Design of high-temperature solar-selective coatings based on aluminium titanium oxynitrides AlyTi1-y(OxN1-x). Part 2: Experimental validation and durability tests at high temperature

Abstract

The durability of two solar-selective aluminium titanium oxynitride multilayer coatings was studied under conditions simulating realistic operation of central receiver power plants. The coatings were deposited by cathodic vacuum arc applying an optimized design concept for complete solar-selective coating (SSC) stacks. Compositional, structural and optical characterization of initial and final stacks was performed by scanning electron microscopy, elastic recoil detection, UV-Vis-NIR-IR spectrophotometry and X-Ray diffraction. The design concept of the solar selective coatings was validated by an excellent agreement between simulated and initial experimental stacking order, composition and optical properties.Both SSC stacks were stable in single stage tests of 12 h at 650°C. At 800°C, they underwent a structural transformation by full oxidation and they lost their solar selectivity. During cyclic durability tests, multilayer 1, comprised of TiN, Al .64 Ti .36 N and an Al 1.37 Ti .54 O top layer, fulfilled the performance criterion (PC) ≤ 5% for 300 symmetric, 3 h long cycles at 600°C in air. Multilayer 2, which was constituted of four Al y Ti 1-y (O x N 1-x ) layers, met the performance criterion for 250 cycles (750 h), but was more sensitive to these harsh conditions. With regard to the degradation mechanisms, the coarser microstructure of multilayer 1 is more resistant against oxidation than multilayer 2 with its graded oxygen content. These results confirm that the designed SSCs based on Al y Ti 1-y (O x N 1-x ) materials withstand breakdown at 600°C in air. Therefore, they can be an exciting candidate material for concentrated solar power applications at high temperature.

High-temperature solar-selective coatings based on Cr(Al)N. Part 1: Microstructure and optical properties of CrNy and Cr1-xAlxNy films prepared by DC/HiPIMS

“…For CrN1.08, the n value increases continuously from n=2.16 at 350 nm to a maximum of 3.38 at ≈1800 nm, reaching a steady-state. The extinction coefficient "k" increases from 0.85 at 350 nm to 1.27 at 1100 nm, and then decreases with the wavelength until 0.54, characteristic of a semiconductor behavior [18,26]. The optical constants match with the trend reported in the literature for a CrN reference [26], although smaller values of n and k are obtained in the whole energy range.…”

“…metallic to covalent), resulting in the variation of the optical properties and electrical resistivity [7,8,[10][11][12][13], as well as improving their mechanical properties and oxidation resistance [14]. In this context, it has been reported that materials as TiNOx (commercially available for mid-temperature SSC [5]) and others materials as TiAlN, TiAlNO, TiAlSiN or NbAlN, display low reflectance and high absorption coefficient in the UV-Vis spectral range, making them excellent candidates to be used as components in mid-and high-temperature SSC [15][16][17][18][19][20][21].…”

Comprehensive microstructural and optical characterization of the thermal stability of aluminum-titanium oxynitride thin films after high temperature annealing in air

“…In this work, two Al y Ti 1-y (O x N 1-x ) thin film samples were analyzed. They are named #1 and #5 according to the notation used in previous works (see Table 2) [27,28]. Samples were grown using only reactive gases (N 2 and O 2 ) without Ar gas assistance.…”

“…The reported work assessed the need of a comprehensive understanding of the chemical bonding and thin film composition in order to properly adjust the final solar selectivity of the stack. The durability of selected multilayers was studied after (i) asymmetric tests of 12 h at 450, 650, and 800 °C and (ii) 900 h of heating-cooling thermal cycles between 300 and 600 °C in air [28]. The designed SSC fulfilled the performance criterion for high-temperature SCC after the long-term thermal cycling between 300 and 600 °C in air.…”

Stress‐Induced Failure Study on a High‐Temperature Air‐Stable Solar‐Selective Absorber Based on W–SiO2 Ceramic Composite

“…[ 26,27 ] The SSAs based on AlyTi 1− y (O x N 1− x ) films using cathodic vacuum arc (CVA) successfully withstood breakdown at 650 °C for 12 h in air. [ 28 ] A novel SSA based on a MoSi 2 −Si 3 N 4 hybrid composite with a Al 2 O 3 capping layer showed exceptional long‐term stability at 600 °C in air. [ 29 ] However, diffusion and oxidation are inevitable in open air atmosphere at high temperature, thus resulting in deterioration in the optical properties of the coatings.…”