A research report submitted in fulfilment of the requirements for the degree of Master of Science in Engineering (50/50) to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, 2018 / Metal dusting (MD) is a severe form of corrosion in which iron, steels, and nickel (Ni) and cobalt (Co) based alloys disintegrate into a metal or carbide powder with a coke deposit when exposed to strongly carburising gases (carbon activity, ac>1) at elevated temperatures (400800°C). Temperature affects both the driving force and rate of the reaction, represented by gas phase supersaturation with carbon, and the rates of the various processes involved in converting that energy difference into the dusting process. Therefore, process streams such as reformer gas can be benign when hot, but becomes aggressive below critical temperatures. There are different views in literature about the effect of temperature on metal dusting of different materials and alloys. Alloy 800 experiences metal dusting (MD) at 525°C, which is the temperature of the tube sheet of reformers in petrochemical industry. This alloy is specifically used for tube ferrules in the reformers. The reformer trains can reach a critical (highest) internal temperature of 650°C. Therefore, these two temperatures were compared. The effect of temperature and exposure time on the metal dusting of Alloy 800 were investigated in terms of the form of attack and the degradation mechanism. From the results obtained, it was observed that the longer exposure periods result in more carbon deposition and the carbon filaments in the coke become finer as compared to the nanotubes obtained after shorter exposure periods. The alloy suffered metal dusting attack after a relatively short exposure period of three days (72 hours) at both temperatures of 525°C and 650°C, with very little coking. / TL2019

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The teeth are amongst the most resilient elements of the human skeleton and are thus often utilised in routine forensic investigation involving the identification of unknown remains. The teeth, however, also have other practical forensic applications. Teeth exposed to thermal stress have the potential to not only aid in identification but also in understanding the circumstances surrounding the fire. Previous investigations have drawn conclusions that if a fire flares up suddenly and intensively, the teeth burst and enamel is lost. If the blaze commences gently and burns slowly, then the first observable morphologic change is the colour. The teeth subsequently are difficult to handle, thus changes in teeth can indicate the history of exposure to thermal conditions. Children are twice as likely to become victims of house fire because of an inability to safely evacuate from areas of danger. The literature demonstrates, however, that research on the effects of incineration on teeth is mostly restricted to the permanent teeth. The apparent lack of knowledge on the effects of incineration on deciduous teeth thus necessitates further research in this area. This research project primarily aims at understanding the effect of extreme temperatures on deciduous teeth. It also aims to relate colour changes that occur post heating with fragility to aid in proper handling of samples in a forensic scenario and to determine the possibility of identifying incineration temperature based on tooth condition. The samples analysed composed of 90 deciduous teeth (45 molars and 45 anteriors) extracted as a part of clinical treatment were used for the study. The project involved exposing extracted deciduous teeth to temperatures ranging from 100°C to 1100°C for 30 minutes using a laboratory Gallenkamp oven. Unheated deciduous teeth were used as controls for the project. Post-incineration the teeth were then analysed under a stereomicroscope and SEM for morphological changes. A colorimetric analysis was also undertaken to evaluate the colour changes induced in the primary teeth due to the thermal stress. It was found that it was possible to identify the incineration temperature based on the tooth condition when the colour changes, stereomicroscopic findings and SEM images were utilised collectively. It was also concluded that the thermally induced changes observed in primary teeth occur at lower temperatures in comparison to the permanent teeth. It was also established that post-incineration deciduous teeth are fragile and show a tendency to fragment after minimal exposure to thermal stress as compared to the permanent teeth. Moreover enamel and dentin remained identifiable in primary teeth even after exposure to 1100°C for 30 minutes while cementum lost its structural morphology at 900°C.

published_or_final_version / abstract / Civil Engineering / Doctoral / Doctor of Philosophy

