Uranium-10wt% zirconium (U-10Zr) alloy nuclear fuels have been used for decades and new variations are under consideration ranging from U-5Zr to U-50Zr. As a precursor to understanding the fission gas behavior in U-Zr alloys using ion implantation, a basic study on the U-Zr metallurgy was completed using EPMA, DSC, XRD, Optical microscopy, and TEM with a focus on solid state phase transformations in alloys containing 2, 5, 10, 20, 30, and 50wt% zirconium. Alloys were cast by crucible melting using high temperature furnace under argon atmosphere in yttrium oxide crucibles and various thermal profiles were used to study phase transformations in these alloys. Using TEM, XRD, and DSC data, it was ascertained that athermal-ω, along with martensitic α1, formed in all alloys quenched from γ phase. XRD could detect the presence of athermal-ω only in U-20, 30 and 50wt%Zr alloys. BSE images for as-cast alloys of 2, 5, 10, 20, and 30wt%Zr had lamellar microstructure with lamellae rich in zirconium. All alloy samples clearly showed a heating transformation pertaining to δ → γ in DSC data while XRD could only confirm the presence of δ phase in U-20, 30, and 50wt%Zr alloys. An explanation is offered for the absence of δ phase peaks in uranium-rich alloys based on its formation mechanism. Alloy samples of U-2, 5, and 10wt%Zr were step-cooled from γ phase by annealing in the (α + δ) phase field before cooling to room temperature revealed broad peaks for δ phase indicating incomplete collapse of {111}γ planes. Both as cast and γ- quenched alloys were annealed at 600degreeC, in the (α + δ) phase field for 1, 3, 7, and 30 days. Microstructures of the samples in both cases contained uranium-rich matrix and zirconium-rich precipitates and WDS analyses were consistent with their being α-U and δ phase respectively. However, XRD data for annealed alloys never showed peaks for δ phase even though it’s area fraction was within the detection limits. Moreover, the peaks which were present in U-20wt%Zr vanished after annealing for 7 days. Based on the data obtained, it is suggested that it is more appropriate to consider the presence of metastable diffusional-ω instead of a stable δ in the as-cast alloys and that it is not stable at 600degreeC.

The PCI technology is well established for reducing the consumption of economic and environmentally expensive coke in blast furnace iron-making. Often, coal blends show unexpected combustion performance which cannot be explained on the basis of individual coal properties particularly coal rank and volatile matter. Several coals were combusted in this study under controlled conditions in a drop tube furnace. Fixed bed reactor, XRD, SEM and BET analyses were used to understand the mechanism of combustion of coal blends. Burnout of the coal blends did not change linearly with volatile matter of blends. The study demonstrated that combustion behaviour of coal blends was influenced by several properties of individual coals and cannot be estimated by using any single coal parameter. Carbon structure of coal as well as the interaction of volatile matter of individual coals was found to have a strong influence on the burnout of coal blends. Pet-cokes were generally found to burn with a greater difficulty. Carbon structure of pet-cokes was found to have a significant effect on the burnout such that coal blends with highly ordered pet-coke indicated lower burnout. The study shows that up to 10% of pet coke did not change the burnout of PCI blends significantly. As far as combustion is concerned, the drop tube furnace test provides a reasonable distinction of the effect of coal properties for PCI application.

