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

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

1985-05-31

1987-02-03

McCarthy, Helen M.

Compositions: ceramic

Ceramic compositions

Refractory

264 60, 501 98, 501103, 501104, 501105, C04B 3558

Patent

active

046409025

ABSTRACT:
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.

REFERENCES:
patent: 4304576 (1981-12-01), Hattori et al.
patent: 4316964 (1982-02-01), Lange
patent: 4506024 (1985-03-01), Claussen et al.
patent: 4511525 (1985-04-01), Tsuge et al.
patent: 4525464 (1985-06-01), Claussen et al.
Stevens, R., "An Introduction to Zirconia" pub. by Magnesium Elektron Ltd., England, Jun. '83, p. 7.
Levin, E. M. et al., Phase Diagrams for Ceramists, 1975, Figure 4452, (ZrO.sub.2 --TiO.sub.2).

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