The rare earth elements are a group of 17 elements consisting of the lantahnide series, scandium and yttrium. The application with the largest rare earth consumption is the permanent rare earth magnets. The neodymium-iron-boron magnets are the strongest permanent magnetic material known and are widely used. There is a concern that there will be a shortage in Nd-Fe-B magnets in short time. This has lead to an increased interest in the recycling of the rare earth magnets in the world.This project gives a very brief introduction to the Nd-Fe-B magnets, their uses and recycling. Two types of experiments that aims at recovery of neodymium from Nd-Fe-B magnets have been performed; extraction of neodymium by the use of molten silver and extraction of neodymium by direct oxidation. In the liquid silver experiments, extraction was obtained, but the analysis gave equivocal results. In the direct oxidation experiment, the separation of an iron phase and a neodymium oxide phase failed, and the experiment was not seen as successful.Magnetic waste from WEEE Recycling was also performed, and it turned out to contain small amounts of rare earth elements.

In this project the main goal was to establish a routine for making a microfluidic flow cell (MFFC) using soft lithography methods, and test the flow cell with different electrolytes, sulphuric acid and a ruthenium red-ox couple, and eventually use the established routine to make a microfluidic fuel cell and test it. A routine was established using the negative photoresist ma-N405. The photoresist was overdeveloped to make sure an undercut profile was reached, which proved to be necessary for the subsequent metal lift-off. Titanium (10 nm) and platinum (25 nm) were vapor deposited on the glass chips, and the lift-off process was completed in a couple of days. Flow channels of two different heights (about 15 and 100 µm) were made by making an impression in PDMS. A low flow channel, height of 15 µm, showed a significant electrolyte resistance in the experimental electrochemical work, and none of the experiments gave the expected results. The electrolyte resistance was measured by electrochemical impedance spectroscopy and taken to be the value corresponding to the high frequency intersection of the real axis. In addition, this resistance was estimated from cyclic voltammetry and taken to be the reciprocal of the slope of the curve, and was found to vary between 104-107 Ω. The results from EIS and CV were compared, and they overlapped quite well. An MFFC with a channel height of 100 µm and 500 µm electrodes, resulted in a significant decrease in measured electrolyte resistance and gave improved electrochemical results. The electrolyte resistance was measured from EIS and was reduced a lot to about 300 - 10000 Ω. These results were not compared with linear regression of the linear hydrogen area since the hydrogen area was no longer linear. The cell was tested with a ruthenium red-ox couple (hexaammineruthenium(II)chloride and hexaammineruthenium(III)chloride), and an external hydrogen reference electrode placed in the outlet was found to be simpler to control than an internal reference electrode. The potential limits were -0.3 and 0.3 V vs. an external hydrogen electrode in the same electrolyte. The effect of flow rate, sweep rate and oxygen content in the electrolyte was investigated.

The possibilities for using CaNb2O6 as a photocatalyst in direct water splitting have been evaluated by investigating the electronic structure of the material. In addition the oxide was doped with nitrogen in order to modify the electronic structure and obtain visible light absorption. Experimental techniques such as electrochemical impedance spectroscopy (EIS), photocurrent, and diffuse reflectance spectroscopy (DRS) were combined with theoretical approaches to determine the bandgap, flatband potential and quasi-Fermi levels of the photocatalyst. CaNb2O6 was prepared by a sol-gel synthesis and doped with nitrogen by heat treatment of the oxide powder in an ammonia atmosphere. X-ray diffraction (XRD) confirmed phase pure orthorhombic CaNb2O6 for both pure and N-doped oxide and excluded a possible transformation of the oxide into an oxynitride. Upon illumination anodic photocurrents were observed implying that CaNb2O6 was an n-type semiconductor due to oxygen vacancies in the lattice. From the wavelength dependency of the photocurrent a direct bandgap of 3.7eV and an indirect bandgap of 3.4eV were determined for undoped CaNb2O6. Doping with nitrogen altered the optical properties of the oxide and shifted the absorption edge into the visible light region. Calculations using the density functional theory (DFT) attributed the change in absorption properties to the formation of narrow energy bands above the valence band of pure CaNb2O6. An alternative explanation could be a hybridization of N 2p and O 2p bands. Correspondingly a reduction of the bandgaps for N-doped CaNb2O6 with respect to the undoped oxide was identified. Impedance was applied to determine the flatband potential of CaNb2O6 from Mott-Schottky plots. However the obtained results seemed to be dominated by contributions from the electrode substrate. Theoretical investigations concluded that pinhole-free oxide layers creating an ohmic contact with the substrate are required in order to designate the observed impedance response to the space charge capacitance. Quasi-Fermi level measurements indicated a low photocatalytic activity of CaNb2O6 as no photocurrent could be detected. Further investigations are needed to identify the cause of the photocurrent limitations. Nevertheless probable explanations could be low conductivity in CaNb2O6, high concentrations of recombination centers or slow charge transfer kinetics. The latter was confirmed for porous oxide layers as the addition of a hole scavenger increased the measured photocurrent. Positive photocurrent transients were also observed for porous CaNb2O6 films and could be related to either the diffusion of electrons through the porous oxide layer or to a photoanodic decomposition of the photocatalyst.

