Master of Science / Department of Chemical Engineering / James H. Edgar / Silicon oxidation has been the cornerstone of the semiconductor industry for many years, so understanding and being able to predict the oxidation process is paramount. The most popular model to date is the Deal-Grove model for the thermal oxidation of planar silicon surfaces. The Deal-Grove model owes its popularity to the overall simplicity in which it was derived and the accuracy in which it predicts the oxidation of planar silicon geometries. Due to this popularity and accuracy it is desirable to extend the Deal-Grove model beyond flat surfaces to other geometries such as cylinders and spheres. Extending the Deal-Grove model to these types of geometries would allow the prediction of the oxidation of silicon nano-wires and silicon nanocrystals. Being able to predict the oxidation is attractive due to the recent progress of integration of silicon nano-wires and silicon nano-crystals into microelectronic devices. Prediction of the oxidation of silicon cylinders (nano-wires) and spheres (nano-crystals) by simply utilizing the established planar Deal-Grovel model results in highly exaggerated oxide thicknesses compared with empirical data. This exaggeration for small silicon cylinders and spheres is due to the effects of the reduction in the available surface area for oxidation along with the stress induced due to the volumetric expansion and viscous flow of the oxide on non-planar surfaces. These stress effects retard the oxidation rate in non-planar silicon geometries with respect to flat surfaces. This reduction in the oxidation rate reduction is caused by the normal compressive stress which is normal to the SiO[subscript]2/Si interface due to the volumetric expansion during oxidation. This compressive stress reduces the reaction rate constant at the SiO[subscript]2/Si interface and thus retards the overall oxidation rate for silicon cylinders and spheres with respect to planar silicon. The focus of this paper will be to contrast cylindrical and spherical versions of the Deal-Grove model to the well established planar version. Surface area and stress effects will also be explored as they help explain the reduction in the oxidation rate for non-planar silicon geometries.

Master of Science / Department of Chemical Engineering / Larry A. Glasgow / The military is interested in stopping suspicious vehicles at checkpoints or security positions while minimizing noncombatant fatalities. Preliminary work has shown that decreasing the oxygen concentration in proximity to the automobile air intake system and blocking the air flow through an automotive induction system provides the greatest probability of success for the broadest possible array of internal combustion engines. A non-lethal foam deployment system was developed that satisfies the military’s needs to stop suspicious vehicles. The foam is discharged from a pressurized tank and engulfs the air intake system of the target vehicle. The foam is drawn into the air intake and the protein additive contained in the foam would occlude pores in the air filter medium. Once the air filter was blocked, the vehicle would become immobilized so that security personnel can secure the vehicle. The work carried out in this project consisted of development and refinement of surfactant solution composition, improvement in the rate of absorption of carbon dioxide for increased foam volume, and characterization of discharge for optimum foam volume. In addition, a half-scale model apparatus was developed to test the foam’s ability to be ingested in an automotive intake system. These experiments demonstrated that the foam deployment system would stop an automobile within six seconds.

Heat transfer through the sidewall accounts for a significant proportion of the energy loss from an aluminium reduction cell. At the same time, the ledge formed on the sidewall has important consequences with regards to the cell service life and the dynamic heat balance during various disturbances associated with the smelting operation such as alumina feeding, anode changing, metal tapping and anode effect. Several studies have been carried out to investigate the ledge heat transfer. However, the reported heat transfer coefficients in the literature not only vary over a wide range of values but provide insufficient information on the ledge heat transfer. A heat transfer probe and measurement techniques were developed for studying the ledge heat transfer in a full-scale 3-D air-water model. Quantitative measurements were conducted to determine the bath/ledge heat transfer characteristics at various positions, and under different operating conditions such as anode-ledge distance, current density and bath depth. Variation of the heat transfer were also examined as a function of the anode bottom inclination, the anode slot width and the position on the side ledge relative to the anode slot. The results illustrate that the ledge profile in an operating cell will take on a different shape in compliance with the heat transfer variation. A similitude analysis was carried out to interpret the measured results in a meaningful manner for use in a reduction cell. As a result, the heat transfer coefficient in industrial cells under various operating parameters, and at different positions on the side ledge, can be estimated using the empirical correlations presented. Gas bubble behaviour and bubble impingement on the side ledge were observed in the water model. Observations made on the 2-D and 3-D water models indicate that anode gas evolution in the 3-D model cell will reflect more closely the flow pattern in actual cells and hence provide more reliable quantitative results. A simple 2-D thermal model for the prediction of ledge thickness and profile as a moving boundary was developed and solved simply and efficiently with a commercial spreadsheet software using the finite difference method. The ledge profile was predicted using the ledge heat transfer coefficients measured extensively from the full-scale 3-D physical model. The results show that the ledge shape is highly sensitive to the positional variation of the heat transfer coefficient. It is also shown that the ledge heat transfer coefficients obtained from industrial measurements assuming 1-D heat flow are much lower than the actual values in a Hall-Heroult cell. A transient thermal model derived by considering the Stefan problem$/sp[*]$ for the sidewall/ledge region was developed. A fixed-grid and deforming-grid spacing were respectively superimposed on the sidewall and the ledge region in order to track the moving front of the phase change zone. Various aspects of the process dynamics with respect to the variation of ledge thickness and sidewall shell temperature were presented. The model considered dynamic heat loss through the sidewall which results in a closer approximation to the real situation. ftn$/sp[*]$N.B.: In the strict sense the problem of the ledge is not a classical Stefan problem. The classical Stefan problem involves conduction on both sides of the interface. The ledge problem involves conduction on the side and convection on the other. / Subscription resource available via Digital Dissertations only.

