Formation and reactivity of nitrides I. Review and introduction

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Abstract
Methods of nitride production are summarised and their thermodynamics surveyed. Crystal structures and types of bonding in binary and ternary nitride compounds are classified and discussed. Kinetics of nitride formation are related to structural changes in the materials, which control diffusion of metals and nitrogen and cause nitride scaling. Metal nitridation with ammonia and nitride formation during ammonia synthesis are discussed.Information so far available on the sintering of nitrides and its effect on their chemical reactivity is reviewed. This effect is influenced by additives or impurities such as oxides formed by partial nitride hydrolysis and oxidation. Sintering and hot pressing increase the resistance of nitrides to hydrolysis and oxidation, so that they become more suitable for use as refractories. Often, corrosion resistance of nitride layers on metal surfaces is impaired by poor scaling resistance in air or oxygen at comparatively low temperatures. The kinetics and products of oxidation of nitrides so far studied, notably AlN, TiN and UN, depend mainly on the intrinsic reactivity of the material and the available surface at which oxidation can occur.Subsequent work will be concerned with changes in phase composition, surface area and crystallite and aggregate sizes and their correlation with production, sintering, hydrolysis and oxidation conditions for single and mixed nitrides. Suitable experimental techniques are summarised in this paper.

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