Renewable energy production featuring silicon photovoltaic solar cells are of considerable interest to reduce pollution and related environmental changes. Improvements in efficiency along with reductions in cost are key elements to large scale implementation of this technology. Some suggested and attempted methods of improvements that deserves mentioning are: modifying the energy of incident light to better suit the existing band gap along with reduction in losses by applying surface texturing and nitride coatings. Looking to nature for inspiration reveals diatoms and their frustules having pore structures displaying excellent light harvesting abilities. Thus an implementation of such structural features with regards to solar cell improvements would be highly desirable. This thesis was aimed at performing modifications of diatom frustules surfaces by deposition of oxides known to possess properties of up and down-conversion of light as well as attempting to convert diatom frustules to silicon nitride replicas. Coating frustules with oxides possessing properties of up and down-conversion of light combines light harvesting properties of frustules with spectral modifications of incident light. This offers possibilities of solar cell improvements upon implementation. Nitriding of diatom frustules preserves structural features of the frustules and offers increased mechanical, chemical, thermal and anti-reflecting properties for possible solar cell use. Diatom frustules of the species Coscinodiscus wailesii and Coscinodiscus sp. were utilized in all experimental work during this thesis. An initial temperature exposure experiment was performed at temperatures ranging from 400oC-1200oC with increments of 200oC, to gage thermal response of the frustules. In another set of experiments diatom frustules were subjected to one, two and four dip coatings in one of two different precursor solutions. One solution consisted of erbium and yttrium chloride dissolved in a mixture of ethylene glycol and acetonitrile while the other solution consisted of manganese and zinc chloride dissolved in ethylene glycol and acetonitrile. Post dip coating, frustules were annealed at 800oC in normal atmosphere, decomposing chloride precursors to corresponding oxides. Nitriding of frustules was attempted by simultaneous metallothermic reduction in a purpose built reactor vessel where necessary nitrogen was supplied in the form of ammonia at 650oC and 800oC. Ammonia was generated by thermal decomposition of ammonium chloride mixed with calcium oxide. Post experiments, frustules were characterized by use of scanning electron microscope (SEM) featuring energy dispersive x-ray spectrometer (EDS), fluorescence microscopy, photoluminescence spectroscopy and Raman spectroscopy. Frustules in the temperature exposure experiment were found to display small changes to the pores at 600oC. At 800oC the changes were more severe and the changes were found to increase with increasing temperature until complete destruction of the pores along with visible external changes took place at 1200oC. For the coating experiments, no photoluminescent properties were found to exist for frustules coated once or twice. Frustules coated four times were found to display photoluminescent behavior for both types of coatings. Frustules subjected to four coatings with Zn/Mn solution were found to display more temperature related changes in the pores as compared to frustules coated four times with Y/Er solution. Frustules coated with Zn/Mn solution, were found to be contaminated by elevated levels of tin, possibly influencing both thermal and photoluminescent properties. Frustules subjected to simultaneous metallothermic reduction and nitriding at 650oC were found to suffer low conversion and thus only superficial nitride formation. Frustules nitrided at 800oC were found to display higher conversion to silicon nitride. The formed nitride was determined to be β-silicon nitride by Raman spectroscopy. The frustules were also found to contain elevated levels of reduced silicon, for the frustules nitrided at 800oC, this silicon was found to be a mixture of amorphous and nanocrystalline. The nanocrystalline silicon was found to have a crystalline size of ~2.2 nm.

