Sample records for solidification thermal outgassing

  1. Inverse thermal analysis method to study solidification in cast iron

    Dioszegi, Atilla; Hattel, Jesper


    Solidification modelling of cast metals is widely used to predict final properties in cast components. Accurate models necessitate good knowledge of the solidification behaviour. The present study includes a re-examination of the Fourier thermal analysis method. This involves an inverse numerical...... solution of a 1-dimensional heat transfer problem connected to solidification of cast alloys. In the analysis, the relation between the thermal state and the fraction solid of the metal is evaluated by a numerical method. This method contains an iteration algorithm controlled by an under relaxation term...... inverse thermal analysis was tested on both experimental and simulated data....

  2. Inverse thermal analysis method to study solidification in cast iron

    Dioszegi, Atilla; Hattel, Jesper


    Solidification modelling of cast metals is widely used to predict final properties in cast components. Accurate models necessitate good knowledge of the solidification behaviour. The present study includes a re-examination of the Fourier thermal analysis method. This involves an inverse numerical...... solution of a 1-dimensional heat transfer problem connected to solidification of cast alloys. In the analysis, the relation between the thermal state and the fraction solid of the metal is evaluated by a numerical method. This method contains an iteration algorithm controlled by an under relaxation term...... was developed in order to investigate the thermal behaviour of the solidifying metal. Three cylindrically shaped cast samples surrounded by different cooling materials were introduced in the same mould allowing a common metallurgical background for samples solidifying at different cooling rates. The proposed...

  3. Rapid solidification in thermal spary deposition: Microstructure and modelling

    Guo-Xiang Wang; V Prasad; S Sampath


    Mechanical, thermal, and adhesive properties of thermal spray coatings are primarily determined by the phase and microstructure of single splats, which ultimately depend on rapid solidification of each splat and on the interactions between the splats and between the splat and the substrate. Significant efforts are being made to develop a better understanding of the physical mechanisms underlying these phenomena. This paper reviews a series of work in the area of mathematical modelling of phase and microstructure formation during the rapid solidification of single splats and coatings. The model development has been complimented by special experiments. Conditions under which plariar interface solidification occurs, columnar cellular or dendriric growth takes place, or banded structure forms, have been identified. A microstructure map can therefore be built using the model presented here. The process parameters that promote crystalline nucleation and grain structure formation can be isolated and the effect of interfacial heat transfer, splat substrate temperature difference, and substrate melting and resolidification can be examined using the model. The model predictions agree qualitatively well with the experimental data for alumina, yttria, partially-stabilized zirconia, and molybdenum.

  4. Surface morphology of amorphous germanium thin films following thermal outgassing of SiO{sub 2}/Si substrates

    Valladares, L. de los Santos, E-mail: [Cavendish Laboratory, Department of Physics, University of Cambridge, J.J. Thomson Ave., Cambridge CB3 0HE (United Kingdom); Dominguez, A. Bustamante [Laboratorio de Cerámicos y Nanomateriales, Facultad de Ciencias Físicas, Universidad Nacional Mayor de San Marcos, Apartado Postal 14-0149, Lima (Peru); Llandro, J.; Holmes, S. [Cavendish Laboratory, Department of Physics, University of Cambridge, J.J. Thomson Ave., Cambridge CB3 0HE (United Kingdom); Quispe, O. Avalos [Laboratorio de Cerámicos y Nanomateriales, Facultad de Ciencias Físicas, Universidad Nacional Mayor de San Marcos, Apartado Postal 14-0149, Lima (Peru); Langford, R. [Cavendish Laboratory, Department of Physics, University of Cambridge, J.J. Thomson Ave., Cambridge CB3 0HE (United Kingdom); Aguiar, J. Albino [Laboratório de Supercondutividade e Materiais Avançados, Departamento de Física, Universidade Federal de Pernambuco, 50670-901, Recife (Brazil); Barnes, C.H.W. [Cavendish Laboratory, Department of Physics, University of Cambridge, J.J. Thomson Ave., Cambridge CB3 0HE (United Kingdom)


    Highlights: • Annealing promotes outgassing of SiO{sub 2}/Si wafers. • Outgassing species embed in the a-Ge film forming bubbles. • The density of bubbles obtained by slow annealing is smaller than by rapid annealing. • The bubbles explode after annealing the samples at 800 °C. • Surface migration at higher temperatures forms polycrystalline GeO{sub 2} islands. - Abstract: In this work we report the surface morphology of amorphous germanium (a-Ge) thin films (140 nm thickness) following thermal outgassing of SiO{sub 2}/Si substrates. The thermal outgassing was performed by annealing the samples in air at different temperatures from 400 to 900 °C. Annealing at 400 °C in slow (2 °C/min) and fast (10 °C/min) modes promotes the formation of bubbles on the surface. A cross sectional view by transmission electron microscope taken of the sample slow annealed at 400 °C reveals traces of gas species embedded in the a-Ge film, allowing us to propose a possible mechanism for the formation of the bubbles. The calculated internal pressure and number of gas molecules for this sample are 30 MPa and 38 × 10{sup 8}, respectively. Over an area of 22 × 10{sup −3} cm{sup 2} the density of bubbles obtained at slow annealing (9 × 10{sup 3} cm{sup −2}) is smaller than that at rapid annealing (6.4 × 10{sup 4} cm{sup −2}), indicating that the amount of liberated gas in both cases is only a fraction of the total gas contained in the substrate. After increasing the annealing temperature in the slow mode, bubbles of different diameters (from tens of nanometers up to tens of micrometers) randomly distribute over the Ge film and they grow with temperature. Vertical diffusion of the outgas species through the film dominates the annealing temperature interval 400–600 °C, whereas coalescence of bubbles caused by lateral diffusion is detected after annealing at 700 °C. The bubbles explode after annealing the samples at 800 °C. Annealing at higher temperatures, such as

  5. Effect of low temperature melt on solidification structure of A356 alloy with melt thermal treatment

    何树先; 王俊; 孙宝德; 周尧和


    The influence of the low temperature melt (LTM) structure on solidification structure of the sample with melt thermal treatment (MTT) process was studied. And the mechanism of the MTT process was analyzed with cluster theory. It is shown that the final solidification structure is dependent mainly on the structure of LTM. Dendrites will appear in the solidification structure if the structure of LTM is dendritic before MTT. Otherwise, non-dendritic grains will appear in the solidification structure. And the lower the temperature of LTM, the more remarkable the effect of the LTM structure is.

  6. A Combined Numerical-Experimental Approach to Quantify the Thermal Contraction of A356 During Solidification

    Macht, J. P.; Maijer, D. M.; Phillion, A. B.


    A process for generating thermal contraction coefficients for use in the solidification modeling of aluminum castings is presented. Sequentially coupled thermal-stress modeling is used in conjunction with experimentation to empirically generate the thermal contraction coefficients for a strontium-modified A356 alloy. The impact of cooling curve analysis on the modeling procedure is studied. Model results are in good agreement with experimental findings, indicating a sound methodology for quantifying the thermal contraction. The technique can be applied to other commercially relevant aluminum alloys, increasing the utility of solidification modeling in the casting industry.

  7. Advanced Durable Flexible Ultra Low Outgassing Thermal Control Coatings for NASA Science Missions Project

    National Aeronautics and Space Administration — This Phase I program proposes to synthesize novel nanoengineered ultra low out gassing elastomers and formulate high temperature capable flexible thermal control...

  8. Development of thermal simulation system for heavy section ductile iron solidification


    A new reliable thermal simulation system for studying solidification of heavy section ductile iron has been developed using computer feedback control and artificial intelligent methods. Results of idle test indicate that the temperature in the system responses exactly to the inputted control data and the temperature control error is less than ± 0.5 %. It is convenient to simulate solidification of heavy section ductile iron using this new system. Results of thermal simulation experiments show that the differences in nodularity and number of graphite nodule per unit area in the thermal simulation specimen and the actual heavy section block is less than 5 % and 10 %, respectively.

  9. Dynamics of liquid solidification thermal resistance of contact layer

    Lipnicki, Zygmunt


    This monograph comprehensively describes phenomena of heat flow during phase change as well as the dynamics of liquid solidification, i.e. the development of a solidified layer. The book provides the reader with basic knowledge for practical designs, as well as with equations which describe processes of energy transformation. The target audience primarily comprises researchers and experts in the field of heat flow, but the book may also be beneficial for both practicing engineers and graduate students.

  10. Modeling and simulation of 3D thermal stresses of large-sized castings in solidification processes


    When heavy machines and large scaled receiver system of communication equipment are manufactured, it always needs to produce large- sized steel castings, aluminum castings and etc. Some defects of hot cracking by thermal stress often appear during solidification process as these castings are produced, which results in failure of castings.Therefore predicting the effects of technological parameters for production of castings on the thermal stress during solidification process becomes an important means. In this paper, the mathematical models have been established and numerical calculation of temperature fields by using finite difference method (FDM) and then thermal stress fields by using finite element method (FEM) during solidification process of castings have been carried out. The technological parameters of production have been optimized by the results of calculation and the defects of hot cracking have been eliminated. Modeling and simulation of 3D thermal stress during solidification processes of large-sized castings provided a scientific basis, which promoted further development of advanced manufacturing technique.

  11. Hydrogen Outgassing from Lithium Hydride

    Dinh, L N; Schildbach, M A; Smith, R A; Balazs1, B; McLean II, W


    Lithium hydride is a nuclear material with a great affinity for moisture. As a result of exposure to water vapor during machining, transportation, storage and assembly, a corrosion layer (oxide and/or hydroxide) always forms on the surface of lithium hydride resulting in the release of hydrogen gas. Thermodynamically, lithium hydride, lithium oxide and lithium hydroxide are all stable. However, lithium hydroxides formed near the lithium hydride substrate (interface hydroxide) and near the sample/vacuum interface (surface hydroxide) are much less thermally stable than their bulk counterpart. In a dry environment, the interface/surface hydroxides slowly degenerate over many years/decades at room temperature into lithium oxide, releasing water vapor and ultimately hydrogen gas through reaction of the water vapor with the lithium hydride substrate. This outgassing can potentially cause metal hydriding and/or compatibility issues elsewhere in the device. In this chapter, the morphology and the chemistry of the corrosion layer grown on lithium hydride (and in some cases, its isotopic cousin, lithium deuteride) as a result of exposure to moisture are investigated. The hydrogen outgassing processes associated with the formation and subsequent degeneration of this corrosion layer are described. Experimental techniques to measure the hydrogen outgassing kinetics from lithium hydride and methods employing the measured kinetics to predict hydrogen outgassing as a function of time and temperature are presented. Finally, practical procedures to mitigate the problem of hydrogen outgassing from lithium hydride are discussed.

  12. Experimental Study on Melting and Solidification of Phase Change Material Thermal Storage

    Ambarita, H.; Abdullah, I.; Siregar, C. A.; Siregar, R. E. T.; Ronowikarto, A. D.


    Melting and solidification process of Phase Change Materials (PCMs) are investigated experimentally. The tested PCMs are Paraffin wax and Steric acid which typically used for solar water heater. The objective is to explore the characteristics of the PCM when it is being melted and solidified. The experiments are performed in a glass box. One side of the box wall is heated while the opposite wall is kept constant and other walls are insulated. Temperature of the heated wall are kept constant at 80°C, 85°C, and 90°C, respectively. Every experiment is carried out for 600 minutes. Temperatures are recorded and the melting and solidification processes are pictured by using camera. The results show that the melting process starts from the upper part of the thermal storage. In the solidification process, it starts from the lower part of the thermal storage. As a thermal energy storage, Paraffin wax is better than Steric acid. This is because Paraffin wax can store more energy. At heat source temperature of 90°C, thermal energy stored by Paraffin wax and Stearic acid is 61.84 kJ and 57.39 kJ, respectively. Thus it is better to used Paraffin wax in the solar water heater as thermal energy storage.

  13. Effect of Grade on Thermal-Mechanical Behavior of Steel During Initial Solidification

    Zappulla, Matthew L. S.; Hibbeler, Lance C.; Thomas, Brian G.


    Thermal-mechanical analysis of solidification is important to understand crack formation, shape problems, and other aspects of casting processes. This work investigates the effect of grade on thermal-mechanical behavior during initial solidification of steels during continuous casting of a wide strand. The employed finite element model includes non-linear temperature-, phase-, and carbon content-dependent elastic-viscoplastic constitutive equations. The model is verified using an analytical solution, and a mesh convergence study is performed. Four steel grades are simulated for 30 seconds of casting without friction: ultra-low-carbon, low-carbon, peritectic, and high-carbon steel. All grades show the same general behavior. Initially, rapid cooling causes tensile stress and inelastic strain near the surface of the shell, with slight complementary compression beneath the surface, especially with lower carbon content. As the cooling rate decreases with time, the surface quickly reverses into compression, with a tensile region developing toward the solidification front. Higher stress and inelastic strain are generated in the high-carbon steel, because it contains more high-strength austenite. Stress in the δ-ferrite phase near the solidification front is always very small, owing to the low strength of this phase. This modeling methodology is a step toward designing better mold taper profiles for continuous casting of different steels.

  14. The mechanics of shallow magma reservoir outgassing

    Parmigiani, A.; Degruyter, W.; Leclaire, S.; Huber, C.; Bachmann, O.


    Magma degassing fundamentally controls the Earth's volatile cycles. The large amount of gas expelled into the atmosphere during volcanic eruptions (i.e., volcanic outgassing) is the most obvious display of magmatic volatile release. However, owing to the large intrusive:extrusive ratio, and considering the paucity of volatiles left in intrusive rocks after final solidification, volcanic outgassing likely constitutes only a small fraction of the overall mass of magmatic volatiles released to the Earth's surface. Therefore, as most magmas stall on their way to the surface, outgassing of uneruptible, crystal-rich magma storage regions will play a dominant role in closing the balance of volatile element cycling between the mantle and the surface. We use a numerical approach to study the migration of a magmatic volatile phase (MVP) in crystal-rich magma bodies ("mush zones") at the pore scale. Our results suggest that buoyancy-driven outgassing is efficient over crystal volume fractions between 0.4 and 0.7 (for mm-sized crystals). We parameterize our pore-scale results for MVP migration in a thermomechanical magma reservoir model to study outgassing under dynamical conditions where cooling controls the evolution of the proportion of crystal, gas, and melt phases and to investigate the role of the reservoir size and the temperature-dependent viscoelastic response of the crust on outgassing efficiency. We find that buoyancy-driven outgassing allows for a maximum of 40-50% volatiles to leave the reservoir over the 0.4-0.7 crystal volume fractions, implying that a significant amount of outgassing must occur at high crystal content (>0.7) through veining and/or capillary fracturing.

  15. Inverse Thermal Analysis of Alloy 690 Laser and Hybrid Laser-GMA Welds Using Solidification-Boundary Constraints

    Lambrakos, S. G.


    An inverse thermal analysis of Alloy 690 laser and hybrid laser-GMA welds is presented that uses numerical-analytical basis functions and boundary constraints based on measured solidification cross sections. In particular, the inverse analysis procedure uses three-dimensional constraint conditions such that two-dimensional projections of calculated solidification boundaries are constrained to map within experimentally measured solidification cross sections. Temperature histories calculated by this analysis are input data for computational procedures that predict solid-state phase transformations and mechanical response. These temperature histories can be used for inverse thermal analysis of welds corresponding to other welding processes whose process conditions are within similar regimes.

  16. What happens to the initial planar instability when the thermal gradient is increased during directional solidification?

    Wang Zhi-Jun; Wang Jin-Cheng; Li Jun-Jie; Yang Gen-Cang; Zhou Yao-He


    The positive thermal gradient is one of the most important parameters during directional solidification.The increase of the thermal gradient usually stabilizes the planar interface in the steady state analysis.However,in the initial transient range of planar instability,the thermal gradient presents complicated effects.Time-dependent analysis shows that the increase of the thermal gradient can enhance both the stabilizing effects and the destabilizing effects on a planar interface.The incubation time first decreases and then increases with the increase of the thermal gradient.Moreover,the initial average wavelength always increases with the thermal gradient increasing,contrary to the effect of the thermal gradient on the steady cellular/dendritic spacing.This reveals the types of spacing adjustment after planar instability.

  17. Thermal effects in rapid directional solidification - Linear theory

    Huntley, D. A.; Davis, S. H.


    We study the morphological instability of the planar solid/liquid interface for a unidirectionally-solidified dilute binary mixture. We use a model developed by Boettinger et al. (1985, 1986), Aziz (1982), and Jackson et al. (1980), which allows for nonequilibrium effects on the interface through velocity-dependent segregation and attachment kinetics. Two types of instabilities are found in the linear stability analysis: (1) a cellular instability, and (2) an oscillatory instability driven by disequilibrium effects. Merchant and Davis (1990) characterized these instabilities subject to the frozen-temperature approximation (FTA). The present work relaxes the FTA by including the effects of latent heat and the full temperature distribution. Thermal effects slightly postpone the onset of the cellular instability but dramatically postpone the onset of the oscillatory instability; however, the absolute-stability conditions, at which at high speed the cellular and oscillatory instabilities are suppressed, remain unchanged from the FTA.

  18. A Thermal Simulation Method for Solidification Process of Steel Slab in Continuous Casting

    Zhong, Honggang; Chen, Xiangru; Han, Qingyou; Han, Ke; Zhai, Qijie


    Eighty years after the invention of continuous cast of steels, reproducibility from few mm3 samples in the laboratory to m3 product in plants is still a challenge. We have engineered a thermal simulation method to simulate the continuous casting process. The temperature gradient ( G L ) and dendritic growth rate ( v) of the slab were reproduced by controlling temperature and cooling intensity at hot and chill end, respectively, in our simulation samples. To verify that our samples can simulate the cast slab in continuous casting process, the heat transfer, solidification structure, and macrosegregation of the simulating sample were compared to those of a much larger continuous casting slab. The morphology of solid/liquid interface, solidified shell thickness, and dendritic growth rate were also investigated by in situ quenching the solidifying sample. Shell thickness ( δ) determined by our quenching experiment was related to solidification time ( τ) by equation: δ = 4.27 × τ 0.38. The results indicated that our method closely simulated the solidification process of continuous casting.

  19. The effect of carbon nanotubes in enhancing the thermal transport properties of PCM during solidification

    Kumaresan, Vellaisamy; Velraj, Ramalingam; Das, Sarit K.


    This study is aimed to prepare a novel class of nanofluid phase change material (NFPCM) by dispersing a small amount of multi-walled carbon nanotubes (MWCNT) in liquid paraffin, to enhance the heat transfer properties and examine the characteristics of the NFPCM during the solidification process. The stable NFPCMs are prepared by dispersing the MWCNT in liquid paraffin at 30°C with volume fractions of 0.15, 0.3, 0.45 and 0.6% without any dispersing agents. The rheology measurement illustrates the Newtonian fluid behavior in the shear stress range of 1-10 Pa. The differential scanning calorimetric results showed that there is no observable variation in the freezing/melting temperature of the NFPCM, and only a small observable change in the latent heat values. The thermal conductivity of various NFPCM is measured. The enhancement in thermal conductivity increases with the increased volume fraction of the MWCNT, and shows a weak dependence on the temperature. Further, for the NFPCM with a volume fraction of 0.6%, there is an appreciable increase in heat transfer with a reduction in the solidification time of 33.64%. The enhancement in the heat transfer performance would alleviate the major problems that have been encountered in the conventional phase change materials since several years.

  20. Spacecraft Material Outgassing Data

    National Aeronautics and Space Administration — This compilation of outgassing data of materials intended for spacecraft use were obtained at the Goddard Space Flight Center (GSFC), utilizing equipment developed...

  1. Phase change material solidification in a finned cylindrical shell thermal energy storage: An approximate analytical approach

    Mosaffa Amirhossein


    Full Text Available Results are reported of an investigation of the solidification of a phase change material (PCM in a cylindrical shell thermal energy storage with radial internal fins. An approximate analytical solution is presented for two cases. In case 1, the inner wall is kept at a constant temperature and, in case 2, a constant heat flux is imposed on the inner wall. In both cases, the outer wall is insulated. The results are compared to those for a numerical approach based on an enthalpy method. The results show that the analytical model satisfactory estimates the solid-liquid interface. In addition, a comparative study is reported of the solidified fraction of encapsulated PCM for different geometric configurations of finned storage having the same volume and surface area of heat transfer.

  2. CFD Simulation of Melting and Solidification of PCM in Thermal Energy Storage Systems of Different Geometry

    Arena, S.; Cau, G.; Palomba, C.


    At the Department of Mechanical, Chemical and Materials Engineering of the University of Cagliari an experimental and numerical research project has begun with the aim of developing highly efficient thermal energy storage (TES) systems using phase change materials (PCM) of particular interest in concentrating small-medium scale solar power (CSP) applications. The present work aims to simulate the melting and solidification processes in containing boxes and heat transfer devices of different geometrical features which may constitute the elementary cell of a more complex TES system. Two-dimensional axisymmetric numerical models, developed with COMSOL Multiphysics are considered and used to simulate TES, heat conduction and natural convection. The models are used to determine the temperature profile inside the PCM to identify which configurations are capable of enhancing thermal response between a solid wall and a PCM. The results obtained will be used for comparison with experimental data acquired from a pilot plant under construction in the DIMCM laboratories. At the current stage the laboratory is being brought to completion.

  3. Novel synthesis and applications of Thiomer solidification for heavy metals immobilization in hazardous ASR/ISW thermal residue.

    Baek, Jin Woong; Mallampati, Srinivasa Reddy; Park, Hung Suck


    The present paper reports the novel synthesis and application of Thiomer solidification for heavy metal immobilization in hazardous automobile shredder residues and industrial solid waste (ASR/ISW) thermal residues. The word Thiomer is a combination of the prefix of a sulfur-containing compound "Thio" and the suffix of "Polymer" meaning a large molecule compound of many repeated subunits. To immobilize heavy metals, either ASR/ISW thermal residues (including bottom and fly ash) was mixed well with Thiomer and heated at 140°C. After Thiomer solidification, approximately 91-100% heavy metal immobilization was achieved. The morphology and mineral phases of the Thiomer-solidified ASR/ISW thermal residue were characterized by field emission-scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction (XRD), which indicated that the amounts of heavy metals detectable on the ASR/ISW thermal residue surface decreased and the sulfur mass percent increased. XRD indicated that the main fraction of the enclosed/bound materials on the ASR/ISW residue contained sulfur associated crystalline complexes. The Thiomer solidified process could convert the heavy metal compounds into highly insoluble metal sulfides and simultaneously encapsulate the ASR/ISW thermal residue. These results show that the proposed method can be applied to the immobilization of ASR/ISW hazardous ash involving heavy metals. Copyright © 2015 Elsevier Ltd. All rights reserved.

  4. Tungsten Alloy Outgassing Measurements

    Rutherfoord, John P; Shaver, L


    Tungsten alloys have not seen extensive use in liquid argon calorimeters so far. Because the manufacturing process for tungsten is different from the more common metals used in liquid argon there is concern that tungsten could poison the argon thereby creating difficulties for precision calorimetry. In this paper we report measurements of outgassing from the tungsten alloy slugs proposed for use in the ATLAS FCal module and estimate limits on potential poisoning with reasonable assumptions. This estimate gives an upper limit poisoning rate of

  5. BET measurements: Outgassing of minerals

    Clausen, Liselotte; Fabricius, Ida Lykke


    Outgassing minerals at elevated temperatures prior to BET measurements can lead to phase changes, especially in the case of amorphous and poorly crystalline materials. In order to evaluate the applicability of the BET method when low outgassing temperatures are required, selected aquifer minerals...... were outgassed at different temperatures and for different times. The studied minerals are 2-line ferrihydrite, goethite, lepidocrocite, quartz, calcite, ®-alumina, and kaolinite. The results demonstrate that measured specific surface areas of iron oxides are strongly dependent on outgassing conditions...... because the surface area increased by 170% with increasing temperature. In the poorly crystalline minerals, phase changes caused by heating were observed at temperatures lower than 100±C. Therefore low outgassing temperatures are preferable for minimizing phase changes. As demonstrated in this study...

  6. Solidification of AM and AZ magnesium alloys characterized by heat-transfer modeled thermal and calorimetric analysis and microsegregation study of directionally solidified microstructure

    Mirkovic, Djordje


    The micro-scale solidification of commercial Mg alloys of the AZ and AM series is in the focus of the present thesis. Two approaches of investigating solidification are implemented, complementary regarding temperature gradient and solidification rate, and also with respect to the generated microstructure. The first approach considers solidification under a negligible spatial temperature gradient. Here the solidification curves, i.e. fraction solid versus temperature, were determined by developing an improved heat-transfer modeling applicable on both differential thermal analysis (DTA) and differential scanning calorimetry (DSC) signals. The correlation between solidification enthalpy and fraction solid during solidification was tested in detail. A better evaluation of the measured DTA and DSC signals is attained through an independent measurement of the time constant as function of temperature for the applied equipment. A further improvement is achieved through a more impartial interpretation of the measured curves. Both improvements enable a better desmearing of measured signals and reduce the error induced by the operator. The novel tantalum encapsulation enabled appropriate handling of challenging Mg-alloys. The viability and limitations of thermal analysis in general to determine start and end of solidification of AZ magnesium alloys was also studied. The second approach is based on directional solidification in a high temperature gradient and at constant solidification rate, achieved by the Bridgman technique. The resulting dendritic microstructure and inherent microsegregation are studied in this work. The solute profiles, i.e. solute content versus solid phase fraction during solidification, are determined by an advanced treatment of the EPMA data. Problems that are demonstrated in this work are Al-loss and melt pollution due to reaction with typical sample container material made of unprotected steel. The development of an optimized boron nitride (BN

  7. Influence of Crucible Thermal Conductivity on Crystal Growth in an Industrial Directional Solidification Process for Silicon Ingots

    Zaoyang Li


    Full Text Available We carried out transient global simulations of heating, melting, growing, annealing, and cooling stages for an industrial directional solidification (DS process for silicon ingots. The crucible thermal conductivity is varied in a reasonable range to investigate its influence on the global heat transfer and silicon crystal growth. It is found that the crucible plays an important role in heat transfer, and therefore its thermal conductivity can influence the crystal growth significantly in the entire DS process. Increasing the crucible thermal conductivity can shorten the time for melting of silicon feedstock and growing of silicon crystal significantly, and therefore large thermal conductivity is helpful in saving both production time and power energy. However, the high temperature gradient in the silicon ingots and the locally concave melt-crystal interface shape for large crucible thermal conductivity indicate that high thermal stress and dislocation propagation are likely to occur during both growing and annealing stages. Based on the numerical simulations, some discussions on designing and choosing the crucible thermal conductivity are presented.

  8. Effects of carbon content and solidification rate on thermal conductivity of grey cast iron


    The thermal conductivity or diffusivity of pearlitic grey irons with various carbon contents is investigated by the laser flash method. The materials are cast in controlled thermal environments and produced in three dissimilar cooling rates. The cooling rate together with the carbon content largely influence the thermal conductivity of grey iron. Linear relationships exist between the thermal conductivity and the carbon content, the carbon equivalent and the fraction of former primary solidified austenite transformed into pearlite. The work shows that optimal thermal transport properties are obtained at medium cooling rates. Equations describing the thermal conductivity of pearlite,solidified as pre-eutectic austenite, and the eutectic of grey iron are derived. The thermal conductivity of pearlitic grey iron is modeled at both room temperature and elevated temperature with good accuracy.

  9. Effects of Carbon Content and Solidification Rate on the Thermal Conductivity of Grey Cast Iron

    Daniel Holmgren; Attila Diószegi; Ingvar L.Svensson


    The thermal conductivity/diffusivity of pearlitic grey irons with various carbon contents was investi- gated by the laser flash method. The materials were cast in controlled thermal environments producing three dissimilar cooling rates. The cooling rates together with the carbon content largely influence the thermal conductivity of grey iron. Linear relationships exist between the thermal conductivity and the carbon content, the carbon equivalent, and the fraction of the former primary solidified austenite transformed into pearlite. The results show that the optimal thermal transport properties are obtained at medium cooling rates. Equa- tions are given for the thermal conductivity of pearlite, solidified as pre-eutectic austenite, and the eutectic of grey iron. The thermal conductivity of pearlitic grey iron is modelled at both room temperature and elevated temperatures with good accuracy.

  10. Effects of carbon content and solidification rate on thermal conductivity of grey cast iron

    Daniel Holmgren


    Full Text Available The thermal conductivity or diffusivity of pearlitic grey irons with various carbon contents is investigated by the laser flash method. The materials are cast in controlled thermal environments and produced in three dissimilar cooling rates. The cooling rate together with the carbon content largely influence the thermal conductivity of grey iron. Linear relationships exist between the thermal conductivity and the carbon content, the carbon equivalent and the fraction of former primary solidified austenite transformed into pearlite. The work shows that optimal thermal transport properties are obtained at medium cooling rates. Equations describing the thermal conductivity of pearlite,solidified as pre-eutectic austenite, and the eutectic of grey iron are derived. The thermal conductivity of pearlitic grey iron is modeled at both room temperature and elevated temperature with good accuracy.

  11. Numerical models of the Earth’s thermal history: Effects of inner-core solidification and core potassium

    Butler, S. L.; Peltier, W. R.; Costin, S. O.


    Recently there has been renewed interest in the evolution of the inner core and in the possibility that radioactive potassium might be found in significant quantities in the core. The arguments for core potassium come from considerations of the age of the inner core and the energy required to sustain the geodynamo [Nimmo, F., Price, G.D., Brodholt, J., Gubbins, D., 2004. The influence of potassium on core and geodynamo evolution. Geophys. J. Int. 156, 363-376; Labrosse, S., Poirier, J.-P., Le Mouël, J.-L., 2001. The age of the inner core. Earth Planet Sci. Lett. 190, 111-123; Labrosse, S., 2003. Thermal and magnetic evolution of the Earth's core. Phys. Earth Planet Int. 140, 127-143; Buffett, B.A., 2003. The thermal state of Earth's core. Science 299, 1675-1677] and from new high pressure physics analyses [Lee, K., Jeanloz, R., 2003. High-pressure alloying of potassium and iron: radioactivity in the Earth's core? Geophys. Res. Lett. 30 (23); Murthy, V.M., van Westrenen, W., Fei, Y.W., 2003. Experimental evidence that potassium is a substantial radioactive heat source in planetary cores. Nature 423, 163-165; Gessmann, C.K., Wood, B.J., 2002. Potassium in the Earth's core? Earth Planet Sci. Lett. 200, 63-78]. The Earth's core is also located at the lower boundary of the convecting mantle and the presence of radioactive heat sources in the core will affect the flux of heat between these two regions and will, as a result, have a significant impact on the Earth's thermal history. In this paper, we present Earth thermal history simulations in which we calculate fluid flow in a spherical shell representing the mantle, coupled with a core of a given heat capacity with varying degrees of internal heating in the form of K40 and varying initial core temperatures. The mantle model includes the effects of the temperature dependence of viscosity, decaying radioactive heat sources, and mantle phase transitions. The core model includes the thermal effects of inner core

  12. Solidification and Biotoxicity Assessment of Thermally Treated Municipal Solid Waste Incineration (MSWI Fly Ash

    Bing Gong


    Full Text Available In the present work, thermal treatment was used to stabilize municipal solid waste incineration (MSWI fly ash, which was considered hazardous waste. Toxicity characteristic leaching procedure (TCLP results indicated that, after the thermal process, the leaching concentrations of Pb, Cu, and Zn decreased from 8.08 to 0.16 mg/L, 0.12 to 0.017 mg/L and 0.39 to 0.1 mg/L, respectively, which well met the limits in GB5085.3-2007 and GB16689-2008. Thermal treatment showed a negative effect on the leachability of Cr with concentrations increasing from 0.1 to 1.28 mg/L; nevertheless, it was still under the limitations. XRD analysis suggested that, after thermal treatments, CaO was newly generated. CaO was a main contribution to higher Cr leaching concentrations owing to the formation of Cr (VI—compounds such as CaCrO4. SEM/EDS tests revealed that particle adhesion, agglomeration, and grain growth happened during the thermal process and thus diminished the leachability of Pb, Cu, and Zn, but these processes had no significant influence on the leaching of Cr. A microbial assay demonstrated that all thermally treated samples yet possessed strong bactericidal activity according to optical density (OD test results. Among all samples, the OD value of raw fly ash (RFA was lowest followed by FA700-10, FA900-10, and FA1100-10 in an increasing order, which indicated that the sequence of the biotoxicity for these samples was RFA > FA700-10 > FA900-10 > FA1100-10. This preliminary study indicated that, apart from TCLP criteria, the biotoxicity assessment was indispensable for evaluating the effect of thermal treatment for MSWI fly ash.

  13. Effects of Manganese Content on Solidification Structures, Thermal Properties, and Phase Transformation Characteristics in Fe-Mn-C Steels

    Yang, Jian; Wang, Yu-Nan; Ruan, Xiao-Ming; Wang, Rui-Zhi; Zhu, Kai; Fan, Zheng-Jie; Wang, Ying-Chun; Li, Cheng-Bin; Jiang, Xiao-Fang


    The solidification structures and the thermal properties of Fe-Mn-C steel ingots containing different manganese contents have been investigated and the phase transformation characteristics have been revealed by Thermo-Calc to assist development of the continuous casting technology of Fe-Mn-C steels. The results show that the thermal conductivity of the 0Mn steel is higher than that of the 3Mn steel. The thermal conductivity of the 6Mn steel is the lowest in the three kinds of steels below 1023 K (750 °C) and the highest above 1173 K (900 °C). The 0Mn steel has the highest value of the proportion of equiaxed grain zone area in the three kinds of steels, whereas the 3Mn steel has the lowest value of it in the steels. Manganese has the effect of promoting the coarsening of grains. The microstructure is martensite and a little retained austenite (3.8 mass pct) in the 6Mn steel, whereas the microstructure is bainite in the 3Mn steel. The 0Mn steel is characterized by ferrite and pearlite. The mean thermal expansion coefficients of the steels are in the range from 1.0 × 10-5 to 1.6 × 10-5 K-1, and the determinations of mold tapers of the 6Mn and 3Mn steels can refer to low-carbon steel. Using RA steel is 873 K to 1073 K (600 °C to 800 °C), whereas those of the 3Mn steel and the 0Mn steel are 873 K to 1123 K (600 °C to 850 °C) and 873 K to 1173 K (600 °C to 900 °C), respectively. In the 6Mn and 3Mn steels, the deformation-induced ferrite (DIF) forms in sufficient quantities cause the recovery of the ductility at the low temperature end. However, since low strains are present when straightening, sufficient quantities of DIF cannot be formed. Thus, the ductility of the 6Mn and 3Mn steels cannot be improved during the continuous casting process. Manganese has the effect of enlarging the austenite phase region and reducing the δ-ferrite phase region and α-ferrite phase region.

  14. Dendritic solidification and thermal expansion of refractory Nb-Zr alloys investigated by electrostatic levitation

    Yang, S. J.; Hu, L.; Wang, L.; Wei, B.


    The dendritic growth and thermal expansion of isomorphous refractory Nb-5%Zr, Nb-10%Zr, and Nb-15%Zr alloys were studied by electrostatic levitation technique. The obtained maximum undercoolings for the three alloys were 534 (0.2 T L), 498 (0.19 T L), and 483 K (0.18 T L), respectively. Within these undercooling ranges, the dendritic growth velocities of the three alloys all exhibited power laws, and achieved 38.5, 34.0, and 27.1 m s-1 at each maximum undercooling. The microstructures were characterized by coarse dendrites at small undercooling, while they transformed into refined dendrites under large undercooling condition. In addition, the measured thermal expansion coefficients of solid Nb-Zr alloys increased linearly with temperature. The values at liquid state were more than double of those at solid state, which also displayed linear dependence on temperature.

  15. Evaluation of Settler Tank Thermal Stability during Solidification and Disposition to ERDF

    Stephenson, David E. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Delegard, Calvin H. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Schmidt, Andrew J. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States)


    Ten 16-foot-long and 20-inch diameter horizontal tanks currently reside in a stacked 2×5 (high) array in the ~20,000-gallon water-filled Weasel Pit of the 105-KW Fuel Storage Basin on the US-DOE Hanford Site. These ten tanks are part of the Integrated Water Treatment System used to manage water quality in the KW Basin and are called “settler” tanks because of their application in removing particles from the KW Basin waters. Based on process knowledge, the settler tanks are estimated to contain about 124 kilograms of finely divided uranium metal, 22 kg of uranium dioxide, and another 55 kg of other radioactive sludge. The Sludge Treatment Project (STP), managed by CH2MHill Plateau Remediation Company (CHPRC) is charged with managing the settler tanks and arranging for their ultimate disposal by burial in ERDF. The presence of finely divided uranium metal in the sludge is of concern because of the potential for thermal runaway reaction of the uranium metal with water and the formation of flammable hydrogen gas as a product of the uranium-water reaction. Thermal runaway can be instigated by external heating. The STP commissioned a formal Decision Support Board (DSB) to consider options and provide recommendations to manage and dispose of the settler tanks and their contents. Decision criteria included consideration of the project schedule and longer-term deactivation, decontamination, decommissioning, and demolition (D4) of the KW Basin. The DSB compared the alternatives and recommended in-situ grouting, size-reduction, and ERDF disposal as the best of six candidate options for settler tank treatment and disposal. It is important to note that most grouts contain a complement of Portland cement as the binding agent and that Portland cement curing reactions generate heat. Therefore, concern is raised that the grouting of the settler tank contents may produce heating sufficient to instigate thermal runaway reactions in the contained uranium metal sludge.

  16. Thermal stress induced dislocation distribution in directional solidification of Si for PV application

    Jiptner, Karolin; Gao, Bing; Harada, Hirofumi; Miyamura, Yoshiji; Fukuzawa, Masayuki; Kakimoto, Koichi; Sekiguchi, Takashi


    This paper presents the limitation of the cast technique for silicon growth and the obstacle to reduce the dislocation density below 103 cm-2. The thermal stress induced dislocation density, independent of other dislocation sources, is determined and the result suggests that local dislocation densities as high as 104 cm-2 are readily introduced alone in the cooling period of the crystal growth. Areas of high residual strain and dislocation densities are identified and presented. The experimental results are correlated with numerical simulation based on a three-dimensional Haasen-Alexander-Sumino (HAS) model. The dislocation introduction is caused by an activation of different slip systems in different ingot areas.

  17. Solidification behavior and thermal conductivity of bulk sodium acetate trihydrate composites with thickening agents and graphite

    Dannemand, Mark; Johansen, Jakob Berg; Furbo, Simon


    . Samples that crystalized without supercooling tended to form solid crystals near the heat transfer surface and cavities away from the heat transfer surface. The measured thermal conductivity was up to 0.7 W/m K in solid sodium acetate trihydrate. Samples that crystalized from supercooled state formed...... of the phase change material limits the heat exchange capacity rate to and from the storage. Another factor that limits the heat transfer is the contraction and expansion of the salt hydrate during the phase change. This density change causes formation of cavities inside the solid storage material...

  18. Measurement of Ultra Low Outgassing Rates for NLC UHV Vacuum Chambers

    Kishiyama, K; Shen, S; Behne, D; Corlett, J N; Atkinson, D; Kennedy, K; Miller, T; Eriksson, L; Ross, M


    Ultra low outgassing rates would be highly advantageous in accelerators and storage rings, such as the Next Linear Collider (NLC), where an outgassing rate of <10{sup -12} Torr liter/sec/cm{sup 2} could eliminate the need for costly distributed pumping. Measuring such low outgassing rates at room temperature has many difficulties. However, by inspection of Fick's law, it can be seen that thermal desorption is proportional to outgassing rate. It is commonly observed that the outgas rate doubles approximately every 15 C for temperatures under 100 C. By measuring outgassing rate versus temperature and time and extrapolating back to room temperature we can measure outgassing rates that would otherwise be difficult to make. To produce a reliable measurement also requires the total surface area under study to be approximately an order of magnitude greater than the area of the measurement chamber walls. To accomplish this, 27 plates of 5083 aluminum were placed in the measurement chamber. This technique will be the basis for future investigation of outgassing rates of other sample plates fabricated with different machining and cleaning techniques.

  19. Effects of laser processing parameters on solidification microstructures of ternary Al_2O_3/YAG/ZrO_2 eutectic in situ composite and its thermal property

    SU Hai-jun; ZHANG Jun; LIU Lin; FU Heng-zhi


    Rapid surface resolidification with a high powered CO_2-laser was performed in preparing directionally solidified Al_2O_3/YAG/ZrO_2 ternary eutectic ceramic in situ composite.The effects of laser processing parameters on the solidification microstructure characteristics and thermal properties were studied by scanning electron microscopy (SEM),energy dispersive spectroscopy (EDS),X-ray diffractometry (XRD) and synthetically thermal analysis (STA).Detailed investigations of the influence of laser power and scanning rate on the preparation and microstructural parameters of the ternary eutectic were presented.Moreover,the eutectic phase separation rule at high temperature was discussed.The results indicate that solidification microstructure of the ternary eutectic composite is greatly influenced by the laser processing parameters.The synthetically thermal analysis shows that the eutectic temperature of ternary Al_2O_3/YAG/ZrO_2 composite is 1 738 ℃,well matching the phase diagram of Al_2O_3-Y_2O_3-ZrO_2.

  20. Effect of thermosolutal convection on directional solidification

    Suresh V Garimella; James E Simpson


    The impact of thermosolutal convection during directional solidification is explored via results of numerical investigations. Results from fully transient numerical simulations of directional solidification in a differentially heated cavity under terrestrial conditions and Bridgman crystal growth in space are discussed. The pivotal role of both thermal and solutal convection in the solidification process is illustrated by examining these two cases. In particular, radial and longitudinal macrosegregation resulting from this thermosolutal convection is discussed.

  1. Thermal processes and solidification kinetcs of evolution of the microstructure of tin-silver-copper solder alloys

    Kinyanjui, Robert Kamau

    The adoption of Sn-Ag-Cu (SAC) Pb-free solders will affect electronic manufacturing processes and joint reliability for electronics packages. Since SAC solder has a higher melting temperature than eutectic Pb-Sn solder, higher processing temperatures will be required. The higher processing temperatures can potentially affect the microstructure of these Pb-free solder joints. We investigated the effect of thermal history on the evolution of the microstructure of Sn-xAg-yCu (0 ≤ x ≤ 4.0; 0 ≤ y ≤ 1.4, concentrations are in weight percent) solder alloys. This family of alloys falls within a class of Sn-rich Sn-Ag-Cu (SAC) alloys recommended by various international consortia for implementation in electronic manufacturing industry to replace the conventional PbSn solders. This investigation was divided into three parts: part one was an investigation of an optimum SAC alloy composition devoid of large (in length scales) intermetallic compounds (IMCs) after thermal treatment. The presence of large IMCs, with different mechanical characteristics from the bulk Sn, may compromise the mechanical integrity of the Pb-free solder interconnect. In part two of this study, we examined the growth morphology of Ag3Sn, Cu6Sn 5, and betaSn in the SAC alloys. In part three, an examination of the effect of sample size on undercooling was carried out. A Sn-Ag-Cu alloy of the composition: 96.5Sn-2.6Ag-0.9Cu (in weight percent) was found to exhibit no growth of large Ag3Sn, Cu6Sn 5 intermetallic compounds at cooling rates from 0.1 to 1°C/s. However, growth of large betaSn dendrites was observed. The crystallized Sn-Ag-Cu balls were found to contain only a few Sn grains. Also the solidification temperature of the 96.5Sn-2.6Ag-yCu (0 ≤ y ≤ 1.4) solder system was found to increase with Cu content. Further, this investigation established a strong correlation between Sn-Ag-Cu sample size and degree of undercooling for these Pb-free solder alloys. The degree of undercooling of Sn in

  2. The use of a directional solidification technique to investigate the interrelationship of thermal parameters, microstructure and microhardness of Bi–Ag solder alloys

    Spinelli, José Eduardo, E-mail: [Department of Materials Engineering, Federal University of São Carlos, UFSCar, 13565-905 São Carlos, SP (Brazil); Silva, Bismarck Luiz [Department of Materials Engineering, Federal University of São Carlos, UFSCar, 13565-905 São Carlos, SP (Brazil); Cheung, Noé; Garcia, Amauri [Department of Manufacturing and Materials Engineering, University of Campinas, UNICAMP, PO Box 6122, 13083-970 Campinas, SP (Brazil)


    Bi–Ag alloys have been stressed as possible alternatives to replace Pb-based solder alloys. Although acceptable melting temperatures and suitable mechanical properties may characterize such alloys, as referenced in literature, there is a lack of comprehension regarding their microstructures (morphologies and sizes of the phases) considering a composition range from 1.5 to 4.0 wt.%Ag. In order to better comprehend such aspects and their correlations with solidification thermal parameters (growth rate, v and cooling rate, T-dot), directional solidification experiments were carried out under transient heat flow conditions. The effects of Ag content on both cooling rate and growth rate during solidification are examined. Microstructure parameters such as eutectic/dendritic spacing, interphase spacing and diameter of the Ag-rich phase were determined by optical microscopy and scanning electron microscopy. The competition between eutectic cells and dendrites in the range from 1.5 to 4.0 wt.%Ag is explained by the coupled zone concept. Microhardness was determined for different microstructures and alloy Ag contents with a view to permitting correlations with microstructure parameters to be established. Hardness is shown to be directly affected by both solute macrosegregation and morphologies of the phases forming the Bi–Ag alloys, with higher hardness being associated with the cellular morphology of the Bi-2.5 and 4.0 wt.%Ag alloys. - Highlights: • Asymmetric zone of coupled growth for Bi–Ag is demonstrated. • Faceted Bi-rich dendrites have been characterized for Bi–1.5 wt.%Ag alloy. • Eutectic cells were shown for the Bi-2.5 and 4.0 wt.%Ag solder alloys. • Interphase spacing relations with G × v are able to represent the experimental scatters. • Hall-Petch type equations are proposed relating microstructural spacings to hardness.

  3. Dendritic Growth, Solidification Thermal Parameters, and Mg Content Affecting the Tensile Properties of Al-Mg-1.5 Wt Pct Fe Alloys

    Gomes, Leonardo F.; Silva, Bismarck L.; Garcia, Amauri; Spinelli, José E.


    Al-Mg-Fe alloys are appointed as favorable ones with respect to the costs and all the required properties for successful vessel service. However, the experimental inter-relations of solidification thermal parameters, microstructure, and mechanical strength are still undetermined. In the present research work, the dependences of tensile properties on the length scale of the dendritic morphology of ternary Al-1.2 wt pct Mg-1.5 wt pct Fe and Al-7 wt pct Mg-1.5 wt pct Fe alloys are examined. Transient heat flow conditions during solidification have been achieved by the use of a directional solidification system, thus permitting a comprehensive characterization of the dendritic microstructures to be performed. Thermo-Calc computations, X-ray diffraction, and scanning electron microscopy analyses are carried out to give support to the extensive microstructural evaluation performed with both ternary Al-Mg-Fe alloys. Experimental growth relations of primary, λ 1, and secondary, λ 2, dendrite arm spacings with cooling rate ( {dot T}_{{L}} ) and of tensile properties with λ 2 are proposed. For both alloys examined, Hall-Petch type formulas show that the tensile strength increases with the decrease in λ 2. The soundest strength-ductility balance is exhibited by the Al-7 wt pct Mg-1.5 wt pct Fe alloy specimen with refined microstructure. This is shown to be due to a more homogeneous distribution of intermetallic particles in connection with solid solution strengthening propitiated by Mg. Functional experimental inter-relations of tensile properties with growth (V L) and cooling rates ( {dot T}_{{L}} ) for both ternary Al-Mg-Fe alloys have also been derived.

  4. Outgassing Properties of Chemically Polished Titanium Materials

    Kurisu, Hiroki; Kimoto, Gou; Fujii, Hiroaki; Tanaka, Kazuhiko; Yamamoto, Setsuo; Matsuura, Mitsuru; Ishizawa, Katsunobu; Nomura, Takeru; Murashige, Nobuyuki

    We developed a chemical polishing (CP) for titanium materials applicable to ultrahigh vacuum (UHV) and extremely high vacuum (XHV) systems. The surface roughness, Ra, of the chemically polished titanium is obtained to be 25 nm by the atomic force microscopy measurement. This value is smaller than those of the base metal (BM) and the buff-polished (BP) samples. The thickness of the surface oxide layer of CP sample is estimated to be 7 nm by the cross section of transmission electron micrograph. Amount of desorption gas of CP sample obtained by the thermal desorption measurement is smaller than those of BM and BP sample, and is the same as that of the mechanochemically polished (MCP) sample. The outgassing rate of CP sample after baking at 150°C×20 h is obtained to be 7×10-13 Pa•m•s-1. This value is lower than that of standard vacuum materials by two orders of magnitude after the ordinary baking.

  5. Outgassed water on Mars - Constraints from melt inclusions in SNC meteorites

    Mcsween, Harry Y., Jr.; Harvey, Ralph P.


    The SNC (shergottite-nakhlite-chassignite) meteorites, thought to be igneous rocks from Mars, contain melt inclusions trapped at depth in early-formed crystals. Determination of the pre-eruptive water contents of SNC parental magmas from calculations of the solidification histories of these amphibole-bearing inclusions indicates that Martian magmas commonly contained 1.4 percent water by weight. When combined with an estimate of the volume of igneous materials on Mars, this information suggests that the total amount of water outgassed since 3.9 billion years ago corresponds to global depths on the order of 200 meters. This value is significantly higher than previous geochemical estimates but lower than estimates based on erosion by floods. These results imply a wetter Mars interior than has been previously thought and support suggestions of significant outgassing before formation of a stable crust or heterogeneous accretion of a veneer of cometary matter.

  6. Combined effect of non-equilibrium solidification and thermal annealing on microstructure evolution and hardness behavior of AZ91 magnesium alloy

    Zhou, Z.Z.; Yang, W., E-mail:; Chen, S.H.; Yu, H.; Xu, Z.F.


    Non-equilibrium solidification of commercial AZ91 magnesium alloy was performed by copper mold spray-casting technique and the thermal stability property of as-formed meta-stable microstructure was investigated by subsequent annealing at different temperatures and times. Remarkable grain refinement appears with increasing cooling rate during solidification process, which is accompanied by a visible cellular/dendrite transition for the grain morphology of primary phase. Moreover, the non-equilibrium solidified alloy exhibits obvious precipitation hardening effect upon annealing at 200 °C, and the precipitation mode of β-Mg{sub 17}Al{sub 12} phase changes from discontinuous to continuous with extending isothermal time from 4 h to 16 h, which generates an increase of resultant micro-hardness value. After solid solution treatment at the elevated temperature of 420 °C, the volume fraction of β-Mg{sub 17}Al{sub 12} phase decreases and a notable grain growth phenomenon occurs, which give rise to a reduction of hardness in comparison with that of as-quenched alloy.

  7. Texturing of high T(sub c) superconducting polycrystalline fibers/wires by laser-driven directional solidification in an thermal gradient

    Varshney, Usha; Eichelberger, B. Davis, III


    This paper summarizes the technique of laser-driven directional solidification in a controlled thermal gradient of yttria stabilized zirconia core coated Y-Ba-Cu-O materials to produce textured high T(sub c) superconducting polycrystalline fibers/wires with improved critical current densities in the extended range of magnetic fields at temperatures greater than 77 K. The approach involves laser heating to minimize phase segregation by heating very rapidly through the two-phase incongruent melt region to the single phase melt region and directionally solidifying in a controlled thermal gradient to achieve highly textured grains in the fiber axis direction. The technique offers a higher grain growth rate and a lower thermal budget compared with a conventional thermal gradient and is amenable as a continuous process for improving the J(sub c) of high T(sub c) superconducting polycrystalline fibers/wires. The technique has the advantage of suppressing weak-link behavior by orientation of crystals, formation of dense structures with enhanced connectivity, formation of fewer and cleaner grain boundaries, and minimization of phase segregation in the incongruent melt region.

  8. Outgassing of stagnant-lid planets

    Dorn, Caroline; Rozel, Antoine; Noack, Lena


    Little is known about compositional and structural diversity of super Earths. Super-Earths are distinct from mini-Neptunes in terms of the origin of their atmospheres, i.e., which are outgassed from the interior. Modeling the outgassing rates that arise from interior dynamics is key in order to inform the interpretation of data from current and future missions (e.g., James Webb Space telescope). Here, we present a comprehensive study on the outgassing of super-Earths of different mass, structure, composition, and temperature. We emphasize that this study is limited to planets in a stagnant-lid convection regime only. We model a convection and melting in a 2-D spherical annulus geometry. The convection code solves the conservation equations for mass, momentum and energy. Partial melt occurs where mantle temperature exceeds the solidus melting temperature. If the melt is gravitationally buoyant, we assume that melt rises immediately to the surface, while tracing the melt depletion in the mantle with particles, that advect along the convective stream lines. The model for convection and melting is applied to planets between 1 and 8 Earth masses. Besides planet mass, we test different aspects that may influence the production of melt and outgassing: (1) core size, (2) mantle composition, especially iron mantle content, (3) upper mantle temperature, (4) amount of radioactive heat sources, (5) temperature jump at the core-mantle-boundary, (6) lithosphere thickness, and (7) model resolution. We present our findings in the form of scaling laws that express the outgassing depending on investigated parameters. We find that first order effects on outgassing are energy-related parameters such as upper mantle temperature and the amount of radioactive heat sources, as well as planet mass. Interestingly, the composition of the mantle has only second-order effects. However, we note that we use reference profiles for pressure and temperature and hence phase transition depths are set

  9. Low-Outgassing Photogrammetry Targets for Use in Outer Space

    Gross, Jason N.; Sampler, Henry; Reed, Benjamin B.


    A short document discusses an investigation of materials for photogrammetry targets for highly sensitive optical scientific instruments to be operated in outer space and in an outer-space-environment- simulating thermal vacuum chamber on Earth. A key consideration in the selection of photogrammetry-target materials for vacuum environments is the need to prevent contamination that could degrade the optical responses of the instruments. Therefore, in addition to the high levels and uniformity of reflectivity required of photogrammetry-target materials suitable for use in air, the materials sought must exhibit minimal outgassing. Commercially available photogrammetry targets were found to outgas excessively under the thermal and vacuum conditions of interest; this finding prompted the investigators to consider optically equivalent or superior, lower-outgassing alternative target materials. The document lists several materials found to satisfy the requirements, but does not state explicitly whether the materials can be used individually or must be combined in the proper sequence into layered target structures. The materials in question are an aluminized polyimide tape, an acrylic pressure- sensitive adhesive, a 500-A-thick layer of vapor-deposited aluminum, and spherical barium titanate glass beads having various diameters from 20 to 63 microns..

  10. Packaging Materials Outgassing Study Final Report

    Smith, R. A. [Oak Ridge Y-12 Plant (Y-12), Oak Ridge, TN (United States)


    An outgassing study was conducted on two polyurethane packaging foams, two polymer bottles (polytetrafluoroethylene and polyethylene), and two polymer lids. The purpose was to measure the volume of gases that diffuse from these packaging materials at a maximum of 400-degrees F when stored in ambient air within sealed containers.

  11. Approximate Analytical Solution for One-Dimensional Solidification Problem of a Finite Superheating Phase Change Material Including the Effects of Wall and Thermal Contact Resistances

    Hamid El Qarnia


    Full Text Available This work reports an analytical solution for the solidification of a superheating phase change material (PCM contained in a rectangular enclosure with a finite height. The analytical solution has been obtained by solving nondimensional energy equations by using the perturbation method for a small perturbation parameter: the Stefan number, ε. This analytical solution, which takes into account the effects of the superheating of PCM, finite height of the enclosure, thickness of the wall, and wall-solid shell interfacial thermal resistances, was expressed in terms of nondimensional temperature distributions of the bottom wall of the enclosure and both PCM phases, and the dimensionless solid-liquid interface position and its dimensionless speed. The developed solution was firstly compared with that existing in the literature for the case of nonsuperheating PCM. The predicted results agreed well with those published in the literature. Next, a parametric study was carried out in order to study the impacts of the dimensionless control parameters on the dimensionless temperature distributions of the wall, the solid shell, and liquid phase of the PCM, as well as the solid-liquid interface position and its dimensionless speed.

  12. Satellite Contamination and Materials Outgassing Knowledge base

    Minor, Jody L.; Kauffman, William J. (Technical Monitor)


    Satellite contamination continues to be a design problem that engineers must take into account when developing new satellites. To help with this issue, NASA's Space Environments and Effects (SEE) Program funded the development of the Satellite Contamination and Materials Outgassing Knowledge base. This engineering tool brings together in one location information about the outgassing properties of aerospace materials based upon ground-testing data, the effects of outgassing that has been observed during flight and measurements of the contamination environment by on-orbit instruments. The knowledge base contains information using the ASTM Standard E- 1559 and also consolidates data from missions using quartz-crystal microbalances (QCM's). The data contained in the knowledge base was shared with NASA by government agencies and industry in the US and international space agencies as well. The term 'knowledgebase' was used because so much information and capability was brought together in one comprehensive engineering design tool. It is the SEE Program's intent to continually add additional material contamination data as it becomes available - creating a dynamic tool whose value to the user is ever increasing. The SEE Program firmly believes that NASA, and ultimately the entire contamination user community, will greatly benefit from this new engineering tool and highly encourages the community to not only use the tool but add data to it as well.

  13. Photoresist outgassing at 157 nm exposure

    Hien, Stefan; Angood, Steve; Ashworth, Dominic; Basset, Steve; Bloomstein, Theodore M.; Dean, Kim R.; Kunz, Roderick R.; Miller, Daniel A.; Patel, Shashikant; Rich, Georgia K.


    Contamination of optical elements during photoresist exposure is a serious issue in optical lithography. The outgassing of photoresist has been identified as a problem at 248nm and 193nm in production because the organic films that can be formed on an exposure lens can cause transmission loss and sever image distortion. At these exposure energies, the excitation of the photo acid generator, formation of acid, and cleavage of the protecting group are highly selective processes. At 157nm, the exposure energy is much higher (7.9 eV compared to 6.4 eV at 193nm) and it is known from laser ablation experiments that direct laser cleavage of sigma bonds occurs. The fragments formed during this irradiation can be considered as effective laser deposition precursors even in the mid ppb level. In this study, methods to quantify photoresist outgassing at 157 nm are discussed. Three criteria have been set up at International SEMATECH to protect lens contamination and to determine the severity of photoresist outgassing. First, we measured film thickness loss as a function of exposure dose for a variety of materials. In a second test we studied the molecular composition of the outgassing fragments with an exposure chamber coupled to a gas chromatograph and a mass spectrometer detector. Our third method was a deposition test of outgassing vapors on a CaF2 proof plate followed by analysis using VUV and X-ray photoelectron spectroscopies (XPS). With this technique we found deposits for many different resists. Our main focus is on F- and Si- containing resists. Both material classes form deposits especially if these atoms are bound to the polymer side chains. Whereas the F-containing films can be cleaned off under 157nm irradiation, cleaning of Si-containing films mainly produces SiO2. Our cleaning studies of plasma deposited F-containing organic films on SiO2 did not indicate damage of this surface by the possible formation of HF. Despite that we strongly recommend engineering

  14. Thermal and structural studies about the solidification process of grey cast irons; Estudio termico y estructural del proceso de solidificacion de funciones de hierro con grafito laminar

    Larranaga, P.; Sertucha, J.


    The grey iron casting manufacture is an industrial process extendly used today. Therefore, the study of the solidification features obtained from this iron and the factors that have influence on such transition becomes a powerful tool in order to support the technological development of this type of material. In the present work, three inoculated alloys with different chemical compositions (hypo eutectic, eutectic and hyper eutectic) have been selected so as to comparatively analyse the structural characteristics of the irons during the liquid-solid transformation. The behaviour of the samples has been controlled recording the cooling curves and then they have been quenched in order to study the structural characteristics at different stages of the solidification. The selected alloys show different solidification features as a function of the chemical composition and the corresponding nucleation potential. The obtained results have been discussed in terms of a comparative analysis, establishing a solidification model that explains the industrial behaviour of the alloys. (Author)

  15. Effects of laser processing parameters on thermal behavior and melting/solidification mechanism during selective laser melting of TiC/Inconel 718 composites

    Shi, Qimin; Gu, Dongdong; Xia, Mujian; Cao, Sainan; Rong, Ting


    A three-dimensional finite element model is proposed to study the effects of laser power and scan speed on the thermal behavior and melting/solidification mechanism during selective laser melting (SLM) of TiC/Inconel 718 powder system. The cooling time during powder delivery is taken into account to simulate the actual production process well. It shows obviously the existence of heat accumulation effect in SLM process and, the tailored set of cooling time of 10 ms during powder delivery alleviates that effectively. The maximum temperature gradient in the molten pool slightly increases from 1.30×104 °C/mm to 2.60×104 °C/mm as the laser power is increased from 75 W to 150 W. However, it is negligibly sensitive to the variation of scan speed. There is a positive corresponding relationship between the maximum rate of temperature change and processing parameters. A low laser power (75 W) or a high scan speed (300 mm/s) is more energy efficient in Z-direction of the molten pool, giving rise to a deep-narrow cross section of the pool. Whereas, a high laser power (150 W) or a low scan speed (50 mm/s) causes a shallow-wide cross section of the molten pool, meaning it is more energy efficient in the Y-direction of the melt. The combination of a laser power of 125 W and a scan speed of 100 mm/s contributes to achieve a sound metallurgical bonding between the neighbor layers and tracks, due to the proper molten pool size (width: 109.3 μm; length: 120.7 μm; depth: 67.8 μm). The SLM experiments on TiC/Inconel 718 powder system are performed to verify the reliability and accuracy of the physical model and, simulation results are proved to be correct.

  16. Outgassing from Open and Closed Magma Foams

    Felix W. von Aulock


    Full Text Available During magma ascent, bubbles nucleate, grow, coalesce, and form a variably permeable porous network. The reorganization, failing and sealing of bubble walls may contribute to the opening and closing of the volcanic system. In this contribution we cause obsidian to nucleate and grow bubbles to high gas volume fraction at atmospheric pressure by heating samples to 950°C for different times and we image the growth through a furnace. Following the experiment, we imaged the internal pore structure of selected samples in 3D and then dissected for analysis of textures and dissolved water content remnant in the glass. We demonstrate that in these high viscosity systems, during foaming and subsequent foam-maturation, bubbles near a free surface resorb via diffusion to produce an impermeable skin of melt around a foam. The skin thickens non-linearly through time. The water concentrations at the outer and inner skin margins reflect the solubility of water in the melt at the partial pressure of water in atmospheric and water-rich bubble conditions, respectively. In this regime, mass transfer of water out of the system is diffusion limited and the sample shrinks slowly. In a second set of experiments in which we polished off the skin of the foamed samples and placed them back in the furnace to allow open system outgassing, we observe rapid sample contraction and collapse of the connected pore network under surface tension as the system efficiently outgasses. In this regime, mass transfer of water is permeability limited. We conclude that diffusion-driven skin formation can efficiently seal connectivity in foams. When rupture of melt film around gas bubbles (i.e., skin removal occurs, then rapid outgassing and consequent foam collapse modulate gas pressurization in the vesiculated magma. The mechanisms described here are relevant to the evolution of pore network heterogeneity in permeable magmas.

  17. Thermal-vacuum response of polymer matrix composites in space

    Tennyson, R. C.; Matthews, R.


    This report describes a thermal-vacuum outgassing model and test protocol for predicting outgassing times and dimensional changes for polymer matrix composites. Experimental results derived from 'control' samples are used to provide the basis for analytical predictions to compare with the outgassing response of Long Duration Exposure Facility (LDEF) flight samples. Coefficient of thermal expansion (CTE) data are also presented. In addition, an example is given illustrating the dimensional change of a 'zero' CTE laminate due to moisture outgassing.

