Bayer Aktiengesellschaft

Gerhard Leimer

Lothar Schonfelder

Lutz Frassek

Ernst Gugel

Stefan Roth

A process for the production of dense silicon nitride materials by the nitriding of moulded bodies of silicon powder, silicon nitride powder and sintering additives under normal pressure and sintering of the moulded bodies at normal nitrogen pressure as well as silicon nitride materials produced correspondingly.

Process for the production of dense silicon nitride materials

Si.sub.3 N.sub.4 -based sintered compositions containing MgO and optionally other sintering additives, which after sintering, has a flexural strength level at room temperatures of .gtoreq.800 MPa, measured by the four-point bending method, and a Weibull modulus of &gt;15, is produced by mixing MgO, any additional sintering additives and Si.sub.3 N.sub.4 powder to form a mixture, calcining the mixture in an oxygen-free atmosphere to obtain a pre-synthesis mixture, and adding the pre-synthesis mixture to uncalcined Si.sub.3 N.sub.4 powder which is then sintered.

Sintered material based on Si.sub.3 N.sub.4 and processes for its

High-strength Si.sub.3 N.sub.4 -based material with a narrow range spread of values for mechanical properties useful for producing thick-walled ceramic parts for internal combustion engines, thick-walled ceramic fittings or cutting tools is produced by molding a powder-form starting mixture comprising powdered Si.sub.3 N.sub.4, finely divided elemental silicon and sintering additives, and subsequently heat treating the mixture to obtain a sintered molding very near the theoretical density of the material.

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Roedental, Germany

Gerhard Leimer