The reactions of atomically clean, titanium film surfaces with oxygen, deuterium, and water have been investigated. Auger Electron Spectroscopy was utilized to monitor the formation 9f a surface oxide in the case of oxygen exposure, and to characterize the deuteride which formed upon deuterium absorption, and its subsequent oxidation. Quantification of surface oxide stoichiometries was facilitated by novel data acquisition and treatment schemes. The quartz crystal microbalance was used to measure the mass of adsorbed oxygen or deuterium with submonolayer sensitivity. Electron energy loss spectroscopy was sensitive to the presence of Ti⁺³ in the surface oxide. The initial oxidation of the titanium surface was characterized by the dissociative adsorption of three mono1ayers of oxygen atoms at a constant rate. The oxide formed during this reaction stage was a Ti₂0₃/Ti0₂ mixture with a total thickness of 13 A. The rate of oxygen adsorption then decreased such that oxide growth was logarithmic with time. When the oxide had attained a total thickness of 20 A, the initial suboxide was converted to Ti0₂, and subsequent oxide formed was purely Ti0₂. Oxide growth occurred by oxygen anion migration under the influence of an electrostatic field, set up across the oxide layer by electron transfer from the metal to adsorbed oxygen species. The pressure dependence of the oxide growth rate and terminal thickness suggested a constant field growth mechanism. Clean titanium films reacted with deuterium to form a bulk deuteride TiDₓ (x<2). The oxide layer which resulted from oxygen exposure was characterized by the above techniques. Oxide layers greater than 20 A completely inhibited deuterium absorption by prohibiting 02 dissociation, but did not act as a diffusional barrier when additional dissociation sites were provided. Iron adlayers were found to accelerate the D₂ absorption reaction. Removal of the titanium films from the vacuum chamber to an isolable electrochemical reaction chamber, without exposure to the atmosphere, allowed a determination of the effect of the various gas/solid reactions on the subsequent electrochemical oxidation processes.

A novel way of producing nanostructures in the past decade has been through the use of an anodized alumina template. This template has dense, self-ordered nanometric pores that grow in the oxide as the aluminum is being anodized. This technique is a fairly new method of processing nanostructures, and much study and research is presently being done to understand the formation mechanisms of the highly ordered pores. Ultra-pure aluminum foil and pure aluminium single crystal plates were anodized to create porous anodized alumina, and using it as a template to electro-deposit Nickel nanostructures. The effects different anodizing parameters have on oxide creation were studied, and the results obtained from studying the effects of substrate purity and texture of the anodized aluminum substrate on the morphology of the alumina template, through the use of X-ray diffraction and scanning electron microscopy. / Nickel nanowires were prepared by DC electrodeposition inside the porous alumina template with a gold-palladium coating serving a conductive base. The nanowires have a diameter of 65 nm, and their length depends on the deposition time. The nanowires can uphold a position perpendicular to the substrate by partially dissolving the alumina template. They also have a tendency to gather together once the template is partially removed.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Bert Bras; Committee Member: David Rosen; Committee Member: Jeannette Yen

Contents: a. The oxidation of metals by atomic and molecular oxygen -- b. Calculation of the heats of formation of point defects in some transition metal oxides.

No description available.

The dehydration of isopropanol over anodic oxides was studied. The catalytic activity of the anodic oxides prepared in phosphoric, sulfuric, and oxalic acid was compared to the activity of ν-Al₂O₃. The effect of various thermal treatments on the catalytic activity was examined. IR spectroscopy proved useful for the study of the effect of thermal treatment on the acidity of the oxides. X-ray photoelectron spectroscopy (XPS) was employed to examine the oxide surfaces both before and after use as a catalyst. The acidity of the oxides was studied by various methods and related to the activity of the oxides. The acidity of the oxide surfaces was studied by the adsorption of pH indicators on the oxide surfaces. The adsorption of gaseous bases, ammonia and pyridine, was studied by IR spectroscopy and temperature programmed desorption mass spectrometry. It was thus possible to differentiate between Lewis and Brønsted acid sites and to determine the quantity of the acid sites on the various oxides. / Ph. D.

An equifield strength model has been established to elucidate the formation mechanism for the highly ordered alumina pore arrays and titanium oxide nanotubular arrays prepared via a common electrochemical methodology, anodisation. The fundamentals of the equifield strength model was the equilibrium between the electric field driven oxidation rate of the metal and electric field enhanced dissolution rate of oxide. During the anodic oxidation of metal, pore initiation was believed to generate based on dissolution rate difference caused by inhomogeneity near the metal/oxide interface. The ionic nanoconvection driven by the electric force exerted on the space charge layer in the vicinity of electrolyte/oxide interface is established to be the main driving force of the pore ordering at the early stage of the anodisation. While the equifield strength requirement governs the following formation of the single pore and the self-ordering of random distributed pore arrays during the anodisation process. Hexagonal patterned Al2O3 nanopore arrays and TiO2 nanotubular arrays have been achieved by anodisation of corresponding metal substrates in proper electrolytes. The two characteristic microstructural features of anodic aluminium oxide (AAO) and anodic titanium oxide (ATO) were investigated using scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The observations of the hemispherical electrolyte/oxide and oxide/metal interfaces, uniform thickness of the oxide layer, as well as self-adjustment of the pore size and pore ordering can be well explained by the equifield strength model. Field enhanced dissociation of water is extremely important in determination of the porosity of anodic metal oxide. The porosity of AAO and ATO films was found to be governed by the relative dissociation rate of water which is dependent on anodisation conditions, such as electrolyte, applied voltage, current density and electric field strength. Using an empirical method, the relations between the porosity of the AAO (ATO) films and the anodisation parameters, such as electric field strength, current density and applied voltage, have been established. Besides, the extent that an external electric field can facilitate the heterolytic dissociation of water molecule has been estimated using quantum-chemical model computations combined with the experimental aspect. With these achievements, the fabrication of anodic metal oxide films can be understood and controlled more precisely. Additionally, the impacts of other factors such as the electrolyte type and the temperature effect on the morphology of the anodic products were also investigated. Some important experimental evidences on the pore diameters variation with applied voltage in the anodisation of aluminium and the titanium were obtained for future investigation of the anodic metal oxide formation processes.