  18. Quantitative measurement of resist outgassing during exposure

    Maxim, Nicolae; Houle, Frances A.; Huijbregtse, Jeroen; Deline, Vaughn R.; Truong, Hoa; van Schaik, Willem


    Determination of both the identity and quantity of species desorbing from photoresists during exposure at any wavelength - 248nm, 193nm and EUV - has proved to be very challenging, adding considerable uncertainty to the evaluation of risks posed by specific photoresists to exposure tool optics. Measurements using a variety of techniques for gas detection and solid film analysis have been reported but analytical results have not in general been easy to compare or even in apparent agreement, in part due to difficulties in establishing absolute calibrations. In this work we describe two measurement methods that can be used for any exposure wavelength, and show that they provide self-consistent quantitative outgassing data for 2 all-organic and 2 Si-containing 193 nm resists. The first method, based upon gas collection, uses two primary chromatographic techniques. Organic products containing C, S and Si are determined by collection of vapors emitted during exposure in a cold trap and analysis by Gas Chromatography-Flame Ionization Detector-Pulsed Flame Photometric Detector-Mass Spectrometry (GC-FID-PFPD-MS). Inorganic products such as SO2 are identified by adsorbent bed with analysis by Gas Particle-Ion Chromatography (GP-IC). The calibration procedure used provides reasonable accuracy without exhaustive effort. The second method analyzes the elemental concentrations in resist films before and after exposure by secondary ion mass spectrometry technique (SIMS), which requires only knowledge of the resist compositions to be quantitative. The extent of outgassing of C and S determined by the two methods is in good agreement for all 4 resists, especially when taking their fundamentally different characters into account. Overall, the gas collection techniques yielded systematically lower outgassing numbers than did SIMS, and the origins of the spread in values, which likely bracket the true values, as well as detection limits will be discussed. The data for Si were found to

  19. Surface Effects of Satellite Material Outgassing Products


    I 8c ADDRF.SS (C//y, Ste~e, and ZlPCode) Air Force Systems Command Arnold Air Force Base, TN 37389-5000 I eor ,;~m~ed OMB N(k 0704-0r88 lb... CO2 is easily identified by the very sharp absorption band located at 2,340 cm -1 (4.3 "m). In cases where there is strong absorption by CO2 , thicknesses of 0.12, 1.00, and 5.24 "m. Water and CO2 were the only major outgassed species observed. Although no total mass loss (TML

  20. Directional Solidification of Ledeburite

    M. Trepczyńska-Łent


    Full Text Available Directional solidification of ledeburite was realised out using a Bridgman’s device. The growth rate for movement sample v=83.3 μm/s was used. In one sample the solidification front was freezing. The value of temperature gradient in liquid at the solidification front was determined. Interfacial distance λ on the samples was measured with NIS-Elements application for image analysis.

  1. MAVEN Contamination Venting and Outgassing Analysis

    Petro, Elaine M.; Hughes, David W.; Secunda, Mark S.; Chen, Philip T.; Morrissey, James R.; Riegle, Catherine A.


    Mars Atmosphere and Volatile EvolutioN (MAVEN) is the first mission to focus its study on the Mars upper atmosphere. MAVEN will study the evolution of the Mars atmosphere and climate, by examining the conduit through which the atmosphere has to pass as it is lost to the upper atmosphere. An analysis was performed for the MAVEN mission to address two distinct concerns. The first goal of the analysis was to perform an outgassing study to determine where species outgassed from spacecraft materials would redistribute to and how much of the released material might accumulate on sensitive surfaces. The second portion of the analysis serves to predict what effect, if any, Mars atmospheric gases trapped within the spacecraft could have on instrument measurements when re-released through vents. The re-release of atmospheric gases is of interest to this mission because vented gases from a higher pressure spacecraft interior could bias instrument measurements of the Mars atmosphere depending on the flow rates and directions.

  2. A Coupled Thermal, Fluid Flow, and Solidification Model for the Processing of Single-Crystal Alloy CMSX-4 Through Scanning Laser Epitaxy for Turbine Engine Hot-Section Component Repair (Part I)

    Acharya, Ranadip; Bansal, Rohan; Gambone, Justin J.; Das, Suman


    Scanning laser epitaxy (SLE) is a new laser-based additive manufacturing technology under development at the Georgia Institute of Technology. SLE is aimed at the creation of equiaxed, directionally solidified, and single-crystal deposits of nickel-based superalloys through the melting of alloy powders onto superalloy substrates using a fast scanning Nd:YAG laser beam. The fast galvanometer control movement of the laser (0.2 to 2 m/s) and high-resolution raster scanning (20 to 200 µm line spacing) enables superior thermal control over the solidification process and allows the production of porosity-free, crack-free deposits of more than 1000 µm thickness. Here, we present a combined thermal and fluid flow model of the SLE process applied to alloy CMSX-4 with temperature-dependent thermo-physical properties. With the scanning beam described as a moving line source, the instantaneous melt pool assumes a convex hull shape with distinct leading edge and trailing edge characteristics. Temperature gradients at the leading and trailing edges are of order 2 × 105 and 104 K/m, respectively. Detailed flow analysis provides insights on the flow characteristics of the powder incorporating into the melt pool, showing velocities of order 1 × 10-4 m/s. The Marangoni effect drives this velocity from 10 to 15 times higher depending on the operating parameters. Prediction of the solidification microstructure is based on conditions at the trailing edge of the melt pool. Time tracking of solidification history is incorporated into the model to couple the microstructure prediction model to the thermal-fluid flow model, and to predict the probability of the columnar-to-equiaxed transition. Qualitative agreement is obtained between simulation and experimental result.

  3. Fundamental Metallurgy of Solidification

    Tiedje, Niels


    The text takes the reader through some fundamental aspects of solidification, with focus on understanding the basic physics that govern solidification in casting and welding. It is described how the first solid is formed and which factors affect nucleation. It is described how crystals grow from ...

  4. 自凝与热凝树脂义齿材料摩擦磨损行为对比%Comparison of friction and wear characteristic of self-solidification and thermal coagulation resin denture material

    田晓; 耿建; 马力辉; 牛建刚; 马凯


    By using a reciprocating sliding wear test machine, friction and wear characteristic of two types of dental resin were investigated and compared under the dry friction condition. A normal force of 20N, reciprocating amplitude 85mm and frequency of 0. 5 Hz were used for all the wear tests. The contact was in a ball-on-flat, the ball was self-solidification resin and thermal coagulation resin, the flat was self-solidification resin. By using dynamic strain instrument measure the strain of strain gauge, and then calculated the friction coefficient. Through the analysis of friction coefficient, wear loss and electron micrograph observation get the wear-resisting performance of the two kinds of materials. Through the observation of electron micrograph, the self-solidification resin denture material emerged plastic flow and surface smooth layer on surface in the process of wear, its wear loss was light. The compactness of the thermal coagulation resin denture was bad, the layer wear was obvious and the material of pores around was easy to fall off, so the friction coefficient of self-solidification resin denture material was less than that of thermal coagulation resin denture material, and the wear-resisting performance showed the opposite.%在自制的往复摩擦磨损实验台上,以球面接触方式,在干摩擦、法向压力为20 N、往复频率为0.5 Hz、摆幅85 mm条件下,研究了牙科用的自凝和热凝树脂球分别对自凝树脂板的摩擦磨损行为.实验过程中利用动态应变仪测量摩擦过程中应变片的应变,进而计算出摩擦系数.结合电镜观察比较得出了自凝与热凝2种义齿材料的耐磨性能:自凝树脂义齿材料磨损过程中会出现材料塑性流动和表面致密的光滑层,磨损轻微,后者材料致密性差有气孔,磨损过程中出现层状磨损,气孔周围材料易脱落,结果自凝材料的摩擦系数低于热凝材料,且耐磨性高于热凝材料.

  5. Eutectic-Free Superalloy Made By Directional Solidification

    Schmidt, Deborah Dianne


    By suitable control of thermal conditions in directional-solidification process, supperalloy structural and machine components (e.g., turbine blades) cast with microstructures enhancing resistance to fatigue. Specific version of process and thermal conditions chosen to reduce micro-segregation during solidification and to minimize or eliminate script carbide and eutectic-phase inclusions, which are brittle inclusions found to decrease resistance to fatigue.

  6. Parabolic aircraft solidification experiments

    Workman, Gary L. (Principal Investigator); Smith, Guy A.; OBrien, Susan


    A number of solidification experiments have been utilized throughout the Materials Processing in Space Program to provide an experimental environment which minimizes variables in solidification experiments. Two techniques of interest are directional solidification and isothermal casting. Because of the wide-spread use of these experimental techniques in space-based research, several MSAD experiments have been manifested for space flight. In addition to the microstructural analysis for interpretation of the experimental results from previous work with parabolic flights, it has become apparent that a better understanding of the phenomena occurring during solidification can be better understood if direct visualization of the solidification interface were possible. Our university has performed in several experimental studies such as this in recent years. The most recent was in visualizing the effect of convective flow phenomena on the KC-135 and prior to that were several successive contracts to perform directional solidification and isothermal casting experiments on the KC-135. Included in this work was the modification and utilization of the Convective Flow Analyzer (CFA), the Aircraft Isothermal Casting Furnace (ICF), and the Three-Zone Directional Solidification Furnace. These studies have contributed heavily to the mission of the Microgravity Science and Applications' Materials Science Program.

  7. Advances in Solidification Processing

    Hugo F. Lopez


    Full Text Available Melt solidification is the shortest and most viable route to obtain components, starting from the design to the finished products. Hence, a sound knowledge of the solidification of metallic materials is essential for the development of advanced structural metallic components that drive modern technological societies. As a result, there have been innumerable efforts and full conferences dedicated to this important subject [1–6]. In addition, there are various scientific journals fully devoted to investigating the various aspects which give rise to various solidification microstructures [7–9]. [...

  8. Modelling directional solidification

    Wilcox, William R.; Regel, Liya L.


    This grant, NAG8-831, was a continuation of a previous grant, NAG8-541. The long range goal of this program has been to develop an improved understanding of phenomena of importance to directional solidification, in order to enable explanation and prediction of differences in behavior between solidification on Earth and in space. Emphasis in the recently completed grant was on determining the influence of perturbations on directional solidification of InSb and InSb-GaSb alloys. In particular, the objective was to determine the influence of spin-up/spin-down (ACRT), electric current pulses and vibrations on compositional homogeneity and grain size.

  9. Numerical Simulation of Thermal Stresses of Castings during Solidification Based on Personal Computer and Its Engineering Application%基于微机的铸件凝固过程应力数值模拟及工程应用

    李培锋; 孙立斌; 康进武; 柳百成


    Based on personal computer, a FDM/FEM integrated analysis system of thermal stresses was developed, and 3D numerical simulaion of thermal stresses in large castings during solidification has been carried out. The residual stress fields in the blower case castings with different technological processes were analyzed and the tendency of hot tearing in the main shaft of water turbine was predicted.%开发了基于微机平台的FDM/FEM集成应力分析系统,对复杂大型铸件的凝固过程热应力进行三维数值模拟;比较了鼓风机机壳在两种不同工艺方案中的残余应力,并且分析了水轮机长轴头的热裂倾向。

  10. Finite element modelling of solidification phenomena

    K N Seetharamu; R Paragasam; Ghulam A Quadir; Z A Zainal; B Sathya Prasad; T Sundararajan


    The process of solidification process is complex in nature and the simulation of such process is required in industry before it is actually undertaken. Finite element method is used to simulate the heat transfer process accompanying the solidification process. The metal and the mould along with the air gap formation is accounted in the heat transfer simulation. Distortion of the casting is caused due to non-uniform shrinkage associated with the process. Residual stresses are induced in the final castings. Simulation of the shrinkage and the thermal stresses are also carried out using finite element methods. The material behaviour is considered as visco-plastic. The simulations are compared with available experimental data and the comparison is found to be good. Special considerations regarding the simulation of solidification process are also brought out.

  11. Melt Flow Control in the Directional Solidification of Binary Alloys

    Zabaras, Nicholas


    Our main project objectives are to develop computational techniques based on inverse problem theory that can be used to design directional solidification processes that lead to desired temperature gradient and growth conditions at the freezing front at various levels of gravity. It is known that control of these conditions plays a significant role in the selection of the form and scale of the obtained solidification microstructures. Emphasis is given on the control of the effects of various melt flow mechanisms on the local to the solidification front conditions. The thermal boundary conditions (furnace design) as well as the magnitude and direction of an externally applied magnetic field are the main design variables. We will highlight computational design models for sharp front solidification models and briefly discuss work in progress toward the development of design techniques for multi-phase volume-averaging based solidification models.

  12. Solidification microstructure development

    G Phanikumar; K Chattopadhyay


    In the present article, evolution of microstructure during solidification, as a function of various parameters, is discussed. Macrosegregation is described as being due to insufficient diffusivity of solute in the solid. Pattern formation is discussed in the light of instabilities at the solidification growth front. An overview of the scaling relations for various microstructures is given. Metastable extensions to equilibrium phase diagrams and corrections to equilibrium quantities are described.

  13. Solidification and casting

    Cantor, Brian


    INDUSTRIAL PERSPECTIVEDirect chillcasting of aluminium alloysContinuous casting of aluminium alloysContinuous casting of steelsCastings in the automotive industryCast aluminium-silicon piston alloysMODELLING AND SIMULATIONModelling direct chill castingMold filling simulation of die castingThe ten casting rulesGrain selection in single crystal superalloy castingsDefects in aluminium shape castingPattern formation during solidificationPeritectic solidificationSTRUCTURE AND DEFECTSHetergeneous nucleation in aluminium alloysCo

  14. In-Space Outgassing Laboratory Distant from Earth (ISOLDE)

    Çay, Yiǧit; Cilden, Demet; Mirzai, Amin; Gençkal, Neslihan; Aydın, Egemen; Kırcı, İrem


    Outgassing is the phenomenon occurring when the gasses dissolved, trapped, frozen or absorbed in materials are released. The phenomenon is proved to be dangerous for spacecraft body and subsystems. Outgassing rates of the materials used on spacecraft should be evaluated while the satellite in ultra-high vacuum environment in order to determine more accurate results than those experimented on ground. Newly designed materials can also be tested so as to show that they manage to prevent the electronic and optical systems on the spacecraft as expected. A small satellite mission, ISOLDE is proposed to investigate outgassing in polar HEO by its interior laboratory units. Payload laboratory will conduct a spectral analysis of outgassing for different materials used as main spacecraft materials both raw and zeolite -a gas absorbing material proposed by NASA- covered. In this study, conceptual design of ISOLDE is presented including preliminary studies of orbit insertion, payload design and subsystem architectures.

  15. Outgassing Studies of Foams for the W80 LEP (FY05)

    Alviso, C; Harvey, C; Vance, A


    Removable epoxy foam (REF) is a novel material developed by researchers at Sandia National Laboratories to simplify the removal of encapsulants from electronic components [McElhanon, et al., Journal of Applied Polymer Science, 2002, 85, 1496-1502]. The material is based on a resin that includes a thermally reversible chemical bond. When the material is heated at relatively mild temperatures ({approx}50-90 C) in the presence of appropriate solvents, the reversible bonds are broken, and the material is easily rinsed away. In order to ease the removal of the encapsulant for surveillance purposes, it was proposed to use REF in the W80 LEP in place of the polyurethane TDI (toluene diisocyanate), which is being phased out at the Kansas City Plant due to toxicity concerns. Colleagues at Sandia noted that REF exhibited especially high outgassing of the liquid fluorinert, FC-72, which is used at a level of 5 wt% as the blowing agent in the foaming process. After obtaining a sample of the material from Sandia, headspace solid phase microextraction gas chromatography-mass spectrometry (SPME GC/MS) measurements were performed. These measurements revealed significant outgassing of fluorinert as well as other solvents and siloxanes [Memo, Vance, 3/3/05 & Vance, Foam PRT presentation UCRL-PRES-212462]. This report is intended to summarize foam outgassing studies performed at LLNL in support of the W80 LEP.

  16. Materials Outgassing Rate Decay in Vacuum at Isothermal Conditions

    Huang, Alvin Y.; Kastanas, George N.; Kramer, Leonard; Soares, Carlos E.; Mikatarian, Ronald R.


    As a laboratory for scientific research, the International Space Station has been in Low Earth Orbit for nearly 20 years and is expected to be on-orbit for another 10 years. The ISS has been maintaining a relatively pristine contamination environment for science payloads. Materials outgassing induced contamination is currently the dominant source for sensitive surfaces on ISS and modeling the outgassing rate decay over a 20 to 30 year period is challenging. Materials outgassing is described herein as a diffusion-reaction process using ASTM E 1559 rate data. The observation of -1/2 (diffusion) or non-integers (reaction limited) as rate decay exponents for common ISS materials indicate classical reaction kinetics is unsatisfactory in modeling materials outgassing. Non-randomness of reactant concentrations at the interface is the source of this deviation from classical reaction kinetics. A diffusion limited decay was adopted as the result of the correlation of the contaminant layer thicknesses on returned ISS hardware, the existence of high outgassing silicone exhibiting near diffusion limited decay, and the confirmation of non-depleted material after ten years in the Low Earth Orbit.Keywords: Materials Outgassing, ASTM E 1559, Reaction Kinetics, Diffusion, Space Environments Effects, Contamination

  17. Variable-Temperature-Gradient Device for Solidification Research

    Kaukler, W. F.


    Device for research in solidification and crystal growth allows crystallization of melt observed as occurs. Temperature gradient across melt specimen increased or decreased rapidly while solidification front proceeds at constant speed across sample. Device moves sample at same speed, thereby holding position of liquid/solid interface stationary within field of optical microscope. Device, variabletemperature-gradient microscope stage, used to study crystal growth at constant rate while thermal driving force is varied.

  18. Models of Rapid Solidification

    Gilmer, G. H.; Broughton, J. Q.


    Laser annealing studies provide much information on various consequences of rapid solidification, including the trapping of impurities in the crystal, the generation of vacancies and twins, and on the fundamental limits to the speed of the crystal-melt interface. Some results obtained by molecular dynamics methods of the solidification of a Lennard-Jones liquid are reviewed. An indication of the relationship of interface speed to undercooling for certain materials can be derived from this model. Ising model simulations of impurity trapping in silicon are compared with some of the laser annealing results. The consequences of interface segregation and atomic strain are discussed.

  19. Solidification modeling: Status and outlook

    Dantzig, J. A.


    Solidification modeling is a complex and highly advanced field. This article examines the state of the art in solidification modeling, including physical phenomena of solidification such as heat extraction, transport processes within a casting, and dimensional changes in the casting and mold during solidification. Also examined are current efforts to model these phenomena and the strengths and weaknesses of these efforts. Finally, obstacles to solidification modeling, such as speed and cost of the process, are considered, along with the likelihood those obstacles will be overcome.


    E. I. Marukovich


    Full Text Available The new method of continuously iterative casting of hollow cylindrical castings from cast iron without application of core, based on the principle of direction of metal solidification is presented in the work. the thermal condition of crystallizer at iterative temperature influences on its internal surface and solidification of casting in the conditions of intensive one-way heat sink and presence of constant overheat on front of solidification is examined.

  1. [Solidification of volatile oil with graphene oxide].

    Yan, Hong-Mei; Jia, Xiao-Bin; Zhang, Zhen-Hai; Sun, E; Xu, Yi-Hao


    To evaluate the properties of solidifying volatile oil with graphene oxide, clove oil and zedoary turmeric oil were solidified by graphene oxide. The amount of graphene oxide was optimized with the eugenol yield and curcumol yield as criteria. Curing powder was characterized by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The effects of graphene oxide on dissolution in vitro and thermal stability of active components were studied. The optimum solidification ratio of graphene oxide to volatile oil was 1:1. Dissolution rate of active components had rare influence while their thermal stability improved after volatile oil was solidified. Solidifying herbal volatile oil with graphene oxide deserves further study.

  2. Seaweed to dendrite transition in directional solidification.

    Provatas, Nikolas; Wang, Quanyong; Haataja, Mikko; Grant, Martin


    We simulate directional solidification using a phase-field model solved with adaptive mesh refinement. For small surface tension anisotropy directed at 45 degrees relative to the pulling direction we observe a crossover from a seaweed to a dendritic morphology as the thermal gradient is lowered, consistent with recent experimental findings. We show that the morphology of crystal structures can be unambiguously characterized through the local interface velocity distribution. We derive semiempirically an estimate for the crossover from seaweed to dendrite as a function of thermal gradient and pulling speed.

  3. Shape of growth cells in directional solidification.

    Pocheau, A; Georgelin, M


    The purpose of this study is to characterize experimentally the whole shape of the growth cells displayed in directional solidification and its evolution with respect to control parameters. A library of cells is first built up from observation of directional solidification of a succinonitrile alloy in a large range of pulling velocity, cell spacing, and thermal gradient. Cell boundaries are then extracted from these images and fitted by trial functions on their whole profile, from cell tip to cell grooves. A coherent evolution of the fit parameters with the control parameters is evidenced. It enables us to characterize the whole cell shape by a single function involving only two parameters which vary smoothly in the control parameter space. This, in particular, evidences a continuous evolution of the cell geometry at the cell to dendrite transition which denies the existence of a change of branch of solutions at the occurrence of sidebranching. More generally, this global determination of cell shape complemented with a previous determination of the position of cells in the thermal field (the cell tip undercooling) provides a complete characterization of growth solutions and of their evolutions in this system. It thus brings about a relevant framework for testing and improving theoretical and numerical understanding of cell shapes and cell stability in directional solidification.

  4. Qualitative and quantitative characterization of outgassing from SU-8

    Melai, J.; Salm, Cora; Wolters, Robertus A.M.; Schmitz, Jurriaan


    SU-8 is often used as a structural material in Microsystems. In this work, the outgassing characteristics from such cross-linked SU-8 layers are studied using mass spectrometry and gas-chromatography techniques. With these methods the composition of the released matter can be identified, also the ou

  5. Outgassing studies of materials for the TRT construction

    Guarino, F; Romaniouk, A; Soutchkov, S; Tartarelli, F


    Systematic outgassing studies of 7 materials and 10 glues candidates to be used in the construction of the TRT are persented. Each sample has been tested before and after irradiation up to 50 Mrad dose. Some results on tests of the electrical and mechanical properties of the materals are also presented.

  6. Measurement of outgassing rate for GTAW welded SS304 materials

    Bukhari, Mohsin; Mukherjee, Samiran; Panchal, Paresh; Gangradey, Ranjana; Shukla, Ajit Kumar


    Outgassing plays an important role to achieve Ultra High Vacuum (UHV) and to maintaining the required vacuum level of the vessel. For a large size machines like Tokamak, accelerators, space simulation chambers, outgassing from the structural materials and their welding sections need to be checked during the design. Hence studies were carried out for the measurement of outgassing rate for the Gas Tungsten Arc Welding (GTAW) welded SS304 materials at OutGassing Measurement System (OGMS) at IPR Extension Lab. The system consists of two chambers, pumping chamber and sample chamber, made up of 304 grades Stainless Steel pre-air baked at 400 °C. The pumping chamber connected to a turbo molecular pump having pumping speed 240 l/s, backed by a rotary vacuum pump having pumping speed 5m3/hour. Pumping chamber and sample chamber connected through a 100 CF flange having a circular aperture of 5.2 mm diameter. The conductance of aperture is 2.47 l/s. Bare SS304 sample & GTAW welded SS304 samples are prepared with 100mmX50mmX5mm and 95mmX55mmX5mm dimensions respectively. The base outgassing rate of the blank system is 2.34×10-11 mbar l/s-cm2. The calculated outgassing rate is 3.66×10-10 & 4.37×10-10 mbar l/s-cm2 for bare sample & welded sample. From the partial pressure analysis it has been found that hydrogen and nitrogen are in the partial level of 3.35×10-9 & 2.36×10-9 for bare sample and 3.14×10-9 mbar & 2.33×10-9 mbar for welded sample. It has been observed that, the GTAW doesn't have major effect on outgassing rate and one can use welded joint for designing a large vessel welding sections.

  7. Outgassing of Flown and Unflown MIR Solar Cells

    Harvey, Gale A.; Kinard, William H.; Wilson, Linda A.


    A solar panel array with more than ten years space exposure was removed from the Mir core module in November 1997, and an eight panel section was returned to Earth in January 1998. Several solar cells were removed from panel eight of the returned array and placed in a high vacuum system with a residual gas analyzer (200 amu mass spectrometer) and a cold finger. Similar unflown solar cells of the same vintage were later obtained from Energia. Several of the unflown cells were also placed in the vacuum system and outgassed residues were collected on the LN2 cold finger. Almost 3 mg of outgassed residue was collected -from a string of three unflown solar cells over a period of 94 hours under vacuum. The collected residue was weighed with a microbalance, and then the residue was analyzed by FTIR spectroscopy, and by gas chromatograph-mass spectroscopy. About 25 outgassed constituents were separated by the gas chromatograph, and a high-resolution mass spectrum was obtained of each constituent. Molecular identifications have been made for the constituents. The constituents are primarily cyclic siloxanes, and several of the constituents are isomers of the same molecule. Most of the outgassed constituents have a molecular mass of about 500 amu. Almost one mg of residue was extracted from one sq cm of coverglass/adhesive from a flown solar cell by soaking in isopropyl alcohol for 30 minutes. The gas chromatograph separated about 20 constituents. The constituents are mostly cyclic siloxanes with linear branches, hydrocarbons, and phthalates. The typical molecular mass is about 600 amu. These identifications of specific outgassing molecules have resulted in a more complete understanding of the SiO(x) contamination on the Mir solar cell coverglasses, and on the MEEP experiment trays and optical specimens during the Shuttle-Mir Phase One flight experiment program. Adjusted outgassing rates based on the data reported here, and/or measured outgassing rates and specific molecular

  8. Outgassing of Flown and Unflown MIR Solar Cells

    Harvey, Gale A.; Kinard, William H.; Wilson, Linda A.


    A solar panel array with more than ten years space exposure was removed from the Mir core module in November 1997, and an eight panel section was returned to Earth in January 1998. Several solar cells were removed from panel eight of the returned array and placed in a high vacuum system with a residual gas analyzer (200 amu mass spectrometer) and a cold finger. Similar unflown solar cells of the same vintage were later obtained from Energia. Several of the unflown cells were also placed in the vacuum system and outgassed residues were collected on the LN2 cold finger. Almost 3 mg of outgassed residue was collected -from a string of three unflown solar cells over a period of 94 hours under vacuum. The collected residue was weighed with a microbalance, and then the residue was analyzed by FTIR spectroscopy, and by gas chromatograph-mass spectroscopy. About 25 outgassed constituents were separated by the gas chromatograph, and a high-resolution mass spectrum was obtained of each constituent. Molecular identifications have been made for the constituents. The constituents are primarily cyclic siloxanes, and several of the constituents are isomers of the same molecule. Most of the outgassed constituents have a molecular mass of about 500 amu. Almost one mg of residue was extracted from one sq cm of coverglass/adhesive from a flown solar cell by soaking in isopropyl alcohol for 30 minutes. The gas chromatograph separated about 20 constituents. The constituents are mostly cyclic siloxanes with linear branches, hydrocarbons, and phthalates. The typical molecular mass is about 600 amu. These identifications of specific outgassing molecules have resulted in a more complete understanding of the SiO(x) contamination on the Mir solar cell coverglasses, and on the MEEP experiment trays and optical specimens during the Shuttle-Mir Phase One flight experiment program. Adjusted outgassing rates based on the data reported here, and/or measured outgassing rates and specific molecular

  9. Directional Solidification of AlSi Alloys with Fe Intermetallic Phases

    Mikołajczak P.


    Full Text Available Directional solidification technique is an important research instrument to study solidification of metals and alloys. In the paper the model [6,7,8] of directional solidification in special Artemis-3 facility was presented. The current work aimed to propose the ease and efficient way in calibrating the facility. The introduced M coefficient allowed effective calibration and implementation of defined thermal conditions. The specimens of AlSi alloys with Fe-rich intermetallics and especially deleterious β-Al5FeSi were processed by controlled solidification velocity, temperature gradient and cooling rate.

  10. Why are plutons dry? Outgassing mechanisms of crustal magmatic bodies

    parmigiani, andrea; Huber, Christian; Bachmann, Olivier; Leclaire, Sébastien


    Magma bodies crystallizing to completion within the crust (i.e., forming plutons) typically undergo significant amounts of second boiling (i.e. cooling and crystallization of dominantly anhydrous minerals lead to volatile saturation and bubble nucleation/growth). The low water content ( 6 wt % H2O for evolved compositions in subduction zones), testify that outgassing from crystalline mushy reservoirs must be an efficient and widespread process. Understanding this outgassing mechanism is key to understand how volatiles are transferred from mantle depths to the surface. From the hydrodynamics point of view, the mass balance of exsolved volatiles in these plutonic bodies is controlled by the difference between the rate of degassing (formation of bubbles by 2nd boiling) and outgassing (transport of gas out of the magma body). In this study, we use pore-scale multiphase modeling to constrain these rates as function of the crystal and volatile contents in the magma. Because second boiling is a slow process, one can consider equilibrium degassing as a valid assumption. Outgassing, on the other end, is controlled by the competition between buoyancy, capillary and viscous forces. Our numerical simulations are used to determine the most efficient setting for gas to escape its magmatic trap. The high viscosity of interstitial melts and capillary forces (due to the non-wetting nature of the gas phase with most of the mineral phases in magmatic systems) strongly limits gas transport until vertically extensive gas channels are generated. We show that channels can readily form in volatile-rich coarse-grained mush zones in the upper crust, and allow efficient outgassing at crystallinities around 50-75 vol%, when millimetric bubbles can still win capillary resistive forces.

  11. The moisture outgassing kinetics of a silica reinforced polydimethylsiloxane

    Sharma, H. N.; McLean, W.; Maxwell, R. S.; Dinh, L. N.


    A silica-filled polydimethylsiloxane (PDMS) composite M9787 was investigated for potential outgassing in a vacuum/dry environment with the temperature programmed desorption/reaction method. The outgassing kinetics of 463 K vacuum heat-treated samples, vacuum heat-treated samples which were subsequently re-exposed to moisture, and untreated samples were extracted using the isoconversional and constrained iterative regression methods in a complementary fashion. Density functional theory (DFT) calculations of water interactions with a silica surface were also performed to provide insight into the structural motifs leading to the obtained kinetic parameters. Kinetic analysis/model revealed that no outgassing occurs from the vacuum heat-treated samples in subsequent vacuum/dry environment applications at room temperature (˜300 K). The main effect of re-exposure of the vacuum heat-treated samples to a glove box condition (˜30 ppm by volume of H2O) for even a couple of days was the formation, on the silica surface fillers, of ˜60 ppm by weight of physisorbed and loosely bonded moisture, which subsequently outgasses at room temperature in a vacuum/dry environment in a time span of 10 yr. However, without any vacuum heat treatment and even after 1 h of vacuum pump down, about 300 ppm by weight of H2O would be released from the PDMS in the next few hours. Thereafter the outgassing rate slows down substantially. The presented methodology of using the isoconversional kinetic analysis results and some appropriate nature of the reaction as the constraints for more accurate iterative regression analysis/deconvolution of complex kinetic spectra, and of checking the so-obtained results with first principle calculations such as DFT can serve as a template for treating other complex physical/chemical processes as well.

  12. The solidification of two-phase heterogeneous materials: Theory versus experiment

    ZHANG Bin; KIM Tongbeum; LU TianJian


    The solidification behavior of two-phase heterogeneous materials such as close-celled aluminum foams was analytically studied. The proposed analytical model can precisely predict the location of solidification front as well as the full solidification time for a two-phase heterogeneous material composed of aluminum melt and non-conducting air pores. Experiments using distilled water simulating the aluminum melt to be solidified (frozen) were subsequently conducted to validate the analytical model for two selected porosities (ε), ε=0 and 0.5. Full numerical simulations with the method of finite difference were also performed to examine the influence of pore shape on solidification. The remarkable agreement between theory and experiment suggests that the delay of solidification in the two-phase heterogeneous material is mainly caused by the reduction of bulk thermal conductivity due to the presence of pores, as this is the sole mechanism accounted for by the analytical model for solidification in a porous medium.

  13. Experimental Verification of Solidification Stress Theory

    Solbrig, C W; Morrison, M C; SImpson, M F; Bateman, K J


    A research program is being conducted to develop a crack-free ceramic waste form (CWF) to be used for long term encasement of fission products and actinides resulting from processing spent nuclear fuel. Cracking usually occurs in the cooldown phase of the glass or ceramic formations. A crack-free formation should have more resistance to leaching than one with many cracks. In the research leading up to producing a CWF, a model was developed that proposes a permanent stress develops when the melt solidifies and that this stress can cause failure as the CWF nears room temperature. This paper reports on how the formation, CWF2, confirms the existence of this stress. The solidification stress is in addition to and of opposite sign of the thermal stress. Its derivation is reported on in Ref. 1. Cracking of the CWF would occur at low temperatures if solidification stress exists but at high temperatures if it doesn’t. If solidification stress occurs, then the cooldown rate during solidification should be reduced. If not, it should be reduced when the thermal stresses are highest. Recording cracking sounds confirm the existence of this solidification stress since cracking occurred during the low temperature phase of the cooldown. As a side purpose of this paper, a cooldown rate is proposed that should eliminate cracking in the next experiment, CWF3. CWF2 is a prototype vertical ceramic waste cylinder formed over a period of 10 days by heating a mixture of 75% zeolite, 25% glass frit in an argon atmosphere furnace through melting to 925 C and then cooling through solidification to room temperature. It is approximately 1 m high, 0.5 m in diameter, weighs about 400 kg, and is formed in a stainless steel can 0.5 cm thick. This cylinder developed many cracks on cooldown. At least 15 loud cracks were recorded over a period of 4 days at the end of cooldown when the temperatures were below 400 C. The CWF2 surface and centerline temperatures at mid height were measured which

  14. Construction and analysis of dynamic solidification curves for non-equilibrium solidification process in lost-foam casting hypo-eutectic gray cast iron

    Ming-guo Xie


    Full Text Available Most lost-foam casting processes involve non-equilibrium solidification dominated by kinetic factors, while construction of a common dynamic solidification curve is based on pure thermodynamics, not applicable for analyses and research of non-equilibrium macro-solidification processes, and the construction mode can not be applied to non-equilibrium solidification process. In this study, the construction of the dynamic solidification curve (DSC for the non-equilibrium macro-solidification process included: a modified method to determine the start temperature of primary austenite precipitation (TAL and the start temperature of eutectic solidification (TES; double curves method to determine the temperature of the dendrite coherency point of primary austenite (TAC and the temperature of eutectic cells collision point (TEC; the “technical solidus” method to determine the end temperature of eutectic reaction (TEN. For this purpose, a comparative testing of the non-equilibrium solidification temperature fields in lost-foam casting and green sand mold casting hypoeutectic gray iron was carried out. The thermal analysis results were used to construct the DSCs of both these casting methods under non-equilibrium solidification conditions. The results show that the transformation rate of non-equilibrium solidification in hypoeutectic gray cast iron is greater than that of equilibrium solidification. The eutectic solidification region presents a typical mushy solidification mode. The results also indicate that the primary austenite precipitation zone of lost-foam casting is slightly larger than that of green sand casting. At the same time, the solid fraction (fs of the dendrite coherency points in lost-foam casting is greater than that in the green sand casting. Therefore, from these two points, lost-foam casting is more preferable for reduction of shrinkage and mechanical burnt-in sand tendency of the hypoeutectic gray cast iron. Due to the fact that

  15. Battery outgassing sensor for electric drive vehicle energy storage systems

    Beshay, Manal; Chandra Sekhar, Jai Ganesh; Kempen, Lothar U.


    Lithium-ion batteries have been proven efficient as high power density and low self-discharge rate energy storage systems, specifically in electrical drive vehicles. An important safety factor associated with these systems is the potential hazardous release and outgassing of toxic chemical vapors such as hydrogen fluoride (HF) and hydrogen sulfides (H2S), and relatively elevated levels of carbon dioxide (CO2). The release and accumulation of such gases emphasizes an in-line monitoring need. Intelligent Optical Systems, Inc. (IOS) has identified a viable approach for the development of an onboard optical sensor array that can be used to monitor battery outgassing. This paper discusses the potential of developing a battery outgas sensing approach that will meet sensitivity and response time requirements.

  16. Effect of chemical polishing in titanium materials for low outgassing

    Ishizawa, K.; Kurisu, H.; Yamamoto, S.; Nomura, T.; Murashige, N.


    A chemical polishing using a nitric acid solution was found to be the most suitable for the titanium materials. 1.8 nm of small surface roughness was observed in a microscopic range in 1 μm square, and 7 nm of a thin oxide layer was shown to exist for the chemically polished titanium. The surface processing for the titanium was developed combining the chemical polishing and the precision cleaning. The chemically polished pure titanium of JIS grade 2 showed extremely low outgassing rate below 10-12 Pams-1 after baking process, which is two orders of magnitude smaller than that for standard vacuum materials under the same baking condition. Outgassing rates of the titanium is about 1/5 of that for a stainless steel without baking process.

  17. Effect of chemical polishing in titanium materials for low outgassing

    Ishizawa, K; Kurisu, H; Yamamoto, S [Graduate School of Science and Engineering, Yamaguchi University, Ube, Yamaguchi 755-8611 (Japan); Nomura, T; Murashige, N [CT division San-ai Plant Industries, Ltd, Kawasaki, Kanagawa 210-0821 (Japan)], E-mail:


    A chemical polishing using a nitric acid solution was found to be the most suitable for the titanium materials. 1.8 nm of small surface roughness was observed in a microscopic range in 1 {mu}m square, and 7 nm of a thin oxide layer was shown to exist for the chemically polished titanium. The surface processing for the titanium was developed combining the chemical polishing and the precision cleaning. The chemically polished pure titanium of JIS grade 2 showed extremely low outgassing rate below 10{sup -12} Pams{sup -1} after baking process, which is two orders of magnitude smaller than that for standard vacuum materials under the same baking condition. Outgassing rates of the titanium is about 1/5 of that for a stainless steel without baking process.

  18. Outgassing of Ordinary Chondritic Material and Some of its Implications for the Chemistry of Asteroids, Planets, and Satellites

    Schaefer, L; Schaefer, Laura; Fegley, Bruce


    We used chemical equilibrium calculations to model thermal outgassing of ordinary chondritic material as a function of temperature, pressure, and bulk compositions and use our results to discuss outgassing on asteroids and the early Earth. The calculations include ~1,000 solids and gases of the elements Al, C, Ca, Cl, Co, Cr, F, Fe, H, K, Mg, Mn, N, Na, Ni, O, P, S, Si, and Ti. The major outgassed volatiles from ordinary chondritic material are CH4, H2, H2O, N2, and NH3(the latter at conditions where hydrous minerals form). Contrary to widely held assumptions, CO is never the major C-bearing gas during ordinary chondrite metamorphism. The calculated oxygen fugacity (partial pressure) of ordinary chondritic material is close to that of the quartz-fayalite-iron (QFI) buffer. Our results are insensitive to variable total pressure, variable volatile element abundances, and kinetic inhibition of C and N dissolution in Fe metal. Our results predict that Earth's early atmosphere contained CH4, H2, H2O, N2, and NH3; ...

  19. Lunar Outgassing, Transient Phenomena & the Return to the Moon, II: Predictions and Tests for Outgassing/Regolith Interactions

    Crotts, Arlin P S


    We follow Paper I with predictions of how gas leaking through the lunar surface could influence the regolith, as might be observed via optical Transient Lunar Phenomena (TLPs) and related effects. We touch on several processes, but concentrate on low and high flow rate extremes, perhaps the most likely. We model explosive outgassing for the smallest gas overpressure at the regolith base that releases the regolith plug above it. This disturbance's timescale and affected area are consistent with observed TLPs; we also discuss other effects. For slow flow, escape through the regolith is prolonged by low diffusivity. Water, found recently in deep magma samples, is unique among candidate volatiles, capable of freezing between the regolith base and surface, especially near the lunar poles. For major outgassing sites, we consider the possible accumulation of water ice. Over geological time ice accumulation can evolve downward through the regolith. Depending on gases additional to water, regolith diffusivity might be...

  20. Monitoring contamination due to materials outgassing by QCM-based sensors

    Dirri, Fabrizio


    F. Dirri, E. Palomba, A. Longobardo, D. Biondi, A. Boccaccini, E. Zampetti, B. Saggin, D. Scaccabarozzi, A. Tortora, A. Nanni, J. Alves, A. Tighe Outgassing from spacecraft materials often occurs and degassing contaminants can degrade critical spacecraft surfaces, such as optical systems, solar panels, thermal radiators and thermal management systems. The main contaminants are the water adsorbed by cold surface, organics from spacecraft structure, electronics, insulation and thrusters firings [1]. Thus, it is fundamental to monitor these low-outgassing rates especially in a long duration mission: Quartz Crystal Microbalance (QCM) based sensors (i.e. single and double crystal configurations) are a suitable instruments to monitor step by step these degradation processes which occur in space conditions. The Contamination Assessment Microbalance (CAM) is a device aimed at monitoring in-orbit contamination of sensitive surfaces and payloads on ESA's future satellites. The device, developed by a consortium of Italian research Institutes, is based on QCM technology, previously considered by NASA and ESA experiments performed on Space Shuttle and satellite missions [2,3,4]. CAM is a low mass (200 grams for the sensor head), low volume (smaller than 5x5x5 cm3 for the sensor head) and low power consumption (less than 1.5 W) sensor. The device is composed by: 1) the Sensor Head, containing a sensing crystal (which measures the deposited contaminant mass), a reference crystal (used as frequency reference), their related Proximity Electronics (PE) and a Temperature Control System (TCS); 2) the Main Electronics Unit (MEU), which acquires the signal in output from Sensor Head unit; 3) the Harness connecting Sensor Head and MEU; 4) the User Interface (UI) to read and display the data. The device shows several improvements, i.e. possibility to measure directly the crystal temperature (with an accuracy better than 0.1°C), large measurable mass range (from 5•10-9 to 7•10-4 g/cm2

  1. Study for Reduction of Outgassing Property of Adsorbed Water Gas for Improved Surface Finished Titanium Material

    Takeda, Masatoshi; Kurisu, Hiroki; Uchida, Takashi; Yamamoto, Setsuo; Ishizawa, Katsunobu; Nomura, Takeru; Eda, Takahiro; Murashige, Nobuyuki

    This paper addresses the development of the surface finishing for a titanium material and the study for the reduction of outgassing property of adsorbed water (H2O) molecules. Developed surface finishing is composed of the buffing for the reduction of the surface roughness and improved chemical polishing for the thick surface oxide layer compared with the chemical polishing so far. The surface roughness of the surface finished titanium material is reduced 35% and the thickness of the surface oxide layer increases by 30%. The total amount of thermal desorbed H2O gas for the new surface finished titanium is reduced 30%. It is considered that the origin for the decrease of the amount of desorption H2O gas is the reduction of the adsorption sites due to the decrease of the surface roughness and the reduction of adsorption energy of H2O gas due to the strong surface oxidation for a titanium material.

  2. The effects of solidification on sill propagation dynamics and morphology

    Chanceaux, L.; Menand, T.


    as observed in the field does not necessarily involve multiple injections, but could instead reflect a continuous, yet complex morphology induced by solidification effects during emplacement. Also, a discontinuous sill propagation induced by solidification effects should be associated with bursts of seismic activity. Finally, our study shows that once a sill has initiated, the dimensionless flux influences the sill thermal state, and in turn its propagation, and final extent and thickness. In restricting the lateral extent of sills, magma cooling and solidification are likely to impact directly the size of plutons constructed by amalgamated sills.

  3. Nonlinear instability and dynamic bifurcation of a planeinterface during solidification

    吴金平; 侯安新; 黄定华; 鲍征宇; 高志农; 屈松生


    By taking average over the curvature, the temperature and its gradient, the solute con-centration and its gradient at the flange of planar interface perturbed by sinusoidal ripple during solidifi-cation, the nonlinear dynamic equations of the sinusoidal perturbation wave have been set up. Analysisof the nonlinear instability and the behaviors of dynamic bifurcation of the solutions of these equationsshows that (i) the way of dynamic bifurcation of the flat-to-cellular interface transition vades with differ-ent thermal gradients. The quasi-subcritical-lag bifurcation occurs in the small interface thermal gradientscope, the supercritical-lag bifurcation in the medium thermal gradient scope and the supercritical bifur-cation in the large thermal gradient scope. (ii) The transition of cellular-to-flat interface is realizedthrough supercritical inverse bifurcation in the rapid solidification area.

  4. Solidification under microgravity

    B K Dhindaw


    The paper outlines the broad areas where studies are being conducted under microgravity conditions worldwide viz., biotechnology, combustion science, materials science and fluid physics. The paper presents in particular a review on the various areas of research being pursued in materials science. These include studies on immiscibles, eutectics, morphology development during solidification or pattern formation, nucleation phenomena, isothermal dendrite growth, macrosegregation and the behaviour of insoluble particles ahead of the solidifying interface. The latter studies are given in detail with description of case studies of experiments conducted by the author on space shuttles. In particular, the technology and the science issues are addressed. Lastly, based on the presentations, some salient features enumerating the advantages of conducting experiments under conditions of microgravity are highlighted in terms of science returns.

  5. Matemathical description of solidification cooling curves of pure metals

    Arno Müller


    Full Text Available The introduction of an "incubation time" to the Schwarz classical mathematical description of metals solidification, resulted in a new model called Modified Schwarz Model. By doing so it was possible to identify and quantify the "delay time" that separates the two heat waves traveling independently in a casting during the solidification: the Supercooled / Superheated Liquid and the Solid / Liquid. The thermal shock produced in the initial stage of the undercooling generation process, can be used as an important parameter in the forecasting of the solidification's behavior of pure metals and alloys, when changing mold's materials, pouring and ambient temperatures. The hypercooling proneness degree of metals and alloys, can also be calculated.

  6. Non-equilibrium solidification of undercooled droplets during atomization process

    Prashant Shukla; R K Mandal; S N Ojha


    Thermal history of droplets associated with gas atomization of melt has been investigated. A mathematical model, based on classical theory of heterogeneous nucleation and volume separation of nucleants among droplets size distribution, is described to predict undercooling of droplets. Newtonian heat flow condition coupled with velocity dependent heat transfer coefficient is used to obtain cooling rate before and after nucleation of droplets. The results indicate that temperature profile of droplets in the spray during recalescence, segregated and eutectic solidification regimes is dependent on their size and related undercooling. The interface temperature during solidification of undercooled droplets rapidly approaches the liquidus temperature of the alloy with a subsequent decrease in solid–liquid interface velocity. A comparison in cooling rates of atomized powder particles estimated from secondary dendrite arm spacing measurements are observed to be closer to those predicted from the model during segregated solidification regime of large size droplets.

  7. Effect of Coating on Instantaneous Interracial Heat Transfer During Near-Rapid Solidification

    ZHANG Wei; YU Yan; FANG Yuan; LI Jian-guo


    For many rapid or near-rapid solidification processes, the interracial heat transfer between the melt and the substrate is a key issue on the cooling and solidification rate of castings. For the purpose of controlling and adjusting of the interfacial thermal resistance, the effects of C/BN, Zn and organic coatings on the instantaneous interracial heat flux and the solidified structure of AISI304 stainless steel solidification on copper substrate have been investiga- ted by using an experimental simulator. The results show that C/BN coatings can improve the uniformity of heat flux and solidified structure; Zn coating can increase the heat flux and solidification rate in the growth stage of the solidified shell; organic coating will decrease the heat flux and the solidification rate and make re-melted structure on the surface of the solidified shell.

  8. Effect of strontium and solidification rate on eutectic grain structure in an AI-13 wt% Si alloy

    Liao Hengcheng; Bi Juanjuan; Zhang Min; Ding Ke; Jiang Yunfeng; Cai Mingdong


    The influence of strontium addition and solidification rate on eutectic grain structure in a near-eutectic AI-Si alloy was investigated. The characteristic temperature of eutectic nucleation (TN),minimum temperature prior to recalescence (TM),and the growth temperature (TG) during cooling were determined by quantitative thermal analysis. All characteristic temperatures were found to decrease continuously with increasing Sr content and solidification rate. Microstructural analysis also revealed that the eutectic grain size decreases with increasing Sr content and solidification rate. Such eutectic grain refinement is attributed to the increased actual under-cooling ahead of the liquid/solid interface during solidification.

  9. Growth directions of microstructures in directional solidification of crystalline materials.

    Deschamps, J; Georgelin, M; Pocheau, A


    In directional solidification, as the solidification velocity increases, the growth direction of cells or dendrites rotates from the direction of the thermal gradient to that of a preferred cristalline orientation. Meanwhile, their morphology varies with important implications for microsegregation. Here, we experimentally document the growth directions of these microstructures in a succinonitrile alloy in the whole accessible range of directions, velocities, and spacings. For this, we use a thin sample made of a single crystal on which the direction of the thermal gradient can be changed. This allows a fine monitoring of the misorientation angle between thermal gradient and preferred crystalline orientation. Data analysis shows evidence of an internal symmetry which traces back to a scale invariance of growth directions with respect to a Péclet number. This enables the identification of the relationship between growth directions and relevant variables, in fair agreement with experiment. Noticeable variations of growth directions with misorientation angles are evidenced and linked to a single parameter.

  10. Standard Test Method for Contamination Outgassing Characteristics of Spacecraft Materials

    American Society for Testing and Materials. Philadelphia


    1.1 This test method covers a technique for generating data to characterize the kinetics of the release of outgassing products from materials. This technique will determine both the total mass flux evolved by a material when exposed to a vacuum environment and the deposition of this flux on surfaces held at various specified temperatures. 1.2 This test method describes the test apparatus and related operating procedures for evaluating the total mass flux that is evolved from a material being subjected to temperatures that are between 298 and 398 K. Pressures external to the sample effusion cell are less than 7 × 10−3 Pa (5 × 10−5 torr). Deposition rates are measured during material outgassing tests. A test procedure for collecting data and a test method for processing and presenting the collected data are included. 1.3 This test method can be used to produce the data necessary to support mathematical models used for the prediction of molecular contaminant generation, migration, and deposition. 1.4 Al...

  11. Numerical analysis on solidification process and heat transfer of FGH95 superalloy droplets during PREP

    Huanming Chen; Benfu Hu; Yiwen Zhang; Quanmao Yu; Huiying Li


    In order to understand the relation between microstructure of superalloy powders and its solidification progress, the processing parameters are optimized during plasma rotating electrode processing (PREP). It was predicted from the results that the droplet velocities, droplet temperature, and fractional solidification with flight time about FGH95 superalloy droplet have been carried out based on Newtonian heat transfer formulation coupled with the classical heterogeneous nucleation and the specific solidification process. It has been found that the droplet dynamic and thermal behavior is strongly affected by the distribution of droplet diameters,the proportion of cooling atmosphere, but is relatively unaffected by the droplet superheat.

  12. Elimination of Hot Tears in Steel Castings by Means of Solidification Pattern Optimization

    Kotas, Petr; Tutum, Cem Celal; Thorborg, Jesper


    the solidification pattern, i.e., establishing directional and progressive solidification with the help of the Niyama criterion, macrosegregation and hot tearing issues can be both minimized or eliminated entirely. An original casting layout was simulated using a transient three-dimensional (3-D) thermal fluid model...... incorporated in a commercial simulation software package to determine potential flaws and inadequacies. Based on the initial casting process assessment, multiobjective optimization of the solidification pattern of the considered steel part followed. That is, the multiobjective optimization problem of choosing...

  13. Investigation of the physical properties of iron nanoparticles in the course of the melting and solidification

    Fedorov, A. V.; Shul'gin, A. V.; Lavruk, S. A.


    The processes of iron-nanoparticles melting and iron-nanodroes solidification have been studied under different thermal actions. The determined values of the phase-transition temperatures for particles with radii of 1.5-4 nm agree with the data calculated by other authors. In the course of calculating the solidification of iron nanoparticles, the dependence of the solidification temperature on the rate of heat removal has been found and the hysteresis of the phase transition has been demonstrated. Based on the determined caloric curves, the heat capacity of the particles has been found and their approximation in the form of dependences on temperature and particle size has been suggested.

  14. Three Dimensional Numerical Simulation for the Driving Force of Weld Solidification Cracking

    Zhibo DONG; Yanhong WEI; Renpei LIU; Zujue DONG


    The double ellipsoidal model of heat source is used to analyze the thermal distributions with a three dimensional finite element method (FEM). In the mechanical model, solidification effects are treated by a dynamic element rebirth scheme. The driving force is obtained in the cracking susceptible temperature range. Moreover, this paper presents the effect of solidification shrinkage, external restraint, weld start locations and material properties on the driving force. The comparison between the simulated driving force and the experimental measurements of the material resistance predicts the susceptibility of weld metal solidification cracking.

  15. Solidification process and infrared image characteristics of permanent mold castings

    Viets, Roman; Breuer, Markus; Haferkamp, Heinz; Kruessel, Thomas; Niemeyer, Matthias


    Interdependence between the development of temperature gradients at the solid-liquid interface during solidification of metals and the formation of local defects demands for thermal investigation. In foundry practice thermocouples are used to control the die's overall cooling-rate, but fluctuations in product quality still occur. Capturing FIR- thermograms after opening the die visualizes the state, when most thermal throughput has already flattened the temperature gradients in the mold. Rapid dissipation of heat from liquid metal to the mold during solidification forces further approach of the process investigation by slowing down the heat flux or the use of transparent mold material. Aluminum gravity casting experiments under technical vacuum conditions lead to decelerated solidification by suppression of convection and image sequences containing explicit characteristics that could be assigned to local shrinkage of the casting. Hence relevant clusters are extracted and thermal profiles are drawn from image series, pointing out correlations between feeding performance from the sink heads and the appearance of local defects. Tracing thermal processes in vacuum casting can scarcely be transferred to image data in foundry practice, since only little analogies exist between atmospheric and vacuum casting. The diagnosis of the casting process requires detection of the still closed mold using a transparent silica- aerogel sheet as part of the die. Hereby thermograms of the initial heat input are recorded by adapting a NIR-camera in addition to the FIR-unit. Thus the entire thermal compensation at the joint face for each casting is visualized. This experimental set-up is used for image sequence analysis related to the intermediate casting phases of mold filling, body formation and solidification shrinkage.

  16. Structures Self-Assembled Through Directional Solidification

    Dynys, Frederick W.; Sayir, Ali


    Nanotechnology has created a demand for new fabrication methods with an emphasis on simple, low-cost techniques. Directional solidification of eutectics (DSE) is an unconventional approach in comparison to low-temperature biomimetic approaches. A technical challenge for DSE is producing microstructural architectures on the nanometer scale. In both processes, the driving force is the minimization of Gibb's free energy. Selfassembly by biomimetic approaches depends on weak interaction forces between organic molecules to define the architectural structure. The architectural structure for solidification depends on strong chemical bonding between atoms. Constituents partition into atomic-level arrangements at the liquid-solid interface to form polyphase structures, and this atomic-level arrangement at the liquid-solid interface is controlled by atomic diffusion and total undercooling due to composition (diffusion), kinetics, and curvature of the boundary phases. Judicious selection of the materials system and control of the total undercooling are the keys to producing structures on the nanometer scale. The silicon-titanium silicide (Si-TiSi2) eutectic forms a rod structure under isothermal cooling conditions. At the NASA Glenn Research Center, directional solidification was employed along with a thermal gradient to promote uniform rods oriented with the thermal gradient. The preceding photomicrograph shows the typical transverse microstructure of a solidified Si-TiSi2 eutectic composition. The dark and light gray regions are Si and TiSi2, respectively. Preferred rod orientation along the thermal gradient was poor. The ordered TiSi2 rods have a narrow distribution in diameter of 2 to 3 m, as shown. The rod diameter showed a weak dependence on process conditions. Anisotropic etch behavior between different phases provides the opportunity to fabricate structures with high aspect ratios. The photomicrographs show the resulting microstructure after a wet chemical etch and a

  17. The water outgassing rate of internal surfaces of vacuum systems

    Rozanov, L. N.


    On the basis of experimental adsorption isotherm the ratio between the real and geometrical surfaces was calculated and the amount of gas required to form a monolayer was defined. Simultaneous usage of Henry and Frendlih equations allowed to determine the dependence of the heat of adsorption on the logarithm of the absorbed gas amount A mathematical model of pumping of the vacuum systems with adsorbing walls is presented. This model uses the parameters of the vacuum system and the dependence of the adsorption heat on the amount of the adsorbed gas .The conditions of the existence of regular pumping regime are discussed. The structure database vacuum adsorption properties of materials was proposed. The experimental data on the determination of the adsorption outgassing rate were released.

  18. Directional Solidification Assisted by Liquid Metal Cooling

    Jian ZHANG; Langhong LOU


    An overview of the development and current status of the directional solidification process assisted by liquid metal cooling (LMC) has been presented in this paper. The driving force of the rapid development of the LMC process has been analyzed by considering the demands of (1) newer technologies that can provide higher thermal gradients for alleviated segregation in advanced alloy systems, and (2) better production yield of the large directionally solidified superalloy components. The brief history of the industrialization of the LMC process has been reviewed, followed by the discussion on the LMC parameters including selection of the cooling media, using of the dynamic baffle, and the influence of withdrawal rates and so on. The microstructure and mechanical properties of the traditional superalloys processed by LMC, as well as the new alloys particularly developed for LMC process were then described. Finally, future aspects concerning the LMC process have been summarized.

  19. Effect of Melt Superheating Treatment on Directional Solidification Interface Morphology of Multi-component Alloy

    Changshuai Wang; Jun Zhang; Lin Liu; Hengzhi Fu


    The influence of melt superheating treatment on the solid/liquid (S/L) interface morphology of directionally solidified Ni-based superalloy DZ125 is investigated to elucidate the relationship between melt characteristic and S/L interface stability. The results indicate that the interface morphology is not only related to the withdrawal velocity (R) but also to the melt superheating temperature (Ts) when the thermal gradient of solidification interface remains constant for different Ts with appropriate superheating treatment regulation. The interface morphology changes from cell to plane at R of 1.1 μm/s when Ts increases from 1500°C to 1650°C, and maintains plane with further elevated Ts of 1750°C. However, the interface morphology changes from coarse dendrite to cell and then to cellular dendrite at R of 2.25 μm/s when Ts increases from 1500°C to 1650°C and then to 1750°C. It is proved that the solidification onset temperature and the solidification interval undergo the nonlinear variation when Ts increases from 1500°C to 1680°C, and the turning point is 1650°C at which the solidification onset temperature and the solidification interval are all minimum. This indicates that the melt superheating treatment enhances the solidification interface stability and has important effect on the solidification characteristics.

  20. Directional solidification of flake and nodular cast iron during KC-135 low-g maneuvers

    Curreri, P. A.; Stefanescu, D. M.; Hendrix, J. C.


    Alloys solidified in a low-gravity environment can, due to the elimination of sedimentation and convection, form unique and often desirable microstructures. One method of studying the effects of low-gravity (low-g) on alloy solidification was the use of the NASA KC-135 aircraft flying repetitive low-g maneuvers. Each maneuver gives from 20 to 30 seconds of low-g which is between about 0.1 and 0.001 gravity. A directional solidification furnace was used to study the behavior of off eutectic composition case irons in a low-g environment. The solidification interface of hypereutectic flake and spheroidal graphite case irons was slowly advanced through a rod sample, 5 mm in diameter. Controlled solidification was continued through a number of aircraft parabolas. The known solidification rate of the sample was then correlated with accelerometer data to determine the gravity level during solidification for any location of the sample. The thermal gradient and solidification rate were controlled independently. Samples run on the KC-135 aircraft exhibited bands of coarser graphite or of larger nodules usually corresponding to the regions solidified under low-g. Samples containing high phosphorous (used in order to determine the eutectic cell) exhibited larger eutectic cells in the low-g zone, followed by a band of coarser graphite.

  1. Effect of outgassing on the field emission property of tetrapod ZnO

    Cui, Yunkang [School of Electronic Science and Engineering, Southeast University, Nanjing (China); Department of Basic Courses, Nanjing Institute of Technology, Nanjing (China); Jiangsu Information Display Engineering Research Center, Nanjing (China); Zhang, Xiaobing; Lei, Wei [School of Electronic Science and Engineering, Southeast University, Nanjing (China); Jiangsu Information Display Engineering Research Center, Nanjing (China); Wang, Jinchan [School of Electronic and Information Engineering, Henan University of Science and Technology, Luoyang (China); Di, Yunsong [Jiangsu Information Display Engineering Research Center, Nanjing (China); Yang, Xiaxi; Chen, Jing [School of Electronic Science and Engineering, Southeast University, Nanjing (China)


    To study the mechanism of current degradation of a cold cathode, the outgassing measurement of a field emission diode with tetrapod zinc oxide (ZnO) cathode has been taken with a quadrupole mass spectrometer (QMS) in an ultra-high vacuum (UHV) system. It was found that the H{sub 2}, CO{sub 2}, CO, and CH{sub 4} were outgassed from the diode during the working process. The partial pressure of outgassing increases with the increased emission current density. The field emission properties of the cold cathode, such as turn-on field, threshold field and the emission current density, were largely related to the pressure of the outgases. From the outgassing experimental results, the relation between the emission current degradation and the outgassing of field emission devices has been found. Due to the outgassing, the work function of ZnO cold cathode increases, while the field enhancement factor decreases. Therefore, the outgassing plays very important role in the current degradation for the field emission devices. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  2. Vacuum Outgassing Behavior of Carbon Nanotube Cathode with High-Intensity Pulsed Electron Emission

    Shen, Yi; Zhang, Huang; Xia, Liansheng; Liu, Xingguang; Pan, Haifeng; Lv, Lu; Yang, Anmin; Shi, Jinshui; Zhang, Linwen; Deng, Jianjun


    Experimental investigations on the vacuum outgassing of a carbon nanotube (CNT) cathode with high-intensity pulsed electron emission on a 2 MeV linear induction accelerator injector are presented. Under the 1.60 MV diode voltage, the CNT cathode could provide 1.67 kA electron beam with the amount of outgassing of about 0.51 Pa·L. It is found that the amount of outgassing, which determines the cathode emission current, depends on the diode voltage and the vacuum.

  3. Density and Mechanical Properties of Aluminum Lost Foam Casting by Pressurization during Solidification


    Porosity is thought to be severe in aluminum alloy castings produced by lost foam process due to the pyrolysis of the polystyrene foam pattern during pouring, which results in detrimental effect in mechanical property.The slow solidification rate promotes the formation of gassing pin holes, and relative weakness of the thermal gradients can cause micro-shrinkage if the outline of the part complicates feeding in the lost foam casting. One of the methods to eliminate the porosity is to apply high pressure to the molten metal like an isostatic forging during solidification. Fundamental experiments were carried out to evaluate the effect of the external pressure on the porosity and mechanical properties of A356.2 alloy bar in the lost foam casting. Solidification time and porosity decreased with increasing the applied pressure during solidification. Applying external pressure was effective in decreasing the porosity and increasing the elongation of the lost foam casting.

  4. Stress/strain distributions for weld metal solidification crack in stainless steels


    This paper has simulated the driving force of solidification crack of stainless steels, that is, stress/strain field in the trail of molten pool. Firstly, the effect of the deformation in the molten pool was eliminated after the element rebirth method was adopted. Secondly, the influence of solidification shrinkage was taken into account by increasing thermal expansion coefficients of the steels at elevated temperatures. Finally, the stress/strain distributions of different conditions have been computed and analyzed. Furthermore, the driving force curves of the solidification crack of the steels have been obtained by converting strain-time curves into strain-temperature curves, which founds a basis for predicting welding solidification crack.

