocks from the Leka ophiolite in Norway and from Alpine Corsica using electron backscatter diffraction (EBSD) data, and calculated the corresponding probability density functions. We compared our results with samples from other studies and localities that have formed under a wide range of stress and strain rate conditions. All distributions collapse onto one universal curve in a log-log diagram where grain sizes are normalized by the mean grain size of each sample. The curve is composed of two straight segments with distinct slopes for grains above and below the mean grain size. These observations indicate that a surprisingly simple and universal power-law scaling describes the grain size distribution in ultramafic rocks during dislocation creep irrespective of stress levels and strain rates. Cross, Andrew J., Susan Ellis, and David J. Prior. 2015. « A Phenomenological Numerical Approach for Investigating Grain Size Evolution in Ductiley Deforming Rocks ». Journal of Structural Geology 76 (juillet): 22-34. doi:10.1016/j.jsg.2015.04.001. De Bresser, J. H. P., J. H. Ter Heege, and C. J. Spiers. 2001. « Grain Size Reduction by Dynamic

  12. Solidification of Suspended Sediments with Two Characteristic Grain Sizes

    Science.gov (United States)

    Zarski, G.; Borja, R. I.

    2010-12-01

    We use mixture theory to formulate the problem of solidification of sediments with two characteristic grain sizes in a suspension. The formulation involves a mixture of larger grains in a thick fluid, where the thick fluid is a mixture of smaller particles in a host fluid. This mixture within a mixture description resembles a double porosity representation in unsaturated soil mechanics. Two independent variables of interest include the volume fraction of the larger grains relative to the total volume of the mixture, and the volume fraction of the smaller grains relative to the volume of the thick fluid. The two volume fractions are coupled by a constitutive law based on the Richardson-Zaki equation. The governing partial differential equations describing the settling velocities of the two solid groups are solved simultaneously in space and time using the finite element method.

  13. Defect and electrical properties of nanocrystalline tungsten trioxide

    Institute of Scientific and Technical Information of China (English)

    Yang Xin-Sheng; Wang Yu; Dong Liang; Qi Li-Zhen; Zhang Feng

    2004-01-01

    Nanocrystalline tungsten trioxide particles were prepared by a wet-chemical method. Transmission electron microscope (TEM) analysis shows that the average grain size is about 15nm. The oxygen deficiency of nanometre-sized sample is higher than that of ordinary tungsten trioxide. The electric conductivity increases because of high oxygen deficiency. Ironic relaxation polarization and crystallographic shear (CS) planes theory were used to explain the unusual dielectric characteristic of nanocrystalline tungsten trioxide.

  14. Colour characteristics of winter wheat grits of different grain size

    Directory of Open Access Journals (Sweden)

    Horváth Zs. H.

    2015-01-01

    Full Text Available Nowadays, wheat has spread all over the world due to its extensive usability. The colour of wheat grits is very important for the milling and baking industry because it determines the colour of the products made from it. The instrumental colour measuring is used, first of all, for durum wheat. We investigated the relationship between colour characteristics and grain size in the case of different hard aestivum wheats. We determined the colour using the CIE (Commission Internationale de l’Eclairage 1976 L*, a*, b* colour system measured by MINOLTA CR-300 tristimulus colorimeter. After screening the colour of the wheat fractions of different grain size, grits was measured wet and dry. We determined the L*, a*, b* colour co-ordinates and the whiteness index, too. To evaluate the values we had obtained, we used analysis of variance and regression analysis. We pointed out that the colour of wheat grits of different grain size is dependent on the hardness index of wheat. The lightness co-ordinate (L* of grits of the harder wheat is smaller, while a* and b* co-ordinates are higher. We also found that while grain size rises, the L* co-ordinate decreases and a*, b* values increase in the case of every type of wheat. The colour of grits is determined by the colour of fractions of 250-400 μm in size, independently from the average grain size. The whiteness index and the L* colour co-ordinate have a linear relation (R2 = 0.9151; so, the determination of whiteness index is not necessary. The L* value right characterizes the whiteness of grits.

  15. Mean grain size mapping with single-beam echo sounders

    NARCIS (Netherlands)

    Van Walree, P.A.; Ainslie, M.A.; Simons, D.G.

    2006-01-01

    Echo energies of single-beam echo sounders are inverted for the sediment mean grain size via a combination of theoretical and empirical relationships. In situ measurements of the seafloor mass density have revealed the presence of a thin transition layer between the water and the sediment. Within th

  16. Thermodynamic properties and phase stability of nanocrystalline metals

    Institute of Scientific and Technical Information of China (English)

    SONG Xiaoyan; LI Lingmei; ZHANG Jiuxing

    2006-01-01

    The fundamental thermodynamic functions of enthalpy, entropy, and Gibbs free energy, as functions of the excess free volume at interfaces, temperature, and grain size, have been derived for single-phase metal nanocrystals. The model was applied to predict the thermal features of nano-grain boundaries and the characteristics of phase transformation in nanocrystalline metals, such as the transformation temperature and the critical grain size for phase transformation at a given temperature. The model predictions have been verified by experimental studies on the β-Co (→) α-Co phase transformation in nanocrystalline Co prepared by ball milling.

  17. Grain Size Dependence of Exchange-Coupling Interaction between Magnetically Soft-Hard Grains and Effective Anisotropy

    Institute of Scientific and Technical Information of China (English)

    韩广兵; 高汝伟; 傅爽; 刘汉强; 冯维存; 陈伟

    2004-01-01

    Taking α-Fe and Nd2Fe14B grains as example, the grain size dependence of the exchange-coupling interaction and effective anisotropy and also their variations depending on the ratio of magnetically soft and hard grain sizes, Ds∶ Dh, were investigated. When grain size D>Lex, the grain's anisotropy is the statistic value of the coupled and uncoupled part. The anisotropy constant of uncoupled part is the common value K1 and that of coupled part varies with the distance to the grain surface. The effective anisotropy constant between magnetically soft and hard grains, Keff, can be expressed as the sum of the products of volume fractions for soft and hard grains, respectively, and the corresponding mean anisotropy constants. The calculation results indicate that the exchange-coupling interaction is enhanced with the reduction of grain size, and the effective anisotropy decreases with reducing grain size and increasing ratio of Ds∶ Dh. In order to get high effective anisotropy constant, Keff, in composite magnetically soft-hard grains, the hard grain size should be larger than 30 nm and the soft grain size should be about 10 nm.

  18. Size-dependent behavior of nanocrystalline titania and iron oxyhydroxide biominerals

    Science.gov (United States)

    Banfield, Jillian F.

    2000-03-01

    Biomineralization and chemical weathering products are predominantly nanocrystalline. Such phases comprise the majority of reactive surface area in soils and sediments. Microbial oxidation of dissolved iron leads to precipitation of nanocrystalline Fe-oxyhydroxides. Initial ~ 2nm diameter ferrihydrite-like particles nucleate on microbial polymers and form submicron-diameter spherical aggregates via floculation in solution. We have used titania (TiO2) as a model system to explore relationships between size and structure, phase stability, crystal growth mechanisms, phase transformation kinetics, and surface properties. Initial amorphous titania sol-gel products restructure to form 2-4 nm particles that, upon heating, grow to ~ 5 nm, then transform to anatase. Molecular dynamics simulations suggest conversion from four and five coordinated Ti4+ in < 3 nm particles to octahedrally coordinated Ti4+ in larger particles. Four and five coordinated Ti sites are supported by prior synchrotron-based studies on nanotitania. Furthermore, calculated XRD patterns for energy-minimized 2 nm particle structures coincide well with experimental patterns. Particle growth primarily occurs via solid state oriented attachment. Small misorientations between adjacent particles introduce new structural components, as well as dislocations and extended defects that can serve as nucleation sites for subsequent phase transformations. 2-3 nm ferrihydrites transform to ~ 3-6 nm randomly oriented feroxyhyte and goethite (FeOOH) crystals. FeOOH nanocrystals aggregate via oriented attachment to form tens of nanometer diameter imperfect single crystals. The sequence of crystallization steps and similarities in crystal growth and defect formation mechanisms in the titania and iron systems suggest oriented attachment is an important pathways for structural change and crystal growth in many natural and synthetic nanophase materials.

  19. Size effect in tension perpendicular to the grain

    DEFF Research Database (Denmark)

    Pedersen, Martin Bo Uhre; Clorius, Christian Odin; Damkilde, Lars;

    1999-01-01

    The strength in tension perpendicular to the grain is known to decrease with an increase in the stressed volume. Usually this size effect is explained on a stochastic basis, that is an explanation relying on an increased probability of encountering a strength reducing flaw when the volume of the ...... that the size effect can be explained on a deterministic basis. Arguments for such a simple deterministic explanation of size effect is found in finite element modelling using the orthotropic stiffness characteristics in the transverse plane of wood....

  20. Solid state consolidation nanocrystalline copper-tungsten using cold spray

    Energy Technology Data Exchange (ETDEWEB)

    Hall, Aaron Christopher [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Sarobol, Pylin [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Argibay, Nicolas [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Clark, Blythe [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Diantonio, Christopher [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2015-09-01

    It is well known that nanostructured metals can exhibit significantly improved properties compared to metals with conventional grain size. Unfortunately, nanocrystalline metals typically are not thermodynamically stable and exhibit rapid grain growth at moderate temperatures. This severely limits their processing and use, making them impractical for most engineering applications. Recent work has shown that a number of thermodynamically stable nanocrystalline metal alloys exist. These alloys have been prepared as powders using severe plastic deformation (e.g. ball milling) processes. Consolidation of these powders without compromise of their nanocrystalline microstructure is a critical step to enabling their use as engineering materials. We demonstrate solid-state consolidation of ball milled copper-tantalum nanocrystalline metal powder using cold spray. Unfortunately, the nanocrystalline copper-tantalum powder that was consolidated did not contain the thermodynamically stable copper-tantalum nanostructure. Nevertheless, this does this demonstrates a pathway to preparation of bulk thermodynamically stable nanocrystalline copper-tantalum. Furthermore, it demonstrates a pathway to additive manufacturing (3D printing) of nanocrystalline copper-tantalum. Additive manufacturing of thermodynamically stable nanocrystalline metals is attractive because it enables maximum flexibility and efficiency in the use of these unique materials.

  1. A New Attempt to Obtain Bulk Nanocrystalline Steel

    Institute of Scientific and Technical Information of China (English)

    Shengjie Yao; Linxiu Du; Xianghua Liu; Guodong Wang

    2009-01-01

    Bulk nanocrystalline steel sample was obtained in laboratory through refining of austenite grains and controlled rolling. Transmission electron microscopy micrographs show that some textures are evolved in the process of the treatment and two typical carbides are classified according to their size and location. The tensile strength of the nanocrystalline sample is obviously lower than conventional consideration, and scanning electron microscopy observation shows that the existence of the first type of carbide is considered as the main reason for the failure.

  2. High Pressure X-Ray Diffraction Studies on Nanocrystalline Materials

    Science.gov (United States)

    Palosz, B.; Stelmakh, S.; Grzanka, E.; Gierlotka, S.; Pielaszek, R.; Bismayer, U.; Werner, S.; Palosz, W.

    2003-01-01

    Application of in situ high pressure powder diffraction technique for examination of specific structural properties of nanocrystals based on the experimental data of SiC nanocrystalline powders of 2 to 30 nrn diameter in diameter is presented. Limitations and capabilities of the experimental techniques themselves and methods of diffraction data elaboration applied to nanocrystals with very small dimensions (nanocrystalline powders under pressure. We offer a tentative interpretation of the distribution of macro- and micro-strains in nanoparticles of different grain size.

  3. Nanocrystalline and Ultra-Fine Grained Tungsten for Kinetic Energy Penetrator and Warhead Liner Applications

    Science.gov (United States)

    2007-06-01

    Tungsten Sheet, J. Less Common Metals, 13, 141-155. Jain, M., Skandan, G., Martin , K., Kapoor, D., Cho, K., Klotz, B., Dowding, R., Agarawal, D., and...2758. Zhilyaev, A.P., Nurislamova, G.V., Kim, B.K., Baro , M.D., Szpunar, J.A., and Langdon, T.G., 2003: Experimental Parameters Influencing Grain

  4. Quantifying the relative importance of flow regulation and grain size regulation of suspended sediment transport α and tracking changes in grain size of bed sediment β

    Science.gov (United States)

    Rubin, David M.; Topping, David J.

    2001-01-01

    To predict changes in sediment transport, it is essential to know whether transport is regulated mainly by changes in flow or by changes in grain size of sediment on the bed. In flows where changes in suspended sediment transport are regulated purely by changes in flow (grain size of bed sediment is constant), increases in flow strength cause increases in both concentration and grain size of sediment in suspension (because stronger flows are able to suspend more sediment and coarser grains). Under this constraint of constant grain size of bed sediment concentration and median diameter of suspended sediment are positively correlated. In contrast, where transport is regulated purely by changes in grain size of sediment on the bed, concentration and median diameter of suspended sediment are negatively correlated (because increasing the median diameter of the bed sediment causes the concentration to decrease while causing the median grain size in suspension to increase). Where both flow strength and grain size on the bed are free to vary, the relation between concentration and grain size in suspension can be used to quantify the importance of grain size regulation relative to flow regulation of sediment transport, a measure defined as α. To predict sediment transport in systems that are regulated dominantly by changes in grain size on the bed, it is more useful to measure sediment input events or changes in grain size on the bed than to measure changes in flow. More commonly, grain size of bed sediment may be secondary to flow in regulating transport but may, nevertheless, be important. The relative coarseness of bed sediment (β) can be measured directly or, like α, can be calculated from measurements of concentration and grain size of suspended sediment.

  5. Quantifying the relative importance of flow regulation and grain size regulation of suspended sediment transport a and tracking changes in grain size of bed sediment B

    Science.gov (United States)

    Rubin, David M.; Topping, David J.

    2001-01-01

    To predict changes in sediment transport, it is essential to know whether transport is regulated mainly by changes in flow or by changes in grain size of sediment on the bed. In flows where changes in suspended sediment transport are regulated purely by changes in flow (grain size of bed sediment is constant), increases in flow strength cause increases in both concentration and grain size of sediment in suspension (because stronger flows are able to suspend more sediment and coarser grains). Under this constraint of constant grain size of bed sediment concentration and median diameter of suspended sediment are positively correlated. In contrast, where transport is regulated purely by changes in grain size of sediment on the bed, concentration and median diameter of suspended sediment are negatively correlated (because increasing the median diameter of the bed sediment causes the concentration to decrease while causing the median grain size in suspension to increase). Where both flow strength and grain size on the bed are free to vary, the relation between concentration and grain size in suspension can be used to quantify the importance of grain size regulation relative to flow regulation of sediment transport, a measure defined as α. To predict sediment transport in systems that are regulated dominantly by changes in grain size on the bed, it is more useful to measure sediment input events or changes in grain size on the bed than to measure changes in flow. More commonly, grain size of bed sediment may be secondary to flow in regulating transport but may, nevertheless, be important. The relative coarseness of bed sediment (β) can be measured directly or, like α, can be calculated from measurements of concentration and grain size of suspended sediment.

  6. Characterisation of interfaces in nanocrystalline palladium

    Indian Academy of Sciences (India)

    R Divakar; V S Raghunathan

    2003-02-01

    Structures of grain boundaries and triple line junctions in nanocrystalline materials are of interest owing to large fractions of atoms in nanocrystalline materials being at these interfacial positions. Grain boundary and triple line junction structures in nanocrystalline palladium have been studied using high-resolution transmission electron microscopy (HRTEM). The main microstructural features observed include the varying atomic structures of grain boundaries and the presence of disordered regions at triple line junctions. Also, there is variation in lattice parameters in different nanocrystalline grains. Geometric phase analysis is used to quantify atomic displacements within nanocrystalline grains. Displacement fields thus detected indicate links to the interface structures.

  7. The dust grain size - stellar luminosity trend in debris discs

    CERN Document Server

    Pawellek, Nicole

    2015-01-01

    The cross section of material in debris discs is thought to be dominated by the smallest grains that can still stay in bound orbits despite the repelling action of stellar radiation pressure. Thus the minimum (and typical) grain size $s_\\text{min}$ is expected to be close to the radiation pressure blowout size $s_\\text{blow}$. Yet a recent analysis of a sample of Herschel-resolved debris discs showed the ratio $s_\\text{min}/s_\\text{blow}$ to systematically decrease with the stellar luminosity from about ten for solar-type stars to nearly unity in the discs around the most luminous A-type stars. Here we explore this trend in more detail, checking how significant it is and seeking to find possible explanations. We show that the trend is robust to variation of the composition and porosity of dust particles. For any assumed grain properties and stellar parameters, we suggest a recipe of how to estimate the "true" radius of a spatially unresolved debris disc, based solely on its spectral energy distribution. The r...

  8. Stress Field of Non-equilibrium Grain Boundaries in Nano-crystalline Metals

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Introducing the stress distribution near grain boundaries to improve the dislocation pileup model for the Hall-Petch (H-P) relation, the continuous distribution of dislocations in the pileup could be solved by means of Tschebysheff polynomials for the Hilbert transformation. An analytical formula of the stress intensity factor for the dislocation pileup is obtained. The reverse H-P relation may be explained by the modified dislocation-pileup-model.

  9. The inverse hall-petch relation in nanocrystalline metals: A discrete dislocation dynamics analysis

    Science.gov (United States)

    Quek, Siu Sin; Chooi, Zheng Hoe; Wu, Zhaoxuan; Zhang, Yong Wei; Srolovitz, David J.

    2016-03-01

    When the grain size in polycrystalline materials is reduced to the nanometer length scale (nanocrystallinity), observations from experiments and atomistic simulations suggest that the yield strength decreases (softening) as the grain size is decreased. This is in contrast to the Hall-Petch relation observed in larger sized grains. We incorporated grain boundary (GB) sliding and dislocation emission from GB junctions into the classical DDD framework, and recovered the smaller is weaker relationship observed in nanocrystalline materials. This current model shows that the inverse Hall-Petch behavior can be obtained through a relief of stress buildup at GB junctions from GB sliding by emitting dislocations from the junctions. The yield stress is shown to vary with grain size, d, by a d 1 / 2 relationship when grain sizes are very small. However, pure GB sliding alone without further plastic accomodation by dislocation emission is grain size independent.

  10. In vitro corrosion, cytotoxicity and hemocompatibility of bulk nanocrystalline pure iron.

    Science.gov (United States)

    Nie, F L; Zheng, Y F; Wei, S C; Hu, C; Yang, G

    2010-12-01

    Bulk nanocrystalline pure iron rods were fabricated by the equal channel angular pressure (ECAP) technique up to eight passes. The microstructure and grain size distribution, natural immersion and electrochemical corrosion in simulated body fluid, cellular responses and hemocompatibility were investigated in this study. The results indicate that nanocrystalline pure iron after severe plastic deformation (SPD) would sustain durable span duration and exhibit much stronger corrosion resistance than that of the microcrystalline pure iron. The interaction of different cell lines reveals that the nanocrystalline pure iron stimulates better proliferation of fibroblast cells and preferable promotion of endothelialization, while inhibits effectively the viability of vascular smooth muscle cells (VSMCs). The burst of red cells and adhesion of the platelets were also substantially suppressed on contact with the nanocrystalline pure iron in blood circulation. A clear size-dependent behavior from the grain nature deduced by the gradual refinement microstructures was given and well-behaved in vitro biocompatibility of nanocrystalline pure iron was concluded.

  11. Grain size control and superplasticity in 6013-type aluminum alloys

    Science.gov (United States)

    Troeger, Lillianne Plaster Whitelock

    Aluminum alloys have been the material of choice for aircraft construction since the 1930's. Currently, the automotive industry is also showing an increasing interest in aluminum alloys as structural materials. 6xxx aluminum alloys possess a combination of strength and formability which makes them attractive to both industries. In addition, 6xxx alloys are highly weldable, corrosion resistant, and low in cost as compared with the 2xxx and 7xxx aluminum alloys. Superplastic forming (SPF) is a manufacturing process which exploits the phenomenon of superplasticity in which gas pressure is used to form complex-shaped parts in a single forming operation. This reduces part counts and the need for fasteners and connectors, resulting in reduced product weight. Reduced product/vehicle weight improves fuel economy. Most alloys must be specially processed for superplasticity. Much research effort has been directed at the development of thermomechanical processes for the grain refinement of aluminum alloys by static or dynamic recrystallization. to induce superplasticity. While large numbers of studies have been conducted on 2xxx, 5xxx, 7xxx, and 8xxx aluminum alloys, very few studies have been focused on the grain refinement of 6xxx aluminum alloys for superplasticity. The current research describes a new thermomechanical process for application to 6xxx aluminum alloys for grain refinement and superplasticity. The process is shown to successfully refine and induce superplasticity in an Al-Mg-Si-Cu alloy which falls within the compositional limits of both 6013 and 6111. The grain refinement is by particle-stimulated nucleation of recrystallization. The microstructural evolution during the thermomechanical processing is characterized in terms of precipitate size, shape, distribution and composition; texture; recrystallization; and grain size, shape, and thermal stability. The new process produces a statically-stable, weakly-textured, equiaxed grain structure with an average

  12. Microhardness studies of nanocrystalline lead molybdate

    Energy Technology Data Exchange (ETDEWEB)

    Anandakumar, V.M. [Department of Physics, University of Kerala, Kariavattom P.O., Thiruvananthapuram 695581 (India); Department of Physics, Mahatma Gandhi College, Pattom Palace P.O., Thiruvananthapuram 695004 (India); Abdul Khadar, M., E-mail: mabdulkhadar@rediffmail.com [Department of Physics, University of Kerala, Kariavattom P.O., Thiruvananthapuram 695581 (India); Centre for Nanoscience and Nanotechnology, University of Kerala, Kariavattom P.O., Thiruvananthapuram 695581 (India)

    2009-08-30

    Nanocrystalline lead molybdate (PbMoO{sub 4}) of four different grain sizes were synthesized through chemical precipitation technique and the grain sizes and crystal structure are determined using the broadening of X-ray diffraction patterns and transmission electron microscopy. The microhardness of nanocrystalline lead molybdate (PbMoO{sub 4}) with different grain sizes were measured using a Vicker's microhardness tester for various applied loads ranging from 0.049 to 1.96 N. The microhardness values showed significant indentation size effect at low indentation loads. The proportional specimen resistance model put forward by Li and Bradt and energy balance model put forward by Gong and Li were used to analyze the behaviour of measured microhardness values under different indentation loads. The microhardness data obtained for samples of different grain sizes showed grain size dependent strengthening obeying normal Hall-Petch relation. The dependence of compacting pressure and annealing temperature on microhardness of the nanostructured sample with grain size of {approx}18 nm were also studied. The samples showed significant increase in microhardness values as the compacting pressure and annealing time were increased. The variation of microhardness of the material with pressure of pelletization and annealing time are discussed in the light of change of pore size distribution of the samples.

  13. Grain-to-Grain Variations in NbC Particle Size Distributions in an Austenitic Stainless Steel

    DEFF Research Database (Denmark)

    Barlow, Claire; Ralph, B.; Silverman, B.

    1979-01-01

    Quantitative information has been obtained concerning the size distributions of NbC precipitate particles in different grains in a deformed and aged austenitic stainless steel specimen. The precipitate size distributions obtained differ from one grain to another. The average disparity measured...... between the mean precipitate sizes was a function of the distance betwen the grains compared. The results obtained are considered in terms of differences in precipitation behaviour due to variations in the levels of plastic strain in constituent grains of the deformed specimen....

  14. Ferromagnetism appears in nitrogen implanted nanocrystalline diamond films

    Energy Technology Data Exchange (ETDEWEB)

    Remes, Zdenek [Institute of Physics ASCR v.v.i., Cukrovarnicka 10, 162 00 Prague 6 (Czech Republic); Sun, Shih-Jye, E-mail: sjs@nuk.edu.tw [Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan (China); Varga, Marian [Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan (China); Chou, Hsiung [Department of Physics, National Sun Yat-Sen University, Kaohsiung 804, Taiwan (China); Hsu, Hua-Shu [Department of Applied Physics, National Pingtung University of Education, Pingtung 900, Taiwan (China); Kromka, Alexander [Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan (China); Horak, Pavel [Nuclear Physics Institute, 250 68 Rez (Czech Republic)

    2015-11-15

    The nanocrystalline diamond films turn to be ferromagnetic after implanting various nitrogen doses on them. Through this research, we confirm that the room-temperature ferromagnetism of the implanted samples is derived from the measurements of magnetic circular dichroism (MCD) and superconducting quantum interference device (SQUID). Samples with larger crystalline grains as well as higher implanted doses present more robust ferromagnetic signals at room temperature. Raman spectra indicate that the small grain-sized samples are much more disordered than the large grain-sized ones. We propose that a slightly large saturated ferromagnetism could be observed at low temperature, because the increased localization effects have a significant impact on more disordered structure. - Highlights: • Nitrogen implanted nanocrystalline diamond films exhibit ferromagnetism at room temperature. • Nitrogen implants made a Raman deviation from the typical nanocrystalline diamond films. • The ferromagnetism induced from the structure distortion is dominant at low temperature.

  15. Calculated Grain Size-Dependent Vacancy Supersaturation and its Effect on Void Formation

    DEFF Research Database (Denmark)

    Singh, Bachu Narain; Foreman, A. J. E.

    1974-01-01

    In order to study the effect of grain size on void formation during high-energy electron irradiations, the steady-state point defect concentration and vacancy supersaturation profiles have been calculated for three-dimensional spherical grains up to three microns in size. In the calculations...... of vacancy supersaturation as a function of grain size, the effects of internal sink density and the dislocation preference for interstitial attraction have been included. The computations show that the level of vacancy supersaturation achieved in a grain decreases with decreasing grain size. The grain size...... dependence of the maximum vacancy supersaturation in the centre of the grains is found to be very similar to the grain size dependence of the maximum void number density and void volume swelling measured in the central regions of austenitic stainless steel grains. This agreement reinforces the interpretation...

  16. Grain Constraint and Size Effects in Shape Memory Alloy Microwires

    Science.gov (United States)

    Ueland, Stian Melhus

    Shape memory alloys exhibit interesting and useful properties, such as the shape memory effect and superelasticity. Among the many alloy families that have been shown to exhibit shape memory properties the ones based on copper are interesting because they are relatively inexpensive and show excellent properties when made as single crystals. However, the performance ofthese alloys is severely compromised by the introduction of grain boundaries, to the point where they are too poor for commercial applications. This thesis studies the mechanical properties of fine Cobased wires with a bamboo microstructure, i.e., where triple junctions are absent and grain boundaries run perpendicular to the wire axis. These microwires are not single crystals, but their microstructure is not as complex as that of polycrystals either: we call this new class of shape memory alloys oligocrystals. This thesis seeks to better understand the relationship between microstructure and properties in these alloys through a combination of mechanical testing, in situ experiments and modeling. First, in situ scanning electron microscopy, together with finite element modeling, is used to understand the role of grain constraint on the martensitic transformation. Grain constraints are observed to be much less severe in oligocrystalline wires as compared to polycrystals. Oligocrystalline microwires are then thermomechanically tested and shown to exhibit excellent properties that approach those of single crystals. Next, property evolution during cycling is investigated, revealing training effects as well as fatigue life and fracture. Finally, size effects in damping and transformation morphology are studied and it is shown that a transition from a many-domain to a single domain martensite morphology takes place when the wire diameter is decreased. (Copies available exclusively from MIT Libraries, libraries.mit.edu/docs - docs@mit.edu)

  17. Diffusion in nanocrystalline solids

    OpenAIRE

    Chadwick, Alan V.

    2016-01-01

    Enhanced atomic migration was an early observation from experimental studies into nanocrystalline solids. This contribution presents an overview of the available diffusion data for simple metals and ionic materials in nanocrystalline form. It will be shown that enhanced diffusion can be interpreted in terms of atomic transport along the interfaces, which are comparable to grain boundaries in coarse-grained analogues. However, the method of sample preparation is seen to play a major role in...

  18. Nanocrystalline cellulose-dispersed AKD emulsion for enhancing the mechanical and multiple barrier properties of surface-sized paper.

    Science.gov (United States)

    Yang, Luming; Lu, Sheng; Li, Juanjuan; Zhang, Fengshan; Cha, Ruitao

    2016-01-20

    In this study, we employed nanocrystalline cellulose (NCC) as an efficient dispersant to perpare alkyl ketene dimer (AKD) emulsion. The particle size and zeta potential of AKD/NCC emulsion were measured, which were approximately 5 μm and -50 mV, respectively. The surface-sized paper possessed multiple barriers properties. The air permeability of surface-sized paper was 0.29 μm/Pas and the sizing degree reached 42 s when the amount of sizing was 12.58 g/m(2) with a 96.83% decrease and a 40.00%, increase, respectively. Furthermore, the mechanical properties were optimal when the amount of sizing was about 8 g/m(2). AKD/NCC emulsion acted as a good reinforcing agent in surface-sized paper.

  19. Effect of annealing on microstructure, grain growth, and hardness of nanocrystalline Fe-Ni alloys prepared by mechanical alloying

    Energy Technology Data Exchange (ETDEWEB)

    Kotan, H., E-mail: hkotan@ncsu.edu [Department of Materials Science and Engineering, NC State University, 911 Partners Way, Room 3078, Raleigh, NC 27606-7907 (United States); Saber, M.; Koch, C.C.; Scattergood, R.O. [Department of Materials Science and Engineering, NC State University, 911 Partners Way, Room 3078, Raleigh, NC 27606-7907 (United States)

    2012-08-30

    Highlights: Black-Right-Pointing-Pointer Iron-nickel powders were hardened to 9.5 GPa by the mechanism of grain refinement strengthening using ball-milling. Black-Right-Pointing-Pointer We annealed the prepared powders and observed reduced hardness and extensive grain growth above 500 Degree-Sign C. Black-Right-Pointing-Pointer The Vickers hardness as a function of the grain size was found to exhibit a Hall-Petch slope. Black-Right-Pointing-Pointer Retained austenite was observed for Fe-8Ni and Fe-10Ni alloys annealed in the two-phase region. Black-Right-Pointing-Pointer As-milled microstructure plays an important role on the formation of austenite in the two-phase region. - Abstract: Fe-xNi alloys from x = 0 to x = 15 with an as-milled grain size and hardness in the range of 8-11 nm and 8.5-9.5 GPa, respectively, were synthesized by ball milling. Microstructural changes, hardness, and grain growth due to annealing were characterized using X-ray diffractometry, microhardness, focused ion beam channeling contrast imaging, and optical microscopy. It was found that the composition range of single bcc phase was extended by ball milling. Subsequent annealing of MA samples resulted in reduction of hardness and extensive grain growth. It indicates that nickel has no significant effect on thermal stabilization of iron. Retained austenite was observed for Fe-8Ni and Fe-10Ni alloys annealed in the two-phase region and effect of as-milled structure on retained austenite formation was discussed.

  20. Mapping Snow Grain Size over Greenland from MODIS

    Science.gov (United States)

    Lyapustin, Alexei; Tedesco, Marco; Wang, Yujie; Kokhanovsky, Alexander

    2008-01-01

    This paper presents a new automatic algorithm to derive optical snow grain size (SGS) at 1 km resolution using Moderate Resolution Imaging Spectroradiometer (MODIS) measurements. Differently from previous approaches, snow grains are not assumed to be spherical but a fractal approach is used to account for their irregular shape. The retrieval is conceptually based on an analytical asymptotic radiative transfer model which predicts spectral bidirectional snow reflectance as a function of the grain size and ice absorption. The analytical form of solution leads to an explicit and fast retrieval algorithm. The time series analysis of derived SGS shows a good sensitivity to snow metamorphism, including melting and snow precipitation events. Preprocessing is performed by a Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm, which includes gridding MODIS data to 1 km resolution, water vapor retrieval, cloud masking and an atmospheric correction. MAIAC cloud mask (CM) is a new algorithm based on a time series of gridded MODIS measurements and an image-based rather than pixel-based processing. Extensive processing of MODIS TERRA data over Greenland shows a robust performance of CM algorithm in discrimination of clouds over bright snow and ice. As part of the validation analysis, SGS derived from MODIS over selected sites in 2004 was compared to the microwave brightness temperature measurements of SSM\\I radiometer, which is sensitive to the amount of liquid water in the snowpack. The comparison showed a good qualitative agreement, with both datasets detecting two main periods of snowmelt. Additionally, MODIS SGS was compared with predictions of the snow model CROCUS driven by measurements of the automatic whether stations of the Greenland Climate Network. We found that CROCUS grain size is on average a factor of two larger than MODIS-derived SGS. Overall, the agreement between CROCUS and MODIS results was satisfactory, in particular before and during the

  1. Grain Size of Recall Practice for Lengthy Text Material: Fragile and Mysterious Effects on Memory

    Science.gov (United States)

    Wissman, Kathryn T.; Rawson, Katherine A.

    2015-01-01

    The current research evaluated the extent to which the grain size of recall practice for lengthy text material affects recall during practice and subsequent memory. The "grain size hypothesis" states that a smaller vs. larger grain size will increase retrieval success during practice that in turn will enhance subsequent memory for…

  2. A grain size distribution model for non-catalytic gas-solid reactions

    NARCIS (Netherlands)

    Heesink, Albertus B.M.; Prins, W.; van Swaaij, Willibrordus Petrus Maria

    1993-01-01

    A new model to describe the non-catalytic conversion of a solid by a reactant gas is proposed. This so-called grain size distribution (GSD) model presumes the porous particle to be a collection of grains of various sizes. The size distribution of the grains is derived from mercury porosimetry measur

  3. Atomic-scale simulations of the mechanical deformation of nanocrystalline metals

    DEFF Research Database (Denmark)

    Schiøtz, Jakob; Vegge, Tejs; Di Tolla, Francesco

    1999-01-01

    Nanocrystalline metals, i.e., metals in which the grain size is in the nanometer range, have a range of technologically interesting properties including increased hardness and yield strength. We present atomic-scale simulations of the plastic behavior of nanocrystalline copper. The simulations show...... leads to a hardening as the grain size is increased (reverse Hall-Fetch effect), implying a maximum in hardness for a grain size above the ones studied here. We investigate the effects of varying temperature, strain rate, and porosity, and discuss the relation to recent experiments. At increasing...

  4. Control of grain size in sublimation-grown CdTe, and the improvement in performance of devices with systematically increased grain size

    Energy Technology Data Exchange (ETDEWEB)

    Major, J.D.; Proskuryakov, Y.Y.; Durose, K. [Department of Physics, Science Laboratories, Durham University, South Road, Durham, DH1 3LE (United Kingdom); Zoppi, G.; Forbes, I. [Northumbria University, Northumbria Photovoltaics Applications Centre, Newcastle upon Tyne NE1 8ST (United Kingdom)

    2010-06-15

    A method to control the grain size of CdTe thin films deposited by close space sublimation using chamber pressure is demonstrated. Grain diameter is shown to increase in the pressure range 2-200 Torr, following the linear relationship D ({mu}m)=0.027 x P (Torr)+0.90. A mechanism is proposed to explain the dominance of the 111 preferred orientation in the small-grained, but not the large-grained films. For a series of CdTe/CdS solar cells in which the only variable was grain size, the performance parameters were seen to increase from 0.54% (0.94 {mu}m grains) up to a plateau of 11.3% ({>=}3.6 {mu}m grains). This corresponds to the point at which the series resistance is no longer dominated by grain boundaries, but by the contacts. (author)

  5. Control of grain size in sublimation-grown CdTe, and the improvement in performance of devices with systematically increased grain size

    OpenAIRE

    Major, Jonathan; Proskuryakov, Yuri; Durose, Ken; Zoppi, Guillaume; Forbes, Ian

    2010-01-01

    A method to control the grain size of CdTe thin films deposited by close space sublimation using chamber pressure is demonstrated. Grain diameter is shown to increase in the pressure range 2–200 Torr, following the linear relationship D (?m)=0.027×P (Torr)+0.90. A mechanism is proposed to explain the dominance of the 111 preferred orientation in the small-grained, but not the large-grained films. For a series of CdTe/CdS solar cells in which the only variable was grain size, the performance p...

  6. Effect of grain size on the domain structures and electromechanical responses of ferroelectric polycrystal

    Science.gov (United States)

    Li, Xinkai; Wang, Jie

    2017-01-01

    The effect of grain size on the domain structures and electromechanical responses of ferroelectric polycrystals is investigated by a phase field model. The phase field simulations show that the different types of domains in different size of grains play an important role in the size-dependent properties of ferroelectric polycrystals. It is found that the remnant polarization, coercive field and dielectric coefficient increase monotonously with the increase of grain size. However, the piezoelectric coefficient increases first and then decreases as the grain size increases. The decrease of vortex domains is responsible for the increase of piezoelectric coefficient in the range of small grain size, the decrease of 90° domain walls results in the decrease of piezoelectric coefficient in the range of large grain size. In addition, different domain structures in different size of grains have also great influence on the mechanical depolarization of the ferroelectric polycrystals subjected to a compressive stress.

  7. Bulk nanocrystalline Al prepared by cryomilling

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Bulk nanocrystalline Al was fabricated by mechanically milling at cryogenic temperature (cryomilling) and then by hot pressing in vacuum. By using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), the microstructure evolution of the material during cryomilling and consolidation was investigated. With increasing the milling time, the grain size decreased sharply and reduced to 42 nm when cryomilled for 12 h. The grains had grown up, and the columnar grain was formed under the hot pressing and extrusion compared with the cryomilled powders. The grain size of as-extruded specimen was approximately 300-500 nm. The reason of high thermal stability of this bulk was attributed primarily to the Zener pinning from the grain boundary of the AlN arising from cryomilling and the solute drag of the impurity. Tensile tests show that the strength of nanocrystalline Al is enhanced with decreasing grain size. The ultimate tensile strength and tensile elongation were 173 MPa and 17.5%, respectively. It appears that the measured high strength in the cryomilled Al is related to a grain-size effect, dispersion strengthening, and dislocation strengthening.

  8. Surface finish effects and the strength-grain size relation in SiC

    Science.gov (United States)

    Cranmer, D. C.; Tressler, R. E.; Bradt, R. C.

    1977-01-01

    The effect of surface finish on the strength-grain size relation was investigated for dense hot-pressed SiC. Failure initiated predominantly via the propagation of extrinsic machining-induced flaws for the range of grain sizes and machining grit sizes studied. These results are consistent with the region of large-grain-size flaw control as delineated by Prochazka and Charles. The severity of machining-induced flaws, relative to the machining grit size, decreased with increasing machining grit size and decreasing SiC grain size.

  9. Research on factors influencing on the microwave permeability of nanocrystalline FeB alloys

    Institute of Scientific and Technical Information of China (English)

    Fu Cheng-Wu; Zhang Shuan-Qin

    2007-01-01

    Nanocrystalline FeB alloys have been prepared with optimized grain size and internal stress. Samples prepared under different annealing conditions are analysed by x-ray diffraction, and the permeability μ(ω) is measured by HP8510B Vector Network Analyser in the frequency range 2-18GHz. The results show that annealing leads to the growth of the grain size and reduces the internal stress, and smaller grain size and larger internal stress favours the magnetic dissipation.

  10. Deltaic processes on Titan - the role of grain size

    Science.gov (United States)

    Witek, Piotr; Czechowski, Leszek

    2015-04-01

    In Titan's polar regions the Cassini spacecraft observed numerous hydrocarbon lakes surrounded by river valley systems. The rivers transport sediments to the lakes which serve as local sedimentary basins. The shape and evolution of the sedimentary deposits depends, among other parameters, on grain size. This is a result of dependence of settling velocity and drag force on diameter of the sediment particle. In consequence the deltas and alluvial cones take different shapes depending on the source of sediments and the distance from the source, due to natural sorting of rocky material. We used numerical models to simulate development of river deltas in Titanian and terrestrial conditions. Despite differences in gravity and composition, affecting effectiveness of sediment transport, we found many similarities in evolution of sedimentary landforms on both bodies. This gives us another tool for understanding the evolution of the surface of this unique moon.

  11. Image - Rice Grain Scanner: a three-dimensional fully automated assessment of grain size and quality traits

    Directory of Open Access Journals (Sweden)

    Rubens Marschalek

    2016-12-01

    Full Text Available The Image is a scanner developed as a grain classifier for quality control at the rice industry based on Brazilian official norms. It orders the dehulled grains ensuring that each grain would pass individually, in free fall, while the grain is analysed from different sides, covering its whole surface. It ensures a precise three-dimensional measurement of grain size, chalkiness, defects of the grain, milling quality, given out a total of 39 traits/classes/defects/values, which are sent to a excel Microsoft spreadsheet. This is managed through a digital platform which analysis routine and layout were developed and designed by Selgron and Epagri to fit the needs of research. The scanner and its software reach outputs that enhance rice breeding efficiency for grain quality, performing it faster, precisely and with a high-throughput phenotyping than ever before, especially interesting in very early breeding generations.

  12. Superplastic Micro-forming Mechanism and Size Effects of Micro-array Made of Nanocrystalline Material%纳米材料微阵列超塑微成形机理与尺度效应

    Institute of Scientific and Technical Information of China (English)

    王国峰; 李优; 刘奇; 赵相禹

    2015-01-01

    微成形技术是未来批量制造高精密微小零件的关键技术,但是,微小尺度下材料的塑性变形行为不仅表现出明显的尺度效应,而且零件尺度已经接近常规材料的晶粒尺寸,每个晶粒的形状、取向、变形特征对整体变形产生复杂的影响,难以保证微成形的工艺稳定性。本项目采用纳米材料进行微成形,制造微阵列,零件内部包含大量的晶粒,可以排除晶粒复杂性的影响,而且纳米材料具有超塑性,在超塑状态下,变形抗力和摩擦力都明显降低,从而显著降低微成形工艺对模具性能的苛刻要求,提高工艺稳定性和成形精度。目前,纳米材料超塑性微成形技术方面的研究极少,变形时纳米材料的力学行为、变形机理、尺度效应、位错演化、力学模型等关键问题还有待研究。采用电沉积技术制备晶粒尺寸可控的纳米材料,将工艺实验研究、性能测试、组织分析、力学性能表征、数值模拟相结合,深入探究了纳米材料微阵列超塑性微成形机理和成形规律,以促进该技术的广泛应用。%ABSTRACT:Micro-forming is a key technique for fabricating high-precision micro-part in large volume. However, plastic deformation at small scale has obvious size effects. The shape, orientation and deformation behavior of each grain have complicated influence on the micro-forming, since the scale of the parts approaches to the size of grain in common materi-als. Consequently, it is very hard to ensure the processing stability of micro-forming. In the current project, nanocrystalline materials were used to form micro-array. The influence of grain complexity could be eliminated since there were a lot of grains in the micro-part. In addition, nanocrystalline materials usually have superplasticity. Under this condition, the de-formation force and friction decrease obviously, which decreases the requirement on the mechanical

  13. Microstructure and Performances of Nanocrystalline Zinc-nickel Alloy Coatings

    Institute of Scientific and Technical Information of China (English)

    LIGuang-yu; LIANJian-she; NIULi-yuan; JIANGZhong-hao

    2004-01-01

    Nanocrystalline zinc-nickel alloy coatings were deposited from an alkaline zincate bath contained an organic additive that can reduce polarization and a complexing agent. SEM and TEM observations and XRD analysis were performed to examine the microstructure and phase composition of the coatings. The nickel content in deposits is 12.0-14.7% and the coating is consisted of single nanectystalline γ-phase structure (Ni5Zn21), with grain average grain size about 15nm. The nanocrystalline zinc-nickel alloy coatings have better corrosion resistance, less brittleness and higher microhardness than the conventional zinc coatings.

  14. Effect of Flake Thickness on Coercivity of Nanocrystalline SmCo5 Bulk Prepared from Anisotropic Nanoflake Powder (Postprint)

    Science.gov (United States)

    2016-08-23

    milling parameter of ball-to-powder weight ratio. XRD analysis revealed that as-milled flake powders possessed nanocrystalline grains with no observable...ball-to-powder weight ratio. XRD anal- ysis revealed that as-milled flake powders possessed nanocrystalline grains with no observable oxide peaks. The...grinded down to the designated particle size. The starting powder was milled in a stainless steel vial on a SPEX 8000 mill. Milling balls with

  15. Grain size reduction due to fracturing and subsequent grain-size-sensitive creep in a lower crustal shear zone in the presence of a CO2-bearing fluid

    Science.gov (United States)

    Okudaira, Takamoto; Shigematsu, Norio; Harigane, Yumiko; Yoshida, Kenta

    2017-02-01

    To understand rheological weakening in the lower continental crust, we studied mylonites in the Paleoproterozoic Eidsfjord anorthosite, northern Norway. The zones of anorthositic mylonites range from a few millimeters to several meters thick, and include ultramylonites and protomylonites. They contain syn-kinematic metamorphic minerals, including Cl-bearing amphibole and scapolite. Thermodynamic analysis reveals that syn-deformational hydration reactions occurred at ∼600 °C and ∼700 MPa under CO2-bearing conditions. The protomylonites contain many fragmented plagioclase porphyroclasts. The fractures in porphyroclasts are filled with fine-grained plagioclase, suggesting that fracturing is a common mechanism of grain size reduction. The anorthite contents of fine-grained polygonal matrix plagioclase are different from those of porphyroclastic plagioclase, suggesting that the matrix grains nucleated and grew during syn-kinematic metamorphism. Plagioclase aggregates in the matrices of mylonites do not exhibit a distinct crystallographic preferred orientation, which implies that the dominant deformation mechanism was grain-size-sensitive creep. Consequently, in the lower crustal anorthositic mylonites, grain size reduction occurred via fracturing, rather than through dynamic recrystallization, leading to grain-size-sensitive creep. The syn-kinematic recrystallization of minor phases at plagioclase grain boundaries may suppress the growth of plagioclase and contribute to the development of grain-size-sensitive creep.

  16. Effect of zirconium on grain growth and mechanical properties of a ball-milled nanocrystalline FeNi alloy

    Energy Technology Data Exchange (ETDEWEB)

    Kotan, Hasan, E-mail: hkotan@ncsu.edu [Department of Materials Science and Engineering, NC State University, 911 Partners Way, Room 3078, Raleigh, NC 27606-7907 (United States); Darling, Kris A. [U.S. Army Research Laboratory, Weapons and Materials Research Directorate, RDRL-WMM-F, Aberdeen Proving Ground, MD 21005-5069 (United States); Saber, Mostafa; Koch, Carl C.; Scattergood, Ronald O. [Department of Materials Science and Engineering, NC State University, 911 Partners Way, Room 3078, Raleigh, NC 27606-7907 (United States)

    2013-02-25

    Highlights: Black-Right-Pointing-Pointer Pure Fe, Fe{sub 92}Ni{sub 8}, and Fe{sub 91}Ni{sub 8}Zr{sub 1} powders were hardened up to 10 GPa by ball milling. Black-Right-Pointing-Pointer Annealing of Fe and Fe{sub 92}Ni{sub 8} leads to reduced hardness and extensive grain growth. Black-Right-Pointing-Pointer The addition of Zr to Fe{sub 92}Ni{sub 8} increases its stability and strength by second phases. Black-Right-Pointing-Pointer The second phases are found to promote the stability of Fe{sub 91}Ni{sub 8}Zr{sub 1} by Zener pinning. Black-Right-Pointing-Pointer The Zr-containing precipitates contribute to the overall strength of the material. - Abstract: Grain growth of ball-milled pure Fe, Fe{sub 92}Ni{sub 8}, and Fe{sub 91}Ni{sub 8}Zr{sub 1} alloys has been studied using X-ray diffractometry (XRD), focused ion beam (FIB) microscopy and transmission electron microscopy (TEM). Mechanical properties with respect to compositional changes and annealing temperatures have been investigated using microhardness and shear punch tests. We found the rate of grain growth of the Fe{sub 91}Ni{sub 8}Zr{sub 1} alloy to be much less than that of pure Fe and the Fe{sub 92}Ni{sub 8} alloy at elevated temperatures. The microstructure of the ternary Fe{sub 91}Ni{sub 8}Zr{sub 1} alloy remains nanoscale up to 700 Degree-Sign C where only a few grains grow abnormally whereas annealing of pure iron and the Fe{sub 92}Ni{sub 8} alloy leads to extensive grain growth. The grain growth of the ternary alloy at high annealing temperatures is coupled with precipitation of Fe{sub 2}Zr. A fine dispersion of precipitated second phase is found to promote the microstructural stability at high annealing temperatures and to increase the hardness and ultimate shear strength of ternary Fe{sub 91}Ni{sub 8}Zr{sub 1} alloy drastically when the grain size is above nanoscale.

