AlN—Mo复合陶瓷的介电性能研究

以AlN和Mo为原料,采用放电等离子体烧结技术（SPS）制备了AlN-Mo复合衰减材料。运用XRD、金相显微镜、介电频谱等测试手段对复合衰减陶瓷的相组成、显微组织、复介电常数和电阻率进行表征,研究了提高渗流阈值的方法和影响复合陶瓷介电性能的因素。结果表明,添加体积分数1％的Ni可以使复合陶瓷的渗流阈值达到23％（体积分数）;复合陶瓷的介电常数、损耗随Mo含量的增加而增大,同一组分复合陶瓷的介电性能可通过改变导电相的分布状态实现可控调节,并从复合陶瓷的显微组织、电阻率及介电理论上对上述结果予以解释。     

AIN-Mo复合陶瓷的介电性能研究

以AlN和Mo为原料,采用放电等离子体烧结技术(SPS)制备了AlN-Mo复合衰减材料.运用XRD、金相显微镜、介电频谱等测试手段对复合衰减陶瓷的相组成、显微组织、复介电常数和电阻率进行表征,研究了提高渗流阁值的方法和影响复合陶瓷介电性能的因素.结果表明,添加体积分数1%的Ni可以使复合陶瓷的渗流阈值达到23%(体积分数);复合陶瓷的介电常数、损耗随Mo含量的增加而增大,同一组分复合陶瓷的介电性能可通过改变导电相的分布状态实现可控调节,并从复合陶瓷的显微组织、电阻率及介电理论上对上述结果予以解释.     

石墨/陶瓷复合导电材料的制备及性能

为了研究片状石墨的掺杂量和取向排列对石墨/陶瓷复合材料结构和性能的影响,以长石、透辉石、石英等作为陶瓷基体并掺杂石墨,经湿混、干燥、干压成型、快速烧结等工艺制备了石墨/陶瓷复合导电材料。用精密伏安表精确测定了材料垂直和平行于成型压力方向的电阻,用XRD、SEM分析了试样的物相组成和断面形貌。实验结果表明：在烧结过程中石墨与陶瓷基体不发生化学反应,未发现有新相生成;片状石墨在复合材料中具有定向排列的特征,即片状石墨的c轴平行于成型压力方向;石墨/陶瓷复合导电材料的电阻率具有明显的各向异性;随着石墨掺量的增加,复合导电材料的电阻率随石墨掺量的增加而急剧减小;但是,当石墨掺量超过15 wt%时,复合材料电阻率的变化趋于平缓。     

烧结温度对1BaO-10NiO-NiFe2O4复合陶瓷导电性能的影响

利用冷压-烧结技术制备了1BaO-10NiO-NiFe2O4复合陶瓷,研究了1BaO-10Ni-NiFe2O4复合陶瓷物相组成和显微结构以及烧结温度对相对密度和导电率的影响.结果表明,1BaO-10NiO-NiFe2O4复合陶瓷烧结样品中主要含有NiO和NiFe2O4两种,BaO与10NiO-NiFe2O4陶瓷组分反应并形成瞬时液相BaFe2O4和Ba2Fe2O5,且Ba2 离子固溶到基体中,促进致密化烧结;随着烧结温度的升高,样品的相对密度无太大变化,均在97%以上.但样品导电率逐渐增大,当烧结温度为1673K时,1BaO-10NiO-NiFe2O4复合陶瓷达到最大电导率21.16S/cm,是烧结温度为1473K时电导率10.17S/cm的2.08倍.     

