<p>Pure and doped CaF₂ single crystals were grown from melts by Czochralski technique. The doped crystals contained two levels of Na⁺, K⁺, V³⁺ and Y³⁺ impurities. The crystals were subsequently annealed and analysed for impurities. Samples were mechanically tested in compression at 450 and 600°C, and the 0.1% proof stress noted. An attempt was made to explain the observed hardening by Fleischer's theory of solid solution hardening in the case of V³⁺ and Y³⁺ -doped CaF₂ and by precipitation hardening theory in the case of Na⁺ and K⁺ -doped crystals.</p> / Master of Engineering (ME)

<p>A numerical Solution to the one dimensional unsteady state heat transfer problem including the latent heat evolution of the pearlite reaction has been developed to predict thermal conditions in a Jominy bar. This has been combined with a model for pearlite nucleation and growth developed by Kirkaldy and used to predict the TTT curves for the austenite → pearlite transformation and the pearlite volume fraction as a function of time and Jominy number. The conversion of the TTT to OCT curves, which is a necessary step in the latter calculation, has been Investigated using the additivity rule and the approximation to it due to Grange and Kieffer. It was concluded that the latter approximation will often not be justified. Inclusion of the latent heat evolution in the heat transfer calculations was proven to be significant and as such should be included in any accurate algorithm for predicting Jominy curves.</p> / Master of Engineering (ME)

<p>The crystal structure of Cu₂V₂O₆ has been studied by X-ray diffraction techniques. CuV₂O₆ has been found to have a structure closely related to the mineral brannerite as do the majority of the metavanadates, but with lower symmetry. The refinement of the structure showed a bonding geometry consistent with the bond strength-bond length correlations for oxides which have been applied to other vanadate structures.</p> <p>The symmetry and unit cell parameters of Ca₂V₂O₇ have been determined. The attempted solutions are described and suggestions are made for future work on this structure.</p> / Master of Science (MS)

<p>A production basic oxygen furnace installation at Dominion Foundries and Steel Ltd., Hamilton, Ontario was used to develop and evaluate a method of measuring the rates of materials ejection during steelmaking. These rates are determined by periodic sampling at the mouth of the BOF with a tubular sampler, during the oxygen blow.</p> <p>The materials ejected are classified into two categories, slopping and metal ejection. From the measured rates and analyses of ejected materials, combined with the composition of the slag and metal bath as obtained by direct sampling, certain insights are made about the mechanisms of materials ejection. Among the process variables examined, the metal bath level, oxygen flow and course of slag development showed the largest influence on ejection rates.</p> / Master of Engineering (ME)

<p>Intrinsic degradation, which leads to the long-term decrease in the electroluminescence efficiency, has been a major limitation facing the new technology of organic light emitting devices (OLED). Traditionally, degradation has been speculated to be caused by morphological instability of the organic layers, especially the less stable hole transport layer (HTL), or by the formation of deep traps at the hole-injecting contact. These speculations were based on experimental observations showing that doping the organic layers or introducing a buffer layer at the hole-injecting contact can dramatically improve device stability. However, the real causes of OLED degradation remained uncertain. In this study, the cause of the long-term degradation of OLEDs based on tris(8-hydroxyquinolato) aluminum (A1Q3), the most widely used electroluminescent molecule, is investigated. OLEDs with various structures are studied. Results reveal that the injection of holes into the AlQ3 layer is the dominant factor responsible for device degradation. Cationic AlQ3 species are found to be unstable and their degradation products are fluorescence quenchers that lower the electroluminescence efficiency of OLEDs. In view of these findings, the effectiveness of stabilizing agents, such as, doping the HTL, introducing a buffer layer at the hole-injecting contact, or using mixed layers of hole and electron transporting molecules, is explained in terms of their role in slowing down the injection of holes into the AlQ 3 , which results in a higher electron density and thus a more rapid electron-hole recombination. Therefore, the lifetime of the unstable cationic AlQ3 species is reduced leading to a significant decrease in AlQ 3 degradation and consequently increases device stability. Other earlier observations pertaining to OLED degradation are also addressed. The degradation mechanism is further demonstrated on OLEDs with dual-layer HTL made of materials with different ionization potentials. The important features of a theoretical framework to model OLED degradation are also discussed.</p> / Doctor of Philosophy (PhD)

