Hydrogen storage has been identified as a primary bottleneck in the large-scale implementation of a hydrogen-based economy. Many research efforts are underway to both improve the capacity of existing hydrogen storage systems and develop new systems. One promising area of research is hydrogen physi-sorbed into carbonbased structures such as nanotubes and graphene. Two novel systems consisting of a phthalocyanine salt with a large cation were studied. Ab initio, density functional theory, and molecular dynamics simulations of tetramethylammonium lithium phthalocyanine (TMA-LiPc) and trimethyl-(2-trimethylazaniumylethyl) azanium phthalocyanine (TMA2-Pc) were undertaken to estimate the H2 gas-solid adsorption uptake (wt/wt) as a function of pressure and temperature. For TMA-LiPc, the maximum H2 binding energy was approximately 0.9 kcal/mol for an isolated system and 1.2 kcal/mol for a crystal. H2 adsorption at the optimal inter-layer distance of 8.49 Å ranged from 2.1% to 6.0% (wt/wt) at 300 K, 2.5% to 6.5% at 273K, 3.3% to 7.2% at 236K, 5.2% to 8.6% at 177K, and 10.4% to 11.7% at 77K. At ILD 10 Å H2 adsorption was about 1.5% (wt/wt) higher at all points. For TMA2-Pc, the maximum H2 binding energy was approximately 1.3 kcal/mol for an isolated system and 1.2 kcal/mol for a crystal. H2 adsorption at the optimal inter-layer distance of 8.12 Å ranged from 0.5% to 2.6% (wt/wt) at 300 K, 0.6% to 2.8% at 273K, 0.8% to 3.2% at 236K, 1.4% to 3.9% at 177K, and 4.5% to 6.0% at 77K. At ILD 10 Å H2 adsorption ranged from about 0.1% (wt/wt) at 40 bar to 0.5% higher at 250 bar. The behavior of H2 adsorption for both TMA-LiPc and TMA2-Pc were compared. The adsorbed H2 probability density was compared to pair correlation function data and surfaces of constant binding energy. Regions of relatively high H2 density appear to correlate well with the binding energy, but the total adsorption does not, indicating that the adsorption is driven by factors other than binding energetics. Lithium ion transport in TMA2-Pc was also investigated for suitability as an electrolyte medium for use in lithium ion battery systems.

Metal membranes are useful for hydrogen separation from mixed gas streams. They can exhibit perfect selectivity for hydrogen. However, in order to be commercially viable, in addition to providing high hydrogen fluxes, they must also be resistant to poisoning, possess long operating lifetimes and be cost effective. Many types of metal membranes such as pure metals, disordered alloys and amorphous metals have been studied for this application. In this work, we aim to identify intermetallic stoichiometric compounds of two or more metals that could be used as potential membrane materials for hydrogen separation. In the past, first principle calculations combined with Monte Carlo methods have been developed that can accurately predict H₂ fluxes through metal membranes at different hydrogen pressures and temperatures. Although these models are accurate, they are computationally intensive. In this work, we use these methods and develop screening criteria based on calculated properties that enable us to perform detailed calculations on a diminishing set of materials and rapidly identify the favorable candidates for hydrogen separation. We screened 1059 intermetallics at this high level of theory, which is the largest set of materials studied for this application. We divided the intermetallics into Pd-based and non-Pd based materials using additional screening algorithms to reduce the number of calculations required to identify potential candidate materials. 8 intermetallics were identified that had permeabilities that was comparable or higher to that of pure Pd. MgZn₂ and MnTi were found to have the highest H permeabilities among all the intermetallics studied. In addition to ground state structures, metastable structures were also found to be stabilized in the presence of hydrogen. Our work demonstrates the ability of these computational methods to identify potential novel materials for specific applications from large sets of materials that would not be possible experimentally. In the models for hydrogen permeability developed above, H-induced metal lattice rearrangements were not considered. Experimental evidence suggests that hydrogen heat treated (HHT) Pd-Au alloys undergo lattice rearrangement that results in an ordered structure which has a higher solubility than the non-HHT alloys. Using a combination of cluster expansion methods developed for predicting hydrogen permeability of disordered alloys and Monte Carlo methods, we predicted the extent of H induced lattice rearrangement in Pd₉₆Au₄ and Pd₈₅Au₁₅ alloys. We also predicted the solubility, diffusivity and permeability of these rearranged phases and found that their H permeability is higher than the non-rearranged phases. Our models capture the H-induced lattice rearrangement and provide useful insight of the conditions where this phenomenon is significant. Using the tools developed in this work, similar alloys that have a tendency to undergo lattice rearrangement that results in enhanced H permeability can be identified.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (p. 169-185).

Thesis (M.S.)--University of Michigan, 1968.

Thesis--University of Illinois at Urbana-Champaign, 1977. / Includes bibliographical references (p. 126-128).

Thesis (M.S.)--University of Michigan, 1968.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1934. / Typescript. Includes bibliographical references.

No description available.

