Abstract
The corrosion inhibition of mild steel in acid mine water of pH 2.5 containing ferric and cupric ions with inhibitors such as urea ([NH2]2CO), guanylurea sulfate (C4H12N8O2·H2SO4), benzotriazole (C6H5N3), butylamine (C4H11N), hexadecyl pyridinium chloride (C21H38ClN·H2O), thiourea (CH4N2S), and potassium oxalate (K2C2O4·H2O) was studied. Thiourea and potassium oxalate gave 77% and 93% inhibition, respectively. Thiourea reduced ferric ions in solution and produced a sulfide film that caused hydrogen embrittlement. Corrosion inhibition by potassium oxalate was photosensitive due to the formation of a trisoxalato iron complex followed by photodecomposition to β-ferrous oxalate and its deposition on the steel sample, thereby inhibiting the corrosion of the steel. The mechanism of this first example of photochemical inhibition is postulated.
