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Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 258-270). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph.D.)--Memorial University of Newfoundland, 2004. / Bibliography: leaves 175-182.

Thesis (Ph. D)--University of Alabama at Birmingham, 2009. / Title from PDF t.p. (viewed June 30, 2010). Additional advisors: Viola L. Acoff, Krishan K. Chawla, Raymond J. Donahue, Gregg M. Janowski, Harry E. Littleton (ad hoc). Includes bibliographical references (p. 143-138).

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisors: Keith P. Johnston and William J. Koros. Vita. Includes bibliographical references.

Pontos quânticos de carbono (C-dots) luminescentes na região do azul-verde aprisionados em matriz de sílica foram produzidos por um processo novo, baseado na pirólise de grupos contendo carbono dispersos nas bordas dos grãos de dimensões nanométricas de sílica (AEROSIL) previamente sinterizados a frio sob alta pressão, onde nenhuma técnica de passivação foi exigida. A análise de difração de elétrons de área selecionada (SAED – Selected Area Electron Diffraction) e espectroscopia de perda de energia de elétrons (EELS – Electron Energy Loss Spectroscopy) confirmaram a formação de C-dots contendo átomos de carbono com ligações do tipo sp2. Foram investigados diferentes valores de pressão (2,5, 4 e 7,7 GPa) para sinterização a frio e diferentes temperaturas de pirólise, a partir de 500 até 900°C. Resultados de análise térmica revelaram pequena perda de massa durante a pirólise das amostras, praticamente independente da pressão utilizada na sinterização. Espectroscopia na faixa do infravermelho revelou alterações nas bandas de aborção na faixa correspondente aos modos de vibração de CH2 e CH3, dependentes da temperatura e da pressão utilizadas. Os espectros de fotoluminescência (FL) foram fortemente dependentes do comprimento de onda de excitação e observou-se uma intensidade de emissão mais elevada no intervalo entre 500-550 nm para a amostra sinterizada a frio em 7,7 GPa e tratada termicamente a 800°C para excitação em 460 nm. Também foi investigado a contribuição da matriz de silica após a sinterização. / Quantum dots in the blue-green region embedded in a silica matrix were produced by a new process based on the pyrolysis of groups containing carbon dispersed on the edges of the grain of nanosized silica (AEROSIL) previously sintered under high pressure, where no passivation technique was required. The Selected Area Electron Diffraction (SAED) and Electron Energy Loss Spectroscopy (EELS) confirmed the formation of Cdots containing carbon atoms with sp2 bonds. Different pressure values (2,5, 4 and 7,7 GPa) were investigated for cold sintering and the pyrolsys was in the temperature range from 500 to 900°C. Results of thermal analysis revealed a small loss of mass during the pyrolysis of the samples, practically independent of the sintering pressure. Infrared spectroscopy revealed changes in the absorption bands in the range corresponding to the CH2 and CH3 vibration modes, depending on the temperature and pressure conditions. Photoluminescence (PL) spectra were strongly dependent on the excitation wavelength and a higher emission intensity was observed in the range 500-550 nm for the sample sintered at 7.7 GPa and pyrolysed at 800°C for excitation at 460 nm. The contribution of the silica matrix after sintering was also investigated.

