No description available.

Conventional physical vapour deposition (PVD) techniques usually result in films of lower quality than the corresponding bulk material. A major problem with PVD films is the presence of columns and voids throughout the thickness of the film. The films may have a low packing density, low micro-hardness and in many cases poor adhesion to the substrate. Many of these problems are a direct consequence of the low energy of the depositing atoms arriving at the substrate during film growth. The resulting film porosity gives rise to a reduction in mechanical strength, and in the case of dielectric optical films, a reduction in the refractive index. The properties of deposited films are greatly improved when the substrate or the growing film is bombarded with more energetic particles. An ideal deposition process requires a high flux of film atoms with an energy of approximately 5-50 eV in order to achieve sufficient surface mobility at the substrate to overcome columnar growth.

<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)

No description available.

<p> Cathodic electrodeposition method has been developed for the fabrication of manganese oxide films for application in electrochemical supercapacitors (ES). The manganese oxide films prepared from KMn04 and NaMn04 aqueous solution showed an increasing deposition yield with the deposition time. The deposition rate decreases with increasing the concentration of deposition precursor. The obtained films were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction analysis (XRD), thermogravimetric and differential thermal analysis (TGA/DTA). The SEM observations revealed uniform films of highly porous nanostructure on different substrates. The capacitive behavior of the deposits was investigated by cyclic voltammetry and chronopotentiometry method in 0.1M NaS04 aqueous solutions. As prepared deposits exhibited pseudocapacitive behavior in the potential window of 0-1.0 V versus SCE with excellent cyclability. A maximum specific capacitance (SC) of 353 Fig was obtained for the 45 μg/cm2 film deposited from KMn04 solution on stainless steel foil, at a scan rate of 2 m V /s in the 0.1 M Na2S04 solution. It was found that the SC decreased with increasing deposit thickness and scan rate. No significant effect was obtained on the films prepared from 20 mM KMn04 on stainless steel after heat treatment at various temperatures. The capacitance of as-prepared electrode did not change by changing the electrolyte from Na2S04 to K2S04 solutions. However, higher capacitance values were observed by using electrolyte with higher concentration. Different structures of manganese oxides were obtained when different deposition precursors were used. No significant difference in capacitive behavior was found between the films prepared from different deposition precursor. However it was concluded that conductivity of the film is key in determining the performance of the electrodes. The effect of substrates on the electrochemical behavior has also been investigated by using stainless steel and nickel foils. </p> / Thesis / Master of Applied Science (MASc)

Metallic additives, also known as anticorrosive pigments, can provide sacrificial cathodic protection and complement the barrier protection afforded by heterogeneous organic coatings to metallic substrates. The unique systematic study of the corrosion resistance of an epoxy coating reinforced with different sizes (80nm, 500nm, 10um) and continuous multiple pigment volume concentration (0, 2%, 10%, 20%, 45%) below global critical pigment volume concentration of zinc particles were studied. The thesis is developing the fundamental understanding to optimize corrosion protection and predicting the protection with time. The properties of these cathodic coatings were investigated by a single-frequency electrochemical impedance spectroscopy (EIS) and open circuit potential (OCP) measurements that can be used as to understand cathodic protective state. Finite Element Analysis (FEA) has been applied here for modeling and simulating part of actual experiments. This thesis will help understanding the sensitivity and efficiency to various size and loading of metallic additives for corrosion protection.

The durability of concrete structures is affected by a number of factors such as environmental exposure, electrochemical reactions, mechanical loading, impact damage and others. Of all of these, corrosion of the reinforcement is probably the main cause for the deterioration of steel reinforced concrete (RC) structures. Corrosion management is becoming increasingly necessary as a result of the growing number of ageing infrastructure assets (e.g. bridges, tunnels etc.) and the increased requirement for unplanned maintenance in order to keep these structures operational throughout their design life (and commonly, beyond). The main RC repair, refurbishment and rehabilitation approaches generally employed can be broadly categorised under a) conventional, b) surface treatments, c) electrochemical treatments and d) design solutions. The overarching aim of this research was to identify the key corrosion management techniques and undertake empirical investigations focused on full-scale RC structures to investigate their long-term performance. To achieve this, individual research packages were identified from the above broad five approaches for repair, replacement and rehabilitation. These were 1) Patch repairs and incipient anodes, 2) Impressed Current Cathodic Protection, 3) Galvanic Cathodic Protection and 4) Hydrophobic treatments. The selection of the above research packages was based on past and present use by the construction industry to repair, refurbish and rehabilitate RC structures. Their contributions may be broadly categorised as i) Investigations on how specific treatments and materials perform, ii) Investigations on the effectiveness of existing methods of measurements and developing alternatives, iii) Changes to the existing theory of corrosion initiation and arrest and iv) Changes to management framework strategies. The key findings from each research package can be summarised as follows: Macrocell activity appears to be a consequence rather than a cause of incipient anode formation in repaired concrete structures, as has previously been presented; ICCP has persistent protective effects even after interruption of the protective current; Discrete galvanic anodes installed in the parent concrete surrounding the patch repair are a feasible alternative to galvanic anodes embedded within the patch repairs of RC structures; Silanes may have a residual hydrophobic effect even after 20 years of service.

