新型对称联苯双酯类液晶材料的合成和晶体结构

设计并合成了4个对称联苯双酯类液晶化合物,化合物结构通过红外和核磁表征,它们的介晶性通过差示扫描量热仪(DSC),X射线衍射仪(XRD)和热台偏光显微镜(POM)进行了研究.并测定了4,4'-3,3',5,5'-四甲基联苯-二(4-甲基苯甲酸酯)(Ⅲa)的单晶结构,结果显示:晶体属于单斜晶系,P21/c空间群,晶胞参数为a=18.525(3)(A),b=12.196(2)(A),c=12.195(2)(A),β=97.142(2)°,V=2733.7(9)(A)3,Z=4,Dc=1.163 Mg/m3,R=0.0521,Rw=0.1161.化合物均为热致型互变液晶,并讨论了氧原子、不饱和端基和端基链长对介晶性的影响.     

两相钛合金再结晶退火组织与织构演变的蒙特卡罗模拟

蒙特卡罗(MC)方法被广泛应用于模拟金属材料在退火过程中的静态再结晶行为. 在已有两相材料晶粒长大MC模型基础上, 引入形核阶段, 综合考虑再结晶晶粒吞并形变晶粒和再结晶晶粒竞争长大两种情况, 建立了退火时两相合金再结晶MC模型.结合电子背散射衍射所测 初始晶粒形貌、相成分、晶体学取向及应变储能相对值, 该模型被应用于TC11钛合金退火过程中的微观组织及织构演变模拟.结果表明, 所建模型能够较好体现退火过程中两相晶粒的形核及晶粒长大行为. 与β相相比较, α相具有较低的再结晶速率和较高的晶粒长大速率, 前者主要归结于α相较低的初始应变储能, 后者则体现了该条件下初始组织形貌、分布及两相比例对晶粒长大具有重要影响; 由于非均匀形核的影响, 模拟得到的再结晶速率变化与 假设均匀形核的Johnson-Mehl-Avrami-Kolmogorov 再结晶方程存在明显差异.同时, 两相的基本织构特征在退火过程中无明显变化, 但织构强度增加. 关键词： 两相钛合金 再结晶 蒙特卡罗方法 织构     

聚合物液晶的奇偶现象及其结晶行为

用直接缩聚法从4,4′-(1,4,7-三氧亚庚基)-二苯甲酸和4 4′-(α,ω-二氧亚烷基)-二苯酚合成了一系列芳香族聚酯(亚烷基碳数为2～6,10)。并对其结构进行了表征。采用DSC和偏光显微镜方法研究了聚合物的液晶行为。发现n=2～6的五个聚合物均具有热致型液晶行为。其中除n=4的聚合物具有近晶相和向列相两个中介相以外均呈向列型中介相。随着n的变化,聚合物液晶转交温度均呈现出奇偶现象,且为奇低偶高。液晶相温度范围在4和5之间出现最大值。本文还研究了热史对转变的影响。并用偏光显徽镜和X-衍射方法,发现此聚合物具有良好的结晶性,不易在淬火条件下保持液晶的织态结构。     

冷轧TA7合金板材织构的完整ODF分析

依取向空间的等体积划分原理,将传统的六方晶系材料特征非对称子空间(等角法)予以改造。并按等面积投影法对 ODF 图进行重建。按此法对实测的冷轧 TA7 合金板材完整ODF 施行织构分析。结果表明,织构分析与原等角法的完全等效;此方法能清晰地建立起反极图与 ODF 图之间的关系。等面积投影法的采用使织构定量简便、易行。     

YBCO涂层导体用Ni5W基带的制备和立方织构的发展

为了制作能满足YBCO涂层导体（coated conductor）所需要的高强度、低磁性的立方织构基带，本工作用粉末冶金方法制作了Ni-5at％W合金基带．为评估基带中立方织构的发展，用March-Dollase函数对各种热处理样品的择优取向度进行了研究，结果与用X射线极图法和电子背散射衍射法得到的结果基本一致．研究结果表明，在实验中所用的工艺参数范围内，随总加工率和热处理温度的提高，基带中立方织构百分数明显增高．提高总加工率实际增加了冷加工样品中立方织构晶粒或立方核心的数量．实验中得到了较好的和实用的工艺制度，用这种工艺可以制作出具有99％～100％立方织构百分数，并具有很好一致取向度的Ni5W基带．     

Synthesis and characterization of poly[4-(4-hydroxyphenoxy) benzoic acid]

Poly[4-(4-hydroxyphenoxy) benzoic acid] was prepared by the bulk polycondensation of 4-(4-acetoxyphenoxy) benzoic acid. Polycondensation was conducted at 350°C for 3 h under a reduced pressure of 0.1 mmHg and gave a polymer with X?n of 255. The polymer was characterized by elemental analysis, IR spectroscopy, differential scanning calorimetry, and wide-angle X-ray measurement. The crystal/nematic and nematic/isotropic phase transition temperatures of polymer, which depend on the molecular weight, were observed at about 300°C and 410°C, respectively. The polymers with low molecular weights showed nematic textures above 300°C. This nematic/isotropic phase transition temperature is lower than that of poly (4-hydroxybenzoic acid). This thermal behavior of polymer comes from ether units, which increase the flexibility (the rotation or torsion of skeletal bonds) of the polymer chain. © 1994 John Wiley & Sons, Inc.     

Grain Growth in Polycrystalline Thin Films of Semiconductors

Grain growth in thin films is usually abnormal, leading not only to an increase in the average grain size, but also to an evolution in the shape of the grain size distribution and to an evolution in the distribution of grain orientations. The latter can be driven by surface, interface or strain energy minimization, depending on film and substrate properties and on deposition conditions, and can lead to different final textures depending on which energy dominates.In semiconductor films, as in other materials, grain growth stagnation coupled with texture-selective driving forces leads to secondary grain growth, the rate of which is higher in thinner films. Self ion-bombardment enhances the rate of pre-stagnation grain growth, and doping of Si with electron donor leads to enhanced pre-stagnation grain growth as well as surface-energy-driven secondary grain growth. The effects of ion-bombardment and dopants on grain growth in Si can be understood in terms of associated increases in point defect concentrations and the effects of point defects on grain boundary mobilities.     

煤体结构对瓦斯突出能量的影响

本文主要从理论方面论述并推导了瓦斯突出能量是以一种潜能形式赋存于煤层及围岩之中;并结合一些实验数据,分析了煤体结构的差异对瓦斯突出能量的某些影响,是一步揭示了瓦斯突出多发生在地质构造破坏带的另一种内在联系.     

数字地面模型的加密与显示

介绍以航测数据重建三维地形模型,改进三次样条曲面算法用于格网加密,提出以格网为基础的地表、地物快速显示算法,实现地物造型、树木及地表纹理的三维表示。