Metal hydrides are used as anode material in nickel metal hydride batteries and are of particular interest because of the potential to be a part of energy systems completely involving renewable sources (e.g. solar power, wind power etc.). Preparation and electrochemical characterization of metal hydride electrodes have not previously been performed at the Department of Chemistry – Ångström Laboratory. Two basic techniques that are desired to be used in the characterization are cyclic voltammetry and chronopotentiometry. This thesis work is aimed at preparation and electrochemical characterization of a metal hydride electrode and, as a complement, study the electrode with X-ray diffraction. LaNi3.55Co0.75Mn0.4Al0.3, a standard material for metal hydride electrodes previously studied by Khaldi et al. was chosen, to ensure that electrochemical absorption of hydrogen was possible, and to be able to compare electrochemical results [1-3]. LaNi3.55Co0.75Mn0.4Al0.3 was synthesized with arc melting, with additional annealing at 900˚C for five days, ground in a cemented carbide ball mill and sieved to less than 56 µm. Electrodes were prepared containing 90 wt.-% of LaNi3.55Co0.75Mn0.4Al0.3 powder, 5 wt.-% of polytetrafluoroethylene and 5 wt.-% of carbon black. The hydrogen absorption and desorption capabilities of the electrode were studied electrochemically with cyclic voltammetry and chronopotentiometry, and the structural changes associated with absorption of hydrogen was studied with X-ray diffraction. The capacity increased, probably from activation of the material, during initial cycling up to the maximum capacity of 294 mAh/g, obtained after 9 cycles, followed by a small decrease, probably caused by corrosion and passivation of the material, in capacity of the remaining 11 cycles. Activation of the material causes the charge and the discharge potential to shift to a more positive and a more negative value, respectively. The final values for the charge potential and the discharge potential were -841mV and -945 mV vs. Hg/HgO, respectively, after 16 cycles. Khalid et al. [1-3]reported a maximum capacity of 300 mAh/g, a charge potential of about -960 mV and a discharge potential of about -840 mV after 16 cycles the results obtained in this study are considered to be in good agreement with those reported. X-ray diffraction of the electrodes revealed, as expected, a cell volume change of the charged electrode compared to the discharged electrode. The change in cell volume corresponds to an estimated capacity of 303 mAh/g, which is very close to the, above mentioned, electrochemically obtained maximum capacity of 294 mAh/g.

In this thesis, we study high quality InN films grown on sapphire (0001) by plasma-assisted molecular beam epitaxy (PAMBE). We used double layers methods to reduce lattice mismatch successfully. In this experiment, we have two series of samples, about series of A use low temperature GaN (LT-GaN) as the buffer layer as compared with series of B use high temperature AlN (HT-AlN) as the buffer layer. By in situ reflection high-energy electron diffraction (RHEED), we got film¡¦s surface situation. Surface morphology of the samples was observed by atomic force microscope (AFM). By high resolution X-ray diffraction (HR-XRD) methods was analyzed quality and composition of InN films. Van der Pauw method (Hall) was used to determine carrier concentration and mobility. The optical properties of InN films under different growth conditions were investigated by photoluminescence (PL). By changing growth temperature of these samples, we found the series of A having some fine characters as the InN(0002) rocking curve was 343 arcsec and InN(10-12) rocking curve was nearly 1000 arcsec. The mobility and carrier density of these samples were approximately 1000 cm2/Vs and 3 x 1018 cm-3 by Van der Pauw method.

Yttrium garnet is an excellent laser host crystal due to its excellent optical, thermal, mechanical properties and high chemical stability. As a rare-earth ion with the simplest energy level construction, Yb3+ belongs to the 4f13 electronic configuration. It possess some important advantages such as long fluorescence lifetime, no excited-state absorption, low quantum defect and larger intrinsic laser slope efficiency. Besides, yttrium garnet crystal doping ytterbium ion can especially dope with high concentrations and lower heat generation. In this thesis, a series of different doping concentration of Yb¡GYAG by Czochralski pulling technique are grown and perform some accurate experiments including Raman, IR, XRD and EXAFS in order to make sure the impact effect of doping on the lattice structure. The study includes following ¡]1¡^the effect of different doping Yb3+ from pure YAG to YbAG¡]2¡^the distances of Yb-O, Yb-Al, Yb-Y, Yb-Yb when Yb3+ ions replace Y3+ ions¡]3¡^the changes of absorption energy level in YAG crystal due to different concentrations of Yb3+ ion.

No description available.

