Deposition of black chromium coating for solar thermal application

Abstract

Deposition of black chromium on the substrates provides the coating surface as a medium for converting solar energy into thermal energy. This work focused on coating black chromium onto two different substrate materials; zinc and aluminium plates. The optical properties of the coated substrates were tested and analysed. It was found that with duplex coating application, both the zinc and aluminium substrates exhibited absorptivity with more than 0.85 and emittance lower than 0.24. Crack was barely seen on zinc coated sample, but obvious on aluminium coated sample with average coating thickness of 5.382 µm on zinc coated sample and 8.168 µm on aluminium coated sample. Chemical composition analysis showed that chromium was the major element present in the coating with a smaller amount of oxygen element. The deficiency in the optical property value could be attributed to the lack of black colorization due to the low amount of oxygen in the coating with higher quantity of Cr, CrO and Cr2O3.