<p>For environmental and economical considerations, it is desirable to use iron ore concentrates directly without agglomeration and coal directly without coking for ironmaking. The present work is a study of the kinetics and mechanisms of iron ore reduction in ore/coal composites. An experimental system has been designed and experiments have been conducted with in-situ measurements of temperature and pressure to establish profiles within the ore/coal packing with the furnace temperature maintained at 1200 or 1300ºC. Samples were taken at various locations for chemical analysis in the partially reacted specimens. These experiments lead to a better understanding of this non-isothermal and non-isobaric system. A non-isothermal and non-isobaric mathematical model has been developed and validated by the experimental data. Mechanisms of heat transfer, mass transfer and interfacial reactions were studied using the mathematical model. The contribution of the individual kinetic steps to the rate of overall reaction were compared to evaluate the rate controlling step. The contribution of the author is the design of the experimental system which has demonstrated the non-isothermal and non-isobaric nature of the reaction system, and the development of the mathematical model. The present study may be used in new ironmaking processes and carbothermic process, such as FASTMET and cokemaking processes.</p> / Doctor of Philosophy (PhD)

<p>Growth of superlattices on V-grooved substrates has become a popular method of producing quantum wires. The success of this technique to date has been limited to the lattice-matched AlGaAs/GaAs system. The unpredictability of the morphology and defects found in lattice-mismatched systems has been a major hindrance in their development. Additionally, the misfit stresses in lattice mismatched systems may play an important role in determining the properties of the laser. In V-grooves, the singular points at the corners of the groove produce a stress distribution completely different from the case of layers grown on a planar substrate. Accurate knowledge of the stress distribution is hence necessary because a stress can affect the optoelectronic properties and lead to defects, limiting the life of the laser. The aim of the project was two fold: first to characterize the InGaAs/InP growth on (211)A and (111)B grooves using molecular beam epitaxy in terms of faceting, thickness variation, and composition variation; second to obtain an analytical and numerical stress distribution for the case of a layer with uniform composition and thickness grown on a sharp V-groove. The characterization was performed using transmission electron microscope and degree of polarization methods. Composition analysis was done with a high resolution scanning transmission electron microscope. Numerical simulation was done using a commercial finite element program, 'ABAQUS'. The results showed a clearly distinct morphology for layers grown on faceted (211)A and (111)B substrates. The differences observed in faceting, thickness variations, and composition variations in the (211)A and (111)B grooves suggest that the lower incorporation rate of group III atoms on (111)B surfaces leads to increased interfacet diffusion compared to (211)A grooves, where a higher incorporation rate produces layers with uniform composition and thickness. Furthermore, the 46.5% increase in In content found at the bottom of (111)B grooves indicates that the mean diffusion length of In is much higher than Ga for the growth conditions used in this study. The large variation in composition in (111)B grooves produced extensive defects at the bottom of the groove and at certain locations of the sidewall where the misfit exceeds the critical limit. The analytical and numerical solution of the stress distribution were in good agreement with experimental results. The stress fields obtained by these methods would be useful in helping to predict the optoelectronic properties of the quantum wire. Furthermore these models are useful in determining the composition and thickness of the layers which need to be grown to obtain specific optical properties.</p> / Doctor of Philosophy (PhD)

