Ferrochrome (FeCr) is a crude alloy containing chromium (Cr) and iron (Fe). FeCr is mainly used for the production of stainless steel, which is an important modern-day alloy. FeCr is produced from chromite ore through various smelting methods. In this study, the focus was on the pelletised chromite pre-reduction process, which is also referred to as the solid state reduction of chromite. In this process, fine chromite ore, a clay binder and a carbon reductant are dry milled, agglomerated (pelletised) and pre-reduced (solid state reduction) in a rotary kiln. The pre-reduced pellets are then charged hot, immediately after exiting the rotary kiln, into a closed submerged arc furnace (SAF). This production process option has the lowest specific energy consumption (SEC), i.e. MWh/ton FeCr produced, of all the FeCr production processes that are commercially applied. Other advantages associated with the application of the pelletised chromite pre-reduction process are that it eliminates the use of chromite fines, has a high Cr recovery, and produces low sulphur- (S) and silicon (Si)-containing FeCr. The main disadvantage of the pelletised chromite pre-reduction process is that it requires extensive metallurgical control due to the variances in the levels of pre-reduction achieved and carbon content of the pre-reduced pelletised furnace feed material. This implies that the metallurgical carbon balance has to be changed regularly to prevent the process from becoming carbon deficient (also referred to as ‘under coke’) or over carbon (also referred to as ‘over coke’). The analytical technique currently applied to determine the level of chromite pre-reduction is time consuming, making it difficult and expensive to deal with large numbers of samples. In an attempt to develop a technique that would be faster to determine the level of chromite pre-reduction, a new analytical method using a combination of scanning electron microscopy (SEM), image processing and computational techniques was investigated in this study. Metallurgical grade chromite (<1 mm), anthracite breeze (<1 mm), and fine FeCr (<1 mm) that were used to prepare pellets in the laboratory, as well as industrially produced pre-reduced pellets that had already been milled in preparation for the determination of the pre-reduction level with wet chemical analysis were received from a large South African FeCr producer. These laboratory prepared pellets and the industrially produced pellet mixtures were considered in this investigation. Samples were moulded in resin and polished in order to obtain SEM micrographs of the polished cross sections. Elements with higher molecular weights are indicated by lighter greyscale, while elements with lower molecular weights are indicated by darker greyscale in SEM micrographs. This basic principle was applied in the development of the new analytical technique to determine the level of chromite pre-reduction, with the hypothesis that the pixel count of white pixels (representing metallised particles), divided by the combined pixel count of white (representing metallised particles) and grey (representing chromite particles) pixels would be directly related to the level of chromite pre-reduction determined with the current wet chemical method. This hypothesis can be mathematically expressed as: The newly-developed analytical method was validated by correlating the white pixel% calculated with the chromite pre-reduction levels (%) determined with wet chemical analysis of laboratory prepared and industrially produced pellet mixtures, which had R2 values of 0.998 and 0.919, respectively. This suggests that the method can be used to determine chromite pre-reduction accurately. / MSc (Engineering Sciences in Chemical Engineering), North-West University, Potchefstroom Campus, 2015

Ternary indium aluminum nitride (InXAl1-XN) semiconductor is an attractive material with a wide-range bandgap energy varied from ultraviolet (Eg(AlN): 6.2 eV) to near infrared (Eg(InN): 0.7 eV). With tuning composition, it can be widely used to many optoelectronic device applications. In this thesis, I have studied InXAl1-XN film deposited on Si (111) substrate using natural and isotopically enriched nitrogen as reactive gas by reactive magnetron sputter epitaxy (MSE). Four series of experiments were performed, which are I. InAlN presputtering, II. InAlN sputter deposition, III. InAlN direct deposition, and IV. InAlN direct deposition using isotopically enriched nitrogen. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). The θ-2θ XRD scan confirms that the designed composition x = 0.17 of InXAl1-XN film was obtained. TEM images shows that an amorphous interlayer with a thickness ranging from 1.2 nm to 1.5 nm was formed between Si substrate and InXAl1-XN film. However, high-resolution TEM shows that the interlayer actually contains partial crystalline structures. EDX line profile indicates that the chemical composition of the amorphous interlayer is silicon nitride (SiNX). By comparing d-spacing measurement of partial crystalline structures with EDX line profile, it reveals that partial SiNX crystal is formed in the interlayer. Nonetheless, the samples (IAD01, IAD02, IAD03, IAD04), grown without presputtering procedure, contain both crystalline SiNX and InXAl1-XN embedded in the amorphous interlayer. It means that SiNX and InXAl1-XN film can be directly grown on the substrate in the beginning of deposition. Moreover, the samples (IAD01, IAD03), quenched directly after deposition, have less crystalline structures in the interlayer then the samples (IAD02, IAD04), maintained at 800℃ for 20 min.

