by Cho, King-sum. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves 108-110). / Text in English; abstracts in English and Chinese. / by Cho, King-sum. / Abstract --- p.i / 摘要 --- p.iii / Acknowledgment --- p.iv / Contents --- p.v / List of figures --- p.x / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Review of non-destructive techniques --- p.2 / Chapter 1.1.1 --- Liquid penetration technique --- p.2 / Chapter 1.1.2 --- Eddy current inspection --- p.2 / Chapter 1.1.3 --- Ultrasonic testing --- p.3 / Chapter 1.1.4 --- Radiography --- p.3 / Chapter 1.1.5 --- Magnetic testing methods --- p.4 / Chapter 1.2 --- Barkhausen emission --- p.4 / Chapter 1.3 --- The development of Barkhausen Emission --- p.5 / Chapter 1.4 --- The advantages of using Barkhausen emission --- p.6 / Figures for chapter1 --- p.8 / Chapter 2 --- Iron-carbon System --- p.9 / Chapter 2.1 --- Iron-iron carbide phase diagram --- p.9 / Chapter 2.2 --- Invariant reactions in the Fe-Fe3C phase diagram --- p.11 / Chapter 2.3 --- Classification of carbon steels --- p.12 / Chapter 2.4 --- Effect of heat treatment on plain-carbon steels --- p.13 / Chapter 2.4.1 --- Annealing and normalizing --- p.14 / Chapter 2.4.2 --- Slow cooling --- p.15 / Chapter 2.5 --- Process of recovery and recrystallization --- p.15 / Chapter 2.5.1 --- Recovery --- p.16 / Chapter 2.5.2 --- Recrystallization --- p.16 / Chapter 2.5.3 --- Grain growth --- p.17 / Figures for chapter2 --- p.18 / Chapter 3 --- Background Theory --- p.23 / Chapter 3.1 --- Ferromagnetism --- p.23 / Chapter 3.1.1 --- Localized moment theory --- p.24 / Chapter 3.1.2 --- Band theory --- p.25 / Chapter 3.1.3 --- Hysteresis loop --- p.25 / Chapter 3.2 --- Domain theory --- p.26 / Chapter 3.2.1 --- Magnetic domain --- p.26 / Chapter 3.2.2 --- Structure of domain wall --- p.27 / Chapter 3.2.3 --- Domain wall motion --- p.29 / Chapter 3.2.4 --- Magnetostatic energy --- p.30 / Chapter 3.2.5 --- Magnetization process --- p.32 / Chapter 3.3 --- Effect of applied stress --- p.33 / Chapter 3.3.1 --- Stress --- p.33 / Chapter 3.3.2 --- Magnetostriction --- p.34 / Chapter 3.3.3 --- Effect of stress on magnetization --- p.34 / Figures for chapter 3 --- p.37 / Chapter 4 --- Instrumentation --- p.39 / Chapter 4.1 --- Introduction --- p.39 / Chapter 4.2 --- Experimental setup for Barkhausen emission --- p.39 / Chapter 4.2.1 --- Magnetizing unit --- p.40 / Chapter 4.2.2 --- Signal detection unit --- p.41 / Chapter 4.2.3 --- Signal processing unit --- p.42 / Chapter 4.3 --- The typical BE profile --- p.42 / Chapter 4.4 --- Specimen treatment --- p.43 / Chapter 4.4.1 --- Optical microscope --- p.43 / Chapter 4.4.2 --- Vickers´ة hardness tester --- p.44 / Chapter 4.4.3 --- Thermal resistance furnace --- p.45 / Chapter 4.4.4 --- Instron loading machine --- p.45 / Figures for chapter4 --- p.47 / Chapter 5 --- Experiments and Results: Evaluation of Carbon Content in Steel --- p.52 / Chapter 5.1 --- Introduction --- p.52 / Chapter 5.2 --- Experiments and results --- p.52 / Chapter 5.3 --- Discussions --- p.53 / Chapter 5.3.1 --- The magnetization process --- p.53 / Chapter 5.3.2 --- The BE profiles 、 --- p.54 / Chapter 5.3.3 --- Hardness --- p.57 / Chapter 5.4 --- Conclusions --- p.57 / Figures for chapter5 --- p.58 / Chapter 6 --- Experiments and Results: The Effects of annealing on Barkhausen Emission in Mild Steel Bars --- p.64 / Chapter 6.1 --- Introduction --- p.64 / Chapter 6.2 --- Experiments --- p.64 / Chapter 6.3 --- Results and discussions --- p.64 / Chapter 6.3.1 --- The mechanical properties --- p.65 / Chapter 6.3.2 --- Grain size --- p.65 / Chapter 6.3.3 --- BE profiles --- p.66 / Chapter 6.4 --- Conclusions --- p.67 / Figures for chapter6 --- p.68 / Chapter 7 --- Experiments and Results: The Effects of Dynamic and Residual Stresses on Barkhausen Emission in Annealed Mild Steel Bars --- p.76 / Chapter 7.1 --- Introduction --- p.76 / Chapter 7.2 --- Experiments --- p.76 / Chapter 7.2.1 --- Measurement of dynamic loading (with samples of Set A) --- p.77 / Chapter 7.2.2 --- Measurement of residual stress (with samples of Set B) --- p.77 / Chapter 7.2.3 --- Measurement of continuous tensile stress (with samples of Set C) --- p.77 / Chapter 7.3 --- Results and discussions --- p.78 / Chapter 7.3.1 --- Peak ratio of the BE profile --- p.78 / Chapter 7.3.2 --- The initial peak value under the effects of increasing tensile stress --- p.81 / Chapter 7.4 --- Conclusions --- p.82 / Figures for chapter7 --- p.83 / Chapter 8 --- Experiments and Results: The Recovery of Strained Steel Bars by Annealing --- p.94 / Chapter 8.1 --- Introduction --- p.94 / Chapter 8.2 --- Experiments --- p.94 / Chapter 8.2.1 --- Measurement of annealed sample (Set D) --- p.95 / Chapter 8.2.2 --- Results of the Set E samples --- p.95 / Chapter 8.3 --- Results and discussions --- p.95 / Chapter 8.3.1 --- Hardness --- p.96 / Chapter 8.3.2 --- Peak ratio of the BE profile --- p.97 / Chapter 8.3.3 --- BE profile for the samples of Set E --- p.98 / Chapter 8.4 --- Conclusions --- p.99 / Figures for chapter8 --- p.100 / Chapter 9 --- Conclusions and Suggestions for Further Studies --- p.104 / Bibliography --- p.108

