WorldWideScience

Sample records for dendritic crystal growth

  1. Velocity selection in the symmetric model of dendritic crystal growth

    Science.gov (United States)

    Barbieri, Angelo; Hong, Daniel C.; Langer, J. S.

    1987-01-01

    An analytic solution of the problem of velocity selection in a fully nonlocal model of dendritic crystal growth is presented. The analysis uses a WKB technique to derive and evaluate a solvability condition for the existence of steady-state needle-like solidification fronts in the limit of small under-cooling Delta. For the two-dimensional symmetric model with a capillary anisotropy of strength alpha, it is found that the velocity is proportional to (Delta to the 4th) times (alpha exp 7/4). The application of the method in three dimensions is also described.

  2. Sidebranching in the Dendritic Crystal Growth of Ammonium Chloride

    Science.gov (United States)

    Dougherty, Andrew

    2012-02-01

    We report measurements of the dendritic crystal growth of NH4Cl from supersaturated aqueous solution at small supersaturations. Sidebranch growth in this regime is challenging to model well, and the origin of the sidebranches is not fully understood. The early detection of sidebranches requires measurements of small deviations from the smooth steady state shape, but that shape is not well known at the intermediate distances relevant for sidebranch measurements. One model is that sidebranches result from the selective amplification of microscopic noise. We compare measurements of the sidebranch envelope with predictions of the noise-induced sidebranching model of Gonz'alez-Cinca, Ram'irez-Piscina, Casademunt, and Hern'andez-Machado [Phys Rev. E, 63, 051602 (2001)]. We find that the measured amplitude is somewhat larger than predicted, and the shape of the sidebranch envelope is also different. A second model is that sidebranches result from small oscillations of the tip. We have observed no such oscillations, but very small ones can not be ruled out. No measurement of the tip region can be completely free of contamination from early sidebranches, so it can be challenging to distinguish between an oscillating tip and a smooth tip with sidebranches starting nearby.

  3. Characterization of Optical Lenses to be Considered for the Imaging of Crystal Dendrite Growth

    Science.gov (United States)

    Wing, Frank M.

    1999-01-01

    Dynamic fracture is a phenomenon that is extremely sensitive to small perturbations in system parameters. This phenomenon is, in some ways, similar to that of dendritic crystal growth, although it is governed by different physical principles. Crystal dendrite growth patterns are affected by parameters such as temperature, pressure, and gravity. By studying the behavior of crystal dendrites in a controlled, microgravity environment, a greater understanding of dynamic fracture could be revealed. A sealed cubical container contains four stingers, which facilitate the growth of crystal dendrites. The container has five windows and is emersed in a liquid, for thermal isolation. The tip of a dendrite can advance in any direction, therefore three-dimensional images of the process are desired. Furthermore, because of the rapid growth rate, a fast image frame rate is required for accurate tracking of dendrite tip velocity. In addition, optical parameters such as field of view, depth of focus, and resolution are examined, as well as the working distance between a lens and the target of observation.

  4. Transport Processes in Dendritic Crystallization

    Science.gov (United States)

    Glicksman, M. E.

    1984-01-01

    Free dentritic growth refers to the unconstrained development of crystals within a supercooled melt, which is the classical dendrite problem. The development of theoretical understanding of dendritic growth and its experimental status is sketched showing that transport theory and interfacial thermodynamics (capillarity theory) are insufficient ingredients to develop a truly predictive model of dendrite formation. The convenient, but incorrect, notion of maximum velocity was used for many years to estimate the behavior of dendritic transformations until supplanted by modern dynamic stability theory. The proper combinations of transport theory and morphological stability seem to be able to predict the salient aspects of dendritic growth, especially in the neighborhood of the tip.

  5. Free dendritic growth

    Science.gov (United States)

    Glicksman, M. E.

    1984-01-01

    Free dendritic growth refers to the unconstrained development of crystals within a supercooled melt, which is the classical 'dendrite problem'. Great strides have been taken in recent years in both the theoretical understanding of dendritic growth and its experimental status. The development of this field will be sketched, showing that transport theory and interfacial thermodynamics (capillarity theory) were sufficient ingredients to develop a truly predictive model of dendrite formation. The convenient, but incorrect, notion of 'maximum velocity' was used for many years to estimate the behavior of dendritic transformations until supplanted by modern dynamic stability theory. The proper combinations of transport theory and morphological stability seem to able to predict the salient aspects of dendritic growth, especially in the neighborhood of the tip. The overall development of cast microstructures, such as equiaxed zone formation, rapidly solidified microstructures, etc., also seems to contain additional non-deterministic features which lie outside the current theories discussed here.

  6. Numerical Simulation of Dendritic crystal growth using phase field method and investigating the effects of different physical parameter on the growth of the dendrite

    OpenAIRE

    Sanal, Rahul

    2014-01-01

    In this journal, we study the phase-field model of solidification for numerical simulation of dendritic crystal growth that occurs during the casting of metals and alloys based on the kobayashi [1] model. Qualitative relationships between shapes of the crystal and physical parameters are studied and visualized.

  7. Comparison of Cellular Automaton and Phase Field Models to Simulate Dendrite Growth in Hexagonal Crystals

    Institute of Scientific and Technical Information of China (English)

    2012-01-01

    A cellular automaton (CA)-finite element (FE) model and a phase field (PF)-FE model were used to simulate equiaxed dendritic growth during the solidification of hexagonal metals. In the CA-FE model, the conservation equations of mass and energy were solved in order to calculate the temperature field, solute concentration, and the dendritic growth morphology. CA-FE simulation results showed reasonable agreement with the previously reported experimental data on secondary dendrite arm spacing (SDAS) vs cooling rate. In the PF model, a PF variable was used to distinguish solid and liquid phases similar to the conventional PF models for solidification of pure materials. Another PF variable was considered to determine the evolution of solute concentration. Validation of both models was performed by comparing the simulation results with the analytical model developed by Lipton-Glicksman-Kurz (LGK), showing quantitatively good agreement in the tip growth velocity at a given melt undercooling. Application to magnesium alloy AZ91 (approximated with the binary Mg-8.9 wt% AI) illustrates the difficulty of modeling dendrite growth in hexagonal systems using CA-FE regarding mesh-induced anisotropy and a better performance of PF-FE in modeling multiple arbitrarily-oriented dendrites growth.

  8. Isothermal Dendritic Growth Experiment - PVA Dendrites

    Science.gov (United States)

    1997-01-01

    The Isothermal Dendritic Growth Experiment (IDGE), flown on three Space Shuttle missions, is yielding new insights into virtually all industrially relevant metal and alloy forming operations. IDGE used transparent organic liquids that form dendrites (treelike structures) similar to those inside metal alloys. Comparing Earth-based and space-based dendrite growth velocity, tip size and shape provides a better understanding of the fundamentals of dentritic growth, including gravity's effects. Shalowgraphic images of pivalic acid (PVA) dendrites forming from the melt show the subtle but distinct effects of gravity-driven heat convection on dentritic growth. In orbit, the dendrite grows as its latent heat is liberated by heat conduction. This yields a blunt dendrite tip. On Earth, heat is carried away by both conduction and gravity-driven convection. This yields a sharper dendrite tip. In addition, under terrestrial conditions, the sidebranches growing in the direction of gravity are augmented as gravity helps carry heat out of the way of the growing sidebranches as opposed to microgravity conditions where no augmentation takes place. IDGE was developed by Rensselaer Polytechnic Institute and NASA/Glenn Research Center. Advanced follow-on experiments are being developed for flight on the International Space Station. Photo Credit: NASA/Glenn Research Center

  9. Isothermal Dendritic Growth Experiment Video

    Science.gov (United States)

    1997-01-01

    This video, captured during the Isothermal Dendritic Growth Experiment (IDGE) flown on STS-87 as a part of the fourth United States Microgravity payload, shows the growth of a dendrite, and the surface solidification that occurred on the front and back windows of the growth chamber. Dendrites are tiny, tree like structures that form as metals solidify.

  10. Numerical simulation of facet dendrite growth

    Institute of Scientific and Technical Information of China (English)

    CHEN Zhi; CHEN Chang-le; HAO Li-mei

    2008-01-01

    Numerical simulation based on phase field method was performed to describe the solidification of silicon. The effect of anisotropy, undercooling and coupling parameter on dendrite growth shape was investigated. It is indicated that the entire facet dendrite shapes are obtained by using regularized phase field model. Steady state tip velocity of dendrite drives to a fixed value when γ≤0.13. With further increasing the anisotropy value, steady state tip velocity decreases and the size is smaller. With the increase in the undercooling and coupling parameter, crystal grows from facet to facet dendrite. In addition, with increasing coupling parameter, the facet part of facet dendrite decreases gradually, which is in good agreement with Wulff theory.

  11. 3D Modeling and Simulation of Dendritic Growth during Solidification

    Institute of Scientific and Technical Information of China (English)

    Zuojian LIANG; Qingyan XU; Baicheng LIU

    2003-01-01

    A mathematical model for the three-dimensional simulation of free dendritic growth and microstructure evolutionwas developed based on the growth mechanism of crystal grains and basic transfer equations such as heat, massand momentum transfer equations. Ma

  12. Phase field modeling of dendrite growth

    Institute of Scientific and Technical Information of China (English)

    Yutuo ZHANG; Chengzhi WANG; Dianzhong LI; Yiyi LI

    2009-01-01

    Single dendrite and multi-dendrite growth for A1-2 mol pct Si alloy during isothermal solidification are simulated by phase field method. In the case of single equiaxed dendrite growth, the secondary and the necking phenomenon can be observed. For multi-dendrite growth, there exists the competitive growth among the dendrites dur-ing solidification. As solidification proceeds, growing and coarsening of the primary arms occurs, together with the branching and coarsening of the secondary arms.When the diffusion fields of dendrite tips come into contact with those of the branches growing from the neighboring dendrites, the dendrites stop growing and being to ripen and thicken.

  13. The Isothermal Dendritic Growth Experiment

    Science.gov (United States)

    Glicksman, M. E.; Koss, M. B.; Malarik, D. C.

    1998-01-01

    The growth of dendrites is one of the commonly observed forms of solidification encountered when metals and alloys freeze under low thermal gradients, as occurs in most casting and welding processes. In engineering alloys, the details of the dendritic morphology directly relates to important material responses and properties. Of more generic interest, dendritic growth is also an archetypical problem in morphogenesis, where a complex pattern evolves from simple starting conditions. Thus, the physical understanding and mathematical description of how dendritic patterns emerge during the growth process are of interest to both scientists and engineers. The Isothermal Dendritic Growth Experiment (IDGE) is a basic science experiment designed to measure, for a fundamental test of theory, the kinetics and morphology of dendritic growth without complications induced by gravity-driven convection. The IDGE, a collaboration between Rensselaer Polytechnic Institute, in Troy NY, and NASA's Lewis Research Center (LeRC) was developed over a ten year period from a ground-based research program into a space flight experiment. Important to the success of this flight experiment was provision of in situ near-real-time teleoperations during the spaceflight experiment.

  14. Modeling of dendritic growth in the presence of convection

    Institute of Scientific and Technical Information of China (English)

    ZHU; Mingfang; DAI; Ting; LEE; Sungyoon; HONG; Chunpyo

    2005-01-01

    A two-dimensional coupling modified cellular automaton (MCA)-transport model has been employed to investigate the asymmetrical dendritic growth behavior in a flowing melt. In the present model, the cellular automaton method for crystal growth is incorporated with a transport model, for numerical calculating of the fluid flow and mass transport by both convection and diffusion. The MCA takes into account the effects of the thermal, the constitutional and the curvature undercoolings on dendritic growth. It also considers the preferred growth orientation of crystal and solute redistribution during solidification. In the transport model, the SIMPLE scheme and a fully implicit finite volume method are employed to solve the governing equations of momentum and species transfers. The present model was applied to simulating the evolution of a single dendrite and multi-dendrites of an Al-3mass%Cu alloy in a forced flow. The simulated results show that dendritic growth morphology is strongly influenced by melt convection.

  15. Phase field simulation of dendrite growth under convection

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The phase-field model coupled with a flow field was used to simulate the solidification of pure materials by the finite difference method.The effects of initial crystal radius,the space step and the interface thickness on the dendrite growth were studied.Results indicate that the grain grows into an equiaxial dendrite during free flow and into a typical branched structure under forced flow.The radius of an initial crystal can affect the growth of side-branches but not the stability of the dendrite s tip whe...

  16. Observation of dendritic growth under the influence of forced convection

    Science.gov (United States)

    Roshchupkina, O.; Shevchenko, N.; Eckert, S.

    2015-06-01

    The directional solidification of Ga-25wt%In alloys within a Hele-Shaw cell was visualized by X-ray radioscopy. The investigations are focused on the impact of melt convection on the dendritic growth. Natural convection occurs during a bottom up solidification because lighter solute is rejected during crystallization. Forced convection was produced by a specific electromagnetic pump. The direction of forced melt flow is almost horizontal at the solidification front. Melt flow induces various effects on grain morphology primarily caused by convective transport of solute, such as a facilitation of the growth of primary trunks or lateral branches, dendrite remelting, fragmentation or freckle formation depending on the dendrite orientation, the flow direction and intensity. Forced flow eliminates solutal plumes and damps local fluctuations of solute. A preferential growth of the secondary arms occurs at the upstream side of the dendrites, whereas high solute concentration at the downstream side inhibits the formation of secondary branches.

  17. Dendritic gold nanowire growth observed in liquid with transmission electron microscopy.

    Science.gov (United States)

    Kraus, Tobias; de Jonge, Niels

    2013-07-02

    The growth of nanoscale gold dendrites was studied in situ in a thin liquid film with transmission electron microscopy (TEM) using a liquid cell with silicon nitride (SiN) windows. Gold nanoparticle seeds were covered by a thin liquid layer containing precursor solution. Dendrite nucleation was induced by the electron beam leading to an initial burst of growth. The growth then settled at tip velocities between 0.1 and 2.0 nm/s for different dendrites. Tip velocities fluctuated as different dendrite geometries grew from the tips. Those dendrites showing granularities in their structure experienced the largest growth speed. Comparison of the observed velocities with diffusion-limited growth rates suggests that dendrite growth in thin films at this scale is limited by diffusion. The described method may find application in research on the mechanisms behind dendrite growth and also to study other types of anisotropic growth of nanomaterials driven by crystal and twin geometries.

  18. A Rayleigh number based dendrite fragmentation criterion for detachment of solid crystals during solidification

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Arvind; Dutta, Pradip [Department of Mechanical Engineering, Indian Institute of Science, Bangalore 560012 (India)], E-mail: pradip@mecheng.iisc.ernet.in

    2008-08-07

    Movement of solid crystals in the form of dendrite fragments causes severe macro-segregation in solidified products. Dendrite fragmentation in the developing mushy zone occurs as a result of remelting (causing dissolution) and subsequent breakage of dendritic side arms from the dendritic stalks. An understanding of the mechanisms of dendrite fragmentation is essential for predicting the transport of fragmented solid crystals for possible control of macro-segregation. In this work, a Rayleigh number based fragmentation criterion is developed for detachment of dendrites from the developing mushy zone, which determines the conditions favourable for fragmentation of dendrites. The Rayleigh number, defined in this paper, measures the ratio of the driving buoyancy force for the flow in the mushy zone to the retarding frictional force associated with the permeability of the mush. The criterion developed is a function of the concentration difference, liquid fraction, permeability, growth rate of mushy layer and thermophysical properties of the material.

  19. A Transition from Eutectic Growth to Dendritic Growth Induced by High Undercooling Conditions

    Institute of Scientific and Technical Information of China (English)

    吕勇军; 魏炳波

    2003-01-01

    Cu-8 wt.%Al eutectic alloy was undercooled by up to 187K (0.14 TE) using a drop tube technique. The crystal growth and phase selection mechanisms were investigated during containerless rapid solidification. It is found that the microstructural morphology is characterized by lamellar eutectic growth at small undercoolings. However,if the liquid alloy is undercooled by more than 25K, eutectic growth will be suppressed completely and the dendritic growth of (Gu) solid solution dominates its solidification process. When the undercooling exceeds 153 K, a microstructural transition from coarse dendrite to equiaxed dendrite takes place.

  20. Degenerate seaweed to tilted dendrite transition and their growth dynamics in directional solidification of non-axially oriented crystals: a phase-field study

    Science.gov (United States)

    Xing, Hui; Dong, Xianglei; Wu, Hongjing; Hao, Guanhua; Wang, Jianyuan; Chen, Changle; Jin, Kexin

    2016-05-01

    We report the results of a phase-field study of degenerate seaweed to tilted dendrite transition and their growth dynamics during directional solidification of a binary alloy. Morphological selection maps in the planes of (G, Vp) and (ε4, Vp) show that lower pulling velocity, weaker anisotropic strength and higher thermal gradient can enhance the formation of the degenerate seaweed. The tip undercooling shows oscillations in seaweed growth, but it keeps at a constant value in dendritic growth. The M-S instability on the tips and the surface tension anisotropy of the solid-liquid interface are responsible for the formation of the degenerate seaweed. It is evidenced that the place where the interfacial instability occurs determines the morphological transition. The transient transition from degenerate seaweed to tilted dendrite shows that dendrites are dynamically preferred over seaweed. For the tilted dendritic arrays with a large tilted angle, primary spacing is investigated by comparing predicted results with the classical scaling power law, and the growth direction is found to be less sensitive to the pulling velocity and the primary spacing. Furthermore, the effect of the initial interface wavelength on the morphological transition is investigated to perform the history dependence of morphological selection.

  1. NUMERICAL SIMULATION OF SUCCINONITRITE DENDRITIC GROWTH IN A FORCED FLOW

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Numerical simulation based on phase field method is performed to describe solidifica-tion process of pure material in a free or forced flow. The evolution of the interface is showed, and the effects of mesh grid and flow velocity on succinonitrite shape are studied. These results indicate that crystal grows into an equiaxial dendrite in a free flow and into an asymmetrical dendritic in a forced flow. With increasing flow velo-city, the upstream dendritic arm tip grows faster and the downstream arm grows slower. However, the evolution of the perpendicular tip has no significant change. In addition, mesh grid has no influence on dendritic growth shape when mesh grid is above 300×300.

  2. Phase field modeling of multiple dendrite growth of AI-Si binary alloy under isothermal solidification

    Institute of Scientific and Technical Information of China (English)

    Sun Qiang; Zhang Yutuo; Cui Haixia; Wang Chengzhi

    2008-01-01

    Phase field method offers the prospect of being able to perform realistic numerical experiments on dendrite growth in metallic systems. In this study, the growth process of multiple dendrites in Ai-2-mole-%-Si binary alloy under isothermal solidification was simulated using phase field model. The simulation results showed the impingement of arbitrarily oriented crystals and the competitive growth among the grains during solidification. With the increase of growing time, the grains begin to coalesce and impinge the adjacent grains. When the dendrites start to impinge, the dendrite growth is obviously inhibited.

  3. Structure defect prediction of single crystal turbine blade by dendrite envelope tracking model

    Institute of Scientific and Technical Information of China (English)

    WANG Tong-min; Itsuo OHNAKA; Hideyuki YASUDA; SU Yan-qing; GUO Jing-jie

    2006-01-01

    The structure defects such as stray grains during unidirectional solidification can severely reduce the performance of single crystal turbine blades. A dendrite envelope tracking model is developed for predicting the structure defects of unidirectional solidification turbine blade. The normal vector of dendrite envelope is estimated by the gradient of dendrite volume fraction,and the growth velocity of the dendrite envelope (dendrite tips) is calculated with considering the anisotropy of grain growth. The solute redistribution at dendrite envelope is calculated by introducing an effective solute partition coefficient. Simulation tests show that the solute-build-up due to the rejection at envelope greatly affects grain competition and consequently solidification structure. The model is applied to predict the structure defects (e.g. stray grain) of single crystal turbine blade during unidirectional solidification. The results show that the developed model is reliable and has the following abilities: reproduce the growth competition among the different-preferential-direction grains:predict the stray grain formation:simulate the structure evolution (single crystal or dendrite grains).

  4. Growth and microstructure of AlN whiskers and dendrites

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    AlN whiskers or dendrites were synthesized with a sublimation-recrystallization method by using Al, AlN powders and some additives as raw materials. Whiskers with different sizes that featured high purity and good crystallinity were obtained by controlling temperature and gas supersaturation in the reaction container. The whiskers were described as long and straight single crystals of approximately 1-30 (m in diameter by the centimeter range in length. However, AlN dendrites were about 1 mm in diameter by 0.5 cm in length, and showed an obviously preferential growth orientation, i.e., perpendicular to and planes. It is concluded that the whiskers or dendrites grow via the vapor-solid mechanism.

  5. Selection Theory of Dendritic Growth with Anisotropic Diffusion

    Directory of Open Access Journals (Sweden)

    Martin von Kurnatowski

    2015-01-01

    Full Text Available Dendritic patterns frequently arise when a crystal grows into its own undercooled melt. Latent heat released at the two-phase boundary is removed by some transport mechanism, and often the problem can be described by a simple diffusion model. Its analytic solution is based on a perturbation expansion about the case without capillary effects. The length scale of the pattern is determined by anisotropic surface tension, which provides the mechanism for stabilizing the dendrite. In the case of liquid crystals, diffusion can be anisotropic too. Growth is faster in the direction of less efficient heat transport (inverted growth. Any physical solution should include this feature. A simple spatial rescaling is used to reduce the bulk equation in 2D to the case of isotropic diffusion. Subsequently, an eigenvalue problem for the growth mode results from the interface conditions. The eigenvalue is calculated numerically and the selection problem of dendritic growth with anisotropic diffusion is solved. The length scale is predicted and a quantitative description of the inverted growth phenomenon is given. It is found that anisotropic diffusion cannot take the stabilizing role of anisotropic surface tension.

  6. Phase-field-crystal investigation of the morphology of a steady-state dendrite tip on the atomic scale.

    Science.gov (United States)

    Tang, Sai; Wang, Jincheng; Li, Junjie; Wang, Zhijun; Guo, Yaolin; Guo, Can; Zhou, Yaohe

    2017-06-01

    Through phase-field-crystal (PFC) simulations, we investigated, on the atomic scale, the crucial role played by interface energy anisotropy and growth driving force during the morphological evolution of a dendrite tip at low growth driving force. In the layer-by-layer growth manner, the interface energy anisotropy drives the forefront of the dendrite tip to evolve to be highly similar to the corner of the corresponding equilibrium crystal from the aspects of atom configuration and morphology, and thus affects greatly the formation and growth of a steady-state dendrite tip. Meanwhile, the driving force substantially influences the part behind the forefront of the dendrite tip, rather than the forefront itself. However, as the driving force increases enough to change the layer-by-layer growth to the multilayer growth, the morphology of the dendrite tip's forefront is completely altered. Parabolic fitting of the dendrite tip reveals that an increase in the influence of interface energy anisotropy makes dendrite tips deviate increasingly from a parabolic shape. By quantifying the deviations under various interface energy anisotropies and growth driving forces, it is suggested that a perfect parabola is an asymptotic limit for the shape of the dendrite tips. Furthermore, the atomic scale description of the dendrite tip obtained in the PFC simulation is compatible with the mesoscopic results obtained in the phase-field simulation in terms of the dendrite tip's morphology and the stability criterion constant.

  7. Phase-field-crystal investigation of the morphology of a steady-state dendrite tip on the atomic scale

    Science.gov (United States)

    Tang, Sai; Wang, Jincheng; Li, Junjie; Wang, Zhijun; Guo, Yaolin; Guo, Can; Zhou, Yaohe

    2017-06-01

    Through phase-field-crystal (PFC) simulations, we investigated, on the atomic scale, the crucial role played by interface energy anisotropy and growth driving force during the morphological evolution of a dendrite tip at low growth driving force. In the layer-by-layer growth manner, the interface energy anisotropy drives the forefront of the dendrite tip to evolve to be highly similar to the corner of the corresponding equilibrium crystal from the aspects of atom configuration and morphology, and thus affects greatly the formation and growth of a steady-state dendrite tip. Meanwhile, the driving force substantially influences the part behind the forefront of the dendrite tip, rather than the forefront itself. However, as the driving force increases enough to change the layer-by-layer growth to the multilayer growth, the morphology of the dendrite tip's forefront is completely altered. Parabolic fitting of the dendrite tip reveals that an increase in the influence of interface energy anisotropy makes dendrite tips deviate increasingly from a parabolic shape. By quantifying the deviations under various interface energy anisotropies and growth driving forces, it is suggested that a perfect parabola is an asymptotic limit for the shape of the dendrite tips. Furthermore, the atomic scale description of the dendrite tip obtained in the PFC simulation is compatible with the mesoscopic results obtained in the phase-field simulation in terms of the dendrite tip's morphology and the stability criterion constant.

  8. Convective heat transfer during dendritic growth

    Science.gov (United States)

    Glicksman, M. E.; Huang, S. C.

    1979-01-01

    Axial growth rate measurements were carried out at 17 levels of supercooling between 0.043 C and 2 C, a temperature range in which convection, instead of diffusion, becomes the controlling mechanism of heat transfer in the dentritic growth process. The growth velocity, normalized to that expected for pure diffusive heat transfer, displays a dependence on orientation. The ratio of the observed growth velocity to that for convection-free growth and the coefficients of supercooling are formulated. The dependence of normalized growth rate in supercooling is described for downward growing dendrites. These experimental correlations can be justified theoretically only to a limited extent.

  9. Primary and secondary dendrite spacing of Ni-based superalloy single crystals

    Directory of Open Access Journals (Sweden)

    SLOBODANKA KOSTIC

    2009-01-01

    Full Text Available Ni-based superalloy single crystals were grown by different methods (gradient method and Bridgman technique with spontaneous nucleation and with seed. In all crystal growth experiments using the Bridgman technique, the temperature gradient along the vertical furnace axes was constant (G = 33.5 °C/cm. The obtained single crystals were cut, mechanical and chemical polished, and chemically etched. Using a metallographic microscope, the spacing of the primary and secondary dendrites was investigated. The dendrite arm spacing (DAS was determined using a Quantimet 500 MC. The obtained results are discussed and compared with published data.

  10. Containerless Undercooled Melts: Ordering, Nucleation, and Dendrite Growth

    Science.gov (United States)

    Herlach, Dieter M.; Binder, Sven; Galenko, Peter; Gegner, Jan; Holland-Moritz, Dirk; Klein, Stefan; Kolbe, Matthias; Volkmann, Thomas

    2015-11-01

    Electromagnetic and electrostatic levitation are applied to containerless undercool and solidify metallic melts. A large undercooling range becomes accessible with the extra benefit that the freely suspended drop is accessible directly for in situ observation. The short-range order in undercooled melts is investigated by combining levitation with elastic neutron scattering and X-ray scattering using synchrotron radiation. Muon Spin Rotation ( µSR) experiments show magnetic ordering in deeply undercooled Co80Pd20 alloys. The onset of magnetic ordering stimulates nucleation. Results on nucleation undercooling of zirconium are presented showing the limit of maximum undercoolability set by the onset of homogeneous nucleation. Metastable phase diagrams are determined by applying energy-dispersive X-ray diffraction of Ni-V alloys with varying concentration. Nucleation is followed by crystal growth. Rapid dendrite growth velocity is measured on levitation-processed samples as a function of undercooling ∆ T by using high-speed video camera technique. Solute trapping in dilute solid solutions and disorder trapping in intermetallic compounds are experimentally verified. Measurements of glass-forming Cu-Zr alloy show a maximum in the V(∆ T) relation that is indicative for diffusion-controlled growth. The influence of convection on dendrite growth of Al50Ni50 is shown by comparative measurements of dendrite growth velocity on Earth and in reduced gravity. Eventually, faceting of a rough interface by convection is presented as observed on Ni2B alloys.

  11. DENDRITE REFINING AND EUTECTIC TRANSFORMATION BEHAVIOR OF NICKEL-BASE SINGLE CRYSTAL (NBSC) SUPERALLOY

    Institute of Scientific and Technical Information of China (English)

    1998-01-01

    Because of the low temperature gradient and growth rate, the microstructure of the conventional single crystal superalloy made by HRS processing is coarse dendrite with well developed sidebranches and has serious segregation. With the help of the high temperature gradient directional solidification equipment (HGDS), the solidification cooling rate is greatly increased. Study on microstructure of the Ni-base single crystal superalloy solidified at much higher cooling rate shows that the dendrite arm spacing is highly refined, of which the primary dendrite arm spacing can be made to be 38μm, just as 1/10 as that by conventional HRS processing. With the increase of the cooling rate, the amount of the eutectic increases and then decreases. In the superfine columnar dendrite, the amount of γ/γ′eutectic is much fewer and its size is very small. This is useful to homogenize the microsegregation and improve the property of the material.

  12. The Isothermal Dendritic Growth Experiment Archive

    Science.gov (United States)

    Koss, Matthew

    2009-03-01

    The growth of dendrites is governed by the interplay between two simple and familiar processes---the irreversible diffusion of energy, and the reversible work done in the formation of new surface area. To advance our understanding of these processes, NASA sponsored a project that flew on the Space Shuttle Columbia is 1994, 1996, and 1997 to record and analyze benchmark data in an apparent-microgravity ``laboratory.'' In this laboratory, energy transfer by gravity driven convection was essentially eliminated and one could test independently, for the first time, both components of dendritic growth theory. The analysis of this data shows that although the diffusion of energy can be properly accounted for, the results from interfacial physics appear to be in disagreement and alternate models should receive increased attention. Unfortunately, currently and for the foreseeable future, there is no access or financial support to develop and conduct additional experiments of this type. However, the benchmark data of 35mm photonegatives, video, and all supporting instrument data are now available at the IDGE Archive at the College of the Holy Cross. This data may still have considerable relevance to researchers working specifically with dendritic growth, and more generally those working in the synthesis, growth & processing of materials, multiscale computational modeling, pattern formation, and systems far from equilibrium.

  13. Growth units model of anion coordination-polyhedra and its application to crystal growth

    Institute of Scientific and Technical Information of China (English)

    ZHANG Xuehua; LUO Haosu; ZHONG Weizhuo

    2004-01-01

    Growth units model of anion coordination-polyhedra ACP model emphasizes the influence of intrinsic structure of crstal upon the crystal growth and the importance of the external conditions on which crystals grow. The ACP model is used to analyze some problems in crystal growth, such as the formation of dendrite in the crystal structure,growth habit of polar crystal, and formation of allomerism and polymorphism.

  14. Growth of dopamine crystals

    Energy Technology Data Exchange (ETDEWEB)

    Patil, Vidya, E-mail: vidya.patil@ruparel.edu; Patki, Mugdha, E-mail: mugdha.patki@ruparel.edu [D. G. Ruparel College, Senapati Bapat Marg, Mahim, Mumbai – 400 016 (India)

    2016-05-06

    Many nonlinear optical (NLO) crystals have been identified as potential candidates in optical and electro-optical devices. Use of NLO organic crystals is expected in photonic applications. Hence organic nonlinear optical materials have been intensely investigated due to their potentially high nonlinearities, and rapid response in electro-optic effect compared to inorganic NLO materials. There are many methods to grow organic crystals such as vapor growth method, melt growth method and solution growth method. Out of these methods, solution growth method is useful in providing constraint free crystal. Single crystals of Dopamine have been grown by evaporating the solvents from aqueous solution. Crystals obtained were of the size of orders of mm. The crystal structure of dopamine was determined using XRD technique. Images of crystals were obtained using FEG SEM Quanta Series under high vacuum and low KV.

  15. Growth of dopamine crystals

    Science.gov (United States)

    Patil, Vidya; Patki, Mugdha

    2016-05-01

    Many nonlinear optical (NLO) crystals have been identified as potential candidates in optical and electro-optical devices. Use of NLO organic crystals is expected in photonic applications. Hence organic nonlinear optical materials have been intensely investigated due to their potentially high nonlinearities, and rapid response in electro-optic effect compared to inorganic NLO materials. There are many methods to grow organic crystals such as vapor growth method, melt growth method and solution growth method. Out of these methods, solution growth method is useful in providing constraint free crystal. Single crystals of Dopamine have been grown by evaporating the solvents from aqueous solution. Crystals obtained were of the size of orders of mm. The crystal structure of dopamine was determined using XRD technique. Images of crystals were obtained using FEG SEM Quanta Series under high vacuum and low KV.

  16. Phase field modeling of multiple dendrite growth of Al-Si binary alloy under isothermal solidifi cation

    Directory of Open Access Journals (Sweden)

    Sun Qiang

    2008-11-01

    Full Text Available Phase field method offers the prospect of being able to perform realistic numerical experiments on dendrite growth in metallic systems. In this study, the growth process of multiple dendrites in Al-2-mole-%-Si binary alloy under isothermal solidifi cation was simulated using phase fi eld model. The simulation results showed the impingement of arbitrarily oriented crystals and the competitive growth among the grains during solidifi cation. With the increase of growing time, the grains begin to coalesce and impinge the adjacent grains. When the dendrites start to impinge, the dendrite growth is obviously inhibited.

  17. Web-dendritic ribbon growth. Annual report, October 1, 1975--September 31, 1976

    Energy Technology Data Exchange (ETDEWEB)

    Hilborn, Jr., R. B.; Faust, Jr., J. W.

    1976-10-01

    The web furnace has been set up, calibrated, and made operational for pulling dendritic-web samples. Considerable work has been completed in the investigation of the effect of changes in the furnace thermal geometry, as accomplished by variations in the number, size, shape, and location of thermal shields, on the growth of dendritic-web. Numerous growth runs were made to grow primitive dendrites for use as the dendritic seed crystals for the web growth. Some preliminary investigations were conducted to try and determine the optimum twin spacing in the dendritic seed crystal for web growth. Models were developed and computer programs applied to ascertain the thermal geometries present in the susceptor, crucible melt, meniscus, and web. A major result of this analysis has been the prediction of an upper limit on the pull rate of approximately 4 cms. per minute with the thermal geometry presented in our furnace. The facilities for obtaining characterization data were set-up and made operational. Data on twin spacings and number of twin planes in the dendritic seed crystals and resulting web samples was obtained. Resistivity and majority charge carrier type determinations were made on a few select web samples. All samples to date have been high resistivity, undoped, p-type. (WDM)

  18. Dendritic growth model of multilevel marketing

    Science.gov (United States)

    Pang, James Christopher S.; Monterola, Christopher P.

    2017-02-01

    Biologically inspired dendritic network growth is utilized to model the evolving connections of a multilevel marketing (MLM) enterprise. Starting from agents at random spatial locations, a network is formed by minimizing a distance cost function controlled by a parameter, termed the balancing factor bf, that weighs the wiring and the path length costs of connection. The paradigm is compared to an actual MLM membership data and is shown to be successful in statistically capturing the membership distribution, better than the previously reported agent based preferential attachment or analytic branching process models. Moreover, it recovers the known empirical statistics of previously studied MLM, specifically: (i) a membership distribution characterized by the existence of peak levels indicating limited growth, and (ii) an income distribution obeying the 80 - 20 Pareto principle. Extensive types of income distributions from uniform to Pareto to a "winner-take-all" kind are also modeled by varying bf. Finally, the robustness of our dendritic growth paradigm to random agent removals is explored and its implications to MLM income distributions are discussed.

  19. Unsteady growth of ammonium chloride dendrites

    Science.gov (United States)

    Martyushev, L. M.; Terentiev, P. S.; Soboleva, A. S.

    2016-02-01

    Growth of ammonium chloride dendrites from aqueous solution is experimentally investigated. The growth rate υ and the radius ρ of curvature of branches are measured as a function of the relative supersaturation Δ for steady and unsteady growth conditions. It is shown that the experimental results are quantitatively described by the dependences ρ=a/Δ+b, υ=cΔ2, where the factors for primary branches are a=(1.3±0.2)·10-7 m, b=(2.5±0.4)·10-7 m, and c=(2.2±0.3)·10-4 m/s. The factor c is found to be approximately 7 times smaller for the side branches than that for the primary branches.

  20. Advanced Crystal Growth Technology

    Energy Technology Data Exchange (ETDEWEB)

    Land, T A; Hawley-Fedder, R A

    2005-03-01

    Although the fundamental mechanism of crystal growth has received and continues to receive deserved attention as a research activity, similar research efforts addressing the need for advanced materials and processing technology required to grow future high quality crystals has been sorely lacking. The purpose of this research effort is to develop advanced rapid growth processing technologies and materials suitable for providing the quality of products needed for advanced laser and photonics applications. In particular we are interested in developing a methodology for growing high quality KDP crystals based on an understanding of the fundamental mechanisms affecting growth. One problem in particular is the issue of control of impurities during the growth process. Many unwanted impurities are derived from the growth system containers and can adversely affect the optical quality and aspect ratio (shape) of the crystals. Previous studies have shown that even trace concentrations ({approx}10{sup -9} M) of impurities affect growth and even 'insignificant' species can have a large impact. It is also known that impurities affect the two growth faces of KDP very differently. Traces of trivalent metal impurities such as Fe{sup 3+}, Cr{sup 3+}, and Al{sup 3+} in solution are known to inhibit growth of the prismatic {l_brace}100{r_brace} faces of KDP while having little effect on the growth of the pyramidal {l_brace}101{r_brace} faces. This differentiation opens the possibility of intentionally adding select ions to control the aspect ratio of the crystal to obtain a more advantageous shape. This document summarizes our research efforts to improve KDP crystal growth. The first step was to control unwanted impurity addition from the growth vessel by developing an FEP liner to act as a barrier to the glass container. The other focus to develop an understanding of select impurities on growth rates in order to be able to use them to control the habit or shape of the

  1. Numerical Simulations of Equiaxed Dendrite Growth Using Phase Field Method

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Phase field method offers the prospect of being able to perform realistic numerical experiments on dendrite growthin a metallic system. In this paper, the equiaxed dendrite evolution during the solidification of a pure material wasnumerically simulated using the phase field model. The equiaxed dendrite growth in a two-dimensional square domainof undercooled melt (nickel) with four-fold anisotropy was simulated. The phase field model equations was solvedusing the explicit finite difference method on a uniform mesh. The formation of various equiaxed dendrite patternswas shown by a series of simulations, and the effect of anisotropy on equiaxed dendrite morphology was investigated.

  2. Shaped Crystal Growth

    Science.gov (United States)

    Tatartchenko, Vitali A.

    Crystals of specified shape and size (shaped crystals) with controlled crystal growth (SCG) defect and impurity structure have to be grown for the successful development of modern engineering. Since the 1950s many hundreds of papers and patents concerned with shaped growth have been published. In this chapter, we do not try to enumerate the successful applications of shaped growth to different materials but rather to carry out a fundamental physical and mathematical analysis of shaping as well as the peculiarities of shaped crystal structures. Four main techniques, based on which the lateral surface can be shaped without contact with the container walls, are analyzed: the Czochralski technique (CZT), the Verneuil technique (VT), the floating zone technique (FZT), and technique of pulling from shaper (TPS). Modifications of these techniques are analyzed as well. In all these techniques the shape of the melt meniscus is controlled by surface tension forces, i.e., capillary forces, and here they are classified as capillary shaping techniques (CST). We look for conditions under which the crystal growth process in each CST is dynamically stable. Only in this case are all perturbations attenuated and a crystal of constant cross section shaping technique (CST) grown without any special regulation. The dynamic stability theory of the crystal growth process for all CST is developed on the basis of Lyapunov's dynamic stability theory. Lyapunov's equations for the crystal growth processes follow from fundamental laws. The results of the theory allow the choice of stable regimes for crystal growth by all CST as well as special designs of shapers in TPS. SCG experiments by CZT, VT, and FZT are discussed but the main consideration is given to TPS. Shapers not only allow crystal of very complicated cross section to be grown but provide a special distribution of impurities. A history of TPS is provided later in the chapter, because it can only be described after explanation of the

  3. Crystal growth and crystallography

    Science.gov (United States)

    Chernov, A. A.

    1998-01-01

    Selected topics that may be of interest for both crystal-structure and crystal-growth communities are overviewed. The growth of protein crystals, along with that of some other compounds, is one of the topics, and recent insights into related phenomena are considered as examples of applications of general principles. The relationship between crystal growth shape and structure is reviewed and an attempt to introduce semiquantitative characterization of binding for proteins is made. The concept of kinks for complex structures is briefly discussed. Even at sufficiently low supersaturations, the fluctuation of steps may not be sufficient to implement the Gibbs-Thomson law if the kink density is low enough. Subsurface ordering of liquids and growth of rough interfaces from melts is discussed. Crystals growing in microgravity from solution should be more perfect if they preferentially trap stress-inducing impurities, thus creating an impurity-depleted zone around themselves. Evidently, such a zone is developed only around the crystals growing in the absence of convection. Under terrestrial conditions, the self-purified depleted zone is destroyed by convection, the crystal traps more impurity and grows stressed. The stress relief causes mosaicity. In systems containing stress-inducing but poorly trapped impurities, the crystals grown in the absence of convection should be worse than those of their terrestrial counterparts.

  4. Crystal Growth Behaviors of Silicon during Melt Growth Processes

    Directory of Open Access Journals (Sweden)

    Kozo Fujiwara

    2012-01-01

    Full Text Available It is imperative to improve the crystal quality of Si multicrystal ingots grown by casting because they are widely used for solar cells in the present and will probably expand their use in the future. Fine control of macro- and microstructures, grain size, grain orientation, grain boundaries, dislocation/subgrain boundaries, and impurities, in a Si multicrystal ingot, is therefore necessary. Understanding crystal growth mechanisms in melt growth processes is thus crucial for developing a good technology for producing high-quality Si multicrystal ingots for solar cells. In this review, crystal growth mechanisms involving the morphological transformation of the crystal-melt interface, grain boundary formation, parallel-twin formation, and faceted dendrite growth are discussed on the basis of the experimental results of in situ observations.

  5. Assessment of scaling factor in modified dendrite growth model

    Institute of Scientific and Technical Information of China (English)

    张瑞丰; 沈宁福; 曹文博

    2002-01-01

    A model for dendrite growth during rapid solidification was established on the basis of BCT model and marginal stability criterion through modified Peclet numbers. Taking into account the interaction of diffusion fields, including solute diffusion field and thermal diffusion field around the dendrite tip, the model obtain a satisfactory results to predict the dendrite velocity and the tip radius, which agrees well with the experimental data from references in Cu-Ni alloy.

  6. Growth of NaBi(WO4)2 Dendrite and Mechanism

    Institute of Scientific and Technical Information of China (English)

    HONG Yong; AI Fei; PAN Xiu-Hong; JIN Wei-Qing; ZHONG Wei-Zhuo; SHINICHI Yoda

    2006-01-01

    @@ The solid-liquid interface motion of NaBi(WO4)2 (NBWO) melt crystal growth is observed in an in situ system,in which the whole processes of interface transition from flat interface and cellular to dendrite are visualized.

  7. Three-dimensional interfacial wave theory of dendritic growth: (Ⅰ). multiple variables expansion solutions

    Institute of Scientific and Technical Information of China (English)

    Chen Yong-Qiang; Tang Xiong-Xin; Xu Jian-Jun

    2009-01-01

    Dendritic pattern formation at the interface between liquid and solid is a commonly observed phenomenon in crystal growth and solidification process. The theoretical investigation of dendritic growth is one of the most profound and highly challenging subjects in the broad areas of intcrfacial pattern formation, condensed matter physics and materials science, preoccupying many researchers from various areas. Some longstanding key issues on this subject finally gained a breakthrough in the late of last century, via the 'Interracial Wave (IFW) Theory' on the ground of systematical global stability analysis of the basic state of dendritic growth. The original form of the IFW theory mainly focus on the investigation of various axi-symmetric unsteady perturbed modes solutions around the axi-symmctric basic state of system of dendritic growth. In reality, the system may allow various non-axi-symmctric, unsteady perturbed states. Whether or not the system of dendritic growth allows some growing non-axi-symmetric modes? Will the stationary dendritic pattern be destroyed by some of such non-axi-symmetric modes? Or, in one word, what is the stability property of the system, once the non-axi-symmetric modes can be evoked? The answers for these questions are important for the solid foundation of IFW theory. The present work attempts to settle down these issues and develop a three-dimensional (3D) interracial wave theory of dendritic growth. Our investigations verify that dendritic growth indeed allows a discrete set of non-axi-symmetric unstable global wave modes, which gives rise to a set of multiple arms spiral waves propagating along the Ivantsov's paraboloid.

  8. Epigenetic regulation of axon and dendrite growth

    Directory of Open Access Journals (Sweden)

    Ephraim F Trakhtenberg

    2012-03-01

    Full Text Available Neuroregenerative therapies for central nervous system (CNS injury, neurodegenerative disease, or stroke require axons of damaged neurons to grow and reinnervate their targets. However, mature mammalian CNS neurons do not regenerate their axons, limiting recovery in these diseases (Yiu and He, 2006. CNS’ regenerative failure may be attributable to the development of an inhibitory CNS environment by glial-associated inhibitory molecules (Yiu and He, 2006, and by various cell-autonomous factors (Sun and He, 2010. Intrinsic axon growth ability also declines developmentally (Li et al., 1995; Goldberg et al., 2002; Bouslama-Oueghlani et al., 2003; Blackmore and Letourneau, 2006 and is dependent on transcription (Moore et al., 2009. Although neurons’ intrinsic capacity for axon growth may depend in part on the panoply of expressed transcription factors (Moore and Goldberg, 2011, epigenetic factors such as the accessibility of DNA and organization of chromatin are required for downstream genes to be transcribed. Thus a potential approach to overcoming regenerative failure focuses on the epigenetic mechanisms regulating regenerative gene expression in the CNS. Here we review molecular mechanisms regulating the epigenetic state of DNA through chromatin modifications, their implications for regulating axon and dendrite growth, and important new directions for this field of study.

  9. Numerical Modeling of Dendrite Growth in Al Alloys

    Institute of Scientific and Technical Information of China (English)

    许庆彦; 柳百成

    2004-01-01

    Dendritic grains are the most often observed microstructure in metals and alloys. In the past decade, more and more attention has been paid to the modeling and simulation of dendritic microstructures. This paper describes a modified diffusion-limited aggregation model to simulate the complex shape of the dendrite grains during metal solidification. The fractal model was used to simulate equiaxed dendrite growth. The fractal dimensions of simulated Al alloy structures range from 1.63-1.88 which compares well with the experimentally-measured fractal dimension of 1.85; therefore, the model accurately predicts not only the dendritic structure morphology, but also the fractal dimension of the dendrite structure formed during solidification.

  10. Heterogeneous nucleation and dendritic growth within undercooled liquid niobium under electrostatic levitation condition

    Science.gov (United States)

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

    2017-09-01

    The physical mechanisms of crystal nucleation and dendritic growth within undercooled niobium were systematically studied by electrostatic levitation and molecular dynamics methods. The maximum undercooling was achieved as 454 K (0.16Tm), while the hypercooling limit was determined as 706 K (0.26Tm). The undercooling probability displayed Poisson distribution and indicated the occurrence of heterogeneous nucleation. The calculated critical nucleus size reduced rapidly with undercooling and the solid-liquid interface energy was deduced to be 0.367 J m-2. In addition, the dendritic growth velocity of pure niobium exhibited a power relation versus undercooling, and reached 41 m s-1 at the maximum undercooling.

  11. Quartz crystal growth

    Science.gov (United States)

    Baughman, Richard J.

    1992-01-01

    A process for growing single crystals from an amorphous substance that can undergo phase transformation to the crystalline state in an appropriate solvent. The process is carried out in an autoclave having a lower dissolution zone and an upper crystallization zone between which a temperature differential (.DELTA.T) is maintained at all times. The apparatus loaded with the substance, solvent, and seed crystals is heated slowly maintaining a very low .DELTA.T between the warmer lower zone and cooler upper zone until the amorphous substance is transformed to the crystalline state in the lower zone. The heating rate is then increased to maintain a large .DELTA.T sufficient to increase material transport between the zones and rapid crystallization. .alpha.-Quartz single crystal can thus be made from fused quartz in caustic solvent by heating to 350.degree. C. stepwise with a .DELTA.T of 0.25.degree.-3.degree. C., increasing the .DELTA.T to about 50.degree. C. after the fused quartz has crystallized, and maintaining these conditions until crystal growth in the upper zone is completed.

  12. Interfacial wave theory for dendritic structure of a growing needle crystal. I - Local instability mechanism. II - Wave-emission mechanism at the turning point

    Science.gov (United States)

    Xu, Jian-Jun

    1989-01-01

    The complicated dendritic structure of a growing needle crystal is studied on the basis of global interfacial wave theory. The local dispersion relation for normal modes is derived in a paraboloidal coordinate system using the multiple-variable-expansion method. It is shown that the global solution in a dendrite growth process incorporates the morphological instability factor and the traveling wave factor.

  13. Simulation of facet dendrite growth with strong interfacial energy anisotropy by phase field method

    Institute of Scientific and Technical Information of China (English)

    袁训锋; 刘宝盈; 李春; 周春生; 丁雨田

    2015-01-01

    Numerical simulations based on a new regularized phase-field model were presented, to simulate the solidification of hexagonal close-packed materials with strong interfacial energy anisotropies. Results show that the crystal grows into facet dendrites, displaying six-fold symmetry. The size of initial crystals has an effect on the branching-off of the principal branch tip along the direction, which is eliminated by setting the b/a (a and b are the semi-major and semi-minor sizes in the initial elliptical crystals, respectively) value to be less than or equal to 1. With an increase in the undercooling value, the equilibrium morphology of the crystal changes from a star-like shape to facet dendrites without side branches. The steady-state tip velocity increases exponentially when the dimensionless undercooling is below the critical value. With a further increase in the undercooling value, the equilibrium morphology of the crystal grows into a developed side-branch structure, and the steady-state tip velocity of the facet dendrites increases linearly. The facet dendrite growth has controlled diffusion and kinetics.

  14. Interactions with Astroglia Influence the Shape of the Developing Dendritic Arbor and Restrict Dendrite Growth Independent of Promoting Synaptic Contacts

    Science.gov (United States)

    Farley, Jennifer R.; Sterritt, Jeffrey R.; Crane, Andrés B.; Wallace, Christopher S.

    2017-01-01

    Astroglia play key roles in the development of neurons, ranging from regulating neuron survival to promoting synapse formation, yet basic questions remain about whether astrocytes might be involved in forming the dendritic arbor. Here, we used cultured hippocampal neurons as a simple in vitro model that allowed dendritic growth and geometry to be analyzed quantitatively under conditions where the extent of interactions between neurons and astrocytes varied. When astroglia were proximal to neurons, dendrites and dendritic filopodia oriented toward them, but the general presence of astroglia significantly reduced overall dendrite growth. Further, dendritic arbors in partial physical contact with astroglia developed a pronounced pattern of asymmetrical growth, because the dendrites in direct contact were significantly smaller than the portion of the arbor not in contact. Notably, thrombospondin, the astroglial factor shown previously to promote synapse formation, did not inhibit dendritic growth. Thus, while astroglia promoted the formation of presynaptic contacts onto dendrites, dendritic growth was constrained locally within a developing arbor at sites where dendrites contacted astroglia. Taken together, these observations reveal influences on spatial orientation of growth as well as influences on morphogenesis of the dendritic arbor that have not been previously identified. PMID:28081563

  15. Ovariectomy attenuates dendritic growth in hormone-sensitive spinal motoneurons.

    Science.gov (United States)

    Hebbeler, S L; Verhovshek, T; Sengelaub, D R

    2001-09-15

    The lumbar spinal cord of rats contains the sexually dimorphic, steroid-sensitive spinal nucleus of the bulbocavernosus (SNB). Dendritic development of SNB motoneurons in male rats is biphasic, initially showing exuberant growth through 4 weeks of age followed by a retraction to mature lengths by 7 weeks of age. The initial growth is steroid dependent, attenuated by castration or aromatase inhibition, and supported by hormone replacement. Dendritic retraction is also steroid sensitive and can be prevented by testosterone treatment, but is unaffected by aromatase inhibition. Together, these results suggest a role for estrogens during the initial growth phase of SNB development. In this study, we tested whether ovarian hormones could support SNB somal and dendritic development. Motoneuron morphology was assessed in normal males and in females perinatally masculinized with dihydrotestosterone and then either ovariectomized or left intact. SNB motoneurons were retrogradely labeled with cholera toxin-HRP at 4 or 7 weeks of age and reconstructed in three dimensions. Initial growth of SNB dendrites was reduced after ovariectomy in masculinized females. However, no differences in dendritic length were seen at 7 weeks of age between intact and ovariectomized masculinized females, and lengths in both groups were significantly lower than those of normal males. Together with previous findings, these results suggest that estrogens are involved in the early growth of SNB dendrites, but not in their subsequent retraction.

  16. Amphiphilic dendritic peptides: Synthesis and behavior as an organogelator and liquid crystal

    Directory of Open Access Journals (Sweden)

    Xinwu Ba

    2011-02-01

    Full Text Available New amphiphilic dendritic peptides on dendritic polyaspartic acid were designed and synthesized. The organogel and liquid crystal properties of these amphiphilic dendritic peptides were fully studied by field-emission SEM, temperature dependent FT-IR, differential scanning calorimetry, polarization optical microscopy and X-ray diffraction experiments. Amphiphilic dendritic peptides G3 show good organogel properties with a minimum gelation concentration as low as 1 wt %. Furthermore, amphiphilic dendritic peptides G3 can form a hexagonal columnar liquid crystal assembly over a wide temperature range.

  17. Laboratory studies of crystal growth in magma

    Science.gov (United States)

    Hammer, J. E.; Welsch, B. T.; First, E.; Shea, T.

    2012-12-01

    The proportions, compositions, and interrelationships among crystalline phases and glasses in volcanic rocks cryptically record pre-eruptive intensive conditions, the timing of changes in crystallization environment, and the devolatilization history of eruptive ascent. These parameters are recognized as important monitoring tools at active volcanoes and interpreting geologic events at prehistoric and remote eruptions, thus motivating our attempts to understand the information preserved in crystals through an experimental appoach. We are performing laboratory experiments in mafic, felsic, and intermediate composition magmas to study the mechanisms of crystal growth in thermochemical environments relevant to volcanic environments. We target features common to natural crystals in igneous rocks for our experimental studies of rapid crystal growth phenomena: (1) Surface curvature. Do curved interfaces and spongy cores represent evidence of dissolution (i.e., are they corrosion features), or do they record the transition from dendritic to polyhedral morphology? (2) Trapped melt inclusions. Do trapped liquids represent bulk (i.e., far-field) liquids, boundary layer liquids, or something intermediate, depending on individual species diffusivity? What sequence of crystal growth rates leads to preservation of sealed melt inclusions? (3) Subgrain boundaries. Natural phenocrysts commonly exhibit tabular subgrain regions distinguished by small angle lattice misorientations or "dislocation lamellae" and undulatory extinction. Might these crystal defects be produced as dendrites undergo ripening? (4) Clusters. Contacting clusters of polymineralic crystals are the building blocks of cumulates, and are ubiquitous features of mafic volcanic rocks. Are plagioclase and clinopyroxene aligned crystallographically, suggesting an epitaxial (surface energy) relationship? (5) Log-normal size distribution. What synthetic cooling histories produce "natural" distributions of crystal sizes, and

  18. Growth habit of polar crystals

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Using coordination polyhedron rule, growth habit of polar crystals such as ZnO, ZnS and SiO2 is investigated. It shows that the growth rates in the positive and negative polar axis directions are different. The theoretical growth habit of ZnO crystal is hexagonal prism and the growth rates of its various faces are:V{0001}>V{0111}-->V{0110}->V{0111}->V{0001}-. The growth habit of ZnS crystal is tetrahedron and its growth rates of different crystal faces are: V{111}>V{001}>V{001} =V{100} =. The growth rate relationship between positive and negative polar axis directions of SiO2 crystal V[1120]-->V[1120]-.is These results are in agreement with the growth habits observed under hydrothermal conditions. The different growth rates between positive and negative polar axis directions cannot be explained by PBC theory.

  19. Dendrite growth characteristics within liquid Fe-Sb alloy

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Bulk samples and small droplets of liquid Fe-10%Sb alloys are undercooled up to 429 K (0.24TL) and 568 K (0.32TL), respectively, with glass fluxing and free fall techniques. The high undercooling does not change the phase constitution, and only the αFe solid solution is found in the rapidly solidified alloy. The experimental results show that when the undercooling is below 296 K, the growth velocity of αFe dendrite rises exponentially with the increase of undercooling and reaches a maximum value 1.38 m/s. Subsequently, the growth velocity begins to decrease if undercooling further increases. The αFe phase grows into coarse dendrites under small undercooling conditions, whereas it becomes vermicular dendrites in highly undercooled melts. The solute trapping is closely related to the dendrite growth velocity and cooling rate rather than undercooling. Although the solute trapping can be remarkably suppressed by the rapid dendrite growth, the segregationless solidification is not observed in the present experiments due to the large solidification temperature range.

  20. Dendrite growth characteristics within liquid Fe-Sb alloy

    Institute of Scientific and Technical Information of China (English)

    WANG WeiLi; Lü YongJun; QIN HaiYan; WEI BingBo

    2009-01-01

    Bulk samples and small droplets of liquid Fe-10%Sb alloys are undercooled up to 429 K (0.24TL) and 568 K (0.32 TL), respectively, with glass fluxing and free fall techniques. The high undercooling does not change the phase constitution, and only the αFe solid solution is found in the rapidly solidified alloy.The experimental results show that when the undercooling is below 296 K, the growth velocity of αFe dendrite rises exponentially with the increase of undercooling and reaches a maximum value 1.38 m/s.Subsequently, the growth velocity begins to decrease if undercooling further increases. The αFe phase grows into coarse dendrites under small undercooling conditions, whereas it becomes vermicular dendrites in highly undercooled melts. The solute trapping is closely related to the dendrite growth velocity and cooling rate rather than undercooling. Although the solute trapping can be remarkably suppressed by the rapid dendrite growth, the segregationless solidification is not observed in the present experiments due to the large solidification temperature range.

  1. Springer Handbook of Crystal Growth

    CERN Document Server

    Dhanaraj, Govindhan; Prasad, Vishwanath; Dudley, Michael

    2010-01-01

    Over the years, many successful attempts have been made to describe the art and science of crystal growth. Most modern advances in semiconductor and optical devices would not have been possible without the development of many elemental, binary, ternary, and other compound crystals of varying properties and large sizes. The objective of the Springer Handbook of Crystal Growth is to present state-of-the-art knowledge of both bulk and thin-film crystal growth. The goal is to make readers understand the basics of the commonly employed growth processes, materials produced, and defects generated. Almost 100 leading scientists, researchers, and engineers from 22 different countries from academia and industry have been selected to write chapters on the topics of their expertise. They have written 52 chapters on the fundamentals of bulk crystal growth from the melt, solution, and vapor, epitaxial growth, modeling of growth processes and defects, techniques of defect characterization as well as some contemporary specia...

  2. Diagenetic Crystal Clusters and Dendrites, Lower Mount Sharp, Gale Crater

    Science.gov (United States)

    Kah, L. C.; Kronyak, R.; Van Beek, J.; Nachon, M.; Mangold, N.; Thompson, L.; Wiens, R.; Grotzinger, J.; Farmer, J.; Minitti, M.; hide

    2015-01-01

    Since approximately Sol 753 (to sol 840+) the Mars Science Laboratory Curiosity rover has been investigating the Pahrump locality. Mapping of HiRise images suggests that the Pahrup locality represents the first occurrence of strata associated with basal Mount Sharp. Considerable efforts have been made to document the Pahrump locality in detail, in order to constrain both depositional and diagenetic facies. The Pahrump succession consists of approximately 13 meters of recessive-weathering mudstone interbedded with thin (decimeter-scale) intervals of more erosionally resistant mudstone, and crossbedded sandstone in the upper stratigraphic levels. Mudstone textures vary from massive, to poorly laminated, to well-laminated. Here we investigate the distribution and structure of unusual diagenetic features that occur in the lowermost portion of the Pahrump section. These diagenetic features consist of three dimensional crystal clusters and dendrites that are erosionally resistant with respect to the host rock.

  3. Dendritic and eutectic growth in Sb60Ag20Cu20 ternary alloy

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The rapid solidification of Sb60Ag20Cu20 ternary alloy was realized by high undercooling method, and the maximum undercooling is up to 142 K (0.18TL). Within the wide undercooling range of 40-142 K, the solidified microstructures are composed of (Sb), θand ε phases. High undercooling enlarges the solute solubility of (Sb) phase, which causes its crystal lattice to expand and its crystal lattice constants to increase. Primary (Sb) phase grows in two modes: at small undercoolings non-faceted dendrite growth is the main growth form; whereas at large undercoolings faceted dendrite growth takes the dominant place. The remarkable difference of crystal structures between (Sb) and θphases leads to (θ+ Sb) pseudobinary eutectic hard to form, whereas strips of θform when the alloy melt reaches the (θ + Sb) pseudobinary eutectic line. The cooperative growth of θand ε phases contributes to the formation of (ε +θ) pseudobinary eutectic easily. In addition, the crystallization route has been determined via microstructural characteristic analysis and DSC experiment.

  4. The plane-to-cellular-to-dendrite transition of the shape of the crystallization front during the crystallization of Al–Cu alloys

    Directory of Open Access Journals (Sweden)

    VESNA RADOJEVIC

    2006-03-01

    Full Text Available The evolution of the crystallization front from a planar to a dendritic one as a function of the GL/(Rc0 parameter was investigated during the crystallization of Al–Cu alloys by the vertical Bridgman method. Six series of alloyswith different initial compositions of Cu were solidified at different growth rates. A mathematical model for the heat transfer during vertical Bridgmen crystal growth was developed. The model was solved using the finite element method. The temperature gradient in the melt at the beginning of crystal growth was calculated using the obtainedmodel. Discrete stages of the crystallization front were identified in the experiments, as the ratio GL/(Rc0 decreased.

