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Hard-burnt magnesium oxide (MgO) has been successfully used in large volume concrete, mainly dam construction in China, for thermal shrinkage reduction since the 1970’s. At ~4% addition to the cement by weight, it is much simpler than conventional shrinkage measures and in particular, reduces the quantity of crack control reinforcement used. The mechanism is similar to conventional ettringite-based and lime-based expansive admixture relying on their expansion to offset concrete shrinkage. In other words, the tensile stresses induced by concrete shrinkage are offset by the compressive stresses induced by MgO expansion under a restrained condition so that shrinkage and cracking can be reduced. While there are technical specifications in China for this application, the production of MgO is not robust enough to produce specified MgOs, and thus specific performance cannot be specified or guaranteed. In addition, there has been very little rigorous scientific research work in the literature on the performance mechanisms and controlling variables. These issues have hindered the application of the unique designable expansion characteristics of MgO and have limited the application in thermal shrinkage reduction. Hence, this PhD study aims to investigate the expansive characteristics of a number of commercially available MgOs used as an additive and evaluate their shrinkage reduction in cement and concrete. This work also presents a literature review of MgOs, particularly from Chinese sources, and a thorough evaluation of the expansion characteristics and shrinkage reduction capabilities of MgOs with different reactivities in both cement paste and concrete. To this end, four different reactivity MgOs obtained from seawater, brine and magnesite were tested. First, cement paste and concrete prisms - both cured in water - were used for correlating MgO reactivities with expansion characteristics under unrestrained and restrained conditions. The changes in length in cement paste and concrete prisms showed that the MgO expansion rate and magnitude increased with MgO content and reactivity as well as water content. Provision of restraint in prisms both decreased the magnitude and rate of expansion. Highly reactive MgOs showed higher early age expansion and plateaued in a relatively short period while less reactive MgOs exhibited delayed expansion. Temperature increase accelerated all MgOs hydration activation. In particular, less reactive MgOs displayed rapid expansion at an early age instead of delayed expansion. With regards to unrestrained compressive strength development, it was found that the higher the MgO expansion, the greater the compressive strength reduction. Microstructural analyses confirmed the existence of MgO hydration product brucite which contributed to the expansion. While the brucite quantity increased in cement paste systems, it had an insignificant influence on cement paste pH and thus potential reinforcement corrosion resistance. Similar expansion characteristic was found in the PC-Slag cement pastes containing different reactivities of MgOs as compared to that of PC cement paste except that the PC-Slag cement pastes displayed a slightly higher expansion than PC cement at an early age but lower ultimate expansion. One high reactivity MgO (MgO-N50) and one medium reactivity MgO (MgO-92/200), with distinct expansion characteristics, were selected for evaluating the shrinkage reduction performance of cement paste in autogenous and drying curing conditions. Autogenous shrinkage of unrestrained cement paste prisms was measured using laser sensors and length comparator at an early age (< 24 hours) and long-term respectively. The results showed that autogenous shrinkage in the cement paste containing the MgOs was reduced and further decreased with MgO reactivity, content, as well as water content. Compared to PC, the slower strength development in PC-Slag cement resulted in smaller autogenous shrinkage reduction. Drying shrinkage reduction was observed at an early age in both PC and PC-Slag unrestrained cement paste containing the MgOs at water-to-bonder (w/b) ratio of 0.5, although the long-term shrinkage was higher than the control. To further investigate the benefit of early age MgO expansion in drying shrinkage reduction, the final part of the study focused on restrained concrete specimens using the restrained ring test. The results showed that drying shrinkage was reduced in PC concrete with the addition of the highly reactive MgO-N50 when the w/b ratio was increased from 0.40 and 0.50. On the contrary, drying shrinkage reduction was not observed in the PC concrete with the less reactive MgO-92/200. Neither MgOs in PC-Slag concrete showed drying shrinkage reduction. The results reaffirmed the earlier findings that MgO expansion is dependent on strength development. The combination of pre-compressive stresses, delay in tensile stress development and smaller modulus of elasticity of MgO concrete contributed to a lower stresses-to-strength ratio and thus higher resistance to cracking caused by drying shrinkage. From an engineering point of view, the high reactivity MgO-N50 characterised by early age expansion can be used for reducing concrete autogenous shrinkage as it is used for drying shrinkage effect. The less reactive MgO-92/200 with delayed expansion can be utilised in mass concrete to address thermal shrinkage.

Undersokningen omfattar problem som kan uppsta vid permanentdrift pa MGO i tvatakts-fartygsdieslar som tidigare har opererats pa HFO. Undersokningen ar utford med hjalp av intervjuer samt en litteraturstudie. Den overgripande slutsatsen ar att det ar fullt mojligt med drift pa MGO, det kraver dock en del anpassningar av systemen. Det enskilt storsta problemet ar den laga viskositeten. Kan inte viskositeten hallas tillrackligt hog sa kommer problem med okat slitage pa bland annat branslepumpar att uppsta. Det kan aven forekomma drifts- och startproblem.