Mixed ionic electronic conducting ceramic oxides are being investigated for use as membranes for oxygen separation from air and as electrodes in solid oxide fuel cells [1, 2]. Oxygen surface exchange rate is an important parameter controlling the oxy- gen permeation rate of these membranes [3]. In this work surface structuring by wet chemical etching is investigated as a possible route to improve the surface exchange rate of La0.2Sr0.8Fe0.8Ta0.2O3−δ (LSFT). Several different etchant solutions have been in- vestigated (HCl, HNO3, H2SO4, H2C2O4, NaHCO3, Na2CO3 and KOH) and evaluated with respect to etch rate, the resulting surface morphology, selectivity and special effects caused by the etchant or the nature of the sample being etched. The resulting surface structure after etching proved to be very dependent on microstructure, showing both el- evated grain boundary and mid grain etching. The mid grain etching was unexpected, and additional experiments were done to investigate the cause of this behaviour. The effect of surface structuring using wet chemical etching was investigated using electri- cal conductivity relaxation at 800◦C and 900◦C. This showed that an increase of the specific surface area 3.6 times gave an increase of the chemical surface exchange coef- ficient about 3.16 times at 800◦C. The influence of temperature and partial pressure of oxygen on the effect of surface structuring is discussed based on the obtained results. LSF-based membranes (La1−xSrxFe1−yMyO3−δ where M = transition metal cation) show limited stability towards CO2 containing atmospheres, forming surface layers of SrCO3 [4, 5]. It is suggested that a subsequent removal of this layer by i.e. chemical etching could lead to a fine surface structuring. In this work, exposure of LSFT-samples to CO2- rich atmospheres was done at 900◦C and 1000◦C without the formation of such a layer. Reasons for this are discussed and alternate experimental conditions are suggested.

The aim of the thesis is to produce high grade silicon from off-grade materials like sculls and process slags from Elkem Thamshavn. The methods investigated are dense medium separation, optical separation, flotation and metallurgical separation by remelting. Dense medium separation trials are conducted using magnetite suspended in water and aim to find the suspension density where only one phase will float. Optical separation experiments are done to identify light intensity thresholds between refractories, silicon and slag. The viability of flotation without surface activators and at neutral pH are investigated by measuring the zeta potential of each phase. Remelting experiments are done, building on previous work by the author, with the aim of investigating whether adding CaO or MgO to the slag will increase the settling efficiency. No results were obtained in the DMS experiments, because the viscosity of the suspension increased to infinity before the density of either slag or silicon was reached. The flotation experiments showed that flotation is not viable at neutral pH without surface activators, as the zeta potential of slag and silicon is nearly identical. The optical separation experiments were a success. The product fraction had an average silicon content of 74 wt%, compared to 52 wt% in the original off-grade material, while the waste fraction contained 7.5 wt% silicon. The separation efficiency was best for coarser grains, which is the expected result based on theory. The remelting experiments concluded that adding CaO or MgO to the slag will increase the settling efficiency. This was established both by chemical analysis and by surface area analysis of slag samples from each experiment. MgO seemed to contribute more to the settling efficiency than CaO, but because of the large variance between samples, this is not conclusive. The quality of the produced silicon was unaffected or improved by adding CaO, but additions of MgO increased the magnesium content slightly.

ABSTRACT

The aluminium smelter at Hydro Sunndal has experienced problems with an unexpected increased loss of AlF3 from the electrolyte when using a certain quality of alumina. One hypothesis considered was that the fluoride loss was a direct result of unusually high HF formation when the quality was added to the cryolitic melt. This work has set out to study the HF formation potential of three different industrial alumina qualities. Alumina A was an alumina quality that worked well in the smelter. Alumina B was the alumina quality where the aforementioned drop in AlF3 was observed and alumina C, made by the same producer, controversially did not to exhibit the same loss at smelter. The present work has been divided into two parts: a characterisation section, where the aluminas have been characterised by techniques such as LOI, TGA, DSC and XRD, and an experimental section, where the industrial aluminas were added to a cryolitic melt. The HF formation and the corresponding H2O concentration were measured in-situ using a tunable diode laser during the alumina additions to the cryolitic melt. Through this work it has been found that both primary and secondary alumina A form less HF than alumina B and C. The LOI, TGA and XRD characterisation has shown that alumina B and C contain a substantial amount of gibbsite, whilst the gibbsite level in alumina A is negligible. A clear correlation between the quantity of moisture found through LOI characterisation and HF formation has been found. It has also been shown that all types of moisture found through LOI testing contribute to HF formation; both physisorbed and chemisorbed types, as well as structural hydroxyl. From the present work it cannot be explained why alumina B caused a drop in AlF3 in the electrolyte, whilst alumina C did not. One explanation postulated is that alumina C has better scrubber efficiency than alumina B. Examining this hypothesis has been outside the scope of this master work. If variations in scrubber efficiency for the two aluminas fail to explain the drop in AlF3, the solution may be found in parameters outwit the alumina quality e.g. weather conditions at the time of production or storage conditions at the calciner.