Hydrogen embrittlement (HE), which results in an unpredictable failure of metals, has been a major limitation in the design of critical components for a wide range of engineering applications, given the near-ubiquitous presence of hydrogen in their service environments. However, the exact mechanisms that underpin HE failure remain poorly understood. It is known that hydrogen, when free to diffuse in these materials, can tend to concentrate at a crack tip front. In turn, this facilitates crack propagation. Hence one of the proposed strategies for mitigating HE is to limit the content of freely diffusing hydrogen within the metal atomic lattice via the introduction of microstructural hydrogen traps. Further, it is empirically known that the introduction of finely-dispersed distribution of nano-sized carbide hydrogen traps in ferritic steel matrix can improve resilience to HE. This resilience has been attributed to the effective hydrogen trapping of the carbides. However, conclusive atomic-scale experimental evidence is still lacking as to the manner by which these features can impede the movement of the hydrogen. This lack of insight limits the further progress for the optimisation of the microstructural design of this type of HE-resistant steel. In order to further understand the hydrogen trapping phenomenon of the nano-sized carbide in steel, an appropriate characterisation method is required. Atom probe tomography (APT) has been known for its powerful combination of high 3D spatial and chemical resolution for the analysis of very fine precipitates. Furthermore, previous studies have shown that the application of isotopic hydrogen (²H) loading techniques, combined with APT, facilitates the hydrogen signal associated to fine carbides to be unambiguously identified. However, the considerable experimental requirements as utilised by these previous studies, particularly the instrumental capability necessary for retention of the trapped hydrogen in the needle-shaped APT specimen, limits the study being reproduced or extended. In this APT study, a model ferritic steel with finely dispersed V-Mo-Nb carbides of 10-20 nm is investigated. Initially, existing specialised instrumentation formed the basis of a cryogenic specimen chain under vacuum, so as to retain loaded hydrogen after an electrolytic charging treatment for APT analysis. This work confirms the importance of cryogenic treatment for the retention of trapped hydrogen in APT specimen. The quality of the obtained experimental data allows a quantitative analysis on the hydrogen trapping mechanism. Thus, it is conclusively determined that interior of the carbides studied in this steel acts as the hydrogen trapping site as opposed to the carbide/matrix interface as commonly expected. This result supports the theoretical investigations proposing that the hydrogen trapping within the carbide interior is enabled by a network of carbon vacancies. Based on the established importance of the specimen cold chain in these APT experiments, this work then successfully develops a simplified approach to cryo-transfer which requires no instrumental modification. In this approach there is no requirement for the charged specimen to be transferred under vacuum conditions. The issue of environmental-induced ice contamination on the cryogenic sample surface in air transfer is resolved by its sublimation in APT vacuum chamber. Furthermore, the temperature of the transferred sample is able to be determined independently by both monitoring changes to vacuum pressure in the buffer chamber and also the thermal response of the APT sample stage in the analysis chamber. This simplified approach has the potential to open up a range of hydrogen trapping studies to any commercial atom probe instrument. Finally, as an example of the use of this simplified cryo-transfer technique, targeted studies for determining the source of hydrogen adsorption during electropolishing and electrolytic loading process are demonstrated. This research provides a critical verification of hydrogen trapping mechanism of fine carbides as well as an achievable experimental protocol for the observation of the trapping of individual hydrogen atoms in alloy microstructures. The methods developed here have the potential to underpin a wide range of possible experiments which address the HE problem, particularly for the design of new mitigation strategies to prevent this critical issue.

The study of hydrogen and the understanding of its response to extended pressure and temperatures is of great importance due to its significant universal abundance. Hydrogen is currently not well understood in these extended regimes due to it being inherently difficult to work with experimentally as well as having a poor response to a wide range of diagnostics. Consequently, there have been long standing predicted phenomena which still remain experimentally elusive: (1) melting driven by large zero point oscillations [Brovman 72] and (2) adopting a purely atomic state at higher pressures [Wigner 35]. Coupling high-pressure, high-temperature techniques with in-situ optical diagnostics, the stability of the solid phases of hydrogen were evaluated over an extended pressure-temperature regime. The first ever H2 solid-solid transitions above 300 K are reported and the evolution of the I-IV phase line after the III-IV-I triple point is constrained. A transition which could be attributed to melting is observed at 480 K and 225 GPa, the lowest known melting temperature for any material under these conditions. A new triple point between phase I-IV-Liquid is identified, the third known triple point in the phase diagram and the first on the melting curve. The possible continuations of the melting line are discussed, ultimately revising the melting transition at 300 K and at 0 K to much higher pressures than previously thought [Bonev 04]. The contributing work also marks a new high pressure achievement, obtaining some of the highest ever recorded static pressures in the laboratory. Hydrogen and its heavier isotopes hydrogen deuteride and deuterium were compressed to pressures of 384 GPa, 388 GPa and 380 GPa respectively. These experimental data are indicative that above 325 GPa H2 and HD adopt a new solid phase, phase V. Analysis of the spectra over the IV-V transition is suggestive that under compression the molecular bonding in the G-layers of the Pc structure lengthen and symmetrise, evolving into the Ibam structure. It is speculated that this phase could be a precursor to the elusive, purely atomic I41/amd structure predicted to be stable at higher pressures (>400 GPa) [McMahon 11, Azadi 14].