Abstract The AAO membrane with nanopore arrays were fabricated by anodizing highly pure aluminum foils (99.9995%) in electrolyte under steady voltage. Pore diameter can be controlled by different anodic voltage(from 30 to 50 V) and electrolyte, on the other hand, thickness is proportioned to anodizing time , and interpore could follow this rule(a = 15.4+2.63¡Ñv) , and minimum radius of pore could reach 15nm . The XRD spectra of AAO without and with annealing, both showed the diffraction peaks of (311)¡B(400)¡B(440), corresponding to the £^-Al2O3 phase . Before fabricating AAO, we would polish under low temperature and then clean alumina foil in order to reduce surface roughness that is good for better order and regular. Through the use of porous anodic alumina masks, Au nanodot arrays deposited on Si by E-gun with AAO mask. Subsequently, the AAO mask was removed by H3PO4. Under the same procedure, we can fabricate 80nm of the diameter of pore and apply this mask on wafer of laser constructure . Because of regular hexagonal pore array, we may get the photonic crystal effect. During PL experiment, we got the result that AAO could increase light extraction of quantum dot from C237 wafer and controlled emission peak from C238 and C196 wafer and position of peak could shift to 1140nm. We hope nanodot array on wafer of laser structure could control emission peak.

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

No description available.

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.

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.

The direct anodic decomposition of copper-rich mattes using packed bed electrodes was investigated, because a practical solution to direct electrorefining of copper matte would lead to the potential elimination of copper converting and its associated sulphur dioxide emissions. Much greater copper extraction has been achieved experimentally at 50° C from a packed bed electrode consisting of 0.5-4mm diameter particles than from a massive or solid flat electrode composed of copper-rich matte, as found in earlier studies. This was shown to be attributable to natural convection mass transport processes within the inter-particle region that is not available in massive electrodes. However, while natural convection mass transfer is an important process in the packed bed electrodes, other factors were shown to be ultimately more important in terms of the maximum copper extraction which may be achieved prior to shut-down caused by total-bed polarization of these electrodes. Total-bed polarization of copper-rich mattes during direct anodic decomposition may be attributed to (a) deteriorating electrical contact (related to the formation of elemental sulphur and lead sulphate) between the current distributor and the adjacent particles, and in thick electrodes, between the particles across the anode, (b) relative nonreactivity of iron-containing phases and (c) physical association of these phases with the reactive phases, and under certain conditions (d) crystallization of copper sulphate within the inter-particle region, blocking ionic conduction paths. The maximum copper extraction from synthetic pure chalcocite, the predominant component of industrial copper-rich mattes, using the packed bed electrodes was found to be about 80%. The presence of 3-4wt% iron in the copper-rich mattes was shown to degrade the copper extraction considerably due to the presence of relatively nonreactive iron-rich phases which form as the matte is cooled from its liquid state. The presence of lead in copper matte was found to be a relatively unimportant impurity in terms of copper extraction, while oxygen was found to partially offset the negative effects of iron. A simple one-dimensional mathematical model was developed to estimate the variation of copper extraction across a 2cm-thick packed bed electrode. The copper extraction was found experimentally to vary by less than a factor of two across the anode. This was attributed to (a) the relatively high electrical conductivity of the electrolyte which minimizes reaction-process overpotential gradients across the anode, and (b) the increasing impedances of the decomposition processes in the most reacted particles. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

No description available.

<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)