Selective Solar Absorber Having a Thick Corrosion-Resistant Passivation and Thermal Barrier Layer for High Temperature Applications and its Process of Preparation

Abstract

A selective solar thermal absorber capable of operating at high temperatures in a corrosive environment, including, successively stacked, a substrate, a selective solar coating, configured in order to absorb a large part of the solar radiation while re-emitting as little as possible of thermal infrared radiation at high temperatures when it is not corroded, and a corrosion-resistant barrier layer. The corrosion-resistant barrier layer is a thick passivation layer which is thermally stable, which has a low optical refractive index and which is optically transparent to solar radiation, the thickness being adjusted as a function of the operating temperature and of the effectiveness of the third material in order to prevent the diffusion of constituent components of the corrosive environment.

1 . Selective solar thermal absorber capable of operating at high temperatures in a corrosive environment, comprising, successively stacked:
 a substrate composed of a first material,   a selective solar coating composed of a second material,   a corrosion-resistant barrier layer composed of a third material,   characterized in that:   the corrosion-resistant barrier layer is a passivation layer having an optical refractive index of less than or equal to 2 over the range of wavelengths between 0.3 μm and 10 μm and being transparent to the radiation of the solar spectrum for which the wavelength is between 0.3 μm and 2.5 μm,   and in that the thickness of the said corrosion-resistant barrier is greater than or equal to 0.5 μm.   
     
     
         2 . Selective solar thermal absorber according to  claim 1 , wherein said corrosion-resistant barrier layer is also transparent to the radiation for which the wavelength is between 2.5 μm and 10 μm. 
     
     
         3 . Selective solar thermal absorber according to  claim 1 , wherein the said corrosion-resistant barrier layer exhibits a transmittance of greater than or equal to 90%. 
     
     
         4 . Selective solar thermal absorber according to  claim 1 , wherein, the said selective solar coating exhibiting an absorption region and an emissivity region, the cut-off wavelength between these two regions is between 1 μm and 3 μm. 
     
     
         5 . Selective solar thermal absorber according to  claim 1 , in which the third material from which the passivation layer is prepared is included in the group of the oxides, nitrides, oxynitrides and complex oxides. 
     
     
         6 . Selective solar thermal absorber according to  claim 5 , in which the oxides are included in the group formed by alumina (Al 2 O 3 ), silicon oxide (SiO 2 ), zirconium oxide (ZrO 2 ) and boron trioxide (B 2 O 3 ),
 the nitride is silicon nitride (Si 3 N 4 ),   the oxynitrides are included in the group formed by silicon oxynitride (SiON) and aluminium oxynitride (AlON),   the complex oxides are included in the group formed by spinel (MgAl 2 O 4 ), calcite (CaCO 3 ) and mullite (3Al 2 O 3 :2SiO 2 ).   
     
     
         7 . Selective solar thermal absorber according to  claim 1 , wherein the compound or compounds of the corrosion-resistant barrier layer is or are in stoichiometric proportion. 
     
     
         8 . Selective solar thermal absorber according to  claim 1 , wherein the corrosion-resistant barrier layer is
 SiO 2  or SiO x  with x other than 2; or   Al 2 O 3  or Al x O y  with x/y other than 2/3.   
     
     
         9 . Selective solar thermal absorber according to  claim 1 , wherein the corrosion-resistant barrier layer is composed of a composite material formed by a mixture of at least two materials or of a multilayer. 
     
     
         10 . Selective solar thermal absorber according to  claim 1 , wherein the selective coating consists of a stack, starting from the substrate, of thin first, second and third layers of tungsten (W), aluminium nitride (AlN) and titanium/aluminium nitride (TiAlN) and of a fourth layer of aluminium nitride (AlN). 
     
     
         11 . Selective solar thermal absorber according to  claim 9 , wherein the thicknesses of the first, second, third and fourth layers are respectively equal to 200 nm, 50 nm, 25 nm and 70 nm. 
     
     
         12 . A Process for the manufacture of a selective solar thermal absorber capable of operating at high temperatures in a corrosive environment, comprising, carried out successively, the stages comprising:
 providing a substrate of a first material,   depositing, on this substrate, a selective solar coating of a second material,   depositing a corrosion-resistant barrier layer of a third material, wherein   the corrosion-resistant barrier layer is a passivation layer having an optical refractive index of less than or equal to 2 over the range of wavelengths between 0.3 μm and 10 μm and being transparent to the radiation of the solar spectrum for which the wavelength is between 0.3 μm and 2.5 μm,   and in that the thickness of the said corrosion-resistant barrier is greater than or equal to 0.5 μm.   
     
     
         13 . Process for the manufacture of a selective solar thermal absorber according to  claim 11 , wherein
 the deposition stages are carried out using one or more deposition techniques, taken alone or in combination, included in the group of the physical vapour deposition (PVD) techniques, chemical vapour deposition techniques, jet deposition techniques and electrodeposition.