低熔点微晶封接玻璃的研究

系统地研究了Ｂ２Ｏ３－ＺｎＯ－ＰｂＯ－ＳｉＯ２系统玻璃的组成与性能，给出玻璃配方与其物化性能测试结果，并就晶核剂以及部分成分对低熔点微晶封接玻璃性能的影响进行了讨论，封接玻璃已广泛地用于微光像增强器，激光器，氙灯，湿敏电阻器等金属与金属，金属与玻璃，玻璃与玻璃，玻璃与陶瓷的封接。     

Ti4+掺杂硼硅酸盐微晶玻璃的光谱特性

制备了Ti4+掺杂硼硅酸盐玻璃,根据玻璃样品的差热分析(DTA)进行微晶化处理,测试了Ti4+掺杂硼硅酸盐微晶玻璃的X射线衍射(XRD)谱、透射电镜(TEM)图像、吸收光谱和发射光谱.根据Scherrer公式计算了BaYF5微晶的平均晶粒尺寸并与TEM图像进行比对.在紫外光激发下,观察到Ti4+掺杂BaYF5硼硅酸盐微...     

二氧化钛纳米微晶的制备及性质的研究

用无水四氯化铁和异丙醇为原料，用溶胶－凝胶法制备二氧化钛纳米微晶，用一系列手段研究了它的结构，结果表明，所得纳米微晶为椭球状，粒径分布范围窄，６００℃焙烧１小时所得微晶为锐矿相和金红石相两种结构共存，其Ｘ射线光电子能谱及红外光谱的特性直接受该微结构的影响。     

微晶玻璃试片的化学抛光研究

光学零件的凹槽、孔道等复杂结构无法进行机械抛光,只能采用化学抛光。分析了化学抛光的机理和微晶玻璃的组成,设计了化学抛光技术方案、工艺流程和操作方法。对微晶玻璃化学抛光前后的光学表面进行了测试、分析。结果表明:化学抛光去除量主要由化学抛光液的温度和抛光时间控制。采用氟化氢铵、氢氟酸与添加剂组成的化学抛光液和合适的化学抛光工艺,可以能够得到光滑、透明的表面,表面粗糙度可降低到100nm;可见光透过率81%~83%。     

独居石微晶玻璃中玻璃相含量的红外光谱定量测定

独居石微晶玻璃由偏磷酸盐玻璃和独居石两相组成。玻璃和独居石的红外吸收谱带彼此不相重叠,且1275和616cm~(-1)谱带的吸收强度随玻璃相的含量变化而变化。两谱带的对数吸光度比值与玻璃相含量(w％)的相关系数r=0.9975,其回归方程为y=48.356 25.93x。合成独居石的IR谱中952和616cm~(-1)谱带的吸光度比值也随不同的Ce_2O_3/La_2O_3比值规律变化。其r=0.9917,回归方程为y=0.2211exp(0.0221x)。高的相关性表明IR技术可在磷酸盐微晶玻璃物相定量分析中得到实际应用。     

氟氧化物微晶玻璃散射效率的研究

本文利用离散偶极子近似[1](Discrete Dipole Approximation,简称DDA),从理论上系统地探究了氟氧化物微晶玻璃纳米微晶的尺寸、周围介质折射率和多粒子周期性排布结构对散射效率的影响,提出降低微晶玻璃散射效率的有效途径,成功解释了氟氧化物微晶玻璃中的"超透明"现象。     

Tb3+掺杂PbF2基氟氧微晶玻璃的发光性能

采用高温熔融法和热处理工艺制备出一种Tb3+掺杂的PbF2基玻璃和微晶玻璃。经XRD分析发现,微晶玻璃内析出了PbF2颗粒,微晶团聚体平均尺寸约为15～75μm。在378 nm紫外光和X射线激发下,掺Tb3+的微晶玻璃与未经热处理的玻璃样品比较,微晶玻璃的发光强度增加了数倍,因而提出PbF2微晶的析出是微晶玻璃发光增强的主要原因。     

退火重结晶制备AlN/C复合泡沫材料及其力学性能研究

为了得到一种轻质、高强度、耐烧灼的新型碳泡沫材料,以无定形AlN为添加剂,在空心微球/网络复合型碳泡沫的基础上,采用退火热处理工艺成功地制备出了AlN/C复合泡沫材料.通过扫描电镜、透射电镜对样品进行表征,测试结果表明无定形AlN在碳微球的表面重结晶为AlN晶须,其直径大约为50nm左右,长度10μm以上,具有较大的长径比.X-射线衍射峰证明样品石墨化程度高,且AlN晶须为六方结构.X-射线光电子能谱测试发现在287.5eV处有较明显的C-N峰出现,这表明AlN和碳泡沫在界面处通过C-N键结合.同时,对其力学性能进行测试,通过分析应力-应变测试结果,AlN/C复合泡沫材料的压缩强度为40.27MPa,相对碳泡沫材料而言提高了近一个数量级.测试结果表明,AlN晶须显著增强了碳泡沫的压缩强度,这种新型复合泡沫材料有望应用于各种抗压减震航空材料.     

