The dust particles generated due to mechanical wear of iron ore pellets and clusters formed in molten stainless steel alloyed with rare earth metals (REM) are considered in this study. Firstly, the influence of the characteristics of iron ore pellets, applied load on a pellet bed and partial reduction of the pellets on the size distribution of the generated dust was investigated. Secondly, REM clusters are investigated to evaluate the size distribution of the clusters. Also, an extreme value distribution (EVD) analysis has been applied for the observed REM clusters. The large sized pellets showed 10-20% higher wear rate than small sized pellets during wear in a planetary mill. Moreover, an increase of ~67% was observed in the friction and dust generation in the pellet bed as the applied load increased from 1 to 3 kg. Also, it was observed that a higher friction in the pellet bed can lead to an increased amount of airborne particles. The mechanical wear experiments of pellets reduced at 500 °C (P500) and 850 °C (P850) showed that P500 pellets exhibit ~16-35% higher wear rate than unreduced pellets. For the P850 pellets, the wear is inhibited by formation of a metallic layer at the outer surface of the pellets. The mechanism of dust generation has been explained using the obtained results. A reliable cluster size distribution of REM clusters was obtained by improving the observation method and it was used to explicate the formation and growth mechanism of REM clusters. The results show that the growth of clusters is governed by different types of collisions depending on the size of the clusters. For EVD analysis three different size parameters were considered. Moreover, using the maximum length of clusters results in a better correlation of EVD regression lines compared to other size parameters. Moreover, a comparison of predicted and observed maximum lengths of clusters showed that further work is required for the application of EVD analyses for REM clusters. / Studien fokuserar på två olika typer av mikropartiklar som är valda från olika delar av järn- och ståltillverkningsprocessen. Dessa partiklar är dels stoft som genereras på grund av mekanisk nötning av partiklar och dels klusters som bildas i flytande rostfria stål legerade med sällsynta jordartsmetaller (REM). Inledningsvis så undersöktes inverkan av tre faktorer på storleksfördelningen hos stoft som bildas vid hantering av järnoxidpellets. De undersökta faktorerna inkluderade karakteristiken hos järnoxidpellets, det applicerade trycket på pelletsbädden och den partiella reduktionen av järnoxidpellets. Därefter så utfördes tredimensionella undersökningar av REM kluster som extraherats med hjälp av elektrolytisk extraction för att bestämma storleksfördelningen hos klustren. Dessutom så utfördes en extremvärdesdistribution (EVD) studie för de studerade klustren. En planetkvarn användes för att undersöka inverkan of karakeristiken hos pellets på stoftbildningen. Resultaten visade att storleken på pellets kan påverka nötningshastigheten under dessa försöksförhållanden. Pellets som hade en större storlek (13.5&lt; Deq &lt;15.0 mm) uppvisade en 10 till 20% högre nötningshastighet i jämförelse med mindre pellets (9.5&lt; Deq &lt;12.5 mm). Baserat på analyserna av stoftet som genererades under nötningsexperimenten så konstaterades att nötningsmekanismerna för dessa pellets var abrasions- och kollisionsnötning. En pelletsbädd skapades för att möjliggöra studier av inverkan av ett applicerat tryck på stoftbildningen och friktionskrafterna i en pelletsbädd. Ett varierat tryck på mellan 1 till 3 kg applicerades på pelletsbädden. Resultaten visade att en ökning på ~67% av friktionskraften och stoftbildningen ägde rum när det applicerade trycket ökades från 1 till 3kg. Dessutom så visade resultaten att en högre friktionskraft i pelletsbädden kan resultera in en ökad mängd luftburna partiklar. Den mekaniska nötningen av pellets som reducerats vid 500 °C (P500) och 850 °C (P850) studerades också genom användande av en planetkvarn. Resultaten visade att P500 pellets uppvisade en ~ 16 till 35% högre nötningshastighet i jämförelse med oreducerade referenspellets.  Resultaten för P850 pellets visade att den mekaniska nötningen motverkades genom bildningen av ett metalliskt skikt på den yttre delen av pelletsen. Resultaten visade också att stoftet som bildats pga mekanisk nötning av reducerade pellets innehöll 3 till 6 gånger mer grova partiklar  (&gt;20µm) i jämförelse med stoft som bildats från oreducerade pellets. Slutligen så diskuterades hur dessa resultat kan relateras till industriella förhållanden med avseende på mekanismerna som är involverade i den mekaniska nötningen av pellets samt med avseende på relationen mellan hastigheten av de utgående gaserna och storlken och morfologin hos stoftpartiklarna. Klusters innehållande REM-oxider som extraherats från en 253MA rostfri stålsort undersöktes med användande av en tredimensionell teknik. En trovärdig