陶瓷高价反离子直接凝固注模成型的基础研究

In the light of problems existed in ceramic colloidal processing, such as toxic gel system, low green strength, poor adaptability and difficulty in preparing large and complex-shape ceramics, direct coagulation casting of ceramics via high valance counter ions (DCC-HVCI) was investigated. Following basic issues would be investigated. Firstly, the influences of ceramic components, types and addition content of dispersant, pH value and solid loading on rheological properties of multiphase ceramic suspensions was systematically investigated. And the rheological equations of ceramic suspensions were established. High solid loading and low viscosity multiphase ceramic suspensions were prepared. Secondly, the effect of high valance counter ions on the coagulation rule of high solid loading suspensions was studied and the coagulation mechanism was revealed. The classical colloidal theory was amended and the coagulation formula for high solid loading ceramic suspenisons would be established. In addition, new methods with good adaptability for controlled release of high valance counter ions to coagulate ceramic suspensions were explored. Water soluble polymers were added to enhance the wet strength of coagulated bodies. Finally, DCC-HVCI and sintering technology were combined to prepare large and complex-shape ceramics with high properties and low shrinkage. The investigations above are the basis for the deeply research and applications of DCC-HVCI.

针对陶瓷胶态成型工艺存在的反应体系有毒、坯体强度低、普适性较弱、制备大尺寸复杂形状陶瓷部件困难等问题，本项目将系统陶瓷高价反离子直接凝固注模成型工艺，拟开展以下几个基础问题的研究。首先，系统探讨陶瓷组分、分散剂类型及添加量、pH值及固相含量对复相陶瓷悬浮体流变性能的影响规律，并建立陶瓷悬浮体流变方程，优化制备高固相含量、低粘度的复相陶瓷悬浮体。其次，系统研究高价反离子对高固相含量陶瓷悬浮体聚沉的影响规律，揭示高价反离子在浓悬浮体中的聚沉机制，修正经典胶体理论并建立适合高固相含量陶瓷悬浮体的聚沉方程式。再次，深入挖掘具有普适性的高价反离子控释固化陶瓷悬浮体的新方法，并通过添加水溶性高分子进一步提高固化坯体的强度。最后，将陶瓷高价反离子直接凝固注模成型与烧结工艺结合制备高性能大尺寸复杂形状陶瓷部件。上述研究为陶瓷高价反离子直接凝固注模成型工艺的理论研究和推广应用提供了新的思路。

本文提出一种以亚微米螯合物作为固化剂来控制释放高价反离子的新方法。采用三聚磷酸钠、聚磷酸铵和柠檬酸铵三种螯合剂控制释放高价反离子，并应用于氧化物陶瓷的高价反离子直接凝固注模成型中。研究了通过添加少量水溶性高分 子来增加陶瓷坯体强度的可能性。采用陶瓷分散剂失效原位凝固注模成型方法制 备了硼化铪基陶瓷并探讨其固化的微观机制。采用三聚磷酸钠作为螯合剂控释高价反离子实现氧化锆悬浮体的直接凝固注模成型。螯合物的粒度分布较窄，d50为0.11μm，粒度分布接近于粉体粒径。湿坯的抗压强度为2.1~3.8MPa，氧化锆陶瓷的相对密度为99.5%，抗弯强度为726±48MPa，韦伯模量为21。采用聚磷酸铵螯合液作为固化剂，在 40~70°C下添加聚磷酸铵螯合液与二乙酸甘油酯实现悬浮体的固化成型。湿坯的抗压强度为2.1±0.9MPa。氧化铝陶瓷的相对密度为97.9%，抗弯强 度为388±23 MPa，韦伯模量为14。发明了一种以柠檬酸铵螯合液制备陶瓷悬浮体，通过调控pH值控制高价 反离子释放固化陶瓷悬浮体的新方法。通过柠檬酸铵与氯化钙制备柠檬酸钙螯合液并制备50vol%的氧化铝悬浮体。在40~70°C下保温2~6 h使氧化铝悬浮体原位固化。湿坯的抗压强度为1.1~2.4 MPa。氧化铝陶瓷的相对密度为98.5%，抗弯强度和韦伯模量分别为455±17 MPa和30。探讨水溶性高分子提高坯体强度的微观机制，在65°C 下，琼脂、卡德兰胶及聚乙烯醇对氧化铝悬浮体粘度影响不大，而 Isobam 的自发凝胶则可使悬浮体粘度增大至 9 Pa s。添加水溶性高分子的氧化铝湿坯抗压强度增大至2 MPa，干坯抗压强度曲线呈塑性变形趋势。添加卡德兰胶的氧化铝干坯强度增大到 3 MPa，坯体的塑性性能获得提高。采用湿磨工艺，球料比为 3:1，球磨时间为 8 h，将硼化铪粉的 d50 减小 至 1.45 μm，满足了胶态成型工艺的要求。利用二乙酸甘油酯缓慢水解产生乙酸，乙酸与分散剂四甲基氢氧化铵发生中和反应的特性，实现了硼化铪悬浮体的可控、均匀固化并制备了性能良好的硼化铪陶瓷。