Thèses sur le sujet « METALLURGICAL INVESTIGATION »

Metallurgical coke is used primarily as a reducing agent for the reduction of iron in the blast furnace. Due to the high cost, high demand and reduced availability of high quality coking coals used in the production of metallurgical coke, alternative resources are being sought. One possible alternative is to use petroleum coke. Petroleum coke has the advantage of having a higher calorific value than traditional coke, at relatively low cost with a low ash content and ready availability. However the drawback to petroleum coke relates to its poor mechanical strength and reactivity. The main focus of this study was therefore to develop a process for producing petroleum coke with the required qualities for blast furnace application. In an initial series of experiments tests including proximate analysis, ultimate analysis, intrinsic reactivity test, DSC, direct tensile strength, calorific value, X-ray computed tomography, X-ray diffraction and scanning electron microscopy were used to characterise a wide range of petroleum coke and compare it with metallurgical coke properties. X-ray computed tomography methodology was also used to provide 3D information on coke lumps. Results show that none of the petroleum coke samples met the full requirements needed for use as a good blast furnace coke.

Hot-pressed aluminium and silicon coated boron steel is used in the car industry where high tensile strength is of great importance, such as in the safety cage of a car where deformation has to be kept to a minimum in case of a collision. After hot-pressing the AlSi-boron steel shows excellent properties with high tensile strength, minimal spring back and also shows good protection against corrosion. A thickness of the AlSi coating of 150 [g/m2] for AlSi coated boron steel is typically used by the car industry today. However the coating thickness would be desirable to be minimized to 80 [g/m2]. Welding of this boron steel with 80 [g/m2]have shown difficulties; and it’s not clear why this occurs. In this report the metallurgical properties of the different coating layers will be investigated, simulations with Thermocalc module Dictra will be used, SEM/EDS will be used to characterize phases in coating layers and correlate to weldability. Resistance spot welding tests will also be performed where the welding parameters of pre-pulse, pulse time, time in between pulses and current will be varied to achieve desirable weld plug diameter without expulsion. Hardness testing in form of micro Vickers will executed. The Materials used will be USIBOR® 1500, AS80 with four different annealing times and one sample of AS150.

The application of powder metallurgy (PM) technologies to the manufacturing of Oil & Gas turbomachineries’ components was investigated in the course of research collaboration with the Material and Processes Engineering Department of General Electric Oil & Gas (Italy). The thesis focused on the study of the pressure-assisted Hot Isostatic Pressing technology for the processing of the corrosion resistant Ni-base alloy N07626. The densification behaviour of the N07626 metal powder in condition of pressure assisted sintering was investigated by experiments conducted on a small scale by uniaxial hot pressing condition using a Spark Plasma Sintering (SPS) machine in the aim of extending the result to the initial stage of densification of HIP. The SPS exepriments demonstrated that the densification rate is strongly affected by the process temperature and it is less sensitive to the variation of applied pressure. The microstructure and mechanical properties of full-dense HIPped N07626 alloy, produced according to a fixed proprietary cycle and several experimental deviations were analyzed. The microstructure was studied by Optical Metallography, Scanning Electron Microscopy, Energy Dispersed X-Ray Spectroscopy and Electron Backscatter Diffraction. The mechanical properties of the alloy were assessed by tensile testing, conventional and instrumented Charpy V-Notch testing, JIC fracture toughness tests and fatigue crack growth rate testing. The tensile and impact toughness properties resulted sensitive to the local accumulation of oxygen in Oxygen Affected Zones (OAZs), that leads to a ductile to brittle transition in the impact toughness of the material. Two models for formation of OAZs were proposed based on the phase transformation and the oxidation/reduction reactions taking place in the HIP. The mechanical properties were discussed on the base of the microstructure of the Prior Particle Boundaries (PPBs) interface, focusing of the phase transformation products, represented by a thin layer of submicrometric oxides and carbides. The fracture mode was explained by the analogy with models of ductile micro-mechanisms of void nucleation and coalescence and with fracture models of particulate reinforced metal-matrix-composite. The Charpy impact toughness and the fracture toughness were correlated to the oxygen concentration and to the density of inclusions. The fatigue crack propagation behavior was discussed focusing on the effect of clustering of inclusions on the crack propagation path. A relation between the Paris slope with the impact toughness was found. Finally the increase of processing temperature (HIP and heat treatment) was found significanty beneficial for the toughness. This effect was investigate by grain-size analysis and was proposed to be related to a reduction of density of PPBs inclusions.

The application of powder metallurgy (PM) technologies to the manufacturing of Oil & Gas turbomachineries’ components was investigated in the course of research collaboration with the Material and Processes Engineering Department of General Electric Oil & Gas (Italy). The thesis focused on the study of the pressure-assisted Hot Isostatic Pressing technology for the processing of the corrosion resistant Ni-base alloy N07626. The densification behaviour of the N07626 metal powder in condition of pressure assisted sintering was investigated by experiments conducted on a small scale by uniaxial hot pressing condition using a Spark Plasma Sintering (SPS) machine in the aim of extending the result to the initial stage of densification of HIP. The SPS exepriments demonstrated that the densification rate is strongly affected by the process temperature and it is less sensitive to the variation of applied pressure. The microstructure and mechanical properties of full-dense HIPped N07626 alloy, produced according to a fixed proprietary cycle and several experimental deviations were analyzed. The microstructure was studied by Optical Metallography, Scanning Electron Microscopy, Energy Dispersed X-Ray Spectroscopy and Electron Backscatter Diffraction. The mechanical properties of the alloy were assessed by tensile testing, conventional and instrumented Charpy V-Notch testing, JIC fracture toughness tests and fatigue crack growth rate testing. The tensile and impact toughness properties resulted sensitive to the local accumulation of oxygen in Oxygen Affected Zones (OAZs), that leads to a ductile to brittle transition in the impact toughness of the material. Two models for formation of OAZs were proposed based on the phase transformation and the oxidation/reduction reactions taking place in the HIP. The mechanical properties were discussed on the base of the microstructure of the Prior Particle Boundaries (PPBs) interface, focusing of the phase transformation products, represented by a thin layer of submicrometric oxides and carbides. The fracture mode was explained by the analogy with models of ductile micro-mechanisms of void nucleation and coalescence and with fracture models of particulate reinforced metal-matrix-composite. The Charpy impact toughness and the fracture toughness were correlated to the oxygen concentration and to the density of inclusions. The fatigue crack propagation behavior was discussed focusing on the effect of clustering of inclusions on the crack propagation path. A relation between the Paris slope with the impact toughness was found. Finally the increase of processing temperature (HIP and heat treatment) was found significanty beneficial for the toughness. This effect was investigate by grain-size analysis and was proposed to be related to a reduction of density of PPBs inclusions.

