Elektroschmelzwerk Kempten Gmbh

Georg Vogt

Karl A Schwetz

Gunther Kratel

Hans Kaiser

Gunter Stohr

A method of producing dense shaped articles of pure boron carbide that optionally contain 0.1 to 8% by weight of free carbon in the form of graphite is disclosed involving the steps of homogeneously mixing boron carbide in submicron powder form with small quantities of a carbon containing additive, forming the powder mixture into a shaped green body and then sintering the body in a controlled atmosphere and in the absence of external pressure at a temperature of about 2100.degree.-2200.degree. C. The shaped articles thus obtained are polycrystalline and, insofar as they correspond to the stoichiometric composition B.sub.4 C, single-phase; they have an average grain size of not more than 10 .mu.m, a density of at least 90% of the theoretical density of boron carbide and a flexural strength of at least 300 N/mm.sup.2. The fracture mode of the sintered articles is completely transcrystalline.

Process for the production of dense sintered shaped articles of

Process for preparing hydrophobic SiO.sub.2 by reacting solid SiO.sub.2 of finest particle size with organosilicon compounds while subjecting the reaction mixture to a mechanical impact treatment which will at the same time result in a comminution of the SiO.sub.2 particles as well as of their aggregates, said process comprising incorporation to the reaction mixture, in addition to the water adsorbed by the SiO.sub.2, an amount of 0.3 to 3% by weight of water calculated on the weight of the SiO.sub.2.

Growing community of inventors

Munich, Georgia

Georg Vogt