Transmission electron microscopy (TEM) is a powerful tool for studying solidstate crystalline systems. With the advances in aberration correction, monochromation, and in situ capabilities, these microscopes are now more useful for addressing fundamental materials chemistry problems than ever before. This dissertation will illustrate the ways in which I have been using high-resolution imaging and in situ heating in the TEM during my Ph.D. research to investigate unique solid state chemistry questions. This dissertation will focus on four unique crystal systems: thermoelectric skutterudite crystals, vapor-liquid-solid (VLS) grown nanowires, and hafnium dioxide nanorods. Although these systems are very different from one another, high resolution and/or in situ heating in TEM is an integral part of each study. Through these techniques, we gain insight and knowledge of these systems that may have gone unknown through different analysis techniques. The experiments I will describe in some cases provide surprising and unexpected results that arise from the nanoscale nature of the materials and would be difficult to observe through bulk analytical methods. The work presented here helps to demonstrate the strength and versatility of TEM to address solid state chemistry questions.

Introduction: Though xenogeneic acellular scaffolds are frequently used for surgical reconstruction, knowledge of their mechanical properties is lacking. This study compared the mechanical, histological and ultrastructural properties of various native and acellular specimens. Materials and methods: Porcine esophagi, ureters and skin were tested mechanically in a native or acellular condition, focusing on the elastic modulus, ultimate tensile stress and maximum strain. The testing protocol for soft tissues was standardized, including the adaption of the tissue’s water content and partial plastination to minimize material slippage as well as templates for normed sample dimensions and precise cross-section measurements. The native and acellular tissues were compared at the microscopic and ultrastructural level with a focus on type I collagens. Results: Increased elastic modulus and ultimate tensile stress values were quantified in acellular esophagi and ureters compared to the native condition. In contrast, these values were strongly decreased in the skin after acellularization. Acellularization-related decreases in maximum strain were found in all tissues. Type I collagens were well-preserved in these samples; however, clotting and a loss of cross-linking type I collagens was observed ultrastructurally. Elastins and fibronectins were preserved in the esophagi and ureters. A loss of the epidermal layer and decreased fibronectin content was present in the skin. Discussion: Acellularization induces changes in the tensile properties of soft tissues. Some of these changes appear to be organ specific. Loss of cross-linking type I collagen may indicate increased mechanical strength due to decreasing transverse forces acting upon the scaffolds, whereas fibronectin loss may be related to decreased load-bearing capacity. Potentially, the alterations in tissue mechanics are linked to organ function and to the interplay of cells and the extracellular matrix, which is different in hollow organs when compared to skin.

Ultrasound contrast agents (CAs) are typically used in clinic for perfusion studies (blood flow through a specific region) and border delineating (differentiate borders between tissue structures) during cardiac imaging. The CAs used during ultrasound imaging usually consist of gas filled microbubbles (MBs) (diameter 1-5 μm) that are injected intravenously into the circulatory system. This thesis partially involves a novel polymer-shelled ultrasound CA that consists of air filled MBs stabilized by a polyvinyl alcohol (PVA) shell. These MBs could be coupled with superparamagnetic iron oxide nanoparticles (SPIONs) in order to serve as a combined CA for ultrasound and magnetic resonance imaging. The first three papers (Paper A-C) in this thesis investigate the structural characteristic and the elimination process of the CA. In Paper A, two types (PVA Type A and PVA Type B) of the novel CA were analyzed using transmission electron microscopy (TEM) images of thin sectioned MBs. The images demonstrated that the SPIONs were either attached to the PVA shell surface (PVA Type A) or embedded in the shell (PVA Type B). The average shell thickness of the MBs was determined in Paper B by introducing a model that calculated the shell thickness from TEM images of cross-sectioned MBs. The shell thickness of PVA Type A was determined to 651 nm, whereas the shell thickness of PVA Type B was calculated to 637 nm. In Paper C, a prolonged blood elimination time was obtained for PVA-shelled MBs compared to the lipid-shelled CA SonoVue used in clinic. In addition, TEM analyzed tissue sections showed that the PVA-shelled MBs were recognized by the macrophage system. However, structurally intact MBs were still found in the circulation 24 h post injection. These studies illustrate that the PVA-shelled MBs are stable and offer large chemical variability, which make them suitable as CA for multimodal imaging. This thesis also involves studies (Paper D-E) of the molecular chaperones (Hsp21 and DNAJB6). The small heat shock protein Hsp21 effectively protects other proteins from unfolding and aggregation during stress. This chaperone ability requires oligomerization of the protein. In Paper D, cryo-electron microscopy together with complementary structural methods, obtained a structure model which showed that the Hsp21 dodecamer (12-mer) is kept together by paired C-terminal interactions.The human protein DNAJB6 functions as a very efficient suppressor of polyglutamine (polyQ) and amyloid-β42 (Aβ42) aggregation. Aggregation of these peptides are associated with development of Huntington’s (polyQ) and Alzheimer’s (Aβ42) disease. In Paper E, a reconstructed map of this highly dynamic protein is presented, showing an oligomer with two-fold symmetry, indicating that the oligomers are assembled by two subunits. / <p>QC 20160527</p>