Heat transfer through the sidewall accounts for a significant proportion of the energy loss from an aluminium reduction cell. At the same time, the ledge formed on the sidewall has important consequences with regards to the cell service life and the dynamic heat balance during various disturbances associated with the smelting operation such as alumina feeding, anode changing, metal tapping and anode effect. Several studies have been carried out to investigate the ledge heat transfer. However, the reported heat transfer coefficients in the literature not only vary over a wide range of values but provide insufficient information on the ledge heat transfer. A heat transfer probe and measurement techniques were developed for studying the ledge heat transfer in a full-scale 3-D air-water model. Quantitative measurements were conducted to determine the bath/ledge heat transfer characteristics at various positions, and under different operating conditions such as anode-ledge distance, current density and bath depth. Variation of the heat transfer were also examined as a function of the anode bottom inclination, the anode slot width and the position on the side ledge relative to the anode slot. The results illustrate that the ledge profile in an operating cell will take on a different shape in compliance with the heat transfer variation. A similitude analysis was carried out to interpret the measured results in a meaningful manner for use in a reduction cell. As a result, the heat transfer coefficient in industrial cells under various operating parameters, and at different positions on the side ledge, can be estimated using the empirical correlations presented. Gas bubble behaviour and bubble impingement on the side ledge were observed in the water model. Observations made on the 2-D and 3-D water models indicate that anode gas evolution in the 3-D model cell will reflect more closely the flow pattern in actual cells and hence provide more reliable quantitative results. A simple 2-D thermal model for the prediction of ledge thickness and profile as a moving boundary was developed and solved simply and efficiently with a commercial spreadsheet software using the finite difference method. The ledge profile was predicted using the ledge heat transfer coefficients measured extensively from the full-scale 3-D physical model. The results show that the ledge shape is highly sensitive to the positional variation of the heat transfer coefficient. It is also shown that the ledge heat transfer coefficients obtained from industrial measurements assuming 1-D heat flow are much lower than the actual values in a Hall-Heroult cell. A transient thermal model derived by considering the Stefan problem$/sp[*]$ for the sidewall/ledge region was developed. A fixed-grid and deforming-grid spacing were respectively superimposed on the sidewall and the ledge region in order to track the moving front of the phase change zone. Various aspects of the process dynamics with respect to the variation of ledge thickness and sidewall shell temperature were presented. The model considered dynamic heat loss through the sidewall which results in a closer approximation to the real situation. ftn$/sp[*]$N.B.: In the strict sense the problem of the ledge is not a classical Stefan problem. The classical Stefan problem involves conduction on both sides of the interface. The ledge problem involves conduction on the side and convection on the other. / Subscription resource available via Digital Dissertations only.

