Anodic Direction Research Articles

The electrochemical behaviour of Al in Na-acetate buffers

High purity aluminium is studied in aqueous sodium acetate solution of various pH values, using the potential step method. The current-time curves resulting from the steps are extrapolated to zero time. When these extrapolated values are plotted against the potential, Tafel lines are found both in anodic and cathodic directions. The intersection of the lines are displaced in cathodic direction, indicating that at least two cathodic reactions are taking place. The Tafel slopes were not constant, but changed with changing stabilization potential, pH and stabilization time. An explanation of the results is given, based on a change in the ionic and electronic behaviour of the oxide film formed on the aluminium surface.

The real condition of electrochemically oxidized platinum surfaces: Part I. Resolution of component processes

Summary The problem that 3 peaks can be resolved in the initial stages of Pt surface oxidation below a monolayer of electrosorbed OH (1 e per Pt atom), even on single crystal faces, is examined. A high degree of solution purity is required for this resolution to be observed. Reversibility with respect to these stages in the formation and reduction of the surface oxide layer has been evaluated. The stages of surface oxidation below the OH monolayer limit are related to the geometries of various sub-lattices of OH on the Pt surface rather than to specific stoichiometries of platinum-oxygen surface compounds. It is shown that the cathodic reduction profile can also be resolved into reversible and irreversible components depending on end potential in the anodic direction of polarization and on temperature. Low temperature measurements enable complete resolution of a fast reversible component from an irreversible one, associated with the normal main cathodic peak in Pt surface oxide reduction. The irreversible component arises from a rearranged form of the surface oxide and is formed already to a significant extent well below a monolayer of “PtOH”. It is reduced at less positive potentials and gives rise to the characteristic hysteresis between oxide formation and reduction processes at Pt. The origin of the shape of the i-V profile at Pt and other noble metals is explained. Optical studies by means of ellipsometry show that in pure solutions and with sensitive instrumentation there is no distinguishability, with respect to potential dependence, between the change of optical properties and the change of the surface coverage determined by surface coulometry down to the lowest coverages that can be detected. The surface oxidation and reduction is shown, however, to be optically irreversible with respect to degree of surface oxidation so that a real change of condition of the surface arises between anodic and cathodic directions of polarization.

Effects of Fe3+ on Corrosion of Iron in Acidic Solutions

Polarization curves of a platinum rotating disk electrode in acidic solutions containing Fe2+ and Fe3+ showed typical shapes of the diffusion-controlled process in both anodic and catholic directions. The process is governed by the diffusion of Fe3+ when the catholic reduction of Fe3+ couples the anodic dissolution of Fe because the anodic process is relatively fast under the given condition of the experiment. The corrosion test on iron rotating disks was carried out under various conditions. Some discussions on aqueous corrosion of iron in acidic solution containing Fe3+ as well as dissolved oxygen have been made.

Electrodissolution Kinetics of Iron in Chloride Solutions: Part II . Alkaline Solutions

The anodic behavior of pure iron in alkaline chloride solution was studied by potential sweep and galvanostatic methods. For active dissolution anodic Tafel slopes of 65 and 66 mV/decade were obtained from the galvanostatic and potential sweep experiments, respectively. These values can be interpreted in terms of the Bockris mechanism with Temkin adsorption. Passivation was also observed. The peak current or critical current which appeared in the potential‐current curve obtained by potential sweeps was proportional to the square root of the sweep rate. The potential associated with the peak current varied linearly in the anodic direction as the log of the sweep rate with a slope of 33 mV/decade. The square root of the passivation time obtained from galvanostatic polarization was inversely proportional to the current. These results were interpreted by assuming that passivation occurred when the iron chloride complex attained its solubility limit.

Corrosion under stress of materials composing dental amalgam.

AbstractCorrosion potentials of materials composing dental amalgam have been measured in artificial saliva as the specimens were subjected to an increasing tensile load. Further, tensile tests have been carried out on specimens which had been previously subjected to controlled corrosion.The corrosion potentials of Cu, Ag, Zn, Ag2Hg3, Ag3Sn and finished dental amalgam showed only a slight increase in the anodic direction as the load increased. The potentials of Sn and Sn amalgams, on the other hand, showed a considerable increase.Most of the above results were explained as being a consequence of the rupture and repair of protective films as stress was applied or released. For Sn, however, it was necessary to postulate a complex attack by the corrodant to explain the large potential change.Of the phases of dental amalgam whose tensile strengths were measured after subjection to controlled corrosion, only the γ2 or Sn‐Hg phase was affected. Its strength was lowered by corrosion, whether or not stress was applied.It was concluded that stress, as such, probably is not a direct factor in the corrosion of dental amalgam under oral conditions.