storleksfördelning av klusters (CSD) erhölls genom att förbättra undersökningsmetoden och denna användes för att studera bildningen och tillväxten av REM oxider. Dessutom så användes cirkularitetsfaktorn hos klusters för att dela in klustren i två olika grupper, vilka bildas och tillväxer enligt olika mekanismer. Resultaten visade också att tillväxten av klusters gynnas av olika typer av kollisioner som beror av av storleken på klusters. För REM-klusters så drogs slutsatsen att turbulenta kollisioner är den huvudsakliga mekanismen som påverkar tillväxten. Avhandlingen behandlar även problemet om hur det är möjligt att hantera synfält där det inte förekommer kluster vid en extremvärdesdistribution (EVD) analys. Tre olika parametrar undersöktes i EVD analysen. Resultaten visar att om den maximala längden på kluster (LC) används i analysen så erhålls den bästa korrelationen gällande regressionslinjen för en EVD analys. Specifikt så var R2 värdet upp till 0.9876 i jämförelse med de andra storleksparametrarna som har värden i intervallet 0.9656 – 0.9774. Slutligen så visar resultaten från en jämförelse mellan beräknade och observerade maximala klusterlängder att EVD analyser för studier av REM kluster behöver undersökas ytterligare i framtiden. / <p>QC 20161128</p>

This dissertation undertakes an analysis of the spatial persistence of population in South Africa over the period 1911 to 2011. A comprehensive review is given of the history and development of geographical economics in order to understand the dynamics of the forces of agglomeration. In addition the history of the development of South Africa is discussed and special focus is directed to the geographical, economic and political factors that gave rise to the unequal distribution of population and wealth in the country. In the empirical analysis Zipf’s law was applied and it was found that South Africa’s population was more evenly spread in 1911. With the application of the law to the 2011 data the Pareto exponent of the OLS log-linear regression indicated that urban agglomeration was more persistent. Although this might indicate that apartheid did not influence agglomeration in South Africa it is argued that the nature of the agglomeration was in fact influenced by restrictive measures placed on the urbanisation of the population and industrial decentralisation policies. It is indicated that the apartheid policy altered the equilibrium spatial distribution of population and wealth which lead to a smaller than optimal primate and second largest magisterial districts, too many secondary cities of similar size, and also too many small and uneconomical rural settlements. / MCom (Economics), North-West University, Potchefstroom Campus, 2015

This dissertation undertakes an analysis of the spatial persistence of population in South Africa over the period 1911 to 2011. A comprehensive review is given of the history and development of geographical economics in order to understand the dynamics of the forces of agglomeration. In addition the history of the development of South Africa is discussed and special focus is directed to the geographical, economic and political factors that gave rise to the unequal distribution of population and wealth in the country. In the empirical analysis Zipf’s law was applied and it was found that South Africa’s population was more evenly spread in 1911. With the application of the law to the 2011 data the Pareto exponent of the OLS log-linear regression indicated that urban agglomeration was more persistent. Although this might indicate that apartheid did not influence agglomeration in South Africa it is argued that the nature of the agglomeration was in fact influenced by restrictive measures placed on the urbanisation of the population and industrial decentralisation policies. It is indicated that the apartheid policy altered the equilibrium spatial distribution of population and wealth which lead to a smaller than optimal primate and second largest magisterial districts, too many secondary cities of similar size, and also too many small and uneconomical rural settlements. / MCom (Economics), North-West University, Potchefstroom Campus, 2015

A new retrieval algorithm has been developed based on the Optimal Estimation (OE) approach, which retrieves lognormal aerosol size distribution parameters from multiwavelength aerosol extinction data, as measured by the Stratospheric Aerosol and Gas Experiment (SAGE) II in the lower stratosphere. Retrieving these aerosol properties becomes increasingly more difficult under aerosol background conditions, when tiny particles (« 0.1 µm) prevail, to which the experiment is nearly or entirely insensitive. A successful retrieval algorithm must then be able (a) to fill the 'blind spot' with suitable information about the practically invisible particles, and (b) to identify 'the best' of many possible solutions. The OE approach differs from other previously used aerosol retrieval techniques by