Cathodic Potential Region Research Articles

Voltametric behaviour of Ti n O2n−1 ceramic electrodes close to the hydrogen evolution reaction

Voltammetric behaviour close to the hydrogen evolution reaction has been studied on metallic conducting oxides from Ti n O2n−1 series with n = 4–6. The Ti4O7, Ti5O9 and Ti6O11 ceramic electrodes were prepared by the reduction of TiO2 compacts with hydrogen. The current-voltage curves (i, E) were obtained by the potentiodynamic method in aqueous solutions. The electrochemical reaction which occurs in the cathodic potential region is discussed in terms of proton insertion into the Ti n O2n−1 structure. The influence of the porosity of the ceramic electrodes on the electrochemical reaction taking place in this potential region was examined using electrodes of different pore size distributions (different values of roughness factor, r). The influence of the degree of reduction of titanium oxide (n in Ti n O2n−1) on the electrolytic activity for the hydrogen evolution reaction on these oxides was examined.

The effect of potential on stress corrosion cracking of type 316 and type 310 austenitic stainless steels

The stress corrosion cracking (SCC) of type 316 and type 310 austenitic stainless steels has been investigated as a function of applied potential and solution temperature in 0.82 kmol m −3 HCl solution under a constant stress condition. The results of type 316 show that the cracking behavior is different at a potential below and above −90 mV(SHE) in the vicinity of the corrosion potential, −60 mV(SHE). Type 310 exhibits no failure at potentials in the cathodic region. The double logarithmic relation between steady state elongation rate and time to failure becomes a linear function irrespective of potential, solution temperature and the materials, although the slope depends upon the potential region (cathodic and anodic) and solution temperature. This implies that the steady state elongation rate becomes a useful parameter for the prediction time to failure as compared to the potential. On the basis of the results obtained, it is suggested that the cracking of type 316 is caused by hydrogen embrittlement (HE) in the cathodic potential region, while in the anodic potential region that of type 316 and type 310 takes place by SCC subjected to anodic dissolution.

Electrochemical studies of the corrosion of molybdenum electrodes in soda-lime glass metls

The corrosion rate of molybdenum electrodes in soda-lime glass melts was studied by electrochemical measurements. An electrochemical cell with three-electrode equipment and a ZrO 2/air reference electrode was used. Current-potential curves on molybdenum electrodes show an “active” potential region in which the corrosion rate is high and a “passive” region at more anodic potential in which the corrosion rate is much lower. At an extremely cathodic potential region the glass melt is decomposed, and a MoSi x layer is formed as shown by scanning electron microscopy. Cyclic voltammograms in MoO 3 doped soda-lime glass melts at platinum electrodes show that Mo is first oxidized to Mo III and in a second step at a more anodic potential to Mo VI. In the “passive” potential region predominantly Mo VI is formed, and therefore it is assumed that only Mo VI compounds are able to form a protective layer which hinders the dissolution of the molybdenum electrode.

Voltametric behaviour of anodic titanium oxide films close to the hydrogen evolution reaction

The behaviour of anodic titanium oxide films grown at voltages higher than 10 V was studied in the cathodic potential region with respect to the flat-band potential. The influence of the morphology of the oxide film on the electrochemical reaction which takes place in this potential region was examined using oxide films of different thickness electroformed in 0.5 M H 2SO 4. The electrochemical reaction which occurs in the cathodic potential region is discussed in terms of a three-layer model for the titanium oxide film. An overall reaction scheme that would explain the electrochemical phenomena is proposed.

Collision Dissociation Model in Ion Nitriding

Specimens of iron and various steels were ion nitrided in different atmospheres at different ionic energy levels. A collision dissociation model of ion nitriding is proposed, based on the results of ion nitriding tests and calculations of the densities of ions and neutral particles in the cathode potential drop region, incorporating analysis of the collision process and cathode sputtering effects. In ion nitriding there are several possible processes of nitrogen atom migration from gas phase to solid phase, but ion nitriding is achieved primarily by penetration of active nitrogen atoms produced by collision dissociation. The energy conditions of N2, NH3, and N2–H2 in collision dissociation were analysed and the amount of active nitrogen atoms was calculated semiquantitatively. The calculated values were in agreement with the results of the nitriding tests. The effects of H2 on collision dissociation and the heating of the cathode during ion nitriding are also discussed.

ChemInform Abstract: SINTERED IRON(III) OXIDE PHOTOANODE DOPED WITH MOLYBDENUM

AbstractEs werden mit M0 dotierte FezOyPhotoanoden durch Sintem bei 1200°C in Gegenwart von 0.2 Atom‐°/o M002 oder l.O Atom‐% MoO3 hergestellt.

Sintered Iron (III) Oxide Photoanode Doped with Molybdenum

Abstract Sintered iron(III) oxide electrodes which contained about 0.01 atomic% of molybdenum showed considerable improvement in generating anodic photocurrent, particularly, in a cathodic potential region. 0.01 Atomic% doping level was found to be attained by sintering at 1200 °C for 12h using 0.2 atomic% of MoO2 or 1.0 atomic% of MOO3.

