In this study, maghemite (&amp / #947 / -Fe2O3) thin films were prepared by chemical solution deposition on glass and quartz substrates. The solution was prepared by using 0.3 M iron (III) nitrate [Fe(NO3)3 - 9H2O] as precursor and dissolved in a mixture of 2-methoxyethanol and acetylacetone in a molar ratio of 20:2, by stirring the solution at RT for 2 hours. Substrates were prepared by either piranha etching method or ultrasonic cleaning method. The solution was spin coated on glass and quartz substrates at 1400 and 4000 rpm for 1 minute. The resultant film thickness was found as 65 and 80 nm by SEM. Viscosity of the main solution was found to be approximately as 0.0035 Pa.s by viscosity measurement. TGA/DTA analyses showed that, to produce maghemite thin film, heat treatment should be done between 330 &deg / C and 440 &deg / C. Homogeneous and crack free maghemite thin films were observed by Energy Dispersive Spectrometry (EDS) and Scanning Electron Microscope (SEM) methods. TEM studies verified maghemite thin film formation by using electron diffraction and SAED (selected area electron diffraction) method. Thin film characteristics were evaluated by changing the experimental parameters which are annealing temperature, annealing time and thickness of the films using XRD (x-ray diffraction) method. Optical band gap of maghemite thin films were found as approximately 2.64 eV by UV-VIS Spectrophotometer. Magnetic properties of maghemite thin films were also examined by VSM (vibrating sample magnetometer).

Titanium-nickel is a unique class of material known as Shape Memory Alloy (SMA). A thermoelastic martensitic phase transformation is responsible for its extraordinary properties such as shape memory effect and superelasticity. The near equiatomic Ti-Ni alloys are the commercially most exploited SMAs because of the unique combination of these properties and superior ductility, strength, fatigue resistance and corrosion resistance. The properties of Ti-Ni SMAs are very sensitive to composition and the processing parameters. The properties of Ti-Ni SMAs can be modified to a great extent by choice of composition, mechanical working and heat treatment. Thermo-mechanical treatments are required to strengthen the matrix and improve the shape memory characteristics. Plastic deformation and subsequent annealing is the common way to improve shape memory properties. In the present study, Ti- 50 at% Ni wire specimens are produced and used for the investigation of the effect of different heat treatment and cold working processes on shape memory characteristics. To investigate the thermomechanical behavior of differently processed wire specimens, a fully computerized servo hydraulic thermomechanical testing machine was designed and constructed. Testing machine was capable to perform different types of tests that are selected by the user. It can both heat and cool the specimen automatically according to the testing sequence by applying DC current directly through the SMA wire or by sending liquid nitrogen into the cooling chamber. Temperature is measured by a K-type thermocouple directly mounted on the wire specimen with a glass tape. Force that is applied to the specimen is produced by hydraulic power unit with a double action cyclinder and it is controlled by a controller which takes the feedback from the loadcell and LVDT (Linear Variable Distance Transducer). During performig thermomechanical-tests all the data of loadcell, LVDT and thermocouple are collected by a data acqusition system integrated with a host computer that operates the program XPC Target. Ti-Ni alloy with equiatomic composition is prepared in vacum induction furnace. Specimen cast in the form of rod was then hot swaged. Subsequent to swaging, cold wire drawing, intermediate annealing at 500 &amp / #61616 / C and water quenching was applied to obtain SMA wire with a diameter of 1.52 mm. Ti-Ni wires produced were subjected to four different processes. All the samples were initially solution heat treated at 925 &amp / #61616 / C for 30 minutes prior to water quenching. Some of the samples were further treated by an intermediate anneal at 500 &amp / #61616 / C. To see the effect of cold working / prior to intermediate annealing, 20 % or 40 % cold work was applied to another group of specimens. To study the shape memory characteristics of specimens subjected to the above mentioned processes, four types of test, namely constant stress free recovery test, constant strain free recovery test, constant stress constrained recovery test and constant strain constrained recovery test, were designed and applied cyclically. The tests have shown that the stress plateau observed in the first cycle of the tests disappear upon cycling and the shape memory characteristics improve and stabilize with cycling. Once trained by cycling, fractional free recovery was observed to reach to 100 % and recovery stress to reach 120% of the applied stress if shape recovery is prevented.

In this work present the broad-band noise structure in the 2-60 keV data of Cataclysmic Variables (CVs) with Anomalous X-Ray Pulsars (AXPs) and Soft Gamma Repeaters (SGRs). We analyzed Rossi X-ray Timing Explorer (RXTE) PCA data and derived time series from 27 CVs, 4 AXPs and 1 SGR using the RXTE archive. In general, CVs of different types all show broad band noise which can be fitted with power laws, using exponentional cut-offs, and Lorentzians in a similar way to power spectral (noise) characteristics of X-ray Binaries (XRBs). In general terms the power spectra show a power law index of (-)1.2-2. A rather large scale flattening of the power spectra exits in nonmagnetic systems in the low to very low frequency range. We observe that in low and high states/outbursts the noise in the high frequency range and low frequency range is changed. CVs show considerably low frequency noise. In addition, we recovered several possible QPOs in the X-ray wavelengths from CVs mainly from Intermediate Polar systems. AXP and SGR sources which are thought to be powered by either magnetic decay or accretion show band limited noise in their low frequencies. We also correlated their equal time interval noise characteristic with their burst states and discovered that in the two AXPs (1E 2259+586, 1E 1048.1-5937) noise correlates with their bursts.

