超重力下燃烧合成大体积凝固态Al2O3/ZrO2（4Y）研究

通过在铝热剂中引入ZrO2(4Y)混合粉末,以超重力下燃烧合成方式,制备出Al2O3/ZrO2(4Y)自生复合陶瓷板材,并研究了复合陶瓷微观结构、生长机理与力学性能.XRD、SEM与EDS结果显示,Al2O3/32%ZrO2(4Y)复合陶瓷基体为亚微米t-ZrO2纤维成三角对称分布其上、取向各异的棒状共晶团,而Al2O3/37%ZrO2(4Y)复合陶瓷则以分布均匀的微米级t-ZrO2球晶为基体.Al2O3/32%ZrO2(4Y)复合陶瓷的强化归因于小尺寸共晶团边界及残余压应力增韧、相变增韧机制引发的高断裂韧性所致;同时,细小t-ZrO2球晶所具有的小尺寸缺陷及相变增韧与微裂纹增韧机制所引发的高断裂韧性也使Al2O3/37%ZrO2(4Y)复合陶瓷得以强化.     

烧结温度对20%ZrO_2(3Y)/Al_2O_3复相陶瓷力学性能和微观结构的影响

20%纳米ZrO2(3Y)粉末加入到高纯亚微米Al2O3粉中,采用高压干压成型方法和恒速升温多阶段短保温烧结方法制备出不同烧结温度下的复相陶瓷。研究烧结温度对复相陶瓷力学性能的影响,通过XRD,EDS和SEM对复相陶瓷进行元素组成和微观结构分析。结果表明:烧结温度在很大程度上影响着复相陶瓷的力学性能和微观结构,常压烧结1600℃保温8h时,相对密度、维氏硬度和断裂韧性达到最大,分别为98.6%,18.54GPa和9.3MPa·m1/2,而基体晶粒尺寸为1.4~8.1μm,ZrO2相变量为34.6%。1600℃下复相陶瓷具有优质的微观结构,断裂方式为沿晶-穿晶混合断裂模式。ZrO2(3Y)粉体的加入,从相变增韧、内晶型颗粒增韧和裂纹偏转等多个方面提高了复相陶瓷的断裂韧性。     

ZrO_2增韧Al_2O_3陶瓷的力学性能和增韧机制

对通过热压烧结法制备的3种陶瓷99.5vol%Al2O3(AD995)、ZrO2(15vol%)/Al2O3和ZrO2(25vol%)/Al2O3的力学性能和增韧机制进行了实验和理论研究。基于复合材料细观力学理论并考虑ZrO2的相变特性,建立了描述ZrO2/Al2O3陶瓷力学性能的本构模型。结果表明:ZrO2的加入细化了基体Al2O3晶粒,ZrO2/Al2O3陶瓷的致密性得到提高;3种陶瓷试件的破坏呈现小变形到脆性破坏的特点,压缩加载下试件应力-应变曲线近似为线性关系;AD995陶瓷的断裂韧性为5.65 MPa·m1/2,ZrO2(25vol%)/Al2O3陶瓷的断裂韧性为8.42 MPa·m1/2,提高了近50%;随ZrO2增韧相含量的增加,ZrO2/Al2O3陶瓷的弹性模量降低而断裂韧性增加,这一变化趋势与实验结果有良好的一致性。     

ZrO2(3Y)/Fe3Al复合材料的显微结构及性能

采用热压烧结制备了ZrO2(3Y)/Fe3Al复合材料,材料的室温抗弯强度、断裂韧性、HRA硬度分别为1321MPa、36MPa.m1/2、86.7,临界热震温差(△T)由单相ZrO2(3Y)的250℃提高至500℃.显微结构研究表明,裂纹桥联、裂纹偏转及相变增韧的协同作用,及位错对裂纹扩展的扰动作用是断裂韧性成倍增加的主要原因.     

