Papers by Keyword: Solar Selective Coating

Abstract: In terms of good optical properties and high thermal stability, Mo/Si₃N₄/Mo/Si₃N₄/SiO₂ coatings based on metal/dielectric multilayer structure were adapted to the solar selective coating at high operating temperatures. The coatings exhibited high solar absorptance in the range of 0.924 ~ 0.936 and low thermal emittance of 0.114 ~ 0.118. The coatings deposited on quartz substrates were thermally stable up to 625 °C in air for 2 h, while they were degraded at 650 °C from the characterization of the absorptance and emittance. The degradation of the coatings was mainly due to the oxidation of molybdenum in air, which was confirmed by Raman spectroscopy. Compared with the thermal stability in air, the coatings were much more stable in vacuum under high temperature. The remarkable thermal stability of the Mo/Si₃N₄/Mo/Si₃N₄/SiO₂ coatings in air and in vacuum makes them suitable to be applied at high temperature applications.

Abstract: Activation energy is an important parameter which determines thermal stability of solar selective absorbing coating. In this investigation, a new performance criterion (PC) was defined for solar selective coating according to our modified equation of photo-thermal conversion. Then the activation energy of Cu/stainless steel (SS)-AlN/SiAlO_x solar selective absorbing coating was measured. Cu/SS-AlN/SiAlO_x tandem films were deposited by magnetron sputtering. Accelerated ageing tests were performed on the coating at 500°C and 550°C, under the atmosphere, calculating PC from the reflectance spectrum and measuring the failure time. According to Arrhenius equation, the activation energy and the equivalent life span of Cu/SS-AlN/SiAlO_x tandem film at 400°C were determined to be about 187.4kJ/mol and more than 16260 hours, respectively.

Abstract: Mo thin films were prepared by Mid-Frequency twin target magnetron sputtering as the high reflectivity coating in high temperature solar selective coating. The structure and optical properties of the coatings were studied by X-ray diffraction, scanning electron microscopy and Fourier Transform Infrared Spectrometer and spectrophotometer, the optical constants were inversely calculated by Handley equation. The highest infrared reflectivity of 94% reached at the bias voltage of-150 V and sputtering current 12A of the Mo cathode source, which satisfy the requirement for low thermal emittance solar selective coating applications. The thin films with body centered cubic structure grew along the (110) surface as column crystal, optical constants of Mo thin film were similar with bulk Mo. The thermal emittance of the infrared high reflectance Mo based selective absorber coating can control in 0.15 (400).

Abstract: A new cermet film Nb-NbN, deposited on the stainless steel substrate by direct reactive magnetron sputtering, was reported as solar selective absorptive coating. Some fundamental studies on microstructure and optical properties of the Nb-NbN cermet films were carried out by XRD, EDX, SEM and spectrophotometer. A solar absorptivity of 0.94 and a normal emissivity of 0.16 at room temperature were achieved for the coating. Thermal stability was investigated at 350°C and 500°C and it was observed that the absorptivity was changed in a range from 0.92 to 0.94 and the surface emissivity varied firstly from 0.16 to 0.14 and then increasing to 0.19 when the temperature was increased from room temperature to 350°C and up to 500°C.

Abstract: Based on double cermet layer structure, Mo-Al2O3 cermet solar selective coating was prepared on stainless steel substrate. A solar absorptance of 0.92 and normal emittance of 0.19 at room temperature have been achieved. Vacuum annealing treatment was done and its influences on the solar selective performance was discussed. Absorptance changed between 0.90 and 0.92 under the selected annealing temperature range of 350-800°C, and emittance varied from 0.19 to 0.23 when heated at 650°C. The microstructures before and after annealing process at different temperatures were investigated.