taking a statistical approach to the multiple solution problem, in which the entire range of possible solutions are considered (including the smallest particles) and characterized by probability density functions. The three main parts of this thesis are (1) the development of the new OE retrieval algorithm, (2) the validation of this algorithm on the basis of synthetic extinction data, and (3) application of the new algorithm to SAGE II measurements of stratospheric background aerosol. The validation results indicate that the new method is able to retrieve the particle size of typical background aerosols reasonably well, and that the retrieved uncertainties are a good estimate of the true errors. The derived surface area densities (A), and volume densities (V ) tend to be closer to the correct solutions than the directly retrieved number density (N), median radius (R), and lognormal distribution width (S). Aerosol properties as retrieved from SAGE II measurements (recorded in 1999) are observed to be close to correlative in situ data. In many cases the OE and in situ data agree within the (OE and/or the in situ ) uncertainties. The retrieved error estimates are of the order of 69% (σN), 33% (σR), 14% (σS), 23% (σA), 12% (σV), and 13% (σReff ). The OE number densities are generally larger, and the OE median particle sizes are generally smaller than those N and R retrieved by Bingen et al. (2004a), who suggest that their results underestimate (N) or overestimate (R) correlative in situ data due to the 'small particle problem'. The OE surface area estimates are generally closer to correlative in situ profiles (courtesy of T. Deshler, University of Wyoming), and larger than Principal Component Analysis (PCA) retrieval solutions of A (courtesy of L. W. Thomason, NASA LaRC) that have been observed to underestimate correlative in situ data by 40-50%. These observations suggest that the new OE retrieval algorithm is a successful approach to the aerosol retrieval problem, which is able to add to the current knowledge by improving current estimates of aerosol properties in the lower stratosphere under low aerosol loading conditions.

Student Number : 0318623R - PhD thesis - School of Geosciences - Faculty of Science / Physical and chemical properties of atmospheric particles are fundamental but not necessarily easily accessible parameters. Uncertainties in these parameters are responsible for some uncertainties associated with radiative impacts of aerosol particles in global climate models. The uncertainties pertain to limitations of sampling and measurement devices, difficulties in modelling aerosols (source strengths, spatial and temporal variability) and in understanding microphysical and optical properties of aerosol particles. Physical and chemical properties can be obtained at single-particle level by microscopy analyses of individual particles. Using refined analytical and interpretative techniques to derive some of these fundamental properties, aerosol particles collected in various field campaigns and laboratory experiments were investigated using two high resolution microscopes. The particles were collected during the LBA-EUSTACH, Large-Scale Biosphere-Atmosphere Experiment part of European Studies on Trace Gases and Atmospheric Chemistry; SMOCC campaign, Smoke Aerosols, Clouds, Rainfall and Climate; CTBH II, Cape Town Brown Haze II campaign; and a controlled combustion experiment. Microscopy techniques were compared and complemented with conventional techniques to characterise particle sizes, shapes, chemical compositions and mixing states. Particle size distributions were compared between geometric equivalent sizes measured from microscopes and aerodynamic equivalent diameters, while taking into account particle densities. Large differences were found between the particle sizing techniques. Microscopy sizes (3D) were systematically lower than expected, and depended on the relative humidity during particle sampling. Differences were attributed to loss of mass, presumably water adsorbed on particles. Losses were high and could not be accounted for by known humidity growth factors suggesting losses of other volatile compounds adsorbed on particles as well. Findings suggest that there are inherent problems in defining particle sizes with different sizing techniques, despite accounting for humidity growth of particles and particle density. For collected particles, there are mass losses on individual particles, as opposed to particle losses to walls during sampling. These losses will inevitably bias observed mass distributions derived from collected particles and hence their number-size distributions. Relatively young aggregated soot particles from wood combustion were investigated for particle morphology (fractality, specific mass) and dynamic properties. Based on a procedure that has been validated on modelled aggregates, several important parameters to characterise geometry and drag-to-mass relationship