Thermophysical properties of PI/SiO2 and PI/C composite films
Yang Liping, Cai An, Luo Caiyun, Xu Zijun and Xi Tonggeng
Thermal diffusivities and specific heats of polyimide (PI), PI/C and PI/SiO2 thin films in the temperature range of 293 to 433 K were measured by laser flash technique and differential scanning calorimeter (DSC), respectively. The thermal conductivity was calculated from the thermal diffusivity, specific heat and density. Besides the effect of temperature, the effects of additions of nanometer silica and carbon on thermophysical properties were investigated. The results showed that both silica and carbon could reduce specific heats and increase thermal conductivities. The increasing trend of thermal conductivities of PI with temperature increasing did not change when silica or carbon was added. The thermal conductivity of PI/SiO2 obviously increased when the content of silica changed from 10% to 20% because the contact between silica particles strengthened the heat conduction and the larger silica particle diameter resulted in the less phonon-particle surface scattering. The thermal conductivity of PI/C with 30% carbon was less than that of PI/SiO2 with 20% silica because the smaller carbon particle diameter resulted in the more phonon-particle surface scattering.
Keywords: Powder compaction, sintering, Flash method, effective thermal diffusivity, porosity.