In engineering practice it is important to know which factors affect the thermal and electrical resistance of metal contacts. This thesis is to investigate some of these factors such as surface roughness and contact pressure. Thermal electrical contact resistance ratios for metal contacts were calculated from the experimental data. The technical literature was searched, and several papers were found in which either thermal or electrical contact resistance was studied separately. However, none of the papers recorded data for both thermal and electrical resistances for the same samples. The information found in these papers has been used as a background for understanding the nature of thermal and electrical contact resistance. Both of these contact resistances are primarily a function of the load on the contact and the condition of the surfaces. At low pressures only a small fraction of the total gross area of the contacts is in metal-to-metal contact. Increasing the load, flattens the “hills” and reduces both the thermal and electrical contact resistance. This phenomenon is called “spreading resistance” since the flow of heat or electrical current must spread out after they pass through the restricted areas that are actually in contact. Another type of thermal and electrical resistance, which is called “interface resistance", is caused by a film of foreign material such as an oxide, etc. on the surfaces of the contacting “hills”. If the space between the “hills” of a contact is filled with air, there is a heat flow by convection currents. The literature indicates this quantity of heat flow is approximately one thousandth of the total heat flow through metal contacts. Since the only electrical current conduction mechanism acting between areas not in actual metallic contact is that due to thermionic emission, the electrical resistance for these areas will be extremely high at room temperature for which thermionic emission is negligible. The experimental apparatus to measure both the thermal and electrical contact resistances consists mainly of a bellows-actuated press which is operated remotely under a vacuum bell. The press pressure loads the sample metal wafers. A thin film heat meter is used to indicate the quantity of heat flowing through the metal contacts. The temperature drop caused by the contacts is measured with thermocouples. The temperature difference and the quantity of heat flowing is used to calculate the thermal contact resistance. A strain gage on the bellows-press stem measures the loading on the contact surfaces. Electrical probes are used to measure the electrica1 resistance across the contact surfaces. The thermocouples and electrical resistance probes are permanently installed in the outer two smooth copper wafers. This makes it possible to quickly change to other sets of sample wafers of other metals and finishes. In order to use this permanent arrangement, it is necessary to finish two mating surfaces of the particular set of metal wafers to be tested, similar to the permanent smooth copper wafers so that these two extra mating contact resistances can be found and thus be subtracted from the overall contact resistance. The data indicates that the thermal-electrical contact resistance ratio can be changed by changing the load on the contacts. The heat meter had performed very well, and this new method of measuring heat flow will undoubtedly become a standard method of measuring heat flux.

When trace quantities of an alkali element are added to a flame, its optical and electrical properties change significantly. Addition of alkali seed to both premixed and diffusion flames has been used in the development of two new techniques, one for flame temperature measurement and the other for enhanced mixing. Advantage has been taken of the spectral characteristics of alkali seeds in the development of a non-invasive optical flame temperature measurement technique. The strongest resonance line of alkalis is in fact a doublet, and the two peaks can be subjected to different optical treatment. A cesium-seeded flame was exposed to