A procedure for texturing of lead-free piezoelectric ceramics based on sodium potassium niobate (KNN) was investigated with respect to texturing procedure and choice of materials.Material compositions that were considered include KNN with and without addition of 0.5 mol% MnO, and KNN modified with Li and Ta (KNNLT), and Mn substituted into the A or B site of the perovskite structure. The two compositions KNN-Mn and KNNLT-Mn(A) compositions were further investigated as candidate materials for texturing.Textured samples of the two materials were made by tape casting and templated grain growth, using needle-shaped KNN particles as templates, while non-textured reference samples were made by conventional sintering of powders. Both textured and non-textured dense materials were characterized with respect to density, degree of texture and piezoelectric and dielectric properties. The non-textured materials sintered to high relative densities of 93.9 % for KNN-Mn and 96.7 % for KNNLT-Mn(A). A converse piezoelectric coefficient of over 250 pm/V was measured for non-textured KNNLT-Mn(A), and around 200 pm/V for KNN-Mn.Texturing led to a lower relative density of both compositions, 89.1 % for KNN-Mn and 92.1 % for KNNLT-Mn(A). The piezoelectric performance of KNN-Mn was not significantly affected by the texturing procedure, while the piezoelectric performance of KNNLT-Mn(A) became significantly poorer. This is due to the formation of a secondary phase in KNNLT-Mn(A) during sintering, which is probably caused by the compositional mismatch between the templates and the fine-grained matrix powder.Based on the results, and a theoretical consideration of the texturing procedure, a different choice of template particles is suggested for further work on texturing of KNN-based materials.

Silicon undergoes oxidation at room temperature, causing a formation of an oxide layer on its surface. Gaining knowledge about the oxide layer formed during ageing, is valuable with regards to production of high quality ceramics, Si3N4, especially with for the slip casting process.In this work silicon powders were exposed to humid air at different temperatures for different periods of time. From the XPS analysis, the oxygen and hydroxide content were found to be higher for powders aged at higher humidity compared to powder aged at lower humidity. This was verified by the estimated oxide thickness, which was larger for powder aged at higher humidity. No obvious difference could be observed for short and long ageing time in low humidity atmosphere. Results from Raman spectroscopy showed a more amorphous powder after storage in humid air. A clear shift and broadening of the crystalline silicon peak were observed for powders exposed to air at low and high humidity. The powders aged in humid air were further reacted with water at pH 9.4 and temperature of 60°C. The onset time for hydrogen evolution was observed to be later for samples exposed longer times to humid air. This indicates that the reactivity of the powder decreases as the oxide layer formed during ageing develops. The amount of hydrogen evolved seemed to be dependent on the hydrogen evolution time rather than the time of exposure to humid air. This was verified by the surface area, which was about the same for all samples, showing only a slightly decrease for increasing exposure time. The oxygen content measured was linearly related to the surface area for the main section of the samples. Higher hydroxide content seemed to catalyse the aqueous oxidation reacting, resulting in an earlier onset time for hydrogen evolution and a higher hydrogen flow. This was stated by a higher surface area and higher oxygen content for these samples.Powder thermally treated, at 300 °C and 900 °C, were also investigated. XPS analysis showed a thicker oxide layer for powder treated at 900 °C. No hydrogen was formed in the aqueous oxidation of powder treated at 300 °C. This was verified by a low surface area.Regarding the slip casting of silicon powders, a defect free green body can be obtained by reducing the hydrogen formation. Based on the results found, this can be obtained by the formation of a passivation oxide layer on the particle surface, formed during ageing of the powders in humid atmosphere before processing.Higher humidity and longer ageing time seems to affect the development of the oxide layer formed on the surface more than low humidity and short ageing time. To minimise the hydrogen formation, it is crucial to be able to control the hydroxide concentration in the aqueous oxidation accurately.