Bibliography: leaves 91-92.
In recent years the development of Machine Vision systems has opened up new possibilities for non-intrusive process performance sensors and process control. There are currently various Machine Vision systems on notation plants worldwide (Metso at Kennecott, Frothcam at Escondida). Extensive research has been done on using froth image analysis in closed loop control (Hyotyniemi et aI, 2000; Kittel et aI, 2001; Holtham and Nguyen, 2002; Cipriano et aI, 1998) and recently plants have been using these systems to control the air or level of a flotation cell as a means of controlling mass pull using the froth velocity output. As yet no flotation plants have reported the use of froth colour in their control strategies, however it is well accepted that an experienced operator can judge the metallurgical state of a flotation cell by the appearance of the froth, using colour as a key descriptor of grade, particularly in the case of copper froths. For this reason an investigation was undertaken to evaluate whether a relationship existed between concentrate grade and the froth colour obtained using a Machine Vision system. This relationship could be used to control reagent addition or for system diagnostics. Both would be invaluable tools for the flotation industry. A Machine Vision system called SmartFroth has been developed at University of Cape Town (VCT) as a research tool to investigate the relationships between froth surface indicators and metallurgical parameters. The relationship between froth colour and % solids was also investigated as it was believed that solids loading could be reflected by froth colour. This work was aimed at evaluating the empirical relationship between froth colour and copper grade in the laboratory and then investigating whether a similar relationship existed on plant. Various colour spaces were examined to find one appropriate for the copper flotation froths in order to allow for accurate colour analysis. It also evaluated the use of calibration objects in the colour analysis of flotation froths. This work also evaluated relating froth colour to % solids on plant. Two batch flotation campaigns were done using different ores as well as a preliminary plant trial.

Gas stirring is currently the most commonly used method of homogenizing liquid steel in commercial processes. However, due to the harsh environment during the process, physical models built out of e.g. plexiglass have been used to easier understand the complex phenomenon occurring in the process. The models are also used to optimize stirring conditions and estimate mixing times. Instead of liquid steel, water has been used for modelling, to increase safety and reduce costs. The water models are usually scaled down to sizes that are easier to handle. Scaling correctly requires fulfilling commonly used criteria and dimensionless numbers. This report investigated the accuracy of these dimensionless numbers and the relations commonly used for scaling. Existing studies and relations were evaluated, and the theoretically best suitable scaling equations were tested. Three bottom blown vessels were built, in order to test the existing relations. By applying scaling criteria and calculating gas flow rates accordingly, the correlation between theoretical mixing time and measured mixing time could be investigated. This thesis concluded that the correlation between the measured mixing times was not significant, however, by implementing the scale factor λ1/2 a better approximation seems to be given.
Gasomrörning är för tillfället den vanligaste metoden som används för att homogenisera flytande stål i kommersiella processer. På grund av de svåra förhållandena under processen har fysiska modeller, byggda av exempelvis plexiglas, använts. Detta för att enklare förstå de komplexa fenomen som uppstår under processen. Modellerna används också för att optimera omrörningsförhållandena och för att uppskatta blandningstider. Istället för flytande stål har vatten använts vid modellering för att öka säkerheten och minska kostnaderna. Vattenmodellerna är vanligtvis nedskalade till storlekar som är lättare att hantera. En korrekt skalning kräver att vanliga kriterier och dimensionslösa tal uppfylls. Denna rapport undersökte noggrannheten för dessa dimensionslösa tal samt relationer som vanligtvis används vid skalning. Befintliga studier och relationer utvärderades och de teoretiskt mest lämpliga skalningsekvationerna testades. Tre stycken kärl med bottenblåsning byggdes för att testa dessa relationer. Genom att tillämpa skalningskriterier och beräkna gasflödeshastigheterna, kunde korrelationen mellan de teoretiska och uppmätta blandningstiderna undersökas. Denna avhandling drog slutsatsen att korrelationen mellan de uppmätta blandningstiderna inte var signifikant. Dock verkade en bättre approximation fås när skalfaktorn λ1/2 implementerades.

The aim of this thesis work is to increase the knowledge of phenomena taking place during the initial stage in a top blown converter. The work has been done in a few steps resulting in four different supplements. Water model experiments have been carried out using particle image velocimetry (PIV) technology. The system investigated was a fundamental top blown converter where an air jet was set to impinge on a water surface. The flow field of the combined blown case, where an air jet was introduced through a bottom nozzle, was also captured by the PIV. The work clearly showed that the flow field caused by an impinging top blown jet alone could not match that of the bottom blown case. The main re-circulation loop (or vortex) was investigated with respect to position and it was found that an increased flow rate pushes the center of the re-circulation loop downwards into the bath. However, for the top-blown case there is a point when the flow rate is too large to cause a distinguishable re-circulation loop since the jet becomes more plunging (i.e. penetrates deep into the bath) than impinging, with large surface agitation and splashing as a result.A numerical model with the same dimensions as the experimental system was then created. Three different turbulence models from the same family were tested: standard-, realizable- and a modified-(slight modification of one of the coefficients in order to produce less spreading of the air jet) k-ε turbulence model. It could be shown that for the family of k-ε turbulence models the difference in penetration depth was small and that the values corresponded well to literature data. However, when it comes to the position of the re-circulation loop it was shown that the realizable k-ε model produced better results when comparing the results to the experimental data produced from the PIV measurements, mentioned earlier.It was then shown how the computational fluid dynamics (CFD) model could be coupled to thermodynamics databases in order to solve for both reactions and transport in the system. Instead of an air-water system, a gas-steel-slag system was created using the knowledge obtained in the previous simulation step described above. Reactions between gas-steel, gas-slag, steel-slag and gas-steel-slag were considered. Extrapolation of data from a few seconds of simulation was used for comparison to experimental data from the literature and showed reasonable agreement. The overall conclusion was that it is possible to make a coupling of the Thermo-Calc databases and a CFD software to make dynamic simulations of metallurgical processes such as a top-blown converter.A parametric study was then undertaken where two different steel grades were tested; one with high initial carbon content (3.85 mass-%) and one with lower carbon content (0.5 mass-%). The initial silicon content was held constant at 0.84 mass-%. Different initial temperatures were tested and also some variation in initial dissolved oxygen content was tried. It was found that the rate of decarburization/desiliconization was influenced by the temperature and carbon concentration in the melt, where a high temperature as well as a high carbon concentration favors decarburization over desiliconization. It was also seen that the region affected by a lower concentration of alloys (or impurities) was quite small close to the axis where the impinging jet hits the bath. Add the oscillating nature of the cavity and it was realized that sampling from this region during an experiment might be quite difficult.
QC 20100720