<p>The mechanical behaviour in uniaxial tension and compression of extruded and aged Mg-8.5wt%Al was studied. In-situ neutron diffraction was used to follow the elastic lattice strains under load in the matrix and the precipitates. The internal stresses determined from these measurements are highest in grains unfavourably oriented for both basal slip and {10Τ2} twinning, lowest in grains oriented favourably for both, and in between for grains oriented favourably for {10Τ2} twinning only. Most variations in scattered peak intensity are due to the lattice reorientation produced by {10Τ2} twinning. A critical resolved shear stress criterion is shown to apply for twinning. Intensity variations which cannot be explained by {10Τ2} twinning occurred in some grains during tensile loading. They are likely due to {10Τ1} twinning which produces c-axis compression, unlike {10Τ2} twinning. Transmission electron microscopy revealed the presence of c- and non-basal a-dislocations in the undeformed alloy. Basal slip is the most common slip system, though non-basal a-slip also occurs. Only {10Τ2} twinning was observed by TEM. Twins often traversed grains completely, despite the presence of the precipitates. Schmid factor considerations show that pure magnesium yields first by basal slip. The early portion of the stress-strain curve should thus be considered a region of rapid strain hardening due to basal dislocation pile-ups at grain boundaries. In compression {10Τ2} twinning can also occur at very low applied stress. Strengthening in the alloy before yield is explained using a Brown and Clarke mean-stress hardening model. Beyond yield, relaxation mechanisms reduce the mean stress contribution essentially to zero in tension. The mechanical and physical properties of the intermetallic were obtained from experiments on a single crystal. Property correlations have been used to estimate the fracture toughness and yield stress, assuming its behaviour is similar to that of a ceramic.</p> / Doctor of Philosophy (PhD)

<p>The most useful properties of ceramics (high temperature strength, chemical inertness and hardness at low density) are accompanied by brittleness. This is still the main factor limiting widespread application of ceramic materials. In the present thesis an energy approach to fracture of ceramics was undertaken and refined to account for a nonelastic behaviour of these materials. A chevron-notched (CN) four-point bend specimen was recognized as effective experimental arrangement for room and elevated temperature tests. Consequently, a number of theoretical studies of the specimen's performance were undertaken. Modelling of the variation of the strain energy release rate with the crack extension revealed that the subcritical crack growth in a CN specimen causes dependence of the measured fracture parameters on the experimental procedure (stressing rate, stiffness of the testing system, crack length). It appears that, as complete fracture is approached (i.e. 100% of the specimen's cross-section), the measured work-of-fracture approaches that required for crack initiation. An electrical potential drop technique for crack length measurement in the CN specimen was developed for elevated temperatures fracture studies in the ionically conducting zirconium oxide ceramics. The resistance-to-fracture versus crack extension was determined for a range of temperatures (25 to 1300℃) for stabilized zirconias and their HfO₂ solid solutions and with second phase p-Al₂O₃ particles dispersed in them. The room temperature results agreed with the literature data and model predictions. Above 1000℃ an energy input of ⁻1 J/m² is required to drive the crack through zirconium oxide ceramics. Viscoelastic effects and crack interaction with p-Al₂O₃ particles result in a total fracture energy dissipation two orders of magnitude higher.</p> / Doctor of Philosophy (PhD)

<p>Currently available theoretical formulation for the kinetics of slag-metal systems have been extended to clarify certain aspects of the system. Coupling factors for electrochemical reactions and for ionic diffusion have been defined to clarify the significance of coupling phenomena in the kinetics of multi-component systems. Theoretical equations for the interfacial reactions and the diffusion processes in both phases, in seven hypothetical pseudo-ternary slag-metal systems have been numerically solved by a finite difference method. Typical features of coupling phenomena, i.e.m acceleration and deceleration of reaction or diffusion, and up hill reaction or diffusion have been clearly demonstrated. Through numerical analysis, a modified form of "Sherwood Number", Shᵢ*≡kᵢL/ρDᵢ for a particular reaction i, is defined and found to be proper to explain the rate controlling steps for the over-all reaction. In the present analysis, the relationships between the modified Sherwood Number and rate controlling steps were found to be as follows: Sh*ᵢ > 360: diffusion control, 0.05 ≲ Sh*ᵢ ≲ 360: mixed control, Sh*ᵢ < 0.05: interfacial reaction control Thus non-trivial numerical solutions for slag-metal systems have been developed for the first time.</p> / Master of Engineering (ME)

