Study of the efficacy of Zinc Oxalate Conversion Coating in Protecting Structures Containing Galvanized Steel in Corrosive Environments with ph Variation

Abstract

Corrosion of reinforcing bars in reinforced concrete significantly compromises the durability of structures. In aggressive environments, measures such as galvanization are common, but surface treatments with zinc chromate (Cr6+), a carcinogenic compound, demand safer alternatives. Organic acids, especially oxalic acid, have shown promise in acidic environments, but their efficacy under alkaline conditions is uncertain. This study evaluates the zinc oxalate conversion coating on galvanized steel exposed to corrosive environments with varied pH. Galvanized sheets were treated with oxalic acid [0.1 m] and exposed to alkaline solutions (pH 13) and slightly acidic nacl solutions (ph 6.5). Corrosion resistance tests and analyses of phase formation (XRD) and morphology (SEM) were conducted. Results showed that the zinc oxalate film acts as a physical barrier in acidic conditions but dissolves in alkaline environments, demonstrating ineffectiveness. In NaCl solution, treatment with oxalic acid promotes the formation of a zinc oxalate layer, which accelerates the formation of corrosion products and improves resistance to corrosive attack. In contrast, treatment with an alkaline solution results in a less effective passivation layer, offering limited protective effects and leading to a higher corrosion rate over time.