Patent ID: 7909029

Claim:
An absorber pipe ( 13 ), especially for a parabolic trough collector, said absorber pipe ( 13 ) comprises a steel pipe ( 1 ) with an outer surface and a radiation selective absorber coating on said outer surface of said steel pipe ( 1 ); wherein said radiation selective absorber coating comprises at least two barrier layers ( 24 a , 24 b ) arranged over each other on said outer surface of said steel pipe ( 1 ), an infrared-range reflective layer ( 21 ) arranged on said at least two barrier layers ( 24 a , 24 b ), an absorption layer ( 22 ) arranged over said infrared-range reflective layer ( 21 ) and an antireflection layer ( 23 ) arranged over said absorption layer ( 22 ); and wherein said at least two barrier layers comprise a first barrier layer ( 24 a ) and a second barrier layer ( 24 b ), said first barrier layer ( 24 a ) consists of oxidized components the steel pipe and is made by thermal oxidation of the steel and said second barrier layer ( 24 b ) consists of at least one aluminum oxide compound and said at least one aluminum oxide compound are each of the formula Al x O y layer, wherein x=1 or 2 and y=1, 2, or 3.