Si3N4 ceramics with Y2O3 and Al2O3 additives set in an Al2O3 sagger with a
Si3N4 powder bed were successfully sintered in air atmosphere furnace at 16
00-1700 degreesC. Bulk densities of the sintered Si3N4 ceramics were 3.10-3
.16 g/cm(3) which were similar to the densities of those sintered in a nitr
ogen gas furnace of 0.1 MPa. No heterogeneous surface layer was observed. W
hen the sagger and powder bed are structured so that SiO gas continuously g
enerated during the sintering, Si3N4 ceramics can be sintered in air withou
t serious oxidation.