A voltammetric study of several 4-substituted benzene-1,2-diols in aqueous solutions as a function of pH has been carried out. From slow linear sweep voltammetry at a rotating disc electrode, diffusion coefficients were obtained which could be correlated, in the main, with molecular size. From cyclic voltammetry at a stationary electrode, it was established that the rate of the redox reaction decreases with increasing pH. The cyclic voltammetric measurements were also used to estimate E1/2 as a function of pH. All systems studied showed regions in which plots of E1/2 against pH were linear with a slope of close to -59 mV per pH unit. Such plots were used to estimate values of E1/2 at pH 0, which were then correlated with the Hammett function. The cyclic voltammetry also showed that the reactivity of the quinone formed by oxidation of the benzene-1,2 diols increased with pH. With the most reactive quinones (e.g. that formed from 3,4-dihydroxyacetophenone), a second pair of cyclic voltammetric peaks could be observed, which were ascribed to the oxidation and reduction of a dimer formed by quinone coupling.

In this paper, cementation (metal displacement) reactions are discussed in terms of Evans diagrams, i.e. diagrams constructed by the superposition of cathodic and anodic polarization curves. The conditions under which the rate of a cementation reaction will be controlled by cation diffusion to the reacting metal surface or some chemical step at the surface are explored. It is found that for the case in which the effective cathodic and anodic areas are approximately equal, the cementation is likely to be diffusion-controlled when its two component oxidation-reduction reactions have standard electrodepotentials which differ by more than 0.36 V. The ratio of cathodic to anodic area is also found to be important in determining the reaction mechanism. The presence of an oxide film on the metal is shown to be another factor which influences the reaction mechanism. Evans diagrams are used to discuss the composition of the product layer formed during a cementation reaction.

A cyclic voltammetric study of the oxidation and reduction of elemental tellurium over the pH range 0-14 has been undertaken with tellurium disk electrodes which could be rotated. In both oxidation and reduction, the behaviour of tellurium is largely that expected from the predictions of the E-pH diagram for this element. Exceptions to this general principle were observed during the oxidation of tellurium at both low and high pH where it was found that tellurous acid was relatively quick to form and slow to dissolve; this led to a type of passivation behaviour. On the reduction side, the system behaved in a complex, fashion between pH 8 and 11 with both HTe - and Te22- being formed.

Kinetic experiments are reported on the chemical formation of AgI layers on polycrystalline silver substrates. The AgI layers, up to several micrometres in average thickness, were grown under ambient conditions by reacting a rotating silver disc with solutions of iodine dissolved in ethanol and with aqueous triiodide solutions. The morphology and structural identity of the AgI layers were determined by scanning electron microscopy and powder X-ray diffraction, respectively. Depending upon the growth conditions employed, either porous or compact AgI deposits could result, and thus the rate of formation of AgI could be limited by a diffusion step in solution, or by some slower transport step across the layers. The AgI layers were inhomogeneous, and often consisted of discrete crystallites. Thus, the metal oxidation theories developed for planar and isotropic product layers could not be applied to the formation of AgI layers under ambient conditions.

The kinetics and electrochemistry of the dissolution of a rotating copper disc in various acidified acetonitrile-water mixtures containing iron(III) as the oxidant are described. The reaction kinetics were investigated by a chronopotentiometric method in which the time taken for a copper film of known thickness to dissolve was determined. The reaction was shown to be diffusion-controlled over the temperature range (270-304 K) and composition range (1.0-14.5 mol dm-3 acetonitrile) investigated, good agreement being obtained between rate constants calculated from kinetic measurements and those calculated from electrochemical (cathodic polarization) measurements. From these and kinematic viscosity data, diffusion coefficients for iron(III) in acetonitrile-water mixtures were calculated. It was found that, associated with a discontinuous change in the kinematic viscosity at 290 K, there was a corresponding change in the diffusion coefficient. The activation energy for the high-temperature diffusion process was lower than that for the low-temperature process. It was also found that the diffusion coefficient decreased with increasing acetonitrile concentration. Corrosion potential measurements as a function of disc rotation speed and iron(III) concentration are reported. From these measurements, it was inferred that the anodic reaction is under mixed control.