The impedance characteristics of corroding iron was studied in acidic solutions with or without inhibitors, with special attention to the inductive impedance behaviour. The inductive behaviour, at low frequencies, was remarkable only in the sulphuric acid containing propargyl alcohol and it faded out with elapse of time. As expected from the theory of impedance, the corrosion reaction resistance R_cor, which is inversely proportional to the corrosion rate i_cor, was estimated from the impedances at high and low frequency. It was confirmed that the corrosion rates estimated from the impedance measurements and that of weight loss method were well consistent and the a-c corrosion monitor, devised by the authors recently, permitted to record the variation of corrosion rates even in the presence of inhibitors. The applicabilities of the a-c corrosion monitor were described.

View full abstract

Growth and dissolution of anodic oxide films formed on pure molybdenum in deaerated boric-borate solutions of pH 6.48, 8.42 and 10.43 proceed simultaneously at anodic potentials higher than 0.43V (HESS). The composition of anodic oxide films formed on molybdenum in the transpassive region was analyzed by Auger electron spectroscopy (AES) and X-ray photo electron spectroscopy (XPS) combined with argon ion sputter-etching. The uppermost layer (about 1nm) of the anodic oxide films consists of hexavalent Mo (VI) ions, O^2- and OH^- ions, whereas low valent Mo (V), Mo (IV) and Mo (III) ions and O^2- ions exist in the inner layer (20-1000nm) whose composition is uniform in depth. The average valency of molybdenum in the inner layer increases from +3.4 to +5 as the solution pH increases from 6.48 to 10.43. The ratio of film dissolution current density i_D to film growth current density i_O also increases with increasing pH of solution. It seems that the composition of inner layer is determined by kinetic parameters of film growth and dissolution.

View full abstract

Anticorrosive properties of inorganic zinc rich paints were investigated in 3wt% NaCl solution using current interrupter method. Dissolution rate of zinc involved in zinc rich paints was measured to investigate protective properties. Polarization resistance which depends mainly on the dissolution of zinc was constant within the range of 5mV polarization potential. It was found that the amount of white product which was caused by zinc dissolution was related to the magnitude of polarization resistance of steel coated with zinc rich paints. It was also found that the coated steel of which polarization resistance was of the order of 10²Ω to 10³Ω had potential of about -1000mV (vs. SCE) and the one of which polarization resistance was about 10⁴Ω had more noble potential of about -1000mV to about -600mV. Measurement of the dissolution rate of zinc involved in zinc rich paints using current interrupter method was helpful for investigation and formulation of protective zinc rich paints.

View full abstract

Corrosion and erosion problems appear to be encountered in the coal liquefaction processes are briefly reviewed referring to the open literature. Corrosion and erosion have been the major cause of troubles experienced in the operating liquefaction pilot plants in the U. S. A. and therefore have to be overcome primarily. Possible corrosion modes may encompass sulphidation, stress corrosion cracking, naphthenic acid corrosion etc., depending upon the site in the plant. Erosion or erosion/corrosion is the other annoying problem in almost all the components which process solid particle laiden fluid. However, the environment may be very complex and its precise conditions are still to be clarified. Although profound knowledge accumulated in the oil refinery technology can be used to solve, especially, corrosion problems, further effort may be necessary to evaluate materials taking account of the conditions specifically of coal liquefaction.

View full abstract