  17. Analysis of EBSD Grain Size Measurements Using Microstructure Simulations and a Customizable Pattern Matching Library for Grain Perimeter Estimation

    Science.gov (United States)

    Coutinho, Y. A.; Rooney, S. C. K.; Payton, E. J.

    2017-03-01

    Grain size data from electron backscatter diffraction (EBSD) maps are often reported as the mean of the circle equivalent diameters of the measured grain areas. Circle equivalent diameters are not directly comparable to the lineal intercept measurements more historically common for grain size characterization in analog optical microscopy. While the value of mean lineal intercept is the same in 2D and 3D for a given probe direction, the mean 2D circle equivalent section diameter is not directly related to any 3D property. Estimation of mean lineal intercept from circle equivalent diameter is usually carried out by again assuming feature circularity, despite the obvious corners that are inherent to grains from the requirements of space filling. A direct conversion between section areas and lineal intercepts can be performed if the grain perimeters are known. In the present work, a novel pattern matching library approach is investigated for measurement of grain perimeters using simulated 2D EBSD maps. The results are compared to alternative approaches for perimeter measurement and assessed with respect to spatial resolution, grain size distribution parameters, and relevant ASTM and ISO measurement standards. The benefits and drawbacks of each approach are discussed. Empirical estimators for conversion between lineal intercept, circle equivalent diameter, and ASTM grain size number are presented.

  18. Two-size approximation: a simple way of treating the evolution of grain size distribution in galaxies

    CERN Document Server

    Hirashita, Hiroyuki

    2014-01-01

    Full calculations of the evolution of grain size distribution in galaxies are in general computationally heavy. In this paper, we propose a simple model of dust enrichment in a galaxy with a simplified treatment of grain size distribution by imposing a `two-size approximation'; that is, all the grain population is represented by small (grain radius a 0.03 micron) grains. We include in the model dust supply from stellar ejecta, destruction in supernova shocks, dust growth by accretion, grain growth by coagulation and grain disruption by shattering, considering how these processes work on the small and large grains. We show that this simple framework reproduces the main features found in full calculations of grain size distributions as follows. The dust enrichment starts with the supply of large grains from stars. At a metallicity level referred to as the critical metallicity of accretion, the abundance of the small grains formed by shattering becomes large enough to rapidly increase the grain abundance by acc...

  19. Preparation and mechanism study of bulk pure rare-earth metals with amorphous and nanocrystalline structures

    Institute of Scientific and Technical Information of China (English)

    LI ErDong; SONG XiaoYan; ZHANG JiuXing; LU NianDuan

    2007-01-01

    The preparation and the mechanism study of bulk pure rare-earth metals with amorphous and nanocrystalline structures, which were produced by spark plasma sintering (SPS), were carried out in this paper. With different processing parameters, the amorphous, two phases of amorphous and nanocrystalline, and complete nanocrystalline microstructures have been obtained. The nano-grain sizes in the bulk nanocrystalline materials are found smaller than the original powder particles sizes, which may change the conventional viewpoint that the grains in the sintered bulk are generally coarser than the raw powder particles. The technique developed in the present work can be extended to the preparation of many other nano bulk metal materials, and thus enables the studies of the nano-size effects on the physical, chemical and mechanical properties of bulk nano materials.

  20. Effects of grain size and grain boundary on critical current density of high T(sub c) superconducting oxides

    Science.gov (United States)

    Zhao, Y.; Zhang, Q. R.; Zhang, H.

    1990-01-01

    By means of adding impurity elements in high T sub c oxides, the effects were studied of grain size and grain boundary on the critical current density of the following systems: YBa2Cu3O(7-y) and Bi-Pr-Sr-Ca-Cu-O. In order to only change the microstructure instead of the superconductivity of the grains in the samples, the impurity elements were added into the systems in terms of the methods like this: (1) substituting Y with the lanthanide except Pr, Ce, and Tb in YBa2Cu3O(7-y) system to finning down grains in the samples, therefore, the effect can be investigated of the grain size on the critical current density of 1:2:3 compounds; (2) mixing the high T sub c oxides with the metal elements, such as Ag, according to the composition of (high T sub c oxide)1-xAgx to metallize the grain boundaries in the samples, studying the effect of the electric conductivity of the grain boundaries on the critical current density; (3) adding SiO2, PbO2, and SnO2 into the high T sub c oxide to form impurity phases in the grain boundaries, trying to find out the effects of the impurity phases or metalloid grain boundaries on the critical current density of the high T sub c superconductors. The experimental results indicate that in the case of of the presence of the metalloid grain boundaries finning down grains fails to enhance the j sub c, but restrains it strongly, the granular high T sub c superconductors with the small size grains coupled weakly is always the low j sub c system.

  1. Numerical modelling of riverbed grain size stratigraphic evolution

    Institute of Scientific and Technical Information of China (English)

    Peng HU; Zhi-xian CAO; Gareth PENDER; Huai-han LIU

    2014-01-01

    For several decades, quantification of riverbed grain size stratigraphic evolution has been based upon the active layer formulation (ALF), which unfortunately involves considerable uncertainty. While it is the sediment exchange across the bed surface that directly affects the riverbed stratigraphy, it has been assumed in the ALF that the sediment fraction at the lower interface of the active layer is a linear function of the sediment fraction in the flow. Here it is proposed that the sediment fraction of the sediment exchange flux is used directly in estimating the sediment fraction at the lower surface of the active layer. Together with the size-specific mass conservation for riverbed sediment, the modified approach is referred to as the surface-based formulation (SBF). When incorporated into a coupled non-capacity modelling framework for fluvial processes, the SBF leads to results that agree as well or better than those using ALF with laboratory and field observations. This is illustrated for typical cases featuring bed aggradation and degradation due to graded bed-load sediment transport. Systematic experiments on graded sediment transport by unsteady flows are warranted for further testing the modified formulation.

  2. Holocene marine transgression as interpreted from bathymetry and sand grain size parameters off Gopalpur

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, K.M.; Rajamanickam, G.V.; Rao, T.C.S.

    Grain size statistical parameters of the surface sediment samples collected from the innershelf off Gopalpur were calculated using graphic and moment methods. Fine-grained sand present up to 15 m water depth shows symmetrical skewness and good...

  3. Grain size effect of monolayer MoS2 transistors characterized by second harmonic generation mapping

    KAUST Repository

    Lin, Chih-Pin

    2015-08-27

    We investigated different CVD-synthesized MoS2 films, aiming to correlate the device characteristics with the grain size. The grain size of MoS2 can be precisely characterized through nondestructive second harmonic generation mapping based on the degree of inversion symmetry. The devices with larger grains at the channel region show improved on/off current ratio, which can be explained by the less carrier scattering caused by the grain boundaries.

  4. Properties of nanocrystalline copper prepared by vacuum-warm-compaction method

    Institute of Scientific and Technical Information of China (English)

    CHU Guang; LIU Wei; YANG Tian-zu; TANG Yong-jian

    2009-01-01

    Nanocrystalline Cu with average grain size of 22.8-25.3 nm was prepared by vacuum-warm-compaction method. Scanning electronic microscope, HMV-2 type microhardness tester, X-ray diffractometer, and 6157 type electrometer were used to determine the microstructure, microhardness and electrical resistivity of as-prepared nanocrystalline Cu, respectively. The results show that the microhardness of nanocrystalline Cu increases with larger pressure, longer duration of pressure or higher temperature. The highest microhardness of nanocrystalline Cu is 3.8 GPa, which is 7 times higher than that of coarse-grained copper. The electrical resistivity of as-prepared specimens is (1.2-1.4)×10-7 Ω·m at temperature 233-293 K, which is 5-6 times higher than that of the coarse-grained copper.

  5. SMALL GRAIN 1, which encodes a mitogen-activated protein kinase kinase 4, influences grain size in rice.

    Science.gov (United States)

    Duan, Penggen; Rao, Yuchun; Zeng, Dali; Yang, Yaolong; Xu, Ran; Zhang, Baolan; Dong, Guojun; Qian, Qian; Li, Yunhai

    2014-02-01

    Although grain size is one of the most important components of grain yield, little information is known about the mechanisms that determine final grain size in crops. Here we characterize rice small grain1 (smg1) mutants, which exhibit small and light grains, dense and erect panicles and comparatively slightly shorter plants. The short grain and panicle phenotypes of smg1 mutants are caused by a defect in cell proliferation. The smg1 mutations were identified, using a map-based cloning approach, in mitogen-activated protein kinase kinase 4 (OsMKK4). Relatively higher expression of OsMKK4/SMG1 was detected in younger organs than in older ones, consistent with its role in cell proliferation. Green fluorescent protein (GFP)-OsMKK4/SMG1 fusion proteins appear to be distributed ubiquitously in plant cells. Further results revealed that OsMKK4 influenced brassinosteroid (BR) responses and the expression of BR-related genes. Thus, our findings have identified OsMKK4 as a factor for grain size, and suggest a possible link between the MAPK pathways and BRs in grain growth. © 2013 The Authors The Plant Journal © 2013 John Wiley & Sons Ltd.

  6. Effects of Technical Conditions on Structure, Morphology and Crystalline Size of Nanocrystalline Nd-Doped Ceria Powders

    Institute of Scientific and Technical Information of China (English)

    Gao Yong; Wang Lingling; Liu Huangqing

    2004-01-01

    Nanocrystalline solid solution CeO2-Nd2O3 powders were prepared by low temperature combustion process.Special attention was paid to the influence of the glycine/metal ratio and calcination temperature on the powders phase structure, morphology and particle size.TG-DSC curves and XRD peaks of different glycine/metal ratio show that smaller particle size can be obtained with a slightly fuel-deficient ratio.XRD results indicate that the as-prepared powders are crystallized in a single fluorite structure.The crystalline size ranges from 9 to 24 nm, which increases with the increase of calcination temperature.The lower SEM images were characterized by the spongy and form-like microstructure of the powders.Organic agent may be gradually eliminated by high temperature calcination process.

  7. Grain growth of ε-iron: Implications to grain size and its evolution in the Earth's inner core

    Science.gov (United States)

    Yamazaki, Daisuke; Tsujino, Noriyoshi; Yoneda, Akira; Ito, Eiji; Yoshino, Takashi; Tange, Yoshinori; Higo, Yuji

    2017-02-01

    Knowledge of grain growth rate of ε-iron can put constraint on estimation of the grain size in the inner core. We determined grain growth rate of ε-iron at ∼55 GPa and 1200-1500 K by means of in-situ X-ray diffraction observation to be Gn - G0n = kt, where G (m) is the grain size at time t (s), G0 (m) is the initial grain size, n is growth exponent (fixed to 2) and k is the growth constant expressed as k =k0 exp ⁡ (-H* / RT) with log k0 (mn /s) = - 5.8 (± 2.4) and activation enthalpy H* = 221 (± 61) kJ /mol, and R is the gas constant and T is the absolute temperature. Extrapolation of the grain growth law of ε-iron to the inner core conditions suggests that the grain size in the inner core is in a range from several hundred meters to several kilometers, which is intermediate among the previous estimations, and hence the dominant deformation mechanism is considered to be Harper-Dorn creep rather than diffusion creep as pointed out by the previous work. This indicates the relatively uniform viscosity in the entire inner core.

  8. Modeling nano-scale grain growth of intermetallics

    Indian Academy of Sciences (India)

    Mohsen Kazeminezhad

    2009-02-01

    The Monte Carlo simulation is utilized to model the nano-scale grain growth of two nanocrystalline materials, Pd81Zr19 and RuAl. In this regard, the relationship between the real time and the time unit of simulation, i.e. Monte Carlo step (MCS), is determined. The results of modeling show that with increasing time of heating, the grain sizes of both nano-crystalline materials increased as in the case of conventional materials. Moreover, it is found that for both nano-crystalline materials the relationship between the real time and MCS is in power law form, which is linear for the conventional materials.

  9. Synthesis and Characterization of Electrodeposited Nanocrystalline Nickel

    Institute of Scientific and Technical Information of China (English)

    DAI Pin-qiang; YU Hui, LI Qiang

    2004-01-01

    Nanocrystalline nickel was synthesize d by direct current electrodeposition from a modified Watts-type bath. X-ray diffraction and transmission electron microscope were used to characterize the microstructure of nickel deposits. The results show that nanocrytalline nickel with grain sizes in the range 20~50nm can be synthesized from saccharin-containing Watts-type baths with current density range 5~30A/dm2. There existed preferred orientation in the deposits and it changed progressively from a (200) fibre texture to a (111) (200) double fibre texture as saccharin concentration increased. The hardness of the deposits increased prominently as grain size decreased to nanometer range.

  10. Synthesis and Characterization of Electrodeposited Nanocrystalline Nickel

    Institute of Scientific and Technical Information of China (English)

    DAIPin-qiang; YUHui; LIQiang

    2004-01-01

    Nanocrystalline nickel was synthesized by direct current electrodeposition from a modified Watts-type bath. X-ray diffraction and transmission electron microscope were used to characterize the microstructure of nickel deposits. The results show that nanocrytalline nickel with grain sizes in the range 20-50nm can be synthesized from saccharin-containing Watts-type baths with current density range 5-30A/dm2. There existed preferred orientation in the deposits and it changed progressively from a (200) fibre texture to a (111) (200) double fibre texture as saccharin concentration increased. The hardness of the deposits increased prominently as grain size decreased to nanometer range.

  11. Grain size influences the corrosion and cavitation of Ni3Al intermetallic alloys

    Directory of Open Access Journals (Sweden)

    D. Zasada

    2015-01-01

    Full Text Available Influence of grain size on corrosion and cavitation of the Ni3Al - based intermetallic alloy was studied in recent paper. The research was conducted on Ni3Al - based intermetallic alloy doped with boron and zirconium. The initial grain size of 6, 20 and 45 μm the investigated samples was obtained through cold rolling followed by recrystallization annealing. It was found that initial grain size does not influence the breakthrough potential neither repassivation potential. On the other hand, various types of pits were found for alloys with different grain size during corrosion tests in sodium chloride solutions. It was found that increase of grain size results with reducing the depth of cavitational pits. However, surface area of the pits increases with increasing grain size.

  12. Determination of grain-size characteristics from electromagnetic seabed mapping data: A NW Iberian shelf study

    Science.gov (United States)

    Baasch, Benjamin; Müller, Hendrik; von Dobeneck, Tilo; Oberle, Ferdinand K. J.

    2017-05-01

    The electric conductivity and magnetic susceptibility of sediments are fundamental parameters in environmental geophysics. Both can be derived from marine electromagnetic profiling, a novel, fast and non-invasive seafloor mapping technique. Here we present statistical evidence that electric conductivity and magnetic susceptibility can help to determine physical grain-size characteristics (size, sorting and mud content) of marine surficial sediments. Electromagnetic data acquired with the bottom-towed electromagnetic profiler MARUM NERIDIS III were analysed and compared with grain size data from 33 samples across the NW Iberian continental shelf. A negative correlation between mean grain size and conductivity (R=-0.79) as well as mean grain size and susceptibility (R=-0.78) was found. Simple and multiple linear regression analyses were carried out to predict mean grain size, mud content and the standard deviation of the grain-size distribution from conductivity and susceptibility. The comparison of both methods showed that multiple linear regression models predict the grain-size distribution characteristics better than the simple models. This exemplary study demonstrates that electromagnetic benthic profiling is capable to estimate mean grain size, sorting and mud content of marine surficial sediments at a very high significance level. Transfer functions can be calibrated using grains-size data from a few reference samples and extrapolated along shelf-wide survey lines. This study suggests that electromagnetic benthic profiling should play a larger role for coastal zone management, seafloor contamination and sediment provenance studies in worldwide continental shelf systems.

  13. Synthesis and characterization of nanocrystalline Ni produced by cryomilling in liquid nitrogen

    Institute of Scientific and Technical Information of China (English)

    YANG Bin; FAN Jianzhong; HAO Bin; TIAN Xiaofeng; CHENG Junsheng; ZHANG Jishan

    2007-01-01

    Nanocrystalline Ni powders were successfully fabricated by mechanically milling at cryogenic temperature (cryomilling) with 1 wt.%Y2O3 particles. The experimental results have shown that the Ni grain size is reduced to 25 nmafter 2 h of cryomilling in the presence of the Y2O3 particles. The cryomilled Ni/Y2O3 powders can maintain their nanocrystalline structure up to 900℃, or 62% of the melting point of Ni. A bulk nanocrystalline Ni/Y2O3 material with a thermally stable grain size of approximately 100 nm was produced by cryomilling, cold isostatic pressing, followed by hot isostatic pressing. The microhardness of bulk nanocrystalline Ni/1wt.%Y2O3 is 315 DPH, which is two times as high as that of conventional Ni.

  14. Recrystallization Behavior Design for Controlling Grain Size in Strip Rolling Process

    Institute of Scientific and Technical Information of China (English)

    ZHU Guo-hui; S V Subramanian

    2008-01-01

    To promote effectively dynamic recrystallization and obtain a homogeneous distribution of ultrafine grain size in strip finish rolling process, the behavior of static and dynamic recrystallization must be appropriately designed to provide an ultrafine austenite microstructure without mixed grain size. The design of rolling schedule was analyzed based on the control of the recrystallization behavior to achieve ultrafine grain size in the strip rolling process of niobium microalloyed steel. The experimental simulations were presented to validate the twice dynamic recrystallization design to achieve ultrafine grain size control.

  15. Material grain size characterization method based on energy attenuation coefficient spectrum and support vector regression.

    Science.gov (United States)

    Li, Min; Zhou, Tong; Song, Yanan

    2016-07-01

    A grain size characterization method based on energy attenuation coefficient spectrum and support vector regression (SVR) is proposed. First, the spectra of the first and second back-wall echoes are cut into several frequency bands to calculate the energy attenuation coefficient spectrum. Second, the frequency band that is sensitive to grain size variation is determined. Finally, a statistical model between the energy attenuation coefficient in the sensitive frequency band and average grain size is established through SVR. Experimental verification is conducted on austenitic stainless steel. The average relative error of the predicted grain size is 5.65%, which is better than that of conventional methods.

  16. Influence of particle size on H2 and H2S sensing characteristics of nanocrystalline zinc ferrite

    Science.gov (United States)

    Ghosh, P.; Das, M. R.; Mitra, P.

    2016-12-01

    Nanocrystalline zinc ferrite ZnFe2O4 was synthesized by sol-gel self-combustion technique. Ball milling at room temperature was carried out to control the particle size. Characterization of synthesized powders was made using X-ray diffraction and transmission electron microscopy analysis. Fine powders resulted from milling were used to prepare gas sensing elements in pellet form. The gas-sensing properties were studied in presence of hydrogen and hydrogen sulphide as test gases. The gas response behavior was found to be strongly influenced by the particle size. Significantly high sensitivity of 82 % was found for 7 nm zinc ferrite in presence of 200 ppm H2S at an operating temperature of 150 °C. Sensitivity was found to increase with temperature before being maximum at a particular operating temperature.

  17. The Effects of Grain Size and Temperature Distributions on the Formation of Interstellar Ice Mantles

    CERN Document Server

    Pauly, Tyler

    2015-01-01

    Computational models of interstellar gas-grain chemistry have historically adopted a single dust-grain size of 0.1 micron, assumed to be representative of the size distribution present in the interstellar medium. Here, we investigate the effects of a broad grain-size distribution on the chemistry on dust-grain surfaces and the subsequent build-up of molecular ices on the grains, using a three-phase gas-grain chemical model of a quiescent dark cloud. We include an explicit treatment of the grain temperatures, governed both by the visual extinction of the cloud and the size of each individual grain-size population. We find that the temperature difference plays a significant role in determining the total bulk ice composition across the grain-size distribution, while the effects of geometrical differences between size populations appear marginal. We also consider collapse from a diffuse to a dark cloud, allowing dust temperatures to fall. Under the initial diffuse conditions, small grains are too warm to promote ...

  18. Nanocrystalline magnetite thin films grown by dual ion-beam sputtering

    Energy Technology Data Exchange (ETDEWEB)

    Prieto, Pilar, E-mail: pilar.prieto@uam.es [Departamento de Física Aplicada M-12, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid (Spain); Ruiz, Patricia [Departamento de Física Aplicada M-12, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid (Spain); Ferrer, Isabel J. [Departamento de Física de Materiales M-4, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid (Spain); Figuera, Juan de la; Marco, José F. [Instituto de Química Física “Rocasolano”, CSIC, Serrano 119, 28006 Madrid (Spain)

    2015-07-05

    Highlights: • We have grown tensile and compressive strained nanocrystalline magnetite thin films by dual ion beam sputtering. • The magnetic and thermoelectric properties can be controlled by the deposition conditions. • The magnetic anisotropy depends on the crystalline grain size. • The thermoelectric properties depend on the type of strain induced in the films. • In plane uniaxial magnetic anisotropy develops in magnetite thin films with grain sizes ⩽20 nm. - Abstract: We have explored the influence of an ion-assisted beam in the thermoelectric and magnetic properties of nanocrystalline magnetite thin films grown by ion-beam sputtering. The microstructure has been investigated by XRD. Tensile and compressive strained thin films have been obtained as a function of the parameters of the ion-assisted beam. The evolution of the in-plane magnetic anisotropy was attributed to crystalline grain size. In some films, magneto-optical Kerr effect measurements reveal the existence of uniaxial magnetic anisotropy induced by the deposition process related with a small grain size (⩽20 nm). Isotropic magnetic properties have observed in nanocrystalline magnetite thin film having larger grain sizes. The largest power factor of all the films prepared (0.47 μW/K{sup 2} cm), obtained from a Seebeck coefficient of −80 μV/K and an electrical resistivity of 13 mΩ cm, is obtained in a nanocrystalline magnetite thin film with an expanded out-of-plane lattice and with a grain size ≈30 nm.

  19. A strain gradient crystal plasticity analysis of grain size effects in polycrystals

    DEFF Research Database (Denmark)

    Borg, Ulrik

    2007-01-01

    individually oriented grains, in a unit cell, each having three planar slip systems. An energy potential that penalizes crystallographic slip at grain boundaries is included in the analyzes. The polycrystal is subjected to plane strain tension for various grain sizes and higher order boundary conditions...

  20. Martensitic transformations in nanostructured nitinol: Finite element modeling of grain size and distribution effects

    DEFF Research Database (Denmark)

    Liu, Hong-Sheng; Mishnaevsky, Leon

    2013-01-01

    A computational model of martensitic phase transformation in nanostructured nitinol is developed which takes into account the grain size effect. On the basis of the theoretical analysis of the thermodynamic transformation criterion and the energy barrier for phase transformation, it was demonstra...... between the coarse and fine grained regions, and expand inside the region with small grains along the shear band direction....

  1. Analytical Investigation of Prior Austenite Grain Size Dependence of Low Temperature Toughness in Steel Weld Metal

    Institute of Scientific and Technical Information of China (English)

    X.F. Zhang; P. Hall; H. Terasak; M. Sato; Y. Komizo

    2012-01-01

    Prior austenite grain size dependence of the low temperature impact toughness has been addressed in the bainitic weld metals by in situ observations.Usually,decreasing the grain size is the only approach by which both the strength and the toughness of a steel are increased.However,low carbon bainitic steel with small grain size shows a weakening of the low temperature impact toughness in this study.By direct tracking of the morphological evolution during phase transformation,it is found that large austenite grain size dominates the nucleation of intragranular acicular ferrite,whereas small austenite grain size leads to grain boundary nucleation of bainite.This kinetics information will contribute to meet the increasing low temperature toughness requirement of weld metals for the storage tanks and offshore structures.

  2. Grain Size Effect on Fracture Behavior of the Axis-Tensile Test of Inconel 718 Sheet

    Science.gov (United States)

    Liu, B. B.; Han, J. Q.; Zhao, R.; Liu, W.; Wan, M.

    2016-11-01

    Change in mechanical parts from macro-size to micro-size has become a trend in the metal- and alloy-forming process, with an increasing demand on micro-parts in the last decades. The material mechanical behaviors of micro-size parts are quite different from the conventional ones of macro-size parts due to size effect. It is necessary to further investigate the effects of grain size on material mechanisms in micro-scales, especially fracture behaviors. The fracture behaviors of Inconel 718 sheet with the thickness of 300 μm are studied by uniaxial tensile tests in different grain sizes ranging from 18 to 130 μm. The results show that fracture stress and strain decrease with the increase of grain size. A critical value in the specimen thickness (t) to grain size (d) ratio divides the strength levels into separate stages on the basis of an increase of the inverse of grain size. In addition, the grain size-dependent fracture morphology is changed in the number of dimples and micro-voids decreasing on the fracture surfaces and the sizes of micro-voids changing larger with the increase of grain size.

  3. Mechanical model for yield strength of nanocrystalline materials under high strain rate loading

    Institute of Scientific and Technical Information of China (English)

    朱荣涛; 周剑秋; 马璐; 张振忠

    2008-01-01

    To understand the high strain rate deformation mechanism and determine the grain size,strain rate and porosity dependent yield strength of nanocrystalline materials,a new mechanical model based on the deformation mechanism of nanocrystalline materials under high strain rate loading was developed.As a first step of the research,the yield behavior of the nanocrystalline materials under high strain rate loading was mainly concerned in the model and uniform deformation was assumed for simplification.Nanocrystalline materials were treated as composites consisting of grain interior phase and grain boundary phase,and grain interior and grain boundary deformation mechanisms under high strain rate loading were analyzed,then Voigt model was applied to coupling grain boundary constitutive relation with mechanical model for grain interior phase to describe the overall yield mechanical behavior of nanocrystalline materials.The predictions by the developed model on the yield strength of nanocrysatlline materials at high strain rates show good agreements with various experimental data.Further discussion was presented for calculation results and relative experimental observations.

  4. WIDE AND THICK GRAIN 1, which encodes an otubain-like protease with deubiquitination activity, influences grain size and shape in rice.

    Science.gov (United States)

    Huang, Ke; Wang, Dekai; Duan, Penggen; Zhang, Baolan; Xu, Ran; Li, Na; Li, Yunhai

    2017-09-01

    Grain size and shape are two crucial traits that influence grain yield and grain appearance in rice. Although several factors that affect grain size have been described in rice, the molecular mechanisms underlying the determination of grain size and shape are still elusive. In this study we report that WIDE AND THICK GRAIN 1 (WTG1) functions as an important factor determining grain size and shape in rice. The wtg1-1 mutant exhibits wide, thick, short and heavy grains and also shows an increased number of grains per panicle. WTG1 determines grain size and shape mainly by influencing cell expansion. WTG1 encodes an otubain-like protease, which shares similarity with human OTUB1. Biochemical analyses indicate that WTG1 is a functional deubiquitinating enzyme, and the mutant protein (wtg1-1) loses this deubiquitinating activity. WTG1 is expressed in developing grains and panicles, and the GFP-WTG1 fusion protein is present in the nucleus and cytoplasm. Overexpression of WTG1 results in narrow, thin, long grains due to narrow and long cells, further supporting the role of WTG1 in determining grain size and shape. Thus, our findings identify the otubain-like protease WTG1 to be an important factor that determines grain size and shape, suggesting that WTG1 has the potential to improve grain size and shape in rice. © 2017 The Authors The Plant Journal © 2017 John Wiley & Sons Ltd.

  5. GS6, A Member of the GRAS Gene Family, Negatively Regulates Grain Size in Rice

    Institute of Scientific and Technical Information of China (English)

    Lianjun Sun; Xiaojiao Li; Yongcai Fu; Zuofeng Zhu; Lubin Tan; Fengxia Liu; Xianyou Sun; Xuewen Sun; Chuanqing Sun

    2013-01-01

    Grain size is an important yield-related trait in rice. Intensive artificial selection for grain size during domestication is evidenced by the larger grains of most of today’s cultivars compared with their wild relatives. However, the molecular genetic control of rice grain size is still not well characterized. Here, we report the identification and cloning of Grain Size 6 (GS6), which plays an important role in reducing grain size in rice. A premature stop at the þ348 position in the coding sequence (CDS) of GS6 increased grain width and weight significantly. Alignment of the CDS regions of GS6 in 90 rice materials revealed three GS6 alleles. Most japonica varieties (95%) harbor the Type I haplotype, and 62.9%of indica varieties harbor the Type II haplotype. Association analysis revealed that the Type I haplotype tends to increase the width and weight of grains more than either of the Type II or Type III haplotypes. Further investigation of genetic diversity and the evolutionary mechanisms of GS6 showed that the GS6 gene was strongly selected in japonica cultivars. In addition, a “ggc” repeat region identified in the region that encodes the GRAS domain of GS6 played an important historic role in the domestication of grain size in rice. Knowledge of the function of GS6 might aid efforts to elucidate the molecular mechanisms that control grain development and evolution in rice plants, and could facilitate the genetic improvement of rice yield.

  6. Synthesis and properties of nanocrystalline nonferrous metals prepared by flow-levitation-molding method

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Nanocrystalline nonferrous metals (Cu, Al, and Ag) were synthesized by flow-levitation-molding method. The microstructure of the as-prepared nanocrystalline metals was characterized by XRD and FESEM. The microhardness and electrical resistivity were tested by the HMV-2 type Microhardness Tester and 6157 type Electrometer, respectively. The synthesis process was also studied. The results show that the spheriform particles in nanocrystalline metals have average grain size of 20-30 nm. The relative density of nanocrystalline Cu, Al, and Ag are 95.1%, 98.1% and 98.3%, respectively. The microhardness of nanocrystalline Cu, Al and Ag are 2.01, 2.11 and 1.26 GPa respectively, which are larger than those of their coarse-grained counterparts by the factor of 4.5, 14, and 2.5, respectively. The electrical resistivity of nanocrystalline Cu at room temperature is 1.5 × 10-7 Ω·m, which is higher than coarse-grained Cu by a factor of 7.5. The pressure is the predominant factor influencing the density of the as-prepared nanocrystalline nonferrous metals.

  7. Characterizing the Large (cm-size) Grains Around Comet 103P/Hartley 2

    Science.gov (United States)

    Sunshine, Jessica M.; Feaga, Lori M.; Farnham, Tony; Protopapa, Silvia; Kelley, Michael S.; Engle, Anna

    2016-10-01

    During the flyby of comet 103P/Hartley 2, two populations of bright grains were identified in the coma. Small, 1 µm-sized, water ice-rich grains were observed near the small end of the nucleus that were dragged from the interior by CO2 gas emissions. At closest approach a population of larger grains was clearly seen in visible images off the large lobe. The estimated brightness of the isolated grains suggests that they are likely cm-sized particles and likely water ice-rich. Both sets of grains were simultaneously observed in visible images, at two different resolutions, and by Deep Impact infrared spectrometer. However, because of the difficulty in finding isolated grains in the infrared slit, the population of larger grains has not previously been characterized. Doing so allows us to determine both the reflected and thermal properties of the grains, which when compared to visible images can be used to constrain the size of the grains. Their spectral properties can also be used to definitively detect water ice as has been assumed from visible albedos. In addition, the infrared spectra can be used estimate the relative abundance and particle sizes of ice and non-ice components. The velocity and dynamics of these larger grains can also be characterized. These data will be compared with those of the population of smaller grains emanated directly from the nucleus.Funding from NASA'S Discovery Data Analysis Program (NNX16AJ93G) is greatfully acknowledged.

  8. Micrometer size grains of hot isostatically pressed alumina and its characterization

    Indian Academy of Sciences (India)

    A K Mallik; S Gangadharan; S Dutta; D Basu

    2010-08-01

    Alumina samples were prepared from two different particle size powders. Finer particle compacts when heated along with coarser particle compacts at same processing temperatures produce bigger grain microstructures due to higher grain growth. An unconventional method of etching by molten V2O5 was adopted to look at the microstructure for accuracy in reported data. On an average starting with finer particles give microstructure with a grain size of 5.5 m and starting with coarser particles, give microstructure with 2.2 m average grain size. The flexural strength is around 400 MPa for alumina samples prepared from finer powder in comparison with about 550 MPa for alumina samples prepared from coarser powder. The Vickers hardness in 5.5 m grain microstructure is around 20 GPa in comparison to about 18 GPa in microstructure with smaller grains of 2.2 m size.

  9. Derivation of Hillert-type 3D grain growth rate model with topological considerations and discussion on its grain size parameter

    Institute of Scientific and Technical Information of China (English)

    Guoquan Liu; Haibo Yu; Xiaoyan Song; Xiangge Qin; Chao Wang

    2004-01-01

    A Hillert-type three-dimensional grain growth rate model was derived through the grain topology-size correlation model,combined with a topology-dependent grain growth rate equation in three dimensions. It shows clearly that the Hillert-type 3D grain growth rate model may also be described with topology considerations of microstructure. The size parameter bearing in the model is further discussed both according to the derived model and in another approach with the aid of quantitative relationship between the grain size and the integral mean curvature over grain surface. Both approaches successfully demonstrate that, if the concerned grains can be well approximated by a space-filling convex polyhedra in shape, the grain size parameter bearing in the Hillert-type 3D grain growth model should be a parameter proportional to the mean grain tangent radius.

  10. Molten salt synthesis and luminescent properties of YVO4:Eu nanocrystalline phosphors

    Institute of Scientific and Technical Information of China (English)

    WANG Fang; LIU Chenglu; ZHOU Zhiqiang; JIA Peiyun; LIN Jun

    2012-01-01

    YVO4:Eu nanocrystalline phosphors were successfully prepared at 400 ℃ in equal moles of NaNO3 and KNO3 molten salts.NaOH concentration and annealing temperature played important roles in phase purity and crystallinity of the nanocrystallines,and the optimum NaOH concentration and annealing temperature were 6∶40 and 400 ℃,respectively.The nanocrystallines were well crystallized with a cubic morphology in an average grain size of 18 nm.Upon excitation of the vanadate groups at 314 nm,YVO4:Eu nanocrystallines exhibited the characteristic emission of Eu3+,which indicated that there was an energy transfer from vanadate groups to Eu3+.Moreover,the influence of superficial effect,especially the dangling bonds on the structure and luminescent properties of the nanocrystallines was discussed in detail.

  11. Deformation behavior and microstructural evolution of nanocrystalline aluminum alloys and composites

    Science.gov (United States)

    Ahn, Byungmin

    Nanocrystalline or ultrafine-grained Al alloys are often produced by severe plastic deformation methods and exhibit remarkably enhanced strength and hardness compared to conventional coarse-grained materials, resulting in great potential for structural applications. To achieve nanocrystalline structure, grains were refined by cryomilling (mechanical milling at cryogenic temperature) pre-alloyed powders. Cryomilling provides capability for rapid grain refinement and synthesis of commercial quantities (30-40 kg). The cryomilled powder was primarily consolidated by hot or cold isostatic pressing in general. Secondary consolidation was achieved by extrusion or forging. Alternatively, quasi-isostatic forging was applied either as an initial consolidation or as a further deformation step. To improve insufficient ductility and toughness of nanocrystalline materials, an intelligent design with microstructural modification was introduced by generation of multiple size scales. A bimodal grain structure consisting of nanocrystalline grains and inclusions of coarse-grained material was produced by consolidation of blended powders. The resulting materials exhibited enhanced ductility compared to 100% nanocrystalline materials, with only moderate decreases in strength. A similar process was used to produce hybrid trimodal microstructures comprised of regions of nanocrystalline and coarse grains, as well as hard ceramic particles, providing super-high compressive strength. For cryomilled nanocrystalline Al alloys, effects of degassing temperature were investigated in terms of microstructural evolution. Higher degassing temperatures resulted in higher density and lower hydrogen content, which can reduce loss of toughness in consolidated materials. Different consolidation methods were compared with regard to the relation between the microstructures and mechanical properties. Quasi-isostatic forging led to greater and more isotropic fracture toughness, compared with other processing

  12. Grain size in lithospheric-scale shear zones: Chicken or Egg?

    Science.gov (United States)

    Thielmann, M.; Rozel, A.; Kaus, B. J. P.; Ricard, Y.

    2012-04-01

    Lithospheric-scale shear zones are commonly defined as regions inhomogeneous and localized deformation. Strain softening has been demonstrated to be necessary for localization in those shear zones, but there is still debate about the physical cause of this softening. As natural shear zones typically have a significantly reduced grain size, it has been proposed that grain size reduction provides the necessary strain softening to localize deformation. As grain size reduces, the dominant deformation mechanism switches from dislocation to diffusion creep, thus requiring less stress to deform the rock. Until recently, the equilibrium grain size has been thought to follow a piezometric relationship, thus indicating the stress under which a shear zone deformed. More recent work (Austin and Evans (2007), Rozel et. al. (2011)) suggests that the equilibrium grain size is not dependent on stress, but rather on the deformational work. Using this relationship, we use numerical models to investigate the effect of grain size evolution on lithospheric deformation. We focus on the question if grain size provides sufficient weakening to effectively localize deformation under lithospheric conditions or if it's effect is rather passive and as such a marker for the deformational work done in a shear zone. We then compare the localization potential of grain size reduction to shear heating and investigate the interplay between the two weakening mechanisms.

  13. Grain-size dependence of superconductivity in dc sputtered Nb films

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The superconducting transition temperature and grain size of dc sputtered Nb films are systematically investigated. The results show that the superconductivity is closely related to the grain size, rather than to the scattering strength of electrons or the surface layer proximity effect of the films.

  14. Eyewitness Recall: Regulation of Grain Size and the Role of Confidence

    Science.gov (United States)

    Weber, Nathan; Brewer, Neil

    2008-01-01

    Eyewitness testimony plays a critical role in Western legal systems. Three experiments extended M. Goldsmith, A. Koriat, and A. Weinberg-Eliezer's (2002) framework of the regulation of grain size (precision vs. coarseness) of memory reports to eyewitness memory. In 2 experiments, the grain size of responses had a large impact on memory accuracy.…

  15. The effect of nitrogen on the formation of nanocrystalline copper thin films.

    Science.gov (United States)

    Calinas, R; Vieira, M T; Ferreira, P J

    2009-06-01

    The current success of nanocrystalline materials is due to their unusual and promising properties compared to coarser grain size materials. However, maintaining the nanocrystalline character during processes or applications is not an easy task, due to the tendency towards grain growth exhibited by nanocrystalline materials. It is well known that the addition of solutes with a strong affinity for grain boundary segregation can act as pinning centers and inhibit grain growth, particularly during the manufacturing process. However, the ideal is to use these elements/compounds only during manufacturing, and after that these elements must disappear in order to attain the desirable properties. The aim of this study is to produce nanocrystalline Cu-based thin films through controlled addition of nitrogen to inhibit grain growth. A detailed chemical composition, structural and grain size analysis of these thin films was made by Electron Probe Microanalysis (EPMA), X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). The results indicate that introduction of nitrogen, even in small amounts, leads to a significant decrease in grain size, particularly if Cu3N is not yielded in the thin film during the deposition process.

  16. A Modified Thermal Treatment Method for the Up-Scalable Synthesis of Size-Controlled Nanocrystalline Titania

    Directory of Open Access Journals (Sweden)

    Aysar Sabah Keiteb

    2016-10-01

    Full Text Available Considering the increasing demand for titania nanoparticles with controlled quality for various applications, the present work reports the up-scalable synthesis of size-controlled titanium dioxide nanocrystals with a simple and convenient thermal treatment route. Titanium dioxide nanocrystals with tetragonal structure were synthesized directly from an aqueous solution containing titanium (IV isopropoxide as the main reactant, polyvinyl pyrrolidone (PVP as the capping agent, and deionized water as a solvent. With the elimination of the drying process in a thermal treatment method, an attempt was made to decrease the synthesis time. The mixture directly underwent calcination to form titanium dioxide (TiO2 nanocrystalline powder, which was confirmed by FT-IR, energy dispersive X-ray spectroscopy (EDX, and X-ray diffraction (XRD analysis. The control over the size and optical properties of nanocrystals was achieved via variation in calcination temperatures. The obtained average sizes from XRD spectra and transmission electron microscopy (TEM images showed exponential variation with increasing calcination temperature. The optical properties showed a decrease in the band gap energy with increasing calcination temperature due to the enlargement of the nanoparticle size. These results prove that direct calcination of reactant solution is a convenient thermal treatment route for the potential large-scale production of size-controlled Titania nanoparticles.

  17. Effect of Grain Size on Mechanical Properties of Nickel-Free High Nitrogen Austenitic Stainless Steel

    Institute of Scientific and Technical Information of China (English)

    LI Hua-bing; JIANG Zhou-hua; ZHANG Zu-rui; YANG Yan

    2009-01-01

    The fine grained structures of nickel-free high nitrogen austenitic stainless steels had been obtained by means of cold rolling and subsequent annealing.The relationship between microstructure and mechanical properties and gain size of nickel-free high nitrogen austenitic stainless steels was examined.High strength and good ductility of the steel were found.In the grain size range,the Hall-Petch dependency for yield stress,tensile strength,and hardness was valid for grain size ranges for the nickel-free high nitrogen austenitic stainless steel.In the present study,the ductility of cold rolled nickel-free high nitrogen austenitic stainless steel decreased with annealing time when the grain size was refined.The fracture surfaces of the tensile specimens in the grain size range were covered with dimples as usually seen in a ductile fracture mode.

  18. A new method to determine the grain size of planetary regolith

    CERN Document Server

    Gundlach, Bastian

    2012-01-01

    Airless planetary bodies are covered by a dusty layer called regolith. The grain size of the regolith determines the temperature and the mechanical strength of the surface layers. Thus, knowledge of the grain size of planetary regolith helps to prepare future landing and/or sample-return missions. In this work, we present a method to determine the grain size of planetary regolith by using remote measurements of the thermal inertia. We found that small bodies in the Solar System (diameter less than ~100 km) are covered by relatively coarse regolith grains with typical particle sizes in the millimeter to centimeter regime, whereas large objects possess very fine regolith with grain sizes between 10 and 100 micrometer.

  19. Grain size, stress and creep in polycrystalline solids

    CSIR Research Space (South Africa)

    Nabarro, FRN

    2000-08-01

    Full Text Available ?Herring sources within the grain and the annihilation of dislocation pairs under their mutual attraction. This process occurs and Harper?Dorn creep is possible if inequality (4) is satisfied. If the inequality is not satisfied, dislocations climb into the grain... by glide. If, in addition, inequality (5) is satisfied, disloca- tions will multiply by glide within the cell much more rapidly than they can annihilate by climb. Harper?Dorn creep gives way to power-law creep [9]. If the product L 1/2 s is less...

  20. Grain Size Dependence of Uniform Elongation in Single-Phase FCC/BCC Metals

    Science.gov (United States)

    Liu, Haiting; Shen, Yao; Ma, Jiawei; Zheng, Pengfei; Zhang, Lei

    2016-09-01

    We studied the dependence of uniform elongation on grain size in the range of submicron to millimeter for single-phase FCC/BCC metals by reviewing recent experimental results and applying crystal plasticity finite element method simulation. In the order of increasing grain size, uniform elongation can be divided into three stages, namely low elongation stage, nearly constant elongation stage, and decreased elongation with large scatters stage. Low elongation stage features a dramatic increase near the critical grain size at the end of the stage, which is primarily attributed to the emergence of dislocation cell size transition from ultrafine to mid-size grain. Other factors can be neglected due to their negligible influence on overall variation trend. In nearly constant elongation stage, uniform elongation remains unchanged at a high level in general. As grain size keeps growing, uniform elongation starts decreasing and becomes scattered upon a certain grain size, indicating the initiation of decreased elongation with large scatters stage. It is shown that the increase is not linear or smooth but rather sharp at the end of low elongation stage, leading to a wider range in nearly constant elongation stage. The grain size dependence of uniform elongation can serve as a guiding principle for designing small uniaxial tensile specimens for mechanical testing, where size effect matters in most cases.

  1. Genetic dissection of grain size and grain number trade-offs in CIMMYT wheat germplasm.

    Directory of Open Access Journals (Sweden)

    Simon Griffiths

    Full Text Available Grain weight (GW and number per unit area of land (GN are the primary components of grain yield in wheat. In segregating populations both yield components often show a negative correlation among themselves. Here we use a recombinant doubled haploid population of 105 individuals developed from the CIMMYT varieties Weebill and Bacanora to understand the relative contribution of these components to grain yield and their interaction with each other. Weebill was chosen for its high GW and Bacanora for high GN. The population was phenotyped in Mexico, Argentina, Chile and the UK. Two loci influencing grain yield were indicated on 1B and 7B after QTL analysis. Weebill contributed the increasing alleles. The 1B effect, which is probably caused by to the 1BL.1RS rye introgression in Bacanora, was a result of increased GN, whereas, the 7B QTL controls GW. We concluded that increased in GW from Weebill 7B allele is not accompanied by a significant reduction in grain number. The extent of the GW and GN trade-off is reduced. This makes this locus an attractive target for marker assisted selection to develop high yielding bold grain varieties like Weebill. AMMI analysis was used to show that the 7B Weebill allele appears to contribute to yield stability.

  2. Genetic dissection of grain size and grain number trade-offs in CIMMYT wheat germplasm.

    Science.gov (United States)

    Griffiths, Simon; Wingen, Luzie; Pietragalla, Julian; Garcia, Guillermo; Hasan, Ahmed; Miralles, Daniel; Calderini, Daniel F; Ankleshwaria, Jignaben Bipinchandra; Waite, Michelle Leverington; Simmonds, James; Snape, John; Reynolds, Matthew

    2015-01-01

    Grain weight (GW) and number per unit area of land (GN) are the primary components of grain yield in wheat. In segregating populations both yield components often show a negative correlation among themselves. Here we use a recombinant doubled haploid population of 105 individuals developed from the CIMMYT varieties Weebill and Bacanora to understand the relative contribution of these components to grain yield and their interaction with each other. Weebill was chosen for its high GW and Bacanora for high GN. The population was phenotyped in Mexico, Argentina, Chile and the UK. Two loci influencing grain yield were indicated on 1B and 7B after QTL analysis. Weebill contributed the increasing alleles. The 1B effect, which is probably caused by to the 1BL.1RS rye introgression in Bacanora, was a result of increased GN, whereas, the 7B QTL controls GW. We concluded that increased in GW from Weebill 7B allele is not accompanied by a significant reduction in grain number. The extent of the GW and GN trade-off is reduced. This makes this locus an attractive target for marker assisted selection to develop high yielding bold grain varieties like Weebill. AMMI analysis was used to show that the 7B Weebill allele appears to contribute to yield stability.

