<p>It is assumed in this study that the protection imparted by passive layers is dependent upon the balance between the breakdown of the protective film and the healing of the produced flaws. Therefore, the occurrence of a pit must coincide with a change in the local conditions in a flaw which did not heal.</p> <p>Using this hypothesis, five proposed theories for pitting corrosion are compared using data published in the literature. The processes assumed to occur during pit nucleation are simulated. The solution compositions and potentials from reported experimental determinations of pitting potentials are used as initial conditions. The potential and concentrations at the base of the flaw are computed by using mass transport equations.</p> <p>The values obtained are then used to compare the five models. For each theory, an expression depending on potential and concentrations at the metal surface was identified, so that where a theory is correct, this expression is smaller (or larger) than a parameter. This parameter, should be constant, and independent of the particular set of experimental conditions (e.g. pH, chloride concentration in the bulk solution), as all the calculations are made for conditions corresponding to the pitting potential, i.e. conditions borderlining between pitting and passivity.</p> <p>The particular case of iron in borate buffers is considered here. The computed results indicate that the most probable mechanism controlling pitting is the adsorption of the chloride ions at the metal surface. The repassivation by precipitation of ferrous hydroxide is always thermodynamically favoured, but apparently slow.</p> / Doctor of Philosophy (PhD)

<p>Thermodynamic measurements were made using the following ionic materials as solid electrolytes in galvanic cells: calcia stabilized zirconia, Naβ and α-alumina, Caβ"-alumina, Kβ- and α-alumina, Laβ- and α-alumina, and Caβ and α-alumina. With the exception of the widely employed calcia stabilized zirconia, the ionic materials utilized in this work have only recently been developed as solid electrolytes. In order to characterize these β-/β"-aluminas for high temperature galvanic cell applications, their chemical stabilities were determined.</p> <p>The following sections give a description of the various galvanic cells used in the present study, and a summary of the thermodynamic information obtained from each cell.