Li-ion batteries have a huge potential for use in electrification of the transportation sector. The major challenge to be met is the limited energy storage capacity of the battery pack: both the amount of energy which can be stored within the space available in the vehicle (defining its range), and the aging of the individual battery cells (determining how long a whole pack can deliver sufficient energy and power to drive the vehicle). This thesis aims to increase our knowledge and understanding of structural changes induced by aging and usage of the Li-ion battery materials involved. Aging processes have been studied in commercial-size Li-ion cells with two different chemistries. LiFePO4/graphite cells were aged under different conditions, and thereafter examined at different points along the electrodes by post mortem characterisation using SEM, XPS, XRD and electrochemical characterization in half-cells. The results revealed large differences in degradation behaviour under different aging conditions and in different regions of the same cell. The aging of LiMn2O4-LiCoO2/Li4Ti5O12 cells was studied under two different aging conditions. Post mortem analysis revealed a high degree of Mn/Co mixing within individual particles of the LiMn2O4-LiCoO2 composite electrode. Structural changes induced by lithium insertion were studied in two negative electrode materials: in Li0.5Ni0.25TiOPO4 using in situ XRD, and in Ni0.5TiOPO4 using EXAFS, XANES and HAXPES. It was shown that Li0.5Ni0.25TiOPO4 lost most of its long-range-order during lithiation, and that both Ni and Ti were involved in the charge compensation mechanism during lithiation/delithiation of Ni0.5TiOPO4, with small clusters of metal-like Ni forming during lithiation. Finally, in situ XRD studies were also made of the reaction pathways to form LiFeSO4F from two sets of reactants: either FeSO4·H2O and LiF, or Li2SO4 and FeF2. During the heat treatment, Li2SO4 and FeF2 react to form FeSO4·H2O and LiF in a first step. In a second step LiFeSO4F is formed. This underlines the importance of the structural similarities between LiFeSO4F and FeSO4·H2O in the formation process of LiFeSO4F.

The overall goal of this research is concerned with understanding the effects of bentonite on the external corrosion of bare mild steel well casing. Na-bentonite is mainly used in enormous amounts in drilling processes, so it used as the main electrochemical environment surrounding the casing at different condition. The major part of the current study was divided into 3 stages; the first stage is constant current cathodic protection (CP) with a range of 0.0 (Open Circuit Potential) to 200mA.m-2 was applied respectively to protect bare mild steel buried vertically inside the bentonite layer contains 45% (w/w) 0.5 M NaCl Solution. This study was attempted to investigate the polarisation potential distribution over depth. The second stage is polarisation potential with a range of OCP to -1.15V/SCE was applied to protect mild steel exposed to 0.5M sodium chloride solution containing different concentration of bentonite, namely 0.0%, 1.0 and 10.0% (w/w). The third stage was concerning with the ZnCl2 added at 500ppm and 1000ppm to the bentonite as cathodic inhibitor to investigate its effects on the corrosion process of mild steel. CP at 0.0mV (OCP) and -1.15 V against saturated calomel electrode (SCE) were applied for this experiment. Weight loss, visual observation, Open Circuit Potential (OCP), cathodic protection and linear polarisation resistance (LPR) techniques were employed for this study. Optical microscope, Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray analysis (EDX), and X-Ray diffraction (XRD) analysis are illustrated to study, examine and analyse the films that formed on the metal surface. It is demonstrated that the corrosion rate produced from LPR measurement data was fairly lower than that obtained by experimental weight loss data. Low corrosion rate was recorded for the specimens immersed in 0.5NaCl solution, containing bentonite compared to that were obtained for solution free of bentonite. Magnesium hydroxide and calcium carbonate were the main chemical compounds that detected on the metal surfaces when cathodic protection (CP) was applied at -1.15V vs. SCE. It was confirmed that, the addition of ZnCl2 at two different concentration, 500ppm and 1000ppm has reduced the current density applied to a considerable value. This was ascribed to the formation of compacted and uniform film on the protected surface. The examination of the specimens using EDX and XRD has shown the formation of zinc containing compounds. Small amount of NaCl in the form of halite for both concentrations was also detected.

No description available.

