The Effect of Crystalline phase of Sodium Molybdate on the Corrosion Inhibition for Carbon Steel

This study is aiming at the effect of crystalline phase of sodium molybdate (Na2MoO4) on the corrosion inhibition of carbon steel. Our TGA result indicated three endothermic events, two of which corresponds to the transition of crystalline phase (i.e. the phase transformation from cubic to orthorrombic phase and from orthorrombic tohexagonal phase) and the last event is owing to the melting of Na2MoO4. Based on the weight-loss measurements, the efficiency of corrosion inhibition performed by Na2MoO4 with different crystalline phase differed as a result of different stacking orientation of MoO42- on the test coupon. For example, the corrosion rate of carbon steel in the presence of MoO42- with orthormobic phase was found at 0.01MPY which was 2.1 times better than that of commercial Na2MoO4 with cubic phase. This result was further supported by the PP (Polarization potential) and EIS (Electrochemical Impedance Spectroscopy) measurements in terms of the thermodynamic and kinetic viewpoints. Therefore, the corrosion inhibition capability of Na2MoO4 could be enhanced after appropriate thermal treatment. Further investigations by XPS are underway for examining the microstructure and chemical composition of MoO42-Fe2+ complex film possibly formed on the test coupon. © 2022, Chinese Mechanical Engineering Society. All right reserved.