Ce travail étudie le potentiel du silicium de type n purifié par voie métallurgique pour la fabrication de cellules photovoltaïques à bas coût. Les teneurs élevées en dopants conduisent à de faibles valeurs de résistivité, ainsi qu'à une diminution de la durée de vie des porteurs de charge. La fabrication de cellules photovoltaïques a permis d'obtenir des rendements de conversion variant de 13.7% à 15.0% sur 148.6cm². Avec un procédé de fabrication amélioré, des rendements de 16.0% pourraient être obtenus. La résistivité des plaquettes a été identifiée comme facteur limitant les performances des cellules. Le co-dopage au gallium a été proposé pour augmenter la gamme de résistivité. Les cellules photovoltaïques réalisées montrent une excellente stabilité sous illumination et de faibles coefficients en température de la tension de circuit-ouvert. Ces travaux de thèse ont permis de définir le potentiel du silicium de type n purifié par voie métallurgique et de définir les spécifications nécessaires initiales au niveau de la charge à purifier pour permettre la fabrication de cellules photovoltaïques efficaces.

The contact fatigue and surface damage of prealloyed (Fe-0.85Mo, Fe-1.5Mo) and diffusion bonded (Ni-free, low-Ni, high-Ni) powder metallurgy (PM) steels were investigated. Materials subjected to contact stress fail due to the nucleation of subsurface cracks (contact fatigue cracks), nucleation of brittle surface cracks, and surface plastic deformation. The occurrence of these contact damage mechanisms was predicted using theoretical models, which were developed by assuming that crack nucleation is preceded either by local plastic deformation (contact fatigue and surface plastic deformation) or local brittleness (brittle surface cracks ) of the metallic matrix. With reference to the mean yield strength of the matrix (mean approach) or the yield strength of soft constituents (local approach), the models predict the theoretical resistance of materials to the formation of damage mechanisms. The models were then verified using experimental evidence from lubricated rolling-sliding contact tests. In addition, the effect of compact density and microstructures of materials on the resistance to contact damage mechanisms was investigated. Density and microstructure were modified by varying green density, alloying elements, sintering temperature and time, and applying strengthening treatments: carburizing and shot peening on prealloyed (homogenous microstructure) and carburizing, sinterhardening and through hardening on diffusion bonded (heterogeneous microstructure) steels. The theoretical resistance to subsurface and surface crack nucleation in prealloyed materials was predicted using the mean approach since the microstructure is homogeneous. But the local approach is applied for diffusion bonded materials (Ni-free and low-Ni); exceptionally, the mean approach was applied for some homogeneous microstructure of Ni-free material sintered at a prolonged time. However, the models have a limitation in predicting the contact damage mechanisms in a high-Ni material. This issue may require further investigation to modify the model. Shot peening provides higher resistance to the nucleation of surface cracks. High compact density, high sintering temperature and time, and sinterhardening improve the resistance to contact damage mechanisms for Ni-free and low-Ni materials.

The contact fatigue and surface damage of prealloyed (Fe-0.85Mo, Fe-1.5Mo) and diffusion bonded (Ni-free, low-Ni, high-Ni) powder metallurgy (PM) steels were investigated. Materials subjected to contact stress fail due to the nucleation of subsurface cracks (contact fatigue cracks), nucleation of brittle surface cracks, and surface plastic deformation. The occurrence of these contact damage mechanisms was predicted using theoretical models, which were developed by assuming that crack nucleation is preceded either by local plastic deformation (contact fatigue and surface plastic deformation) or local brittleness (brittle surface cracks ) of the metallic matrix. With reference to the mean yield strength of the matrix (mean approach) or the yield strength of soft constituents (local approach), the models predict the theoretical resistance of materials to the formation of damage mechanisms. The models were then verified using experimental evidence from lubricated rolling-sliding contact tests. In addition, the effect of compact density and microstructures of materials on the resistance to contact damage mechanisms was investigated. Density and microstructure were modified by varying green density, alloying elements, sintering temperature and time, and applying strengthening treatments: carburizing and shot peening on prealloyed (homogenous microstructure) and carburizing, sinterhardening and through hardening on diffusion bonded (heterogeneous microstructure) steels. The theoretical resistance to subsurface and surface crack nucleation in prealloyed materials was predicted using the mean approach since the microstructure is homogeneous. But the local approach is applied for diffusion bonded materials (Ni-free and low-Ni); exceptionally, the mean approach was applied for some homogeneous microstructure of Ni-free material sintered at a prolonged time. However, the models have a limitation in predicting the contact damage mechanisms in a high-Ni material. This issue may require further investigation to modify the model. Shot peening provides higher resistance to the nucleation of surface cracks. High compact density, high sintering temperature and time, and sinterhardening improve the resistance to contact damage mechanisms for Ni-free and low-Ni materials.

