High performance polymer composites are materials with emphasis on specific chemical and mechanical properties due to their broad scope of applications. The main advantages are high strenght and toughness in comparison with their low weight and density. An increased adhesion at composite interfaces is important to ensure excellent composite properties. Bundles of glass fibers were coated by plasma-polymerised interlayers of tetravinylsilane (pp-TVS) of different thicknesses and at different effective powers. The prepared interlayers of pp-TVS were analyzed to evaluate chemical composition (RBS, FTIR, XPS) and mechanical properties (NI-AFM). Microindentation test and fiber-bundle pull-out test were used to determine the interfacial shear strenght.

The doctoral thesis is aimed at preparation of glass fiber reinforced polymer composites with controlled interphase formed by plasma-polymerized tetravinylsilane and tetravinylsilane/oxygen thin films. The thin polymer films of specific physico-chemical properties and thickness were deposited to improve interfacial adhesion of glass fiber/polyester composites. The fiber surface modification was performed by using plasma enhanced chemical vapor deposition in low-temperature RF plasma operating in an various effective power range and different treatment time. Test results were examined in relation to the interlayer thickness and different treatment conditions. The prepared interlayers were analyzed to evaluate physico-chemical composition and properties (XPS, RBS, ERDA, FTIR and spectroscopic elipsometry). Selected mechanical properties were evaluated by AFM. Mechanical response of plasma interlayers was evaluated by short beam shear test and direct method of testing the interfacial shear strength using microindentation. The interphase shear failure was controlled by the shear strength at the interlayer/fiber interface as follows from experimental and model data.

<p>  </p> <p>Room-temperature sodium-sulfur (RT Na-S) batteries are an emergent new technology that are highly attractive due to their low raw materials cost and large theoretical specific energy. However, many fundamental problems still plague RT Na-S batteries that prevent their progression from the research and development phase to the commercial phase. Sulfur and its final discharge product are insulators, and intermediate polysulfide discharge products are soluble in commonly used liquid electrolytes. As a result, RT Na-S cells exhibit large capacity defects, low coulombic efficiencies, and rapid capacity fading. Additionally, the reactive sodium metal anode can form dendrites during cycling, which reduces capacity and shortens cell life. One way to combat these issues is the judicious selection of electrolyte components. In this study, the effects of monoglyme (G1), diglyme (G2), and tetraglyme (G4) glyme ether electrolyte solvents on RT Na-S cell performance are investigated. Galvanostatic cycling of Na/Na symmetric coin cells reveals that the G2 solvent enable stable cycling at low overpotentials over a wide range of current densities. In contrast, the G1-based cells show evidence of dendritic plating, and G4-based cells are not suitable for use at high current densities. Electrochemical impedance spectroscopy during cycling confirms that the G2 solvent facilitates the formation of a strong, stable SEI on the Na electrode surface. Results from galvanostatic cycling of RT Na-S full coin cells demonstrates that G1-based cells deliver the highest initial specific discharge capacities among the three cell types, but G4-based cells are the most reversible. Infinite charging, the indefinite accrual of charge capacity at the high charge voltage plateau, affects all cell types at different cycle numbers and to different extents. This behavior is linked to the strength of the polysulfide shuttle during charge. Optical microscopy experiments show that G2 and G4 facilitate the formation of the S3•- sulfur radical, which reduces capacity. G1 minimizes the radical formation and thus delivers higher initial specific discharge capacity. In order to fully optimize the electrolyte for RT Na-S cells, future work should study glyme solvent blends, additives, and concentrated salts.</p>

炭素繊維強化樹脂系複合材料(CFRP)の界面あるいは界面層においては、CFの陽極酸化処理条件やサイジング剤の存在により、その化学的、物理的な機能が影響を受け、CFとマトリックス樹脂との接着性やCFRPの機械的特性に影響を及ぼすことを明らかにした。また、界面/界面層の化学的、物理的機能を把握し、その構造制御を行うことにより、CFRPの優れた機械的特性を有効活用できることを示した。 / Chemical and physical functions of interface/interphase of CFRP are affected by the condition of surface treatment of CF and the existence of sizing resin and consequently will make some significant effects on the mechanical properties of CFRP. In order to make the best use of the superior mechanical properties of CFRP, it is important to know the chemical/physical functions of interface/interphase of CFRP and control their strctures. / 博士(工学) / Doctor of Philosophy in Engineering / 同志社大学 / Doshisha University

