Title: Effect of Solid State Diffusion on Microsegregation in Steels, Author: Dipak B. Moharil, Location: Thode / <p>Controlled solidification of Fe-2wt% Ni binary and Fe-2 wt% Ni-Xwt%C ternary alloys was carried out in a travelling furnace. Metallographic studies were used to observe the effect of carbon on the morphology of growth. Electron probe microanalysis was carried out to obtain quantitative results on the microsegregation of Ni in the binary and ternary alloys. The extent of homogenization of Ni, occurring both during and after solidification was quantitatively estimated.</p> / Thesis / Master of Engineering (ME)

Title: Thermodynamics and Kinetic study of the Iron-Manganese-Sulfur System at 1300°C, Author: Hitoji Nakao, Location: Thode / <p>In this thesis, a thermodynamic and kinetic study of the ironmanganese- sulfur system is described which is relevant to sulfide transformations in commercial steel at soaking temperatures (~1300°C). Equilibrium and diffusion couple experiments have been carried out to explain the characteristics of formation of sulfides at 1300°C using electron probe microanalysis and metallographic techniques. Apparent semi-conductive behaviour of MnS, which cannot be understood on the basis of simple diffusion kinetics, was observed in the diffusion experiments. The concept of the "virtual" diffusion path adequately rationalized the reaction between Fe-Mn alloys and FeS. Information about the constitution of the 1300°C ternary isotherm was obtained.</p> / Thesis / Master of Engineering (ME)

Title: Surface Tension Measurements on Iron and Iron-Oxygen Alloys by the Oscillating Drop Technique, Author: Ram N. Murarka, Location: Thode / <p>The oscillating drop technique was used to measure the surface tension of pure liquid iron and its oxygen alloys in the range 0 to 600 ppm oxygen. An attempt has been made to investigate how these measurements can be used for future kinetics studies.</p> / Thesis / Master of Engineering (ME)

<p> The kinetics of the hematite to rnagnetite reduction have been studied in H2-H2O, and H2-H2O-N2 gas mixtures, using natural as well as synthetic specimens. The reactivity of hematite was found to be related to the structural defects formed during the preparation of the specimens. The type of defects formed and their effect on reactivity are discussed. Kinetic studies are performed on the specimens with reproducible properties. Rate expressions based upon suitable reaction mechanisms are derived and their validity checked with the experimental data. Reaction rate parameters for the expressions accurately interpreting the experimental results are evaluated, and the effect of nitrogen is separately established. Values of enthalpies and entropies for the mechanistic steps a.re calculated from the temperature dependence of these parameters, which reasonably support the proposed mechanism. </p> / Thesis / Doctor of Philosophy (PhD)

Title: The Role of Structural Defects in the Growth of Thin Nickel Oxide Films, Author: John M. Perrow, Location: Thode / <p>In this these, the nature and distribution of the structural defects present in thin nickel oxide films formed at 500° and 600°C have been determined, as a function of oxidation time, by means of transmission electron microscopy. For nickel oxide films of thickness up to at least 3500 and 5000Å, formed at 500° and 600°C respectively, the films were relatively uniform in thickness on individual metal grains and were composed of small oxide crystallites. The increase in crystallite size with oxidation time has been related to recrystalization and grain growth processes occurring in the films. An oxide film model has been advanced correlating the oxidation kinetics and simultaneous lattice diffusion and short-circuit diffusion via crystallite boundaries.</p> <p>At a later stage of growth the films consisted of large oxide grains containing randomly distributed dislocations of well defined sub-boundaries. These films exhibited non-uniform growth which has been attributed to the short-circuit diffusion of nickel via dislocations of sub-boundaries oriented approximately perpendicular to the plane of the film.<P> / Thesis / Doctor of Philosophy (PhD)

The interstitial concentration and temperature dependence of the diffusion coefficient ratio D12/D11 in ternary austenites containing silicon or manganese has been experimentally determined using diffusion couples based on the concept of "transient equilibrium". The results are compared with values predicted theoretically from statistical and thermodynamic considerations. </p> <p> The kinetics of the growth of proeutectoid ferrite in binary and ternary austenites have been determined, using two-phase diffusion couples. The results are consistent with the premise that carbon diffusion controls the rate of interface migration. It is demonstrated, theoretically and experimentally, that the ternary results fall into two classes - one in which local equilibrium may be assumed, and one in which "constrained local equilibrium" may be postulated. / Thesis / Doctor of Philosophy (PhD)

Title: Decarburization of an Iron-0.8% Carbon Alloy in the Presence of a Wustile Scale, Author: Andrew S. Reeves, Location: Thode / <p>The kinetics of the oxidation and decarburization of an iron-0.8% carbon alloy in carbon dioxide at 950°C have been studied. Both processes are controlled by surface reactions. Decarburization through the wustite scale has been studied by allowing oxide reduction by carbon to proceed under vacuum and in argon atmosphere . Oxide reduction is influenced both by surface reaction steps and by carbon diffusion in the metal. Transport of the gaseous reaction products through the scale is accomplished primarily by porosity in the oxide, with occasional evidence of mechanical failure of wustite. The effectiveness of the pores as a means of transport of carbon gases is dependent on the wustite scale thickness and a critical concentration of carbon at the metal-oxide interface.</p> / Thesis / Master of Science (MS)

<p> The equilibrium and kinetic properties of semicoherent interfaces between γ precipitates and β matrix in Cu-Zn-Sn are examined using a simple dislocation model. The predicted surface energies and mobilities are compared to those observed in experiments which also assess the validity of current theories of interfacial stability in diffusion-controlled growth.</p> / Thesis / Master of Science (MSc)

<p> An Experimental investigation has been conducted to determine the effects on degree of reduction and efficiency of utilization of gases of changes in the levels of several variables when reducing fixed beds of commercial hematite pellets. The effects on reduction behaviour of changes in the levels of reducing gas composition and flow rate, and reaction temperature, were determined by graphical and numerical techniques.</p> / Thesis / Master of Engineering (MEngr)

<p> An investigation is reported on the oxidation properties of alpha-zirconium at 850°C and beta-zirconium at 950°C in oxygen for periods extending to 400 hr. and 100 hr. , respectively. Nitriding kinetics of zirconium in the range of 750° to 1000°C up to 200 hr. were investigated. The kinetics wen determined by volumetric and gravimetric techniques and may be represented by' a parabolic relationship after a period of more rapid oxidation. The uptakes of oxygen or nitrogen were consistent with the mathematical evaluations based on multi-phase diffusion models. Two diffusion models were advanced; one based upon differential and the other upon integral solutions of diffusion equations. It was possible to separate quantatively the oxygen or nitrogen partitions in the scale, alpha and beta phases of zirconium. </p> <p> The diffusivity of nitrogen in alpha-zirconium was determined by using transverse microhardness measurements. The diffusivity is: D = 0.15 exp (-54100/RT)cm/sec^2 for the temperature range of 750°- l000°C. </p> <p> The influence of oxygen-nitrogen atmospheres on the scaling rate of alpha-zirconium at 850°C was investigated. Small additions of either gas to the other increased the sealing rate. A definite breakaway point was observed in the scaling kinetics and the time interval to the transition point varied with the relative amounts of nitrogen to oxygen. </p> <p> Scaling rates of zirconium at 850° and 950°C in the oxygen-water vapor atmospheres initially obeyed to a good approximation a parabolic relationship which was followed by a much faster scaling rate. </p> / Thesis / Doctor of Philosophy (PhD)