Optimization of sputtered zirconium thin films as an infrared reflector for use in spectrally-selective solar absorbers

Thermal emittance is an important parameter for the solar thermal collectors as thermal radiative losses from the solar thermal collector increase to the fourth power of temperature. This should be minimized using infrared reflectors in designing spectrally selective absorber coatings for solar thermal applications. The thermal emittance of zirconium (Zr) film as an infrared reflector has been investigated for the use in the spectrally selective absorber. The Zr metallic films are deposited using DC magnetron sputtering process on stainless steel and glass substrates and the deposition process has been optimized to achieve the minimum thermal emittance. The effect of structural, microstructural and surface morphological properties of Zr films is investigated on the emittance of fabricated structures. The X-ray diffraction analysis revealed that the Zr film coatings consist of both cubic and hexagonal Zr crystallographic phase. The optimized deposition time and temperature showed 0.12 and 0.14 emittance values for Zr film coatings on stainless steel and glass substrates respectively. - Highlights: • Zr films for infrared reflector in high temperature spectrally selective coatings • Zr film structure evolution as a function of deposition time and temperature • Impact of residual oxygen on ZrO₂ phase in Zr metallic films & emittance • Emittance ~ 0.12 on stainless steel substrates to minimize the reradiative losses