Suitability of ultra-refractory diboride ceramics as absorbers for solar energy applications

Ultra-refractory diborides are currently studied mainly as thermal protection materials for aerospace and military applications. However, their favourable properties (very high melting points and good thermo-mechanical properties at high temperatures) can be advantageously exploited to increase the operating temperature of thermodynamic solar plants in concentrating solar power systems. This paper reports on the spectral reflectance characterization of hafnium and zirconium diborides containing MoSi2 as secondary phase to evaluate their potential as novel solar absorbers. To assess the spectral selectivity properties, room-temperature hemispherical reflectance spectra were measured from the UV wavelength region to the mid-infrared, considering different levels of porosity for each system. Moreover, for zirconium diboride and hafnium diboride composites containing 10 vol% of MoSi2 sintering aid, the thermal emittance was measured in the 1100-1400 K temperature range. Room temperature spectral characteristics and high temperature emittance were compared to that of a monolithic silicon carbide.