  5. Solidification at the High and Low Rate Extreme

    Meco, Halim [Iowa State Univ., Ames, IA (United States)


    The microstructures formed upon solidification are strongly influenced by the imposed growth rates on an alloy system. Depending on the characteristics of the solidification process, a wide range of growth rates is accessible. The prevailing solidification mechanisms, and thus the final microstructure of the alloy, are governed by these imposed growth rates. At the high rate extreme, for instance, one can have access to novel microstructures that are unattainable at low growth rates. While the low growth rates can be utilized for the study of the intrinsic growth behavior of a certain phase growing from the melt. Although the length scales associated with certain processes, such as capillarity, and the diffusion of heat and solute, are different at low and high rate extremes, the phenomena that govern the selection of a certain microstructural length scale or a growth mode are the same. Consequently, one can analyze the solidification phenomena at both high and low rates by using the same governing principles. In this study, we examined the microstructural control at both low and high extremes. For the high rate extreme, the formation of crystalline products and factors that control the microstructure during rapid solidification by free-jet melt spinning are examined in Fe-Si-B system. Particular attention was given to the behavior of the melt pool at different quench-wheel speeds. Since the solidification process takes place within the melt-pool that forms on the rotating quench-wheel, we examined the influence of melt-pool dynamics on nucleation and growth of crystalline solidification products and glass formation. High-speed imaging of the melt-pool, analysis of ribbon microstructure, and measurement of ribbon geometry and surface character all indicate upper and lower limits for melt-spinning rates for which nucleation can be avoided, and fully amorphous ribbons can be achieved. Comparison of the relevant time scales reveals that surface-controlled melt

  6. Structural modification of boron-doped ZnO layers caused by hydrogen outgassing

    Lovics, R.; Csik, A.; Takáts, V.; Hakl, J.; Vad, K.


    Results of annealing experiments of boron-doped zinc oxide (ZnO:B) layers prepared by low pressure chemical vapor deposition method on polished Si, soda-lime glass for windows, and AF45 Schott alkali free thin glass substrates are presented. It is shown that short annealing of samples at 150 °C and 300 °C in air causes serious surface degradation of samples prepared on Si and soda-lime glass substrate. The characteristic feature of degradation is the creation of bubbles and craters on the sample surface which fully destroy the continuity of zinc oxide layers. The results of depth distribution mapping of elements indicate that the formation of bubbles is linked to increase in hydrogen concentration in the layer. The surface degradation was not noticed on samples deposited on AF45 Schott alkali free thin glass which has a SiO2 diffusion barrier layer on the surface, only much fewer and smaller bubbles were visible. The results indicate the important role of hydrogen outgassing from the substrate induced by a thermal shock.

  7. Structural modification of boron-doped ZnO layers caused by hydrogen outgassing

    Lovics, R.; Csik, A., E-mail:; Takáts, V.; Hakl, J.; Vad, K.


    Results of annealing experiments of boron-doped zinc oxide (ZnO:B) layers prepared by low pressure chemical vapor deposition method on polished Si, soda-lime glass for windows, and AF45 Schott alkali free thin glass substrates are presented. It is shown that short annealing of samples at 150 °C and 300 °C in air causes serious surface degradation of samples prepared on Si and soda-lime glass substrate. The characteristic feature of degradation is the creation of bubbles and craters on the sample surface which fully destroy the continuity of zinc oxide layers. The results of depth distribution mapping of elements indicate that the formation of bubbles is linked to increase in hydrogen concentration in the layer. The surface degradation was not noticed on samples deposited on AF45 Schott alkali free thin glass which has a SiO{sub 2} diffusion barrier layer on the surface, only much fewer and smaller bubbles were visible. The results indicate the important role of hydrogen outgassing from the substrate induced by a thermal shock.

  8. Pits formation from volatile outgassing on 67P/Churyumov-Gerasimenko

    Mousis, O; Brugger, B; Jorda, L; Kargel, J S; Bouquet, A; Auger, A -T; Lamy, P; Vernazza, P; Thomas, N; Sierks, H


    We investigate the thermal evolution of comet 67P/Churyumov-Gerasimenko's subsurface in the Seth_01 region, where active pits have been observed by the ESA/Rosetta mission. Our simulations show that clathrate destabilization and amorphous ice crystallization can occur at depths corresponding to those of the observed pits in a timescale shorter than 67P/Churyumov-Gerasimenko's lifetime in the comet's activity zone in the inner solar system. Sublimation of crystalline ice down to such depths is possible only in the absence of a dust mantle, which requires the presence of dust grains in the matrix small enough to be dragged out by gas from the pores. Our results are consistent with both pits formation via sinkholes or subsequent to outbursts, the dominant process depending on the status of the subsurface porosity. A sealed dust mantle would favor episodic and disruptive outgassing as a result of an increasing gas pressure in the pores, while a high porosity should allow the formation of large voids in the subsur...

  9. Isothermal solidification based packaging of biosensors at low temperatures

    Sharma, R.P., E-mail: [Electronic Science Department, Kurukshetra University, Kurukshetra-136119, Haryana (India); Central Electronics Engineering Research Institute (CEERI)/Council of Scientific and Industrial Research (CSIR), Pilani-333031, Rajasthan (India); Khanna, P.K., E-mail: pkk@ceeri.ernet.i [Central Electronics Engineering Research Institute (CEERI)/Council of Scientific and Industrial Research (CSIR), Pilani-333031, Rajasthan (India); Kumar, D., E-mail: [Electronic Science Department, Kurukshetra University, Kurukshetra-136119, Haryana (India)


    Thick film Au printed square contact pads are interconnected to Cu substrates at constant pressure and temperature using the isothermal solidification of Bi-In alloy on the joining surfaces. The effect of reaction time on the mechanical strength of the package has been analyzed. Thermal stability of the fabricated specimens have been measured and discussed. The delaminated surfaces examined optically reveal the morphology of the metallization zones on the joining substrates. The scanning electron microscopy of these surfaces is reported in this paper. Tests for thermal shock, pH resistivity and shelf life have been carried out to predict the reliability of the packaging for long term applications.

  10. Gas migration regimes and outgassing in particle-rich suspensions

    Julie eOppenheimer


    Full Text Available Understanding how gases escape from particle-rich suspensions has important applications in nature and industry. Motivated by applications such as outgassing of crystal-rich magmas, we map gas migration patterns in experiments where we vary (1 particle fractions and liquid viscosity (10 Pa s – 500 Pa s, (2 container shape (horizontal parallel plates and upright cylinders, and (3 methods of bubble generation (single bubble injections, and multiple bubble generation with chemical reactions. We identify two successive changes in gas migration behavior that are determined by the normalized particle fraction (relative to random close packing, and are insensitive to liquid viscosity, bubble growth rate or container shape within the explored ranges. The first occurs at the random loose packing, when gas bubbles begin to deform; the second occurs near the random close packing, and is characterized by gas migration in a fracture-like manner. We suggest that changes in gas migration behavior are caused by dilation of the granular network, which locally resists bubble growth. The resulting bubble deformation increases the likelihood of bubble coalescence, and promotes the development of permeable pathways at low porosities. This behavior may explain the efficient loss of volatiles from viscous slurries such as crystal-rich magmas.

  11. Outgassing of planets in relation to their obital frequencies

    Kochemasov, G.

    venusian 6000 km (πR/3) 0.07 khz. Venusian oscillations thus 2.33 times more frequent. If a degassing difference of two planets is the square (degassing goes through surface) of the production of differences in granulation and oscillation frequencies, then Venus is 62 times more outgassed [Dv /De = (3.38 x 2.33)2 =62.1]. Actually the venusian atmosphere is 90 times more massive than the terrestrial one. Comparing Mars (1/10th of the Earth's mass) and Earth by the same method we get 920 times less massive martian atmosphere (actually only about 200 times). The discrepancy probably is due to large amounts of volatiles in soils and crust (ice, aqueous salts, zeolites) exchanging them with atmosphere under changing conditions. On contrary, Mercury is completely "shaken out", 1 dry, its would-be massive atmosphere is completely eliminated by solar wind. The smaller volatile rich Titan with high orbital frequency has an important atmosphere -probably only remnants of what was totally outgassed during eons. All Titan's dark plains (frozen methane?) are intensively warped by cross-cutting ridge-groove systems -a consequence of an important subsidence, loosing radius. So, there is an inverse relation between atmospheric masses and a volatile stock in planets. Dry Venus has a massive atmosphere, wet Mars has a weak one. Earth is in the middle: rather wet interior and an important atmosphere. Most outgassed Mercury with distinct traces of earlier contraction (escarps or lobate ledges), alas, has lost its gaseous envelope. Asteroids , next to Mars, as show carboneceous chondrites are rich in volatiles. Sharing an angular momentum between a solid body and a massive gaseous envelope enforces this body rotate slower (Venus, Mercury). This observation could perhaps explain one enigmatic situation: the larger asteroids rotate faster than smaller ones. A reason: the former less wasted their "original" momentum not spending it with loosing volatiles than the latter, more degassed

  12. Analysis of EUV resist outgassing depended on the dosage

    Shiobara, E.; Takagi, I.; Kikuchi, Y.; Sasami, T.; Minegishi, S.; Fujimori, T.; Watanabe, T.; Harada, T.; Kinoshita, H.; Inoue, S.


    The suppression of extreme ultraviolet (EUV) photoresist-related outgassing is one of the challenges in high-volume manufacturing with EUV lithography (EUVL), because it contributes to the contamination of the EUV scanner mirror optics, resulting in reflectivity loss. Witness sample pragmatic outgas qualification has been developed into the general method for clarifying commercially available, chemically amplified resists. Preliminary results have suggested a linear correlation between contamination thickness in the electron-beam-based and the EUV-based evaluation systems. In fact, a positive relationship was observed between contamination thickness and exposure dose. However, recent experiments indicate that in some resists, this relationship is not linear. In the present study, a resist outgas model is proposed and tested to investigate the contamination thickness' dependency on exposure dose. The model successfully explains the experimental outgas phenomenon. It is estimated that increasing exposure dose, in resists with low activation energies (Ea) in deprotection reactions, results in extreme increase in contamination thickness. Furthermore, the low-Ea resists have high contamination risk when exposure is extensive.

  13. The Effect of Heat Treatments and Coatings on the Outgassing Rate of Stainless Steel Chambers

    Mamum, Md Abdullah A. [Old Dominion Univ., Norfolk, VA (United States); Elmustafa, Abdelmageed A, [Old Dominion Univ., Norfolk, VA (United States); Stutzman, Marcy L. [JLAB, Newport News, VA (United States); Adderley, Philip A. [JLAB, Newport News, VA (United States); Poelker, Matthew [JLAB, Newport News, VA (United States)


    The outgassing rates of four nominally identical 304L stainless steel vacuum chambers were measured to determine the effect of chamber coatings and heat treatments. One chamber was coated with titanium nitride (TiN) and one with amorphous silicon (a-Si) immediately following fabrication. One chamber remained uncoated throughout, and the last chamber was first tested without any coating, and then coated with a-Si following a series of heat treatments. The outgassing rate of each chamber was measured at room temperatures between 15 and 30 deg C following bakes at temperatures between 90 and 400 deg C. Measurements for bare steel showed a significant reduction in the outgassing rate by more than a factor of 20 after a 400 deg C heat treatment (3.5 x 10{sup 12} TorrL s{sup -1}cm{sup -2} prior to heat treatment, reduced to 1.7 x 10{ sup -13} TorrL s{sup -1}cm{sup -2} following heat treatment). The chambers that were coated with a-Si showed minimal change in outgassing rates with heat treatment, though an outgassing rate reduced by heat treatments prior to a-Si coating was successfully preserved throughout a series of bakes. The TiN coated chamber exhibited remarkably low outgassing rates, up to four orders of magnitude lower than the uncoated stainless steel. An evaluation of coating composition suggests the presence of elemental titanium which could provide pumping and lead to an artificially low outgassing rate. The outgassing results are discussed in terms of diffusion-limited versus recombination-limited processes.

  14. A finite element modeling on the fluid flow and solidification in a continuous casting process

    Kim, T.H.; Kim, D.S. [Hanyang University Graduate School, Seoul (Korea); Choi, H.C. [Agency for Defence Development, Taejon (Korea); Kim, S.W. [Hanyang University, Seoul (Korea); Lee, S.K. [Chung Buk National University, Chungju (Korea)


    The coupled turbulent flow and solidification is considered in a typical slab continuous casting process using commercial program FIDAP. Standard {kappa}-{epsilon} turbulence model is modified to decay turbulent viscosity in the mushy zone and laminar viscosity is set to a sufficiently large value at the solid region. This coupled turbulent flow and solidification model also contains thermal contact resistance due to the mold powder and air gap between the strand and mold using an effective thermal conductivity. From the computed flow pattern, the trajectory of inclusion particles was calculated. The comparison between the predicted and experimental solidified shell thickness shows a good agreement. (author). 27 refs., 11 figs., 2 tabs.

  15. Solidification characterization of a new rapidly solidified Ni-Cr-Co based superalloy

    Wu, Kai, E-mail: [School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China); Liu, Guoquan [School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China); State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Hu, Benfu [School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China); Li, Feng [Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB2 3QZ (United Kingdom); Zhang, Yiwen [School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083 (China); High Temperature Materials Research Institution, CISRI, Beijing 100081 (China); Tao, Yu; Liu, Jiantao [High Temperature Materials Research Institution, CISRI, Beijing 100081 (China)


    The solidification characterization of a new rapidly solidified Ni-Cr-Co based superalloy prepared by plasma rotating electrode process was investigated by means of optical microscope, scanning electron microscope, and transmission electron microscope. The results show that the solidification microstructure changes from dendrites to cellular and microcrystal structures with decreasing powder size. The elements of Co, Cr, W and Ni are enriched in the dendrites, while Mo, Nb and Ti are higher in the interdendritic regions. The relationships between powder size with the average solid-liquid interface moving rate, the average interface temperature gradient and the average cooling rate are established. Microsegregation is increased with larger powder size. The geometric integrity of MC Prime type carbides in the powders changes from regular to diverse with decreasing powder size. The morphology and quantity of carbides depend on the thermal parameters and non-equilibrium solute partition coefficients during rapid solidification. - Highlights: Black-Right-Pointing-Pointer The relations of solidification thermal parameters with powder size are established. Black-Right-Pointing-Pointer The relation of non-equilibrium solute partition with powder size is investigated. Black-Right-Pointing-Pointer The solidification microstructure is related to thermal parameters. Black-Right-Pointing-Pointer The segregation behavior is linked to non-equilibrium partition coefficients. Black-Right-Pointing-Pointer The morphology and quantity of carbides depend on the above combined factors.

  16. Structure and dynamics of cold water super-Earths: the case of occluded CH{sub 4} and its outgassing

    Levi, A.; Podolak, M. [Department of Geophysics and Planetary Science, Tel Aviv University, Tel Aviv 69978 (Israel); Sasselov, D., E-mail: [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)


    In this work, we study the transport of methane in the external water envelopes surrounding water-rich super-Earths. We investigate the influence of methane on the thermodynamics and mechanics of the water mantle. We find that including methane in the water matrix introduces a new phase (filled ice), resulting in hotter planetary interiors. This effect renders the super-ionic and reticulating phases accessible to the lower ice mantle of relatively low-mass planets (∼5 M{sub E} ) lacking a H/He atmosphere. We model the thermal and structural profile of the planetary crust and discuss five possible crustal regimes which depend on the surface temperature and heat flux. We demonstrate that the planetary crust can be conductive throughout or partly confined to the dissociation curve of methane clathrate hydrate. The formation of methane clathrate in the subsurface is shown to inhibit the formation of a subterranean ocean. This effect results in increased stresses on the lithosphere, making modes of ice plate tectonics possible. The dynamic character of the tectonic plates is analyzed and the ability of this tectonic mode to cool the planet is estimated. The icy tectonic plates are found to be faster than those on a silicate super-Earth. A mid-layer of low viscosity is found to exist between the lithosphere and the lower mantle. Its existence results in a large difference between ice mantle overturn timescales and resurfacing timescales. Resurfacing timescales are found to be 1 Ma for fast plates and 100 Ma for sluggish plates, depending on the viscosity profile and ice mass fraction. Melting beneath spreading centers is required in order to account for the planetary radiogenic heating. The melt fraction is quantified for the various tectonic solutions explored, ranging from a few percent for the fast and thin plates to total melting of the upwelled material for the thick and sluggish plates. Ice mantle dynamics is found to be important for assessing the composition of

  17. Onset of sidebranching in directional solidification.

    Echebarria, Blas; Karma, Alain; Gurevich, Sebastian


    We use a computationally efficient phase-field formulation [B. Echebarria, Phys. Rev. E 70, 061604 (2004)] to investigate the origin and dynamics of sidebranching in directional solidification for realistic parameters of a dilute alloy previously studied experimentally [M. Gorgelin and A. Pocheau, Phys. Rev. E 57, 3189 (1998)]. Sidebranching is found to result either from noise amplification or from deterministic oscillations that exist both in two dimensions and in a three-dimensional thin-sample geometry. The oscillatory branch of growth solutions bifurcates subcritically from the main steady-state branch of solutions and exists over a finite range of large array spacings. In contrast, noise-induced sidebranching is associated with a smooth transition where the sidebranching amplitude increases exponentially with spacing up to nonlinear saturation due to the overlap of diffusion fields from neighboring cells, as observed experimentally. In the latter case where sidebranching is noise-induced, we find that increasing the externally imposed thermal gradient reduces the onset velocity and wavelength of sidebranching, as also observed experimentally. We show that this counterintuitive effect is due to tip blunting with increasing thermal gradient that promotes noise amplification in the tip region.

  18. Geometrical modulus of a casting and its influence on solidification process

    F. Havlicek


    Full Text Available Object: The work analyses the importance of the known criterion for evaluating the controlled solidification of castings, so called geometrical modulus defined by N. Chvorinov as the first one. Geometrical modulus influences the solidification process. The modulus has such specificity that during the process of casting formation it is not a constant but its initial value decreases with the solidification progress because the remaining melt volume can decrease faster than its cooling surface.Methodology: The modulus is determined by a simple calculation from the ratio of the casting volume after pouring the metal in the mould to the cooled mould surface. The solidified metal volume and the cooled surface too are changed during solidification. That calculation is much more complicated. Results were checked up experimentally by measuring the temperatures in the cross-section of heavy steel castings during cooling them.Results: The given experimental results have completed the original theoretical calculations by Chvorinov and recent researches done with use of numerical calculations. The contribution explains how the geometrical modulus together with the thermal process in the casting causes the higher solidification rate in the axial part of the casting cross-section and shortening of solidification time. Practical implications: Change of the geometrical modulus negatively affects the casting internal quality. Melt feeding by capillary filtration in the dendritic network in the casting central part decreases and in such a way the shrinkage porosity volume increases. State of stress character in the casting is changed too and it increases.

  19. The solidification of two-phase heterogeneous materials:Theory versus experiment

    KIM; Tongbeum


    The solidification behavior of two-phase heterogeneous materials such as close-celled aluminum foams was analytically studied.The proposed analytical model can precisely predict the location of solidification front as well as the full solidification time for a two-phase heterogeneous material composed of aluminum melt and non-conducting air pores.Experiments using distilled water simulating the aluminum melt to be solidified(frozen)were subsequently conducted to validate the analytical model for two selected porosities(ε),ε=0 and 0.5.Full numerical simulations with the method of finite difference were also performed to examine the influence of pore shape on solidification.The remarkable agreement between theory and experiment suggests that the delay of solidification in the two-phase heterogeneous material is mainly caused by the reduction of bulk thermal conductivity due to the presence of pores,as this is the sole mechanism accounted for by the analytical model for solidification in a porous medium.

  20. Drone Detects Hotspots of Radiation and CO2 Outgassing

    Takac, M.; Kletetschka, G.


    Market availability of environmental sensors and drones allow drones to become part of the education activities promoting environmental science both in high schools and grade schools. Here we provide one mode of drone operation for potential use in educational framework.Drone can carry devices that are capable of measuring various parameters of the environment. Commercial radiation and gas (CO2) sensors can be attached to the commercial drone. Our specific drone acquired data set of CO2 measurements over the natural outgassing of CO2 and another set of measurements over old uranium mine. Measurements of CO2 gave a poor signal to noise ratio. Its sensitivity, however, was enough to detect an increase in CO2 in the closed room with humans present compared to the fresh air outside. We could measure an increase of CO2 when directly over the source of natural CO2 outburst. Our data showed that CO2 concentration quickly dilutes in air few meters from the source to concentrations that are within the noise limit. However, the radiation measurements provided a map that correlates well with radiation survey obtained by ground measurements with more sophisticated instrument. We used the most common conventional drone, which is on the market and highly effective personal dosimeter, which can also be used for fire and rescue for its durability. Experimental field measurements were done at Třebsko site, where a map of radioactivity using standard spot measurements was already done. A field experiment was done in winter months when demand for the drone was higher due to cold and wet weather. We tested profiles and height versus the intensity of the recorded signal measurements. We consulted our results and ability to measure radioactivity with the regional fire-fighting units headquarters and verify the applicability and use of this technology for their needs.

  1. Simulation of continuous cast steel product solidification

    Ardelean, E.


    Full Text Available Primary cooling – inside the tundish – has a great impact over the thickness of the solidified steel crust. If on exiting the tundish the crust is too thin, it can punch and break, as a result of the ferrostatic pressure exerted from the inside by the liquid steel as well as because of the weight of the molten steel. The parameters that influence the amount of dissipated heat depend on the cooling water flow of the tundish, on the pressure and temperature of the cooling water but also on the overheating of the continuously cast steel. The secondary cooling takes place at the exit of the semi-finished product from the tundish, when the solidification is supposed to take place all along the cross section of the strand. In order to achieve it, in addition to a correctly managed primary cooling, it is necessary to obtain the proper correlation of the factors that influence the secondary cooling as well: the water flow rate long the three zones of the installation and its pressure in the secondary circuit. All these have in view a proper solidification length; an intense cooling can generate cracks due to the thermal stress, while a too slow cooling can generate a partial solidification of the strand up to the cropping machine area. The paper presents a mathematical simulation of the continuously cast steel solidification.

    El enfriamiento primario del cristalizador tiene una gran importancia sobre el espesor de la costra de acero solidificado. Si al salir del cristalizador, esta costra es demasiado sutil, bajo la acción de la presión ferro estática ejercitada por el acero líquido del interior y gracias el peso propio del hilo, ésta, puede perforar resultando su rompimiento. Los parámetros que influenyen sobre la cantidad de calor cedida dependen del agua de enfriamiento del catalizador, de la presión y de la temperatura de agua de enfriamiento, pero también del sobrecalentamiento del acero fundido continuamente. A la salida del

  2. Influence of Forced Convection on the Solidification of Metal in Cast-Iron and Ceramic Ingot Molds

    Kalashnikova, O. A.; Dremov, V. V.


    A nonstationary problem of solidification of an ingot in molds with walls of varying thermal conductivity has been solved by the variational method with account taken of forced convection in the liquid phase of the metal. A formula for the temperature distribution in the liquid phase and the dependence of the time of advance of the solidification front on its coordinates have been obtained. Numerical calculations of the time of solidification of the ingot in castiron and ceramic molds have been done at different convection rates.

  3. Towards a Map of Solidification Cracking Risk in Laser Welding of Austenitic Stainless Steels

    Bermejo, María-Asunción Valiente; DebRoy, Tarasankar; Hurtig, Kjell; Karlsson, Leif; Svensson, Lars-Erik

    In this work, two series of specimens with Hammar and Svensson's Cr- and Ni-equivalents (Creq+Nieq) = 35 and 45 wt% were used to cover a wide range of austenitic grades. These were laser welded with different energy inputs achieving cooling rates in the range of 103 °C/s to 104 °C/s. As high cooling rates and rapid solidification conditions could favour fully austenitic solidification and therefore raise susceptibility to solidification cracking, the solidification modes of the laser welded specimens were compared to the ones experienced by the same alloys under arc welding conditions. It was found that high cooling rates experienced in laser welding promoted fully austenitic solidification for a wider range of compositions, for example specimens with (Creq+Nieq) = 35% under arc welding cooling conditions at 10 °C/s showed fully austenitic solidification up to Creq/Nieq = 1.30, whilst the same specimens laser cooled at 103 °C/s showed fully austenitic solidification up to Creq/Nieq = 1.50 and those cooled at 104 °C/s showed it up to Creq/Nieq = 1.68. Therefore, high cooling rates extended the solidification cracking risk to a wider range of Creq/Nieq values. This work also compares the cooling rates experimentally determined by thermocouples to the computed cooling rates calculated by a highly-advanced computational model. The distance between the thermocouple's wires and the thermal resistance of thermocouples together with the small size of the weld pools proved to be practical limitations in the experimental determination of cooling rates. However, an excellent agreement was found between computed and experimental solidus isotherms at high energy input settings. For low energy input settings cooling rate was in the order of magnitude of 104 °C/s, whilst for high energy input settings cooling rate was found to be in the order of magnitude of 103 °C/s.

  4. Effect of process parameters on hardness, temperature profile and solidification of different layers processed by direct metal laser sintering (DMLS)

    Ahmed, Sazzad Hossain; Mian, Ahsan; Srinivasan, Raghavan


    In DMLS process objects are fabricated layer by layer from powdered material by melting induced by a controlled laser beam. Metallic powder melts and solidifies to form a single layer. Solidification map during layer formation is an important route to characterize micro-structure and grain morphology of sintered layer. Generally, solidification leads to columnar, equiaxed or mixture of these two types grain morphology depending on solidification rate and thermal gradient. Eutectic or dendritic structure can be formed in fully equiaxed zone. This dendritic growth has a large effect on material properties. Smaller dendrites generally increase ductility of the layer. Thus, materials can be designed by creating desired grain morphology in certain regions using DMLS process. To accomplish this, hardness, temperature distribution, thermal gradient and solidification cooling rate in processed layers will be studied under change of process variables by using finite element analysis, with specific application to Ti-6Al-4V.

  5. Effect of process parameters on hardness, temperature profile and solidification of different layers processed by direct metal laser sintering (DMLS)

    Ahmed, Sazzad Hossain; Mian, Ahsan, E-mail:; Srinivasan, Raghavan [Department of Mechanical and Materials Engineering, Wright State University, Dayton, Ohio 45435 (United States)


    In DMLS process objects are fabricated layer by layer from powdered material by melting induced by a controlled laser beam. Metallic powder melts and solidifies to form a single layer. Solidification map during layer formation is an important route to characterize micro-structure and grain morphology of sintered layer. Generally, solidification leads to columnar, equiaxed or mixture of these two types grain morphology depending on solidification rate and thermal gradient. Eutectic or dendritic structure can be formed in fully equiaxed zone. This dendritic growth has a large effect on material properties. Smaller dendrites generally increase ductility of the layer. Thus, materials can be designed by creating desired grain morphology in certain regions using DMLS process. To accomplish this, hardness, temperature distribution, thermal gradient and solidification cooling rate in processed layers will be studied under change of process variables by using finite element analysis, with specific application to Ti-6Al-4V.

  6. Simulation on solidification of an Al-Ni alloy under electromagnetic stirring

    Sha Minghong


    Full Text Available The microstructure of Al-Ni alloy has a significant influence on its performance, while electromagnetic stirring is one of the most effective methods for control of solidification structure of Al alloy. To investigate the effect of electromagnetic stirring on the solidification of the ingot, the solidification of the Al-50Ni alloy in vacuum with electromagnetic stirring was described by numerical simulation in this paper; and a three dimensional mathematical model was established. The electromagnetic field was simulated by ANSYS software and the thermal-flow field was simulated by FLUENT software. The coupling between the electromagnetic field and the thermal-flow field was implemented by user-defined subroutines. It is found that the current intensity has significant influences on the fluid flow and the microstructure of the alloy. The simulation results agree well with the experimental results, and the optimum current intensity under the exprimental conditions is 80 A, while the frequency is 50 Hz.

  7. A Multi-Chamber System for Analyzing the Outgassing, Deposition, and Associated Optical Degradation Properties of Materials in a Vacuum

    Singal, J; Chang, C; Czodrowski, P; Kim, P


    We report on the Camera Materials Test Chamber, a multi-vessel apparatus which analyzes the outgassing consequences of candidate materials for use in the vacuum cryostat of a new telescope camera. The system measures the outgassing products and rates of samples of materials at different temperatures, and collects films of outgassing products to measure the effects on light transmission in six optical bands. The design of the apparatus minimizes potential measurement errors introduced by background contamination.

  8. Morphology of solidification front in eutectic

    M. Trepczyńska - Łent


    Full Text Available In this paper the analysis of morphology of solidification front in eutectic made. It was present influence of composition, solidification velocity, concentration micro-field and capillarity effects on the morphology of the solid/liquid interface. It was introduced phase-field model.

  9. Solidification phenomena in metal matrix nanocomposites

    de Cicco, Michael Peter


    Nanoparticles in metal matrix nanocomposites (MMNCs) were shown to act as catalysts for nucleation of solidification of the matrix alloy, as well as to alter the intermetallic phase formation. These phenomena were studied in zinc, aluminum, and magnesium alloys. In all alloys studied, a refinement of the microstructure was seen with the addition of the nanoparticles. Various types of nanoparticles were used and had varying degrees of refinement. In a zinc alloy, AC43A, SiC, TiC, and Al2O3 gamma nanoparticles were all found to refine the alloy. Thermal analysis of bulk samples showed the onset of solidification at reduced undercoolings, indicating nucleation catalysis. Nucleation of the primary phase was also observed by employing the droplet emulsion technique (DET). DET results showed that the secondary phase nucleation was also catalyzed by the nanoparticles. Exploiting the nucleation catalysis of the nanoparticles and the associated grain refinement, a semi-solid casting (SSC) process was demonstrated in AC43A + SiC nanocomposites. This novel process successfully incorporated the strength enhancement of MMNCs and the casting quality benefits of SSC. This process required no additional processing steps or material handling typical of existing SSC processes. The nucleation catalysis of the nanoparticles was sufficient to create semi-solid slurries appropriate for SSC. Nanoparticle induced nucleation catalysis was also examined in a common aluminum alloy, A356, using the DET. All nanoparticles catalyzed nucleation of the primary Al phase. However, undercoolings varied depending on the nanoparticle identity and average diameter. The variation in undercoolings generally agreed with a modified lattice disregistry theory and the free growth theory. For nanoparticles with a small lattice spacing mismatch with the Al phase, undercoolings approached the size dependent free growth limit. Binary alloys of magnesium and zinc showed significant strength and ductility

  10. Numerical modelling of rapid solidification

    Pryds, Nini; Hattel, Jesper Henri


    A mathematical model of the melt spinning process has been developed based on the control-volume finite-difference method. The model avoids some of the limitations of the previous models, for example including the effect of the wheel in the heat how calculations and the temperature dependence...... of the thermophysical parameters of the material. The nucleation temperature was calculated based on the heterogeneous nucleation theory. The effect of various parameters, such as the heat transfer coefficient, the nucleation temperature and the heating and type of the wheel on the rapid solidification behaviour...

  11. Directional Solidification of Eutectic Ceramics

    Sayir, Ali


    Two major problems associated with structural ceramics are lack of damage tolerance and insufficient strength and creep resistance at very high temperatures of interest for aerospace application. This work demonstrated that the directionally solidified eutectics can have unique poly-phase microstructures and mechanical properties superior to either constituent alone. The constraining effect of unique eutectic microstructures result in higher resistance to slow crack growth and creep. Prospect of achieving superior properties through controlled solidification are presented and this technology can also be beneficial to produce new class of materials.

  12. Extremely low-outgassing material: 0.2% beryllium copper alloy

    Watanabe, Fumio


    Exploration for low-outgassing materials for use in ultrahigh vacuum and extreme high-vacuum systems is one of the most important topics of a vacuum researcher. We have found that a copper alloy containing 0.2% beryllium (0.2% BeCu) can attain an extremely low hydrogen outgassing rate of 10-14 Pa (H2) m/s order. Almost the entire surface of 0.2% BeCu is dominated by a BeO layer, after a 400 °C×72 h prebakeout treatment in an ultrahigh vacuum. This layer functions as a barrier to the processes of oxidization and permeation of hydrogen. In addition, this layer resists carbon contamination. Temperature-programmed desorption spectra show only a single peak for water at 150 °C and small quantities of any other desorption gases. Therefore, an in situ bakeout process in which the temperature simply ramps up to 150 °C and immediately ramps back down is enough for degassing; it does not require an ordinary sustained-temperature bakeout. Using an outgassing sample consisting of 0.2% BeCu disks housed in a 0.2% BeCu nipple chamber, a lowest outgassing rate of the 5.6×10-14 Pa (H2) m/s was measured by the pressure-rise method after pump cutoff. The pressure-rise versus time curve was completely nonlinear. It rises over time to a constant slope of 1/2 in a log-log plot, due to hydrogen diffusion from the bulk, but this requires over a week at room temperature. The hydrogen outgassing from the 0.2% BeCu bulk is completely dominated by a diffusion-limited mechanism. This article will describe why we obtain such low-outgassing rates with 0.2% BeCu. It is based on the observed surface changes with prebakeout treatment seen by x-ray photoelectron spectroscopy, and the improvement of hydrogen outgassing measurements by the pressure-rise method. A comparison is made to ordinary stainless steel. In addition, the concept of an outgassing reduction method will be discussed from a review of the published ultralow-outgassing data and reduction methods. .


    Charles W. Solbrig; Kenneth J. Bateman


    The goal of this work is to produce a ceramic waste form (CWF) that permanently occludes radioactive waste. This is accomplished by absorbing radioactive salts into zeolite, mixing with glass frit, heating to a molten state 915 C to form a sodalite glass matrix, and solidifying for long-term storage. Less long term leaching is expected if the solidifying cooling rate doesn’t cause cracking. In addition to thermal stress, this paper proposes that a stress is formed during solidification which is very large for fast cooling rates during solidification and can cause severe cracking. A solidifying glass or ceramic cylinder forms a dome on the cylinder top end. The temperature distribution at the time of solidification causes the stress and the dome. The dome height, “the length deficit,” produces an axial stress when the solid returns to room temperature with the inherent outer region in compression, the inner in tension. Large tensions will cause cracking of the specimen. The temperature deficit, derived by dividing the length deficit by the coefficient of thermal expansion, allows solidification stress theory to be extended to the circumferential stress. This paper derives the solidification stress theory, gives examples, explains how to induce beneficial stresses, and compares theory to experimental data.

  14. Outgassing measurement of an LHC collimator and estimation for the NEG performances

    Kamiya, Junichiro; Jimenez, J M; Bregliozzi, G


    The outgassing rate of the collimators in the Large Hadron Collider (LHC) at CERN has an important role for the life-time of the Non-Evaporable Getter (NEC), and an accurate analysis allows the definition of future activities, like NEC vacuum activation. For these reasons, both, total outgassing rate and gas composition of a secondary collimator have been measured in the laboratory. The outgassing rate decreases by about two orders of magnitude by after bake-out and moreover, repeated bake-out further reduced the outgassing rate. The gas transmission through the NEC coated beam pipes and the resulting pressure distributions near the collimator were also measured in a dedicated setup. It is found that the main gas component after just 2 m of NEC coated beam pipe is CH(4) due to the extreme pumping speed of NEC for the other gases. Large amount of outgassing for H(2) and carbon related molecules are released when moving the collimator jaws. It is found that the NEC is very effective even in such case with large...

  15. Kinetics of CO(2) fluxes outgassing from champagne glasses in tasting conditions: the role of temperature.

    Liger-Belair, Gérard; Villaume, Sandra; Cilindre, Clara; Jeandet, Philippe


    Measurements of CO(2) fluxes outgassing from a flute poured with a standard Champagne wine initially holding about 11 g L(-1) of dissolved CO(2) were presented, in tasting conditions, all along the first 10 min following the pouring process. Experiments were performed at three sets of temperature, namely, 4 degrees C, 12 degrees C, and 20 degrees C, respectively. It was demonstrated that the lower the champagne temperature, the lower CO(2) volume fluxes outgassing from the flute. Therefore, the lower the champagne temperature, the lower its progressive loss of dissolved CO(2) concentration with time, which constitutes the first analytical proof that low champagne temperatures prolong the drink's chill and helps retains its effervescence. A correlation was also proposed between CO(2) volume fluxes outgassing from the flute poured with champagne and its continuously decreasing dissolved CO(2) concentration. Finally, the contribution of effervescence to the global kinetics of CO(2) release was discussed and modeled by the use of results developed over recent years. The temperature dependence of the champagne viscosity was found to play a major role in the kinetics of CO(2) outgassing from a flute. On the basis of this bubbling model, the theoretical influence of champagne temperature on CO(2) volume fluxes outgassing from a flute was discussed and found to be in quite good accordance with our experimental results.

  16. Algorithms of optimum location of sensors for solidification parameters estimation

    J. Mendakiewicz


    Full Text Available The algorithms of optimal sensor location for estimation of solidification parameters are discussed. These algorithms base on the Fisher Information Matrix and A-optimality or D-optimality criterion. Numerical examples of planning algorithms are presented and next foroptimal position of sensors the inverse problems connected with the identification of unknown parameters are solved. The examplespresented concern the simultaneous estimation of mould thermophysical parameters (volumetric specific heat and thermal conductivityand also the components of volumetric latent heat of cast iron.

  17. Boundary-layer model of pattern formation in solidification

    Ben-Jacob, E.; Goldenfeld, N.; Langer, J. S.; Schon, G.


    A model of pattern formation in crystal growth is proposed, and its analytic properties are investigated. The principal dynamical variables in this model are the curvature of the solidification front and the thickness (or heat content) of a thermal boundary layer, both taken to be functions of position along the interface. This model is mathematically much more tractable than the realistic, fully nonlocal version of the free-boundary problem, and still recaptures many of the features that seem essential for studying dendritic behavior, for example. Preliminary numerical solutions produce snowflakelike patterns similar to those seen in nature.

  18. Lunar Outgassing, Transient Phenomena and The Return to The Moon, I: Existing Data

    Crotts, Arlin P S


    Herein the transient lunar phenomena (TLP) report database is subjected to a discriminating statistical filter robust against sites of spurious reports, and produces a restricted sample that may be largely reliable. This subset is highly correlated geographically with the catalog of outgassing events seen by the Apollo 15, 16 and Lunar Prospector alpha-particle spectrometers for episodic Rn-222 gas release. Both this robust TLP sample and even the larger, unfiltered sample are highly correlated with the boundary between mare and highlands, as are both deep and shallow moonquakes, as well as Po-210, a long-lived product of Rn-222 decay and a further tracer of outgassing. This offers another significant correlation relating TLPs and outgassing, and may tie some of this activity to sagging mare basalt plains (perhaps mascons). Additionally, low-level but likely significant TLP activity is connected to recent, major impact craters (while moonquakes are not), which may indicate the effects of cracks caused by the ...

  19. A Reducing Atmosphere From Out-gassing of the Early Earth

    Schaefer, L.; Fegley, B., Jr.


    Earth's present atmosphere originated from out-gassing of volatile-bearing grains. We calculated the composition of volatiles out-gassed from chondritic planetary bodies. We present results for average CI, CM, CV, H, L, and EH chondrites, which are the building blocks of the Earth. From the oxygen-isotope mixing (OIM) model, we calculated a composition of 70% EH, 21% H, 5% CV, and 4% CI chondritic matter for the early Earth. The major out-gassed volatiles for these starting compositions are CH4, N2, NH3, H2, and H2O. The Miller-Urey experiment demonstrated that a reducing atmosphere like this generates amino acids and other organic compounds that are essential for the formation of life. This work is supported by the NASA Astrobiology Program. \\leavevmode \\epsfxsize=0.9\\hsize \\epsfbox{49.eps}

  20. Interface Pattern Selection in Directional Solidification

    Trivedi, Rohit; Tewari, Surendra N.


    The central focus of this research is to establish key scientific concepts that govern the selection of cellular and dendritic patterns during the directional solidification of alloys. Ground-based studies have established that the conditions under which cellular and dendritic microstructures form are precisely where convection effects are dominant in bulk samples. Thus, experimental data can not be obtained terrestrially under pure diffusive regime. Furthermore, reliable theoretical models are not yet possible which can quantitatively incorporate fluid flow in the pattern selection criterion. Consequently, microgravity experiments on cellular and dendritic growth are designed to obtain benchmark data under diffusive growth conditions that can be quantitatively analyzed and compared with the rigorous theoretical model to establish the fundamental principles that govern the selection of specific microstructure and its length scales. In the cellular structure, different cells in an array are strongly coupled so that the cellular pattern evolution is controlled by complex interactions between thermal diffusion, solute diffusion and interface effects. These interactions give infinity of solutions, and the system selects only a narrow band of solutions. The aim of this investigation is to obtain benchmark data and develop a rigorous theoretical model that will allow us to quantitatively establish the physics of this selection process.

  1. Solidification of gold nanoparticles in carbon nanotubes.

    Arcidiacono, S; Walther, J H; Poulikakos, D; Passerone, D; Koumoutsakos, P


    The structure and the solidification of gold nanoparticles in a carbon nanotube are investigated using molecular dynamics simulations. The simulations indicate that the predicted solidification temperature of the enclosed particle is lower than its bulk counterpart, but higher than that observed for clusters placed in vacuum. A comparison with a phenomenological model indicates that, in the considered range of tube radii (R(CNT)) of 0.5 < R(CNT) < 1.6 nm, the solidification temperature depends mainly on the length of the particle with a minor dependence on R(CNT).

  2. Petrology of Deep Storage, Ingassing, and Outgassing of Terrestrial Carbon (Invited)

    Dasgupta, R.


    net ingassing of carbon into the mantle in the modern Earth, but in the hotter subduction zones that prevailed during the Hadean, Archean, and most of Proterozoic, recycled carbonate likely was released at shallow mantle wedge depths and may have returned to the exosphere more efficiently through arc volcanism. Release of primordial carbon through magmatism was also likely more vigorous owing to deeper intersection of solidi and hotter mantle adiabat. Inefficient ingassing, along with efficient outgassing, may have maintained the ancient mantle carbon-poor. If this is accurate, then the present-day carbon budget of the mantle is likely shaped mostly from NeoProterozoic through Phanerozoic, a time when thermal state of the planet allowed deep subduction of carbonated crustal rocks.

  3. Rapid solidification of immiscible alloys

    Bosco, Enrica; Rizzi, Paola; Baricco, Marcello E-mail:


    Immiscible alloys have been rapidly solidified for the preparation of granular materials with giant magnetoresistance properties. Au-based (Au-Co and Au-Fe) and Cu-based (Cu-Co and Cu-Fe) systems have been investigated. Single supersaturated solid solution has been obtained for Au-Fe, whereas three FCC solid solutions with different Co content have been found for Au-Co. For Cu-Co and Cu-Fe a limit of solubility in Cu has been observed. Ni additions to Cu-Fe strongly enhance solid solubility. A thermodynamic analysis has been used to describe the competition between partition-less solidification and phase separation in undercooled liquid.

  4. Theoretical - Experimental Analysis of Cellular and Primary Dendritic Spacings during Unidirectional Solidification of Sn-Pb Alloys

    Otávio F.L. da Rocha


    Full Text Available Structural parameters as grain size, dendritic and cellular spacings, segregated products, porosity and other phases are strongly influenced by the thermal behavior of the metal/mold system during solidification, imposing a close correlation between this and the resulting microstructure. Several unidirectional solidification studies with the objective of characterizing cellular and dendritic spacings have been developed in large scale involving solidification in steady-state heat flow. The main objective of this work is to determine the thermal solidification parameters during the cellular/dendritic transition as well as to compare theoretical models that predict cellular and primary dendritic spacings with experimental results for solidification situations in unsteady-state heat flow. Experiments were carried out in a water cooled unidirectional solidification apparatus and dilute alloys of the Sn-Pb system were used (Sn 1.5wt%Pb, Sn 2.5wt%Pb and Sn 5wt%Pb. The upper limit of the Hunt-Lu cellular growth model closely matched the experimental spacings. The lower limit calculated with the Hunt-Lu dendritic model best generated the experimental results. The cellular/dendritic transition was observed to occur for the Sn 2.5wt%Pb alloy over a range of analytical cooling rates from 0.28 K/s to 1.8 K/s.

  5. Estimation of solidification time during casting by use of a heat transfer model.

    Okazaki, M; Takahashi, J; Kimura, H; Ida, K


    Time-dependent temperature profiles in dental casting molds were analyzed by an unsteady heat conduction model. The thermal conductivity and initial temperature of the mold greatly affected the heat transfer in the mold. The thermal conductivities of gypsum- and phosphate-bonded investments at high temperatures were accurately measured by means of the hot wire method. From the data obtained, the solidification times of Ag, Ag alloy, and Co-Cr alloy were calculated and compared with the experimental results.

  6. Evolution of solidification texture during additive manufacturing

    Wei, H L; Mazumder, J; DebRoy, T


    Striking differences in the solidification textures of a nickel based alloy owing to changes in laser scanning pattern during additive manufacturing are examined based on theory and experimental data...

  7. Alternating grain orientation and weld solidification cracking

    Kou, S.; Le, Y.


    A new mechanism for reducing weld solidification cracking was proposed, based on the concept of the crack path and resistance to crack propagation, and its effectiveness was verified in magnetically oscillated GTA welds of a rather crack susceptible material 2014 aluminum alloy. This mechanism, i.e., alternating grain orientation, was most pronounced in welds made with transverse arc oscillation of low frequency and high amplitude, and solidification cracking was dramatically reduced in these welds. The effect of the arc oscillation pattern, amplitude, and frequency on the formation of alternating columnar grains and the reduction of solidification cracking in GTA welds of 2014 aluminum alloy was examined and explained. The present study demonstrated for the first time that columnar grains can, in fact, be very effective in reducing solidification cracking, provided that they are oriented favorably.

  8. A visualization of the eutectic solidification process

    E. Olejnik


    Full Text Available The study presents a visualization of the sequence of formation of eutectic grains during solidification in volume and directional solidification of model organic materials from the system of salol (faceted phase - camphor (non-faceted phase and carbon tetrabromide (non-faceted phase - hexachloroethane (non-faceted phase. It has been proved that the faceted phase may act as a substrate for nucleation of the non-faceted phase, while the non-faceted phase in a eutectic grain is of polycrystalline character. The directional solidification of non-faceted/non-faceted eutectic enabled disclosing various structural defects, while solidification in volume explained in what way the, so called, halo effect is formed.

  9. Evolution of solidification texture during additive manufacturing.

    Wei, H L; Mazumder, J; DebRoy, T


    Striking differences in the solidification textures of a nickel based alloy owing to changes in laser scanning pattern during additive manufacturing are examined based on theory and experimental data. Understanding and controlling texture are important because it affects mechanical and chemical properties. Solidification texture depends on the local heat flow directions and competitive grain growth in one of the six preferred growth directions in face centered cubic alloys. Therefore, the heat flow directions are examined for various laser beam scanning patterns based on numerical modeling of heat transfer and fluid flow in three dimensions. Here we show that numerical modeling can not only provide a deeper understanding of the solidification growth patterns during the additive manufacturing, it also serves as a basis for customizing solidification textures which are important for properties and performance of components.

  10. A Citizen's Guide to Solidification and Stabilization

    This guide describes how solidification and stabilization refer to a group of cleanup methods that prevent or slow the release of harmful chemicals from wastes, such as contaminated soil, sediment, and sludge.

  11. Thermal gradient analysis of solidifying casting

    J. Suchoń


    Full Text Available For description of casting solidification and crystallization process the thermal derivative analysis (TDA is commonly used. Besides the process kinetics considered in TDA method to describe the solidification process, the thermal gradient analysis can be also used for this purpose [1, 2]. In conducted studies analysis of thermal gradient distribution inside the solidifying wedge casting was shown which enabled determination of heat flow intensity on casting section.

  12. Solidification fronts in large magma chambers: insights from the anomalies

    VanTongeren, J. A.


    The emplacement of hot viscous magma into the cold rigid crust causes a thermal disturbance within both the country rock and the magma. With time, heat loss from the molten interior to the walls causes solidification at the floor, roof and margins of the magma chamber. As is observed in both experiment and theory, in the absence of hydrothermal convection, the majority of heat is lost via conduction through the roof of the intrusion. In basaltic sills and layered mafic intrusions (LMIs), this solidification front is manifest in the deposition of mineral assemblages and compositions that become progressively more evolved from the floor of the intrusion upwards (the 'Layered Series'; LS) and from the roof downwards (the UBS) such that the most chemically evolved rocks are found in the interior of the magma body at a 'Sandwich Horizon'. The formation of a UBS, as typified by the Skaergaard Intrusion, is a natural outcome of the progression of the solidification front from the cold roof to the hot center of the magma chamber. There are, however, a few unique LMIs for which little or no UBS exists. Convection of the molten magma, reinjection and mixing of new magma, compaction of cumulates, and porous flow of interstitial liquid, among other processes, can affect the final location and composition of the most differentiated liquids; but ultimately, all are linked to the nature of heat loss from the magma chamber. In this study, I examine the thermal evolution of several classic LMIs as it is recorded in the extent of the preserved upper solidification front (or Upper Border Series; 'UBS'). For those intrusions that have experienced crystallization at the roof, such as the Skaergaard Intrusion, the development of a UBS reduces the temperature gradient at the roof and effectively slows the rate of heat loss from the main magma body. However, for those intrusions that do not have an UBS, such as the Bushveld Complex, the cooling rate is controlled only by the maximum rate

  13. Outgassing rate of the copper-plated beam tube for ISABELLE

    Hseuh, H.C.; Gaudet, E.F.


    The ultrahigh vacuum system of the intersecting storage accelerator, ISABELLE, will consist of two interlaced rings of stainless steel beam tubes with a circumference 2-1/2 miles each. To obtain a good heat conduction during bakeout and to reduce the resistive wall instability during beam operation, a lmm thick copper coating will be electroplated to the outer surface of this 1.5 mm thick beam tube. To minimize the beam loss due to beam-gas collision, the pressure inside the beam tube is required to be 1 x 10/sup -11/ Torr (N/sub 2/ equivalent) or less. To achieve this ultrahigh vacuum, the outgassing rate of the 304 LN stainless steel tubes has been reduced to approx. 1 x 10/sup -13/ Torr. l/cm/sup 2/. sec by vacuum firing at 950/sup 0/C for one hour. However, during acid-bath electroplating of copper, significant amount of hydrogen will be reintroduced and trapped in stainless steel which will substantially increase the outgassing rate (to approx. 2 x 10/sup -12/ Torr . l/cm/sup 2/ sec). The outgassing characteristics of these copper-plated beam tubes are studied and discussed within the scope of diffusion and energy of activation. Methods to reduce the outgassing rate to an acceptable level (approx. 1 x 10/sup -13/ Torr . l/cm/sup 2/ . sec) are also given.

  14. Outgassing measurements for the turn insulation of CFETR poloidal field coils

    Zou, C.; Song, Y.; Wu, H., E-mail:; Shen, G.; Wu, W.; Lu, K.; Wei, J.


    Highlights: • Outgassing rate of turn insulation will affect VPI process and conductor leak test. • The outgassing rate of turn insulation structure was measured by dynamic flow method. • The interleaved polyimide decreases the insulation outgassing rate. - Abstract: China Fusion Engineering Test Reactor (CFETR) is a new tokamak device. The poloidal field (PF) system plays an important role in controlling the location and shape of the plasma. In order to satisfy the electrical and mechanical requirements, the turn insulation shall be applied on the conductor during winding. Before vacuum pressure impregnation (VPI) process, the conductor with dry (un-impregnated) insulation should be leak tested in a chamber, and the material shall be degassed in the VPI mold before impregnation with epoxy. The gas released from the insulation material will affect the vacuum of leak test vessel and VPI quality. In this paper, the dynamic flow method was used to measure the outgassing rate of insulation material in special structure, and the results were shown and discussed.

  15. Kinetic measurement and prediction of the hydrogen outgassing from the polycrystalline LiH/Li2O/LiOH system

    Dinh, L N; Grant, D M; Schildbach, M A; Smith, R A; Siekhaus, W J; Balazs, B; Leckey, J H; Kirkpatrick, J; McLean II, W


    Due to the exothermic reaction of lithium hydride (LiH) salt with water during transportation and handling, there is always a thin film of lithium hydroxide (LiOH) present on the LiH surface. In dry or vacuum storage, this thin LiOH film slowly decomposes. We have used temperature-programmed reaction/decomposition (TPR) in combination with the isoconversion method of thermal analysis to determine the outgassing kinetics of H{sub 2}O from pure LiOH and H{sub 2} and H{sub 2}O from this thin LiOH film. H{sub 2} production via the reaction of LiH with LiOH, forming a lithium oxide (Li{sub 2}O) interlayer, is thermodynamically favored, with the rate of further reaction limited by diffusion through the Li{sub 2}O and the stability of the decomposing LiOH. Lithium hydroxide at the LiOH/vacuum interface also decomposes easily to Li{sub 2}O, releasing H{sub 2}O which subsequently reacts with LiH in a closed system to form H{sub 2}. At the onset of dry decomposition, where H{sub 2} is the predominant product, the activation energy for outgassing from a thin LiOH film is lower than that for bulk LiOH. However, as the reactions at the LiH/Li{sub 2}O/LiOH and at the LiOH/vacuum interfaces proceed, the overall activation energy barrier for the outgassing approaches that of bulk LiOH decomposition. The kinetics developed here predicts a hydrogen evolution profile in good agreement with hydrogen release observed during long term isothermal storage.

  16. EUV resist outgassing analysis for the new platform resists at EIDEC

    Shiobara, Eishi; Kikuchi, Yukiko; Mikami, Shinji; Sasami, Takeshi; Kamizono, Takashi; Minegishi, Shinya; Kimoto, Takakazu; Fujimori, Toru; Watanabe, Takeo; Harada, Tetsuo; Kinoshita, Hiroo; Tanaka, Satoshi


    The suppression of outgassing from the EUV resist is one of the significant challenges, which has to be addressed for realizing EUV lithography (EUVL). The outgassing might be the main contributor involved in the contamination of the mirror optics in scanners. This may result in reflectivity losses. The pragmatic outgassing test that utilizes the witness sample (WS) was used as a general method to quantify the outgassing level for commercially available chemically amplified resists (CAR). There are two types of contaminations. The first type of contamination involves a cleanable contamination that mainly comprises hydrocarbons that can be removed by the hydrogen radical cleaning. Another type of contamination includes the noncleanable contamination that remains on the WS even after hydrogen radical cleaning. Several outgas qualification results were evaluated at the EIDEC [1, 2]. The data indicated that contaminations by the CAR mainly comprised the cleanable contaminations. The data also indicated that there were almost negligible noncleanable contaminations from the CAR. EUV resist communities accelerate the development of high sensitivity resists to compensate the low power of the EUV source. Nonchemically amplified resist (nonCAR) with a new platform is a candidate for high sensitivity resists. The nonCAR includes some types of metal elements with high absorbance for EUV light. There is very limited research on the outgassing characteristics of the nonCAR. In this study, we considered an EUV exposure process in the actual EUV scanner and EUV resists were exposed in a hydrogen environment. A potential risk could result from the reaction of the hydrogen radicals generated by the EUV light with the metal elements in the nonCAR and the metal hydride outgases from the resist. This would result in a noncleanable contamination on the EUV mirror [3]. The knowledge with respect to outgassing from an organic metal complex is insufficient even in a vacuum condition. Hence

  17. An abrupt outgassing revealed by a slow decompression experiment of cristal-bearing syrup foam

    Kanno, Y.; Namiki, A.


    Distribution of volcanic gasses in a conduit determines eruption style. Outgassing changes the distribution of volcanic gasses in a conduit.We here simulated the outgassing from ascending magma by slow decompression experiments. As molten magma ascends in a conduit, surrounding pressure becomes low and bubbles in magma expand. In our previous work, we found that the bubble expansion causes film rupturing and makes paths for outgassing. The crystals in magma may affect this newly found outgassing style. Accordingly, we slowly decompressed syrup foam including solid particles as a magma analogue. Experiments are conducted in an acrylic tank. We observed the expansion of three-phase magma analog from the front of the tank using a digital video camera. From the images and pressure measurements, we calculated time evolution of the syrup volume and permeability. We consider that there is no bubble segregation by the ascent of individual bubbles from the Stoke's velocity. We conducted our experiments with a viscosity range of 10-20 Pa s which is the same orders of magnitude of that of basaltic magma, 10-103 Pa s. At the beginning of the decompression, the volume change of the syrup foam is well explained by isothermal expansion. When the gas fractions reached to the 85-90%, we observed that deformations of bubble films caused film rupturing so that bubbles coalesce vertically to clear a path. As time elapsed, the measured gas volume in the foam becomes smaller than that estimated by the isothermal expansion, indicating the occurrence of outgassing. In the experiments with high volume fraction of solid particles (>30 vol.% for bubble-free liquid), we observed another new style of outgassing. Several large voids (> 10 mm in radius) appear at a middle height of the foam and connect each other to make a horizontally elongated cavity. The roof of the cavity collapses, and then massive outgassing occurs. At the beginning of the decompression until the foam collapses, outgassing

  18. Gravimetric measurements of materials outgassing applied to graphite-epoxy laminates

    Scialdone, John J.


    The outgassing rates of two graphite-epoxy laminates, American Cyanamide 985B-626 and HST-7B-112, were obtained using a gravimetric method. The rates as a function of time and temperature were derived from the measurements of their mass losses at temperatures varying from 25 to 150 C and for a time span of up to 400 hours in a vacuum. The data from those measurements were reduced to obtain the outgassing activation energies, the mass losses per unit mass or area, and the corresponding outgassing rates. The rates are expressed in closed-form equations and are directly usable for modeling computations. The procedures to obtain these parameters are shown and may be used for the evaluation of other materials. The results of the tests show that the activation energies of the two materials are: 4630 cal/mole for the 985B-626 materials and 4791 cal/mole for the HST-7B-112 sample no. 10 Graphite Epoxy. The outgassing rates of these materials are in the 1OE-5 g sq cm/hr range and they decay according to a power of time of 0.60 at 25 C, indicating that the outgassing process is mainly a diffusion at that temperature. The normalized mass losses versus time obtained from these tests were compared to the discrete results obtained from the ASTM-E595 tests. The comparison provides general indications on the effects of temperature and time in relation to the ASTM test values obtained at 125 C for a 24-hour test duration.

  19. Dynamic outgassing of deuterium, helium and nitrogen from plasma-facing materials under DEMO relevant conditions

    Möller, S.; Matveev, D.; Martynova, Y.; Unterberg, B.; Rasinski, M.; Wegener, T.; Kreter, A.; Linsmeier, Ch.


    In confined plasma magnetic fusion devices significant amounts of the hydrogen isotopes used for the fusion reaction can be stored in the plasma-facing materials by implantation. The desorption of this retained hydrogen was seen to follow a t α law with α  ≈  -0.7 in tokamaks. For a pulsed fusion reactor this outgassing can define the inter-pulse waiting time. This work presents new experimental data on the dynamic outgassing in ITER grade tungsten exposed under the well-defined conditions of PSI-2 to pure and mixed D2 plasmas. A peak ion flux of 1022 D+ m-2 s is applied for up to 6 h at sample temperatures of up to 900 K. Pure D2 and mixed D2  +  He, D2  +  N2 and D2  +  He  +  N2 plasmas are applied to the sample at 68 V bias. The D2, He, N outgassing at 293 K and 580 k are observed via in-vacuo quadrupole mass spectrometry covering the range of 40 s-200 000 s after exposure. The outgassing decay follows a single power law with exponents α  =  -0.7  to  -1.1 at 293 K, but at 580 K a drop from α  =  -0.25 to  -2.35 is found. For DEMO a pump-down time to 0.5 mPa in the order of 1-5 h can be expected. The outgassing is in all cases dominated by D2.

  20. Thermoelastic Stability Analysis of Solidification of Pure Metals on a Coated Planar Mold of Finite Thickness

    Demir, Mehmet Hakan; Yigit, Faruk


    A theoretical model for investigating the thermoelastic instability/mechanism during pure metal solidification on a coated mold of finite thickness is developed. This study extends the previous theoretical works on growth instability during solidification process by investigating the effects of an added coating layer. Mold coating is one of the most important factors controlling the heat transfer rate, and hence it has a very important role on the solidification rate and the development of microstructure. In this model, thermal and mechanical problems are coupled through the pressure-dependent contact resistances at mold/coating and coating/shell interfaces. The thermal diffusivities of solidified shell, coating, and mold materials are assumed to be zero. This assumption provides us to solve heat transfer problem analytically. A linear perturbation method is used to simplify complexity of the modeled solidification problem, and governing equations are solved numerically using a variable step variable order predictor-corrector algorithm. The effects of coating layer thickness and coupling rates at shell/coating and coating/mold interfaces are investigated in detail. The results show that coating thickness has destabilizing effect on the growth instability when the coupling rates are small. However, when these coupling rates are increased individually or together, the destabilizing effect of coating thickness turns to be stabilizing. On the other hand, coupling rates have generally destabilizing effects on the process, but an increase in the thickness of coating leads to diminishing coupling rates effect in some cases.

  1. Graphite curtain vacuum outgassing and heat transfer. Final report

    Fivel, H.J.; Lang, G.P.; Kipp, H.W.


    Thermal conductivity of a bundle of high conductivity graphite fibers (T-50) was measured as a function of temperature, density and fiber orientation at pressures of 10/sup -4/ to 10/sup -5/ torr. All 3 variables had a significant influence on thermal conductivity. The highest conductivity fiber bundle tested had a conductivity significantly less than dense, bulk nuclear grade graphite. The incorporation of heat pipes into a graphite spectral shaper will permit a 2-fold thicker shaper. Heat pipes not only increase the transport of heat within the spectral shaper but can increase heat transfer at the shaper-first wall interface and potentially serve as a means of attaching shaper modules to the first wall. A heat pipe using a liquid metal working fluid was fabricated and tested in magnetic fields of 1 and 2 Tesla. Liquid metal heat pipes can be used in a magnetic field of at least up to 2 Tesla. Much more work needs to be done to establish the capabilities for high performance heat pipes when used in magnetic fields. Four different types of graphite fibers were exposed in EBR-II to a neutron fluence of 3.5 x 10/sup 21/ cm/sup -2/ EFF at 470/sup 0/C. Large axial shrinkages of 6.6 to 8.6% resulted.

  2. Influence of directional solidification variables on primary dendrite arm spacing of Ni-based superalloy DZ125

    Zhang Weiguo; Liu Lin; Huang Taiwen; Zhao Xinbao; Qu Min; Yu Zhuhuan; Fu Hengzhi


    The primary dendrite morphology and spacing of DZ125 superalloy have been observed during directional solidification under high thermal gradient about 500 K/cm. The results reveal that the primary dendrite arm spacing decreases from 94 μm to 35.8 μm with the increase of directional solidification cooling rate from 2.525 K/s to 36.4 K/s. The regression equation of the primary dendrite arm spacings λ1 versus cooling rate is λ1=0.013(GV)-0.32. The predictions of Kurz/Fisher model and Hunt/Lu model accord reasonably well with the experimental data. The influence of directional solidification rate under variable thermal gradient on the primary dendrite arm spacing has also been investigated.

