AlN陶瓷的介电性能

着重探讨了ＡｌＮ陶瓷的极化机理,应用基本的电介质物理理论,结合ＡｌＮ陶瓷的组成特点,研究了ＡｌＮ陶瓷介电性能随测量温度、测量频率变化而变化的温度特性和频率特性,结果表明：ＡｌＮ陶瓷的主要极化机理及空间电荷极化;经典的极化理论适用于ＡｌＮ陶瓷;ＡｌＮ陶瓷因介电性能较好,导热率较高崦有望成为比Ａｌ２Ｏ３陶瘊性能更加优良的基板材料。     

AlN—BN复合陶瓷的介电性能

以ＡｌＮ－ＢＮ复合陶瓷为研究对象，着重探讨了ＡｌＮ－ＢＮ复合陶瓷的极化机理，应用基本的介电介质物理理论，结合ＡｌＮ－ＢＮ复合陶瓷组成和结构特点，研究了ＡｌＮ－ＢＮ复合陶瓷介电性能（介电常数，介电损耗角正切值）随测量温度，测量频率变化而发生变化的温度特性和频率特性。     

影响AlN陶瓷热导率的本征氧缺陷

对ＡｌＮ晶格中的铝空位，延展缺陷等进行了研究，研究表明，在固溶氧浓度较低（〈０．７５，原子百分数）的高热导率ＡｌＮ试样中，铝空位的存在会造成的ＡｌＮ晶胞局域收缩的现象，并观察到了铝空位的存在；固溶氧浓度较高（〉０．７５％）时，孤立的缺陷产生团聚，形成铝氧八面体；在氧浓度很高（〉０．７５％）的低热导率试样中观察到了反相区，多型体等延展缺陷。     

制备工艺对BNBT陶瓷介电性能的影响

BNT(BaO-Nd2O3-TiO2)系统陶瓷是一种介电性能优良的陶瓷材料.在BNT中添加一定量的Bi2O3,可以得到介电性能更优的BNBT(BaO-Nd2O3-Bi2O3 -TiO2)陶瓷.该文分别研究了球磨时间、烧结温度和保温时间对BNBT陶瓷介电性能的影响.结果表明:当球磨时间为10 h、烧结温度为1160 ℃、保温时间为9 h时,BNBT陶瓷的介电性能为:介电常数ε=99.8281,介电损耗tanδ=2.65×10-4,介电常数温度系数αε≤±30 ppm/℃.     

锰掺杂对压电陶瓷介电性能的影响

采用传统的电子陶瓷工艺制备了高性能四元系压电陶瓷（PZN-PMS-PZT）。考察了不同剂量锰掺杂对压电陶瓷的室温介电常数（εTr)，介电常数温度谱以及居里温度（Tc)的影响。实验结果表明：随着Mn含量的增加，压电陶瓷的室温介电常数εTr减小；由于内偏置场的影响，居里温度Tc随锰含量的增加而增加。     

球磨工艺对钛酸钡陶瓷介电性能的影响

研究了固相法合成BaTjO3粉体时,在滚筒磨和搅拌磨中球磨BaCO3和TiO2粉体过程中,浆料的粒度、凝聚程度与球磨时间、筒容积的关系,分析了粉体均匀性对BaTiO3、陶瓷介电性能的影响.研究结果表明:TiO2粉体在球磨过程中,粒度大小没有显著变化,导致粉体凝聚的主要原因是BaCO3粉体;应先球磨BaCO3粉体10小时后再加入TjO2粉体继续球磨2小时所得的物料颗粒要比钡钛一起球磨所得的颗粒均匀,合成BaTiO3均匀性好;采用搅拌磨时,制备的BaTiO3陶瓷介电性能优于滚筒磨.     

稀土氧化物和CaF_2对AlN陶瓷烧结性能及热导率的影响

以4%Y_2O_3、3%Y_2O_3–1%CeO_2、3%Y_2O_3–1%CaF_2和3%Y_2O_3–0.5%CeO_2–0.5%CaF_2(质量分数)为助烧剂,于1 860℃制备得到了AlN陶瓷。研究了不同助烧剂体系对AlN陶瓷物相组成、显微结构、烧结性能及热导率的影响。结果表明:所得样品的物相组成中均含有AlN与钇铝酸盐相,在含有CeO_2助烧剂的样品中还检测到少量的铈铝氧化物相;样品晶粒尺寸分布均在3~8μm之间。与添加一元及二元助烧剂相比,三元助烧剂的引入能更有效促进AlN陶瓷烧结致密化,强化其导热性能。添加三元助烧剂制备得到AlN陶瓷的体积密度为3.29 g/cm~3,气孔率为0.58%,热导率为184.8 W/(m·K)。     

