京都大学 / 新制・課程博士 / 博士(工学) / 甲第23913号 / 工博第5000号 / 新制||工||1780(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 作花 哲夫, 教授 安部 武志, 教授 阿部 竜 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

<p> Pure zinc and zinc/yttria stabilized zirconia (YSZ) composite coatings for combined wear and corrosion protection of ferrous substrates were prepared by electrodeposition using acidic zinc sulphate solutions containing YSZ and gelatin. The morphology of the electrodeposit was studied by Field Emission Scanning Electron Microscopy (FESEM) with energy dispersive spectroscopy (EDS). X-ray diffraction was employed to determine the texture of the zinc deposits. In the electrodeposition of pure zinc coatings, the influence of electrodeposition parameters, including current density, deposition time and solution pH was studied. It was found that the deposition rate was controlled by the current density and that an increase in deposition time resulted in the formation of deposit microstructures with coarse, columnar grains. The deposits prepared from solutions with lower pH were composed of uniform, fine grains and exhibited a basal plane preferred orientation.</p> <p> The effects of gelatin on zinc electrodeposition were investigated. It was found that the addition of gelatin profoundly modified the microstructure and crystallographic orientation of the zinc deposit. As the gelatin concentration increased, the mean grain size of zinc deposit was reduced and the basal plane preferred orientation was inhibited. The modification of the microstructure and orientation by gelatin increased microhardness of the zinc coating. However, the corrosion protection property which was assessed by potentiodynamic polarization test was not significantly changed.</p> <p> In the study on composite coatings, the incorporation of ceramic particles in the zinc deposit was characterized as a function of the deposition solution composition. The effect of ceramic particles on the hardness of the composite coatings was assessed by microhardness. The corrosion potential of the composite coating was determined by potentiodynamic polarization tests. The results showed that decrease in solution pH and addition of gelatin promoted the co-deposition of ceramic particles with zinc. The mechanical and corrosion properties of conventional zinc coatings were improved by the incorporation of ceramic particles.</p> / Thesis / Master of Applied Science (MASc)

京都大学 / 新制・課程博士 / 博士(エネルギー科学) / 甲第24713号 / エネ博第456号 / 新制||エネ||85(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 野平 俊之, 教授 萩原 理加, 教授 佐川 尚 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

Engineered components can gain desirable properties when coated with surface materials. Wear-resistant coatings can improve the performance of contacting surfaces and allow for an extended life of the parts. Hard chromium has been the plating material of choice for certain wear and corrosion- resistant coatings because of its desirable combination of chemical resistance, adhesion, and mechanical properties. However, hexavalent chromium, a component of the process for applying hard chromium coatings, has been recognized by the EPA as having hazardous health and environmental impacts. Existing and planned environmental regulations restricts the use of process chemicals containing hexavalent chromium ions. This substantiates a need to develop an environmental friendly process for alternative coatings. Praxair has reported that Cr-Ni-C particles have a better corrosion resistance than current chromium carbide and nickel chromium powders. Today, Cr-Ni-C provides great qualities for flame spray and does not contain the toxic compounds used to deposit hard chromium, but is not compatible with application by cold spray. The purpose of this thesis project is to compare two processes for plating metal powder, chromium nickel carbide (Cr-Ni-C, CRC-410-1 from Praxair), with nickel. The particles were encapsulated using three different methods: one electroplating method previously used on particles, and two electroless plating processes using different solutions. The Cr-Ni-C particles were successfully encapsulated with Ni by one of the electroless deposition methods. The electrolytic deposition experiments did not yield the uniformity of coating without agglomeration that is being attained in industrial practice today. Further research on this method is recommended, due to the material operational cost in an industrial setting that is projected to be over 200 times cheaper than electroless deposition method. In the meantime, it should be possible to produce enough coated powder by electroless deposition to validate the utility of this coated powder in depositing wear- and corrosion-resistant coatings of Cr-Ni-C by cold spray.

