[No abstract available] / Science, Faculty of / Chemistry, Department of / Graduate

The rate of oxidation of 99.99% and 99.999% pure copper samples at 1220°C by low-momentum jets of pure oxygen has been studied at gas flow rates of from 500 to 2000 cm³ min⁻¹. Oxidation rates at a given gas flow rate were found to be constant and were governed by starvation mass transfer kinetics. Factors studied for the reaction include: effect of lance height, effect of small additions of silicon and sulphur to the melt prior to oxidation, and effect of oxide patch area. Interfacial tension-generated flow, radially outward from the point of jet impingement, was observed during oxidation and surface velocity studies showed that such flow had a mean value of 26.1 ± 5.5 cm sec⁻¹ for all of the experiments and was independent of oxygen gas flow rate and copper bath oxygen concentration. Surface-blockage studies indicated that the bulk of the oxygen transfer to the copper occurred over the area described by the oxide patch. Liquid-phase oxygen mass transfer coefficients were calculated using the oxidation rates and oxide patch areas, and a mean value was found to be 0.104 ± 0.012 cm sec⁻¹ independent of oxygen flow rate, bath oxygen content, and dissolved sulphur and silicon contents. The rate of oxidation of 99.995% pure silver at 1100°C was studied using low-momentum jets of pure oxygen at flow rates of 1500 and 2000 cm³ min⁻¹ and was found not to be governed by starvation mass transfer kinetics. The oxidation rate was not dependent on oxygen gas flow rate and was found to be a factor of about 50 times less than those observed for copper. No spontaneous interfacial tension-generated flow was observed during oxidation of the molten silver and a possible explanation was postulated. Liquid-phase oxygen mass transfer coefficients were found to have a mean value of 2.88 ± .41 (10⁻³) cm sec⁻¹, independent of gas flow rate and bath oxygen content. The effect of interfacial turbulence on liquid-phase oxygen mass transfer coefficients in molten copper was to enhance the value by about 40 times over that observed in molten silver, where interfacial turbulence does not occur on oxidation. Copper deoxidation at 1220°C using low-momentum jets of pure hydrogen at flow rates of 1500 and 3000 cm³ min⁻¹ was studied, and was found not to depend on hydrogen flow rate, lance height, and starting oxygen concentration. The rate-controlling step was found to be the gas-phase mass transfer of hydrogen to the liquid surface for the first 3000 sec. of deoxidation. After this, liquid-phase oxygen mass transport control predominated. Dissolved silicon was found to retard the deoxidation rate, while dissolved sulphur was found to enhance the deoxidation rate through continued SO2 elimination. Interfacial tension-generated flow was observed during deoxidation and approximate surface velocities of 10 to 15 cm sec⁻¹ towards the point of jet impingement were observed. A mechanism for this flow was postulated. The gas-phase mass transfer coefficient was found to be 1.28 ± 0.25 cm sec⁻¹ for copper-oxygen alloys, and was 0.89 cm sec⁻¹ in the 1.28 ± 0.25 cm sec⁻¹ for copper-oxygen alloys, and was 0.89 cm sec⁻¹ in the presence of dissolved silicon and 2.68 cm sec⁻¹ in the presence of dissolved sulphur. An approximate value for the liquid-phase oxygen mass transfer coefficient in the liquid-phase control region was found to be 4.9 (10⁻³) cm sec⁻¹, and was found to be influenced by the presence of bubbling during this phase of deoxidation. The rate of deoxidation of molten silver at 1100°C by low-momentum hydrogen jets was studied at hydrogen flow rates of 1500 and 2000 cm³ min⁻¹ The rate was found not to depend upon hydrogen flow rate, but was found to decrease with decreasing starting bath oxygen concentration. Interfacial tension-generated flow was observed, during silver deoxidation, with approximate surface velocities of 10 to 15 cm sec⁻¹ towards the point of jet impingement. The rate-controlling step was found to be liquid-phase mass transfer of oxygen, and liquid-phase oxygen mass transfer coefficients were found to decrease with decreasing initial oxygen content. These values were enhanced by the presence of bubbling during deoxidation. Interfacial turbulence during the dissolution of solid CU₂S CU₂O, Se, and Te in molten copper was shown to occur. Values calculated for the spreading coefficient S, indicated that the spreading of these materials on molten copper was predictable. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

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.

