A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. / A quartz microbalance electrode (QME) was constructed for the investigation of the electrochemistry of electroless plating baths. To this end, the electronic oscillator circuitry required for the microbalance was developed from literature examples, and the techniques of forming electrodes and mounting the crystal in an appropriate holder were established. The device thus developed was compact, allowing for in situ frequency and electrochemical measurements to be made in a commercially available 100 mL Metrohm cell. The precision .and accuracy obtained with the home-built device were shown to be adequate for electrochemical research, and the sensitivity was found to be consistent with the value expected from the Sauerbrey equation.(Abbreviation abstract) / Andrew Chakane 2018

by Lam Ka. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 54-60). / Abstracts in English and Chinese. / ABSTRACT --- p.i / ACKNOWLEDGEMENT --- p.ii / TABLE OF CONTENT --- p.iii / LIST OF TABLES --- p.v / LIST OF FIGURES --- p.vii / Chapter CHAPTER ONE: --- INTRODUCTION --- p.1 / Chapter 1.1 --- Metal deposition --- p.1 / Chapter 1.2 --- Electroless Nickel Plating --- p.3 / Chapter 1.2.1 --- Historical Review and Applications --- p.3 / Chapter 1.2.2 --- General Chemical Principles --- p.5 / Chapter 1.2.3 --- Previous Studies --- p.7 / Chapter 1.3 --- Scope of Work --- p.12 / Chapter CHAPTER TWO: --- EXPERIMENTAL --- p.13 / Chapter 2.1 --- Bath Composition --- p.13 / Chapter 2.1.1 --- Theoretical Description --- p.13 / Chapter 2.2.2 --- Materials --- p.15 / Chapter 2.2 --- Procedure and Experimental Conditions --- p.17 / Chapter 2.3 --- Characterization of EN Coatings --- p.18 / Chapter 2.3.1 --- Theory --- p.18 / Chapter 2.3.1.1 --- Energy Dispersive X-ray Detection of Scanning Electron Microscopy --- p.18 / Chapter 2.3.1.2 --- Polycrystalline X-ray Diffraction --- p.18 / Chapter 2.3.1.3 --- X-ray Photoelectron Spectroscopy --- p.20 / Chapter 2.3.1.4 --- Microhardness --- p.22 / Chapter 2.3.1.5 --- Corrosion resistance --- p.23 / Chapter 2.3.1.6 --- Thickness Measurement --- p.23 / Chapter 2.4 --- Application --- p.24 / Chapter CHAPTER THREE: --- RESULTS AND DISCUSSION --- p.26 / Chapter 3.1 --- Appearance --- p.28 / Chapter 3.2 --- Microstructure --- p.30 / Chapter 3.2.1 --- Effect of Phosphorus Content --- p.30 / Chapter 3.2.2 --- Effect of heat treatment --- p.32 / Chapter 3.3 --- Corrosion Resistance --- p.37 / Chapter 3.3.1 --- Effect of Phosphorus Content --- p.37 / Chapter 3.3.2 --- Effect of Heat Treatment --- p.45 / Chapter 3.3.2.1 --- Temperature --- p.45 / Chapter 3.3.2.2 --- Cooling Rate --- p.47 / Chapter 3.4 --- Microhardness --- p.49 / Chapter 3.4.1 --- Effect of Phosphorus Content --- p.49 / Chapter 3.4.2 --- Effect of Heat Treatment --- p.49 / Chapter CHAPTER FOUR: --- CONCLUSION --- p.52 / REFERENCES --- p.54

