Determination of thermal conductivity and specific heat by a combined 3ω/decay technique

A technique is presented that allows measurement of both the thermal effusivity and diffusivity of the specimen. It employs the thermal excitation of a sample with a plane-surface heater at frequency ω and the observation of the 3ω thermal response of this metal element. In addition the temperature decay of the surface is observed, after the periodic heating current is switched off. Using this technique, the temperature dependence of the thermal conductivity and the specific heat of fused silica have been determined over a wide temperature range. For measurements on electrically conducting solids a technique for preparation of a dielectric insulating magnesiumoxide (MgO) film has been developed. A theoretical model is discussed, that allows to investigate not only bulk materials, but layered structures, also. Applying this model, the thermal effusivity of the upper polymethylmetacrylate (PMMA) layer of a PMMA-aluminum system and the effusivity of the substrate in a MgO stainless-steel system has been measured.