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1

Fluid mechanics in crystal growth - The 1982 Freeman scholar lecture  

Microsoft Academic Search

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

Simon Ostrach

1983-01-01

2

The Mechanism of Protein Crystal Growth from Lipid Layers  

Microsoft Academic Search

Two-dimensional (2D) crystals of proteins on lipid monolayers can initiate the formation of large three-dimensional (3D) crystals suitable for X-ray diffraction studies. The role of the 2D crystals in this process has not been firmly established. While it is likely that the 2D crystals serve as nuclei for epitaxial crystal growth, other mechanisms, such as non-specific nucleation induced by the

Sally A. Hemming; Alexey Bochkarev; Seth A. Darst; Roger D. Kornberg; Paul Ala; Daniel S. C. Yang; Aled M. Edwards

1995-01-01

3

Growth mechanisms in laser crystallization and laser interference crystallization  

Microsoft Academic Search

The processes involved in the pulsed laser crystallization of amorphous silicon thin films were studied using transient reflection measurements. A model of the melting and solidification induced by the laser exposure, based on a one-dimensional calculation of the heat flow, was used to simulate the time-dependent reflectivity, yielding agreement with the experiments. Two laser beams interfering on the sample surface

G. Aichmayr; D. Toet; M. Mulato; P. V. Santos; A. Spangenberg; R. B. Bergmann

1998-01-01

4

Stable growth mechanisms of ice disk crystals in heavy water.  

PubMed

Ice crystal growth experiments in heavy water were carried out under microgravity to investigate the morphological transition from a disk crystal to a dendrite. Surprisingly, however, no transition was observed, namely, the disk crystal or dendrite maintained its shape throughout the experiments, unlike the results obtained on the ground. Therefore, we introduce a growth model to understand disk growth. The Gibbs-Thomson effect is taken into account as a stabilization mechanism. The model is numerically solved by varying both an interfacial tension of the prism plane and supercooling so that the final sizes of the crystals can become almost the same to determine the interfacial tension. The results are compared with the typical experimental ones and thus the interfacial tension is estimated to be 20 mJ/m(2). Next, the model is solved under two supercooling conditions by using the estimated interfacial tension to understand stable growth. Comparisons between the numerical and experimental results show that our model explains well the microgravity experiments. It is also found that the experimental setup has the capability of controlling temperature on the order of 1/100 K. PMID:22181428

Adachi, Satoshi; Yoshizaki, Izumi; Ishikawa, Takehiko; Yokoyama, Etsuro; Furukawa, Yoshinori; Shimaoka, Taro

2011-11-22

5

Growth of Crystals. Vol. 13  

Microsoft Academic Search

This book contains information on the crystallization of proteins, mechanisms and kinetics of crystal growth by vapor deposition, epitaxy, mechanisms and kinetics of crystal growth from the melt and from high-temperature solutions, growth of crystals from the melt, growth of crystals from solution, defect structure in crystals, and new materials (equipment for crystal growth). Specific articles include: equilibrium adsorption layers

E. I. Givargizov; E. A. D. White

1986-01-01

6

Solid mechanics and material strength studies on the melt growth of bulk single crystals  

Microsoft Academic Search

Microdefects such as dislocations and macrocracking should be controlled during the crystal growth process to obtain high-quality bulk single crystals. Solid mechanics and material strength studies on the single crystals are of importance to solve the problems related to the generation and multiplication of dislocations and the cracking of single crystals. The present paper reviews such research activities that comprise

Noriyuki Miyazaki

2007-01-01

7

Mechanisms of protein and virus crystal growth: An atomic force microscopy study of canavalin and STMV crystallization  

SciTech Connect

The evolution of surface morphology and step dynamics during growth of rhombohedral crystals of the protein canavalin and crystals of the cubic satellite tobacco mosaic virus (STMV) have been investigated for the first time by in situ atomic force microscopy. These two crystals were observed to grow by very different mechanisms. Growth of canavalin occurs on complex vicinal hillocks formed by multiple, independently acting screw dislocations. Small clusters were observed on the terraces. STMV on the other hand, was observed to grow by 2D nucleation of islands. No dislocations were found on the crystal. The results are used to determine the growth mechanisms and estimate the fundamental materials parameters. The images also illustrate the important mechanism of defect incorporation and provide insight to the processes that limit the growth rate and uniformity of these crystals.

Land, T.A.; De Yoreo, J.J. [Lawrence Livermore National Lab., CA (United States). Dept. of Chemistry and Materials Science; Malkin, A.J.; Kutznesov, Yu.G.; McPherson, A. [Univ. of California, Riverside, CA (United States). Dept. of Biochemistry

1996-05-01

8

A study of growth mechanism of KDP and ADP crystals by means of quantum chemistry  

NASA Astrophysics Data System (ADS)

Impurity adsorption, crystal growth by adsorption of growth unit and step-pinning mechanism of metal ion adsorption were investigated for potassium dihydrogen phosphate (KDP; KH 2PO 4) and ammonium dihydrogen phosphate (ADP; NH 4H 2PO 4) by quantum chemistry. In this study, the ideal crystal morphologies, the growth unit and the crystal surface with and without metal ions were calculated and analyzed by using electrostatic property. It is found that the computational results based on electrostatic potential distribution can account for the observed behaviours on KDP and ADP crystal growth.

Asakuma, Yusuke; Li, Qin; Ang, H. Ming; Tade, Moses; Maeda, Kouji; Fukui, Keisuke

2008-05-01

9

Growth Units and Formation Mechanisms of the Crystals under Hydrothermal Conditions.  

National Technical Information Service (NTIS)

The growth units and formation mechanisms of quartz (SiO2) and barium titanate (BaTiO3) crystals under hydrothermal conditions have been investigated by means of cataphoretic experiments. It is proposed that the growth units of the crystals in hydrotherma...

W. Z. Zhong G. Liu E. Shi S. Hua D. Tang Q. Zhao

1994-01-01

10

Deducing growth mechanisms for minerals from the shapes of crystal size distributions  

USGS Publications Warehouse

Crystal size distributions (CSDs) of natural and synthetic samples are observed to have several distinct and different shapes. We have simulated these CSDs using three simple equations: the Law of Proportionate Effect (LPE), a mass balance equation, and equations for Ostwald ripening. The following crystal growth mechanisms are simulated using these equations and their modifications: (1) continuous nucleation and growth in an open system, during which crystals nucleate at either a constant, decaying, or accelerating nucleation rate, and then grow according to the LPE; (2) surface-controlled growth in an open system, during which crystals grow with an essentially unlimited supply of nutrients according to the LPE; (3) supply-controlled growth in an open system, during which crystals grow with a specified, limited supply of nutrients according to the LPE; (4) supply- or surface-controlled Ostwald ripening in a closed system, during which the relative rate of crystal dissolution and growth is controlled by differences in specific surface area and by diffusion rate; and (5) supply-controlled random ripening in a closed system, during which the rate of crystal dissolution and growth is random with respect to specific surface area. Each of these mechanisms affects the shapes of CSDs. For example, mechanism (1) above with a constant nucleation rate yields asymptotically-shaped CSDs for which the variance of the natural logarithms of the crystal sizes (??2) increases exponentially with the mean of the natural logarithms of the sizes (??). Mechanism (2) yields lognormally-shaped CSDs, for which ??2 increases linearly with ??, whereas mechanisms (3) and (5) do not change the shapes of CSDs, with ??2 remaining constant with increasing ??. During supply-controlled Ostwald ripening (4), initial lognormally-shaped CSDs become more symmetric, with ??2 decreasing with increasing ??. Thus, crystal growth mechanisms often can be deduced by noting trends in ?? versus ??2 of CSDs for a series of related samples.

Eberl, D. D.; Drits, V. A.; Srodon, J.

1998-01-01

11

Prismatic faces of KDP crystal, kinetic and mechanism of growth from solutions  

Microsoft Academic Search

Growth kinetic of (100) typefaces of KDP crystals in impure solutions were measured and analyzed. The dual action of impurities as promoters of nucleation at higher supersaturations and as stopper of the spreading layer on the crystal surface at smaller supersaturations is underlined. 2D heterogeneous nucleation mechanism was found to be dominant at higher supersaturations, where the surface coverage of

H. V. Alexandru; S. Antohe

2003-01-01

12

Crystal growth mechanisms in miarolitic cavities in the Lake George ring complex and vicinity, Colorado  

USGS Publications Warehouse

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.

Kile, D. E.; Eberl, D. D.

1999-01-01

13

TEM investigation of the microporous compound VSB-1: Building units and crystal growth mechanisms  

SciTech Connect

Surface fine structure and structural defects in the open framework material VSB-1 have been investigated by electron microscopy. Crystal growth phenomena are proposed by a building unit model: (i) a unit is formed by two building units; (ii) they are linked to form first channels; and (iii) the whole network is grown via a layer-by-layer growth mechanism. A planar defect was observed in high-resolution transmission electron microscope (HRTEM) image taken with the [0001] incidence, and diffuse streaks related to the presence of defects were observed in a series of electron diffraction (ED) patterns. The microstructure model derived from the defect structure gives information on crystal growth. These defects highlight an open site that could be the pillar of a new crystal growth process. The study of defects and crystal growth is important in understanding physical properties such as catalytic or magnetic properties, and in synthesising a new open framework structure. - Graphical abstract: TEM investigation of the microporous compound VSB-1 evidenced defects and information about building units and crystal growth. As usually observed for microporous materials, the crystal growth via a layer by layer mechanism.

Colmont, Marie [Structural Chemistry, Arrhenius Laboratory, Stockholm University, S-10691 Stockholm (Sweden)], E-mail: marie.Colmont@ensc-lille.fr; Terasaki, Osamu [Structural Chemistry, Arrhenius Laboratory, Stockholm University, S-10691 Stockholm (Sweden)

2007-03-15

14

Insights into the crystal growth mechanisms of zeolites from combined experimental imaging and theoretical studies.  

PubMed

Detailed investigations into surface mediated crystal growth at zeolite external surfaces are presented. High resolution TEM is able to directly resolve surface and bulk crystallographic features and the unusual surface structural features are interpreted from simulation work. The growth of the double 4 ring is found to be a crucial and rate-determining step in the surface mediated, post-nucleation crystal growth mechanism of zeolite Beta C. Growth of 4 rings is found to be more favourable on fast growing rather than slow growing faces, explaining the relative growth rate of crystal faces in this materials. Similarly, the terminating structures of zeolite Y/Faujasite can be partly explained by considering the condensation of 6 ring and double 6 ring species at the crystal surface. Whilst 4-ring and double 4 rings are known solution species, 6 rings and double 6 rings are not, and hence it is speculated that post-nucleation crystal growth may involve competition between primary building unit and secondary building unit mediated crystal growth mechanisms. PMID:17955806

Slater, Ben; Ohsuna, Tetsu; Liu, Zheng; Terasaki, Osamu

2007-01-01

15

Atomic force microscopy studies on growth mechanisms of LAP crystals grown in solution containing excessive amount of l-arginine  

Microsoft Academic Search

Atomic force microscopy (AFM) has been used to investigate the growth mechanisms of the l-arginine phosphate monohydrate (LAP) crystal grown from the aqueous solution containing excessive amount of l-arginine molecules. Under this condition, the LAP crystals grow by both 2D nucleation mechanism and spiral dislocation mechanism. 2D nucleation growth is the intrinsical growth mechanism owing to the crystal structure of

Y. L. Geng; D. Xu; D. L. Sun; W. Du; H. Y. Liu; G. H. Zhang; X. Q. Wang

2005-01-01

16

Growth mechanism changes in pseudo-dewetted monolayer poly(ethylene oxide) crystallization  

NASA Astrophysics Data System (ADS)

Crystal growth mechanism changes have been observed in pseudo-dewetted monolayers of low molecular weight (LMW) (PEO) on freshly cleaved hydrophilic mica surfaces [HPEO(4250) which have -OH groups at both ends and MHPEO(4700) which has one -OH and one -OCH3 as end groups]. X-ray scattering reflectivity measurements show a wetted monolayer of molten PEO with a thickness of ˜ 4.5 nm on the mica surface. Non-adsorbed PEO droplets sit on top of the wetted monolayer. A two-step process for PEO single crystal growth under isothermal conditions was identified utilizing in-situ atomic force microscopy at different crystallization temperatures (Tx). In the first step, the crystal grows within the droplet which supplies the molten PEO that participates in the crystal formation. In this second-step, the wetted monolayer at the growth front is depleted by about 1.5 - 2.5 nm. The growing crystal lateral sizes obey a power law of t^? (t: time). At a high Tx of 63 C for MHPEO(4700), the growth behavior obeys r t (? = 1). While in the case of HPEO(4250), its growth behavior follows r t^0.5 (? = 0.5) in the whole Tx range. With decreasing Tx, the growth of MHPEO(4700) falls into a scaling law of r t^? (0.5 < ? < 1).

Zhu, Dun-Shen; Chen, Er-Qiang; Shi, An-Chang; Cheng, Stephen

2006-03-01

17

Characterization of the growth mechanism of YIG crystal fibers using the laser heated pedestal growth method  

NASA Astrophysics Data System (ADS)

Yttrium iron garnet (YIG, Y3Fe5O12) single-crystal fibers were grown by the laser heated pedestal growth (LHPG) method. Different compositions, with various Y2O3 and Fe2O3 ratios seeds were used. The microstructure and the compositional variation of the obtained crystals show that YIG single-crystal fibers could be directly grown at the stable freezing interface when the melt had a composition of 78 87 mol% Fe2O3. When the seed's Fe2O3 concentration was below 78 mol%, the yttrium orthoferrite (YFeO3) would crystallize out until the composition of the melt increased along the liquidus curve until it needed a concentration of 78 mol% Fe2O3 or higher, whereupon YIG started to crystallize from the liquid. With the LHPG method, however, when Fe-rich ceramic rod used as a seed was employed to grow YIG crystal, the crystallographic orientation was indefinite. Therefore, YIG single-crystal fibers with the desired crystallographic orientation could only be obtained using a two-pass method. During the forward pass, YIG single crystal could be directly grown using a Fe-rich solvent, while during the backward pass, the crystallographic orientation of the grown crystal would be the same as that of the YIG seed.

Mao, Tze-Chern; Chen, Jyh-Chen; Hu, Chao-Chang

2005-08-01

18

Growth of Crystals. Vol. 13  

SciTech Connect

This book contains information on the crystallization of proteins, mechanisms and kinetics of crystal growth by vapor deposition, epitaxy, mechanisms and kinetics of crystal growth from the melt and from high-temperature solutions, growth of crystals from the melt, growth of crystals from solution, defect structure in crystals, and new materials (equipment for crystal growth). Specific articles include: equilibrium adsorption layers on GaAs (Ill) and Si (lll) surfaces in CVD growth; the role of adsorption layer in chemical vapor deposition; the kinetics and mechanism of gallium arsenide growth in gas-transporrt systems; the application of electron microscopy to a study of kinetics and mechansm of crystallization; general approach to Monte Carlo simulation of crystal growth; stability of crystallization in edge-defined film-fed growth from the melt; progress in flux growth of large crystals; growth defects in semiconductor crystals; the defect structure of Sb2S/sub 3/ crystals revealed by electron microscope crystal lattice imaging techniques; and application of laser heating to crystal growth.

Givargizov, E.I.; White, E.A.D.

1986-01-01

19

Advanced Crystal Growth Technology  

SciTech Connect

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 crystal for yield improvement.

Land, T A; Hawley-Fedder, R A

2005-03-01

20

Growth, photoluminescence, thermal and mechanical behaviour of Ethyltriphenylphosphonium bromide dihydrate crystal  

NASA Astrophysics Data System (ADS)

Single crystal of Ethyltriphenylphosphonium bromide dihydrate (ETPB) was grown by slow evaporation solution growth technique. The grown crystal was confirmed by single crystal X-ray diffraction. The functional groups and vibrational frequencies were identified using FT-IR and FT-Raman spectral analyses. Optical properties were studied by UV-Visible and photoluminescence spectroscopic techniques to explore its efficacy towards device fabrication. Thermal characteristics of ETPB were studied using the TGA/DTA and DSC response curves. The mechanical behaviour of the grown crystal was studied using Vicker's microhardness tester and the work hardening coefficient was evaluated. The second harmonic generation of the title compound was tested by Kurtz-Perry powder technique.

Parthasarathy, M.; Gopalakrishnan, R.

2013-10-01

21

User's Guide to Galoper: A Program for Simulating the Shapes of Crystal Size Distributions from Growth Mechanisms - and Associated Programs  

USGS Publications Warehouse

GALOPER is a computer program that simulates the shapes of crystal size distributions (CSDs) from crystal growth mechanisms. This manual describes how to use the program. The theory for the program's operation has been described previously (Eberl, Drits, and Srodon, 1998). CSDs that can be simulated using GALOPER include those that result from growth mechanisms operating in the open system, such as constant-rate nucleation and growth, nucleation with a decaying nucleation rate and growth, surface-controlled growth, supply-controlled growth, and constant-rate and random growth; and those that result from mechanisms operating in the closed system such as Ostwald ripening, random ripening, and crystal coalescence. In addition, CSDs for two types weathering reactions can be simulated. The operation of associated programs also is described, including two statistical programs used for comparing calculated with measured CSDs, a program used for calculating lognormal CSDs, and a program for arranging measured crystal sizes into size groupings (bins).

Eberl, Dennis D.; Drits, V. A.; Srodon, J.

2000-01-01

22

Understanding of crystal growth mechanisms through experimental studies of semiconductor epitaxy  

NASA Astrophysics Data System (ADS)

Elementary crystal growth mechanisms in solution and vapor growths are discussed taking semiconductor as a model material. Solution growth mechanism is argued at first taking liquid phase epitaxy (LPE) as a model system. On the surface of the LPE layer, macrosteps are often generated as a result of step bunching. By studying the behavior of the macrosteps using photoluminescence image and chemical etching of the cleaved cross section, it was found that the shape of the macrostep is governed by bulk diffusion and growth kinetics. This has been confirmed by space experiments. It is concluded that the growth on the macrostep terrace is conducted by steps generated at screw dislocations. A technique, which is called microchannel epitaxy, was developed to realize macrostep-free and dislocation-free layers. Vapor growth mechanism is discussed next taking molecular beam epitaxy of III V compound as a model system. Here, the mechanism of inter-surface diffusion is investigated. The surface diffusion of group-III elements between facets was studied by changing group-V pressure. It was found that the direction of the inter-surface diffusion is reversed twice as the group-V pressure is increased. This has been attributed to the different group-V pressure dependence of group-III ad-atom lifetime on different facet. It was concluded that in MBE the growth on the facet is conducted by birth and spread of two-dimensional nuclei and by mass transports from next facet and from effusion cell.

Nishinaga, Tatau

2005-02-01

23

New type of compositional zoning in calcite: Insights into crystal-growth mechanisms  

NASA Astrophysics Data System (ADS)

Compositional zoning of trace elements is observed in time-equivalent regions within 1014 growth sectors of natural and synthetic calcite single crystals, and has been called "intrasectoral zoning" to distinguish it from conventional sectoral zoning. Differential interference contrast microscopy shows that {10114} faces grow by the spiral mechanism. Cathodoluminescence microscopy and electron probe microanalyses reveal that trace element partitioning differences on {10114} faces correspond exactly to crystallographically controlled orientations of growth steps. Effective partitioning of Mg and Mn varies up to a factor of four between time-correlative growth steps spreading in different directions. Effective Sr partitioning varies by approximately 20% and is inversely correlated with enrichment trends of Mg and Mn. Preferential incorporation of different aqueous species at different growth steps may provide an explanation for morphological and chemical variation in natural calcites.

Paquette, Jeanne; Reeder, Richard J.

1990-12-01

24

Crystal growth mechanisms and morphological control of the prototypical metal-organic framework MOF-5 revealed by atomic force microscopy.  

PubMed

Crystal growth of the metal-organic framework MOF-5 was studied by atomic force microscopy (AFM) for the first time. Growth under low supersaturation conditions was found to occur by a two-dimensional or spiral crystal growth mechanism. Observation of developing nuclei during the former reveals growth occurs through a process of nucleation and spreading of metastable and stable sub-layers revealing that MOFs may be considered as dense phase structures in terms of crystal growth, even though they contain sub-layers consisting of ordered framework and disordered non-framework components. These results also support the notion this may be a general mechanism of surface crystal growth at low supersaturation applicable to crystalline nanoporous materials. The crystal growth mechanism at the atomistic level was also seen to vary as a function of the growth solution Zn/H(2)bdc ratio producing square terraces with steps parallel to the <100> direction or rhombus-shaped terraces with steps parallel to the <110> direction when the Zn/H(2)bdc ratio was >1 or about 1, respectively. The change in relative growth rates can be explained in terms of changes in the solution species concentrations and their influence on growth at different terrace growth sites. These results were successfully applied to the growth of as-synthesized cube-shaped crystals to increase expression of the {111} faces and to grow octahedral crystals of suitable quality to image using AFM. This modulator-free route to control the crystal morphology of MOF-5 crystals should be applicable to a wide variety of MOFs to achieve the desired morphological control for performance enhancement in applications. PMID:23055448

Cubillas, Pablo; Anderson, Michael W; Attfield, Martin P

2012-10-10

25

On the genetic nature of isomorphism: Mechanism of component selection during crystal growth  

NASA Astrophysics Data System (ADS)

The concept of mixed-crystal formation, which has developed since the early 1980s, suggests the leading role of the metasomatic exchange between the crystal and solution. Compositions of solid and liquid phases shift to meet one another up to achieving thermodynamic equilibrium. This mechanism provides the regulation of the crystal composition during the process of isomorphism. The principles of the proposed assembly mechanism of selecting isomorphic components in the proportions dictated by a given combination of conditions (composition of the solution, supercooling or superheating, and temperature) are set forth as follows. The particle assemblages characterize a certain statistical distribution by the composition precipitate on the surface. Only those assemblages, which satisfy the aforementioned conditions, survive, whereas the other assemblages are dissolved, initiating the salting-out of the former assemblages. The validity of the proposed model is corroborated by the development of the assembly structure of autoepitaxial (K,Rb)HC8H4O4 nuclei on a KHC8H4O4 crystal observed with a Park CP atomic force microscope. The nuclei are widely scattered in composition, degree of faceting, and size, demonstrating their different stability and growth rate. Another example is the distribution of spontaneously precipitated mixed K(Br,Cl) crystals by isomorphic composition and size. The small and large fractions are enriched in KBr in comparison with medium-size fractions, while the volumetric proportions of the fractions reveal a bimodality with the complete absence of fractions 30-50 ?m. The traditionally discussed statistical selection of particular ions, which is probably second in importance; however, it may become crucial when the amount of one of the isomorphic components is rather small. While oversaturation is fairly high, crystallization without selection may be expected.

Glikin, A. E.

2007-12-01

26

Growth, mechanical, thermal and spectral properties of Cr3+:MgMoO4 crystal.  

PubMed

This paper reports the growth, mechanical, thermal and spectral properties of Cr(3+):MgMoO(4) crystals. The Cr(3+):MgMoO(4) crystals with dimensions up to 30 mm×18 mm×14 mm were obtained by TSSG method. The absorption cross-sections of (4)A(2)?(4)T(1) and (4)A(2)?(4)T(2) transitions are 12.94×10(-20) cm(2) at 493 nm and 7.89×10(-20) cm(2) at 705 nm for E//N(g), respectively. The Cr(3+):MgMoO(4) crystal shows broad band emission extending from 750 nm to 1300 nm with peak at about 705 nm. The emission cross-section with FWHM of 188 nm is 119.88×10(-20) cm(2) at 963 nm for E//N(g). The investigated results showed that the Cr(3+):MgMoO(4) crystal may be regarded as a potential tunable laser gain medium. PMID:22291935

Li, Lingyun; Huang, Yisheng; Zhang, Lizhen; Lin, Zhoubin; Wang, Guofu

2012-01-24

27

Growth of silver nanowires from solutions: a cyclic penta-twinned-crystal growth mechanism.  

PubMed

Silver nanowires are synthesized by simple reduction of the silver ions with reductants such as glucose, sodium citrate, and sodium hypophosphite, etc., in the absence of the so-called surfactants or capping reagents at the temperature from 80 to 200 degrees C. Regardless of the reductants, the nanowires prepared at a given temperature are uniform in diameters, ranging from 30 to 50 nm at 100 degrees C. Nanoparticles coexist with nanowires in the products with larger diameters (usually larger than 50 nm). We find that all the silver nanowires in the as-prepared products are of cyclic penta-twinned structure, where five crystallites bond by the {111} facets. We propose that the intrinsic factor of the cyclic penta-twinned structure, i.e., the angular mismatch of the five crystallites in forming a gapless rod, controls the size of the nanowires and guides the directional growth of the nanowires with {110} as the active facets. The nanoparticles in the products are aggregates of imperfect penta-twinned crystals, which inhibits them from growing into nanowires and results in larger size. From the structural information of the nanoparticles synthesized at room temperature, we propose that the formation of the cyclic penta-twinned structure is due to the stacking fault and the intrinsic equilibrium structures of the lower energy. PMID:16852129

Zhang, Shu-Hong; Jiang, Zhi-Yuan; Xie, Zhao-Xiong; Xu, Xin; Huang, Rong-Bin; Zheng, Lan-Sun

2005-05-19

28

Supra- and nanocrystallinity: specific properties related to crystal growth mechanisms and nanocrystallinity.  

PubMed

The natural arrangement of atoms or nanocrystals either in well-defined assemblies or in a disordered fashion induces changes in their physical properties. For example, diamond and graphite show marked differences in their physical properties though both are composed of carbon atoms. Natural colloidal crystals have existed on earth for billions of years. Very interestingly, these colloidal crystals are made of a fixed number of polyhedral magnetite particles uniform in size. Hence, opals formed of assemblies of silicate particles in the micrometer size range exhibit interesting intrinsic optical properties. A colorless opal is composed of disordered particles, but changes in size segregation within the self-ordered silica particles can lead to distinct color changes and patterning. In this Account, we rationalize two simultaneous supracrystal growth processes that occur under saturated conditions, which form both well-defined 3D superlattices at the air-liquid interface and precipitated 3D assemblies with well-defined shapes. The growth processes of these colloidal crystals, called super- or supracrystals, markedly change the mechanical properties of these assemblies and induce the crystallinity segregation of nanocrystals. Therefore, single domain nanocrystals are the primary basis in the formation of these supracrystals, while multiply twinned particles (MTPs) and polycrystals remain dispersed within the colloidal suspension. Nanoindentation measurements show a drop in the Young's moduli for interfacial supracrystals in comparison with the precipitated supracrystals. In addition, the value of the Young's modulus changes markedly with the supracrystal growth mechanism. Using scanning tunneling microscopy/spectroscopy, we successfully imaged very thick supracrystals (from 200 nm up to a few micrometers) with remarkable conductance homogeneity and showed electronic fingerprints of isolated nanocrystals. This discovery of nanocrystal fingerprints within supracrystals could lead to promising applications in nanotechnology. PMID:23003577

Pileni, M P

2012-09-24

29

Mechanism of Ice Crystal Growth Habit and Shape Instability Development Below Water Saturation.  

National Technical Information Service (NTIS)

Ice phase process in supercooled clouds play dominant roles in development of updrafts and downdrafts as well as various forms of precipitation. In a supercooled cloud, an ice phase process begins normally with vapor diffusional growth of ice crystals. Co...

G. D. Swoboda

1981-01-01

30

Growth of ice discs from the vapor and the mechanism of habit change of ice crystals  

NASA Astrophysics Data System (ADS)

Ice crystals nucleated on a liquid nitrogen cooled glass fiber grow first as thin disks which subsequently transform to plates and columns as they thicken and extend to regions of higher supersaturation. Crystals are often found to be dislocation-free, which suggests that growth results from surface nucleation, the habit depending on preferential nucleation in an adsorbed multilayer on basal or prism face.

Keller, V. W.; McKnight, C. V.; Hallett, J.

1980-07-01

31

Crystal growth and dielectric, mechanical, electrical and ferroelectric characterization of n-bromo succinimide doped triglycine sulphate crystals  

NASA Astrophysics Data System (ADS)

Single crystals of triglycine sulphate (TGS) doped with n-bromo succinimide (NBS) were grown at ambient temperature by the slow evaporation technique. An aqueous solution containing 1-20 mol% of n-bromo succinimide as dopant was used for the growth of NBSTGS crystals. The incorporation of NBS in TGS crystals has been qualitatively confirmed by FTIR spectral data. The effect of the dopant on morphology and crystal properties was investigated. The cell parameters of the doped crystal were determined by the powder X-ray diffraction technique. The dielectric constant of NBS doped TGS crystal was calculated along the ferroelectric direction over the temperature range of 30-60 °C. The dielectric constant of NBSTGS crystals decrease with the increase in NBS concentration and considerable shift in the phase transition temperature (TC) towards the higher temperature observed. Pyroelectric studies on doped TGS were carried out to determine the pyroelectric coefficient. The emergence of internal bias field due to doping was studied by collecting P-E hysteresis data. Temperature dependence of DC conductivity of the doped crystals was studied and gradual increase in the conductivity with the increase of dopant concentration was observed. The activation energy (?E) calculated was found to be lower in both the ferroelectric and the paraelectric phases for doped crystals compared to that of pure TGS. The micro-hardness studies were carried out at room temperature on thin plates cut perpendicular to the b-axis. Less doped TGS crystals show higher hardness values compared to pure TGS. Piezoelectric measurements were also carried out on 010 plates of doped TGS crystals at room temperature.

Rai, Chitharanjan; Byrappa, K.; Dharmaprakash, S. M.

2011-09-01

32

Growth, thermal and mechanical properties of new nonlinear optical barium bis-paranitrophenolate paranitrophenol tetrahydrate single crystal  

SciTech Connect

Barium bis paranitrophenolate paranitrophenol tetrahydrate, a new semiorganic nonlinear optical single crystal has been grown by slow evaporation solution growth technique at room temperature of 30 deg. C. Crystal of dimensions of 29 mm x 11 mm x 5 mm was obtained in a period of 30 days. X-ray diffraction analysis reveal the newness of the crystal structure belonging to the orthorhombic class with lattice parameters a = 19.899(5) A, b = 28.019(8) A, c = 10.745(4) A and {alpha} = {beta} = {gamma} = 90{sup o}. The grown crystal is examined for its nonlinear optical nature with Kurtz powder technique after being sieved for particle sizes between 5 and 100 {mu}m and analyzed for its thermal and mechanical properties. The effective nonlinear optical coefficient being 16 times greater than that of KDP crystal, good thermal stability up to 120 deg. C with the Meyer's constant n < 2 helps fashion the crystal towards device geometry.

Varjula, A. Jonie; Ramanand, A. [Department of Physics, Loyola College, Chennai 600034 (India); Das, S. Jerome [Department of Physics, Loyola College, Chennai 600034 (India)], E-mail: sjeromedas2004@yahoo.com

2008-02-05

33

Growth, Mechanical and Thermal Properties of Bi4Si3O12 Single Crystals  

NASA Astrophysics Data System (ADS)

Bi4Si3O12 (BSO) is an excellent scintillation crystal, and is becoming the desirable candidate for dual-readout calorimeters in high-energy physics. In this work, high quality BSO crystals are successfully grown by the modified Bridgman method. For the first time, its mechanical and thermal properties are investigated and compared with those of the famous scintillation crystal Bi4Ge3O12 (BGO). The Vickers hardness and fracture toughness of BSO crystal are higher than those of BGO crystal. Its specific heat, thermal diffusivity and thermal conductivity are measured to be 0.319 J·g-1K-1, 1.54 mm2·s-1 and 3.29 W·m-1K-1 at 298 K, respectively. The average thermal expansion coefficient is calculated to be 7.07 × 10-6K-1 from 300 to 1173 K. Compared with BGO crystal, BSO crystal possesses larger specific heat, thermal conductivity and smaller thermal expansion. These results indicate that BSO crystals possess better mechanical and thermal properties, which will benefit its practical applications.

Shen, Hui; Xu, Jia-Yue; Ping, Wei-Jie; He, Qing-Bo; Zhang, Yan; Jin, Min; Jiang, Guo-Jian

2012-07-01

34

Studies on growth, spectral, optical and mechanical properties of new organic NLO crystal: guanidinium L-glutamate (GuGL).  

PubMed

Good optical quality single crystal of guanidinium l-glutamate is grown by slow evaporation solution growth technique. The cell parameters and crystallinity are determined from the single crystal and powder X-ray diffraction analysis. The formation of synthesized compound was confirmed by FT-IR and FT-Raman spectroscopic analysis. Wide band gap of 4.98eV with high transmittance up to 2000 nm is observed for the grown crystal in UV-Vis-NIR spectral analysis. The optical constants such as refractive index and extinction coefficient of the grown crystal are obtained as 2.1 and 8.64×10(-6) respectively. The nonlinear optical study reveals that the second harmonic generation efficiency of guanidinium l-glutamate is 2.8 times that of potassium dihydrogen phosphate (KDP). The mechanical stability of the grown crystal was analyzed by Vickers microhardness test and the results are discussed. PMID:22902572

Arumanayagam, T; Ananth, S; Murugakoothan, P

2012-07-20

35

Studies on growth, spectral, optical and mechanical properties of new organic NLO crystal: Guanidinium L-glutamate (GuGL)  

NASA Astrophysics Data System (ADS)

Good optical quality single crystal of guanidinium L-glutamate is grown by slow evaporation solution growth technique. The cell parameters and crystallinity are determined from the single crystal and powder X-ray diffraction analysis. The formation of synthesized compound was confirmed by FT-IR and FT-Raman spectroscopic analysis. Wide band gap of 4.98 eV with high transmittance up to 2000 nm is observed for the grown crystal in UV-Vis-NIR spectral analysis. The optical constants such as refractive index and extinction coefficient of the grown crystal are obtained as 2.1 and 8.64 × 10-6 respectively. The nonlinear optical study reveals that the second harmonic generation efficiency of guanidinium L-glutamate is 2.8 times that of potassium dihydrogen phosphate (KDP). The mechanical stability of the grown crystal was analyzed by Vickers microhardness test and the results are discussed.

Arumanayagam, T.; Ananth, S.; Murugakoothan, P.

2012-11-01

36

Kinetics and growth mechanism of gallium arsenide crystals in gas-phase epitaxy  

Microsoft Academic Search

In conclusion, we note that gallium arsenide itself is the material with which the physicochemical and crystallophysical fundamentals of gas-phase epitaxy are presently being developed. It is hoped that the basic principles or crystal growth in gas-phase systems discovered in gallium arsenide will prove sufficiently general to be applied to other analogous systems.

L. G. Lavrent'eva

1980-01-01

37

Crystal growth of semiconductor bulk crystals  

SciTech Connect

This course is aimed at showing how to grow bulk crystals by using several methods. The course involves the following points. The growth methods of Bridgman and Czochralski will be introduced. The course also focuses on the mechanism of some processes with consideration of the basic phenomenon. Experimental and numerical examples of the methods will also be introduced.

Kakimoto, Koichi [Research Institute for Applied Mechanics, Kyushu University, 6-1, Kasuga-Koen, Kasuga, 816-8580 (Japan)

2010-07-22

38

Crystal Growth and Design  

NSDL National Science Digital Library

An electronic version of this journal from the American Chemical Society is available for free through June 30, 2001. Crystal Growth and Design is "a new journal from the American Chemical Society, dedicated to publishing articles on the physical, chemical, and biological phenomena and processes related to crystal growth and design of new materials."

39

Crystal growth, structural, crystalline perfection, optical and mechanical properties of Nd3+ doped sulfamic acid (SA) single crystals  

NASA Astrophysics Data System (ADS)

Sulfamic acid (SA) single crystals, both pure and doped with 1, 2.5 and 5 mol% Nd, were grown successfully in an aqueous solution by the slow cooling method. Powder X-ray diffraction patterns were recorded to check the variation in the lattice parameters and phase of the crystals. The optical transparency was found to be higProd. Type: FTPhest (˜80%) for the 1 mol% Nd3+ doped SA single crystal. The optical band gap was also calculated and found to be ˜4.31, 4.20 and 3.67 eV. The influence of Nd3+ doping on the crystalline perfection was assessed by a high resolution X-ray diffractometer (HRXRD) and shows that the grown crystals could accommodate Nd3+ at the interstitial positions in the crystalline matrix of SA up to some critical concentration without any deterioration in the crystalline perfection. The etching studies were carried out and the etch pits densities were calculated. The mechanical property of grown single crystals was also studied.

Shkir, Mohd.; Riscob, B.; Ganesh, V.; Vijayan, N.; Gupta, Rahul; Plaza, J. L.; Dieguez, E.; Bhagavannarayana, G.

2013-10-01

40

Self-catalytic crystal growth, formation mechanism, and optical properties of indium tin oxide nanostructures  

NASA Astrophysics Data System (ADS)

In-Sn-O nanostructures with rectangular cross-sectional rod-like, sword-like, and bowling pin-like morphologies were successfully synthesized through self-catalytic growth. Mixed metallic In and Sn powders were used as source materials, and no catalyst layer was pre-coated on the substrates. The distance between the substrate and the source materials affected the size of the Sn-rich alloy particles during crystal growth in a quartz tube. This caused In-Sn-O nanostructures with various morphologies to form. An X-ray photoelectron spectroscope and a transmittance electron microscope with an energy-dispersive X-ray spectrometer were used to investigate the elemental binding states and compositions of the as-synthesized nanostructures. The Sn doping and oxygen vacancies in the In2O3 crystals corresponded to the blue-green and yellow-orange emission bands of the nanostructures, respectively.

Liang, Yuan-Chang; Zhong, Hua

2013-08-01

41

Self-catalytic crystal growth, formation mechanism, and optical properties of indium tin oxide nanostructures.  

PubMed

In-Sn-O nanostructures with rectangular cross-sectional rod-like, sword-like, and bowling pin-like morphologies were successfully synthesized through self-catalytic growth. Mixed metallic In and Sn powders were used as source materials, and no catalyst layer was pre-coated on the substrates. The distance between the substrate and the source materials affected the size of the Sn-rich alloy particles during crystal growth in a quartz tube. This caused In-Sn-O nanostructures with various morphologies to form. An X-ray photoelectron spectroscope and a transmittance electron microscope with an energy-dispersive X-ray spectrometer were used to investigate the elemental binding states and compositions of the as-synthesized nanostructures. The Sn doping and oxygen vacancies in the In2O3 crystals corresponded to the blue-green and yellow-orange emission bands of the nanostructures, respectively. PMID:23965167

Liang, Yuan-Chang; Zhong, Hua

2013-08-22

42

The role of hydration and complexing in the mechanism of impurity influence on crystal growth  

NASA Astrophysics Data System (ADS)

The influence of impurities of chlorides and nitrates of divalent Ca2+ and Ba2+ cations on the kinetic growth of potassium dihydrophosphate KH2PO4 crystals at a saturation temperature of 323 K and relative supersaturation of 0.03 has been investigated experimentally. It is established that the impurity acts differently, depending on the face index, the impurity concentration, cation hydration, and the stability of the complexes formed in the solution by impurity salt ions. A model is proposed to explain the different influence of impurity ions on the growth of crystal faces. This influence is determined by the different hydration of cations and enhanced association of cations and anions of impurity salts in the surface layer with a lower dielectric constant.

Efremova, E. P.; Okhrimenko, T. M.; Lyashchenko, A. K.

2012-05-01

43

Self-catalytic crystal growth, formation mechanism, and optical properties of indium tin oxide nanostructures  

PubMed Central

In-Sn-O nanostructures with rectangular cross-sectional rod-like, sword-like, and bowling pin-like morphologies were successfully synthesized through self-catalytic growth. Mixed metallic In and Sn powders were used as source materials, and no catalyst layer was pre-coated on the substrates. The distance between the substrate and the source materials affected the size of the Sn-rich alloy particles during crystal growth in a quartz tube. This caused In-Sn-O nanostructures with various morphologies to form. An X-ray photoelectron spectroscope and a transmittance electron microscope with an energy-dispersive X-ray spectrometer were used to investigate the elemental binding states and compositions of the as-synthesized nanostructures. The Sn doping and oxygen vacancies in the In2O3 crystals corresponded to the blue-green and yellow-orange emission bands of the nanostructures, respectively.

2013-01-01

44

TPA-silicalite crystallization from homogeneous solution: kinetics and mechanism of nucleation and growth  

Microsoft Academic Search

The formation and growth of tetrapropylammonium-templated crystal nuclei of silicalite from a clear homogeneous solution was recorded in situ as a function of time at temperatures between 90 and 115 C using small-angle X-ray scattering (SAXS). The kinetics of the nucleation process was studied and give an apparent activation energy of 70 kJ mol-1. A small-angle neutron scattering (SANS) contrast

Jonathan N. Watson; Lennox E. Iton; Roland I. Keir; John C. Thomas; Trevor L. Dowling; John W. White

1997-01-01

45

Nucleation and crystal growth in batch crystallizers  

Microsoft Academic Search

The aim of the present work is to gain knowledge of the mechanism of formation of the crystal size distribution in batch crystallizers in order to give directives for design and operation of batch crystallizers. The crystal size distribution is important for the separation of crystals and mother liquid, the subsequent washing and drying of the crystals, and the product

A. H. Janse

1977-01-01

46

The secrets of crystal growth  

SciTech Connect

Lawrence Livermore researchers are using the atomic-force microscope (AFM) to elucidate the growth mechanisms and three-dimensional structures of widely different solution-based crystals on the nanometer (billionth-of-a-meter) scale. Much of the AFM work has been in support of the Laser Programs` need to better understand KDP (potassium dihydrogen phosphate) crystal growth because of its direct impact on advanced lasers such as the National Ignition Facility. A second avenue of research has focused on the growth of solution-based crystals of biological macromolecules, specifically the protein canavalin and the satellite tobacco mosaic virus. The AFM images have revealed how solution-based crystals grow and how they are affected by impurities, defects, and solution conditions. The results are likely to affect many disciplines and technologies, from pharmaceuticals to materials synthesis.

De Yoreo, J.; Land, T. [Lawrence Livermore National Lab., CA (United States)

1996-11-01

47

Shaped Crystal Growth  

NASA Astrophysics Data System (ADS)

Crystals of specified shape and size (shaped crystals) with controlled 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 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 fundamental principles of shaping. Some shaped crystals, especially sapphire and silicon, have specified structures. The crystal growth of these materials, and some metals, including crystal growth in space, is discussed.

Tatartchenko, Vitali A.

48

Impurity trapping during crystal growth  

Microsoft Academic Search

A computer simulation of dendritic crystal growth was developed and used to derive a relationship between solution trapping and system and process parameters during crystal growth. The relation predicts that trapping will increase with increasing crystal growth velocity and decreasing positive and negative temperature gradients. A flow crystallizer was used to experimentally study the growth of calcium sulphate, potassium aluminum

A. S. Myerson

1977-01-01

49

Quartz crystal growth  

SciTech Connect

This patent describes a process for growing high quality single crystals of a nutrient substance that can undergo phase transformation from the amorphous to the crystalline state in an appropriate solvent, charging the substance, seed crystals of the substance, and the solvent in an autoclave having a lower dissolution zone connecting with an upper crystallization zone; allowing the close charged autoclave to stand at ambient temperature for a time sufficient to reach internal equilibrium; gradually heating the autoclave at a rate such that a very small temperature differential ([Delta]T) is maintained between the cooler upper zone and the warmer lower zone until the nutrient substance has undergone transformation to the crystalline phase; and increasing the heating rate to achieve and maintain a larger temperature differential ([Delta]T) between the zones sufficient to allow increased material transport between the zones and rapid controlled crystal growth.

Baughman, R.J.

1992-08-04

50

Organic-inorganic interaction and the growth mechanism of hydroxyapatite crystals in gelatin matrices between 37 and 80 degrees C.  

PubMed

The crystal development of hydroxyapatite[HAp] phase in gelatin[GEL] matrices was investigated in the temperature range 37 to 80 degrees C by using X-ray diffraction, scanning electron microscopy(SEM), thermoanalytical measurement(DT/TGA), Fourier-Transformed Infra-Red(FT-IR) spectroscopy, and transmission electron microscopy(TEM) with electron diffraction(ED). It was found that during the coprecipitation of apatite phase in GEL matrices and the next aging process the crystallites were formed and developed through the two reaction mechanisms of organic-inorganic interaction between apatite phase and GEL molecules, and thermodynamic reaction for the crystal growing. The analytical evidences showed that there was a definite competition between these two mechanisms with the reaction temperature. Below 50 degrees C the crystal development of HAp was greatly suppressed by the existence of the GEL molecules, indicating the heterogeneous nucleation by the supposed number of carboxyl groups in GEL. Above 50 degrees C the effective organic components as a template for the heterogeneous nucleation of apatite crystallites were greatly degraded and so more amount of inorganic ions could be favorably accredited on the preexisting crystallites in virtue of the limited nucleation chance, finally resulting in the crystal growth. At higher temperature pretty big HAp crystals were developed with the depletion of the organics to be bound with crystallites in the slurry solution. Presumably it is believed that the poisoning of the functional groups in GEL molecules was vigorously occurred in the phosphoric acid environment above approximately 50 degrees C. PMID:16617418

Chang, Myung Chul; Douglas, William H; Tanaka, Junzo

2006-04-01

51

Physical Phenomena Related to Crystal Growth in the Space Environment.  

