In this master thesis experiments were conducted to determine the abrasion-corrosion properties of a steel designed for TBM tunnelling. This was done by three different tests, reciprocal ball-on-plate, rubber wheel and hyperbaric soil abrasion test. The reciprocal tests were done by rubbing steel balls onto rock obtained from a tunnel boring site in the Faroe Islands. The test were performed in dry conditions, in water from the same site as rock and a mixture of the water and a foam designed for use in hard rock tunnel boring. During these tests no measurable weight loss was produced, but the water and the foam caused some pitting to occur on the steel surface. The water and foam also provided some lubrication, where the foam clearly was the best lubricant by producing elastohydrodynamic lubrication (EHL). The rubber wheel tests were performed in different combinations of water, sand, oil and a foam specially designed for soft ground tunnel boring. The sands used were sand used for making casting moulds and sand obtained from a soft ground tunnel boring site in Israel. The two different water samples used were obtained from the site in the Faroe Islands mentioned above and the previous mentioned Israel site. The tests showed that adding foam to the sand and water mixture significantly reduced the measured weight loss. However, as for the reciprocal ball-on-plate test, the foam caused pitting to occur. The same corrosion effect was observed for the oil additive, but the oil did not provide enough lubrication to avoid abrasive wear. Consequently, the test with the oil additive produced the biggest weight loss of all the rubber wheel tests. The hyperbaric soil abrasion tests were performed in the sand obtained at the site in Israel. The sand was tested both dry and saturated with water from Israel. Tests showed that the measured weight loss from these two tests was similar. However, SEM pictures revealed that in the test with sand saturated with water, both abrasion and corrosion had occurred. While in the dry sand, only abrasion had occurred. This indicates that in this test the hardness of the steel and abrasiveness of the sand is more decisive for the weight loss than the corrosivity of the solution.

When a liquid SiMn alloy is cooled, carbon is dissolved from the melt. The dissolved carbon either forms graphite or reacts with silicon from the melt to form SiC. The goal of this thesis has been to determine how temperature fluctuations affect the formation of SiC and graphite in the SiMn process. The focus of this thesis has been on dissolved carbon from the SiMn alloy due to cooling of the system, and the formation of graphite and SiC from this dissolution of carbon.The experiments conducted in this thesis is done with near constant silicon content, and temperature as the main variable in addition to carbon. The investigation was carried out by heating SiMn alloys several times, forming SiC and graphite. Carbon from the crucibles dissolved into the liquid SiMn alloy to reach equilibrium between carbon and silicon. This is equivalent to an industrial furnace where coke can dissolve carbon into the SiMn alloy, and thus form SiC or graphite. Accumulation of graphite and SiC is believed to be bad for furnace operations.SiC that forms in a Mn-Si-Fe-C saturated alloy can have an interface structure of granular, angular grains and as dendrites. When SiC accumulates in the Mn-Si-Fe-C system, clusters of SiC particles with intermediate SiMn metal can form. This study shows that SiC clusters is typically a decade larger than the average SiC particle. The SiC particles settles at the top of the melt when a cooling rate of 18°C per minute is used.Graphite that forms in the Mn-Si-Fe-C system have an interface structure of flakes. When the carbon content of the liquid SiMn is high enough, nucleation of new graphite grains happens instead of grain growth. The graphite flakes did not settle, but remained evenly dispersed in the SiMn alloy. This may be due to high viscosity in the melt, high friction on the graphite flakes or the buoyancy can be fairly equal to the drag of the graphite particles.The rate of formation of SiC and graphite in Mn-Si-Fe-C saturated alloys is reduced slightly by each consecutive temperature cycle. This suggest that SiC and graphite formed during the first cycles only partly dissolve into the liquid SiMn alloy to reach equilibrium in the system.