</p> <p>Calcia Stabilized Zirconia (and Naβ- and α-alumina) Solid Electrolytes in Galvanic Cells for Equlibrium Studies in M-S-O Systems</p> <p>(M = Ca, Mg, La, K and Na)</p> <p>The following electrochemical cells were used for thermodynamic equilibrium studies in metal-sulphur-oxygen systems:</p> <p>Cell I</p> <p>Pt⎮Cu(s), Cu₂S(s), CaS(s), CaO(s)⎮CSZ⎮Air⎮Pt</p> <p>Cell II</p> <p>Pt⎮CaS(s), CaSO₄(s)⎮CSZ⎮Air⎮Pt</p> <p>Cell III</p> <p>Pt⎮Cu(s), Cu₂S(s), CaSO₄(s), CaO(s)⎮CSZ⎮Air⎮Pt</p> <p>Cell IV</p> <p>Pt⎮Ag(s), Ag₂S(s), MgS(s), MgO(s)⎮CSZ⎮Air⎮Pt</p> <p>Cell V</p> <p>Pt⎮Ag(s), Ag₂S(s), MgS(s), MgO(s)⎮Naβ-and α-alumina⎮Ni(s), NiO(s)⎮Pt</p> <p>Cell VI</p> <p>Pt⎮Cu(s), Cu₂S(s), La₂O₂S(s), La₂O₃(s)⎮CSZ⎮Air⎮Pt</p> <p>Cell VII</p> <p>Pt⎮Ag(s), Ag₂S(s), La₂S₃(s), La₂O₂S(s)⎮CSZ⎮Air⎮Pt</p> <p>Cell VIII</p> <p>Pt⎮Ag(s), Ag₂S(s), La₂S₃(s), La₂O₂S(s)⎮Naβ-and α-alumina⎮Ni(s), NiO(s)⎮Pt</p> <p>Cell IX</p> <p>Pt⎮K₂S(s), K₂SO₄(s)⎮CSZ⎮Air⎮Pt</p> <p>Cell X</p> <p>Pt⎮Na₂S(s), Na₂SO₄(s)⎮CSZ⎮Air⎮Pt</p> <p>The results from Cells I, III and VI were each combined with the values of ΔGfº for Cu₂S in order to calculate the ΔGº of the following reactions:</p> <p>CaO + 1/2S₂→CaS + 1/2O₂ Cell I</p> <p>CaO + 3/2O₂ + 1/2S₂→CaSO₄ Cell III</p> <p>La₂O₃ + 1/2S₂→La₂O₂S + 1/2O₂ Cell VI</p> <p>Cells II, IX and X were used to determine the standard free energies of oxidation of CaS, K₂S and Na₂S to their corresponding sulphates.</p> <p>The results from cells IV and VII were each combined with the values of ΔGfº for Ag₂S to determine the ΔGº of the following reactions:</p> <p>MgO + 1/2S₂→MgS + 1/2O₂ Cell IV</p> <p>La₂O₂S + S₂→La₂S₃+ O₂ Cell VII</p> <p>Cells V and VII were used to confirm that the oxygen pressures developed in the anodes of cells IV and VII were within the electrolytic domain of the CSZ solid electrolyte.</p> <p>Thermodynamic Stabilities of β-/β"-Aluminas</p> <p>CSZ solid electrolytes were also used to study the chemical stabilities of Caβ"-alumina, Laβ-alumina, Kβ-alumina, and Naβ-alumina. The following cells were employed in this investigation:</p> <p>Cell XI</p> <p>Pt⎮Ag(s), Ag₂S(s), CaSO₄(s)/(CaO)β-(s)⎮CSZ⎮Air⎮Pt</p> <p>(CaO)β-(s) refers to Caβ-alumina in coexistence with MgO-Al₂O₃(s) and α-Al₂O₃(s).</p> <p>The results from cell Xl were employed for determining the CaO activities in α-AI₂O₃(s)/MgO-AI₂O₃(s)/Caβ"-alumina coexistence.</p> <p>Cell XII</p> <p>Pt⎮Ag(s), Ag₂S(s), La₂O₂SO₄(s), (La₂O₃)β/α(s)⎮CSZ⎮Air⎮Pt</p> <p>(La₂O₃)β/α refers to Laβ-alumina in coexistence with α-Al₂O₃</p> <p>Cell XIII</p> <p>Pt⎮Ag(s), Ag₂S(s), La₂O₂SO₄(s), (La₂O₃)β/ʟᴀ(s)⎮CSZ⎮Air⎮Pt</p> <p>(La₂O₃)β/ʟᴀ refers to Laβ-alumina in coexistence with La₂O₃-Al₂O₃(s).</p> <p>Cells XII and XIII were used to obtain the values of La₂O₃ activities in α- Al₂O₃/Laβ-Al₂O₃ and La₂O₃-Al₂O₃/Laβ-Al₂O₃ coexistences.</p> <p>Cell XIV</p> <p>Pt⎮Ag(s), Ag₂S(s), K₂S(s), (K₂O)β/α(s)⎮CSZ⎮Air⎮Pt</p> <p>(K₂O)β/α refers to the Kβ-alumina in coexistence with α-Al₂O₃.</p> <p>Cell XV</p> <p>Pt⎮Ag(s), Ag₂S(s), Na₂S(s), (Na₂O)β/α(s)⎮CSZ⎮Air⎮Pt</p> <p>(Na₂O)β/α refers to Naβ-alumina in coexistence with α-Al₂O₃.