ZnO nanostructures have great promise in a wide range of applications such as sensors, optoelectronics, piezoelectronics, healthcare. Preparation of oxide films by electrodeposition from aqueous solution presents several advantages over other techniques such as controlling the rate and morphology through several well-defined parameters (electrode potential, current, temperature, pH, etc.), the fact that electrolytic processing is a well-established technology and readily scalable for production, and the non-equilibrium nature of the electrochemical interface often gives rise to morphologies and compositions not attainable through other, usually high-temperature, routes. Despite a large amount of research in this area the detailed mechanism of nucleation and growth is still controversial. Only a good understanding of it will allow the expected industrial applications to be achieved. One of the main difficulties to overcome is that tiny amounts of material are involved and the required in-situ measurements are thus very delicate. The ability of synchrotron radiation to probe material structure during deposition makes it the ideal tool for the study of nucleation and growth of these materials as a function of the processing parameters. Here we will present two synchrotron-based approaches involving both X-ray absorption and scattering. The first method, together with ex-situ characterisation, provides detailed information about how the kinetics of the growth and/or dissolution is influenced by the electrochemical parameters. The effect of time, potential, zinc ions concentration, oxygen precursor, temperature and electrolyte composition have been studied. Following this understanding of the influence of the parameters, films of desired structure can be synthesised and new structures have been made. Beside the electrochemical parameters, the growth of the film is influenced by the interaction with substrate in the early stage of nucleation. The second synchrotron technique allows the direct observation of the development of the crystal orientation of the films during the deposition. It gives promising results to study how the substrate influences the growth and thus the properties of the films.

The concept of sustainability on the one hand and the extraction and processing of primary resources on the other, at first glance, appear to be in conflict, since the production processes deplete resources that are strictly considered finite. In addition, these processes inevitably disturb the environment. This is especially true in copper production considering this is a metal with a high global demand, currently mined at increasingly low grades. Life Cycle Assessment (LCA) is an established method to assess the sustainability profile of products, processes and systems that has become important in recent years through the establishment of the ISO 14040 series of standards. Although LCA studies on mining and mineral processing systems, including copper, have been carried out since the mid- to late 1990s; these studies are limited to the ore extraction and mineral processing, not considering waste management, which is absent from all LCA based sustainability assessment of metal production systems reported in literature. In addition the low level of detail used in conventional LCA tools (not accounting for emissions at unit process level) lead to oversimplifications and underestimation of the true impacts. In this PhD research an LCA model has been developed to assess the impacts of copper mining and processing, considering the mine, mineral processing and waste disposal facilities life cycles as part of the copper production. The model is designed at unit process level and integrates the mining (open-pit and underground), mineral processing and waste management processes and accounts for emissions to the different environmental compartments (air, water, soil). The life cycle inventory (LCI) models developed are designed using specific activity data at component unit-process level together with emission factors from literature (US EPA, Australian NPI) and engineering calculations or models. The model developed uses mass balance/equilibrium calculations from intermediate products, resource consumption rates or activity levels to estimate life cycle estimates. The model functionality is illustrated using a true Chilean mine case study which was parameterised using mining, mineral processing and waste disposal facilities information for a baseline year when detailed operational data and key variables were recorded. The different LCA impact indicators estimated are carbon footprint (or global warming potential), water footprint, human toxicity, resource depletion and ecotoxicity (USEtox). Different Life Cycle Impact Assessment (LCIA) methods, chosen from the most recent and widely used LCIA methods, are utilised to compare the different methods results. Extensive Sensitivity and Monte Carlo analysis is performed to assess the uncertainty of key parameters. The response of the LCA impact indicator scores to the variation of variables such as the copper ore grade, copper recovery efficiency, average stripping ratio, electricity grid mix, are evaluated and presented.

The creep rupture properties of cast !Cr!Mo!V and ICrlMo!V alloy steel used in the manufacture of power station steam generating plant, have been investigated. The effects of constraint and geometry on the creep rupture properties are also considered. The validity of various criteria controlling macroscopic creep crack growth in cast CrMoV alloys has been examined. It is found that neither the stress intensity factor nor reference stress correlate satisfactorily the creep crack growth rates at the test temperature of 5500C. Certain minimum displacements must be achieved for crack initiation and propagation. It is found that this displacement as measured by crack opening displacement or crack aspect ratio, is the same in both compact tension and centre-cracked panel geometries, is invariant with crack length and decreases with increasing constraint. The effect of constraint on creep crack growth rate in the two geometries is less conclusive. A new model describing creep crack growth in cast CrMoV alloy steels has been developed. The model is based on the results from a numerical finite element creep analysis of the relaxation and redistribution of stress ahead of an incubating creep crack. It is found that macroscopic creep crack growth in a material undergoing either plane stress or plane strain deformation can be described by a fracture stress which is based on the Von Mises equivalent stress. It has been shown that this model is capable of rationalising all of the experimental crack velocity data from the cast CrMoV alloys. The resultant degree of data correlation is far superior to that obtained when using the stress intensity factor or reference stress. A cumulative damage creep fracture model based upon the results from the numerical analysis has been developed. It is found that the model is capable of predicting the behaviour of propagating creep cracks in cast CrMoV alloys from smooth bar creep rupture data.