Thesis (MScIng)--University of Stellenbosch, 2007.
ENGLISH ABSTRACT: Due to economic and environmental constraints mining operations are placed under increasing pressure to effectively manage and operate tailings disposal operations. Restrictions imposed on water usage and tailings operations footprint have led to higher density and wider particle size distribution slurries conveyed to tailings areas. One means of efficiently disposing the tailings is co-disposal. In this method a concentrated fine vehicle slurry is used to convey a coarser fraction. This produces a higher density of tailings, with a number of advantages both upstream and downstream of the tailings process. Limited research has been conducted on the effect of coarse particles on the non-Newtonian rheological properties of these slurries. This lack of information complicates the design and reliable operation of these systems. This project aims at gaining a clearer understanding as to the mechanisms involved in the addition of coarse particles to a fine clay slurry vehicle; and to provide a means of estimating the measured slurry rheological properties. A number of experiments were designed to test the slurry (both Kaolin only, and Kaolin-coarse particle mixtures) rheological properties using a Couette viscometer (for the dynamic flow properties of yield stress and plastic viscosity) and a vane instrument (for the static yield stress measurements). The slurries were prepared in varying Kaolin clay solids concentrations with reverse osmosis water. Glass beads and two types of industrial sand were used as the coarse fractions. All of the coarse particles had a similar size but varied significantly in shape. Slurry pH and temperature readings were monitored throughout the tests. Tests were done initially on clay only slurries. The rheological properties of these slurries were repeatable, and no noticeable variations of properties with time were observed. The yield stress (both static and dynamic) and plastic viscosity data were well correlated with established relationships. Coarse particles were added to the clay only slurries, and then removed. The remaining clay only slurry exhibited the same rheological properties as the initial clay only slurry. The presence of coarse particles increased all the measured rheological properties (i.e. dynamic yield stress, Bingham viscosity, and static vane yield stress) in a fashion resembling the effect of adding clay to a clay only slurry. In addition, the change in measured rheological property by addition of coarse particle was independent of the clay fraction in the clay slurry. Furthermore, with both the clay only slurries and clay and coarse sand slurries, a constant linear relationship existed between the static and dynamic yield stress. Several correlations from the literature were found to provide reasonable prediction of the rheological property variations observed. These empirical and semi-empirical models however did little to explain the mechanisms involved in coarse particle addition. A new correlation has been proposed, Residual Clay Concentration, which predicts the change in rheological property based on an additional clay concentration, which in turn is a linear function of the coarse particle concentration. The accuracy of this model further strengthens the belief that the coarse particle acts in a similar fashion to a floc. By means of a case study example the importance of selecting an appropriate model for design was illustrated. The Residual Clay Concentration method provided the most conservative results. This combined with its theoretical basis strengthens the models recommendation for use in design.
AFRIKAANSE OPSOMMING: As gevolg van ekonomiese en omgewings beperkinge word mynwese nywerhede onder toenemende druk geplaas om doeltreffende afvalstroom bestuur en operasie toe te pas. Beperkinge geplaas op water gebruik en afvalstroom area-groote ly tot hoër digthede en wyer partikel-grooteverspreidings van flodders vervoer na afval areas. Een manier om van die afval doeltreffend ontslae te raak en te berg is deur medeberging. In die metode word ‘n gekonsentreerde fyn flodder gebruik as draer van ‘n growwer partikel-fraksie. Dit ly tot ‘n hoër digtheid flodder, met verskeie voordele in beide die op – en afstroom prosesse. Beperkte navorsing is gedoen op die effek van growwe partikels op die nie-Newoniese rheolgiese eienskappe van hierdie flodders. Hierdie tekort aan informasie maak die effektiewe, betroubare bedryf en operasie van die sisteme meer ingewikkeld. Hierdie projek is daarheen gemik om ‘n beter begrip te ontwikkel met betrekking tot die meganismes betrokke in die byvoeging van growwe partikels aan ‘n fyn klei-agtige flodder draer; en om ‘n manier te voorsien wat die rheologiese eienskappe kan beraam. Verskeie eksperimente was ontwerp om die flodders (beide slegs Kaolien, en Kaoliengrowwe partikel mengsels) se rheologiese eienskappe te toets deur die gebruik van ‘n Couette-viskometer. Die Couette viskometer was gebruik om die dinamiese eienskappe (van grens-spanning, en plastiese viskositet) te meet. ‘n Vaan apparaat is gebruik om die eienskap van statiese grens-spanning te meet. Die flodders was voorberei in verskeie Kaolien konsentrasies met tru-osmosis water. Glas krale en twee tipes industriële sand is gebruik as die growwe fraksies. Al die growwe partikels het soortgelyke groottes gehad, maar het grootliks verskil in vorm. Die flodder pH en temperatuur lesings is deurentyd nagegaan. Toetse was aanvanklik gedoen op die klei-alleenlike flodders. Die gemete reologiese eienskappe van die flodders was herhaalbaar, en geen opmerkbare veranderinge van die eienskappe met betrekking tot tyd is gemeet nie. Die grens-spanning (beide statiese en dinamiese) en plastiese viskositeit is goed gekorrelleer met gevestigde verhoudinge. Growwe partikels is aan die klei-alleenlike flodders bygevoeg, en daarnae verwyder. Die oorblywende klei-alleenlike flodder het dieselfde gemete rheologiese eienskappe getoon as die oorspronklike klei-allenlike flodder. Die teenwoordigheid van growwe partikels het na ‘n toename van al die gamete rheologiese eienskappe gelei wat fisies baie soortgelyk is aan die byvoeging van klei tot ‘n klei-alleenlike flodder. Verder, met beide die klei-alleenlike en klei-growwe partikel flodders het ‘n konstante liniëre funksie tussen die statiese en dinamiese grens-spannings bestaan. Verskeie verhoudings uit die literatuur het goeie korrelasie bewerkstellig met die waargenome rheologie veranderinge. Hierdie empiriese en semi-empiriese modelle doen egter min om die megansimes betrokke in die toevoeging van growwe partikels te verduidelik. ‘n Nuwe korrelasie is voorgestel, naamlik die Residu Klei Konsentrasie. Hierdie model voorspel die verandering in reologiese eienskappe gebaseer op ‘n addisionele klei konsentrasie, wat ‘n liniëre funkise is van die growwe partikel konsentrasie. Die goeie korrelasie gesien met die model versterk die idée dat die growwe partikel in ‘n soortgelyke manier as ‘n flok gedra in die teenwoordigheid van ander flokke. Deur middel van ‘n tipiese industriële voorbeeld is die belangrikheid in die keuse van die regte korrelasie geillustreer. Die Residu Klei Konsentrasie metode het die mees konservatiewe resultate gelewer. Hierdie feit gekombineerd met die model se soliede teoreitiese beginsels versterk dit as voorgestelde korrelasie vir ontwerp.

