INVESTIGATION OF AISI 316 STAINLESS STEEL CORROSION IN PERCHLORIC ACID

The authors study the corrosion of AISI 316 stainless steel in 1M perchloric acid at 90 °C, including in the presence of the benzotriazole corrosion inhibitor. Electrochemical experiments were carried out in a three-electrode glass cell with a platinum counter electrode and a saturated silver chloride electrode as a reference electrode. The authors carried out the potentiodynamic measurements at the temperature of (90±2) °C and the potential sweep speed of 1 mV/s; the impedance measurements within the frequency range from 20 kHz to 0.1 Hz at the voltage amplitude of ±10 mV. Cyclic polarization curves show that the cathode direction currents are always lower than the anode direction currents of the potential sweep. Consequently, the curves of anode and cathode directions of the potential sweep are analyzed separately. When analyzing, the authors use the modified Tafel equation, which is linear at any overload that allow determining the corrosion currents more accurately. The study shows that with an increase in the inhibitor concentration, the potentiodynamic curves shift to the cathode side, and the cathode currents decrease more strongly than the anode currents. Therefore, benzotriazole in perchloric acid is an inhibitor of cathodic action, i.e. slows down the cathodic reaction of the perchloric acid anion reduction to chloride ions. The authors identified that benzotriazole inhibits corrosion at concentrations of more than 10^-4 mol/L. At the concentration of 1×10^-3 mol/L, the inhibition efficiency is 33±10 %, and at the concentration of 1×10^-2 mol/L, it is 36±13 %. The inhibiting effect of a benzotriazole molecule in the acidic medium is caused by the possibility of its protonated form to be adsorbed on the metal surface. The protonated form of benzotriazole in acidic medium allows explaining the slow-down of the cathode depolarization reaction as the inhibitor is adsorbed predominantly on metal surface areas charged more negatively. The impedance measurements showed that the corrosion process is modeled by the element parallel circuit with the constant phase shift and corrosion resistance.

AISI 316 stainless steel, perchloric acid, corrosion, electrochemical polarization, benzotriazole corrosion inhibitor