高温熔体晶体生长的三维实时观察实验装置

最近开发了三维光学实时观察法,应用透视魔镜法实时观察并记录透明晶体的生长和溶解过程,最高使用温度为1000℃配合三维观察,设计并制造了一套独特的生长炉和坩埚,有二组互相垂直的光路可同时实时观察晶体生长过程,并通过CCD摄像头进行同步记录.应用这组设备,观察并记录了KCl枝蔓晶的生长过程．     

微重力条件下晶体生长的实验研究

本文提供了在空间晶体生长观察装置上,实时观察记录了空间高温氧化物晶体生长过程的新方法．该装置具有自动光电调焦、多工位、自动图像记录等特点,通过设置不同的温控程序,利用该装置测定了高温熔体内的温度分布,同时对高温氧化物晶体材料界面形貌变化及其周围的熔体流动状态进行了分析,并首次观察到空间高温溶质的均匀扩散现象和空间高温溶液内均匀胞状结构的形成过程,最后对比空间和地面的实验结果,阐述重力对流和表面张力对流在微重力条件下对晶体生长的影响机制．     

高温氧化物晶体界面非稳定性研究

设计了一套模拟实验,以获得关于晶体形态和界面非稳定性的差异的可靠数据,如高温溶液生长的骸晶和枝蔓晶．这些实验是在高温实时观察装置（ＨＩＴＩＳＯＴ）内进行的．高温溶液晶体生长实验是在环形铂金丝炉圈内进行的．炉圈直径为２ｍｍ．铂金丝既起加热又起支撑熔体的作用．选用ＫＮｂＯ_３和Ｌｉ_２Ｂ_４Ｏ_７的混合物进行晶体生长实验．在只存在扩散机制的快速生长过程中,会形成不同的晶体不完整性,如晶面凹坑、骸晶和枝蔓晶．采用淬火实验以分辨不同的ＫＮｂＯ_３晶体形态,并用扫描电镜研究Ｌｉ_２Ｂ_４Ｏ_７溶体中ＫＮｂＯ_３晶体生长的形貌．在一般情况下,当晶体在气液界面附近液相区成核时,会产生晶体界面非稳定性．导致晶体形状不稳定的溶液层的厚度为６０μｍ．通过扫描电镜观察,发现晶体在这一溶液层中由多面体晶变为枝蔓晶．骸晶和枝蔓晶的各向异性反映了ＫＮｂＯ_３的立方特性,也反映了界面非稳定性是沿［１１０］晶棱扩大的,［１１０］晶棱方向的分支证实了晶体生长形状的各向异性·形成界面非稳定性的临界尺寸为１０μｍ．与此相反,中持稳定的晶面形状是通过６０μｍ厚度以下的溶液内的晶体生长来实现的．晶体生长过程是由高温实时观察装置进行实时观察和记录的,并能观察到晶体固液     

铝合金直接氨化生长氮化铝反应机制研究

针对铝合金直接氮化生长ＡＩＮ过程中的晶体生长过程进行分析,通过Ｘ－ｒａｙ衍射和ＳＥＭ观察,获得了不同生长阶段ＡＩＮ晶体的生长特征,研究了铝合金直接氨化生长氮化铝的反应机制．提出了一种气－液－固－固）晶体生长机制,简称ＶＬＳＳ机制,并着重对ＶＬＳＳ机制的实现条件、实现过程以及与传统的ＶＬＳ晶体生长机制的相同点和差异进行了讨论．     

光学干涉技术在晶体生长研究中的应用

利用光学干涉法对晶体生长过程中所引起的溶液折射率微小变化进行监测,分析所采集到的干涉图像,可得出与光程差相关的溶液浓度场及温度场的精确分布、晶体微观形貌变化及溶液对流等信息,对晶体生长机理研究有重要的意义.回顾了干涉技术测量晶体生长参数的基本原理,同时综述了近年来干涉技术在晶体生长研究中的应用及发现,并分析了该技术在晶体生长研究领域中的发展方向.     

