Le titane contenu dans un acier maraging se combine avec l'azote résiduel pour former des inclusions de nitrure de titane (TiN), néfastes du point de vue des propriétés en fatigue de l'alliage. La compréhension de leur origine doit permettre de trouver les moyens de réduire leur taille. Des expériences de Sieverts ont été réalisées pour étudier d'un point de vue thermodynamique et cinétique les réactions de dénitruration de l'alliage et de précipitation des TiN. Au regard de ces expériences et des données thermodynamiques disponibles dans la littérature et compte-tenu des teneurs en azote résiduel, la formation des TiN est supposée avoir lieu lors de la solidification sous l’effet de la ségrégation interdendritique. Un certain nombre d'inclusions de TiN sont associées à un germe de type oxyde ou sulfure. L'observation au MET d'une de ces inclusions mixte révèle l'existence d’une relation d'orientation entre le nitrure TiN, un sulfure CaS et un spinelle MgAl2O4, ce qui suggère une croissance par épitaxie du TiN sur ces deux germes. L’étude a été complétée par des calculs ab initio d’énergies de surface et d’énergies d’adsorption. Ces travaux appuient l'hypothèse d'une germination hétérogène des nitrures de titane sur des particules préexistantes et stables dans l'acier liquide. Un modèle numérique de précipitation couplée à la ségrégation interdendritique a été développé puis intégré au logiciel SOLAR simulant la solidification du lingot VAR. Ces calculs quantifient l'influence déterminante sur la taille des plus grands nitrures de la teneur initiale en azote, de la densité de germes, et du temps local de solidification / The titanium contained in maraging steels combines itself with residual Nitrogen to form Titanium nitride precipitates (TiN), which are detrimental to fatigue properties. Understanding their formation may give some ways to reduce their sizes. A Sieverts apparatus was used to study denitriding reactions and precipitation reactions from a thermodynamic and kinetic point of view. According to these experiments, to thermodynamical data from literature, and to the Nitrogen content in the steel, the TiN inclusions are supposed to form during the solidification of the steel thanks to interdendritic segregation. A certain number of the TiN inclusions are found under SEM observations to be located next to another oxide or sulfur particle. A TEM observation reveals the existence of an orientation relationship between a nitride, a sulfur CaS and a spinel MgAl2O4. It suggests an epitaxial growth of the TiN on these two germs. This study was completed with ab initio calculations of surface energies and adsorption energies. This work supports the hypothesis of a heterogeneous nucleation of the Titanium nitrides on preexisting, stable particles in the liquid steel. A numerical model of the precipitation coupled to the interdendritic segregation of solutes is developed and introduced in the SOLAR software modelling the VAR ingot solidification. It evaluates the determinant influence of the initial Nitrogen mass fraction, germ number density and local solidification time on the TiN sizes

Artefacts relating to tin smelting from tin mills or ¿blowing houses¿ in Devon and Cornwall, plus material from smelting sites that cover a range of dates from the Bronze Age through to the 19th Century, were examined: these include metallic tin, furnace linings, ore samples and slag. Analysis of tin slags from over forty sites was carried out, to determine microstructure and chemical composition. Techniques employed included optical and scanning electron microscopy, X-ray fluorescence and ICP mass spectrometry. Analysis indicates that slag appearance and composition are heavily influenced by local geology. Composition, particularly iron content, is shown to have a strong effect on slag melting point and viscosity, and the implications for the purity of metal produced are discussed. Bringing together the evidence provided by slag chemistry, documentary sources and smelting remains in the archaeological record, changes in tin smelting technology through time, and the consequences thereof, are considered. / R. F. Tylecote Memorial Fund, administered by the Historical Metallurgy Society, and the Francis Raymond Hudson Memorial Fund.

