The aim of the project was to establish the rate and mechanisms of solid stage reduction of titania and ilmenite ores. The project examined carbothermal reduction of titania and various types of ilmenite ores in argon, helium, hydrogen, and their mixtures. Effect of CO in the gas atmosphere on reduction behavior of titania and primary ilmenite ore was also studied. Isothermal and non-isothermal reduction experiments were conducted in a fixed bed reactor in the high temperature furnace in the temperature range up to 1500oC. The off-gas composition in the reduction process was monitored by a CO/CO2/CH4 infrared analyser. The extent of reduction was calculated using data on gas composition and LECO oxygen analysis. Phase composition and morphology of reduced samples were studied using XRD, SEM and optical microscopy. The major findings of this project are as follows: • The reduction of titania to titanium oxycarbide occurred in the following sequence: TiO2 → Ti5O9 → Ti4O7 → Ti3O5 → Ti2O3 → (TiO-TiC) solid solution. • Carbothermal reduction of ilmenite concentrates proceeded in two main stages. In the first stage pseudorutile and ilmenite were reduced to metallic iron and titania. Second stage involved the reduction of titania to titanium oxycarbide. • Rate and degree of reduction of titania and ilmenite concentrates increased with increasing temperature. • Reduction rate of titania and ilmenite concentrates was faster in hydrogen than in helium and argon. The difference in the reduction behavior in helium and argon was insignificant; reduction rate of ilmenite was slightly faster in helium than in argon. • High rate of reduction of titania and ilmenite in hydrogen was attributed to formation of methane which facilitated mass transfer of carbon from graphite to oxide. Hydrogen was also directly involved in reduction of titania and ilmenite concentrates; hydrogen reduced pseudorutile to iron and titania. Titania was further reduced to titanium oxycarbide by carbon through methane. • Increased gas flow rate slightly improved the reduction rate in hydrogen and suppressed the reduction in inert gases. • Addition of CO to hydrogen and inert gases above 3 vol% suppressed the reduction process.

The aim of the project was to establish the rate and mechanisms of solid stage reduction of titania and ilmenite ores. The project examined carbothermal reduction of titania and various types of ilmenite ores in argon, helium, hydrogen, and their mixtures. Effect of CO in the gas atmosphere on reduction behavior of titania and primary ilmenite ore was also studied. Isothermal and non-isothermal reduction experiments were conducted in a fixed bed reactor in the high temperature furnace in the temperature range up to 1500oC. The off-gas composition in the reduction process was monitored by a CO/CO2/CH4 infrared analyser. The extent of reduction was calculated using data on gas composition and LECO oxygen analysis. Phase composition and morphology of reduced samples were studied using XRD, SEM and optical microscopy. The major findings of this project are as follows: • The reduction of titania to titanium oxycarbide occurred in the following sequence: TiO2 → Ti5O9 → Ti4O7 → Ti3O5 → Ti2O3 → (TiO-TiC) solid solution. • Carbothermal reduction of ilmenite concentrates proceeded in two main stages. In the first stage pseudorutile and ilmenite were reduced to metallic iron and titania. Second stage involved the reduction of titania to titanium oxycarbide. • Rate and degree of reduction of titania and ilmenite concentrates increased with increasing temperature. • Reduction rate of titania and ilmenite concentrates was faster in hydrogen than in helium and argon. The difference in the reduction behavior in helium and argon was insignificant; reduction rate of ilmenite was slightly faster in helium than in argon. • High rate of reduction of titania and ilmenite in hydrogen was attributed to formation of methane which facilitated mass transfer of carbon from graphite to oxide. Hydrogen was also directly involved in reduction of titania and ilmenite concentrates; hydrogen reduced pseudorutile to iron and titania. Titania was further reduced to titanium oxycarbide by carbon through methane. • Increased gas flow rate slightly improved the reduction rate in hydrogen and suppressed the reduction in inert gases. • Addition of CO to hydrogen and inert gases above 3 vol% suppressed the reduction process.

This research deals with the synthesis and characterization of titanium diboride (TiB2) from novel carbon coated precursors. This work provides information on using different boron sources and their effect on the resulting powders of TiB2.The process has two steps in which the oxide powders were first coated with carbon by cracking of a hydrocarbon gas, propylene (C3H6) and then, mixed with boron carbide and boric acid powders in a stoichiometric ratio. These precursors were treated at temperatures in the range of 1200-1400° C for 2 h in flowing Argon atmosphere to synthesize TiB2.The process utilizes a carbothermic reduction reaction of novel carbon coated precursor that has potential of producing high-quality powders (sub-micrometer and high purity). Single phase TiB2 powders produced, were compared with commercially available titanium diboride using X-ray diffraction and Transmission electron microscopy obtained from boron carbide and boric acid containing carbon coated precursor.