Методом ориентационной микроскопии (EBSD) исследованы текстурные состояния сплава Ti-6Al-4V, изготовленного методом селективного электронно-лучевого плавления (СЭЛС). Установлено, что текстура β-фазы представлена текстурой кристаллизации, при которой направление <100>β параллельно направлению синтеза изделия. Текстура α-фазы является многокомпонентной и наследует текстуру β-фазы через ОС Бюргерса. Показано, что при последующем охлаждении в сплаве Ti-6Al-4V выделяется вторичная βII-фаза, кристаллографически отличная от высокотемпературной β-фазы. Предложена схема протекающих фазовых превращений. / The textural states of the Ti-6Al-4V alloy fabricated by a method of electron beam melting (EBM) were studied by orientation microscopy (EBSD). It was found that the texture of the β-phase is represented by the texture of crystallization, where the direction <100>β is parallel to the building direction. The texture of the α-phase is multicomponent and inherits the texture of the β-phase following the Burgers OR. It was shown that upon subsequent cooling in the Ti-6Al-4V alloy, a secondary βII-phase is precipitated, which is crystallographically different from the high-temperature β-phase. A scheme of the ongoing phase transformations is proposed.

<p>Sodium (Na)-ion battery displays many properties similar to Lithium (Li)-ion battery, such as operating principles and capacity, which noticeably compressed the Na-ion battery cathode exploration period. Having said that, anode materials of Na-ion battery is still underperforming as commercial graphite is inadequate in storing bulky Na ions. In the search for anode materials, both alloy-type and Na metal anode materials have gained popularity as these materials can absorb more charges and have higher storage capacity. It is essential to remember that such materials exhibit massive volume expansion upon sodiation and hence experience considerable mechanical stress upon cycling, leading to fractures and pulverization of the electrodes. In addition to electrode stability, ionic motions between the electrode and electrolyte are pivotal in determining the battery response. The decomposition of the electrolyte cocktails forms a passivation layer on the electrode surface, known as solid electrolyte interphase (SEI), which can rupture and regenerate in unstable cycles. Rickety SEI can cause the consumption of active Na and the formation of local hotspots for notorious dendrite growth, leading to short battery durability.</p> <p><br></p> <p>In the first part of the thesis, Tin (Sn) has been selected as an exemplar system to study the dynamic changes in a Na-ion battery. Higher ion-uptake capabilities of Sn electrode come with a price of large structural and morphological changes and can be controlled by careful charting of non-active phases such as binder and suitable electrolyte solution. This work comprehensively studies the technical challenges associated with Sn with different binder domains and in different liquid electrolyte environments. Parallelly, the sensitivity of the Na-Sn system towards the operating potential window and the crosstalk between the working electrode (alloying and de-alloying) and the counter electrode (plating and stripping) has been untied. Also, a fundamental understanding of the materials-transport-interface interactions during thermal abuse tests and their implication on the safety aspects of Na-ion batteries has been addressed. </p> <p><br></p> <p>Following that, the morphological stability of the Na metal anode is investigated based on the distinct electrochemical reactions arising from the composition of different liquid electrolytes. The role heterogeneity in the SEI layer of Na metal for the growth of dendritic patterns has been discussed. A unified framework incorporating a detailed electrochemical study of various electrolyte formulations, cognizant of the reactions and kinetics at the electrode-electrolyte interface, has been developed. To mechanistically counter the heterogeneity implications and synergistically leverage the electrolyte-additive-driven improvement in ionic transport, a flux-homogenizing separator has been introduced to extend the battery cycling. Based on this synergistic approach, the complex interplay between the homogeneity in SEI composition, electrodeposition/dissolution morphology, and cell performance in Na-metal-based batteries has been identified.</p> <p><br></p> <p>This work tried to offer fresh insights on fundamental mechanisms governing the evolution of the electrode-electrolyte interphases and their role in determining electro-chemo-mechano-thermal stability for future research endeavors in the Na-ion battery field. </p>

No description available.