Šioje daktaro disertacijoje pirmoje dalyje nustatyta šiuolaikinės, o antroje dalyje – archeologinės keramikos gaminių elementinė ir fazinė sudėtis, bei ištirta morfologija. Šiuolaikinės ir archeologinės keramikos pavyzdžių elementinė sudėtis nustatyta Rentgeno spindulių dispersinės analizės (EDX), liepsnos atominės absorbcinės spektrometrijos (LAAS), titrimetrinės ir spektrofotometrinės analizės metodais. Parodyta, kad visų keraminių pavyzdžių kokybinė bei kiekybinė sudėtis yra skirtinga Nustatyta, kad visuose keramikos mėginiuose pagrindiniai elementai yra silicis ir aliuminis. SiO2 sudaro 46 – 60% keramikos sudėties, Al2O3 – apie 17 – 33%. Fe, Na, Mg, K, Ca ir Ti mėginiuose rasta kelis kartus mažiau. EDX analizė gali būti sėkmingai naudojama nustatant pagrindinius elementus, kurių kiekiai viršija 0,5 % bendros elementinės sudėties. Norint nustatyti tikslią keramikos sudėtį ir pėdsakinius elementus reikia naudoti LAAS analizės metodą. Aliuminio kiekį keramikoje patikimai galima nustatyti titrimetriniu, o silicio ir titano kiekį – spektrofotometriniais metodais. Ištyrus šiuolaikę ir archeologinę keramiką Rentgeno spindulių difrakcine analize (XRD), nustatyta, kad visų keramikų pagrindinė fazė yra vienoda – silicio dioksidas SiO2, tačiau jų bendra fazinė sudėtis skiriasi. Skirtinguose kermikos pavyzdžiuose buvo aptikos šios fazės: kvarcas, dolomitas, kaolinas, albitas, mikroklinas, muskovitas, mulitas, hematitas, rutilas, diopsidas, korundas, titanitas, natrio anortitas... [toliau žr. visą tekstą] / The elemental composition of the samples of modern and archaeological ceramics was determined using the energy dispersive X-ray analysis, flame atomic absorption spectrometry, titrimetric and spectrophotometric analysis methods. It has been shown that the qualitative and quantitative composition of all the samples is different. It has been established that silicon and aluminium are the main elements in all the samples. SiO2 accounts for 46–60 % of the composition of the ceramics, Al2O3 – for some 17–33%. The amounts of Fe, Na, Mg, K, Ca and Ti discovered in the samples are several times lesser. EDX analysis can successfully be used in determining the main elements whose amounts exceed 0.5% of the overall elemental composition. In order to determine the exact composition of ceramics one has to employ the FAAS analysis method. To determine in a credible manner the amount of aluminium in ceramics, one can use the titrimetric method, and the amount of silicon and titanium – spectrophotometric methods. Upon examination of the modern and archaeological ceramics by diffraction analysis it has been established that the main phase of all the samples is the same – quartz SiO2, however their phase composition varies. In different samples the following phases have been discovered: calcite, dolomite, kaolinite, albite, microcline, muscovite, mullite, hematite, rutile, diopside, corundum, titanite, and sodium anorthite. Being aware of the phase composition, it has been established that the... [to full text]

Les nanostructures ont des propriétés mécaniques qui diffèrent de celles des matériaux massifs. La compréhension des propriétés mécaniques aux échelles nanométriques requièrent la mise en place d’essais mécaniques combinés à des observations structurales. Au cours de cette thèse nous avons développé un microscope à force atomique (AFM) dédié permettant de solliciter mécaniquement un nano-objet unique sur une ligne de lumière synchrotron. Les possibilités offertes par cette nouvelle approche expérimentale sont démontrées sur deux exemples de sollicitation mécanique in situ: (i) la nanoindentation in situ de cristaux d’or combinée à la diffraction cohérente des rayons X; (ii) la flexion trois points de nanofils d’or associée à la micro-diffraction de Laue. Ces expériences permettent d'accéder au comportement élastique ainsi qu’au comportement plastique du nanomatériau et permettent de déterminer la limite d'élasticité et le type de défauts induits par le chargement mécanique. / Nanostructures were found to exhibit different mechanical properties compared to their bulk counterpart. For obtaining further insight into the mechanical behaviour on the nanoscale, mechanical tests are combined with observation techniques allowing for monitoring the structural evolution. Within this thesis a special atomic force microscope has been developed which is compatible with different X-ray diffraction techniques at synchrotron sources for in situ mechanical testing on single nano-objects. The great potential of the new experimental approach is demonstrated on two kinds of in situ mechanical tests: (i) in situ nano-indentation on Au crystals with coherent X-ray diffraction. (ii) In situ three point bending tests on Au nanowires with μLaue diffraction. These experiments give access to the elastic as well as the plastic behavior of the nanomaterial and allows for determining the elastic limit and the type of defects induced by the mechanical loading.