of aggregates were derived. Three techniques were used to derive fractal dimension of soot aggregates. Averaged fractal dimension was found to be Df = 1.82 ± 0.08. Dynamic shape factors of soot particles were 1.7 to 2.5 and increasing with mass of aggregates. In the regime 0.2 < Kn < 0.7 (Knudsen number, Kn = 2#21;/dmob) the mobility diameter dmob was observed to be proportional to the radius of gyration with a ratio dmob/2Rg = 0.81 ± 0.07. Specific surface area of aggregates was determined to be 70 ± 10 m2g−1 based on SEM image analysis. These parameters can be used directly in modelling microphysical behaviour of freshly formed soot particles from biomass combustion with fractal dimension of Df ≈ 1.80. Chemical composition and size distributions of particles were investigated on filter samples collected during intense winter brown haze episodes in Cape Town. The sampling technique offered the capability to characterise highly heterogeneous aerosols over a polluted urban environment. Based on morphology and elemental composition, particles were categorised into seven particle groups of: aggregated soot particles, mineral dust, sulphates (SO2− 4 ), sea-salt, tar balls/fly ash, rod-shaped particles associated with soot agglomerates and those that could not be attributed to any of these groups were labelled as ‘others’. Apportionments of chemical species were highly variable both spatially and temporally. These variations indicate lack of lateral mixing and dependence of particle chemical compositions on localised and point sources within the Cape Town area. Sulphate and aggregated soot particles were externally mixed with fractional number concentrations of 0− 82% and 11%−46%, respectively. Aerosol complex refractive indices were derived from the chemical apportionment and particle abundance determined in microscopy analyses. The refractive indices were combined with in-situ measurements of number-size distribution to determine optical properties of aerosols. Single scattering albedo, !0, varied from 0.61 to 0.94 with a mean value of 0.72±0.08. The !0 is much lower than is generally reported in literature, and this was attributed to high concentrations of highly absorbing anthropogenic soot observed in SEM analysis. The mean extinction coefficient #27;ep was 194 ± 195 Mm−1. #27;ep and !0 clearly demonstrated and explained quantitatively the visibility reduction due to particles in the Cape Town atmosphere, reduction observed as the brown haze phenomenon. In all the three case studies, microscopy single particle analysis played a critical role in advancing knowledge of understanding properties of aerosol particles in the atmosphere.

Aerosol particles, especially in the high Arctic are still not very well represented in climate models. Particle size and number concentrations are strongly under-predicted and temporal variations of aerosol composition and size are still not very well understood, mainly due to the sparsity of observations. The main objective of this thesis is the characterization of the high Arctic summer aerosol by means of electron microscopy in order to extend the existing data set from previous expeditions by size resolved data on aerosol number, morphology and chemical composition and to gain a better understanding of the evolution of the aerosol in the atmosphere. Ambient aerosol was collected over the pack ice during the Arctic Summer Cloud and Ocean (ASCOS) campaign to the high Arctic in summer 2008. Aerosol particles were evaluated with scanning electron microscopy and subsequent digital image processing to assess particle size and morphology. More than 3900 aerosol particles from 9 sampling events were imaged with scanning electron microscopy and merged into groups of similar morphology which contributed to different degrees to the total aerosol: single particles (82%), gel particles (11%) and halo particles (7%). Single particles were observed over the whole size range with a maximum at 64 nm in diameter, gel particles appeared &gt; 45 nm with a maximum in number at 174 nm, halo particles appeared &gt; 75 nm with a maximum in number at 161 nm. The majority of particles showed the morphology of marine gels, no sea salt or otherwise crystalline particles were observed. Transmission electron microscopy enabled more subtle insights into particle morphology and allowed further subdivision of gel particles into aggregates, aggregates with film and mucus-like particles. Energy dispersive X-ray spectroscopy of individual particles revealed a gradual transition in the content of Na+/K+ and Ca2+/Mg2+ between particle morphologies. Single particles and aggregate particles preferentially contained Na+/K+ whereas aggregate with film particles and mucus-like particles mainly contained Ca2+/Mg2+ suggesting a connection between particle morphology and ion content. Back-trajectory analysis was used to identify aerosol sources and to understand the evolution of the aerosol as a function of