</p> <p>The result from these two cells were utilized in order to calculate the respective alkali oxide activities in α-Al₂O₃/β-Al₂O₃ coexistences.</p> <p>The thermodynamic stability of Caβ-alumina (CaO-6AI₂O₃) was determined by measuring the CaO activities in α-Al₂O₃/β-Al₂O₃ and CaO-2Al₂O₃/β-Al₂O₃ coexistences. These measurements were undertaken by using Caβ"-alumina as solid electrolyte in the following two calcium concentration cells:</p> <p>Cell XVI</p> <p>Pt⎮Air⎮CaO(s),Pt(s)⎮Caβ"-alumina⎮Pt(s),CaO-6Al₂O₃(s),α-Al₂O₃(s)⎮Air⎮Pt</p> <p>Cell XVII</p> <p>Pt⎮Air⎮CaO(s),Pt(s)⎮Caβ"-alumina⎮Pt(s),CaO-6Al₂O₃(s),CaO-2Al₂O₃(s)⎮Air⎮Pt</p> <p>Thermodynamics of CaO-AI₂O₃ System Using Caβ"-Alumina Solid Electrolyte</p> <p>Caβ"-alumina solid electrolytes were utilized to measure the CaO activities in the CaO-Al₂O₃ system in the following cells (in addition to cells XVI and XVII):</p> <p>Cell XVIII</p> <p>Pt⎮Air⎮CaO(s),Pt(s)⎮Caβ"-alumina⎮Pt(s),CaO-Al₂O₃(s),CaO-2Al₂O₃(s)⎮Air⎮Pt</p> <p>Cell XIX</p> <p>Pt⎮Air⎮CaO(s),Pt(s)⎮Caβ"-alumina⎮Pt(s),3CaO-Al₂O₃(s),CaO-Al₂O₃(s)⎮Air⎮Pt</p> <p>Cell XX</p> <p>Pt⎮Air⎮CaO(s),Pt(s)⎮Caβ"-alumina⎮Pt(s),CaO(s),3CaO-Al₂O₃(s)⎮Air⎮Pt</p> <p>Two-Phase β- and α-Alumina Solid Electrolytes in Oxygen Concentration Cells</p> <p>The reversibility of two phase β- and α-alumina solid electrolytes to oxygen potentials were tested using the following cells:</p> <p>Cell XXI</p> <p>Pt⎮Fe(s), FeO(s)⎮Naβ- and α-alumina⎮Ni(s), NiO(s)⎮Pt</p> <p>Cell XXII</p> <p>Pt⎮Fe(s), FeO(s)⎮Kβ- and α-alumina⎮Ni(s), NiO(s)⎮Pt</p> <p>Cell XXIII</p> <p>Pt⎮Fe(s), FeO(s)⎮Laβ- and α-alumina⎮Ni(s), NiO(s)⎮Pt</p> <p>Cell XXIV</p> <p>Pt⎮Fe(s), FeO(s)⎮Caβ- and α-alumina⎮Ni(s), NiO(s)⎮Pt</p> <p>Applications</p> <p>(i) The data obtained from cells I to X were used to construct the metal- sulphur-oxygen phase stability diagrams at high temperature for the elements Ca, Mg, La, K and Na.</p> <p>(ii) The phase stability diagrams for Ca-S-O, La-S-O, K-S-O and Na-S-O systems were further extended by including the data for CaO-Al₂O₃ systems (cells XI, XVI to XX),, La₂O₃-Al₂O₃ system (cells XII and XIII), Kβ-alumina (cell XIV) and Naβ-alumina (cell XV) respectively.</p> <p>(iii) The thermodynamic information from the phase stability diagrams for Ca-S-O (extended), Mg-S-O and La-S-O (extended) were combined with available data in the literature to construct deoxidation- desulfurization diagrams for liquid iron at 1643K and liquid steel at 1873K.</p> <p>(iv) The results for the chemical stabilities of β/β"-aluminas (cells XI to XVII) were extrapolated to different conditions of temperatures and oxygen partial pressures. These results were used to determine the feasibility of their utilization as solid electrolytes in galvanic cells for industrial applications in iron and steelmaking.</p> / Doctor of Philosophy (PhD)

