Influence of phase and morphology on thermal conductivity of alumina particle/silicone rubber composites

Silicone rubber filled with thermally conductive alumina is fabricated as a class of thermal interface materials in this work. The thermal conductivity of the prepared alumina/silicone rubber composite is measured as a function of alumina loading. The effects of alumina filler with different phases and morphologies on the thermal conductivity of the composite are investigated by comparative method. When the filler loading is low, the composite filled with porous irregular-shaped alpha-alumina exhibits a higher thermal conductivity than that filled with gamma-Al2O3 and spherical alpha-Al2O3. In order to achieve a high loading, spherical alpha-Al2O3 has the most pronounced effect due to its intrinsic high thermal conductivity and unique morphology for homogeneous dispersion in the polymer matrix, which is superior to irregular-shaped alpha- and gamma-Al2O3. Our results demonstrate that the composite filled with spherical alumina by the mass concentration of 82 % has six times thermal conductivity higher than pure silicone rubber. Thermogravimetric analysis studies exhibit that the thermal stability of the composite distinctly increases with filler loadings. The obtained data were compared with theoretical equations in the literatures that are used to predict the properties of two-phase mixtures.