On the existence of bivalent ions in the apatite channels: A new example—Phosphocalcium cyanamido-apatite
A new apatite, phosphocalcium cyanamido-apatite Ca 10(PO 4) 6 CN 2 □, is obtained by treatment under low pressure at high temperature (900-1000°C) of a mixture of the corresponding hydroxyapatite and calcium cyanamide. In this apatite, one CN 2-2 ion associated with a vacancy replaces two hydroxyl ions in the channels. The formation of a cyanamide-containing apatite also occurs by treatment of an A-type carbonated apatite by ammonia at 600-900°C: in the latter case, the reaction seems more difficult and more limited than in the former. The cyanamido apatite is decomposed by heating in air, and it gives rise first to an A-type carbonated apatite, with release of both ammonia and nitrogen oxide and second to hydroxyapatite by hydrolysis of the A-type carbonated apatite.