The Effective Thermal Transport in Composite Materials

Bashir M. Suleiman

Department of Applied Physics, College of Sciences, University of Sharjah, P. O. Box 27272, Sharjah, United Arab Emirates

1. Introduction

Composite materials are promising materials, which should exhibit an improve on several aspects of the physical properties such as mechanical, thermal, electrical etc.. A composite material is a system of materials composed of two or more components randomly mixed and bonded on a macroscopic scale. For example, metal-alloys Silicon carbides such as Aluminum Silicon Carbide (AlSiC) is made up of Aluminum, Silicon and Carbone on a microscopic scale. It is a metal matrix composite (MMC) packages that have a unique set of material properties. It is ideally suited to thermal management performance, and a functionality that supports high-density interconnection microelectronic packaging applications (Hollecka et al., 1988) & (Zhang et al., 2004). This example is one of the concrete evidences that thermal conduction is an important feature of composites’ application for electronic packaging, which are associated with thermal insulation, and heat spreader. General speaking, we should have different composite materials which are suitable for different applications (Xu, & Yagi, 2004), and this can be achieved because of the unique character of the detailed microstructure of the composites.

In particular, a composite material is composed of strengthening items (reinforcement) such as particles, flakes, fibers, etc.., embedded in a matrix of metals, ceramics, or polymers. The matrix holds these items to form the desired shape while the items improve the overall physical properties of the matrix. When designed properly, the new combined material exhibits better physical property than would each individual material. When composites are selected over traditional materials such as metal alloys or plastics, it is usually because of one or more desired properties regarding cost, weight, size, surface condition, strength, thermal and electrical conduction etc…

For example, SliconCarbide SiC/SiC composites, which are relatively cheap, have upper limit for thermal conductivity that exceeds the corresponds obtained in single crystal and high-purity chemically vapor deposited CVD SiC. Effective thermal conductivity (Xeff) of such composites reaches maximum values of ~320 W/m oC at room temperature (Zinkle & Snead, 1999). This value is comparable if not higher than the thermal conductivity of some precious expensive metals such gold and silver.

A new generation of functionally graded fibrous composites called functionally graded materials (FGMs) (Suresh, 1998), (Koizumi, 1993) and (Fung & Hu, 2008). FGMs have dynamic effective thermal properties and the volume fraction of the materials changes

gradiently. It is the non-homogeneous microstructures in these materials that produce continuous graded macroscopic properties, such as the thermal conductivity, specific heat, mass density and elastic modulus. FGMs have been developed as the super-resistant materials for propulsion systems and airframe of the space planes in order to decrease thermal stresses and to increase the effect of protection from heat (Gray et al., 2003) and (Kuo & Chen, 2005). FGMs can reduce the thermal stress in such structures working in high temperature environment. All the effective thermal properties of FGMs can provide great help in predicting the overall behavior under various loading conditions. The least to say is that the theoretical and experimental investigation of the effective thermal properties of all composites including FGMs is an area which has received great interest in recent years.