Transport Processes in Composite Media

Transport processes in two types of composite media were investigated. In one type, exemplified by hydrogen diffusion in steel with microvoids present, short-lived trapping reactions result in a lowering of the effective or overall diffusion coefficient. The other type of composite consists of randomly mixed parts or phases having no interfacial resistance or trapping. The percolation properties of such systems are reviewed, and thermal conductivity, self- diffusivity, and gas permeability in certain porous solids are analyzed in the light of percolation theory.