Thermal diffusion in thin plates and coatings: in uence of thickness andsubstrate material

Abstract

The dependence of thermal diffusivity/conductivity on thickness for a variety of coatings and free-standingthin metallic plates was measured using a traveling photothermal technique. The selected materials have large differencesin terms of their thermal conductivity. Measurements were carried out on coatings prepared on substrates with two widelydifferent values for thermal conductivity to bring out the in uence of substrate thermal conductivity on the thermaldiffusivity/conductivity of the coating. Thermal diffusivity/conductivity increases exponentially with coating thicknesswith the value saturating at a de nite thickness. The variation follows an empirical relation, which can predict thermaldiffusivity of a coating at any thickness in the low thickness regime. In the region where thermal diffusivity increasesexponentially 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, beyondthe saturation thickness the thermal diffusivity is independent of substrate material. Thermal conductivity of coatingsas well as thin metallic plates follows analogous variations with thickness and substrate material. The results will helpin providing a better theoretical description of heat transport in low dimensional structures.