空间微重力环境下蛋白质晶体生长的研究进展

空间微重力环境可消除或减弱常重力场下溶液中存在的对流和沉降,为蛋白质晶体生长提供一个相对均一和稳定的环境,有利于得到尺寸更大、衍射分辨率更高的蛋白质晶体。通过对这些高质量空间晶体进行X射线衍射分析,可获得多种蛋白质的精细三维结构。从空间蛋白质晶体生长的发展历史、研究成果、生长机理、存在的问题与对策等方面总结了空间微重力环境下蛋白质晶体生长的研究进展,展望了空间蛋白质结晶的未来。     

光电功能晶体材料研究进展

光电功能晶体,包括激光晶体、非线性光学晶体、电光晶体、介电体超晶格、闪烁晶体和PMN-PT驰豫电单晶等,在高技术发展中具有不可替代的重要作用。近年来,我国在这些重要晶体材料的生长、基础研究和应用方面都获得了很大成绩。综述了光电功能晶体材料研究和应用的部分进展。在此基础上,提出进一步发展晶体理论,扩大理论的应用范围,注重晶体生长基本理论研究,发展新的晶体生长方法和技术,加强晶体生长设备研制,加强晶体从原料到加工、后处理、检测及镀膜等全过程的结合等建议,以全面提高我国光电功能晶体研究发展及其产业化水平。     

KDP/KD*P晶体生长过程中柱面扩展的研究

目前在KDP/KD*P晶体的实际生长过程中,仍以传统降温法为主.在传统降温速度的基础上适当提高降温速度,可以加快KDP/KD*P晶体的生长速度,但与此同时有可能产生柱面扩展.为此,我们对不同生长环境下的KDP/KD*P晶体生长过程中柱面扩展进行了一系列研究.实验中所用KDP原料和去离子水均与生长大口径KDP晶体相同,其它各项条件也尽量模拟大口径KDP晶体生长过程中的实际情况.在晶体生长实验过程中通过研究不同条件下KDP/KD*P晶体的柱面扩展情况来研究柱面扩展对KDP/KD*P晶体光学质量影响的共同特点.通过分析和研究实验数据及晶体生长过程,我们认为在正常生长条件下引起柱面扩展的主要因素有两个溶液的过饱和度和籽晶柱面存在的缺陷.扩展部分的晶体的光学质量与本体部分差别较大,扩展部分对光的透过率在紫外部分下降很快,明显低于本体部分在这一波段的透过率.本体部分和扩展部分对光的透过率在其它波段差别不十分突出.     

实时控制过饱和度降温法生长KDP晶体

用变压器型电导仪实现了ＫＤＰ晶体生长过程中溶液的浓度和过饱和度的实时测量与控制,测量精度±０．０３ｇ ＫＤＰ／１００ｇ Ｈ_２Ｏ（±０．１０％相对过饱和度）,控制精度与测量精度相当．过饱和度实时控制系统提供了一种方法,可以研究在不同工艺条件生长ＫＤＰ晶体时,过饱和度与晶体生长和性能的关系．用分析纯原料生长ＫＤＰ晶体,发现随着过饱和度的增大,晶体的生长速度加快,晶体的均匀性降低．过饱和度实时控制系统可以使ＫＤＰ晶体在相对恒定的过饱和度下生长,提高了晶体生长的均匀性,抑制了生长层和散射颗粒的产生,有利于提高晶体的光学透过率和光伤阈值．     

快速生长KDP晶体中的包裹体

利用底部热能输入晶体生长装置进行了KDP晶体快速生长,晶体生长速度达25mm/d.利用激光透射成像法、断面显微观察、SEM及电子能谱对快速生长晶体中的各种包裹体进行了观察,分别观察到了平行于生长面的层状包裹及其分布、线形排列的液相包裹以及微观包裹体的形貌、尺度和分布等,讨论了快速生长KDP晶体中包裹体出现的条件,分析了这些包裹体形成的原因.     

Visualization of dynamic 3-D water behavior in polymer electrolyte fuel cell by using neutron image intensifier

Visualization of dynamic three-dimensional water behavior in a polymer electrolyte fuel cell (PEFC) stack was carried out by neutron CT using a neutron image intensifier. The neutron radiography system at JRR-3 in Japan Atomic Energy Agency was used. An operating stack with three cells based on Japan Automobile Research Institute standard was visualized. A consecutive CT reconstruction method by rotating the fuel stack continuously was developed using a neutron image intensifier and a C-MOS high speed video camera. The dynamic water behavior in channels in the operating PEFC stack was clearly visualized in 15 s intervals by the present dynamic neutron CT system.     

