Kinetics Of Anodic Process Research Articles

The Effect of Chemiadsorbed Layers of Nitrilotris–Methylenephosphonate Complexes of Lead(II) with Bridging and Chelate Coordination on the Electrochemical Behavior of a Steel 20 Surface. Thermochemical Induction of Secondary Inhibition

The effect of the chemiadsorbed layers of two lead(II) complexes of nitrilotris–methylenephosphonic acid, differing from one another in coordination of the Pb(II) atom, on the corrosion-electrochemical behavior of a Steel 20 surface in neutral aqueous medium with natural aeration, after deposition of the adsorption layers of the complexes and their heat treatment in air, was investigated. The adsorption layer of the complex with a bridging structure weakly retards the anodic dissolution of steel, and the heat treatment has almost no effect on the protective effectiveness. The adsorption layer of a complex with a chelate structure at medium temperatures also has a weak effect on the kinetics of anodic process; however, the change of the structure of the surface layer after heat treatment at 300°C results in a sharp decrease in the anode current and to refining of the steady-state corrosion potential. The conclusion was drawn that heat treatment induces chelate decomplexation and results in secondary inhibition of the surface of steel by products of the thermochemical transformation.

ELECTROCHEMICAL PROCESSES ON DISPERSE GRAPHITE ELECTRODES IN HNO3 SOLUTIONS

The mechanism and kinetics of anodic processes on a dispersed graphite electrode are investigated by a potentiodynamic method. Variation of the reversal potential in the anode zone on potentiodynamic curves PDC allow to estimate the ratio of the anode and cathode capacities and to determine the coefficient of reversibility of electrochemical reactions. By the degree of reversibility of electrochemical reactions, three potential zones are distinguished: Ist - E ... 1.15 V; II-1,15 ... 1,4V; III -> 1.4B corresponding to the sequential course of the intercalation of graphite with nitrate ions, oxidation of the surface functional groups, the formation of oxide-like graphite compounds. In the zone of potentials I, the maximum reversibility of the anodic process is noted, due to the intercalation-deintercalation process, with the formation of graphite intercalation compounds. Then, a regular decrease in the coefficient of reversibility associated with the occurrence of reactions involving surface oxygen-containing groups and reactions involving oxygen is noticed. This complex of electrochemical processes is accompanied by the formation of graphite intercalation compounds of non-stoichiometric composition and, probably, the oxide of similar structures. The transition to the potential of zone III is characterized by an abrupt decrease in the coefficient of reversibility and the growth of anode currents, which decrease with cycling. Under these conditions, oxidation reactions of the graphite matrix are likely to occur with the formation of CO and CO2. An increase in the rate of irreversible reactions is revealed with a decrease in the concentration of HNO3. In 45% HNO3, the re-oxidation reactions of graphite intercalation compound and the formation of oxide compounds of graphite are significantly accelerated. In 30% HNO3, the highest anode currents of the first cycle from the solutions studied are recorded on a dispersed graphite electrode, and the reversibility of the anode processes is lower than in 60% HNO3. It has been shown that in HNO3 with a concentration of less than 15%, the intercalation of graphite proceeds at a low rate and is accompanied by the surface reactions involving oxygen.For citation:Yakovlev A.V., Yakovleva E.V., Rakhmetulina L.A., Solovyova N.D., Lopukhova M.I. Electrochemical processes on disperse graphite electrodes in HNO3 solutions. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 7. P. 121-128

Effect of nature of side anion on kinetics of anodic processes in ‘Chromispel’ electrolytes developed for chromium plating

Electrochemical chromium plating was carried out in non-standard ‘Chromispel’ electrolytes containing halogenide instead of sulphate anions. The amount of halogenide anions were varied through changing the CrO3∶I− and CrO3∶Cl− ratios within the range from 15∶1 to 35∶1. Some of the electrolytes used were also contained. Cyclic voltammetry and a kinetic method were applied for electrode polarisation determination. A anode, plate cathodes and a saturated calomel electrode were used. It was found that the nature of the side anion affected the values. In the Cl− containing electrolytes they were found twice as high as those in the presence of I− ions. The polarisation curves recorded in the iodide (‘Chromispel-I’) electrolytes were characterised by a single step, while those obtained in the chloride (‘Chromispel-C’) electrolytes were found to have a second step, although not so well resolved. It was suggested that oxygen and chlorine evolution reactions determined the first and the second step, correspondingly. The value of first step activation energy found in the chloride electrolytes was essentially lower than that calculated for the Cl− containing electrolytes which showed evidence that the oxygen evolution was facilitated there. The experimental data obtained indicated that the electrode polarisation in all electrolytes studied was a concentration one but some chemical interactions or electrochemical hindrances could be expected to interfere in the complex anodic process examined.

