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Zr-Nb-Mn alloys were developed to investigate hydrogen diffusion and its effects among different manganese additions. Thermo-Calc® and TC-Prisma simulations were used to determine the studied chemical compositions and to estimate the volume fraction and the mean radius of precipitates. Three compositions were chosen to be melted and thermomechanically processed, resulting in an α-Zr matrix with fine β-Nb precipitation. TDS results indicated that hydrogen diffusion coefficient was 10-12 m2.s-1 for all the analyzed compositions. The manganese addition increased the strength while ductility was maintained. Although optical microscopy revealed that the increase of manganese content resulted in less oriented hydrides, the reduction in ductility was similar for the three studied compositions. Results showed manganese as a promising addition element for zirconium alloys due to the increase of hydrogen solubility, the good relationship between strength and ductility and the morphology of the hydrides.

The addition of Al, Cu and Mn in Zr–Nb-based alloys was evaluated through corrosion and hydrogen absorption tests in cold rolled and annealed conditions. For the studied alloys, the heat treatment resulted in an α-Zr matrix with β-Nb precipitates and X-ray diffraction (XRD) confirmed the formation of hydrides after hydrogenation in all conditions evaluated. It was observed that the alloy with Al addition absorbed the largest amount of hydrogen and the alloy containing Cu took more time to begin the absorption. The alloy with Mn absorbed little hydrogen but the onset of absorption occurred in a short time. The results indicate that the alloy with Cu addition is the most promising and the alloy with Al addition is inadequate for nuclear application.

The purpose of this study was to investigate the kinetics of hydrogen absorption and hydride formation and their effect on the mechanical properties in Zr-1Nb and Zr-1Nb-1Sn-0.1Fe alloys, which were thermomechanically processed and gaseously hydrided at 320ºC under 10 bar hydrogen pressure. X-ray diffraction (XRD) confirmed the formation of α-Zr matrix after final heat treatment. The alloys absorbed almost the same amount of hydrogen, although with different kinetics. Absorption began almost immediately in Zr-1Nb alloy whilst in Zr-1Nb-1Sn-0.1Fe hydrogen absorption started after 11 h besides a faster hydrogen kinetics. Results showed that tensile strengths for both alloys were nearly independent of absorbed hydrogen. Fractographic examinations indicated ductile fractures for unhydrided condition whereas quasi-cleavage features were observed for all hydrided specimens.

The present work shows the results of kinetic crystallization of the amorphous metallic alloy Fe 73.5 Cu 1 Nb 3 Si 8.5 B 14 by isothermal annealing, measured by ferromagnetic resonance (FRM) and small angle scattering X-ray in situ (SAXS/WAXS), and by non-isothermal annealing treatment, measured by differential scanning calorimetry (DSC). Only one crystalline phase was observed by WAXS and only one peak was observed by DSC. The activation energies, calculated from FMR and DSC data were 287 and 313.4 kJ mol −1 respectively, showing a good correlation between the two experimental techniques, since the difference is within the limits of experimental error. The values calculated for the Avrami exponent were 1.0 (FMR) and 1.4 (DSC). These values correspond to different mechanisms of nucleation and growth; however, the SAXS/WAXS results suggest that the dominant mechanisms are nucleation and growth of crystals from small dimensions.

Crystallization of the amorphous metallic alloy Fe73.5 Cu1Nb3 Si8.5 B14 was investigated by ferromagnetic resonance (FMR), small angle in situ X-ray scattering (SAXS/WAXS) and differential scanning calorimetry (DSC). Only one crystalline phase was observed by WAXS and only one peak was observed by DSC. The activation energies, calculated from FMR and DSC data, were 287 kJ.mol-1 and 313.4 kJ.mol-1, respectively. The values calculated for the Avrami exponent were 0.98 (FMR) and 1.4 (DSC). These values correspond to different mechanisms of nucleation and growth; however, the SAXS /WAXS results suggest that the dominant mechanisms are nucleation and growth of crystals from small dimensions.

The crystallization kinetics of the (Fe50Co50)73.5Ag1Nb3Si13.5B9 amorphous alloy was studied using ferromagnetic resonance (FMR) measurements on samples annealed at 693 K for several periods of time and differential scanning calorimetry (DSC) measurements using several heating rates between 5 and 30 K/s. The increase of the FMR linewidth with annealing time is attributed to crystallization. Assuming a linear relation between the linewidth increase and the transformed volume fraction, it is possible to determine the Avrami exponent, n, from the FMR results: n=1.83±0.10. The DSC measurements show two exothermal peaks, suggesting a crystallization process involving more than one phase. The Avrami exponents calculated from the DSC measurements are n=1.80±0.10 for the first peak and n=1.50±0.10 for the second peak; these results are consistent with a diffusion-controlled process with a decreasing nucleation rate for the first peak and with a nucleation rate close to zero for the second peak. There is a reasonable agreement between the FMR results and the DSC results for the first peak. The activation energies are 353.5±2.8 and 424.9±10.2 kJ/mol for the first and second peaks, respectively.

Samples of amorphous and partially crystallized Fe40Ni38Mo4B18 alloy were submitted to hydrogen gas permeation from 523 to 643 K. The hydrogen permeation curves exhibited a single sigmoidal shape, typical of tests where no hydride formation occurs. It was observed that the hydrogen diffusivity increases for the amorphous samples and partially crystallized alloy with the temperature increase. The hydrogen diffusion coefficient as a function of temperature was found to be D = 5.1 ± 0.5 × 10-12 exp (-11.0 ± 3.5/RT) (m2.s-1) for amorphous condition and D = 3.6 ± 0.5 × 10-11 exp (-19.8 ± 3.3/RT) (m2.s-1) for the partially crystallized condition. This suggests that the annihilation of defects in the amorphous structure and the crystalline phase precipitate contributes to the increase of the hydrogen diffusion.