Anodic alumina nanohoneycombs (AAO) have been widely used because of its convenient fabrication and controllable pores’ geometry. A lot of investigations have been conducted to study its physical and chemical properties. However, the mechanical properties, especially tribological properties, of such a popular nanomaterial still remain almost unknown. In this project, a series of scratch experiments were conducted on AAO films fabricated by a two-step anodisation method. The testing system is a G200 Nanoindenter provided by Agilent Corporation. A standard diamond Berkovich tip is used as the scratch tip. A scanning electron microscope was used to image the microstructure of the material deformation after scratching. Strengths of AAO domains with different pore regularities were compared by performing the scratch tests at constant normal loads crossing the boundaries separating these domains. Ramping load tests were carried out to show the effects of the normal load on the deformation and friction of the AAO. Scratch cycles and velocities were also varied to see their influence on friction and wear. The results show that the more ordered AAO structure has higher strength than disordered counterparts under scratch testing. The friction coefficient reduces rapidly on increasing normal load, and an explanation of this unusual behaviour is offered by considering the row-by-row deformation of the AAO structure. In multicycle scratch tests, the friction reaches a maximum at the fourth cycle. A step-like deformation behaviour was observed when the scratch velocity became extremely large, and this is probably due to the dynamic response of the instrument. / published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

Self-ordered anodic porous alumina with a nano-honeycomb structure has recently been extensively used as templates for the synthesis of various nanomaterials for diverse applications. However, due to the insufficient knowledge on the combined electro-chemo-mechanical processes, the formation mechanism of self-ordering has been under debate for decades without clear conclusions. Also, fast fabrication of highly self-ordered and mechanically stable anodic porous alumina is still a challenge. Furthermore, the actuation behavior of anodic porous alumina upon external mechanical and electrical triggering in an electrochemical cell has not been exploited. In this work, firstly, we investigated the self-ordering mechanism by establishing a kinetics model involving the Laplacian electric potential distribution and a continuity equation for current density within the oxide body. Current densities governed by the Cabrera-Mott equation are formed by ion migration within the oxide as well as across the interfaces. The pore channel growth, due to electric-field-assisted reactions, is governed by Faraday’s law. Real-time evolution of pre-patterned pore channel growth was simulated in two-dimensional cases by finite element method. The simulations revealed a parameter domain within which pre-patterned pore channels will continue to grow in a stable manner during the subsequent anodization if the pre-patterns are commensurate with the self-ordered configurations, or these are driven into stable if the pre-patterns do not initially match the self-ordered configurations. This was verified in experimentally observed pore channel growth under the guidance of pre-patterns made by focused-ion-beam milling. Furthermore, the simulations revealed that ionization reaction on (001) oriented Al grain is relatively easier than that on (101) grain, which results in stable and unstable pore channel growth on (001) and (101) Al grains, respectively, both of which were observed from the simulations and experiments. Secondly, a scheme on quantitative evaluation of self-ordering qualities in anodic porous alumina has been developed, based on which we systematically searched the optimum self-ordering conditions, by varying the key anodization factors, including substrate grain orientation, electrolyte concentration, temperature, voltage, and time. A high acid concentration and high temperature anodization method was found. Compared with conventional methods, the present method can realize fast formation of highly self-ordered, and mechanically stable anodic porous alumina under a continuous range of anodization voltage with tunable interpore distances. Thirdly, reversible bending was found in anodic porous alumina-Al composites upon cyclic electric actuation, as directly observed by an optical microscope and detected by in situ nanoindentation. The bending is thought to be the result of charge-induced surface stresses in the nanoporous alumina. The results suggest a new type of composite materials for applications as micro-scale actuators to transform electrical energy into mechanical energy. Furthermore, the composite exhibits significant softening during in situ nanoindentation when the estimated maximum stress underneath the indenter is exerted on the metal/oxide interface. Softening was further verified by in situ microindentation. Electron microscopy examination indicated that the softening is due to a combination of high compression stress and electric field acting near the interface, which enhance ionization reaction and cause the interface to move faster into the substrate. / published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

