Diffusion-Limited Reactions of Non-Oxide Ceramics with Transition Metals

Thermodynamic and diffusion models are given to describe morphological evolution of the reaction zone during diffusion-limited interaction between non-oxide Si-containing ceramics (SiC and Si3N4) and transition metals (Cr, Mo, Ti, Ni, Co, Pt). In the case of diffusion-controlled process in the ternary metal-ceramic systems, reaction phenomena can be rationalized using chemical potential diagrams. However, in some cases, a periodic layered morphology is found in the transition zone, which is not fully understood, and it is difficult to predict a priori. Silicide formation in systems based on dense Silicon Nitride and non-nitride forming metals can be explained by assuming a nitrogen pressure build-up at the contact surface. This pressure determines the chemical potential of Silicon at the interface, and hence, the product phases in the diffusion zone. Traces of Oxygen in the ambient atmosphere might affect the interaction in non-oxide ceramic/transition metal systems. The thermodynamic stability of the condensed phases in the systems where volatile species may form can be interpreted using predominant area-type diagrams.