  3. Metal-assisted chemical etching of CIGS thin films for grain size analysis

    Energy Technology Data Exchange (ETDEWEB)

    Xue, Chaowei [Research and Development Centre, Hanergy Thin Film Power Group Limited, Chengdu (China); Loi, Huu-Ha; Duong, Anh; Parker, Magdalena [Failure Analysis Department, MiaSole Hi-Tech Corp., Santa Clara, CA (United States)

    2016-09-15

    Grain size of the CIGS absorber is an important monitoring factor in the CIGS solar cell manufacturing. Electron backscatter diffraction (EBSD) analysis is commonly used to perform CIGS grain size analysis in the scanning electron microscope (SEM). Although direct quantification on SEM image using the average grain intercept (AGI) method is faster and simpler than EBSD, it is hardly applicable on CIGS thin films. The challenge is that, not like polycrystalline silicon, to define grain boundaries by selective chemical etching is not easily realizable for the multi-component CIGS alloy. In this Letter, we present direct quantification of CIGS thin film grain size using the AGI method by developing metal-assisted wet chemical etching process to define CIGS grain boundaries. The calculated value is similar to EBSD result. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  4. Grain size distribution of quartz isolated from Chinese loess/paleosol

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Grain size distribution of bulk loess-paleosol and quartz chemically extracted from the loess/paleosol shows that mean size of the bulk samples is always finer than that of the quartz. The original aeolian depositions have been modified to various degrees by post-depositional weathering and pedogenic processes. The grain size distribution of the isolated quartz should be close to that of the primary aeolian sediment because the chemical pretreatment excludes secondary produced minerals. Therefore, the grain size of the quartz may be considered to more clearly reflect the variations of winter monsoon intensity.

  5. Creating bulk nanocrystalline metal.

    Energy Technology Data Exchange (ETDEWEB)

    Fredenburg, D. Anthony (Georgia Institute of Technology, Atlanta, GA); Saldana, Christopher J. (Purdue University, West Lafayette, IN); Gill, David D.; Hall, Aaron Christopher; Roemer, Timothy John (Ktech Corporation, Albuquerque, NM); Vogler, Tracy John; Yang, Pin

    2008-10-01

    Nanocrystalline and nanostructured materials offer unique microstructure-dependent properties that are superior to coarse-grained materials. These materials have been shown to have very high hardness, strength, and wear resistance. However, most current methods of producing nanostructured materials in weapons-relevant materials create powdered metal that must be consolidated into bulk form to be useful. Conventional consolidation methods are not appropriate due to the need to maintain the nanocrystalline structure. This research investigated new ways of creating nanocrystalline material, new methods of consolidating nanocrystalline material, and an analysis of these different methods of creation and consolidation to evaluate their applicability to mesoscale weapons applications where part features are often under 100 {micro}m wide and the material's microstructure must be very small to give homogeneous properties across the feature.

  6. Grain Size Effect on Electrical Conductivity and Giant Magnetoresistance of Bulk Magnetic Polycrystals

    Institute of Scientific and Technical Information of China (English)

    LUO Wei; ZHU Lin-Li; ZHENG Xiao-Jing

    2009-01-01

    By solving the Boltzmann transport equation and considering the spin-dependent grain boundary scattering, the distribution of electrons in grains and the electrical transport properties in the applied magnetic field are studied. With regard to the dominant influence of grain boundary scattering which is taken as a boundary condi-tion for the electrical transport, the grain size-dependent electrical conductivity is investigated. In addition, the reorientation of the relative magnetization between grains brings the change of the electron spin when the magne-tonanocrystalline material is subjected to the magnetic field, resulting in the remarkable giant magnetoresistance effect.

  7. A statistical mixture model for estimating the proportion of unreduced pollen grains in perennial ryegrass (Lolium perenne L.) via the size of pollen grains

    NARCIS (Netherlands)

    Jansen, R.C.; Nijs, A.P.M. den

    1993-01-01

    The size of pollen grains is commonly used to indicate the ploidy level of pollen grains. In this paper observations of the diameter of pollen grains are evaluated from one diploid accession of perennial ryegrass (Lolium perenne L.), which was expected to produce diploid (unreduced) pollen grains in

  8. Investigating feedback mechanisms between stress and grain-size: preliminary findings from finite-element modelling

    Science.gov (United States)

    Cross, A. J.; Prior, D. J.; Ellis, S. M.

    2012-12-01

    It is widely accepted that changes in stress and grain size can induce a switch between grain-size insensitive (GSI) and sensitive (GSS) creep mechanisms. Under steady-state conditions, grains evolve to an equilibrium size in the boundary region between GSS and GSI, described by the paleopiezometer for a given material. Under these conditions, significant rheological weakening is not expected, as grain size reduction processes are balanced by grain growth processes. However, it has been shown that the stress field surrounding faults varies through the seismic cycle, with both rapid loading and unloading of stress possible in the co- and post-seismic stages. We propose that these changes in stress in the region of the brittle-ductile transition zone may be sufficient to force a deviation from the GSI-GSS boundary and thereby cause a change in grain size and creep mechanism prior to system re-equilibration. Here we present preliminary findings from numerical modelling of stress and grain size changes in response to loading of mechanical inhomogeneities. Our results are attained using a grain-size evolution (GSE) subroutine incorporated into the SULEC finite-element code developed by Susan Ellis and Susanne Buiter, which utilises an iterative approach of solving for spatial and temporal changes in differential stress, grain size and active creep mechanism. Preliminary models demonstrate that stress changes in response to the opening of a fracture in a flowing medium can be significant enough to cause a switch from GSI to GSS creep. These results are significant in the context of understanding spatial variations and feedback between stress, grain size and deformation mechanisms through the seismic cycle.

  9. Molecular dynamics investigation of the fracture behavior of nanocrystalline α-Fe

    Science.gov (United States)

    Latapie, A.; Farkas, D.

    2004-04-01

    We carried out classical atomistic studies of crack propagation in fully three-dimensional nanocrystalline α-Fe (body-centered cubic structure) to examine the influence of temperature and average grain size on the fracture mechanisms and properties. Digital samples with grain sizes ranging from 6 to 12 nm are reported at temperatures ranging from 100 K to 600 K using atomistic simulations. For all grain sizes, a combination of intragranular and intergranular fracture is observed. Mechanisms such as grain boundary accommodation, grain boundary triple junction activity, grain nucleation and grain rotation are observed to dictate the plastic deformation energy release. Intergranular fracture is shown to proceed by the coalescence of nanovoids formed at the grain boundaries ahead of the crack. The simulations also show that at an atomistic scale the fracture resistance and plastic deformation energy release mechanisms increase with increasing temperature. The observed fracture toughness increases with decreasing grain size.

  10. Effective anisotropy and coercivity in nanocrystalline single-phase NdFeB permanent magnetic material

    Institute of Scientific and Technical Information of China (English)

    韩广兵; 高汝伟; 冯维存; 刘汉强; 王标; 张鹏; 陈伟; 李卫; 郭永权

    2003-01-01

    The effect of exchange-coupling interaction on the effective anisotropy and its varying tendency in nanocrystalline single-phase NdFeB permanent magnetic material have been investigated. The results show that the exchange-coupling interaction between grains makes the effective anisotropy of material, Keff, decrease with the reduction of grain size. The variation of Keff is basically the same as that of coercivity. The decrease in effective anisotropy is the main reason of the reduction of coercivity for nanocrystalline single-phase NdFeB permanent magnetic material. In order to get high anisotropy and coercivity in nanocrystalline single-phase NdFeB permanent material, the grain size should be larger than 35 nm.

  11. Size Matters: FTIR Spectral Analysis of Apollo Regolith Samples Exhibits Grain Size Dependence.

    Science.gov (United States)

    Martin, Dayl; Joy, Katherine; Pernet-Fisher, John; Wogelius, Roy; Morlok, Andreas; Hiesinger, Harald

    2017-04-01

    The Mercury Thermal Infrared Spectrometer (MERTIS) on the upcoming BepiColombo mission is designed to analyse the surface of Mercury in thermal infrared wavelengths (7-14 μm) to investigate the physical properties of the surface materials [1]. Laboratory analyses of analogue materials are useful for investigating how various sample properties alter the resulting infrared spectrum. Laboratory FTIR analysis of Apollo fine (60%) causes a 'flattening' of the spectrum, with reduced reflectance in the Reststrahlen Band region (RB) as much as 30% in comparison to samples that are dominated by a high proportion of crystalline material. Apollo 15401,147 is an immature regolith with a high proportion of volcanic glass pyroclastic beads [2]. The high mafic mineral content results in a systematic shift in the Christiansen Feature (CF - the point of lowest reflectance) to longer wavelength: 8.6 μm. The glass beads dominate the spectrum, displaying a broad peak around the main Si-O stretch band (at 10.8 μm). As such, individual mineral components of this sample cannot be resolved from the average spectrum alone. Apollo 67481,96 is a sub-mature regolith composed dominantly of anorthite plagioclase [2]. The CF position of the average spectrum is shifted to shorter wavelengths (8.2 μm) due to the higher proportion of felsic minerals. Its average spectrum is dominated by anorthite reflectance bands at 8.7, 9.1, 9.8, and 10.8 μm. The average reflectance is greater than the other samples due to a lower proportion of glassy material. In each soil, the smallest fractions (0-25 and 25-63 μm) have CF positions 0.1-0.4 μm higher than the larger grain sizes. Also, the bulk-sample spectra mostly closely resemble the 0-25 μm sieved size fraction spectrum, indicating that this size fraction of each sample dominates the bulk spectrum regardless of other physical properties. This has implications for surface analyses of other Solar System bodies where some mineral phases or components

  12. ON ESTIMATION AND HYPOTHESIS TESTING OF THE GRAIN SIZE DISTRIBUTION BY THE SALTYKOV METHOD

    Directory of Open Access Journals (Sweden)

    Yuri Gulbin

    2011-05-01

    Full Text Available The paper considers the problem of validity of unfolding the grain size distribution with the back-substitution method. Due to the ill-conditioned nature of unfolding matrices, it is necessary to evaluate the accuracy and precision of parameter estimation and to verify the possibility of expected grain size distribution testing on the basis of intersection size histogram data. In order to review these questions, the computer modeling was used to compare size distributions obtained stereologically with those possessed by three-dimensional model aggregates of grains with a specified shape and random size. Results of simulations are reported and ways of improving the conventional stereological techniques are suggested. It is shown that new improvements in estimating and testing procedures enable grain size distributions to be unfolded more efficiently.

  13. Dislocation-mediated creep process in nanocrystalline Cu

    Institute of Scientific and Technical Information of China (English)

    Mu Jun-Wei; Sun Shi-Cheng; Jiang Zhong-Hao; Lian Jian-She; Jiang Qing

    2013-01-01

    Nanocrystalline Cu with average grain sizes ranging from ~ 24.4 to 131.3 nm were prepared by the electric brushplating technique.Nanoindentation tests were performed within a wide strain rate range,and the creep process of nanocrystalline Cu during the holding period and its relationship to dislocation and twin structures were examined.It was demonstrated that creep strain and creep strain rate are considerably significant for smaller grain sizes and higher loading strain rates,and are far higher than those predicted by the models of Cobble creep and grain boundary sliding.The analysis based on the calculations and experiments reveals that the significant creep deformation arises from the rapid absorption of high density dislocations stored in the loading regime.Our experiments imply that stored dislocations during loading are highly unstable and dislocation activity can proceed and lead to significant post-loading plasticity.

  14. The effect of grain size on dynamic tensile extrusion behaviour

    Directory of Open Access Journals (Sweden)

    Park Leeju

    2015-01-01

    Full Text Available Dynamic tensile extrusion (DTE tests were conducted on coarse grained and ultrafine grained (UFG OFHC Cu, Interstitial free (IF Steel, and pure Ta. Equal channel angular pressing (ECAP of 16passes with Bc for Cu, IF Steel and 4 passes for Ta was employed to fabricated UFG materials. DTE tests were carried out by launching the sphere samples (Dia. 7.62 mm to the conical extrusion die at a speed of ∼500 m/sec. The fragmentation behavior of the soft-recovered fragments were examined and compared with each other. The DTE fragmentation behavior of CG and UFG was numerically simulated by the LS-DYNA FEM code.

  15. Geochemical indicator of original eolian grain size and implications on winter monsoon evolution

    Institute of Scientific and Technical Information of China (English)

    彭淑贞; 郭正堂

    2001-01-01

    Grain size of eolian deposits from the Loess Plateau in China has been widely used to reconstruct the history of the East Asian winter monsoon. However, the grain size of bulk samples is only partially indicative to the strength of the winter monsoon because post-depositional weathering processes have significantly changed the grain size of original eolian particles. Here, non-weathered loess samples were separated into eight different particle fractions, and major chemical elements were determined in order to establish a geochemical indicator of original eolian grain size. The results show that SiO2and AI2O3contents and the SiO2/AI203 ratio in different fractions vary regularly with grain size, and that a good linear relation exists between the SiO2/AI2O3 ratio and grain size for the fractions<50μm. Because Al and Si are among the most stable elements and pedogenic processes in the Loess Plateau cannot affect the SiO2/AI2O3 ratio, this index can be used to reflect the grain size of original eolian part

  16. Preparation of nanocrystalline BaTiO3 ceramics

    Institute of Scientific and Technical Information of China (English)

    DENG XiangYun; LI DeJun; LI JianBao; WANG XiaoHui; LI LongTu

    2009-01-01

    The high-dense nanocrystalline BaTiO3 (BT) ceramics with grain size smaller than 100 nm have been successfully prepared by the two step sintering and the spark plasma sintering (SPS) process. The successive transitions in nanograin BT ceramics from rhombohedrel to orthorhombic, tetragonal and cubic transitions, similar to those in coarse BT ceramics, were revealed by in-situ temperature dependent Raman spectrum. The multiphase coexistence and the diffused phase transition character were demonstrated in the 8 nm nanocrystalline BT ceramics.

  17. Preparation of nanocrystalline BaTiO3 ceramics

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The high-dense nanocrystalline BaTiO3(BT)ceramics with grain size smaller than 100nm have been successfully prepared by the two step sintering and the spark plasma sintering(SPS)process.The successive transitions in nanograin BT ceramics from rhombohedral to orthorhombic,tetragonal and cubic transitions,similar to those in coarse BT ceramics,were revealed by in-situ temperature dependent Raman spectrum.The multiphase coexistence and the diffused phase transition character were demonstrated in the 8nm nanocrystalline BT ceramics.

  18. Study on pore characteristics and microstructure of sandstones with different grain sizes

    Science.gov (United States)

    Li, Huigui; Li, Huamin; Gao, Baobin; Wang, Wen; Liu, Chuang

    2017-01-01

    The grain sizes have a pronounced influence on the pore characteristics and microstructure of sandstone. This work examined the pore structure and characteristics of three kinds of sandstones with different grain sizes using the scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) methods and analyzed their grain size distributions, pore size distributions, T2-distributions, and porosity variations. The experimental results showed that sandstones with different grain sizes have significant differences in the microstructures grain size distribution, pore size distribution, T2-distribution, and porosity variation. The results show that coarse, medium and fine sandstones have two peaks in T2-distributions, mean grain size of 398.5, 145.1 and 25.1 μm, respectively, mean pore size of 46.3, 25.9, and 8.4 μm, respectively, porosity of 7.52%, 5.88% and 1.55%, respectively, indicating that both coarse and medium sandstones contain big pores, while fine sandstone contains small pores. This study is of significance for understanding of water migration characteristics in aquifers and gas in coal seams after the working face exploitation.

  19. Grain size evolution in the mantle and its effect on geodynamics, seismic velocities and attenuation

    Science.gov (United States)

    Dannberg, Juliane; Eilon, Zach; Gassmoeller, Rene; Moulik, Pritwiraj; Myhill, Robert; Faul, Ulrich; Asimow, Paul

    2015-04-01

    Dynamic models of Earth's convecting mantle usually implement flow laws with constant grain size, stress-independent viscosity and a limited treatment of variations associated with changes in mineral assemblage. These simplifications greatly reduce computational requirements but preclude effects such as shear localisation and transient changes in rheology associated with phase transitions, which have the potential to fundamentally change flow patterns in the mantle. Here we use the finite-element code ASPECT (Bangerth et al., 2013) to model grain size evolution and the interplay between grain size, stress and strain rate in the convecting mantle. We include the simultaneous and competing effects of dynamic recrystallisation resulting from work done by dislocation creep, grain growth in multiphase assemblages and recrystallisation at phase transitions. Grain size variations also affect seismic properties of mantle materials. We use several published formulations to relate intrinsic variables (P, T, and grain size) from our numerical models to seismic velocity (Vs) and attenuation (Q). Our calculations use thermodynamically self-consistent anharmonic elastic moduli determined for the mineral assemblages in the mantle using HeFESTo (Stixrude and Lithgow-Bertelloni, 2013). We investigate the effect of realistically heterogeneous grain sizes by computing body wave travel times, ray paths, and attenuation (t*) at different frequencies. We highlight the frequency-dependent sensitivity of seismic waves to grain size, which is important when interpreting Vs and Q observations in terms of mineral assemblage and temperature. Our models show that rapid metamorphic reactions in mantle upwellings and downwellings lead to high lateral viscosity contrasts, as a result of gradual grain size evolution. Positive feedback between grain size reduction and viscosity reduction results in shear localisation. As a result, the edges of thermal plumes have smaller grain sizes and lower

  20. Effect of Grain Size on the Threshold Voltage for Double-Gate Polycrystaline Silicon MOSFET

    Directory of Open Access Journals (Sweden)

    Alka Panwar

    2011-01-01

    Full Text Available The effect of grain size (D on the threshold voltage (Vth for double gate polycrystalline silicon MOSFET is investigated theoretically in terms of grain boundary trap states (NT. It is found that the threshold voltage (Vth increases non-linearly with increasing silicon-oxide thickness (tox for all values of grain size (D. However the threshold voltage is seen to have smaller values for same tox for the larger grains. This may be attributed to the reduction in the number of trap states in the depletion regions on either side of a grain boundary. Finally the dependence of threshold voltage (Vth on various parameters such as the doping concentration, interface trap state density and field penetration from drain to source are explored out. The results of these findings are in good agreement with those available in the literature. For large grain poly silicon MOSFET the threshold voltage is seen to approach the single crystal value.

  1. High-pressure structural behavior of nanocrystalline Ge

    DEFF Research Database (Denmark)

    Wang, H.; Liu, J. F.; Yan, H.;

    2007-01-01

    The equation of state and the pressure of the I-II transition have been studied for nanocrystalline Ge using synchrotron x-ray diffraction. The bulk modulus and the transition pressure increase with decreasing particle size for both Ge-I and Ge-II, but the percentage volume collapse at the transi......The equation of state and the pressure of the I-II transition have been studied for nanocrystalline Ge using synchrotron x-ray diffraction. The bulk modulus and the transition pressure increase with decreasing particle size for both Ge-I and Ge-II, but the percentage volume collapse...... at the transition remains constant. Simplified models for the high-pressure structural behaviour are presented, based on the assumption that a large fraction of the atoms reside in grain boundary regions of the nanocrystalline material. The interface structure plays a significant role in affecting the transition...

  2. The Role of Grain Size and Shape on the Electrical Conductivity of Volcanic Ash

    Science.gov (United States)

    Woods, T.; Genareau, K. D.; Cloer, S.

    2016-12-01

    Volcanic lightning is a common, yet understudied, phenomenon. The exact mechanisms of electric charge generation and transmission in explosive eruption plumes are poorly understood. Ash is a probable charge carrier, and thus, the physical properties of ash may factor into charge generation and transmission. Specifically, the shape and size of ash grains, volatiles bound within the grains, and the efficiency of grains to act as ice nuclei may be contributing factors. To examine the relationship between conductivity and grain size/shape, this research compares conductivity measurements to grain size distribution and shape from five minimally processed ash samples collected from explosive eruptions in Alaska, U.S.A. (Katmai, 1912; Crater Peak, 1992; Augustine, 2006; Okmok, 2008; Redoubt, 2009) that produced volcanic lightning and a set of homogenized (with respect to grain size and shape) ash samples from Lathrop Wells (Nevada, U.S.A.), Taupo (New Zealand), and the Valles Caldera (New Mexico, U.S.A.). Grain size distribution was measured using a laser diffractometer particle size analyzer and grain shapes (aspect ratios, concavity indices) were characterized using backscattered electron images that were processed with ImageJ freeware. The resistance of minimally compressed samples was measured using a current amplifier and converted to conductivity. A general effective media (GEM) equation was then applied using the assumption that the grains are oblate ellipsoids under the influence of minimal compaction. Preliminary analyses suggest that compaction, and therefore shape and contact points, controls ash conductivity and not bulk composition, as homogenized samples provide variable resistance measurements from 1.6 x 10-3 to 9.9 x 10-1 S/m. Non-homogenized Alaskan samples are hypothesized to have higher concavity indices and conductivities when compared to the homogenized samples, due to wider variations in grain size and shape, and these data will be presented.

  3. Measurement and Simulation of Grain Size in Strong Textured and Coarse-Grained Metal Sheets

    Institute of Scientific and Technical Information of China (English)

    Leng CHEN; Weimin MAO; Yongning YU; Huiping FENG

    2003-01-01

    An X-ray diffractometer that equipped with a two-dimensional detector is used for developing the technique of grainsize measurement for strong textured and coarse-grained Si steel sheet. The method is based on the concept thatthe position of diffraction s

  4. Microhardness studies of nanocrystalline calcium tungstate

    Energy Technology Data Exchange (ETDEWEB)

    Anandakumar, V.M. [Department of Physics, Mahatma Gandhi College, Thiruvananthapuram (India); Khadar, M.A. [Centre for Nanoscience and Nanotechnology and Department of Physics, University of Kerala, Thiruvananthapuram (India)

    2008-02-15

    Nanocrystals of calcium tungstate (CaWO{sub 4}) of three different grain sizes were synthesized through chemical precipitation technique and the grain sizes and crystal structure were determined using the broadening of X-ray diffraction patterns and transmission electron microscopy. The microhardness of compacted pellets of nanocrystalline calcium tungstate (CaWO{sub 4}) with different grain sizes were measured using a Vickers microhardness tester for various applied loads ranging from 0.049 N to 1.96 N. The values of microhardness showed significant reverse indentation size effect at low indentation loads. The microhardness data obtained for samples of different grain sizes showed grain size dependent strengthening obeying normal Hall-Petch relation. The dependence of compacting pressure and annealing temperature on microhardness of the nanostructured sample with grain size of 13 nm were also studied. The samples showed significant increase in microhardness as the compacting pressure and annealing time were increased. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  5. Anomalous grain growth in nanocrystalline Fe73.5Cu1Nb3Su13.5B9 alloys

    DEFF Research Database (Denmark)

    Jiang, Jianzhong

    1997-01-01

    The grain growth of the FeSi phase during the crystallization process of the amorphous Fe73.5Cu1Nb3Si13.5B9 alloy was studied using transmission electron microscopy and x-ray diffractometry. An anomalous grain growth behaviour of the FeSi phase in the samples annealed in temperature range from 74...

  6. Influence of Grain Size on Electrical and Optical Properties of InP Films

    Institute of Scientific and Technical Information of China (English)

    Mustafa (O)ztas

    2008-01-01

    InP film samples were prepared by spray pyrolysis technique using aqueous solutions of lnCl3 and Na2HPO4,which were atomized with compressed air as carrier gas onto glass substrates at 500℃ with different thicknesses of the films. It is found that the resistivity of the polycrystalline films strongly depends on the grain size. It is observed that the grain size of the films increase with the decrease of the energy band gap and strain of the film.The changes observed in the energy band gap and strain related to the film grain size of the films are discussed in detail.

  7. Mechanical properties for irradiated face-centred cubic nanocrystalline metals

    Science.gov (United States)

    Xiao, X. Z.; Song, D. K.; Chu, H. J.; Xue, J. M.; Duan, H. L.

    2015-01-01

    In this paper, a self-consistent plasticity theory is proposed to model the mechanical behaviours of irradiated face-centred cubic nanocrystalline metals. At the grain level, a tensorial crystal model with both irradiation and grain size effects is applied for the grain interior (GI), whereas both grain boundary (GB) sliding with irradiation effect and GB diffusion are considered in modelling the behaviours of GBs. The elastic-viscoplastic self-consistent method with considering grain size distribution is developed to transit the microscopic behaviour of individual grains to the macroscopic properties of nanocrystals (NCs). The proposed theory is applied to model the mechanical properties of irradiated NC copper, and the feasibility and efficiency have been validated by comparing with experimental data. Numerical results show that: (i) irradiation-induced defects can lead to irradiation hardening in the GIs, but the hardening effect decreases with the grain size due to the increasing absorption of defects by GBs. Meanwhile, the absorbed defects would make the GBs softer than the unirradiated case. (ii) There exists a critical grain size for irradiated NC metals, which separates the grain size into the irradiation hardening dominant region (above the critical size) and irradiation softening dominant region (below the critical size). (iii) The distribution of grain size has a significant influence on the mechanical behaviours of both irradiated and unirradiated NCs. The proposed model can offer a valid theoretical foundation to study the irradiation effect on NC materials. PMID:27547091

  8. Grain-Size-Limited Mobility in Methylammonium Lead Iodide Perovskite Thin Films

    Energy Technology Data Exchange (ETDEWEB)

    Reid, Obadiah G.; Yang, Mengjin; Kopidakis, Nikos; Zhu, Kai; Rumbles, Garry

    2016-09-09

    We report a systematic study of the gigahertz-frequency charge carrier mobility found in methylammonium lead iodide perovskite films as a function of average grain size using time-resolved microwave conductivity and a single processing chemistry. Our measurements are in good agreement with the Kubo formula for the AC mobility of charges confined within finite grains, suggesting (1) that the surface grains imaged via scanning electron microscopy are representative of the true electronic domain size and not substantially subdivided by twinning or other defects not visible by microscopy and (2) that the time scale of diffusive transport across grain boundaries is much slower than the period of the microwave field in this measurement (-100 ps). The intrinsic (infinite grain size) minimum mobility extracted form the model is 29 +/- 6 cm2 V-1 s-1 at the probe frequency (8.9 GHz).

  9. Intensity and degree of segregation in bimodal and multimodal grain size distributions

    Science.gov (United States)

    Katra, Itzhak; Yizhaq, Hezi

    2017-08-01

    The commonly used grain size analysis technique which applies moments (sorting, skewness and kurtosis) is less useful in the case of sediments with bimodal size distributions. Herein we suggest a new simple method for analyzing the degree of grain size segregation in sand-sized sediment that has clear bimodal size distributions. Two main features are used to characterize the bimodal distribution: grain diameter segregation, which is the normalized difference between coarse and fine grain diameters, and the frequency segregation which is the normalized difference in frequencies between two modes. The new defined indices can be calculated from frequency plot curves and can be graphically represented on a two dimensional coordinate system showing the dynamical aspects of the size distribution. The results enable comparison between granular samples from different locations and/or times to shed new light on the dynamic processes involved in grain size segregation of sediments. We demonstrate here the use of this method to analyze bimodal distributions of aeolian granular samples mostly from aeolian megaripples. Six different aeolian cases were analyzed to highlight the method's applicability, which is relevant to wide research themes in the Earth and environmental sciences, and can furthermore be easily adapted to analyze polymodal grain size distributions.

  10. Relationship between ferromagnetic properties and grain size of Inconel alloy 600

    Energy Technology Data Exchange (ETDEWEB)

    Kikuchi, H., E-mail: hkiku@iwate-u.ac.jp; Takahashi, H.; Yanagiwara, H.; Murakami, T.

    2015-05-01

    Inconel alloy 600 is widely used in steam generator tubings where sensitization due to chromium depletion occurs at grain boundaries and the sensitization induces tubing failures. Though the alloy usually exhibits paramagnetic properties, it shows ferromagnetic properties along grain boundaries when chromium depletion occurs. This means that magnetic nondestructive evaluation of sensitization is possible. Therefore, as a fundamental study to develop magnetic nondestructive evaluation technique for sensitization, the relationship between ferromagnetic properties and grain size in Inconel 600 was investigated using isothermal heat treatment. The grain was controlled using solution annealing, and then, specimens were heat treated at 873, 923, and 973 K within 400 h. The saturation magnetization increases as heat treatment time increases and eventually peaks. The peak time depends on the heat treatment temperature. The coercivity increases during the initial heat treatment stage, and decreases as the duration of heat treatment increases. The maximum saturation magnetization decreases as the grain diameter increases and is inversely proportional to the grain diameter squared, which is consistent with the fact that the ferromagnetic phase only formed along grain boundaries. - Highlights: • Relationship between ferromagnetism and grain size in Inconel 600 was clarified. • The saturation magnetization increases and eventually peaks during heat treatment. • The coercivity increases during the initial heat treatment stage, and then decreases. • The saturation magnetization is inversely proportional to the grain diameter squared. • The magnetic property changes are explained by the Cr depletion at grain boundaries.

  11. A Galvanostatic Modeling for Preparation of Electrodeposited Nanocrystalline Coatings by Control of Current Density

    Institute of Scientific and Technical Information of China (English)

    Ali Mohammad Rashidi

    2012-01-01

    The correlation between the grain size of electrodeposited coatings and the current densities was modeled by considering galvanostatic conditions. In order to test the model by experimental results, nanocrystalline (NC) nickel samples were deposited at different current densities using a Watts bath. The grain size of the deposits was evaluated by X-ray diffraction (XRD) technique. Model predictions were validated by finding a curve being the best-fit to the experimental results which were gathered from literature for different NC coatings in addition to those data measured in this research for NC nickel coatings. According to our model, the variation of grain size with the reciprocal of the current density follows a power law. A good agreement between the experimental results and model predictions was observed which indicated that the derived analytical model is applicable for producting the nanocrystalline electrodeposits with the desired grain size by controling current density.

  12. Extreme creep resistance in a microstructurally stable nanocrystalline alloy

    Science.gov (United States)

    Darling, K. A.; Rajagopalan, M.; Komarasamy, M.; Bhatia, M. A.; Hornbuckle, B. C.; Mishra, R. S.; Solanki, K. N.

    2016-09-01

    Nanocrystalline metals, with a mean grain size of less than 100 nanometres, have greater room-temperature strength than their coarse-grained equivalents, in part owing to a large reduction in grain size. However, this high strength generally comes with substantial losses in other mechanical properties, such as creep resistance, which limits their practical utility; for example, creep rates in nanocrystalline copper are about four orders of magnitude higher than those in typical coarse-grained copper. The degradation of creep resistance in nanocrystalline materials is in part due to an increase in the volume fraction of grain boundaries, which lack long-range crystalline order and lead to processes such as diffusional creep, sliding and rotation. Here we show that nanocrystalline copper-tantalum alloys possess an unprecedented combination of properties: high strength combined with extremely high-temperature creep resistance, while maintaining mechanical and thermal stability. Precursory work on this family of immiscible alloys has previously highlighted their thermo-mechanical stability and strength, which has motivated their study under more extreme conditions, such as creep. We find a steady-state creep rate of less than 10-6 per second—six to eight orders of magnitude lower than most nanocrystalline metals—at various temperatures between 0.5 and 0.64 times the melting temperature of the matrix (1,356 kelvin) under an applied stress ranging from 0.85 per cent to 1.2 per cent of the shear modulus. The unusual combination of properties in our nanocrystalline alloy is achieved via a processing route that creates distinct nanoclusters of atoms that pin grain boundaries within the alloy. This pinning improves the kinetic stability of the grains by increasing the energy barrier for grain-boundary sliding and rotation and by inhibiting grain coarsening, under extremely long-term creep conditions. Our processing approach should enable the development of

  13. Extreme creep resistance in a microstructurally stable nanocrystalline alloy.

    Science.gov (United States)

    Darling, K A; Rajagopalan, M; Komarasamy, M; Bhatia, M A; Hornbuckle, B C; Mishra, R S; Solanki, K N

    2016-09-15

    Nanocrystalline metals, with a mean grain size of less than 100 nanometres, have greater room-temperature strength than their coarse-grained equivalents, in part owing to a large reduction in grain size. However, this high strength generally comes with substantial losses in other mechanical properties, such as creep resistance, which limits their practical utility; for example, creep rates in nanocrystalline copper are about four orders of magnitude higher than those in typical coarse-grained copper. The degradation of creep resistance in nanocrystalline materials is in part due to an increase in the volume fraction of grain boundaries, which lack long-range crystalline order and lead to processes such as diffusional creep, sliding and rotation. Here we show that nanocrystalline copper-tantalum alloys possess an unprecedented combination of properties: high strength combined with extremely high-temperature creep resistance, while maintaining mechanical and thermal stability. Precursory work on this family of immiscible alloys has previously highlighted their thermo-mechanical stability and strength, which has motivated their study under more extreme conditions, such as creep. We find a steady-state creep rate of less than 10(-6) per second-six to eight orders of magnitude lower than most nanocrystalline metals-at various temperatures between 0.5 and 0.64 times the melting temperature of the matrix (1,356 kelvin) under an applied stress ranging from 0.85 per cent to 1.2 per cent of the shear modulus. The unusual combination of properties in our nanocrystalline alloy is achieved via a processing route that creates distinct nanoclusters of atoms that pin grain boundaries within the alloy. This pinning improves the kinetic stability of the grains by increasing the energy barrier for grain-boundary sliding and rotation and by inhibiting grain coarsening, under extremely long-term creep conditions. Our processing approach should enable the development of

  14. The role of grain-size ratio in the mobility of mixed granular beds

    Science.gov (United States)

    Staudt, Franziska; Mullarney, Julia C.; Pilditch, Conrad A.; Huhn, Katrin

    2017-02-01

    The main goal of the study was to understand the effects of grain-size distribution on the stability of beds in the sand-silt range, which is a critical subject for the understanding of geomorphological processes in aquatic environments. Although theoretical models can explain the mobilization of a mixed bed, there is a clear lack in knowledge regarding the stabilizing effect of non-cohesive fine material. To connect existing findings, we analysed bed stability in relation to grain-size distribution in laboratory experiments. Erosion experiments in an annular flume were conducted using beds of different size compositions of spherical glass beads, i.e. a) the grain-size ratio RD = D50,coarse/D50,fine (the relative size of coarse and fine grains; D50 = 39-367 μm) and b) the amount of fines. Several glass-bead combinations with unimodal and bimodal grain-size distributions (RD = 3.9, 5.8, and 9.4) and varying fine fractions (10-40% dry weight) were subjected to increasing flow speeds (0.01-0.19 m s-1). Using acoustic Doppler velocimetry (ADV) and optical backscatter, the flow profile in the vicinity of the bed surface, the changes in bed morphology, and the suspended sediment concentration (SSC) were measured. A new method was developed to evaluate the bed-level changes detected by the ADV as a proxy for the bed mobility. We found different modes of bed mobility depending on the grain-size ratio. For low grain-size ratios, an increase in the fine fraction (to 40%) led to increased bed-level changes during the experiment and the mobilization of the mixed bed at the highest flow speed. For high ratios an increase in fine fraction (to 40%) led to a decrease of bed-level changes and the beds remained stable, i.e. no bed forms developed even at the highest flow speed. Therefore, increasing the amount of fine particles can lead to different modes of behaviour depending on the grain-size ratio. For a bimodal sediment bed with spherical grains under unidirectional flow

  15. Location and sizes of forsterite grains in protoplanetary disks: Interpretation from the Herschel DIGIT programme

    NARCIS (Netherlands)

    K.M. Maaskant; B.L. de Vries; M. Min; L.B.F.M. Waters; C. Dominik; F. Molster; A.G.G.M. Tielens

    2015-01-01

    Context. The spectra of protoplanetary disks contain mid- and far- infrared emission features produced by forsterite dust grains. The spectral features contain information about the forsterite temperature, chemical composition and grain size. Aims. We aim to characterize how the 23 and 69 μm feature

  16. Millimeter-sized grains in the protostellar envelopes: Where do they come from?

    Science.gov (United States)

    Wong, Yi Hang Valerie; Hirashita, Hiroyuki; Li, Zhi-Yun

    2016-08-01

    Grain growth during star formation affects the physical and chemical processes in the evolution of star-forming clouds. We investigate the origin of the millimeter (mm)-sized grains recently observed in Class I protostellar envelopes. We use the coagulation model developed in our previous paper and find that a hydrogen number density of as high as 1010 cm-3, instead of the typical density 105 cm-3, is necessary for the formation of mm-sized grains. Thus, we test a hypothesis that such large grains are transported to the envelope from the inner, denser parts, finding that gas drag by outflow efficiently "launches" the large grains as long as the central object has not grown to ≳0.1 M⊙. By investigating the shattering effect on the mm-sized grains, we ensure that the large grains are not significantly fragmented after being injected in the envelope. We conclude that the mm-sized grains observed in the protostellar envelopes are not formed in the envelopes but formed in the inner parts of the star-forming regions and transported to the envelopes before a significant mass growth of the central object, and that they survive in the envelopes.

  17. Millimeter-sized grains in the protostellar envelopes: where do they come from?

    CERN Document Server

    Wong, Yi Hang Valerie; Li, Zhi-Yun

    2016-01-01

    Grain growth during star formation affects the physical and chemical processes in the evolution of star-forming clouds. We investigate the origin of the millimeter (mm)-sized grains recently observed in Class I protostellar envelopes. We use the coagulation model developed in our previous paper and find that a hydrogen number density of as high as $10^{10}~{\\rm cm^{-3}}$, instead of the typical density $10^5~{\\rm cm^{-3}}$, is necessary for the formation of mm-sized grains. Thus, we test a hypothesis that such large grains are transported to the envelope from the inner, denser parts, finding that gas drag by outflow efficiently "launches" the large grains as long as the central object has not grown to $\\gtrsim 0.1$ M$_{\\odot}$. By investigating the shattering effect on the mm-sized grains, we ensure that the large grains are not significantly fragmented after being injected in the envelope. We conclude that the mm-sized grains observed in the protostellar envelopes are not formed in the envelopes but formed i...

  18. Size Distribution and Rate of Dust Generated During Grain Elevator Handling

    Science.gov (United States)

    Dust generated during grain handling is an air pollutant that produces safety and health hazards. This study was conducted to characterize the particle size distribution (PSD) of dust generated during handling of wheat and shelled corn in the research elevator of the USDA Grain Marketing and Product...

  19. Optical dating of single sand-sized grains of quartz: Sources of variability

    DEFF Research Database (Denmark)

    Duller, G.A.T.; Bøtter-Jensen, L.; Murray, A.S.

    2000-01-01

    Optically stimulated luminescence (OSL) measurements have been made of over 3000 sand-sized grains of quartz. Analysis at this scale highlights the variability in the luminescence sensitivity and the dose saturation characteristics of individual quartz grains. Using a new instrument capable of me...... intensity, dose saturation characteristics and instrument uncertainty in equivalent dose calculation. (C) 2000 Elsevier Science Ltd. All rights reserved....

  20. Thermal Conductivity of Amorphous and Nanocrystalline Silicon Films Prepared by Hot-Wire Chemical-Vapor Deposition

    Energy Technology Data Exchange (ETDEWEB)

    Nemeth, William M [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Jugdersuren, B. [Sotera Defense Solutions, Inc.; Kearney, B. T. [Naval Research Laboratory; Queen, D. R. [Naval Research Laboratory; Metcalf, T. H. [Naval Research Laboratory; Culbertson, J. C. [Naval Research Laboratory; Chervin, C. N. [Naval Research Laboratory; Stroud, R. M. [Naval Research Laboratory; Wang, Q. [Formerly NREL; Liu, Xiao [Naval Research Laboratory

    2017-07-31

    We report 3..omega.. thermal conductivity measurements of amorphous and nanocrystalline silicon thin films from 85 to 300 K prepared by hot-wire chemical-vapor deposition, where the crystallinity of the films is controlled by the hydrogen dilution during growth. The thermal conductivity of the amorphous silicon film is in agreement with several previous reports of amorphous silicon prepared by a variety of deposition techniques. The thermal conductivity of the as-grown nanocrystalline silicon film is 70% higher and increases 35% more after an anneal at 600 degrees C. They all have similarly weak temperature dependence. Structural analysis shows that the as-grown nanocrystalline silicon is approximately 60% crystalline, nanograins and grain boundaries included. The nanograins, averaging 9.1 nm in diameter in the as-grown film, are embedded in an amorphous matrix. The grain size increases to 9.7 nm upon annealing, accompanied by the disappearance of the amorphous phase. We extend the models of grain boundary scattering of phonons with two different non-Debye dispersion relations to explain our result of nanocrystalline silicon, confirming the strong grain size dependence of heat transport for nanocrystalline materials. However, the similarity in thermal conductivity between amorphous and nanocrystalline silicon suggests the heat transport mechanisms in both structures may not be as dissimilar as we currently understand.

  1. Thermal conductivity of amorphous and nanocrystalline silicon films prepared by hot-wire chemical-vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Jugdersuren, B.; Kearney, B. T.; Queen, D. R.; Metcalf, T. H.; Culbertson, J. C.; Chervin, C. N.; Stroud, R. M.; Nemeth, W.; Wang, Q.; Liu, Xiao

    2017-07-01

    We report 3..omega.. thermal conductivity measurements of amorphous and nanocrystalline silicon thin films from 85 to 300 K prepared by hot-wire chemical-vapor deposition, where the crystallinity of the films is controlled by the hydrogen dilution during growth. The thermal conductivity of the amorphous silicon film is in agreement with several previous reports of amorphous silicon prepared by a variety of deposition techniques. The thermal conductivity of the as-grown nanocrystalline silicon film is 70% higher and increases 35% more after an anneal at 600 degrees C. They all have similarly weak temperature dependence. Structural analysis shows that the as-grown nanocrystalline silicon is approximately 60% crystalline, nanograins and grain boundaries included. The nanograins, averaging 9.1 nm in diameter in the as-grown film, are embedded in an amorphous matrix. The grain size increases to 9.7 nm upon annealing, accompanied by the disappearance of the amorphous phase. We extend the models of grain boundary scattering of phonons with two different non-Debye dispersion relations to explain our result of nanocrystalline silicon, confirming the strong grain size dependence of heat transport for nanocrystalline materials. However, the similarity in thermal conductivity between amorphous and nanocrystalline silicon suggests the heat transport mechanisms in both structures may not be as dissimilar as we currently understand.

  2. Thermal conductivity of amorphous and nanocrystalline silicon films prepared by hot-wire chemical-vapor deposition

    Science.gov (United States)

    Jugdersuren, B.; Kearney, B. T.; Queen, D. R.; Metcalf, T. H.; Culbertson, J. C.; Chervin, C. N.; Stroud, R. M.; Nemeth, W.; Wang, Q.; Liu, Xiao

    2017-07-01

    We report 3 ω thermal conductivity measurements of amorphous and nanocrystalline silicon thin films from 85 to 300 K prepared by hot-wire chemical-vapor deposition, where the crystallinity of the films is controlled by the hydrogen dilution during growth. The thermal conductivity of the amorphous silicon film is in agreement with several previous reports of amorphous silicon prepared by a variety of deposition techniques. The thermal conductivity of the as-grown nanocrystalline silicon film is 70% higher and increases 35% more after an anneal at 600 ∘C . They all have similarly weak temperature dependence. Structural analysis shows that the as-grown nanocrystalline silicon is approximately 60 % crystalline, nanograins and grain boundaries included. The nanograins, averaging 9.1 nm in diameter in the as-grown film, are embedded in an amorphous matrix. The grain size increases to 9.7 nm upon annealing, accompanied by the disappearance of the amorphous phase. We extend the models of grain boundary scattering of phonons with two different non-Debye dispersion relations to explain our result of nanocrystalline silicon, confirming the strong grain size dependence of heat transport for nanocrystalline materials. However, the similarity in thermal conductivity between amorphous and nanocrystalline silicon suggests the heat transport mechanisms in both structures may not be as dissimilar as we currently understand.

  3. Transport, retention, and size perturbation of graphene oxide in saturated porous media: Effects of input concentration and grain size

    Science.gov (United States)

    Accurately predicting the fate and transport of graphene oxide (GO) in porous media is critical to assess its environmental impact. In this work, sand column experiments were conducted to determine the effect of input concentration and grain size on transport, retention, and size perturbation of GO ...

  4. Modeling grain size variations of aeolian gypsum deposits at White Sands, New Mexico, using AVIRIS imagery

    Science.gov (United States)

    Ghrefat, H.A.; Goodell, P.C.; Hubbard, B.E.; Langford, R.P.; Aldouri, R.E.

    2007-01-01

    Visible and Near-Infrared (VNIR) through Short Wavelength Infrared (SWIR) (0.4-2.5????m) AVIRIS data, along with laboratory spectral measurements and analyses of field samples, were used to characterize grain size variations in aeolian gypsum deposits across barchan-transverse, parabolic, and barchan dunes at White Sands, New Mexico, USA. All field samples contained a mineralogy of ?????100% gypsum. In order to document grain size variations at White Sands, surficial gypsum samples were collected along three Transects parallel to the prevailing downwind direction. Grain size analyses were carried out on the samples by sieving them into seven size fractions ranging from 45 to 621????m, which were subjected to spectral measurements. Absorption band depths of the size fractions were determined after applying an automated continuum-removal procedure to each spectrum. Then, the relationship between absorption band depth and gypsum size fraction was established using a linear regression. Three software processing steps were carried out to measure the grain size variations of gypsum in the Dune Area using AVIRIS data. AVIRIS mapping results, field work and laboratory analysis all show that the interdune areas have lower absorption band depth values and consist of finer grained gypsum deposits. In contrast, the dune crest areas have higher absorption band depth values and consist of coarser grained gypsum deposits. Based on laboratory estimates, a representative barchan-transverse dune (Transect 1) has a mean grain size of 1.16 ??{symbol} (449????m). The error bar results show that the error ranges from - 50 to + 50????m. Mean grain size for a representative parabolic dune (Transect 2) is 1.51 ??{symbol} (352????m), and 1.52 ??{symbol} (347????m) for a representative barchan dune (Transect 3). T-test results confirm that there are differences in the grain size distributions between barchan and parabolic dunes and between interdune and dune crest areas. The t-test results

  5. Diffusion of Oxygen Isotopes in Thermally Evolving Planetesimals and Size Ranges of Presolar Silicate Grains

    Science.gov (United States)

    Wakita, Shigeru; Nozawa, Takaya; Hasegawa, Yasuhiro

    2017-02-01

    Presolar grains are small particles found in meteorites through their isotopic compositions, which are considerably different from those of materials in the solar system. If some isotopes in presolar grains diffused out beyond their grain sizes when they were embedded in parent bodies of meteorites, their isotopic compositions could be washed out, and hence the grains could no longer be identified as presolar grains. We explore this possibility for the first time by self-consistently simulating the thermal evolution of planetesimals and the diffusion length of 18O in presolar silicate grains. Our results show that presolar silicate grains smaller than ˜0.03 μm cannot keep their original isotopic compositions even if the host planetesimals experienced a maximum temperature as low as 600 °C. Since this temperature corresponds to that experienced by petrologic type 3 chondrites, isotopic diffusion can constrain the size of presolar silicate grains discovered in such chondrites to be larger than ˜0.03 μm. We also find that the diffusion length of 18O reaches ˜0.3-2 μm in planetesimals that were heated up to 700-800°C. This indicates that, if the original size of presolar grains spans a range from ˜0.001 μm to ˜0.3 μm like that in the interstellar medium, then the isotopic records of the presolar grains may be almost completely lost in such highly thermalized parent bodies. We propose that isotopic diffusion could be a key process to control the size distribution and abundance of presolar grains in some types of chondrites.

