Annealing effects on the structural and optical properties of vanadium oxide film obtained by the hot-filament metal oxide deposition technique (HFMOD)

Vanadium oxide films amorphous, nonstoichiometric and highly absorbing in the optical region were depositedon ITO-coated glass and on silicon substrates, by the hot-filament metal oxide deposition technique(HFMOD) and oxidized by ex-situ annealing in a furnace at 200, 300, 400 and 500 ºC, under an atmosphereof argon and rarefied oxygen. X-ray diffraction, Raman and Rutherford backscattering spectroscopy as wellas optical transmission were employed to characterize the amorphous and annealed films. When annealed at200 and 300 ºC the as-deposited opaque films become transparent but still amorphous. Under treatments at400 and 500 ºC a crystalline nonstoichiometric V2O5 structure is formed. All the annealed films became semiconducting,with their optical absorption coefficients changing with the annealing temperature. An opticalgap of 2.25 eV was measured for the films annealed at 400 and 500 ºC. The annealing in rarefied oxygenatmosphere proved to be a useful and simple ex-situ method to modulate the structural and optical propertiesof vanadium oxide films deposited by HFMOD technique. This technique could be applied to other amorphousand non-absorbing oxide films, replacing the conventional and sometimes expensive method of modulatedesirable film properties by controlling the film deposition parameters. Even more, the HFMOD techniquecan be an inexpensive alternative to deposit metal oxide films

Li diffusion and electrochromism in amorphous and crystalline vanadium oxide thin film electrodes

Amorphous vanadium oxide films were synthesized onto ITO-coated glass substrates by the hot filament metal oxide deposition technique. The as-deposited samples were heat-treated in an argon atmosphere. X-ray diffraction analysis revealed that the films treated at 200 and 300 ºC were still amorphous, while those treated at 400 and 500 ºC were crystalline, with a V2O5 structure. All electrodes were electrochemically reversible for Li+ intercalation, exhibiting the electrochromic effect, observed from optical transmittance measurements at 632.8 nm. The Li-diffusion coefficient, DC, was measured by the galvanostatic intermittent titration technique (GITT) as function of the inserted charge. For the crystalline films it was observed that the optical absorbance and the DC increase with increasing Li insertion in the single-phase regions of crystalline Li xV2O5 and decrease in the two-phase regions. For the latter, an effective DC was considered. The presence of other vanadium oxides mixed to the V2O5 matrix was inferred for the crystalline films from the chronopotentiometric and DC measurements

Recovering the Cathode Material Adhered to the Collector and Separator of Spent Lithium-Ion Batteries for Recycling Purposes

Depleted Li-ion batteries (LIBs) must be recycled for environmental and sustainability reasons. Most recycling processes are dedicated to the recovery of Li, Co, Mn, and Ni present in the cathode material of LIBs. However, separating the cathode material strongly adhered to the aluminum collector and those mechanically trapped into the polymeric separator is still challenging. Processes to separate the cathode material by dissolving its aluminum collector in NaOH solution and to extract part of this material encrusted in the separator by ultrasonic cavitation and mechanical friction are presented in tests with NMC batteries on a laboratory scale. Tests of LIB discharges were also carried out in different MnO4 solution concentrations, and the related electrochemical reactions were discussed

Propriedades mecânicas em filmes de Nb/Pd

Orientador: Sergio MoehleckeTese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb WataghinResumo: Fizemos um estudo da tensão mecânica (interna e térmica), falhas mecânicas e adesão, em filmes poli cristalinos de Nb/Pd depositados pelas técnicas de "sputtering" e evaporação. Observou-se que a tensão residual depende das condições de deposição, em especial da pressão do gás do plasma de argônio nos filmes obtidos por "sputtering" .Verificou-se também que padrões caracterizam as falhas por trincas e descolamentos, as quais ocorrem dependentemente dos parâmetros tensão residual, espessura do filme e adesão. Obteve-se ainda para estes filmes, as tensões de compressão críticas para a ocorrência de falhas por descolamentos. Com os resultados obtidos discutiu-se os modelos teóricos para a origem da tensão e falhas mecânicas em filmes finos. Um resumo atualizado das propriedades mecânicas destes materiais é também apresentadoAbstract: Stress (internal and thermal), mechanical failures and adhesion were studied for Nb/Pd polycrystalline films, deposited by sputtering and evaporation techniques. A dependence between residual stress and depositions conditions, mainly with the plasma pressure in sputtered films was observed. Specific patterns characterize the failures by cracking and buckling, with occur depending on residual stress film thickness and adhesion parameters. The critical compressive stress to failures by bucking in these films was obtained experimentally. Based on these results theoretical models of the origin of stress and of mechanical failures in thin films were discussed. An up-to-date abstract about the mechanical properties in these materials is also presentedDoutoradoFísicaDoutor em Ciência

