Thesis (Ph.D.) - University of Queensland, 2005. / Includes bibliography.

Thesis (M.S.)--University of Wisconsin--Madison, 1970. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (PH. D.)--University of Michigan, 1929. / "Reprinted from Physical review ... vol. 34, no. 1, July 1, 1929."

>Magister Scientiae - MSc / Spinel lithium manganese oxide (LiMn2O4), for its low cost, easy preparation and nontoxicity, is regarded as a promising cathode material for lithium-ion batteries. However, a key problem prohibiting it from large scale commercialization is its severe capacity fading during cycling. The improvement of electrochemical cycling stability is greatly attributed to the suppression of Jahn-Teller distortion (Robertson et al., 1997) at the surface of the spinel LiMn2O4 particles. These side reactions result in Mn2+ dissolution mainly at the surface of the cathode during cycling, therefore surface modification of the cathode is deemed an effective way to reduce side reactions. The utilization of a nanocomposite which comprises of metallic Cu and Au were of interest because their oxidation gives rise to a variety of catalytically active configurations which advances the electrochemical property of Li-ion battery. In this research study, an experimental strategy based on doping the LiMn2O4 with small amounts of Cu-Au nanocomposite cations for substituting the Mn3+ ions, responsible for disproportionation, was employed in order to increase conductivity, improve structural stability and cycle life during successive charge and discharge cycles. The spinel cathode material was synthesized by coprecipitation method from a reaction of lithium hydroxide and manganese acetate using 1:2 ratio. The Cu-Au nanocomposite was synthesized via a chemical reduction method using copper acetate and gold acetate in a 1:3 ratio. Powder samples of LiMxMn2O4 (M = Cu-Au nanocomposite) was prepared from a mixture of stoichiometric amounts of Cu-Au nanocomposite and LiMn2O4 precursor. The novel LiMxMn2O4 material has a larger surface area which increases the Li+ diffusion coefficient and reduces the volumetric changes and lattice stresses caused by repeated Li+ insertion and expulsion. Structural and morphological sample analysis revealed that the modified cathode material have good crystallinity and well dispersed particles. These results corroborated the electrochemical behaviour of LiMxMn2O4 examined by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The diffusion coefficients for LiMn2O4 and LiMxMn2-xO4 obtained are 1.90 x10-3 cm2 / s and 6.09 x10-3 cm2 / s respectively which proved that the Cu-Au nanocomposite with energy band gap of 2.28 eV, effectively improved the electrochemical property. The charge / discharge value obtained from integrating the area under the curve of the oxidation peak and reduction peak for LiMxMn2-xO4 was 263.16 and 153.61 mAh / g compared to 239.16 mAh / g and 120 mAh / g for LiMn2O4. It is demonstrated that the presence of Cu-Au nanocomposite reduced side reactions and effectively improved the electrochemical performance of LiMn2O4.

>Magister Scientiae - MSc / A study on carbon paste electrode (CPE) materials containing 1-methyl-3-octylimidazolium bis (trifluoromethylsulfonyl) imide [MOIM[Tƒ2N] – a hydrophobic room temperature ionic liquid (IL) - is reported. CPEs with (a) the IL as the only binder (ILCPE) and (b) 1:1 (v/v) IL: paraffin mixture as the binder (ILPCPE) were prepared, characterized, and applied to the electrodeposition of films of multivalent transition metal oxides (MV-TMO) from five precursor ions (Fe2+, Mn2+, Cu2+, Co2+, Ce4+) in aq. KCl. Cyclic voltammetry (CV) showed a potential window of +1.5 V to -1.8 V regardless of the electrode type, including the traditional paraffin CP electrode (PCPE). However, the IL increased the background current by 100-folds relative to paraffin. The electrochemical impedance spectroscopy (EIS) of ILPCPE in aq. KCl (0.1M) revealed two phase angle maxima in contrast with the single maxima for PCPE and ILCP. The study also included the CV and EIS investigation of the electrode kinetics of the Fe(CN)6 3-/4 redox system at these electrodes. The electrodeposition of Fe2+, Co2+, and Mn2+ possibly in the form of the MV-TMOs FexOy, CoxOy, and MnxOy, respectively, onto the electrodes was confirmed by the observation of new and stable cathodic and anodic peaks in a fresh precursor ion –free medium. CVs of H2O2 as a redox probe supported the same conclusions. Both ATR-FTIR spectra and SEM image of surface samples confirmed the formation of electrodeposited films. This study demonstrated that the use of this hydrophobic IL alone or in combination with paraffin as a binder gives viable alternative CPE materials with better performance for the electrodeposition of MV-TMOs films than the paraffin CPE. Thus, in combination with the easy preparation methods and physical “morpheability” in to any shape, these CPEs are potentially more useful in electrochemical technologies based on high surface-area MV-TMO films in general, and MnxOy films in particular.

