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Master of Science / Department of Chemical Engineering / John Schlup / This study investigated the specular reflectance properties of 6061-T6 aluminum alloy anodized in accordance with military specification MIL-A-8625 as a function of both etch process time and anodization process potential. Both process parameters affect the specular reflectance characteristics when measured using a 660 nm, collimated diode laser source. The etch process time, when varied between 0.5 to 20 minutes, resulted in a decrease in specular reflectivity with increasing time. The anodization process potential was varied between 10 and 21 volts, with a 15 volt condition producing samples with the greatest specular reflectivity. Between the two parameters, the etch time had the greater effect. Additionally, the dependence of the incident beam angle on specular reflectivity was shown not to have a significant effect when compared to the etch process time and process potential.

A system for the analysis of urine bioassay samples for the purpose of inversely investigating an unknown exposure to uranium has been developed. This technique involves the use of a thin flow electrochemical cell in conjunction with an anodized glassy carbon electrode to selectively separate uranium atoms out of solution for later analysis on an inductively coupled plasma mass spectrometer. A series of uranium urinalysis bioassay sample results can be used to investigate the time frame and type of exposure. This analysis uses an exposure database and regression analysis to best fit urinalysis uranium excretion data to expected profiles using commercially available mathematics software. The least number of data points to determine an acceptable confidence interval is ten bioassay samples taken at least a week apart. The system was benchmarked using a random sampling of urinary excretion samples from a known case at the Y-12 plant in the 1960’s. The electrochemical system was characterized using U.S. Department of Energy synthetic urine quality assurance standards from an inter-laboratory exercise in 2012. The separation apparatus was able to consistently separate uranium from the synthetic urine solutions with a consistent recovery between ten and fifteen percent and up to fifty percent. The method is isotope independent and maintains the enrichment of any excreted material. This allows for the material to be compared to operational logbooks at facilities using multiple enrichments in the nuclear fuel cycle. This methodology is recommended for spot estimation in support of a traditional bioassay program.

This dissertation describes experimental studies of the structures and properties, and their correlations in ferromagnetic nanowires and nanotubes fabricated using porous templates. Ferromagnetic Ni and Fe nanowires with diameters 30 ~ 250 nm were electroplated into the pores of anodic aluminum oxide membranes. The effects of nanowire diameter on structural and magnetic properties were investigated. The microstructures of these nanowires were studied using X-ray diffraction and selected-area electron diffraction measurements. The magnetic properties of the nanowires were investigated using magnetic hysteresis measurements and magnetic force microscopy. Additionally, ferromagnetic Ni-P nanotubes were fabricated using an electroless chemical deposition method. Structure and composition analyses were conducted using X-ray diffraction and energy-dispersive spectroscopy. The magnetic properties of the nanotube arrays and the electronic properties of individual nanotubes were studied. Hysteresis measurements revealed that the 250-nm diameter Ni nanowires had a poor squareness in their hysteresis loops, indicating the existence of multi-domain states. In comparison, the squareness in the hysteresis loops of 60-nm and 30-nm Ni nanowires was much improved, suggesting the existence of single domain states in these smaller diameter nanowires. Magnetic force microscopy measurements confirmed the magnetic domain structures suggested by magnetic hysteresis measurements. Similar investigations of Fe nanowires with diameters of 250 nm and 60 nm found that they all have multidomain magnetic structures. This is expected based on their material properties and polycrystalline structures. Furthermore, magnetic structures of Y-branches and multi-wire clusters were also studied using magnetic force microscopy. The as-prepared Ni-P nanotubes had an amorphous structure. Following a heat treatment, however, a structural phase transformation from the amorphous phase to a crystalline phase was observed using X-ray diffraction measurements. The tetragonal crystalline phase of Ni3P and the face-centered-cubic phase of Ni were confirmed via simulations by the GSAS software. The high Ni3P content accounts for the semiconducting behavior and a low magnetic anisotropy observed in the Ni-P nanotubes.

No description available.

