It has been suggested by others that hot working is an extension of high temperature creep because of the similar observed dependencies of stress, strain rate, temperature and the similar activation energies of the two types of deformation. This suggestion has been evaluated for commercial purity aluminum by obtaining stress, strain rate and temperature data in the strain rate range 10⁻⁴ to 10¹/second. Published hot compression, hot torsion, and high temperature creep work of others is used to provide supplementary data. A combination of the published work of others with the present experimental work provides data in the strain rate range 10⁻⁷ to 10⁺²/second. From the present analysis, contradictions arise against the theory that hot working is an extension of high temperature creep. First, the method of evaluation of the material constant α in the hyperbolic stress-strain rate relation, [formula omitted], must change in going from creep to hot working. Secondly, the activation energy varies. Those that have suggested that hot working is an extension of high temperature creep found that α and the activation energy were independent of strain rate. Their work is compared to the present analysis and many discrepancies were found. The work in the literature left a data gap in the strain rate range 10⁻³ to 10⁰/second. Hot tensile tests and hot rolling tests were used to provide data in this gap. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

by Kwong Tsz-kin. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1993. / Includes bibliographical references (leaves 90-96). / Chapter I. --- Abstract --- p.i / Chapter II. --- Acknowledgment --- p.ii / Chapter III. --- Table of contents --- p.iii / Chapter IV. --- List of Tables and Figures 、 --- p.iv / Chapter Chapter 1. --- Introduction --- p.1 / Chapter 1.1. --- General introduction / Chapter 1.2. --- Review of analytical methods for aluminium analysis / Chapter 1.3. --- Spectrofluorimetric determination of aluminium / Chapter 1.4. --- Project aim / Chapter Chapter 2. --- Experimental --- p.14 / Chapter 2.1. --- Apparatus / Chapter 2.2. --- Reagents & Material / Chapter 2.3. --- Procedure / Chapter 2.4. --- Treatment of data / Chapter Chapter 3. --- Results and discussion --- p.24 / Chapter 3.1. --- Optimization of experimental conditions / Chapter 3.2. --- Analytical Parameters / Chapter 3.3. --- Analytical results / Chapter Chapter 4. --- Conclusion --- p.89 / Chapter Chapter 5. --- References --- p.90 / Appendix --- p.97

Using Fe57 Mossbauer spectroscopy, two alternative sites occupied by cobalt (10-4 at. % ) impurity atoms in aluminum have been isolated. The substitutional site A is the stable position after annealing the sample above 840 K, followed by a rapid quench. The impurity atoms in site A are characterized by a single line Mossbauer spectrum (indicative of a cubic environment), a room-temperature f = 0.502 (r. m. s. displ. 0.071 A) and an I. S. (reI. to Fe) = -0.421 mm/sec. For anneals below 770 K the cobalt atoms migrate to site B, which is characterized by a well resolved quadrupole doublet (indicative of a non-cubic environment), a large change in the value of the room-temperature f = - 0.766 (r. m. s. displ. 0.071 A), I. S. = -0.150 mm/sec (increased s-electron density at the nucleus). All linewidths· are approximately 0.21 mm/sec, indicating high uniformity of impurity sites. The site distribution [A] / [B} varies from about 5 % to 95 % for anneals between 770 K and 830 K.

Kinetics and mechanisms of Al adsorption on Ca-saturated kaolinite, montmorillonite, and peat were studied using miscible displacement methods. Unneutralized and partially neutralized Al solutions (OH/Al=1.0) were leached through monomineralic columns and effluent analyzed for monomeric and polymeric Al, titratable acidity, and desorbed Ca as a function of time. Observed breakthrough curves (BTC) for continuous injection of the various Al solutions through kaolinite suggested the existence of at least two mechanisms for Al adsorption. It was shown that a relatively rapid reaction, where solution Al was in equilibrium with the solid phase, involved Ca-Al exchange and a slower reaction involved Al polymerization on the adsorbent. This scenario was supported by rigorous modeling of observed BTC with nonequilibrium transport theory, analysis of desorbed Ca effluent, and potentiometric titrations of effluent solutions. The occurrence of two mechanisms for Al adsorption on montmorillonite and peat was also evident. Polymeric Al was preferentially adsorbed by kaolinite throughout the displacement experiment whereas montmorillonite preferentially adsorbed monomers at short times and polymers at longer times. Selective adsorption of either form of Al on peat was not evident. In order to accurately distinguish between monomeric and polymeric Al in solution and on solids, a method was developed which evaluates the interaction of ferron with Al. The colorimetric complexation of aqueous Al with ferron was largely described by a binary species first-order rate function. Based on the differential kinetic reactions of ferron with monomeric and polymeric Al, the fraction of the former species was well predicted using the binary species model. The method avoids arbitrary separation times for the distinction of monomeric and polymeric Al since the duration of monomer interactions with ferron depend on the initial basicity of the Al solution. / Ph. D.