Thesis (MMed (Biomedical Sciences. Anatomy and Histology))--University of Stellenbosch, 1993. / Glial fibrillary acidic protein (GFAP) is found in varying amounts in the cytoplasm of most normal and neoplastic cells of astroglial origin. Though not glial specific, immunoelectron microscopy has shown that vimentin and GFAP are coexpressed as monomers of glial intermediate filaments. These structures display irreversible assembly and a slow metabolic turnover. Although currently applied as astroglial markers, these intermediate filament proteins may reflect the functional and developmental differentiation status of the cells in which they are expressed. Some authors have tried to apply these aspects as diagnostic parameters for grades of malignancy and anaplasia whilst other workers have indicated variable concentrations of GFAP in different astroglial cell types and entities. Different processing protocols, including the use of epoxy and acrylic resins, omission of osmium tetroxide and variations in concentration and incubation time of primary fixatives, were evaluated to find a compromise between antigen availability and acceptable ultrastructure. Thin sections were labelled on grid for GFAP (Dako A561) and vimentin (Dako M725) by means of the indirect immunogold method. For semi- quantification of relative antigen concentrations, a novel method was devised to calculate the labelling density, percentage heterogeneity of the particle distribution and the surface area investigated. This allowed expression of labelling results as a three figure unit. Standardized post-embedding immunoelectron microscopy was performed on 11 normal and neoplastic human tissue specimens. The tissue was exposed to conventional immersion fixation in glutaraldehyde and osmium tetroxide prior to modified embedding in LR White resin. The validity of these results was verified by correlation with conventional histopathological, immunohistochemical and clinical data obtained for each specimen. The presence of epoxy resin in thin sections was shown to reduce antigen availability to such an extent that very low to negative labelling was encountered. Acrylic LR White resin allowed more acceptable immunodetection, but at the cost of inferior ultrastructure and greater instability of thin sections in the electron beam. This masked the effects of glutaraldehyde fixation on the density of the tissuefixative matrix which included destruction of the vimentin and some GFAP associated epitopes. Although osmium tetroxide was required for acceptable ultrastructure, it reduced the labelling sensitivity by 20% and was responsible for premature curing of acrylic resin during impregnation of tissue. Despite superior resolution gained by electron microscopy and the advantage of semi-quantification of labeling results, the labelling sensitivity of this technique is lesser than that of light microscopical immunohistochemistry. Immunoelectron microscopy confirmed the association between GFAP and glial intermediate filaments in almost all the glial tumours studied, correlating well with GFAP expression in matching specimens demonstrated at light microscopical level. In the absence of intermediate filaments, no positivity for GFAP or vimentin was found in oligodendroglial components of mixed tumours. GFAP positivity in astrocytomas was demonstrated by between 17 and 126 particles / µm2, whilst lower figures were obtained for the glioblastoma (PD = 8) and some of the mixed gliomas (Pd = 6). Rosenthal fibres showed both peripheral and central positive labelling for GFAP, thus providing more evidence for their hypothetical degenerative, astroglial nature. The meningioma studied, was GFAP negative, but produced low density positivity for vimentin. Coexpression of GFAP and vimentin was demonstrated in an astroblastoma and degenerative infant brain tissue, thus supporting the presence of both these proteins development of glial structures. Although sites of likely glial intermediate filament synthesis were found, the antigen availability for vimentin was too low to allow a reliable assessment of specific vimentin localization and determination of the GFAP : vimentin ratio in individual intermediate filaments and/or astroglial fibres. Variations in particle densities (PD) which demonstrated GFAP in the various astroglial entities studied, were considered to be a result of variable technical and tissue processing factors rather than truly significant differences in expression of GFAP in individual intermediate filaments. This lead to the conclusion that the GFAP concentration / glial intermediate filament area is likely to be constant for mature glial intermediate filaments and therefore cannot be used to distinguish between different astroglial cells or entities. Whether each cell has a different number of glial intermediate filaments, has not been established satisfactorily. Following complementary conventional immunohistochemistry and careful orientation of biopsy material, the procedure can be applied to suitable specimens for the electron microscopical localization of high concentrations of aldehyde resistant, cytoplasmic antigens.