Ferroelectric-reinforced metal matrix composites (FR-MMCs) offer the potential to improve damping characteristics of structural materials. Many structural materials are valued based on their stiffness and strength; however, stiff materials typically have limited inherent ability to dampen mechanical or acoustic vibrations. The addition of ferroelectric ceramic particles may also augment the strength of the matrix, creating a multifunctional composite. The damping behavior of two FR-MMC systems has been examined. One involved the incorporation of barium titanate (BaTiO3) particles into a Cu- 10w%Sn (bearing bronze) matrix and the other incorporating them into an electroformed Ni matrix. Here the damping properties of the resulting ferroelectric reinforced metal matrix composites (FR-MMCs) have been investigated versus frequency, temperature (above and below the Curie temperature of the reinforcement), and number of strain cycles. FR-MMCs currently represent a material system capable of exhibiting increased damping ability, as compared to the structural metal matrix alone. Dynamic mechanical analysis and neutron diffraction have shown that much of this added damping ability can be attributed to the ferroelectric/ferroelastic nature of the reinforcement. / Ph. D.

Nonwetting surfaces including superhydrophobic (SHS) and liquid infused surfaces (SLIPS) exhibit diverse exceptional characteristics promoting numerous application opportunities. Engineered textured surfaces demonstrate multiple features including drag reduction, fouling reduction, corrosion resistance, anti-fogging, anti-icing, and condensation enhancement. Integrating these properties, nonwetting surfaces have shown significant potential in improving the efficiency of energy applications. The first part of the thesis work aims at developing a fundamental mathematical understanding of the wetting process on the solid surface followed by presenting fabrication methodologies specifically focused on metallic substrates. The second part of this thesis presents an exhaustive survey on recent advancements and researches about features of nonwetting surfaces that could be implemented in major industrial applications. To establish how realistically these features could enhance the real-life applications, the third part of this work investigates the dynamic performance and economic benefits of using textured surfaces fabricated using an electrodeposition process for condenser tubes in thermoelectric power plants. The textured surfaces are expected to provide enhanced performance by deterring fouling and promoting dropwise condensation of the steam on the shell side. Using a thermal resistance network of a shell and tube condenser, detailed parametric studies are carried out to investigate the effect of various design parameters on the annual condenser performance measured in terms of its electric energy output of a representative 550 MW coal-fired power plant. A cost modeling tool and a new Levelized cost of condenser (LCOC) metric have been developed to evaluate the economic and performance benefits of enhanced condenser designs. The LCOC is defined as the ratio of the lifetime cost of the condenser (and associated costs such as coating, operation and maintenance) to the total electric energy produced by the thermoelectric power plant. The physical model is coupled with a numerical optimization method to identify the optimal design and operating parameters of the textured tubes that minimizes LCOC. Altogether, the study presents the first effort to construct and analyze enhanced condenser design with textured tube surfaces on annual thermoelectric power plant performance and compares it against the baseline condenser design with plain tubes. / Master of Science / Liquid repellant surfaces have attracted lots of attention due to their numerous promising characteristics including promoting condensation, drag reduction, prohibiting fouling/deposition, corrosion, and fog/dew harvesting. These attributes have the potential to inspire a variety of applications for these surfaces in power plants, automotive and aviation industries, oils/organic solvents clean-up, fuel cells, solar panels, membrane distillation, stone/concrete protection, surgical fabrics, and biological applications, to name a few. Some of these applications have reached their potential for real-life implementation and more are still at the research phase needing more experimental and fundamental studies to get them ready. The first part of this study presents the fundamentals of the wetting process. Next, fabrication methods for metallic surfaces have been explored to identify the most scalable and cost-effective approaches which could be administered in large scale industrial applications. A comprehensive review of recent publications on features of nonwetting surfaces has been carried out and presented in the second part of this thesis. To establish how realistically these features could enhance the real-life applications of a thermo-economic a performance model is developed for a powerplant condenser in the third section. Through a simple and cost-effective electrodeposition process, the common condenser tubes are modified to achieve textured tubes with superhydrophobic properties. The influence of using textured tubes on the plant's performance and its economic benefits are investigated to predict the potential promises of nonwetting surfaces.

The optimal conditions for deposition of nickel coating and Ni-layered double hydroxide metal matrix composite coatings onto stainless steel discs in a modified all-sulfate solutions have been examined. Nickel films provide good general corrosion resistance and mechanical properties as a protective layer on many metallic substrates. In recent years, there has been interest in incorporation nano-dimensional ceramic materials, such as montemorillonite, into the metal matrices to improve upon the corrosion and mechanical properties. Layered double hydroxides have been used as corrosion enhancer in polymer coatings by increasing mechanical strength and lowering the corrosion rate but until now, have not been incorporated in a metal matrix by any means. Layered double hydroxides can be easily synthesized in a variety of elemental compositions and sizes but typically require the use of non-polar solvents to delaminate into nanodimensional colloidal suspensions. The synthesis of a Zn-Al LDH has been studied and characterized. The effects of the non-polar solvents dimethylformamide and n-butanol on the deposition and corrosion resistance of nickel coatings from a borate electrolyte bath have been studied, a nickel-LDH nanocomposite coating has been synthesized by electrochemical deposition and the corrosion resistance has been studied. Results indicate an improvement in corrosion resistance for the coatings with minimal change in the nickel matrix's internal strain and crystallite size.