Hemp, eucalyptus, coal, hemp and coal blended fuel, and eucalyptus and coal blended fuel were ashed and then heat treated for 1 hour at temperatures from 600-1100°C. X-ray diffraction analysis indicated reactions between the phases present after initial ashing of the fuel showed biomass-biomass, biomass-coal and coal-coal interactions. Two phase systems were identified as dominant in the biomass and coal ash blends, these were CaO-MgO-SiO2 and CaO-Al2O3-SiO2. The phases identified in these systems have also been identified in ceramics produced at high temperatures which have similar compositions to the ash matrix of the laboratory synthesised ash; this indicates that phase diagrams can be powerful tools in phase formation prediction. Structures identified as trichomes (phosphate-silicate structures with melting points above 1100°C) from the hemp fuel which had not decomposed were present in both the hemp ash and the hemp and coal ash. The composition determined by Energy-dispersive X-ray spectroscopy analysis of laboratory synthesised ashes was also in agreement with the phases identified through X-ray diffraction. Hemp and coal, eucalyptus and coal, and eucalyptus ash samples (deposited, quenched, cyclone, and bottom ash) removed from a full scale 1MWth combustion rig were analysed. Phase composition of the fly ash samples are similar to those identified in the analagous samples produced in the laboratory with several of the same phases present; confirming that laboratory testing is useful for the predictions of phases present on the industrial scale combustion rig. Particle morphology is one of the largest differences between the laboratory scale tests and combustion rig samples. The dominant particle shape of fly ash particles removed from the combustion rig is spherical. These particles of characteristic shape are often referred to as plerospheres and cenospheres and were first identified in coal fly ash. The presence of the spheres in the combustion rig when only biomass (eucalyptus) is present indicates the formation mechanism of the particles is similar to that of coal. There are similarities between the chemical composition of the spheres which are solely of biomass origin and co-fired; it is likely that phase composition of the sphere and not the fuel origin contributes to the formation of the spheres. Phases identified in the bottom ash are similar to those identified in the fly ash. High temperature phases such as (e.g. Ca9MgK(PO4)7) ocur in the bottom ash suggesting that higher temperatures are reached in the bottom of the rig than in the flue gas. Analysis of 15Mo3 alloy corrosion coupons with fly ash deposited onto the surface, alongside the interactions between gas phases and coupons, deposits and coupons, and gas phases and deposits, showed that some oxidation/reduction of the metal had occurred. The presence vi of metal oxide flakes indicated corrosion. Oxidation of 15Mo3 alloy was observed in hemp and coal, and eucalyptus and coal combustion trials, likely due to the observed deposition of potassium chloride which has caused detachment of several scales. Between the metal-deposit interface, hematite whiskers were observed; magnetite octahedra were also present on the surface of scales. The phases present in the coupon deposit ash differ from those observed in the laboratory and fly ash due to the length of time spent in the high temperature environment. This indicates that some phases will not form until the deposits have built up and are in the furnace for an extended period of time. When the coupon samples were coated, fewer metal scales were observed meaning that the coatings are an affective method of corrosion reduction leading to an increased lifetime of boiler components. The dominant particle morphology present in the combustion rig is the cenospheres and plerospheres. The phases formed can be broadly catergorised into CaO-MgO-SiO2, CaO-Al2O3-SiO2, and K2O-Al2O3-SiO2 phases. Potassium chloride is observed in the laboratory ash and combustion rig ash indicating, alongside the presence of metal oxide scales, that the fuel blends are likely to lead to corrosion during combustion.

