process for the manufacture of smooth and rissefreien staeben from high-purity boron from the melt

摘要

In the production of a high purity boron rod free from strains p and cracks by zone-melting using induction heating, the temperature in each plane perpendicular to the axis of the rod in the "plastic" region of the rod is maintained constant over the entire cross-section of the rod by means of a shield heated to at least 1,500 DEG C or by the supply of heat. The shield may be a cylinder of carbon, tungsten, tantalum, or boron situated between concentric cylinders of boron nitride (Fig. 2 or 3). The shield is purged by an inert gas except in the case of boron which may be melted. The shield may be heated by the primary induction coil, an additional induction coil, or resistance. Heat may be supplied by electron bombardment (Fig. 4) or a plasma which may be produced by the primary induction coil (Fig. 5).