2-D sizing of sodium oxalate crystals by automated optical image analysis

A new automated static optical image analysis (SOIA) method was developed for characterising the shape of sodium oxalate crystals by separately measuring their length and width. The automated size analysis combines crystal image acquisitioning with a custom-developed numerical algorithm for morphological analysis of crystals. The automation of the two main measuring steps enables characterisation of a large number of crystals ensuring statistically meaningful results. As part of the numerical algorithm, a rectangularity-based morphological filter was implemented to eliminate overlapping crystals and crystal networks. The developed optical sizing technique has a low detection limit of 0.25 μm, which is close to the theoretical resolution of optical microscopy. It is demonstrated that the new automated SOIA sizing technique is very sensitive in identifying oxalate crystals of different shape. The measured crystal size distributions are compared to those obtained by an AccuSizer sizing instrument to confirm that they are consistent with the measurements obtained by a conventional crystal sizing instrument.     

Three-dimensional atomic imaging of Y and (B12)13 clusters in YB56 by HREM and crystallographic image processing

The three-dimensional atomic image of YB₅₆ was obtained by inverse Fourier transformation of three-dimensional phases and amplitudes in three high-resolution images along [100], [110] and [111] of YB₅₆ crystals. After crystallographic image processing, the image directly showed the three-dimensional potential map of the crystal, which showed (B₁₂)₁₃ clusters and Y atom positions. The present method would be useful for three-dimensional structure analysis in nanoscale regions.     

Stress intensity factors and crack propagation in a single crystal nickel-based superalloy

A three-dimensional finite element method was used to calculate the stress intensity factors for corner cracked specimens of a single crystal nickel-based superalloy. The anisotropic material properties and inclinations of the cracks were shown to have significant effects on the stress intensities. Then the two-dimensional resolved shear stress approach for predicting the crack planes and crack growth directions in single crystals was extended to the three-dimensional case. Using this approach, the fatigue crack growth behaviour in single crystal corner cracked specimens could be explained.     

Three-dimensional atomic imaging of Y and (B12)13 clusters in YB56 by HREM and crystallographic image processing

The three-dimensional atomic image of YB₅₆ was obtained by inverse Fourier transformation of three-dimensional phases and amplitudes in three high-resolution images along [100], [110] and [111] of YB₅₆ crystals. After crystallographic image processing, the image directly showed the three-dimensional potential map of the crystal, which showed (B₁₂)₁₃ clusters and Y atom positions. The present method would be useful for three-dimensional structure analysis in nanoscale regions.     

锗酸铅晶体枝蔓晶生长的实时观察研究

利用实时观察方法对锗酸铅晶体生长枝蔓晶的生长过程进行了描述和分析．发现，枝蔓晶的产生与杂质相关，杂质作为一个成核中心，在其周围存在一个溶质扩散层，这个溶质扩散层的厚度随着晶体生长而增大．当该扩散层的厚度超过某个临界值时，出现枝蔓晶生长，溶质扩散层的临界厚度约为12μm．枝蔓晶主干的生长速度受分支出现以及主干转向的影响．     

3D Modeling and Simulation of Dendritic Growth during Solidification

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

Noninvasive OCT imaging of the retinal morphology and microvasculature based on the combination of the phase and amplitude method

To implement the optical coherence tomography (OCT) angiography on the low scanning speed OCT system, we developed a joint phase and amplitude method to generate 3-D angiograms by analysing the frequency distribution of signals from non-moving and moving scatterers and separating the signals from the tissue and blood flow with high-pass filter dynamically. This approach firstly compensates the sample motion between adjacent A-lines. Then according to the corrected phase information, we used a histogram method to determine the bulk non-moving tissue phases dynamically, which is regarded as the cut-off frequency of a high-pass filter, and separated the moving and non-moving scatters using the mentioned high-pass filter. The reconstructed image can visualize the components of moving scatters flowing, and enables volumetric flow mapping combined with the corrected phase information. Furthermore, retinal and choroidal blood vessels can be simultaneously obtained by separating the B-scan into retinal part and choroidal parts using a simple segmentation algorithm along the RPE. After the compensation of axial displacements between neighbouring images, three-dimensional vasculature of ocular vessels has been visualized. Experiments were performed to demonstrate the effectiveness of the proposed method for 3-D vasculature imaging of human retina and choroid. The results revealed depth-resolved vasculatures in retina and choroid, suggesting that our approach can be used for noninvasive and three-dimensional angiography with a low-speed clinical OCT, and it has a great potential for clinic application.