Materials Based on Amorphous Al 2 O 3 and Composite W-Al 2 O 3 for Solar Coatings Deposited by High-Rate Sputter Processes.

In parabolic trough technology, the development of thermally and structurally stable solar coatings plays a key role in determining the efficiency, durability, and economic feasibility of tube receivers. A cermet-based solar coating is typically constituted by a thin film stratification, where a multilayer graded cermet is placed between an infrared metallic reflector and an antireflection filter. This work reports the realization of materials based on Al₂O₃ and W characterized by high structural and chemical stability in vacuum at high temperature, obtained through the optimization of high-deposition-rate processes. Al₂O₃ material, employed as the antireflection layer, was deposited through a reactive magnetron sputtering process at a high deposition rate. Cermet materials based on W-Al₂O₃ were deposited and employed as absorber layers by implementing reactive magnetron co-sputtering processes. An investigation into the stability of the realized samples was carried out by means of several material characterization methods before and after the annealing process in vacuum (1 × 10⁻³ Pa) at high temperature (620 °C). The structural properties of the samples were evaluated using Raman spectroscopy and XRD measurements, revealing a negligible presence of oxides that can compromise the structural stability. Spectrophotometric analysis showed little variations between the deposited and annealed samples, clearly indicating the high structural stability. [ABSTRACT FROM AUTHOR]