<p> The main objective of this study was to gain an understanding of the oxidation properties of iron at low oxygen pressures and at high temperature. </p> <p> A thermogravimetric technique was employed to investigate the oxidation of iron in oxygen over the pressure range 2.5×10⁻³ - 3.0×10⁻¹ torr at temperatures ranging between 750ºC and 1000ºC. The oxidation curves exhibited distinct intervals of linear kinetics followed by transition to intervals of parabolic kinetics during exposures extending to 125 min. Linear kinetics governing the growth of uniformly thick wustite scales; the linear rate constants showed a proportional dependence on oxygen pressure due to reaction control by a phase boundary reaction involving non-dissociation adsorption of oxygen. Parabolic kinetics governed growth of wustite-magnetite scales containing magnetite as outermost layers. The value of the parabolic rate constants were independent of oxygen pressure since scale growth was directly dependent on the iron vacancy gradient in wustite established by the oxygen activities at the Fe/FeO and FeO/Fe₃O₄ interfaces. </p> <p> Scanning electron microscopy techniques were used to gain information on the growth of magnetite and hematite layers in the multilayer scale consisting largely of wustite formed at high temperature in the pressure range 2.5×10⁻³ to 760 torr. </p> / Thesis / Master of Science (MSc)

Increased DOC and Fe concentrations from terrestrial landscapes has led to the browning of boreal surface waters. The negative societal and ecological impacts of brownification are increased cost of water purification, increased presences of algae and cyanobacteria, loss of ecosystem services and reduced recreational value. Impacts of climate change, changes in land use and reduced sulfur deposition have been identified as drivers of brownification. While it has been recognized that DOC and Fe from terrestrial landscapes is increasing, little has been done to understand the impact of different land use practices on brownification. This research aims at evaluating the DOC and Fe runoff from spruce plantations, clear-cuts and wetland landscapes and determining the export of DOC from these landscapes into humic lakes. To do that, streams running through these three different land use types were sampled for water colour, pH, temperature, conductivity, DOC and Fe both at upstream and downstream of each land use type. Further, water discharge was calculated with the help of flow speed measurements and stream profiling (width, depth and channel shape). DOC (but not Fe) concentrations changed significantly depending on land use type. Wetlands lead to reduced DOC concentrations, whereas especially spruce plantations lead to increased stream water DOC concentrations.

Philosophiae Doctor - PhD / The commercial need to improve the performance of low-cost organic solar cells has led to the idea for this research. The study discusses the synthesis of one dimensional TiO2 and ZnO nanowire arrays synthesised using a hydrothermal autoclave method and their application in bulk heterojunction inverted organic solar cells. Previous literature has shown that the precise manipulation, positioning and assembly of 1D nanostructures remain one of the greatest challenges in the field of nanotechnology, with much of the difficulty arising primarily from the lack of size and scale of the materials as well as the inability to visualise the nanostructures. In particular, one dimensional metal-oxides such as TiO2, ZnO and Fe2O3 have emerged as attractive alternatives to traditional semiconductor structures such as Si and GaAs as they are simple and inexpensive to manufacture, with research showing that application of ZnO nano-cones yield efficiencies of 8.4%, which is very attractive given the scope that exists in optimising the metal-oxide architecture. Much is still to be learned from the precise structural features of these materials and their influence on device performance. In this regard, this work largely focuses on this aspect of metal-oxide nanowires prior their application in organic solar cells.