Si-nanowires are being introduced as an attempt to decrease the high recombination rate present in silicon based thin-film solar cells by employing radial pn-junctions instead of conventional planar pn-junctions. Previous publications have also shown an additional increase in the amount of absorbed light when covering a silicon-substrate in silicon nanowires which may result in a further increase in the total efficiency of a thin-film solar cell. Successful growth of Si-nanowires has earlier been performed by Chemical Vapour Deposition (CVD), employing gold (Au) as catalytic material. Au is a very stable catalytic material for nanowire growth but Au-residues are unwanted in solar cell applications, and the current experiment has therefore investigated aluminium (Al) as an alternative catalyst material. However, stable Al-catalysed growth has been proven to be difficult and is assumed to be mainly due to rapid oxidation of Al to Al2O3. Most of the nanowires were short, tapered and consisted of worm-like structures. Several unsuccessful in-situ NH3-based cleaning (CVD) processes were attempted. Tin (Sn) was also attempted as a protective coating for the Al-film in order to protect Al from exposure to air during sample transport, without any luck. As solar cells require both p-doped and n-doped sections in order to form pn-junctions, initial investigations were performed on the effect from the addition of dopant gases (B2H6 and PH3) on nanowire morphology. The addition of B2H6 to the gas flow seemed to have much larger effects than PH3 on the nanowire morphology compared to intrinsic nanowires. Both gases resulted in a continuous reduction in the average nanowire length with increasing dopant⁄SiH4 ratios, ultimately leading to a complete inhibition of nanowire growth. The highest usable dopant⁄SiH4 ratios before complete growth-inhibition were found to ~10^-3 for B2H6 and ~10^-1 for PH3. An undesirable tapering effect was also found when adding B2H6 to the gas-flow, resulting in radial growth of amorphous silicon on the nanowire walls already at the lowest dopant ratio (~10^-5). This may complicate the use of B2H6 as a dopant gas for p-type nanowires. Ignoring the fact that the addition of PH3 to the gas-flow reduces the nanowire growth rate PH3 may be assumed to be a good alternative for n-type doping of nanowires as no further effects on the nanowire morphology is observed. The actual implementation of dopant atoms into the nanowire structure may be determined by measuring the electrical resistivity in the nanowire, and a possible four-contact structure has been designed and partly optimized for this purpose. The contact structure has been designed in three layers where two of them are produced by photolithography while the smallest layer by electron-beam-lithography. Note that the structure has not been finalized because of time limitations. Some optimization of the four nanowire contacts remains as some final lift-off problems appeared, and is assumed to be related to either an incomplete development of the smallest features or an observed resist-bubbling because of high Titanium (Ti) deposition temperature. However, a robust three-point alignment procedure has been investigated and found useful for producing accurate contacts to single nanowires and leads to the conclusion of a promising structure.

