Resumo: Dentre os compostos mais pesquisados atualmente encontram-se os eletrólitos sólidos com elevada condutividade iônica, pois estes apresentam potenciais aplicações em baterias de estado sólido, entretanto, na literatura, há poucos trabalhos que descrevam o processo de preparação e caracterização de pós com estrutura tipo perovskita para aplicações como catodos em baterias de lítio. Assim, este projeto teve como objetivo o desenvolvimento do processo de preparação do pó de La0.50Li0.50TiO3 pelo método de precursores poliméricos. O comportamento térmico do pó obtido a 350ºC foi avaliado através das técnicas de Análise Termogravimétrica (TGA) e Análise Térmica Diferencial (DTA); já a evolução térmica do pó obtido a 350 e 700ºC foi analisada por meio das técnicas espectroscópicas de Infravermelho (IR) e Raman. O processo de cristalização do pó foi realizado por Difração de Raios X (DRX), em conjunto com o Método de Rietveld que identificou uma fase pervskita altamente cristalina durante o processo de cristalização, no entanto, uma fase secundária, LiTi2O4, também foi detectada. A morfologia do pó foi observada por Microscopia Eletrônica de Varredura (MEV-FEG), que revelou uma microestrutura de grãos esféricos e homogêneos. Quanto às medidas eletroquímicas, foram utilizadas as técnicas de Titulação Galvanostática Intermitente (GITT), Cronopotenciometria e Voltametria Cíclica que evidenciaram a presença de dois processos cinéticos diferentes / Abstract: Among the most researched compounds currently are the solid electrolytes with high ionic conductivity, because of their potential applications in solid state batteries, however, in the literature there are few studies that describe the preparation and characterization of powders with perovskite structure for applications such as cathodes in lithium batteries. Thus this project aimed to develop the process of preparing the powder La 0.50Li0.50TiO3 by the polymeric precursor method. The thermal behavior of the power obtained at 350ºC was evaluated using the techniques of Thermogravimetric analysis (TGA) and Differential Thermal Analysis (DTA), whereas the thermal evolution of the power obtained at 350 and 700ºC was analyzed by spectroscopic techiniques IR and Raman. The crystallization process was analyzed by X-ray powder diffraction together with the Rietveld Method that identified a highly crystalline perovskite phase during the crystallization process; however, a secondary phase LiTi2O4 was also detected. The morphology of the powder was observed by field emission gun scanning electron microscopy (FEG-SEM), which revealed a microstructure of spherical and homogeneous grains. As for the eletrochemical measurements, we have used the Galvanostatic Intermittent Intermittent Titration Technique (GITT), Chronopotenciometry and Cyclic Voltammetry demonstrating the presence of two different kinetic processes / Orientador: Carlos Frederico de Oliveira Graeff / Coorientador: Alejandra Hortencia Miranda González / Banca: Fritz Cavalcante Huguenin / Banca: Fenelon Martinho Lima Pontes / Banca: Roberto Manuel Torresi / Banca: Maria Aparecida Z. Bertochi / O programa de Pós graduação em Ciência e Tecnologia de Materiais, POSMAT, tem carater institucional e integra as atividades de pesquisa em diversos materiais de diversos campi da Unesp / Doutor

In the current age of fast-depleting conventional energy sources, top priority is given to exploring non-conventional energy sources, designing highly efficient energy storage systems and converting existing machines/instruments/devices into energy-efficient ones. ‘Energy efficiency’ is one of the important challenges for today’s scientific and research community, worldwide. In line with this demand, the current research was focused on developing two highly energy-efficient devices – field emitters and Li-ion batteries, using beneficial properties of carbon nanotubes (CNT). Interface-engineered, directly grown CNTs were used as cathode in field emitters, while similar structure was applied as anode in Li-ion batteries. Interface engineering was found to offer minimum resistance to electron flow and strong bonding with the substrate. Both field emitters and Li-ion battery anodes were benefitted from these advantages, demonstrating high energy efficiency. Field emitter, developed during this research, could be characterized by low turn-on field, high emission current, very high field enhancement factor and extremely good stability during long-run. Further, application of 3-dimensional design to these field emitters resulted in achieving one of the highest emission current densities reported so far. The 3-D field emitter registered 27 times increase in current density, as compared to their 2-D counterparts. These achievements were further followed by adding new functionalities, transparency and flexibility, to field emitters, keeping in view of current demand for flexible displays. A CNT-graphene hybrid structure showed appreciable emission, along with very good transparency and flexibility. Li-ion battery anodes, prepared using the interface-engineered CNTs, have offered 140% increment in capacity, as compared to conventional graphite anodes. Further, it has shown very good rate capability and an exceptional ‘zero capacity degradation’ during long cycle operation. Enhanced safety and charge transfer mechanism of this novel anode structure could be explained from structural characterization. In an attempt to progress further, CNTs were coated with ultrathin alumina by atomic layer deposition technique. These alumina-coated CNT anodes offered much higher capacity and an exceptional rate capability, with very low capacity degradation in higher current densities. These highly energy efficient CNT based anodes are expected to enhance capacities of future Li-ion batteries.

