Corrosion and its mechanism of aluminum in methanol environment

The corrosion of Al (99.99 % in mass) in deaerated methanol with and without H₂O, NaCl, and HCOOH as contaminants was investigated using immersion corrosion tests, potentiodynamic polarization tests, electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). The content of H₂O in deaerated methanol was changed from 0.1% to 30%, that of NaCl from 0% to 0.1%, and that of HCOOH from 0% to 0.1%. The immersion corrosion tests showed that Al did not suffer from corrosion in deaerated methanol containing 0.1-30%H₂O. When 0.1%NaCl was added to methanol containing 0.1-30%H₂O, the corrosion occurred only at 0.1%H₂O. The ElS measurement endorsed that corrosion resistance of Al was higher in methanol containing 30%H₂O than that in methanol containing 0.1%H₂O. In case that 0.1% HCOOH was added, the corrosion occurred only at 30%H₂O. Potentiodynamic polarization curves obtained in deaerated methanol with 0.01-0.1%NaCl showed that pitting potential increased with increasing H₂O content. In this case, the passive region became obvious with increasing H₂O content. The passive films composed of Al₂O₃ and Al(OH)₃ were identified by XPS.