Thermal conductivity of composites

The paper shows that the conductivity properties of a composite regarded as a two- or multiphase material do not obey the rule of mixtures. The discussion concerns the conductivity of a quasihomogeneous composite defined as a composite material in which the distribution of stereometric parameters (volume fraction, shape factor, and orientation of constituent particles) is constant in a representative volume which is large compared to the size of the single particles involved. The theory of the conductivity of quasihomogeneous composites is examined relative to the type of structure (dispersion type and interconnecting-phases type) shape factor, and orientation. The concept of quasihomogeneous material does not consider transport mechanisms for the thermal conductivity, so that consideration of particle size limits the application of the concept of quasihomogeneity to the thermal conductivity of composites. Also discussed are an analysis of the microstructure of a composite, experimental evidence in support of the theory, and the special case of porous materials.