The objective of this research work was to develop a methodology for experimentally estimating the interfacial properties at slag-metal interfaces. From previous experiments carried out in the division, it was decided to use surface active elements like sulfur or oxygen to trace any motion at the interface. For this purpose the following experimental investigations were carried out. Firstly the density of slag was estimated using the Archimedes Principle and the Sessile Drop technique. The density of the slag would give the molten slag height required for the surface active element to travel before reaching the slag-metal interface. Diffusivity measurements were uniquely designed in order to estimate the sulfur diffusion through slag media. It was for the first time that the chemical diffusivity was estimated from the concentration in the metal phase. Experiments carried out validated the models developed earlier. The density and diffusivity value of sulfur in the slag was used to accurately capture the time for sulfur to reach the slag-metal interface. The oscillations were identified by calculating the contact angle variations and the interfacial velocity was estimated from the change in the surface area of the liquid iron drop. The interfacial tension was estimated from the contact angles and the interfacial dilatational modulus was calculated. Based on cold model experiments using water as well as mercury, an equation of the dependence of the interfacial shear viscosity on the interfacial velocity and interfacial tension was established. This paved way for the estimation of the interfacial shear viscosity at the slag-metal interface. The present study is expected to have a strong impact on refining reactions in pyometallurgical industries where slag/metal interfaces play an important role. From a fundamental view point, this provides a deeper insight into interfacial phenomena and presents an experimental technique to quantify the same.
QC 20101130

With the progress of high alloy steelmaking processes, it is essential to minimize the loss of valuable metals, like chromium and vanadium during the decarburization process, from both economic as well as environmental view points. One unique technique to realize this aim, used in the present work, is the decarburization of high alloy steel grades using oxygen with CO2 in order to reduce the partial pressure of oxygen. In the present work, the investigation on the oxidation of iron-chromium and iron-vanadium molten alloys under CO2-O2 mixtures was carried out and presented in this dissertation. For oxidation study on Fe-Cr molten alloy with CO2-O2 mixtures, on the basis of thermodynamic analysis, energy balance calculation and modeling results, experimental validation in laboratory was carried out, and later on, the oxidation kinetics of Fe-Cr and Fe-Cr-C melts under controlled partial pressure of oxygen was investigated. Thermodynamics calculation and energy balance estimation demonstrated that, it is possible to use CO2 or CO2-O2 mixtures as decarburizers during EAF process and high initial carbon contents in the steel can be adopted at the beginning in order to reduce the cost. A generic model has been developed to describe the overall process kinetics prevailing in metallurgical reactors containing liquid metal and gas bubbles. This model is general and can be extended further to consider any gas liquid reactions in any chemical engineering reactor, and especially the metallurgical ones, like AOD. In the present dissertation, the model is applied in predicting the evolution of Cr and C contents in a Fe-C-Cr melt during injection of different O2-CO2 mixtures. The related simulation results illustrated that CO2 is efficient in Cr retention. In order to verify the modeling results, 1kg induction furnace experiments were carried out in the present laboratory. The results indicated that the predictions of the model are in good agreement with the experimental results. Meanwhile, the experimental results indicated that the Cr-losses can be significantly lowered by replacing the oxygen with CO2 in the injected gas, specifically for Fe-Cr-C melts with carbon levels higher than about 0.8 mass%. Subsequently, the oxidation kinetics of Fe-Cr and Fe-Cr-C melts was investigated under different CO2-O2 mixtures. It is indicated that, the oxidation rate is controlled by the chemical reaction at the initial stage and the reaction rate can be expressed as  at the Cr range of 11-21 mass% in the Fe-Cr melt. For oxidation study on Fe-V liquid alloy, the investigation of the oxidation kinetics was carried out under CO2-O2 mixtures, which is followed by the study on thermodynamic properties of vanadium containing slags. During oxidation of Fe-V melt, in the case of alloys with vanadium contents exceeding 10 mass%, there exists an incubation period before the chemical reactions prevail the process. In addition, the ‘incubation time’ increased with the increase of temperature and the vanadium content, whereas it decreased with the increase of oxygen partial pressure in the oxidant gas. High-temperature mass spectrometric method was used to determine the activity of the vanadium oxide in CaO-MgO-Al2O3-SiO2-V2O3 slags, whereas, the oxidation states of vanadium in the CaO-MgO-Al2O3-SiO2-VOxslag system was studied by XANES method. The results indicated that, higher basicities stabilize higher vanadium oxidation state, whereas, higher temperature stabilizes lower vanadium oxidation state. The present work, which was carried out within the ECO-STEELMAKING project funded by MISTRA via Jernkontoret is expected to lead to implementation of some modifications in high alloy steel production based on fundamental concepts towards more environment-friendly steel processing.

QC20100628

The objective of this research is to increase the understanding of the solidification behaviour of some industrially important wrought aluminium alloys. The investigation methods range from direct investigations of as-cast ingots to laboratory-scale techniques in which ingot casting is simulated. The methods span from directional solidification at different cooling rates to more fundamental and controlled techniques such as DTA and DSC. The microstructure characteristics of the castings have been investigated by optical and Scanning Electron microscopy. Hardness tests were used to evaluate the mechanical properties. The effects of adding alloying elements to 3XXX and 6XXX aluminium alloys have been studied with special focus on the effects of Zn, Cu, Si and Ti. These elements influence the strength and corrosion properties, which are important for the performance of final components of these alloys. Solidification studies of 0-5wt% Zn additions to 3003 alloys showed that the most important effect on the microstructure was noticed at 2.5 wt% Zn, where the structure was fine, and the hardness had a maximum. Si addition to a level of about 2% gave a finer structure, having a relatively large fraction of eutectic structure, however, it also gave a long solidification interval. The addition of small amounts of Cu, 0.35 and 1.0 wt%, showed a beneficial effect on the hardness. Differences have been observed in the ingot surface microstructures of 6xxx billets with different Mg and Si ratios. Excess Si compositions showed a coarser grain structure and more precipitations with possible negative implications for surface defect formation during DC casting. The comparison of alloys of different Ti content showed that the addition of titanium to a level of about 0.15 wt% gave a coarser grain structure than alloys with a normal Ti content for grain refinement, i.e. < 0.02 wt%, although a better corrosion resistance can be obtained at higher Ti contents. The larger grain size results in crack sensitivity during DC casting. A macroscopic etching technique was developed, based on a NaOH solution, and used in inclusion assessment along DC cast billets. Good quantitative data with respect to the size and spatial distribution of inclusions were obtained. The results from studied billets reveal a decreasing number of inclusions going from bottom to top, and the presence of a ring-shaped distribution of a large number of small defects in the beginning of the casting. The present study shows how composition modifications, i.e. additions of certain amounts of alloying elements to the 3xxx and 6xxx Al alloys, significantly change the microstructures of the materials, its castability, and consequently its mechanical properties
QC 20100901

