Surface Modification of AISI 316 Stainless Steel by Oxynitrocarburizing for Solar Collector Applications
Abstract
The surface modification of AISI 316 stainless steel was studied using a mixture of cyanate and sodium carbonate salts. This mixture was placed in paste form on previously polished steel substrates. The oxinitrocarburizing treatment was carried out at 580 °C for 5 to 20 minutes by the eutectic mixture paste of sodium cyanate (NaCNO) and sodium carbonate (Na2CO3) salts. Characterization of the materials was carried out using XRD, SEM/EDS, UV/Vis, FT-IR spectroscopy techniques. The oxynitrocarburizing time played an important role in the surface modification of the stainless steel, in terms of the nature of the phases formed in the resulting oxidized and nitrided layers, thickness of both layers and surface optical properties of the treated samples. The development of a thick surface oxidized layer was detrimental for the surface optical properties of the samples. In this sense, a 5 min oxynitrocarburizing treatment produced the best results. The best optical properties obtained at the surface of the steel were an absorptance (α) of 0.90 and an emittance (ε) of 0.1.