Measurement of the Thermal Diffusivity of Glass at High Temperatures

Abstract

Abstract The effective thermal diffusivity of a glass sample is extracted at different temperatures using a modified Angstrom’s method. A modulated CO2 laser beam (λ = 10.6 μm) with a Gaussian profile is incident on one surface of the sample. This wavelength couples well to the silicate phonon modes and is strongly absorbed by the glass (an optical penetration depth of less than 5 μm). The opposite surface is observed with a thermal camera. The thermal camera is fitted with a filter to block direct CO2 laser radiation from affecting the measurements. The experiments are performed in the frequency domain with a modulated laser. The amplitude and phase of the temperature on the back surface of the glass slide is determined using a least-square algorithm. In this approach, the laser heat flux can be decomposed to a sinusoidal and constant portion. The steady-state portion heats the glass. The relatively small thickness of the glass slide results in minimal differences in the steady-state temperature. The frequency-dependent amplitude and phase of the back surface temperature are compared to finite-difference conduction models solved in the frequency domain. A 1D model is developed to extract the thermal diffusivity by minimizing the error between the model and experiment. Adjusting the constant offset of the laser allows the material to be heated and the diffusivity estimated at elevated temperatures. The experimental results compare well to literature for fused quartz glass up to 1200 °C.