Calculate the corrosion current density of a steel metal in contact with a copper metal, given that the corrosion potential of steel and copper are -0.58 V and +0.34 V, respectively. The temperature and pH of the solution are 25°C and 7, respectively. The surface area of the steel metal is 10 cm2 and the copper metal is a large area electrode.

Question

Calculate the corrosion current density of a steel metal in contact with a copper metal, given that the corrosion potential of steel and copper are -0.58 V and +0.34 V, respectively. The temperature and pH of the solution are 25°C and 7, respectively. The surface area of the steel metal is 10 cm2 and the copper

Answer 1

To calculate the corrosion current density of the steel metal in contact with the copper metal, we need to use the mixed potential theory and the Tafel equation. The mixed potential theory states that when two metals are in contact, the potential difference between them drives the corrosion process. The Tafel equation relates the corrosion current density  i_corr  to the potential difference  E  between the two metals.E = E_copper - E_steel = 0.34 V -  -0.58 V  = 0.92 VThe Tafel equation is given by:i_corr = i_0 *  10^E / b_a  - 10^-E / b_c  where i_0 is the exchange current density, b_a is the anodic Tafel slope, and b_c is the cathodic Tafel slope. The values of i_0, b_a, and b_c depend on the specific metals and the solution conditions. For steel in a neutral solution  pH 7  at 25C, typical values are:i_0 = 1 x 10^-6 A/cmb_a = 0.12 V/decadeb_c = 0.12 V/decadePlugging these values into the Tafel equation:i_corr =  1 x 10^-6 A/cm  *  10^0.92 V / 0.12 V/decade  - 10^-0.92 V / 0.12 V/decade  i_corr  0.0002 A/cmThe corrosion current density of the steel metal in contact with the copper metal is approximately 0.0002 A/cm.