FABRICATION OF SI3N4 AND SI3N4 SIC COMPOS ITES BY PRESSURELESS SINTERING USING NITRATE AS SINTERING ADDITIVES/

The effect of nitrates as sintering additives on the densification of Si3N4 based ceramics by pressureless sintering was compared with that of oxide additives. The surface of Si3N4 particles milled with a metha nol solution of Al and Y nitrates, was coated with a layer containing Al, Y and O. Homogeneous distribution of sintering additives increased the sinterability of Si3N4 Monolithic Si3N4 with nitrate additives co uld be sintered to 94% T.D. at 1500 degrees C, Furthermore, after pres sureless sintering at 1750 degrees C for 2h in Nz, the bulk density of a Si3N4/20 mass% SiC composite reached 95% T.D. with nitrate additive s. The enhancement of densification in the case of nitrate additives w as attributed to the enhancement of primary particle rearrangement due to the homogeneous distribution of liquid phase, a consequence of the homogeneous distribution of sintering additives, during sintering.