No description available.

The depletion of natural resources has long been a concern since the rapid increase in energy consumption in recent years. The gradual increase of pollution worldwide accompanied by energy generation process also started to post threats to the environment. With the evolution of technology and materials, power generation and energy storage with significant improved efficiency can be made possible, and further benefits the reduction of degree of pollution generated. In this research, synthesis, processing, characterization and application of nano materials towards energy generation and energy storage devices are studied. In chapter 2, superior corrosion resistance properties of HVOF thermal spray of TiC and TiB2 coatings on 304H stainless steel, 430, and P91 steels were reported. The coatings successfully served at a protection layer by limiting oxygen penetration, sulfur attack, and decreased the formation of pits and cracks on the substrates at 750°C for up to 800 hours. In chapter 3, continuous smooth TiC nanofibers were successfully synthesized by carbothermal reduction of electrospun titanium based nanofibers. XRD and HR-TEM analysis results indicated the synthesized nanofibers were composed of high purity TiC. Electric conductivity of a single fiber was in the 2.00×10^5 range. Symmetrical cyclic voltammetry curve further indicated good electrochemical properties of the fibers. In addition, the TiC nanofibers also exhibited excellent sintering properties over TiC or TiB2 nanoparticles. Studies on morphology and electrochemical properties of MnOx nanofiber and nanoparticles is reported in chapter 4. MnOx, MnOx/SnO2, and MnOx/CNT nanofibers synthesized using electrospinning method showed specific capacitance of 166.12 F/g, 182 F/g for, and 472 F/g at scan rate of 10mV/s. Analysis results also showed positive impact of conductivity and fiber morphology on the electrochemical properties of the fibers. morphology and electrochemical properties of the MnOx nanoparticles synthesized using solvents with different polarity with gelation pH of 8.5, 9.0 and 10.0 were also studied. Analysis results show the impact of particle sized and morphology on the electrochemical properties. Highest specific capacitance measured for the synthesized nanoparticles was 231.38F/g@10mV/s and 165.13F/g@10mV/s for methanol and mixture of methanol and propanol based MnOx respectively. Effect of solvent polarity of the manganese sol on MnOx formation and phase transformation temperature is also shown in the chapter.

