Mechanochemical Nitride Synthesis

A frequent criticism of nitride materials during the last 30 years, and especially those designed for structural applications has been that the cost is too high by a factor of (say) 10. In the competition with cheaper materials (albeit with poorer properties and shorter lifetimes), users have generally preferred to go for the cheaper option, rather than the more expensive nitrides. Despite many attempts to address this issue, the cost of nitride processing has remained high – due to the high price of starting materials, the high temperatures needed for firing, and also the finishing costs (often involving diamond machining), and this has been a major factor limiting the market share enjoyed by these materials. A number of studies have been reported recently using the technique of mechanochemical synthesis, in which nitrogen is incorporated (usually via ammonia) into the starting powders during a high-energy milling process (at room temperature). In the subsequent firing, considerably lower temperatures are needed to produce the resulting final nitride product(s). In this presentation, the technique of mechanochemical synthesis is discussed, the range of materials that have been produced are reviewed, and the potential of this technique for reducing the cost of bulk nitride production is reviewed.