The complexity of electronic systems in vehicles is rapidly increasing, and as a consequence, the long-term reliability of automotive connectors has become an important issue. The aims of this thesis have been: 1. to characterize the friction, wear and electrical properties of tin coatings, 2. to achieve an improved fundamental understanding of the deterioration processes caused by wear and fretting corrosion, 3. to propose improvements of tin coatings systems for electrical connectors. The required insertion force has a significant impact on the design and the cost of a connector. A reduced insertion force can be achieved by reduced contact load and/or reduced tin coating thickness, but this will increase the risk of fretting corrosion. Wear during the insertion stroke is essential in order to wipe off the non-conductive oxide layer. However, a thin tin layer may become worn off after only a few insertion strokes. The rider will then partly slide on the hard intermetallic compound formed between the substrate and the residual tin. Due to the restricted wear when sliding on the intermetallic compound more oxide will be formed during sliding than is removed and consequently the electrical contact resistance will increase. Two semi-empirical models are proposed, the first describing the contact resistance when the rider plows the free tin layer, and the second describing the contact resistance increase due to oxidation when the rider slides on the intermetallic compound. Two novel methods to improve the performance of pre-tinned material were evaluated. The first involves the use of a lubricant in combination with a textured surface, to improve the supply of lubricant into the contact spot. The second involves the addition of small amounts of a preferential oxidation additive to the tin. This increases the possibility of achieving a cold-welded contact spot, which results in an ultimately stable connection.

The strain introduced by lattice mismatch is a built-in characteristic in Si/SiGe heterostructures, which has significant influences on various material properties. Proper design and precise control of strain within Si/SiGe heterostructures, i.e. the so-called “strain engineering”, have become a very important way not only for substantial performance enhancement of conventional microelectronic devices, but also to allow novel device concepts to be integrated with Si chips for new functions, e.g. Si-based optoelectronics. This thesis thus describes studies on two subjects of such strain-engineered Si/SiGe heterostructures grown by molecular beam epitaxy (MBE). The first one focuses on the growth and characterizations of delicately strain-symmetrized Si/SiGe multi-quantum-well/superlattice structures on fully relaxed SiGe virtual substrates for light emission in the THz frequency range. The second one investigates the strain relaxation mechanism of thin SiGe layers during MBE growth and post-growth processes in non-conventional conditions. Two types of THz emitters, based on different quantum cascade (QC) intersubband transition schemes, were studied. The QC emitters using the diagonal transition between two adjacent wells were grown with Si/Si0.7Ge0.3 superlattices up to 100 periods. It was shown that nearly perfect strain symmetry in the superlattice with a high material quality was obtained. The layer parameters were precisely controlled with deviations of ≤ 2 Å in layer thickness and ≤ 1.5 at. % in Ge composition from the designed values. The fabricated emitter devices exhibited a dominating emission peak at ~13 meV (~3 THz), which was consistent with the design. An attempt to produce the first QC THz emitter based on the bound-to-continuum transition was made. The structures with a complicated design of 20 periods of active units were extremely challenging for the growth. Each unit contained 16 Si/Si0.724Ge0.276 superlattice layers, in which the thinnest one was only 8 Å. The growth parameters were carefully studied, and several samples with different boron δ-doping concentrations were grown at optimized conditions. Extensive material characterizations revealed a high crystalline quality of the grown structures with an excellent growth control, while the heavy δ-doping may introduce layer undulations as a result of the non-uniformity in the strain field. Moreover, carrier lifetime dynamics, which is crucial for the THz QC structure design, was also investigated. Strain-symmetrized Si/SiGe multi-quantum-well structures, designed for probing the carrier lifetime of intersubband transitions inside a well between heavy hole 1 (HH1) and light hole 1 (LH1) states with transition energies below the optical phonon energy, were grown on SiGe virtual substrates. The lifetime of the LH1 excited state was determined directly with pump-probe spectroscopy. The measurements indicated an increase of lifetime by a factor of ~2 due to the increasingly unconfined LH1 state, which agreed very well with the theory. It also showed a very long lifetime of several hundred picoseconds for the holes excited out of the well to transit back to the well through a diagonal process. Strained SiGe grown on Si (110) substrates has promising potentials for high-speed microelectronics devices