Made available in DSpace on 2014-06-11T19:29:08Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-06-29Bitstream added on 2014-06-13T19:58:46Z : No. of bitstreams: 1 santos_bas_me_araiq_parcial.pdf: 140847 bytes, checksum: e8b2160128eaa3da3d1484fbcf67ae66 (MD5) Bitstreams deleted on 2015-05-28T14:25:11Z: santos_bas_me_araiq_parcial.pdf,. Added 1 bitstream(s) on 2015-05-28T14:26:14Z : No. of bitstreams: 1 000712512_20150603.pdf: 130802 bytes, checksum: bdb6945e08e2e94a92c03994c911bda2 (MD5) Bitstreams deleted on 2015-06-03T11:42:39Z: 000712512_20150603.pdf,. Added 1 bitstream(s) on 2015-06-03T11:44:06Z : No. of bitstreams: 1 000712512.pdf: 693882 bytes, checksum: 00545a9471b1789616ed3f2c302bb891 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este trabalho descreve estratégias instrumentais para a determinação de Mn em amplo intervalo de concentração por espectrometria absorção atômica em chama com fonte contínua e de alta resolução (HR-CS FAAS), por meio do uso de diferentes linhas atômicas (principal, secundária, alternativa ou o ajuste do arranjo instrumental) desde que seus intervalos de concentração se completem, sem a necessidade de amplas diluições da amostra. O método proposto foi aplicado as amostras de água de abastecimento, fertilizante foliar, poli vitamínico e material certificado de ligas metálicas. A exaltidão e precisão foram avaliadas por testes de significância (t de student e t - pareado), adição e recuperação, e materiais de referência do Instituto de Pesquisa Tecnológica do Estado de São Paulo, e os resultados foram concordantes ao nível de 95% de confiança em sua grande maioria. Obteve-se curvas analíticas nos intervalos 0,1-2 mg L-1 (279,482 nm), 2-25 mg L-1 (403,075 nm), 25-500 mg L-1 (209,250 nm ou 403,075 nm com queimador a 90 graus), com coeficiente de correlação linear melhor do que 0,9936 em ambas as técnicas (utilizou a espectrometria de absorção atômica em chama com fonte de linhas - LS FAAS - como técnica comparativa). Os limites de detecção para a HR-CS FAAS foram 1,1x10-3 mg L-1 (279,482 nm), 9,8 x 10-3 mg L-1 (403,075 nm), 1,7 mg L-1 (209,250 nm), 7,3x10-2 mg L-1 (403,075 nm com queimador a 90 graus), e para a LS FAAS foram 1,0x10-2 mg L-1, 0,10 mg L-1, 24,8 mg L-1, 7,0 mg L-1, respectivamente. Em HR-CS FAAS, o RSD% variou 0,9 a 1,3, enquanto para a LS FAAS variou 1,1 a 11,8%. As concentrações encontradas pela HR-CS FAAS foram: < 1,1x10-3 mg L-1 (água de abastecimento)... / This paper describes instrumental strategies for the determination of Mn in a wide range concentration by high-resolution continuum source flame atomic absorption spectrometry technique (HR-CS FAAS) by means of different atomic lines (primary, secondary, alternative or adjusting the instrumental arrangement) provided that their concentration intervals complete one another, without need for large sample dilutions. The proposed method was applied to water, foliar fertilizer, poly vitamin and metal alloys certified materials. Accuracy and precision were evaluated by tests of significance (Student's t test and paired - t test), addition and recovery, and reference materials from the Institute of Technological Research of São Paulo. Analytical curves in the intervals 0.1-2 mg L-1 (279.482 nm), 2-25 mg L-1 (403.075 nm), 25-500 mg L-1 (209.250 nm or 403.075 nm burner 90 degrees) were obtained with linear correlation coefficient better than 0.9936. Line source flame atomic absorption spectrometry (LS FAAS) were used as a comparative technique. The detection limits HR-CS FAAS were 1.1x10-3 mg L-1 (279.482 nm), 9.8 x 10-3 mg L-1 (403.075 nm), 1.7 mg L-1 (209.250 nm), 7.3x10-2 mg L-1 (403.075 nm burner 90 degrees). And by LS FAAS were 1.0x10-2 mg L-1, 0.10 mg L-1, 24.8 mg L-1, 7.0 mg L-1 respectively. In HR-CS FAAS, the RSD ranged from 0.9 to 1.3%, while for LS FAAS from 1.1 to 11.8%. The Mn concentrations found by HR-CS FAAS were < 1.1x10-3 mg L-1 (water supply), 4728 ± 62 mg L-1 (foliar fertilizer), 3.65 ± 2 mg g-1 (poly vitamin), 0.709 ± 0.116 mg L-1 (Alloy 14A), 0.998 ± 0.042 mg L-1 (alloy 25). For LS FAAS, the concentrations wer... (Complete abstract click electronic access below)