National Technical Information Service (NTIS)

The mechanism of crystal growth which may be affected by the space environment was studied. Conclusions as to the relative technical and scientific advantages of crystal growth in space over earth bound growth, without regard to economic advantage, were d...

T. L. Chu

1973-01-01

52

Effect of pH on the growth, crystalline perfection, nonlinear optical and mechanical properties of tris-glycine zinc chloride single crystals  

NASA Astrophysics Data System (ADS)

Bulk single crystals of tris-glycine zinc chloride (TGZC) have been grown from aqueous solutions at three different pH values. The influence of pH on the morphology, structure, optical and mechanical properties has been investigated. The single crystal X-ray diffraction was used to analyze the influence on the lattice parameters of the grown crystals. The growth morphology obtained at three pH values was analyzed to infer about the growth rate of the different crystallography habit faces. The optical quality was assessed by recording UV-vis transmission spectrum, birefringence interferometry and laser damage threshold studies. The hardness of the grown crystals was compared by Vickers hardness measurements. It is found that TGZC crystals grown at pH 3 results in better optical and mechanical properties.

Sugandhi, K.; Verma, Sunil; Jose, M.; Joseph, V.; Das, S. Jerome

2013-12-01

53

Crystal Growth from the Melt: A Review  

Microsoft Academic Search

This paper reviews four aspects of crystal growth theory: the nature of the rate-controlling process, the mechanism controlling molecular attachment onto the growing crystal surface, the nature of the crystal-melt interface, and the stability of planar interfaces relative to cellular interfaces. The rate-controlling process may be diffusion in the melt, heat flow, or the reaction at the crystal-melt interface. Diffusion

R. Jeuss Knrpnrnrcr

54

Synthesis, Growth, Structural, Spectroscopic, Optical, Thermal and Mechanical Studies of a Semi-Organic Nonlinear Optical Crystal:. L-Glutamic Acid Hydrochloride  

NASA Astrophysics Data System (ADS)

The semi-organic nonlinear optical single crystal of L-glutamic acid hydrochloride was grown by slow evaporation solution growth technique at room temperature. The cell parameters of the grown crystal were estimated by single crystal X-ray diffraction analysis. The presence of various functional groups was identified from Fourier transform infrared analysis. The transmission spectrum of this crystal show that the lower cut-off wavelength lies at 248 nm. Thermal analysis was performed to study the thermal stability of the grown crystal. The Kurtz powder second harmonic generation test shows that the crystal is a potential candidate for optical second harmonic generation. Mechanical properties of the grown crystal were determined and Vickers' hardness number was calculated.

Selvaraju, K.; Kirubavathi, K.; Vijayan, N.; Kumararaman, S.

55

Growth morphologies of crystal surfaces  

NASA Astrophysics Data System (ADS)

We have expanded our earlier Monte Carlo model [Phys. Rev. A 38, 2447 (1988); J. Crystal Growth 100, 313 (1990)] to three dimensions and included reevaporation after accommodation and growth on dislocation-induced steps. We found again that, for a given set of growth parameters, the critical size, beyond which a crystal cannot retain its macroscopically faceted shape, scales linearly with the mean free path in the vapor. However, the three-dimensional (3D) the systems show increased shape stability compared to corresponding 2D cases. Extrapolation of the model results to mean-free-path conditions used in morphological stability experiments leads to order-of-magnitude agreement of the predicted critical size with experimental findings. The stability region for macroscopically smooth (faceted) surfaces in the parameter space of temperature and supersaturation depends on both the surface and bulk diffusion. While surface diffusion is seen to smooth the growth morphology on the scale of the surface diffusion length, bulk diffusion is always destabilizing. The atomic surface roughness increases with increase in growth temperature and supersaturation. That is, the tendency of surface kinetics anisotropies to stabilize the growth shape is reduced through thermal and kinetic roughening. It is also found that the solid-on-solid assumption, which can be advantageously used at low temperatures and supersaturations, is insufficient to describe the growth dynamics of atomically rough interfaces where bulk diffusion governs the process. For surfaces with an emerging screw dislocation, we find that the spiral growth mechanism dominates at low temperatures and supersaturations. The polygonization of a growth spiral decreases with increasing temperature or supersaturation. When the mean free path in the nutrient is comparable to the lattice constant, the combined effect of bulk and surface diffusion reduces the terrace width of a growth spiral in its center region. At elevated temperatures and supersaturations, 2D nucleation-controlled growth can dominate in corner and edge regions of a facet, while the spiral growth mode prevails in its center. Thus, in addition to confirming the experimental observation that the critical size of a growing crystal depends on the prevailing growth mechanism, we are able to obtain detailed insight into the processes leading to the loss of face and facet stability.

Xiao, Rong-Fu; Alexander, J. Iwan D.; Rosenberger, Franz

1991-03-01

56

Study of the mechanism of crystallization electromotive force during growth of congruent LiNbO3 using a micro-pulling-down method  

NASA Astrophysics Data System (ADS)

We have investigated the crystallization electromotive force (EMF) during the growth of congruent LiNbO3 (LN) by exploiting the features of a micro-pulling-down (?-PD) method. The electric potential distribution around the growth interface that was measured in the ?-PD system was attributed to the Seebeck effect and several mV of crystallization EMF. The mechanism of the crystallization EMF during the growth of congruent LN from the melt was explained using a model wherein segregation of the ionic species in the melt formed a net ionic charge at the growth interface resulting in the development of an EMF. Redistribution of the net ionic charge, which was analyzed on the basis of a one-dimensional differential equation that included electric-field-driven transport in the melt, well reproduced the experimental data of the nonlinear dependence of crystallization EMF on the growth rate. We concluded that the crystallization EMF occurred during crystal growth of the congruent LN owing to the ionic-charge accumulation at the growth interface.

Koh, Shinji; Uda, Satoshi; Nishida, Masahiro; Huang, Xinming

2006-12-01

57

Protein Crystal Growth in Microgravity  

NASA Astrophysics Data System (ADS)

The crystals of most proteins or other biological macromolecules are poorly ordered and diffract to lower resolutions than those observed for most crystals of simple organic and inorganic compounds. Crystallization in the microgravity environment of space may improve crystal quality by eliminating convection effects near growing crystal surfaces. A series of 11 different protein crystal growth experiments was performed on U.S. space shuttle flight STS-26 in September 1988. The microgravity-grown crystals of ? -interferon D1, porcine elastase, and isocitrate lyase are larger, display more uniform morphologies, and yield diffraction data to significantly higher resolutions than the best crystals of these proteins grown on Earth.

Delucas, Lawrence J.; Smith, Craig D.; Smith, H. Wilson; Vijay-Kumar, Senadhi; Senadhi, Shobha E.; Ealick, Steven E.; Carter, Daniel C.; Snyder, Robert S.; Weber, Patricia C.; Salemme, F. Raymond; Ohlendorf, D. H.; Einspahr, H. M.; Clancy, L. L.; Navia, Manuel A.; McKeever, Brian M.; Nagabhushan, T. L.; Nelson, George; McPherson, A.; Koszelak, S.; Taylor, G.; Stammers, D.; Powell, K.; Darby, G.; Bugg, Charles E.

1989-11-01

58

Growth of ADP-KDP mixed crystal and its optical, mechanical, dielectric, piezoelectric and laser damage threshold studies  

NASA Astrophysics Data System (ADS)

Good quality ADP-KDP mixed crystal (90:10) is grown by slow cooling method. The size of the grown crystal is 80×10×10 mm3. The mounted seed size was 5×10×10 mm3 and the crystal was grown along the ‘c’ axis. HRXRD studies have been done in the near and far regions of the seed crystal. The FWHM of these diffraction curves are 28 and 29 arcsec, which are almost the same. The close values of FWHM of both the specimens indicate that the quality of the crystal remains nearly the same throughout the crystal. 80% of transparency is observed from the UV-vis studies in the entire visible region. Vickers hardness studies indicate that the mixed crystal is mechanically more stable compared to the ADP. Higher piezoelectric coefficient is observed in mixed crystals. Dielectric measurements are carried out. From the laser damage threshold studies, it is observed that higher energy is required to damage the mixed crystal and it indicates that the laser stability of the mixed crystal is high.

Rajesh, P.; Ramasamy, P.; Bhagavannarayana, G.

2013-01-01

59

Growth, structural, spectral, mechanical and optical properties of pure and metal ions doped sulphamic acid single crystals.  

PubMed

Bulk single crystals of pure and metal ions (Mn(2+), Cu(2+) and Ni(2+)) doped sulphamic acid (SA) have been grown by conventional and unidirectional solution growth methods. Intensities of powder X-ray diffraction peaks of metal ions doped SA reveal that these dopants enhanced the crystallanity. The peak broadening and intensity variation in some frequency regions in FT-IR spectra show the incorporation of dopants in the SA lattice. Mn(2+) and Cu(2+) doped SA single crystals show high crystalline perfection (FWHM 5.5arcs) compared to pure and Ni(2+) metal ions doped SA crystals. The grown pure and Mn(2+), Cu(2+) and Ni(2+) ions doped SA crystals have transparency in the order SA>Mn:SA>Cu:SA>Ni:SA. The hardness value of Ni(2+) doped crystal is relatively less than that of the pure and other metal ions doped SA crystals. Pure and Ni(2+) ions doped SA crystals possess high dielectric constants than that of Cu(2+) and Mn(2+) ions doped crystals. From the SEM micrograph analyses, it is observed that the doping of these metal ions modify the surface morphology of the grown crystals. PMID:20493763

Ramesh Babu, R; Ramesh, R; Gopalakrishnan, R; Ramamurthi, K; Bhagavannarayana, G

2010-04-24

60

On the mechanism of trace-element uptake during the hydrothermal growth of sulfide mineral crystals  

Microsoft Academic Search

The stable species of cadmium and mercury are formed in iron and lead sulfides at elevated temperatures and pressures under\\u000a hydrothermal conditions. Their formation proceeds through different mechanisms. The most general mechanism involves the uptake\\u000a of trace elements in the form of structural species due to isomorphous exchange. The results obtained for cadmium in pyrrhotite\\u000a indicate that structural defects substantially

V. L. Tauson; D. N. Babkin; I. Yu. Parkhomenko; V. I. Men’shikov

2004-01-01

61

Synthesis, growth, structural, spectral, thermal, chemical etching, linear and nonlinear optical and mechanical studies of an organic single crystal 4-chloro 4-nitrostilbene (CONS): a potential NLO material.  

PubMed

4-Chloro 4-nitrostilbene (CONS) a new organic nonlinear optical material has been synthesized. Employing slow evaporation method, good optical quality single crystals (dimensions up to 6×2×3 mm(3)) have been grown using ethyl methyl ketone (EMK) as a solvent. The grown crystals have been subjected to various characterizations such as single crystal X-ray diffraction, powder XRD, Fourier Transform Infrared spectroscopy (FTIR), proton NMR, solid UV absorption, SHG studies. Single crystal X-ray diffraction reveals that the crystal system belongs to monoclinic with noncentrosymmetric space group P21. The UV-Vis absorption spectrum has been recorded and found that the cut off wavelength is 380 nm. Functional groups and the structure of the title compound have been confirmed by FTIR and (1)H NMR spectroscopic analyses respectively. Molecular mass of the CONS confirmed by the high resolution mass spectral analysis .The thermal behavior of the grown crystal has been studied by TG/DTA analysis and it shows the melting point is at 188.66 °C. Dislocations and growth pattern present in the grown crystal revealed by the etching study. The mechanical strength of the CONS crystal has been studied by Vicker's hardness measurement. The SHG efficiency of the grown crystal has been determined by Kurtz and Perry powder test which revealed that the CONS crystal (327 mV) has 15 times greater efficiency than that of KDP (21.7 mV). PMID:23624038

Dinakaran, Paul M; Kalainathan, S

2013-03-20

62

Synthesis, growth, structural, spectral, thermal, chemical etching, linear and nonlinear optical and mechanical studies of an organic single crystal 4-chloro 4-nitrostilbene (CONS): A potential NLO material  

NASA Astrophysics Data System (ADS)

4-Chloro 4-nitrostilbene (CONS) a new organic nonlinear optical material has been synthesized. Employing slow evaporation method, good optical quality single crystals (dimensions up to 6 × 2 × 3 mm3) have been grown using ethyl methyl ketone (EMK) as a solvent. The grown crystals have been subjected to various characterizations such as single crystal X-ray diffraction, powder XRD, Fourier Transform Infrared spectroscopy (FTIR), proton NMR, solid UV absorption, SHG studies. Single crystal X-ray diffraction reveals that the crystal system belongs to monoclinic with noncentrosymmetric space group P21. The UV-Vis absorption spectrum has been recorded and found that the cut off wavelength is 380 nm. Functional groups and the structure of the title compound have been confirmed by FTIR and 1H NMR spectroscopic analyses respectively. Molecular mass of the CONS confirmed by the high resolution mass spectral analysis .The thermal behavior of the grown crystal has been studied by TG/DTA analysis and it shows the melting point is at 188.66 °C. Dislocations and growth pattern present in the grown crystal revealed by the etching study. The mechanical strength of the CONS crystal has been studied by Vicker's hardness measurement. The SHG efficiency of the grown crystal has been determined by Kurtz and Perry powder test which revealed that the CONS crystal (327 mV) has 15 times greater efficiency than that of KDP (21.7 mV).

Dinakaran, Paul M.; Kalainathan, S.

2013-07-01

63

Characterization and modeling of illite crystal particles and growth mechanisms in a zoned hydrothermal deposit, Lake City, Colorado  

USGS Publications Warehouse

Mean thickness measurements and crystal-thickness distributions (CTDs) of illite particles vary systematically with changes in hydrothermal alteration type, fracture density, and attendant mineralization in a large acid-sulfate/Mo-porphyry hydrothermal system at Red Mountain, near Lake City, Colorado. The hydrothermal illites characterize an extensive zone of quartz-sericite-pyrite alteration beneath two deeply rooted bodies of magmatic-related, quartz-alunite altered rock. Nineteen illites from a 3000 ft vertical drill hole were analyzed by XRD using the PVP-10 intercalation method and the computer program MudMaster (Bertaut-Warren-Averbach technique). Mean crystallite thicknesses, as determined from 001 reflections, range from 5-7 nanometers (nm) at depths from 0-1700 ft, then sharply increase to 10-16 nm at depths between 1800-2100 ft, and decrease again to 4-5 nm below this level. The interval of largest particle thickness correlates strongly with the zone of most intense quartz-sericite-pyrite alteration (QSP) and attendant high-density stockwork fracturing, and with the highest concentrations of Mo within the drill core. CTD shapes for the illite particles fall into two main categories: asymptotic and lognormal. The shapes of the CTDs are dependent on conditions of illite formation. The asymptotic CTDs correspond to a nucleation and growth mechanism, whereas surface-controlled growth was the dominant mechanism for the lognormal CTDs. Lognormal CTDs coincide with major through-going fractures or stockwork zones, whereas asymptotic CTDs are present in wallrock distal to these intense fracture zones. The increase in illite particle size and the associated zone of intense QSP alteration and stockwork veining was related by proximity to the dacitic magma(s), which supplied both reactants and heat to the hydrothermal system. However, no changes in illite polytype, which in other studies reflect temperature transitions, were observed within this interval.

Bove, D. J.; Eberl, D. D.; McCarty, D. K.; Meeker, G. P.

2002-01-01

64

Growth, structural, spectral, mechanical, thermal and dielectric characterization of phosphoric acid admixtured L-alanine (PLA) single crystals.  

PubMed

Phosphoric acid admixtured L-alanine (PLA) single crystals were grown successfully by solution method with slow evaporation technique at room temperature. Crystals of size 18 mm×12 mm×8 mm have been obtained in 28 days. The grown crystals were colorless and transparent. The solubility of the grown samples has been found out at various temperatures. The lattice parameters of the grown crystals were determined by X-ray diffraction technique. The reflection planes of the sample were confirmed by the powder X-ray diffraction study and diffraction peaks were indexed. Fourier transform infrared (FTIR) studies were used to confirm the presence of various functional groups in the crystals. UV-visible transmittance spectrum was recorded to study the optical transparency of grown crystal. The nonlinear optical (NLO) property of the grown crystal was confirmed by Kurtz-Perry powder technique and a study of its second harmonic generation efficiency in comparison with potassium dihydrogen phosphate (KDP) has been made. The mechanical strength of the crystal was estimated by Vickers hardness test. The grown crystals were subjected to thermo gravimetric and differential thermal analysis (TG/DTA). The dielectric behavior of the sample was also studied. PMID:21775196

Rose, A S J Lucia; Selvarajan, P; Perumal, S

2011-06-28

65

Growth, structural, spectral, mechanical, thermal and dielectric characterization of phosphoric acid admixtured L-alanine (PLA) single crystals  

NASA Astrophysics Data System (ADS)

Phosphoric acid admixtured L-alanine (PLA) single crystals were grown successfully by solution method with slow evaporation technique at room temperature. Crystals of size 18 mm × 12 mm × 8 mm have been obtained in 28 days. The grown crystals were colorless and transparent. The solubility of the grown samples has been found out at various temperatures. The lattice parameters of the grown crystals were determined by X-ray diffraction technique. The reflection planes of the sample were confirmed by the powder X-ray diffraction study and diffraction peaks were indexed. Fourier transform infrared (FTIR) studies were used to confirm the presence of various functional groups in the crystals. UV-visible transmittance spectrum was recorded to study the optical transparency of grown crystal. The nonlinear optical (NLO) property of the grown crystal was confirmed by Kurtz-Perry powder technique and a study of its second harmonic generation efficiency in comparison with potassium dihydrogen phosphate (KDP) has been made. The mechanical strength of the crystal was estimated by Vickers hardness test. The grown crystals were subjected to thermo gravimetric and differential thermal analysis (TG/DTA). The dielectric behavior of the sample was also studied.

Rose, A. S. J. Lucia; Selvarajan, P.; Perumal, S.

2011-10-01

66

Direct flow crystal growth system  

DOEpatents

A crystal is grown in a constantly filtered solution which is flowed directly into the growing face of a crystal. In a continuous flow system, solution at its saturation temperature is removed from a crystal growth tank, heated above its saturation temperature, filtered, cooled back to its saturation temperature, and returned to the tank.

Montgomery, Kenneth E. (Tracy, CA); Milanovich, Fred P. (Lafayette, CA)

1992-01-01

67

Direct flow crystal growth system  

DOEpatents

A crystal is grown in a constantly filtered solution which is flowed directly into the growing face of a crystal. In a continuous flow system, solution at its saturation temperature is removed from a crystal growth tank, heated above its saturation temperatue, filtered, cooled back to its saturation temperature, and returned to the tank. 2 figs.

Montgomery, K.E.; Milanovich, F.P.

1989-10-30

68

What Variables Affect Crystal Growth?  

NSDL National Science Digital Library

Students investigate variables that may influence the growth of crystals which they have learned to make. There are two options for implementing this activity. The first is open-ended, with the students deciding what variables affect crystal growth and then deciding on the manipulating variables they would like to study. The second is prescriptive and explains to students how to test three variables in making crystals: temperature, method of mixing (such as shaking or stirring), and concentration.

69

A comparative study on growth, structural, optical, thermal and mechanical properties of undoped and dye doped bis glycine cadmium chloride single crystals  

Microsoft Academic Search

Dye inclusion crystals have attracted researchers in the context of crystal growth for applications in solid state lasers. Attempt to grow tris glycine cadmium chloride (TGCC) crystals yielded bis glycine cadmium chloride crystals. Single crystals of bis glycine cadmium chloride (BGCC) and organic dye, namely xylenol orange tetra sodium salt (XO) doped BGCC crystals, were grown from aqueous solutions by

B. Raju; A. Saritha; G. Bhagavannarayana; K. A Hussain

2011-01-01

70

Crystal Growth by Evaporation  

NSDL National Science Digital Library

This activity introduces students to the idea that crystals 'grow' (crystallize or precipitate) and that minerals or rocks also form this way, providing a very general idea of the nature of magma (molten material that eventually crystallizes into igneous rocks). Using solutions mixed by the teacher, they will observe and sketch the formation of crystals of potassium dichromate and copper II acetate by placing drops of the solutions on microscope slides and drying them on a hot plate. Discussion questions are provided.

71

Photographic appraisal of crystal lattice growth technique.  

PubMed

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. PMID:16327137

Kapoor, D N; Mahendru, D V; Sharma, V P; Tandon, P

72

Crystal growth inside an octant  

NASA Astrophysics Data System (ADS)

We study crystal growth inside an infinite octant on a cubic lattice. The growth proceeds through the deposition of elementary cubes into inner corners. After rescaling by the characteristic size, the interface becomes progressively more deterministic in the long-time limit. Utilizing known results for the crystal growth inside a two-dimensional corner, we propose a hyperbolic partial differential equation for the evolution of the limiting shape. This equation is interpreted as a Hamilton-Jacobi equation, which helps in finding an analytical solution. Simulations of the growth process are in excellent agreement with analytical predictions. We then study the evolution of the subleading correction to the volume of the crystal, the asymptotic growth of the variance of the volume of the crystal, and the total number of inner and outer corners. We also show how to generalize the results to arbitrary spatial dimension.

Olejarz, Jason; Krapivsky, P. L.

2013-08-01

73

Crystal growth inside an octant.  

PubMed

We study crystal growth inside an infinite octant on a cubic lattice. The growth proceeds through the deposition of elementary cubes into inner corners. After rescaling by the characteristic size, the interface becomes progressively more deterministic in the long-time limit. Utilizing known results for the crystal growth inside a two-dimensional corner, we propose a hyperbolic partial differential equation for the evolution of the limiting shape. This equation is interpreted as a Hamilton-Jacobi equation, which helps in finding an analytical solution. Simulations of the growth process are in excellent agreement with analytical predictions. We then study the evolution of the subleading correction to the volume of the crystal, the asymptotic growth of the variance of the volume of the crystal, and the total number of inner and outer corners. We also show how to generalize the results to arbitrary spatial dimension. PMID:24032777

Olejarz, Jason; Krapivsky, P L

2013-08-07

74

Plenum type crystal growth process  

DOEpatents

Crystals are grown in a tank which is divided by a baffle into a crystal growth region above the baffle and a plenum region below the baffle. A turbine blade or stirring wheel is positioned in a turbine tube which extends through the baffle to generate a flow of solution from the crystal growing region to the plenum region. The solution is pressurized as it flows into the plenum region. The pressurized solution flows back to the crystal growing region through return flow tubes extending through the baffle. Growing crystals are positioned near the ends of the return flow tubes to receive a direct flow of solution.

Montgomery, Kenneth E. (Tracy, CA)

1992-01-01

75

The crystallization of potassium nitrate. II. Growth rate dispersion  

Microsoft Academic Search

The effect of growth rate dispersion (GRD) had to be examined. Therefore, the face-specific growth rate of KNO3 {1 1 1} faces was determined, carrying out single crystal growth experiments with crystals treated in different ways (untreated, hurt, annealed, mechanically strained). For a supersaturation ? > 0.001, the growth can be described by the random fluctuation (RF) model. An even

A. Herden; R. Lacmann

1997-01-01

76

Growth of Gray Tin Crystals  

Microsoft Academic Search

A method is proposed for growing large a-Sn single crystals without their disintegration as a result of the ß ? a phase transition. a-Sn crystals are prepared by freezing the closed system water–Sn–seed in such a way that the pressure exerted by the expanding ice minimizes the amount of a-Sn nuclei and reduces the growth rate.

A. D. Styrkas

2003-01-01

77

An Introduction to Crystal Growth.  

National Technical Information Service (NTIS)

The report describes in some detail the growth of alum single crystals by both evaporation and suspension methods. There are many other types of crystals that can be similarly synthesized. The solutions that are listed in Appendix I have been chosen for t...

M. A. DiPietro

1969-01-01

78

Protein Crystal Nucleation and Growth  

NASA Astrophysics Data System (ADS)

We have developed a microfluidic emulsion based technique to determine the homogeneous and heterogeneous nucleation rates of protein crystallization under conditions of high supersaturation. We utilize the fact that the nucleation rate is constant if no crystal nucleus is formed and count the number of protein droplets with no crystals with time, which decays exponentially with decay constant inversely proportional to nucleation rate and drop volume. We report results of experiments on nucleation and growth rates of lysozyme crystallization. The emulsions are placed on a temperature gradient stage allowing simultaneous measurement of rates as a function of temperature. We routinely scan 30,000 drops in each experiment.

Akella, Sathish; Fraden, Seth

2012-02-01

79

Ultraslow growth rates of giant gypsum crystals  

PubMed Central

Mineralogical processes taking place close to equilibrium, or with very slow kinetics, are difficult to quantify precisely. The determination of ultraslow dissolution/precipitation rates would reveal characteristic timing associated with these processes that are important at geological scale. We have designed an advanced high-resolution white-beam phase-shift interferometry microscope to measure growth rates of crystals at very low supersaturation values. To test this technique, we have selected the giant gypsum crystals of Naica ore mines in Chihuahua, Mexico, a challenging subject in mineral formation. They are thought to form by a self-feeding mechanism driven by solution-mediated anhydrite-gypsum phase transition, and therefore they must be the result of an extremely slow crystallization process close to equilibrium. To calculate the formation time of these crystals we have measured the growth rates of the {010} face of gypsum growing from current Naica waters at different temperatures. The slowest measurable growth rate was found at 55?°C, 1.4 ± 0.2 × 10-5 nm/s, the slowest directly measured normal growth rate for any crystal growth process. At higher temperatures, growth rates increase exponentially because of decreasing gypsum solubility and higher kinetic coefficient. At 50?°C neither growth nor dissolution was observed indicating that growth of giant crystals of gypsum occurred at Naica between 58?°C (gypsum/anhydrite transition temperature) and the current temperature of Naica waters, confirming formation temperatures determined from fluid inclusion studies. Our results demonstrate the usefulness of applying advanced optical techniques in laboratory experiments to gain a better understanding of crystal growth processes occurring at a geological timescale.

Van Driessche, A. E. S.; Garcia-Ruiz, J. M.; Tsukamoto, K.; Patino-Lopez, L. D.; Satoh, H.

2011-01-01

80

Interplay between size and crystal structure of molybdenum dioxide nanoparticles--synthesis, growth mechanism, and electrochemical performance.  

PubMed

A detailed study is presented on the formation of MoO(2) nanoparticles from the dissolution of the precursor to the final rodlike product, with a focus on the exploration of the inorganic reaction occurring ahead of the nucleation step, and interplay between size and crystal structure of MoO(2). In situ X-ray absorption spectroscopy experiments show that the crystallization and the growth process of MoO(2) nanorods is initiated by rapid reduction of the MoO(2) Cl(2) precursor in benzyl alcohol and acetophenone. This reaction triggers the nucleation of 2 nm MoO(2) particles with spherical shape and hexagonal crystal structure. The transformation from spheres into rods emerges as a complex process driven by oriented attachment. High-resolution transmission electron microscopy and X-ray diffraction results provide evidence that the 2 nm particles first aggregate into 5-20 nm-large oriented assemblies. The increase in particle size induces the phase transition from hexagonal to the less symmetrical monoclinic crystal structure, and finally the transformation into rods. Is it shown that electrodes for lithium-ion batteries based on MoO(2) nanorods have a long-term cycling life. The specific discharge capacity even after 200 cycles at a discharge rate of 1 C is about 300 Ah kg(-1) . PMID:21294267

Koziej, Dorota; Rossell, Marta D; Ludi, Bettina; Hintennach, Andreas; Novák, Petr; Grunwaldt, Jan-Dierk; Niederberger, Markus

2010-12-20

81

Crystal Growth - Fast and Slow  

NSDL National Science Digital Library

This lab is divided into two exercises that may be completed within a single three-hour session. The first exercise requires the mixture of aqueous solutions that will precipitate large euhedral crystals over the course of 1 to 2 weeks. These experiments are intended to mimic the slow growth of macroscopic minerals in thermal and chemical equilibrium. In the second exercise, students observe rapid growth of dendritic crystals in strongly undercooled solutions in order to visualize the disequilibrium growth processes that occur in the atmosphere, at chilled margins, and in highly supersaturated solutions.

82

Biomolecular Modification of Inorganic Crystal Growth  

SciTech Connect

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. Finally, we show that the molecular scale observations are well correlated with macroscopic growth rate data.

De Yoreo, J J

2007-04-27

83

Submicrometer intermediates in the citrate synthesis of gold nanoparticles: new insights into the nucleation and crystal growth mechanisms.  

PubMed

The reduction of tetrachloroaurate by citrate ions in aqueous solutions yielding gold nanoparticles (GNPs) has been studied using in situ tapping mode atomic force microscopy (AFM), UV-vis absorption and dynamic light scattering (DLS) spectroscopies, small-angle X-ray scattering (SAXS) along with ex situ TEM, EDX and XPS. Special attention is given to mesoscale intermediates responsible for the intense coloring of the transient solutions and their role in nucleation and crystal growth. AFM detects liquid droplet-like domains, globules 30-50 nm in diameter arranged in submicrometer aggregates in the gray and blue solutions, and well separated individual particles in the final red sols. DLS shows abrupt appearance of species about 30 nm and larger but not growing Au nanoparticles, while SAXS reveals gradually increasing nanoparticles and no aggregates. The mesoscale structures observed in TEM become looser as the reaction proceeds; they contain signatures of oxidized Au and other solutes. The results are interpreted in terms of decomposition of supersaturated solutions to afford domains ("dense droplets") enriched by gold, and then, after nucleation and coalescence of Au nuclei inside them, rather slow growth of gold nanoparticles within the associated globules; the color changes of the transient solutions are due to increasing interparticle distances. PMID:21798551

Mikhlin, Yuri; Karacharov, Anton; Likhatski, Maxim; Podlipskaya, Tatyana; Zubavichus, Yan; Veligzhanin, Alexey; Zaikovski, Vladimir

2011-07-07

84

Crystallization kinetics and growth mechanism of 8 mol% yttria-stabilized zirconia (8YSZ) nano-powders prepared by a sol–gel process  

Microsoft Academic Search

Eight mol% yttria-stabilized zirconia (8YSZ) gel powders were synthesized at 348K for 2h using ZrOCl2·8H2O and Y(NO3)3·6H2O as starting materials in an ethanol–water solution by a sol–gel process. The crystallization kinetics and growth mechanism of the 8YSZ gel powders have been investigated using differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected

Chih-Wei Kuo; Yueh-Hsun Lee; I-Ming Hung; Moo-Chin Wang; Shaw-Bing Wen; Kuan-Zong Fung; Chi-Jen Shih

2008-01-01

85

Mechanically tunable photonic crystal  

NASA Astrophysics Data System (ADS)

Many technologies have been developed to actively change the band gap of a photonic crystal. While reasonable tuning speeds have been achieved, large simultaneous changes in band gap have not. This is suitable for optical switching and routing, however, a much larger tuning range is required for optical switching of multiple wavelength signals. In this paper, we show the design and analysis of a MEMS device which allows for higher tuning capabilities by leveraging the high strain achievable within a polydimethylsiloxane (PDMS) polymer attached to silicon comb drives. This novel design can lead to photonic crystals with more tunability than other state-or-the-art designs while maintaining acceptable speeds over 1 kHz.

Schrader, Steven; Truxal, Steven; Gandhi, Sheeba; Kurabayashi, Katsuo

2007-10-01

86

Efg Crystal Growth Apparatus And Method  

DOEpatents

An improved mechanical arrangement controls the introduction of silicon particles into an EFG (Edge-defined Film-fed Growth) crucible/die unit for melt replenishment during a crystal growth run. A feeder unit injects silicon particles upwardly through a center hub of the crucible/die unit and the mechanical arrangement intercepts the injected particles and directs them so that they drop into the melt in a selected region of the crucible and at velocity which reduces splashing, whereby to reduce the likelihood of interruption of the growth process due to formation of a solid mass of silicon on the center hub and adjoining components. The invention also comprises use of a Faraday ring to alter the ratio of the electrical currents flowing through primary and secondary induction heating coils that heat the crucible die unit and the mechanical arrangement.

Mackintosh, Brian H. (Concord, MA); Ouellette, Marc (Nashua, NH)

2003-05-13

87

Crystal growth and dendritic solidification  

Microsoft Academic Search

The motion of complex solid\\/liquid boundaries in crystal growth is presently computed by a numerical model encompassing such physical effects as crystalline anisotropy, surface tension, molecular kinetics, and undercooling. The model recasts the equations of motion as a single, history-dependent boundary integral equation on the solid\\/liquid boundary, and moves the boundary by solving an equation formulated by Osher and Sethian

James A. Sethian; John Strain

1992-01-01

88

Proceedings of the Soviet Conference on Crystal Growth (3RD).  

National Technical Information Service (NTIS)

The USSR symposium on crystal growth covered basic theories and methods for crystal growth, testing and determination. Discussions were made on crystal growth theories, the water-heating crystal growing method, the flame melting crystal growing method, th...

Chang Shou-ch'ing

1968-01-01

89

Crystal growth and annealing method and apparatus  

DOEpatents

A method and apparatus for producing crystals that minimizes birefringence even at large crystal sizes, and is suitable for production of CaF.sub.2 crystals. The method of the present invention comprises annealing a crystal by maintaining a minimal temperature gradient in the crystal while slowly reducing the bulk temperature of the crystal. An apparatus according to the present invention includes a thermal control system added to a crystal growth and annealing apparatus, wherein the thermal control system allows a temperature gradient during crystal growth but minimizes the temperature gradient during crystal annealing. An embodiment of the present invention comprises a secondary heater incorporated into a conventional crystal growth and annealing apparatus. The secondary heater supplies heat to minimize the temperature gradients in the crystal during the annealing process. The secondary heater can mount near the bottom of the crucible to effectively maintain appropriate temperature gradients.

Gianoulakis, Steven E. (Albuquerque, NM); Sparrow, Robert (North Brookfield, MA)

2001-01-01

90

Cluster Mechanism of Homogeneous Crystallization (Computer Study)  

NASA Astrophysics Data System (ADS)

A molecular dynamics (MD) study of homogeneous crystallization of liquid rubidium is conducted with an inter-particle pair potential. The equilibrium crystallization temperature of the models was 313 K. Models consisted of 500, 998, and 1968 particles in a basic cube. The main investigation method was as follows: to detect (along the MD run) the atoms with Voronoi polyhedrons (VP) of 0608 type (“0608-atoms,” as in a bcc crystal) and to detect the bound groups of 0608-atoms (“0608-clusters”) that could play the role of the seeds in crystallization. Full crystallization was observed only at temperatures lower than 185 K with the creation of a predominant bcc crystal. The crystallization mechanism of Rb models differs drastically from the mechanism adopted in classical nucleation theory. It consists of the growth of the total number of 0608-atoms on cooling and the formation of 0608-clusters, analogous to the case of coagulation of solute for a supersaturated two-component solution. At the first stage of the process the clusters have a very loose structure (something like medusa or octopus with many tentacles) and include inside atoms with other Voronoi polyhedron types. The dimensions of clusters quickly increase and approach those of the basic cube. 0608-atoms play the leading role in the crystallization process and activate the transition of the atoms involved in the 0608-coordination. The fast growth of the maximum cluster begins after it attains a critical size (about 150 0608-atoms). The fluctuations of cluster sizes are very important in the creation of a 0608-cluster of critical (threshold) size. These fluctuations are especially large in the interval from 180 K to 185 K.

Belashchenko, D. K.

2008-12-01

91

Crystal growth and high-temperature properties of intermetallic compound nickel aluminide  

Microsoft Academic Search

Investigations have been performed to the studying single crystal growth mechanism of intermetallic compound Ni3Al and to understand its mechanical behavior in single crystal and polycrystalline form at elevated temperatures under an oxidizing environment. Two crystal growth techniques, electron beam zone melting and Bridgman method, are combined together to grow single crystals in this work. The effects of the concentration

Zhigang Xiao

1999-01-01

92

On the mechanism of impurity influence on growth kinetics and surface morphology of KDP crystals—II: experimental study of influence of bivalent and trivalent impurity ions on growth kinetics and surface morphology of KDP crystals  

Microsoft Academic Search

The experimental results of the influence of bivalent (Ni2+, Co2+, Fe2+, Mn2+, Ba2+, Ca2+, Sr2+) and trivalent (Fe3+, Mn3+, Y3+, La3+) impurity ions on growth rates and surface morphology of potassium dihydrogen phosphate (KDP) crystal faces are presented and discussed. The analysis of the obtained results is performed in conjunction with the theoretical results presented in our previous paper (Rak

T. A. Eremina; V. A. Kuznetsov; N. N. Eremin; T. M. Okhrimenko; N. G. Furmanova; E. P. Efremova; Miros?awa Rak

2005-01-01

93

Growth, thermal, dielectric and mechanical properties of L-phenylalanine-benzoic acid: A nonlinear optical single crystal  

NASA Astrophysics Data System (ADS)

An efficient amino acid family nonlinear optical single crystal L-phenylalanine-benzoic acid (LPB) was conveniently grown by slow evaporation technique at room temperature. The crystal system and the lattice parameters were analyzed by single crystal X-ray diffraction studies. The grown crystal has excellent transmission in the entire visible region and its lower cut-off wavelength was found to be 248 nm. The SHG efficiency of the grown crystal was found to be 1.6 times higher than that of KDP crystal. The Laser damage threshold value of LPB has been found to be 6.5 GW/cm2. The sample was thermally stable up to 134 °C. Microhardness, dielectric and AC/DC conductivity measurements were made along (0 0 1) plane and reported for the first time. Microhardness studies revealed that the sample belongs to hard nature. Frequency dependent dielectric constant was measured for different temperatures and found maximum dielectric constant of 14 for 363 K. Photoconductivity studies of LPB divulged its negative photoconducting nature.

Tamilselvan, S.; Vimalan, M.; Vetha Potheher, I.; Rajasekar, S.; Jeyasekaran, R.; Antony Arockiaraj, M.; Madhavan, J.

2013-10-01

94

Possible origin of enhanced crystal growth in a glass  

NASA Astrophysics Data System (ADS)

Contrary to the common belief that a glassy state is stable against crystallization, Oguni and co-workers discovered unusual enhancement of the crystal growth rate of a few molecular liquids below the glass transition temperature Tg . We studied this phenomenon using o -terphenyl (OTP) and phenyl salicylate (salol), focusing on the roles of volume contraction ?V upon crystallization. We confirmed enhancement of crystal growth below Tg for OTP. For salol, which has two kinds of crystal, the crystal growth rate below Tg is faster for a crystal of larger ?V than for another crystal of smaller ?V . Our results suggest the following physical scenario for the phenomenon: for a material having large ?V , the volume contraction upon crystallization provides a crystal-glass interface with large excess free volume, which results in the mobility increase at the growth front and leads to enhancement of the crystal growth. This mechanism may be effective only below Tg , where density fluctuations cannot be quickly relaxed by hydrodynamic transport.

Konishi, Takashi; Tanaka, Hajime

2007-12-01

95

Mechanics of Cell Growth  

PubMed Central

Cell growth describes an essential feature of biological tissues. This growth process may be modeled by using a set of relatively simple governing equations based on the axioms of mass and momentum balance, and using a continuum framework that describes cells and tissues as mixtures of a solid matrix, a solvent and multiple solutes. In this model the mechanics of cell growth is driven by osmotic effects, regulated by the cells’ active uptake of solutes and passive uptake of solvent. By accounting for the anisotropy of the cells’ cytoskeletal structures or extracellular matrix, as well as external constraints, a wide variety of growing shapes may be produced as illustrated in various examples.

Ateshian, Gerard A.; Morrison, Barclay; Holmes, Jeffrey W.; Hung, Clark T.

2012-01-01

96

Controlled growth of semiconductor crystals  

DOEpatents

A method is disclosed 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 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. 7 figs.

Bourret-Courchesne, E.D.

1992-07-21

97

Controlled growth of semiconductor crystals  

DOEpatents

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.

Bourret-Courchesne, Edith D. (Richmond, CA)

1992-01-01

98

Growth and optical parameters of GaSe:Te crystals  

NASA Astrophysics Data System (ADS)

A series of technological experiments on the growth of GaSe:Te single crystals by the Bridgman-Stockbarger method is performed. Surface micromorphology and mechanical properties of crystals with different doping levels are studied. Spectral dependences of the complex refractive index are obtained using ellipsometry. The experimental data are approximated within the Lorentz-Drude model.

Sarkisov, S. Yu.; Atuchin, V. V.; Gavrilova, T. A.; Kruchinin, V. N.; Bereznaya, S. A.; Korotchenko, Z. V.; Tolbanov, O. P.; Chernyshev, A. I.

2010-09-01

99

CuBi 2O 4 single crystal nanorods prepared by hydrothermal method: Growth mechanism and optical properties  

Microsoft Academic Search

The synthesis of copper bismuth oxide (CuBi2O4) nanorods with single crystal structure by hydrothermal method is first reported here. The prepared CuBi2O4 nanorods are characterized by X-ray diffractometer, scanning electron microscopy, transmission electron microscopy (TEM) and high resolution TEM. It is found that the concentration of reagent cupric acetate has strong effect on the purity and microstructure of the prepared

A. M. Abdulkarem; Jialin Li; A. A. Aref; Lu Ren; E. M. Elssfah; Hui Wang; Yunke Ge; Ying Yu

2011-01-01

100

Determination of relative growth rates of natural quartz crystals  

PubMed

Although the theory describing crystal growth in the geological environment is well established, there are few quantitative studies that delimit the absolute time involved in the growth of natural crystals. The actual mechanisms responsible for the variation in size and shape of individual crystal faces are, in fact, not well understood. Here we describe a micro-infrared spectroscopic study of a single, gem-quality quartz crystal that allows us to measure the size, shape and relative growth rate of each of the crystal faces that are active throughout its growth history. We demonstrate that the abundances of hydrogen-bearing impurities can serve as 'speedometers' to monitor the growth rate of advancing crystal faces. Our technique can be applied to crystals from a variety of geological environments to determine their growth histories. Within the electronics industry, the technique might facilitate the production of defect-free synthetic crystals required for high-quality resonators and, ultimately, might allow determination of the absolute time involved in geological processes such as the crystallization of magmas, fluid flow in metamorphism and the sealing of open cracks in earthquake rupture zones. PMID:10786791

Ihinger; Zink

2000-04-20

101

MCT crystal growth. Final report  

SciTech Connect

Convection and segregation in directional solidification and crystal growth by the Bridgman-Stockbarger technique are traditionally treated by assuming axisymmetric thermal condition on the ampoule wall. It is, however, difficult to achieve such a condition in an experimental setup. Any deviation from an axisymmetric temperature field on the wall of a vertical ampoule represents a horizontal temperature gradient. The horizontal density gradient that results from thermal expansion in the melt under this condition must lead on earth to some buoyance-driven convection, no matter what the axial (vertical) temperature distribution that is imposed on the melt. The magnitude of such convective flows for conditions representative of the MSFC mercury-cadmium-telluride (MCT) Bridgman setup is studied.

Baird, J.K.

1988-02-01

102

Analytics of Crystal Growth in Space.  

National Technical Information Service (NTIS)

Two crystal growth processes considered for spacelab experiments were studied to anticipate and understand phenomena not ordinarily encountered on earth. Computer calculations were performed on transport processes in floating zone melting and on growth of...

W. R. Wilcox C. E. Chang P. J. Shlichta P. S. Chen C. K. Kim

1974-01-01

103

Optical diagnostics of mercuric iodide crystal growth.  

National Technical Information Service (NTIS)

Two optical methods were recently developed for in situ monitoring of the growth process of mercuric iodide crystals. The first method uses resonance fluorescence spectroscopy (RFS) for the determination of iodine vapor present in the growth ampule, which...

A. Burger S. H. Morgan E. Silberman D. Nason

1991-01-01

104

Computer simulations of crystal growth defects  

NASA Astrophysics Data System (ADS)

In highly supersaturated solutions, potassium dichromate crystals exhibit a growth anomaly on (001): this face is rough and covered by many potassium dichromate platelets that are only a few ?m thick, even though the structure is centrosymmetric. The following study is based on the crystallite orientation and dichromate classification. The force field method showed that intergrowths of complete structural units (crystal nuclei) in the twin position are energetically favourable on (001) but not on the symmetrically equivalent (001) face. The energetically favourable intergrowth laws occur in nature as macroscopic twins. The necessary potential parameters were determined using a combination of empirical fitting, quantum mechanical ab initio calculations, and normal coordinate analysis of the vibration spectra. The empirical fitting was preformed using GULP program.

Heide, G.; Follner, H.; Jackson, R. A.; Wilde, P. J.

