Obtaining Extra High Purity Tungsten.

Single crystals of high-purity tungsten with the content of the main impurities (including molybdenum and carbon) at the level of sensitivity of the mass-spectrum analysis (approximately 1 multiplied by (times) 10** minus **5%) and with the ratio of electric resistances at the room and helium temperatures of 70,000 have been obtained. Tungsten trioxide was used as the initial raw material. It was then heated in oxygen with subsequent hydrogen reduction and zonal recrystallization of the purified metal in a vacuum.