  5. Micromorphology of pure and PbI{sub 2}-doped CdI{sub 2} dendritic single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Binay [Department of Physics and Astrophysics, University of Delhi, Delhi-110007 (India); Sinha, Nidhi [Department of Electronics, SGTB Khalsa College, University of Delhi, Delhi-7 (India)

    2005-09-01

    Undoped and PbI{sub 2}-doped dendritic single crystals were grown by vapour growth technique. The basal surfaces of the as grown crystals were examined by optical and electron microscopy to observe wide variety of growth and defect features. Apart from typical features of dendritic growth, features of overgrowth, slip bands, growth steps and their bunching, etc. were observed. The basal surfaces of the crystals were then etched by controlled condensation of water vapour, after optimizing the etching condition, and the microscopic studies were repeated. Etch pits of hexagonal and triangular shape, both symmetric and asymmetric, and of different density, were observed in the case of undoped and doped crystals, respectively. In some cases, crystallographic hillocks were also observed. The crystals were also examined by X-ray diffraction for their polytypism and related behaviour. The results are analyzed to elicit information on the correlation of structure, defects and surface features of the crystals. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  6. 3D anisotropy simulation of dendrites growth with phase field method

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The anisotropy problem of 3D phase-field model was studied,and various degrees of anisotropy were simulated by numerical calculation method.The results show that with the change of interface anisotropy coefficients,from smooth transition to the appearance of angle,equilibrium crystals shape morphology has a critical value,and 3D critical value is 0.3.The growth of dendrites is stable and the interface is smooth when it is less than critical value;the interface is unstable,rolling edge appears and the growth is discontinuous when it is more than critical value.With the increase of anisotropy coefficients,the dendrites grow faster under the same condition.

  7. Dendrite crystal morphology evolution mechanism of β-BaB2O4 crystal

    Institute of Scientific and Technical Information of China (English)

    HE ChongJun; ZHONG WeiZhuo; LIU YouWen

    2009-01-01

    Existence of [B3-O6]3- hexagonal ring growth unit in melt solution of β-BaB2O4 crystal was proved by the results of high temperature Raman measurements. A morphology evolution process of β-BaB2O4 crys-tal was observed by a high temperature in-situ observation device. The crystal morphology varied with the supersaturation of growth melt solution. The mechanism of β-BaB2O4 crystal morphology evolution was analyzed through the growth unit model.

  8. Dendrite crystal morphology evolution mechanism of β-BaB2O4 crystal

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Existence of [B3-O6]3- hexagonal ring growth unit in melt solution of β-BaB2O4 crystal was proved by the results of high temperature Raman measurements.A morphology evolution process of β-BaB2O4 crys-tal was observed by a high temperature in-situ observation device.The crystal morphology varied with the supersaturation of growth melt solution.The mechanism of β-BaB2O4 crystal morphology evolution was analyzed through the growth unit model.

  9. Surrogate Seeds For Growth Of Crystals

    Science.gov (United States)

    Shlichta, Paul J.

    1989-01-01

    Larger crystals of higher quality grown. Alternative method for starting growth of crystal involves use of seed crystal of different material instead of same material as solution. Intended for growing single-crystal proteins for experiments but applicable in general to growth of crystals from solutions and to growth of semiconductor or other crystals from melts.

  10. Analyzing dendritic growth in a population of immature neurons in the adult dentate gyrus using laminar quantification of disjointed dendrites

    Directory of Open Access Journals (Sweden)

    Shira eRosenzweig

    2011-03-01

    Full Text Available In the dentate gyrus of the hippocampus, new granule neurons are continuously produced throughout adult life. A prerequisite for the successful synaptic integration of these neurons is the sprouting and extension of dendrites into the molecular layer of the dentate gyrus. Thus, studies aimed at investigating the developmental stages of adult neurogenesis often use dendritic growth as an important indicator of neuronal health and maturity. Based on the known topography of the dentate gyrus, characterized by distinct laminar arrangement of granule neurons and their extensions, we have developed a new method for analysis of dendritic growth in immature adult-born granule neurons. The method is comprised of laminar quantification of cell bodies, primary, secondary and tertiary dendrites separately and independently from each other. In contrast to most existing methods, laminar quantification of dendrites does not require the use of exogenous markers and does not involve arbitrary selection of individual neurons. The new method relies on immonuhistochemical detection of endogenous markers such as doublecortin to perform a comprehensive analysis of a sub-population of immature neurons. Disjointed, orphan dendrites that often appear in the thin histological sections are taken into account. Using several experimental groups of rats and mice, we demonstrate here the suitable techniques for quantifying neurons and dendrites, and explain how the ratios between the quantified values can be used in a comparative analysis to indicate variations in dendritic growth and complexity.

  11. Characteristics of the Dendrite Growth in the Electrochemical Alane Production Process

    Directory of Open Access Journals (Sweden)

    Park Hyun-Kyu

    2016-01-01

    Full Text Available The electrochemical alane production process was proposed for a feasible production of alane. The operation of process was difficult because of short circuit by a dendrite growth in the reactor. Therefore, characteristics of the dendrite growth in the process were investigated. We conducted the electrochemical alane production process using Teflon block for inhibition of the dendrite growth. The obtained dendrite was characterized by XRD, SEM and ICP-AES. It was concluded that the dendrite growth was attributed to a melting and agglomeration of Al fine particles existed in the solution.

  12. Computer modeling of dendritic web growth processes and characterization of the material

    Science.gov (United States)

    Seidensticker, R. G.; Kothmann, R. E.; Mchugh, J. P.; Duncan, C. S.; Hopkins, R. H.; Blais, P. D.; Davis, J. R.; Rohatgi, A.

    1978-01-01

    High area throughput rate will be required for the economical production of silicon dendritic web for solar cells. Web width depends largely on the temperature distribution on the melt surface while growth speed is controlled by the dissipation of the latent heat of fusion. Thermal models were developed to investigate each of these aspects, and were used to engineer the design of laboratory equipment capable of producing crystals over 4 cm wide; growth speeds up to 10 cm/min were achieved. The web crystals were characterized by resistivity, lifetime and etch pit density data as well as by detailed solar cell I-V data. Solar cells ranged in efficiency from about 10 to 14.5% (AM-1) depending on growth conditions. Cells with lower efficiency displayed lowered bulk lifetime believed to be due to surface contamination.

  13. Computer modeling of dendritic web growth processes and characterization of the material

    Science.gov (United States)

    Seidensticker, R. G.; Kothmann, R. E.; Mchugh, J. P.; Duncan, C. S.; Hopkins, R. H.; Blais, P. D.; Davis, J. R.; Rohatgi, A.

    1978-01-01

    High area throughput rate will be required for the economical production of silicon dendritic web for solar cells. Web width depends largely on the temperature distribution on the melt surface while growth speed is controlled by the dissipation of the latent heat of fusion. Thermal models were developed to investigate each of these aspects, and were used to engineer the design of laboratory equipment capable of producing crystals over 4 cm wide; growth speeds up to 10 cm/min were achieved. The web crystals were characterized by resistivity, lifetime and etch pit density data as well as by detailed solar cell I-V data. Solar cells ranged in efficiency from about 10 to 14.5% (AM-1) depending on growth conditions. Cells with lower efficiency displayed lowered bulk lifetime believed to be due to surface contamination.

  14. Czochralski crystal growth: Modeling study

    Science.gov (United States)

    Dudukovic, M. P.; Ramachandran, P. A.; Srivastava, R. K.; Dorsey, D.

    1986-01-01

    The modeling study of Czochralski (Cz) crystal growth is reported. The approach was to relate in a quantitative manner, using models based on first priniciples, crystal quality to operating conditions and geometric variables. The finite element method is used for all calculations.

  15. Investigation of atom-attaching pro cess of three-dimensional b o dy-center-cubic dendritic growth by phase-field crystal mo del%BCC枝晶生长原子堆垛过程的晶体相场研究∗

    Institute of Scientific and Technical Information of China (English)

    郭灿; 王锦程; 王志军; 李俊杰; 郭耀麟; 唐赛

    2015-01-01

    通过在自由能泛函中引入各向异性参数得到了一个基于高斯内核的改进晶体相场模型,并采用该模型研究了体心立方结构(BCC)枝晶生长的原子堆垛过程。结果表明,在BCC由正十二面体平衡形貌演化为枝晶组织过程中,形核位置经历了由面心({110}面)到尖端(⟨100⟩取向)的转移,进而发生界面失稳形成枝晶组织;枝晶生长过程中,新的固相原子首先在枝晶尖端附近形核,并快速向尖端及根部生长,枝晶尖端被新原子完全包覆后将再次诱发液相原子附着形核及生长;随初始液相密度的增加,固-液界面移动速率增加,速率系数的各向异性也增强。%On the basis of the Gaussian kernel phase field crystal model (PFC), we propose a modified PFC model. The atom-attaching process of three-dimensional body-center-cubic (BCC) dendritic growth is examined by using the modified PFC model. Our simulations indicate that in the process of the morphology evolution from regular dodecahedron to dendrite shape, the nucleation position of new layer is transferred from the center of {110} planes into the region of{110}plane near the⟨100⟩tips, and then the BCC dendritic morphology is obtained. In the process of dendritic growth, first, new solid atom absorption takes place near dendrite tips, then liquid atoms start to grow up on the existing solid phase rapidly. After the dendrite tips are completely occupied by new atoms, new nuclei begin to form again. Increasing the initial atom density n will increase the velocity coefficient C and the anisotropy of C.

  16. Solidification in a Supercomputer: From Crystal Nuclei to Dendrite Assemblages

    Science.gov (United States)

    Shibuta, Yasushi; Ohno, Munekazu; Takaki, Tomohiro

    2015-08-01

    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.

  17. The Growth of KLN Crystals

    Institute of Scientific and Technical Information of China (English)

    1999-01-01

    The growth temperature curve of the growth system for the potass ium li thium niobate (KLN) has been measured and the temperature decrease program has b een calculated. KLN crystals with a size up to 30mm × 15mm × 5 mm have be en grown by flux method. The primary factors of the cracking of KLN crystal hav e been discussed. A blue laser light output has been obtained by optical parame tric oscillator pumping.

  18. Protein Crystal Growth in Microgravity

    Institute of Scientific and Technical Information of China (English)

    毕汝昌; 桂璐璐; 师珂; 王耀萍; 陈世芝; 韩青; 胡永林; 沈福苓; 牛秀田; 华子谦; 卢光莹; 张健; 李松林; 龚为民; 牛立文; 黄其辰

    1994-01-01

    Protein crystal growth is quite important for the determination of protein structureswhich are essential to the understanding of life at molecular level as well as to the development of molecu-lar biotechnology.The microgravity environment of space is an ideal place to study the complicated pro-tein crystallization and to grow good-quality protein crystals.A number of crystal-growth experiments of10 different proteins were carried out in August,1992 on the Chinese re-entry satellite FSW-2 in spaceusing a tube crystallization equipment made in China.A total of 25 samples from 6 proteins producedcrystals,and the effects of microgravity on protein crystal growth were observed,especially for an acidicphospholipase A2 and henegg-white lysozyme which gave better crystals in space than earth-grown crys-tals in ground control experiments.The results have shown that the microgravity in space favors the im-provement of the size,perfection,morphology and internal order of the grown protein crytals.

  19. Dendritic growth in the presence of convection. Ph.D. Thesis

    Science.gov (United States)

    Beaghton, Pantelis John

    1988-01-01

    The motion of the freezing front between a dendritic crystal and a supercooled liquid is studied using an interface evolution equation derived from a boundary integral transformation of the transient convective-diffusion equation. A new steady-state theory is introduced that incorporates the effects of convection in dendritic growth. It is shown that in the absence of capillary effects the shape of the crystal-melt interface is a paraboloid of revolution, similar to that found in situations where diffusion is the sole heat transfer mechanism. A relation between the supercooling, the product of the tip velocity and tip radius, and the strength of the flow is derived which reduces to the well-known Ivantsov theory in the absence of convection. A non-linear interface-tracking algorithm is developed and used to study the temporal and spatial evolution of the dendritic interface. The important role of capillarity and convection on the interface dynamics is established and the response of the interface to finite amplitude disturbances is examined for the first time. Tip splitting is identified as the dominant destabilization mechanism in the limit of zero surface tension. Finite surface tension leads to interface stabilization, irrespective of the magnitude and structure of the external perturbations. Finally, convection significantly decreases the magnitude of the freezing velocity.

  20. Rapid dendrite growth in quaternary Ni-based alloys

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The high undercooling and rapid solidification of Ni-10%Cu-10%Fe-10%Co quaternary alloy were achieved by electromagnetic levitation and glass fluxing techniques. The maximum undercooling of 276 K (0.16TL) was obtained in the experiments. All the solidified samples are determined to be α-Ni single-phase solid solutions by DSC thermal analysis and X-ray diffraction analysis. The microstructure of the α-Ni solid solution phase transfers from dendrite to equiaxed grain with an increase in undercooling, accompanied by the grain refinement effect. When the undercooling is very large, the solute trapping effect becomes quite significant and the microsegregation is suppressed. The experimental measurement of α-Ni dendrite growth velocity indicates that it increases with undercooling according to the relation, V=8×10-2×△T1.2.

  1. Crystal growth in salt efflorescence

    Science.gov (United States)

    Zehnder, Konrad; Arnold, Andreas

    1989-09-01

    Salt efflorescences strongly affect wall paintings and other monuments. The external factors governing the crystal habits and aggregate forms are studied phenomenologically in laboratory experiments. As salt contaminated materials dry, slats crystallize forming distinct sequences of crystal habits and aggregate forms on and underneath the surfaces. Four phases may be distinguished: (1) Large individual crystals with equilibrium forms grow immersed in a thick solution film; (2) granular crusts of small isometric crystals grow covered by a thin solution film; (3) fibrous crusts of columnar crystals grow from a coherent but thin solution film so that the crystals are in contact with solution only at their base; (4) whiskers grow from isolated spots of very thin solution films into the air. The main factor governing these morphologies is the humidity of the substrate. A porous material cracks while granular crystals (approaching their equilibrium forms) grow within the large pores. As the fissures widen, the habits pass into columnar crystals and then into whiskers. Because this succession corresponds to the crystallization sequence on the substrate surface it can be traced back to the same growth conditions.

  2. Dendrite Growth Kinetics in Undercooled Melts of Intermetallic Compounds

    Directory of Open Access Journals (Sweden)

    Dieter M. Herlach

    2015-09-01

    Full Text Available Solidification needs an undercooling to drive the solidification front. If large undercoolings are achieved, metastable solid materials are solidified from the undercooled melt. Containerless processing provides the conditions to achieve large undercoolings since heterogeneous nucleation on container walls is completely avoided. In the present contribution both electromagnetic and electrostatic levitation are applied. The velocity of rapidly advancing dendrites is measured as a function of undercooling by a High-Speed-Camera. The dendrite growth dynamics is investigated in undercooled melts of intermetallic compounds. The Al50Ni50 alloy is studied with respect to disorder trapping that leads to a disordered superlattice structure if the melt is undercooled beyond a critical undercooling. Disorder trapping is evidenced by in situ energy dispersive diffraction using synchrotron radiation of high intensity to record full diffraction pattern on levitated samples within a short time interval. Experiments on Ni2B using different processing techniques of varying the level of convection reveal convection-induced faceting of rapidly growing dendrites. Eventually, the growth velocity is measured in an undercooled melt of glass forming Cu50Zr50 alloy. A maximum in the growth velocity–undercooling relation is proved. This is understood by the fact that the temperature dependent diffusion coefficient counteracts the thermodynamic driving force for rapid growth if the temperature of the undercooled melt is approaching the temperature regime above the glass transition temperature. The analysis of this result allows for determining the activation energy of atomic attachment kinetics at the solid–liquid interface that is comparable to the activation energy of atomic diffusion as determined by independent measurements of the atomic diffusion in undercooled Cu50Zr50 alloy melt.

  3. Growth and Characterization of Agar Gel Grown Brushite Crystals

    Directory of Open Access Journals (Sweden)

    V. B. Suryawanshi

    2014-01-01

    Full Text Available Brushite [CaHPO4·2H2O] or calcium hydrogen phosphate dihydrate (CHPD also known as urinary crystal is a stable form of calcium phosphate. The brushite crystals were grown by single and double diffusion techniques in agar-agar gel at room temperature. Effects of different growth parameters were discussed in single diffusion and double diffusion techniques. Good quality star, needle, platy, rectangular, and prismatic shaped crystals in single diffusion and nuclei with dendritic growth were obtained in double diffusion. These grown nuclei were characterized by scanning electron microscopy (SEM, Fourier transform infrared (FTIR spectroscopy, X-ray diffraction (XRD, and thermogravimetric analysis (TGA. SEM has shown the different morphologies of crystals; FTIR has confirmed the presence of functional groups; crystalline nature was supported by XRD, whereas the TGA indicates total 24.68% loss in weight and formation of stable calcium pyrophosphate (Ca2P2O7 at 500°C.

  4. Suppressing The Growth Of Dendrites In Secondary Li Cells

    Science.gov (United States)

    Davies, Evan D.; Perrone, David E.; Shen, David H.

    1996-01-01

    Proposed technique for suppressing growth of lithium dendrites in rechargeable lithium electrochemical power cells involves periodic interruption of steady charging current with short, high-current discharge pulses. Technique applicable to lithium cells of several different types, including Li/TiS(2), Li/NbSe(3), Li/CoO(2), Li/MoS(2), Li/Vo(x), and Li/MnO(2). Cells candidates for use in spacecraft, military, communications, automotive, and other applications in which high-energy-density rechargeable batteries needed.

  5. Bimodal control of dendritic and axonal growth by the dual leucine zipper kinase pathway.

    Directory of Open Access Journals (Sweden)

    Xin Wang

    Full Text Available Knowledge of the molecular and genetic mechanisms underlying the separation of dendritic and axonal compartments is not only crucial for understanding the assembly of neural circuits, but also for developing strategies to correct defective dendrites or axons in diseases with subcellular precision. Previous studies have uncovered regulators dedicated to either dendritic or axonal growth. Here we investigate a novel regulatory mechanism that differentially directs dendritic and axonal growth within the same neuron in vivo. We find that the dual leucine zipper kinase (DLK signaling pathway in Drosophila, which consists of Highwire and Wallenda and controls axonal growth, regeneration, and degeneration, is also involved in dendritic growth in vivo. Highwire, an evolutionarily conserved E3 ubiquitin ligase, restrains axonal growth but acts as a positive regulator for dendritic growth in class IV dendritic arborization neurons in the larva. While both the axonal and dendritic functions of highwire require the DLK kinase Wallenda, these two functions diverge through two downstream transcription factors, Fos and Knot, which mediate the axonal and dendritic regulation, respectively. This study not only reveals a previously unknown function of the conserved DLK pathway in controlling dendrite development, but also provides a novel paradigm for understanding how neuronal compartmentalization and the diversity of neuronal morphology are achieved.

  6. Investigating the Effects of Anisotropic Mass Transport on Dendrite Growth in High Energy Density Lithium Batteries

    Energy Technology Data Exchange (ETDEWEB)

    Tan, Jinwang; Tartakovsky, Alexandre M.; Ferris, Kim F.; Ryan, Emily M.

    2016-01-01

    Dendrite formation on the electrode surface of high energy density lithium (Li) batteries causes safety problems and limits their applications. Suppressing dendrite growth could significantly improve Li battery performance. Dendrite growth and morphology is a function of the mixing in the electrolyte near the anode interface. Most research into dendrites in batteries focuses on dendrite formation in isotropic electrolytes (i.e., electrolytes with isotropic diffusion coefficient). In this work, an anisotropic diffusion reaction model is developed to study the anisotropic mixing effect on dendrite growth in Li batteries. The model uses a Lagrangian particle-based method to model dendrite growth in an anisotropic electrolyte solution. The model is verified by comparing the numerical simulation results with analytical solutions, and its accuracy is shown to be better than previous particle-based anisotropic diffusion models. Several parametric studies of dendrite growth in an anisotropic electrolyte are performed and the results demonstrate the effects of anisotropic transport on dendrite growth and morphology, and show the possible advantages of anisotropic electrolytes for dendrite suppression.

  7. Growth of Solid Solution Crystals

    Science.gov (United States)

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

    1985-01-01

    The major objective of this program is to determine the conditions under which single crystals of solid solutions can be grown from the melt in a Bridgman configuration with a high degree of chemical homogeneity. The central aim is to assess the role of gravity in the growth process and to explore the possible advantages for growth in the absence of gravity. The alloy system being investigated is the solid solution semiconductor with x-values appropriate for infrared detector applications in Hg sub (1-x) Cd sub x Te the 8 to 14 micro m wavelength region. Both melt and Te-solvent growth are being considered. The study consists of an extensive ground-based experimental and theoretical research effort followed by flight experimentation where appropriate. Experimental facilities have been established for the purification, casting, and crystal growth of the alloy system. Facilities have been also established for the metallurgical, compositional, electric and optical characterization of the alloys. Crystals are being grown by the Bridgman-Stockbarger method and are analyzed by various experimental techniques to evaluate the effects of growth conditions on the longitudinal and radial compositional variations and defect densities in the crystals.

  8. Crystallization Growth of Single Crystal Cu by ContinuousCasting

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Crystallization growth of single-crystal Cu by continuous casting has been investigated using selfdesigned horizontal continuous casting equipment and XRD. Experimental results showed that the crystallization plane of (311), (220) and (111) were eliminated sequentially in evolutionary process. The final growth plane of crystal was (200), the direction of crystallization was [100],the growth direction of both sides of the rod inclined to axis, and the degree of deviation of direction [100] from the crystal axis was less than 10. In order to produce high quality single crystal, the solid-liquid interface morphology must be smooth, even be planar.

  9. Dendritic grain growth simulation in weld pool of nickel base alloy

    Institute of Scientific and Technical Information of China (English)

    Zhan Xiaohong; Wei Yanhong; Ma Rui; Dong Zhibo

    2008-01-01

    Dendritic grain growth at the edge of the weld pool is simulated using a stochastic numerical model of cellular automaton algorithm. The grain growth model is established based upon the balance of solute in the solid/liquid interface of the dendrite tip. Considering the complicated nucleation condition and competitive growth, the dendrite morphologies of different nucleation condition are simulated. The simulated results reproduced the dendrite grain evolution process at the edge of the weld pool. It is indicated that the nucleation condition is an important factor influencing the grain morphologies especially the morphologies of secondary and tertiary arms.

  10. Rapid dendritic growth of Al-Ge hypoeutectic alloy in a drop tube

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    Dendritic growth in Al-45% Ge hypoeutectic alloy has been investigated during free fall in a 3 m drop tube. Calculations indicate that the undercooling obtained for the falling Al-45% Ge droplets ranges from 13 K to 201 K. The maximum undercooling attains 0.27TL. With the increase of undercooling, the primary (Al) phase undergoes a "columnar dendrite to equiaxed dendrite" structural transition. According to the current rapid dendritic growth theory, the growth of primary (Al) phase is always controlled by solute diffusion.

  11. Determination of crystal residence timescales in magma reservoirs by diffusion modeling of dendritic phosphorus zoning patterns in olivine

    Science.gov (United States)

    Chakraborty, S.; Potrafke, A.

    2016-12-01

    Deciphering the early stages of crystallization and the chronological evolution of phenocrysts in magma reservoirs is one of the main goals in volcanology. Established approaches that model the concentration evolution of fast diffusing elements like Fe/Mg carry limited information on timescales once the concentration gradients are homogenized. Elements that diffuse more slowly, such as P and Al, become useful in these cases. We present a novel modeling tool that combines high-resolution EMP mapping of slow diffusing phosphorus in olivine with 2D kinetic modeling of the diffusive relaxation of initial chemical zoning pattern of P as well as Fe/Mg. The modeling approach offers a new possibility for determining crystal residence times in magma reservoirs. P diffusion coefficients from the experimental determination of [1] and Fe/Mg diffusion coefficients from [2] were used. The method yields a time-bracket between the minimum time required to homogenize the zoning of fast-diffusing Fe/Mg and the maximum time period for which details of chemical zoning of slow-diffusing P may be retained. To illustrate the approach we have studied the compositional zoning patterns of 7 olivine crystals from Piton de la Fournaise volcano, La Réunion. All crystals show a narrow range of forsterite contents (=Fo82-84) with fully homogenized Fe/Mg distribution, whereas P-mapping reveals oscillatory to dendritic zoning patterns [3]. P concentrations scatter in the range of 0.4 wt-% to below detection limit. Revealed phosphorus zoning patterns were considered to display the initial crystal architecture, whereas Fe and Mg zoning has been wiped out due to faster diffusion. For La Réunion magmas at 1453 K, timescales between few days to weeks were determined to be the time brackets for growth and residence of the olivine crystals in the magmas. These short residence times combined with knowledge of very fast developing dendritic crystals that have recently been revealed worldwide [e.g. 3

  12. Microstructure and crystal growth direction of Al-Mg alloy

    Directory of Open Access Journals (Sweden)

    Ti-jun Chen

    2015-03-01

    Full Text Available The microstructures and crystal growth directions of permanent mould casting and directionally solidified Al-Mg alloys with different Mg contents have been investigated. The results indicate that the effect of Mg content on microstructure is basically same for the alloys prepared by these two methods. The primary grains change from cellular crystals to developed columnar dendrites, and then to equiaxed dendrites as the Mg content is increased. Simultaneously, both the cellular or columnar grain region and the primary trunk spacing decrease. All of these changes are mainly attributed to the constitutional supercooling resulting from Mg element. Comparatively, the cellular or columnar crystals of the directionally solidified alloys are straighter and more parallel than those of the permanent mould casting alloys. These have straight or wavy grain boundaries, one of the most important microstructure characteristics of feathery grains. However, the transverse microstructure and growth direction reveal that they do not belong to feathery grains. The Mg seemingly can affect the crystal growth direction, but does not result in the formation of feathery grains under the conditions employed in the study.

  13. A Century of Sapphire Crystal Growth

    Science.gov (United States)

    2004-05-17

    Crystal growth storage cabinet from Frémy’s lab.5,6 Flame Fusion and the Verneuil Process In 1885 rubies selling for $1000-2500...1891: Working with his student, M. Pacquier, Verneuil had developed most of what we now call Verneuil flame-fusion crystal growth . Verneuil ... Verneuil ) Crystal Growth Nassau, Gems Made by Man 11 • 1892: Verneuil eliminated crystal cracking by making contact area between ruby crystal

  14. Properties of mouse retinal ganglion cell dendritic growth during postnatal development

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The property of dendritic growth dynamics during development is a subject of intense interest.Here,we investigated the dendritic motility of retinal ganglion cells (RGCs) during different developmental stages,using ex vivo mouse retina explant culture,Semliki Forest Virus transfection and time-lapse observations.The results illustrated that during development,the dendritic motility underwent a change from rapid growth to a relatively stable state,i.e.,at P0 (day of birth),RGC dendrites were in a highly active state,whereas at postnatal 13 (P13) they were more stable,and at P3 and P8,the RGCs were in an intermediate state.At any given developmental stage,RGCs of different types displayed the same dendritic growth rate and extent.Since the mouse is the most popular mammalian model for genetic manipulation,this study provided a methodological foundation for further exploring the regulatory mechanisms of dendritic development.

  15. Phase-field-lattice Boltzmann studies for dendritic growth with natural convection

    Science.gov (United States)

    Takaki, Tomohiro; Rojas, Roberto; Sakane, Shinji; Ohno, Munekazu; Shibuta, Yasushi; Shimokawabe, Takashi; Aoki, Takayuki

    2017-09-01

    Simulating dendritic growth with natural convection is challenging because of the size of the computational domain required when compared to the dendrite scale. In this study, a phase-field-lattice Boltzmann model was used to simulate dendritic growth in the presence of natural convection due to a difference in solute concentration. To facilitate and accelerate the large-scale simulation, a parallel computing code with multiple graphics processing units was developed. The effects of the computational domain size as well as those of gravity on the dendritic morphologies were examined by performing two-dimensional free dendritic growth simulations with natural convection. The effects of the gravity direction on the dendrite spacing and morphology were also investigated by simulating unidirectional solidification from multiple seeds.

  16. Measurements of Dendritic Growth Velocities in Undercooled Melts of Pure Nickel Under Static Magnetic Fields

    Science.gov (United States)

    Gao, Jianrong; Zhang, Zongning; Zhang, Yingjie

    2012-01-01

    Dendritic growth velocities in undercooled melts of pure Ni have been intensively studied over the past fifty years. However, the literature data are at marked variance with the prediction of the widely accepted model for rapid dendritic growth both at small and at large undercoolings. In the present work, bulk melts of pure Ni samples of high purity were undercooled by glass fluxing treatment under a static magnetic field. The recalescence processes of the samples at different undercoolings were recorded using a high-speed camera, and were modeled using a software to determine the dendritic growth velocities. The present data confirmed the effect of melt flow on dendritic growth velocities at undercoolings below 100 K. A comparison of the present data with previous measurements on a lower purity material suggested an effect of impurities on dendritic growth velocities at undercoolings larger than 200 K as well.

  17. Electroless Growth of Aluminum Dendrites in NaCl-AlCl3 Melts

    DEFF Research Database (Denmark)

    Li, Qingfeng; Hjuler, H.A.; Berg, Rolf W.

    1989-01-01

    The spontaneous growth of aluminum dendrites after deposition was observed and examined in sodium chloride-aluminumchloride melts. The concentration gradient of AlCl3 in the vicinity of the cathode surface resulting from electrolysisconstitutes a type of concentration cell with aluminum dendrites...... as electrodes. The short-circuit discharge of thecell is found to be the driving force for the growth of aluminum dendrites. Such a concentration gradient is proposed to beone of the causes for dendrite formation in the case of metal deposition....

  18. GPU phase-field lattice Boltzmann simulations of growth and motion of a binary alloy dendrite

    Science.gov (United States)

    Takaki, T.; Rojas, R.; Ohno, M.; Shimokawabe, T.; Aoki, T.

    2015-06-01

    A GPU code has been developed for a phase-field lattice Boltzmann (PFLB) method, which can simulate the dendritic growth with motion of solids in a dilute binary alloy melt. The GPU accelerated PFLB method has been implemented using CUDA C. The equiaxed dendritic growth in a shear flow and settling condition have been simulated by the developed GPU code. It has been confirmed that the PFLB simulations were efficiently accelerated by introducing the GPU computation. The characteristic dendrite morphologies which depend on the melt flow and the motion of the dendrite could also be confirmed by the simulations.

  19. Zeolite crystal growth in space

    Science.gov (United States)

    Sacco, Albert, Jr.; Thompson, Robert W.; Dixon, Anthony G.

    1991-01-01

    The growth of large, uniform zeolite crystals in high yield in space can have a major impact on the chemical process industry. Large zeolite crystals will be used to improve basic understanding of adsorption and catalytic mechanisms, and to make zeolite membranes. To grow large zeolites in microgravity, it is necessary to control the nucleation event and fluid motion, and to enhance nutrient transfer. Data is presented that suggests nucleation can be controlled using chemical compounds (e.g., Triethanolamine, for zeolite A), while not adversely effecting growth rate. A three-zone furnace has been designed to perform multiple syntheses concurrently. The operating range of the furnace is 295 K to 473 K. Teflon-lined autoclaves (10 ml liquid volume) have been designed to minimize contamination, reduce wall nucleation, and control mixing of pre-gel solutions on orbit. Zeolite synthesis experiments will be performed on USML-1 in 1992.

  20. Reactive oxygen species are involved in BMP-induced dendritic growth in cultured rat sympathetic neurons.

    Science.gov (United States)

    Chandrasekaran, Vidya; Lea, Charlotte; Sosa, Jose Carlo; Higgins, Dennis; Lein, Pamela J

    2015-07-01

    Previous studies have shown that bone morphogenetic proteins (BMPs) promote dendritic growth in sympathetic neurons; however, the downstream signaling molecules that mediate the dendrite promoting activity of BMPs are not well characterized. Here we test the hypothesis that reactive oxygen species (ROS)-mediated signaling links BMP receptor activation to dendritic growth. In cultured rat sympathetic neurons, exposure to any of the three mechanistically distinct antioxidants, diphenylene iodinium (DPI), nordihydroguaiaretic acid (NGA) or desferroxamine (DFO), blocked de novo BMP-induced dendritic growth. Addition of DPI to cultures previously induced with BMP to extend dendrites caused dendritic retraction while DFO and NGA prevented further growth of dendrites. The inhibition of the dendrite promoting activity of BMPs by antioxidants was concentration-dependent and occurred without altering axonal growth or neuronal cell survival. Antioxidant treatment did not block BMP activation of SMAD 1,5 as determined by nuclear localization of these SMADs. While BMP treatment did not cause a detectable increase in intracellular ROS in cultured sympathetic neurons as assessed using fluorescent indicator dyes, BMP treatment increased the oxygen consumption rate in cultured sympathetic neurons as determined using the Seahorse XF24 Analyzer, suggesting increased mitochondrial activity. In addition, BMPs upregulated expression of NADPH oxidase 2 (NOX2) and either pharmacological inhibition or siRNA knockdown of NOX2 significantly decreased BMP-7 induced dendritic growth. Collectively, these data support the hypothesis that ROS are involved in the downstream signaling events that mediate BMP7-induced dendritic growth in sympathetic neurons, and suggest that ROS-mediated signaling positively modulates dendritic complexity in peripheral neurons.

  1. Growth and study of barium oxalate single crystals in agar gel

    Indian Academy of Sciences (India)

    P V Dalal; K B Saraf

    2006-10-01

    Barium oxalate was grown in agar gel at ambient temperature. The effect of various parameters like gel concentration, gel setting time and concentration of the reactants on the growth of these crystals was studied. Prismatic platy shaped spherulites and dendrites were obtained. The grown crystals were characterized by X-ray powder diffractometry, infrared spectroscopy, thermogravimetric and differential thermal analysis. An attempt is made to explain the spherulitic growth mechanism.

  2. Formation and growth mechanism of TiC crystal in TiCp/Ti composites

    Institute of Scientific and Technical Information of China (English)

    金云学; 王宏伟; 曾松岩; 张二林

    2002-01-01

    Ti-C and Ti-Al-C alloys were prepared using gravity and directional solidification processes. Morphologies of TiC crystal were investigated by using SEM, XRD and EDX. Also, the formation and growth mechanism of TiC crystal have been analyzed on the basis of coordination polyhedron growth unit theory. During solidification of titanium alloys, the coordination polyhedron growth unit is TiC6. TiC6 growth units stack in a linking mode of edge to edge and form octahedral TiC crystal with {111} planes as present faces. Although the growing geometry of TiC crystal is decided by its lattice structure, the final morphology of TiC crystal depends on the effects of its growth environment. In solute concentration distribution, the super-saturation of C or TiC6 at the corners of octahedral TiC crystal is much higher than that of edges and faces of octahedral TiC crystal. At these corners the driving force for crystal growth is greater and the interface is instable which contribute to quick stacking rate of growth units at these corners and result in secondary dendrite arms along TiC crystallographic 〈100〉 directions. TiC crystal finally grows to be dendrites.

  3. Mapping single-crystal dendritic microstructure and defects in nickel-base superalloys with synchrotron radiation

    Energy Technology Data Exchange (ETDEWEB)

    Husseini, Naji S. [Applied Physics Program, University of Michigan, Ann Arbor, MI 48109 (United States)], E-mail: najihuss@umich.edu; Kumah, Divine P. [Applied Physics Program, University of Michigan, Ann Arbor, MI 48109 (United States); Yi, Jian Z.; Torbet, Christopher J. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109 (United States); Arms, Dohn A.; Dufresne, Eric M. [Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439 (United States); Pollock, Tresa M.; Wayne Jones, J. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109 (United States); Clarke, Roy [Applied Physics Program, University of Michigan, Ann Arbor, MI 48109 (United States)

    2008-10-15

    Solidification of single-crystal nickel-base superalloys introduces large-scale segregation of constituent elements and defects such as dislocations and mosaicity. By exploiting the energy tunability and interference capabilities of high-brilliance X-ray radiation, key structural features of the dendritic single crystals were mapped over large areas. Interference and diffraction of synchrotron X-rays revealed significant misorientations between individual dendrites in the as-solidified state. For the first time this mosaic structure was quantified for an array of dendrites and correlated with the density of 'grown-in' dislocations whose density ranged from 10{sup 7} to 10{sup 8} cm{sup -2}. Absorption contrast permitted simultaneous mapping of the distribution of refractory metal additives (e.g. rhenium and tungsten), which segregated preferentially to the dendrite cores with a linear composition gradient toward the interdendritic regions. The results demonstrate that synchrotron X-ray imaging is promising for in situ studies of single-crystal structure and defects in nickel-base superalloys.

  4. Numerical Simulation on Dendrite Growth During Solidification of Al-4%Cu Alloy

    Directory of Open Access Journals (Sweden)

    ZHANG Min

    2016-06-01

    Full Text Available A new two-dimensional cellular automata and finite difference (CA-FD model of dendritic growth was improved, which a perturbation function was introduced to control the growth of secondary and tertiary dendrite, the concentration of the solute was clearly defined as the liquid solute concentration and the solid-phase solute concentration in dendrite growth processes, and the eight moore calculations method was used to reduce the anisotropy caused by the shape of the grid in the process of redistribution and diffusion of solute. Single and multi equiaxed dendrites along different preferential direction, single and multi directions of columnar dendrites of Al-4% Cu alloy were simulated, as well as the distribution of liquid solute concentration and solid solute concentration. The simulation results show that the introduced perturbation function can promote the dendrite branching, liquid/solid phase solute calculation model is able to simulate the solute distribution of liquid/solid phase accurately in the process of dendritic growth, and the improved model can realize competitive growth of dendrite in any direction.

  5. Crystal growth of various ruthenates

    Energy Technology Data Exchange (ETDEWEB)

    Kunkemoeller, Stefan; Braden, Markus [II. Physikalisches Institut, Universitaet zu Koeln (Germany); Nugroho, Agung [Institut Teknologi Bandung (Indonesia)

    2013-07-01

    Ruthenates of the Ruddlesdon-Popper series exhibit a variety of interesting phenomena ranging from unconventional superconductivity to orbitally polarized Mott insulators. Unfortunately the crystal growth of most of these ruthenates is extremely difficult partially due to the high evaporation of ruthenium; this strongly limits the research on these fascinating materials. We have started to grow single crystals of layered and perovskite ruthenates by the travelling floating-zone method using a Canon SC1-MDH mirror furnace. For the layered Ca{sub 2-x}Sr{sub x}RuO{sub 4} series we focused first on the range of concentration where recent My-SR experiments reveal spin-density wave ordering to occur at relatively high temperature and with a sizeable ordered moment. Good quality crystals of Ca{sub 1.5}Sr{sub 0.5}RuO{sub 4} can be obtained, when an excess of 15 percent of ruthenium is added to the initial preparation of the rod and when a high growth speed up to 40mm/h is used. Even slight modifications of the growing conditions result in large amounts of (Sr/Ca)RuO{sub 3} and (Sr/Ca){sub 3}Ru{sub 2}O{sub 7} intergrowth phases. First attempts to grow perovskite and double-layered ruthenates are discussed as well.

  6. Transcriptional responses of cultured rat sympathetic neurons during BMP-7-induced dendritic growth.

    Directory of Open Access Journals (Sweden)

    Michelle M Garred

    Full Text Available BACKGROUND: Dendrites are the primary site of synapse formation in the vertebrate nervous system; however, relatively little is known about the molecular mechanisms that regulate the initial formation of primary dendrites. Embryonic rat sympathetic neurons cultured under defined conditions extend a single functional axon, but fail to form dendrites. Addition of bone morphogenetic proteins (BMPs triggers these neurons to extend multiple dendrites without altering axonal growth or cell survival. We used this culture system to examine differential gene expression patterns in naïve vs. BMP-treated sympathetic neurons in order to identify candidate genes involved in regulation of primary dendritogenesis. METHODOLOGY/PRINCIPAL FINDINGS: To determine the critical transcriptional window during BMP-induced dendritic growth, morphometric analysis of microtubule-associated protein (MAP-2-immunopositive processes was used to quantify dendritic growth in cultures exposed to the transcription inhibitor actinomycin-D added at varying times after addition of BMP-7. BMP-7-induced dendritic growth was blocked when transcription was inhibited within the first 24 hr after adding exogenous BMP-7. Thus, total RNA was isolated from sympathetic neurons exposed to three different experimental conditions: (1 no BMP-7 treatment; (2 treatment with BMP-7 for 6 hr; and (3 treatment with BMP-7 for 24 hr. Affymetrix oligonucleotide microarrays were used to identify differential gene expression under these three culture conditions. BMP-7 significantly regulated 56 unique genes at 6 hr and 185 unique genes at 24 hr. Bioinformatic analyses implicate both established and novel genes and signaling pathways in primary dendritogenesis. CONCLUSIONS/SIGNIFICANCE: This study provides a unique dataset that will be useful in generating testable hypotheses regarding transcriptional control of the initial stages of dendritic growth. Since BMPs selectively promote dendritic growth in

  7. Phase-field simulation of dendritic growth for binary alloys with complicate solution models

    Institute of Scientific and Technical Information of China (English)

    LI Xin-zhong; GUO Jing-jie; SU Yan-qing; WU Shi-ping; FU Heng-zhi

    2005-01-01

    A phase-field method for simulation of dendritic growth in binary alloys with complicate solution models was studied. The free energy densities of solid and liquid used to construct the free energy of a solidification system in the phase-field model were derived from the Calphad thermodynamic modeling of phase diagram. The dendritic growth of Ti-Al alloy with a quasi-sub regular solution model was simulated in both an isothermal and a nonisothermal regime. In the isothermal one, different initial solute compositions and melt temperatures were chosen.And in the non-isothermal one, release of latent heat during solidification was considered. Realistic growth patterns of dendrite are derived. Both the initial compositions and melt temperatures affect isothermal dendritic morphology and solute distributions much, especially the latter. Release of latent heat will cause a less developed structure of dendrite and a lower interfacial composition.

  8. Introduction to crystal growth and characterization

    CERN Document Server

    Benz, Klaus-Werner

    2014-01-01

    This new textbook provides for the first time a comprehensive treatment of the basics of contemporary crystallography and crystal growth in a single volume. The reader will be familiarized with the concepts for the description of morphological and structural symmetry of crystals. The architecture of crystal structures of selected inorganic and molecular crystals is illustrated. The main crystallographic databases as data sources of crystal structures are described. Nucleation processes, their kinetics and main growth mechanism will be introduced in fundamentals of crystal growth. Some phase d

  9. Pressure-Reduction Technique for Crystal Growth

    Science.gov (United States)

    Shlichta, P. J.

    1981-01-01

    Large crystals grown by varying pressure rather than temperature. In constant temerature pressure-reduction process crystal growth promoted as solubility decreases by factor of more than 10. Technique used to study crystal growth kinetics by "pressure wave"" analog of conventional "thermal wave" experiments. Technique has advantages of faster response and freedom from convective interference.

  10. Dendritic web silicon for solar cell application

    Science.gov (United States)

    Seidensticker, R. G.

    1977-01-01

    The dendritic web process for growing long thin ribbon crystals of silicon and other semiconductors is described. Growth is initiated from a thin wirelike dendrite seed which is brought into contact with the melt surface. Initially, the seed grows laterally to form a button at the melt surface; when the seed is withdrawn, needlelike dendrites propagate from each end of the button into the melt, and the web portion of the crystal is formed by the solidification of the liquid film supported by the button and the bounding dendrites. Apparatus used for dendritic web growth, material characteristics, and the two distinctly different mechanisms involved in the growth of a single crystal are examined. The performance of solar cells fabricated from dendritic web material is indistinguishable from the performance of cells fabricated from Czochralski grown material.

  11. Glycan Sulfation Modulates Dendritic Cell Biology and Tumor Growth

    Directory of Open Access Journals (Sweden)

    Roland El Ghazal

    2016-05-01

    Full Text Available In cancer, proteoglycans have been found to play roles in facilitating the actions of growth factors, and effecting matrix invasion and remodeling. However, little is known regarding the genetic and functional importance of glycan chains displayed by proteoglycans on dendritic cells (DCs in cancer immunity. In lung carcinoma, among other solid tumors, tumor-associated DCs play largely subversive/suppressive roles, promoting tumor growth and progression. Herein, we show that targeting of DC glycan sulfation through mutation in the heparan sulfate biosynthetic enzyme N-deacetylase/N-sulfotransferase-1 (Ndst1 in mice increased DC maturation and inhibited trafficking of DCs to draining lymph nodes. Lymphatic-driven DC migration and chemokine (CCL21-dependent activation of a major signaling pathway required for DC migration (as measured by phospho-Akt were sensitive to Ndst1 mutation in DCs. Lewis lung carcinoma tumors in mice deficient in Ndst1 were reduced in size. Purified CD11c+ cells from the tumors, which contain the tumor-infiltrating DC population, showed a similar phenotype in mutant cells. These features were replicated in mice deficient in syndecan-4, the major heparan sulfate proteoglycan expressed on the DC surface: Tumors were growth-impaired in syndecan-4–deficient mice and were characterized by increased infiltration by mature DCs. Tumors on the mutant background also showed greater infiltration by NK cells and NKT cells. These findings indicate the genetic importance of DC heparan sulfate proteoglycans in tumor growth and may guide therapeutic development of novel strategies to target syndecan-4 and heparan sulfate in cancer.

  12. Glycan Sulfation Modulates Dendritic Cell Biology and Tumor Growth.

    Science.gov (United States)

    El Ghazal, Roland; Yin, Xin; Johns, Scott C; Swanson, Lee; Macal, Monica; Ghosh, Pradipta; Zuniga, Elina I; Fuster, Mark M

    2016-05-01

    In cancer, proteoglycans have been found to play roles in facilitating the actions of growth factors, and effecting matrix invasion and remodeling. However, little is known regarding the genetic and functional importance of glycan chains displayed by proteoglycans on dendritic cells (DCs) in cancer immunity. In lung carcinoma, among other solid tumors, tumor-associated DCs play largely subversive/suppressive roles, promoting tumor growth and progression. Herein, we show that targeting of DC glycan sulfation through mutation in the heparan sulfate biosynthetic enzyme N-deacetylase/N-sulfotransferase-1 (Ndst1) in mice increased DC maturation and inhibited trafficking of DCs to draining lymph nodes. Lymphatic-driven DC migration and chemokine (CCL21)-dependent activation of a major signaling pathway required for DC migration (as measured by phospho-Akt) were sensitive to Ndst1 mutation in DCs. Lewis lung carcinoma tumors in mice deficient in Ndst1 were reduced in size. Purified CD11c+ cells from the tumors, which contain the tumor-infiltrating DC population, showed a similar phenotype in mutant cells. These features were replicated in mice deficient in syndecan-4, the major heparan sulfate proteoglycan expressed on the DC surface: Tumors were growth-impaired in syndecan-4-deficient mice and were characterized by increased infiltration by mature DCs. Tumors on the mutant background also showed greater infiltration by NK cells and NKT cells. These findings indicate the genetic importance of DC heparan sulfate proteoglycans in tumor growth and may guide therapeutic development of novel strategies to target syndecan-4 and heparan sulfate in cancer.

  13. A three-dimensional cellular automaton model for simulation of dendritic growth of magnesium alloy

    Institute of Scientific and Technical Information of China (English)

    Mengwu WU; Shoumei XIONG

    2012-01-01

    A numerical model based on the cellular automaton method for the three-dimensional simulation of dendritic growth of magnesium alloy was developed.The growth kinetics was calculated from the complete solution of the transport equations.By constructing a three-dimensional anisotropy model with the cubic CA cells,simulation of dendritic growth of magnesium alloy with six-fold symmetry in the basal plane was achieved.The model was applied to simulate the equiaxed dendritic growth and columnar dendritic growth under directional solidification,and its capability was addressed by comparing the simulated results to experimental results and those in the previously published works.Meanwhile,the three-dimensional simulated results were also compared with that of in two dimensions,offering a deep insight into the microstructure formation of magnesium alloy during solidification.

  14. Type I TARPs promote dendritic growth of early postnatal neocortical pyramidal cells in organotypic cultures.

    Science.gov (United States)

    Hamad, Mohammad I K; Jack, Alexander; Klatt, Oliver; Lorkowski, Markus; Strasdeit, Tobias; Kott, Sabine; Sager, Charlotte; Hollmann, Michael; Wahle, Petra

    2014-04-01

    The ionotropic α-amino-3-hydroxy-5-methyl-4-isoxazole propionate glutamate receptors (AMPARs) have been implicated in the establishment of dendritic architecture. The transmembrane AMPA receptor regulatory proteins (TARPs) regulate AMPAR function and trafficking into synaptic membranes. In the current study, we employ type I and type II TARPs to modulate expression levels and function of endogenous AMPARs and investigate in organotypic cultures (OTCs) of rat occipital cortex whether this influences neuronal differentiation. Our results show that in early development [5-10 days in vitro (DIV)] only the type I TARP γ-8 promotes pyramidal cell dendritic growth by increasing spontaneous calcium amplitude and GluA2/3 expression in soma and dendrites. Later in development (10-15 DIV), the type I TARPs γ-2, γ-3 and γ-8 promote dendritic growth, whereas γ-4 reduced dendritic growth. The type II TARPs failed to alter dendritic morphology. The TARP-induced dendritic growth was restricted to the apical dendrites of pyramidal cells and it did not affect interneurons. Moreover, we studied the effects of short hairpin RNA-induced knockdown of endogenous γ-8 and showed a reduction of dendritic complexity and amplitudes of spontaneous calcium transients. In addition, the cytoplasmic tail (CT) of γ-8 was required for dendritic growth. Single-cell calcium imaging showed that the γ-8 CT domain increases amplitude but not frequency of calcium transients, suggesting a regulatory mechanism involving the γ-8 CT domain in the postsynaptic compartment. Indeed, the effect of γ-8 overexpression was reversed by APV, indicating a contribution of NMDA receptors. Our results suggest that selected type I TARPs influence activity-dependent dendritogenesis of immature pyramidal neurons.

  15. Controlled growth of semiconductor crystals

    Science.gov (United States)

    Bourret-Courchesne, Edith D.

    1992-01-01

    A method for growth of III-V, II-VI and related semiconductor single crystals that suppresses random nucleation and sticking of the semiconductor melt at the crucible walls. Small pieces of an oxide of boron B.sub.x O.sub.y are dispersed throughout the comminuted solid semiconductor charge in the crucible, with the oxide of boron preferably having water content of at least 600 ppm. The crucible temperature is first raised to a temperature greater than the melt temperature T.sub.m1 of the oxide of boron (T.sub.m1 =723.degree. K. for boron oxide B.sub.2 O.sub.3), and the oxide of boron is allowed to melt and form a reasonably uniform liquid layer between the crucible walls and bottom surfaces and the still-solid semiconductor charge. The temperature is then raised to approximately the melt temperature T.sub.m2 of the semiconductor charge material, and crystal growth proceeds by a liquid encapsulated, vertical gradient freeze process. About half of the crystals grown have a dislocation density of less than 1000/cm.sup.2. If the oxide of boron has water content less than 600 ppm, the crucible material should include boron nitride, a layer of the inner surface of the crucible should be oxidized before the oxide of boron in the crucible charge is melted, and the sum of thicknesses of the solid boron oxide layer and liquid boron oxide layer should be at least 50 .mu.m.

  16. Coordination polyhedron growth mechanism model and growth habit of crystals

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A new growth mechanism model, coordination polyhedron growth mechanism model, is introduced from the angle of the coordination of anion and cation to each other at the interface. It is pointed out that the force driving the growth unit to enter the crystal lattice is the electrostatic attraction force between ions, whose relative size can be approximately measured by the electrostatic bond strength (EBS) that reaches a nearest neighbor anion (or cation) in the parent phase from a cation (or anion) at the interface. The growth habits of NaCl, ZnS, CaF2 and CsI crystals are discussed, and a new growth habit rule is proposed as follows. When the growth rate of a crystal is determined by the step generation rate, the growth habit of this crystal is related to the coordination number of the ion with the smallest coordination rate at the interface of various crystal faces. The smaller the coordination number of the ion at the interface, the faster the growth rate of corresponding crystal face. When the growth of a crystal depends on the step movement rate, the growth habit of this crystal is related to the density of the ion with the smallest coordination rate at the interface of various crystal faces. The smaller the densities of the ion at the interface is, the faster the growth rate of corresponding crystal face will be.

  17. Involvement of α2-antiplasmin in dendritic growth of hippocampal neurons.

    Science.gov (United States)

    Kawashita, Eri; Kanno, Yosuke; Asayama, Haruka; Okada, Kiyotaka; Ueshima, Shigeru; Matsuo, Osamu; Matsuno, Hiroyuki

    2013-07-01

    The α2-Antiplasmin (α2AP) protein is known as a principal physiological inhibitor of plasmin, but we previously demonstrated that it acts as a regulatory factor for cellular functions independent of plasmin. α2AP is highly expressed in the hippocampus, suggesting a potential role for α2AP in hippocampal neuronal functions. However, the role for α2AP was unclear. This study is the first to investigate the involvement of α2AP in the dendritic growth of hippocampal neurons. The expression of microtubule-associated protein 2, which contributes to neurite initiation and neuronal growth, was lower in the neurons from α2AP⁻/⁻ mice than in the neurons from α2AP⁺/⁺ mice. Exogenous treatment with α2AP enhanced the microtubule-associated protein 2 expression, dendritic growth and filopodia formation in the neurons. This study also elucidated the mechanism underlying the α2AP-induced dendritic growth. Aprotinin, another plasmin inhibitor, had little effect on the dendritic growth of neurons, and α2AP induced its expression in the neurons from plaminogen⁻/⁻ mice. The activation of p38 MAPK was involved in the α2AP-induced dendritic growth. Therefore, our findings suggest that α2AP induces dendritic growth in hippocampal neurons through p38 MAPK activation, independent of plasmin, providing new insights into the role of α2AP in the CNS.

  18. Measurements of Protein Crystal Face Growth Rates

    Science.gov (United States)

    Gorti, S.

    2014-01-01

    Protein crystal growth rates will be determined for several hyperthermophile proteins.; The growth rates will be assessed using available theoretical models, including kinetic roughening.; If/when kinetic roughening supersaturations are established, determinations of protein crystal quality over a range of supersaturations will also be assessed.; The results of our ground based effort may well address the existence of a correlation between fundamental growth mechanisms and protein crystal quality.

  19. Polar Growth Habit of KABO Crystal

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The polar growth habit of KABO crystal was discussed by the growth-units model of anionic coordination-polyhedra (ACP), and the relationship between stabilities of incorporation of those growth-units into various group faces and their corresponding morphologies was studied. It is put forward that the growth interface of crystal will be concave when negative plane is used as growth interface. Concave growth interface is very unfavorable for the quality of the crystal, because it is unsuitable for the transfer of the latent heat and impurities released during the deposition.

  20. Recrystallization phenomena of solution grown paraffin dendrites

    NARCIS (Netherlands)

    Hollander, F.F.A.; Stasse, O.; Suchtelen, van J.; Enckevort, van W.J.P.

    2001-01-01

    Paraffin crystals were grown from decane solutions using a micro-Bridgman set up for in-situ observation of the morphology at the growth front. It is shown that for large imposed velocities, dendrites are obtained. After dendritic growth, aging or recrystallization processes set in rather quickly, c

  1. Anomalous α-Mg Dendrite Growth During Directional Solidification of a Mg-Zn Alloy

    Science.gov (United States)

    Shuai, Sansan; Guo, Enyu; Wang, Mingyue; Callaghan, Mark D.; Jing, Tao; Zheng, Qiwei; Lee, Peter D.

    2016-09-01

    Dendritic morphology was investigated in a directionally solidified magnesium-zinc alloy using synchrotron X-ray tomography and electron backscattered diffraction. Unexpectedly, primary dendrites grew along {directions. Further, seven asymmetric sets of side branches formed, instead of six-fold symmetric arms, evolving with three coexisting morphologies per trunk of: traditional, seaweed structure, and free growth. The anomalous growth is attributed to the imposed thermal gradient and zinc-induced interfacial energy anisotropy variations.

  2. Rapid Growth of Ice Dendrite in Acoustically Levitated and Highly Undercooled Water

    Institute of Scientific and Technical Information of China (English)

    吕勇军; 解文军; 魏炳波

    2002-01-01

    Water drops with diameters ranging from 2.5 to 4 mm are highly undercooled by up to 24 K with the acousticlevitation technique. Compared to the case of water contained in a tube, acoustic levitation has efficientlyavoided the heterogeneous nucleation from container walls and consequently increased the undercooling level.However, the cavitation effect induced by ultrasound may prematurely catalyse nucleation, which hinders thefurther achievement of bulk undercooling. The growth velocity of ice dendrite determined experimentally inhighly undercooled water is characteristic of rapid dendritic growth, which reaches 0.17m/s at the undercoolingof 24 K. The Lipton-Kurz-Trivedi dendritic growth model is used to predict the kinetic characteristics of rapidgrowth of ice dendrite under high undercooling conditions, which shows good agreement with the experimentalresults.

  3. Bone morphogenetic protein-5 (BMP-5 promotes dendritic growth in cultured sympathetic neurons

    Directory of Open Access Journals (Sweden)

    Higgins Dennis

    2001-09-01

    Full Text Available Abstract Background BMP-5 is expressed in the nervous system throughout development and into adulthood. However its effects on neural tissues are not well defined. BMP-5 is a member of the 60A subgroup of BMPs, other members of which have been shown to stimulate dendritic growth in central and peripheral neurons. We therefore examined the possibility that BMP-5 similarly enhances dendritic growth in cultured sympathetic neurons. Results Sympathetic neurons cultured in the absence of serum or glial cells do not form dendrites; however, addition of BMP-5 causes these neurons to extend multiple dendritic processes, which is preceded by an increase in phosphorylation of the Smad-1 transcription factor. The dendrite-promoting activity of BMP-5 is significantly inhibited by the BMP antagonists noggin and follistatin and by a BMPR-IA-Fc chimeric protein. RT-PCR and immunocytochemical analyses indicate that BMP-5 mRNA and protein are expressed in the superior cervical ganglia (SCG during times of initial growth and rapid expansion of the dendritic arbor. Conclusions These data suggest a role for BMP-5 in regulating dendritic growth in sympathetic neurons. The signaling pathway that mediates the dendrite-promoting activity of BMP-5 may involve binding to BMPR-IA and activation of Smad-1, and relative levels of BMP antagonists such as noggin and follistatin may modulate BMP-5 signaling. Since BMP-5 is expressed at relatively high levels not only in the developing but also the adult nervous system, these findings suggest the possibility that BMP-5 regulates dendritic morphology not only in the developing, but also the adult nervous system.

  4. Economic analysis of crystal growth in space

    Science.gov (United States)

    Ulrich, D. R.; Chung, A. M.; Yan, C. S.; Mccreight, L. R.

    1972-01-01

    Many advanced electronic technologies and devices for the 1980's are based on sophisticated compound single crystals, i.e. ceramic oxides and compound semiconductors. Space processing of these electronic crystals with maximum perfection, purity, and size is suggested. No ecomonic or technical justification was found for the growth of silicon single crystals for solid state electronic devices in space.

  5. Effect of strontium on columnar growth of dendritic α phase in near-eutectic Al-11.6%Si alloys

    Institute of Scientific and Technical Information of China (English)

    廖恒成; 丁毅; 孙国雄

    2004-01-01

    For Al-11.6 % Si alloy, the influence of the addition of Sr on the morphology of the dendrite α phase was investigated, and the characteristic parameters of the dendrite α phase, the primary dendrite spacing and the secondary dendrite arm spacing, were also measured. The addition of strontium promotes the columnar dendrite growth and leads to a decrease of both the primary dendrite spacing and secondary dendrite arm spacing with the increase of the content of strontium in the modified near-eutectic Al-Si alloys. It is thought that the addition of Sr leads to a reduction of the solid-liquid interfacial energy of the dendrite α phase, consequently resulting in a decrease of the growth undercooling of dendrite tips. And hence, the nucleation of the equiaxed grains in the liquid in front of the columnar dendrite tips is restrained, thus the addition of strontium in Al-Si alloys promotes the growth of the columnar dendrites. The reduction of the solid-liquid interfacial energy also leads to the decreases in the primary dendrite spacing and the secondary dendrite arm spacing.

  6. Crystal Shape Evolution in Detached Bridgman Growth

    Science.gov (United States)

    Volz, M. P.; Mazuruk, K.

    2013-01-01

    Detached (or dewetted) Bridgman crystal growth defines that process in which a gap exists between a growing crystal and the crucible wall. Existence of the gap provides several advantages, including no sticking of the crystal to the crucible wall, reduced thermal and mechanical stresses, reduced dislocations, and no heterogeneous nucleation by the crucible. Numerical calculations are used to determine the conditions in which a gap can exist. According to crystal shape stability theory, only some of these gap widths will be dynamically stable. Beginning with a crystal diameter that differs from stable conditions, the transient crystal growth process is analyzed. In microgravity, dynamic stability depends only on capillary effects and is decoupled from heat transfer. Depending on the initial conditions and growth parameters, the crystal shape will evolve towards the crucible wall, towards a stable gap width, or towards the center of the crucible, collapsing the meniscus. The effect of a tapered crucible on dynamic stability is also described.

  7. Crystal growth as an excitable medium.

    Science.gov (United States)

    Cartwright, Julyan H E; Checa, Antonio G; Escribano, Bruno; Sainz-Díaz, C Ignacio

    2012-06-28

    Crystal growth has been widely studied for many years, and, since the pioneering work of Burton, Cabrera and Frank, spirals and target patterns on the crystal surface have been understood as forms of tangential crystal growth mediated by defects and by two-dimensional nucleation. Similar spirals and target patterns are ubiquitous in physical systems describable as excitable media. Here, we demonstrate that this is not merely a superficial resemblance, that the physics of crystal growth can be set within the framework of an excitable medium, and that appreciating this correspondence may prove useful to both fields. Apart from solid crystals, we discuss how our model applies to the biomaterial nacre, formed by layer growth of a biological liquid crystal.

  8. Simulation of fluctuation effect on dendrite growth by phase field method

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The dendrite growth process was simulated with the phase field model coupling with the fluctuation.The effect of fluctuation intensity on the dendrite morphology and that of the thermal fluctuation together with the phase field fluctuation on the forming of side branches were investigated.The results indicate that with the decrease of thermal fluctuation amplitude.the furcation of dendrite tip also decreases,transverse dendrites become stronger,longitudinal dendrites become degenerated,Doublon structure disappears,and a quite symmetrical dendrite structure appears finally.Thermal fluctuation can result in the unsteadiness of dendrites side branches,and it is also the main reason for forming side branches.The phase field fluctuation has a little contribution to the side branches,and it is usually ignored in calculation.When the thermal fluctuation amplitude(Fu)is appropriate,the thermal noise can result in the side branches,but cannot change the steadY behavior of the dendrites tip.