Law, Man Fai. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references (leaves 84-86). / Text in English; abstract also in Chinese. / Law, Man Fai. / Contents --- p.i / Abstract --- p.iii / Acknowledgement --- p.iv / List of Figures --- p.v / List of Tables --- p.ix / Chapter Chapter 1. --- Introduction --- p.1 / Chapter Chapter 2. --- Spectral Representation of Composite Materials --- p.4 / Chapter 2.1 --- Spectral method --- p.6 / Chapter 2.2 --- General properties --- p.10 / Chapter 2.3 --- Duality --- p.12 / Chapter 2.4 --- Dilute limit --- p.13 / Chapter 2.5 --- Effective-medium approximation (EMA) --- p.15 / Chapter 2.6 --- Moment expansions --- p.16 / Chapter Chapter 3. --- Local Field Effect and Depolarization Factor --- p.19 / Chapter 3.1 --- Isotropic homogeneous media --- p.20 / Chapter 3.2 --- Linear anisotropic homogeneous media --- p.22 / Chapter 3.3 --- Inhomogeneous anisotropic media --- p.24 / Chapter Chapter 4. --- Simulation on Correlated Microstructures --- p.26 / Chapter 4.1 --- Solving the nonlinear impedance networks --- p.27 / Chapter 4.2 --- Models of correlated microstructure --- p.29 / Chapter 4.2.1 --- Two-site correlated microstruture --- p.29 / Chapter 4.2.2 --- Environment correlated microstructure --- p.38 / Chapter 4.3 --- Conclusions --- p.45 / Chapter Chapter 5. --- Simulation on Anisotropic Microstructure --- p.46 / Chapter 5.1 --- Solving anisotropic impedance networks --- p.50 / Chapter 5.2 --- Simulation and results --- p.50 / Chapter 5.2.1 --- Parallel response --- p.51 / Chapter 5.2.2 --- Perpendicular response --- p.57 / Chapter 5.2.3 --- Unpolarized response --- p.61 / Chapter 5.3 --- Conclusions --- p.65 / Chapter Chapter 6. --- Conclusions --- p.66 / Appendix A. Symbolic Simulation --- p.67 / Chapter A.1 --- Formalism --- p.67 / Chapter A.2 --- Scaling Properties --- p.69 / Chapter A.3 --- The simulation --- p.71 / Appendix B. Fluctuation of Local Field in Composite Materials --- p.74 / Chapter B.l --- Simulations and Results --- p.74 / Appendix C. Lattice Animals in Correlated Network --- p.82 / Bibliography --- p.84

Free machining alloys containing soft immiscible phases in the aluminium (Al) matrix, like lead (Pb) and bismuth (Bi), are of great industrial interest. Typical applications in automotive industry are components requiring very high machinability, such as braking pistons and antiblocking system (ABS) housings. Presence of soft immiscible phases is giving their machining properties to this class of alloys. These phases melt due to localised heat build-up generated by machining process and induce chips breaking. Such type of alloys offers best in class performance when the soft phase is uniformly distributed in the Al matrix. The main objective of this work was to develop a method to tailor the distribution of the immiscible phase particles in the final solidified structure of DC cast billets in order to provide enhanced machinability while keeping low levels of Pb and/or Bi additions. As a consequence, another objective of this study was to improve recyclability of such alloys as well as to reduce their environmental impact. Three categories of Al-Pb alloys and different solidification paths were studied: hypermonotectic Al-3Pb, monotectic Al-1.2Pb and industrial hypo-monotectic free machining alloy containing both Pb and Bi. A newly developed melt conditioning combines mechanical, thermal and chemical treatments to obtain a very fine and uniform distribution of the immiscible phase droplets and eliminate compositional heterogeneities. The effect of these new melt treatments on microstructure was evaluated. For the soft phase droplets size was reduced and distribution becomes finer and more homogeneous under the individual effect of each of the treatments and optimum results obtained with the combination of them. These new melt treatments affect not only the nucleation of the Pb/Bi droplets, enhancing their heterogeneous nucleation but reduces considerably the Marangoni motion and Stokes sedimentation reducing therefore the droplet coalescence and restricting their growth. As a consequence of this improved microstructure, mechanical properties and machining performance were enhanced considerably. The results from this study provide a promising new microstructure with a fine and uniform distribution of droplets.

