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Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Poro-viscoelastic materials are well modelled with Biot-Allard equations. This model needs a number of geometrical parameters in order to describe the macroscopic geometry of the material and elastic parameters in order to describe the elastic properties of the material skeleton. Several characterisation methods of viscoelastic parameters of porous materials are studied in this thesis. Firstly, quasistatic and resonant characterization methods are described and analyzed. Secondly, a new inverse dynamic characterization of the same modulus is developed. The latter involves a two layers metal-porous beam, which is excited at the center. The input mobility is measured. The set-up is simplified compared to previous methods. The parameters are obtained via an inversion procedure based on the minimisation of the cost function comparing the measured and calculated frequency response functions (FRF). The calculation is done with a general laminate model. A parametric study identifies the optimal beam dimensions for maximum sensitivity of the inversion model. The advantage of using a code which is not taking into account fluid-structure interactions is the low computation time. For most materials, the effect of this interaction on the elastic properties is negligible. Several materials are tested to demonstrate the performance of the method compared to the classical quasi-static approaches, and set its limitations and range of validity. Finally, conclusions about their utilisation are given.

published_or_final_version / Civil Engineering / Master / Master of Philosophy

Microporous titanosilicates and vanadosilicates were synthesised characterized and photoreactivity studies were carried out.  The titanosilicates synthesised were the titanosilicate pharmacosiderite and AM – 18 and the vanadosilicates were AM – 6, ETVS – 10, AM – 14 and VSH -13Na.  A variety of different techniques were used in the characterisation studies including different X-Ray methods, vibrational spectroscopy, electron microscopy, and solid state NMR spectroscopy.  The studies showed that the synthesised products were homogeneous and an insight into the structures of AM – 18 and AM – 14 was obtained. Raman spectroscopy was used to assess the levels of defects in large crystals of ETS – 10 and ETS – 4 by measuring the variation in the frequency of the Ti – O band and the width of this band.  A similar study was done on large crystals of AM – 6.  Raman spectroscopy showed that Ti – O stretching bands containing Ti(V) and Ti(IV) were present in AM – 18 structure.  The frequency of the vanadyl bands in AM – 14 indicated that it could contain vanadyl chains. Photoreactivity studies using EPR spectroscopy, on the potassium titanosilicate pharmacosiderite showed an O^- species, after UV irradiation in the presence of oxygen.  When the partial pressure was reduced a superoxide and the anomalous ozonide species were observed.  On changing the cation to a proton form, a superoxide anion radical was observed but no other oxygen radicals were observed. Attempted oxidation and reduction studies on VSH – 13Na were unsuccessful and HRTEM and nitrogen adsorption studies showed that the one-dimensional channels were blocked. Oxidation and reduction studies on AM – 14 indicated that the vanadium sites were easily accessible to gas phase.

The aim of this project was to investigate the different porous media flow regimes and to clarify the mechanisms of stream-subsurface exchange at the pore scale. The Ultrasonic Velocity Profiler (UVP) system was used to measure the velocity distribution when the porous media was housed in a closed conduit, i.e. no stream flow could develop. It was found that the time-averaged velocity profiles have a wavy variation due to the flow decelerating and accelerating in the widest and narrowest sections of the pore-space. The spatially averaged higher order moments of velocity showed that a transition of flow properties occurred twice. There is a clear distinction between low, medium and high Reynolds number tests. These relate to three (micro-scale) porous media flow regimes: (1) the unsteady laminar regime, (2) the transitional regime and (3) the turbulent regime. Experiments were then performed in a tilting laboratory flume, which housed the same porous media (i.e. nine layers of spheres). This time there was a turbulent free-surface flow (of depth H) above the porous layer, which acted like a rough permeable wall. A set of reference measurements were also taken at a flow depth of <i>H </i>= 0mm. Particle Image Velocimetry (PIV) was used to measure the velocity distribution of both the stream flow, and the perturbed subsurface flow. From the stream flow experiments a distinct band of high turbulence was found just above the porous media. It is caused by intense shearing just above the roughness elements and is enhanced to some extent, by stream-subsurface interaction. The stream flow velocity statistics resemble those of a plane mixing layer.

As societies depart from current economic models which are built around affordable and easily accessible fossil fuels to energy systems increasingly based on the use of renewable energies, the need grows for a wide-scale clean and sustainable energy vector. Hydrogen fulfils most of the needed equirements, but implementation and large scale penetration, especially for mobile applications, is precluded by technical issues. Among these, arguably the most complex is how to safely, economically and efficiently store hydrogen. Storage in a porous material offers some attractive features, which include fast kinetics, reversibility and moderate energy penalties. A new methodology to analyse hydrogen adsorption isotherms in microporous materials is presented in this thesis. The methodology is applied to hydrogen adsorption in different classes of high-surface area materials but could in principle be used for any supercritical fluid adsorbed onto a microporous material. To illustrate the application of the methodology, high-pressure hydrogen adsorption isotherms of four different materials were analysed, metal-organic frameworks MIL-101 and NOTT-101 and carbons AX-21 and TE7. The analysis extracts important information on the adsorptive capacities of the materials and compares them with conventional storage methods, which include compression, liquefaction and cryogenic compression. The methodology also aids in the calculation of the thermodynamics of adsorption, providing a more accurate calculation method than currently reported techniques, demonstrated with the calculation of the differential isosteric enthalpies for metal-organic framework NOTT-101. NMR and INS are used in a novel way at the same operating conditions of sorption experiments to validate the findings of the analysis. Both methods provide a qualitative validation for the analysis. Remarkably, the INS reveals that the adsorbed hydrogen in TE7 is in a solid-like state. GCMC simulations were also used to compare with the application and findings of the methodology, using silicalite-1 as a test material.

The objectives of the present work are to produce porous polymeric scaffolds with Poly (ƒÕ-Caprolactone), PCL, by electrospinning. The structure in the electrospun polymer has been characterized by scanning electron microscopy. The effects of process variables such as voltage, solution concentration and deposition distance on the structure have been studied. The physical phenomena associated with the electrospinning process have been highlighted through high speed digital photography. The feasibility of using additives to the solution to control the structure of the porous construct has been examined. The data indicate that a range of structural morphologies can be produced in the electrospun polymer. Solid and hollow sub-micron beads can be produced by electrospraying of dilute solutions. Beyond a critical solution concentration of about 4 wt% PCL, elongational flow stabilizes the fibrous structure and a web of interconnected sub-micron fibers may be obtained. The average fiber diameter increases with concentration. A combination of elongated beads and fibers, known as the bead-on-string morphology is also observed under many conditions. The fibrous structure is stabilized at high voltages. The fiber diameter in the electrospun polymer typically exhibits a bimodal distribution. The addition of DMF (N,N-dimethylformamide) to the solution increases the deposition rate significantly and leads to extensive splaying, thereby reducing the fiber diameter to about 150 nm. DSC data indicate that electrospinning may lower the degree of crystallinity in the polymer. The wide of range of structural characteristics that may be obtained in the electrospun polymer make it suitable for many biomedical applications including medical textiles, drug delivery, membrane separation, tissue engineering and organ regeneration.