Effect of silica sol addition on sintering properties of porous alumina ceramics

Porous alumina ceramics were prepared by using calcined α-Al2O3 as raw material,nano silica sol as high temperature binder and carboxymethy cellulose as molding binder with processes of mixing,aging,molding and sintering.The effect of silica sol addition on sintering properties was investigated by test method of SEM and XRD. The linear shrinkage,volume density,porosity and flexural strength were also tested.The results show that the quartz silicon dioxide which is pyrolysed product from silica sol could bond the alumina particles together to form porous ceramics and improve the mechanical properties.The essence of silica sol bonding is physical bonding.The silicon dioxide in the sol begins to react with alumina to form mullite when the sintering temperature reaches 1500 ℃,and the porous ceramics tend to be compact with excellence mechanical properties.The flexural strength is about (105.5±8.0) MPa.The content of mullite phase increases with sintering temperature.However,with much higher content of mullite generation,the porosity increases and the mechanical performance degrades.The porous alumina ceramics with excellence performance can be obtained when the sintering temperature is between 1400 ℃ and 1500 ℃