Importance

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Abstract

The invention relates to cast parts which contain at least 87 wt. % silicon nitride and up to 13 wt. % of an additive combination comprised of Al.sub.2O.sub.3 and Y.sub.2O.sub.3. The initial composition of the mass formulation starts with Y.sub.2O.sub.3/Al.sub.2O.sub.3 ratios of less than 1.1, preferably with Y.sub.2O.sub.3 Al.sub.2O.sub.3 ratios of 0.2 to 1.09. 1% to 20% of the Y.sub.2O.sub.3 portion can thus be substituted by an additional element group of IVb of the periodic table or by the oxide thereof. The cast parts can comprise up to 1.0 wt. % HfO.sub.2 and/or ZrO.sub.2. Said cast parts preferably have a thickness >98% of the theoretic thickness. At room temperature, the bending strength of the inventive cast parts amounts to .gtoreq.1100 MPa and amounts to .gtoreq.850 MPa at 1000.degree. C. The inventive cast parts correspond to the formula Si.sub.6-zAl.sub.zO.sub.zN.sub.8-z. The degree of substitution z thus amounts to 0.20 to 0.60, preferably from 0.22 to 0.54, especially from 0.3 to 0.35.

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First Claim