Isuzu Motors Limited

Isuzu Ceramics Research Institute Co. Ltd.

Wenjea J Tseng

Hideki Kita

Toshiyuki Yamada

A composite ceramic is produced by forming a mixed powder of Si and a compound oxide as the starting material into a formed material, nitriding and firing the formed material to form a sinter, and subjecting the sinter to oxidation treatment. The composite ceramic, which is:lightweight and reduced in heat conductivity, has a specific gravity of at most 2.6, and comprises a phase composed of all of elements Si, O and N, and at least one element selected from the element group consisting of A1, Zr, Li, P and Mg, in which phase a subphase composed of Si, Al, 0 and N and a subphase composed of Si, O and N are formed. Another composite ceramic has pores and a disperse phase in a matrix phase composed of Si.sub.3 N.sub.4 crystal grains, an oxide and an oxynitride, and further comprises coarse Si.sub.3 N.sub.4 grains dispersed in the matrix phase with O-containing boundary reaction product layers formed in the boundaries between the matrix phase and the coarse Si.sub.3 N.sub.4 grains. Thus, this composite ceramic, though reduced in heat conductivity, has a high toughness and a high strength due to dispersion of the coarse Si.sub.3 N.sub.4 grains in the matrix phase.

Composite ceramic

A silicon nitride based sintered product produced with Si powder, a Si.sub.3 N.sub.4 powder, and an assistant component effective for sintering silicon nitride as raw materials. A resultant sintered product has fine tissue, exhibits little presence of pores and remaining silicon, and possesses high mechanical strength which can be enhanced by calcinating the product under low pressure after it has been reacted and first sintered.

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Fujisawa, Japan

Wenjea J Tseng