The hydrogen absorption and desorption of Ti53Zr27Ni20 icosahedral quasicrystal (ICQ) and Ti50Ni50 shape memory alloy (SMA) melt-spun ribbons was studied. Samples were exposed to hydrogen gas at 623 K and 4 MPa for 1000 minutes. The total capacity of hydrogen obtained for Ti53Zr27Ni20 and Ti50Ni50 was 3.2 and 2.4 wt. % respectively. The Thermal Desorption Spectrometry (TDS) of the hydrogenated alloys shows that both alloys start to desorb hydrogen around 750 K. X-ray diffraction (XRD) patterns, performed after hydrogenation, indicate a complete amorphization of the Ti53Zr27Ni20 i-phase alloy, while the Ti50Ni50 alloy remained crystalline after hydride formation.

CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico FAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas Gerais CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior Hydrogen (H2) is a substance with a wide range of important applications like NH3 production. H2 can be obtained according to different processes, including the Na-O-H (sodium-oxygen-hydrogen) thermochemical cycle that breaks water through cyclic chemical reactions sustained by a heat source at specified temperature levels. In this context, GEN-IV (Generation IV) nuclear reactors are suitable energy options for these kind of processes because they are designed to provide electricity together with high temperature applications. At the same time, water could be get by means of MED (Multi-Effect Distillation), a desalination method that harvest waste heat from thermal systems to get fresh water from saline one. Then, H2 production from Na-O-H cycle through the heat supplied by GEN-IV reactors coupled to a MED unit enables the trigeneration of electricity, H2 and H2O, three important goods for society. Therefore, the first main aim of this thesis is to evaluate the thermal performance of this trigeneration process, a new one, considering three 1000 MWth GEN-IV technologies as the heat sources for both Na-O-H cycle plus a MED installation. This goal is developed by implementing mass, energy, entropy and exergy balances in the Engineering Equation Solver (EES) software to determine the amount of H2, electricity and desalinated H2O acquired. Consonant with preliminary results, this trigeneration process has potential to produce around 5 kg/s of H2, 400 MWe and 800 kg/s of H2O. These are theoretical and maximized values in function of all simplifications considered in the research. In the second main aim is investigated if there are other variations (b, c, d and e) of the Na-O-H cycle that have higher thermal performance when compared to its classic form, variation (a), evaluated in the first maim objective. According to the results, variation (e) has energy efficiency around 77% while variation (a) has energy efficiency near 52%. In the third main aim is established the thermodynamic limits (the minimum requirements of enthalpy change and other thermodynamic parameters) for thermochemical water splitting cycles starting from systems similar to the Na-O-H cycle. The results showed that all thermochemical cycles must have enthalpy change superior to 283.83 kJ to produce 1 mol of H2 gas. As it is being demonstrated in this study, it is possible to conclude that the trigeneration process of H2, water and electricity has potential to attempt the demand for such goods through more research and development of the systems analyzed. O hidrogênio (H2) é uma substância com uma ampla gama de aplicações. Ele pode ser obtido de acordo com diferentes processos, incluindo o ciclo termoquímico Na-O-H (sódio-oxigênio-hidrogênio) que quebra moléculas de água por meio de reações químicas cíclicas sustentadas por uma fonte de calor. Nesse contexto, os reatores nucleares de quarta geração (GEN-IV) são opções energéticas adequadas para atender a esse tipo de processos, pois são projetados para fornecer eletricidade em conjunto com aplicações que demandam altas temperaturas. Ao mesmo tempo, água potável poderia ser obtida por meio do processo de dessalinização MED (Multi-Effect Distillation) que reutiliza o calor residual de sistemas térmicos. Ainda, a produção de H2 a partir do ciclo Na-O-H através do calor fornecido por reatores GEN-IV acoplados a uma unidade MED possibilita a trigeração de eletricidade, H2 e H2O, três importantes insumos para a sociedade. Então, o primeiro objetivo principal desta tese é avaliar o desempenho térmico de um novo processo de trigeração, considerando três tecnologias GEN-IV de 1000 MW como fontes de calor para o ciclo Na-O-H e instalação MED. Este objetivo é desenvolvido através da implementação de balanços de massa, energia, entropia e exergia no software Engineering Equation Solver (EES) para determinar a quantidade desses três insumos. De acordo com os resultados, o processo avaliado tem potencial para produzir cerca de 5 kg/s de H2, 400 MW de eletricidade e 800 kg/s de água. Tais valores obtidos são teóricos e maximizados em função de todas as simplificações consideradas na pesquisa. No segundo objetivo principal é investigado se existem outras variações (b, c, d ou e) do ciclo Na-O-H que apresentam desempenho térmico superior à forma clássica desse sistema, variação (a), avaliada no primeiro objetivo. Os resultados indicaram que a variação (e) apresenta eficiência energética de aproximadamente 77% enquanto a variação (a) apresenta eficiência próxima de 52%. No terceiro objetivo principal são estabelecidos os limites termodinâmicos para ciclos termoquímicos partir de sistemas semelhantes ao Na-O-H. Os resultados mostraram que todos os ciclos termoquímicos devem ter variação de entalpia superior a 283,83 kJ para produzir 1 mol de H2. Finalmente, concluiu-se que o processo de trigeração de H2, água e eletricidade avaliado no trabalho tem potencial para atender a demanda por tais insumos pelo desenvolvimento futuro dos sistemas analisados.