Surface modification is a process that is applied to the surfaces of titanium substrates in order to improve the biocompatibility after implanting in the body. Two methods were used in the present work: Anodisation and gel oxidation. Anodisation was performed at room temperature in strong mineral acids (sulphuric acid (H2SO4) and phosphoric acid (H3PO4)), an oxidising agent (hydrogen peroxide (H2O2)), mixed solutions of the preceding three, and a weak organic acid mixture (β-glycerophosphate + calcium acetate). The parameters used in anodisation were: Concentrations of the electrolytes, applied voltage, current density, and anodisation time. Gel oxidation was carried out by soaking titanium substrates in sodium hydroxide (NaOH) aqueous solutions at different concentrations (0.5 M, 1.0 M, 5.0 M, and 10.0 M) at 60??C for 24 h, followed by oxidation at 400??, 600??, and 800??C for 1 h. Conceptual models representing changes in the microstructure as a function of the experimental parameters were developed using the anodisation data. The relevant parameters were: Applied voltage, current density, acid concentration, and anodisation time: ?? The model for anodisation using the strong acid (H2SO4) illustrates the growth rate of the film, identification of the threshold for the establishment of a consistent microstructure, and prediction of the properties of the film. ?? For the oxidising agent (H2O2), two models were developed: Current-control and voltage-control, the applicability of which depends on the scale of the current density (high or low, respectively). These models are interpreted in terms of the coherency/incoherency of the corrosion gel, arcing, and porosity. ?? The model for the strongest acid (H3PO4) is similar to that of H2O2 in current-control mode, although this system showed the greatest intensity of arcing and consequent pore size. ?? Anodisation in mixed solutions uses Ohm??s law to explain four stages of film growth in current-control mode. These stages describe the thickness of the gel, its recrystallisation, and the achievement of a consistent microstructure. ?? Anodisation in weaker organic acids allows the most detailed examination of the anodisation process. Both current density and voltage as a function time reveal the nature of the process in six stages: (1) instrumental response, (2 and 3) gel thickening, (4) transformation of the amorphous gel to amorphous titania, (5) recrystallisation of the amorphous titania, and (6) subsurface pore generation upon establishment of a consistent microstructure. Gel oxidation was done at low and high NaOH concentrations followed by oxidation. Three models were developed to represent the gel oxidation process: (1) Low concentration, (0.5 M and 1.0 M NaOH), (2) Medium concentration (5.0 M NaOH), and (3) high concentration (10.0 M NaOH). For the low concentrations with increasing temperature, the model involves: (1) amorphous sodium titanate forms over a layer of amorphous anatase and (2) a dense layer of rutile forms. For the high concentrations with increasing temperature, the model involves: (1) amorphous sodium titanate forms over a layer of amorphous anatase, (2) a dense layer of anatase forms and raises up the existing porous anatase layer, and (3) the dense and porous anatase layers transform to dense and porous rutile layers, respectively. The main difference between the two is the retention of crystalline sodium titanate in the higher NaOH concentration. Anodised and gel oxidised samples subsequently were soaked in simulated body fluid in order to study the precipitation of hydroxyapatite in the absence and presence of long UV irradiation, which has not been investigated before. With the anodised surfaces, the porous and rough titania coating facilitated both the precipitation of hydroxyapatite and the attachment of bone-like cells. UV irradiation showed greatly enhanced hydroxyapatite precipitation, which is attributed to its photocatalytic properties. With the gel oxidised surfaces, the greatest amount of hydroxyapatite precipitation occurred with the presence of both anatase and amorphous sodium titanate. Rutile suppressed precipitation.