Eu3+离子在微晶玻璃研究中的探针作用

制备出单掺Eu3+离子的氟氧化物玻璃陶瓷系列样品,利用Eu3+离子作为荧光探针,通过热处理前后Eu3+离子发射光谱中电偶极子跃迁与磁偶极子跃迁强度比值的变化表征在玻璃材料中微晶是否形成,分析了Eu3+离子荧光发射谱中电偶极子跃迁与晶体场对称性的关系,进一步表征了稀土离子所处微晶晶格场的变化.     

低熔点微晶封接玻璃的应用研究

探讨低熔点微晶封接玻璃的技术要求和封接件的匹配封接条件，并给出部分低熔点微晶封接玻璃的性质和典型封接工艺。     

铁电体中新畴成核经典模型的改进

新畴成核是外加低场下铁电体中铁电畴反转的一个重要的过程.首先介绍了新畴成核的经典模型,采用该模型研究了铁电畴反转的新畴成核过程,发现理论计算的成核速率与外场关系和实验观测结果不一致.在Tagantsev模型的基础上,选取不同的成核形状对新畴成核的经典模型进行了改进,并获得了和实验观测相符的理论计算结果. 关键词： 铁电体 铁电畴 成核速率     

一种新型引燃电极材料的研究

 根据引燃电极的性能要求,选取碳化硼、氮化硼等原料,采用粉末冶金法制得了无毒、引燃率高、性能稳定的新型引燃电极。然后用X射线衍射仪(XRD)和扫描电子显微镜(SEM)分析了材料的微观结构,并分析了引燃电极成分、表面形貌及冷热电阻对电极的引燃性能的影响。研究表明：引燃电极主体材料中的碳化硼将增强电极的导电性能,氮化硼可以增加热导率并调节电阻,使电极在高温下保持较高的电阻而正常工作;表面形貌将影响样品的引燃性能,致密度高、孔隙率低的样品,其导电能力和耐压能力强,引燃性能好;引燃电极冷电阻的大小只能给电极与水银的接触情况和工作状态提供判断依据,给电极引燃性能的好坏提供粗略的参考,不能为其提供判断依据。     

磁记录硬盘介质研究进展

硬盘磁记录介质是磁性材料应用的一个重要方面,目前在信息存储领域占有重要的地位.文章概述了磁记录硬盘介质的发展过程以及研究和开发的状况,并对硬盘未来的发展前景作了分析.     

Effect of titanium powder assisted surface pretreatment process on the nucleation enhancement and surface roughness of ultrananocrystalline diamond thin films

A superior, easy and single-step titanium (Ti) powder assisted surface pretreatment process is demonstrated to enhance the diamond nucleation density of ultrananocrystalline diamond (UNCD) films. It is suggested that the Ti fragments attach to silicon (Si) surface form bond with carbon at a faster rate and therefore facilitates the diamond nucleation. The formation of smaller diamond clusters with higher nucleation density on Ti mixed nanodiamond powder pretreated Si substrate is found to be the main reason for smooth UNCD film surface in comparison to the conventional surface pretreatment by only nanodiamond powder ultrasonic process. The X-ray photoelectron spectroscopic study ascertains the absence of SiC on the Si surface, which suggests that the pits, defects and Ti fragments on the Si surface are the nucleation centers to diamond crystal formation. The glancing-incidence X-ray diffraction measurements from 100 nm thick UNCD films evidently show reflections from diamond crystal planes, suggesting it to be an alternative powerful technique to identify diamond phase of UNCD thin films in the absence of ultra-violet Raman spectroscopy, near-edge X-ray absorption fine structure and transmission electron microscopy techniques.     

