Journal of Applied Electrochemistry

Vitkova, St.; Kjuchukova, M.; Raichevski, G.

doi: 10.1007/BF01016891pmid: N/A

Optimum conditions have been established for the electrodeposition of amorphous fe-P alloys from sulphate electrolytes, containing complex-forming additives (glycine and oxalic acid) and sodium hypophosphite. It was shown that the increase of pH, current density and glycine content in the plating solution leads to a decrease of the amount of phosphorus in the Fe-P alloy. The cathodic current yield decreases with the increase of glycine concentration in the electrolyte. Small amounts of Cu2+ and Mn2+ act as brighteners. Sodium hypophosphite exerts a depolarizing effect on the alloy formation process. This effect is more pronounced at low hypophosphite concentrations and low cathodic current densities (CCD). The measurement of the cathodic potential during the deposition of the investigated alloy provides no evidence for a concentration change of phosphorus in the electrodeposited layers. No qualitative alterations of the surface morphology of the amorphous coatings studied have been established as the composition of the alloy and the plating conditions are changed.

Holze, Rudolf; Luna, Ana-Maria

doi: 10.1007/BF01016892pmid: N/A

The electrochemical oxidation of formic acid HCOOH at porous PTFE-bonded platinum-carbon electrodes in acidic electrolyte has been studied using the AC-impedance method. A reaction sequence based on known details of this process was transferred into an equivalent circuit which was used to simulate successfully the measured impedance data. The results confirm earlier data obtained with smooth platinum electrodes and allow, for the first time, a correlation between the electrode overpotential and the contribution of the various reaction steps. Further improvements of the porous electrode based on these results are suggested.

Yudi, L.; Baruzzi, A.; Solis, V.

doi: 10.1007/BF01016893pmid: N/A

High material yields were obtained in the indirect electrochemical reduction of 7,7-dibromobicyclo-[4-1-0]heptane (dibromonorcarane) to give the corresponding monobromo derivative in an ethylene chloride/water emulsion. The reducing agent was Cr(II) generated by current controlled electrolysis of aqueous chromic chloride at a silver cathode. The effect of the concentration of Cr(II) and the temperature was studied. At 0.1 M Cr(II) and at 40° C the best results were obtained (90% yield).

López Teijelo, M.; Vilche, J.; Arvia, A.

doi: 10.1007/BF01016894pmid: N/A

The voltammetric behaviour of vitreous carbon/chemically precipitated silver hydroxide layer and silver/electrochemically formed silver oxide layer electrodes are compared. As the former type of electrode is free from silver substrate contributions during the oxidation-reduction cycles (ORC) the voltammetric data indicate the occurrence of soluble Ag(I) species in the gel-like silver hydroxide matrix. Soluble species can be formed during the ORC as a consequence of AgOH formation at the early stages of the oxidation and reduction processes. Nucleation and growth of new phases produce a non-homogeneous layer structure and a decrease in the amount of active material participating in the ORC under preset conditions.

Tilak, B.; Fitzgerald, S.; Hoover, C.

doi: 10.1007/BF01016895pmid: N/A

A generalized current efficiency equation was derived from material balance considerations to estimate the caustic current efficiency in ion exchange chlor-alkali membrane cells taking into account the presence of NaHCO3, Na2CO3, and NaOH in the feed brine. The validity and the accuracy of this equation was established by comparing the ‘gas analysis’ results with the data obtained from caustic collection measurements. It is also shown that this general expression can be easily extended to deduce the current efficiency applicable for diaphragm cell operations.

Kuwabara, K.; Hanafusa, K.; Sugiyama, K.

doi: 10.1007/BF01016896pmid: N/A

Solid electrolyte cells Cu, X/X/(MO, C, X), have been investigated (X; Rb4Cu16I7Cl13, MO; metal oxide, and C; graphite). An electrolytic manganese dioxide was used as a model oxide for preparing three types of cathode: (1) only MO, (2) a mixture of MO and C, and (3) a mixture of MO, C and X. Cell performances depended not only on the composition of the mixed-phase cathode, but also on the uniformity of the mixture of the materials. Several cells with metal oxides such as MnO2, V2O5, and WO3, showed high and stable electromotive forces of 0.546–0.575 V and good discharge behaviour at room temperature.

Eklund, A.; Simonsson, D.

doi: 10.1007/BF01016897pmid: N/A

A study of the rotating concentric cylindrical electrode has been made, in which the enhanced mass transfer rate by turbulence promotors to a smooth cylinder has been measured. When a special polypropene cloth was applied in the annulus an increase in the Sherwood number was detected, up to six times the value for a smooth cylinder at low Taylor numbers.

Bohnke, Cl.; Bohnke, O.

doi: 10.1007/BF01016898pmid: N/A

Electrochromic tungsten oxide thin films, obtained by vacuum evaporation, were studied before and after heat treatment between 25 and 250°C for 2 h in air. Electrochromic properties were investigated in acid electrolyte by simultaneous measurements of the electrical and optical parameters. A.c. complex impedance techniques and voltammetry were used to characterize the films from an electrical point of view. We observed an enhancement of the electrochromic response times during both coloration and bleaching after heat treatment carried out between 150 and 220°C. This phenomenon was associated with a decrease of the ohmic drop in the electrode and a continuous variation of the impedance diagrams of these electrochromic electrodes. Moreover, we observed that the diffusion coefficient of H+ ions into WO3, obtained on colored thin films, increased as the electrochromic kinetics increased.

Wijngaarden, M.; Geldenhuis, J.; Dippenaar, R.

doi: 10.1007/BF01016899pmid: N/A

A technique is déscribed that permits the high-temperature gas-tight extension of short solid electrolyte tubes, discs or rods. It is demonstrated that this technique can be successfully used in the assessment, by coulometric titration, of mixed ionic and electronic conduction in the short solid electrolyte tubes that are commonly used in practical oxygen sensors.

Sum, E.; Skyllas-Kazacos, M.

doi: 10.1007/BF01016900pmid: N/A

The rate of dissolution of electrolytically deposited aluminium was determined by the method of current reversal chronopotentiometry at a tungsten electrode in NaF−AlF3−Al2O3 melts of varying NaF/AlF3 molar ratios or cryolite ratios (CR). The temperature was maintained at 1031±3°C and the alumina content at 4 wt%. More accurate data were obtained by introducing delay times of various lengths (at zero current) between the cathodic and anodic current pulses, compared to direct current reversal chronopotentiometry with varying forward (deposition) times. The rate of aluminium dissolution increased with increasing NaF/AlF3 molar ratio, the curve showing an inflexion in the vicinity of CR=3. This inflexion indicates two dissolution mechanisms, one being predominant depending on the CR. The main reaction in acidic melts (CR<3) may be represented by $$2Al(l) + AlF_6^{3 - } \rightleftarrows 3Al(I)F_x^{1 - x} + (6 - 3x)F^ - $$ while in basic melts (CR>3) $$Al(l) + 3Na^ + \rightleftarrows 3Na(soln) + Al(III)$$ is the likely dominant mechanism. For 0.8<CR<5.7 the rate of dissolution is of the order of 10−7 mol cm−2s−1.