Zinc phosphate

Zinc phosphate (CAS 7779-90-0) is an inorganic salt used primarily as a corrosion-inhibiting pigment in protective coatings and as a surface treatment agent.

Where is Zinc phosphate used?

• Industrial and architectural coatings: anti-corrosion pigment in primers for steel structures, pipelines and metal fabrications
• Concrete and masonry: pH buffer and binder component in phosphate cement systems for construction repair products
• Textile and leather: surface finishing and flame-retardant treatments
• Adhesives and sealants: improved adhesion to metal substrates and extended service life
• It provides rust protection through a passivation mechanism.
• Generally used in combination with other pigments such as ion-exchange silicas.
• Applied to steel surfaces using solutions of zinc phosphate, phosphoric acid, and activators.
• Used as a colourant component in ceramics and ceramic glazes.

Good to know: Unlike traditional heavy-metal inhibitors, it provides rust protection through a passivation mechanism, relevant where regulatory pressure limits chromate or lead-based alternatives.

Formulation notes

• Best performance is obtained at concentrations of 5 to 12% by weight.
• Best performance is obtained at a PVC (pigment volume concentration) between 20 and 40%.

Typical specification

• Lead content is maximum 90 ppm, tested by ICP.
• Low solubility, making it compatible with a wide range of solvent-borne or water-borne systems.
• Available in fine-grain and coarse-grain forms and widely used for equipment exposed to harsh outdoor conditions before powder coating and electroplating.

Regulatory status

• Not classified as hazardous under GHS according to its Safety Data Sheet.

Storage, packaging and handling

• Should be stored in a dry, covered area.

Frequently asked questions about Zinc phosphate

What is the minimum assay of zinc phosphate?

Zinc phosphate has an assay of minimum 98% Zn3(PO4)2.

Does the M Family grade contain soluble salts?

The M Family grade contains no soluble salts that could adversely affect corrosion protection.

On which substrates can zinc phosphate conversion coatings be used?

Zinc phosphate conversion coatings can be used on galvanized steel, electrogalvanized steel, zinc alloy coated steel, aluminum, zinc, cadmium, silver and tin.

Technical content is compiled and updated by the SoleChem product team from public technical sources; the certificate of analysis (COA) governs product-specific specifications.