Shrinkage and flexural strength improvement of silica-based composites for ceramic cores by colloidal alumina infiltration

Abstract The effects of colloidal alumina infiltration on porous silica-based composites for complex designed ceramic cores were investigated. The specimens pre-sintered at 1100 °C for 2 h were immersed into colloidal alumina and were sintered at 1300 °C for 2 h. Infiltrated alumina particles were coagulated on the surface of fused silica via their opposite electrical charges in the infiltrating solution. The infiltrated alumina was reacted with the surface of fused silica, and mullite was formed thereafter. The shrinkage and microcracking induced by surface crystallization of fused silica to cristobalite was prevented by mullitization. As a result, the formation of mullite by alumina infiltration for 150 min dramatically improved the flexural strength (3.3 MPa to 9.6 MPa) and reduced the linear shrinkage (2% to 1%) of the silica-based composites. However, longer infiltration time over 150 min has no significant effects on flexural strength and linear shrinkage.