The main aim of this work was to analyze an impedance model for porous semiconductor electrodes consisting of spherical particles. The model should make it possible to analyze the flatband potential for this type of electrodes. The analysis was conducted by simulating the model in MATLAB®. Cyclic voltammetry and electrochemical impedance spectroscopy was performed on titanium oxide, TiO2 P25, anodized titanium and some iridium tin oxides, Ir(1-x)SnxO2. The aim was to use the experimental data as a reference and compare the simulated data with the experimental results. This could not be done because the recorded data for the oxides were too strongly influenced by the support material. The supports tested in this work were Au, Ti and ITO. The simulations show that the capacitance of the models spherical particle is only weakly dependent on the particles surface potential. This indicates that this one-dimensional version of the model might not be sufficient to analyze the spherical particles. However, another analysis method for investigation of Mott-Schottky behavior for porous electrodes was confirmed by the result for the anodized titanium.

Ceramics with mixed ionic and electronic conductivity are being investigated for oxygen separation from air, intended for the production of syngas. Asymmetric membranes, consisting of a dense membrane co-sintered with a porous support are expected to achieve a high flux of oxygen and at the same time adequate strength. As the porous substrate is mainly intended for strength contribution, it is crucial that the flux of oxygen through the dense membrane is not limited by the flow of air through the porous substrate. An oxygen flux of 10 ml min-1 cm-2 should be achieved at operating temperatures (800-1000 °C) for the substrate to be commercially attractive. A biaxial strength of 34MPa has been obtained by similar porous substrates.Four different strategies for achieving high permeating substrates made by solid state La0.2Sr0.8Fe0.8Ta0.2O3-x have been evaluated. Pressed porous substrates were produced both with and without the use of pore formers. The most promising compositions with respect to porosity and permeability were tape casted and characterized with respect to porosity, permeability and strength.

Coin cells with lithium and graphite electrodes were assembled using different combinations of graphite material and electrolyte. Specifically, three commercially available graphite materials and five electrolyte compositions were studied. The cells were discharge-charge cycled with varying parameters in order to determine the performance of the graphite materials and electrolytes. Particularly, a temperature chamber was employed to cycle some cells at temperatures between 0 and 40°C to find the significance of the electrolyte composition and graphite material on the cell performance at these temperatures. The cycled cells were disassembled and samples from the graphite electrode soaked with electrolyte were prepared for thermal analysis, specifically differential scanning calorimetry (DSC). The thermal stability of the graphite electrodes and the influence from the graphite and electrolyte properties and the cycling parameters were analysed. In order to facilitate the interpretation of the results from discharge-charge cycling at different temperatures, DSC analysis from -80 to +50°C was performed on the pure electrolytes.Confirming previous studies, it was found that both the thermal stability and cycling performance were highly influenced by the properties of a solid electrolyte interphase (SEI), situated between the graphite surface and the electrolyte and formed during cycling. The three graphites were good substrates for stable SEI formation, exhibited by high thermal stability after being cycled at room temperature. After cycling with a temperature program, subjecting the cells to temperatures between 0 and 40°C, the thermal stability was generally reduced. This was attributed to increased SEI formation. The properties of both the electrolyte and graphite influenced the SEI and consequent thermal stability, though in different ways.The cell capacity was considerably reduced upon cycling at lower temperatures, such as 10 and 0°C. The results indicate that the electrolyte properties, particularly the viscosity and resulting conductivity, played the most important role in determining the cell performance. Low viscosity electrolyte components should be utilised, maintaining the electrolyte conductivity even at reduced temperatures. The graphite properties did not influence the cell performance at the temperatures studied. Advice is given on which electrolyte components should be avoided to build Li-ion cells performing acceptably at temperatures from 0 to 40°C.

