TiB2 particle reinforced aluminum matrix composites have been the subject of several investigations. An M.Sc. thesis on production of TiB2 reinforced aluminum composites by reaction between liquid aluminum and B2O3 and TiO2 dissolved in cryolite has been completed in this Department in 2005. This study is a continuation of the mentioned M.Sc.study. Composition of the starting cryolite-B2O3-TiO2 system, temperature and time were used as experimental variables. The resulting composite was squeeze cast and its microstructure was examined. Mechanical properties of the produced composite were measured and how mechanical properties of the composite vary with TiB2 content of the composite was determined.

The aim of this thesis study was to extract nickel and cobalt from Sivrihisar limonitic nickel laterite ore by high pressure acid leaching (HPAL) method under most economical operating parameters. Optimizing the conditions to yield a saleable quality mixed hydroxide product from the pregnant leach solution (PLS) was also investigated. To extract high amounts of nickel and cobalt from the laterite matrix / leaching duration, leaching temperature and sulfuric acid/ore ratio were studied at fixed conditions of -850 &micro / limonitic ore particle size and 40% solids concentration. The Sivrihisar limonitic nickel laterite ore was found to be readily leachable. It was found that 95.4% of Ni and 91.5% of Co were extracted at the optimized conditions of 235oC, 0.23 acid/ore ratio in 60 minutes. The real pregnant leach solution produced at the optimized conditions of HPAL was purified in two iron removal stages under the determined optimum conditions. Nearly all of the Al and Cr were removed from the PLS in the two stages of iron removal. Then, nickel and cobalt were taken out from the PLS in the form of mixed hydroxide precipitates (MHP) in two stages. A MHP 1 product containing 33.41 wt.% Ni, 2.93 wt.% Co was obtained with a Mn contamination of 3.69 wt.% at the optimized conditions of pH=7, 50oC and 60 minutes. The MHP 1 product was also contaminated with Fe (2.83 wt.%) since it could not be completely removed from the PLS without the critical losses of nickel and cobalt during the two iron removal stages.

In recent years, the risks created by the import of energy on the security of energy supply has encouraged countries to utilize local resources to a greater extend, and for many countries including Turkey coal is at the top of the local resources. However, it is not sufficient for countries to have an energy resource itself. Intens competition in today&#039 / s globalized system requires the resources to be produced and utilized in the most economical manner. The supply of the resources to the market in a competitive way is possible by employing an efficient operation, which is then possible only through the business units producing these resources working efficiently. In this study, the efficiencies of the eight establishments of the Turkish Coal Enterprises (TKI) between 2006 to 2009 were analyzed by using Data Envelopment Analysis (DEA), Super Efficiency (SE) and Malmquist Total Factor Productivity Index (MI) methodologies. For the analyses, three output oriented models were constructed and used: Production Efficiency, Revenue Efficiency and Work Safety Efficiency models. In determining the input and output data used in the analyses, it was benefited from similar studies searched in the literature, knowledge of business and economics and a series of brainstorming of the expert panel consisting of ten high level representatives of the public and private lignite mining companies as well as that of the Turkish Ministry of Energy and Natural Resources. As a part of the analyses, first the production and revenue efficiencies of the establishments were analyzed by using Constant Return to Scale (CRS) and Variable Return to Scale (VRS) methods of DEA. Within this context, efficient and inefficient establishments for the years between 2006 to 2009, and benchmarks for inefficient establishments to move to becoming efficient were determined. Furthermore, for the production and revenue efficiency models, the target values and improvement potentials for the inefficient establishments in CRS analyses to becoming more efficient were calculated by using benchmarks tables and 2009 realized values of inputs and outputs. Second, the efficiency rankings of the efficient establishments among themselves between 2006 to 2009 were determined by using SE methodology. Third, to provide the dynamic analysis of the development of the establishments&#039 / s efficiency levels in time, the changes of production, revenue and work safety efficiencies of the establishments between 2006 to 2009 were analyzed using the Malmquist Index (MI) methodology. MI analyses included the analysis of the efficiencies in four efficiency components (Technical, Technological, Pure and Scale efficiencies) as well as the calculation of the Total Factor Productivity Indexes of the establishments.