In the iron production processes, sinters and pellets are mostly used as raw materials due to their consistency with respect to physical and chemical properties. However, natural iron ores, as mined, are rarely used directly as a feed material for iron processing. This is mainly due to the fact that they have small contents of iron and high concentration of impurities. Moreover, they swell and disintegrate during the descent in the furnace as well as due to low melting and softening temperatures. This work involves an investigation of the parameters that influence the use of natural iron ores as a direct feed material for iron production. Furthermore, it points out ways in which these can be mitigated so as to increase their direct use in iron production. Natural iron ore from Muko deposits in south-western Uganda was used in this study. Initially, characterisation of the physical and chemical properties was performed, to understand the natural composition of the ore. In addition, investigations were done to study the low temperature strength of the ore and its behaviour in the direct reduction zone. Also, simulations were performed with three models using the experimental data from the direct reduction experiments in order to determine the best model for predicting the direct reduction kinetics of natural iron ores. Chemical analyses showed that the Muko ore represents a high grade of hematite with an Fe content of 68% on average. The gangue content (SiO2+Al2O3) in 5 of the 6 investigated iron ore samples was < 4%, which is within the tolerable limits for the dominant iron production processes. The S and P contents were 0001-0.006% and 0.02-0.05% respectively. These can be reduced in the furnace without presenting major processing difficulties. With respect to the mechanical properties, the Muko ore was found to have a Tumble Index value of 88-93 wt%, an Abrasion Index value of 0.5-3.8 wt% and a Shatter Index value of 0.6-2.0 wt%. Therefore, the ore holds its form during the handling and charging processes. Under low temperature investigations, new parameters were discovered that influence the low temperature strength of iron oxides. It was discovered that the positioning of the samples in the reduction furnace together with the original weight (W0) of the samples, have a big influence on the low temperature strength of iron oxide. Higher mechanical degradation (MD) values were obtained in the top furnace reaction zone samples (3-25% at 500oC and 10-21% at 600oC). These were the samples that had the first contact with the reducing gas, as it was flowing through the furnace from top to bottom. Then, the MD values decreased till 5-16% at a 500oC temperature and 6-20% at a 600oC temperature in the middle and bottom reaction zones samples. It was found that the obtained difference between the MD values in the top and other zones can be more than 2 times, particularly at 500oC temperature. Furthermore, the MD values for samples with W0 < 5 g varied from 7-21% well as they decreased to 5-10% on average for samples with W0 ≥ 5 g. Moreover, the MD values for samples taken from the top reaction zone were larger than those from the middle and bottom zones. During direct reduction of the ores in a H2 and CO gas mixture with a ratio of 1.5 and a constant temperature, the reduction degree (RD) increased with a decreased flow rate until an optimum value was established. The RD also increased when the flow rate was kept constant and the temperature increased. An optimum range of 3-4g was found for natural iron ores, within which the highest RD values that are realised for all reduction conditions. In addition, the mechanical stability is greatly enhanced at RD values > 0.7. In the case of microstructure, it was observed that the original microstructure of the samples had no significant impact on the final RD value (only 2-4%). However, it significantly influenced the reduction rate and time of the DR process. The thermo-gravimetric data obtained from the reduction experiments was used to calculate the solid conversion rate. Three models: the Grain Model (GM), the Volumetric Model (VM) and the Random Pore Model (RPM), were used to estimate the reduction kinetics of natural iron ores. The random pore model (RPM) provided the best agreement with the obtained experimental results (r2 = 0.993-0.998). Furthermore, it gave a better prediction of the natural iron oxide conversion and thereby the reduction kinetics. The RPM model was used for the estimation of the effect of original microstructure and porosity of iron ore lumps on the parameters of the reduction process.

