Coatings for solar applications

Abstract

The present invention discloses coating compositions comprising: I) at least one highly absorbing material selected from the group consisting of ruthenium, iridium and osmium compounds, and mixtures thereof; II) an inorganic glass binder or a precursor thereof; III) a ceramic filler comprising metal oxides, metal powders and mixtures thereof; and V) a liquid organic vehicle. The invention further discloses methods for preparing these coatings and uses thereof in solar applications.

1 . A coating composition comprising:
 I) at least one highly absorbing material selected from the group consisting of ruthenium, iridium and osmium compounds, and mixtures thereof;   II) an inorganic glass binder or a precursor thereof;   III) a ceramic filler comprising metal oxides, metal powders and mixtures thereof; and   IV) a liquid organic vehicle.   
     
     
         2 . The composition of  claim 1 , wherein said highly absorbing material contains one or more Ru compounds. 
     
     
         3 . The composition of  claim 1 , wherein said highly absorbing material ranges from 7 to 30% weight. 
     
     
         4 . The composition of  claim 2 , wherein said Ru compound is selected from RuO 2 , BaRuO 3 , and pyrochlore-like Ru compounds, or mixtures thereof. 
     
     
         5 . The composition of  claim 1 , wherein said inorganic glass binder is selected from boroaluminosilicates of Na, K, Li, Ca, Sr, Mg, Ba, with or without transition metals oxides. 
     
     
         6 . The composition of  claim 1 , wherein said precursor of said silicon dioxide binder is a silicon resin selected from polydimethylsiloxanes, polymethydro-dimethylsiloxane copolymer, vinyl terminated silicone polymers and vinyl backbone silicone polymers. 
     
     
         7 . The composition of  claim 1 , wherein said inorganic glass binder or said precursor thereof ranges from 15 to 55% weight. 
     
     
         8 . The composition of  claim 1 , wherein said liquid organic vehicle is selected from aliphatic alcohols or esters thereof, terpens, terpineols, solutions of resins. 
     
     
         9 . The composition of  claim 1 , wherein the amount of said liquid organic vehicle ranges from 25% weight to 50% weight of the total weight of the composition. 
     
     
         10 . The composition of  claim 1 , wherein the amount of said ceramic filler ranges from 0.1% weight to 30% weight of the total weight of solids dispersed in said composition. 
     
     
         11 . The composition of  claim 1 , comprising from 1 to 99.5% weight RuO 2 , from 5 to 80% weight glass particles, from 0.1% weight to 30% weight of said ceramic filler and from 10% weight to 50% weight of said liquid organic vehicle. 
     
     
         12 . The composition of  claim 1 , wherein said ceramic filler contains from 0.1 to 12.0% weight Co 3 O 4 ; from 0.1 to 12.0% weight Nb 2 O 5 ; and from 0 to 12.0% weight ZrO 2 . 
     
     
         13 . The composition of  claim 12 , wherein said ceramic filler optionally further contains up to 20% silver powder. 
     
     
         14 . The composition of  claim 1 , being in the form of a paste or a paint. 
     
     
         15 . A method of coating a metal substrate, said method comprising applying the coating composition of  claim 1  on a metal substrate, and curing said composition by heating thereof. 
     
     
         16 . The method of  claim 15 , wherein said metal substrate is selected from a solar tower coated parts which are exposed to concentrated solar power, a trough pipe, a stirling engine or a domestic solar collector. 
     
     
         17 . The method of  claim 15 , wherein said metal substrate is composed of a carbon steel, stainless steel, Inconel™ and super alloys. 
     
     
         18 . The method of  claim 17 , wherein said heating is conducted by firing said composition. 
     
     
         19 . The method of  claim 17 , wherein said heating is conducted by naturally curing said composition. 
     
     
         20 . The method of  claim 19 , wherein said heating is conducted at a temperature which is lower than 750° C. 
     
     
         21 . A metal substrate coated by a ceramic coating, said coating comprising at least one highly absorbing material selected from the group consisting of ruthenium, iridium and osmium compounds, and mixtures thereof, crystallized glass, and one or more a ceramic filler comprising metal oxides, metal powders and mixtures thereof. 
     
     
         22 . A solar absorber coated by a ceramic coating, said coating comprising at least one highly absorbing material selected from the group consisting of ruthenium, iridium and osmium compounds, and mixtures thereof, crystallized glass, and one or more a ceramic filler comprising metal oxides, metal powders and mixtures thereof.