105

GROWTH OF SINGLE CRYSTALS OF INCONGRUENTLY MELTING YTTRIUM IRON GARNET BY FLAME FUSION PROCESS  

Microsoft Academic Search

Single crystals of yttrium iron garnet (YâFeâOââ) were ; grown using the flame fusion process, even though the compcund is reported to ; melt incongruently. The growth of these single crystals involves a mechanism ; different from that which has been proposed for the growth of single crystals of ; incongruently melting mullite. Crystal boules were grown at varying linear

R. G. Rudness; R. W. Kebler

1960-01-01

106

Convective instability in protein crystal growth.  

PubMed

The conditions for the onset of convection during protein crystalization from a solution are studied theoretically on the basis of diffusion-convection evolution equations for the concentrations coupled to the Navier-Stokes equation describing the flow velocity. We consider that the density of the solution depends on the concentration of two species, namely, a protein and a precipitating agent, a salt. While the protein is crystallized at the crystal/solution interface, the salt is rejected, and these mechanisms are described by means of boundary conditions for the interface. We find the base profiles for both protein and salt concentrations and perform a linear stability analysis of this basic state with regard to buoyancy induced perturbations. This gives information on the critical diameter of capillaries above which convection may be observed, as well as on the influence of the speed of growth V of the crystal interface on the stability of the system. Numerical integration of the model shows good agreement with the predictions of the linear stability analysis. PMID:15447499

Lima, D; De Wit, A

2004-08-17

107

Theoretical model of crystal growth shaping process  

Microsoft Academic Search

A theoretical investigation of the crystal growth shaping process is carried out on the basis of the dynamic stability concept. The capillary dynamic stability of shaped crystal growth processes for various forms of the liquid menisci is analyzed using the mathematical model of the phenomena in the axisymmetric case. The catching boundary condition of the capillary boundary problem is considered

V. A. Tatarchenko; V. S. Uspenski; E. V. Tatarchenko; J. Ph. Nabot; T. Duffar; B. Roux

1997-01-01

108

Innovation in crystal growth: A personal perspective  

Microsoft Academic Search

The evolution of crystal growth has been crucially dependent on revolutionary innovations and initiatives involving ideas, technology and communication. A personal perspective is presented on some of these aspects in connection with the early history of semiconductors that have helped evolve our knowledge and advance the science and technology of crystal growth. The presentation considers examples from work on germanium,

J. B. Mullin

2008-01-01

109

Growth of Garnet Crystals for Laser Applications.  

National Technical Information Service (NTIS)

The objective of the Phase I effort was to establish feasibility of growth of Gd3Ga5O12(GGG) crystals as a precursor to growth of other garnet crystals, e.g. Gd35c2Ga3O12 (GSGG), for laser applications. Experimental work showed that Ga2O3 has a high vapor...

C. P. Khattak

1984-01-01

110

Simulation of Sublimation Growth of SiC Single Crystals  

NASA Astrophysics Data System (ADS)

Modelling of sublimation growth of SiC is discussed with the goal to describe the mathematical models necessary to optimize the process and design of the growth system. An analysis of the mechanisms of growth of bulk silicon carbide crystals is performed. Growth conditions which provide stable growth of single SiC crystals without formation of secondary phases are considered. The phase diagram of the formation of extra phases during the sublimation growth of SiC is presented. Modelling of the growth of bulk SiC crystals is considered. Results of modelling the temperature distribution inside the inductively heated system for the growth of bulk SiC crystals are shown. A mechanism of material transport inside the closed Ta container in the absence of an inert gas atmosphere is proposed which is different from that of diffusive or free-molecular transport. First results of the model analysis of chemical processes inside the volume of SiC powder during the sublimation growth are demonstrated. It is shown that the sublimation and re-crystallization of the SiC source is sensitive to the temperature distribution in the source.

Karpov, S. Yu.; Makarov, Yu. N.; Ramm, M. S.

1997-07-01

111

Rapid growth of KDP-type crystals  

Microsoft Academic Search

Growth of KDP-type crystals on the point seed made possible to accelerate growth rates from traditional 1 mm\\/day up to 50 mm\\/day. This acceleration gave base to a development of the rapid growth technique for production of single crystals with the linear sizes up to 90 cm to obtain plates for laser radiation conversion in world-largest lasers. Scientific bases and

N. Zaitseva; L. Carman

2001-01-01

112

Crack propagation driven by crystal growth  

SciTech Connect

Crystals that grow in confinement may exert a force on their surroundings and thereby drive crack propagation in rocks and other materials. We describe a model of crystal growth in an idealized crack geometry in which the crystal growth and crack propagation are coupled through the stress in the surrounding bulk solid. Subcritical crack propagation takes place during a transient period, which may be very long, during which the crack velocity is limited by the kinetics of crack propagation. When the crack is sufficiently large, the crack velocity becomes limited by the kinetics of crystal growth. The duration of the subcritical regime is determined by two non-dimensional parameters, which relate the kinetics of crack propagation and crystal growth to the supersaturation of the fluid and the elastic properties of the surrounding material.

A. Royne; Paul Meaking; A. Malthe-Sorenssen; B. Jamtveit; D. K. Dysthe

2011-10-01

113

Microscopic model of protein crystal growth.  

PubMed

A microscopic, reversible model to study protein crystal nucleation and growth is presented. The probability of monomer attachment to the growing crystal was assumed to be proportional to the protein volume fraction and the orientational factor representing the anisotropy of protein molecules. The rate of detachment depended on the free energy of association of the given monomer in the lattice, as calculated from the buried surface area. The proposed algorithm allowed the simulation of the process of crystal growth from free monomers to complexes having 10(5) molecules, i.e. microcrystals with already formed faces. These simulations correctly reproduced the crystal morphology of the chosen model system--the tetragonal lysozyme crystal. We predicted the critical size, after which the growth rate rapidly increased to approximately 50 protein monomers. The major factors determining the protein crystallisation kinetics were the geometry of the protein molecules and the resulting number of kinetics traps on the growth pathway. PMID:11036969

Kierzek, A M; Pokarowski, P; Zielenkiewicz, P

2000-09-15

114

Nucleation and growth kinetics of struvite crystallization.  

PubMed

Struvite crystallization technology is being widely applied in full-scale due to a surge in nutrient demand and phosphate price increases. Past investigations on struvite crystallization focused on process efficiency and thermodynamics, and less on kinetics, while mainly using fluidized bed type crystallizer. In this work, nucleation and growth kinetic data were measured using stirred vessel. The primary and secondary nucleation was measured in synthetic wastewater, and crystal growth in digested supernatant. The measured kinetic data was correlated with solution supersaturation. The dependence of growth rate on relative supersaturation in the digested was higher compared to synthetic wastewater. The crystal polymorph in synthetic wastewater and real wastewater was comparable. Products from the growth studies showed narrow size distribution and favorable separation characteristics. The secondary nucleation rate showed second order dependence on relative supersaturation. The nucleation induction time decreased with an increase in supersaturation ratio with a clear distinction between homogenous and heterogeneous primary nucleation. PMID:23541308

Mehta, Chirag M; Batstone, Damien J

2013-03-19

115

Crystal growth in nanoporous framework materials.  

PubMed

Future applications of nanoporous materials will be in opto-electronic devices, magnetic and chemical sensors, shape-selective and bio-catalysis, structural materials and nuclear waste management. Crucially, in all such applications, an understanding of crystal growth to the same depth as has been achieved in semiconductor technology is needed. Therefore, defects, intergrowths, dopants and isomorphous substitution must be controlled, and crystal habit and size (e.g. single crystal films) must be fabricated with precision. These goals elude the community because of lack of understanding of crystal growth processes. Modern microscopy techniques including AFM, ultra-high resolution SEM and HREM coupled with theoretical calculations are beginning to reveal the details of these growth processes yielding the important thermodynamic data crucial to effect synthetic control such as: controlling defects; controlling intergrowths: introducing chirality; modifying surface access; altering diffusion pathways; controlling crystal habit; synthesising templated materials cheaply in order to render them economically viable; controlling crystal size for instance as single crystal films. In this paper we will discuss recent results including: the details of surface alteration processes in nanoporous materials, measured in situ, under different chemical environments and the ability to switch processes on and off by the control of growth conditions. Further we illustrate an approach to theoretically model the crystal growth in such complex systems which ultimately delivers activation energies for fundamental growth processes. PMID:17955807

Anderson, Michael W; Agger, Jonathan R; Meza, L Itzel; Chong, Chin B; Cundy, Colin S

2007-01-01

116

A Mechanism of Crystallization of Cometary Silicates  

NASA Astrophysics Data System (ADS)

We propose a mechanism of crystallization of cometary silicate grains on the basis of the Greenberg model of cometary dust which is composed of a silicate core an organic mantle and an outermost icy mantle. The crystallization mechanism we propose is due to energy release by polymerization of the organic mantle when the grains are released from a cometary nucleus and heated by solar radiation. We formulate the crystallization mechanism and calculate the degree of crystallization of the silicate core. We show the results of the calculations of the crystallization degree for plausible values of the physical parameters and of the infrared emission spectra.

Yamamoto, Tetsuo; Chigai, Takeshi

2005-01-01

117

Growth of faceted needle crystals: theory  

Microsoft Academic Search

Needle crystals have been observed to be faceted at low velocities of growth. This can be explained by the theory of diffusion-limited growth with the addition of a supplementary condition fixing the shape of the facet depending on the average temperature on it. This leads to a relation between the size of the facet and the growth velocity in a

M. Ben Amar; Y. Pomeau

1988-01-01

118

Studies on the growth, structural, thermal, mechanical and optical properties of the semiorganic nonlinear optical crystal L-glutamic acid hydrobromide  

NASA Astrophysics Data System (ADS)

Single crystals of optically significant L-glutamic acid hydrobromide were grown from aqueous solutions and their various properties were characterized. The title compound was synthesized with stoichiometric ratio 1:1, purified by recrystallization, confirmed by powder X-ray diffraction and its solubility in double distilled water in the temperature range 30-80 °C was determined by the gravimetric method. Large dimensional (45×26×14 mm3) optically transparent single crystal of the compound was grown by a controlled slow cooling method combined with the reversible seed rotation technique. The morphological importance of the grown crystal was studied in accordance with equilibrium morphology. Samples of the grown crystal were subjected to single crystal X-ray diffraction study for structural analysis, Fourier transform infrared spectroscopy for functional group analysis, TG-DTA/DSC for thermal analysis, Vickers microhardness study for mechanical strength, UV-vis-NIR spectral analysis for optical transparency and the Kurtz powder method for SHG efficiency of the grown crystal. Results indicate that the grown crystal has significant improvement in its thermal, optical and SHG properties when compared to pure L-glutamic acid polymorphs.

Dhanasekaran, P.; Srinivasan, K.

2013-07-01

119

Ground-based vapor crystal growth experiments  

NASA Astrophysics Data System (ADS)

We report on a novel computer-controlled experiment set-up for growing organic nonlinear optical (NLO) crystals by effusive- ampoule physical vapor transport (EAPVT). In this approach, incongruent or impurity vapor components are continuously removed from the vicinity of the growing crystal to vacuum. This results in considerably higher transport rates than are obtained in closed ampoule arrangements. As a consequence, crystal growth can be conducted with reduced temperature gradients, which is important for the growth of structurally perfect crystals. We present design considerations for an EAPVT apparatus, its construction, and its application to the growth of single crystals of 4-(N,N-dimethylamino)-3- acetamidonitrobenzene (DAN), an organic NLO material. The insight gained from this ground-based experimental work was used for the design of the flight hardware used aboard the U.S. Space Shuttle.

Zugrav, Maria I.; Rosenberger, Franz

1997-07-01

120

Growth of Zno Single Crystals.  

National Technical Information Service (NTIS)

Single crystals of ZnO have been grown by subliming both ZnS and ZnSe and reacting them with oxygen in an argon gas flow. Using ZnS as the starting material, both platelet- and prism-type ZnO crystals were grown. Prisms having a cross-sectional area in th...

Y. S. Park D. C. Reynolds

1966-01-01

121

Solvothermal crystal growth of functional materials  

Microsoft Academic Search

Hydrothermal crystal growth was associated with the development of ? -quartz single crystals for devices based on piezoelectric materials. This technology was then used to elaborate single crystals of different functional materials such as quartz-like oxides (AlPO4, GaPO4, GaAsO4, etc.), calcite CaCO3, etc. During the last few years two materials, GaN (using non-aqueous solvent) and ZnO, have been particularly investigated

Alain Largeteau; Stephane Darracq; Graziella Goglio; Gerard Demazeau

2008-01-01

122

Nucleation and Growth of Ice Crystals.  

National Technical Information Service (NTIS)

The basic information regarding nucleation in supercooled water was reviewed. Measurements were performed with water drops and water in bulk. Ice growth was measured as a function of crystal orientation, temperature, flow velocity of solution, salt concen...

J. Farrar W. S. Hamilton

1965-01-01

123

Convective Flow Effects on Protein Crystal Growth.  

National Technical Information Service (NTIS)

During the fourth semi-annual period under this grant we have pursued the following activities: (1) crystal growth morphology and kinetics studies with tetragonal lysozyme. These clearly revealed the influence of higher molecular weight protein impurities...

F. Rosenberger L. A. Monaco

1995-01-01

124

Illusory spirals and loops in crystal growth.  

PubMed

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. PMID:24101507

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

2013-10-07

125

Convection Analysis on Various Crystal Growth Systems.  

National Technical Information Service (NTIS)

Specific work done during an indicated contract period was reviewed. An extensive survey of crystal growth literature and related topics was accomplished during this time. Specific attention was given to those areas dealing with the effects of transport p...

1977-01-01

126

The Growth of Large Single Crystals.  

ERIC Educational Resources Information Center

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)

Baer, Carl D.

1990-01-01

127

Convective Flow Effects on Protein Crystal Growth.  

National Technical Information Service (NTIS)

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 ...

F. Rosenberger

1995-01-01

128

Growth Of Oriented Crystals At Polymerized Membranes  

DOEpatents

The present invention relates to methods and compositions for the growth and alignment of crystals at biopolymeric films. The methods and compositions of the present invention provide means to generate a variety of dense crystalline ceramic films, with totally aligned crystals, at low temperatures and pressures, suitable for use with polymer and plastic substrates.

Charych, Deborah H. (Albany, CA), Berman, Amir (Ben-Shiva, IL)

2000-01-25

129

On growth rate hysteresis and catastrophic crystal growth  

NASA Astrophysics Data System (ADS)

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.

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

2013-04-01

130

Growth, spectral, thermal, dielectric, mechanical, linear and nonlinear optical, birefringence, laser damage threshold studies of semi-organic crystal: Dibrucinium sulfate heptahydrate  

NASA Astrophysics Data System (ADS)

Dibrucinium sulfate heptahydrate (DBSH), a semi-organic nonlinear optical material, has been synthesized and single crystals were grown from water-ethanol solution at room temperature up to dimensions of 10 × 7 × 2 mm3. The unit cell parameters were determined from single crystal and powder X-ray diffraction studies. The structural perfection of the grown crystal has been analyzed by high-resolution X-ray diffraction (HRXRD) study. FTIR and Raman studies were performed to identify the functional groups present in the title compound. The activation energy (E), entropy (?S), enthalpy (?H) and Gibbs free energy (?G), of the thermal decomposition reaction have been derived from thermo gravimetric (TGA) and differential thermal (DTA) analysis curves, using Coats-Redfern method. The variation of dielectric properties of the grown crystal with respect to frequency has been investigated at different temperatures. Microhardness measurements revealed the mechanical strength of grown crystal. The optical parameters, the optical band gap Eg and width of localized states Eu were determined using the transmittance data in the spectral range 200-800 nm. The relative second harmonic efficiency of the compound is found to be 1.4 times greater than that of KDP. Birefringence and Laser damage threshold studies were carried out for the grown crystal.

Krishnan, P.; Gayathri, K.; Bhagavannarayana, G.; Jayaramakrishnan, V.; Gunasekaran, S.; Anbalagan, G.

2013-08-01

131

Growth, spectral, thermal, dielectric, mechanical, linear and nonlinear optical, birefringence, laser damage threshold studies of semi-organic crystal: dibrucinium sulfate heptahydrate.  

PubMed

Dibrucinium sulfate heptahydrate (DBSH), a semi-organic nonlinear optical material, has been synthesized and single crystals were grown from water-ethanol solution at room temperature up to dimensions of 10×7×2 mm(3). The unit cell parameters were determined from single crystal and powder X-ray diffraction studies. The structural perfection of the grown crystal has been analyzed by high-resolution X-ray diffraction (HRXRD) study. FTIR and Raman studies were performed to identify the functional groups present in the title compound. The activation energy (E), entropy (?S), enthalpy (?H) and Gibbs free energy (?G), of the thermal decomposition reaction have been derived from thermo gravimetric (TGA) and differential thermal (DTA) analysis curves, using Coats-Redfern method. The variation of dielectric properties of the grown crystal with respect to frequency has been investigated at different temperatures. Microhardness measurements revealed the mechanical strength of grown crystal. The optical parameters, the optical band gap E(g) and width of localized states Eu were determined using the transmittance data in the spectral range 200-800 nm. The relative second harmonic efficiency of the compound is found to be 1.4 times greater than that of KDP. Birefringence and Laser damage threshold studies were carried out for the grown crystal. PMID:23666350

Krishnan, P; Gayathri, K; Bhagavannarayana, G; Jayaramakrishnan, V; Gunasekaran, S; Anbalagan, G

2013-04-22

132

Growth kinetics and morphology of polymer crystals  

NASA Astrophysics Data System (ADS)

Originating from the nature of chain folding, polymer single crystals are quite unique in the growth kinetics and morphology. The developments of the understanding in the past 50 years are discussed and the unsolved important issues will be suggested. Polymer single crystals are thin lamellae with the thickness in the order of 10nm determined by the period of chain folding, which keeps a constant value for the isothermal crystallization. The growth of polymer single crystals is modeled by the kinetics of creation and annihilation of growth steps on a rectangular substrate with the pre-determined thickness. The growth face is therefore regarded as a one-dimensional substrate and the kinks and anti-kinks on the substrate correspond to the growth steps propagating in the opposite directions. The kinetic equations of those kinks proposed by Seto and Frank well describe the transition of growth regime as a crossover from single nucleation to multi-nucleation on the basis of the standard model of chain-folded polymer crystallization with surface nucleation proposed by Lauritzen and Hoffman. However, the analysis of the growth kinetics and morphology of single crystals having curved growth front suggests an unusual behavior of the step propagation velocity. The anomaly can be accounted for by a self-poisoning of the growth step interrupted by polymer chains with folding shorter than required. An entropic barrier of pinning proposed by Sadler and Gilmer is a possible candidate of the self-poisoning and is in accordance with recent computer simulation results suggesting the kinetics on a rugged free energy landscape having a resemblance to protein folding. Therefore, the quantitative evaluation of the kinetic barriers of surface nucleation and pinning has been an important issue. In addition, examination of the kinetics of melting will have valuable information because melting of a crystal must be free from nucleation but can still be limited by the entropic barrier.

Toda, Akihiko

2007-03-01

133

CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: High-Rate Growth and Nitrogen Distribution in Homoepitaxial Chemical Vapour Deposited Single-crystal Diamond  

Microsoft Academic Search

High rate (> 50 mum\\/h) growth of homoepitaxial single-crystal diamond (SCD) is carried out by microwave plasma chemical vapour deposition (MPCVD) with added nitrogen in the reactant gases of methane and hydrogen, using a polycrystalline-CVD-diamond-film-made seed holder. Photoluminescence results indicate that the nitrogen concentration is spatially inhomogeneous in a large scale, either on the top surface or in the bulk

Hong-Dong Li; Guang-Tian Zou; Qi-Liang Wang; Shao-Heng Cheng; Bo Li; Jian-Nan Lü; Xian-Yi Lü; Zeng-Sun Jin

2008-01-01

134

Growth and observation of micro-organic crystals in two-dimensional glass nanovolume cell  

NASA Astrophysics Data System (ADS)

A simple type of glass cell to control the organic crystal growth in microsize by electrochemical method is presented. We fabricated growth cells with electrodes patterned by photolithograph and nanoliter volume. They have several merits for growth of organic conductors in microsize, including confined growth volume, observable growth space, rapid growth cycle relative to conventional methods, and compatibility with existing microfabrication techniques. The real time observation of the crystal growth was performed. The results are discussed in terms of the growth mechanism, suggesting a possibility of another microscopic view of crystal growth.

Kobayashi, Kaya; Koyama, Hiroko; Ishikura, Kodai; Mitsui, Toshiyuki

2008-10-01

135

Growth of calcium carbonate crystal imitating stalagmite growth in nature  

Microsoft Academic Search

Calcite crystals were prepared by dropping a saturated calcium carbonate aqueous solution on a substrate. The calcite crystals were grown with a growth rate of approximately 0.7?m\\/day under the condition of aqueous temperature of 2°C, aqueous concentration of 0.006mol\\/l, and substrate temperature of 40°C. When the calcite substrate was used, calcite crystals were grown epitaxially. Na2CO3 and CaCl2 aqueous solutions

H. Miyazaki; M. Mizutani; T. Yamashita; H. Aoyama; H. Seue; T. Ota

2006-01-01

136

Historical review of quartz crystal growth  

Microsoft Academic Search

The history of quartz crystal growth is reviewed from the origin to the industrialization. The developing process of growth techniques is divided into the following three stages: (1) The fundamental work based on the mineralogical genetic view point, which was performed in Italy during the end of the 19th to the beginning of the 20th centuries. (2) The works to

Fumiko Iwasaki; Hideo Iwasaki

2002-01-01

137

Synthesis, growth, structural, spectral, linear and nonlinear optical and mechanical studies of a novel organic NLO single crystal 4-Bromo 4-Nitrostilbene (BONS) for nonlinear optical applications  

NASA Astrophysics Data System (ADS)

Single crystal of 4-Bromo 4-Nitrostilbene (BONS), a new organic nonlinear optical material was synthesized and crystals were grown with dimensions up to 8 × 6 × 3 mm3 from ethyl methyl ketone (EMK) solvent by slow evaporation method. Single crystal X-ray diffractometer was used to measure the unit cell parameters and confirmed the BONS structure as orthorhombic with the space group P212121. The sample has been subjected to powder X-ray diffraction to identify the crystalline nature and the prominent peaks were indexed. The functional groups were identified from Fourier transform infrared (FTIR) spectral analysis. Proton NMR analysis confirms the protonation in the structure of the title compound. Optical behaviour of BONS has been observed by UV-Vis absorption spectral analysis which shows the low cut off wavelength lies at 405 nm and found that the energy band gap of the crystal is 2.90 eV. Thermal stability of the material has been confirmed by TG/DTA analyses. The BONS compound formation analyzed by mass spectroscopic analysis. The mechanical strength of the crystal was found using Vickers microhardness measurement. The laser damage threshold (LDT) for the grown crystal was measured by using Nd:YAG laser. Photoluminescence spectrum indicated green light emission at 515.44 nm. The Kurtz powder second harmonic generation test shows that the BONS crystal (1.5 V) is a very potential NLO candidate for optical generation and it has SHG efficiency 69 times greater than that of KDP (21.7 mV).

Dinakaran, Paul M.; Kalainathan, S.

2013-03-01

138

CRYSTAL GROWTH IN RAT ENAMEL  

Microsoft Academic Search

Observations have been made, using electron microscopy and x-ray diffraction, on the changes in crystal size and shape which occur in developing rodent enamel during minerali- zation. Small enamel pieces isolated from ground sections of rat molars and incisors were either embedded in methacrylate and sectioned with a diamond knife for electron micros- copy, or they were mounted intact on

M. U. Nylen; E. D. EANES; K.-A. OMNELL

1963-01-01

139

Fluctuations in growth rate of gypsum crystals  

Microsoft Academic Search

Growth of needlelike gypsum crystals from highly supersaturated aqueous solutions has been studied by the methods of the optical\\u000a and electron microscopies. The average growth rates of the end faces and their fluctuations are determined. It is shown that\\u000a the fluctuations in the growth rates of end faces are described by the Fokker-Planck equation and that the end faces of

V. F. Komarov; A. V. Severin; I. V. Melikhov

2000-01-01

140

Bridgman growth of paratellurite single crystals  

Microsoft Academic Search

The growth of paratellurite single crystals by the vertical-gradient freezing technique is reported for the first time. Boules of 120mm long and 25mm in diameter were obtained under a temperature gradient of 10°Ccm?1 and translation rates lower than 0.6mmh?1. The spatial distribution of defects along the growth axis reveals a continuous evolution of the free convective fluid-flow regime as growth

P. Veber; J. Mangin; P. Strimer; P. Delarue; C. Josse; L. Saviot

2004-01-01

141

Rapid growth of potassium dihydrogen phosphate crystals  

SciTech Connect

The authors report the development of a process for high rate (15 mm/d) growth of potassium dihydrogen phosphate single crystals. Correlations for mass transport by convective diffusion (to cones or disks under axially-impinging flow) are applied to published rate data on 3-mm KDP crystals to derive a semi-empirical kinetic equation for (101) growth rate measured in the z direction: g/sub z/ = k/sub g/ exp(-H/sub g//RT)(c/sub s/-c/sub sat)/sup n/, where the coefficients found by linear regression are k/sub g/ = 3493 m/s. H/sub g/ = 41,399 J/mol and n = 2.277; and c/sub s/ and c/sub sat/ are, respectively, the surface and saturation concentrations (kg-KDP/kg-water). Material properties, transport, and kinetic equations are then solved numerically to predict the dependence of growth rate on temperature, supersaturation, and the ratio of flow rate to a crystal dimension. The model is experimentally verified for 20-25 mm crystals grown at rates of 5-25 mm/d using a turbine to enhance solute flux to the pyramidal faces. The authors conclude that high growth rate of large crystals is possible and scales according to the ratio of characteristic velocity to crystal dimension.

Cooper, J.F.; Singleton, M.F.

1984-01-01

142

Rapid growth of potassium dihydrogen phosphate crystals  

SciTech Connect

We report the development of a process for high rate (15 mm/d) growth of potassium dihydrogen phosphate single crystals. Correlations for mass transport by convective diffusion (to cones or disks under axially-impinging flow) are applied to published rate data on 3-mm KDP crystals to derive a semi-empirical kinetic equation for (101) growth rate measured in the z direction: g/sub z/ = k/sub g/ exp(-H/sub g//RT)(c/sub s/-c/sub sat/)/sup n/, where the coefficients found by linear regression are k/sub g/ = 3492 m/s, H/sub g/ = 41,399 J/mol and n = 2.277; and c/sub s/ and c/sub sat/ are, respectively, the surface- and saturation concentrations (kg-KDP/kg-water). Material properties, transport, and kinetic equations are then solved numerically to predict the dependence of growth rate on temperature, supersaturation, and the ratio of flow rate to a crystal dimension. The model is experimentally verified for 20 to 25 mm crystals grown at rates of 5 to 25 mm/d using a turbine to enhance solute flux to the pyramidal faces. We conclude that high growth rate of large crystals is possible and scales according to the ratio of characteristic velocity to crystal dimension. 22 references, 8 figures.

Cooper, J.F.; Singleton, M.F.

1985-01-24

143

[Crystal growth on human dentin surface].  

PubMed

Gypsum crystal growth on human dentin surface was investigated using a crystal growth agent composed of 4-20% ammonium sulfate and 5-60% acrylic acid aqueous admixtures. In the treatment with 4% ammonium sulfate which contains the concentration of acrylic acid from 5% to 60%, fine half-spherical aggregates of 25 microns in diameter of needle-like crystals were obtained from 35% acrylic acid and large ones from 30% acrylic acid. Using the crystal growth agent of 4% ammonium sulfate-35% acrylic acid aqueous admixture, the human dentin surface pretreated with sulfates of different cations was evaluated from crystal growth. All sulfates without 4% ZnSO4 formed half-spherical aggregates of needle-like crystals. Diameter of their half-spherical aggregates increased as follows; 4% Na2SO4 less than none-treatment less than saturated CaSO4.2H2O less than 4% K2SO4 less than 4% MgSO4 less than 4% ZnSO4. The half-spherical aggregates from sulfates of Na+ and K+ (alkali metal) grew finer than those from sulfates of Ca2+ and Mg2+ (alkali-earth metal) and Zn2+ (zinc) and their area on dentin surface increased more with sulfates of alkali metal than with those of alkali-earth. PMID:2603093

Oyamada, S

1989-03-01

144

Model for the mechanical stress due to the salt crystallization in porous materials  

Microsoft Academic Search

This paper deals with the experimental investigation and the mathematical modelling of crystal growth in porous materials and resulting mechanical stress due to the crystallization pressure.Crystallization of potassium nitrate and of sodium sulphate was induced in two bricks by cooling down at constant rate. The measured temperatures describe indirectly the crystallization and the dissolution rates. Thus, the time-dependent amount of

R. M. Espinosa; L. Franke; G. Deckelmann

2008-01-01

145

New strategies for protein crystal growth.  

PubMed

Protein crystallization is the most difficult and time-consuming step in the determination of a protein's atomic structure. As X-ray diffraction becomes a commonly available tool in structural biology, the necessity for rational methodologies and protocols to produce single, high-quality protein crystals has come to the forefront. The basics of protein crystallization conform to the classical understanding of crystallization of small molecules. Understanding the effect of solution variables such as pH, temperature, pressure, and ionicity on protein solubility allows the proper evaluation of the degree of supersaturation present in protein crystallization experiments. Physicochemical measurements such as laser light scattering, X-ray scattering, X-ray diffraction, and atomic force microscopy provide a clearer picture of protein crystal nucleation and growth. This ever deepening knowledge base is generating rational methods to produce protein crystals as well as means to improve the diffraction quality of such protein crystals. Yet, much remains unclear, and the protein crystallization research community will be quite active for many years to come. PMID:11701498

Wiencek, J M

1999-01-01

146

Structural, spectral and mechanical studies of bimetallic crystal: cadmium manganese thiocyanate single crystals  

NASA Astrophysics Data System (ADS)

A nonlinear optical bimetallic thiocyanate complex crystal, cadmium manganese thiocyanate (CMTC) has been successfully synthesized. The growth of single crystals of cadmium manganese thiocyanate has been accomplished from aqueous solution using slow evaporation method. The presence of manganese and cadmium in the synthesized material was confirmed through energy dispersive spectrum (EDS) analysis. Structural analysis was carried out using powder X-ray diffractometer (PXRD) and crystalline perfection of the grown crystals was ascertained by high-resolution X-ray diffraction (HRXRD) analysis. Fourier transform infrared (FTIR) spectrum was taken to confirm the functional groups. The transmittance spectrum of the crystal in the UV-visible region has been recorded and the cutoff wavelength has been determined. The dielectric measurements for the crystals were performed for various frequencies and temperatures. The mechanical properties were evaluated by Vickers microhardness testing, which reveals hardness and stiffness constant of the crystals.

Manikandan, M.; Vijaya Prasath, G.; Bhagavannarayan, G.; Vijayan, N.; Mahalingam, T.; Ravi, G.

2012-09-01

147

An Apparatus for Growth of Small Crystals From Solutions.  

ERIC Educational Resources Information Center

|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)|

Mitrovic, Mico M.

1995-01-01

148

An Apparatus for Growth of Small Crystals From Solutions.  

ERIC Educational Resources Information Center

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)

Mitrovic, Mico M.

1995-01-01

149

Phase-Field Simulations of Crystal Growth  

SciTech Connect

This course gives an elementary introduction to the phase-field method and to its applications for the modeling of crystal growth. Two different interpretations of the phase-field variable are given and discussed. It can be seen as a physical order parameter that characterizes a phase transition, or as a smoothed indicator function that tracks domain boundaries. Elementary phase-field models for solidification and epitaxial growth are presented and are applied to the dendritic growth of a pure substance and the step-flow growth on a vicinal surface.

Plapp, Mathis [Physique de la Matiere Condensee, Ecole Polytechnique, CNRS, 91128 Palaiseau (France)

2010-07-22

150

Zinc Crystal Growth in Microgravity  

Microsoft Academic Search

We report one of the first direct measurements of the efficiency of vapor-to-crystalline-solid growth in a microgravity environment aboard NASA's Reduced Gravity Research Facility. Zinc vapor is produced from a heater in a vacuum chamber containing argon gas. Vapor-phase nucleation is induced by cooling as the vapor expands away from the heat source, and its onset is easily detected visually

B. P. Michael; Joseph A. Nuth III; Lembit U. Lilleleht

2003-01-01

151

Crystal growth simulations of H(2)S hydrate.  

PubMed

In this paper, we report a molecular simulation study exploring the crystal growth behavior of H(2)S hydrates within two-phase (H(2)S hydrate crystal and H(2)S aqueous solution) and three-phase (H(2)S hydrate crystal, liquid H(2)S, and H(2)S aqueous solution) systems. The microscopic mechanisms of growth, as well as the interfacial properties during the heterogeneous crystal growth process, are probed. We find that the H(2)S hydrate can be grown at a higher rate than methane hydrates under comparable conditions (Vatamanu, J.; Kusalik, P. G. J. Phys. Chem. B 2006, 110, 15896). The three-phase simulations, which also allow us to identify the simulation conditions on the experimental phase diagram, demonstrate that the present models reasonably reproduce the phase behavior of this system. We find that the crystal interface has a strong affinity for water molecules. We observed a relatively low level of defects in the newly formed H(2)S hydrate crystal. PMID:20597531

Liang, Shuai; Kusalik, Peter G

2010-07-29

152

The kinetics of nucleation and crystal growth and scaling laws for magmatic crystallization  

Microsoft Academic Search

Magmatic crystallization depends on the kinetics of nucleation and crystal growth. It occurs over a region of finite thickness called the crystallization interval, which moves into uncrystallized magma. We present a dimensional analysis which allows a simple understanding of the crystallization characteristics. We use scales for the rates of nucleation and crystal growth, denoted by Im and Ym respectively. The

Genevieve Brandeis; Claude Jaupart

1987-01-01

153

Inclusion free cadmium zinc tellurium and cadmium tellurium crystals and associated growth method  

DOEpatents

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.

Bolotnikov, Aleskey E. (South Setauket, NY); James, Ralph B. (Ridge, NY)

2010-07-20

154

Thermocapillary Free Boundaries in Crystal Growth.  

National Technical Information Service (NTIS)

In the paper a two-dimensional free boundary arising from the steady thermo-capillary flow in a viscous incompressible fluid is studied from the numerical point of view. The problem is considered in the context of open boat crystal growth technique. The m...

C. Cuvelier J. M. Driessen

1985-01-01

155

Stochastic resonance in photonic crystal growth  

Microsoft Academic Search

We study the role of noise during the growth process of opal-based photonic crystals, and demonstrate that noise significantly improves their structural properties. We observe a stochastic resonance-like behaviour, where the ordering of the resulting structure improves up to a certain optimal noise level and then deteriorates for larger noise volumes. This demonstrates that noise can have a nontrivial effect

Andreas Amann; Worawut Khunsin; Gudrun Kocher; Clivia M. Sotomayor Torres; Eoin P. O'Reilly

2007-01-01

156

Surface Phenomena and Parameters of Crystal Growth: Simple Basics  

SciTech Connect

Basic concepts of crystal growth and their practical use to semi-quantitatively estimate growth processes are explained: surface energy and free energy, driving force of crystallization, atomically rough vs smooth interface structure and the corresponding normal vs layer-by-layer growth modes, application of the activated complex concept to derive kinetic coefficient characterizing crystal growth rate at a given driving force. The Reader is supposed to be familiar with general physics and chemistry. No specific knowledge in crystal growth is required.

Chernov, A. A. [Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore CA, 94551 (United States)

2010-07-22

157

Carbon nanotube seeded silicon crystal growth  

NASA Astrophysics Data System (ADS)

Crystal growth of liquid silicon on the heterogeneous surfaces of carbon nanotubes (CNTs) is simulated. Silicon atoms are concentrated to form perfect coaxial cylindrical configurations around CNT cores. The heredity effect makes silicon imprint cylindrical shapes of CNTs during the solidification. The CNTs have a great influence on the stacking sequence of silicon atoms. Growth competition between CNT cores is clearly observed, which results in defects at the shared interface. The internal potential field around CNTs is responsible for growth competition and the heredity effect.

Li, Y. F.; Li, H.; Sun, F. W.; Zhang, X. Q.; Liew, K. M.

2011-07-01

158

Laser crystallization and localized growth of nanomaterials for solar applications  

NASA Astrophysics Data System (ADS)

Laser-assisted localized growth of semiconducting nanostructures is reported. As is the case of conventional crystal growth, localized laser enables three kinds of crystal growth: (1) melt growth (recrystallization) of amorphous silicon nanopillars by pulsed laser; (2) vapor growth (chemical vapor deposition) of germanium nanowires; (3) solution growth (hydrothermal growth) of zinc oxide nanowires. The results not only demonstrate programmable and digital fabrication of laser-assisted crystal growth, but also reveal unusual growth chacracteristics (grain morphologies, growth kinetics). Related to solar applications, it is suggested that these structures can act as epitaxial seeds for growth of coarse grains and as multi-spectral centers for enhanced and engineered light absorption.

In, Jungbin; Ryu, Sang-Gil; Lee, Daeho; Ahn, Sanghoon; Zheng, Andy Cheng; Hwang, David Jae-Seok; Grigoropoulos, Costas P.

2013-09-01

159

Crystal growth and annealing for minimized residual stress  

DOEpatents

A method and apparatus for producing crystals that minimizes birefringence even at large crystal sizes, and is suitable for production of CaF.sub.2 crystals. The method of the present invention comprises annealing a crystal by maintaining a minimal temperature gradient in the crystal while slowly reducing the bulk temperature of the crystal. An apparatus according to the present invention includes a thermal control system added to a crystal growth and annealing apparatus, wherein the thermal control system allows a temperature gradient during crystal growth but minimizes the temperature gradient during crystal annealing.

Gianoulakis, Steven E. (Albuquerque, NM)

2002-01-01

160

Growth Habits and Growth Rates of Snow Crystals  

Microsoft Academic Search

Equations are derived for the growth rates of snow crystals as they fall through the atmosphere in terms of the air temperature, supersaturation and their terminal velocities. The predicted maximum attainable diameters of regular hexagonal plates (0.84 mm), sector plates (ca. 2 mm) and stellar dendrites (3.5 mm) are in good agreement with observations based on Nakaya's large collection of

B. J. Mason

1993-01-01

161

Enhancing the Mechanical Properties of Single-Crystal CVD Diamond  

SciTech Connect

Approaches for enhancing the strength and toughness of single-crystal diamond produced by chemical vapor deposition (CVD) at high growth rates are described. CVD processes used to grow single-crystal diamond in high density plasmas were modified to incorporate boron and nitrogen. Semi-quantitative studies of mechanical properties were carried out using Vickers indentation techniques. The introduction of boron in single-crystal CVD diamond can significantly enhance the fracture toughness of this material without sacrificing its high hardness ({approx}78 GPa). Growth conditions were varied to investigate its effect on boron incorporation and optical properties by means of photoluminescence, infrared, and ultraviolet-visible absorption spectroscopy. Boron can be readily incorporated into single-crystal diamond by the methods used, but with nitrogen addition, the incorporation of boron was hindered. The spectroscopic measurements indicate that nitrogen and boron coexist in the diamond structure, which helps explain the origin of the enhanced fracture toughness of this material. Further, low pressure/high temperature annealing can enhance the intrinsic hardness of single-crystal CVD diamond by a factor of two without appreciable loss in fracture toughness. This doping and post-growth treatment of diamond may lead to new technological applications that require enhanced mechanical properties of diamond.

Liang, Q.; Yan, C; Meng, Y; Lai, J; Krasnicki, S; Mao, H; Hemley, R

2009-01-01

162

Lysozyme crystal growth kinetics in microgravity.  

PubMed

Mach-Zehnder interferometry is applied to quantitatively characterize growth of lysozyme crystals in microgravity. Experiments were performed by the Free Interface Diffusion technique into APCF FID reactors using large seeds. Tracking of the experiments using interferometry allowed to monitor the onset of supersaturation and the seed growth. A large and stable concentration depletion zone around the growing crystal developed, whose time evolution was analyzed. The interferograms were analyzed taking into account finite thickness of the cell by integrating the concentration over the straight lines through the optical path. It was concluded that there may be a quasi-steady state growth mode at the stage when the spacial concentration distribution did not change but its absolute value over all the cell was slowly diminishing. From this portion of the data, an estimate was made of the dimensionless parameter beta R/D where beta is the face kinetic coefficient, R is the effective crystal size and D is the lysozyme diffusivity in solution, as followed from the steady state model. For the assumed quasi steady state data portion, the parameter varies between 0.7 and 0.9 suggesting mixed diffusion-interface kinetic controlled growth. PMID:12351886

Otálora, Fermín; García-Ruiz, Juan Manuel; Carotenuto, Luigi; Castagnolo, Dario; Novella, María Luisa; Chernov, Alexander A

2002-09-26

163

Bulk Crystal Growth - Methods and Materials  

NASA Astrophysics Data System (ADS)

This chapter covers the field of bulk single crystals of materials used in electronics and optoelectronics. These crystals are used in both active and passive modes (to produce devices directly in/on bulk-grown slices of material, or as substrates in epitaxial growth, respectively). Single-crystal material usually provides superior properties to polycrystalline or amorphous equivalents. The various bulk growth techniques are outlined, together with specific critical features, and examples are given of the types of materials (and their current typical sizes) grown by these techniques. Materials covered range from Group IV (Si, Ge, SiGe, diamond, SiC), Group III-V (such as GaAs, InP, nitrides) Group II-IV (including CdTe, ZnSe, MCT) through to a wide range of oxide/halide/phosphate/borate materials. This chapter is to be treated as a snapshot only; the interested reader is referred to the remainder of the chapters in this Handbook for more specific growth and characterization details on the various materials outlined in this chapter. This chapter also does not cover the more fundamental aspects of the growth of the particular materials covered; for these, the reader is again referred to relevant chapters within the Handbook, or to other sources of information in the general literature.

Capper, Peter

164

Crystal Splitting in the Growth of Bi2S3  

SciTech Connect

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.

Tang, Jing; Alivisatos, A. Paul

2006-06-15

165

On the propulsion mechanism of "jumping" crystals.  

PubMed

A crystalline metal-organic complex undergoes a polymorphic transformation upon cooling below 215 K. Depending on the cooling rate, crystals exhibit different behaviours that include breaking and "jumping". Variable temperature X-ray diffraction (XRD) and optical microscopy have been employed to analyze the anisotropic changes of the crystallographic axes and propose a mechanism by which the crystals acquire the momentum for the jump. PMID:23999755

Lusi, Matteo; Bernstein, Joel

2013-09-17

166

Direction-specific interactions control crystal growth by oriented attachment.  

PubMed

The oriented attachment of molecular clusters and nanoparticles in solution is now recognized as an important mechanism of crystal growth in many materials, yet the alignment process and attachment mechanism have not been established. We performed high-resolution transmission electron microscopy 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 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. PMID:22628650

Li, Dongsheng; Nielsen, Michael H; Lee, Jonathan R I; Frandsen, Cathrine; Banfield, Jillian F; De Yoreo, James J

2012-05-25

167

Lead isotope variation with growth zoning in a galena crystal  

USGS Publications Warehouse

A large crystal of lead sulfide from Picher, Oklahoma, has significant differences in isotopic composition of lead in successive growth zones. Lead isotope ratios in the parent ore-fluid evidently changed with time during crystal growth. The growth history of this crystal, interpreted quantitatively, points to a tentative hypothesis of genesis of Mississippi Valley deposits of lead and zinc.

Cannon, Jr. , R. S.; Pierce, A. P.; Delevaux, M. H.

1963-01-01

168

Determining crystal growth kinetic parameters using optical fibre sensors  

NASA Astrophysics Data System (ADS)

The capability of an ‘intrinsic exposed core optical fibre sensor’ (IECOFS) as a monitoring device of scale formation has been evaluated. The IECOFS has been used to measure kinetics parameters of calcium carbonate heterogeneous crystal growth such as the activation energy, the crystal growth rate and the induction time. The IECOFS was able to evaluate crystal growth inhibition through the use of chemical inhibitors.

Boerkamp, M.; Lamb, D. W.; Lye, P. G.

