Abstract: The invention concerns a new and improved method for the production of porous and formed bodies with polycrystalline structure that meets the high quality requirements of the usually excellent material characteristics of porous and formed bodies based on silicon nitride and, at the same time, at least considerably reduces known disadvantages of other state-of-the-art techniques. In this, it is provided to first precompress the silicon nitride powder mix with a modal particle distribution of coarse and fine particles to form a green body, and to subsequently bake it using a temperature-based sintering process.

Abstract: The use is described of oxide ceramic materials for compression molds for shaping elements made from glass or a glass-containing ceramic and having high surface quality and tight tolerances. The materials are polycrystalline, monophasal or polyphasal materials which are contact-inert towards the optical elements to be pressed and which, in addition, have significantly better mechanical and thermal properties than monocrystalline substances, which, in principle, exhibit an anisotropic behavior as a consequence of their geometrical anisotropy. The material intended for use according to the invention can comprise a Al.sub.2 O.sub.3 ceramic or a ZrO.sub.2 -- and/or HfO.sub.2 -containing ceramic. The material can also be built up in several phases, i.e. can contain a matrix component and at least one particle component dispersed discretely in it. They are preferably ZrO.sub.

Abstract: The invention is substantially pore-free shaped articles which consist essentially of polycrystalline .alpha.- or .beta.-silicon carbide in the form of a single-phase homogeneous microstructure having grain sizes not exceeding 8 .mu.m, and which are manufactured from SiC powder, without the concomitant use of sintering aides, by isostatic hot-pressing in a vacuum-tight casing at temperatures of from about 1900.degree. C. to 2300.degree. C. and at pressures of from about 100 to 400 MPa. The SiC starting materials have .alpha.- and/or .beta.-SiC powders having a total content of metallic impurities not exceeding 0.1% by weight and a particle size of 4 .mu.m and finer.

Abstract: The invention relates to dense shaped articles of polycrystalline .alpha.-silicon carbide containing from 0.1 to 0.4%, by weight, of aluminum and optionally, a small amount of nitrogen and/or phosphorus, having a homogeneous virtually single-phase microstructure. The additional constituents are substantially in the form of a solid solution in the .alpha.-SiC lattice. The shaped articles are distinguished by flexural strength of at least 600 N/mm.sup.2 up to 1450.degree. C. and low subcritical crack propagation under mechanical stress. The fracture mechanism is trans granular up to at least 1450.degree. C. The shaped articles are manufactured by simultaneously shaping and hot pressing pulverulent .alpha.-silicon carbide containing a small amount of an aluminum-containing additive, such as aluminum powder, aluminum nitride and/or aluminum phosphide, at temperatures between 1850.degree. C. and 2300.degree. C. under a pressure of at least 100 bar (10 MPa).

Abstract: The invention relates to dense shaped articles of polycrystalline .beta.-silicon carbide containing small amounts of aluminum and optionally, nitrogen and/or phosphorus, having a virtually single-phase microstructure since the additional constituents are substantially in the form of a solid solution in the .beta.-SiC lattice. The shaped articles are characterized by high temperature flexural strengths of at least 600 N/mm.sup.2 at temperatures up to 1450.degree. C. The fracture mechanism is transgranular up to at least 1450.degree. C. The shaped articles are manufactured by hot-pressing and simultaneously shaping pulverulent .beta.-silicon carbide with small amounts of an aluminum-containing additive, such as aluminum powder or aluminum nitride and/or aluminum phosphide, at temperatures between 1750.degree. C. and 2200.degree. C. under a pressure of at least 100 bar (10 MPa).