Covering that selectively absorbs visible and infrared radiation, and method for the production thereof

Abstract

The present invention relates to a covering that selectively absorbs visible and infrared radiation, which comprises: (a) a first anti-diffusion barrier layer ( 2 ); (b) an IR-reflecting metallic layer ( 3 ) made from at least one metallic element selected from a group comprising An, Ag, Al, Cu, Ti and Pt; (c) at least a second anti-diffusion barrier layer ( 4 ) formed by oxidation of the layer ( 3 ); (d) a structure that absorbs in the UV-VIS range, which comprises at least a first film ( 5 ) and a second film ( 6 ) made from cermet, which in turn comprises a metallic fraction made from a metal selected from Pt, Cr, Mo, W, Zr, Nb, Ta and Pd, or any alloy thereof, and a ceramic comprising an oxygen-free nitride which is constituted by a metallic oxide in which the metal is selected from aluminium, silicon and chromium; and (e) a dielectric layer that is non-reflecting in the UV-VIS range, which comprises a nitride of at least one metal selected from silicon, aluminium and chromium. A further subject matter of the invention is the method for producing said covering and the use thereof in thermal solar energy collectors.

1 . Covering that selectively absorbs visible and infrared radiation, characterised in that it comprises:
 (a) at least one first anti-diffusion barrier layer ( 2 ) obtained by means of an oxidisation process on the surface layer of the substratum ( 1 ) upon which the covering is deposited;   (b) an IR reflecting metallic layer ( 3 ) located on said first anti-diffusion barrier layer ( 2 ), which comprises at least one metallic element selected from a group consisting of Au, Ag, Al, Cu, Ti and Pt, as well as any combination thereof;   (c) at least a second anti-diffusion barrier layer ( 4 ) located on the IR reflecting metallic layer ( 3 ), where said second anti-diffusion barrier layer ( 4 ) is formed by at least one metallic oxide obtained by means of a passivation process with oxygen on the IR reflecting metallic layer ( 3 );   (d) an absorbent structure in the UV-VIS range, located on said second anti-diffusion barrier layer ( 4 ), comprising at least a first film ( 5 ) and a second film ( 6 ) made of cermet, where said cermet comprises a metallic fraction of at least one metal selected from a group formed by Pt, Cr, Mo, W, Zr, Nb, Ta and Pd or any alloy thereof and a ceramic comprising an oxygen-free nitride of a metal selected from aluminium, silicone and chromium, as well as any combination thereof; and,   (e) an anti-reflecting dielectric layer in the UV-VIS range ( 7 ) located on the absorbent structure in the UV-VIS range, which comprises a nitrite of at least one metal selected from a group formed by silicone, aluminium and chromium, as well as any combination thereof.   
     
     
         2 . Covering according to  claim 1 , wherein the substratum ( 1 ) upon which the covering is located is a glass or metal selected from any kind of steel, copper, zinc or aluminium or any alloy thereof. 
     
     
         3 . Covering according to  claim 1 , wherein the first anti-diffusion barrier layer ( 2 ) comprises at least one oxide of at least one chemical element forming the substratum ( 1 ). 
     
     
         4 . Covering according to  claim 1 , wherein the IR reflecting metallic layer ( 3 ) is between 10 nm and 500 nm thick. 
     
     
         5 . Covering according to  claim 1 , wherein the absorbent structure in the UV-VIS range comprises at least one cermet which is between 10 nm and 500 nm thick. 
     
     
         6 . Covering according to  claim 5 , wherein the cermet comprises molybdenum and silicone nitrite, with a value of the metallic fraction by volume of between 5% and 60%. 
     
     
         7 . Method for obtaining a covering according to  claim 1 , characterised in that it comprises:
 (a) obtaining at least a first anti-diffusion barrier layer ( 2 ) by means of oxidising the surface layer of the substratum ( 1 ), upon which the covering is deposited;   (b) depositing an IR reflecting metallic layer ( 3 ) on said first anti-diffusion barrier layer ( 2 ), wherein said IR reflecting metallic layer ( 3 ) comprises at least one metallic element selected from a group formed by Au, Ag, Al, Cu, Ti and Pt, in addition to any combination thereof;   (c) obtaining at least a second anti-diffusion barrier layer ( 4 ) on the IR reflecting metallic layer ( 3 ) by means of a passivation process with oxygen of the IR reflecting metallic layer ( 3 );   (d) forming an absorbent structure in the UV-VIS range on said second anti-diffusion barrier layer ( 4 ) and   (e) depositing an anti-reflecting dielectric layer in the UV-VIS range ( 7 ) onto the absorbent structure in the UV-VIS range by means of depositing at least one metal selected from a group formed by silicone, aluminium and chromium, in addition to any combination thereof.   
     