A Thesis Submitted Towards the Partial Fulfilment Degree of Master of Technology (M.Tech.) FACULTY OF ENGINEERING MECHANICAL ENGINEERING DEPARTMENT Cape Peninsula University of Technology 2011 / The split Hopkinson pressure bar (SHPB) test is the most commonly used method for determining material properties at high rates of strain. The theory governing the specifics of Hopkinson bar testing has been around for decades; however, it has only been for the last decade or so that significant data processing advancements have been made. It is the intent of this thesis to offer the insight of application of SHPB to determine the compressive dynamic behaviour for welded low carbon steel (mild steel). It also focuses on the tensile behaviour for unheat-treated and heat-treated welded carbon steel. The split Hopkinson Pressure bar apparatus consists of two long slender bars that sandwich a short cylindrical specimen between them. By striking the end of a bar, a compressive stress wave is generated that immediately begins to traverse towards the specimen. Upon arrival at the specimen, the wave partially reflects back towards the impact end. The remainder of the wave transmits through the specimen and into the second bar, causing irreversible plastic deformation in the specimen. It is shown that the reflected and transmitted waves are proportional to the specimen's strain rate and stress, respectively. Specimen strain can be determined by integrating the strain rate. By monitoring the strains in the two bars and the specimen's material, stress-strain properties can be calculated. Several factors influence the accuracy of the results, including the size and type of the data logger, impedance mismatch of the bars with the specimens, the utilization of the appropriate strain gauges and the strain amplifier properties, among others. A particular area of advancement is a new technique to determine the wave's velocity in the specimen with respect to change in medium and mechanical properties, and hence increasing the range of application of SHPB. It is shown that by choosing specimen dimensions based on their impedance, the transmitted stress signal-to-noise ratio can be improved. An in depth discussion of realistic expectations of strain gages is presented, along with closed form solutions validating any claims. The thesis concludes with an analysis of experimental and predicted results. Several recommendations and conclusions are made with regard to the results obtained and areas of improvement are suggested in order to achieve accurate and more meaningful results.

Pontos quânticos de carbono (C-dots) luminescentes na região do azul-verde aprisionados em matriz de sílica foram produzidos por um processo novo, baseado na pirólise de grupos contendo carbono dispersos nas bordas dos grãos de dimensões nanométricas de sílica (AEROSIL) previamente sinterizados a frio sob alta pressão, onde nenhuma técnica de passivação foi exigida. A análise de difração de elétrons de área selecionada (SAED – Selected Area Electron Diffraction) e espectroscopia de perda de energia de elétrons (EELS – Electron Energy Loss Spectroscopy) confirmaram a formação de C-dots contendo átomos de carbono com ligações do tipo sp2. Foram investigados diferentes valores de pressão (2,5, 4 e 7,7 GPa) para sinterização a frio e diferentes temperaturas de pirólise, a partir de 500 até 900°C. Resultados de análise térmica revelaram pequena perda de massa durante a pirólise das amostras, praticamente independente da pressão utilizada na sinterização. Espectroscopia na faixa do infravermelho revelou alterações nas bandas de aborção na faixa correspondente aos modos de vibração de CH2 e CH3, dependentes da temperatura e da pressão utilizadas. Os espectros de fotoluminescência (FL) foram fortemente dependentes do comprimento de onda de excitação e observou-se uma intensidade de emissão mais elevada no intervalo entre 500-550 nm para a amostra sinterizada a frio em 7,7 GPa e tratada termicamente a 800°C para excitação em 460 nm. Também foi investigado a contribuição da matriz de silica após a sinterização. / Quantum dots in the blue-green region embedded in a silica matrix were produced by a new process based on the pyrolysis of groups containing carbon dispersed on the edges of the grain of nanosized silica (AEROSIL) previously sintered under high pressure, where no passivation technique was required. The Selected Area Electron Diffraction (SAED) and Electron Energy Loss Spectroscopy (EELS) confirmed the formation of Cdots containing carbon atoms with sp2 bonds. Different pressure values (2,5, 4 and 7,7 GPa) were investigated for cold sintering and the pyrolsys was in the temperature range from 500 to 900°C. Results of thermal analysis revealed a small loss of mass during the pyrolysis of the samples, practically independent of the sintering pressure. Infrared spectroscopy revealed changes in the absorption bands in the range corresponding to the CH2 and CH3 vibration modes, depending on the temperature and pressure conditions. Photoluminescence (PL) spectra were strongly dependent on the excitation wavelength and a higher emission intensity was observed in the range 500-550 nm for the sample sintered at 7.7 GPa and pyrolysed at 800°C for excitation at 460 nm. The contribution of the silica matrix after sintering was also investigated.

