IR Radiative Properties of Solid and Liquid Alumina: Effects of Temperature and Gaseous Environment

An infrared spectrometer (spectral range 2–6μm), coupled with a 9μm pyrometer (Christiansen’s wavelength), has been developed to collect timeresolved measurements (32 spectra/s) of the spectral emissivity of alumina droplets (d ≈3 mm) freely cooling in an aerodynamic levitation system from the liquid-to-solid phases [2800→1500 K]. The temperature and nature of the gaseous atmosphere surrounding the droplet (oxidizing/neutral/reducing) are two important parameters affecting the spectral emissivity in the semi-transparent range. Observations are discussed in the framework of the thermal activation and of the chemical iInteractions of alumina with the environment.