Effect of Oxygen on the Electrochemical and Corrosion Behavior of Rotating Nickel Disks in H₂SO₄

The electrochemical and corrosion behavior of nickel in deoxygenated and oxygenated H₂SO₄ (pH = 0.3) have been studied by the rotating disk technique. Some preliminary corrosion inhibition results of nickel by benzotriazole(BTA) have also been obtained. In the absence of oxygen, three distinct Tafel regions have been observed for the anodic dissolution of nickel with corresponding Tafel slopes of 0.065, 0.040, and 0.115 V/dec. On the other hand, for nickel in solutions containing benzotriazole, an anodic Tafel region of about three decades with a slope of 0.040 V/dec was obtained. The corrosion potential and corrosion rate of nickel in H₂SO₄ was dependent on the dissolved oxygen content and the hydrodynamic conditions. The corrosion of nickel is controlled by the rate of mass transfer of oxygen above disk rotation rates of 500 rpm and above partial pressures of oxygen of 0.1 atmosphere. For example, the corrosion rates were 0.19 and 7.3 mA/cm² at 500 rpm and 0.1 atmosphere oxygen, and 4500 rpm and 1 atmosphere oxygen, respectively. The corrosion rates were 10 and 0.6 μA/cm² for uninhibited and inhibited (BTA) nickel in deoxygenated 1N H₂SO₄. The limiting diffusion currents for oxygen reduction follow the Levich equation. The diffusion coefficient for oxygen in 1N H₂SO₄ was determined to be 1.6 ± 0.1 × 10⁻⁵ cm²/s.