No description available.

No description available.

Thorium is currently produced primarily as an impure by product of the mining and processing of the rare earth phosphate mineral monazite. Thorium concentrates are currently purified industrially by solvent extraction with PC-88a, but this extractant cannot separate uranium and iron from thorium. In this work mixtures of PC-88a and HDEHP were investigated for the mutual separation of uranium, thorium and iron. The extracted complexes were identified. U and Fe were extracted by cation exchange, while Th was extracted by a mixed cation exchange/solvation mechanism. It was found that three contact stages could extract > 99% of the thorium. A flowsheet was proposed. The first modern use of thorium as a nuclear fuel is most likely to be as an oxide fuel within Generation III+ nuclear reactors. In this work a uranium-plutonium mixed oxide was investigated as a fissile driver for thorium in the Enhanced CANDU 6 reactor, as an alternative to the proposed UK CANMOX fuel for irradiation of the UK plutonium inventory. A large number of fuel concepts were considered, and several were analysed by Monte Carlo simulation. It was found that U-Pu-Th fuels could offer transmutation of the plutonium, irradiate UK reprocessed uranium and give improved coolant void reactivities, while irradiating thorium and converting it to fissile 233U. Thorium and uranium may be recovered from spent nuclear fuel by the Acid THOREX process, which uses TBP solvent extraction. However, TBP has a number of disadvantages. In this work several alternative solvent extraction systems were investigated for the separation of Th, U, Fe and Zr. PC-88a was mixed with ten other extractants as potential synergists, extracting from hydrochloric, nitric and sulfuric acids. Several promising systems were identified based on distribution ratios and separation factors.

No description available.

A study has been made of the hydrogen absorbed by a high-strength steel during cathodic polarization in near-neutral solutions using rigidly controlled experimental conditions. Direct hydrogen analysis by the vacuum heating technique has been utilized and it has been established that use of high extraction temperatures (i.e. > 300°C) can lead to errors which are probably associated with a reaction between adsorbed water and the steel. Extraction at 200°C has been found to give satisfactory results free from this error. The linear relationship between hydrogen absorption and time observed during the early stages of polarization in solutions above pH 4.0 was considered to be characteristic of a rate-controlled slow discharge mechanism of hydrogen evolution. The relationship between hydrogen absorption and overvoltage has been studied in the range pH 4 - 10; the results were found to conform with those anticipated from the kinetics of hydrogen evolution. Metallurgical structure was found to exert a strong influence on the ability of the steel to absorb hydrogen, and a modification of previous theories on delayed failure due to hydrogen has been proposed on the basis of the present study. The influence of arsenic additions to the solution on hydrogen absorption during cathodic polarization have been studied. It has been found that there is a region of pH and overvoltage where hydrogen uptake is inhibited and these results have been correlated with sustained load experiments. The results of this study have been utilized in an attempt to establish whether delayed failure may result from galvanic action produced by discontinuous coatings of electronegative metals (Cd and Zn) on high-tensile steels.

No description available.

A critical review of the literature pertaining to acid copper sulphate electrodeposition preceded the following two paths of research:- 1. A study of electrode kinetic factors using plating solutions without addition agents. A new experimental polarisation technique (called the Reproducible Substrate method) was developed which ensured, in particular, that the cathode had no significant time-dependent properties. This enabled reproducible and linear Tafel plots to be obtained even for those solutions that, with classical polarisation methods, did not previously conform to Tafel behaviour. Special solution preparation methods enabled the properties of super-pure solutions (virtually free of chloride ions) to be studied. The marked effect of trace amounts of chloride ions was shown. The super-pure solutions possessed linear Tafel behaviour, but each plot of n a versus log i showed a change in slcpe at n a = 0.1V - these results were the first to directly confirm a previous prediction made that a change in the cathodic rate-step should occur at this overpotential. 2. A study of addition agent action. Initial trials of many active addition agents were effected in order to select only those that were sufficiently stable and marked in effect to warrant further study. In particular, benzotriazole was studied in detail since it markedly raised n a and affected electrodeposit stuctures(in some cases fully bright coherent deposits were obtained). A mechanism of its action was proposed based on the formation of insoluble cuprous benzotriazolate arising from the formation of cuprous ions in the normal discharge process. A physical model was proposed to explain the phenomenon of banding. Analysis showed that the cuprous benzotriazolate inclusions could be quantitatively retrieved by dissolving up the electrodeposits in acidified silver sulphate. The analysis of trace amounts of these inclusions was carried out by"Polarisation Analysis".