abstract: Expansive soils impose challenges on the design, maintenance and long-term stability of many engineered infrastructure. These soils are composed of different clay minerals that are susceptible to changes in moisture content. Expansive clay soils wreak havoc due to their volume change property and, in many cases, exhibit extreme swelling and shrinking potentials. Understanding what type of minerals and clays react in the presence of water would allow for a more robust design and a better way to mitigate undesirable soil volume change. The relatively quick and widely used method of X-ray Diffraction (XRD) allows identifying the type of minerals present in the soil. As part of this study, three different clays from Colorado, San Antonio Texas, and Anthem Arizona were examined using XRD techniques. Oedometer-type testing was simultaneously preformed in the laboratory to benchmark the behavior of these soils. This analysis allowed performing comparative studies to determining if the XRD technique and interpretation methods currently available could serve as quantitative tools for estimating swell potential through mineral identification. The soils were analyzed using two different software protocols after being subjected to different treatment techniques. Important observations include the formation of Ettringite and Thaumasite, the effect of mixed-layer clays in the interpretation of the data, and the soils being subject to Gypsification. The swelling data obtained from the oedometer-type laboratory testing was compared with predictive swelling functions available from literature. A correlation analysis was attempted in order to find what index properties and mineralogy parameters were most significant to the swelling behavior of the soils. The analysis demonstrated that Gypsification is as important to the swelling potential of the soil as the presence of expansive clays; and it should be considered in the design and construction of structures in expansive soils. Also, the formation of Ettringite and Thaumasite observed during the treatment process validates the evidence of Delayed Ettringite Formation (DEF) reported in the literature. When comparing the measured results with a proposed method from the University of Texas at Arlington (UTA), it was found that the results were somewhat indicative of swell potential but did not explain all causes for expansivity. Finally, it was found that single index properties are not sufficient to estimate the free swell or the swell pressure of expansive soils. In order to have a significant correlation, two or more index properties should be combined when estimating the swell potential. When properties related to the soil mineralogy were correlated with swell potential parameters, the amount of Gypsum present in the soil seems to be as significant to the swell behavior of the soil as the amount of Smectite found. / Dissertation/Thesis / M.S. Civil Engineering 2014

This work was performed as part of the MUZIC-2 (Mechanical Understanding of Zirconium Corrosion) collaboration, established with the goal of understanding the mechanism of hydrogen pickup in zirconium alloys. Hydrogen pickup is one of the least understood and most significant degradation mechanisms affecting zirconium alloys in nuclear reactors. These alloys are used as cladding and structural materials in the reactor core, mainly due to their low thermal neutron absorption cross section and excellent corrosion resistance. This project aims to investigate the effect of oxide texture (i.e. the degree of preferred orientation) on the corrosion performance of zirconium alloys. The texture of the oxide is expected to affect the microstructural development of the oxide, the grain boundary distribution and the stress state. It is therefore considered to be one of the most important factors in determining how the corrosion process occurs, and why different alloys exhibit significantly different corrosion performance. It is hoped that this project will add to the current knowledge of the corrosion process, and in particular hydrogen pickup, so that the route of hydrogen through the protective oxide can be identified. This will lead to the development of a new generation of alloys that provide improved oxidation and hydrogen pickup performance, whilst maintaining the required mechanical properties. This work focuses on four zirconium alloys; Zircaloy-4, ZIRLO™, low-Sn ZIRLO™ and Zr-1.0Nb-0.1Fe. The alloys all have different chemical compositions and therefore exhibit different corrosion performance. The macrotexture of the oxide formed on different alloys was measured by glancing angle X-ray diffraction (XRD) and Electron Backscatter Diffraction (EBSD). A fibre texture was formed in all cases, with the (10-3) to (10-5) planes oriented parallel to the metal-oxide interface for the monoclinic phase. The major orientation was found to be independent of alloy chemistry, substrate orientation and oxidation conditions. The monoclinic texture strength was found to be weakened with increasing oxidation temperature, The major orientation of the tetragonal phase was also found to be a fibre texture, with the (001) planes oriented approximately parallel with the interface. Although significant variation from this texture component was observed. It is suggested that the main driving force for oxide texture development is the transformation stress induced by the Zr-ZrO2 transformation. The microtexture of the oxides was measured using two novel techniques, Transmission Kikuchi Diffraction (TKD) and automated crystal orientation mapping with transmission electron microscopy (TEM). The techniques revealed an oxide microstructure consisting of an outer layer of equiaxed grains with a large range of orientations and an inner layer consisting of well-aligned columnar monoclinic grains. This layer of equiaxed grains was observed to form again after the transition in corrosion kinetics. A large fraction of transformation twin boundaries were observed throughout the oxides. Some of these boundaries were observed to surround large monoclinic grains, providing evidence that the tetragonal grains from which they transformed had grown considerably larger than the critical grain size for stabilisation. Without the presence of Sn, larger monoclinic grains were observed to form with a greater degree of preferred orientation, and with a lower fraction of transformation twin boundaries than Sn-containing alloys. In addition, an increased number of well-oriented tetragonal grains was correlated with the presence of Sn. It is therefore concluded that a reduction in Sn will lead to the formation of an oxide microstructure that is more resistant to both oxidation and hydrogen pickup. An analysis of the crystallography and morphology of a ZrO phase present at the metal-oxide interface was also performed. Finally, the observations have been used to construct a model of the corrosion process.