Heat transfer through the sidewall accounts for a significant proportion of the energy loss from an aluminium reduction cell. At the same time, the ledge formed on the sidewall has important consequences with regards to the cell service life and the dynamic heat balance during various disturbances associated with the smelting operation such as alumina feeding, anode changing, metal tapping and anode effect. Several studies have been carried out to investigate the ledge heat transfer. However, the reported heat transfer coefficients in the literature not only vary over a wide range of values but provide insufficient information on the ledge heat transfer. A heat transfer probe and measurement techniques were developed for studying the ledge heat transfer in a full-scale 3-D air-water model. Quantitative measurements were conducted to determine the bath/ledge heat transfer characteristics at various positions, and under different operating conditions such as anode-ledge distance, current density and bath depth. Variation of the heat transfer were also examined as a function of the anode bottom inclination, the anode slot width and the position on the side ledge relative to the anode slot. The results illustrate that the ledge profile in an operating cell will take on a different shape in compliance with the heat transfer variation. A similitude analysis was carried out to interpret the measured results in a meaningful manner for use in a reduction cell. As a result, the heat transfer coefficient in industrial cells under various operating parameters, and at different positions on the side ledge, can be estimated using the empirical correlations presented. Gas bubble behaviour and bubble impingement on the side ledge were observed in the water model. Observations made on the 2-D and 3-D water models indicate that anode gas evolution in the 3-D model cell will reflect more closely the flow pattern in actual cells and hence provide more reliable quantitative results. A simple 2-D thermal model for the prediction of ledge thickness and profile as a moving boundary was developed and solved simply and efficiently with a commercial spreadsheet software using the finite difference method. The ledge profile was predicted using the ledge heat transfer coefficients measured extensively from the full-scale 3-D physical model. The results show that the ledge shape is highly sensitive to the positional variation of the heat transfer coefficient. It is also shown that the ledge heat transfer coefficients obtained from industrial measurements assuming 1-D heat flow are much lower than the actual values in a Hall-Heroult cell. A transient thermal model derived by considering the Stefan problem$/sp[*]$ for the sidewall/ledge region was developed. A fixed-grid and deforming-grid spacing were respectively superimposed on the sidewall and the ledge region in order to track the moving front of the phase change zone. Various aspects of the process dynamics with respect to the variation of ledge thickness and sidewall shell temperature were presented. The model considered dynamic heat loss through the sidewall which results in a closer approximation to the real situation. ftn$/sp[*]$N.B.: In the strict sense the problem of the ledge is not a classical Stefan problem. The classical Stefan problem involves conduction on both sides of the interface. The ledge problem involves conduction on the side and convection on the other. / Subscription resource available via Digital Dissertations only.

Heat transfer through the sidewall accounts for a significant proportion of the energy loss from an aluminium reduction cell. At the same time, the ledge formed on the sidewall has important consequences with regards to the cell service life and the dynamic heat balance during various disturbances associated with the smelting operation such as alumina feeding, anode changing, metal tapping and anode effect. Several studies have been carried out to investigate the ledge heat transfer. However, the reported heat transfer coefficients in the literature not only vary over a wide range of values but provide insufficient information on the ledge heat transfer. A heat transfer probe and measurement techniques were developed for studying the ledge heat transfer in a full-scale 3-D air-water model. Quantitative measurements were conducted to determine the bath/ledge heat transfer characteristics at various positions, and under different operating conditions such as anode-ledge distance, current density and bath depth. Variation of the heat transfer were also examined as a function of the anode bottom inclination, the anode slot width and the position on the side ledge relative to the anode slot. The results illustrate that the ledge profile in an operating cell will take on a different shape in compliance with the heat transfer variation. A similitude analysis was carried out to interpret the measured results in a meaningful manner for use in a reduction cell. As a result, the heat transfer coefficient in industrial cells under various operating parameters, and at different positions on the side ledge, can be estimated using the empirical correlations presented. Gas bubble behaviour and bubble impingement on the side ledge were observed in the water model. Observations made on the 2-D and 3-D water models indicate that anode gas evolution in the 3-D model cell will reflect more closely the flow pattern in actual cells and hence provide more reliable quantitative results. A simple 2-D thermal model for the prediction of ledge thickness and profile as a moving boundary was developed and solved simply and efficiently with a commercial spreadsheet software using the finite difference method. The ledge profile was predicted using the ledge heat transfer coefficients measured extensively from the full-scale 3-D physical model. The results show that the ledge shape is highly sensitive to the positional variation of the heat transfer coefficient. It is also shown that the ledge heat transfer coefficients obtained from industrial measurements assuming 1-D heat flow are much lower than the actual values in a Hall-Heroult cell. A transient thermal model derived by considering the Stefan problem$/sp[*]$ for the sidewall/ledge region was developed. A fixed-grid and deforming-grid spacing were respectively superimposed on the sidewall and the ledge region in order to track the moving front of the phase change zone. Various aspects of the process dynamics with respect to the variation of ledge thickness and sidewall shell temperature were presented. The model considered dynamic heat loss through the sidewall which results in a closer approximation to the real situation. ftn$/sp[*]$N.B.: In the strict sense the problem of the ledge is not a classical Stefan problem. The classical Stefan problem involves conduction on both sides of the interface. The ledge problem involves conduction on the side and convection on the other. / Subscription resource available via Digital Dissertations only.

