用于直接凝固注模成型工艺的氮化硅粉体表面改性方法与机理研究

Direct coagulation casting (DCC) process has been one of the most effective methods to prepare the silicon nitride ceramics with high quality and precision. Silicon nitride powders are difficult to disperse due to their surface features, therefore it is critical to improve the dispersity and rheological behavior of the silicon nitride aqueous slurry. Dispersant and surface modification techniques like inorganic and organic coating methods were used, but can not lead to the practical application of the native silicon nitride powders. In this project we will develop a quantitative determination method of the surface functional groups on the silicon nitride powders, which is based on the developments in this research area, and focus on the step-by-step grafted modification of the surface functional groups with various types of organic structures to adjust the dispersity and rheological behavior of the silicon nitride aqueous slurry. The relationship between various grafted organic structures and the zeta potential absolute value, steric hindrance and apparent viscosity of the silicon nitride powders in aqueous slurry will be studied. The influence of various types of grafted organic molecules on the dispersity and rheological characteristics of the silicon nitride powders will also be studied, and the universal surface modification method of silicon nitrides or similar powders will be investgated. Finally, modified silicon nitride powders will be prepared for application in direct coagulation casting process. The completement of this project will provide more scientific basis for the preparation of the silicon nitride aqueous slurry with high solid volume fraction and low viscosity, and will provide a new surface modification method for the other similar non-oxide powders.

直接凝固注模成型工艺是制备高性能精细氮化硅陶瓷的有效方法之一，由于氮化硅粉体的表面特性，如何提高其水基浆料的分散性和流变性是实现此工艺的关键技术，采用分散剂处理、无机或有机包覆等表面改性技术难以使国产氮化硅粉体满足应用要求。本项目拟以氮化硅粉体表面基团性质研究为基础，建立表面基团定量检测方法。通过对粉体表面基团的接枝或分步接枝，在氮化硅粉体表面连接上不同性质的有机分子，以调节氮化硅粉体水基浆料的分散性和流变性。研究不同特征基团有机分子与氮化硅粉体表面接枝对其在水基浆料中Zeta电位、空间位阻和表观粘度的影响及其与分散性和流变性的关系，探索氮化硅粉体或其它非氧化物粉体表面改性的普适方法，从而制备出适用于直接凝固注模成型工艺的氮化硅粉体。本项目的完成有望为制备适用于高固相含量低粘度水基浆料的氮化硅粉体提供更充分的科学依据，同时也为非氧化物粉体的表面改性提供一种新的方法。

采用表面改性的方法提高其水基浆料的分散性和流变性是制备高固相体积分数、低粘度的氮化硅水基浓悬浮液的必由之路，也是近年来广受关注的研究领域。因此研究氮化硅粉体表面改性技术有着非常重要科学和应用价值，目前也得到了越来越多的关注。本项目旨在进行适用于直接凝固注模成型工艺的氮化硅粉体表面改性研究。. 本项目的研究内容如下：（a）氮化硅与碳化硅粉体表面羟基定量检测方法和粉体预处理研究。建立了氮化硅及碳化硅粉体表面基团的分析、检测、活化与普适性预处理技术。（b）研究了小分子分散剂如醇、二酸、丙烯酸及其酯直接或分步接枝改性氮化硅粉体。（c）研究了聚合物分散剂如不同分子量的聚乙二醇和聚乙二醇单甲醚直接或分步接枝改性氮化硅粉体。. 本项目主要研究成果如下：（a）发现酸或碱洗可有效调控粉体表面羟基浓度，并建立了两种方法来定量检测表面羟基浓度，为接枝改性及效果评价奠定了基础；（b）基于氮化硅和碳化硅表面羟基较高的反应活性，通过直接接枝和分步接枝小分子及大分子分散剂对氮化硅表面进行改性，发现利用甲基氯硅烷分步接枝小分子或大分子分散剂可有效提高氮化硅粉体浆料固相体积分数。其中采用二甲基二氯硅烷与聚乙二醇8000或聚乙二醇单甲醚1000分步接枝改性的方法可使氮化硅水基浆料固相体积分数达到57%（1P.s）。. 本项目研究有效提高了氮化硅水基浆料的固相体积分数，为其应用于直接凝固注模成型工艺研究奠定了基础，对于其他常见非氧化物粉体的表面接枝改性研究也具有重要的参考价值。