<p>Pitting corrosion is one of the major causes of industrial failure of metallic parts. Unfortunately, such attack cannot always be detected before perforation occurs. Understanding the mechanism of pit development will provide us with a clue of how to prevent pitting corrosion in advance. From an engineering point of view, it is important to keep the pit, once it forms, repassivated rather than allow continuous growth, leading to the perforation. The key factors controlling pit development must therefore be determined. A comprehensive model of pitting processes is proposed which considers interfacial dissolution, salt film formation, multiple species in solution, reaction equilibria, migration and diffusion. The model is capable of determining local chemistry within pits and characterizing the conditions necessary for stabilization of pitting corrosion. The model is experimentally verified using microelectrodes developed to measure the local properties of pitting sites. The electrodes were characterized through studies on their potential stability, spatial resolution, and the interference of other ions involved in the corrosion of nickel. The study was performed on a nickel model pit in a saline environment. The in situ measurements obtained by microelectrodes provide the direct evidence of existence of a salt layer, comprised of corrosion products, at the bottom of a developing pit. The condition for formation of the salt film in active pits appears to require that the pit depth be sufficient to ensure the maintenance of a critical local solution chemistry. The experimental results are consistent with the theoretically predicted critical depth at which a metal chloride salt layer starts to form at the pit bottom. The measurements of the potential distribution within the salt film have provided data for the potential drop across the salt film, its thickness and therefore its conductivity. These help us to achieve a better understanding of the nature of the salt film. The anodic behaviour of nickel was studied in solutions which simulate the pit electrolyte, based on the in situ measurements of the local pH and chloride ion concentration within a pit at different stages of development. The factors controlling the pit growth were deduced.</p> / Doctor of Philosophy (PhD)

<p>A study consisting of theoretical and experimental work on kinetics of simultaneous interfacial reactions in multi-component metallic/ionic systems has been carried out in the present work. General rate expressions for simultaneous interfacial reactions are proposed based on the application of mass action law to the electrodic half-cell reactions and the constraint of no net electric current. The nature of coupling among interfacial reactions is discussed by defining the coupling factor which is a collective property of the system, contributed by and common to all interfacial reactions. Kinetic behavior of each element can be individually and simultaneously described. Experimental work is conducted in slag/metal system for the study of coupled interfacial reactions and diffusion. Considering interfacial reactions as the boundary conditions for diffusion in both phases, a mathematical model is developed. Computed results, based on thermochemical parameters mostly reported in the literature, are compared with diffusion profiles measured by electron probe microanalysis (EPMA) in silicate slag and Fe-Mn-Si alloy at 1763$\sp\circ$K. Values of reaction rate constants for transfer of iron, manganese and silicon are recommended through curve fitting with the experimental data. The conventional pseudo-binary approach in the formulation of rate equations for interfacial reactions in multi-component slag/metal systems may be deduced from the present theory with simplifying assumptions and as a limiting case.</p> / Doctor of Philosophy (PhD)

<p>Bubbly plume flow, which is encountered in many refining processes of the iron and steel making industry, has been studied with a water model ladle and simulated with a novel mathematical model. The main achievements of this project can be summarized as following: (1) A new experimental technique based on the Laser Doppler Anemometry and Electrical Probe has been developed to measure various flow parameters of the plume, such as: mean and turbulent liquid velocities, bubble velocities and distributions of void fraction and bubble frequency. (2) The turbulence feature and bubble behaviour in the gas/liquid two-phase zone has been experimentally studied with the newly developed LDA/EP technique in a water model ladle. It has been found that turbulence in the plume zone is close to an isotropic one and the relative velocity of bubbles is not affected by the void fraction in the plume. (3) A mathematical model based on the modified k-ε turbulence model has been developed to simulate the plume flow. The coefficients of the extra source terms of the modified k-ε model have been determined experimentally. The mathematical model yielded good predictions of both the mean and the turbulent liquid velocities. The behaviour of bubbles in the plume has also been dealt with to produce good predictions of the void fraction distributions.</p> / Doctor of Philosophy (PhD)

