Paper published on: Solar Energy Materials and Solar Cells, vol. 109, pp. 8-16 (2013), DOI: 10.1016/j.solmat.2012.10.004 http://www.sciencedirect.com/science/article/pii/S0927024812004710
Suitability of ultra-refractory diboride ceramics as absorbers for solar energy applications Diletta Scitia, Laura Silvestronia, Luca Mercatellib, Jean-Louis Sansc and Elisa Sani*b a CNR-ISTEC,Institute of Science and Technology for Ceramics, Via Granarolo 64, I-48018 Faenza (Italy) b CNR-INO National Institute of Optics, Largo E. Fermi, 6, I-50125 Firenze, Italy b PROMES-CNRS Processes, Materials and Solar Energy Laboratory,7 rue du Four Solaire, 66120 Font Romeu, France * corresponding author: Tel: +39(0)55.23081 Fax:+39(0)55.233775 email
[email protected] Abstract: 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. Keywords: borides; optical properties; emittance; solar absorbers; solar plants; concentrating solar power. 1. Introduction Concentrating Solar Power (CSP) is considered to be one of the most promising and sustainable technologies for electricity production in the future [1]. For thermodynamic sunlight exploitation, the sun radiation must be collected and concentrated upon a receiver [2-7]. The heat is used to produce steam that drives an electricity turbo-generation unit. The ideal sunlight absorber material is spectrally selective against the thermal radiation: it has a low reflectance 1
(ideally approaching zero) at the solar spectrum wavelengths (λ
