Abstract: There are provided shaped articles of polycrystalline silicon carbide having densities of at least 97% and improved mechanical properties particularly at high temperatures, said articles consisting ofat least 95.4% by weight of .alpha.-silicon carbide,about 0.1 to 2.0% by weight of additional carbon,about 0.2 to 2.0% by weight of aluminium,about 0 to 0.5% by weight of nitrogen, andabout 0 to 0.1% by weight of oxygen,the .alpha.-silicon carbide being in the form of a homogeneous microstructure with an average grain size of less than 10 .mu.m.There is also provided a process for the preparation of such articles by pressureless sintering submicron powder compacts consisting of .alpha.-silicon carbide and aluminium- and carbon-containing additives as sintering aids.

Abstract: A process for the production of oxygen free copper castings and moldings, which contain 0.05 to 0.2% by weight of boron as micro-alloy element, by deoxidation of oxygen containing copper melts by means of calcium hexaboride, comprising introducing 0.3-1% by weight of a CaB.sub.6 into the copper melt, the CaB.sub.6 containing at least 3% C calculated on the weight of the CaB.sub.6, subsequently subjecting the cooled melt, if desired while molding the same, to a solution annealing operation and following up with a storage for an extended time.

Abstract: Process for the manufacture of hexagonal boron nitride which comprises causing a starting material containing an alkali metal boride or an alkaline earth metal boride, preferably a hexa- or dodecaboride, to react with nitrogen at temperatures of at least 900.degree. C and, if desired, up to 2500.degree. C, in the presence of impurities or additives of other boron compounds or compounds of the alkaline earth metals or of carbon compounds. Boron nitride has many uses in various fields, among them, electronics and crucible melting for most non-metallic melts.

Abstract: The present invention relates to powdered boriding compositions for the production of single-phase boride layers on metal articles being substantially free from cracks in the case of mechanical stress, which comprise an activator and a mixture of a boron-releasing agent and an unreactive refractory material, such as silicon carbide.