包含少於1000 個原子的金屬納米顆粒會與此金屬的常規尺寸材料有很大差別。它們擁有一些特殊的物理和化學的性質，因而在過去的二十年中吸引了大量的研究工作。但是由於尺寸太小，對於這些納米結構的深入和全面的研究十分困難。掃描隧道顯微鏡方法是一種強大的研究此類問題的技術。它擁有的極強的空間分辨力和原子操縱的能力使得我們可以獲得一些納米顆粒的細緻信息。在這篇論文中，我將報道我的關於在半導體Si(111)-(7x7)的重構表面的貴金屬（銀/金）顆粒的研究。 / 我首先研究了在Si(111)-(7x7)上的金屬顆粒的製備方法。使用熱蒸發方法，我製備了在Si(111)-(7x7)上的金屬顆粒。在研究了這些金屬顆粒在半元胞中的的整體生長過程之後，我的研究集中在本論文的主要目標--獨立的銀納米顆粒上。通過仔細觀察記錄單個銀原子的擴散過程，我們確認了Ag3‐Ag13 顆粒中的原子數目。這些掃描隧道顯微鏡的圖像同時也指出了這些顆粒的動態性質，包括自發跳動、分解和與鄰近的單個Ag 原子的合成。為了獲得對這些Ag 顆粒的控制，我們找到了一種垂直操縱單個Ag 原子的方法。在樣品的表面，掃描隧道顯微鏡的針尖通過特定的程序被用來抓起和放下單個Ag 原子。它被用來組裝和拆裝Ag的顆粒。各種Ag 顆粒在半元胞中被組裝，同時我們發現單個半元胞中的最大的顆粒是Ag25。同時這項技術被用來組裝複雜的Ag 顆粒的圖形。 / 使用上面這些操縱的技術（熱蒸發方法和原子操縱方法），我們細緻的研究了顆粒的兩方面性質：第一，我們發現對於單個元胞中的Ag 顆粒都存在着顯著的電學的整流效應，同時我們比較了它們各自的特點。通過實驗測量和第一性原理計算，我們發現這種電學整流效應源自電子態密度的耦合效應。當這些顆粒在平面內連接起來從而增加橫向的尺寸時，這種顆粒的整流效應將會繼續存在；但當顆粒形成多層Ag 的結構即垂直方向尺寸增加時，這個整流效應將會消失。另外一個所研究的性質是所有的Ag顆粒都存在一種對周圍單個Ag原子的吸引作用，從而讓自身長大的過程。這一過程對於Ag 顆粒的生長起到了至關重要的作用。我們選擇了幾個有代表性的顆粒，通過原子操縱的方法測量了它們與一個鄰近的Ag 原子的融合過程。測量的結果說明一個顆粒的存在通常會降低一個鄰近Ag 原子向此顆粒擴散的勢壘高度，同時也會影響此單個原子在靠近此顆粒的吸附位上的吸附能。 / Metal nanoclusters with less than 1000 atoms differ very much from their bulk counterparts. They possess many unique chemical and physical properties and have attracted extensive studies during the past two decades. However, in-depth and comprehensive researches of these structures are difficult for their small size. Scanning tunneling microscopy (STM) is a versatile technique to study the nanostructures. Its extreme powerful spatial resolution as well as its atomic manipulation capability enabled us to obtain the detailed information of some nano-clusters. In this thesis, I report on my studies on the noble metal (mainly Ag) clusters on the reconstructed Si(111)-(7x7) surface. / I firstly studied the fflbrication methods of the metal clusters on the Si(111)-(7x7) surface. By thermal deposition, I fabricated Ag clusters on Si(111)-( 7x7). After studying the overall growth process of the Ag clusters in half unit cells, I focused on the main target of this thesis: individual Ag clusters. By carefully observing the diffusion process of the Ag atoms on the surface, we identified of the number of atoms inside Ag3-Ag13 clusters. The STM images also showed the dynamic behaviors of each cluster, including self-hopping, dissociation and association with nearby Ag atoms. For a better controllability, a vertical manipulation technique was developed to transfer single Ag atoms across difference locations on the Si(111)-(7x7) surface. The STM tip was used to pick up or drop off metal atoms from or to the sud"ace following specific procedures. The assembly and disassembly of Ag clusters were achieved by this method. Various Ag clusters were built and the largest occupation of a FRUC was found to be 25 Ag atoms. This technique was demonstrated to be able to manipulate Au atoms and to assemble Au clusters. / With the developed fabrication methods, by thermal deposition as well as by atomic manipulation, two properties of the clusters were studied carefully: first, a prominent electrical rectifying behavior was observed for all the Ag clusters. Their individual behaviors were compared with each other. A combination of experimental measurements and first principle calculations unveiled the mechanism of the electronic rectifying behaviors to be a wave function coupling effect. The rectifying behavior for the clusters was found to persist when clusters connected laterally, whereas to disappear when the vertical size of the cluster increased to form multiple Ag layers. The second property studied is that all the clusters are found to attract nearby single Ag atoms to grow larger. This behavior plays a critical role in the growth process of the Ag clusters. we chose several typical Ag clusters and measured the merging process with single neighboring Ag atoms by atomic manipulation. The results indicate that the presence of a Ag cluster will mostly reduce the diffusion barrier of a single Ag atom in the neighboring half unit cells to diffuse to the cluster and even affect / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Ming, Fangfei = 在Si(111)-(7x7)表面的金屬納米顆粒的製備和性質 / 明方飛. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 116-122). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Ming, Fangfei = Zai Si(111)-(7x7) biao mian de jin shu na mi ke li de zhi bei he xing zhi / Ming Fangfei. / Chapter 1 --- Introduction: metal nano-clusters on semiconductor surfaces --- p.2 / Chapter 1.1 --- Background and Motivation --- p.2 / Chapter 1.1.1 --- Nano-science and nano-technology --- p.2 / Chapter 1.1.2 --- Metal nano-clusters --- p.3 / Chapter 1.2 --- Scanning tunneling microscopy (STM) --- p.6 / Chapter 1.2.1 --- Introduction to STM --- p.6 / Chapter 1.2.2 --- Basic components of STM --- p.7 / Chapter 1.2.3 --- STM working modes --- p.9 / Chapter 1.2.4 --- STM experiments in this thesis --- p.11 / Chapter 1.3 --- Substrate: the Si(111)-(7 x 7) reconstruction surface --- p.12 / Chapter 1.3.1 --- Atomic Structure --- p.12 / Chapter 1.3.2 --- Preparation in ultra high vacuum --- p.14 / Chapter 1.4 --- Growth of Ag on Si(111)-(7 x 7) at room temperature --- p.14 / Chapter 1.4.1 --- Growth method --- p.15 / Chapter 1.4.2 --- Adsorption and diffusion of single Ag atoms --- p.17 / Chapter 1.4.3 --- Forming Ag clusters --- p.20 / Chapter 1.4.4 --- Forming Ag islands --- p.23 / Chapter 1.5 --- Conclusion --- p.25 / Chapter 2 --- Individual Ag clusters: size, dynamics and stability --- p.27 / Chapter 2.1 --- Introduction --- p.27 / Chapter 2.2 --- Experiment --- p.29 / Chapter 2.3 --- Results and discussion --- p.31 / Chapter 2.3.1 --- Growth kinetics --- p.31 / Chapter 2.3.2 --- STrvr images of typical Ag structures Intra-HUC diffusion --- p.33 / Chapter 2.3.3 --- Inter-HUC diffusion --- p.37 / Chapter 2.3.4 --- Inter-HUC diffusion & identification of the number of atoms inside each cluster --- p.38 / Chapter 2.3.5 --- Stability of Ag structures. --- p.45 / Chapter 2.4 --- Conclusion --- p.49 / Chapter 3 --- Assembling and disassembling Ag/ Au clusters by atomic manipulation --- p.51 / Chapter 3.1 --- Introduction --- p.51 / Chapter 3.2 --- Experiment --- p.54 / Chapter 3.3 --- Results and disscussion --- p.55 / Chapter 3.3.1 --- Basic procedures for manipulating a single Ag atom --- p.55 / Chapter 3.3.2 --- Assembly of Ag clusters --- p.58 / Chapter 3.3.3 --- Disassembly of Ag clusters --- p.66 / Chapter 3.3.4 --- Assembly of Ag cluster patterns --- p.70 / Chapter 3.3.5 --- Comparison with the manipulation of Au atoms --- p.71 / Chapter 3.3.6 --- STrvr tip for atomic manipulation --- p.74 / Chapter 3.4 --- Conclusion --- p.75 / Chapter 4 --- Study on the electronic properties of the Ag clusters --- p.76 / Chapter 4.1 --- Introduction --- p.76 / Chapter 4.2 --- Experiment --- p.78 / Chapter 4.2.1 --- Experimental parameters. --- p.78 / Chapter 4.2.2 --- Precise tip positioning --- p.79 / Chapter 4.2.3 --- First principle calculation parameters --- p.80 / Chapter 4.3 --- Results and Discussion --- p.81 / Chapter 4.3.1 --- Grow Ag clusters --- p.81 / Chapter 4.3.2 --- I-V of the clusters. --- p.82 / Chapter 4.3.3 --- Theoretical calculation --- p.88 / Chapter 4.3.4 --- Transition from cluster to bulk in I-V. --- p.91 / Chapter 4.4 --- Conclusion --- p.94 / Chapter 5 --- Dynamics of Ag atoms near an interacting Ag cluster --- p.95 / Chapter 5.1 --- Introduction --- p.95 / Chapter 5.2 --- Results and Discussion --- p.97 / Chapter 5.2.1 --- Different Ag clusters and their orientations --- p.97 / Chapter 5.2.2 --- Association time measurement --- p.99 / Chapter 5.2.3 --- Energy barrier and diffusion prefactor --- p.101 / Chapter 5.2.4 --- Influenced intra-HUC diffusion --- p.105 / Chapter 5.2.5 --- Energy diagram --- p.107 / Chapter 5.3 --- Conclusion --- p.109 / Chapter 6 --- Conclusion and Future Work --- p.111 / Chapter 6.1 --- Conclusion --- p.111 / Chapter 6.2 --- Future work --- p.113 / Bibliography --- p.116