<p>Steelmaking dust is generated in high temperature refining step at a rate of about 2% of the steel produced. Electric Arc Furnace (EAF) dust is classified as a hazardous material due to its content of leachable heavy metals, i.e., Pb, Cd, and Cr. Therefore, it must be treated before disposal to meet certain environmental regulations. Most processes for the treatment of EAF dust involve recovery of valuable metals, such as zinc. In most cases alkali halides and lead in the dust are problematic in both processing and product quality. In the present work a pre-treatment is proposed to separate "more volatile species" which include the alkali halides, lead compounds and cadmium oxide, from "less volatile species" which include iron, zinc and calcium oxides. Evaporation of volatile species in this process takes place at about 900° C in a virtually closed system under reduced pressure, and condensation of the vapors occurs at a lower temperature. The thermodynamic aspects of the process are considered. With the use of three different experimental apparatuses the kinetics of the system are studied. The rate of individual kinetic steps; evaporation, condensation, heat and mass transfer, are calculated and compared with the observed overall rate of reaction. A numerical model for the heat transfer inside the dust bed is developed. Applying the principles of mass and heat transfer to the system under investigation, and using the results of the experiments and the numerical model of heat transfer, it is shown that heat transfer across the porous dust bed is most likely the rate controlling step. A rotary reaction chamber is designed to facilitate the heat transfer to dust particles and eliminate the slow kinetic step of heat transfer across the stationary dust bed. With the use of the rotary reaction chamber the duration of treatment is significantly reduced under otherwise identical conditions. The benefit of the rotational movement may be appreciated by direct comparison of the treatment of twenty five grains EAF dust. At a furnace temperature of 1100°C for 95% removal of the volatile species the time required (from the introduction of the apparatus at 25°C to its withdrawal from the furnace) is 12 minutes for the stationary and 8 minutes for the rotational chamber. At a lower furnace temperature of 950°C , the degrees of removal of lead and potassium are about 51% and 27% for 12 minutes in the stationary reaction chamber and about 83% and 78% for 10 minutes in the rotary reaction chamber. A secondary incinerator dust is also investigated in the present work. In 6 minutes at a furnace temperature of 950°C about 99% of the volatile species including NaCl , KCl , and lead compounds are removed from twenty five grams dust. The residue has an enrichment of zinc from 27%wt to 78%wt . This environmentally friendly and energy efficient process may be applicable for the separation of "more volatile species" in dust generated from most high temperature processes such as steelmaking, incineration, nonferrous processes and cement manufacturing.</p> / Doctor of Philosophy (PhD)

<p>The ionic stability of oxide particles in polar non-aqueous media is studied. Surface chemistry and interparticle forces are manipulated by controlling the acidity and ionic strength of the suspensions without dispersants. The acidity of ethanolic solution is determined using ion transfer functions, wherein the relationships between acidity, oxide particle-surface-charge, zeta-potential, stability and suspension rheological behaviour are established. The ionic stability of oxide particles in ethanol can be controlled by combination of potential determining ions and indifferent electrolyte to optimize the values of repulsive potential and repulsive force. It is shown oxide particles can be charge-stabilized, as in aqueous suspensions. The viscosity and flow curves for oxide/ethanol suspensions are acidity dependent. The flow curves of the suspensions follow the Casson model and the Casson yield value is used to evaluate their stability. Positive isoelectric point shifts were observed for alumina and magnesia in ethanol on increasing the solid concentration. However both dilute and concentrated aqueous suspensions of alumina give the same isoelectric point. Silica/ethanol suspensions are stable near the IEP. This result suggests the colloidal stability of silica in ethanol can not be explained exclusively by the ionic stability mechanism of DLVO theory. The discrepancy is believed due to a steric barrier consisting of a silicic acid gel network. The surface chemistry and rheological properties of alumina suspensions in EtOH and DMSO are strongly influenced by the ionic strength of the suspensions. Rheological measurements show the viscosity of the suspensions decreases with increasing salt concentration due to suppression of the second electroviscous effect. Solvent is found to have a marked influence on suspension rheology. The heterocoagulation behaviour of oxide-mixture/ethanol suspension systems is examined, elucidating the general principles underlying structure formation in mixed dispersions. It is demonstrated that the architecture of composites can be controlled by manipulation of the relative colloidal stability of the constituent primary particles.</p> / Doctor of Philosophy (PhD)

<p>In the manufacture of sulphuric acid more stringent environmental standards and operation economics have forced the industry to improve product utilization, energy efficiency and reliability. A key to improving both the thermal efficiency and reliability is the use and/or development of more corrosion resistance materials including stainless steels, especially in the parts of the plant that handle the condensed acid. Application of more corrosion resistant material requires a better understanding of the corrosion mechanism involved in concentrated H2 SO4 -H2 O (>90 wt.%) solutions. While corrosion kinetics of carbon steel, the traditional material of construction, are relatively well understood, this is much less true in the case of the cyclic active-passive corrosion of stainless steels. Models proposed to explain the cyclic active-passive corrosion involve a periodic formation of either a protective metal sulphate film or an insoluble sulphur layer. To better understand the reactivity and/or passivity of stainless steel in concentrated H2 SO4 -H2 O solutions a study employing immersion and electrochemical techniques, including rotating electrodes, was conducted in order to clarify the following: (1) The state of stainless steel passivity. (2) The conditions in which passivity is stable. (3) The role played by the major alloying elements in establishing and maintaining the passive state. The study involved evaluating the corrosion behaviour of stainless steels S30403 and S43000 along with iron, chromium and nickel in 93.5 wt.% H2 SO4 at temperatures between 25-80°C. Major discoveries of the study include: (1) A content of 17-18 wt.% chromium is sufficient to anodically passivate S43000 as the potential is made more noble. Passivity is not stable and requires anodic polarization. (2) Alloyed nickel plays an active role in improving the corrosion resistance of stainless steel. A content of 8 wt.% nickel is sufficient promote a periodic passivation of the base Fe-(17-18)wt.% Cr stainless steel under open-circuit conditions which reduces the corrosion rate by at least an order of magnitude. (3) The electrolysis of concentrated H2 SO4 -H 2 O solutions involves a potential-dependent reduction of H2 SO 4 molecules to sulphur-containing species with an oxidation state lower than six (6). The various reduction products have a significant effect on the stainless steel corrosion resistance. (4) Successful modelling of the corrosion of nickel has been accomplished by using a galvanic interaction between a noncontinuous nickel sulphide (NiS) deposit, formed in situ, and the uncovered nickel metal. (5) Successful modelling of the active-passive corrosion of S30403 has been accomplished using a galvanic interaction between NiS(Ni) and S43000.</p> / Doctor of Philosophy (PhD)