  3. 新型平板热管相变换热器储放能过程的研究%Experimental Study on Heat Transfer Characteristics of the Melting and Solidification Process for a New Type of Flat Pipe/PCM Thermal Storage System

    李嘉琪; 刁彦华; 赵耀华; 郭娜娜; 张冀


    A new type energy storage system of fiat pipe as the heat transfer component was used in latent heat ttmrmal And a set of flat pipe/PCM phase change thermal storage was designed and manufactured. Paratfm was adopted as phase change material, and a series of experiments about melting and solidification of the storage system were performed. With the temperature distribution of paraffin obtained from the experiments, the analysis of the effects of the inlet water temperature on the clmrging and discharging process were carried out. The homogetteous distribution of temperature and the efficiency of the system were also analyzed. The results showed that the new flat heat pipe thermal storage system works well in the experiment.%将新型平板热管作为换热元件引入相变蓄热系统,研制了一套新型的平板热管式相变蓄热换热器。蓄热换热器采用石蜡作为蓄热材料,对其蓄、放热过程进行了实验研究,得到了不同时刻换热器内石蜡温度分布。改变供、取热流体温度,分析了流体入口温度对换热器蓄放热过程的影响,分析了新型平板热管在蓄放热过程的均温性能以及换热器的蓄放热效率。结果表明,新型平板热管相变换热器蓄、放热效果良好。

  4. Micro/macro solidification modeling of columnar eutectic growth

    Judson, Ward Michael


    A general multidimensional model of alloy solidification is presented in which a velocity-dependent freezing temperature is coupled with the macroscale energy equation. The velocity dependence of the freezing temperature ( Tf˜v ) results from the microscale species diffusion for microstructures with coupled eutectic growth. At solidification rates ( ˜ 1--10 mm/s) that are representative of gravity permanent mold and die casting processes, consideration of the nonequilibrium conditions at the interface affects the prediction of the macroscale thermal field. Near-eutectic alloys freeze with a macroscopically discrete solid-liquid interface at a temperature below the equilibrium eutectic temperature. The model is illustrated with unidirectional solidification of a near-eutectic alloy in a finite domain and solved numerically with a fixed-grid Galerkin finite element method. The numerical algorithm includes inexpensive steps to compute the interface speed explicitly. By nondimensionalizing the governing equations the effect of coupled eutectic growth on heat transport is clearly identified so that the model's sensitivity to important parameters can be investigated. Additionally, the average eutectic spacing can be determined with the temperature field, rather than post-determination from a standard, uncoupled solution of the energy equation. The eutectic coupling results indicate that the predicted solid-liquid interface location lags behind the uncoupled solution; therefore, decreasing the amount of solid formed, increasing the total solidification time, and increasing the average eutectic spacing. A procedure is also illustrated for computing mechanical properties using experimental correlations and the computed interface velocity history. The effect of the eutectic undercooling is then studied in a square domain and a realistic three-dimensional production casting geometry. In order to address the multidimensional cases, a phase-field formulation is developed

  5. Solidification and crystal growth of solid solution semiconducting alloys

    Lehoczky, S.L.; Szofran, F.R.


    Problems associated with the solidification and crytal growth of solid-solution semiconducting alloy crystals in a terrestrial environment are described. A detailed description is given of the results for the growth of mercury cadmium telluride (HgCdTe) alloy crystals by directional solidification, because of their considerable technological importance. A series of HgCdTe alloy crystals are grown from pseudobinary melts by a vertical Bridgman method using a wide range of growth rates and thermal conditions. Precision measurements are performed to establish compositional profiles for the crystals. The compositional variations are related to compositional variations in the melts that can result from two-dimensional diffusion or density gradient driven flow effects ahead of the growth interface. These effects are discussed in terms of the alloy phase equilibrium properties, the recent high temperature thermophysical data for the alloys and the highly unusual heat transfer characteristics of the alloy/ampule/furnace system that may readily lead to double diffusive convective flows in a gravitational environment.

  6. Solidification and crystal growth of solid solution semiconducting alloys

    Lehoczky, S. L.; Szofran, F. R.


    Problems associated with the solidification and crytal growth of solid-solution semiconducting alloy crystals in a terrestrial environment are described. A detailed description is given of the results for the growth of mercury cadmium telluride (HgCdTe) alloy crystals by directional solidification, because of their considerable technological importance. A series of HgCdTe alloy crystals are grown from pseudobinary melts by a vertical Bridgman method using a wide range of growth rates and thermal conditions. Precision measurements are performed to establish compositional profiles for the crystals. The compositional variations are related to compositional variations in the melts that can result from two-dimensional diffusion or density gradient driven flow effects ahead of the growth interface. These effects are discussed in terms of the alloy phase equilibrium properties, the recent high temperature thermophysical data for the alloys and the highly unusual heat transfer characteristics of the alloy/ampule/furnace system that may readily lead to double diffusive convective flows in a gravitational environment.

  7. Solidification control in continuous casting of steel

    S Mazumdar; S K Ray


    An integrated understanding of heat transfer during solidification, friction/lubrication at solid-liquid interface, high temperature properties of the solidifying shell etc. is necessary to control the continuous casting process. The present paper elaborates upon the knowledge developed in the areas of initial shell formation, mode of mould oscillation, and lubrication mechanism. The effect of these issues on the caster productivity and the quality of the product has been discussed. The influence of steel chemistry on solidification dynamics, particularly with respect to mode of solidification and its consequence on strength and ductility of the solidifying shell, has been dealt with in detail. The application of these basic principles for casting of stainless steel slabs and processing to obtain good quality products have been covered.

  8. Non newtonian annular alloy solidification in mould

    Moraga, Nelson O.; Garrido, Carlos P. [Universidad de La Serena, Departamento de Ingenieria Mecanica, La Serena (Chile); Castillo, Ernesto F. [Universidad de Santiago de Chile, Departamento de Ingenieria Mecanica, Santiago (Chile)


    The annular solidification of an aluminium-silicon alloy in a graphite mould with a geometry consisting of horizontal concentric cylinders is studied numerically. The analysis incorporates the behavior of non-Newtonian, pseudoplastic (n=0.2), Newtonian (n=1), and dilatant (n=1.5) fluids. The fluid mechanics and heat transfer coupled with a transient model of convection diffusion are solved using the finite volume method and the SIMPLE algorithm. Solidification is described in terms of a liquid fraction of a phase change that varies linearly with temperature. The final results make it possible to infer that the fluid dynamics and heat transfer of solidification in an annular geometry are affected by the non-Newtonian nature of the fluid, speeding up the process when the fluid is pseudoplastic. (orig.)

  9. Structure and Dynamics of Cold Water Super-Earths: The Case of Occluded CH4 and its Outgassing

    Levi, Amit; Podolak, Morris


    We study the transport of methane in the external water envelopes surrounding water-rich super-Earths and estimate its outgassing into the atmosphere. We investigate the influence of methane on the thermodynamics and mechanics of the water mantle. We find that including methane in the water matrix introduces a new phase (filled ice) resulting in hotter planetary interiors. This effect renders the super-ionic and reticulating phases accessible to relatively low mass planets lacking a H/He atmosphere. We model the thermal and structural profile of the planetary crust and discuss five possible crustal regimes. The formation of methane clathrate in the subsurface is shown to inhibit the formation of a subterranean ocean. This effect results in increased stresses on the lithosphere making modes of ice plate tectonics possible. The dynamics of the tectonic plates are analysed. We derive overturn and resurfacing time scales as well as the melt fraction underneath spreading centers. Ice mantle dynamics is found to be...


    Molina, A. [Departamento de Fisica Aplicada, Universidad de Granada, Facultad de Ciencias, Avda. Severo Ochoa s/n, E-18071 Granada (Spain); Moreno, F. [Instituto de Astrofisica de Andalucia, CSIC, Glorieta de la Astronomia s/n, E-18008 Granada (Spain)


    We obtain the diameter of the most massive grains that might be ejected from the nuclear surface of the comets C/1861 G1 (Thatcher) and 109P/Swift-Tuttle using an outgassing model. The prevenient meteoroids of these two comets produce the known Lyrids and Perseids showers and it is thought that they produce electrophonic sounds. We compare our results with the minimum sized of such meteoroids capable of generating such sounds and we reconcile the discrepancy found by Beech in the case of the Lyrids. However, we conclude that the only outgassing mechanism is not compatible with the existence of electrophonic sounds due to Perseid meteoroids, and other mechanisms must be invoked to justify the presence of meter-sized boulders in the Perseid stream.

  11. AL-SX (H1616) Container Support: Out-gassing of Polyethylene and Polycarbonate Resins

    G.Cook Story; Leon Seibel and Linda Domeier


    Out-gassing tests were carried out on samples of polyethylene and polycarbonate packaging components used within the AL-SX (H1616) shipping container and compared to known samples of high and low density polyethylene and polycarbonate. Polyethylene is used to fabricate the shipping container overpack for the MC3007A/MC4059 and 1X-Acorn; LEXAN{reg_sign} polycarbonate (General Electric) is used to fabricate the lid of the Protective Container utilized to package the MC4213/MC4240 and MC4524 for shipment in the AL-SX (H1616). Pressure was monitored up to about 650 F and all the samples showed similar increases in pressure which were only slightly above those measured for control runs using no resin sample. None of the polymer samples showed out-gassing behavior that would lead to excessive pressure increases in the H1616 within that temperature range.

  12. Segregation effects and phase developments during solidification of alloy 625

    Højerslev, Christian; Tiedje, Niels Skat; Hald, John


    The solidification behaviour of pure Alloy 625, and Alloy 625 enriched respectively in iron and carbon, was investigated in situ by hot-stage light optical microscopy. Using this technique planar front solidification for distances of several hundred microns was facilitated. After solidification...

  13. Solidification of ternary systems with a nonlinear phase diagram

    Alexandrov, D. V.; Dubovoi, G. Yu.; Malygin, A. P.; Nizovtseva, I. G.; Toropova, L. V.


    The directional solidification of a ternary system with an extended phase transition region is theoretically studied. A mathematical model is developed to describe quasi-stationary solidification, and its analytical solution is constructed with allowance for a nonlinear liquidus line equation. A deviation of the liquidus equation from a linear function is shown to result in a substantial change in the solidification parameters.

  14. Timescales of bubble coalescence, outgassing, and foam collapse in decompressed rhyolitic melts

    Martel, Caroline; Iacono-Marziano, Giada


    The timescale of degassing and outgassing in hydrous rhyolitic melts is investigated in a wide range of conditions by means of decompression experiments. The evolution of vesicularity, bubble diameter, and number density is characterized as a function of time either of decompression or spent at final pressure, in order to determine the effect of final pressure, temperature, syn- versus post-decompression degassing, melt composition, and microlites, on the timescale of bubble growth, coalescence, and outgassing. The result suggest that different bubble evolution and degassing-outgassing timescale corresponding to explosive and effusive eruption regimes can be cast in bulk viscosity (melt + bubbles; nbulk) versus decompression time (rather than path) space. The nbulk-time relationships defines three domains of (i) bubble nucleation and growth, restricted to short durations and high nbulk ( 10-13 m2) to extensive (permeability ˜10-11-12 m2), and (iii) outgassing, restricted to long durations and low nbulk(> ˜10 h for nbulk 10-10 m2) that eventually leads to foam collapse. These findings are applied to the case studies of Mt Pelée and Mt Pinatubo to infer the transition from pumice to dense pyroclasts in volcanic eruptions and the possibility of evolving from an explosive Plinian eruption to an effusive dome-growth event by giving the vesicular magma enough time to outgas and collapse (i.e. hundreds to tens of hours for nbulk ˜105 to 104 Pa.s, respectively). We also show the drastic effect of microlites on re-arranging preexistent bubbles and potentially triggering a late nucleation event.

  15. Transient convective instabilities in directional solidification

    Meca, Esteban


    We study the convective instability of the melt during the initial transient in a directional solidification experiment in a vertical configuration. We obtain analytically the dispersion relation, and perform an additional asymptotic expansion for large Rayleigh number that permits a simpler analytical analysis and a better numerical behavior. We find a transient instability, i.e. a regime in which the system destabilizes during the transient whereas the final unperturbed steady state is stable. This could be relevant to growth mode predictions in solidification.

  16. Conditions Of Directional Solidification Affect Superalloy

    Schmidt, D. D.; Alter, W. S.; Hamilton, W. D.; Parr, R. A.


    Report describes experiments to determine effects of gradient of temperature and rate of solidification on microstructure and fatigue properties of nickel-based superalloy MAR-M246(Hf). Enhancement of properties extends lifespans of objects, including turbo-pump blades of Space Shuttle Main Engines. Results indicate significant improvements in fatigue properties derived through manipulation of parameters of directional solidification. Particularly MAR-M246(Hf) for turbine blades contains small, well-dispersed blocky carbide and microstructure with small distances between dendrite arms, and without eutectic phase.

  17. Solidification Based Grain Refinement in Steels


    likely to form, the author conducted a Schiel solidification analysis using Thermo-Calc. Table 2 lists the steel chemistry used based on the actual...the phases present during freezing were calculated. Table 3 Steel chemistry used fur Schiel analysis. C (wt. %) Mn (wt %) AKwt. %) Ti(wt. %) N(wt...0.4 0.6 0.8 Mole fraction of all solid phases Figure 23 Schiel solidification analysis for 0.1 % Ti containing 1030 steel. Figure 25 depicts the

  18. Solidification on fly ash, Yugoslav experiences

    Knezevic, D. [Mining Institute, Belgrade (Yugoslavia); Popov, S.; Salatic, D. [Faculty of Mining and Geology, Belgrade (Yugoslavia)


    A study was performed on ashes produced in the combustion process of coal from the Kosovo coal basin, in order to determine the potential and conditions of ash self-solidification. Investigations showed that the ash properties allows for the transformation into a solid mass through a controlled mixing with water. The optimal concentration of ash is 50 percent and the hydro-mixture is behaving as a Bingham plastic fluid. Solidification is obtained in a relatively short period (within 3 to 5 days) without additives. The resulting solidified mass is very consistent and stable

  19. Observations of a monotectic solidification interface morphology

    Kaukler, W. F.; Frazier, D. O.


    For detailed studies of the region around a solidification interface on a microscopic scale, a very thin (essentially two-dimensional) test cell may be translated across two temperature-controlled heating/cooling blocks and viewed with a microscope. Such a device is sometimes referred to as a temperature gradient microscope stage (TGS). Of particular interest in this study is the behavior of a monotectic type solution during solidification. Succinonitrile based model systems for metallic monotectic alloys, when solidified on a TGS, form an unusual 'worm-like' micromorphology. These interfaces are observable in situ under high optical magnification during growth.

  20. Effects of Atomic Oxygen and Grease on Outgassing and Adhesion of Silicone Elastomers for Space Applications

    deGroh, Henry C., III; Puleo, Bernadette J.; Steinetz, Bruce M.


    An investigation of silicone elastomers for seals used in docking and habitat systems for future space exploration vehicles is being conducted at NASA. For certain missions, NASA is considering androgynous docking systems where two vehicles each having a seal would be required to: dock for a period of time, seal effectively, and then separate with minimum push-off forces for undocking. Silicone materials are generally chosen for their wide operating temperatures and low leakage rates. However silicone materials are often sticky and usually exhibit considerable adhesion when mated against metals and silicone surfaces. This paper investigates the adhesion unit pressure for a space rated silicone material (S0383-70) for either seal-on-seal (SoS) or seal-on-aluminum (SoAl) operation modes in the following conditions: as-received, after ground-based atomic-oxygen (AO) pre-treatment, after application of a thin coating of a space-qualified grease (Braycote 601EF), and after a combination of AO pre-treatment and grease coating. In order of descending adhesion reduction, the AO treatment reduced seal adhesion the most, followed by the AO plus grease pre-treatment, followed by the grease treatment. The effects of various treatments on silicone (S0383-70 and ELA-SA-401) outgassing properties were also investigated. The leading adhesion AO pretreatment reduction led to a slight decrease in outgassing for the S0383-70 material and virtually no change in ELA-SA-401 outgassing.

  1. Volcanism and outgassing of stagnant-lid planets: Implications for the habitable zone

    Noack, L.; Rivoldini, A.; Van Hoolst, T.


    Rocky exoplanets are typically classified as potentially habitable planets, if liquid water exists at the surface. The latter depends on several factors like the abundance of water but also on the amount of available solar energy and greenhouse gases in the atmosphere for a sufficiently long time for life to evolve. The range of distances to the star, where surface water might exist, is called the habitable zone. Here we study the effect of the planet interior of stagnant-lid planets on the formation of a secondary atmosphere through outgassing that would be needed to preserve surface water. We find that volcanic activity and associated outgassing in one-plate planets is strongly reduced after the magma ocean outgassing phase for Earth-like mantle compositions, if their mass and/or core-mass fraction exceeds a critical value. As a consequence, the effective outer boundary of the habitable zone is then closer to the host star than suggested by the classical habitable zone definition, setting an important restriction to the possible surface habitability of massive rocky exoplanets, assuming that they did not keep a substantial amount of their primary atmosphere and that they are not in the plate tectonics regime.

  2. Temperature Histories of Structural Steel Welds Calculated Using Solidification-Boundary Constraints

    Lambrakos, S. G.


    Temperature histories of structural steel deep-penetration welds are presented, which are calculated using numerical-analytical basis functions and solidification-boundary constraints. These weld temperature histories can be adopted as input data to various types of computational procedures, which include numerical models for prediction of solid-state phase transformations and mechanical response. In addition, these temperature histories can be used parametrically for inverse thermal analysis of welds corresponding to other welding processes whose process conditions are within similar regimes. The present study applies an inverse thermal analysis procedure that uses three-dimensional constraint conditions whose two-dimensional projections are mapped within transverse cross sections of experimentally measured solidification boundaries. In addition, the present study uses experimentally measured estimates of the heat effect zone edge to examine the consistency of calculated temperature histories for steel welds.

  3. The solidification behaviour of the UO2–ThO2 system in a laser heating study

    Böhler, R.; Quaini, A.; Capriotti, L.; Cakir, P.; Benes, O.; Boboridis, K.; Guiot, A.; Luzzi, L.; Konings, R.J.M.; Manara, D.


    The high-temperature phase diagram of the UO2–ThO2 system has been experimentally revisited in the present study for the first time since 1970, using a laser heating approach combined with fast pyrometry in a thermal arrest method. The melting/solidification temperature, which is of fundamental info

  4. Eutectic Solidification in Al-13.0%Si Alloys with Combined Addition of Strontium and Boron

    Hengcheng Liao; Ke Ding; Juanjuan Bi; Min Zhang; Huipin Wang; Lei Zhao


    The influence of addition of boron (B) on eutectic solidification in a near-eutectic AI-13.0%Si alloy modified with strontium (Sr) was investigated using thermal analysis and macro/microstructure observation. Addition of B in the Sr-modified alloy leads to a considerable increase in nucleation temperature (Tn, the minimum temperature prior to recalescence (TM) and growth temperature (TG). In the Sr-modified alloy, nucleation of eutectic might originate at the heterogeneous sites on the mold wall or in the melt near the wall, and eutectic solidification proceeds gradually towards the center, controlled by undercooling of melt. However, with addition of B in the Sr-modified alloy, undercooling required for eutectic nucleation became small, and hence eutectic solidification might occur almost simultaneously within whole casting, controlled by amount of heterogeneous sites. With excessive addition of B in the Sr-modified alloy, nucleation of eutectic grains was explosive within the whole casting and the power of Sr on eutectic solidification was completely poisoned.

  5. Break-down of a planar liquid-solid interface during directional solidification - Influence of convection

    Tewari, S. N.; Chopra, M. A.


    The influence of convection on the development of morphological instability at the liquid-solid interface during directional solidification in a positive thermal gradient has been examined in Pb-10 wt pct Sn and succinonitrile-1.9 wt pct acetone. The onset of interfacial breakdown occurs at higher growth speeds in the presence of convection. The linear stability analysis due to Favier and Rouzaud which uses the 'deformable' mass flow boundary layer concept shows a good agreement with the experimentally observed behavior.

  6. Modelling of binary alloy solidification in the MEPHISTO experiment

    Leonardi, Eddie; de Vahl Davis, Graham; Timchenko, Victoria; Chen, Peter; Abbaschian, Reza


    A modified enthalpy method was used to numerically model experiments on solidification of a bismuth-tin alloy which were performed during the 1997 flight of the MEPHISTO-4 experiment on the US Space Shuttle Columbia. This modified enthalpy method was incorporated into an in-house code SOLCON and a commercial CFD code CFX; Soret effect was taken into account by including an additional thermo-diffusion term into the solute transport equation and the effects of thermal and solutal convection in the microgravity environment and of concentration-dependent melting temperature on the phase change processes were also included. In this paper an overview of the results obtained as part of MEPHISTO project is presented. The numerical solutions are compared with actual microprobe results obtained from the MEPHISTO experiment. To cite this article: E. Leonardi et al., C. R. Mecanique 332 (2004).

  7. Advanced powder metallurgy aluminum alloys via rapid solidification technology

    Ray, R.


    Aluminum alloys containing 10 to 11.5 wt. pct. of iron and 1.5 to 3 wt. pct. of chromium using the technique of rapid solidification powder metallurgy were studied. Alloys were prepared as thin ribbons (.002 inch thick) rapidly solidified at uniform rate of 10(6) C/second by the melt spinning process. The melt spun ribbons were pulverized into powders (-60 to 400 mesh) by a rotating hammer mill. The powders were consolidated by hot extrusion at a high reduction ratio of 50:1. The powder extrusion temperature was varied to determine the range of desirable processing conditions necessary to yield useful properties. Powders and consolidated alloys were characterized by SEM and optical metallography. The consolidated alloys were evaluated for (1) thermal stability, (2) tensile properties in the range, room temperature to 450 F, and (3) notch toughness in the range, room temperature to 450 F.

  8. Solidification of hypermonotectic Al-In alloys under microgravity conditions

    Potard, C.


    Four samples of the Al-In system having monotectic and hypermonotectic compositions that were solidified under microgravity during the NASA-SPAR IX flight of January 20, 1981, are considered. The experimental thermal and physicochemical conditions that were actually achieved are analyzed. Radiographic and metallographic observations of the samples reveal a nonregular dispersed primary phase inside the monotectic matrix. These observations are discussed in relation to capillarity and solidification aspects. A key finding is the preservation of a certain degree of dispersion of the indium primary phase. This result differs fundamentally from the results obtained under microgravity conditions on the same system and compositions (Gelles and Markworth, 1980; Alborn and Loehberg, 1979). The results are seen as clearly establishing that the space environment can be used to obtain dispersed structures from hypermonotectic alloys.

  9. Application of simplified model to sensitivity analysis of solidification process

    R. Szopa


    Full Text Available The sensitivity models of thermal processes proceeding in the system casting-mould-environment give the essential information concerning the influence of physical and technological parameters on a course of solidification. Knowledge of time-dependent sensitivity field is also very useful in a case of inverse problems numerical solution. The sensitivity models can be constructed using the direct approach, this means by differentiation of basic energy equations and boundary-initial conditions with respect to parameter considered. Unfortunately, the analytical form of equations and conditions obtained can be very complex both from the mathematical and numerical points of view. Then the other approach consisting in the application of differential quotient can be applied. In the paper the exact and approximate approaches to the modelling of sensitivity fields are discussed, the examples of computations are also shown.

  10. Rapid solidification of Cu-Fe-Ni alloys

    Baricco, M.; Bosco, E.; Acconciaioco, G.; Rizzi, P.; Coisson, M


    Cu{sub 80-x}Ni{sub x}Fe{sub 20} (x=0, 5 and 20) alloys have been rapidly solidified by planar flow casting. X-ray diffraction (XRD) analysis of as-quenched ribbons shows bcc-Fe precipitates embedded in an fcc phase (x=0), two co-existing fcc solid solutions (x=5) and a complete solid solution of the parent elements (x=20). Thermal treatments in the temperature range between 400 and 600 deg. C give precipitation and spinodal decomposition reactions. These phase transformations have been evidenced from a variation of lattice constants, from a broadening of diffraction peaks and from TEM observations. The role of Ni content on competition between precipitation and decomposition reactions during rapid solidification and annealing is discussed in terms of thermodynamic arguments. Recent CALPHAD assessment of thermodynamic properties for Cu-Fe-Ni system has been used for an estimation of composition and volume fraction of equilibrium phases.

  11. Solidification of oils and organic liquids

    Clark, D.E.; Colombo, P.; Neilson, R.M. Jr.


    The suitability of selected solidification media for application in the disposal of low-level oil and other organic liquid wastes has been investigated. In the past, these low-level wastes (LLWs) have commonly been immobilized by sorption onto solid absorbents such as vermiculite or diatomaceous earth. Evolving regulations regarding the disposal of these materials encourage solidification. Solidification media which were studied include Portland type I cement; vermiculite plus Portland type I cement; Nuclear Technology Corporation's Nutek 380-cement process; emulsifier, Portland type I cement-sodium silicate; Delaware Custom Materiel's cement process; and the US Gypsum Company's Envirostone process. Waste forms have been evaluated as to their ability to reliably produce free standing monolithic solids which are homogeneous (macroscopically), contain < 1% free standing liquids by volume and pass a water immersion test. Solidified waste form specimens were also subjected to vibratory shock testing and flame testing. Simulated oil wastes can be solidified to acceptable solid specimens having volumetric waste loadings of less than 40 volume-%. However, simulated organic liquid wastes could not be solidified into acceptable waste forms above a volumetric loading factor of about 10 volume-% using the solidification agents studied.

  12. Solidification studies of automotive heat exchanger materials

    Carlberg, T.; Jaradeh, M.; Kamgou Kamaga, H.


    Modifications of the aluminum alloy AA 3003 have been studied to improve and tailorits properties for applications in automotive heat exchangers. Laboratory techniques have been applied to simulate industrial direct-chill casting, and some basic solidification studies have been conducted. The results are coupled to structures observed in industrial-size ingots and discussed in terms of structure-property relations.

  13. Detached Growth of Germanium by Directional Solidification

    Palosz, W.; Volz, M. P.; Cobb, S.; Motakef, S.; Szofran, F. R.


    The conditions of detached solidification under controlled pressure differential across the meniscus were investigated. Uncoated and graphite- or BN-coated silica and pBN crucibles were used. Detached and partly detached growth was achieved in pBN and BN-coated crucibles, respectively. The results of the experiments are discussed based on the theory of Duffar et al.

  14. Microstructure Development during Solidification of Aluminium Alloys

    Ruvalcaba Jimenez, D.G.


    This Thesis demonstrates studies on microstructure development during the solidification of aluminium alloys. New insights of structure development are presented here. Experimental techniques such as quenching and in-situ High-brilliance X-ray microscopy were utilized to study the microstructure evo

  15. Characterization of the Al-3wt.%Si alloy in unsteady-state horizontal directional solidification

    Diego Brito Carvalho


    Full Text Available The main purpose of this paper is to investigate both the columnar to equiaxed transition and primary dendritic arm spacings of Al-3wt.%Si alloy during the horizontal directional solidification. The transient heat transfer coefficient at the metal-mold interface is calculated based on comparisons between the experimental thermal profiles in castings and the simulations provided by a finite difference heat flow program. Simulated curve of the interfacial heat transfer coefficient was used in another numerical solidification model to determine theoretical values of tip growth rates, cooling rates and thermal gradients that are associated with both columnar to equiaxed transition and primary dendritic arm spacings. A good agreement was observed between the experimental values of these thermal variables and those numerically simulated for the alloy examined. A comparative analysis is carried out between the experimental data of this work and theoretical models from the literature that have been proposed to predict the primary dendritic spacings. In this context, this study may contribute to the understanding of how to manage solidification operational parameters aiming at designing the microstructure of Al-Si alloys.

  16. Development of a High Chromium Ni-Base Filler Metal Resistant to Ductility Dip Cracking and Solidification Cracking

    Hope, Adam T.

    Many nuclear reactor components previously constructed with Ni-based alloys containing 20 wt% Cr have been found to be susceptible to stress corrosion cracking. The nuclear power industry now uses high chromium (˜30wt%) Ni-based filler metals to mitigate stress corrosion cracking. Current alloys are plagued with weldability issues, either solidification cracking or ductility dip cracking (DDC). Solidification cracking is related to solidification temperature range and the DDC is related to the fraction eutectic present in the microstructure. It was determined that an optimal alloy should have a solidification temperature range less than 150°C and at least 2% volume fraction eutectic. Due to the nature of the Nb rich eutectic that forms, it is difficult to avoid both cracking types simultaneously. Through computational modeling, alternative eutectic forming elements, Hf and Ta, have been identified as replacements for Nb in such alloys. Compositions have been optimized through a combination of computational and experimental techniques combined with a design of experiment methodology. Small buttons were melted using commercially pure materials in a copper hearth to obtain the desired compositions. These buttons were then subjected to a gas tungsten arc spot weld. A type C thermocouple was used to acquire the cooling history during the solidification process. The cooling curves were processed using Single Sensor Differential Thermal Analysis to determine the solidification temperature range, and indicator of solidification cracking susceptibility. Metallography was performed to determine the fraction eutectic present, an indicator of DDC resistance. The optimal level of Hf to resist cracking was found to be 0.25 wt%. The optimal level of Ta was found to be 4 wt%. gamma/MC type eutectics were found to form first in all Nb, Ta, and Hf-bearing compositions. Depending on Fe and Cr content, gamma/Laves eutectic was sometimes found in Nb and Ta-bearing compositions, while

  17. A physical simulation study of the effect of thermal variations on the secondary dendrite arm spacing in a Ni-based superalloy

    Rahimian, Mehdi; Milenkovic, Srdjan; Sabirov, Ilchat


    The effect of thermal variations on the secondary dendrite arm spacing (SDAS) in a MAR-M247 Ni-based superalloy has been studied by a novel method based on a physical simulation of melting/solidification experiments with a constant cooling rate and variable temperature gradient. The method proved to be effective as it yielded a spread of microstructures corresponding to a range of well-controlled solidification rates in a single melting/solidification experiment. In addition, it has been demonstrated that SDAS is better related to the solidification rate than to the cooling rate in cases when significant variations of thermal parameters during the solidification process occur.

  18. Simulation of microstructural evolution in directional solidification of Ti-45at.%Al alloy using cellular automaton method

    Wang Kuangfei


    Full Text Available The microstructural evolution of Ti-45 at.%Al alloy during directional solidification was simulated by applying a solute diffusion controlled solidification model. The obtained results have shown that under high thermal gradients the stable primary spacing can be adjusted via branching or competitive growth. For dendritic structures formed under a high thermal gradient, the secondary dendrite arms are developed not very well in many cases due to the branching mechanism under a constrained dendritic growth condition. Furthermore, it has been observed that, with increasing pulling velocity, there exists a cell/dendrite transition region consisting of cells and dendrites, which varies with the thermal gradient in a contradicting way, i.e. increase of the thermal gradient leading to the decrease of the range of the transition region. The simulations agree reasonably well with experiment results.

  19. Application of Solidification Theory to Rapid Solidification Processing


    on the OW150olŝtQ S4blty of . jpt 10to CalCulo @ e fe(@t Of laterfaCe Ikneliti o apowut graw. As iutwface Ii ,’elic Caeffionvt baW~ on the fttinet,0d W...where p- VR/2 L is the Peclet number, El is. the exponential integral , L isthe thermal diffusivity of the liquid, Lv is -the latent heat per unit volume...Phys. 18, 1331 (1950). 20. F. P. Bundy and II . M. Strong, Solid State Physics (Eds. F. Seitz and D. Turnbul1) 13, 134, Academic Press, Y (T9b621_ 21. M

  20. ASTM E 1559 method for measuring material outgassing/deposition kinetics has applications to aerospace, electronics, and semiconductor industries

    Garrett, J. W.; Glassford, A. P. M.; Steakley, J. M.


    The American Society for Testing and Materials has published a new standard test method for characterizing time and temperature-dependence of material outgassing kinetics and the deposition kinetics of outgassed species on surfaces at various temperatures. This new ASTM standard, E 1559(1), uses the quartz crystal microbalance (QCM) collection measurement approach. The test method was originally developed under a program sponsored by the United States Air Force Materials Laboratory (AFML) to create a standard test method for obtaining outgassing and deposition kinetics data for spacecraft materials. Standardization by ASTM recognizes that the method has applications beyond aerospace. In particular, the method will provide data of use to the electronics, semiconductor, and high vacuum industries. In ASTM E 1559 the material sample is held in vacuum in a temperature-controlled effusion cell, while its outgassing flux impinges on several QCM's which view the orifice of the effusion cell. Sample isothermal total mass loss (TML) is measured as a function of time from the mass collected on one of the QCM's which is cooled by liquid nitrogen, and the view factor from this QCM to the cell. The amount of outgassed volatile condensable material (VCM) on surfaces at higher temperatures is measured as a function of time during the isothermal outgassing test by controlling the temperatures of the remaining QCM's to selected values. The VCM on surfaces at temperatures in between those of the collector QCM's is determined at the end of the isothermal test by heating the QCM's at a controlled rate and measuring the mass loss from the end of the QCM's as a function of time and temperature. This reevaporation of the deposit collected on the QCM's is referred to as QCM thermogravimetric analysis. Isothermal outgassing and deposition rates can be determined by differentiating the isothermal TML and VCM data, respectively, while the evaporation rates of the species can be obtained as a

  1. A moving boundary solution for solidification of lava lake and magma intrusion in the presence of time-varying contact temperature

    Ajay Manglik


    During the solidification of a lava lake heat is released convectively from the top surface as well as conductively into the country rock from the base, leading to non-uniform solidification. The upper solidified layer grows at a faster rate than the lower solidified layer. Similarly, solidification of magma intrusion within the crust is also non-uniform due to the presence of thermal gradient in the crust. Available analytical solution for solidification of a melt layer assumes only symmetric cooling about the centre of the layer. In the present work a moving boundary solution for thermal evolution and non-uniform solidification of a melt layer incorporating time-varying contact temperature conditions at both of its boundaries is developed. The solution is obtained by using the Fourier spectral approach in the space domain and a modified finite difference scheme in the time domain, and is validated with available analytical solutions for simple cases and a semi-analytical solution for the case involving temperature gradient in the country rock. This solution can be used to analyse solidification of lava lakes and magma intrusions experiencing time-dependent temperature variation at their contacts with the country rock.

  2. Simulation of thermos-solutal convection induced macrosegregation in a Sn-10%Pb alloy benchmark during columnar solidification

    Zheng, Y.; Wu, M.; Kharicha, A.; Ludwig, A.


    In order to investigate the effect of thermo-solutal convection on the formation of macrosegregation during columnar solidification, simulations with a liquid-columnar two phase model were carried out on a 2D rectangular benchmark of Sn-10%Pb alloy. The solidification direction in the benchmark is unidirectional: (') downwards from top to bottom or (2) upwards from bottom to top. Thermal expansion coefficient, solutal expansion coefficient and liquid diffusion coefficient of the melt are found to be key factors influencing the final macrosegregation. The segregation range and distribution are also strongly influenced by the benchmark configurations, e.g. the solidifying direction (upwards or downwards) and boundary conditions, et al. The global macrosegregation range increases with the velocity magnitude of the melt during the process of solidification.

  3. Finite element modeling of the effect of welding parameters on solidification cracking of Austenitic Stainless Steel 310

    Eslam Ranjbarnodeh


    Full Text Available A transient thermo-mechanical model is employed to study the effects of welding parameters on the occurrence of solidification cracking. A finite element program, ANSYS, is employed to solve the thermal and mechanical equations while the different variables such as welding current, speed and sequence are considered in the simulation. The studied geometry was butt joint of two stainless steel plates with the thickness of 2 mm. Then, the samples were welded by TIG method without filler. To verify the numerical results, the model outputs were checked with the experimental observations and good agreement was observed. It was found that the increasing of welding current from 70 A to 100 A resulted in the increase in transverse tensile strain from 1.2 to 2.1 which can facilitate the occurrence of solidification cracking. Furthermore, the application of symmetric welding layout is an effective method to prevent solidification cracking.

  4. Solidification of Liquid Distributed in its Primary Matrix Phase of Al-10Cu-Fe Alloy and Their Tribological Characteristics

    Rao, L. Sankara; Jha, A. K.; Ojha, S. N.


    Solidification behavior of liquid phase entrained in its primary solid has been investigated. A hypoeutectic alloy based on Al-Cu-Fe system containing Fe and Si was thermal cycled between semisolid regions to low temperatures. The freezing characteristics of the liquid were recorded in inverse rate cooling curves. The continuous network of the liquid phase progressively changed into isolated droplets with their different size and size distribution. Such droplets revealed undercooling of the melt varying from 20 to 35 °C below the eutectic temperature of the alloy. This behavior of melt undercooling is discussed in light of independent nucleation events associated with freezing of droplets. Solidification structure of droplets revealed particulate eutectic phases in contrast to lamellar eutectic microstructure in the interdendritic region of the as-cast alloy. The droplet distribution and their solidification structure resulted in an improvement in tribological characteristics of the alloy. This effect is correlated with features of wear surfaces generated on the matting surfaces.

  5. A phenomenological approach of solidification of polymeric phase change materials

    Bahrani, Seyed Amir; Royon, Laurent; Abou, Bérengère; Osipian, Rémy; Azzouz, Kamel; Bontemps, André


    Phase Change Materials (PCMs) are widely used in thermal energy storage and thermal management systems due to their small volume for a given stored energy and their capability for maintaining nearly constant temperatures. However, their performance is limited by their low thermal conductivity and possible leaks while in the liquid phase. One solution is to imprison the PCM inside a polymer mesh to create a Polymeric Phase Change Material (PPCM). In this work, we have studied the cooling and solidification of five PPCMs with different PCMs and polymer fractions. To understand the heat transfer mechanisms involved, we have carried out micro- and macrorheological measurements in which Brownian motion of tracers embedded in PPCMs has been depicted and viscoelastic moduli have been measured, respectively. Beyond a given polymer concentration, it was shown that the Brownian motion of the tracers is limited by the polymeric chains and that the material exhibits an elastic behavior. This would suggest that heat transfer essentially occurs by conduction, instead of convection. Experiments were conducted to measure temperature variation during cooling of the five samples, and a semi-empirical model based on a phenomenological approach was proposed as a practical tool to choose and size PPCMs.

  6. Lateral carbon fluxes and CO2 outgassing from a tropical peat-draining river

    D. Müller


    Full Text Available Tropical peatlands play an important role in the global carbon cycle due to their immense carbon storage capacity. However, pristine peat swamp forests are vanishing due to deforestation and peatland degradation, especially in Southeast Asia. CO2 emissions associated with this land use change might not only come from the peat soil directly, but also from peat-draining rivers. So far, though, this has been mere speculation, since there was no data from undisturbed reference sites. We present the first combined assessment of lateral organic carbon fluxes and CO2 outgassing from an undisturbed tropical peat-draining river. Two sampling campaigns were undertaken on the Maludam river in Sarawak, Malaysia. The river catchment is covered by protected peat swamp forest, offering a unique opportunity to study a peat-draining river in its natural state, without any influence from tributaries with different characteristics. The two campaigns yielded consistent results. Dissolved organic carbon (DOC concentrations ranged between 3222 and 6218 μmol L−1 and accounted for more than 99 % of the total organic carbon (TOC. Radiocarbon dating revealed that the riverine DOC was of recent origin, suggesting that it derives from the top soil layers and surface runoff. We observed strong oxygen depletion, implying high rates of organic matter decomposition and consequently CO2 production. The measured median pCO2 was 7795 and 8400 μatm during the two campaigns, respectively. Overall, we found that only 26 ± 15 % of the carbon was exported by CO2 evasion, while the rest was exported by discharge. CO2 outgassing seemed to be moderated by the short water residence time. Since most Southeast Asian peatlands are located at the coast, this is probably an important limiting factor for CO2 outgassing from most of its peat-draining rivers.

  7. Lateral carbon fluxes and CO2 outgassing from a tropical peat-draining river

    Müller, D.; Warneke, T.; Rixen, T.; Müller, M.; Jamahari, S.; Denis, N.; Mujahid, A.; Notholt, J.


    Tropical peatlands play an important role in the global carbon cycle due to their immense carbon storage capacity. However, pristine peat swamp forests are vanishing due to deforestation and peatland degradation, especially in Southeast Asia. CO2 emissions associated with this land use change might not only come from the peat soil directly but also from peat-draining rivers. So far, though, this has been mere speculation, since there has been no data from undisturbed reference sites. We present the first combined assessment of lateral organic carbon fluxes and CO2 outgassing from an undisturbed tropical peat-draining river. Two sampling campaigns were undertaken on the Maludam River in Sarawak, Malaysia. The river catchment is covered by protected peat swamp forest, offering a unique opportunity to study a peat-draining river in its natural state, without any influence from tributaries with different characteristics. The two campaigns yielded consistent results. Dissolved organic carbon (DOC) concentrations ranged between 3222 and 6218 μmol L-1 and accounted for more than 99 % of the total organic carbon (TOC). Radiocarbon dating revealed that the riverine DOC was of recent origin, suggesting that it derives from the top soil layers and surface runoff. We observed strong oxygen depletion, implying high rates of organic matter decomposition and consequently CO2 production. The measured median pCO2 was 7795 and 8400 μatm during the first and second campaign, respectively. Overall, we found that only 32 ± 19 % of the carbon was exported by CO2 evasion, while the rest was exported by discharge. CO2 outgassing seemed to be moderated by the short water residence time. Since most Southeast Asian peatlands are located at the coast, this is probably an important limiting factor for CO2 outgassing from most of its peat-draining rivers.

  8. Lateral carbon fluxes and CO2 outgassing from a tropical peat-draining river

    D. Müller


    Full Text Available Tropical peatlands play an important role in the global carbon cycle due to their immense carbon storage capacity. However, pristine peat swamp forests are vanishing due to deforestation and peatland degradation, especially in Southeast Asia. CO2 emissions associated with this land use change might not only come from the peat soil directly but also from peat-draining rivers. So far, though, this has been mere speculation, since there has been no data from undisturbed reference sites. We present the first combined assessment of lateral organic carbon fluxes and CO2 outgassing from an undisturbed tropical peat-draining river. Two sampling campaigns were undertaken on the Maludam River in Sarawak, Malaysia. The river catchment is covered by protected peat swamp forest, offering a unique opportunity to study a peat-draining river in its natural state, without any influence from tributaries with different characteristics. The two campaigns yielded consistent results. Dissolved organic carbon (DOC concentrations ranged between 3222 and 6218 μmol L−1 and accounted for more than 99 % of the total organic carbon (TOC. Radiocarbon dating revealed that the riverine DOC was of recent origin, suggesting that it derives from the top soil layers and surface runoff. We observed strong oxygen depletion, implying high rates of organic matter decomposition and consequently CO2 production. The measured median pCO2 was 7795 and 8400 μatm during the first and second campaign, respectively. Overall, we found that only 32 ± 19 % of the carbon was exported by CO2 evasion, while the rest was exported by discharge. CO2 outgassing seemed to be moderated by the short water residence time. Since most Southeast Asian peatlands are located at the coast, this is probably an important limiting factor for CO2 outgassing from most of its peat-draining rivers.

  9. The effect of outgassing upon the closure of cracks and the strength of lunar analogues

    Mizutani, H.; Spetzler, H.; Getting, I.; Martin, R. J., III; Soga, N.


    The effect of an ultrahigh vacuum and low water vapor pressure on the stress-strain relation in rocks was studied in order to understand geologic and tectonic processes of the moon. Terrestrial basaltic rocks carefully outgassed in high vacuum provided the sample material for the compression tests reported here. The tests were conducted either under 1 atm air saturated with moisture, or under high vacuum. Results of the stress-strain determinations indicated that the dry rocks could show as much as twice the strength of the wet rocks. The data may also provide a means of reconciling the high strength and high temperature exhibited by the lunar interior.

  10. Study of neutron induced outgassing from tungsten alloy for ATLAS FCAL

    Leroy, C; Cheplakov, A P; Golikov, V; Golubyh, S M; Kulagin, E; Kukhtin, V; Luschikov, V


    The use of sintered tungsten alloy slugs as absorber in the ATLAS Forward Calorimeter (FCAL) raised concern that it could possibly poison the liquid argon during the detector operation in the hard radiation environment expected at LHC. A vacuum container filled with tungsten slugs was exposed to the fast neutron fluence of 1.5$\\cdot$10$^{16}$~n~cm$^{-2}$ at the IBR-30 reactor of JINR, Dubna. The residual gas pressure was analysed. The study was completed by mass spectrometer measurements. An upper limit value of 0.1~ppm was determined for the pollution of liquid argon in FCAL due to outgassing from tungsten slugs under irradiation.

  11. Unravelling textural heterogeneity in obsidian: Shear-induced outgassing in the Rocche Rosse flow

    Shields, J. K.; Mader, H. M.; Caricchi, L.; Tuffen, H.; Mueller, S.; Pistone, M.; Baumgartner, L.


    Obsidian flow emplacement is a complex and understudied aspect of silicic volcanism. Of particular importance is the question of how highly viscous magma can lose sufficient gas in order to erupt effusively as a lava flow. Using an array of methods we study the extreme textural heterogeneity of the Rocche Rosse obsidian flow in Lipari, a 2 km long, 100 m thick, ~ 800 year old lava flow, with respect to outgassing and emplacement mechanisms. 2D and 3D vesicle analyses and density measurements are used to classify the lava into four textural types: 'glassy' obsidian ( 40% vesicles), high aspect ratio, 'shear banded' lava (20-40% vesicles) and low aspect ratio, 'frothy' obsidian with 30-60% vesicles. Textural heterogeneity is observed on all scales (m to μm) and occurs as the result of strongly localised strain. Magnetic fabric, described by oblate and prolate susceptibility ellipsoids, records high and variable degrees of shearing throughout the flow. Total water contents are derived using both thermogravimetry and infrared spectroscopy to quantify primary (magmatic) and secondary (meteoric) water. Glass water contents are between 0.08-0.25 wt.%. Water analysis also reveals an increase in water content from glassy obsidian bands towards 'frothy' bands of 0.06-0.08 wt.%, reflecting preferential vesiculation of higher water bands and an extreme sensitivity of obsidian degassing to water content. We present an outgassing model that reconciles textural, volatile and magnetic data to indicate that obsidian is generated from multiple shear-induced outgassing cycles, whereby vesicular magma outgasses and densifies through bubble collapse and fracture healing to form obsidian, which then re-vesiculates to produce 'dry' vesicular magma. Repetition of this cycle throughout magma ascent results in the low water contents of the Rocche Rosse lavas and the final stage in the degassing cycle determines final lava porosity. Heterogeneities in lava rheology (vesicularity, water

  12. Laser Surface Melting of Stainless Steel Anodes for Reduced Hydrogen Outgassing (Postprint)


    carried out at atmospheric pressure under con- stant N2 flow into the capped stage (O2 levels ɘ.2%), as shown in Fig. 1. The beam expander telescope...electronic high power terahertz sources, IEEE Trans. Terahertz Sci . Technol. 1 (2011) 54–75. [4] S.D. Korovin, V.V. Rostov, S.D. Polevin, I.V. Pegel, E...9] M. Bernardini, Air bake-out to reduce hydrogen outgassing from stainless steel, J. Vac. Sci . Technol. A Vacuum, Surfaces, Film 16 (1998) 188–193.4

  13. Numerical analysis of ALADIN optics contamination due to outgassing of solar array materials

    Markelov, G [Advanced Operations and Engineering Services (AOES) Group BV, Postbus 342, 2300 AH Leiden (Netherlands); Endemann, M [ESA-ESTEC/EOP-PAS, Postbus 299, 2200 AG Noordwijk (Netherlands); Wernham, D [ESA-ESTEC/EOP-PAQ, Postbus 299, 2200 AG Noordwijk (Netherlands)], E-mail:


    ALADIN is the very first space-based lidar that will provide global wind profile and a special attention has been paid to contamination of ALADIN optics. The paper presents a numerical approach, which is based on the direct simulation Monte Carlo method. The method allows one to accurately compute collisions between various species, in the case under consideration, free-stream flow and outgassing from solar array materials. The collisions create a contamination flux onto the optics despite there is no line-of-sight from the solar arrays to the optics. Comparison of obtained results with a simple analytical model prediction shows that the analytical model underpredicts mass fluxes.

  14. The heliocentric variation of the outgassing rate and molecular abundances in the coma of 67P as seen by MIRO

    Biver, Nicolas; Hofstadter, Mark; von Allmen, Paul; Bockelee-Morvan, Dominique; Choukroun, Mathieu; Gulkis, Samuel; Lee, Seungwon; Schloerb, F. Peter; Rezac, Ladislav; Leyrat, Cedric; Davidsson, Bjorn; Ip, Wing-Huen; MIRO team


    During the two years around the Aug. 2015 perihelion, the MIRO instrument on board the Rosetta spacecraft has been regularly mapping the emission of 8 molecular lines around 560 GHz (H2O and its isotopes, CO, NH3 and CH3OH) in the inner coma of comet 67P/Churyumov-Gerasimenko. We have used those observations to estimate the mean outgassing rates as a function of time in 2014-2016 and heliocentric distance (Rh=1.2-4 AU). The peak outgassing rate of water (~1028 molec./s), based on maps of H218O was reached slightly after perihelion. We have also measured the evolution of the abundances relative to water of CO, CH3OH and NH3. The abundances of CH3OH and CO significantly increased around and after perihelion time when most of the outgassing was coming from the illuminated southern pole. We have also retrieved the 3-D outgassing patterns, which enabled us to track the location of the bulk of outgassing for each molecule.

  15. Immiscible phase incorporation during directional solidification of hypermonotectics

    Andrews, J. Barry; Merrick, Roger A.


    Solidification processes in immiscible samples were investigated by directly observing the events taking place at the solid-liquid interface during directional solidification. Visualization of these events was made possible through the use of a transparent metal analog system and a temperature gradient stage assembly fitted to an optical microscope. The immiscible transparent analog system utilized was the succinonitrile-glycerol system. This system has been shown to exhibit the same morphological transitions as observed in metallic alloys of monotectic composition. Both monotectic and hypermonotectic composition samples were directionally solidified in order to gain an improved understanding of the manner in which the excess hypermonotectic liquid is incorporated into the solidifying structure. The processing conditions utilized prevented sedimentation of the excess hypermonotectic liquid by directionally solidifying the samples in very thin (13 microns), horizontally oriented cells. High thermal gradient to growth rate ratios (G/R) were used in an effort to prevent constitutional supercooling and the subsequent formation of L(sub 2) droplets in advance of the solidification front during the growth of fibrous composite structures. Results demonstrated that hypermonotectic composites could be produced in samples up to two weight percent off of the monotectic composition by using a G/R ratio greater than or equal to 4.6 x 10(exp 4) C(s)/mm(sup 2) to avoid constitutional supercooling. For hypermonotectic samples processed with G/R ratios below 4.6 x 10(exp 4) C(s)/mm(sup 2), constitutional supercooling occurred and resulted in slight interfacial instability. For these samples, two methods of incorporation of the hypermonotectic liquid were observed and are reported. The correlation between the phase spacing, lambda, and the growth rate, R, was examined and was found to obey a relationship generally associated with a diffusion controlled coupled growth process. For

  16. Transport Phenomena During Equiaxed Solidification of Alloys

    Beckermann, C.; deGroh, H. C., III


    Recent progress in modeling of transport phenomena during dendritic alloy solidification is reviewed. Starting from the basic theorems of volume averaging, a general multiphase modeling framework is outlined. This framework allows for the incorporation of a variety of microscale phenomena in the macroscopic transport equations. For the case of diffusion dominated solidification, a simplified set of model equations is examined in detail and validated through comparisons with numerous experimental data for both columnar and equiaxed dendritic growth. This provides a critical assessment of the various model assumptions. Models that include melt flow and solid phase transport are also discussed, although their validation is still at an early stage. Several numerical results are presented that illustrate some of the profound effects of convective transport on the final compositional and structural characteristics of a solidified part. Important issues that deserve continuing attention are identified.

  17. Complex banded structures in directional solidification processes.

    Korzhenevskii, A L; Rozas, R E; Horbach, J


    A combination of theory and numerical simulation is used to investigate impurity superstructures that form in rapid directional solidification (RDS) processes in the presence of a temperature gradient and a pulling velocity with an oscillatory component. Based on a capillary wave model, we show that the RDS processes are associated with a rich morphology of banded structures, including frequency locking and the transition to chaos.

  18. Molecular dynamics modelling of solidification in metals

    Boercker, D.B.; Belak, J.; Glosli, J. [Lawrence Livermore National Lab., CA (United States)


    Molecular dynamics modeling is used to study the solidification of metals at high pressure and temperature. Constant pressure MD is applied to a simulation cell initially filled with both solid and molten metal. The solid/liquid interface is tracked as a function of time, and the data are used to estimate growth rates of crystallites at high pressure and temperature in Ta and Mg.

  19. Direct numerical simulation of solidification microstructures affected by fluid flow

    Juric, D.


    The effects of fluid flow on the solidification morphology of pure materials and solute microsegregation patterns of binary alloys are studied using a computational methodology based on a front tracking/finite difference method. A general single field formulation is presented for the full coupling of phase change, fluid flow, heat and solute transport. This formulation accounts for interfacial rejection/absorption of latent heat and solute, interfacial anisotropies, discontinuities in material properties between the liquid and solid phases, shrinkage/expansion upon solidification and motion and deformation of the solid. Numerical results are presented for the two dimensional dendritic solidification of pure succinonitrile and the solidification of globulitic grains of a plutonium-gallium alloy. For both problems, comparisons are made between solidification without fluid flow and solidification within a shear flow.

  20. Study on undercooling of metal droplet in rapid solidification

    GAO; Yulai; GUAN; Wanbing; ZHAI; Qijie; XU; Kuangdi


    A mathematical model for the undercooling of the metal droplet during the rapid solidification is established, by which the factors that influence the undercooling of the metal droplet during the rapid solidification are analyzed, and the parameter ζ=σSL3/ (TLΔH 2 ) is defined as the impact factor of the undercooling for the droplet solidification. Different undercoolings of droplets induced by various rapid solidification conditions are mainly ascribed to the change of the impact factor. Moreover, it is shown that the larger of ζ, the higher the relative undercooling can be gained. Meanwhile, the parameters such as solid-liquid interfacial energy σSL and latent heat of solidification ΔH also vary with the rapid solidification conditions of droplets.

  1. Modelling of Mould Filling and Solidification of Castings

    Xu Zhian


    An experimental casting for validation has been designed. The casting is composed of two 50×600×2.5 (width×length×thick) thin-wall pieces. One downsprue is located in the middle. A pouring cup with a stopper is used. This design allows to using two different types of moulds simultaneously. An Al-10%Si alloy has been poured at different temperatures. Two effects have been studied: one is the pouring temperature and the other is the moulding method (namely by machine or manually). The filling length is proportional to the pouring temperature. The influence of different moulding methods on mould filling is more complicated. The filling length in the manual-made mould is 1.5 times as long as the one in the machine-made mould due to the different thermal conductivities. Vents have little influence. A finite volume based computer code which can simulate fluid flow during mould filling coupled with heat transfer as well as solidification has been developed in WTCM Foundry Center.. The code can predict cold shut during mould filling and shrinkage defects during solidification. The simulated results are in good agreement with the experiments.In the second part of the paper, an example is given which illustrates how to use computer simulation to aid designing the casting system. The final computational result is compared with the industrial casting. The process of designing castings by using simulation is completely different from the traditional way. The computer aided casting design offers the possibility to obtain a sound casting from the first time.




    Full Text Available Welding processes induce a state of residual stress into materials and jobs. This poses a series of problems, in terms of dimensional stability, corrosion cracking, reduced fatigue life and structural integrity . Thermal cycle produced near weld line generates residual stress and inhomogeneous plastic deformation in weldments. Understanding of grain nucleation and grain growth becomes necessary that are influenced under welding conditions. After completion of nucleation, the solidification process will continue with nucleus growth .With vibratory weld conditioning, the enhancement of weld metal microstructure can be achieved. The mechanical properties, level of residual stresses, and deformation can also be affected . Structural changes of the welds prepared under vibratory conditions affects the mechanical properties of the welds. The vibration duringwelding benefits energy absorbed in impact toughness test of weld metal and improves fracture behavior. This paper presents the microstructure, solidification behaviour and residual stress relaxation under vibratory welding condition.

  3. Simulation of the solidification in a channel of a water-cooled glass flow

    G. E. Ovando Chacon


    Full Text Available A computer simulation study of a laminar steady-state glass flow that exits from a channel cooled with water is reported. The simulations are carried out in a two-dimensional, Cartesian channel with a backward-facing step for three different angles of the step and different glass outflow velocities. We studied the interaction of the fluid dynamics, phase change and thermal behavior of the glass flow due to the heat that transfers to the cooling water through the wall of the channel. The temperature, streamline, phase change and pressure fields are obtained and analyzed for the glass flow. Moreover, the temperature increments of the cooling water are characterized. It is shown that, by reducing the glass outflow velocity, the solidification is enhanced; meanwhile, an increase of the step angle also improves the solidification of the glass flow.

  4. Numerical simulation of solidification in a horizontal cylindrical annulus charged with an aqueous salt solution

    Neilson, D. G.; Incropera, F. D.; Bennon, W. D.


    A computational study of solidification of a binary Na2CO3 solution in a horizontal cylindrical annulus is performed using a continuum formulation with a control-volume based, finite-difference scheme. The initial conditions were selected to facilitate the study of counter thermal and solutal convection, accompanied by extensive mushy region growth. Numerical results are compared with experimental data with mixed success. Qualitative agreement is obtained for the overall solidification process and associated physical phenomena. However, the plume thickness calculated for the solutally-driven convective upflow is substantially smaller than the observed value. Evolution of double-diffusive layers is predicted, but over a time scale much smaller than that observed experimentally. Good agreement is obtained between predicted and measured results for solid growth, but the mushy region thickness is significantly overpredicted.

  5. A Review on Solidification and Change in Mechanical Properties Under Vibratory Welding Condition

    Jyoti Prakash


    Full Text Available Welding has been applied to various industries in particular, automotive, aerospace and microelectronics. Thermal cycle produced near weld line generates residual stress and inhomogeneous plastic deformation in weldments. However there are many methods for welding the workpieces and one of the method among these is vibratory welding. It has the advantages of less investment, more convenient operation, less pollution and shorter manufacturing period. In vibratory welding, workpiece vibrates in the whole welding process and it mainly effects the welding solidification to improve the quality. Vibration facilitates the release of dissolved gases and the resulting weld beads greatly exhibit reduced porosity. Mechanical properties of the welds prepared under vibratory conditions are dependent on the structural changes of the welds This paper presents the solidification behaviour and changes occurs in mechanical properties under vibratory welding condition.

  6. Phase field modeling of grain structure evolution during directional solidification of multi-crystalline silicon sheet

    Lin, H. K.; Lan, C. W.


    Evolution of grain structures and grain boundaries (GBs), especially the coincident site lattice GBs, during directional solidification of multi-crystalline silicon sheet are simulated by using a phase field model for the first time. Since the coincident site lattice GBs having lower mobility, tend to follow their own crystallographic directions despite thermal gradients, the anisotropic energy and mobility of GBs are considered in the model. Three basic interactions of GBs during solidification are examined and they are consistent with experiments. The twinning process for new grain formation is further added in the simulation by considering twin nucleation. The effect of initial distribution of GB types and grain orientations is also investigated for the twinning frequency and the evolution of grain size and GB types.

  7. Long-lived magnetism from solidification-driven convection on the pallasite parent body

    Bryson, James F.J.; Nichols, Claire I. O.; Herrero-Albillos, Julia


    Palaeomagnetic measurements of meteorites suggest that, shortly after the birth of the Solar System, themolten metallic cores ofmany small planetary bodies convected vigorously and were capable of generating magnetic fields. Convection on these bodies is currently thought to have been thermally...... driven, implying that magnetic activity would have been short-lived. Here we report a time-series palaeomagnetic record derived fromnanomagneticimaging10 of the Imilac and Esquel pallasite meteorites, a group of meteorites consisting of centimetre-sized metallic and silicate phases. We find a history...... of long-lived magnetic activity on the pallasite parent body, capturing the decay and eventual shutdown of the magnetic field as core solidification completed.We demonstrate that magnetic activity driven by progressive solidification of an inner core is consistent with our measuredmagnetic field...

  8. Autonomous Optimization of a Solidification Pattern and Its Effect on Porosity and Segregation in Steel Castings

    Kotas, Petr; Tutum, Cem Celal; Hattel, Jesper Henri


    The present paper considers optimization of a solidification pattern of a gravity sand-cast steel part. That is, the choice of proper riser and chill designs has been investigated using genetic algorithms while simultaneously considering their impact on centerline porosity and macrosegregation...... distribution. This was accomplished by coupling a casting simulation software package with an optimization module. The casting process of the original casting design was simulated using a transient 3D thermal model incorporated in a commercial simulation software package to determine potential flaws...... and inadequacies. After this initial assessment, a new geometrical model was suggested with the redesigned gating system and rearranged chills to obtain better filling and solidification patterns. Based on the improved model, relevant optimization targets and constraints were defined. One multi...

  9. [Recent advance in solidification/stabilization technology for the remediation of heavy metals-contaminated soil].

    Hao, Han-zhou; Chen, Tong-bin; Jin, Meng-gui; Lei, Mei; Liu, Cheng-wu; Zu, Wen-pu; Huang, Li-mi


    Remediation of heavy metals-contaminated soil is still a difficulty and a hotspot of international research projects. At present, the technologies commonly adopted for the remediation of contaminated sites mainly include excavation, solidification/stabilization (S/S), soil washing, soil vapor extraction (SVE), thermal treatment, and bioremediation. Based on the S/S technical guidelines of Unite State Environmental Protection Agency (EPA) and United Kingdom Environment Agency (EA) and the domestic and foreign patents, this paper introduced the concepts of S/S and its development status at home and abroad, and discussed its future development directions. Solidification refers to a process that binds contaminated media with a reagent, changing the media's physical properties via increasing its compressive strength, decreasing its permeability, and encapsulating the contaminants to form a solid material. Stabilization refers to the process that involves a chemical reaction which reduces the leachability of a waste, chemically immobilizes the waste and reduces its solubility, making the waste become less harmful or less mobile. S/S technology includes cement solidification, lime pozzolanic solidification, plastic materials stabilization, vitrification, and regent-based stabilization. Stabilization (or immobilization) treatment processes convert contaminants to less mobile forms through chemical or thermal interactions. In stabilization technology, the aim of adding agents is to change the soil physical and chemical properties through pH control technology, redox potential technology, precipitation techniques, adsorption technology, and ion-exchange technology that change the existing forms of heavy metals in soil, and thus, reduce the heavy metals bioavailability and mobility. This review also discussed the S/S evaluation methods, highlighted the need to enhance S/S technology in the molecular bonding, soil polymers, and formulation of China's S/S technical guidelines.

  10. Examining the Possibilities of Analyzing the Solidification Process of Al-Si Alloy with the Infrared Camera

    Władysiak R.


    Full Text Available The paper presents the results of the crystallization process of silumin by the TDA thermographic method and the results of the cast microstructure obtained in the sampler ATD-10, that was cooling down in ambient air. The study was conducted for silumins AlSi8 and AlSi11 unmodified. The work demonstrated that the use of thermal imaging camera allows for the measurement and recording the solidification process of silumin. Thermal curve was registered with the infrared camera and derivative curve that was calculated on the base of thermal curve have both a very similar shape to adequate them TDA curves obtained from measurements using a thermocouple. Test results by TDA thermographic method enable quantitative analysis of the kinetics of the cooling and solidification process of hypo-and neareutectic silumins.

