The field of mesoporous silica has been studied for about 20 years but it is still an area attracting a lot of attention. The use of novel templating molecules and several issues related to the synthesis and fine structural details are still poorly understood. These aspects are of special relevance to the theme of this thesis, which includes novel work on three fronts; the synthesis, characterization and applications of mesoporous materials. The work described in this thesis aims to contribute to the mesoporous field by developing novel methods of mesoporous silica synthesis without relying on surfactant micelles as the templating agent but focusing instead on the stacking arrangement of aromatic molecules such as folic acid. The novel route presented here leads to 2D hexagonal structures with p6mm symmetry possessing high mesoporosity and large surface areas. The versatility of this route at various synthesis temperatures and using hydrothermal treatments has also been investigated. A novel strategy is also proposed for the synthesis of mesocaged materials with Pm3n symmetry structures. The mechanism relies on the penetration of the neutral propylamino moiety of a co-structure directing agent into the hydrophobic core of the surfactant micelles. Beside these novel pathways, the effect of hydrothermal treatment (HT) at 100 oC on the 3D cubic Ia3d structure (AMS-6) over a long period of time was also examined, and the results show a phase transformation from a 3D cubic Ia3d to a 2D hexagonal p6mm structure and a return to the 3D cubic Ia3d structure at a later stage in the synthesis. This unexpected result is discussed. In this work, the detailed structural characterization of mesoporous materials using electron microscopy techniques is an important task. In particular, to extend previous knowledge, the fine structural details of mesocaged materials possessing Pm3n symmetry prepared with various amphiphilic surfactants under acidic and alkaline conditions has been investigated using electron crystallography and sorption studies. The results show subtle fine structural differences with materials prepared under alkaline conditions exhibiting the largest mesocage sizes. The cage and window sizes are primarily determined by the charge density of the surfactant and the thickness of the hydration layer surrounding the surfactant micelles. The relationship between the mesoporous structure and its function has been investigated by evaluating the rate of release of amphiphilic molecules, used as model molecules, from the internal pore structures of mesoporous materials with different pore geometries. In a similar study, the rate of proton diffusion from a liquid surrounding the mesoporous nanoparticles into the pore system of AMS-n was also assessed. The results show that the diffusion coefficients for the proton absorption process are higher than those for the release of the surfactant template molecules, with more complex 3D mesocaged particles showing the highest diffusion coefficients in both cases. Finally, the quantity of CO2 adsorption was measured by modifying the internal surfaces of mesocaged material with n-propylamino groups. Results show that the cage-connecting window sizes limit the surface coverage of n-propylamino groups by pore blocking and affect the volume of CO2 adsorption. In addition, at the molecular level, CO2 adsorption shows physisorption or chemisorption depending on the localized distribution of n-propylamino groups, as studied by in-situ infrared spectroscopy.

Forging ingots are hot worked to consolidate structural imperfections and refine the microstructure. Possible imperfections are segregations, porosities, cracks, and inclusions. In this thesis, techniques and methods for the characterisation of behaviour and properties of ingots and forgings. The root causes for quality issues in open-die forgings are shown to be numerous. Ingot structure in cast tool steel was analyzed, and the main imperfections were centre macrosegregation, and mid radius A-segregations.For overheated steel forgings and low reductions after reheating, a high ultrasonic attenuation and low Charpy-V toughness was found. It could be related to the coarse grain structure found. Only a high forging reduction after reheating will break down the coarse structure. Shorter reheating times and lower forging temperatures gave higher toughness and lower ultrasonic attenuation. Some reduction in toughness was also found from the inclusion field from the bottom of the ingot. Accurate attenuation measurements require a lathe turned surface, complicating in-between-measurements in heat treatment sequences. But on carefully surface prepared forgings, attenuation measurement can be used to determine the success of grain refinement in the heat treatment. A new method for ultrasonic macrography of cast ingot samples is presented. In addition, a new method for hot compression testing of cylindrical metal samples is presented. / QC 20100809