In this work, a high-performance hybrid supercapacitor is assembled with N-doped reduced graphene oxide (N-rGO) decorated with Fe2O3 (Fe2O3/N-rGO) as the anode, and NiCo layered double hydroxide integrated with conductive Co(OH)2 (NiCo LDH/Co(OH)2) as the cathode. The two main pseudo-capacitive materials are modified by different materials (N-rGO and Co(OH)2) to enhance the conductivity. For anode, the Fe2O3 nanoparticles are uniformly dispersed on N-rGO via a facile solvent-thermal method. The highly conductive Fe2O3/N-rGO exhibits a superior capacitance of 912.9F/g at 1 A/g and retains 84% at 30 A/g. The NiCo LDH/Co(OH)2 cathode also synthesized by a convenient solvent-thermal method delivers a high specific capacitance of 2220.0F/g at 1 A/g and retains 70% at a high current density of 50 A/g. Utilizing these electrodes, we successfully fabricate a hybrid battery-like supercapacitor with an excellent energy density of 103.3 Wh/kg at an outstanding power density of 790 W/kg, an excellent capacitance of 296.3F/g at 1 A/g and a remarkable cyclic stability with 92% retention after 1000 cycles at 10 A/g. Due to the elaborately designed electrode materials, the battery-like supercapacitor exhibits excellent electrochemical properties and is an inspiration for future energy storage devices.

In recent years, the automotive industry has turned to press hardened steels (PHS) to improve passenger safety while enabling vehicle weight reduction. To form the complex shapes required for this purpose, they are often direct hot press formed. It is possible to provide corrosion resistance to these parts by galvanizing the PHS sheets prior to direct hot press forming (DHPF). However, the austenitization of the galvanized steel causes the Zn-based coating to transform into two intermetallic phases. These are iron-rich α-Fe(Zn) and zinc-rich Г-Fe3Zn10. The Г-Fe3Zn10 is liquid during traditional DHPF, and the applied stress can result in liquid metal embrittlement (LME). Recently, two new grades of PHS have been developed, which allow for DHPF at 600-700°C, below the Fe-Zn peritectic temperature at 782°C, thus avoiding LME. These prototype PHS grades are designated 2%Mn (0.2C-2Mn-0.25Si-0.005B (wt%)) and 2.5%Mn (0.2C-2.5Mn-0.25Si-0.005B (wt%)). The objective of this work is to determine the effect of DHPF on the ability of a Zn-based coating to provide robust cathodic protection to the two prototype PHS. Galvanized panels of both the 2%Mn and 2.5%Mn steel were DHPF with a U-shape die at 700°C. The surface and cross-section of the coating were examined to determine the effects of DHPF on the coating surface. Die friction during DHPF resulted in die wiping on the wall of the part, leading to removal of surface Г-Fe3Zn10. In cross-section, coating cracks were present at the wall and corner of the U-shape part due to the deformation during DHPF. Potentiodynamic polarization scans were used to determine the corrosion potential of the coating, and this was used to calculate the driving force for cathodic protection using the difference in corrosion potential between the coating phases and the substrate. It was found that only Γ-Fe3Zn10 provided robust cathodic protection to both steel substrates, and the driving force for cathodic protection was lower for the coated DHPF 2.5%Mn steel. Galvanostatic scans were used to evaluate dissolution kinetics of coating phases. Robust cathodic protection was provided by the galvanized coating for austenitization times of 30 - 120 s for the 2%Mn substrate and 30 - 60 s for the 2.5%Mn substrate. The duration that robust cathodic protection was provided was shortest at the wall of the U-shape part. This result was attributed to die wiping caused by DHPF, where the surface is smoothed by die friction. When there is less Г-Fe3Zn10 in the coating, such as at longer austenization times, surface Г-Fe3Zn10 was removed and an increased amount of α-Fe(Zn) is exposed, which does not provide robust cathodic protection. In addition, coating cracks form along α-Fe(Zn) grain boundaries after austenitization for 180 s on all examined regions of the U-shape part, allowing a greater surface area of the coating exposed to electrolyte, further increasing dissolution of the coating. / Thesis / Master of Applied Science (MASc)