  6. The Effect of Grain Size on the Radiation Response of Silicon Carbide and its Dependence on Irradiation Species and Temperature

    Science.gov (United States)

    Jamison, Laura

    In recent years the push for green energy sources has intensified, and as part of that effort accident tolerant and more efficient nuclear reactors have been designed. These reactors demand exceptional material performance, as they call for higher temperatures and doses. Silicon carbide (SiC) is a strong candidate material for many of these designs due to its low neutron cross-section, chemical stability, and high temperature resistance. The possibility of improving the radiation resistance of SiC by reducing the grain size (thus increasing the sink density) is explored in this work. In-situ electron irradiation and Kr ion irradiation was utilized to explore the radiation resistance of nanocrystalline SiC (nc-SiC), SiC nanopowders, and microcrystalline SiC. Electron irradiation simplifies the experimental results, as only isolated Frenkel pairs are produced so any observed differences are simply due to point defect interactions with the original microstructure. Kr ion irradiation simulates neutron damage, as large radiation cascades with a high concentration of point defects are produced. Kr irradiation studies found that radiation resistance decreased with particle size reduction and grain refinement (comparing nc-SiC and microcrystalline SiC). This suggests that an interface-dependent amorphization mechanism is active in SiC, suggested to be interstitial starvation. However, under electron irradiation it was found that nc-SiC had improved radiation resistance compared to single crystal SiC. This was found to be due to several factors including increased sink density and strength and the presence of stacking faults. The stacking faults were found to improve radiation response by lowering critical energy barriers. The change in radiation response between the electron and Kr ion irradiations is hypothesized to be due to either the change in ion type (potential change in amorphization mechanism) or a change in temperature (at the higher temperatures of the Kr ion

  7. Condition for the formation of micron-sized dust grains in dense molecular cloud cores

    CERN Document Server

    Hirashita, Hiroyuki

    2013-01-01

    We investigate the condition for the formation of micron-sized grains in dense cores of molecular clouds. This is motivated by the detection of the mid-infrared emission from deep inside a number of dense cores, the so-called `coreshine,' which is thought to come from scattering by micron-sized grains. Based on numerical calculations of coagulation starting from the typical grain size distribution in the diffuse interstellar medium, we obtain a conservative lower limit to the time $t$ to form micron-sized grains: $t/t_\\mathrm{ff}>3 (5/S) (n_\\mathrm{H}/10^5 \\mathrm{cm}^{-3})^{-1/4}$ (where $t_\\mathrm{ff}$ is the free-fall time at hydrogen number density $n_\\mathrm{H}$ in the core, and $S$ the enhancement factor to the grain-grain collision cross-section to account for non-compact aggregates). At the typical core density $n_\\mathrm{H}=10^5 \\mathrm{cm}^{-3}$, it takes at least a few free-fall times to form the micron-sized grains responsible for coreshine. The implication is that those dense cores observed in co...

  8. Grain-size dynamics beneath mid-ocean ridges: Implications for permeability and melt extraction

    CERN Document Server

    Turner, Andrew J; Behn, Mark D

    2014-01-01

    Grain size is an important control on mantle viscosity and permeability, but is difficult or impossible to measure in situ. We construct a two-dimensional, single phase model for the steady-state mean grain size beneath a mid-ocean ridge. The mantle rheology is modelled as a composite of diffusion creep, dislocation creep, dislocation accommodated grain boundary sliding, and a plastic stress limiter. The mean grain size is calculated by the piezometric relationship of Austin and Evans [2007]. We investigate the sensitivity of our model to global variations in grain growth exponent, potential temperature, spreading-rate, and mantle hydration. We interpret the mean mean grain-size field in the context of permeability. The permeability structure due to mean grain size may be approximated as a high permeability region beneath a low permeability region. The transition between high and low permeability regions forms a boundary that is steeply sloped toward the ridge axis. We hypothesise that such a permeability str...

  9. Synthesis of nanocrystalline CdS thin films in PVA matrix

    Indian Academy of Sciences (India)

    R Devi; P Purkayastha; P K Kalita; B K Sarma

    2007-04-01

    Nanocrystalline thin films of CdS are deposited on glass substrates by chemical bath deposition technique using polyvinyl alcohol (PVA) matrix solution. Crystallite sizes of the nanocrystalline films are determined from broadening of X-ray diffraction lines and are found to vary from 5.4–10.2 nm. The band gap of the nanocrystalline material is determined from the UV spectrograph. The absorption edge is shifted towards the lower wave length side (i.e. blue shift) and are found to be within the range from 2.48–2.8 eV as grain sizes decrease from 10.2–5.4 nm. This is also supported by the spectral response curves. An increase of molarity decreases the grain size which in turn increases the band gap.

  10. Grain-size analysis of sediment cores collected in 2009 offshore from Palos Verdes, California

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — This part of the data release includes grain-size analysis of sediment cores collected in 2009 offshore of Palos Verdes, California. It is one of seven files...

  11. National Marine Fisheries Service Grain Size Data from the Baltimore Canyon Trough

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Grain size analyses produced by Robert Reid of the NOAA National Marine Fisheries Service for the NOAA/BLM Outer Continental Shelf Mid-Atlantic Project, Baltimore...

  12. Evaluating grain size in polycrystals with rough surfaces by corrected ultrasonic attenuation.

    Science.gov (United States)

    Li, Xiongbing; Han, Xiaoqin; Arguelles, Andrea P; Song, Yongfeng; Hu, Hongwei

    2017-02-27

    Surface roughness of a sample has a great effect on the calculated grain size when measurements are based on ultrasonic attenuation. Combining modified transmission and reflection coefficients at the rough interface with a Multi-Gaussian beam model of the transducer, a comprehensive correction scheme for the attenuation coefficient is developed. An approximate inverse model of the calculated attenuation, based on Weaver's diffuse scattering theory, is established to evaluate grain size in polycrystals. The experimental results showed that for samples with varying surface roughness and matching microstructures, the fluctuation of evaluated average grain size was ±1.17μm. For polished samples with different microstructures, the relative errors to optical microscopy were no more than ±3.61%. The presented method provides an effective nondestructive tool for evaluating the grain size in metals with rough surfaces.

  13. Laboratory Liquefaction Test of Sand Based on Grain Size and Relative Density

    Directory of Open Access Journals (Sweden)

    Abdul Hakam

    2016-08-01

    Full Text Available Liquefaction due to strong earthquakes often occurs in sandy soil under low water table conditions with certain physical properties. The physical properties of sandy soil that give effect to liquefaction resistance include grain size and relative density. This paper presents the physical properties of sand soils related to their resistance to vibration. Vibration tests were conducted by using a shaking table. The acceleration and settlement of the samples were recorded during shaking. The tests were conducted with variation of soil density and mean grain size. The test results showed that average grain size and relative density of sand have a unique effect on liquefaction resistance. It can be concluded that there is a density limit with respect to the mean grain size of the sand particles associated with the liquefaction resistance for a certain acceleration.

  14. Surface-sediment grain-size distributions from the Elwha River delta, Washington, July 2015

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — This portion of the data release presents sediment grain-size data from samples collected on the Elwha River delta, Washington, between July and August 2015 (USGS...

  15. Surface-sediment grain-size distributions from the Elwha River delta, Washington, May 2014

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — This portion of the data release presents sediment grain-size data from samples collected on the Elwha River delta, Washington, in May 2014 (USGS Field Activity...

  16. Surface-sediment grain-size distributions from the Elwha River delta, Washington, March 2013

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — This portion of the data release presents sediment grain-size data from samples collected on the Elwha River delta, Washington, in March 2013 (USGS Field Activity...

  17. Surface-sediment grain-size distributions of the Elwha River delta, Washington, July 2016

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — This portion of the data release presents sediment grain-size data from samples collected on the Elwha River delta, Washington, in July 2016 (USGS Field Activity...

  18. Surface-sediment grain-size distributions of the Elwha River delta, Washington, January 2015

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — This portion of the data release presents sediment grain-size data from samples collected on the Elwha River delta, Washington, in January 2015 (USGS Field Activity...

  19. Surface-sediment grain-size distributions from the Elwha River delta, Washington, September 2013

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — This portion of the data release presents sediment grain-size data from samples collected on the Elwha River delta, Washington, in September 2013 (USGS Field...

  20. Sediment grain size in the Elwha River estuary, Washington, from 2013 and 2014.

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — This portion of the data release presents sediment grain-size data from samples collected in the Elwha River estuary, Washington, in July 2013 and June 2014 (USGS...

  1. Surface-sediment grain-size distributions from the Elwha River delta, Washington, September 2014

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — This portion of the data release presents sediment grain-size data from samples collected on the Elwha River delta, Washington, in September 2014 (USGS Field...

  2. Surface-sediment grain-size distributions from the Elwha River delta, Washington, August 2012

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — This portion of the data release presents sediment grain-size data from samples collected on the Elwha River delta, Washington, in August 2012 (USGS Field Activity...

  3. Geostatistical modeling of regionalized grain-size distributions using Min/Max Autocorrelation Factors

    National Research Council Canada - National Science Library

    Desbarats, A J

    2001-01-01

    .... Since the number of classes may be large and abundances in adjacent classes may be highly cross-correlated, practical simulation of regionalized grain-size distributions requires an efficient method...

  4. Measuring spatiotemporal variation in snow optical grain size under a subalpine forest canopy using contact spectroscopy

    National Research Council Canada - National Science Library

    Molotch, Noah P; Barnard, David M; Burns, Sean P; Painter, Thomas H

    2016-01-01

    .... In this study, we address one of many measurement gaps by using contact spectroscopy to measure snow optical grain size at high spatial resolution in trenches dug between tree boles in a subalpine forest...

  5. Grain Size Data from the NOAA Outer Continental Shelf Environmental Assessment Program (OCSEAP)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This data set contains grain size data from samples acquired under the NOAA Outer Continental Shelf Environmental Assessment Program (OCSEAP) from the Outer...

  6. Influence of austenite grain size on recrystallisation-precipitation interaction in a V-microalloyed steel

    Energy Technology Data Exchange (ETDEWEB)

    Quispe, A. [National University ' Jorge Basadre' , Av. Miraflores s/n, University City, Tacna (Peru)]. E-mail: abqc@unjbg.edu.pe; Medina, S.F. [National Center for Metallurgical Research (CENIM), Av. Gregorio del Amo 8, 28040-Madrid (Spain)]. E-mail: smedina@cenim.csic.es; Gomez, M. [National Center for Metallurgical Research (CENIM), Av. Gregorio del Amo 8, 28040-Madrid (Spain); Chaves, J.I. [National Center for Metallurgical Research (CENIM), Av. Gregorio del Amo 8, 28040-Madrid (Spain)

    2007-02-25

    By means of torsion tests using small specimens, the influence of austenite grain size on strain induced precipitation kinetics has been determined in a vanadium microalloyed steel. Determination of recrystallisation-precipitation-time-temperature (RPTT) diagrams for two austenite grain sizes allows values of the aforementioned magnitudes to be determined. An ample discussion is made of the quantitative influence found and its relation with nucleation and growth mechanisms of precipitates. The results are compared with the quantitative influence exerted by the other variables, reaching the conclusion that the austenite grain size has a notable influence on strain induced precipitation kinetics which should not be underestimated. Finally, the influence of austenite grain size is included in a strain induced precipitation model constructed by the authors of this work and which also takes into account the other aforementioned variables.

  7. Laboratory Application of Laser Grain-Size Analyzer in Determining Suspended Sediment Concentration

    Institute of Scientific and Technical Information of China (English)

    LIU Xiao; FENG Xiuli; LIU Jie; LIN Lin

    2014-01-01

    Suspended sediment concentration (SSC) is an important parameter in marine sedimentology. With the development of technology, many acoustic and optical devices, such as the Laser In-Situ Scattering and Transmissometry, have been designed to meas-ure in situ SSC and grain size distribution. But due to fund or other restrictions, many experiments were only conducted in laboratory, using an indoor laser grain-size analyzer and gravimetric method to measure grain size distribution and concentration, respectively. In this study the laboratory experiment is simplified by omitting the tiring step of gravimetric method. The connections between SSC and other parameters (obscuration, D50 and sorting index) were investigated based on 124 surface sediment samples collected from different offshore areas. A new method is developed for determining SSC in laboratory using a laser grain-size analyzer.

  8. How to form asteroids from mm-sized grains

    CERN Document Server

    Carrera, Daniel; Davies, Melvyn B

    2016-01-01

    The size distribution of asteroids in the solar system suggests that they formed top-down, with 100-1000 km bodies forming from the gravitational collapse of dense clumps of small solid particles. We investigate the conditions under which solid particles can form dense clumps in a protoplanetary disc. We used a hydrodynamic code to model the solid-gas interaction in disc. We found that particles down to millimeter size can form dense clumps, but only in regions where solids make $\\sim$ 8% of the local surface density. More generally, we mapped the range of particle sizes and concentrations that is consistent with the formation of particle clumps.

  9. The influence of grain size, grain color, and suspended-sediment concentration on light attenuation: why fine-grained terrestrial sediment is bad for coral reef ecosystems

    Science.gov (United States)

    Storlazzi, Curt; Norris, Benjamin; Rosenberger, Kurt

    2015-01-01

    Sediment has been shown to be a major stressor to coral reefs globally. Although many researchers have tested the impact of sedimentation on coral reef ecosystems in both the laboratory and the field and some have measured the impact of suspended sediment on the photosynthetic response of corals, there has yet to be a detailed investigation on how properties of the sediment itself can affect light availability for photosynthesis. We show that finer-grained and darker-colored sediment at higher suspended-sediment concentrations attenuates photosynthetically active radiation (PAR) significantly more than coarser, lighter-colored sediment at lower concentrations and provide PAR attenuation coefficients for various grain sizes, colors, and suspended-sediment concentrations that are needed for biophysical modeling. Because finer-grained sediment particles settle more slowly and are more susceptible to resuspension, they remain in the water column longer, thus causing greater net impact by reducing light essential for photosynthesis over a greater duration. This indicates that coral reef monitoring studies investigating sediment impacts should concentrate on measuring fine-grained lateritic and volcanic soils, as opposed to coarser-grained siliceous and carbonate sediment. Similarly, coastal restoration efforts and engineering solutions addressing long-term coral reef ecosystem health should focus on preferentially retaining those fine-grained soils rather than coarse silt and sand particles.

  10. Advance in orientation microscopy: quantitative analysis of nanocrystalline structures.

    Science.gov (United States)

    Seyring, Martin; Song, Xiaoyan; Rettenmayr, Markus

    2011-04-26

    The special properties of nanocrystalline materials are generally accepted to be a consequence of the high density of planar defects (grain and twin boundaries) and their characteristics. However, until now, nanograin structures have not been characterized with similar detail and statistical relevance as coarse-grained materials, due to the lack of an appropriate method. In the present paper, a novel method based on quantitative nanobeam diffraction in transmission electron microscopy (TEM) is presented to determine the misorientation of adjacent nanograins and subgrains. Spatial resolution of twin boundaries is substantially higher than that observed in bright-field images in the TEM; small angle grain boundaries are prominent; there is an obvious dependence of the grain boundary characteristics on grain size distribution and mean grain size.

  11. Grain size record of microparticles in the Muztagata ice core

    Institute of Scientific and Technical Information of China (English)

    WU; Guangjian; YAO; Tandong; XU; Baiqin; LI; Zheng; TIAN; Lide; DUAN; Keqin; WEN; Linke

    2006-01-01

    The dust transport and sediment characteristics are discussed based on analysis of microparticle size and size distribution in the Muztagata ice core at 6350 m a.s.l. The finer particles with diameter of 1―5μm are the dominant fraction in number, while middle and coarse particles mainly contribute to the total volume. The lognormal distribution characteristics can be seen for some high concentration samples, showing that model size and standard variation are greater than that in the Greenland ice cores. However, size-volume distribution of some low concentration samples is abnormal. Those distributions reflect the dust deposit process in high mountain glaciers at mid-low latitudes and show differences from those in polar ice sheet.

  12. Nano-scale machining of polycrystalline coppers - effects of grain size and machining parameters.

    Science.gov (United States)

    Shi, Jing; Wang, Yachao; Yang, Xiaoping

    2013-11-22

    In this study, a comprehensive investigation on nano-scale machining of polycrystalline copper structures is carried out by molecular dynamics (MD) simulation. Simulation cases are constructed to study the impacts of grain size, as well as various machining parameters. Six polycrystalline copper structures are produced, which have the corresponding equivalent grain sizes of 5.32, 6.70, 8.44, 13.40, 14.75, and 16.88 nm, respectively. Three levels of depth of cut, machining speed, and tool rake angle are also considered. The results show that greater cutting forces are required in nano-scale polycrystalline machining with the increase of depth of cut, machining speed, and the use of the negative tool rake angles. The distributions of equivalent stress are consistent with the cutting force trends. Moreover, it is discovered that in the grain size range of 5.32 to 14.75 nm, the cutting forces and equivalent stress increase with the increase of grain size for the nano-structured copper, while the trends reserve after the grain size becomes even higher. This discovery confirms the existence of both the regular Hall-Petch relation and the inverse Hall-Petch relation in polycrystalline machining, and the existence of a threshold grain size allows one of the two relations to become dominant. The dislocation-grain boundary interaction shows that the resistance of the grain boundary to dislocation movement is the fundamental mechanism of the Hall-Petch relation, while grain boundary diffusion and movement is the reason of the inverse Hall-Petch relation.

  13. Fatigue Resistance of the Grain Size Transition Zone in a Dual Microstructure Superalloy Disk

    Science.gov (United States)

    Gabb, T. P.; Kantzos, P. T.; Telesman, J.; Gayda, J.; Sudbrack, C. K.; Palsa, B. S.

    2010-01-01

    Mechanical property requirements vary with location in nickel-based superalloy disks. To maximize the associated mechanical properties, heat treatment methods have been developed for producing tailored microstructures. In this study, a specialized heat treatment method was applied to produce varying grain microstructures from the bore to the rim portions of a powder metallurgy processed nickel-based superalloy disk. The bore of the contoured disk consisted of fine grains to maximize strength and fatigue resistance at lower temperatures. The rim microstructure of the disk consisted of coarse grains for maximum resistance to creep and dwell crack growth at high temperatures up to 704 C. However, the fatigue resistance of the grain size transition zone was unclear, and needed to be evaluated. This zone was located as a band in the disk web between the bore and rim. Specimens were extracted parallel and transverse to the transition zone, and multiple fatigue tests were performed at 427 and 704 C. Mean fatigue lives were lower at 427 C than for 704 C. Specimen failures often initiated at relatively large grains, which failed on crystallographic facets. Grain size distributions were characterized in the specimens, and related to the grains initiating failures as well as location within the transition zone. Fatigue life decreased with increasing maximum grain size. Correspondingly, mean fatigue resistance of the transition zone was slightly higher than that of the rim, but lower than that of the bore. The scatter in limited tests of replicates was comparable for all transition zone locations examined.

  14. Dependence of corrosion properties of AISI 304L stainless steel on the austenite grain size

    Energy Technology Data Exchange (ETDEWEB)

    Sabooni, Soheil; Rashtchi, Hamed; Eslami, Abdoulmajid; Karimzadeh, Fathallah; Enayati, Mohammad Hossein; Raeissi, Keyvan; Imani, Reihane Faghih [Isfahan Univ. of Technology, Isfahan (Iran, Islamic Republic of). Dept. of Materials Engineering; Ngan, Alfonso Hing Wan [The Univ. of Hong Kong (China). Dept. of Mechanical Engineering

    2017-07-15

    The corrosion resistance of austenitic stainless steels is known to be hampered by the loss of chromium available for passive surface layer formation as a result of chromium carbide precipitation at austenite grain boundaries during annealing treatments. Although high-temperature annealing can promote carbide dissolution leading to better corrosion resistance, grain coarsening also results, which would lead to poorer mechanical properties. Processing methods to achieve both good corrosion resistance and mechanical properties are thus highly desirable for austenitic stainless steels. In the present study, we show that the corrosion resistance of AISI 304L stainless steel can be improved by grain refinement into the ultrafine-grained regime. Specifically, samples with different austenite grain sizes in the range of 0.65-12 μm were studied by potentiodynamic polarization and electrochemical impedance spectroscopy tests in a 3.5 wt.% NaCl solution. All samples showed a typical passive behavior with similar corrosion potential, but the corrosion current density decreased significantly with decreasing grain size. The results show that the sample with the finest grain size had the best corrosion resistance due to a higher resistance of the passive layer to pitting attacks. This study indicates that grain refinement which improves mechanical properties can also significantly improve the corrosion resistance of AISI 304L stainless steel.

  15. Graded composite diamond coatings with top-layer nanocrystallinity and interfacial integrity: Cross-sectional Raman mapping

    Energy Technology Data Exchange (ETDEWEB)

    Dumpala, Ravikumar [Manufacturing Engineering Section, Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036 (India); Nano Functional Materials Technology Centre, Department of Physics, Indian Institute of Technology Madras, Chennai 600036 (India); Ramamoorthy, B. [Manufacturing Engineering Section, Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036 (India); Rao, M.S. Ramachandra, E-mail: msrrao@iitm.ac.in [Nano Functional Materials Technology Centre, Department of Physics, Indian Institute of Technology Madras, Chennai 600036 (India)

    2014-01-15

    Cross-sectional structural characteristics of the CVD diamond coatings deposited on the tungsten carbide (WC-Co) substrates were analysed using Raman imaging technique. The grain size of the nanocrystalline diamond (NCD) coatings was observed to deviate from the nanocrystallinity with increasing thickness and exhibited the surface characteristics of microcrystalline diamond (MCD). However, thick diamond coatings with surface nanocrystallinity is the key requirement for load-bearing tribological applications. Tribological tests have clearly indicated the significance and need for the top-layer nanocrystallinity. Graded composite diamond coatings with an architecture of NCD/transition-layer/MCD/WC-Co are potentail candiadates to realize thick diamond coatings with top-layer nanocrystallinity. Residual stresses along the cross-section of the graded composite diamond coatings were analysed using Raman imaging technique, which confirmed the improved interfacial integrity of the graded composite diamond coatings.

  16. Mechanical properties of nanocrystalline metals, intermetalics and multiphase materials determined by tension, compression and disk-bend techniques

    Energy Technology Data Exchange (ETDEWEB)

    Eastman, J.A.; Thompson, L.J.; DiMelfi, R.J. [Argonne National Lab., IL (United States); Choudry, M. [Argonne National Lab., IL (United States)]/[Illinois Inst. of Tech., Chicago, IL (United States); Dollar, M. [Illinois Inst. of Tech., Chicago, IL (United States); Weertman, J.R. [Northwestern Univ., Evanston, IL (United States); Rittner, M.N.; Youngdahl, C.J. [Argonne National Lab., IL (United States)]/[Northwestern Univ., Evanston, IL (United States)

    1997-02-01

    The mechanical behavior of nanocrystalline metallic, intermetallic, and multiphase materials was investigated using tension, compression, and disk-bend techniques. Nanocrystalline NiAl, Al-Al{sub 3}Zr, and Cu were synthesized by gas condensation and either resistive or electron beam heating followed by high temperature vacuum compaction. Disk- bend tests of nanocrystalline NiAl show evidence of improved ductility at room temperature in this normally extremely brittle material. In contrast, tension tests of multiphase nanocrystalline Al- Al{sub 3}Zr samples show significant increases in strength by substantial reductions in ductility with decreasing grain size. Compression tests of nanocrystalline copper result in substantially higher yield stress and total elongation values than those measured in tensile tests. Implications for operative deformation mechanisms in these materials are discussed.

  17. Characterization of nanocrystalline Pd by x-ray diffraction and EXAFS

    Energy Technology Data Exchange (ETDEWEB)

    Eastman, J.A. (Argonne National Lab., IL (USA)); Fitzsimmons, M.R.; Mueller-Stach, M.; Wallner, G. (Ludwig-Maximilians-Universitaet, Munich (Germany, F.R.)); Elam, W.T. (Naval Research Lab., Washington, DC (USA))

    1990-12-01

    Since the fraction of atoms located within a few atomic distances of one or more internal interfaces increases rapidly with decreasing grain size in the nanometer regime, it is expected that the structure of grain boundaries plays an important role in determining and controlling the properties of nanocrystalline materials. A high resolution electron microscopy study of nanocrystalline Pd found no evidence for extended, disordered boundary regions that would differ from boundaries in coarse-grained materials. Recent results from x-ray diffraction, EXAFS and hydriding studies have yielded clear evidence that the boundaries in nanocrystalline Pd are ordered and/or extremely localized in nature. The present paper will summarize and discuss the principal results of these three studies. 12 refs., 4 figs.

  18. Modeling and simulation of boron-doped nanocrystalline silicon carbide thin film by a field theory.

    Science.gov (United States)

    Xiong, Liming; Chen, Youping; Lee, James D

    2009-02-01

    This paper presents the application of a multiscale field theory in modeling and simulation of boron-doped nanocrystalline silicon carbide (B-SiC). The multiscale field theory was briefly introduced. Based on the field theory, numerical simulations show that intergranular glassy amorphous films (IGFs) and nano-sized pores exist in triple junctions of the grains for nanocrystalline B-SiC. Residual tensile stress in the SiC grains and compressive stress on the grain boundaries (GBs) were observed. Under tensile loading, it has been found that mechanical response of 5 wt% boron-SiC exhibits five characteristic regimes. Deformation mechanism at atomic scale has been revealed. Tensile strength and Young's modulus of nanocrystalline SiC were accurately reproduced.

  19. Structural modification of nanocrystalline ceria by ion beams.

    Science.gov (United States)

    Zhang, Yanwen; Edmondson, Philip D; Varga, Tamas; Moll, Sandra; Namavar, Fereydoon; Lan, Chune; Weber, William J

    2011-07-07

    Exceptional size-dependent electronic-ionic conductivity of nanostructured ceria can significantly alter materials properties in chemical, physical, electronic and optical applications. Using energetic ions, we have demonstrated effective modification of interface volume and grain size in nanocrystalline ceria from a few nm up to ∼25 nm, which is the critical region for controlling size-dependent material property. The grain size increases and follows an exponential law as a function of ion fluence that increases with temperature, while the cubic phase is stable under the irradiation. The unique self-healing response of radiation damage at grain boundaries is utilized to control the grain size at the nanoscale. Structural modification by energetic ions is proposed to achieve desirable electronic-ionic conductivity.

  20. The Importance of Grain Size to Mantle Dynamics and Seismological Observations: A Multidisciplinary Approach

    Science.gov (United States)

    Gassmöller, Rene; Dannberg, Juliane; Eilon, Zach; Moulik, Pritwiraj; Myhill, Robert; Faul, Ulrich

    2016-04-01

    Dynamic models of Earth's convecting mantle usually implement flow laws with constant grain size, stress-independent viscosity and a limited treatment of variations associated with changes in mineral assemblage. These simplifications greatly reduce computational requirements but preclude effects such as shear localisation and transient changes in rheology associated with phase transitions, which have the potential to fundamentally change flow patterns in the mantle. Here we use the finite-element code ASPECT [Bangerth et al., 2013] to model grain size evolution and the interplay between grain size, stress and strain rate in the convecting mantle. We include the simultaneous and competing effects of dynamic recrystallisation resulting from work done by dislocation creep, grain growth in multiphase assemblages and recrystallisation at phase transitions. Grain size variations also affect seismic properties of mantle materials. We apply published formalisms [Jackson & Faul, 2010; McCarthy et al., 2011; Takei et al., 2014] to relate intrinsic variables (P, T, and grain size) from our numerical models to seismic velocity (Vs) and attenuation (Q). We investigate these formalisms for consistency with seismic observations at conditions beyond the range of the experiments upon which they are based; this requires constraining the range of pre-factors and activation volumes relevant for the lower mantle. Our calculations use thermodynamically self-consistent anharmonic elastic moduli determined for the mineral assemblages in the mantle using HeFESTo [Stixrude and Lithgow-Bertelloni, 2013]. We investigate the effect of realistically heterogeneous grain sizes by computing synthetic seismological data; these highlight the frequency-dependent sensitivity of seismic waves to grain size, which is important when interpreting Vs and Q observations in terms of mineral assemblage and temperature. Our models show that grain size evolution can lead to lateral viscosity variations of six

  1. Multiscale architectured materials with composition and grain size gradients manufactured using high-pressure torsion.

    Science.gov (United States)

    Kang, Ji Yun; Kim, Jung Gi; Park, Hyo Wook; Kim, Hyoung Seop

    2016-05-27

    The concept of multiscale architectured materials is established using composition and grain size gradients. Composition-gradient nanostructured materials are produced from coarse grained interstitial free steels via carburization and high-pressure torsion. Quantitative analyses of the dislocation density using X-ray diffraction and microstructural studies clearly demonstrate the gradients of the dislocation density and grain size. The mechanical properties of the gradient materials are compared with homogeneous nanostructured carbon steel without a composition gradient in an effort to investigate the gradient effect. Based on the above observations, the potential of multiscale architecturing to open a new material property is discussed.

  2. Grain size of loess and paleosol samples: what are we measuring?

    Science.gov (United States)

    Varga, György; Kovács, János; Szalai, Zoltán; Újvári, Gábor

    2017-04-01

    Particle size falling into a particularly narrow range is among the most important properties of windblown mineral dust deposits. Therefore, various aspects of aeolian sedimentation and post-depositional alterations can be reconstructed only from precise grain size data. Present study is aimed at (1) reviewing grain size data obtained from different measurements, (2) discussing the major reasons for disagreements between data obtained by frequently applied particle sizing techniques, and (3) assesses the importance of particle shape in particle sizing. Grain size data of terrestrial aeolian dust deposits (loess and paleosoil) were determined by laser scattering instruments (Fritsch Analysette 22 Microtec Plus, Horiba Partica La-950 v2 and Malvern Mastersizer 3000 with a Hydro Lv unit), while particles size and shape distributions were acquired by Malvern Morphologi G3-ID. Laser scattering results reveal that the optical parameter settings of the measurements have significant effects on the grain size distributions, especially for the fine-grained fractions (Innovation Office (Hungary) under contract NKFI 120620 is gratefully acknowledged. It was additionally supported (for G. Varga) by the Bolyai János Research Scholarship of the Hungarian Academy of Sciences.

  3. Microstructure and magnetic characteristics of nanocrystalline Ni0.5Zn0.5 ferrite synthesized by a spraying-coprecipitation method

    Institute of Scientific and Technical Information of China (English)

    Liu Yin; Qiu Tai

    2007-01-01

    Nanocrystalline Ni0.5Zn0.5 ferrite with average grain sizes ranging from 10 to 100 nm is prepared by using a spraying-coprecipitation method. The results indicate that the nanocrystalline Ni0.5Zn0.5 ferrite is ferromagnetic without the superparamagnetic phenomenon observed at room temperature. Specific saturation magnetization of nanocrystalline Ni0.5Zn0.5 ferrite increases from 40.2 to 75.6 emu/g as grain size increases from 11 to 94nm. Coercivity of nanocrystalline Ni0.5Zn0.5 ferrite increases monotonically when d < 62 nm. The relationship between the coercivity and the mean grain size is well fitted into a relation Hc ~ d3. A theoretically evaluated value of the critical grain size is 141nm larger than the experimental value 62nm for nanocrystalline Ni0.5Zn0.5 ferrite. The magnetic behaviour of nanocrystalline Ni0.5Zn0.5 ferrite may be explained by using the random anisotropy theory.

  4. EFFECT OF INITIAL GRAIN SIZE ON STATIC RECRYSTALLIZA-TION SOFTENING IN Cr STEEL USING STRESS RELAXATION TECHNIQUE

    Institute of Scientific and Technical Information of China (English)

    A.R. Morgridge

    2002-01-01

    Effect of initial grain size (I.G.S.) on static recrystallization softening in Cr steel(0.77wt.% CR) has been investigated through the use of interrupted hot compressiontests and stress relaxation curves from Gleeble 1500. Initial grain sizes were variedbetween 20 and 93 microns. Stress strains curves for Cr steel for different initialgrain sizes and recrystallization times have been highlighted. Similar observation wasmade for metadynamic recrystallization with shorter retardation times. Staticallyrecrystallized grain size also increased as initial grain size increases. It is found thatthe values of initial grain size have significant effects on the mean flow stress andstatic recrystallization kinetics as well as the peak strain values to initiate dynamicrecrystallization.

  5. Grain-Size Analysis of Debris Flow Alluvial Fans in Panxi Area along Jinsha River, China

    Directory of Open Access Journals (Sweden)

    Wen Zhang

    2015-11-01

    Full Text Available The basic geometric parameters of 236 debris flow catchments were determined by interpreting SPOT5 remote sensing images with a resolution of 2.5 m in a 209 km section along the Jinsha River in the Panxi area, China. A total of 27 large-scale debris flow catchments were selected for detailed in situ investigation. Samples were taken from two profiles in the deposition zone for each debris flow catchment. The φ value gradation method of the grain size was used to obtain 54 histograms with abscissa in a logarithmic scale. Five types of debris flows were summarized from the outline of the histogram. Four grain size parameters were calculated: mean grain size, standard deviation, coefficient of skewness, and coefficient of kurtosis. These four values were used to evaluate the features of the histogram. The grain index that reflects the transport (kinetic energy information of debris flows was defined to describe the characteristics of the debris-flow materials. Furthermore, a normalized grain index based on the catchment area was proposed to allow evaluation of the debris flow mobility. The characteristics of the debris-flow materials were well-described by the histogram of grain-size distribution and the normalized grain index.

  6. Role of grain size and particle velocity distribution in secondary electron emission in space plasmas

    Science.gov (United States)

    Chow, V. W.; Mendis, D. A.; Rosenberg, M.

    1993-01-01

    By virtue of being generally immersed in a plasma environment, cosmic dust is necessarily electrically charged. The fact that secondary emission plays an important role in determining the equilibrium grain potential has long been recognized, but the fact that the grain size plays a crucial role in this equilibrium potential, when secondary emission is important, has not been widely appreciated. Using both conducting and insulating spherical grains of various sizes and also both Maxwellian and generalized Lorentzian plasmas (which are believed to represent certain space plasmas), we have made a detailed study of this problem. In general, we find that the secondary emission yield delta increases with decreasing size and becomes very large for grains whose dimensions are comparable to the primary electron penetration depth, such as in the case of the very small grains observed at comet Halley and inferred in the interstellar medium. Moreover, we observed that delta is larger for insulators and equilibrium potentials are generally more positive when the plasma has a broad non-Maxwellian tail. Interestingly, we find that for thermal energies that are expected in several cosmic regions, grains of different sizes can have opposite charge, the smaller ones being positive while the larger ones are negative. This may have important consequences for grain accretion in polydisperse dusty space plasmas.

  7. The Influence of Grain Size on Decomposition Reaction of Limestone in Dispersing State

    Institute of Scientific and Technical Information of China (English)

    XU De-long; WEI Hon-gen; LUO Yong-qin

    2004-01-01

    The thermal behavior and kinetic parameters of decomposition reaction of limestone in a temperature-programmed mode were investigated by means of TG. The experimental results show that the kinetic model functions in different forms for the thermal decomposition reactions of different limestone grain sizes in dispersing state under the atmosphere of static air are 4(1-α)3/4 for small size limestone and (1-α) for large size limestone. Information was obtained on the relationship among the decomposition temperature, decomposition time, decomposition fraction, decomposition reaction rate constant and grain size of limestone.

  8. Self-composite comprised of nanocrystalline diamond and a non-diamond component useful for thermoelectric applications

    Science.gov (United States)

    Gruen, Dieter M.

    2009-08-11

    One provides nanocrystalline diamond material that comprises a plurality of substantially ordered diamond crystallites that are sized no larger than about 10 nanometers. One then disposes a non-diamond component within the nanocrystalline diamond material. By one approach this non-diamond component comprises an electrical conductor that is formed at the grain boundaries that separate the diamond crystallites from one another. The resultant nanowire is then able to exhibit a desired increase with respect to its ability to conduct electricity while also preserving the thermal conductivity behavior of the nanocrystalline diamond material.

  9. A new look at grain size and load effects in the hardness of ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Krell, A. [Fraunhofer-Institut fuer Keramische Technologien und Sinterwerkstoffe (IKTS), Dresden (Germany)

    1998-05-01

    A simple model describes the load effect (size effect) in the hardness, assuming an increasing microplastic deformability, when the further extension of the plastic zone growth and multiplication of pre-existing elements of plasticity are more effective than the generation of new dislocations or twins in the virgin material around the indentation site. The model explains experiments with sintered alumina which indicate a reduced load effect in increasingly fine-grained microstructures due to a grain size effect that is more pronounced at higher testing loads (larger indents) than in the microhardness range. A large difference between the hardness of plastically deformed volumes in single crystals and in polycrystalline microstructures consisting of grains with the same size, respectively, reveals a substantial contribution of the grain boundaries to plastic deformation at the indentation site even at room temperature and even for coarser microstructures. (orig.) 18 refs.

  10. Effect of grain size on superelasticity in Fe-Mn-Al-Ni shape memory alloy wire

    Directory of Open Access Journals (Sweden)

    T. Omori

    2013-09-01

    Full Text Available Effects of grain size on superelastic properties in Fe-34Mn-15Al-7.5Ni alloy wires with a ⟨110⟩ fiber-texture were investigated by cyclic tensile tests. It was confirmed that the critical stress for induced martensitic transformation and the superelastic strain are functions of relative grain size d/D (d: mean grain diameter, D: wire diameter, and that the critical stress is proportional to (1–d/D2 as well as in Cu-based shape memory alloys. A large superelastic strain of about 5% was obtained in the specimen with a large relative grain size over d/D = 1.

  11. Experimental evidence of tunable space-charge-layer-induced electrical properties of nanocrystalline ceria thin films.

    Science.gov (United States)

    Lee, Kyung-Ryul; Lee, Jong-Ho; Yoo, Han-Ill

    2013-10-07

    Fully dense nanocrystalline ceria films were successfully deposited on a MgO single crystal by pulsed laser deposition (PLD). The electrical conductivity of the nanocrystalline thin film was 20 times higher than that of the bulk sample. The activation energy of bulk ceria was 2.3 eV, whereas the activation energy of the nanocrystalline sample was only 1.2 eV. After post-annealing at 1273 K in which the grain size of the nanocrystalline thin film increased to ~400 nm, the electrical conductivity and activation energy of the film were changed similar to those of bulk. These unique electrical properties of the nano-crystalline thin-film can be attributed to the grain size effect, or more specifically, to the space charge layer (SCL) effect. Furthermore, the electrical conductivity of the nanocrystalline thin film became similar to that of the bulk in an extremely reducing atmosphere because of the unusual dependence of the SCL effect on the oxygen partial pressure.

  12. Characterization of grain sizes and roughness of HfOsub>2sub> single layers.

    Science.gov (United States)

    Zhang, Lei; Cheng, Xinbin; Zhang, Jinlong; Jiao, Hongfei; Bao, Ganghua; Ding, Tao; Wang, Zhanshan

    2017-02-01

    The grain sizes and their influence on the roughness of an HfOsub>2sub> single layer prepared with ion-assisted deposition were investigated. Three methods, x ray diffractometry, atomic force microscopy, and the k-correlated power spectral density function model, were used to obtain the grain sizes in two HfOsub>2sub> single layers with 16 and 20 nm thicknesses. X ray diffractometry showed that the grain sizes were about 7 and 9 nm, respectively, whereas the other two methods demonstrated that the grain sizes were about 14 and 16 nm. It was thought that x ray diffractometry underestimated the grain size due to micro strain or a shallow penetration depth. The grains in an HfOsub>2sub> single layer lead to a rough surface, which had a significant bulge at the middle-high frequency range in a power spectral density function curve. The coating intrinsic roughness of the HfOsub>2sub> single layer was separated from the substrate roughness.

  13. Investigations of grain size dependent sediment transport phenomena on multiple scales

    Science.gov (United States)

    Thaxton, Christopher S.

    Sediment transport processes in coastal and fluvial environments resulting from disturbances such as urbanization, mining, agriculture, military operations, and climatic change have significant impact on local, regional, and global environments. Primarily, these impacts include the erosion and deposition of sediment, channel network modification, reduction in downstream water quality, and the delivery of chemical contaminants. The scale and spatial distribution of these effects are largely attributable to the size distribution of the sediment grains that become eligible for transport. An improved understanding of advective and diffusive grain-size dependent sediment transport phenomena will lead to the development of more accurate predictive models and more effective control measures. To this end, three studies were performed that investigated grain-size dependent sediment transport on three different scales. Discrete particle computer simulations of sheet flow bedload transport on the scale of 0.1--100 millimeters were performed on a heterogeneous population of grains of various grain sizes. The relative transport rates and diffusivities of grains under both oscillatory and uniform, steady flow conditions were quantified. These findings suggest that boundary layer formalisms should describe surface roughness through a representative grain size that is functionally dependent on the applied flow parameters. On the scale of 1--10m, experiments were performed to quantify the hydrodynamics and sediment capture efficiency of various baffles installed in a sediment retention pond, a commonly used sedimentation control measure in watershed applications. Analysis indicates that an optimum sediment capture effectiveness may be achieved based on baffle permeability, pond geometry and flow rate. Finally, on the scale of 10--1,000m, a distributed, bivariate watershed terain evolution module was developed within GRASS GIS. Simulation results for variable grain sizes and for

  14. Can high resolution 3D topographic surveys provide reliable grain size estimates in gravel bed rivers?

    Science.gov (United States)

    Pearson, E.; Smith, M. W.; Klaar, M. J.; Brown, L. E.

    2017-09-01

    High resolution topographic surveys such as those provided by Structure-from-Motion (SfM) contain a wealth of information that is not always exploited in the generation of Digital Elevation Models (DEMs). In particular, several authors have related sub-metre scale topographic variability (or 'surface roughness') to sediment grain size by deriving empirical relationships between the two. In fluvial applications, such relationships permit rapid analysis of the spatial distribution of grain size over entire river reaches, providing improved data to drive three-dimensional hydraulic models, allowing rapid geomorphic monitoring of sub-reach river restoration projects, and enabling more robust characterisation of riverbed habitats. However, comparison of previously published roughness-grain-size relationships shows substantial variability between field sites. Using a combination of over 300 laboratory and field-based SfM surveys, we demonstrate the influence of inherent survey error, irregularity of natural gravels, particle shape, grain packing structure, sorting, and form roughness on roughness-grain-size relationships. Roughness analysis from SfM datasets can accurately predict the diameter of smooth hemispheres, though natural, irregular gravels result in a higher roughness value for a given diameter and different grain shapes yield different relationships. A suite of empirical relationships is presented as a decision tree which improves predictions of grain size. By accounting for differences in patch facies, large improvements in D50 prediction are possible. SfM is capable of providing accurate grain size estimates, although further refinement is needed for poorly sorted gravel patches, for which c-axis percentiles are better predicted than b-axis percentiles.

  15. Relationship between Spectral Induced Polarization Measurements and Grain Size of Sandstones

    Science.gov (United States)

    Seleznev, N. V.; Hou, C. Y.; Freed, D.; Fellah, K.; Feng, L.; Xu, G.; Slater, L. D.

    2016-12-01

    Frequency dependence of the complex conductivity of ion-conductive soils and sediments in the range from millihertz to kilohertz can exhibit what is called the spectral induced polarization (SIP) effect, in which the impedance phase shows a near-resonance peak at a characteristic frequency as a result of a strong polarization response. Because the conventional Maxwell-Wagner interfacial polarization related to rock texture cannot provide an adequate explanation, the electrochemical polarization related to the electrical double layer formed in the presence of grains with surface charge is often invoked as a main mechanism for the SIP effect. Several studies demonstrating the link between SIP effect and the dominant grain size have previously been conducted on loose sands. Although loose sands provide good control of the grain size, they are not entirely representative of the consolidated sedimentary rocks common in the subsurface. In the present study we investigate the relationship between SIP effect and dominant grain size of well-characterized quarried consolidated sandstones. The choice of samples minimizes the influence of other factors, such as the presence of clays, on the SIP effect. Dominant grain size was determined using digital image analysis of scanning electron microscope (SEM) images obtained on thin sections. SIP spectra were measured on a collection of quarried clay-free sandstones saturated with brines. All rocks displayed a distinct peak in the imaginary conductivity dispersion curve. Also, we establish a rock model based on differential effective medium approach that accounts for both the interfacial polarization and electrochemical polarization due to the presence of charged grains. Experimental data is inverted with the model to obtain the dominant grain size. The model is shown to be capable of reproducing experimental data, and the inverted dominant grain size compares favorably with values determined from image analysis.

  16. Grain size effect on yield strength of titanium alloy implanted with aluminum ions

    Energy Technology Data Exchange (ETDEWEB)

    Popova, Natalya, E-mail: natalya-popova-44@mail.ru [Tomsk State University of Architecture and Building, 2, Solyanaya Sq., 634003, Tomsk (Russian Federation); Institute of Strength Physics and Materials Science, SB RAS, 2/4, Akademicheskii Ave., 634021, Tomsk (Russian Federation); Nikonenko, Elena, E-mail: vilatomsk@mail.ru [Tomsk State University of Architecture and Building, 2, Solyanaya Sq., 634003, Tomsk (Russian Federation); National Research Tomsk Polytechnic University, 30, Lenin Str., 634050, Tomsk (Russian Federation); Yurev, Ivan, E-mail: yiywork@mail.ru [Tomsk State University of Architecture and Building, 2, Solyanaya Sq., 634003, Tomsk (Russian Federation); Kalashnikov, Mark, E-mail: kmp1980@mail.ru [Institute of Strength Physics and Materials Science, SB RAS, 2/4, Akademicheskii Ave., 634021, Tomsk (Russian Federation); Kurzina, Irina, E-mail: kurzina99@mail.ru [National Research Tomsk State University, 36, Lenin Str., 634050, Tomsk (Russian Federation)

    2016-01-15

    The paper presents a transmission electron microscopy (TEM) study of the microstructure and phase state of commercially pure titanium VT1-0 implanted by aluminum ions. This study has been carried out before and after the ion implantation for different grain size, i.e. 0.3 µm (ultra-fine grain condition), 1.5 µm (fine grain condition), and 17 µm (polycrystalline condition). This paper presents details of calculations and analysis of strength components of the yield stress. It is shown that the ion implantation results in a considerable hardening of the entire thickness of the implanted layer in the both grain types. The grain size has, however, a different effect on the yield stress. So, both before and after the ion implantation, the increase of the grain size leads to the decrease of the alloy hardening. Thus, hardening in ultra-fine and fine grain alloys increased by four times, while in polycrystalline alloy it increased by over six times.

  17. Determination of Size Distributions in Nanocrystalline Powders by TEM, XRD and SAXS

    DEFF Research Database (Denmark)

    Jensen, Henrik; Pedersen, Jørgen Houe; Jørgensen, Jens Erik

    2006-01-01

    available powders showed different morphologies. The SSEC78 powder showed the narrowest sizes distribution while UV100 and TiO2_5nm consisted of the smallest primary particles. SSEC78, UV100, and TiO2_5nm consisted of both primary particles as well as a secondary structure comprised of nanosized primary......Crystallite size distributions and particle size distributions were determined by TEM, XRD, and SAXS for three commercially available TiO2 samples and one homemade. The theoretical Guinier Model was fitted to the experimental data and compared to analytical expressions. Modeling of the XRD spectra...

  18. Sol-Gel Synthesis of LaMO3 (M = Cr, Mn, Fe, Co, Ni) Nanocrystalline Powders

    Institute of Scientific and Technical Information of China (English)

    Chen Zhanheng; Xing Xianran; Dai Jing; Huang Xiaowei; Li Hongwei

    2004-01-01

    Sol-gel synthesis of LaMO3 ( M = Cr, Mn, Fe, Co, Ni) nanocrystalline Powders was investigated. DSC measurement shows that precursors decomposed at about 403 K and 620 K to bum out of N, C, and H. The calcined samples at 1073 K were determined by XRD to be single phase. SEM observation shows that the prepared samples are nanocrystalline powders in broad sense. The average grain size of LaM'O3 (M'= Cr, Mn, Fe, Ni) is 150 ~700 nm,and the grain size of LaCoO3 is about 30 nm.

  19. Effects of Strain Energy and Grain Size on Corrosion Resistance of Ultrafine Grained Fe-20%Cr Steels with Extremely low C and N Fabricated by ECAP

    Directory of Open Access Journals (Sweden)

    Muhammad Rifai

    2015-01-01

    Full Text Available Effect of strain energy and grain size on corrosion resistance of ultrafine grained (UFG Fe-20%Cr steels with extremely low C and N fabricated by equal channel angular pressing (ECAP was investigated. UFG structures of initial grain size of 144 nm exhibited the typical three-stage softening comprising recovery, recrystallization, and grain growth. Potentiodynamic polarization measurements were carried out with a conventional three-electrode cell to evaluate pitting potential. Pitting potential in 1000 mol·m−3 NaCl solution was nobler in UFG state, but pitting potential started to decrease monotonously at lower temperature compared to hardness. The degradation of corrosion resistance in the early stage of annealing is attributed to stability change of passivation by recovery of dislocation structures inside grains and in nonequilibrium grain boundaries. We therefore conclude that nobler potentials of UFG states were realized by not only grain size reduction but also defective deformation-induced UFG.