<p>This project was planed in order to study the effect of growth and crystalline quality of GaN on lattice matched Al1-xInxN seed layer. The GaN lattice matched Al0.81Ino.19N seed layer was grown by co-sputtering of Al and In target using only N2 as a sputtering gas in a direct current (DC) reactive magnetron sputter deposition chamber under UHV conditions at low temperature (230 oC) on different substrates. The Indium composition was calculated using vegards law from lattice parameters determined by XRD. The Indium composition was determined by Rutherford Backscattering Spectroscopy (RBS) as well. X-rays diffraction (XRD) showed high crystalline quality wurtzite hexagonal Al1-xInxN seed layers grown at this temperature. The GaN was grown on top of Al0.81Ino.19N seed layer by halide vapour phase epitaxy (HVPE) using a mixture of N2 and H2 and only N2 as a carrier gas in order to study the effect of carrier gas on crystalline quality of GaN. The GaN films were characterised by high resolution X-rays diffraction (HRXRD), scanning electron microscopy (SEM), cathode luminescence (CL) and high resolution transmission electron microscopy (HRTEM) in order to study stress, strain, crystalline quality, surface morphology and optoelectronic properties in relation with the defect density and the microstructure of grown GaN films.</p>

This project was planed in order to study the effect of growth and crystalline quality of GaN on lattice matched Al1-xInxN seed layer. The GaN lattice matched Al0.81Ino.19N seed layer was grown by co-sputtering of Al and In target using only N2 as a sputtering gas in a direct current (DC) reactive magnetron sputter deposition chamber under UHV conditions at low temperature (230 oC) on different substrates. The Indium composition was calculated using vegards law from lattice parameters determined by XRD. The Indium composition was determined by Rutherford Backscattering Spectroscopy (RBS) as well. X-rays diffraction (XRD) showed high crystalline quality wurtzite hexagonal Al1-xInxN seed layers grown at this temperature. The GaN was grown on top of Al0.81Ino.19N seed layer by halide vapour phase epitaxy (HVPE) using a mixture of N2 and H2 and only N2 as a carrier gas in order to study the effect of carrier gas on crystalline quality of GaN. The GaN films were characterised by high resolution X-rays diffraction (HRXRD), scanning electron microscopy (SEM), cathode luminescence (CL) and high resolution transmission electron microscopy (HRTEM) in order to study stress, strain, crystalline quality, surface morphology and optoelectronic properties in relation with the defect density and the microstructure of grown GaN films.

The final properties of an alloy are highly interlaced with its microstructure. It is therefore essential to control the evolution of the microstructure of the material during the fabrication process. Nowadays, materials design involves an increasing part of computational design to complement the traditional experimental trial and error approach. Such simulations of the process can decrease the number of material prototypes and shorten the development time for new alloys. In this thesis several microstructure models, aimed for process design, have been suggested. The ambition has been to develop physically based models that are capable to represent the evolution of hundreds of grain or particle sizes, where the models should be possible to run on a standard computer with simulation times less than one day. To achieve this goal, simplified approaches have been suggested, which are accurate enough for the growth rate of grains and particles. The microstructure models have all in common that size distributions of grains or particles are simulated with mean-field approaches. Several of the models also utilize composition and temperature dependent thermodynamic and kinetic properties continually throughout the simulations. These properties have been calculated with programming interfaces to Thermo-Calc and DICTRA together with appropriate thermodynamic and kinetic databases. The materials that have been considered in the present thesis are low alloyed steels, aluminium alloys and cemented carbides. The models are however generic in the sense that all materials can be handled if appropriate thermodynamic, kinetic and property databases exist for the alloy. / QC 20110316

Volume change during solidification is an important concept in achieving of casting soundness. The solidification shrinkage can cause different defects in the ingot casting as well as the shape casting. The volume change due to phase transformation during solidification is the other concept which has to be studied. In addition, the solidification shrinkage can be affected by the volume change of liquid metals due to the structure change of liquid. In this work, first, the solidification shrinkage was measured in copper-lead base alloys by a dilatometer which was developed to use for melting and solidification processes. The volume change was measured during primary solidification and monotectic reaction. The macrostructure evaluation of samples was used to explain the volume change results. A shrinkage model was used to explain the volume changes during solidification. In addition, the microsegregation of alloying elements was studied in the alloys.   In the second part, the solidification of brass alloys was investigated in different cooling rates. Microstructure evaluation showed that the peritectic transformation occurred as diffusionless (partitionless) as well as the diffusion-controlled transformation. In addition, the volume change was measured in the peritectic alloys. A theoretical analysis was developed to evaluate the volume change effect on the peritectic reaction.   Hot crack formation was investigated during the solidification of peritectic steels as a volume change concept during the transformation of ferrite to austenite. A series of in situ solidification experiments was performed using a MTS tensile testing machine combined with a mirror furnace to measure the sample temperature and the force change during solidification. It was observed that a rise in tensile force began with the start of solidification and suddenly dropped. The sudden drop of force, which occurred around the peritectic temperature of the alloy, was accompanied by a crack or a refilled crack in the microstructure. Furthermore, the peritectic reaction types were studied theoretically and experimentally to understand their effects on the force change during solidification. The analyses showed that the volume change due to the peritectic transformation is a reason for crack formation. In addition, when the peritectic reaction occurred as a diffusionless manner (partitionless), the crack formation is more probable.   In the last study, the effect of cooling rate and super heat temperature were studied on the precipitation of primary silicon in Al-Si hypereutectic alloys. The liquidus temperature was found to decrease with cooling rate. In addition, the fraction of primary silicon decreased with increasing the cooling rate and the super heat temperature. Furthermore, the morphology of the primary silicon changed as an effect of cooling rate and super heat temperature. It was concluded that the solidification characteristic and silicon morphology relate to the liquid structure. / QC 20100726