泡沫碳化硅陶瓷的导电性能

采用高分子热解和反应烧结方法制备出泡沫碳化硅陶瓷，研究了泡沫碳化硅陶瓷的体积分数变化和钛的掺杂对泡沫碳化硅陶瓷骨架导电性能的影响．结果表明：随着泡沫碳化硅陶瓷的体积分数提高，泡沫碳化硅陶瓷的电阻率降低，这是泡沫碳化硅陶瓷筋中部碳化硅的面积增加所引起的；掺杂的钛转变成TiSi2导电相改善了泡沫碳化硅陶瓷的导电性能．TiSi2呈现离散和团聚两种形态分布，以不规则的形状位于碳化硅晶界之间，在碳化硅中作为施主杂质．泡沫碳化硅陶瓷表现出的正或负温度系数取决与掺杂的钛量的多少．     

二相粒子复合陶瓷内应力的有限元分析及其增韧机理

本文建立了二相粒子复合陶瓷的有限元模型,分析了模型内部的应力分布状况,并总结了二相粒子体积比V_p变化时的应力分布的变化规律,讨论了颗粒热膨胀系数α_p与基体热膨胀系数α_m的匹配关系变化时,复合陶瓷内的应力分布状况,在此基础上,对二相粒子复合陶瓷的增韧机理做了探讨．     

TiN／O′-sialon复相陶瓷的常温导电性能研究

对原位TiN／O′-sialon纳米复相陶瓷（NTS）和采用“二步法”制备的TiN／O′-sialon复相陶瓷（TS）的常温导电性能进行了对比研究，并对材料TS进行了放电加工。研究结果表明，初始原料中20％（质量分数）和25％（质量分数）左右的TiO2加入量是决定材料NTS和TS中TiN能否形成导电网络的最低TiO2加入量，该导电临界值同基相O′-sialon与导电相TiN的颗粒尺寸比有关，此时相应材料的电阻率为1.6×10^-2和1.8×10^-2Ω·cm，满足放电加工的需要。烧结温度升高，两种材料的电阻率略有降低。随放电加工速度的增加，材料TS加工表面粗糙度明显增加。     

红外辐射陶瓷的导电化

本文根据单相的个体特性选择堇青石和ＴｉＣ两相复合制备出了导电型的红外辐射陶瓷材料。对体系电性能进行研究发现，体系电导率值随ＴｉＣ含量的变化呈非线性变化，ＴｉＣ含量在９％ｗｔ以下时，体系电导率在１０￣（－１）Ｓ／ｃｍ以下，而从９％ｗｔ开始，随着ＴｉＣ含量的增加，体系的电导率迅速增加，幅度达几个数量级之多。通过电子探针分析我们认为，材料的导电是由ＴｉＣ相形成的导电通路所提供的，其导通过程是一种逾渗过程。根据渗流理论对体系的导电特性进行分析，可以很好地说明电导率发生的突跃现象，由此得到了本复合体系的导电模型。利用这种模型可以从理论上预测某一给定ＴｉＣ含量时系统电导率值的大小，使体系的电导率可控可调。     

溶胶凝胶法0.5PbTiO_3/0.5NiFe_2O_4两相复合陶瓷的制备

通过sol-gel原位复合方法制备了两相比例为1∶1的铁电PbTiO3(PTO)/铁磁NiFe2O4(NFO)复合粉末以及陶瓷材料,利用XRD对复合体系的物相结构进行了研究,利用SEM对复相粉体及陶瓷的形貌进行了观察,采用阻抗分析仪(Agilent 4294A)测试了复合陶瓷的介电性能以及磁性能。结果表明,在550℃热处理温度下制备的原料粉末形成了PbO相及少量PTO和NFO相,650~700℃下形成了PTO和NFO两相,750℃以上则形成PTO、NFO和PbFe12O19(PFO)三相,热处理时间则对粉末形成影响不大。不同的原料粉末在1150℃下烧结后均形成了PTO和NFO两相均匀分布的复相陶瓷。控制在粉末先驱体中预先形成需要的两相,并控制相对较高的PTO相含量,可得到介电性能相对较好的陶瓷。控制相对较低的原料粉末制备温度,抑制PTO相在原料粉末中的形成,有利于得到较好磁性能的复相陶瓷,也即控制原料中的晶相形成,可以调节这种铁电铁磁两相复合陶瓷的性能。     

