No description available.

No description available.

The suitability of metal-metal oxide electrodes and the drawbacks of established pII measuring electrodes are reviewed. A well-established metal-metal oxide system was chosen for initial examination and various experimental techniques of evaluation were developed. This work was extended to include a brief investigation of certain other systems, bismuth, tungsten, platinum, rhodium. and gold, Finally, the viability of an electrode prepared by the electrodeposition of rhodium was established and detailed studies made. Further experiments were designed to determine the chemical and physical nature of the electrode surface, as well as the, reactions responsible for some of the deviations from the theorctical pH response. The techniques employed for this purpose included Energy Dispersive Analysis, Stereoscan Electron Microscopy, X-ray Photoelectron Spectroscopy as well as various Electrochemical methods.

The reduction of dichromate to chromic ion has been studied in sulphuric and perchloric acid solutions, in connection with the possible use of dichromate as a depolariser in a primary battery. Gold and pyrolytic graphite electrodes have been used. At a gold electrode the current increases rapidly to a limiting value. Potential-sweep experiments and electron diffraction studies indicate that the rate of reduction is controlled by the properties of surface film. The nature of this film is altered by potential and is also modified by addition of foreign anions. On a pyrolytic graphite electrode in perchloric acid, film deposition and modification again considerably modify the rate of reduction. In sulphuric acid solutions, however, the form of the current-potential curves obtained is not determined primarily by the properties of a surface film. Under these conditions it was shown that dimeric CrVI species are reduced at more positive potentials than the monomeric species. The kinetics of the reduction of the monomeric species has been investigated.

Thermoelectric generation of electrical energy from heat energy has been reviewed, the histor.f of the subject has been reassessed, and the materials used for thermoelectric generation have been examined. The suitability of a material for thermoelectric generation is determined by the product of the figure of merit, Z, and the 2.bsolutetemperature, T. The figure of merit of a material depends upon the thermoelectric potential, eX. , and the ratio of the electrical conductivity, 0-, to the thermal conductivity, K : Z T = 0< 2 T a-/ K The most suitable semiconductor materials have (dimensionless) ZT values between 0.5 and 1, and the most suitable molten salts developed in this work have ZT values of about 0.5. The advantages of molten salt cells over semiconductol' thermoelements are the absence of conta.ct junction, doping and thermal expansion problems, and the low cost of the materials. The major disadvantage is the mass transfer between the electrodes, and this caused the failure of many of the initial generation thermocells de signed by the author. Pure molten salts are found to have ZT values ranging up to 0.3 and mixtures of salts have been examined in an attempt to increase the ZT value. The .A{,-cI - AgI system has been studied as an example of a. common-cation The thermoelectric potential has been measured up to a temperature of a.bout 12000C and. the thermal conductivity has been measured using a transient hot wire method which was adapted for measurements on molten salts at high temperatures. The maximum ZT value is 0.4 for the AgCl - AgI eutectic mixture. The AgCl - CuCl - LiOl 2 system has been studied as an example of a common anion mixture. A theory to the thermoelectric potential of common anion mixtures has been developed and partially substantiated by experiment. Some salt mixtures are expected to havo ZT values in excess of unity, yielding actual conversion efficiencies of 7 - 10%. The thermoelectric effect in a molten salt thermocell is due to the flow of ions between the electrodes, and this flow of ions causes an electrochemical mass transfer. In addition there is a mass transfer between the electrodes caused by natural convection currents in the salt. A cell has been developed in which the mass transfer problem has been overcome by arranging for the mechanisms just described to transfer metal from a molten metal alloy electrode to another electrode situated above it, and allowing gravity to return the metal to the lower electrode. Convection currents have been decreased by inserting a fibrous material in the salt. to the thermoelectric potential of a thermocell with alloy (rather than pure metal) electrodes has been developed and confirmed. In order to demonstrate the feasibility of thermocell generation a smaIl generator consisting of up to 44 of these cells has been constructed and has given an open circuit potential of 13 volts and a short circuit current of 0.6 amps. This is believed to be the first thermoelectric generator using a liquid thermoelectric material and also the first utilising the thermoelectric effect of the flow of ions.

No description available.