Conducting research experiments on plutonium electrorefining is difficult due to the significant hazards and regulations associated with nuclear materials. Finding a surrogate for plutonium electrorefining studies would enable more fundamental research to be conducted. Potential surrogates were identified by determining the physical properties required to conduct electrorefining using a molten metal and molten salt in CaCl2 at 1123 K. More potential surrogates were identified by changing the matrix salt to be a LiCl-KCl-CaCl2 eutectic salt with electrorefining conducted at 673-773 K. Ce-CeCl3, In-InCl3, Zn-ZnCl2, Sn-SnCl2, and Bi-BiCl¬3 were investigated as potential plutonium electrorefining surrogates. Ce electrorefining in molten CaCl2 resulted in a difficult to separate colloid mixture of Ce, Ca and Cl. Electrorefining rates for In were too slow due to InCl3 volatilizing out of the molten salt. Zn was successfully electrorefined, but the metal obtained did not coalesce into one piece. Sn and Bi were successfully electrorefined and coalesced into solid product rings with high yields and coulombic efficiencies. While a surrogate could not be identified using the same conditions as plutonium electrorefining, two possible surrogates, Sn-SnCl2 and Bi-BiCl3,¬ were found that could imitate the physical configuration (i.e., molten salt on top of molten metal) of plutonium electrorefining at a reduced temperature using a eutectic LiCl-KCl-CaCl2 salt in place of CaCl2. Using this surrogate enables fundamental studies of aspects of plutonium electrorefining. One aspect of plutonium electrorefining research is to improve its efficiency and yield. Plutonium electrorefining is a time-intensive process which generates radioactive waste. Improvements in efficiency and yield can reduce process time and waste. One possible way of improving the efficiency of plutonium electrorefining is to study the impact of using an AC superimposed DC waveform. Four AC superimposed DC and two DC electrorefining runs were performed using bismuth as a plutonium surrogate. All six runs showed a high level of yield and coulombic efficiency. All six cathode rings were confirmed to be high-purity bismuth using scanning electron microscopy with energy dispersive x-ray analysis (SEM-EDS). While the results were inconclusive about the ability of AC superimposed DC waveforms to increase the efficiency of bismuth electrorefining, applying an AC superimposed DC waveform did not appear to decrease the efficiency or yield of the process. The change in waveform also did not result in impurities being present in the product cathode ring. Bismuth, in addition to being identified as a viable plutonium surrogate, has been investigated as a potential liquid electrode for molten salt electrorefining. Because of this, its electrochemical properties are of interest. However, bismuth's electrochemical behavior has received scant attention in eutectic LiCl-KCl melts and no studies were found in the ternary LiCl-KCl-CaCl2 melts. LiCl-KCl-CaCl2 melts offer some advantages over eutectic LiCl-KCl, such as lower melting point and higher oxide solubility. Cyclic voltammetry, square wave voltammetry, chronoamperometry, chronopotentiometry and open-circuit chronopotentiometry were used to measure electrochemical parameters, such as diffusivity and standard redox potential of bismuth electrodeposition in LiCl-KCl and LiCl-KCl-CaCl2 eutectics.