Kinetics and mechanisms of electrochemical reactions on platinum with solutions of iodine—sodium-iodide in dimethylsulphoxide

The kinetics and mechanisms of the iodine and tri-iodide ion reduction and iodide and tri-iodide ion oxidation on platinum have been determined, from a study of the electrochemical kinetic behaviour of DMSO solutions containing an iodine/sodium-iodide ratio greater than one. The likely mechanisms are the same as those recently discussed for the iodine—sodium-iodide solutions in acetonitrile, and all comprise consecutive reaction schemes involving, for the processes in the anodic direction, an ion-plus-atom reaction as rate-determining step, and the reverse reaction for the cathodic processes.

Patterns of soluble proteins and multiple forms of dehydrogenases in amphibian development.

AbstractIn the three amphibian species Bombina variegata, Rana temporaria and Triturus alpestris there is a two‐ to threefold increase in the total content of saline‐soluble proteins during development (prior to feeding). Analyses by polyacrylamide gel electrophoresis revealed the appearance of one or two new protein fractions at gastrulation. Protein bands of transitional occurrence were also observed at various developmental stages. In general, during early embryogenesis protein components with relatively low migrating rates in the anodal direction predominate, whereas in the late larvae fractions of higher mobilities are more abundant.The isozymic patterns of four dehydrogenases in both embryonic and adult tissues of the three amphibians have been analysed. Three molecular forms of lactate dehydrogenase (LDH) are present in Bombina and Triturus, and two in Rana. Triturus and Rana have only a single malate dehydrogenase (MDH), whereas Bombina has two with, however, a clear difference in the mobility of the minor band between embryonic and adult stages. The total number of molecular forms of glucose‐6‐phosphate dehydrogenase (GDH) varies from four in Bombina to two in Rana and Triturus. There are probably four to five isozymes of alcohol dehydrogenase (ADH) of very low activity.Morphogenetic changes of the isozymic patterns include the appearance of one MDH in Bombina and the gradual increases in activities of LDH, GDH and MDH in Rana at gastrulation. After hatching further appearance of ADH isozymes occurs. The new synthesis of one GDH in the late Bombina larvae seems largely associated with the differentiation of heart and fat body. The formation of one MDH in this amphibian is probably delayed until after metamorphosis. A shift in the relative synthesis of isozymes during Bombina development is indicated by the temporary loss of one LDH band at tail‐bud formation and after hatching.

Study of the catalytic and adsorption properties of ruthenium catalysts in the hydrogenation of cyclohexene

1. Ruthenium blacks are comparatively active catalysts of the liquid-phase hydrogenation of cyclohexene. 2. In the presence of catalysts containing ruthenium oxide, the hydrogenation of cyclohexene proceeds with an induction period, which is accompanied by a sharp shift of the potential in the anodic direction, to 400 mV. 3. Charging curves of ruthenium black were obtained. A measurement of the surface according to the double-layer capacitance of ruthenium black is impossible, since together with charging of the surface there is an adsorption of oxygen. More reliable values are obtained when the surface is determined according to the hydrogen region. 4. The bond energies of the surface ruthenium atoms to hydrogen and to carbon at the double bond in the cyclohexene molecule were calculated, and it was demonstrated that the presence of oxides in the catalyst decreases the bond energy of the catalyst to hydrogen and increase the bond energy to carbon.

Kinetics of electrode processes of dissolution and deposition of cadmium

The mechanism of me multi-step electrochemical reactionCd0 ⇌ −e0− Cd+ ⇌ −e0− Cd2+ on a stationary drop of Cd-amalgam in Cd2+ ion solution with and without surface active-agents has been investigated by a galvanostatic method.In the absence of surfactants, the process appears to be a mixed one, accompanied by Cd+-ion disproportionation,2Cd+→Cd2+ + Cd0. so that in both the anodic and cathodic directions the first step of the reaction is the slowest (nc* = 1, na* = 1).When phenol and gelatin are added the process becomes purely electrochemical. The slowest step in the cathodic direction in this process is then nc* = 1, and in the anodic na* = 2. This can be explained by supposing that surfactants in cathodic polarization cause partial blocking of the surface by adsorption, whilst in anodic polarization they inhibit the process of disproportionation.