The widespread use of Liquid Petroleum Gas (LPG) for cooking and as fuel for automobile vehicles requires fast and selective detection of LPG to precisely measure the leakage of gas for preventing the occurrence of accidental explosions. The adoption of Micro-Electro-Mechanical-System (MEMS) technology for fabricating the gas sensor provides other potential advantages for sensing applications, which includes low power consumption, low fabrication cost, high quality, small size and reliability. MEMS based gas sensor requires a sensitive layer of oxide material like ZnO, SnO2, TiO2, Fe2O3, etc. The tin oxide material used in the present work changes its electrical properties, as it interacts with the reducing gas like LPG. The sensor material becomes active only at high temperature such as 400ºC, thereby realizing the need of a micro heater to reach the desired temperature. To control the temperature of micro heater and to determine the change in electrical properties of the sensor due to its interaction with LPG an Application Specific Integrated Circuit (ASIC) forms an essential constituent of the MEMS based gas sensor. In the present work, an attempt has been made to improve the sensitivity of LPG gas sensor and it is correlated with other properties by different characterization techniques. The work also includes the design as well as testing of ASIC for gas sensor system. Process parameters particularly deposition time and substrate temperature have a profound influence on the microstructure of the tin oxide film, which in turn affects the gas sensing properties. To study the effects of these parameters, RF magnetron sputtering system is used for depositing tin oxide films onto the silicon substrate, which is compatible with CMOS technology. The effects of structural properties, optical properties and the porosity of the films are also studied and correlated with the gas sensing properties. In this direction the deposited films are characterized using X-Ray Diffraction (XRD) to determine the structure orientation. The morphology of the sensor films are analyzed by Scanning Electron Microscope (SEM) while the refractive index, thickness and porosity of the films are determined using ellipsometry studies. The thickness of the deposited films is also confirmed by the surface profilometer. The change in composition of the deposited film along its depth is determined using Secondary Ion Mass Spectrometer (SIMS). Maximum sensitivity 5.5 is obtained for 470 nm thick films, which corresponds to a grain size of 38nm at the operating temperature of 4000C. Following these studies, an ASIC has been designed using Tanner EDA Tools on AMIS 0.7 µm CMOS process, fabricated through Euro practice’s ASIC prototyping service, Belgium and tested successfully after fabrication. The temperature control module of ASIC has been designed using relaxation oscillator technique to control the temperature of the in house developed heater. The resistance to period conversion technique is explored for the design of the sensor read out module of ASIC. The heater is integrated successfully with the sensor film, ASIC and microcontroller based LCD module. The test results show good agreement with the simulation results.

published_or_final_version / Transport Policy and Planning / Master / Master of Arts in Transport Policy and Planning

The primary aim of this dissertation is to map the geology of the East Rand Basin accurately by creating a 3D model. This was done by using borehole data from the National Groundwater Archive Geodatabase, which the Department of Water and Sanitation collected, and the average depths derived from the literature. Triangulated irregular networks (TINs) and digital elevation models (DEMs) surfaces were created from these data points to determine the depths for areas with no borehole data. Using these surfaces, three methods were used to create three main models. These models were then compared to one another, other geological maps and cross-sections to determine the most accurate and practical model of the three. It was found that the quality and quantity of the data from the National Groundwater Archive Geodatabase were not sufficient for these models; therefore, the results and accuracy of each layer was questionable. This dissertation found that these methods can be used for basic geological studies if the data are of the same quality and quantity. However, if the data are more evenly distributed and higher in quantity, these methods can be used to create more accurate models. Furthermore, the use of commercial software was recommended in this study. The reason for recommending these tools is that they have been specifically designed to create geological layers from boreholes within the ArcGIS software. These tools also allow the user to create cross-sections within ArcGIS. / MSc (Geography and Environmental Management), North-West University, Potchefstroom Campus, 2015

The primary aim of this dissertation is to map the geology of the East Rand Basin accurately by creating a 3D model. This was done by using borehole data from the National Groundwater Archive Geodatabase, which the Department of Water and Sanitation collected, and the average depths derived from the literature. Triangulated irregular networks (TINs) and digital elevation models (DEMs) surfaces were created from these data points to determine the depths for areas with no borehole data. Using these surfaces, three methods were used to create three main models. These models were then compared to one another, other geological maps and cross-sections to determine the most accurate and practical model of the three. It was found that the quality and quantity of the data from the National Groundwater Archive Geodatabase were not sufficient for these models; therefore, the results and accuracy of each layer was questionable. This dissertation found that these methods can be used for basic geological studies if the data are of the same quality and quantity. However, if the data are more evenly distributed and higher in quantity, these methods can be used to create more accurate models. Furthermore, the use of commercial software was recommended in this study. The reason for recommending these tools is that they have been specifically designed to create geological layers from boreholes within the ArcGIS software. These tools also allow the user to create cross-sections within ArcGIS. / MSc (Geography and Environmental Management), North-West University, Potchefstroom Campus, 2015

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

published_or_final_version / abstract / Urban Design / Master / Master of Urban Design

No description available.

No description available.