Heat transfer through the sidewall accounts for a significant proportion of the energy loss from an aluminium reduction cell. At the same time, the ledge formed on the sidewall has important consequences with regards to the cell service life and the dynamic heat balance during various disturbances associated with the smelting operation such as alumina feeding, anode changing, metal tapping and anode effect. Several studies have been carried out to investigate the ledge heat transfer. However, the reported heat transfer coefficients in the literature not only vary over a wide range of values but provide insufficient information on the ledge heat transfer. A heat transfer probe and measurement techniques were developed for studying the ledge heat transfer in a full-scale 3-D air-water model. Quantitative measurements were conducted to determine the bath/ledge heat transfer characteristics at various positions, and under different operating conditions such as anode-ledge distance, current density and bath depth. Variation of the heat transfer were also examined as a function of the anode bottom inclination, the anode slot width and the position on the side ledge relative to the anode slot. The results illustrate that the ledge profile in an operating cell will take on a different shape in compliance with the heat transfer variation. A similitude analysis was carried out to interpret the measured results in a meaningful manner for use in a reduction cell. As a result, the heat transfer coefficient in industrial cells under various operating parameters, and at different positions on the side ledge, can be estimated using the empirical correlations presented. Gas bubble behaviour and bubble impingement on the side ledge were observed in the water model. Observations made on the 2-D and 3-D water models indicate that anode gas evolution in the 3-D model cell will reflect more closely the flow pattern in actual cells and hence provide more reliable quantitative results. A simple 2-D thermal model for the prediction of ledge thickness and profile as a moving boundary was developed and solved simply and efficiently with a commercial spreadsheet software using the finite difference method. The ledge profile was predicted using the ledge heat transfer coefficients measured extensively from the full-scale 3-D physical model. The results show that the ledge shape is highly sensitive to the positional variation of the heat transfer coefficient. It is also shown that the ledge heat transfer coefficients obtained from industrial measurements assuming 1-D heat flow are much lower than the actual values in a Hall-Heroult cell. A transient thermal model derived by considering the Stefan problem$/sp[*]$ for the sidewall/ledge region was developed. A fixed-grid and deforming-grid spacing were respectively superimposed on the sidewall and the ledge region in order to track the moving front of the phase change zone. Various aspects of the process dynamics with respect to the variation of ledge thickness and sidewall shell temperature were presented. The model considered dynamic heat loss through the sidewall which results in a closer approximation to the real situation. ftn$/sp[*]$N.B.: In the strict sense the problem of the ledge is not a classical Stefan problem. The classical Stefan problem involves conduction on both sides of the interface. The ledge problem involves conduction on the side and convection on the other. / Subscription resource available via Digital Dissertations only.

Doctor of Philosophy / Department of Biological & Agricultural Engineering / Donghai Wang, Scott Bean / The performance of soybean hulls and forage sorghum as feed stocks for ethanol production was studied. The main goal of this research was to increase fermentable sugars' yield through high-efficiency pretreatment technology. Soybean hulls are a potential feedstock for production of bio-ethanol due to their high carbohydrate content ([approximately equals]50%) of nearly 37% cellulose. Soybean hulls could be the ideal feedstock for fuel ethanol production, because they are abundant and require no special harvesting and additional transportation costs as they are already in the plant. Dilute acid and modified steam-explosion were used as pretreatment technologies to increase fermentable sugars yields. Effects of reaction time, temperature, acid concentration and type of acid on hydrolysis of hemicellulose in soybean hulls and total sugar yields were studied. Optimum pretreatment parameters and enzymatic hydrolysis conditions for converting soybean hulls into fermentable sugars were identified. The combination of acid (H[subscript]2SO[subscript]4, 2% w/v) and steam (140 °C, 30 min) efficiently solubilized the hemicellulose, giving a pentose yield of 96%. Sorghum is a tropical grass grown primarily in semiarid and dry parts of the world, especially in areas too dry for corn. The production of sorghum results in about 30 million tons of byproducts mainly composed of cellulose, hemicellulose, and lignin. Forage sorghum such as brown midrib (BMR) sorghum for ethanol production has generated much interest since this trait is characterized genetically by lower lignin concentrations in the plant compared with conventional types. Three varieties of forage sorghum and one variety of regular sorghum were characterized and evaluated as feedstock for fermentable sugar production. Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and X-Ray diffraction were used to determine changes in structure and chemical composition of forage sorghum before and after pretreatment and enzymatic hydrolysis process. Up to 72% of hexose yield and 94% of pentose yield were obtained using "modified" steam explosion with 2% sulfuric acid at 140°C for 30 min and enzymatic hydrolysis with cellulase (15 FPU/g cellulose) and [Beta]-glucosidase (50 CBU/g cellulose).