  9. The microRNA bantam regulates a developmental transition in epithelial cells that restricts sensory dendrite growth.

    Science.gov (United States)

    Jiang, Nan; Soba, Peter; Parker, Edward; Kim, Charles C; Parrish, Jay Z

    2014-07-01

    As animals grow, many early born structures grow by cell expansion rather than cell addition; thus growth of distinct structures must be coordinated to maintain proportionality. This phenomenon is particularly widespread in the nervous system, with dendrite arbors of many neurons expanding in concert with their substrate to sustain connectivity and maintain receptive field coverage as animals grow. After rapidly growing to establish body wall coverage, dendrites of Drosophila class IV dendrite arborization (C4da) neurons grow synchronously with their substrate, the body wall epithelium, providing a system to study how proportionality is maintained during animal growth. Here, we show that the microRNA bantam (ban) ensures coordinated growth of C4da dendrites and the epithelium through regulation of epithelial endoreplication, a modified cell cycle that entails genome amplification without cell division. In Drosophila larvae, epithelial endoreplication leads to progressive changes in dendrite-extracellular matrix (ECM) and dendrite-epithelium contacts, coupling dendrite/substrate expansion and restricting dendrite growth beyond established boundaries. Moreover, changes in epithelial expression of cell adhesion molecules, including the beta-integrin myospheroid (mys), accompany this developmental transition. Finally, endoreplication and the accompanying changes in epithelial mys expression are required to constrain late-stage dendrite growth and structural plasticity. Hence, modulating epithelium-ECM attachment probably influences substrate permissivity for dendrite growth and contributes to the dendrite-substrate coupling that ensures proportional expansion of the two cell types.

  10. Phase-field simulation of dendritic growth in a binary alloy with thermodynamics data

    Institute of Scientific and Technical Information of China (English)

    Long Wen-Yuan; Xia Chun; Xiong Bo-Wen; Fang Li-Gao

    2008-01-01

    This paper simulates the dendrite growth process during non-isothermal solidification in the A1-Cu binary alloy by using the phase-field model. The heat transfer equation is solved simultaneously. The thermodynamic and kinetic parameters are directly obtained from existing database by using the Calculation of Phase Diagram (CALPHAD)method. The effects of the latent heat and undercooling on the dendrite growth, solute and temperature profile during the solidification of binary alloy are investigated. The results indicate that the dendrite growing morphologies could be simulated realistically by linking the phase-field method to CALPHAD. The secondary arms of solidification dendritic are better developed with the increase of undercooling. Correspondingly, the tip speed and the solute segregation in solid-liquid interface increase, but the tip radius decreases.

  11. Quantification of dendritic and axonal growth after injury to the auditory system of the adult cricket Gryllus bimaculatus.

    Science.gov (United States)

    Pfister, Alexandra; Johnson, Amy; Ellers, Olaf; Horch, Hadley W

    2013-01-01

    Dendrite and axon growth and branching during development are regulated by a complex set of intracellular and external signals. However, the cues that maintain or influence adult neuronal morphology are less well understood. Injury and deafferentation tend to have negative effects on adult nervous systems. An interesting example of injury-induced compensatory growth is seen in the cricket, Gryllus bimaculatus. After unilateral loss of an ear in the adult cricket, auditory neurons within the central nervous system (CNS) sprout to compensate for the injury. Specifically, after being deafferented, ascending neurons (AN-1 and AN-2) send dendrites across the midline of the prothoracic ganglion where they receive input from auditory afferents that project through the contralateral auditory nerve (N5). Deafferentation also triggers contralateral N5 axonal growth. In this study, we quantified AN dendritic and N5 axonal growth at 30 h, as well as at 3, 5, 7, 14, and 20 days after deafferentation in adult crickets. Significant differences in the rates of dendritic growth between males and females were noted. In females, dendritic growth rates were non-linear; a rapid burst of dendritic extension in the first few days was followed by a plateau reached at 3 days after deafferentation. In males, however, dendritic growth rates were linear, with dendrites growing steadily over time and reaching lengths, on average, twice as long as in females. On the other hand, rates of N5 axonal growth showed no significant sexual dimorphism and were linear. Within each animal, the growth rates of dendrites and axons were not correlated, indicating that independent factors likely influence dendritic and axonal growth in response to injury in this system. Our findings provide a basis for future study of the cellular features that allow differing dendrite and axon growth patterns as well as sexually dimorphic dendritic growth in response to deafferentation.

  12. Quantification of dendritic and axonal growth after injury to the auditory system of the adult cricket Gryllus bimaculatus

    Directory of Open Access Journals (Sweden)

    Alexandra ePfister

    2013-08-01

    Full Text Available Dendrite and axon growth and branching during development are regulated by a complex set of intracellular and external signals. However, the cues that maintain or influence adult neuronal morphology are less well understood. Injury and deafferentation tend to have negative effects on adult nervous systems. An interesting example of injury-induced compensatory growth is seen in the cricket, Gryllus bimaculatus. After unilateral loss of an ear in the adult cricket, auditory neurons within the central nervous system sprout to compensate for the injury. Specifically, after being deafferented, ascending neurons (AN-1 and AN-2 send dendrites across the midline of the prothoracic ganglion where they receive input from auditory afferents that project through the contralateral auditory nerve (N5. Deafferentation also triggers contralateral N5 axonal growth. In this study, we quantified AN dendritic and N5 axonal growth at 30 hours, as well as at 3, 5, 7, 14 and 20 days after deafferentation in adult crickets. Significant differences in the rates of dendritic growth between males and females were noted. In females, dendritic growth rates were non-linear; a rapid burst of dendritic extension in the first few days was followed by a plateau reached at 3 days after deafferentation. In males, however, dendritic growth rates were linear, with dendrites growing steadily over time and reaching lengths, on average, twice as long as in females. On the other hand, rates of N5 axonal growth showed no significant sexual dimorphism and were linear. Within each animal, the growth rates of dendrites and axons were not correlated, indicating that independent factors likely influence dendritic and axonal growth in response to injury in this system. Our findings provide a basis for future study of the cellular features that allow differing dendrite and axon growth patterns as well as sexually dimorphic dendritic growth in response to deafferentation.

  13. Transport and Growth Kinetics in Microgravity Protein Crystal Growth

    Science.gov (United States)

    Otalora, F.; Garcia-Ruiz, J. M.; Carotenuto, L.; Castagnolo, D.; Novella, M. L.; Chernov, A. A.

    2002-01-01

    The dynamic coupling between mass transport and incorporation of growth units into the surface of a crystal growing from solution in microgravity is used to derive quantitative information on the crystal growth kinetics. To this end, new procedures for experiment preparation, interferometric data processing and model fitting have been developed. The use of experimental data from the bulk diffusive maw transport together with a model for steady state stagnant crystal growth allows the detailed quantitative understanding of the kinetics of both the concentration depletion zone around the crystal and the growth of the crystal interface. The protein crystal used in the experiment is shown to be growing in the mixed kinetic regime (0.2 x 10(exp -6) centimeters per second less than beta R/D less than 0.9 x 10(exp -6) centimeters per second).

  14. Growth of single crystals of BaFe12O19 by solid state crystal growth

    Science.gov (United States)

    Fisher, John G.; Sun, Hengyang; Kook, Young-Geun; Kim, Joon-Seong; Le, Phan Gia

    2016-10-01

    Single crystals of BaFe12O19 are grown for the first time by solid state crystal growth. Seed crystals of BaFe12O19 are buried in BaFe12O19+1 wt% BaCO3 powder, which are then pressed into pellets containing the seed crystals. During sintering, single crystals of BaFe12O19 up to ∼130 μm thick in the c-axis direction grow on the seed crystals by consuming grains from the surrounding polycrystalline matrix. Scanning electron microscopy-energy dispersive spectroscopy analysis shows that the single crystal and the surrounding polycrystalline matrix have the same chemical composition. Micro-Raman scattering shows the single crystal to have the BaFe12O19 structure. The optimum growth temperature is found to be 1200 °C. The single crystal growth behavior is explained using the mixed control theory of grain growth.

  15. Promotion of protein crystal growth by actively switching crystal growth mode via femtosecond laser ablation

    Science.gov (United States)

    Tominaga, Yusuke; Maruyama, Mihoko; Yoshimura, Masashi; Koizumi, Haruhiko; Tachibana, Masaru; Sugiyama, Shigeru; Adachi, Hiroaki; Tsukamoto, Katsuo; Matsumura, Hiroyoshi; Takano, Kazufumi; Murakami, Satoshi; Inoue, Tsuyoshi; Yoshikawa, Hiroshi Y.; Mori, Yusuke

    2016-11-01

    Large single crystals with desirable shapes are essential for various scientific and industrial fields, such as X-ray/neutron crystallography and crystalline devices. However, in the case of proteins the production of such crystals is particularly challenging, despite the efforts devoted to optimization of the environmental, chemical and physical parameters. Here we report an innovative approach for promoting the growth of protein crystals by directly modifying the local crystal structure via femtosecond laser ablation. We demonstrate that protein crystals with surfaces that are locally etched (several micrometers in diameter) by femtosecond laser ablation show enhanced growth rates without losing crystal quality. Optical phase-sensitive microscopy and X-ray topography imaging techniques reveal that the local etching induces spiral growth, which is energetically advantageous compared with the spontaneous two-dimensional nucleation growth mode. These findings prove that femtosecond laser ablation can actively switch the crystal growth mode, offering flexible control over the size and shape of protein crystals.

  16. Effects of impurities on crystal growth in fructose crystallization

    Science.gov (United States)

    Chu, Y. D.; Shiau, L. D.; Berglund, K. A.

    1989-10-01

    The influence of impurities on the crystallization of anhydrous fructose from aqueous solution was studied. The growth kinetics of fructose crystals in the fructose-water-glucose and fructose-water-difructose dianhydrides systems were investigated using photomicroscopic contact nucleation techniques. Glucose is the major impurity likely to be present in fructose syrup formed during corn wet milling, while several difructose dianhydrides are formed in situ under crystallization conditions and have been proposed as a cause in the decrease of overall yields. Both sets of impurities were found to cause inhibition of crystal growth, but the mechanisms responsible in each case are different. It was found that the presence of glucose increases the solubility of fructose in water and thus lowers the supersaturation of the solution. This is probably the main effect responsible for the decrease of crystal growth. Since the molecular structures of difructose dianhydrides are similar to that of fructose, they are probably "tailor-made" impurities. The decrease of crystal growth is probably caused by the incorporation of these impurities into or adsorption to the crystal surface which would accept fructose molecules in the orientation that existed in the difructose dianhydride.

  17. N-methyl-D-aspartate receptor blockade inhibits estrogenic support of dendritic growth in a sexually dimorphic rat spinal nucleus.

    Science.gov (United States)

    Hebbeler, Sara Louise; Verhovshek, Tom; Sengelaub, Dale Robert

    2002-09-16

    The lumbar spinal cord of rats contains the sexually dimorphic, steroid-sensitive spinal nucleus of the bulbocavernosus (SNB). Dendritic development of SNB motoneurons requires the action of both androgens and estrogens. Estrogenic effects are limited to the initial growth of SNB dendrites through 4 weeks of age. During this postnatal period, dendritic growth in other spinal motoneurons is regulated by N-methyl-D-aspartate (NMDA) receptor activation. In this study, we tested whether NMDA receptor activation was involved in SNB dendritic growth and whether the estrogenic support of SNB dendritic growth was dependent on the activation of NMDA receptors. Motoneuron morphology was assessed in normal males, intact males treated daily with the NMDA receptor antagonist MK-801, castrated males treated with estradiol benzoate (EB), and castrated males treated with both EB and MK-801. SNB motoneurons were retrogradely labeled with cholera toxin-horseradish peroxidase at 4 weeks of age (when dendritic length is normally maximal) and reconstructed in three dimensions. Somal area and dendritic length of SNB motoneurons in MK-801-treated, intact males were below those of normal males. Dendritic growth was partially supported in EB-treated castrates, but this growth was blocked by MK-801 treatment. These results suggest that, as in other motoneurons, dendritic development in the SNB involves NMDA receptors and, furthermore, that the estrogen-sensitive component of SNB dendritic development requires their activation. Copyright 2002 Wiley-Liss, Inc.

  18. Low-level laser therapy promotes dendrite growth via upregulating brain-derived neurotrophic factor expression

    Science.gov (United States)

    Meng, Chengbo; He, Zhiyong; Xing, Da

    2014-09-01

    Downregulation of brain-derived neurotrophic factor (BDNF) in the hippocampus occurs early in the progression of Alzheimer's disease (AD). Since BDNF plays a critical role in neuronal survival and dendrite growth, BDNF upregulation may contribute to rescue dendrite atrophy and cell loss in AD. Low-level laser therapy (LLLT) has been demonstrated to regulate neuronal function both in vitro and in vivo. In the present study, we found that LLLT rescued neurons loss and dendritic atrophy via the increase of both BDNF mRNA and protein expression. In addition, dendrite growth was improved after LLLT, characterized by upregulation of PSD95 expression, and the increase in length, branching, and spine density of dendrites in hippocampal neurons. Together, these studies suggest that upregulation of BDNF with LLLT can ameliorate Aβ-induced neurons loss and dendritic atrophy, thus identifying a novel pathway by which LLLT protects against Aβ-induced neurotoxicity. Our research may provide a feasible therapeutic approach to control the progression of Alzheimer's disease.

  19. Phase-field simulation of dendrite growth in the presence of lateral constraints

    Directory of Open Access Journals (Sweden)

    Lifei Du

    2014-06-01

    Full Text Available The effect of a sudden change in the crossing section on the microstructural evolution as well as solute and heat diffusions during solidification of the Ni-40.8% Cu alloy was investigated by implementing a non-isothermal phase-field model. Simulations with lateral constraints of different sizes were carried out to study the changes of the dendritic growth manner. Significant changes in microstructures had been observed as the interface encountered a sharply reduced crossing section; a cellular–dendrite transition could be achieved with lateral constraints, and the tip velocity significantly changed during the development of dendrite microstructures, and also, lateral constraints of different sizes had different effects on changes of the tip positions as well as tip velocities during the dendritic growing through constraints, which agreed well with experimental results.

  20. Phase-field simulation of dendrite growth in the presence of lateral constraints

    Institute of Scientific and Technical Information of China (English)

    Lifei Du; Rong Zhang

    2014-01-01

    The effect of a sudden change in the crossing section on the microstructural evolution as well as solute and heat diffusions during solidification of the Ni-40.8%Cu alloy was investigated by implementing a non-isothermal phase-field model. Simulations with lateral constraints of different sizes were carried out to study the changes of the dendritic growth manner. Significant changes in microstructures had been observed as the interface encountered a sharply reduced crossing section; a cellular-dendrite transition could be achieved with lateral constraints, and the tip velocity significantly changed during the development of dendrite microstructures, and also, lateral constraints of different sizes had different effects on changes of the tip positions as well as tip velocities during the dendritic growing through constraints, which agreed well with experimental results.

  1. Phase field simulation of the columnar dendritic growth and microsegregation in a binary alloy

    Institute of Scientific and Technical Information of China (English)

    Li Jun-Jie; Wang Jin-Cheng; Yang Gen-Cang

    2008-01-01

    This paper applies a phase field model for polycrystalline solidification in binary alloys to simulate the formation and growth of the columnar dendritic array under the isothermal and constant cooling conditions.The solidification process and microsegregation in the mushy zone are analysed in detail.It is shown that under the isothermal condition solidification will stop after the formation of the mushy zone,but dendritic coarsening will progress continuously,which results in the decrease of the total interface area.Under the constant cooling condition the mushy zone will solidify and coarsen simultaneously. For the constant cooling solidification,microsegregation predicted by a modified Brody Flemings model is compared with the simulation results.It is found that the Fourier number which characterizes microsegregation is different for regions with different microstructures.Dendritic coarsening and the larger area of interface should account for the enhanced Fourier number in the region with well developed second dendritic arms.

  2. Dynamic Characterization of Dendrite Deposition and Growth in Li-Surface by Electrochemical Impedance Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Hernandez-Maya, R; Rosas, O; Saunders, J; Castaneda, H

    2015-01-13

    The evolution of dendrite formation is characterized by DC and AC electrochemical techniques. Interfacial mechanisms for lithium deposition are described and quantified by electrochemical impedance spectroscopy (EIS) between a lithium electrode and a graphite electrode. The initiation and growth of dendrites in the lithium surface due to the cathodic polarization conditions following anodic dissolution emulate long term cycling process occurring in the lithium electrodes. The dendrite initiation at the lithium/organic electrolyte interface is proposed to be performed through a combination of layering and interfacial reactions during different cathodic conditions. The growth is proposed to be performed by surface geometrical deposition. In this work, we use EIS in galvanostatic mode to assess the initiation and growth stages of dendrites by the accumulation of precipitates formed under different current conditions. The lithium/organic solvent experimental system using frequency domain techniques is validated by the theoretical approach using a deterministic model that accounts for the faradaic processes at the interface assuming a coverage fraction of the electrodic surface affected by the dendritic growth. (C) 2015 The Electrochemical Society. All rights reserved.

  3. Making Li-metal electrodes rechargeable by controlling the dendrite growth direction

    Science.gov (United States)

    Liu, Yadong; Liu, Qi; Xin, Le; Liu, Yuzi; Yang, Fan; Stach, Eric A.; Xie, Jian

    2017-07-01

    The long-standing issue of Li-dendrite formation and growth during repeated plating or stripping processes prevents the practical application of Li-metal anodes for high-specific-energy batteries. Here we develop an approach to control dendrite growth by coating the separator with functionalized nanocarbon (FNC) with immobilized Li ions. During cycling, the Li dendrites grow toward each other simultaneously from both the FNC layer on the separator and the Li-metal anode; when the dendrites meet, the growth changes direction: rather than penetrating the separator, a dense Li layer is formed between the separator and the Li anode. This controlled growth alleviates the solid electrolyte interphase formation, reduces the decomposition of the electrolyte, and improves the cyclability of the Li-metal cell. In a Li/LiFePO4 coin cell with three different electrolytes, we show that this approach enables a long stable cycle life (>800 cycles with 80% retention of the initial capacity) and improved efficiency (>97%). Our method offers promise for application in practical Li-metal batteries, and it may also be useful for tackling dendrite issues for other metals.

  4. Determination of interface width value in phase-field simulation of dendritic growth into undercooled melt

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The influence of the interface width value on the simulation results and its dependence upon thermo-physical parameters in the phase-field simulation of dendritic growth into undercooled melt are investigated. After choosing the reasonable interface width value, the tip velocities of dendritic growth in Ni melt under different undercoolings are calculated and compared with the experimental data in order to benchmark our results. It is shown that the reasonable interface width value, which is determined by the undercooling, anisotropy, interface kinetic, and thermal diffusivity, has to be taken low enough, and the agreement of our results with experimental data verifies that the credible results can be achieved as long as the interface width value is adequately low. This paper provides the basis of determining interface width value in simulating dendritic growth into undercooled melt by phase-field approach.

  5. Photographic appraisal of crystal lattice growth technique

    Directory of Open Access Journals (Sweden)

    Kapoor D

    2005-01-01

    Full Text Available Concept of creating mechanical retention for bonding through crystal growth has been successfully achieved in the present study. By using polyacrylic acid, sulphated with sulphuric acid as etchant, abundant crystal growth was demonstrated. Keeping in view the obvious benefits of crystal growth technique, the present SEM study was aimed to observe and compare the changes brought about by different etching agents (phosphoric acid, polyacrylic acid and polyacrylic acid sulphated and to evaluate their advantages and disadvantages in an attempt to reduce iatrogenic trauma caused due to surface enamel alteration. Control and experimental groups were made of 24 and 30 premolars, respectively, for scanning electron microscopic appraisal of normal unetched and etched enamel surface and fracture site and finished surface evaluation. When compared with conventional phosphoric acid and weaker polyacrylic acid, investigations indicated that crystal growth treatment on enamel surface caused minimal iatrogenic trauma and surface alteration were restored to the original untreated condition to a large extent.

  6. Illusory spirals and loops in crystal growth.

    Science.gov (United States)

    Shtukenberg, Alexander G; Zhu, Zina; An, Zhihua; Bhandari, Misha; Song, Pengcheng; Kahr, Bart; Ward, Michael D

    2013-10-22

    The theory of dislocation-controlled crystal growth identifies a continuous spiral step with an emergent lattice displacement on a crystal surface; a mechanistic corollary is that closely spaced, oppositely winding spirals merge to form concentric loops. In situ atomic force microscopy of step propagation on pathological L-cystine crystals did indeed show spirals and islands with step heights of one lattice displacement. We show by analysis of the rates of growth of smaller steps only one molecule high that the major morphological spirals and loops are actually consequences of the bunching of the smaller steps. The morphology of the bunched steps actually inverts the predictions of the theory: Spirals arise from pairs of dislocations, loops from single dislocations. Only through numerical simulation of the growth is it revealed how normal growth of anisotropic layers of molecules within the highly symmetrical crystals can conspire to create features in apparent violation of the classic theory.

  7. The Growth of Large Single Crystals.

    Science.gov (United States)

    Baer, Carl D.

    1990-01-01

    Presented is an experiment which demonstrates principles of experimental design, solubility, and crystal growth and structure. Materials, procedures and results are discussed. Suggestions for adapting this activity to the high school laboratory are provided. (CW)

  8. Crystal growth and structural analysis of zirconium sulphoselenide single crystals

    Indian Academy of Sciences (India)

    K R Patel; R D Vaidya; M S Dave; S G Patel

    2008-08-01

    A series of zirconium sulphoselenide (ZrSSe3–, where = 0, 0.5, 1, 1.5, 2, 2.5, 3) single crystals have been grown by chemical vapour transport technique using iodine as a transporting agent. The optimum condition for the growth of these crystals is given. The stoichiometry of the grown crystals were confirmed on the basis of energy dispersive analysis by X-ray (EDAX) and the structural characterization was accomplished by X-ray diffraction (XRD) studies. The crystals are found to possess monoclinic structure. The lattice parameters, volume, particle size and X-ray density have been carried out for these crystals. The effect of sulphur proportion on the lattice parameter, unit cell volume and X-ray density in the series of ZrSSe3– single crystals have been studied and found to decrease in all these parameters with rise in sulphur proportion. The grown crystals were examined under optical zoom microscope for their surface topography study. Hall effect measurements were carried out on grown crystals at room temperature. The negative value of Hall coefficient implies that these crystals are -type in nature. The conductivity is found to decrease with increase of sulphur content in the ZrSSe3– series. The electrical resistivity parallel to c-axis as well as perpendicular to -axis have been carried out in the temperature range 303–423 K. The results obtained are discussed in detail.

  9. Vapor Crystal Growth (VCG) experiment Cell

    Science.gov (United States)

    1992-01-01

    The image shows a test cell of Crystal Growth experiment inside the Vapor Crystal Growth System (VCGS) furnace aboard the STS-42, International Microgravity Laboratory-1 (IML-1), mission. The goal of IML-1, a pressurized marned Spacelab module, was to explore in depth the complex effects of weightlessness of living organisms and materials processing. More than 200 scientists from 16 countires participated in the investigations.

  10. Technology of gallium nitride crystal growth

    CERN Document Server

    Ehrentraut, Dirk; Bockowski, Michal

    2010-01-01

    This book deals with the important technological aspects of the growth of GaN single crystals by HVPE, MOCVD, ammonothermal and flux methods for the purpose of free-standing GaN wafer production. Leading experts from industry and academia report in a very comprehensive way on the current state-of-the-art of the growth technologies and optical and structural properties of the GaN crystals are compared.

  11. On growth rate hysteresis and catastrophic crystal growth

    Science.gov (United States)

    Ferreira, Cecília; Rocha, Fernando A.; Damas, Ana M.; Martins, Pedro M.

    2013-04-01

    Different crystal growth rates as supersaturation is increasing or decreasing in impure media is a phenomenon called growth rate hysteresis (GRH) that has been observed in varied systems and applications, such as protein crystallization or during biomineralization. We have recently shown that the transient adsorption of impurities onto newly formed active sites for growth (or kinks) is sensitive to the direction and rate of supersaturation variation, thus providing a possible explanation for GRH [6]. In the present contribution, we expand on this concept by deriving the analytical expressions for transient crystal growth based on the energetics of growth hillock formation and kink occupation by impurities. Two types of GRH results are described according to the variation of kink density with supersaturation: for nearly constant density, decreasing or increasing supersaturation induce, respectively, growth promoting or inhibiting effects relative to equilibrium conditions. This is the type of GRH measured by us during the crystallization of egg-white lysozyme. For variable kink density, slight changes in the supersaturation level may induce abrupt variations in the crystal growth rate. Different literature examples of this so-called 'catastrophic' crystal growth are discussed in terms of their fundamental consequences.

  12. Effect of heat source on the growth of dendritic drying patterns

    Indian Academy of Sciences (India)

    Kiran M Kolwankar; Pulkit Prakash; Shruthi Radhakrishnan; Swadhini Sahu; Aditya K Dharmadhikari; Jayashree A Dharmadhikari; Deepak Mathur

    2015-03-01

    Shining a tightly-focussed but low-powered laser beam on an absorber dispersed in a biological fluid gives rise to spectacular growth of dendritic patterns. These result from localized drying of the fluid because of efficient absorption and conduction of optical energy by the absorber. We have carried out experiments in several biologically relevant fluids and have analysed patterns generated by different types of absorbers. We observe that the growth velocity of branches in the dendritic patterns can decrease below the value expected for natural drying.

  13. Noncrystallographic calcite dendrites from hot-spring deposits at Lake Bogoria, Kenya

    Energy Technology Data Exchange (ETDEWEB)

    Jones, B. [Univ. of Alberta, Edmonton, Alberta (Canada). Dept. of Geology; Renaut, R.W. [Univ. of Saskatchewan, Saskatoon (Canada). Dept. of Geological Sciences

    1995-01-02

    Complex calcite crystals are an integral component of precipitates that form around the orifices of the Loburu and Mawe Moto hot springs on the shores of Lake bogoria, Kenya. Two types of large (up to 4 cm long) noncrystallographic dendrites are important components of these deposits. Feather dendrites are characterized by multiple levels of branching with individual branches developed through crystal splitting and spherulitic growth. Scandulitic (from Latin meaning shingle) dendrites are formed of stacked calcite crystals and are generally more compact than feather dendrites. These developed through the incremental stacking of rectangular-shaped calcite crystals that initially grew as skeletal crystals. Feather and scandulitic dendrites precipitated from the same waters in the same springs. The difference in morphology is therefore related to microenvironments in which they grew. Feather dendrites grew in any direction in pools of free-standing water provided that they were in constant contact with the solute. Conversely, scandulitic dendrites grew on rims of dams where water flowed over the surface in concert with the pulses of spring water. Thus, each calcite crystal in these dendrites represents one episode of crystal growth. The orientation of the component crystals in scandulitic dendrites is controlled by the topography of the dam or surface, not crystallographic criteria. The noncrystallographic dendrites formed from spring waters with initial temperatures of 90--99 C. Surficial water cooling, loss of CO{sub 2}, and presence of other elements that can interfere with crystal growth contributed to the formation of these unusual crystals.

  14. On the Origin of Grid Anisotropy in the Simulation of Dendrite Growth by a VFT Model

    Science.gov (United States)

    Djaraoui, Afaf; Nebti, Samia

    2016-10-01

    A virtual front tracking model, based on solute and heat diffusion in two dimensions, is chosen to capture the full microstructural behavior of dendritic solidification in a binary alloy. We use a simple method of calculation, easy to perform, with relatively high stable time step, to simulate the dendrite growth in an Al-8 wt pct Mg alloy for which no numerical simulation has been carried out in the past. Local equilibrium at the liquid solid interface and the buildup of solute ahead of the interface are solved, and the dendrite growth process is simulated in isothermal solidification conditions. We show that the artificial grid anisotropy originates from the four cell neighborhood method adopted for capturing the moving front. By a correct neighborhood configuration, a grid independent set of results and expected phenomena are reproduced for a free dendrite growing either aligned or inclined with the grid. The dendrite morphology and orientation, and the growth velocity are explored via physical simulation parameters such as undercooling and surface tension anisotropy.

  15. In situ study on dendrite growth of metallic alloy by a synchrotron radiation imaging technology

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    This study was trying to observe the real-time dendrite growth of Sn-Bi and Sn-Pb binary alloys by a synchrotron radiation imaging technology.The imaging system includes an intense and high brightness synchrotron radiation source,a high-resolution and fast-readout charge coupled device camera,an alloy sample and a Bridgman solidification system.The imaging experiments were done at Beijing Synchrotron Radiation Facility with an updated synchrotron radiation imaging technique,diffraction-enhanced imaging,which was firstly used to study the dendrite growth of metallic alloy.A series of growth behavior and morphology evolution of dendrite have been in situ observed,such as columnar-to-equiaxed transition,dendrite competition,dendrite fragmentation and floating,etc.,which can offer the direct proofs to verify or improve the solidification theories of metallic alloy.This research opens a novel window for the study of alloy solidification and enables the unambiguous understanding of solidification processes in optically opaque,metallic alloys.

  16. Historical aspects of crystal growth technology

    Science.gov (United States)

    Scheel, Hans J.

    2000-04-01

    The father of crystal fabrication technology is A. Verneuil with his flame-fusion growth method 1902. His principles of nucleation and growth control are adapted in most later growth methods from melt. The Czochralski method was essentially developed by Teal, Little and Dash. The multidisciplinary nature of crystal growth and epitaxy technology and the complex multiparameter processes, and also the scaling problem, have impeded the scientific development of this important area. Only recently it was possible to solve the striation problem and to understand the control of epitaxial growth modes for achieving structurally perfect layers of GaAs and high- Tc superconductors with atomically flat surfaces. The formation of crystal growth and epitaxy engineers and scientists as well as centers of excellence are necessary in order to develop crystal and epilayer fabrication technologies required for development of highest-efficiency white light-emitting diodes and photovoltaic solar cells for energy-saving lighting and as alternative source of energy. Also laser-fusion energy and other high technologies have to wait for progress in crystal growth technology.

  17. Over-limiting Current and Control of Dendritic Growth by Surface Conduction in Nanopores

    CERN Document Server

    Han, Ji-Hyung; Bai, Peng; Bazant, Martin Z

    2014-01-01

    Understanding over-limiting current (faster than diffusion) is a long-standing challenge in electrochemistry with applications in desalination and energy storage. Known mechanisms involve either chemical or hydrodynamic instabilities in unconfined electrolytes. Here, it is shown that over-limiting current can be sustained by surface conduction in nano pores, without any such instabilities, and used to control dendritic growth during electrodeposition. Copper electrode posits are grown in anodized aluminum oxide membranes with polyelectrolyte coatings to modify the surface charge. At low currents, uniform electroplating occurs, unaffected by surface modification due to thin electric double layers, but the morphology changes dramatically above the limiting current. With negative surface charge, growth is enhanced along the nanopore surfaces, forming surface dendrites and nanotubes behind a deionization shock. With positive surface charge, dendrites avoid the surfaces and are either guided along the nanopore cen...

  18. A critical examination of the dendrite growth models Comparison of theory with experimental data

    Science.gov (United States)

    Tewari, S. N.; Laxmanan, V.

    1987-01-01

    Three dendrite growth models for directionally solidified succinonitrile-acetone, succinonitrile-salol, aluminum-copper, and lead-paladium alloys are evaluated. The characteristics of the Burden and Hunt (1974) model, the Laxmanan (1985) model, and the Trivedi (1980) model are described. The dendrite tip temperature, tip radius, liquid composition, and primary arm spacing for the alloys are analyzed in terms of growth speed, alloy composition, and temperature gradient. It is observed that the Burden and Hunt model accurately predicts the proper behavior of the parameters, but does not provide good quantitative predictions. A good fit between the experimental data and the Trivedi and Laxmanan models is detected. The advantages of the Trivedi marginal stability analysis and the Laxmanan minimum dendrite tip undercooling approaches are discussed.

  19. Numerical simulation of dendrite growth and microsegregation formation of binary alloys during solidification process

    Institute of Scientific and Technical Information of China (English)

    Li Qiang; Guo Qiao-Yi; Li Rong-De

    2006-01-01

    The dendrite growth and solute microsegregation of Fe-C binary alloy are simulated during solidification process by using cellular automaton method.In the model the solid fraction is deduced from the relationship among the temperature,solute concentration and curvature of the solid/liquid interface unit,which can be expressed as a quadric equation,instead of assuming the interface position and calculating the solid fraction from the interface velocity.Then by using this model a dendrite with O and 45 degree of preferential growth direction are simulated respectively.Furthermore,a solidification microstructure and solute microsegregation are simulated by this method. Finally,different GibbsThomson coefficient and liquid solute diffusing coefficient are adopted to investigate their influences on the morphology of dendrite.

  20. Rapid growth of primary dendrite in highly undercooled copper-antimany alloy

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The droplets of Cu-11wt.%Sb hypoeutectic alloy have been rapidly solidified during containerless processing in a 3 m drop tube. The undercooling and cooling rates are estimated, and both play a dominant role in the dendritic growth of primary Cu phase. Undercoolings up to 200 K (0.16TL, where TL is the liquidus temperature) have been obtained in the experiment. With the increase of undercooling, the microstructural evolution of primary Cu phase proceeds from remelted dendrites to the equiaxed grains. A coarse dendritic grain microstructure can form in the undercooling range of 61~102 K and at cooling rates of 1.35×102~2.66×103 K/s. The segregationless solidification of Cu-11wt.%Sb hypoeutectic alloy occurs when undercooling is more than 176 K. The growth of primary Cu phase is mainly controlled by solute diffusion.

  1. Anisotropic corner diffusion as origin for dendritic growth on hexagonal substrates

    DEFF Research Database (Denmark)

    Brune, H.; Röder, H.; Bromann, K.

    1996-01-01

    and stick mechanism, form. Dendrites are characterized by preferential growth in the [2]-directions, i.e., perpendicular to A-steps. The key process for their formation has been found to be diffusion of one-fold comer atoms towards neighboring steps. Calculations with the effective medium...... theory show that this relaxation is highly asymmetric with respect to the two different kinds of close-packed steps. It leads to dendritic growth as verified by kinetic Monte-Carlo simulations which agree well with experiment.......Ag aggregation on Ag(111), Pt(111), and 1 ML Ag pseudomorphically grown on Pt(111), has been studied with variable temperature STM. These systems all have in common that dendritic patterns with trigonal symmetry rather than randomly ramified aggregates, which would be expected for a simple hit...

  2. INTERFACIAL MASS TRANSPORT IN OXIDE CRYSTAL GROWTH

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    @@ A space high temperature in situobservation instrument (SHITISOI) is dedicated to visualize and record the whole growth process of oxide crystal in high temperature melts and solutions. Model experiments using transparent liquids such as KNbO3,Li2B4O7+KNbO3 were chosen to investigate effects of interracial mass transport in oxide crystal growth. For the scaling of the coupled velocity, heat and concentration fields in KNbO3 crystal growth, a rotating crystal growth process was performed and the widths of interfacial concentration, heat and momentum transition zones (The "boundary layers") are obtained, which are 7.5×10-a, 8.6×10-2 and 4.4×10-1 cm,respectively. Hence one can expect that interfacial concentration gradient will be confined to a narrow layer and in region of major concentration change at the in terface. In order to study a mechanism based on the interfacial mass transport resulting from hydrodynamics, the growth of KNbO3 grain in high temperature Li2B4O7 and KNbO3 solutin was studied. The result shows that the pivotal feature in the KNbO3 crystal growth is the initiated by KNbO3 solute surface tension gra dient which is caused by the slow diffusion of KNbO3 solutes. Direct comparison of the model predictions and experimental observed phenomena demonstrate the predictive capability of this model.

  3. Convective flow effects on protein crystal growth

    Science.gov (United States)

    Rosenberger, Franz

    1995-01-01

    During the fifth semi-annual period under this grant we have pursued the following activities: (1) Characterization of the purity and further purification of lysozyme solutions, these efforts are summarized in Section 2; (2) Crystal growth morphology and kinetics studies with tetragonal lysozyme, our observation on the dependence of lysozyme growth kinetics on step sources and impurities has been summarized in a manuscript which was accepted for publication in the Journal of Crystal Growth; (3) Numerical modelling of the interaction between bulk transport and interface kinetics, for a detailed summary of this work see the manuscript which was accepted for publication in the Journal of Crystal Growth; and (4) Light scattering studies, this work has been summarized in a manuscript that has been submitted for publication to the Journal of Chemical Physics.

  4. Lattice Boltzmann Simulation of Water Isotope Fractionation During Growth of Ice Crystals in Clouds

    Science.gov (United States)

    Lu, G.; Depaolo, D.; Kang, Q.; Zhang, D.

    2006-12-01

    The isotopic composition of precipitation, especially that of snow, plays a special role in the global hydrological cycle and in reconstruction of past climates using polar ice cores. The fractionation of the major water isotope species (HHO, HDO, HHO-18) during ice crystal formation is critical to understanding the global distribution of isotopes in precipitation. Ice crystal growth in clouds is traditionally treated with a spherically- symmetric steady state diffusion model, with semi-empirical modifications added to account for ventilation and for complex crystal morphology. Although it is known that crystal growth rate, which depends largely on the degree of vapor over-saturation, determines crystal morphology, there are no existing quantitative models that directly relate morphology to the vapor saturation factor. Since kinetic (vapor phase diffusion-controlled) isotopic fractionation also depends on growth rate, there should be a direct relationship between vapor saturation, crystal morphology, and crystal isotopic composition. We use a 2D Lattice-Boltzmann model to simulate diffusion-controlled ice crystal growth from vapor- oversaturated air. In the model, crystals grow solely according to the diffusive fluxes just above the crystal surfaces, and hence crystal morphology arises from the initial and boundary conditions in the model and does not need to be specified a priori. The input parameters needed are the isotope-dependent vapor deposition rate constant (k) and the water vapor diffusivity in air (D). The values of both k and D can be computed from kinetic theory, and there are also experimentally determined values of D. The deduced values of k are uncertain to the extent that the sticking coefficient (or accommodation coefficient) for ice is uncertain. The ratio D/k is a length that determines the minimum scale of dendritic growth features and allows us to scale the numerical calculations to atmospheric conditions using a dimensionless Damkohler number

  5. Substrate effect on the growth of monolayer dendritic MoS2 on LaAlO3 (100) and its electrocatalytic applications

    Science.gov (United States)

    Li, Cong; Zhang, Yu; Ji, Qingqing; Shi, Jianping; Chen, Zhaolong; Zhou, Xiebo; Fang, Qiyi; Zhang, Yanfeng

    2016-09-01

    In accommodating the rapid development of two-dimensional (2D) nanomaterials, chemical vapor deposition (CVD) has become a powerful tool for their batch production with desirable characteristics, such as high crystal quality, large domain size, and tunable domain shape. The crystallinity and morphology of the growth substrates usually play a crucial role in the CVD synthesis of high-quality monolayer MoS2, a kind of 2D layered material which has ignited huge interest in nanoelectronics, optoelectronics and energy harvesting, etc. Herein, by utilizing a low-pressure chemical vapor deposition (LPCVD) system, we demonstrate a regioselective synthesis of monolayer MoS2 on the corrugated single-crystal LaAlO3 (100) with twin crystal domains induced by the second-order phase transition. Unique dendritic morphologies with tunable nucleation densities were obtained in different regions of the undulated substrate, presenting a strong substrate modulation effect. Interestingly, the exposure of abundant active edge sites along with the rather high nucleation density makes the monolayer dendritic MoS2 a good electrocatalyst for hydrogen evolution reaction (HER), particularly featured by a rather high exchange current density (70.4 μA cm-2). Furthermore, uniform monolayer MoS2 films can also be obtained and transferred to arbitrary substrates. We believe that this work provides a new growth system for the controllable synthesis of 2D layered materials with unique dendritic morphologies, as well as its great application potential in energy conversion and harvesting.

  6. Multi-GPUs parallel computation of dendrite growth in forced convection using the phase-field-lattice Boltzmann model

    Science.gov (United States)

    Sakane, Shinji; Takaki, Tomohiro; Rojas, Roberto; Ohno, Munekazu; Shibuta, Yasushi; Shimokawabe, Takashi; Aoki, Takayuki

    2017-09-01

    Melt flow drastically changes dendrite morphology during the solidification of pure metals and alloys. Numerical simulation of dendrite growth in the presence of the melt flow is crucial for the accurate prediction and control of the solidification microstructure. However, accurate simulations are difficult because of the large computational costs required. In this study, we develop a parallel computational scheme using multiple graphics processing units (GPUs) for a very large-scale three-dimensional phase-field-lattice Boltzmann simulation. In the model, a quantitative phase field model, which can accurately simulate the dendrite growth of a dilute binary alloy, and a lattice Boltzmann model to simulate the melt flow are coupled to simulate the dendrite growth in the melt flow. By performing very large-scale simulations using the developed scheme, we demonstrate the applicability of multi-GPUs parallel computation to the systematical large-scale-simulations of dendrite growth with the melt flow.

  7. Method for solid state crystal growth

    Science.gov (United States)

    Nolas, George S.; Beekman, Matthew K.

    2013-04-09

    A novel method for high quality crystal growth of intermetallic clathrates is presented. The synthesis of high quality pure phase crystals has been complicated by the simultaneous formation of both clathrate type-I and clathrate type-II structures. It was found that selective, phase pure, single-crystal growth of type-I and type-II clathrates can be achieved by maintaining sufficient partial pressure of a chemical constituent during slow, controlled deprivation of the chemical constituent from the primary reactant. The chemical constituent is slowly removed from the primary reactant by the reaction of the chemical constituent vapor with a secondary reactant, spatially separated from the primary reactant, in a closed volume under uniaxial pressure and heat to form the single phase pure crystals.

  8. The growth of Nd: YAG single crystals

    Directory of Open Access Journals (Sweden)

    ANDREJA VALCIC

    2002-04-01

    Full Text Available Y3Al5O12 doped with 0.8 % wt. Nd (Nd:YAG single crystals were grown by the Czochralski technique under an argon atmosphere. The conditions for growing the Nd: YAG single crystals were calculated by using a combination of Reynolds and Grashof numbers. The critical crystal diameter and the critical rate of rotation were calculated from the hydrodynamics of the melt. The crystal diameter Dc = 1.5 cm remained constant during the crystal growth, while the critical rate of rotation changed from wc = 38 rpm after necking to wc = 13 rpm at the end of the crystal. The value of the rate of crystal growth was experimentally found to be 0.8–1.0 mm/h. According to our previous experiments, it was confirmed that 20 min exposure to conc. H3PO4 at 603 K was suitable for chemical polishing. Also, one-hour exposure to conc. H3PO4 at 493 K was found to be suitable for etching. The lattice parameter a = 1.201 (1 nm was determined by X-ray powder diffraction. The obtained results are discussed and compared with published data.

  9. Thalamus-derived molecules promote survival and dendritic growth of developing cortical neurons.

    Science.gov (United States)

    Sato, Haruka; Fukutani, Yuma; Yamamoto, Yuji; Tatara, Eiichi; Takemoto, Makoto; Shimamura, Kenji; Yamamoto, Nobuhiko

    2012-10-31

    The mammalian neocortex is composed of various types of neurons that reflect its laminar and area structures. It has been suggested that not only intrinsic but also afferent-derived extrinsic factors are involved in neuronal differentiation during development. However, the role and molecular mechanism of such extrinsic factors are almost unknown. Here, we attempted to identify molecules that are expressed in the thalamus and affect cortical cell development. First, thalamus-specific molecules were sought by comparing gene expression profiles of the developing rat thalamus and cortex using microarrays, and by constructing a thalamus-enriched subtraction cDNA library. A systematic screening by in situ hybridization showed that several genes encoding extracellular molecules were strongly expressed in sensory thalamic nuclei. Exogenous and endogenous protein localization further demonstrated that two extracellular molecules, Neuritin-1 (NRN1) and VGF, were transported to thalamic axon terminals. Application of NRN1 and VGF to dissociated cell culture promoted the dendritic growth. An organotypic slice culture experiment further showed that the number of primary dendrites in multipolar stellate neurons increased in response to NRN1 and VGF, whereas dendritic growth of pyramidal neurons was not promoted. These molecules also increased neuronal survival of multipolar neurons. Taken together, these results suggest that the thalamus-specific molecules NRN1 and VGF play an important role in the dendritic growth and survival of cortical neurons in a cell type-specific manner.

  10. Biomolecular Modification of Inorganic Crystal Growth

    Energy Technology Data Exchange (ETDEWEB)

    De Yoreo, J J

    2007-04-27

    The fascinating shapes and hierarchical designs of biomineralized structures are an inspiration to materials scientists because of the potential they suggest for biomolecular control over materials synthesis. Conversely, the failure to prevent or limit tissue mineralization in the vascular, skeletal, and urinary systems is a common source of disease. Understanding the mechanisms by which organisms direct or limit crystallization has long been a central challenge to the biomineralization community. One prevailing view is that mineral-associated macromolecules are responsible for either inhibiting crystallization or initiating and stabilizing non-equilibrium crystal polymorphs and morphologies through interactions between anionic moieties and cations in solution or at mineralizing surfaces. In particular, biomolecules that present carboxyl groups to the growing crystal have been implicated as primary modulators of growth. Here we review the results from a combination of in situ atomic force microscopy (AFM) and molecular modeling (MM) studies to investigate the effect of specific interactions between carboxylate-rich biomolecules and atomic steps on crystal surfaces during the growth of carbonates, oxalates and phosphates of calcium. Specifically, we how the growth kinetics and morphology depend on the concentration of additives that include citrate, simple amino acids, synthetic Asp-rich polypeptides, and naturally occurring Asp-rich proteins found in both functional and pathological mineral tissues. The results reveal a consistent picture of shape modification in which stereochemical matching of modifiers to specific atomic steps drives shape modification. Inhibition and other changes in growth kinetics are shown to be due to a range of mechanisms that depend on chemistry and molecular size. Some effects are well described by classic crystal growth theories, but others, such as step acceleration due to peptide charge and hydrophylicity, were previously unrealized

  11. Studies of laser crystal growth. 1. Production of crystal growth furnaces and operating results

    Energy Technology Data Exchange (ETDEWEB)

    Sugiyama, Akira; Sasuga, Tsuneo; Arisawa, Takashi; Takuma, Hiroshi [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment; Anzai, Yutaka; Katsurayama, Masamichi; Yamazaki, Takafumi; Yamagishi, Kiyoshi

    1997-10-01

    Table top short pulse Peta-watt laser system is the most promising light source to drive studying high energy field physics in advance photon research. To achieve high efficiency laser oscillation in stable condition, it is required to pull out the best performance from laser crystals as the gain medium. Therefore, we have conducted cooperative investigation with Mitsui Mining and Smelting Co., LTD. to create large ideal laser crystals by improved growth methods which solve several problems in usual growth techniques. This report describes specifications, results of operation, and improvements in two different types of growth furnaces which make homogeneous doped concentration along growth direction of Nd:YAG laser crystal and large fluoride laser crystals with a wide band gap, respectively. It also describes the first four results of crystals such as YAG, Nd:YAG, YLF, and LBO grown by these furnaces. (author)

  12. An Apparatus for Growth of Small Crystals From Solutions.

    Science.gov (United States)

    Mitrovic, Mico M.

    1995-01-01

    Describes an apparatus for crystal growth that was designed to study growth kinetics of small crystals from solutions and to obtain crystals of various substances. Describes the use of the apparatus in laboratory practical experiments in the field of crystal growth physics within the course "Solid State Physics". (JRH)

  13. A model for grain growth based on the novel description of dendrite shape

    Directory of Open Access Journals (Sweden)

    O. Wodo

    2007-12-01

    Full Text Available We use novel description of dendritic shape in the micro solid phase growth model. The model describes evolution of both primary solid solution dendrite and eutectic that forms between arms and grains in the last stage of solidification. Obtained results show that our approach can be used in grain growth model to determine more reliable eutectic distribution. In the paper no kinetics connected with the eutectic transformation is taken into account. However, this does not affect the eutectic distribution because at the beginning of eutectic reaction all liquid phase was assumed to fully transform into eutectic. Results for solid phase growth model based on this description are presented. The obtained results of eutectic distribution are especially important in the hypoeutectic alloy solidification case, where the eutectic grains grow between formed solid solution grains. Thus, the distribution of solid solution grain becomes crucial due to its influence on the delay in solid fraction increase of eutectic grains.

  14. Effects of cyclic structure inhibitors on the morphology and growth of tetrahydrofuran hydrate crystals

    Science.gov (United States)

    Li, Sijia; Wang, Yanhong; Lang, Xuemei; Fan, Shuanshi

    2013-08-01

    Morphology and growth of hydrate crystals with cyclic structure inhibitors at a hydrate-liquid interface were directly observed through a microscopic manipulating apparatus. Tetrahydrofuran (THF) hydrate was employed as an objective. The effects of four kind of cyclic structure inhibitors, polyvinylpyrrolidone (PVP), poly(N-vinyl-2-pyrrolidone-co-2-vinyl pyridine) (PVPP), poly(2-vinyl pyridine-co-N-vinylcaprolactam) (PVPC) and poly(N-vinylcaprolactam) (PVCap), were investigated. Morphological patterns between each hydrate crystal growth from hydrate-liquid interface into droplet were found differ significantly. Lamellar structure growth of hydrate crystal was observed without inhibitor, while with PVP was featheriness-like, PVPP was like long dendritic crystal, PVPC was Mimosa pudica leaf-like and PVCap was like weeds. The growth rate of hydrate crystal without inhibitor was 0.00498 mm3/s, while with PVPP, PVPC and PVCap, were 0.00339 mm3/s, 0.00350 mm3/s, 0.00386 mm3/s and 0.00426 mm3/s, respectively. Cyclic structure inhibitors can decrease the growth rate, degree of reduction in growth rate of hydrate crystals decrease with the increase of cylinder number.

  15. Direct observation of dendritic domain growth in perpendicular magnetic anisotropy CoFe/Pt multilayers

    Energy Technology Data Exchange (ETDEWEB)

    Liu Haoliang [State Key Laboratory of Magnetism and Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); He Wei, E-mail: hewei@aphy.iphy.ac.cn [State Key Laboratory of Magnetism and Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Du Haifeng; Wu Qiong; Fang Yapeng [State Key Laboratory of Magnetism and Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Zhu Yun [College of Physics and Electronic Information Science, Tianjin Normal University, Tianjin 300387 (China); Cai Jianwang [State Key Laboratory of Magnetism and Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Cheng Zhaohua, E-mail: zhcheng@aphy.iphy.ac.cn [State Key Laboratory of Magnetism and Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)

    2011-09-15

    We present the experimental results on thermally activated magnetization reversal for [Co{sub 0.9}Fe{sub 0.1}(5.0 A)/Pt(20 A)]{sub 4} multilayer. Direct domain observations show that magnetization reversal is initiated with rare nucleation and followed by dendritic growth of domain walls. Based on macroscopic magnetic parameters from experimental data, the dendritic domain growth mode is qualitatively interpreted by Monte Carlo simulations in terms of a simple uniaxial magnetic anisotropy model. Moreover, both time evolution of domain growth observation and magnetic relaxation measurements reveal that CoFe/Pt multilayer has a relatively large activation volume compared with Co/Pt multilayers. - Highlights: > We investigate magnetization reversal of [Co{sub 0.9}Fe{sub 0.1}(5.0 A)/Pt(20 A)]{sub 4} multilayer. > Magnetization reversal is governed by thermally activated mechanism. > Magnetic domains evolve in dendritic domain growth mode. > Relatively large activation volume is obtained for the multilayer. > Monte Carlo simulation reproduces the domain growth mode well.

  16. The growth of sapphire single crystals

    Directory of Open Access Journals (Sweden)

    STEVAN DJURIC

    2001-06-01

    Full Text Available Sapphire (Al2O3 single crystals were grown by the Czochralski technique both in air and argon atmospheres. The conditions for growing sapphire single crystals were calculated by using a combination of Reynolds and Grashof numbers. Acritical crystal diameter dc = 20 mm and the critical rate of rotation wc = 20 rpm were calculated from the hydrodynamics of the melt. The value of the rate of crystal growth was experimentally found to be 3.5 mm/h. According to our previous experiments, it was confirmed that three hours exposures to conc. H3PO4 at 593 K was suitable for chemical polishing. Also, three hours exposure to conc.H3PO4 at 523 K was found to be a suitable etching solution. The lattice parameters a = 0.47573 nm and c = 1.29893 nm were determined by X-ray powder diffraction. The obtained results are discussed and compared with published data.

  17. Growth of single-crystal gallium nitride

    Science.gov (United States)

    Clough, R.; Richman, D.; Tietjen, J.

    1970-01-01

    Use of ultrahigh purity ammonia prevents oxygen contamination of GaN during growth, making it possible to grow the GaN at temperatures as high as 825 degrees C, at which point single crystal wafers are deposited on /0001/-oriented sapphire surfaces.

  18. Numerical simulation for isothermal dendritic growth of succinonitrile-acetone alloy

    Institute of Scientific and Technical Information of China (English)

    CHEN Zhi; CHEN Chang-le; HAO Li-mei

    2008-01-01

    Numerical simulation based on phase field method was developed to describe the solidification of two-dimensional isothermal binary alloys.The evolution of the interface morphology was shown and the effects of phase field parameters were formulated for succinonitrile-acetone alloy.The results indicate that an anti-trapping current (ATC) can suppress many trapped molten packets,which is caused by the thickened interface.With increasing the anisotropy value from 0 to 0.05,a small circular seed grows to develope secondary dendritic,dendritic tip velocity increases monotonically,and the solute accumulation of solid/liquid interface is diminished distinctly.Furthermore,with the increase of the coupling parameter value,the interface becomes unstable and the side branches of crystals appear and grow gradually.

  19. Microscopic properties of lithium, sodium, and magnesium battery anode materials related to possible dendrite growth

    Energy Technology Data Exchange (ETDEWEB)

    Jäckle, Markus; Groß, Axel [Institute of Theoretical Chemistry, Ulm University, 89069 Ulm, Germany and Helmholtz Institut Ulm (HIU) Electrochemical Energy Storage, 89069 Ulm (Germany)

    2014-11-07

    Lithium and magnesium exhibit rather different properties as battery anode materials with respect to the phenomenon of dendrite formation which can lead to short-circuits in batteries. Diffusion processes are the key to understanding structure forming processes on surfaces. Therefore, we have determined adsorption energies and barriers for the self-diffusion on Li and Mg using periodic density functional theory calculations and contrasted the results to Na which is also regarded as a promising electrode material in batteries. According to our calculations, magnesium exhibits a tendency towards the growth of smooth surfaces as it exhibits lower diffusion barriers than lithium and sodium, and as an hcp metal it favors higher-coordinated configurations in contrast to the bcc metals Li and Na. These characteristic differences are expected to contribute to the unequal tendencies of these metals with respect to dendrite growth.

  20. High undercooling and rapid dendritic growth of Cu-Sb alloy in drop tube

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Droplets of Cu-20%Sb hypoeutectic alloy has been rapidly solidified in drop tube within the containerless condition. With the decrease of droplet diameter, undercooling increases and the microstructures of primary copper dendrite refines. Undercooling up to 207 K (0.17 TL) is obtained in experiment. Theoretic analysis indicated that, because of the broad temperature range of solidification, the rapid growth of primary copper dendrite is controlled by the solutal diffusion. Judging from the calculation of T0 curve in the phase diagram, it is shown that the critical undercooling of segregationless solidification is (T0 = 474 K. At the maximum undercooling of 207 K, the growth velocity of primary copper phase exceeds to 37 mm/s, and the distinct solute trapping occurs.

  1. Flux growth of BPO 4 crystals

    Science.gov (United States)

    Li, Zhihua; Wu, Yicheng; Fu, Peizhen; Pan, Shilie; Chen, Chuangtian

    2004-10-01

    Single crystals of BPO4 with sizes up to 15×10×12 mm3 were grown by top-seeded solution growth method using Li2O-Li4P2O7 as fluxes. The components volatilized from the melt were characterized by the method of X-ray powder diffraction. The defects of grown crystals have also been investigated. The measured ultraviolet cutoff edge of BPO4 was about 130 nm. Its density was 2.82 g/cm3 determined using drainage method.

  2. Class 3 semaphorin mediates dendrite growth in adult newborn neurons through Cdk5/FAK pathway.

    Directory of Open Access Journals (Sweden)

    Teclise Ng

    Full Text Available Class 3 semaphorins are well-known axonal guidance cues during the embryonic development of mammalian nervous system. However, their activity on postnatally differentiated neurons in neurogenic regions of adult brains has not been characterized. We found that silencing of semaphorin receptors neuropilins (NRP 1 or 2 in neural progenitors at the adult mouse dentate gyrus resulted in newly differentiated neurons with shorter dendrites and simpler branching in vivo. Tyrosine phosphorylation (Tyr 397 and serine phosphorylation (Ser 732 of FAK were essential for these effects. Semaphorin 3A and 3F mediate serine phosphorylation of FAK through the activation of Cdk5. Silencing of either Cdk5 or FAK in newborn neurons phenocopied the defects in dendritic development seen upon silencing of NRP1 or NRP2. Furthermore, in vivo overexpression of Cdk5 or FAK rescued the dendritic phenotypes seen in NRP1 and NRP2 deficient neurons. These results point to a novel role for class 3 semaphorins in promoting dendritic growth and branching during adult hippocampal neurogenesis through the activation of Cdk5-FAK signaling pathway.

  3. Crystallization and Growth of Colloidal Nanocrystals

    CERN Document Server

    Leite, Edson Roberto

    2012-01-01

    Since the size, shape, and microstructure of nanocrystalline materials strongly impact physical and chemical properties, the development of new synthetic routes to  nanocrystals with controlled composition and morphology is a key objective of the nanomaterials community. This objective is dependent on control of the nucleation and growth mechanisms that occur during the synthetic process, which in turn requires a fundamental understanding of both classical nucleation and growth and non-classical growth processes in nanostructured materials.  Recently, a novel growth process called Oriented Attachment (OA) was identified which appears to be a fundamental mechanism during the development of nanoscale  materials. OA is a special case of aggregation that provides an important route by which nanocrystals grow, defects are formed, and unique—often symmetry-defying—crystal morphologies can be produced. This growth mechanism involves reversible self-assembly of primary nanocrystals followed by reorientati...

  4. Bridgman growth of bismuth tellurite crystals

    Indian Academy of Sciences (India)

    Anhua Wu; Jiayue Xu; Guoxing Qian; Baoliang Lu; Zengwei Ge; Linyao Tang; Xianjun Wu

    2005-10-01

    The photorefractive crystal, Bi2TeO5, was grown by the modified Bridgman method for the first time. High purity Bi2O3 and TeO2 were used as starting materials and were mixed thoroughly with molar ratio of Bi2O3/TeO2 = 1 : 1. Platinum crucible was fabricated with a seed well of 10 mm in diameter and several folds were pressed so that the spontaneous nuclei could be eliminated through competition. The crucible was sealed during the growth so that the evaporation of TeO2 was controlled effectively. By optimizing growth parameters, transparent and crack-free Bi2TeO5 crystal up to 25 mm in diameter and 40 mm in length was grown successfully.

  5. Facile fabrication of dendritic silver structures and their surface enhanced Raman spectroscopic properties

    Indian Academy of Sciences (India)

    Jisheng Yang; Zhengdong Jiang

    2015-01-01

    A simple and efficient approach was developed to fabricate silver dendrites by Cu reducing Ag+ in AgNO3 solution. The growth speed, morphologies and structures of the silver dendrites strongly depend on AgNO3 concentration and reaction time. The silver dendrites were formed from nanosheets and the crystal structure is face-centered cubic. Rhodamine 6G was used as probe molecule to show that the silver dendrites have high sensitivity to surface enhanced Raman spectroscopy response.

  6. Engineering crystal growth of calcium hydrogenphosphate dihydrate

    Energy Technology Data Exchange (ETDEWEB)

    Sikiric, M.; Babic-Ivancic, V. [Institut Rudjer Boskovic, Zagreb (Croatia); Milat, O. [Zagreb Univ. (Croatia). Inst. za Fiziku; Sarig, S.; Fueredi-Milhofer, H. [Hebrew Univ., Jerusalem (Israel). Inst. of Applied Chemistry

    2001-07-01

    The factors underlying calcium hydrogenphosphate dihydrate (CaHPO{sub 4}.2H{sub 2}O, DCPD) interactions with several structurally different additives: glutamic and aspartic acid, sodium citrate, hexaammonium tetrapolyphosphate, calcium phytate and polyaspartic acid were studied. DCPD crystals were prepared under controlled conditions by fast mixing of the anionic and cationic reactant solutions and subsequent growth without further stirring in the course of 24 hours at 37 C. The initial conditions were c(CaCl{sub 2}) = c(Na{sub 2}HPO{sub 4}) = 0.021 mol dm{sup -3}, c(NaCl) = 0.3 mol dm{sup -3}, pH{sub i} 5.5. The respective additive was added to the anionic component prior to pH adjustment. Crystals were characterized by X-ray diffraction, while their morphology was observed by optical and scanning electron microscopy (SEM). The Miller indices of the crystal faces were determined from SEM micrographs, after the orientation of the most prominent face was ascertained by the Weissenberg method. Mechanism of additive-DCPD crystals interaction depends on size and structure of additive molecule, structural fit between organic molecule and the ionic structure of particular crystal face. Small molecules (ions) specifically adsorb on lateral faces by electrostatic interactions, while macromolecules and molecules with hindered structure specifically adsorb on dominant (010) face, for which certain degree of structural fit is necessary. (orig.)

  7. Growth of piezoelectric crystals by Czochralski method

    OpenAIRE

    Cochet-Muchy, D.

    1994-01-01

    The Czochralski method is one of the most widely used industrial technique to grow single-crystals, since it applies to a very large range of compounds, such as semiconductors, oxides, fluorides, etc... Many exhibit piezoelectric properties and some of them find applications in Surface-Acoustic-Waves or Bulk-Acoustic-Waves devices. That explains the large amount of work made on the development of the corresponding growth processes and the high levels of production achieved in the world today....

  8. Sealed silica pressure ampoules for crystal growth

    Science.gov (United States)

    Holland, L. R.

    1984-01-01

    The properties of vitreous silica and the mechanics of thick walled pressure vessels are reviewed with regard to the construction of sealed silica crucibles such as are used in the growth of mercury-cadmium telluride crystals. Data from destructive rupture tests are reported, failure modes discussed, and recommendations for design given. Ordinary commercial clear vitreous silica from flame fused quartz can withstand a surface stress of 20 MPa or more in this application.

