“…3 shows the reflectance in the sunlight spectral region, the sunlight spectrum is also superimposed for reference.Figure 3Reflectance spectra of samples, compared to dense samples of hafnium and zirconium borides from ref. 41.
…”
We investigate the optical properties of LaB6 – based materials, as possible candidates for solid absorbers in Concentrating Solar Power (CSP) systems. Bulk LaB6 materials were thermally consolidated by hot pressing starting from commercial powders. To assess the solar absorbance and spectral selectivity properties, room-temperature hemispherical reflectance spectra were measured from the ultraviolet to the mid-infrared, considering different compositions, porosities and surface roughnesses. Thermal emittance at around 1100 K has been measured. Experimental results showed that LaB6 can have a solar absorbance comparable to that of the most advanced solar absorber material in actual plants such as Silicon Carbide, with a higher spectral selectivity. Moreover, LaB6 has also the appealing characteristics to be a thermionic material, so that it could act at the same time both as direct high-temperature solar absorber and as electron source, significantly reducing system complexity in future concentrating solar thermionic systems and bringing a real innovation in this field.
“…3 shows the reflectance in the sunlight spectral region, the sunlight spectrum is also superimposed for reference.Figure 3Reflectance spectra of samples, compared to dense samples of hafnium and zirconium borides from ref. 41.
…”
We investigate the optical properties of LaB6 – based materials, as possible candidates for solid absorbers in Concentrating Solar Power (CSP) systems. Bulk LaB6 materials were thermally consolidated by hot pressing starting from commercial powders. To assess the solar absorbance and spectral selectivity properties, room-temperature hemispherical reflectance spectra were measured from the ultraviolet to the mid-infrared, considering different compositions, porosities and surface roughnesses. Thermal emittance at around 1100 K has been measured. Experimental results showed that LaB6 can have a solar absorbance comparable to that of the most advanced solar absorber material in actual plants such as Silicon Carbide, with a higher spectral selectivity. Moreover, LaB6 has also the appealing characteristics to be a thermionic material, so that it could act at the same time both as direct high-temperature solar absorber and as electron source, significantly reducing system complexity in future concentrating solar thermionic systems and bringing a real innovation in this field.
“…Very recently, our group has studied several non-oxide materials belonging to the family of ultra-high temperature ceramics (UHTCs) [5][6][7][8][9][10], showing promising characteristics for solar absorber applications.…”
“…Due to these excellent qualities, borides of early transition metals are considered candidates for aerospace applications, such as engine components and leading edges for hypersonic reentry vehicles. Other prospective uses include concentrated solar thermal absorbers, nuclear fuel cladding, and neutron absorbers . In particular, combined with silicon carbide or carbon fiber as ceramic matrix composites (CMCs), they provide a combination of improved failure tolerance and ablation resistance .…”
The synthesis of early transition nanocrystals using NaBH 4 and the respective metal oxides at atmospheric pressure was studied at temperatures between 400 and 1000°C. Reaction products were analyzed by x-ray diffraction, the crystallite size was determined after Rietveld refinement of diffraction patterns, while the morphology was analyzed by scanning and transmission electron microscopy. For all the investigated systems the lowest temperature to complete the synthesis was 700°C and the reaction occurred in three subsequent steps: (i) decomposition of NaBH 4 , (ii) formation of crystalline ternary species Na-M-O and Na-B-O, (iii) conversion of intermediary species to MB 2 and NaBO 2 . Syntheses carried out at T > 700°C only caused coarsening of the powders. The synthetized boride powders had the morphology of highly agglomerated nanocrystals.
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