The main object was to investigate the effect of donors, thermal donors and defects on the lifetime on n-type Czochralsky (Cz) silicon. Cz is a technique for making monocrystals by dipping a monocrystalline seed into the melt, and pulling the ingot up as the melt solidifies. Samples were prepared by sawing, grinding and polishing. Copper decoration and preferential etching was done to reveal the defects. Resistivity measurements were performed to investigate the donor distribution. The lifetime and oxygen concentration was measured.The lifetime may be influenced by donors and traps. Traps may be metallic or non-metallic. Dopants and metal contaminants are usually Scheil distributed, which typically involves a relatively stable distribution in most part of the ingot, and a rapid increase in concentration close to the bottom. Metal contaminants may be introduced from the feedstock, and dopants (either n or p dopants) are added to the melt.Oxygen is dissolved from the crucible. The oxygen concentration typically decreases with increasing length, and is controlled by the rotation speed. This was confirmed by the interstitial oxygen measurements. The oxygen concentration showed no change after heat treatment, but the presence of oxygen in itself may contribute to produce lifetime reducing agents, such as precipitates and thermal donors. Thermal donors were found in the first 18cm of the ingot. Both the resistivity and lifetime measurements was used to calculate estimated lifetimes and donor concentrations, respectively. This estimated values were compared with the measured ones, revealing that the lifetime in the ingot was SRH dominated. Thermal donors were found to have less influence on the lifetime than the trapping. Oxygen precipitations may explain the low lifetime found in the center of the ingot up to about 30cm from the crown. Such precipitations are often gathered in defect bands in the sample. CDI of a Cu decorated sample revealed a pattern of different defect densities, which also showed up at the surface of the sample after preferential etching. An H- or L- band was believed to be situated here, which both consist of small oxygen precipitates. Defects arize as a funktion of the pulling parameters, and a low growth rate was connected to the low lifetime here. Indications of the presence of non-metallic traps were found throughout the ingot. However, oxygen precipitates could not explain the non-metallic traps that was found on the outside of the ingot, and the cause of these is therefore unknown. It is however likely that these traps may be connected to the pullrate/temperature gradient-ratio. Most likely metallic traps were also present. It is uncertain whether the non-metallic or metallic traps were the most important to the lifetime of this ingot, as the relative distribution of the two cannot be decided with certainty from the results in this thesis.Contrasts in CDI and steep curves using PCD measurements vs length plots were believed to be due to the lifetime degrading agent that changes the fastest. Metallic traps and the phosphorous dopant are known to be Scheil distributed, hence they appear transparent for the lifetime measurements in areas where the distribution is stable. Thermal donors and non-metallic traps are thus more likely to create contrast in the top parts of an ingot. However, it is not necessarily the phenomenon that causes the contrast that is the major lifetime degradation contributor.

The recycling of aluminium from used aluminium scrap leads to an unavoidable presence of pollutions in the form of elements of various amounts. Two such elements are iron and silicon. These will always be present to some extent in an aluminium alloy as they are introduced to the alloy during processing. Iron and silicon are accumulative elements, meaning that they can never be completely eliminated once introduced into the aluminium. Some alloys have very narrow compositional windows, they have strict regulations concerning amount of alloying elements allowed. This is of grave importance for the recycling process; to be able to produce specific alloys with limitations regarding content and mechanical properties. A project to uncover the effects of common elements in aluminium such as Mg, Si and Fe has been initiated by the industry. This work is closely related to the project and was carried out as a report during fall 2010 and continued as a master thesis during spring 2011. The aim of this work was to study the effects of variation of small amounts of iron and silicon in 4 different alloys of high and ultra high purity (>99.7 and >99.999 wt% Al, respectively). The main focus was to uncover the effect of the elements on mechanical properties. Tensile test experiments with specimens in uniaxial tension were conducted to uncover the mechanical properties of the alloys. In addition to the tensile tests other parameters like texture, particles, recrystallisation and micro structure development were investigated. DC-cast, extruded flat profiles and rolled and recrystallised versions of the 4 alloys were used during the work.The results from tensile tests performed on the rolled and recrystallised aluminium showed that an initial introduction of 0.066 wt % Fe and Si 0.068 wt % to an alloy containing no pollutions lead to a dramatic increase in strength properties (up to 100% for the tensile strength) and a mild decrease in elongation. The increased strength properties and reduced formability was traced to iron and silicon in solid solution. From the same tensile tests it was concluded that a further increase of iron and an introduction of a small amount of pollutions had close to no effect on the mechanical properties.

