Electrolysis of molten fluorides is one of the promising methods for the recovery and recycling of rare earth metals from used magnets. Due to the dearth of phase equilibria data for molten fluoride systems, thermodynamic modelling of LiF-DyF3-NdF3 system using the CALPHAD approach was carried out. Gibbs energy modelling for LiF-NdF3 and LiF-DyF3 systems was performed using the constitutional data from literature. Ab initio calculations were used to obtain enthalpy of reaction of LiDyF4, an intermediate phase that is found to exist in the LiF-DyF3 system. Differential thermal analysis was carried out for selected compositions in the NdF3-DyF3 system, in order to determine liquidus and solidus temperatures. The Gibbs energy parameters for the limiting binaries determined in this work is used for modelling the Gibbs energy functions of equilibrium phases in the ternary system. Selected compositions of LiF-NdF3-DyF3 were subjected to DTA in order to validate the calculated phase temperatures involving melt.

Since the investigation of wear particles in rail transport started in late-1910s, the high mass concentration of these particles has raised worries among researchers concerned with air quality. However, effective action has yet to be taken because of lack of relevant knowledge. This thesis provides applicable information for the airborne wear particles in rail transport. Some aspects of their characteristics such as diameter size, mass concentration, number concentration, and morphology of particles were investigated in field tests and laboratory tests.The effects on particle characterisations from different operational conditions in the field tests, and applying different braking materials, conducting tests in different applied loads or sliding velocities in the laboratory tests were studied. The main advantage of conducting laboratory tests was to focus on studying particles from one source. The possibility of repetition, using high sensitive instruments and conducting tests at low costs are the other advantages of laboratory studies. Paper A describes how a pin-on-disc machine was used to reproduce similar real operational conditions during mechanical braking in a train. The results were validated by comparing the field tests results with the laboratory studies. The particles morphology and size distribution were also studied.Paper B presents a summary of field tests results. The effects of curve negotiating and applying braking in different real conditions were investigated with an on-board measurement.The element composition of the particles and their potential sources were also investigated outside of the particles morphologies.Paper C presents comprehensive results from laboratory studies on airborne particles from different braking materials. The differences in the particle characteristics in similar test conditions were attributable to different material compositions and dominant wear mechanisms. A new index was introduced in this paper and is suggested to be used as a qualitative factor with regard to the airborne wear particle emission rate.Paper D is a review of the recent studies of exhaust emission and non-exhaust emission from rail vehicles. A summary of results, measurements, adverse health effects, and proposed or applied solutions are reviewed in this paper.

Autonomising industrial robots is the main goal in this paper; imagine humanoid robots that have several degrees of freedom (DOF) mechanisms as their arms. What if the humanoid's arms could be programmed to be responsive to their surrounding environment, without any hard-coding assigned? This paper presents the idea of an autonomous system, where the system observes the surrounding environment and takes action on its observation. The application here is that of rebuffing an object that is thrown towards a robotic arm's workspace. This application mimics the idea of high dynamic responsiveness of a robot's arm. This paper will present a trajectory generation framework for rebuffing incoming flying objects. The framework bases its assumptions on inputs acquired through image processing and object detection. After extensive testing, it can be said that the proposed framework managed to fulfil the real-time system requirements for this application, with an 80% successful rebuffing rate. 

This thesis explores the formation of segregation and inclusions during solidification of steel and cast iron. A better understanding of the formation mechanism should result in decreasing fraction of defects during solidification of ingot and strand material.

Density driven macrosegregation was studied both experimentally and theoretically to see the effect of channel segregation on the total segregation. Formation of these pencil-like segregations is due to natural convection in the solidifying metal caused by liquid enrichment of elements with lower density compared to the bulk. It is suggested to change the composition to compensate for this density difference.

Inclusion precipitation can be finite by limitations in segregation. Saturated liquid is found in the last solidified areas, often between dendrites. Here the enrichment of the liquid is possible due to microsegregation. Meanwhile crystals form and solidify the elements with low solubility in the solid is pushed out in the remaining liquid. Soon the liquid is saturated to the level where spontaneous formation of inclusions occurs. Microstructure studies by aid of SEM and micro-probe measurements are analysed to find at what point during solidification process the inclusions start to form. In steel making this formation has a detrimental effect on the mechanical properties in contrary to the production of nodular cast iron where the inclusions have a beneficial effect on the graphite formation.

Inoculation of cast iron aims at reaching higher number density of graphite nodules, nodule morphology modification and control of nodule distribution during solidification. Late precipitation of nucleation sites has shown to have a positive impact on preventing chill. To find the most potent inoculation agent different additives were tested. Special effort has been made to analyse the effect of oxides and sulphides as nucleation sites.

The use of magnesium alloys has been rapidly increased due to their ability to maintain high strengths at light weights. However weldability of steels and aluminum alloys by using resistance spot weld (RSW) process is a major issue, because it cannot be directly utilized for magnesium alloys. In this study, a structural-thermal-electrical finite element (FE) model has been developed to predict the distribution of residual stresses in RSW AZ61 magnesium alloy. Thermophysical and thermomechanical properties of AZ61 magnesium alloy have been experimentally determined, and have been used in FE model to increase the accuracy of the model. X-ray diffraction (XRD) technique has been utilized to measure the residual stresses in welded samples, and its results have been used to validate the FE model. Comparison study shows that the results obtained by using FE model have a good agreement with the experimental XRD data. In specific, the results show that the maximum tensile residual stress occurs at the weld center while decreases towards the nugget edge. In addition, the effects of welding parameters such as electrical current, welding time, and electrode force have been investigated on the maximum tensile residual stress. The results show that the tensile residual stress in welded joints rises by increasing the electrical current; however, it declines by prolonging the welding time as well as increasing the electrode force.

Particle-reinforced polymers are widely used in load-carrying applications. The effect of particle size on damage development in the polymer is still relatively unexplored. In this study, the effect of glass-sphere size on the damage development in tensile loaded epoxy has been investigated. The diameter of the glass spheres ranged from approximately 0.5-50 mu m. The first type of damage observed was debonding at the sphere poles, which subsequently grew along the interface between the glass spheres and epoxy matrix. These cracks were observed to kink out into the matrix in the radial direction perpendicular to the applied load. The debonding stresses increased with decreasing sphere diameter, whereas the length to diameter ratio of the resulting matrix cracks increased with increasing sphere diameter. These effects could not be explained by elastic stress analysis and linear-elastic fracture mechanics. Possible explanations are that a thin interphase shell may form in the epoxy close to the glass spheres, and that there is a length-scale effect in the yield process which depends on the strain gradients. Cohesive fracture processes can contribute to the influence of sphere size on matrix-crack length. Better knowledge on these underlying size-dependent mechanisms that control damage development in polymers and polymer composites is useful in development of stronger materials. From a methodology point of view, the glass-sphere composite test can be used as an alternative technique (although still in a qualitative way) to hardness vs. indentation depth to quantify length-scale effects in inelastic deformation of polymers.

Experimental observations have indicated that the presence of strain gradients has an influence on the inelastic behavior of polymers as well as in other materials such as ceramics and metals. The present study has experimentally quantified length-scale effects in inelastic deformations of the polymer material polystyrene (PS) with respect to the molecular length. The experimental technique that has been used is nano-indentation to various depths with a Berkovich indenter. The hardness has been calculated with the method by Oliver and Pharr, and also by direct measurements of the area from atomic force microscopy. The experiments showed that the length-scale effects in inelastic deformations exist in polystyrene at ambient conditions. The direct method gave a smaller hardness than the Oliver-Pharr method. It was also shown that the length-scale parameter according to Nix and Gao increases with increasing molecular weight. For high molecular weights above a critical value of entanglement, there was no pertinent increase in the length-scale parameter. The length-scale parameter for strain-gradient plasticity has a size of around 0.1 μm for polystyrene.