Ti-6Al-4V alloy has been used as biomedical implants for decades because of its superior mechanical properties, good biocompatibility, lack of allergic problems and good corrosion resistance. It is widely used as the tibial components in total knee arthroplastry and hip cup in total hip replacement. However, the mechanical properties of Ti-6Al-4V implant can be deteriorated due to corrosion pits. In the past decades, the rapid developments in additive manufacturing have broadened their applications in biomedical area due to the high geometrical freedom in fabricating patient-friendly implants. However, the high-localized thermal input and fast cooling rate during laser processing usually result in non-equilibrium phase with high residual stress. Therefore, it is necessary to apply proper post-treatments on the as-printed parts to ensure better properties. In this work, various post-treatments (e.g. post-heat treatments, hot isostatic pressing) were applied aim to improve the corrosion behavior of direct metal laser sintered Ti-6Al-4V parts. The effect of post-treatment temperature on the mechanical properties and corrosion behavior were examined experimentally. A discussion on factors influencing corrosion rate was presented, and the corrosion mechanism on the Ti-6Al-4V part in simulated body fluid was proposed. Based on the electrochemical measurement results, enhanced corrosion resistance was observed in the samples after high temperature HIPing at the annealing temperature (α+β region) of 799°C.

Les carraghénanes (Car) sont des polysaccharides linéaires sulfatés extraits d’algues rouges et sont très utilisés en tant qu’épaississants et gélifiant en industrie. Les rendements d’extraction ainsi que les propriétés physicochimiques de Car extraits de différentes espèces cultivées dans la baie de Cam Ranh au Vietnam ont été déterminés. Pour les variantes kappa et iota, les propriétés rhéologiques et de la microstructure en solution seuls ou en mélange à différentes concentrations en présence de CaCl2 ou de KCl. Leurs mélanges présentent une gélification thermique en deux étapes qui correspondent chacune aux gélifications du kappa et iota seuls. Cependant, pour les mélanges, l’élasticité du gel est nettement supérieure à la somme de celle des Car seuls. Des mesures en microscopie confocale et de turbidimétrie ont démontré que les gels obtenus avec le kappa étaient toujours plus turbides que ceux avec l’iota mais étaient moins turbides dans les mélanges. Au vus des résultats, un mécanisme de séparation de phase microscopique entre les deux Car semble très peu probable. Des mesures de FRAP (Recouvrance de Fluorescence Après Photo-blanchiment) ont permis de sonder la mobilité des chaînes de Car dans les gels pour les systèmes individuels ou les mélange. Dans tous les cas, il a été observée qu’une fraction des chaînes de Car reste mobile dans les gels. Cette fraction mobile varie de 25% à 75% selon le type de Car et le type/concentration en sel. Cette fraction n’est pas corrélée à la dureté du gel quelles que soient les conditions opératoires. De plus, il a été démontré que les chaines relarguées sont plus petites que la moyenne de l’échantillon initial. / Carrageenan (Car) is a polysaccharide extracted from red algae and is widely used as thickener, stabilizer and gelling agent in various products. Properties of Car extracted from different algae species cultured at Cam Ranh Bay in Vietnam were characterized. Kappa car extracted from K. alvarezii and iota Car from E.denticulatum were selected to study the rheological properties and the microstructure of individual and mixed car solutions in presence of CaCl2 and KCl. Mixtures showed a two-step gelation process with gelation temperatures that coincided with those of corresponding individual kappa and iota Car solutions. However, the stiffness of the mixed gels was much higher than the sum of the corresponding individual gels. Confocal laser scanning microscopy and turbidity measurements showed that the kappa Car gel was always more heterogeneous than the iota Car gel, but less in the mixture than in the individual system. The results show that microphase separation of iota and kappa Car in mixed gels is highly unlikely.The mobility of Car chains in individual gels of kappa and iota Car and their mixtures was determined using fluorescence recovery after photobleaching. Slow recovery was observed for the gels showing that a fraction of the Car chains remained mobile. The fraction of mobile chains in the gels varied between 25% and 75% depending on the type of Car and the type and concentration of salt. The fraction of mobile chains in gels was not correlated to the gel stiffness. These results were confirmed by the release of Car from gel fragments into excess solvent. It was found that released Car chains were smaller than the average size of the initial Car sample.

