zincphosphate

Zinc phosphate refers to an inorganic compound with the chemical formula Zn3(PO4)2. It is a white, crystalline solid that is sparingly soluble in water. In nature, a hydrated form occurs as the mineral hopeite, Zn3(PO4)2·4H2O, illustrating that zinc phosphate can exist both as anhydrous and hydrated species.

Preparation and forms of zinc phosphate are diverse. It can be produced by combining zinc salts (such as zinc oxide or zinc sulfate) with phosphate sources (for example, phosphoric acid or sodium phosphate) in aqueous solution, leading to precipitation of zinc phosphate and its hydrates. In industrial practice, zinc phosphate is especially valued as a conversion coating on iron and steel surfaces, formed by treating the metal in phosphate-containing baths to deposit a protective, porous layer of zinc phosphate crystals. This coating enhances corrosion resistance and provides improved paint adhesion.

Applications and variants. The primary use of zinc phosphate coatings is as a corrosion-resistant primer for steel prior to painting or plating. Neutral and basic zinc phosphate coatings are common variants, with the latter often incorporating additives to boost rust inhibition and coating performance. Beyond coatings, zinc phosphate is involved in various niche chemical formulations, where its low solubility and phosphate content can influence material properties.

Properties and safety. Zinc phosphate is relatively insoluble in water and acids, and it may decompose at high temperatures to oxides and phosphates. Handling should follow standard chemical safety practices; dust may irritate the respiratory tract, and prolonged exposure should be avoided.