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, in fulfilment of the requirements for the degree of Master of Science in Engineering 15 October 2016 / The alloys Ti-52.5Al-10.0Ni (at.%) and Ti-52.5Al-10.0Ni-0.2Ru (at.%) were made by mixing, and melting their powders in a button arc furnace under an argon atmosphere. The high temperature oxidation and room temperature corrosion of behaviour of the alloys was investigated. Isothermal oxidation in air at 950°C for 120 hours and 720 hours was done. Cyclic oxidation behaviour of the alloys was also investigated in air and in a hot salt (Na2SO4) environment. The corrosion tests were conducted in 5 wt% and 25 wt% HCl. All the samples were characterised using scanning electron microscopy with energy dispersive X-ray spectroscopy, X-ray diffraction and hardness measurements. On solidification, the Ti-52.5Al-10.0Ni (at.%) alloy formed dendrites of γ-TiAl (~55 at.% Al) surrounded by a eutectic of γ-TiAl + Ti2NiAl3 (τ3) phases. Most of the nickel was found in the Ti2NiAl3 (τ3) phase (~12 at.%) with trace amounts in the dendrites (~0.5 at.%). The Ti-52.5Al-10.0Ni-0.2Ru (at.%) alloy formed dendrites of γ-TiAl (~53 at.% Al) surrounded by a eutectic of γ-TiAl + Ti2NiAl3 (τ3). Most of the nickel (~15 at.%) and ruthenium (~0.3 at.%) were in solid solution in the Ti2NiAl3 (τ3) phase, although small amounts of both metals were present in the dendrites (~1 at.% Ni and 0.1 at.% Ru). Under isothermal oxidation conditions, both alloys showed good oxidation resistance with a low mass gain (< 2%). The alloys formed a continuous scale of TiO2 and Al2O3 with good adherence to the substrate, but as exposure time increased, the scale was severely degraded and exfoliated from the surface. Cyclic oxidation conditions were more aggressive for both alloys. The Ti-52.5Al-10.0Ni-0.2Ru (at.%) alloy was more resistant and formed a nickel-rich sub-surface zone between the substrate and intermixed oxide layer. Both alloys had a fairly good corrosion resistance in HCl due to the presence of nickel. They formed a thin and non-continuous Al2O3 oxide scale on the surface of the γ-TiAl dendrites, with Ti3NiAl2O on the γ-TiAl + Ti2NiAl3 (τ3) eutectic regions. The acid mainly corroded the τ3 phase, thus attacking the eutectic and leaving the γ-TiAl dendrites exposed. / MT2017

Une interface de capteur intégré haute température est proposée. L'interface de capteur a une architecture dans le domaine temporel et entièrement différentielle. Cette approche offre l'avantage d'une meilleure stabilité thermique par rapport aux architectures analogiques classiques. L'interface du capteur est basée sur des oscillateurs à verrouillage d'injection (ILO) utilisés comme déphaseurs. Une paire d’ILOs convertit la tension de sortie du capteur en une différence de déphasage qui est ensuite numérisée à l'aide d'un convertisseur temps-numérique. La sortie de l'interface du capteur dépend uniquement du rapport des valeurs de ses paramètres plutôt que de leurs valeurs absolues, ce qui entraîne une faible dépendance à température. L'interface du capteur est fabriquée à l'aide d'une technologie de silicium sur isolant partiellement déplété (PD-SOI) de 0.18μm de XFAB, qui est choisie pour sa robustesse thermique. Les mesures montrent que l’interface de capteur a une variation thermique de 178ppm / ° C sur ± 60mV de pleine échelle d'entrée et une variation thermique de 65ppm / ° C sur ± 40mV de pleine échelle d'entrée sur une large plage de température de fonctionnement étendue de -20 ° C à 220 ° C. / A high temperature integrated sensor interface is proposed. The sensor interface has a fully differential time domain architecture. This approach offers the advantage of better thermal stability compared to typical analog based architectures. The sensor interface is based on Injections Locked Oscillators (ILO) used as phase shifters. A pair of ILOs converts the sensor output voltage into a phase shift difference which is then digitized using a time to digital converter. The sensor interface output depends only on the ratio of its parameters values rather than their absolute values thus leading to a low temperature dependency. The sensor interface is fabricated using a 0.18µm Partially-Depleted Silicon on Insulator technology (PD-SOI) from XFAB which is chosen for its thermal robustness. Measurements show that the sensor interface achieves a thermal variation of 178ppm/°C over ±60mV input full scale and a thermal variation of 65ppm/°C over ±40mV input full scale over a wide operation temperature range extended from -20°C to 220°C.

The spacetime dimensions of the particle source in proton-lead collisions at √sNN = 5.02 TeV are measured with the ATLAS detector at the Large Hadron Collider. Femtoscopic measurements are made from correlation functions built with charged pions identified by their ionization energy loss. The measured HBT radii that represent the source dimensions are presented differentially as a function of centrality, transverse momentum, and rapidity. The effect of jet fragmentation on the two-particle correlation function is studied, and a method using opposite-charge pair data to constrain its contributions to the measured correlations is described. The measured source sizes are substantially larger in more central collisions and are observed to decrease with increasing pair transverse momentum. A correlation of the radii with the local charged-particle density dN/dy is demonstrated. The scaling of the extracted radii with the mean number of participating nucleons is also used to compare a parameterization of an initial-geometry model that allows for fluctuations in the proton cross-section. The cross-term R_ol is measured as a function of rapidity, and a nonzero value is observed that agrees with hydrodynamic predictions. The HBT radii are also shown for central events in intervals of azimuthal angle relative to the 2nd-order event plane, pair transverse momentum, and flow vector magnitude, where the correlation functions are corrected for the event plane resolution. Significant modulations of the transverse HBT radii R_out, R_side, and R_os are observed. The orientation of this modulation is the same as that in heavy-ion collisions, in which they are attributed to hydrodynamic evolution from an elliptic initial geometry. The sign and transverse momentum dependence of these modulations are consistent with a hydrodynamic evolution of a short-lived medium.

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Thesis (Ph. D.)--Institute of Paper Chemistry, 1959. / Includes bibliographical references (p. 107-109).