<p>A series of plane strain compression experiments and finite element method (FEM) calculations were performed on continuous fibre composites to examine the role of volume fraction and fibre arrangement on the mechanical behaviour when the fibre axis was perpendicular to the loading direction. The flow pattern in the matrix was quantified by measuring the shape change of a fine gold grid which had been fabricated on the surface of the sample prior to deformation. It was determined that the pattern of deformation in the matrix was controlled by the spacing and geometric arrangement of the fibres. The damage process (i.e. by fibre cracking or interfacial decohesion) can be understood by the local distribution of stresses (as calculated by FEM) in the fibres and at the fibre matrix interface. The development of the deformation texture in the matrix and the observations of the pattern of subsequent recrystallization events can be related to the flow pattern in the matrix. The combination of careful experiments with finite element method calculations represents a powerful approach to studying problems involving composite materials.</p> / Doctor of Philosophy (PhD)

<p>Thin films of ZnS and ZnO(1-x)Sx were prepared by electrodeposition and chemical vapour atomic layer deposition (CVALD), respectively. This represents the first effort to apply the technique of electrodeposition to ZnS for the purposes of electroluminescence. This is also the first time thin films of ZnO(1-x)Sx were grown by CVALD and represents the first analysis of how the films properties vary with a known stoichiometry. Characterization methods performed on the thin films include: Auger spectroscopy, Rutherford backscattering spectroscopy, scanning electron microscopy, x-ray powder diffraction, Hall measurements and uv/visible transmittance. The as electrodeposited films were nearly stoichiometric but conductive and oriented in a <200> direction. After annealing the films became discontinuous and lost their crystallinity, but their absorption characteristics more closely resembled that of evaporated films. Ion implantation with Mn was successful and the films exhibited yellow-orange cathodoluminescence. The value of x in the formula ZnO(1-x)Sx could be varied from 0 to 0.95 by changing the amount of hydrogen sulphide admitted to the reaction chamber. Films with values of x near 0 grow in the <200> direction (of ZnO) and have a fine grained structure. As the value of x increases the films become more and more amorphous but split into a two phase structure close to x = 0.55. At this point the films exhibit a minimum bandgap. As x increases further the films become one phase again and become oriented into the <111> direction of ZnS. The cathodoluminescent characteristics of these films also change with x. When x is zero the films appear to luminescence green or yellow depending on the deposition temperature. Even 5% S removes this luminescence however and the spectrum is dominated by a peak in the red. This peak steadily decreases then increases again as x increases.</p> / Doctor of Philosophy (PhD)

<p>The energies of one and two-dimensional dislocation arrays lying near<br />a free surface are evaluated directly from the stress fields of single dislocations<br />in a half-space. These results are used to obtain expressions giving the<br />equilibrium spacings of a number of different arrays relieving misfit in a<br />strained epitaxial system. Numerical calculations are performed for the case of<br />edge and 60º dislocations relieving strain in a silicon-germanium layer<br />deposited on a silicon substrate. This method is also used to calculate the<br />energies of various low angle grain boundaries in a half-space.</p> <p>Single-ended dislocation sources are observed using transmission<br />electron microscopy in two short-period Si-Ge superlattices grown on Si(100).<br />Their formation is linked to the development of non-planar layers during the<br />growth of the superlattices. The relaxation of these superlattices takes place<br />at significantly lower temperatures than equivalently strained homogeneous<br />epilayers.</p> <p>Si-Ge short period superlattices deposited on Si(100) are shown to<br />relax through twinning on {111} planes if the deposited layers become grossly<br />non-planar. Twinning is accompanied by the formation of a diamond<br />hexagonal phase. No 60· a/2(110) dislocations relieving misfit are present in the strained layer structure.</p> <p>The nature and origin of a new type of defect in Si₁_ᵪGeᵪ/Si strained<br />layer structures, the "pagoda" defect, is studied using transmission electron<br />microscopy. The defects are found to propagate in a direction determined by<br />the position of the Si source in unrotated substrates, and to have their origin<br />in the role played by SiC particles (left after cleaning the substrate) during<br />the growth process. Pits that form at the SiC particles are preserved during<br />MBE growth and perturb the strained layers, leading to the formation of<br />pagodas.</p> / Doctor of Philosophy (PhD)

