Structural, optical, and mechanical properties of cobalt copper oxide coatings synthesized from low concentrations of sol-gel process.

Thin films of Co xCu yO z have been coated on aluminum substrates via sol-gel route using low concentration of copper and cobalt precursors at annealing temperatures in range of 500-650 °C. The coatings were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-Vis-NIR spectrophotometry, and nanoindentation. The XRD analysis in 2 θ-range of 30°-42° revealed that the coatings exhibited low crystallinity of CoCu2O3, CoCuO2, and CuCoO2. The surface bonding structure analyzed using XPS indicated that the coating contained: Cu (tetrahedral Cu+ and octahedral Cu2+), Co (octahedral Co3+, tetrahedral Co2+, and mixed Co2+ and Co3+), and O (lattice, surface, and sub-surface oxygens). The optical properties characterized using UV-Vis-NIR showed that the reflectance spectra of coatings formed a spectrally solar selective absorber profile associated with the interference peaks and the absorption edges around wavelengths of below 1.2 μm. The maximum absorptance ( α = 75.8%) was shown by coating synthesized at 500 °C. The mechanical properties of coatings showed that the increase of annealing temperature increased the coating's hardness ( H) and the elastic modulus ( E) due to the enhancement of the [CoCuO2/CuCoO2]:[CoCu2O3] oxide phases ratio, as the result, an excellent stability of the wear resistance ( H/E) of around ∼0.035 was recorded. [ABSTRACT FROM AUTHOR]