As propriedades de superfícies de pós cerâmicos desempenham um papel importante na produção de dispositivos de alta qualidade, elevado desempenho e confiabilidade. Muitas dessas propriedades estão relacionadas a interações com o meio em que o material esta presente. Um exemplo, são materiais cerâmicos utilizados em sensores de gases. A perovisquita BaSnO3 (estanato de bário) é um de material cerâmico promissor a sensor de gás. Neste sentido, a proposta do presente trabalho consistiu em realizar a síntese do composto BaSnO3 por reação no estado sólido e preparar cerâmicas com o objetivo de estudar suas propriedades estruturais, microestruturais e seu comportamento elétrico em função da atmosfera. As amostras foram caracterizadas utilizando-se as técnicas de termogravimetria, calorimetria exploratória diferencial, difratometria de raios x, microscopia eletrônica de varredura, dilatometria e espectroscopia de impedância. Para a produção do BaSnO3 foram utilizadas duas metodologias de síntese. A primeira, chamada de rota 1, a preparação foi realizada a partir da mistura direta dos pós precursores, sem aquecimento prévio. A segunda metodologia, denominada rota 2, os pós precursores foram submetidos a um aquecimento separadamente antes da mistura e síntese. Os resultados obtidos utilizando a rota 1 mostraram a presença de fases secundárias (SnO2 e BaCO3) ao material pretendido, além da formação de fase líquida durante o processo de sinterização das cerâmicas. Contudo, os resultados obtidos com o procedimento adotado na rota 2 mostraram apenas a presença da fase desejada e ausência de fase líquida durante a sinterização. Com o objetivo de assegurar que a presença de fases secundárias na rota 1 e a fase líquida observadas nas microestruturas foram devido a presença de água adsorvida nos pós precursores, corpos cerâmicos `a verde produzidos pela rota 2 foram submetidos a imersão em água por aproximadamente 10 horas antes da sinterização. Este procedimento não resultou no aparecimento de fases secundárias, como era esperado, porém verificou-se a formação de fase líquida durante o processo de sinterização. As cerâmicas assim processadas apresentaram menor densidade relativa e maior tamanho médio de grão. Para a caracterização elétrica das cerâmicas foram utilizados as seguintes atmosferas: ar, em condição de pressão distinta, argônio contendo 5% de hidrogênio e argônio contendo 15% de hidrogênio. Os resultados mostraram que o estanato de bário apresenta significativa sensibilidade relativa da condutividade elétrica para as atmosferas estudadas a temperaturas acima de 100oC. / The surface properties of ceramic powders play an important role in the production of devices of high quality, high performance and reliability. Many of these properties are related to interactions with the environment. One example, ceramics are used in gas sensor devices. A ceramic material that has been reported as promising gas sensor is perovskite BaSnO3 (barium stannate). In this work we performed the synthesis of the BaSnO3 compound by solid state reaction to study its structural properties, microstructure and electrical behavior in function of atmosphere. The samples were characterized by thermogravimetry, differential scanning calorimetry, x-ray diffraction, scanning electron microscopy, dilatometry and impedance spectroscopy. For the production of BaSnO3 used two methods of synthesis. the first method, called route 1, the preparation was performed directly from the mixing of powder precursors. The second, named as route 2, the precursor powders were subjected to heating separately before mixing. The results obtained using the route 1 showed the presence of secondary phases (SnO2 and BaCO3) and the formation of liquid phase during sintering of the ceramics. The results obtained with the procedure adopted in the route 2 showed only the presence of the desired (BaSnO3) phase and no liquid phase during sintering. In order to investigate what the effects caused by the water adsorption by perovskite BaSnO3, the green-ceramic bodies produced by route 2 were submitted to immersion in water prior to sintering. This procedure did not result in the appearance of secondary phases, but was verified the presence of the liquid phase, and the ceramics showed lower density and larger average grain size. For the electrical characterization we used the following atmospheres: vacuum, air, argon containing 5% hydrogen and argon containing 15% hydrogen. The results showed that the barium stannate shows a significant sensitivity to the conductivity in the studied atmospheres at temperatures above 100oC.