The importance of surface topology for the generation of cavitating flows in micro scale has been emphasized during the last decade. In this regard, the utilization of surface roughness elements is not only beneficial in promoting mass transportation mechanisms, but also in improving the surface characteristics by offering new interacting surface areas. Therefore, it is possible to increase the performance of microfluidic systems involving multiphase flows via modifying the surface. In this study, we aim to enhance generation and intensification of cavitating flows inside microfluidic devices by developing artificial roughness elements and trapping hydrophobic fluorinated lubricants. For this, we employed different microfluidic devices with various hydraulic diameters, while roughness structures with different lengths were formed on the side walls of microchannel configurations. The surface roughness of these devices was developed by assembling various sizes of silica nanoparticles using the layer-by-layer technique (D2). In addition, to compare the cavitating flow intensity with regular devices having plain surfaces (D1), highly fluorinated oil was trapped within the pores of the existing thin films in the configuration D2 via providing the Slippery Liquid-Infused Porous Surface (D3). The microfluidic devices housing the short microchannel and the extended channel were exposed to upstream pressures varying from 1 to 7.23 MPa. Cavitation inception and supercavitation condition occured at much lower upstream pressures for the configurations of D2 and D3. Interestingly, hydraulic flip, which rarely appears in the conventional conical nozzles at high pressures, was observed at moderate upstream pressures for the configuration D2 proving the air passage existence along one side of the channel wall.

Although high strength steels represent yield strength up to 1300 MPa, welded structures reveal lowerstrength values. The strongest commercially available electrode provides the yield strength of about900 MPa. Therefore, in welded steels with strength above this type of filler metal, achieving anacceptable global strength is a crucial issue.

In this master thesis, affects of different welding procedures on static strength of welded jointsof Weldox 960 and Weldox 1100 steels, were studied. These steels are produced by SSAB inOxelösund. Meanwhile, finite element method analyses were applied in order to investigatethe static strength behavior of such weldments under uniaxial tension.

The welding parameters which were selected as variables are:

•  Heat input
• Weld joint geometry
• Filler metal

When weld metal is undermatching in strength levels than the base material, by applyingtension the soft weld metal begins to deform before parent metal. At that point thedeformation of resulted soft zone, including the weld metal and the heat affected zone, ishindered by high strength parent metal. Thus, uniaxial stress caused by uniaxial load isconverted to multiaxial stress. This conversion in tension results in increase in the staticstrength of weldment. The increase in strength is emphasized by increase in the width of thewelded joint while the thickness of the plate is kept as constant.

After experiments and performing FEM studies, it was revealed that the static strength ofWeldox 960 welded joints approaches towards the tensile strength of parent metal by increasein the width of the weldment. In Weldox 1100 joints; a slight increase in tensile properties ofthe weldments, when the width of the sample increases, was observed.

CFF s are used to filter liquid metal in the aluminum industry. CFFs are classified in grades or pores per inch (PPI), ranging froml0-100 PPI. Their properties vary in everything from pore and strut size to window size. CFFs of 80-100 PPI are generally not practical for use by industry, as priming of the filters by gravitational forces requires an excessive metal head. Recently, co-authors have invented a method to prime such filters using electromagnetic Lorentz forces, thus allowing filters to be primed with a low metal head. In the continuation of this research work, an improved experimental setup was developed in the present study to validate previous results and to measure the permeability of different filters, as well as a stack of filters. The study of permeability facilitates estimation of the required pressure drop to prime the filters and the head required to generate a given casting rate.

Lower hot ductility can lead to cracks in steels. Hot ductility is affected by grain boundary sliding at temperatures higher than A3 and by the presence of thin films of ferrite at grain boundaries at temperatures lower than A3. Grain boundary sliding might occur because of the segregation of harmful elements like sulphur, etc. While thin films of ferrite at grain boundaries lead to easy interlinking of MnS precipitates at grain boundaries and ultimately may cause cracks in the material. Also, stress concentration is higher at thin ferrite films at grain boundaries which for being softer as compared to austenite matrix lead to cracks in the material. Elongated  (Fe, Mn)S sulphides are more detrimental for the hot ductility as compared to round ones. Higher aspect ratio of the precipitates is also dependent on sulphur content. The higher the sulphur content, the higher would be the hot ductility. Silicon, being a ferrite stabilizer, causes the volume fraction of ferrite to increase which improves the hot ductility of the steels. Hot ductility can be improved by adding Boron that segregates to grain boundaries instead of sulphur improving the strength of grain boundaries. Increasing silicon content can lead to higher volume fraction of ferrite thus improving ductility because stress would uniformly be distributed across the grain and not merely on the grain boundaries. Apart from that, decreasing the solution treatment temperature and increasing holding time on solution treatment temperature can lead to lower dissolved content of sulphur and coarser MnS precipitates hence improving hot ductility. 

Pin-on-disc testing was used to investigate the sliding behavior and the wear products of a low-steel friction material against a cast iron disc at different applied loads, to investigate the effect of the temperature rise induced by frictional heating. The testing rig was operated in a clean chamber with a purified incoming air flux. The outgoing flux carries the wear particles to an impactor that counted and sorted them by average diameter and weight. At increasing applied loads, corresponding to a proportional increase of the pin-disc contact temperature, the coverage of both the pin and disc surface by a friction layer was found to increase too. The relevant X-Ray diffraction patterns revealed the presence of a large amount of graphite and different compounds originating from the friction material and from the counterface disc, mainly iron oxides, as concerns this latter. After the test at the lowest investigated load, i.e., 1 kg, the disc worn surface exhibited abrasive grooves and a discontinuous friction layer mainly made of compacted iron oxide particles. After the test at higher loads, i.e., 5 and 7 kg, the disc surface was covered by a compact friction layer. As concerns the friction layer on the pins, most of the ingredients from the friction material were detected, in association with the iron oxides from the disc. These results can be interpreted in terms of the temperature stability range of the phenolic resin used as a binder of the friction material. The characterization of the collected airborne wear debris showed that the particles produced by the low temperature (i.e., low load) test were mostly equiaxed; whereas those produced by the high temperature (i.e., high loads) tests, predominantly displayed a plate-like morphology. The mechanisms of their formation in relation to the characteristics of the friction layers are illustrated and discussed.

In this paper, the experimental flow boiling visualization results of a microchannel are presented and discussed. A series of visualization experiments have been conducted in a horizontal, circular, uniformly heated microchannel, to record the two-phase flow patterns evolved during the boiling process and to study the ebullition process. A high speed camera (REDLAKE HG50LE) with a maximum of 100000 fps together with tungsten lights was used to capture the images along the test section. Microchannel was made of circular fused silica tube having an internal diameter of 0.781 mm and a uniformly heated length of 191 mm. Outside of the test tube was coated with a thin, electrically conductive layer of Indium Tin Oxide (ITO) for direct heating of the test section. Refrigerant R134a was used as working fluid and experiments were performed at two different system pressures corresponding to saturation temperatures of 25 degrees C and 30 degrees C. Mass flux was varied from 100 kg/m(2)s to 400 kg/m(2)s and heat flux ranged from 5 kW/m(2) to 45 kW/m(2). Visualization results show that the bubble growth is restricted by the tube diameter which results in very short existence of isolated bubbly flow regime except essentially restricted to a very short length of test tube. Flow patterns observed along the length were: Isolated bubble, elongated bubble, slug flow, semi annular and annular flow. Rigorous boiling and increased coalescence rates were observed with increase in heat flux. Bubble frequency was observed to increase with both heat and mass flux. A comparison with our previous flow boiling visualization studies, carried out for a test tube of 1.33 mm internal diameter, shows that the number of active nucleation sites is less while the bubble frequency is higher for the current study. Mean bubble length and bubble velocity during elongated bubble flow pattern have also been calculated from the images obtained during the tests.