Surface modification is a process that is applied to the surfaces of titanium substrates in order to improve the biocompatibility after implanting in the body. Two methods were used in the present work: Anodisation and gel oxidation. Anodisation was performed at room temperature in strong mineral acids (sulphuric acid (H2SO4) and phosphoric acid (H3PO4)), an oxidising agent (hydrogen peroxide (H2O2)), mixed solutions of the preceding three, and a weak organic acid mixture (β-glycerophosphate + calcium acetate). The parameters used in anodisation were: Concentrations of the electrolytes, applied voltage, current density, and anodisation time. Gel oxidation was carried out by soaking titanium substrates in sodium hydroxide (NaOH) aqueous solutions at different concentrations (0.5 M, 1.0 M, 5.0 M, and 10.0 M) at 60??C for 24 h, followed by oxidation at 400??, 600??, and 800??C for 1 h. Conceptual models representing changes in the microstructure as a function of the experimental parameters were developed using the anodisation data. The relevant parameters were: Applied voltage, current density, acid concentration, and anodisation time: ?? The model for anodisation using the strong acid (H2SO4) illustrates the growth rate of the film, identification of the threshold for the establishment of a consistent microstructure, and prediction of the properties of the film. ?? For the oxidising agent (H2O2), two models were developed: Current-control and voltage-control, the applicability of which depends on the scale of the current density (high or low, respectively). These models are interpreted in terms of the coherency/incoherency of the corrosion gel, arcing, and porosity. ?? The model for the strongest acid (H3PO4) is similar to that of H2O2 in current-control mode, although this system showed the greatest intensity of arcing and consequent pore size. ?? Anodisation in mixed solutions uses Ohm??s law to explain four stages of film growth in current-control mode. These stages describe the thickness of the gel, its recrystallisation, and the achievement of a consistent microstructure. ?? Anodisation in weaker organic acids allows the most detailed examination of the anodisation process. Both current density and voltage as a function time reveal the nature of the process in six stages: (1) instrumental response, (2 and 3) gel thickening, (4) transformation of the amorphous gel to amorphous titania, (5) recrystallisation of the amorphous titania, and (6) subsurface pore generation upon establishment of a consistent microstructure. Gel oxidation was done at low and high NaOH concentrations followed by oxidation. Three models were developed to represent the gel oxidation process: (1) Low concentration, (0.5 M and 1.0 M NaOH), (2) Medium concentration (5.0 M NaOH), and (3) high concentration (10.0 M NaOH). For the low concentrations with increasing temperature, the model involves: (1) amorphous sodium titanate forms over a layer of amorphous anatase and (2) a dense layer of rutile forms. For the high concentrations with increasing temperature, the model involves: (1) amorphous sodium titanate forms over a layer of amorphous anatase, (2) a dense layer of anatase forms and raises up the existing porous anatase layer, and (3) the dense and porous anatase layers transform to dense and porous rutile layers, respectively. The main difference between the two is the retention of crystalline sodium titanate in the higher NaOH concentration. Anodised and gel oxidised samples subsequently were soaked in simulated body fluid in order to study the precipitation of hydroxyapatite in the absence and presence of long UV irradiation, which has not been investigated before. With the anodised surfaces, the porous and rough titania coating facilitated both the precipitation of hydroxyapatite and the attachment of bone-like cells. UV irradiation showed greatly enhanced hydroxyapatite precipitation, which is attributed to its photocatalytic properties. With the gel oxidised surfaces, the greatest amount of hydroxyapatite precipitation occurred with the presence of both anatase and amorphous sodium titanate. Rutile suppressed precipitation.

<p> Cyclic voltammetric oxidation of 1,2,3,4,5-pentaphenylcyclopentadiene has been studied in non-polar chloroalkane solvents (CH2Cl2 and CH2ClCH2Cl). The oxidation is reversible if tetra-n-butylammonium hexafluorophosphate (TBA^+PF6^-) is used as supporting electrolyte, but irreversible when tetra-n-butylammonium perchlorate (TBA^+ClO4^-) or tetra-n-butylammonium trifluoromethane sulfonate (TBA^+OTf^-) are used, and partially reversible when tetra-n-butylammonium tetrafluoroborate (TBA^+BF4^-) is used. Oxidation of 1,2,3,4,5-pentaphenyl-1-methylcyclopentadiene, which has no relatively acidic protons, was reversible with all four supporting electrolytes.</p> <p> The criteria for reversibility were observation of cathodic wave on scan reversal, equal anodic and cathodic peak currents, minor dependence of peak potentials on scan rate, v, and linearity of anodic peak current, ipa with the square root of scan rate, v^1/2 , corresponding to Randles-Sevcik equation for reversible processes.</p> <p> It is proposed that perchlorate (ClO4^-) and triflate (OTf^-) anions are sufficiently basic to accept a proton from 1,2,3,4,5-pentaphenylcyclopentadiene cation-radical intermediate, while tetrafluoroborate (BF4^-) and particularly hexafluorophosphate (PF6^-) are less basic, and therefore less reactive.</p> <p> Controlled potential electrolysis of 1,2,3,4,5-pentaphenylcyclopentadiene with tetra-n-butylammonium perchlorate as supporting electrolyte affords the cation, which is consistent with an ECE mechanism in which the chemical step is proton loss.</p> / Thesis / Master of Science (MSc)

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.

Part I: Pyrrolidine derivatives were attached a methoxy group on a-C position of pyrrolidine-ring via anodic oxidation. Followed with alkylation and series of transformation under Lewis acids to obtain tropane alkaloids. Part II: Application of intramolecular radical cyclization toward the synthesis of aporphine alkaloids. Tributyltinhydride and AIBN were used to generate aryl radicals. Trapping of aryl radicals with unsaturated alkenes led to products.