Este trabalho avalia as propriedades mecânicas, microestrutura resultante e força de estampagem da liga DIN 27MnCrB5 para o processo de estampagem a quente nas temperaturas de aquecimento de 750°C, 850°C e 950°C. Para isso foram realizados ensaios nas três temperaturas e medidos os valores da força necessária para a estampagem da chapa, que foi aplicada em uma área de 30mm x 1,50mm. A partir da peça estampada foram realizadas análises metalográficas da microestrutura resultante e medições de dureza para a correlação com as propriedades mecânicas. Para as temperaturas de aquecimento de 750°C e 850°C não foi verificada microestrutura martensítica nas peças estampadas. Para o ensaio realizado com uma temperatura de aquecimento de 950°C ocorreu transformação martensítica na peça na região que esteve em contato com o prensa chapa e a matriz. Esta transformação metalúrgica resultou em valores de dureza de 715±17HV0,2 em comparação com a condição inicial da chapa, cuja dureza era de 187±5HV0,2. As medições de força de estampagem para as três temperaturas de ensaio indicam uma redução da força com o aumento da temperatura de aquecimento da chapa. Para a temperatura de aquecimento da chapa de 750°C o valor médio da força de estampagem foi de 14kN, para a temperatura de 850°C o valor médio da força de estampagem foi de 9kN, enquanto para a temperatura de 950°C foi encontrado o valor médio de 5kN. / This work evaluates the mechanical properties, resulting microstructure and stamping force of the DIN 27MnCrB5 alloy for the hot stamping process at the heating temperatures of 750°C, 850°C and 950°C. For this, tests were carried out at the three temperatures and the values of the force required for the stamping of the sheet were measured, which was applied in an area of 30mm x 1,50mm. From the stamped part metallographic analyzes of the resulting microstructure and hardness measurements were performed for the correlation with the mechanical properties. For the heating temperatures of 750°C and 850°C, no martensitic microstructure was observed in the stamped parts. For the test performed with a heating temperature of 950°C martensitic transformation occurred in the part in the region that was in contact with the blank holder and the die. This metallurgical transformation resulted in hardness values of 715±17HV0,2 compared to the initial condition of the sheet, whose hardness was 187±5HV0,2. Stamping force measurements for the three test temperatures indicate a reduction in force with the increase of the sheet heating temperature. For the sheet heating temperature of 750°C the average value of the stamping force was 14kN, at the temperature of 850°C the average value of the stamping force was 9kN, while at the temperature of 950°C it was found The average value of 5kN.

Osteoporosis is a major metabolic bone disease that causes reduced bone mass, deteriorated bone microstructural and increased fracture risk. In clinical practice, the gold standard to examine bone quality and evaluate fracture risk is using dual energy X-ray absorptiometry through measurements of areal bone mineral density (aBMD). However, it has been well accepted that in addition to aBMD, bone geometry, microstructure and material properties also play important roles in determining overall bone mechanical competence, which is directly related to fracture risk. High-resolution peripheral quantitative computed tomography (HR-pQCT) has the capability to image three-dimensional (3D) bone microstructures in vivo and provide quantitative measurements of bone mineral density as well as cortical and trabecular microstructure. Based on the HR-pQCT images, micro finite element (µFE) models can be constructed to directly estimate bone strength. HR-pQCT has become a widely used imaging tool in clinical research to evaluate the effect of aging, drug treatment, and metabolic bone disease on bone quality. The work in this thesis focuses on evaluating the accuracy and capability of HR-pQCT in quantifying microstructural properties of human radius and tibia bone, exploring its prediction power of whole bone strength and discussing potential applications in clinical studies. In this thesis, we quantified the accuracy of the standard HR-pQCT microstructural measurements of human distal radius and tibia through comparisons with gold standard µCT-based morphological measures. The results showed that the BV/TVd, Tb.N*, Tb.Th and Tb.Sp from HR-pQCT were significantly and highly correlated with those from gold-standard µCT measurements. Strong correlations between the HR-pQCT µFE predictions and direct mechanical testing measures suggest that HR-pQCT µFE is a robust method to determine bone mechanical properties. In a clinical setting, standard HR-pQCT scans are performed on the non-dominant wrist (usually the left) and the corresponding tibia. However, the contralateral side is selected for scanned when there is a fracture the non-dominant wrist. It remains unclear whether the dominant side is representative of the non-dominant side and how much error it will bring into a study where subjects include mixed scans of both sides. In this thesis, we applied HR-pQCT and µCT based morphological and mechanical measurements to characterize the symmetric nature of distal radius and tibia. We found that the right radius tend to be larger than the left radius. However, at the tibia, the bone size was found to be similar between left and right. By micro computed tomography (µCT), microstructural parameters such as BV/TV were also found to be larger at the right radius, while no difference was found at the tibia. Trabecular number, trabecular thickness, trabecular separation and cortical thickness were not different between left and right radius. µFE analyses demonstrated that stiffness and strength of right radius were significantly higher than left radius, while there was no difference at the tibia. The standard clinical region of interest HR-pQCT is recommended by the manufacturer; however, it is not clear whether a segment HR-pQCT scan is representative of whole bone mechanical properties. Therefore we quantified the associations of microstructural and mechanical measurements of the radius and tibia segments with whole bone stiffness and examined if we can improve the correlation when we select a different region. The microstructural and mechanical measurements at the two regions next to the standard HR-pQCT segment (proximal and distal) were also examined. The results showed that the bone microstructure from proximal and distal sections is highly correlated to standard region at both distal radius and tibia. The mechanical properties of the three segments were strongly correlated with overall bone mechanical properties. The microstructural measurements at the most distal section were correlated with whole bone stiffness better compared to those from standard and proximal regions. DXA is incapable of discriminating patients with wrist fracture from those without. In this study, we examined the microstructural and mechanical properties in patients with and without wrist fracture through HR-pQCT based analyses. We demonstrated that wrist fracture patients had lower plate and rod bone volume fraction, less plate and rod trabecular number, thinner cortex and lower whole bone stiffness and strength, compared to healthy controls. Failure analyses also depicted significantly lower trabecular plate compression and tension failure fraction in wrist fracture patients.