无助剂AlN陶瓷的高压烧结制备及热导率

以碳热还原法生产的AlN粉体为原料,用国产六面顶压机,在5.0GPa,1 300～1 800℃,在无烧结助剂的情况下,高压烧结制备了AlN陶瓷.用X射线衍射、扫描电镜对高压烧结AlN陶瓷微观结构进行了表征.结果表明:经1 300℃烧结50 min制备的AlN陶瓷的相对密度达94.8%.经1 400℃烧结50min制备的AlN陶瓷的断裂模式为穿晶断裂.经1 800℃烧结50min制备的AlN陶瓷由单相多晶等轴晶粒组成,该样品的热导率达115.0W/(m·K).高压烧结制备的AlN陶瓷的晶格常数比AlN粉体的略有减小.高压烧结温度的提高和烧结时间的延长有助于提高AlN陶瓷的热导率.     

热处理工艺对石英纤维复合材料介电性能的影响

通过热处理温度、热处理气氛和防潮涂层对石英纤维增强复合材料介电性能影响的研究,结果表明:在800℃或500℃通氧条件下进行热处理,才可以较彻底的排除石英纤维增强复合材料中残余的游离碳。经高温处理后介电性能较好,进行防潮处理后能达到更好的效果,更好的应用于航天领域。     

SrCO3掺杂对BMT陶瓷结构及介电性能的影响

采用固相烧结法制备SrCO3掺杂Ba（Mg1/3Ta2/3）O3（BMT）微波介质陶瓷,研究SrCO3质量（下同）掺量w（SrCO3）=2%～8%对BMT微波介质陶瓷结构和介电性能的影响。结果表明：添加适量SrCO3可以促进烧结并在一定程度上提高BMT陶瓷体系的B位离子1：2有序度;当w（SrCO3）=6%时,陶瓷致密...     

关于氮化铝陶瓷导热性的讨论

本从声子机理出发，探讨了影响氮化铝陶瓷导热性的主要因素；提出了提高导热率的努力方向，即结构上努力减少晶格缺陷（主要是杂质固溶）和晶界缺陷（包括第二相析出，晶界玻璃相，气孔），并使相的分布尽量合理；指出了提高A1N陶瓷导热率的可能途径，即严格控制A1N粉末质量，选择合理的烧结助剂，采用还原气氛烧成等。     

无压烧结高导热AlN陶瓷的研究进展

AlN以其优异的高热导率、与Si相匹配的热膨胀系数及其它优良的物理化学性能受到了国内外学术界的广泛关注,被誉为新一代高密度封装的首选基板材料.本文详细综述了AlN陶瓷的导热机理和无压烧结工艺等方面的研究进展,并介绍了烧结助剂的选取原则和AlN陶瓷热导率与温度的关系,以及展望了AlN基板的发展趋势和前景.     

浸渍及热处理对常压烧结AlN/h-BN复相陶瓷微观结构及性能的影响

采用常压烧结方法在1 700℃保温2 h制备出AlN/20%(体积分数)h-BN复相陶瓷,对烧结后的样品分别采用A10铝溶胶和硅溶胶/酚醛树脂进行浸渍处理,随后在1 450℃氮气气氛下热处理2 h。对比研究了浸渍及热处理前后复相陶瓷的致密度、抗弯强度、Vickers硬度、微观结构和物相组成,并分析了复相陶瓷的强化机理。结果表明:A10铝溶胶浸渍处理后样品的抗弯强度和Vickers硬度略有提高;经过硅溶胶/酚醛树脂处理的样品抗弯强度和Vickers硬度大幅提高,抗弯强度和Vickers硬度分别从81.5MPa和1.99 GPa提高到130.1 MPa和3.58GPa;硅溶胶/酚醛树脂处理后的样品在孔隙界面处生成的碳化硅及氮氧化铝是样品抗弯强度和Vickers硬度显著提高的主要原因。     

高导热AlN陶瓷烧结助剂的研究现状

在分析了陶瓷的导热机理的基础上，着重评述介绍了几种复合烧结助剂在制备高导热AIN陶瓷过程中的作用机理，对比了AIN陶瓷样品的热导率值。分析了晶界相的形成和AIN晶格的净化，从而减少了氧缺陷，提高了陶瓷材料的致密度和热导率。     

Dielectric and Electrical Conductivity Properties of PMS–PZT Ceramics

The dielectric and electrical conductivity properties of x Pb(Mn_1/3Sb_2/3)O₃–(1− x )Pb(Zr_0.52Ti_0.48)O₃ (PMS–PZT) ceramics were studied. X-ray diffraction indicated that all samples exhibit a single-phase perovskite structure. Dielectric study revealed that the dielectric relaxor behavior was induced by co-doping Mn²⁺ and Sb⁵⁺ into Pb(Zr_0.52Ti_0.48)O₃ ceramics. Electrical conductivity measurements showed that the concentration of carriers are increased with the increase in PMS contents. After annealing in an oxygen atmosphere for 30 h, the direct current conductivity of PMSZ15 was much lower than that of the as-sintered sample. The reason why this phenomenon occurs may be the reduction of oxygen-vacancy concentration.     