炭黑填充BST/PVDF复合薄膜的制备与介电性研究

以聚偏氟乙烯(PVDF)为聚合物基体,钛酸锶钡(BST)为陶瓷相,成本低廉的导电炭黑(CB)为导电相。采用流延加低温热处理的方法制备了一系列高介电柔性复合薄膜。利用阻抗分析仪对薄膜的介电性进行了测试,结果表明,炭黑的填充能有效提高复合材料的介电性能,当体积分数接近渗流阈值6.2%时,CB/BST/PVDF复合材料的介电常数、介质损耗、电导率急剧增加。结合经典渗流理论研究了材料在渗流转变时介电性变化特征及微观机理,利用微电容模型、界面极化理论对这一现象进行解释。     

PZT95/5铁电陶瓷晶粒度对冲击波作用下击穿电压的影响

在气炮加载条件下,分别测试了两种晶粒度的PZT95/5铁电陶瓷样品在冲击波作用下的击穿电压,并采用Weibull分布分析了所获得数据.结果表明,PZT95/5铁电陶瓷在冲击波作用下的击穿电压分布可以用二参数Weibull分布模型描述,从击穿电压密度分布函数和失效率函数来看,晶粒度为2.5μm的PZT95/5样品的击穿电压分布优于晶粒度为7μm的PZT95/5样品击穿电压分布.     

用碳热还原法制备多孔氮化硅陶瓷

以廉价的二氧化硅和活性碳为起始粉料, 用碳热还原法制备了高气孔率, 孔结构均匀的多孔氮化硅陶瓷.考察了二氧化硅粉末粒径对多孔氮化硅陶瓷微观组织和力学性能的影响. 借助X射线衍射(XRD), 扫描电子显微(SEM)和三点弯曲法对多孔氮化硅陶瓷的微观组织和力学性能进行了研究. XRD分析表明在烧结后的试样中, 除了微量的α-Si₃N₄相和晶界结晶相Y₈Si₄N₄O₁₄外, 其余的都是β-Si₃N₄相; SEM分析显示多孔氮化硅陶瓷是由柱状β-Si₃N₄晶粒和均匀的孔组成, 通过改变二氧化硅的粒径, 制备了不同孔隙率, 力学性能优异的多孔氮化硅陶瓷.     

PMN和PZN基复相陶瓷的制备及其介电温度稳定性的研究

以PZN基和PMN基粉本为起始组元，采用两相混合烧结法成功的制备了两相共存的复相陶瓷，介电性能测试表明，复相陶瓷的室温介电常数为5377（1kHz)，其介质电温谱在－15℃－＋90℃温度范围内相当平坦，介电温度稳定性大幅提高，据键价理讨论了复相陶瓷的设计和组成控制，并初步探讨了复相陶瓷提高介电温度稳定性的机制。     

铁电体中相变临界尺寸的研究现状

从铁电薄膜和铁电颗粒两大方面回顾了处理尺寸效应的理论研究方法(包括宏观的热力学唯像理论、微观的横场Ising模型和第一性原理计算)和铁电相变临界尺寸的理论预测. 总结了从50年代以来实验中观测到的各种铁电材料的临界尺寸, 简单介绍了铁电纳米陶瓷的一些尺寸效应, 并叙述了近几年才开始报道的铁电纳米线中的铁电相变. 最后指出了目前研究现状中存在的一些问题.     

SiC对烧结堇青石材料性能的影响

以高岭土、滑石和工业氧化铝为矿物原料烧结制备了堇青石陶瓷,通过X射线衍射仪、扫描电镜、万能材料试验机和热膨胀仪等测试手段,研究了添加不同含量SiC对烧结堇青石陶瓷相组成和性能的影响,并比较了添加不同颗粒尺寸的SiC对烧结陶瓷强度的影响。试验表明,随着SiC添加量的增加,堇青石陶瓷的弯曲强度、致密度和热膨胀系数逐渐增大。当添加SiC的质量分数为5%、粒径为5.0μm时,烧结堇青石陶瓷的强度较未添加时增大了41.9%,而热膨胀系数的增幅不大。     

Effect of grain size on elastic modulus and hardness of nanocrystalline ZrO2-3 wt% Y2O3 ceramic

Dense nanocrystalline ZrO₂-3 wt% Y₂O₃ ceramics with grain sizes ranging between 23 to 130 nm were tested by ultrasonic pulse echo and Vickers hardness. The elastic modulus and hardness results were corrected for the residual porosity and the phase content. The corrected elastic moduli exhibited continuous decrease with decrease in the grain size. In contrast, no correlation was found between the corrected hardness and grain size. The percolative composite model was used to describe the changes in the elastic moduli in terms of percolation of the elastic wave through the intercrystalline phase at the percolation threshold. The absence of correlation with the hardness results was explained due to the other energy absorbing mechanisms such as microcracking beneath the indenter.     