In this study we present the results of electroless deposition of silver (Ag) and electrophoretic deposition (EPD) of Al2O3 layers on glass for application in thin film transistor (TFT). Since Ag exhibits excellent resistivity, it is selected to be the material of conductive layer. Ag thin film electrical and physical parameters are studied as a function of the deposition time and working temperature. We study the thin-film electrical and mechanical properties using 4-point Probe, surface analyzer and nano indenter. The Ag film, thicker than 200 nm, exhibited a specific electrical sheet resistivity of about 500 m£[/¡¼. We also study the thin-film morphology and composition using SEM and FTIR, respectively. In this study, Mechanism and kinetics of the electrophoretic process in an Al2O3 cell are also studied. Al2O3 concentration levels are set from 1.25 to 7.5%, and deposition time from 5~20 seconds. Deposition time and Al2O3 particle concentration is experimentally discussed and characterized. The result shows that a linear relationship between the deposition rate and applied voltage is obtained. Besides, in this study, deposition of conductive layer silver and insulating layer Al2O3 for TFT are studied. A new process to deposit Ag layer and Al2O3 layer to be the conductivity layer and insulating layer of TFT is presented. First, the circuit pattern is defined by lithography process. Then, Ag is deposited with thickness of 200 nanometers. Second, the wafer is immersed in the stripper solution to remove the resist. After the deposition of the Ag on glass is finished, Al2O3 nano-scale particle concentration is prepared for electrophoretic deposition.

Hydrogen is considered to be the fuel of the future as it is clean and abundant. Together with the rapidly developing fuel cell technology, it can sustain an environmentally sound and efficient energy supply system. Developing the technologies of palladium-based membrane for hydrogen separation and palladium nanostructured materials for hydrogen sensing and hydrogenation catalysts makes the "hydrogen economy" possible. This is because these technologies will allow for commercially viable production of comparatively cheap and high-quality hydrogen, and safety of its application. Based on the market requirements and interest in the development of a hydrogen economy, the purposes of this thesis are to develop thin palladium membrane for hydrogen separation and to explore an economic method for the synthesis of palladium nanowires in potential engineering applications. The original contributions of this thesis are outlined below: / The investigation of deposition progress of a palladium membrane on porous stainless steel substrate illustrates that palladium deposits will form a network structure on pore areas of the substrate surface in the initial stages. A bridge model is presented to describe the formation of a membrane. This model is confirmed from the cross-section of the deposited membranes. Based on the bridge model and the experimental measurements of palladium membranes deposited on the pore area of the substrates, the thickness of a palladium membrane deposited on 0.2 mum grade porous stainless steel substrate can be effectively controlled around 1.5∼2 mum, and the thickness of a palladium membrane deposited on 2 mum grade porous Inconel substrate can be effectively controlled around 7.5∼8 mum. Comparing the thickness and quality of palladium membranes deposited on the same substrates with the data in the literature, the thicknesses of the membranes prepared in this program are lower. The obtained result will be beneficial in the design and manufacture of suitable membranes using the electroless deposition process. / In the initial deposition stages, palladium nanoparticles cannot be deposited at the surface of the SiO2 inclusions that appear at the substrate surface. With the extension of deposition time, however, palladium nanoparticles gradually cover the SiO2 inclusions layer by layer due to the advance deposited palladium nanoparticles on the steel substrate surrounding them. The effect of the SiO2 inclusions on palladium deposits cannot be neglected when an ultra-thin membrane having the thickness similar to the size of inclusions is to be built. / The chemical reaction between phosphorus (or phosphate) and palladium at high temperature can take place. This reaction causes surface damage of the membranes. If palladium membranes are built on the porous substrates that contain phosphorus or phosphate used in the inorganic binders, they cannot be used over 550°C. This result also implies that palladium membranes cannot be employed on the work environment of phosphorus or phosphates. / Palladium nanowires are well arranged by nanoparticles at the rough stainless steel surface. The formation procedures consist of 3 stages. In the initial stage, palladium nanoparticles are aligned in ore direction, then the nanowire is assembled continuously using follow-up palladium deposits, and finally the nanowire is built smoothly and homogeneously. It is also found that palladium nanoparticles generated from the autocatalytic reaction are not wetting with the steel substrate and they are not solid and easily deformed due to the interfacial tension when they connect to each other. / Various palladium nanowire arrays possessing the morphologies of single wires, parallel and curved wires, intersections and network structures are illustrated. The results demonstrate that palladium nanowires can be built in a self-assembled manner by palladium nanoparticles in the initial deposition stages. Such self-assembled nanowires may attract engineering applications because electroless deposition process and preparation of a substrate are simple and inexpensive. / The diameter of palladium nanowires can be effectively controlled by the concentration of PdCl2 in the plating solution and deposition time. The size of palladium nanoparticles generated from the autocatalytic reaction is directly dependent on the concentration of PdCl2 in the plating solution. The higher the concentration of PdCl2 in the plating solution is, the smaller the deposited palladium nanoparticles are. The experimental results provide a controllable method for the fabrication of palladium nanowire arrays with potential engineering applications.