This master thesis has the objective to improve the mechanical properties of Super Duplex steel by adding Elkem Grain Refiner (EGR). EGR is commercial grain refiner where the active element is cerium. Cerium is a strong oxide and sulphide former whose inclusions are to act as sites for heterogeneous nucleation during casting. The cerium inclusions will form at low undercooling making it possible to grow equiaxed grains ahead of the solidifying front, reducing the size of the columnar zone normally seen in an ingot. By reducing the columnar zone the steel will have a larger zone of equiaxed, and smaller, grains improving the mechanical properties of the steel and reducing the segregation throughout the ingot. The experiment was performed with S4501 Super Duplex steel provided by Scana Steel Stavanger. The casting was done at Frekhaug stål, Bergen by adding 0.05, 0.075 and 0.1 wt% cerium to 120 kg casts. There were a total of 3 parallels, where 1 was cast at 1525ºC and 2 series at 1540ºC. The as cast structure was significantly refined, the columnar zone was reduced from 22 mm to being absent in the cast with most cerium added. The mechanical results show a linear increase in both yield and ultimate tensile strength with increasing amount of cerium. The elongation increased somewhat, but the impact toughness decreased linearly with increasing cerium content. The casting temperature did not seem to have an effect on the grain refining.

Due to recent fractures in grade 70 anchor chains in the fish farming industry, chain supplier Erling Haug AS has initiated an examination of a sandblasted anchor they sell today. The sandblasted anchor chain is of the same strength category as the chains associated with the mentioned accidents. The mechanical properties of the sandblasted chain were characterized in 2010 in a student project work[1]. The report expressed concern about the sandblasted grade 70 chains since the material fulfilled requirements to be susceptible to hydrogen induced stress cracking (HISC). Therefore, further research on the material was needed. Another grade 70 chain, of an unknown origin, was obtained to make a comparison. This chain had fractured in-service. It was therefore necessary to characterize the mechanical properties of the fractured chain before examining the two chain grades susceptibility to HISC. The fractured chain was examined in terms of its microstructure, hardness, transition temperature and strength. An attempt was made to explain why the fractured chain failed in-service.The tensile test of the fractured chain revealed that its yield strength was 140MPa lower than that of the sandblasted chain. It was considered possible that the fracture chain were weaker than they should have been and that the reason it failed in-service was due to overload.The susceptibility of the two chains to HISC was tested by submerging tensile specimens into a 3.5% NaCl solution in CorTest Proof rings, while exposed to hydrogen. Specimens were either hot dip galvanized (HDG), protected by an external potential of -1050mV vs. Ag/AgCl or freely exposed at their corrosion potential. Some specimens were pulled in steps till fracture, while others were held at a constant load for 14 days.Different loading and corrosion potentials were applied to the two chain qualities during the HISC test, but the experiment was unable to provoke brittle fractures in either of them. No cracking was observed in the SEMivfor any of the HDG tensile specimens. It was found that hydrogen have no influence the mechanical properties of the HDG tensile specimens, while hydrogen appear to assist in the development of cracks on the polarized specimens.

Stability and compatibility of the proton conducting electrolyte material La6WO12 with the potential cathode materials LaCoO3 and La2NiO4 were investigated by means of solid-solid diffusion couples. Reactivity studies were carried out at 1450 °C for various times. Reaction products were analysed by SEM and EDS. The study suggests a high reactivity between the electrolyte and the electrodes, which is detrimental for the fuel cell system.In the case of LaCoO3 as a cathode material a secondary phase of LaCo1-xWxO3 were formed at the interface and as precipitates in La6WO12. Theoretical models for both diffusion or interface controlled reactions failed to fit the experimental data. This failure is probably related to the reaction going towards equilibrium after a certain time, or poor connectivity between the materials. The solid- state reaction between La6WO12 and La2NiO4 showed formation of a composite layer of La2O3 and La6WO12 at the interface. The reaction kinetics of this product layer was diffusion controlled. In addition to the interface reaction, precipitates of La2O3 and La6WO12 were formed in the La2NiO4 phase.