Bi-component hard (H) (hexaferrite) and soft (S) (spinel) ferrites nanocomposites are gaining interest scientifically and technically, not only for combining the high magnetization of spinel ferrite nanomaterials and the high coercivity of hexaferrite magnetic nanomaterials but also for the outstanding exchange-coupling behavior among hard and soft magnetic phase. The improved magnetic features lead to produce a new nanocomposite with higher microwave absorption capacity in comparison with ferrites with a single absorption mechanism. Exchange-coupled effect has a potential application based on microwave absorption, recording media, permanent magnets, biomedical and other applications. Intensive studies have been conducted on this topic to produce hard/soft (H/S) ferrite nanocomposites with establishment of exchange coupled effect between the two phases. Preparation methods, microstructure, magnetics features, microwave and dielectric properties, and applications are elaborated. Consequently, a comprehensive effort has been made to contain an original reference investigating in detail the precise outcomes of the published papers. 

Detta projekt bygger på framställningen och analysen av en tidigare outforskad chitosan-stearinsyra (CS-SA) färg med bi pollen som mikrokapslar för inkapsling av 2-mercaptobenzothiazole (MBT) som en vattenlöslig och biokompatibel anti-korrosions färg. CS-SA var tillverkat med en carbodiimide reaktion för att bilda miceller som ska omslutna pollenkornen, och även ett försök med vidare tvärbindning mellan chitosanen med glutaraldehyde (GA) gjordes. Stearinsyra fick interagera hydrofobiskt med den modifierade pollen och tvärbindes sedan med chitosan, som visade sig vara lyckad med hjälp av FTIR analys. Enkapsuleringen av MBT visade sig med UV-Vis spektroskopi vara lyckad, dock på grund av pollens stora korn (ca 20 μm) orsakade problem med att bilda en stabil barriär mot omgivningen. Storleken av pollen och dess reaktivitet med carbodiimide tvärbindningen är de mest allvarliga problemen med pollen som mikrokapslar, och därav gjordes inga vidare tester av korrosions egenskaperna då detta kräver en täckande och stabil film genom hela mätningen. Då även referensfärgen som gjordes utan pollen gav avsevärt mycket bättre resultat i det avseendet är slutsatsen att reaktiviteten av pollen gör det problematiskt att tvärbinda med chitosan och valet av en kapsel av rätt storlek och hur den inkapslar är avgörande för att utveckla en bra korrosionsskyddande färg.

Under senare år har materialet grafit studerats omfattande eftersom dess användning i diverse applikationer har ökat. Detta omfattar områden som batterier, bilar och solceller. När behovet av denna typ av material ökar måste metodernas effektivitet beaktas för processen. Denna avhandling presenterar en alternativ metod för att framställa grafit från biokol som är förnybar. Biokol i kombination med en katalysator användes istället för den traditionella metoden som är känd för sina höga temperaturer och tidskrävande processer. Ett viktförhållande av rent järn till biokol på cirka 22,4 viktprocent i grafit användes i produktionsprocessen. Resultatet analyserades med röntgendiffraktion och metoden lyckades producera en högkristallin grafit vid en temperatur av 1300 ° C och inom ett tidsintervall på ca 3 timmar. Resultatet visade även att genom användningen av en katalysator i processen uppnåddes en hög "grad av grafitisering" med en måttlig kristallstorlek.

Kärnkraftsteknologin genomgår just nu en revolutionerande utvecklingspro- cess och dess användning debatteras över hela världen där hållbarhet är en av de viktigaste ståndpunkterna i materialvetenskapsområdet. Vissa komponenter i ett kärnkraftverk blir utsatta för en bestrålande miljö vilket orsakat stor skada på materialet över tid. Det är därför av högsta vikt att dessa material är desig- nade för att motstå sådana miljöer på grund av kärnkraftverkens långa livstid. De högenergetiska partiklarna som är förekommande vid kärnreaktioner gene- rerar punktdefekter i materialets mikrostruktur vilka ändrar de makroskopiska egenskaperna hos materialet.

Värmehantering är kritiskt i ett kärnkraftverk och därför är detta arbete de- dikerat till att modellera effekten av försämring av värmeledningsförmågan i kristallgittret, som resultat av punktdefekterna, och att definiera sambandet. Detta uträttas genom ab initio simuleringar av superceller där de kvantmekaniska krafterna beräknas med täthetsfunktionalsteori med en generaliserad approximation av täthetsgradienten för den tillhörande utbytes- och korrela- tionstermen. Boltzmann ekvationen löses med hjälp av linjärisering och med en approximation av relaxationstiden vilket används för att beräkna värmeledningen i gittret för modellen. Fononernas band-moder och tillståndstäthet undersöks därtill.

För närvarande finns det inga rapporter bland litteraturen där detta ämne behandlas med samma metoder.

Användningen av fiberförstärkta polymerer (FRP)-­kompositmaterial i strukturella applikationer har ökat under de senaste decennierna i högpresterande sektorer, såsom i fordons­ och flygindustrin, för viktminskningsändamål. FRP-­kompositmaterial kan dock erbjuda mer betydande innovationspotential. Användningen av CNTs i kombination med kompositmaterial kan möjliggöra skapandet av multifunktionella material, beroende på FRP för den strukturella sidan och CNT för avkänningsförmågan. I denna masteruppsats undersöktes inbäddningen av ett Vertical Aligned Carbon Nanotube (VACNT) lager i den interlaminära regionen av Carbon Fiber (CF) laminat för att ge polyvalent avkänningsförmåga till materialet. För att få exakta resultat måste sensorn isoleras från resten av laminatet. Av denna anledning var huvudproblemet som skulle lösas i detta projekt den elektriska isoleringen på CNT-­lagret och dess kontakter från lagren av CF­-laminat. Denna studie syftar till att hitta en lämplig isoleringsteknik för att tillämpa CNT­sensorteknologin, utvecklad i tidigare studier, i CF-­laminat. Även om de är tänkta för flygtillämpningar, kan dessa sensorer appliceras på olika strukturella komponenter inom olika områden.

A project to construct a high-speed road deflection tester was initiated in the 1991. A mid-sized truck was used as a carrier for the first prototype. The results were promising and it was decided to build a full-size truck system. The new vehicle, based on a Scania R143 ML, was completed in 1997.

The Road Deflection Tester (RDT) is equipped with two arrays of twenty noncontact laser sensors that collects transversal surface profiles at normal traffic speeds. One profile, placed between the wheel axles, constitutes an unloaded case. The other profile, just behind the rear axle of the vehicle, constitutes the loaded case. By subtracting the front cross profile from the corresponding rear one, the "deflection profile" is assessed. The deflection is assumed to vary with the stiffness of the road.

In order to produce a large load on the rear wheels the engine was mounted in the back of the vehicle, slightly behind the rear axle. In testing mode the rear axle force is approximately 112 kN, and the front axle force is about 30 kN. An incremental wheel pulse transducer, two force transducers and two accelerometers, an optical speedometer and a gyroscope are also mounted on the RDT.

The first test programme was carried out in 1998. Due to the careful choice of test sections, data from these sections still produce the best results. A smaller test programme was carried out in 2001, and a larger one in 2002 when the RDT was taken to England and France for demonstration. Promising results, both on an aggregated scale and for individual test sections, have been obtained. The RDT compares favourably with the Falling Weight Deflectometer.

Short histories of road construction and road research give some historical and cultural background to the more recent developments. A more comprehensive history of rolling deflectographs presents all devices found in the literature from the start in the mid-fifties when the California Traveling Deflectograph and Lacroix Deflectograph were constructed, to the latest laser based High-Speed Deflectograph. Many references are given for further reading.

The data acquisition hardware on the RDT system consist of sensors, signal converters, signal processing cards, an industrial computer for data communication, and an ordinary PC for operating the equipment and data storage. The software used to evaluate the data is written entirely in Matlab. Many levels of pre-processing make evaluation relatively fast, and the modularised design makes it easy to implement new evaluation algorithms in a clean and efficient way.

