Enhanced mechanical properties for porous ceramics with an in situ formation of anorthite crystals during vitrification

Abstract

Porous anorthite ceramics are widely applied as catalysis supports, separation membranes, and thermal insulations at high temperatures. In situ formation of anorthite crystals during vitrification is herein employed to improve mechanical properties of porous anorthite with modulated grain sizes on pore walls. Sintering parameters of shrinkage (5%-30%), open porosity (31.0%-58.3%), density (1.18-1.71 g/cm 3 ), and mass loss (12.20%-18.26%) are estimated to investigate the influences of sintering aids of calcite, fused mullite, and silicon carbide or talcum on the densification processes of porous anorthite. The Kissinger equation is used to determine the activation energy of 783 kJ/mol for the crystallization of anorthite, which is significantly low for the formation of anorthite crystals through surface nucleation mechanism in present flux-rich melt. In situ crystallization and simultaneous densification under liquid drainages are favored for whiskersreinforced mechanism to enhance flexural strengths (6.9-19.4 MPa) for porous anorthite with the porosity of 49.6%-58.3% through the formation of hierarchical nano-and microscale structures during vitrification.