Polarography of substituted and bridged bis(cyclopentadienyl)-titanium dichlorides in tetrahydrofuran

1. Substituted and bridged bis (cyclopentadienyl) titanium dichlorides such as Cp2TiCl2, in THF solution at a dropping mercury electrode undergo stepwise irreversible two-electron reduction. 2. In the absence of steric effects the increase in electron density at the Ti atom whan the ring contains alkyl substituants causes first-step E1/2 to shift to the cathodic potential region, and second-step E1/2 to shift to the anodic region. 3. When the ring contains bulky alkyl substituents, or alkylidene bridges that connect the cyclopentadiene ligands, the main influence on E1/2 of the complexes is that of steric effects that facilitate the first reduction step. The rigid alkylidene bridges hinder the second reduction step.

銀の変色，腐食に対するベンゾトリアゾールの抑制効果

The inhibition effects and mechanism of benzotriazole (B.T.A.) on tarnishing and corrosion of silver were studied by means of potentiostatic polarization curves, differential capacity-electrode potential curves, and accelerated testings in H2S and SO2 atmospheres. It was recognized that B.T.A. had little inhibition effects in acidic solutions (pH 2.5), but had great effects in almost neutral solutions; because, B.T.A.-Ag complex was formed on the surface in anodic potential region, and B.T.A. was adsorbed on the surface with lone electron-pairs of N-atoms in cathodic potential region. Silver treated with B.T.A. had an enhanced resistance to tarnishing in H2S atmosphere. It was considered that the prevention would be due to the formation of stable B.T.A.-Ag film on the surface. The galvanic corrosion of silver-plated panels occurred in SO2 atmosphere, leading to the copper base owing to the presence of pores, was much more markedly inhibited by electrolytic treatment than immersion treatment in B.T.A. solution. It was found that the change in the surface coverage (θ) of B.T.A. treated copper conformed to Langmuir's adsorption formula expressed as follows: θ=Km/(1+Km), where K: adsorption constant and m: concentration of B.T.A. Then, the changes of K by immersion treatment and by electrolytic treatment were measured. As the results, a larger value of K was obtained by electrolytic treatment. Therefore, it was considered that the adsorption of B.T.A. on copper through pores became easier by electrolytic treatment.

Electrode processes at mercury in the far cathodic potential region V. The reduction of Ba2+ from aqueous 0.5 M BaCl2, BaI2 and MgCl2

Electrode processes at mercury in the far cathodic potential region V. The reduction of Ba2+ from aqueous 0.5 M BaCl2, BaI2 and MgCl2

Electrode processes at mercury in the far cathodic potential region: V. The reduction of Ba 2+ from aqueous 0.5 M BaCl 2, BaI 2 and MgCl 2

Summary The reduction of Ba2+ at the DME from aqueous solutions of 0.5 M BaCl2, 0.5 M BaI2 and 0.002 M BaCl2+0.5 M MgCl2 has been studied with the aid of impedance measurements combined with d.c. polarograms. Values of the double layer capacity in the non-faradaic as well as in the faradaic region are reported. The electrode process appears to be a single quasi-irreversible electrode reaction. The kinetic parameters are compared with each other and with those of the reaction in 1 M LiCl reported previously. The values of the kinetic parameters are found to be independent of the nature of the supporting electrolyte anion, but dependent on the supporting electrolyte cation.

銅の腐食に対するベンゾトリアゾールの抑制効果

Inhibition effects and mechanism of benzotriazole (B.T.A.) on corrosion of Cu in NaCl, NaClO4, and HClO4 solutions were studied by potentiostatic polarization curves, electrical double layer (e.d.l.), and capacity-electrode potential curves; and by the relation between inhibition efficiency (P) determined by immersion test and degree of surface coverage (Q) obtained from e.d.l. capacity in Cu-NaCl-B.T.A. system. Each of the values of P and Q were measured as functions of B.T.A. concentration (m). The results obtained were as follows: (1) The inhibition effect of B.T.A. in Cu-NaCl system depended on its concentration and electrode potential. In anodic potential region, it was found that B.T.A. had little effects in low concentration, but a good inhibition effect was obtained in high concentration, because B.T.A. -Cu complex was formed and adsorbed on the surface. Whereas, in cathodic potential region, inhibition effects were found in both of low and high concentrations, owing to chemisorption of B.T.A. on the surface with a lone electron-pair of N-atom. (2) However, in Cu-NaClO4 system, it was observed that B.T.A. in low concentration had good inhibition effects in anodic and cathodic potential regions. (3) It was also found that B.T.A. had little inhibition effects in acid solutions such as of HClO4, but it had maximum effects in neutral solutions such as of NaCl and NaClO4. (4) The P-m and Q-m curves obtained in Cu-NaCl-B.T.A. system were typical Langmuir's adsorption isotherms. Proper linear correlation was observed between P and Q, but the correlation coefficient varied according to the range of B.T.A. concentration.