due to the enhanced carrier mobility. Strain relaxation of SiGe/Si(110) subjected to different annealing treatments was studied by X-ray reciprocal space mapping. The in-plane lattice mismatch was found to be asymmetric with the major strain relaxation observed in the lateral [001] direction. It was concluded that this was associated to the formation and propagation of conventional a/2<110> dislocations oriented along [110]. This was different from the relaxation observed during growth, which was mainly along in-plane [110]. A novel MBE growth process to fabricate thin strain-relaxed Si0.6Ge0.4 virtual substrates involving low-temperature (LT) buffer layers was investigated. At a certain LT-buffer growth temperature, a dramatic increase in the strain relaxation accompanied with a decrease of surface roughness was observed in the top SiGe, together with a cross-hatch/cross-hatch-free transition in the surface morphology. It was explained by the association with a certain onset stage of the ordered/disordered transition during the growth of the LT-SiGe buffer. / Kisel(Si)-baserad mikroelektronik har utvecklats under en femtioårsperiod till att bli basen för vår nuvarande informationsteknologi. Förutom att integrera fler och mindre komponenter på varje kisel-chip så utvecklas metoder att modifiera och förbättra materialegenskaperna för att förbättra prestanda ytterligare. Ett sätt att göra detta är att kombinera kisel med germanium (Ge) bl.a. för att skapa kvantstrukturer av nanometer-storlek. Eftersom Ge-atomerna är större än Si-atomerna kan man skapa en töjning i materialet vilket kan förbättra egenskaperna, ex.vis hur snabbt laddningarna (elektronerna) rör sig i materialet. Genom att variera Gekoncentrationen i tunna skikt kan man skapa skikt som är antingen komprimerade eller expanderade och därmed ger möjlighet att göra strukturer för tillverkning av nya typer av komponenter för mikroelektronik eller optoelektronik. I detta avhandlingsarbete har Si/SiGe nanostrukturer tillverkats med molekylstråle-epitaxi-teknik (molecular beam epitaxy, MBE). Med denna teknik byggs materialet upp på ett substrat, atomlager för atomlager, med mycket god kontroll på sammansättningen av varje skikt. Samtidigt kan töjningen av materialet designas så att inga defekter skapas alternativt många defekter genereras på ett kontrollerat sätt. I denna avhandling beskrivs detaljerade studier av hur töjda i/SiGe-strukturer kan tillverkas och ge nya potentiella tillämpningar ex.vis som källa för infraröd strålning. Studierna av de olika töjda skikten har framför allt gjorts med avancerade röntgendiffraktionsmätningar och transmissionselektronmikroskopi.

In this work an extended literature survey on ceramics and porcelains in particular, has been documented. Samples from two Ugandan deposits of each feldspar and quartz were characterised by means of X-ray diffraction, thermal analysis, chemical analysis and scanning electron microscopy and found to possess requisite properties for making electro porcelain insulators. Five porcelain bodies were formulated and samples were fabricated from materials collected from selected deposits in Uganda using different mixing proportions of clay, feldspar and quartz. The properties of the formulated bodies were studied in relation to workability, firing temperature, dielectric and bending strengths. The strengths (both mechanical and dielectric) were found to decrease as the firing temperature was increased above 1250°C. Additionally, ten formulations with components in the range of 30-60% clay, 20-45% feldspar and 20-25% sand were prepared. Specimens for mechanical and physical characterisation were made using the plastic extrusion method. The samples were characterised in terms of constituent oxide composition, flexural strength, fracture toughness, dielectric strength along with microstructural and phase properties using ICP-AES analyses, 4-point load bending strength test, Vicker’s indentation method, SEM and XRD analyses respectively. XRD studies revealed that the crystalline phases formed were mullite and quartz and their intensity was almost identical for all samples fired at 1250°C but there was a decrease inquartz content as temperature was increased above 1250°C. Samples with 20% sandcontent resulted in higher density, MOR and fracture toughness compared to thosecontaining 25% sand. Mullite content on the other hand did not change at temperatures above 1200°C but there were significant differences in the morphologies of the mullite crystals in the samples. Optimum mechanical and electrical properties were found at maximum vitrification and a microstructure showing small closely packed mullite needles. This occurred at a firing temperature of 1250°C. Three promising porcelain formulations from the above investigations were chosen and five glazes formulated to fit on biscuit fired specimens. The best-fitting glaze was adopted. The formulated specimens were investigated using dilatometry, Steger test, FEG-SEM, XRD, 4-point bending, dielectric strength and fracture toughness tests. A porcelain specimen consisting of 68% SiO2, 19% Al2O3, 4.7% K2O and a glaze of Seger formula RO:0.57Al2O3:4.86SiO2 exhibited MOR of 105MPa with Weibull modulus of 5.6 and a dielectric strength of 18kV/mm upon firing at a heating rate of 6ºC/min to 1250ºC, soaking for 2h at the top temperature and cooling down to 500°C at a rate of 6°C/min, followed by furnace cooling. The microstructure of the high strength specimen exhibited round mullite needles, quartz and glass. Holding samples for 2h at peak temperature resulted in a 22% increase in MOR compared to 1h holding. Glazing further improved strength by 67% for the best sample. Compressive stresses in glaze contributed to the strengthening effect. The dielectric and mechanical strengths obtained make the ormulated sample suitable for application in low voltage electrical insulation. / QC20100609

Over the past centuries, a number of process routes for extraction of metal values from an ore or other resources have been developed. These can generally be classifiedinto pyrometallurgical, hydrometallurgical or electrometallurgical routes. In the caseof the latter two processes, the reaction medium consists of liquid phase electrolytesthat can be aqueous, non-aqueous as well as molten salts. The present dissertationpresents the work carried out with two aspects of the above-mentioned electrolytes.First part is about the electrolyte solutions, which can be used in solvent extractionrelevant to many hydrometallurgical or chemical engineering processes; the secondpart is about the molten salts, which is often used in the electrometallurgical processesfor production of a variety of many kinds of metals or alloys, especially those that arehighly reactive.In the first part of this thesis, the focus is given to the thermodynamics ofelectrolyte solutions. Since the non-ideality of high concentration solution is not wellsolved, a modified three-characteristic-parameter correlation model is proposed,which can calculate the thermodynamic properties of high concentration electrolytesolutions accurately. Model parameters for hundreds of systems are obtained foraqueous as well as non-aqueous solutions. Moreover, a new predictive method tocalculate the freezing point depression, boiling point elevation and vaporizationenthalpy of electrolyte solutions is also proposed. This method has been shown to be agood first approximation for the prediction of these properties.In the second part, a process towards the extraction of metal values from slags,low-grade ores and other oxidic materials such as spent refractories using molten saltsis presented. Firstly, this process is developed for the recovery of Cr, Fe values fromEAF slag as well as chromite ore by using NaCl-KCl salt mixtures in the laboratoryscale. The slags were allowed to react with molten salt mixtures. This extraction stepwas found to be very encouraging in the case of Cr and Fe present in the slags. Byelectrolysis of the molten salt phase, Fe-Cr alloy was found to be deposited on thecathode surface. The method is expected to be applicable even in the case of V, Mnand Mo in the waste slags.Secondly, this process was extended to the extraction of copper/iron from copperore including oxidic and sulfide ores under controlled oxygen partial pressures.Copper or Cu/Fe mixtures could be found on the cathode surface along with theemission of elemental sulphur that was condensed in the cooler regions of the reactor.Thus, the new process offers a potential environmentally friendly process routereducing SO2 emissions.Furthermore, the cyclic voltammetric studies of metal ions(Cr, Fe, Cu, Mg, Mn)in (CaCl2-)NaCl-KCl salt melt were performed to understand the mechanisms, such asthe deposition potential, electrode reactions and diffusion coefficients, etc. In addition,another method using a direct electro-deoxidation concept(FFC Cambridge method),was also investigated for the electrolysis of copper sulfide. Sintered solid porouspellets of copper sulfide Cu2S and Cu2S/FeS were electrolyzed to elemental Cu, S andCu, Fe, S respectively in molten CaCl2-NaCl at 800oC under the protection of Argongas. This direct electrolysis of the sulfide to copper with the emission of elementalsulfur also offers an attractive green process route for the treatment of copper ore. / QC 20100714

Atmospheric corrosion takes place on most metals as they interact with thesurrounding environment. A degradation of the metal is the common result,which often leads to a shortened lifespan of the material. Hence, knowledge onthe fundamental interaction between a gas containing corrosive constituentsand a metal surface, which is the starting point of atmospheric corrosion, isimportant in many contexts. As the nature of atmospheric corrosion is inherentlycomplex, it imposes demands on the analytical studies that are neededin order to understand the fundamentals on a molecular level. Consequently,in-situ vibrational techniques, providing molecular information, have beenutilized in this work to study atmospheric corrosion by targeting the initialstages of the interaction between corrosive air and a metal surface. The initialstages (from minutes until days of exposure) were studied as these havea large influence on the atmospheric corrosion for prolonged exposure times. More specifically, the interaction between humidified air to which organicacids were added, and zinc was targeted in order to address a situation inindoor atmospheric corrosion, where organic acids are of importance. Zinc isa constituent in e.g. brass, which is an alloy used in many indoor applications. A systematic investigation utilizing complementary acting vibrational techniquesthus enabled detailed information on the mechanisms of the onsetof atmospheric corrosion of zinc induced by acetic and formic acid. Corrosionproducts of both two dimensional and three dimensional character couldbe separately studied by combining VSFS (interface sensitive), IRAS (nearsurfacesensitive), and CRM (bulk sensitive). The Zn surface was found to be heterogeneous with different hydroxylgroups present on the surface. As this surface was exposed to formic or aceticacid, the OH groups on the surface were rapidly displaced in a ligand exchangewith formate or acetate. These ligands, organised in two dimensionalstructures, promoted corrosion by weakening the bonds of the Zn atoms totheir surrounding matrix. The subsequent growth of three dimensional corrosion products, Zn hydroxyacetate and formate, observed within short exposure times of Zn exposedto acetic and formic acid, was found to be electrochemical in nature.Cathodic areas consisting of more crystalline ZnO were observed. The potentialdifference between these more noble areas on the surface and those of lessnoble character created an electrochemical cell, initiating release of Zn ionsinto the aqueous adlayer in the anodic reactions. These Zn ions precipitatedas localised corrosion products. The cathodic areas increased the local pHon the surface, thereby promoting precipitation in their vicinity. The resultson initial stages of this type of corrosion were found to have similarities withprevious field studies of Zn exposed to real indoor environments. One way to decrease the corrosion rate of zinc is by adsorbing a corrosioninhibitor to the metal surface in order to protect it. As a model for sucha corrosion inhibitor, octadecanethiol (CH3(CH2)17SH) was seen to provideincreased corrosion protection of both reduced and oxidised Zn substrates byforming an adsorbed surface layer with an ordered structure. / QC 20100719

Welds in materials intended for service at temperatures above the creep activation temperature often develop damage before the base metal. The weld is a discontinuity in the material and stresses and strains often accumulate in the weld. Knowledge of the properties of the weld is essential to the safe operation of the component containing the weld. The work in this thesis has been aimed at the study of welds in service at high temperatures: The work is divided into two main chapters. The first chapter deals with welds in stainlesssteels and dissimilar metal welds and includes three papers, and the second chapter dealswith welds in copper intended for nuclear waste disposal, also including three papers. Common to both parts is that the temperature is high enough for most of the damage in the welds to result from creep. In the first part the role of the weld microstructure on the creep crack propagation properties has been studied. Experiments using compact tension specimens have been performed on service exposed, low alloyed heat resistant steels. The results show good correlation with the crack tip parameter, C*, during steady state creep crack growth. The test methodology has also been reviewed and sensitive test parameters have been identified. The results from the creep crack propagation tests on service exposed material has been modeled using uniaxial creep data on both new and ex-service material. The development of the weld microstructure in a dissimilar metal weld between two heat resistant steels has also been investigated. A weld was made between one ferritic and one martensitic steel and the development of the microstructure during welding and post-weldheat treatments has been studied. The results show that the carbon depleted zone that develops near the weld metal in the lower alloyed steel depends on the formation and dissolution of the M23C6-carbide. Variations of the weld parameters and the post-weld heat treatment affect the size and shape of this zone. The process has been successfully modeled by computer simulation. The second part focuses on oxygen free copper intended for nuclear waste disposal containers. The containers are made with an inner core of cast nodular iron and an outer core of copper for corrosion protection. The copper shell has to be welded and two weld methods has been tested, electron beam welding and friction stir welding. Creep specimens taken from both weld types have been tested as have base metal specimens. The technical specifications of the waste canisters demand that the creep ductility of both the copper shell and the welds has to be as high as possible. The creep test results show that base material doped with at least 30 ppm phosphorus has high creep ductility, and friction stir welds made from this material has almost as high creep strength and creep ductility. Copper without phosphorus does not exhibit the same ductility. The creep properties evaluated from testing has been modeled and extrapolated for the intended purpose / QC20100719

The present thesis was mainly to study the preparation of nickel composite materials by chemical plating process. Nickel coated boron nitride particles, nickel coated spherical silica particles and nickel viscose composite fibres were prepared. Both experiment and model development were carried out to study the kinetics of the processes. Preparation of hollow nickel fibres was also investigated. NiSO4-(NH4)2SO4-NH3·H2O-N2H4·H2O was found a suitable system for nickel plating. This system could be employed in preparing nickel coating layer on surface of boron nitride particles, spherical silica powder and viscose fibres. The main factors which could affect the plating process were investigated. The optimum conditions were suggested for different substrate materials based on the experimental results. It was found that Pd on the surface of substrate materials acted as an active center for nickel deposition at the initial stage of the process. Thereafter, Ni itself would act as an active center to catch Ni from the solution through the reaction: Ni2+ + 2H* ad ⇒ Ni + 2H+. The rate of the process was found to be controlled by the reaction at the interface under the present experimental conditions. A kinetic model was developed on the basis of the mechanism study. The model predictions were found to be in agreement with the experimental data for different substrate materials. Since the kinetic model does not have any parameters related to the shape and surface area of the substrate, it could be used as a general model to describe the processes controlled by interface reaction with growing interface area. Hollow nickel fibers were prepared by thermal decomposition method from nickel viscose composite. The experiments showed that viscose filling could be removed by heat treatment in air atmosphere. Experiments showed that hollow nickel fiber could be prepared by direct thermal decomposition in air flow at low temperature, e.g. 573 K. But slight surface oxide is inevitable. Decomposition of the viscose filling could also be carried at higher temperature. However, serious oxidation of nickel would also take place during the decomposition. To remove nickel oxide, reduction by hydrogen gas could be applied. Preliminary effort was made to extend the application of the present method to prepare copper viscose composite fibres. Promising result was obtained. More detailed study is required to confirm the applicability of the technique. / QC 20100804

Good toughness properties in base and weld material enable the use of duplex stainless steels (DSS) in critical applications. DSS offer high strength compared to common austenitic stainless steels. The high strength can be utilized to reduce the wall thickness and accordingly accomplish reduction of cost, welding time and transportation weight, contributing to ecological and energy savings. Although DSS have been used successfully in many applications the last decades, the full utilisation in pressure vessels has been restricted due to conservative design rules. The consequences of failure in a pressure vessel are often very severe and it is accordingly important to verify a high ductility and fracture toughness. In this study fracture toughness data has been generated that has been used to analyse the brittle failure model in the European pressure vessel code EN 13445. The evaluation of the results has been made successfully by the master curve analysis, previously applied to ferritic steels. The master curve analysis includes calculation of a reference temperature, which can be correlated to an impact toughness transition temperature. A correlation between fracture and impact toughness results is necessary for a practically applicable design code. The heat distribution and austenite reformation have been modelled to verify satisfactory toughness properties in the heat affected zone. A similar model was used to evaluate the nucleation and diffusional growth of sigma phase during isothermal heat treatment or continuous cooling. For future stainless steel development, the availability of satisfactory correlations between composition, microstructure and mechanical properties are essential to optimize alloy design. Stainless steel data has been analysed to find approximate relations between mechanical properties and the chemical composition, grain size, ferrite content, product thickness and solution hardening size misfit parameter. The solution hardening effect was successfully predicted by the Labusch-Nabarro relation and multiple regression analyses were used to evaluate hardening equations for stainless steel. / QC 20100920

The recent development of tool steels and high-speed steels has led to a significant increase in alloy additions, such as Co, Cr, Mo, N, V, and W. Knowledge about the phase relations in these multicomponent alloys, that is, the relative stability between different carbides or the solubility of different elements in the carbides and in the matrix phase, is essential for understanding the behaviour of these alloys in heat treatments. This information is also the basis for improving the properties or designing new alloys by controlling the amount of alloying elements. Thermodynamic calculations together with a thermodynamic database is a very powerful and important tool for alloy development of new tool steels and high-speed steels. By thermodynamic calculations one can easily predict how different amounts of alloying elements influence on the stability of different phases. Phase fractions of the individual phases and the solubility of different elements in the phases can be predicted quickly. Thermodynamic calculations can also be used to find optimised processing temperatures, e.g. for different heat treatments. Combining thermodynamic calculations with kinetic modelling one can also predict the microstructure evolution in different processes such as solidification, dissolution heat treatments, carbide coarsening, and the important tempering step producing secondary carbides. The quality of predictions based on thermodynamic calculations directly depends on the accuracy of the thermodynamic database used. In the present work new experimental phase equilibria information, both in model alloys containing few elements and in commercial alloys, has been determined and was used to evaluate and improve the thermodynamic description. This new experimental investigation was necessary because important information concerning the different carbide systems in tool steels and high-speed steels were lacking. A new thermodynamic database for tool steels and high-speed steels, TOOL05, has been developed within this thesis. With the new database it is possible to calculate thermodynamic properties and phase equilibria with high accuracy and good reliability. Compared with the previous thermodynamic description the improvements are significant. In addition the composition range of different alloying elements, where reliable results are obtained with the new thermodynamic database, have been widened significantly. As the available kinetic data did not always predict results in agreement with new experiments the database was modified in the present work. By coupling the new thermodynamic description with the new kinetic description accurate diffusion simulations can be performed for carbide coarsening, carbide dissolution and micro segregation during solidification. / QC 20100929

The objective of the present thesis is to optimize the electric arc furnace (EAF) practice from an environmental view point. Two aspects that meet the requirements of the secondary steelmaking industries today, viz. Mo alloying with maximum retainment of the alloying element in molten steel and optimization of foaming by carbonate addition with a view to optimize the energy need of the process. Both these aspects would also have a significant impact on the process economy. Iron molybdate (Fe2MoO4) has been synthesized from commercial grade materials and proposed as a new potential precursor for steel alloying with Mo. The thermal stabilities of different molybdates, viz. Fe2MoO4, CaMoO4 and MgMoO4, were studied using thermogravimetry analysis (TGA). It was found that Fe2MoO4 is the most stable one and doesn’t evaporate in Ar atmosphere when heating up to 1573 K. The synthesis of Fe2MoO4 requires high temperature (1373 K) and long holding time (up to 16 hours). In a view of this, the possibilities for in-situ formation of Fe2MoO4 and CaMoO4 from their precursor mixtures were studied with the aid of high-temperature X-ray diffraction (XRD) and TGA analysis. Laboratory and industrial trials on steel alloying with Mo were conducted using precursor mixtures as sources of Mo. It was found that the mixture, which contains FeOx, MoO3 and C (Fe2MoO4 precursor), can provide the Mo yield up to 98 % at both the laboratory as well as industrial trials. The Mo yields even in the case of C+MoO3 and C+MoO3+CaO mixtures were around 93 % in these trials. The higher yield for the MoO3+C+FeOx mixture was attributed to the stabilization of Mo in the precursor (marked by the decrease in the Gibbs energy of Mo) and the readiness to dissolve in the steel bath. The heat effect of the slag foaming with carbonates addition was studied at 1623 and 1673 K with the aid of thermal analysis technique with a new crucible design. Experiments were conducted by adding limestone and dolomite pieces of defined shapes (together with iron sinkers) in molten slag and monitoring the temperature changes accompanying the decomposition of carbonates. It was found that the decomposition energies for dolomite and limestone for the studied slag composition are in the range 56-79 % of theoretical values, which is linked to the energy saving effect of slag foaming. No influence of sample shape on decomposition energy was found both for limestone and dolomite. The kinetics of slag foaming by limestone particles was studied at 1773 K with the aid of X-ray imaging system. A model was proposed to describe the decrease in foam height with time on the basis of CaO shell formation during decomposition reaction. The energy impact of limestone and raw dolomite addition was examined in a 100-ton EAF. It was found that, in the case of addition of carbonates after the scrap is completely molten; the endothermic heat effects for limestone and dolomite (2255 and 2264 kJ/kg respectively) were only 70 % from theoretical values. This is indicative of the resistance to heat transfer due to increased foaming. / QC 20100914