A literature survey on the deformations of solids under static and moving load is presented in Appendix A. The static case started with Boussinesq in 1885, was much developed in the sixties, but since the eighties only a very limited amount of new results have been published. The moving load case, on the other hand, is still an field of active research and development.

Zr-based materials have found their main application in the nuclear field having high corrosion resistance and low neutron absorption cross-section. The oxide layer that is formed on the surface of these alloys is meant to be the barrier between the metal and the corrosive environment. The deterioration of this protective layer limits the lifetime of these alloys. A better understanding of the transport phenomena, which take place in the oxide layer during oxidation, could be beneficial for the development of more resistant alloys.

In the present study, oxygen and hydrogen transport through the zirconia layer during oxidation of Zr-based materials at temperatures around 400C have been investigated using the isotope-monitoring techniques Gas Phase Analysis and Secondary Ion Mass Spectrometry. The processes, which take place at oxide/gas and oxide/metal interface, in the bulk oxide and metal, have to be considered in the investigation of the mechanism of hydration and oxidation. Inward transport of oxygen and hydrogen species can be influenced by modification of the surface properties. We found that CO molecules adsorbed on Zr surface can block the surface reaction centers for H₂ dissociation, and as a result, hydrogen uptake in Zr is reduced. On the other hand, coating the Zr surface with Pt, resulted in increased oxygen dissociation rate at the oxide/gas interface. This generated enhanced oxygen transport towards the oxide/metal interface and formation of thicker oxides. Our results show that at temperatures relevant for the nuclear industry, oxygen dissociation efficiency decreases in the order: Pt > Zr₂Fe > Zr₂Ni > ZrCr₂ ≥ Zircaloy-2.

Porosity development in the oxide scales generates easy diffusion pathways for molecules across the oxide layer during oxidation. A novel method for evaluation of the gas diffusion, gas concentration and effective pore size of oxide scales is presented in this study. Effective pore sizes in the nanometer range were found for pretransition oxides on Zircaloy-2.

A mechanism for densification of oxide scales by obtaining a better balance between inward oxygen and outward metal transport is suggested. Outward Zr transport can be influenced by the presence of hydrogen in the oxide/metal substrate. Inward oxygen transport can be promoted by oxygen dissociating elements such as Fe-containing second phase particles. The results suggest furthermore that a proper choice of the second-phase particle composition and size distribution can lead to the formation of dense oxides, which are characterized by low oxygen and hydrogen uptake rates during oxidation.

Industriella nanopartiklar används i allt större utsträckning. Därför är det av stor vikt attundersöka hela livscykeln som dessa produkter går igenom for att säkerhetsställa att de inte utgör någon fara för miljön och ekosystemen som de kan komma att hamna i. Som ett resultat av deras storlek interagerar nanopartiklar annorlunda med sin omgivning om man jämför med bulkmaterial av samma sammansättning, detta nanopartiklar både sina unika fördelar och risker. Riskerna innefattar ofta oönskade interaktioner med biologiska  kretslopp som kan resultera i toxicitet. I den här rapporten läggs fokus på just denna typ av kemiska omvandlingar som nanopartiklar av mangan och manganoxid kan tänkas genomgå i det naturliga kretsloppet. Applikationer man ofta ser dessa partiklar i är batteriteknologi och katalys. De medium som används för att studera omvandlingarna är en lösning som efterliknar ytvatten från en klar sjö. Exponeringar gjordes både med denna lösning så som den är och med tillsatt naturligt organiskt material, NOM.En rad olika experiment gjordes så som analyser med AAS för att undersöka partiklarnas upplösning, NTA för partikelstorlekar och ATR-FTIR som undersökte adsorption på partiklarna. Även en studie med en DCFH metod där ökat ROS aktivitet undersöktes och en rad med SHM simuleringar gjorda i Visual MINTEQ utfördes.

Resultaten från NTA och AAS analysen visade sig inte vara särskilt tillförlitliga på grund av tvetydliga resultat som troligen orsakats av problem med provpreparationen. Men resultaten från båda dessa pekar mot att upplösningshastigheten blir något hämmad då man tillsätter naturligt organiskt material, för båda partiklarna. Från ART-FTIR och simuleringarna kunde de säkerhetsställas att adsorption av NOM, karbonat och svavel sker på båda partiklarna, möjligen i fler än ett lager. När det kommer till ROS studien kunde inga bevis på ökad ROS aktivitet hittas med den använda metoden. Dock så kunde inte ökat väteperoxid aktivitet mätas med den metod som användes så detta hade varit av intresse att testa i framtiden. Andra studier som också skulle vara hjälpsamma för att ge en mer nyanserad bild av detta system är en studie om partiklarnas zeta potential och merundersökningar om vilken typ av adsorptions mekanism som sker vid partiklarnas yta.

Biomass is an important source of energy and the most important fuel worldwide after coal, oil and natural gas. Biomass does not add carbon dioxide to the atmosphere as it absorbs the same amount of carbon in growing as it releases when consumed as a fuel. Its advantage is that it can be used to generate electricity with the same equipment or power plants that are now burning fossil fuels. However, the low energy density of the biomass requires developments and advances in conversion technologies in order to increase process efficiency and reduce pollution. One of the most promising converting methods for treatment of biomass and waste feedstock is gasification. In this study a highly preheated air/steam of temperatures >800^oC is introduced to the gasifier which is fed with wood pellets’ feeding rate 40-50 kg/h.

The system is redesigned to work as a continuous type updraft HTAG. The aim of the studies was to test the performance of an Updraft configuration in various operating conditions using Biomass (wood pellets) as the feedstock, and facing primarily technological difficulties and process limitations. Determining the Temperature distribution along the reactor and synthesis gas composition of the process are reported for various operating parameters.

During the experiment it is observed that the introduction of more steam flow rate increases the LHV (lower heating value) of the synthesis gases. Three case studies (Case1, Case2, and Case3) are conducted, each case having different biomass feeding rate, steam flow rate and process air flow rate. The result show that the amount of LHV of gas varied from 3 to 4.2 MJ/Nm3, the H2: CO ratio is between 0.5-0.9 and the CO/CO2 ratio has range 1.0-1.7.  Case 3, in which 40 kg/h biomass feeding rate and 80 kg/h Steam flow rate is maintained gives High LHV, high H2/CO ratio and more CO/CO2 ratio among the rest case studies.

Further improvement can be done within the reactor, increase in retention time and variation of more parameters can examine, in order to get the optimum result in future.

Korrosion är en mekanism som kraftigt reducerar livslängden för metaller i olika miljöer, särskilt i vatten- eller fuktmiljö. De globala underhållskostnaderna på grund av korrosion uppskattas i miljarder dollar per år, och faktiska lösningar med avseende på beläggning innehåller vanligtvis giftiga eller miljöfarliga arter. Med en ständigt ökande begränsning genom miljörestriktioner och bestämmelser krävs det en hållbar lösning.

Kitosan, den näst vanligaste biopolymeren, kan vara lösningen på många problem. Skaldjuravfall är en av de viktigaste källorna till kitosan. Dess resurseffektivitet, biokompatibilitet och mångsidiga fysikalisk-kemiska egenskaper för kelering och tvärbindning gör kitosan till en lovande kandidat som matrismaterial för biobaserade antikorrosiva applikationer.

Syftet med denna masteruppsats är att kombinera egenskaperna hos kitosan med den höga porositeten hos bipollen som antikorrosivt medel för att erhålla en helt hållbar lösning för korrosionsskydd. Målet med detta mycket ambitiösa projekt är att producera ett sammansatt material med en tredubbel verkan: korrosionsskydd för metallytor, självhelande egenskap hos beläggningen och anti- biobeväxningsaktivitet.