the synoptic weather situation. Particle numbers, size and morphology changed with the days the air mass spent over the pack-ice. A morphological descriptor applied to gel particles showed a clear trend suggesting that the contour of the particles becomes sharper and more distinct with increased time spent over the pack-ice. For a very long time over the pack-ice, however, we observed a morphology comparable to freshly emitted particles suggesting aerosol sources over the inner pack-ice. Size resolved aerosol chemical composition measurements were utilized to investigate the inorganic composition of laboratory generated nascent sea spray aerosol particles and ambient aerosol samples collected during ASCOS. A significant enrichment of Ca2+ was observed in submicrometer particles in either case with a tendency for increasing Ca2+ enrichment with decreasing particle size. This has strong implications for the alkalinity of sea spray aerosol particles with consequences for the sulfur chemistry in the marine boundary layer, the hygroscopicity and thus the potential of sea spray aerosol particles to act as cloud condensation nuclei. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.</p>

Cascade impactors, routinely used for in vitro particle size characterization of pharmaceutical aerosols, are calibrated using dilute, charge-neutralized, monodisperse aerosols. But pharmaceutical aerosols are known to generate concentrated, inherently charged, polydisperse aerosol clouds. A computational model of the Andersen Cascade Impactor (ACI) suggested that the presence of charge on aerosol particles may influence their deposition within the ACI, but experimental validation of the model is warranted. This dissertation investigates the influence of electrostatic charge upon the deposition behavior of aerosols within cascade impactors, to address the impact of charge on particle size characterization. The influence of applied charge upon the deposition pattern and aerodynamic particle size distribution (APSD) of commercially available pressurized metered dose inhalers (pMDIs) within the Electrical Low Pressure Impactor (ELPI) was examined. Electrostatic properties were modified using an external voltage source in conjunction with the ELPI corona charger and observed to be dependent on the formulation and device packaging. Induced artificial charge on the aerosol particles influenced the deposition pattern within the impactor, but did not result in a significant change in the apparent APSD. An experimental apparatus capable of producing charge neutralized and charged aerosol, with targeted deposition on the CFD predicted ‘charge sensitive’ ACI stages, was developed. In vitro results were observed to be in partial agreement with the CFD predictions. While charge influenced the deposition pattern in the ACI with increased deposition observed in the charger and on the upper stages of the ACI, it did not influence the apparent APSD of the aerosol. Electrostatic charge effects on deposition behavior within cascade impactors were delineated with respect to space charge and image charge effects by investigating the influence of impactor grounding, particle size, stage coating and loading. While the deposition pattern within the ACI was influenced by charge, only stage coating and stage loading resulted in a small, significant difference in the apparent APSD, which may not be practically relevant due to the variability associated with in vitro aerosol testing. Similar trends were observed in the deposition behavior of charge neutralized and charged aerosol within an abbreviated ACI system compared to the full resolution ACI.

Texture of igneous rocks, which includes size, shape and spatial distribution of grains, represents the final record of kinetic and mechanical processes operating during ascent and final emplacement of a magma. However, traditional geochemical approaches cannot assess and verify the physical processes of magma solidification, in particular, crystal nucleation and growth, textural coarsening, or mechanical crystal-melt interactions. In this work, I apply stereological methods to quantitatively characterize the textures and to interpret the crystallization history of granitic rocks in the Western Krušné hory/Erzgebirge and Vogtland. The Western Krušné hory/Erzgebirge granites consist of three suites: biotite granites (Kirchberg), muscovite-biotite microgranites (Walfischkopf), and topaz-zinnwaldite alkali- feldspar granites (Eibenstock), which consist of eight intrusive units and two aplite dyke sets. The entire granite sequence exhibits an extreme and nearly continuous differentiation range, but in detail the evolutionary trends of each suite are independent, and individual intrusive units are also clearly compositionally separated. The granites consist of 29-43 vol.% quartz, 20-30 vol. % plagioclase, 22-31 vol. % K-feldspar, 2-9 vol. % biotite, <2 vol. % muscovite, and minor topaz and apatite. All...