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When bonded joints are subjected to harsh environmental conditions, the interphase, the three-dimensional region surrounding the adhesive/substrate interface, becomes critically important. Frequently, failure occurs in this region after adhesively bonded systems are subjected to elevated temperature oxidative aging. In a previous study, this was found to be the case with a polyimide adhesive bonded to chromic acid anodized (CAA) Ti-6Al-4V. The objective of the current research has been twofold: 1) to investigate the effect of thermal aging on the interphase region of polyimide/titanium adhesive joints, and 2) to evaluate the method used in the current study for durability characterization of other adhesive/substrate systems. The method used in this research has been to characterize the effect of elevated temperature aging on the following systems: 1) Notched coating adhesion (NCA) specimens and 2) bulk samples of dispersed substrate particles in an adhesive matrix. The NCA test has the advantages of an accelerated aging geometry and a mode mix that leads to failure through the interphase, the region of interest. The bulk samples have the advantage of an increased interphase volume and allow for the application of bulk analysis techniques to the interphase, a region that is traditionally limited to surface analysis techniques. The adhesive systems studied consisted of one of two polyimide adhesives, LaRC© PETI-5 or Cytec Fiberite© FM-5, bonded to CAA Ti-6Al-4V. The model filled system consisted of a PETI-5 matrix with amorphous titanium dioxide filler. Through the use of the NCA test, it was determined that bonded specimens made with FM-5 lose approximately 50% of their original fracture energy when aged in air at 177°C for 30 days. This aging temperature is well below the glass transition temperature of the adhesive, 250°C. At the same time, the failure location moves from the anodized oxide layer to the adhesive that is directly adjacent to the substrate surface, the interphase region. Through surface analysis of this region, it is determined that the adhesive penetrates the pores of the CAA surface to a depth of 70 to 100 nm, promoting adhesion at the interface. With aging, the adhesive in the interphase region appears to be weakening, although analysis of the bulk adhesive after aging shows little change. This indicates that adhesive degradation is enhanced in the interphase compared to the bulk. Analysis of the model filled system gave similar information. Specimens containing titanium dioxide filler had glass transition temperatures that were approximately 20°C lower than the neat polyimide samples. In addition, the filled samples contained a significant portion of low molecular weight extractable material that was not present in the neat specimens. The tan delta spectra from dynamic mechanical thermal analysis of the filled specimens exhibited a shoulder on the high-temperature side of the glass transition peak. This shoulder is attributed to the glass transition of the interphase, a distinct phase of the polyimide which is constrained by adsorption onto the filler particle surfaces. As a function of aging time at 177° or 204°C, the shoulder decreases substantially in magnitude, which may relate to loss of adhesive strength between the polyimide and the filler particles. From this research, it has been illustrated that information relating to the durability of adhesively bonded systems is gained using an interfacially debonding adhesive test and a model system of substrate particles dispersed in an adhesive matrix / Ph. D.

Over the past ten years, there has been increased use of electronic power processing in alternative, sustainable, and distributed energy sources, as well as energy storage systems, transportation systems, and the power grid. Three-phase voltage source converters (VSCs) have become the converter of choice in many ac medium- and high-power applications due to their many advantages, such as high efficiency and fast response. For transportation applications, high power density is the key design target, since increasing power density can reduce fuel consumption and increase the total system efficiency. While power electronics devices have greatly improved the efficiency, overall performance and power density of power converters, using power electronic devices also introduces EMI issues to the system, which means filters are inevitable in those systems, and they make up a significant portion of the total system size and cost. Thus, designing for high power density for both power converters and passive components, especially filters, becomes the key issue for three-phase converters. This dissertation explores two different approaches to reducing the EMI filter size. One approach focuses on the EMI filters itself, including using advanced EMI filter structures to improve filter performance and modifying the EMI filter design method to avoid overdesign. The second approach focuses on reducing the EMI noise generated from the converter using a three-level and/or interleaving topology and changing the modulation and control methods to reduce the noise source and reduce the weight and size of the filters. This dissertation is divided into five chapters. Chapter 1 describes the motivations and objectives of this research. After an examination of the surveyed results from the literature, the challenges in this research area are addressed. Chapter 2 studies system-level EMI modeling and EMI filter design methods for voltage source converters. Filter-design-oriented EMI modeling methods are proposed to predict the EMI noise analytically. Based on these models, filter design procedures are improved to avoid overdesign using in-circuit attenuation (ICA) of the filters. The noise propagation path impedance is taken into consideration as part of a detailed discussion of the interaction between EMI filters, and the key design constraints of inductor implementation are presented. Based on the modeling, design and implementation methods, the impact of the switching frequency on EMI filter weight design is also examined. A two-level dc-fed motor drive system is used as an example, but the modeling and design methods can also be applied to other power converter systems. Chapter 3 presents the impact of the interleaving technique on reducing the system passive weight. Taking into consideration the system propagation path impedance, small-angle interleaving is studied, and an analytical calculation method is proposed to minimize the inductor value for interleaved systems. The design and integration of interphase inductors are also analyzed, and the analysis and design methods are verified on a 2 kW interleaved two-level (2L) motor drive system. Chapter 4 studies noise reduction techniques in multi-level converters. Nearest three space vector (NTSV) modulation, common-mode reduction (CMR) modulation, and common-mode elimination (CME) modulation are studied and compared in terms of EMI performance, neutral point voltage balancing, and semiconductor losses. In order to reduce the impact of dead time on CME modulation, the two solutions of improving CME modulation and compensating dead time are proposed. To verify the validity of the proposed methods for high-power applications, a 100 kW dc-fed motor drive system with EMI filters for both the AC and DC sides is designed, implemented and tested. This topology gains benefits from both interleaving and multilevel topologies, which can reduce the noise and filter size significantly. The trade-offs of system passive component design are discussed, and a detailed implementation method and real system full-power test results are presented to verify the validity of this study in higher-power converter systems. Finally, Chapter 5 summarizes the contributions of this dissertation and discusses some potential improvements for future work. / Ph. D.