Effects of sample holder characteristics on thermal diffusivity measurement using the laser flash method

The laser flash method is commonly adopted to measure the thermal diffusivity of solid material since its advantages, such as a wide measuring range of thermal diffusivity, a small amount of samples, a high measuring temperature, and so on. However, the sample holders used by this method are limited and costly, which seriously affects the convenience and economy of this method. So, in order to develop and design more kinds of sample holders, it is necessary to study the effects of sample holder characteristics on measuring results. A transient flow and heat transfer calculation model was developed to analyse effects of pulse energy, pulse time, laser beam area, protective gas flow and sample holder materials on the thermal diffusivity measurement. It is found that the temperature increase of the sample upper surface ∆T obviously increases with pulse energy, pulse time and laser beam area increasing, but the half heating up time t₅₀ slightly decreases with theses parameters increasing. ∆T and t₅₀ are independent to the volume flow rate of protective gas. The heat transfer process and mechanism between sample and holders with various materials were analysed. The heat loss of samples depends on the heat conduction and radiation between sample and holder, the heat convection and radiation from sample to protective gas. The thermal conductivity, specific heat and emissivity of holder materials can affect the heat conduction and radiation between sample and holder slightly. So the ∆T and t₅₀ are nearly independent to the holder material properties. Based on these conclusions, a new SUS310 holder was made, and the thermal diffusivity of a sample was experimentally measured using the new holder. As a result, the measuring error is less than ±3%.