Progressive bone loss and weakening bone strength associated with aging predispose the elderly population to osteoporosis and millions of costly fragility fractures. Micro finite element (µFE) analysis based on clinical high-resolution skeletal imaging provides an accurate computational solution to assessing the mechanical properties of bone, which can be used as the dominant factors for fracture risk. However, the current µFE analysis technique is impractical for clinical use due to its prohibitive computational costs, which result from the “voxel-to-element” approach of modeling human bone regardless of its microstructural pattern. I developed a novel plate-rod microstructural modeling technique for highly efficient patient-specific µFE analysis and translated it to clinical research for the assessment of bone strength in osteoporosis and fragility fractures. Trabecular microstructure is composed of interconnected plate-like and rod-like trabeculae. Instead of converting every image voxel directly into an element, the plate-rod modeling approach created mechanical characterization for every individual trabecular plate and rod. The validation studies demonstrated that the PR model was able to reproduce the morphology and mechanical behavior of the original trabecular microstructure, while reducing the size of the µFE model and improving the efficiency of µFE simulations. First, the PR models of trabecular bone were developed based on high-resolution micro computed tomography (µCT), and evaluated in comparison with computational gold standard-voxel µFE models and experimental gold standard-mechanical testing for estimating Young’s modulus and yield strength of human trabecular bone. Results suggested that PR model predictions of the trabecular bone mechanical properties were strongly correlated with voxel models and mechanical testing results. Moreover, the PR models were indistinguishable from the corresponding voxel models constructed from the same images in the prediction of trabecular bone Young’s modulus and yield strength. In addition, PR model nonlinear µFE analyses resulted in over 200-fold reduction in computation time compared with voxel model µFE analyses. In the effort of studying the heterogeneous bone mineralization in trabecular plates and rods, I developed an individual trabecula mineralization (ITM) analysis technique that allows quantification of the tissue mineral density of each individual trabecular plate and rod. By examining the variation of mineral density with trabecular types and orientations, it was found that trabecular plates were higher mineralized than trabecular rods. Furthermore, trabecular plate mineral density varied with trabecular orientation, increasing from the longitudinal direction to the transverse direction. ITM provided measurement of mineral density of each trabecular plate and rod, which was converted to trabecula-specific tissue modulus and used in the PR models to incorporate mineral heterogeneity in µFE simulations. Results suggested that heterogeneous PR models did not differ from the homogeneous PR models or specimen-specific PR models in their predictions of apparent Young’s modulus and yield strength of the human trabecular bone specimens from non-diseased donors. Based on the trabecular bone PR model, a whole bone PR model was developed for assessing whole bone mechanical strength at the distal radius and the distal tibia from high-resolution peripheral quantitative computed tomography (HR-pQCT). The accuracy of the whole bone PR model was evaluated on human cadaver radius and tibia specimens which were imaged using HR-pQCT and µCT, respectively, and tested to failure. The whole bone stiffness and yield load of the radius and tibia segments predicted by HR-pQCT PR models were strongly correlated with those predicted by corresponding HR-pQCT voxel models, µCT voxel models, and mechanical testing measurements. The PR models µFE results were indistinguishable from the voxel models constructed from the same HR-pQCT images. Moreover, the PR models significantly reduced the computational time for nonlinear µFE assessment of whole bone strength. After evaluating the accuracy and efficiency of the newly developed whole bone PR model, it was employed in a clinical study aimed at characterizing the abnormalities of trabecular plate and rod microstructure, cortical bone, and whole bone mechanical properties in postmenopausal women with vertebral fractures. Women with vertebral fractures had thinner cortical bone, and larger trabecular area compared to their non-fractured peers. ITS analyses suggested vertebral fracture subjects had deteriorated trabecular microstructure, evidenced by fewer trabecular plates, less axially aligned trabeculae and less trabecular connectivity at both radius and tibia. These microstructural deficits translated into reduced whole bone stiffness and yield load at radius and tibia as predicted by PR model nonlinear µFE simulation. More importantly, logistic regression indicated that whole bone yield load was effective in discriminating the vertebral fracture subjects from the non-fractured controls.