The causes of the bud eccentricity and the large divergence angles between leaves in Cucurbitaceae

In Cucurbitaceae the axillary buds are eccentric, being much displaced in the anodic or up-hill direction of the genetic leaf spiral: also the angles between successive leaves are unusually large. In the young seedling the leaf spiral and the bud eccentricity both start with the third leaf from the base. If a radial vertical cut of some little depth is made in the apex at the kathodic side of P 1 , the youngest leaf primordium, or of I 1 , the next primordium due to arise, the bud of the P 1 or I 1 is often median or nearly so. Also, if P 1 or I 1 is isolated from the apex with a vertical cut made in the tangential direction and is then extirpated, the bud of the next primordium, I 1 or I 2 , is often subeccentric or nearly median. But shaving down the upstanding part of P 1 flush with the apex, or preventing with shallow cuts P 1 or its bud or both from developing does not diminish the eccentricity of any subsequent bud. It is concluded that an axillary bud is made anodic by some repelling influence, perhaps a hormone, which originates from an older leaf primordium and travels in the anodic direction of the leaf spiral. This influence is interrupted by a cut of moderate depth in the apex, but not by a very shallow cut. The changes in the positions of certain younger leaves due to the formation of median or nearly median buds after these operations strongly support an explanation of the large angles between successive leaves based on a space-filling theory of phyllotaxis. This explanation is that the position in which any leaf n is determined is displaced in the anodic direction by the anodic axillary bud of leaf n — 3, which encroaches from the kathodic side upon the space available for n between n — 3 and n — 2. When the bud of n — 3 is median or nearly so, the position of n is much less far anodic. The repelling influence that makes the buds anodic is further discussed in relation to the course of the conducting strands and other relevant facts.

Short‐Pulse Techniques: I . Kinetics of the Triiodide/Iodide Reaction on a Platinum Electrode in Neutral Solution

The subject application permits observation of polarization changes on an electrode surface in times as short as 25 nanosec. The required miniaturization of the electrolytic cell is achieved by the use of a solion. Short pulses limit electrochemical processes so that only those reactants already present at the metal/solution interface are available for reaction. The perturbation time of iodide ions in the compact double layer was estimated to be . Kinetic relations for polarization build‐up and decay are derived and applied to this redox system for both anodic and cathodic polarization. The variability of the transfer coefficient, α, found by Newson and Riddiford, is confirmed over a wide range in both the anodic and cathodic directions. Kinetic parameters are determined, and the equations based on the Vetter electron transfer step, with some modifications, are verified. Surface coverage determinations indicate that the fraction of available platinum surface covered with adsorbed iodine atoms at zero overvoltage for adsorbed iodine atoms is 0.09. Parameters are also determined for the hydrogen formation reaction at potentials where all of the iodine is reduced. A model for the adsorption of iodine species on the electrode surface is given in order to explain the relationship between surface coverage of these species and the exchange current density.

Electrophoretic behaviour of i-urobilin and stercobilin.

As the urobilinoid pigments i-urobilin and stercobilin are known to contain both basic and acidic groups, we have investigated their electro-phoretic behaviour—yet unstudied—at various pH values. Paper electrophoresis was performed at 120 V., in acetate buffer (a mixture of M/5 acetic acid–sodium acetate buffer and 0.9 per cent sodium chloride solution) in the pH. range less than 6.0, and barbital buffer (Michaelis sodium barbital-sodium acetate-hydrochloric acid buffer) at pH greater than 6.0; the positions of the coloured spots were observed directly during the procedure, but even minute quantities of urobilinoid pigments could be seen at the end of the run after spraying the papers with Schlesinger reagent (saturated zinc acetate solution in ethanol), and observing the green fluorescence in ultra-violet light. With the exception of the sharply defined pH. value of 4.41 at which both urobilinoid pigments became immobile in the electric field, they moved towards the cathode at pH less than 4.41 and toward the anode at pH. greater than this value, the direction of movement, which was the same for both pigments, being dependent only on the pH. However, the rate of movement of these materials differed at various pH. levels: thus in buffers around pH 5.0 and at pH less than 4.41 stercobilin migrated faster toward the anode or cathode, respectively, whereas at higher pH values (8.6) urobilin was found to move faster than stercobilin in the anode direction.