The topic of this thesis is the design of an automatic preanodizer to be used to preadjust precision tantalum resistors by anodizing their surfaces. The purpose of the preanodizer is to generate a controllable voltage ramp to be applied to a set of tantalum resistors which are immersed in a suitable electrolyte. The slope and maximum value of the voltage ramp are set to produce the current required for proper anodization of the resistors. The rate of anodization determines the rate of change of the resistor value. This thesis covers the design of an electronic device to meet a set of requirements specified by the Western Electric Company. The primary tasks the device has to perform are the generation of a linear voltage ramp of adjustable slope and maximum voltage and the supply of a given maximum current. Metering circuits are provided to measure, store and display the current and the maximum value reached by the ramp voltage.

An electrochemical investigation of the corrosion of iron and Fe18Cr based stainless steel alloys was undertaken with particular emphasis on the nucleation and growth of surface films. Chronoamperometry was shown to be a sensitive technique to investigate the initial stages of film formation and growth. In a variety of acidic (pH < 7), alkaline and alkaline cyanide electrolytes, providing dissolution of the substrate metal could occur rising current transients, similar to those reported in electrocrystallisation studies, were observed when the electrode was stepped to the appropriate potential. This indicated that at these potentials the surface film formed via the nucleation and growth of discrete nuclei. A significant aspect of this study was visual evidence of this nucleation and subsequent growth of the film provided by scanning electron microscopy which supported the electrochemical data and interpretation thereof. Existing electrocrystallisation models were used to evaluate the experimental rising current transients. While these models gave an indication as to the prevailing nucleation and growth mechanism, they were found to be inadequate in describing anodic oxide formation on an oxidising substrate. A qualitative model was proposed. In acidic electrolytes, rising chronoamperometric transients were observed for Fe, Cr and Fe18Cr at passive potentials and for FexCr (x = 16,18, 20,23% Cr) and alloys 444, 4732, 4733, 304L and 316L at transpassive potentials. The transients were shown to be sensitive to variations of potential, temperature, electrolyte and alloy composition. A systematic investigation of the influence of temperature (20 0 C - 1200 C) on the chronoamperometric, cyclic voltammetric and rotating ring - disc electrode behaviour of Fe in O.5M and 1.0M NaOH was also undertaken. In alkaline electrolytes, the formation of a duplex surface film was proposed, with x-ray photoelectron spectroscopy indicating that the protective base layer consisted of FeO while Fez03 and FeOOH constituted the upper layer. Base layer formation was favoured with increasing temperature and increasing hydroxide ion concentration of the electrolyte. Addition of OAM NaCN to O.5M and 1.0M NaOH had a marked effect on the electrochemistry of the system, with CN- inhibiting surface film formation, particularly of the upper layer. A mechanism for the oxidation of Fe in alkaline and alkaline cyanide electrolytes was proposed. / Thesis (Ph.D.)-University of Natal, 1994.

Biologically inspired design is used as an approach for sustainable engineering. Taking a biologically inspired approach, one abstracts ideas and principles from nature, an inherently sustainable system, and uses them in engineering applications with the goal of producing environmentally superior designs. One such biological idea with potential environmental benefits for engineering is microscale and nanoscale surface roughness found on the Lotus plant and many other surfaces in nature. These surfaces repel water and aid in contaminant removal; this self-cleaning phenomenon is called the "Lotus Effect," in honor of the plant first observed to exhibit it. The structures responsible for the Lotus Effect inspired research and development of many technologies capable of creating hydrophobic, self-cleaning surfaces, and many potential self-cleaning surface applications exist beyond nature's intended application of cleaning. While statements have been made about the environmental benefits of using a self-cleaning surface, only limited scientific data exist. Artificial self-cleaning surfaces are successfully cleaned using fog or mist. This shows that such surfaces can be cleaned with less energy and water intensive methods than the more conventional methods used to clean regular surfaces, such as spray or solvent cleaning. This research investigates the potential environmental burden reductions associated with using these surfaces on products. A life cycle assessment is performed to determine the environmental burdens associated with manufacturing a self-cleaning surface, for three production methods: a chemical coating, a laser ablated steel template, and an anodized aluminum template. The environmental benefits and burdens are quantified and compared to those of more conventional cleaning methods. The results indicate that self-cleaning surfaces are not necessarily the environmentally superior choice.