Varias técnicas de física nuclear tem sido aplicadas no estudo de artefatos arqueológicos e de arte contribuindo para seu restauro e preservação. A aplicação destas técnicas são indicadas por não serem destrutivas, preservando o material a ser analisado. Neste trabalho, propomos um procedimento para a investigação indireta da dureza de espadas antigas, por meio de técnicas não destrutivas. Com este proposito as técnicas PIXE, NRA, XRD e RBS se adequam ao nosso estudo de espadas antigas, especificamente uma espada Indiana (Damascena) e outra Japonesa (Wakizashi). Com a técnica PIXE esperávamos identificar os elementos presentes nas laminas das espadas e em suas empunhaduras. Na espada Indiana os elementos identificados foram: Cr, Mn, Fe, Ni, Cu, Zn e As. Para a espada Japonesa somente o elemento Fe foi identificado, mas com o auxílio da técnica RBS identificamos também, um filme fino de carbono na superfície da lamina, medindo 0; 75 _m de espessura. Nas empunhaduras foram identificados os elementos Cr, Fe, Cu e Au para a espada Indiana; Fe, Cu, As e Ag na peca Habaki e S, Cl, K, CA, Fe, As e Au na peca Fuchi, estas duas pecas fazem parte da empunhadura da espada Japonesa. A técnica XRD foi usada para verificarmos as estruturas cristalinas que se formam na superfície das laminas durante o processo de forja (variação de 6 temperatura e deformações plástica). Estas informações possibilitam inferir sobre a temperatura de forja e consequências da deformação plásticas. A fase cristalina da superfície das laminas foi identificada como ferro na forma cristalina cubica de corpo centrado. Nesta estrutura, ha a formação de pequenos cristais orientados (cristalitos), que apresentaram tamanho médio da ordem de 200 _A. Foi verificado que ha também uma fase amorfa do ferro na espada Japonesa, sugerindo que o processo de forja alcançou temperaturas menores quando comparada com a espada Indiana. A espada Damascena _e muito famosa pela dureza e ductibilidade apresentada por sua lamina. Um elemento que pode contribuir para estas caraterísticas e o nitrogênio, que pode ser identificado usando a técnica NRA, mais especificamente a reação 15N(p; _)12C. O nitrogênio poderia ser introduzido na lamina durante o processo de endurecimento da região de corte. Neste processo a lamina era resfriada em urina animal, composta principalmente por acido úrico (C5H4N4O3) e ureia (NH2)2CO. Não foi possível identificarmos a presença de nitrogênio dentro do nosso limite de detecção (acima de 0; 263(4)% em massa de nitrogênio, valor referenciado para a amostra padrão CRM-298). / A set of physical techniques have been applied to characterize archaeological and art artifacts and contribute to its preservation and restoration. The application of these techniques are indicated because they are non invasive methods, preserving the material to be analyzed. In this work, we propose a procedure to investigate indirectly the hardness of ancient swords, by nondestructive techniques. With this aim, we decided to apply the techniques PIXE, NRA, XRD and RBS in the study of ancient swords, specially Indian (Damascus blade) and a Japanese (Wakizashi) swords. With PIXE we identified the major compounds in the blades and in their grips. In the Indian blade were identified the following elements: Cr, Mn, Fe, Ni, Cu, Zn e As. In the Japanese only iron was identified, although, with RBS we could identified a thin _lm of carbon on its surface. The grips were also analyzed and the results indicated to Indian were: Cr, Fe, Cu and Au; and to Japanese: Fe, Cu, As e Ag in the peace Habaki, and S, Cl, K, CA, Fe, As e Au in the peace Fuchi, those pieces are part of the grip. The XRD technique was applied to verify the crystalline structure which were formed during the forging process (hammering and quenching). These information can help to understand more about the quenching and hammering process. The crystalline phase in the surface of the blade was identified as iron. The surface is composed by crystallites oriented with grain size in order to 200_A, oriented as the result of hammering process. Also there is an amorphous phase in the Japanese blade, suggesting that in the forje process the temperature achieved was lower when compared with the Indian sword. The Damascus blade is famous due its hardness and ductility. An element that can improve these characteristics is the nitrogen. Its determination is possible using NRA technique, more specially the reaction 15N(p; _)12C. The nitrogen could been insert in the blade during the edge hardness process (in this process the blade was quenched into animal urine that its main compound are uric acid (C5H4N4O3) and urea (NH2)2CO, or in a brine). It was not possible to identify the presence of nitrogen within our limit of quantification.