Chemical Phosphatizing of Carbon Steel

Abstract

Kinetics of formation of phosphate coatings (PCs) on St3 carbon steel in zinc nitrate–phosphate solution (0.65 М Zn²⁺ + 0.3 М \({\text{PO}}_{{\text{4}}}^{{{\text{3}} - }}\) + 1.0 М \({\text{NO}}_{{\text{3}}}^{ - },\) рН 1.95) with various additives has been studied at 25°С. It has been shown that introduction of effective silicon-containing additive to phosphatizing solution and further treatment of phosphate films in aqueous solution containing silicon compounds has provided corrosion-stable PCs on St3. Using mathematical planning of Box–Wilson extreme experiment, preparation of PCs with increased protective ability has been optimized under these conditions.