Call number: LD2668 .T4 1965 G47 / Master of Science

Three of the most important questions concerning hydrogen storage in metals are how much hydrogen can be absorbed, how fast it can be absorbed (or released) and finally how strongly the hydrogen is bonded. In transition metals hydrogen occupies interstitial sites and the absorption as well as desorption of hydrogen can be fast. The enthalpy of the hydride formation is determined by the electronic structure of the absorbing material, which determines the amount of energy released in the hydrogen uptake and the energy needed to release the hydrogen. This thesis concerns the possibility of tuning hydrogen uptake by changing the extension of the absorbing material and the boundary conditions of extremely thin layers. When working with extremely thin layers, it is possible to alter the strain state of the absorbing material, which is used to influence the site occupancy of hydrogen isotopes. Vanadium is chosen as a model system for these studies. V can be grown in the form of thin films as well as superlattices using MgO as a substrate. Special emphasis are on Fe/V(001) and Cr/V(001) superlattices as these can be grown as high quality single crystals on a routine basis. The use of high quality samples ensured well-defined conditions for all the measurements. In these experiments the hydrogen concentration is determined by the light transmittance of the thin films.  By changing the temperature and the pressure of the hydrogen gas, it is possible to determine the thermodynamic properties of hydrogen in the samples, from the obtained concentrations.  Measurements of the electrical resistivity is used to increase the accuracy in the measurements at low concentrations as well as to provide information on ordering at intermediate and high hydrogen concentrations. The thermodynamic properties and the electrical resistivity of VH are strongly affected by the choice of boundary layers. For example, when hydrogen is absorbed in V embedded by Fe, Cr or Mo in the form of superlattices, both the thermodynamic properties and the changes in the resistivity are strongly influenced. The critical temperature and H-H interactions of hydrogen in thin V(001) layers are found to increase with thickness of the thin films and superlattices. The observed finite size effects resemble same scaling with the thickness of the layers as does the magnetic ordering temperature. The results were validated by investigations of isotope effects in the obtained thermodynamic properties. Close to negligible effects are obtained when replacing hydrogen by deuterium, with respect to the thermodynamic properties. These observations are rationalised by an octahedral occupancy in the strained layers, as compared to tetrahedral occupancy in unstrained bulk. The octahedral site occupancy is found to strongly alter the diffusion coefficient of hydrogen in thin V layers.

The extent of hydrogen bonding in ethanethiol is determined using a correlation between the chemical shift of the sulphydryl proton and the stretching frequencies of the component bands of the vS-H infrared band The component bands having stretching frequencies at 2585 cm-1 and 2570 cm-1 for non hydrogen bonded and mono-hydrogen bonded thiol groups respectively. It is calculated that the pure liquid at 22°C. contains ca. 49% free SH bonds. A dimerisation constant of 0.038 dm3 mol-1 is estimated at 22°C. 2-Hydroxyethanethiol is used to investigate the strength of hydrogen bonding to the thiol group in aqueous solutions. The results of the IR and NIR studies are consistent with the formation of hydrogen bonds of S-H O type between thiol and water molecules. Salt and solvent effects upon the phosphate and thiophosphate groups of Sodium Dimethyphosphate (NaDMP) and Sodium Dimethylthiophosphate (NaDMSP) are investigated. Infrared spectra in the and v3P-O of DMP and DMSP suggest that the order of strength of binding of metal ion to phosphate/thiophosphate group is Na+ < Mg2+ < Ca2f. The results indicate that solvent-separated ion pairs dominate in aqueous solutions, whereas, mono- and bi-dentate contact ion pairs are favoured in DMSO and methanol solutions. The thiophosphate group is solvated by methanol and water, primarily at the oxygen site. No evidence was found to support hydrogen bond formation to the anionic sulphur site. Infrared spectra were also consistent with Mg2+ and Ca2+ interacting with the Oxygen atom, but not the Sulphur atom. DNA hydration is investigated using high field NMR spectrometry. Frozen aqueous DNA solutions were found to have a broad NMR signal due to hydration water. From this signal it is estimated that, at -12°C., the DNA samples are hydrated by ca. 25 water molecules per base pair of DNA.

No description available.

No description available.

No description available.

No description available.

No description available.

The hydrogen embrittlement of two HSLA steels was studied in conditions typical of the marine environment. Double cantilever beam specimens, heat treated to produce the microstructure in the heat affected zone of a weld, were tested in seawater containing sulphate reducing bacteria (SRB) over a range of cathodic protection (CP) potentials and the threshold stress intensities ([Threshold Stress Intensity]) were recorded. The hydrogen concentration absorbed by the steel ([Surface Hydrogen Concentration]) was measured and shown to be higher at more negative CP potentials and significantly increased when SRB were present. An inverse relationship was established between log [Threshold Stress Intensity] and [Surface Hydrogen Concentration]. It was concluded that crack propagation occurs by a single mechanism whether or not SRB are present. Three point bend specimens of both steels were machined from welded plate. Corrosion fatigue tests were carried out in seawater with and without SRB. The presence of active SRB caused increased crack growth rates. Sediment samples were collected from the River Mersey and the base of a North Sea platform. In addition, SRB were added as an inoculum to artificial seawater. SRB numbers were enumerated and their activities assessed by measuring the concentrations of sulphide generated. Hydrogen permeation tests were performed on steel held at a range of CP potentials and exposed to each environment. Measurements were also carried out in seawater containing chemically prepared sulphides. Hydrogen absorption was shown to be enhanced when SRB were present and to be related to the total sulphide (TS) concentration in the environment. High hydrogen concentrations were produced by chemically prepared sulphides and the nature and thickness of the sulphide film appeared to be important in determining the extent of hydrogen absorption. Chemically produced sulphide gave sustained levels of absorbed hydrogen, but those generated biogenically decayed rapidly unless the TS concentration was maintained in the solution.

No description available.