No description available.

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Herbert E. Allen, Dept. of Civil & Environmental Engineering. Includes bibliographical references.

No description available.

Thesis--University of Florida. / Typescript. Vita. Description based on print version record. Bibliography: leaves 87-88.

Thesis (M.S.)--University of Missouri, School of Mines and Metallurgy, 1946. / The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed June 14, 2010) Includes bibliographical references (p. 40) and index (p. 41).

Thesis (M.S.)--University of Wisconsin--Madison. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 82-83).

An investigation of precipitation was carried out on the system Cu-Ni-Co at temperatures varying from 600°C to 800°C over a wide range of composition . The precipitation process was studied primarily by use of X-ray diffraction techniques. The precipitation was observed to procede by a spinodal decomposition process. The initial wavelength of the modulated structure was in the range 40 to 55Å, in good agreement with the theory for spinodal decomposition. On ageing, a coarsening was observed for all alloys aged inside the spinodal. This coarsening appeared to follow a law of the form Q[superscript: m] – Qo[superscript: m] = k (t-to) where Q = wavelength at time t Qo = wavelength before the coarsening begins at time to k and m = constants The activation energy of the coarsening process was found to be 65 kcal/mole + 10 kcal suggesting that volume diffusion was the controlling factor. RESUME Le présent travail étudie la formation de précipités dans divers alliages du systéme Cu-Ni-Co au cours de vieillissements à des temperatures de 600°C a 800°C. L’évolution de la précipitation a été suivie principalement par diffraction des rayons X. On a observé que la précipitation procède par décomposition spinodale. La longeur d'onde initiale de la structure modulée est comprise entre 40 et 55Å; en bon accord avec la théorie de la décomposition spinodale de Cahn. Au cours du vieillissement on a mesuré un accroissement de la longeur d'onde pourtous les alliages traités à l'intérieur du spinodal. Cet accroissement de longeur d'onde obéit à une loi de la forme Q[superscript: m] – Qo[superscript: m] = k (t-to) ou Q = longeur d'onde au temps t Qo = longeur d’onde avant que le grossisement commence, à to k et m = constantes if energie d'activation du mécanisme de croissance des précipités a été déterminée; sa valeur, 65 kcal/mole suggére que la diffusion en volume est le facteur préponderant. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Mode I and Mode III fatigue tests were performed on copper nickel alloys in helium, salt water environments. The hydrogen, oxygen, two alloys used air and in this investigation were 90-10 and 70-30 copper nickel. Both alloys contained iron which was added to improve the erosion corrosion resistance. The extent of cracking varied with the test environment. Tests showed that oxygen and humid air promoted cracking while salt water helium was used as the baseline retarded cracking when environment. Hydrogen promoted cracking when compared to helium but retarded cracking if comparisons were made with oxygen or humid air. The environmental effects (helium as the base case} in the Mode I tests in gaseous environments were manifested in the form of shorter fatigue lives, easier crack initiation, marginally higher crack growth rates and the development of intergranular fracture at the surface. These effects were accompanied by a change in the near surface deformation characteristics. The increases in fatigue life induced by testing in aqueous environments were greatly extended if the copper nickel was galvanically coupled to steel. Mode III tests showed the same ranking of environmental effects as Mode I tests and also showed multiple initiation, brittle fracture and secondary cracking. Two models were proposed to explain the observed results. One was based on the dilation-aided diffusion of oxygen ahead of the crack tip and subsequent oxidation of internal iron particles. The oxidation caused a volume expansion which produced internal tensile strains and facilitated fracture. The other mechanism was based on dilation-aided transport of hydrogen with subsequent accumulation of hydrogen at interfaces, resulting in a lowering of the interfacial strength and promoting intergranular fracture. The observed increases in life in the aqueous environments were rationalized by the reduced oxygen content available in the stagnant solutions. These observations suggest that the presence of iron accelarates fatigue in copper nickel alloys exposed to aggressive environments. Thus, any application involving fatigue loading with simultaneous exposure to aggressive environments should attempt to ensure that the iron content of the copper nickel alloys is minimized. / Doctor of Philosophy

There is significant concern about the accumulation of potentially toxic elements (PTEs) in soils because of both direct and indirect impacts on human and ecosystem health. Knowledge of the fate and distribution of such contamination can lead to an effective assessment of the hazards to soil biota and the need for protective or mitigation activities. This is a particular challenge due to the heterogeneity of the soil matrix and complexity of the processes that determine PTE availability to soil biota. While whole-cell bacterial biosensors have been proposed as tools in enabling greater confidence in addressing such biological and chemical interfaces their genuine value remains to be realised. The underpinning objective of this work was to link the response of microbial biosensors to detailed chemical analysis and to relate the dose response sensitivity to other biological measurements. To better understand the phenomena of PTE bioavailability, the study considered changes in toxicity within the context of ion competition in both freshly amended and historically impacted soils. The interaction of test bacteria with both free (soil pore water) and sorbed (solid phase) fractions of the target analytes (copper, nickel and zinc) has enabled a better estimation of bioavailability/toxicity of PTEs in soils. In comparison to other assays, the responses of the microbial sensor to Cu, Ni and Zn highlighted its relative sensitivity to PTE contamination. The use of luminescence marked microbial sensors complements the performance of rigorous analytical soil chemistry approaches. Their value in soil pollution should be considered a technique that should be interpreted alongside chemical analysis rather than an alternative as their performance in complex environmental matrixes is yet to be validated.

No description available.