Doctor of Philosophy / Department of Chemical Engineering / Jennifer L. Anthony / Zeolites and zeolite-like materials have well-ordered structures and pores creating varying capacities for molecules based upon size, functional groups, polarity, and intermolecular forces making the materials useful for molecular sensing as well for molecules that are considered hazardous at very low concentrations with reproducible results because of these properties. This study will identify and characterize applications for zeolite and zeolite-like materials in gas and liquid phases based upon the dominating physical and chemical properties of the materials. The properties of interest include liquid phase ion exchange capacities, selectivities, gas/vapor phase adsorption capacity, and initial adsorption uptake rate. Zincosilicates have similar framework structures to aluminosilicate zeolites; however, they have distinct advantages over traditional zeolites. Zincosilicates typically have a higher ion density, lack “cages” in their structure which leads to all the cations being accessible for ion exchange, and have the ability to form three-membered rings which lead to large void spaces in their structure. These features lead to high capture capacities for divalent heavy metal mercury ions. In this work, the potential to use zincosilicates as ion exchangers such as VPI-7, VPI-9 and VPI-10 is presented. Results have shown that zincosilicates have capture capacities greater than traditional zeolites, even greater than those that have been synthesized with functional groups intended to increase metal sorption capacities. The selectivity coefficients in a binary ion exchange system were successfully modeled using the Gibbs-Donnan selectivity model. The selectivities for the zincosilicates were Pb>Na>Hg>K>Ca. Zeolites are also able to adsorb chemical species and therefore can be used as the recognition element in sensing devices. The sorption capacity of 2-chloroethyl ethyl sulfide, dimethyl methanephosphonate, ethanol, and n-butanethiol were examined with zeolites 13X, 4A, MCM-41, VPI-7, VPI-9, and ZSM-5. The zeolites selected provided very different framework composition, countercation, and surface area features for determining the most significant properties in adsorption. Zeolite 13X had the highest equilibrium and initial uptake rate for most compounds tested, whereas the low surface area zincosilicates, VPI-7 and VPI-9, had the lowest capacity. Based on these results, a piezoelectric device with an array of zeolites can be successfully employed as a sensor.

Master of Science / Department of Chemical Engineering / Larry E. Erickson / The reaction chemistry of uranium metal has been well documented for use in the development of nuclear fuels. The oxidation of uranium from the thermal stress of nearby combustion is different than that of a reactor environment due to the selectivity of the various competing reactions. This work extracts available information in literature and various experiments over the last 60 years to provide a critical look at the response of uranium metal to thermal stress. The oxide fume formed and the equilibrium phase shifts during the dispersal of the airborne particulate are of principal interest when determining potential consequences to the health and safety of the workers, members of the public, and the environment. The transport phenomena and reaction kinetics of the oxide fume are also discussed at various distances from the source material. Uranium is a versatile element that can form numerous compounds, of which the oxides are the forms that are most readily generated under thermal stress and also pose the largest health risk to human beings, primarily through inhalation. A general summary of uranium and the dry compounds (oxides and carbides) is provided discussing the different structures of each state. The reaction kinetics and selectivity as the oxidation progresses is discussed for typical uranium metal forms at temperatures above and below the ignition point. Characteristics of potential fires are qualified for determining thermal stress. The creation of the oxide fume is outlined followed by dispersal characteristics of the aerosol. These molecular processes are related to the release fractions of uranium under fire scenarios which are compared with available experimental data from the regulatory handbooks. A critical look at the conclusions of the handbook with recommendations for revising the existing guidelines and additional testing are made in the interest of ensuring that derived controls are appropriate to reduce the risk of accidents involving the oxidation of uranium metal.