Resultaten visar att en biopolymerkomposit i form av suspension eller beläggningar med alla önskade komponenter kan uppnås. Specifikt har en biopolymer-nanokomposit sammansatt av kitosanmatris med inbäddade pollenkorn, som i förväg packats med antikorrosionsmedlet 2-mercaptobenzotiazol (MBT) och med zinkoxid-nanopartiklar, producerats.

Den fysikalisk-kemiska karakteriseringen av biopolymerkompositen och dess beläggningar, liksom elektrokemiska impedansspektroskopimätningar (EIS) på rostfri stålplåt med sådana beläggningar tyder på att en enhetlig och kompakt beläggning erhålls. Trots sin goda hydrofobi med maximal kontaktvinkel 134,32 ± 3,84° med toppbeläggningen, är nanokompositbeläggningen av kitosan fortfarande permeabel för vatten, delvis på grund av den relativt stora storleken hos pollen (ca. 20 μm) som introducerar luckor och stör integriteten hos beläggningen. Därför uppnås inte en fullständig immersionskorrosionsbeständighet. Sammanfattningsvis genomfördes fasövergång av hydrofobt pollen till hydrofil kitosanmatris, MBT-packning i pollen, ZnO-inkapsling i kitosan, samt tvärbindning av kitosan med framgång. En beläggning baserad på sådan biopolymer-nanokomposit framställs på rostfritt stål och undersöks med avseende på dess korrosionsegenskaper. Framtida arbete kommer att bestå i att välja en lämplig storlek av pollen som en mikrobehållare för att förbättra beläggningens integritet, och så småningom förse beläggningen med tre-i-ett-funktionen, dvs.antikorrosion, antimikrobiell och självhelande.

For the purpose of modeling internal corrosion of the stainless steel fuel pins in fast nuclear reactors, the present work presents a thermodynamic description of the Fe–Ni–Te system modeled via the Calphad method. The liquid phase was modeled using the ionic 2-sublattice liquid model. Only binary parameters were optimized in the β2, δ and τ solid phases, to fit the isothermal section at 600 °C. The liquid did not require much adjustment from the extrapolation from the binary Fe–Te, Ni–Te and Fe–Ni systems. The paper presents a re-optimization of the Fe–Te liquid description in order to remove inverted liquid miscibility gaps at high temperatures. The resulting phase diagrams reproduce experimental isothermal sections well, and fits liquidus and solidus data very well. The description will be incorporated into the Thermodynamics of Advanced Fuels - International Database (TAF-ID). This will then be coupled with the Germinal system code to model the fission-product induced corrosion in nuclear fuel pins.

I jakten på säkrare, renare och mer uthålliga energislag för att täcka våra växande behov, utvecklas en ny typ av kärnreaktor som kyls av flytande metall istället för vatten. Men, specifikt för denna typ av kärnreaktor har man upptäckt en unik form av korrosion av inkapslingsmaterialet till kärnbränslet i härden, så kallad bränsle-inkapsling kemisk interaktion (FCCI) och sönderfallsproduktsinducerad smältmetallförsprödning (FPLME). Detta är en invecklad kemisk process som har observerats i bränslestavarna för natriumkylda snabba reaktorer (SFR). För att kunna förutsäga risker och konsekveser relaterade till denna korrosionsprocess, behöver man simulera förloppet. Och för detta krävs en termodynamisk beskrivning av de involverade ämnena, d.v.s Cr--Cs--Fe--Ni--Te--O. Denna avhandling behandlar utvecklingen av en sådan termodynamisk beskrivning av systemet Cr--Fe--Ni--Te med hjälp av numerisk optimering av modellparametrar, med stöd från ab-initio beräkningar och experimentalla studier.

Within the field of neuroprosthetics the possibility to use implanted electrodes for communication with the nervous system is explored. Much effort is put into the material aspects of the electrode implant to increase charge injection capacity, suppress foreign body response and build micro sized electrode arrays allowing close contact with neurons. Conducting polymers, in particular poly(3,4-ethylene dioxythiophene) (PEDOT), have been suggested as materials highly interesting for such neural communication electrodes. The possibility to tailor the material both mechanically and biochemically to suit specific applications, is a substantial benefit with polymers when compared to metals. PEDOT also have hybrid charge transfer properties, including both electronic and ionic conduction, which allow for highly efficient charge injection.

Part of this thesis describes a method of tailoring PEDOT through exchanging the counter ion used in electropolymerisation process. Commonly used surfactants can thereby be excluded and instead, different biomolecules can be incorporated into the polymer. The electrochemical characteristics of the polymer film depend on the ion. PEDOT electropolymerised with heparin was here determined to have the most advantageous properties. In vitro methods were applied to confirm non-cytotoxicity of the formed PEDOT:biomolecular composites. In addition, biocompatibility was affirmed for PEDOT:heparin by evaluation of inflammatory response and neuron density when implanted in rodent cortex.

One advantage with PEDOT often stated, is its high stability compared to other conducting polymers. A battery of tests simulating the biological environment was therefore applied to investigate this stability, and especially the influence of the incorporated heparin. These tests showed that there was a decline in the electroactivity of PEDOT over time. This also applied in phosphate buffered saline at body temperature and in the absence of other stressors. The time course of degradation also differed depending on whether the counter ion was the surfactant polystyrene sulphonate or heparin, with a slightly better stability for the former.

One possibility with PEDOT, often overlooked for biological applications, is the use of its semi conducting properties in order to include logic functions in the implant. This thesis presents the concept of using PEDOT electrochemical transistors to construct textile electrode arrays with in-built multiplexing. Using the electrolyte mediated interaction between adjacent PEDOT coated fibres to switch the polymer coat between conducting and non conducting states, then transistor function can be included in the conducting textile. Analogue circuit simulations based on experimentally found transistor characteristics proved the feasibility of these textile arrays. Developments of better polymer coatings, electrolytes and encapsulation techniques for this technology, were also identified to be essential steps in order to make these devices truly useful.

In summary, this work shows the potential of PEDOT to improve neural interfaces in several ways. Some weaknesses of the polymer and the polymer electronics are presented and this, together with the epidemiological data, should point in the direction for future studies within this field.

Electrodes intended for neural communication must be designed to meet boththe electrochemical and biological requirements essential for long term functionality. Metallic electrode materials have been found inadequate to meet theserequirements and therefore conducting polymers for neural electrodes have emergedas a field of interest. One clear advantage with polymerelectrodes is the possibility to tailor the material to haveoptimal biomechanical and chemical properties for certain applications. To identifyand evaluate new materials for neural communication electrodes, three chargedbiomolecules, fibrinogen, hyaluronic acid (HA), and heparin are used ascounterions in the electrochemical polymerization of poly(3,4-ethylenedioxythiophene) (PEDOT). The resultingmaterial is evaluated electrochemically and the amount of exposed biomoleculeon the surface is quantified. PEDOT:biomolecule surfaces are also studiedwith static contact angle measurements as well as scanning electronmicroscopy and compared to surfaces of PEDOT electrochemically deposited withsurfactant counterion polystyrene sulphonate (PSS). Electrochemical measurements show that PEDOT:heparinand PEDOT:HA, both have the electrochemical properties required for neuralelectrodes, and PEDOT:heparin also compares well to PEDOT:PSS. PEDOT:fibrinogen isfound less suitable as neural electrode material.

