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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
531

Degradation of e-glass fibre in selected organic acids

Zahir, Aishath Zehereen January 2008 (has links)
E-glass has been widely used as a reinforcing material for years, especially as a plastic reinforcer in the production of GRP (Glass Reinforced Plastic). Failure of GRP materials under stress came in to the picture quite recently. Since then studies have been conducted in an attempt to understand the causes and the underlying behaviour. / Except for the last section of the research (analysis using a kinetic approach) where glass fibre was cut out to weigh approximately 1.0g, standard sized specimens were soaked in the required acid solutions of desired concentrations for varying temperatures and time frames. Wherever tensile strength retention was measured, LLOYD instrument was employed. Leaching of the cations were analysed using Inductively Coupled Plasma – Optical Emission Spectroscopy (ICP-OES and also know and ICP-AES). / The scope of this project can be divided in to four sections; first section involved investigating the effects of malonic acid. The study of malonic acid was narrowed to investigating the trend in strength retention. A rapid strength loss was observed initially followed by a much steady decline in the strength. However the continuation of the loss of strength was unmistakable throughout the time period of exposure. Furthermore, temperature can be observed as a facilitating factor in this degradation reaction. / Secondly the corrosive effect of glyoxylic acid on E-glass fibre was studied. This was explored at two different temperatures for two specific time frames using various concentrations of the acid of interest. The influence of this acid on the glass fibre was found out in terms of strength retention and loss of cations from the glass matrix. The mildness of this acid was accentuated by the fact that 70% or more of the strength was retained at all the conditions employed. A minima in strength retention was observed at 2M acid concentration similar to the trends observed in the past (Betz and Jones 2003 and Jones and Chandler 1986). Leaching of cations reflected this trend. The large strength retention could be related to the fewer amounts of Ca and K leached from the glass matrix (Kumosa and Qui, 1997). Similar to malonic acid, an unusually large amount of B was leached out that could be due to the favourable orientation of the anion with the trivalent ions during the complex formation. Yet again temperature was found to enhance the degradation process. / Next the extent of passivation (if any) showed by malonic acid was investigated using E-glass fibre pre-treated in 5M malonic acid and post treated in known corrosive acids hydrochloric acid and oxalic acid. Passivation of malonic acid was put to test through examination of strength retention of the fibres under these conditions. This segment was carried out as an extension of a finding (a behaviour synonymous to passivation) shown by malonic that surfaced the previous year by the present researcher. Increasing the pre-treatment time showed a great improvement in the retained strength for all the post-treatment acid mediums. Furthermore, while Jones and Betz (2004) featured 20-40% strength retention within a short time frame in 3M HCl, the immense amount of strength retention (60-70%) preceding pre-treatment should definitely be noted. Similarly strength retention of about 80% was observed when post-treated with the severely corrosive oxalic acid. Hence its is clear that passivation can be induced through prolonged pre-treatment in 5M malonic acid that could inhibit the attack of corrosive acid at least for a period of time. / The last fragment of the study focussed on understanding and working out the mechanism behind the reactions between the E-glass fibre and acid medium in terms of kinetics. The acids utilized were 1.5M malonic acid and 3M glyoxylic acid and the assessments were made through the analysis of the weight changes brought about by the acid medium at various temperatures and time frames. In addition leaching patterns of cations were evaluated as this could contribute in achieving the objective. Maximum weight loss reached 4% in glyoxylic acid while that for malonic acid exceeded 20%. The general trend was that the glass fibres lost weight in both acids for a period of time followed by an evident weight gain. Furthermore the weight loss results fit the first order rate law. While the leaching of cations reflects the weight loss for the shorter time frames, steady loss of ions was visible even for the longer time frames where the weight has increased. The weight gain could be explained in terms of binding of anions to certain cations on the glass surface, accounting for the hindrance in the loss of cations at the longer time frames as well. About 50% of weight loss was associated to Ca while 20% was to Al, leaving 6% to B where as the rest of the ions had shown almost insignificant contribution to the weight loss.
532

Reincarnating the micro universe /

Bae, Jeon Ah. January 2008 (has links)
Thesis (M.F.A.)--Rochester Institute of Technology, 2008. / Typescript. Includes bibliographical references (leaf 36).
533

A comparison between in vivo and in vitro bond strengths of a glass ionomer cement a clinical study : a thesis submitted in partial fulfillment ... restorative dentistry, operative ... /

Tyler, Michael W. January 1986 (has links)
Thesis (M.S.)--The University of Michigan, 1986. / Also issued in print.
534

Time-dependent fluoride uptake into dentin from a resin-modified glass ionomer a thesis submitted in partial fulfillment ... for the degree of Master of Science in Restorative Dentistry ... /

McLaren, Charles I. January 2003 (has links)
Thesis (M.S.)--University of Michigan, 2003. / Includes bibliographical references.
535

The windows of the trades at Chartres Cathedral

Williams, Jane Welch. January 1987 (has links)
Thesis (Ph. D.)--University of California, Los Angeles, 1987. / Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 326-355).
536

A comparison between in vivo and in vitro bond strengths of a glass ionomer cement a clinical study : a thesis submitted in partial fulfillment ... restorative dentistry, operative ... /

Tyler, Michael W. January 1986 (has links)
Thesis (M.S.)--The University of Michigan, 1986. / eContent provider-neutral record in process. Description based on print version record.
537

Marketing exclusive brands in Hong Kong : a strategic approach /

Yung, Kar, Frontane. January 1995 (has links)
Thesis (M.B.A.)--University of Hong Kong, 1995. / Includes bibliographical references (leaves 97-98).
538

Damage analysis and mechanical response of as-received and heat-treated Nicalon/CAS-II glass-ceramic matrix composites /

Lee, Shin Steven. January 1993 (has links)
Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 170-175). Also available via the Internet.
539

Simultaneous and sequential multi-site impact response of composite laminates

Bartus, Shane D. January 2006 (has links) (PDF)
Thesis (Ph. D.)--University of Alabama at Birmingham, 2006. / Additional advisors: James S. Davidson, Derrick R. Dean, Gregg M. Janowski, Mark L. Weaver. Description based on contents viewed Jan. 24, 2007; title from title screen. Includes bibliographical references (p. 235-246).
540

The dynamic mechanical response of polymer-based nanocomposites and network glasses

Putz, Karl William, Green, Peter F., January 2004 (has links) (PDF)
Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: Peter F. Green. Vita. Includes bibliographical references.

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