  20. GRAIN SIZE DISTRIBUTION OF SEDIMENT IN THE NORTHERN EAST CHINA SEA AND THE RELATIONSHIP WITH THE SEA CURRENTS

    Institute of Scientific and Technical Information of China (English)

    LEI Kun; YANG Zuosheng; GUO Zhigang

    2002-01-01

    This paper discusses the relationship between the grain size distribution of sediment and currents in the northern East China Sea on the basis of the grain size analysis. The results show that grain size distribution of suspended sediment is controlled by the currents. Suspended sediment in the littoral water is finer than those in the open sea currents. Grain size distribution of surface sediment is affected by the sea currents to some extent. And the grain size of suspended sediment and surface sediment do not agree with each other in positions.

  1. Species sensitivity distributions for suspended clays, sediment burial, and grain size change in the marine environment.

    Science.gov (United States)

    Smit, Mathijs G D; Holthaus, Karlijn I E; Trannum, Hilde C; Neff, Jerry M; Kjeilen-Eilertsen, Grete; Jak, Robbert G; Singsaas, Ivar; Huijbregts, Mark A J; Hendriks, A Jan

    2008-04-01

    Assessment of the environmental risk of discharges, containing both chemicals and suspended solids (e.g., drilling discharges to the marine environment), requires an evaluation of the effects of both toxic and nontoxic pollutants. To date, a structured evaluation scheme that can be used for prognostic risk assessments for nontoxic stress is lacking. In the present study we challenge this lack of information by the development of marine species sensitivity distributions (SSDs) for three nontoxic stressors: suspended clays, burial by sediment, and change in sediment grain size. Through a literature study, effect levels were obtained for suspended clays, as well as for burial of biota. Information on the species preference range for median grain size was used to assess the sensitivity of marine species to changes in grain size. The 50% hazardous concentrations (HC50) for suspended barite and bentonite based on 50% effect concentrations (EC50s) were 3,010 and 1,830 mg/L, respectively. For burial the 50% hazardous level (HL50) was 5.4 cm. For change in median grain size, two SSDs were constructed; one for reducing and one for increasing the median grain size. The HL50 for reducing the median grain size was 17.8 mum. For increasing the median grain size this value was 305 mum. The SSDs have been constructed by using information related to offshore oil- and gas-related activities. Nevertheless, the results of the present study may have broader implications. The hypothesis of the present study is that the SSD methodology developed for the evaluation of toxic stress can also be applied to evaluate nontoxic stressors, facilitating the incorporation of nontoxic stressors in prognostic risk assessment tools.

  2. Size Effect Of Glulam Beams In Tension Perpendicular To Grain

    DEFF Research Database (Denmark)

    Astrup, Thomas; Odin Clorius, Christian; Damkilde, Lars;

    2007-01-01

    The strength of wood is reduced when the stressed volume is increased. The phenomenon is termed size effect and is often explained as being stochastic in the sense that the probability of weak locations occurring in the wood increases with increased volume. This paper presents the hypothesis...... that the lower strength is caused by stress concentrations. The stress concentrations arise from the anisotropic structure of wood, and are therefore deterministic. The hypothesis is substantiated through extensive FEM-calculations and experiments. A reasonable agreement between ultimate stresses determined...

  3. Size effect of glulam beams in tension perpendicular to grain

    DEFF Research Database (Denmark)

    Astrup, Thomas; Clorius, Christian Odin; Damkilde, Lars;

    2007-01-01

    that the lower strength is caused by stress concentrations. The stress concentrations arise from the anisotropic structure of wood, and are therefore deterministic. The hypothesis is substantiated through extensive FEM-calculations and experiments. A reasonable agreement between ultimate stresses determined......The strength of wood is reduced when the stressed volume is increased. The phenomenon is termed size effect and is often explained as being stochastic in the sense that the probability of weak locations occurring in the wood increases with increased volume. This paper presents the hypothesis...

  4. Size dependent magnetic and electrical properties of Ba-doped nanocrystalline BiFeO3

    Directory of Open Access Journals (Sweden)

    Mehedi Hasan

    2016-03-01

    Full Text Available Improvement in magnetic and electrical properties of multiferroic BiFeO3 in conjunction with their dependence on particle size is crucial due to its potential applications in multifunctional miniaturized devices. In this investigation, we report a study on particle size dependent structural, magnetic and electrical properties of sol-gel derived Bi0.9Ba0.1FeO3 nanoparticles of different sizes ranging from ∼ 12 to 49 nm. The substitution of Bi by Ba significantly suppresses oxygen vacancies, reduces leakage current density and Fe2+ state. An improvement in both magnetic and electrical properties is observed for 10 % Ba-doped BiFeO3 nanoparticles compared to its undoped counterpart. The saturation magnetization of Bi0.9Ba0.1FeO3 nanoparticles increase with reducing particle size in contrast with a decreasing trend of ferroelectric polarization. Moreover, a first order metamagnetic transition is noticed for ∼ 49 nm Bi0.9Ba0.1FeO3 nanoparticles which disappeared with decreasing particle size. The observed strong size dependent multiferroic properties are attributed to the complex interaction between vacancy induced crystallographic defects, multiple valence states of Fe, uncompensated surface spins, crystallographic distortion and suppression of spiral spin cycloid of BiFeO3.

  5. Concepts on Low Temperature Mechanical Grain Growth

    Energy Technology Data Exchange (ETDEWEB)

    Sharon, John Anthony [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Metallurgy and Materials Joining Dept.; Boyce, Brad Lee [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Metallurgy and Materials Joining Dept.

    2013-11-01

    In metals, as grain size is reduced below 100nm, conventional dislocation plasticity is suppressed resulting in improvements in strength, hardness, and wears resistance. Existing and emerging components use fine grained metals for these beneficial attributes. However, these benefits can be lost in service if the grains undergo growth during the component’s lifespan. While grain growth is traditionally viewed as a purely thermal process that requires elevated temperature exposure, recent evidence shows that some metals, especially those with nanocrystalline grain structure, can undergo grain growth even at room temperature or below due to mechanical loading. This report has been assembled to survey the key concepts regarding how mechanical loads can drive grain coarsening at room temperature and below. Topics outlined include the atomic level mechanisms that facilitate grain growth, grain boundary mobility, and the impact of boundary structure, loading scheme, and temperature.

  6. Preliminary analysis of grain-size populations with environmentally sensitive terrigenous components in marginal sea setting

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    Terrigenous components were separated from the bulk sediment of Core A7 from the Okinawa Trough and Core A37 from the Ryukru Trench and grain-size distributions of these sub-samples were analyzed. Based upon an analysis of the grain-size data of the two sedimentary sequences, grain-size populations are identified to be sensitive to sedimentary environmental changes. The modal values and size ranges of the two main grain-size populations in Core A7 are evidently different from those of Core A37, indicating the spatial variability of sediment sources and transport processes between the two places. The downcore variations in the content of the environmentally sensitive grain-size populations reveal that during the accumulation of sedimentary material the environment remained relatively stable at the site where Core A7 was collected, except for the apparent events for the formation of two turbidite layers and a volcanic ash layer. However, the sedimentary sequence of Core A37 shows six sedimentary cycles, indicating a highly variable sedimentary environment at this location.

  7. Fatigue Failure Modes of the Grain Size Transition Zone in a Dual Microstructure Disk

    Science.gov (United States)

    Gabb, Timothy P.; Kantzos, Pete T.; Palsa, Bonnie; Telesman, Jack; Gayda, John; Sudbrack, Chantal K.

    2012-01-01

    Mechanical property requirements vary with location in nickel-based superalloy disks. In order to maximize the associated mechanical properties, heat treatment methods have been developed for producing tailored grain microstructures. In this study, fatigue failure modes of a grain size transition zone in a dual microstructure disk were evaluated. A specialized heat treatment method was applied to produce varying grain microstructure in the bore to rim portions of a powder metallurgy processed nickel-based superalloy disk. The transition in grain size was concentrated in a zone of the disk web, between the bore and rim. Specimens were extracted parallel and transversely across this transition zone, and multiple fatigue tests were performed at 427 C and 704 C. Grain size distributions were characterized in the specimens, and related to operative failure initiation modes. Mean fatigue life decreased with increasing maximum grain size, going out through the transition zone. The scatter in limited tests of replicates was comparable for failures of uniform gage specimens in all transition zone locations examined.

  8. The influence of grain size ratio upon the relative mobility in bimodal sediment mixtures

    Science.gov (United States)

    Dudill, Ashley; Frey, Philippe

    2014-05-01

    The behaviour of grain mixtures varies from that of uniform grain, which has implications for bedload sediment transport in gravel-bed rivers. In particular, sediment mixtures act to modify the level of mobility within the bed, leading to aggradation or degradation, which has significant implications for river stability. Previous work has reported upon this change in mobility within bimodal mixtures; however we do not know how far grain size ratio influences these results. We hypothesise that there is a link between the change in levels of mobility and the grain size ratio due to varying amounts of infiltration, which controls the hiding/exposure function. This poster will present experimental results from an investigation designed to isolate the influence of grain size ratio upon the change in levels of mobility in bimodal sediment mixtures. This experimental investigation was undertaken using various sizes of spherical particles in a relatively narrow flume. Using this arrangement, we are able to observe effects at the particle scale in order to understand the individual and bulk grain behaviour.

  9. Model for evolution of grain size in the rim region of high burnup UO2 fuel

    Science.gov (United States)

    Xiao, Hongxing; Long, Chongsheng; Chen, Hongsheng

    2016-04-01

    The restructuring process of the high burnup structure (HBS) formation in UO2 fuel results in sub-micron size grains that accelerate the fission gas swelling, which will raise some concern over the safety of extended the nuclear fuel operation life in the reactor. A mechanistic and engineering model for evolution of grain size in the rim region of high burnup UO2 fuel based on the experimental observations of the HBS in the literature is presented. The model takes into account dislocations evolution under irradiation and the grain subdivision occur successively at increasing local burnup. It is assumed that the original driving force for subdivision of grain in the HBS of UO2 fuel is the production and accumulation of dislocation loops during irradiation. The dislocation loops can also be annealed through thermal diffusion when the temperature is high enough. The capability of this model is validated by the comparison with the experimental data of temperature threshold of subdivision, dislocation density and sub-grain size as a function of local burnup. It is shown that the calculated results of the dislocation density and subdivided grain size as a function of local burnup are in good agreement with the experimental results.

  10. Film Grain-Size Related Long-Term Stability of Inverted Perovskite Solar Cells.

    Science.gov (United States)

    Chiang, Chien-Hung; Wu, Chun-Guey

    2016-09-22

    The power conversion efficiency (PCE) of the perovskite solar cell is high enough to be commercially viable. The next important issue is the stability of the device. This article discusses the effect of the perovskite grain-size on the long-term stability of inverted perovskite solar cells. Perovskite films composed of various sizes of grains were prepared by controlling the solvent annealing time. The grain-size related stability of the inverted cells was investigated both in ambient atmosphere at relative humidity of approximately 30-40 % and in a nitrogen filled glove box (H2 Osolar cell based on a perovskite film having the grain size larger than 1 μm (D-10) decreases less than 10 % with storage in a glove box and less than 15 % when it was stored under an ambient atmosphere for 30 days. However, the cell using the perovskite film composed of small (∼100 nm) perovskite grains (D-0) exhibits complete loss of PCE after storage under the ambient atmosphere for only 15 days and a PCE loss of up to 70 % with storage in the glove box for 30 days. These results suggest that, even under H2 O-free conditions, the chemical- and thermal-induced production of pin holes at the grain boundaries of the perovskite film could be the reason for long-term instability of inverted perovskite solar cells.

  11. Effect of time and temperature on grain size of V and V-Cr-Ti alloys

    Energy Technology Data Exchange (ETDEWEB)

    Natesan, K.; Rink, D.L. [Argonne National Lab., IL (United States)

    1996-10-01

    Grain growth studies were conducted to evaluate the effect of time and temperature on the grain size of pure V, V-4 wt.%Cr-4 wt.%Ti, and V-5 wt.%Cr-5 wt.%Ti alloys. The temperatures used in the study were 500, 650, 800, and 1000{degrees}C, and exposure times ranged between 100 and {approx}5000 h. All three materials exhibited negligible grain growth at 500, 650, and 800{degrees}C, even after {approx}5000 h. At 1000{degrees}C, pure V showed substantial grain growth after only 100 h, and V-4Cr-4Ti showed growth after 2000 h, while V-5Cr-5Ti showed no grain growth after exposure for up to 2000 h.

  12. Thermal Stability: The Next Frontier for Nanocrystalline Materials

    Energy Technology Data Exchange (ETDEWEB)

    Mathaudhu, Suveen; Boyce, Brad L.

    2015-11-06

    For the past quarter decade, the science and technology of nanocrystalline materials (materials with grain sizes less than 100 nm) has been an extremely rich and diverse field of study.1,2 Generally, it has been observed that tremendous improvements in physical and mechanical properties, including order-of-magnitude increases in yield strength, are possible.2 As predicted by the Hall– Petch equation,3,4 a reduction in grain size should be accompanied by an increase in strength. But, despite the promise of nanocrystalline materials for a host of structural and functional applications, their use has been severely limited by their lack of microstructural stability at elevated temperatures5 or under mechanical loads.6,7 In the case of pure metals, this coarsening often occurs even at ambient temperatures.5 Ironically, the same features that often result in the enhancement of properties in nanocrystalline materials, namely the high volume fraction of high-energy grain boundaries, are responsible for the observed grain growth or phase transformation.8

  13. Local electrical and dielectric properties of nanocrystalline solid oxide fuel cell electrolytes

    Science.gov (United States)

    Perry, Nicola Helen

    Reducing the operating temperature of solid oxide fuel cells (SOFCs), to improve durability and lower cost, requires an increase in the low temperature oxygen-ion conductivity of the electrolyte. This work investigates whether the electrolyte conductivity could be increased by decreasing the grain size into the nanoscale. Bulk electrolytes - cubic yttria-stabilized zirconia (YSZ, with 8mol% Y2O3), tetragonal zirconia polycrystal (TZP, with 3mol% Y2O3), and Sr- and Mg- co-doped LaGaO3 (LSGM) - were fabricated with grain sizes ranging from 10nm to 3mum, using commercial or sol-gel-derived nanopowders and various sintering techniques. Local grain boundary and grain core conductivities and dielectric constants were analyzed over a range of temperatures and atmospheres using AC-impedance spectroscopy and our novel nano-Grain Composite Model, and interpreted in terms of grain-size dependent defect chemistry (e.g. space charge models, local thermodynamics, and impurity/ acceptor segregation). All three oxides exhibited qualitatively similar electrical/ dielectric behavior. Their single crystal/ grain core dielectric constants exhibited an upturn with temperature, which was attributed to the onset of dipolar relaxation. Grain boundary dielectric constants were consistently higher than grain core dielectric constants at the nanoscale. n-GCM-derived electrical grain boundary half-widths agreed well with measured acceptor dopant segregation widths at grain boundaries. The local grain boundary conductivity was consistently increased in nanocrystalline vs. microcrystalline samples, although the mechanisms responsible for this behavior differed in each material. Grain core conductivity did not change with grain size in each case. Despite the increase in local grain boundary conductivity at the nanoscale, the total conductivity decreased monotonically with decreasing grain size in all three electrolytes; the grain boundaries remain barriers to transport (relative to grain cores

  14. Lost in Jupiter's Shadow: Can Resonant Charge Variations Explain Dust Grain Sizes in the Main Ring?

    Science.gov (United States)

    Jontof-Hutter, Daniel; Hamilton, D. P.

    2012-10-01

    Interplanetary impacts onto the tiny moons Metis and Adrastea replenish Jupiter's main ring with dusty ejecta of all sizes. The equilibrium size distribution present in the rings at a given time is a function of production and loss mechanisms, both of which may be vary with particle size. Loss mechanisms include collisions and dynamical processes. Here we explore some of the latter. Grains tend to pick up negative electric charges due to motion through Jupiter's plasma environment, and positive charges from the photoelectric effect of sunlight. The periodic interruption of sunlight in Jupiter's shadow causes the equilibrium electric charge, and hence the Lorentz force, to resonate with the Kepler orbital frequency. The eccentricity increases for grains moving radially inwards during the shadow transit, and decreases when grains move outward in the shadow, hence the azimuthal location of pericenter is important. For smaller grains, the eccentricity increases monotonically until they collide with Jupiter. For much larger grains, precession due to both the Lorentz force and planetary oblateness causes the eccentricity to oscillate periodically. We explore the shadow instability in the main ring for a variety of uniform plasma density models, comparing numerical data with a semi-analytic approximation. We find that the effect of the shadow dwindles in importance for plasma that is either too sparse or too dense. In sparse plasma, the charging timescale slows, limiting the change in electric potential from sunlight to shadow. In dense plasma, charging currents from the plasma overwhelm the photoelectric effect in sunlight, also resulting in a small change in electric potential. Between these two regimes, the shadow resonance efficiently removes grains up to a particular size threshold in the main ring. This size-dependent loss mechanism may contribute to the observed flattening in the size distribution index for smaller grains.

  15. Dependence of coercivity on phase distribution and grain size in nanocomposite Nd2Fe14B/α-Fe magnets

    Institute of Scientific and Technical Information of China (English)

    Feng Wei-Cun; Gao Ru-Wei; Li Wei; Han Guang-Bing; Sun Yan

    2005-01-01

    The dependence of coercivity on the grain size in nanocomposite Nd2Fe14B/α-Fe magnets with different distributions of magnetically soft and hard phases is investigated by means of statistical mean. The calculations show that when there exists no soft phase, the coercivity of magnets decreases monotonically with hard grain size reducing. For a given volume fraction of hard phase, the coercivity of nanocomposite Nd2Fe14B/α-Fe magnets with a random distribution of soft and hard grains shows a peak value as a function of hard grain size. When the hard grain size is larger than an optimum value of soft grain size (15nm), the nanocomposite Nd2Fe14B/α-Fe magnets with the multilayer structure of soft and hard grains can possess a higher coercivity than that with the random distribution of soft and hard grains.

  16. Grain size and texture changes of magnesium alloy AZ31 during multi-directional forging

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Grain size and texture changes of magnesium alloy AZ31 were studied in multidirectional forging(MDF) under decreasing temperature conditions. MDF was carried out up to large cumulative strains of 4.8 with changing the loading direction during decrease in temperature from pass to pass. MDF can accelerate the uniform development of fine-grained structures and increase the plastic workability at low temperatures. As a result, the MDFed alloy shows excellent higher strength as well as moderate ductility at room temperature even at the grain size below 1 μm. Superplastic flow takes place at 423 K and depends on the anisotropy of MDFed samples. The mechanisms of strain-induced free-grained structure development and of the plastic deformation were discussed in detail.

  17. Trend analysis of sediment grain size and sedimentary process in the central South Yellow Sea

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    With the method of trend analysis of sediment grain size, the sediment transport trend of the fine-grained sediments area in the central South Yellow Sea was studied. The results demonstrated that there is a sedimentation center around the point of 123.4°E, 35.1°N, and the sediments outside the center are transported to it. The patterns of sediment transportation and deposition in the Yellow Sea should be controlled by cyclonic circulation (including the Yellow Sea Cold Water Mass) and cold water gyre. The study also showed that the method of trend analysis of sediment grain size has prospective utilization in the fine-grained sediment deposited area on large-scale continental shelf.

  18. Analysis of EBSD Grain Size Measurements Using Microstructure Simulations and a Customizable Pattern Matching Library for Grain PerimeterEstimation (Postprint)

    Science.gov (United States)

    2017-03-08

    member of grain #1. The crystal misorientation between the seed point and its neighbors is checked, and it is assumed that the adjacent pixel is a member...than circles, and whether the performance is a function of grain size dispersion . The EBSD technique-specific ASTM standard, E2627,[17] generally builds...of realistic looking microstructures with varied grain size dispersions and the ability to apply different pixel sampling resolutions to instances of

  19. [The measurement and retrieval of the spectral reflectance of different snow grain size on Northern Xinjiang, China].

    Science.gov (United States)

    Hao, Xiao-Hua; Wang, Jie; Wang, Jian; Zhang, Pu; Huang, Chun-Lin

    2013-01-01

    The retrieval of snow grain size is one of the important research directions for cryosphere snow remote sensing. In the present study, we designed the measurement plan of different snow grain size by different snow layer. A SVC HR-1024 ground-based spectral radiometer was used for measuring the spectral property of different snow grain size in northern Xinjiang, China. At the same time, the snow grain size and shape were measured by a hand-loupe with scale. Then the DSPP method was used to calculate the equivalent snow grain size. Finally, the asymptotic radiative transfer (ART) theory was applied to retrieve the snow grain size from measured snow spectral reflectance of different snow layer by optimizing the inversion band and the snow grain size factor "b". The retrieved snow grain size was validated by the measured snow grain size from DSPP method. The results showed that the DSPP method is an effective means of measuring the equivalent snow grain size. However, there is a large deviation of the snow grain size sample in the same snow layer. It is necessary to improve the measurement method of the single snow grain size sample; The study showed that the near-infrared bands are the most effective selection for retrieval of snow grain size. The retrieval algorithm from ART is feasible. When the snow is dry, the authors optimize the inversion band and the snow grain size factor b in the Northern Xinjiang, China. The optimal band wavelength is 1.20 microm and b is 3.62.

  20. A variational multiscale constitutive model for nanocrystalline materials

    KAUST Repository

    Gurses, Ercan

    2011-03-01

    This paper presents a variational multi-scale constitutive model in the finite deformation regime capable of capturing the mechanical behavior of nanocrystalline (nc) fcc metals. The nc-material is modeled as a two-phase material consisting of a grain interior phase and a grain boundary effected zone (GBAZ). A rate-independent isotropic porous plasticity model is employed to describe the GBAZ, whereas a crystal-plasticity model which accounts for the transition from partial dislocation to full dislocation mediated plasticity is employed for the grain interior. The constitutive models of both phases are formulated in a small strain framework and extended to finite deformation by use of logarithmic and exponential mappings. Assuming the rule of mixtures, the overall behavior of a given grain is obtained via volume averaging. The scale transition from a single grain to a polycrystal is achieved by Taylor-type homogenization where a log-normal grain size distribution is assumed. It is shown that the proposed model is able to capture the inverse HallPetch effect, i.e., loss of strength with grain size refinement. Finally, the predictive capability of the model is validated against experimental results on nanocrystalline copper and nickel. © 2010 Elsevier Ltd. All rights reserved.

  1. Estimate the influence of snow grain size and black carbon on albedo

    Institute of Scientific and Technical Information of China (English)

    ZhongMing Guo; NingLian Wang; XiaoBo Wu; HongBo Wu; YuWei Wu

    2015-01-01

    Estimation of the influence of snow grain size and black carbon on albedo is essential in obtaining the accurate albedo. In this paper, field measurement data, including snow grain size, snow depth and density was obtained. Black carbon samples were collected from the snow surface. A simultaneous observation using Analytical Spectral Devices was employed in the Qiyi Glacier located in the Qilian Mountain. Analytical Spectral Devices spectrum data were used to analyze spectral re-flectance of snow for different grain size and black carbon content. The measurements were compared with the results obtained from the Snow, Ice, and Aerosol Radiation model, and the simulation was found to correlate well with the ob-served data. However, the simulated albedo was near to 0.98 times of the measured albedo, so the other factors were as-sumed to be constant using the corrected Snow, Ice, and Aerosol Radiation model to estimate the influence of measured snow grain size and black carbon on albedo. Field measurements were controlled to fit the relationship between the snow grain size and black carbon in order to estimate the influence of these factors on the snow albedo.

  2. Grain-size-independent plastic flow at ultrahigh pressures and strain rates.

    Science.gov (United States)

    Park, H-S; Rudd, R E; Cavallo, R M; Barton, N R; Arsenlis, A; Belof, J L; Blobaum, K J M; El-dasher, B S; Florando, J N; Huntington, C M; Maddox, B R; May, M J; Plechaty, C; Prisbrey, S T; Remington, B A; Wallace, R J; Wehrenberg, C E; Wilson, M J; Comley, A J; Giraldez, E; Nikroo, A; Farrell, M; Randall, G; Gray, G T

    2015-02-13

    A basic tenet of material science is that the flow stress of a metal increases as its grain size decreases, an effect described by the Hall-Petch relation. This relation is used extensively in material design to optimize the hardness, durability, survivability, and ductility of structural metals. This Letter reports experimental results in a new regime of high pressures and strain rates that challenge this basic tenet of mechanical metallurgy. We report measurements of the plastic flow of the model body-centered-cubic metal tantalum made under conditions of high pressure (>100  GPa) and strain rate (∼10(7)  s(-1)) achieved by using the Omega laser. Under these unique plastic deformation ("flow") conditions, the effect of grain size is found to be negligible for grain sizes >0.25  μm sizes. A multiscale model of the plastic flow suggests that pressure and strain rate hardening dominate over the grain-size effects. Theoretical estimates, based on grain compatibility and geometrically necessary dislocations, corroborate this conclusion.

  3. Grain-size distribution in suspension over a sand-gravel bed in open channel flow

    Institute of Scientific and Technical Information of China (English)

    Koeli GHOSHAL; Debasish PAL

    2014-01-01

    Grain-size distributions of suspended load over a sand-gravel bed at two different flow velocities were studied in a laboratory flume. The experiments had been performed to study the influence of flow velocity and suspension height on grain-size distribution in suspension over a sand-gravel bed. The experimental findings show that with an increase of flow velocity, the grain-size distribution of suspended load changed from a skewed form to a bimodal one at higher suspension heights. This study focuses on the determination of the parameter βn which is the ratio of the sediment diffusion coefficient to the momentum diffusion coefficient of n th grain-size. A new relationship has been proposed involvingβn , the normalizing settling velocity of sediment particles and suspension height, which is applicable for widest range of normalizing settling velocity available in literature so far. A similar parameter β for calculating total suspension concentration is also developed. The classical Rouse equation is modified with βn and β and used to compute grain-size distribution and total concentration in suspension, respectively. The computed values have shown good agreement with the measured values of experimental data.

  4. Variance in Dominant Grain Size Across the Mississippi River Delta

    Science.gov (United States)

    Miller, K. L.; Chamberlain, E. L.; Esposito, C. R.; Wagner, R. W.; Mohrig, D. C.

    2016-02-01

    Proposals to restore coastal Louisiana often center on Mississippi River diversion projects wherein water and sediment are routed into wetlands and shallow waters in an effort to build land. Successful design and implementation of diversions will include consideration of behavior and characteristics of sediment, both in the river and in the receiving basin. The Mississippi River sediment load is primarily mud (roughly 75%), with the remainder being very-fine to medium sand or organic detritus. The dominance of muds leads many to suggest that diversions should focus on capturing the mud fraction despite the smaller size and longer settling times required for these particles compared to sand; others believe that sand should be the focus. We present a systemic analysis of the texture of land-building sediment in the Mississippi Delta using borehole data from various depositional environments representing a range of spatial scales, system ages, and fluvial and basin characteristics. We include subdelta-scale data from the incipient Wax Lake Delta and from the distal plain of the abandoned Lafourche subdelta, as well as crevasse-scale data from modern Cubit's Gap and the Attakapas splay, an inland Lafourche crevasse. Comparison of these sites demonstrates a large variance in the volumetric mud to sand ratios across the system. We consider the differences to be emblematic of the various forcings on each lobe as it formed and suggest that the most efficient building block for a diversion is a function of the receiving basin and is not uniform across the entire delta.

  5. Healing mechanism of nanocrack in nanocrystalline metals during creep process

    Science.gov (United States)

    Meraj, Md.; Pal, Snehanshu

    2017-02-01

    Molecular dynamics (MD) simulation has been performed to demonstrate the fate of cracks present inside ultrafine-grained (grain size 7 nm) nanocrystalline Ni specimen during creep deformation process. It is observed that internal nanocracks are healed within a few pico-seconds of initial part of creep process even if the constant applied load on the specimen is tensile in nature and acting normal to crack surface in the outward direction. This kind of crack-healing phenomenon can be accounted by the facts such as stress-driven grain boundary migration, grain boundary diffusion and amorphization of specimen as per results obtained from this MD simulation. This MD study also reveals that the presence of nanocrack inside ultrafine-grained NC Ni in fact slightly improves creep properties and such enhancement of the creep properties is intensified as the size of internal crack increases.

  6. Scratching of nanocrystalline metals: A molecular dynamics study of Fe

    Science.gov (United States)

    Gao, Yu; Urbassek, Herbert M.

    2016-12-01

    Using molecular dynamics simulation we study the influence of grain boundaries on the indentation and scratching of Fe crystals by a hard repulsive tip. By comparing the results for nanocrystalline Fe with those for single crystals, the effect of grain boundaries on the normal and tangential forces, the hardness and the friction coefficient can be determined. We use nanocrystals of various grain sizes, and also vary the tip diameter. This allows us to determine the influence of these parameters on the scratching process. We find that with increasing size of the grains relative to the indenter the normal force needed for indentation or in scratch increases, and the friction coefficient is reduced. However, grain orientation has a dominant effect on the pile-up shape, and also influences the friction coefficient strongly.

  7. Effect of Grain Size Distribution on Processing Maps for Isothermal Compression of Inconel 718 Superalloy

    Science.gov (United States)

    Wang, Jianguo; Liu, Dong; Hu, Yang; Yang, Yanhui; Zhu, Xinglin

    2016-02-01

    Cylindrical specimens of Inconel 718 alloys with three types of grain size distribution were used in the compression tests and processing maps were developed in 940-1040 °C and 0.001-10 s-1. The equiaxed fine grain is more effective on the dynamic softening behavior. For partial recrystallized microstructure, the peak efficiency of power dissipation occurs at the strain rate of 0.001 s-1, and the temperature range of 1000-1020 °C. In order to obtain homogeneous microstructure with fine grains, the partial recrystallized microstructure should be deformed at the low temperature and slow strain rates. The area fraction of instability domains decreases with strain increasing. The peak efficiency of power dissipation increases with average grain size decreasing. The efficiency of power dissipation will be stimulated by the precipitation of δ phase at slow strain rate of 0.001-0.01 s-1, and the initial deformed substructure at the strain rate of 0.1-1 s-1. Equiaxed fine grain is the optimum state for forging process and dynamic recrystallization. The grain size distribution has slight influence on the microstructure evolution at high temperatures.

  8. Correlation vs. Causation: The Effects of Ultrasonic Melt Treatment on Cast Metal Grain Size

    Directory of Open Access Journals (Sweden)

    J. B. Ferguson

    2014-10-01

    Full Text Available Interest in ultrasonic treatment of liquid metal has waxed and waned for nearly 80 years. A review of several experiments representative of ultrasonic cavitation treatment of Al and Mg alloys shows that the theoretical mechanisms thought to be responsible for grain refinement are (1 cavitation-induced increase in melting temperature predicted by the Clausius-Clapeyron equation and (2 cavitation-induced wetting of otherwise unwetted insoluble particles. Neither of these theoretical mechanisms can be directly confirmed by experiment, and though they remain speculative, the available literature generally assumes that one or the other or both mechanisms are active. However, grain size is known to depend on temperature of the liquid, temperature of the mold, and cooling rate of the entire system. From the reviewed experiments, it is difficult to isolate temperature and cooling rate effects on grain size from the theoretical effects. Ultrasonic treatments of Al-A356 were carried out to isolate such effects, and though it was found that ultrasound produced significant grain refinement, the treatments also significantly chilled the liquid and thereby reduced the pouring temperature. The grain sizes attained closely correlated with pouring temperature suggesting that ultrasonic grain refinement is predominantly a result of heat removal by the horn and ultrasonic stirring.

  9. The Effect of Grain Size and Strain on the Tensile Flow Stress of Aluminium at Room Temperature

    DEFF Research Database (Denmark)

    Hansen, Niels

    1977-01-01

    Tensile-stress-strain data over a strain range from 0.2 to 30% were obtained at room temperature for 99.999 and 99.5% aluminium as a function of grain size. The yield stress-grain size relationship can be expressed by a Petch-Hall relation with approximately the same slope for the two materials. ...... stress-grain size relationship was analyzed in terms of matrix strengthening and grain boundary strengthening according to the dislocation concept of Ashby. At intermediate strains this approach gives a good description of the effect of strain, grain size and purity on the flow stress....

  10. The prediction of the evolution of grain size of land-gear forging during the die-forging process

    Directory of Open Access Journals (Sweden)

    Lin Gao

    2015-01-01

    Full Text Available The land-gear forgings are the most important structure parts, made of high strength steel 300M. Because of the bad service environment, the microstructure and performance of the part are very strict requirements. In this article the evolution of grain size during the die-forging process is predicted, the volume fraction of dynamic recrystallization, grain refinement and development of grain size in-homogeneity, and the affection of billet shape on the grain size distribution are analyzed. The simulated results show that the grain size differences on the different billet positions are very large at the deformation beginning. But in final forging stage, the difference of the average grain size is smaller. At some center zones of the part the maximum difference of grain size is bigger than 100 μm.

  11. A new database sub-system for grain-size analysis

    Science.gov (United States)

    Suckow, Axel

    2013-04-01

    Detailed grain-size analyses of large depth profiles for palaeoclimate studies create large amounts of data. For instance (Novothny et al., 2011) presented a depth profile of grain-size analyses with 2 cm resolution and a total depth of more than 15 m, where each sample was measured with 5 repetitions on a Beckman Coulter LS13320 with 116 channels. This adds up to a total of more than four million numbers. Such amounts of data are not easily post-processed by spreadsheets or standard software; also MS Access databases would face serious performance problems. The poster describes a database sub-system dedicated to grain-size analyses. It expands the LabData database and laboratory management system published by Suckow and Dumke (2001). This compatibility with a very flexible database system provides ease to import the grain-size data, as well as the overall infrastructure of also storing geographic context and the ability to organize content like comprising several samples into one set or project. It also allows easy export and direct plot generation of final data in MS Excel. The sub-system allows automated import of raw data from the Beckman Coulter LS13320 Laser Diffraction Particle Size Analyzer. During post processing MS Excel is used as a data display, but no number crunching is implemented in Excel. Raw grain size spectra can be exported and controlled as Number- Surface- and Volume-fractions, while single spectra can be locked for further post-processing. From the spectra the usual statistical values (i.e. mean, median) can be computed as well as fractions larger than a grain size, smaller than a grain size, fractions between any two grain sizes or any ratio of such values. These deduced values can be easily exported into Excel for one or more depth profiles. However, such a reprocessing for large amounts of data also allows new display possibilities: normally depth profiles of grain-size data are displayed only with summarized parameters like the clay

  12. Biomolecularly capped uniformly sized nanocrystalline materials: glutathione-capped ZnS nanocrystals

    Science.gov (United States)

    Torres-Martínez, Claudia L.; Nguyen, Liem; Kho, Richard; Bae, Weon; Bozhilov, Krassimir; Klimov, Victor; Mehra, Rajesh K.

    1999-09-01

    Micro-organisms such as bacteria and yeasts form CdS to detoxify toxic cadmium ions. Frequently, CdS particles formed in yeasts and bacteria were found to be associated with specific biomolecules. It was later determined that these biomolecules were present at the surface of CdS. This coating caused a restriction in the growth of CdS particles and resulted in the formation of nanometre-sized semiconductors (NCs) that exhibited typical quantum confinement properties. Glutathione and related phytochelatin peptides were shown to be the biomolecules that capped CdS nanocrystallites synthesized by yeasts Candida glabrata and Schizosaccharomyces pombe. Although early studies showed the existence of specific biochemical pathways for the synthesis of biomolecularly capped CdS NCs, these NCs could be formed in vitro under appropriate conditions. We have recently shown that cysteine and cysteine-containing peptides such as glutathione and phytochelatins can be used in vitro to dictate the formation of discrete sizes of CdS and ZnS nanocrystals. We have evolved protocols for the synthesis of ZnS or CdS nanocrystals within a narrow size distribution range. These procedures involve three steps: (1) formation of metallo-complexes of cysteine or cysteine-containing peptides, (2) introduction of stoichiometric amounts of inorganic sulfide into the metallo-complexes to initiate the formation of nanocrystallites and finally (3) size-selective precipitation of NCs with ethanol in the presence of Na+. The resulting NCs were characterized by optical spectroscopy, high-resolution transmission electron microscopy (HRTEM), x-ray diffraction and electron diffraction. HRTEM showed that the diameter of the ZnS-glutathione nanocrystals was 3.45+/-0.5 nm. X-ray diffraction and electron diffraction analyses indicated ZnS-glutathione to be hexagonal. Photocatalytic studies suggest that glutathione-capped ZnS nanocrystals prepared by our procedure are highly efficient in degrading a test model

  13. Effects of grain size on high temperature creep of fine grained, solution and dispersion hardened V-1.6Y-8W-0.8TiC

    Energy Technology Data Exchange (ETDEWEB)

    Furuno, T. [Ehime Univerisity, 3 Bunkyo-cho, Matsuyama 790-8577 (Japan); Kurishita, H., E-mail: kurishi@imr.tohoku.ac.jp [International Research Center for Nuclear Materials Science, Institute for Materials Research (IMR), Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Nagasaka, T.; Nishimura, A.; Muroga, T. [Fusion Engineering Research Center, National Institute for Fusion Science (NIFS), Oroshi-cho 322-6, Tok, Gifu 292 (Japan); Sakamoto, T.; Kobayashi, S.; Nakai, K. [Department of Materials Science and Biotechnology, Ehime Univerisity, 3 Bunkyo-cho, Matsuyama 790-8577 (Japan); Matsuo, S.; Arakawa, H. [International Research Center for Nuclear Materials Science, Institute for Materials Research (IMR), Tohoku University, Oarai, Ibaraki 311-1313 (Japan)

    2011-10-01

    Creep resistance is the major concern of vanadium and its alloys for fusion reactor structural applications. In order to elucidate the effects of grain size on the creep behavior of solution and dispersion strengthened vanadium alloys, V-1.6Y-8W-0.8TiC specimens with fine grain sizes from 0.58 to 1.45 {mu}m were prepared by mechanical alloying and HIP without any plastic working and tested at 1073 K and 250 MPa in vacuum. It is shown that the creep resistance of V-1.6Y-8W-0.8TiC depends strongly on grain size and increases with increasing grain size: The creep life for the grain size of 1.45 {mu}m is almost one order longer than that of 0.58 {mu}m, and about two orders longer than that of V-4Cr-4Ti (NIFS-Heat 2) although the grain size of V-4Cr-4Ti is as large as 17.8 {mu}m. The observed creep behavior is discussed in terms of grain size effects on dislocation glide and grain boundary sliding.

  14. Scattering and Absorption Properties of Polydisperse Wavelength-sized Particles Covered with Much Smaller Grains

    Science.gov (United States)

    Dlugach, Jana M.; Mishchenko, Michael I.; Mackowski, Daniel W.

    2012-01-01

    Using the results of direct, numerically exact computer solutions of the Maxwell equations, we analyze scattering and absorption characteristics of polydisperse compound particles in the form of wavelength-sized spheres covered with a large number of much smaller spherical grains.The results pertain to the complex refractive indices1.55 + i0.0003,1.55 + i0.3, and 3 + i0.1. We show that the optical effects of dusting wavelength-sized hosts by microscopic grains can vary depending on the number and size of the grains as well as on the complex refractive index. Our computations also demonstrate the high efficiency of the new superposition T-matrix code developed for use on distributed memory computer clusters.

  15. Grain-size related nitrogen distribution in southern Yellow Sea surface sediments

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    Forty-eight surface sediments of the southern Yellow Sea are separated into three grain-size fractions. Four forms of extractable nitrogen (nitrogen in ion-exchangeable form (Nie), nitrogen in weak-acid extractable form (Nwa), nitrogen in strong-alkali extractable form (Nsa) and nitrogen in strong-oxidant form (Nso)) are obtained by the sequential extraction. The results show that the contents and the distributions of the extractable nitrogen in the southern Yellow Sea surface sediments are closely related to sediment grain size. The distributions of Nie, Nso and total nitrogen (TN) present positive correlations with fine particles content, while Nwa and Nsa does not have such correlation. The net contents of all the forms of nitrogen increase with sediment grain size finer.

  16. Effects of grain size and porosity on strength of Li2TiO3 tritium breeding pebbles and its grain growth behavior

    Science.gov (United States)

    Xiang, Maoqiao; Zhang, Yingchun; Zhang, Yun; Wang, Chaofu; Liu, Wei; Yu, Yonghong

    2016-12-01

    Tons of Li2TiO3 tritium breeding pebbles will be filled in the blanket for obtaining tritium fuel. In this work, isothermal sintering was carried out to study the grain growth behavior of the Li2TiO3 pebbles fabricated by agarose method. The grain growth exponent (n) and the activation energy (Q) calculated by the phenomenological kinetic equation were 2 and 435.65 kJ/mol, respectively. The grain growth was controlled by vapor transport (p = 2S/r). In addition, effects of porosity and grain-size on the strength of Li2TiO3 pebbles were investigated. The strength was affected by the grain size and the porosity of Li2TiO3 pebbles, and high strength (about 72 MPa) depended partly on achieving the optimum balance between the porosity (about 10%) and grain size (about 2 μm).

  17. Tailoring the thermal and electrical transport properties of graphene films by grain size engineering

    Science.gov (United States)

    Ma, Teng; Liu, Zhibo; Wen, Jinxiu; Gao, Yang; Ren, Xibiao; Chen, Huanjun; Jin, Chuanhong; Ma, Xiu-Liang; Xu, Ningsheng; Cheng, Hui-Ming; Ren, Wencai

    2017-02-01

    Understanding the influence of grain boundaries (GBs) on the electrical and thermal transport properties of graphene films is essentially important for electronic, optoelectronic and thermoelectric applications. Here we report a segregation-adsorption chemical vapour deposition method to grow well-stitched high-quality monolayer graphene films with a tunable uniform grain size from ~200 nm to ~1 μm, by using a Pt substrate with medium carbon solubility, which enables the determination of the scaling laws of thermal and electrical conductivities as a function of grain size. We found that the thermal conductivity of graphene films dramatically decreases with decreasing grain size by a small thermal boundary conductance of ~3.8 × 109 W m-2 K-1, while the electrical conductivity slowly decreases with an extraordinarily small GB transport gap of ~0.01 eV and resistivity of ~0.3 kΩ μm. Moreover, the changes in both the thermal and electrical conductivities with grain size change are greater than those of typical semiconducting thermoelectric materials.

  18. Inhomogeneity of the grain size of aircraft engine turbine polycrystalline blades

    Directory of Open Access Journals (Sweden)

    J. Chmiela

    2011-10-01

    Full Text Available The determination of the behaviour of inhomogeneous materials with a complex microstructure requires taking into account the inhomogeneity of the grain size, as it is the basis for the process of designing and modelling effective behaviours. Therefore, the functional description of the inhomogeneity is becoming an important issue. The paper presents an analytical approach to the grain size inhomogeneity, based on the derivative of a logarithmic-logistic function. The solution applied enabled an effective evaluation of the inhomogeneity of two macrostructures of aircraft engine turbine blades, characterized by a high degree of diversity in the grain size. For the investigated single-modal and bimodal grain size distributions on a perpendicular projection and for grains with a non-planar surface, we identified the parameters that describe the degree of inhomogeneity of the constituents of weight distributions and we also derived a formula describing the overall degree of inhomogeneity of bimodal distributions. The solution presented in the paper is of a general nature and it can be used to describe the degree of inhomogeneity of multi-modal distributions. All the calculations were performed using the Mathematica® package.

  19. Grain size evaluation of structural materials in nuclear power plant using a thickness independent ultrasonic method

    Energy Technology Data Exchange (ETDEWEB)

    Li, Xiongbing, E-mail: lixb_ex@163.com [CAD/CAM Institute, Central South University, Changsha 410075 (China); State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083 (China); Song, Yongfeng [CAD/CAM Institute, Central South University, Changsha 410075 (China); Ni, Peijun [The Ningbo Branch of Ordnance Science Institute of China, Ningbo 315103 (China); Wang, Zi; Liu, Feng [State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083 (China); Du, Hualong [Mechanical and Aerospace Engineering Department, North Carolina State University, Raleigh, NC 27606 (United States)

    2015-05-15

    Highlights: •We derive a coefficient of ultrasonic attenuation rate related to the grain size. •The mean grain size of the pipe can be evaluated without measuring its thickness. •Experiments show this method is better suited to square pipe than other methods. -- Abstract: It is important to accurately and nondestructively evaluate the grain size of structural materials used in nuclear power plants. The current ultrasonic non-destructive methods are so dependent on the thickness measurement of a square pipe that it reduces their practicality and reliability. In this paper, a novel method using the coefficient of ultrasonic attenuation rate is developed by using the transmission and reflection coefficients. As a result, the mean grain size of the pipe can be nondestructively evaluated without measuring its thickness. Moreover, the signal preprocessing is studied to improve the stability and accuracy of evaluation results. The experimental results show that the dependence of the attenuation rate on grain sizes is much higher than that of the ultrasonic velocity. The relative error of the attenuation rate method is lower than that of the backscatter method if the thickness of the sample is less than 5 mm. When evaluating a TP304 stainless steel square pipe whose thickness is not convenient to measure, the mean grain sizes are measured 103.5 ± 2.6 μm, 96.9 ± 3.5 μm and 94.0 ± 1.7 μm by the attenuation method, the attenuation rate method and the electron backscattering diffraction method, respectively. The result verifies that the presented method works better than the attenuation method due to the fact that the error of the thickness measurement has no effect on the ultrasonic attenuation rate.

  20. A universal approximation to grain size from images of non-cohesive sediment

    Science.gov (United States)

    Buscombe, D.; Rubin, D.M.; Warrick, J.A.

    2010-01-01

    The two-dimensional spectral decomposition of an image of sediment provides a direct statistical estimate, grid-by-number style, of the mean of all intermediate axes of all single particles within the image. We develop and test this new method which, unlike existing techniques, requires neither image processing algorithms for detection and measurement of individual grains, nor calibration. The only information required of the operator is the spatial resolution of the image. The method is tested with images of bed sediment from nine different sedimentary environments (five beaches, three rivers, and one continental shelf), across the range 0.1 mm to 150 mm, taken in air and underwater. Each population was photographed using a different camera and lighting conditions. We term it a “universal approximation” because it has produced accurate estimates for all populations we have tested it with, without calibration. We use three approaches (theory, computational experiments, and physical experiments) to both understand and explore the sensitivities and limits of this new method. Based on 443 samples, the root-mean-squared (RMS) error between size estimates from the new method and known mean grain size (obtained from point counts on the image) was found to be ±≈16%, with a 95% probability of estimates within ±31% of the true mean grain size (measured in a linear scale). The RMS error reduces to ≈11%, with a 95% probability of estimates within ±20% of the true mean grain size if point counts from a few images are used to correct bias for a specific population of sediment images. It thus appears it is transferable between sedimentary populations with different grain size, but factors such as particle shape and packing may introduce bias which may need to be calibrated for. For the first time, an attempt has been made to mathematically relate the spatial distribution of pixel intensity within the image of sediment to the grain size.