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Magnetic tunnel junctions (MTJs), which consist of a thin insulation layer sandwiched by two ferromagnetic (FM) layers, are among the key devices of spintronics that have promising technological applications for computer hard disk drives, magnetic random access memory (MRAM) and other future spintronic devices. The work presented here is related to the development of relevant techniques for the preparation and characterization of magnetic films, exchanged biased systems and MTJs. The fabrication and characterization of PtMn/CoFe exchange biased systems and MTJs with Al-O barriers were undertaken when the new Aviza StratIon fxP ion beam deposition tool was developed by the project consortium funded by DTI MNT. After the Nordiko 9550 spintronic deposition tool was installed at Plymouth, the work focused on the development of MTJ multilayer stacks with layer structures of CoFeB/MgO/CoFe/IrMn and IrMn/CoFeB/MgO/CoFeB to achieve coherent tunneling with a crystalline MgO barrier. The film deposition, microfabrication, magnetic field annealing, microstructural and nano-scale characterization, magnetic and magneto-transport measurement for these devices have been systematically studied to achieve smooth interfaces and desired crystallographic textures and magnetic properties of layer stacks. Magnetoresistance (MR) of up to 200% was obtained from MTJs with a layer structure of Ta/CuN/Ta/CoFeB/MgO/CoFe/IrMn/Ta and a CuN bottom electrode. Enhanced exchange anisotropy from the bottom pinned IrMn/CoFeB stacks has been obtained, which demonstrated the possibility of fabricating MTJs with CoFeB as both the top and bottom FM electrodes with strong exchange bias. The origin of the enhanced exchange bias field was studied by employing high resolution transmission electron microscopy (HRTEM) and x-ray magnetic circular dichroism (XMCD) to examine the mmicrostructure properties and element specific magnetic properties of the stacks. Results demonstrate that the enhanced exchange anisotropy in the IrMn/CoFeB system is closely associated with the increased uncompensated interfacial spins. MTJs with layered structures of IrMn/CoFeB/MgO/CoFeB were prepared based on this exchange bias system. However, further work is required for the optimisation of the (001) crystallographic textures of the CoFeB/MgO/CoFeB stack to achieve coherent tunneling.

Pulsed laser deposition method was employed to grow MgO thin films with preferred orientation on bare Si(100) and SiO₂/Si(100) substrates. The orientation of MgO thin films was systematically investigated by varying deposition parameters. XRD analysis showed that the preferred orientation of MgO thin films would change from (111) to (100) when laser fluence decreased and oxygen pressure increased to certain extend. But it was difficult to fabricate completely (100)-oriented MgO films. Substrate temperature seemed to have little influence on the orientation of MgO thin films at high laser fluence. SEM images of the MgO thin films on Si(100) deposited at 400°C and the laser fluence of 5J/cm² in the oxygen ambient of 200mTorr demonstrated that there was no presence of interfacial reactions or cracks and the film surface was very smooth. Such film is suitable as buffer layers for the growth of high-quality ferroelectric and superconducting overlayers. / Singapore-MIT Alliance (SMA)

When nuclear fuel, fabricated for the purpose of transmuting spent fuel is irradiated, significant amounts of He is produced from alpha particles mainly emitted when 242Cm decays into 238Pu. From irradiation experiments it is known that the presence of He in the solids alters the swelling behaviour of the material. The thesis presents the theoretical background from which nucleation models of He bubbles can be formulated. Such models are presented for He in metals, and the case of He in Mo is studied as an example. MgO, which together with Mo is suggested as a matrix material in transmutation fuel is also studied and the stability of He containing bubbles in this material is discussed. By calculating parameters for a rate theory model derived from atomistic modelling, it is shown that He can stabilise vacancy clusters and cause cluster growth at temperatures and irradiation doses where nucleation and growth would not otherwise occur. At the initial stages of nucleation He can stabilise small bubbles while larger bubbles are unstable. This results in an incubation time of swelling, which implies that He does not always cause increased swelling, but can at certain irradiation conditions slow down the growth of large vacancy clusters and thereby delay swell\-ing beyond the time of the irradiation. When comparing the behaviour of bubble nucleation in Mo and MgO, it is found that He has a significant impact even at very low concentrations in Mo. In contrast, the concentration of He has to be considerably higher in MgO to affect the swelling behaviour. For an inert matrix fuel, designed for transmutation purposes, this implies that the Mo matrix will have a tendency to swell considerably at rather high temperatures due to He stabilised vacancy clusters. If operated at lower temperatures, the swelling could instead be reduced due to the incubation time. In a MgO matrix, the swelling behaviour will instead depend largely on the production rate of He. For a low production rate, the material will have a swelling behaviour similar to the one seen when He is not present in the material. A high production rate implies that He will remain in vacancy clusters, thereby stabilising the clusters and enhancing the growth and swelling.