The aim of this work was experimental study of features of high pressure influence onto tows of double-walled and single-walled carbon nanotubes. The structural transitions for carbon nanotubes subjected to external pressure with changes in the cross section of nanotubes were discovered by the method of molecular dynamics simulation and experimentation study. At higher pressures observed polymerization of carbon nanotubes. In the first section, an overview of current concepts about the structure of single-walled and multi-walled nanotubes and their electrical and mechanical properties are shown, as well as the methods of experimental study of the structure and properties are listed. Raman spectroscopy as one of the most sensitive and informative methods of research of carbon materials has been allocated in a separate paragraph. In the "EXPERIMENTAL" basic characteristics and principle of operation of two used in the work settings: press for creation high pressures and the displays system of the Raman confocal microscope WiTecAlpha AR + 300 have been described. The main conclusions:  Features on the curve of the electrical resistance dependence from the pressure of single-walled CNT correspond to known structural transitions in nanotubes related to changes in the cross section of nanotubes, found at 2 and 7 GPa. The pressure of 50 GPa is not critical for the investigated samples of single-walled nanotubes.  Similar features are found on the curve of the pressure resistance of double-walled CNT at 2 and 21 GPa. It was found that the resistance feature of about 24 GPa associated with the destruction of the external nanotubes structure of the double-walled nanotube. Thus, the assumption of a two-stage mechanism of destruction of double-wall CNT large diameter confirmed.  50 GPa pressure is critical for the investigated double -walled nanotubes. Based on the results, it can be concluded about the destruction of the double-walled CNT is happening at a pressure of 50 GPa. Those data allow us to judge the partial polymerization of double-walled CNT reaching the critical pressure of 50 GPa. / Целью работы являлось экспериментальное исследование особенностей воздействия высокого давления на жгуты двустенных и одностенных углеродных нанотрубок. Методами молекулярно-динамического моделирования и экспериментальным путем были обнаружены структурные переходы для углеродных нанотрубок подвергнутых внешнему давлению, связанные с изменением поперечного сечения нанотрубок. При более высоких давлениях наблюдалась полимеризация углеродных нанотрубок. В первом разделе приведен обзор современных представлений о структуре однослойных и многослойных нанотрубок, их электрических и механических свойствах, а также перечислены методы экспериментального исследования их структуры и свойств. В отдельный пункт была выделена спектроскопия комбинационного рассеяния света, как один из наиболее чувствительных и информативных методов исследования углеродных материалов. В разделе «МЕТОДИКА ЭКСПЕРИМЕНТА» были описаны основные характеристики и принцип работы двух использовавшихся в работе установок: пресса для создания высоких давлений и системы отображающей конфокальной микроскопии комбинационного рассеяния WiTecAlpha 300 AR+. Основные выводы работы:  Обнаружены особенности на кривой зависимости электросопротивления от давления одностенных УНТ при 2 и 7 ГПа, соответствующие известным структурным переходам в нанотрубках, и связанные с изменением сечения нанотрубок. Давление 50 ГПа не является критическим для исследованного образца одностенных УНТ.  Обнаружены аналогичные особенности на кривой зависимости сопротивления от давления двустенных УНТ при 2 и 21 ГПа. Было установлено, что особенность сопротивления около 24 ГПа связана с разрушением внешних нанотрубок в структуре двустенных УНТ. Таким образом, подтверждается предположение о двухступенчатом механизме разрушения двустенных УНТ большого диаметра.  Давление 50 ГПа является критическим для исследованных двустенных УНТ. Исходя из полученных результатов, можно сделать вывод о происходящем разрушении ДУНТ при давлении 50 ГПа. Те же данные позволяют судить о частичной полимеризации двустенных УНТ при достижении критического давления 50 ГПа.

Thesis. 1975. Ph.D.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences. / Vita. / Includes bibliographical references. / Ph.D.