Arctic steels, like the API X70 steel explored in this master thesis, are developed to withstand very low temperatures, with a ductile/brittle transition temperature below −60◦C. However, during welding, brittle phases like martensite-austenite (M-A) islands may form in the heat affected zone (HAZ). In this master thesis in situ heat treatment and quenching experiments have been combined with electron backscatter diffraction (EBSD) inside a field emission scanning electron microscope in order to simulate a second weld cycle simulation. In conjunction with this a quenching device has been designed with respect to an existing hot stage.Inside the SEM, it was found difficult to recreate the characteristic microstructure of API X70 steel from a traditional second cycle thermal weld simulation. This was probably due to the slow heating rate and the excessive high temperature holding time. The developed quenching device was based on gas quenching and produced a steel sample cooling time from 600◦C to 400◦C, ∆t6/4, of approximately 6.5 seconds in every experiment. As a result of the gas quenching substantial amounts of oxide contamination, covered the sample surface following the experiments. This contamination layer produced artifacts, such as unreasonable amounts of austenite in the EBSD phase maps.Despite the quenching, islands of austenite (FCC) observed at elevated temperatures transformed into a low strain BCC structure. Some austenite islands showed a memory- effect during phase transformation, while others adapted the orientation of the surround- ing structure. No retained austenite was observed in the API X70 steel after the in situ gas quenching, probably due to insufficient cooling rates.

Det er aktuelt å bruke restaluminium fra produksjonsindustrien som råmaterialet til skrueekstrudering. Restaluminiumet inneholder forurensinger som blant annet skjæreolje. Dette arbeidet har fokusert på ulike rensemetoder av råmaterialet som skal skrueekstruderes og kvaliteten på ekstrudatene. Råmaterialet ble systematisk forurenset med en olje fra maskineringsindustrien og behandlet på fire ulike måter før ekstrudering, hhv. ubehandlet, vannrenset, acetonrenset og termisk renset. Mikrostruktur og mekaniske egenskaper ble undersøkt, og det var en klar sammenheng mellom kvalitet og innhold av olje i ekstrudatene. Høyere innhold av olje førte til økt spredning i strekkresultater, redusert bruddforlengelse, økt gassutvikling og delaminering. Termisk rensing gir et ekstrudat av høy kvalitet, som viser svært gode resultater med lav spredning i mekaniske egenskaper, høy styrke og god duktilitet.

The mechanisms in the carbothermic production of silicon have been examined in this report. Through the investigation of a pilot scale furnace as well as five small scale induction furnace experiments, a better understanding of this comlex process has been obtained. Especially the silicon producing reactions and mechanisms have been studied.Samples of all raw material as they travelled downwards in the pilot scale furnace was investigated along with samples from the induction furncace. SiO gas formed in the hot zone (2000 °C) travelled upwards and deposited as a condensate mixture of SiO2 and Si. In the pilot scale furnace this condensate went back down with raw material as the furnace was stoked or the raw materials slowly melted. The condensate decomposed as the temperatures increased; silicon accumulated and escaped from the SiO2-matrix in the condensate.A typical experiment conducted in the induction furnace had a specic power consumption of roughly 62 MWh per ton silicon produced, far more than normal industrial power consumption of 11-13 MWh per ton Si produced. Mass balance demonstrated that just over half of the silicon produced were left in the silicon pool in the bottom of the crucible. The other mere half had to end as silicon droplets in the condensate deposited in the upper portion of the crucible.The main silicon producing reaction is: SiO(g) + SiC(s) = 2Si(s,l) + CO(g), but the findings in this thesis have shown that the perspiration of silicon from the condensate is very important. A significant contribution to the total amount of silicon produced can therefore come from the following reaction: 2SiO(g) = SiO2(s,l)+ Si(s,l)Compression tests have been made on the agglomerate caused by the deposits of condensate (SiO2+Si). The compression strength varied from 115 to 396 MPa. Samples exposed to temperatures above 1670 °C had the lowest strenght, while those exposed to lower temperatures were the strongest.

Optimalization of PLD deposition of YSZ for micr-SOFC electrolyte applications by varying deposition pressure and target-substrate distance.Substrate used was Si-based chips and wafers (large area PLD), and the substrate temperature was held at 600. Dense films were obtained at 20 mTorr.

Lette våpen som håndvåpen, rifler og granater står for de fleste dødsfall i moderne konflikter, og behovet for robuste materialer til vern mot slike våpen er stort. Denne rapporten har tatt sikte på å avdekke hvilken effekt introduksjon av aluminafliser til en stålmatriks har på de ballistiske egenskapene, i hvor stor grad beskyttelsesevnen er redusert ved et skudd nummer 2 i samme flis og om treff mellom flisene vil gi redusert beskyttelse. For å avdekke dette ble det støpt inn 12 mm tykke fliser av alumina i den ferrittisk-martensittiske støpelegeringen S165M, med spalteavstander mellom flisen på 0, 3 og 10 mm. Det ble utført ballistiske tester med 7,62 mm AP og 12,7 mm AP ammunisjon, samt gjort undersøkelser av mikrostruktur og penetrasjonsområdet i etterkant av forsøkene. Ballistiske forsøk viste ingen klar forbedring av penetrasjonsmotstanden ved innstøping av aluminafliser. Årsaken til manglende forbedring skyldes i hovedsak oppsprekking av keramet under støping, grunnet termisk sjokk. Reduksjon i ballistisk grense ved skudd nummer 2 i samme flis var ca. 6 %. På grunn av manglende fylling av de 3 mm brede spaltene under støping, gav skudd i spaltene ingen klare resultater.

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.