  11. Analysis of solidification and melting of Pcm with energy generation

    Jiji, Latif M. [Department of Mechanical Engineering, The City College of the City University of New York, New York, NY 10031 (United States); Gaye, Salif [Ecole Superieure Polytechnique, Enseignant a l' ESP BP A10, Universite Cheikh Anta Diop, Thies (Senegal)


    One-dimensional solidification and melting of a slab with uniform volumetric energy generation is examined analytically. A sudden change in surface temperature triggers phase transformation and interface motion. Analytic solutions are obtained using a quasi-steady approximation. Unlike solidification, the melting case is characterized by a pure liquid phase and a mixture of solid and liquid at the fusion temperature. The solution is governed by a single energy generation parameter. Temperature profiles, interface location and steady state conditions are presented for solidification and melting. Results are applied to two examples: solidification of a nuclear material and melting of ice. [Author].

  12. A Numerical Study of Directional Solidification and Melting in Microgravity

    Chen, P. Y. P.; Timchenko, V.; Leonardi E.; deVahlDavis, G.; deGroh, H. C., III


    A computational model is presented for the study of the solidification and melting of a pure substance and of a binary alloy. The enthalpy method has been used, and incorporated into a commercial CFD code. Three examples of the use of the model are described: the three-dimensional solidification of a pure substance (succinonitrile), the results of which are compared with experiment; an example of the solidification of a bismuth-tin alloy; and a simulation of a solidification and melting experiment done in space known as the MEPHISTO program.

  13. Effect of solidification rate on competitive grain growth in directional solidification of a nickel-base superalloy

    ZHOU YiZhou; SUN XiaoFeng


    The mechanism of grain structure evolution during directional solidification is a fundamental subject in material science.Within the published research there exist conflicting views on the mechanism of grain overgrowth.To study the effect of solidification rate on grain structure evolution,bi-crystals samples were produced in a nickel-base superalloy at different solidification rates.It was found that at the convergent grain boundaries those grains better aligned with respect to the heat flux more readily overgrew neighbouring grains with misaligned orientations and the effect became more pronounced as solidification rate was increased.However,at diverging grain boundaries the rate of overgrowth was invariant to the solidification rate.These experimental results were compared with models in the literature.Thus,a better insight into competitive grain growth in directional solidification processes was obtained.

  14. Effects of the location of a cast in the furnace on flatness of the solidification front in directional solidification

    Lian, Yuanyuan; Li, Dichen; Zhang, Kai


    Many defects of single crystals are caused by the nonplanar solidification front. The transverse temperature gradient at melt-crystal interface results in nonplanar solidification fronts. The location of a cast in the directional solidification furnace affects heat dissipation and thus influences the transverse temperature gradient. This paper presents a criterion and a searching algorithm to find the optimal location of the cast for flattening the solidification front. A numerical simulation was employed for the verification of our method. Additionally, the effects of the size of the cooling device of the furnace on the optimal location, the transverse temperature gradient and the solidification time were discussed. The transverse temperature gradient is reduced about 50% without increasing much solidification time when setting the cast with a varying thickness mould at the optimal location. In addition, the optimal location is mainly influenced by the radius of the cooling ring.

  15. Online process control for directional solidification by ultrasonic pulse echo technique.

    Drevermann, A; Pickmann, C; Tiefers, R; Zimmermann, G


    A method of controlling the actual growth velocity during directional solidification based on ultrasound has been developed. For this purpose a pulse echo technique is used to measure the actual solidification rate online. This quantity is used to control the furnace velocity. Solidification experiments with metallic alloys and constant furnace velocity often result in non-steady actual solidification rates. Experiments carried out with online process control demonstrate that a really steady-state solidification with a constant solidification rate is achieved.

  16. Thermal Convection Affects Shape Of Solid/Liquid Interface

    Mennetrier, C.; Chopra, M. A.; Yao, M.; De Groh, H. C., III; Yeoh, G. H.; De Vahl Davis, G.; Leonardi, E.


    Report describes experimental and theoretical study of effect of thermal convection on shape of interface between solid and liquid succinonitrile, clear commercially available plastic, in Bridgman (directional-solidification) apparatus in vertical and horizontal orientations.

  17. Mold Simulator Study of Heat Transfer Phenomenon During the Initial Solidification in Continuous Casting Mold

    Zhang, Haihui; Wang, Wanlin


    In this paper, mold simulator trials were firstly carried out to study the phenomena of the initial shell solidification of molten steel and the heat transfer across the initial shell to the infiltrated mold/shell slag film and mold. Second, a one-dimensional inverse heat transfer problem for solidification (1DITPS) was built to determine the temperature distribution and the heat transfer behavior through the solidifying shell from the measured shell thickness. Third, the mold wall temperature field was recovered by a 2DIHCP mathematical model from the measured in-mold wall temperatures. Finally, coupled with the measured slag film thickness and the calculations of 1DITPS and 2DIHCP, the thermal resistance and the thickness of liquid slag film in the vicinity of the meniscus were evaluated. The experiment results show that: the total mold/shell thermal resistance, the mold/slag interfacial thermal resistance, the liquid film thermal resistance, and the solid film thermal resistance is 8.0 to 14.9 × 10-4, 2.7 to 4.8 × 10-4, 1.5 to 4.6 × 10-4, and 3.9 to 6.8 × 10-4 m2 K/W, respectively. The percentage of mold/slag interfacial thermal resistance, liquid film thermal resistance, and solid film thermal resistance over the total mold/shell thermal resistance is 27.5 to 34.4, 17.2 to 34.0, and 38.5 to 48.8 pct, respectively. The ratio of radiation heat flux is around 14.1 to 51.9 pct in the liquid slag film.

  18. Pattern and phase selection of peritectic reaction during directional solidification

    HUANG; Weidong; (黄卫东); LIN; Xin; (林鑫); WANG; Meng; (王猛); SHEN; Shujuan; (沈淑娟); SU; Yunpeng; (苏云鹏); LIU; Zhenxia; (刘振侠)


    Based on the growth competition between different pattern and phases, the pattern and phase selection during peritectic solidification is analysed by applying the maximum interface temperature criterion to the interface response functions calculated from a numerical model for single phase solidification. The theoretical results agree very well with the experimental results published in literature.

  19. A Computer Aided System for Simulating Weld Metal Solidification Crack


    A computer-aided system for simulating weld solidification crack has been developed by which a welding engineer can carry out the welding solidification crack simulation on the basis of a commercial finite element analysis software package. Its main functions include calculating the heat generations of the moving arc, mesh generation, calculating stress-strain distributions with element rebirth technique.

  20. Processing of alnico permanent magnets by advanced directional solidification methods

    Zou, Min; Johnson, Francis; Zhang, Wanming; Zhao, Qi; Rutkowski, Stephen F.; Zhou, Lin; Kramer, Matthew J.


    Advanced directional solidification methods have been used to produce large (>15 cm length) castings of Alnico permanent magnets with highly oriented columnar microstructures. In combination with subsequent thermomagnetic and draw thermal treatment, this method was used to enable the high coercivity, high-Titanium Alnico composition of 39% Co, 29.5% Fe, 14% Ni, 7.5% Ti, 7% Al, 3% Cu (wt%) to have an intrinsic coercivity (Hci) of 2.0 kOe, a remanence (Br) of 10.2 kG, and an energy product (BH)max of 10.9 MGOe. These properties compare favorably to typical properties for the commercial Alnico 9. Directional solidification of higher Ti compositions yielded anisotropic columnar grained microstructures if high heat extraction rates through the mold surface of at least 200 kW/m2 were attained. This was achieved through the use of a thin walled (5 mm thick) high thermal conductivity SiC shell mold extracted from a molten Sn bath at a withdrawal rate of at least 200 mm/h. However, higher Ti compositions did not result in further increases in magnet performance. Images of the microstructures collected by scanning electron microscopy (SEM) reveal a majority α phase with inclusions of secondary αγ phase. Transmission electron microscopy (TEM) reveals that the α phase has a spinodally decomposed microstructure of FeCo-rich needles in a NiAl-rich matrix. In the 7.5% Ti composition the diameter distribution of the FeCo needles was bimodal with the majority having diameters of approximately 50 nm with a small fraction having diameters of approximately 10 nm. The needles formed a mosaic pattern and were elongated along one crystal direction (parallel to the field used during magnetic annealing). Cu precipitates were observed between the needles. Regions of abnormal spinodal morphology appeared to correlate with secondary phase precipitates. The presence of these abnormalities did not prevent the material from displaying superior magnetic properties in the 7.5% Ti composition

  1. Low Melt Height Solidification of Superalloys

    Montakhab, Mehdi; Bacak, Mert; Balikci, Ercan


    Effect of a reduced melt height in the directional solidification of a superalloy has been investigated by two methods: vertical Bridgman (VB) and vertical Bridgman with a submerged baffle (VBSB). The latter is a relatively new technique and provides a reduced melt height ahead of the solidifying interface. A low melt height leads to a larger primary dendrite arm spacing but a lower mushy length, melt-back transition length, and porosity. The VBSB technique yields up to 38 pct reduction in the porosity. This may improve a component's mechanical strength especially in a creep-fatigue type dynamic loading.

  2. Novel Directional Solidification of Hypermonotectic Alloys

    Grugel, R. N.; Fedoseyev, A. I.; Rose, M. Franklin (Technical Monitor)


    There are many metal alloy systems that separate into two different liquids upon cooling from a higher temperature. Uniform microstructural development during solidification of these immiscible liquids on Earth is hampered by inherent density differences between the phases. Microgravity processing minimizes settling but segregation still occurs due to gravity independent wetting and coalescence phenomena. Experiments with the transparent organic, metal analogue, succinonitrile-glycerol system were conducted in conjunction with applied ultrasonic energy. The processing parameters associated with this technique have been evaluated in view of optimizing dispersion uniformity. Characterization of the experimental results in terms of an initial modeling effort will also be presented.

  3. Alternating tip splitting in directional solidification.

    Utter, B; Ragnarsson, R; Bodenschatz, E


    We report experimental results on the tip splitting dynamics of seaweed growth in directional solidification of succinonitrile alloys. Despite the random appearance of the growth, a tip splitting morphology was observed in which the tip alternately splits to the left and to the right. The tip splitting frequency f was found to be related to the growth velocity V as a power law f~V1.5. This finding is consistent with the predictions of a tip splitting model that is also presented. Small anisotropies are shown to lead to different kinds of seaweed morphologies.

  4. ORNL liquid low-level waste solidification

    Schultz, R.M.; Monk, T.H.; du Mont, S.P.; Helms, R.E.; Keigan, M.V.; Morris, M.I.


    The solidification of LLLW at ORNL has developed two basic strategies, a near-term or backup flowsheet is planned to alleviate the immediate capacity problem for storage of concentrated LLLW and a long-term or reference flowsheet is planned to incorporate filtration of the settleable TRU and cesium and strontium decontamination of the LLLW. Presently a feasibility study is evaluating the process alternatives for segregating LLLW from remote-handled transuranic (RH-TRU) sludges, decontamination of the LLLW for beta-gamma radionuclides such as cesium and strontium, and the handling and storage of the RH-TRU sludges and decontamination media. 14 refs.

  5. Effect of phosphor addition on eutectic solidification and microstructure of an Al-13%Si alloy

    Liao Hengcheng


    Full Text Available As the refiner or modifier, the master alloys containing high concentration phosphor are widely used in preparing eutectic or hypereutectic Al-Si alloys. To study the effect of phosphor addition on the eutectic solidification and microstructure of the Al-13%Si alloy, an investigation has been undertaken by means of thermal analysis and micro/macro-structure observation. Results indicate that addition of phosphor in near eutectic Al-Si alloy promotes the nucleation of eutectic but has little refinement impact on primary Si particles as expected. Conversely, both primary Si particles and eutectic Si flakes become slightly coarser in P-rich alloys. The coarsening of eutectic Si flakes ties closely to the increased eutectic growth temperature with phosphor addition. The eutectic solidification of the alloy proceeds from the near mold zone towards the center, and it is also found that a few independent nucleation regions emerge in liquid at the solidification front due to the addition of phosphor.

  6. Effect of current and atomized grain size distribution on the solidification of Plasma Transferred Arc coatings

    Danielle Bond


    Full Text Available Plasma Transferred Arc (PTA is the only thermal spray process that results in a metallurgical bond, being frequently described as a hardfacing process. The superior properties of coatings have been related to the fine microstructures obtained, which are finer than those processed under similar heat input with welding techniques using wire feedstock. This observation suggests that the atomized feedstock plays a role on the solidification of coatings. In this study a model for the role of the powders grains in the solidification of PTA coatings is put forward and discussed. An experiment was setup to discuss the model which involved the deposition of an atomized Co-based alloy with different grain size distributions and deposition currents. X ray diffraction showed that there were no phase changes due to the processing parameters. Microstructure analysis by Laser Confocal Microscopy, dilution with the substrate steel and Vickers microhardness were used the characterized coatings and enriched the discussion confirming the role of the powdered feedstock on the solidification of coatings.

  7. Macrosegregation in Al-7Si alloy caused by abrupt cross-section change during directional solidification

    Ghods, M.; Johnson, L.; Lauer, M.; Grugel, R. N.; Tewari, S. N.; Poirier, D. R.


    Hypoeutectic Al-7 wt .% Si alloys were directionally solidified vertically downward in cylindrical molds that incorporated an abrupt cross-section decrease (9.5 mm to 3.2 mm diameter) which, after 5 cm, reverted back to 9.5 mm diameter in a Bridgman furnace; two constant growth speeds and thermal gradients were investigated. Thermosolutal convection and cross-section-change-induced shrinkage flow effects on macrosegregation were investigated. Dendrite clustering and extensive radial macrosegregation was seen, particularly in the larger cross-sections, before contraction and after expansion, this more evident at the lower growth speed. This alloy shows positive longitudinal macrosegregation near cross-section decrease followed by negative macrosegregation right after it; the extent of macrosegregation, however, decreases with increasing growth speed. Primary dendrite steepling intensified as solidification proceeded into the narrower section and negative longitudinal macrosegregation was seen on the re-entrant shelves at expansion. A two-dimensional model accounting for both shrinkage and thermo-solutal convection was used to simulate solidification and the resulting mushy-zone steepling and macrosegregation. The experimentally observed longitudinal and radial macrosegregation associated with the cross-section changes during directional solidification of an Al-7Si alloy is well captured by the numerical simulations.

  8. Comparison between numerical simulation and experimental measurement of solute segregation during directional solidification

    Stelian, Carmen; Duffar, Thierry; Nicoara, Irina


    The effect of Bridgman furnace configuration on the temperature field, melt convection and the solute distribution in the resulting crystal are experimentally and numerically analyzed for the semiconductor diluted alloy solidification. The governing equations of the heat and mass transfer are solved by using the finite element method with help of the commercial software FIDAP ®. Two different solidification experiments of Ga 1- xIn xSb ( x=0.01 and 0.04) are simulated in order to compare the numerical results for thermal, velocity and solute fields. The central objective of the work is to give the conditions for which a more uniform distribution of the solute in the crystal can be obtained. It is found that crystals obtained in conditions of a strong convective regime in the vicinity of the solid-liquid interface are more homogeneous radially and on a significant length than the crystals for which solidification occurred in a quasi-diffusive regime. The results, in terms of axial and radial segregation, are compared to experimental chemical analysis.

  9. Solute segregation in directional solidification of GaInSb concentrated alloys under alternating magnetic fields

    Stelian, Carmen; Delannoy, Yves; Fautrelle, Yves; Duffar, Thierry


    Numerical simulations of the vertical Bridgman solidification of Ga 1- xIn xSb concentrated alloys are performed by using the commercial codes FIDAP ® and FLUENT ®. The transient axi-symmetric simulation of heat, mass and species transport during highly doped ( x=0.2) crystal growth, shows a strong solute effect on the melt convection. The thermally driven flow is damped by the heavier solute (InSb) rejected at the solid-liquid interface. A diffusive transport regime is established in the melt a short time after the beginning of solidification and as a consequence, the radial segregation increases. This leads to a significant increase of the interface curvature because of the melting point dependency on the interface composition. Finally, the crystals are not chemically homogeneous with large variations of InSb concentration on the axial and radial directions. In order to improve the chemical homogeneity of highly doped Ga 1- xIn xSb crystals, it is proposed to apply an alternating magnetic field in the vicinity of the solid-liquid interface. The magnetic parameters for which an optimal level of convection arises in the melt are derived from the numerical simulation. It is shown that during solidification under optimized electromagnetic stirring, the radial segregation and interface deflection can be maintained at low values.

  10. The effect of ultrasonic processing on solidification microstructure and heat transfer in stainless steel melt.

    Zhang, Xiaopeng; Kang, Jinwu; Wang, Shuo; Ma, Jiyu; Huang, Tianyou


    The heat transfer in the ultrasonic processing of stainless steel melt is studied in this thesis. The temperature field is simulated when the metal melt is treated with and without ultrasound. In order to avoid the erosion of high temperature melt, ultrasound was introduced from the bottom of melt. It is found that the temperature of melt apparently increases when processed with ultrasound, and the greater the ultrasonic power is, the higher the melt temperature will be; ultrasonic processing can reduce the temperature gradient, leading to more uniform temperature distribution in the melt. The solidification speed is obviously brought down due to the introduction of ultrasound during solidification, with the increasing of ultrasonic power, the melt temperature rises and the solidification speed decreases; as without ultrasound, the interface of solid and mushy zone is arc-shaped, so is the interface of liquid and mushy zone, with ultrasound, the interface of solid and mushy zone is still arc-shaped, but the interface of liquid and mushy zone is almost flat. The simulation results of temperature field are verified in experiment, which also indicates that the dendrite growth direction is in accord with thermal flux direction. The effect of ultrasonic treatment, which improves with the increase of treating power, is in a limited area due to the attenuation of ultrasound.

  11. Modeling of Filling and Solidification Process for TiAl Exhaust Valves During Suction Casting

    Chao XIONG; Yingche MA; Bo CHEN; Kui LIU; Yiyi LI


    Investment and suction casting (ISC) represents an economic and promising process route to fabricate automotive exhaust valves ofγ-TiAl based alloys,but information available on the metal flow and the temperature changes during mould filling and solidification process for the ISC process is meager.A sequentially coupled mathematical flow-thermal model,based on the commercial finite-volume/finite-difference code FLOW-3D and the finite-element code PROCAST,has been developed to investigate the ISC process.In term of calculating the flow and temperature fields during the filling and solidification stages,potential defects including the gas bubbles and the surface air entrainment occurred in the mould filling process and the shrinkage porosities formed in the solidification process are predicted and the reasons for the formation of these defects are also analyzed.The effects of filling pressure difference control methods and moulds on gas bubble and surface air entrainment behavior are presented.It is found that by changing the filling pressure difference control methods from general suction casting to "air leakage" suction casting and reducing air leakage flow rates,the gas bubbles are eliminated effectively,and the surface air entrainment attenuate dramatically.With resort to a mould with a tetragonal runner,the surface air entrainment decrease to the lowest level.Finally,the water analogue and suction casting experiments of exhaust valves are implemented for further validation of the simulation results.

  12. Nanoparticle-induced unusual melting and solidification behaviours of metals

    Ma, Chao; Chen, Lianyi; Cao, Chezheng; Li, Xiaochun


    Effective control of melting and solidification behaviours of materials is significant for numerous applications. It has been a long-standing challenge to increase the melted zone (MZ) depth while shrinking the heat-affected zone (HAZ) size during local melting and solidification of materials. In this paper, nanoparticle-induced unusual melting and solidification behaviours of metals are reported that effectively solve this long-time dilemma. By introduction of Al2O3 nanoparticles, the MZ depth of Ni is increased by 68%, while the corresponding HAZ size is decreased by 67% in laser melting at a pulse energy of 0.18 mJ. The addition of SiC nanoparticles shows similar results. The discovery of the unusual melting and solidification of materials that contain nanoparticles will not only have impacts on existing melting and solidification manufacturing processes, such as laser welding and additive manufacturing, but also on other applications such as pharmaceutical processing and energy storage.

  13. Relationships between Microbial Activities and Subduction-related Outgassing and Volatile Flux at Aleutian Arc Volcanoes

    Miller, H.; Lopez, T. M.; Fischer, T. P.; Schrenk, M. O.


    Subduction-related processes, including the movement and alteration of carbon compounds, are an important component of global geochemical cycles. Actively degassing volcanoes of the Aleutian Island arc offer interesting opportunities to not only characterize the composition and abundance of volatiles, but also to identify the origin of the discharging gases (e.g. mantle, organic matter, or carbonates). Taking this approach a step further, microbial activities in and around volcanic fumarole areas may impact the composition and flux of reduced volcanic gases, either through their modification or their assimilation into fixed biomass. Microbiological studies of these systems can be used to develop predictive models to complement those based upon geochemical data while providing greater understanding of the causal relationships between microbial populations and their environment, and ultimately refine estimates of volcanic outgassing. Coupled fumarole soil and gas samples were collected from several Aleutian Island volcanoes in 2015 (Gareloi, Kanaga, Kiska, Little Sitkin) and 2016 (Okmok, Resheschnoi). DNA was extracted from the soil and used to describe microbial community composition, while gas samples were analyzed through chromatography and mass spectrometry. Preliminary data suggests a relationship between the abundance of specific groups of prokaryotes known to metabolize reduced gases, such as sulfur-oxidizers and methanotrophs, and the abundances of the degassing volatiles, including sulfur dioxide and methane. Ongoing studies aimed at investigating the relationship between the genomic composition of the fumarolic microbial community and the physical and chemical properties of the soil (i.e. mineralogy, bulk geochemistry, nutrient concentration, gas flux, and environmental measurements) are underway. These data will be used to evaluate the potential for microbial communities to remove volcanic carbon and store it as biomass, or to modify the volatile carbon

  14. Outgassing of plasma facing antenna front for lower hybrid wave launcher

    Maebara, Sunao E-mail:; Goniche, Marc; Kazarian, Fabienne; Seki, Masami; Ikeda, Yoshitaka; Imai, Tsuyoshi; Bibet, Philippe; Froissard, Philippe; Rey, Guy


    A 3.7 GHz mock-up antenna module using carbon fiber composite (CFC) was fabricated and tested for the development of a heat-resistive front of the lower hybrid current drive (LHCD) antenna. This module has four waveguides and a water cooling channel, the length is 206 mm. The CFC surface was coated with a thin titanium layer and was plated with copper in order to reduce RF losses, to bond rods and septum plates and to assemble them with cooling channel. The RF losses and the outgassing rates of this CFC module at high RF power were measured during long pulses. When the injected power varies between 30 and 100 kW, the RF losses measured by calorimetery, were found to be in the range of 1.0-1.2%. It is found that this experimental value is 2.5-3.0 times higher than the theoretical value of pure copper. Stationary operation of the CFC module with water cooling is performed at the RF power density of 45 MW m{sup -2} during 1000 s. The outgassing rates from the CFC module are in the range of 0.93{approx}1.3x10{sup -6} Pam{sup -3} s{sup -1} m{sup -2} at the module temperature of 120 deg. C, it is low enough for an antenna material. No significant bonding defects occurred during the steady-state operation. It is assessed that a CFC module is an attractive candidate for a heat-resistive front of LHCD antenna.

  15. Real Time Characterization of Solid/Liquid Interfaces During Directional Solidification

    Sen, S.; Kaukler, W. K.; Curreri, P. A.; Peters, P.


    A X-Ray Transmission Microscope (XTM) has been developed to observe in real time and in-situ solidification phenomenon at the solid/liquid interface. Recent improvements in the horizontal Bridgman furnace design provides real-time magnification (during solidification) up to 12OX. The increased magnification has enabled for the first time the XTM imaging of real-time growth of fibers and particles with diameters of 3-6 micrometers. Further, morphological transitions from planar to cellular interfaces have also been imaged. Results from recent XTM studies on Al-Bi monotectic system, Al-Au eutectic system and interaction of insoluble particles with s/I interfaces in composite materials will be presented. An important parameter during directional solidification of molten metal is the interfacial undercooling. This parameter controls the morphology and composition at the s/I interface. Conventional probes such as thermocouples, due to their large bead size, do not have sufficient resolution for measuring undercooling at the s/I interface. Further, the intrusive nature of the thermocouples also distorts the thermal field at the s/I interface. To overcome these inherent problems we have recently developed a compact furnace which utilizes a non-intrusive technique (Seebeck) to measure undercooling at the S/I interface. Recent interfacial undercooling measurements obtained for the Pb-Sn system will be presented. The Seebeck measurement furnace in the future will be integrated with the XTM to provide the most comprehensive tool for real time characterization of s/I interfaces during solidification.

  16. Preservation of Thermal Control Specular Gold Baffle Surface on the James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) Electronics Compartment (IEC)

    MonteedeGarcia, Kristina; Patel, Jignasha; Perry, Radford, III


    Extremely tight thermal control property degradation allowances on the vapor-deposited, gold-coated IEC baffle surface, made necessary by the cryogenic JWST Observatory operations, dictate tight contamination requirements on adjacent surfaces. Theoretical degradation in emittance with contaminant thickness was calculated. Maximum allowable source outgassing rates were calculated using worst case view factors from source to baffle surface. Tight requirements pushed the team to change the design of the adjacent surfaces to minimize the outgassing sources

  17. The melting and solidification of nanowires

    Florio, B. J.; Myers, T. G.


    A mathematical model is developed to describe the melting of nanowires. The first section of the paper deals with a standard theoretical situation, where the wire melts due to a fixed boundary temperature. This analysis allows us to compare with existing results for the phase change of nanospheres. The equivalent solidification problem is also examined. This shows that solidification is a faster process than melting; this is because the energy transfer occurs primarily through the solid rather than the liquid which is a poorer conductor of heat. This effect competes with the energy required to create new solid surface which acts to slow down the process, but overall conduction dominates. In the second section, we consider a more physically realistic boundary condition, where the phase change occurs due to a heat flux from surrounding material. This removes the singularity in initial melt velocity predicted in previous models of nanoparticle melting. It is shown that even with the highest possible flux the melting time is significantly slower than with a fixed boundary temperature condition.

  18. The Advanced Automated Directional Solidification Furnace

    Gillies, D. C.; Reeves, F. A.; Jeter, L. B.; Sledd, J. D.; Cole, J. M.; Lehoczky, S. L.


    The Advanced Automated Directional Solidification Furnace (AADSF) is a five zone tubular furnace designed for Bridgman-Stockbarger, other techniques of crystal growth involving multiple temperature zones such as vapor transport experiments and other materials science experiments. The five zones are primarily designed to produce uniform hot and cold temperature regions separated by an adiabatic region constructed of a heat extraction plate and an insert to reduce radiation from the hot to the cold zone. The hot and cold zone temperatures are designed to reach 1600 C and 1100 C, respectively. AADSF operates on a Multi-Purpose Experiment Support Structure (MPESS) within the cargo bay of the Space Shuttle on the United States Microgravity Payload (USMP) missions. Two successful flights, both employing the directional solidification or Bridgman Stockbarger technique for crystal growth have been made, and crystals of HgCdTe and PbSnTe grown in microgravity have been produced on USMP-2 and USMP-3, respectively. The addition of a Sample Exchange Mechanism (SEM) will enable three different samples to be processed on future flights including the USMP-4 mission.

  19. Carburizer Effect on Cast Iron Solidification

    Janerka, Krzysztof; Kondracki, Marcin; Jezierski, Jan; Szajnar, Jan; Stawarz, Marcin


    This paper presents the effect of carburizing materials on cast iron solidification and crystallization. The studies consisted of cast iron preparation from steel scrap and different carburizers. For a comparison, pig iron was exclusively used in a solid charge. Crystallization analysis revealed the influence of the carburizer material on the crystallization curves as well as differences in the solidification paths of cast iron prepared with the use of different charge materials. The carburizers' influence on undercooling during the eutectic crystallization process was analyzed. The lowest undercooling rate was recorded for the melt with pig iron, then for synthetic graphite, natural graphite, anthracite, and petroleum coke (the highest undercooling rate). So a hypothesis was formulated that eutectic cells are created most effectively with the presence of carbon from pig iron (the highest nucleation potential), and then for the graphite materials (crystallographic similarity with the carbon precipitation in the cast iron). The most difficult eutectic crystallization is for anthracite and petroleum coke (higher undercooling is necessary). This knowledge can be crucial when the foundry plant is going to change the solid charge composition replacing the pig iron by steel scrap and the recarburization process.

  20. Solidification microstructure of centrifugally cast Inconel 625

    Silvia Barella


    Full Text Available Centrifugal casting is a foundry process allowing the production of near net-shaped axially symmetrical components. The present study focuses on the microstructural characterization of centrifugally cast alloys featuring different chemical compositions for the construction of spheres applied in valves made of alloy IN625 for operation at high pressure. Control of the solidification microstructure is needed to assure the reliability of the castings. Actually, a Ni-base superalloy such as this one should have an outstanding combination of mechanical properties, high temperature stability and corrosion resistance. Alloys such as IN625 are characterised by a large amount of alloying elements and a wide solidification range, so they can be affected by micro-porosity defects, related to the shrinkage difference between the matrix and the secondary reinforcing phases (Nb-rich carbides and Laves phase. In this study, the microstructure characterization was performed as a function of the applied heat treatments and it was coupled with a calorimetric analysis in order to understand the mechanism ruling the formation of micro-porosities that can assure alloy soundness. The obtained results show that the presence of micro-porosities is governed by morphology and by the size of the secondary phases, and the presence of the observed secondary phases is detrimental to corrosion resistance.

  1. Inversion Solidification Cladding of H90-Steel

    LI Bao-mian; XU Guang-ming; CUI Jian-zhong


    The variation law of cladding thickness as well as the structures and properties of H90-steel clad strip produced by inversion solidification was studied.The interface bonding mechanisms were approached.It is found that the thickness of H90 cladding goes sequentially through the solidification growth stage,holding stage,and remelting stage,with an increase in immersion time.The higher the preheating temperature of the steel coil,the thicker is the maximum cladding thickness.Observation by using optical microscopy (OM) and the electron probe microanalyzer (EPMA) shows that the microstrueture of H90 cladding is composed of equiaxed grains,and that interdiffusion between Cu and Fe at interface occurs but obvious diffusion of Zn and the intermetallic layer are not observed.The diffusion layer is thin and about 4 μm.Multipass small reduction cold rolling and repeated bending tests show that the interface is firmly bonded.Tensile test shows that the mechanical properties of the as-clad strips can meet the requirements of GB5213-2001 for the F-grade deep-drawing steel plate though there is a slight difference in the mechanical properties among the clad strips with different cladding thickness.

  2. Synergic effect of atomic oxygen and outgassing phenomena on Carbon/SiC composites for space applications

    Albano, Marta

    The space environment is one of the most critical for space structures. The low earth orbit (LEO) space environment includes hazards such as atomic oxygen, UV radiation, ionizing radiation (electrons, protons), high vacuum, plasma, micrometeoroids and debris, as well as severe temperature cycles. Exposure of composites to the space environment may result in different detrimental effects via modification of their chemical, electrical, thermal, optical and mechanical properties as well as surface erosion. The high vacuum induces material outgassing (e.g. low-molecular weight residues, plasticizers and additives) and consequent contamination of nearby surfaces. At LEO altitudes the neutral atmosphere consists primarily of ATOX (˜80%) and nitrogen molecules (˜20%). ATOX, which is formed by photo-dissociation of molecular oxygen in the upper atmosphere, is a severe hazard for composites. The number density of ATOX at about 300 km altitude is ˜2 × 109 to 8 × 109 atoms/cm3, for minimum and maximum solar activity, respectively. Front surfaces (ram direction) of space vehicles orbiting at a velocity of about 8 km/s collide with the ATOX species with impingement kinetic energy of approximately 5 eV. The ATOX flux is determined by such parameters as altitude, orbital inclination, solar activity and time of day. A nominal range of values for LEO is 1014-1015 atoms/cm2 s. The Low Earth Orbit is a complex and dynamic environment where constituents vary with position, local time, season and solar activity. Effects of different constituents of the space environment on spacecraft materials play an important role in determining the system function, reliability and lifetime. This is more crucial if the structure has to be used for the re-entry as thermal protection systems for example. In this case the integrity of the surface and its coating is crucial for the success of the entire mission. During the re-entry, resistance of materials is hard tested by fast chemical reactions

  3. Residual thermal stresses in injection molded products

    Zoetelief, W.F.; Douven, L.F.A.; Ingen Housz, A.J.


    Nonisothermal flow of a polymer melt in a cold mold cavity introduces stresses that are partly frozen-in during solidification. Flow-induced stresses cause anisotropy of mechanical, thermal, and optical properties, while the residual thermal stresses induce warpage and stress-cracking. In this study

  4. Numerical modelling on stress and dislocation generation in multi-crystalline silicon during directional solidification for PV applications

    Srinivasan, M.; Karuppasamy, P.; Ramasamy, P.; Barua, A. K.


    Numerical modelling has emerged as a powerful tool for the development and optimization of directional solidification process for mass production of multicrystalline silicon. A transient global heat transfer model is performed to investigate the effect of bottom grooved furnace upon the directional solidification (DS) process of multi-crystalline silicon (mc-Si). The temperature distribution, von Mises stress, residual stress and dislocation density rate in multi-crystalline silicon ingots grown by modified directional solidification method have been investigated for five growth stages using finite volume method at the critical Prandtl number, Pr = 0.01. This paper discusses bottom groove furnace instead of seed crystal DS method. It achieves an advanced understanding of the thermal and mechanical behaviour in grown multi-crystalline ingot by bottom grooved directional solidification method. The von Mises stress and dislocation density were reduced while using the bottom grooved furnace. This work was carried out in the different grooves of radius 30 mm, 60 mm and 90 mm of the heat exchanger block of the DS furnace. In this paper, the results are presented for 60 mm radius groove only because it has got better results compared to the other grooves. Also, the computational results of bottom grooved DS method show better performance compared the conventional DS method for stress and dislocation density in grown ingot. [Figure not available: see fulltext.

  5. Heterogeneous nucleation of the primary phase in the rapid solidification of Al-4.5wt%Cu alloy droplet

    Maitre, A.; Bogno, A-A; Bedel, M; Reinhart, G; Henein, H


    International audience; This paper reports on rapid solidification of Al-Cu alloys. A heterogeneous nucleation/growth model coupled with a thermal model of a falling droplet through a stagnant gas was developed. The primary undercooling as well as the number of nucleation points was compared with Al-Cu alloy droplets produced by Impulse Atomization (IA). Based on experimental results from Neutron Diffraction, secondary (eutectic) phases were obtained. Then, primary and secondary undercoolings...

  6. Numerical Simulation of Transport Phenomena in Solidification of Multicomponent Ingot Using a Continuum Model


    A continuum model proposed for dendrite solidification of multicomponent alloys, with any partial solid back diffusion, was used to numerically simulate the macroscopic solidification transport phenomena and macrosegregations in an upwards directionally solidified plain carbon steel ingot. The computational results of each macroscopic field of the physical variables involved in the solidification process at a middle solidification stage were presented.

  7. Crossover scaling of wavelength selection in directional solidification of binary alloys.

    Greenwood, Michael; Haataja, Mikko; Provatas, And Nikolas


    We simulate cellular and dendritic growth in directional solidification in dilute binary alloys using a phase-field model solved with adaptive-mesh refinement. The spacing of primary branches is examined for a wide range of thermal gradients and alloy compositions and is found to undergo a maximum as a function of pulling velocity, in agreement with experimental observations. We demonstrate that wavelength selection is unambiguously described by a nontrivial crossover scaling function from the emergence of cellular growth to the onset of dendritic fingers. This result is further validated using published experimental data, which obeys the same scaling function.

  8. Control of deflection deformation of plate-shape castings in solidification

    郑贤淑; 金英达


    The deformation mechanism during the solidification was analyzed based on the experimental results ofthe castings. An approximate quadratic differential equation and its discrete model of calculation deflection were pro-posed. The model indicates that the key factors leading to the deflection deformation are the thermal bending mo-ment M and the flexural rigidity E.J. The smaller the former and the larger the latter is, the smaller the deflectiondeformation will be. The experiments are carried out at various technical conditions, and their results appear good a-greement with calculation ones. A method was proposed to predict and control the casting deformation.

  9. Quantitative phase-field modeling of nonisothermal solidification in dilute multicomponent alloys with arbitrary diffusivities.

    Ohno, Munekazu


    A quantitative phase-field model is developed for simulating microstructural pattern formation in nonisothermal solidification in dilute multicomponent alloys with arbitrary thermal and solutal diffusivities. By performing the matched asymptotic analysis, it is shown that the present model with antitrapping current terms reproduces the free-boundary problem of interest in the thin-interface limit. Convergence of the simulation outcome with decreasing the interface thickness is demonstrated for nonisothermal free dendritic growth in binary alloys and isothermal and nonisothermal free dendritic growth in a ternary alloy.

  10. Hydrothermal Solidification of Diatomite and Its Heat Insulating Property

    TONG Yu; GAO Jian; XIA Feng; XU Dawei; SONG Lili; YANG Wenrui; ZENG You


    To meet the commercial requirements of inorganic heat insulators,the mixture of diatomite and Ca(OH) 2 are evenly dispersed,mold-compacted,and then hydrothermally solidified due to the formation of tobermorite under an autoclaved process.Systematic investigations of the preparation conditions (including mix ratio,autoclaved factors,mold pressure,etc)were carried out to optimize the serving properties of such toberrnorite-based products.As a result,a compressive strength of more than 30 MPa was realized for the specimen in high density( about 1.30( g·cm-3) ).On the contrary,the specimen in light weight for example 0.63 ( g ·cm-3 ) typically showed a thermal conductivity of around 0.12 ( W· m-1· K-1 ).The present work developed a feasible way to produce and to control the serving properties of diatomite-based heat insulators by a process of hydrothermal solidification,in which the optimized value of Ca/Si ratio was proposed to be 0.6 ~ 0.7,while the water content is 25 % in weight,and hydrothermal reaction is performed at 180 ℃ for no more than 24 hours.

  11. Evolution of grain structures during directional solidification of silicon wafers

    Lin, H. K.; Wu, M. C.; Chen, C. C.; Lan, C. W.


    The evolution of grain structures, especially the types of grain boundaries (GBs), during directional solidification is crucial to the electrical properties of multicrystalline silicon used for solar cells. To study this, the electric molten zone crystallization (EMZC) of silicon wafers at different drift speeds from 2 to 6 mm/min was considered. It was found that orientation was dominant at the lower drift velocity, while orientation at the higher drift velocity. Most of the non-∑GBs tended to align with the thermal gradient, but some tilted toward the unfavorable grains having higher interfacial energies. On the other hand, the tilted ∑3GBs tended to decrease during grain competition, except at the higher speed, where the twin nucleation became frequent. The competition of grains separated by ∑GBs could be viewed as the interactions of GBs that two coherent ∑3n GBs turned into one ∑3nGB following certain relations as reported before. On the other hand, when ∑ GBs met non-∑ GBs, the non-∑ GBs remained which explained the decrease of ∑ GBs at the lower speed.

  12. Directional Solidification of Bi-Sn on USMP-4

    Abbaschian, Reza; deGroh, H., III; Leonardi, E.; Timchenko, V.; deVahlDavis, G.


    The experiments used MEPHISTO hardware to study the solidification and melting behavior of bismuth alloyed with 1 at% tin. Three samples, each approximately 900 mm long and 6mm in diameter, were used. A portion of each sample also included a 2 mm diameter growth capillary, to assist in the formation of a single grain. One sample provided the Seebeck voltage generated during melting and freezing processes. Another provided temperature data and Peltier pulsed demarcation of the interface shape for post flight analysis. The third sample provided resistance and growth velocity measurements, as well as additional thermal data. The third sample was also quenched at the end of the mission to preserve the composition of the liquid near the interface for post flight determination. A total of 450mm of directionally solidified samples were preserved for post mission structural and compositional characterization. Substantial differences were observed in the Seebeck signal between the ground-based experiments and the space-based experiments. The temperature gradient in the liquid for the ground-based experiments was significantly lower than the temperature gradient in the liquid for the space-based experiments.

  13. Solidification science in cast MMCs: The influence of merton flemings

    Rohatgi, Pradeep; Asthana, Rajiv


    The solidification science of cast metalmatrix composites (MMC) evolved as a subset of the broad field of solidification of monolithic alloys pioneered by Merton Flemings and his students. As a result of advances in solidification, the cast MMC field has evolved from its early incarnation—employing empirical research to engineer novel materials using versatile and cost-effective casting techniques—to using solidification-science-based approaches to tailor advanced materials for application-specific needs. The current and emerging applications of cast MMCs in a variety of automotive, aerospace, electronic packaging, and consumer-good industries exemplify the maturity of the field and the materials. Innovations in composite-forming techniques and efforts at wider industrial acceptance of MMCs will undoubtedly continue. However, the scientific principles underlying the solidification microstructure evolution that governs the composite properties have become well established, to a great extent, due to Flemings’ early, pioneering work on monolithic alloys and some of his more recent studies on solidification of reinforced metals. This paper reviews some aspects of solidification of discontinuously reinforced cast metals that owe their current understanding to Flemings’ contributions, in particular, the scientific understanding of macro- and microsegregation, fluidity and rheology of multiphase slurries, and stircasting, semi-solid casting, and preform infiltration. Current research to develop and test prototype components made from cast composites, including Al-flyash, Cu-graphite, Al-graphite, Al-alumina, and SiC-Al, is also presented, along with directions for future research.

  14. Thermoelectric and morphological effects of Peltier pulsing on directional solidification of eutectic Bi-Mn

    Silberstein, R. P.; Larson, D. J., Jr.; Dressler, B.


    Extensive in situ thermal measurements using Peltier Interface Demarcation (PID) during directional solidification of eutectic Bi/MnBi were carried out. Observations indicate that significant thermal transients occur throughout the sample as a result of the Peltier pulsing. The contributions of the Peltier, Thomson, and Joule heats were separated and studied as a function of pulse intensity and polarity. The Joule and the combined Peltier and Thomson thermal contributions were determined as a function of time during and after the current pulses, close to the solid/liquid interface. Variations of the Bi/MnBi particle morphology clearly reveal the interface shape, changes in interface velocity, meltback, and temporary loss of cooperative growth, as a result of the pulsing.

  15. Thermoelectric and morphological effects of peltier pulsing on directional solidification of eutectic Bi-Mn

    Silberstein, R. P.; Larson, D. J.; Dressler, B.


    We have carried out extensive in situ thermal measurements during Peltier Interface Demarcation (PID) during directional solidification of eutectic Bi/MnBi. We have observed that significant thermal transients occur throughout the sample as a result of the Peltier pulsing. We have separated the contributions of the Peltier, Thomson, and Joule heats, and studied them as a function of pulse intensity and polarity. The Joule and the combined Peltier and Thomson thermal contributions were determined as a function of time during and after the current pulses, close to the solid/liquid interface. Variations of the Bi/MnBi particle morphology clearly reveal the interface shape, changes in interface velocity, meltback, and temporary loss of cooperative growth, as a result of the pulsing.

  16. Oscillatory cellular patterns in three-dimensional directional solidification.

    Tourret, D; Debierre, J-M; Song, Y; Mota, F L; Bergeon, N; Guérin, R; Trivedi, R; Billia, B; Karma, A


    We present a phase-field study of oscillatory breathing modes observed during the solidification of three-dimensional cellular arrays in microgravity. Directional solidification experiments conducted onboard the International Space Station have allowed us to observe spatially extended homogeneous arrays of cells and dendrites while minimizing the amount of gravity-induced convection in the liquid. In situ observations of transparent alloys have revealed the existence, over a narrow range of control parameters, of oscillations in cellular arrays with a period ranging from about 25 to 125 min. Cellular patterns are spatially disordered, and the oscillations of individual cells are spatiotemporally uncorrelated at long distance. However, in regions displaying short-range spatial ordering, groups of cells can synchronize into oscillatory breathing modes. Quantitative phase-field simulations show that the oscillatory behavior of cells in this regime is linked to a stability limit of the spacing in hexagonal cellular array structures. For relatively high cellular front undercooling (i.e., low growth velocity or high thermal gradient), a gap appears in the otherwise continuous range of stable array spacings. Close to this gap, a sustained oscillatory regime appears with a period that compares quantitatively well with experiment. For control parameters where this gap exists, oscillations typically occur for spacings at the edge of the gap. However, after a change of growth conditions, oscillations can also occur for nearby values of control parameters where this gap just closes and a continuous range of spacings exists. In addition, sustained oscillations at to the opening of this stable gap exhibit a slow periodic modulation of the phase-shift among cells with a slower period of several hours. While long-range coherence of breathing modes can be achieved in simulations for a perfect spatial arrangement of cells as initial condition, global disorder is observed in both

  17. Localized microstructures induced by fluid flow in directional solidification.

    Jamgotchian, H; Bergeon, N; Benielli, D; Voge, P; Billia, B; Guérin, R


    The dynamical process of microstructure localization by multiscale interaction between instabilities is uncovered in directional solidification of transparent alloy. As predicted by Chen and Davis, morphological instability of the interface is observed at inward flow-stagnation regions of the cellular convective field. Depending on the driving force of fluid flow, focus-type and honeycomb-type localized patterns form in the initial transient of solidification, that then evolves with time. In the case of solute-driven flow, the analysis of the onset of thermosolutal convection in initial transient of solidification enables a complete understanding of the dynamics and of the localization of morphological instability.

  18. Capillary-wave description of rapid directional solidification.

    Korzhenevskii, Alexander L; Bausch, Richard; Schmitz, Rudi


    A recently introduced capillary-wave description of binary-alloy solidification is generalized to include the procedure of directional solidification. For a class of model systems a universal dispersion relation of the unstable eigenmodes of a planar steady-state solidification front is derived, which readjusts previously known stability considerations. We moreover establish a differential equation for oscillatory motions of a planar interface that offers a limit-cycle scenario for the formation of solute bands and, taking into account the Mullins-Sekerka instability, of banded structures.

  19. Experimental Investigations of Halogen and Noble Gas Geochemistry as Constraints on Planetary Outgassing

    Musselwhite, D. S.; Drake, M. J.; Swindle, T. D.


    Introduction The ^129Xe/^132Xe ratio in Mid-Ocean Ridge Basalts (MORBs) is higher than in the atmosphere and Ocean Island Basalts. Enhanced ^129Xe/^132Xe ratios are widely regarded to be the result of ^129I decay (t(sub)1/2 = 16 m.y.) early in solar system history (e.g. Swindle et al., 1986). Allegre et al. (1983, 1988) proposed a catastrophic degassing scheme to explain this excess. Both Musselwhite et al. (1990) and Hiyagon and Ozima (1990) have noted that because mineral/melt partition coefficients (D) for I appear lower than for Xe, the I/Xe ratio may not be enhanced in the mantle by mineral/melt fractionation. Musselwhite et al. (1990) proposed recycling of I back into the mantle following outgassing, and Hiyagon and Ozima (1990) proposed impact degassing of the mantle as a way around this problem. Knowledge of the relative values of D(I) and D(Xe) is important to the discussion of early planetary outgassing models. Although the dataset for D(I) values is not complete, the known values so far are uniformly low. The dataset for Xe on the other hand is quite ambiguous. Experimentally determined values for D(Xe) vary widely--ranging from 0.05 to >> 1 (Hiyagon and Ozima, 1986; Broadhurst et al., 1992), and it is unclear which of the values is the geologically significant one. Particularly important is the question of whether D(Xe) is greater than or less than unity. Partitioning Experiments: We have undertaken to simultaneously determine the D(I) and D(Ar) values directly, then calculate the D(Xe) from D(Ar). This approach is possible because experiments investigating the mineral/melt partitioning of noble gases, while not consistent in an absolute sense between experiments, do display a consistent trend with the lightest noble gases being most incompatible and Xe most compatible. We are adapting our technique to determine D(Kr) and D(Xe) directly. Finely crushed silica glass (~100 micrometer grain size) was placed in a gas pressure vessel. The vessel was

  20. Solidification of Al alloys under electromagnetic field



    New theories and technology in the electromagnetic field were put forward about DC casting of Al alloys, including the fundamental research works, I.e, effects of the electromagnetic field on solidus and liquidus, macrosegregation of the main alloying elements, microstructures, content of alloying elements in grains and grain size after solidification under electromagnetic field, and also including a new process-DC casting under low frequency electromagnetic field(LFEMC), which can refine microstructure, eliminate macrosegregation, increase the content of alloying elements within grains, decrease the residual stress, avoid cracks and improve surface quality, and another new process-DC casting under low frequency electromagnetic vibration(LFEVC), which is a high effective method for grain refining.

  1. Convection and morphological stability during directional solidification

    Coriell, Sam R.; Chernov, A. A.; Murray, Bruce T.; Mcfadden, G. B.


    For growth of a vicinal face at constant velocity, the effect of anisotropic interface kinetics on morphological stability is calculated for a binary alloy. The dependence of the interface kinetic coefficient on crystallographic orientation is based on the motion and density of steps. Anisotropic kinetics give rise to traveling waves along the crystal-melt interface, and can lead to a significant enhancement of morphological stability. The stability enhancement increases as the orientation approaches a singular orientation and as the solidification velocity increases. Shear flows interact with the traveling waves and, depending on the direction of the flow, may either stabilize or destabilize the interface. Specific calculations are carried out for germanium-silicon alloys.

  2. The cement solidification systems at LANL

    Veazey, G.W.


    There are two major cement solidification systems at Los Alamos National Laboratory. Both are focused primarily around treating waste from the evaporator at TA-55, the Plutonium Processing Facility. The evaporator receives the liquid waste stream from TA-55's nitric acid-based, aqueous-processing operations and concentrates the majority of the radionuclides in the evaporator bottoms solution. This is sent to the TA-55 cementation system. The evaporator distillate is sent to the TA-50 facility, where the radionuclides are precipitated and then cemented. Both systems treat TRU-level waste, and so are operated according to the criteria for WIPP-destined waste, but they differ in both cement type and mixing method. The TA-55 systems uses Envirostone, a gypsum-based cement and in-drum prop mixing; the TA-50 systems uses Portland cement and drum tumbling for mixing.

  3. The Complex Outgassing of Comets and the Resulting Coma, a Direct Simulation Monte-Carlo Approach

    Fougere, Nicolas

    During its journey, when a comet gets within a few astronomical units of the Sun, solar heating liberates gases and dust from its icy nucleus forming a rarefied cometary atmosphere, the so-called coma. This tenuous atmosphere can expand to distances up to millions of kilometers representing orders of magnitude larger than the nucleus size. Most of the practical cases of coma studies involve the consideration of rarefied gas flows under non-LTE conditions where the hydrodynamics approach is not valid. Then, the use of kinetic methods is required to properly study the physics of the cometary coma. The Direct Simulation Monte-Carlo (DSMC) method is the method of choice to solve the Boltzmann equation, giving the opportunity to study the cometary atmosphere from the inner coma where collisions dominate and is in thermodynamic equilibrium to the outer coma where densities are lower and free flow conditions are verified. While previous studies of the coma used direct sublimation from the nucleus for spherically symmetric 1D models, or 2D models with a day/night asymmetry, recent observations of comets showed the existence of local small source areas such as jets, and extended sources via sublimating icy grains, that must be included into cometary models for a realistic representation of the physics of the coma. In this work, we present, for the first time, 1D, 2D, and 3D models that can take into account the full effects of conditions with more complex sources of gas with jets and/or icy grains. Moreover, an innovative work in a full 3D description of the cometary coma using a kinetic method with a realistic nucleus and outgassing is demonstrated. While most of the physical models used in this study had already been developed, they are included in one self-consistent coma model for the first time. The inclusion of complex cometary outgassing processes represents the state-of-the-art of cometary coma modeling. This provides invaluable information about the coma by

  4. Outgassing in the lab: Permeability development in two-phase magmas during simple shear

    Kushnir, Alexandra; Martel, Caroline; Champallier, Rémi; Arbaret, Laurent


    The mechanisms governing permeability development in rising magmas influence the nature of volcanic outgassing and, consequently, eruption style. Of particular interest for any given system are: 1) the conditions under which permeability develops; 2) when permeability develops; and 3) the structure of the permeable network. To explore this, we performed a series of in-situ permeability measurements made during non-coaxial deformation of two-phase magmas at various shear strain rates. Samples were synthesized prior to each experiment by sintering a haplogranitic (HPG8) powder at a temperature of 1150° C. During synthesis, both the confining (PC) and pore fluid (Pf) pressures were equal to 300 MPa; the confining medium and pore fluid were argon. An effective pressure of 0 MPa (PC=Pf) ensured that bubbles trapped between the sintering grains were pressurized while the sample retained its cylindrical geometry. The magmas were then isothermally decompressed to 60 MPa to allow bubble expansion. Synthesized samples were impermeable and had bubble fractions between 0.11 and 0.14. Prior to deformation, the temperature was lowered to 880° C and a differential pore fluid pressure was applied across the sample. The magmas were deformed in torsion until the pore fluid pressures above and below the samples equilibrated, providing an in-situ measure of permeability. At low strain rates (7). In these samples, bubbles acted as passive strain markers and recorded the total strain on the sample. At shear strain rates between ˜2×10-4 and 4.5×10-4 s-1, samples experienced strain hardening until they became permeable at high strain (γ >3). The permeable network in these samples was constructed of en echelon, Mode I fractures distributed around the sample periphery. The bubble density adjacent to these features was reduced with respect to the rest of the sample, suggesting aspiration of surrounding bubbles into the fractures. Above shear strain rates of 4.5×10-4 s-1, permeability

  5. Experimental Determination of the Primary Solidification Phase dependency on the solidification velocity for 17 different austenitic stainless steel compositions

    Laursen, Birthe Nørgaard; Olsen, Flemming Ove; Yardy, John;


    to the austenite phase.Most stainless steels are weldable by conventional welding techniques. However, during laser weldng the solidification velocities can be very much higher than by conventional welding techniques. By increasing the solidification velocity to a critical value known as the transition velocity......, the primary solidification phase is found to change from ferrite to austenite.A novel laser remelting technique has been modified to enable the transition velocity for laser welded austenitic stainless steels to be deermined experimentally and on the basis of results from 17 different alloy compositions...... an equation for the calculation of the transition velocity from alloy composition is proposed....

  6. Fundamentals of Alloy Solidification Applied to Industrial Processes


    Solidification processes and phenomena, segregation, porosity, gravity effects, fluid flow, undercooling, as well as processing of materials in the microgravity environment of space, now available on space shuttle flights were discussed.

  7. Progress of Solidification Researches and the Applications in Materials Processing


    The research achievements of solidification theories and technologies in the last decades are reviewed with the stresses on some new development in the recent years. Some new interesting areas emerged in the last years are also pointed out.

  8. Effect Of Natural Convection On Directional Solidification Of Pure Metal

    Skrzypczak T.


    Full Text Available The paper is focused on the modeling of the directional solidification process of pure metal. During the process the solidification front is sharp in the shape of the surface separating liquid from solid in three dimensional space or a curve in 2D. The position and shape of the solid-liquid interface change according to time. The local velocity of the interface depends on the values of heat fluxes on the solid and liquid sides. Sharp interface solidification belongs to the phase transition problems which occur due to temperature changes, pressure, etc. Transition from one state to another is discontinuous from the mathematical point of view. Such process can be identified during water freezing, evaporation, melting and solidification of metals and alloys, etc.

  9. Rapid Solidification of AB5 Hydrogen Storage Alloys

    Gulbrandsen-Dahl, Sverre


    This doctoral thesis is concerned with rapid solidification of AB5 materials suitable for electrochemical hydrogen storage. The primary objective of the work has been to characterise the microstructure and crystal structure of the produced AB5 materials as a function of the process parameters, e.g. the cooling rate during rapid solidification, the determination of which has been paid special attention to.The thesis is divided in to 6 parts, of which Part I is a literature review, starting wit...

  10. Young organic matter as a source of carbon dioxide outgassing from Amazonian rivers

    Mayorga, E; Aufdenkampe, A K; Masiello, C A; Krusche, A V; Hedges, J I; Quay, P D; Richey, J E; Brown, T A


    Rivers are generally supersaturated with respect to carbon dioxide, resulting in large gas evasion fluxes that can be a significant component of regional net carbon budgets. Amazonian rivers were recently shown to outgas more than ten times the amount of carbon exported to the ocean in the form of total organic carbon or dissolved inorganic carbon. High carbon dioxide concentrations in rivers originate largely from in situ respiration of organic carbon, but little agreement exists about the sources or turnover times of this carbon. Here we present results of an extensive survey of the carbon isotope composition ({sup 13}C and {sup 14}C) of dissolved inorganic carbon and three size-fractions of organic carbon across the Amazonian river system. We find that respiration of contemporary organic matter (less than 5 years old) originating on land and near rivers is the dominant source of excess carbon dioxide that drives outgassing in mid-size to large rivers, although we find that bulk organic carbon fractions transported by these rivers range from tens to thousands of years in age. We therefore suggest that a small, rapidly cycling pool of organic carbon is responsible for the large carbon fluxes from land to water to atmosphere in the humid tropics.

  11. Increased CO2 outgassing in February-May 2010 in the tropical Atlantic

    Lefèvre, Nathalie; Caniaux, Guy; Janicot, Serge; Gueye, Abdou Karim


    The tropical Atlantic is a source of CO2 for the atmosphere but the magnitude of this source and its evolution with time are still poorly known. A CO2 network has been set up in the Atlantic to monitor the fugacity (partial pressure) of CO2 in the ocean. Two merchant ships sailing from France to French Guyana and from France to Brazil have been equipped with an automated CO2 system. On the France-Brazil line, the fCO2 distribution shows very high values in 2010 compared to 2009 and 2011. This anomaly occurred mainly in boreal spring (from February to May) between 10oS and 10oN with values as high as 10 to 15% than during the other years. At the basin scale, this anomaly was associated with higher than usual sea surface temperature and salinity. Moreover, reduced northeasterly winds were observed in the north-western Atlantic basin. In addition, the inter-tropical convergence zone was shifted northwards in boreal spring, an exceptional position never reached during the last 50 years. The anomalous physical conditions observed in 2010 led to an increased fCO2 outgassing in the tropical Atlantic compared to the years 2009 and 2011. This situation can be put in correlation with the high Pacific Nino index in 2009, an elevated AMO index and a strongly negative NAO index in 2010.

  12. Bubble dynamics inside an outgassing hydrogel confined in a Hele-Shaw cell

    Haudin, Florence; Noblin, Xavier; Bouret, Yann; Argentina, Médéric; Raufaste, Christophe


    We report an experimental study of bubble dynamics in a non-Newtonian fluid subjected to a pressure decrease. The fluid is a hydrogel, composed of water and a synthetic clay, prepared and sandwiched between two glass plates in a Hele-Shaw geometry. The rheological properties of the material can be tuned by the clay concentration. As the imposed pressure decreases, the gas initially dissolved in the hydrogel triggers bubble formation. Different stages of the process are observed: bubble nucleation, growth, interaction, and creation of domains by bubble contact or coalescence. Initially bubble behave independently. They are trapped and advected by the mean deformation of the hydrogel, and the bubble growth is mainly driven by the diffusion of the dissolved gas through the hydrogel and its outgassing at the reactive-advected hydrogel-bubble interface. In this regime, the rheology of the fluid does not play a significant role on the bubble growth. A model is proposed and gives a simple scaling that relates the bubble growth rate and the imposed pressure. Carbon dioxide is shown to be the gas at play, and the hydrogel is degassing at the millimeter scale as a water solution does at a smaller scale. Later, bubbles are not independent anymore. The growth rate decreases, and the morphology becomes more anisotropic as bubbles interact because they are separated by a distance smaller than the individual stress field extension. Our measurements show that the interaction distance scales with the bubbles' size.

  13. Substantial outgassing of CO from comet Hale-Bopp at large heliocentric distance.

    Biver, N; Rauer, H; Despois, D; Moreno, R; Paubert, G; Bockelée-Morvan, D; Colom, P; Crovisier, J; Gérard, E; Jorda, L


    When comet C/1995 O1 (Hale-Boop) was discovered, at a distance of seven astronomical units from the sun, it was more than one hundred times brighter than comet Halley at the same distance. A comet's brightness is derived from the reflection of sunlight from dust grains driven away from the nucleus by the sublimation of volatile ices. Near the sun, sublimation of water ice (a main constituent of comet nuclei) is the source of cometary activity; but at its current heliocentric distance, Hale-Boop is too cold for this process to operate. Other comets have shown activity at large distances, and in the case of comet Schwassmann-Wachmann 1, carbon monoxide has been detected in quantities sufficient to generate its observed coma. Here we report the detection of CO emission from Hale-Boop, at levels indicating a very large rate of outgassing. Several other volatile species were searched for, but not detected. Sublimation of CO therefore appears to be responsible for the present activity of this comet, and we anticipate that future observations will reveal the onset of sublimation of other volatile species as the comet continues its present journey towards the sun.

  14. Evidence for multiple magma ocean outgassing and atmospheric loss episodes from mantle noble gases

    Tucker, Jonathan M


    The energy associated with giant impacts is large enough to generate global magma oceans during Earth's accretion. However, geochemical evidence requiring a terrestrial magma ocean is scarce. Here we present evidence for at least two separate magma ocean outgassing episodes on Earth based on the ratio of primordial 3He to 22Ne in the present-day mantle. We demonstrate that the depleted mantle 3He/22Ne ratio is at least 10 while a more primitive mantle reservoir has a 3He/22Ne ratio of 2.3 to 3. The 3He/22Ne ratios of the mantle reservoirs are higher than possible sources of terrestrial volatiles, including the solar nebula ratio of 1.5. Therefore, a planetary process must have raised the mantle's 3He/22Ne ratio. We show that long-term plate tectonic cycling is incapable of raising the mantle 3He/22Ne ratio and may even lower it. However, ingassing of a gravitationally accreted nebular atmosphere into a magma ocean on the proto-Earth explains the 3He/22Ne and 20Ne/22Ne ratios of the primitive mantle reservoir....

  15. The relationship between dissolution, gas oversaturation and outgassing of solutions determined by Broadband Acoustic Resonance Dissolution Spectroscopy (BARDS).

    Fitzpatrick, Dara; Evans-Hurson, Rachel; Krüse, Jacob; Vos, Bastiaan; McSweeney, Seán; Casaubieilh, Pierre; O'Gorman, Eadaoin


    The addition of a solute to a solvent is known to reduce the solubility of dissolved gases in solution which leads to gas oversaturation and outgassing of the solvent. The importance of the processes involved have received relatively little attention due to a limited capacity to elucidate their effects in real time. Broadband Acoustic Resonance Dissolution Spectroscopy (BARDS) is a recently introduced acoustic approach which can monitor changes in the compressibility of a solvent due to outgassing. BARDS spectra show that a time dependent and quantitative reduction in gas oversaturation, following the dissolution of a simple salt, takes place over several hours. It is shown how vigorous agitation quickly equilibrates a solution, post dissolution, by removing gas oversaturation consistently. The level of oversaturation can be elucidated by further dissolving a marker compound into a solution consecutively. BARDS spectra indicate that the dissolution of a compound produces a consistent and quantifiable oversaturation of a solvent and a consistent and quantifiable outgassing. Low frequency sonication in an immersion bath is also shown to play no significant role in removing gas oversaturation post dissolution.

  16. Analytical investigation of the decrease in the size of the habitable zone due to limited CO$_2$ outgassing rate

    Abbot, Dorian S


    The habitable zone concept is important because it focuses the scientific search for extraterrestrial life and aids the planning of future telescopes. Recent work has shown that planets near the outer edge of the habitable zone might not actually be able to stay warm and habitable if CO$_2$ outgassing rates are not large enough to maintain high CO$_2$ partial pressures against removal by silicate weathering. In this paper I use simple equations for the climate and CO$_2$ budget of a planet in the habitable zone that can capture the qualitative behavior of the system. With these equations I derive an analytical formula for an effective outer edge of the habitable zone, including limitations imposed by the CO$_2$ outgassing rate. I then show that climate cycles between a Snowball state and a warm climate are only possible beyond this limit if the weathering rate in the Snowball climate is smaller than the CO$_2$ outgassing rate (otherwise stable Snowball states result). I derive an analytical solution for the c...

