High-Temperature Thermal Diffusivity Measurements Using a Modified Ångström's Method With Transient Infrared Thermography

Abstract

This work reports a method to measure thermal diffusivity of thin disk samples at high temperatures (approximately 900–1150 K) using a modified Ångström's method. Conventionally, samples are heated indirectly from the surroundings to reach high temperatures for such measurements, and this process is time-consuming, typically requiring hours to reach stable temperatures. In this work, samples are heated directly in a custom instrument by a concentrated light source and are able to reach high steady-periodic temperatures in approximately 10 min, thus enabling rapid thermal diffusivity characterization. Further, existing Ångström's methods for high temperature characterization use thermocouples for temperature detection that are commonly attached to samples via drilling and welding, which are destructive to samples and introduce thermal anomalies. We use an infrared camera calibrated to 2000 °C for noncontact, nondestructive, and data-rich temperature measurements and present an image analysis approach to process the infrared (IR) data that significantly reduces random noise in temperature measurements. We extract amplitude and phase from processed temperature profiles and demonstrate that these metrics are insensitive to uncertainty in emissivity. Previous studies commonly use regression approaches for parameter estimation that are ill-posed (i.e., nonunique solutions) and lack rigorous characterization of parameter uncertainties. Here, we employ a surrogate-accelerated Bayesian framework and a “no-U-turn” sampler for uncertainty quantification. The reported results are validated using graphite and copper disks and exhibit excellent agreement within 5% as compared to reference values obtained by other methods.