radiation which was selectively filtered to yield different apparent source temperatures at the wavelengths corresponding to the doublet resonance lines. The ratio of the emission peak heights at the two wavelengths relates directly to flame temperature. This technique allows real-time measurement of flame temperatures up to 2800 K. A second process has been investigated which takes advantage of the enhanced electrical conductivity of alkali-seeded diffusion flames. The study first required a characterization of electrical discharges through planar diffusion flames. Because of the increase in conductivity, alkali-seeded diffusion flames can carry current when a transverse electric potential is applied. The behavior of diffusion flames carrying electrical current has been investigated. The dependence on electrode position and gap is reported and the behavior is contrasted with that described in the literature for premixed flames. A planar diffusion flame was subjected to a steady magnetic field parallel to the flow direction while an orthogonal, oscillating current passed through the flame sheet. A Lorentz body force was induced on the flame sheet which acted to move it alternately toward the fuel and oxidizer streams, improving bulk mixing in the flame. High-speed video images of the oscillating flame were analyzed to obtain its maximum lateral velocity. The results compared well with predictions from a simple theoretical model. / Graduation date: 1992

Yin, Weixin = 非晶液態鈀-鎳-磷合金相位分離的證據 / 殷瑋欣. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references. / Abstracts in English and Chinese. / Yin, Weixin = Fei jing ye tai ba-nie-lin he jin xiang wei fen li de zheng ju / Yin Weixin. / Acknowledgement --- p.i / Abstract --- p.ii / Contents --- p.iv / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- A Brief Introduction to Metallic Glass --- p.1 / Chapter 1.2 --- Homogeneous Nucleation Frequency --- p.3 / Chapter 1.3 --- Heterogeneous Nucleation Frequency --- p.4 / Chapter 1.4 --- Spinodal Decomposition --- p.5 / Chapter 1.5 --- Conditions for Metallic Glasses Formation --- p.8 / Chapter 1.6 --- How to Get Large Undercooling --- p.9 / Chapter 1.7 --- Liquid Phase Separation --- p.10 / References --- p.12 / Figures --- p.13 / Chapter Chapter 2 --- Experimental Procedures and Techniques of Transmission Electron Microscopy --- p.18 / Chapter 2.1 --- Sample preparation --- p.18 / Chapter 2.1.1 --- Ni2P Preparation --- p.18 / Chapter 2.1.2 --- Alloying --- p.18 / Chapter 2.1.3 --- Fluxing --- p.18 / Chapter 2.2 --- Introduction to TEM Specimen Preparation --- p.19 / Chapter 2.2.1 --- "Grinding, Polishing and Punching" --- p.19 / Chapter 2.2.2 --- Final Thinning by Ion Miller --- p.20 / Chapter 2.2.3 --- Final Thinning by Twin Jet --- p.20 / Chapter 2.3 --- Introduction to Transmission Electron Microscopy Techniques --- p.21 / Chapter 2.3.1 --- Basic Instrumentations of TEM --- p.21 / Chapter 2.3.2 --- Elastic Scattering and Inelastic Scattering --- p.21 / Chapter 2.3.3 --- Image Contrast --- p.22 / Chapter 2.3.4 --- Dark Field Image and Bright Field Image --- p.24 / Chapter 2.3.5 --- EDX Mapping --- p.24 / Chapter 2.3.6 --- High Resolution Images --- p.25 / References --- p.26 / Figures --- p.27 / Chapter Chapter 3 --- Evidence of amorphous/liquid phase separation in Pd41.25Ni41.25P17.5 alloy --- p.32 / Chapter 3.1 --- Introduction --- p.32 / Chapter 3.2 --- Experimental --- p.34 / Chapter 3.3 --- Discussions --- p.42 / References --- p.44 / Figures --- p.45 / Chapter Chapter 4 --- Conclusions --- p.68