The effect of replacing fine ore by coarse ore on sintering reactions was investigated using an infrared furnace on laboratory scale and sinter pots on pilot plant scale. Five sinter mixes were prepared by changing the percentage coarse ore from 0% to 100% in 25% increments. Coarse ore fraction, sintering temperature, holding time and oxygen partial pressure were selected as sintering parameters, and two-level factorial design was used for identification of parameters that significantly influence the formation of sinter phases. Experimental results showed that the coarse ore fraction has a higher effect on the sintering process compared to those of other parameters. The experiment design also enabled to set these parameters to their optimum values. The porosity of compacted pellets was measured using a helium pycnometer. The replacement of fine ore by coarse ore resulted in a decrease in porosity (increase in packing density) of compacted pellets. The particles are closer to each other in pellets consisting of more coarse particles than fine particles. Laboratory experiments were performed at 1300°C in air, using a high heating rate (15°C/s). The holding time was set to 2.5 minutes. X-ray diffraction (XRD), reflected light microscopy (RLM), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) were used to characterize sintering reactions and sinter phases. XRD analysis revealed that sintered pellets consisted of hematite, SFCA, SFCA-I and calcium silicate. The proportions of SFCA slightly increased when the fraction of coarse ore varied from 0% to 25%, but decreased with a further increase in percentage coarse ore. At 25% coarse ore fraction, the porosity of the compacted pellets decreased, resulting in an increase in packing density and sintering rate. More hematite reacted, resulting in the formation of high amounts of SFCA. Above 25% coarse ore fraction, the amount of hematite increased, and the concentrations of columnar SFCA decreased despite a further decrease in porosity. This was attributed to the decrease in reaction surface area for coarse ore, and the short reaction time, which limited the extent of reaction of the coarse particles. The variation of SFCA-I and calcium silicate was not significant under laboratory conditions. Reflected light microscopy and SEM analysis easily identified two major sinter phases: hematite and SFCA. A clear distinction between the different types of SFCA could not be made using EDS analysis. Sinter pot tests were carried out in order to examine the effect of coarse ore fraction on physical and metallurgical properties of sinters. The tumbler and reduction disintegration indexes increased with increasing coarse ore fraction in the sinter bed. This was presumably due to the increase in amounts of hematite and decrease in surface area for reaction. Consequently, the reducibility of sinter decreased as the percentage coarse ore increased. This study has concluded that the presence of 25% coarse ore in the sinter mix led to enhance sintering reactions. The amounts of SFCA increased, and sinter quality was improved. It is recommended that in future work, sintering reactions should further be investigated by also measuring the permeability of the sinter bed and the reaction surface area of solid particles. Copyright / Dissertation (MSc)--University of Pretoria, 2012. / Materials Science and Metallurgical Engineering / unrestricted

