| Summary: | 博士 === 國立清華大學 === 材料科學工程學系 === 94 === This thesis reports a novel method of using electrochemical process in the synthesis of monodispersed metal nanoparticles. The fabrication of the noble electrodes devised for the electrochemical system was also studied. The synthesis of monodispersed Ag and Au nanosphere particles in ethylene glycol and aqueous solution at room temperature by electrochemical method was demonstrated. Poly(N-vinylpyrrolidone) (PVP) was chosen as the stabilizer and tested for electrochemically stablility. Further characterization by high-resolution transmission electron microscopy (HRTEM) and nano-beam electron diffraction (NBED) pattern was carried out to investigate the particles size and growth direction of the nanosphere particles. For the large scale production of Ag nanoparticles for industrial uses, investigation has been focused on the effect of the electrochemical parameters on the formation of monodisperse Ag nanoparticles. The time evolution of absorption spectra by UV-Visible spectroscopy was employed to illustrate that silver nanoparticles in the electrolyte increase upon electrochemical process under the effect of different electrolyte compositions, applied potential and electrode materials. Suitability of the BDD (boron-doped diamond) electrode and IrO2 coated Ti electrode for the electrochemical synthesis of the Ag nanoparticles was demonstrated.
The electrode properties of BDD thin films grown by a hot-filament chemical vapor deposition technique on the surface modified Ti substrates were evaluated. The BDD films deposited thereon were characterized with various methods, including Raman spectroscopy, scanning electron microscopy (SEM), film adhesion using Vicker’s indentation method, and e.t.c.. Influence of the BDD film quality on the electrochemical performance and electrode stability has also been evaluated. The substrate roughened surface obviously reduces the film inner stress thus improved the film adhesion. In addition, the preetching of the Ti substrate produces the titanium hydride layer that can affect the BDD film growth significantly. The electrodes reveal minimal background current and better stability.
The Ti substrate surface, associated with an intense micro-roughness and a layer of protective Ti oxide, exhibits a significant contribution to the durability of the IrO2-Ta2O5 coated Ti electrode. The IrO2-Ta2O5 coated Ti-supported anodes were examined using c.p. grade 1 Ti plates as the starting substrate material which were given various treatment processes including annealing, chemical etching and thermal oxidation prior to the coating of IrO2-Ta2O5 active layer by the conventional thermo-decomposition method. The attempts analyzed the result of a modified approach to form a significant intense roughness to provide additional bonding and anchoring for the catalyst oxide coating. The roughened Ti substrate was further given protection by a thin thermal oxide layer on the surface. The service life of the IrO2-Ta2O5 coated Ti base electrode was assessed in aqueous solution of H2SO4 in order to clarify the effect of improved bonding durability between IrO2-Ta2O5 coating layer and Ti base metal. The surface morphology and phase structure properties of the Ti substrates and as well as the IrO2-Ta2O5 coating layer were investigated by scanning electron microscope (SEM), X-ray energy dispersive spectroscopy (EDS), X-ray diffraction technique (XRD) and Auger electron spectroscopy (AES) analyses.
Microstructure effect on chemical etching behavior of the annealed Ti–6Al–4Vand Ti–3Al–2.5V titanium (Ti) alloys was compared with that of unalloyed c.p titanium. The microstructural evolution of structure phases after annealing the titanium and its alloys at temperature near and above β transus and followed by furnace cooling to room temperature was studied using optical microscope, SEM and XRD. The microstructure study illustrates that the heat treatment enhanced partitioning effect allows extensive formation of hemispherical and near spherical pits roughened surface to be readily acquired by chemically etching the annealed α+β titanium alloys. The increasing networks of grain boundary β phase near surface act as a barrier over the underneath α grain. The kinetics of the chemical etching reaction process shows that the annealed α+β titanium alloys exhibit relatively lower weight loss and thickness reduction rate, thus illustrate less chemical activity than the annealed unalloyed c.p. titanium.
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