Aluminum Corrosion in Slightly Alkaline Sodium Sulfate Solutions at Different Hydrostatic Pressures

The effect of variable SO₄^{− −}concentrations (10⁻² to 10⁻¹ M) in slightly alkaline solutions (pH 8.2) on aluminum corrosion has been studied at different hydrostatic pressures (1, 100, and 300 atm). The solution temperature was 20 C, and it contained ~8 ppm of dissolved oxygen. It was observed that SO₄^{− −} ions have an inhibiting effect on aluminum corrosion for the entire pressure interval. At 10⁻² M Na₂SO₄ concentration, the aluminum corrosion rate increases as the hydrostatic pressure increases. This increase is attributed to the preferential formation of aluminum hydroxide in the oxidized film, which is more soluble at 300 atm than at atmospheric pressure and is therefore less protective. At higher SO₄^{− −} concentrations, the aluminum corrosion rate does not seem to be markedly affected by an increase in hydrostatic pressure.