2012-12-01

169

Thermocapillary free boundaries in crystal growth  

Microsoft Academic Search

A two-dimensional free boundary arising from the steady thermocapillary flow in a viscous incompressible fluid is studied numerically. The problem is considered in the context of the open-boat crystal-growth technique. The problem is solved numerically by a finite-element-method discretization. Three iterative methods are introduced for the computation of the free boundary. The nondimensional form of the problem gives rise to

C. Cuvelier; J. M. Driessen

1986-01-01

170

Dynamic pressure-induced dendritic and shock crystal growth of ice VI  

PubMed Central

Crystal growth mechanisms are crucial to understanding the complexity of crystal morphologies in nature and advanced technological materials, such as the faceting and dendrites found in snowflakes and the microstructure and associated strength properties of structural and icy planetary materials. In this article, we present observations of pressure-induced ice VI crystal growth, which have been predicted theoretically, but had never been observed experimentally to our knowledge. Under modulated pressure conditions in a dynamic-diamond anvil cell, rough single ice VI crystal initially grows into well defined octahedral crystal facets. However, as the compression rate increases, the crystal surface dramatically changes from rough to facet, and from convex to concave because of a surface instability, and thereby the growth rate suddenly increases by an order of magnitude. Depending on the compression rate, this discontinuous jump in crystal growth rate or “shock crystal growth” eventually produces 2D carpet-type fractal morphology, and moreover dendrites form under sinusoidal compression, whose crystal morphologies are remarkably similar to those predicted in theoretical simulations under a temperature gradient field. The observed strong dependence of the growth mechanism on compression rate, therefore, suggests a different approach to developing a comprehensive understanding of crystal growth dynamics.

Lee, Geun Woo; Evans, William J.; Yoo, Choong-Shik

2007-01-01

171

Crystal growth mechanism of VLS-Sm1+xBa2-xCu3Oy films including self-assembled BaZrO3 nanorods  

NASA Astrophysics Data System (ADS)

In order to improve a critical current density (Jc) under applied magnetic fields, an addition of BaMO3 (BMO; M = Zr, Sn) nanorods into REBa2Cu3Oy (REBCO) films is actively discussed. Although superconducting properties of the REBCO films are dramatically enhanced by self-assembled BMO nanorods, the growth mechanisms of the BMO nanorods have not been clarified yet. In this study, in order to clarify the growth mechanisms of the BZrO3 (BZO) nanorods and to further improve the superconducting properties, we fabricated a BZO-doped Sm1+xBa2-xCu3Oy (Sm+BZO) film by using modified Vapor-Liquid-Solid (VLS) technique (VLS-Sm+BZO/i). The in-field Jc of the VLS-Sm+BZO/i film showed 4.5 times higher than that of Sm+BZO film fabricated by conventional pulsed laser deposition method (PLD-Sm+BZO) at B = 4 T and the Jc-B-? curves of the VLS-Sm+BZO/i film was higher than that of the PLD-Sm+BZO film around the applied field angle of 40° against the c-axis of the SmBCO. From a TEM observation, we found that the BZO nanorods of VLS-Sm+BZO/i film grew discontinuously along the c-axis of the SmBCO.

Funaki, S.; Yoshida, Y.; Ichino, Y.; Takai, Y.; Ichinose, A.; Matsumoto, K.; Mukaida, M.; Horii, S.; Kita, R.

2009-10-01

172

Growth and adhesion properties of monosodium urate monohydrate (MSU) crystals  

NASA Astrophysics Data System (ADS)

The presence of monosodium urate monohydrate (MSU) crystals in the synovial fluid has long been associated with the joint disease gout. To elucidate the molecular level growth mechanism and adhesive properties of MSU crystals, atomic force microscopy (AFM), scanning electron microscopy, and dynamic light scattering (DLS) techniques were employed in the characterization of the (010) and (1-10) faces of MSU, as well as physiologically relevant solutions supersaturated with urate. Topographical AFM imaging of both MSU (010) and (1-10) revealed the presence of crystalline layers of urate arranged into v-shaped features of varying height. Growth rates were measured for both monolayers (elementary steps) and multiple layers (macrosteps) on both crystal faces under a wide range of urate supersaturation in physiologically relevant solutions. Step velocities for monolayers and multiple layers displayed a second order polynomial dependence on urate supersaturation on MSU (010) and (1-10), with step velocities on (1-10) generally half of those measured on MSU (010) in corresponding growth conditions. Perpendicular step velocities on MSU (010) were obtained and also showed a second order polynomial dependence of step velocity with respect to urate supersaturation, which implies a 2D-island nucleation growth mechanism for MSU (010). Extensive topographical imaging of MSU (010) showed island adsorption from urate growth solutions under all urate solution concentrations investigated, lending further support for the determined growth mechanism. Island sizes derived from DLS experiments on growth solutions were in agreement with those measured on MSU (010) topographical images. Chemical force microscopy (CFM) was utilized to characterize the adhesive properties of MSU (010) and (1-10). AFM probes functionalized with amino acid derivatives and bio-macromolecules found in the synovial fluid were brought into contact with both crystal faces and adhesion forces were tabulated into histograms for comparison. AFM probes functionalized with -COO-, -CH3, and -OH functionalities displayed similar adhesion force with both crystal surfaces of MSU, while adhesion force on (1-10) was three times greater than (010) for -NH2+ probes. For AFM probes functionalized with bovine serum albumin, adhesion force was three times greater on MSU (1-10) than (010), most likely due to the more ionic nature of (1-10).

Perrin, Clare M.

173

Mechanics and growth of tissues  

NASA Astrophysics Data System (ADS)

During development or during tumor growth, cells organize collectively by cell division and apoptosis in a tissue. The aim of our work is to build up theoretical tools based on non-equilibrium statistical mechanics and continuum mechanics to describe the mechanical properties of tissues and to apply them to various biologically relevant situations. We first show that because of the coupling between cell division and the local stress, a tissue can be considered as a visco-elastic liquid at time scales larger than the cell division time. We then show recent model experiments on cell aggregates showing the effect of mechanical stress on tissue growth. Finally, we use the hydrodynamic description to discuss the steady state structure of villis which are the protrusions of the surface of the intestine. We describe the formation of villis as a buckling instability of a polar cell monolayer. Similar instabilities occur as well for tube-like cellular structures such as arteries.

Joanny, Jean-Francois

2013-03-01

174

Synthesis, growth, structural, optical, spectral, thermal and mechanical studies of 4-methoxy 4-nitrostilbene (MONS): a new organic nonlinear optical single crystal.  

PubMed

4-Methoxy 4-nitrostilbene (MONS), a new organic nonlinear optical material has been synthesized. Based on the solubility data good quality single crystal with dimensions up to 38×11×3 mm(3) has been grown by slow evaporation method using ethyl methyl ketone (MEK) as a solvent. Powder XRD confirms the crystalline property and also the diffraction planes have been indexed. The lattice parameters for the grown MONS crystals were determined by using single crystal X-ray diffraction analysis and it reveals that the crystal lattice system is triclinic. The crystalline perfection of the grown crystals has been analysed by high resolution X-ray diffraction (HRXRD) rocking curve measurements. Fourier transform infrared (FTIR) spectrum for powdered MONS sample confirms the functional groups present in the grown crystal. The UV-vis absorption spectrum has been recorded in the range of 190-1100 nm and the cut off wavelength 499 nm has been determined. The optical constants of MONS have been determined through UV-vis-NIR spectroscopy. The MONS crystals were further subjected to other characterizations. i.e., (1)H NMR, TG/DTA, photoluminescence and microhardness test. The Kurtz and Perry powder technique confirms the NLO property of the grown crystal and the SHG efficiency of MONS was found to be 1.55× greater than that of KDP crystal. PMID:22929904

Dinakaran, Paul M; Bhagavannarayana, G; Kalainathan, S

2012-08-08

175

Synthesis, growth, structural, optical, spectral, thermal and mechanical studies of 4-methoxy 4-nitrostilbene (MONS): A new organic nonlinear optical single crystal  

NASA Astrophysics Data System (ADS)

4-Methoxy 4-nitrostilbene (MONS), a new organic nonlinear optical material has been synthesized. Based on the solubility data good quality single crystal with dimensions up to 38 × 11 × 3 mm3 has been grown by slow evaporation method using ethyl methyl ketone (MEK) as a solvent. Powder XRD confirms the crystalline property and also the diffraction planes have been indexed. The lattice parameters for the grown MONS crystals were determined by using single crystal X-ray diffraction analysis and it reveals that the crystal lattice system is triclinic. The crystalline perfection of the grown crystals has been analysed by high resolution X-ray diffraction (HRXRD) rocking curve measurements. Fourier transform infrared (FTIR) spectrum for powdered MONS sample confirms the functional groups present in the grown crystal. The UV-vis absorption spectrum has been recorded in the range of 190-1100 nm and the cut off wavelength 499 nm has been determined. The optical constants of MONS have been determined through UV-vis-NIR spectroscopy. The MONS crystals were further subjected to other characterizations. i.e., 1H NMR, TG/DTA, photoluminescence and microhardness test. The Kurtz and Perry powder technique confirms the NLO property of the grown crystal and the SHG efficiency of MONS was found to be 1.55× greater than that of KDP crystal.

Dinakaran, Paul M.; Bhagavannarayana, G.; Kalainathan, S.

2012-11-01

176

Alloy Semiconductor Crystal Growth Under Microgravity  

SciTech Connect

Microgravity studies on the dissolution and crystallization of In{sub x}Ga{sub 1-x}Sb have been done using a sandwich combination of InSb and GaSb as the starting material using the Chinese recoverable satellite. The same type of experiment was performed under 1G gravity condition for comparison. From these experiments and the numerical simulation, it is found that the shape of the solid/liquid interface and composition profile in the solution was found to be significantly affected by gravity. GaSb seed was dissolved faster than GaSb feed even though the GaSb feed temperature was higher than that of GaSb seed temperature. These results clearly indicate that solute transport due to gravity affects dissolution and growth processes of alloy semiconductor bulk crystals.

Hayakawa, Yasuhiro; Arivanandhan, Mukannan; Rajesh, Govindasamy; Tanaka, Akira [Research Institute of Electronics, Shizuoka University, Johoku 3-5-1, Naka-Ku, Hamamatsu, Shizuoka 432-8011 (Japan); Ozawa, Tetsuo [Shizuoka Institute of Science and Technology, 2200-2 Toyozawa, Fukuroi, Shizuoka 437-8555 (Japan); Okano, Yasunori [Graduate School of Engineering Science, Osaka University, 1-3 Machiganeyama, Osaka 560-8531 (Japan); Sankaranarayanan, Krishnasamy [Alagappa University, Karaikudi, Tamilnadu (India); Inatomi, Yuko [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510 (Japan)

2010-12-01

177

Thermocapillary free boundaries in crystal growth  

NASA Astrophysics Data System (ADS)

A two-dimensional free-boundary problem arising from the steady thermocapillary flow in a viscous fluid, whose motion is governed by the Navier-Stokes equations coupled with the heat conduction equation, is considered in the context of the open boat technique in crystal growth. The problem is formulated in a nondimensional form, producing six characteristic numbers. For the computation of the free boundary three iterative methods were used. Numerical experiments show the influence of the characteristic numbers on the flow field variables and on the shape of the free boundary.

Cuvelier, C.; Driessen, J. M.

178

Thermocapillary free boundaries in crystal growth  

NASA Astrophysics Data System (ADS)

A two-dimensional free boundary arising from the steady thermocapillary flow in a viscous incompressible fluid is studied numerically. The problem is considered in the context of the open-boat crystal-growth technique. The problem is solved numerically by a finite-element-method discretization. Three iterative methods are introduced for the computation of the free boundary. The nondimensional form of the problem gives rise to the following characteristic parameters: Reynolds, Grashof, Prandtl, Marangoni, Bond, Ohnesorge, and Biot numbers. The influence of these parameters on the flow field, the temperature distribution, and the shape of the free boundary is studied.

Cuvelier, C.; Driessen, J. M.

1986-08-01

179

Solid State Pathways to Complex Shape Evolution and Tunable Porosity during Metallic Crystal Growth.  

PubMed

Growing complex metallic crystals, supported high index facet nanocrystal composites and tunable porosity metals, and exploiting factors that influence shape and morphology is crucial in many exciting developments in chemistry, catalysis, biotechnology and nanoscience. Assembly, organization and ordered crystallization of nanostructures into complex shapes requires understanding of the building blocks and their association, and this relationship can define the many physical properties of crystals and their assemblies. Understanding crystal evolution pathways is required for controlled deposition onto surfaces. Here, complex metallic crystals on the nano- and microscale, carbon supported nanoparticles, and spinodal porous noble metals with defined inter-feature distances in 3D, are accomplished in the solid-state for Au, Ag, Pd, and Re. Bottom-up growth and positioning is possible through competitive coarsening of mobile nanoparticles and their site-specific crystallization in a nucleation-dewetted matrix. Shape evolution, density and growth mechanism of complex metallic crystals and porous metals can be imaged during growth. PMID:24026532

Valenzuela, Carlos Díaz; Carriedo, Gabino A; Valenzuela, María L; Zúñiga, Luis; O'Dwyer, Colm

2013-09-12

180

Solid State Pathways to Complex Shape Evolution and Tunable Porosity during Metallic Crystal Growth  

PubMed Central

Growing complex metallic crystals, supported high index facet nanocrystal composites and tunable porosity metals, and exploiting factors that influence shape and morphology is crucial in many exciting developments in chemistry, catalysis, biotechnology and nanoscience. Assembly, organization and ordered crystallization of nanostructures into complex shapes requires understanding of the building blocks and their association, and this relationship can define the many physical properties of crystals and their assemblies. Understanding crystal evolution pathways is required for controlled deposition onto surfaces. Here, complex metallic crystals on the nano- and microscale, carbon supported nanoparticles, and spinodal porous noble metals with defined inter-feature distances in 3D, are accomplished in the solid-state for Au, Ag, Pd, and Re. Bottom-up growth and positioning is possible through competitive coarsening of mobile nanoparticles and their site-specific crystallization in a nucleation-dewetted matrix. Shape evolution, density and growth mechanism of complex metallic crystals and porous metals can be imaged during growth.

Valenzuela, Carlos Diaz; Carriedo, Gabino A.; Valenzuela, Maria L.; Zuniga, Luis; O'Dwyer, Colm

2013-01-01

181

On the origin of size-dependent and size-independent crystal growth: Influence of advection and diffusion  

USGS Publications Warehouse

Crystal growth experiments were conducted using potassium alum and calcite crystals in aqueous solution under both non-stirred and stirred conditions to elucidate the mechanism for size-dependent (proportionate) and size-independent (constant) crystal growth. Growth by these two laws can be distinguished from each other because the relative size difference among crystals is maintained during proportionate growth, leading to a constant crystal size variance (??2) for a crystal size distribution (CSD) as the mean size increases. The absolute size difference among crystals is maintained during constant growth, resulting in a decrease in size variance. Results of these experiments show that for centimeter-sized alum crystals, proportionate growth occurs in stirred systems, whereas constant growth occurs in non-stirred systems. Accordingly, the mechanism for proportionate growth is hypothesized to be related to the supply of reactants to the crystal surface by advection, whereas constant growth is related to supply by diffusion. Paradoxically, micrometer-sized calcite crystals showed proportionate growth both in stirred and in non-stirred systems. Such growth presumably results from the effects of convection and Brownian motion, which promote an advective environment and hence proportionate growth for minute crystals in non-stirred systems, thereby indicating the importance of solution velocity relative to crystal size. Calcite crystals grown in gels, where fluid motion was minimized, showed evidence for constant, diffusion-controlled growth. Additional investigations of CSDs of naturally occurring crystals indicate that proportionate growth is by far the most common growth law, thereby suggesting that advection, rather than diffusion, is the dominant process for supplying reactants to crystal surfaces.

Kile, D. E.; Eberl, D. D.

2003-01-01

182

Nucleation-growth kinetics of the oxidation of silver nanocrystals to silver halide crystals  

Microsoft Academic Search

The electrochemical oxidation of silver nanocrystals to silver halide crystals proceeds by a process of nucleation and growth. The mechanism is confirmed by analyzing chronopotentiograms using a new extension of nucleation theory. The theory makes it possible to derive plots of nucleation-growth currents vs potential, and growth rates vs potential, directly from experimental data. Such plots yield powerful insights into

Ulrich Hasse; Stephen Fletcher; Fritz Scholz

2006-01-01

183

Dendritic Growth in Nematic Liquid Crystals  

NASA Astrophysics Data System (ADS)

The experimental study of the onset of electrohydrodynamic convection (EHC) through a dendritic growth is reported. If a magnetic Freedericksz-distorted liquid crystal of negative dielectric anisotropy is subjected to an electric field parallel to the magnetic field, EHC sets in through the nucleation of dendrites [1,2]. Measurements of tip speeds of the dendrites as a function of applied voltage at a fixed magnetic field are made. The goal is to explore the effect of the magnetic and electric fields on the dendritic growth. In addition, pattern dynamics is monitored once the final state of spatio-temporal chaos is reached by the system. [1] J. T. Gleeson, Nature 385, 511 (1997). [2] J. T. Gleeson, Physica A 239, 211 (1997). This research was supported by NSF grants DMR 9704579 and DMR 9619406.

Martin, Joshua; Garg, Shila

2000-03-01

184

Special phase transformation and crystal growth pathways observed in nanoparticles+  

PubMed Central

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.

Gilbert, Benjamin; Zhang, Hengzhong; Huang, Feng; Finnegan, Michael P; Waychunas, Glenn A; Banfield, Jillian F

2003-01-01

185

Growth and morphology of crystals: Theory and observations  

NASA Astrophysics Data System (ADS)

In the thesis, crystal growth and morphology, and the relationship between morphology and structure are investigated. Experimental observations and theoretical predictions on the growth and morphology of NH4N03, ((CH3)4N)2ZnCl(4-x)Br(x), and beta-triacyl-glycerol crystals based on the periodic bond chain approach are compared. The results of a study of in situ crystal growth of potassium hydrogenphthalate utilizing an on line digital imaging processing technique are presented.

Vogels, L.

186

Comment on "Evaluation of X-ray diffraction methods for determining the crystal growth mechanisms of clay minerals in mudstones, shales and slates," by L. N. Warr and D. R. Peacor  

USGS Publications Warehouse

A recent paper by Warr and Peacor (2002) suggested that our use of the Bertaut-Warren-Averbach technique (MudMaster computer program) for studying changes in crystallite thickness distributions (CTDs) of clay minerals during diagenesis and very low-grade metamorphism is not reliable because it is dependent on many variables which can not be fully controlled. Furthermore, the authors implied that the measured shapes of CTDs cannot be used with confidence to deduce crystal growth mechanisms and histories for clays, based on our CTD simulation approach (using the Galoper computer program). We disagree with both points, and show that the techniques are powerful, reliable and useful for studying clay mineral alteration in rocks. ?? 2003 Schweiz. Mineral. Petrogr. Ges.

Eberl, D. D.; Srodon, J.; Drits, V. A.

2003-01-01

187

New Aspects of Crystal Growth of Solid 4He Studied by Acoustic Wave  

NASA Astrophysics Data System (ADS)

The new aspects of crystal growth in solid 4He at low temperatures are revealed by manipulating the crystal with a radiation pressure of acoustic waves. The acoustic radiation pressure is generally a tiny nonlinear effect, but it has given unexpected effect on the surface of 4He owing to the markedly high growth rate of the crystal. Radiation pressure induces crystallization or melting. Owing to the strong temperature dependences of the growth rate of an atomically rough surface, which increases divergingly towards T=0, and the numerical value of the ratio of the sound velocities in both phases, the crystal melts at high temperatures when the sound wave is applied from the solid side, while it grows at low temperatures under the same conditions. We found a new type of growth mechanism of a c-facet driven by a strong radiation pressure. The growth rate of a c-facet was found to be much higher than the conventional screw-dislocation-mediated mechanism. Theoretical analysis that treated elementary steps as quantum mechanical quasi-particles reproduced the observed important feasures. The superflow around steps was taken into account as the kinetic energy of the steps. Finally, it was demonstrated that the use of radiation pressure enables the creation of negative crystals or superfluid bubbles in the crystal. Various interesting motions and shapes of the negative crystal were observed and interpreted using a simple model.

Okuda, Yuichi; Nomura, Ryuji

2008-11-01

188

Diffusion-controlled crystal growth in deeply undercooled melt on approaching the glass transition  

NASA Astrophysics Data System (ADS)

Crystal-growth velocity in metallic melts has been reported by others to increase monotonically with undercooling. Nevertheless, such an observation is not predicted by conventional growth theory. In this work, the metallic melt of Zr50Cu50 is studied to address the problem by measuring the growth velocity over a wide range of undercooling up to 325 K. A maximum growth velocity is observed at an undercooling of 200 K instead of the monotonic increase reported in the literature. We find that the planar or dendrite growth theories can explain the value of the maximum growth velocity, but the predicted location of the maximum in undercooling is far less than that seen by experiment. With the assistance of current results, a general pattern of crystal growth is established for melts of a variety of substances, where all sluggish crystal-growth kinetics is explained by the diffusion-controlled mechanism at deep undercooling.

Wang, Q.; Wang, Li-Min; Ma, M. Z.; Binder, S.; Volkmann, T.; Herlach, D. M.; Wang, J. S.; Xue, Q. G.; Tian, Y. J.; Liu, R. P.

2011-01-01

189

Growth and characterization of L-tryptophan doped KDP crystals  

NASA Astrophysics Data System (ADS)

Potassium Dihydrogen Phosphate crystals are one of the most popular crystals used for Non-linear Optical applications. Most of the amino acids also exhibit NLO properties. The effect of doping of one of the amino acids, L-tryptophan in KDP crystals has been investigated. Pure and L-tryptophan doped KDP crystals were grown by slow solvent evaporation solution growth technique. Good quality transparent crystals were obtained. Doping of L-tryptophan in KDP crystal was confirmed by FT-IR spectroscopy studies. The value of second harmonic generation efficiency and optical transmission in UV-Vis spectra increased as doping of L-tryptophan increased in KDP crystals.

Parikh, K. D.; Dave, D. J.; Parekh, B. B.; Joshi, M. J.

2013-06-01

190

Crystal growth of YBCO coated conductors by TFA MOD method  

NASA Astrophysics Data System (ADS)

The crystal growth mechanism of TFA (trifluoroacetates) MOD (metal organic deposition) derived YBa2Cu3Oy has been investigated to understand the process for higher production rates of the conversion process. YBCO films were prepared by TFA MOD on CeO2/Gd2Zr2O7/Hastelloy C276 substrates. The growth rates of YBCO derived from Y:Ba:Cu = 1:2:3 and 1:1.5:3 starting solutions were investigated by XRD and TEM analyses. YBCO growth proceeds in two steps of the epitaxial one from the substrate and solid state reaction. The overall growth rate estimated from the residual amounts of BaF2 with time measured by XRD is proportional to a square root of P(H2O). The trend was independent of the composition of starting solutions, however, the growth rate obtained from the 1:1.5:3 starting solutions was high as twice as that of 1:2:3, which could not be explained by the composition of BaF2 included in the precursor films. On the other hand, the growth rate measured from the thickness of the YBCO quenched film at the same process time showed no difference between the samples of 1:2:3 and 1:1.5:3. The epitaxial growth rate of 1:1.5:3 was also the same as the overall growth rate of that, which means there was no solid state reaction to form YBCO after the epitaxial growth. The YBCO growth mechanism was found to be as follows; YBCO crystals nucleate at the surface of the substrate and epitaxially grow into the precursor by layer-by-layer by a manner with trapping unreacted particles. The amounts of YBCO and the unreacted particles trapped in the YBCO film are independent of the composition of the starting solution in this step. Unreacted particles react with each other to form YBCO and pores by solid state reaction as long as there is BaF2 left in the film. The Ba-poor starting solution gives little BaF2 left in the film and so the solid state reaction is completed within a short time, resulting in the fast overall growth rate.

Yoshizumi, M.; Nakanishi, T.; Matsuda, J.; Nakaoka, K.; Sutoh, Y.; Izumi, T.; Shiohara, Y.

2008-09-01

191

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

NASA Astrophysics Data System (ADS)

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.

Chauhan, Chetan K.; Joshi, Mihir J.

2013-01-01

192

Crystal growth and properties of Yb:FAP laser crystal  

NASA Astrophysics Data System (ADS)

A large and transparent Yb:FAP crystal with dimensions up to ?30 mm×85 mm has been grown by the Czochralski method. The preparation of the raw material has been investigated. X-ray power diffraction studies of Yb:FAP crystal confirm that the as-grown crystal is isostructural with the FAP crystal. The crystalline quality has been studied using X-ray rocking curve analysis. The segregation coefficient of Yb3+ in the Yb:FAP crystal has been also determined. Linear thermal expansion coefficients in [0 0 1] and [1 0 0] directions have been measured in the 30 800 °C temperature range.

Song, Pingxin; Zhao, Zhiwei; Xu, Xiaodong; Deng, Peizhen; Xu, Jun

2005-04-01

193

Flux growth of (Pb,La)(Zr, Sn,Ti)O 3 single crystals and their characterization  

Microsoft Academic Search

Lead lanthanum zirconate titanate stannate (PLZST) single crystals have been successfully grown by a flux method using KF as flux. Well-developed single crystals with sizes of 2.0mm×2.0mm×1.5mm were obtained for the first time. The crystal morphology was studied and related to a layer growth mechanism controlled by two-dimensional growth. Crystal structure measured by X-ray diffraction technique was single perovskite. The

Lihong Xue; Qiang Li; Yiling Zhang; Xihe Zhen; Rui Liu; Lin Wang

2005-01-01

194

Growth phenomena in the surface layer and step generation from the edges of faceted crystals  

SciTech Connect

The mechanism of growth step generation from the edges of faceted crystals obtained from experimental results with KDP crystals is described. It shows that growth from the crystal edges is initiated by the deviation of the edges from their crystallographic orientation and formation of incomplete shapes of singular facets. The conditions for formation of the incomplete faceted shapes during dislocation growth are considered. It is shown that the process of step generation from the edges is determined by the mutual positions of the vicinal slopes on the adjacent faces.

Carman, L; Smolsky, I; Zaitseva, N P

1999-07-29

195

Vapor-phase hydrothermal growth of novel segmentally configured nanotubular crystal structure.  

PubMed

A new form of nanotubular crystal structure is directly grown by a vapor-phase hydrothermal method via an epitaxial orientated crystal growth mechanism. The as-prepared nanotubes possess a unique multi-tunnel core-shell layered nanotubular structure with droplet shaped polygonal periphery and segmental crystal configuration. They are dimension-tunable and demonstrate superior ion exchange properties in terms of exchange rate and ion accommodating capacity. PMID:23589320

Liu, Porun; Zhang, Haimin; Liu, Hongwei; Wang, Yun; An, Taicheng; Cai, Weiping; Yang, Huagui; Yao, Xiangdong; Zhu, Guangshan; Webb, Robyn; Zhao, Huijun

2013-04-16

196

Rapid growth of KDP crystal with new additive  

Microsoft Academic Search

A chelating reagent sulfosalicylic acid (SSA) as a new additive was added into the KDP solutions in a small amount (1wt%) and metastable zone widths were measured for different saturation temperatures when compared to the pure system. Potassium dihydrogen orthophosphate crystals were rapidly grown from both pure and SSA-added solutions by adopting the same crystal growth procedure. The crystal grown

Guohui Li; Genbo Su; Xinxin Zhuang; Zhengdong Li; Youping He

2004-01-01

197

Investigation on Growth and Surface Analysis of DAST Single Crystals  

SciTech Connect

We have explored the growth of bulk size N, N-dimethylamino-N'-methylstilbazolium p-toluenesulphonate (DAST) using slope nucleation method. The grown crystal was characterized by single crystal X-ray diffraction (XRD), and CHN analyses. The surface morphology of the crystal was analyzed using Scanning electron microscopy (SEM).

Thomas, Tina; Vijay, R. Jerald; Gunaseelan, R.; Sagayaraj, P. [Department of Physics, Loyola College, Chennai - 600 034 (India)

2011-07-15

198

Czochralski silicon crystal growth: Modeling and simulation study  

Microsoft Academic Search

Czochralski (CZ) crystal growth process is a widely used technique in the manufacturing of silicon crystals and other semiconductor materials such as germanium (Ge) and gallium arsenide (GaAs). The ultimate goal for the Integrated Circuit (IC) industry is to have the highest quality substrate. There is a huge interest to manipulate the thermal field in both the melt and crystal

Massoud Javidi

2006-01-01

199

Study of growth of calcium carbonate crystals on chitosan film  

Microsoft Academic Search

Biomimetic heterogeneous nucleation and growth of calcium carbonate crystals on the chitosan film as the template took place in supersaturated calcium bicarbonate solution. The specimen were characterized by optical microscopy, scanning electron microscopy, X-ray diffraction, attenuated total reflectance infrared spectroscopy. The obtained crystals proved to be calcite in sheets composed of fine crystal particles. Lab results indicated that proper additives

Fengying Zhang; Jie Wang; Zhengchi Hou; Ming Yu; Leidong Xie

2006-01-01

200

Nucleation and crystal growth of calcium sulfite hemihydrate  

Microsoft Academic Search

In slurry scrubbing processes for flue gas desulfurization the precipitation rate of calcium sulfite affects scrubber solution composition, SOâ absorption, sulfite oxidation, and limestone utilization. Sludge quality and disposal costs are also a function of precipitation kinetics. The nucleation and crystal growth rates of calcium sulfate hemihydrate were measured in a continuous flow crystallizer at conditions that produced agglomerate crystals,

C. L. Gleason; G. T. Rochelle

2009-01-01

201

Luminescence labeling and dynamics of growth active crystal surface structures  

NASA Astrophysics Data System (ADS)

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 only recognize some propagating steps as opposed to others, but preferentially choose between kinks propagating in opposing directions on the same step. Beyond providing the first experimental test of the CS proposal, this work is aimed at understanding the nucleation, evolution, and impurity interactions of growth-induced screw dislocations, a necessary ingredient for the growth of crystals at low supersaturation.

Bullard, Theresa Vivian

202

Effect of ferricenium salts on the crystal growth of hydroxyapatite in aqueous solution  

Microsoft Academic Search

The crystal growth of hydroxyapatite (HAP), the thermodynamically most stable calcium phosphate phase at 37°C, pH7.40 and ionic strength 0.15M in the presence of ferrocene complexes has been investigated by the constant composition technique. The kinetic results showed a surface diffusion controlled mechanism. The presence of ferricenium salts inhibited the crystal growth of HAP possibly through adsorption onto the active

S. Koutsopoulos; E Pierri; E Dalas; N Tzavellas; N Klouras

2000-01-01

203

Crystal Growth Kinetics of Nanocrystalline ZnS under Surface Adsorption  

Microsoft Academic Search

The crystal growth mechanism, kinetics, and microstructure development play a fundamental role in tailoring the materials with controllable size and morphology. In this study, by introducing the strong surface adsorption of the concentrated NaOH, two-stage crystal growth kinetics of ZnS nanoparticles was observed. In the first stage, the primary particles grow into a size over a hundred times of the

ZHANG Jinga

204

Crystal growth and characterization of 9,10-diphenylanthracene  

NASA Astrophysics Data System (ADS)

In this paper we report on the crystal growth and characterization of 9,10-diphenylanthracene. Crystals of 9,10-diphenylanthracene (DPA) were grown by the solution growth technique as well as the vertical Bridgman method. In case of the solution growth technique, several organic solvents were investigated including heptane, cyclohexane, toluene, and p-xylene. The largest crystals of the highest quality were obtained from toluene and xylene. In the case of vertical Bridgman, evacuated silica ampoules were used to grow large single crystals of DPA. Crystals grown by this method exhibit excellent scintillation properties.Radioluminescence spectra of DPA crystals exhibit a broad emission band peaking at 475 nm. DPA crystals show high light yields of up to 20,000 ph/MeV and a fast scintillation decay of less than 20 ns. Fast neutron detection was achieved using a 252Cf source.

van Loef, Edgar V.; Mukhopadhyay, Sharmistha; Zaitseva, Natalia; Payne, Steve; Shah, Kanai S.

2012-08-01

205

Effect of L-Valine on the growth and characterization of Sodium Acid Phthalate (SAP) single crystals  

NASA Astrophysics Data System (ADS)

Undoped and amino acid doped good quality single crystals of Sodium Acid Phthalate crystals (SAP) were grown by slow evaporation solution growth technique which are semiorganic in nature. The effect of amino acid (L-Valine) dopant on the growth and the properties of SAP single crystal was investigated. The single crystal X-ray diffraction studies and FT-IR studies were carried out to identify the crystal structure and the presence of functional groups in undoped and L-Valine doped SAP crystals. The transparent nature of the grown crystal was observed using UV-Visible spectrum. The thermal decomposition of the doped SAP crystals was investigated by thermo gravimetric analysis (TGA) and differential thermal analysis (DTA). The enhancement in the NLO property of the undoped and L-Valine doped SAP crystals using KDP crystal as a reference was studied using SHG measurements. Vickers micro hardness measurements are used for the study of mechanical strength of the grown crystals.

Nirmala, L. Ruby; Prakash, J. Thomas Joseph

2013-06-01

206

Taylor vortices formed in the melt during paratellurite crystal growth  

SciTech Connect

The hydrodynamics of tellurium dioxide melt during Czochralski growth of paratellurite crystals with a diameter up to 80 mm was experimentally investigated. The images of the melt surface during crystal growth are obtained. It is shown that a stable system of Taylor vortices in the form of two convection cells is formed at definite Reynolds numbers.

Kolesnikov, A. I., E-mail: Ivan.Kaplunov@tversu.ru; Grechishkin, R. M.; Tret'yakov, S. A.; Gritsunova, O. V.; Vorontsova, E. Yu. [Tver State University (Russian Federation)

2008-12-15

207

Growth rate dispersion of single potassium alum crystals  

Microsoft Academic Search

The dispersion of growth rates is a lively discussed matter. However, still no acceptable explanation exists for the reason of the phenomenon describing that crystals of the same size growing under the same constant environmental conditions (as supersaturation, temperature and hydrodynamics) might grow with different rates. The individual face-specific growth rates of potassium aluminium alum crystals (diameter 1–3 mm) have

Rolf Lacmann; Ulrike Tanneberger

1995-01-01

208

Oscillatory zoning: a pathological case of crystal growth  

Microsoft Academic Search

A new theory of oscillatory zoning in naturally grown plagioclase crystals is presented. This describes explicitly the coupling between the interface kinetics and the diffusion of chemical species in the melt. The crystal growth rate R responds with a finite delay time to concentration changes at the interface. Thus the growth rate cannot be simply some function of the supersaturation.

Claude J. Allègre; Ariel Provost; Claude Jaupart

1981-01-01

209

Hard sphere crystal nucleation and growth near large spherical impurities  

NASA Astrophysics Data System (ADS)

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.

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

210

Sizes and spatial relationships of crystals in granitic plutons: Exploring the crystallization gaps, heterogeneous nucleation, and mechanical clustering of crystals  

NASA Astrophysics Data System (ADS)

Quantitative measurements on magmatic textures provide an important insight into nucleation and growth rates as well as mechanical effects such as crystal settling and melt extraction in magma reservoirs. Crystal size distribution (CSD) measurements and spatial analysis are routinely applied to dilute volcanic suspensions but comparable data on holocrystalline multiphase plutonic rocks are uncommon. We present quantitative description of CSDs and spatial relationships for all rock-forming minerals from an intrusive suite of the Fichtelgebirge/Smr?iny granite batholith in central Europe. This composite body represents two spatially unrelated chambers, consisting of peraluminous biotite, two-mica, and tourmaline-muscovite granites, crystallized as texturally diverse batches covering equigranular, serial porphyritic, and hiatal porphyritic fine- to coarse-grained types. All granite samples exhibit straight to concave-up CSDs in the natural log of population density vs. crystal size projection. Straight CSDs were only found in fine-grained biotite-rich granites representing early crystallizing roof facies of the batholith. For all other samples, the slope decreases from -65 to nearly 0 mm-1 as grain size increases. The curvature can result from superposition of two quasilinear segments. It cannot be produced by two separate crystallization events because the population of larger grains is about 10 times more abundant by volume than the fine one. Instead, we propose that the concave-up CSDs developed in situ, with enhanced nucleation and/or reduced growth rates during the final stage of solidification. Spatial analysis and measurements of contact relationships reveal significant clustering of crystals except near the roof of the batholith. The clustering index decreases to 0.6 for the smallest crystals (random = 1), Ripley's Ľ-function reaches 0.8 mm, and the clusters are mineral sensitive: pairs of like phases appear to be more clustered than the unlike pairs. The observed parameters were reproduced by a three-dimensional numerical model with time-dependent nucleation and growth rates, and with variable degree of clustering induced by changing the ratio of homogeneous vs. heterogeneous nucleation rate, between

Špillar, V.; Dolejš, D.

2012-04-01

211

Controlled Growth of Organic Semiconductor Films Using Liquid Crystal Solvents  

NASA Astrophysics Data System (ADS)

Interest in using organic semiconductors in applications such as large area displays, photovoltaic devices, and RFID tags stems in part from their prospects for enabling significantly reduced manufacturing costs compared to traditional inorganic semiconductors. However many of the best performing prototype devices produced so far have involved expensive or time-consuming fabrication methods, such as the use of single crystals or thin films deposited under high vacuum conditions. We present a new approach for growing low molecular weight organic crystalline films at ambient conditions based on a vapor-liquid-solid growth mechanism using thermotropic nematic liquid crystal (LC) solvents. Tetracene is deposited via atmospheric-pressure sublimation onto substrates coated by a LC layer oriented using rubbed polyimide, producing films that are highly crystalline, with large grain sizes, and possessing macroscopic uniaxial orientation. This poster will describe the growth mechanism, discuss the effects of processing conditions such as LC layer thickness, substrate temperature and flux rate, and compare the results to a model of diffusion limited aggregation accounting for the finite thickness of the solvent layer.

Bufkin, Kevin; Ohlson, Brooks; Hillman, Ben; Johnson, Brad; Patrick, David

2008-03-01

212

Controlled Growth of Organic Semiconductor Films Using Liquid Crystal Solvents  

NASA Astrophysics Data System (ADS)

Interest in using organic semiconductors in applications such as large area displays, photovoltaic devices, and RFID tags stems in part from their prospects for enabling significantly reduced manufacturing costs compared to traditional inorganic semiconductors. However many of the best performing prototype devices produced so far have involved expensive or time-consuming fabrication methods, such as the use of single crystals or thin films deposited under high vacuum conditions. We present a new approach for growing low molecular weight organic crystalline films at ambient conditions based on a vapor-liquid-solid growth mechanism using thermotropic nematic liquid crystal (LC) solvents. Tetracene is deposited via atmospheric-pressure sublimation onto substrates coated by a LC layer oriented using rubbed polyimide, producing films that are highly crystalline, with large grain sizes, and possessing macroscopic uniaxial orientation. This poster will describe the growth mechanism, discuss the effects of processing conditions such as LC layer thickness, substrate temperature and flux rate, and compare the results to a model of deposition-diffusion aggregation accounting for the finite thickness of the solvent layer.

Bufkin, Kevin; Ohlson, Brooks; Hillman, Ben; Johnson, Brad; Patrick, David

2008-05-01

213

Continuum models of crystal growth from atomic beams with and without desorption  

Microsoft Academic Search

Continuum equations appropriate to describe crystal growth from atom beams are derived in various cases. When desorption is important, the growth is described on very long lengthscales by the Kardar-Parisi-Zhang equation, but should be corrected for shorter lengthscales where surface diffusion is the dominant mechanism. In the absence of desorption, an important effect at sufficiently low temperature comes from the

J. Villain

1991-01-01

214

Crystallization mechanisms in convective particle assembly.  

PubMed

Colloidal particles are continuously assembled into crystalline particle coatings using convective fluid flows. Assembly takes place inside a meniscus on a wetting reservoir. The shape of the meniscus defines the profile of the convective flow and the motion of the particles. We use optical interference microscopy, particle image velocimetry, and particle tracking to analyze the particles' trajectory from the liquid reservoir to the film growth front and inside the deposited film as a function of temperature. Our results indicate a transition from assembly at a static film growth front at high deposition temperatures to assembly in a precursor film with high particle mobility at low deposition temperatures. A simple model that compares the convective drag on the particles to the thermal agitation explains this behavior. Convective assembly mechanisms exhibit a pronounced temperature dependency and require a temperature that provides sufficient evaporation. Capillary mechanisms are nearly temperature independent and govern assembly at lower temperatures. The model fits the experimental data with temperature and particle size as variable parameters and allows prediction of the transition temperatures. While the two mechanisms are markedly different, dried particle films from both assembly regimes exhibit hexagonal particle packings. We show that films assembled by convective mechanisms exhibit greater regularity than those assembled by capillary mechanisms. PMID:22559295

Born, Philip; Munoz, Andres; Cavelius, Christian; Kraus, Tobias

2012-05-18

215

Needs and Opportunities in Crystal Growth.  

ERIC Educational Resources Information Center

|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)|

Mroczkowski, Stanley

1980-01-01

216

Needs and Opportunities in Crystal Growth.  

ERIC Educational Resources Information Center

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)

Mroczkowski, Stanley

1980-01-01

217

Calcite crystal growth rate inhibition by polycarboxylic acids  

USGS Publications Warehouse

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.

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

2001-01-01

218

Growth and defects of explosives crystals.  

National Technical Information Service (NTIS)

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 ...

H. H. Cady

1992-01-01

219

Calcite Crystal Growth Rate Inhibition by Polycarboxylic Acids  

Microsoft Academic Search

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

Michael M. Reddy; Anthony R. Hoch

2001-01-01

220

Progress in the crystal growth of Ce:LiSAF  

Microsoft Academic Search

Although the growth of chromium doped LiSrAlF6 has been developed to produce long boules of near-scatter-free material, the doping of LiSAF with cerium introduces different variables into the growth of high optical quality laser crystals. The main crystal growth issue for Ce:LiSAF is the charge compensation mandated by the substitution of the trivalent cerium ion for divalent strontium, which is

V. K. Castillo; G. J. Quarles

1995-01-01

221

Programmed crystallization via epitaxial growth and ligand replacement towards hybridizing porous coordination polymer crystals.  

PubMed

Hybridized porous coordination polymers (PCPs) are synthesized through epitaxial growth or ligand replacement. Whereas epitaxial growth on the core crystal leads to a sandwich type PCP, ligand replacement near the surface of core crystal results in a core-shell type PCP. PMID:23612878

Hirai, Kenji; Chen, Kebi; Fukushima, Tomohiro; Horike, Satoshi; Kondo, Mio; Louvain, Nicolas; Kim, Chiwon; Sakata, Yoko; Meilikhov, Mikhail; Sakata, Osami; Kitagawa, Susumu; Furukawa, Shuhei

2013-04-23

222

Theory of the intermediate stage of crystal growth with applications to protein crystallization  

Microsoft Academic Search

A closed form solution is found for the Buyevich–Mansurov theory of the intermediate stage of crystal growth. Using a common model for the growth rate, expressions for the time-dependent relative supersaturation and the distribution function for crystal sizes are found. With these results, the rate of homogeneous nucleation is established and need not be given as a boundary condition. The

D. A. Barlow

2009-01-01

223

Crystal growth history of quartz in the Ordovician Millbrig K-bentonite  

NASA Astrophysics Data System (ADS)

Crystal size distribution (CSD) analysis has been applied to quartz crystals of the Ordovician Millbrig K-bentonite, which represents one of the largest known fallout ash deposits in the Phanerozoic Era, to establish crystal growth histories and conditions in the magma chamber prior to eruption. Specific CSDs of the quartz crystals of the Millbrig K-bentonite were examined to establish their growth conditions prior to the eruption. On the crystal size distribution plot, all Millbrig samples exhibit concave-down shapes in agreement with previously reported CSDs on large silicic systems [1] but in contrast to more mafic systems characterized by linear CSDs. Crystal growth mechanisms responsible for the concave down CSDs are thought to be surface-controlled crystal growth followed by a episode of textural coarsening. Although all samples follow concave-down shapes, two samples exhibit rather different CSD shapes. These findings appear to fingerprint a separate magma batch with different crystal growth conditions. These ash beds appear to be a product of a series of separate eruptions that represent separate magma layers or batches, each with slightly different crystal growth conditions. Haynes [2] interpreted the multiple ash layers as either a product of several periods of eruptive activity or the cumulative effect of an evolving magma chamber during a single massive eruptive event. Our data support the model of several periods of eruptive activity that was closely spaced in time. The two of the eight Millbrig samples must have come from an earlier phase eruption and are part of a basal section that have not been preserved in the stratigraphic record and lacks lateral continuity in distal parts of the deposits. Therefore, the multiple ash beds in the Millbrig must have been a product of series of separate eruptions that represent separate magma layers or batches that had different crystal growth conditions. Although conclusions on crystallization processes and the origin of deposits cannot be drawn from CSD shapes alone, it is shown here that CSDs of a fallout ash deposit can be used to fingerprint separate magma batches, provide valuable information on crystal growth rates as well as the nature of the crystal growth mechanisms of quartz crystals. [1] Bindeman (2003) Geology 31, 367-370. [2] Haynes (1994) Geol. Soc. Am Spec. Pap. 290, 1-80.

Huff, W. D.; Inanli, F. O.

2011-12-01

224

Simulating micrometre-scale crystal growth from solution.  

