<p> The growth kinetics of a plates and rods in B-brass have been calculated using a local equilibrium model. These are in good agreement with published experimental data. Along with this, quantitative microanalysis of deep etched specimens ts cited in support of the proposed diffusional mechanism for their formation. </p> <p> The model was also employed to calculated the growth rates of upper bainitic rods in the Fe-C-Nisystem at 400° C. A "phase diagram" was constructed in order to supply the effective supersaturations required by the local equilibrium model$ Lengthening rates were also calculated using a paraequilibrtum Interface condition. The experimental data were correctly predicted assuming the former case but failed at the "phase" boundary. It seems that a solute drag might well operate in this system. These results have provided some further indication of the part alloying elements play in the formation of the microstructural constituents of steel. </p> / Thesis / Master of Engineering (MEngr)

No description available.

Rate constants for chemical reactions in various aqueous and micro- heterogeneous systems have been measured and analysed. A large part of the thesis is concerned with interpreting kinetic trends in two water-in-oil microemulsions. Kinetic data for inorganic reactions involving low-spin iron (II) di-imine oorplexes and for reactions involving the organic substrates, 2,4-dinitrochlorobenzene, crystal violet and malachite green in microemulsions have been collected and used to identify different structural zones in these solvent systems. The kinetic data are interpreted in terms of a model in which reaction occurs at an interfuse. Reactions involving cis-bis(pyridine)tetracarbonylmolybdenum (0) in oil- in-water, water-in-oil microemulsions and organic solvent mixtures have been studied. Aquation reactions of iron (II) hexadentate Schiff base have been used to identify microheterogeneous phases in water-rich '2-butoxyethanol + water' mixtures. Solvent effects on initial and transition states are discussed for reactions of iron (II) glyoxal bis-N methylamine with hydroxide ions in 'methanol + water' mixtures and reactions of iron(II) 1,10-phenan- throline with hydroxide ions in 'isopropanol + water' mixtures. Transfer chemical potentials for single ions, in 'acetone + water' mixtures, have been estimated, using solubility data for salts in conjunction with the assumption that transfer chemical potentials for tetraphenylboronate and tetraphenylarsonium ions are equal. Effects of added salt on the neutral hydrolysis of phenyldichloro- acetate in aqueous solutions are examined in terms of solvent cosphere interactions between ions. The temperature dependence of rate constants for reactions of iron (II) 4-methyl, 1,10-phenanthroline have been examined. The results are discussed in terms of isobaric, isothermal and isochoric activation parameters. The meaning of the term 'isochoric' is clarified in this context.

Rate constants for chemical reactions in various aqueous systems have been measured and analysed. A major part of this thesis discusses the effect of added salts on the reaction kinetics of organic substrates and the effect of added cosolvent on iron(II) complexes in solution. The thesis discusses the properties of aqueous solutions with reference to the prediction of trends in kinetic parameters. Transfer chemical potentials for single ions in 'urea + water' mixtures have been estimated, using solubility data for salts in conjunction with the tetraphenylarsonium tetraphenylboronate assumption. Solvent effects on the initial and transition states for reactions between iron (II) 1,10-phenanthroline and iron(II) glyoxal bis-N methylamine with hydroxide ions are also reported. Solvent effects on initial and transition states for reaction between three iron (II) complexes and hydroxide ions in 'methanol + water' mixtures are reported. Effects of added salt on the neutral hydrolysis of phenyldichloroacetate and the para-methoxy derivative are discussed in terms of solvent cosphere interactions between ions. With regard to computer-based studies osmotic coefficients for ammonium, alkylammonium and azoniaspiroalkane halides have been used with Pitzer's equations and the ideas of Wood et al to produce pairwise Gibbs function cosphere-cosphere interaction parameters. The effects of added salt on rate constants for the alkaline hydrolysis of the sodium salt of bromophenol blue are reported and analysed using Pitzer's equation for the activity coefficients of single ions in aqueous salt solutions. Internal pressures of water and deuterium oxide in the region 273.15? T/K ?373.15 and 0? P/bar ?1000 have been calculated and fitted to an equation based on a Taylor expansion about internal pressure ?i (?,0) at temperature T = 0 and pressure p = n. Calculations are reported which shed light on the controversy concerning the isobaric heat capacities for activation for the solvolysis of alkyl halides in water.

toc / Chemistry / Master / Master of Science

published_or_final_version / Chemistry / Master / Master of Science

published_or_final_version / Chemistry / Master / Master of Science

published_or_final_version / Chemistry / Master / Master of Science

published_or_final_version / Chemistry / Master / Master of Science

published_or_final_version / Chemistry / Master / Master of Philosophy