Radiation-selective absorber coating and absorber tube with said radiation-selective absorber coating
The radiation-selective absorber coating for absorber tubes of parabolic trough collectors includes two or more barrier layers ( 24 a, 24 b ); an infrared reflective layer ( 21 ) on the barrier layers ( 24 a, 24 b ); at least one cermet absorption layer ( 22 ) above the infrared reflective layer ( 21 ) and an antireflection layer ( 23 ) above the at least one cermet absorption layer ( 22 ). The two or more barrier layers ( 24 a, 24 b ) include a first barrier layer ( 24 a ) of thermally produced oxide and a second barrier layer ( 24 b ) arranged above it. The second barrier layer ( 24 b ) is a cermet material including at least one oxide compound and at least one metal. The oxide compound is aluminium oxide, silicon oxide, nickel oxide and/or chromium oxide. The metal is molybdenum, nickel, tungsten and/or vanadium. The invention also includes an absorber tube with the absorber coating on it.
1. A radiation-selective absorber coating ( 20 ), in particular for absorber tubes ( 13 ) of parabolic trough collectors ( 10 ), said radiation-selective absorber coating ( 20 ) comprising
at least two barrier layers ( 24 a , 24 b );
an infrared reflective layer ( 21 ) that reflects infrared radiation, said infrared reflective layer ( 21 ) being arranged on said at least two barrier layers ( 24 a , 24 b );
at least one absorption layer ( 22 ) arranged above the infrared reflective layer ( 21 ); and
an antireflection layer ( 23 ) arranged above the at least one absorption layer ( 22 );
wherein the at least two barrier layers ( 24 a , 24 b )comprise a first barrier layer ( 24 a ) and a second barrier layer ( 24 b ) arranged above the first barrier layer, said first barrier layer consisting of a thermally produced oxide;
wherein said second barrier layer ( 24 b ) consists of a cermet material composed of aluminum oxide and molybdenum; and
wherein said second barrier layer ( 24 b ) comprises 20 to 70% by volume of said molybdenum.
2. The absorber coating ( 20 ) according to claim 1 , further comprising at least one adhesion-enhancing layer ( 25 ) arranged between the first barrier layer ( 24 a ) and the second barrier layer ( 24 b ).
3. The absorber coating ( 20 ) according to claim 2 , wherein said at least one adhesion-enhancing layer ( 25 ) is composed of molybdenum.
4. The absorber coating ( 20 ) according to claim 1 , wherein the second barrier layer ( 24 b ) has a thickness of 5 nm to 200 nm.
5. The absorber coating ( 20 ) according to claim 1 , wherein the absorption layer ( 22 ) consists of said cermet material.
6. The absorber coating ( 20 ) according to claim 1 , wherein the infrared reflective layer ( 21 ) comprises gold, silver, platinum or copper.
7. The absorber coating ( 20 ) according to claim 1 , wherein the infrared reflective layer ( 21 ) consists of gold, silver, platinum or copper.
8. The absorber coating ( 20 ) according to claim 1 , wherein the infrared reflective layer has a thickness of 50 nm to 150 nm.
9. The absorber coating ( 20 ) according to claim 1 , wherein the first barrier layer ( 24 a ) is a chromium iron oxide layer.
10. The absorber coating ( 20 ) according to claim 1 , wherein the absorption layer ( 22 ) has a thickness of 60 nm to 140 nm.
11. An absorber tube ( 13 ), in particular for parabolic trough collectors, said absorber tube ( 13 ) comprising a steel tube ( 1 ), on an outer side of which is applied a radiation-selective absorber coating ( 20 ), and wherein said radiation-selective absorber coating ( 20 ) comprises
at least two barrier layers ( 24 a , 24 b );
an infrared reflective layer ( 21 ) that reflects infrared radiation, said infrared reflective layer ( 21 ) being applied on said at least two barrier layers ( 24 a , 24 b b);
at least one absorption layer ( 22 ) arranged above the infrared reflective layer ( 21 ); and
an antireflection layer ( 23 ) arranged above the at least one absorption layer ( 22 );
wherein the at least two barrier layers ( 24 a , 24 b ) comprise a first barrier layer ( 24 a ) and a second barrier layer ( 24 b ) arranged above the first barrier layer, said first barrier layer consisting of a thermally produced oxide;
wherein said second barrier layer ( 24 b ) consists of a cermet material composed of aluminum oxide and molybdenum; and
wherein said second barrier layer ( 24 b ) comprises 20 to 70% by volume of said molybdenum.
12. The absorber tube ( 13 ) according to claim 11 , wherein said radiation-selective absorber coating ( 20 ) comprises at least one adhesion-enhancing layer ( 25 ) arranged between the first barrier layer ( 24 a ) and the second barrier layer ( 24 b ).
13. The absorber tube ( 13 ) according to claim 12 , wherein said at least one adhesion-enhancing layer ( 25 ) is composed of molybdenum.