煅烧预处理改善氮化硅的凝胶注模成型工艺

Improvement of Gelcasting of Si_3N_4 by Calcination

凝胶注模成型工艺要求制备高固相含量、低粘度的浓悬浮体。商业氮化硅粉体表面特性复杂 ,难于制备符合工艺要求的悬浮体 ,而且在水基凝胶注模成型中固液界面上发生的放气反应也会导致坯体中存在显气孔缺陷。因此 ,本文在 85 0℃下煅烧氮化硅粉 2h ,改善了粉体表面特性 ,在颗粒表面生成SiO2 和Si2 N2 O包覆层 ,使成型过程中产生气孔的有害反应得到有效抑制 。

Concentrated suspension with high solid loading and low viscosity is required for gelcasting process. Usually it is difficult to use Si 3N 4 to prepare the concentrated suspension suitable for gelcasting because of its complex surface status, furthermore, during the process of water-based gelcasting, some gas often discharges out of the solid-liquid interface due to the chemical reactions, which leads to a great deal of bubbles in the green bodies. In this paper, after Si 3N 4 powder was calcined at 850℃ for 2h, its surface status was modified, and a layer of SiO 2 and Si 2N 2O was formed on its surface, which effectively prohibited the gas discharge, so, the homogeneous green bodies were obtained by gelcasting process.