Abstract: 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.

Abstract: 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 >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.

Abstract: 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.

Abstract: Method for the production of a polycrystalline shaped body of silicon carbide of a density of at least 98% of the theoretical density of silicon carbide, prepared through pressureless sintering at temperatures from 1,900 to 2,200 C. from at least 97 weight % of .alpha.-silicon carbide and/or .beta.-silicon carbide under addition of up to 3 weight % of boron, characterized by the fact that the shaped body is prepared without any carbon additions to the batch and is pressureless sintered in a carbon containing protective gas atmosphere.

Abstract: Polycrystalline shaped body of a density of at least 98% of the theoretical density of silicon carbide, consisting of at least 92 weight % of .alpha.-silicon carbide and/or .beta.-silicon carbide, which is present in the form of a homogeneous texture with grains of maximal 10 .mu.m, and is characterized by the fact that, besides a content of up to 3 weight % of boron, a share of about 0.5 to 5 weight % of a metal or rare earth element that acts reducing or mixtures thereof is present, and the body shows a transverse rupture strength (determined by the four-point method) of at least 500 N/mm.sup.2 up to 1,400 C and is essentially free of free carbon.A method for the production of shaped bodies through the pressureless sintering of the silicon carbide starting material, characterized by the fact that about 0.