INTERFACIAL CHEMISTRY - REACTIONS IN INORGANIC SYSTEMS

The use of equilibrium thermodynamics in describing interfacial reacti ons in inorganic systems is demonstrated using examples of interaction s between non-oxide materials (C, Si, SiC, Si3N4) and transition metal s (Ti, Mo, Pt): In the case of diffusion-controlled process, solid-sta te reactions can be interpreted with chemical potenial diagrams. Howev er, in some cases a periodic,layered morphology is found in the reacti on zone, which is not fully understood and it is difficult to predict a priori. The interfacial phenomena in systems based on dense Si3N4 an d non-nitride forming metals can be explained by assuming a nitrogen p ressure build-up at the contact surface. This pressure determines the chemical potential of Si at the interface and, hence, the reaction pro ducts formed in the diffusion zone. Traces of oxygen in the ambient at mosphere might affect the interaction at the interfaces. This is espec ially of importance when both members of the diffusion couple can form gaseous products. The thermodynamic stability of the condensed phases in the systems where volatile species may form can be described using predominance-type thermochemical diagrams.