The present thesis deals with some aspects concerning secondary metallurgy of steel where there is little or very inconsistent information in the literature. More specifically, it is devoted to the studies on high temperature phase equilibria in the Al2O3-CaO-MgO-SiO2 system, the formation of ladle glaze and the thermodynamics of magnesium in liquid iron. First, the solidification of different slags on MgO based refractories was studied in order to reveal the mechanism behind the formation of “ladle glaze”. The formation of the slag glaze layer was studied by dipping MgO rods, dense or porous, into liquid slags at 1873 K. The rods were thereafter cooled at a predetermined rate. From a later SEM-EDS microscopy, it was found that the initial slag composition had the most profound effect on the phases found in the solidified slag layer. It was found that the type of MgO rod used and cooling speed had a minor impact on the morphology on the solidified samples. In addition, the slags used in the study were equilibrated at 1773 K, 1673 K and 1573 K in order to get an understanding of the equilibrium phases and their relationship during cooling. On the basis of the experimental results, the mechanism regarding entrainment of exogenous inclusions from the refractory lining was also discussed. Secondly, phase diagram studies in the high basicity region of the Al2O3-CaO-MgO-SiO2 system were performed using the quench technique followed by EPMA analysis. The main focus in the study was to find the liquidus surfaces for MgO and CaO saturation at 1773 and 1873 K. Based on the experimental data, phase diagrams for the 25, 30 and 35 mass percent alumina sections were constructed for silica contents generally less than 20 mass percent.. The results generally agreed very well with previous, well established phase diagrams. In addition, the activities of MgO, CaO and Al2O3 were estimated using the phase diagram information. At last, the thermodynamics of magnesium in liquid iron at 1823 K were studied. In a pre-study, the thermodynamics of Ag-Mg solutions were studied, necessary for the Fe-Mg system. For the Ag-Mg system, two different experimental techniques were used; the vapor pressure method and the gas equilibration technique. The temperature range of the Ag-Mg study was 1573 to 1823 K. It was found that the excess Gibbs energy of this system can be described quite well with a sub-regular solution model. In the Fe-Mg study, the partition of Mg between liquid iron and liquid silver were studied at 1823 K. Using the results from the pre-study, the activity coefficient of Mg in liquid iron and the self-interaction parameter <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Cxi%5Cfrac%7BMg%7D%7BMg%7D" />were determined at 1823 K. / QC 20110314

The present work describes the use of atomistic computer simulations in the area of Condensed Matter Physics, and speci cally its application to the study of two problems: the dynamics of the melting phase transition and the properties of materials at extremely high pressures and temperatures, problems which defy experimental measurements and purely analytical calculations. A good sampling of techniques including classical and rst-principles Molecular Dynamics, and Metropolis Monte Carlo simulation have been applied in this study. It includes the calculation of melting curves for a wide range of pressures for elements such as Xe and H2, the comparison of two di erent models for molecular interactions in ZrO2 with respect to their ability to reproduce the melting point of the stable cubic phase, the study of the elastic constants of Fe at the extreme conditions of the Earth's inner core, and the stability of its crystalline phases. One of the most interesting results in this work is the characterization of di usion and defects formation in generic models of crystalline solids (namely Lennard-Jones and Embedded-atom) at the limit of superheating, including the role they play in the triggering of the melting process itself. / QC 20100708