In the presented work we study Al and Sn on a Si(100)2$\times$1 surface by means of STM. Peculiarities of displaying and morphology of metallic structures are investigated. Utilizing the STM to investigate Al and Sn, we obtain the growth characteristics for various coverage and temperatures at deposition. It is shown, that island size distribution is scalable for both metals and has a qualitatively different character. In order to interpret the growth characteristics and obtain unknown microscopic parameters, a new software tool for kinetic Monte Carlo (kMC) simulations of aluminum was conceived.

Buildings consume around half of the UK's total energy consumption and are responsible for almost 50% of UK's total carbon dioxide (CO2) emissions. Use of high thermal resistance insulation in buildings is critical to save the substantial amounts of space heating energy lost through building fabric. Conventional building insulation materials have higher thermal conductivity values ranging from 40 mWm-1K-1 (Glass fibre) - 26 mWm-1K-1 (Polyurethane foam) and require larger thicknesses to achieve stringent building regulation requirements which may not be feasible due to techno-economic constraints. Vacuum Insulation Panel (VIP) is a relatively new insulation for building applications that offers 5-8 times higher thermal resistance and can achieve significant space savings in buildings. VIPs are produced as a rigid panel comprising inner core board laminated in an outer high barrier envelope under evacuated conditions (< 5mbar). However, the main challenge for large scale acceptance of VIPs in building applications is their higher cost. VIPs have been shown to have an approximately 10 times longer payback compared to conventional EPS insulation due to their high initial cost. Expensive materials currently being used for VIP manufacturing such as fumed silica contribute to high cost of VIPs and it is critical to identify alternative low cost materials for VIP components to overcome the challenge of high cost. The aim of this thesis was to develop an alternative low cost material and investigate its suitability for use as VIP core. Expanded perlite, a low cost material was identified as a replacement of expensive fumed silica in a VIP core. Composite samples containing expanded perlite, fumed silica, silicon carbide (SiC) and polyester fibres were developed by dry mixing of the constituents in different mass ratios and their different properties were experimentally measured to identify optimum composition of composite. Gaseous thermal conductivity at different pressures was calculated from the pore size data obtained using Mercury Intrusion Porosimetry (MIP), gas adsorption and electron microscopy. Radiative conductivity of composite samples was measured using Fourier Transform Infrared (FTIR) to ascertain the opacifying effect of expanded perlite and opacifier (SiC). Centre of panel thermal conductivity of core boards of size 100mm x 100mm made of composite material at atmospheric pressure was measured by using a small guarded hot plate device. Average pore diameter values of expanded perlite decreased with the partial filling of fumed silica aggregates and was found to be in the range of 150-300 nm yielding lower gaseous conductivity values of 1.2-2.1 mWm-1K-1 at 100mbar and became negligible upon further decreasing pressures below 10 mbar. Core boards made of optimised composite containing 30% expanded perlite and 50% fumed silica along with SiC and polyester fibres was found to achieve centre of panel thermal conductivity of 28 mWm-1K-1 at atmospheric pressure and the average radiative conductivity of 0.67 mWm-1K-1 at 300K with its gaseous thermal conductivity at 1 mbar being 0.016 mWm-1K-1. According to the results of the thesis VIP prototypes consisting of core made with optimised composite consisting (50 mass% of fumed silica, 30 mass% of expanded perlite along with 8 mass% of fibre and 12 mass% of SiC) yielded centre of panel thermal conductivity of 7.4-7.6 mWm-1K-1 at pressure of 0.53-0.64 mbar. Opacifying properties of expanded perlite were observed and quantified. Expanded perlite reduced the radiative conductivity of the composite requiring smaller quantities of high density opacifiers such as SiC. For sample containing no expanded perlite, average radiative conductivity was calculated to be 1.37 mWm-1K-1 and radiative conductivity values decreased to 1.12 mWm-1K-1, 0.67 mWm-1K-1, 0.63 mWm-1K-1 and 0.50 mWm-1K-1 with mass ratio of expanded perlite 20%, 30%, 40% and 60% respectively. It was concluded that the solid conductivity of prototypes VIPs was 1.8-2 times higher compared to those of commercially available VIPs and is the main reason for higher centre of panel thermal conductivity.