云母微晶玻璃/Y-TZP复相材料的制备和力学性能

本文用烧结法制备了云母微晶玻璃／－TZP复相材料,用X光衍射分析（XRD）法测定了材料断裂过程中氧化锆的相变体积分数,用拉曼微探针谱测定了相变区宽度,并对增韧机制进行了研究．结果表明：氧化锆的加入可以显著提高材料的力学性能．当加入40vol％ZrO₂时,云母微晶玻璃的强度和断裂韧性分别可达446MPa和4．8MPam^1／2氧化锆的相变分数随氧化锆含量的增加而减小,而相变区宽度随氧化锆含量的增加而增大;氧化锆主要通过应力诱导相交增韧机制来提高云母微晶玻璃的断裂韧性,但随着氧化锆含量的增加,裂纹在氧化锆颗粒附近的偏转会进一步提高材料的断裂韧性．     

四方相氧化锆多晶陶瓷的力学性能及其增韧机理的研究

研究了 Y_2O_3的含量和热压工艺对四方相 ZrO_2多晶陶瓷(Y—TZP)力学性能的影响。含有2.8mol%Y_2O_3的热压 Y—TZP 的断裂韧性 K_(1c) 和断裂强度分别为15.3±1.9MPam~(1/2)和15.7±0.9×10~2MPa。观察了微裂纹尖端及其周围的相变过程。并非所有从四方相 ZrO_2到单斜相的相变对增韧和增强具有相同的作用.     

Al2O3/ZrO2/ZrSiO4复合材料的研究

在Al2O3颗粒补强锆英石陶瓷的研究基础上,探讨了Al2O3与ZrO2共同对锆英石陶瓷的协同补强增韧行为.制备的锆英石基复合材料的室温抗弯强度和断裂韧性分别可达383.31MPa、4.39 MPa·m12.采用XRD分析了复合材料的相组成,采用SEM观察复合材料的断面形貌.结果显示:ZrSiO4为主要晶相,另外还有少量Al2O3和ZrO2存在;第二种增强体ZrO2的最佳引入量为20％(质量分数);确定复合材料的强韧化是由Al2O3和ZrO2颗粒引起的裂纹偏转、微裂纹增韧与ZrO2颗粒引起的相变增韧共同作用而实现的,断裂方式主要为穿晶断裂.     

氧化锆基复合材料的裂纹扩展和疲劳性能

氧化锆(ZrO2)陶瓷中的应力诱导相变概念,在陶瓷领域颇具新意.70年代业已证明,ZrO2陶瓷确实有一个抗裂纹扩展的相变韧化机理.应力诱导相变就是裂纹尖端的亚稳四方晶体向单斜晶体转变,伴随体积膨胀诱导出压缩应力,起着减小裂纹扩展驱动力的作用.四方晶体的ZrO2陶瓷(TZP),通过添加不同氧化物,例如铈氧化物(Ce-TZP)或钇氧化物(Y-TZP),以四方对称的形式保持稳定.ZrO2陶瓷也能以四方晶体形式存在于立方基体中.     

ZrO2纤维/莫来石轻质复合材料的凝胶注模制备及其增韧机理研究

采用凝胶注模成型工艺制备了ZrO2纤维增韧莫来石复合陶瓷材料.借助透射电子显微镜(TEM)、扫描电子显微镜(SEM)、平板导热仪、单边切口梁法(SENB)等测试手段对样品微观形貌、导热系数、断裂韧性等进行研究;研究了分散剂对凝胶注模浆料团聚体的影响;讨论了ZrO2纤维增韧莫来石复合材料的增韧机理;概述了同时获得高韧性和高强度材料的途径.结果表明:添加ZrO2纤维能够明显提高莫来石的断裂韧性;当ZrO2纤维添加量(体积分数)为25％左右时可使莫来石轻质耐火复合材料兼具较低的热导率(λ=0.35 W·m-1·K-1,298 K)和优异的综合力学性能(KIC=7.6 MPa·m1/2,σb=270 MPa).     

氧化锆层状复合陶瓷表面压应力与相变增韧的关系

利用维氏硬度仪和X射线应力分析仪、X射线衍射仪等手段分别对单层和层状氧化锆陶瓷进行了力学性能测试和分析,研究结果表明,在ZrO2层状复合陶瓷中,压痕裂纹的形成除了因塑性区体积变化产生的残余应力外,还与相变应力和表面压应力有关,表面压应力对表面裂纹具有较大的抑制作用.层状陶瓷断裂韧性提高,主要是通过表面压应力对压痕裂纹区应力强度因子的贡献、提高断裂相变量,强化相变增韧效果、细化晶粒等几个方面来实现的.     