<p>The steady-state growth of cells in binary alloy single phase solidification is examined theoretically and experimentally. The failure of the marginal-stability calculations to predict and describe the growth of stable cells indicates a theoretical gap in this field. The Zener-Hillert type model for cellular solidification proposed by Kirkaldy is discussed. In this theory the physics of cell growth demands that the interface be a non-equilibrium interface stabilized by Kinetic and crystallographic effects. A quantitative model following this line is advanced for the steady-state growth of two-dimensional cells. The solution to the free boundary diffusion problem requires, in addition to the boundary conditions, two extra constraints. A principle of minimum cell root radius, surrogate to the principle of minimum rate of entropy production, is used to provide the additional conditions. Cell growth in the succinonitrile-salol system was studied experimentally. For a given set of growth conditions the cells have a unique steadystate spacing and length. Perturbation experiments about the steady-state support the validity of the optimization procedure used in the calculations. Quantitative predictions on steady-state growth are verified by the experiments.</p> / Doctor of Philosophy (PhD)

<p>A new metallurgical reactor called the LB furnace is being developed at McMaster University for potential applications in ironmaking, cokemaking and waste oxide recycling.</p> <p>A bench-scale LB furnace has been built in our laboratory and a series of experiments on ironmaking was carried out with the use of this furnace. The mass balance and thermal efficiency were analyzed for the overall process.</p> <p>A two-dimensional mathematical model for the turbulent, reacting flows in a confined system has been developed to determine the rates of fluid flow, combustion and heat transfer in the reduction/combustion chamber of this furnace. Measurements of velocity and tracer concentration distributions in two room temperature physical models of the chamber were conducted and were used to assess, the validity of the mathematical model.</p> <p>The following-conclusions can be drawn: (1) The LB furnace has the potential to efficiently produce sponge iron or liquid hot metal of desired composition.</p> <p>(2) The mathematical modelling has been shown to be effective in the study of transport phenomena of the turbulent, reacting flows in this metallurgical reactor and has contributed to a better design of the process.</p> / Doctor of Philosophy (PhD)

<p>The effect of hydrogen has been studied on a grade X65 high strength low alloy (HSLA) pipeline steel using a four point bend test. Hydrogen was introduced into single V-notched test samples by a standard BP method. Slow bend tests were conducted on both the base metal and on the heat affected zone (HAZ) of a commercially welded plate. It was found that hydrogen reduced the plastic strain required for crack initiation and increased the rate of crack propagation in three orientations of the base metal and in one orientation of the HAZ. Tests using a higher strain rate, showed that hydrogen still promoted crack initiation but did not affect the rate of crack propagation. Metallographic examination indicated that the orientations of inclusions played an important role in determining the path of crack propagation and delamination.</p> / Master of Engineering (ME)

