INFLUENCE OF SOL-GEL SIO2/TIO2 PROTECTIVE COATINGS ON THE OPTICAL AND THERMAL-PROPERTIES OF NICKEL-PHOSPHORUS SELECTIVE SURFACES

A sol-gel coating was applied to an electroless acid-etched Ni-P spectrally selective surface in order to investigate its influence on the optical and thermal properties of the selective surface. The sol-gel process is a low-temperature preparation of glasses, which is of interest considering the lack of resistance of selective surfaces at the high temperatures generally needed to prepare glasses by the melting technique. The application of a glass coating on the Ni-P layer increases its oxidation resistance at high temperatures and improves the optical and thermal properties of this selective surface for heat treatments in air, up to 400-degrees-C.