Stability of Crystal Growth Face and Dissolution Face in Crystallization from Solution under Microgravity

The stability of the shapes of crystal growth face and dissolution face in a two-dimensional mathematical model of crystal growth from solution under microgravity is studied. It is proved that the stable shapes of crystal growth face and dissolution face do exist, which are suitably shaped curves with their upper parts inclined backward properly.The stable shapes of crystal growth faces and dissolution faces are calculated for various values of parameters, Ra, Pr and Sc. It is shown that the stronger the convection relative to the diffusion in solution is, the more backward the upperparts of the stable crystal growth face and dissolution face are inclined. The orientation and the shape of dissolution face hardly affect the stable shape of crystal growth face and vice versa.

氨基酸系列改性TGS晶体研究

TGS (triglycine sulfate) is a pyroelectric crystal material which has an excllent pyroelectricity.The LATGS,a kind of doped TGS crystal,in which L α alanine (LA) substitues for glycine partially and induces an internal bias in TGS resulting in permanently poled single domain crystal,becomes the comprehensively used pyroelectric material. Based on the study which was about the locked polarization in LATGS,we select many kinds of aminoacids which have a strong polarity group and a unsymmetry atom to dope into TGS crystals.The aninoacids are LB (L asparagine),LL (L lysine),LH (L histidine) and LG (L glutamid acid).The saturated solutions for above four crystals growth are prepared by TGS doped with different aminoacids in water. Transparent crystals up to several centinetres in size have been grown by circling plate method and the reversible rotation rate of the platform with the crystal was about 90 r/min.There was a prefered growth in the b axis direction,with a growth rate of the b axis of about 1.0-1.2mm/day.The concentrations of aminoacids doped in TGS crystals were determined by a liquid chromatography,the concentrations of different aminoacids are about 10 -3 . It shows that the lattice parameters ( a,b and V )of TGS doped with aminoacids are significant longer than that of pure TGS crystal. We conclude that the pyroelectic cofficient,pyroelectric merit and the locked polarization of four TGS crystals,especially,the internal bield ( E b ) of LLTGS is larger than the LATGS,so that the LLTGS crystal is a promising pyroelectrc material for infrared detector.

氯酸钠晶体生长动力学的研究

Sodium chlorate is a no coloured,no smell and no poisonous transparent crystal with the formula of NaClO 3.Its structure belongs to the cubic( T 23)class and exhibits optical activity.The space group is P 2 13 and there are four molecules per cubic unit cell with a =0.6570nm.We chose the crystal as a research system based on two reasons:(1)since the crystal structure belongs to the cubic class,the crystal faces,such as(100),(010),(001)are possessed of homogeneity,it is the suitable system for studying kinetics of crystal growth;(2)since the solubility of the NaClO 3 is higher in the H 2O and the crystal could be grown from low temperature solution,this is a suitable system for studying a influence of gravity on the boundary layer characteristics of the crystal growth under the microgravity condition.

Phase Diagram, Growth and Optical Property of the LaBWO_6 Crystal

The phase diagram, growth and optical property of LaBWO6 crystal are reported. LaBWO6 crystal melts congruently at 1078 ℃. Based on the pseudo-ternary phase diagram of LaBWO6-（Li2WO4/LiF） -B203, the LaBWO6 crystals have been firstly grown by the flux method. LaBWO6 crystal crystallizes in the orthorhombic system, space group P222 with a = 4.1, b = 10.31 and c = 21.71 A. LaBWO6 Crystal exhibits high transparency in a range from 327 to 1100 nm. The absorption edge of the crystal in the UV range is at 293 nm. The SHG efficient of LaBWO6 crystal is 0.3 times as large as that of the KDP crystal.

Facile and green route to highly luminescent ZnS-shelled CdSe nanocrystals

Highly luminescent CdSe/ZnS nanocrystals were obtained by adapting non-TOP-based synthesis and a subsequent two-phase ZnS shelling procedure:the core CdSe nanocrystals were synthesized in sole solvent paraffin liquid with cadmium oxide,elemental sele-nium,and oleic acid; the deposition of the ZnS shell was conducted by using zinc stearate in toluene and sodium sulfide in deionized water. The green and low-cost route was proved to be more efficient to constrain the size of core nanocrystals while tuning the ...

Preparation and characterization of nanostructured Bi_2Se_3 and Sn_(0.5)-Bi_2Se_3

Nanostructured Bi2Se3 and Sn0.5-Bi2Se3 were successfully synthesized by hydrothermal coreduction from SnCl2?H2O and the oxides of Bi and Se. The products were characterized by X-ray diffraction (XRD),transmission electron microscopy (TEM),and field emission scanning electron microscope (FESEM). Bi2Se3 powders obtained at 180°C and 150°C consist of hexagonal flakes of 50-150 nm in side length and nanorods of 30-100 nm in diameter and more than 1 μm in length. The product obtained at 120°C is composed of thin...

