Authors: HARSHAN SOUMYA, JACOB PHILIP
Abstract: The dependence of thermal diffusivity/conductivity on thickness for a variety of coatings and free-standing thin metallic plates was measured using a traveling photothermal technique. The selected materials have large differences in terms of their thermal conductivity. Measurements were carried out on coatings prepared on substrates with two widely different values for thermal conductivity to bring out the influence of substrate thermal conductivity on the thermal diffusivity/conductivity of the coating. Thermal diffusivity/conductivity increases exponentially with coating thickness with the value saturating at a definite thickness. The variation follows an empirical relation, which can predict thermal diffusivity of a coating at any thickness in the low thickness regime. In the region where thermal diffusivity increases exponentially with thickness, thermal diffusivity of the coating is lower when the substrate is a better thermal conductor, implying that thermal waves diffuse into substrate causing an overall reduction in thermal diffusivity. However, beyond the saturation thickness the thermal diffusivity is independent of substrate material. Thermal conductivity of coatings as well as thin metallic plates follows analogous variations with thickness and substrate material. The results will help in providing a better theoretical description of heat transport in low dimensional structures.
Keywords: Thermal conductivity, thin plates, coatings, photothermal technique
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