Boron carbide is produced in a heat resistance furnace using boric oxide and petroleum coke as the raw materials. In this process, a large current is passed through the graphite rod located at the center of the cylindrical furnace, which is surrounded by the coke and boron oxide mixture. Heat generated due to resistance heating is responsible for the reaction of boron oxide with coke which results in the formation of boron carbide. The whole process is highly energy intensive and inefficient in terms of the production of boron carbide. Only 15% charge gets converted into boron carbide. The aim of the present work is to develop a mathematical model for this batch process and validate the model with experiments and to optimize the operating parameters to increase the productivity. To mathematically model the process and understand the influence of various operating parameters on the productivity, existing simple one-dimensional (1-D) mathematical model in radial direction is modified first. Two-dimensional (2-D) model can represent the process better; therefore in second stage of the project a 2-D mathematical model is also developed. For both, 1-D and 2-D models, coupled heat and mass balance equations are solved using finite volume technique. Both the models have been tested for time step and grid size independency. The kinetics of the reaction is represented using nucleation growth mechanism. Conduction, convection and radiation terms are considered in the formulation of heat transfer equation. Fraction of boron carbide formed and temperature profiles in the radial direction are obtained computationally. Experiments were conducted on a previously developed experimental setup consisting of heat resistance furnace, a power supply unit and electrode cooling device. The heating furnace is made of stainless steel body with high temperature ceramic wool insulation. In order to validate the mathematical model, experiments are performed in various conditions. Temperatures are measured at various locations in the furnace and samples are collected from the various locations (both in radial and angular directions) in the furnace for chemical analysis. Also, many experimental data are used from the previous work to validate the computed results. For temperatures measurement, pyrometer, C, B and K type thermocouple were used. It is observed that results obtained from both the models (1-D and 2-D) are in reasonable agreement with the experimental results. Once the models are validated with the experiments, sensitivity analysis of various parameters such as power supply, initial percentage of B4C in the charge, composition of the charge, and various modes of power supply, on the process is performed. It is found that linear power supply mode, presence of B4C in the initial mixture and increase in power supply give better productivity (fraction reacted). In order to have more confidence in the developed models, the parameters of one the computed results in the sensitivity analysis parameters are chosen (in present case, linear power supply is chosen) to perform the experiment. Results obtained from the experiment performed under the same simulated conditions as computed results are found in excellent match with each other.

ZnO nanowires are a promising material with great semiconductor properties. ZnO nanowires were prepared by carbothermal reduction and vapor-liquid-solid growth mechanism. Altering a variety of parameters ranging from mole to mole ratio of ZnO to C all the way to gas flow rate was examined. The nanowires were then characterized and their morphology examined under a SEM to observe what effect the parameter had on the morphology of the nanowires. From the experiments and the parameters tested it was observed that in order to produce the highest quality straight nanowires one should use a mole to mole ratio of ZnO to C graphite of 1 to 3. With a dwell temperature and time of 900 °C for 3 hours. A gold seed catalyst of 4nm and a gas flow rate of 50 to 100sccm of Ar provides the straightest nanowires. Understanding the effect of each parameter on the morphology of ZnO nanowires is vital for the current research. This will only lead to further the research and provide a better understanding of the growth mechanism of these wires and how the production of specific wires with certain morphologic features and characteristics can be achieved.

Nanocrystalline beta-silicon carbide (ß-SiC) was synthesized at relatively low temperature (<1300C) by carbothermal reduction (CTR) reaction in fine scale carbon/silica mixtures. The fine scale mixing of the reactants (i.e., carbon and silica) was achieved by solution-based processing and subsequent heat treatment. The mechanism of the CTR reaction in the current system was investigated from different aspects. The condensates of the volatile species generated during the CTR reaction was collected and analyzed. The results supported previous investigations which suggested that the CTR reaction is a multi-step process that involves silicon monoxide (SiO) vapor as a reaction intermediate. The kinetics of the CTR reaction was investigated by isothermal weight loss study and by the study which determined the amount of SiC formed via quantitative X- ray diffraction (QXRD) analysis. The results of kinetic study were consistent with the "shrinking-core" model, in which the reaction between SiO vapor and carbon at the carbon surface to produce SiC is the rate-controlling step. In addition, several techniques, including XRD, gas adsorption analysis, laser diffraction particle size analysis, SEM, TEM, etc., had been used to study the structural evolutions of the reaction product of CTR. It was demonstrated that the evolutions of product structure characteristics such as crystallite size, specific surface area, specific pore volume, pore size distribution, particle size distribution, and powder morphology, etc. were consistent with each other and provided support to the reaction mechanism proposed.