<p>The dielectric and semiconducting properties of two types of ceramics (n-type BaTiO₃ and dielectric Ba(B'⅓ B''⅔ )O₃ where B' = Mg, Zn, Ni, and B'' = Nb₁ Ta) were characterized. Complex impedance analysis and dc conductivity measurements of samples prepared at various [Special Characters Removed] have ruled out oxygen chemisorption in favor of interfacial segregation of cation vacancies as the cause of the positive temperature coefficient of resistivity (PTCR) effect in n-type BaTiO₃ . The effect of preparation conditions, sintering atmosphere, stoichiometry, and post-sinter anneal on the defect chemistry of BaTiO₃ was studied using the electron paramagnetic resonance (EPR) technique. Several paramagnetic defects such as, Ti³⁺ , [Special Characters Removed] were detected and identified by EPR. Current-voltage characteristics (I-V ) of PTCR BaTiO₃ were analyzed in light of space-charge-limited-current, trap-filled-limited-current, Frenkel-Poole, small polaron, and double-Schottky barrier models. It was shown that for the double-Schottky barrier model, a partial stabilisation of the potential barrier is expected when the Fermi level is pinned at grain boundaries by a high density of the interface states. The deviation of I-V characteristics of BaTiO₃ in the region of the PTCR effect can be explained by dependence of the population of the interface electron states on applied voltage. Based on the Seebeck and Hall effect measurements, it was found that in the range of 100-300 K, the drift mobility of electrons in BaTiO₃ is not thermally activated, which supports the concept of conduction band electron transport rather than small radii polaron hopping. However, further study over a wider temperature range and on better quality crystals is required to unequivocally clarify the electron transport mechanism in BaTiO₃ . Phase composition, degree of cation ordering, and dielectric properties of complex perovskites with general formula Ba(B' ⅓ B''⅔ )O₃ where B' = Mg, Zn, Ni, and B'' = Nb₁ Ta were analyzed. It was shown that in Ba(Mg⅓ Ta⅔ )O₃ both intrinsic and extrinsic dielectric loss affect the Q-factor, whereas in Ba(Mg⅓ Nb⅔ )O₃ and Ba(Ni⅓ Nb⅔ )O₃ extrinsic factors such as the second phase and point defects dominate the dielectric loss at microwave frequencies.</p> / Doctor of Philosophy (PhD)

<p>Silicon nitride is sintered with the use of additives, such as Y₂O₃ and Al₂O₃, in order to enhance densification. After sintering, these additives along with SiO₂, present on the starting Si₃N₄ powder, form an intergranular amorphous phase. The presence of a glassy phase is generally thought to be detrimental to the high temperature creep properties. In the material analyzed, Kyocera SN220, this intergranular glassy phase partially devitrifies upon annealing. Thus the effect of a fully amorphous or a partially crystalline intergranular phase on the creep properties could be assessed. The creep resistance of the material is only modestly affected by partial grain, boundary devitrification in both flexural and compressive creep. However the creep life is reduced significantly.</p> <p>Extensive analytical microscopy was done on the amorphous and partially crystalline material in order to determine what changes were occurring due to anneling and due to creep deformation. A quantitative methodology was developed for electron energy loss spectroscopy to analyze the intergranular phase composition. Using this technique concentrations of light elements, such as oxygen and nitrogen, and heavier elements could be determined. Different crystalline grain boundary products were found near the surface of samples annealed in air compared to the centre of these and throughout samples annealed in an inert atmosphere. However the residual amorphous phase composition was the same regardless of annealing atmosphere or location. In addition, phases present after devitrification did not depend on the stress state. Extensive cavitation, a commonly observed effect of creep, did not occur in samples containing the maximum obtainable strain in flexure of 2.7%.</p> <p>The observed microstructural information and creep data was taken into consideration in developing a creep model. This model describes creep due to non-linear viscous flow of an amorphous intergranular phase around a hexagonal array of grains. An initial constant strain rate is predicted at low strains, followed by a decrease in strain rate as the intergranular phase is squeezed out from between grains. This decrease occurs at smaller strains in compression than in tension or flexure. The creep behaviour observed experimentally corresponds well with that predicted theoretically.</p> / Doctor of Philosophy (PhD)

