Anodic behaviour of manganese germanide Mn5Ge3 in a sodium sulphate aqueous solution

Germanides are an interesting class of two-component systems which consist of metal and germanium. They are similar in their structure with silicides but have the specific properties. The target of the investigation was finding the main anodic electrochemical behaviour mechanisms for magnesium germanide Mn5Ge3 in an Na2SO4 aqueous solution.Electrochemical behaviour of manganese germanide obtained by Czochralski method was investigated by polarization curves and electrochemical impedance spectroscopy methods and accomplished by microscopy data. Individual manganese and germanium were investigated in the same way for comparison. It was established that in the anodic oxidation process germanium is the potential-determining component. The passivation process associated with the formation of surface oxide films was accomplished by the current density oscillations appearing due to the bad adhesion of oxide film to the surface of the sample, its imperfection and discontinuity. The nature of oxide film formed in the polarization process waspartially established. The dependence of the anodic behaviour of the sample on the sulphate concentration was established: in the diluted solutions the passivation occurs at more positive potentials than in the concentrated. This phenomenon can be explained by the different mechanisms of anodic oxidation in the solutions of different concentrations.

Anodic behaviour of Zn0.5Al doped with molybdenum in acidic, neutral and alkaline media

The paper presents the results of a potentiodynamic study of the anodic behaviour of Zn0.5Al doped with molybdenum in the acidic (0.1 M, pH = 1; 0.01 M, pH = 2; 0.001 M, pH = 3), neutral (0.03, 0.3, 3%, pH = 7) and alkaline (0.001 M, pH = 10; 0.01 M, pH = 11; 0.1 M, pH = 12) media of HCl, NaCl and NaOH electrolytes. In the potentiodynamic mode with an electrode potential sweep rate of 2 mV/s, all Zn0.5Al-Mo samples containing from 0.01 to 1.0 wt% of molybdenum demonstrated a shift in the potentials of corrosion, pitting formation and repassivation. These potentials shift towards negative values in acidic and alkaline media, while shifting to positive values in a neutral medium. It was established that an increase in the concentration of electrolytes led to a shift of all the considered potentials towards negative values in all media - acidic, neutral and alkaline. This dependence is associated with the specific features of the process of anodic dissolution of alloys during the formation of an oxide film on their surface. The significance of the dependence of the stationary potential of free corrosion of alloys on time for establishing the passivity of surfaces in acidic, neutral and alkaline media was shown. It was determined that zinc alloys doped with molybdenum are resistant to pitting corrosion in all the investigated media. This resistivity is particularly high in acidic (0.001 M), neutral (0.03%) and alkaline (0.001 M) media of HCl, NaCl and NaOH electrolytes. The favourable effect of molybdenum on both the anodic behaviour of Zn0.5Al and the overall increase in the corrosion resistance of alloys was demonstrated. In comparison with undoped Zn0.5Al alloys, the corrosion rate of alloys doped with molybdenum (0.01-1.0 wt%) is 2-2.5 times lower. The proposed compositions of Zn0.5Al-Mo alloys can be used as noncorrosive coatings for steel products.

Electrochemical synthesis of new Bi(III) complex by anodic oxidation of Bi in an aqueous solution of 4-toluenesulfonic acid

The anodic behaviour of bismuth in aqueous p-toluenesulfonic acid at three different concentrations and in the potential range from 0 to 1.0 V volt is studied. A significant amount of...

Investigation of anodic behaviour of phenylethers in non-aqueous solvents on platinum and glassy carbon electrodes

Electrooxidation of selected phenylethers was investigated (2-phenoxyethanol, anisole, o-nitrophenyl octyl ether, diphenylether, fenoxycarb) on platinum and glassy carbon electrodes. The chosen solvents were acetonitrile, dimethyl sulphoxide, 1-propanol and mesityl oxide. In acetonitrile, at around 2 V characteristic voltammetric peaks appeared for all compounds. In dimethyl sulphoxide and 1-propanol, no relevant peak appeared due to the high overlapping with solvent electrooxidation. During anodic oxidation of o-nitrophenyl octyl ether and fenoxycarb, a bimolecular reaction takes place predominantly. In mesityl oxide due to its unsaturated bond, identical behaviour was observed for majority of compounds and the differences between the two electrodes are also highlighted in the surface studies. The images made with the aid of an optical microscope showed the formation of islands of products for each substrate after deposition from mesityl oxide.

Pitting Suppression of AISI 316 Stainless Steel Plates in Conditions of Ultrasonic Vibration

Plate heat exchangers are widespread type of equipment that suffers from pitting corrosion in chloride containing solutions. Anodic behaviour of AISI 316 stainless steel was tested in 3.5% NaCl solution in conditions of ultrasound vibration (27 kHz, 10 W). The potentiodynamic sweep, potentiostatic technique, and galvanostatic technique were used coupled with surface morphology investigation after polarization. The pitting potential increased from 0.26 ± 0.02 V/SSCE to 0.42 ± 0.05 V/SSCE, and repassivation potential increased from 0.03 ± 0.01 V/SSCE to 0.18 ± 0.04 V/SSCE when vibration was applied. The anodic current at applied potential in pitting region was two orders of magnitude lower in conditions of ultrasound vibration. A possible mechanism of vibration influence on pitting is proposed, which is the elimination of pit covers from the vibrating surface, vibration-induced electrolyte motion in and out of the pits, and repassivation of active metal inside the pits.