This thesis investigates the application of plasma immersion ion implantation (PIII) to polymers. PIII requires that a high negative potential be applied to the surface of the material while it is immersed in a plasma. This presents a problem for insulating materials such as polymers, since the implanting ions carry charge to the surface, resulting in a charge accumulation that effectively neutralises the applied potential. This causes the plasma sheath at the surface to collapse a short time after the potential is applied. Measurements of the sheath dynamics, including the collapsing sheath, are performed using an electric probe. The results are compared to theoretical models of the plasma sheath based on the Child-Langmuir law for high voltage sheaths. The theoretical model predicts well the sheath dynamics for conductive substrates. For insulating substrates the model can account for the experimental observations if the secondary electron coefficient is modified, justified on the basis of the poly-energetic nature of the implanting ions. If a conductive film is applied to the insulator surface the problem of charge accumulation can be avoided without compromising the effectiveness of PIII. The requirement for the film is that it be conductive, yet transparent to the incident ions. Experimental results are presented which confirm the effectiveness of the method. Theoretical estimates of the surface potential show that a film of the order of 5nm thickness can effectively circumvent the charge accumulation problem. Efforts to produce and characterise such a film form the final two chapters of this thesis. The optimal thickness is determined to be near the percolation threshold, where a marked increase in conductivity occurs. Spectroscopic ellipsometry is shown to be an excellent method to determine the film thickness and percolation threshold non-invasively. Throughout this work cathodic vacuum arcs are used to deposit thin films and as a source of metal plasmas. The design and construction of a pulsed cathodic vacuum arc forms a significant part of this thesis. Investigations of the cathode spots and power supply requirements are presented.

Graduation date: 1999

This dissertation explores cathodic electrodeposition mechanisms that describe the synthesis of redox-active electrode materials. Several interesting elements are known to deposit at negative potentials (e.g., Mo, Re, Se), and by extending this work, we can tailor the growth of new binary systems (e.g., MoxRe₁₋xOy, MoxSe₁₋xOy) that have enhanced optical and electronic properties. To grasp the subtleties of deposition and understand how the growth of a particular phase is influenced by other species in solution, several analytical methodologies are used to thoroughly characterize film deposition, including chronocoulometry, voltammetry, nanogravimetry, UV-Visible spectroelectrochemistry, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and inductively coupled plasma mass spectrometry (ICPMS). Chapter 1 is a general introduction that discusses the growth of redox-active metal oxides and alloys with an emphasis on tuning the composition to enhance material performance. Chapter 2 proposes a mechanistic pathway for the deposition of rhenium films from an acidic perrhenate (ReVIIO₄⁻) solution containing both metallic and oxide components. Unlike many other metal anions, it was observed that ReVIIO₄⁻ adsorbs to the electrode surface prior to reduction. As such, ReVIIO₄⁻ is ideally situated to be a redox-active mediator for other electrochemical reactions, and in Chapter 3, this dissertation explores how ReVIIO₄⁻ increases the deposition efficiency of Mo oxide deposition. Depth profiling XPS supported by electrochemical studies demonstrated that Mo and Re deposit separately to form an inhomogeneous material, MoxRe₁₋xOy (0.6 < x ≤ 1.0). Over a limited potential range from –0.3 V to –0.7 V (vs Ag/AgCl) the rhenium mole fraction increases linearly with the applied voltage. Chapter 4 explores the deposition of MoxSe₁₋xOy, and in this case, the incorporation of Mo species in solution shifts the deposition of Se⁰ to more positive potentials. Depending on the applied potential used, voltammetry experiments suggest that a small amount of Mo (<5%) reduces to the zero-valent phase to yield the photosensitive alloy, MoxSey. Chapter 5 discusses future work and presents preliminary data describing the deposition of Se⁰ on ITO using adsorbed ReVIIO₄⁻ as a redox mediator. / text