by Chan Kim Wai. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references. / by Chan Kim Wai. / Chapter Chapter I --- Introduction / Chapter 1.1 --- Rapid solidification / Chapter 1.1.1 --- Rapid quenching --- p.1-1 / Chapter 1.1.2 --- Undercooling --- p.1-2 / Chapter 1.2 --- Grain refinement / Chapter 1.2.1 --- What is grain refinement? --- p.1-5 / Chapter 1.2.2 --- Previous results in grain refinement / Chapter 1.2.2.1 --- Pure metals (or dilute alloys) --- p.1-5 / Chapter 1.2.2.2 --- Alloys --- p.1-9 / Chapter 1.2.2.3 --- Semiconductor --- p.1-10 / Chapter 1.2.3 --- Critical crystal growth velocity V* --- p.1-11 / Chapter 1.2.4 --- Proposed models to grain refinement / Chapter 1.2.4.1 --- Dynamic nucleation and cavitation --- p.1-12 / Chapter 1.2.4.2 --- Remelting (melt-back) --- p.1-14 / Chapter 1.2.4.3 --- Interdendritic fluid flow --- p.1-15 / Chapter 1.2.5 --- Volumetric manifestation of grain refinement --- p.1-15 / Chapter 1.3 --- Aim of this project --- p.1-16 / References / Figures / Chapter Chapter II --- Experimental / Chapter 2.1 --- Pure palladium / Chapter 2.1.1 --- Sample preparation and procedure --- p.2-1 / Chapter 2.1.2 --- Limitation and choice of flux --- p.2-2 / Chapter 2.1.3 --- High temperature furnace --- p.2-3 / Chapter 2.1.4 --- Measurement of specific volume / Chapter 2.1.4.1 --- Theory --- p.2-4 / Chapter 2.1.4.2 --- Setup --- p.2-5 / Chapter 2.1.5 --- Observing internal morphology --- p.2-5 / Chapter 2.2 --- Palladium with insoluble impurity / Chapter 2.2.1 --- Choice of insoluble impurities --- p.2-6 / Chapter 2.2.2 --- Sample preparation --- p.2-7 / References / Figures / Chapter Chapter III --- Results and Discussion / Results / Chapter 3.1 --- Pure palladium / Chapter 3.1.1 --- Specific volume --- p.3-1 / Chapter 3.1.2 --- Grain structure and internal voids --- p.3-2 / Chapter 3.2 --- Palladium with insoluble impurity / Chapter 3.2.1 --- Pinning effect of insoluble impurities --- p.3-3 / Chapter 3.2.2 --- Pd-Ni-S system / Chapter 3.2.2.1 --- Grain refinement in Pd99.9Ni-S)0.1 --- p.3-4 / Chapter 3.2.2.2 --- Change of ΔT* with addition of sulfur --- p.3-5 / Chapter 3.2.2.3 --- Internal voids --- p.3-5 / Discussion / Chapter 3.3 --- Dynamic nucleation of Pd-Ni-S system --- p.3-6 / Chapter 3.4 --- Void formation of pure palladium and Pd-Ni-S --- p.3-6 / Chapter 3.5 --- Grain refinement and specific volume --- p.3-7 / Reference / Figures

by Yuen Cheong Wing. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references (leaves [138]-[142]). / by Yuen Cheong Wing. / Acknowledgments --- p.ii / Abstract --- p.iii / Table of Contents --- p.v / Chapter Chapter 1: --- Introduction --- p.1-1 / Chapter 1.1 --- What is Metallic Glass? --- p.1-1 / Chapter 1.2 --- Use of Metallic Glass --- p.1-3 / Chapter 1.3 --- A Dilemma --- p.1-4 / Chapter 1.4 --- Glass Forming Ability --- p.1-5 / Chapter 1.5 --- Role of Liquid State Phase Separation in GFA --- p.1-6 / References --- p.1-9 / Figure --- p.1-10 / Chapter Chapter 2: --- Phase Separation Theory --- p.2-1 / Chapter 2.1 --- Free Energy Curve --- p.2-1 / Chapter 2.2 --- Nucleation and Growth --- p.2-2 / Chapter 2.2.1 --- Liquid state nucleation and growth --- p.2-2 / Chapter 2.2.2 --- Nucleation and growth during solidification --- p.2-4 / Chapter 2.3 --- Spinodal Decomposition --- p.2-5 / Chapter 2.3.1 --- Cahn-Hilliard linearized equation --- p.2-6 / Chapter 2.3.2 --- Temporal evolution --- p.2-9 / References --- p.2-12 / Figures --- p.2-15 / Chapter Chapter 3 ： --- Experimental Setup and Techniques --- p.3-1 / Chapter 3.1 --- Technique in Achieving High Undercooling --- p.3 -1 / Chapter 3.1.1 --- Effects and limitation of B203 --- p.3-1 / Chapter 3.1.2 --- Preparation of B203 --- p.3-3 / Chapter 3.1.3 --- Cleansing of apparatus --- p.3-4 / Chapter 3.2 --- Experimental --- p.3-5 / Chapter 3.2.1 --- Sample preparation --- p.3-6 / Chapter 3.2.2 --- Experimental setup --- p.3-7 / Chapter 3.2.3 --- Procedures --- p.3-8 / Chapter 3.3 --- Observing the Microstructure --- p.3-9 / Chapter 3.3.1 --- Cutting --- p.3-10 / Chapter 3.3.2 --- Molding --- p.3-10 / Chapter 3.3.3 --- Polishing --- p.3-11 / Chapter 3.3.4 --- Etching --- p.3-12 / Chapter 3.3.5 --- Observation --- p.3-12 / References --- p.3-14 / Table --- p.3-15 / Figures --- p.3-16 / Chapter Chapter 4: --- Metastable liquid phase separationin undercooled molten PD40. 5]\l40.5P19 --- p.4-1 / Abstract --- p.4-1 / References --- p.4-9 / Figures --- p.4-10 / Chapter Chapter 5 ： --- Transformation in undercooled molten PD40.5NI40.5P19 --- p.5-1 / Chapter 5.1 --- Abstract --- p.5-1 / Chapter 5.1 --- Introduction --- p.5-2 / Chapter 5.3 --- Experimental --- p.5-4 / Chapter 5.4 --- Results --- p.5-6 / Chapter 5.5 --- Discussions --- p.5-13 / References --- p.5-20 / Figures --- p.5-22 / Chapter Chapter 6 ： --- Solidification of liquid spinodal in undercooled PD40.5NI40.5P19 --- p.6-1 / Chapter 6.1 --- Abstract --- p.6-1 / Chapter 6.2 --- Introduction --- p.6-2 / Chapter 6.3 --- Experimental --- p.6-3 / Chapter 6.4 --- Results --- p.6-5 / Chapter 6.5 --- Discussions --- p.6-10 / References --- p.6-17 / Figures --- p.6-18 / Chapter Chapter 7: --- Conclusion --- p.7-1 / References --- p.7-4 / Bibliography --- p.B-1