     
         8 . Method according to  claim 7 , wherein the absorbent structure in the UV-VIS range is formed on said second anti-diffusion barrier layer ( 4 ) by means of a process in which films formed by at least one metal selected from a group formed by silicone, aluminium and chromium, in addition to any combination thereof are successively deposited, by means of a vapour stage deposition technique in a nitrogen atmosphere, as well as by means of s vapour stage deposition technique in an inert atmosphere of films made of at least one metal selected from a group formed by Pt, Cr, Mo, W, Zr, Nb, Ta Pd and W, in addition to any combination thereof. 
     
     
         9 . Method according to  claim 7 , wherein the absorbent structure in the UV-VIS range mentioned in step (d) is formed by means of preparing a cermet by sequentially depositing a ceramic and at least one metal and repeating the process until the desired thickness is attained. 
     
     
         10 . Method according to  claim 7 , where the anti-reflecting dielectric layer in the UV-VIS range ( 7 ) included in step (e) is deposited by means of a vapour stage deposition technique in a reactive atmosphere, with a partial nitrogen pressure of between 1×10 −5  mbar and 1 mbar and a partial oxygen pressure of less than 1×10 −4  mbar in order to form an oxygen-free nitride. 
     
     
         11 . Method according to  claim 10 , wherein when the metal deposited in step (e) is silicone, the reactive cathode pulverisation is carried out with a partial nitrogen pressure of between 1×10 −3  mbar and 1 mbar, forming a layer of Si x N y , with a y/x relationship of between 1.2 and 1.4, where said layer is between 10 nm and 500 nm thick. 
     
     
         12 . Method according to  claim 7 , where the covering is applied to the external surface of a tube with a roughness Ra comprised between 100 nm and 500 nm made of glass or metal selected from any kind of steel, copper, zinc or aluminium or any combination thereof. 
     
     
         13 . Method according to  claim 7 , where the first anti-diffusion barrier layer ( 2 ) is between 10 and 200 nm thick. 
     
     
         14 . Method according to  claim 7 , where the IR reflecting metallic layer ( 3 ) is between 10 nm and 500 nm thick, being deposited by means of a vapour stage deposition technique. 
     
     
         15 . Method according to  claim 7 , wherein the second anti-diffusion barrier layer ( 4 ) is less than or equal to 2 nm thick. 
     
     
         16 . Method according to  claim 7 , wherein the absorbent structure in the UV-VIS range comprises depositing at least one cermet by means of a vapour stage deposition technique, this cermet being between 10 and 500 nm thick, with a metallic fraction value by volume comprised between 5% and 60%. 
     
     
         17 . Method according to  claim 16 , wherein the metal selected from silicone, aluminium and chromium comprised by the absorbent structure in the UV-VIS range and the anti-reflecting dielectric layer ( 7 ) is deposited when nitrogen is supplied in an oxygen-free environment, corresponding to a partial oxygen pressure of less than 1×10 −4  mbar. 
     
     
         18 . Use of a covering according to  claim 1 , to be deposited on glass or metal supports used in thermal solar energy collectors. 
     
     
         19 . Use of a covering according to  claim 18 , wherein these supports consist of glass tubes or metal tubes selected from copper, zinc and aluminium or any combination thereof, through which a fluid circulates at a temperature of between room temperature and 300° C. 
     
     
         20 . Use of a covering according to  claim 18 , where said supports consist of steel tubes and where the thermal solar energy collectors consist of thermal solar energy parabolic collectors, in which the steel tube is in vacuum conditions with a partial oxygen pressure of less than 1×10 −1  mbar. 
     
     
         21 . Use of a covering according to  claim 20 , characterised in that it comprises a fluid circulating inside said steel tubes at a temperature of between 300° C. and 600° C.