The use of offshore wind turbines as a source of renewable energy is promising. However, many challenges have to be solved before they will be cost effective. The operation time, without any maintenance required, is desired to be as long as possible, because downtime and maintenance costs are high. Thus it is important that the rotating parts in the turbine have a long operational time. The harsh marine environment, combined with the desire for elongated operating times and little or no maintenance, give rise to many tribological challenges. It is important that the chosen materials and lubricants can withstand the marine environment, and the high loads. The effect of marine environment on lubricating properties of lubricants is not well understood. The objective of this thesis has been to investigate this effect. Two lubricants that are commonly used as gear lubricants in onshore wind turbines were tested in this work; polyalphaolefin and polyalkylene glycol. They were both contaminated with different amounts of artificial seawater in order to investigate the effect on the lubricating properties. The lubricants were tested in a rotating ball-on-disc tribometer, with self-mated stainless steel, and self-mated silicon carbide. Stainless steel was selected as it is commonly used in gear bearings, whereas silicon carbide was chosen due to its promising excellent properties. The results obtained from this work show that PAO has a very low saturation limit for water, and an emulsion will be formed even at low contamination levels. This made the lubricant unstable, and the measured COF were unstable. It was found that the amount of two-body abrasive wear increased as a function of seawater content. The PAG lubricant managed to dissolve much larger quantities of seawater that PAO. But even though the system was one-phased, the results for COF were unstable. Wear induced pitting was found for both clean and contaminated lubricant. It is believed that it is caused by the additive package of the lubricant. For dry tribological testing COF was found to be mush less for self-mated silicon carbide than for self-mated stainless steel. This is as expected, since silicon carbide has shown outstanding tribological properties in previous work.For self-mated silicon carbide testing only abrasive wear could be found for both dry contact, and lubricated. The results from PAO contaminated with seawater, showed a clear increase in COF as a function of seawater content. Further, the COF all stabilized after the running-in period. PAG showed no such trend with increasing amounts of seawater, but the standard deviation of the measurements increased.