QC 20130531

Sustainable Technology Development in the Lake Victoria Region

Gli acciai inossidabili duplex presentano proprietà meccaniche, resistenza alla corrosione e tenacità superiori rispetto agli acciai inossidabili ferritici, austenitici e martensitici. L’ottimo bilanciamento delle loro proprietà è dovuto alla particolare microstruttura che è costituita da percentuali pressoché uguali di ferrite (δ) e di austenite (γ). L’austenite è responsabile della resistenza a corrosione e della tenacità, la ferrite fornisce l’elevata resistenza meccanica; grazie a questa combinazione di proprietà l’acciaio inossidabile duplex offre molti vantaggi rispetto agli acciai inossidabili monofasici. Gli acciai duplex possono sopportare condizioni di esercizio più gravose e possono essere utilizzati in svariati settori industriali come l’alimentare, il petrolchimico, l’oil & gas, la trasmissione di potenza ed in ambiente marino. La saldatura è il principale metodo per la fabbricazione delle strutture in acciaio inossidabile e molteplici sono i processi che possono essere utilizzati a tale scopo. Tuttavia, la saldatura determina inevitabilmente un cambiamento delle proprietà del materiale base nella zona interessata dell’alterazione microstrutturale. Nella zona di saldatura si può assistere alla perdita del giusto bilanciamento delle due principali fasi, nonché si può verificare la precipitazione di fasi intermetalliche complesse. I processi di saldatura applicabili agli acciai inossidabili duplex possono essere molteplici; in questo lavoro sono stati studiati gli effetti prodotti da alcune varianti del tradizionale processo TIG sulla saldatura dell’acciaio duplex UNS S32304 e dell’acciaio superduplex UNS S32570. In particolare, sono stati considerati gli effetti dell’aggiunta di polveri di nichel, dell’utilizzo di azoto come gas di processo e dell’esecuzione di uno specifico trattamento termico a valle della realizzazione dei giunti saldati. È stata successivamente effettuata una caratterizzazione microstrutturale al microscopio ottico metallografico (MO) e sono state utilizzate tecniche di analisi di immagine al fine di studiare l’evoluzione delle percentuali di fase nelle diverse zone dei giunti. Prove di trazione e prove di microdurezza hanno consentito di valutare i miglioramenti ottenuti sulle proprietà meccaniche. Inoltre, su campioni ricavati dai giunti stessi sono state eseguite prove elettrochimiche per studiare la resistenza a corrosione al variare delle condizioni di processo e del trattamento termico. I risultati ottenuti mostrano che, sia l’aggiunta delle polveri di nichel, sia l’utilizzo dell’azoto come gas di processo determinano un incremento delle proprietà meccaniche e microstrutturali dei giunti. Risulta tuttavia che il processo che consente il miglior incremento prestazionale è l’esecuzione del trattamento termico post saldatura, in quanto tende a ripristinare le percentuali delle fasi ferritica e austenitica a livelli confrontabili con quelli del metallo base. Nella seconda parte della tesi sono state studiate le proprietà di un riporto a base di polveri di nichel e particelle di carburo di tungsteno applicato mediante processo PTA (Plasma Transferred Arc) sulla superficie dell’acciaio da utensili D2, adatto per lavorazioni a freddo. Con un riporto superficiale di tale tipologia è possibile incrementare sia la qualità dell’acciaio sia aumentare la sua vita in esercizio in molte applicazioni industriali. Per ottenere una appropriata combinazione dei parametri di processo e per eseguire il numero minimo di prove, è stato utilizzato la metodologia DoE (Design of Experiment). Come parametri variabili sono stati considerati la corrente, la velocità di avanzamento e il preriscaldamento. Questi parametri sono importanti per ottenere un riporto finale con una appropriata geometria del cordone di saldatura e con buone proprietà metallurgiche. Tutti i campioni sono stati preparati per le necessarie caratterizzazioni metallografiche ed è stato considerato l’effetto dei parametri di processo sulla geometria del cordone di saldatura. Nel corso di ciascun esperimento sono stati misurati i parametri della geometria del cordone tra cui la diluizione, la penetrazione e il rinforzo. Le microstrutture e la distribuzione delle particelle di carburo di tungsteno sono stati analizzati sia al microscopio ottico metallografico (OM) sia al microscopio elettronico a scansione (SEM) dotato di microsonda EDS. Inoltre, sono state eseguite prove di microdurezza per valutare le proprietà meccaniche dei riporti realizzati. Infine, fra tutti gli esperimenti, è stato selezionato il campione con l’appropriata geometria del cordone e l’adeguata microstruttura. Nell’ultima parte della tesi si è cercato di valutare l’effetto dell’aggiunta di nanoparticelle di carburo di tungsteno sul comportamento meccanico e metallurgico dell’esistente polvere di nichel. Per questi campioni, in aggiunta a quelli sopra menzionati, sono stati eseguiti test di usura ed analisi mediante profilometro sulla superficie, al fine di confrontare e selezionare l’ottima percentuale di aggiunta di nanoparticelle. I dettagli degli esperimenti e dei metodi sono descritti negli abstracts relativi a ciascun capitolo.
Duplex stainless steels show high mechanical strength, corrosion resistance and toughness with respect to ferritic, austenitic and martensitic stainless steels. These favourable properties are largely conferred by the peculiar microstructure of the material, which contains roughly equal percentage of ferrite (δ) and austenite (γ). Austenite is responsible for toughness and corrosion resistance and ferrite provides high strength; thanks to this combination, duplex stainless steel has many advantages over monophase stainless steels. This makes them better able to withstand harsher conditions, and therefore they are more applicable in different sectors such as the food, petrochemical, oil and gas, marine and power industries. As it is clear, welding is the main method for fabrication of steel structures, which cause to change the base metal properties on that zone. In fusion zone, due to melting, the balance between ferrite and austenite is destroyed and the risk of precipitation of intermetallic phases increase. Different welding methods can be applied to duplex stainless steels for the production of several equipments and structures. Nevertheless, fusion welding processes, due to intrinsic properties, cause to destroy the equal percentage of ferrite and austenite phases in the fusion zone, which is responsible for their good engineering properties. In this study I tried to use different methods to to solve these problems especially for the duplex UNS S32304 and superduplex UNS S32570. Due to that, effect of addition of nickel powder, nitrogen gas, post weld heat treatment (PWHT) and combination of these methods were applied. After that, the joints were characterized by optical microscopy (OM) and the evolution of the phase percentages in the different zones was studied by means of the image analysis technique. Tensile and microhardness tests were carried out on the joints in order to evaluate the improvement of the mechanical properties. In addition electrochemical tests were applied on the samples to observe the corrosion resistance of the joints after modifications. The results showed that both the addition of nickel powder and nitrogen gas during the welding process cause to improve the welding characteristics but the effect of applying PWHT is better than addition of alloying elements especially in restoring the phase percentages close to the base metal. In another part of the thesis, a nickel-base powder mixed with tungsten carbide particles was applied by Plasma Transferred Arc welding (PTA) on the surface of the D2 cold work tool steel in order to improve the surface quality and to extend its life time during industrial applications. To obtain appropriate combination of hardfacing parameters and to run minimum number of tests, the Design of Experiment (DoE) method was applied. Current, travel speed and preheat were considered as variable parameters. These parameters are important to reach a final layer with an appropriate bead geometry, accompanied with good metallurgical properties. All samples were prepared for metallurgical investigations and effects of process parameters on the weld bead geometry were considered. For each run of experiment, weld bead geometry parameters including dilution, penetration and reinforcement were measured. Microstructures and the distribution of tungsten carbide particles after welding were analysed by Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) equipped with EDS microprobe. In addition, microhardness tests were performed to evaluate the mechanical properties of the weld bead layers. Finally, among all the experiments, the best sample with appropriate bead geometry and microstructure was selected. In the last part, I tried to study the effect of addition of tungsten carbide nanoparticles on the mechanical and metallurgical behavior of the existing nickel powder. For these samples, in addition to the above tests mentioned, wear test and surface profilometry analysis was performed for comparison and selecting optimum percentage of the addition of nanoparticles. Details of each experiments and methods are explained in the abstract of each chapter separately.