A Method for the Strength Prediction of Porous Ceramics

We present a fracture model for ceramic materials, according to which ceramics is regarded as a porous inhomogeneous material with a composite structure. The role of pores as stress raisers is taken into account, and their size, geometric shape, and orientation with respect to the direction of the maximum tensile stresses are shown to be important factors. The stress on the pore surface at the places of highest stress concentration, which is equal to the ultimate strength of the ceramics bonding phase, was taken as limiting (failure) stress. Probable pore sizes and shapes have been considered in terms of filler crystal size and volume content. A fracture model and a method for the mathematical determination of the strength of ceramics have been proposed, the method taking into account the strength of the constituents, their volume content, and the shape and size of possible internal defects.     

Strength and fatigue properties of three-step sintered dense nanocrystal hydroxyapatite bioceramics

Dense hydroxyapatite (HA) ceramic is a promising material for hard tissue repair due to its unique physical properties and biologic properties. However, the brittleness and low compressive strength of traditional HA ceramics limited their applications, because previous sintering methods produced HA ceramics with crystal sizes greater than nanometer range. In this study, nano-sized HA powder was employed to fabricate dense nanocrystal HA ceramic by high pressure molding, and followed by a three-step sintering process. The phase composition, microstructure, crystal dimension and crystal shape of the sintered ceramic were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Mechanical properties of the HA ceramic were tested, and cytocompatibility was evaluated. The phase of the sintered ceramic was pure HA, and the crystal size was about 200 nm. The compressive strength and elastic modulus of the HA ceramic were comparable to human cortical bone, especially the good fatigue strength overcame brittleness of traditional sintered HA ceramics. Cell attachment experiment also demonstrated that the ceramics had a good cytocompatibility.     

Development and Characterization of Low-Emitting Ceramics

The infrared-optical properties of ceramics are correlated with the complex index of refraction of the material and the structure of the ceramic. By changing these parameters, the infrared-optical properties can be changed over a relatively wide range. The correlation of the structural properties (like the porosity or the pore sizes) and the material properties (such as the complex index of refraction on the one hand and the infrared-optical properties such as emittance on the other) are described by a solution of the equation of radiative transfer and the Mie-theory. Within this work, low-emitting ceramics, which have significantly lower emittances than conventional ceramics, were prepared by optimizing their composition and structure. The spectral emittance of these ceramics was measured, and a total emittance dependent on temperature was calculated from the spectral emittance. As a result, one obtains ceramics which have a total emittance of 0.2 at a temperature of 1,100 K. In comparison to conventional ceramics with a typical total emittance of 0.8 at 1,100 K, the use of such low-e ceramics leads to a reduction in heat transfer of about 70% via thermal radiation. The results of our calculations were compared with experimental data to validate the theory. Paper presented at the Seventh European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic.     

Piezoelectricity and microstructures of modified lead titanate ceramics

Modified lead titanate ceramics with the composition Pb_0.70 Ca_0.30 Ti_0.94 (Co_1/2W_1/2)_0.06 O₃ with 1 mol% MnO were prepared by the mixed oxide route. By varying the sintering temperature, ceramics with average grain sizes between 2.8 and 5m were obtained. An increase in grain size resulted in an increased electromechanical anisotropy and a decreased dielectric constant. Transmission electron microscopy was used to examine the ferroelectric domain boundaries and intergranular phases. Indications are that during poling favourably oriented domains approximately doubled in size by 90 ° type domain wall switching. Evidence was found for the existence of a vitreous intergranular phase at multiple grain junctions. EDS microanalysis indicated that the amorphous grain boundary phase had a lower lead content than the bulk material.