In order to optimize the metallurgical processes it is necessary to improve the understandings of the industrial slag properties, which include thermophysical and thermochemical properties. In the present study Mass Triangle Model was applied to predict these properties. According to the model formula, a program was developed in Visual C++ environment to calculate different properties in limited solubility ternary system. Successful applications of this model in predicting viscosity, surface tension, and density have been demonstrated in the case of a number of ternary slags in liquid state, as for example, RExOy-CaF2-SiO2 (RE refer to rare earth metal), MnO-TiO2-SiO2, CaO-Al2O3-SiO2, BaO-FeO-Fe2O3, CaO-MnO-SiO2 etc. In addition, the method has also been extended to predict electrical conductivities and sulphide capacities, which is first attempt to compute properties. Furthermore, an extension of this model has also been performed in the present study to obtain the corresponding properties in a homogeneous ternary system. Good agreement between model calculation and literature values had demonstrated that mass triangle model offers a powerful and efficient tool for estimations of various properties of molten system only based on limited experimental information. Knowledge of the thermodynamic properties of chromium oxides-containing slags is of great importance to chromium retention in stainless steel production, in view of chromium impacts on economic costs and environmental protection. Thus, the oxidation states of chromium in slags as well as sulphide capacity of CrOx-containing slag have been studied. In the studies of oxidation state of chromium in slags, gas/slag equilibrium technique was used for CaO-SiO2-CrOx system and the ratio of Cr2+/Cr3+ in multicomponent slags was measured by X-ray absorption near edge spectra (XANES). High-temperature mass spectrometry method was also used to obtain the distribution of chromium oxides in CaO-MgO(-FeO)-Al2O3-SiO2-CrOx system. It is to be noted that the present work is probably the first to employ Knudsen cell-mass spectrometry as an effective way to estimate chromium valences through vapor species. Utilizing the data obtained in present study as well as those reported in literature, a mathematical correlation was established for estimating the ratio of Cr2+/Cr3+ as a function of temperature, partial pressure of oxygen and slag basicity. The comparison between experimental valence ratio values and estimated ones presents a satisfactory agreement. The sulphide capacities of CaO-SiO2-CrOx pseudo-ternary slags were measured using the gas-slag equilibration technique in the temperature range 1823–1923 K under two different oxygen partial pressures 9.80×10-3 and 9.88×10-4 Pa. The results showed that log10Cs varied linearly with the reciprocal temperature, and the slope was higher than the corresponding value reported in the case of the binary CaO-SiO2 of corresponding composition. By using the equation developed as part of this project relating Cr2+/Cr3+ with basicity, oxygen partial pressure and temperature, it was possible to understand the effect of CrO on the sulphide capacities; viz. the sulphide capacity shows a decreasing trend as Cr2+ replaces Ca2+ in the slag. With further increase of Cr2+ content, there are indications of the occurrence of a minimum point beyond which the sulphide capacities show a slight increasing trend. The latter is attributed to the increasing extent of the polymerization reaction releasing oxygen ions for sulphide reactions in the metasilicate region. The behavior of CrO in the slag was found to be analogous to FeO. Estimation of liquidus and solidus temperature of slag was also carried out in the present study. The results indicated that it is possible to get a reasonable idea of the solidus temperature from X-ray radiography while DSC would indicate the liquidus temperature of slag / <p>QC 20100813</p> / MISTRA

This thesis mainly treats the fabrication and applications of micro-optical elements in the semiconductor materials gallium arsenide (GaAs) and diamond. The recent trend in high-capacity data transfer using light as the information carrier creates new demands on the optoelectronic systems, such as small size, low cost and the integration of many components. Micro-optical components are key elements for building compact optoelectronic systems and are well suited for integration with other devices. Another area where micro-optical elements can play an important role is the use of lasers in medicine, industrial machining, metrology, etc. In most cases, the laser beam characteristic is not directly suited for the application and external optics is needed to focus, shape or split the laser beam. In the first part of this thesis, the fabrication of continuous-relief diffractive optical elements, such as diffractive lenses and blazed gratings, in GaAs is examined. The manufacturing technology uses electron-beam lithography followed by plasma etching in an inductively coupled plasma etching system. In the next step, these diffractive elements were monolithically integrated with vertical-cavity surface-emitting lasers. In the second part of this thesis a novel topic is examined, diamond micro-optics. Diamond is a unique material in many aspects, it is the hardest material mankind knows, it has an extremely wide optical transmission window, and it possesses the highest thermal conductivity of all solids. Until today, due to difficulties in machining diamond, the realization of diamond optics has been limited. By using the same technology we earlier developed for the fabrication of GaAs optics we demonstrate for the first time continuous-relief structures in diamond of optical quality. Several diamond micro-optical structures are presented; sub-wavelength gratings for reduction of unwanted Fresnel reflections, diffractive fan-out elements used to split a CO2-laser beam and refractive microlens arrays. The accuracy of the fabrication process by plasma etching was evaluated by optical and topographical measurements, in all cases the optical components were of very high quality.