PubMed

Understanding crystal growth is essential for controlling the crystallization used in industrial separation and purification processes. Because solids interact through their surfaces, crystal shape can influence both chemical and physical properties. The thermodynamic morphology can readily be predicted, but most particle shapes are actually controlled by the kinetics of the atomic growth processes through which assembly occurs. Here we study the urea-solvent interface at the nanometre scale and report kinetic Monte Carlo simulations of the micrometre-scale three-dimensional growth of urea crystals. These simulations accurately reproduce experimentally observed crystal growth. Unlike previous models of crystal growth, no assumption is made that the morphology can be constructed from the results for independently growing surfaces or from an a priori specification of surface defect concentration. This approach offers insights into the role of the solvent, the degree of supersaturation, and the contribution that extended defects (such as screw dislocations) make to crystal growth. It also connects observations made at the nanometre scale, through in situ atomic force microscopy, with those made at the macroscopic level. If extended to include additives, the technique could lead to the computer-aided design of crystals. PMID:16267550

Piana, Stefano; Reyhani, Manijeh; Gale, Julian D

2005-11-01

225

Numerical computations of faceted pattern formation in snow crystal growth.  

PubMed

Faceted growth of snow crystals leads to a rich diversity of forms with remarkable sixfold symmetry. Snow crystal structures result from diffusion-limited crystal growth in the presence of anisotropic surface energy and anisotropic attachment kinetics. It is by now well understood that the morphological stability of ice crystals strongly depends on supersaturation, crystal size, and temperature. Until very recently it was very difficult to perform numerical simulations of this highly anisotropic crystal growth. In particular, obtaining facet growth in combination with dendritic branching is a challenging task. We present numerical simulations of snow crystal growth in two and three spacial dimensions using a computational method recently introduced by the present authors. We present both qualitative and quantitative computations. In particular, a linear relationship between tip velocity and supersaturation is observed. In our computations, surface energy effects, although small, have a pronounced effect on crystal growth. We compute solid plates, solid prisms, hollow columns, needles, dendrites, capped columns, and scrolls on plates. Although all these forms appear in nature, it is a significant challenge to reproduce them with the help of numerical simulations for a continuum model. PMID:23005427

Barrett, John W; Garcke, Harald; Nürnberg, Robert

2012-07-26

226

Critical Supersaturation for Ice Crystal Growth: Laboratory Measurements and Atmospheric Modeling Implications  

NASA Astrophysics Data System (ADS)

An improved understanding of ice crystal growth, particularly at low temperatures, is much in demand for the advancement of numerical modeling of atmospheric processes. Cirrus models must contend with the complexity of ice crystals growing in cold temperatures, low pressures, low supersaturations, and with multiple nucleation mechanisms. Recent observations have allowed increasingly realistic parameterizations of cirrus ice crystal microphysics, but these observations need to be supplemented by a fundamental understanding of growth processes affecting low-temperature crystals. Several experimental studies have demonstrated that certain ice crystals require a minimum "critical" supersaturation before exhibiting detectable growth. These crystals are presumed to be essentially defect-free, preventing vicinal hillock growth at the site of crystal dislocations. In the case of crystal growth by spiral dislocation, advancement of faces begins as soon as supersaturation is present. The finding of conditional critical supersaturations have analogies in other materials (metals, semiconductors, potassium dihydrogen phosphate) and are thermodynamically predicted given a two-dimensional nucleation growth mechanism. Previous measurements have determined the critical supersaturation for ice as a function of temperature and crystallographic face from 0 to --15° C with extrapolation to --30° C. For both basal and prism faces, critical supersaturation is seen to increase with decreasing temperature, suggesting that low-temperature, low-supersaturation processes are most likely to be affected by this critical contingency. We present laboratory results to verify and extend prior critical supersaturation measurements using a novel approach for supersaturation generation, control, and measurement. The crystals are grown on the tip of a fine glass fiber ( ˜10 microns in diameter) under varying conditions of temperature, pressure, and saturation. Supersaturation is generated when a pre-saturated airflow passes over a coil of ice warmed by electrical resistance upstream from the growing crystal. Supersaturation is determined by a system of differential thermocouples calibrated to sulfuric acid drop size measurements. Measurements follow those made in earlier studies, but also extend to temperatures of --45° C, mimicking conditions found in some high altitude clouds.

Magee, N.; Moyle, A.; Lamb, D.

2003-12-01

227

Dynamic crystallization of cocoa butter. II. Morphological, thermal, and chemical characteristics during crystal growth  

Microsoft Academic Search

After an induction period, crystallization of cocoa butter under dynamic conditions at 26.5C occurs in two stages, primary\\u000a and secondary. The primary stage involves nucleation, crystal growth, aggregation, and sintering. Crystals formed during the\\u000a primary stage were slightly or non-birefringent, and had long, irregular-shaped filaments. The secondary stage was initiated\\u000a by the formation of spherulites. Total crystallization time may depend

Siree Chaiseri I; Paul S. Dimick

1995-01-01

228

Effects of anions on rapid growth and growth habit of KDP crystals  

Microsoft Academic Search

The synthesis of KDP from its raw material has been found exist in the growth solution. In the crystal growth experiment, significant extension of specific faces was observed at low dopant concentration. At high doping concentration, the growth rate of the whole crystal decreased with no significant habit modification. The inhibiting effects of phosphite and other H-bonding anionic ions on

You-Jun Fu; Zhang-Shou Gao; Xun Sun; Shen-Lai Wang; Yi-ping Li; Hong Zeng; Jian-Ping Luo; Ai-Dong Duan; Ji-Yang Wang

2000-01-01

229

Second harmonic chalcone crystal: Synthesis, growth and characterization  

NASA Astrophysics Data System (ADS)

The novel nonlinear optical chalcone derivative (2E)-3-[4-(methylsulfanyl)phenyl]-1-(3-bromophenyl)prop-2-en-1-one (3Br4MSP) crystals have been grown by slow evaporation technique at ambient temperature. The crystal was subjected to different types of characterization method in order to study its possible application in nonlinear optics. The structure determination of the grown crystal was done by single crystal X-ray diffraction study. The morphology of the crystal is studied. The crystal was subjected to thermal analysis to find its thermal stability. The grown crystals were characterized for their optical transmission and mechanical hardness. The second harmonic generation (SHG) efficiency of the crystal is obtained by classical powdered technique. The laser damage threshold for 3Br4MSP crystal was determined using Q-switched Nd:YAG laser.

D'Silva, E. D.; Narayan Rao, D.; Philip, Reji; Butcher, Ray J.; Rajnikant; Dharmaprakash, S. M.

2011-05-01

230

Control of Protein Crystal Nucleation and Growth Using Stirring Solution  

NASA Astrophysics Data System (ADS)

We have previously developed a protein crystallization technique using a stirring protein solution and revealed that (i) continuous stirring prevents excess spontaneous nucleation and accelerates the growth of protein crystals and (ii) prestirring (solution stirring in advance) promotes the crystal nucleation of hen egg-white lysozyme. In bovine adenosine deaminase (ADA) crystallization, continuous stirring improves the crystal quality but elongates the nucleation time. In this paper, in order to control both the crystal nucleation and growth of ADA using a Micro-Stirring technique, we carried out five different stirring patterns such as (i) no stirring, (ii) continuous stirring, (iii) prestirring, (iv) poststirring (stirring late in the growth period) and (v) restirring (combined pre- and poststirring). The results showed that high-quality well-shaped crystals were obtained under the continuous stirring and restirring conditions and the nucleation time under the prestirring and restirring conditions was shorter than that under the continuous stirring and poststirring conditions. Consequently, high-quality crystals were promptly obtained under the restirring condition. These results suggest that we are able to control both the nucleation and growth of protein crystals with the stirring techniques.

Niino, Ai; Adachi, Hiroaki; Takano, Kazufumi; Matsumura, Hiroyoshi; Kinoshita, Takayoshi; Warizaya, Masaichi; Inoue, Tsuyoshi; Mori, Yusuke; Sasaki, Takatomo

2004-11-01

231

Supersaturation dependence of crystal growth in solutions in the presence of impurity  

NASA Astrophysics Data System (ADS)

It is proposed to describe the rate of crystal growth in solution in the presence of impurity as a function of supersaturation. The theoretical equations are based on the pinning mechanism of Cabrera and Vermilyea for the inhibition of step advancement, assuming that impurity species are adsorbed one-dimensionally on the step lines. The Langumir adsorption isotherm is assumed to hold for impurity adsorption. Experimental growth rate data from the literature are used to assess the model. The supersaturation dependence of crystal growth rate in the presence of impurity is also well described with the model. The critical supersaturation below which a crystal does not grow is correlated with the impurity concentration. For the case where an impurity has no effect at high supersaturation, two possible mechanisms are discussed: one related to a change of rate-determining process and the other related to competition between impurity adsorption and growth unit deposition processes.

Kubota, Noriaki; Yokota, Masaaki; Mullin, J. W.

1997-12-01

232

Protein Single Crystal Growth under Microgravity  

NASA Astrophysics Data System (ADS)

The preparation of suitably large protein single crystals is essentially the rate-determining step of protein x-ray structure determinations. Attempts to produce single crystals with two model compounds--? -galactosidase and lysozyme--under conditions of microgravity were successful. Crystals formed by salting out from solutions kept free of convection were 27 and 1000 times larger in volume, respectively, than those produced in the same apparatus but exposed to terrestrial gravitation.

Littke, Walter; John, Christina

1984-07-01

233

The effects of polydispersity and metastability on crystal growth kinetics  

NASA Astrophysics Data System (ADS)

We investigate the effect of metastable gas-liquid (G-L) separation on crystal growth in a system of either monodisperse or slightly size-polydisperse square well particles, using a simulation setup that allows us to focus on the growth of a single crystal. Our system parameters are such that, inside the metastable G-L binodal, a macroscopic layer of the gas phase "coats" the crystal as it grows, consistent with experiment and theoretical free energy considerations. Crucially, the effect of this metastable G-L separation on the crystal growth rate depends qualitatively on whether the system is polydisperse. We measure reduced polydispersity and qualitatively different local size ordering in the crystal relative to the fluid, proposing that the required fractionation is dynamically facilitated by the gas layer. Our results show that polydispersity and metastability, both ubiquitous in soft matter, must be considered in tandem if their dynamical effects are to be understood.

Williamson, John J.; Evans, R. Mike L.

234

Growth of large KDP crystals in the form of plates  

SciTech Connect

This paper suggests a new technique of growth-oriented KDP crystals in the form of plates. The technique includes: using small oriented seeds spaced between two parallel platforms with a rapid growth of crystals between these two platforms, in a tank containing a KDP solution. As a result, crystals in the form of plates can be obtained. The thickness of the crystal plate depends on the distance between platforms. The horizontal dimensions of the plate depend on the volume of solution and the diameter of the platforms. The orientation of the plates are defined by the orientation of the seed. KDP crystals in the form of plates of two orientations are grown. The peculiarities of morphology and some characteristics of crystals are discussed.

Beriot, E; Tatartchenko, V

1998-05-01

235

Investigation of Crystal Growth from Solutions.  

National Technical Information Service (NTIS)

The quality was investigated of a crystal of Rochelle salt grown from a solution placed in the zero-gravity environment of Skylab 4. The crystal has the following unique features: (1) the typical cavity is a long tube extending along the c-axis, the avera...

I. Miyagawa

1974-01-01

236

Hydrothermal Growth of Crystals of LAALO3.  

National Technical Information Service (NTIS)

Two new molten salt solvent systems were found from which LaAlO3 could be crystallized, PbF2-B2O3 and Bi2O3 - B2O3. The conditions and compositions for using these solvents were developed so that crystals one half to one inch on edge were grown. In the Pb...

1966-01-01

237

Atomic scale modeling of vicinal surface growth from melts using the phase-field crystal method  

NASA Astrophysics Data System (ADS)

Using the phase-field crystal method, we investigated the bcc {1 1 0} vicinal surface growth from melts at the atomic scale with emphasis on the growth kinetics of two growth modes: step flow growth and island growth on terrace. Simulation results show that, for step flow growth, with the decrease of terrace width, the competition for feeding atoms between neighboring steps causes growth rate vs. step density to deviate from a linear relationship, and finally converge to a finite value. The step crystal direction also strongly influences the growth kinetics: vicinal surface with steps along the closest packed direction—[1 1 1] grows slower than that with [0 0 1] step. For island growth on terrace, the growth exponent of each layer in multi-layer island gradually transits from 1/2 for the top layer to 1/3 for the bottom layer, which demonstrates the transition from global diffusion controlled growth for top layer to surface diffusion controlled growth for bottom layer. The growth mechanism selection map with respect to terrace width and supersaturation is summarized and atom attaching rates of different growth mechanisms are also compared.

Tang, Sai; Wang, Zhijun; Guo, Yaolin; Wang, Jincheng; Yu, Yanmei; Zhou, Yaohe

2013-07-01

238

Effect of storage temperature on crystal formation rate and growth rate of calcium lactate crystals on smoked Cheddar cheeses.  

PubMed

Previous studies have shown that storage temperature influences the formation of calcium lactate crystals on vacuum-packaged Cheddar cheese surfaces. However, the mechanisms by which crystallization is modulated by storage temperature are not completely understood. The objectives of this study were to evaluate the effect of storage temperature on smoked Cheddar cheese surfaces for (1) the number of discrete visible crystals formed per unit of cheese surface area; (2) growth rate and shape of discrete crystals (as measured by area and circularity); (3) percentage of total cheese surface area occupied by crystals. Three vacuum-packaged, random weight (?300 g) retail samples of naturally smoked Cheddar cheese, produced from the same vat of cheese, were obtained from a retail source. The samples were cut parallel to the longitudinal axis at a depth of 10mm from the 2 surfaces to give six 10-mm-thick slabs, 4 of which were randomly assigned to 4 different storage temperature treatments: 1, 5, 10°C, and weekly cycling between 1 and 10°C. Samples were stored for 30 wk. Following the onset of visible surface crystals, digital photographs of surfaces were taken every other week and evaluated by image analysis for number of discrete crystal regions and total surface area occupied by crystals. Specific discrete crystals were chosen and evaluated biweekly for radius, area, and circularity. The entire experiment was conducted in triplicate. The effects of cheese surface, storage temperature, and storage time on crystal number and total crystal area were evaluated by ANOVA, according to a repeated-measures design. The number of discrete crystal regions increased significantly during storage but at different rates for different temperature treatments. Total crystal area also increased significantly during storage, at rates that varied with temperature treatment. Storage temperature did not appear to have a major effect on the growth rates and shapes of the individual crystals that were chosen for analysis. The data indicated that the effect of storage temperature was complex, likely involving solubility changes, the formation of d(-) and l(+) lactic acid, and the occurrence of syneresis, which in turn affected the number of crystal formation sites and total crystal area on the cheese surface. PMID:23548293

Rajbhandari, P; Patel, J; Valentine, E; Kindstedt, P S

2013-03-30

239

Liquid Crystal Elastomers: Optics and Mechanics  

NASA Astrophysics Data System (ADS)

Rubber elasticity is a unique feature of polymer networks or elastomers formed from long polymer chains connected to one another by crosslinkages. An implanting of rod-like mesogenic monomer units into the network chains can induce the liquid crystalline state of the elastomers. The interplay between network chain conformation and liquid crystalline phase creates material with remarkable properties. Detailed investigations proved a direct coupling between chain conformation and anisotropic state of order of the liquid crystalline phase. Introducing an anisotropic chain conformation a priori by a suitable synthesis concept, networks can be obtained that are macroscopic uniformly ordered (liquid single crystal elastomers, LSCE). Depending on the liquid crystalline phase structure, LSCE exhibit exceptional properties, e.g. · Nematic LSCE change their macroscopic dimensions when the state of order is modified by external stimuli. This effect can be applied to novel thermo- and opto-mechanical actuators. · Chiral nematic (cholesteric) LSCE, because of their birefringence and periodic, helicoidal structure, are 1-d photonic band-gap materials which enable mirrorless lasing. Mechanical deformation of the networks couples to the phase structure and causes a shift of the emission wave length.

Finkelmann, Heino

2004-03-01

240

Holographic Observation of Crystal Growth from the Melt.  

National Technical Information Service (NTIS)

A holographic recording technique is used to observe the interface morphology of transparent crystals during growth from the melt. Microscopic detail with spatial resolution of 300 line pairs/mm can be recorded within a volume several centimeters long by ...

R. H. McFee

1969-01-01

241

Filamentary crystal growth associated with impact craters from hypervelocity microparticles.  

PubMed

A filamentary crystal growth is associated with impacts of hypervelocity microparticles upon copper foil. They are copper whiskers formed by the condensation of the target material vaporzied by the impact. PMID:17768911

Berg, O E; McDonnell, J A

1970-05-15

242

Crystal growth and roughening of solid D{sub 2}  

SciTech Connect

Near the triple point, growth shapes of vapor deposited hexagonal close packed D{sub 2} crystals reveal two crystal orientations contain facets which persist up to the melt. This observation is in contrast with previous experiments on rare gas solids and H{sub 2} where the highest T{sub r} measured is 0.8 T{sub tp}.

Kozioziemski, B.J.; Collins, G.W.; Bernat, T.P.

1997-03-26

243

m-dinitrobenzene: optical nonlinear organic crystal growth for optoelectronics  

NASA Astrophysics Data System (ADS)

A high purity dinitro derivate of benzene for crystal growth has been obtained by chemical purification, vacuum distillation and two stages directional freezing. The crystallization process of m-dinitrobenzene has been investigated by a Bridgman method using a special heating and displacement arrangement. The quality of organic crystalline material has been analyzed by chemical and optical methods.

Stanculescu, Anca I.; Popina, Alexandru

1996-05-01

244

Gallium arsenide crystal growth from metallic solution under microgravity  

Microsoft Academic Search

Homogeneous and low-defect crystals are important to improving semiconductor devices. This paper reports the properties of GaAs crystals grown from a metallic solution under microgravity. Growth was free from convection caused by surface tension and by gravity. Our experiment was performed aboard the Second German Spacelab Mission D-2.

Y Suzuki; S Kodama; O. Ueda; O. Ohtsuki

1995-01-01

245

Growth of Vaterite and Calcite Crystals in Gels.  

National Technical Information Service (NTIS)

Crystals of vaterite and calcite have been simultaneously grown in sodium metasilicate-acetic acid gels. The crystals were characterized by x-ray diffraction and infrared spectroscopy. The growth ratios of vaterite and calcite are functions of gel pH valu...

A. Schwartz D. Eckart J. O'Connell K. Francis

1971-01-01

246

Imaging and interferometric analysis of protein crystal growth  

NASA Astrophysics Data System (ADS)

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 VDXTM 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.

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

2008-05-01

247

Growth and characterization of rare earths doped triglycine sulfate crystals  

Microsoft Academic Search

Ferroelectric triglycine sulfate (TGS) single crystals have been grown by a temperature-lowering technique from the aqueous solution by doping with samarium sulfate, ytterbium sulfate and terbium sulfate in the ferroelectric phase. The effects of these different dopants on the morphology, growth and various properties such as dielectric, pyroelectric and piezoelectric of doped TGS crystals have been investigated. The decrease in

A. K. Batra; Padmaja Guggilla; Dewanna Cunningham; M. D. Aggarwal; R. B. Lal

2006-01-01

248

Photostimulated growth of whiskers in AgI-type superionic crystals  

NASA Astrophysics Data System (ADS)

The growth of whiskers inside and on the surface of superionic crystals (AgI, CuI, RbAg4I5) is considered. The crystals are exposed to radiations with different spectral compositions at temperatures above and below the temperature of the superionic phase transition. The chemical composition, structure, and properties of whiskers are studied with optical microscopy, scanning electron microscopy, transmission electron microscopy, and photoluminescence. The mechanisms of photostimulated growth of whiskers in semiconductors with a high ionic conductivity are discussed, and the role of the "molten" cation sublattice during nucleation and growth of whiskers is considered.

Akopyan, I. Kh.; Labzovskaya, M. E.; Novikov, B. V.; Tsagan-Mandzhieva, D. A.

2012-02-01

249

Acquisition of Single Crystal Growth and Characterization Equipment  

Microsoft Academic Search

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

M. Brian Maple; Diego A. Zocco

2008-01-01

250

Definition study for temperature control in advanced protein crystal growth  

NASA Astrophysics Data System (ADS)

Some of the technical requirements for an expedient application of temperature control to advanced protein crystal growth activities are defined. Lysozome was used to study the effects of temperature ramping and temperature gradients for nucleation/dissolution and consecutive growth of sizable crystals and, to determine a prototype temperature program. The solubility study was conducted using equine serum albumin (ESA) which is an extremely stable, clinically important protein due to its capability to bind and transport many different small ions and molecules.

Nyce, Thomas A.; Rosenberger, Franz; Sowers, Jennifer W.; Monaco, Lisa A.

1990-09-01

251

Gallium arsenide advanced crystal growth and beam processing  

Microsoft Academic Search

This report describes the progress made during a fifteen month program to study the feasibility of growth of high purity epitaxial quality bulk GaAs crystals from solution and annealing of implanted layers and Ohmic contacts for device applications using laser and electron beams. Millimeter-thick crystals have been grown by the low-temperature solution-growth process. Room-temperature n-type carrier concentrations of 2 times

C. L. Anderson

1980-01-01

252

Progress in the crystal growth of Ce : colquiriites  

Microsoft Academic Search

The search for an efficient solid-state laser with tunable emission in the ultraviolet wavelength region has resulted in the growth and development of cerium-doped colquiriite crystals, such as LiCaAlF6 (LiCAF) and LiSrAlF6 (LiSAF). Unfortunately, the doping of LiSAF and LiCAF with Ce3+ introduces different variables into the growth of high optical quality crystals, due to the charge imbalance induced when

Vida K. Castillo; Gregory J. Quarles

1997-01-01

253

Czochralski growth of gallium indium antimonide alloy crystals  

NASA Astrophysics Data System (ADS)

Attempts were made to grow alloy crystals of Gasb{1-x}Insb{x}Sb by the conventional Czochralski process. A transparent furnace was used, with hydrogen purging through the chamber during crystal growth. Single crystal seeds up to around 2 to 5 mole % InSb were grown from seeds up to around 1 to 2 mole % InSb, which were grown from essentially pure GaSb seeds of the (111) direction. Single crystals were grown with InSb rising from around 2 to 6 mole % at the seed ends to around 14 to 23 mole % InSb at the finish ends. A conical reflector was installed above the melt and coaxially around the growing crystal to help the crystal grow monocrystalline. Floating crucible technique that had been effective in reducing segregation in doped crystals, was used to reduce segregation in Czochralski growth of alloy crystals of Gasb{1-x}Insb{x}Sb. Crystals close to the targeted composition of 1 mole % InSb were grown. However, difficulties were encountered in reaching higher targeted InSb concentrations. Crystals around 2 mole % were grown when 4 mole % was targeted. It was observed that mixing occurred between the melts and render the compositions of the melts and hence the resultant crystal unpredictable. The higher density of the growth melt than the replenishing melt could have triggered thermosolutal convection to cause such mixing. It was also observed that the floating crucible stuck to the outer crucible when the liquidus temperature of the replenishing melt was significantly higher than that of the growth melt. The homogeneous Gasb{1-x}Insb{x}Sb single crystals were grown successfully by pressure-differential technique that a quartz tube was separated into an upper chamber for crystal growth and a lower chamber for replenishing. The melts were connected by a capillary tube to suppress mixing between them. A constant pressure differential was maintained between the chambers to keep the growth melt up in the growth chamber. The method was first tested with a low temperature alloy Bisb{1-x}Sbsb{x}. Single crystals of Gasb{1-x}Insb{x}Sb were grown with uniform compositions up to nearly 5 mole % InSb.

Tsaur, Shuenn-Ching

254

Microfluidic experiments reveal that antifreeze proteins bound to ice crystals suffice to prevent their growth.  

PubMed

Antifreeze proteins (AFPs) are a subset of ice-binding proteins that control ice crystal growth. They have potential for the cryopreservation of cells, tissues, and organs, as well as for production and storage of food and protection of crops from frost. However, the detailed mechanism of action of AFPs is still unclear. Specifically, there is controversy regarding reversibility of binding of AFPs to crystal surfaces. The experimentally observed dependence of activity of AFPs on their concentration in solution appears to indicate that the binding is reversible. Here, by a series of experiments in temperature-controlled microfluidic devices, where the medium surrounding ice crystals can be exchanged, we show that the binding of hyperactive Tenebrio molitor AFP to ice crystals is practically irreversible and that surface-bound AFPs are sufficient to inhibit ice crystal growth even in solutions depleted of AFPs. These findings rule out theories of AFP activity relying on the presence of unbound protein molecules. PMID:23300286

Celik, Yeliz; Drori, Ran; Pertaya-Braun, Natalya; Altan, Aysun; Barton, Tyler; Bar-Dolev, Maya; Groisman, Alex; Davies, Peter L; Braslavsky, Ido

2013-01-08

255

Microfluidic experiments reveal that antifreeze proteins bound to ice crystals suffice to prevent their growth  

PubMed Central

Antifreeze proteins (AFPs) are a subset of ice-binding proteins that control ice crystal growth. They have potential for the cryopreservation of cells, tissues, and organs, as well as for production and storage of food and protection of crops from frost. However, the detailed mechanism of action of AFPs is still unclear. Specifically, there is controversy regarding reversibility of binding of AFPs to crystal surfaces. The experimentally observed dependence of activity of AFPs on their concentration in solution appears to indicate that the binding is reversible. Here, by a series of experiments in temperature-controlled microfluidic devices, where the medium surrounding ice crystals can be exchanged, we show that the binding of hyperactive Tenebrio molitor AFP to ice crystals is practically irreversible and that surface-bound AFPs are sufficient to inhibit ice crystal growth even in solutions depleted of AFPs. These findings rule out theories of AFP activity relying on the presence of unbound protein molecules.

Celik, Yeliz; Drori, Ran; Pertaya-Braun, Natalya; Altan, Aysun; Barton, Tyler; Bar-Dolev, Maya; Groisman, Alex; Davies, Peter L.; Braslavsky, Ido

2013-01-01

256

A kinetic model to simulate protein crystal growth in an evaporation-based crystallization platform  

SciTech Connect

The quality, size, and number of protein crystals grown under conditions of continuous solvent extraction are dependent on the rate of solvent extraction and the initial protein and salt concentration. An increase in the rate of solvent extraction leads to a larger number of crystals. The number of crystals decreases, however, when the experiment is started with an initial protein concentration that is closer to the solubility boundary. Here we develop a kinetic model capable of predicting changes in the number and size of protein crystals as a function of time under continuous evaporation. Moreover, this model successfully predicts the initial condition of drops that will result in gel formation. We test this model with experimental crystal growth data of hen egg white lysozyme for which crystal nucleation and growth rate parameters are known from other studies. The predicted and observed rates of crystal growth are in excellent agreement, which suggests that kinetic constants for nucleation and crystal growth for different proteins can be extracted by applying a kinetic model in combination with observations from a few evaporation-based crystallization experiments.

Talreja, S.; Kenis, P; Zukoski, C

2007-01-01

257

Growth of highly doped Nd:YAG laser crystals  

NASA Astrophysics Data System (ADS)

During the last decade, Nd:YVO4 has been developed as a promising substitutes for Nd:YAG in diode-pumped lasers due to its high absorption and emission cross-sections. However, the applications of YVO4 are limited due to its poor physical- mechanical properties and growth difficulty etc. Now, in this present paper, we have developed the high-doped Nd:YAG(SUPER- Nd:YAG) crystals. It shows high absorption cross-section and has many advantages over Nd:YVO4: (1) Due to the cubic symmetry and high quality, Nd:YAG is easy to operate with TEM00 mode. (2) Nd:YAG can be Q-switched with Cr4+:YAG directly (sandwich). (3) Nd:YAG can produce blue laser with the frequency-doubling of 946 nm. (4) Nd:YAG can be operated in a very high power laser up to kW level.

Xu, Jun; Zhou, Yongzong; Li, Hongjun; Deng, Peizhen

2000-04-01

258

Growth of single crystals of mercuric iodide (HgI/sub 2/) in spacelab III  

SciTech Connect

Continued development of a system designed to grow crystals by physical vapor transport in the environment of Spacelab III will be described, with special emphasis on simulation of expected space conditions, adjustment of crystal growth parameters, and on board observation and control of the experiment by crew members and ground personnel. A critical factor in the use of mercuric iodide for semiconductor detectors of x-rays and gamma-rays is the crystalline quality of the material. The twofold purpose of the Spacelab III experiment is therefore to grow single crystals with superior electronic properties as an indirect result of the greatly reduced gravity field during the growth, and to obtain data which will lead to improved understanding of the vapor transport mechanism. The experiments planned to evaluate the space crystals, including gamma-ray diffractometry and measurements of stoichiometry, lattice dimensions, mechanical strength, luminescense, and detector performance are discussed.

Van Den Berg, L.; Schnepple, W.F.

1981-01-01

259

Crystal growth 1989; Proceedings of the Ninth International Conference, Sendai, Japan, Aug. 22-25, 1989  

NASA Astrophysics Data System (ADS)

Papers are presented on the stoichiometry control and Bridgman modeling of crystal growth, as well as the fundamentals of crystal growth. Dendritic crystals and other crystallization phenomena are also covered. Papers are also presented on thin films and epitaxial growth. Among the topics covered in this area are: (1) silicon and related materials, (2) group III-V compounds, (3) group II-VI compounds, (4) atomic layer epitaxy, and (5) metals and metal oxides. Other papers covering semiconductor crystals; II-VI compound crystals; chalcopyrite and related crystals; oxide crystals; superconductor crystals; metal, halide, carbide, and boride crystals; and organic and biological crystals are also presented. Papers on industrial crystallization, diamond crystals, natural crystallization, crystal growth under microgravity, and crystal growth characterization techniques conclude the proceedings.

Chikawa, J.; Mullin, J. B.; Woods, J.

1990-01-01

260

Growth kinematics of the regeneration surfaces of crystals  

NASA Astrophysics Data System (ADS)

A formula for the propagation velocity of the regeneration surface front is derived under the assumption of equal growth rates of the polyhedral crystal faces and the corresponding faces forming subindividuals of the regeneration surface. It is shown that both sharp minima (increase of the face) and sharp maxima (decrease of the face) can correspond to faces in the growth rate diagram. An experimental diagram of the growth rates of the [110] zone of potash alum crystals is constructed which confirms the analytical conclusions. It is established that the regeneration surface growth rate decreases with time. This effect is caused by the disappearance of rapidly growing faces from subindividual faceting. The faceting of a regenerating crystal changes in the direction of successive disappearance of sharp maxima in the growth rate diagram.

Gavryushkin, P. N.; Thomas, V. G.

2009-03-01

261

Analytics of Crystal Growth in Space.  

National Technical Information Service (NTIS)

The variation of radial impurity distribution induced by surface tension driven flow increases as the zone length decreases in silicon crystals grown by floating zone melting. In combined buoyancy driven and surface tension driven convection at the gravit...

C. E. Chang R. A. Lefever W. R. Wilcox

1975-01-01

262

A new method of growth ferroelectrics crystal  

Microsoft Academic Search

TGS crystals were grown from solution with ethyl alcohol additions. The TGS crystals weighed more than 100 grams.Ferroelectric hysteresis loop, dielectric and pyroelectric properties have been measured. The Curie temperature is 50.2°C. It is found that the properties of TGS grown by this method are similar to that grown by slowly lowering the temperature at constant supersaturation.An infrared detactor constructed

Deng Zhao-De

1981-01-01

263

Nanoindentation in crystal engineering: quantifying mechanical properties of molecular crystals.  

PubMed

Nanoindentation is a technique for measuring the elastic modulus and hardness of small amounts of materials. This method, which has been used extensively for characterizing metallic and inorganic solids, is now being applied to organic and metal-organic crystals, and has also become relevant to the subject of crystal engineering, which is concerned with the design of molecular solids with desired properties and functions. Through nanoindentation it is possible to correlate molecular-level properties such as crystal packing, interaction characteristics, and the inherent anisotropy with micro/macroscopic events such as desolvation, domain coexistence, layer migration, polymorphism, and solid-state reactivity. Recent developments and exciting opportunities in this area are highlighted in this Minireview. PMID:23315913

Varughese, Sunil; Kiran, M S R N; Ramamurty, Upadrasta; Desiraju, Gautam R

2013-01-11

264

Epitaxial Growth of WOx Nanorod on Single Crystal Tungsten Substrate  

NASA Astrophysics Data System (ADS)

Nanorods of substoichiometric tungsten oxide (WOx) were grown on single crystal tungsten substrate. The grown nanorods were investigated with scanning electron micrope and atomic force microscope. WOx nanorods were grown on W(001) in accordance with epitaxial relationship between WO3 crystals and W(001) surface. The results indicate that the WO3 crystals formed at the initial stage act as the nuclei of WOx nanorods. Nanorod growth of certain epitaxial directions can be selectively enhanced by choosing growth methods or choosing suitable crystallographic orientation of substrate surface.

Shingaya, Yoshitaka; Nakayama, Tomonobu

265

Growth and Characterization of New Nonlinear Optical Single Crystals of 3-AMINOPHENOL Orthophosphoric Acid (3-AMPHPH)  

NASA Astrophysics Data System (ADS)

The semi-organic 3-aminophenol-orthophosphoric acid (denoted as 3-amphph) single crystals were grown by slow evaporation solution technique with water as solvent. The resulted crystal has well-defined surface morphology and is transparent and colorless with a size of 29 × 17 × 4 mm3. The powder X-ray diffraction (XRD), NMR spectroscopic technique, UV-vis-NIR, TG/DTA and dielectric analysis are used to characterize the crystals. XRD analysis revealed that the crystal lattice of 3-amphph is orthorhombic having cell parameters a = 4.481(2) Å, b = 9.782(4) Å, c = 18.326(4) Å with non-centrosymmetric space group P212121. Nonlinear optical studies indicated that the second harmonic generation (SHG) efficiency is 2.22 times that of the standard potassium dihydrogen phosphate (KDP) crystals. Growth mechanism and surface textures of the as-grown single crystals were analyzed by chemical etching analysis.

Raj, K. Russel; Murugakoothan, P.

266

Crystal growth of optical materials for advanced lasers  

SciTech Connect

During FY96, two specific projects were addressed, Yb-doped fluoroapatite and Cr:ZnSe crystals, which are being used as the gain media to develop diode-pumped solid-state lasers. Both materials have unique properties for near infrared to mid-infrared applications. However, defects in the crystals create optical losses and reduce the efficiency of the lasers. The source of the losses in the crystals were studied and techniques developed to reduce and/or eliminate defects to aid in the growth of high optical quality crystals to increase laser efficiency.

Schaffers, K.I.; Payne, S.A.

1997-02-04

267

Anomalous Crystal Growth In Supercooled OTP On Temperature Cycling  

NASA Astrophysics Data System (ADS)

It has been previously observed [1] that when the fragile glass former o-terphenyl (OTP) is supercooled to -23 ^oC, well below its normal freezing temperature but above its glass transition temperature, an anomalous growth mode appears indicated by a sudden increase in the crystal growth velocity. We report observations of this anomalous crystal growth when the temperature is raised briefly above the apparent transition temperature and then cooled back down. We find that when the temperature is raised to -20.5 ^oC or less the original anomalous growth continues to grow, apparently uninterrupted. When the temperature is raised above -19 ^oC the original anomalous growth does not continue to grow, although new anomalous growth nucleates. One interpretation of these results is that the transition temperature for the anomalous growth is around -20 ^oC. [4pt] [1] M. Hatase, M. Hanaya, and M. Oguni, J. Non-Cryst. Solids 333, 129 (2004)

Hall, Stephen C.; Lindsay, Sean

2010-03-01

268

Predicting crystal structure by merging data mining with quantum mechanics  

Microsoft Academic Search

Modern methods of quantum mechanics have proved to be effective tools to understand and even predict materials properties. An essential element of the materials design process, relevant to both new materials and the optimization of existing ones, is knowing which crystal structures will form in an alloy system. Crystal structure can only be predicted effectively with quantum mechanics if an

Christopher C. Fischer; Kevin J. Tibbetts; Dane Morgan; Gerbrand Ceder

2006-01-01

269

Kinetics of non-isothermal crystallization process and activation energy for crystal growth in amorphous materials  

Microsoft Academic Search

An equation expressing the volume fraction,x, of crystals precipitating in a glass heated at a constant rate, a, was derived. When crystal particles grow m-dimensionally,x is expressed as In [- ln(1 -x)] = -n (na - 1.052mE\\/RT + Constant whereE is the activation energy for crystal growth andn is a numerical factor depending on the nucleation process. When the nuclei

Kazumasa Matusita; Takayuki Komatsu; Ryosuke Yokota

1984-01-01

270

Effects of Solution Stirring on Protein Crystal Growth  

NASA Astrophysics Data System (ADS)

We report the influence of solution stirring on the growth of hen egg white lysozyme crystals. Solution stirring rate was controlled by varying the rotation speed of a rotary shaker. A range of precipitation agent (sodium chloride) concentrations was also investigated. The time required for crystal nucleation to occur was observed to be much greater in stirred samples than in unstirred samples. Solution stirring resulted in a reduced number of crystals (at sodium chloride concentrations from 6 to 9%). These crystals were larger and of a higher quality. However, the time required for nucleation to occur was reduced by gentle stirring (25 and 50 rpm) in a 12.5% sodium chloride concentration solution, suggesting that stirring can stimulate nucleation. These results indicate that the optimization of solution stirring rates is a useful technique for controlling protein crystal growth.

Yaoi, Mari; Aadachi, Hiroaki; Takano, Kazufumi; Matsumura, Hiroyoshi; Inoue, Tsuyoshi; Mori, Yusuke; Sasaki, Takatomo

2004-05-01

271

Bulk III-V compound semiconductor crystal growth  

NASA Astrophysics Data System (ADS)

This paper discusses the production of III-V compound semiconductor substrates characterized by structural perfection and chemical homogeneity. Special attention is given to the use of vertical-gradient-freeze (VGF) technique for producing large high-quality GaP, InP, and GaAs crystals. The characteristics of VGF-grown GaAs crystals are described, including the dislocation-count distribution, etch-pit density, and electrical properties. The VGF-grown crystals have very low levels of crystalline defects distributed uniformly throughout the crystal; growth striations are planar and are greatly reduced in comparison with those observed in materials produced by the liquid-encapsulated Czochralski method. Yields obtained with the VGF method compare favorably with those of other commercial crystal-growth processes.

Clemans, Jim E.; Ejim, Theophilus I.; Gault, William A.; Monberg, Eric M.

1989-02-01

272

Molecular tagging velocimetry characterization of rapid KDP crystal growth  

SciTech Connect

Measurements of the tangential and axial velocities near the prism faces of a rotating mock crystal mounted on a rotating platform are presented. These measurements were made using molecular tagging velocimetry and are significant to the rapid growth of KDP crystals because they provide a description of the flow field and the evolution of the relative tangential and axial velocities near the prism faces and in the bulk flow region. These data represent the first measurements of fluid velocities around rotating crystal geometries, and thus provide a benchmark for future computer simulations of the crystal growth process at higher Re than previously obtainable. The measurements provide a temporal and spatial description of the evolving velocity field in the vicinity of a rotating crystal. Rotational conditions and locations on the prism faces where low shear rates are likely to occur, based on the measurements presented, are discussed qualitatively.

Maynes, D.

2000-03-01

273

A novel method for measurement of crystal growth rate  

NASA Astrophysics Data System (ADS)

A new method for measurement of crystal growth rate is proposed, in an attempt to make the measuring of growth rate more convenient than the existing methods. In this newly proposed method, the point of nucleation under a constant cooling rate condition was measured as changing the amount of seeds. The growth kinetics parameters were then estimated using the experimental data to match the points of nucleation. Experiments were performed with potash alum in the water system and growth kinetic parameters were estimated. Compared with existing results, the proposed method showed tolerable discrepancy in the growth kinetic parameters. The proposed method can be an alternative technique for measurement of growth rate.

Kim, Do Yeon; Yang, Dae Ryook

2013-06-01

274

Crystal Growth of Berlinite: Methods for Growing Longer Crystals and Improving the Quality.  

National Technical Information Service (NTIS)

A study to find a hydrothermal method for growing berlinite crystals of sufficently large sizes to use as piezoelectric materials is presented. Natural berlinite of large size are not known. Studies of the optimal conditions of growth were performed using...

X. Buisson A. Zarka R. Arnaud B. Capelle Y. Zheng

1992-01-01

275

Hydrothermal crystal growth of the potassium niobate and potassium tantalate family of crystals  

SciTech Connect

Single crystals of KNbO{sub 3} (KN), KTaO{sub 3} (KT), and KTa{sub 1-x}Nb{sub x}O{sub 3} (x=0.44, KTN) have been prepared by hydrothermal synthesis in highly concentrated KOH mineralizer solutions. The traditional problems of inhomogeneity, non-stoichiometry, crystal striations and crystal cracking resulting from phase transitions associated with this family compounds are minimized by the hydrothermal crystal growth technique. Crystals of good optical quality with only minor amounts of metal ion reduction can be grown this way. Reactions were also designed to provide homogeneous distribution of tantalum and niobium metal centers throughout the KTN crystal lattice to maximize its electro-optic properties. Synthesis was performed at relatively low (500-660 {sup o}C) temperatures in comparison to the flux and Czochralski techniques. This work represents the largest crystals of this family of compounds grown by hydrothermal methods to date. -- Graphical Abstract:

Mann, Matthew [Department of Chemistry, Clemson University, Clemson, SC 29634 (United States); Center for Optical Materials Science and Engineering Technologies (COMSET), 91 Technology Drive, Anderson, SC 29625 (United States); Jackson, Summer [Department of Chemistry, Clemson University, Clemson, SC 29634 (United States); Kolis, Joseph, E-mail: kjoseph@clemson.ed [Department of Chemistry, Clemson University, Clemson, SC 29634 (United States); Center for Optical Materials Science and Engineering Technologies (COMSET), 91 Technology Drive, Anderson, SC 29625 (United States)

2010-11-15

276

Protein crystal growth in microgravity: Status and commercial implications  

NASA Astrophysics Data System (ADS)

Since 1985, The Center for Macromolecular Crystallography has conducted an extensive program of macromolecular crystal growth experiments in microgravity. This Center has designed and built crystal growth flight hardware that has an excellent productivity and reliability record. In addition, several other crystallography laboratories have conducted macromolecular crystal growth experiments in microgravity and developed hardware to house their experiments. These experiments have successfully demonstrated that the low gravity environment can be used to produce crystals of proteins and other macromolecules that are superior to crystals of the same compounds grown on earth. Improved, extended x-ray diffraction data collected from space-grown crystals has contributed to the solution of the three-dimensional structures of many proteins and has augmented structure-based drug design studies targeting several diseases and degenerative conditions. The production of produce high-quality crystals of medically relevant macromolecules is important because of the rapidly growing role of macromolecular crystallography in biology and medicine. Large, high-quality crystals are critical to solving the structures of biologically important macromolecules, but it is often difficult to obtain these crystals because of the physical and chemical properties of the compounds. Work by this and other crystallography laboratories has shown that conducting macromolecular crystallization experiments in the microgravity environment alleviates convection and sedimentation effects, and frequently results in crystals that yield x-ray diffraction data that is superior to their earth-grown counterparts. The improved diffraction data translates directly to faster, more accurate solutions to the three-dimensional structures of the target molecules.

Moore, Karen M.; Long, Marianna M.; Delucas, Lawrence J.

1999-01-01

277

Crystal Growth of Device Quality GaAs in Space.  

National Technical Information Service (NTIS)

The program on Crystal Growth of Device Quality GaAs in Space was initiated in 1977. The initial stage covering 1977 to 1984 was devoted strictly to ground-based research. By 1985 the program had evolved into its next logical stage aimed at space growth e...

H. C. Gatos J. Lagowski

1989-01-01

278

Growth and Morphology of Crystals: Theory and Observations.  

National Technical Information Service (NTIS)

In the thesis, crystal growth and morphology, and the relationship between morphology and structure are investigated. Experimental observations and theoretical predictions on the growth and morphology of NH4N03, ((CH3)4N)2ZnCl(sub 4-x)Br(sub x), and beta-...

L. Vogels

1993-01-01

279

Crystal growth and the formation of chemical zoning in garnets  

Microsoft Academic Search

A crystal growth model is developed which generalizes the Rayleigh fractionation process. The new growth model allows some insight into the interpretation of nonequilibrium behavior of minerals, primarily the chemical zoning profiles exhibited by metamorphic minerals. A nonlinear equilibrium term for exchange of constituents between a growing mineral and a reservoir is initially incorporated into the usual isothermal fractionation model.

Randall T. Cygan; Antonio C. Lasaga

1982-01-01

280

Growth and characterization of pure and doped btzs single crystals  

NASA Astrophysics Data System (ADS)

The growth and characterization of pure and doped BTZS single crystals are discussed. In the present study powder X-Ray diffraction data of the grown crystal were recorded using BRUKER D8 Advance powder crystal X-ray diffractometer with 2.2 KW Cu anode ceramic X-ray tube. The various functional groups present in the grown crystals were identified and confirmed by recording the FTIR spectrum using BRUKER IFS-66V spectrophotometer by KBr Pellet Technique in the region 4000 â?? 400 cm The UV - Vis - NIR optical spectra of the crystals were recorded using the VARIAN CARY 5E model spectrophotometer. The degree of dopant inclusion was estimated by using Atomic Absorption Spectroscopy. The SHG efficiencies of the crystals were studied using Nd:YAG Q - switched laser.

