Gypsum plaster with high fire resistance - obtd. by adding boric acid, and esp. by using impure calcium sulphate obtd. as by. prod., in mfg. boric acid from natural borates

摘要

The plaster consists of natural or synthetic calcium sulphate-dihydrate which has been partly dehydrated and also contains boric acid. The pref. plaster contains 0.05-12.0% boric acid w.r.t. the dry prod. The plaster is pref. made by crushing a natural or synthetic plaster and/or their mixts. and/or natural and/or synthetic gypsum, and adding boric acid or borates to the mixt.. An alternative mfg. method consists of treating calcium borate with sulphuric acid so both boric acid and calcium sulphate is obtd., the latter prod. being heated so it loses its water of crystallisation. The plaster obtd. pref. has fungicidal properties. In addn. to providing a plaster with high fire resistance, the invention permits the use of a residual prod. obtd. during the mfr. of boric acid by treating natural calcium borates, e.g. borocalcite, with H2SO4. The residual prod. is CaSO4 contg. max. 12% boric acid.