The precipitation reactions occurring in a series of copper-based alloys selected from the system copper-chromium-zirconium have been studied by resistometric and metallographic techniques. A survey of the factors influencing the development of copper-based alloys for high strength, high conductivity applications is followed by a more general review of contemporary materials, and illustrates that the most promising alloys are those containing chromium and zirconium. The few systematic attempts to study alloys from this system have been collated, discussed, and used as a basis for the selection of four alloy compositions viz:- Cu - 0.4% Cr Cu - 0.24. Zr Cu - 0. 3% Cr - 0.1% Zr Cu - 0.2% Cr - 0.2% Zr A description of the experimental techniques used to study the precipitation behaviour of these materials is preceeded by a discussion of the currently accepted theories relating to precipitate nucleation and growth. The experimental results are presented and discussed for each of the alloys independently, and are then treated jointly to obtain an overall assessment of the way in which the precipitation kinetics, metallography and mechanical properties vary with alloy composition and heat treatment. The metastable solid solution of copper-chromium is found to decompose by the rejection of chromium particles which maintain a coherent interface and a Kurdjumov-Sachs type crystallographic orientation relationship with the copper matrix. The addition of 0.1% zirconium to the alloy retards the rate of transformation by a factor of ten and modifies the dispersion characteristics of the precipitate without markedly altering the morphology. Further additions of zirconium lead to the growth of stacking faults during ageing, which provide favourable nucleation sites for the chromium precipitate. The partial dislocations bounding such stacking faults are also found to provide mobile heterogeneous nucleation sources for the precipitation reactions occurring in copper-zirconium.

No description available.

No description available.

No description available.

No description available.

Fatigue crack propagation has been investigated in single edge notched mild steel specimens under constant and programmed loading conditions. Results have been analysed by the fracture mechanics approach and the Palmgren-Miner summation. Fracture surfaces were examined with a Cambridge Stereoscan scanning electron microscope. In tests where both load rises and load drops were included, the cumulative cycle ratio was always slightly greater than unity, irrespective of block size, load level, rate of load change or sequence. When the programme consisted only of load rises, the cumulative cycle ratio decreased below unity. These results have been explained in terms of residual stresses developed at the crack tip during load changes. The fracture mechanics analysis was found to provide a satisfactory method of data correlation, provided the effects of material and experimental variables were fully appreciated. However, no single value of slope of the log∆K-log da/dN relationship will apply to all materials and conditions. In the absence of residual stresses due to manufacturing processes, computer integration of the constant amplitude fracture mechanics data will provide a satisfactory method of life prediction. Fractographic observations showed that striation spacings were often larger than the macroscopic crack growth rate. This effect was discussed in terms of discontinuous crack front movement. Striation spacing measurements were not therefore useful as a technique of correlating macroscopic crack growth rate with the microscopic observations. However, two distinct modes of fracture were observed to occur. The first (designated stage Ila) was structure sensitive, whilst the second (designated stage IIb) was structure insensitive. The transition from stage Ila to stage llb occurred when the radius of the plastic zone ahead of the crack tip reached a value of about four times the mean grain diameter. Under programmed loading conditions, stage IIa was found to occur after a high to low load change even though the prevailing stress intensity was at the level sufficient to produce stage IIb in a single stress level test. It is suggested that this effect is caused by substantial residual compressive stresses acting in opposition to the applied stress intensity and estimates of the minimal levels of these residual stresses have been made. The mechanisms of residual stress formation and decay have been explained in terms of sizes of plastic zones at the crack tip.

Pulsating; tension fatigue tests have been carried out on edge notched specimens of a mild steel. An electrical potential drop technique was used to determine the number of cycles taken to initiate cracks and the rate at which the cracks grew across the specimen. The results could be described by the range of stress intensity factor, which for crack initiation was modified to take account of the notch root radius. Analysis of elastic stress distributions at cracks and notches and models of plasticity at crack tips are used to discuss the results. Limited evidence in the literature indicates that the fracture mechanics approach may provide a general description of crack initiation and growth in notched specimens, and a simple graphical method of calculating fatigue lives is described. The results are used to illustrate the effects of specimen size and geometry on the fatigue life of notched specimens. The relevance of the work to the assessment of the significance of defects in welds is discussed.