Nb-NbN Cermet Film as Solar Selective Coating

A new cermet film Nb-NbN, deposited on the stainless steel substrate by direct reactive magnetron sputtering, was reported as solar selective absorptive coating. Some fundamental studies on microstructure and optical properties of the Nb-NbN cermet films were carried out by XRD, EDX, SEM and spectrophotometer. A solar absorptivity of 0.94 and a normal emissivity of 0.16 at room temperature were achieved for the coating. Thermal stability was investigated at 350°C and 500°C and it was observed that the absorptivity was changed in a range from 0.92 to 0.94 and the surface emissivity varied firstly from 0.16 to 0.14 and then increasing to 0.19 when the temperature was increased from room temperature to 350°C and up to 500°C.