The thermal decomposition of silver permanganate, pre-irradiated in BEPO and in a ⁶°C₀ Ϫ 'hot spot' has been investigated in the temperature range 100 - 125°C. The results are similar to those for irradiated KMn0₄ and the mechanism proposed for the latter is again suggested. The activation energy for the migration of point defects over the induction period is 1.03 ev. The decompositions of unirradiated and irradiated crystals differ in that the latter undergo physical disintegration over the acceleratory period. X-ray studies immediately prior to disintegration show strain and fragmentation in the irradiated crystal. An explanation involving the annealing of point defects at dislocation is advanced to explain the changes produced in the p/t plots with increased dosage, and fixed decomposition temperature. Summary, p. 94.

A thesis submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy (Metallurgical Engineering) 2017 / The alloy Ti-2.7Al-5.7Fe-6Mo-6V (wt%), commercially known as Timetal 125, is used as a high strength fastener in aerostructure assemblies. Very little information is available on its properties and processing, and this study investigated its consolidation from low cost elemental powders, to achieve the minimum mechanical properties for use as a high strength fastener. Reactions during alloying and its beta transus were investigated by differential thermal analysis. The α+β phase region was established to lie between 590oC and 800oC by thermal analysis, metallography and XRD. The alloy was consolidated to ~99% theoretical density by semi-centrifugal casting, and spark plasma sintering of the blended powders. Various heat treatments were undertaken, and the microstructures were evaluated by optical and scanning electron microscopy. Tensile properties, hardness and density were measured after each heat treatment, to establish the optimal combination of mechanical properties. The experimental Timetal 125 style alloy was found to be a metastable beta titanium alloy, which could be strengthened by ageing. It had a microstructure consisting of alpha grains with fine beta precipitates in the as-cast condition, while the sintered samples had acicular precipitates and larger grains, due to the unusually long period that was required to sinter the samples. The ultimate tensile strength was >1500MPa, and elongation was ~3% in the as-cast condition, thus failing to conform to the Airbus EN6116 standard’s specification for ultimate tensile strength and elongation for a high strength fastener in the as-cast or sintered condition. After annealing the castings at 900oC for 1 hour, the ultimate tensile strength decreased to ~760MPa, while elongation increased to ~15%, which still did not conform to the Airbus standard, due to the low strength. The alloy was solution-annealed at 900oC, followed by water quenching to retain a fully βTi microstructure. The minimum properties for the Airbus standard were achieved after ageing between 500oC and 590oC for 1 hour, with an ultimate tensile strength of ~1285MPa, and elongation of ~6.3%. The strengthening depended on the amount and morphology of αTi precipitates from ageing. The αTi/βTi ratio increased with increasing temperature and holding time (shown by XRD), up to 590oC where the precipitates progressively transformed to βTi. Extending isothermal holding time coarsened the precipitates, which was deleterious to strength. There was generally a positive correlation between mean grain size and temperature or holding time, although competing