Absorption surface of solar collector

A selective absorption surface of a solar collector comprising a coating surface of metal oxide at a thickness of 500 - 2,000 A on the substrate having a mirror-like surface, said substrate surface having a roughness of Ra of less than 0.07 .mu. or Rz of less than 0.2 .mu. determined according to the method of ISO recommendation R 468, said metal oxide consisting of those of 0.001 - 0.15 wt % of C, 0.005 - 3.00 wt % of Si, 0.005 - 10.00 wt % of Mn, 11.00 - 30.00 wt % of Cr and 0.001 - 5.00 wt % of at least one additional element selected from the group comprising N, Cu, Al, V, Y, Ti, Nb, Ta, U, Th, W, Zr, and Hf, optionally, 0.75 - 5.00 wt % of Mo and the balance being Fe and possessing properties of high energy absorption factor at a wave length of 0.3 - 2.5 .mu.m and low energy radiative factor at a wave length of 3 - 50 .mu.m.

A selective absorption surface of a solar collector comprising a coating surface of metal oxide at a thickness of 500 - 2,000 A on the substrate having a mirror-like surface, said substrate having a roughness of Ra of less than 0.07 .mu. or Rz of less than 0.2 .mu. determined according to the method of ISO recommendation R 468, said metal oxide consisting of those of 0.001 - 0.15 wt % of C, 0.005 - 3.00 wt % of Si, 0.005 - 10.00 wt % of Mn, 11.00 - 30.00 wt % of Cr, 0.005 - 22.00 wt % of Ni, and 0.001 - 5.00 wt % of at least one additional element selected from the group comprising N, Cu, Al, V, Y, Ti, Nb, Ta, U, Th, W, Zr and Hf, optionally, 0.75 - 5.00 wt % of Mo and the balance being Fe and possessing properties of high energy absorption factor at a wave length of 0.3 - 2.5 .mu.m and low energy radiative factor at a wave length of 3 - 50 .mu.m.

A process for manufacturing the selective absorption surface of the solar collector, in which the stainless steel having a mirror-like surface having a roughness of Ra of less than 0.07 .mu. or Rz of less than 0.2 .mu. determined according to the method of ISO Recommendation R 468, and the metal composition comprising;

• 0.001 - 0.15 wt % of C, 0.005 - 3.00 wt % of Si, 0.005 - 10.00 wt % of Mn, 11.00 - 30.00 wt % of Cr, 0.005 - 22.00 wt % of Ni, optionally 0.75 - 5.00 wt % of Mo, and the balance being Fe, is chemically oxidized in an acidic bath consisting of 150 - 800 g/l of sulfuric acid and a compound selected from the class consisting of 100 - 400 g/l of sodium, 100 - 400 g/l of potassium bichromate or 40 - 700 g/l of chromium trioxide, at the temperature of 50.degree. C to the boiling point, a dipping time of 3 - 40 minutes to form the oxide film at a thickness of 500 to 2,000 A.