Spray pyrolytically grown NiAlOx cermets for solar thermal selective absorbers: spectral properties and thermal stability

After deposition of NiAlOx thin films on stainless-steel substrates by the spray pyrolysis technique, various properties of the films were investigated using Fourier transform infrared spectroscopy, UV-visible reflectance spectrophotometry, energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Optical quantities were determined using reflectance spectra in the relevant spectrum region. At first the optimal substrate temperature was selected and then different nickel to aluminium ratios were examined to find the efficient solar absorber. The SEM revealed changes in morphology due to different molar ratios. The XRD of the selected sample showed a mixture of nickel and nickel oxide phases with the strong presence of substrate peaks and without the presence of alumina phase while in the EDX test the peaks corresponding to O, Al and Ni appeared. Long-term thermal stability study was performed by means of performance criterion concept.