Denne masteroppgaven har tatt for seg undersøkelser av stål designet for lavtemperaurappliksjoner ved bruk av elektronmikroskop i kombinasjon med diffraksjon av tilbakespredte elektroner (Electron Backscatter Diffraction - EBSD). Målet med oppgaven var å bruke EBSD-teknikken i kombinasjon med in situ deformasjon og en spesiallaget kaldfinger for å kunne studere materialene ved lave temperaturer. To ulike stål ble undersøkt; et smidd finkornet strukturelt stål (F70) og et varmvalset supermartensittisk rustfritt stål (Supermartensitic Stainless Steel - SMSS).F70-stålet ble sveisesimulert for å oppnå en mikrostruktur tilsvarende interkritisk grovkornet HAZ (Heat Affected Zone). Dette ble gjort ved en tosykel sveisesimulering. Prøvestaver av materialet ble varmet opp med en ønsket makstempertur på Tp1= 1350°C og Tp2= 780°C. For å undersøke effekten av ulike avkjølingshastigheter ble halvparten av prøvestavene avkjølt med Dt8/5 = 5 sekund, og den andre halvparten med Dt8/5 = 15 sekund. Ved sveising av stål kan det dannes lokale sprø soner som martensitt/austenitt-faser (MA-faser). Bilder tatt i lysmikroskop viser at strukturen til sveisesimulert F70-stål består av martensitt og noe bainitt. MA-faser er lokalisert langs korngrensene.EBSD-teknikken krever at materialet på forhånd gjennomgår en tilfredsstillende prøvepreparering for å gi gode resultater. Det var tidligere etablert en tilfredsstillende prepareringsteknikk for SMSS. I denne oppgaven ble to ulike prepareringsmetoder testet på sveisesimulerte prøver av F70-stål, som er et forholdsvis nytt materiale. Metodene som ble testet var ionesputtering og elektropolering. Preparerte prøver ble undersøkt med EBSD for å analysere kvaliteten på prepareringen. Det viste seg at MA-fasene reagerte annerledes på prepareringen enn resten av strukturen, og det var derfor vanskelig å få disse fram på EBSD-skann. De to prepareringsmetodene ga også forskjellige utfall for andel austenitt (g-fase) i stålet. Da det i hovedsak er MA-fasene som er interessante ved in situ undersøkelser ble det besluttet å ikke gjennomføre disse på F70-stålet, da en tilfredsstillende preparering må etableres først. Ved bruk av EBSD-teknikken kan orienteringsdataene som lagres behandles i programvaren TSL OIM Analysis 5.32, som tilbyr ulike renseoperasjoner. Grain CI Standarization gir alle punktene i et korn, innenfor en gitt vinkeltoleranse, samme CI-verdi som den maksimale CI-verdien funnet blant punktene i dette kornet. Det er også mulig å legge på et CI-filter som fjerner alle punkter med en CI ≤ 0,05, og erstatter disse med svarte eller grå piksler. Effekten av disse to operasjonene ble undersøkt på et EBSD-skann av SMSS tatt ved romtemperatur, uten noe form for deformasjon. Renseoperasjonene førte til at 8,1 % av alle punkter ble fjernet. 3,8 % av disse var av g-fasen, som utgjør kun 17,3 % av skannet før renseoperasjonene ble benyttet. Punkter som fjernes ligger i hovedsak i forbindelse med korngrenser eller øyer av restaustenitt. For SMSS som inneholder rundt 20 vol.% restaustenitt i opprinnelig (dvs. interkristisk glødet) tilstand, ble det gjennomført undersøkelser av deformasjonsindusert fasetransformasjon ved bruk av in situ strekktesting med påfølgende EBSD karakterisering. Undersøkelsene ble utført ved romtemperatur og -80°C. Et spesiallaget strekkbord ble montert på SEM (Scanning Electron Microscope) stagen med prøven fastmontert, og en kaldfinger ble brukt for å kjøle ned prøven. EBSD karakteriseringen ble foretatt uten deformasjon og ved 1, 2, 3 og 4 % forlengelse. En sammenligning av resultatene ved romtemperatur og -80°C ble deretter utført. Det ble konkludert med at øyer av restaustenitt transformeres til martensitt som følge av plastisk deformasjon i større grad ved -80°C, som følge av høyere termodynamiske drivkrefter for reaksjonen. Ved romtemperatur var det mulig å verifisere at martensitten som ble dannet oppfyller Kurdjomov-Sachs kriteriet som beviser at den er korrekt indisert. Dette var vanskelig å verifisere for lavtemperatursforsøkene, da skannene har en mye lavere kvalitet.

AISI 316/316L has traditionally been used in offshore topside environments when operating under low temperatures. It has been observed that the AISI 316/316L piping suffer from severe attacks of pitting and crevice corrosion on external surfaces. It is therefore important to emphasise the comments within the statements that give the limitations on the use of the material. While temperature is the main parameter in the standards, there seem to be others, such as location, presence of tags and coating, which affect the initiation and propagation of pitting and crevice corrosion. This thesis discusses the various operating parameters that affect the susceptibility to pitting and crevice corrosion of AISI 316/316L piping and proposes procedures for identifying piping that are most prone to attack, and calculations of the probability of failure of such piping.In the first part of the thesis, a literature survey of the parameters that affect the pitting and crevice corrosion of AISI 316/316L in an offshore environment is presented. In the second part, a procedure for the identification of piping that is prone to pitting and crevice corrosion is presented. This procedure has been developed taking into consideration the parameters that are assumed to be important and suitable for use in RBI analysis. In the first step, the parameters that affect both pitting and crevice corrosion, that is, the chloride content due to the location of the pipe, coating and temperature, were considered to be the most important ones. In the second step, the possibility of crevice corrosion was assessed. In the third part, a procedure for assessing the possibility of pitting corrosion in the offshore topside environment based on the pitting potential was developed. The temperature of the external pipe surface was used to find the solubility of NaCl in water. The chloride concentration was used to determine the in order to find the possibility of pitting in the topside offshore environment. The last step was to develop a procedure for calculating the probability of failure of a pipe as a function of time. In this step, the functional life of the coating and the rate of pitting corrosion have been considered.