  9. Studying Crystal Growth With the Peltier Effect

    Science.gov (United States)

    Larsen, David J., Jr.; Dressler, B.; Silberstein, R. P.; Poit, W. J.

    1986-01-01

    Peltier interface demarcation (PID) shown useful as aid in studying heat and mass transfer during growth of crystals from molten material. In PID, two dissimilar "metals" solid and liquid phases of same material. Current pulse passed through unidirectionally solidifying sample to create rapid Peltier thermal disturbance at liquid/solid interface. Disturbance, measured by thermocouple stationed along path of solidification at or near interface, provides information about position and shape of interface.

  10. Rapid growth of nickel dendrite in highly undercooled Ni-Mo alloys

    Institute of Scientific and Technical Information of China (English)

    姚文静; 魏炳波

    2003-01-01

    Ni-39.3%Mo, Ni-45%Mo hypoeutectic alloys and Ni-47.7%Mo eutectic alloy have been rapidly solidified with different droplet sizes by containerless processing in a drop tube. For Ni-39.3%Mo hypoeutectic alloy, which corresponds to the maximum solid solubility of nickel phase, the solidification microstructure is characterized by nickel dendrite plus (Ni+NiMo) eutectic structure. The undercooling of this alloy up to 182 K has been realized in the experiments. With an increase in undercooling, the dendritic microstructure is refined. The microstructural evolution of primary Ni phase in Ni-45%Mo hypoeutectic alloy evolves from remelted dendrite to equiaxed grains, whereas Ni-47.7%Mo eutectic alloy exhibits a structural transition from lamellar eutectic to anomalous eutectic. Theoretical analyses indicate that, for Ni-39.3%Mo, Ni-45%Mo and Ni-47.7%Mo alloys, the nickel phase shows a transition from solutal-diffusion-controlled growth to thermal-diffusion-controlled growth at undercoolings of 66.6, 81.9 and 85.0 K. The critical transition temperature decreases with a reduction in the nickel content.

  11. In situ observation of NaBi(WO4)2 dendrite growth and the study on microstructure of solidification

    Institute of Scientific and Technical Information of China (English)

    AI Fei; HONG Yong; JIN WeiQing; LUO HaoSu; LIU Yan; PAN XiuHong

    2007-01-01

    The dendrite growth process of transparent NaBi(WO4)2 with small prandtl and high melting point was studied by using the in-situ observation system. According to the dynamic images and detailed information, there are two kinds of restriction effect on the dendrite growth, the competition between arms and branches and the convection in the melt. The dendrite growth rate was time dependent, and the rate of arm growth reached the maximum 5.8 mm/s in the diffusive-advective region and rapidly decreased in the diffusive-convective region. The growth rate of branch had the same change trends as the arm's. Based on the EPMA-EDS data of solidification structure of quenched NaBi(WO4)2 melt, it was found that there were component differences from stoichiometric concentration in the melt near the interface during the growth process.

  12. In situ observation of NaBi(WO4)2 dendrite growth and the study on microstructure of solidification

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The dendrite growth process of transparent NaBi(WO4)2 with small prandtl and high melting point was studied by using the in-situ observation system. According to the dynamic images and detailed information, there are two kinds of restriction effect on the dendrite growth, the competition between arms and branches and the convection in the melt. The dendrite growth rate was time dependent, and the rate of arm growth reached the maximum 5.8 mm/s in the diffusive-advective region and rapidly decreased in the diffusive-convective region. The growth rate of branch had the same change trends as the arm’s. Based on the EPMA-EDS data of solidifica- tion structure of quenched NaBi(WO4)2 melt, it was found that there were compo- nent differences from stoichiometric concentration in the melt near the interface during the growth process.

  13. Pattern selection in a boundary-layer model of dendritic growth in the presence of impurities

    Science.gov (United States)

    Karma, A.; Kotliar, B. G.

    1985-01-01

    Presently analyzed, in the context of a boundary-layer model, is the problem of pattern selection in dendritic growth in a situation where impurities are present in the undercooled liquid. It is found that the tip-velocity selection criterion that has been proposed recently for the geometrical model and the boundary-layer model of a pure substance can be extended, in a nontrivial way, to this more complex situation where two coupled diffusion fields (temperature and solute) determine the interface dynamics. This model predicts a sharp enhancement of tip velocity in good qualitative agreement with experiment. This agreement is consistent with the conjecture that a solvability condition can be used to determine the operating point of the dendrite in the full nonlocal problem.

  14. Electromagnetic induction heating for single crystal graphene growth: morphology control by rapid heating and quenching.

    Science.gov (United States)

    Wu, Chaoxing; Li, Fushan; Chen, Wei; Veeramalai, Chandrasekar Perumal; Ooi, Poh Choon; Guo, Tailiang

    2015-03-12

    The direct observation of single crystal graphene growth and its shape evolution is of fundamental importance to the understanding of graphene growth physicochemical mechanisms and the achievement of wafer-scale single crystalline graphene. Here we demonstrate the controlled formation of single crystal graphene with varying shapes, and directly observe the shape evolution of single crystal graphene by developing a localized-heating and rapid-quenching chemical vapor deposition (CVD) system based on electromagnetic induction heating. Importantly, rational control of circular, hexagonal, and dendritic single crystalline graphene domains can be readily obtained for the first time by changing the growth condition. Systematic studies suggest that the graphene nucleation only occurs during the initial stage, while the domain density is independent of the growth temperatures due to the surface-limiting effect. In addition, the direct observation of graphene domain shape evolution is employed for the identification of competing growth mechanisms including diffusion-limited, attachment-limited, and detachment-limited processes. Our study not only provides a novel method for morphology-controlled graphene synthesis, but also offers fundamental insights into the kinetics of single crystal graphene growth.

  15. Web-dendritic ribbon growth. Quarterly report, 1 January 1976--31 March 1976. USC solar report No. Q-2

    Energy Technology Data Exchange (ETDEWEB)

    Hilborn, R.B. Jr.; Faust, J.W. Jr.

    1976-03-17

    The purpose of this investigation is to develop web-dendritic process methods that will: (1) minimize the cost of processing silicon into ribbons of solar cell quality with a terrestrial energy conversion efficiency greater than 10 percent, and (2) be suitable for large quantity production. The report for this second quarter describes the work of the program during this period and presents the plan for the program for the full length of the contract. Work is described on: (1) the procedures used to calibrate and operate the web-dendritic growth furnace; (2) use of the furnace to grow web-dendritic ribbon; (3) considerations applied for the thermal analysis and modeling of the web-dendritic growth system; and (4) procedures, facilities, and initial results for the structural and electrical characterization of web material. (WDM)

  16. Growth of the (001 face of borax crystals

    Directory of Open Access Journals (Sweden)

    Suharso Suharso

    2010-06-01

    Full Text Available he growth rates of borax crystals from aqueous solutions in the (001 direction at various relative supersaturations were measured using in situ cell optical microscopy method. The result shows that the growth mechanism of the (001 face of borax crystal at temperature of 20 °C is spiral growth mechanism.   Keywords: Growth mechanism, borax.

  17. Growth of the (001) face of borax crystals

    OpenAIRE

    Suharso, Suharso

    2010-01-01

    he growth rates of borax crystals from aqueous solutions in the (001) direction at various relative supersaturations were measured using in situ cell optical microscopy method. The result shows that the growth mechanism of the (001) face of borax crystal at temperature of 20 °C is spiral growth mechanism.   Keywords: Growth mechanism, borax.

  18. Enhancement of Amygdaloid Neuronal Dendritic Arborization by Fresh Leaf Juice of Centella asiatica (Linn during Growth Spurt Period in Rats

    Directory of Open Access Journals (Sweden)

    K. G. Mohandas Rao

    2009-01-01

    Full Text Available Centella asiatica (CeA is a creeping herb, growing in moist places in India and other Asian Countries. Ayurvedic system of medicine, an alternate system of medicine in India, uses leaves of CeA for memory enhancement. Here, we have investigated the role of CeA fresh leaf juice treatment during growth spurt period of rats on dendritic morphology of amygdaloid neurons, one of the regions concerned with learning and memory. The present study was conducted on neonatal rat pups. The rat pups (7-days-old were fed with 2, 4 and 6 ml/kg body of fresh leaf juice of CeA for 2, 4 and 6 weeks. After the treatment period, the rats were killed, brains removed and amygdaloid neurons impregnated with Silver nitrate (Golgi staining. Amygdaloid neurons were traced using camera lucida and dendritic branching points (a measure of dendritic arborization and intersections (a measure dendritic length quantified. These data were compared with those of age-matched control rats. The results showed a significant increase in dendritic length (intersections and dendritic branching points along the length of dendrites of the amygdaloid neurons of rats treated with 4 and 6 ml/kg body weight/day of CeA for longer periods of time (i.e. 4 and 6 weeks. We conclude that constituents/active principles present in CeA fresh leaf juice has neuronal dendritic growth stimulating property; hence it can be used for enhancing neuronal dendrites in stress and other neurodegenerative and memory disorders.

  19. The impact of space research on semiconductor crystal growth technology

    Science.gov (United States)

    Witt, A. F.

    1983-01-01

    Crystal growth experiments in reduced gravity environment and related ground-based research have contributed significantly to the establishment of a scientific basis for semiconductor growth from the melt. NASA-sponsored research has been instrumental in the introduction of heat pipes for heat and mass transfer control in crystal growth and in the development of magnetic field induced melt stabilization, approaches primarily responsible for recent advances in crystal growth technology.

  20. In-situ detection of growth striations by crystallization electromotive force measurement during Czochralski crystal growth

    Science.gov (United States)

    Zhu, Yunzhong; Ma, Decai; Long, Siwei; Tang, Feng; Lin, Shaopeng; Wang, Biao

    2017-10-01

    Growth striations, as macrodefects of crystalline materials, are mainly caused by convection and temperature fluctuations in growth interface. For decades, striations have been widely regarded as an inherent problem. Even in the well-developed Czochralski method, the striation formation process is difficult to inspect in situ. In view of this long-standing issue, after systematically studying the temperature, weight, and output power during crystal growth and numerically modeling the growth process, we found that the regularity of the growth interface electromotive force (GEMF) is related to the distribution of striations. Furthermore, the GEMF quantifies interface fluctuations (711.2 s, 16.6 μm) and thermal hysteresis (107 s), presenting finer details than those provided by a thermocouple and a load cell. In this paper, GEMF is found to be an outstanding choice for monitoring the crystal growth status in real time. As an additional feedback, a new automatic control method could be developed for reducing growth striations and promoting crystal quality.

  1. Physicochemical principles of high-temperature crystallization and single crystal growth methods

    Science.gov (United States)

    Bagdasarov, Kh. S.

    The mechanisms of crystal growth are reviewed, with attention given to the physicochemical reactions taking place in the melt near the phase boundary; phenomena determining physical and chemical kinetics directly at the growth front; solid-phase processes occurring within the crystal. Methods for growing refractory single crystals are discussed with particular reference to the Verneuil method, zone melting, Czhochralskii growth, horizontal directional solidification, and the Stockbarger method. Methods for growing crystals of complex geometrical shapes are also discussed.

  2. Advances in the understanding of crystal growth mechanisms

    CERN Document Server

    Nishinaga, T; Harada, J; Sasaki, A; Takei, H

    1997-01-01

    This book contains the results of a research project entitled Crystal Growth Mechanisms on an Atomic Scale, which was carried out for 3 years by some 72 reseachers. Until recently in Japan, only the technological aspects of crystal growth have been emphasized and attention was paid only to its importance in industry. However the scientific aspects also need to be considered so that the technology of crystal growth can be developed even further. This project therefore aimed at understanding crystal growth and the emphasis was on finding growth mechanisms on an atomic scale.

  3. Single crystal growth and anisotropic crystal-fluid interface tension in soft colloidal systems

    NARCIS (Netherlands)

    Nguyen, V.D.; Hu, Z.; Schall, P.

    2011-01-01

    We measure the anisotropy of the crystal-fluid interfacial free energy in soft colloidal systems. A temperature gradient is used to direct crystal nucleation and control the growth of large single crystals in order to achieve well-equilibrated crystal-fluid interfaces. Confocal microscopy is used to

  4. CRYSTAL GROWTH OF RARE EARTH COMPOUNDS IN CLOSED SYSTEM

    OpenAIRE

    1991-01-01

    Remarkable improvements have been made on the crystal growth of rare earth pnictides and chalchogenides by the development of new growth technique and the construction of several new equipments for the crystal growth such as electron beam welding system of tungsten crucible provided with large glove box and vacuum HF furnace. This system has really worked on obtaining excellent quality of single crystals and made easier to explore unknown materials of rare earth compounds. Interesting and att...

  5. Growth of Hydroxyapatite Crystal in the Presence of Origanic Film

    Institute of Scientific and Technical Information of China (English)

    Yong LIU; Suping HUANG; Xiaohong DAN; Kechao ZHOU

    2004-01-01

    The growth of hydroxyapatite (Hap) crystal in the presence of hexadecylamine was investigated. Due to its high polarity and high charge density, the organic film could increase the ion supersaturation on its surface. Therefore the growth of pure Hap crystals was accelerated. Moreover, the positive headgroups of the organic film could act as recognized nucleation sites and orient the growth of Hap crystals along thedirection.

  6. Anion-switchable supramolecular gels for controlling pharmaceutical crystal growth

    Science.gov (United States)

    Foster, Jonathan A.; Piepenbrock, Marc-Oliver M.; Lloyd, Gareth O.; Clarke, Nigel; Howard, Judith A. K.; Steed, Jonathan W.

    2010-12-01

    We describe the use of low-molecular-weight supramolecular gels as media for the growth of molecular crystals. Growth of a range of crystals of organic compounds, including pharmaceuticals, was achieved in bis(urea) gels. Low-molecular-weight supramolecular gelators allow access to an unlimited range of solvent systems, in contrast to conventional aqueous gels such as gelatin and agarose. A detailed study of carbamazepine crystal growth in four different bis(urea) gelators, including a metallogelator, is reported. The crystallization of a range of other drug substances, namely sparfloxacin, piroxicam, theophylline, caffeine, ibuprofen, acetaminophen (paracetamol), sulindac and indomethacin, was also achieved in supramolecular gel media without co-crystal formation. In many cases, crystals can be conveniently recovered from the gels by using supramolecular anion-triggered gel dissolution; however, crystals of substances that themselves bind to anions are dissolved by them. Overall, supramolecular gel-phase crystallization offers an extremely versatile new tool in pharmaceutical polymorph screening.

  7. Crystal growth in zinc borosilicate glasses

    Science.gov (United States)

    Kullberg, Ana T. G.; Lopes, Andreia A. S.; Veiga, João P. B.; Monteiro, Regina C. C.

    2017-01-01

    Glass samples with a molar composition (64+x)ZnO-(16-x)B2O3-20SiO2, where x=0 or 1, were successfully synthesized using a melt-quenching technique. Based on differential thermal analysis data, the produced glass samples were submitted to controlled heat-treatments at selected temperatures (610, 615 and 620 °C) during various times ranging from 8 to 30 h. The crystallization of willemite (Zn2SiO4) within the glass matrix was confirmed by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). Under specific heat-treatment conditions, transparent nanocomposite glass-ceramics were obtained, as confirmed by UV-vis spectroscopy. The influence of temperature, holding time and glass composition on crystal growth was investigated. The mean crystallite size was determined by image analysis on SEM micrographs. The results indicated an increase on the crystallite size and density with time and temperature. The change of crystallite size with time for the heat-treatments at 615 and 620 °C depended on the glass composition. Under fixed heat-treatment conditions, the crystallite density was comparatively higher for the glass composition with higher ZnO content.

  8. Brain-derived neurotrophic factor mediates activity-dependent dendritic growth in nonpyramidal neocortical interneurons in developing organotypic cultures.

    Science.gov (United States)

    Jin, Xiaoming; Hu, Hang; Mathers, Peter H; Agmon, Ariel

    2003-07-02

    Brain-derived neurotrophic factor (BDNF) promotes postnatal maturation of GABAergic inhibition in the cerebral and cerebellar cortices, and its expression and release are enhanced by neuronal activity, suggesting that it acts in a feedback manner to maintain a balance between excitation and inhibition during development. BDNF promotes differentiation of cerebellar, hippocampal, and neostriatal inhibitory neurons, but its effects on the dendritic development of neocortical inhibitory interneurons remain unknown. Here, we show that BDNF mediates depolarization-induced dendritic growth and branching in neocortical interneurons. To visualize inhibitory interneurons, we biolistically transfected organotypic cortical slice cultures from neonatal mice with green fluorescent protein (GFP) driven by the glutamic acid decarboxylase (GAD)67 promoter. Nearly all GAD67-GFP-expressing neurons were nonpyramidal, many contained GABA, and some expressed markers of neurochemically defined GABAergic subtypes, indicating that GAD67-GFP-expressing neurons were GABAergic. We traced dendritic trees from confocal images of the same GAD67-GFP-expressing neurons before and after a 5 d growth period, and quantified the change in total dendritic length (TDL) and total dendritic branch points (TDBPs) for each neuron. GAD67-GFP-expressing neurons growing in control medium exhibited a 20% increase in TDL, but in 200 ng/ml BDNF or 10 mm KCl, this increase nearly doubled and was accompanied by a significant increase in TDBPs. Blocking action potentials with TTX did not prevent the BDNF-induced growth, but antibodies against BDNF blocked the growth-promoting effect of KCl. We conclude that BDNF, released by neocortical pyramidal neurons in response to depolarization, enhances dendritic growth and branching in nearby inhibitory interneurons.

  9. Bonding Energy and Growth Habit of Lithium Niobate Single Crystals

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    On the basis of crystallographic structure of lithium niobate (LN), the bonding energy was quantitatively calculated by the bond valence sum model, which was employed to investigate the crystal growth. A possible relationship between the crystal growth habit and chemical bonding energy of LN crystals are found. It is found that the higher the bond energy, the slower the growth rate, and the more important the plane. The analytical results indicate that (012) plane is the most influential face for the LN crystal growth, which consists well with the standard card (JCPDS Card: 20-0631) and our previous experimental observation. The current work shows that the chemical bond analysis of LN crystals allows us to predict its growth habit and thus to obtain the expected morphology during the spontaneous growth.

  10. Crystal growth in fluid flow: Nonlinear response effects

    Science.gov (United States)

    Peng, H. L.; Herlach, D. M.; Voigtmann, Th.

    2017-08-01

    We investigate crystal-growth kinetics in the presence of strong shear flow in the liquid, using molecular-dynamics simulations of a binary-alloy model. Close to the equilibrium melting point, shear flow always suppresses the growth of the crystal-liquid interface. For lower temperatures, we find that the growth velocity of the crystal depends nonmonotonically on the shear rate. Slow enough flow enhances the crystal growth, due to an increased particle mobility in the liquid. Stronger flow causes a growth regime that is nearly temperature-independent, in striking contrast to what one expects from the thermodynamic and equilibrium kinetic properties of the system, which both depend strongly on temperature. We rationalize these effects of flow on crystal growth as resulting from the nonlinear response of the fluid to strong shearing forces.

  11. Nucleation and crystal growth in laser patterned lines in glasses

    Directory of Open Access Journals (Sweden)

    Takayuki Komatsu

    2016-07-01

    Full Text Available Laser-induced crystallization is a new method for the design and control of the crystallization of glasses and opens a new door in the study of nucleation and crystal growth in glasses. Nonlinear optical Sm-doped -BaB2O4 (-BBO crystal lines were patterned by continuous wave Yb:YVO4 fiber laser (wavelength 1080 nm in 8Sm2O3-42BaO-50B2O3 glass as an example, and nucleation and crystal growth behaviors in the laser-patterned bending and crossing lines were examined. It was confirmed that the growth of c-axis oriented -BBO crystals follows along the laser scanning direction even if laser scanning direction changes. The model of self-organized homo-epitaxial crystal growth was demonstrated for the orientation of -BBO crystals at the crossing point of two lines, in which the first crystal line at the crossing point acts as nucleation site for the second crystal line. This study proposes a new crystal growth technology.

  12. Reinvestigation of growth of 'L-valine zinc sulphate' crystal.

    Science.gov (United States)

    Srinivasan, Bikshandarkoil R; Jyai, Rita N

    2014-01-01

    A reinvestigation of the growth of l-valine zinc sulphate crystal is reported. The slow evaporation of an aqueous solution containing l-valine and zinc sulphate heptahydrate results in the fractional crystallization of l-valine and not the organic inorganic hybrid nonlinear optical l-valine zinc sulphate crystal, as reported by Puhal Raj and Ramachandra Raja (2012).

  13. Stability of melt crystal growth under microgravity conditions

    Science.gov (United States)

    Tatarchenko, V. A.

    The conception of dynamic stability of melt crystal growth has been developed. The method based on the Lyapunov stability theory has been used to the study stability of crystallization by capillary shaping techniques including Czokhralsky, Stepanov, Kiropoulos, Verneuil and floating zone methods. Preliminary results of the stability analysis of crystallization by floating zone technique under microgravity conditions are presented here.

  14. Differential activation of dendritic cells by nerve growth factor and brain-derived neurotrophic factor.

    Science.gov (United States)

    Noga, O; Peiser, M; Altenähr, M; Knieling, H; Wanner, R; Hanf, G; Grosse, R; Suttorp, N

    2007-11-01

    Neurotrophins are involved in inflammatory reactions influencing several cells in health and disease including allergy and asthma. Dendritic cells (DCs) play a major role in the induction of inflammatory processes with an increasing role in allergic diseases as well. The aim of this study was to investigate the influence of neurotrophins on DC function. Monocyte-derived dendritic cells were generated from allergic and non-allergic donors. Neurotrophin receptors were demonstrated by western blotting, flow cytometry and fluorescence microscopy. Activation of small GTPases was evaluated by pull-down assays. DCs were incubated with nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) and supernatants were collected for measurement of IL-4, IL-6, IL-10, IL-12p70, TNF-alpha and TGF-beta. Receptor proteins were detectable by western blot, fluorescence activated cell sorting analysis and fluorescence microscopy. Signalling after neurotrophin stimulation occurred in a ligand-specific pattern. NGF led to decreased RhoA and increased Rac activation, while BDNF affected RhoA and Rac activity in a reciprocal fashion. Cells of allergics released a significantly increased amount of IL-6, while for healthy subjects a significantly higher amount of IL-10 was found. These data indicate that DCs are activated by the neurotrophins NGF and BDNF by different pathways in a receptor-dependant manner. These cells then may initiate inflammatory responses based on allergic sensitization releasing preferred cytokines inducing tolerance or a T-helper type 2 response.

  15. Thermal diffusion dominated dendritic growth — an analysis of the wall proximity effect

    Science.gov (United States)

    Pines, Vladimir; Chait, Arnon; Zlatkowski, Marianne

    1996-09-01

    It is demonstrated that using a simple correction to the original Ivantsov solution to account for wall proximity effects is sufficient to describe the Peclet number microgravity data of Glicksman et al. [M.E. Glicksman, M.B. Koss and E.A. Winsa, Phys. Rev. Lett. 73 (1994) 573; M.E. Glicksman, M.B. Koss, L.T. Bushnell, J.C. LaCombe and E.A. Winsa, ISLJ International 35 (1995) 1216; MRS Fall Meeting, Symp. P, Boston MA, 1995, in press] at low supercooling. The analytical correction provides for the enhanced diffusive heat transfer when the thermal diffusion length becomes comparable to the physical chamber dimension. The wall proximity effect is also responsible for the existence of a lower supercooling limit below which the dendrite cannot grow in a steady-state manner. It is concluded that Glicksman's USMP-2 microgravity data is thermal diffusion dominated and thus entirely appropriate for comparison with dendritic growth theories.

  16. Simulation of Single Crystal Growth: Heat and Mass Transfer

    CERN Document Server

    Zhmakin, A I

    2015-01-01

    The heat transfer (conductive, convective, radiative) and the related problems (the unknown phase boundary fluid/crystal, the assessment of the quality of the grown crystals) encountered in the melt and vapour growth of single crystal as well as the corresponding macroscopic models are reviewed. The importance of the adequate description of the optical crystal properties (semitransparency, absorption, scattering, refraction, diffuse and specular reflecting surfaces) and their effect on the heat transfer is stressed. The problems of the code verification and validation are discussed; differences between the crystal growth simulation codes intended for the research and for the industrial applications are indicated.

  17. On the growth of calcium tartrate tetrahydrate single crystals

    Indian Academy of Sciences (India)

    X Sahaya Shajan; C Mahadevan

    2004-08-01

    Calcium tartrate single crystals were grown using silica gel as the growth medium. Calcium formate mixed with formic acid was taken as the supernatant solution. It was observed that the nucleation density was reduced and the size of the crystals was improved to a large extent compared to the conventional way of growing calcium tartrate crystals with calcium chloride. The role played by formate–formic acid on the growth of crystals is discussed. The grown crystals were characterized by atomic absorption spectroscopy (AAS), X-ray diffraction analysis (XRD), microhardness measurement, Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG) and differential thermal analysis (DTA). The results obtained are compared with the previous work.

  18. Nucleation and crystal growth in laser patterned lines in glasses

    OpenAIRE

    Takayuki Komatsu; Tsuyoshi Honma

    2016-01-01

    Laser-induced crystallization is a new method for the design and control of the crystallization of glasses and opens a new door in the study of nucleation and crystal growth in glasses. Nonlinear optical Sm-doped -BaB2O4 (-BBO) crystal lines were patterned by continuous wave Yb:YVO4 fiber laser (wavelength 1080 nm) in 8Sm2O3-42BaO-50B2O3 glass as an example, and nucleation and crystal growth behaviors in the laser-patterned bending and crossing lines were examined. It was confirmed that the...

  19. On the elastic contribution to crystal growth in complex environments

    Science.gov (United States)

    Gadomski, A.; Siódmiak, J.

    2005-03-01

    Based on a number of experimental studies, we propose to consider how elastic interactions between a crystal and its surroundings change crystal growing conditions. To aim to do this, we analyze the influence of some nonequilibrium modification of the Gibbs-Thomson thermodynamic condition, prescribed at the crystal boundary, on some properties of a kinetic model of protein crystal growth in a mass-convection regime. Next, to draw the physical picture more realistically, we study the influence of a certain stochastic perturbation on the crystal growth rate. To fulfill the task we apply the description of crystal growth in terms of nonequilibrium thermodynamics at a mesoscopic level. The proposed model offers a quite comprehensive picture of the formation of modern organic crystalline materials such as non-Kossel crystals.

  20. Space manufacturing in an automated crystal growth facility

    Science.gov (United States)

    Quinn, Alberta W.; Herrmann, Melody C.; Nelson, Pamela J.

    1989-01-01

    An account is given of a Space Station Freedom-based robotic laboratory system for crystal growth experiments; the robot must interface with both the experimental apparatus and such human input as may be required for control and display. The goal of the system is the simultaneous growth of several hundred protein crystals in microgravity. The robot possesses six degrees-of-freedom, allowing it to efficiently manipulate the cultured crystals as well as their respective growth cells; the crystals produced are expected to be of sufficiently high quality for complete structural determination on the basis of XRD.

  1. Preparation for microgravity science investigation of compound semiconductor crystal growth

    Science.gov (United States)

    Fripp, A. L.; Debnam, W. J.; Clark, I. O.; Crouch, R. K.; Carlson, F. M.

    1985-01-01

    Preparatory work on Bridgman directional solidification (BDS) of PbSnTe crystals prior to microgravity crystal growth experiments on Shuttle flights are reported. Gravitational effects become important in crystal growth when density gradients are present. The situation is critical in BDS of PbSnTe because of the necessity of obtaining homogeneous compositional distributions, which can be disturbed when convective processes occur. Numerical models have been defined which quantify the effects of convection in the crystal growth solution. The models were verified by earth-based crystal-growth tests in a two-zone furnace using equal concentrations of each of the elements. Data are provided to demonstrate the differences in composition among crystals grown at different orientations to the gravitational field vector.

  2. A PKC-dependent recruitment of MMP-2 controls semaphorin-3A growth-promoting effect in cortical dendrites.

    Directory of Open Access Journals (Sweden)

    Bertrand Gonthier

    Full Text Available There is increasing evidence for a crucial role of proteases and metalloproteinases during axon growth and guidance. In this context, we recently described a functional link between the chemoattractive Sema3C and Matrix metalloproteinase 3 (MMP3. Here, we provide data demonstrating the involvement of MMP-2 to trigger the growth-promoting effect of Sema3A in cortical dendrites. The in situ analysis of MMP-2 expression and activity is consistent with a functional growth assay demonstrating in vitro that the pharmacological inhibition of MMP-2 reduces the growth of cortical dendrites in response to Sema3A. Hence, our results suggest that the selective recruitment and activation of MMP-2 in response to Sema3A requires a PKC alpha dependent mechanism. Altogether, we provide a second set of data supporting MMPs as effectors of the growth-promoting effects of semaphorins, and we identify the potential signalling pathway involved.

  3. Effect of growth hormone on the immune function of dendritic cells

    Institute of Scientific and Technical Information of China (English)

    LIU Qiu-liang; WANG Yi-sheng; WANG Jia-xiang

    2010-01-01

    Background Dendritic cells (DCs) are one of the most important antigen presenting cells in the human body, and DCs at various stages of maturation possess different or even opposite functions. The aim of this study was to investigate the influence of growth hormones on the functional status of cord blood-derived DCs encompassing immunophenotype, ability to excrete interleukin (IL)-12 and provoke autologous leukomonocyte.Methods Mononuclear cells were isolated from fresh cord blood, with IL-4 and granulocyte-macrophage colony-stimulating factor (GM-CSF) used to induce and stimulate the mononuclear cells. Growth hormone at different concentrations was used to modify DCs, and then DCs morphology, number and growth status were observed. The immunophenotype of DCs was detected with a flow cytometer. The concentration of IL-12 in the DCs supernatant was determined by enzyme linked immunosorbent assay (ELISA) and DCs functional status was evaluated by autologous mixed lymphocyte reactions. Results Mononuclear cells from cord blood can be differentiated into DCs by cytokine induction and growth hormone modification. With the increase in growth hormone concentrations (5-100 μ g/L), the expression of DCs HLA-DR, CD1α, CD80 and CD83 were significantly increased (P<0.05). The ability of DCs to secrete IL-12 was significantly improved (P <0.05), and the ability of DCs to activate autologous lymphocytes was significantly enhanced (P <0.05). Pegvisomant was able to ablate the effects of growth hormone on DCs.Conclusions Growth hormone may facilitate DCs induction and maturation, and improve the reproductive activity of autologous lymphocytes in a dose-dependent manner. Growth hormone may serve as a factor of modifying DCs to achieving maturity.

  4. Issues in the growth of bulk crystals of infrared materials

    Science.gov (United States)

    Bachmann, K. J.; Golowsky, H.

    1987-01-01

    Attention is given to the relevant criteria governing materials choice in the growth of IR optoelectronic bulk single crystals of III-V and II-VI alloy and I-III-VI2 compound types. The most important considerations concern the control of crystal purity, microstructural perfection, stoichiometry, and uniformity during crystal growth, as well as the control of surface properties in wafer fabrication. Specific examples are given to illustrate the problems encountered and their preferred solutions.

  5. Computing the crystal growth rate by the interface pinning method

    DEFF Research Database (Denmark)

    Pedersen, Ulf Rørbæk; Hummel, Felix; Dellago, Christoph

    2015-01-01

    -phase configurations are stabilized by adding a spring-like bias field coupling to an order-parameter that discriminates between the two phases. Crystal growth is a Smoluchowski process and the crystal growth rate can, therefore, be computed from the terminal exponential relaxation of the order parameter. The approach...... from first principles. A generalized version of the method may be used for computing the rates of crystal nucleation or other rare events....

  6. Hard sphere crystal nucleation and growth near large spherical impurities

    Science.gov (United States)

    de Villeneuve, V. W. A.; Verboekend, D.; Dullens, R. P. A.; Aarts, D. G. A. L.; Kegel, W. K.; Lekkerkerker, H. N. W.

    2005-11-01

    We report how large spherical impurities affect the nucleation and growth of hard sphere colloidal crystals. Both the impurities and the colloids are fluorescently labelled polymethylmetacrylate particles and are dispersed in an optically and density matching solvent mixture. Crystal growth, initiated either at the impurity surface, or at the sample bottom, was studied by imaging sequences of two-dimensional xy-slices in the plane of the impurity's centre of mass with a laser scanning confocal microscope. At least two factors determine whether a large impurity can function as a seed for heterogeneous nucleation: timescales and impurity curvature. The curvature needs to be sufficiently low for crystal nuclei to form on the impurity surface. If bulk crystal growth has already approached the impurity, bulk growth is dominant over growth of crystallites on the impurity surface. Such surface crystallites eventually reorient to adapt to the overall bulk crystal symmetry.

  7. Needs and Opportunities in Crystal Growth.

    Science.gov (United States)

    Mroczkowski, Stanley

    1980-01-01

    Presents a survey of the scientific basis for single crystals production, discussing some of the theoretical and experimental advances in the area. Future prospects for semiconductors, magnetic lasers, nonlinear optics, piezoelectrics, and other crystals are surveyed. (Author/CS)

  8. Numerical Simulation of Three-Dimensional Dendritic Growth of Alloy: Part I—Model Development and Test

    Science.gov (United States)

    Wang, Weiling; Luo, Sen; Zhu, Miaoyong

    2016-03-01

    To improve the computational efficiency of the three-dimensional (3D) cellular-automaton-finite-volume-method (CA-FVM) model for describing the dendritic growth of alloy, the block-correction technique (BCT) and the parallel computation approach are introduced. Accordingly, a serial of investigations on the efficiency of the optimized codes in dealing with the designed cases for the melt flow and the heat transfer problems is carried out. Moreover, the accuracy of the present codes is evaluated by the comparisons between the solution to the melt flow and the heat transfer problems and the results from analytical equations and the commercial software. Additionally, the capability of the present CA model is evaluated by comparing the steady growth parameters of the equiaxed dendritic tip and the morphology and the secondary dendrite arm spacing (SDAS) of columnar dendrites with the LGK analytical model and the experimental results of the unidirectional solidification of high-carbon steels. The results show that with the introduction of the 3D BCT, the iteration process of the serial tri-diagonal matrix algorithm (TDMA) code changes from the fluctuation type to the smooth one, and thus, the computational cost is reduced significantly. Moreover, the parallel Jacobi code with one two-dimensional (2D) iteration in 3D BCT is proved to be the most efficient one among the codes compiled in the present work, and therefore, accordingly it is employed to simulate the 3D dendritic growth of alloys. The calculated velocity distribution and temperature variation agree well with the results from the analytical equations and the commercial software. The predicted steady tip velocities agree with the LGK analytical model as the undercooling is 6 K to 7 K. Moreover, the predicted columnar dendritic morphology and SDAS of high-carbon Fe-C alloys during the unidirectional solidification agree with the experimental results.

  9. Inhibition mechanism of aspartic acid on crystal growth of hydroxyapatite

    Institute of Scientific and Technical Information of China (English)

    HUANG Su-ping; ZHOU Ke-chao; LI Zhi-you

    2007-01-01

    The effects of aspartic acid on the crystal growth, morphology of hydroxyapatite(HAP) crystal were investigated, and the inhibition mechanism of aspartic acid on the crystal growth of hydroxyapatite was studied. The results show that the crystal growth rate of HAP decreases with the increase of the aspartic acid concentration, and the HAP crystal is thinner significantly compared with that without amino acid, which is mainly due to the (10(-)10) surface of HAP crystal being inhibited by the aspartic acids. The calculation analysis indicates that the crystal growth mechanism of HAP, following surface diffusion controlled mechanism, is not changed due to the presence of aspartic acid. AFM result shows that the front of terrace on vicinal growth hillocks is pinned, which suggests that the aspartic acid is adsorbed onto the (10(-)10) surface of HAP and interacts with the Ca2+ ions of HAP surface, so as to block the growth active sites and result in retarding of the growth of HAP crystal.

  10. Single Crystal Growth of Zirconia Utilizing a Skull Melting Technique,

    Science.gov (United States)

    1979-08-01

    help eliminate many crystal growth problems. The flame-fusion apparatus was invented by A. Verneuil 3 over 75 years ago and has been used for growth of...AOAO2 23 OMEAIRDEVLOPENT CNT RI RIFISS AFB NY F /S .7/ NGLE CRYSTAL GROWTH OF Z RONA UT IXZIN A SKULL MELTING TE-SCUl AUG 79 A C MARSHALL, J A ADAMSK...Crucible-less synthesis 50. ABSTRACT (Ceefiw.. - eooe edi. ,.e.eimwd identiby Slek ~b.,) Investigation into the growth of single crystal materials are

  11. Characterization of the Bridgman crystal growth process by radiographic imaging

    Science.gov (United States)

    Fripp, Archibald L.; Debnam, W. J.; Woodell, G. W.; Berry, R. F.; Simchick, R. T.; Sorokach, S. K.; Barber, P. G.

    1991-01-01

    Elemental (Ge) and alloy (PbSnTe) crystal growth that is monitored via radiography to reveal both the interface position and the shape in real time is discussed for both seeded and unseeded growth. It is concluded that the interface position and the actual growth rate of a Bridgman grown crystal is dependent on the growth conditions. The actual growth rate which is a strong function of the degree of supercooling exceeded the pull rate by a factor of greater than two. The interface shape changed from concave to flat to convex during the growth.

  12. Characterization of the Bridgman crystal growth process by radiographic imaging

    Science.gov (United States)

    Fripp, Archibald L.; Debnam, W. J.; Woodell, G. W.; Berry, R. F.; Simchick, R. T.; Sorokach, S. K.; Barber, P. G.

    1991-01-01

    Elemental (Ge) and alloy (PbSnTe) crystal growth that is monitored via radiography to reveal both the interface position and the shape in real time is discussed for both seeded and unseeded growth. It is concluded that the interface position and the actual growth rate of a Bridgman grown crystal is dependent on the growth conditions. The actual growth rate which is a strong function of the degree of supercooling exceeded the pull rate by a factor of greater than two. The interface shape changed from concave to flat to convex during the growth.

  13. Study on buoyancy convection phenomenon in the crystal growth process

    Institute of Scientific and Technical Information of China (English)

    DUAN Li; KANG Qi

    2009-01-01

    Real-time phase shift Mach-Zehnder interference technique,imaging technique,and computer image processing technique were combined to perform a real-time diagnosis of NaCIO3 crystal,which described both the dissolution process end the crystallization process of the NaCIO3 crystal in real-time condition.The dissolution fringes and the growth fringes in the process were obtained.Moreover,a distribution of concentration field in this process was obtained by inversion calculation.Finally,the buoyancy convection phenomenon caused by gravity in the crystal growth process was analyzed.The results showed that this convection phenomenon directly influences the growth rate of each crystal face in the crystal.

  14. Study on buoyancy convection phenomenon in the crystal growth process

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Real-time phase shift Mach-Zehnder interference technique, imaging technique, and computer image processing technique were combined to perform a real-time diagnosis of NaClO3 crystal, which de- scribed both the dissolution process and the crystallization process of the NaClO3 crystal in real-time condition. The dissolution fringes and the growth fringes in the process were obtained. Moreover, a distribution of concentration field in this process was obtained by inversion calculation. Finally, the buoyancy convection phenomenon caused by gravity in the crystal growth process was analyzed. The results showed that this convection phenomenon directly influences the growth rate of each crystal face in the crystal.

  15. Calcite crystal growth rate inhibition by polycarboxylic acids

    Science.gov (United States)

    Reddy, M.M.; Hoch, A.R.

    2001-01-01

    Calcite crystal growth rates measured in the presence of several polycarboxyclic acids show that tetrahydrofurantetracarboxylic acid (THFTCA) and cyclopentanetetracarboxylic acid (CPTCA) are effective growth rate inhibitors at low solution concentrations (0.01 to 1 mg/L). In contrast, linear polycarbocylic acids (citric acid and tricarballylic acid) had no inhibiting effect on calcite growth rates at concentrations up to 10 mg/L. Calcite crystal growth rate inhibition by cyclic polycarboxyclic acids appears to involve blockage of crystal growth sites on the mineral surface by several carboxylate groups. Growth morphology varied for growth in the absence and in the presence of both THFTCA and CPTCA. More effective growth rate reduction by CPTCA relative to THFTCA suggests that inhibitor carboxylate stereochemical orientation controls calcite surface interaction with carboxylate inhibitors. ?? 20O1 Academic Press.

  16. Growth and Characterization on PMN-PT-Based Single Crystals

    Directory of Open Access Journals (Sweden)

    Jian Tian

    2014-07-01

    Full Text Available Lead magnesium niobate—lead titanate (PMN-PT single crystals have been successfully commercialized in medical ultrasound imaging. The superior properties of PMN-PT crystals over the legacy piezoelectric ceramics lead zirconate titanate (PZT enabled ultrasound transducers with enhanced imaging (broad bandwidth and improved sensitivity. To obtain high quality and relatively low cost single crystals for commercial production, PMN-PT single crystals were grown with modified Bridgman method, by which crystals were grown directly from stoichiometric melt without flux. For ultrasound imaging application, [001] crystal growth is essential to provide uniform composition and property within a crystal plate, which is critical for transducer performance. In addition, improvement in crystal growth technique is under development with the goals of improving the composition homogeneity along crystal growth direction and reducing unit cost of crystals. In recent years, PIN-PMN-PT single crystals have been developed with higher de-poling temperature and coercive field to provide improved thermal and electrical stability for transducer application.

  17. Growth kinetics of nanometric dendrites in metal-carbon thin films

    Energy Technology Data Exchange (ETDEWEB)

    Corbella, C., E-mail: corbella@ub.edu [FEMAN Research Group, Institute of Nanoscience and Nanotechnology of the Universitat de Barcelona, c/Marti i Franques 1, E-08028 Barcelona (Spain); Echebarria, B.; Ramirez-Piscina, L. [Departament de Fisica Aplicada, Universitat Politecnica de Catalunya, Av. Doctor Maranon 44, E-08028 Barcelona (Spain); Pascual, E.; Andujar, J.L.; Bertran, E. [FEMAN Research Group, Institute of Nanoscience and Nanotechnology of the Universitat de Barcelona, c/Marti i Franques 1, E-08028 Barcelona (Spain)

    2009-10-15

    Tungsten-carbon films deposited by pulsed-DC reactive magnetron sputtering show the formation of a dendritic structure at the nanometric scale. The structure is formed by a combination of a polycrystalline {beta}-W phase together with a non-stoichiometric WC{sub 1-x} phase. The nanodendrites coincide with W-rich zones, whereas C-rich regions are located at the interstices. The characteristics of this nanostructure have been modulated by varying the metal concentration of the films. The composition, structure and morphology were characterized by X-ray photoelectron spectroscopy, electron probe microanalysis, transmission electron microscopy, X-ray diffraction and atomic force microscopy, and the mechanical and tribological properties were evaluated by profilometry, nanoindentation and microscratch. The observed growth pattern is interpreted as the result of nucleation and growth of a W phase into a W-C amorphous matrix, whose growth is controlled by diffusion of carbon. A simulation model based on phase field modelling and presenting similar morphologies is formulated. This special structure combines properties of W and diamond-like carbon films, which enlarges the scope of applications towards self-lubricating hard and low-friction coatings with improved stability.

  18. An assessment of calcite crystal growth mechanisms based on crystal size distributions

    Science.gov (United States)

    Kile, D.E.; Eberl, D.D.; Hoch, A.R.; Reddy, M.M.

    2000-01-01

    Calcite crystal growth experiments were undertaken to test a recently proposed model that relates crystal growth mechanisms to the shapes of crystal size distributions (CSDs). According to this approach, CSDs for minerals have three basic shapes: (1) asymptotic, which is related to a crystal growth mechanism having constant-rate nucleation accompanied by surface-controlled growth; (2) lognormal, which results from decaying-rate nucleation accompanied by surface-controlled growth; and (3) a theoretical, universal, steady-state curve attributed to Ostwald ripening. In addition, there is a fourth crystal growth mechanism that does not have a specific CSD shape, but which preserves the relative shapes of previously formed CSDs. This mechanism is attributed to supply-controlled growth. All three shapes were produced experimentally in the calcite growth experiments by modifying nucleation conditions and solution concentrations. The asymptotic CSD formed when additional reactants were added stepwise to the surface of solutions that were supersaturated with respect to calcite (initial Ω = 20, where Ω = 1 represents saturation), thereby leading to the continuous nucleation and growth of calcite crystals. Lognormal CSDs resulted when reactants were added continuously below the solution surface, via a submerged tube, to similarly supersaturated solutions (initial Ω = 22 to 41), thereby leading to a single nucleation event followed by surface-controlled growth. The Ostwald CSD resulted when concentrated reactants were rapidly mixed, leading initially to high levels of supersaturation (Ω >100), and to the formation and subsequent dissolution of very small nuclei, thereby yielding CSDs having small crystal size variances. The three CSD shapes likely were produced early in the crystallization process, in the nanometer crystal size range, and preserved during subsequent growth. Preservation of the relative shapes of the CSDs indicates that a supply-controlled growth mechanism

  19. Growth and micro-topographical studies of gel grown cholesterol crystals

    Indian Academy of Sciences (India)

    Anit Elizabeth; Cyriac Joseph; M A Ittyachen

    2001-08-01

    Cholesterol (C27H46O) is the most abundant and best-known steroid in the animal kingdom. The in vitro crystallization of this important biomaterial has been attempted by few researchers. Here we are reporting crystallization of pure cholesterol monohydrate crystals in gel medium. It is found that the morphology of the crystals depends on various parameters. The effect of solvent has been studied in detail. The different morphologies observed are fibrous, needle, platelet, dendrite etc. Micro topographical studies have been made and it is found that the crystals grow, at least in the last stage, by spreading of layers. However, at initial stage microcrystals formed and developed into dendrite or needle forms. These one-dimensional crystals developed into platelets and finally thickened. Further studies reveal that micro impurities play a vital role in the development of these crystals as seen by dissolution figures on the crystals. These crystals are characterized by using the XRD and IR spectroscopic methods.

  20. Crystal growth mechanisms of the (0 1 0) face of α-lactose monohydrate crystals

    Science.gov (United States)

    Dincer, T. D.; Ogden, M. I.; Parkinson, G. M.

    2009-04-01

    The growth rates of the (0 1 0) face of α-lactose monohydrate crystals were measured at 30, 40 and 50 °C in the relative supersaturation range 0.55-2.33 in aqueous solutions. The mechanisms of growth were investigated. Spiral growth was found to be the mechanism of growth up to a critical relative supersaturation ( s-1) crit=1.9 at 30 °C. Above the critical relative supersaturation, the crystal growth mechanisms were predicted to change. All growth models fit equally well to the growth rates. No two-dimensional nucleation was observed above critical supersaturation by AFM. On the other hand increased step height and roughness on the edges of steps were observed. It was concluded that the growth mechanism of the (0 1 0) face of α-lactose monohydrate crystal is spiral growth. A parabolic relationship was obtained below critical supersaturation followed by a linear relationship with relative supersaturation.

  1. Chemical Bond Calculations of Crystal Growth of KDP and ADP

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    A novel method was proposed to calculate the crystal morphology (or growth habit) on the basis of chemical bond analysis. All constituent chemical bonds were distinguished as relevant and independent bonds according to their variations during the crystallization process. By employing the current method, the influence of specific growth conditions on the crystal morphology can be considered in the structure analysis process. The ideal morphologies of both KDP (KH2PO4) and ADP (NH4H2PO4) crystals were calculated and compared with our obtained crystallites at room temperature, which validates the present calculation method very well.

  2. Universality classes for unstable crystal growth.

    Science.gov (United States)

    Biagi, Sofia; Misbah, Chaouqi; Politi, Paolo

    2014-06-01

    Universality has been a key concept for the classification of equilibrium critical phenomena, allowing associations among different physical processes and models. When dealing with nonequilibrium problems, however, the distinction in universality classes is not as clear and few are the examples, such as phase separation and kinetic roughening, for which universality has allowed to classify results in a general spirit. Here we focus on an out-of-equilibrium case, unstable crystal growth, lying in between phase ordering and pattern formation. We consider a well-established 2+1-dimensional family of continuum nonlinear equations for the local height h(x,t) of a crystal surface having the general form ∂_{t}h(x,t)=-∇·[j(∇h)+∇(∇^{2}h)]: j(∇h) is an arbitrary function, which is linear for small ∇h, and whose structure expresses instabilities which lead to the formation of pyramidlike structures of planar size L and height H. Our task is the choice and calculation of the quantities that can operate as critical exponents, together with the discussion of what is relevant or not to the definition of our universality class. These aims are achieved by means of a perturbative, multiscale analysis of our model, leading to phase diffusion equations whose diffusion coefficients encapsulate all relevant information on dynamics. We identify two critical exponents: (i) the coarsening exponent, n, controlling the increase in time of the typical size of the pattern, L∼t^{n}; (ii) the exponent β, controlling the increase in time of the typical slope of the pattern, M∼t^{β}, where M≈H/L. Our study reveals that there are only two different universality classes, according to the presence (n=1/3, β=0) or the absence (n=1/4, β>0) of faceting. The symmetry of the pattern, as well as the symmetry of the surface mass current j(∇h) and its precise functional form, is irrelevant. Our analysis seems to support the idea that also space dimensionality is irrelevant.

  3. Growth and defects of explosives crystals

    Science.gov (United States)

    Cady, H. H.

    Large single crystals of PETN, RDX, and TNT can be grown easily from evaporating ethyl acetate solutions. The crystals all share a similar type of defect that may not be commonly recognized. The defect generates conical faces, ideally mosaic crystals, and may account for the 'polymorphs' of TNT and detonator grades of PETN. TATB crystals manufactured by the amination of trichlorotrinitrobenzene in dry toluene entrain two forms of ammonium chloride. One of these forms causes 'worm holes' in the TATB crystals that may be the reason for its unusually low failure diameters. Strained HMX crystals form mechanical twins that can spontaneously revert back to the untwinned form when the straining force is removed. Large strains or temperatures above 100 C lock in the mechanical twins.

  4. Phase Relationship in Phenol-Insulin Crystal Growth System

    Institute of Scientific and Technical Information of China (English)

    梁栋材; 宋浪舟; 万柱礼; 常文瑞

    1994-01-01

    Based on the crystal growth system of rhombohedral 2Zn-insulin,the phase transition ofinsulin crystals has been investigated with the phenol concentration as an independent component.The dia-gram of the phase relationship in this crystal growth system was established,and two points of phase transi-tion were found.The transition point Ⅰ indicates the phase transition between rhombohedral 2Zn-insulin crys-tal and rhombohedral 4Zn-insulin crystal,and these two phases coexist within a narrow region of phenol con-centration (0.028%-0.029% (g/ml)).Point Ⅱ at 0.76%-0.77% (g/ml) of phenol concentration showsthe phase transition between rhombohcdral crystal and monoclinic crystals,and a new phase of monocliniccrystal (B-form monoclinic insulin crystal) has been observed.This paper reports the diagram of phase rela-tionship obtained from our experiments,and analyses and discusses the dependence of phase transition of in-sulin crystals on phenol concentration in crystal growth system.

  5. Progress in modeling of fluid flows in crystal growth processes

    Institute of Scientific and Technical Information of China (English)

    Qisheng Chen; Yanni Jiang; Junyi Yan; Ming Qin

    2008-01-01

    Modeling of fluid flows in crystal growth processes has become an important research area in theoretical and applied mechanics.Most crystal growth processes involve fluid flows,such as flows in the melt,solution or vapor.Theoretical modeling has played an important role in developing technologies used for growing semiconductor crystals for high performance electronic and optoelectronic devices.The application of devices requires large diameter crystals with a high degree of crystallographic perfection,low defect density and uniform dopant distribution.In this article,the flow models developed in modeling of the crystal growth processes such as Czochralski,ammono-thermal and physical vapor transport methods are reviewed.In the Czochralski growth modeling,the flow models for thermocapillary flow,turbulent flow and MHD flow have been developed.In the ammonothermal growth modeling,the buoyancy and porous media flow models have been developed based on a single-domain and continuum approach for the composite fluid-porous layer systems.In the physical vapor transport growth modeling,the Stefan flow model has been proposed based on the flow-kinetics theory for the vapor growth.In addition,perspectives for future studies on crystal growth modeling are proposed.

  6. Method of Promoting Single Crystal Growth During Melt Growth of Semiconductors

    Science.gov (United States)

    Su, Ching-Hua (Inventor)

    2013-01-01

    The method of the invention promotes single crystal growth during fabrication of melt growth semiconductors. A growth ampoule and its tip have a semiconductor source material placed therein. The growth ampoule is placed in a first thermal environment that raises the temperature of the semiconductor source material to its liquidus temperature. The growth ampoule is then transitioned to a second thermal environment that causes the semiconductor source material in the growth ampoule's tip to attain a temperature that is below the semiconductor source material's solidus temperature. The growth ampoule so-transitioned is then mechanically perturbed to induce single crystal growth at the growth ampoule's tip.

  7. Control of dendrite growth by a magnetic field during directional solidification

    Science.gov (United States)

    Dai, Yanchao; Du, Dafan; Hou, Long; Gagnoud, Annie; Ren, Zhongming; Fautrelle, Yves; Moreau, Rene; Li, Xi

    2016-04-01

    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.

  8. The steady-state solution of dendritic growth from the undercooled binary alloy melt with the far field flow

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The steady-state dendritic growth from the undercooled binary alloy melt with the far field flow is considered. By neglecting the interface energy, interface kinetics and buoyancy effects in the system, we obtaine the steady-state solution for the case of the large Schmidt number, in terms of the multiple variable expansion method. The changes of the temperature and concentration fields, the morphology of the interface, the normalization parameter and the Peclet number of the system induced by uniform external flow are derived. The results show that, compared with the system of dendritic growth from undercooled pure melt, the convective flow in the system of growth from undercooled binary alloy has stronger effects on the morphology of the interface. Nevertheless, the shape of the interface still remains nearly a paraboloid.

  9. The steady-state solution of dendritic growth from the undercooled binary alloy melt with the far field flow

    Institute of Scientific and Technical Information of China (English)

    CHEN MingWen; WANG ZiDong; XU JianJun

    2009-01-01

    The steady-state dendritic growth from the undercooled binary alloy melt with the far field flow is considered.By neglecting the interface energy,interface kinetics and buoyancy effects in the system,we obtaine the steady-state solution for the case of the large Schmidt number,in terms of the multiple variable expansion method.The changes of thtemperature and concentration fields,the morphology of the interface,the normalization parameter and the Peclet number of the system induced by uniform external flow are derived.The results show that,compared with the system of dendritic growth from undercooled pure melt,the convective flow in the system of growth from undercooled binary alloy has stronger effects on the morphology of the interface.Nevertheless,the shape of the interface still remains nearly a paraboloid.

  10. Growth of Solid Solution Single Crystals

    Science.gov (United States)

    Lehoczky, Sandor L.; Szofran, F. R.; Gillies, Donald C.

    2001-01-01

    The solidification of a solid solution semiconductor, having a wide separation between liquidus and solidus has been extensively studied in ground based, high magnetic field and Spacelab experiments. Two alloys of mercury cadmium telluride have been studied; with 80.0 mole percent of HgTe and 84.8 mole percent of HgTe respectively, the remainder being cadmium telluride. Such alloys are extremely difficult to grow by directional solidification on earth due to high solutal and thermal density differences that give rise to fluid flow and consequent loss of interface shape and composition. Diffusion controlled growth is therefore impossible to achieve in conventional directional solidification. The ground based experiments consisted of growing crystals in several different configurations of heat pipe furnaces, NASA's Advanced Automated Directional Solidification Furnace (AADSF), and a similar furnace incorporated in a superconducting magnet capable of operating at up to 5T. The first microgravity experiment took place during the flight of STS-62 in March 1994, with the AADSF installed on the second United States Microgravity Payload (USMP-2). The alloy was solidified at 3/4 inch per day over a 9 day period, and for the first time a detailed evaluation was performed correlating composition variations to measured residual acceleration. The second flight experiment took place in the fourth United States Microgravity Payload Mission (USMP-4) in November 1997. Due to contamination of the furnace system, analysis shows that the conditions prevailing during the experiment were quite different from the requirements requested prior to the mission. The results indicate that the sample did accomplish the desired objectives.

  11. Crystal growth methods dedicated to low solubility actinide oxalates

    Energy Technology Data Exchange (ETDEWEB)

    Tamain, C., E-mail: christelle.tamain@cea.fr [CEA, Nuclear Energy Division, Marcoule, RadioChemistry & Processes Department, F-30207 Bagnols sur Cèze (France); Arab-Chapelet, B. [CEA, Nuclear Energy Division, Marcoule, RadioChemistry & Processes Department, F-30207 Bagnols sur Cèze (France); Rivenet, M. [University Lille Nord de France, Unité de Catalyse et de Chimie du Solide, UCCS UMR CNRS 8181, ENSCL-USTL, B.P. 90108, F-59652 Villeneuve d’Ascq Cedex (France); Grandjean, S. [CEA, Nuclear Energy Division, Marcoule, RadioChemistry & Processes Department, F-30207 Bagnols sur Cèze (France); Abraham, F. [University Lille Nord de France, Unité de Catalyse et de Chimie du Solide, UCCS UMR CNRS 8181, ENSCL-USTL, B.P. 90108, F-59652 Villeneuve d’Ascq Cedex (France)

    2016-04-15

    Two novel crystal growth syntheses dedicated to low solubility actinide-oxalate systems and adapted to glove box handling are described. These methods based on the use of precursors of either actinide metal or oxalic acid have been optimized on lanthanide systems (analogue of actinides(III)) and then assessed on real actinide systems. They allow the synthesis of several actinide oxalate single crystals, Am{sub 2}(C{sub 2}O{sub 4}){sub 3}(H{sub 2}O){sub 3}·xH{sub 2}O, Th(C{sub 2}O{sub 4}){sub 2}·6H{sub 2}O, M{sub 2+x}[Pu{sup IV}{sub 2−x}Pu{sup III}{sub x}(C{sub 2}O{sub 4}){sub 5}]·nH{sub 2}O and M{sub 1−x}[Pu{sup III}{sub 1−x}Pu{sup IV}{sub x}(C{sub 2}O{sub 4}){sub 2}·H{sub 2}O]·nH{sub 2}O. It is the first time that these well-known compounds are formed by crystal growth methods, thus enabling direct structural studies on transuranic element systems and acquisition of basic data beyond deductions from isomorphic (or not) lanthanide compounds. Characterizations by X-ray diffraction, UV–visible solid spectroscopy, demonstrate the potentialities of these two crystal growth methods to obtain oxalate compounds. - Graphical abstract: Two new single crystal growth methods dedicated to actinide oxalate compounds. - Highlights: • Use of diester as oxalate precursor for crystal growth of actinide oxalates. • Use of actinide oxide as precursor for crystal growth of actinide oxalates. • Crystal growth of Pu(III) and Am(III) oxalates. • Crystal growth of mixed Pu(III)/Pu(IV) oxalates.

  12. Growth and characterization of DAST crystal with large-thickness

    Science.gov (United States)

    Cao, Lifeng; Teng, Bing; Zhong, Degao; Hao, Lun; Sun, Qing

    2016-10-01

    Highly nonlinear optical 4-N, N-dimethylamino-4-N-methyl stilbazolium tosylate (DAST) crystals with large surface and thickness was grown by the slope nucleation technology with slow-cooling in a high concentration solution. The structure and composition of the crystal were confirmed by X-ray diffraction (XRD). The surface morphology of the crystal was characterized by optical microscope. Growth layers were observed on the (001) surface and several isolated "island layers" were also found. The mechanism of crystal growth was analyzed. Etching behavior of the (001) and (00 1 bar) faces of the crystal was studied with methanol, respectively. Optical properties of the crystal were also characterized by UV-vis-NIR spectrometer. The dielectric constants and the dielectric loss were tested by impedance analyzer.

  13. Development of novel growth methods for halide single crystals

    Science.gov (United States)

    Yokota, Yuui; Kurosawa, Shunsuke; Shoji, Yasuhiro; Ohashi, Yuji; Kamada, Kei; Yoshikawa, Akira

    2017-03-01

    We developed novel growth methods for halide scintillator single crystals with hygroscopic nature, Halide micro-pulling-down [H-μ-PD] method and Halide Vertical Bridgman [H-VB] method. The H-μ-PD method with a removable chamber system can grow a single crystal of halide scintillator material with hygroscopicity at faster growth rate than the conventional methods. On the other hand, the H-VB method can grow a large bulk single crystal of halide scintillator without a quartz ampule. CeCl3, LaBr3, Ce:LaBr3 and Eu:SrI2 fiber single crystals could be grown by the H-μ-PD method and Eu:SrI2 bulk single crystals of 1 and 1.5 inch in diameter could be grown by the H-VB method. The grown fiber and bulk single crystals showed comparable scintillation properties to the previous reports using the conventional methods.

  14. Large-volume protein crystal growth for neutron macromolecular crystallography.

    Science.gov (United States)

    Ng, Joseph D; Baird, James K; Coates, Leighton; Garcia-Ruiz, Juan M; Hodge, Teresa A; Huang, Sijay

    2015-04-01

    Neutron macromolecular crystallography (NMC) is the prevailing method for the accurate determination of the positions of H atoms in macromolecules. As neutron sources are becoming more available to general users, finding means to optimize the growth of protein crystals to sizes suitable for NMC is extremely important. Historically, much has been learned about growing crystals for X-ray diffraction. However, owing to new-generation synchrotron X-ray facilities and sensitive detectors, protein crystal sizes as small as in the nano-range have become adequate for structure determination, lessening the necessity to grow large crystals. Here, some of the approaches, techniques and considerations for the growth of crystals to significant dimensions that are now relevant to NMC are revisited. These include experimental strategies utilizing solubility diagrams, ripening effects, classical crystallization techniques, microgravity and theoretical considerations.

