Tuning of surface characteristics of composite (WO3/BiVO4) zinc phosphate coatings for industrial applications

The paper reports about a simple strategy for improvements of zinc phosphate coated steel for protection from corrosion with an added advantage of energy saving by enhanced NIR reflectance. In this work, WO3/BiVO4 composite was synthesized by a simple double precipitation method with a tuned composition of 1:4 WBV. Accordingly, the band gap energy, electronic transitions, particle size, stability and color characteristics were effectively controlled to enhance the NIR reflectance efficiency. The weight percentage of the tuned composite (1:4 WBV) additive was optimized to achieve NIR reflectance as high as 64% as compared to the galvanized steel (25%). The addition of an optimum amount (0.2 wt%) of the tuned composite (1:4 WBV) into the phosphating bath could effectively act as a nucleating agent for the formation of zinc phosphate crystals by reducing the activation energy for the formation of new phases resulting in the development of more compact and dense phosphate coating. The resultant coating yielded very high surface coverage and thereby enhanced NIR reflectance (64%), chemical stability and high corrosion resistance (0.0753 mmpy) as compared to other coatings. The developed composite zinc phosphate coating (BP-0.2WBV) with enhanced NIR reflectance can be used as an energy saving 'cool coating' for structural engineering materials such as roofing and automotive body parts.