No description available.

Thesis (Ph.D.)--Worcester Polytechnic Institute. / Keywords: composite Pd and Pd/Ag membranes, alloying, Pd/Ag barrier, intermetallic diffusion, bi-metal multi-layer BMML deposition, electroless plating kinetics, high temperature x-ray diffraction, aluminum hydroxide surface grading, porous sintered metal supports, hydrogen separation. Includes bibliographical references (leaves 279-296 ).

One of the key elements to the success of Pd-Ag membrane based reactor for the H2 production is the synthesis of thin and highly selective membranes using the electroless plating method. This work describes the effect of electroless plating conditions on the obtained Pd and Ag deposits properties (morphology, compactness, phase structure, compositional homogeneity and adhesion) important from synthesis of thin and H2 selective membrane viewpoint. Both sequential and co-deposition deposition methods were investigated. The conventional Pd and Ag plating conditions (NH3+EDTA based bath) produced dendritic and non-uniform sequential (multi layer) deposits, not suitable for synthesizing the thin and H2 selective Pd-Ag membranes. Ag under the conventional plating conditions deposited at high overpotential resulting in the dendritic and non-uniform sequential deposits. The modified Ag plating conditions eliminated Ag deposition at high overpotential and the sequential deposits obtained were non-dendritic and uniform. Thin (< 10 µm thick) and H2 selective Pd-Ag membranes were successfully synthesized using the modified Ag plating conditions. The membranes were then successfully annealed at 550 oC. After the annealing step, the membranes showed activation energy for the H2 permeation (4.3-11.5 kJ/mole) lower than that of the pure Pd membrane (12-16.4 kJ/mole) meaning that the Pd-Ag membranes were more effective for the H2 separation at lower temperatures than the pure Pd membrane. A Pd-Ag (20 wt%) membrane showed H2 permeance higher by a factor of 2.47 at 250 oC than the pure Pd foil. The Pd-Ag membranes also showed decline in the H2/He selectivity on exposure to the annealing and H2 permeation (300-500 oC) study conditions. The Pd-Ag co-deposits obtained (using NH3+EDTA bath) were dendritic, inhomogeneous with poor substrate adhesion, therefore not suitable for the membrane synthesis. The co-deposits were bi-metallic and required the annealing step to form the Pd-Ag alloy. There existed a large difference in the deposition potentials (600 to 650 mV) of Pd and Ag. The Ag deposition was severely controlled by its mass transfer in the solution resulting in the dendritic and inhomogeneous deposits. Among the different complexing agents investigated, KCl showed the least difference between the Pd and Ag deposition potentials. The co-deposits obtained using the KCl bath were non-dendritic, homogeneous and were Pd-Ag alloy therefore required no annealing step. Finally, the multi step plating, annealing and polishing approach was used to avoid the decline in the selectivity of the sequentially prepared Pd-Ag membranes. The membranes prepared by the plating, annealing and polishing approach showed very high selectivity (H2/He) and no decline in the selectivity was observed between 300-450 oC for the total exposure time > 550 h (> 200 h at 450 oC).

No description available.

No description available.

No description available.