Mathematical modelling using differential equations is an important tool to predict the behaviorof vanadium redox batteries, since it may contribute to improve the device performance and leadto a better understanding of the principles of its operation. Modelling can be complementedby asymptotic analysis as a mean to promote reductions or simplifications that make modelsless complex. Such simplifications are useful in this context, whereas these models usuallyaddresses one cell only – the smallest operating unit – while real applications demand tensor hundreds cells implying on larger computational requirements. In this research, severaloptions for asymptotic reductions were investigated and, applied to different models, were ableto speed up the processing time in 2.46× or reduce the memory requirements up to 11.39%. Thecomputational simulations were executed by COMSOL Multiphysics v.4.4, also by in-housecode developed in MATLAB. The validation of results was done by comparing it to experimentalresults available in literature. Additionally, correlating the results provided by COMSOL withthe ones arising from the implemented sub-routines allowed to validate the developed algorithm.Key-words:

The increase in bearing capacity over time (i.e. set-up) of driven piles in non-cohesive soils is often substantial. However, the basic mechanisms behind the phenomenon are still not fully understood. In order to investigate the mechanisms related to set-up a comprehensive field test was performed involving a full-scale driven pile. The pile was instrumented with earth pressure cells and piezometers on the shaft, as well as a pressure cell at the pile toe. The pile was static load tested at different points in time during a period of almost two years. During the whole time period the long-term increase in the horizontal stress, due to stress relaxation, was monitored. However, during the actual loading of the pile a large increase in horizontal stress on the shaft was observed, as a result of confined dilatancy. The results showed that this mechanism had a major influence on the pile capacity and was clearly time-dependent. Furthermore, it was concluded that it was the predominant cause behind the observed set-up. The results provide a valuable insight into how piles behave during loading, as well as clarifying the basic mechanisms involved during set-up.

The current work is devoted to studying the evolution of deep level defects in the lower half of the 4H-SiC bandgap after high temperature processing and ion implantation. Two as-grown and pre-oxidized 4H-SiC sets of samples have been thermally treated at temperatures up to 1950 °C for 10 min duration using RF inductive heating. Another set of as grown samples was implanted by 4.2 MeV Si ions at room temperature (RT) with different doses (1- 4×108 cm-2). The so-called “D-center” at EV+0.6 eV dominates and forms after the elevated heat treatments, while it shows no change after the ion implantations (EV denotes the valence band edge). In contrast, the concentration of the so-called HK4 level at EV+1.44 eV increases with the implantation dose, whereas it anneals out after heat treatment at ≥ 1700 °C.

A technique based on Fourier Transform Infrared Spectroscopy-Attenuated Total Reflectance (FTIR-ATR) was developed and used to study movement of water into bitumen/substrate interfaces, as well as to characterize stripping. Bitumens from different sources were used and applied on various substrates (silicon, germanium and zinc selenide) as thin films. The influence of bitumen type, substrate type, temperature, film thickness and modification with amines, on water damage was studied. The technique gave information on water flow into interfaces and how stripping possibly occurs. It distinguished between stripping and non-stripping bitumens. At least one of three processes occurred, namely water diffusion, film fracture, and bitumen displacement by water, respectively. The diffusion of water did not obey Fick's law. Stripping was influenced by bitumen source when silicon and germanium substrates were used. Notching the films made the process of water entry almost occur immediately. Additives significantly reduced stripping in the moisture-sensitive bitumen on silicon and germanium substrates, even after film notching. Although, good agreement was observed between tests for the bitumens that did not strip, the tests on stripping bitumens showed poor agreement.

Spinodal decomposition is a phase separation mechanism within the miscibility gap. Its importance in case of Fe-Cr system, the basis of the whole stainless steel family, stems from a phenomenon known as the “475^oC embrittlement” which results in a ruin of mechanical properties of ferritic, martensitic and duplex stainless steels. This work is aimed at a better understanding of the phase separation process in   the Fe-Cr system.

Alloys of 10 to 55 wt.% Cr , each five percent, were homogenized to achieve fully ferritic microstructure and then isothermally aged at 400, 500 and 600^oC for different periods of time ranging from 30min to 1500 hours. Hardness of both homogenized and aged samples were measured by the Vickers micro-hardness method and then selected samples were studied by means of Transmission Electron Microscopy (TEM).

 It was observed that hardness of homogenized samples increased monotonically with increasing Cr content up to 55 wt.% which can be attributed to solution hardening as well as higher hardness of pure chromium compared to pure iron.  At 400^oC no significant change in hardness was detected for aging up to 1500h, therefore we believe that phase separation effects at 400^oC are very small up to this time. Sluggish kinetics is imputed to lower diffusion rate at lower temperatures. At 500^oC even after 10h a noticeable change in hardness, for alloys containing 25 wt.% Cr and higher, was observed which indicates occurrence of phase separation. The alloy with 10 wt.% Cr did not show change in hardness up to 200h which suggests that this composition falls outside the miscibility gap at 500^oC. For compositions of 15 and 20 wt.% Cr only a small increase in hardness was detected even after 200h of aging at 500^oC, which could be due to the small amounts of α´ formed. However, it means that alloys of 15 wt.% Cr and higher are suffering phase separation. For compositions inside the miscibility gap, hardening effect is a result of phase separation either by nucleation and growth or spinodal decomposition. To distinguish between these two mechanisms, TEM studies were performed and we found evidence that at 500^oC the Fe-25 wt.% Cr sample decomposes by nucleation  and growth  while that of 35 wt.% Cr  shows characteristics of the spinodal mechanism. For compositions inside the miscibility gap, with increasing Cr content up to 40% the change in hardness generally increased and for 45% and higher it always decreased. This suggests that the composition range corresponding to the spinodal region at 500^oC is biased towards the Fe-rich side of the phase diagram. At 600^oC only samples of 25, 30 and 35 wt.% Cr were studied because according to the previous studies, the spinodal boundary is most probably located in this composition range. However, no change in hardness was observed even up to 24h. We believe that this means the miscibility line lies below 600^oC for alloys containing 35 wt.% Cr and lower. Further investigations are needed to confirm and explain this result. 

In this work we study electromagnetic properties of a resonator recently suggested for the search of axions-a hypothetical candidate to explain dark matter. A wire medium loaded resonator (called a plasma haloscope when used to search for dark matter) consists of a box filled with a dense array of parallel wires electrically connected to top and bottom walls. We show that the homogenization model of a wire medium works for this resonator without mesoscopic corrections, and that the resonator quality factor Q at the frequency of our interest drops versus the growth of the resonator volume V until it is dominated by resistive losses in the wires. We find that even at room temperature metals like copper can give quality factors in the thousands-an order of magnitude higher than originally assumed. Our theoretical results for both loaded and unloaded resonator quality factors were confirmed by building an experimental prototype. We discuss ways to further improve wire medium loaded resonators.

This study aims to understand crack opening-closing behavior on pre-fatigued welded joints repaired by High Frequency Mechanical Impact (HFMI). Detailed rat-hole specimen models inserting different depths of rectangle slit in the weld toes to simulate initial cracks were used in the HFMI treatment simulation. Induced compressive residual stress, change of slit geometry, and opening-closing behavior of the slit after HFMI treatment simulation were investigated numerically. The amount of induced compressive residual stress around the slit tip is reduced when slit depth becomes larger, and slit size of about 0.4 mm remains when the slit depth is 2.0 mm. The opening-closing behavior of HFMI treated slit was examined based on change of strains along the slit face. The slit is opened from the bottom side prior to its treated surface. Additionally, the crack opening-closing behavior was investigated experimentally using pre-fatigued out-of-plane gusset welded joints repaired by impact crack closure retrofit treatment. Phased array ultrasonic testing system was used to examine the change of echo height from cracks. It could be concluded that similar behavior as the numerical investigation is observed. From both investigations, experimentally and numerically, the behavior on pre-fatigue welded joints repaired by HFMI could be studied successfully. 

This study aims to investigate influence of under- and over-treatment on residual stress state induced by HFMI numerically. Finite element simulations were performed using a flat plate model considering S355 where feed rate and the number of hits were varied. To reduce computational time, the mass scaling method was adopted to the simulations. In addition, in order to survey influence of surface removal on residual stress state, electropolishing was conducted after the HFMI simulation. Additional simulations were performed on bead on plate model considering JIS-SM400 in order to investigate applicability of isotropic hardening model for residual stress estimation. From the results, the mass scaling method can result in reducing computational time more than 90% with reasonable good estimation of the residual stresses.The investigations regarding under- and over-treatment reveal that high feed rate mainly influences residual stress state on the treated surface and the number of hits is independent of amount of induced residual stress. Surface removal after the simulation can result in slightly improving the accuracy of the estimated residual stresses. The simulations to bead on plate model give reasonable results in a depth of around 0.2 mm even when the residual stresses due to welding is disregarded. 