transformations suppressed grain growth, particularly after heat treatment close to transformation temperatures. Although grain size had an effect on the strength of the Timetal 125 style alloy, the main mechanism was precipitation hardening by the secondary αTi. Extended ageing resulted in the formation of allotriomorphic alpha titanium, and a corresponding decrease in the ultimate tensile strength. It was not possible to subject the sintered samples to tensile testing, due to their shape. However, the sintered samples were less porous and had higher Vickers’ values than the castings, suggesting they had similar, if not higher tensile strengths. The acicular precipitates in the sintered samples were possibly martensite or omega titanium (ωTi, Pearson symbol hP3 and space group P6/mmm) although they were too fine to be detected by X-ray diffraction and too fine analyse separately by energy dispersive X-ray spectrometry. / MT 2017

by Guo Wenhua. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

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Orientador: Amauri Garcia / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-08T17:48:12Z (GMT). No. of bitstreams: 1 Silva_JorgeAyrtonda_M.pdf: 5941604 bytes, checksum: 9ec8b76ce4cbb57c06994f1a8307f767 (MD5) Previous issue date: 2007 / A análise térmica é amplamente utilizada como método de controle de processos metalúrgicos e na investigação da composição química de ferros fundidos na prática de fundição. Um meio confiável de avaliação da composição de ferros fundidos é disponibilizado pela técnica do Carbono Equivalente, que é baseada na mudança de inclinação da curva de resfriamento na temperatura liquidus durante o resfriamento de uma amostra de ferro fundido a partir do estado líquido. O presente trabalho é focado no desenvolvimento de um novo sensor para análise térmica, um sensor de imersão, que objetiva contribuir com determinações mais confiáveis de composição durante as operações de fundição. Foram desenvolvidos experimentos em diferentes empresas de fundição, utilizando-se tanto o sensor de imersão quanto o tradicional sensor tipo cápsula, normalmente utilizado na prática de fundição. As comparações de composições químicas, medidas por essas duas técnicas e medidas fornecidas por análise de espectrometria de emissão óptica, demonstram que geralmente o sensor de imersão fornece resultados mais confiáveis. Uma análise térmica realizada durante o resfriamento de ferro fundido em um dispositivo unidirecional com uma coquilha, e utilizando um conjunto de termopares, permitiu também a determinação quantitativa de variáveis térmicas de solidificação, tais como: coeficientes transitórios de transferência de calor metal/molde e molde/ambiente e taxa de resfriamento à frente da isoterma liquidus / Abstract: Thermal analysis is a widely used method for metallurgical process control and investigation of alloy composition of cast irons in foundry practice. A reliable means of rapidly evaluating the composition of cast irons is available by the Carbon-Equivalent technique, which is based on the change in thermal arrest temperature of the liquidus as the sample of molten cast iron freezes. The present work focuses on the development of a new sensor for thermal analysis, a dip-sensor, wich aims to contribute to more reliable determination of alloy composition during casting operation. Experiments were carried-out in different foundries by using both the dipsensor and the traditional capsule-sensor, which is normally used in foundry practice. The comparison of alloy compositions measured by these two techniques with analysis performed by Arc/Spark spectrometry has shown that generally the dip-sensor provides more reliable results. Thermal analysis conducted during cooling of molten cast iron in a unidirectional chill apparatus, by using a set of thermocouples, has also permitted the quantitative determination of solidification thermal variables, such as: transient metal/mold and mold/ambient heat transfer coefficients and tip cooling rates / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica