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京都大学 / 新制・課程博士 / 博士(工学) / 甲第23503号 / 工博第4915号 / 新制||工||1768(附属図書館) / 京都大学大学院工学研究科機械理工学専攻 / (主査)教授 黒瀬 良一, 教授 花崎 秀史, 教授 岩井 裕 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Two types of solder samples, pins and through-holes were tested by SERA™ (Sequential Electrochemical Reduction Analysis) and Wetting Balance after various length of steamaging treatment. It was shown that after steam-aging, both types of specimen gave a similar electrochemical reduction curve, and solderabilty predictions made from SERA™ test agree with results obtained from Wetting Balance test on a qualitative base. Wetting balance test of pin samples after SERA™ test confirmed that SERA™ is a non-destructive testing method -- it even restored solderability. Comparison of electrochemical reduction behavior of samples under different treatment indicates that steam-aging can not reproduce exactly the effect of naturally atmospheric aging, and may not be the best artificial accelerating environment adopted.

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other / no / The effect of sulphuric acid on the chemical and physical behaviour of the piston ring lubricant in a marine engine cylinder was investigated. To reveal the basic influence of H2SO4 on the lubricant film, the saturated hydrocarbon Squalane (C30H62) was chosen as a simple model oil. The interfacial tension between aqueous H2SO4 (0-98% w/w) and C30H62 was measured between -3 and 165 degrees C to understand droplet formation in the lubricant. Interfacial tension decreases with increasing acid concentration and is temperature dependent. / The wettability of engine parts with corrosive sulphuric acid was characterised by the contact angle. The contact angle of H2SO4 (0-98% w/w) on a grey cast iron cylinder liner material (Wartsila, RT84) and a piston ring chrome-ceramic coating (Federal Mogul Goetze, CKS, empty set960 mm) immersed in C30H62 was measured over a temperature range from 20 to 165 degrees C. In general, larger contact angles were measured under higher temperature conditions and on chrome surfaces. / In addition to the physical measurements, chemical reaction between H2SO4 and C30H62 was observed which influenced the interfacial tension, visual appearance, phase separation and formation of solid matter. The reaction time was found to be faster than the neutralisation times of commercially formulated lubricants. The reaction products were analysed using FTIR spectroscopy and EDX to find oxidation and sulphonation.

In the atmosphere in the height of 18000ft to 25000ft, there are some metastable droplets called supercooled liquid water in the temperature range of 0◦C to 40◦C. When these droplets impinge on the wings of an airplane, a very thin layer of ice is formed on the surface. This natural phenomenon calls “impact icing”. In this research, I studied the nanoscale impact icing on structured graphite surfaces, as the substrates at the atomistic scale using Molecular Dynamics (MD) simulations. This research focuses on the first steps of the development of a predictive multiscale strategy for molecular simulations of impact ice adhesion on nanostructured substrates. Through the simulations, the molecular level physics such as molecular interactions, interfacial energy, and nanoscale surface roughness are processed into a “microscopic ice adhesion strength” that describes the energy cost for breaking the nanoscale interfacial layer. In this work, the simulation strategy is designed based on the postulate that at the nanoscale the fracture strength of impact ice on a given substrate is controlled by the extent of the ice interdigitating the substrate. The interdigitating interfacial structure is then determined by the process of wetting the substrate by a supercooled impinged water droplet and the process of penetrating of supercooled water crystallizing into ice crystals under graphene nanoconfinement. Following this line of reasoning, I divided my impact icing simulations into three separate sections including (1) simulations of dynamic wetting of supercooled water on nanostructured graphene substrate, (2) simulations of water crystallization under nano-confinement, and (3) simulations of fracture of prescribed ice-substrate interfacial structure. Based on the results, it is concluded that the degree of surface hydrophobicity, depth of penetrated water, the order of interlocked water molecules, size of surface roughness, texture structure of the surface, and ice temperature are the key roles that dominate the investigation of fracture strength of impact ice at the solid interface. Furthermore, MD simulation results demonstrate that the surface roughness lower than 3.0nm is enabled to stop water from crystallization, a piece of useful information to design anti-icing surfaces.