In this study, to evaluate the influence of grid blast following to the peening process on the fatigue strength improvement, residual stress measurement and fatigue tests have been conducted. Examined peening processes were UIT, PPP and HP with ICR apparatus. For the residual stress measurement, plate and on-bead specimens made of JIS-SM400, SBHS400, SBHS500 and SBHS700 were used, and X-ray diffraction method was applied to the measurement. The results concluded that the differences in the compressive residual stress distribution in the vicinity of peened area with and without blast are not so significant. For the fatigue tests, out-of-plane gusset welded joint specimens made of JIS-SM490 and SBHS500 were used. Fatigue tests were conducted under stress ratio R=0.0 and 0.5. Fatigue tests showed that fatigue strength of peened specimens with blast are almost the same as that of peened specimens without blast, and those results were observed independently of steel grade and of peening methods.

A set of Be and W tiles removed after the first ITER-like wall campaigns (JET-ILW) from 2011 to 2012 has been analysed. The results indicate that the primary erosion site is in the main chamber (Be) as in previous carbon campaigns (JET-C). In particular the limiters tiles near the mid-plane are eroded probably during the limiter phases of discharges. W is found at low concentrations on all plasma-facing surfaces of the vessel indicating deposition via plasma transport initially from the W divertor and from main chamber W-coated tiles; there are also traces of Mo (used as an interlayer for these coatings). Deposited films in the inner divertor have a layered structure, and every layer is dominated by Be with some W and O content.

This licentiate thesis is generally concerned with the ductile failure and rupture mechanisms encountered under combined tension and torsion loading. In the first part entitled Paper A, an experimental investigation of the rupture mechanisms in a mid-strength and a high strength steel was conducted employing a novel test configuration. The specimen used was a double notched tube specimen loaded in combined tension and torsion at a fixed ratio. The effective plastic strain, the stress triaxiality and the Lode parameter was determined in the centre of the notch at failure. Scanning electron microscopy of the fractured surfaces revealed two distinctively different ductile rupture mechanisms depending on the stress state. At high stress triaxiality the fractured surfaces were covered with large and deep dimples, suggesting that growth and internal necking of voids being the governing rupture mechanism. At low triaxiality it was found that the fractured surfaces were covered with elongated small shear dimples, suggesting internal void shearing being the governing rupture mechanism. In the fractured surfaces of the high-strength steel, regions with quasi-cleavage were also observed. The transition from the internal necking mechanism to the internal shearing mechanism was accompanied by a significant drop in ductility.

In the second part entitled Paper B, a micromechanics model based on the theoretical framework of plastic localization into a band introduced by Rice is developed. The model employed consists of a planar band with a square array of equally sized cells, with a spherical void located in the centre of each cell. The periodic arrangement of the cells allows the study of a single unit cell for which fully periodic boundary conditions are applied. The micromechanics model is applied to analyze failure by ductile rupture in experiments on double notched tube specimens subjected to combined tension and torsion carried out by the present authors. The stress state is characterized in terms of the stress triaxiality and the Lode parameter. Two rupture mechanisms can be identified, void coalescence by internal necking at high triaxiality and void coalescence by internal shearing at low triaxiality. For the internal necking mechanism, failure is assumed to occur when the deformation localizes into a planar band and is closely associated with extensive void growth. For the internal shearing mechanism, a simple criterion based on the attainment of a critical value of shear deformation is utilized. The two failure criteria capture the transition between the two rupture mechanisms successfully and are in good agreement with the experimental result.

På den yttersta ytan av däggdjurshår återfinns den grenade fettsyran 18-methyleikosansyra tillsammans en mindre mängd av de raka fettsyrornapalmitinsyra och stearinsyra. Den exakta rollen av 18-MEA är dock ännu inte heltklarlagd. Ett monoskikt av 18-MEA på en subfas innehållande kadmiumklorid påtvingar en krökning av vatten–luftgränsytan. Det leder till bildandet av 3D-domäner som lätt kan överföras från vattenytan till fasta ytor vilket möjliggör att dekorera dessa ytor med komplexa och multifunktionella strukturer. Detta projekt undersöker om andra, miljövänliga motjoner i subfasen också skulle leda till bildandet av 3D-domäner eller om det är en inneboende egenskap hos kadmiumklorid. Det här ger även insikt om hur motjoner kan användas för att påverka och kontrollera domänbildningen. En kombination av Langmuirtråg och atomkraftsmikroskopi används för att karakterisera monoskikten. Det visas att en subfas innehållande kadmium inte är nödvändig och att en mer miljövänlig natriumsubfas kan användas för att bilda 3D-domäner. Det visas också att olika kedjors längd interagerar olika med den grenade fettsyran 18-MEA, vilket resulterar i bildandet av olika strukturer i deponerade monoskikt. Det visas också att yttrycket vid deponering och sammansättningen av fettsyror i mono skiktet påverkar egenskaperna hos monoskiktet, vilket leder till varierande storlek och struktur på de bildade domänerna, där cirkulära och långsträckta domäner, kontinuerliga labyrintstrukturer och dendritiska tusenfotingsliknande strukturer observeras.

Theoretical studies of point defect interactions and structural stability of compounds have been performed using density functional theory. The defect-related properties, such as activation energy of diffusion, electronic and magnetic structure of selected materials have been studied.

The major part of the present work is devoted to a very important material for semiconductor industry, GaAs. The formation energies of intrinsic point defects and the solution energies of 3d transitions in GaAs have been calculated from first principles. Based on the calculated energies, we analysed the site preference of defects in the crystal. The tendency of defects to form clusters has been investigated for the intrinsic defects as well as for impurities in GaAs. The magnetic moment of 3d impurities has been calculated as a function of the chemical environment. The possibility of increasing the Curie temperature in (Ga,Mn)As by co-doping it with Cr impurities has been examined on the basis of calculated total energy difference between the disordered local moment and the ferromagnetically ordered spin configurations. We found that, in order to reach the highest critical temperature, GaAs should be separately doped with either Cr or Mn impurities. Also, we have shown that diffusion barrier of interstitial Mn depends on the charge state of this impurity in (Ga, Mn)As. The formation of defect complexes between interstitial and substitutional Mn atoms, and their influence on the value of diffusion barrier for interstitial Mn, has been studied.

The pair interactions energies between interstitial oxygen atoms in hcp Zr, Hf and Ti have been calculated using first principles. Based on the calculated energies, the oxygen ordering structures in IVB transition metal solid solutions have been explained. A prediction of nitrogen ordering in Hf-N solid solution has been made.

The thermodynamic description of intermetallic compounds in the Zr-Sn binary system has been obtained. The conclusion has been made that Zr substitution on the Sn sites takes place in the Zr₄Sn phase, which accounts for the unusual stoichiometry of this Cr3Si structure type compound.

The influence of pressure on the phase stability in the Fe-Si system has been investigated. We have found instability of the hcp Fe_0.9Si_0.1 random alloy with respect to the decomposition onto the Si-poor hcp Fe alloy and the B2 FeSi under high pressure. The tendency of this decomposition becomes stronger with increasing the applied pressure.

The formation energies of intrinsic point defects and solution energies of transition metal impurities in gallium arsenide are determined on the basis of ab initio calculations using the method of a locally self-consistent Green's function, which is a generalization of the coherent potential approximation. Based on the calculated energies, the conclusion is made that the As-Ga antisite defect is the most common intrinsic defect in GaAs. Calculations showed that transition metal impurities, except for Ni, preferentially occupy gallium sites substitutionally. The magnetic moments of impurity atoms are calculated as a function of the chemical environment. It is shown that, in compensated GaAs, Mn atoms tend to form clusters.

