Nitridation in the processing and preparation of metals and ceramics

Abstract

The formation and separation of metal nitrides from a variety of materials including ferroalloys, oxides, natural materials and minerals is an important component in current materials processing practice. Ferroalloys like ferroniobium and ferrovanadium undergo nitridation by ammonia yielding a mixture of iron nitrides and the refractory metal nitride. Acid leaching effectively separates the iron nitride from the mixture. Niobium nitride thus obtained is used to produce niobium metal by pyrovacuum treatment. Vanadium nitride converts to metal when pyrovacuum treatment is followed by electrorefining. Nitride suitable for decomposition to metal can be obtained from niobium pentoxide by reacting ammonia or by reacting a mixture of carbon and nitrogen. Rice husk is a ready-made intimate mixture of silica and carbon. It can be converted to silicon nitride or to a mixture of silicon carbide and silicon nitride by carbonitrothermic reduction. β sialon can be directly prepared from kaolinite by carbonitrothermic reduction. Ilmenite is another mineral amenable to nitridation processing. It yields after reaction with nitrogen in presence of carbon, a separable titanium nitride-iron mixture. All these attractive features of nitridation have been discussed in this paper. The possibility of incorporating nitridation into the process flowsheets has been highlighted.