High purity silicon material in solar cell fabrication constitutes 40% of the total cost for conventional solar cell production. One approach to reduce costs would be to use less of this expensive silicon by making thin film solar cells and use a cheaper substrate as mechanical carrier.In this work the main objective has been to manufacture silicon substrates from powder by hot-pressing. The effect of the sintering parameters has been characterized. A secondary objective was to look at the possibility to achieve larger grains by recrystallization.Samples processed by hot-pressing silicon powder of metallurgical grade with varying temperatures (1200-1375 °C), pressures (30-50 MPa) and sintering time (30-60 min) has been carried out. Halogen lamps were used for heat treatment for specific samples after hot-pressing. Microstructure and porosity were characterized using optical and electronic microscopy. EBSD was used to determine the grain size and grain orientation. The density was determined by Archimedes’ method. Resistivity was measured by a conductive probe.Densities higher than 90 % were obtained at high temperatures and pressures. The time conducted at maximum temperature during hot-pressing was not of vital importance with respect to density.The mean particle size of the powder was determined to ~20 μm, while hot-pressed samples had an average grain size of ~30 μm. The samples showed low resistivity due to high impurities of the silicon powder. High surface porosity was found for the less dense samples. Recrystallization was successfully achieved for the sample hot-pressed at 1350 °C, 30 MPa and 30 min, resulting in elimination of pores and significant grain growth from 31,83 to 56,96 μm.Characterizations of the hot-pressed samples are limited to the methods and techniques described above.

Fasetransformasjoner som skjer ved sveising av F 70 arktisk stål fører til at ugunstige mikrostrukturer oppstår i den varmepåvirkede sonen av grunnmaterialet (HAZ). Ved gjentatt oppvarming av HAZ vil det kunne dannes områder med martensitt/austenitt-fase (MA-fase) langs tidligere austenittkorngrenser. For at den karakteristiske mikrostrukturen som er forbundet med sveising skal kunne oppstå kreves det en rask nedkjøling fra tofaseområdet for stål. Teknikken med å skanne overflaten av en prøve for å ta opp diffraksjonsmønster fra tilbakesprette elektroner (EBSD-teknikken) i SEM, er tidligere blitt brukt for å karakterisere framveksten av austenitt under oppvarming av stål til tofaseområdet. Da det er vakuum i SEM under kjøring vil prøver kjøles sakte ned. Det er aldri før blitt gjort in situ –forsøk på å bråkjøle stål fra tofaseområdet i SEM. Det har derfor ikke vært mulig å studere effektene bråkjøling har på dannelsen av mikrostrukturer som er avhengig av rask nedkjøling, deriblant dannelsen av MA-fase. For å EBSD-karakterisere dannelsen av MA-fase ble en metode for bråkjøling i SEM utviklet. Ved bruk av metoden for bråkjøling i SEM ble det oppnådd en kjølehastighet på ca. 40 oC/s. Dette var tilstrekkelig rask kjøling til å danne MA-faser ved bråkjøling av F 70-stål. Under in situ-forsøkene ble prøver varmet til tofaseområdet for ferritt og austenitt og holdt ved en temperatur i tofaseområdet i 5 minutter før EBSD-skann ble gjort. Prøver som ble varmet for høyt opp i tofaseområdet fikk så store forandringer i mikrostrukturen at mikrostrukturen før oppvarming og etter bråkjøling ikke var sammenliknbar. Da det viste seg vanskelig å måle en pålitelig temperaturen på varme prøver, var det vanskelig å finne en temperatur som gav en mengde austenitt som gjorde det mulig å sammenlikne in situ oppvarmede prøver med tosykel sveisesimulerte prøver. Målet for denne oppgaven var å utvikle et kjølesystem som gir tilstrekkelig rask kjøling for å oppnå sveisesimulering. Det var også viktig å oppnå en mikrostruktur som er lik den som oppstår ved sveisesimulering. En gunstig holdetemperatur måtte derfor finnes ved prøving og feiling.Prøver som ble varmet like over A1 –temperaturen for F 70-stål fikk MA-faser langs tidligere austenittkorngrenser etter bråkjøling. På grunn av holdetid i tofaseområdet ble framveksten av austenitt større ved in situ-forsøk enn ved sveisesimulering. Morfologien av MA-fasen som dannes fra in situ-forsøk ble derfor forskjellig fra de som observeres i tosykel sveisesimulerte prøver.Austenitten som vokser fram i tofaseområdet oppfyller K-S-orienteringssammenheng med BCC-strukturen inne i tidligere austenittkorn. Austenitten er derfor riktig indisert og ikke en artifakt.Ved oppvarming av prøver var det mulig å benyttes dobbelt så høy skannhastighet i forhold til før oppvarming. Dette gjør at større områder av oppvarmede prøver kunne skannes uten å bruke lang tid.