<p>The thermodynamics of Fe-Nb-C, Fe-Ti-C, Fe-Nb-N austenites and that of binary carbides and nitrides of Ti and Nb essential in the understanding of the precipitation behaviour in microalloyed steels has been investigated in this study. A dynamic gas equilibration technique has been used in the experimental investigation of the thermodynamics of ternary austenites and binary carbides of Ti and Nb. The results obtained in this study have been analyzed using the modified Wagner formalism for dilute ternary austenites and the sublattice - subregular model suggested by Hillert and Staffansson for the interstitial carbides and nitrides. The solubilities of NbC, TiC and NbN in austenite have been determined from the isoactivity measurements done in this study. The solubility minimum and the variation of solubility limits of carbides of Ti and Nb and the increase in carbon content at constant carbon activity have been quantitatively related to the ternary interaction parameter. The C-Nb, C-Ti and N-Nb interaction parameters have been determined. The dissolution free energies of Nb and Ti in fee Fe have been obtained from the analysis of the solubilities of NbC, NbN and TiC in their respective austenites.</p> <p>Expressions describing the variation of the partial molar free energies of the components in the binary carbides and nitrides of transition metals have been obtained via statistical mechanical considerations. The pair interaction free energies involved in the statistical mechanical description of interstitial solutions have been related to the interaction parameters in the sublattice model. The carbon activity measurements in the NbCy and TiCy phases and the nitrogen activity measurements in the NbNy phase obtained in this study together with the data available in the literature have been analyzed to obtain the interaction parameters in the sublattice model. The limitations in applying the classical Wagner-Schottky model to highly nonstoichiometric compounds have been discussed. The necessary modifications to this classical model have been made by referring to the expressions obtained via the statistical mechanical approach.</p> <p>The microalloyed ternary austenite - nonstoichiometric carbide equilibrium has been evaluated for the Fe-Nb-C and Fe-Ti-C systems. The effects due to solute interactions and the nonstoichiometry of the precipitate have been clarified. The solubility of TiN in Fe-Ti-N austenite has been calculated using the dissolution free energy of Ti evaluated in this study. Rational correlations between the ternary interaction parameters and the free energies of formation of carbides and nitrides have been established. Using this correlation an approximate value of the nitrogen-titanium interaction parameter has been evaluated.</p> / Doctor of Philosophy (PhD)

<p>The elastic interaction of the new phase coherent particles with tetragonal distortion is considered. The analysis shows that the elastic energy may be minimized by the formation of regular tridimensional arrays.</p> <p>Studies of the variations of the interaction energy of the Tyapkin array with respect to displacements and volume perturbation of the particles (in the finite approximation) lead to the conclusion that the periodic distribution is stable.</p> / Master of Engineering (ME)

<p>An experimental investigation has been conducted to study the factors influencing the formation and behaviour of the primary slag phase formed in commercial iron ore pellets when reduced under conditions simulating those encountered in the iron blast furnace. Weight loss during reduction, metallographic and electron microprobe analysis techniques have been employed. Possible implications for blast furnace operation are discussed.</p> / Master of Science (MS)

<p>PubIished standard free energy changes and activity data for iron and its binary and ternary alloys have been used to evaluate the general linear series (Wagner) expansion of the activity coefficient and these were employed in turn for the accurate thermodynamic determinations of the liquids line and the field in steels with additions of Mn, Si, Ni, Cr, Mo, Cu, V, Nb and Co. Computer programs based on several derived analytic formulae were used to predict multicomponent constant composition and isothermal phase diagrams for total alloy additions up to 5 wt%.</p> / Master of Engineering (ME)

<p>The rate of corrosion of silica and alumino-silicate refractories in Armco iron and iron-carbon melts was measured. An interpretation of the rate data required an experimental investigation of the kinetics of the reactions between iron oxide and silica, and carbon and silica.</p> <p>A standard "immersion" technique was used under both static and dynamic conditions. The corrosion of the refractories in Armco iron melts was initially controlled by a chemical reaction process but changed rapidly to a steady-state, diffusion-controlled process. A liquid silicate product layer built up at the interface during the induction period. The steady-state rate of corrosion was independent of the oxygen content of the melt and was also found to be a linear function of the peripheral velocity of the refractory specimen. The rate of corrosion for the various refractories was measured and found to be controlled by diffusion of iron and oxygen in the silicate layer.</p> <p>The rate of corrosion of these refractories in carbon-saturated iron melts was also studied. The rate was found to be independent of the silicon concentration and the carbon concentration in the melt (in the range 2.3%C to saturation). The rate was independent of the rate of rotation of the refractory specimen. The results were interpreted in terms of chemical reaction control at the refractory/metal interface, with the dissociation of silica proposed as the controlling reaction. The rate was found to be strongly temperature dependent indicating reaction control.</p> <p>This experimental investigation has provided new insights into the mechanism of corrosion of silica and alumino-silicate refractories in iron melts.</p> / Doctor of Philosophy (PhD)