  1. Electrical characterization of nanocrystalline zinc selenide thin films

    Science.gov (United States)

    Sharma, Jeewan; Shikha, Deep; Tripathi, Surya Kant

    2012-08-01

    In the present paper, we have studied the effect of photo-illumination on electrical properties of nanocrystalline ZnSe thin films. The ZnSe thin films with different grain sizes (coherently diffracting domains) have been prepared. The semiconducting material with the composition Zn25Se75 has been prepared using melt-quenching technique. Thermal evaporation technique has been used to prepare nanocrystalline ZnSe thin films on highly cleaned glass substrates at different partial pressures of Ar gas. The grain size has been controlled by the partial pressure of inert gas. The grain size has been calculated using X-ray diffraction plots. Mobility activation has been studied from the photocurrent decay curves. The effective density of states ( N eff), frequency factor ( S), and trap depth ( E) have been calculated for all the films having different grain sizes. Three different types of trap levels have been found in these films. There is a linear distribution of traps having different energies below the conduction band. The increase in photoconductivity is explained in terms of built in potential barriers ( ϕ b) at the grain boundaries.

  2. The effect of grain size on the mechanical response of a metastable austenitic stainless steel

    Directory of Open Access Journals (Sweden)

    Sinclair C.W.

    2013-11-01

    Full Text Available The combination of high environmental resistance and excellent strength, elongation and energy absorption make austenitic stainless steels potentially attractive for transportation applications. In the case of metastable grades that undergo a strain induced martensitic transformation it is possible to significantly change the mechanical properties simply by changing the austenite grain size. Predicting such behaviour using physically based models is, however, extremely challenging. Here, some recent work on the coupling between grain size and mechanical response will be presented for a metastable AISI 301 LN stainless steel. Successes and continuing challenges will be highlighted.

  3. Effect of grain size of polycrystalline diamond on its heat spreading properties

    Science.gov (United States)

    Simon, Roland B.; Anaya, Julian; Faili, Firooz; Balmer, Richard; Williams, Gruffudd T.; Twitchen, Daniel J.; Kuball, Martin

    2016-06-01

    The exceptionally high thermal conductivity of polycrystalline diamond (>2000 W m-1 K-1) makes it a very attractive material for optimizing the thermal management of high-power devices. In this paper, the thermal conductivity of a diamond sample capturing grain size evolution from nucleation towards the growth surface is studied using an optimized 3ω technique. The thermal conductivity is found to decrease with decreasing grain size, which is in good agreement with theory. These results clearly reveal the minimum film thickness and polishing thickness from nucleation needed to achieve single-crystal diamond performance, and thus enable production of an optimal polycrystalline diamond for heat-spreading applications.

  4. Grain size and film thickness effect on the thermal expansion coefficient of FCC metallic thin films.

    Science.gov (United States)

    Hwang, Seulgi; Kim, Youngman

    2011-08-01

    Thin films are used in wide range of applications in industry, such as solar cells and LEDs. When thin films are deposited on substrates, various stresses are generated due to the mechanical difference between the film and substrate. These stresses can cause defects, such as cracking and buckling. Therefore, knowledge of the mechanical properties is important for improving their reliability and stability. In this study, the thermal expansion coefficient of FCC metallic thin films, such as Ag and Cu, which have different grain sizes and thicknesses, were calculated using the thermal cycling method. As a result, thermal expansion coefficient increased with increasing grain size. However, the film thickness had no remarkable effect.

  5. Effect the Grain Size on the Polymer Matrix Composites Reinforced by Reenia Particles

    Directory of Open Access Journals (Sweden)

    Kdhim khaion kahlol

    2013-01-01

    Full Text Available Synthetic polymers such as polyurethane are used widely in the field of biomedical applications such as implants or part of implant systems.This paper focuses on the preparation of base polymer matrix composite materials by (Hand Lay-Up method, and studying the effect of selected grain size (32, 53, 63, 75, and 90 µm of (Reenia particles on some properties of the prepared composite.Mechanical tests were used to evaluate the prepared system (Tensile, Compression, Impact, and Hardness tests, and a physical test of (Water absorption %, and all tests were accomplished at room temperature.Where results showed tensile test (maximum tensile strength and modulus of elasticity high at small grain size while the percentage of elongation decreased with increasing size. As the compressive strength increased with small grain size. And also the values of hardness and fracture energy affected by particle size where the hardness and fracture energy increased at small particles size of compared to larger particles size. While the percentage of water absorption increased at large particle size.In general the results showed clear improvement in properties and maximum values which get it of tensile strength, Modulus of elasticity, elongation percentage, compression strength, fracture energy, hardness and water absorption were as follows ((34.8 MPa, (10%, (268 N/mm2, ( 54.2 MPa,( o.408 J, (78.9 Shor (D, (0.2668 % at using (32µm except water absorption was at (90µm .

  6. Linking differential domain functions of the GS3 protein to natural variation of grain size in rice

    OpenAIRE

    Mao, Hailiang; Sun, Shengyuan; Yao, Jialing; Wang, Chongrong; Yu, Sibin; Xu, Caiguo; Li, Xianghua; Zhang, Qifa

    2010-01-01

    Grain yield in many cereal crops is largely determined by grain size. Here we report the genetic and molecular characterization of GS3, a major quantitative trait locus for grain size. It functions as a negative regulator of grain size and organ size. The wild-type isoform is composed of four putative domains: a plant-specific organ size regulation (OSR) domain in the N terminus, a transmembrane domain, a tumor necrosis factor receptor/nerve growth factor receptor (TNFR/NGFR) family cysteine-...

  7. Synthesis and Characterizations of Nanocrystalline WC-Co Composite Powders by a Unique Ball Milling Process

    Institute of Scientific and Technical Information of China (English)

    Jun SHEN; Jianfei SUN; Faming ZHANG

    2004-01-01

    In order to explore the high efficiency of fabricating nanocrystalline WC-Co composite powders, this paper presented a unique high energy ball milling process with variable rotation rate and repeatious circulation, by which nanocrystalline WC-10Co0.8VC-0.2Cr3C2 (wt pct) composite powders with mean grain size of 25 nm were prepared in 32 min, and the quantity of the powders for a batch was as much as 800 grams. The as-prepared powders were analyzed and characterized by chemical analysis,X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential thermal analysis (DTA). The results show that high energy ball milling with variable rotation rates and repeatious circulation could be used to produce nanocrystalline WC-Co powder composites with high efficiency. The compositions of the powders meet its specifications with low impurity content. The mean grain size decreases, lattice distortion and system energy increase with increasing the milling time. The morphology of nanocrystalline WC-Co particles displays dominantly sphere shape and their particle sizes are all lower than 80nm. The eutectic temperature of the nanocrystalline WC-10Co-0.8VC-0.2Cr3C2 composites is about 1280℃.

  8. Plasticity of nanocrystalline alloys with chemical order: on the strength and ductility of nanocrystalline Ni-Fe.

    Science.gov (United States)

    Schäfer, Jonathan; Albe, Karsten

    2013-01-01

    Plastic deformation and alloying of nanocrystalline Ni-Fe is studied by means of atomic scale computer simulations. By using a combination of Monte-Carlo and molecular dynamics methods we find that solutes have an ordering tendency even if grain sizes are in the nanometer regime, where the phase field of the ordered state is widened as compared to larger grain sizes. Tensile testing of disordered structures with various elemental distributions and the simultaneous analysis of intragranular defects reveal that solid solution strengthening is absent for the studied grain sizes. The composition and relaxation state of the grain boundary control the strength of the material, which is also found for ordered structures (L12), where dislocation activity is suppressed.

  9. Plasticity of nanocrystalline alloys with chemical order: on the strength and ductility of nanocrystalline Ni–Fe

    Science.gov (United States)

    Albe, Karsten

    2013-01-01

    Summary Plastic deformation and alloying of nanocrystalline Ni–Fe is studied by means of atomic scale computer simulations. By using a combination of Monte-Carlo and molecular dynamics methods we find that solutes have an ordering tendency even if grain sizes are in the nanometer regime, where the phase field of the ordered state is widened as compared to larger grain sizes. Tensile testing of disordered structures with various elemental distributions and the simultaneous analysis of intragranular defects reveal that solid solution strengthening is absent for the studied grain sizes. The composition and relaxation state of the grain boundary control the strength of the material, which is also found for ordered structures (L12), where dislocation activity is suppressed. PMID:24205450

  10. The grain-size distribution of pyroclasts: Primary fragmentation, conduit sorting or abrasion?

    Science.gov (United States)

    Kueppers, U.; Schauroth, J.; Taddeucci, J.

    2013-12-01

    Explosive volcanic eruptions expel a mixture of pyroclasts and lithics. Pyroclasts, fragments of the juvenile magma, record the state of the magma at fragmentation in terms of porosity and crystallinity. The grain size distribution of pyroclasts is generally considered to be a direct consequence of the conditions at magma fragmentation that is mainly driven by gas overpressure in bubbles, high shear rates, contact with external water or a combination of these factors. Stress exerted by any of these processes will lead to brittle fragmentation by overcoming the magma's relaxation timescale. As a consequence, most pyroclasts exhibit angular shapes. Upon magma fragmentation, the gas pyroclast mixture is accelerated upwards and eventually ejected from the vent. The total grain size distribution deposited is a function of fragmentation conditions and transport related sorting. Porous pyroclasts are very susceptible to abrasion by particle-particle or particle-conduit wall interaction. Accordingly, pyroclastic fall deposits with angular clasts should proof a low particle abrasion upon contact to other surfaces. In an attempt to constrain the degree of particle interaction during conduit flow, monomodal batches of washed pyroclasts have been accelerated upwards by rapid decompression and subsequently investigated for their grain size distribution. In our set-up, we used a vertical cylindrical tube without surface roughness as conduit. We varied grain size (0.125-0.25; 0.5-1; 1-2 mm), porosity (0; 10; 30 %), gas-particle ratio (10 and 40%), conduit length (10 and 28 cm) and conduit diameter (2.5 and 6 cm). All ejected particles were collected after settling at the base of a 3.3 m high tank and sieved at one sieve size below starting size (half-Φ). Grain size reduction showed a positive correlation with starting grain size, porosity and overpressure at the vent. Although milling in a volcanic conduit may take place, porous pyroclasts are very likely to be a primary product

  11. Regolith grain sizes of Saturn's rings inferred from Cassini-CIRS far-infrared spectra

    CERN Document Server

    Morishima, Ryuji; Spilker, Linda

    2012-01-01

    We analyze far-infrared (10-650 cm$^{-1}$) emissivity spectra of Saturn's main rings obtained by the Cassini Composite Infrared Spectrometer (CIRS). In modeling of the spectra, the single scattering albedos of regolith grains are calculated using the Mie theory, diffraction is removed with the delta-Eddington approximation, and the hemispherical emissivities of macroscopic free-floating ring particles are calculated using the Hapke's isotropic scattering model. Only pure crystalline water ice is considered and the size distribution of regolith grains is estimated. We find that good fits are obtained if the size distribution is broad ranging from 1 $\\mu$m to 1-10 cm with a power law index of $ \\sim 3$. This means that the largest regolith grains are comparable to the smallest free-floating particles in size and that the power law indices for both free-floating particles and regolith grains are similar to each other. The apparent relative abundance of small grains increases with decreasing solar phase angle (or...

  12. Numerical modelling of intergranular fracture in polycrystalline materials and grain size effects

    Directory of Open Access Journals (Sweden)

    P. Wriggers

    2011-07-01

    Full Text Available In this paper, the phenomenon of intergranular fracture in polycrystalline materials is investigated using a nonlinear fracture mechanics approach. The nonlocal cohesive zone model (CZM for finite thickness interfaces recently proposed by the present authors is used to describe the phenomenon of grain boundary separation. From the modelling point of view, considering the dependency of the grain boundary thickness on the grain size observed in polycrystals, a distribution of interface thicknesses is obtained. Since the shape and the parameters of the nonlocal CZM depend on the interface thickness, a distribution of interface fracture energies is obtained as a consequence of the randomness of the material microstructure. Using these data, fracture mechanics simulations are performed and the homogenized stress-strain curves of 2D representative volume elements (RVEs are computed. Failure is the result of a diffuse microcrack pattern leading to a main macroscopic crack after coalescence, in good agreement with the experimental observation. Finally, testing microstructures characterized by different average grain sizes, the computed peak stresses are found to be dependent on the grain size, in agreement with the trend expected according to the Hall-Petch law.

  13. Role of grain size on the magnetic properties of La{sub 0.7}Sr{sub 0.3}MnO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Yadav, P.A. [Center for Advanced Studies in Materials Science and Condensed Matter Physics, Department of Physics, University of Pune, Pune 411007 (India); Deshmukh, A.V. [Department of Physics, Fergusson College, Pune 411004 (India); Adhi, K.P. [Center for Advanced Studies in Materials Science and Condensed Matter Physics, Department of Physics, University of Pune, Pune 411007 (India); Kale, B.B. [Centre for Materials for Electronics Technology, Pune 411008 (India); Basavaih, N. [Indian Institute of Geomagnetism, New Mumbai 410218 (India); Patil, S.I., E-mail: patil@physics.unipune.ac.in [Center for Advanced Studies in Materials Science and Condensed Matter Physics, Department of Physics, University of Pune, Pune 411007 (India)

    2013-02-15

    Nanophasic La{sub 0.7}Sr{sub 0.3}MnO{sub 3} samples were synthesized using the citrate-gel method. The samples were annealed at different temperatures ranging from 600 to 1200 Degree-Sign C. Grain size was observed to increase with the increase in annealing temperature. Furthermore, the magnetization data of these samples show well defined hysteresis. Saturation magnetization was observed to increase with increase in particle size. This gives evidence of formation of a magnetically dead layer at the surface. The thickness of the dead layer has also been calculated. The coercivity of nanoparticles follows the same trend as predicted theoretically and particles below 22 nm are found to be single domain. The ferromagnetic to paramagnetic transition temperature also increases with increase in particle size. - Highlights: Black-Right-Pointing-Pointer Synthesis of nanocrystalline La{sub 0.7}Sr{sub 0.3}MnO{sub 3} by the citrate-gel method. Black-Right-Pointing-Pointer Saturation magnetization increases with increase in particle size. Black-Right-Pointing-Pointer Formation of dead magnetic layer.

  14. Investigation on grain size effect in high strain rate ductility of 1100 pure aluminum

    Science.gov (United States)

    Bonora, N.; Bourne, N.; Ruggiero, A.; Iannitti, G.; Testa, G.

    2017-01-01

    The effect of the initial grain size on the material ductility at high strain rates in 1100 pure aluminum was investigated. Dynamic tensile extrusion (DTE) tests, at different impact velocities, were performed. Samples have been annealed at 350°C for different exposure times to induce grain growth. Extruded fragments were soft-recovered and the overall length of the extruded jets was used as a measure of material ductility at high strain rates. Numerical simulation of DTE test at different velocity was performed using the modified Rusinek-Klepaczko constitutive model. Results indicates that, as reported for pure copper, the overall ductility of the aluminum increases when grain size decreases. Numerical simulation results were in quite good agreement with experimental data.

  15. Influence of Processing Parameters on Grain Size Evolution of a Forged Superalloy

    Science.gov (United States)

    Reyes, L. A.; Páramo, P.; Salas Zamarripa, A.; de la Garza, M.; Guerrero-Mata, M. P.

    2016-01-01

    The microstructure evolution of nickel-based superalloys has a great influence on the mechanical behavior during service conditions. Microstructure modification and the effect of process variables such as forging temperature, die-speed, and tool heating were evaluated after hot die forging of a heat-resistant nickel-based alloy. Forging sequences in a temperature range from 1253 to 1323 K were considered through experimental trials. An Avrami model was applied using finite element data to evaluate the average grain size and recrystallization at different evolution zones. It was observed that sequential forging at final temperatures below 1273 K provided greater grain refinement through time-dependent recrystallization phenomena. This investigation was aim to explore the influence of forging parameters on grain size evolution in order to design a fully homogenous and refined microstructure after hot die forging.

  16. Response of grain size of Quaternary gravels to climate and tectonics in the northern Tibetan Plateau

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The widely distributed thick gravel deposits along the rim of the Tibetan Plateau have been long thought to be the product of rapid tectonic uplift of the plateau. However, this has been challenged by recent works that suggest these thick gravels may be the result of climate change. In this paper we carried out a detailed field measurement of gravel grain sizes from the Jiuquan and Gobi Gravel Beds in the top of the Laojunmiao section in the Jiuxi Basin in the northern margin of Qilian Mts. (northern Tibetan Plateau). The results suggest that the grain sizes of the Jiuquan and Gobi Gravel Beds over the last 0.8 Ma are characterized by nine coarse-fine cycles having strong 100-ka and 41-ka periodicities that correlate well with the loess-paleosol monsoon record and isotopic global climatic record from deep sea sediments as well as by a long trend of coarsening in gravel grain size. The coarse gravel layers were formed during the warm-humid interglaciations while the fine layers correspond to the cold-dry glaciations. Because the paleoclimate in NW China began to get dramatically drier after the mid-Pleistocene, we think the persistent coarsening of gravel grain size was most probably caused by the rapid uplift of the northern Tibetan Plateau, and that the orbital scale cyclic variations in gravel grain size were driven by orbital forcing factors that were superimposed on the tectonically-forced long-term coarsening trend in gravel size. These findings also shed new light on the interaction results of climate and tectonics in relation to the uplift of the Tibetan Plateau.

  17. The grain-size characteristics of Quaternary deposits at Xingshan near Siping in Jilin province, China

    Institute of Scientific and Technical Information of China (English)

    Maxwell A Boateng; Xikui Wang

    2006-01-01

    This research paper analyses the grain-size characteristics of the Quaternary deposits at Xingshan near Siping, Jilin province in China by employing graphic measures to study the grain size distribution and its mode of transport and deposition. The Quaternary deposits at Xingshan lie unconformable on Cretaceous rocks made of siltstone, mudstone and sandstone. The average grain size is between 8.06 to 8.55Φ (0.002 6 ~0.003 7 mm). The Quaternary deposits at Xingshan mainly compose of very fine silt to clay. The compositions of the grade are clay 63% and silt 37%. The clay size components are weathered debris transported and deposited by flowing water from the SE highlands or hills to the low lying NW Xingshan plains whereas the silty components accumulated by aoelian process. The Quaternary deposits at Xingshan accumulated in the middle and late Pleistocene interglacial periods from (459.12~39.03) ka to (88.92~7.56) ka. The standard deviation ranged from 0.96 to 1.36Φ, indicating that the sediments are moderately to poorly sorted, Coefficient of skewness ranged from 0.16~0.31 with an average skewness of 0.218, (Positively skewed towards fine). Kurtosis values (0.84~1.05) from the grain size distribution and visual inspection of the frequency curves indicate platykurtic to mesokurtic curves and unimodal to bimodal grain-size distribution. The type of deposit formation is sand dune and the source is at a distal from its provenance.

  18. THE RATE-INDEPENDENT CONSTITUTIVE MODELING FOR POROUS AND MULTI-PHASE NANOCRYSTALLINE MATERIAL

    Institute of Scientific and Technical Information of China (English)

    Zhou Jianqiu; Li Yuanling; Zhang Zhenzhong

    2007-01-01

    To determine the time-independent constitutive modeling for porous and multiphase nanocrystalline materials and understand the effects of grain size and porosity on their mechanical behavior, each phase was treated as a mixture of grain interior and grain boundary, and pores were taken as a single phase, then Budiansky's self-consistent method was used to calculate the Young's modulus of porous, possible multi-phase, nanocrystalline materials, the prediction being in good agreement with the results in the literature. Further, the established method is extended tosimulate the constitutive relations of porous and possible multi-phase nanocrystalline materials with small plastic deformation in conjunction with the secant-moduli approach and iso-strain assumption. Comparisons between the experimental grain size and porosity dependent mechanical data and the corresponding predictions using the established model show that it appears to be capable of describing the time-independent mechanical behaviors for porous and multi-phase nanocrystalline materials in a small plastic strain range. Further discussion on the modification factor, the advantages and limitations of the model developed were present.

  19. Microstructure and mechanical strength of near- and sub-micrometre grain size copper prepared by spark plasma sintering

    DEFF Research Database (Denmark)

    Zhu, K. N.; Godfrey, A.; Hansen, Niels

    2017-01-01

    Spark plasma sintering (SPS) has been used to prepare fully dense samples of copper in a fully recrystallized condition with grain sizes in the near- and sub-micrometre regime. Two synthesis routes have been investigated to achieve grain size control: (i) SPS at different temperatures from 800 to...... been probed using hardness measurements and tensile testing, revealing an enhanced strength for samples with grain sizes less than ≈ 1 μm....

  20. Influence of temperature, grain size and cobalt content on the hardness of WC-Co alloys

    CSIR Research Space (South Africa)

    Milman, YV

    1999-01-01

    Full Text Available The Vickers hardness of WC-Co alloys has been measured at temperatures ranging from -196 to 900 degrees C. The cobalt content of the alloys ranged from 10 to 24 vol% and the grain size from 0.5 to 2.3 um. It was found that, at all cobalt contents...

  1. Discrimination of sediment provenance in the Yellow Sea: Secondary grain-size effect and REE proxy

    Science.gov (United States)

    Jung, Hoi-Soo; Lim, Dhongil; Jeong, Do-Hyun; Xu, Zhaokai; Li, Tiegang

    2016-06-01

    This study analyzed grain size and elemental concentrations (Al, Mg, Fe, and rare earth elements (REEs)) in 91 surface sediments to elucidate sediment provenance in the Yellow Sea. Elemental concentrations were normalized by Al concentration (Celement/CAl) to minimize the sediment grain-size effect (GSE). However, noticeable linear relationships between Al concentration (or mean grain size) and the ratio (e.g., Mg/Al or Fe/Al) appeared unexpectedly in pair diagrams. The spatial distribution patterns of Fe/Al and Mg/Al ratios were also similar to the pattern of mean grain size. This implies that the GSE was not removed completely, even after the normalization process. Thus, great care must be taken when applying the ratios of Celement/CAl as a proxy of sediment provenance. To improve provenance discrimination of the sediments in the Yellow Sea, the difference between the REE distribution patterns of Chinese and Korean river sediments, expressed as δ (δ = REE∗(La) - REE∗(Lu)), was calculated, and the spatial distribution patterns of the δ values were mapped. The δ values gradually increased from the western to the eastern part of the Yellow Sea, except for low δ values in the southeastern part of the Yellow Sea. This result indicates that the majority of Chinese and Korean river sediments are accumulating near to their respective coasts, except for a deposit along the southwestern coast of Korea in which a considerable amount of sediment from Chinese rivers has been accumulating.

  2. Using LiDAR derivatives to estimate sediment grain size on beaches in False Bay

    CSIR Research Space (South Africa)

    Burns, J

    2017-05-01

    Full Text Available to global and climate change in particular, continues to have a big impact on coastal environments. The vulnerability of the sandy coast is dependent on the physical characteristics such as orientation/exposure, beach slope, and sand grain size...

  3. Agriproteomics of Bread Wheat: Comparative Proteomics and Network Analyses of Grain Size Variation.

    Science.gov (United States)

    Dawkar, Vishal V; Dholakia, Bhushan B; Gupta, Vidya S

    2015-07-01

    Agriproteomics signifies the merging of agriculture research and proteomics systems science and is impacting plant research and societal development. Wheat is a frequently consumed foodstuff, has highly variable grain size that in effect contributes to wheat grain yield and the end-product quality. Very limited information is available on molecular basis of grain size due to complex multifactorial nature of this trait. Here, using liquid chromatography-mass spectrometry, we investigated the proteomics profiles from grains of wheat genotypes, Rye selection 111 (RS111) and Chinese spring (CS), which differ in their size. Significant differences in protein expression were found, including 33 proteins uniquely present in RS111 and 32 only in CS, while 54 proteins were expressed from both genotypes. Among differentially expressed proteins, 22 were upregulated, while 21 proteins were downregulated in RS111 compared to CS. Functional classification revealed their role in energy metabolism, seed storage, stress tolerance and transcription. Further, protein interactive network analysis was performed to predict the targets of identified proteins. Significantly different interactions patterns were observed between these genotypes with detection of proteins such as Cyp450, Sus2, and WRKY that could potentially affect seed size. The present study illustrates the potentials of agriproteomics as a veritable new frontier of plant omics research.

  4. Optimal foraging in the thalassinidean shrimp Callianassa subterranea - Improving food quality by grain size selection

    NARCIS (Netherlands)

    Stamhuis, EJ; Videler, JJ; de Wilde, PAWJ

    1998-01-01

    The grain size distributions and organic content of habitat sediment, stomach content and faecal pellets of the endobenthic shrimp C. subterranea were analyzed to study food selection and its nutritional yield. Sub-samples of sediment from the shrimps' habitat and the stomach content were fractioned

  5. Effects of grain size distribution on the packing fraction and shear strength of frictionless disk packings

    Science.gov (United States)

    Estrada, Nicolas

    2016-12-01

    Using discrete element methods, the effects of the grain size distribution on the density and the shear strength of frictionless disk packings are analyzed. Specifically, two recent findings on the relationship between the system's grain size distribution and its rheology are revisited, and their validity is tested across a broader range of distributions than what has been used in previous studies. First, the effects of the distribution on the solid fraction are explored. It is found that the distribution that produces the densest packing is not the uniform distribution by volume fractions as suggested in a recent publication. In fact, the maximal packing fraction is obtained when the grading curve follows a power law with an exponent close to 0.5 as suggested by Fuller and Thompson in 1907 and 1919 [Trans Am. Soc. Civ. Eng. 59, 1 (1907) and A Treatise on Concrete, Plain and Reinforced (1919), respectively] while studying mixtures of cement and stone aggregates. Second, the effects of the distribution on the shear strength are analyzed. It is confirmed that these systems exhibit a small shear strength, even if composed of frictionless particles as has been shown recently in several works. It is also found that this shear strength is independent of the grain size distribution. This counterintuitive result has previously been shown for the uniform distribution by volume fractions. In this paper, it is shown that this observation keeps true for different shapes of the grain size distribution.

  6. Comparison of geostatistical kriging algorithms for intertidal surface sediment facies mapping with grain size data.

    Science.gov (United States)

    Park, No-Wook; Jang, Dong-Ho

    2014-01-01

    This paper compares the predictive performance of different geostatistical kriging algorithms for intertidal surface sediment facies mapping using grain size data. Indicator kriging, which maps facies types from conditional probabilities of predefined facies types, is first considered. In the second approach, grain size fractions are first predicted using cokriging and the facies types are then mapped. As grain size fractions are compositional data, their characteristics should be considered during spatial prediction. For efficient prediction of compositional data, additive log-ratio transformation is applied before cokriging analysis. The predictive performance of cokriging of the transformed variables is compared with that of cokriging of raw fractions in terms of both prediction errors of fractions and facies mapping accuracy. From a case study of the Baramarae tidal flat, Korea, the mapping method based on cokriging of log-ratio transformation of fractions outperformed the one based on cokriging of untransformed fractions in the prediction of fractions and produced the best facies mapping accuracy. Indicator kriging that could not account for the variation of fractions within each facies type showed the worst mapping accuracy. These case study results indicate that the proper processing of grain size fractions as compositional data is important for reliable facies mapping.

  7. Comparison of Geostatistical Kriging Algorithms for Intertidal Surface Sediment Facies Mapping with Grain Size Data

    Directory of Open Access Journals (Sweden)

    No-Wook Park

    2014-01-01

    Full Text Available This paper compares the predictive performance of different geostatistical kriging algorithms for intertidal surface sediment facies mapping using grain size data. Indicator kriging, which maps facies types from conditional probabilities of predefined facies types, is first considered. In the second approach, grain size fractions are first predicted using cokriging and the facies types are then mapped. As grain size fractions are compositional data, their characteristics should be considered during spatial prediction. For efficient prediction of compositional data, additive log-ratio transformation is applied before cokriging analysis. The predictive performance of cokriging of the transformed variables is compared with that of cokriging of raw fractions in terms of both prediction errors of fractions and facies mapping accuracy. From a case study of the Baramarae tidal flat, Korea, the mapping method based on cokriging of log-ratio transformation of fractions outperformed the one based on cokriging of untransformed fractions in the prediction of fractions and produced the best facies mapping accuracy. Indicator kriging that could not account for the variation of fractions within each facies type showed the worst mapping accuracy. These case study results indicate that the proper processing of grain size fractions as compositional data is important for reliable facies mapping.

  8. Retrieval of snow albedo and grain size using reflectance measurements in Himalayan basin

    Directory of Open Access Journals (Sweden)

    H. S. Negi

    2011-03-01

    Full Text Available In the present paper, spectral reflectance measurements of Himalayan seasonal snow were carried out and analysed to retrieve the snow albedo and effective grain size. The asymptotic radiative transfer (ART theory was applied to retrieve the plane and spherical albedo. The retrieved plane albedo was compared with the measured spectral albedo and a good agreement was observed with ±10% differences. Retrieved integrated albedo was found within ±6% difference with ground observed broadband albedo. The retrieved snow grain sizes using different models based on the ART theory were compared for various snow types and it was observed that the grain size model using two channel method (one in visible and another in NIR region can work well for the Himalayan seasonal snow and it was found consistent with temporal changes in grain size. This method can work very well for clean, dry snow as in the upper Himalaya, but sometimes, due to the low reflectances (<20% using wavelength 1.24 μm, the ART theory cannot be applied, which is common in lower and middle Himalayan old snow. This study is important for monitoring the Himalayan cryosphere using air-borne or space-borne sensors.

  9. Modeling grain-size dependent bias in estimating forest area: a regional application

    Science.gov (United States)

    Daolan Zheng; Linda S. Heath; Mark J. Ducey

    2008-01-01

    A better understanding of scaling-up effects on estimating important landscape characteristics (e.g. forest percentage) is critical for improving ecological applications over large areas. This study illustrated effects of changing grain sizes on regional forest estimates in Minnesota, Wisconsin, and Michigan of the USA using 30-m land-cover maps (1992 and 2001)...

  10. Retrieval of snow albedo and grain size using reflectance measurements in Himalayan basin

    Directory of Open Access Journals (Sweden)

    H. S. Negi

    2010-11-01

    Full Text Available In the present paper spectral reflectance measurements of Himalayan seasonal snow were carried out and analysed to retrieve the snow albedo and effective grain size. The asymptotic radiative transfer (ART theory was applied to retrieve the plane and spherical albedo. The retrieved plane albedo was compared with the measured spectral albedo and a good agreement was observed with ±10% measured error accuracy. Retrieved integrated albedo was found within ±6% difference with ground observed broadband albedo. The snow grain sizes retrieved using different models based on ART theory are compared for different snow types and it was observed that presently grain size model using two channel method (one in visible and another in NIR region can work well for Himalayan seasonal snow and it was found consistence with temporal increased grain size. This method can work very well for clean dry snow like in upper Himalaya but sometime due to low reflectances (<0.2 using wavelength 1.24 μm ART theory can not be applied, which is common in lower and middle Himalayan old snow. This study is of importance for monitoring the Himalayan cryosphere using air-borne or space-borne sensors.

  11. Ceramography and segmentation of polycristalline ceramics: application to grain size analysis by automatic methods

    Energy Technology Data Exchange (ETDEWEB)

    Arnould, X.; Coster, M.; Chermant, J.L.; Chermant, L. [LERMAT, ISMRA, Caen (France); Chartier, T. [SPCTS, ENSCI, Limoges (France)

    2002-07-01

    The knowledge of the mean grain size of ceramics is a very important problem to solve in the ceramic industry. Some specific methods of segmentation are presented to analyse, by an automatic way, the granulometry and morphological parameters of ceramic materials. Example presented concerns cerine materials. Such investigations lead to important information on the sintering process. (orig.)

  12. Distribution of grain size and clay minerals in sediments from the INDEX area, central Indian Basin

    Digital Repository Service at National Institute of Oceanography (India)

    Valsangkar, A.B.; Ambre, N.V.

    ,R.,H. L. Howa,and D. Michel. 1996. Application of grain size trend analysis for the determination of sediment transport pathways in intertidal areas. Marine Geology135:35–49.Pettijohn,F. G.,P. D. Potter,and R. Siever. 1972. Sand and Sandstone.New York...

  13. X-ray peak broadening analysis of Fe50Ni50 nanocrystalline alloys prepared under different milling times and BPR using size strain plot (SSP) method

    Indian Academy of Sciences (India)

    L Hosseinzadeh; J Baedi; A Khorsand Zak

    2014-08-01

    Fe50Ni50 nanocrystalline alloys were prepared by mechanical alloying method at different milling times of 2, 5, 10, 30, 50 and 70 h and ball powder ratios (BPR) of 10 : 1, 20 : 1 and 30 : 1. The structures of prepared powders were studied by X-ray diffraction (XRD). The broadening of the diffraction peaks were analysed using size strain plot (SSP) method and the lattice strain and crystallite size of the nanocrystals were calculated. In addition, the typical morphological studies were performed by scanning electron and transmission electron microscopies (SEM and TEM). The results showed that the crystallite size of the nanocrystals decreased with the milling time and BPR increases; whereas, the lattice constant () increased. Vibrating sample magnetometer (VSM) study of the powder prepared at 50 h and BPR 30 : 1 showed that the sample exhibits both the superparamagnetic and ferromagnetic properties in nanocrystallite size range.

  14. Dolomite microstructures between 390° and 700 °C: Indications for deformation mechanisms and grain size evolution

    Science.gov (United States)

    Berger, Alfons; Ebert, Andreas; Ramseyer, Karl; Gnos, Edwin; Decrouez, Danielle

    2016-08-01

    Dolomitic marble on the island of Naxos was deformed at variable temperatures ranging from 390 °C to >700 °C. Microstructural investigations indicate two end-member of deformation mechanisms: (1) Diffusion creep processes associated with small grain sizes and weak or no CPO (crystallographic preferred orientation), whereas (2) dislocation creep processes are related with larger grain sizes and strong CPO. The change between these mechanisms depends on grain size and temperature. Therefore, sample with dislocation and diffusion creep microstructures and CPO occur at intermediate temperatures in relative pure dolomite samples. The measured dolomite grain size ranges from 3 to 940 μm. Grain sizes at Tmax >450 °C show an Arrhenius type evolution reflecting the stabilized grain size in deformed and relative pure dolomite. The stabilized grain size is five times smaller than that of calcite at the same temperature and shows the same Arrhenius-type evolution. In addition, the effect of second phase particle influences the grain size evolution, comparable with calcite. Calcite/dolomite mixtures are also characterized by the same difference in grain size, but recrystallization mechanism including chemical recrystallization induced by deformation may contribute to apparent non-temperature equilibrated Mg-content in calcite.

  15. Enhanced crystal grain size by bromine doping in electrodeposited Cu{sub 2}O

    Energy Technology Data Exchange (ETDEWEB)

    Han Kunhee; Kang Feng [Department of Electrical Engineering, University of Texas at Arlington, Arlington, TX 76019 (United States); Han Xiaofei [Department of Material Science and Engineering, University of Texas at Arlington, Arlington, TX 76019 (United States); Tao Meng, E-mail: meng.tao@asu.edu [Department of Electrical Engineering, University of Texas at Arlington, Arlington, TX 76019 (United States)

    2012-06-01

    Extremely large crystal grains are obtained by bromine doping in electrodeposited Cu{sub 2}O on indium tin oxide (ITO) substrate through an acetate bath. The grains are as large as 10,000 {mu}m{sup 2} in area, or {approx} 100 {mu}m in linear dimension, while the film is only 1-5 {mu}m thick. The enhanced grain size is explained by the effect of over-potential for the Cu{sup 2+}/Cu{sup +} redox couple on nucleation density of Cu{sub 2}O on ITO substrate. The over-potential is a function of several deposition conditions including solution pH, deposition potential, deposition temperature, bromine precursor concentration, and copper precursor concentration. In addition, undoped Cu{sub 2}O displays a high resistivity of 100 M{Omega}cm. Bromine doping in Cu{sub 2}O significantly reduces the resistivity to as low as 42 {Omega}cm after vacuum annealing. Br-doped Cu{sub 2}O shows n-type behavior. - Highlights: Black-Right-Pointing-Pointer Extremely large crystal grains ({approx} 100 {mu}m) achieved in electrodeposited Br-doped Cu{sub 2}O. Black-Right-Pointing-Pointer Large grains reduce carrier recombination and carrier scattering at grain boundaries. Black-Right-Pointing-Pointer N-type behavior demonstrated in naturally p-type Cu{sub 2}O by Br doping.

  16. Enhanced Sucrose Loading Improves Rice Yield by Increasing Grain Size1[OPEN

    Science.gov (United States)

    Wang, Liang; Lu, Qingtao

    2015-01-01

    Yield in cereals is a function of grain number and size. Sucrose (Suc), the main carbohydrate product of photosynthesis in higher plants, is transported long distances from source leaves to sink organs such as seeds and roots. Here, we report that transgenic rice plants (Oryza sativa) expressing the Arabidopsis (Arabidopsis thaliana) phloem-specific Suc transporter (AtSUC2), which loads Suc into the phloem under control of the phloem protein2 promoter (pPP2), showed an increase in grain yield of up to 16% relative to wild-type plants in field trials. Compared with wild-type plants, pPP2::AtSUC2 plants had larger spikelet hulls and larger and heavier grains. Grain filling was accelerated in the transgenic plants, and more photoassimilate was transported from the leaves to the grain. In addition, microarray analyses revealed that carbohydrate, amino acid, and lipid metabolism was enhanced in the leaves and grain of pPP2::AtSUC2 plants. Thus, enhancing Suc loading represents a promising strategy to improve rice yield to feed the global population. PMID:26504138

  17. Hardening by ion implantation of VT1-0 alloy having different grain size

    Energy Technology Data Exchange (ETDEWEB)

    Nikonenko, Alisa, E-mail: aliska-nik@mail.ru; Kurzina, Irina, E-mail: kurzina99@mail.ru [National Research Tomsk State University, 36, Lenin Str., 634050, Tomsk (Russian Federation); Popova, Natalya, E-mail: natalya-popova-44@mail.ru [Tomsk State University of Architecture and Building, 2, Solyanaya Sq., 634003, Tomsk (Russian Federation); Institute of Strength Physics and Materials Science, SB RAS, 2/4, Akademicheskii Ave., 634021, Tomsk Russia (Russian Federation); Nikonenko, Elena, E-mail: vilatomsk@mail.ru [Tomsk State University of Architecture and Building, 2, Solyanaya Sq., 634003, Tomsk (Russian Federation); National Research Tomsk Polytechnic University, 30, Lenin Str., 634050, Tomsk (Russian Federation); Kalashnikov, Mark, E-mail: kmp1980@mail.ru [Institute of Strength Physics and Materials Science, SB RAS, 2/4, Akademicheskii Ave., 634021, Tomsk Russia (Russian Federation)

    2016-01-15

    The paper presents a transmission electron microscopy (TEM) study of the structural and phase state of commercially pure titanium implanted by aluminum ions. TEM study has been carried out for two types of grains, namely coarse (0.4 µm) and small (0.5 µm). This paper presents details of the yield stress calculations and the analysis of strength components for the both grain types in two areas of the modified layer: at a distance of 0-150 nm (surface area I) and ∼300 nm (central area II) from the irradiated surface. It is shown that the ion implantation results in a considerable hardening of the entire thickness of the implanted layer in the both grain types. The grain size has, however, a different effect on the yield stress in areas I and II. Thus, near the ion-alloyed layer, the yield stress decreases with the increase of the grain size, whilst area II demonstrates its increase. Moreover, the contribution to the general hardening of the alloy made by certain hardening mechanisms differs from contributions made by each of these mechanisms in each certain case.

  18. Magnetic properties in an ash flow tuff with continuous grain size variation: a natural reference for magnetic particle granulometry

    Science.gov (United States)

    Till, J.L.; Jackson, M.J.; Rosenbaum, J.G.; Solheid, P.

    2011-01-01

    The Tiva Canyon Tuff contains dispersed nanoscale Fe-Ti-oxide grains with a narrow magnetic grain size distribution, making it an ideal material in which to identify and study grain-size-sensitive magnetic behavior in rocks. A detailed magnetic characterization was performed on samples from the basal 5 m of the tuff. The magnetic materials in this basal section consist primarily of (low-impurity) magnetite in the form of elongated submicron grains exsolved from volcanic glass. Magnetic properties studied include bulk magnetic susceptibility, frequency-dependent and temperature-dependent magnetic susceptibility, anhysteretic remanence acquisition, and hysteresis properties. The combined data constitute a distinct magnetic signature at each stratigraphic level in the section corresponding to different grain size distributions. The inferred magnetic domain state changes progressively upward from superparamagnetic grains near the base to particles with pseudo-single-domain or metastable single-domain characteristics near the top of the sampled section. Direct observations of magnetic grain size confirm that distinct transitions in room temperature magnetic susceptibility and remanence probably denote the limits of stable single-domain behavior in the section. These results provide a unique example of grain-size-dependent magnetic properties in noninteracting particle assemblages over three decades of grain size, including close approximations of ideal Stoner-Wohlfarth assemblages, and may be considered a useful reference for future rock magnetic studies involving grain-size-sensitive properties.

  19. Absorption Efficiencies of Forsterite. I: DDA Explorations in Grain Shape and Size

    Science.gov (United States)

    Lindsay, Sean S.; Wooden, Diane; Harker, David E.; Kelley, Michael S.; Woodward, Charles E.; Murphy, Jim R.

    2013-01-01

    We compute the absorption efficiency (Q(sub abs)) of forsterite using the discrete dipole approximation (DDA) in order to identify and describe what characteristics of crystal grain shape and size are important to the shape, peak location, and relative strength of spectral features in the 8 - 40 micron wavelength range. Using the DDSCAT code, we compute Q(sub abs) for non-spherical polyhedral grain shapes with a(sub eff) = 0.1 micron. The shape characteristics identified are: 1) elongation/reduction along one of three crystallographic axes; 2) asymmetry, such that all three crystallographic axes are of different lengths; and 3) the presence of crystalline faces that are not parallel to a specific crystallographic axis, e.g., non-rectangular prisms and (di)pyramids. Elongation/reduction dominates the locations and shapes of spectral features near 10, 11, 16, 23.5, 27, and 33.5 micron, while asymmetry and tips are secondary shape effects. Increasing grain sizes (0.1 - 1.0 micron) shifts the 10, 11 micron features systematically towards longer wavelengths and relative to the 11 micron feature increases the strengths and slightly broadens the longer wavelength features. Seven spectral shape classes are established for crystallographic a-, b-, and c-axes and include columnar and platelet shapes plus non-elongated or equant grain shapes. The spectral shape classes and the effects of grain size have practical application in identifying or excluding columnar, platelet or equant forsterite grain shapes in astrophysical environs. Identification of the shape characteristics of forsterite from 8 - 40 micron spectra provides a potential means to probe the temperatures at which forsterite formed.

  20. ABSORPTION EFFICIENCIES OF FORSTERITE. I. DISCRETE DIPOLE APPROXIMATION EXPLORATIONS IN GRAIN SHAPE AND SIZE

    Energy Technology Data Exchange (ETDEWEB)

    Lindsay, Sean S. [Department of Earth and Planetary Sciences, University of Tennessee, 1421 Circle Drive, Knoxville, TN 37996-2366 (United States); Wooden, Diane H. [Space Science Division, NASA Ames Research Center, MS 245-3, Moffett Field, CA 94035-0001 (United States); Harker, David E. [Center for Astrophysics and Space Sciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0424 (United States); Kelley, Michael S. [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Woodward, Charles E. [Minnesota Institute of Astrophysics, 116 Church Street S. E., University of Minnesota, Minneapolis, MN 55455 (United States); Murphy, Jim R., E-mail: slindsay@utk.edu, E-mail: diane.h.wooden@nasa.gov, E-mail: dharker@uscd.edu, E-mail: msk@astro.umd.edu, E-mail: chelsea@astro.umn.edu, E-mail: murphy@nmsu.edu [Department of Astronomy, New Mexico State University, P.O. Box 30001, MSC 4500, Las Cruces, NM 88003-8001 (United States)

    2013-03-20

    We compute the absorption efficiency (Q{sub abs}) of forsterite using the discrete dipole approximation in order to identify and describe what characteristics of crystal grain shape and size are important to the shape, peak location, and relative strength of spectral features in the 8-40 {mu}m wavelength range. Using the DDSCAT code, we compute Q{sub abs} for non-spherical polyhedral grain shapes with a{sub eff} = 0.1 {mu}m. The shape characteristics identified are (1) elongation/reduction along one of three crystallographic axes; (2) asymmetry, such that all three crystallographic axes are of different lengths; and (3) the presence of crystalline faces that are not parallel to a specific crystallographic axis, e.g., non-rectangular prisms and (di)pyramids. Elongation/reduction dominates the locations and shapes of spectral features near 10, 11, 16, 23.5, 27, and 33.5 {mu}m, while asymmetry and tips are secondary shape effects. Increasing grain sizes (0.1-1.0 {mu}m) shifts the 10 and 11 {mu}m features systematically toward longer wavelengths and relative to the 11 {mu}m feature increases the strengths and slightly broadens the longer wavelength features. Seven spectral shape classes are established for crystallographic a-, b-, and c-axes and include columnar and platelet shapes plus non-elongated or equant grain shapes. The spectral shape classes and the effects of grain size have practical application in identifying or excluding columnar, platelet, or equant forsterite grain shapes in astrophysical environs. Identification of the shape characteristics of forsterite from 8 to 40 {mu}m spectra provides a potential means to probe the temperatures at which forsterite formed.

  1. Strain Amount Dependent Grain Size and Orientation Developments during Hot Compression of a Polycrystalline Nickel Based Superalloy

    Directory of Open Access Journals (Sweden)

    Guoai He

    2017-02-01

    Full Text Available Controlling grain size in polycrystalline nickel base superalloy is vital for obtaining required mechanical properties. Typically, a uniform and fine grain size is required throughout forging process to realize the superplastic deformation. Strain amount occupied a dominant position in manipulating the dynamic recrystallization (DRX process and regulating the grain size of the alloy during hot forging. In this article, the high-throughput double cone specimen was introduced to yield wide-range strain in a single sample. Continuous variations of effective strain ranging from 0.23 to 1.65 across the whole sample were achieved after reaching a height reduction of 70%. Grain size is measured to be decreased from the edge to the center of specimen with increase of effective strain. Small misorientation tended to generate near the grain boundaries, which was manifested as piled-up dislocation in micromechanics. After the dislocation density reached a critical value, DRX progress would be initiated at higher deformation region, leading to the refinement of grain size. During this process, the transformations from low angle grain boundaries (LAGBs to high angle grain boundaries (HAGBs and from subgrains to DRX grains are found to occur. After the accomplishment of DRX progress, the neonatal grains are presented as having similar orientation inside the grain boundary.

  2. Gibbs-Thomson effect in nanocrystalline Fe-Ge

    Science.gov (United States)

    Sarkar, S.; Bansal, C.; Chatterjee, Ashok

    2000-08-01

    We studied the phase transformation behavior of chemically disordered bcc (α) phase Fe1-xGex alloys near the Fe3Ge stoichiometry synthesized in the nanocrystalline state by mechanical alloying of the elemental constituents. The evolution of the equilibrium L12 ordered (ɛ') phase was seen to occur via a metastable DO3-ordered (α1) phase, but a significant α1-->ɛ' phase transformation took place only after the growth of the grains. This behavior is understood with the help of a capillary effect or the Gibbs-Thomson effect wherein the grain boundary energy of the nanosize grains raises the Gibbs free energy of the ɛ' phase relative to the α1 phase for small sizes and the ɛ' phase grows only after a certain grain size is reached.