Efeitos da composição e tratamento termico no composto supercondutor : SnMo6S8

Orientador: Sergio MoehleckeDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb WataghinResumo: Fizemos um estudo da dependência de temperatura crítica supercondutora (Tc) e dos parâmetros de rede cristalográfico (aR e aR) com o tempo e a temperatura, para diferentes tratamentos térmicos, nos compostos ternários Chevrel Sn-Mo-S. Observamos a existência de condições ótimas nestes parâmetros para a obtenção de um máximo em Tc e aR. Notou-se que a fase Chevrel pode ser formada apenas aquecendo-se a amostra da temperatura ambiente até a temperatura de síntese e que existe uma região de homogeneidade bem definida desta fase para tratamentos a 1100ºC. Foi obtido uma dependência linear crescente entre os parâmetros Tc e aR para as várias amostras. Alguns modelos teóricos foram confrontados com estes resultados, onde algumas interpretações podem ser feitasAbstract: The dependence of the superconducting critical temperature (Tc) and the lattice parameters (aR and aR) on the time and temperature for differents heat treatments were here studied on the ternary Chevrel compounds Sn-Mo-S. We observe the occurrence of optimal conditions for a maximum Tc and aR. It was also noticed that the Chevrel phase can be formed by just warming up the sample from room temperature to the synthesizing temperature and the existence of a well define homogeneity range for this phase at 1100ºC. In all ours samples a linear dependence between Tc and aR were observed. Finally, a few theoretical predictions were compared with ours results where some interpretations could be madeMestradoFísicaMestre em Físic

Medida da potência térmica de refrigeração a água de uma bomba de vácuo difusora

Bombas de vácuo difusoras são utilizadas na indústria e na ciência para produção de alto vácuo. Considerando que os sistemas de vácuo operam por horas e são refrigerados com água corrente, o consumo excessivo de água pode ser evitado se a refrigeração for realizada em circuito fechado. Contudo, para implementação de um destes circuitos é necessário se conhecer a potência térmica dissipada pela bomba, que pode ser obtida através do manual de operações do sistema, literatura técnica ou pela medida da própria potência dissipada pelo sistema, caso não se possa consultar o manual. Neste trabalho, a potência térmica de uma bomba difusora foi obtida medindo-se a vazão e a variação da temperatura da água, e calculada através da equação da variação de quantidade de calor em função do tempo. O valor encontrado foi de 935,6 W, que ao ser comparado com o manual de operações, está 397 W menor que a máxima potência e 35 W maior do que a mínima potência térmica da bomba. Com este procedimento é possível determinar com precisão, agilidade e facilidade, a potência térmica da bomba difusora ou de qualquer sistema que se pretende refrigerar a circuito fechado de água

ANALYSIS OF A COMMERCIAL PORTABLE LITHIUM-ION BATTERY UNDER LOW CURRENT CHARGE-DISCHARGE CYCLES

The dependence between the transferred charge and the corresponding transference time to charge and discharge a portable cell phone Li-ion battery (LiCoO2/C) under cycles of low intensity currents was studied in detail. The voltage curve profile between 3.0 and 4.2 V and the charging and discharging time are strongly influenced by the applied current intensity. A linear dependence between the stored and extracted charges, into and from the battery, with the intensity of applied current was also observed. Allometric equations were found to describe the correlation between the charge transference time and the applied current intensity to charge and discharge the battery