THE OPTICAL CHARACTERISTICS OF BLACK CHROME SOLAR SELECTIVE FILMS COATED BY THE PULSE CURRENT ELECTROLYSIS METHOD

The application of the pulse current method for black chrome oxide electrocrystallization has been investigated. Plating parameters to optimize the optical properties of the solar selective film included the bath composition, current density, plating time, duty cycle and substrate. The bath composition was 250-300 g/l of chromic acid, 10-15 g/l of propionic acid and 0.5 g/l of a proprietary additive. It has been observed that the black chrome coatings exhibited reasonable optical properties for commercialization when the plating parameters were properly controlled; absorptance (alpha) was 0.944 and 0.94, and emittance (epsilon) was 0.084 and 0.15 for nickel and copper substrates, respectively. Thermal stability of the black chrome coatings was also studied by aging at 300-degrees-C and 450-degrees-C in air for 24 h. This study implies that the pulse current electrolysis method could enhance the optical properties of black chrome solar selective coatings for practical solar applications.