Durant ce travail, la réactivité des dioxydes du groupe IVb (TiO2, ZrO2, HfO2) en contact avec du carbone turbostratique a été étudiée afin de comprendre les mécanismes réactionnels de la réduction carbothermique. Cette voie de synthèse a également permis d’obtenir des phases oxycarbures sous forme pulvérulente afin d’étudier les différents domaines de stabilité des solutions solides en fonction de la température de traitement thermique. L’ajout d’oxygène à la structure cristalline des carbures modifie le comportement de ces matériaux au frittage ainsi que leurs propriétés macroscopiques. Par conséquent, la détermination des limites des différentes solutions solides requiert l’utilisation d’une méthodologie précise. En couplant les différentes techniques de caractérisation (analyse chimique élémentaire, DRX, dosage de phases, MET), les compositions des phases oxycarbures synthésisées ont ainsi pu être déterminées. Afin de compléter cette étude, la réactivité de monolithes de carbure de titane en contact avec du dioxyde de titane a été étudiée lors de traitements thermiques de recuit sous charge en atmosphère confinée. L’identification des phases en équilibre constituent des données diagrammatiques nécessaires aux première tentatives de modélisation thermodynamique des diagrammes de phases ternaires Me-C-O (ou Me = Ti, Zr, Hf) par la méthode semi-empirique CALPHAD. / During this work, the reactivity of group IVb dioxides (TiO2, ZrO2, HfO2) in contact with turbostractic carbon has been investigated in order to understand the reactional mechanisms of the carbothermal reduction. This way of synthesis has also allowed us to obtain oxycarbides phases in powder form to study the different stability domains of solids solutions with respect to the temperature of heat treatment. The addition of oxygen within the crystalline structure modifies the sintering behaviour of these materials and also their macroscopic properties. Consequently, the determination of solid solution boundaries requires an accurate methodology. A broad panoply of characterization techniques are coupled (Elemental analysis, XRD, Quantification of phases, TEM) to determine the compositions of oxycarbide phases. In order to complete this study, the reactivity of titanium carbide monoliths in contact with titanium dioxide has been studied during heat treatments of annealing under pressure in confined atmosphere. The identification of phases in equilibrium constitutes diagrammatic data which are necessary for the preliminary attempts of thermodynamic modeling of ternary phases diagrams Me-C-O (where Me = Ti, Zr, Hf) using the semi-empirical CALPHAD method.

Zirconium carbide (ZrC) is a high modulus ceramic with an ultra-high melting temperature and, consequently, is capable of withstanding extreme environments. Carbon-carbon composites (CCCs) are important structural materials in future hypersonic aircraft; however, these materials may be susceptible to degradation when exposed to elevated temperatures during extreme velocities. At speeds of exceeding Mach 5, intense heating of leading edges of the aircraft triggers rapid oxidation of carbon in CCCs resulting in degradation of the structure and probable failure. Environmental/thermal barrier coatings (EBC/TBC) are employed to protect airfoil structures from extreme conditions. Yttria stabilized zirconia (YSZ) is a well-known EBC/TBC material currently used to protect metallic turbine blades and other aerospace structures. In this work, 3 mol% YSZ has been studied as a potential EBC/TBC on CCCs. However, YSZ is an oxygen conductor and may not sufficiently slow the oxidation of the underlying CCC. Under appropriate conditions, ZrC can form at the interface between CCC and YSZ. Because ZrC is a poor oxygen ion conductor in addition to its stability at high temperatures, it can reduce the oxygen transport to the CCC and thus increase the service lifetime of the structure. This dissertation investigates the thermodynamics and kinetics of the YSZ/ZrC/CCC system and the resulting structural changes across multiple size scales. A series of experiments were conducted to understand the mechanisms and species involved in the carbothermal reduction of ZrO2 to form ZrC. 3 mol% YSZ and graphite powders were uniaxially pressed into pellets and reacted in a graphite (C) furnace. Rietveld x-ray diffraction phase quantification determined that greater fractions of ZrC were formed when carbon was the majority mobile species. These results were validated by modeling the process thermochemically and were confirmed with additional experiments. Measurements were conducted to examine the effect of carbothermal reduction on the bond lengths in YSZ and ZrC. Subsequent extended x-ray absorption fine structure (EXAFS) measurements and calculations showed Zr-O, Zr-C and Zr-Zr bond lengths to be unchanged after carbothermal reduction. Energy dispersive spectroscopy (EDS) line scan and mapping were carried out on carbothermaly reduced 3 mol% YSZ and 10 mol% YSZ powders. Results revealed Y2O3 stabilizer forming agglomerates with a very low solubility in ZrC.