Electrochemical anodization is a facile technique to synthesize ordered oxide nanostructures. Though the number of materials exhibiting anodized nanostructures has increased considerably in the recent years, only nanoporous alumina and nanotubular titania have been investigated extensively for various applications. Anodized nanostructures, nanotubes and nanopores, of zirconia are also of considerable interest for applications such as templates, sensors and solid-oxide fuel cells. In spite of the potential applications of zirconia, these nanostructures have been barely studied. As most of these applications require elevated temperatures in excess of 400C, thermal stability becomes an important attribute. Even though zirconia (Tm=2715C) has as higher melting point than alumina(Tm = 2072C), literature reports and initial research showed that the thermal stability of anodized zirconia was limited to 500C-1 h compared to 1000C-4 h for alumina. The work carried out as a part of this research showed that halide ions used in the synthesis are the possible cause for the lower thermal stability. Chemical treatment of the zirconia membranes to neutralize the halide ions helped enhance the stability to 1000C-1 h, thus, improving their usability for most of the applications mentioned above. Most of the current reported work on aluminum, zirconium, and titanium is predominantly limited to anodization of foils which can only yield free-standing nanostructures. As synthesis of these nanostructures on a substrate would further facilitate their usage, supported anodized zirconia nanostructures were synthesized by anodizing sputtered zirconium films. This study showed that the anodized morphology depends strongly on the sputtered film microstructure, which changes in accordance with the Thornton’s zone diagrams. A general approach thus developed is expected to be applicable to anodization of all metallic films. Most applications involving zirconia also require stabilization against a tetragonal-monoclinic phase transformation by suitable alloying such as with yttria. Towards this end, routes to develop anodized yttria-stabilized zirconia nanostructures, which are nonexistent, were explored. The synthesis of yttria stabilized zirconia nanostructures with no detectable monoclinic phase was achieved. Yttrium alloying using a solution treatment was found to enhance stability of the supported nanostructures to 900C-16 h, which makes it possible to now evaluate these nanostructures, especially for micro-SOFC applications.

"Recently, nanomaterials have been vigorously studied for the development of biosensors. Among them, carbon nanotubes (CNTs) have stimulated enormous interest for constructing biosensors due to their unique physical and chemical properties such as high surface-to-volume ratio, high conductivity, high strength and chemical inertness. Our study is to develop a general design of biosensors based on vertically aligned CNT arrays. Glucose biosensor is selected as the model system to verify the design of biosensors. In the preliminary design, glucose oxidase (GOx) is attached to the walls of the porous alumina membrane by adsorption. Porous highly ordered anodized aluminum oxide (AAO) prepared by two-step anodization are used as templates. Deposited gold on both sides of template surfaces serve as a contact and prevent non-specific adhesion of GOx on the surface. In order to find out optimized thickness of gold coating, the oxidation and reduction (redox) reaction in [Fe(CN)6]3¨C /[Fe(CN)6]4¨C system is monitored by Cyclic Voltammetry (CV). Subsequently, enzymatic redox reaction in glucose solutions is also attempted by CV. We expect protein layers with GOx form a conductive network. However, no obvious enzymatic redox reaction is detected in the voltammogram. To take advantage of the attractive properties of CNTs, the design of enzyme electrodes is modified by attaching CNT onto the sidewalls of AAO template nanopores and then immobilizing GOx to the sidewalls and tips of CNTs. AAO templates provided vertical, parallel, well separated and evenly spacing nanochannels for CNT growth. Cobalt is used as a catalyst to fabricate CNTs. As a result, multi-walled carbon nanotubes (MWCNTs) are fabricated inside the AAO templates by catalytic chemical vapor deposition (CCVD). Characterization of AAO templates and cobalt electrochemical deposition are employed by scanning electron microscope (SEM), and energy dispersive X-ray spectrometry (EDS). Detailed structure and texture of CNTs are examined by transmission electron microscope (TEM). "

Multi-walled carbon nanotubes (MWCNTs) are a potential alternative to commonly used catalyst support structures in hydrotreating processes. Synthesis of MWCNTs with specific pore diameters can be achieved by chemical vapor deposition (CVD) of a carbon source onto an anodic aluminum oxide (AAO) template. AAO films consist of pore channels in a uniform hexagonal arrangement that run parallel to the surface of the film. These films are created by the passivation of an aluminum anode within an electrolysis cell consisting of certain weak acid electrolytes. Changing the concentration of the electrolyte (oxalic acid) and the electrical potential of the electrolysis cell altered the pore channel diameter of these AAO films. Controlling the pore diameter of these templates enabled the pore diameter of MWCNTs synthesized by CVD to be controlled as well. The produced MWCNTs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Raman spectroscopy, and N2 adsorption analysis. Anodizing conditions of 0.40 M oxalic acid concentration and 40.0 V maximum anodizing potential were found to produce AAO films that resulted in MWCNTs with optimum surface characteristics for a catalyst support application. CVD parameter values of 650°C reaction temperature and 8.00 mL/(min·g) C2H2-to-AAO ratio were found to produce the highest yield of MWCNT product.<p> The MWCNTs were synthesized for the purpose of supporting hydroprocessing catalysts, with several grades of NiMo/MWCNT sulfide catalysts being prepared to determine the optimum pore size. These catalysts were characterized by techniques of TEM, CO chemisorption, N2 adsorption, and H2 temperature programmed reduction (TPR). A MWCNT grade with 67 nm inner diameters (found from TEM analysis) was found to offer the best hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activities for the treatment of coker light gas oil (CLGO). After determining the most suitable pore diameter, the optimum catalyst metal loadings were found to be 2.5 wt.% for Ni and 19.5 wt.% for Mo. The optimum catalyst was found to offer HDS conversions of 90.5%, 84.4%, and 73.5% with HDN conversions of 75.9%, 65.8%, and 55.3% for temperatures of 370°C, 350°C, and 330°C, respectively. An equal mass loading of commercial NiMo/ã-Al2O3 catalyst offered HDS conversions of 91.2%, 77.9%, and 58.5% with HDN conversions of 71.4%, 53.2%, and 31.3% for temperatures of 370°C, 350°C, and 330°C, respectively.<p> A kinetic study was performed on the optimum NiMo/MWCNT catalyst to help predict its HDS and HDN activities while varying the parameters of temperature, liquid hourly space velocity (LHSV), pressure, and gas-to-oil flow rate ratio. Rate expressions were then developed to predict the behavior of both the HDS and HDN reactions. Power law models were best fit with reaction orders of 2.6 and 1.2, and activation energies of 161 kJ/mol and 82.3 kJ/mol, for the HDS and HDN reactions, respectively. Generalized Langmuir-Hinshelwood models were found to have reaction orders of 3.0 and 1.5, and activation energies of 155 kJ/mol and 42.3 kJ/mol, for the HDS and HDN reactions, respectively.