  17. Analytical Investigation of the Decrease in the Size of the Habitable Zone Due to a Limited CO2 Outgassing Rate

    Abbot, Dorian S.


    The habitable zone concept is important because it focuses the scientific search for extraterrestrial life and aids the planning of future telescopes. Recent work has shown that planets near the outer edge of the habitable zone might not actually be able to stay warm and habitable if CO2 outgassing rates are not large enough to maintain high CO2 partial pressures against removal by silicate weathering. In this paper, I use simple equations for the climate and CO2 budget of a planet in the habitable zone that can capture the qualitative behavior of the system. With these equations I derive an analytical formula for an effective outer edge of the habitable zone, including limitations imposed by the CO2 outgassing rate. I then show that climate cycles between a snowball state and a warm climate are only possible beyond this limit if the weathering rate in the snowball climate is smaller than the CO2 outgassing rate (otherwise stable snowball states result). I derive an analytical solution for the climate cycles including a formula for their period in this limit. This work allows us to explore the qualitative effects of weathering processes on the effective outer edge of the habitable zone, which is important because weathering parameterizations are uncertain.

  18. Getting in shape: molten wax drop deformation and solidification at an immiscible liquid interface.

    Beesabathuni, Shilpa N; Lindberg, Seth E; Caggioni, Marco; Wesner, Chris; Shen, Amy Q


    The controlled production of non-spherical shaped particles is important for many applications such as food processing, consumer goods, adsorbents, drug delivery, and optical sensing. In this paper, we investigated the deformation and simultaneous solidification of millimeter size molten wax drops as they impacted an immiscible liquid interface of higher density. By varying initial temperature and viscoelasticity of the molten drop, drop size, impact velocity, viscosity and temperature of the bath fluid, and the interfacial tension between the molten wax and bath fluid, spherical molten wax drops impinged on a cooling water bath and were arrested into non-spherical solidified particles in the form of ellipsoid, mushroom, disc, and flake-like shapes. We constructed cursory phase diagrams for the various particle shapes generated over a range of Weber, Capillary, Reynolds, and Stefan numbers, governed by the interfacial, inertial, viscous, and thermal effects. We solved a simplified heat transfer problem to estimate the time required to initiate the solidification at the interface of a spherical molten wax droplet and cooling aqueous bath after impact. By correlating this time with the molten wax drop deformation history captured from high speed imaging experiments, we elucidate the delicate balance of interfacial, inertial, viscous, and thermal forces that determine the final morphology of wax particles.

  19. Influence of Lanthanum on Solidification, Microstructure, and Mechanical Properties of Eutectic Al-Si Piston Alloy

    Ahmad, R.; Asmael, M. B. A.


    The effects of Lanthanum (La) concentration on the solidification parameters of the α-Al, Al-Si, and Al-Cu phases and on the microstructure, tensile, and hardness properties of eutectic Al-Si-Cu-Mg alloy were systematically investigated. The solidification parameters were examined using computer-aided cooling curve thermal analysis (CA-CCTA). The cooling curve and microstructure analysis showed that La altered the Si structure. The nucleation and growth temperatures of eutectic Si decreased when 0.3 wt.% La was added, and a high depression temperature was obtained with 1.0 wt.% La. High amounts of La considerably modified the Si structure and decreased the area and aspect ratio by 69.9 and 51%, respectively. The thermal analysis result recorded a faster freezing time with the La addition and a 36% alteration in the secondary dendrite arm spacing. Two secondary or ternary La-rich intermetallic phases were formed with needle- and plate-like structures. Furthermore, the mechanical properties were investigated by hardness and tensile tests with different La concentrations. The addition of small amounts of La (0.1 wt.%) significantly improved the ultimate tensile strength and quality index of the Al-Si-Cu-Mg alloy. In addition, the hardness value of Al-11Si-Cu increased by 7-8% with the increasing amount of La added.

  20. Finite volume modeling of the solidification of an axial steel cast impeller

    M. Copur


    Full Text Available In the foundry industry, obtaining the solidification contours in cast geometries are extremely important to know the last location(s to solidify in order to define the correct feeding path and the number of risers. This paper presents three-dimensional simulation of transient conduction heat transfer within an axial impeller, made of AISI 1016 steel, poured and solidified in chemically bonded mold and core medium, by using FVM technique and ANSYS CFX. Specific heat, density and thermal conductivity of AISI 1016 steel, mold and Core materials are considered as functions of temperatures. In this transient thermal analysis, the convection heat transfer phenomenon is also considered at the outer surfaces of the mold. In order to shorten the run-time, the nonlinear transient analysis has been made for 600/3600 segment of the impeller, core and mold. The solidification contours of the impeller as well as isothermal lines in core and mold have been obtained in 3-D. The cooling curves of diff erent points are also shown in the result section.

  1. Transient Simulation of Mold Heat Transfer and Solidification Phenomena of Continuous Casting of Steel

    El-Bealy, Mostafa Omar


    A comprehensive model of heat transfer and solidification phenomena has been developed including microstructure evolution and fluctuation macrosegregation in continuously cast steel slabs with an objective of evaluation of various mold cooling conditions. The study contains plant trials, metallographic examinations, and formulation of mathematical modeling. The plant trials involved sample collection from three slab casters in use at two different steel plants. The metallographic study combined measurements of dendrite arm spacings and macrosegregation analysis of collected samples. A one-dimensional mathematical model has been developed to characterize the thermal, solidification phases, microstructure evolution, interdendritic strain, and therefore, the macrosegregation distributions. Two cooling approaches were proposed in this study to evaluate the Newtonian heat transfer coefficient in various mold regions. The first approach is a direct estimation approach (DEA), whereas the second one is a coupled approach of the interfacial resistor model and direct estimation approach (CIR/DEA). The model predictions and standard analytical models as well as the previous measurements were compared to verify and to calibrate the model where good agreements were obtained. The comparison between the model predictions and the measurements of dendrite arm spacings and fluctuated carbon concentration profiles were performed to determine the model accuracy level with different cooling approaches. Good agreements were obtained by different accuracy levels with different cooling approaches. The model predictions of thermal parameters and isotherms were analyzed and discussed.

  2. Proceedings of the 2010 international solidification-stabilization technology forum

    Lake, C.B. [Dalhousie Univ., Halifax, NS (Canada). Dept. of Civil and Resource Engineering; Hills, C.D. [Greenwich Univ. (United Kingdom). Centre for Contaminated Land Remediation] (eds.)


    Solidification/stabilization (S/S) is remediation technology used to manage the risk associated with contaminated soils, wastes, and brownfield sites. Canada is now facing considerable challenges in ensuring that sites impacted by hydrocarbon contaminants are efficiently and effectively remediated. This forum was held to bring together leading researchers and practitioners in S/S remediation technology. Recent advances in research were presented, as well as new developments in the implementation of S/S technologies in the field, and methods of safely stabilizing and using potentially hazardous waste products. The conference was divided into the following 8 sessions: (1) stabilization/solidification of organics, (2) stabilization/solidification case studies, (3) stabilization/solidification of metals, (4) performance assessment, (5) mining applications, (6) new stabilization/solidification applications and approaches, (7) marine/coastal applications, and (8) stabilization/solidification amendments or alternatives. The forum featured 28 presentations, of which 6 have been catalogued separately for inclusion in this database. refs., figs.

  3. Experimental Determination of the Primary Solidification Phase dependency on the solidification velocity for 17 different austenitic stainless steel compositions

    Laursen, Birthe Nørgaard; Olsen, Flemming Ove; Yardy, John


    When studying laser welding of austenitic stainless steel, hot cracking is frequently observed. To prevent hot cracking in laser welded stainless steel it is advantageous to obtain primary solidification of the ferrite phase that subsequently, on cooling, transforms in the solid state...... to the austenite phase.Most stainless steels are weldable by conventional welding techniques. However, during laser weldng the solidification velocities can be very much higher than by conventional welding techniques. By increasing the solidification velocity to a critical value known as the transition velocity......, the primary solidification phase is found to change from ferrite to austenite.A novel laser remelting technique has been modified to enable the transition velocity for laser welded austenitic stainless steels to be deermined experimentally and on the basis of results from 17 different alloy compositions...

  4. Numerical Simulation of Steady State Conduction Heat Transfer During the Solidification of Aluminum Casting in Green Sand Mould

    Victor ANJO


    Full Text Available The solidification of molten metal during the casting process involves heat transfer from the molten metal to the mould, then to the atmosphere. The mechanical properties and grain size of metals are determined by the heat transfer process during solidification. The aim of this study is to numerically stimulate the steady conduction heat transfer during the solidification of aluminum in green sand mould using finite difference analysis 2D. The properties of materials used are industrial AI 50/60 AFS green sand mould, pure aluminum and MATLAB 7.0.1. for the numerical simulation. The method includes; the finite difference analysis of the heat conduction equation in steady (Laplace’s and transient states and using MATLAB to numerically stimulate the thermal flow and cooling curve. The results obtained are: the steady state thermal flow in 2D and transient state cooling curve of casting. The results obtain were consider relevant in the control of the grain size and mechanical properties of the casting.

  5. Melting and solidification characteristics of a mixture of two types of latent heat storage material in a vessel

    Yu, JikSu; Horibe, Akihiko; Haruki, Naoto; Machida, Akito; Kato, Masashi


    In this study, we investigated the fundamental melting and solidification characteristics of mannitol, erythritol, and their mixture (70 % by mass mannitol: 30 % by mass erythritol) as potential phase-change materials (PCMs) for latent heat thermal energy storage systems, specifically those pertaining to industrial waste heat, having temperatures in the range of 100-250 °C. The melting point of erythritol and mannitol, the melting peak temperature of their mixture, and latent heat were measured using differential scanning calorimetry. The thermal performance of the mannitol mixture was determined during melting and solidification processes, using a heat storage vessel with a pipe heat exchanger. Our results indicated phase-change (fusion) temperatures of 160 °C for mannitol and 113 and 150 °C for the mannitol mixture. Nondimensional correlation equations of the average heat transfer during the solidification process, as well as the temperature and velocity efficiencies of flowing silicon oil in the pipe and the phase-change material (PCM), were derived using several nondimensional parameters.

  6. Numerical study on morphology and solidification characteristics of successive droplet depositions on a substrate

    Adaikalanathan, Vimalan

    Successive droplet impingement finds extensive applications in additive manufacturing technologies such as 3D printing, Liquid Metal Jetting and Net Form Manufacturing. Deposition, deformation and solidification of droplets are the constitutive stages in the process which determine the final outcome. Detailed knowledge about the flow behaviour, phase transformation and free surface deformation is required to have a complete understanding and optimization of the process parameters. Experimental research in this field is only limited to imaging techniques and post solidification analysis which only provide superficial information while overlooking most of the governing phenomenon. Knowledge of the physics governing the fluid and thermal behaviours can be applied to study the process with real time data pertaining to flow field, temperature profiles and solidification. However, free surface tracking, surface tension modelling, non-isothermal solidification and convection dominant heat transfer pose mathematical challenges in the solution of the governing equations. Moreover, deposition of droplets on pre-solidified splats or non-flat surfaces requires accurate special attention. The objective of the present work is to model the successive droplet impacts and simultaneous solidification and deformation. The highly non-linear flow field governed by the Navier Stokes equation is solved using a Two Step Projection method. The surface tension effects are accounted for through a Continuum Surface Force technique. One of the crucial elements in the study is the interface tracking algorithm. A Coupled Level Set Volume of Fluid (CLSVOF) method is formulated to give an accurate orientation of the drastically deforming interface and also facilitates generation of multiple droplets in a fixed domain at a user defined frequency, thereby conserving computational resources. The phase change is modelled using an enthalpy formulation of the energy equation with an implicit source term

  7. The solidification and structure of Al-17wt.%Si alloy modified with intermetallic phases containing Ti and Fe

    J. Piątkowski


    Full Text Available The article describes the process of casting and solidification of Al-17wt.%Si alloy that have been modified with composite powdercontaining the intermetallic phases of Ti and Fe. The chemical and phase composition of the applied modifier was described with thefollowingformula:FeAlx–TiAlx–Al2O3. Applying the method of thermal analysis ATD, the characteristic parameters of the solidificationprocess were determined, and exo-and endothermic effects of the modifying powder on the run of the silumin solidification curves wereobserved. By the methods of light, scanning, and X-ray microscopy, the structure of alloy and the chemical composition of the dispersionhardening precipitates were examined. A change in the morphology of Al-Si eutectic from the lamellar to fibrous type was reportedtogether with changes in the form of complex eutectics of an Al-Si-Ti and Al-Si-Fe type and size reduction of primary silicon crystals.

  8. Is it reasonable to assume a uniformly distributed cooling-rate along the microslide of a directional solidification stage?



    It is commonly assumed that the cooling-rate along the microslide of a directional solidification stage is uniformly distributed, an assumption which is typically applied in low cooling-rates studies. A new directional solidification stage has recently been presented, which is specified to achieve high cooling-rates of up to 1.8 x 104 degrees C min-1, where cooling-rates are still assumed to be uniformly distributed. The current study presents a closed-form solution to the temperature distribution and to the cooling-rate in the microslide. Thermal analysis shows that the cooling-rate is by no means uniformly distributed and can vary by several hundred percent along the microslide in some cases. Therefore, the mathematical solution presented in this study is essential for experimental planning of high cooling-rate experiments.

  9. Numerical study of the spreading and solidification of a molten particle impacting onto a rigid substrate under plasma spraying conditions

    Oukach Soufiane


    Full Text Available This paper deals with simulation of the spreading and solidification of a fully molten particle impacting onto a preheated substrate under traditional plasma spraying conditions. The multiphase problem governing equations of mass, momentum and energy conservation taking into account heat transfer by conduction, convection and phase change are solved by using a Finite Element approach. The interface between molten particle and surrounding air, is tracked using the Level Set method. The effect of the Reynolds number on the droplet spreading and solidification, using a wide range of impact velocities (40-250m/s, is reported. A new correlation that predicts the final spread factor of splat as a function of Reynolds number is obtained. Thermal contact resistance, viscous dissipation, wettability and surface tension forces effects are taken into account.

  10. Photochemically reversible liquefaction and solidification of multiazobenzene sugar-alcohol derivatives and application to reworkable adhesives.

    Akiyama, Haruhisa; Kanazawa, Satoshi; Okuyama, Yoko; Yoshida, Masaru; Kihara, Hideyuki; Nagai, Hideki; Norikane, Yasuo; Azumi, Reiko


    Multiazobenzene compounds, hexakis-O-[4-(phenylazo)phenoxyalkylcarboxyl]-D-mannitols and hexakis-O-[4-(4-hexylphenylazo)phenoxyalkylcarboxyl]-D-mannitols, exhibit photochemically reversible liquefaction and solidification at room temperature. Their photochemical and thermal phase transitions were investigated in detail through thermal analysis, absorption spectroscopy, and dynamic viscoelasticity measurements, and were compared with those of other sugar-alcohol derivatives. Tensile shear strength tests were performed to determine the adhesions of the compounds sandwiched between two glass slides to determine whether the compounds were suitable for application as adhesives. The adhesions were varied by alternately irradiating the compounds with ultraviolet and visible light to photoinduce phase transitions. The azobenzene hexyl tails, lengths of the methylene spacers, and differences in the sugar-alcohol structures affected the photoresponsive properties of the compounds.

  11. Aluminum alloy weldability. Identification of weld solidification cracking mechanisms through novel experimental technique and model development

    Coniglio, Nicolas


    The objective of the present thesis is to make advancements in understanding solidification crack formation in aluminum welds, by investigating in particular the aluminum 6060/4043 system. Alloy 6060 is typical of a family of Al-Mg-Si extrusion alloys, which are considered weldable only when using an appropriate filler alloy such as 4043 (Al-5Si). The effect of 4043 filler dilution (i.e. weld metal silicon content) on cracking sensitivity and solidification path of Alloy 6060 welds are investigated. Afterwards, cracking models are developed to propose mechanisms for solidification crack initiation and growth. Cracking Sensitivity. Building upon the concept that silicon improves weldability and that weldability can be defined by a critical strain rate, strain rate-composition combinations required for solidification crack formation in the Al- 6060/4043 system were determined using the newly developed Controlled Tensile Weldability (CTW) test utilizing local strain extensometer measurements. Results, presented in a critical strain rate - dilution map, show a crack - no crack boundary which reveals that higher local strain rates require higher 4043 filler dilution to avoid solidification cracking when arc welding Alloy 6060. Using the established crack - no crack boundary as a line of reference, additional parameters were examined and their influence on cracking characterized. These parameter influences have included studies of weld travel speed, weld pool contaminants (Fe, O, and H), and grain refiner additions (TiAl{sub 3} + Boron). Each parameter has been independently varied and its effect on cracking susceptibility quantified in terms of strain rate - composition combinations. Solidification Path. Solidification path of the Al-6060/4043 system was characterized using thermal analysis and phase identification. Increasing 4043 filler dilution from 0 to 16% in Alloy 6060 arc welds resulted in little effect on thermal arrests and microstructure, no effect on

  12. Stabilization/solidification of TSCA incinerator ash

    Spence, R.D.; Trotter, D.R.; Francis, C.L.; Morgan, I.L.


    Stabilization/solidification is a well-known waste treatment technique that utilizes different additives and processes. The Phoenix Ash Technology of the Technical Innovation Development Engineering Company is such a technique that uses Cass C fly ash and mechanical pressure to make brick waste forms out of solid wastes, such as the bottom ash from the Toxic Substances Control Act incinerator at the Oak Ridge K-25 Site. One advantage of this technique is that no volume increase over the bulk volume of the bottom ash occurs. This technique should have the same high pH stabilization for Resource Conservation and Recovery Act metals as similar techniques. Also, consolidation of the bottom ash minimizes the potential problems of material dispersion and container corrosion. The bottom ash was spiked with {sup 99}{Tc} to test the effectiveness of the bricks as a physical barrier. The {sup 99}{Tc} leachability index measured for these bricks was 6.8, typical for the pertechnetate anion in cementitious waste forms, indicating that these bricks have accessible porosity as high as that of other cementitious waste forms, despite the mechanical compression, higher waste form density, and water resistant polymer coating.

  13. Crustal fingering: solidification on a moving interface

    Fu, Xiaojing; Jimenez-Martinez, Joaquin; Porter, Mark; Cueto-Felgueroso, Luis; Juanes, Ruben


    Viscous fingering-the hydrodynamic instability that takes place when a less viscous fluid displaces a more viscous fluid-is a well known phenomenon. Motivated by the formation of gas hydrates in seafloor sediments and during the ascent of gas bubbles through ocean water, here we study the interplay of immiscible viscous fingering with solidification of the evolving unstable interface. We present experimental observations of the dynamics of a bubble of Xenon in a water-filled and pressurized Hele-Shaw cell. The evolution is controlled by two processes: (1) the formation of a hydrate "crust" around the bubble, and (2) viscous fingering from bubble expansion. To reproduce the experimental observations, we propose a phase-field model that describes the nucleation and thickening of a porous solid shell on a moving gas-liquid interface. We design the free energy of the three-phase system (gas-liquid-hydrate) to rigorously account for interfacial effects, mutual solubility, and phase transformations (hydrate formation and disappearance). We introduce a pseudo-plasticity model with large variations in viscosity to describe the plate-like rheology of the hydrate shell. We present high-resolution numerical simulations of the model, which illustrate the emergence of complex "crustal fingering" patterns as a result of gas fingering dynamics modulated by hydrate growth at the interface.

  14. A new coupled model for alloy solidification

    LI Daming; LI Ruo; ZHANG Pingwen


    A new coupled model in the binary alloy solidification has been developed. The model is based on the cellular automaton (CA)technique to calculate the evolution of the interface governed by temperature, solute diffusion and Gibbs-Thomson effect. The diffusion equation of temperature with the release of latent heat on the solid/liquid (S/L) interface is valid in the entire domain.The temperature diffusion without the release of latent heat and solute diffusion are solved in the entire domain. In the interface cells, the energy and solute conservation, thermodynamic and chemical potential equilibrium are adopted to calculate the temperature, solid concentration, liquid concentration and the increment of solid fraction. Compared with other models where the release of latent heat is solved in implicit or explicit form according to the solid/liquid (S/L) interface velocity, the energy diffusion and the release of latent heat in this model are solved at differentscales, I.e. The macro-scale and micro-scale. The variation ofsolid fraction in this model is solved using several algebraicrelations coming from the chemical potential equilibrium andthermodynamic equilibrium which can be cheaply solved insteadof the calculation of S/L interface velocity. With the assumptionof the solute conservation and energy conservation, the solidfraction can be directly obtained according to the thermodynamicdata. This model is natural to be applied to multiple (>2)spatial dimension case and multiple (>2) component alloy. Themorphologies of equiaxed dendrite are obtained in numericalexperiments.

  15. Weld solidification cracking in 304 to 204L stainless steel

    Hochanadel, Patrick W [Los Alamos National Laboratory; Lienert, Thomas J [Los Alamos National Laboratory; Martinez, Jesse N [Los Alamos National Laboratory; Johnson, Matthew Q [Los Alamos National Laboratory


    A series of annulus welds were made between 304 and 304L stainless steel coaxial tubes using both pulsed laser beam welding (LBW) and pulsed gas tungsten arc welding (GTAW). In this application, a change in process from pulsed LBW to pulsed gas tungsten arc welding was proposed to limit the possibility of weld solidification cracking since weldability diagrams developed for GTAW display a greater range of compositions that are not crack susceptible relative to those developed for pulsed LBW. Contrary to the predictions of the GTAW weldability diagram, cracking was found.This result was rationalized in terms of the more rapid solidification rate of the pulsed gas tungsten arc welds. In addition, for the pulsed LBW conditions, the material compositions were predicted to be, by themselves, 'weldable' according to the pulsed LBW weldability diagram. However, the composition range along the tie line connecting the two compositions passed through the crack susceptible range. Microstructurally, the primary solidification mode (PSM) of the material processed with higher power LBW was determined to be austenite (A), while solidification mode of the materials processed with lower power LBW apparently exhibited a dual PSM of both austenite (A) and ferrite-austenite (FA) within the same weld. The materials processed by pulsed GTAW showed mostly primary austenite solidification, with some regions of either primary austenite-second phase ferrite (AF) solidification or primary ferrite-second phase austenite (FA) solidification. This work demonstrates that variations in crack susceptibility may be realized when welding different heats of 'weldable' materials together, and that slight variations in processing can also contribute to crack susceptibility.

  16. Weld solidification cracking in 304 to 304L stainless steel

    Hochanadel, Patrick W [Los Alamos National Laboratory; Lienert, Thomas J [Los Alamos National Laboratory; Martinez, Jesse N [Los Alamos National Laboratory; Martinez, Raymond J [Los Alamos National Laboratory; Johnson, Matthew Q [Los Alamos National Laboratory


    A series of annulus welds were made between 304 and 304L stainless steel coaxial tubes using both pulsed laser beam welding (LBW) and pulsed gas tungsten arc welding (GTAW). In this application, a change in process from pulsed LBW to pulsed gas tungsten arc welding was proposed to limit the possibility of weld solidification cracking since weldability diagrams developed for GTAW display a greater range of compositions that are not crack susceptible relative to those developed for pulsed LBW. Contrary to the predictions of the GTAW weldability diagram, cracking was found. This result was rationalized in terms of the more rapid solidification rate of the pulsed gas tungsten arc welds. In addition, for the pulsed LBW conditions, the material compositions were predicted to be, by themselves, 'weldable' according to the pulsed LBW weldability diagram. However, the composition range along the tie line connecting the two compositions passed through the crack susceptible range. Microstructurally, the primary solidification mode (PSM) of the material processed with higher power LBW was determined to be austenite (A), while solidification mode of the materials processed with lower power LBW apparently exhibited a dual PSM of both austenite (A) and ferrite-austenite (FA) within the same weld. The materials processed by pulsed GT A W showed mostly primary austenite solidification, with some regions of either primary austenite-second phase ferrite (AF) solidification or primary ferrite-second phase austenite (FA) solidification. This work demonstrates that variations in crack susceptibility may be realized when welding different heats of 'weldable' materials together, and that slight variations in processing can also contribute to crack susceptibility.


    Meech, Karen J.; Yang, Bin; Kleyna, Jan; Chiang, Hsin-Fang; Riesen, Timm; Keane, Jacqueline V.; Reipurth, Bo; Hsieh, Henry H. [NASA Astrobiology Institute, Honolulu, HI 96822 (United States); Ansdell, Megan [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Hainaut, Olivier [European Southern Observatory, Santiago 19001 (Chile); Vincent, Jean-Baptiste; Boehnhardt, Hermann [Max-Planck-Institut fur Sonnensystemforschung, Max-Planck-Strasse 2, D-37191 Katlenburg-Lindau (Germany); Fitzsimmons, Alan [Queens University Belfast, Belfast BT7 1NN (United Kingdom); Rector, Travis [Department of Physics and Astronomy, University of Alaska Anchorage, 3211 Providence Drive, Anchorage, AK 99508 (United States); Michaud, Peter [Gemini Observatory, Northern Operations Center, 670 North A' ohoku Place, Hilo, HI 96720 (United States); Milani, Giannantonio [Associazione Astronomica Euganea, via Tommaseo, I-35131 Padova (Italy); Bryssinck, Erik [BRIXIIS Observatory, Eyckensbeekstraat, B-9150 Kruibeke (Belgium); Ligustri, Rolando [Talmassons Observatory (C.A.S.T.), via Cadorna, I-33030 Talmassons (Italy); Trabatti, Roberto [Stazione Astronomica Descartes, via Lambrinia 4, I-2013 Chignolo Po' (Italy); Tozzi, Gian-Paolo, E-mail: [INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-40125 Firenze (Italy); and others


    We report photometric observations for comet C/2012 S1 (ISON) obtained during the time period immediately after discovery (r = 6.28 AU) until it moved into solar conjunction in mid-2013 June using the UH2.2 m, and Gemini North 8 m telescopes on Mauna Kea, the Lowell 1.8 m in Flagstaff, the Calar Alto 1.2 m telescope in Spain, the VYSOS-5 telescopes on Mauna Loa Hawaii and data from the CARA network. Additional pre-discovery data from the Pan STARRS1 survey extends the light curve back to 2011 September 30 (r = 9.4 AU). The images showed a similar tail morphology due to small micron sized particles throughout 2013. Observations at submillimeter wavelengths using the James Clerk Maxwell Telescope on 15 nights between 2013 March 9 (r = 4.52 AU) and June 16 (r = 3.35 AU) were used to search for CO and HCN rotation lines. No gas was detected, with upper limits for CO ranging between 3.5-4.5 × 10{sup 27} molecules s{sup –1}. Combined with published water production rate estimates we have generated ice sublimation models consistent with the photometric light curve. The inbound light curve is likely controlled by sublimation of CO{sub 2}. At these distances water is not a strong contributor to the outgassing. We also infer that there was a long slow outburst of activity beginning in late 2011 peaking in mid-2013 January (r ∼ 5 AU) at which point the activity decreased again through 2013 June. We suggest that this outburst was driven by CO injecting large water ice grains into the coma. Observations as the comet came out of solar conjunction seem to confirm our models.

  18. Preparation of the initial solid liquid interface and melt in directional solidification

    Nguyen Thi, H.; Drevet, B.; Debierre, J. M.; Camel, D.; Dabo, Y.; Billia, B.


    The preparation of the initial conditions (solid-liquid interface morphology and solute segregation in the liquid phase) on which growth is started is a very critical step in directional-solidification experiments. Dedicated experiments on Al-1.5 wt% Ni consisting in directional melting followed by thermal stabilisation with different lengths, show that precise control is in practice not straightforward. Indeed, in the mushy zone created by melting the original solid sample, temperature gradient zone melting (TGZM) causes migration of solute-rich liquid droplets and channels. A model is proposed to describe this process and validate the physical interpretation of the experiments through numerical simulation. Knowing the status of the preparation, the intriguing observations in the partially melted region of the Al-1.5 wt% Ni alloys solidified in the Advanced Gradient Heating Facility of European Space Agency during the LMS and STS-95 space missions can now be explained. Finally, the influence of initial interface morphology and melt segregation on directional-solidification transient is discussed, based on a comparison of Al-Ni alloys with hypoeutectic Al-Li alloys previously grown on Earth and in space. It follows that for experiments achieved on original rods with equiaxed microstructure, the efficiency of the preparatory melting and stabilisation phases can be evaluated from the solute macrosegregation profile in the region in between the non-melted solid and directional solidification. The major conclusion is that when the melt is mixed by fluid flow, the initial conditions are near to their asymptotic state at the end of TGZM whereas, when solute diffusion is the mode of transport into the bulk liquid, the condition of homogeneous melt becomes limiting and too much time-consuming to be fulfilled, which in particular holds for the 3D-experiments carried out in the reduced-gravity environment of space.

  19. Thermal and structural characteristics of the AM50 magnesium alloy

    M. Sahoo


    Full Text Available Purpose: The goal of this publication is to demonstrate the laboratory metal casting simulation methodology based on controlled melting and solidification experiments. The thermal characteristics of the AM50 magnesium alloy during melting and solidification cycles were determined and correlated with the test samples’ microstructural parameters.Design/methodology/approach: A novel methodology allowed to perform variable solidification rates for stationary test samples. The experiments were performed using computer controlled induction heating and cooling sources using Argon for melt protection and test sample cooling.Findings: Thermal analysis data indicated that the alloy’s melting range was between approximately 434 and 640°C. Increasing the cooling rate from 1 to 4°C/s during solidification process reduced the Secondary Dendrite Arm Spacing from approximately 64 to 43μm. The temperatures of the metallurgical reactions were shifted toward the higher values for faster solidification rates. Fraction liquid curve indicates that at the end of melting of the α(Mg-β(Mg17Al12 eutectic, i.e., 454.2ºC the alloy had a 2% liquid phase.Research limitations/implications: Future research is intended to address the development of a physical simulation methodology representing very high solidification rates used by High Pressure Die Casting (HPDC and to assess the microstructure refinement as a function of solidification rates.Practical implications: Advanced simulation capabilities including non-equilibrium thermal and structural characteristics of the magnesium alloys are required for the development of advanced metal casting technologies like vacuum assisted HPDC and its heat treatment.Originality/value: The presented results point out the direction for future research needed to simulate the alloy solidification in a laboratory environment representing industrial casting processes.

  20. Investigation of Melting and Solidification of Thin Polycrystalline Silicon Films via Mixed-Phase Solidification

    Wang, Ying

    Melting and solidification constitute the fundamental pathways through which a thin-film material is processed in many beam-induced crystallization methods. In this thesis, we investigate and leverage a specific beam-induced, melt-mediated crystallization approach, referred to as Mixed-Phase Solidification (MPS), to examine and scrutinize how a polycrystalline Si film undergoes the process of melting and solidification. On the one hand, we develop a more general understanding as to how such transformations can transpire in polycrystalline films. On the other hand, by investigating how the microstructure evolution is affected by the thermodynamic properties of the system, we experimentally reveal, by examining the solidified microstructure, fundamental information about such properties (i.e., the anisotropy in interfacial free energy). Specifically, the thesis consists of two primary parts: (1) conducting a thorough and extensive investigation of the MPS process itself, which includes a detailed characterization and analysis of the microstructure evolution of the film as it undergoes MPS cycles, along with additional development and refinement of a previously proposed thermodynamic model to describe the MPS melting-and-solidification process; and (2) performing MPS-based experiments that were systematically designed to reveal more information on the anisotropic nature of Si-SiO2 interfacial energy (i.e., sigma Si-SiO2). MPS is a recently developed radiative-beam-based crystallization technique capable of generating Si films with a combination of several sought-after microstructural characteristics. It was conceived, developed, and characterized within our laser crystallization laboratory at Columbia University. A preliminary thermodynamic model was also previously proposed to describe the overall melting and solidification behavior of a polycrystalline Si film during an MPS cycle, wherein the grain-orientation-dependent solid-liquid interface velocity is identified

  1. Temporal magma dynamics during solidification of the mafic-silicic complex of Isle au Haut, Maine

    Patwardhan, Kaustubh

    The Isle au Haut Igneous Complex provides a unique opportunity to examine in detail the in situ physical and chemical interactions between contemporaneously emplaced mafic and silicic magmas. The complex contains a 600 m thick sequence of 11 alternating layers of gabbro and diorite (typically 15--40 m thick). Purely on the basis of density contrasts (2.65 g/cm 3 gabbro vs. 2.55 g/cm3 diorite), the entire system should have undergone wholesale instability and mixing; it is instead arrested in a grossly unstable state of interaction while molten. Chilled margins along the lower contacts of the gabbros and structural integrity of the diorite layers indicate that near liquidus gabbroic magma invaded partly crystalline, cooler diorite. Mineral assemblages, chemical analyses, and phase equilibria calculations indicate initial temperatures during emplacement of ˜1180°C (gabbro) and ˜1000°C (diorite). Conductive thermal models yield solidification timescales of 15--60 years for individual gabbro layers and about a thousand years for the entire complex. There is ample evidence for two phases of small-scale interfacial Rayleigh-Taylor type instabilities of dioritic melt into the gabbros. Phase I occurred immediately upon gabbro emplacement whereas evenly spaced, slender more silicic pipes represent a much later stage (Phase II). Pipe geometry and spacing, estimated viscosities of the gabbroic magma and silicic melt, and the sudden increase in silica near the upper contact of the diorite, all indicate a thin (˜18--53 cm) buoyant layer at the upper contact of the diorite as the source of the pipes. Compaction of the diorite produced this layer over a period of about ten years. Simultaneous solidification along the lower contact of the overlying gabbro, thickening inwards, increased viscosity enough to arrest pipe ascent after a few meters. Crystal size distribution (CSD) analyses of the gabbro layers yield crystal growth rates (G0 = 2--4 x 10-10 cm/s) and nucleation rates

  2. Modeling of multiphase flow with solidification and chemical reaction in materials processing

    Wei, Jiuan

    moving the side insulation layer upward. It is possible to produce high quality crystal with a good combination of heating and cooling. SiC based ceramic materials fabricated by polymer pyrolysis and synthesis becomes a promising candidate for nuclear applications. To obtain high uniformity of microstructure/concentration fuel without crack at high operating temperature, it is important to understand transport phenomena in material processing at different scale levels. In our prior work, a system level model based on reactive porous media theory was developed to account for the pyrolysis process in uranium-ceramic nuclear fabrication In this thesis, a particle level mesoscopic model based on the Smoothed Particle Hydrodynamics (SPH) is developed for modeling the synthesis of filler U3O8 particles and SiC matrix. The system-level model provides the thermal boundary conditions needed in the particle level simulation. The evolution of particle concentration and structure as well as composition of composite produced will be investigated. Since the process temperature and heat flux play the important roles in material quality and uniformity, the effects of heating rate at different directions, filler particle size and distribution on uniformity and microstructure of the final product are investigated. Uncertainty issue is also discussed. For the multiphase flow with directional solidification, a system level based on FVM is established. In this model, melt convection, temperature distribution, phase change and solidification interface can be investigated. For the multiphase flow with chemical reaction, a particle level model based on SPH method is developed to describe the pyrolysis and synthesis process of uranium-ceramic nuclear fuel. Due to its mesh-free nature, SPH can easily handle the problems with multi phases and components, large deformation, chemical reactions and even solidifications. A multi-scale meso-macroscopic approach, which combine a mesoscopic model based

  3. Rapid solidification processing of iron-base alloys for structural applications

    Flinn, J.E.


    The response of iron-base alloys to rapid solidification is reviewed with an emphasis on the effects of processing on the microstructure and mechanical property behavior. The processing topics addressed are powder atomization, powder consolidation, joining, and thermal-mechanical exposure. The value of rapid solidification processing (RSP) lies in the ability to promote compositional homogeneity and retention of fine and stable (to high temperatures) microstructures. Achieving the maximum benefit from RSP requires proper application of the basic principles of composition control and rapid crystallization. This investigation has disclosed two very important facets of the RSP approach that can be applied using current technologies. Dissociated oxygen appears to play a significant role in stabilizing microstructural features. In conjunction with oxygen, vacancies trapped during crystallization provide a very stable matrix dispersion for enhanced strengthening. With a fundamental understanding of the response of iron-base alloys to RSP, alloys can be designed that will have substantially better properties and performance than their conventionally processed counterparts. 77 refs., 94 figs., 14 tabs.

  4. Interfacial instabilities in directional solidification of dilute binary alloys: The Kuramoto-Sivashinsky equation

    Novick-Cohen, A.


    Directional solidification processes in the presence of an impurity are studied in the limit in which the dimensionless parameter overlineW = {GD}/{VC}0( g + ⨍ c) is small. Here G is the imposed temperature gradient, D is the diffusion coefficient of the impurity, V is the imposed transport velocity, g is equal to minus the slope of the liquidus line, C0 is the impurity concentration at the liquid side of a planar interface, and ⨍ c is a coefficient reflecting deviations from local thermal equilibrium. The dynamics of interfacial kinetics becomes important in this limit and the phenomenological model of Coriell and Sekerka [J. Cryst. Growth 61 (1983) 499-508] is used to model these processes. In this limit, the Kuramoto-Sivashinsky equation is shown to be an asymptotically valid description of the interfacial dynamics. The Kuramoto-Sivashinsky equation is known to exhibit intermittancy superimposed on a relatively stable array of cusps or wrinkles [Michelson and Sivashinsky, Acta Astronautica 4 (1977) 1207-1221] and thus may give a reasonable limiting description of the solidification interface just before coherency is lost. These cusps may also be important in the initiation of dendritic growth by serving as defect points [Schaefer and Glicksman, Met. Trans. 1 (1970) 1973-1978].

  5. Effects of argon flow on impurities transport in a directional solidification furnace for silicon solar cells

    Li, Zaoyang; Liu, Lijun; Ma, Wencheng; Kakimoto, Koichi


    A global simulation including coupled oxygen and carbon transport was carried out to study the argon flow effects on the impurities transport in a directional solidification furnace for silicon solar cells. The simulation is based on a fully coupled calculation of the thermal and flow fields in a furnace including argon gas flow and melt convection. Five chemical reactions are considered in the impurity transport model. The effects of both the argon flow rate and the furnace pressure were examined. It was found that the argon flow has an important effect on the silicon melt convection, which will further influence the evaporation characteristic of SiO at the melt free surface. The amount of SiO carried away by the argon flow increases with increase in the argon flow rate while the CO gas can be prevented from being transported to the melt free surface. There exists a peak value for the concentration of impurities in the furnace chamber regarding argon flow rate due to the correlation among SiO evaporated, reacted and taken away. The pressure also influences the impurity transport in the furnace by modifying the pattern of argon flow. The numerical results demonstrate a method to control the oxygen and carbon transport in a directional solidification furnace by adjusting the argon flow rate and the furnace pressure.

  6. Directional Solidification of Mercury Cadmium Telluride During the Second United States Microgravity Payload Mission (USMP-2)

    Gillies, D. C.; Lehoczky, S. L.; Szofran, F. R.; Watring, D. A.; Alexander, H. A.; Jerman, G. A.


    As a solid solution semiconductor having, a large separation between liquidus and solidus, mercury cadmium telluride (MCT) presents a formidable challenge to crystal growers desiring an alloy of high compositional uniformity. To avoid constitutional supercooling during Bridgman crystal growth it is necessary to solidify slowly in a high temperature gradient region. The necessary translation rate of less than 1 mm/hr results in a situation where fluid flow induced by gravity on earth is a significant factor in material transport. The Advanced Automated Directional Solidification Furnace (AADSF) is equipped to provide the stable thermal environment with a high gradient, and the required slow translation rate needed. Ground based experiments in AADSF show clearly the dominance of flow driven transport. The first flight of AADSF in low gravity on USMP-2 provided an opportunity to test theories of fluid flow in MCT and showed several solidification regimes which are very different from those observed on earth. Residual acceleration vectors in the orbiter during the mission were measured by the Orbital Acceleration Research Experiment (OARE), and correlated well with observed compositional differences in the samples.

  7. Exploring new concepts in directional solidification by electron beam melting and selective laser melting

    Martinez, Edwin

    Unlike more conventional directional solidification, electron and laser-beam melting technologies involve building 3D components through layer-by-layer melt/solidification thermal cycling which creates novel, directional microstructural architectures. In this study we compared various the columnar microstructures of various components manufactured by EBM and SLM; image composite observations of columnar microstructural architectures in Cu, Co-29-Cr-6Mo-0.2C alloy, Ni-22Cr-9Mo-4Nb (alloy 625) fabricated by electron beam melting (EBM), and Ni-19Cr-19Fe-5Nb-1Al (alloy 718) by selective laser melting (SLM) as well as stainless steel 17-4 PH (SLM). Cu produced discontinuous columns of Cu2O precipitates while the Co-base alloy exhibited similar columns of Cr 23C6 precipitates. The alloy 625 produced columns of Ni 3Nb (Upsilon"-bct) precipitates. All of the EBM-produced columnar microstructure arrays were spaced ˜2 microm. In contrast, the SLM fabricated alloy 718 contained columnar microstructural arrays of Ni3 Nb (Upsilon") spaced ˜ 0.8microm, the 17-4 PH stainless steel produced martensitic structures dependent on the gas used for manufacturing. The manufactured components were observed by optical microscopy, SEM, XRD and by TEM in order to understand the microstructural development.

  8. Impact of the Solidification Rate on the Chemical Composition of Frozen Cryolite Bath

    Sándor Poncsák


    Full Text Available Solidification of cryolite (Na3AlF6-based bath takes place at different rates along the sideledge, and around alumina rafts and new anodes. The solidification rate has a significant impact on the structure and the chemical composition that determine the thermal conductivity and thus the thickness of sideledge, or the duration of the existence of the temporary frozen bath layers in other cases. Unfortunately, samples that can be collected in industrial cells are formed under unknown, spatially and temporally varying conditions. For this reason, frozen bath samples were created under different heat flux conditions in a well-controlled laboratory environment using the so-called cold finger technique. The samples were analyzed by X-ray Diffractometer (XRD and Scanning Electron Microscope (SEM in Back Scattering (BS mode in order to obtain spatial distribution of chemical composition. Results were correlated with structural analysis. XRD confirmed our earlier hypothesis of recrystallization of cryolite to chiolite under medium heat flux regime. Lower α-alumina, and higher γ-alumina content in the samples obtained with very high heating rate suggest that fast cooling reduces α–γ conversion. In accordance with the expectation, SEM-BS revealed significant variation of the Na/Al ratio in the transient sample.

  9. Solidification of Magnesium (AM50A) / vol%. SiCp composite

    Zhang, X.; Hu, H.


    Magnesium matrix composite is one of the advanced lightweight materials with high potential to be used in automotive and aircraft industries due to its low density and high specific mechanical properties. The magnesium composites can be fabricated by adding the reinforcements of fibers or/and particles. In the previous literature, extensive studies have been performed on the development of matrix grain structure of aluminum-based metal matrix composites. However, there is limited information available on the development of grain structure during the solidification of particulate-reinforced magnesium. In this work, a 5 vol.% SiCp particulate-reinforced magnesium (AM50A) matrix composite (AM50A/SiCp) was prepared by stir casting. The solidification behavior of the cast AM50A/SiCp composite was investigated by computer-based thermal analysis. Optical and scanning electron microscopies (SEM) were employed to examine the occurrence of nucleation and grain refinement involved. The results indicate that the addition of SiCp particulates leads to a finer grain structure in the composite compared with the matrix alloy. The refinement of grain structure should be attributed to both the heterogeneous nucleation and the restricted primary crystal growth.

  10. Carbon isotope fractionation of dissolved inorganic carbon (DIC) due to outgassing of carbon dioxide from a headwater stream

    Doctor, D.H.; Kendall, C.; Sebestyen, S.D.; Shanley, J.B.; Ohte, N.; Boyer, E.W.


    The stable isotopic composition of dissolved inorganic carbon (??13C-DIC) was investigated as a potential tracer of streamflow generation processes at the Sleepers River Research Watershed, Vermont, USA. Downstream sampling showed ?? 13C-DIC increased between 3-5??? from the stream source to the outlet weir approximately 0??5 km downstream, concomitant with increasing pH and decreasing PCO2. An increase in ??13C-DIC of 2.4 ?? 0??1??? per log unit decrease of excess PCO2 (stream PCO2 normalized to atmospheric PCO2) was observed from downstream transect data collected during snowmelt. Isotopic fractionation of DIC due to CO2 outgassing rather than exchange with atmospheric CO2 may be the primary cause of increased ?? 13C-DIC values downstream when PCO2 of surface freshwater exceeds twice the atmospheric CO2 concentration. Although CO2 outgassing caused a general increase in stream ??13C-DIC values, points of localized groundwater seepage into the stream were identified by decreases in ??13C-DIC and increases in DIC concentration of the stream water superimposed upon the general downstream trend. In addition, comparison between snowmelt, early spring and summer seasons showed that DIC is flushed from shallow groundwater flowpaths during snowmelt and is replaced by a greater proportion of DIC derived from soil CO2 during the early spring growing season. Thus, in spite of effects from CO2 outgassing, ??13C of DIC can be a useful indicator of groundwater additions to headwater streams and a tracer of carbon dynamics in catchments. Copyright ?? 2007 John Wiley & Sons, Ltd.

  11. Relationship between resist outgassing and EUV witness sample contamination in NXE outgas qualification using electrons and EUV photons

    Pollentier, I.; Tirumala Venkata, A.; Gronheid, R.


    EUV photoresists are considered as a potential source of optics contamination, since they introduce irradiation-induced outgassing in the EUV vacuum environment. Therefore, before these resists can be used on e.g. ASML NXE:3100 or NXE:3300, they need to be tested in dedicated equipment according to a well-defined procedure, which is based on exposing a witness sample (WS) in the vicinity of a simultaneously exposed resist as it outgasses. Different system infrastructures are used at multiple sites (e.g. NIST, CNSE, Sematech, EIDEC, and imec) and were calibrated to each other by a detailed test plan. Despite this detailed tool qualifications, a first round robin comparison of identical materials showed inconsistent outgas test results, and required further investigation by a second round robin. Since the resist exposure mode is different at the various locations (some sites are using EUV photons while others use E-gun electrons), this difference has always a point of concern for variability of test results. In this work we compare the outgas test results from EUV photon and electron exposure using the resist materials of the second round robin. Since the imec outgas tester allows both exposure methods on the resist, a within-system comparison is possible and showed limited variation between photon and electron exposure mode. Therefore the system-to-system variability amongst the different outgas test sites is expected to be related to other parameters than the electron/photon exposure mode. Initial work showed that the variability might be related to temperature, E-gun emission excursion, and/or residual outgassing scaled by different wafer areas at the different sites.

  12. Shape sensitivity analysis in numerical modelling of solidification

    E. Majchrzak


    Full Text Available The methods of sensitivity analysis constitute a very effective tool on the stage of numerical modelling of casting solidification. It is possible, among others, to rebuilt the basic numerical solution on the solution concerning the others disturbed values of physical and geometrical parameters of the process. In this paper the problem of shape sensitivity analysis is discussed. The non-homogeneous casting-mould domain is considered and the perturbation of the solidification process due to the changes of geometrical dimensions is analyzed. From the mathematical point of view the sensitivity model is rather complex but its solution gives the interesting information concerning the mutual connections between the kinetics of casting solidification and its basic dimensions. In the final part of the paper the example of computations is shown. On the stage of numerical realization the finite difference method has been applied.

  13. Simulation of shrinkage cavity formation during solidification of binary alloy

    T. Skrzypczak


    Full Text Available Presented paper is focused on numerical modeling of binary alloy solidification process with connection to shrinkage cavity formation phenomenon. Appropriate matching of cooling parameters during solidification process of the cast with raiser is essential to obtain suitable properties of the manufactured part. Localization, structure and depth of the shrinkage cavity is connected to these parameters. The raiser is removed after process, so defect localization in the top part of the manufactured element is of great importance. Mathematical model of solidification process is presented in the paper. The main focus is put on the algorithm of shrinkage cavity creation process. On the basis of mathematical model the numerical approach using finite element method is proposed. On the base of mathematical and numerical model computer program is made. It is able to perform simulation of the shrinkage cavity formation in 2D region. Shape and localization of shrinkage cavity obtained from simulation is compared to defect which was created during experiment.

  14. Stabilization/Solidification Remediation Method for Contaminated Soil: A Review

    Tajudin, S. A. A.; Azmi, M. A. M.; Nabila, A. T. A.


    Stabilization/Solidification (S/S) is typically a process that involves a mixing of waste with binders to reduce the volume of contaminant leachability by means of physical and chemical characteristics to convert waste in the environment that goes to landfill or others possibly channels. Stabilization is attempts to reduce the solubility or chemical reactivity of the waste by changing the physical and chemical properties. While, solidification attempt to convert the waste into easily handled solids with low hazardous level. These two processes are often discussed together since they have a similar purpose of improvement than containment of potential pollutants in treated wastes. The primary objective of this review is to investigate the materials used as a binder in Stabilization/Solidification (S/S) method as well as the ability of these binders to remediate the contaminated soils especially by heavy metals.

  15. Nonequilibrium Solidification, Grain Refinements, and Recrystallization of Deeply Undercooled Ni-20 At. Pct Cu Alloys: Effects of Remelting and Stress

    Xu, Xiaolong; Hou, Hua; Zhao, Yuhong; Liu, Feng


    Grain refinement phenomena during the microstructural evolution upon nonequilibrium solidification of deeply undercooled Ni-20 at. pct Cu melts were systematically investigated. The dendrite growth in the bulk undercooled melts was captured by a high-speed camera. The first kind of grain refinement occurring in the low undercooling regimes was explained by a current grain refinement model. Besides, for the dendrite melting mechanism, the stress originating from the solidification contraction and thermal strain in the FMZ during rapid solidification could be a main mechanism causing the second kind of grain refinement above the critical undercooling. This internal stress led to the distortion and breakup of the primary dendrites and was semiquantitatively described by a corrected stress accumulation model. It was found that the stress-induced recrystallization could make the primary microstructures refine substantially after recalescence. A new method, i.e., rapidly quenching the deeply undercooled alloy melts before recalescence, was developed in the present work to produce crystalline alloys, which were still in the cold-worked state and, thus, had the driven force for recrystallization.

  16. In-Situ Analysis of Coarsening during Directional Solidification Experiments in High-Solute Aluminum Alloys

    Ruvalcaba, D.; Mathiesen, R.H.; Eskin, D.G.; Arnberg, L.; Katgerman, L.


    Coarsening within the mushy zone during continuous directional solidification experiments was studied on an Al-30 wt pct Cu alloy. High brilliance synchrotron X-radiation microscopy allowed images to be taken in-situ during solidification. Transient conditions were present during directional solidif

  17. Effects of Pulse Current on Solidification Structure of Austenitic Stainless Steel

    FAN Jin-hui; CHEN Yu; LI Ren-xing; ZHAI Qi-jie


    The 1Cr18Ni9Ti specimens were treated respectively with pulse current under 520 V and 2 600 V during solidification and the solidification structure was observed. The results showed that pulse current can refine solidification grains, cut primary dentrities remarkably and reduce second dentritic arm spacing. The mechanism and effect are changed with operation parameters.

  18. Application of modern software packages to calculating the solidification of high-speed steels

    Morozov, S. I.


    The solidification of high-speed steels is calculated with the Pandat and JMatPro software packages. The results of calculating equilibrium and nonequilibrium solidification are presented and discussed. The nonequilibrium solidification is simulated using the Shelley-Gulliver model. The fraction of carbides changes as a function of the carbon content in the steels.

  19. Modelling of convection during solidification of metal and alloys

    A K Singh; R Pardeshi; B Basu


    The role of convection during solidification is studied with the help of a mathematical model. The effect of various mush models on convection and consequent macrosegregation is examined with the help of numerical simulations. The predicted macrosegregation profiles are compared with published experimental data. Subsequently, the importance of proper auxiliary relationship for thermo-solutal coupling in the mushy region is highlighted through some careful numerical simulations. Finally, the role of material parameters on double-diffusive convection is illustrated through comparative study of solidification of aqueous ammonium chloride, iron-carbon and lead-tin binary systems. Important results of these studies are presented and discussed.

  20. Modeling solidification structure evolution and microsegregation under pressure condition

    Qiang Li; Qiaoyi Guo; Rongde Li


    Solidification microstructure and microsegregation were simulated under a constant pressure condition using the cellular automaton method. First, a single dendrite evolution was simulated and compared under pressure condition and under normal condition,respectively. The solidification microstructure and microsegregation were then simulated. Through simulation, it may be concluded that if the growth direction of the dendrite is parallel to the pressure direction, dendrite growth will be hindered. On the other hand,pressure has no influence on the dendrite evolution. However, when two dendrites grow in close contact, solute enrichment occurs in the dendrites, which hinders the growth of the dendrites. In addition, the solute is preferentially enriched along the pressure direction.

  1. Heat Transfer and Its Effect on Solidification in Combined Mould

    QIU Sheng-tao; TAO Hong-biao; TANG Hong-wei; ZHANG Hui; ZHAO Pei


    The nucleation can be enhanced by decreasing the superheat of molten steel, thus reducing temperature gradient on the solidification front can retard the growth of columnar crystals and enlarge the equiaxed zone in continuous casting strand. The billets with equiaxed zone more than 90% were cast with a combined mould and the heatflux was measured. The heat transfer of the combined mould and traditional mould was compared. The results show that under same casting conditions, the temperature gradient on the solidification front in the combined mould is smaller than that in traditional mould at a distance within 0-150 mm from the meniscus.

  2. Solidification microstructure of directionally solidified superalloy under high temperature gradient


    The effect of solidification rate on the microstructure development of nickel-based superalloy under the temperature gradient of 500 K·cm-1 was studied. The results show that, with the increase of directional solidification rate from 50 to 800 μm·s-1, both the primary and the secondary dendrite arm spacings of the alloy decrease gradually, and the dendrite morphologies transform from coarse dendrite to superfine dendrite. The sizes of all precipitates in the superalloy decrease gradually. The morphology of ...

  3. Phase-field modelling of microstructure formation during the solidification of continuously cast low carbon and HSLA steels

    Böttger, B.; Apel, M.; Santillana, B.; Eskin, D. G.


    Cracking in continuous casting of steels has been one of the main problems for decades. Many of the cracks that occur during solidification are hot tears. To better understand the factors leading to this defect, microstructure formation is simulated for a low carbon (LCAK) and two high strength low alloyed (HSLA) steel grades during the initial stage of the process where the first solidified shell is formed inside the mould and where breakouts typically occur. 2D simulation is performed using the multiphase-field software MICRESS [1], which is coupled to the thermodynamic database TCFE6 [2] and the mobility database MOB2 [2], taking into account all elements which may have a relevant effect on the mechanical properties and structure formation during or subsequent to solidification. The use of a moving-frame boundary condition allows travelling through the entire solidification history starting from the slab surface, and tracking the morphology changes during growth of the shell. A heterogeneous nucleation model is included to permit the description of morphological transitions between the initial solidification and the subsequent columnar growth region. Furthermore, a macroscopic one-dimensional temperature solver is integrated to account for the transient and nonlinear temperature field during the initial stage of continuous casting. The external heat flux boundary conditions for this process were derived from thermal process data of the industrial slab caster. The simulation results for the three steel grades have been validated by thickness measurements of breakout shells and microstructure observation of the corresponding grades. Furthermore, the primary dendrite spacing has been measured across the whole thickness of the shell and compared with the simulated microstructures. Significant microstructure differences between the steel grades are discussed and correlated with their hot-cracking behavior.

  4. Influence of solidification variables on the cast microstructure and porosity in directionally solidified Mar-M247

    Whitesell, Harry Smith, III

    The solidification microstructure is critical in determining the amount and distribution of porosity that develops during the freezing of castings. As the solidification velocity Vs increases, the microstructural length scales (primary and secondary dendrite arm spacings) decrease; thus (1) the mushy zone permeability would be expected to decrease; and (2) nucleated pores would be increasingly isolated. Although the first effect would tend to increase the observed porosity, the second effect would tend to decrease the porosity. As solidification velocity decreases, the cooling rate decreases allowing additional time for carbide growth. Large carbide size may block feeding in the intercellular spaces increasing observed porosity. To better understand these competitive mechanisms, a series of controlled unidirectional experiments were performed on bars of nickel-base superalloy Mar-M247. Samples were produced with constant dendrite arm spacing throughout an extended length of each cast bar. The axial thermal gradient and withdrawal velocity imposed on each casting were varied between castings to produce a range of microstructures from aligned cellular dendritic to aligned dendritic to misaligned dendritic. Macrosegregation effects along the lengths of the bars were evaluated and the resultant impact upon the density along the lengths of each casting was also characterized. The density measurements were found to be very sensitive to both (1) compositional macrosegregation in these castings and (2) internal porosity. Statistical analyses of microporosity in castings were based upon metallographic measurements. The development of microporosity in the unidirectionally solidified castings is shown to be dependent upon the hydrogen gas content of the samples and the imposed solidification velocity through the sample's cast microstructures. An optimum intermediate withdrawal velocity of 0.005--0.01 cm/s was found, which led to closely spaced dendrite arms, a large number of

  5. Transient Thermal State of an Active Braille Matrix with Incorporated Thermal Actuators by Means of Finite Element Method

    Alutei, Alexandra-Maria; Szelitzky, Emoke; Mandru, Dan


    In this article the authors present the transient thermal analysis for a developed thermal linear actuator based on wax paraffin used to drive the cells of a Braille device. A numerical investigation of transient heat transfer phenomenon during paraffin melting and solidification in an encapsulated recipient has been carried out using the ANSYS…

  6. Potential Flow Interactions With Directional Solidification

    Buddhavarapu, Sudhir S.; Meiburg, Eckart


    The effect of convective melt motion on the growth of morphological instabilities in crystal growth has been the focus of many studies in the past decade. While most of the efforts have been directed towards investigating the linear stability aspects, relatively little attention has been devoted to experimental and numerical studies. In a pure morphological case, when there is no flow, morphological changes in the solid-liquid interface are governed by heat conduction and solute distribution. Under the influence of a convective motion, both heat and solute are redistributed, thereby affecting the intrinsic morphological phenomenon. The overall effect of the convective motion could be either stabilizing or destabilizing. Recent investigations have predicted stabilization by a flow parallel to the interface. In the case of non-parallel flows, e.g., stagnation point flow, Brattkus and Davis have found a new flow-induced morphological instability that occurs at long wavelengths and also consists of waves propagating against the flow. Other studies have addressed the nonlinear aspects (Konstantinos and Brown, Wollkind and Segel)). In contrast to the earlier studies, our present investigation focuses on the effects of the potential flow fields typically encountered in Hele-Shaw cells. Such a Hele-Shaw cell can simulate a gravity-free environment in the sense that buoyancy-driven convection is largely suppressed, and hence negligible. Our interest lies both in analyzing the linear stability of the solidification process in the presence of potential flow fields, as well as in performing high-accuracy nonlinear simulations. Linear stability analysis can be performed for the flow configuration mentioned above. It is observed that a parallel potential flow is stabilizing and gives rise to waves traveling downstream. We have built a highly accurate numerical scheme which is validated at small amplitudes by comparing with the analytically predicted results for the pure

  7. Wet inside and out? Constraints on water in the Martian mantle and on outgassed water, based on melt inclusions in SNC meteorites

    Mcsween, H. Y., Jr.; Harvey, R. P.


    Constraints on the volatile inventory and outgassing history of Mars are critical to understanding the origin of ancient valley systems and paleoclimates. Planetary accretion models for Mars allow either a volatile-rich or volatile-poor mantle, depending on whether the accreted materials were fully oxidized or whether accretion was homogeneous so that water was lost through reaction with metallic iron. The amount of water that has been outgassed from the interior is likewise a contentious subject, and estimates of globally distributed water based on various geochemical and geological measurements vary from a few meters to more than a thousand meters. New data on SNC meteorites, which are thought to be Martian igneous rocks, provide constraints on both mantle and outgassed water.




    Full Text Available In this research solidification characteristic of metal matrix composites consisted of titanium carbide particulate reinforced aluminium-11.8% silicon alloy matrix is performed. Vortex mixing and permanent casting method are used as the manufacturing method to produce the specimens. Temperature measurements during the casting process are captured and solidification graphs are plotted to represent the solidification characteristic. The results show, as volume fraction of particulate reinforcement is increased, solidification time is faster. Particulate reinforcement promotes rapid solidification which will support finer grain size of the casting specimen. Hardness test is performed and confirmed that hardness number increased as more particulate are added to the system.


    KORTI, Abdel Illah Nabil


    In this paper, two dimensional unsteady flow and energy equations are employed for simulating the fluid flow, heat transfer and solidification during direct chill continuous casting of Al-Mg alloy billet. In these processes, the formation of some macro defects such as thermal cracking, hot tearing, surface cracking, etc, has been found to initiate during the starting phase of the operation. International Journal of Computational Methods.

  10. Impact of External Pressure on the Heat Transfer Coefficient during Solidification of Al-A356 Alloy

    Jabbari, Masoud; Ilkhchy, A.Fardi; Moumani, E.

    In this paper the interfacial heat transfer coefficient (IHTC) is correlated to applied external pressure, in which IHTC at the interface between A356 aluminum alloy and metallic mold during the solidification of the casting under different pressures were obtained using the Inverse Heat Conduction...... Problem (IHCP) method. The method covers the expedient of comparing theoretical and experimental thermal histories. Temperature profiles obtained from thermocouples were used in a finite difference heat flow program to estimate the transient heat transfer coefficients. The new simple formula was presented...

  11. Effects of an Applied Magnetic Field on the Directional Solidification of Hg(1-x)Zn(x)Se Alloys

    Cobb, S. D.; Lehoczky, S. L.; Szofran, F. R.; Jones, K. S.


    Directionally solidified Hg(0.9)Zn(0.1)Se alloys were studied as an alternative to HgCdTe for the detection of electromagnetic radiation because of predicted improvements in lattice stability. Several boules were grown using a modified Bridgman-Stockbarger method and in an applied magnetic field. Axial compositional profiles showed mass transfer was primarily diffusion controlled. Radial compositional variations were greatly reduced when solidification occurred in an applied magnetic field. Microstructural characteristics and dislocation etch pit densities were greatly improved over HgTe based alloys. The extreme importance of processing conditions on defect generation was illustrated by comparing ampoule configurations and thermal profiles.

  12. Identification of the heat transfer coefficient in the two-dimensional model of binary alloy solidification

    Hetmaniok, Edyta; Hristov, Jordan; Słota, Damian; Zielonka, Adam


    The paper presents the procedure for solving the inverse problem for the binary alloy solidification in a two-dimensional space. This is a continuation of some previous works of the authors investigating a similar problem but in the one-dimensional domain. Goal of the problem consists in identification of the heat transfer coefficient on boundary of the region and in reconstruction of the temperature distribution inside the considered region in case when the temperature measurements in selected points of the alloy are known. Mathematical model of the problem is based on the heat conduction equation with the substitute thermal capacity and with the liquidus and solidus temperatures varying in dependance on the concentration of the alloy component. For describing this concentration the Scheil model is used. Investigated procedure involves also the parallelized Ant Colony Optimization algorithm applied for minimizing a functional expressing the error of approximate solution.