<p>Two model systems, Co-Rh and Ni-Co, were used to study surface segregation and oxidation phenomena on binary alloys.</p> <p>Cobalt was found to sputter preferentially from five Co-Rh alloys ranging in composition from 19.3 to 84.7 at % Rh when irradiated by 4 keY Ar⁺ ions. Surface segregation experiments on this system in the temperature range 623 to 1123 K showed that cobalt was enriched on the surface of a 84.7Rh alloy while rhodium enrichment was determined for a 19.3Rh alloy. No conclusive segregation could be measured on the surface of a 47.8Rh alloy. The variation of surface concentration with temperature indicated enthalpy values of 1 ± 1 kJ mol‾¹ and -3 ± 7 kJ mol‾¹ for the 19.3Rh and 84.7Rh alloys, respectively. Reasonable agreement was found between these measured enthalpy values and those calculated from the combined bond breaking and lattice strain models of surface segregation.</p> <p>Oxidation experiments were performed on (110) Ni-3.86Co and Ni-4.0Co polycrystalline alloys at temperatures in the range 673 to 1073 K and a pressure of 5x10‾³ Torr. The effects of surface pretreatment and orientation of the alloy surfaces were correlated to differences in oxide morphology and growth rates. Single crystal specimens which were chemically polished, annealed in vacuum and initially exposed to oxygen at room temperature showed a tendency to form (100) (NiCo)O ⎮⎮ (110) Ni-3.86Co. These layers also exhibited the slowest growth rates and greater enrichment of CoO from the inner to outer oxide surfaces. Single crystal surfaces prepared by chemical polishing, annealing in vacuum and initial exposure to oxygen at the reaction temperatures developed additional oxide orientations parallel to the underlying alloys. Finally, the polycrystalline Ni-4.0Co specimens which were prepared by mechanical polishing followed by exposure to room temperature oxygen developed polycrystalline oxide films. These types of structures were associated with higher rates of oxide growth and lower enrichments of CoO from the inner to the outer oxide surfaces.</p> <p>The experimentally measured composition profiles were analysed according to the Wagner(⁶) model of oxidation, modified to include the effects of short circuit grain boundary diffusion. Effective alloy interdiffusion coefficients were calculated which showed that the rate of transport in the alloy zone beneath the growing oxide layer was enhanced relative to that expected solely on the basis of volume diffusion in this phase. The results were rationalized according to a dislocation model for the accomodation of plastic strain and vacancy annihilation in cation conducting scales(¹⁴⁹).</p> / Doctor of Philosophy (PhD)