Electronic structure, thermodynamic, and magnetic properties of 3d-transition metal (TM) impurities in GaAs have been studied from first principles using Green's function approach. The studied TM impurities (V, Cr, Mn, and Fe) are found to form substitutional alloys on the Ga sublattice. The possibility of raising the Curie temperature TC in (GaMn) As by co-doping it with Cr impurities was examined on the basis of total energy difference between the disordered local moment (DLM) and the ferromagnetically ordered (FM) spin configurations. The calculated Curie temperature and magnetic moment have maxima for GaAs doped with Cr and Mn. The magnetic properties of Mn-doped GaAs are shown to be more sensitive to antisite As defects than those of Cr-doped GaAs. However, the Cr impurities are sensitive to the presence of acceptor defects, such as vacancies on the Ga sublattice. The investigation of the electronic structure of pseudo-ternary alloys (Ga(1-x-y)MnxCry) As has shown a mutual compensation of Mn and Cr impurities. Therefore, in order to reach the highest critical temperature, GaAs has to be separately doped with Cr or Mn impurities. The GaAs doped with Fe is found to be non-ferromagnetic.

The first section of this chapter presents an NMPC strategy for underwater robotic vehicles operating under various constraints. The purpose of the controller is to guide the vehicle towards specific way -points. Various constraints such as obstacles, workspace boundaries and control input saturation as well as predefined upper bound of the vehicle velocity (requirements for several underwater tasks such as seabed inspection scenario and mosaicking) are considered during the control design. The proposed scheme incorporates the full dynamics of the vehicle in which the ocean currents are also involved. The controller is designed in order to find the optimal thrusts required for minimizing the way -point tracking error. Moreover, the controlinputs calculated by the proposed approach are formulated in a way that the vehicle will exploit the ocean currents, when they are in favor of the way -point tracking mission, which results in reduced energy consumption by the thrusters. In the second part of this chapter, novel position- and trajectory -tracking control schemes for AUVs are presented. The proposed controllers do not utilize the vehicle’s dynamic model parameters and guarantee prescribed transient and steady-state performance despite the presence of external disturbances and kinematic constraints for the case of underactuated vehicles. Moreover, through the appropriate selection of certain performance functions, the proposed scheme can also guarantee the satisfaction of motion and performance constraints imposed by the desired task.

Thermal fatigue occurs in most metals under cyclic heat loads and can threaten the structural integrity of metal parts. Detailed knowledge of these loads is of utter importance to prevent such issues. In this study, a large eddy simulation (LES) with wall-adapting local eddy viscosity (WALE) subgrid model is performed to better understand turbulent thermal mixing in an annulus with a pair of opposing cold inlets at a low axial level (z = 0.15 m) and with a pair of opposing hot inlets at a higher axial level (z = 0.80 m). Each inlet pair is 90 degrees from each other in the azimuthal direction. Conjugate heat transfer between fluid and structure is accounted for. The geometry simplifies a control-rod guide tube (CRGT) in a boiling water reactor (BWR). LES results are compared with measurement data. This is one of the first times BWR conditions are met in both experiments and LES: pressure equals 7.2 MPa, while the temperature difference between hot and cold inlets reaches 216 K. LES temperatures at the fluid-structure interface are fairly correlated with their experimental equivalents, with regard to mean values, local variances, and dangerous oscillation modes in fatigue-prone areas (z = 0.65 - 0.67 m). An elastic analysis of the structure is performed to evaluate stress intensities there. From them, cumulative fatigue usage factors (CUFs) are estimated and used as screening criteria in the subsequent frequency analysis of temperature time series at the fluid-structure interface. The likelihood of initiating a fatigue crack is linked to the maximum CUF, which is 3.2 x 10(-5) for a simulation time of similar to 10 s.

We present theoretical calculations of the magnetic and electronic structure of Mn-doped GaAs (in the zinc-blende structure). The magnetic properties are shown to be very sensitive to structural defects, in particular, As antisite defects and Mn at interstitial positions. Only when considering such defects can the experimental magnetic moments be reproduced by first-principles theory. We present a simple model for understanding the connection between the magnetic ordering and the As antisites, and the way in which the defects help to stabilize a partial disordered local-moment state. The connection between the energetics of the Mn substitution and the As antisite concentration is also analyzed. In addition, we compare the calculated magnetic properties and electronic structures of Mn situated on substitutional sites (Mn replacing a Ga atom) and on interstitial sites, where in agreement with observations the interstitial site is found to be less favorable. Finally, combining our first-principles calculations of the spin-wave excitation energies with a classical Heisenberg Hamiltonian we have calculated interatomic exchange interactions, and using Monte Carlo simulations we present theoretical values of the critical temperature as a function of Mn concentration.

A computerized Fast Fourier Transform system has been used to analyse vibration measurements sampled from a 100-ton electric arc furnace. It has been the hypothesis that patterns in the vibration data would correlate to specific events in the electric arc furnace during the melting process. The theory was that the vibration patterns would be most powerful in multiples of 50 Hz, as the electric arcs operate with a frequency of 50 Hz. It was concluded that the multiples of 50 Hz were dominant. Investigation was made regarding how the amount of scrap affects the amplitude in the vibrations after a defined amount of energy input. It was confirmed that the intensity of the vibrations decreased with increasing mass and basket volume. Another discovery was the M-shaped pattern at the beginning of the melting process. This pattern was statistically analysed. It was found that 71 % of the 41 charges showed an M-shaped correlation. The appearance of this M-shape was analysed regarding power usage, and steel-type. It was concluded that the steel type affected the appearance of the M-shape. The occurrence of flat-bath was also investigated. The theory was that the vibration data would be fairly constant with the occurrence of flat-bath. It was discovered that the vibration data experienced a somewhat constant behaviour towards the end of the melting process in approximately 57 % of the 41 charges. Difficulties were encountered regarding detection of patterns, and correlating them to specific conditions, due to the many parameters that affect the vibration measurements from charge to charge. It was concluded that vibration analysis are unlikely to be used as an absolute way to foresee every event in the electric arc furnace during each charge. But can rather serve as a statistical tool, upon which decisions of how the melting process should be conducted could be based on.

Sandvik Coromant in Gimo is in need of a good quality evaluation method of adhesion for PVD layers; since the existing testing method is located in Sandvik Coromant’s other location in Västberga. Different micro-blasting methods were investigated in this thesis and the results show that some of the methods could potentially be used for evaluation of adhesion, more specifically the wet blasting methods, M1 and M2. The results also show that the investigated geometry received varying adhesion quality when lower etching bias in the PVD process was used and when different sides was pointing upwards in the PVD furnace. Further investigation will have to be made in order to fully implement micro-blasting as a testing method in production. 

Stålindustrin släpper ut stora mängder koldioxid. Industrins huvudsakliga utsläpp produceras iprocessen där stål värms upp i industriella ugnar, exempelvis ljusbågsugnar (EAF). Syftet meddetta projekt var att utvärdera och föreslå en process för att reformera biogas till vätgas. Dettaför att kunna användas som bränsle för industriella ugnar och resultera i koldioxidneutrala ellernegativa koldioxidutsläpp. Projektet har utförts genom en litteraturstudie som granskatnuvarande metoder för reformering av biogas till vätgas, datorsimuleringar i Aspen Plus därtermodynamiska beräkningar och en jämförelse med förbränning av ren metan utfördes. Studienresulterade i en process som är teoretiskt möjlig, och som skulle ge negativa koldioxidutsläpp tillföljd av tekniker för avskiljning och lagring av koldioxid. Däremot är den föreslagna processen ärinte lika effektiv som processen att bränna ren metan, men eftersom det kan ge negativakoldioxid utsläpp är det fortfarande ett fördelaktigt alternativ med hänsyn till miljöaspekter.