No description available.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

By using cryo-electron microscopy, we analyzed the morphology and structure of long double-stranded DNA chains condensed upon addition of varying amounts of the tetravalent polycation spermine (polyamine). Experiments have been performed i) with chains diluted in the bulk and ii) with individual chains confined in a virus capsid.Bulk experiments have been done with lambda DNA (48.5 kbp) at low concentration (0.03 mM Ph) and in low salt conditions (10 mM Tris HCl, 1 mM EDTA, pH 7.6). We explored a wide range of spermine concentration, from the onset of precipitation (0.05 mM sp) up to above the resolubilization limit (400 mM sp). Sixteen min after mixing spermine and DNA, samples have been trapped in thin films and vitrified in liquid ethane to keep ionic conditions unchanged, and imaged at low temperature with low doses of electrons (cryoTEM). DNA chains mostly form large aggregates of toroids in which DNA chains are hexagonally packed with interhelical spacings of 2.93, 2.88, and 2.95 nm at 0.05, 1 and 100 mM spermine, respectively, in agreement with previous X-ray data. At higher spermine concentration (200 mM), hexagonal toroids are replaced by cholesteric bundles with a larger interhelical spacing (3.32 nm). We conclude that the shape and the structure of the liquid crystalline sp-DNA condensates are linked to the DNA interhelix spacing and determined by the ionic conditions i.e. by the cohesive energy between DNA strands. Outside of the precipitation domain (400 mM spermine), DNA chains form a soluble network of thin fibers (4-6 nm in diameter) that let us reconsider the state of these DNA chains in excess of spermine. We also designed experiments to visualize condensates formed 6-60 sec after mixing Lambda DNA with 0.05 mM spermine, under identical buffer conditions. Among multiple original shapes (not found after 16 min), the presence of stretched and helical elongated fibers seen only 9sec after addition of spermine let us propose that DNA chains are immediately stretched upon addition of spermine, relax into helical structures and finally form small toroids (containing in some cases less than one Lambda chain) that further grow and aggregate. We also analyzed the dimensions and structural details of the complete collection of toroids, and reveal the existence of geometric constraints that remain to be clarified. Since it was only exceptionally possible to prevent the aggregation of DNA in dilute solution, we used another approach to observe the collapse of single DNA chains. We handled a population of T5 viruses containing a fraction of their initial genome (12-54 kbp long). The Na-DNA chain, initially confined in the small volume of the capsid (80nm in diameter) is collapsed by the addition of spermine. Compared to the first set of experiments, we explored a higher DNA concentration range (0.45 mM Phosphates in the whole sample) and the spermine concentration was varied from 0.05 to 0.5 mM (which corresponds to much lower +/- charge ratios). Experiments are thus performed close to the precipitation line, in the coexistence region, between the region where all chains are in a coil conformation, and the region where all chains are collapsed into toroids. We describe the existence of intermediate states between the coil and the toroidal globule that were not reported yet. In these "hairy toroids", part of the DNA chain is condensed in the toroid and the other part stays uncondensed outside of it. The interhelical spacing was also measured; it is larger in these partly-condensed toroids than in the fully organized toroids formed at higher spermine concentration.These two series of experiments show the interest of cryoEM to analyze the structural polymorphism and local structure of spermine-DNA aggregates. We also demonstrated how the confinement interferes with DNA condensation and the interest to investigate such effects that are important in the biological context.

No description available.