Hovedmålet i masteroppgaven har vært å utforske nye gullkatalyserte reaksjoner og anvendelser av propargylestere og allenestere. Allen 14, ble syntetisert fra propargylbromid over to trinn, ved en kjent prosedyre. Kationiske gullkomplekser har en sterk alkynofil karakter som aktiverer alle typer π-systemer for nukleofilt angrep. Dette gjør allen 14 godt egnet som substrat i gullkatalyserte transformasjoner. E-Dien 22a-b, samt Z-dien 23a-b, ble syntetisert i en stereoselektiv gull(I)katalysert reaksjon. Dette er første gang diener har blitt fremstilt fra 2-substituerte allenestere, og det ble observert en høyere Z-selektivitet enn hva som tidligere har blitt observert for usubstituerte allenestere. Dien 22a og 23a ble isolert i et utbytte på henholdsvis 35% og 33% med et E/Z-forhold på 47:53. For dien 22b og 23b var E/Z-forholdet 52:48, og de ble isolert utbytter på 38% og 28%. Elektrofil addisjon til allen 14, etterfulgt av et 1,2-arylskift, ga aldehyd 25 i et utbytte på 45%. Tre nye forbindelser er blitt fremstilt ved en helt ny metode for gull(I)katalysert jodhydroksylering av allenestere. Vinyljodid 24 og 26 ble dannet i utbytter på henholdsvis 59% og 39%, mens omleiret produkt 27, ble isolert i et utbytte på 20%. Syklopropylforbindelse 28 ble syntetisert i en ny gull(I)katalysert ”tandem”-syklopropaneringsreaksjon, fra propargylester 4, i et utbytte på 34%.Fire nye syklopropylforbindelser 18a-b og 19a-b har blitt syntetisert. Disse er dannet i en sykliseringsreaksjon mellom vinylester 17 og propargylester 1b eller 4. Syklopropylforbindelse 18 og 19 er isolert i utbytter på henholdsvis 52% og 76%. Et kiralt NHC-basert gullkompleks 41 har blitt syntetisert, og testet som gull-ligand i syklopropanerings-reaksjon. Det ble funnet et enantiomert overskudd på 5% for cis-forbindelse 43a, og et enantiomert overskudd på 6% for trans-forbindelse 43b. Dette er første gang en kiral NHC-basert gullkatalysator er blitt testet i en gullkatalysert asymmetrisk syklopropaneringsreaksjon.

Et kiralt triazoliumbasert N-heterosykliskkarben-salt (NHC) 1 har blitt fremstilt fra L-fenylalanin 2 og fenylhydrazinhydroklorid 12 i en synteserute som går over fem trinn, og med et totalutbytte på 10%. NHC-salt 1 er blitt testet som organokatalysator i en sykliseringsreaksjon mellom aldehyd 4 og keton 5. Produktet, butyrolakton 6, ble dannet i et trans/cis-forhold på 59:41, og med et enantiomert overskudd på henholdsvis 10% og 19% for trans- og cis-forbindelse 6a og 6b.NHC-salt 1 ble testet som ligand i en gullkatalysert syklopropaneringsreaksjon. Gullkatalysator 15a og 15b ble syntetisert fra NHC-salt 1 og 16 ved hjelp av Ag2O og AuCl(Me2S) i et utbytte på henholdsvis 82% og 85%. Syklopropaneringsreaksjon mellom alkyn 18 og alken 19 ga syklopropylforbindelse 20 i et trans/cis-forhold på 41:59 for gullkatalysator 15a og 38:62 for gullkatalysator 15b. Gullkatalysator 15a ga et enantiomert overskudd på 8% og 6% for henholdsvis trans- og cis-forbindelse 20a og 20b. Gullkatalysator 15b ga et enantiomert overskudd på 10% og 9% for de samme forbindelsene. Dette er første gang en kiral triazolbasert NHC-gullkatalysator har blitt brukt i asymmetrisk syntese.

