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abstract: In the United States, 95% of the industrially produced hydrogen is from natural gas reforming. Membrane-based techniques offer great potential for energy efficient hydrogen separations. Pd77Ag23 is the bench-mark metallic membrane material for hydrogen separation at high temperatures. However, the high cost of palladium limits widespread application. Amorphous metals with lower cost elements are one alternative to replace palladium-based membranes. The overall aim of this thesis is to investigate the potential of binary and ternary amorphous metallic membranes for hydrogen separation. First, as a benchmark, the influence of surface state of Pd77Ag23 crystalline metallic membranes on the hydrogen permeability was investigated. Second, the hydrogen permeability, thermal stability and mechanical properties of Cu-Zr and Ni60Nb35M5 (M=Sn, Ti and Zr) amorphous metallic membranes was evaluated. Different heat treatments were applied to commercial Pd77Ag23 membranes to promote surface segregation. X-ray photoelectron spectroscopy (XPS) analysis indicates that the membrane surface composition changed after heat treatment. The surface area of all membranes increased after heat treatment. The higher the surface Pd/(Pd+Ag) ratio, the higher the hydrogen permeability. Surface carbon removal and surface area increase cannot explain the observed permeability differences. Previous computational modeling predicted that Cu54Zr46 would have high hydrogen permeability. Amorphous metallic Cu-Zr (Zr=37, 54, 60 at. %) membranes were synthesized and investigated. The surface oxides may result in the lower experimental hydrogen permeability lower than that predicted by the simulations. The permeability decrease indicates that the Cu-Zr alloys crystallized in less than two hours during the test (performed at 300 °C) at temperatures below the glass transition temperature. This original experimental results show that thermal stability of amorphous metallic membranes is critical for hydrogen separation applications. The hydrogen permeability of Ni60Nb35M5 (M=Sn, Ti and Zr) amorphous metallic membranes was investigated. Nanoindentation shows that the Young’s modulus and hardness increased after hydrogen permeability test. The structure is maintained amorphous after 24 hours of hydrogen permeability testing at 400°C. The maximum hydrogen permeability of three alloys is 10-10 mol m-1 s-1 Pa-0.5. Though these alloys exhibited a slight hydrogen permeability decreased during the test, the amorphous metallic membranes were thermally stable and did not crystalize. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2015

Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-04-04T20:26:12Z No. of bitstreams: 1 ALANA PEREIRA RAMOS - DISSERTAÇÃO PPG-CEMat 2014..pdf: 2592489 bytes, checksum: 5e82ab454a76e1050981da9019ce8fec (MD5) / Made available in DSpace on 2018-04-04T20:26:12Z (GMT). No. of bitstreams: 1 ALANA PEREIRA RAMOS - DISSERTAÇÃO PPG-CEMat 2014..pdf: 2592489 bytes, checksum: 5e82ab454a76e1050981da9019ce8fec (MD5) Previous issue date: 2017-08-07 / As ligas ternárias de Ti-Cu-Ni com memória de forma são conhecidas por apresentarem transformação de fase característica e propriedades semelhantes às ligas binárias Ti–Ni. Estudos realizados com ligas ricas em cobre mostraram que a adição de cobre nas ligas de Ti-Ni reduz a histerese de resposta do efeito de memória de forma e aumenta a TFA (tendência de formação de fase amorfa) ainda pouco estudada com altas porcentagens de cobre. Diante disso, este trabalho teve como objetivo avaliar a influência da velocidade de resfriamento nas temperaturas de transformação e na tendência de amorfização em fitas de Ti-CuNi resfriadas rapidamente. Para tanto, foram produzidas duas fitas Ti01 (Ti 43,5 Cu 37,8 Ni 18,7) e Ti02 (Ti 58,4 Cu 25,6 Ni 16,0) pelo processo melt spinning, variando-se a velocidade linear da roda em 21 m/s e 63 m/s. As amostras foram caracterizadas utilizando-se técnicas DSC, DR-X, RET e MO. Após essa caracterização pode-se afirmar que a técnica de melt spinning permite a produção de fitas muito finas, da ordem de micrômetros, em apenas uma etapa de processamento, assim como também foi possível a produção de fitas amorfas, do sistema Ti-Cu-Ni, sem nenhuma fase cristalina como observado na fita Ti01 e Ti 02 obtidas com velocidade linear de 63m/s. O tratamento térmico foi suficiente para remover todos os defeitos produzidos pelo processo de solidificação rápida e produzir um rápido crescimento de grão, favorecendo o aumento das temperaturas de transformação martensíticas e austeníticas. / Ternary alloys with shape memory Ti-Cu-Ni are known to submit a characteristic phase transformation and properties similar to the and Ti-Ni binary alloy . Studies with rich-copper alloys showed that the addition of copper in alloys Ti-Ni reduces the hysteresis response of the shape memory effect and increases the TFA (tendency to form amorphous phase) still little studied with high percentages of copper. Thus, this study aimed to evaluate the influence of cooling rate on the transformation temperatures and on the tendency of Cu-Ni-Ti ribbons rapidly solidified. Therefore, two ribbons TI01 (Ti 43.5 Cu 37.8 Ni 18.7) and Ti02 (Ti 58.4 Cu 25.6 Ni 16.0) were produced by melt spinning process, varying the wheel linear velocity 21 m/s and 63 m/s. The samples were characterized using DSC, X-DR, RET and MO and techniques. Melt spinning technique allows the production of very thin ribbons of the order of microns, in one processing step, as it was also possible to produce amorphous ribbons, the system Ti-Cu-Ni, without crystalline phase as observed in TI01 and 02 Ti02 with linear velocity of 63m/s. The heat treatment was sufficient to remove all defects produced by rapid solidification process and produce a rapid grain growth, favoring the increase of temperatures of martensitic and austenitic transformation.