An Ultrawideband System for Measuring the Dielectric Properties of Mineral Compounds in a Heat-Reaction Chamber at High Temperatures

A measurement system for the measurement of microwave dielectric properties of mineral compounds at temperatures up to +1000 °C is presented. It includes the simultaneous measurement of mass and temperature. Samples’ volumes in the range of 0.01–0.1
$\text{m}^{3}$
can be studied. The system comprises a heat reaction chamber on a mass scale with mounted ultrawideband (UWB) radio sensors and temperature probes. The complex refractive index is determined from the UWB signals using a technique with windowing to suppress interference and fitting of a modeled signal to the experimental ones. The developed method is validated by measuring the complex refractive index of water from +82 °C down to +23 °C and comparing with literature values. The system is used to study the calcination of limestone, i.e., the chemical decomposition of CaCO3 to CaO and CO2 when heated up to +1000 °C. The chemical decomposition is clearly seen as a decrease in mass and as significant changes in the complex refractive index. The system could also be used for other mineral compounds and other types of materials.