Polycrystalline sintered compacts based on europium hexaboride and process for their manufacture

The invention relates to polycrystalline sintered compact based on europium hexaboride having a density of at least 85% of the theoretical density. The compacts comprise EuB6, from about 0.1 to 10% by weight of B4C and, optionally, amorphous carbon, and have a total of Eu+B+C of at least 98.5% by weight. They have a homogeneous microstructure with mean grain sizes of less than 20 mu m, in which, in addition to the crystalline phase EuB6-xCx, in which x has values of from 0 to 0.25, B4C can be detected as a separate, finely divided, crystalline phase. The sintered compacts can be manufactured from powder mixtures comprising europium hexaboride of stoichiometric composition and additions of boron carbide and/or mixtures of a carbon-containing material and a boron component by means of hot pressing in graphite moulds, by means of isostatic hot pressing in casings that can be sealed so that they are gas-impermeable, or by means of pressureless sintering.