Low thermal conductivity Si.sub.3 N.sub.4 /ZrO.sub.2 composite ceramics

摘要

Improved Si.sub.3 N.sub.4 /ZrO.sub.2 composite ceramics are described, having low thermal conductivity and which are substantially free of surface spalling and material degradation. Such composites are produced by incorporating an additive, e.g. MgO, CaO or Y.sub.2 O.sub.3, preferably Y.sub.2 O.sub.3, in suitable molar proporations based on ZrO. sub.2, and sintering the mixture with Si.sub.3 N.sub.4. In a preferred embodiment a powder mixture of 70% Si.sub.3 N.sub.4 and 30% ZrO.sub.2, by volume, and containing 6.6 mole percent Y.sub.2 O.sub.3 based on ZrO.sub. 2, is formed and is sintered to produce a composite ceramic. The Y.sub.2 O.sub.3 is preferably pre-reacted with the ZrO.sub.2 to form a solid solution. A sintering aid, preferably Al.sub.2 O.sub.3, e.g. in an amount of about 2 to about 4%, by weight of the total mixture, can be added to permit production of the Si.sub.3 N.sub.4 /ZrO.sub.2 composite by pressureless sintering.