In this study, prealloyed austenitic stainless steel and premixed soft magnetic Ni-Fe permalloy compacts were consolidated through microwave and conventional sintering routes at combinations of various sintering temperatures and compaction pressures. Sintered alloys were characterized in terms of their densification, microstructural evolution as well as mechanical and magnetic properties. The effect of sintering method in terms of the applied sintering parameters on the final properties of the compacts were investigated in a comparative manner. It was determined that microwave sintered permalloys are superior compared to their conventionally sintered counterparts in densification response, microstructural characteristics such as pore shape and distribution as well as mechanical properties for both austenitic stainless steel and permalloy compacts. However, permeability of the microwave sintered permalloys was inferior to their conventionally sintered counterparts in some cases due to microstructural refinement associated with microwave sintering route.

ABSTRACT AN INVESTIGATION OF THE MICROSTRUCTURAL AND MECHANICAL PROPERTIES OF TRI-CALCIUM PHOSPHATES DOPED WITH ALUMINUM AND FLUORIDE IONS Tahmasebifar, Aydin M. Sc., Department of Engineering Sciences Supervisor: Assoc. Prof. Dr. Zafer Evis August / 88 Pages The aim of this study was to investigate the microstructure and mechanical properties of pure tricalcium phosphate (TCP) and tricalcium phosphates doped with aluminum (Al3+) and fluoride (F-) ions at different compositions. TCP was synthesized via precipitation method and sintered at 1100

Carbothermic production of hexagonal BN by using boric acid and ground colemanite mined from Bigadi&ccedil / Region in Turkey was investigated by subjecting pellets prepared from B2O3, activated carbon and colemanite mixtures to nitrogen gas at 1500&deg / C. Similar to CaCO3 addition, colemanite addition to the B2O3-C mixtures resulted in higher amounts of h-BN in the final products. As a result of the experiments conducted with colemanite and CaCO3 additions providing the same quantity of CaO to the initial mixtures, similar amounts of hexagonal BN in the reaction products were observed. As a result of the experiments conducted with different compositions of colemanite- B2O3- C mixtures, 5 wt % colemanite addition was determined to be the optimum composition giving the highest amount of hexagonal BN in the reaction products. Increasing duration of the experiments increased the amount and particle size of h-BN formed in the products. Optimum amount of colemanite addition resulted in higher amounts and coarser particles of h-BN in the products than the optimum amounts of CaCO3 addition.

In Diesel engine blocks properties such as tensile strength, heat conductivity, sound damping, engine vibration and noise are strongly influenced by graphite shape and volume percent in the matrix microstructure. In this study, the engine blocks were produced at ELBA Basin&ccedil / li D&ouml / k&uuml / m Od&ouml / ksan Cast iron foundry in Osmaneli Turkey by performing casting into furan resin sand and preparing cast iron liquid alloy in induction furnace that were treated with Mg by using ladle method. The main purpose of this study is to achive 0 &ndash / 25% volume nodularity and remaining is compacted graphite in the produced engine blocks. The shape and volume percent of graphite particles were characterized by an image analyze system. In the first part of this work, after the diesel engine blocks were produced at ELBA Basin&ccedil / li D&ouml / k&uuml / m Od&ouml / ksan Cast iron foundry in Osmaneli Turkey, the blocks were cut and samples were obtained from 14 different thicknesses of diesel engine blocks. Afterwards, the samples were examined under optical microscope, Soif XJP-6A. The nodularity and compacted graphite values were obtained numerically with the help of Materials Plus image analyzer systems, which is attached to the optical microscope. v In the second part of the study, the diesel engine blocks which are produced at Od&ouml / ksan were examined by ultrasonic test that was done by using USM 35 flaw detector test machine. Solidification &ndash / time and temperature &ndash / time simulations were also done by using NovaCast NovaFlow simulation code. Finally mathematical formulas for 13 different thickness of diesel engine blocks were obtained by using excel linest code. The compacted graphite volume percent observed at different sections of the diesel engine blocks were found to be a function of cooling rate and chemical composition. Best results were obtained when chemical Mg/S ratio was approximately 1 and C.E.V. was between 4.40 &ndash / 4.50.

