GB789403A - Improvements in or relating to the purification of elementary boron - Google Patents

Abstract

Boron is purified by roasting impure boron with a reagent comprising boron fluoride, hydrogen fluoride, or an ammonium or alkali metal fluoride, or mixtures or combinations of any two or more of these, and leaching the product with hot acid. 5-20 per cent of the reagent may be sufficient, but preferably 50-200 per cent is used. The heating may be for 30-60 minutes at a temperature within the range 300-1000 DEG C. in an inert atmosphere, e.g. helium or argon, or in a reducing atmosphere, e.g. hydrogen, and may be at subatmospheric pressure. The boron may be prepared by reaction of B2O3 and magnesium in a ratio 1.5-2.0, and the impure boron may be leached with hot acid before heating with the reagent. The heated product may be leached with water, and is then boiled with 20 per cent HCl, washed and dried. In examples, impure boron is roasted for 40 minutes with KBF4, KHF2, or KF at 1000 DEG C. in argon at 0.4 mm., and at 1000 DEG C. with BF3 or HF, produced by thermal decomposition of KBF4 or KHF2, respectively, contained in a separate boat in the roasting chamber. KBF4, KHF2 and mixtures thereof are particularly effective for removing magnesium impurities. A mixture of KBF4, KHF2 and KF may be used, or the boron may be subjected to successive treatments with KF and a mixture of KBF4 and KHF2.