Anti-Corrosion Coatings Chemicals

Zinc phosphate and its modified versions (zinc aluminum phosphate, zinc molybdate phosphate) are the standard lead-free anticorrosion pigments. For cathodic protection, zinc dust at 80–95% loading in epoxy or silicate binders forms galvanic primers that protect steel even if the coating is scratched.

Liquid bisphenol A/F epoxy with amine or polyamide hardeners forms the backbone of most marine and industrial anticorrosion primers. Epoxy novolac resins with high crosslink density are used for immersion service. Zinc-rich epoxy primers provide cathodic protection for offshore steel structures.

Silane coupling agents (amino or glycidoxy silanes) significantly improve adhesion to metals, especially on clean steel. Adhesion promoters based on phosphate ester chemistry are widely used in waterborne anticorrosion systems. Proper surface preparation (Sa 2.5) combined with suitable wetting agents is equally important.

For C5-M (marine/industrial) corrosivity per ISO 12944, total DFT is 240–320 µm in three coats: zinc-rich epoxy primer (60–80 µm) + epoxy MIO intermediate (100–160 µm) + polyurethane topcoat (60–80 µm). For C3 (urban/industrial), 160–200 µm total is sufficient. Holiday testing (low-voltage wet sponge) and DFT measurement per ISO 19840 verify coverage on every batch.

Solvent-free (100% solids) epoxy tank linings cure with no shrinkage and no entrapped solvent, allowing 500–1000 µm in a single application — preferred for potable water and chemical storage tanks. They require heated airless spray, careful pot-life management, and disciplined surface prep. Solventborne epoxies are more forgiving but limited to thinner coats and not approved for many immersion services.

Micaceous iron oxide (MIO) is a lamellar pigment that aligns parallel to the substrate during film formation, creating a tortuous path that dramatically reduces water and oxygen permeability. MIO-pigmented epoxy intermediate coats at 100–160 µm DFT are standard in heavy-duty C5 systems. MIO grade and particle size are critical — coarse grades (D90 ~120 µm) give the best barrier and adhesion to overcoat.