<p>Steel-clad calcium wire was fed into 40 kg heats of AISI steel with various sulphur and aluminum contents under argon atmosphere. Samples were taken continuously during and after calcium injection for chemical and inclusion analysis from more than twelve heats of injection. Calcium dissolution was found to be enhanced by instantaneous reactions with oxygen and sulfur in the boundary layer. The unreacted calcium diffuses through the gas-liquid film into the melt for oxide and sulfide inclusion modification. The overall interaction between oxides and sulfides with the bulk drives towards the equilibrium of (CaO) + S = (CaS) + O. The system paths from the initial state to the final state were kinetically studied with the assistance of a_CaS-a_MnS diagrams, which were calculated by applying a regular solution model to the solid phase and an ideal model to the liquid phase of the CaS-MnS phase diagram at various steelmaking temperatures. A mathematical model for the multiphase kinetics was developed to interpret the calcium dissolution, deoxidation, desulphurization, oxide and sulfide inclusion modification during and after calcium injection. The implications for full-scale operation were discussed.</p> / Doctor of Philosophy (PhD)

<p>Measurements by dielectric spectroscopy, ultrasonics and calorimetry ofseveral low viscosity monomeric liquids undergoing spontaneous chemical reaction, to form three new, linear chain polymers under isothermal conditions, have been used to determine how the number ofcovalent bonds formed during the growth of a linear chain affects the dielectric and ultrasonic properties, their respective relaxation times, and their spectral shape. The dielectric properties changed in the following manner. During this reaction, the static permittivity decreased and the relaxation time increased towards limiting values. As the number of covalent bonds increased towards the Avogadro number, the change in the complex permittivity as measured for a fixed frequency was phenomenologically similar to that observed on varying the frequency, although the exact formalisms in both cases differed. In both cases the relaxation function could be well described by a stretched exponential or sum ofexponentials, characterized by a temperature and system dependent exponent that decreased as the state of the system changed from a monomeric liquid to a fully reacted polymer. At later stages of chemical reaction a second relaxation process at higher frequencies is revealed. The dielectric manifestation of the irreversible process of covalent bond formation is remarkably similar to that observed on supercooling a molecular or polymeric liquid.</p> <p>Longitudinal velocity and attenuation of ultrasonic waves travelling through the three molecular liquids at different temperatures have been measured as its molecules combine irreversibly to form large entities and thereby decrease the diffusivity and increase the configurational restrictions to their dynamics. From these data, the longitudinal modulus and compliance are calculated, and the molecular relaxation time and related properties are deduced and interpreted in terms ofthe number of covalent bonds formed, by a formalism that connects the size ofthe molecules in the liquid with its elastic behaviour. This relaxation time increases monotonically with increase in the molecule's size, tending to infinity as the number ofcovalent bonds formed approaches Avogadro's number. The complex plane plots ofthe modulus and compliance have a shape which is described by a skewed arc function, with a temperature dependent exponent ϒ, that ranges in values from 0.33- 0.31 for modulus and 0.39-0.45 for compliance. Departure from this shape is shown to be due to contributions from non-zero shear viscosity for relatively small size of molecules, and contributions from a faster, or sub Tg-relaxation process when the molecular size is large, which is similar to the behaviour for the dielectric properties. Simulation of the data suggests that this sub Tg-relaxation process, which is progressively more separated from the main relaxation process as the molecular size increases, contributes significantly to the high frequency elastic properties. The measured longitudinal modulus has been deconvoluted to show that the increase in the bulk modulus, and not the shear modulus, dominates the elastic properties when the molecular size increases. Comparison ofthe calculated relaxation times for the longitudinal modulus and compliance with the dielectric relaxation time show that the compliance and dielectric data change in a remarkably similar manner with increasing time of chemical reaction, which is unexpected owing to their different mechanisms.</p> <p>In the last part of this work, the dipolar diffusion in the glassy and supercooled liquid states of 9 additional molecular liquids and oftheir linear chain or network polymerized states formed by condensation-polymerization at different temperatures and times have been studied by measuring the dielectric properties for a fixed ac frequency of 1 kHz. The study showed that as the extent of polymerization increased with increasing isothermal temperature of polymerization, the sub-Tg relaxation peak due to localized molecular motions in the molecular state became gradually extinct, and a corresponding peak at a higher temperature evolved and reached its maximum height. The temperature of the sub-Tg relaxation peak in the polymerized state differed from that of the α-relaxation peak of the supercooled molecular liquid by as much as 70K, but, in several cases, the two temperatures were similar. Reasons for the latter occurrence are given in phenomenogical terms. It is concluded that the localized relaxation modes of the polar segments of the macromolecule are not related to the modes of molecular diffusion in the monomeric liquid state above its Tg. The localized relaxation characteristic of the glassy molecular state persists in the incompletely polymerized state, where it is seen as a ϒ-relaxation.</p> / Doctor of Philosophy (PhD)

