Resonant Ultrasound Spectroscopy Studies Of Poroelasticity In Porous Ceramics And Elasticity Of Thermoelectric Snse

This dissertation primarily focuses on use of resonant ultrasound spectroscopic (RUS) measurements to investigate temperature- and pressure-dependent elastic properties of select materials: porous ceramics, which are used in a wide range of material applications, and thermoelectric tin selenide (SnSe), which is widely studied as an efficient thermoelectric material. RUS experiments were conducted on: ceramics used in LG fuel cells, alumina, zircona and titania, to explore their elastic behavior under the variation of hydrostatic pressure over the low- and high-pressure regimes (0.02 – 800 psi). All the porous ceramics exhibited a reversible material softening mechanism with increasing hydrostatic pressure. The comparison of material stiffening with increasing pressure observed from fully dense ceramics validates the poroelastic behavior of porous ceramics described by Biot’s theory of poroelasticity. The influence of saturated gas type and their physical properties on the above elasticity variation with hydrostatic pressure was analyzed qualitatively as well as quantitatively by using the helium, nitrogen, and argon gas saturation. The observed porous material stiffness with increasing temperature was explained by the partial sintering and microcrack healing mechanisms. Single crystalline SnSe has an orthorhombic Pnma phase that undergoes a displacive phase transition transforming into a Cmcm phase at ~810 K. Temperature dependence of elastic constants (C_ij) of SnSe were measured at elevated temperatures in the range of 295 – 773 K. The measured elastic constants were then used to explain the elastic anisotropic behavior, structural change, and the thermal transportation mechanisms of SnSe at higher temperatures. The occurrence of the phase transition at 803 10 K was analyzed by the temperature-dependent normal mode frequency trends. The validation of the measured elastic constants and derived elastic properties are discussed using the previously reported theoretical and experimental studies

Ultrasonic Study of Water Adsorbed in Nanoporous Glasses

Thermodynamic properties of fluids confined in nanopores differ from those observed in the bulk. To investigate the effect of nanoconfinement on water compressibility, we performed water sorption experiments on two nanoporous glass samples while concomitantly measuring the speed of longitudinal and shear ultrasonic waves in these samples. These measurements yield the longitudinal and shear moduli of the water laden nanoporous glass as a function of relative humidity that we utilized in the Gassmann theory to infer the bulk modulus of the confined water. This analysis shows that the bulk modulus (inverse of compressibility) of confined water is noticeably higher than that of the bulk water at the same temperature. Moreover, the modulus exhibits a linear dependence on the Laplace pressure. The results for water, which is a polar fluid, agree with previous experimental and numerical data reported for non-polar fluids. This similarity suggests that irrespective of intermolecular forces, confined fluids are stiffer than bulk fluids. Accounting for fluid stiffening in nanopores may be important for accurate interpretation of wave propagation measurements in fluid-filled nanoporous media, including in petrophysics, catalysis, and other applications, such as in porous materials characterization

Biological Conversion of Algefiber® to Carboxylic Acids for Chemical Upgrading to Ketones

Biomass is a renewable resource which can be used for energy production as a substitute for fossil fuels. Conversion of terrestrial lignocellulosic biomass in to ethanol is the widely known conventional process to produce liquid biofuel. However the conversion of marine macro algae to biofuel draws attention at present. Use of marine biomass sources have some advantages over terrestrial lignocellulosic biomass such as less competition for land and fresh water resources, no interference with food crops, little or no lignin content, and high growth rates. The conversion of biomass to carboxylic acids via mixed culture acidogenic digestion offers many advantages over conventional sterile fermentation process such as: no need for sterilization, no need of genetically modified organisms, low capital cost, and ability to produce longer chain carboxylic acids. The produced carboxylic acids can be chemically up graded in to value added chemicals or mixed alcohol biofuel. In this study a seaweed-derived biomass source was biologically converted into a mixture of carboxylic acids using a mixed culture of microorganisms. Algefiber® was the biomass used; it is a waste biomass from seaweed processing (FMC Biopolymer, Rockland, ME). It is an alkaline treated industrial waste which has higher ash content than conventional terrestrial lignocellulosic biomass sources. Despite its high ash content, acidogenic fermentation of Algefiber® carried out under conditions of inhibited methanogenesis produced carboxylic acids ranging from one to seven carbons (Formic acid to Heptanoic acid). Fermentations were carried out at two temperatures, 35°C and 55°C. Acetic acid was the prominent acid produced at both temperatures, though mesophilic temperature (35°C) gave higher carboxylic acid yield and a higher percentage of longer chain acids. A combination of Algefiber® and chicken manure gave the highest acid concentration of 18 g/L at 15 % solid concentration. Carboxylate salts of the fermentation-derived acids were thermally decomposed in to mixture ketones which had acetone, 3-pentanone, 2-hexanone, 3-heptanone, 2-heptanone, and 4-octanone as major products. These ketones can be hydrogenated to form the longer chain mixed alcohols which contain higher energy density than ethanol due to presence of longer chain alcohols such as propanol, butanol etc