<p>The evolution of molecular dynamics during the polymerization of linear-chain and network forming liquids was studied using dielectric spectroscopy and differential scanning calorimetry. Polymerization was carried out using step-addition reactions between epoxide and amine molecules, and by catalysis of epoxide molecules with tertiary amines. The former resulted in linear-chain or network structured polymers while the latter resulted in network polymers. The step-addition polymerizations resulted in linear-chain polymers by reacting stoichiometric quantities of diepoxide and monoamine molecules, and network structure polymers by reacting stoichiometric quantities of triepoxide and monoamine molecules, or diepoxide and diamine molecules. The growth and extinction of localized (or secondary) relaxation processes during the polymerization were studied by measuring the changing dielectric properties using two techniques; fixed frequency dielectric measurements during heating of the partially polymerized samples, and isothermal dielectric measurements over the frequency range of 1 MHz to 20 GHz. The number of covalent bonds formed at any instant during the polymerization was determined by isothermal calorimetric measurements. Thus, the change in the dielectric properties during polymerization was associated with the increase in the number of covalent bonds. It was found that the localized relaxations evolve in a manner that is independent of the spontaneous increase in configurational entropy. The results also tend evidence towards the concept that these relaxations occur in regions of relatively high energy, and the collapse of such regions led to the observed changes in the dielectric properties. As well, an analogy was made between the structural relaxation of a physically metastable glass and the polymerization of a chemically metastable liquid. This has lead to the concept of a chemical fictive temperature to describe the state of the polymerizing liquid. The effects of pressure on the dielectric properties of the polymerizing liquids was studied using fixed frequency dielectric measurements. Pressure was step-increased, both at the beginning of the polymerization and at a time during the polymerization, then maintained. An increase in pressure increased the rate of polymerization, and thus the dielectric properties evolved more rapidly with time. The chemical effects of pressure during polymerization were examined using transition state theory and the concept of negative feed-back. The physical effects of pressure were investigated in terms of its effects on the equilibrium dielectric properties. It was shown that the polymerization kinetics are increased with increased pressure when the kinetics are in the mass-controlled regime, and decreased with increased pressure when the kinetics are in the diffusion-controlled regime. The transition from mass- to diffusion-controlled kinetics was investigated using the rate of change of the dielectric loss. Finally, the chemical and physical effects of step-increased pressure upon the dielectric properties of polymerizing liquids in the mass-controlled regime were mathematically simulated using current concepts and formalisms. The simulated results were qualitatively similar to those obtained experimentally, demonstrating the adequacy of the understanding.</p> / Doctor of Philosophy (PhD)

<p>This work has involved a study of diffusion and ion implantation enhanced diffusion in GaAs based semiconductor heterostructures. A knowledge of kinetic parameters underlying the diffusion process is of practical value in the fabrication of optoelectronic devices. Two main problems have been explored. (a) Thermal interdiffusion of (InGaAs/GaAs)quantum well structures and superlattices. Transmission electron microscopy, X-ray diffraction and photoluminescence experiments have been undertaken to follow the temporal evolution of the indium composition during annealing of the superlattice. A linear model of diffusion has been utilized to calculate the evolution of strain, indium composition and the X-ray diffraction intensity during annealing. Calculation of energy levels of the electrons and holes in the superlattice structure and their evolution with annealing have also been performed following a transfer matrix approach. This has been used to predict the experimentally observed trends in photoluminescence. Non linear aspects of diffusion including composition dependence and strain dependence (by growth on 311A substrates) have also been experimentally examined. (b) Ion implantation enhanced disordering of III-V compound semiconductor heterostructures (InGaAs/GaAs, GaAs/AlGaAs). Various parameters which influence the disordering process, namely the implant energy, ion species, implant temperature and heterostructure composition have been studied with transmission electron microscopy (conventional/high resolution) and photoluminescence techniques. Several interesting phenomena with respect to the position and crystallographic nature of implant damage have been observed. A phenomenological model to rationalize data has been developed by numerically solving the governing diffusion equations.</p> / Doctor of Philosophy (PhD)