Second-phase nucleation on an edge dislocation

A model for nucleation of second phase at or around a dislocation in a crystalline solid is considered. The model employs the Ginzburg–Landau theory of phase transitions comprising the sextic term in the order parameter (η⁶) in the Landau free energy. The ground state solution of the linearised time-independent Ginzburg–Landau equation is derived, through which the spatial variation of the order parameter is delineated. Moreover, a generic phase diagram indicating tricritical behaviour near and away from the dislocation is depicted. The relation between classical nucleation theory and the Ginzburg–Landau approach is discussed, for which the critical formation energy of the nucleus is related to the maximum of the Landau potential energy. A numerical example illustrating the application of the model to the case of nucleation of hydrides in zirconium alloys is provided.     

Determination of the colloidal crystal nucleation rate density

Colloidal suspensions of charged latex microspheres in water exhibit liquid-like or crystalline ordering depending on particle interaction and concentration. By virtue of large particle spacing and slow dynamics, colloidal systems offer a unique opportunity to study interfacial structure and dynamics. This paper presents the first reported experimental study of the nucleation rate density, c, of an nonequilibrium (supercooled) colloidal liquid to colloidal crystal first order phase transition. Local and global observations of colloidal crystals growing from a metastable colloidal liquid were used to determine c. Microscopic local observations revealed homogeneous nucleation and constant interface velocity growth of quasispherical crystallites in the bulk and heterogeneous nucleation of a crystalline sheet with lower growth velocity at the cell wall. Complementary global observations of the recrystallization transition made by measuring the time dependence of the suspension transparency (the fraction of transmitted laser light) determined c by fitting this curve to a model based on an extension of Avrami's theory of crystallization.     

Characteristics of acoustic emissions during nucleation of superheated droplets

Superheated droplet nucleation and subsequent bubble oscillation produces an acoustic pressure pulse that contains valuable information about the nucleation process. Spectral analysis of the pressure pulse indicates excitation of different modes of bubble oscillations in the nucleation process. In the present study it is observed that gamma induced droplet nucleation excites higher modal oscillations and also emits higher intensity acoustic emission compared to that of spontaneous nucleations.     

Adsorption and nucleation on smooth surfaces

The nucleation and growth of condensate nuclei on smooth surfaces, e.g., an immiscible liquid or a smooth solid, can occur both by the direct addition of molecules from the vapor and from those adsorbed on the substrate. We show how to generalize nucleation theory to allow for the simultaneous occurrence of both mechanisms. The vapor-condensate-substrate interfacial forces, the contact angle, the critical supersaturation, and the coefficient in the adsorption isotherm are different ways of expressing the affinity between vapor molecules and the substrate surface. The critical supersaturations for nucleation on the surface of an immiscible liquid and nucleation on the surface of a perfectly smooth solid are predicted in terms of these parameters and the relationships among them. For most values of these parameters we find that adsorbed molecules are usually far more important to the nucleation process than those in the vapor phase.     

纳米尺度下气泡核化生长的分子动力学研究

采用分子动力学方法模拟纳米尺度下液体在固体壁面上发生核化沸腾的过程,主要研究壁面浸润性对气泡初始核化过程和气泡生长速率的影响以及固-液界面效应在液体核化沸腾的能量传递过程中所起到的作用.研究结果发现：壁面浸润性越强,气泡在固壁处越容易核化.该结果与经典核化理论中“疏水壁面易于产生气泡”的现象产生了明显的区别.其根本原因是在纳米尺度下,固-液界面热阻效应不能被忽略.一方面,在相同的壁温下,通过增强固-液相互作用,可以显著降低界面热阻,使得热量传递效率提高,导致靠近壁面处的流体温度升高,气泡核化等待时间缩短,有利于液体沸腾核化.另一方面,气泡的生长速率随着壁面浸润性的增强而明显升高.当气泡体积生长到一定程度时,会在壁面处形成气膜,从而导致壁面传热性能恶化.因此,通过壁面的热流密度呈现出先增大后减小的规律.     

基于Wenzel模型的粗糙界面异质形核分析

异质形核是形核发生的主要形式. 经典形核理论对基底界面作了理想化平面假设,然而实际异质形核体系中理想平直的固体界面是不存在的,这导致了异质形核描述与实际情况的偏差. 考察了固相晶胚在非平整界面上的异质形核过程,基于Wenzel润湿模型,分析了非理想界面的粗糙度因子对固相晶胚形核功的影响规律. 结果表明:当基底与晶核之间的本征润湿角小于90°时,基底界面越粗糙越有利于形核;本征润湿角大于90°时,基底界面越粗糙越不利于形核. 同时,游离晶胚在基底上润湿是球冠晶胚形成的重要途径,粗糙界面润湿过程中界面自由能的 关键词： 异质形核 粗糙界面 Wenzel模型 润湿过程