  15. Nucleation and structural growth of cluster crystals

    CERN Document Server

    Leitold, Christian

    2016-01-01

    We study the nucleation of crystalline cluster phases in the generalized exponential model with exponent n=4. Due to the finite value of this pair potential for zero separation, at high densities the system forms cluster crystals with multiply occupied lattice sites. Here, we investigate the microscopic mechanisms that lead to the formation of cluster crystals from a supercooled liquid in the low-temperature region of the phase diagram. Using molecular dynamics and umbrella sampling, we calculate the free energy as a function of the size of the largest crystalline nucleus in the system, and compare our results with predictions from classical nucleation theory. Employing bond-order parameters based on a Voronoi tessellation to distinguish different crystal structures, we analyze the average composition of crystalline nuclei. We find that even for conditions where a multiply-occupied fcc crystal is the thermodynamically stable phase, the nucleation into bcc cluster crystals is strongly preferred. Furthermore, w...

  16. Nonlinear Optical BBO Crystals: Growth, Properties and Applications

    Institute of Scientific and Technical Information of China (English)

    唐鼎元

    2000-01-01

    Low temperature phase barium metaborate β-BaB2O4 (BBO) is an important nonlinear optical material. Up to now, the BBO single crystals with large size and good optical quality were grown from Na2O or NaF fluxed solvents by the top-seeded solution growth (TSSG) technique with or without pulling. In order to improve the growth rate and quality of BBO crystals, several new techniques such as continuous feeding, forced stirring and cooling growing crystals etc. have been suggested. Applications of BBO as an excellent nonlinear optical crystal include mainly frequency conversion of various laser radiation, high average power frequency conversion, frequency doubling of ultrashort pulses and broadly tunable optical parametric oscillators (OPO).This paper is a brief review on the growth, properties and applications of BBO crystals.

  17. Modelling of Heat Transfer in Single Crystal Growth

    CERN Document Server

    Zhmakin, Alexander I

    2014-01-01

    An attempt is made to review the heat transfer and the related problems encountered in the simulation of single crystal growth. The peculiarities of conductive, convective and radiative heat transfer in the different melt, solution, and vapour growth methods are discussed. The importance of the adequate description of the optical crystal properties (semitransparency, specular reflecting surfaces) and their effect on the heat transfer is stresses. Treatment of the unknown phase boundary fluid/crystal as well as problems related to the assessment of the quality of the grown crystals (composition, thermal stresses, point defects, disclocations etc.) and their coupling to the heat transfer/fluid flow problems is considered. Differences between the crystal growth simulation codes intended for the research and for the industrial applications are indicated. The problems of the code verification and validation are discussed; a brief review of the experimental techniques for the study of heat transfer and flow structu...

  18. Zeolite Crystal Growth (ZCG) Flight on USML-2

    Science.gov (United States)

    Sacco, Albert, Jr.; Bac, Nurcan; Warzywoda, Juliusz; Guray, Ipek; Marceau, Michelle; Sacco, Teran L.; Whalen, Leah M.

    1997-01-01

    The extensive use of zeolites and their impact on the world's economy has resulted in many efforts to characterize their structure, and improve the knowledge base for nucleation and growth of these crystals. The zeolite crystal growth (ZCG) experiment on USML-2 aimed to enhance the understanding of nucleation and growth of zeolite crystals, while attempting to provide a means of controlling the defect concentration in microgravity. Zeolites A, X, Beta, and Silicalite were grown during the 16 day - USML-2 mission. The solutions where the nucleation event was controlled yielded larger and more uniform crystals of better morphology and purity than their terrestrial/control counterparts. The external surfaces of zeolite A, X, and Silicalite crystals grown in microgravity were smoother (lower surface roughness) than their terrestrial controls. Catalytic studies with zeolite Beta indicate that crystals grown in space exhibit a lower number of Lewis acid sites located in micropores. This suggests fewer structural defects for crystals grown in microgravity. Transmission electron micrographs (TEM) of zeolite Beta crystals also show that crystals grown in microgravity were free of line defects while terrestrial/controls had substantial defects.

  19. A Multiscale simulation method for ice crystallization and frost growth

    Science.gov (United States)

    Yazdani, Miad

    2015-11-01

    Formation of ice crystals and frost is associated with physical mechanisms at immensely separated scales. The primary focus of this work is on crystallization and frost growth on a cold plate exposed to the humid air. The nucleation is addressed through Gibbs energy barrier method based on the interfacial energy of crystal and condensate as well as the ambient and surface conditions. The supercooled crystallization of ice crystals is simulated through a phase-field based method where the variation of degree of surface tension anisotropy and its mode in the fluid medium is represented statistically. In addition, the mesoscale width of the interface is quantified asymptotically which serves as a length-scale criterion into a so-called ``Adaptive'' AMR (AAMR) algorithm to tie the grid resolution at the interface to local physical properties. Moreover, due to the exposure of crystal to humid air, a secondary non-equilibrium growth process contributes to the formation of frost at the tip of the crystal. A Monte-Carlo implementation of Diffusion Limited Aggregation method addresses the formation of frost during the crystallization. Finally, a virtual boundary based Immersed Boundary Method (IBM) is adapted to address the interaction of ice crystal with convective air during its growth.

  20. Imaging and interferometric analysis of protein crystal growth

    Science.gov (United States)

    Raghunandan, Ranjini; Gupta, Anamika Sethia; Muralidhar, K.

    2008-04-01

    Protein crystals are grown under controlled temperature, concentration and vapor pressure conditions, usually by vapor diffusion, liquid-liquid diffusion and dialysis techniques. The present study examines the effects of protein concentration, drop size and reservoir height on the crystal growth of Hen Egg White Lysozyme (HEWL). Crystals are grown by the hanging drop vapor diffusion method using Modular VDX TM Plates. Due to the vapor pressure difference created between the protein drop and the reservoir, evaporation takes place till equilibrium is attained. Crystal formation takes place after a certain level of supersaturation is attained when the protein precipitates out in crystalline form. The observations revealed that the growth is faster for higher lysozyme concentration, smaller drop sizes and larger reservoir heights. The morphology of the crystals is viewed during the growth process using stereomicroscope. The number of crystals formed is the maximum for higher concentrations, drop sizes and reservoir heights. When the number of crystals formed is less, the size of the crystals is comparatively larger. The effect of evaporation of water vapor from the protein drop into the reservoir is studied using Mach-Zehnder interferometry. The recorded interferograms and shadowgraph images indicate the diffusion of condensed water into the reservoir. The radius of the drop is determined using the shadowgraph images of the growth process. The radius decreases with evaporation and the rate of decrease of radius is highest for higher protein concentrations, smaller drop sizes and larger reservoir heights.

  1. Growth features of ammonium hydrogen -tartrate single crystals

    Indian Academy of Sciences (India)

    G Sajeevkumar; R Raveendran; B S Remadevi; Alexander Varghese Vaidyan

    2004-08-01

    Ammonium hydrogen -tartrate (-AHT) single crystals were grown in silica gel. The growth features of these crystals with variation of parameters like specific gravity of the gel, gel pH, acid concentrations, concentration of the feed solution and gel age were studied in detail.

  2. Cross-twinning model of fcc crystal growth

    NARCIS (Netherlands)

    Waal, van de Benjamin W.

    1996-01-01

    The theory developed in 1960 by Wagner, Hamilton and Seidensticker (WHS-theory) to explain observed crystal growth phenomena in Ge is critically reviewed and shown to be capable of explaining preservation of ABC stacking order in two dimensions in fcc crystals of effectively spherical closed shell m

  3. An automatic system for crystal growth studies at constant supersaturation

    Science.gov (United States)

    March, J. G.; Costa-Bauzá, A.; Grases, F.; Söhnel, O.

    1992-01-01

    An automatic system for growing crystals from seeded supersaturated solutions at constant supersaturation is described. Control of burettes and data acquisition are controlled by computer. The system was tested with a study of the calcium oxalate kinetics of crystal growth. PMID:18924950

  4. Modeling and simulation of Si crystal growth from melt

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Lijun; Liu, Xin; Li, Zaoyang [National Engineering Research Center for Fluid Machinery and Compressors, School of Energy and Power Engineering, Xi' an Jiaotong University, Xi' an, Shaanxi 710049 (China); Miyazawa, Hiroaki; Nakano, Satoshi; Kakimoto, Koichi [Research Institute for Applied Mechanics, Kyushu University, Kasuga 816-8580 (Japan)

    2009-07-01

    A numerical simulator was developed with a global model of heat transfer for any crystal growth taking place at high temperature. Convective, conductive and radiative heat transfers in the furnace are solved together in a conjugated way by a finite volume method. A three-dimensional (3D) global model was especially developed for simulation of heat transfer in any crystal growth with 3D features. The model enables 3D global simulation be conducted with moderate requirement of computer resources. The application of this numerical simulator to a CZ growth and a directional solidification process for Si crystals, the two major production methods for crystalline Si for solar cells, was introduced. Some typical results were presented, showing the importance and effectiveness of numerical simulation in analyzing and improving these kinds of Si crystal growth processes from melt. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  5. The crystal growth of barium flouride in aqueous solution

    Science.gov (United States)

    Barone, J. P.; Svrjcek, D.; Nancollas, G. H.

    1983-06-01

    The kinetics of growth of barium flouride seed crystals were investigated in aqueous solution at 25°C using a constant composition method, in which the supersaturation and ionic strength were maintained constant by the addition of titrants consisting of barium nitrate and potassium flouride solutions. The rates of reaction, studied over a range of supersaturation (σ ≈ 0.4 to 1.0), were interpreted in terms of crystal growth models. A spiral growth mechanism best describes the data, and scanning electron microscopy indicates a three-dimensional growth. In the presence of inorganic additives such as phosphate, however, induction periods precede a morphological two-dimensional crystallization. Coulter Counter results show little crystal agglomeration.

  6. Crystal size growth in the liquid phase methanol synthesis catalyst

    Energy Technology Data Exchange (ETDEWEB)

    Sawant, A.; Lee, S.; Foos, A.

    1988-01-01

    The phenomenon of crystal growth in the methanol synthesis catalyst has been studied. Crystallite size distributions in the CuO/ZnO/Al/sub 2/O/sub 3/ methanol synthesis catalyst have been determined. The effects of temperature, reaction environment and time under reaction conditions have been studied. It is observed that water in the reaction mixture promotes crystal growth. 26 refs., 10 figs., 1 tab.

  7. Kinetics of the growth of filamentary KH2PO4 crystals on a seed crystal

    Science.gov (United States)

    Titaeva, E. K.; Kuritsyn, M. S.; Noskova, A. N.; Portnov, V. N.

    2017-08-01

    At oversaturations exceeding the inert range end for face {101} due to the presence of admixture Al(NO3)3 · 9H2O, a new phase is observed during the growth of this face in the form of filamentary crystals. Some experimental dependences of the growth rate of filamentary potassium dihydrophosphate (KH2PO4) crystals on the oversaturation have been obtained at different admixture concentrations. The growth of filamentary crystals occurs by the mechanism of two-dimensional nucleation. Their formation is governed by the effect of [AlHPO4]+ complexes in the form of Cabrera and Vermilyea stoppers.

  8. Theory of the intermediate stage of crystal growth with applications to insulin crystallization

    Science.gov (United States)

    Barlow, D. A.

    2017-07-01

    A theory for the intermediate stage of crystal growth, where two defining equations one for population continuity and another for mass-balance, is used to study the kinetics of the supersaturation decay, the homogeneous nucleation rate, the linear growth rate and the final distribution of crystal sizes for the crystallization of bovine and porcine insulin from solution. The cited experimental reports suggest that the crystal linear growth rate is directly proportional to the square of the insulin concentration in solution for bovine insulin and to the cube of concentration for porcine. In a previous work, it was shown that the above mentioned system could be solved for the case where the growth rate is directly proportional to the normalized supersaturation. Here a more general solution is presented valid for cases where the growth rate is directly proportional to the normalized supersaturation raised to the power of any positive integer. The resulting expressions for the time dependent normalized supersaturation and crystal size distribution are compared with experimental reports for insulin crystallization. An approximation for the maximum crystal size at the end of the intermediate stage is derived. The results suggest that the largest crystal size in the distribution at the end of the intermediate stage is maximized when nucleation is restricted to be only homogeneous. Further, the largest size in the final distribution depends only weakly upon the initial supersaturation.

  9. Growth and characterization of lead bromide crystals

    Science.gov (United States)

    Singh, N. B.; Gottlieb, M.; Henningsen, T.; Hopkins, R. H.; Mazelsky, R.; Glicksman, M. E.; Coriell, S. R.; Santoro, G. J.; Duval, W. M. B.

    1992-01-01

    Lead(II) bromide was purified by a combination of directional freezing and zone-refining methods. Differential thermal analysis of the lead bromide showed that a destructive phase transformation occurs below the melting temperature. This transformation causes extensive cracking, making it very difficult to grow a large single crystal. Energy of phase transformation for pure lead bromide was determined to be 24.67 cal/g. To circumvent this limitation, crystals were doped by silver bromide which decreased the energy of phase transformation. The addition of silver helped in achieving the size, but enhanced the inhomogeneity in the crystal. The acoustic attenuation constant was almost identical for the pure and doped (below 3000 ppm) crystals.

  10. Effects of temperature boundary conditions on equiaxed dendritic growth in phase-field simulations of binary alloy

    Institute of Scientific and Technical Information of China (English)

    于艳梅; 杨根仓; 赵达文; 吕衣礼

    2002-01-01

    By the phase-field approach, the dendritic growth in binary alloy melt was simulated respectively using two types of temperature boundary conditions, i.e., the constant temperature boundary by which the boundary temperature was fixed at the initial temperature, and Zero-Neumann temperature boundary. The influences of the temperature boundary conditions on numerical results are investigated. How to choose appropriate temperature boundary conditions is proposed. The results show that: 1) when the computation region is limited to a changeless size, the Zero-Neumann and constant temperature boundary conditions lead to the different dendritic growth behaviors, and the Zero-Neumann condition is preferable to the constant temperature condition; 2) when the computation region is enlarged continually with the computational time according to the increasing thermal diffusion scale, the two types of temperature boundary conditions achieve the consistent tip velocities and tip radii, and they both are appropriate choices.

  11. Growth and characterization of strontium tartrate pentahydrate crystals

    Energy Technology Data Exchange (ETDEWEB)

    Firdous, A.; Ahmad, M.M. [Department of Physics, National Institute of Technology, Kashmir (India); Quasim, I.; Kotru, P.N. [Crystal Growth and Materials Research Laboratory, Department of Physics and Electronics, University of Jammu (India)

    2008-10-15

    Silica gel impregnated with L-tartaric acid and using strontium nitrate as the second reactant leads to the growth of well faceted strontium tartrate pentahydrate single crystals.The morphological developmen and internal cell dimensions are observed to be different from the ones reported in the literature for strontium tartrate trihydrate crystals. The crystals are characterized using XRD, CH analysis, SEM, FTIR spectroscopy and thermoanalytical techniques. The crystals are observed to be thermally stable upto about 105 C but thereafter start decomposing and ejecting water of hydration at various stages, finally reducing to strontium oxide. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  12. Growth morphology and structural characteristic of C70single crystals

    Institute of Scientific and Technical Information of China (English)

    周维亚; 解思深; 吴源; 常保和; 王刚; 钱露茜

    1999-01-01

    Large size C70 single crystals with the dimension of more than 5 mm are grown from the vapor phase by controlling nucleation. X-ray diffraction and electron diffraction confirm that in the C70 single crystal a phase of the hexagonal close-packed (hcp) structure coexists with a minor face-center-cubic (fcc) phase at room temperature. The morphologies and their formation mechanism of the C70 single crystals are investigated by means of scanning electron microscopy and optical microscopy. The influence of growth conditions on the morphologies of C70 single crystals is discussed.

  13. Growth and characterization of CdS crystals

    Science.gov (United States)

    Su, Ching-Hua; Lehoczky, S. L.; Szofran, F. R.

    1990-01-01

    A growth method for the physical vapor transport of compound semiconductors in closed ampoules is described. With the unique techniques applied in the heat treatment of the starting materials and the temperature profiles provided by the three-zone translational furnace, large crystals of CdS have been grown successfully by the method at lower temperatures than previously used. Both unseeded and seeded growth have been investigated. The CdS crystals were examined using optical and scanning electron microscopies (SEM) to study the microstructure and the dislocation etch-pits. The crystals were further characterized by infrared (IR) and ultraviolet (UV) transmission measurements.

  14. Skylab experiments on semiconductors and alkali halides. [single crystal growth

    Science.gov (United States)

    Lundquist, C. A.

    1974-01-01

    The space processing experiments performed during the Skylab missions included one on single crystal growth of germanium selenide and telluride, one on pure and doped germanium crystals, two on pure and doped indium antimonide, one on gallium-indium-antimony systems, and one on a sodium chloride-sodium fluoride eutectic. In each experiment, three ampoules of sample were processed in the multipurpose electric furnace within the Skylab Materials Processing Facility. All were successful in varying degrees and gave important information about crystal growth removed from the effects of earth surface gravity.

  15. Fluid mechanics in crystal growth - The 1982 Freeman scholar lecture

    Science.gov (United States)

    Ostrach, S.

    1983-01-01

    An attempt is made to unify the current state of knowledge in crystal growth techniques and fluid mechanics. After identifying important fluid dynamic problems for such representative crystal growth processes as closed tube vapor transport, open reactor vapor deposition, and the Czochralski and floating zone melt growth techniques, research results obtained to date are presented. It is noted that the major effort to date has been directed to the description of the nature and extent of bulk transport under realistic conditions, where bulk flow determines the heat and solute transport which strongly influence the temperature and concentration fields in the vicinity of the growth interface. Proper treatment of near field, or interface, problems cannot be given until the far field, or global flow, involved in a given crystal growth technique has been adequately described.

  16. Dendrite growth kinetics of βZr phase within highly undercooled liquid Zr-Si hypoeutectic alloys under electrostatic levitation condition

    Science.gov (United States)

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

    2017-04-01

    The liquid Zr100-xSix (x = 1, 3, and 5) alloys were substantially undercooled by up to 392 K (0.19TL), 423 K (0.21TL), and 451 K (0.23TL), respectively, under the electrostatic levitation condition. The measured dendrite growth velocity of the primary βZr phase increased with the enhancement of liquid undercooling. Although the undercooling ability showed an increasing tendency with the increase in the Si content, dendrite growth was obviously depressed due to the dominance of solute diffusion controlled growth. Their critical undercoolings for kinetics transition from solute diffusion to thermal diffusion controlled growth were determined. It demonstrates a remarkable refinement of dendrites and an increasing trend of Si solubility in αZr dendrites with increasing undercooling.

  17. Growth and characterization of diammonium copper disulphate hexahydrate single crystal

    Energy Technology Data Exchange (ETDEWEB)

    Siva Sankari, R. [Department of Physics, Agni College of Technology, Thalambur, Chennai 603103 (India); Perumal, Rajesh Narayana, E-mail: r.shankarisai@gmail.com [Department of Physics, SSN College of Engineering, Kalavakkam, Chennai 603110 (India)

    2014-03-01

    Graphical abstract: Diammonium copper disulphate hexahydrate (DACS) is one of the most promising inorganic dielectric crystals with exceptional mechanical properties. Good quality crystals of DACS were grown by using solution method in a period of 30 days. The grown crystals were subjected to single crystal X-ray diffraction analysis in order to establish their crystalline nature. Thermo gravimetric, differential thermal analysis, FTIR, and UV–vis–NIR analysis were performed for the crystal. Several solid state physical parameters have been determined for the grown crystals. The dielectric constant and the dielectric loss and AC conductivity of the grown crystal were studied as a function of frequency and temperature has been calculated and plotted. - Highlights: • Diammonium copper disulphate is grown for the first time and CCDC number obtained. • Thermal analysis is done to see the stability range of the crystals. • Band gap and UV cut off wavelength of the crystal are determined to be 2.4 eV and 472.86 nm, respectively. • Dielectric constant, dielectric loss and AC conductivity are plotted as a function of applied field. - Abstract: Diammonium copper disulphate hexahydrate is one of the most promising inorganic crystals with exceptional dielectric properties. A good quality crystal was harvested in a 30-day period using solution growth method. The grown crystal was subjected to various characterization techniques like single crystal X-ray diffraction analysis, thermo gravimetric, differential thermal analysis, FTIR, and UV–vis–NIR analysis. Unit cell dimensions of the grown crystal have been identified from XRD studies. Functional groups of the title compounds have been identified from FTIR studies. Thermal stability of the samples was checked by TG/DTA studies. Band gap of the crystal was calculated. The dielectric constant and dielectric loss were studied as a function of frequency of the applied field. AC conductivity was plotted as a function

  18. Protein crystal growth and the International Space Station

    Science.gov (United States)

    DeLucas, L. J.; Moore, K. M.; Long, M. M.

    1999-01-01

    Protein structural information plays a key role in understanding biological structure-function relationships and in the development of new pharmaceuticals for both chronic and infectious diseases. The Center for Macromolecular Crystallography (CMC) has devoted considerable effort studying the fundamental processes involved in macromolecular crystal growth both in a 1-g and microgravity environment. Results from experiments performed on more than 35 U.S. space shuttle flights have clearly indicated that microgravity can provide a beneficial environment for macromolecular crystal growth. This research has led to the development of a new generation of pharmaceuticals that are currently in preclinical or clinical trials for diseases such as cutaneous T-cell lymphoma, psoriasis, rheumatoid arthritis, AIDS, influenza, stroke and other cardiovascular complications. The International Space Station (ISS) provides an opportunity to have complete crystallographic capability on orbit, which was previously not possible with the space shuttle orbiter. As envisioned, the x-ray Crystallography Facility (XCF) will be a complete facility for growing protein crystals; selecting, harvesting, and mounting sample crystals for x-ray diffraction; cryo-freezing mounted crystals if necessary; performing x-ray diffraction studies; and downlinking the data for use by crystallographers on the ground. Other advantages of such a facility include crystal characterization so that iterations in the crystal growth conditions can be made, thereby optimizing the final crystals produced in a three month interval on the ISS.

  19. Incorporating an extended dendritic growth model into the CAFE model for rapidly solidified non-dilute alloys

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Jie; Wang, Bo [State Key Laboratory of Advanced Special Steel, Shanghai University, Shanghai 200072 (China); Shanghai Engineering Technology Research Center of Special Casting, Shanghai 201605 (China); Zhao, Shunli [Research Institute, Baoshan Iron & Steel Co., Ltd, Shanghai 201900 (China); Wu, Guangxin [State Key Laboratory of Advanced Special Steel, Shanghai University, Shanghai 200072 (China); Shanghai Engineering Technology Research Center of Special Casting, Shanghai 201605 (China); Zhang, Jieyu, E-mail: zjy6162@staff.shu.edu.cn [State Key Laboratory of Advanced Special Steel, Shanghai University, Shanghai 200072 (China); Shanghai Engineering Technology Research Center of Special Casting, Shanghai 201605 (China); Yang, Zhiliang [State Key Laboratory of Advanced Special Steel, Shanghai University, Shanghai 200072 (China); Shanghai Engineering Technology Research Center of Special Casting, Shanghai 201605 (China)

    2016-05-25

    We have extended the dendritic growth model first proposed by Boettinger, Coriell and Trivedi (here termed EBCT) for microstructure simulations of rapidly solidified non-dilute alloys. The temperature-dependent distribution coefficient, obtained from calculations of phase equilibria, and the continuous growth model (CGM) were adopted in the present EBCT model to describe the solute trapping behaviors. The temperature dependence of the physical properties, which were not used in previous dendritic growth models, were also considered in the present EBCT model. These extensions allow the present EBCT model to be used for microstructure simulations of non-dilute alloys. The comparison of the present EBCT model with the BCT model proves that the considerations of the distribution coefficient and physical properties are necessary for microstructure simulations, especially for small particles with high undercoolings. Finally, the EBCT model was incorporated into the cellular automaton-finite element (CAFE) model to simulate microstructures of gas-atomized ASP30 high speed steel particles that were then compared with experimental results. Both the simulated and experimental results reveal that a columnar dendritic microstructure preferentially forms in small particles and an equiaxed microstructure forms otherwise. The applications of the present EBCT model provide a convenient way to predict the microstructure of non-dilute alloys. - Highlights: • A dendritic growth model was developed considering non-equilibrium distribution coefficient. • The physical properties with temperature dependence were considered in the extended model. • The extended model can be used to non-dilute alloys and the extensions are necessary in small particles. • Microstructure of ASP30 steel was investigated using the present model and verified by experiment.

  20. Tocotrienol-adjuvanted dendritic cells inhibit tumor growth and metastasis: a murine model of breast cancer.

    Directory of Open Access Journals (Sweden)

    Sitti Rahma Abdul Hafid

    Full Text Available Tocotrienol-rich fraction (TRF from palm oil is reported to possess anti-cancer and immune-enhancing effects. In this study, TRF supplementation was used as an adjuvant to enhance the anti-cancer effects of dendritic cells (DC-based cancer vaccine in a syngeneic mouse model of breast cancer. Female BALB/c mice were inoculated with 4T1 cells in mammary pad to induce tumor. When the tumor was palpable, the mice in the experimental groups were injected subcutaneously with DC-pulsed with tumor lysate (TL from 4T1 cells (DC+TL once a week for three weeks and fed daily with 1 mg TRF or vehicle. Control mice received unpulsed DC and were fed with vehicle. The combined therapy of using DC+TL injections and TRF supplementation (DC+TL+TRF inhibited (p<0.05 tumor growth and metastasis. Splenocytes from the DC+TL+TRF group cultured with mitomycin-C (MMC-treated 4T1 cells produced higher (p<0.05 levels of IFN-γ and IL-12. The cytotoxic T-lymphocyte (CTL assay also showed enhanced tumor-specific killing (p<0.05 by CD8(+ T-lymphocytes isolated from mice in the DC+TL+TRF group. This study shows that TRF has the potential to be used as an adjuvant to enhance effectiveness of DC-based vaccines.

  1. Cellular Automaton Study of Hydrogen Porosity Evolution Coupled with Dendrite Growth During Solidification in the Molten Pool of Al-Cu Alloys

    Science.gov (United States)

    Gu, Cheng; Wei, Yanhong; Yu, Fengyi; Liu, Xiangbo; She, Lvbo

    2017-09-01

    Welding porosity defects significantly reduce the mechanical properties of welded joints. In this paper, the hydrogen porosity evolution coupled with dendrite growth during solidification in the molten pool of Al-4.0 wt pct Cu alloy was modeled and simulated. Three phases, including a liquid phase, a solid phase, and a gas phase, were considered in this model. The growth of dendrites and hydrogen gas pores was reproduced using a cellular automaton (CA) approach. The diffusion of solute and hydrogen was calculated using the finite difference method (FDM). Columnar and equiaxed dendrite growth with porosity evolution were simulated. Competitive growth between different dendrites and porosities was observed. Dendrite morphology was influenced by porosity formation near dendrites. After solidification, when the porosities were surrounded by dendrites, they could not escape from the liquid, and they made pores that existed in the welded joints. With the increase in the cooling rate, the average diameter of porosities decreased, and the average number of porosities increased. The average diameter of porosities and the number of porosities in the simulation results had the same trend as the experimental results.

  2. Slanted stacking faults and persistent face centered cubic crystal growth in sedimentary colloidal hard sphere crystals

    NARCIS (Netherlands)

    Hilhorst, J.; Wolters, J. R.; Petukhov, A.V.

    2010-01-01

    Hard sphere crystal growth is a delicate interplay between kinetics and thermodynamics, where the former is commonly thought to favour a random hexagonal close packed structure and the latter leads to a face centered cubic crystal. In this article, we discuss the influence of slanted stacking faults

  3. Global deprivation of brain-derived neurotrophic factor in the CNS reveals an area-specific requirement for dendritic growth.

    Science.gov (United States)

    Rauskolb, Stefanie; Zagrebelsky, Marta; Dreznjak, Anita; Deogracias, Rubén; Matsumoto, Tomoya; Wiese, Stefan; Erne, Beat; Sendtner, Michael; Schaeren-Wiemers, Nicole; Korte, Martin; Barde, Yves-Alain

    2010-02-03

    Although brain-derived neurotrophic factor (BDNF) is linked with an increasing number of conditions causing brain dysfunction, its role in the postnatal CNS has remained difficult to assess. This is because the bdnf-null mutation causes the death of the animals before BDNF levels have reached adult levels. In addition, the anterograde axonal transport of BDNF complicates the interpretation of area-specific gene deletion. The present study describes the generation of a new conditional mouse mutant essentially lacking BDNF throughout the CNS. It shows that BDNF is not essential for prolonged postnatal survival, but that the behavior of such mutant animals is markedly altered. It also reveals that BDNF is not a major survival factor for most CNS neurons and for myelination of their axons. However, it is required for the postnatal growth of the striatum, and single-cell analyses revealed a marked decreased in dendritic complexity and spine density. In contrast, BDNF is dispensable for the growth of the hippocampus and only minimal changes were observed in the dendrites of CA1 pyramidal neurons in mutant animals. Spine density remained unchanged, whereas the proportion of the mushroom-type spine was moderately decreased. In line with these in vivo observations, we found that BDNF markedly promotes the growth of cultured striatal neurons and of their dendrites, but not of those of hippocampal neurons, suggesting that the differential responsiveness to BDNF is part of a neuron-intrinsic program.

  4. Crystal growth of CVD diamond and some of its peculiarities

    CERN Document Server

    Piekarczyk, W

    1999-01-01

    Experiments demonstrate that CVD diamond can form in gas environments that are carbon undersaturated with respect to diamond. This fact is, among others, the most serious violation of principles of chemical thermodynamics. In this $9 paper it is shown that none of the principles is broken when CVD diamond formation is considered not a physical process consisting in growth of crystals but a chemical process consisting in accretion of macro-molecules of polycyclic $9 saturated hydrocarbons belonging to the family of organic compounds the smallest representatives of which are adamantane, diamantane, triamantane and so forth. Since the polymantane macro-molecules are in every respect identical with $9 diamond single crystals with hydrogen-terminated surfaces, the accretion of polymantane macro- molecules is a process completely equivalent to the growth of diamond crystals. However, the accretion of macro-molecules must be $9 described in a way different from that used to describe the growth of crystals because so...

  5. Chemical Bond Analysis of Single Crystal Growth of Magnesium Oxide

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Starting from the crystallographic structure of magnesium oxide (MgO), both the chemical bond model of solids and Pauling's third rule (polyhedral sharing rule) were employed to quantitatively analyze the chemical bonding structure of constituent atoms and single crystal growth. Our analytical results show that MgO single crystals prefer to grow along the direction and the growth rate of the {100} plane is the slowest one. Therefore, the results show that the {100} plane of MgO crystals can be the ultimate morphology face, which is in a good agreement with our previous experimental results. The study indicate that the structure analysis is an effective tool to control the single-crystal growth.

  6. Relationship between crystal growth mode, preferred orientation and magnetostriction of (Tb0.3Dy0.7)Fe1.95 alloys

    Institute of Scientific and Technical Information of China (English)

    ZHANG Shirong; LI Kuoshe; YU Dunbo; LI Yongsheng; YANG Hongchuan; LI Hongwei; TU Ganfeng

    2008-01-01

    The relationship between crystal growth mode, preferred orientation and magnetostrictive properties of (Tb0.3Dy0.7)Fe1.95 alloys was investigated at different directional solidification rates. The results showed that preferred orientation had a strong influence on the characteristics of (Tb0.3Dy0.7)Fe1.95 alloys. At lower solidification rates, the sample with preferred orientation showed larger low-field magnetostriction and apparent compressive stress effect. The excessive solidification rate resulted in failure of preferred orientation and a poor magnetostrictive performance. With an increase in solidification rates, the crystal growth modes changed gradually from cellular and primary dendrite morphology to developed dendritic morphology. In addition, domain configurations were observed using magnetic force microscopy, and the change of magnetostrictive properties was interpreted in terms of revealing the domain configurations.

  7. Selectivity of Crystal Growth Direction in Layered Double Hydroxides

    Institute of Scientific and Technical Information of China (English)

    赵芸; 梁吉; 李峰; 段雪

    2004-01-01

    Investigation of selectivity of crystal growth direction in layered double hydroxides is helpful to control their particle sizes in different directions. Mg-Al layered double hydroxides (LDHs) were synthesized using a coprecipitation method. The influences of aging temperature, aging time, and Mg/Al molar ratio on the crystal structure, the LDHs particle size, and the selectivity of crystal growth in different directions were investigated. The results show that the size of the crystallites in the a direction is larger than that in the c direction for all experimental conditions, indicating faster crystal growth in the a direction than in the c direction. The crystallite sizes in the a and c directions both increase with decreasing Mg/Al molar ratio but with less difference between the sizes in the two directions. Therefore, the crystal growth rate in the c direction increases more than that in the a direction as the Mg/Al molar ratio decreases. The influence of the aging time, aging temperature, and Mg/Al molar ratio on the selectivity of the crystal growth direction can be used to prepare LDHs with selected sizes in the a and c directions.

  8. Crystal Growth and Characterization of Bil3

    Science.gov (United States)

    Hayes, Julia; Chen, Kuo-Tong; Burger, Arnold

    1997-01-01

    Bismuth tri-iodide (BiI3) have been grown by physical vapor transport (PVT), and by the Bridgman (melt) method. These crystals along with pure and stoichiometric BiI3 powder have been investigated by differential scanning calorimetry (DSC). The DSC results show that pure BiI3 powder has no phase transition and melts around 408 C. While we found no evidence for the high temperature dissociation of BiI3, the DSC measurements show that crystals grown from melt method contain a significantly large amount of Bi-rich phases than crystals grown from PVT method, as indicated by phase transition detected at 270, 285, 298 and 336 C.

  9. The growth of ruby single crystals

    Directory of Open Access Journals (Sweden)

    ALEKSANDAR GOLUBOVIC

    2005-02-01

    Full Text Available Ruby (Cr:Al2O3 single crystals were grown by the Czochralski technique in an argon atmosphere. The critical crystal diameter dc = 1.0 cm and the critical rate of rotation wc = 20 rpm were calculated by equations of the hydrodynamics of the melt. The rate of crystal growthwas experimentally obtained to be 2.7 mm/h. For chemical polishing, conc. H3PO4 at 593 K for an exposure of 3 hours was determined. Conc. H3PO4 at 523 K for an exposure of 3 h was found to be a suitable etching solution. The lattice parameters a = 0.47627(6 nm and c = 1.301(1 nm were determined by X-ray powder diffraction. The obtained results are discussed and compared with published data.

  10. Growth and characterization of doped LiF crystals

    Energy Technology Data Exchange (ETDEWEB)

    Khan, S.; Kim, H. J. [Kyungpook National University, Daegu (Korea, Republic of); Rooh, G. [Abdul Wali Khan University, Mardan (Pakistan); Kim, S. H. [Cheongju University, Cheongju (Korea, Republic of)

    2014-12-15

    Transparent and crack-free crystals of LiF:x (x = Ca, Pb, Na, Tl) were successfully grown by using the Czochralski method. Growth parameters such as the pulling and the rotation rates were optimized. The grown crystals were characterized and compared by using X-ray luminescence. Tl- and Na-doped crystals showed better luminescence intensity than crystals with other dopants. Thermoluminescence (TL) glow curves were obtained to study the crystal defects in the grown samples. Activation energies were calculated from the TL glow curves. The temperature dependence of the light yield in the temperature range from 10 to 300 K under alpha particle excitation was also investigated. The light yield was found to be larger at low temperatures. Na- and Tl-doped crystals showed 35% and 20% increases in the light yield, respectively, at low temperatures as compared to room temperature.

  11. Growth of Tungsten Bronze Family Crystals

    Science.gov (United States)

    1989-03-01

    retracti e index nuclear activation of undoped and cerium-doped SBN. Since undoped SBN is photorefractie while containing only trace These equations %ere...Boules as large as 2 to 2.5 cm in diameter are now routinely grown. AXIS APERTURlE OMAA RETICON ABERRATOR r. POLARIZATIONI , ~ SSN ETALI Rt EAM ’SPLITTER...1tMl-R 1A, (REFERENCE OMIA WITH CRYSTAL SBN Cxi SEIN CeRETICON PHOTODIODE RETICON PHOTODIODE I POLARIZED EXTRAORDINARY OMAA (REFERENCE C2= CRYSTAL 9O I

  12. Effects of impurities on growth habit of KDP crystal

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The effects of metaphosphate, boric acid and quaternary ammonium cations with different concentration on the growth habit of KDP crystal are reported. The results are analyzed and discussed, which show that the effects of different impurities on the growth habit of KDP are not the same. It is due to the different adsorption mechanism of the impurities.

  13. Molecular modifiers reveal a mechanism of pathological crystal growth inhibition

    Science.gov (United States)

    Chung, Jihae; Granja, Ignacio; Taylor, Michael G.; Mpourmpakis, Giannis; Asplin, John R.; Rimer, Jeffrey D.

    2016-08-01

    Crystalline materials are crucial to the function of living organisms, in the shells of molluscs, the matrix of bone, the teeth of sea urchins, and the exoskeletons of coccoliths. However, pathological biomineralization can be an undesirable crystallization process associated with human diseases. The crystal growth of biogenic, natural and synthetic materials may be regulated by the action of modifiers, most commonly inhibitors, which range from small ions and molecules to large macromolecules. Inhibitors adsorb on crystal surfaces and impede the addition of solute, thereby reducing the rate of growth. Complex inhibitor-crystal interactions in biomineralization are often not well elucidated. Here we show that two molecular inhibitors of calcium oxalate monohydrate crystallization—citrate and hydroxycitrate—exhibit a mechanism that differs from classical theory in that inhibitor adsorption on crystal surfaces induces dissolution of the crystal under specific conditions rather than a reduced rate of crystal growth. This phenomenon occurs even in supersaturated solutions where inhibitor concentration is three orders of magnitude less than that of the solute. The results of bulk crystallization, in situ atomic force microscopy, and density functional theory studies are qualitatively consistent with a hypothesis that inhibitor-crystal interactions impart localized strain to the crystal lattice and that oxalate and calcium ions are released into solution to alleviate this strain. Calcium oxalate monohydrate is the principal component of human kidney stones and citrate is an often-used therapy, but hydroxycitrate is not. For hydroxycitrate to function as a kidney stone treatment, it must be excreted in urine. We report that hydroxycitrate ingested by non-stone-forming humans at an often-recommended dose leads to substantial urinary excretion. In vitro assays using human urine reveal that the molecular modifier hydroxycitrate is as effective an inhibitor of nucleation

  14. A microfluidic, high throughput protein crystal growth method for microgravity.

    Directory of Open Access Journals (Sweden)

    Carl W Carruthers

    Full Text Available The attenuation of sedimentation and convection in microgravity can sometimes decrease irregularities formed during macromolecular crystal growth. Current terrestrial protein crystal growth (PCG capabilities are very different than those used during the Shuttle era and that are currently on the International Space Station (ISS. The focus of this experiment was to demonstrate the use of a commercial off-the-shelf, high throughput, PCG method in microgravity. Using Protein BioSolutions' microfluidic Plug Maker™/CrystalCard™ system, we tested the ability to grow crystals of the regulator of glucose metabolism and adipogenesis: peroxisome proliferator-activated receptor gamma (apo-hPPAR-γ LBD, as well as several PCG standards. Overall, we sent 25 CrystalCards™ to the ISS, containing ~10,000 individual microgravity PCG experiments in a 3U NanoRacks NanoLab (1U = 10(3 cm.. After 70 days on the ISS, our samples were returned with 16 of 25 (64% microgravity cards having crystals, compared to 12 of 25 (48% of the ground controls. Encouragingly, there were more apo-hPPAR-γ LBD crystals in the microgravity PCG cards than the 1g controls. These positive results hope to introduce the use of the PCG standard of low sample volume and large experimental density to the microgravity environment and provide new opportunities for macromolecular samples that may crystallize poorly in standard laboratories.

  15. Crystal Growth Models of Dexamethasone Sodium Phosphate in a MSMPR Reactive Crystallizer

    Institute of Scientific and Technical Information of China (English)

    郝红勋; 王静康; 王永莉; 侯宝红

    2005-01-01

    The reactive crystallization process of dexamethasone sodium phosphate was investigated in a continuous mixed-suspension, mixed-product-removal(MSMPR) crystallizer. Analyzing experimental data, it was found that the growth of product crystal was size-dependent. The Bransom, CR, ASL, M J2 and M J3 size-dependent growth models were discussed in details. Using experimental steady state population density data of dexamethasone sodium phosphate, parameters of five size-dependent growth models were determined by the method of non-linear least-squares. By comparison of experimental population density and linear growth rate data with those obtained from the five size-dependent growth models, it was found that the MJ3 model predicts the growth more accurately than do the other four models. Based on the theory of population balance, the crystal nucleation and growth rate equations of dexamethasone sodium phosphate were determined by non-linear regression method. The effects of different operation parameters such as supersaturation, magma density and temperature on the quality of product crystal were also discussed, and the optimal operation conditions were derived.

  16. Synthesis, crystal growth and mechanical properties of Bismuth Silicon Oxide (BSO) single crystal

    Energy Technology Data Exchange (ETDEWEB)

    Riscob, B. [CSIR – National Physical Laboratory, Crystal Growth and X-ray Analysis, New Delhi 110 012 (India); Institute for Plasma Research, Bhat, Gandhinagar 382428, Gujarat (India); Shkir, Mohd. [CSIR – National Physical Laboratory, Crystal Growth and X-ray Analysis, New Delhi 110 012 (India); Ganesh, V. [Department of Physics, Kakatiya University, Warangal 506 009 (India); Vijayan, N.; Maurya, K.K. [CSIR – National Physical Laboratory, Crystal Growth and X-ray Analysis, New Delhi 110 012 (India); Kishan Rao, K. [Department of Physics, Kakatiya University, Warangal 506 009 (India); Bhagavannarayana, G., E-mail: bhagavan@mail.nplindia.ernet.in [CSIR – National Physical Laboratory, Crystal Growth and X-ray Analysis, New Delhi 110 012 (India)

    2014-03-05

    Highlights: • Synthesis of Bismuth Silicon Oxide (BSO). • Single crystal growth of BSO by Czochralski (Cz) method. • Complete mechanical analysis by device fabrication point of view. • Theoretical and experimental calculations of mechanical properties. -- Abstract: Bismuth Silicon Oxide (BSO) is an efficient material for piezo-electric and electro-optic applications. In this article, growth of BSO single crystal by high temperature Czochralski melt growth technique and its detailed mechanical characterization by Vickers microhardness, fracture toughness, crack propagation, brittleness index and yield strength have been reported. The raw material was synthesized by solid state reaction using the stoichiometric ratio of high purity bismuth tri-oxide and silicon di-oxide. The synthesized material was charged in the platinum crucible and then melted. The required rotation and pulling rate was optimized for BSO single crystal growth and good quality single crystal has been harvested after a time span of 5 days. Powder X-ray diffraction analysis confirms the parent crystallization phase of BSO. The experimentally studied mechanical behavior of the crystal is explained using various theoretical models. The anisotropic nature of the crystals is studied using Knoop indentation technique.

  17. Growth of aluminum nitride bulk crystals by sublimation

    Science.gov (United States)

    Liu, Bei

    The commercial potential of III-nitride semiconductors is already being realized by the appearance of high efficiency, high reliability, blue and green LEDS around the world. However, the lack of a native nitride substrate has hindered the full-realization of more demanding III-nitride devices. To date, single aluminum nitride (AlN) crystals are not commercially available. New process investigation is required to scale up the crystal size. New crucibles stable up to very high temperatures (˜2500°C) are needed which do not incorporate impurities into the growing crystals. In this thesis, the recent progresses in bulk AlN crystal growth by sublimation-recondensation were reviewed first. The important physical, optical and electrical properties as well as chemical and thermal stabilities of AlN were discussed. The development of different types of growth procedures including self-seeding, substrate employed and a new "sandwich" technique were covered in detail. Next, the surface morphology and composition at the initial stages of AlN grown on 6H-SiC (0001) were investigated. Discontinuous AlN coverage occurred after 15 minutes of growth. The initial discontinuous nucleation of AlN and different lateral growth of nuclei indicated discontinuous AIN direct growth on on-axis 6H-SiC substrates. At the temperature in excess of 2100°C, the durability of the furnace fixture materials (crucibles, retorts, etc.) remains a critical problem. The thermal and chemical properties and performance of several refractory materials, including tantalum carbide, niobium carbide, tungsten, graphite, and hot-pressed boron nitride (HPBN), in inert gas, as well as under AIN crystal growth conditions were discussed. TaC and NbC are the most stable crucible materials in the crystal growth system. HPBN crucible is more suitable for AlN self-seeding growth, as crystals tend to nucleate in thin colorless platelets with low dislocation density. Finally, clear and colorless thin platelet Al

  18. Crystal Growth of Ternary Compound Semiconductors in Low Gravity Environment

    Science.gov (United States)

    Su, Ching-Hua

    2014-01-01

    A low gravity material experiment will be performed in the Material Science Research Rack (MSRR) on International Space Station (ISS). There are two sections of the flight experiment: (I) crystal growth of ZnSe and related ternary compounds, such as ZnSeS and ZnSeTe, by physical vapor transport (PVT) and (II) melt growth of CdZnTe by directional solidification. The main objective of the project is to determine the relative contributions of gravity-driven fluid flows to the compositional distribution, incorporation of impurities and defects, and deviation from stoichiometry observed in the grown crystals as results of buoyancy-driven convection and growth interface fluctuations caused by irregular fluid-flows on Earth. The investigation consists of extensive ground-based experimental and theoretical research efforts and concurrent flight experimentation. This talk will focus on the ground-based studies on the PVT crystal growth of ZnSe and related ternary compounds. The objectives of the ground-based studies are (1) obtain the experimental data and conduct the analyses required to define the optimum growth parameters for the flight experiments, (2) perfect various characterization techniques to establish the standard procedure for material characterization, (3) quantitatively establish the characteristics of the crystals grown on Earth as a basis for subsequent comparative evaluations of the crystals grown in a low-gravity environment and (4) develop theoretical and analytical methods required for such evaluations. ZnSe and related ternary compounds have been grown by vapor transport technique with real time in-situ non-invasive monitoring techniques. The grown crystals have been characterized extensively by various techniques to correlate the grown crystal properties with the growth conditions.

  19. Rapid solidification and dendrite growth of ternary Fe-Sn-Ge and Cu-Pb-Ge monotectic alloys

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The phase separation and dendrite growth characteristics of ternary Fe-43.9%Sn- 10%Ge and Cu-35.5%Pb-5%Ge monotectic alloys were studied systematically by the glass fluxing method under substantial undercooling conditions. The maximum undercoolings obtained in this work are 245 and 257 K, respectively, for these two alloys. All of the solidified samples exhibit serious macrosegregation, indicating that the homogenous alloy melt is separated into two liquid phases prior to rapid solidification. The solidification structures consist of four phases including α-Fe, (Sn), FeSn and FeSn2 in Fe-43.9%Sn-10%Ge ternary alloy, whereas only (Cu) and (Pb) solid solution phases in Cu-35.5%Pb-5%Ge alloy under different undercool- ings. In the process of rapid monotectic solidification, α-Fe and (Cu) phases grow in a dendritic mode, and the transition "dendrite→monotectic cell" happens when alloy undercoolings become sufficiently large. The dendrite growth velocities of α-Fe and (Cu) phases are found to increase with undercooling according to an exponential relation.

  20. Rapid solidification and dendrite growth of ternary Fe-Sn-Ge and Cu-Pb-Ge monotectic alloys

    Institute of Scientific and Technical Information of China (English)

    ZHANG XueHua; RUAN Ying; WANG WeiLi; WEI BingBo

    2007-01-01

    The phase separation and dendrite growth characteristics of ternary Fe-43.9%Sn- 10%Ge and Cu-35.5%Pb-5%Ge monotectic alloys were studied systematically by the glass fluxing method under substantial undercooling conditions. The maximum undercoolings obtained in this work are 245 and 257 K, respectively, for these two alloys. All of the solidified samples exhibit serious macrosegregation, indicating that the homogenous alloy melt is separated into two liquid phases prior to rapid solidification. The solidification structures consist of four phases including α-Fe, (Sn), FeSn and FeSn2 in Fe-43.9%Sn-10%Ge ternary alloy, whereas only (Cu) and (Pb) solid solution phases in Cu-35.5%Pb-5%Ge alloy under different undercoolings. In the process of rapid monotectic solidification, α-Fe and (Cu) phases grow in a dendritic mode, and the transition "dendrite→monotectic cell" happens when alloy undercoolings become sufficiently large. The dendrite growth velocities of α-Fe and (Cu) phases are found to increase with undercooling according to an exponential relation.

  1. Crystal growth and physical properties of Ferro-pnictides

    Energy Technology Data Exchange (ETDEWEB)

    Aswartham, Saicharan

    2012-11-08

    The thesis work presented here emphasizes important aspects of crystal growth and the influence of chemical substitution in Fe-As superconductors. High temperature solution growth technique is one of most powerful and widely used technique to grow single crystals of various materials. The biggest advantage of high temperature solution growth technique is the, possibility of growing single crystals from both congruently and incongruently melting materials. Solution growth technique has the potential to control high vapour pressures, given the fact that, in Fe-based superconductors elements with high vapour pressure like As, K, Li and Na have to be handled during the crystal growth procedure. In this scenario high temperature solution growth is the best suitable growth technique to synthesize sizable homogeneous single crystals. Using self-flux high temperature solution growth technique, large centimeter-sized high quality single crystals of BaFe{sub 2}As{sub 2} were grown. This pristine compound BaFe{sub 2}As{sub 2} undergoes structural and magnetic transition at T{sub S/N} = 137 K. By suppressing this magnetic transition and stabilizing tetragonal phase with chemical substitution, like Co-doping and Na-doping, bulk superconductivity is achieved. Superconducting transitions of as high as T{sub c} = 34 K with Na substitution and T{sub c} = 25 K with Co-doping were obtained. A combined electronic phase diagram has been achieved for both electron doping with Co and hole doping with Na in BaFe{sub 2}As{sub 2}. Single crystals of LiFe{sub 1-x}Co{sub x}As with x = 0, 0.025, 0.05 and 0.075 were grown by a self-flux high temperature solution growth technique. The charge doping in LiFeAs is achieved with the Co-doping in Fe atoms. The superconducting properties investigated by means of temperature dependent magnetization and resistivity revealed that superconductivity is shifted to lower temperatures and with higher amount of charge carriers superconductivity is killed

  2. Aluminum nitride bulk crystal growth in a resistively heated reactor

    Science.gov (United States)

    Dalmau, Rafael Federico

    A resistively heated reactor capable of temperatures in excess of 2300°C was used to grow aluminum nitride (AlN) bulk single crystals from an AlN powder source by physical vapor transport (PVT) in nitrogen atmosphere. AlN crystals were grown at elevated temperatures by two different methods. Self-seeded crystals were obtained by spontaneous nucleation on the crucible walls, while seeded growth was performed on singular and vicinal (0001) surfaces of silicon carbide (SiC) seeds. During self-seeded growth experiments a variety of crucible materials, such as boron nitride, tungsten, tantalum, rhenium, tantalum nitride, and tantalum carbide, were evaluated. These studies showed that the morphology of crystals grown by spontaneous nucleation strongly depends on the growth temperature and contamination in the reactor. Crucible selection had a profound effect on contamination in the crystal growth environment, influencing nucleation, coalescence, and crystal morphology. In terms of high-temperature stability and compatibility with the growth process, the best results for AlN crystal growth were obtained in crucibles made of sintered tantalum carbide or tantalum nitride. In addition, contamination from the commercially purchased AlN powder source was reduced by presintering the powder prior to growth, which resulted in a drastic reduction of nearly all impurities. Spontaneously grown single crystals up to 15 mm in size were characterized by x-ray diffraction, x-ray topography, glow discharge mass spectrometry, and secondary ion mass spectrometry. Average dislocation densities were on the order of 103 cm -3, with extended areas virtually free of dislocations. High resolution rocking curves routinely showed peak widths as narrow as 7 arcsec, indicating a high degree of crystalline perfection. Low-temperature partially polarized optical reflectance measurements were used to calculate the crystal-field splitting parameter of AlN, Deltacr = -230 meV, and a low-temperature (1

  3. Crystal growth and magnetic property of YFeO3 crystal

    Indian Academy of Sciences (India)

    Anhua Wu; Hui Shen; Jun Xu; Zhanliang Wang; Linwen Jiang; Liqing Luo; Shujuan Yuan; Shixun Cao; Huaijin Zhang

    2012-04-01

    YFeO3 and other rare earth substituted crystals with distorted orthorhombic pervoskite-like structure (space group, ) have attracted much attention due to their remarkable magnetic properties of primary significance for technological applications. In the present work, the floating zone growth of YFeO3 crystals has been systematically investigated and high quality YFeO3 crystal was obtained by optimized process. The magnetic properties of YFeO3 crystal were investigated, and it indicated the high magneto-optical property in YFeO3 crystals with specific orientation due to its anisotropy. YFeO3 crystals display superior performance in the application magneto-optical current sensors and fast latching optical switches.

  4. Control of nucleation and growth in protein crystal growth

    Science.gov (United States)

    Rosenberger, Franz; Meehan, Edward J.

    1988-01-01

    The potential advantages of nucleation and growth control through temperature, rather than the addition of precipitants or removal of solvent, are discussed. A simple light scattering arrangement for the characterization of nucleation and growth conditions in solutions is described. The temperature dependence of the solubility of low ionic strength lysozyme solutions is applied in preliminary nucleation and growth experiments.

  5. Hydrothermal crystal growth of oxides for optical applications

    Science.gov (United States)

    McMillen, Colin David

    2007-12-01

    The manipulation of light has proven to be an integral part of today's technology-based society. In particular, there is great interest in obtaining coherent radiation in all regions of the optical spectrum to advance technology in military, medical, industrial, scientific and consumer fields. Exploring new crystal growth techniques as well as the growth of new optical materials is critical in the advancement of solid state optics. Surprisingly, the academic world devotes little attention to the growth of large crystals. This shortcoming has left gaps in the optical spectrum inaccessible by solid state devices. This dissertation explores the hydrothermal crystal growth of materials that could fill two such gaps. The first gap exists in the deep-UV region, particularly below 200 nm. Some materials such as LiB3O5 and beta-BaB2O4 can generate coherent light at wavelengths as low as 205 nm. The growth of these materials was explored to investigate the feasibility of the hydrothermal method as a new technique for growing these crystals. Particular attention was paid to the descriptive chemistry surrounding these systems, and several novel structures were elucidated. The study was also extended to the growth of materials that could be used for the generation of coherent light as low as 155 nm. Novel synthetic schemes for Sr2Be2B2O7 and KBe2BO 3F2 were developed and the growth of large crystals was explored. An extensive study of the structures, properties and crystal growth of related compounds, RbBe2BO3F2 and CsBe2BO 3F2, was also undertaken. Optimization of a number of parameters within this family of compounds led to the hydrothermal growth of large, high quality single crystal at rates suitable for large-scale growth. The second gap in technology is in the area of high average power solid state lasers emitting in the 1 mum and eye-safe (>1.5 mum) regions. A hydrothermal technique was developed to grow high quality crystals of Sc 2O3 and Sc2O3 doped with suitable

  6. Pathways to self-organization: crystallization via nucleation and growth

    CERN Document Server

    Jungblut, Swetlana

    2016-01-01

    Crystallization, a prototypical self-organization process during which a disordered state spontaneously transforms into a crystal characterized by a regular arrangement of its building blocks, usually proceeds by nucleation and growth. In the initial stages of the transformation, a localized nucleus of the new phase forms in the old one due to a random fluctuation. Most of these nuclei disappear after a short time, but rarely a crystalline embryo may reach a critical size after which further growth becomes thermodynamically favorable and the entire system is converted into the new phase. In these lecture notes, we will discuss several theoretical concepts and computational methods to study crystallization. More specifically, we will address the rare event problem arising in the simulation of nucleation processes and explain how to calculate nucleation rates accurately. Particular attention is directed towards discussing statistical tools to analyze crystallization trajectories and identify the transition mech...

  7. Growth, crystalline perfection and characterization of benzophenone oxime crystal

    Science.gov (United States)

    Rajasekar, M.; Muthu, K.; Meenatchi, V.; Bhagavannarayana, G.; Mahadevan, C. K.; Meenakshisundaram, SP.

    Single crystals of benzophenone oxime (BPO) have been grown by slow evaporation solution growth technique from ethanol at room temperature. The single crystal X-ray diffraction study reveals that the crystal belongs to monoclinic system and cell parameters are, a = 9.459 Å, b = 8.383 Å, c = 26.690 Å, v = 2115 Å3 and β = 92.807°. The structure and the crystallinity of the materials were further confirmed by powder X-ray diffraction analysis. The various functional groups present in the molecule are confirmed by FT-IR analysis. The TG/DSC studies reveal the purity of the material and the crystals are transparent in the entire visible region having a lower optical cut-off at ˜300 nm. The crystalline perfection was evaluated by high-resolution X-ray diffraction (HRXRD). The crystal is further characterized by Kurtz powder technique, dielectric studies and microhardness analysis.

  8. Controlled Growth of Rubrene Nanowires by Eutectic Melt Crystallization

    Science.gov (United States)

    Chung, Jeyon; Hyon, Jinho; Park, Kyung-Sun; Cho, Boram; Baek, Jangmi; Kim, Jueun; Lee, Sang Uck; Sung, Myung Mo; Kang, Youngjong

    2016-03-01

    Organic semiconductors including rubrene, Alq3, copper phthalocyanine and pentacene are crystallized by the eutectic melt crystallization. Those organic semiconductors form good eutectic systems with the various volatile crystallizable additives such as benzoic acid, salicylic acid, naphthalene and 1,3,5-trichlorobenzene. Due to the formation of the eutectic system, organic semiconductors having originally high melting point (Tm > 300 °C) are melted and crystallized at low temperature (Te = 40.8–133 °C). The volatile crystallizable additives are easily removed by sublimation. For a model system using rubrene, single crystalline rubrene nanowires are prepared by the eutectic melt crystallization and the eutectic-melt-assisted nanoimpinting (EMAN) technique. It is demonstrated that crystal structure and the growth direction of rubrene can be controlled by using different volatile crystallizable additives. The field effect mobility of rubrene nanowires prepared using several different crystallizable additives are measured and compared.

  9. Vapor Growth of Mercuric Iodide Tetragonal Prismatic Crystals

    Science.gov (United States)

    2013-03-01

    These steps were followed by immersion in 1% potassium iodide (KI) solution. The apparatus were then cleaned and rinsed thoroughly with deionized (DI...Pergamon Press, 1973. [34] N. Lyakh, “Composition and kinetic characteristics of vapour phase during mercuric iodide growing,” Crystal Res. Technol...DTRA-TR-13-6 Vapor Growth of Mercuric Iodide Tetragonal Prismatic Crystals Approved for public release, distribution is unlimited. March 2013

  10. Defect reduction in seeded aluminum nitride crystal growth

    Science.gov (United States)

    Bondokov, Robert T.; Morgan, Kenneth E.; Schowalter, Leo J.; Slack, Glen A.

    2017-06-06

    Bulk single crystal of aluminum nitride (AlN) having an areal planar defect density .ltoreq.100 cm.sup.-2. Methods for growing single crystal aluminum nitride include melting an aluminum foil to uniformly wet a foundation with a layer of aluminum, the foundation forming a portion of an AlN seed holder, for an AlN seed to be used for the AlN growth. The holder may consist essentially of a substantially impervious backing plate.

  11. Defect reduction in seeded aluminum nitride crystal growth

    Energy Technology Data Exchange (ETDEWEB)

    Bondokov, Robert T.; Morgan, Kenneth E.; Schowalter, Leo J.; Stack, Glen A.

    2017-04-18

    Bulk single crystal of aluminum nitride (AlN) having an areal planar defect density.ltoreq.100 cm.sup.-2. Methods for growing single crystal aluminum nitride include melting an aluminum foil to uniformly wet a foundation with a layer of aluminum, the foundation forming a portion of an AlN seed holder, for an AlN seed to be used for the AlN growth. The holder may consist essentially of a substantially impervious backing plate.

  12. Growth of lead molybdate crystals by vertical Bridgman method

    Indian Academy of Sciences (India)

    Hongbing Chen; Congxin Ge; Rongsheng Li; Jinhao Wang; Changgen Wu; Xianling Zeng

    2005-10-01

    The growth of PbMoO4 crystals by the modified Bridgman method has been reported in this paper. The feed material with strict stoichiometric composition is desirable for the Bridgman growth of the crystals. The continuous composition change of the melts during growth can be avoided because the volatilization of melts is limited by sealed platinum crucibles. By means of the optimum growth parameters such as the growth rate of < 1.2 mm/h and the temperature gradient of 20 ∼ 40°C/cm across the solid–liquid interface under the furnace temperature of 1140 ∼ 1200°C, large size crystals with high optical uniformity were grown successfully. The distribution of Pb and Mo concentration along the growth axis was measured by X-ray fluorescence analysis. The single crystallinity of the grown sample was evaluated by the double-crystal X-ray rocking curve. The transmission spectra were measured in the range of 300–800 nm at room temperature.

  13. Zeolite crystal growth in space - What has been learned

    Science.gov (United States)

    Sacco, A., Jr.; Thompson, R. W.; Dixon, A. G.

    1993-01-01

    Three zeolite crystal growth experiments developed at WPI have been performed in space in last twelve months. One experiment, GAS-1, illustrated that to grow large, crystallographically uniform crystals in space, the precursor solutions should be mixed in microgravity. Another experiment evaluated the optimum mixing protocol for solutions that chemically interact ('gel') on contact. These results were utilized in setting the protocol for mixing nineteen zeolite solutions that were then processed and yielded zeolites A, X and mordenite. All solutions in which the nucleation event was influenced produced larger, more 'uniform' crystals than did identical solutions processed on earth.

  14. Stability limits for the horizontal ribbon growth of silicon crystals

    Science.gov (United States)

    Daggolu, Parthiv; Yeckel, Andrew; Bleil, Carl E.; Derby, Jeffrey J.

    2013-01-01

    A rigorous, thermal-capillary model, developed to couple heat transfer, melt convection and capillary physics, is employed to assess stability limits of the HRG system for growing silicon ribbons. Extending the prior understanding of this process put forth by Daggolu et al. [Thermal-capillary analysis of the horizontal ribbon growth of silicon crystals, Journal of Crystal Growth 355 (2012) 129-139], model results presented here identify additional failure mechanisms, including the bridging of crystal onto crucible, the spilling of melt from the crucible, and the undercooling of melt at the ribbon tip, that are consistent with prior experimental observations. Changes in pull rate, pull angle, melt height, and other parameters are shown to give rise to limits, indicating that only narrow operating windows exist in multi-dimensional parameter space for stable growth conditions that circumvent these failure mechanisms.

  15. Directed Growth of Orthorhombic Crystals in a Micropillar Array.

    Science.gov (United States)

    Holzner, Gregor; Binder, Claudia; Kriel, Frederik H; Priest, Craig

    2017-02-14

    We report directed growth of orthorhombic crystals of potassium permanganate in spatial confinement of a micropillar array. The solution is introduced by spontaneous wicking to give a well-defined film (thickness 10-15 μm; volume ∼600 nL) and is connected to a reservoir (several microliters) that continuously "feeds" the evaporating film. When the film is supersaturated, crystals nucleate and preferentially grow in specific directions guided by one of several possible linear paths through the pillar lattice. Crystals that do not initially conform are stopped at an obstructing pillar, branch into another permitted direction, or spontaneously rotate to align with a path and continue to grow. Microspectroscopy is able to track the concentration of solute in a small region of interest (70 × 100 μm(2)) near to growing crystals, revealing that the solute concentration initially increases linearly beyond the solubility limit. Crystal growth near the region of interest resulted in a sharp decrease in the local solute concentration (which rapidly returns the concentration to the solubility limit), consistent with estimated diffusion time scales (crystal orientation in nanoliter samples will provide new insight into microscale dynamics of microscale crystallization.

  16. A novel dendritic surfactant for enhanced microcystin-LR detection by double amplification in a quartz crystal microbalance biosensor.

    Science.gov (United States)

    Xia, Yuetong; Zhang, Jianping; Jiang, Long

    2011-08-01

    Enhanced sensitivity for the hepatotoxin microcystin-LR (MC-LR) was achieved in a quartz crystal microbalance (QCM) system via double amplification. For primary amplification, an innovative interface on the QCM was obtained as a matrix by the vesicle layer formed by our synthetic dendritic surfactant, bis (amidoethyl-carbamoylethyl) octadecylamine (C18N3). The vesicle matrix was then functionalised by an optimised concentration of monoclonal antibodies against MC-LR (anti-MC-LR) to detect the analyte. The results showed that a detection limit of 100 ng/mL was achieved by primary amplification. To achieve higher sensitivity, secondary amplification was implemented with anti-MC-LR gold nanoparticle (AuNPs) conjugates as probes, which lowered the detection limit for MC-LR to 1 ng/mL (the maximum concentration recommended by the World Health Organization [WHO] in drinking water for humans). The QCM immunosensor reported here has advantages such as high sensitivity, portability, simplicity, and cost-effectiveness for MC-LR detection. It would be uniquely superior compared with current MC-LR detection techniques for on-the-spot water detection. Furthermore, the methodology described here is also potentially significant in many fields for the routine monitoring of environmental and food safety.

  17. Crystal growth of aragonite in the presence of phosphate

    Science.gov (United States)

    Tadier, Solène; Rokidi, Stamatia; Rey, Christian; Combes, Christèle; Koutsoukos, Petros G.

    2017-01-01

    The crystal growth of aragonite was investigated at pH 7.8, 37 °C and constant solution supersaturation from aragonite-seeded supersaturated solutions. The effect of the presence of orthophosphate ions in the supersaturated solution on the kinetics of crystallization of aragonite was investigated over the range of orthophosphate concentrations of 0.25 μM-1 mM. In the presence of orthophosphate in the range of 0.25 μM-8 μM, the crystal growth rate of aragonite decreased with increasing phosphate concentration. At orthophosphate concentration levels exceeding 2 μM, induction times were measured and were found to increase with orthophosphate concentration. At orthophosphate concentration levels >8 μM, the crystal growth of aragonite was inhibited, suggesting the blockage of the active growth sites by the adsorption of orthophosphate ions. Adsorption was confirmed by the investigation of orthophosphate uptake on aragonite, which was: i) found to depend on the equilibrium concentration of orthophosphate in aqueous solutions saturated with respect to aragonite; ii) not influenced by the ionic strength of the electrolyte up to 0.15 M NaCl, showing that electrostatic interactions between orthophosphate and CaCO3 did not play a significant role in this concentration range. Adsorption data of orthophosphate on the aragonite crystals gave satisfactory fit to the Langmuir adsorption model and was confirmed by XPS analysis.

  18. Modelling of transport phenomena and defects in crystal growth processes

    Indian Academy of Sciences (India)

    S Pendurti; H Zhang; V Prasad

    2001-02-01

    A brief review of single crystal growth techniques and the associated problems is presented. Emphasis is placed on models for various transport and defect phenomena involoved in the growth process with the ultimate aim of integrating them into a comprehensive numerical model. The sources of dislocation nucleation in the growing crystal are discussed, and the propagation and multiplication of these under the action of thermal stresses is discussed. A brief description of a high-level numerical technique based on multiple adaptive grid generation and finite volume discretization is presented, followed by the result of a representative numerical simulation.

  19. Crystal-growth Underground Breeding Extra-sensitive Detectors

    Science.gov (United States)

    Mei, Dongming

    2012-02-01

    CUBED (Center for Ultra-Low Background Experiments at DUSEL) collaborators from USD, SDSMT, SDSU, Sanford Lab, and Lawrence Berkeley National Laboratory are working on the development of techniques to manufacture crystals with unprecedented purity levels in an underground environment that may be used by experiments proposed for DUSEL. The collaboration continues to make significant progress toward its goal of producing high purity germanium crystals. High quality crystals are being pulled on a weekly basis at the temporary surface growth facility located on the USD campus. The characterization of the grown crystals demonstrates that the impurity levels are nearly in the range of the needed impurity level for detector-grade crystals. Currently, the crystals are being grown in high-purity hydrogen atmosphere. With an increase in purity due to the zone refining, the group expects to grow high-purity crystals by the end of 2011. The one third of the grown crystals will be manufactured to be detectors; the remaining will be fabricated in to wafers that have large applications in electro and optical devices as well as solar panels. This would allow the research to be connected to market and create more than 30 jobs and multi millions revenues in a few years.

  20. Growth and study of mixed crystals of Ca–Cd iodate

    Indian Academy of Sciences (India)

    S L Garud; K B Saraf

    2008-08-01

    Mixed crystals of calcium–cadmium iodate were grown by a simple gel technique using diffusion method. The optimum conditions were established by varying various parameters such as pH of gel solution, gel concentration, gel setting time, concentration of reactants etc. Crystals having different morphologies and habits were obtained. Prismatic, dendritic crystals of calcium–cadmium iodate and prismatic needle shaped, hopper crystals of mixed iodate were obtained. Some of them were transparent, some transluscent and a few others were opaque. The crystals were characterized using FT–IR, EDAX, XRD, TGA and DTA.

  1. The dynamic nature of crystal growth in pores

    Science.gov (United States)

    Godinho, Jose R. A.; Gerke, Kirill M.; Stack, Andrew G.; Lee, Peter D.

    2016-09-01

    The kinetics of crystal growth in porous media controls a variety of natural processes such as ore genesis and crystallization induced fracturing that can trigger earthquakes and weathering, as well as, sequestration of CO2 and toxic metals into geological formations. Progress on understanding those processes has been limited by experimental difficulties of dynamically studying the reactive surface area and permeability during pore occlusion. Here, we show that these variables cause a time-dependency of barite growth rates in microporous silica. The rate is approximately constant and similar to that observed on free surfaces if fast flow velocities predominate and if the time-dependent reactive surface area is accounted for. As the narrower flow paths clog, local flow velocities decrease, which causes the progressive slowing of growth rates. We conclude that mineral growth in a microporous media can be estimated based on free surface studies when a) the growth rate is normalized to the time-dependent surface area of the growing crystals, and b) the local flow velocities are above the limit at which growth is transport-limited. Accounting for the dynamic relation between microstructure, flow velocity and growth rate is shown to be crucial towards understanding and predicting precipitation in porous rocks.

  2. Effect of Co2+ doping on solubility, crystal growth and properties of ADP crystals

    Science.gov (United States)

    Ganesh, V.; Shkir, Mohd.; AlFaify, S.; Yahia, I. S.

    2016-09-01

    Bulk size crystal growth of ADP with different concentrations doping of cobalt (Co2+) has been done by low cost slow evaporation technique at ambient conditions. The solubility measurement was carried out on pure and doped crystals and found that the solubility is decreasing with doping concentrations. The presence of Co2+ ion in crystalline matrix of ADP has been confirmed by structural, vibrational and elemental analyses. Scanning electron microscopic study reveals that the doping has strong effect on the quality of the crystals. The optical absorbance and transmission confirms the enhancement of quality of ADP crystals due to Co2+ doping and so the optical band gap. Further the dislocation, photoluminescence, dielectric and mechanical studies confirms that the properties of grown crystals with Co2+ doping has been enriched and propose it as a better candidate for optoelectronic applications.

  3. Controlling protein crystal growth rate by means of temperature

    Energy Technology Data Exchange (ETDEWEB)

    SantamarIa-Holek, I; Gadomski, A [Institute of Mathematics and Physics, University of Technology and Life Sciences, PL-85796 Bydgoszcz (Poland); RubI, J M, E-mail: isholek.fc@gmail.com, E-mail: agad@utp.edu.pl, E-mail: mrubi@ub.edu [Departament de Fisica Fonamental, University of Barcelona, Av. Diagonal 647, E-08028 Barcelona (Spain)

    2011-06-15

    We have proposed a model to analyze the growth kinetics of lysozyme crystals/aggregates under non-isothermal conditions. The model was formulated through an analysis of the entropy production of the growth process which was obtained by taking into account the explicit dependence of the free energy on the temperature. We found that the growth process is coupled with temperature variations, resulting in a novel Soret-type effect. We identified the surface entropy of the crystal/aggregate as a decisive ingredient controlling the behavior of the average growth rate as a function of temperature. The behavior of the Gibbs free energy as a function of temperature is also analyzed. The agreement between theory and experiments is very good in the range of temperatures considered.

  4. Controlling protein crystal growth rate by means of temperature.

    Science.gov (United States)

    Sanamaría-Holek, I; Gadomski, A; Rubí, J M

    2011-06-15

    We have proposed a model to analyze the growth kinetics of lysozyme crystals/aggregates under non-isothermal conditions. The model was formulated through an analysis of the entropy production of the growth process which was obtained by taking into account the explicit dependence of the free energy on the temperature. We found that the growth process is coupled with temperature variations, resulting in a novel Soret-type effect. We identified the surface entropy of the crystal/aggregate as a decisive ingredient controlling the behavior of the average growth rate as a function of temperature. The behavior of the Gibbs free energy as a function of temperature is also analyzed. The agreement between theory and experiments is very good in the range of temperatures considered.

  5. Accumulated distribution of material gain at dislocation crystal growth

    Science.gov (United States)

    Rakin, V. I.

    2016-05-01

    A model for slowing down the tangential growth rate of an elementary step at dislocation crystal growth is proposed based on the exponential law of impurity particle distribution over adsorption energy. It is established that the statistical distribution of material gain on structurally equivalent faces obeys the Erlang law. The Erlang distribution is proposed to be used to calculate the occurrence rates of morphological combinatorial types of polyhedra, presenting real simple crystallographic forms.

  6. Formation and growth of crystal defects in directionally solidified multicrystalline silicon for solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Ryningen, Birgit

    2008-07-01

    crucible bottom and the subsequent growth is governed by dislocations. For the other type of ingots which is dominated by twins and has a higher minority carrier lifetime, a higher undercooling has occurred before crystal nucleation. It is suggested that this undercooling can reach the critical value for dendritic nucleation to occur (10 K). After dendritic nucleation, subsequent crystal growth is dominated by twins. Nucleation and multiplication mechanisms for dislocations are complex, and investigations on a microscopic scale have been performed. Mechanisms such as punch-out from precipitates with a thermal expansion coefficient different from that of the silicon matrix, intergranular - and intragranular hardening and development of strain fields due to differences in the elasticity module between different grains are thought to play a role in the nucleation of dislocations higher up in the cast. The multiplication has been explained by a macroscopic stress field at the solidification front, stresses developed during cooling and pinning by oxygen impurities. For dislocations nucleated by an angular grain boundary a multiplication and growth mechanism is proposed where dislocations can cross slip and line up at certain crystallographic directions during crystal growth. (Author). 134 refs., 29 figs., 4 tabs

  7. Growth and high pressure studies of zirconium sulphoselenide single crystals

    Indian Academy of Sciences (India)

    K R Patel; R D Vaidya; M S Dave; S G Patel

    2009-11-01

    Transition metal trichalcogenides are well suited for extreme pressure lubrication. These materials being semiconducting and of layered structure may undergo structural and electronic transition under pressure. In this paper authors reported the details about synthesis and characterization of zirconium sulphoselenide single crystals. The chemical vapour transport technique was used for the growth of zirconium sulphoselenide single crystals. The energy dispersive analysis by X-ray (EDAX) gave the confirmation about the stoichiometry of the as-grown crystals and other structural characterizations were accomplished by X-ray diffraction (XRD) study. The variation of electrical resistance was monitored in a Bridgman opposed anvil set-up up to 8 GPa pressure to identify the occurrence of any structural transition. These crystals do not possess any structural transitions upto the pressure limit examined.

  8. Crystal nucleation and near-epitaxial growth in nacre

    CERN Document Server

    Olson, Ian C; Tamura, Nobumichi; Kunz, Martin; Gilbert, Pupa U P A

    2013-01-01

    Nacre, the iridescent inner lining of many mollusk shells, interests materials scientists because of its unique brick-and-mortar periodic structure at the sub-micron scale and its remarkable resistance to fracture. However, it remains unclear how nacre forms. Here we present 20-nm, 2{\\deg}-resolution Polarization-dependent Imaging Contrast (PIC) images of shells from 15 species, mapping nacre tablets and their orientation patterns, showing where crystals nucleate and how they grow in nacre. In all shells we found stacks of co-oriented aragonite (CaCO3) tablets arranged into vertical columns or staggered diagonally. Only near the nacre-prismatic boundary are disordered crystals nucleated, as spherulitic aragonite. Overgrowing nacre tablet crystals are most frequently co-oriented with the underlying spherulitic aragonite or with another tablet, connected by mineral bridges. Therefore aragonite crystal growth in nacre is epitaxial or near-epitaxial, with abrupt or gradual changes in orientation, with c-axes with...

  9. Second harmonic generation and crystal growth of new chalcone derivatives

    Science.gov (United States)

    Patil, P. S.; Dharmaprakash, S. M.; Ramakrishna, K.; Fun, Hoong-Kun; Sai Santosh Kumar, R.; Narayana Rao, D.

    2007-05-01

    We report on the synthesis, crystal structure and optical characterization of chalcone derivatives developed for second-order nonlinear optics. The investigation of a series of five chalcone derivatives with the second harmonic generation powder test according to Kurtz and Perry revealed that these chalcones show efficient second-order nonlinear activity. Among them, high-quality single crystals of 3-Br-4'-methoxychalcone (3BMC) were grown by solvent evaporation solution growth technique. Grown crystals were characterized by X-ray powder diffraction (XRD), laser damage threshold, UV-vis-NIR and refractive index measurement studies. Infrared spectroscopy, thermogravimetric analysis and differential thermal analysis measurements were performed to study the molecular vibration and thermal behavior of 3BMC crystal. Thermal analysis does not show any structural phase transition.

  10. Maintenance of supersaturation II: indomethacin crystal growth kinetics versus degree of supersaturation.

    Science.gov (United States)

    Patel, Dhaval D; Anderson, Bradley D

    2013-05-01

    This study compares the kinetics of crystal growth of indomethacin from supersaturated suspensions at varying degrees of supersaturation (2 ≤ S ≥ 9) in the presence of seed crystals of the γ-form of indomethacin, the lowest energy polymorph. At high S (6 ≤ S ≥ 9), the crystal growth was first order with rate coefficients (kG ) that were nearly constant and consistent with the value predicted for bulk-diffusion control. At lower S (supersaturation suggesting that a higher energy surface layer was deposited on the γ-form seed crystals during crystal growth. When growth experiments were repeated at low S in the presence of indomethacin seed crystals isolated from a previous crystal growth experiment (i.e., seed crystals having higher energy surface), kG matched the higher values observed for bulk diffusion-controlled crystal growth. Crystal growth experiments were also conducted at S supersaturation during oral absorption. Copyright © 2013 Wiley Periodicals, Inc.

  11. Phase-field simulation of dendritic sidebranching induced by thermal noise

    Institute of Scientific and Technical Information of China (English)

    朱昌盛; 王智平; 荆涛; 柳百成

    2004-01-01

    The influence of undercooling and noise magnitude on dendritic sidebranching during crystal growth was investigated by simulation of a phase-field model which incorporates thermal noise. It is shown that, the sidebranching is not influenced with inclusion of the nonconserved noise, therefore, in order to save the computational costs it is often neglected; while conserved noise drives the morphological instability and is dominant origin of sidebranching. The dependence of temperature field on magnitude of thermal noise is apparent, when Fu gets an appropriate value, noise can induce sidebranching but not influence the dendritic tip operating state. In the small undercooled melt, the thermal diffusion layer collected around the dendrite is thick, which suppresses the growth of its sidebranching and makes the dendrite take on the morphology of no sidebranching, but when the undercooling is great,the thermal diffusion layer is thin, which is advantageous to the growth of the sidebranching and the dendrite presents the morphology of the developed sidebranching.

  12. Transient natural convection heat and mass transfer in crystal growth

    Science.gov (United States)

    Han, Samuel S.

    1990-01-01

    A numerical analysis of transient combined heat and mass transfer across a rectangular cavity is performed. The physical parameters are selected to represent a range of possible crystal growth in solutions. Good agreements with measurement data are observed. It is found that the thermal and solute fields become highly oscillatory when the thermal and solute Grashof numbers are large.

  13. Solidification and crystal growth of solid solution semiconducting alloys

    Energy Technology Data Exchange (ETDEWEB)

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

    1984-10-01

    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.

  14. Phase field simulations of ice crystal growth in sugar solutions

    NARCIS (Netherlands)

    Sman, Van Der R.G.M.

    2016-01-01

    We present the first model ever, that describes explicitly ice crystal growth in a sugar solution during freezing. This 2-D model uses the phase field method, supplemented with realistic, and predictive theories on the thermodynamics and (diffusion) kinetics of this food system. We have to make u

  15. Solidification and crystal growth of solid solution semiconducting alloys

    Science.gov (United States)

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

    1984-01-01

    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.

  16. Growth of Cd0.96Zn0.04Te single crystals by vapor phase gas transport method

    Directory of Open Access Journals (Sweden)

    S. H. Tabatabai Yazdi

    2006-03-01

    Full Text Available   Cd0.96Zn0.04Te crystals were grown using vapor phase gas transport method (VPGT. The results show that dendritic crystals with grain size up to 3.5 mm can be grown with this technique. X-ray diffraction and Laue back-reflection patterns show that dendritic crystals are single-phase, whose single crystal grains are randomly oriented with respect to the gas-transport axis. Electrical measurements, carried out using Van der Pauw method, show that the as-grown crystals have resistivity of about 104 Ω cm and n-type conductivity.

  17. Crystal Growth of Solid Solution HgCdTe Alloys

    Science.gov (United States)

    Lehoczky, Sandor L.

    1997-01-01

    The growth of homogenous crystals of HgCdTe alloys is complicated by the large separation between their liquidus and solidus temperatures. Hg(1-x)Cd(x)Te is representative of several alloys which have electrical and optical properties that can be compositionally tuned for a number of applications. Limitations imposed by gravity during growth and results from growth under reduced conditions are described. The importance of residual accelerations was demonstrated by dramatic differences in compositional distribution observed for different attitudes of the space shuttle that resulted in different steady acceleration components.

  18. Growth of lead-tin telluride crystals under high gravity

    Science.gov (United States)

    Regel, L. L.; Turchaninov, A. M.; Shumaev, O. V.; Bandeira, I. N.; An, C. Y.; Rappl, P. H. O.

    1992-04-01

    The influence of high gravity environment on several growth habits of lead-tin telluride crystals began to be investigated. Preliminary experiments with Pb 0.8Sn 0.2te grown by the Bridgman technique had been made at the centrifuge facilities of the Y.A. Gagarin Cosmonauts Center in the USSR, using accelerations of 5 g, 5.2 g and 8 g. The Sn distribution for these crystals was compared with that obtained for growth at normal gravity and the results show the existence of significant compositional inhomogeneities along the axial direction. Convection currents at high gravity seem to help multiple nucleation and subsequent random orientation of growth. Analyses of carrier concentrations as well as morphological characteristics were also made.

  19. Using Microfluidics to Decouple Nucleation and Growth of Protein Crystals.

    Science.gov (United States)

    Shim, Jung-Uk; Cristobal, Galder; Link, Darren R; Thorsen, Todd; Fraden, Seth

    2007-01-01

    A high throughput, low volume microfluidic device has been designed to decouple the physical processes of protein crystal nucleation and growth. This device, called the Phase Chip, is constructed out of poly(dimethylsiloxane) (PDMS) elastomer. One of the Phase Chip's innovations is to exploit surface tension forces to guide each drop to a storage chamber. We demonstrate that nanoliter water-in-oil drops of protein solutions can be rapidly stored in individual wells thereby allowing the screening of 1000 conditions while consuming a total of only 10 mug protein on a 20 cm(2) chip. Another significant advance over current microfluidic devices is that each well is in contact with a reservoir via a dialysis membrane through which only water and other low molecular weight organic solvents can pass, but not salt, polymer, or protein. This enables the concentration of all solutes in a solution to be reversibly, rapidly, and precisely varied in contrast to current methods, such as the free interface diffusion or sitting drop methods, which are irreversible. The Phase Chip operates by first optimizing conditions for nucleation by using dialysis to supersaturate the protein solution, which leads to nucleation of many small crystals. Next, conditions are optimized for crystal growth by using dialysis to reduce the protein and precipitant concentrations, which leads small crystals to dissolve while simultaneously causing only the largest ones to grow, ultimately resulting in the transformation of many small, unusable crystals into a few large ones.

  20. Vapor Growth of Alloy-Type Semiconductor Crystals

    Science.gov (United States)

    Wiedemeier, H.

    1985-01-01

    The present effort is part of a continuing research program directed towards the investigation of basic vapor transport phenomena and of crystal growth properties of electronic materials. The primary purpose of ground-based studies is the development and definition of optimum experimental parameters for flight experiments. The ground-based effort includes the investigation of gravity-driven convection effects on mass transport rates and on crystal morphology for different orientations of the density gradient with respect to the gravity vector, and as a function of pressure and of temperature. In addition to the experimental tasks, theoretical efforts involve the quantitative thermodynamic analysis of the systems under investigation, the computation of fluid dynamic parameters, and the consideration of other possible effects on fluid flow under vertical, stabilizing and microgravity conditions. The specific experiments to be performed in a microgravity environment include the investigation of vapor transport and crystal growth phenomena of the GeSe-Xenon system and of the mass flux and growth of bulk and layer-type crystals of Hg sub (1-x) Cd sub x Te using HgI as a transport agent.

  1. Twin-mediated crystal growth: an enigma resolved

    Science.gov (United States)

    Shahani, Ashwin J.; Gulsoy, E. Begum; Poulsen, Stefan O.; Xiao, Xianghui; Voorhees, Peter W.

    2016-06-01

    During crystal growth, faceted interfaces may be perturbed by defects, leading to a rich variety of polycrystalline growth forms. One such defect is the coherent Σ3 {111} twin boundary, which is widely known to catalyze crystal growth. These defects have a profound effect on the properties of many materials: for example, electron-hole recombination rates strongly depend on the character of the twin boundaries in polycrystalline Si photovoltaic cells. However, the morphology of the twinned interface during growth has long been a mystery due to the lack of four-dimensional (i.e., space and time resolved) experiments. Many controversial mechanisms have been proposed for this process, most of which lack experimental verification. Here, we probe the real-time interfacial dynamics of polycrystalline Si particles growing from an Al-Si-Cu liquid via synchrotron-based X-ray tomography. Our novel analysis of the time evolution of the interfacial normals allows us to quantify unambiguously the habit plane and grain boundary orientations during growth. This, when combined with direct measurements of the interfacial morphology provide the first confirmation of twin-mediated growth, proposed over 50 years ago. Using the insights provided by these experiments, we have developed a unified picture of the phenomena responsible for the dynamics of faceted Si growth.

  2. Phase-field simulation of formation of cellular dendrites and fine cellular structures at high growth velocities during directional solidification of Ti56Al44 alloy

    Institute of Scientific and Technical Information of China (English)

    LI Xin-zhong; GUO Jing-jie; SU Yan-qing; WU Shi-ping; FU Heng-zhi

    2005-01-01

    A phase-field model whose free energy of the solidification system derived from the Calphad thermodynamic modeling of phase diagram was used to simulate formation of cellular dendrites and fine cellular structures of Ti56Al44 alloy during directional solidification at high growth velocities. The liquid-solid phase transition of L→β was chosen. The dynamics of breakdown of initially planar interfaces into cellular dendrites and fine cellular structures were shown firstly at two growth velocities. Then the unidirectional free growths of two initial nucleations evolving to fine cellular dendrites were investigated. The tip splitting phenomenon is observed and the negative temperature gradient in the liquid represents its supercooling directional solidification. The simulation results show the realistic evolution of interfaces and microstructures and they agree with experimental one.

  3. Study of Growth Mechanism of Lysozyme Crystal by Batch Crystallization Method

    Institute of Scientific and Technical Information of China (English)

    Hai Liang CUI; Yong YU; Wan Chun CHEN; Qi KANG

    2006-01-01

    The lysozyme crystals were made by batch crystallization method and the distribution of aggregate in solution were measured by dynamic light scattering. The results showed that the dimension of aggregate increased with the increase of the concentration of lysozyme and NaC1,lysozyme molecules aggregated gradually in solution and finally arrived at balance each other.The higher the concentrations of lysozyme and NaC1 were, the faster the growth rate of (110) face was. The growth rates of lysozyme crystal were obtained by a Zeiss microscope, and the effective surface energy (α) of growing steps were calculated about 4.01×l0-8 J.cm-2 according to the model of multiple two-dimensional nucleation mechanism.

  4. Crystal Splitting in the Growth of Bi2S3

    Energy Technology Data Exchange (ETDEWEB)

    Tang, Jing; Alivisatos, A. Paul

    2006-06-15

    Novel Bi{sub 2}S{sub 3} nanostructures with a sheaf-like morphology are obtained via reaction of bismuth acetate-oleic acid complex with elemental sulfur in 1-octadecence. We propose these structures form by the splitting crystal growth mechanism, which is known to account for the morphology some mineral crystals assume in nature. By controlling the synthetic parameters, different forms of splitting, analogous to observed in minerals, are obtained in our case of Bi{sub 2}S{sub 3}. These new and complex Bi{sub 2}S{sub 3} nanostructures are characterized by TEM, SEM, XRD and ED.

  5. III-V semiconductor solid solution single crystal growth

    Science.gov (United States)

    Gertner, E. R.

    1982-01-01

    The feasibility and desirability of space growth of bulk IR semiconductor crystals for use as substrates for epitaxial IR detector material were researched. A III-V ternary compound (GaInSb) and a II-VI binary compound were considered. Vapor epitaxy and quaternary epitaxy techniques were found to be sufficient to permit the use of ground based binary III-V crystals for all major device applications. Float zoning of CdTe was found to be a potentially successful approach to obtaining high quality substrate material, but further experiments were required.

  6. Control of crystal growth in water purification by directional freeze crystallization

    Science.gov (United States)

    Conlon, William M. (Inventor)

    1996-01-01

    A Directional Freeze Crystallization system employs an indirect contact heat exchanger to freeze a fraction of liquid to be purified. The unfrozen fraction is drained away and the purified frozen fraction is melted. The heat exchanger must be designed in accordance with a Growth Habit Index to achieve efficient separation of contaminants. If gases are dissolved in the liquid, the system must be pressurized.

  7. Dependence of calcite growth rate and Sr partitioning on solution stoichiometry: Non-Kossel crystal growth

    NARCIS (Netherlands)

    Nehrke, G.; Reichart, G.-J.; Van Cappellen, P.; Meile, C.; Bijma, J.

    2007-01-01

    Seeded calcite growth experiments were conducted at fixed pH (10.2) and two degrees of supersaturation (Ω = 5, 16), while varying the Ca2+ to CO3 2- solution ratio over several orders of magnitude. The calcite growth rate and the incorporation of Sr in the growing crystals strongly depended on

  8. Dendritic design as an archetype for growth patterns in Nature: fractal and constructal views

    Directory of Open Access Journals (Sweden)

    Antonio F. Miguel

    2014-02-01

    Full Text Available The occurrence of configuration (design, shape, structure, rhythm is a universal phenomenon that occurs in every flow system. Dendritic configuration (or tree-shaped configurations is ubiquitous in nature and likely to arise in both animate and inanimate flow systems. Why is it so important? Is there a principle from which this configuration can be deduced? In this review paper we show that these systems own two of the most important properties of fractals that are self-similarity and scaling. Their configuration do not develop by chance. It´s occurrence is a universal phenomenon of physics covered by a principle. Here we also show that the emergence of dendritic configuration in flow systems constitutes a basic supportive flow path along which order need to persist is propagated.

  9. In situ atomic force microscopy of layer-by-layer crystal growth and key growth concepts

    Science.gov (United States)

    Rashkovich, L. N.; de Yoreo, J. J.; Orme, C. A.; Chernov, A. A.

    2006-12-01

    Contradictions that have been found recently between the representations of classical theory and experiments on crystal growth from solutions are considered. Experimental data show that the density of kinks is low in many cases as a result of the low rate of their fluctuation generation, the Gibbs-Thomson law is not always applicable in these cases, and there is inconsistency with the Cabrera-Vermilyea model. The theory of growth of non-Kossel crystals, which is to be developed, is illustrated by the analysis of the experimental dependence of the growth rate on the solution stoichiometry.

  10. Crystal growth in a three-phase system: diffusion and liquid-liquid phase separation in lysozyme crystal growth.

    Science.gov (United States)

    Heijna, M C R; van Enckevort, W J P; Vlieg, E

    2007-07-01

    In the phase diagram of the protein hen egg-white lysozyme, a region is present in which the lysozyme solution demixes and forms two liquid phases. In situ observations by optical microscopy show that the dense liquid droplets dissolve when crystals grow in this system. During this process the demixed liquid region retracts from the crystal surface. The spatial distribution of the dense phase droplets present special boundary conditions for Fick's second law for diffusion. In combination with the cylindrical symmetry provided by the kinetically roughened crystals, this system allows for a full numerical analysis. Using experimental data for setting the boundary conditions, a quasi-steady-state solution for the time-dependent concentration profile was shown to be valid. Comparison of kinetically rough growth in a phase separated system and in a nonseparated system shows that the growth kinetics for a three-phase system differs from a two-phase system, in that crystals grow more slowly but the duration of growth is prolonged.

  11. Nanoparticle-mediated nonclassical crystal growth of sodium fluorosilicate nanowires and nanoplates

    Directory of Open Access Journals (Sweden)

    Hongxia Li

    2011-12-01

    Full Text Available We observed nonclassical crystal growth of the sodium fluorosilicate nanowires, nanoplates, and hierarchical structures through self-assembly and aggregation of primary intermediate nanoparticles. Unlike traditional ion-by-ion crystallization, the primary nanoparticles formed first and their subsequent self-assembly, fusion, and crystallization generated various final crystals. These findings offer direct evidences for the aggregation-based crystallization mechanism.

  12. Microgravity protein crystal growth; results and hardware development

    Science.gov (United States)

    DeLucas, Lawrence J.; Smith, Graig D.; Carter, Daniel C.; Snyder, Robert S.; McPherson, A.; Koszelak, S.; Bugg, Charles E.

    1991-02-01

    Protein crystal growth experiments have been performed on a series of US shuttle missions. Crystallographic studies of proteins and nucleic acids have played key roles in establishing the structural foundations of molecular biology and biochemistry and for revealing structure/function relationships that are of major importance in understanding how macromolecules operate in biological systems. A number of major advances in the technology involved in determining protein structures have shortened the time span involved in structure determination. The major bottleneck in the widespread application of protein crystallography is the ability to produce high quality crystals that are suitable for a complete structural analysis. Evidence from several investigations indicates that crystals of superior quality can be obtained in a microgravity environment. This paper summarizes results obtained from a series of US shuttle missions and describes new hardware currently being developed for future shuttle missions.

  13. Physical modelling of Czochralski crystal growth in horizontal magnetic field

    Science.gov (United States)

    Grants, Ilmārs; Pal, Josef; Gerbeth, Gunter

    2017-07-01

    This study addresses experimentally the heat transfer, the temperature azimuthal non-uniformity and the onset of oscillations in a low temperature physical model of a medium-sized Czochralski crystal growth process with a strong horizontal magnetic field (HMF). It is observed that under certain conditions the integral heat flux may decrease with increasing magnetic field strength at the same time as the flow velocity increases. The azimuthal non-uniformity of the temperature field in the melt near the crystal model rim is only little influenced by its rotation rate outside of a narrow range where the centrifugal force balances the buoyant one. The flow oscillation onset has been observed for two values of the HMF strength. Conditions of this onset are little influenced by the crystal rotation. The critical temperature difference of the oscillation onset considerably exceeds that of the Rayleigh-Bénard (RB) cell in a strong HMF.

  14. The nacre protein perlucin nucleates growth of calcium carbonate crystals.

    Science.gov (United States)

    Blank, S; Arnoldi, M; Khoshnavaz, S; Treccani, L; Kuntz, M; Mann, K; Grathwohl, G; Fritz, M

    2003-12-01

    Atomic force microscopy (AFM) in aqueous solution was used to investigate native nacre of the marine snail Haliotis laevigata on the microscopic scale and the interaction of purified nacre proteins with calcium carbonate crystals on the nanoscopic scale. These investigations were controlled by scanning electron microscopy (SEM), light microscopy (LM) and biochemical methods. For investigations with AFM and SEM, nacre was cleaved parallel to the aragonite tablets in this biogenic polymer/mineral composite. Multilamellar organic sheets consisting of a core of chitin with layers of proteins attached on both sides lay between the aragonite layers consisting of confluent aragonite tablets. Cleavage appeared to occur between the aragonite tablet layer and the protein layer. AFM images revealed a honeycomb-like structure to the organic material with a diameter of the 'honeycombs' equalling that of the aragonite tablets. The walls of the structures consisted of filaments, which were suggested to be collagen. The flat regions of the honeycomb-like structures exhibited a hole with a diameter of more than 100 nm. When incubated in saturated calcium carbonate solution, aragonite needles with perfect vertical orientation grew on the proteinacous surface. After treatment with proteinase K, no growth of orientated aragonite needles was detected. Direct AFM measurements on dissolving and growing calcite crystals revealed a surface structure with straight steps the number of which decreased with crystal growth. When the purified nacre protein perlucin was added to the growth solution (a super-saturated calcium carbonate solution) new layers were nucleated and the number of steps increased. Anion exchange chromatography of the water-soluble proteins revealed a mixture of about 10 different proteins. When this mixture was dialysed against saturated calcium carbonate solution and sodium chloride, calcium carbonate crystals precipitated together with perlucin leaving the other proteins

  15. Analysis of the carbon source for diamond crystal growth

    Institute of Scientific and Technical Information of China (English)

    LI Li; XU Bin; LI MuSen

    2008-01-01

    The lattice constants of diamond and graphite at high pressure and high temperature (HPHT) were calculated on the basis of linear expansion coefficient and elastic constant. According to the empirical electron theory of solids and molecules (EET), the valence electron structures (VESs) of diamond, graphite crystal and their common planes were calculated. The relationship between diamond and graphite structure was analyzed based on the boundary condition of the improved Thomas-Fermi-Dirac theory by Cheng (TFDC). It was found that the electron densities of common planes in graphite were not continuous with those of planes in diamond at the first order of approximation. The results show that during the course of diamond single crystal growth at HPHT with metal catalyst, the carbon sources forming diamond structure do not come from the graphite structure directly. The diamond growth mechanism was discussed from the viewpoint of valence electron structure.

  16. Growth morphology of zinc tris(thiourea) sulphate crystals

    Indian Academy of Sciences (India)

    Sunil Verma; M K Singh; V K Wadhawan; C H Suresh

    2000-06-01

    The growth morphology of crystals of zinc tris(thiourea) sulphate (ZTS) is investigated experimentally, and computed using the Hartman–Perdok approach. Attachment energies of the observed habit faces are calculated for determining their relative morphological importance. A computer code is developed for carrying out these calculations. A special procedure is adopted for computing the cohesive energy of a slice of the structure parallel to any rational crystallographic plane. For estimating the cohesive energies, formal charges on the experimentally determined atomic positions in the molecules of ZTS are calculated by ab initio molecular-orbital computations, with wave functions obtained by the Hartree–Fock procedure. Fairly good agreement with the observed crystal morphology is obtained for a model of growth mechanism in which ZTS is assumed to exist in solution as zinc tris(thiourea) ions and sulphate ions.

  17. A new approach to the CZ crystal growth weighing control

    Science.gov (United States)

    Kasimkin, P. V.; Moskovskih, V. A.; Vasiliev, Y. V.; Shlegel, V. N.; Yuferev, V. S.; Vasiliev, M. G.; Zhdankov, V. N.

    2014-03-01

    The aim of a new approach was to improve the robustness of the weighing control of CZ growth especially for semiconductors, for which the “anomalous“ behavior of the apparent weight provokes instability of the servo-loop. In the described method, the periodic reciprocating measuring motion of small amplitude is superposed on the uniform pull-rod movement. The cross-sectional area is determined from the weight sensor responses that are modulated mainly by the forces of hydrostatic pressure. By the example of germanium crystal growth, it is shown that in the control system, based on such a way of the diameter measuring, a simple PI control law provides a good close loop system's stability and dynamics for the materials with the “anomalous” behavior of a weighing signal. The effect of a meniscus on the modulation measuring of a crystal diameter is also discussed.

  18. Mathematical modeling and numerical simulation of Czochralski Crystal Growth

    Energy Technology Data Exchange (ETDEWEB)

    Jaervinen, J.; Nieminen, R. [Center for Scientific Computing, Espoo (Finland)

    1996-12-31

    A detailed mathematical model and numerical simulation tools based on the SUPG Finite Element Method for the Czochralski crystal growth has been developed. In this presentation the mathematical modeling and numerical simulation of the melt flow and the temperature distribution in a rotationally symmetric crystal growth environment is investigated. The temperature distribution and the position of the free boundary between the solid and liquid phases are solved by using the Enthalpy method. Heat inside of the Czochralski furnace is transferred by radiation, conduction and convection. The melt flow is governed by the incompressible Navier-Stokes equations coupled with the enthalpy equation. The melt flow is numerically demonstrated and the temperature distribution in the whole Czochralski furnace. (author)

  19. Solar furnace satellite for large diameter crystal growth in space

    Science.gov (United States)

    Overfelt, Tony; Wells, Mark; Blake, John

    1993-02-01

    Investigators worldwide are preparing experiments to test the influence of low gravity found in space on the growth of many crystalline materials. However, power limitations prevent existing space crystal growth furnaces from being able to process samples any larger than about 2 cm, and in addition, the background microgravity levels found on the Space Shuttle are not low enough to significantly benefit samples much larger than 2 cm. This paper describes a novel concept of a free-flying platform utilizing well-established solar furnace technology to enable materials processing in space experiments on large-diameter crystals. The conceptual design of this Solar Furnace Satellite is described along with its operational scenario and the anticipated g levels.

  20. Growth morphologies and optical properties of LTA single crystal.

    Science.gov (United States)

    Liu, Xiaojing; Ren, Miaojuan; Chen, Gang; Wang, Peiji

    2013-12-01

    Atomic force microscopy (AFM) has been used to study the growth morphologies of l-threonine acetate (abbreviated as LTA) crystal. Spiral growth hillocks and typical step patterns are described and discussed. Nuclei with various shapes often distribute at the larger step terraces. Eventually, in order to investigate microscopic second order nonlinear optical properties of LTA crystals, the molecular dipole moment (μ), polarizability (α), and first hyperpolarizability (β) were computed using a series of basis sets including polarized and diffuse functions at the framework of Hartree-Fock and density functional theory methods. The study is helpful to the further development of l-threonine analogs with improved nonlinear optical properties. Copyright © 2013 Elsevier B.V. All rights reserved.

  1. Synthesis, crystal structure, crystal growth and physical properties of N,N-diethyl anilinium picrate

    Science.gov (United States)

    Subramaniyan @ Raja, R.; Anandha Babu, G.; Ramasamy, P.

    2011-11-01

    Crystalline substance of N,N-diethyl anilinium picrate (NNDEAP) has been synthesized and single crystals of NNDEAP were successfully grown for the first time by the slow evaporation solution growth technique at room temperature with dimensions 14×10×10 mm3. The formation of the new crystal has been confirmed by single crystal X-ray diffraction studies. The structural perfection of the grown crystal was analyzed by high resolution X-ray diffraction (HRXRD) measurements. The functional groups of NNDEAP have been identified by Fourier transform infrared spectral studies. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) have also been carried out and the thermal behavior of NNDEAP has been studied. The UV-vis-NIR studies have been carried out to identify the optical transmittance and the cut off wavelength of NNDEAP is identified. The dielectric loss and the dielectric constant as a function of frequency and temperature were measured for the grown crystal and the nature of variation of dielectric constant εr and dielectric losses (tan δ) were studied. Vicker's hardness test has been carried out on NNDEAP to measure the load dependent hardness. The laser induced surface damage threshold for the grown crystal was measured using Nd:YAG laser.

  2. Crystal growth and reflectivity studies of Zn1–MnTe crystals

    Indian Academy of Sciences (India)

    K Veera Brahmam; D Raja Reddy; B K Reddy

    2005-08-01

    Single crystals of Zn1–MnTe were prepared by vertical Bridgman crystal growth method for different concentrations of Mn. Chemical analysis and reflectivity studies were carried out for compositional and band structure properties. Microscopic variation in composition between starting and end compounds was observed from EDAX analysis. Linear dependence of fundamental absorption edge (0) as a function of Mn concentration () was expressed in terms of a straight line fit and a shift in 0 towards higher energy was observed in reflectivity spectra of Zn1–MnTe.

  3. Screening and Crystallization Plates for Manual and High-throughput Protein Crystal Growth

    Science.gov (United States)

    Thorne, Robert E. (Inventor); Berejnov, Viatcheslav (Inventor); Kalinin, Yevgeniy (Inventor)

    2010-01-01

    In one embodiment, a crystallization and screening plate comprises a plurality of cells open at a top and a bottom, a frame that defines the cells in the plate, and at least two films. The first film seals a top of the plate and the second film seals a bottom of the plate. At least one of the films is patterned to strongly pin the contact lines of drops dispensed onto it, fixing their position and shape. The present invention also includes methods and other devices for manual and high-throughput protein crystal growth.

  4. Reduced Insulin/Insulin-Like Growth Factor Receptor Signaling Mitigates Defective Dendrite Morphogenesis in Mutants of the ER Stress Sensor IRE-1

    Science.gov (United States)

    Salzberg, Yehuda; Cohen-Berkman, Moran; Biederer, Thomas; Bülow, Hannes E.

    2017-01-01

    Neurons receive excitatory or sensory inputs through their dendrites, which often branch extensively to form unique neuron-specific structures. How neurons regulate the formation of their particular arbor is only partially understood. In genetic screens using the multidendritic arbor of PVD somatosensory neurons in the nematode Caenorhabditis elegans, we identified a mutation in the ER stress sensor IRE-1/Ire1 (inositol requiring enzyme 1) as crucial for proper PVD dendrite arborization in vivo. We further found that regulation of dendrite growth in cultured rat hippocampal neurons depends on Ire1 function, showing an evolutionarily conserved role for IRE-1/Ire1 in dendrite patterning. PVD neurons of nematodes lacking ire-1 display reduced arbor complexity, whereas mutations in genes encoding other ER stress sensors displayed normal PVD dendrites, specifying IRE-1 as a selective ER stress sensor that is essential for PVD dendrite morphogenesis. Although structure function analyses indicated that IRE-1’s nuclease activity is necessary for its role in dendrite morphogenesis, mutations in xbp-1, the best-known target of non-canonical splicing by IRE-1/Ire1, do not exhibit PVD phenotypes. We further determined that secretion and distal localization to dendrites of the DMA-1/leucine rich transmembrane receptor (DMA-1/LRR-TM) is defective in ire-1 but not xbp-1 mutants, suggesting a block in the secretory pathway. Interestingly, reducing Insulin/IGF1 signaling can bypass the secretory block and restore normal targeting of DMA-1, and consequently normal PVD arborization even in the complete absence of functional IRE-1. This bypass of ire-1 requires the DAF-16/FOXO transcription factor. In sum, our work identifies a conserved role for ire-1 in neuronal branching, which is independent of xbp-1, and suggests that arborization defects associated with neuronal pathologies may be overcome by reducing Insulin/IGF signaling and improving ER homeostasis and function. PMID

  5. Growth of crystalline semiconductor materials on crystal surfaces

    CERN Document Server

    Aleksandrov, L

    2013-01-01

    Written for physicists, chemists, and engineers specialising in crystal and film growth, semiconductor electronics, and various applications of thin films, this book reviews promising scientific and engineering trends in thin films and thin-films materials science. The first part discusses the physical characteristics of the processes occurring during the deposition and growth of films, the principal methods of obtaining semiconductor films and of reparing substrate surfaces on which crystalline films are grown, and the main applications of films. The second part contains data on epitaxial i

  6. Effect of dendrite arm spacing and the γ’ phase size on stress rupture properties of Ni3Al-base single crystal superalloy IC6SX

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The effect of dendrite arm spacing and the size of γ’ phase on stress rupture properties of as-cast Ni3Al-based single crystal superalloy IC6SX was studied.It has been found that the stress rupture properties were affected by dendrite arm spacing and the size of γ’ phase significantly,i.e.,the stress rupture lives of as-cast specimens under the test condition of 1100°C/120 MPa were significantly increased from about 10 h to 31 h with decreasing dendrite arm spacing and the size of γ’ phase from 3.0 μm and 1.6 μm to 1.3 μm and 0.8 μm,respectively.The creep cracks generated easily in the brittle Y-NiMo phase.Then the cracks gradually mergered and grew up during creep,and finally led to specimens fracture.The orientated coarsening of γ’ phase has been found in the stress ruptured specimens,due to the elements diffusion.However,the γ’ phase did not form the integrated structure during the short periods of 10-31 h as the creep tests lasted.

  7. RAB-10 Regulates Dendritic Branching by Balancing Dendritic Transport.

    Directory of Open Access Journals (Sweden)

    Caitlin A Taylor

    2015-12-01

    Full Text Available The construction of a large dendritic arbor requires robust growth and the precise delivery of membrane and protein cargoes to specific subcellular regions of the developing dendrite. How the microtubule-based vesicular trafficking and sorting systems are regulated to distribute these dendritic development factors throughout the dendrite is not well understood. Here we identify the small GTPase RAB-10 and the exocyst complex as critical regulators of dendrite morphogenesis and patterning in the C. elegans sensory neuron PVD. In rab-10 mutants, PVD dendritic branches are reduced in the posterior region of the cell but are excessive in the distal anterior region of the cell. We also demonstrate that the dendritic branch distribution within PVD depends on the balance between the molecular motors kinesin-1/UNC-116 and dynein, and we propose that RAB-10 regulates dendrite morphology by balancing the activity of these motors to appropriately distribute branching factors, including the transmembrane receptor DMA-1.

  8. Special phase transformation and crystal growth pathways observed in nanoparticles†

    Directory of Open Access Journals (Sweden)

    Finnegan Michael P

    2003-11-01

    Full Text Available Phase transformation and crystal growth in nanoparticles may happen via mechanisms distinct from those in bulk materials. We combine experimental studies of as-synthesized and hydrothermally coarsened titania (TiO2 and zinc sulfide (ZnS with thermodynamic analysis, kinetic modeling and molecular dynamics (MD simulations. The samples were characterized by transmission electron microscopy, X-ray diffraction, synchrotron X-ray absorption and scattering, and UV-vis spectroscopy. At low temperatures, phase transformation in titania nanoparticles occurs predominantly via interface nucleation at particle–particle contacts. Coarsening and crystal growth of titania nanoparticles can be described using the Smoluchowski equation. Oriented attachment-based crystal growth was common in both hydrothermal solutions and under dry conditions. MD simulations predict large structural perturbations within very fine particles, and are consistent with experimental results showing that ligand binding and change in aggregation state can cause phase transformation without particle coarsening. Such phenomena affect surface reactivity, thus may have important roles in geochemical cycling.

  9. Effect of traveling magnetic field on solute distribution and dendritic growth in unidirectionally solidifying Sn-50 wt%Pb alloy: An in situ observation

    Science.gov (United States)

    Cao, Fei; Yang, Fenfen; Kang, Huijun; Zou, Cunlei; Xiao, Tiqiao; Huang, Wanxia; Wang, Tongmin

    2016-09-01

    Synchrotron X-ray radiography was used to in situ study the solute distribution and the dendritic growth during the bottom-up solidification of Sn-50 wt%Pb alloy under a traveling magnetic field (TMF) for the first time. The buoyance driven evolution and motion of the plumes containing Sn-rich melt are directly observed in the solidification front before the application of TMF. A forced melt flow from left to right is induced with the application of TMF, which results in the redistribution of the solute concentration (facilitate the solute transportation and reduce the local fluctuations considerably) and the change of the dendrite morphologies (promote/suppress the growth of the secondary arms, remelting and fragmentation of dendrites). Meanwhile, the concentration variations of Sn around the solidification front are quantitatively analyzed through the extraction of gray level from sequenced X-ray images.

  10. Autism-associated Dyrk1a truncation mutants impair neuronal dendritic and spine growth and interfere with postnatal cortical development.

    Science.gov (United States)

    Dang, T; Duan, W Y; Yu, B; Tong, D L; Cheng, C; Zhang, Y F; Wu, W; Ye, K; Zhang, W X; Wu, M; Wu, B B; An, Y; Qiu, Z L; Wu, B L

    2017-02-07

    Autism is a prevailing neurodevelopmental disorder with a large genetic/genomic component. Recently, the dual-specificity tyrosine-(Y)-phosphorylation-regulated kinase 1 A (DYRK1A) gene was implicated as a risk factor for autism spectrum disorder (ASD). We identified five DYRK1A variants in ASD patients and found that the dose of DYRK1A protein has a crucial role in various aspects of postnatal neural development. Dyrk1a loss of function and gain of function led to defects in dendritic growth, dendritic spine development and radial migration during cortical development. Importantly, two autism-associated truncations, R205X and E239X, were shown to be Dyrk1a loss-of-function mutants. Studies of the truncated Dyrk1a mutants may provide new insights into the role of Dyrk1a in brain development, as well as the role of Dyrk1a loss of function in the pathophysiology of autism.Molecular Psychiatry advance online publication, 7 February 2017; doi:10.1038/mp.2016.253.

  11. Non-linear optical titanyl arsenates: Crystal growth and properties

    Science.gov (United States)

    Nordborg, Jenni Eva Louise

    Crystals are appreciated not only for their appearance, but also for their unique physical properties which are utilized by the photonic industry in appliances that we come across every day. An important part of enabling the technical use of optical devices is the manufacture of crystals. This dissertation deals with a specific group of materials called the potassium titanyl phosphate (KIP) family, known for their non-linear optical and ferroelectric properties. The isomorphs vary in their linear optical and dielectric properties, which can be tuned to optimize device performance by forming solid solutions of the different materials. Titanyl arsenates have a wide range of near-infrared transmission which makes them useful for tunable infrared lasers. The isomorphs examined in the present work were primarily RbTiOASO4 (RTA) and CsTiOAsO4 (CTA) together with the mixtures RbxCs 1-xTiOAsO4 (RCTA). Large-scale crystals were grown by top seeding solution growth utilizing a three-zone furnace with excellent temperature control. Sufficiently slow cooling and constant upward lifting produced crystals with large volumes useable for technical applications. Optical quality RTA crystals up to 10 x 12 x 20 mm were grown. The greater difficulty in obtaining good crystals of CTA led to the use of mixed RCTA materials. The mixing of rubidium and cesium in RCTA is more favorable to crystal growth than the single components in pure RTA and CTA. Mixed crystals are rubidium-enriched and contain only 20-30% of the cesium concentration in the flux. The cesium atoms show a preference for the larger cation site. The network structure is very little affected by the cation substitution; consequently, the non-linear optical properties of the Rb-rich isomorphic mixtures of RTA and CTA can be expected to remain intact. Crystallographic methods utilizing conventional X-ray tubes, synchrotron radiation and neutron diffraction have been employed to investigate the properties of the atomic

  12. Protracted dendritic growth in the typically developing human amygdala and increased spine density in young ASD brains.

    Science.gov (United States)

    Weir, R K; Bauman, M D; Jacobs, B; Schumann, C M

    2017-09-20

    The amygdala is a medial temporal lobe structure implicated in social and emotional regulation. In typical development (TD), the amygdala continues to increase volumetrically throughout childhood and into adulthood, while other brain structures are stable or decreasing in volume. In autism spectrum disorder (ASD), the amygdala undergoes rapid early growth, making it volumetrically larger in children with ASD compared to TD children. Here we explore: 1) if dendritic arborization in the amygdala follows the pattern of protracted growth in TD and early overgrowth in ASD and 2), if spine density in the amygdala in ASD cases differs from TD from youth to adulthood. The amygdala from 32 postmortem human brains (7-46 years of age) was stained using a Golgi-Kopsch impregnation. Ten principal neurons per case were selected in the lateral nucleus and traced using Neurolucida software in their entirety. We found that both ASD and TD individuals show a similar pattern of increasing dendritic length with age well into adulthood. However, spine density is i) greater in young ASD cases compared to age-matched TD controls (ASD age into adulthood, a phenomenon not found in typical development. Therefore, by adulthood, there is no observable difference in spine density in the amygdala between ASD and TD age-matched adults (≥18 years old). Our findings highlight the unique growth trajectory of the amygdala and suggest that spine density may contribute to aberrant development and function of the amygdala in children with ASD. This article is protected by copyright. All rights reserved. © 2017 Wiley Periodicals, Inc.

  13. Luminescence labeling and dynamics of growth active crystal surface structures

    Science.gov (United States)

    Bullard, Theresa Vivian

    One aspect of the multifaceted proposal by A. G. Cairns-Smith (CS), that imperfect crystals have the capacity to act as primitive genes by transferring the disposition of their imperfections from one crystal to another, is investigated. An experiment was designed in a model crystalline system unrelated to the composition of the pre-biotic earth but suited to a well-defined test. Plates of potassium hydrogen phthalate were studied in order to ascertain whether, according to CS, parallel screw dislocations could serve as an information store with cores akin to punches in an old computer card. Evidence of screw dislocations was obtained from their associated growth hillocks through differential interference contrast microscopy, atomic force microscopy, and luminescence labeling of hillocks in conjunction with confocal laser scanning microscopy. Inheritance was evaluated by the corresponding patterns of luminescence developed in 'daughter' crystals grown from seed in the presence of fluorophores. The dispositions and evolution of growth active hillock patterns were quantified by fractal correlation analysis and statistical analysis. Along the way, we came to realize that transferring information encoded in the disposition of screw dislocations is complicated by several factors that lead to 'mutations' in the information stored in the pattern of defects. These observations forced us to confront the fundamental mechanisms that give rise to screw dislocations. It became clear that inter-hillock correlations play a significant role in the appearance of new dislocations through growth, and cause the overall pattern of hillocks to be non-random. Tendencies for clustering and correlations along various crystallographic directions were observed. Investigations into the dye-crystal surface chemistries and interactions with hillock steps also ensued through a combination of experimental techniques and force-field calculations. It was established that certain dye molecules not

  14. Oriented growth and assembly of zeolite crystals on substrates

    Institute of Scientific and Technical Information of China (English)

    ZHOU Ming; ZHANG BaoQuan; LIU XiuFeng

    2008-01-01

    The aligned array and thin film of zeolites and molecular sieves possess a variety of potential applica-tions in membrane separation and catalysis, chemical sensors, and microelectronic devices. There are two main synthesis methods for manufacturing the aligned arrays and thin films of zeolites and mo-lecular sieves, i.e. in situ hydrothermal reaction and self-assembly of crystal grains on substrates. Both of them have attracted much attention in the scientific community worldwide. A series of significant progress has been made in recent years. By the in situ hydrothermal synthesis, the oriented nucleation and growth of zeolite and molecular sieve crystals can be achieved by modifying the surface properties of substrates or by changing the composition of synthesis solutions, leading to the formation of uni-formly oriented multicrystal-aligned arrays or thin films. On the other hand, the crystal grains of zeo-lites and molecular sieves can be assembled onto the substrate surface in required orientation using different bondages, for instance, the microstructure in the array or thin film can be controlled. This review is going to summarize and comment the significant results and progress reported recently in manufacturing highly covered and uniformly aligned arrays or thin films of zeolites and molecular sieves. It involves (1) in situ growth of highly aligned zeolite arrays and thin films via embedding func-tional groups on the substrate surface, modifying the surface microstructure of substrates, as well as varying the composition of synthesis solutions; (2) assembly of zeolite and molecular sieve crystals on various substrates to form aligned arrays and thin films with full coverage by covalent, ionic, and in-termolecular coupling interactions between crystals and substrates; (3) coupling surface assembly with microcontact printing or photoetching technique to produce patterned zeolite arrays and thin films. Finally, the functionality and applications of zeolite

  15. Growth and properties of Lithium Salicylate single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Zaitseva, N; Newby, J; Hull, G; Saw, C; Carman, L; Cherepy, N; Payne, S

    2009-02-13

    An attractive feature of {sup 6}Li containing fluorescence materials that determines their potential application in radiation detection is the capture reaction with slow ({approx}< 100 keV) neutrons: {sup 6}Li + n = {sup 4}He + {sup 3}H + 4.8MeV. The use of {sup 6}Li-salicylate (LiSal, LiC{sub 6}H{sub 5}O{sub 3}) for thermal neutron detection was previously studied in liquid and polycrystalline scintillators. The studies showed that both liquid and polycrystalline LiSal scintillators could be utilized in pulse shape discrimination (PSD) techniques that enable separation of neutrons from the background gamma radiation. However, it was found that the efficiency of neutron detection using LiSal in liquid solutions was severely limited by its low solubility in commonly used organic solvents like, for example, toluene or xylene. Better results were obtained with neutron detectors containing the compound in its crystalline form, such as pressed pellets, or microscopic-scale (7-14 micron) crystals dispersed in various media. The expectation drown from these studies was that further improvement of pulse height, PSD, and efficiency characteristics could be reached with larger and more transparent LiSal crystals, growth of which has not been reported so far. In this paper, we present the first results on growth and characterization of relatively large, a cm-scale size, single crystals of LiSal with good optical quality. The crystals were grown both from aqueous and anhydrous (methanol) media, mainly for neutron detection studies. However, the results on growth and structural characterization may be interesting for other fields where LiSal, together with other alkali metal salicylates, is used for biological, medical, and chemical (as catalyst) applications.

  16. Researches on the Growth Habit and Optical Properties of Fe3+ Ion Doped KDP Crystal

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    During the process of KDP crystal growth, metal ions strongly affect the growth habit and optical properties of KDP single crystal. In this paper, KDP crystals were grown from an aqueous solution doped with different concentration of Fe3+ dopant by traditional temperaturereduction method and "point-seed" rapid growth method. Furthermore, we examined the light scatter and measured the transmission of these KDP crystals. It is found that the dopant of Fe3+ ion can improve the stability of the KDP growth solution when its concentration is less than 30 ppm.The effects of Fe3+ ion on the growth habit and optical properties of KDP crystal are also obvious.

  17. Growth, spectral and crystallization perfection studies of semi organic non linear optical crystal - L-alanine lithium chloride

    Science.gov (United States)

    Redrothu, Hanumantharao; Kalainathan, S.; Bhagavannarayana, G.

    2012-06-01

    Single crystals of L-alanine lithium chloride single crystals were successfully grown using slow evaporation solution growth technique at constant temperature (303K). The formation of the new crystal has been confirmed by single-crystal X-ray diffraction, FT-IR studies. The crystalline perfection was analyzed by high-resolution X-ray diffraction (HRXRD) rocking curve measurements. The powder second harmonic generation (SHG) has been confirmed by Nd: YAG laser. The results have been discussed in detail.

  18. Growth and study of some gel grown group II single crystals of iodate

    Indian Academy of Sciences (India)

    Sharda J Shitole; K B Saraf

    2001-10-01

    Single crystals of calcium iodate and barium iodate were grown by simple gel technique by single diffusion method. The optimum conditions were established by varying various parameters such as pH of gel solution, gel concentration, gel setting time, concentration of the reactants etc. Crystals having different morphologies and habits were obtained. Prismatic, dendritic crystals of barium iodate and prismatic, needle shaped, hopper crystals of calcium iodate were obtained. Some of them were transparent, some transluscent, and few others were opaque. Both the crystals were studied using XRD, FT-IR, and thermal analysis. The crystals were doped by iron impurity. The effect of doping was studied using IR spectroscopy and thermal analysis.

  19. Crystal growth of LiIn1-xGaxSe2 crystals

    Science.gov (United States)

    Wiggins, Brenden; Bell, Joseph; Woodward, Jonathan; Goodwin, Brandon; Stassun, Keivan; Burger, Arnold; Stowe, Ashley

    2017-06-01

    Lithium containing chalcogenide single crystals have become very promising materials for photonics and radiation detection. Detection applications include nuclear nonproliferation, neutron science, and stellar investigations for the search of life. Synthesis and single crystal growth methods for lithium containing chalcogenide, specifically LiIn1-xGaxSe2, single crystals are discussed. This study elucidates the possibility of improving neutron detection by reducing the indium capture contribution; with the incorporation of the lithium-6 isotope, gallium substitution may overcome the neutron detection efficiency limitation of 6LiInSe2 due to appreciable neutron capture by the indium-115 isotope. As a figure of merit, the ternary parent compounds 6LiInSe2 and 6LiGaSe2 were included in this study. Quality crystals can be obtained utilizing the vertical Bridgman method to produce quaternary compounds with tunable optical properties. Quaternary crystals of varying quality depending on the gallium concentration, approximately 5×5×2 mm3 or larger in volume, were harvested, analyzed and revealed tunable absorption characteristics between 2.8-3.4 eV.