  3. Grain size distribution and annual variation along the beaches from Poompuhar to Nagoor, Tamilnadu, India

    Digital Repository Service at National Institute of Oceanography (India)

    Chandrasekaran, R.; Angusamy, N.; Manickaraj, D.S.; Loveson, V.J.; Gujar, A.R.; Chandrasekar, N.; Rajamanickam, G.V.

    samples, peaks are represented in the order of dominance by 1.86, 2.35, 2.87 Ø, whereas it is found to be the reverse in the post-tsunami sample. In Kuttiyandiur, polymodal distribution of LT and HT samples of pre and post- tsunami displays similar... (Tab.2). In the present study region, graphic mean size of the LT, HT samples of Poompuhar show that sediments are of medium grained in pre and post-tsunami whereas the berm samples display a change in characteristics from medium grained...

  4. Grain size dependent optical band gap of CdI2 films

    Indian Academy of Sciences (India)

    Pankaj Tyagi; A G Vedeshwar

    2001-06-01

    The thermally evaporated stoichiometric CdI2 films show good -axis alignment normal to substrate plane for film thickness up to 200 nm. The optical absorption data indicate an allowed direct interband transition across a gap of 3.6 eV in confirmation with earlier band structure calculations. However, part of the absorption data near band edge can be fitted to an indirect band gap of 3 eV. The dependence of band gap on film thickness (> 200 nm) can be explained qualitatively in terms of decreasing grain boundary barrier height with grain size.

  5. On Techniques to Characterize and Correlate Grain Size, Grain Boundary Orientation and the Strength of the SiC Layer of TRISO Coated Particles: A Preliminary Study

    Energy Technology Data Exchange (ETDEWEB)

    I.J.van Rooyen; J.L. Dunzik Gougar; T. Trowbridge; Philip M van Rooyen

    2012-10-01

    The mechanical properties of the silicon carbide (SiC) layer of the TRi-ISOtropic (TRISO) coated particle (CP) for high temperature gas reactors (HTGR) are performance parameters that have not yet been standardized by the international HTR community. Presented in this paper are the results of characterizing coated particles to reveal the effect of annealing temperature (1000 to 2100°C) on the strength and grain size of unirradiated coated particles. This work was further expanded to include possible relationships between the grain size and strength values. The comparative results of two strength measurement techniques and grain size measured by the Lineal intercept method are included. Preliminary grain boundary characterization results determined by electron backscatter diffraction (EBSD) are included. These results are also important for future fission product transport studies, as grain boundary diffusion is identified as a possible mechanism by which 110mAg, one of the fission activation products, might be released through intact SiC layers. Temperature is a parameter known to influence the grain size of SiC and therefore it is important to investigate the effect of high temperature annealing on the SiC grain size. Recommendations and future work will also be briefly discussed.

  6. Conditions necessary for capillary hysteresis in porous media: Tests of grain size and surface tension influences

    Science.gov (United States)

    Tokunaga, Tetsu K.; Olson, Keith R.; Wan, Jiamin

    2004-05-01

    Hysteresis in the relation between water saturation and matric potential is generally regarded as a basic aspect of unsaturated porous media. However, the nature of an upper length scale limit for saturation hysteresis has not been previously addressed. Since hysteresis depends on whether or not capillary rise occurs at the grain scale, this criterion was used to predict required combinations of grain size, surface tension, fluid-fluid density differences, and acceleration in monodisperse systems. The Haines number (Ha), composed of the aforementioned variables, is proposed as a dimensionless number useful for separating hysteretic (Ha 15) behavior. Vanishing of hysteresis was predicted to occur for grain sizes greater than 10.4 ± 0.5 mm, for water-air systems under the acceleration of ordinary gravity, based on Miller-Miller scaling and Haines' original model for hysteresis. Disappearance of hysteresis was tested through measurements of drainage and wetting curves of sands and gravels and occurs between grain sizes of 10 and 14 mm (standard conditions). The influence of surface tension was tested through measurements of moisture retention in 7 mm gravel, without and with a surfactant (sodium dodecylbenzenesulfonate (SDBS)). The ordinary water system (Ha = 7) exhibited hysteresis, while the SDBS system (Ha = 18) did not. The experiments completed in this study indicate that hysteresis in moisture retention relations has an upper limit at Ha = 16 ± 2 and show that hysteresis is not a fundamental feature of unsaturated porous media.

  7. SPEED DEPENDENCE OF ACOUSTIC VIBRATION PROPAGATION FROM THE FERRITIC GRAIN SIZE IN LOW-CARBON STEEL

    Directory of Open Access Journals (Sweden)

    I. A. Vakulenko

    2015-08-01

    Full Text Available Purpose. It is determining the nature of the ferrite grain size influence of low-carbon alloy steel on the speed propagation of acoustic vibrations. Methodology. The material for the research served a steel sheet of thickness 1.4 mm. Steel type H18T1 had a content of chemical elements within grade composition: 0, 12 % C, 17, 5 % Cr, 1 % Mn, 1, 1 % Ni, 0, 85 % Si, 0, 9 % Ti. The specified steel belongs to the semiferritic class of the accepted classification. The structural state of the metal for the study was obtained by cold plastic deformation by rolling at a reduction in the size range of 20-30 % and subsequent recrystallization annealing at 740 – 750 ° C. Different degrees of cold plastic deformation was obtained by pre-selection of the initial strip thickness so that after a desired amount of rolling reduction receives the same final thickness. The microstructure was observed under a light microscope, the ferrite grain size was determined using a quantitative metallographic technique. The using of X-ray structural analysis techniques allowed determining the level of second-order distortion of the crystal latitude of the ferrite. The speed propagation of acoustic vibrations was measured using a special device such as an ISP-12 with a working frequency of pulses 1.024 kHz. As the characteristic of strength used the hardness was evaluated by the Brinell’s method. Findings. With increasing of ferrite grain size the hardness of the steel is reduced. In the case of constant structural state of metal, reducing the size of the ferrite grains is accompanied by a natural increasing of the phase distortion. The dependence of the speed propagation of acoustic vibrations up and down the rolling direction of the ferrite grain size remained unchanged and reports directly proportional correlation. Originality. On the basis of studies to determine the direct impact of the proportional nature of the ferrite grain size on the rate of propagation of sound

  8. The rate sensitivity and plastic deformation of nanocrystalline tantalum films at nanoscale

    Directory of Open Access Journals (Sweden)

    Huang Yongli

    2011-01-01

    Full Text Available Abstract Nanoindentation creep and loading rate change tests were employed to examine the rate sensitivity (m and hardness of nanocrystalline tetragonal Ta films. Experimental results suggested that the m increased with the decrease of feature scale, such as grain size and indent depth. The magnitude of m is much less than the corresponding grain boundary (GB sliding deformation with m of 0.5. Hardness softening behavior was observed for smaller grain size, which supports the GB sliding mechanism. The rate-controlling deformation was interpreted by the GB-mediated processes involving atomic diffusion and the generation of dislocation at GB.

  9. Porous media grain size distribution and hydrodynamic forces effects on transport and deposition of suspended particles.

    Science.gov (United States)

    Ahfir, Nasre-Dine; Hammadi, Ahmed; Alem, Abdellah; Wang, HuaQing; Le Bras, Gilbert; Ouahbi, Tariq

    2017-03-01

    The effects of porous media grain size distribution on the transport and deposition of polydisperse suspended particles under different flow velocities were investigated. Selected Kaolinite particles (2-30μm) and Fluorescein (dissolved tracer) were injected in the porous media by step input injection technique. Three sands filled columns were used: Fine sand, Coarse sand, and a third sand (Mixture) obtained by mixing the two last sands in equal weight proportion. The porous media performance on the particle removal was evaluated by analysing particles breakthrough curves, hydro-dispersive parameters determined using the analytical solution of convection-dispersion equation with a first order deposition kinetics, particles deposition profiles, and particle-size distribution of the recovered and the deposited particles. The deposition kinetics and the longitudinal hydrodynamic dispersion coefficients are controlled by the porous media grain size distribution. Mixture sand is more dispersive than Fine and Coarse sands. More the uniformity coefficient of the porous medium is large, higher is the filtration efficiency. At low velocities, porous media capture all sizes of suspended particles injected with larger ones mainly captured at the entrance. A high flow velocity carries the particles deeper into the porous media, producing more gradual changes in the deposition profile. The median diameter of the deposited particles at different depth increases with flow velocity. The large grain size distribution leads to build narrow pores enhancing the deposition of the particles by straining. Copyright © 2016. Published by Elsevier B.V.

  10. Grain size fraction of heavy metals in soil and their relationship with land use

    Directory of Open Access Journals (Sweden)

    M. H. Sayadi

    2017-03-01

    Full Text Available The aim of the present study was to investigate the distribution of heavy metals (Pb, Ni, Cr and Cd in different grain-size fractions of the surface soils. The soil samples of different land uses were taken from 20 cm depth at 12 stations where is located at Amir Abad of Birjand city, Iran. The air-dried samples were passed through sieves of different sizes to collect the fractions lesser than 63 μm, 63-125 μm, 125-250 μm, 250-500 μm, 500-1000 μm and 1000-2000 μm. The samples were digested by perchloric acid and nitric acid; and the concentrations of heavy metals were determined using Atomic Absorption Spectrophotometer (model AAcontr700. The highest concentrations for Pb, Cr, Ni and Cd (139.5, 195.4, 98.4 and 3.15 mg/kg respectively were obtained in the fractions less than 63 μm from the road-side soils. The contamination factor values for the fractions less than 63 μm were higher than other fractions. The comparison of different toxic metals concentration from various grain-size fractions demonstrated higher Cr levels, especially in the 63-125 μm size fractions from the road-side lands. Thus, the comparison of grain size factors from different soils revealed that Cr exhibited highest values in relation to the other toxic elements studied.

  11. Effect of grain size reduction on high temperature oxidation ofbinary two-phase alloys

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The effect of grain size reduction on the high temperature oxidation of binary two-phase alloys was discussed based on the recent research progress. The results show that for those two-phase alloys with coarse grain prepared by the conventional methods, complex oxide scales are easily formed after oxidation under high oxygen pressure or under oxygen pressure below the stability limit of the less reactive component oxides. On the contrary, for the nano-sized alloys, an exclusive external oxidation of the most reactive component usually occurs during oxidation in air or pure oxygen even for much lower content of the most reactive component. So the gain size reduction is not always beneficial to improve the oxidation resistance of the materials, but exhibits different effects depending mainly on the protective feature of the scales. The transition mechanisms between the different oxidation modes are discussed with respect to the thermodynamic and dynamic aspects.

  12. Relationship among grain size, annealing twins and shape memory effect in Fe-Mn-Si based shape memory alloys

    Science.gov (United States)

    Wang, Gaixia; Peng, Huabei; Zhang, Chengyan; Wang, Shanling; Wen, Yuhua

    2016-07-01

    In order to clarify the relationship among grain size, annealing twins and the shape memory effect in Fe-Mn-Si based shape memory alloys, the Fe-21.63Mn-5.60Si-9.32Cr-5.38Ni (weight %) alloy with a grain size ranging from 48.9 μm-253.6 μm was obtained by adjusting the heating temperature or heating time after 20% cold-rolling. The densities of grain boundaries and annealing twins increase with a decrease in grain size, whereas the volume fraction and width of stress-induced ɛ martensite after 9% deformation at Ms + 10 K decrease. This result indicates that grain refinement raises the constraint effects of grain boundaries and annealing twins upon martensitic transformation. In this case, the ability to suppress the plastic deformation and facilitate the stress-induced ɛ martensite transformation deteriorates after grain refinement owing to the enhancement of the constraint effects. It is demonstrated by the result that the difference at Ms + 10 K between the critical stress for plastic yielding and that for inducing martensitic transformation is smaller for the specimen with a grain size of 48.9 μm than for the specimen with a grain size of 253.6 μm. Therefore, the shape memory effect declined by decreasing the grain size.

  13. Effect of alloy grain size on the high-temperature oxidation behavior of the austenitic steel TP 347

    Directory of Open Access Journals (Sweden)

    Vicente Braz Trindade

    2005-12-01

    Full Text Available Generally, oxide scales formed on high Cr steels are multi-layered and the kinetics are strongly influenced by the alloy grain boundaries. In the present study, the oxidation behaviour of an austenite steel TP347 with different grain sizes was studied to identify the role of grain-boundaries in the oxidation process. Heat treatment in an inert gas atmosphere at 1050 °C was applied to modify the grain size of the steel TP347. The mass gain during subsequent oxidation was measured using a microbalance with a resolution of 10-5 g. The scale morphology was examined using SEM in combination with energy-dispersive X-ray spectroscopy (EDS. Oxidation of TP347 with a grain size of 4 µm at 750 °C in air follows a parabolic rate law. For a larger grain size (65 µm, complex kinetics is observed with a fast initial oxidation followed by several different parabolic oxidation stages. SEM examinations indicated that the scale formed on specimens with smaller grain size was predominantly Cr2O3, with some FeCr2O4 at localized sites. For specimens with larger grain size the main oxide is iron oxide. It can be concluded that protective Cr2O3 formation is promoted by a high density of fast grain-boundary diffusion paths which is the case for fine-grained materials.

  14. Thermal stability of the in-plane magnetic anisotropy and the coercivity of nanocrystalline CoFeNi films

    NARCIS (Netherlands)

    van Voorthuysen, EHD; ten Broek, FT; Chechenin, NG; Boerma, DO

    2003-01-01

    By choosing the right production parameters, in-plane, uniaxial anisotropy up to about 15 Oe (1250 J/m(3)) could be induced in electrodeposited layers of Co59Fe26Ni15. This compound consists of a mixture of FCC and BCC phases. The layers were magnetically soft and nanocrystalline with grain sizes of

  15. Effects of Moisture and Grain Sizes on Rainsplash Transport with Implications for Desert Plant-Soil Interactions

    Science.gov (United States)

    Taube, S. R.; Furbish, D. J.; Roberts, A. S.

    2009-12-01

    Soil mounds beneath desert shrubs can develop from sediment transport associated with rainsplash of soil grains around the plants. As the canopy of a plant protects the underlying soil from the raindrop impacts, sediment accumulates beneath the shrub canopy due to differential rainsplash of grains. Previous work has clarified how rainsplash transport varies with raindrop momentum and with different sizes of dry sediment, focusing on the transfer of momentum of the drops to grains during drop impacts. Details of this transfer of momentum and grain mobilization for moist sediment conditions are not well known, which is important for understanding sediment transport by rainsplash during the progression of storms. Moreover, related work suggests that relatively immobile coarse soil grains are less likely to be splashed beneath shrub canopies than are small grains, so that smaller grains are more likely to accumulate within shrub mounds. However, systematic measurements of sediment grain sizes around and beneath desert shrubs in the Cibola National Forest, New Mexico, suggest that, aside from the coarsest lag material, larger grain sizes (0.5 - 1.5 mm) are preferentially concentrated within the mound surfaces close to the shrubs. This pattern of grain-size sorting is likely associated with effects of moisture, wherein small grains tend to be ejected during drop impacts as grain clumps rather than individually due to surface tension, and thereby behave as relative coarse grains with shorter splash distances. High-speed imaging of drop impacts on sediment reveals this clumping behavior. These results may be useful in determining the dispersal of nutrients and contaminants that preferentially adhere to the smaller grain sizes. This information also extends our understanding of rainsplash transport beyond dry conditions, that is, to storm conditions where soil moisture and grain detachment rates are changing.

  16. Nanocrystalline Heterojunction Materials

    Science.gov (United States)

    Elder, Scott H.; Su, Yali; Gao, Yufei; Heald, Steve M.

    2004-02-03

    Mesoporous nanocrystalline titanium dioxide heterojunction materials and methods of making the same are disclosed. In one disclosed embodiment, materials comprising a core of titanium dioxide and a shell of a molybdenum oxide exhibit a decrease in their photoadsorption energy as the size of the titanium dioxide core decreases.

  17. Grain size distributions of chalk from image analysis of electron micrographs

    DEFF Research Database (Denmark)

    Røgen, Birte; Gommesen, Lars; Fabricius, Ida Lykke

    2001-01-01

    In the chalk of the Ekofisk formation in the Chalk Group of the North Sea, substantial depth-related variations in porosityare observed. With the aim of obtaining a textural interpretation of these porositydata, we have developed a method to assess the grain size distribution of the chalk from...... image analysis. The chalk is composed of a fine-grained matrix of nannofossils and predominantlycalcitic fossil debris with larger microfossil grains, but the chalk may also contain significant amounts of silica and siliciclastic clay. For image analysis, we used backscatter electron images of epoxy......-impregnated, polished samples from the Ekofisk Formation, Tyra field, Danish North Sea. On backscatter images the calcite phase will appear light as opposed to the dark pore space. The procedure involves the combination of data acquired at two magnifications and bythis method analysis of only four images per sample...

  18. Effects of Additive AlCl3 on Crystal Phase, Particle Size and Microstructural Parameters of Nanocrystalline TiO2 Prepared by HF-PCVD

    Institute of Scientific and Technical Information of China (English)

    Haiping XU; Yanping SUN; Xinmou CHEN

    2004-01-01

    Nanocrystalline TiO2 was prepared by high frequency plasma chemical vapor deposition (HF-PCVD). The effects of additive AlCl3 on crystal phase, particle size and microstructural parameters of TiO2 nanocrystallites were investigated by X-ray diffraction(XRD) and transmission electron microscopy (TEM). The nanocrystallites obtained experimentally are mixture of anatase and rutile, the uniform diameters of particles are about 30 nm. The phase transformation from anatase to rutile was accelerated by AlCl3, and rutile content is increased from 26.7 wt pct to 53.6 wt pct with increasing of addition of AlCl3 from 0.0 wt pct to 5.0 wt pct. The particle size is reduced and the size distribution becomes very narrow. The crystal lattice constants have the trend to decrease, and cell volumes appear as shrinkable.

  19. Linking differential domain functions of the GS3 protein to natural variation of grain size in rice.

    Science.gov (United States)

    Mao, Hailiang; Sun, Shengyuan; Yao, Jialing; Wang, Chongrong; Yu, Sibin; Xu, Caiguo; Li, Xianghua; Zhang, Qifa

    2010-11-09

    Grain yield in many cereal crops is largely determined by grain size. Here we report the genetic and molecular characterization of GS3, a major quantitative trait locus for grain size. It functions as a negative regulator of grain size and organ size. The wild-type isoform is composed of four putative domains: a plant-specific organ size regulation (OSR) domain in the N terminus, a transmembrane domain, a tumor necrosis factor receptor/nerve growth factor receptor (TNFR/NGFR) family cysteine-rich domain, and a von Willebrand factor type C (VWFC) in the C terminus. These domains function differentially in grain size regulation. The OSR domain is both necessary and sufficient for functioning as a negative regulator. The wild-type allele corresponds to medium grain. Loss of function of OSR results in long grain. The C-terminal TNFR/NGFR and VWFC domains show an inhibitory effect on the OSR function; loss-of-function mutations of these domains produced very short grain. This study linked the functional domains of the GS3 protein to natural variation of grain size in rice.

  20. Continuous Single-Step Fabrication of Nonaggregated, Size-Controlled and Cubic Nanocrystalline Y2O3:Eu3+ Phosphors Using Flame Spray Pyrolysis

    Science.gov (United States)

    Chang, Hankwon; Lenggoro, I. Wuled; Okuyama, Kikuo; Kim, Tae-Oh

    2004-06-01

    Continuous single-step fabrication of cubic nanocrystalline Y2O3:Eu3+ phosphor particles using flame spray pyrolysis was successfully conducted without any post-heat treatments. The morphology of the as-prepared particles was spherical and nonaggregated. The mean size of as-prepared particles was easily controlled by adjusting the precursor concentration. On varying the overall concentration of the precursor solution from 0.01 to 0.5 M, the crystallite size and geometric mean particle diameter varied from 38.4 nm to 50.6 nm and 263 nm to 741 nm, respectively. XRD spectra of as-prepared particles indicated that all products, regardless of the precursor concentration, showed the cubic phase with high crystallinity without any post-treatments, although residence times in the flame were very short. Upon excitation with 254 nm light, all of the as-prepared particles showed bright red emission due to the 4f-4f transitions of Eu3+ ions, and the highest photoluminescent intensity at 611 nm was found at a Eu3+ content of about 12 mol%. These results indicate the possibility of the fabrication of cubic nanocrystalline Y2O3:Eu3+ phosphors with a high production rate and high purity.

  1. Grain Size Distribution in Mudstones: A Question of Nature vs. Nurture

    Science.gov (United States)

    Schieber, J.

    2011-12-01

    Grain size distribution in mudstones is affected by the composition of the source material, the processes of transport and deposition, and post-depositional diagenetic modification. With regard to source, it does make a difference whether for example a slate belt is eroded vs a stable craton. The former setting tends to provide a broad range of detrital quartz in the sub 62 micron size range in addition to clays and greenschist grade rock fragments, whereas the latter may be biased towards coarser quartz silt (30-60 microns), in addition to clays and mica flakes. In flume experiments, when fine grained materials are transported in turbulent flows at velocities that allow floccules to transfer to bedload, a systematic shift of grain size distribution towards an increasingly finer grained suspended load is observed as velocity is lowered. This implies that the bedload floccules are initially constructed of only the coarsest clay particles at high velocities, and that finer clay particles become incorporated into floccules as velocity is lowered. Implications for the rock record are that clay beds deposited from decelerating flows should show subtle internal grading of coarser clay particles; and that clay beds deposited from continuous fast flows should show a uniform distribution of coarse clays. Still water settled clays should show a well developed lower (coarser) and upper (finer) subdivision. A final complication arises when diagenetic processes, such as the dissolution of biogenic silica, give rise to diagenetic quartz grains in the silt to sand size range. This diagenetic silica precipitates in fossil cavities and pore spaces of uncompacted muds, and on casual inspection can be mistaken for detrital quartz. In distal mudstone successions close to 100 % of "apparent" quartz silt can be of that origin, and reworking by bottom currents can further enhance a detrital perception by producing rippled and laminated silt beds. Although understanding how size

  2. Grain-size evidence for multiple origins of the reticulate red clay in southern China

    Institute of Scientific and Technical Information of China (English)

    HU Xuefeng; ZHU Yu; SHEN Mingneng

    2005-01-01

    Grain-size distributions of the reticulate red clay in Xuancheng, Anhui Province, and Jiujiang, Taihe and Ganzhou, Jiangxi Province, are analyzed. The results are as follows: (1) Generally fine and uniform, grain-size characteristics of the reticulate red clay in Xuancheng and Jiujiang are much similar, with no >2 mm gravels, 0.30% and 1.14% of >63 μm fraction on average, respectively, and 34.65% and 37.20% of 10―50 μm fraction, which is apparently accumulated. The patterns of the grain-size distribution curves of the uppermost yellow-brown earth of the profiles in the two areas much resemble those of the loess in northern China and the Xiashu loess in southeastern China, while the patterns of the other layers also apparently show some attributes inherited from the above. The grain-size distribution patterns of the quartz separated from the whole profiles in the areas are almost identical, which could also be compared with those of the loess and the Xiashu loess. All the features above reveal aeolian characteristics of the reticulated red clay in these two areas. (2) The reticulate red clay in Taihe and Ganzhou is much coarser than that in Xuancheng and Jiujiang, with high content of >63 μm fraction and relatively low content of 10―50 μm fraction. The variations in grain-size distributions of the profiles are also observed. The grain-size distribution patterns of both the original samples and the quartz of the red clay could hardly be compared with those of the loess and the Xiashu loess. All the features above reveal their alluvial or diluvial origins. (3) The multiple origins of the reticulate red clay in the areas reflect the diversity and complexity of the Quaternary environment in southern China. The existence of the reticulate red clay with aeolian characteristics brings forth objective evidence for the occurrence of large-scale dust deposition in southern China during the Quaternary glacial periods. Further investigation and study on the regional

  3. MinSORTING: an Excel macro for modelling sediment composition and grain-size distribution

    Science.gov (United States)

    Resentini, Alberto; Malusà, Marco G.; Garzanti, Eduardo

    2013-04-01

    Detrital mineral analyses are gaining increasing attention in the geosciences as new single-grain analytical techniques are constantly improving their resolution, and consequently widening their range of application, including sedimentary petrology, tectonic geomorphology and archaeology (Mange and Wright, 2007; von Eynatten and Dunkl, 2012). We present here MinSORTING, a new tool to quickly predict the size distribution of various minerals and rock fragments in detrital sediments, based on the physical laws that control sedimentation by tractive wind or water currents (Garzanti et al., 2008). The input values requested by the software are the sediment mean size, sorting, fluid type (seawater, freshwater, air) and standard sediment composition chosen from a given array including nine diverse tectonic settings. MinSORTING calculates the bulk sediment density and the settling velocity. The mean size of each single detrital component, assumed as lognormally-distributed, is calculated from its characteristic size-shift with respect to bulk sediment mean size, dependent in turn on its density and shape. The final output of MinSORTING is the distribution of each single detrital mineral in each size classes (at the chosen 0.25, 0.5 or 1 phi intervals). This allows geochronolgists to select the most suitable grain size of sediment to be sampled in the field, as well as the most representative size-window for analysis. Also, MinSORTING provides an estimate of the volume/weight of the fractions not considered in both sizes finer and coarser than the selected size-window. A beta version of the software is available upon request from: alberto.resentini@unimib.it Mange, M., and Wright, D. (eds), 2007. Heavy minerals in use. Developments in Sedimentology Series, 58. Elsevier, Amsterdam. Garzanti, E., Andò, S., Vezzoli, G., 2008. Settling-equivalence of detrital minerals and grain-size dependence of sediment composition. Earth and Planetary Science Letters 273, 138-151. von

  4. Variations in CYP78A13 coding region influence grain size and yield in rice.

    Science.gov (United States)

    Xu, Fan; Fang, Jun; Ou, Shujun; Gao, Shaopei; Zhang, Fengxia; Du, Lin; Xiao, Yunhua; Wang, Hongru; Sun, Xiaohong; Chu, Jinfang; Wang, Guodong; Chu, Chengcai

    2015-04-01

    Grain size is one of the most important determinants of crop yield in cereals. Here, we identified a dominant mutant, big grain2 (bg2-D) from our enhancer-trapping population. Genetic analysis and SiteFinding PCR (polymerase chain reaction) revealed that BG2 encodes a cytochrome P450, OsCYP78A13. Sequence search revealed that CYP78A13 has a paralogue Grain Length 3.2 (GL3.2, LOC_Os03g30420) in rice with distinct expression patterns, analysis of transgenic plants harbouring either CYP78A13 or GL3.2 showed that both can promote grain growth. Sequence polymorphism analysis with 1529 rice varieties showed that the nucleotide diversity at CYP78A13 gene body and the 20 kb flanking region in the indica varieties were markedly higher than those in japonica varieties. Further, comparison of the genomic sequence of CYP78A13 in the japonica cultivar Nipponbare and the indica cultivar 9311 showed that there were three InDels in the promoter region and eight SNPs (single nucleotide polymorphism) in its coding sequence. Detailed examination of the transgenic plants with chimaeric constructs suggested that variation in CYP78A13 coding region is responsible for the variation of grain yield. Taken together, our results suggest that the variations in CYP78A13 in the indica varieties hold potential in rice breeding for application of grain yield improvement.

  5. Influence of charging process and size distribution of dust grain on the electric conductivity of dusty plasma

    Energy Technology Data Exchange (ETDEWEB)

    Duan Jizheng; Wang Canglong; Zhang Jianrong; Ma Shengqian; Hong Xueren; Sun Jianan [College of Physics and Electronic Engineering and Joint Laboratory of Atomic and Molecular Physics of NWNU and IMP CAS, Northwest Normal University, Lanzhou 730070 (China) and Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); Duan Wenshan [College of Physics and Electronic Engineering and Joint Laboratory of Atomic and Molecular Physics of NWNU and IMP CAS, Northwest Normal University, Lanzhou 730070 (China) and Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); Key Laboratory of Atomic and Molecular Physics and Functional Materials of Gansu Province, College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070 (China); Yang Lei [College of Physics and Electronic Engineering and Joint Laboratory of Atomic and Molecular Physics of NWNU and IMP CAS, Northwest Normal University, Lanzhou 730070 (China) and Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); Department of Physics, Lanzhou University, Lanzhou 730000 (China)

    2012-08-15

    The effects of dust size distribution and charging process of dust grains on the complex electric conductivity of dusty plasmas have been investigated in the present paper. Comparisons are made between real dusty plasma in which there are many different dust grain species and the mono-sized dusty plasma (MDP) in which there is only one kind of dust grain whose size is the average dust size. In some cases the complex electric conductivity of real dusty plasma is larger than that of MDP, while in other cases it is smaller than that of MDP, it depends on the dust size distribution function.

  6. Estimating the settling velocity of bioclastic sediment using common grain-size analysis techniques

    Science.gov (United States)

    Cuttler, Michael V. W.; Lowe, Ryan J.; Falter, James L.; Buscombe, Daniel D.

    2017-01-01

    Most techniques for estimating settling velocities of natural particles have been developed for siliciclastic sediments. Therefore, to understand how these techniques apply to bioclastic environments, measured settling velocities of bioclastic sedimentary deposits sampled from a nearshore fringing reef in Western Australia were compared with settling velocities calculated using results from several common grain-size analysis techniques (sieve, laser diffraction and image analysis) and established models. The effects of sediment density and shape were also examined using a range of density values and three different models of settling velocity. Sediment density was found to have a significant effect on calculated settling velocity, causing a range in normalized root-mean-square error of up to 28%, depending upon settling velocity model and grain-size method. Accounting for particle shape reduced errors in predicted settling velocity by 3% to 6% and removed any velocity-dependent bias, which is particularly important for the fastest settling fractions. When shape was accounted for and measured density was used, normalized root-mean-square errors were 4%, 10% and 18% for laser diffraction, sieve and image analysis, respectively. The results of this study show that established models of settling velocity that account for particle shape can be used to estimate settling velocity of irregularly shaped, sand-sized bioclastic sediments from sieve, laser diffraction, or image analysis-derived measures of grain size with a limited amount of error. Collectively, these findings will allow for grain-size data measured with different methods to be accurately converted to settling velocity for comparison. This will facilitate greater understanding of the hydraulic properties of bioclastic sediment which can help to increase our general knowledge of sediment dynamics in these environments.

  7. Physical conditions in three high-z H2-bearing DLAs: implications for grain size

    CERN Document Server

    Rawlins, Katherine; Srianand, Raghunathan

    2016-01-01

    We present results of our numerical simulation of three H2-bearing damped Lyman alpha absorbers (DLAs) in the redshift interval ~ 2-3. The systems we have modelled are the DLAs at zabs = 2.3377 towards the quasar LBQS 1232+0815, at zabs = 2.41837 towards SDSS J143912.04+111740.5 and at zabs = 2.6265 towards FBQS J081240.6+320808. We have used the spectral synthesis code CLOUDY to simulate the physical environment of these DLAs, and constrain the density, radiation field, geometry and dust-grain properties of the DLAs self-consistently based on the observed column densities of various atomic and molecular species such as H I, fine structure lines of C I and the rotational level population of H2. In our models, we explore the effect of grain size distribution on the predicted column densities of different species. Within the allowed uncertainties in the inferred dust-to-gas ratio, both models with standard ISM grains and smaller-sized grains reproduce the observations equally well. Improved constraints on dust-...

  8. Determination of grain-size distribution function using two-dimensional Fourier transforms of tone-pulse-encoded images

    Science.gov (United States)

    Generazio, E. R.

    1988-01-01

    Microstructural images may be tone pulse encoded and subsequently Fourier transformed to determine the two-dimensional density of frequency components. A theory is developed relating the density of frequency components to the density of length components. The density of length components corresponds directly to the actual grain-size distribution function from which the mean grain shape, size, and orientation can be obtained.

  9. Determination of grain size distribution function using two-dimensional Fourier transforms of tone pulse encoded images

    Science.gov (United States)

    Generazio, E. R.

    1986-01-01

    Microstructural images may be tone pulse encoded and subsequently Fourier transformed to determine the two-dimensional density of frequency components. A theory is developed relating the density of frequency components to the density of length components. The density of length components corresponds directly to the actual grain size distribution function from which the mean grain shape, size, and orientation can be obtained.

  10. Grain-size distribution patterns of suspended sediment in response to hydrodynamics on the Dafeng intertidal flat, Jiangsu, China

    Institute of Scientific and Technical Information of China (English)

    LI Zhanhai; GAO Shu; CHEN Shenliang; WANG Yaping

    2006-01-01

    Patterns of grain-size distributions of suspended sediment in relation to resuspension, settling, and tidal processes are investigated, based on in situ measurements over the Dafeng intertidal flat, on the Jiangsu coast, in the summer of 2002 and 2003. The suspended sediment here is dominated by fine and very fine silt, with a mean grain-size of 7~13 μm. The patterns of the grain-size distributions of suspended sediment during a tidal cycle are characterized by two types: one stable type representing insignificant spatial and temporal variations; and the other bimodal type with significant variations. The main factors influencing the grain-size distributions include resuspension, settling, suspended sediment imported into intertidal flats during the flood phase, and the grain-size distribution of seabed sediment. Resuspension increases the coarse particle content, enhances the mean grain-size of suspended sediment, and results in grain-size distributions for the suspended sediment similar to those of seabed sediment; the settling process has opposite effects on the suspended sediment. When resuspension occurs, the gain-size distributions of suspended sediment in the lower part of water column respond significantly to the current velocity. Where the influence of resuspension and settling processes is weak, the grain-size distributions of suspended sediment appear to be stable and almost identical for the various parts of intertidal flats during different measurement periods. Such distributions are referred to the background grain-size distribution, for which the mean grain-size over the Dafeng intertidal flat is around 7 μm.

  11. Reading acquisition, developmental dyslexia, and skilled reading across languages: a psycholinguistic grain size theory.

    Science.gov (United States)

    Ziegler, Johannes C; Goswami, Usha

    2005-01-01

    The development of reading depends on phonological awareness across all languages so far studied. Languages vary in the consistency with which phonology is represented in orthography. This results in developmental differences in the grain size of lexical representations and accompanying differences in developmental reading strategies and the manifestation of dyslexia across orthographies. Differences in lexical representations and reading across languages leave developmental "footprints" in the adult lexicon. The lexical organization and processing strategies that are characteristic of skilled reading in different orthographies are affected by different developmental constraints in different writing systems. The authors develop a novel theoretical framework to explain these cross-language data, which they label a psycholinguistic grain size theory of reading and its development.

  12. Grain-size cycles in Salawusu River valley since 150 ka BP

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The palaeo-mobile dune sands and fluvio-lacustrine facies with palaeosols in Milanggouwan stratigraphic section of the Salawusu River valley situated at the southeast of the Mu Us Desert experienced abundant remarkable alternative changes of coarse and fine rhythms in grainsize since 150 ka BP, and the grain-size parameters - Mz, σ, Sk, Kg and SC/I also respond to the situation of multi-fluctuational alternations between peak and valley values. Simultaneity the grainsize eigenvalues - Ф5, Ф16, P25, Ф50, Ф75, Ф84 and Ф95 are respondingly manifested as greatly cadent jumpiness. Hereby, the Milanggouwan section can be divided into 27 grain-size coarse and fine sedimentary cycles, which can be regarded as a real and integreted record of climate-geological process of desert vicissitude resulted from the alternative evolvement of the ancient winter and summer monsoons of East Asia since 150 ka BP.

  13. Influence of the Matrix Grain Size on the Apparent Density and Bending Strength of Sand Cores

    Directory of Open Access Journals (Sweden)

    Dańko R.

    2017-03-01

    Full Text Available The results of investigations of the influence of the matrix grain sizes on properties of cores made by the blowing method are presented in the hereby paper. Five kinds of matrices, differing in grain size compositions, determined by the laser diffraction method in the Analysette 22NanoTec device, were applied in investigations. Individual kinds of matrices were used for making core sands in the Cordis technology. From these sands the shaped elements, for determining the apparent density of compacted sands and their bending strength, were made by the blowing method. The shaped elements (cores were made at shooting pressures being 3, 4 and 5 atn. The bending strength of samples were determined directly after their preparation and after the storing time of 1 hour.

  14. Grain size analysis and depositional environment of shallow marine to basin floor, Kelantan River Delta

    Science.gov (United States)

    Afifah, M. R. Nurul; Aziz, A. Che; Roslan, M. Kamal

    2015-09-01

    Sediment samples were collected from the shallow marine from Kuala Besar, Kelantan outwards to the basin floor of South China Sea which consisted of quaternary bottom sediments. Sixty five samples were analysed for their grain size distribution and statistical relationships. Basic statistical analysis like mean, standard deviation, skewness and kurtosis were calculated and used to differentiate the depositional environment of the sediments and to derive the uniformity of depositional environment either from the beach or river environment. The sediments of all areas were varied in their sorting ranging from very well sorted to poorly sorted, strongly negative skewed to strongly positive skewed, and extremely leptokurtic to very platykurtic in nature. Bivariate plots between the grain-size parameters were then interpreted and the Coarsest-Median (CM) pattern showed the trend suggesting relationships between sediments influenced by three ongoing hydrodynamic factors namely turbidity current, littoral drift and waves dynamic, which functioned to control the sediments distribution pattern in various ways.

  15. Formation of nanocrystalline layers by surface severe plastic deformation and pulsed plasma electrolytic carburizing.

    Science.gov (United States)

    Aliofkhazraei, M; Rouhaghdam, A Sabour

    2010-07-01

    Surfaces of various kinds of metallic materials spheres were treated by nanocrystalline surface severe plastic deformation and then pulsed nanocrystalline plasma electrolytic carburizing to study nanocrystalline substrate effect on formation and nano-hardness of hard nanocrystalline layer. The surface layers of the metallic materials developed by the nanocrystalline surface severe plastic deformation were characterized by means of high resolution scanning electron microscope. Nearly equiaxed nanocrystals with grain sizes ranging from 15 to 90 nm were observed in the near surface regions of all metallic materials, which are low carbon steel and commercially pure titanium. The effect of substrate nanocrystallization on growth kinetics and hardness of formed nanocrystalline carbide layer was studied with the means of figure analysis and nanohardness tests. Figure analysis show the length to diameter ratio and distribution curve of nanocrystals and it has been found that the achieved properties of hard layer (growth rate, nano-hardness, nanostructure...) are related to these factors. It was also clarified that these techniques and surface nanocrystallization can be easily achieved in most of metallic materials. Results indicate that the resultant hardened carburized layers exhibited excellent hardness profile. Investigation of the layer characteristics showed strong dependence followed from the treatment experimental parameters as well as the shape of nanocrystals.

  16. Disk Radii and Grain Sizes in Herschel-resolved Debris Disks

    Science.gov (United States)

    Pawellek, Nicole; Krivov, Alexander V.; Marshall, Jonathan P.; Montesinos, Benjamin; Ábrahám, Péter; Moór, Attila; Bryden, Geoffrey; Eiroa, Carlos

    2014-09-01

    The radii of debris disks and the sizes of their dust grains are important tracers of the planetesimal formation mechanisms and physical processes operating in these systems. Here we use a representative sample of 34 debris disks resolved in various Herschel Space Observatory (Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA) programs to constrain the disk radii and the size distribution of their dust. While we modeled disks with both warm and cold components, and identified warm inner disks around about two-thirds of the stars, we focus our analysis only on the cold outer disks, i.e., Kuiper-belt analogs. We derive the disk radii from the resolved images and find a large dispersion for host stars of any spectral class, but no significant trend with the stellar luminosity. This argues against ice lines as a dominant player in setting the debris disk sizes, since the ice line location varies with the luminosity of the central star. Fixing the disk radii to those inferred from the resolved images, we model the spectral energy distribution to determine the dust temperature and the grain size distribution for each target. While the dust temperature systematically increases toward earlier spectral types, the ratio of the dust temperature to the blackbody temperature at the disk radius decreases with the stellar luminosity. This is explained by a clear trend of typical sizes increasing toward more luminous stars. The typical grain sizes are compared to the radiation pressure blowout limit s blow that is proportional to the stellar luminosity-to-mass ratio and thus also increases toward earlier spectral classes. The grain sizes in the disks of G- to A-stars are inferred to be several times s blow at all stellar luminosities, in agreement with collisional models of debris disks. The sizes, measured in the units of s blow, appear to decrease with the luminosity

  17. Disk radii and grain sizes in Herschel-resolved debris disks

    Energy Technology Data Exchange (ETDEWEB)

    Pawellek, Nicole; Krivov, Alexander V. [Astrophysikalisches Institut und Universitätssternwarte, Friedrich-Schiller-Universität Jena, Schillergäßchen 2-3, 07745 Jena (Germany); Marshall, Jonathan P. [School of Physics, University of New South Wales, Sydney NSW 2052 (Australia); Montesinos, Benjamin [Departmento de Astrofísica, Centro de Astrobiología (CAB, CSIC-INTA), ESAC Campus, P.O. Box 78, E-28691 Villanueva de la Cañada, Madrid (Spain); Ábrahám, Péter; Moór, Attila [Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, P.O. Box 67, H-1525 Budapest (Hungary); Bryden, Geoffrey [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Eiroa, Carlos [Departamento de Física Teórica, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, E-28049 Madrid (Spain)

    2014-09-01

    The radii of debris disks and the sizes of their dust grains are important tracers of the planetesimal formation mechanisms and physical processes operating in these systems. Here we use a representative sample of 34 debris disks resolved in various Herschel Space Observatory (Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA) programs to constrain the disk radii and the size distribution of their dust. While we modeled disks with both warm and cold components, and identified warm inner disks around about two-thirds of the stars, we focus our analysis only on the cold outer disks, i.e., Kuiper-belt analogs. We derive the disk radii from the resolved images and find a large dispersion for host stars of any spectral class, but no significant trend with the stellar luminosity. This argues against ice lines as a dominant player in setting the debris disk sizes, since the ice line location varies with the luminosity of the central star. Fixing the disk radii to those inferred from the resolved images, we model the spectral energy distribution to determine the dust temperature and the grain size distribution for each target. While the dust temperature systematically increases toward earlier spectral types, the ratio of the dust temperature to the blackbody temperature at the disk radius decreases with the stellar luminosity. This is explained by a clear trend of typical sizes increasing toward more luminous stars. The typical grain sizes are compared to the radiation pressure blowout limit s {sub blow} that is proportional to the stellar luminosity-to-mass ratio and thus also increases toward earlier spectral classes. The grain sizes in the disks of G- to A-stars are inferred to be several times s {sub blow} at all stellar luminosities, in agreement with collisional models of debris disks. The sizes, measured in the units of s {sub blow}, appear to decrease

  18. Identifying grain-size dependent errors on global forest area estimates and carbon studies

    Science.gov (United States)

    Daolan Zheng; Linda S. Heath; Mark J. Ducey

    2008-01-01

    Satellite-derived coarse-resolution data are typically used for conducting global analyses. But the forest areas estimated from coarse-resolution maps (e.g., 1 km) inevitably differ from a corresponding fine-resolution map (such as a 30-m map) that would be closer to ground truth. A better understanding of changes in grain size on area estimation will improve our...

  19. Test of magnetic susceptibility and grain-size age models of loess

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Ages of the stratigraphic boundary MIS1/2 and MIS3/4 of the Yuanbu loess section in Linxia are used as the basis of the nodal control age. The age of MIS1/2 and MIS3/4 are obtained from the latest international research result-the climatic events recorded in the stalagmite in the Hulu Cave in Nanjing, that MIS1/2 is 11.5 kaB. P. and MIS3/4 is 59.8 kaB.P.. The ages of the two climatic events contain three nodal age control models (Model 1: 0 kaB. P. -59.8 kaB. P.; Model 2: 0 kaB. P. -11.5 kaB. P. and 11.5kaB. P. -59.8 kaB. P.; Model 3: 11.5 kaB. P. -59.8 kaB. P. ), which are used as the nodal control age separately. The deposition times of various stratigraphic horizons are calculated by using the magnetic susceptibility age model and grain-size age model, and then compared with each other. In addition, the AMS14C age, OSL age and the ages of YD and H events are compared with the ages of the corresponding horizons calculated by the three models of nodal control ages. From the analyses of lithologic characters and climatic stages it has been found that both the magnetic susceptibility age model and the grain-size age model have some defects. Because the accurate control ages are selected as the nodal points of the glacial period or interglacial period, the stratigraphic deposition times determined by the high resolution of magnetic susceptibility age model and grain-size age model approximate to the actual ages. As for the relative accuracy of the two age models, the magnetic susceptibility age model is more accurate than the grain-size age model.

  20. The detection of QTLs in barley associated with endosperm hardness, grain density, grain size and malting quality using rapid phenotyping tools.

    Science.gov (United States)

    Walker, Cassandra K; Ford, Rebecca; Muñoz-Amatriaín, María; Panozzo, Joe F

    2013-10-01

    Using a barley mapping population, 'Vlamingh' × 'Buloke' (V × B), whole grain analyses were undertaken for physical seed traits and malting quality. Grain density and size were predicted by digital image analysis (DIA), while malt extract and protein content were predicted using near infrared (NIR) analysis. Validation of DIA and NIR algorithms confirmed that data for QTL analysis was highly correlated (R (2) > 0.82), with high RPD values (the ratio of the standard error of prediction to the standard deviation, 2.31-9.06). Endosperm hardness was measured on this mapping population using the single kernel characterisation system. Grain density and endosperm hardness were significantly inter-correlated in all three environments (r > 0.22, P hardness QTLs were found on 1H, 5H, and 7H. In this study, the majority of the genomic regions associated with grain texture were also coincident with QTLs for grain size, yield, flowering date and/or plant development genes. This study highlights the complexity of genomic regions associated with the variation of endosperm hardness and grain density, and their relationships with grain size traits, agronomic-related traits, and plant development loci.

  1. Determination of hydraulic conductivity from grain-size distribution for different depositional environments.

    Science.gov (United States)

    Rosas, Jorge; Lopez, Oliver; Missimer, Thomas M; Coulibaly, Kapo M; Dehwah, Abdullah H A; Sesler, Kathryn; Lujan, Luis R; Mantilla, David

    2014-01-01

    Over 400 unlithified sediment samples were collected from four different depositional environments in global locations and the grain-size distribution, porosity, and hydraulic conductivity were measured using standard methods. The measured hydraulic conductivity values were then compared to values calculated using 20 different empirical equations (e.g., Hazen, Carman-Kozeny) commonly used to estimate hydraulic conductivity from grain-size distribution. It was found that most of the hydraulic conductivity values estimated from the empirical equations correlated very poorly to the measured hydraulic conductivity values with errors ranging to over 500%. To improve the empirical estimation methodology, the samples were grouped by depositional environment and subdivided into subgroups based on lithology and mud percentage. The empirical methods were then analyzed to assess which methods best estimated the measured values. Modifications of the empirical equations, including changes to special coefficients and addition of offsets, were made to produce modified equations that considerably improve the hydraulic conductivity estimates from grain size data for beach, dune, offshore marine, and river sediments. Estimated hydraulic conductivity errors were reduced to 6 to 7.1 m/day for the beach subgroups, 3.4 to 7.1 m/day for dune subgroups, and 2.2 to 11 m/day for offshore sediments subgroups. Improvements were made for river environments, but still produced high errors between 13 and 23 m/day.

  2. Determination of hydraulic conductivity from grain-size distribution for different depositional environments

    KAUST Repository

    Rosas, Jorge

    2013-06-06

    Over 400 unlithified sediment samples were collected from four different depositional environments in global locations and the grain-size distribution, porosity, and hydraulic conductivity were measured using standard methods. The measured hydraulic conductivity values were then compared to values calculated using 20 different empirical equations (e.g., Hazen, Carman-Kozeny) commonly used to estimate hydraulic conductivity from grain-size distribution. It was found that most of the hydraulic conductivity values estimated from the empirical equations correlated very poorly to the measured hydraulic conductivity values with errors ranging to over 500%. To improve the empirical estimation methodology, the samples were grouped by depositional environment and subdivided into subgroups based on lithology and mud percentage. The empirical methods were then analyzed to assess which methods best estimated the measured values. Modifications of the empirical equations, including changes to special coefficients and addition of offsets, were made to produce modified equations that considerably improve the hydraulic conductivity estimates from grain size data for beach, dune, offshore marine, and river sediments. Estimated hydraulic conductivity errors were reduced to 6 to 7.1m/day for the beach subgroups, 3.4 to 7.1m/day for dune subgroups, and 2.2 to 11m/day for offshore sediments subgroups. Improvements were made for river environments, but still produced high errors between 13 and 23m/day. © 2013, National Ground Water Association.

