Spectrally selective absorbing coating for solar receivers acting in air

A process for implementing a spectrally selective absorbing coating, for receivers acting in air of solar thermal and thermodynamic systems, the process comprising the steps of:

• providing a substrate of the receiver;
• applying a spectrally selective absorbing coating overall or on a portion of a surface of the substrate by PVD deposition techniques,
• wherein a metal layer of a protective structure of the coating consists of an alloy of at least a first and a second metal, the first metal, present in alloy with atomic percentages comprised between 50% and 90%, being selected from the group consisting of:
• W, Mo, Ta, Nb, Ni, Co, Cu, Hf, Fe, Ag, Au, Pt, Pd, Cr, Rh, and the second metal, present in alloy with atomic percentages comprised between 10% and 50%, being selected from the group consisting of:
• Cr, Al, Si, Ti, Zr, said second metal having Gibbs free energy of formation of an oxide thereof lower than that of said first metal, and wherein, the ceramic layer of the protective structure, deposited on said metal layer, consists of a sub-stoichiometric oxide of a metal material selected from the group consisting of:
• Al, Si, alloy of Al and Si, said metal material having Gibbs free energy of formation of an oxide thereof lower than or equal to that of said second metal.