Wetting behaviors influence many aspects of life and industry from consumer product goods to oil recovery to cosmetics. While the traditional solid-liquid-vapor (SLV) system has been studied for many years now, wetting transitions in the solid-liquid-liquid (SLL) system has remained relatively unexplored. The purpose of this work is to bring light to the wetting transition of the solid-liquid-liquid system and to understand the replacement rates of initially hydrocarbon-filled microscopic cavities with water and the factors affecting these rates. Factors studied were viscosity, density, diffusion related properties, and surface related properties in both hydrocarbon-saturated and hydrocarbon-non-saturated conditions. Cylindrical microscopic cavities were etched in a silicon wafer, filled with various organic solvents dyed with fluorophores, then submerged in water. Through fluorescence microscopy techniques, the transition or replacement rates of the initially hydrocarbon-filled cavities with water in both hydrocarbon-saturated and hydrocarbon-absent water conditions are observed. Among the factors we investigated, namely viscosity, density, surface chemistry, and diffusive flux (composed of solubility and diffusivity), diffuse flux dominated replacement rates in hydrocarbon-absent water conditions. By using hydrocarbon-saturated water, diffusive flux was minimized, allowing for deeper investigation of other factors. In the hydrocarbon-saturated scenario, replacement rates are largely affected by initial fluid motion, specific cavity geometry, and cavity penetration mechanisms. Image analysis reveals the geometry of the oils in the cavities and shows how the transition from hydrocarbon-fully-filled to hydrocarbon-partially-filled states occurs in the SLL system.

Third-generation advanced high-strength steels (3G AHSS) are being developed to assist in vehicle light weighting so that fuel efficiency may be improved without sacrificing passenger safety. 3G-AHSS have received significant interest from the automotive industry as a critical candidate for their unique combination of high strength and ductility. However, due to selective oxidation of the principal alloying elements such as Mn, Si, Al, and Cr at the steel surface during the annealing stage prior to immersion in the galvanizing Zn(Al, Fe) bath, the process of continuous hot-dip galvanizing of these steel is challenging. This thesis determined the influence of annealing process parameters such as oxygen partial pressure and annealing time, on the selective oxidation and reactive wetting of an Fe-0.15C-5.56Mn-1.17Si-1Al (wt%) prototype 3G AHSS during intercritical annealing as well as continuous galvanizing. Simulated annealing and galvanizing were conducted on the prototype Fe-0.15C-5.56Mn-0117Si-1Al (wt%) 3G steel; Intercritical annealing heat treatments were carried out at 690˚C in a N2-5 vol pct H2 process atmosphere under dew points of 223 K (–50 °C), 243 (–30 °C) and 268 K (–5 °C). MnO was the major oxide formed at the outmost layer of the external oxides on all annealed samples. The experimental parameters, on the other hand, had a substantial impact on the morphology, distribution, thickness, and surface oxide coverage. The greatest Mn surface concentration as well as maximum surface oxide coverage and thickness was obtained by annealing the panels under the 223 K (–50 °C) and 243 (–30 °C) dp process atmospheres. The oxides formed under these process atmospheres largely comprised coarse, compact, and continuous film nodules. In contrast, MnO nodules formed under the 268 K (–5 °C) dewpoint process, exhibited wider spacing between finer and thinner nodules, which was consistent with the internal oxidation mode, while under 223 K (–50 °C) dp process atmosphere, generally external oxidation took place. Poor reactive wetting was obtained for the panels annealed under the 223 K (–50 °C) dp process atmosphere for both the 60 s and 120 s holding times as well as the 243 K (–30 °C) dp process atmosphere for 120 s. This was attributed to the formation of a thick, compact oxide layer on the steel surface, which acted as a barrier between the substrate and Zn bath, preventing Fe dissolution from the substrate surface for the formation of the desired Fe2Al5Znx interfacial layer. However, a well-developed interfacial Fe-Al intermetallic layer was formed under the 268 K (–5 °C) and 243 (–30 °C) dp process atmospheres for intercritical annealing times of 60 s, which is indicative of a good reactive wetting since the thinner and nodule-like oxides on the steel surface after annealing encourage the reactive wetting. External oxides morphology plays a dominant role in facilitating the contact between Zn-alloy bath and the substrate via different mechanisms such as aluminothermic reduction which occurred for the sample annealed under the 268 K (–5 °C) dp process atmosphere. / Thesis / Master of Applied Science (MASc)

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