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dc.contributor.advisorReimanis, Ivar E. (Ivar Edmund)
dc.contributor.authorRamalingam, Subramanian
dc.date.accessioned2007-01-03T04:48:23Z
dc.date.accessioned2022-02-09T08:39:55Z
dc.date.available2014-04-01T04:18:44Z
dc.date.available2022-02-09T08:39:55Z
dc.date.issued2013
dc.identifierT 7197
dc.identifier.urihttps://hdl.handle.net/11124/78484
dc.descriptionIncludes illustrations (some color).
dc.descriptionIncludes bibliographical references (pages 100-123).
dc.description.abstractBeta-eucryptite (LiAlSiO4) has received widespread attention, both industrially and academically because of its low negative average coefficient of thermal expansion (CTE) and one dimensional Li-ion conductivity. Beta-eucryptite is also known to undergo a reversible pressure-induced phase transformation under compression at ~0.8 GPa to a metastable polymorph, epsilon-eucryptite. The present work evaluates the thermal and mechanical behavior of beta-eucryptite and eucryptite composites with several different experiments. In the first set of experiments, nanoindentation was used to determine the activation volume of the pressure-induced phase transformation in polycrystalline and single crystal beta-eucryptite. It is shown that the phase transformation is a thermally activated event. It is the first time that nanoindentation has been used to find the activation volume in a pressure-induced phase transformation. Results suggest that the nucleation event that marks the onset of the phase transformation is approximately the size of the silica and alumina tetrahedra comprising the beta-eucryptite structure. The effect of Zn doping on the phase transformation was also examined using in situ diamond anvil cell-Raman spectroscopy and nanoindentation experiments. The present work is the first to employ both techniques in a comparative manner to investigate pressure-induced phase transformation in the same material. This study demonstrates that, though the data obtained from the two techniques are complementary, important differences including the loading rate and the state of stress between the two techniques must be noted when understanding data from the two experiments. The next set of experiments examined the effect of Zn doping on the thermal expansion of beta-eucryptite to understand the structure-property relationship in the material. The results revealed that doping significantly increases the bulk CTE - negative for pure beta-eucryptite to slightly positive for Zn-doped beta-eucryptite in the range from 25°C to 1000°C, and also lowers the tendency to microcracking. No difference in grain size was observed between the pure and doped samples, and all the ceramics exhibited high relative densities. It is believed that an intrinsic modification in the beta-eucryptite structure is responsible for the observed behavior. In the final study, the potential of transformation toughening was examined by fabricating composites of 10 mol % yttria stabilized zirconia reinforced with varying amounts (0 to 20 vol. %) of beta-eucryptite (LiAlSiO4) with the intent of stabilizing in situ the high-pressure eucryptite polytype, epsilon-eucryptite, so that the reverse transformation to beta-eucryptite under a crack tip stress field may impart toughening by volume expansion. The results indicate that the change in toughness with volume fraction of beta-eucryptite is best explained by considering a transformation toughening mechanism in conjunction with the toughening decrement predicted due to matrix tensile stresses which arise due to the thermal expansion mismatch.
dc.format.mediumborn digital
dc.format.mediumdoctoral dissertations
dc.languageEnglish
dc.language.isoeng
dc.publisherColorado School of Mines. Arthur Lakes Library
dc.relation.ispartof2013 - Mines Theses & Dissertations
dc.rightsCopyright of the original work is retained by the author.
dc.subjectdiamond anvil cell - Raman spectroscopy
dc.subjectbeta eucryptite
dc.subjectnanoindentation
dc.subjectthermal residual stresses
dc.subjectphase transformations
dc.subjecttransformation toughening
dc.subject.lcshMaterials -- Mechanical properties
dc.subject.lcshCeramics
dc.subject.lcshComposite materials
dc.subject.lcshPhase transformations (Statistical physics)
dc.titleThermo-mechanical behavior of beta-eucryptite and eucryptite based composites
dc.typeText
dc.contributor.committeememberPackard, Corinne E.
dc.contributor.committeememberGorman, Brian P.
dc.contributor.committeememberCiobanu, Cristian V.
dc.contributor.committeememberOlson, D. L. (David LeRoy)
dcterms.embargo.terms2014-04-01
dcterms.embargo.expires2014-04-01
thesis.degree.nameDoctor of Philosophy (Ph.D.)
thesis.degree.levelDoctoral
thesis.degree.disciplineMetallurgical and Materials Engineering
thesis.degree.grantorColorado School of Mines
dc.rights.access1-year embargo


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