High cost and a short lifetime are the two main reasons why the PEM fuel cell is yet to be commercialized. The bipolar plate in a PEM fuel cell is alone responsible for about 45% of the cost and 85% of the total weight of a single cell. stainless steel has been suggested as material for the bipolar plate because of its good mechanical properties, easy manufacturing and relatively low price. A problem with stainless steel is the Chromium oxide film formed on the surface which causes a high contact resistance. In order to prevent this oxide formation, the stainless steel can be coated. Gold has been suggested as coating, but it is too expensive to be considered a viable alternative. The objective of this thesis was to investigate stainless steel as bipolar plate material for PEM fuel cells. In cooperation with SINTEF polarization tests were done on stainless steel bipolar plates with and without two different coatings; gold and Coating A. The tests were performed in H2SO4 electrolytes with different molarities and additives. Before and after each polarization test Interfacial Contact Resistance (ICR) measurements where done to see how the oxide layer on the stainless steel surface changed during polarization. Gold coated stainless steel was chosen as standard for both the polarization tests and the ICR measurements because of its corrosion resistance.The results obtained from both polarization tests and corresponding ICR measurements showed that the reproducibility was not as good as one had hoped, but this can be explained by low absolute values of the current densities. Gold coated steel proved to be a good standard for the ICR measurements, but due to pitting corrosion the corresponding polarization results were not as promising. The pH in an operating fuel cell was found to be approximately 3.5, and the tests done at different molarities showed that at a lower pH the oxide layer seemed to be thinner and the stainless steel surface thus became more exposed to corrosion. Additions of fluoride and chloride in the amounts expected in an operating fuel cell did not seem to cause any changes for neither the polarization results nor the contact resistance measurements. Stainless steel plates with Coating A showed very small changes in contact resistance after being put trough the polarization tests, but at low potentials the current densities in the polarization test were very high, indicating that components in the coating either catalyzed hydrogen evolution or were reduced themselves. Out of all the ICR measurements, gold coated stainless steel was the only plate satisfying US department Of Energy’s (DOE) resistance requirement for bipolar plates of less than 10 mΩ cm2. The stainless steel plates with Coating A were close to DOE’s requirements for both corrosion current and contact resistance. Non-coated stainless steel was ruled out as bipolar plate material due to high contact resistance measurements.

Silicon quantum dots were synthesised wet-chemically by three different methods based on reduction of silicon tetrachloride with the reduction agents potassium naphthalide, sodium cyclopentadiene and the alkalide of potassium. The purpose of these quantum dots was to deposit them on a substrate in order to use them as down converters on top of photovoltaic solar cells for enhanced solar cell efficiency. One possible method for the formation of down converting layers is to incorporate quantum dots into silica thin films by deposition of quantum dots in an ethanol based silica sol, followed by spin coating. It is believed that when the quantum dots are water dispersible, this will make it easier to bind them to the silica network, and a good dispersion in the film is facilitated. The different hydrophilic functionalisations investigated were pentenoxy capping, oxidised pentenoxy capping, oxidised acrylic acid capping and ethanolamine capping. Challenges were encountered during the synthesis of water dispersible quantum dots, the most important were related to agglomeration and purification of the quantum dots. This was believed to be due to the tendency of hydrophilic surface groups to attract each other, interaction with the polar solvent and similar solubility characteristics of the quantum dots and the byproduct salts.Si quantum dots with hydrophobic octoxy capping were also synthesised. Dispersions of these quantum dots were deposited onto solid substrates followed by solvent evaporation. This was done to see whether it was possible to deposit the synthesised quantum dots by this simple approach, to investigate the fundamentals upon evaporation, the degree of agglomeration and the byproducts present in the quantum dot dispersions. It was found that agglomeration was very pronounced after the solvent had evaporated and that quite large amounts of byproducts were present in the final quantum dot dispersions. The most important reasons to this were believed to be too weak steric repulsive forces between the particles, too fast evaporation of the solvent and an insufficient purification procedure. For the use of Si quantum dots synthesised wet-chemically as down converters in solar cells, improvements of the particles are needed.