Ultra-black coating due to surface morphology

Abstract

The invention provides a method of producing an ultra-black surface coating, having an extremely high light absorption capacity, on a substrate, such as a metal, ceramic, glass, or plastic, the blackness being associated with a unique surface morphology consisting of a dense array of microscopic pores etched into the surface, as well as the resulting coated substrate. The method involves preparing the substrate for plating with a nickel-phosphorus alloy, as by cleaning and/or activating it, immersing the thus-prepared substrate in an electroless plating bath containing nickel and hypophosphite ions in solution until an electroless nickel-phosphorus alloy coating has been deposited on the substrate, and then removing the substrate, coated with the electroless nickel-phosphorus alloy, from the plating bath and washing and drying it. The dried substrate, coated with the electroless nickel-phosphorus alloy, is then immersed in an etchant bath consisting of an aqueous solution of nitric acid, wherein the nitric acid concentration ranges from a 1:5 ratio with distilled or de-ionized water to concentrated, until the coated surface of the substrate develops ultra-blackness, the blackness being associated with the surface morphology as described above. The resulting substrate, covered with the ultra-black coating is thereafter washed and dried. The ultra-black surface, which has a spectral reflectance on the order of about from 0.5 to 1.0% at wavelengths of light of about from 320 to 2140 nanometers, finds use as a solar collector in the field of solar energy.