Ultrasonic metal welding (USMW) is a new and emerging concept used in the industries over the past twenty years and serving to the manufacturing sectors like aviation, medical, microelectronics, automotive and much more due to various hurdles faced by conventional fusion welding process. USMW is a clean and reliable technique in which the welding takes place with a high energy, no flux or filler metal needed, longer tool life and it takes very short time (less than one second) to weld materials in a perfect controllable environment with greater efficiency.To acquire high vibration amplitude in USMW, there is a necessity to design a welding system that consists of components like a booster and horn. The principal purpose of these parts is to amplify the input amplitude of vibration so that the energy transferred to the welding spot should be sufficient for creating a joint. In the present study, new type of booster and horn are proposed and modelled with adequate precision not only to produce high-quality welds but also to solve a lot of issues faced while designing these types of ultrasonic tools. The modal analysis module of finite element method (FEM) is used to analyze the effects of different step lengths and fillet radius on its natural frequency of 20 kHz, ensuring that these components will be in a resonating condition with other parts of the system. It is found that there were 1.11 % and 2.52 % errors in the length calculation of both parts. Similarly, 0.61 % error is obtained for both while calculating the magnification ratio. However, such low levels of errors may be considered to be insignificant. The dynamic analysis has also been performed to find out the stress distribution in both parts under cyclic loading conditions. Due to these cyclic loading conditions, the nodal regions (hot areas) are under highly stressed, and the relevant temperature field is consequently determined. The results obtained from the simulation, and experimental results were found to be close to each other and an error of 2% was noticed. Other welding components are also fabricated such as anvil, specimen-holder and backing plate for producing a satisfactory weld. Meanwhile, the complex mechanism behind the USMW has been addressed and modelled analytically. This model can predict the forces as well as temperatures those occur during the welding process and also explains the effects of various material properties and surface conditions on the weld behaviour. The experiments have been performed on the aluminium, copper, brass and stainless steel metal sheets with a number of different configurations, anvil designs, and surface conditions. The fundamental aspect of this study is to control the process parameters like vibration amplitude, weld pressure and weld time so that, an appreciable weld strength can be obtained. Thus, tensile shear and T-peel failure load studies suggest that increase in vibration amplitude means the increase of scrubbing action between the faying surfaces, resulting a better bonding strength. Similarly, increase in weld pressure also increases these weld failure loads and reach a peak value at a particular pressure. But, subsequently, these failure loads decrease due to suppression of relative motion between sheets and initiation of cracks. Excessive weld time also causes cracks around the weld spot. Likewise, if the thickness of the sheets increased, weld strengths are also increased due to absorption of more amount of ultrasonic energy. Moreover, the highest weld interface temperatures and weld areas are observed at the end of weld time because of the larger plastic deformation at the mating surfaces. For all the experiments, first anvil design shows maximum failure loads due to its non-cutting width and angle of knurls. Likewise, on the increase of surface roughness, the tensile shear, and T-peel failure loads decrease. It is found that, in lubricating condition, the highest failure loads are obtained. Furthermore, the polynomial regression, artificial neural network (ANN) and adaptive neuro-fuzzy inference system (ANFIS) methods are developed and compared for each performance measure so that the whole welding process can be accurately described by a best predictive model. A welding mechanics based numerical model has been developed which can predict the temperatures during USMW process for various surface conditions. For all the experimental investigations, the predictive results show good agreement with the experimental values. In addition to it, acoustic softening during ultrasonic welding is found to very significant for the reduction in yield strength of the weld material up to 95 %. It is seen that the quality of welding depends on the material properties, process parameters, and thickness of the workpiece. The present investigation also explains in details the effect of process parameters on the responses through metallurgical analysis. A quality lobe of welding like “under weld”, “good weld” and “over weld” is proposed after observing the fractured samples in optical microscopy and scanning electron microscopy (SEM). Meantime, energy dispersive spectroscopy (EDS) and X- ray diffraction (XRD) analyses are also used to reveal the thickness of interatomic diffusion and IMCs along the weld interface.

In recent years, the complex equipment/systems require a variety of materials with contradictory properties to improve performance and to reduce cost. This has resulted in increased demands for techniques to weld dissimilar materials and for use in large scale industrial production. Particularly the joining of AISI 304 stainless steel and commercially pure copper dissimilar metal couple is extensively employed for various industrial applications, i.e., in the field of electrical and electronics, cryogenics, power generation and transmission, food processing plants, neutron absorbent coolant system, automotive turbo compressor fan and shaft joints, etc. The main purpose of this combination is to utilize the high strength of the steel and high electrical conductivity of copper simultaneously with significant corrosion resistance. The objectives of the present research work are to characterize and determine the weldability of AISI 304 SS and CP copper dissimilar metal couples without use of any kind of filler materials based on experimental, numerical simulation and statistical modeling approaches. The investigations are carried out by three different types of fusion welding processes such as continuous wave CO2 laser, pulsed wave TIG arc and pulsed wave Nd:YAG laser. The experimental work aimed to investigate the welding induces microstructure, microhardness, residual stress, compositional analysis and tensile properties of butt joint of SS-Cu weldments under different welding conditions separately. The numerical simulation (using ANSYS 15.0 FLUENT® environment) including weld pool shape and temperature obtained during welding have been investigated for laser welding and validate with the experimental results. The aim of statistical modeling is to predict and optimize the SS-Cu weldments in industrial application through desired weld structure with proper microstructure and minimum defects. The design of experiments (DOE) approaches are implemented to design the experiments, develop mathematical models and optimize the welding operations with proper parametric settings. Although joining of dissimilar metals is a tough task due to their mismatch in properties like physical, chemical thermal, etc., the experimental results showed that a successful weldment of SS-Cu butt joint has been achieved by all three welding processes. The HAZ in CO2 laser welded specimens are found minimum i.e. 10 μm compared to other welding processes, and it is narrower for SS side in comparison to Cu side. The microhardness in the weld zone found to be more than the base materials. The numerical simulation results shows a good agreement with the experimental results in terms of shape of the weld pool and temperature profile for CO2 laser and Nd:YAG laser respectively. A greater fitness of the Taguchi orthogonal array design model for all welding processes, confirms from the corresponding ANOVA table, probability and residual plots. In pulsed TIG arc welding, the formation of weld craters at the end of the weld is resolved by varying ramp down time experimentally. Welding approaches like proper selection of input process parameters and preheating of welding specimens are successfully applied for improvement of weld strength as well as penetration depth during pulsed wave Nd:YAG laser welding processes.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, 2015.
Excavations conducted at Thaba Nkulu, an Early Farming Community homestead with associated metal working debris, led to the recovery of iron slag, tuyères, furnace lining, iron ore, copper artefacts and iron artefacts. Using the material recovered, this dissertation identified chemical signatures for metal artefacts and metal smelting and smithing associated material. This was achieved through the use of a combination of X-ray fluorescence spectrometry (XRF) and Scanning Electron Microscopy coupled with Energy-Dispersive X-Ray Spectroscopy (SEM-EDX). The artefacts recovered were analysed, and 3 sets of possible chemical signatures were recorded.