Enhancement of Densification and Thermal Conductivity in AlN Ceramics by Addition of Nano-Sized Particles

The effect of addition of nano-sized particles on densification and thermal conductivity of AlN ceramics was investigated. The commercially available AlN powder (∼0.9 μm) was mixed with 1.89 mass% nano-sized AlN particles (<0.1 μm), 3.53 mass% Y₂O₃, and 2.0 mass% CaO as sintering aid. The mixture was fired at 1500° and 1600°C in a tungsten resistance furnace under flowing N₂ atmosphere. The results showed that a fully densified specimen was obtained at the lower temperature of 1600°C by addition of nano-sized particles. The thermal conductivity of the resulting product was 133 W/m°C. The value is much higher than the 52 W/m°C for the sample prepared without adding the nano-sized AlN powder. This study indicates a strong potential for the use of nano-sized particles as additives in the densification of AlN ceramics.     

Effect of Grain Thermal Expansion Mismatch on Thermal Conductivity of Porous Ceramics

Many ceramics contain microcracks, which are often situated between sintered grains. These microcracks constitute thermal resistances, which may affect heat transfer through the material and its effective thermophysical properties. The thicknesses and the contact areas of the microcracks change with temperature as a result of the thermal expansion mismatch between the grains on opposite sides of the microcracks. This physical mechanism affects changes of the material's thermal conductivity, k , with temperature. The above mechanism usually plays a minor role at atmospheric pressure, where heat may flow via the gas filling the cracks. Hence, the temperature-induced changes of the crack geometry have little effect on heat transfer. However, at low gas pressures, where the heat flow between the grains occurs mainly via the contact areas, the grains' thermal expansion mismatch causes unusual temperature behavior of the material's thermal conductivity observed for several industrial refractories. In this paper, the influence of the above physical mechanism is discussed relative to other heat transfer mechanisms described in the literature. A simple physical model of the thermal expansion of grains bonded by an agent, having different thermal expansion coefficients, is developed. This model allows calculation of the contact area and the average microcrack opening between the grains as functions of the temperature, the characteristic grains sizes and their thermal expansion coefficients, and the permanent crack area. These parameters are evaluated and used to calculate the effective thermal conductivity of ceramic materials containing microcracks that appear as a result of thermal contraction of grains. The calculated thermal conductivity satisfactorily correlates with the experimental data collected for several chrome-magnesite refractories over a wide range of temperatures and gas pressures.     

多孔陶瓷热导率的影响因素及其有效热导率的数值计算方法

多孔陶瓷因具有孔隙率高、体积密度小、比表面积大等独特的表面物理特性而被广泛应用于保温材料、炉膛材料、热障涂层材料、高温烟气过滤材料等,研究多孔陶瓷导热机制并给出其有效热导率的计算方法既是重点又是难点。本文总结了国内外研究的多孔陶瓷热导率的影响因素,概述了多孔陶瓷有效热导率的计算方法,并重点分析了不同显微结构的不同计算方法。针对不同的应用领域对材料热导率的不同要求,提出通过控制显微结构控制热导率是今后多孔陶瓷热导率研究得发展趋势。     

Thermal Conductivity: XIII, Effect of Microstructure on Conductivity of Single-Phase Ceramics

The thermal conductivity of Al₂O₃, MgO, TiO₂, and CaF₂ single crystals and single-phase poly-crystalline aggregates of controlled microstructure was measured between 0° and 1000°C. The conductivity of pure single-phase dense polycrystalline aggregates agrees with that of the corresponding single crystals at temperatures below the onset of radiant-heat transfer. Small amounts of impurities and the pore geometry may considerably affect the conductivity of aggregates.     

NZP陶瓷组成与显微结构对其导热系数的影响

研究了化学组成及显微结构对Ｍ１位ＮＺＰ陶瓷导热系数的影响，随着Ｍ１位离子种类数的增加，ＮＺＰ陶瓷的导热和降低。ＣＭＳ的导热系数随着气孔率的增加而降低。