Gunasekaran, Sethu; Venkatesan, Padmapriya

2012-05-01

281

Progress in the crystal growth of Ce:LiSAF  

NASA Astrophysics Data System (ADS)

The search for an efficient solid state laser with tunable emission in the ultraviolet wavelength region has resulted in the growth and development of cerium doped colquiriite crystals, such as LiCaAlF6 (LiCAF) and LiSrAlF6 (LiSAF). Results from preliminary research at Lawrence Livermore National Laboratory indicate that Ce:LiSAF is the preferred material of the colquiriite hosts, since it shows higher gains than Ce:LiCAF. Although the growth of chromium doped LiSAF has been developed to produce long boules of near-scatter-free material, the doping of LiSAF with cerium introduces different variables into the growth of high optical quality crystals. The main crystal growth issue for Ce:LiSAF is the charge compensation mandated by the substitution of the trivalent cerium ion for divalent strontium, which is located in the only site large enough to support the cerium ion. Initial growth runs produced opaque, heavily cracked crystals with less than 10 mm of cleaner, single crystal material. The addition of charge compensating ions into the starting charge and their effect in attaining higher doped and less-stressed material is discussed. The selection of growth parameters needed to produce higher-doped, near-scatter-free Ce:LiSAF will also be described.

Castillo, Vida K.; Quarles, Gregory J.

1995-04-01

282

Crystal Growth and Magnetic Anisotrophy of Copper Ferrite (CuFe2O4).  

National Technical Information Service (NTIS)

This report examines some of the basic crystalline properties of single crystal copper ferrite. Crystal growth of single crystal copper ferrite at Stanford and by other investigators is reviewed. Ferromagnetic resonance experiments on crystals grown at lo...

D. A. Herman

1975-01-01

283

Macromolecular crystal growth experiments on International Microgravity Laboratory--1.  

PubMed Central

Macromolecular crystal growth experiments, using satellite tobacco mosaic virus (STMV) and canavalin from jack beans as samples, were conducted on a US Space Shuttle mission designated International Microgravity Laboratory--1 (IML-1), flown January 22-29, 1992. Parallel experiments using identical samples were carried out in both a vapor diffusion-based device (PCG) and a liquid-liquid diffusion-based instrument (CRYOSTAT). The experiments in each device were run at 20-22 degrees C and at colder temperatures. Crystals were grown in virtually every trial, but the characteristics of the crystals were highly dependent on the crystallization technique employed and the temperature experience of the sample. In general, very good results, based on visual inspection of the crystals, were obtained in both PCG and CRYOSTAT. Unusually impressive results were, however, achieved for STMV in the CRYOSTAT instrument. STMV crystals grown in microgravity by liquid-liquid diffusion were more than 10-fold greater in total volume than any STMV crystals previously grown in the laboratory. X-ray diffraction data collected from eight STMV crystals grown in CRYOSTAT demonstrated a substantial improvement in diffraction quality over the entire resolution range when compared to data from crystals grown on Earth. In addition, the extent of the diffraction pattern for the STMV crystals grown in space extended to 1.8 A resolution, whereas the best crystals that were ever grown under conditions of Earth's gravity produced data limited to 2.3 A resolution. Other observations indicate that the growth of macromolecular crystals is indeed influenced by the presence or absence of gravity. These observations further suggest, consistent with earlier results, that the elimination of gravity provides a more favorable environment for such processes.

Day, J.; McPherson, A.

1992-01-01

284

Commercial Protein Crystal Growth: Protein Crystallization Facility (CPCG-H)  

NASA Astrophysics Data System (ADS)

Within the human body, there are thousands of different proteins that serve a variety of different functions, such as making it possible for red blood cells to carry oxygen in our bodies. Yet proteins can also be involved in diseases. Each protein has a particular chemical structure, which means it has a unique shape. It is this three-dimensional shape that allows each protein to do its job by interacting with chemicals or binding with other proteins. If researchers can determine the shape, or shapes, of a protein, they can learn how it works. This information can then be used by the pharmaceutical industry to develop new drugs or improve the way medications work. The NASA Commercial Space Center sponsoring this experiment - the Center for Biophysical Sciences and Engineering at the University of Alabama at Birmingham - has more than 60 industry and academic partners who grow protein crystals and use the information in drug design projects.

DeLucas, Lawrence J.

2002-12-01

285

Shallow Melt Apparatus for Semicontinuous Czochralski Crystal Growth  

DOEpatents

In a single crystal pulling apparatus for providing a Czochralski crystal growth process, the improvement of a shallow melt crucible (20) to eliminate the necessity supplying a large quantity of feed stock materials that had to be preloaded in a deep crucible to grow a large ingot, comprising a gas tight container a crucible with a deepened periphery (25) to prevent snapping of a shallow melt and reduce turbulent melt convection; source supply means for adding source material to the semiconductor melt; a double barrier (23) to minimize heat transfer between the deepened periphery (25) and the shallow melt in the growth compartment; offset holes (24) in the double barrier (23) to increase melt travel length between the deepened periphery (25) and the shallow growth compartment; and the interface heater/heat sink (22) to control the interface shape and crystal growth rate.

Wang, T.; Ciszek, T. F.

2006-01-10

286

Growth mechanism of carbon nanocoils  

NASA Astrophysics Data System (ADS)

Carbon nanocoils were prepared by catalytic pyrolysis of acetylene using iron-coated indium tin oxide as the catalyst. The effects of the constitution of catalyst, the growth temperature and time, the flow rate of acetylene gas on the growth of carbon nanocoils were investigated. It is found that the coils grow mainly from the interface of iron and indium tin oxide films. The coils generally consist of two or more nanotubes. Each coil has its own external diameter and pitch, which is determined by the structure of the catalyst at its tip. The growth of the carbon nanocoil is considered to be due to the nonuniformity of the carbon extrusion speed at different parts of the catalyst particle containing iron, tin, indium and/or oxygen. It is confirmed that iron is crucial in the formation of a nanotubule and indium tin oxide induces the helical growth of the nanotubule.

Pan, Lujun; Zhang, Mei; Nakayama, Yoshikazu

2002-06-01

287

Effect of a strong magnetic field on protein crystal growth  

NASA Astrophysics Data System (ADS)

Recently, a superconducting magnet has been used to obtain better quality protein crystals. It is possible to reduce effective gravity and damp natural convection by applying a vertical magnetic field gradient to cause an upward magnetization (Kelvin) force. When protein crystals (snake muscle fructose-1,6-bisphosphatase) were formed in 0.7-0.8 g, their resolutions of X-ray diffraction were improved by 30% compared with those formed outside the magnet. On the other hand, in a uniform field of 10 T which did not cause an upward force, the improvement of the quality of orthorhombic lysozyme crystals was found. In this paper, besides through the upward magnetization force, we studied how a strong magnetic field damps natural convection and influences the crystal quality. First, we discussed the damping of natural convection by Lorentz force, and concluded it almost negligible because Hartman number is about 3.5 for the typical protein crystal formation experiments. Second, we studied the magnetic effect on the viscosity of protein solutions and found that the viscosity increases under 10 T when the solution contains suspended small crystals. Numerical simulations showed that the viscosity increase causes the damping of natural convection during protein crystal growth. Furthermore, the effect of magnetic orientation of suspended crystals on the crystal quality was also discussed. These types of magnetic effect will occur both in gradient and uniform magnetic fields. If we use these kinds of magnetic effects efficiently, it will be possible to improve the crystal quality.

Wakayama, Nobuko I.; Wang, L. B.; Ataka, M.

2002-09-01

288

Comment on the paper "Synthesis, growth, structural, spectral, thermal, chemical etching, linear and nonlinear optical and mechanical studies of an organic single crystal 4-Chloro 4-Nitrostilbene (CONS): A potential NLO material" by P.M. Dinakaran, S. Kalainathan [Spectrochim. Acta A 111 (2013) 123-130].  

PubMed

We argue that (trans)-4-chloro-4'-nitrostilbene is not a new organic nonlinear optical material as claimed by Dinakaran and Kalainathan [P.M. Dinakaran, S. Kalainathan, Synthesis, growth, structural, spectral, thermal, chemical etching, linear and nonlinear optical and mechanical studies of an organic single crystal 4-Chloro 4-Nitrostilbene (CONS): a potential NLO material, Spectrochim. Acta A 111 (2013) 123-130], but instead a well-known compound whose synthesis, spectral data, single crystal structure and second harmonic generation (SHG) efficiency are well documented in the literature. The title paper is completely erroneous. PMID:24152596

Srinivasan, Bikshandarkoil R; Dhuri, Sunder N; Nadkarni, V S

2013-10-08

289

Silicon Crystal Growth by the Electromagnetic Czochralski (EMCZ) Method  

NASA Astrophysics Data System (ADS)

A new method for growing silicon crystals by using electromagnetic force to rotate the melt without crucible rotation has been developed. We call it electromagnetic Czochralski (EMCZ) growth. An electromagnetic force in the azimuthal direction is generated in the melt by the interaction between an electric current (I) through the melt in the radial direction and a vertical magnetic field (B). The rotation rate (?m) of the silicon melt is continuously changed from 0 to over 105 rpm under I = 0 to 8 A and B = 0 to 0.1 T. Thirty-mm-diameter silicon single crystals free of dislocations could be grown under two conditions: I = 2.0 A and B = 0.05 T (?m = 105 rpm); and I =0.2 A and B = 0.1 T (?m = 15 rpm). The oxygen concentration in the crystals was 8 ×1017 atoms/cm3 for the high rotation rate and 1×1017 atoms/cm3 for the low rotation rate. The oxygen-concentration distributions in the radial direction in both crystals were more homogeneous than those in the crystals grown by conventional CZ and/or MCZ growth. This new crystal-growth method can be easily adopted for growing large-diameter silicon crystals.

Watanabe, Masahito; Eguchi, Minoru; Hibiya, Taketoshi

1999-01-01

290

Novel protein crystal growth technology: Proof of concept  

NASA Astrophysics Data System (ADS)

A technology for crystal growth, which overcomes certain shortcomings of other techniques, is developed and its applicability to proteins is examined. There were several unknowns to be determined: the design of the apparatus for suspension of crystals of varying (growing) diameter, control of the temperature and supersaturation, the methods for seeding and/or controlling nucleation, the effect on protein solutions of the temperature oscillations arising from the circulation, and the effect of the fluid shear on the suspended crystals. Extensive effort was put forth to grow lysozyme crystals. Under conditions favorable to the growth of tetragonal lysozyme, spontaneous nucleation could be produced but the number of nuclei could not be controlled. Seed transfer techniques were developed and implemented. When conditions for the orthorhombic form were tried, a single crystal 1.5 x 0.5 x 0.2 mm was grown (after in situ nucleation) and successfully extracted. A mathematical model was developed to predict the flow velocity as a function of the geometry and the operating temperatures. The model can also be used to scaleup the apparatus for growing larger crystals of other materials such as water soluble non-linear optical materials. This crystal suspension technology also shows promise for high quality solution growth of optical materials such as TGS and KDP.

Nyce, Thomas A.; Rosenberger, Franz

1989-03-01

291

Tooth enamel proteins enamelin and amelogenin cooperate to regulate the growth morphology of octacalcium phosphate crystals.  

PubMed

To examine the hypothetical cooperative role of enamelin and amelogenin in controlling the growth morphology of enamel crystals in the post-secretory stage, we applied a cation selective membrane system for the growth of octacalcium phosphate (OCP) in the truncated recombinant porcine amelogenin (rP148) with and without the 32kDa enamelin fragment. Enamelin alone inhibited the growth in the c-axis direction more than rP148, yielding OCP crystals with the smallest aspect ratio of all conditions tested. When enamelin was added to the amelogenin "gel-like matrix", the inhibitory action of the protein mixture on the growth of OCP in the c-axis direction was diminished, while that in the b-axis direction was increased. As a result, the length to width ratio (aspect ratio) of OCP crystal was markedly increased. Addition of enamelin to amelogenin enhanced the potential of amelogenin to stabilize the amorphous calcium phosphate (ACP) transient phase. The ratio of enamelin and amelogenin was crucial for stabilization of ACP and the growth of OCP crystals with larger aspect ratio. The cooperative regulatory action of enamelin and amelogenin was attained, presumably, through co-assembling of enamelin and amelogenin. These results have important implications in understanding the growth mechanism of enamel crystals with large aspect ratio. PMID:21483648

Iijima, Mayumi; Fan, Daming; Bromley, Keith M; Sun, Zhi; Moradian-Oldak, Janet

2010-11-01

292

Tooth enamel proteins enamelin and amelogenin cooperate to regulate the growth morphology of octacalcium phosphate crystals  

PubMed Central

To examine the hypothetical cooperative role of enamelin and amelogenin in controlling the growth morphology of enamel crystals in the post-secretory stage, we applied a cation selective membrane system for the growth of octacalcium phosphate (OCP) in the truncated recombinant porcine amelogenin (rP148) with and without the 32kDa enamelin fragment. Enamelin alone inhibited the growth in the c-axis direction more than rP148, yielding OCP crystals with the smallest aspect ratio of all conditions tested. When enamelin was added to the amelogenin “gel-like matrix”, the inhibitory action of the protein mixture on the growth of OCP in the c-axis direction was diminished, while that in the b-axis direction was increased. As a result, the length to width ratio (aspect ratio) of OCP crystal was markedly increased. Addition of enamelin to amelogenin enhanced the potential of amelogenin to stabilize the amorphous calcium phosphate (ACP) transient phase. The ratio of enamelin and amelogenin was crucial for stabilization of ACP and the growth of OCP crystals with larger aspect ratio. The cooperative regulatory action of enamelin and amelogenin was attained, presumably, through co-assembling of enamelin and amelogenin. These results have important implications in understanding the growth mechanism of enamel crystals with large aspect ratio.

Iijima, Mayumi; Fan, Daming; Bromley, Keith M.; Sun, Zhi; Moradian-Oldak, Janet

2010-01-01

293

Single Crystal Growth of Photorefractive Sillenites.  

National Technical Information Service (NTIS)

The compounds, crystallized in the cubic form similar to sillenite structure, occur in a number of isomorphs. The well-known representatives of this family are bismuth germanium (BGO) and bismuth silicon oxides (BSo), both of which can be grown from their...

V. V. Volkov Y. F. Kargin V. M. Skorikov

1992-01-01

294

Single Crystal Growth by Laser CVD.  

National Technical Information Service (NTIS)

CO2 gas lasers prove to be a superb heat source for use in various applications. Using the lasers, thin monocrystals with a diameter of less than 1 mm were grown. The processes are discussed for creation of the crystals, including a report on related work...

S. Hayashi

1988-01-01

295

Studies in Tantalum Oxide Crystal Growth.  

National Technical Information Service (NTIS)

Crystals of beta-Ta2O5 and gamma-Nb2O5 have been grown from molten KPO3 and mixtures of KPO3 and KVO3. A search for additional polymorphs of beta-Ta2O5 in this system has instead revealed five not hitherto reported tantalum compounds containing potassium ...

G. M. Wolten A. B. Chase

1969-01-01

296

Verneuil Growth Experiments with Magnesium Oxide Crystals.  

National Technical Information Service (NTIS)

A plasma torch having very high gas enthalpy and low contamination was developed for growing single crystals of very refractory materials. The torch consisted of a wall-stabilized, constricted-arc, nitrogen-plasma jet using 20-50 kilowatts of d-c power. A...

H. C. Early F. J. Martin E. A. Martin

1969-01-01

297

Liquid phase growth of bulk GaSe crystal implemented with the temperature difference method under controlled vapor pressure  

NASA Astrophysics Data System (ADS)

GaSe crystal has been expected as one of the promising nonlinear optical crystals for highly efficient terahertz (THz) wave generation. However there are several reasons why it is difficult to grow the bulk crystals with high quality. To overcome some difficulties, the temperature difference method under controlled vapor pressure (TDM-CVP) is applied for crystal growth. According to this method, stoichiometric composition can be controlled by the application of Se vapor during crystal growth. Crystal growth is carried out at a constant growth temperature without any mechanical disturbance or vibration. It is also noticed that lower temperature growth enables the reduction of point defect concentration in equilibrium. In this article, surface morphology is observed by an optical microscope using the Nomarski interference method. To identify polytypes of grown crystals, backscattered Raman spectra were measured. X-ray diffraction confirmed the polytypes and single crystalline phase. Infrared (?=1 ?m) and terahertz wave (1–3 THz) transmittance measurements were performed to calculate the absorption coefficient in these wavelength regions. From these results, it is shown that the grown crystals have shown ?-type single phase and the absorption coefficients of grown crystals have been improved according to the increase of applied Se vapor pressure during crystal growth.

Onai, Takahide; Nagai, Yuki; Dezaki, Hikari; Oyama, Yutaka

2013-10-01

298

Methane hydrate crystallization mechanism from in-situ particle sizing  

SciTech Connect

A new experimental setup that makes possible in-situ determinations of the population density function of the methane hydrate particles during its crystallization in a pressurized reactor is used. Thanks to this equipment, new results can be obtained, in particular concerning the granular aspects of the crystallization processes and the influence of the stirring rate. These results are discussed in the framework of a model including gas absorption, primary and secondary nucleation, crystal growth, agglomeration, and breakage. From this discussion, the relevant processes and parameters of methane hydrate crystallization can be determined and quantified.

Herri, J.M. [Ecole des Mines de Saint-Etienne (France)]|[Institut Francais du Petrole, Rueil-Malmaison (France); Pic, J.S.; Gruy, F.; Cournil, M. [Ecole des Mines de Saint-Etienne (France)

1999-03-01

299

Deformation behavior during thermo-mechanical fatigue of a nickel-based single crystal superalloy  

Microsoft Academic Search

The deformation and damage mechanisms of a single crystal nickel-based superalloy CMSX-4 have been investigated under out-of-phase thermo-mechanical fatigue (OP TMF) condition. The failure mechanism was oxide-layered surface initiated crack followed by its planar growth along ? channel. However, the deformation was highly localized to area near crack tip, where multiple groups of parallel twin plates on {111} planes formed

H. U. Hong; B. G. Choi; I. S. Kim; Y. S. Yoo; C. Y. Jo

2011-01-01

300

Nucleation and growth of polytypic-layered crystals from the network liquid zinc chloride  

NASA Astrophysics Data System (ADS)

The liquid to solid crystallization for zinc (II) chloride is studied by molecular dynamics computer simulation. The transition is unusual in that it involves a change from a three-dimensional network liquid structure to a pseudo-two-dimensional layered crystal. The crystallization events are observed from four distinct liquid starting configurations and are identified by reference to the time evolution of the system energetics and Bragg peaks associated with the cation layering. Order parameters and molecular graphics are applied to understand the transitions at an atomistic length scale. Mechanisms are presented for the initial layer growth, the coherent joining of the layered crystallites, and the destruction of high-energy grain boundaries. The growth kinetics are analyzed by defining times for catastrophic and critical nucleation. The final crystal structures are shown to have essentially random anion close-packed stacking sequences consistent with the large number of experimentally observed polytypic structures. The formation of grain boundary stacking faults is also observed.

Wilson, Mark

2003-06-01

301

Reinvestigation of growth of thiourea urea zinc sulfate crystal.  

PubMed

Reinvestigation of the growth of thiourea urea zinc sulfate crystal is reported. Aqueous reaction of thiourea, urea and zinc sulfate in 1:1:1mol ratio results in the formation of the well known [Zn(tu)3(SO4)] (1) (tu=thiourea) crystal and not the 'so called' novel semiorganic nonlinear optical thiourea urea zinc sulfate (2) crystal, as claimed by Redrothu Hanumantha Rao, S. Kalainathan, Spectroscopic investigation, nucleation, growth, optical, thermal and second harmonic studies of novel semi-organic nonlinear optical crystal - Thiourea urea zinc sulfate, Spectrochim. Acta A97 (2012) 456-463. In this work, we demonstrate the usefulness of elemental analytical data, infrared and NMR spectra and X-ray powder pattern, for accurate product characterization. PMID:24060627

Srinivasan, Bikshandarkoil R; Naik, Teja A; Tylczy?ski, Zbigniew; Priolkar, K R

2013-08-28

302

Determination of the activation energy for crystal growth by differential thermal analysis  

Microsoft Academic Search

A method for determining the activation energy for crystal growth was calculated on the basis of the heat balance in the differential thermal analysis (DTA) measurements and the mechanism of nucleation and growth. The theoretical analysis showed that the term ln[Cpd(dT)\\/dt+KdT] should be a linear function of l\\/T, whereCp is the heat capacity of sample and sample holder,K is the

K. Matusita; S. Sakka; Y. Matsui

1975-01-01

303

Numerical simulation of Cz crystal growth in rotating magnetic field with crystal and crucible rotations  

NASA Astrophysics Data System (ADS)

Three-dimensional numerical simulations were carried out to analyze the effect of crystal and crucible rotating directions on heat and oxygen transport in Czochralski crystal growth system under rotating magnetic field. A low-Reynolds number k-? model was used for the description of the turbulent processes. The computational results show that when rotations of crystal, melt and crucible are in the same direction, the oxygen concentration in the melt is the lowest and a low concentration crystal can be obtained. Under rotating magnetic field, the heat transport is dominated by lorentz force induced streaming field and the influence of crystal and crucible rotations on heat transport is weak. Moreover, the effect of crystal rotation on the melt turbulent flow and oxygen transport is stronger than that of crucible.

Zhou, Xiaoming; Huang, Hulin

2012-02-01

304

Crystal growth and characterization of L-histidine hydrochloride monohydrate semiorganic nonlinear optical single crystals  

NASA Astrophysics Data System (ADS)

Nearly perfect single crystals of L-histidine hydrochloride monohydrate have been grown from the solution prepared from the mixture of L-histidine and hydrochloric acid using slow evaporation solution growth technique. Single crystal X-ray diffraction analysis, High resolution X-ray diffraction analysis, fourier transform infrared and FT-Raman analyzes were employed for structural characterization. Linear and nonlinear optical properties have been studied by UV-Vis transmission spectrum and Kurtz Perry technique respectively. The refractive index, redox behavior and hardness of the grown crystal have been found by suitable methods. Thermogravimetric, differential thermal analysis were employed to characterize the as-grown crystals. The second harmonic generation conversion efficiency of the grown crystal and other properties show the suitability of the grown crystal for frequency conversion applications.

Anandan, P.; Jayavel, R.; Saravanan, T.; Parthipan, G.; Vedhi, C.; Mohan Kumar, R.

2012-05-01

305

Effect of Pressure on Crystal Growth  

Microsoft Academic Search

I HAVE been greatly interested in the comments arising from my suggestion that the expansion of setting plaster-of-Paris might be due to the pressure exerted by crystals of gypsum growing non-isotropically in a not completely confined space1. The original suggestion was speculative, and it was made clear that it had no direct experimental confirmation. Undoubtedly, more direct proof would be

F. R. Himsworth

1946-01-01

306

Crystal growth furnace with trap doors  

DOEpatents

An improved furnace is provided for growing crystalline bodies from a melt. The improved furnace is characterized by a door assembly which is remotely controlled and is arranged so as to selectively shut off or permit communication between an access port in the furnace enclosure and a hot zone within that enclosure. The invention is especially adapted to facilitate use of crystal growing cartridges of the type disclosed in U.S. Pat. No. 4,118,197.

Sachs, Emanual M. (Watertown, MA); Mackintosh, Brian H. (Lexington, MA)

1982-06-15

307

Beneficial effect of solubility enhancers on protein crystal nucleation and growth.  

PubMed

Crystallizing solutions of proteins often contain various nonelectrolyte additives that arise from the purification process of proteins or from the reagents employed in the screening kits. Currently, limited knowledge exists about the influence of these additives on the mechanisms underlying the crystallization process, in particular on the nucleation stage of crystals. To address this need, we studied crystallization of two proteins, D-xylose isomerase and chicken egg-white lysozyme, in small batches and in the presence of two solubility-enhancing additives, acetonitrile and glycerol. We have also measured the nucleation rates of crystals of these proteins in the presence and in the absence of acetonitrile using the method of initial rates. With the addition of the solubility enhancers, both proteins exhibited an increase in crystal nucleation at any given supersaturation. Solubility enhancing additives appear to lower the energy barrier to nucleation by influencing the strength of attraction between the protein molecules. We have characterized the quality of D-xylose isomerase crystals by determining the crystal mosaicity, which showed considerable improvement for crystals grown in the presence of additives. When compared to the crystals of chicken egg-white lysozyme, D-xylose isomerase crystals required higher supersaturations to nucleate. We attribute this result to the large size of the D-xylose isomerase molecule, which influences the energy barrier to nucleation by increasing the surface area of the critical nucleus. Contrary to the common expectation that reagents that solubilize the protein may hinder the crystallization process, our results suggest that solubility enhancers, in fact, can have a beneficial effect on the nucleation and growth of crystals. These findings are of importance in formulating successful strategies toward crystallizing new proteins. PMID:19309115

Gosavi, Rajendrakumar A; Bhamidi, Venkateswarlu; Varanasi, Sasidhar; Schall, Constance A

2009-04-21

308

Crystal growth in tellurium flux and characterization of ruthenium dichalcogenides  

Microsoft Academic Search

Growth of RuX2(X = S, Se, Te) by flux method were attempted. Large crystals of RuS2, RuSe0.32Te1.68 and RuTe2 measuring up to 15 × 10 × 10 mm3 with mirror-like surfaces have been grown in tellurium flux by the slow cooling technique with seeds. The stoichiometry of selected crystals are examined by energy dispersive X-ray analysis (EDXA). The difficulties of

Ming-Yih Tsay; Jeng-Kuang Huang; Chia-Shin Chen; Ying-Sheng Huang

1995-01-01

309

Kinetics of gypsum crystal growth on a reverse osmosis membrane  

Microsoft Academic Search

The development of calcium sulfate dihydrate (gypsum) mineral scale in reverse osmosis (RO) membrane desalting was investigated by direct real-time observation of crystal growth. Gypsum scaling studies were conducted in a specially modified plate-and-frame reverse osmosis cell fitted with an optical window, with dark-field membrane lighting arrangement within the membrane cell to enhance crystal boundaries and allow recording of digital

Michal Uchymiak; Eric Lyster; Julius Glater; Yoram Cohen

2008-01-01

310

Investigation of Energy-Transfer Mechanisms in Pyrene Crystals  

Microsoft Academic Search

In this paper we have examined the fluorescence emission spectra, intensity, and decay characteristics and the excitation spectra of pure pyrene crystals and of perylene-doped pyrene crystals at temperatures down to 1.7°K. From these observations we conclude that energy transfer in pyrene crystals occurs by four different mechanisms with the following characteristics: (i) Reabsorption of emitted photons: important at high

Nori Y. C. Chu; Kenji Kawaoka; David R. Kearns

1971-01-01

311

Approach for growth of high-quality and large protein crystals  

PubMed Central

Three crystallization methods for growing large high-quality protein crystals, i.e. crystallization in the presence of a semi-solid agarose gel, top-seeded solution growth (TSSG) and a large-scale hanging-drop method, have previously been presented. In this study the effectiveness of crystallization in the presence of a semi-solid agarose gel has been further evaluated by crystallizing additional proteins in the presence of 2.0% (w/v) agarose gel, resulting in complete gelification with high mechanical strength. In TSSG the seed crystals are hung by a seed holder protruding from the top of the growth vessel to prevent polycrystallization. In the large-scale hanging-drop method, a cut pipette tip was used to maintain large-scale droplets consisting of protein–precipitant solution. Here a novel crystallization method that combines TSSG and the large-scale hanging-drop method is reported. A large and single crystal of lysozyme was obtained by this method.

Matsumura, Hiroyoshi; Sugiyama, Shigeru; Hirose, Mika; Kakinouchi, Keisuke; Maruyama, Mihoko; Murai, Ryota; Adachi, Hiroaki; Takano, Kazufumi; Murakami, Satoshi; Mori, Yusuke; Inoue, Tsuyoshi

2011-01-01

312

Spiral crystal growth of potassium dichromate in gelatin  

NASA Astrophysics Data System (ADS)

Huge spiral crystals of potassium dichromate (K2Cr2O7) have been found to grow three-dimensionally in a gelatin medium when gelatin containing K2Cr2O7 was dried slowly in a test tube at a low temperature. These spirals were all right-handed, and their widths, axial pitches and lengths were 2-3 mm, 5-6 mm and 20-25 mm, repectively. When the gelatin concentration in the medium was decreased, ordinary plate-like crystals were observed to grow, instead of the spiral crystals. To the best of our knowledge, inorganic compounds such as K2Cr2O7 have so far not been reported to form such huge spiral crystals. It is conjectured that collagen molecules, which compose the gelatin medium and have right-handed triple helix structure lead to the growth of spiral crystals.

Suda, Jun-Ichiro; Matsushita, Mitsugu

1995-02-01

313

Crystal growth of device quality GaAs in space  

NASA Astrophysics Data System (ADS)

The program on Crystal Growth of Device Quality GaAs in Space was initiated in 1977. The initial stage covering 1977 to 1984 was devoted strictly to ground-based research. By 1985 the program had evolved into its next logical stage aimed at space growth experiments; however, since the Challenger disaster, the program has been maintained as a ground-based program awaiting activation of experimentation in space. The overall prgram has produced some 80 original scientific publications on GaAs crystal growth, crystal characterization, and new approaches to space processing. Publication completed in the last three years are listed. Their key results are outlined and discussed in the twelve publications included as part of the report.

Gatos, Harry C.; Lagowski, Jacek

1989-02-01

314

Synthesis, growth and characterization of L-Phenylalanine-4-nitrophenol (LPNP) single crystal  

NASA Astrophysics Data System (ADS)

Single crystals of L-Phenylalanine-4-nitrophenol (LPNP) were synthesis and grown by slow cooling solution growth technique. The grown crystals have been subjected to various characterization techniques such as single crystal X-ray diffraction and Powder X-ray diffraction studies to confirm the lattice parameters. Transmittance of the grown crystals was analysed and optical band gap calculated to be 1.54 eV. Thermogravimetric analysis and differential thermal analysis showed that the compound decomposes beyond 170°C. Mechanical behavior of the grown LPNP crystal was analyzed by Vicker's microhardness test. The relative second harmonic efficiency of the compound is found to be 0.3 greater than that of KDP.

Rajalakshmi, M.; Indirajith, R.; Gopalakrishnan, R.

2012-06-01

315

Growth and concentration dependencies of rare-earth doped lithium niobate single crystals  

NASA Astrophysics Data System (ADS)

A series of lithium niobate LiNbO3 (LN) single crystals doped by rare-earth elements (Tm, Er, Dy, Tb, Gd, Pr) were grown under the same conditions by the Czochralski technique in a wide range of dopant concentrations. The distribution coefficients of rare-earth elements in the “crystal—melt” system of LN were determined at the beginning of the crystal growth. Their dependence on the dopant concentration in melt ranging from 0.1 to 3.5 wt% was investigated. Concentration dependences of physicochemical, ferroelectric and structural characteristics of doped LN single crystals were studied using X-ray diffraction, thermal analysis and Raman scattering measurements. A mechanism of rare-earth elements incorporation into the crystal lattice of LN was proposed for a wide range of dopant concentrations.

Palatnikov, M. N.; Biryukova, I. V.; Sidorov, N. V.; Denisov, A. V.; Kalinnikov, V. T.; Smith, P. G. R.; Shur, V. Ya.

2006-06-01

316

Silicon crystal growth in a cusp magnetic field  

NASA Astrophysics Data System (ADS)

In the present Czochralski growth of an Si crystal at the site of an axially symmetric magnetic field cusp, the free surface of the melt is centered between two superconducting coils. It is found that both dopant and oxygen distributions are homogenized by the magnetic field; the controllability of oxygen concentration is due to the ability of the magnetic field cusp to effect a localized control of thermal convection at the melt-crucible interface, independently of convection at the free surface of the melt. High crystal homogeneity is due to the obviation of crystal and crucible rotation changes to preclude oxygen concentrations.

Hirata, Hiroshi; Hoshikawa, Keigo

1989-08-01

317

Lead sulfate scintillator crystal growth for PET applications  

SciTech Connect

It has recently been shown that lead sulfate (PbSO[sub 4]) is a promising scintillator material for use in PET detector systems. However, for lead sulfate scintillators to be useful in such an application, a technique must be developed to grow large optical quality crystals of this material. This paper describes the research into the high-temperature solution growth of PbSO[sub 4] crystals. The authors report on the systematic selection of solvent materials including KCl, LiCl, PbCl[sub 2], Na[sub 2]SO[sub 4] and Li[sub 2]SO[sub 4]. The studies indicate that Na[sub 2]SO[sub 4] is the best solvent. With Na[sub 2]SO[sub 4] as the flux, the authors obtained PbSO[sub 4] single crystals of several millimeters in size by Bridgmann crystal growth method. The authors employed ACRT (Accelerated Crucible Rotation Technique), to resolve the constitutional supercooling problem, thus increase the crystal yield and reduced the number of grains. Finally, the authors compared the scintillation properties of synthetic PbSO[sub 4] crystals the authors grew with previous measurements on natural anglesite and other synthetic crystals, and found them nearly identical.

Zhang, J.G.; Lund, J.C.; Cirignano, L.; Shah, K.S.; Squillante, M.R. (Radiation Monitoring Devices, Inc., Watertown, MA (United States)); Moses, W.W. (Lawrence Berkeley Lab., CA (United States))

1994-08-01

318

Molecular Weight Dependence of Crystal Growth Rate and Its Corresponding States  

NASA Astrophysics Data System (ADS)

Poly(ethylene succinate) (PESU) was crystallized from the melt at a wide range of crystallization temperature. The paper will discuss on molecular weight dependent of spherulite growth rate. PESU was fractionated by GPC method. The fractionated molecular weight (Mp) was in the range of 1,000-10,000. PESU was isothermally crystallized on a slide glass at various temperatures from the melt. Each fractionated sample showed the maximum growth rate (Gmax). The Gmax increased with a decrease in molecular weight up to a certain molecular weight (Mp*=ca. 3,000) and then decreased with a decrease in molecular weight (below Mp*). When the growth rates and crystallization temperatures were normalized with the maximum growth rate and its temperature, a single master curve was observed. The universal plot indicates that the ratio of Go/Gmax shows constant. The molecular weight dependence of growth rate is only associated with Go and Gmax. In the region of molecular weight above Mp*, Log(Gmax) showed a linear relation to Log(Mp) and its slope was about -0.5. On the other hand below Mp*, the molecular weight dependence showed a positive slope of 1. The value of Mp* was coincided with a critical molecular weight of transition from ECC to FCC. The molecular weight dependence will be discussed on the basis of molecular adsorption and its diffusion mechanism on the crystal growing surface.

Okui, Norimasa

2001-03-01

319

Micromechanisms of fatigue crack growth in a single crystal Inconel 718 nickel-based superalloy  

SciTech Connect

The fatigue crack growth behavior of an experimental, single crystal alloy, of equivalent nominal chemical composition to Inconel 718 is presented. Fracture modes under cyclic loading were determined by scanning electron microscopy. The results of the fractographic analyses are presented on a fracture mechanism map that shows the dependence of the fatigue fracture mechanisms on the maximum stress intensity factor, K[sub max], and the stress intensity factor range, [Delta]K. Crack-tip deformation mechanisms associated with fatigue crack growth were studied using transmission electron microscopy. The relative effects of [Delta]K and K[sub max] on the fatigue crack growth behavior of this material are discussed within the context of a two-parameter crack growth law. The influence of grain boundaries on the fatigue crack growth resistance of materials such as Inconel 718 is also discussed in light of the results of this investigation.

Mercer, C.; Soboyejo, A.B.O.; Soboyejo, W.O. (Ohio State Univ., Columbus, OH (United States))

1999-07-09

320

Mechanics of soft-solid-liquid-crystal interfaces  

Microsoft Academic Search

The interfacial mechanics of soft elastic solids and nematic liquid crystals is presented. The theory can be applied to interfaces involving gels, elastomers, biomaterials, and thermotropic nematic liquid crystals. A model of anisotropic elastic interfaces is formulated and used to derive two fundamental capillary quantities: (i) interfacial torques on the nematic orientation, and (ii) capillary pressure. The couplings between soft-solid

Alejandro D. Rey

2005-01-01

321

Dendritic crystal growth in pure /sup 4/He  

SciTech Connect

Dendritic crystal growth of pure hcp and fcc /sup 4/He was observed at pressures between 210 and 6500 bar. Dendrite morphology depends on fluid supercooling and crystal phase. At large supercooling, dendrites with side arms are observed, whereas at low supercooling dendrites grow without side arms. The morpholpogy of hcp /sup 4/He dendrites is strongly influenced by crystalline anisotropy. Comparison with present theories of dendrite growth show good agreement with the power law dependencies of velocity, tip radius, and Peclet number on supercooling. Numerically, theory predicts much larger velocities than are observed. The stability parameter sigma is found to be much smaller than theoretically predicted.

Franck, J.P.; Jung, J.

1986-08-01

322

Crystals  

NSDL National Science Digital Library

In this earth science/math/art activity, learners use simple ingredients to grow crystals and examine the repeating geometric shapes and patterns. Learners compare the growth of crystals from four types of crystal-starters (table salt, Borax, sand, and Epsom salt) to see which starter grows the most crystals in 14 days. Learners report their results online and find out what other learners discovered. Afterward, learners can use the crystals they grew to create works of art.

Science, Lawrence H.

2009-01-01

323

The mechanical properties of single crystal {alpha}-Si{sub 3}N{sub 4}  

SciTech Connect

The ambient and high temperature mechanical properties of single crystal {alpha}{minus}Si{sub 3}N{sub 4} synthesized by chemical vapor deposition are reported. Crack patterns in the as-grown crystals and around Vicker`s indentations reveal that significant residual stresses develop during growth. Indentation studies indicate that the cleavage is essentially isotropic in {alpha}{minus}Si{sub 3}N{sub 4} at 25 C as well as at 1400 C. Transmission electron microscopy on crystals deformed at high temperatures, confirmed previous observation that high-temperature slip occurs primarily on (1011)[1120] system.

Reimanis, I.E.; Suematsu, H.; Petrovic, J.J.; Mitchell, T.E.

1993-11-01

324

Unidirectional growth of Methyl 2-amino-5-bromobenzoate crystal by Sankaranarayanan-Ramasamy method and its characterization  

NASA Astrophysics Data System (ADS)

Bulk single crystal of Methyl 2-amino-5-bromobenzoate (M2A5B) nonlinear optical single crystal of size 60 mm length and 15 mm diameter was successfully grown from solution by Unidirectional growth method of Sankaranarayanan-Ramasamy (SR) for the first time in the literature. The growth conditions were optimized and the growth rate of 1.5 mm per day was observed for the SR grown crystal. The crystal system and its lattice parameters were confirmed by single crystal X-ray diffraction studies. The UV-vis transmission, Photoluminescence, Chemical Etching And Mechanical behavior of M2A5B were studied for conventional and SR methods grown crystals and compared. The second harmonic generation efficiency of M2A5B was confirmed by Kurtz-Perry powder method.

Parthasarathy, M.; Gopalakrishnan, R.

2013-06-01

325

A generalized electrochemical aggregative growth mechanism.  

PubMed

The early stages of nanocrystal nucleation and growth are still an active field of research and remain unrevealed. In this work, by the combination of aberration-corrected transmission electron microscopy (TEM) and electrochemical characterization of the electrodeposition of different metals, we provide a complete reformulation of the Volmer-Weber 3D island growth mechanism, which has always been accepted to explain the early stages of metal electrodeposition and thin-film growth on low-energy substrates. We have developed a Generalized Electrochemical Aggregative Growth Mechanism which mimics the atomistic processes during the early stages of thin-film growth, by incorporating nanoclusters as building blocks. We discuss the influence of new processes such as nanocluster self-limiting growth, surface diffusion, aggregation, and coalescence on the growth mechanism and morphology of the resulting nanostructures. Self-limiting growth mechanisms hinder nanocluster growth and favor coalescence driven growth. The size of the primary nanoclusters is independent of the applied potential and deposition time. The balance between nucleation, nanocluster surface diffusion, and coalescence depends on the material and the overpotential, and influences strongly the morphology of the deposits. A small extent of coalescence leads to ultraporous dendritic structures, large surface coverage, and small particle size. Contrarily, full recrystallization leads to larger hemispherical monocrystalline islands and smaller particle density. The mechanism we propose represents a scientific breakthrough from the fundamental point of view and indicates that achieving the right balance between nucleation, self-limiting growth, cluster surface diffusion, and coalescence is essential and opens new, exciting possibilities to build up enhanced supported nanostructures using nanoclusters as building blocks. PMID:23809002

Ustarroz, Jon; Hammons, Joshua A; Altantzis, Thomas; Hubin, Annick; Bals, Sara; Terryn, Herman

2013-07-17

326

Emittance concept and growth mechanisms  

SciTech Connect

The authors present an introduction to the subjects of emittance and space-charge effects in charged-particle beams. This is followed by a discussion of three important topics that are at the frontier of this field. The first is a simple model, describing space-charge-induced emittance growth, which yields scaling formulas and some physical explanations for some of the surprising results. The second is a discussion of beam halo, an introduction to the particle-core model, and a brief summary of its results. The third topic is an introduction to the hypothesis of equipartitioning for collisionless particle beams.

Wangler, T.P. [Los Alamos National Lab., NM (United States). Accelerator Operations and Technology Div.

1996-05-01

327

Manipulating the Crystal Growth of Organic Energetic Materials on Substrates  

NASA Astrophysics Data System (ADS)

Organic energetic materials (OMEs) have been attracted a lot of attention due to its wide application in military weapon. One of the most compelling researches is manipulating the crystal structure of OEMs due to their performances, such as ignition and burning rate, which depend strongly on the crystalline structure. The crystalline structure of OEMs on substrates has strong dependence on the experimental parameters, such as the deposition rate and external factors. This report demonstrates a new technique for manipulating the crystal growth of OEMs on substrates by micro-contact printing. The methodology depends on coating a polymer stamp with a surfactant, which has a strong affinity for the OEMs deposited on the substrate. The coated stamp selectively removes OEMs in contact areas when the stamp was lifted. And then the OEMs that were left on the substrates grew to the crystals. By careful choice facile film preparation method and optimal stamp pattern, this technique provides a new methodology for fabricating OEMs crystals from hexagon single crystals, dendrite crystals to micro-rod crystals and manipulating the size and distribution of these crystals.

Zhang, Xin; Zhang, Gengxin; Weeks, Brandon

2012-10-01

328

Crystal growth in porous materials—I: The crystallization pressure of large crystals  

Microsoft Academic Search

A critical review of the existing literature on the pressure exerted by growing crystals in porous materials reveals that a number of different equations are in use. A derivation of an equation for the crystallization pressure based on the chemical potentials of the loaded and the unloaded faces of a growing crystal is provided. The equation obtained is compared to

Michael Steiger

2005-01-01

329

Structural and mechanical studies of cadmium manganese thiocyanate crystal  

NASA Astrophysics Data System (ADS)

Single crystals of cadmium manganese thiocyanate (CMTC) have been synthesized successfully and grown by slow evaporation method. The structural perfection of the grown crystals has been analyzed by High resolution X-ray diffraction (HRXRD), which shows the crystalline perfection of the grown crystal is quite good. Optical behavior was assessed by UV-Vis analysis and found that no absorption in the UV visible region and it may be useful for second harmonic applications. The mechanical hardness of the grown crystals was studied and Vicker's microhardness, Stiffness constant was calculated.

Manikandan, M. R.; Vijayaprasath, G.; babu, G. Anandha; Bhagavannarayan, G.; Vijayan, N.; Ravi, G.

2012-06-01

330

Hydrothermal Growth of Crystals of LAALO3.  

National Technical Information Service (NTIS)

LaAlO3 has been successfully grown in a hydrothermal system below and above the transition temperature of 435C. Using small autoclaves, growth has been observed in the temperature range of 400C - 600C in 7 m K2CO3 at 10,000 to 20,000 psi. A high pressure ...

1964-01-01

331

Visual Simulation of Ice Crystal Growth  

Microsoft Academic Search

The beautiful, branching structure of ice is one of the most striking visual phenomena of the winter landscape. Yet there is little study about modeling this effect in computer graphics. In this paper, we present a novel approach for visual simulation of ice growth. We use a numerical simulation technique from computational physics, the \\

Theodore Kim; Ming C. Lin

2003-01-01

332

Physical mechanism of crystal hyaline cortex emulsification with YAG laser  

NASA Astrophysics Data System (ADS)

Thirty-six cases of crystal hyaline cortex emulsification operations for immature cataract with an YAG laser are reported in this paper. According to the basic theory of interaction between laser and tissues, the mechanisms of laser induced hyaline cortex emulsification in the operation are discussed, and it is put forward that the mechanical effect of laser plasma shock wave and photochemical effect of plasma flash on eye tissues result in degeneration and coagulation of the crystal hyaline cortex tissue protein.

