【作者】 祝琳华；

【导师】 张昭；

【作者基本信息】 四川大学 ， 化学工程， 2000， 硕士

【摘要】 NZP族陶瓷材料因其低热膨胀特性和热膨胀系数的可裁剪性而受到广泛的研究，使它成为在催化剂载体、汽车发动机元件、小型换热器以及在航天技术上作为涂层方面都有应用潜力的一种新材料。 对此类材料，通过组成的调整，可以得到接近零膨胀的组成，若能同时使晶格的热膨胀异向性最小，则可减少冷却过程中微裂纹的产生，提高材料的耐热冲击性。为此，经过理论分析，设计了一种新型二元固溶体型NZP族磷酸盐陶瓷—Ca_1-xBa_xZr₄P_bO₂₄（0≤x≤1）系列，简称CBZP。本研究的目的是通过组成的调整，得到一种具有良好力学性能的近零膨胀的新材料，并使其有较小的热膨胀异向性。 首先用共沉淀法合成了化学组成准确均匀的CBZP系列粉体，进行了共沉淀法反应机理和粉体分散性的研究。然后进一步将粉料添加ZnO或MgO为烧结助剂，在80Mpa干压成型，于1100℃-1300℃烧结，研究了烧结条件对致密化进程以及对材料抗压强度、显微结构发展和热膨胀特性的影响。 实验结果表明： （1） 共沉淀反应的加料顺序对控制产物化学组成及其均匀性非常重要，应采取逆加法并保持沉淀剂过量。 （2） 调节液相反应过程的pH为9，可以在颗粒表面形成稳定的双电层，产生的静电排斥力能够避免团聚现象；用低分子有机溶剂处理共沉淀物，可以消除液固分离及干燥过程的团聚，制得平均粒径1.6-2.3μm，粒度分布窄的CBZP系列粉体。 四川大学硕士学位论文摘要 （3）X射线衍射结果显示共沉淀反应的产物是无定形的，需经过 900 ’C 锻烧后，才能转化为单相的结晶良好的CBZP系列化合物。 （4）添加Zno和Mgo可以有效促进CBZP的烧结，合适的烧结温度为1100 C和 1300’C，合适的添加剂用量是 3wt％Zno和 4－swt％Mgo。该系列 陶瓷的抗压强度最高可达287．92Mpa。 （5）烧结时间以120min为宜，过长的烧结时间会导致晶粒过度生长， 进而影响材料的显微结构、强度和耐热冲击性。 u)以吨0为添加剂时，会使整个 CBZP系列陶瓷的热膨胀系数升高， 原因是在烧结过程中有第＝相产生；而以h 为烧结助剂，则得到 的CBZP系列陶瓷均为低热膨胀材料，20－1000C的平均线膨胀系数 低于2．0X10“／℃。 （7）通过调节 Ca／Ba的配比，可以得到不同烧结条件下的近零膨胀组 成，但这些组成的材料其热膨胀异向性仍然较大，耐热冲击性不理 想。 （8）要提高 CBIP系列的热震稳定性，通过调整组成的方式很难实现， 从添加抑制剂抑制晶粒生长入手，可望使晶粒粒径保持在临界粒径 以下，以避兔微裂纹的产生。更多还原

【Abstract】 The [NZP] family of materials has attracted worldwide attention for its low and tailorable thermal expansion coefficient and other useful properties. They now have emerged as potential candidates in many applications, including catalyst supports, automobile engine components, heat exchangers, and coating materials for space technology.It is possible to develop the suitable compositions in the [NZP] family with the near-zero bulk thermal expansion and the minimal thermal expansion anisotropy of crystal, thereby minimizing the production of microcracks during cooling. For these purposes, a new type of [NZP] materials-Ca1-xBaxZr4P6O24(0<x<1,abbreviation CBZP) ,which is a crystalline solid-solution series, was designed and prepared successfully. The purposes of this work were to study the Ca1-xBaxZr4P6O24 system and to find a composition possessing the near-zero thermal expansion coefficient (TEC) and the low thermal expansion anisotropy(TEA).The ultrafine powder with some advantages, including precise chemical composition and homogeneity, narrow size distribution, and no agglomeration, was synthesized by coprecipitation method at first. The conditions of synthesizingreaction, the mechanism of coprecipitation, and the method of dispersion were investigated. After this, the powders with the ZnO or MgO as a sintering additive were compacted by cold pressing under 80Mpa for 15min. The compacts were sintered at the temperature range of 1100℃-1300℃. The effects of sintering conditions on the change of apparent density, compressive strength and thermal expansion were studied.The experimental results indicate:(1) The feeding method is very important to precisely control the chemical composition of precipitate and its homogeneity in the synthesis of powder.(2) By adjusting the pH value of the reaction system is 9, the agglomeration of particles can be decreased. These copreciptaters were dispersed by a organic solvent of small molecular quantity in order to avoid the agglomeration during the separation stage of solid and liquid. The powders with the average size range of 1.6-2.3 u m are prepared.(3) The coprecipitating method produces amporphous precursor of the needed powders. After calcination at 900℃ for 2h, the single phase materials with [NZP] structure-type were formed.(4) The sintering process can be promoted by addition of MgO or ZnO, the proper sintering temperature is 1300℃ and 1100℃ respectively, the amount of additives is 4wt%MgO or 3wt%ZnO.(5) The sintering time should be 90min-120min. A too long time will result in the excess growth of grain, and then influence on the microstructure, strength, and thermal expansion property of the CBZP ceramics.(6) When MgO is used as additive, the thermal expansion coefficients of this series will increase because of forming the second phase. The CBZP series are the low thermal expansion materials when sintering with addition of ZnO, their line thermal expansion coefficients(TEC) are smaller than 2.0 ×10-6/℃.(7) By adjusting the ratio of Ca and Ba, the composition with the near-zero TEC can be attained. But these compositions still possess significant thermal expansion anisotropy, and their property of thermal shock resistance is notperfect. (8) In order to prevent the formation of microcracks, the grain growth beyond thetransition grain size must be suppressed with an additive during the sinteringperiod.更多还原