Aspects of the electrochemistry of iron and its oxides have been reviewed, emphasis has been placed on discussion of the factors relevant to the dissolution processes. The preparation of electrodes of magnetite (Fe3O4) with suitable characteristics for electrochemical studies is described. The responses of stationary electrodes to potentiostatic, potentiodynamic and alternating currents have been investigated. The results can be interpreted in terms of solid phase reactions at the electrode at short times. Subsequently nucleation and growth processes have been identified at negative overpotentials. Dissolution processes giving rise to cathodic currents are investigated at positive overpotentials. The role of the flux of dissolution products from the electrode on dissolution rate is also discussed. The semi conducting nature of iron oxides is shown to have a profound effect on the electrochemistry of these materials. Parallels are drawn between the semiconducting properties of the crystals and their electrochemical response. The dissolution of magnetite under potentiostatic control has been studied. Faradaic processes are followed coulometrically and the overall removal of iron species (crystal dissolution) followed analytically using atomic absorption spectroscopy. The results have indicated a variation in current efficiency of the dissolution process with applied potential.

The conditions under which insulating oxide films can be formed on uranium by anodic oxidation have been investigated, and a number of experimental techniques has been developed for controlling the conditions of formation and for estimating film thickness during the growth of the layer. A survey of a range of possible anodising electrolytes has been carried out and it is shown that consistent anodising is only obtained within the ternary electrolyte system ammonia-water-glycol. A detailed account of the anodic oxidation in this electrolyte of uranium having different degrees of purity is described. Film formation on uranium is found to be critically dependent not only on the electrolyte composition and the mode of surface preparation, but also on the purity of both electrolyte and metal. The physical and chemical properties of the films have been investigated. The film is found to consist of a nearly amorphous material whose composition lies between UO[2.3] and UO[2.7], depending upon the purity of the metal used. The results obtained are more complex than those which have been noted in other studies of anodic oxidation, and it has not been found possible to account for the kinetics of film formation by applying the theory of Cabrera and Mott.

The electrical conductances of aqueous solutions of magnesium and manganese (H) oxalates and diothionates, barium dithionate and of acetic acid have been measured at various frequencies in the range 1 KHz to 50 Mz, using a conventional audio-frequency Wheatstone bridge and two radio-frequency transformer ratio-arm bridges. The measurements of the radio-frequency conductances were determined with respect to potassium chloride which is taken as the reference electrolyte. The evaluation of the conductance data was carried out by extrapolation and minimisation techniques using the following theoretical conductance equations: the complete and modified forms of Pitts (8,29) and Fuoss-Hsia(19,30) and those of Falkenhagen-Leist-Kelbg(5) D'Aprano(20). and Murphy-Cohen(25). Quantitative results showed that magnesium, manganese and barium dithionates could be only treated as essentially fully dissociated electrolytes which exhibit ion pairing. All the oxalate and dithionate salts showed an increase in their conductances in a high-frequency field (normal Falkenhagen effect). This could be explained in terms of two effects: the ion atmosphere relaxation(5), and the relaxation of ion-pair equilibrium as calculated by Gilkerson(50). The above-mentioned electrolytes exhibited variations in the values of their association constants (second Falkenhagen effect) with frequency. Estimation has been made for the rate constants of the ion-pair dissociation rate by using Gilkerson theory. The results indicate that acetic acid does not exhibit any effect other than relaxation Of the ionic atmosphere, corresponding to the frequency of the alternating field. It is concluded that this electrolyte is present in neutral molecules which can not be dissociated by the alternating field.

The work reported in this thesis has been concerned with the study of the electrochemical behaviour of unsymmetrical electrolytes in propylene carbonate. Zinc halides were found to be soluble in this solvent, while zinc oxide, sulphate and carbonate and potassium carbonate were sparingly soluble. The electrical conductances of zinc halides, zinc perchlorate and ferric chloride in PC have been measured at 25&deg;C. The results indicate that all of these solutes behave as "weak" electrolytes. Zinc perchlorate was found to be anomalous in showing unusually high molar conductance in this solvent, and in exhibiting a pronounced maximum conductance at low concentration. The Murphy-Cohen equation was modified to allow for "weak" electrolytes and for different modes of ionisation of unsymmetrical electrolytes. The conductance data were analysed by a minimisation technique using the modified Murphy-Cohen equation and the limiting law. It was found that for zinc salts in propylene carbonate solution at 25 C the mode of ionisation is specific for the anion involved. The effect of the variation of the distance parameter a on the values of Lambda[O] and K[A] was fully investigated. Single ion conductances, calculated from conductance and transport number data, suggested that the mobilities of the cations decreases along the series: ZnI[+] > ZnBr[+] > Zn[2+]. Electrodeposition of zinc from a solution of zinc chloride in propylene carbonate proceeded with very high efficiency. Polarographic reduction of cations was possible, with a range of half wave potentials similar to those for aqueous solutions.