  3. The origin of bimodal grain-size distribution for aeolian deposits

    Science.gov (United States)

    Lin, Yongchong; Mu, Guijin; Xu, Lishuai; Zhao, Xue

    2016-03-01

    Atmospheric dust deposition is a common phenomenon in arid and semi-arid regions. Bimodal grain size distribution (BGSD) (including the fine component and coarse component) of aeolian deposits has been widely reported. But the origin of this pattern is still debated. Here, we focused on the sedimentary process of modern dust deposition, and analyzed the grain size distribution of modern dust deposition, foliar dust, and aggregation of the aeolian dust collected in Cele Oasis, southern margin of Tarim Basin. The results show that BGSD also appear in a dust deposition. The content of fine components (dust storm is significant less than that from subsequent floating dust. Fine component also varies with altitude. These indicate that modern dust deposition have experienced changing aerodynamic environment and be reworked during transportation and deposition, which is likely the main cause for BGSD. The dusts from different sources once being well-mixed in airflow are hard to form multiple peaks respectively corresponding with different sources. In addition, the dust deposition would appear BGSD whether aggregation or not. Modern dust deposition is the continuation of ancient dust deposition. They both may have the same cause of formation. Therefore, the origin of BGSD should provide a theoretical thinking for reconstructing the palaeo-environmental changes with the indicator of grain size.

  4. New empirical relationship between grain size distribution and hydraulic conductivity for ephemeral streambed sediments

    KAUST Repository

    Rosas, Jorge

    2014-07-19

    Grain size distribution, porosity, and hydraulic conductivity were determined for 39 sediment samples collected from ephemeral streams (wadis) in western Saudi Arabia. The measured hydraulic conductivity values were then compared to values calculated using 20 different empirical equations commonly used to estimate hydraulic conductivity from grain size analyses. It was found that most of the hydraulic conductivity values estimated from the empirical equations correlated very poorly with the measured hydraulic conductivity values. Modifications of the empirical equations, including changes to special coefficients and statistical offsets, were made to produce modified equations that considerably improved the hydraulic conductivity estimates from grain size data for wadi sediments. The Chapuis, Hazen, Kozeny, Slichter, Terzaghi, and Barr equations produced the best correlations, but still had relatively high predictive errors. The Chapius equation was modified for wadi sediments by incorporating mud percentage and the standard deviation (in phi units) into a new equation that reduced the predicted hydraulic conductivity error to ±14.1 m/day. The equation is best applied to ephemeral stream samples that have hydraulic conductive values greater than 2 m/day.

  5. The Influence of Grain Size and Crystal Content on Rheology and Deformation of Pyroclastic Material

    Science.gov (United States)

    Paquereau-Lebti, P.; Robert, G.; Grunder, A. L.; Russell, K. J.

    2007-12-01

    Pyroclastic deposits undergo variable degrees of sintering, viscous deformation of particles and loss of pore space, which combine to produce the dramatic textural variations that define welded facies. We here investigate the effects of grain size and crystal content on the rheology and welding of pyroclastic material.Uniaxial deformation experiments were conducted using sintered cores of natural rhyolite ash under conditions consistent with welding. Experiments were done in the University of British Columbia Volcanology Deformation Rig (VDR). This apparatus is designed to run experiments relevant to volcanology, by supporting low-load, high temperature, deformation experiments (Quane et al., 2004). We ran experiments at constant displacement rate (2.5.10-6 m.s-1), under ambient water pressure ("Dry"), at temperatures of 850 and 900°C and to maximal strain of 50%. Grain-size effect was investigated using sintered cores from three different sieving fractions of Rattlesnake Tuff (RST, Eastern Oregon, USA) ash: fine ash (grain size 15% crystal content inhibited sintering in a sample that welded under the same experimental conditions when phenocryst depleted (phenocryst content around 1% in whole Rattlesnake Tuff ash). Reference: Quane, S.L., Russell, J.K., and Kennedy, L.A. (2004). A low-load, high-temperature deformation apparatus for volcanological studies. American mineralogist, 89, 873-877.

  6. Energy saving cement production by grain size optimisation of the raw meal

    Directory of Open Access Journals (Sweden)

    B. Simons

    Full Text Available The production of cement clinker is an energy consuming process. At about 50% of the energy is associated with grinding and milling of the raw meal, that normally is in the range 100% <200 μm with 90% <90 μm. Question: is it possible to use coarser components of the raw meal without reducing the clinker quality. With synthetic raw meals of various grain sizes the clinker formation was studied at static (1100 - 1450°C and dynamic conditions (heating microscope. A routine to adjust the grain size of the components for industrial raw meals is developed. The fine fraction <90 μm should mainly contain the siliceous and argileous components, whereas the calcitic component can be milled separately to a grain size between 200-500 μm, resulting in lower energy consumption for milling. Considering the technical and economical realizability the relation fine/coarse should be roughly 1:1. The energy for milling can be reduced significantly, that in addition leads to the preservation of natural energy resources.

  7. Computer program for the calculation of grain size statistics by the method of moments

    Science.gov (United States)

    Sawyer, Michael B.

    1977-01-01

    A computer program is presented for a Hewlett-Packard Model 9830A desk-top calculator (1) which calculates statistics using weight or point count data from a grain-size analysis. The program uses the method of moments in contrast to the more commonly used but less inclusive graphic method of Folk and Ward (1957). The merits of the program are: (1) it is rapid; (2) it can accept data in either grouped or ungrouped format; (3) it allows direct comparison with grain-size data in the literature that have been calculated by the method of moments; (4) it utilizes all of the original data rather than percentiles from the cumulative curve as in the approximation technique used by the graphic method; (5) it is written in the computer language BASIC, which is easily modified and adapted to a wide variety of computers; and (6) when used in the HP-9830A, it does not require punching of data cards. The method of moments should be used only if the entire sample has been measured and the worker defines the measured grain-size range. (1) Use of brand names in this paper does not imply endorsement of these products by the U.S. Geological Survey.

  8. Effect of grain size on high-temperature oxidation behavior of Cu-80Ni alloy

    Institute of Scientific and Technical Information of China (English)

    曹中秋; 牛焱; 曹丽杰; 吴维(山又)

    2003-01-01

    The thermogravimetric analysis of binary Cu-80Ni alloys prepared respectively by conventional casting(CA) and mechanical alloying(MA) techniques and presenting widely different grain sizes was performed at 800 ℃ in air in order to study the effect of grain size change on the oxidation behavior of a solid solution alloy. The results show that the kinetic curves for the oxidation of the two alloys are complex and deviate from the parabolic rate law and usually are not composed of a single stage. Mixed scales were produced on the CACu-80Ni alloy surface, which consists of a mixture of copper and nickel oxides. However, oxide scale for MACu-80Ni alloy is mainly composed of a thick compact and continuous inner layer of nickel oxide. The reduction in the alloy grain size speeds up the diffusion of the more reactive component nickel from the alloy to alloy/oxide scale interface and completes the transition from a mixed scale to continuous scale of nickel oxide.

  9. How well does end-member modelling analysis of grain size data work?

    Science.gov (United States)

    Schulte, Philipp; Dietze, Michael; Dietze, Elisabeth

    2014-05-01

    End-member modelling analysis (EMMA) is a powerful and flexible statistic approach to identify and quantify generic sediment transport processes from multimodal grain-size distributions. EMMA has been introduced over 15 years ago and is now available in different approaches as encapsulated FORTRAN code (Weltje, 1997), Matlab-script (Dietze et al., 2012) and the R-package EMMAgeo (Dietze and Dietze, 2013). EMMA was mainly used to reconstruct past sedimentation processes in a variety of sedimentary environments (marine, aeolian, lacustrine). Typically, it is rather difficult to assess how meaningful and well the model performs in a certain environment, since neither the actual process end-members (generic grain-size distributions sorted by a certain sediment transport) nor their individual contributions to each sample are known a priori. To allow a comprehensive performance test, we sampled a set of four known process end-members: alluvial sand (main mode: 0.70±0.55 φ), dune sand (main mode: 1.35±0.60 φ), loess (main mode: 4.71±0.65 φ) and overbank deposit (main mode: 5.81±1.62 φ). High resolution grain-size information is based on laser-diffraction analysis (116 classes). The four process end-members were artificially mixed with random, but known proportions to yield 100 samples. This mixed data set was measured again with the laser particle size analyser and served as input for EMMA within the R-package EMMAgeo. This contribution discusses the ability of EMMA to identify and characterise the four distinct process end-members and quantify their contributions to each sample. Different ways to estimate uncertainties are presented. Further evaluations focus on the influence of numbers of included samples, numbers of grain-size classes, vertical mixing of samples (simulating turbation) and self-similarity of process end-members. Dietze E, et al. 2012. An end-member algorithm for deciphering modern detrital processes from lake sediments of Lake Donggi Cona, NE

  10. Can we use only Grain Size Data for Paleo-Flow Reconstructions?

    Science.gov (United States)

    Perillo, M. M.; Pohl, F.; Eggenhuisen, J. T.; Fedele, J.; Hoyal, D. C. J. D.; Mohrig, D. C.

    2015-12-01

    Paleo-flow and paleo-environmental reconstruction from ancient deposits is a critical task for earth surface scientists interested in the sedimentary record. Forming processes are commonly interpreted from the architectural characteristics of sedimentary deposits using quantitative relationships derived from experiments or geomorphic studies. However, very little attention has been paid to the equivalent problem at the scale of micro-facies: can we interpret the conditions at the time of sediment accumulation from grain size information in a small sample? Here we investigate the use of grain size distributions alone to reconstruct the flow conditions based on a set of experiments conducted in a 2D flume tank in the Eurotank facilities at Utrecht University. The experiments are designed for the examination of grain size distributions within sediments which were deposited by flows with known conditions (e.g. velocity, turbulence, shear velocity, concentration). By changing the slope of the flume tank we were able to create a range of flows from strongly depositional (depletive) to bypassing. Inspired by Eastwood et al (2012), we propose a working methodology to link the grain size distribution of the deposit to flow conditions. Our method utilizes the following empiric relations: i) the finer fraction of the deposit was deposited while most of that range surpass the Bagnold (1966)'s suspension threshold (shear velocity υ* approx. 3 times the settling velocity ωs); ii) the mean fraction was at incipient suspension stage (υ* ~ ωs); iii) the finer portion of the coarser grains were at bedload/saltation stage, where u* is approx. υ*c (critical shear velocity for initiation of motion); and iv) the coarser portion of the coarser grains were at creep-bedload stage, where υ* is approx. 0.7υ*c . We test whether this set of rules can be applied to the probability distribution function of deposit grainsize in an inversion that converges on a single value for the shear

  11. Only pick the right grains: Modelling the bias due to subjective grain-size interval selection for chronometric and fingerprinting approaches.

    Science.gov (United States)

    Dietze, Michael; Fuchs, Margret; Kreutzer, Sebastian

    2016-04-01

    Many modern approaches of radiometric dating or geochemical fingerprinting rely on sampling sedimentary deposits. A key assumption of most concepts is that the extracted grain-size fraction of the sampled sediment adequately represents the actual process to be dated or the source area to be fingerprinted. However, these assumptions are not always well constrained. Rather, they have to align with arbitrary, method-determined size intervals, such as "coarse grain" or "fine grain" with partly even different definitions. Such arbitrary intervals violate principal process-based concepts of sediment transport and can thus introduce significant bias to the analysis outcome (i.e., a deviation of the measured from the true value). We present a flexible numerical framework (numOlum) for the statistical programming language R that allows quantifying the bias due to any given analysis size interval for different types of sediment deposits. This framework is applied to synthetic samples from the realms of luminescence dating and geochemical fingerprinting, i.e. a virtual reworked loess section. We show independent validation data from artificially dosed and subsequently mixed grain-size proportions and we present a statistical approach (end-member modelling analysis, EMMA) that allows accounting for the effect of measuring the compound dosimetric history or geochemical composition of a sample. EMMA separates polymodal grain-size distributions into the underlying transport process-related distributions and their contribution to each sample. These underlying distributions can then be used to adjust grain-size preparation intervals to minimise the incorporation of "undesired" grain-size fractions.

  12. DUST DYNAMICS IN PROTOPLANETARY DISK WINDS DRIVEN BY MAGNETOROTATIONAL TURBULENCE: A MECHANISM FOR FLOATING DUST GRAINS WITH CHARACTERISTIC SIZES

    Energy Technology Data Exchange (ETDEWEB)

    Miyake, Tomoya; Suzuki, Takeru K.; Inutsuka, Shu-ichiro, E-mail: miyake.tomoya@e.mbox.nagoya-u.ac.jp, E-mail: stakeru@nagoya-u.jp [Department of Physics, Nagoya University, Nagoya, Aichi 464-8602 (Japan)

    2016-04-10

    We investigate the dynamics of dust grains of various sizes in protoplanetary disk winds driven by magnetorotational turbulence, by simulating the time evolution of the dust grain distribution in the vertical direction. Small dust grains, which are well-coupled to the gas, are dragged upward with the upflowing gas, while large grains remain near the midplane of a disk. Intermediate-size grains float near the sonic point of the disk wind located at several scale heights from the midplane, where the grains are loosely coupled to the background gas. For the minimum mass solar nebula at 1 au, dust grains with size of 25–45 μm float around 4 scale heights from the midplane. Considering the dependence on the distance from the central star, smaller-size grains remain only in an outer region of the disk, while larger-size grains are distributed in a broader region. We also discuss the implications of our result for observations of dusty material around young stellar objects.

  13. Superb nanocrystalline alloys for plating

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    @@ With high rigidity and antiwear performance,nanocrystalline metals and their alloys can find wide applications in surface protection.However, the existence of grain boundaries often leads to erosive micro-batteries which accelerate the process of corrosion.Therefore, it has already become a key issue for surface engineering researchers to find nano materials with higher lubricating, anticorrosion and antiwear capacities.

  14. Effects of particle optical properties on grain size measurements of aeolian dust deposits

    Science.gov (United States)

    Varga, György; Újvári, Gábor; Kovács, János; Szalai, Zoltán

    2015-04-01

    Particle size data are holding crucial information on the sedimentary environment at the time the aeolian dust deposits were accumulated. Various aspects of aeolian sedimentation (wind strength, distance to source(s), possible secondary source regions and modes of sedimentation and transport) can be reconstructed from proper grain size distribution data. Laser diffraction methods provide much more accurate and reliable information on the major granulometric properties of wind-blown sediments compared to the sieve and pipette methods. The Fraunhofer and Mie scattering theories are generally used for laser diffraction grain size measurements. () The two different approaches need different 'background' information on the medium measured. During measurements following the Fraunhofer theory, the basic assumption is that parcticles are relatively large (over 25-30 µm) and opaque. The Mie theory could offer more accurate data on smaller fractions (clay and fine silt), assuming that a proper, a'priori knowledge on refraction and absorption indices exists, which is rarely the case for polymineral samples. This study is aimed at determining the effects of different optical parameters on grain size distributions (e.g. clay-content, median, mode). Multiple samples collected from Hungarian red clay and loess-paleosol records have been analysed using a Malvern Mastersizer 3000 laser diffraction particle sizer (with a Hydro LV unit). Additional grain size measurements have been made on a Fritsch Analysette 22 Microtec and a Horiba Partica La-950 v2 instrument to investigate possible effects of the used laser sources with different wavelengths. XRF and XRD measurements have also been undertaken to gain insight into the geochemical/mineralogical compositions of the samples studied. Major findings include that measurements using the Mie theory provide more accurate data on the grain size distribution of aeolian dust deposits, when we use a proper optical setting. Significant

  15. Debris flow grain size scales with sea surface temperature over glacial-interglacial timescales

    Science.gov (United States)

    D'Arcy, Mitch; Roda Boluda, Duna C.; Whittaker, Alexander C.; Araújo, João Paulo C.

    2015-04-01

    Debris flows are common erosional processes responsible for a large volume of sediment transfer across a range of landscapes from arid settings to the tropics. They are also significant natural hazards in populated areas. However, we lack a clear set of debris flow transport laws, meaning that: (i) debris flows remain largely neglected by landscape evolution models; (ii) we do not understand the sensitivity of debris flow systems to past or future climate changes; and (iii) it remains unclear how to interpret debris flow stratigraphy and sedimentology, for example whether their deposits record information about past tectonics or palaeoclimate. Here, we take a grain size approach to characterising debris flow deposits from 35 well-dated alluvial fan surfaces in Owens Valley, California. We show that the average grain sizes of these granitic debris flow sediments precisely scales with sea surface temperature throughout the entire last glacial-interglacial cycle, increasing by ~ 7 % per 1 ° C of climate warming. We compare these data with similar debris flow systems in the Mediterranean (southern Italy) and the tropics (Rio de Janeiro, Brazil), and find equivalent signals over a total temperature range of ~ 14 ° C. In each area, debris flows are largely governed by rainfall intensity during triggering storms, which is known to increase exponentially with temperature. Therefore, we suggest that these debris flow systems are transporting predictably coarser-grained sediment in warmer, stormier conditions. This implies that debris flow sedimentology is governed by discharge thresholds and may be a sensitive proxy for past changes in rainfall intensity. Our findings show that debris flows are sensitive to climate changes over short timescales (≤ 104 years) and therefore highlight the importance of integrating hillslope processes into landscape evolution models, as well as providing new observational constraints to guide this. Finally, we comment on what grain size

  16. Effect of grain size on optical transmittance of birefringent polycrystalline ceramics

    Science.gov (United States)

    Wen, Tzu-Chien

    Polycrystalline ceramics are increasingly used for fabricating windows and domes for the mid infra-red regime (3-5 mum) due to their superior durability as compared to glass and the lower cost of their fabrication and finishing relative to single crystals without significant compromise in optical properties. Due to the noncubic structure, MgF2 and Al2O3 are birefringent ceramics. Birefringence causes scatter of light at the grain boundaries and diminishes in-line transmittance and optical performance. This dissertation presents experimental results and analyses of the grain-size and wavelength dependence of the in-line transmittance of polycrystalline MgF2 and Al2O3. Chapter 2 presents experimental results and analyses of light transmission in polycrystalline MgF2 as a function of the mean grain size at different wavelengths. The scattering coefficient of polycrystalline MgF 2 increased linearly with the mean grain size and inversely with the square of the wavelength of light. These trends are consistent with theoretical models based on both a limiting form of the Raleigh-Gans-Debye theory of particle scattering and light retardation theories that take refractive-index variations along the light path. Chapter 3 investigates the applicability of particle light scattering theories to light attenuation in birefringent polycrystalline ceramics by measuring light transmittance in a model two-phase system. The system consisted of microspheres of silica dispersed in a solution of glycerol in water. It was found that RGD theory showed the systematic deviation for higher particle volume fraction (φ > 0.2) and larger particle size (d p > 1 mum). This result suggested that light scattering models based on single particle scattering are unlikely to provide viable physical explanation for the effect of grain size on light transmittance in birefringent polycrystalline ceramics due to the high volume fraction in dense polycrystalline ceramics. Chapter 4 analyses light

  17. Determination of the total grain size distribution in a vulcanian eruption column, and its implications to stratospheric aerosol perturbation

    Science.gov (United States)

    Murrow, P. J.; Rose, W. I., Jr.; Self, S.

    1980-11-01

    The total grain distribution of tephra from the eruption by the Fuego volcano in Guatemala on Oct. 14, 1974 was determined by grain size analysis. The region within each isopach has a grain distribution which was weighted proportionally to its percentage volume; the total distribution had a median grain size of 0.6 mm and a sorting coefficient of 2.3. The ash composed of fine particles did not fall in the volcano area as part of the recognizable tephra blanket; the eruption column reached well into the stratosphere to the height of 10-12 km above sea level, with mass flux rate estimated altitudes of 18-23 km

  18. The effect of oxide particles on the strength and ductility of bulk iron with a bimodal grain size distribution

    Energy Technology Data Exchange (ETDEWEB)

    Casas, C.; Tejedor, R. [Department of Materials Science and Metallurgical Engineering, ETSEIB, Universitat Politècnica de Catalunya, Av. Diagonal 647, 08028 Barcelona (Spain); Rodríguez-baracaldo, R. [Department of Mechanical Engineering, Universidad Nacional de Colombia, Bogotá. Colombia (Colombia); Benito, J.A., E-mail: Josep.a.benito@upc.edu [Department of Materials Science and Metallurgical Engineering, EUETIB, Universitat Politècnica de Catalunya, Comte d' Urgell 187, 08036 Barcelona (Spain); Fundació CTM Centre Tecnològic de Manresa, Plaça de la Ciencia, 2, 08243 Manresa (Spain); Cabrera, J.M. [Department of Materials Science and Metallurgical Engineering, ETSEIB, Universitat Politècnica de Catalunya, Av. Diagonal 647, 08028 Barcelona (Spain); Fundació CTM Centre Tecnològic de Manresa, Plaça de la Ciencia, 2, 08243 Manresa (Spain)

    2015-03-11

    The strength and ductility of bulk nanostructured and ultrafine-grained iron containing 0.39% oxygen by weight was determined by tensile tests. Samples were obtained by consolidation of milled iron powder at 500 °C. Heat treatments were designed to cover a wide range of grain sizes spanning from 100 to 2000 nm with different percentages of coarse and nanostructured grain areas, which was defined as a bimodal grain size distribution. Transmission electron microscopy was used to determine the diameter, volume fraction and location of oxides in the microstructure. The strength was analysed following two approaches. The first one was based on the strong effect of oxides and involved the use of a mixed particle-grain boundary strengthening model, and the second one was based on simple grain boundary strengthening. The mixed model underestimated the strength of nanostructured samples, whereas the simple grain boundary model worked better. However, for specimens with a bimodal grain size, the fitting of the mixed model was better. In this case, the more effective particle strengthening was related to the dispersion of oxides inside the large ferrite grains. In addition, the bimodal samples showed an acceptable combination of strength and ductility. Again, the ferrite grains containing oxides promoted strain hardening due to the increase in dislocation activity.

  19. Light emission, light detection and strain sensing with nanocrystalline graphene.

    Science.gov (United States)

    Riaz, Adnan; Pyatkov, Feliks; Alam, Asiful; Dehm, Simone; Felten, Alexandre; Chakravadhanula, Venkata S K; Flavel, Benjamin S; Kübel, Christian; Lemmer, Uli; Krupke, Ralph

    2015-08-14

    Graphene is of increasing interest for optoelectronic applications exploiting light detection, light emission and light modulation. Intrinsically, the light-matter interaction in graphene is of a broadband type. However, by integrating graphene into optical micro-cavities narrow-band light emitters and detectors have also been demonstrated. These devices benefit from the transparency, conductivity and processability of the atomically thin material. To this end, we explore in this work the feasibility of replacing graphene with nanocrystalline graphene, a material which can be grown on dielectric surfaces without catalyst by graphitization of polymeric films. We have studied the formation of nanocrystalline graphene on various substrates and under different graphitization conditions. The samples were characterized by resistance, optical transmission, Raman and x-ray photoelectron spectroscopy, atomic force microscopy and electron microscopy measurements. The conducting and transparent wafer-scale material with nanometer grain size was also patterned and integrated into devices for studying light-matter interaction. The measurements show that nanocrystalline graphene can be exploited as an incandescent emitter and bolometric detector similar to crystalline graphene. Moreover the material exhibits piezoresistive behavior which makes nanocrystalline graphene interesting for transparent strain sensors.

  20. Microplastics in the Mediterranean Sea: Deposition in coastal shallow sediments, spatial variation and preferential grain size.

    Science.gov (United States)

    Alomar, Carme; Estarellas, Fernando; Deudero, Salud

    2016-04-01

    Marine litter loads in sea compartments are an emergent issue due to their ecological and biological consequences. This study addresses microplastic quantification and morphological description to test spatial differences along an anthropogenic gradient of coastal shallow sediments and further on to evaluate the preferential deposition of microplastics in a given sediment grain fraction. Sediments from Marine Protected Areas (MPAs) contained the highest concentrations of microplastics (MPs): up to 0.90 ± 0.10 MPs/g suggesting the transfer of microplastics from source areas to endpoint areas. In addition, a high proportion of microplastic filaments were found close to populated areas whereas fragment type microplastics were more common in MPAs. There was no clear trend between sediment grain size and microplastic deposition in sediments, although microplastics were always present in two grain size fractions: 2 mm > x > 1 mm and 1 mm > x 0.5 mm.

  1. Influence of grain size and exchange interaction on the LLB modeling procedure

    Science.gov (United States)

    Vogler, Christoph; Abert, Claas; Bruckner, Florian; Suess, Dieter; Praetorius, Dirk

    2016-12-01

    Reliably predicting bit-error rates in realistic heat-assisted magnetic recording simulations is a challenging task. Integrating the Landau-Lifshitz-Bloch (LLB) equation, within a coarse graining approach, can reduce the computational effort to determine the magnetization dynamics in the vicinity of the Curie temperature, compared to solving the atomistic Landau-Lifshitz-Gilbert equation. If the aim is that the dynamics of both approaches coincide, temperature dependent material functions, such as the zero-field equilibrium magnetization as well as the parallel and normal susceptibilities, must be modeled carefully in order to use them as input in the LLB equation. We present an extensive study on how these functions depend on grain size and exchange interactions. We show that, if the size or the exchange constant of a reference grain is modified, the material functions can be scaled, according to the changed Curie temperature, yielding negligible errors. This is shown to be valid for volume changes of up to ±40% and variations of the exchange constant of up to ±10%. Besides the temperature dependent material curves, computed switching probabilities also agree well with probabilities separately determined for each system. Our study suggests that there is no need to recalculate the required LLB input functions for each particle. Within the presented limits, it is sufficient to scale them to the Curie temperature of the altered system.

  2. DEPENDENCE OF GRAIN SIZE OF AUSTENITE STEEL OF RAILWAY WHEEL FROM PARAMETERS OF HOT DEFORMATION

    Directory of Open Access Journals (Sweden)

    L. I. Vakulenko

    2015-03-01

    Full Text Available Purpose. The estimation of heat temperature influence and degree of hot reduction of carbon steel on the size of grain аustenite at making of railway wheels. Methodology. The material for research was carbon steel, mark 60 with carbon content of 0,55 and 0,65 %, selected from the fragments of railway wheels. The size of grain аustenite depending on a temperature (from 800 to 1 150 ºC and degrees of hot deformation (10−50 % was determined. The size of grain was determined under a light microscope with the use of quantitative metallography methods. Findings. The use of cooling in the process of hot reduction of the railway wheel will allow dispergating the structure of аustenite on large distances from the surface of the rim. The reason for this is that the volumes of metal after cooling have an increased strength and will be exposed in less degree to the plastic deformation. To compare the cooling layers near-by with the surface of rim, they are more warmed-up in internal volumes of metal. In the conditions of continuity of plastic deformation distribution, having a high temperature, they will be exposed to the reduction on the large total degree of deformation. In consequence of the resulted decisions more even austenitic structure must be formed on the section of rim of railway wheel. To obtain the effect of disperse grain of аustenite at making of the whole-rolled railway wheels it is necessary to decrease the heat temperature of billet under rolling or increase the degree of reduction on the lasts stages of shape-generating deformation. The pause by duration of 1,5 min. after reduction of 20 % at a temperature 950 ºC is sufficiently for processes completion of dynamic and static recrystalization of аustenite carbon steel of the railway wheel. Originality. Increase of plastic deformation degree, especially in the central volumes of rim is accompanied by the decrease of heterogeneity of austenitic structure on his section. The

  3. Experimental investigation of dynamic effects in capillary pressure: Grain size dependency and upscaling

    Science.gov (United States)

    Camps-Roach, Geremy; O'Carroll, Denis M.; Newson, Timothy A.; Sakaki, Toshihiro; Illangasekare, Tissa H.

    2010-08-01

    The macroscopic flow equations used to predict two-phase flow typically utilizes a capillary pressure-saturation relationship determined under equilibrium conditions. Theoretical reasoning, experimental evidence, and numerical modeling results have indicated that when one fluid phase replaces another fluid, this relationship may not be unique but may depend on the rate at which the phase saturations change in response to changes in phase pressures. This nonuniqueness likely depends on a variety of factors including soil-fluid properties and possibly physical scale. To quantify this dependency experimentally, direct measurements of equilibrium and dynamic capillary pressure-saturation relationships were developed for two Ottawa sands with different grain sizes using a 20 cm long column. A number of replicate air-water experiments were conducted to facilitate statistical comparison of capillary pressure-saturation relationships. Water and air pressures and phase saturations were measured at three different vertical locations in the sand column under different desaturation rates (1) to measure local capillary pressure-saturation relationships (static and dynamic); (2) to quantify the dynamic coefficient τ, a measure of the magnitude of observed dynamic effects, as a function of water saturation for different grain sizes and desaturation rates; (3) to investigate the importance of grain size on measured dynamic effects; and (4) to assess the importance of sample scale on the magnitude of dynamic effects in capillary pressure. A comparison of the static and dynamic Pc-Sw relationships showed that at a given water saturation, capillary pressure measured under transient water drainage conditions is statistically larger than capillary pressure measured under equilibrium or static conditions, consistent with thermodynamic theory. The dynamic coefficient τ, used in the expression relating the static and dynamic capillary pressures to the desaturation rate was dependant on

  4. The effect of grain size and phosphorous-doping of polycrystalline 3C-SiC on infrared reflectance spectra

    Energy Technology Data Exchange (ETDEWEB)

    Rooyen, I.J. van, E-mail: Isabella.vanRooyen@inl.gov [Fuel Performance and Design Department, Idaho National Laboratory, Idaho Falls, ID 83415-6188 (United States); Department of Physics, Nelson Mandela Metropolitan University, Port Elizabeth (South Africa); Engelbrecht, J.A.A. [Department of Physics, Nelson Mandela Metropolitan University, Port Elizabeth (South Africa); Henry, A.; Janzen, E. [Department of Physics, Chemistry and Biology, Semiconductor Materials, Linkoeping University, Linkoeping 58183 (Sweden); Neethling, J.H. [Department of Physics, Nelson Mandela Metropolitan University, Port Elizabeth (South Africa); Rooyen, P.M. van [Philip M van Rooyen Network Consultants, Midlands Estates (South Africa)

    2012-03-15

    Highlights: Black-Right-Pointing-Pointer IR is investigated as a technique to measure grain size and P-doping of polycrystalline SiC. Black-Right-Pointing-Pointer Infrared plasma minima can be used to determine doping levels in 3C-SiC for doping levels greater than 5 Multiplication-Sign 10{sup 17} cm{sup -3}. Black-Right-Pointing-Pointer A linear relationship is found between FWHM and the inverse of grain size of 3C-SiC irrespective of P-doping level. Black-Right-Pointing-Pointer It is further found that {omega}{sub p} is not influenced by the grain size. Black-Right-Pointing-Pointer P-doping level has no significant effect on the linear relationship between grain size and surface roughness. - Abstract: The effect of P-doping and grain size of polycrystalline 3C-SiC on the infrared reflectance spectra is reported. The relationship between grain size and full width at half maximum (FWHM) suggest that the behavior of the 3C-SiC with the highest phosphorous doping level (of 1.2 Multiplication-Sign 10{sup 19} at. cm{sup -3}) is different from those with lower doping levels (<6.6 Multiplication-Sign 10{sup 18} at. cm{sup -3}). It is also further demonstrated that the plasma resonance frequency ({omega}{sub p}) is not influenced by the grain size.

  5. Effect of grain size on the mechanical properties of dual phase Fe/Si/C steels

    Energy Technology Data Exchange (ETDEWEB)

    Ahn, J.H.

    1983-08-01

    For an Fe/2Si/0.1C steel with an intermediate quenching heat treatment, it was found that as the prior austenite grain size is refined, significant improvements in total elongation, reduction in area and impact toughness can be achieved, while uniform elongation, yield and tensile strengths are not affected. These improvements are analyzed in terms of microstructure and fracture characteristics. The cleavage cracks propagate nearly straight without deviation at the ferrite/martensite interfaces within the sub-units of the DFM structure, but change their path at high angle sub-unit boundaries. The crack is less likely to be deflected at the ferrite/martensite interface because the interface is coherent. Comparison of optical micrographs and SEM fractographs has shown that there is close agreement between the sub-unit size and cleavage facet size. The observations lead to the conclusion that the sub-unit size is the basic microstructure unit controlling the fracture behavior of DFM steels produced by the intermediate quenching heat treatment. A controlled rolling process was undertaken to obtain grain refined DFM steels. Results showed that this produces micro-duplex structures with attractive mechanical properties in an economicl way.

  6. The potential for adaptive evolution of pollen grain size in Mimulus guttatus.

    Science.gov (United States)

    Lamborn, Ellen; Cresswell, James E; Macnair, Mark R

    2005-07-01

    We tested whether pollen grain size (PGS) shows heritable variation in three independent populations of Mimulus guttatus by imposing artificial selection for this character. In addition, we looked for correlated responses to selection in a range of 15 other floral characters. Heritable variation in PGS was found in all three populations, with heritabilities of between 19 and 40% (average 30%). After three generations, upward and downward lines differed on average by 30% in pollen volume. No consistent patterns of correlated response were found in other characters, indicating that PGS can respond to selective forces acting on PGS alone. Possible selection mechanisms on PGS in this species could include intermale selection, if large pollen grains produce more competitive gametophytes; or optimization of patterns of resource allocation, if local mate competition varies.

  7. Influence of grain size, shape and compaction on georadar waves: example of an Aeolian dune

    CERN Document Server

    Guillemoteau, Julien; Dujardin, Jean-Rémi; 10.1111/j.1365-246X.2012.05577.x

    2012-01-01

    Many Ground Penetrating Radar (GPR) profiles acquired in dry aeolian environment have shown good reflectivity inside present-day dunes. We show that the origin of this reflectivity is related to changes in grain size distribution, packing and/or grain shape in a sandy material. We integrate these three parameters into analytical models for bulk permittivity in order to predict the reflections and the velocity of GPR waves. We consider two GPR cross-sections acquired over Aeolian dunes in the Chadian desert. The 2D migration of GPR data suggests that dunes contain different kinds of bounding surfaces. We discuss and model three kinds of reflections using reasonable geological hypothesis about Aeolian sedimentation processes. The propagation and the reflection of radar waves are calculated using the 1D wavelet modelling method in spectral domain. The results of the forward modelling are in good accordance with real observed data.

  8. Location, Identification, and Size Distribution of Depleted Uranium Grains in Reservoir Sediments

    Science.gov (United States)

    Lo, D.; Fleischer, R. L.; Albert, E. A.; Arnason, J. G.

    2006-05-01

    The location, isotopic composition, and size distribution of uranium-rich grains in sediment layers can be identified by analysis of etched particle tracks. Samples are pressed against track detectors, irradiated with thermal neutrons, and the detectors are chemically etched to reveal fission tracks. The total track abundance from the sample is a measure of the U-235 content; hence, if the bulk uranium (mostly U-238) has been measured, the two sets of results give the depletion or enrichment of the uranium. Each uranium-rich particle produces a sunburst of tracks where the number of tracks is proportional to the size of the particle. From 1958 to 1984, National Lead Industries processed depleted uranium (DU) at its plant in Colonie, NY (just west of Albany). Radioactive materials, principally DU, that were emitted from its exhaust stacks have been found 40 km away (Dietz, 1981). We have studied a sediment core taken by Arnason and Fletcher (2003, 2004) from a small body of water, the Patroon Reservoir, which is 1 km east-southeast of the National Lead plant. Examination of portions of that core demonstrates the usefulness of induced nuclear tracks (1) to locate microscopic high-uranium grains for further mineralogical study ; (2) to determine the size distribution of uranium grains; and (3) to help analyze the average isotopic depletion of the uranium when total U concentrations are known. We infer that the size of DU particles in the sediment was controlled by both atmospheric transport from stack to reservoir and fluvial transport within the reservoir.

  9. Beyond the threshold for motion: river channel geometry and grain size reflect sediment supply

    Science.gov (United States)

    Pfeiffer, A.; Finnegan, N. J.; Willenbring, J. K.

    2016-12-01

    In many gravel-bedded rivers, floods that fill the ch­­annel banks create just enough shear stress to move the median-sized gravel particles on the bed surface (D50). Because this observation is common and is supported by theory, the coincidence of bankfull flow and the incipient motion of D50 has become a­­ commonly employed assumption. However, not all natural gravel channels actually conform to this simple relationship; some channels maintain bankfull stresses far in excess of the critical stress required to initiate sediment transport. We use a database of >300 gravel-bedded rivers and >600 10Be-derived erosion rates from across North America to explore the hypothesis that sediment supply drives the magnitude of bankfull shear stress relative to the critical stress required to mobilize the median bed surface grain size. We find that the ratio of bankfull to critical stress is significantly higher in West Coast river reaches (2.47, n= 84) than in river reaches in the rest of the continent (1.03, n = 245). This pattern parallels trends in erosion rates (and hence sediment supplies). Supporting our hypothesis, we find a significant correlation between upstream erosion rate and local τ*bf/τ*c at sites where this comparison is possible. Our analysis reveals a decrease in bed surface armoring with increasing τ*bf/τ*c, suggesting that channels accommodate changes in sediment supply through adjustments in bed surface grain size, as predicted through numerical modeling. Our findings demonstrate that sediment supply is encoded in the bankfull hydraulic geometry of gravel-bedded channels through its control on bed surface grain size.

  10. High strength and high ductility in as-deposited nanocrystalline Ni

    Energy Technology Data Exchange (ETDEWEB)

    Dai Pinqiang; Xu Weichang; Tang Dian, E-mail: pqdai@126.co [School of Materials Science and Engineering, Fuzhou University, Fuzhou 350108 (China)

    2010-07-01

    In the present study, an electrodeposited nanocrystalline (nc) Ni sample with high strength and superior ductility relative to many other electrodeposited nc-Ni was prepared. The superior ductility in the present nc-Ni sample free of defects was ascribed to mixed grains, the size of which spanned nano- and sub-micro scales at its as-deposited state with a grain size distribution ranged from 5 to 120nm. Obvious dislocation motion happening in coarse-grained polycrystalline was observed in large grains of nc-Ni matrix resulting in a remarkable enhanced ductility without a decrease in the strength. The present nc-Ni with an average grain size of 27.2nm prepared by direct current electrodeposition shows the average ultimate tensile strength of 1200MPa and the average elongation to failure of 10.4%.

  11. Five-fold twin formation during annealing of nanocrystalline Cu

    Energy Technology Data Exchange (ETDEWEB)

    Bringa, E M; Farkas, D; Caro, A; Wang, Y M; McNaney, J; Smith, R

    2009-05-20

    Contrary to the common belief that many-fold twins, or star twins, in nanophase materials are due to the action of significant external stresses, we report molecular dynamics simulations of annealing in 5 nm grain size samples annealed at 800 K for nearly 0.5 nsec at 0 external pressure showing the formation of five-fold star twins during annealing under the action of the large internal stresses responsible for grain growth and microstructural evolution. The structure of the many-fold twins is remarkably similar to those we have found to occur under uniaxial shock loading, of samples of nanocrystalline NiW with a grain size of {approx}5-30 nm. The mechanism of formation of the many-fold twins is discussed in the light of the simulations and experiments.

  12. Properties and processing of nanocrystalline materials. Quarterly report

    Energy Technology Data Exchange (ETDEWEB)

    Valiev, R.Z.

    1996-01-22

    The present Report completes the investigations in the frame of the project for the first year. It is important to estimate our achievements in the investigation of properties of nanocrystalline materials obtained by severe plastic deformation and their production. We think that the main results obtained can be summarized as follows: (1) We performed an improvement of the die-set for equal channel (ECA) pressing and torsion under high pressure with the aim to increase dimensions of the samples produced and to conduct processing of low ductile materials. (2) It was established that in pure metals severe plastic deformation led to the formation of an ultra fine-grained structure with a mean grain size of 100-200 nm, while in alloys due to severe plastic deformation and/or special methods of treatment (a decrease in the temperature of deformation, an increase of the pressure applied etc.) the grain size could be decreased down to a few tens of manometers.

  13. Preparation and characterization of nanocrystalline ZnO by direct precipitation method

    Institute of Scientific and Technical Information of China (English)

    Siqingaowa; Zhaorigetu; Yao Hongxia; Garidi

    2006-01-01

    Nanocrystalline ZnO was prepared with ZnCl2·2H2O and (NH4)2CO3 as raw materials by direct precipitation method.The precursor was proved to be [Zn5(OH)6(CO3)2] by TG-DTG-DTA and IR analysis.This precursor was calcined at 300℃ for 1,2 and 3 hours respectively,and then the nanocrystalline ZnO of different grain size were obtained.The nanocrystalline ZnO was characterized using X-ray diffraction (XRD),TEM and Brunner-Emmett-Teller method (BET).Experimental results for nanocrystalline ZnO showed that the minimum size was about 8nm,the maximum was about 15 nm and the mean grain size was 12 nm,the surface area was 80.56 m2/g and the purity was 99.9% when the precursor was calcined at 300℃ for 2 h.

  14. Exploring the effects of temperature and grain size on plumes associated with PDCs through analogue experimentation

    Science.gov (United States)

    Mitchell, S. J.; Eychenne, J.; Rust, A.

    2015-12-01

    Pyroclastic density currents (PDCs) often loft upwards into convective, buoyant co-PDC plumes. Recent analogue experiments using a unimodal grain size of 22 ± 6 μm (Andrews & Manga, 2012) have established that plume generation is aided by PDC interaction with a topographic barrier. Here, we have simulated the onset of co-PDC plumes from the collapse of concentrated particle-gas mixtures comprised of unimodal or bimodal grain size distributions (GSD) of glass beads, using combinations of lognormal populations with modes of 35, 195 and 590 μm. The collapse of a mixture, with constant mass 2950 ± 150 g, induced the propagation of a gravity current channelized down a 13° sloping tank; a barrier in the tank caused the gravity current to produce a plume of particles. Experiments were recorded with high speed visible and thermal-infrared cameras. Initial GSD and temperature of the mixture were varied to assess the effects of the addition of a coarser component on plume generation. Analogue co-PDC plumes were only produced when a proportion of fine grains (35 μm) was present in the initial granular mixture. Sampling of the particles entrained in the co-PDC plumes revealed that fine grains (35 μm) are preferentially lofted, although a few coarser particles (195 or 590 μm) are also entrained in the co-PDC plumes and settle closer to the area of uplift. Increasing the initial temperature of the mixture increases plume height measured at 1 and 2s after onset; this is supported by repeat experiments at specific conditions. Bimodal mixtures containing both fine (35 μm) and coarser (195 or 590 μm) grains result in plume heights and initial flow velocities higher than observed in unimodal fine-grained experiments of the same total mass of particles. Repeat experiments identify the natural variability in plume generation under the same nominal conditions, which is likely due to the combined variations of momentum during flow propagation and heat-driven buoyancy, as well

  15. Comparison of Automated Image-Based Grain Sizing to Standard Pebble Count Methods

    Science.gov (United States)

    Strom, K. B.

    2009-12-01

    This study explores the use of an automated, image-based method for characterizing grain-size distributions (GSDs) of exposed, open-framework gravel beds. This was done by comparing the GSDs measured with an image-based method to distributions obtained with two pebble-count methods. Selection of grains for the two pebble-count methods was carried out using a gridded sampling frame and the heel-to-toe Wolman walk method at six field sites. At each site, 500-partcle pebble-count samples were collected with each of the two pebble-count methods and digital images were systematically collected over the same sampling area. For the methods used, the pebble counts collected with the gridded sampling frame were assumed to be the most accurate representations of the true grain-size population, and results from the image-based method were compared to the grid derived GSDs for accuracy estimates; comparisons between the grid and Wolman walk methods were conducted to give an indication of possible variation between commonly used methods for each particular field site. Comparison of grain sizes were made at two spatial scales. At the larger scale, results from the image-based method were integrated over the sampling area required to collect the 500-particle pebble-count samples. At the smaller sampling scale, the image derived GSDs were compared to those from 100-particle, pebble-count samples obtained with the gridded sampling frame. The comparisons show that the image-based method performed reasonably well on five of the six study sites. For those five sites, the image-based method slightly underestimate all grain-size percentiles relative to the pebble counts collected with the gridded sampling frame. The average bias for Ψ5, Ψ50, and Ψ95 between the image and grid count methods at the larger sampling scale was 0.07Ψ, 0.04Ψ, and 0.19Ψ respectively; at the smaller sampling scale the average bias was 0.004Ψ, 0.03Ψ, and 0.18Ψ respectively. The average bias between the

  16. Preparation of grain size controlled boron-doped diamond thin films and their applications in selective detection of glucose in basic solutions

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Boron-doped diamond (BDD) thin films with different crystal grain sizes were prepared by controlling the reacting gas pressure using hot filament chemical vapor deposition (HFCVD).The morphologies and structures of the prepared diamond thin films were characterized by scanning electron microscopy (SEM) and Raman spectroscopy.The electrochemical responses of K4Fe(CN)6 on different BDD electrodes were investigated.The results suggested that electron transfer was faster at the boron-doped nanocrystalline diamond (BDND) thin film electrodes in comparison with that at other BDD thin film electrodes.The prepared BDD thin film electrodes without any modification were used to directly detect glucose in the basic solution.The results showed that the as-prepared BDD thin film electrodes exhibited good selectivity for detecting glucose in the presence of ascorbic acid (AA) and uric acid (UA).The higher sensitivity was observed on the BDND thin film grown on the boron-doped microcrystalline diamond (BDMD) thin film surface,and the linear response range,sensitivity and the low detection limit were 0.25–10 mM,189.1 μA mmol-1 cm-2 and 25 μM (S/N=3) for glucose in the presence of AA and UA,respectively.

  17. Grain-size-induced weakening of H2O ices I and II and associated anisotropic recrystallization

    Science.gov (United States)

    Stern, L.A.; Durham, W.B.; Kirby, S.H.

    1997-01-01

    Grain-size-dependent flow mechanisms tend to be favored over dislocation creep at low differential stresses and can potentially influence the rheology of low-stress, low-strain rate environments such as those of planetary interiors. We experimentally investigated the effect of reduced grain size on the solid-state flow of water ice I, a principal component of the asthenospheres of many icy moons of the outer solar system, using techniques new to studies of this deformation regime. We fabricated fully dense ice samples of approximate grain size 2 ?? 1 ??m by transforming "standard" ice I samples of 250 ?? 50 ??m grain size to the higher-pressure phase ice II, deforming them in the ice II field, and then rapidly releasing the pressure deep into the ice I stability field. At T ??? 200 K, slow growth and rapid nucleation of ice I combine to produce a fine grain size. Constant-strain rate deformation tests conducted on these samples show that deformation rates are less stress sensitive than for standard ice and that the fine-grained material is markedly weaker than standard ice, particularly during the transient approach to steady state deformation. Scanning electron microscope examination of the deformed fine-grained ice samples revealed an unusual microstructure dominated by platelike grains that grew normal to the compression direction, with c axes preferentially oriented parallel to compression. In samples tested at T ??? 220 K the elongation of the grains is so pronounced that the samples appear finely banded, with aspect ratios of grains approaching 50:1. The anisotropic growth of these crystallographically oriented neoblasts likely contributes to progressive work hardening observed during the transient stage of deformation. We have also documented remarkably similar microstructural development and weak mechanical behavior in fine-grained ice samples partially transformed and deformed in the ice II field.

  18. Rainfall-runoff properties of tephra: Simulated effects of grain-size and antecedent rainfall

    Science.gov (United States)