Hydrogen transport membranes have gained interest from industry as an alternative to pressure swing adsorption or cryogenic distillation, and are aimed to reduce cost, equipment size, energy consumption and waste generation. Doped strontium cerate stabilized with zirconium exhibit high proton conductivity and chemical stability and is therefore considered to be a promising material for hydrogen transport membranes.The purpose of the work was to investigate if phase pure strontium cerates, stabilized with zirconium and doped with thulium, ytterbium or yttrium, could be synthesized by the Pechini method, and if the membranes exhibited sufficient density. Determination of optimal calcination and sintering parameters was also important parts in the study.SrCe0.75Zr0.20M0.05O3-d, (M=Tm,Y,Yb) were synthesized via the Pechini method, followed by calcination, pressing of green bodies and sintering of dense membranes. Phase purity of powders and sintered membranes was examined by X-ray diffraction. Surface investigation and microstructure was investigated in a scanning electron microscope. Sintering behavior and thermal expansion coefficients was determined by dilatometry. Phase pure and dense orthorhombic perovskite structured SrCe0.75Zr0.20M0.05O3-d;, (M=Tm,Y,Yb) membranes, were obtained by powder calcination at 1000 C, followed by milling and conventional sintering at 1500-1600 C. SrCe0.75Zr0.20Tm0.05O3-d demonstrated the highest density of 98,6%, when sintered at 1500 C. Sintered membranes had a average grain size in the range from 3,2 – 4,9 um. Ball milling is concluded to be of vital importance to obtain sufficient density in the membranes.The membrane characterization is limited to the methods and techniques described above. Hydrogen flux across the membrane, total conductivity, stability in reducing atmosphere and thorough investigation of thermal properties are recommended for further work.

Copper are used as an alloying element in aluminum alloys to increase the strength of the material. By mixing copper and aluminum the good corrosion resistance of the pure aluminum decreases giving the alloy a lower corrosion resistance. After years of investigation on corrosion of aluminum alloys several results have shown increasing corrosion rates of aluminum that have been alloyed with both copper and zinc, giving a “grainy appearance” on the surface of the alloy. By adding copper to the aluminum increased intergranular corrosion and preferential etching of surface grains has been found after heat treatment and etching of the alloy.Before etching the aluminum alloys in alkaline and acidic environments, Glow Discharge Mass Spectroscopy (GDMS) measurements was done for all the alloys to determine the correct amount of alloying elements and impurities in each alloy. Preliminary etching trials have been performed on pure aluminum (Al 5N), aluminum containing 10 ppm copper (AlCu10), aluminum containing 100 ppm copper (AlCu100), and aluminum containing 1000 ppm copper (AlCu1000), as well as corrosion potential tests. Further, the surface of all the etched test specimens has been investigated in light microscope, Scanning Electron Microscope (SEM), Electron Backscattered Diffraction (EBSD), Confocal Microscope (IFM), Energy Dispersive Spectroscopy (EDS),and Glow Discharge Optical Electron Spectroscopy (GD-OES). These methods have been used to determine height differences between etched neighboring grains, the crystallographic orientation of grains, surface roughness, detecting elements occurring on the surface of etched specimens, and giving a depth profile of the etched specimens.For the alkaline etching trials, an increasing etching rate was found by increasing the amount of copper in the alloys, however the AlCu10-alloy showed little or no difference from the pure aluminum both in the etching trials and the corrosion potential tests. By increasing the copper amount in the aluminum the corrosion potential increased drastically for AlCu100-alloy and the AlCu1000-alloy. Further an increasing etching rate of grains having close to [111] crystallographic orientation could be seen in alkaline environment, a difference in the surface roughness between grains with different crystallographic orientations could also be seen for the alkaline etched test specimens. The GD-OES investigations done on test specimens that had been alkaline etched revealed differences in their depth profiles dependent on the etching temperature and how the specimens was treated after being etched. AlCu1000-alloys etched in acidic environment showed a different type of etching and surface after etching than the other alloys etched in the same environment. A clear difference could also be seen between the alkaline and the acidic etched AlCu1000 specimens.