At Nouryon Stockvik the Expancel production site is located. Expandable microspheres areused in for many types of applications and is a technically challenging product. At ExpancelStockvik they are constantly striving to improve product properties in line with customerexpectations. To be able to do this, it is important to understand the properties of themicrospheres such as crystallinity and crystallite size.Films was prepared from microspheres dissolved in DMA and analyzed with High-resolutionSEM, Powder X-Ray Diffraction and Raman Spectroscopy. The aim was to develop a methodto investigate and determine crystalline ratios and crystallite size within the microsphere filmsand the microspheres before film preparation. The eventual correlation between morphologyand crystallinity was also studied. An attempt of finding an amorphous reference sample wasalso performed, this was done by grinding microspheres in liquid nitrogen, unfortunately, nosuccess was reached. Gauss-fitting was therefore performed to be able to find the amorphousregions of the XRD Diffractogram for the calculations of crystallinity and crystallite size. TheGauss-fitting was successfully performed with good R-square values.During the Raman analysis some fluorescence problems occurred, this problem will probablybe solved if a laser source with higher excitation frequency is used in future analysis. Evenwith fluorescence problems, Raman analysis could successfully be performed and giveinformation of the composition. The crystallite size was in general larger for the microspheresbefore they were prepared from dissolving them to make films. Generally, it seems as there isa correlation between the morphology, crystallinity, and crystallite size.

Within this thesis, a comprehensive study of the initial growth process of pure Fe3O4 films and Fe3O4/NiO bilayers on Nb:SrTiO3(001) substrates including the thermal interdiffusion behavior of these bilayers is presented. The sensitive interplay between magnetic, electronic and structural properties of these materials has been investigated in detail. In the first study, the initial growth behavior of high-quality ultrathin magnetite films on SrTiO3(001) deposited by reactive molecular beam epitaxy depending on the deposition temperature has been analyzed. For this purpose, the growth process has been monitored in situ and during the deposition by grazing incidence x-ray diffraction (GIXRD). The second part provides a comparative study of Fe3O4/NiO bilayers grown on both MgO(001) and Nb:SrTiO3(001) substrates exploring morphological, structural and magnetic properties. These structures have been investigated by means of x-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), x-ray reflectivity (XRR) and diffraction (XRD), as well as vibrating sample magnetometry (VSM). Subsequently, thermal stability of these bilayers and the thermally induced interdiffusion process have been studied successively accompanied by a comprehensive characterization of the fundamental electronic, structural and magnetic properties using additional techniques such as angle resolved hard x-ray photoelectron spectroscopy (AR-HAXPES) and x-ray magnetic circular dichroism (XMCD). Finally, an alternative pathway for the preparation of ultrathin nickel ferrite films through interdiffusion is provided.

A strategy based on reticulating metal ions and organic ligands into atomically precise gold and silver nanoclusters (NCs) with high monodispersity has been advanced to a point that allows the design of NCs with strict stoichiometries, functionalities and valence. Of the Ag NCs discovered, Ag44 is the most studied, not only due to its high absorption that transcends the visible spectrum suitable for photovoltaics but also because of its long excited state lifetime, as revealed by nanosecond transient absorption spectroscopy. A major principle discovered in this dissertation is the ability to produce Ag44 in scalable amounts and with high stability in addition to modulation of the functional groups of the organic ligands via a fast and complete ligand exchange process. This new discovery has led to the development of synthetic designs in which new sizes were obtained by varying the reaction parameters (e.g., ligands functionality, reaction temperature and time), namely, Ag29 using dithiols and phosphines. The synthesized NCs possess tetravalent functionalities that facilitate their crystallization and characterization. Furthermore, Ag29 glows red and is therefore a possible candidate for sensing and imaging applications.

In this project, we focus on developing a method to produce synthetic spider silk thin films. Using these films we optimized mechanical properties, lowered cost, and improved the environmental impact using different processing methods. Applications for spider silk films are broad, ranging from physical protection to biocompatible materials. This project was designed to improve mechanical properties and production methods of films made from synthetic forms of MaSp1 and MaSp2 from the dragline silk of Nephila clavipes. We have increased the mechanical stress (200 MPa) to more than 4 times that of similar products with elongations as high as 35%. The films have also been analyzed using NMR, XRD, and AFM or SEM showing that the secondary structure in as-poured films is mainly alpha-helical and after processing this structure turns to an aligned betasheet formation similar to that in spider silk fibers.