Hydrothermal surface treatment of 434-L stainless-steel for spectra solar absorber application

Abstract

This work aims to improve the absorption properties of stainless-steel (SS) (434-L) using a hydrothermal treatment method. Therefore, four SS films were prepared at different treatment times, i.e., 1 h, 2 h, 3 h and 24 h. The XRD results revealed the transformation of the crystal structure of the as-received SS from Body-centered cubic (BCC) to Face-centered cubic (FCC) of FeFe2O4 after treatment at 200 °C. The SEM results showed micro-pores distributed across the surface of the films, whereas the AFM results revealed an increment in surface roughness of the films as the duration of the treatment extended. The absorptance (α) of the SS was enhanced from 0.350 to 0.931 after the treatment. This improvement was attributed to surface oxidation and micro-pores distributed across the surface of the films, as confirmed by EDS and SEM results. On the other hand, the high emissivity (0.41) recorded was attributed to the large surface roughness (137.8 nm) of the film. Based on the UV–vis results, the optical reflectance of the film in the short wavelength of the solar spectrum was reduced from ~80 to ~8% resulting in a significant improvement in the absorptance of the SS.