Made available in DSpace on 2017-07-25T19:29:47Z (GMT). No. of bitstreams: 1 ValterAssami.pdf: 1493027 bytes, checksum: b7055c6cb6163590aa97d192d094742d (MD5) Previous issue date: 2010-10-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Surface application of lime in no-till system (NTS), result in a gradient between surface and subsurface soil layers due to acidity amelioration. Liming and nitrogen fertilization can change chemical soil profile and modify soil quality (biological, physical and chemical). The aim of this study was to investigate the magnitude of the chemical and physical changes of soil due to surface liming, cover crop management and nitrogen fertilization. The experimental design was a complete randomized block, in a split-plot on loamy, kaolinitic, thermic Typic Hapludox in Ponta Grossa, Parana State, Brazil, and 30 years under NTS. The main plots consisted of dolomite lime applied on soil surface without incorporation (control, 4, 8 and 12 Mg ha-1 of lime) in May 2004. The subplots were represented by winter crop management: without black oat cover crop (SCA); with black oat cover crop (CCA) and black oat fertilized with 180 kg ha-1 of N (CCA+N). After corn (Zea mays L.) harvest, in May 2009 (60 months after liming application), samples of soil layers 0 - 5, 5 - 10 and 10 - 20 cm were collected for determination of: pH; point of zero salt effect (PZSE), ΔpH, electrical conductivity (EC), total acidity (H+Al); content of exchangeable aluminum (Al), calcium (Ca), magnesium (Mg) and potassium (K); effective cation exchange capacity (CECE), available phosphorus (P), total nitrogen (TN) and total organic carbon (TOC). In this occasion, samples undisturbed were token from 0-10 and 10-20 cm layers and performed to macroporosity, microporosity, total porosity (TP) and bulk density (BD). Samples blocks of soil were also collected to measure the tensile strength of aggregates (TS). The surface liming, after five years of its use in soil managed for 30 years in NTS provides increase of Ca and Mg in all layers studied. When high levels of ammonium nitrate were applied on black oat, had an increase of soil acidification and reduction of Ca and Mg in the layer 0 - 5 and 5 - 10 cm. The liming and cover crop of black oat, with and without N application favored the accumulation of TOC and TN in all layers studied. Treatments with black oat provided increment of pH, EC, Ca, Mg, and TN in the layer 10 - 20 cm, showing the importance of vegetation for the improvement of soil fertility. The cover crop of black oat allied to liming under NTS consolidated had little change in the attributes PZSE, ΔpH and EC, but the values of the electrochemical properties obtained were adequate to the soil managed in the NTS. The treatments with black oat combined with liming reduced the macroporosity and contributed to the increase in RT at 0 - 10 cm. It was found that the lime in the level of 8 Mg ha-1 combined with lime and without black oat increased the microporosity at the layer 0 - 10 cm of the soil. In the layer 10 - 20 cm, the limestone associated with treatments of oat reduced macroporosity and increase microporosity of the soil. Key-words: electrochemical properties, tropical soil, dolimitic lime, agriculture conservationist. / A aplicação superficial de calcário, no sistema plantio direto (SPD), resulta em um gradiente entre a superfície e camadas subsuperficiais do solo na correção da acidez. A calagem e a fertilização nitrogenada proporcionam modificações químicas no perfil do solo capaz de influenciar a qualidade (biológica, física e química) do solo. O objetivo desse trabalho foi verificar a magnitude das alterações químicas, eletroquímicas e físicas do solo devido à calagem superficial, manejo da cobertura vegetal e adubação nitrogenada. O delineamento experimental empregado foi o de blocos completos ao acaso com parcelas subdivididas em um Latossolo Vermelho textura média manejado há 30 anos no SPD no Paraná, Brasil. As parcelas receberam calagem superficial (controle, 4, 8 e 12 Mg ha-1 de calcário) em maio de 2004. Nas subparcelas, foram estabelecidos os seguintes tratamentos: sem cobertura de aveia (SCA); com cobertura de aveia (CCA) e com cobertura de aveia fertilizada anualmente com 180 kg ha-1 de nitrogênio mineral (nitrato de amônio) (CCA+N). Em maio de 2009 (60 meses após a calagem), amostras de solo das camadas de 0 - 5, 5 - 10 e 10 - 20 cm foram coletadas para determinação de: pH, ponto de efeito salino nulo (PESN), delta pH (ΔpH), condutividade elétrica (CE), acidez total; teores trocáveis de alumínio (Al), cálcio (Ca), magnésio (Mg) e potássio (K); capacidade de troca catiônica efetiva (CTCe), fósforo disponível (P Mehlich-1), nitrogênio total (NT) e carbono orgânico total (COT). Amostras de solo indeformados das camadas de 0 - 10 e 10 - 20 cm foram coletadas, na mesma ocasião, visando à determinação dos atributos: macroposidade, microporosidade, porosidade total (PT) e densidade do solo (Ds). Blocos de solo foram coletados para quantificar a resistência tênsil (RT) de agregados. A calagem superficial, após 5 anos de sua aplicação em solo manejado há 30 anos no SPD proporcionou correção da acidez, aumento de Ca e Mg trocáveis em todas as camadas estudadas. Quando altas doses de nitrato de amônio foram aplicadas na aveia preta, ocorreu aumento da acidificação do solo e redução dos teores de Ca e Mg trocáveis na camada de 0 - 5 e 5 - 10 cm. A calagem e a cobertura de aveia preta, sem e com aplicação de N, favoreceram o acúmulo de COT e NT em todas as camadas estudadas. Os tratamentos com aveia preta proporcionaram incremente de pH, CE, Ca, Mg e NT na camada de 10 - 20 cm, evidenciando importância da cobertura vegetal para o melhoria da fertilidade do solo. A cobertura de aveia preta aliada à calagem superficial sob SPD consolidado pouco alteraram os atributos PESN, ΔpH e CE, porém os valores dos atributos eletroquímicos obtidos foram adequados ao manejo do solo no SPD. Os tratamentos com aveia preta aliada a calagem superficial reduziu a macroporosidade e contribui para o aumento da RT na camada de 0 - 10 cm. Verificou-se que na dose de 8 Mg ha-1 de calcário (saturação por bases estimada de 65%) aliado aos tratamentos com e sem aveia preta favoreceram os maiores valores de microporosidade na camada de 0 - 10 cm. A calagem associado aos tratamentos da aveia preta reduziu a macroporosidade e aumento da microporosidade na camada de 10 - 20 cm do solo.