Ni, Xiao-Wu; Lu, Jian-Feng; He, An-Zhi; Li, Yong-Nian

1994-06-01

333

Growth and characterization of sulphate mixed L-arginine phosphate and ammonium dihydrogen phosphate/potassium dihydrogen phosphate mixed crystals  

NASA Astrophysics Data System (ADS)

Our investigations on the growth of the mixed crystals of L-arginine phosphate sulphate and ammonium dihydrogen phosphate/potassium dihydrogen phosphate (ADP/KDP) are presented. The structural, mechanical, electrical and optical properties of L-arginine phosphate (LAP) and L-arginine phosphate sulphate (LAPS) crystals are discussed. Pure and mixed crystals of KDP and ADP have been grown on KDP seeds for the entire range of compositions.

Ravi, G.; Srinivasan, K.; Anbukumar, S.; Ramasamy, P.

1994-04-01

334

2D modeling of the regeneration surface growth on crystals  

NASA Astrophysics Data System (ADS)

A physical model is proposed to describe the growth of regeneration surfaces (flat crystal surfaces that are not parallel to any possible faces). According to this model, the change in the growth rate of a regeneration surface during its evolution and the decrease in the number of subindividuals forming the growth front can be explained by the implementation of two types of geometric selection: within each subindividual (the absorption of rapidly growing faces by slowly growing ones) and between subindividuals (when subindividuals absorb each other). A numerical modeling of the growth of the regeneration surface (30.30.19) of potassium alum crystals showed quantitative agreement between the model proposed and the experimental data.

Thomas, V. G.; Gavryushkin, P. N.; Fursenko, D. A.

2012-11-01

335

Mechanism of plant growth promotion by rhizobacteria.  

PubMed

Plant growth results from interaction of roots and shoots with the environment. The environment for roots is the soil or planting medium which provide structural support as well as water and nutrients to the plant. Roots also support the growth and functions of a complex of microorganisms that can have a profound effect on the growth anti survival of plants. These microorganisms constitute rhizosphere microflora and can be categorized as deleterious, beneficial, or neutral with respect to root/plant health. Beneficial interactions between roots and microbes do occur in rhizosphere and can be enhanced. Increased plant growth and crop yield can be obtained upon inoculating seeds or roots with certain specific root-colonizing bacteria- 'plant growth promoting rhizobacteria'. In this review, we discuss the mechanisms by which plant growth promoting rhizobacteria may stimulate plant growth. PMID:12561941

Gupta, A; Gopal, M; Tilak, K V

2000-09-01

336

Recent Advances in High-Growth Rate Single-Crystal CVD Diamond  

SciTech Connect

There have been important advances in microwave plasma chemical vapor deposition (MPCVD) of large single-crystal CVD diamond at high growth rates and applications of this diamond. The types of gas chemistry and growth conditions, including microwave power, pressure, and substrate surface temperatures, have been varied to optimize diamond quality and growth rates. The diamond has been characterized by a variety of spectroscopic and diffraction techniques. We have grown single-crystal CVD diamond over ten carats and above 1 cm in thickness at growth rates of 50-100 {micro}m/h. Colorless and near colorless single crystals up to two carats have been produced by further optimizing the process. The nominal Vickers fracture toughness of this high-growth rate diamond can be tuned to exceed 20 MPa m{sup 1/2} in comparison to 5-10 MPa m{sup 1/2} for conventional natural and CVD diamond. Post-growth high-pressure/high-temperature (HPHT) and low-pressure/high-temperature (LPHT) annealing have been carried out to alter the optical, mechanical, and electronic properties. Most recently, single-crystal CVD diamond has been successfully annealed by LPHT methods without graphitization up to 2200 C and < 300 Torr for periods of time ranging from a fraction of minute to a few hours. Significant changes observed in UV, visible, infrared, and photoluminescence spectra are attributed to changes in various vacancy centers and extended defects.

Liang, Q.; Yan, C; Meng, Y; Lai, J; Krasnicki, S; Mao, H; Hemley, R

2009-01-01

337

An experimental study of crystallization and crystal growth of methane hydrates from melting ice  

Microsoft Academic Search

An experiment with well defined gas-water interfacial surface area was developed to study the crystallization and crystal growth of methane hydrates. Measurable formation rates were observed only when melting ice was involved. No hydrates nucleated from liquid water or from non-melting ice. It is concluded that melting ice, which like hydrate water is hydrogen-bonded, provides a template for hydrate nucleation

M. J. Hwang; D. A. Wright; A. Kapur; G. D. Holder

1990-01-01

338

Crystal growth of device quality GaAs in space  

Microsoft Academic Search

The program on Crystal Growth of Device Quality GaAs in Space was initiated in 1977. The initial stage covering 1977 to 1984 was devoted strictly to ground-based research. By 1985 the program had evolved into its next logical stage aimed at space growth experiments; however, since the Challenger disaster, the program has been maintained as a ground-based program awaiting activation

Harry C. Gatos; Jacek Lagowski

1989-01-01

339

Kinetics of Crystal Growth From Silicate Melts: Anorthite and Diopside  

Microsoft Academic Search

Rates of linear crystal growth have been measured for diopside and anorthite growing from their own melts by using a microscope heating stage. Rates were obtained for undercoolings of as little as 13øC. The rates are higher for diopside than for anorthite. Maximum growth rates observed are 1.5 X 10 -' cm\\/s (AT = 194øC) for anorthite and 2.2 X

R. James Kirkpatrick; Gilpin R. Robinson; James Fred Hays

1976-01-01

340

SIMULATION OF CRYSTALLIZATION KINETICS AND MORPHOLOGICAL DEVELOPMENT DURING ISOTHERMAL CRYSTALLIZATION OF POLYMERS: EFFECT OF NUMBER OF NUCLEI AND GROWTH RATE  

Microsoft Academic Search

The effect of number of nuclei and growth rate on crystallization kinetics and detailed morphological development during isothermal crystallization of a polymer was investigated using a stochastic simulation. The results show that number of nuclei significantly affects both crystallization kinetics and polymer morphology. An increase in the number of nuclei hastens the crystallization process by speeding up the impingement phenomenon

Saraporn Ketdee; Siripon Anantawaraskul

2008-01-01

341

The mechanisms of fatigue crack growth at low growth rates  

NASA Astrophysics Data System (ADS)

The thesis described the mechanisms of crack growth at low growth rates in 1018 steel. For a comparison purpose a 2519 aluminum was also investigated. Further, a detailed study of the striation formation process at high growth rates where striations were readily seen was carried out for the later comparison with that at low growth rates. The environment effect, such as air vs vacuum, was also undertaken. Sawtooth type striations are found on the fracture surface at high growth rates and they are formed cycle by cycle, indicating the crack growth is continuous in this range. "Striation-like" markings are found on the fracture surface at low growth rates and they are actually the reflection of underlying dislocation structures. Fine striations are also found between the "striation-like" markings and they are the continuation of the striations at high growth rates. Crack proceeds along (011) planes through the underlying subgrains cycle by cycle and form the fine striations on the crack surface. The environment, such as vacuum, changes the fracture features at high growth rates to some extent but does not change those at low growth rates. Striations in 2519 aluminum are found to have underlying dislocation bands, which is similar to the situation in 1018 steel.

Cai, Hengfeng

342

Physico-mechanical and dissolution behaviours of ibuprofen crystals crystallized in the presence of various additives  

PubMed Central

Background and the purpose of the study The success of any direct-tableting procedure is strongly affected by the quality of the crystals used in the process. Ibuprofen is a poorly compactible drug with a high tendency for capping. In order to use ibuprofen in direct compression formulations, physico-mechanical properties of ibuprofen should be improved considerably. The aim of the present investigation was to employ crystallization techniques in order to improve the physico- mechanical properties of ibuprofen for direct compression. Methods The experimental methods involved the preparation of ibuprofen crystals by solvent change technique. Ibuprofen was dissolved in ethanol and crystallized out with water in the absence or presence of various hydrophilic additives (PEG 6000, 8000, Brij 98P and polyvinyl alcohol 22000, PVA 22000) with different concentrations. The physico-mechanical properties of the ibuprofen crystals were studied in terms of flow, density, tensile strength and dissolution behaviour. Morphology of ibuprofen crystals was studied by scanning electron microscopic (SEM). Solid state of the recrystallized particles was also investigated using differential scanning calorimeter (DSC) and FT-IR. Results Ibuprofen samples crystallized in the presence of PEG 6000 and 8000 and PVA showed remarkable increase in the tensile strengths of the directly compressed tablets, while some other additives, i.e. Brij 98P did not produce improved ibuprofen crystals. Ibuprofen powders made from particles obtained in the presence of PVA and Brij 98P showed similar dissolution profiles to the commercial ibuprofen particles. DSC and FT-IR results ruled out any significant interaction between ibuprofen and additives except for the samples crystallized in the presence of PEG 8000. Conclusion The crystal habit of ibuprofen can be altered successfully by the crystallization technique which was developed in this study. The crystals developed in the presence of certain additives can be recommended for direct compression.

Nokhodchi, A.; Amire, O.; Jelvehgari, M.

2010-01-01

343

Crystal growth of clathrate hydrate in gas/liquid/liquid system: variations in crystal-growth behavior.  

PubMed

This paper reports the visual observations of the formation and growth of structure-II hydrate crystals on a water droplet partially immersed in liquid cyclopentane and exposed to difluoromethane gas. Each of the experiments was performed under prescribed temperature and pressure conditions in the range from 281.7 to 297.0 K and from 0.12 to 1.10 MPa in order to investigate the effect of the driving force for the hydrate crystal growth. The experiments were conducted at 25 different temperature-pressure conditions. It was found that the behavior of the hydrate crystal growth in this three-component system can be classified into three modes, which we called "cover", "expansion" and "line", depending on the temperature and pressure. The descriptions of the three types are summarized as follows. "COVER": Hydrate crystals first formed on the water-droplet surface and then grew to form a polycrystalline layer covering the surface. After complete surface coverage, no more hydrate growth and little change in the shape of the hydrate-covered water droplet were observed. "EXPANSION": Like "cover", the first crystals were observed on the water-droplet surface. They grew not only along the surface, but also toward the gas phase, and then continued to grow for more than several tens of minutes after complete coverage. "LINE": Unlike the other two modes, hydrate crystals first formed at the three-phase interfacial line and grew along this line. The shape of the hydrate crystals eventually became like a doughnut, since the center of the water droplet collapsed when they grew. PMID:21735490

Ishida, Yosuke; Sakemoto, Riki; Ohmura, Ryo

2011-07-06

344

AlN Bulk Crystal Growth by Physical Vapor Transport  

NASA Astrophysics Data System (ADS)

Despite considerable research in thin-film growth of wide-bandgap group III nitride semiconductors, substrate technology remains a critical issue for the improvement of nitride devices. With applications ranging from high-power electronics to optoelectronics, an increasing number of nitride semiconductor devices are becoming commercially available. Currently, many of these devices are being grown heteroepitaxially on nonnative substrates, leading to a high defect density in the active layers, which limits device performance and lifetime. Aluminum nitride (AlN) is considered a highly desirable candidate as a native substrate material for III-nitride epitaxy, especially for AlGaN devices with high Al concentrations. AlN crystals have been grown by a variety of methods. High-temperature growth of AlN bulk crystals by physical vapor transport (PVT) has emerged as the most promising growth technique to date for production of large, high-quality single crystals. This chapter reviews recent growth and characterization results of AlN bulk crystals grown by PVT and discusses several issues that remain to be addressed for continued development of this technology.

Dalmau, Rafael; Sitar, Zlatko

345

The Clapeyron effect in succinonitrile: applications to crystal growth  

Microsoft Academic Search

This paper describes experiments that measure the Clapeyron effect, i.e., the change in melting temperature with static pressure in succinonitrile (SCN), a common model material used in crystal growth experiments. The Clapeyron results also yield information about the density change upon solidification – a parameter that is difficult to measure accurately and directly in SCN due to void formation in

J. C LaCombe; M. B Koss; L. A Tennenhouse; E. A Winsa; M. E Glicksman

1998-01-01

346

Nucleation, crystal growth and the thermal regime of cooling magmas  

Microsoft Academic Search

Crystallization at the margin of a quiet cooling magma has been studied numerically, taking into account the kinetics of crystalligation. The variables are the latent heat value, the growth and nucleation functions, the initial magma temperature, and the thermal contrast between magma and country rock. We have investigated a wide range of values for these parameters corresponding to natural conditions.

Geneviéve Brandeis; Claude Jaupart; Claude J. Allégre

1984-01-01

347

Ampoule failure sensor development for semiconductor crystal growth experiments  

Microsoft Academic Search

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

Dale A. Watring; Martin Johnson

1994-01-01

348

Second harmonic generation and crystal growth of new chalcone derivatives  

NASA Astrophysics Data System (ADS)

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.

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

2007-05-01

349

Aluminium segregation of TiAl during single crystal growth  

SciTech Connect

{gamma}-TiAl single crystals have been successfully prepared by an induction-heated cold crucible Czochralski technique which offers more flexibility than vertical float zoning. Compositional analysis of the Czochralski grown single crystals indicates a homogeneous composition after initial transition; and the average composition is close to the peritectic composition. However, {gamma}-TiAl single crystals prepared by vertical float zoning show a small aluminium segregation profile along the growth direction; and the average composition of the as-grown crystals is close to that of the starting alloy. Compositional analysis further demonstrated the banded structure with alternative single {gamma}-phase and {alpha}{sub 2} + {gamma} lamellar regions in the vertical float zoned Ti-54 at.% Al.

Bi, Y.J.; Abell, J.S. [Univ. of Birmingham (United Kingdom). School of Metallurgy and Materials

1997-09-15

350

Titanium Nitride Epitaxy on Tungsten (100) by Sublimation Crystal Growth  

SciTech Connect

Titanium nitride crystals were grown from titanium nitride powder on tungsten by the sublimation-recondensation technique. The bright golden TiN crystals displayed a variety of shapes including cubes, truncated tetrahedrons, truncated octahedrons, and tetrahedrons bounded by (111) and (100) crystal planes. The TiN crystals formed regular, repeated patterns within individual W grains that suggested epitaxy. X-ray diffraction and electron backscattering diffraction revealed that the tungsten foil was highly textured with a preferred foil normal of (100) and confirmed that the TiN particles deposited epitaxially with the orientation TiN(100)/W(100) and TiN[100]/W[110], that is, the unit cells of the TiN crystals were rotated 45{sup o} with respect to the tungsten. Because of its larger coefficient of thermal expansion compared to W, upon cooling from the growth temperature, the TiN crystals were under in-plane tensile strain, causing many of the TiN crystals to crack.

Mercurio, Lisa [Kansas State University; Du, Li [Kansas State University; Edgar, J H [Kansas State University; Kenik, Edward A [ORNL

2007-01-01

351

Epitaxial growth of single crystal films  

NASA Astrophysics Data System (ADS)

An experiment in gallium arsenide liquid phase epitaxy (LPE) on a flight of the SPAR 6 is described. A general purpose LPE processor suitable for either SPAR or Space Transportation System flights was designed and built. The process was started before the launch, and only the final step, in which the epitaxial film is grown, was performed during the flight. The experiment achieved its objectives; epitaxial films of reasonably good quality and very nearly the thickness predicted for convection free diffusion limited growth were produced. The films were examined by conventional analytical techniques and compared with films grown in normal gravity.

Lind, M. D.; Kroes, R. L.; Immorlica, A. A., Jr.

1981-10-01

352

The effect of nucleation and crystal growth on isotope fractionation  

NASA Astrophysics Data System (ADS)

A set of "free-drift" experiments is conducted to precipitate aragonites from seawater at controlled temperature (25-55oC) and CO2 degassing rate in the lab. These experiments help to calibrate a coupled degassing-nucleation-crystal growth model, which not only can reproduce measured pH and alkalinity over the course of the experiments, but also predict crystal size within a factor of two of the measured values, the activation energy of the precipitation reaction constant to be 24.3±1.3 kJ/mol, the surface energy of aragonite crystals that is consistent with estimation by atomistic simulation and crystal morphology. Forward simulation of our precipitation experiments using calibrated parameters reveal the supersaturation of seawater arrives at a critical value (~13-50 in our experiment) before nucleation initiates and when the concentration of the total dissolved inorganic carbon (DIC) reduces to that of Ca. This result cannot be explained by classical nucleation theory (CNT), but is consistent with recently proposed "two-step" nucleation model, implying solution chemistry determines when the nucleation starts but the surface properties of crystal (surface energy and crystal morphology) determine the size of the crystal. It also requires not only carbonate ions but all other DIC species within a sphere of a-few-micron radius actively participate into the nucleation process. This model is then used as a framework to understand oxygen and Mg isotope fractionation between carbonates and fluid. Our results suggest nucleation and crystal growth will affect isotope fractionation at different levels depending on experimental conditions. A quantitative analysis using our model can help reconcile the isotope fractionation factors determined by various experimental approaches.

Wang, Z.; Gaetani, G. A.; Liu, C.; Hu, P.; Cohen, A. L.

2011-12-01

353

Crystal Growth in the Presence of Surface Melting and Impurities: An Explanation of Snow Crystal Growth Morphologies  

Microsoft Academic Search

We examine the molecular dynamics of crystal growth in the presence of\\u000asurface melting and surface impurities, and from this propose a detailed\\u000amicroscopic model for the growth of ice from the vapor phase. Our model\\u000anaturally accounts for many aspects of the experimental data that are otherwise\\u000adifficult to explain, and it suggests a variety of measurements that can

Kenneth G. Libbrecht

2008-01-01

354

Crystal growth of YBCO coated conductors by TFA–MOD method  

Microsoft Academic Search

The crystal growth mechanism of TFA (trifluoroacetates)–MOD (metal organic deposition) derived YBa2Cu3Oy has been investigated to understand the process for higher production rates of the conversion process. YBCO films were prepared by TFA–MOD on CeO2\\/Gd2Zr2O7\\/Hastelloy C276 substrates. The growth rates of YBCO derived from Y:Ba:Cu=1:2:3 and 1:1.5:3 starting solutions were investigated by XRD and TEM analyses. YBCO growth proceeds in

M. Yoshizumi; T. Nakanishi; J. Matsuda; K. Nakaoka; Y. Sutoh; T. Izumi; Y. Shiohara

2008-01-01

355

Crystal growth, EPR and site-selective laser spectroscopy of Gd 3+-activated LiCaALF 6 single crystals  

Microsoft Academic Search

Ce3+-activated LiCaAlF6 (LiCAF) and LiSrAlF6 (LiSAF) single crystals are the most prospective active media for directly pumped UV solid-state tunable lasers. Due to the geterovalent activation nature of these crystals, crystal spectroscopic properties as well as their laser efficiency strongly depend on the actual crystal growth conditions. In order to establish the growth-related peculiarities of activator center formation in LiCAF,

R. Yu. Abdulsabirov; M. A. Dubinskii; S. L. Korableva; A. K. Naumov; V. V. Semashko; V. G. Stepanov; M. S. Zhuchkov

2001-01-01

356

Mechanical properties of single crystal YAg  

SciTech Connect

YAg, a rare earth-precious metal 'line compound', is one member of the family of B2 rare earth intermetallic compounds that exhibit high ductilities. Tensile tests of polycrystalline YAg specimens have produced elongations as high as 27% before failure. In the present work, single crystal specimens of YAg with the B2, CsCl-type crystal structure were tensile tested at room temperature. Specimens with a tensile axis orientation of [0 1 1-bar] displayed slip lines on the specimen faces corresponding to slip on the {l_brace}1 1 0{r_brace}<0 1 0> with a critical resolved shear stress of 13 MPa. A specimen with a tensile axis orientation of [1 0 0] showed no slip lines and began to crack at a stress of 300 MPa. The test specimens also displayed some slip lines whose position corresponded to slip on the {l_brace}1 0 0{r_brace}<0 1 0>; these slip lines were found near intersections of {l_brace}1 1 0{r_brace}<0 1 0> slip lines, which suggests that the {l_brace}1 0 0{r_brace}<0 1 0> may be a secondary slip system in YAg. Transmission electron microscope (TEM) examination of the crystals was performed after tensile testing and the dislocations observed were analyzed by g {center_dot} b=0 out of contrast analysis. This TEM analysis indicated that the predominant Burgers vector for the dislocations present was <1 1 1> with some <0 1 1> dislocations also being observed. This finding is inconsistent with the <0 1 0> slip direction determined by slip line analysis, and possible explanations for this surprising finding are presented.

Russell, A.M.; Zhang, Z.; Lograsso, T.A.; Lo, C.C.H.; Pecharsky, A.O.; Morris, J.R.; Ye, Y.; Gschneidner, K.A.; Slager, A.J

2004-08-02

357

Growth of Tourmaline Crystals (Based on Natural Observations and Experimental Data).  

National Technical Information Service (NTIS)

The method of growth of an individual crystal determines its internal structure, which in turn characterizes the quality of the crystal. This is especially important for crystals of minerals that are used directly in technology. Tourmaline is one such min...

M. M. Slivko I. E. Voskresenskaya

1966-01-01

358

Peculiarities of the growth of KDP single crystals with incorporated aluminium oxyhydroxide nanoparticles  

NASA Astrophysics Data System (ADS)

Grown for the first time are KH2PO4 (KDP) crystals with incorporated aluminium oxyhydroxide Al2O3·nH2O nanoparticles (n=3.5-3.6). The influence of the nanoparticles on the structure perfection and the growth kinetics of the crystal faces are studied. The presence of the nanoparticles in the crystal matrix is confirmed by the results of chemical analysis, X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM). The most essential inhibiting effect of the nanoparticles is observed for the {100} faces. The mechanism of influence of the nanoparticles on the {100} faces growth is explained on the base of the Cabrera-Vermilyea (C-V) model using Langmuir adsorption isotherm.

Pritula, I. M.; Kosinova, A. V.; Vorontsov, D. A.; Kolybaeva, M. I.; Bezkrovnaya, O. N.; Tkachenko, V. F.; Vovk, O. M.; Grishina, E. V.

2012-09-01

359

Growth and morphology of ruby crystals with unusual chromium concentration  

NASA Astrophysics Data System (ADS)

Single crystals of ruby have been obtained from fluxed melts based on the systems Li2O MoO3, Li2O WO3, Na2O WO3, 2PbO 3V2O5, PbO V2O5 WO3, PbF2 Bi2O3 and Na3AlF6 by both the TSSG method and spontaneous crystallization at the temperatures 1330 900 °C. Al2O3 solubility has been measured for the flux composition of 2Bi2O3 5PbF2 in the temperature range 1200 1000 °C and dissolution enthalpy has been defined as 29.4 KJ/Mol. The composition of grown crystals was studied by electron microprobe analysis. The synthetic ruby contains from 0.51 to 6.38 at% of chromium admixture depending on the crystal growth conditions. Experimental results on growth conditions, composition and morphology of grown crystals are presented for each flux and temperature interval.

Leonyuk, N. I.; Lyutin, A. V.; Maltsev, V. V.; Barilo, S. N.; Bychkov, G. L.; Kurnevich, L. A.; Emelchenko, G. A.; Masalov, V. M.; Zhokhov, A. A.

2005-07-01

360

Using Microfluidics to Decouple Nucleation and Growth of Protein Crystals.  

PubMed

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. PMID:19590751

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

2007-01-01

361

Using Microfluidics to Decouple Nucleation and Growth of Protein Crystals  

PubMed Central

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 ?g protein on a 20 cm2 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.

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

2009-01-01

362

Role of lamellar thickness in the kinetics of polymer crystal growth  

NASA Astrophysics Data System (ADS)

The lamellar thickness of polymer crystals reflects their thermodynamic metastability and meanwhile decides the linear crystal growth rates on their lateral sides. The traditional theories about the growth kinetics of polymer crystals, like Lauritzen-Hoffman theory and Sadler-Gilmer theory, attributed the effect of lamellar thickness to the free energy barrier at the lateral growth front, in order to explain the slower growth of thicker crystals observed at higher temperatures. We studied the linear growth rates of flat-on-oriented polymer crystals in ultra-thin films, by means of dynamic Monte Carlo simulations of lattice polymers. We found that at the same temperatures, the thicker crystals are actually growing faster. The effect of lamellar thickness has no relation with the free energy barrier; rather, it is only related with the driving force for crystal growth. On the basis of the intramolecular crystal nucleation model, we discussed a reasonable microscopic image on the growth kinetics of polymer crystals.

Hu, Wenbing

2012-02-01

363

Crystal Growth, Thermal, Optical and Microhardness Studies of Tris (thiourea) Magnesium Sulphate:. a Semiorganic Nlo Material  

NASA Astrophysics Data System (ADS)

Single crystals of tris (Thiourea) magnesium sulphate (MTS) were grown from aqueous solution by low temperature solution growth technique. The grown crystals have been characterized by X-ray diffraction to confirm the formation of the crystalline phases. The presence of functional groups was identified by Fourier transform infrared spectroscopy. The optical transmission spectrum showed that a lower cut-off wavelength of MTS crystal is below 300 nm and it has a wide transparency window, which is suitable for second harmonic generation of laser in the blue region. The thermal stabilities were studied by differential thermal analysis (DTA) and thermo gravimetric analysis (TGA). Nonlinear optical characteristics of MTS were studied using Q-switched Nd:YAG laser (?=1064 nm). The micro-hardness studies reveal the mechanical properties of the grown crystals.

Pasupathi, G.; Philominathan, P.

364

Mutiple Czochralski growth of silicon crystals from a single crucible  

NASA Astrophysics Data System (ADS)

An apparatus for the Czochralski growth of silicon crystals is presented which is capable of producing multiple ingots from a single crucible. The growth chamber features a refillable crucible with a water-cooled, vacuum-tight isolation valve located between the pull chamber and the growth furnace tank which allows the melt crucible to always be at vacuum or low argon pressure when retrieving crystal or introducing recharge polysilicon feed stock. The grower can thus be recharged to obtain 100 kg of silicon crystal ingots from one crucible, and may accommodate crucibles up to 35 cm in diameter. Evaluation of the impurity contents and I-V characteristics of solar cells fabricated from seven ingots grown from two crucibles reveals a small but consistent decrease in cell efficiency from 10.4% to 9.6% from the first to the fourth ingot made in a single run, which is explained by impurity build-up in the residual melt. The crystal grower thus may offer economic benefits through the extension of crucible lifetime and the reduction of furnace downtime.

Lane, R. L.; Kachare, A. H.

1980-10-01

365

Growth promoting effect of organic impurities on growth kinetics of KAP and KDP crystals  

Microsoft Academic Search

The experimental results of the influence of a variety of organic impurities differing in their chemical behavior on the growth rates of different faces of KAP and KDP crystals are presented. It was observed that, with increasing additive concentration in practically all experiments, an impurity leads first to an increase and then a decrease in the growth rate, passing through

V. A Kuznetsov; T. M Okhrimenko; Miros?awa Rak

1998-01-01

366

Curved faces in polymer crystals with asymmetrically spreading growth patches  

NASA Astrophysics Data System (ADS)

Polymer crystals often have curved faces. Understanding such morphology is of major interest since it allows distinction between fundamentally different theories of polymer crystallization. E.g. Sadler's ``roughness-pinning'' theory assumes that the curvature is a result of roughening transition on lateral faces. It has since been shown by Mansfield that the curvature can be explained quantitatively, essentially within the Lauritzen-Hoffman nucleation theory. However, the step propagation rates v implied in their treatment are substantially lower than predicted by the LH theory. The retardation appears to be due to the ``self-poisoning'' or ``pinning'' effect of incorrect chain attachment, effectively demonstrated by the extreme cases of growth rate minima in long-chain monodisperse n-alkanes. Recently crystals of poly(vinylidene fluoride) and alkanes C162H326 and C198H398 have been found with habits that can be best described as bounded by curved 110 faces. The interesting feature is the asymmetry of the curvature: while the faces are curved at one end, they are straight at the other. We carried out mathematical analysis of the curvature, generalizing the Mansfield model. We suggest that such asymmetric curvature arises from the propagation rates to the left, vl, and to the right, vr, being different because of the lack of mirror bisecting planes such as (110). By solving appropriate equations with moving boundaries, we obtained the shape of the growth front y(x,t). Calculated crystal habits gave excellent fits to the observed growth shapes of a-axis lenticular crystals of long alkanes and PVDF, as well as of single crystals of PEO. This explains some hitherto poorly understood morphologies and, in principle, allows independent measurements of step initiation and propagation rates in all polymers.

Ungar, Goran

2006-03-01

367

Crystal growth and characterization of a semiorganic nonlinear optical single crystal of gamma glycine  

NASA Astrophysics Data System (ADS)

Gamma glycine has been successfully synthesized by taking glycine and potassium chloride and single crystals have been grown by solvent evaporation method for the first time. The grown single crystals have been analyzed with XRD, Fourier transform infrared (FTIR), and thermo gravimetric and differential thermal analyses (TG/DTA) measurements. Its mechanical behavior has been assessed by Vickers microhardness measurements. Its nonlinear optical property has been tested by Kurtz powder technique. Its optical behavior was examined by UV vis., and found that the crystal is transparent in the region between 240 and 1200 nm. Hence, it may be very much useful for the second harmonic generation (SHG) applications.

Prakash, J. Thomas Joseph; Kumararaman, S.

2008-11-01

368

Growth of (Perylene)2 [Pd(mnt)2] crystals  

NASA Astrophysics Data System (ADS)

The conditions for the growth of (Perylene)2 [Pd(mnt)2] crystals either by chemical oxidation and electrochemical routes are described. The electrocrystallisation is limited by close proximity of the oxidation potentials of the perylene donor and [Pd(mnt)2]- anion, and depending on the experimental conditions different morphologies can be obtained. (Per)2 [Pd(mnt)2] crystals obtained by elecrocrystallisation were found to be mainly of the ?-polymorph with properties comparable to the Cu, Ni and Pt analogues previously described at variance with those obtained by chemical oxidation which are mainly of the ?-polymorph .

Afonso, M. L.; Silva, R. A. L.; Matos, M.; Lopes, E. B.; Coutinho, J. T.; Pereira, L. C. J.; Henriques, R. T.; Almeida, M.

2012-02-01

369

Computer Simulation of Growth Process of Binary Quasi Crystal  

NASA Astrophysics Data System (ADS)

We performed Monte Carlo simulation of the aggregation process of a two-component Lennard-Jones system on the two-dimensional (2D) Penrose lattice for the purpose of studying the details of the creation and growth process of quasi crystals. We adopted the potential parameter values proposed by Widom et al. [Phys. Rev. Lett. 58 (1987) 706]. The present simulation clarified that the stability of the formed quasi crystals depends on temperature and the strength of the potential and that the transition from solid state to liquid state occurs when the value of the inverse of the dimensionless temperature is approximately 4.0.

Sasajima, Yasushi; Adachi, Katsumi; Tanaka, Hideki; Ichimura, Minoru; Itaba, Masanori; Ozawa, Satoru

1994-05-01

370

Observation of Growth Pulsations in Polymer Dendritic Crystallization in PEO/PMMA Blend Films  

NSDL National Science Digital Library

We investigate the existence of growth pulsations in dendritic growth using polymer blend films where the crystallization morphology can be studied at high undercooling and over long timescales due to the relatively slow rate of crystallization.

Douglas, Jack; Ferreiro, Vincent; Warren, James A.; Karim, Alamgir

2002-01-01

371

Large volume single crystal growth of cadmium zinc telluride with minimal secondary phases for room temperature radiation detector application  

NASA Astrophysics Data System (ADS)

Two major aspects of Cadmium Zinc Telluride (CdZnTe) crystal growth for room temperature radiation detection application namely tellurium rich second phase defects and single crystal yield have been addressed. Various approaches were considered towards the minimization of these defects both during growth and post growth thermal treatment in cadmium environment. Since the issue of retrograde solubility in CdZnTe pseudo binary alloy system causes tellurium precipitation, different cooling mechanisms were also devised to achieve minimal secondary phases. Some important and encouraging results were obtained relative to the size and distribution of secondary phases upon growing the crystal with different growth rate and different cooling rate of the crystal after growth. Thermomigration of tellurium were also observed while post processing samples in a temperature gradient, in (Cd,Zn) atmosphere. Results indicated orders of magnitude reduction on secondary phases at the expense of sample resistivity. Apart from the issue of secondary phases, CdZnTe also suffers from low single crystal yield. Since grain boundaries and twins are known to hinder the transport properties of charge carriers, it is necessary to have large single crystal volumes with good uniformity for better charge collection efficiency. In our crystal growth facility, single crystal volumes up to 25x25x20 mm3 have been grown using unseeded vertical Bridgman technique. However reproducibility has been a major issue as far as single crystal yield is concerned. In order to consistently produce large volume detector grade material, seeding was attempted in vertical Bridgman set up in which crystals are grown on top of another appropriately oriented seed crystal. Certain important requirements for successful seeded growth are partial melting of the seed from top, proper melt mixing before starting growth and maintaining a convex interface shape to promote outward grain growth. To achieve these conditions, extreme care was taken in designing our experimental set up. Seed crystals with various orientations have been used in different growths. Preliminary results on these growths indicate success in achieving partial seed melting and proper control on the thermal environment. The grown crystals exhibited large number of twins suggesting that the use of seed crystal with proper orientation is critical.

Swain, Santosh Kumar

372

Dynamic mechanisms of blood vessel growth  

PubMed Central

The formation of a polygonal configuration of proto-blood-vessels from initially dispersed cells is the first step in the development of the circulatory system in vertebrates. This initial vascular network later expands to form new blood vessels, primarily via a sprouting mechanism. We review a range of recent results obtained with a Monte Carlo model of chemotactically migrating cells which can explain both de novo blood vessel growth and aspects of blood vessel sprouting. We propose that the initial network forms via a percolation-like instability depending on cell shape, or through an alternative contact-inhibition of motility mechanism which also reproduces aspects of sprouting blood vessel growth.

Merks, Roeland M H; Glazier, James A

2009-01-01

373

Mechanics of soft-solid-liquid-crystal interfaces  

NASA Astrophysics Data System (ADS)

The interfacial mechanics of soft elastic solids and nematic liquid crystals is presented. The theory can be applied to interfaces involving gels, elastomers, biomaterials, and thermotropic nematic liquid crystals. A model of anisotropic elastic interfaces is formulated and used to derive two fundamental capillary quantities: (i) interfacial torques on the nematic orientation, and (ii) capillary pressure. The couplings between soft-solid deformation and liquid-crystal anisotropic interfacial tension is shown to lead to strain-induced anchoring transitions, and strain-induced morphological instabilities.

Rey, Alejandro D.

2005-07-01

374

Ultrasonic reactivation of phosphonate poisoned calcite during crystal growth.  

PubMed

The effect of ultrasonic irradiation (42,150 Hz, 17 W dm(-3)/7.1 W cm(-2)) on the growth of calcite in the presence of the inhibitor nitrilotris(methylene phosphonic acid) (NTMP) was investigated at constant composition conditions. In seeded growth experiments, it was found that the inhibiting effect of NTMP on crystal growth could be seriously mitigated under influence of ultrasonic irradiation. An approximately twofold increase in volumetric growth rate was achieved during ultrasonic irradiation, and recovery of the growth rate following inhibition was strongly enhanced compared to growth experiments without ultrasonic irradiation. The results could be explained in part by the physical effect of ultrasound that causes breakage and attrition of poisoned crystals, which resulted in an increase in fresh surface area. Mass spectroscopy analysis of sonicated NTMP solutions revealed that there is also a chemical effect of ultrasound that plays an important role. Several breakdown products were identified, which showed that ultrasound caused the progressive loss of phosphonate groups from NTMP, probably by means of physicochemically generated free radicals and/or pyrolysis in the hot bubble-bulk interface. PMID:21463963

Boels, L; Wagterveld, R M; Witkamp, G J

2011-04-03

375

Oriented Growth of Single-Crystal Ni Nanowires onto Amorphous SiO(2).  

PubMed

Highly oriented, single-crystal Ni nanowire arrays have been synthesized atop amorphous SiO(2)?Si substrates using a single-step chemical vapor deposition method in the absence of any foreign catalyst. Electron and X-ray diffraction confirm the crystalline quality of the Ni nanowires while magnetoresistance measurements probe the magnetic response and the behavior is explained using simulation results for nanoscale, single-crystal Ni. A growth mechanism involving competing chemical, energetic, and kinetic influences is presented. PMID:21033695

Chan, Keith T; Kan, Jimmy J; Doran, Christopher; Ouyang, Lu; Smith, David J; Fullerton, Eric E

2010-10-29

376

Temperature and Enhanced Adduct Mobility on the Growth of MMTWNMP Single Crystals  

NASA Astrophysics Data System (ADS)

A novel organometallic nonlinear optical crystal material; diaquatetrakis (thiocyanato) manganese (II) mercury (II)-N-methyl-2-pyrrolidone, MnHg(SCN)4(H2O)2.2(C3H6CONCH3), (abbreviated as MMTWNMP) of very good transparency was grown by low temperature solution growth method. The improvement on the quality of the single crystal was analyzed and explained based on the temperature effect and the mobility of adduct N-Methyl Pyrrolidone molecules. A mechanism for the basic mass transport is proposed and reasoned.

Srinivasan, R.; Raghavan, C. M.; Saravanan, L.; Jayavel, R.; Baskar, K.

2011-07-01

377

Crystal growth: A comparison of Monte Carlo simulation nucleation and normal growth theories  

Microsoft Academic Search

We simulated the growth of a (001) Kossel crystal surface on a special-purpose computer. Different nearest-neighbor bond energies in the two lateral directions of our solid-on-solid model were possible (anisotropy). The values which we obtained for the growth rate are much more accurate than previous results on a general-purpose computer. The supersaturation dependence of the growth rate was compared with

J. P. van der Eerden; C. van Leeuwen; P. Bennema; W. L. van der Kruk; B. P. Th. Veltman

1977-01-01

378

Effect of thermal environment evolution on AlN bulk sublimation crystal growth  

NASA Astrophysics Data System (ADS)

To obtain a large and thick AlN single crystal during sublimation growth, it is very important to maintain the thermal environment suitable for growth inside the crucible during a long period of time (>50 h). In this paper, an in-house developed integrated model capable of describing inductive, radiative and conductive heat transfer will be used to simulate the transient behavior of thermal environment inside the crucible during a 40-h experiment growth. Effects of graphite insulation degradation on temperature distribution inside the crucible will be investigated. Simulation results will be compared with the experimental data to study the effects of the insulation degradation-induced particle deposition, geometric variation of source material and crystal size enlargement on the temperature distribution in the crucible and the growth rate. The relationship between graphite insulation degradation and power input change of the induction-heated system will be established. The evolution of temperature difference between the source material and crystal, which is the driving force for growth, will be presented. This study will also provide the explanation of mechanism underling substantial reduction of growth rate after a long experiment run.

Cai, D.; Zheng, L. L.; Zhang, H.; Zhuang, D.; Herro, Z. G.; Schlesser, R.; Sitar, Z.

2007-08-01

379

Time-dependent, protein-directed growth of gold nanoparticles within a single crystal of lysozyme.  

PubMed

Gold nanoparticles are useful in biomedical applications due to their distinct optical properties and high chemical stability. Reports of the biogenic formation of gold colloids from gold complexes has also led to an increased level of interest in the biomineralization of gold. However, the mechanism responsible for biomolecule-directed gold nanoparticle formation remains unclear due to the lack of structural information about biological systems and the fast kinetics of biomimetic chemical systems in solution. Here we show that intact single crystals of lysozyme can be used to study the time-dependent, protein-directed growth of gold nanoparticles. The protein crystals slow down the growth of the gold nanoparticles, allowing detailed kinetic studies to be carried out, and permit a three-dimensional structural characterization that would be difficult to achieve in solution. Furthermore, we show that additional chemical species can be used to fine-tune the growth rate of the gold nanoparticles. PMID:21278750

Wei, Hui; Wang, Zidong; Zhang, Jiong; House, Stephen; Gao, Yi-Gui; Yang, Limin; Robinson, Howard; Tan, Li Huey; Xing, Hang; Hou, Changjun; Robertson, Ian M; Zuo, Jian-Min; Lu, Yi

2011-01-30

380

Time-dependent Protein-directed Growth of Gold Nanoparticles within a Single Crystal of Lysozyme  

SciTech Connect

Gold nanoparticles are useful in biomedical applications due to their distinct optical properties and high chemical stability. Reports of the biogenic formation of gold colloids from gold complexes has also led to an increased level of interest in the biomineralization of gold. However, the mechanism responsible for biomolecule-directed gold nanoparticle formation remains unclear due to the lack of structural information about biological systems and the fast kinetics of biomimetic chemical systems in solution. Here we show that intact single crystals of lysozyme can be used to study the time-dependent, protein-directed growth of gold nanoparticles. The protein crystals slow down the growth of the gold nanoparticles, allowing detailed kinetic studies to be carried out, and permit a three-dimensional structural characterization that would be difficult to achieve in solution. Furthermore, we show that additional chemical species can be used to fine-tune the growth rate of the gold nanoparticles.

H Wei; Z Wang; J Zhang; S House; Y Gao; L Yang; H Robinson; L Tan; H Xing; C Hou

2011-12-31

381

Time-dependent, protein-directed growth of gold nanoparticles within a single crystal of lysozyme  

SciTech Connect

Gold nanoparticles are useful in biomedical applications due to their distinct optical properties and high chemical stability. Reports of the biogenic formation of gold colloids from gold complexes has also led to an increased level of interest in the biomineralization of gold. However, the mechanism responsible for biomolecule-directed gold nanoparticle formation remains unclear due to the lack of structural information about biological systems and the fast kinetics of biomimetic chemical systems in solution. Here we show that intact single crystals of lysozyme can be used to study the time-dependent, protein-directed growth of gold nanoparticles. The protein crystals slow down the growth of the gold nanoparticles, allowing detailed kinetic studies to be carried out, and permit a three-dimensional structural characterization that would be difficult to achieve in solution. Furthermore, we show that additional chemical species can be used to fine-tune the growth rate of the gold nanoparticles.

Wei, H.; Robinson, H.; Wang, Z.; Zhang, J.; House, S.; Gao, Y.-G.; Yang, L.; Tan, L. H.; Xing, H.; Hou, C.; Robertson, I. M.; Zuo, J.-M.; Lu, Y.

2011-01-30

382

Crystal growth and characterization of calcium metaborate scintillators  

NASA Astrophysics Data System (ADS)

Calcium metaborate CaB2O4 single crystals were grown by the Czochralski (CZ) method with the radio-frequency (RF) heating system. In these crystals, a plane cleavage was observed along the growth direction. The crystals had an 80% transparency, and no absorption bands were detected in the 190-900 nm wavelength range. The 241Am 5.5 MeV ?-ray-excited radioluminescence spectrum of CaB2O4 demonstrated a broad intrinsic luminescence peak at 300-400 nm, which originated from the lattice defects or an exciton-based emission. According to the pulse height spectrum, when irradiated by neutrons from a 252Cf source, the scintillation light yielded approximately 3200 photons per neutron (ph/n).

Fujimoto, Y.; Yanagida, T.; Kawaguchi, N.; Fukuda, K.; Totsuka, D.; Watanabe, K.; Yamazaki, A.; Chani, V.; Nikl, M.; Yoshikawa, A.

2013-03-01

383

Fracture and fatigue crack-growth behavior of single crystal NiAl  

SciTech Connect

Single crystal intermetallics have significant potential for gas turbine applications where high temperature strength and oxidation resistance are required. With its low density, high thermal conductivity, and superior oxidation resistance, NiAl + X is a leading candidate as an alternative to conventional superalloys. Typical gas turbine applications will expose the material to significant cyclic and vibrational loading. However, very limited reliable fracture and subcritical crack-growth data currently exists, together with little fundamental understanding of damage and failure modes for NiAl single crystals, particularly at elevated temperatures. There is virtually no knowledge of what constitutes a fracture or fatigue-resistant microstructure or composition, and there is a real uncertainty in potential life-prediction procedures. Accordingly, this work describes progress made in characterizing fracture and fatigue crack-growth behavior in a Nial + Fe single crystal using fracture mechanics based techniques. The authors believe the fatigue crack-growth data presented in this paper to be quite unique, representing the first reported subcritical crack-growth data in such intermetallic single crystals. Surprisingly, their observations appear to indicate that under fatigue loading conditions. cracks may leave the low energy cleavage plane and actually propagate along higher index planes.

Flores, K.M.; Dauskardt, R.H. [Stanford Univ., CA (United States). Dept. of Materials Science and Engineering

1997-06-15

384

Mechanisms for the Crystallization of ZBLAN.  