Cuprous oxide (Cu2O) was first investigated in the 1920s as a semiconductor material with Eg~2.17 eV. It is ideal for applications in solar cells, electrochromic devices, oxygen and humidity sensors because of its high optical absorption coefficient, non-toxic nature, abundant availability and low cost for production. Many groups have tried different ways to grow the cuprous oxide by, for instance, sputtering, CVD, PLD, MBE, and electro-deposition etc. Among them, the sputtering method is probably the most cost-effective and easy to operate. In this work, the cuprous oxide thin films were grown on R-Al2O3 and (110)-MgO substrates by DC reactive magnetron sputtering. Thin films grown at different temperatures under various oxygen partial pressures were studied by X-ray diffraction (XRD) to test their structural perfections. Samples with the Cu2O on Al2O3(1012) and MgO(110) were studied via measurement of cathodoluminescence(CL) spectroscopy, photoluminescence (PL) spectroscopy, transmission spectroscopy and magneto transport behaviors. The correlation of growth condition and physical properties are discussed.

O controle das características da escória de refino primário pode ser realizado pela adição de fluxantes, sendo comumente utilizado a Fluorita (CaF2), isto porque a Fluorita aumenta a solubilidade de CaO e, por conseguinte, aumenta a capacidade de desfosforação de escória. Apesar disso, alguns estudos advertem sobre o risco de liberação de gás tetra fluoreto de silício, que tem caráter nocivo para o meio ambiente. Outro problema relatado é o aumento do desgaste do revestimento refratário impactando nos custos de produção. Neste trabalho de mestrado o uso de Sodalita Nefelínica como fluxante foi comparado com a Fluorita em relação ao desgaste de refratários a base de MgO-C e à fluidez. Os ensaios consistiram em dopar escória de conversor LD com diferentes quantidades de Fluorita e Sodalita (1, 2, 3, 4 % em massa). Os resultados demonstraram que a Fluorita fornece uma escória com menor ponto de fusão e mais fluida, porém ela causa maior desgaste no revestimento refratário, mais que o dobro do desgaste causado pela Sodalita. Acredita-se que isso tenha ocorrido devido a Fluorita ser capaz de aumentar a dissolução tanto do CaO presente na escória quanto do MgO presente no refratário. Este processo é intensificado pela baixa viscosidade apresentada com este fluxante. / The control of the slag characteristics from primary refining can be accomplished by adding fluxes, being commonly used Fluorite (CaF2). This happens because the fluorite increases the solubility of CaO and thus increases the ability of the slag dephosphorization. Nevertheless, some studies warn about the risk of releasing silicon tetra-fluoride gas which has harmful character to the environment. Another problem reported is the increased wear of the refractory lining impacting on production costs. In this master dissertation the use of Sodalite Nepheline as flux was compared with Fluorite concerning MgO-C based refractories wear and fluidity. The tests consisted of doping LD converter slag with different amounts of Fluorite and Sodalite (1, 2, 3, 4 % mass). The results showed that the Fluorite provides a slag with a lower melting point and becomes more fluid, but it causes greater wear on the refractory lining, more than double the wear caused by Sodalite. It is believed that this has occurred due Fluorite be able to enhance the dissolution of the CaO in slag as well as MgO present in the refractory. This process is intensified by the low slag viscosity presented with this flux.

Ce manuscrit se concentre sur l'analyse du GISAXS d'îlots sur un substrat. Les données GISAXS doivent être analysées de façon quantitative afin d'obtenir des paramètres morphologiques précis (courbes de croissance, forme d'équilibre de l'îlot et énergie interfaciale) pour le processus d'élaboration. L'accent est mis sur le facteur de forme de l'îlot, c'est-à-dire la transformée de Fourier de la forme de l'îlot. On montre que la forme de l'îlot et la taille peuvent être obtenues à partir de la symétrie de l'îlot, la présence de facettes de l''îlot, le comportement asymptotique loin dans l'espace réciproque pour une grande polydispersité et les zéros ou les minima de l'intensité pour une faible polydispersité. Une comparaison approfondie entre l'approximation de Born et l'approximation plus précise de l'onde distordue (DWBA) met en évidence la spécificité apportée par la géométrie en incidence rasante. L'analyse quantitative est illustrée pour des images GISAXS acquises in situ pendant l'épitaxie par jet moléculaire de nano-îlots Ag ou Pd sur MgO(001) pour différentes épaisseurs et températures. Les paramètres morphologiques obtenus sont en très bon accord avec des résultats de microscopie électronique à transmission. Finalement, la diffusion incohérente a été mise en évidence en GISAXS et a pour origine des corrélations entre les îlots.