陶瓷分散剂反应失效原位凝固注模成型的机理研究

Colloidal processing of ceramics is the key procedure for high performance complex-shape ceramic parts, and the development of colloidal processing is helpful to ceramic preparation science. There are a lot of problems existed in ceramic colloidal processing, such as internal stress in green bodies and low reliability of ceramics. To reveal two basic scientific issues, namely dispersion stabilization mechanism and reaction failure mechanism of ceramic dispersants, this project will study in-situ coagulation casting of ceramic suspensions via dispersant reaction failure method, which is controlled by the reaction between dispersants and coagulating agents. First of all, the effect of dispersant on the dispersion stability of ceramic suspensions is investigated and the dispersion stabilization mechanism is revealed. Secondly, the influence of the ceramic powder characteristics, dispersant, pH value and solid loading on the colloidal behaviors and rheological properties of ceramic suspensions is studied, and rheological model of ceramic suspensions is established. Optimal conditions for preparation of high solid loading and low viscosity ceramic suspensions are obtained. Again, the universal method for in-situ coagulation casting of ceramic suspensions via dispersant reaction failure is developed, and the mechanism of liquid-solid transformation process is studied to obtain complex-shape green bodies. Finally, complex-shape ceramic parts with high performance and high reliability were prepared by the combination of in-situ coagulation casting process and sintering process. This project will further enrich the research and development of advanced ceramic colloidal processing theory and method, and provide a new way for the preparation of high performance and high reliability complex-shaped ceramic parts.

陶瓷胶态成型是制备高性能复杂形状陶瓷部件的关键环节，对其深入研究有助于陶瓷制备科学的发展。针对陶瓷胶态成型存在的坯体内应力、陶瓷可靠性差等问题，围绕陶瓷分散剂的分散稳定机制及反应失效机制两个关键科学问题，本项目将系统研究陶瓷分散剂反应失效原位凝固注模成型的机理。首先，研究分散剂对陶瓷悬浮体分散稳定的影响规律并揭示其分散稳定机制。其次，探讨陶瓷粉体特性、分散剂、pH值及固相含量对陶瓷悬浮体胶体行为及流变特性的影响规律，建立陶瓷悬浮体流变方程，优化高固相含量、低粘度陶瓷悬浮体的制备条件。最后，发展具有普适性的分散剂反应失效原位凝固陶瓷悬浮体的新方法，揭示陶瓷悬浮体液-固转变过程的变化规律并阐明分散剂反应失效机制，实现陶瓷坯体的近净尺寸成型，结合烧结工艺制备高性能、高可靠性复杂形状陶瓷部件。本项目研究将进一步丰富和发展先进陶瓷胶态成型理论和方法，为高性能、高可靠性复杂形状陶瓷部件制备提供新思路。

陶瓷分散剂失效原位凝固注模成型工艺可以成型近净尺寸复杂形状陶瓷坯体，具有固化时间短，坯体强度高，有机添加剂少，工艺过程简单等优点。但是根据悬浮体分散稳定机制的不同，分散剂的失效方法和悬浮体的固化机理也不相同，因此针对分散剂失效工艺普适性研究的问题亟待解决。本项目以氧化铝、碳化硅、氮化铝及钛酸锶钡陶瓷为研究对象，分别采用多聚磷酸铵水解失效、聚电解质交联失效、低温诱导分散剂失效及Isobam基凝胶流延成型实现陶瓷悬浮体的原位凝固成型，制备出高性能、高可靠性复杂形状陶瓷部件，为批量制备高性能复杂形状陶瓷提供基础。主要研究成果如下：（1）采用聚磷酸铵为分散剂，添加0.3 wt%质量分数的聚磷酸铵，可以制备固相含量为50 vol%，粘度为0.45 Pa s的高固相含量、低粘度的氧化铝陶瓷悬浮体。氧化铝陶瓷湿坯抗压强度最高为3.37±0.27 MPa，烧结样品抗弯强度最高为412±15 MPa。（2）采用聚乙烯亚胺为分散剂制备碳化硅悬浮体，羧甲基纤维素钠分子链上的羧酸钠基团，与聚乙烯亚胺分子链上的伯胺发生反应是导致悬浮体原位固化的主要原因。采用热压烧结制备的碳化硅陶瓷相对密度和弯曲强度分别为99.38％和754±68 MPa。（3）采用油酸作为分散剂可以有效的改善氮化铝悬浮体的流动性，添加0.6 wt%的油酸，可以获得固相含量最大为54 vol%，粘度为0.40 Pa s的氮化铝悬浮体。氮化铝悬浮体可以在−20ºC的温度下可以发生原位固化。当固相含量为54 vol%时，氮化铝陶瓷的相对密度可以达到99.8%，最大抗弯强度可达到427 MPa。（4）采用Isobam基凝胶流延成型结合模板籽晶生长法成功制备出晶粒择优取向的钛酸锶钡织构陶瓷。含5wt%籽晶的钛酸锶钡陶瓷织构度达61.1%，介电可调性为47% (1 kV/mm)。