Yes / The tribological performance of a nanocrystalline coating is heavily influenced by its composition, morphology, and microstructural characteristics. This research work describes the effect of heat treatment temperature on the microstructural, morphological, and mechanical behavior of nanocrystalline Ni/TiO2 coatings produced by electrophoresis. The surface morphology and coating cross section were characterized by scanning electron microscopy (SEM). The composition of coatings and the percentage of TiO2 nanoparticles incorporated in the Ni matrix were studied and estimated by using an energy-dispersive spectroscopic (EDS) analysis, while x-ray diffractometry (XRD) was used to investigate the effect of heat treatment temperature on phase structure. The results showed agglomeration of TiO2 nanoparticles on the surface of the coating. The high hardness and wear resistance recorded for the as-deposited coating was attributed to the uniform distribution of TiO2 nanoparticle clusters throughout the cross section of the coating. Heat treatment of the Ni/TiO2 coatings to temperatures above 200 °C led to significant grain growth that changed the surface morphology of the coating and reduced the strengthening effects of the nanoparticles, thus causing a reduction in the hardness and wear resistance of the coatings.

<div>Self-assembled templates allow the creation of many complex arrays of nanostructures, which would be extremely difficult and expensive, if not impossible, to realize using any of the other available fabrication techniques. The complexity of these advanced nanostructures, synthesized using the various template assisted electrodeposition techniques, can be controlled to nanometer scale range by tuning the structural properties of the template, which is achieved by adjusting its various growth parameters during the self-assembly process.</div><div>Electrodeposition allows the creation of arrays of various metallic and semiconducting nanostructures. Monitoring the electrodeposition conditions permit the creation of single crystalline nanostructures of a particular material, or the formation of heterostructures using multiple electrodeposition steps. This work demonstrates the template assisted electrodeposition of vertically aligned nanowire arrays, both straight and branched, of metals, and a direct bandgap, III-V semiconductor, indium antimonide (InSb), which has one of the smallest known bandgap of any material. The template assisted electrodeposition of metallic, and InSb inverse opal (IO) structures is also shown, and the fabrication of a novel zipper shaped nanostructure by laser photomodification of a Ni IO structure is reported.</div><div>The optical characterization of the various nanostructures realized in this work have been examined. The results from this work confirm the ability to tune the optical spectra of nanostructures of the same material with similar volume fill fractions by structural modulation, where the different optical responses can be attributed to the structural differences of the actual structure as opposed to the material properties of the solid.</div>

Ni electrodeposition is a suitable process for producing thick deposits and thick metallic microstructures, especially for producing relatively deep micromoulds in Microsystems industry. Ni-P deposits, due to their better properties compared to Ni deposits – particularly high mechanical properties (hardness, wear resistivity), corrosion resistance, magnetic properties, a higher fatigue limit and lower macroscopic deformation – can be a very good alternative for producing Microsystems, especially for MEMS or Microengines. According to few limited literature and our primary investigations, dispersion coating and adding particle into the electrolyte can be considered as an approach in order to decrease the stress and ease the deposition of Ni-P galvanically. Although in the last decades the influence of particles embedment in the matrix by electroplating techniques have attracted the scientific interest, there are still contradictions among the research community concerning the influence of codeposited particles on the microstructure and strengthening properties of Ni-based composites coatings. In many cases, it is believed that the enhanced mechanical performance of the coatings is mainly caused by a change in the microstructure of the metal matrix and not so much by the presence of the particles themselves. In other words, the role of particle characteristics - like their nature, size and concentration - on the layer features and strengthening mechanism of electrodeposited Ni-based composite coating with different matrix is not cleared well. Furthermore, the incorporation of particles into the deposit is mainly considered as a key factor for determining the composite coatings properties. Despite of existing models of ECD, the mechanism of particle incorporation into the film under influence of different particle characteristics has not been well understood yet. Therefore, the main aim of this study is to shed light on the effect of particle characteristics (size, concentration, type) on the codeposition process, microstructure and strengthening mechanisms in Ni and Ni-P electrodeposited composite coatings.