A B S T R A C TThe aim of this work was to demonstrate the feasibility of producing Portland cement clinker upon direct exposure of the raw materials under concentrated solar radiation using the PSA high concentration solar furnace SF40. For this purpose, a short thermal cycle (< 40 min) was devised including 5 min dwell times at temperatures in the range 900-950°C and 1250-1300°C, followed by 10-15 min at 1500-1550°C. The chemical and mineralogical data of the grey clinker produced are encouraging since values of 51.0 ± 6.9% C 3 S, 22.7 ± 5.3% C 2 S, 8.6 ± 0.4% C 3 A and 10.8 ± 0.7% C 4 AF are similar to those observed for conventional clinker used for the production of Portland cement in accordance to EN 197-1 standard. White clinker, in turn, could not be produced by direct irradiation in this setup conditions because of its low absorptance of solar energy.

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Nitriding experiments for powder specimens of Mo and Fe were carried out using a solar furnace SF40 at PSA (Plataforma Solar de Almería) in Tabernas (Spain) in uncracked ammonia NH 3 gas (NH 3 gas with suppressed extent of dissociation by flowing) aiming at determining the range of linear velocity v of NH 3 gas flow to yield higher nitride phases, δ-MoN for Mo and ε-Fe 2 N for Fe. Standard solar exposure duration at a specified reaction temperature T was set to be 60 min over range of v between 1.14 mm•s -1 and 11.4 mm•s -1 . By X-ray diffraction (XRD) analysis, presence of δ-MoN was detected besides γ-Mo 2 N and metallic Mo for Mo powder specimen heated to 900 ºC in NH 3 gas flow at v = 1.14 mm•s -1 but XRD peaks identifiable as δ-MoN became indiscernible when v was increased to 11.4 mm•s -1 . On the other hand, for Fe powder specimen exposed to NH 3 gas flow at v = 1.14 mm•s -1 at T = 500 ºC, remnant metallic α-Fe was detectable by XRD at the down-stream side of the specimen holder but no metallic α-Fe was detected at the up-stream side of the specimen holder suggesting that chemical activity a(N) of N atom in uncracked NH 3 gas tended to decrease along the NH 3 gas flow path on going from the up-stream side to the down-stream side.

Three semi-closed open cell ceramic foams, namely mullite, brown alumina and ceria-based materials, were subjected to thermal cycles by direct concentrated solar irradiation to study their thermal resistance in view of their potential application as photothermal devices, such as volumetric solar absorbers. After cycling, the extent of the damage in the samples was determined by measuring the retained crushing (compressive) strength. The extent of the damage was found to depend on the composition, the applied surface temperature difference (ΔT) of thermal cycling and the temperature gradient across the foams. It was found that the retained crushing strength gradually decreased with an increase in ΔT and was independent of the number of thermal cycles in the range investigated. The ceria foams displayed the poorest thermal shock resistance. Experimental data fit the Gibson-Ashby model for the thermal shock resistance of ceramic foams, for a constant C = 0.65.