  13. Investigation of Intermetallic Compound Formed from Rapid Solidification of Al-Ti-RE Alloy

    杨明珊; 王振飞


    Al-Ti alloy containing rare earth elements can produce fine,uniform dispersion intermetallic phase through rapid solidification(RS)technology.RS Al-Ti-RE alloy can be designed for applications at elevated-temperature since the intermetallic compound has good thermal stability.A transmission electron microscopy investigation shows the intermetallic phase has a diamond cubic structure(a=1.47736 nm),with space group Fd3m.The chemical stoichiometry is Al20Ti2La.The particle is formed from the melting directly,prior to other phases,and the nucleus is formed from icosahedrons composed with twenty tetrahedrons.Twin crystal structure plays an important role in the nucleation stage.

  14. Effect of partition coefficient on microsegregation during solidification of aluminium alloys

    MH Avazkonandeh-Gharavol; M Haddad-Sabzevar; H Fredriksson


    In the modeling of microsegregation, the partition coefficient is usually calculated using data from the equilibrium phase diagrams. The aim of this study was to experimentally and theoretically analyze the partition coefficient in binary aluminum-copper alloys. The sam-ples were analyzed by differential thermal analysis (DTA), which were melted and quenched from different temperatures during solidifica-tion. The mass fraction and composition of phases were measured by image processing and scanning electron microscopy (SEM) equipped with an energy-dispersive X-ray spectroscopy (EDS) unit. These data were used to calculate as the experimental partition coefficients with four different methods. The experimental and equilibrium partition coefficients were used to model the concentration profile in the primary phase. The modeling results show that the profiles calculated by the experimental partition coefficients are more consistent with the experi-mental profiles, compared to those calculated using the equilibrium partition coefficients.

  15. Study of Solidification of Continuously Cast Steel Round Billets Using Numerical Modelling

    Tkadlečková M.


    Full Text Available The paper is dedicated to the verification of solidification of continuously cast round steel billets using numerical modelling based on the finite element method. The aim of numerical modelling is to optimize the production of continuously cast steel billets of round format. The paper describes the pre-processing, processing and post-processing phases of numerical modelling. Also, the problems with determination of the thermodynamic properties of materials and the heat transfer between the individual parts of the casting system, including the definition of the heat losses along the casting strand in the primary and secondary cooling, were discussed. The first results of numerical simulation show the so-called thermal steady state of continuous casting. The temperature field, the metallurgical length and the thickness of the shell at the end of the mould were predicted. The further research will be concentrated on the prediction the risk of the cracks and the porosity based on the different boundary conditions.

  16. Macrosegregation during Plane Front Solidification of Cesium Iodide wt Percent Thallium Iodide Alloy

    Sidawi, Ibrahim M. S.

    Macrosegregation produced during directional solidification of CsI-1 wt% TlI by vertical Bridgman technique has been examined in crucibles of varying diameter, from 0.5 to 2.0 cm. Phase diagram and temperature dependence of the thermal conductivity have been determined. The experimentally observed liquid-solid interface shape and the fluid flow behavior have been compared with that computed from the commercially available code FIDAP. Thallium iodide content of the alloy was observed to increase along the length of the directionally solidified specimens, resulting in continuously decreasing light output. The experimentally observed solutal distribution agrees with predictions from the boundary layer model of Favier. The observed macrosegregation behavior suggests that there is a significant convection in the melt even in the smallest crucible diameter of 0.5 cm.

  17. Phase-field simulation of peritectic solidification closely coupled with directional solidification experiments in an Al-36 wt% Ni alloy.

    Siquieri, R; Doernberg, E; Emmerich, H; Schmid-Fetzer, R


    In this work we present experimental and theoretical investigations of the directional solidification of Al-36 wt% Ni alloy. A phase-field approach (Folch and Plapp 2005 Phys. Rev. E 72 011602) is coupled with the CALPHAD (calculation of phase diagrams) method to be able to simulate directional solidification of Al-Ni alloy including the peritectic phase Al(3)Ni. The model approach is calibrated by systematic comparison to microstructures grown under controlled conditions in directional solidification experiments. To illustrate the efficiency of the model it is employed to investigate the effect of temperature gradient on the microstructure evolution of Al-36 wt% Ni during solidification.

  18. Particle Trapping and Banding in Rapid Colloidal Solidification

    Elliott, J. A. W.


    We derive an expression for the nonequilibrium segregation coefficient of colloidal particles near a moving solid-liquid interface. The resulting kinetic phase diagram has applications for the rapid solidification of clay soils, gels, and related colloidal systems. We use it to explain the formation of bandlike defects in rapidly solidified alumina suspensions. © 2011 American Physical Society.

  19. Solidification in a Supercomputer: From Crystal Nuclei to Dendrite Assemblages

    Shibuta, Yasushi; Ohno, Munekazu; Takaki, Tomohiro


    Thanks to the recent progress in high-performance computational environments, the range of applications of computational metallurgy is expanding rapidly. In this paper, cutting-edge simulations of solidification from atomic to microstructural levels performed on a graphics processing unit (GPU) architecture are introduced with a brief introduction to advances in computational studies on solidification. In particular, million-atom molecular dynamics simulations captured the spontaneous evolution of anisotropy in a solid nucleus in an undercooled melt and homogeneous nucleation without any inducing factor, which is followed by grain growth. At the microstructural level, the quantitative phase-field model has been gaining importance as a powerful tool for predicting solidification microstructures. In this paper, the convergence behavior of simulation results obtained with this model is discussed, in detail. Such convergence ensures the reliability of results of phase-field simulations. Using the quantitative phase-field model, the competitive growth of dendrite assemblages during the directional solidification of a binary alloy bicrystal at the millimeter scale is examined by performing two- and three-dimensional large-scale simulations by multi-GPU computation on the supercomputer, TSUBAME2.5. This cutting-edge approach using a GPU supercomputer is opening a new phase in computational metallurgy.

  20. Changes in porosity of foamed aluminum during solidification


    In order to control the porosity of foamed aluminum, the changes in the porosity of foamed aluminum melt in the processes of foaming and solidification, the distribution of the porosity of foamed aluminum, and the relationship between them were studied. The results indicated that the porosity of foamed aluminum coincides well with the foaming time.

  1. Overview of the Tusas Code for Simulation of Dendritic Solidification

    Trainer, Amelia J. [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Newman, Christopher Kyle [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Francois, Marianne M. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)


    The aim of this project is to conduct a parametric investigation into the modeling of two dimensional dendrite solidification, using the phase field model. Specifically, we use the Tusas code, which is for coupled heat and phase-field simulation of dendritic solidification. Dendritic solidification, which may occur in the presence of an unstable solidification interface, results in treelike microstructures that often grow perpendicular to the rest of the growth front. The interface may become unstable if the enthalpy of the solid material is less than that of the liquid material, or if the solute is less soluble in solid than it is in liquid, potentially causing a partition [1]. A key motivation behind this research is that a broadened understanding of phase-field formulation and microstructural developments can be utilized for macroscopic simulations of phase change. This may be directly implemented as a part of the Telluride project at Los Alamos National Laboratory (LANL), through which a computational additive manufacturing simulation tool is being developed, ultimately to become part of the Advanced Simulation and Computing Program within the U.S. Department of Energy [2].

  2. Three-dimensional solidification and melting using magnetic field control

    Dulikravich, George S.; Ahuja, Vineet


    A new two-fluid mathematical model for fully three dimensional steady solidification under the influence of an arbitrary acceleration vector and with or without an arbitrary externally applied steady magnetic field have been formulated and integrated numerically. The model includes Joule heating and allows for separate temperature dependent physical properties within the melt and the solid. Latent heat of phase change during melting/solidification was incorporated using an enthalpy method. Mushy region was automatically captured by varying viscosity orders of magnitude between liquidus and solidus temperature. Computational results were obtained for silicon melt solidification in a parallelepiped container cooled from above and from a side. The results confirm that the magnetic field has a profound influence on the solidifying melt flow field thus changing convective heat transfer through the boundaries and the amount and shape of the solid accrued. This suggests that development of a quick-response algorithm for active control of three dimensional solidification is feasible since it would require low strength magnetic fields.

  3. Multi-crystalline silicon solidification under controlled forced convection

    Cablea, M.; Zaidat, K.; Gagnoud, A.; Nouri, A.; Chichignoud, G.; Delannoy, Y.


    Multi-crystalline silicon wafers have a lower production cost compared to mono-crystalline wafers. This comes at the price of reduced quality in terms of electrical properties and as a result the solar cells made from such materials have a reduced efficiency. The presence of different impurities in the bulk material plays an important role during the solidification process. The impurities are related to different defects (dislocations, grain boundaries) encountered in multi-crystalline wafers. Applying an alternative magnetic field during the solidification process has various benefits. Impurities concentration in the final ingot could be reduced, especially metallic species, due to a convective term added in the liquid that reduces the concentration of impurities in the solute boundary layer. Another aspect is the solidification interface shape that is influenced by the electromagnetic stirring. A vertical Bridgman type furnace was used in order to study the solidification process of Si under the influence of a travelling magnetic field able to induce a convective flow in the liquid. The furnace was equipped with a Bitter type three-phase electromagnet that provides the required magnetic field. A numerical model of the furnace was developed in ANSYS Fluent commercial software. This paper presents experimental and numerical results of this approach, where interface markings were performed.

  4. The Effect of Solidification Rate on Morphological Stability

    Sekerka, R. F.


    At low solidification rates, the criterion for the onset of morphological instability parallels closely the criterion of constitutional supercooling. At somewhat larger rates of solidification, however, the results of the perturbation theory of morphological instability differ significantly from the predictions of constitutional supercooling. This arises because the critical wave length for instability decreases as solidification rate increases and thus the effects of capillarity (solid-liquid surface tension) play a strong stabilizing role. This gives rise to the concept of absolute stability, according to which the system will always be stable for a sufficiently large rate of solidification. This enhanced stabilization by capillarity is present only so long as local equilibrium is maintained at the solid-liquid interface. If the interfacial temperature drops below its equilibrium value by an amount dependent on growth rate, oscillatory morphological instabilities can occur. The differences among these various stability criteria are illustrated by means of some simple two-dimensional diagrams that should supplant the conventional plots of (temperature gradient)/(growth rate) vs. alloy concentration.

  5. Microstructural Development in Al-Si Powder During Rapid Solidification

    Genau, Amber Lynn [Iowa State Univ., Ames, IA (United States)


    Powder metallurgy has become an increasingly important form of metal processing because of its ability to produce materials with superior mechanical properties. These properties are due in part to the unique and often desirable microstructures which arise as a result of the extreme levels of undercooling achieved, especially in the finest size powder, and the subsequent rapid solidification which occurs. A better understanding of the fundamental processes of nucleation and growth is required to further exploit the potential of rapid solidification processing. Aluminum-silicon, an alloy of significant industrial importance, was chosen as a model for simple eutectic systems displaying an unfaceted/faceted interface and skewed coupled eutectic growth zone, Al-Si powder produced by high pressure gas atomization was studied to determine the relationship between microstructure and alloy composition as a function of powder size and atomization gas. Critical experimental measurements of hypereutectic (Si-rich) compositions were used to determine undercooling and interface velocity, based on the theoretical models which are available. Solidification conditions were analyzed as a function of particle diameter and distance from nucleation site. A revised microstructural map is proposed which allows the prediction of particle morphology based on temperature and composition. It is hoped that this work, by providing enhanced understanding of the processes which govern the development of the solidification morphology of gas atomized powder, will eventually allow for better control of processing conditions so that particle microstructures can be optimized for specific applications.

  6. Solidification of Hypereutectic Thin Wall Ductile Cast Iron

    Pedersen, Karl Martin; Tiedje, Niels Skat


    Hypereutectic ductile iron was cast in green sand moulds with four plates with thickness of 1.5, 2, 3 and 4 mm in each mould. Temperatures were measured in the 3 and 4 mm plate. The temperature curves showed that eutectic solidification was divided into two stages: primary and secondary eutectic...

  7. Solidification paths in modified Inconel 625 weld overlay material

    Chandrasekaran, Karthik; Tiedje, Niels Skat; Hald, John


    Inconel 625 is commonly used for overlay welding to protect the base metal against high temperature corrosion. The efficiency of corrosion protection depends on effective mixing of the overlay weld with the base metal and the subsequent segregation of alloy elements during solidification...

  8. Climate change increases riverine carbon outgassing, while export to the ocean remains uncertain

    Langerwisch, F.; Walz, A.; Rammig, A.; Tietjen, B.; Thonicke, K.; Cramer, W.


    , independent of the SRES scenario. The export of carbon to the atmosphere increases as well, with an average of about 30 %. In contrast, changes in future export of organic carbon to the Atlantic Ocean depend on the SRES scenario and are projected to either decrease by about 8.9 % (SRES A1B) or increase by about 9.1 % (SRES A2). Such changes in the terrigenous-riverine system could have local and regional impacts on the carbon budget of the whole Amazon basin and parts of the Atlantic Ocean. Changes in riverine carbon could lead to a shift in the riverine nutrient supply and pH, while changes in the exported carbon to the ocean lead to changes in the supply of organic material that acts as a food source in the Atlantic. On larger scales the increased outgassing of CO2 could turn the Amazon basin from a sink of carbon to a considerable source. Therefore, we propose that the coupling of terrestrial and riverine carbon budgets should be included in subsequent analysis of the future regional carbon budget.

  9. Some inner satellites of giant planets are still outgassing: Triton, Enceladus, Io

    Kochemasov, Gennady G.


    plumes of sulfur and sulfur dioxide hundreds of kilometers high. It is admitted that Io's orbital eccentricity is a main reason for volcanism creating its patchy atmosphere and plasma tore ("detached atmosphere"). It is interesting that the latest MESSENGER data show that spacious volcanic effusions cover Mercury and one region appears to have experienced a high level of volcanic activity. Chains of small deep pits occur in the region along with the larger 30 km across crater. The innermost planet Mercury is deeply degassed and almost dry. Areal volcanic effusions, clear traces of contraction (escarps or lobate ledges), numerous chains of deep pits (craters) controlled by lineaments or weakness zones witness this. Not able to keep an atmosphere in the close vicinity to mighty Sun, Mercury still has traces of Na, K, Ca, Mg, and noble gases in its exosphere (but it seems that sputtering from the surface is a main reason for their appearance). References: [1] Kochemasov G.G. (2006) Venus, Earth, Mars, Titan: intensity of wiping out volatiles from celestial bodies and building atmospheres //36th COSPAR Scientific Assembly, Beijing, China, 16-23 July 2006, Abstr. COSPAR2006-A-00789, CD-ROM; [2] Kochemasov G.G. (2009) A regular row of planetary relief ranges connected with tectonic granulations of celestial bodies // New Concepts in Global Tectonics Newsletter, # 51, 58-61. [3] Kochemasov, G.G. (2006). Outgassing of planets in relation to their orbital frequencies // EUROPLANET-2006 Sci. Conference, Sept.22-26, 2006, Berlin, EPSC Abstracts, Vol. 1, EPSC2006-A-00043, CD-ROM.

  10. Experimental and Numerical Simulations of the Solidification Process in Continuous Casting of Slab

    Liang Bai


    Full Text Available Thermal simulation equipment (TSE was recently developed to simulate the solidification process in the industrial continuous casting of slab. The grain growth, solid-liquid interface movement, and columnar-to-equiaxed transition (CET in the continuous casting process can be reproduced using this equipment. The current study is focused on the effects of different cooling rates and superheat conditions on the grain growth in the solidification process of chromium-saving ferritic stainless steel (B425. The temperature distribution and microstructure evolution are simulated by a Cellular Automaton-Finite Element (CAFE model. The experimental results demonstrate that the temperature gradient and the grain growth rate of the sample can be effectively controlled by the equipment. It is observed from optical micrographs of the microstructure that the average equiaxed grain ratio increases when the superheat temperature decreases. The average equiaxed grain ratio is approximately 26% and 42% under superheat conditions of 40 °C and 30 °C, respectively, and no apparent columnar grain generation in the samples occurs under superheat conditions of 10 °C and 20 °C, as the result of a large thermal resistance at the copper-sample interface and low superheat inside the sample. A lower cooling rate results in a higher equiaxed crystal ratio in the sample. As the cooling rate decreases, the equiaxed crystal ratio becomes 14%, 23%, and 42%. Comparing the simulation results with the experimental observations, a reasonable qualitative agreement is achieved for the chilled layer thickness, grain morphology, and CET in the sample. Thus, the CAFE model in the current study can accurately predict the grain growth under different superheating and cooling rate conditions.

  11. Modeling fluid interactions with the rigid mush in alloy solidification

    Plotkowski, Alexander J.

    Macrosegregation is a casting defect characterized by long range composition differences on the length scale of the ingot. These variations in local composition can lead to the development of unwanted phases that are detrimental to mechanical properties. Unlike microsegregation, in which compositions vary over the length scale of the dendrite arms, macrosegregation cannot be removed by subsequent heat treatment, and so it is critical to understand its development during solidification processing. Due to the complex nature of the governing physical phenomena, many researchers have turned to numerical simulations for these predictions, but properly modeling alloy solidification presents a variety of challenges. Among these is the appropriate treatment of the interface between the bulk fluid and the rigid mushy zone. In this region, the non-linear and coupled behavior of heat transfer, fluid mechanics, solute transport, and alloy thermodynamics has a dramatic effect on macrosegregation predictions. This work investigates the impact of numerical approximations at this interface in the context of a mixture model for alloy solidification. First, the numerical prediction of freckles in columnar solidification is investigated, and the predictive ability of the model is evaluated. The model is then extended to equiaxed solidification, in which the analogous interface is the transition of free-floating solid particles to a rigid dendritic network. Various models for grain attachment are investigated, and found to produce significant artifacts caused by the discrete nature of their implementation on the numerical grid. To reduce the impact of these artifacts, a new continuum grain attachment model is proposed and evaluated. The differences between these models are compared using uncertainty quantification, and recommendations for future research are presented.

  12. Simulating the Effect of Space Vehicle Environments on Directional Solidification of a Binary Alloy

    Westra, D. G.; Heinrich, J. C.; Poirier, D. R.


    for the rate of change of fraction of liquid as the liquid in an element solidifies. The new method enables us to contrast results of simulations in which the alloy is subjected to no gravity or a steady-state acceleration versus simulations when the alloy is subjected to vibration disturbances; therefore, the effect of vibration disturbances can be assessed more accurately. To assess the impact of these vibration-perturbations, transient accelerometer data from a space shuttle mission are used as inputs for the simulation model. These on-orbit acceleration data were obtained from the Microgravity Science Division at Glenn Research Center (GRC- MSD) and are applied to the buoyancy term of the momentum equation in a simulation of a Pb-5.8 wt. % Sb alloy that solidifies in a thermal gradient of 4000 K/m and a translation velocity of 3 p d s . Figure 2 shows the vertical velocity of a node that begins in the all-liquid region and subsequently solidifies; the vibrations are applied at 5000 seconds in this simulation. An important difficulty, common to all solidification models based on finite elements or 2 The magnitudes of the velocity oscillations that are vibration-induced are very small and acceptable. The biggest concern is whether the concentration of the liquid near the dendrite tips is distorted because of the vibration-induced perturbations. Results for this case show no concentration oscillations present in the all-liquid region.

  13. Rates and Mechanisms of Solidification in Large Magma Bodies: Implications for Melt Extraction in all Tectonic Settings

    VanTongeren, J. A.


    As is observed in both experiment and theory, in the absence of hydrothermal convection, the majority of magma chamber heat loss occurs via conduction through the roof of the intrusion and into the cold country rock above. The formation of an upper solidification front (or Upper Border Series, UBS), recorded in the rocks both geochemically and texturally, is a natural outcome of the progression of the solidification front from the cold roof to the hot center of the magma chamber. There are, however, a few unique layered mafic intrusions for which little or no UBS exists. In this study, I examine the thermal evolution and crystallization rates of several classic layered intrusions as it is recorded in the extent of the preserved UBS. For those intrusions that have experienced crystallization at the roof, such as the Skaergaard Intrusion, the development of a UBS reduces the temperature gradient at the roof and effectively slows the rate of heat loss from the main magma body. However, for those intrusions that do not have an UBS, such as the Bushveld Complex, the cooling rate is controlled only by the maximum rate of conductive heat loss through the overlying roof rocks, which decreases with time. The implications are two-fold: (1) The relative thickness of the UBS in large intrusions may be the key to quantifying their cooling and solidification rates; and (2) The nature of the magma mush zone near the roof of an intrusion may depend principally on the long-term thermal evolution of the magma body. Particularly at the end stages of crystallization, when the liquids are likely to be highly evolved and high viscosities may inhibit convection, intrusions lacking a well-defined UBS may provide important insights into the mechanics of crystal-liquid separation, melt extraction, and compaction in felsic plutons as well as mafic intrusions. These results are important for long-lived (>500 kyr) or repeatedly replenished magma chambers in all tectonic settings.

  14. Outgassing properties of ferrite materials after different treatments%不同处理方法下铁氧体出气性能的研究

    杨伟顺; 张军辉; 罗成; 蒙峻; 郭迪舟; 杨晓天; 赵玉刚; 胡振军; 侯生军


    As the main material of ion beam extraction component used in accelerator system, ferrite has to be treated to satisfy lower outgassing rate for vacuum up to 10~7~10~10 Pa. By the method of switching two pumping paths (SPP), outgassing properties of ferrite materials, which were treated by normal cleaning, high vacuum degassing and TiN coating, baking after exposing to air or N2, were measured and compared. The results show that all treatments can reduce the outgassing rate, but the TiN-coated sample after degassing and baking, exposing to N2, has the lowest outgassing rate.%为减少加速器束流快引出元件铁氧体材料真空出气量,对铁氧体材料进行真空除气、镀膜以及烘烤工艺处理.采用旁路切换法( SPP)测量不同处理条件下的出气率.结果表明,铁氧体材料经真空除气后镀TiN膜,在测试罩中经烘烤,冷却后充氮气测得的出气率最低.

  15. Mathematical Modeling of Binary Alloy Solidification

    R. Černý


    Full Text Available Te is simulated. Moving boundary conditions for temperatures are taken into account, which makes it possible to simulate the Bridgman method of crystal growth for instance. The computational experiments reveal a qualitative agreement of the numerically simulated and experimentally measured concentration fields. The influence of principal parameters of Bridgman growth and of the accuracy of material parameters is studied as well. Concerning the material parameters, the liquid/solid thermal conductivity ratio at the melting temperature is found to be the most important because it can affect the shape of the phase interface significantly, and therefore the temperature and concentration fields as well.

  16. Convective heat transfer during dendritic solidification

    Glicksman, M. E.; Huang, S. C.


    Experiments on succinonitrile are described in which the dependence of dendritic growth velocity is studied as a function of orientation with respect to gravity. Growth rate measurements were carried out at a relatively small supercooling, requiring high specimen purity as well as extreme thermal stability and precision temperature measurement. The normalized growth velocity showed a dependence on orientation described by the ratio of observed growth velocity to that expected for convection-free growth being equal to 3.52 times the n-th power of Cos half the orientation angle, where n lies between 0.5 and 0.75.

  17. Transport processes in directional solidification and their effects on microstructure development

    Mazumder, Prantik [Iowa State Univ., Ames, IA (United States)


    The processing of materials with unique electronic, mechanical, optical and thermal properties plays a crucial role in modern technology. The quality of these materials depend strongly on the microstructure and the solute/dopant fields in the solid product, that are strongly influenced by the intricate coupling of heat and mass transfer and melt flow in the growth systems. An integrated research program is developed that include precisely characterized experiments and detailed physical and numerical modeling of the complex transport and dynamical processes. Direct numerical simulation of the solidification process is carried out that takes into account the unsteady thermo-solutal convection in the vertical Bridgman crystal growth system, and accurately models the thermal interaction between the furnace and the ampoule by appropriately using experimentally measured thermal profiles. The flow instabilities and transitions and the nonlinear evolution following the transitions are investigated by time series and flow pattern analysis. A range of complex dynamical behavior is predicted with increasing thermal Rayleigh number. The route to chaos appears as: steady convection → transient mono-periodic → transient bi-periodic → transient quasi-periodic → transient intermittent oscillation-relaxation → stable intermittent oscillation-relaxation attractor. The spatio-temporal dynamics of the melt flow is found to be directly related to the spatial patterns observed experimentally in the solidified crystals. The application of the model to two phase Sn-Cd peritectic alloys showed that a new class of tree-like oscillating microstructure develops in the solid phase due to unsteady thermo-solutal convection in the liquid melt. These oscillating layered structures can give the illusion of band structures on a plane of polish. The model is applied to single phase solidification in the Al-Cu and Pb-Sn systems to characterize the effect of convection on the macroscopic

  18. Numerical Analysis of Temperature Gradients and Interface Shape During Directional Solidification of Al and Al-Cu Alloy Under Microgravity Conditions

    Bune, Andris V.; Sen, Subhayu; Mukherjee, Sundeep; Catalina, Adrian; Stefanescu, Doru M.


    Numerical modeling was undertaken to analyze the influence of radial thermal gradient on solid/liquid (s/1) interface shape and convection patterns during solidification of pure Al and Al-4 wt% Cu alloy. The objective of the numerical task was to predict the influence of convective velocity on an insoluble particle near a s/l interface. These predictions would then be used to define the minimum gravity level (g) required to investigate the fundamental physics of interaction between a particle and a s/I interface. To satisfy this objective, steady state calculations were performed for different gravity levels and orientations with the gravity vector. ne furnace configuration used in this analysis is the proposed International Space Station Furnace, Quench Module Insert (QMI) 1. Results from a thermal model of the furnace core were used as initial boundary conditions for solidification modeling. General model of binary alloy solidification was based on the finite element code FIDAP. It was found that for the worst case orientation of 90 degrees with the gravity vector and a g level of 10(exp -4)g(sub o) (g(sub o) = 9.8 m/s(exp 2)) the dominant forces acting on the particle would be the fundamental drag and interfacial forces.

  19. Structural Properties of Liquid SiC during Rapid Solidification

    WanJun Yan


    Full Text Available The rapid solidification of liquid silicon carbide (SiC is studied by molecular dynamic simulation using the Tersoff potential. The structural properties of liquid and amorphous SiC are analyzed by the radial distribution function, angular distribution function, coordination number, and visualization technology. Results show that both heteronuclear and homonuclear bonds exist and no atomic segregation occurs during solidification. The bond angles of silicon and carbon atoms are distributed at around 109° and 120°, respectively, and the average coordination number is <4. Threefold carbon atoms and fourfold silicon atoms are linked together by six typical structures and ultimately form a random network of amorphous structure. The simulated results help understand the structural properties of liquid and amorphous SiC, as well as other similar semiconductor alloys.

  20. Kinetic model of ductile iron solidification with experimental verification

    W. Kapturkiewicz


    Full Text Available A solidification model for ductile iron, including Weibull formula for nodule count has been presented. From this model, the following can be determined: cooling curves, kinetics of austenite and eutectic nucleation, austenite and eutectic growth velocity, volume fraction, distribution of Si and P both in austenite and eutectic grain with distribution in casting section.In the developed model of nodular graphite iron casting solidification, the correctness of the mathematical model has been experimentally verified in the range of the most significant factors, which include temperature field, the value of maximum undercooling, and the graphite nodule count interrelated with the casting cross-section. Literature offers practically no data on so confronted process model and simulation program.

  1. Modeling of solidification of MMC composites during gravity casting process

    R. Zagórski


    Full Text Available The paper deals with computer simulation of gravity casting of the metal matrix composites reinforced with ceramics (MMC into sand mold. The subject of our interest is aluminum matrix composite (AlMMC reinforced with ceramic particles i.e. silicon carbide SiC and glass carbon Cg. The created model describes the process taking into account solidification and its influence on the distribution of reinforcement particles. The computer calculation has been carried out in 2D system with the use of Navier-Stokes equations using ANSYS FLUENT 13. The Volume of Fluid approach (VOF and enthalpy method have been used to model the air-fluid free surface (and also volume fraction of particular continuous phases and the solidification of the cast, respectively.

  2. Solidification zoning and metallographic cooling rates of chondrites

    Willis, J.; Goldstein, J. I.


    The cooling rates of chondrites have been determined according to the cooling rate method of Wood (1967) which involves the measurement of the concentration of nickel in the interiors of taenite grains of various sizes. The present paper presents an investigation of the effect of zoning produced during solidification on the use of the Wood method. Cooling rate curves were obtained in a computer simulation based on a model of kamacite formation on the outer edge of a taenite sphere of uniform initial composition, followed by the inward radial progression of the kamacite-taenite interface. When a concentration gradient produced by solidification is present in the initial conditions, deviations from the cooling rate curves for uniform 10% Ni are obtained only at cooling rates greater than 1000 K/million years, which would result in an overestimation of the cooling rates based on observed Ni gradients in grains of radius greater than 20 microns.

  3. Computer modelling of solidification of pure metals and alloys

    Barkhudarov, M R


    differencing advection algorithm used in the simulations, the Leith's method is incorporated into the public domain two-dimensional SOLA code. It is shown that the resulting scheme is unconditionally stable despite being explicit. Two numerical models have been developed to describe the volumetric changes during solidification in pure metals and alloys and to predict shrinkage defects in the castings of general three-dimensional configuration. The first model is based on the full system of the Continuity, Navier-Stokes and Enthalpy Equations. Volumetric changes are described by introducing a source term in the Continuity Equation which is a function of the rate of local phase transformation. The model is capable of simulating both volumetric shrinkage and expansion. The second simplified shrinkage model involves the solution of only the Enthalpy Equation. Simplifying assumptions that the feeding flow is governed only by gravity and solidification rate and that phase transformation proceeds only from liquid to...

  4. Solidification and ordering during directional drying of a colloidal dispersion.

    Goehring, Lucas; Clegg, William J; Routh, Alexander F


    During drying, colloidal dispersions undergo processes such as solidification, cracking, and the draining of interstitial pores. Here we show that the solidification of polystyrene and silica dispersions, during directional drying, occurs in two separate stages. These correspond to the initial ordering and subsequent aggregation of the colloidal particles. Transitions between these stages are observed as changes in transparency and color that propagate as distinct fronts along the drying layer. The dynamics of these fronts are shown to arise from a balance between compressive capillary forces and the electrostatic and van der Waals forces described by DLVO theory. This suggests a simple method by which the maximum interparticle repulsion between particles can be measured through the optical inspection of the dynamics of a drying dispersion, under a microscope.

  5. Inverse problem for porosity estimation during solidification of TNT

    Aldélio Bueno Caldeira


    Full Text Available In the present study, the porosity formed during the solidification process is estimated by an inverse problem technique based on particle swarm optimization. The effective heat capacity method is adopted to model the heat transfer problem. The transient-diffusive heat transfer equation is solved numerically by the finite volume method with an explicit scheme, employing the central difference interpolation function. The solution of the direct problem is compared to reference solutions. The model is applied to trinitrotoluene (TNT solidification process. The results show that the proposed procedure was able to estimate the porosity for different Stefan numbers. The analysis of the heat flux in the mold is indicated to predict the porosity formation during the casting process.

  6. Fluid mechanics of directional solidification at reduced gravity

    Chen, C. F.


    The primary objective of the proposed research is to provide additional groundbased support for the flight experiment 'Casting and Solidification Technology' (CAST). This experiment is to be performed in the International Microgravity Laboratory-1 (IML-1) scheduled to be flown on a space shuttle mission scheduled for 1992. In particular, we will provide data on the convective motion and freckle formation during directional solidification of NH4Cl from its aqueous solution at simulated parameter ranges equivalent to reducing the gravity from the sea-level value down to 0.1 g or lower. The secondary objectives of the proposed research are to examine the stability phenomena associated with the onset of freckles and the mechanisms for their subsequent growth and decline (to eventual demise of some) by state-of-the-art imaging techniques and to formulate mathematical models for the prediction of the observed phenomena.

  7. Supporting the model of ductile iron dendritic solidification

    Santos, H.M.C.M. [Porto Univ. (Portugal). Metall. and Mater. Dept.; Pinto, A.M.P. [Minho Univ. (Portugal). Mechanical Engineering Dept.; Jacinto, M.C.P.L. [Porto Polytechnic Inst. and INEGI, Porto (Portugal). Mechanical Engineering Dept.; Sa, C.P.M. [Porto Univ. (Portugal). Materials Center


    Microsegregation in ductile iron is generally accepted as modelled by a regular pattern: the graphite promoter elements are assumed to concentrate in the neighborhood of the graphite nodules and the carbide forming elements in the eutectic cell boundaries. The authors have conducted several microanalyses in several ductile irons and concluded that the microsegregation pattern does not agree with this model but supports the mechanism of dendritic ductile iron solidification. (orig.)

  8. [Application of solidification technology in ecological protection of rural riverbank].

    Fu, Rong-bing; Chen, Xiao-hua; Luo, Qi-shi; Zhang, Shu-jiu; Li, Xiao-ping; Geng, Chun-nü


    A self-developed binder was used for the solidification of construction refuse piles and whole soil matrix, and a technology of this solidification combining with grass-planting was adopted to ecologically protect the rural riverbanks at Tianshan Village of Shanghai. This technology and other ecological engineering techniques were also employed to reconstruct the ecological environment of a sewage pond at the Village. The results showed that the solidified piles had an anti-compression strength of up to 7.3 MPa, with good hydraulic permeability, fast hardening rate, and low drying shrinkage, which met the requirements for ecological safety. The solidified stakes could be used at a low temperature of above -18 degrees C with addition of certain anti-freezing agents. The riverbank underpinned with the solidified stakes had higher anti-compressive strength, higher ability of anti-soil erosion, and better hydraulic permeability; and its soil had the similar moisture content to bare riverbank soil, with no detrimental effects on the root growth of planted grass. After soil solidification, the shearing strength of the riverbank increased by 50 times, and its soil loss was only 5% of the bare riverbank. In the first 10 days after adopting this technology, parts of Cynodon dactylon roots on the surface of solidified soil matrix began to extend into soil; after one month, 60% of the roots penetrated into deeper soil layer; and 11 months later, the grass roots completely grew in-depth in the soil. The combination of our solidification technique with vegetation reconstruction satisfied the requirements of both stabilizing riverbank and improving riparian habitat.

  9. Development Of A Magnetic Directional-Solidification Furnace

    Aldrich, Bill R.; Lehoczky, Sandor L.


    Report describes development of directional-solidification furnace in which axial magnetic field is imposed by surrounding ring permanent magnets and/or electromagnets and pole pieces. Furnace provides controlled axial temperature gradients in multiple zones, through which ampoule containing sample of material to be solidified is translated at controlled speed by low-vibration, lead-screw, stepping-motor-driven mechanism. Intended for use in low-gravity (spaceflight) experiments on melt growth of high-purity semiconductor crystals.

  10. Interface Pattern Selection Criterion for Cellular Structures in Directional Solidification

    Trivedi, R.; Tewari, S. N.; Kurtze, D.


    The aim of this investigation is to establish key scientific concepts that govern the selection of cellular and dendritic patterns during the directional solidification of alloys. We shall first address scientific concepts that are crucial in the selection of interface patterns. Next, the results of ground-based experimental studies in the Al-4.0 wt % Cu system will be described. Both experimental studies and theoretical calculations will be presented to establish the need for microgravity experiments.

  11. Advances on Microstructure Modeling of Solidification Process of Shape Casting

    柳百成; 许庆彦


    Simulation technology for shape casting at macro-scale has been successfully put into engineering application in a number of casting plants and as a result the quality of castings is assured, the research and development time is shortened, and the manufacturing cost is greatly saved as well. In this paper, modeling and simulation technologies of solidification process of shape casting at microstructure-scale, especially deterministic, cellular automaton, and phase field models are studied and reviewed.

  12. Fluid mechanics and solidification investigations in low-gravity environments

    Fichtl, G. H.; Lundquist, C. A.; Naumann, R. J.


    Fluid mechanics of gases and liquids and solidification processes were investigated under microgravity conditions during Skylab and Apollo-Soyuz missions. Electromagnetic, acoustic, and aerodynamic levitation devices, drop tubes, aircraft parabolic flight trajectories, and vertical sounding rockets were developed for low-g simulation. The Spacelab 3 mission will be carried out in a gravity gradient flight attitude; analyses of sources of vehicle dynamic accelerations with associated g-levels and angular rates will produce results for future specific experiments.

  13. Solidification and microstructure of thin walled ductile cast iron

    Pedersen, Karl Martin


    In the recent years there has been an increasing interest in light constructions in order to save weight in e.g. cars. Ductile cast iron has good mechanical properties but it is necessary to re­duce the wall thicknesses of the castings in order to reduce the weight. Reducing the wall thicknesses...... of the casting will increase the cooling rates and by that change the conditions for nucleation and growth during solidification....

  14. Accelerated aging of solid lubricants for the W76-1 TSL : effects of polymer outgassing.

    Dugger, Michael Thomas; Wallace, William O.; Huffman, Elizabeth M.


    The behavior of MoS{sub 2} lubricants intended for the W76-1 TSL was evaluated after 17 and 82 thermal cycles, each lasting seven days and including a low temperature of -35 C and a high temperature of 93 C, in a sealed container containing organic materials. The MoS{sub 2} was applied by tumbling with MoS{sub 2} powder and steel pins (harperized), or by spraying with a resin binder (AS Mix). Surface composition measurements indicated an uptake of carbon and silicon on the lubricant surfaces after aging. Oxidation of the MoS{sub 2} on harperized coupons, where enough MoS{sub 2} was present at the surface to result in significant Mo and S concentrations, was found to be minimal for the thermal cycles in an atmosphere of primarily nitrogen. Bare steel surfaces showed a reduction in friction for exposed coupons compared to control coupons stored in nitrogen, at least for the initial cycles of sliding until the adsorbed contaminants were worn away. Lubricated surfaces showed no more than a ten percent increase in steady-state friction coefficient after exposure. Initial coefficient of friction was up to 250 percent higher than steady-state for AS Mix films on H950 coupons after 82 thermal cycles. However, the friction coefficient exhibited by lubricated coupons was never greater than 0.25, and more often less than 0.15, even after the accelerated aging exposures.

  15. Solidification microstructures and solid-state parallels: Recent developments, future directions

    Asta, M. [Department of Chemical Engineering and Materials Science, University of California at Davis, Davis, CA 95616 (United States); Beckermann, C. [Department of Mechanical and Industrial Engineering, University of Iowa, Iowa City, IA 52242 (United States); Karma, A. [Department of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston, MA 02115 (United States); Kurz, W. [Institute of Materials, Ecole Polytechnique Federale de Lausanne (EPFL), 1015 Lausanne (Switzerland)], E-mail:; Napolitano, R. [Department of Materials Science and Engineering, Iowa State University, and Ames Laboratory USDOE, Ames, IA 50011 (United States); Plapp, M. [Physique de la Matiere Condensee, Ecole Polytechnique, CNRS, 91128 Palaiseau (France); Purdy, G. [Department of Materials Science and Engineering, McMaster University, Hamilton, Ont., L8S 4L7 (Canada); Rappaz, M. [Institute of Materials, Ecole Polytechnique Federale de Lausanne (EPFL), 1015 Lausanne (Switzerland); Trivedi, R. [Department of Materials Science and Engineering, Iowa State University, and Ames Laboratory USDOE, Ames, IA 50011 (United States)


    Rapid advances in atomistic and phase-field modeling techniques as well as new experiments have led to major progress in solidification science during the first years of this century. Here we review the most important findings in this technologically important area that impact our quantitative understanding of: (i) key anisotropic properties of the solid-liquid interface that govern solidification pattern evolution, including the solid-liquid interface free energy and the kinetic coefficient; (ii) dendritic solidification at small and large growth rates, with particular emphasis on orientation selection; (iii) regular and irregular eutectic and peritectic microstructures; (iv) effects of convection on microstructure formation; (v) solidification at a high volume fraction of solid and the related formation of pores and hot cracks; and (vi) solid-state transformations as far as they relate to solidification models and techniques. In light of this progress, critical issues that point to directions for future research in both solidification and solid-state transformations are identified.

  16. Microstructural development of rapid solidification in Al-Si powder

    Jin, Feng [Iowa State Univ., Ames, IA (United States)


    The microstructure and the gradient of microstructure that forms in rapidly solidificated powder were investigated for different sized particles. High pressure gas atomization solidification process has been used to produce a series of Al-Si alloys powders between 0.2 μm to 150 μm diameter at the eutectic composition (12.6 wt pct Si). This processing technique provides powders of different sizes which solidify under different conditions (i.e. interface velocity and interface undercooling), and thus give different microstructures inside the powders. The large size powder shows dendritic and eutectic microstructures. As the powder size becomes smaller, the predominant morphology changes from eutectic to dendritic to cellular. Microstructures were quantitatively characterized by using optical microscope and SEM techniques. The variation in eutectic spacing within the powders were measured and compared with the theoretical model to obtain interface undercooling, and growth rate during the solidification of a given droplet. Also, nucleation temperature, which controls microstructures in rapidly solidified fine powders, was estimated. A microstructural map which correlates the microstructure with particle size and processing parameters is developed.

  17. Non-Equilibrium Solidification of Undercooled Metallic Melts

    Dieter M. Herlach


    Full Text Available If a liquid is undercooled below its equilibrium melting temperature an excess Gibbs free energy is created. This gives access to solidification of metastable solids under non-equilibrium conditions. In the present work, techniques of containerless processing are applied. Electromagnetic and electrostatic levitation enable to freely suspend a liquid drop of a few millimeters in diameter. Heterogeneous nucleation on container walls is completely avoided leading to large undercoolings. The freely suspended drop is accessible for direct observation of rapid solidification under conditions far away from equilibrium by applying proper diagnostic means. Nucleation of metastable crystalline phases is monitored by X-ray diffraction using synchrotron radiation during non-equilibrium solidification. While nucleation preselects the crystallographic phase, subsequent crystal growth controls the microstructure evolution. Metastable microstructures are obtained from deeply undercooled melts as supersaturated solid solutions, disordered superlattice structures of intermetallics. Nucleation and crystal growth take place by heat and mass transport. Comparative experiments in reduced gravity allow for investigations on how forced convection can be used to alter the transport processes and design materials by using undercooling and convection as process parameters.

  18. Solidification of sediment contaminated with volatile chlorinated hydrocarbons

    Schwarz, E.J. [Anchor QEA LLC, Portland, OR (United States)


    A series of bench-scale treatability tests were used to evaluate the effectiveness of various solidification reagents in treating sediments contaminated with high concentrations of chlorinated hydrocarbons. The effectiveness of Portland cement, cement kiln dust, lime kiln dust, fly ash, and a combination of silica and lime were was assessed relative to their ability to reduce the leaching of contaminants, increase the strength of the contaminated sediment, and reduce the hydraulic conductivity of the sediments. The aim of the study was to develop a design for treating sediments in a stagnant water body located on the grounds of an industrial facility. The sediments were predominantly fine-grained and high in organic content. Preliminary tests identified Portland cement and the silica and lime mixture as achieving the desired strength and resistance to leaching. The solidification reagents were used to solidify more than 11,000 cubic yards of sediment with a mixture of 2 fly ashes. The full-scale solidification project surpassed the required standards for strength and permeability. 10 refs., 4 tabs., 3 figs.

  19. Impact of Metal Droplets: A Numerical Approach to Solidification

    Koldeweij, Robin; Mandamparambil, Rajesh; Lohse, Detlef


    Layer-wise deposition of material to produce complex products is a subject of increasing technological relevance. Subsequent deposition of droplets is one of the possible 3d printing technologies to accomplish this. The shape of the solidified droplet is crucial for product quality. We employ the volume-of-fluid method (in the form of the open-source code Gerris) to study liquid metal (in particular tin) droplet impact. Heat transfer has been implemented based on the enthalpy approach for the liquid-solid phase. Solidification is modeled by adding a sink term to the momentum equations, reducing Navier-Stokes to Darcy's law for high solid fraction. Good agreement is found when validating the results against experimental data. We then map out a phase diagram in which we distinguish between solidification behavior based on Weber and Stefan number. In an intermediate impact regime impact, solidification due to a retracting phase occurs. In this regime the maximum spreading diameter almost exclusively depends on Weber number. Droplet shape oscillations lead to a broad variation of the morphology of the solidified droplet and determine the final droplet height. TNO.

  20. Solidification microstructure formation in HK40 and HH40 alloys

    Ding, Xian-fei; Liu, Dong-fang; Guo, Pei-liang; Zheng, Yun-rong; Feng, Qiang


    The microstructure formation processes in HK40 and HH40 alloys were investigated through JmatPro calculations and quenching performed during directional solidification. The phase transition routes of HK40 and HH40 alloys were determined as L → L + γ → L + γ + M7C3 → γ + M7C3 → γ + M7C3 + M23C6→ γ + M23C6 and L → L + δ → L + δ + γ→ L + δ + γ + M23C6 δ + γ + M23C6, respectively. The solidification mode was determined to be the austenitic mode (A mode) in HK40 alloy and the ferritic-austenitic solidification mode (FA mode) in HH40 alloy. In HK40 alloy, eutectic carbides directly precipitate in a liquid and coarsen during cooling. The primary γ dendrites grow at the 60° angle to each other. On the other hand, in HH40 alloy, residual δ forms because of the incomplete transformation from δ to γ. Cr23C6 carbide is produced in solid delta ferrite δ but not directly in liquid HH40 alloy. Because of carbide formation in the solid phase and no rapid growth of the dendrite in a non-preferential direction, HH40 alloy is more resistant to cast defect formation than HK40 alloy.

  1. Successful Completion of Outward Transport Disposal Stage Ⅰ of Radioactive Cement Solidification

    DU; Hong-ming; LIU; Fu-guo; JIN; Song


    As the last batch of solidification barrels arriving at the repository on May 5th,2013,the outward transport disposal stage I of radioactive cement solidification completed successfully.This project started in May,2011,lasted for 19 months,during which 9 batches,3 300 barrels of cement solidification,had been retrieved and transferred.It is a lot of preparation work and continuous improvement that to ensure the safety of the outbound work.

  2. Characterization of Solidification and Solid State Transformation in Duplex Cast Steel: Thermo-Calc Investigation


    The paper presents a characteristic of solidification process and changes occurring in the solid state in a duplex cast steel. Theoretical chemical composition of individual phases, its changes during solidification and cooling after solidification and also changes in volume fractions of phases versus temperature have been determined. Theoretical results of Thermo-Calc analysis have been correlated with the microstructure of as-cast cast steel as well as with analysis of chemical composition ...

  3. Effect of solidification rate on microstructure evolution in dual phase microalloyed steel.

    Kostryzhev, A G; Slater, C D; Marenych, O O; Davis, C L


    In steels the dependence of ambient temperature microstructure and mechanical properties on solidification rate is not well reported. In this work we investigate the microstructure and hardness evolution for a low C low Mn NbTi-microalloyed steel solidified in the cooling rate range of 1-50 Cs(-1). The maximum strength was obtained at the intermediate solidification rate of 30 Cs(-1). This result has been correlated to the microstructure variation with solidification rate.

  4. Analysis of a solidification interface stability Al - Cu by the heat balance integral method

    B. Magiera


    Full Text Available The aim of his thesis is the analysis of a planar interface solidification stability of alloys. The stability of a planar interface solidification is tested by means of solving the heat conduction equation for solids and liquid and a mass diffusion equation for liquid, under assumed boundary, initial and continuity conditions. The solidification equations are solved using the method of heat balance integral and the theorem of the derivative integrals, whose limitsdepend on the parameter.

  5. Gas flow analysis during thermal vacuum test of a spacecraft.

    Scialdone, J. J.


    The pressures indicated by two tubulated ionization gages, one pointing to a spinning spacecraft undergoing thermal vacuum test and the other the walls of the chamber, have been used in a computer program to calculate important parameters of flow kinetics in the vacuum chamber. These parameters calculated as a function of time are: the self-contamination of the spacecraft (defined as the return of outgassed molecules on its critical surfaces either in orbit or while undergoing vacuum test); the spacecraft outgassing including leaks from sealed compartments; and the gas pumping performance of the vacuum chamber. The test indicated the feasibility of this type of evaluation and the improvements in instrumentations and arrangements needed for future tests.

  6. Numerical simulation on directional solidification of Al-Ni-Co alloy based on FEM

    Yang Zhili


    Full Text Available The ratio, of the temperature gradient at the solidification front to the solidification rate of solid-liquid interface, plays a large part in columnar grain growth. The transient temperature fields of directional solidification of Al-Ni-Co alloy were studied by employing a finite element method. The temperature gradient at the solidification front and the solidification rate were analyzed for molten steels pouring at different temperatures. The results show that with different initial pouring temperatures, the individual ratio of the temperature gradient at solidification front to the solidification rate soars up in the initial stage of solidification, then varies within 2,000-6,000 ℃·s·cm-2, and finally goes down rapidly and even tend to be closed to each other when the solidification thickness reaches 5-6 cm. The simulation result is consistent with the practical production which can provide an available reference for process optimization of directional solidified Al-Ni-Co alloy.

  7. The Solidification Velocity of Undercooled Nickel and Titanium Alloys with Dilute Solute

    Algoso, Paul R.; Altgilbers, A. S.; Hofmeister, William H.; Bayuzick, Robert J.


    The study of solidification velocity is important for two reasons. First, understanding the manner in which the degree of undercooling of the liquid and solidification velocity affect the microstructure of the solid is fundamental. Second, there is disagreement between theoretical predictions of the relationship between undercooling and solidification velocity and experimental results. Thus, the objective of this research is to accurately and systematically quantify the solidification velocity as a function of undercooling for dilute nickel-and titanium-based alloys. The alloys chosen for study cover a wide range of equilibrium partition coefficients, and the results are compared to current theory.

  8. MPS Solidification Model. Volume 2: Operating guide and software documentation for the unsteady model

    Maples, A. L.


    The operation of solidification Model 2 is described and documentation of the software associated with the model is provided. Model 2 calculates the macrosegregation in a rectangular ingot of a binary alloy as a result of unsteady horizontal axisymmetric bidirectional solidification. The solidification program allows interactive modification of calculation parameters as well as selection of graphical and tabular output. In batch mode, parameter values are input in card image form and output consists of printed tables of solidification functions. The operational aspects of Model 2 that differ substantially from Model 1 are described. The global flow diagrams and data structures of Model 2 are included. The primary program documentation is the code itself.

  9. Numerical investigation of a binary solidification design problem

    Hale, Scott Wayne

    This exposition presents the development and application of a methodology for control of unidirectional solidification of a binary alloy. In particular, it is desired to produce a casting that has a uniform cast structure throughout its entire length. Furthermore, the methodology allows the specification, a priori, of the cast structure with respect to both scale, i.e., fine or coarse, and morphology, i.e., dentritic or cellular. This specification is in the form of a map that relates solidification characteristics, i.e., scale and morphology, to the solidification velocity and liquid-side interfacial temperature gradient. Thus design is accomplished by controlling these two parameters during the solidification process. With this in mind, the goal of what is termed the binary solidification design problem is the prediction of a set of boundary temperatures and heat fluxes which when applied will result in the desired interfacial motion and temperature gradient and therefore cast structure. Mathematical models for problems of this type lead to what are termed ill-posed systems in that they may not exhibit existence, uniqueness, or continuous dependence on boundary data. The resolution of this class of problems requires advanced techniques to overcome the instabilities encountered due to their ill-posed nature. The methodology developed herein employs the classical weight residual approach in a innovative manner. Normally, in the solution of a parabolic partial differential equation, such as the heat equation, a spatial series expansion with time varying coefficients is utilized along with a minimization technique to reduce the partial differential equation to a set of first order ordinary differential equations. This set can be solved using any number of numerical technique, i.e., Runge-Kutta, to obtain the temporal variation of the coefficients. These types of time stepping techniques eventually lead to the onset of instability when employed for the resolution of

  10. Skaergaard vs Sudbury: Solidification Times and Crystal Sizes

    Marsh, B. D.; Mittal, T.; Currier, R. M.; Jordon, E.


    The overall cooling time of a batch of magma is intimately reflected in the nature of the crystal sizes. The thinner are dikes and sills the finer grained are the crystals they display. And the spatial variations in crystal size and abundance record the spatial progression of solidification. Chilled margins are fine grained because of rapid solidification, and a progressive inward increase in crystal size is perfectly predictable by coupling a law of crystal growth with a suitable solidification front-based cooling model. When observed crystal sizes are much larger than predicted, as in finding phenocrysts near or in chilled margins, this is a clear indication of crystals grown and entrained prior to final emplacement and solidification. This is exactly the process exhibited by volcanics carrying swarms of large crystals. But in plutonic rocks there is frequent confusion over what crystal sizes to expect, especially when the pluton size and shape is poorly known, and there is often an unexpressed feeling that fine grained (i.e., non-phenocryst bearing) bodies almost regardless of size somehow cool fundamentally different than large bodies, especially layered intrusions. An invaluable standard state body to which to compare the crystal sizes of other large bodies is the Sudbury impact melt sheet. Formed in a few minutes, the 3km thick 200 km wide superheated melt sheet cooled and crystallized to produce a systematic and predictable internal variation in crystal size and abundance (Zieg & Marsh, 2002, JPet). Buried by 3km of fallback debris, the sheet took about 100,000 to solidify. The Skaergaard intrusion is of a similar thickness (3.4-4 km), but is much less extensive, being more like a thin-edged elliptical laccolith (Norton et. al., 1984, JGR) or a fault-bounded loaf of bread (7.75 x 10.55 x 3.7 km; Nielsen, 2004, JPet). In spite of its limited extent, the extent is large enough for solidification of the thickest parts time to approach that of an infinite sheet

  11. Effects of cooling rate on solidification behavior of dilute Al-Sc and Al-Sc-Zr solid solution

    金头男; 聂祚仁; 徐国富; 阮海琼; 杨军军; 付静波; 左铁镛


    Six alloys with different compositions of Al-0.1%Sc, Al-0.3%Sc, Al-0.3%Zr, Al-0.1% Sc-0. 1%Zr,Al-0.3%Sc-0.1%Zr and Al-0.3%Sc-0.3%Zr were prepared by casting in a wedge shaped copper mould. The hardness test, microstructure observation, and DSC thermal analysis were applied to fully investigate the solidification behavior of the wedge tip (whose cooling rate is 1 000 K/s) and the top surface (cooling rate 100 K/s) of each casting. The results show that the cast structures in the hypoeutectic region of Al-Sc alloys are slightly affected by cooling rates during the solidification. In the case of hypereutectic alloy of Al-0.3%Sc-0.3%Zr , the cast grains were remarkably refined under the condition of a 100 K/s cooling rate, however, under a 1 000 K/s cooling rate condition,solute atoms contribute nothing to the grain-refinement, due to the eutectic concentration becomes higher. The hardness can be improved to a greater degree by Sc single addition, compared to single Zr addition, but it can be improved even greater when Sc added together with Zr. It is sensitive to cooling rate, the higher the cooling rate, the greater the hardness. By combining the results of TEM examination and DSC analysis, it can be seen that a supersaturated Al solid solution forms during the solidification, and the solubility of Sc in Al solution can be improved by increasing the cooling rate.

  12. Heat flow model for pulsed laser melting and rapid solidification of ion implanted GaAs

    Kim, Taeseok; Pillai, Manoj R.; Aziz, Michael J.; Scarpulla, Michael A.; Dubon, Oscar D.; Yu, Kin M.; Beeman, Jeffrey W.; Ridgway, Mark C.


    In order to further understand the pulsed-laser melting (PLM) of Mn and N implanted GaAs, which we have used to synthesize thin films of the ferromagnetic semiconductor Ga1-xMnxAs and the highly mismatched alloy GaNxAs1-x, we have simulated PLM of amorphous (a-) and crystalline (c-) GaAs. We present a numerical solution to the one-dimensional heat equation, accounting for phase-dependent reflectivity, optical skin depth, and latent heat, and a temperature-dependent thermal conductivity and specific heat. By comparing the simulations with experimental time-resolved reflectivity and melt depth versus laser fluence, we identify a set of thermophysical and optical properties for the crystalline, amorphous, and liquid phases of GaAs that give reasonable agreement between experiment and simulation. This work resulted in the estimation of thermal conductivity, melting temperature and latent heat of fusion of a-GaAs of 0.008 W/cm K at 300 K, 1350 K, and 2650 J/cm3, respectively. These materials properties also allow the prediction of the solidification velocity of crystalline and ion-amorphized GaAs.

  13. Adjoint analyses of enhanced solidification for shape optimization in conjugate heat transfer problem

    Morimoto, Kenichi; Kinoshita, Hidenori; Suzuki, Yuji


    In the present study, an adjoint-based shape-optimization method has been developed for designing extended heat transfer surfaces in conjugate heat transfer problems. Here we specifically consider heat conduction-dominated solidification problem under different thermal boundary conditions: (i) the isothermal condition, and (ii) the conjugate condition with thermal coupling between the solidified liquid and the solid wall inside the domain bounded by the extended heat transfer surface. In the present shape-optimization scheme, extended heat transfer surfaces are successively refined in a local way based on the variational information of a cost functional with respect to the shape modification. In the computation of the developed scheme, a meshless method is employed for dealing with the complex boundary shape. For high-resolution analyses with boundary-fitted node arrangement, we have introduced a bubble-mesh method combined with a high-efficiency algorithm for searching neighboring bubbles within a cut-off distance. The present technique can be easily applied to convection problems including high Reynolds number flow. We demonstrate, for the isothermal boundary condition, that the present optimization leads to tree-like fin shapes, which achieve the temperature field with global similarity for different initial fin shapes. We will also show the computational results for the conjugate condition, which would regularize the present optimization due to the fin-efficiency effect.

  14. Thermal-vacuum effects on polymer matrix composite materials

    Tennyson, R. C.; Mabson, G. E.


    Results are presented on the thermal-vacuum response of a variety of fiber reinforced polymers matrix composites that comprised the UTIAS experiment on the LDEF satellite. Theoretical temperature-time predictions for this experiment are in excellent agreement with test data. Results also show quite clearly the effect of outgassing in the dimensional changes of these materials and the corresponding coefficients of thermal expansion. Finally, comparison with ground-based simulation tests are presented as well. Use of these data for design purposes are also given.

  15. Constrained/unconstrained solidification within the massive cast steel/iron ingots

    W. S. Wołczyński


    Full Text Available Some properties of the ingot and especially of the steel forging ingots depend on the ratio of a columnar structure area to an equiaxed structure area created during solidification. The C-E transition is fundamental phenomenon that can be applied to characterize massive cast steel ingots produced by the casting house. The mentioned ratio is created spontaneously due to the rate of heat transfer towards the ceramic mould and then to the environment. The ceramic mould operates as an isolator. So that the thickness of the mould together with a growing solid fraction control the heat transfer and finally the ratio of the columnar structure area to the equiaxed structure area. At first the increase of heat accumulation within the ceramic mould is observed. Next the stationary state for heat transfer is created and finally a gentle abatement of the mould temperature associated with the heat output to the environment is expected. The steep thermal gradients correspond to the increase of heat accumulation in the ceramic mould. The steep thermal gradients are required to promote the columnar structure formation. The full heat accumulation in the mould corresponds well with the C-E transformation while the appearance of the moderate thermal gradients is referred to the gentle temperature abatement within the ceramic mould. The equiaxed structure is expected within this period of heat transfer behavior. The steep thermal gradients involve the activity of viscosity gradient in the liquid. As the result a sedimentary cones are formed at the bottom of the ingot. The C-E transformation is associated with competition between columnar and equaixed structure formation. At the end of competition a fully equiaxed structure is formed. The viscosity gradient is replaced by the thermophoresis which is the driving force for the deposition of some equiaxed grain layers onto the surface of C+E zone. The convection together with the gravity allow the layers to be uniform

  16. Minimizing Segregation during the Controlled Directional Solidification of Dendric Alloys

    Grugel, Richard N.; Fedoseyev, Alex; Kim, Shin-Woo


    Gravity-driven convection induced in the liquid by density gradients of temperature or composition disrupts uniform dendritic growth during controlled directional solidification and promotes severe macrosegregation. The solute-rich region about the dendrite tip appears to play a pivotal role in channel initiation. Allen and Hunt referred to this region as an "initial transient" or dynamic region constituting steep concentration gradients. Experimental investigation also point to the role the tip region plays in developing microstructure. Hellawell and co-workers showed that flow-through dendritic channels could be effectively disrupted, and segregation minimized, during the gradient freezing of bulk castings by rotating the melt through a slight angle with respect to Earth's gravity vector. Adapting this principle to controlled directional solidification, it has been shown" that segregation in dendritic alloys can be minimized, and properties improved, by processing the sample near horizontal in conjunction with a slow axial rotation of the crucible. It is postulated that the observed microstructural uniformity arises by maintaining the developing solute field about the dendrite tip. Solute rejected during vertical directional solidification will rise or sink parallel to the primary dendrite arms during axial rotation setting the stage for accumulation, instabilities, and segregation. In contrast, during horizontal growth, the rejected solute will sink or rise perpendicular to the primary dendrite. Now, in the presence of a slight axial rotation, solute that was initially sinking (or rising) will find itself above (or below) its parent dendrite, i.e., still about the tip region. The following is intended to experimentally demonstrate the viability of this concept in coordination with a model that gives predictive insight regarding solute distribution about growing dendrites. Alloys based on the lead-tin eutectic system were used in this study. The system is well

  17. Effect of solidification parameters on the secondary dendrite arm spacing in MAR M-247 superalloy determined by a novel approach

    Milenkovic S.; Rahimian M.; Sabirov I.; Maestro L.


    The effect of solidification parameters on the secondary dendrite arm spacing in a MAR-M247 Ni-based superalloy has been studied by a novel approach, based on physical simulation of melting/solidification experiment with a constant cooling rate and variable temperature gradient. The applied experimental method proved to be efficient as it yielded a spread of microstructures corresponding to a range of well controlled solidification rates in a single melting/solidification experiment. In addit...

  18. Widmannstätten laths in Ti48Al2Cr2Nb alloy by undercooled solidification

    Liu, Yi; Hu, Rui, E-mail:; Yang, Guang; Kou, Hongchao; Zhang, Tiebang; Wang, Jun; Li, Jinshan


    Widmannstätten laths in Ti48Al2Cr2Nb alloy were obtained by containerless electromagnetic levitation during undercooled solidification rather than heat treatments in most cases. The nucleation of γ{sub Widmannstätten} is confirmed by the thermal history of the second recalescence behaviour. High dislocation density, stacking faults and dislocation slip are observed by transmission electron microscopy. By quantitative analysis of the transformation energy, the driving force for γ{sub Widmannstätten} in the solid state phase transformation is calculated, compared with that of heat treatments. Meanwhile, the proper undercoolings (ΔT = 257–300 K), post-solidification cooling rates (11.1–29.1 K/s), the fine lamellar colony sizes (306–467 μm) and proper undercoolings in the solid state phase transformation are in favour of promoting the formation of Widmannstätten laths at moderate undercoolings. - Graphical abstract: Display Omitted - Highlights: • Widmannstätten laths were observed in undercooled TiAl alloy. • The influencing factors were discussed in undercooled TiAl alloy. • An analysis of the nucleation of γ{sub Widmannstätten} is carried out.

  19. Phase transformation of cordierite ceramics in solidification of the melt. Gyoko katei niokeru cordierite ceramics no so hentai

    Takebe, H. (Kyushu Univ., Fukuoka (Japan)); Morinaga, K., (Kyushu Univ., Fukuoka (Japan). Graduate School of Engineering Sciences)


    Cordierite ceramics which has such properties as low thermal expansion and low permittivity, etc. is generally made by the sintering process and the vitrification. In this study, an examination was made on the conditions to obtain cordierite ceramics during the process of the solidification and crystallization of the melt of the cordierite composition (2MgO, 2Al {sub 2} O {sub 3}, 5SiO {sub 2} ) and the phase transformation of cordierite in the solidification process was discussed. The main conclusions are as follows: the cordierite phase was not crystallized even when the melt of cordierite composition was put under the continuous cooling process; the above phase was crystallized when the melt was cooled quickly down to a specified temperature without crystallization and then was crystallized in the isothermal condition. In other words, at 1673k, mullite was crystallized first, then at 1623k, LOW-cordierite was identified. Furthermore, at 1253k, {mu} -cordierite was crystallized first, then at 1223k, the transformation from the {mu} -cordierite to the {alpha} -cordierite was identified. 17 refs., 7 figs., 1 tab.