The aim of the project was to establish rate and mechanisms of solid state reduction of manganese ores. The project studied carbothermal reduction of manganese oxide MnO, two Groote Eylandt (Australian) and Wessels (South African) manganese ores in hydrogen, helium and argon atmospheres at temperatures up to 1400C for MnO and 1200C for manganese ores. Experiments were conducted in the fixed bed reactor with on-line off-gas analysis. The major findings are as follows. ?? Rate and degree of reduction of MnO and ores increased with increasing temperature. ?? Reduction of MnO and manganese ores at temperatures up to 1200C was faster in helium than in argon, and much faster in hydrogen than in helium. The difference in MnO reduction in hydrogen and helium decreased with increasing temperature to 1400C. ?? Addition of up to 7 vol% of carbon monoxide to hydrogen had no effect on MnO reduction at 1200C. ?? In the process of carbothermal reduction of ores in hydrogen at 1200C, silica was reduced. ?? Reduction of both GE ores was slower than of Wessels ore. This was attributed to high content of iron oxide in the Wessels ore. ?? Carbon content in the graphite-ore mixture had a strong effect on phases formed in the process of reduction; thus, in the reduction of Wessels ore with 12-16 wt% C, a-Mn and Mn23C6 were formed; when carbon content was above 20 wt%, oxides were reduced to carbide (Mn,Fe)7C3. ?? Kinetic analysis showed that mass transfer of intermediate CO2 from oxide to graphite in carbothermal reduction in inert atmosphere was a contributing factor in the rate control. ?? High rate of reduction of manganese oxide in hydrogen was attributed to formation of methane which facilitated mass transfer of carbon from graphite to oxide. Hydrogen was also directly involved in reduction of manganese ore reducing iron oxides to metallic iron and higher manganese oxides to MnO. Reduction of Wessels and Groote Eyland Premium Fines ores in the solid state is feasible at temperatures up to 1200C; while temperature for solid state reduction of Groote Eyland Premium Sands is limited by 1100C.

The aim of the project was to establish rate and mechanisms of solid state reduction of manganese ores. The project studied carbothermal reduction of manganese oxide MnO, two Groote Eylandt (Australian) and Wessels (South African) manganese ores in hydrogen, helium and argon atmospheres at temperatures up to 1400C for MnO and 1200C for manganese ores. Experiments were conducted in the fixed bed reactor with on-line off-gas analysis. The major findings are as follows. ?? Rate and degree of reduction of MnO and ores increased with increasing temperature. ?? Reduction of MnO and manganese ores at temperatures up to 1200C was faster in helium than in argon, and much faster in hydrogen than in helium. The difference in MnO reduction in hydrogen and helium decreased with increasing temperature to 1400C. ?? Addition of up to 7 vol% of carbon monoxide to hydrogen had no effect on MnO reduction at 1200C. ?? In the process of carbothermal reduction of ores in hydrogen at 1200C, silica was reduced. ?? Reduction of both GE ores was slower than of Wessels ore. This was attributed to high content of iron oxide in the Wessels ore. ?? Carbon content in the graphite-ore mixture had a strong effect on phases formed in the process of reduction; thus, in the reduction of Wessels ore with 12-16 wt% C, a-Mn and Mn23C6 were formed; when carbon content was above 20 wt%, oxides were reduced to carbide (Mn,Fe)7C3. ?? Kinetic analysis showed that mass transfer of intermediate CO2 from oxide to graphite in carbothermal reduction in inert atmosphere was a contributing factor in the rate control. ?? High rate of reduction of manganese oxide in hydrogen was attributed to formation of methane which facilitated mass transfer of carbon from graphite to oxide. Hydrogen was also directly involved in reduction of manganese ore reducing iron oxides to metallic iron and higher manganese oxides to MnO. Reduction of Wessels and Groote Eyland Premium Fines ores in the solid state is feasible at temperatures up to 1200C; while temperature for solid state reduction of Groote Eyland Premium Sands is limited by 1100C.