The predominant site for the initiation of pitting on austenitic stainless steel has been shown to be sulfide inclusions and notably the manganese types of sulfides. Dissolution of inclusions has been observed and suggested to be the initial step for pit initiation, though several explanations for the mechanisms causing initiation has been proposed. Regarding welded stainless steels, several microstructural changes have been described and suggested to contribute to the decreased corrosion resistance in the weld zone. An area which has not been investigated much is the contribution of inclusions, in particular MnS inclusions, to the reduced corrosion resistance and the initiation of pitting in the weld zone. In the present work a literature review of the investigations focusing on the initiation of pitting by sulfide inclusions in austenitic stainless steels has been provided. A literature review of investigations focusing on the effects of welding on the microstructure, inclusions and the corrosion properties in the weld zone of austenitic stainless steels has also been provided.Experimental work was performed to obtain results which could be compared to or verify findings and suggestions from the reviewed literature regarding the initiation of pitting by inclusions. Observations of MnS inclusions as the preferential site for pit initiation in austenitic stainless steel was tried recreated. The hypothesis saying that dissolution of MnS inclusions occur prior to the initiation of pitting was also tried verified. It was also performed experiments to obtain results which could give knowledge about the effects of MnS inclusions on the corrosion properties and the initiation of pitting in the weld zone of an austenitic stainless steel. Along with this, the corrosion behaviour and microstructural changes in the weld zone in general and compared with the base metal were studied. A part of the work was also to study the effect of a lacking inert shielding gas during welding.Samples of a 316L stainless steel were first examined in SEM to study the microstructure and to identify inclusions. Then, some samples were welded, followed by SEM examination. Then all samples were polarized electrochemically in synthetic seawater with the purpose of initiating pitting. After the polarization, all samples were examined in SEM again to correlate pitting attack to inclusions and to compare microstructural changes and the corrosion behaviour in the base metal and the weld zone.It was verified that the main initiation site for pitting in the base metal was MnS inclusions. It was indicated that dissolution of the MnS inclusions started the pit initiation process, with the contribution of released compounds from the inclusions. An average percent of inclusions showing an inactive behavior regarding the initiation of pitting was 38 %, verifying similar observations reported in earlier investigations. A nitric acid treatment to remove MnS inclusions improved the pitting resistance significantly.The welding caused the initiation of corrosion at lower potentials when performing electrochemical polarization in synthetic seawater. The corrosion mechanism was probably grain boundary corrosion caused by precipitation of chromium carbides in the grain boundaries. A lacking inert shielding gas during welding did not have any effect on the potential for the initiation of corrosion when comparing two samples welded with and without shielding gas.It was indicated that compositional changes had occurred for MnS inclusions in a certain distance from the fusion line. These changes may have caused the inclusions to be more prone to initiate pitting. Further investigation should be performed to clarify the behaviour of such inclusions, and their susceptibility towards the initiation of corrosion. Grain boundary corrosion in various grades had occurred in the HAZ in certain distances from the fusion line. In a further distance from the fusion line pitting-like corrosion in clusters, possibly induced by chromium depletion after forming chromium oxides combined with a thin oxide film, had occurred. The grain boundary corrosion and the pitting cluster attack are from the experimental results believed to be more important for the failure of the welded stainless steel investigated in this work, than pitting initiated at MnS inclusions changed by the welding process.