National Technical Information Service (NTIS)

The objective of this ground based study is to test the hypothesis that shear thinning (the non-Newtonian response of viscosity to shear rate) is a viable mechanism to explain the observation of enhanced glass formation in numerous low-g experiments. In 1...

E. C. Ethridge D. S. Tucker W. Kaukler B. Antar

2003-01-01

385

Growth and morphology of W18O49 crystals produced by microwave decomposition of ammonium paratungstate  

NASA Astrophysics Data System (ADS)

By microwave irradiation of ammonium paratungstate (APT, (NH4)10H2W12O42 × 4H2O), needle crystals of W18O49 with a wide variety of size and morphology were formed. Their sizes and morphologies varied depending on various facets of individual APT pseudomorphous particles on which whiskers were grown, and among neighbouring decomposed APT pseudomorphous particles. Based on scanning electron and transmission electron-microscopic observations, it has been concluded that individual whiskers were monocrystalline and grew by a root growth mechanism from a nucleus formed in the amorphous layer, and that a rapid leader-like whisker growth in length was followed by a subsequent slower growth in thickness. Any evidence supporting a screw dislocation mechanism or tip growth by vapour-liquid-solid have not been detected.

Pfeifer, J.; Badaljan, E.; Tekula-Buxbaum, P.; KováCs, T.; Geszti, O.; TóTh, A. L.; Lunk, H.-J.

1996-12-01

386

The Elastic Constants and Related Mechanical Properties of the Monoclinic Polymorph of the Carbamazepine Molecular Crystal  

NASA Astrophysics Data System (ADS)

Polymorphism is the property of a compound to crystallize in two or more crystalline phases containing different arrangements and/or conformations of the molecules in the crystal lattice. The Phenomenon of polymorphism is a major issue in the pharmaceutical industry especially in relation to drug uptake in the body, tablet processing and growth. This has led to considerable interest in predicting and understanding properties of drug polymorphs, and more recently the mechanical properties of the polymorphs. In this work, Brillouin scattering is used to probe the acoustic phonons of the monoclinic (P21/c) polymorph of the drug, carbamazepine (CBZ). By sampling a variety of acoustic phonons, the complete elastic constant tensor has been determined for this CBZ polymorph. The observed trend in the elastic constants: C11< C22˜C33 is qualitatively associated with the crystal growth pattern seen in CBZ. Investigation into the anisotropy of the intermolecular interactions has been investigated further by calculation of linear compressibilities.

Mohapatra, Himansu; Eckhardt, Craig J.

2007-03-01

387

Microscopic examination of the growth of thin silica colloidal crystals formed by convective assembly  

NASA Astrophysics Data System (ADS)

One simple route to three-dimensional microstructures is to utilize convective assembly, a coating process in which thin colloidal crystals are deposited on a substrate from suspensions of nearly monodisperse spheres. Such crystals (also known as opaline films) have been shown to he highly ordered with a strong tendency toward the face-centered cubic (FCC) structure. Thus, they have become a very popular starting material for a wide range of applications from batteries to microfiltration to photonic crystals. However, the crystallization mechanism of convective assembly is not yet well understood. Hence we explored this issue by examining the microscopic details of convective assembly. We assembled a real-time optical microscopic system with the ability to discern single submicron particles. We then used it to study the kinetics of crystallization quantitatively. The structure of dried crystals was studied by electron microscopy and scanning confocal microscopy. Using real-time microscopic visualization, electron microscopy, and scanning confocal microscopy, we uncovered the interesting and unexpected features of the crystallization process. To help understand our experimental results, we modeled and simulated the flow through sphere packings by using a simplified network analysis. The study examined the ability of fluid flow to steer the motion of colloidal spheres as they attach to the surface of the growing crystal. This helped elucidate the role of flow in the crystal formation. This thesis research should provide a better understanding of the mechanism of growth as well as an avenue for developing a new class of self-assembly techniques. By clever design of the process, new micro- and nanostructured films may be obtained.

Meng, Linli

388

Effect of L-Valine on the growth and characterization of Sodium Acid Phthalate (SAP) single crystals.  

PubMed

Undoped and amino acid doped good quality single crystals of Sodium Acid Phthalate crystals (SAP) were grown by slow evaporation solution growth technique which are semiorganic in nature. The effect of amino acid (L-Valine) dopant on the growth and the properties of SAP single crystal was investigated. The single crystal X-ray diffraction studies and FT-IR studies were carried out to identify the crystal structure and the presence of functional groups in undoped and L-Valine doped SAP crystals. The transparent nature of the grown crystal was observed using UV-Visible spectrum. The thermal decomposition of the doped SAP crystals was investigated by thermo gravimetric analysis (TGA) and differential thermal analysis (DTA). The enhancement in the NLO property of the undoped and L-Valine doped SAP crystals using KDP crystal as a reference was studied using SHG measurements. Vickers micro hardness measurements are used for the study of mechanical strength of the grown crystals. PMID:23583879

Nirmala, L Ruby; Thomas Joseph Prakash, J

2013-03-25

389

Minoxidil: mechanisms of action on hair growth  

Microsoft Academic Search

Summary We have known for over 30 years that minoxidil stimulates hair growth, yet our understanding of its mechanism of action on the hair follicle is very limited. In animal studies, topical minoxidil shortens telogen, causing premature entry of resting hair follicles into anagen, and it probably has a similar action in humans. Minoxidil may also cause prolongation of anagen

A. G. Messenger; J. Rundegren

2004-01-01

390

Interface shape and growth rate analysis of Se GaAs bulk crystals grown in the NASA crystal growth furnace (CGF)  

Microsoft Academic Search

Selenium-doped gallium arsenide, SeGaAs, bulk crystals have been grown on earth using NASA's crystal growth furnace (CGF) in preparation for microgravity experimentation on the USML-2 spacelab mission. Peltier cooling pulses of 50 ms duration, 2040 A magnitude, and 0.0033 Hz frequency were used to successfully demark the melt-solid interface at known times during the crystal growth process. Post-growth characterization included

J. M. Bly; M. L. Kaforey; D. H. Matthiesen; A. Chait

1997-01-01

391

The influences of gypsum water-proofing additive on gypsum crystal growth  

Microsoft Academic Search

The gypsum water-proofing additives were composed of organic emulsion that were emulsified by polyvinyl alcohol and stearic acid and saline water-proofing additive made of alunite, carboxylic acid sodium, aluminium sulfate, etc. Using modern testing instrument, such as SEM, EPS, the influences of gypsum water-proofing additives on the crystal growth of gypsum products and its water-proof mechanism were analyzed from the

Jianquan Li; Guozhong Li; Yanzhen Yu

2007-01-01

392

In situ observation of antisite defect formation during crystal growth  

SciTech Connect

In situ x-ray diffraction (XRD) coupled with molecular dynamics (MD) simulations have been used to quantify antisite defect trapping during crystallization. Rietveld refinement of the XRD data revealed a marked lattice distortion which involves an a axis expansion and a c axis contraction of the stable C11b phase. The observed lattice response is proportional in magnitude to the growth rate, suggesting that the behavior is associated with the kinetic trapping of lattice defects. MD simulations demonstrate that this lattice response is due to incorporation of 1% to 2% antisite defects during growth.

Kramer, M. J.; Mendelev, M. I.; Napolitano, R. E.

2010-12-07

393

Diffuse interface model of diffusion-limited crystal growth  

Microsoft Academic Search

A general approach to diffusion-limited crystal growth is proposed. It consists of a modified (nonequilibrium) Cahn-Hilliard representation of the interface coupled to a diffusion equation. Arguments are given as to its superiority over previous models. These are illlustrated in a one-dimensional solution which shows how the system selects a unique interface velocity. The selection can be interpreted as the requirement

Joseph B. Collins; Herbert Levine

1985-01-01

394

Computer Simulation of Growth Process of Binary Quasi Crystal  

Microsoft Academic Search

We performed Monte Carlo simulation of the aggregation process of a two-component Lennard-Jones system on the two-dimensional (2D) Penrose lattice for the purpose of studying the details of the creation and growth process of quasi crystals. We adopted the potential parameter values proposed by Widom et al. [Phys. Rev. Lett. 58 (1987) 706]. The present simulation clarified that the stability

Yasushi Sasajima; Katsumi Adachi; Hideki Tanaka; Minoru Ichimura; Masanori Itaba; Satoru Ozawa

1994-01-01

395

Metastable Solution Thermodynamic Properties and Crystal Growth Kinetics.  

National Technical Information Service (NTIS)

The crystal growth rates of NH4H2PO4, KH2PO4, (NH4)2SO4, KAl(SO4)2 central dot 12H2O, NaCl, and glycine and the nucleation rates of KBr, KCl, NaBr central dot 2H2O, (NH4)2Cl, and (NH4)2SO4 were expressed in terms of the fundamental driving force of crysta...

S. Kim A. S. Myerson

1996-01-01

396

Modeling and design of PVT growth of silicon carbide crystals  

Microsoft Academic Search

Physical vapor transport method (PVT) is an important technique for growing SiC bulk crystals, which is a promising semiconductor material for electrical and optoelectronic applications in the areas of high power, high temperature, high frequency and strong radiation. The ever-increasing demand for SiC substrates of high quality and large diameter has motivated extensive research effort on the growth of SiC

Ronghui Ma

2003-01-01

397

Progress in the crystal growth of Ce:LiSAF  

Microsoft Academic Search

The search for an efficient solid state laser with tunable emission in the ultraviolet wavelength region has resulted in the growth and development of cerium doped colquiriite crystals, such as LiCaAlF6 (LiCAF) and LiSrAlF6 (LiSAF). Results from preliminary research at Lawrence Livermore National Laboratory indicate that Ce:LiSAF is the preferred material of the colquiriite hosts, since it shows higher gains

Vida K. Castillo; Gregory J. Quarles

1995-01-01

398

Growth of high-quality DAST crystals for THz applications  

Microsoft Academic Search

Growth of high-quality 4-N,N-dimethylamino-4?-N?-methyl stilbazolium tosylate (DAST) crystal by slope nucleation method with controlled nucleation has been achieved when the DAST solution was subjected to a few successive thermal cycles. The ionic conductivities measured for the stirred and unstirred pre-crystalline solutions showed that the persisting cluster formation in the unstirred solution might have facilitated controlled nucleation. These efficient and high-quality

S. Brahadeeswaran; S. Onduka; M. Takagi; Y. Takahashi; H. Adachi; M. Yoshimura; Y. Mori; T. Sasaki

2006-01-01

399

Surface-engineered growth of AgIn?S? crystals.  

PubMed

The growth of semiconductor crystals and thin films plays an essential role in industry and academic research. Considering the environmental damage caused by energy consumption during their fabrication, a simpler and cheaper method is desired. In fact, preparing semiconductor materials at lower temperatures using solution chemistry has potential in this research field. We found that solution chemistry, the physical and chemical properties of the substrate surface, and the phase diagram of the multicomponent compound semiconductor have a decisive influence on the crystal structure of the material. In this study, we used self-assembled monolayers (SAMs) to modify the silicon/glass substrate surface and effectively control the density of the functional groups and surface energy of the substrates. We first employed various solutions to grow octadecyltrichlorosilane (OTS), 3-mercaptopropyl-trimethoxysilane (MPS), and mixed OTS-MPS SAMs. The surface energy can be adjusted between 24.9 and 50.8 erg/cm(2). Using metal sulfide precursors in appropriate concentrations, AgIn5S8 crystals can be grown on the modified substrates without any post-thermal treatment. We can easily adjust the nucleation in order to vary the density of AgIn5S8 crystals. Our current process can achieve AgIn5S8 crystals of a maximum of 1 ?m in diameter and a minimum crystal density of approximately 0.038/?m(2). One proof-of-concept experiment demonstrated that the material prepared from this low temperature process showed positive photocatalytic activity. This method for growing crystals can be applied to the green fabrication of optoelectronic materials. PMID:23551172

Lai, Chia-Hung; Chiang, Ching-Yeh; Lin, Po-Chang; Yang, Kai-Yu; Hua, Chi Chung; Lee, Tai-Chou

2013-04-22

400

Growth of oxide fibers by the internal crystallization method  

Microsoft Academic Search

A new approach is developed for growing relatively inexpensive single-crystal and eutectic oxide fibers suitable for the fabrication\\u000a of high-temperature composite materials. Sapphire (Al2O3), YAG (Y3Al5O12), mullite (3Al2O3 2SiO2), YAP (YAlO3), and eutectic (Al2O3-Y3Al5O12, Al2O3-ZrO2 (Y2O3), and Al2O3-Gd2O3) fibers are produced by the internal crystallization method, and their mechanical strength and micro-structures are studied.

V. N. Kurlov; S. T. Mileiko; A. A. Kolchin; M. Yu. Starostin; V. M. Kiiko

2002-01-01

401

Virtual Crystallizer  

SciTech Connect

Large dihydrogen phosphate (KDP) crystals are grown in large crystallizers to provide raw material for the manufacture of optical components for large laser systems. It is a challenge to grow crystal with sufficient mass and geometric properties to allow large optical plates to be cut from them. In addition, KDP has long been the canonical solution crystal for study of growth processes. To assist in the production of the crystals and the understanding of crystal growth phenomena, analysis of growth habits of large KDP crystals has been studied, small scale kinetic experiments have been performed, mass transfer rates in model systems have been measured, and computational-fluid-mechanics tools have been used to develop an engineering model of the crystal growth process. The model has been tested by looking at its ability to simulate the growth of nine KDP boules that all weighed more than 200 kg.

Land, T A; Dylla-Spears, R; Thorsness, C B

2006-08-29

402

Mechanisms for Membrane Protein Crystallization Measured by Small Angle Neutron Scattering  

NASA Astrophysics Data System (ADS)

Crystallization of integral membrane proteins is of critical importance for structural biology, although the mechanism is only poorly understood. Membrane protein crystallization is complicated by the necessity of having a solubilizing detergent in crystallization mixtures. Optimal conditions vary appreciably for specific proteins, and currently there appears to be no general rule that can reliably predict which combination of detergent, amphiphile, and precipitant will be successful for crystallization of a new protein. We have begun a characterization of the molecular structures present in crystallization mixtures of the detergent-solubilized Rhodobacter sphaeroides photosynthetic reaction center, RC, using small angle neutron scattering, SANS. This work provides quantitative data on the mechanism of crystallization, and criteria for developing rational schemes for membrane protein crystallization. Neutron scattering is well-suited for analyzing structures in complex crystallization mixtures. Scattering for individual components within heterogeneous samples can be detected by isotopic substitution, and by varying solution 2H2O/1H2O ratios to eliminate the scattering contrast between a second, unlabeled component and the solvent. We are using these techniques to selectively resolve RC, detergent, and possibly solvation layer structures during the time-course of RC crystallization. SANS studies were carried out with fully deuterated RCs, and with the solution D2O/H2O ratio adjusted so that the scattering length density of the solvent matched that of the detergent. These conditions selectively enhanced scattering for the RC protein, while eliminating scattering from the detergent in the small angle domain. These measurements permitted resolution of the RC solution structure during the crystallization time course without interference from detergent structures. SANS measurements taken during presaturation, nucleation, and crystal growth phases of crystallization found that the RC in solution remains in the monomeric state throughout this process. Before addition of the precipitating agents the detergent solubilized RC was found to exist predominately in the monomeric form, although aggregated states were seen, accounting for 5of the protein in different preparations. The addition of polyethylene glycol, PEG, below the crystallization threshold caused precipitation of the aggregated species. Guinier analysis of neutron scattering from mixtures at the onset of nucleation showed that the RC is in a homogeneous, monomeric state with undetectable amounts of aggregated species. Fitting of the scattering data with scattering calculated from RC crystal structures showed that less than 7form of dimers or other small aggregates. During further crystal nucleation and growth, the solution state of the protein was found not to change. These findings indicate that a monodispersed RC-detergent particle is likely to serve as the precursor for nucleation, and as the crystal growth unit. These results are in marked contrast with analogous studies on water- soluble proteins, suggesting that the mechanism of crystallization differs significantly in these cases. Complementary SANS studies have begun that examine detergent structures. SANS from samples containing either deuterated n-octyl-B-D-glucoside, OG, and protonated RC, or with protonated OG and RC, show that OG micelle structures are variable and heterogeneous in samples before the addition of PEG. Following PEG addition, OG micelle number and size were found to be reduced, and scattering from a RC associated OG layer can be detected. The results suggest that the PEG induced change in OG micelle structures may be responsible for the unique success in using PEG as a precipitant for OG-containing crystallization mixtures.

Tiede, David

1997-03-01

403

Manipulating crystal growth and polymorphism by confinement in nanoscale crystallization chambers.  

PubMed

The phase behaviors of crystalline solids embedded within nanoporous matrices have been studied for decades. Classic nucleation theory conjectures that phase stability is determined by the balance between an unfavorable surface free energy and a stabilizing volume free energy. The size constraint imposed by nanometer-scale pores during crystallization results in large ratios of surface area to volume, which are reflected in crystal properties. For example, melting points and enthalpies of fusion of nanoscale crystals can differ drastically from their bulk scale counterparts. Moreover, confinement within nanoscale pores can dramatically influence crystallization pathways and crystal polymorphism, particularly when the pore dimensions are comparable to the critical size of an emerging nucleus. At this tipping point, the surface and volume free energies are in delicate balance and polymorph stability rankings may differ from bulk. Recent investigations have demonstrated that confined crystallization can be used to screen for and control polymorphism. In the food, pharmaceutical, explosive, and dye technological sectors, this understanding and control over polymorphism is critical both for function and for regulatory compliance. This Account reviews recent studies of the polymorphic and thermotropic properties of crystalline materials embedded in the nanometer-scale pores of porous glass powders and porous block-polymer-derived plastic monoliths. The embedded nanocrystals exhibit an array of phase behaviors, including the selective formation of metastable amorphous and crystalline phases, thermodynamic stabilization of normally metastable phases, size-dependent polymorphism, formation of new polymorphs, and shifts of thermotropic relationships between polymorphs. Size confinement also permits the measurement of thermotropic properties that cannot be measured in bulk materials using conventional methods. Well-aligned cylindrical pores of the polymer monoliths also allow determination and manipulation of nanocrystal orientation. In these systems, the constraints imposed by the pore walls result in a competition between crystal nuclei that favors those with the fastest growth direction aligned with the pore axis. Collectively, the examples described in this Account provide substantial insight into crystallization at a size scale that is difficult to realize by other means. Moreover, the behaviors resulting from nanoscopic confinement are remarkably consistent for a wide range of compounds, suggesting a reliable approach to studying the phase behaviors of compounds at the nanoscale. Newly emerging classes of porous materials promise expanded explorations of crystal growth under confinement and new routes to controlling crystallization outcomes. PMID:22035061

Hamilton, Benjamin D; Ha, Jeong-Myeong; Hillmyer, Marc A; Ward, Michael D

2011-10-28

404

Investigation on the influence of foreign metal ions in crystal growth and characterization of l-Alaninium Maleate (LAM) single crystals.  

PubMed

A Nonlinear Optical, good quality, single crystals of doped and undoped l-Alaninium Maleate (LAM) were grown by slow evaporation solution growth technique at room temperature. The lattice parameters were analyzed by single crystal X-ray diffraction technique. The identification of Cadmium ion in the doped crystals was done using the EDAX spectrum. The presence of functional group of the dopant with LAM molecule was studied using FTIR spectra. The results of UV-Vis study is used to compare the transparencies of the doped and undoped LAM crystals. The optical band gap energy of the grown crystal was also calculated. The relative second harmonic generation (SHG) efficiency measurement with KDP reference is used to find the incorporation of metal to l-Alaninium Maleate crystals and the parent material. Also the thermal stability of the grown crystals was studied by TGA/DTA spectrum. The mechanical stability of the grown crystals was confirmed through Vickers micro hardness study. By parallel plate capacitor technique, the dielectric response was studied over a wide range of frequencies at different temperatures. The various studies showed the incorporation of the impurity Cd(2+) into LAM crystals and the investigations indicated that the impurity played an important role in the changes of the spectral and structural properties of LAM crystals. PMID:23892119

Ruby Nirmala, L; Thomas Joseph Prakash, J

2013-07-05

405

The role of an alkali halide flux in the growth of YBa2Cu3O7-? single crystals  

NASA Astrophysics Data System (ADS)

In order to understand the precise role of a NaCl-KCl flux in controlling the crystal growth process of YBa2Cu3O7-?, the microstructure of pellets prepared with various amounts of flux were studied by means of optical microscopy. Quenching experiments indicate significant flux loss during the growth cycle and DTA reveals liquid phase formation below the peritectic decomposition. The observations suggest a complex liquid phase-promoted growth mechanism.

Abell, J. S.; Gencer, F.

1991-12-01

406

ZnTe single crystal growth by the liquid encapsulated pulling method  

NASA Astrophysics Data System (ADS)

Large diameter ZnTe single crystals were grown by the liquid-encapsulated pulling method using a double crucible. Crystals of around 80 mm in diameter and 40 mm in length were reproducibly obtained by this method. Both 100 and 110 crystals were successfully grown. The strong facet growth was observed when the shoulder part of the bulk was formed. Rectangular facet growth was observed in 100 growth and hexagonal facet growth was observed in 110 growth. The etch pit density of the grown crystal was lower than 10000 cm-2 and the strain in the crystal was lower than that of modified liquid encapsulated Kyropoulos method.

Asahi, T.; Yabe, T.; Sato, K.

2004-02-01

407

Crystal growth of calcite from calcium bicarbonate solutions at constant PCO2 and 25??C: a test of a calcite dissolution model  

USGS Publications Warehouse

A highly reproducible seeded growth technique was used to study calcite crystallization from calcium bicarbonate solutions at 25??C and fixed carbon dioxide partial pressures between 0.03 and 0.3 atm. The results are not consistent with empirical crystallization models that have successfully described calcite growth at low PCO2 (< 10-3 atm). Good agreement was found between observed crystallization rates and those calculated from the calcite dissolution rate law and mechanism proposed by Plummer et al. (1978). ?? 1981.

Reddy, M. M.; Plummer, L. N.; Busenberg, E.

1981-01-01

408

Growth and Characterization of Graphene on Single Crystal Cu Substrates  

NASA Astrophysics Data System (ADS)

One of the key issues for the use of CVD graphene in device applications is the influence of defects on the transport properties of the graphene. Therefore, it is important to understand the influence of the substrate on the orientation of the graphene. Growth of graphene films on Cu(111) has the potential for producing films with a low defect density because of the hexagonal symmetry of the substrate and relatively small lattice mismatch, whereas growth on Cu(100) is expected to result in multi-domain growth because of its square symmetry. In this study, graphene films were grown on Cu single crystal substrates, and characterized with LEEM, LEED, SEM, AFM, and Raman spectroscopy. The clean Cu substrates were prepared by sputtering and annealing in UHV. For the initial growth studies, the samples were transferred to a tube furnace for graphene growth using a technique optimized for Cu foils. The UHV system has recently been modified with a button heater compatible with the conditions needed for graphene growth to enable in-situ growth and characterization.

Robinson, Z. R.; Tyagi, P.; Geisler, H.; Ventrice, C. A., Jr.; Bol, A. A.; Hannon, J. B.

2012-02-01

409

Growth and properties of Lithium Salicylate single crystals  

SciTech Connect

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.

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

2009-02-13

410

Crystal grain growth during room temperature high pressure Martensitic alpha to omega transformation in zirconium  

SciTech Connect

Systematic increase in transition pressure with increase in interstitial impurities is observed for the martensitic {alpha} {yields} {omega} structural phase transition in Zr. Significant room temperature crystal grain growth is also observed for the two highest purity samples at this transition, while in the case of the lowest purity sample interstitial impurities obstruct grain growth even as the sample is heated to 1279 K. Our results show the importance of impurities in controlling structural phase stability and other mechanical properties associated with the {alpha} {yields} {omega} structural phase transition.

Velisavljevic, Nenad [Los Alamos National Laboratory; Chesnut, Gary N [Los Alamos National Laboratory; Stevens, Lewis L [Los Alamos National Laboratory; Dattelbaum, Dana M [Los Alamos National Laboratory

2008-01-01

411

Ductile-regime turning mechanism of single-crystal silicon  

Microsoft Academic Search

Diamond turning of single-crystal silicon was carried out along all the crystallographic directions on the (001) and (111) planes at depths of cut of 100 nm and 1 ?m, and then the mechanism involved in ductile-regime turning was studied. Pitting damage occurred along certain specific crystallographic orientations. The crystallographic orientation dependence of the surface features also changed with the depth

Takayuki Shibata; Shigeru Fujii; Eiji Makino; Masayuki Ikeda

1996-01-01

412

Colouring mechanism of dyed KDP crystal by quantum chemistry  

Microsoft Academic Search

Dye adsorption mechanism, in particular, colouring mechanism of KDP (KH2PO4) crystal was investigated by quantum chemistry in this study. Phenomena, such as different preferentially coloured faces of KDP when co-crystallised with different dyes, are explained by the minimum and maximum values of electrostatic potential (ESP). Furthermore, it is found that the ESP distribution of a dye molecule may not necessarily

Yusuke Asakuma; Motosuke Nishimura; Qin Li; H. Ming Ang; Moses Tade; Kouji Maeda; Keisuke Fukui

2007-01-01

413

Growth and characterization of Fe:Ti:Al2O3 single crystal by floating zone method  

NASA Astrophysics Data System (ADS)

Fe:Ti:Al2O3 single crystals were successfully grown by the floating zone (FZ) method in different atmospheres. The grown crystals, typically about 7–8 mm in diameter and 50–70 mm in length, have been obtained from the materials of Al2O3 doped with FeTiO3 and Fe2O3. The effect of the atmosphere on the growth was studied, and the obtained single crystals presented the best crystal quality when grown in argon. The optimum growth parameters by the FZ method for this single crystal were also studied in order to grow the highest quality single crystal. The crystal has been characterized by means of X-ray diffraction (XRD) and X-ray single crystal diffraction. Meanwhile, the Raman spectroscopy indicates that the single crystal grown in argon is similar to the natural blue sapphire. The transmittance was also measured by ultraviolet and visible spectrophotometry. Coloration mechanism in the single crystals of Fe:Ti:Al2O3 was analyzed by an electron probe X-ray microanalyser (EPMA). It is proved that iron is the main coloring element.

Xu, Hong; Jiang, Yijian; Fan, Xiujun; Wang, Yue; Liu, Guoqing

2013-06-01

414

Crystal growth of vanadium silicides from high-temperature metal solutions and some properties of the crystals  

Microsoft Academic Search

Crystals of vanadium silicides were grown from high-temperature tin and copper solutions in an argon atmosphere using vanadium metal chips and silicon powder as starting materials. The crystals grown were V3Si, V5Si3 and VSi2. The growth conditions for obtaining single crystals of relatively large size were established. The as-grown V3Si, V5Si3 and VSi2 crystals were used for chemical analysis and

Shigeru Okada; Tomoko Suda; Akio Kamezaki; Kunio Kudou; Ken-ichi Takagi

1996-01-01

415

Crystal growth of Pt-doped IrTe2  

NASA Astrophysics Data System (ADS)

IrTe2, a layered compound with a triangular iridium lattice, exhibits a structural phase transition at approximately 250 K. Electric resistivity and magnetic susceptibility exhibit anomalies at the transition with hysteresis [1]. Charge-orbital density wave or orbitally induced Peierls effect, a crystal field effect are suggested as candidates of the origin of the transition [2-4]. On the other hand, superconducting phase emerges when the structural phase transition is suppressed by chemical substitution or intercalation [2,5]. Analysis of physical property using single crystal should be helpful to clarifying the relation between the ground states of IrTe2 and superconductivity. Recently, Fang et al. reported the growth of single crystal of parent compound [4]. However, single crystal of superconducting sample had not been reported yet. For these reason, we studied superconductivity and the structural transition in platinum doped IrTe2 single crystals. We successfully synthesized several composition of the Ir1-xPtxTe2 single crystal by flux method. From magnetization and transport measurement, we confirm the suppression of structural phase transition and emergence of superconductivity. Detail of the experiment will be discussed.[4pt] [1] N. Matsumoto et al., J. Low Temp. Phys. 117 (1999) 1129.[0pt] [2] J. J. Yang et al., Phys. Rev. Lett. 108 (2012) 116402.[0pt] [3] D. Ootsuki et al., Phys. Rev. B. 86 (2012) 014519.[0pt] [4] A. F. Fang et al., arXiv:1203.4061 (2012).[0pt] [5] S. Pyon et al., J. Phys. Soc. Jpn. 81, 053701 (2012).

Pyon, Sunseng; Kudo, Kazutaka; Nohara, Minoru

2013-03-01

416

A payload for investigating the influence of convection on GaAs crystal growth  

Microsoft Academic Search

A comparative study of the influence of buoyancy driven fluid flow on gallium arsenide (GaAs) crystal growth was undertaken. Crystals will be grown from melts with different degrees of convective flow including growth in the microgravity environment of space. The space growth of GaAs will be performed in a Get Away Special payload. A well insulated growth furnace was designed

Alfred H. Bellows; Glenn A. Duchene

1988-01-01

417

Atomic force microscopy of insulin single crystals: direct visualization of molecules and crystal growth.  

PubMed Central

Atomic force microscopy performed on single crystals of three different polymorphs of bovine insulin revealed molecularly smooth (001) layers separated by steps whose heights reflect the dimensions of a single insulin hexamer. Whereas contact mode imaging caused etching that prevented molecular-scale resolution, tapping mode imaging in solution provided molecular-scale contrast that enabled determination of lattice parameters and polymorph identification while simultaneously enabling real-time examination of growth modes and assessment of crystal quality. Crystallization proceeds layer by layer, a process in which the protein molecules assemble homoepitaxially with nearly perfect orientational and translational commensurism. Tapping mode imaging also revealed insulin aggregates attached to the (001) faces, their incorporation into growing terraces, and their role in defect formation. These observations demonstrate that tapping mode imaging is ideal for real-time in situ investigation of the crystallization of soft protein crystals of relatively small proteins such as insulin, which cannot withstand the lateral shear forces exerted by the scanning probe in conventional imaging modes. Images FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 4

Yip, C M; Ward, M D

1996-01-01

418

A simple method for systematically controlling ZnO crystal size and growth orientation  

SciTech Connect

We present a simple, easy and reproducible method to systematically control the dimension and shape evolution of zinc oxide (ZnO) as thin film on glass substrate by chemical bath deposition (CBD). The only varying factor to control crystal transformation is the molar ratio of Cd{sup 2+}/Zn{sup 2+}, R{sub m}, in the initial chemical solution. With the increase of R{sub m}, ZnO crystals transformed from long-and-slim hexagonal rods to fat-and-short hexagonal pyramids, and then to twinning hexagonal dots as observed by scanning electron microscopy (SEM). Film crystallinity was characterized by X-ray diffraction (XRD). Chemical component analysis by energy dispersive spectroscopy (EDS) showed that most cadmium was present in the residual solution instead of the developed film and the precipitate at the bottom of beaker. The mechanism of the cadmium effect, with different initial concentrations, on ZnO crystal transformation was tentatively addressed. We believe that cadmium influences the chelate ligands adsorption onto (0001-bar) plane of ZnO crystals, alters the crystal growth orientation, and thus directs the transformation of the size and shape of ZnO crystals.

Zhang Rong [Department of Paper and Chemical Engineering, Miami University, Oxford, OH 45056 (United States); Kerr, Lei L. [Department of Paper and Chemical Engineering, Miami University, Oxford, OH 45056 (United States)], E-mail: kerrll@muohio.edu

2007-03-15

419

Crystallization mechanisms in cream during ripening and initial butter churning.  

PubMed

The temperature treatment of cream is the time-consuming step in butter production. A better understanding of the mechanisms leading to partial coalescence, such as fat crystallization during ripening and churning of the cream, will contribute to optimization of the production process. In this study, ripening and churning of cream were performed in a rheometer cell and the mechanisms of cream crystallization during churning of the cream, including the effect of ripening time, were investigated to understand how churning time and partial coalescence are affected. Crystallization mechanisms were studied as function of time by differential scanning calorimetry, nuclear magnetic resonance and by X-ray scattering. Microstructure formation was investigated by small deformation rheology and static light scattering. The study demonstrated that viscosity measurements can be used to detect phase inversion of the emulsion during churning of the cream in a rheometer cell. Longer ripening time (e.g., 5h vs. 0h) resulted in larger butter grains (91 vs. 52µm), higher viscosity (5.3 vs. 1.3 Pa·s), and solid fat content (41 vs. 13%). Both ripening and churning time had an effect on the thermal behavior of the cream. Despite the increase in solid fat content, no further changes in crystal polymorphism and in melting behavior were observed after 1h of ripening and after churning. The churning time significantly decreased after 0.5h of ripening, from 22.9min for the cream where no ripening was applied to 16.23min. Therefore, the crystallization state that promotes partial coalescence (i.e., aggregation of butter grains) is obtained within the first hour of cream ripening at 10°C. The present study adds knowledge on the fundamental processes of crystallization and polymorphism of milk fat occurring during ripening and churning of cream. In addition, the dairy industry will benefit from these insights on the optimization of butter manufacturing. PMID:24035028

Buldo, Patrizia; Kirkensgaard, Jacob J K; Wiking, Lars

2013-09-12

420

Crystal growth of Cu2ZnSnS4 solar cell absorber by chemical vapor transport with I2  

NASA Astrophysics Data System (ADS)

Single crystals of Cu2ZnSnS4 have been produced within sealed quartz ampoules via the chemical vapour transport technique using I2 as the transporting agent. The effects of temperature gradient and I2 load on the crystal habit and composition are considered. Crystals have been analyzed with XRD, SEM, and TEM for compositional and structural uniformities at both microscopic and nanoscopic levels. The synthesized crystals have suitable (I2-load dependent) properties and are useful for further solar absorber structural and physical characterizations. A new chemical vapour transport method based on longitudinally isothermal treatments is attempted. Based on a proposed simplistic mechanism of crystal growth, conditions for crystal enlargement with the new method are envisaged.

Colombara, D.; Delsante, S.; Borzone, G.; Mitchels, J. M.; Molloy, K. C.; Thomas, L. H.; Mendis, B. G.; Cummings, C. Y.; Marken, F.; Peter, L. M.

2013-02-01

421

GSGG crystal growth and quality: a status report  

NASA Astrophysics Data System (ADS)

Gadolinium scandium gallium garnet (GSGG) co-doped with Cr and Nd is the crystalline-laser material with the highest measured efficiency (5% absolute) under flashlamp pumping. It is presently being developed for a variety of laser applications. We report measurements of the present crystal quality of 1.5 to 2-inch diameter boules, finding 0.24 m-1 loss coefficient; ?/50 homogeneity in a 1/4-inch by 3-inch rod; and 0.4 nm/cm, birefringence. We have evidence that a one-micron absorption band, which appears frequently in Cr doped GSGG, is caused by Cr4+, which is generated to compensate for Ca2+ impurities in the crystal. Scale-up boule growth to 5-inch diameter is now underway.

Stokowski, S.; Caird, J.; Shinn, M.; Smith, L.; Wilder, R.

1986-08-01

422

Growth Mechanisms of Metal Nanoparticles via First Principles  

SciTech Connect

Despite the important applications of nanoparticles (NPs), their mechanisms of growth still remain elusive. Herein we elucidate the growth mechanisms of silver NPs via first-principle calculations to elucidate anisotropic growth and shape selectivity by a symmetry-break mechanism. The capping agent (citrate) can play a multifunctional action: under certain conditions, it blocks NP growth via an electrostatic or a van der Waals stabilization mechanism, and under others, it induces NP growth.

Mpourmpakis, Giannis; Vlachos, Dionisios G. [Department of Chemical Engineering, University of Delaware, Newark, Delaware 19716 (United States)

2009-04-17

423

Gallium arsenide advanced crystal growth and beam processing  

NASA Astrophysics Data System (ADS)

This report describes the progress made during a fifteen month program to study the feasibility of growth of high purity epitaxial quality bulk GaAs crystals from solution and annealing of implanted layers and Ohmic contacts for device applications using laser and electron beams. Millimeter-thick crystals have been grown by the low-temperature solution-growth process. Room-temperature n-type carrier concentrations of 2 times 10 to the 15th power/cu cm and liquid nitrogen mobilities of 30,000 sq cm/V/sec have been achieved. Theoretical studies of a variety of potential growth configurations were performed. A detailed study of the laser of annealing implanted layers and Ohmic contacts was performed using several Q-switched and cw lasers. State-of-the-art results were achieved in both the implant-annealing and Ohmic-contact areas. Preliminary investigations of the annealing of implanted layers and Ohmic contacts using pulsed electron beams were also performed.

Anderson, C. L.

1980-01-01

424

Reactive atmosphere growth of 2.06 micron laser crystals  

NASA Astrophysics Data System (ADS)

A specified formula Y(0.428)Er(0.500)Tm(0.067)Ho(0.005)LiF4 was used as a first approximation to a laser system whereby the necessary broad pump bands and fast, efficient laser excitation could be obtained. Laser rods were cut from single crystal ingots grown by a reactive atmosphere process (RAP). Thermal conductivity, hardness, elastic modulus, rupture strength, radiative characteristics, and laser test data were measured to determine the laser performance characteristics of Ho:YLF. Development of RAP Ho:YLF growth procedures provided proof of practical, congruent melting behavior. Electron probe, spectrographic analysis, and backscatter measurements showed R(3+) (R + Y + Er + Tm + Ho in Ho:YLF) acted as one ionic species in crystal growth. Glass-like optical quality Ho:YLF was RAP Czochralski grown at 5 mm/hour. A short investigation of Bridgman growth indicated that higher yields and inexpensively scaled-up rod production technology can be developed.

Devor, D. P.; Pastor, R. C.; Robinson, M.; Akutagawa, W. M.; Arita, K.

1974-10-01

425

On the Growth Dynamics of 4He Crystals near the First Roughening Transition  

NASA Astrophysics Data System (ADS)

The first roughening transition of a surface of hcp 4He crystals was carefully studied in Paris in 1980s. By investigating the growth dynamics of the (0001) facet, the free energy of an elementary step was measured in the close vicinity of the transition and a good agreement was found with the theory of critical fluctuations developed by Nozières and Gallet. We believe, however, that the interpretation of the growth data near the roughening transition made by the Paris group is not self-consistent. We argue that with the step energies they obtained, assuming that the growth is due to the process of 2D-nucleation of terraces, another growth mechanism provided by screw dislocations should be much more effective.

Todoshchenko, I. A.; Alles, H.; Junes, H. J.; Parshin, A. Ya.

2006-09-01

426

Theoretical investigation of crystal growth shaping process with the wetting boundary condition  

Microsoft Academic Search

A theoretical investigation of crystal growth shaping process (to elaborate crystals in the form of tubes or rods with different cross sections, and other complicated forms) is carried out on the basis of the dynamic stability concept. The capillary dynamic stability of shaped crystal growth from the melt is analyzed using a mathematical model based on the proposal of axisymmetry

V. A Tatarchenko; V. S Uspenski; E. V Tatarchenko; B Roux

2000-01-01

427

Finite element modeling solution crystal growth at a meso-scale  

Microsoft Academic Search

We present a multi-scale model of the growth of a vicinal crystal surface from a supersaturated liquid solution that couples bulk fluid dynamics with surface step growth. We consider relatively simple flows within boundary layers adjacent to the macroscopic, vicinal surface of a crystal growing from a liquid solution. There is a depletion of solute due to the crystallization at

Bing Dai

2005-01-01

428

Growth of epitaxial ice crystals on covellite (CuS) under reduced air pressure  

Microsoft Academic Search

The advance velocity of nonthickening crystals and basal steps were measured as a function of temperature, supersaturation, and air pressure, using an optical interference technique. Ice crystal growth at -7 C in a thermal diffusion chamber was also investigated as a function of supersaturation. The radial growth rates of nonthickening crystals and the advance velocity of a 0.08 micrometer step

N. K. Cho

1982-01-01

429

CALCIUM OXALATE CRYSTAL FORMATION IS NOT ESSENTIAL FOR GROWTH OF MEDICAGO TRUNCATULA  

Technology Transfer Automated Retrieval System (TEKTRAN)

Plants invest a considerable amount of resources and energy into the formation of calcium oxalate crystals. A number of roles for crystal formation in plant growth and development have been assigned based on the prevalence of crystals, their spatial distribution, and the variety of crystal shapes. ...

430

Designed additives for controlled growth of crystals of phospholipid interacting proteins: Short chain phospholipids  

Microsoft Academic Search

A new approach to crystallization of proteins that interact with lipids has been applied to the protein crambin. Short chain phospholipids are water-soluble additives and effectively lower the amount of protein needed to form crambin crystals by lowering protein solubility and inhibiting crystal growth in the fastest growing direction. Compared with optimal crystallization conditions without phospholipid, which gave large crambin

Ofer Markman; Cecilia Roh; Mary F. Roberts; Martha M. Teeter

1996-01-01

431

Influence of Filler on the Mechanical Properties and Kinetic Crystallization Behavior of Polylactic Acid (PLA)  

NASA Astrophysics Data System (ADS)

The kinetic crystallization behavior of PLA (polylactic acid) and PLA/MMT nanocomposites containing 3 wt% montmorillonite (MMT) was examined in order to develop a new technique for obtaining the relative crystallization degree of a material from the spherulite occupation area based on images obtained using a charge-coupled device (CCD) camera. In addition, the relative crystallization degree is discussed in terms of the Ozawa theory. The effect of MMT filler on the mechanical properties of PLA/MMT nanocomposites, the number of spherulites generated in the nanocomposites, and the linear growth rate of these spherulites were also examined experimentally. The relative crystallization curves obtained by CCD and by DSC measurement were found to be approximately the same. Moreover, it was found that the Ozawa theory could be applied not only to PLA but also to PLA/MMT nanocomposites. In these nanocomposites, the number of spherulites decreased and the linear growth rate slightly increased ; moreover, the rate of crystallization also increased. The tensile and flexural modulus of the PLA/MMT nanocomposites containing 3 wt% MMT were 5.2-14.3% greater than those of PLA, and annealing resulted in a further increase of about 4.0-20.7%. However, the Izod impact value decreased due to the increase in rigidity caused by annealing and the addition of filler.

Mitsuta, Ryo; Inoue, Ryohei; Hara, Ryosuke; Sato, Sadao

432

Numerical simulation of crystal growth in a vertical Bridgman furnace  

NASA Astrophysics Data System (ADS)

The method of global calculation of heat transfer is applied to the numerical simulation of crystal growth in a vertical Bridgman furnace. Specific consideration is given to the Mellen electrodynamic gradient furnace, where a large number of heating elements make it possible to generate arbitrary temperature fields within the load. By means of the global analysis, it is possible to obtain a full description of the temperature field in terms of a limited number of parameters. Also shown is the importance of a precise measurement of material parameters.

Crochet, M. J.; Dupret, F.; Ryckmans, Y.; Geyling, F. T.; Monberg, E. M.

1989-09-01

433

Mechanical characterization of ibuprofen, naproxen, and their spherically crystallized products  

NASA Astrophysics Data System (ADS)

The objectives of this study were to establish a rational basis for choosing parameters for conducting the tensile strength and indentation hardness test on pharmaceutical compacts, to describe the changes in tableting indices based on the different parameters, to develop a method to spherically crystallize ibuprofen, and to compare the mechanical and micromeritic properties of spherically crystallized ibuprofen and naproxen to the starting materials. This work described the importance of establishing the appropriate test parameters for tensile strength and indentation hardness tests so that reliable and predictive tableting indices could be determined. The fracture strength for diametral compression of ibuprofen compacts was determined for two modes of stress application, constant stress rate and constant strain rate. The tensile strength for diametral compression of ibuprofen and naproxen compacts was determined using a constant strain rate (0.05 to 16 mm/min). The static indentation hardness (Meyer hardness) of ibuprofen and naproxen compacts was determined at varying solid fractions and indentor depth of penetration. Results from these studies were used to establish an appropriate rate of stress application during diametral compression and an appropriate depth of penetration for indentation hardness testing in order to calculate tableting indices. The tableting indices calculated from the aforementioned properties were: the brittle fracture index (BFI), the best case bonding index (BIsb{b}), the worst case bonding index (BIsb{w}), the brittle/viscoelastic bonding index (bBIsb{v}), and the viscoelastic index (VI). In addition, changes in compactibility between the starting materials and their spherically crystallized products were assessed through the analysis of Athy-Heckel profiles. A comparison of micromeritic properties included particle size, porosity, surface area, bulk density, tap density, true density, and flowability as measured by the Carr Index. The spherically crystallized products of ibuprofen and naproxen were shown to be free flowing, less compressible, and more compactible than the starting materials. The spherically crystallized ibuprofen product was optimized for improved tensile strength, bonding index, and minimal particle size using response surface experimental design methodology. Key process factors in the quasi-emulsion solvent diffusion method employed to spherically crystallize ibuprofen were: the amount of additive, hydroxypropylmethyl cellulose, added to the nonsolvent, the agitation rate during the crystallization process, and the