Document Type : Research Article

Authors

• Ajoy K. Saha ¹
• Rajesh Kumar ^{1, 2}
• Belal Usmani ^{1, 2}
• Laltu Chandra ^{1, 3}
• Ambesh Dixit ^{1, 2}

¹ Center for Solar Energy, Indian Institute of Technology, Jodhpur, Old Residency Road, Ratanada, Jodhpur, 342011, India

² Department of Physics, Indian Institute of Technology, Jodhpur, Old Residency Road, Ratanada, Jodhpur, 342011, India

³ Department of Mechanical Engineering, Indian Institute of Technology, Jodhpur, Old Residency Road, Ratanada, Jodhpur, 342011, India

Abstract

We report the development of Fe₃O₄/Cu, and Ni-Fe₃O₄/Cu based spectrally selective coatings for solar absorber applications using two different electrochemical baths. The deposition processes were optimized for both electrochemical baths and it was observed that the controlled introduction of nickel in Fe₃O₄ matrix is important to achieve enhanced solar thermal response. The fabricated coatings were characterized to understand the structural, micro-structural and optical properties, to investigate their phase, chemical composition, surface morphology, thickness and solar thermal properties. Ni-Fe₃O₄ composite coatings exhibited improved adhesion to Cu substrate and allowed better thickness control when compared to Fe₃O₄ structures without Ni. Improved substrate adhesion and optimized thickness resulted in better optical properties for these coatings. The optimized Ni-Fe₃O₄ coatings exhibit maximum spectrally averaged absorptivity (α = 0.87) in the 300 – 900 nm wavelength range, and minimum spectrally averaged emissivity (ε = 0.18) in the 2.5 – 25 µm infrared range at room temperature. For Fe₃O₄ coatings developed on Cu substrates without Ni, maximum absorptance and minimum emittance values obtained were 0.76 and 0.08 respectively. Ni-Fe₃O₄ coating thickness was measured ~32 μm. 

Keywords

• Solar selective coatings
• electrochemical deposition
• absorptance
• emittance
• copper substrate