SOLAR SELECTIVE COATING HAVING HIGHER THERMAL STABILITY USEFUL FOR HARNESSING SOLAR ENERGY AND A PROCESS FOR THE PREPARATION THEREOF

摘要

The present invention provides an improved solar selective multilayer coating having higher thermal stability and a process for the preparation thereof. Solar selective coatings having higher thermal stability are useful in solar steam generation, solar steam turbines to produce electricity and also on automobile engine components. In the present invention, a tandem stack of three layers of TiAlN, TiAlON and Si₃N₄ is deposited on metal and non-metal substrates at room temperature using a planar reactive direct current magnetron sputtering process. The first two layers function as the absorber and the third antireflection layer further enhances the coating's absorptance. The solar selective coatings were annealed in air and vacuum to test the thermal stability at different temperatures and durations. The coatings of the present invention deposited on copper substrates are stable in air up to a temperature of 625° C. for a duration of 2 hours and exhibit higher solar selectivity in the order of 9-10 and these coating also show no change in the absorptance and the emittance values even after vacuum annealing at 600° C. for 3 hours. Coatings deposited on copper substrates showed no significant degradation in the optical properties even after continuous heating in air at 525° C. for 50 hours. The solar selective coatings of the present invention exhibit high hardness, high oxidation resistance, chemical inertness and stable microstructure.