Coating that selectively absorbs radiation, and method thereof for achieving ambient temperature

Abstract

The instant invention relates to thermal applications. More specifically, it relates to coatings applied on metals, used for harnessing solar radiation or artificial illumination. The object of this coating is to improve the efficacy of solar energy collection, maximizing visible light harnessing and minimizing heat emission in the metal. The procedure including the composition and obtainment of the solar absorbing coating operating in the low and medium temperature range from 25° C. to 300° C., and that can be used in devices generating heat through solar radiation or artificial illumination is described.

1 . A radiation selective absorbing coating comprising:
 a metal substrate; and   at least one metallic layer;   wherein said at least one metallic layer possesses reflecting and anti-reflecting characteristics.   
     
     
         2 . A process for obtaining the radiation selective absorbing coating according to  claim 1 , wherein the process includes the steps of:
 at least one cleaning step;   at least one stripping step;   at least one first rinsing step;   at least one immersion step in an aqueous solution; and   at least one second rinsing step.   
     
     
         3 . The radiation selective absorbing coating according to  claim 1 , wherein said metallic substrate have surfaces of various configurations and textures, wherein the surfaces are selected from the group consisting of smooth, rough, pipes, sheets, wires, filaments, spheres, and mixtures thereof. 
     
     
         4 . The radiation selective absorbing coating according to  claim 1 , wherein said metallic layer is made of chromium oxide. 
     
     
         5 . The process according to  claim 2 , wherein said steps are conducted at room temperature between 20° C. and 40° C. and within a humidity ranging from 0% to 80% relative humidity. 
     
     
         6 . The process according to  claim 2 , wherein in the cleaning step, the metal surface is covered with solvents, the solvents are selected from the group consisting of a mixture of silicates, phosphates, carbonates, sulfates, trichloroethylene, acetone, and mixture thereof. 
     
     
         7 . The process according to  claim 6 , wherein the cleaning step optionally includes acetone. 
     
     
         8 . The process according to  claim 2 , wherein in the first immersion step, the aqueous solution is hydrofluoric acid at a concentration ranging from 0% to 5% plus nitric acid at a concentration ranging from 5% to 15%. 
     
     
         9 . The process according to  claim 8 , wherein in the immersion step the surface to be coated is immersed during 8 to 16 minutes. 
     
     
         10 . The according to  claim 2 , wherein the first and second rinsing steps are conducted with water or with an impurity removing liquid. 
     
     
         11 . The process according to  claim 2 , wherein in a second immersion step, the aqueous solution is chromium acid at a concentration ranging from 200 g/L to 300 g/L and sulfuric acid at a concentration ranging from 350 g/L and 450 g/L and during 9 to 13 hours. 
     
     
         12 . (canceled) 
     
     
         13 . The process according to  claim 2 , wherein the solvents and the solutions are reused. 
     
     
         14 . The radiation selective absorbing coating according to  claim 1 , wherein the radiation selective absorbing coating operates at a low and medium temperature ranging from 25° C. to 300° C. 
     
     
         15 . The radiation selective absorbing coating according to  claim 1 , wherein the coating is designed be applied to a device to generate heat through a solar radiation or an artificial illumination. 
     
     
         16 . The radiation selective absorbing coating according to  claim 1 , wherein the coating is used in thermosolar applications, the thermosolar application are selected from the group consisting of a food industry, production processes, or a textile product including fabric or thread, and patches or inserts in the textile industry. 
     
     
         17 . The radiation selective absorbing coating according to  claim 1 , wherein the coating is use for heating water and liquids where a heat process heat is required. 
     
     
         18 . The process according to  claim 2 , wherein pre-polishing process is not required. 
     
     
         19 . The radiation selective absorbing coating according to  claim 1 , wherein level of absorption in a wavelength from 0.25 to 1.0 μm of 89%. 
     
     
         20 . The radiation selective absorbing coating according to  claim 1 . wherein the coating has a reflectance level in a wavelength from 2 to 15 μm of 21%. 
     
     
         21 . The radiation selective absorbing coating according to  claim 1 , wherein the thickness of the chromium oxide film obtained is 200 nm.