Electrode processes at mercury in the far cathodic potential region: IV. Inhibition of the K + reduction by electrogenerated hydrogen in the case of mixed KCl+HCl solutions

The reduction of K+ from 1 M KCl solution was studied in the presence of HCl at concentrations 0–5×10−3 M. The primary K+ reduction process is reversible at all values of pH within the limitations of the measuring technique. The primary process is accompanied by a parallel irreversible reaction due to an amalgam dissolution reaction. The characteristics of this process were similar at all values of pH to systems previously studied. An increase in the Warburg coefficients of the potassium ion reduction with decreasing pH was observed. The only plausible explanation was considered to be the blocking of the electrode by a product of the hydrogen ion reduction. The parallel amalgam decomposition reaction was similarly impeded. These results are compared briefly with previous studies of hydrogen ion reduction.

Electrode processes at mercury in the far cathodic potential region IV. Inhibiton of the K+ reduction by electrogenerated hydrogen in the case of mixed KCl+HCl solutions

The reduction of K + from 1 M KCl solution was studied in the presence of HCl at concentrations 0–5×10 −3 M . The primary K + reduction process is reversible at all values of pH within the limitations of the measuring technique. The primary process is accompanied by a parallel irreversible reaction due to an amalgam dissolution reaction. The characteristics of this process were similar at all values of pH to systems previously studied. An increase in the Warburg coefficients of the potassium ion reduction with decreasing pH was observed. The only plausible explanation was considered to be the blocking of the electrode by a product of the hydrogen ion reduction. The parallel amalgam decomposition reaction was similarly impeded. These results are compared briefly with previous studies of hydrogen ion reduction.

Electrode processes at mercury in the far cathodic potential region: III. The reduction of K + from KOH solution

The reduction of K + , in 0.88 M concentration, from KOH solution has been studied at the dropping mercury electrode using d.c. polarography and electrode impedance measurements as a function of frequency and electrode potential. The K + reduction is reversible within the limitations of the measuring technique. The K + reduction process was accompanied by a secondary irreversible process as had already been found in neutral aqueous solutions. From the similarity between the results in neutral and alkaline media, it was concluded that water and not the proton is the primary species reduced during the amalgam dissolution process.

Electrode processes at mercury in the far cathodic potential region III. The reduction of K+ from KOH solution

Electrode processes at mercury in the far cathodic potential region III. The reduction of K+ from KOH solution

Electrode processes at mercury in the far cathodic potential region: II. The reduction of Li + and m M Na + from aqueous 1 M LiCl solution

The reduction of Li + ions in 1 M concentration and the reduction of Na + ions in m M concentration in aqueous solution, has been studied at the dropping mercury electrode, using d.c. polarography and electrode impedance measurements, as a function of frequency and electrode potential. The reduction of Li + was found to be quasireversible ( k f sh =0.08±0.04 cm s −1 ). The reduction process was accompanied by an irreversible secondary process as was found previously for K + and Na + reductions. This is attributed to the reaction of the alkali metal amalgam with water. The error in potentiometric measurements of the standard potential of the lithium/lithium ion couple has been calculated (21 mV). The reversibility of the Na + reaction was confirmed by the measurements in m M concentration. The presence of the irreversible reaction due to water reduction was detected over the entire polarographic reduction range of the Na + ion. This irreversible reaction was found to be in agreement with the theory developed for the process in the presence of 1 M alkali metal ions.

Electrode processes at mercury in the far cathodic potential region I. The reduction of K+ and Na+ in neutral aqueous media

Electrode processes at mercury in the far cathodic potential region I. The reduction of K+ and Na+ in neutral aqueous media

Electrode processes at mercury in the far cathodic potential region: I. The reduction of K + and Na + in neutral aqueous media

The reduction of K + and Na + ions at the dropping mercury electrode in 1 M aqueous solutions of halide salts has been studied using d.c. polarography and electrode impedance measurements as a function of frequency and electrode potential. The results confirm that the reductions are reversible but that the primary reduction process is accompanied by an irreversible secondary process which seems likely to be reduction of water. The influence of this process on the analysis of the K + wave is discussed. The implications of the observation of a coupled process are more generally discussed. In particular, it is concluded that potentiometric measurements of the standard potentials of alkali-amalgam/alkali ion redox couples are always in error because a mixed potential is observed instead of the Nernst potential. Two principally different correction procedures are suggested.

Electrode processes at mercury in the far cathodic potential region II. The reduction of Li+ and mM Na+ from aqueous 1 M LiCl solution

Electrode processes at mercury in the far cathodic potential region II. The reduction of Li+ and mM Na+ from aqueous 1 M LiCl solution