Optical constant measurements of solar thermochemical reaction catalysts and optical window

Because of the ultra-high operation temperature in solar thermochemical reactors, radiative transfer accounts for the majority of the total heat transfer. Determining the radiative characteristics of catalysts during solar thermochemical reactions is critical for numerical calculations. Optical constant of material is only determined by the intrinsic properties of materials and not related to the micro-structural morphology. In this study, optical constants of four typical types of metal oxides often used as catalysts during solar thermochemical reactions were obtained by using infrared variable angle spectroscopic ellipsometry. In addition, the variation of optical constant of quartz window with temperature was also investigated using infrared variable angle spectroscopic ellipsometry in the far infrared spectral region. The experimental results indicated that the peak values of the refractive index and extinction coefficient of the optical window decreased with increasing temperature, and the degree of polarization of optical window decreased with increasing temperature and already decreased to 40% at 673 K in the spectral range of 7.2–7.5 μm. In addition, the refractive index and extinction coefficient varied sharply with increasing wavelength for both the catalysts and optical window.