Über künstlich erzeugte laufende Schichten in der Argon‐Niederdruckentladung

AbstractOberhalb der Puppschen Grenzstromstärke iG können durch periodische äußere Störungen passender Frequenz künstlich stationäre laufende Schichten in der positiven Säule der Edelgas‐Niederdruckentladung angeregt werden. Die Schichten laufen aus der Anodenrichtung kommend bis zur Erregungsstelle der Störung. Die Schichtamplituden zeigen dabei je nach Strom und Frequenz einen exponentiellen Anstieg oder Abfall. Dieses Verhalten wurde eingehender für Argon bei 1 Torr untersucht; es wurde die Dispersion und die Amplifikation der künstlichen laufenden Schichten in Abhängigkeit von der Frequenz gemessen. Die sich aus der Dispersion bei der natürlichen Schichtungsfrequenz ergebende Gruppengeschwindigkeit stimmt überein mit der Ausbreitungsgeschwindigkeit der Pekárekschen Schichtungswelle. Hieraus ergibt sich unter Benutzung einer von Pekárek abgeleiteten Beziehung, daß die natürliche Schichtungsfrequenz in gewissen Bereichen der Entladungsparameter ein Viertel der Stoßfrequenz des Elektrons für ionisierende Stöße beträgt. Die Amplifikation zeigt in Nähe der natürlichen Schichtungsfrequenz ein Maximum, das um so größer wird, je näher man der Grenzstromstärke kommt, bis die Amplifikation schließlich bei iG so groß wird, daß Selbsterregung einsetzt.

Investigation of Inorganic Inhibitors for Minimizing Galvanic Corrosion of Magnesium Coupled to Aluminum★

Abstract A fundamental study has been conducted of some inhibitors found to be effective in reducing galvanic corrosion between magnesium alloy AZ31B and aluminum alloy 2024-T3 in saline solutions. The object of the study was to determine the mechanism of protection afforded by the inhibitors, Mg(V03)2, BaK2(CrO4)2, and CaS, singly and in combination. The effect of these inhibitors on the polarization characteristics of the metals was determined with the electrodes isolated in separate compartments, bridging being accomplished with agar-NaC1 bridges. In this group of tests, the polarization potentials, recovery potentials, and corrosion currents were measured, the latter by means of the zero resistance ammeter circuit. Additional tests were made with the electrodes in the same beaker, corrosion currents and corrosion rates being determined under these conditions. Correlation of results from the potential, corrosion current, and corrosion rate data indicates that the Mg(VO3)2 and BaK2CCrO4)2 polarize the aluminum strongly in the anodic direction, thereby reducing the galvanic current and the weight loss of magnesium. Weight loss on aluminum was related to the increase in alkalinity occurring in experiments made in the same beaker. Corrosion current measurements may serve as a useful tool for the determination of effectiveness of inhibitors, but the method should not be used indiscriminately. Practical conclusions should only be drawn from the results obtained in experiments with both metals exposed in the same compartment. 5.8.3

Inhibition of Iron Dissolution in Acid Solutions

The inhibition of iron dissolution from rotating cylinders has been studied in solutions of dilute hydrochloric or perchloric acid with excess nitrate as depolarizer. No better over‐all oxidizing inhibitor than dichromate was found. Complexing and chelating agents greatly improve protection by dichromate in hydrochloric acid although they simultaneously shift the iron potential in the anodic direction. Iron is protected better by dichromate alone in perchloric acid; chelants tend to make the potential more cathodic, but shorten the time of protection.Neocupferron, which forms insoluble chelate salts with iron ions, protects iron for many hours in these solutions. Carbon monoxide was studied as an adsorption inhibitor.

