Development of microstructurally tuned zinc phosphate coating containing bismuth-doped iron vanadate (BFV) with high NIR reflectance, corrosion resistance and thermal shielding

The present work investigated the role of bismuth-doped iron vanadate (BFV) in changing the morphology of zinc phosphate (hopeite) crystals in zinc phosphate (ZP) coating to enhance the NIR reflectance, corrosion resistance and thermal shielding performance through a proposed mechanism of altering the crystal grain size and boundary density. The ingression of an optimum amount of BFV particles is shown to modify the crystal morphology of ZP crystals from elongated plate-like structure to uniform flat morphology with a reduction in their crystal size due to the increased number of nucleation sites, remarkable surface coverage and reduced roughness. Tuning the morphology of the developed BFV-ZP coating resulted in NIR reflectance as high as 83 % due to the increase in the number of hopeite crystals with better coverage and subsequent increase in the crystal grain boundaries. The corrosion resistance of the bare ZP coating by barrier protection is well improved by the presence of BFV particles through the effective morphology-controlled fabrication providing a suitable environment for the crystal nucleation of hopeite crystals leading to a length-wise extension of crystals rather than height-wise growth. The as-developed coatings achieved a considerable temperature difference of 13.1 °C in front and behind the coated surface with excellent chemical and photostability. Our findings illustrate the inevitable role of BFV in tuning the morphology and crystal size of the ZP coating to be employed as multifunctional anti-corrosive energy-saving cool coatings.