Multi-walled carbon nanotubes (MWCNTs) are a potential alternative to commonly used catalyst support structures in hydrotreating processes. Synthesis of MWCNTs with specific pore diameters can be achieved by chemical vapor deposition (CVD) of a carbon source onto an anodic aluminum oxide (AAO) template. AAO films consist of pore channels in a uniform hexagonal arrangement that run parallel to the surface of the film. These films are created by the passivation of an aluminum anode within an electrolysis cell consisting of certain weak acid electrolytes. Changing the concentration of the electrolyte (oxalic acid) and the electrical potential of the electrolysis cell altered the pore channel diameter of these AAO films. Controlling the pore diameter of these templates enabled the pore diameter of MWCNTs synthesized by CVD to be controlled as well. The produced MWCNTs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Raman spectroscopy, and N2 adsorption analysis. Anodizing conditions of 0.40 M oxalic acid concentration and 40.0 V maximum anodizing potential were found to produce AAO films that resulted in MWCNTs with optimum surface characteristics for a catalyst support application. CVD parameter values of 650°C reaction temperature and 8.00 mL/(min·g) C2H2-to-AAO ratio were found to produce the highest yield of MWCNT product.<p> The MWCNTs were synthesized for the purpose of supporting hydroprocessing catalysts, with several grades of NiMo/MWCNT sulfide catalysts being prepared to determine the optimum pore size. These catalysts were characterized by techniques of TEM, CO chemisorption, N2 adsorption, and H2 temperature programmed reduction (TPR). A MWCNT grade with 67 nm inner diameters (found from TEM analysis) was found to offer the best hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activities for the treatment of coker light gas oil (CLGO). After determining the most suitable pore diameter, the optimum catalyst metal loadings were found to be 2.5 wt.% for Ni and 19.5 wt.% for Mo. The optimum catalyst was found to offer HDS conversions of 90.5%, 84.4%, and 73.5% with HDN conversions of 75.9%, 65.8%, and 55.3% for temperatures of 370°C, 350°C, and 330°C, respectively. An equal mass loading of commercial NiMo/ã-Al2O3 catalyst offered HDS conversions of 91.2%, 77.9%, and 58.5% with HDN conversions of 71.4%, 53.2%, and 31.3% for temperatures of 370°C, 350°C, and 330°C, respectively.<p> A kinetic study was performed on the optimum NiMo/MWCNT catalyst to help predict its HDS and HDN activities while varying the parameters of temperature, liquid hourly space velocity (LHSV), pressure, and gas-to-oil flow rate ratio. Rate expressions were then developed to predict the behavior of both the HDS and HDN reactions. Power law models were best fit with reaction orders of 2.6 and 1.2, and activation energies of 161 kJ/mol and 82.3 kJ/mol, for the HDS and HDN reactions, respectively. Generalized Langmuir-Hinshelwood models were found to have reaction orders of 3.0 and 1.5, and activation energies of 155 kJ/mol and 42.3 kJ/mol, for the HDS and HDN reactions, respectively.

A process with aim to prepare an oxidically and thermal resistant layer was performed on the samples from clear aluminium (99,99+ %, VÚK čisté kovy, s. r. o.) and on the samples from clear titanium (99,95 % Goodfellow) with a layer from sputtered aluminium (99,99 %, VÚK čisté kovy, s. r. o.), An oxidic layer was prepared on the samples by anodization in the oxalic acid. The layer had fine, hexagonally organized pores with the diameter of 30 nm. During the following processing was the structure prepared for the electrochemical deposition of copper to the pores. The aim of the electrodeposition was preparation of copper nanowires deposited into the pores of the oxidic layer. The process was performed in the solution of copper sulfate and sulfuric acid in water. The controlling parameter of the deposition was voltage which had a very asymmetric period. The period had to be optimized for a successful preparation of the wires. The result of the whole process was structure with oxidic matrix whose most of the pores were filled with copper.