  20. Acquisition of Single Crystal Growth and Characterization Equipment

    Energy Technology Data Exchange (ETDEWEB)

    Maple, M. Brian; Zocco, Diego A.

    2008-12-09

    Final Report for DOE Grant No. DE-FG02-04ER46178 'Acquisition of Single Crystal Growth and Characterization Equipment'. There is growing concern in the condensed matter community that the need for quality crystal growth and materials preparation laboratories is not being met in the United States. It has been suggested that there are too many researchers performing measurements on too few materials. As a result, many user facilities are not being used optimally. The number of proficient crystal growers is too small. In addition, insufficient attention is being paid to the enterprise of finding new and interesting materials, which is the driving force behind much of condensed matter research and, ultimately, technology. While a detailed assessment of this situation is clearly needed, enough evidence of a problem already exists to compel a general consensus that the situation must be addressed promptly. This final report describes the work carried out during the last four years in our group, in which a state-of-the-art single crystal growth and characterization facility was established for the study of novel oxides and intermetallic compounds of rare earth, actinide and transition metal elements. Research emphasis is on the physics of superconducting (SC), magnetic, heavy fermion (HF), non-Fermi liquid (NFL) and other types of strongly correlated electron phenomena in bulk single crystals. Properties of these materials are being studied as a function of concentration of chemical constituents, temperature, pressure, and magnetic field, which provide information about the electronic, lattice, and magnetic excitations at the root of various strongly correlated electron phenomena. Most importantly, the facility makes possible the investigation of material properties that can only be achieved in high quality bulk single crystals, including magnetic and transport phenomena, studies of the effects of disorder, properties in the clean limit, and spectroscopic and

  1. Treatment of transplanted CT26 tumour with dendritic cell vaccine in combination with blockade of vascular endothelial growth factor receptor 2 and CTLA-4

    DEFF Research Database (Denmark)

    Pedersen, Anders Elm; Buus, S; Claesson, M H

    2005-01-01

    We investigated the anti CT26 tumour effect of dendritic cell based vaccination with the MuLV gp70 envelope protein-derived peptides AH1 and p320-333. Vaccination lead to generation of AH1 specific cytotoxic lymphocytes (CTL) and some decrease in tumour growth of simultaneously inoculated CT26...

  2. Optimal Control of Oxygen Concentration in a Magnetic Czochralski Crystal Growth by Response Surface Methodology

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Concepts and techniques of response surface methodology have been widely applied in many branches of engineering, especially in the chemical and manufacturing areas. This paper presents an application of the methodology in a magnetic crystal Czochralski growth system for single crystal silicon to optimize the oxygen concentration at the crystal growth interface in a cusp magnetic field. The simulation demonstrates that the response surface methodology is a feasible algorithm for the optimization of the Czochralski crystal growth process.

  3. Growth and Characterization of Lead-free Piezoelectric Single Crystals

    Directory of Open Access Journals (Sweden)

    Philippe Veber

    2015-11-01

    Full Text Available Lead-free piezoelectric materials attract more and more attention owing to the environmental toxicity of lead-containing materials. In this work, we review our first attempts of single crystal grown by the top-seeded solution growth method of BaTiO3 substituted with zirconium and calcium (BCTZ and (K0.5Na0.5NbO3 substituted with lithium, tantalum, and antimony (KNLSTN. The growth methodology is optimized in order to reach the best compositions where enhanced properties are expected. Chemical analysis and electrical characterizations are presented for both kinds of crystals. The compositionally-dependent electrical performance is investigated for a better understanding of the relationship between the composition and electrical properties. A cross-over from relaxor to ferroelectric state in BCTZ solid solution is evidenced similar to the one reported in ceramics. In KNLSTN single crystals, we observed a substantial evolution of the orthorhombic-to-tetragonal phase transition under minute composition changes.

  4. Diagenetic Crystal Growth in the Murray Formation, Gale Crater, Mars

    Science.gov (United States)

    Kah, L. C.; Kronyak, R. E.; Ming, D. W.; Grotzinger, J. P.; Schieber, J.; Sumner, D. Y.; Edgett, K. S.

    2015-01-01

    The Pahrump region (Gale Crater, Mars) marks a critical transition between sedimentary environments dominated by alluvial-to-fluvial materials associated with the Gale crater rim, and depositional environments fundamentally linked to the crater's central mound, Mount Sharp. At Pahrump, the Murray formation consists of an approximately 14-meter thick succession dominated by massive to finely laminated mudstone with occasional interbeds of cross-bedded sandstone, and is best interpreted as a dominantly lacustrine environment containing tongues of prograding fluvial material. Murray formation mudstones contain abundant evidence for early diagenetic mineral precipitation and its subsequent removal by later diagenetic processes. Lenticular mineral growth is particularly common within lacustrine mudstone deposits at the Pahrump locality. High-resolution MAHLI images taken by the Curiosity rover permit detailed morphological and spatial analysis of these features. Millimeter-scale lenticular features occur in massive to well-laminated mudstone lithologies and are interpreted as pseudomorphs after calcium sulfate. The distribution and orientation of lenticular features suggests deposition at or near the sediment-water (or sediment-air) interface. Retention of chemical signals similar to host rock suggests that original precipitation was likely poikilotopic, incorporating substantial amounts of the primary matrix. Although poikilotopic crystal growth is common in burial environments, it also occurs during early diagenetic crystal growth within unlithified sediment where high rates of crystal growth are common. Loss of original calcium sulfate mineralogy suggests dissolution by mildly acidic, later-diagenetic fluids. As with lenticular voids observed at Meridiani by the Opportunity Rover, these features indicate that calcium sulfate deposition may have been widespread on early Mars; dissolution of depositional and early diagenetic minerals is a likely source for both calcium

  5. In vitro crystallization, characterization and growth-inhibition study of urinary type struvite crystals

    Science.gov (United States)

    Chauhan, Chetan K.; Joshi, Mihir J.

    2013-01-01

    The formation of urinary stones, known as nephrolithiasis or urolithiasis, is a serious, debilitating problem throughout the world. Struvite—NH4MgPO4·6H2O, ammonium magnesium phosphate hexahydrate, is one of the components of urinary stones (calculi). Struvite crystals with different morphologies were grown by in vitro single diffusion gel growth technique with different growth parameters. The crystals were characterized by powder XRD, FT-IR, thermal analysis and dielectric study. The powder XRD results of struvite confirmed the orthorhombic crystal structure. The FT-IR spectrum proved the presence of water of hydration, metal-oxygen bond, N-H bond and P-O bond. For thermal analysis TGA, DTA and DSC were carried out simultaneously. The kinetic and thermodynamic parameters of dehydration/decomposition process were calculated. Vickers micro-hardness and related mechanical parameters were also calculated. The in vitro growth inhibition studies of struvite by the juice of Citrus medica Linn as well as the herbal extracts of Commiphora wightii, Boerhaavia diffusa Linn and Rotula aquatica Lour were carried out and found potent inhibitors of struvite.

  6. Some Aspects of PVT Low Supersaturation Nucleation and Contactless Crystal Growth

    Science.gov (United States)

    Grasza, K.; Palosz, W.

    1996-01-01

    The basic principles of the contactless growth of crystals from the vapor in combination with the process of low-supersaturation nucleation are discussed. The mathematical formulation of the morphological stability criterion in vapor growth systems is given and its implications for contactless growth technique are analyzed. A diagram for selection of proper temperature conditions for growth of CdTe crystals is presented.

  7. Single Crystals of Organolead Halide Perovskites: Growth, Characterization, and Applications

    KAUST Repository

    Peng, Wei

    2017-04-01

    crystals will be discussed in Chapter 3 and 4. Despite their outstanding charge transport characteristics, organolead halide perovskite single crystals grown by hitherto reported crystallization methods are not suitable for most optoelectronic devices due to their small aspect ratios and free standing growth. As the other major part of work of this dissertation, explorative work on growing organolead halide perovskite monocrystalline films and further their application in solar cells will be discussed in Chapter 5.

  8. In-situ study of the dendritic growth in lithium/polymer electrolyte-salt/lithium cells; Etude in-situ de la croissance dendritique dans des cellules lithium/POE-sel/lithium

    Energy Technology Data Exchange (ETDEWEB)

    Brissot, C.; Rosso, M.; Chazalviel, J.N. [Ecole Polytechnique, 91 - Palaiseau (France); Baudry, P.; Lascaud, S. [Electricite de France, 77 - Moret sur Loing (France). Direction des Etudes et Recherches

    1996-12-31

    The in-situ observation of dendritic growth in lithium/polymer electrolyte-LiTFSI/lithium battery cells shows that dendrites grow up with about the same rate as anion migration. Memory effects have been evidenced in cycling experiments and limit the dendrites length. An overall movement of the electrolyte due to variations of electrolyte concentration in the vicinity of the electrodes has been observed too. (J.S.) 13 refs.

  9. Validation, verification, and benchmarking of crystal growth simulations

    Science.gov (United States)

    Dadzis, K.; Bönisch, P.; Sylla, L.; Richter, T.

    2017-09-01

    The variety of physical phenomena in crystal growth processes requires diverse software tools for the numerical simulations. Both, dedicated 2D or 3D ready-to-use software for coupled simulations of a crystallization furnace and general-purpose 3D simulation packages have been used in the literature. This work proposes a general strategy for model development: validation of the physical model using model experiments; verification of the numerical model using analytical or high-accuracy solutions; testing of the computational efficiency using complex benchmark cases. The application of these steps is demonstrated for various models in directional solidification of silicon showing the capabilities of various open source or commercial software packages.

  10. Modelling of Verneuil process for the sapphire crystal growth

    Science.gov (United States)

    Barvinschi, Floricica; Santailler, Jean-Louis; Duffar, Thierry; Le Gal, Hervé

    1999-03-01

    The finite element software FIDAP was used to simulate the Verneuil crystal growth process. The turbulent combustion between hydrogen and oxygen, giving water, the hydrodynamics of the gas phase, the inlet and outlet chemical species flow resulting from the combustion and the heat transfer in the furnace (including internal wall-to-wall radiation) are taken into account. A problem with 10 degrees of freedom per node is generated, solved and the results of the axisymmetric model have shown that the coupling of all these phenomena can be achieved in one numerical model. The effects of transparency of the crystal is discussed. A qualitative agreement between some experimental observations and the model is found, so that modelling may be a good tool for studying the Verneuil process. Nevertheless, some improvements of the model in conjunction with other experimental validations appear necessary.

  11. Model of apparent crystal growth rate and kinetics of seeded precipitation from sodium aluminate solution

    Institute of Scientific and Technical Information of China (English)

    LI Xiao-bin; LIU Zhi-jian; XU Xiao-hui; ZHOU Qiu-sheng; PENG Zhi-hong; LIU Gui-hua

    2005-01-01

    Based on the population balance equation in a batch crystallizer characteristic of seeded precipitation, a model to calculate the rate of apparent crystal growth of aluminum hydroxide from the size distribution was deve-loped. The simulation results indicate that the rate of apparent crystal growth during seeded precipitation exhibits a manifest dependence on the crystal size. In general, there is an obvious increase in the apparent crystal growth rate with the augment in crystal size. The apparent activation energy increases with the increase of characteristic crystal size, which indicates that the growth of small crystals is controlled by surface chemical reaction; it is gradually controlled by both the surface reaction and diffusion with the augment in crystal size.

  12. In situ investigation of growth rates and growth rate dispersion of α-lactose monohydrate crystals

    Science.gov (United States)

    Dincer, T. D.; Ogden, M. I.; Parkinson, G. M.

    2009-02-01

    The growth rates and growth rate dispersion (GRD) of four different faces of α-lactose monohydrate crystal were measured at 30, 40 and 50 °C in the relative supersaturation range 0.55-2.33 in aqueous solutions. The overall growth rate of the crystal is around 50-60% of the (0 1 0) face of the crystal. The power law was applied to the growth rates of the four faces and the activation energies were calculated to be between 9.5 and 13.7 kcal/mol. This indicates a diffusion-controlled growth, but the exponents calculated are between 2.5 and 3.1 which are higher than unity. Introduction of critical supersaturation decreased the exponents to between 1.8 and 2.4. The variance of GRD for the (0 1 0) face is twice the variance of the GRD of the (1 1 0) and (1 0 0) faces and 10 times higher than the (1 1¯ 1¯) face at the same supersaturations and temperatures. The GRD of the four faces were similar when expressed as a function of growth rate. However, the (0 1 1) face displayed lower GRD than the other faces at the same temperatures and supersaturations.

  13. Potential productivity benefits of float-zone versus Czochralski crystal growth

    Science.gov (United States)

    Abe, T.

    1985-01-01

    Efficient mass production of single-crystal silicon is necessary for the efficient silicon solar arrays needed in the coming decade. However, it is anticipated that there will be difficulty growing such volumes of crystals using conventional Czochralski (Cz) methods. While the productivity of single crystals might increase with a crystal diameter increase, there are two obstacles to the mass production of large diameter Czochralski crystals, the long production cycle due to slow growth rate and the high heat requirements of the furnaces. Also counterproductive would be the large resistivity gradient along the growth direction of the crystals due to impurity concentration. Comparison between Float zone (FZ) and Cz crystal growth on the basis of a crystal 150 mm in diameter is on an order of two to four times in favor of the FZ method. This advantage results from high growth rates and steady-state growth while maintaining a dislocation-free condition and impurity segregation.

  14. Recovery of surfaces from impurity poisoning during crystal growth

    Science.gov (United States)

    Land, Terry A.; Martin, Tracie L.; Potapenko, Sergey; Palmore, G. Tayhas; de Yoreo, James J.

    1999-06-01

    Growth and dissolution of crystal surfaces are central to processes as diverse as pharmaceutical manufacturing,, corrosion, single-crystal production and mineralization in geochemical and biological environments,. Impurities are either unavoidable features of these processes or intentionally introduced to modify the products. Those that act as inhibiting agents induce a so-called `dead zone', a regime of low supersaturation where growth ceases. Models based on the classic theory of Cabrera and Vermilyea explain behaviour near the dead zone in terms of the pinning of elementary step motion by impurities,. Despite general acceptance of this theory, a number of commonly investigated systems exhibit behaviour not predicted by such models. Moreover, no clear microscopic picture of impurity-step interactions currently exists. Here we use atomic force microscopy to investigate the potassium dihydrogen phosphate {100} surface as it emerges from the dead zone. We show that traditional models are not able to account for the behaviour of this system because they consider only elementary steps, whereas it is the propagation of macrosteps (bunches of monolayer steps) that leads to resurrection of growthout of the dead zone. We present a simple physical model of this process that includes macrosteps and relates characteristics of growth near the dead zone to the timescale for impurity adsorption.

  15. Kinetics of faceting of crystals in growth, etching, and equilibrium

    Science.gov (United States)

    Vlachos, D. G.; Schmidt, L. D.; Aris, R.

    1993-03-01

    The faceting of crystals in equilibrium with the gas phase and also during crystal growth and etching conditions is studied using the Monte Carlo method. The dynamics of the transformation of unstable crystallographic orientations into hill and valley structures and the spatial patterns that develop are examined as functions of surface temperature, crystallographic orientation, and strength of interatomic potential for two transport processes: adsorption-desorption and surface diffusion. The results are compared with the continuum theory for facet formation. Thermodynamically unstable orientations break into hill and valley structures, and faceting exhibits three time regimes: disordering, facet nucleation, and coarsening of small facets to large facets. Faceting is accelerated as temperature increases, but thermal roughening can occur at high temperatures. Surface diffusion is the dominant mechanism at short times and small facets but adsorption-desorption becomes important at long times and large facets. Growth and etching promote faceting for conditions close to equilibrium but induce kinetic roughening for conditions far from equilibrium. Simultaneous irreversible growth and etching conditions with fast surface diffusion result in enhanced faceting.

  16. Modeling of crystal morphology : growth simulation on facets in arbitrary orientations

    NARCIS (Netherlands)

    Boerrigter, Stephan Xander Mattheus

    2003-01-01

    Many aspects of crystal morphology modeling are studied in this thesis. Most important of all, is the dependence of crystal growth on supersaturation--the driving force for crystallization--which not only influences the crystal morphology, but also polymorphism and nucleation. It is shown that an

  17. A study about some phosphate derivatives as inhibitors of calcium oxalate crystal growth

    Science.gov (United States)

    Grases, F.; March, P.

    1989-08-01

    The kinetic of crystal growth of calcium oxalate monohydrate seed crystals were investigated potentiometrically in the presence of several phosphate derivatives, D-fructose-1,6-diphosphate, pyrophosphate, methylene diphosphonate and phytate, and it was found that in some cases they strongly inhibited crystal growth. The inhibitory action of the different substances assayed was comparatively evaluated.

  18. Growth Defects in Langasite Crystals Observed with White Beam Synchrotron Radiation Topography

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Langasite single crystal was grown by the Czochralski method and its perfection was assessed by white beam synchrotron radiation topography. It is found that the growth core and the growth striations are the primary growth defects and they show strong X-ray kinematical contrast in the topographs. Another typical defect in LGS crystal is dislocation. The formation mechanisms of these growth defects in LGS crystals were discussed.

  19. Essential role for vav Guanine nucleotide exchange factors in brain-derived neurotrophic factor-induced dendritic spine growth and synapse plasticity.

    Science.gov (United States)

    Hale, Carly F; Dietz, Karen C; Varela, Juan A; Wood, Cody B; Zirlin, Benjamin C; Leverich, Leah S; Greene, Robert W; Cowan, Christopher W

    2011-08-31

    Brain-derived neurotrophic factor (BDNF) and its cognate receptor, TrkB, regulate a wide range of cellular processes, including dendritic spine formation and functional synapse plasticity. However, the signaling mechanisms that link BDNF-activated TrkB to F-actin remodeling enzymes and dendritic spine morphological plasticity remain poorly understood. We report here that BDNF/TrkB signaling in neurons activates the Vav family of Rac/RhoA guanine nucleotide exchange factors through a novel TrkB-dependent mechanism. We find that Vav is required for BDNF-stimulated Rac-GTP production in cortical and hippocampal neurons. Vav is partially enriched at excitatory synapses in the postnatal hippocampus but does not appear to be required for normal dendritic spine density. Rather, we observe significant reductions in both BDNF-induced, rapid, dendritic spine head growth and in CA3-CA1 theta burst-stimulated long-term potentiation in Vav-deficient mouse hippocampal slices, suggesting that Vav-dependent regulation of dendritic spine morphological plasticity facilitates normal functional synapse plasticity.

  20. Viscosity solutions for a polymer crystal growth model

    CERN Document Server

    Cardaliaguet, Pierre; Monteillet, Aurélien

    2010-01-01

    We prove existence of a solution for a polymer crystal growth model describing the movement of a front $(\\Gamma(t))$ evolving with a nonlocal velocity. In this model the nonlocal velocity is linked to the solution of a heat equation with source $\\delta_\\Gamma$. The proof relies on new regularity results for the eikonal equation, in which the velocity is positive but merely measurable in time and with H\\"{o}lder bounds in space. From this result, we deduce \\textit{a priori} regularity for the front. On the other hand, under this regularity assumption, we prove bounds and regularity estimates for the solution of the heat equation.

  1. Growth of bulk gadolinium pyrosilicate single crystals for scintillators

    Science.gov (United States)

    Gerasymov, I.; Sidletskiy, O.; Neicheva, S.; Grinyov, B.; Baumer, V.; Galenin, E.; Katrunov, K.; Tkachenko, S.; Voloshina, O.; Zhukov, A.

    2011-03-01

    Ce, Pr, and La-doped gadolinium pyrosilicate Gd2Si2O7 (GPS) single crystals were grown by the Czochralski and Top Seeded Solution Growth (TSSG) techniques for the first time. Formation conditions of different pyrosilicate phases were determined. X-ray luminescence integral intensity of Ce-doped GPS is about one order of magnitude higher in comparison with gadolinium oxyorthosilicate Gd2SiO5:Ce (GSO:Ce). All samples demonstrate temperature stability of luminescence yield up to 400 K.

  2. Direction-specific interactions control crystal growth by oriented attachment

    DEFF Research Database (Denmark)

    Li, Dongsheng; Nielsen, Michael H; Lee, Jonathan R.I.

    2012-01-01

    initiated at the contact point. Interface elimination proceeds at a rate consistent with the curvature dependence of the Gibbs free energy. Measured translational and rotational accelerations show that strong, highly direction-specific interactions drive crystal growth via oriented attachment....... using a fluid cell to directly observe oriented attachment of iron oxyhydroxide nanoparticles. The particles undergo continuous rotation and interaction until they find a perfect lattice match. A sudden jump to contact then occurs over less than 1 nanometer, followed by lateral atom-by-atom addition...

  3. Fluid flow and solute segregation in EFG crystal growth process

    Science.gov (United States)

    Bunoiu, O.; Nicoara, I.; Santailler, J. L.; Duffar, T.

    2005-02-01

    The influence of the die geometry and various growth conditions on the fluid flow and on the solute distribution in EFG method has been studied using numerical simulation. The commercial FIDAP software has been used in order to solve the momentum and mass transfer equations in the capillary channel and in the melt meniscus. Two types of shaper design are studied and the results are in good agreement with the void distribution observed in rod-shaped sapphire crystals grown by the EFG method in the various configurations.

  4. Kinetic Processes Crystal Growth, Diffusion, and Phase Transformations in Materials

    CERN Document Server

    Jackson, Kenneth A

    2004-01-01

    The formation of solids is governed by kinetic processes, which are closely related to the macroscopic behaviour of the resulting materials. With the main focus on ease of understanding, the author begins with the basic processes at the atomic level to illustrate their connections to material properties. Diffusion processes during crystal growth and phase transformations are examined in detail. Since the underlying mathematics are very complex, approximation methods typically used in practice are the prime choice of approach. Apart from metals and alloys, the book places special emphasis on th

  5. Viscosity solutions for a polymer crystal growth model

    OpenAIRE

    Cardaliaguet, Pierre; Ley, Olivier; Monteillet, Aurélien

    2011-01-01

    International audience; We prove existence of a solution for a polymer crystal growth model describing the movement of a front $(\\Gamma(t))$ evolving with a nonlocal velocity. In this model the nonlocal velocity is linked to the solution of a heat equation with source $\\delta_\\Gamma$. The proof relies on new regularity results for the eikonal equation, in which the velocity is positive but merely measurable in time and with H\\"{o}lder bounds in space. From this result, we deduce \\textit{a pri...

  6. Fabrication of 2D and 3D dendritic nanoarchitectures of CdS

    Institute of Scientific and Technical Information of China (English)

    GU Li

    2008-01-01

    The controlled preparation of two-dimensional (2D) and three-dimensional (3D) dendritic nanostructures of CdS was reported. 2D dendritic patterns are obtained through the self-assembly of nanoparticles under the entropy-driven force. 3D dendritic needle-like nanocrystals are prepared through an aqueous solution synthesis regulated by oleic acid molecules. Their growth mechanism is presumed to be the selective binding of OA molecules onto growing crystal planes. Techniques such as SEM, TEM, XRD, and FT-IR were employed to characterize the morphologies and structures of the obtained products.

  7. Numerical Simulation of Three-Dimensional Dendritic Growth of Alloy: Part II—Model Application to Fe-0.82WtPctC Alloy

    Science.gov (United States)

    Wang, Weiling; Luo, Sen; Zhu, Miaoyong

    2016-03-01

    In the second part (Part II) of the present simulation work, the three-dimensional (3D) dendritic growth of Fe-0.82wtpctC alloy is investigated with the 3D CA-FVM cellular automaton-finite volume method model developed in Part I. The influences of the melt undercooling, the interfacial anisotropy, and the forced flow on the equiaxed dendritic growth, especially the formation of secondary arms, are discussed. The comparisons of equiaxed dendritic growth in 3D and two-dimensional (2D) are also carried out. Finally, the columnar dendritic growth under different cooling conditions is investigated including the morphology and the secondary dendrite arm spacing (SDAS). The results show that the high undercooling can promote the formation of secondary arms as the anisotropy parameter is 0.04. With the increase of the anisotropy parameter, the secondary arms first reduce and then well develop again; meanwhile the tertiary arms are gradually developed. However, the secondary arms vanish at the undercooling of 5 K as the anisotropy parameter increases to 0.04. With the introduction of the forced flow with the inlet velocity of 0.001 m/s along the x axis, the secondary arms at the left (upstream) arm become more developed. However, they become slightly less developed with the forced flow intensifying. Secondary arms at the left side (upstream) of the perpendicular arms and in the y-z symmetrical plane become more and more developed as the inlet velocity increases. The competition of the secondary arms at the right side (downstream) of the perpendicular arms and at the right (downstream) arm becomes significant as the undercooling increases from 10 to 15 K. The solute-enriched envelope in 2D is much thicker than in the 3D case, so that the dendritic growth in 2D is influenced more by the melt flow and the undercooling; moreover, the secondary arms in 2D are hard to form even at the undercooling of 15 K and with the forced convection in the present article. Meanwhile, the

  8. Inclusion free cadmium zinc tellurium and cadmium tellurium crystals and associated growth method

    Science.gov (United States)

    Bolotnikov, Aleskey E.; James, Ralph B.

    2010-07-20

    The present disclosure provides systems and methods for crystal growth of cadmium zinc tellurium (CZT) and cadmium tellurium (CdTe) crystals with an inverted growth reactor chamber. The inverted growth reactor chamber enables growth of single, large, high purity CZT and CdTe crystals that can be used, for example, in X-ray and gamma detection, substrates for infrared detectors, or the like. The inverted growth reactor chamber enables reductions in the presence of Te inclusions, which are recognized as an important limiting factor in using CZT or CdTe as radiation detectors. The inverted growth reactor chamber can be utilized with existing crystal growth techniques such as the Bridgman crystal growth mechanism and the like. In an exemplary embodiment, the inverted growth reactor chamber is a U-shaped ampoule.

  9. Growth and evaluation of lanthanoids orthoniobates single crystals processed by a miniature pedestal growth technique

    Energy Technology Data Exchange (ETDEWEB)

    Octaviano, E.S. [Universidade Camilo Castelo Branco, Descalvado, SP (Brazil); Reyes Ardila, D. [Departmento de Fisica, Universidad de Santiago de Chile (Chile); Andrade, L.H.C.; Siu Li, M.; Andreeta, J.P. [Instituto de Fisica de Sao Carlos, Departamento de Fisica e Ciencia dos Materiais, Universidade de Sao Paulo, Sao Carlos, SP (Brazil)

    2004-10-01

    Optimized conditions for the growth of lanthanoids orthoniobates (LnNbO{sub 4}, Ln=lanthanide elements) single crystal minirods by a floating zone technique were investigated. Adequate atmospheres and pulling to feeding speed ratios to grow these materials were determined. Emphasis is given to the study of LaNbO{sub 4} because of their more favorable growth conditions and crystalline quality. This material can be efficiently doped with rare earth elements such as erbium. It grows with high crystallinity and its preferential growth direction is [110]. A preliminary evaluation of optical properties of Er{sup 3+}-doped LaNbO{sub 4} single crystal under the Judd-Ofelt formalism indicates spectral parameters {omega}{sub t} close and even larger than for Er{sup 3+} ions in YVO{sub 4}. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. Dendritic Cell

    OpenAIRE

    Sevda Söker

    2005-01-01

    Dendritic cells, a member of family of antigen presenting cells, are most effective cells in the primary immune response. Dendritic cells originated from dendron, in mean of tree in the Greek, because of their long and elaborate cytoplasmic branching processes. Dendritic cells constitute approximately 0.1 to 1 percent of the blood’s mononuclear cell. Dendritic cells are widely distributed, and specialized for antigen capture and T cell stimulation. In this article, structures and functions of...

  11. Numerical computation of sapphire crystal growth using heat exchanger method

    Science.gov (United States)

    Lu, Chung-Wei; Chen, Jyh-Chen

    2001-05-01

    The finite element software FIDAP is employed to study the temperature and velocity distribution and the interface shape during a large sapphire crystal growth process using a heat exchanger method (HEM). In the present study, the energy input to the crucible by the radiation and convection inside the furnace and the energy output through the heat exchanger is modeled by the convection boundary conditions. The effects of the various growth parameters are studied. It is found that the contact angle is obtuse before the solid-melt interface touches the sidewall of the crucible. Therefore, hot spots always appear in this process. The maximum convexity decreases significantly when the cooling-zone radius (RC) increases. The maximum convexity also decreases significantly as the combined convection coefficient inside the furnace (hI) decreases.

  12. On the origin of radiation growth of hcp crystals

    Energy Technology Data Exchange (ETDEWEB)

    Golubov, Stanislav I [ORNL; Barashev, Aleksandr [University of Liverpool; Stoller, Roger E [ORNL

    2012-03-01

    The aim of the present work is to study theoretically the radiation growth (RG) of hcp-type materials with a particular focus on the effect of one-dimensionally (1-D) migrating clusters of self-interstitial atoms (SIAs), which are steadily produced in displacement cascades under neutron or heavy-ion irradiation. A reaction-diffusion model is developed for the description of RG in single hcp-type metallic crystals. The model reproduces all RG stages observed in neutron-irradiated annealed samples of pure Zr and Zr alloys, such as high strain rate at low, strain saturation at intermediate and breakaway growth at relatively high irradiation doses. In addition, it accounts for the striking observations of negative strains in prismatic directions and coexistence of vacancy- and SIA-type prismatic loops. The role of cold work in RG behavior and alignment of the vacancy-type loops along basal planes are revealed and the maximum strain rate is estimated.

  13. Semiconductor Crystal Growth in Static and Rotating Magnetic fields

    Science.gov (United States)

    Volz, Martin

    2004-01-01

    Magnetic fields have been applied during the growth of bulk semiconductor crystals to control the convective flow behavior of the melt. A static magnetic field established Lorentz forces which tend to reduce the convective intensity in the melt. At sufficiently high magnetic field strengths, a boundary layer is established ahead of the solid-liquid interface where mass transport is dominated by diffusion. This can have a significant effect on segregation behavior and can eliminate striations in grown crystals resulting from convective instabilities. Experiments on dilute (Ge:Ga) and solid solution (Ge-Si) semiconductor systems show a transition from a completely mixed convective state to a diffusion-controlled state between 0 and 5 Tesla. In HgCdTe, radial segregation approached the diffusion limited regime and the curvature of the solid-liquid interface was reduced by a factor of 3 during growth in magnetic fields in excess of 0.5 Tesla. Convection can also be controlled during growth at reduced gravitational levels. However, the direction of the residual steady-state acceleration vector can compromise this effect if it cannot be controlled. A magnetic field in reduced gravity can suppress disturbances caused by residual transverse accelerations and by random non-steady accelerations. Indeed, a joint program between NASA and the NHMFL resulted in the construction of a prototype spaceflight magnet for crystal growth applications. An alternative to the suppression of convection by static magnetic fields and reduced gravity is the imposition of controlled steady flow generated by rotating magnetic fields (RMF)'s. The potential benefits of an RMF include homogenization of the melt temperature and concentration distribution, and control of the solid-liquid interface shape. Adjusting the strength and frequency of the applied magnetic field allows tailoring of the resultant flow field. A limitation of RMF's is that they introduce deleterious instabilities above a

  14. The influence of crystal morphology on the kinetics of growth of calcium oxalate monohydrate

    Science.gov (United States)

    Millan, A.; Sohnel, O.; Grases, F.

    1997-08-01

    The growth of several calcium oxalate monohydrate seeds in the presence and absence of additives (phytate, EDTA and citrate) has been followed by potentiometry measurements. Growth rates have been calculated from precipitate curves by a cubic spline method and represented in logarithmic plots versus supersaturation. Crystal growth kinetics were found to be dependent on crystal morphology, crystal perfection and degree of aggregation. Some seeds were dissolving in supersaturated solutions. Other seeds showed an initial growth phase of high-order kinetics. The effect of the additives was also different on each seed. Three alternative mechanisms for calcium oxalate crystal growth are proposed.

  15. A preliminary review of organic materials single crystal growth by the Czochralski technique

    Science.gov (United States)

    Penn, B. G.; Shields, A. W.; Frazier, D. O.

    1988-01-01

    The growth of single crystals of organic compounds by the Czochralski method is reviewed. From the literature it is found that single crystals of benzil, a nonlinear optical material with a d sub 11 value of 11.2 + or - 1.5 x d sub 11 value of alpha quartz, has fewer dislocations than generally contained in Bridgman crystals. More perfect crystals were grown by repeated Czochralski growth. This consists of etching away the defect-containing portion of a Czochralski grown crystal and using it as a seed for further growth. Other compounds used to grow single crystals are benzophenone, 12-tricosanone (laurone), and salol. The physical properties, growth apparatus, and processing conditions presented in the literature are discussed. Moreover, some of the possible advantages of growing single crystals of organic compounds in microgravity to obtain more perfect crystals than on Earth are reviewed.

  16. Crystal Nucleation and Growth of Al-based Alloys Produced by Electrolysis

    Institute of Scientific and Technical Information of China (English)

    Zhiyong LIU; Mingxing WANG; Yonggang WENG; Tianfu SONG; Yuping HUO; Jingpei XIE

    2003-01-01

    The nucleation and growth of grains in a series of Al-based alloys produced by electrolysis are observed under SEM. The atomicTi/Al ratios of the nuclei and the distribution of Ti at certain points are analyzed by point EDS. The particles in differentatomic Ti/Al ratios might act as the nuclei of α-Al. At the early stage of growth, the spherical Ti-enriched regions might formaround these particles within very limited temperature ranges in which the reactions such as the peritectic reactions etc occur.At the latter stage of growth, the dendrites freely develop in the radial orientations, and the concentration of Ti decreaseslinearly along the dendrite arm and becomes negligible in the region near the periphery of the dendrite. It is believed that thenucleation is closely related with the number and dispersion of primary spherical areas in the melts, and the segregation of Tileads to the free growth of dendrite, which is necessary for the formation of equiaxial grains.

  17. Solution Growth and Characterization of Single Crystals on Earth and in Microgravity

    Science.gov (United States)

    Aggarwal, M. D.; Currie, J. R.; Penn, B. G.; Batra, A. K.; Lal, R. B.

    2007-01-01

    Crystal growth has been of interest to physicists and engineers for a long time because of their unique properties. Single crystals are utilized in such diverse applications as pharmaceuticals, computers, infrared detectors, frequency measurements, piezoelectric devices, a variety of high-technology devices, and sensors. Solution crystal growth is one of the important techniques to grow a variety of crystals when the material decomposes at the melting point and a suitable solvent is available to make a saturated solution at a desired temperature. In this Technical Memorandum (TM) an attempt is made to give the fundamentals of growing crystals from solution including improved designs of various crystallizers. Since the same solution crystal growth technique could not be used in microgravity, the authors proposed a new cooled-sting technique to grow crystals in space. The authors experience from conducting two Space Shuttle solution crystal growth experiments are also detailed in this TM and the complexity of solution growth experiments to grow crystals in space are also discussed. These happen to be some of the early experiments performed in space, and various lessons learned are described. A brief discussion of protein crystal growth that shares basic principles of the solution growth technique is given, along with some flight hardware information for growth in microgravity.

  18. VO{sub 2} (A): Reinvestigation of crystal structure, phase transition and crystal growth mechanisms

    Energy Technology Data Exchange (ETDEWEB)

    Rao Popuri, Srinivasa [ICMCB, CNRS, UPR 9048, F-33608 Pessac (France); University of Bordeaux, ICMCB, UPR 9048, F-33608 Pessac (France); National Institute for Research and Development in Electrochemistry and Condensed Matter, Timisoara, Plautius Andronescu Str. No. 1, 300224 Timisoara (Romania); Artemenko, Alla [ICMCB, CNRS, UPR 9048, F-33608 Pessac (France); University of Bordeaux, ICMCB, UPR 9048, F-33608 Pessac (France); Labrugere, Christine [CeCaMA, University of Bordeaux 1, ICMCB, 87 Avenue du Dr. A. Schweitzer, F-33608 Pessac (France); Miclau, Marinela [National Institute for Research and Development in Electrochemistry and Condensed Matter, Timisoara, Plautius Andronescu Str. No. 1, 300224 Timisoara (Romania); Villesuzanne, Antoine [ICMCB, CNRS, UPR 9048, F-33608 Pessac (France); University of Bordeaux, ICMCB, UPR 9048, F-33608 Pessac (France); Pollet, Michaël, E-mail: pollet@icmcb-bordeaux.cnrs.fr [ICMCB, CNRS, UPR 9048, F-33608 Pessac (France); University of Bordeaux, ICMCB, UPR 9048, F-33608 Pessac (France)

    2014-05-01

    Well crystallized VO{sub 2} (A) microrods were grown via a single step hydrothermal reaction in the presence of V{sub 2}O{sub 5} and oxalic acid. With the advantage of high crystalline samples, we propose P4/ncc as an appropriate space group at room temperature. From morphological studies, we found that the oriented attachment and layer by layer growth mechanisms are responsible for the formation of VO{sub 2} (A) micro rods. The structural and electronic transitions in VO{sub 2} (A) are strongly first order in nature, and a marked difference between the structural transition temperatures and electronic transitions temperature was evidenced. The reversible intra- (LTP-A to HTP-A) and irreversible inter- (HTP-A to VO{sub 2} (M1)) structural phase transformations were studied by in-situ powder X-ray diffraction. Attempts to increase the size of the VO{sub 2} (A) microrods are presented and the possible formation steps for the flower-like morphologies of VO{sub 2} (M1) are described. - Graphical abstract: Using a single step and template free hydrothermal synthesis, well crystallized VO{sub 2} (A) microrods were prepared and the P4/ncc space group was assigned to the room temperature crystal structure. Reversible and irreversible phase transitions among different VO{sub 2} polymorphs were identified and their progressive nature was highlighted. Attempts to increase the microrods size, involving layer by layer formation mechanisms, are presented. - Highlights: • Highly crystallized VO{sub 2} (A) microrods were grown via a single step hydrothermal process. • The P4/ncc space group was determined for VO{sub 2} (A) at room temperature. • The electronic structure and progressive nature of the structural phase transition were investigated. • A weak coupling between structural and electronic phase transitions was identified. • Different crystallite morphologies were discussed in relation with growth mechanisms.

  19. GROWTH OF CRYSTALS OF PRIMARY ALUMINIUM WITH ROSETTE MORPHOLOGY AT CASTING OF SILUMINS

    Directory of Open Access Journals (Sweden)

    E. I. Marukovich

    2011-01-01

    Full Text Available The work is devoted to actual theme of alloy solidifi – investigation of infl of overlapping of thermal and concentration fi of neighboring crystals to forming of non- dendrite structures. Experimental research of microstructure of Al-Si alloy for wide range of silicon concentration is conducted, and corresponding numerical simulation develop too. The conclusion about different schemes of forming of rosette structures is adopted.

  20. SiGe crystal growth aboard the international space station

    Science.gov (United States)

    Kinoshita, K.; Arai, Y.; Tsukada, T.; Inatomi, Y.; Miyata, H.; Tanaka, R.

    2015-05-01

    A silicon germanium mixed crystal Si1-xGex (x~0.5) 10 mm in diameter and 9.2 mm in length was grown by the traveling liquidus-zone (TLZ) method in microgravity by suppressing convection in a melt. Ge concentration of 49.8±2.5 at% has been established for the whole of the grown crystal. Compared with the former space experiment, concentration variation in the axial direction increased from ±1.5 at% to ±2.5 at% although average Ge concentration reached to nearly 50 at%. Excellent radial Ge compositional uniformity 52±0.5 at% was established in the region of 7-9 mm growth length, where axial compositional uniformity was also excellent. The single crystalline region is about 5 mm in length. The interface shape change from convex to concave is implied from both experimental results and numerical analysis. The possible cause of increase in concentration variation and interface shape change and its relation to the two-dimensional growth model are discussed.

  1. Diet-induced obesity alters dendritic cell function in the presence and absence of tumor growth.

    Science.gov (United States)

    James, Britnie R; Tomanek-Chalkley, Ann; Askeland, Eric J; Kucaba, Tamara; Griffith, Thomas S; Norian, Lyse A

    2012-08-01

    Obesity is a mounting health concern in the United States and is associated with an increased risk for developing several cancers, including renal cell carcinoma (RCC). Despite this, little is known regarding the impact of obesity on antitumor immunity. Because dendritic cells (DC) are critical regulators of antitumor immunity, we examined the combined effects of obesity and tumor outgrowth on DC function. Using a diet-induced obesity (DIO) model, DC function was evaluated in mice bearing orthotopic RCC and in tumor-free controls. Tumor-free DIO mice had profoundly altered serum cytokine and chemokine profiles, with upregulation of 15 proteins, including IL-1α, IL-17, and LIF. Tumor-free DIO mice had elevated percentages of conventional splenic DC that were impaired in their ability to stimulate naive T cell expansion, although they were phenotypically similar to normal weight (NW) controls. In DIO mice, intrarenal RCC tumor challenge in the absence of therapy led to increased local infiltration by T cell-suppressive DC and accelerated early tumor outgrowth. Following administration of a DC-dependent immunotherapy, established RCC tumors regressed in normal weight mice. The same immunotherapy was ineffective in DIO mice and was characterized by an accumulation of regulatory DC in tumor-bearing kidneys, decreased local infiltration by IFN-γ-producing CD8 T cells, and progressive tumor outgrowth. Our results suggest that the presence of obesity as a comorbidity can impair the efficacy of DC-dependent antitumor immunotherapies.

  2. Growth of BPO4 single crystals from Li2Mo3O10 flux

    Science.gov (United States)

    Xu, Guogang; Li, Jing; Han, Shujuan; Guo, Yongjie; Wang, Jiyang

    2010-12-01

    Transparent single crystal of BPO4 with a typical sizes of 5 × 7 × 9 mm3 have been grown by the top-seeded solution growth (TSSG) slow-cooling method using Li2Mo3O10 as the flux. X-ray powder diffraction result shows that the as-grown crystal was well crystallized and indexed in a tetragonal system. The processing parameters and the effects of the flux on the crystal growth were investigated.

  3. Structures and growth mechanisms of poly-(3-hydroxybutyrate) (PHB) crystallized from solution and thin melt film

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The spherulitic structures and morphologies of poly-(3-hydroxybutyrate) (PHB) crystallized from a so- lution and a thin melt film were investigated in this study. The formation mechanisms of banded spherulites under different crystallization conditions are proposed. It was found that the formation of banded spherulites was caused by the rhythmic crystal growth of the spherulites and lamellar twisting growth for the polymer crystallization from a thin melt film and a solution, respectively.

  4. Study on Characteristics of Crystal Growth of NdFeB Cast Alloys

    Institute of Scientific and Technical Information of China (English)

    李波; 郭炳麟; 王东玲; 刘涛; 喻晓军

    2004-01-01

    The characteristic of crystal growth of NdFeB cast alloys was studied.It is found that the crystal growth orientation of conventional ingots is along or .As the cooling rate increases,the crystallization orientation changes from a axis to c axis,along which the grain is easy to be magnetized.Meanwhile,by analyzing the change of crystallization orientation,the influence on the property of magnets was discussed.

  5. TGF-β Signaling in Dopaminergic Neurons Regulates Dendritic Growth, Excitatory-Inhibitory Synaptic Balance, and Reversal Learning

    Directory of Open Access Journals (Sweden)

    Sarah X. Luo

    2016-12-01

    Full Text Available Neural circuits involving midbrain dopaminergic (DA neurons regulate reward and goal-directed behaviors. Although local GABAergic input is known to modulate DA circuits, the mechanism that controls excitatory/inhibitory synaptic balance in DA neurons remains unclear. Here, we show that DA neurons use autocrine transforming growth factor β (TGF-β signaling to promote the growth of axons and dendrites. Surprisingly, removing TGF-β type II receptor in DA neurons also disrupts the balance in TGF-β1 expression in DA neurons and neighboring GABAergic neurons, which increases inhibitory input, reduces excitatory synaptic input, and alters phasic firing patterns in DA neurons. Mice lacking TGF-β signaling in DA neurons are hyperactive and exhibit inflexibility in relinquishing learned behaviors and re-establishing new stimulus-reward associations. These results support a role for TGF-β in regulating the delicate balance of excitatory/inhibitory synaptic input in local microcircuits involving DA and GABAergic neurons and its potential contributions to neuropsychiatric disorders.

  6. 3D dendritic gold nanostructures: seeded growth of a multi-generation fractal architecture.

    Science.gov (United States)

    Pan, Ming; Xing, Shuangxi; Sun, Ting; Zhou, Wenwen; Sindoro, Melinda; Teo, Hui Hian; Yan, Qingyu; Chen, Hongyu

    2010-10-14

    In this report, we focus on the synthetic challenges for nanoscale 3D fractal architectures, namely the multi-generation growth with control in both size uniformity and colloidal stability; by directing the simultaneous growth of Au and polyaniline on Au seeds, fractal nanoparticles can be achieved with a topology distinctively different from those of spheres, cubes or rods.

  7. A peek into the history of sapphire crystal growth

    Science.gov (United States)

    Harris, Daniel C.

    2003-09-01

    After the chemical compositions of sapphire and ruby were unraveled in the middle of the 19th century, chemists set out to grow artificial crystals of these valuable gemstones. In 1885 a dealer in Geneva began to sell ruby that is now believed to have been created by flame fusion. Gemnologists rapidly concluded that the stones were artificial, but the Geneva ruby stimulated A. V. L. Verneuil in Paris to develop a flame fusion process to produce higher quality ruby and sapphire. By 1900 there was brisk demand for ruby manufactured by Verneuil's method, even though Verneuil did not publicly announce his work until 1902 and did not publish details until 1904. The Verneuil process was used with little alteration for the next 50 years. From 1932-1953, S. K. Popov in the Soviet Union established a capability for manufacturing high quality sapphire by the Verneuil process. In the U.S., under government contract, Linde Air Products Co. implemented the Verneuil process for ruby and sapphire when European sources were cut off during World War II. These materials were essential to the war effort for jewel bearings in precision instruments. In the 1960s and 1970s, the Czochralski process was implemented by Linde and its successor, Union Carbide, to make higher crystal quality material for ruby lasers. Stimulated by a government contract for structural fibers in 1966, H. LaBelle invented edge-defined film-fed growth (EFG). The Saphikon company, which is currently owned by Saint-Gobain, evolved from this effort. Independently and simultaneously, Stepanov developed edge-defined film-fed growth in the Soviet Union. In 1967 F. Schmid and D. Viechnicki at the Army Materials Research Lab grew sapphire by the heat exchanger method (HEM). Schmid went on to establish Crystal Systems, Inc. around this technology. Rotem Industries, founded in Israel in 1969, perfected the growth of sapphire hemispheres and near-net-shape domes by gradient solidification. In the U.S., growth of near

  8. Effect of gallbladder hypomotility on cholesterol crystallization and growth in CCK-deficient mice.

    Science.gov (United States)

    Wang, Helen H; Portincasa, Piero; Liu, Min; Tso, Patrick; Samuelson, Linda C; Wang, David Q-H

    2010-02-01

    We investigated the effect of gallbladder hypomotility on cholesterol crystallization and growth during the early stage of gallstone formation in CCK knockout mice. Contrary to wild-type mice, fasting gallbladder volumes were enlarged and the response of gallbladder emptying to a high-fat meal was impaired in knockout mice on chow or the lithogenic diet. In the lithogenic state, large amounts of mucin gel and liquid crystals as well as arc-like and tubular crystals formed first, followed by rapid formation of classic parallelogram-shaped cholesterol monohydrate crystals in knockout mice. Furthermore, three patterns of crystal growth habits were observed: proportional enlargement, spiral dislocation growth, and twin crystal growth, all enlarging solid cholesterol crystals. At day 15 on the lithogenic diet, 75% of knockout mice formed gallstones. However, wild-type mice formed very little mucin gel, liquid, and solid crystals, and gallstones were not observed. We conclude that lack of CCK induces gallbladder hypomotility that prolongs the residence time of excess cholesterol in the gallbladder, leading to rapid crystallization and precipitation of solid cholesterol crystals. Moreover, during the early stage of gallstone formation, there are two pathways of liquid and polymorph anhydrous crystals evolving to monohydrate crystals and three modes for cholesterol crystal growth.

  9. Growth of Bi-2212 single crystals by a horizontal Bridgman method using different oxygen pressure

    Energy Technology Data Exchange (ETDEWEB)

    Fujiwara, M.; Makino, T.; Nakabayashi, T. [Department of Electrical and Electronic Engineering, Tottori University, Koyama-Minami, Tottori 680-8552 (Japan); Tanaka, H. [Yonago National College of Technology, 4448 Hikona Yonago, Tottori 683-8502 (Japan); Kinoshita, K., E-mail: kinoshita@ele.tottori-u.ac.j [Department of Electrical and Electronic Engineering, Tottori University, Koyama-Minami, Tottori 680-8552 (Japan); Kishida, S. [Department of Electrical and Electronic Engineering, Tottori University, Koyama-Minami, Tottori 680-8552 (Japan)

    2009-10-15

    We compared the crystallinity of the Bi-2212 single crystals grown by the horizontal Bridgman (HB) method with those grown by the vertical Bridgman (VB) method in terms of resistivity, rho. It was clarified that crystals far inside the ingot grown by HB method showed the equivalent crystallinity to crystals grown by VB method, whereas crystals near the surface of the ingot grown by HB method showed the similar crystallinity to crystals grown by TSFZ method, which is sensitive to the growth atmosphere.

  10. Effect of Crystal Growth Direction on Domain Structure of Mn-Doped (Na,K)NbO3 Crystal

    Science.gov (United States)

    Tsuchida, Kohei; Kakimoto, Ken-ichi; Kagomiya, Isao

    2013-09-01

    Single crystals of (Na0.55K0.45)(Nb0.995Mn0.005)O3 have been grown by a floating zone method in N2 and decompression atmosphere to avoid alkaline metal volatilization on the SrTiO3 material base. The variation of their ferroelectric domain structure and the chemical composition of the grown crystal in the growth direction were evaluated. In the crystal grown in N2 atmosphere, the Na and K are not distributed homogeneously. In addition, the phase transition temperature TC and TO-T showed different values between the grown crystal and raw material. By using laser scanning confocal microscope, the domain structures of the grown crystal revealed random patterns in the initial growth stage and lamellar patterns in the progressing crystal growth. In decompression atmosphere, the TC and TO-T values of the grown crystal were similar to those of the raw material and the domain structures showed a constant domain size. The electrical property of the crystal became stable and the domain structure was easily switched against applied electrical field because the oriented lamellar domain was created during cooling of the crystal.

  11. EFFECT OF SODIUM DODECYLBENZENESULFONIC ACID (SDBS ON THE GROWTH RATE AND MORPHOLOGY OF BORAX CRYSTAL

    Directory of Open Access Journals (Sweden)

    Suharso Suharso

    2010-06-01

    Full Text Available An investigation of the effect of sodium dodecylbenzenesulfonic acid (SDBS on both growth rate and morphology of borax crystal has been carried out.  This experiment was carried out at temperature of 25 °C and relative supersaturation of 0.21 and 0.74 under in situ cell optical microscopy method.  The result shows that SDBS inhibits the growth rate and changes the morphology of borax crystal.   Keywords: Borax; growth rate; crystallization, SDBS

  12. EFFECT OF SODIUM DODECYLBENZENESULFONIC ACID (SDBS) ON THE GROWTH RATE AND MORPHOLOGY OF BORAX CRYSTAL

    OpenAIRE

    Suharso, Suharso

    2010-01-01

    An investigation of the effect of sodium dodecylbenzenesulfonic acid (SDBS) on both growth rate and morphology of borax crystal has been carried out.  This experiment was carried out at temperature of 25 °C and relative supersaturation of 0.21 and 0.74 under in situ cell optical microscopy method.  The result shows that SDBS inhibits the growth rate and changes the morphology of borax crystal.   Keywords: Borax; growth rate; crystallization, SDBS

  13. Crystal growth, structural and thermal studies of amino acids admixtured L-arginine phosphate monohydrate single crystals

    Science.gov (United States)

    Anandan, P.; Saravanan, T.; Parthipan, G.; Kumar, R. Mohan; Bhagavannarayana, G.; Ravi, G.; Jayavel, R.

    2011-05-01

    To study the improved characteristics of L-arginine phosphate monohydrate (LAP) crystals, amino acids mixed LAP crystals have been grown by slow cooling method. Amino acids like glycine, L-alanine, and L-valine have been selected for doping. Optical quality bulk crystals have been harvested after a typical growth period of about twenty days. The effect of amino acids in the crystal lattice and molecular vibrational frequencies of various functional groups in the crystals have been studied using X-ray powder diffraction and Fourier Transform infrared (FTIR) analyses respectively. Thermal behavior of the amino acids mixed LAP crystals have been studied from the TG and DTG analyses. High-resolution X-ray diffraction studies have been carried out to find the crystalline nature. Optical transmission studies have been carried out by UV-vis spectrophotometer. The cut off wavelength is below 240 nm for the grown crystals.

  14. Phase field modeling of dendritic coarsening during isothermal

    Directory of Open Access Journals (Sweden)

    Zhang Yutuo

    2011-08-01

    Full Text Available Dendritic coarsening in Al-2mol%Si alloy during isothermal solidification at 880K was investigated by phase field modeling. Three coarsening mechanisms operate in the alloy: (a melting of small dendrite arms; (b coalescence of dendrites near the tips leading to the entrapment of liquid droplets; (c smoothing of dendrites. Dendrite melting is found to be dominant in the stage of dendritic growth, whereas coalescence of dendrites and smoothing of dendrites are dominant during isothermal holding. The simulated results provide a better understanding of dendrite coarsening during isothermal solidification.

  15. A phase-field-lattice Boltzmann method for modeling motion and growth of a dendrite for binary alloy solidification in the presence of melt convection

    Science.gov (United States)

    Rojas, Roberto; Takaki, Tomohiro; Ohno, Munekazu

    2015-10-01

    In this study, a combination of the lattice Boltzmann method (LBM) and the phase-field method (PFM) is used for modeling simultaneous growth and motion of a dendrite during solidification. PFM is used as a numerical tool to simulate the morphological changes of the solid phase, and the fluid flow of the liquid phase is described by using LBM. The no-slip boundary condition at the liquid-solid interface is satisfied by adding a diffusive-forcing term in the LBM formulation. The equations of motion are solved for tracking the translational and rotational motion of the solid phase. The proposed method is easily implemented on a single Cartesian grid and is suitable for parallel computation. Two-dimensional benchmark computations show that the no-slip boundary condition and the shape preservation condition are satisfied in this method. Then, the present method is applied to the calculation of dendritic growth of a binary alloy under melt convection. Initially, the solid is stationary, and then, the solid moves freely due to the influence of fluid flow. Simultaneous growth and motion are effectively simulated. As a result, it is found that motion and melt convection enhance dendritic growth along the flow direction.

  16. Confined Crystal Growth in Space. Deterministic vs Stochastic Vibroconvective Effects

    Science.gov (United States)

    Ruiz, Xavier; Bitlloch, Pau; Ramirez-Piscina, Laureano; Casademunt, Jaume

    The analysis of the correlations between characteristics of the acceleration environment and the quality of the crystalline materials grown in microgravity remains an open and interesting question. Acceleration disturbances in space environments usually give rise to effective gravity pulses, gravity pulse trains of finite duration, quasi-steady accelerations or g-jitters. To quantify these disturbances, deterministic translational plane polarized signals have largely been used in the literature [1]. In the present work, we take an alternative approach which models g-jitters in terms of a stochastic process in the form of the so-called narrow-band noise, which is designed to capture the main statistical properties of realistic g-jitters. In particular we compare their effects so single-frequency disturbances. The crystalline quality has been characterized, following previous analyses, in terms of two parameters, the longitudinal and the radial segregation coefficients. The first one averages transversally the dopant distribution, providing continuous longitudinal information of the degree of segregation along the growth process. The radial segregation characterizes the degree of lateral non-uniformity of the dopant in the solid-liquid interface at each instant of growth. In order to complete the description, and because the heat flux fluctuations at the interface have a direct impact on the crystal growth quality -growth striations -the time dependence of a Nusselt number associated to the growing interface has also been monitored. For realistic g-jitters acting orthogonally to the thermal gradient, the longitudinal segregation remains practically unperturbed in all simulated cases. Also, the Nusselt number is not significantly affected by the noise. On the other hand, radial segregation, despite its low magnitude, exhibits a peculiar low-frequency response in all realizations. [1] X. Ruiz, "Modelling of the influence of residual gravity on the segregation in

  17. The brain-specific RasGEF very-KIND is required for normal dendritic growth in cerebellar granule cells and proper motor coordination

    Science.gov (United States)

    Hayashi, Kanehiro; Furuya, Asako; Sakamaki, Yuriko; Akagi, Takumi; Shinoda, Yo; Sadakata, Tetsushi; Hashikawa, Tsutomu; Shimizu, Kazuki; Minami, Haruka; Sano, Yoshitake; Nakayama, Manabu

    2017-01-01

    Very-KIND/Kndc1/KIAA1768 (v-KIND) is a brain-specific Ras guanine nucleotide exchange factor carrying two sets of the kinase non-catalytic C-lobe domain (KIND), and is predominantly expressed in cerebellar granule cells. Here, we report the impact of v-KIND deficiency on dendritic and synaptic growth in cerebellar granule cells in v-KIND knockout (KO) mice. Furthermore, we evaluate motor function in these animals. The gross anatomy of the cerebellum, including the cerebellar lobules, layered cerebellar cortex and densely-packed granule cell layer, in KO mice appeared normal, and was similar to wild-type (WT) mice. However, KO mice displayed an overgrowth of cerebellar granule cell dendrites, compared with WT mice, resulting in an increased number of dendrites, dendritic branches and terminals. Immunoreactivity for vGluT2 (a marker for excitatory presynapses of mossy fiber terminals) was increased in the cerebellar glomeruli of KO mice, compared with WT mice. The postsynaptic density around the terminals of mossy fibers was also increased in KO mice. Although there were no significant differences in locomotor ability between KO and WT animals in their home cages or in the open field, young adult KO mice had an increased grip strength and a tendency to exhibit better motor performance in balance-related tests compared with WT animals. Taken together, our results suggest that v-KIND is required for compact dendritic growth and proper excitatory synaptic connections in cerebellar granule cells, which are necessary for normal motor coordination and balance. PMID:28264072

  18. The Durability of Various Crucible Materials for Aluminum Nitride Crystal growth by Sublimation

    Energy Technology Data Exchange (ETDEWEB)

    Liu,B.; Edgar, J.; Gu, Z.; Zhuang, D.; Raghothamachar, B.; Dudley, M.; Sarua, A.; Kuball, M.; Meyer, H.

    2004-01-01

    Producing high purity aluminum nitride crystals by the sublimation-recondensation technique is difficult due to the inherently reactive crystal growth environment, normally at temperature in excess of 2100 C. The durability of the furnace fixture materials (crucibles, retorts, etc.) at such a high temperature remains a critical problem. In the present study, the suitability of several refractory materials for AlN crystal growth is investigated, including tantalum carbide, niobium carbide, tungsten, graphite, and hot-pressed boron nitride. The thermal and chemical properties and performance of these materials in inert gas, as well as under AlN crystal growth conditions are discussed. TaC and NbC are the most stable crucible materials with very low elemental vapor pressures in the crystal growth system. Compared with refractory material coated graphite crucibles, HPBN crucible is better for AlN self-seeded growth, as crystals tend to nucleate in thin colorless platelets with low dislocation density.

  19. The growth of Nd:CaWO4 single crystals

    Directory of Open Access Journals (Sweden)

    ALEKSANDAR GOLUBOVIC

    2003-12-01

    Full Text Available CaWO4 doped with 0.8 % at. Nd (Nd:CaWO4 single crystals were grown from the melt in air by the Czochralski technique. The critical diameter dc = 1.0 cm and the critical rate of rotation wc = 30 rpm were calculated from hydrodynamic equations for buoyancy-driven and forced convection. The rate of crystal growth was experimentally obtained to be 6.7 mm/h. For chemical polishing, a solution of 1 part saturated chromic acid (CrO3 in water and 3 parts conc. H3PO4 (85 % at 433 K with an exposure time of 2 h was found to be adequate. A mixture of 1 part concentrated HF and 2 parts chromic acid at room temperature after exposure for 30 min was found to be a suitable etching solution. The lattice parameters a = 0.52404 (6 nm, c = 1.1362 (6 nm and V0 = 0.312 (2 nm3 were determined by X-ray powder diffraction. The obtained results are discussed and compared with published data.

  20. Preparation of anhydrous lanthanum bromide for scintillation crystal growth

    Institute of Scientific and Technical Information of China (English)

    ZHANG Tong; LI Hongwei; ZHAO Chunlei; YU Jinqiu; HU Yunsheng; CUI Lei; HE Huaqiang

    2012-01-01

    This paper reported an efficient and economical method for preparation of anhydrous LaBr3 for scintillation crystal growth.High purity anhydrous LaBr3 powders in large quantities were successfully obtained by stepped dehydration of LaBr3·7H2O using NH4Br as additive.Experiments revealed that adding proper amount of NH4Br could effectively restrain the hydrolysis of LaBr3 during dehydration and thus decreased the yield of deleterious impurity of LaOBr.Optimum preparation conditions,including the amount of NH4Br in use,the dehydration temperature and atmosphere,were investigated by DTA/TG and water/oxygen analysis.The Raman characterization of the as-prepared anhydrous LaBr3 was also presented.

  1. Growth of single-crystal YAG fiber optics.

    Science.gov (United States)

    Nie, Craig D; Bera, Subhabrata; Harrington, James A

    2016-07-11

    Single-crystal YAG (Y3Al5O12) fibers have been grown by the laser heated pedestal growth technique with losses as low as 0.3 dB/m at 1.06 μm. These YAG fibers are as long as about 60 cm with diameters around 330 μm. The early fibers were grown from unoriented YAG seed fibers and these fibers exhibited facet steps or ridges on the surface of the fiber. However, recently we have grown fibers using an oriented seed to grow step-free fibers. Scattering losses made on the fibers indicate that the scattering losses are equal to about 30% of the total loss.

  2. High Speed Crystal Growth by Q-switched Laser Melting

    Science.gov (United States)

    Cullis, A. G.