<p>Atomic mixing resulting from heavy-ion bombardment of thin-film Ni/Pd bilayers and thin Pd markets sandwiched between two Ni layers has been investigated. Experiments were carried out using 120 keV Ar⁺ and 145 keV Kr⁺ ions for doses 0-4x10¹⁶cm⁻² over a wide temperature range (40-673K). The resulting interdiffusion was measured using 2 MeV ⁴He⁺ ion backscattering in-situ. In some cases, additional depth analysis was undertaken using Auger Electron Spectroscopy (AES) with sputter depth profiling. The influence of film microstructure and bombardment-induced microstructural changes on the mixing have been assessed with transmission electron microscopy (TEM). The electrocatalytic behavior of the ion-mixed bilayer samples was determined for the hydrogen evolution reaction in strong KOH solution, using potentiostatic polarization techniques. The amount of ion beam mixing is found to vary with the square root of the ion dose for temperatures ≤ 573K. Also, at 40K, where it is assumed that no significant thermally activated process contributes to the mixing, it is found that the mixing is dependent on the damage energy, FD(subscript, see original file), deposited at the interface region. Between 40 and ~400K, the mixing parameter shows a weak temperature dependence with an apparent activation energy Ea ~ 0.1eV. This suggests that some interstitial diffusion contributes to the inter-mixing in this temperature regime. Above ~ 473K, the mixing (at each temperature) increases rapidly with ion dose for ir radiation doses ≤ 5x10¹⁵cm⁻² with high initial mixing efficiencies of 6-35 atoms/ion between 573-673K. This initial rapid mixing level eventually slows to a less rapid (~1.2 atoms/ion at 673K) rate for doses ≥ 5x10¹⁵cm⁻². TEM observations of the irradiated and unirradiated films suggests that the change to a less rapid mixing rate is correlated with an increase in the average grain diameter (10-80nm) in the film following ion bombardment, and therefore with a reduction in the contribution of grain boundary diffusion to the intermixing. For samples annealed, without irradiation, below ~ 473K, no measurable interdiffusion of the Ni/Pd layers was observed. For samples annealed above ~473K, Whipple analyses of the interdiffusion show two distinct regions - lattice diffusion-dominated region near the original interface and grain boundary diffusion dominated region further away from the interface. The lattice diffusivities, Dℓ(subscript), under thermal annealing conditions were evaluated and ranged from ~ 0.22 to 52x16⁻¹⁶cm⁻²-sec⁻¹ for Pd diffusing in Ni, and 0.33 to 56.6x10⁻¹⁶cm²-sec⁻¹ for Ni diffusing in Pd between 523-673K. These lattice diffusivities are high because of enhancement of diffusion by defects present in the as-prepared films. The grain boundary diffusion coefficients (for Pd diffusion in Ni boundaries) DB(subscript) varied from ~ 5.4x10⁻¹⁴cm²-sec⁻¹ at 523K to ~ 3x10⁻¹¹cm²-sec⁻¹ at 623K, with an apparent activation energy EB(subscript) ~ 1.35 eV and a prefactor D⁰B(subscript) ~ 0.75 cm²-sec⁻¹. Under irradiation conditions, ion irradiation results in an enhancement of the mixing especially below ~ 400K where almost an order of magnitude enhancement over thermal anneal only, was observed. At ~ 673K, the contribution of equilibrium defects to interdiffusion over-whelms the irradiation effects. The diffusion coefficients under irradiation, Drad(subscript), were also evaluated and ranged from ~4 to 70x10⁻¹⁶cm²-sec⁻¹ at 523 and 673K with apparent activation energy Ea ~ 0.57 eV. For Pd films deposited on large-grain Ni substrates, thermal annealing and/or bombardment result in mixing levels that are almost two orders of magnitude lower than observed from small-grained Ni/Pd couples, though under irradiation conditions, radiation enhancement of the mixing was also observed. As potential electrocatalysts for the H₂ evolution reaction in strong KOH solution, the ion-beam mixed surface alloys (in the over-potential range ≤ 0.4 V) show superior performance over smooth Ni, and Ni coated with evaporated Pd.</p> / Doctor of Philosophy (PhD)

<p>This thesis is a report on a series of measurements of ion-bombardment effects on α-quartz crystals. Damage was produced in α-quartz (single-crystal SiO₂) by bombarding with ions of ⁴He⁺ to ²⁰⁹Bi⁺⁺ in the energy range of 15 - 200 keV, at both 300 K and ≤ 50 K. The samples were analysed in - situ with Rutherford backscattering/channeling, using 1 - 2 MeV ⁴He⁺ ions; data was obtained from both the oxygen and silicon peaks, so that damage stoichiometry could be calculated. At low ion fluences (~ 10¹⁰ - 10¹¹ ions/mm²) the apparent damage level increases linearly with fluence, but at rates of about 3 - 19 times greater than predicted by the modified Kinchin-Pease equation. At higher fluences (~ 10¹¹ - 10¹² ions/mm²) the rate of damage increases with fluence for elastic energy deposition rates of less than :::= 0.08 eV/atom, but remains constant for greater elastic energy deposition rates. At even higher ion fiuences saturation of the damage occurs. It has been observed that the analysis beam creates damage at a rate dependent on the level of damage already present in the crystal; furthermore, the damage created by the analysis ions appears to be predominantly due to the inelastically deposited energy. Strain effects seem to greatly exaggerate the level of damage indicated by simple channeling calculations. A simple model is proposed to explain both the high rates of damage production and the non-stoichiometry of the damage. The model indicates that the effects of elastic energy deposition, inelastic energy deposition, strain produced by damage, and lattice relaxation into a '"quasi-amorphous" state. all contribute to the apparent damage levels synergistically.</p> / Doctor of Philosophy (PhD)