Анодный процесс на платине в расплаве на основе CaCl2-CaO

Methods potentiostatic polarization and cyclic voltammetry obtained new data on the mechanism and kinetics of anodic processes on platinum in the molten CaCl2-KCl-CaO when 725–775 °C. Given thermodynamic values of potential difference probable total reactions in the range of the studied temperature. Using potentiostatic polarization and cyclic voltammetry obtained new data on the mechanism and kinetics of anodic process on platinum in the molten CaCl2-KCl-CaO when 725–775 °C thermodynamic assessment of the probability of occurrence total reactions during electrolysis melt on the basis of CaCl2-CaO using non-carbon anode. It is shown that at high current densities anodic process takes place mainly in the conditions of slow diffusion of electrically active particles to the anode, and at low densities (up to 10 mA/cm2) to their discharge to the atomic and lecular oxygen is preceded by a stage, which can be associated with adsorption of atoms of oxygen or with the formation of an oxide film on the surface of platinum. To detect the nature of this stage, further research is needed.

Anodic Dissolution of Nickel from the Individual and NiZn Intermetallic Phases in Acidic Sulfate Solutions. II. NiZn Intermetallic Compound

Comparative investigation of the anodic behavior of nickel in its own phase and in NiZn intermetallic compound in acidic sulfate solutions showed that the kinetics of anodic process is the same in both cases, but the partial anodic curve and the passivation potentials of nickel in NiZn phase are shifted in the negative direction by 140 mV. The passivation current is larger, and the dissolution rate of nickel from NiZn phase at the cathodic polarization is higher. The peculiarity of the behavior of nickel in NiZn phase is related to the activity of surface nickel atoms and the increase in the number of active sites of anodic dissolution. It is shown that introducing an electrochemically negative metal into an alloy can, under certain conditions, facilitate the passivation of the latter irrespective of the passivability of the former.

Adsorption kinetics of electrode processes and the mechanism of Kolbe electrosynthesis: Part II: The role of adsorption in processes taking place during electrolysis of carboxylic acid salts

The kinetics of anodic processes taking place during the electrolysis of carboxylic acids in aqueous and non-aqueous solutions on platinum electrodes was studied over a broad potential range. Direct comparison of adsorption and kinetic studies conducted under the same conditions made it possible to draw conclusions on the role of adsorption in the processes taking place on the electrodes. At low potentials in aqueous solutions, the carboxylic acid is shown to undergo destructive oxidation via its alkyl group through a stage of chemisorption, the mechanism of which is analogous to that of electro-oxidation of hydrocarbons on platinum. In aqueous and most non-aqueous solvents, solvent oxidation precedes carboxylic acid anion discharge. The transition from solvent discharge to discharge of the carboxylic acid anion becomes possible owing to an increase in anion adsorption with increasing potential and to the displacement of the solvent molecules from the electrode surface by the adsorbed anions.

Structure of the double layer and kinetics of anodic processes at high potentials

Structure of the double layer and kinetics of anodic processes at high potentials

Kinetics of Anodic Processes on Iron in Alkaline Solutions

Anodic transients of iron in 1N solution have been investigated. After the electrode was maintained at a potential until steady state was achieved, either an anodic potential step or a potential sweep were imposed. For a potential step, the current transient followed the relations and where is the time after the imposition of the potential step. For a potential sweep of sweep rate, λ, a peak current was observed where For the current transients for both potential step and potential sweep polarization were interpreted in terms of the logarithmic growth of an oxide. For , a duplex structure of the oxide layer, mixed oxide/solution, was assumed, where the mixed oxide consisted of Fe(II) and Fe(III) oxy compounds. The current transient behavior was attributed to composition changes in the mixed oxide layer due to diffusion of Fe(II). The experimental results can be satisfactorily interpreted by assuming the existence of the complex ions, , in the oxide film.