abstract: Sensitivity is a fundamental challenge for in vivo molecular magnetic resonance imaging (MRI). Here, I improve the sensitivity of metal nanoparticle contrast agents by strategically incorporating pure and doped metal oxides in the nanoparticle core, forming a soluble, monodisperse, contrast agent with adjustable T2 or T1 relaxivity (r2 or r1). I first developed a simplified technique to incorporate iron oxides in apoferritin to form "magnetoferritin" for nM-level detection with T2- and T2* weighting. I then explored whether the crystal could be chemically modified to form a particle with high r1. I first adsorbed Mn2+ ions to metal binding sites in the apoferritin pores. The strategic placement of metal ions near sites of water exchange and within the crystal oxide enhance r1, suggesting a mechanism for increasing relaxivity in porous nanoparticle agents. However, the Mn2+ addition was only possible when the particle was simultaneously filled with an iron oxide, resulting in a particle with a high r1 but also a high r2 and making them undetectable with conventional T1-weighting techniques. To solve this problem and decrease the particle r2 for more sensitive detection, I chemically doped the nanoparticles with tungsten to form a disordered W-Fe oxide composite in the apoferritin core. This configuration formed a particle with a r1 of 4,870mM-1s-1 and r2 of 9,076mM-1s-1. These relaxivities allowed the detection of concentrations ranging from 20nM - 400nM in vivo, both passively injected and targeted to the kidney glomerulus. I further developed an MRI acquisition technique to distinguish particles based on r2/r1, and show that three nanoparticles of similar size can be distinguished in vitro and in vivo with MRI. This work forms the basis for a new, highly flexible inorganic approach to design nanoparticle contrast agents for molecular MRI. / Dissertation/Thesis / Ph.D. Bioengineering 2012

Orientador: Celio Pasquini / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-08T16:03:21Z (GMT). No. of bitstreams: 1 Cortez_Juliana_M.pdf: 4343113 bytes, checksum: d1746c525a8d51ede4e8432a525eecf2 (MD5) Previous issue date: 2007 / Resumo: Neste trabalho um instrumento LIBS com resolução temporal (TRELIBS) foi construído e seu desempenho foi avaliado para análise qualitativa e quantitativa. Além disso, este trabalho apresenta estudos exploratórios acerca da influência de parâmetros que afetam as análises em LIBS. O instrumento foi montado empregando-se óptica e sistema de detecção de última geração: um detector ICCD, um policromador echelle e um laser Q-switched de Nd:YAG. Três configurações do sistema LIBS foram avaliadas. No último arranjo do sistema, o pulso de laser era refletido por um espelho dicróico à 45º para uma lente de distância focal de 25 cm que focava o pulso de laser na superfície da amostra. A radiação foi coletada por uma lente de curta distância focal e depois enviada para o echelle, por uma fibra óptica, e posteriormente para o ICCD. Na análise qualitativa foram avaliados os espectros de uma placa de cobre e zinco, obtendo-se espectros condizentes com a literatura, de acordo com a resolução do echelle. Na avaliação quantitativa, determinou-se manganês em aços acalmados. O sistema apresentou resposta às diferentes concentrações de manganês em 293,30 nm e curvas analíticas foram obtidas. A energia do pulso de laser mostrou ser um fator determinante no desempenho da análise quantitativa. Outros parâmetros como tempo de integração do sinal, tempo de atraso, ganho do MCP, co-adição de pulsos e distância foco-amostra também mostraram ter influência na análise quantitativa. Imagens de MEV e mapeamentos de EDS das crateras formadas pelo laser foram ferramentas importantes para o entendimento do processo de interação laser-amostra-atmosfera / Abstract: In this work a time resolved LIBS instrument (TRELIBS) was built and its performance evaluated in qualitative and quantitative analysis. Additionally, exploratory studies are presented on the influence of parameters that affect the LIBS analysis. The instrument was built employing optical systems and devices of modern technology: an ICCD device, an echelle polychromator and an Q-switched Nd:YAG laser. Three configurations of LIBS system were evaluated. In the last configuration, the laser pulse was reflected by a dicroic mirror at 45º to a lens of 25 cm focal distance that focused the laser pulse on the sample surface. The plasma emission was collected by a lens of short focal distance and sent to the echelle, through of an optical fiber, and later to the ICCD. In qualitative analysis, spectra of copper and zinc foils were evaluated and the spectral lines were found in agreement with literature, considering the echelle resolution. In quantitative analysis, manganese was determined in killed steel. The system presented signals at 293,30 nm whose intensities changes in function of manganese concentration and analytical curves were obtained. The laser pulse energy showed to be an important factor for the success of quantitative analysis. Others parameters such as width, delay time, MCP gain, accumulated laser pulses and distance sample-focusing lens also showed have influence in quantitative analysis. MEV images and surface scanner by EDS of the craters formed by laser were important tools to understanding laser-sample-atmosphere interaction processes / Mestrado / Quimica Analitica / Mestre em Química