Optically and thermally stimulated luminescence of KMgF3:Ce3 and NaMgF3:Ce3+

The potentialities of optically stimulated luminescence (OSL) for personal dosimetry of ionising radiation have stimulated the search for new synthetic materials with good dosimetric properties. The sensitivity of two new OSL materials KMgF3 and NaMgF3 doped with Ce3+ ions has been evaluated and found to be of the same order of magnitude as that of Al2O3:C. Several other characteristics have also been investigated. Promising results for KMgF3:Ce are the high sensitivity and the low fading. However, this material suffers from a high self-dose due to the presence of 40K. NaMgF5:Ce is sensitive as well but shows strong fading. Interesting information on the mechanism has been obtained by correlating the signals of OSL and TL. Furthermore, the different bleachabilities under blue LED illumination of the strongly overlapping glow peaks allowed the extraction of one single peak for KMgF3:Ce3+. The results demonstrate new possibilities offered by the combination of TL and OSL.     

LiTaO3 and LiNbO3 Epitaxial Films

The preparation of film-forming peroxide solutions of LiTaO₃ and LiNbO₃ precursors is described. The solutions are used to produce LiTaO₃ films on single-crystal corundum and LiNbO₃ substrates by the spinning process and dip coating, followed by heat treatment, and LiNbO₃ films on single-crystal corundum substrates by the spinning process.     

Heat capacities and latent heats of LiNO3, NaNO3, and KNO3

Enthalpies of fusion and transition together with heat capacities in both solid and liquid phases have been measured on LiNO₃, NaNO₃, and KNO₃ with a high accuracy by differential scanning calorimetry (DSC). Polynomial expressions of heat capacities are given.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Dielectric Relaxation and Conductivity of Ba(Mg1/3Ta2/3)O3and Ba(Zn1/3Ta2/3)O3

The frequency dependent dielectric properties of barium magnesium tantalate(BMT),Ba(Mg_(1/3)Ta(2/3))O_3 and barium zinc tantalate(BZT),Ba(Zn_(1/3)Ta_(2/3))O_3 synthesized by solid state reaction technique have been investigated at various temperatures by impedance spectroscopy.BMT and BZT possess cubic structure with lattice parameter a = 0.708 and 0.451 nm,respectively.The resonance peaks due to dielectric relaxation processes are observed in the loss tangent of these oxides.The relaxation in the samples is polydispersive in nature.The temperature dependence of dc conductivity,the most probable relaxation frequency(ω_m) obtained from tanδ vs logw plots and ω_m obtained from imaginary parts of the complex electrical modulus vs logw plots follow the Arrhenius behavior.According to these Arrhenius plots the activation energies of BMT and BZT are about 0.54 and 0.40 eV,respectively.Thus the results indicate that samples are semiconducting in nature.The frequency-dependent electrical data are analyzed in the framework of conductivity and electric modulus formalisms.Both these formalisms show qualitative similarities in relaxation time.Our study points that for complex perovskite oxides with general formula A(B'B")O_3,the dielectric properties significantly depend on the atomic radii of both A and B type cations.BMT and BZT exhibit enhancement in dielectric property compared to their niobate counterparts.They may find several technological applications such as in capacitors,resonators and filters owing to their high dielectric constant and low loss tangent.     

溶液法CH3NH3PbCl3单晶的生长与性能研究

分别采用蒸发结晶法和逆温结晶法生长尺寸约为4 mm×3 mm×3 mm的CH₃NH₃PbCl₃单晶。对两种方法生长的单晶粉体的XRD分析结果显示, 单晶具有立方晶系结构, 其晶格常数分别为0.56833、0.56891 nm。实验测量了CH₃NH₃PbCl₃单晶的红外光谱(FT-IR)和拉曼光谱, 并对谱峰进行了指认; 使用UV-VIS-NIR分光光度计、荧光光度计对CH₃NH₃PbCl₃单晶的光学性能进行了测试。结果表明: CH₃NH₃PbCl₃晶体的吸收边约为423 nm, 光致发光峰为433 nm, 带隙值为2.97 eV, 与CH₃NH₃PbCl₃薄膜的光学特性相比, CH₃NH₃PbCl₃单晶更具潜在的应用前景。最后, 结合第一性原理研究了CH₃NH₃PbCl₃晶体的能带结构, 计算得出带隙值2.428 eV, 与实验值吻合较好。