Enhancing the long-term solar absorptance of ceramic particles through spinel coatings by resonance acoustic mixer

Abstract

The use of solid particles as direct heat absorbance and storage media promises enhanced storage densities in concentrated solar power (CSP) technologies [1]. Spherical particles based on bauxite-type raw materials, commonly referred as proppants, are state-of-the-art for particle receivers of concentrated solar power plants [2]. Despite several beneficious properties such as high thermal shock resistance, sphericity, heat capacity, proppants exhibit a significant decrease in solar weighted absorptance after thermal exposure [3,4]. Moreover, due to the scattering chemical composition of the raw materials, end-properties may exhibit drastic changes among various batches, which affects in turn their efficiency in CPS applications [5]. In the scope of EU H2020 CompassCO2 project, novel particle compositions were developed with reproducible and enhanced properties. Beyond new particles development, surface modification of the proppants and these new iron oxide-based particles were studied in order to enhance long-time solar weighted absorptance with structural stability. In this work, we present a novel dry coating process, utilizing a resonance acoustic mixer to deposit a commercial deep-black pigment powder on the ceramic particles surface followed by heat treatment and reaction-bonding. Particles were analyzed in as-received condition and after coating in terms of their phase components, microstructure, abrasion resistance and solar absorptance in a comparative manner, emphasizing the possible outperformance of spinel-coated particles in long-term CSP operation. Moreover, depending on the chemical composition of the particle, pigment composition and sintering process were modified and coating mechanisms were discussed.