大尺寸KDP晶体生长

KDP and its deuterated analog DKDP (K (D x H 1- x ) 2PO 4) are the first ch oice materials in the fabrication of optical switcher and frequency converter fo r inertial confinement fusion study.In the past years,the growth technique has b een d eveloped greatly.Large aperture crystals can be grown with various methods,such as,temperature decreasing,solution circular flow,and rapid growth method,which i ntend to reduce the cost of production and satisfy the requirement of ICF.As to rapid growth method,much attention has been paid to solution stability and the K DP crystal qualities of this method which has been proved that high speed can be obtained.LLNL has grown KDP crystal with dimension of 57mm×57mm×55mm,260 kil ogram in 59 days.This method is very different from conventional method for grow ing KDP crystal in three directions uniformly.In addition to the growth of the pyramidal faces,rapid crystallization from supersaturated solution results in si gnificant growth of prismatic faces.Inclusions of growth solution and incorporat ion of metal impurities will occur in the prism sector as prism extends very muc h by this method.Fast growth needs high supersaturation(10%—30%),so the grow th condition,such as ,raw materials,apparatus,temperature lowing proceed should be controlled very strictly.In order to improve the utilization of KDP crystal g rown by point seed method,we developed 4 vessels circular technique on the bas e of 3 vessels circular technique recently.

块状晶体生长中的输运现象——从数值的非线性分析到工艺的改进

The quality of substrate crystals is critical to the performance of devices used in electronic and optoelectronic applications.These bulk crystals are mostly grown from the melt or solution,with a well controlled solidification or supersaturation,which is affected significantly by the heat and mass flows.Particularly,in the melt growth,the interface kinetics is so fast that the growth is mainly controlled by the transport processes.Hence,the intricate coupling of heat and mass transfer and melt flow strongly influences the grown crystal quality,but its analysis and control is not a trivial task.For most materials,such as semiconductors and oxides,a detailed analysis of the transport processes through experiments is extremely difficult due to the long growth period at high temperature.Therefore,numerical simulation is inevitable.For the past ten years,crystal growth modeling has become one of the most active research fields in materials processing.Indeed,as long as the melt crystal growth of semiconductors remains a mainstay of the microelectronics industry,its modeling continues to be important.In this talk,the role of transport phenomena in bulk crystal growth and their detailed nonlinear analysis are illustrated through our research work over the years.Particular interests will be paid to the zone melting and Bridgman crystal growth.The control of convection and interface shape through external forces,such as rotation,magnetic fields,and vibration will be discussed.Interface instability leading to“pit formation”and interface breakdown due to thermal and solutal flows will also be illustrated.

Adsorption of Cholesterol on Carbon Powders

Carbon powders have the ability to remove cholesterol from solution by adsorption. Various combinations from among 12 different types of carbon powders （including two medical carbons）, having a wide range of surface area and porosity, were used to perform cholesterol adsorption experiments. The cholesterol concentration in a cyclohexane solvent （37 ~C, shaking 200 rpm） was detected at 215 nm using ultraviolet spectroscopy. Most adsorption occurred in the first 30 to 60 minutes. A Langmuir model was used to fit the amount of cholesterol adsorbed per gram of carbon. The medical carbon, Natural Elements Activated Charcoal, adsorbed 234 mg of cholesterol adsorption per gram of carbon. The experimental percentages of cholesterol removed from solution （maximum 98%） were correlated with nitrogen Branauer-Emmett-Teller （BET） surface areas and micro, meso, and macropore volume distributions. Surface area alone was not a suitable predictor of cholesterol adsorption. However, carbon powders exhibiting a large surface area along with significant meso and macropores were shown to be effective in adsorbing cholesterol from a nonpolar environment. Ingestion of a medically approved carbon powder with a large surface area and sufficient meso and macroporosity may be able to adsorb cholesterol in the intestinal tract and thereby lower cholesterol levels in the body.

Synthesis, Growth and Characterization of Benzophenone Added Sodium Acid Phthalate Crystal—A Potential Material for Nonlinear Optical Applications

Sodium acid phthalate C8H5NaO4 is one of the suitable semiorganic single crystals hired in second harmonic generation conversion applications. In the present work, optically transparent Benzophenone doped with sodium acid phthalate (SAPB) single crystals were grown successfully by slow evaporation solution technique. Single crystal XRD analyses exposed that the crystal lattice of SAPB crystal is a monoclinic crystal system with unit cell parameters a = 6.77 Å, b = 9.31 Å, c = 13.58 Å, and space group B2cb. The crystalline nature of SAPB material was confirmed by powder XRD pattern. The functional groups present in the grown crystals were identified by the FTIR analysis ranging between 4000 and 500 cm−1. The optical transparency and band gap of grown crystals were measured from UV-Visible spectroscopy. The fluorescence emission spectrum of the SAPB crystal having a strong Yellow emission peak at 574 nm and the red emission at 631 nm are identified. The Vickers microhardness number (Hv) increases with increasing load. Meyer’s index number (n) calculated from Hv shows that the material belongs to the soft material category. Preliminary measurement using Kurtz powder technique with Nd-YAG laser light of wavelength 1064 nm indicates that their second harmonic generation (SHG) efficiencies of the grown crystals were presented 2 times in comparison with Potassium Dihydrogen Phosphate (KDP) was confirmed.