6 - Reactive Phase Formation: Some Theory and Applications

Abstract

In general, the expression “reactive phase formation” encompasses all phenomena whereby the reaction between two adjacent phases leads to the formation of one or several product phases. This chapter is composed of two main parts. In first part, the modalities of reactive diffusion are considered from a more or less theoretical point of view. The conditions leading to linear or linear-parabolic kinetics and nucleation-controlled reactions are analyzed. A distinction is made between the formation of intermediate phases from reacting elements, which seems dominated by kinetic effects and subsequent reactions when new phases are born from already formed phases. Then nucleation can play the dominant role in the process of phase formation and, in some cases, in the absence of such formation. The second part considers the process of phase formation with silicides that are of current technical importance in the electronics industry: TiSi2, CoSi2, and NiSi. Most of the effects reported are well established. However, to be up to date, some tentative explanations are advanced in considering the nucleation of the C49 phase of TiSi2, or enthalpy effects in solutions of CoSi2 and NiSi2.