<p>The central argument of this paper is that efforts to rationalise the European defence industrial base are both pre-requisite to and incompatible with the broader goal of Alliance wide specialisation and rationalisation, at least withiin NATO as it is presently configured. Broadly, the contention is that rising weapons costs in the context of stable or shrinking defence budgets are moving the NATO alliance toward structural disarmament. In response to this trend, the Alliance has been forced to consider means of reforming the highly wasteful defence industrial effort so that the price of military preparedness can be kept within reasonable limits. From a simple economic perspective, the creation of a NATO-wide free-trade regime in defence goods wold seem to be the optimal approach to this program. Free trade, however, is fraught with political hazards that make it largely unacceptable to most Alliance governments.</p> <p>An apparently attainable alternative to free trade in this connexion is "managed specialisation." Managed specialisation, however, also has its limitations. Put simply, in order to rationalise the Allied development and production effort, Europe must first of all "get itself together" and begin producing competitive equipment at competitive prices. In order to achieve this, however, Europe must reform its own domestic market in order to realise US-scale production economies and capitalisation rates. The crux of the problem is that this necessarily requires greater European collaboration and protectionism, and ultimately suggests that Europe will begin to offer the US more global competition. As this is unlikely to sit well with the Americans, it would seem that--contrary to the original intent--European rationalisation seems destined to result in more, not less, fracture within the Alliance defence industrial base. Although the verdict is not yet final, the Eurofighter programme would seem to confirm this hypothesis.</p> / Master of Arts (MA)

<p>In this thesis, solutions to the problem of low power density caused by pH<br />deviation in anode and cathode of a glucose/oxygen based enzymatic fuel cell using GOx and FMCA are provided. Moreover, conclusive evidence of a large active area in this type of fuel cell is determined using a transient state study. The complete process of electrical double layers formation is described.<br />A survey of the solutions to low power density caused by pH deviation is conducted and two feasible alternatives are suggested. The first alternative, using Tris buffer with no alkaline ions resulted in even larger pH gradient. The second alternative: using anion exchange membrane (AEM) successfully reduced the pH gradient by introducing lower power density than the biofuel cells using a Nafion membrane. It was proven that the high internal resistance of the AEM is responsible for the drop in energy output ofthe biofuel cell.<br />A transient study was conducted on the biofuel cells in order to investigate the<br />internal resistance of the components. A discrepancy was found when applying the<br />rarely-mentioned internal circuit model to biofuel cells. The model predicted a much<br />larger surface area for the electrode than was physically measured for the cells. It is<br />therefore concluded that the proposed electrochemical double layers are in the electrolyte as well as on the interface. Finally, a detailed description of electron/proton double layer in the electrolyte associated with each reaction step is given, assuming that double layers can be found on the enzymes and mediators.<br />A complete list of requirements for equivalent circuit is portrayed for our glucose/oxygen enzymatic biofuel cell. The equivalent circuit suggests a possible<br />direction for future biofuel cell research.</p> / Master of Applied Science (MASc)