BeO瓷的金属化和封接

综述了氧化铍瓷的金属化及其封接技术,指出氧化铍瓷和Al2O3瓷在金属化工艺上的差异,论文最后汇集了国内外常用烧结金属粉末法15种配方和工艺参数,以资同行专家参考.     

从微孔洞起始的热冲击裂纹的数值研究——Ⅰ: 热应力分析

陶瓷材料在热冲击荷载作用下的典型破坏模式是裂纹的起始和扩展。当高温的材料或构件突然处于低温环境时,裂纹将由材料或构件的表面开始产生和发展。因此,材料表面及其表面附近的材料微结构对裂纹的起始有着非常重要的影响。实验表明:某些具有微孔洞结构的陶瓷材料比相应的密实材料的抗热冲击性能有所提高,但相关的机制目前还没有得到定量的解释。本文作者利用商业有限元软件ABAQUS,分析了受热冲击表面上的开口微孔洞、处于表面附近的闭口微孔洞周围的热应力场,以及微孔洞的大小、微孔洞与表面的距离对热应力场的影响,其目的是为进一步分析裂纹的起始和扩展做准备。数值结果表明:一般情况下,闭口微孔洞引起的应力集中比开口微孔洞引起的应力集中更为严重,特别当闭口微孔洞与表面之间的距离很小时,和没有微孔洞情况相比,闭口微孔洞引起的最大的应力集中系数超过6。     

无团聚,纳米ZrO2增韧Al2O3基陶瓷材料

本文通过微波加热ＺｒＯＣｌ２·８Ｈ２Ｏ的醇水深液．用ＨＰＣ作分散剂．制备出无团聚、单分散的纳米水合二氧化锆。然后采用胶体工艺制备出Ａｌ２Ｏ３－ＺｒＯ２先躯体均混合的粉体。用ＸＲＤ分析ＺＴＡ的相结构。用ＳＥＭ观察断口形貌。结果发现，ＺｒＯ２均匀地分布在ＺＴＡ陶瓷中。粒径小于５００ｎｍ，并且主要以ｔ－ＺｒＯ２形式稳定存在。最后探讨了ＺＴＡ的增韧机制。     

Machinability evaluation of machinable ceramics with fuzzy theory

The property parameters and machining output parameters were selected for machinability evaluation of machinable ceramics. Based on fuzzy evaluation theory, two-stage fuzzy evaluation approach was applied to consider these parameters. Two-stage fuzzy comprehensive evaluation model was proposed to evaluate machinability of machinable ceramic materials. Ce-ZrO2/CePO4 composites were fabricated and machined for evaluation of machinable ceramics. Material removal rates and specific normal grinding forces were measured. The parameters concerned with machinability were selected as alternative set. Five grades were chosen for the machinability evaluation of machnable ceramics. Machinability grades of machinable ceramics were determined through fuzzy operation. Ductile marks are observed on Ce-ZrO2/CePO4 machined surface. Five prepared Ce-ZrO2/CePO4 composites are classified as three machinability grades according to the fuzzy comprehensive evaluation results. The machinability grades of Ce-ZrO2/CePO4 composites are concerned with CePO4 content.     

(Ta2O5)0.92(TiO2)0.08介电陶瓷的激光烧结改性研究

采用CO2 激光对 (Ta2 O5) 0 .92 (TiO2 ) 0 .0 8陶瓷的烧结改性进行了系统研究 ,分析了改性微观机理。所制备的陶瓷试样比普通炉烧试样的介电常数值提高了约 3倍 ,平均值约为 4 5 0 ,同时具有良好的热稳定性。通过X射线衍射相结构分析 ,确定激光烧结陶瓷试样中存在H -TiTa18O47高温相 ,采用金相和扫描电镜的分析方法 ,首次获得了陶瓷试样的 3D显微结构信息 ,激光烧结试样具有与普通炉烧试样明显不同的显微结构特征。相结构及显微结构的差异应是激光烧结试样介电性能改善的主要原因。     

Transformation ratio of “ring-dot” planar piezoelectric transformer

A piezoelectric transformer (PT) is a device, which can be used for transforming an ac voltage via ultrasonic vibrations. The best characteristics are achieved in the vicinity of mechanical vibration resonance. “Ring-dot” type design of homogeneously poled disk PT was originally proposed by Berlincourt. Only experimental data were published in preceding studies. An analytical continuum model is presented in this work. The effects of dimensions, material properties and electrical load on the voltage gain as well as on the efficiency are calculated. Hard lead zirconate titanate ceramics (PZT, APC841 type) was used for sample fabrication. Studied PTs typically attain transformation ratio equal 20 without load. For load impedance around 5 kΩ, the observed efficiency was above 90%, whereas the transformation ratio dropped down to the values around 2. The model correspondence with experiment is limited by employed approximations. Model limitations are discussed with respect to experimental data.     

烧成工艺对Fe-Cu系陶瓷材料负阻特性的影响

通过大量的实验研究证明：Ｆｅ－Ｃｕ系陶瓷材料对烧成温度比较敏感，样品的烧成温区比较窄，只有２０°左右。同一烧成温度下，保温时间越长，负阻特性能越坏，击穿电压、负值系数下降。降温速率对其负阻特性没有多大影响，采取随炉降温即可获得负阻特性较好的样品。     

Effect of Sintering Temperature on Phase Transition and Mechanical Properties of Lead Zirconate Ceramics

Phase transition and mechanical properties of PbZrO₃ (PZ) at different sintering temperatures were studied. The Curie temperature depends on the sintering temperature. Hardness and fracture toughness of the PZ were measured using Vickers and Knoop microhardness testers. The lower density at the higher sintering temperature resulting from the loss of lead oxide (PbO) causes the lower value of the Curie temperature, hardness and fracture toughness. The results were well corresponding to the microstructure of the PZ ceramics.     

La^3＋、Li^1＋对CaTiO3微波介电性能的影响

研究了La^3＋、Li^1＋取代对CaTiO3微波介电性能的影响。在1400℃以下烧结制备Ca1-xLa2x/3TiO3（简称CLT）微波陶瓷，分析了容差因子τ对谐振频率温度系数τf的影响。在1350℃烧结4h，可制备出εr=118，τf=＋2．95×10^-4/℃，Qf=10360GHz的CLT（x=0．4）微波陶瓷。以（1叫）Ca0.6La0.2667TiO3-yLi1/2Nd1/2TiO3为代表，对（1-y）Ca1-xLa2x/3TiO3叫-yLi1/2Nd1/2TiO3（简称CLLNT）系列材料的微波介电性能进行了探讨。随着烧结温度的提高，CLLNT（x=0．4）的εr略有下降，而Q·f值略有上升。随着y值的增加，CLLNT（x=0．4）的即Q·f、τf都下降。与CLT（X=0．4）相比，虽然CLLNT（x=0．4）的Q·f值下降了，但τf得到较大的改善，同时ε仍很高，保持在100以上。     

各向异性压电陶瓷材料

本工作制备了添有少量Pb(Zn_(1/3) Nb_(2/3))O_3,Bi(Zn_(1/2) Ti_(1/2))O_3和MnO_2的高电阻率,高密度的改性(PbCa)TiO_3压电陶瓷。这种陶瓷在150℃和施加40—50kV/cm电场条件下极化之后显示出大的各向异性压电特性。它具有高的厚度扩张模式机电藕合系数Kt,高的机械品质因素Qm低的介电常数,而平面耦合系数Kp值极小。于是,这种新的压电材料适于制作高频陶瓷滤波器超声换能器,金属探伤检测器,以及声表面波器件等。