Effective thermal and electromagnetic properties of composite materials containing ellipsoidal-coated fillers oriented randomly

Abstract

This study aims to derive explicit solutions for the effective thermal and electromagnetic properties of composite materials containing coated fillers oriented randomly. In this study, the coated fillers are modeled as double inhomogeneous inclusions with anisotropic properties and ellipsoidal shapes, without loss of generality. This model is analyzed by combining the double inclusion method with the self-consistent method or the Mori–Tanaka method. The derived solutions for the effective properties are expressed in explicit form by the physical properties of constituents and the difference in shape between the inner and outer regions of the coated fillers, and confirmed to be consistent in the limit of no coating layer. In addition, the solutions of effective properties are also derived for composite materials containing many kinds of coated fillers with different shapes and physical properties. The solutions allow the prediction of thermal conductivity, permittivity, electrical conductivity, and magnetic permeability of a wide range of composite materials by analogy with thermal and electromagnetic properties. These solutions are applied to the following two composites: diamond fillers coated with TiC/Al, and Co fillers coated with Co 3 O 4/Mg. The effect of the thickness of the coating layer on the effective thermal conductivity of these materials is investigated. As a result, our analytical results for these composite materials generally agree with the experimental results. Moreover, from the viewpoint of maximizing the thermal conductivity of diamond fillers coated with TiC/Al, the optimal combinations of the thickness of the coating layer and the shape of the diamond fillers are identified. For Co coated with Co 3 O 4/Mg, we find that the shape of Co fillers should be long fibrous from the viewpoint of giving high magnetic permeability while maintaining high thermal conductivity due to Mg. Thus, the analytical solutions are demonstrated to be powerful tools for designing composite materials containing coated fillers.