    1984-01-01

    The modification of the structural and electrical properties of semiconductors short radiation pulses obtained from Q-switched lasers is described. These modifications are accomplished by high heating and cooling rates. This processing revealed novel crystal growth and high speed resolidification phenomena. The behavior of semiconductor Si is analyzed. The annealing process typically employs short pulses of radiation in or near the visible region of the spectrum. The Q-switched ruby and Nd-YAG lasers are commonly used and these are sometimes mode locked to reduce the pulse length still further. Material to be annealed can be processed with a single large area radiation spot. Alternatively, a small radiation spot size can be used and a large sample area is covered by overlapping irradiated regions.

  3. Electrochemical migration of tin in electronics and microstructure of the dendrites

    DEFF Research Database (Denmark)

    Minzari, Daniel; Grumsen, Flemming Bjerg; Jellesen, Morten Stendahl

    2011-01-01

    The macro-, micro-, and nano-scale morphology and structure of tin dendrites, formed by electrochemical migration on a surface mount ceramic chip resistor having electrodes consisting of tin with small amounts of Pb (∼2wt.%) was investigated by scanning electron microscopy and transmission electron...... microscopy including Energy dispersive X-ray spectroscopy and electron diffraction. The tin dendrites were formed under 5 or 12V potential bias in 10ppm by weight NaCl electrolyte as a micro-droplet on the resistor during electrochemical migration experiments. The dendrites formed were found to have...... heterogeneous microstructure along the growth direction, which is attributed to unstable growth conditions inside the micro-volume of electrolyte. Selected area electron diffraction showed that the dendrites are metallic tin having sections of single crystal orientation and lead containing intermetallic...

  4. A THREE-DIMENSIONAL CELLULAR AUTOMATON SIMULATION FOR DENDRITIC GROWTH%枝晶生长的三维元胞自动机模拟

    Institute of Scientific and Technical Information of China (English)

    江鸿翔; 赵九洲

    2011-01-01

    Perhaps dendrite is the most observed solidification microstructure of many metallic materials. The dendritic morphologies show a dominating effect on the performance of casting products. A lot of work has been carried out to investigate the formation mechanism of dendritic microstructure. It is found that the development of dendritic microstructures is a complicated process controlled by the interplay of many factors such as thermal and solute transfer, capillary etc. Cellular automaton (CA) can simulate the solidification process with a high computational efficiency, thus, attracts great attentions. In recent years, progress has been made on the two dimensional CA models for the solidification microstructure formation. But up to date researches on three dimensional CA model are very limited. A combined cellular automaton-finite difference (CA-FD) model for the three dimensional simulation of dendritic growth was developed in this paper. Simulations were performed to investigate the dendritic growth in an undercooled Al-Cu alloy as well as in a directionally solidified Al-Cu alloy. The numerical results showed clearly the development of the free dendrite in the under-cooled melt and the microstructure evolution in the directionally solidified alloy and agreed well with the theoretical predictions and the experimental results.%通过将元胞自动机和有限差分方法相耦合,建立了立方体系金属和合金枝晶生长的三维模型.应用该模型,模拟了Al-Cu合金过冷熔体中自由枝晶的生长和定向凝固条件下Al-Cu合金凝固组织演变过程.模拟结果清楚展现了过冷熔体中自由枝晶的生长过程和定向凝固过程中枝晶的形成与淹没,与理论预测和实验结果相吻合,表明所发展的模型能够较准确地描述立方体系金属和合金的凝固组织演变过程.

  5. Transforming growth factor beta-activated kinase 1 (TAK1)-dependent checkpoint in the survival of dendritic cells promotes immune homeostasis and function

    OpenAIRE

    Wang, Yanyan; Huang, Gonghua; Vogel, Peter; Neale, Geoffrey; Reizis, Boris; Chi, Hongbo

    2012-01-01

    Homeostatic control of dendritic cell (DC) survival is crucial for adaptive immunity, but the molecular mechanism is not well defined. Moreover, how DCs influence immune homeostasis under steady state remains unclear. Combining DC-specific and -inducible deletion systems, we report that transforming growth factor beta-activated kinase 1 (TAK1) is an essential regulator of DC survival and immune system homeostasis and function. Deficiency of TAK1 in CD11c+ cells induced markedly elevated apopt...

  6. In-Situ Crystallization of a Lithium Disilicate Glass--Effect of Pressure on Crystal Growth Rate

    Science.gov (United States)

    Fuss, T.; Ray, C. S.; Lesher, C. E.; Day, D. E.

    2006-01-01

    Crystallization of a Li2O.2SiO2 (LS2) glass subjected to a uniform hydrostatic pressure of 4.5 GPa and 6 GPa was investigated up to a temperature of 750 C. The density of the compressed glass is about 2% greater at 4.5 GPa than at 1 atm and, depending upon the processing temperature, up to 10% greater at 6 GPa. Crystal growth rates investigated as a function of temperature and pressure show that lithium disilicate crystal growth is an order of magnitude slower at 4.5 GPa than 1 atm resulting in a shift of +45 C (plus or minus 10 C) in the growth rate curve at high pressure compared to 1 atm condition. At 6 GPa lithium disilicate crystallization is suppressed entirely, while a new high pressure lithium metasilicate crystallizes at temperatures 95 C (plus or minus 10 C) higher than those reported for lithium disilicate crystallization at 1 atm. The decrease in crystal growth rate with increasing pressure for lithium disilicate glass up to 750 C is related to an increase in viscosity with pressure associated with fundamental changes in glass structure accommodating densification.

  7. Synthesis, crystal growth, solubility, structural, optical, dielectric and microhardness studies of Benzotriazole-4-hydroxybenzoic acid single crystals

    Science.gov (United States)

    Silambarasan, A.; Krishna Kumar, M.; Thirunavukkarasu, A.; Mohan Kumar, R.; Umarani, P. R.

    2015-06-01

    Organic Benzotriazole-4-hydroxybenzoic acid (BHBA), a novel second-order nonlinear optical single crystal was grown by solution growth method. The solubility and nucleation studies were performed for BHBA crystal at different temperatures 30, 35, 40 45 and 50 °C. Single crystal X-ray diffraction study reveals that the BHBA belongs to Pna21 space group of orthorhombic crystal system. The crystal perfection of BHBA was examined from powder and high resolution X-ray diffraction analysis. UV-visible and photoluminescence spectra were recorded to study its transmittance and excitation, emission behaviors respectively. Kurtz powder second harmonic generation test reveals that, the frequency conversion efficiency of BHBA is 3.7 times higher than that of potassium dihydrogen phosphate (KDP) crystal. The dielectric constant and dielectric loss values were estimated for BHBA crystal at various temperatures and frequencies. The mechanical property of BHBA crystal was studied on (110), (010) and (012) planes by using Vicker's microhardness test. The chemical etching study was performed on (012) facet of BHBA crystal to analyze its growth feature.

  8. Crystal growth iron based pnictide compounds; Kristallzuechtung eisenbasierter Pniktidverbindungen

    Energy Technology Data Exchange (ETDEWEB)

    Nacke, Claudia

    2012-11-15

    The present work is concerned with selected crystal growth method for producing iron-based superconductors. The first part of this work introduces significant results of the crystal growth of BaFe{sub 2}As{sub 2} and the cobalt-substituted compound Ba(Fe{sub 1-x}Co{sub x}){sub 2}As{sub 2} with x{sub Nom} = 0.025, 0.05, 0.07, 0.10 and 0.20. For this purpose a test procedure for the vertical Bridgman method was developed. The second part of this work contains substantial results for growing a crystal of LiFeAs and the nickel-substituted compound Li{sub 1-δ}Fe{sub 1-x}Ni{sub x}As with x{sub Nom} = 0.015, 0.025, 0.05, 0.06, 0.075 and 0.10. For this purpose a test procedure for the melt flow process has been developed successfully. [German] Die vorliegende Arbeit befasst sich mit ausgewaehlten Kristallzuechtungsverfahren zur Herstellung eisenbasierter Supraleiter. Der erste Teil dieser Arbeit fuehrt wesentliche Ergebnisse der Kristallzuechtung von BaFe{sub 2}As{sub 2} sowie der Cobalt-substituierten Verbindung Ba(Fe{sub 1-x}Co{sub x}){sub 2}As{sub 2} mit x{sub Nom} =0.025, 0.05, 0.07, 0.10 und 0.20 auf. Hierzu wurde eine Versuchsdurchfuehrung fuer das vertikale Bridgman-Verfahren konzipiert, mit welcher erfolgreich Kristalle dieser Zusammensetzungen gezuechtet wurden. Der zweite Teil dieser Arbeit enthaelt wesentliche Ergebnisse zur Kristallzuechtung von LiFeAs sowie der Nickel-substituierten Verbindung Li{sub 1-δ}Fe{sub 1-x}Ni{sub x}As mit x{sub Nom} = 0.015, 0.025, 0.05, 0.06, 0.075 und 0.10. Hierfuer wurde erfolgreich eine Versuchsdurchfuehrung fuer das Schmelzfluss-Verfahren entwickelt.

  9. Crystal growth and scintillation properties of undoped and Ce3+-doped GdI3 crystals

    Science.gov (United States)

    Ye, Le; Li, Huanying; Wang, Chao; Shi, Jian; Chen, Xiaofeng; Wang, Zhongqing; Huang, Yuefeng; Xu, Jiayue; Ren, Guohao

    2017-02-01

    The growth and scintillation properties of undoped and Ce3+-doped GdI3 crystals were reported in this paper. These GdI3:χ%Ce (χ = 0, 1, 2) crystals were grown by the vertical Bridgman growth technique in evacuated quartz crucibles. X-ray excited optical luminescence spectra of GdI3:Ce exhibit a broad emission band (450 nm-650 nm) peaking at 520 nm corresponding to 5d1→4f1 transition of Ce3+ while the undoped GdI3 crystal consists of a broad band (400 nm-600 nm) and several sharp lines peaking at 462 nm, 482 nm, 492 nm, 549 nm, 579 nm owing to the impurities ions and defects. The excitation spectra of Ce3+ doped GdI3 consist of two broad bands between 300 nm and 500 nm corresponding to 4f1→5d1 absorption of Ce3+. The other absorption peaking at 262 nm in the spectrum of GdI3:2%Ce is assigned to band-to-band exciton transition. The excitation spectrum of undoped GdI3 contains a flat absorption band from 330 to 370 nm and a broad band between 390 and 450 nm peaking at 414 nm corresponding to the absorption of the unintentionally doped Ce3+, Dy3+, Ho3+ impurities and other defects. The emission spectrum of undoped GdI3 under 332 nm excitation has the identical line peaks with the spectrum measured under X-ray excitation. The emission spectra of GdI3:2%Ce and GdI3:1%Ce show a broad band in the range of 450-750 nm with the maximum at 550 nm corresponding to 5d1→4f1 transitions of Ce3+ ion. The GdI3, GdI3:1%Ce and GdI3:2%Ce show fast principle decay time constant 73 ns, 69 ns and 58 ns respectively, besides, the undoped also shows a slow decay constant 325 ns which doesn't appear in Ce3+-doped GdI3 crystal. The energy resolutions of GdI3:χ%Ce (χ = 1, 2) measured at 662 KeV are about 3%-5% and the undoped GdI3 is 13.3%.

  10. On geological interpretations of crystal size distributions: Constant vs. proportionate growth

    Science.gov (United States)

    Eberl, D.D.; Kile, D.E.; Drits, V.A.

    2002-01-01

    Geological interpretations of crystal size distributions (CSDs) depend on understanding the crystal growth laws that generated the distributions. Most descriptions of crystal growth, including a population-balance modeling equation that is widely used in petrology, assume that crystal growth rates at any particular time are identical for all crystals, and, therefore, independent of crystal size. This type of growth under constant conditions can be modeled by adding a constant length to the diameter of each crystal for each time step. This growth equation is unlikely to be correct for most mineral systems because it neither generates nor maintains the shapes of lognormal CSDs, which are among the most common types of CSDs observed in rocks. In an alternative approach, size-dependent (proportionate) growth is modeled approximately by multiplying the size of each crystal by a factor, an operation that maintains CSD shape and variance, and which is in accord with calcite growth experiments. The latter growth law can be obtained during supply controlled growth using a modified version of the Law of Proportionate Effect (LPE), an equation that simulates the reaction path followed by a CSD shape as mean size increases.

  11. Predicting crystal growth via a unified kinetic three-dimensional partition model.

    Science.gov (United States)

    Anderson, Michael W; Gebbie-Rayet, James T; Hill, Adam R; Farida, Nani; Attfield, Martin P; Cubillas, Pablo; Blatov, Vladislav A; Proserpio, Davide M; Akporiaye, Duncan; Arstad, Bjørnar; Gale, Julian D

    2017-04-03

    Understanding and predicting crystal growth is fundamental to the control of functionality in modern materials. Despite investigations for more than one hundred years, it is only recently that the molecular intricacies of these processes have been revealed by scanning probe microscopy. To organize and understand this large amount of new information, new rules for crystal growth need to be developed and tested. However, because of the complexity and variety of different crystal systems, attempts to understand crystal growth in detail have so far relied on developing models that are usually applicable to only one system. Such models cannot be used to achieve the wide scope of understanding that is required to create a unified model across crystal types and crystal structures. Here we describe a general approach to understanding and, in theory, predicting the growth of a wide range of crystal types, including the incorporation of defect structures, by simultaneous molecular-scale simulation of crystal habit and surface topology using a unified kinetic three-dimensional partition model. This entails dividing the structure into 'natural tiles' or Voronoi polyhedra that are metastable and, consequently, temporally persistent. As such, these units are then suitable for re-construction of the crystal via a Monte Carlo algorithm. We demonstrate our approach by predicting the crystal growth of a diverse set of crystal types, including zeolites, metal-organic frameworks, calcite, urea and l-cystine.

  12. Predicting crystal growth via a unified kinetic three-dimensional partition model

    Science.gov (United States)

    Anderson, Michael W.; Gebbie-Rayet, James T.; Hill, Adam R.; Farida, Nani; Attfield, Martin P.; Cubillas, Pablo; Blatov, Vladislav A.; Proserpio, Davide M.; Akporiaye, Duncan; Arstad, Bjørnar; Gale, Julian D.

    2017-04-01

    Understanding and predicting crystal growth is fundamental to the control of functionality in modern materials. Despite investigations for more than one hundred years, it is only recently that the molecular intricacies of these processes have been revealed by scanning probe microscopy. To organize and understand this large amount of new information, new rules for crystal growth need to be developed and tested. However, because of the complexity and variety of different crystal systems, attempts to understand crystal growth in detail have so far relied on developing models that are usually applicable to only one system. Such models cannot be used to achieve the wide scope of understanding that is required to create a unified model across crystal types and crystal structures. Here we describe a general approach to understanding and, in theory, predicting the growth of a wide range of crystal types, including the incorporation of defect structures, by simultaneous molecular-scale simulation of crystal habit and surface topology using a unified kinetic three-dimensional partition model. This entails dividing the structure into ‘natural tiles’ or Voronoi polyhedra that are metastable and, consequently, temporally persistent. As such, these units are then suitable for re-construction of the crystal via a Monte Carlo algorithm. We demonstrate our approach by predicting the crystal growth of a diverse set of crystal types, including zeolites, metal-organic frameworks, calcite, urea and L-cystine.

  13. Size effects on void growth in single crystals with distributed voids

    DEFF Research Database (Denmark)

    Borg, Ulrik; Niordson, Christian Frithiof; Kysar, J.W.

    2008-01-01

    The effect of void size on void growth in single crystals with uniformly distributed cylindrical voids is studied numerically using a finite deformation strain gradient crystal plasticity theory with an intrinsic length parameter. A plane strain cell model is analyzed for a single crystal...

  14. Growth of Single Crystals and Fabrication of GaN and AlN Wafers

    Science.gov (United States)

    2006-03-01

    in nature and thus must be synthesized. Crystal growth of this group using standard methods ( Czochralski , Bridgman) is extremely difficult because of...reaction zone in which deposition occurs. High growth rates of up to 0.5 mm/h were obtained with this method ; however, the crystals grew only for short...Chapter Five presents the growth of GaN on sapphire with a modified sandwich growth method which is a variation of vapor phase transport process. Optimum

  15. Large single crystal growth of MnWO4-type materials from high-temperature solutions

    Science.gov (United States)

    Gattermann, U.; Röska, B.; Paulmann, C.; Park, S.-H.

    2016-11-01

    A simple high-temperature growth apparatus was constructed to obtain large crystals of chemically gradient (In, Na)-doped MnWO4solid-solutions. This paper presents the crystal growth and characterisation of both MnWO4and epitaxially grown (In, Na): MnWO4crystals on MnWO4. These large monolithic crystals were made in two steps: A MnWO4 crystal was grown in the crystallographic main direction [001] applying the Czochralski method, followed by the top seeded growth of (In, Na): MnWO4 solid-solutions with an oriented seed crystal of MnWO4. Such a monolithic crystal will serve to fundamental investigation of coupling properties at boundaries between various multiferroic MnWO4-typesolid-solutions.

  16. Study of growth of single crystal ribbon in space

    Science.gov (United States)

    Wood, V. E.; Markworth, A. J.

    1975-01-01

    The technical feasibility is studied of growing single-crystal silicon ribbon in the space environment. Procedures are described for calculating the electromagnetic fields produced in a silicon ribbon by an rf shaping coil. The forces on the ribbon and the degree of shaping to be expected are determined. The expected steady-state temperature distribution in the ribbon is calculated in the one-dimensional approximation. Calculations on simplified models indicate, that lack of flatness of the shaped ribbon and excessive heating of the melt by the eddy currents induced by the shaping fields may pose problems. An analysis of the relative effects of various kinds of forces other than electromagnetic showed that in the space environment capillarity forces would dominate, and that the shape of the melt is thus principally determined by the shape of any solids with which it comes in contact. This suggests that ribbon may be produced simply by drawing between parallel wires. A concept is developed for a process of off-angle growth, in which the ribbon is pulled at an angle to the solidification front. Such a process promises to offer increased growth rate, better homogeneity, and thinner ribbon.

  17. Crystal growth of new charge-transfer salts based on π-conjugated donor molecules

    Energy Technology Data Exchange (ETDEWEB)

    Morherr, Antonia, E-mail: morherr@stud.uni-frankfurt.de [Physikalisches Institut, Goethe-Universität Frankfurt am Main, 60438 Frankfurt am Main (Germany); Witt, Sebastian [Physikalisches Institut, Goethe-Universität Frankfurt am Main, 60438 Frankfurt am Main (Germany); Chernenkaya, Alisa [Graduate School Materials Science in Mainz, 55128 Mainz (Germany); Institut für Physik, Johannes Gutenberg-Universität, 55099 Mainz (Germany); Bäcker, Jan-Peter [Physikalisches Institut, Goethe-Universität Frankfurt am Main, 60438 Frankfurt am Main (Germany); Schönhense, Gerd [Institut für Physik, Johannes Gutenberg-Universität, 55099 Mainz (Germany); Bolte, Michael [Institut für anorganische Chemie, Goethe-Universität Frankfurt am Main, 60438 Frankfurt am Main (Germany); Krellner, Cornelius [Physikalisches Institut, Goethe-Universität Frankfurt am Main, 60438 Frankfurt am Main (Germany)

    2016-09-01

    New charge transfer crystals of π-conjugated, aromatic molecules (phenanthrene and picene) as donors were obtained by physical vapor transport. The melting behavior, optimization of crystal growth and the crystal structure are reported for charge transfer salts with (fluorinated) tetracyanoquinodimethane (TCNQ-F{sub x}, x=0, 2, 4), which was used as acceptor material. The crystal structures were determined by single-crystal X-ray diffraction. Growth conditions for different vapor pressures in closed ampules were applied and the effect of these starting conditions for crystal size and quality is reported. The process of charge transfer was investigated by geometrical analysis of the crystal structure and by infrared spectroscopy on single crystals. With these three different acceptor strengths and the two sets of donor materials, it is possible to investigate the distribution of the charge transfer systematically. This helps to understand the charge transfer process in this class of materials with π-conjugated donor molecules.

  18. Crystal growth of new charge-transfer salts based on π-conjugated donor molecules

    Science.gov (United States)

    Morherr, Antonia; Witt, Sebastian; Chernenkaya, Alisa; Bäcker, Jan-Peter; Schönhense, Gerd; Bolte, Michael; Krellner, Cornelius

    2016-09-01

    New charge transfer crystals of π-conjugated, aromatic molecules (phenanthrene and picene) as donors were obtained by physical vapor transport. The melting behavior, optimization of crystal growth and the crystal structure are reported for charge transfer salts with (fluorinated) tetracyanoquinodimethane (TCNQ-Fx, x=0, 2, 4), which was used as acceptor material. The crystal structures were determined by single-crystal X-ray diffraction. Growth conditions for different vapor pressures in closed ampules were applied and the effect of these starting conditions for crystal size and quality is reported. The process of charge transfer was investigated by geometrical analysis of the crystal structure and by infrared spectroscopy on single crystals. With these three different acceptor strengths and the two sets of donor materials, it is possible to investigate the distribution of the charge transfer systematically. This helps to understand the charge transfer process in this class of materials with π-conjugated donor molecules.

  19. Crystal Growth of new charge-transfer salts based on $\\pi$-conjugated molecules

    CERN Document Server

    Morherr, Antonia; Chernenkaya, Alisa; Bäcker, Jan-Peter; Schönhense, Gerd; Bolte, Michael; Krellner, Cornelius

    2016-01-01

    New charge transfer crystals of $\\pi$-conjugated, aromatic molecules (phenanthrene and picene) as donors were obtained by physical vapor transport. The melting behavior, optimization of crystal growth and the crystal structure is reported for charge transfer salts with (fluorinated) tetracyanoquinodimethane (TCNQ-F$_x$, x=0, 2, 4), which was used as acceptor material. The crystal structures were determined by single-crystal X-ray diffraction. Growth conditions for different vapor pressures in closed ampules were applied and the effect of these starting conditions for crystal size and quality is reported. The process of charge transfer was investigated by geometrical analysis of the crystal structure and by infrared spectroscopy on single crystals. With these three different acceptor strengths and the two sets of donor materials, it is possible to investigate the distribution of the charge transfer systematically. This helps to understand the charge transfer process in this class of materials with $\\pi$-conjug...

  20. Synthesis, Crystal Growth and Characterization of bis Dl-Valine Picrate Single Crystal for Second-Order Nonlinear Optical Applications

    Science.gov (United States)

    Silambarasan, A.; Krishna Kumar, M.; Sudhahar, S.; Thirunavukkarasu, A.; Mohan Kumar, R.; Umarani, P. R.

    2013-08-01

    An organic compound Bis DL-Valine picrate (BDLVP) was synthesized successfully and single crystal was grown by slow evaporation solution growth method. The presence of functional groups in the compound was identified by FTIR spectral analysis. Single crystal X-ray diffraction study revealed that the grown crystal belongs to P21/n space group of monoclinic crystal system. Powder X-ray diffraction pattern was recorded to know the crystalline perfection of the grown crystal. The reaction mechanism, thermal decomposition stages and thermal stability of the grown crystal were studied by using TG/DTA analysis. From the UV-visible spectral study, the electronic band gap energy (Eg) of the grown crystal was found to be 2.43 eV. The second harmonic generation (SHG) efficiency of grown crystal was found to be 1.3 times higher than KDP crystal by using Kurtz powder SHG technique. The microhardness property of the grown crystal was examined by Vicker's microhardness test.

  1. Single crystal growth in spin-coated films of polymorphic phthalocyanine derivative under solvent vapor

    Energy Technology Data Exchange (ETDEWEB)

    Higashi, T.; Ohmori, M.; Ramananarivo, M. F.; Fujii, A., E-mail: afujii@opal.eei.eng.osaka-u.ac.jp; Ozaki, M. [Division of Electrical, Electronic, and Information Engineering, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871 (Japan)

    2015-12-01

    The effects of solvent vapor on spin-coated films of a polymorphic phthalocyanine derivative were investigated. Growth of single crystal films via redissolving organic films under solvent vapor was revealed by in situ microscopic observations of the films. X-ray diffraction measurement of the films after exposing to solvent vapor revealed the phase transition of polymorphs under solvent vapor. The direction of crystal growth was clarified by measuring the crystal orientation in a grown monodomain film. The mechanism of crystal growth based on redissolving organic films under solvent vapor was discussed in terms of the different solubilities of the polymorphs.

  2. Single crystal growth in spin-coated films of polymorphic phthalocyanine derivative under solvent vapor

    Directory of Open Access Journals (Sweden)

    T. Higashi

    2015-12-01

    Full Text Available The effects of solvent vapor on spin-coated films of a polymorphic phthalocyanine derivative were investigated. Growth of single crystal films via redissolving organic films under solvent vapor was revealed by in situ microscopic observations of the films. X-ray diffraction measurement of the films after exposing to solvent vapor revealed the phase transition of polymorphs under solvent vapor. The direction of crystal growth was clarified by measuring the crystal orientation in a grown monodomain film. The mechanism of crystal growth based on redissolving organic films under solvent vapor was discussed in terms of the different solubilities of the polymorphs.

  3. Industrial growth of yttria-stabilized cubic zirconia crystals by skull melting process

    Institute of Scientific and Technical Information of China (English)

    徐家跃; 雷秀云; 蒋新; 何庆波; 房永征; 张道标; 何雪梅

    2009-01-01

    We reported the development of a Ф100 cm growth apparatus for skull melting growth of yttria-stabilized cubic zirconia(YSZ) crystals and more than 1000 kg crystals have been grown in the furnace each time.The growth conditions were optimized and the structure of the as-grown crystals was characterized by X-ray diffraction.The transmittance of 15 mol.% yttria-stabilized cubic zirconia crystal was nearly 80% in the range of 400-1600 nm.The refractive indices were measured and fitted the Sellmeier equation whi...

  4. Method for the growth of large low-defect single crystals

    Science.gov (United States)

    Powell, J. Anthony (Inventor); Neudeck, Philip G. (Inventor); Trunek, Andrew J. (Inventor); Spry, David J. (Inventor)

    2008-01-01

    A method and the benefits resulting from the product thereof are disclosed for the growth of large, low-defect single-crystals of tetrahedrally-bonded crystal materials. The process utilizes a uniquely designed crystal shape whereby the direction of rapid growth is parallel to a preferred crystal direction. By establishing several regions of growth, a large single crystal that is largely defect-free can be grown at high growth rates. This process is particularly suitable for producing products for wide-bandgap semiconductors, such as SiC, GaN, AlN, and diamond. Large low-defect single crystals of these semiconductors enable greatly enhanced performance and reliability for applications involving high power, high voltage, and/or high temperature operating conditions.

  5. Growth Habit of Polar Crystal ZnO by Solid-vapor Method

    Institute of Scientific and Technical Information of China (English)

    MA Shufang; LIANG Jian; LIU Xuguang; ZHAO Junfu; XU Bingshe

    2011-01-01

    Crystals of semiconductor ZnO were fabricated by means of solid-vapor growth method-carbon thermal reduction. Powder X-ray diffraction and field emission scanning electron microscope were used to characterize the phase and morphology of the samples. The results showed that the samples were wurtzite ZnO crystals and anisotropy of crystal growth relied on reaction temperature in solid-vapor process. The crystals synthesized at different temperatures were of short column-like shape, flat top hexagon pyramidal-like shape and polyhedron shape. The growth mechanisms of the above three kinds of crystal were consistent with the theory of growth basic structural unit of negative ion coordination polyhedron. At first, Zn2+ and four O2- form [Zn-O4]6- coordination tetrahedron at any temperature. Then, tetrahedrons stack in different ways into different morphology crystal at different temperatures.

  6. Growth and Characterization of Organic NLO Crystal: β-Naphthol

    Institute of Scientific and Technical Information of China (English)

    S.Janarthanan; R.Sugaraj Samuel; S.Selvakumar; Y.C.Rajan; D.Jayaraman; S.Pandi

    2011-01-01

    Single crystals ofβ-Naphthol (βN), an organic nonlinear optical (NLO) material was successfully grown by temperature lowering method using chloroform as solvent. The initial compound was purified by repeated recrystallization process. As-grown crystals were characterized by single crystal X-ray diffraction (XRD) studies to ascertain that βN crystal crystallized in the monoclinic system with a noncemtrosymmetric space group. Vibrational frequencies of various functional groups in the crystals were derived from Fourier transform infrared (FTIR) spectroscopy and proton nuclear magnetic resonance (NMR) spectrum. Optical characterization was done using UV-Visible near-infrared (NIR) spectroscopy. The thermal behaviour of the material was studied by thermo gravimetric and differential thermal plots. Scanning electron microscopy (SEM) study was carried out on the surface of the grown crystals to investigate the nature of defects in the crystal surface and the NLO property of the crystal was tested by Nd:YAG laser as a source.

  7. Chronic Lead Exposure and Mixed Factors of Gender×Age×Brain Regions Interactions on Dendrite Growth, Spine Maturity and NDR Kinase.

    Directory of Open Access Journals (Sweden)

    Yang Du

    Full Text Available NDR1/2 kinase is essential in dendrite morphology and spine formation, which is regulated by cellular Ca2+. Lead (Pb is a potent blocker of L-type calcium channel and our recent work showed Pb exposure impairs dendritic spine outgrowth in hippocampal neurons in rats. But the sensitivity of Pb-induced spine maturity with mixed factors (gender×age×brain regions remains unknown. This study aimed to systematically investigate the effect of Pb exposure on spine maturity in rat brain with three factors (gender×age×brain regions, as well as the NDR1/2 kinase expression. Sprague-Dawley rats were exposed to Pb from parturition to postnatal day 30, 60, 90, respectively. Golgi-Cox staining was used to examine spine maturity. Western blot assay was applied to measure protein expression and real-time fluorescence quantitative PCR assay was used to examine mRNA levels. The results showed chronic Pb exposure significantly decreased dendritic length and impaired spine maturity in both rat hippocampus and medial prefrontal cortex. The impairment of dendritic length induced by Pb exposure tended to adolescence > adulthood, hippocampus > medial prefrontal cortex and female > male. Pb exposure induced significant damage in spine maturity during adolescence and early adult while little damage during adult in male rat brain and female medial prefrontal cortex. Besides, there was sustained impairment from adolescence to adulthood in female hippocampus. Interestingly, impairment of spine maturity followed by Pb exposure was correlated with NDR1/2 kinase. The reduction of NDR1/2 kinase protein expression after Pb exposure was similar to the result of spine maturity. In addition, NDR2 and their substrate Rabin3 mRNA levels were significantly decreased by Pb exposure in developmental rat brain. Taken together, Pb exposure impaired dendrite growth and maturity which was subject to gender×age×brain regions effects and related to NDR1/2 signal expression.

  8. Real-time processing of interferograms for monitoring protein crystal growth on the Space Station

    Science.gov (United States)

    Choudry, A.; Dupuis, N.

    1988-01-01

    The possibility of using microscopic interferometric techniques to monitor the growth of protein crystals on the Space Station is studied. Digital image processing techniques are used to develop a system for the real-time analysis of microscopic interferograms of nucleation sites during protein crystal growth. Features of the optical setup and the image processing system are discussed and experimental results are presented.

  9. Real-time processing of interferograms for monitoring protein crystal growth on the Space Station

    Science.gov (United States)

    Choudry, A.; Dupuis, N.

    1988-01-01

    The possibility of using microscopic interferometric techniques to monitor the growth of protein crystals on the Space Station is studied. Digital image processing techniques are used to develop a system for the real-time analysis of microscopic interferograms of nucleation sites during protein crystal growth. Features of the optical setup and the image processing system are discussed and experimental results are presented.

  10. Crystal growth, FTIR and thermal characterization of bis(ethyltriphenylphosphonium) tetrabromomanganate(II) dihydrate crystals

    Indian Academy of Sciences (India)

    C Ilamaran; M Sethuram; M Dhandapani; G Amirthaganesan

    2012-05-01

    Single crystals of a novel compound, bis(ethyltriphenylphosphonium) tetrabromomanganate(II) dihydrate (BTP-Mn) were grown by solution growth-slow evaporation technique from aqueous solution of the compound at ambient temperature. The grown crystals were characterized by elemental analysis, powder X-ray diffraction, thermal analysis, nuclear magnetic resonance spectroscopy (NMR) and Fourier transform infra-red spectroscopy (FTIR) techniques. The chemical composition of the compound was revealed by elemental analysis and its crystallinity was confirmed by powder X-ray diffraction. Thermal analysis confirmed that the compound was stable up to 125°C. The various kinds of protons and carbons present in the compound were confirmed by 1H NMR and 13C NMR technique respectively and the presence of phosphorous was confirmed by 31P NMR spectrum in the compound. The modes of vibration of different molecular groups present in the compound were identified by FTIR spectral analysis. The second harmonic generation behaviour was tested by Nd:YAG laser source.

  11. Growth of ZnO Single Crystal by Chemical Vapor Transport Method

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    ZnO crystals were grown by CVT method in closed quartz tube under seeded condition. Carbon was used as a transport agent to enhance the chemical transport of ZnO in the growth process. ZnO single crystals were grown by using GaN/sapphire and GaN/Si wafer as seeds. The property and crystal quality of the ZnO single crystals was studied by photoluminescence spectroscopy and X-ray diffraction technique.

  12. Morphology and Growth of Methyl Stearate as a Function of Crystallization Environment

    OpenAIRE

    Camacho, DM; Roberts, KJ; Muller, FL; Thomas, D.; More, I; Lewtas, K

    2017-01-01

    In situ studies of methyl stearate growing from supersaturated n-dodecane, kerosene, and toluene solutions reveal strong evidence that solvent choice influences the crystal morphology and crystal growth kinetics. Crystals with similar habit are observed in all solvents, with the exception of lower supersaturations in kerosene, where a less symmetric morphology was observed. BFDH analysis based on the monoclinic C2 crystal structure of methyl stearate yielded the morphological indexation to be...

  13. Growth of lithium triborate single crystals from molten salt solution under various temperature gradients

    Science.gov (United States)

    Guretskii, S. A.; Ges, A. P.; Zhigunov, D. I.; Ignatenko, A. A.; Kalanda, N. A.; Kurnevich, L. A.; Luginets, A. M.; Milovanov, A. S.; Molchan, P. V.

    1995-12-01

    Single crystals of lithium triborate LiB 3O 5 (LBO) have been grown by the top-seeded solution growth method with B 2O 3 as a solvent using different temperature gradients in the zone of crystallization. Optical and nonlinear optical properties of LBO single crystals have been investigated. The influence of post-growth thermal treatment in oxygen atmosphere on the optical properties has been studied.

  14. Effect of anisotropy on deep cellular crystal growth in directional solidification

    Science.gov (United States)

    Jiang, Han; Chen, Ming-Wen; Shi, Guo-Dong; Wang, Tao; Wang, Zi-Dong

    2016-06-01

    The effect of anisotropic surface tension and anisotropic interface kinetics on deep cellular crystal growth is studied. An asymptotic solution of deep cellular crystal growth in directional solidification is obtained by using the matched asymptotic expansion method and the multiple variable expansion method. The results show that as the anisotropic parameters increase, the total length of deep cellular crystal increases and the root depth increases, whereas the curvature of the interface near the root increases or the curvature radius decreases.

  15. The Effect of Ionic Liquids on the CaCO3 Crystal Growth

    Institute of Scientific and Technical Information of China (English)

    Zhi Guo HU; Shi Li SONG; Jian Ji WANG; Lin YANG

    2004-01-01

    In this paper, the effect of ionic liquids on the CaCO3 crystal growth has been studied for the first time. The obtained CaCO3 crystals were charactered by the X-ray diffraction and scanning electron micrographs. The results showed that the control ability of ionic liquids for CaCO3 crystals growth was dependent on the counter anion very much.

  16. Essential Role for Vav GEFs in Brain-derived Neurotrophic Factor (BDNF)-induced Dendritic Spine Growth and Synapse Plasticity

    OpenAIRE

    Hale, Carly F.; Dietz, Karen C.; Varela, Juan A.; Wood, Cody B.; Zirlin, Benjamin C.; Leah S. Leverich; Greene, Robert W.; Cowan, Christopher W.

    2011-01-01

    Brain-derived neurotrophic factor (BDNF) and its cognate receptor, TrkB, regulate a wide range of cellular processes, including dendritic spine formation and functional synapse plasticity. However, the signaling mechanisms that link BDNF-activated TrkB to F-actin remodeling enzymes and dendritic spine morphological plasticity remain poorly understood. We report here that BDNF/TrkB signaling in neurons activates the Vav family of Rac/RhoA guanine nucleotide exchange factors (GEFs) through a no...

  17. Dependence of crack growth kinetics on dendrite orientation and water chemistry for Alloy 182 weld metal in high-temperature water

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Zhanpeng, E-mail: zplu@shu.edu.cn [Institute of Materials Science, School of Materials Science and Engineering, Shanghai University, Shanghai 200072 (China); New Industry Creation Hatchery Center, Tohoku University, Sendai 980-8579 (Japan); Chen, Junjie [Institute of Materials Science, School of Materials Science and Engineering, Shanghai University, Shanghai 200072 (China); Shoji, Tetsuo [New Industry Creation Hatchery Center, Tohoku University, Sendai 980-8579 (Japan); Meng, Fanjiang [Shanghai Nuclear Engineering Research & Design Institute, Shanghai 200233 (China)

    2015-03-15

    Highlights: • SCC paths along dendrite directions in both T–S and T–L specimens of Alloy 182. • Higher SCC growth rates in T–S orientation specimen than in T–L orientation specimen. • CGR increased with increasing dissolved oxygen. • Apparently negative da/dt curve by ACPD in hydrogen saturated water. - Abstract: Stress corrosion cracking growth rates of Alloy 182 weld metals in T–S and T–L orientations in 288 °C pure water with various dissolved oxygen and hydrogen concentrations were measured. Extensive inter-dendritic stress corrosion cracking paths on the side surfaces and fracture surfaces were observed. The crack growth path in the T–S orientation specimen was perpendicular to the applied loading direction, and parallel to the loading direction in the T–L specimen. Crack growth rates of the T–S specimen were significantly higher than those of the T–L specimen under the same test conditions. The crack growth rate decreased significantly with decreasing dissolved oxygen concentration. Adding dissolved hydrogen in water caused an apparent decrease of the alternating current potential drop signal during crack growth monitoring.

  18. Crystal growth of compound semiconductors in a low-gravity environment (InGaAs crystals) (M-22)

    Science.gov (United States)

    Tatsumi, Masami

    1993-01-01

    Compound semiconductor crystals, such as gallium arsenide and indium phosphide crystals, have many interesting properties that silicon crystals lack, and they are expected to be used as materials for optic and/or electro-optic integrated devices. Generally speaking, alloy semiconductors, which consist of more than three elements, demonstrate new functions. For example, values of important parameters, such as lattice constant and emission wavelength, can be chosen independently. However, as it is easy for macroscopic and/or microscopic fluctuations of composition to occur in alloy semiconductor crystals, it is difficult to obtain crystals having homogeneous properties. Macroscopic change of composition in a crystal is caused by the segregation phenomenon. This phenomenon is due to a continuous change in the concentration of constituent elements at the solid-liquid interfacing during solidification. On Earth, attempts were made to obtain a crystal with homogeneous composition by maintaining a constant melt composition near the solid-liquid interface, through suppression of the convection flow of the melt by applying a magnetic field. However, the attempt was not completely successful. Convective flow does not occur in microgravity because the gravity in space is from four to six orders of magnitude less than that on Earth. In such a case, mass transfer in the melt is dominated by the diffusion phenomenon. So, if crystal growth is carried out at a rate that is higher than the rate of mass transfer due to this phenomenon, it is expected that crystals having a homogeneous composition will be obtained. In addition, it is also possible that microscopic composition fluctuations (striation) may disappear because microscopic fluctuations diminish in the absence of convection. We are going to grow a bulk-indium gallium arsenide (InGaAs) crystal using the gradient heating furnace (GHF) in the first material processing test (FMPT). The structure of the sample is shown where In

  19. Crystal growth mechanisms in miarolitic cavities in the Lake George ring complex and vicinity, Colorado

    Science.gov (United States)

    Kile, D.E.; Eberl, D.D.

    1999-01-01

    The Crystal Peak area of the Pikes Peak batholith, near Lake George in central Colorado, is world-renowned for its crystals of amazonite (the blue-green variety of microcline) and smoky quartz. Such crystals, collected from individual miarolitic pegmatites, have a remakably small variation in crystal size within each pegmatite, and the shapes of plots of their crystal size distributions (CSDs) are invariably lognormal or close to lognormal in all cases. These observations are explained by a crystal growth mechanism that was governed initially by surface-controlled kinetics, during which crystals tended to grow larger in proportion to their size, thereby establishing lognormal CSDs. Surface-controlled growth was followed by longer periods of supply controlled growth, during which growth rate was predominantly size-independent, consequently preserving the lognormal shapes of the CSDs and the small size variation. The change from surface- to supply controlled growth kinetics may have resulted from an increasing demand for nutrients that exceeded diffusion limitations of the system. The proposed model for crystal growth in this locality appears to be common in the geologic record, and can be used with other information, such as isotopic data, to deduce physico-chemical conditions during crystal formation.

  20. Growth and characterization of propyl-para-hydroxybenzoate single crystals

    Indian Academy of Sciences (India)

    N Karunagaran; P Ramasamy; R Perumal Ramasamy

    2014-10-01

    Single crystals of propyl--hydroxybenzoate have been grown by slow evaporation solution technique. The structure of the compound was confirmed by FT–IR, FT–Raman spectroscopy and single crystal X-ray diffraction studies. The crystalline perfection of the grown single crystals has been analysed by high resolution X-ray diffraction measurements. Optical properties of the grown single crystals were studied by UV–Vis NIR spectrum. The luminescence behaviour of the single crystal has been analysed by photoluminescence analysis and found maximum luminescence in the lower wavelength region. A simple interferometric technique was used for measuring birefringence of the crystal. The laser damage threshold of the crystal is 1.3 GW/cm2. The mechanical strength of the grown crystal is measured using Vickers microhardness tester. The dielectric properties have been investigated.

  1. Growth and characterization of hexamethylenetetramine crystals grown from solution

    Science.gov (United States)

    Babu, B.; Chandrasekaran, J.; Balaprabhakaran, S.

    2014-06-01

    Organic nonlinear optical single crystals of hexamethylenetetramine (HMT; 10 × 10 × 5 mm3) were prepared by crystallization from methanol solution. The grown crystals were subjected to various characterization techniques such as single crystal XRD, powder XRD, UV-Vis and electrical studies. Single crystal XRD analysis confirmed the crystalline structure of the grown crystals. Their crystalline nature was also confirmed by powder XRD technique. The optical transmittance property was identified from UV-Vis spectrum. Dielectric measurements were performed as a function of frequency at different temperatures. DC conductivity and photoconductivity studies were also carried out for the crystal. The powder second harmonic generation efficiency (SHG) of the crystal was measured using Nd:YAG laser and the efficiency was found to be two times greater than that of potassium dihydrogen phosphate (KDP).

  2. Modelling the crystal growth in highly undercooled alloy melts by non-isothermal phase-field method

    Institute of Scientific and Technical Information of China (English)

    Li Mei-E; Yang Gen-Cang; Zhou Yao-He

    2005-01-01

    A non-isothermal phase-field model is used to simulate the rapid solidification of highly undercooled alloy melts.The influence of undercooling on the solidification process is studied. It is indicated that with the increase of undercooling, the dendrite morphology changes from poorly developed dendrite, via the well-developed dendrite containing secondary and ternary arms, to the compact diamond-shaped grain. With increasing undercooling, the tip radius changes in the following rule: decrease → increase → decrease while the growth velocity increases constantly, which is consistent with the results predicted by the Boettinger-Coriell-Trivedi model. The thermal, solutal and kinetic undercooling contributions under different initial undercooling are also determined. It is shown that when the undercooling is increased beyond a certain value, the thermal undercooling contribution exceeds the solutal contribution and the dendrite growth transits from solutal diffusion controlled to thermal diffusion controlled one.

  3. Growth and characterization of gel grown pure and mixed iron–manganese levo-tartrate crystals

    Indian Academy of Sciences (India)

    S J Joshi; B B Parekh; K D Vohra; M J Joshi

    2006-06-01

    Several applications of iron tartrate and manganese tartrate compounds are reported in the literature. In the present investigation, we have grown pure and mixed iron (II)–manganese levo-tartrate crystals by single diffusion gel growth technique. Crystals with spherulitic morphology were harvested. The colouration of the crystals changed from black to pinkish brown upon increasing the content of manganese in the crystals. The crystals were characterized by FTIR spectroscopy, powder XRD, TGA, VSM and dielectric study. Crystal structures of different mixed crystals were studied. From TGA it was observed that on heating the hydrated crystals became anhydrous and then converted into oxides. Paramagnetic nature of the crystals was revealed from VSM study. The variation of the dielectric constant with frequency was studied. The results are discussed.

  4. Progress in art and science of crystal growth and its impacts on modern society

    Science.gov (United States)

    Nishinaga, Tatau

    2015-05-01

    The impacts of the progress in the art and science of crystal growth on human life are reviewed. Even before the invention of the transistor, quartz and corundum crystals were used as crystal oscillators and jewel bearings, respectively. However, a major impact of crystal growth on society was experienced with the invention of the transistor, which required high-purity and perfect germanium crystals. Once the importance of crystal growth was clearly recognized, the science of crystal growth also extensively developed. The growth of single crystalline silicon allows us to produce integrated circuits, which are used in all the electronic devices in everyday use. The technological developments in the growth of compound semiconductors have also had a large impact on society through the inventions of the laser diode for optical communication and the p-n junction nitride light-emitting diode toward the realization of a less energy-intensive society. The latter invention was awarded the 2014 Nobel Prize in Physics. Finally, future aspects of crystal growth are discussed.

  5. Extracellular matrix protein in calcified endoskeleton: a potential additive for crystal growth and design

    Science.gov (United States)

    Azizur Rahman, M.; Fujimura, Hiroyuki; Shinjo, Ryuichi; Oomori, Tamotsu

    2011-06-01

    In this study, we demonstrate a key function of extracellular matrix proteins (ECMPs) on seed crystals, which are isolated from calcified endoskeletons of soft coral and contain only CaCO 3 without any living cells. This is the first report that an ECMP protein extracted from a marine organism could potentially influence in modifying the surface of a substrate for designing materials via crystallization. We previously studied with the ECMPs from a different type of soft coral ( Sinularia polydactyla) without introducing any seed crystals in the process , which showed different results. Thus, crystallization on the seed in the presence of ECMPs of present species is an important first step toward linking function to individual proteins from soft coral. For understanding this interesting phenomenon, in vitro crystallization was initiated in a supersaturated solution on seed particles of calcite (1 0 4) with and without ECMPs. No change in the crystal growth shape occurred without ECMPs present during the crystallization process. However, with ECMPs, the morphology and phase of the crystals in the crystallization process changed dramatically. Upon completion of crystallization with ECMPs, an attractive crystal morphology was found. Scanning electron microscopy (SEM) was utilized to observe the crystal morphologies on the seeds surface. The mineral phases of crystals nucleated by ECMPs on the seeds surface were examined by Raman spectroscopy. Although 50 mM Mg 2+ is influential in making aragonite in the crystallization process, the ECMPs significantly made calcite crystals even when 50 mM Mg 2+ was present in the process. Crystallization with the ECMP additive seems to be a technically attractive strategy to generate assembled micro crystals that could be used in crystals growth and design in the Pharmaceutical and biotechnology industries.

  6. Crystal front shape control by use of an additional heater in a Czochralski sapphire single crystal growth system

    Science.gov (United States)

    Hur, Min-Jae; Han, Xue-Feng; Choi, Ho-Gil; Yi, Kyung-Woo

    2017-09-01

    The quality of sapphire single crystals used as substrates for LED production is largely influenced by two defects: dislocation density and bubbles trapped in the crystal. In particular, the dislocation density has a higher value in sapphire grown by the Czochralski (CZ) method than by other methods. In the present study, we predict a decreased value for the convexity and thermal gradient at the crystal front (CF) through the use of an additional heater in an induction-heated CZ system. In addition, we develop a solute concentration model by which the location of bubble formation in CZ growth is calculated, and the results are compared with experimental results. We further calculate the location of bubble entrapment corresponding with the use of an additional heater. We find that sapphire crystal growth with an additional heater yields a decreased thermal gradient at the CF, together with decreased CF convexity, improved energy efficiency, and improvements in terms of bubble formation location.

  7. Crystallization Kinetics of Organic–Inorganic Trihalide Perovskites and the Role of the Lead Anion in Crystal Growth

    KAUST Repository

    Moore, David T.

    2015-02-18

    © 2015 American Chemical Society. Methylammonium lead halide perovskite solar cells continue to excite the research community due to their rapidly increasing performance which, in large part, is due to improvements in film morphology. The next step in this progression is control of the crystal morphology which requires a better fundamental understanding of the crystal growth. In this study we use in situ X-ray scattering data to study isothermal transformations of perovskite films derived from chloride, iodide, nitrate, and acetate lead salts. Using established models we determine the activation energy for crystallization and find that it changes as a function of the lead salt. Further analysis enabled determination of the precursor composition and showed that the primary step in perovskite formation is removal of excess organic salt from the precursor. This understanding suggests that careful choice of the lead salt will aid in controlling crystal growth, leading to superior films and better performing solar cells.

  8. Crystallization kinetics of organic-inorganic trihalide perovskites and the role of the lead anion in crystal growth.

    Science.gov (United States)

    Moore, David T; Sai, Hiroaki; Tan, Kwan W; Smilgies, Detlef-M; Zhang, Wei; Snaith, Henry J; Wiesner, Ulrich; Estroff, Lara A

    2015-02-18

    Methylammonium lead halide perovskite solar cells continue to excite the research community due to their rapidly increasing performance which, in large part, is due to improvements in film morphology. The next step in this progression is control of the crystal morphology which requires a better fundamental understanding of the crystal growth. In this study we use in situ X-ray scattering data to study isothermal transformations of perovskite films derived from chloride, iodide, nitrate, and acetate lead salts. Using established models we determine the activation energy for crystallization and find that it changes as a function of the lead salt. Further analysis enabled determination of the precursor composition and showed that the primary step in perovskite formation is removal of excess organic salt from the precursor. This understanding suggests that careful choice of the lead salt will aid in controlling crystal growth, leading to superior films and better performing solar cells.

  9. Expression and clinical significance of dendritic cell and transforming growth factor-beta 1 in cervical cancer

    Institute of Scientific and Technical Information of China (English)

    Zhao; Shan; Rong; Fengnian

    2006-01-01

    Objective:To explore the density and mature status of Dendritic cell(DC) in cervical cancer and correlation with the expression of transforming growth factor-beta 1(TGF-β1).Methods:Streptavidin-peroxidase(SP) immunohistochemistry methods were used to detect S-100 DC and the expression of TGF-β1 in 20 normal cervical tissues and 53 cervical cancer tissues without any sort of chemotherapy or radiation therapy prior to resection.Medical records were reviewed,clinicopathological variables were retrieved and used for analysis.Results:Two types of DC were observed under the microscope.The expression of DC in cervical cancer was significantly higher than that in normal tissues(23.34 cells/mm2 vs 29.91 cells/mm2,P<0.05),and significantly higher in early stage than that in advanced stage(P<0.05).The expression of TGF-β1 was significantly higher in cervical cancer than that in normal tissues (P<0.025).However,there was no correaction between TGF-β1 and lymph nodes metastasis.The index of DC in cervical cancer was negatively correlated to the expression of TGF-β1 in tumor cells (r=-0.8875,P=0.0001).Conclusion:Maturation of DC in cervical cancer is inhibited.The decreased number of DC and the higher expression of TGF-β1 are due to the failure of the immunity,these may play an important role in the development of the cervical cancer.

  10. Thermodynamic reactivity, growth and characterization of mercurous halide crystals

    Science.gov (United States)

    Singh, N. B.; Gottlieb, M.; Henningsen, T.; Hopkins, R. H.; Mazelsky, R.; Singh, M.; Glicksman, M. E.; Paradies, C.

    1992-01-01

    Thermodynamic calculations were carried out for the Hg-X-O system (X = Cl, Br, I) to identify the potential sources of contamination and relative stability of oxides and oxy-halide phases. The effect of excess mercury vapor pressure on the optical quality of mercurous halide crystal was studied by growing several mercurous chloride crystals from mercury-rich composition. The optical quality of crystals was examined by birefringence interferometry and laser scattering studies. Crystals grown in slightly mercury-rich composition showed improved optical quality relative to stoichiometric crystals.

  11. Ground based experiments on the growth and characterization of L-Arginine Phosphate (LAP) crystals

    Science.gov (United States)

    Rao, S. M.; Cao, C.; Batra, A. K.; Lal, R. B.; Mookherji, T. K.

    1991-01-01

    L-Arginine Phosphate (LAP) is a new nonlinear optical material with higher efficiency for harmonic generation compared to KDP. Crystals of LAP were grown in the laboratory from supersaturated solutions by temperature lowering technique. Investigations revealed the presence of large dislocation densities inside the crystals which are observed to produce refractive index changes causing damage at high laser powers. This is a result of the convection during crystal growth from supersaturated solutions. It is proposed to grow these crystals in a diffusion controlled growth condition under microgravity environment and compare the crystals grown in space with those grown on ground. Physical properties of the solutions needed for modelling of crystal growth are also presented.

  12. Simulation of the flow and mass transfer for KDP crystals undergoing 2D translation during growth

    Science.gov (United States)

    Zhou, Chuan; Li, Mingwei; Hu, Zhitao; Yin, Huawei; Wang, Bangguo; Cui, Qidong

    2016-09-01

    In this study, a novel motion mode for crystals during growth, i.e., 2D translation, is proposed. Numerical simulations of flow and mass transfer are conducted for the growth of large-scale potassium dihydrogen phosphate (KDP) crystals subjected to the new motion mode. Surface supersaturation and shear stress are obtained as functions of the translational velocity, distance, size, orientation of crystals. The dependence of these two parameters on the flow fields around the crystals is also discussed. The thicknesses of the solute boundary layer varied with translational velocity are described. The characteristics of solution flow and surface supersaturation distribution are summarized, where it suggests that the morphological stability of a crystal surface can be enhanced if the proposed 2D translation is applied to crystal growth.

  13. Investigation on Growth and Optical Properties of LVCC Single Crystals

    Directory of Open Access Journals (Sweden)

    N. Sheen Kumar

    2014-11-01

    Full Text Available L-valine cadmium chloride (LVCC single crystals were grown by slow evaporation technique with different concentrations (0.25, 0.5, 0.75 and 1.0 mole of CdCl2. All the grown crystals were subjected to single crystal X-ray diffraction analysis. Solid state parameters were calculated for the grown crystals. The optical properties of the crystals were investigated by UV-Vis. absorption spectroscopy. The results revealed that, the wider bandgap and large transparency in the visible region along with higher polarizability of the grown crystals are highly useful in optoelectronic devices. Also according to our needs, one can tune the optical and electrical properties of LVCC crystals by adjusting the concentration of CdCl2 in LVCC.

  14. Crystal growth inhibitors for the prevention of L-cystine kidney stones through molecular design.

    Science.gov (United States)

    Rimer, Jeffrey D; An, Zhihua; Zhu, Zina; Lee, Michael H; Goldfarb, David S; Wesson, Jeffrey A; Ward, Michael D

    2010-10-15

    Crystallization of L-cystine is a critical step in the pathogenesis of cystine kidney stones. Treatments for this disease are somewhat effective but often lead to adverse side effects. Real-time in situ atomic force microscopy (AFM) reveals that L-cystine dimethylester (L-CDME) and L-cystine methylester (L-CME) dramatically reduce the growth velocity of the six symmetry-equivalent {100} steps because of specific binding at the crystal surface, which frustrates the attachment of L-cystine molecules. L-CDME and L-CME produce l-cystine crystals with different habits that reveal distinct binding modes at the crystal surfaces. The AFM observations are mirrored by reduced crystal yield and crystal size in the presence of L-CDME and L-CME, collectively suggesting a new pathway to the prevention of L-cystine stones by rational design of crystal growth inhibitors.

  15. Crystal Growth Inhibitors for the Prevention of L-Cystine Kidney Stones Through Molecular Design

    Energy Technology Data Exchange (ETDEWEB)

    Rimer, Jeffrey D.; An, Zhihua; Zhu, Zina; Lee, Michael H.; Goldfarb, David S.; Wesson, Jeffrey A.; Ward, Michael D. (NY Univ.); (MCW)

    2010-11-12

    Crystallization of L-cystine is a critical step in the pathogenesis of cystine kidney stones. Treatments for this disease are somewhat effective but often lead to adverse side effects. Real-time in situ atomic force microscopy (AFM) reveals that L-cystine dimethylester (L-CDME) and L-cystine methylester (L-CME) dramatically reduce the growth velocity of the six symmetry-equivalent {l_brace}100{r_brace} steps because of specific binding at the crystal surface, which frustrates the attachment of L-cystine molecules. L-CDME and L-CME produce L-cystine crystals with different habits that reveal distinct binding modes at the crystal surfaces. The AFM observations are mirrored by reduced crystal yield and crystal size in the presence of L-CDME and L-CME, collectively suggesting a new pathway to the prevention of L-cystine stones by rational design of crystal growth inhibitors.

  16. Raman Spectrum Analysis on the Solid-Liquid Boundary Layer of BGO Crystal Growth

    Institute of Scientific and Technical Information of China (English)

    ZHANG Xia; YIN Shao-Tang; WAN Song-Ming; YOU Jing-Lin; CHEN Hui; ZHAO Si-Jie; ZHANG Qing-Li

    2007-01-01

    We study the Raman spectra of Bi4Ge3O12 crystal at different temperatures, as well as its melt. The structure characters of the single crystal, melt and growth solid-liquid boundary layer of BGO are investigated by their high-temperature Raman spectra for the first time. The rule of structure change of BGO crystal with increasing temperature is analysed. The results show that there exists [GeO4] polyhedral structure and Bi ion independently in BGO melt. The bridge bonds Bi-O-Bi and Bi-O-Ge appear in the crystal and at the boundary layer, but disappear in the melt. The structure of the growth solid-liquid boundary layer is similar to that of BGO crystal. In the melt, the long-range order structure of the crystal disappears. The thickness of the grovth solid-liquid boundary layer of BGO crystal is about 50 μm.

  17. Methodology of Single Crystal Growth and Microstructure Analysis of CoTi(Zr) Intermetallic Compounds

    Institute of Scientific and Technical Information of China (English)

    Lijuan ZHANG; Mike L.JENKINS; Glyn TAYLOR

    2005-01-01

    The effects of preparation and crystal growth methods on the microstructure, composition, and oxidation of CoTi(Zr)intermetallics were dealt with. A group of methods has been used to produce CoTi and CoTi(Zr) crystals to prevent the formation of titanium oxide particles during melting and crystal growth. The results show that more oxides formed when using powdered starting materials even though the metals handled were and melted under an inert gas atmosphere; using bulk starting materials produced alloys showed less oxidation than powders, but adding a small amount of Al to getter the oxygen was not sufficient to prevent TiO2 formation. However, using a slightly reducing atmosphere during initial melting was highly effective in reducing the formation of oxide. Crystal growth carried out in Ar did not reduce the amount of oxide but only redistributed the particles. TiO2 particles were found only inthe grain boundaries after crystal growing, where they obstructed grain growth. Crystal growth in a vacuum was found to be essential in producing oxide free crystals. A seed selection technique was developed and used in growing CoTi single crystals. The microstructures of the samples were determined using optical microscopy, scanning electron microscopy and transmission electron microscopy, including the morphologies, grain sizes, oxide distributions and crystal structure confirmation.

  18. Development of compartment for studies on the growth of protein crystals in space.

    Science.gov (United States)

    Yamazaki, T; Tsukamoto, K; Yoshizaki, I; Fukuyama, S; Miura, H; Shimaoka, T; Maki, T; Oshi, K; Kimura, Y

    2016-03-01

    To clarify the growth mechanism of a protein crystal, it is essential to measure its growth rate with respect to the supersaturation. We developed a compartment (growth cell) for measuring the growth rate (materials for these components with care. The equipment was successfully used to examine the growth of a lysozyme crystal at a controlled supersaturation in space, where convection is negligible because of the microgravity environment, thereby advancing our understanding of the mechanism of protein crystal growth from solution. The technique used to develop the growth cell is useful not only for space experiments but also for kinetic studies of materials with very slow growth and dissolution rates (<10(-3) nm s(-1)).

  19. Ampoule failure sensor development for semiconductor crystal growth experiments

    Science.gov (United States)

    Watring, Dale A.; Johnson, Martin

    1994-01-01

    Currently there are no devices to detect an ampoule failure in semiconductor crystal growth experiments. If an ampoule fails, it will go undetected until the containing cartridge is breached due to chemical degradation. The experiment will then be terminated resulting in a failed experiment and a loss of data. The objective of this research was to develop a reliable failure sensor that would detect a specific liquid or vapor material before the metallic cartridge is degraded and the processing furnace contaminated. The sensor is a chemical fuse made from a metal with which the semiconductor material reacts more rapidly than it does with the containing cartridge. Upon ampoule failure, the sensor is exposed to the vapor or liquid semiconductor and the chemical reaction causes a resistance change in the sensor material. The sensor shows a step change in resistance on the order of megohms when exposed to mercury zinc telluride (HgZnTe), mercury cadmium telluride (HgCdTe), or gallium arsenide (GaAs). This ampoule failure sensor is being tested for possible use on the second United States Microgravity Mission (USML-2) and is the subject of a NASA patent application.

  20. The effect of tailor-made additives on crystal growth of methyl paraben: Experiments and modelling

    Science.gov (United States)

    Cai, Zhihui; Liu, Yong; Song, Yang; Guan, Guoqiang; Jiang, Yanbin

    2017-03-01

    In this study, methyl paraben (MP) was selected as the model component, and acetaminophen (APAP), p-methyl acetanilide (PMAA) and acetanilide (ACET), which share the similar molecular structure as MP, were selected as the three tailor-made additives to study the effect of tailor-made additives on the crystal growth of MP. HPLC results indicated that the MP crystals induced by the three additives contained MP only. Photographs of the single crystals prepared indicated that the morphology of the MP crystals was greatly changed by the additives, but PXRD and single crystal diffraction results illustrated that the MP crystals were the same polymorph only with different crystal habits, and no new crystal form was found compared with other references. To investigate the effect of the additives on the crystal growth, the interaction between additives and facets was discussed in detail using the DFT methods and MD simulations. The results showed that APAP, PMAA and ACET would be selectively adsorbed on the growth surfaces of the crystal facets, which induced the change in MP crystal habits.