Role of Al₂O₃ Antireflective Layer on the Exceptional Durability of Mo–Si–N-Based Spectrally Selective Coatings in Air at High Temperature

Abstract

Enhancing the stability of spectrally selective coatings (SSC) at high temperatures in air is necessary to push the concentrated solar power (CSP) technology to the next level. To avoid failures that might not be discovered for years, advanced knowledge of the chemical properties related to the degradation mechanisms with temperature is required. For this purpose, the Mo local environment is investigated here for Mo−Si 3 N 4 and MoSi 2 − Si 3 N 4 nanocomposites SSCs. The atomic short-range order around Mo proves that MoSi 2 is the stable form that appears in high temperature vacuum annealing and that MoO 3 formation is associated with optical degradation in air annealing. Deposition of Al 2 O 3 capping layers with different techniques is found of paramount relevance in the long term performance of MoSi 2 −Si 3 N 4 based SSCs. MoSi 2 −Si 3 N 4 hybrid composite with Al 2 O 3 capping layer shows exceptional functional stability even after 2900 h at 600 °C in air. Antireflective Al 2 O 3 layer synthesized by atomic layer deposition (ALD) shows an extraordinarily efficient protection against oxidation with unprecedented MoSi 2 stability in MoSi 2 −Si 3 N 4 hybrid composite, and optimum long-term optical performance. On the other hand, Al 2 O 3 layer deposited by sputtering blocks the formation of detrimental MoO 3 at 600 °C but allows the formation of MoO 2 in MoSi 2 −Si 3 N 4 for long annealing times which, however, also provides excellent and stable optical functionality related to MoO 2 high stability. KEYWORDS: spectrally selective coating (SSC), concentrated solar power (CSP), solar selective absorbers, high temperature air stability, MoSi 2 −Si 3 N 4 nanocomposite, Al 2 O 3 capping layer, aging

Cu(Mn0.748Ni0.252)2O4/SiO2 Nanoparticle Layers for Wide-Angle Spectral Selectivity and High Thermal Stability

“…It may be due to subjecting the sample to a longer duration (250 h at 500 °C), which alters the thickness of coatings slightly. A similar observation was reported by Céspedes et al after subjecting SS/MoSiO 2 –Si 3 N 4 /Si 3 N 4 /Al 2 O 3 for 2900 h at 600 °C, which altered the optical properties. Additionally, while subjecting our tandem absorber to 250 h, there is a diffusion of metal ions toward the absorber and AR layer, which helps to form a graded SS/(Cu­(Mn 0.748 Ni 0.252 ) 2 O 4 )/SiO 2 SSAC.…”

Temperature- and Angle-Dependent Emissivity and Thermal Shock Resistance of the W/WAlN/WAlON/Al2O3-Based Spectrally Selective Absorber

“…Spectrally selective absorber coatings on the receiver tube of concentrating solar power systems (CSP) should exhibit a high absorptance in the solar spectrum and low infrared emissivity at high temperature, and these properties would enable to realize the capability of spectrally selective absorbers in solar thermal systems. − For an ideal spectrally selective absorber, the absorptance should be ∼0.95 in the solar spectrum with heat loss fraction of 0.05. − The aforementioned criteria indicate that performance of a solar thermal system is limited not only by how efficiently the solar irradiation is captured by the absorber but also by how effectively the absorbed energy can be utilized to heat the fluid flowing through the receiver with minimal heat loss. − This can be determined in terms of the heliothermal efficiency (η), which is calculated by estimating the difference between the absorbed energy by the surface and the radiated energy from the material with respect to total incident concentrated radiation. − The expression of the heliothermal efficiency (η) is the following: where α is solar absorptance, ε­( T ) represents thermal emissivity of the selective coating at a temperature T , σ indicates Stefan–Boltzmann constant, and C and I are concentration factor and solar flux intensity on the earth’s surface (1000 W/m 2 ), respectively.…”

Enabling Highly Enhanced Solar Thermoelectric Generator Efficiency by a CuCrMnCoAlN-Based Spectrally Selective Absorber

“…40 The obvious decrease in absorption at the beginning of the annealing process may stem from the sputtering gas removal in the absorber, and a similar result was reported previously. 41 After that, the SSA becomes more stable (Figure 2d,e). Then, a weather test was carried out to investigate the oxidation resistance of the absorber in practical conditions.…”