Transparent aluminum oxynitride (AlON) ceramics have been prepared through a method based on direct reaction sintering of alumina and aluminum nitride powders using MgO and Y2O3 as co-additives. The sintering additives could cause the formation of liquid phase during sintering, which would greatly promote the densification and eliminate pores. The grain size of AlON is about 50-100μm. The influence of different component of Al2O3 and AlN as well as sintering temperature on microstructure and optical properties of AlON have been studied. High transparent AlON ceramics with the in-line transmittance of 80.3% at 2000 nm wavelength have been prepared when the concentration of sintering additives was 0.16wt% Y2O3 and 0.02wt% MgO.

This work studies the effects of microstructure and relative density on the dielectric constant of porous silica prepared by two different techniques: gelcasting of suspension (GCS) and gelcasting of foams (GCF). Both routes are carried out from the preparation of silica suspension containing starch granules. In GCS route, the resultant suspensions were heated for consolidation, while in GCF route, the suspension was foamed before consolidation. The results indicated that the dielectric constant of porous silica was obviously determined by relative density, but scarcely influenced by microstructure. The logarithmic fitting equation lnε = ρ·lnεs was a good model to describe the relationship between the dielectric constant and the relative density of porous silica prepared by both GCS and GCF routes.

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