No description available.

The present study represents an investigation of the effect of thiourea, and molecularly related compounds, on the anodic behaviour of nickel in chloride solutions which were either O[2]-free or in equilibrium with in the atmosphere. The results have been presented in the form of E[H]/i plots and Tafel relationships, and it has been shown that the action of thiourea at a nickel anode is concentration dependent. A mechanism has been suggested to explain the effects of thiourea concentration in terms of thiourea adsorption by the nickel electrode, and further experiments in the presence of both thiourea and hydrogen sulphide, and also a three stage experiment have produced results which support this theory. A similar sequence of experiments has been carried out using thioacetamide, and thiosemicarbazide, and almost identical results obtained. Electron microscopy has been used in an attempt to relate the metallographic aspects of nickel dissolution with the electrochemical results. It has been shown that additions of thiourea - and molecularly related compounds -significantly alter the type of attack on nickel in chloride solutions, producing crystallographically orientated etch pits. Although this work is directed towards a better understanding of the anodic behaviour of nickel, an extensive literature survey of the effects of sulphur containing organic compounds on the cathodic electrodeposition of nickel has indicated that the effects of concentration noted during the present studies are reflected in the effects of thiourea concentration on the properties of nickel electrodeposits. A comparison of these results, Maurer's(1) results, and those of the present work, indicates a possible grouping of thio compounds with respect to their effects at nickel electrodes, depending on the electron bonding and hence the reactivity of the sulphur atom (or atoms) in the molecule. Some observations have been made on the mechanism of thiourea action as an inhibitor and the reported abnormal effects of thiourea on the o scale of potentials have been explained in terms of the incapability of the o scale to account for strong chemisorptive links in the corroding metal/inhibitor system.

An electronic fatigue machine has been constructed and used to fatigue stable and metastable beta brass in reverse bending beneath the lens of a microscope provided with stroboscopic illumination. This enabled the progress of fatigue to be continously observed during tests. A study has been made of resulting fatigue damage using X-ray and various metallographic techniques such as taper sectioning and the removal of surface layers by electro-polishing. The fatigue behaviour of stable beta brass is shown to be in some respects unusual and to exhibit certain features previously unreported. One of the most important observations has been the initiation of fatigue cracks and the formation of extrusions in short slip markings adjacent to grain boundaries. Subsequent removal of fatigue damage by electro-polishing has revealed 'persistent markings' which indicate that these cracks originate in the layers adjoining grain boundaries and not in the grain boundaries. These cracks afterwards propagated into and across grain boundaries. Fatigue cracks have also been seen to be initiated at triple point intersections of grain boundaries. Intense and 'permanent' slip markings excluding those described occurring adjacent to grain boundaries have not been observed to form. Extrusions were found to be rare and comparatively small. Fatigue debris considered to be an attrition product consisting of oxidised fragments of metal has been observed. An endeavour has been made to explain these phenomena in terms of the nature of dislocations and their movements in the superlattice. It is thought that cross slip is unlikely to occur and that this inhibits the formation of intense slip markings and extrusions. A disordered grain boundary layer had been proposed to account for the initiation of cracks adjacent to grain boundaries. A fatigue induced precipitate has been described in metastable beta and an explanation has been given in terms of enhanced diffusion due to the generation of vacancies by moving dislocations during fatigue.