Binder free vertical aligned (VA) CNT/sulfur composite electrodes with high sulfur loadings up to 70 wt% were synthesized delivering discharge capacities higher than 800 mAh g−1 of the total composite electrode mass. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Cette thèse présente un travail sur l’obtention d’aérogels d’HDL par séchage en conditions CO2 supercritique et l’élaboration de nouveaux bionanocomposites formés par la coprécipitation d’hydroxydes doubles lamellaire (HDL) dans l'espace confiné des billes d'alginate. Grâce à la combinaison d’une synthèse par coprécipitation Flash et d’un séchage en conditions supercritiques au CO2, des aérogels d’HDL possédant des surfaces spécifiques élevées sont élaborés. Parallèlement, l’alginate est utilisé comme une matrice de confinement pour la précipitation inorganique d’HDL. D’une part, les billes d'alginate sont synthétisées par complexation des ions Ca2+ et la coprécipitation des phases HDL s’effectue en réalisant des imprégnations successives de réactifs. D’autre part, des billes d'alginate sont formées directement en présence des cations divalents (Mg2+, Ni2++, Co2+, ...) et des cations des métaux trivalents (Al3+), précurseurs des composés inorganiques. La coprécipitation des HDL se produit dans ce cas lors d'une étape d'imprégnation dans une solution d'hydroxyde de sodium. Tous les composés HDL, aérogels ou encore bionanocomposites sont caractérisés en détail par DRX, spectroscopie IR, MEB/MET, adsorption/désorption d’azote et ATG/DTG, pour obtenir un meilleur aperçu de la structure des particules, de leur taille et de leur morphologie. Des études menées sur l’adsorption de la trypsine pour les aérogels ou encore sur les performances d’électrodes modifiées HDL-alginate ont permis de montrer qu’il était possible d'améliorer les performances des HDL en augmenter leur porosité et en élaborant des bionanocomposites. / In this work, we investigated both the use of CO2 supercritical drying conditions and the use of biopolymer to modify the growth and aggregation of inorganic Layered Double Hydroxide (LDH) particles. Indeed, one possibility to enhance their performances is to increase the LDH porosity and to design them as nanostructured open structure. Thanks to the combinaison of fast coprecipitation and CO2 supercritical drying, highly porous LDH aerogels were obtained with enhanced textural properties. In parallel, the coprecipitation of Layered Double Hydroxides (LDH) in the confined space of alginate beads is reported. In our approach, Alginate acts as a template to support and confined the inorganic precipitation. In one hand, beads made of Alginate are synthesized by complexation of Ca2+ ions and LDH phases are coprecipitated using successive impregnations of reactants. In another hand, Alginate beads are formed directly in presence of the divalent (Mg2+, Ni2+, Co2+,…) and trivalent metal cations (Al3+), precursors of the inorganic compounds. LDH coprecipitation then occurs during a further impregnation step in a sodium hydroxide solution. All the LDH aerogels and LDH nanocomposites beads are deeply characterized using XRD, SEM/TEM, FTIR spectroscopic, adsorption/desorption of nitrogen and TGA/DTG to get better insight on particle structure, size and morphology Aerogels display enhanced adsorption behavior toward trypsine immobilization whereas a net improvement of the electrochemical response is noticed for the NiAl based bionanocomposites prepared by confined coprecipitation into Alginate.

Binder free vertical aligned (VA) CNT/sulfur composite electrodes with high sulfur loadings up to 70 wt% were synthesized delivering discharge capacities higher than 800 mAh g−1 of the total composite electrode mass. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23515号 / 工博第4927号 / 新制||工||1769(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 安部 武志, 教授 陰山 洋, 教授 作花 哲夫 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM