NICKEL-COBALT SELECTIVE COATINGS BY CONVERSION PROCESS

Abstract

ABSTRACT Black nickel-cobalt coatings have been found to be selective in the solar spectral region and to be more stable than the widely used conventional selective black nickel (NiS-ZnS) coatings. Solar selective black nickel-cobalt coatings formed on zincated aluminium, zinc electroplated aluminium and galvanised iron substrates by conversion process is described. Optical and thermal properties of the coatings are also reported. These coatings show an integrated solar absorptance ( α ) value in the range of 0.90 to 0.94 and a room temperature emittance (e ) in the range of 0.07 to 0.12. The effect of various deposition parameters and substrate preparation on the optical properties and microstructure has been reported. The plating parameters of various coatings have been determined, which yield the optimum optical and thermal properties of the final selective coatings. The thermal stability of the coatings as a function of annealing temperature and time, and the effect of thermal treatment on the optical...