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 0.01 to 0.1 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> can be studied. The system comprises a heat reaction chamber on a mass scale with mounted ultra-wideband (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 modelled 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 systems is used to study calcination of limestone, i.e. the chemical decomposition of CaCO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> to CaO and CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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 be used also for other mineral compounds and other types of materials.