Directional Breakdown in Alkali Halide Crystals

The dc breakdown strength of sodium chloride, shown by von Hippel and Davisson to be independent of orientation at room temperature, also proves to be direction-independent at liquid nitrogen temperature. Experiments at room temperature reveal the existence of three types of breakdown paths: anodic, cathodic, and homogeneous field paths. Anodic paths are initiated by prebreakdown discharges at the anode and are precisely orientated with respect to the crystallographic axes. Cathodic breakdown paths are initiated at point cathodes; their direction dependence differs from that of anodic paths. Finally, in strictly homogeneous fields the paths follow the direction of the field.Measurements on various alkali halides between -160\ifmmode^\circ\else\textdegree\fi{} and 325\ifmmode^\circ\else\textdegree\fi{}C under strictly controlled field conditions confirm the findings of Davisson that the anodic path directions follow the sequence: random \ensuremath{\rightarrow} [100] \ensuremath{\rightarrow} [111] \ensuremath{\rightarrow} [110] with increasing temperature. [111] paths, observed only in sodium salts, are usually accompanied by [110] or [100] paths. While the random \ensuremath{\rightarrow} [100] transition takes place gradually over a temperature range of more than 100\ifmmode^\circ\else\textdegree\fi{}C, the [100] \ensuremath{\rightarrow} [110] transition in potassium and rubidium salts is sharp. With overvoltage this acuteness of the transition disappears, the path directions are shifted towards lower temperature forms and the temperature range of [111] paths in sodium salts is greatly extended. Mechanical deformation has little effect on the path directions. A phonon-Brillouin zone picture, as used by Offenbacher and Callen, but modified for inhomogeneous fields, is in good qualitative agreement with our observations. The electronic-Brillouin zone boundary and the crystalline potential may also influence the path directions.

Corrosion of Aluminum in Potassium Chloride Solutions: I . Effects of Concentrations of and Dissolved Oxygen

The corrosion of aluminum was studied by weight loss measurements in 0.0001N to 1N neutral electrolyte solutions at constant temperature. Oxygen concentration in these solutions was varied over a wide range either by bubbling the gas through the solution or by increasing the partial pressure above the solutions.Weight loss increased with time and increasing oxygen concentration, but decreased with increasing electrolyte concentration. The electrode potential increased in anodic direction with time and increasing electrolyte concentration. Chloride solutions were more aggressive than any other solutions used. Hydrogen peroxide, which might have been a corrosion accelerator in experiments under high oxygen pressure, was found absent in all cases.Results are discussed in the light of the electrochemical theory of corrosion. The relation of oxygen solubility in potassium chloride solutions to corrosion is also discussed.

Studies on the Mechanism of Formation of Optically Active Substances in Living Organisms. Part I. General Consideration on the Stereospecificities of Enzymes and on the Possible Occurence of A New Supposed Enzyme

Anti-corrosion behaviour of rebar embedded in cement mortar containing chloride ions was investigated by electrochemical chloride extraction(ECE). of the initial chloride ions of the cement mortar was fixed to Friedel salts and the soluble chloride ions were successfully extracted by ECE method. Concentration profiles of the chloride ions were estimated by Fick's 2nd law with time and depth, and it was close to the real value. The corrosion potential increased to anodic direction after ECE test, and the corrosion of rebar was reduced as a result of AC impedance spectroscopy.

Influence of Sulphate-reducing Bacteria on the Corrosion Potential of Iron

THE potential assumed by an iron electrode immersed in a culture of sulphate-reducing bacteria has been studied by Hadley1, using a heterotrophic medium. These experiments indicated that the inoculation of the sterile medium, in which the potential of an iron electrode had been allowed to reach a steady value, was followed by a movement of the potential in the anodic (negative) direction. This, in turn, was followed by a rise to a steady value more cathodic (positive) than the initial value in a sterile medium. These changes of potential are shown diagrammatically in the accompanying graph. We feel, however, unable to agree with the explanation given for the first fall of potential, namely, that it is due to bacterial utilization of hydrogen with consequent depolarization of the cathodic areas. Such a depolarization should lead to a potential change in the cathodic (positive) direction, as may be seen from a consideration of the Evans polarization diagram for a corroding system. We also feel unable to accept the statement that the final steady potential(− 0.370 V., normal hydrogen scale) is due to the establishment of the Fe/FeS/S″ equilibrium, on the grounds that this value is too positive for such an equilibrium. It is, in fact, more positive than the standard Fe/Fe++ potential(− 0.441 V.) and would thus imply a concentration of ferrous ions of greater than 1 M. Such a concentration seems impossible in the presence of the large amounts of sulphide produced under heterotrophic conditions.