High Pressure Die Casting (HPDC) is low-cost technique for the mass production of complex, non-ferrous parts. Despite its benefits such as dimensional accuracy, surface quality and high production rate / some mechanical drawbacks limit use of HPDC in production of critical parts especially under dynamical loads. This study aims to improve impact resistance and surface hardness of die cast parts by means of tool steel inserts. These inserts act as a barrier between the impactor and die casting alloy, in order to avoid surface deformation and reduce stress localization which leads crack formation. Except the impact surface, whole insert is embedded into the die casting alloy by placing them on specially machined die casting molds prior to the metal injection. The mentioned method was evaluated by mechanical test and micro-examinations which were applied on AISI D2 tool steel inserted A518.0, A413.2 and Zamak5 alloy samples. To see the effect of inserts on energy absorbance under single destructive loads, both monolithic (conventional) and inserted (produced by mentioned technique) samples were subjected to Charpy impact test. In order to observe its behavior under non-destructive, cyclic, low velocity impacts / a dedicated real rifle part was produced by this method and tested in the real service loads. Explicit Finite Elemental Analysis was also carried out to understand how the inserts increases the energy absorbance and protect the die cast body by simulating both destructive and non-destructive impact loads. In addition to these, micro-examinations were also conducted especially on insert-die casting alloy interface for chemical and physical interactions, defects and stability. In regards of experimental findings, mechanical feasibility of the method was achieved. It was proved that steel inserts improve energy absorbance, stress distribution and impact-surface hardness of die cast products.

Magnesium (Mg) thin films with various thicknesses ranging from 50 to 1000 nm capped with nominally 20 nm Palladium (Pd) were prepared by a thermal evaporation unit. A total of 25 glass substrates were used in each experiment. The unit had a rotatable macro shutter, rectangular in shape, rotation axes opposite to the Mg source, which allowed controlled exposure of the substrates. Thin films of 50, 100, 150, 200, 300, 400, 500, 600, 800 nm and 1000 nm were produced in a single experiment. Hydrogenation and dehydrogenation of the films were examined using a gas loading chamber which allowed in-situ resistance measurement. Samples were hydrogenated isochronally up to 453 K with a heating rate of 1.5 K/min. Samples cooled to room temperature were subjected to dehydrogenation test. The chamber was taken under vacuum (~10-2 mbar) and the sample was heated up to 453 K at a rate of 1.5 K/min. The results showed that the hydrogenation and dehydrogenation temperatures correlate with the film thickness, thinner films reacting with hydrogen at low temperatures. While 200 nm thin film hydrogenated at 420 K and desorbed it at 423 K, 50 nm thin film hydrogenated at room temperature and desorbed it at 405 K. Thicker films needed higher temperatures to react with hydrogen. It is concluded that films thinner than 200 nm react fully with hydrogen / while a considerable portion of the thicker films remain unreacted. Significance of this is discussed with reference to the design of hydrogen storage systems based on thin films or nanoparticles.

Albite (Na-feldspar) and orthoclase (K-feldspar) are the major feldspar minerals used in the production of glass and ceramics. They are found together with impurities like biotite, muscovite, quartz and rutile which are not desired for ceramics and glass industries. Therefore, these have to be removed to make the ore available for industrial use. In order to shed light on the actual feldspar ores, in this study / the flotation characteristics of albite, biotite, muscovite, orthoclase, quartz and rutile were investigated separately in their pure forms. In the investigation, the electrokinetic potential measurements and micro-flotation studies have been carried out to get information about their flotation characteristics under the effect of three different collectors, Aero 704, Aero 3000C and Aero 825, and the pH of the medium. The flotation recoveries were found to be pH dependent and the effective between the pH range of 7.0 and 11.5 in the presence of Aero 704. In the case of flotation with Aero 3000C, the recoveries reached up to 95.0% at certain concentrations and pH values and decreased sharply below pH 3.0 and above pH 9.5 for all the minerals tested. In the presence of Aero 825, the flotation recoveries of the minerals except for rutile, were found to be insufficient even with its highest concentration. In order to evaluate the adsorption mechanism of the collectors, Atomic Force Microscopy (AFM) and Fourier Transform Infrared Spectroscopy (FTIR) analyses were carried out. From the AFM results it might be deduced that the behavior of Aero 3000C and Aero 825 was found to be almost similar for biotite and muscovite as monolayer adsorption and for the remaining minerals, albite, orthoclase, quartz and rutile, as monolayer and bilayer adsorption together. In the case of Aero 704, for albite and orthoclase, the adsorption of the collector might be the reason for monolayer and bilayer formation on their surfaces. The strength of the interaction of the collectors on the mineral surfaces was followed by FTIR analyses before and after acetone washing. The interaction of all the collectors was found to be weak in the case of albite, orthoclase, quartz and rutile whereas the interaction of Aero 704 and Aero 3000C was found to be strong in the case of biotite and muscovite.