The use of ceramic solid particle technology in TES-integrated CSP plants offers a high solar-to-electricity ratio and enhanced storage densities, thanks to their high operational temperatures and wide temperature ranges. Metallurgical slags with composition similar to that of the state-of-art bauxite particles can be used as a sustainable and economical secondary raw material to prepare solid particles. In this study, the as-received state and the high-temperature phase and microstructural changes of two fayalite slags from copper and lead production were elucidated by XRD and SEM/EDS methods in a comparative manner. Solid particles were prepared from slags by the oil dropping method, with subsequent heat treatment. Solar-thermal-application-related functional properties of slag particles, such as heat capacity, absorptance, and thermophysical properties, were evaluated by differential scanning calorimetry (DSC), spectrophotometer, heating microscope, and high-temperature compressive tests, respectively. Owing to the formation of more stable Fe-rich phase components and less amount of glassy phase, copper slag is found to be a more promising secondary resource than lead slag in terms of material and functional properties.

Spherical particles based on bauxite-type raw materials, commonly referred to as proppants, are state-of-the-art for particle receivers of concentrated solar power plants. Particles are heated in a fluidized reactor by focused sunlight and are transported to a heat-exchanger or a storage tank. Therefore, key properties for absorber particles are high solar absorptance and mechanical endurance. Due to their relatively poor content of color-giving transition-metal cations, bauxite-derived proppants show limited solar absorptance, which is even deteriorating by long-term heat exposure. A deep-black Cu, Mn, Fe- pigment with a spinel structure was employed to coat standard proppants in order to improve solar absorptance. The coating process was performed by high-energy, high-speed mixing of proppants and small quantities of spinel powders in a resonant acoustic mixer. A continuous powder coating is achieved by electrostatic attraction between the proppant surface and the coating particles. Consolidation and strong attachment of the coating is achieved by the subsequent sintering beyond the spinel melting temperature. Chemical reaction and bonding between spinel coating and proppant lead to the incorporation of Al, Mg and Ti into the spinel structure. Coated bauxite proppants exhibit a significantly improved, long-term stable solar absorption accompanied by a promising abrasion resistance. The presented coating methodology is considered to be scalable to industrial production.

Polygonal Pt nanoparticles were synthesized using ultrasonic spray pyrolysis (USP) at different precursor concentrations. Physicochemical analysis of the synthesized Pt particles involved thermogravimetric, microscopic, electron diffractive, and light absorptive/refractive characteristics. Electrochemical properties and activity in the oxygen reduction reaction (ORR) of the prepared material were compared to commercial Pt black. Registered electrochemical behavior is correlated to the structural properties of synthesized powders by impedance characteristics in ORR. The reported results confirmed that Pt nanoparticles of a characteristic and uniform size and shape, suitable for incorporation on the surfaces of interactive hosts as catalyst supports, were synthesized. It is found that USP-synthesized Pt involves larger particles than Pt black, with the size being slightly dependent on precursor concentration. Among ORR-active planes, the least active (111) structurally defined the synthesized particles. These two morphological and structural characteristics caused the USP-Pt to be made of lower Pt-intrinsic capacitive and redox currents, as well as of lower ORR activity. Although being of lower activity, USP-Pt is less sensitive to the rate of ORR current perturbations at higher overpotentials. This issue is assigned to less-compact catalyst layers and uniform particle size distribution, and consequently, of activity throughout the catalyst layer with respect to Pt black. These features are considered to positively affect catalyst stability and thus promote USP synthesis for improved properties of host-supported Pt catalysts.

The use of solid particles as direct heat absorbance and storage media promises enhanced storage densities in concentrated solar power (CSP) technologies. The long-term optical performance of those particles, which aim to be operational over years, is crucial. Dry powder coating with a deep black Cu-Mn-oxide pigment in a resonant acoustic mixer and subsequent sintering was employed to improve the long-term optical performance of hematite-rich spherical particles, which aimed to replace the state-of-the-art bauxite proppants. Due to the specific reactivity of the hematite particles, a new strategy using an Al-modified composition of the initial deep black pigment was required. The Al modification diminishes cation diffusion into hematite, allowing the formation of spinel-type Fe-Mn-Cu-Al-oxide coatings with favorable long-term temperature and optical stability. The effect of chemical composition of the coating layer on the coating process mechanism was discussed and the need for an elongated sintering time was noticed to ensure the termination of stable spinel phase formation. The structural and optical measurements revealed the enhancement of the properties of hematite absorber particles through this new modified coating process.

Solid particles as heat absorptances and storage mediums promise enhanced energy storage densities in concentrated solar power/thermal (CSP/T) plants. Employment of metallurgical slags as a secondary precursor material for solid particle preparation is ecologically and economically beneficial. Although these processed wastes, comprised of several oxides, exhibit generally promising high-temperature properties, chemical scattering from batch to batch may result in distinct material and functional properties, which may be an obstacle for their utilization. In this study, a steelmaking slag, LiDonit (LD), produced using a unique controlled slag treatment with high reproducibility is investigated as a candidate material. The aforementioned subsequent unique slag treatment makes LD a very promising and distinguishable secondary raw material for high-temperature applications. The as-received microstructure, phase components, and chemical composition of the LD material were analyzed to understand its material properties and to assess its reproducibility. The as-received LD chunks were transferred into pellets by subsequent milling, gel-casting, and sintering stages to reveal the potential processing routes. The CSP/T-related properties of sintered pellets, such as high temperature stability, heat capacity, and solar absorptance, were also examined to reveal their potential use in CSP/T applications and expand application areas with high added value.

Various commercial proppants originally produced for fracking industry were examined as candidate materials to be used in concentrating solar power (CSP) plants