Flere studier har vist at saltinntaket til mennesker er for høyt, noe som kan føre til økt risiko for blant annet høyt blodtrykk og hjerte- og karsykdommer. Den største delen av saltinntaket kommer fra mat som er bearbeidet. En reduksjon i saltinnholdet i bearbeidede næringsmidler vil ikke bare påvirke smak, men også funksjonelle egenskaper som vannbindingsevne, koketap, geldanning, proteinløselighet og tekstur. Disse egenskapene påvirker også de sensoriske egenskapene. Det er derfor nødvendig med kunnskap om tilsetninger som kan brukes ved lavere saltkonsentrasjoner for å opprettholde både funksjonelle og sensoriske egenskaper i produktet.Hensikten med denne oppgaven var å studere de fysiokjemiske egenskapene til et modellprodukt av fiskepudding tilsatt en lav saltkonsentrasjon (NaCl), natriumalginat (NA) (1,1%) og disse i kombinasjon. Det ble også målt reologi for fiskefarse tilsatt NA og for et gelet system tilsatt NA, CaCO3 og glukono-δ-lakton (GDL).Tilsats av NA (1,1 %), CaCO3 (0,2 %) og GDL (0,6 %) til fiskefarse ga signifikant økt vannbinding og redusert koketap i fiskepudding sammenliknet med fiskepudding av farse som kun var tilsatt NaCl (0,4 %). Det var også tendenser til at fiskepudding tilsatt NA dannet en sterkere gel for varmebehandlet fiskepudding sammenliknet med fiskepudding tilsatt NaCl. Dette var tilfellet både for fiskepudding laget av ferskt og av fryst råstoff av hyse. Proteinløseligheten til fiskefarsen tydet på at tilsats av NA bidro i større grad til dannelse av gel enn geling av myofibrillproteiner.Ved å tilsette NA (1 %), CaCO3 og GDL til fiskemasse (fisk og vann) ble det dannet en gel uten varmebehandling av fiskefarsen, reologiske målinger viste at gelen økte i styrke i løpet av 20 timer.Dette tyder på at tilsats av NA, CaCO3 og GDL til fiskefarse bedrer de fysiokjemiske egenskapene til varmebehandlet fiskefarse både av fryst og ferskt råstoff, samt danner en gel i fiskefarse ved lave temperaturer.

The skin is the largest organ of the human body and it constitutes a great protective barrier against entry of harmful microbial species and foreign materials into the body. The barrier function is a result of the highly hydrophobic nature and compact structure of the outermost skin layer, which makes transdermal delivery of drugs difficult. The aim of this study was to investigate diffusion of hydrophilic fish gelatin peptides and alginate oligomers (G-blocks) into human skin, and to evaluate the effect of skin pretreatments, vehicles and the different characteristics of the test samples on transdermal diffusion.Fish gelatin was degraded by acid hydrolysis to produce peptides of varying molecular size, and the molecular weight distribution and molecular weight averages of the peptides were determined. Further, peptides were conjugated to fluorescent dyes, and together with fluorescently labeled G-block oligomers, they were utilized as traceable model drugs in the transdermal diffusion experiments. Full-scale skins, from healthy human adults after abdominal plastic surgery, were used and the transdermal diffusion experiments were performed in Franz-type diffusion cells. The surface of the skin tissues mounted in the diffusion cells was either untreated or treated with micro-needles or lasers, to disrupt the skin barrier. The model drugs were applied on the epidermal side of the skins in both a 60% dimethyl sulfoxide (DMSO) and a 10% polyethylene glycol 200 (PEG200) vehicle, and the vehicles were also separately applied on skins as control samples. After the transdermal diffusion experiments, imaging of the skin tissues were performed by confocal laser scanning microscopy.An incubation time of 22 hours was determined for the transdermal diffusion experiments and pretreatments were necessary for the model drugs to successfully diffuse into the skin. Pretreatments with micro-needles and laser resulted in enhanced diffusion of the test molecules into the skin tissues compared to diffusion into untreated skin. Laser treatment was found to have the most profound enhancing effect on transdermal diffusion, and enabled efficient diffusion both into and through the skin. Of the four model drugs chosen for use in the experiments, the smallest fish gelatin peptide sample, with an estimated average molecular weight of 3000 g/mol, applied on skin tissues in a 10% PEG200 vehicle, showed the most efficient diffusion into and through human skin.