Freshwater bodies have been long observed to become browner within the northern hemisphere. This brownification, has made drinking water production difficult, since increased organic content in freshwaters requires higher dosages of chemicals during water treatment.  Changes in land use through increased industrial forestry, decreased sulphur deposition from reduced industrial emissions, changing patterns of hydrological and meteorological parameters resulting from climate change, including recently highlighted increase in iron concentrations have been proposed to explain brownification. Drained peat bogs are man-made source of brownifying substances, capable of causing brownification in the rivers and lakes where the water ends up. This research is aimed at investigating dissolved organic matter, total organic carbon, iron, phosphorous, nitrogen and colour in bog ditches draining into the Storån River and Lake Bolmen in southern Sweden, in order to answer these research questions: (1) What are the differences in the level of water quality parameters, pH, conductivity, temperature, DOM, TOC, total phosphorous, total nitrogen, Fe and colour, between bog ditches and Storån River? And what could be the outcome of Colour absorbance comparison, between bog ditches, Storån and lake Bolmen as a single control sample? (2) Is there any association among the different water quality parameters, pH, conductivity, temperature, DOM, TOC, total phosphorous, total nitrogen, Fe and colour within the bog ditch water? Water samples from bog ditches and their corresponding Storån River locations, were used in the analysis. DOM and flow showed significant differences, after statistical test for difference. Conductivity, DOM, total nitrogen and total phosphorous exhibited significant correlations with pH.  TOC also had a correlation with DOM., while colour correlated and depended strongly on Fe, within the bog ditches. Therefore, the bog ditch has behaved to contribute some amount of the brownification, found in Southern Swedish Lakes and Rivers. This knowledge might be useful in future, for more studies and control of Swedish fresh water brownification.

Shelf seas represent an important source of iron (Fe) to the open ocean. Additionally, shelf seas are highly productive environments which contribute to atmospheric carbon dioxide drawdown and support large fisheries. The work presented in this thesis describes the seasonal cycle of Fe in the Celtic and Hebridean Shelf Seas, and determines the physico-chemical speciation of Fe supplied from oxic margins. The results from repeated field surveys of the central Celtic Sea showed a nutrient type seasonal cycling of dissolved Fe (< 0.2 µm; dFe), which is surprising in a particle rich shelf system, suggesting a balance of scavenging and remineralisation processes. Coincident drawdown of dFe and nitrate (NO3-) was observed during the phytoplankton spring bloom. During the bloom, preferential drawdown of soluble Fe (< 0.02 µm; sFe) over colloidal Fe (0.02-0.2 µm; cFe) indicated greater bioavailability of the soluble fraction. Throughout summer stratification, it is known that NO3- is drawn down to < 0.02 µM in surface waters. This study revealed that both dFe and labile particulate Fe (LpFe) were also seasonally drawn down to < 0.2 nM. Consequently, it is hypothesised that the availability of Fe seasonally co-limits primary production in this region. At depth both dFe and NO3- concentrations increased from spring to autumn, indicating that remineralisation is an important process governing the seasonal cycling of dFe in the central Celtic Sea. In spring, summer and autumn, distinctive intermediate nepheloid layers (INL) were observed emanating from the Celtic Sea shelf slope. The INLs were associated with elevated concentrations of dFe (up to 3.25 ± 0.16 nM) and particulate Fe (up to 315 ± 1.8 nM) indicating that they are a persistent conduit for the supply of Fe to the open ocean. Typically > 15% of particulate Fe was labile and 60-90% of dFe was in the colloidal fraction. Despite being < 50 km from the 200 m isobath, the concentration of dFe was < 0.1 nM in surface waters at several stations. Broadly, the concentration of nutrients in surface waters described an oligotrophic environment where co-limitation between multiple nutrients, including Fe, appears likely. Over the Hebridean shelf break, residual surface NO3- concentrations (5.27 ± 0.79 µM) and very low concentrations of dFe (0.09 ± 0.04 nM) were observed during autumn, implying seasonal Fe limitation. The dFe:NO3- ratio observed is attributed to sub-optimal vertical supply of Fe relative to NO3- from sub-surface waters. In contrast to the shelf break, surface water in coastal regions contained elevated dFe concentrations (1.73 ± 1.16 nM) alongside low NO3-. Seasonal Fe limitation is known to occur in the Irminger and Iceland Basins; therefore, the Hebridean shelf break likely represents the eastern extent of sub-Arctic Atlantic seasonal Fe limitation, thus indicating that the associated weakening of the biological carbon pump exists over a wider region of the sub-Arctic Atlantic than previously recognised. These key findings demonstrate that the availability of Fe to phytoplankton may seasonally reach limiting levels in temperate shelf waters and that oxic margins persistently supply Fe dominated by colloidal and particulate fractions to the ocean.