  20. Containerless Solidification and Characterization of Industrial Alloys (NEQUISOL)

    Ilbagi, A.; Henein, H.; Chen, J.; Herlach, D. M.; Lengsdorf, R.; Gandin, Ch-A.; Tourret, D.; Garcia-Escorial, A.


    Containerless solidification using electromagnetic levitator (EML), gas atomization and an instrumented drop tube, known as impulse atomization is investigated for Al-Fe and Al-Ni alloys. The effects of primary phase and eutectic undercooling on the microstructure of Al-Fe alloys are investigated using the impulse drop tube and parabolic flight. The TEM characterization on the eutectic microstructure of impulse-atomized Al-Fe powders with two compositions showed that the metastable AlmFe formed in these alloys. Also, the growth undercooling that the dendritic front experiences during the solidification of the droplet resulted in variation of dendrite growth direction from to . For Al-4 at%Fe, it was found that in reduced-gravity and in the impulse-atomized droplets the primary intermetallic forms with a flower-like morphology, whereas in the terrestrial EML sample it has a needle like morphology. For Al-Ni, the effect of primary phase undercooling on dendrite growth velocity under terrestrial and reduced-gravity condition is discussed. It is shown that under terrestrial conditions, in the Ni-rich alloys with increasing undercooling the growth velocity increases, whereas in the Al-rich alloys the growth velocity decreases. However, the Al-rich alloy that was studied in reduced-gravity showed similar behavior to that of Ni-rich alloys. Furthermore, the effect of cooling rate on the phase fractions and metastable phase formation of impulse-atomized Al-Ni alloys is compared with EML. A microsegregation model for the solidification of Al-Ni alloys is applied to impulse atomized powders. The model accounts for the occurrence of several phase transformations, including one or several peritectic reactions and one eutectic reaction.

  1. Development of Stable Solidification Method for Insoluble Ferrocyanides-13170

    Ikarashi, Yuki; Masud, Rana Syed; Mimura, Hitoshi [Dept. of Quantum Science and Energy Engineering, Graduate School of Engineering, Tohoku University, Aramaki-Aza-Aoba6-6-01-2, Sendai, 980-8579 (Japan); Ishizaki, Eiji; Matsukura, Minoru [UNION SHOWA K.K. 17-20, Mita 2-chome, Minato-ku, Tokyo 108-0073 (Japan)


    The development of stable solidification method of insoluble ferrocyanides sludge is an important subject for the safety decontamination in Fukushima NPP-1. By using the excellent immobilizing properties of zeolites such as gas trapping ability and self-sintering properties, the stable solidification of insoluble ferrocyanides was accomplished. The immobilization ratio of Cs for K{sub 2}[CoFe(CN){sub 6}].nH{sub 2}O saturated with Cs{sup +} ions (Cs{sub 2}[CoFe(CN){sub 6}].nH{sub 2}O) was estimated to be less than 0.1% above 1,000 deg. C; the adsorbed Cs{sup +} ions are completely volatilized. In contrast, the novel stable solid form was produced by the press-sintering of the mixture of Cs{sub 2}[CoFe(CN){sub 6}].nH{sub 2}O and zeolites at higher temperature of 1,000 deg. C and 1,100 deg. C; Cs volatilization and cyanide release were completely depressed. The immobilization ratio of Cs, under the mixing conditions of Cs{sub 2}[CoFe(CN){sub 6}].nH{sub 2}O:CP= 1:1 and calcining temperature: 1,000 deg. C, was estimated to be nearly 100%. As for the kinds of zeolites, natural mordenite (NM), clinoptilolite (CP) and Chabazite tended to have higher immobilization ratio compared to zeolite A. This may be due to the difference in the phase transformation between natural zeolites and synthetic zeolite A. In the case of the composites (K{sub 2-X}Ni{sub X/2}[NiFe(CN){sub 6}].nH{sub 2}O loaded natural mordenite), relatively high immobilization ratio of Cs was also obtained. This method using zeolite matrices can be applied to the stable solidification of the solid wastes of insoluble ferrocyanides sludge. (authors)

  2. Analysis of Solidification in the Presence of High Rayleigh Number Convection in an Enclosure


    A simple and convenient analysis of the process of time-dependent solidification in an enclosed liquid cooled from the side in the presence of natural convection is presented.the influence of each parameter on the process of solidification is carried out systematically,The accuracy of this model is justified by comparing its predicting values with the previous results.

  3. Feasibility of integrated seed making and directional solidification of TiAl alloy using cold crucible

    ZHANG Cheng-jun; FU Heng-zhi; XU Da-ming; GUO Jing-jie; BI Wei-sheng; SU Yan-qing


    A new seed making method with cold crucible by power off technique was proposed. The cold crucible quenched seed with columnar structure has a similar cross-section shape as that of the cold crucible, and can be directly used for the directional solidification processes. The proposed method can significantly simplify the seeded directional solidification process and avoid the contamination from the seed machining.

  4. Nucleation and solidification of thin walled ductile iron - Experiments and numerical simulation

    Pedersen, Karl Martin; Tiedje, Niels Skat


    Investigation of solidification of thin walled ductile cast iron has been performed based on experiments and numerical simulation. The experiments were based on temperature and microstructure examination. Results of the experiments have been compared with a 1-D numerical solidification model...

  5. Outgassing of icy bodies in the Solar System - II. Heat transport in dry, porous surface dust layers

    Gundlach, Bastian


    In this work, we present a new model for the heat conductivity of porous dust layers in vacuum, based on an existing solution of the heat transfer equation of single spheres in contact. This model is capable to distinguish between two different types of dust layers: dust layers composed of single particles (simple model) and dust layers consisting of individual aggregates (complex model). Additionally, we describe laboratory experiments, which were used to measure the heat conductivity of porous dust layers, in order to test the model. We found that the model predictions are in an excellent agreement with the experimental results. Furthermore, the implications of this new model on the modeling of cometary activity are discussed. Finally, the two variants of the model are used to calculate the H2O ice outgassing rate of comets as a function of the thickness of the ice-free dust layer. Therewith, the pressure inside the dust layer is derived and compared with the tensile strength of the material in order to dis...

  6. Numerical Simulation of Dendrite Evolution during Solidification Process

    LI Qiang; GUO Qiao-yi; REN Chuan-fu


    In order to precisely describe the dendrite evolution during solidification process, especially in microscale, a continuous method is presented to deal with the discontinuous physical properties beside the solid/liquid interface. In this method, the physical properties are used as averaging physical properties of solid phase and liquid phase in the interface zone, which can smooth the property gap between solid and liquid phases, and make the properties from liquid phase to solid phase. The simulated results show that the method can represent the sidebranches and the solute micro-segregation well.

  7. Divorced Eutectic Solidification of Mg-Al Alloys

    Monas, Alexander; Shchyglo, Oleg; Kim, Se-Jong; Yim, Chang Dong; Höche, Daniel; Steinbach, Ingo


    We present simulations of the nucleation and equiaxed dendritic growth of the primary hexagonal close-packed -Mg phase followed by the nucleation of the -phase in interdendritic regions. A zoomed-in region of a melt channel under eutectic conditions is investigated and compared with experiments. The presented simulations allow prediction of the final properties of an alloy based on process parameters. The obtained results give insight into the solidification processes governing the microstructure formation of Mg-Al alloys, allowing their targeted design for different applications.

  8. Fractal growth in impurity-controlled solidification in lipid monolayers

    Fogedby, Hans C.; Sørensen, Erik Schwartz; Mouritsen, Ole G.


    A simple two-dimensional microscopic model is proposed to describe solidifcation processes in systems with impurities which are miscible only in the fluid phase. Computer simulation of the model shows that the resulting solids are fractal over a wide range of impurity concentrations and impurity...... diffusional constants. A fractal-forming mechanism is suggested for impurity-controlled solidification which is consistent with recent experimental observations of fractal growth of solid phospholipid domains in monolayers. The Journal of Chemical Physics is copyrighted by The American Institute of Physics....

  9. Numerical prediction of the incremental melting and solidification process

    Jun Wang; Chengchang Jia; Sheng Yin


    A mathematical formulation is applied to represent the phenomena in the incremental melting and solidification process (IMSP), and the temperature and electromagnetic fields and the depth of steel liquid phase are calculated by a finite difference technique using the control volume method. The result shows that the predicted values are in good agreement with the observations. In accordance with the calculated values for different kinds of materials and different size of molds, the technological parameter of the IMS process such as the power supply and the descending speed rate can be determined.

  10. Instabilities in rapid solidification of multi-component alloys

    Altieri, Anthony L.; Davis, Stephen H.


    Rapid solidification of multi-component liquids occurs in many modern applications such as additive manufacturing. In the present work the interface departures from equilibrium consist of the segregation coefficient and liquidus slope depending on front speed, the one-sided, frozen-temperature approximation, and the alloy behaving as the superposition of individual components. Linear-stability theory is applied, showing that the cellular and oscillatory instabilities of the binary case are modified. The addition of components tends to destabilize the interface while the addition of a single large-diffusivity material can entirely suppress the oscillatory mode. Multiple minima in the neutral curve for the cellular mode occur.

  11. Cellular instability in rapid directional solidification - Bifurcation theory

    Braun, R. J.; Davis, S. H.


    Merchant and Davis performed a linear stability analysis on a model for the directional solidification of a dilute binary alloy valid for all speeds. The analysis revealed that nonequilibrium segregation effects modify the Mullins and Sekerka cellular mode, whereas attachment kinetics has no effect on these cells. In this paper, the nonlinear stability of the steady cellular mode is analyzed. A Landau equation is obtained that determines the amplitude of the cells. The Landau coefficient here depends on both nonequilibrium segregation effects and attachment kinetics. This equation gives the ranges of parameters for subcritical bifurcation (jump transition) or supercritical bifurcation (smooth transition) to cells.

  12. Competitive growth of high purity aluminum grains in directional solidification

    ZHANG Jiao; SHU Da; WANG De-lin; SUN Bao-de; CHEN Gang


    A self-made directional solidification setup was used to prepare high purity aluminum ingots of 100mm in diameter. The morphology of the growth interface was detected by SEM and AFM, and the grain lattice orientation was detected by XRD. The results indicate that the grains suffer competitive growth under any conditions in experiments. The lattice orientation of the preferred grains is determined by the flow field above the solid-liquid interface. The horizontal lattice position does not change during the growth process. However, the lattice orientation in the growth direction varies with the growth velocity and approaches to [100]gradually during the growth process.

  13. Rapid Solidification of AB{sub 5} Hydrogen Storage Alloys

    Gulbrandsen-Dahl, Sverre


    This doctoral thesis is concerned with rapid solidification of AB{sub 5} materials suitable for electrochemical hydrogen storage. The primary objective of the work has been to characterise the microstructure and crystal structure of the produced AB{sub 5} materials as a function of the process parameters, e.g. the cooling rate during rapid solidification, the determination of which has been paid special attention to. The thesis is divided into 6 parts, of which Part I is a literature review, starting with a short presentation of energy storage alternatives. Then a general review of metal hydrides and their utilisation as energy carriers is presented. This part also includes more detailed descriptions of the crystal structure, the chemical composition and the hydrogen storage properties of AB{sub 5} materials. Furthermore, a description of the chill-block melt spinning process and the gas atomisation process is given. In Part II of the thesis a digital photo calorimetric technique has been developed and applied for obtaining in situ temperature measurements during chill-block melt spinning of a Mm(NiCoMnA1){sub 5} hydride forming alloy (Mm = Mischmetal of rare earths). Compared with conventional colour transmission temperature measurements, this technique offers a special advantage in terms of a high temperature resolutional and positional accuracy, which under the prevailing experimental conditions were found to be {+-}29 K and {+-} 0.1 mm, respectively. Moreover, it is shown that the cooling rate in solid state is approximately 2.5 times higher than that observed during solidification, indicating that the solid ribbon stayed in intimate contact with the wheel surface down to very low metal temperatures before the bond was broken. During this contact period the cooling regime shifted from near ideal in the melt puddle to near Newtonian towards the end, when the heat transfer from the solid ribbon to the wheel became the rate controlling step. In Part III of the

  14. Permeability in a state of partial solidification of aqueous solution

    Okada, Masashi; Kang, Chaedong; Okiyama, Haruhiko

    A mushy region was formed by solidifying NaCl aqueous solution in a circular tube or a rectangular tube. The measurements of permeability were performed by changing volume fraction of liquid region in the mushy region. The dendritic ice in the solidification process was observed with a CCD microscope. The following results were obtained. The permeability increases with the volume fraction of liquid phase, and decreases with increasing the super-cooling degree of the solution or increasing the initial concentration of the solution, and is constant after the mushy region was formed. The arm space of dendrite becomes narrower as the super-cooling degree of the solution increases.

  15. Crystal Growth and Fluid Mechanics Problems in Directional Solidification

    Tanveer, Saleh A.; Baker, Gregory R.; Foster, Michael R.


    Our work in directional solidification has been in the following areas: (1) Dynamics of dendrites including rigorous mathematical analysis of the resulting equations; (2) Examination of the near-structurally unstable features of the mathematically related Hele-Shaw dynamics; (3) Numerical studies of steady temperature distribution in a vertical Bridgman device; (4) Numerical study of transient effects in a vertical Bridgman device; (5) Asymptotic treatment of quasi-steady operation of a vertical Bridgman furnace for large Rayleigh numbers and small Biot number in 3D; and (6) Understanding of Mullins-Sererka transition in a Bridgman device with fluid dynamics is accounted for.

  16. Verification of a binary fluid solidification model in the finite-volume flow solver

    Waclawczyk, Tomasz


    The aim of this paper is to verify the new numerical implementation of a binary fluid, heat conduction dominated solidification model. First, we extend a semi-analytical solution to the heat diffusion equation, next, the range of its applicability is investigated. It was found that the linearization introduced to the heat diffusion equation negatively affects the ability to predict solidus and liquidus lines positions whenever the magnitude of latent heat of fusion exceeds a certain value. Next, a binary fluid solidification model is coupled with a flow solver, and is used in a numerical study of Al-4.1%Cu alloy solidification in a two-dimensional rectangular cavity. An accurate coupling between the solidification model and the flow solver is crucial for the correct forecast of solidification front positions and macrosegregation patterns.

  17. Effect of Mould Wall Thickness on Rate of Solidification of Centrifugal Casting



    Full Text Available In Centrifugal Casting process the centrifugal force presses the metal against the inner wall of the metal mould, resulting in rapid solidification of the molten metal. However the solidification structures like structural uniformity and structural character of the solidified metal of centrifugal casting is of great importance, regarding to its mechanical properties. The solidification time of the casting is dependent upon the various parameters like speed ofrotation of the mold, mould wall temperature, heat transfer coefficient at the metal-mold interface, mould wall thickness, material of the mould and so on. In this paper experimental study of effect of mould wall thickness on solidification of the centrifugal casting has been discussed. As the mould wall thickness increases, due to the chilling effect, the solidification time decreases. Fine grains are observed in castings produced in thick walled mould and coarse grains are observed in thin walled moulds. Brinel Hardness of the casting was measured.

  18. Solidification microstructure selection of the peritectic Nd-Fe-B alloys

    ZHONG Hong; LI ShuangMing; L(U) HaiYan; LIU Lin; ZOU GuangRong; FU HengZhi


    Bridgman directional solidification and laser remelting experiments were carried out on Nd11.76Fe82.36B5.88 and Nd13.5Fe79.75B6.75 alloys. Microstructure evolutions along with solidification parameters (temperature gradient G, growth velocity V and initial alloy composition C0) were investigated. A solidification microstructure selection map was established, based on the consideration of solidification characteristics of peritectic T1 phase. In Bridgman directional solidification experiments, with the increasing growth velocities, the morphology of T1 phase changed from plane front or faceted plane front to dendrites. In laser remelting experiments, a transition from primary γ-Fe dendrites to T1 dendrites was found. Theoretical predictions are in good agreement with experimental results.

  19. Fabrication of directional solidification components of nickel-base superalloys by laser metal forming

    Liping Feng; Weidong Huang; Darong Chen; Xin Lin; Haiou Yang


    Straight plates, hollow columns, ear-like blade tips, twist plates with directional solidification microstructure made of Rene 95 superalloys were successfully fabricated on Nickel-base superalloy and DD3 substrates, respectively. The processing conditions for production of the parts with corresponding shapes were obtained. The fabrication precision was high and the components were compact. The solidification microstructure of the parts was analyzed by optical microscopy. The results show that the solidification microstructure is composed of columnar dendrites, by epitaxial growth onto the directional solidification substrates. The crystallography orientation of the parts was parallel to that of the substrates. The primary arm spacing was about 10 μm, which is in the range of superfine dendrites, and the secondary arm was small or even degenerated. It is concluded that the laser metal forming technique provides a method to manufacture directional solidification components.

  20. Solidification analysis of a centrifugal atomizer using the Al-32.7wt.% Cu alloy

    Osborne, Matthew G. [Iowa State Univ., Ames, IA (United States)


    A centrifugal atomizer (spinning disk variety) was designed and constructed for the production of spherical metal powders, 100-1,000 microns in diameter in an inert atmosphere. Initial atomization experiments revealed the need for a better understanding of how the liquid metal was atomized and how the liquid droplets solidified. To investigate particle atomization, Ag was atomized in air and the process recorded on high-speed film. To investigate particle solidification, Al-32.7 wt.% Cu was atomized under inert atmosphere and the subsequent particles were examined microscopically to determine solidification structure and rate. This dissertation details the experimental procedures used in producing the Al-Cu eutectic alloy particles, examination of the particle microstructures, and determination of the solidification characteristics (e.g., solidification rate) of various phases. Finally, correlations are proposed between the operation of the centrifugal atomizer and the observed solidification spacings.

  1. Solidification microstructure selection of the peritectic Nd-Fe-B alloys


    Bridgman directional solidification and laser remelting experiments were carried out on Nd11.76Fe82.36B5.88 and Nd13.5Fe79.75B6.75 alloys.Microstructure evolutions along with solidification parameters(temperature gradient G,growth velocity V and initial alloy composition C0)were investigated.A solidification microstructure selection map was established,based on the consideration of solidification characteristics of peritectic T1 phase.In Bridgman directional solidification experiments,with the increasing growth velocities,the morphology of T1 phase changed from plane front or faceted plane front to dendrites.In laser remelting experiments,a transition from primary γ-Fe dendrites to T1 dendrites was found.Theoretical predictions are in good agreement with experimental results.

  2. 2,4-二硝基苯甲醚与 TNT 凝固行为的差异性分析%Analysis on Differences of Solidification Behavior of DNAN and TNT

    罗一鸣; 蒋秋黎; 赵凯; 王浩


    为了解2,4-二硝基苯甲醚(DNAN)凝固缺陷的特征及产生的原因,采用量筒称量法测试了 DNAN 和 TNT样品的液相密度,并计算出样品的体积收缩率;用工业 CT 和扫描电镜对 DNAN 和 TNT 药柱的凝固缺陷分布情况进行观测;用 DSC 和导热系数测定仪测试了 DNAN 和 TNT 药柱的热性能参数;用自制的凝固速率测试装置测试了 DNAN 和 TNT 药柱中不同部位温度随时间的变化规律,计算了不同凝固层厚度下的平均凝固线速度。结果表明,DNAN 的体积收缩率为13.2%,高于 TNT;其凝固缺陷的分散度高于 TNT;在凝固过程初期,DNAN 的平均凝固线速率与 TNT 相当,随着凝固层厚度的增加,其凝固速率快速增加并显著高于 TNT。DNAN 的凝固行为不同于 TNT,不是逐层凝固,而属于中间凝固。%To understand the characteristics and the causes of 2,4-dinitroanisole(DNAN)solidification defects,the liquid-phase density of DNAN and TNT samples was measured by a cylinder weighing method and the two sample′s volume shrinkages were calculated.The distribution of solidification defect of DNAN and TNT grains was observed by industrial CT and SEM,respectively.Thermal property parameters of DNAN and TNT samples were tested by DSC and thermal conductivity measuring instrument.The change rule of temperature of the different position in DNAN and TNT grains with time was measured by a home-made solidification rate measuring device.The average linear solidification rate under different solidifying layer thicknesses was obtained through calculation.Results show that the volume shrinkage of DNAN is 13.2%,higher than that of TNT.The rate of divergence of solidification de-fect of DNAN is higher than that of TNT.The solidification rate of DNAN is close to that of TNT during the early solidification process.With increasing the solidified layer thickness,DNAN solidification rate increases rapidly, significantly

  3. Thermoelectric properties of Tl-doped PbTeSe crystals grown by directional solidification

    Su, Ching-Hua


    Three Tl-doped PbTe and two Tl-doped PbTeSe crystals were grown by vertical un-seeded directional solidification method. Among them, two Tl-doped PbTe ingots, with starting composition of (Pb0.99Tl0.01)Te, were grown under Pb or Te pressure over the melt provided by a Pb or Te reservoir, respectively, whereas another ingot, with starting composition of (Pb0.98Tl0.02)Te, was grown under Te overpressure. Two Tl-doped PbTeSe crystals, with starting composition of (Pb0.98Tl0.02)(Te0.85Se0.15) and (Pb0.96Tl0.04)(Te0.85Se0.15), were grown without any over-pressure. Disk-shaped samples were sliced at different locations along the growth axis and their thermal conductivities were determined from thermal diffusivity, density, and heat capacity measurements. The electrical conductivity and Seebeck coefficient were simultaneously measured as a function of temperature for each disk sample. The Figure of Merit for the thermoelectric application, zT, was calculated from these properties from room temperature to about 640 °C. The Tl-doped PbTeSe samples have the highest zT value of 1.63 at temperature range of 425 to 475 °C, comparing to 1.13 at 410 °C for the Tl-doped PbTe samples. By substituting 15% of the Te atoms in the Tl-doped PbTe by Se atoms, the Figure of Merit of PbTeSe was enhanced by reducing the thermal conductivity about 26% and, at the same time, increasing the electrical conductivity by 43%.

  4. Solidification/Stabilization of Elemental Mercury Waste by Amalgamation

    Yim, S. P.; Ahn, B. G.; Lee, H. J.; Shon, J. S.; Chung, H.; Kim, K. J.; Lee, C. K.


    Experiments on solidification of elemental mercury waste were conducted by amalgamation with several metal powders such as copper, zinc, tin, brass and bronze. Unlike the previous studies which showed a dispersible nature after solidification, the waste forms were found to possess quite large compressive strengths in both copper and bronze amalgam forms. The durability was also confirmed by showing very minor changes of strength after 90 days of water immersion. Leachability from the amalgam forms is also shown to be low: measured mercury concentration in the leachate by the Toxicity Characteristic Leaching Procedure (TCLP) was well below the Environmental Protection Agency (EPA) limit. Long term leaching behavior by Accelerated Leach Test (ALT) has shown that the leaching process was dominated by diffusion and the effective diffusion coefficient was quite low (around 10-19 cm2/sec). The mercury vapor concentration from the amalgam forms were reduced to a 20% level of that for elemental mercury and to one-hundredth after 3 months.

  5. Numerical modelling of the binary alloys solidification with solutal undercooling

    T. Skrzypczak


    Full Text Available In thc papcr descrip~ion of mathcmn~icaI and numerical modcl of binay alloy sot idification is prcscntcd. Mctal alloy consisting of maincomponent and solulc is introduced. Moving, sharp solidification rmnt is assumcd. Conaitulional undcrcooling phcnomcnon is tnkcn intoconsidcralion. As a solidifica~ionf ront advances, solutc is rcdistributcd at thc intcrfacc. Commonly, solutc is rejccted into Itlc liquid. whcrcit accumuIatcs into solittc boundary laycr. Depending on thc tcmpcrature gradient, such tiquid may be undcrcoolcd hclow its mclting point,cvcn though it is hot~crth an liquid at thc Front. This phcnomcnon is orten callcd constitutional or soIr~talu ndcrcool ing, to cmphasizc that itariscs from variations in solutal distribution or I iquid. An important conscqucncc of this accurnulntion of saIutc is that it can cause thc frontto brcak down into cclls or dendri~csT. his occurs bccausc thcrc is a liquid ahcad of thc front with lowcr solutc contcnt, and hcncc a highcrme1 ting tcmpcraturcs than liquid at thc front. In rhc papcr locarion and shapc of wndcrcoolcd rcgion dcpcnding on solidification pararnctcrsis discussed. Nurncrical mcthod basing on Fini tc Elelncnt Mctbod (FEM allowi~lgp rcdiction of breakdown of inoving planar front duringsolidification or binary alloy is proposed.

  6. Modified enthalpy method for the simulation of melting and solidification

    Niranjan N Gudibande; Kannan N Iyer


    Enthalpy method is commonly used in the simulation of melting and solidification owing to its ease of implementation. It however has a few shortcomings. When it is used to simulate melting/solidification on a coarse grid, the temperature time history of a point close to the interface shows waviness. While simulatingmelting with natural convection, in order to impose no-slip and impermeability boundary conditions, momentum sink terms are used with some arbitrary constants called mushy zone constants. The values of these are very large and have no physical basis. Further, the chosen values affect the predictions and hence have to be tuned for satisfactory comparison with experimental data. To overcome these deficiencies, a new cell splitting method under the framework of the enthalpy method has been proposed. This method does not produce waviness nor requires mushy zone constants for simulating melting with natural convection. The method is then demonstrated for a simple onedimensional melting problem and the results are compared with analytical solutions. The method is then demonstrated to work in two-dimensions and comparisons are shown with analytical solutions for problems with planar and curvilinear interfaces. To further benchmark the present method, simulations are performed for melting in a rectangular cavity with natural convection in the liquid melt. The solid–liquid interface obtained is compared satisfactorily with the experimental results available in literature.

  7. Simulation of spreading with solidification: assessment synthesis of Thema code

    Spindler, B.; Veteau, J.M. [CEA Grenoble, Direction de l' Energie Nucleaire, Dept. de Technologie Nucleaire, Service d' Etudes Thermohydrauliques et Technologiques, 38 (France)


    After a presentation of the models included in THEMA code, which simulates the spreading of a fluid with solidification, the whole assessment calculations are presented. The first series concerns the comparison with analytical or numerical solutions: dam break, conduction for the heat transfer in the substrate, crust growth. The second series concerns the comparison with the CORINE isothermal tests (simulating fluid at low temperature). The third series concerns the CORINE tests with heat transfer. The fourth series concerns the tests with simulating materials at medium or high temperature (RIT, KATS). The fifth series concerns the tests with prototypical materials (COMAS, FARO, VULCANO). Finally the blind simulations of the ECOKATS tests are presented. All the calculations are performed with the same physical models (THEMA version 2.5), without any variable tuning parameter according to the test under consideration. Sensitivity studies concern the influence of the viscosity model in the solidification interval, and for the tests with prototypical materials the inlet temperature and the solid fraction. The relative difference between the calculated and measured spreading areas is generally less than 20 % except for the test with prototypical materials, for which the assessment is not easy due to the large experimental uncertainties. The level of validation of THEMA is considered as satisfactory, taking into account the required accuracy. (authors)

  8. Wax solidification of drying agents containing tritiated water

    Mishikawa, M.; Kido, H.


    It is necessary to immobilize the tritium not to give any impact on the environmental biosphere because tritium may give profound effects in the metabolic pathway. One of the most probable methods of immobilizing tritium would be incorporation of tritiated water in solid forms. Any drying or dehydration technique would be effective in a tritium cleanup system for off-gas streams containing tritium or tritiated water. Commonly used drying agents such as activated alumina, silica gel, molecular sieves and calcium sulfate are of value for removal of water vapour from air or other gases. For long term tritium storage, however, these adsorptive materials should be enveloped to prevent contact with water or water vapour because the rate of leaching, evaporation or diffusion of tritium from these porous materials is so large. The beeswax solidification method of the packed bed of drying agents adsorbing tritiated water is developed in this study, where the wax solidification procedure is performed by pouring the melt of wax into the void space of the packed bed of the drying agents and successive gradual cooling. The observed values of diffusivity or permeability of tritium in the wax solidified materials are about one-thousandth of those obtained for the cement block. Effect of coating on the rate of leaching is also discussed.

  9. Stability of a directional solidification front in subdiffusive media.

    Hamed, Mohammad Abu; Nepomnyashchy, Alexander A


    The efficiency of crystal growth in alloys is limited by the morphological instability, which is caused by a positive feedback between the interface deformation and the diffusive flux of solute at the front of the phase transition. Usually this phenomenon is described in the framework of the normal diffusion equation, which stems from the linear relation between time and the mean squared displacement of molecules 〈x2(t)〉∼K1t (K1 is the classical diffusion coefficient) that is characteristic of Brownian motion. However, in some media (e.g., in gels and porous media) the random walk of molecules is hindered by obstacles, which leads to another power law, 〈x2(t)〉∼Kαtα, where 0directional solidification front in the case of an anomalous diffusion. Linear stability of a moving planar directional solidification front is studied, and a generalization of the Mullins-Sekerka stability criterion is obtained. Also, an asymptotic nonlinear long-wave evolution equation of Sivashinsky's type, which governs the cellular structures at the interface, is derived.

  10. Microdomain patterns from directional eutectic solidification and epitaxy

    De Rosa C; Park; Thomas; Lotz


    Creating a regular surface pattern on the nanometre scale is important for many technological applications, such as the periodic arrays constructed by optical microlithography that are used as separation media in electrophoresis, and island structures used for high-density magnetic recording devices. Block copolymer patterns can also be used for lithography on length scales below 30 nanometres (refs 3-5). But for such polymers to prove useful for thin-film technologies, chemically patterned surfaces need to be made substantially defect-free over large areas, and with tailored domain orientation and periodicity. So far, control over domain orientation has been achieved by several routes, using electric fields, temperature gradients, patterned substrates and neutral confining surfaces. Here we describe an extremely fast process that leads the formation of two-dimensional periodic thin films having large area and uniform thickness, and which possess vertically aligned cylindrical domains each containing precisely one crystalline lamella. The process involves rapid solidification of a semicrystalline block copolymer from a crystallizable solvent between glass substrates using directional solidification and epitaxy. The film is both chemically and structurally periodic, thereby providing new opportunities for more selective and versatile nanopatterned surfaces.

  11. A study on polypropylene encapsulation and solidification of textile sludge.

    Kumari, V Krishna; Kanmani, S


    The textile sludge is an inevitable solid waste from the textile wastewater process and is categorised under toxic substances by statutory authorities. In this study, an attempt has been made to encapsulate and solidify heavy metals and dyes present in textile sludge using polypropylene and Portland cement. Sludge samples (2 Nos.) were characterized for pH (8.5, 9.5), moisture content (1.5%, 1.96%) and chlorides (245mg/L, 425.4mg/L). Sludge samples were encapsulated into polypropylene with calcium carbonate (additive) and solidified with cement at four different proportions (20, 30, 40, 50%) of sludge. Encapsulated and solidified cubes were made and then tested for compressive strength. Maximum compressive strength of cubes (size, 7.06cm) containing sludge (50%) for encapsulation (16.72 N/mm2) and solidification (18.84 N/mm2) was more than that of standard M15 mortar cubes. The leachability of copper, nickel and chromium has been effectively reduced from 0.58 mg/L, 0.53 mg/L and 0.07 mg/L to 0.28mg/L, 0.26mg/L and BDL respectively in encapsulated products and to 0.24mg/L, BDL and BDL respectively in solidified products. This study has shown that the solidification process is slightly more effective than encapsulation process. Both the products were recommended for use in the construction of non-load bearing walls.

  12. Investigation of solidification dynamics of Zr-based alloys

    Kobold, Raphael; Herlach, Dieter [Institut fuer Materialphysik im Weltraum, Deutsches Zentrum fuer Luft- und Raumfahrt, 51170 Koeln (Germany); Ruhr-Universitaet Bochum, 44780 Bochum (Germany)


    In contrast to experiments with most undercooled binary alloys the velocity of dendritic growth of a Cu50Zr50 alloy does not increase monotonically with undercooling but passes through a maximum and then decreases. To study this behaviour we investigate Zr-based alloys such as CuZr, NiZr and NiZrAl with Zirconium concentrations ranging from 36 to 64 at.% including eutectic and intermetallic phases. We use electrostatic levitation technique to melt and undercool samples with a diameter of 2-3 mm under ultra-high-vacuum conditions. Containerless processing is an effective tool for undercooling metallic melts far below their equilibrium melting temperatures since heterogeneous nucleation on container walls is completely avoided. During crystallisation of the undercooled melt the heat of crystallisation is released. The rapid increase of the temperature at the solid-liquid interface makes the solidification front visible. The velocities of the solidification front are recorded by using a high-speed camera with a maximum rate of 50.000 frames per second and are analyzed with a software for optical ray tracing. Furthermore, we try to model the growth velocity vs. the undercooling temperature and perform sample EBSD analysis with a scanning electron microscope.

  13. Rapid solidification of undercooled Al-Cu-Si eutectic alloys

    RUAN Ying; WEI BingBo


    Under the conventional solidification condition,a liquid aluminium alloy can be hardly undercooled because of oxidation.In this work,rapid solidification of an undercooled liquid Al,80.4Cu,13.6Si,6 ternary eutectic alloy was realized by the glass fluxing method combined with recycled superheating.The re-lationship between superheating and undercooling was investigated at a certain cooling rate of the alloy melt.The maximum undercooling is 147 K (0.18 TE).The undercooled ternary eutectic is composed of α(Al) solid solution,(Si) semiconductor and β(CuAl,2) intermetallic compound.In the (Al+Si+θ) ternary eutectic,(Si) faceted phase grows independently,while (Al) and θ non-faceted phases grow coopera-tively in the lamellar mode.When undercooling is small,only (Al) solid solution forms as the leading phase.Once undercooling exceeds 73 K,(Si) phase nucleates firstly and grows as the primary phase.The alloy microstructure consists of primary (Al) dendrite,(Al+9) pseudobinary eutectic and (Al+Si+θ) ternary eutectic at small undercooling,while at large undercooling primary (Si) block,(Al+θ) pseudo-binary eutectic and (Al+Si+θ) ternary eutectic coexist.As undercooling increases,the volume fraction of primary (Al) dendrite decreases and that of primary (Si) block increases.

  14. A Review of Permanent Magnet Stirring During Metal Solidification

    Zeng, Jie; Chen, Weiqing; Yang, Yindong; Mclean, Alexander


    Rather than using conventional electromagnetic stirring (EMS) with three-phase alternating current, permanent magnet stirring (PMS), based on the use of sintered NdFeB material which has excellent magnetic characteristics, can be employed to generate a magnetic field for the stirring of liquid metal during solidification. Recent experience with steel casting indicates that PMS requires less than 20 pct of the total energy compared with EMS. Despite the excellent magnetic density properties and low power consumption, this relatively new technology has received comparatively little attention by the metal casting community. This paper reviews simulation modeling, experimental studies, and industrial trials of PMS conducted during recent years. With the development of magnetic simulation software, the magnetic field and associated flow patterns generated by PMS have been evaluated. Based on the results obtained from laboratory experiments, the effects of PMS on metal solidification structures and typical defects such as surface pinholes and center cavities are summarized. The significance of findings obtained from trials of PMS within the metals processing sector, including the continuous casting of steel, are discussed with the aim of providing an overview of the relevant parameters that are of importance for further development and industrial application of this innovative technology.

  15. Energetics of nonequilibrium solidification in Al-Sm

    Zhou, S. H.; Napolitano, R. E.


    Solution-based thermodynamic modeling, aided by first-principles calculations, is employed here to examine phase transformations in the Al-Sm binary system which may give rise to product phases that are metastable or have a composition that deviates substantially from equilibrium. In addition to describing the pure undercooled Al liquid with a two-state model that accounts for structural ordering, thermodynamic descriptions of the fcc phase, and intermediate compounds ( Al4Sm-β , Al11Sm3-α , Al3Sm-δ , and Al2Sm-σ ) are reanalyzed using special quasirandom structure and first-principles calculations. The possible phase compositions are presented over a range of temperatures using a “Baker-Cahn” analysis of the energetics of solidification and compared with reports of rapid solidification. The energetics associated with varying degrees of chemical partitioning are quantified and compared with experimental observations of the metastable Al11Sm3-α primary phase and reports of amorphous solids.

  16. Solidification of Trapped Liquid in Rocks and Crystals

    Morse, S. A.


    Trapped liquid in an igneous cumulate solidifies over a range of time and temperature that can be retrieved by use of the lever rule in binary solutions applied to plagioclase using the range in the An content found for the individual rock studied. The resident crystals in the cumulate count in the phase equilibria as though deposited by the resident liquid in pure fractional crystallization at the moment of trapping. The An range (Morse JPet 53:891, 2012) when measured in sufficient detail, defines the solidification history. The instantaneous solid composition along the solidus defines the zoning of the plagioclase as it follows the trapped liquid on the liquidus. The reference bulk composition of the trapped liquid is given by an intercept on the initial solid-liquid lever, defined by the fraction of plagioclase in the trapped parent magma times the residual porosity. The mafic fraction is assumed to solidify by reaction independently of the plagioclase zoning. The residual porosity is calculated from the An range when that is calibrated to a value independently determined from the evolved components. Examples from a recent treatment of residual porosity (cited above) will be given for the solidification of selected rock compositions from the Kiglapait and Skaergaard intrusions. The same principles apply to the solidification of melt inclusions, with the difference that the latter tend to sample an evolved sheath by capture, rather than a parent magma trapped by closure of a cumulate. Melt inclusions are evolved from birth, and then are likely to evolve further with continued growth and re-equilibration of the container. The cumulate, by contrast, given any small degree of adcumulus growth, has had time to exchange the evolved rejected solute owing to its slow solidification, so its trapped liquid is the contemporaneous magma at the cumulate interface. Experimental results on melt inclusions in mafic magma demonstrate their intrinsic evolved nature. For example

  17. Microstructural Development during Directional Solidification of Peritectic Alloys

    Lograsso, Thomas A.


    A thorough understanding of the microstructures produced through solidification in peritectic systems has yet to be achieved, even though a large number of industrially and scientifically significant materials are in this class. One type of microstructure frequently observed during directional solidification consists of alternating layers of primary solid and peritectic solid oriented perpendicular to the growth direction. This layer formation is usually reported for alloy compositions within the two-phase region of the peritectic isotherm and for temperature gradient and growth rate conditions that result in a planar solid-liquid interface. Layered growth in peritectic alloys has not previously been characterized on a quantitative basis, nor has a mechanism for its formation been verified. The mechanisms that have been proposed for layer formation can be categorized as either extrinsic or intrinsic to the alloy system. The extrinsic mechanisms rely on externally induced perturbations to the system for layer formation, such as temperature oscillations, growth velocity variations, or vibrations. The intrinsic mechanisms approach layer formation as an alternative type of two phase growth that is inherent for certain peritectic systems and solidification conditions. Convective mixing of the liquid is an additional variable which can strongly influence the development and appearance of layers due to the requisite slow growth rate. The first quantitative description of layer formation is a model recently developed by Trivedi based on the intrinsic mechanism of cyclic accumulation and depiction of solute in the liquid ahead of the interface, linked to repeated nucleation events in the absence of convection. The objective of this research is to characterize the layered microstructures developed during ground-based experiments in which external influences have been minimized as much as possible and to compare these results to the current the model. Also, the differences

  18. Melting and solidification processes in a moving graphite-covered titanium surface subjected to multi-pulse laser irradiation

    Courant, B.; Hantzpergue, J.-J.; Benayoun, S.; L'Huillier, J.-P.


    Experimental results of surface melting by pulsed Nd-YAG laser irradiation of titanium covered with graphite powder were analysed in comparison with the results of numerical simulations. The simulations of the thermal events, such as the maximum of temperature gradient at the surface and the duration of the liquid state after irradiation, were found due to a semi-analytic model of the space-time temperature distributions which were induced by the irradiation treatments. These simulations were required in order to calculate a series of integrals by Simpson's numerical method. They have allowed us to explain the experimental results such as the incorporation of carbon in melted zone, which produces titanium carbide and possible graphite inclusions, as a function of the irradiation parameters. The perpetual absence in the thickness and the exceptional presence at the surface of the solidification structure resulting from the plane-front growth of titanium carbide have, moreover, been justified.

  19. Measurement and control of the liquid/solid interface temperature during the directional solidification by using the Seebeck effect

    Cambon, G.; Cadet, G.; Favier, J. J.; Rouzaud, A.; Comera, J.

    The morphological stability and the segregation in the vicinity of the solid/liquid interface moving during the directional solidification of a metallurgical sample are depending on the undercooling phenomena which occurs during the growth. An interesting means to know this undercooling effect is to measure the Seebeck signal produced by the solid/liquid interface moving, with comparison with another static S/L interface of the sample. The in situ measurement techniques developed by CEA/CENG/LES and CNES/GERME gives the possibility to measure this temperature with 0.01 K differential accuracy in the severe mechanical, thermal and electromagnetic environment of the MEPHISTO space instrument on board of the U.S. Space Shuttle. After a brief scientific description of the interest of such undercooling measurement, a technical description of the adequate hardware, with the performance obtained during scientific tests, is presented in this paper.

  20. Weakly faceted cellular patterns versus growth-induced plastic deformation in thin-sample directional solidification of monoclinic biphenyl.

    Börzsönyi, Tamás; Akamatsu, Silvère; Faivre, Gabriel


    We present an experimental study of thin-sample directional solidification (T-DS) in impure biphenyl. The platelike growth shape of the monoclinic biphenyl crystals includes two low-mobility (001) facets and four high-mobility {110} facets. Upon T-DS, biphenyl plates oriented with (001) facets parallel to the sample plane can exhibit either a strong growth-induced plastic deformation (GID), or deformation-free weakly faceted (WF) growth patterns. We determine the respective conditions of appearance of these phenomena. GID is shown to be a long-range thermal-stress effect, which disappears when the growth front has a cellular structure. An early triggering of the cellular instability allowed us to avoid GID and study the dynamics of WF patterns as a function of the orientation of the crystal.

  1. Effects of Gravity on the Double-Diffusive Convection during Directional Solidification of a Non-Dilute Alloy with Application to the HgCdTe

    Bune, Andris; Gillies, Donald; Lehoczky, Sandor


    General 2-D and 3-D finite element model of non-dilute alloy solidification was used to simulate growth of HgCdTe in terrestrial and microgravity conditions. Parametric research was undertaken to investigate effects of gravity level, gravity vector orientation and growth velocity on the pattern of melt convection, shape of crystal/melt interface and radial thermal gradient. Verification of the model was undertaken by comparison with previously published results. For low growth velocities plane front solidification occurs. The location and the shape of the interface was determined using melting temperatures obtained from the HgCdTe liquidus curve. The low thermal conductivity of the solid HgCdTe causes thermal short circuit through the ampoule walls, resulting in curved isotherms in the vicinity of the interface. Double-diffusive convection in the melt is caused by radial temperature gradients and by material density inversion with temperature. Cooling from below and the rejection at the solid-melt interface of the heavier HgTe-rich solute each tend to reduce convection. Because of these complicating factors dimensional rather then non-dimensional modeling was performed. For gravity levels higher then 10(exp -7) of terrestrial one it was found that the maximum convection velocity is extremely sensitive to gravity vector orientation and can be reduced at least by 50% by choosing proper orientation of the ampoule. The predicted interface shape is in agreement with one obtained experimentally by quenching.

  2. Quantitative investigation of cellular growth in directional solidification by phase-field simulation.

    Wang, Zhijun; Wang, Jincheng; Li, Junjie; Yang, Gencang; Zhou, Yaohe


    Using a quantitative phase-field model, a systematic investigation of cellular growth in directional solidification is carried out with emphasis on the selection of cellular tip undercooling, tip radius, and cellular spacing. Previous analytical models of cellular growth are evaluated according to the phase-field simulation results. The results show that cellular tip undercooling and tip radius not only depend on the pulling velocity and thermal gradient, but also depend on the cellular interaction related to the cellular spacing. The cellular interaction results in a finite stable range of cellular spacing. The lower limit is determined by the submerging mechanism while the upper limit comes from the tip splitting instability corresponding to the absence of the cellular growth solution, both of which can be obtained from phase-field simulation. Further discussions on the phase-field results also present an analytical method to predict the lower limit. Phase-field simulations on cell elimination between cells with equal spacing validate the finite range of cellular spacing and give deep insight into the cellular doublon and oscillatory instability between cell elimination and tip splitting.

  3. A Pore-Centric Model for Combined Shrinkage and Gas Porosity in Alloy Solidification

    Khalajzadeh, Vahid; Carlson, Kent D.; Backman, Daniel G.; Beckermann, Christoph


    A unified model has been developed for combined gas- and shrinkage-induced pore formation during solidification of metal alloys. The model is based on a pore-centric approach, in which the temporal evolution of the pore radius is calculated as a function of cooling rate, thermal gradient, gas diffusion, and shrinkage. It accounts for the effect of porosity formation on the liquid velocity within the mushy zone. Simulations for an aluminum alloy show that the porosity transitions smoothly from shrinkage-induced to gas-induced as the Niyama value is increased. A Blake (cavitation) instability is observed to occur when the porosity is both gas- and shrinkage-driven. A revised dimensionless Niyama curve for pure shrinkage is presented. The experimentally observed gas porosity trend that the pore volume decreases with increasing cooling rate is well predicted. The pore-centric formulation allows the present model to be solved locally, at any point in a casting, during a regular casting simulation.

  4. Near-isothermal furnace for in situ and real time X-ray radiography solidification experiments

    Becker, M., E-mail:; Dreißigacker, C.; Klein, S.; Kargl, F. [Institut für Materialphysik im Weltraum, Deutsches Zentrum für Luft- und Raumfahrt (DLR), 51170 Köln (Germany)


    In this paper, we present a newly developed near-isothermal X-ray transparent furnace for in situ imaging of solidification processes in thin metallic samples. We show that the furnace is ideally suited to study equiaxed microstructure evolution and grain interaction. To observe the growth dynamics of equiaxed dendritic structures, a minimal temperature gradient across the sample is required. A uniform thermal profile inside a circular sample is achieved by positioning the sample in the center of a cylindrical furnace body surrounded by a circular heater arrangement. Performance tests with the hypo-eutectic Al-15wt.%Cu and the near-eutectic Al-33wt.%Cu alloys validate the near-isothermal character of the sample environment. Controlled cooling rates of less than 0.5 K min{sup −1} up to 10 K min{sup −1} can be achieved in a temperature range of 720 K–1220 K. Integrated in our rotatable laboratory X-ray facility, X-RISE, the furnace provides a large field of view of 10.5 mm in diameter and a high spatial resolution of ∼4 μm. With the here presented furnace, equiaxed dendrite growth models can be rigorously tested against experiments on metal alloys by, e.g., enabling dendrite growth velocities to be determined as a function of undercooling or solutal fields in front of the growing dendrite to be measured.

  5. Solidification characteristics of Fe-Ni peritectic alloy thin strips under a near-rapid solidification condition

    Chang-jiang Song


    Full Text Available This paper is an experimental investigation of the structure evolution and the solute distribution of 2 mm thick strips of Fe-(2.6, 4.2, 4.7, 7.9wt.%Ni peritectic alloy under a near-rapid solidification condition, which were in the regions of δ-ferrite single-phase, hypo-peritectic, hyper-peritectic and γ-austenite single-phase, respectively. The highest area ratio of equiaxed grain zone in the hyper-peritectic of Fe-4.7wt.%Ni alloy strip was observed, while other strips were mainly columnar grains. The lowest micro-segregation was obtained in the Fe-7.9wt.%Ni alloy strip, while micro-segregation in the Fe-4.7wt.%Ni alloy was the highest. As opposed to the micro-segregation, the macro-segregation of all the Fe-Ni strips was suppressed due to the rapid solidification rate. Finally, the structure formation mechanism of Fe-Ni alloy strips was analyzed.

  6. Modeling of columnar and equiaxed solidification of binary mixtures; Modelisation de la solidification colonnaire et equiaxe de melanges binaires

    Roux, P


    This work deals with the modelling of dendritic solidification in binary mixtures. Large scale phenomena are represented by volume averaging of the local conservation equations. This method allows to rigorously derive the partial differential equations of averaged fields and the closure problems associated to the deviations. Such problems can be resolved numerically on periodic cells, representative of dendritic structures, in order to give a precise evaluation of macroscopic transfer coefficients (Drag coefficients, exchange coefficients, diffusion-dispersion tensors...). The method had already been applied for a model of columnar dendritic mushy zone and it is extended to the case of equiaxed dendritic solidification, where solid grains can move. The two-phase flow is modelled with an Eulerian-Eulerian approach and the novelty is to account for the dispersion of solid velocity through the kinetic agitation of the particles. A coupling of the two models is proposed thanks to an original adaptation of the columnar model, allowing for undercooling calculation: a solid-liquid interfacial area density is introduced and calculated. At last, direct numerical simulations of crystal growth are proposed with a diffuse interface method for a representation of local phenomena. (author)

  7. The Asymmetric Coma of Comets. I. Asymmetric Outgassing from the Nucleus of Comet 2P/Encke

    Festou, M. C.; Barale, O.


    Very little is known about how outgassing regions are distributed over the nucleus of comets. In periodic comets, active regions are believed to be few and of small extent. Since periodic comets are notorious for their lack of (small) solid particles that efficiently scatter sunlight, we try to find traces of the existence of production sites by examining the morphology of the gas coma. We use a new coma model in which results from hydrodynamics calculations describing the inner coma are used as limit conditions for a collisionless description of the outer coma. The production pattern of the parent species mainly depends on the extent and location of the production region(s) and on the rotational state of the nucleus. Analyzing 1980 observations of comet 2P/Encke, we find that free emission from a single, small, active region located near the subsolar point of a nonrotating nucleus is excluded. But such an active region on a rotating nucleus produces well the observed coma morphology. Our data then allow us to determine the orientation of the comet spin axis and the cometocentric latitude of the source. Emission from a few small production regions spread over the sunward part of a nonrotating nucleus or emission at a very low rate from a larger subsolar area could also fit the data. Although we do not find a unique solution to our problem, the excellent quality of our fits indicates that our approach, if used with enough care, can provide a new tool to investigate the properties of comet nuclei when the coma is far from spherically symmetric and, ultimately, to study the effects of the nongravitational force that is acting on comet nuclei.

  8. The Molecular Composition of Comet C/2007 W1 (Boattini): Evidence of a Peculiar Outgassing and a Rich Chemistry

    Villanueva, G. L.; Mumma, M. J.; DiSanti, M. A.; Bonev, B. P.; Gibb, E. L.; Magee-Sauer, K.; Blake, G. A.; Salyk, C.


    We measured the chemical composition of Comet C/2007 W1 (Boattini) using the long-slit echelle grating spectrograph at Keck-2 (NIRSPEC) on 2008 July 9 and 10. We sampled 11 volatile species (H2O, OH*, C2H6, CH3OH, H2CO, CH4, HCN, C2H2, NH3, NH2, and CO), and retrieved three important cosmogonic indicators: the ortho-para ratios of H2O and CH4, and an upper-limit for the D/H ratio in water. The abundance ratios of almost all trace volatiles (relative to water) are among the highest ever observed in a comet. The comet also revealed a complex outgassing pattern, with some volatiles (the polar species H2O and CH3OH) presenting very asymmetric spatial profiles (extended in the anti-sunward hemisphere), while others (e.g., C2H6 and HCN) showed particularly symmetric profiles. We present emission profiles measured along the Sun-comet line for all observed volatiles, and discuss different production scenarios needed to explain them. We interpret the emission profiles in terms of release from two distinct moieties of ice, the first being clumps of mixed ice and dust released from the nucleus into the sunward hemisphere. The second moiety considered is very small grains of nearly pure polar ice (water and methanol, without dark material or apolar volatiles). Such grains would sublimate only very slowly, and could be swept into the anti-sunward hemisphere by radiation pressure and solar-actuated non-gravitational jet forces, thus providing an extended source in the anti-sunward hemisphere.

  9. ThermoCalc Application for the Assessment of Binary Alloys Non-Equilibrium Solidification

    Zyska A.


    Full Text Available The paper presents the possibility of application of the developed computer script which allows the assessment of non-equilibrium solidification of binary alloys in the ThermoCalc program. The script makes use of databases and calculation procedures of the POLY-3 module. A solidification model including diffusion in the solid state, developed by Wołczyński, is used to describe the non-equilibrium solidification. The model takes into account the influence of the degree of solute segregation on the solidification process by applying the so-called back-diffusion parameter. The core of the script is the iteration procedure with implemented model equation. The possibility of application of the presented calculation method is illustrated on the example of the Cr-30% Ni alloy. Computer simulations carried out with use of the developed script allow to determine the influence of the back-diffusion parameter on the course of solidification curves, solidus temperature, phase composition of the alloy and the fraction of each phase after the solidification completion, the profile of solute concentration in liquid during solidification process, the average solute concentration in solid phase at the eutectic temperature and many other quantities which are usually calculated in the ThermoCalc program.

  10. Experimental investigation of performances of microcapsule phase change material for thermal energy storage

    Li, H. [Department of Material Science and Engineering, Nanjing University, Nanjing (China); Liu, X.; Wu, S. [Department of Physics, Nanjing University, Nanjing (China); Fang, G.


    Performances of microcapsule phase change material (MPCM) for thermal energy storage are investigated. The MPCM for thermal energy storage is prepared by a complex coacervation method with gelatin and acacia as wall materials and paraffin as core material in an emulsion system. A scanning electron microscope (SEM) was used to study the microstructure of the MPCM. In thermal analysis, a differential scanning calorimeter (DSC) was employed to determine the melting temperature, melting latent heat, solidification temperature, and solidification latent heat of the MPCM for thermal energy storage. The SEM micrograph indicates that the MPCM has been successfully synthesized and that the particle size of the MPCM is about 81 {mu}m. The DSC output results show that the melting temperature of the MPCM is 52.05 C, the melting latent heat is 141.03 kJ/kg, the solidification temperature is 59.68 C, and the solidification latent heat is 121.59 kJ/kg. The results prove that the MPCM for thermal energy storage has a larger phase change latent heat and suitable phase change temperature, so it can be considered as an efficient thermal energy storage material for heat utilizing systems. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  11. Numerical investigation of thermal history and residual stress of grown multi-crystalline silicon at the various growth stages for PV applications

    Srinivasan, M.; Ramasamy, P.


    The directional solidification is a very important technique for growing high quality multi-crystalline silicon at large scale for PV solar cells. Time dependent numerical modelling of the temperature distribution, residual stress in multi-crystalline silicon ingots grown by directional solidification has been investigated for five growth stage. The computation was carried in a 2D axis symmetric model by the finite volume method. The history of temperature distribution, stress generation, are tracked in our modelling continuously to consider the growth process from the beginning to the end of solidification process. This paper is aimed to achieve an advanced understanding of the thermal and mechanical behavior of grown crystal.

  12. Thermal evolution of plutons: a parameterized approach.

    Spera, F


    A conservation-of-energy equation has been derived for the spatially averaged magma temperature in a spherical pluton undergoing simultaneous crystallization and both internal (magma) and external (hydrothermal fluid) thermal convection. The model accounts for the dependence of magma viscosity on crystallinity, temperature, and bulk composition; it includes latent heat effects and the effects of different initial water concentrations in the melt and quantitatively considers the role that large volumes of circulatory hydrothermal fluids play in dissipating heat. The nonlinear ordinary differential equation describing these processes has been solved for a variety of magma compositions, initial termperatures, initial crystallinities, volume ratios of hydrothermal fluid to magma, and pluton sizes. These calculations are graphically summarized in plots of the average magma temperature versus time after emplacement. Solidification times, defined as the time necessary for magma to cool from the initial emplacement temperature to the solidus temperature vary as R(1,3), where R is the pluton radius. The solidification time of a pluton with a radius of 1 kilometer is 5 x 10(4) years; for an otherwise identical pluton with a radius of 10 kilometers, the solidification time is approximately 10(6) years. The water content has a marked effect on the solidification time. A granodiorite pluton with a radius of 5 kilometers and either 0.5 or 4 percent (by weight) water cools in 3.3 x 10(5) or 5 x 10(4) years, respectively. Convection solidification times are usually but not always less than conduction cooling times.

  13. Immobilisation/solidification of hazardous toxic waste in cement matrices

    Macías, A.


    Full Text Available Immobilization and solidification of polluting waste, introduced into the industrial sector more than 20 years ago, and throughout last 10 years is being the object of a growing interest for engineers and environment scientists, has become a remarkable standardized process for treatment and management of toxic and hazardous liquid wastes, with special to those containing toxic metals. Experimental monitorization of the behaviour of immobilized waste by solidification and stabilisation in life time safe deposits is not possible, reason why it is essential to develop models predicting adequately the behaviour of structures that have to undergo a range of conditions simulating the environment where they are to be exposed. Such models can be developed only if the basic physical and chemical properties of the system matrix/solidifying-waste are known. In this work immobilization/solidification systems are analyzed stressing out the formulation systems based on Portland cement. Finally, some examples of the results obtained from the study of interaction of specific species of wastes and fixation systems are presented.

    La inmovilización y solidificación de residuos contaminantes, implantada en el sector comercial desde hace más de 20 años y que desde hace diez es objeto de creciente interés por parte de ingenieros y científicos medioambientales, se ha convertido en un proceso estandarizado único para el tratamiento y gestión de residuos tóxicos y peligrosos líquidos y, en especial, de los que contienen metales pesados. La monitorización experimental del comportamiento de un residuo inmovilizado por solidificación y estabilización en el tiempo de vida de un depósito de seguridad no es posible, por lo que es imprescindible desarrollar modelos que predigan satisfactoriamente el comportamiento del sistema bajo un rango representativo de condiciones del entorno de exposición. Tales modelos sólo pueden ser desarrollados si se

  14. Numerical calculation on temperature field of FGH95 alloy droplet during rapid solidification

    Huanming Chen; Benfu Hu


    The temperature field of FGH95 alloy droplet atomized by plasma rotating electrode processing (PREP) during solidifica-tion has been calculated through numerical analysis based on equivalent sensible heat capacity method. And thus the relational cul-ves among temperature gradient of solid-liquid interface, moving velocity of solid-liquid interface and solid fraction during solidifi-cation have been presented. The results indicate that the relation between average temperature gradient of solid-liquid interface anddroplet size, and the relation between average moving velocity of solid-liquid interface and droplet size can be expressed during solidification.

  15. Anisotropic growth of multigrain in equiaxial solidification simulated with the phase field method

    Li Mei-E; Xiao Zhi-Ying; Yang Gen-Cang; Zhou Yao-He


    The phase field method has been mainly used to simulate the growth of a single crystal in the past. But polycrystalline materials predominate in engineering. In this work, a phase field model for multigrain solidification is developed, which takes into account the random crystallographic orientations of crystallites and preserves the rotational invariance of the free energy. The morphological evolution of equiaxial multigrain solidification is predicted and the effect of composition on transformation kinetics is studied. The numerical results indicate that due to the soft impingement of grains the Avrami exponent varies with the initial melt composition and the solidification fraction.

  16. Long-time dynamics of the directional solidification of rodlike eutectics.

    Perrut, Mikaël; Akamatsu, Silvère; Bottin-Rousseau, Sabine; Faivre, Gabriel


    We report long-duration real-time observations of the dynamics of hexagonal (rodlike) directional-solidification patterns in bulk samples of a transparent eutectic alloy. A slight forward curvature of the isotherms induces a slow dilatation of the growth pattern at constant solidification rate and triggers the rod-splitting instability. At long times, the rod-splitting frequency exactly balances the dilatation driven by the curved isotherms. The growth pattern is then disordered and nonstationary but has a sharply selected mean spacing. Well-ordered growth patterns can be grown using time-dependent solidification rates.

  17. Control of dendrite growth by a magnetic field during directional solidification

    Dai, Yanchao; Du, Dafan; Hou, Long; Gagnoud, Annie; Ren, Zhongming; Fautrelle, Yves; Moreau, Rene; Li, Xi


    In this work, the alignment behavior of three kinds of dendrites (Al3Ni, α-Al and Al2Cu dendrites) with a remarkable crystalline anisotropy during directional solidification under an axial magnetic field is studied by the EBSD technology. Experimental results reveal that the magnetic field is capable of tailoring the dendrite alignment during directional solidification. Further, based on the crystalline anisotropy, a method to control the dendrite alignment by adjusting the angle between the magnetic field and the solidification direction is proposed.

  18. Modeling of thermosolutal convection during Bridgman solidification of semiconductor alloys in relation with experiments

    Stelian, Carmen; Duffar, Thierry


    Thermosolutal convection during vertical Bridgman directional solidification of Ga 1- xIn xSb alloys has been studied by numerical simulation. The transient analysis of heat, momentum and species transport has been performed by using the finite element code FIDAP ®. In the case of vertical Bridgman configuration, the thermal convection is driven by the radial temperature gradients. The solute (InSb) rejected at the solid-liquid interface, which is heavier than the GaSb component, damps the thermally driven convection. The solutal effect on the melt convection has been analyzed for low ( x=0.01) and high ( x=0.1) doped Ga 1- xIn xSb alloys. It is found that the damping effect is negligible for Ga 0.99In 0.01Sb alloy grown at low pulling rates ( V= 1 μm/s ), but cannot be neglected if the pulling rate is increased. In the case of concentrated alloys, the low level of convection intensity leads to an increase of radial segregation and interface curvature during the whole growth process as also shown by experiments. The effect of solutal buoyancy force on the melt convection is analyzed for the horizontal Bridgman configuration under microgravity conditions. An inverse but lower solutal effect on the melt convection, as compared with vertical Bridgman arrangement, is observed. The results are in good agreement with the experimental data, and show that convective transport can be observed even for low (2×10 -6g0) residual gravity levels.

  19. J series thruster thermal test results

    Bechtel, R. T.; Dulgeroff, C. R.


    Test experience with J series ion thrusters have indicated that the present thruster design may result in excessive temperatures in areas which utilize organic materials such as wire insulation, with the resultant outgassing and potential contamination of insulating materials. Further, it appears that thermal data obtained with earlier thruster designs, such as the 700 series thruster, may not be directly applicable to the J series design. Two J series thrusters were fitted with thermocouples and critical temperatures measured for a variety of configurations and operating parameters. Completely enclosing the thruster to reduce facility contamination significantly increased temperatures prompting the selection of a compromise geometry for life testing. The operating parameter having the largest effect on temperatures was discharge power, while beam power affected little else than extraction system temperatures. Several off-normal operating modes were also investigated. Data believed to be sufficient to effectively modify existing thermal models were obtained from the tests.

  20. Detection of inner core solidification from observations of antipodal PKIIKP

    Cormier, Vernon F.


    PKIIKP waves, reflected from the underside of the inner core boundary, are very sensitive to the S velocity in the uppermost 80 km of the inner core at antipodal distances, undergoing a phase change and a factor of 4 amplification as the distance approaches 180°. Modeled PKIIKP waveforms are consistent with a near-zero shear modulus in the uppermost inner core in a 20-40 km thick patch beneath the eastern equatorial hemisphere. This bright spot of PKIIKP reflection correlates with a thin zone of low P velocity inferred from the complexity of PKIKP waveforms sampling this patch. Estimates of grain sizes from seismic attenuation, the absence of backscattered PKiKP coda in this region, and a prediction for enhanced heat flow through this patch suggest that it is a region of solidification rather than melting.