Effect of pH, milling time, and Isobam content on porous silicon nitride ceramics prepared by gel casting

Abstract

As a non-toxic copolymer of isobutylene and maleic anhydride, Isobam was successfully used as a dispersant and a gelling agent for fabricating porous Si 3 N 4 ceramics by gel casting. The dispersity and rheological properties of the Si 3 N 4 slurry were influenced by the pH, milling time, and Isobam content, which varied from 0.1 wt.% to 0.6 wt.%, and these factors were investigated. The slurry with 40 vol.% solid content and milled for 4 h had a high zeta potential at pH 12 (adjusted by Tetramethyl ammonium hydroxide (TMAH)), which meant that the particles were well dispersed. The mechanisms of TMAH were electrostatic repulsion and steric hindrance. The viscosity of the slurry increased with increasing Isobam content. After pressureless sintering at 1700 °C for 2 h, a uniform unique interlocking microstructure of rod-like β-Si 3 N 4 grains was observed, which may improve the flexural strength of the ceramics by intergranular fracture and particle pullout of β-Si 3 N 4 grains. The density and porosity of the samples fluctuated negligibly with increasing Isobam content, and the Si 3 N 4 ceramic with 0.1 wt.% Isobam exhibited the highest bending strength of 251.6 MPa among all samples.