This aim of this thesis is to examine the possibility of using Magnetic Barkhausen Noise (MBN) technique in characterizing the microstructures of quenched and tempered low alloy steels as well as annealed low carbon steels. To determine the average grain size by MBN, SAE 1010 steel consisting of dominantly ferrite was used. The specimens were slowly cooled in the furnace after austenitizing at different time and temperature variations. By metallographic examination the average ferrite grain size of specimens was determined. The magnetic parameters were measured by a commercial MBN system. With increasing ferrite grain size, the magnetic Barkhausen jumps caused by the microstructure were decreased due to the reduction in grain boundary density per unit volume. A clear relationship has been observed between average grain size and the magnetic Barkhausen noise signals. SAE 4140, 5140 and 1040 steels were used to characterize the microstructures of quenched and tempered specimens. After austenitizing and quenching identically, the specimens were tempered at various temperatures between 200oC and 600oC. Formation of the desired microstructures was ensured by metallographic examinations and hardness measurements. The results show that as tempering temperature increases the Barkhausen activity increases due to the enhancement of domain wall displacement with softening of the martensite. It has been shown that MBN is a powerful tool for evaluating the microstructures of martensitic and annealed steels.

Titanium diboride was produced both by volume combustion synthesis (VCS) and by mechanochemical synthesis through the reaction of TiO2, B2O3 and metallic Mg. Reaction products were expected to be composed of TiB2 and MgO. However, side products such as Mg2TiO4, Mg3B2O6, MgB2 and TiN were also present in the products obtained by volume combustion synthesis. Formation of TiN could be prevented by conducting the volume combustion synthesis under argon atmosphere. Mg2TiO4 did not form when 40% excess Mg was used. Wet ball milling of the products before leaching was found to be effective in removal of Mg3B2O6 during leaching in 1M HCl. When stoichiometric starting mixtures were used, all of the side products could be removed after wet ball milling in ethanol and leaching in 5 M HCl. Thus, pure TiB2 was obtained with a molar yield of 30%. Pure TiB2 could also be obtained at a molar yield of 45.6% by hot leaching of VCS products at 75oC in 5 M HCl, omitting the wet ball milling step. By mechanochemical processing, products containing only TiB2 and MgO were obtained after 15 hours of ball milling. Leaching in 0.5 M HCl for 3 minutes was found to be sufficient for elimination of MgO. Molar yield of TiB2 was 89.6%, much higher than that of TiB2 produced by volume combustion synthesis. According to scanning electron microscope analyses, produced TiB2 had average particle size of 0.27&plusmn / 0.08 &amp / #956 / m.

In this thesis, it was aimed to select and propose a feasible method, or series of methods, for the recovery of zinc (Zn) and lead (Pb) that are present in disposed &Ccedil / iNKUR leach residues having 12.43 % Zn, 15.51 % Pb and 6.27 % Fe. Initially, physical, chemical and mineralogical characterizations of the leach residues were done. Results of these analyses showed that lead was present as lead sulfate (PbSO4), and zinc was present as zinc sulfate heptahydrate (ZnSO4.7H2O), zinc ferrite (ZnFe2O4) and zinc silicate (2ZnO.SiO2) in the leach residues. Initially, water leaching experiments were carried out to determine water soluble amount of blended leach residue, and the maximum zinc recovery was obtained as 18 %. After these trials, sulphuric acid and brine leaching were used to recover zinc and lead, respectively. Firstly, due to the insufficient recovery in water leaching trials acid leaching experiments were done for zinc recovery and the parameters studied were acid concentration, reaction duration, leaching temperature and solid-liquid ratio (pulp density). About 72 % Zn was recovered after hot acid leaching by using 150 g/l H2SO4 at 95 oC in 2 hours with a pulp density of 200 g/l. For lead recovery brine leaching experiments were done with the secondary leach residue obtained after H2SO4 leaching. In brine leaching experiments, NaCl concentration, pulp density (solid/liquid ratio), reaction duration and leaching temperature were chosen as variables. Effect of HCl addition was also investigated. In brine leaching while lead recoveries up to 98 % could be attained at a low pulp density in laboratory scale, the maximum recovery obtained was 84.9 % at a high pulp density (200 g/l) with 300 g/l NaCl concentration in 10 minutes at 95 oC.

In the present study, production of titanium and Ti6Al4V alloy foams has been investigated using powder metallurgical space holder technique in which magnesium powder were utilized to generate porosities in the range 30 to 90 vol. %. Also, sintering of titanium and Ti-6Al-4V alloy powders in loose and compacted condition at various temperatures (850-1250oC) and compaction pressures (120-1125 MPa), respectively, were investigated to elucidate the structure and mechanical properties of the porous cell walls present due to partial sintering of powders in the specimens prepared by space holder technique. In addition, microstructure and mechanical response of the porous alloys were compared with the furnace cooled bulk samples of Ti-6Al-4V-ELI alloy subsequent to betatizing. It has been observed that the magnesium also acts as a deoxidizer during foaming experiments, and its content and removal temperature is critical in determining the sample collapse. Stress-strain curves of the foams exhibited a linear elastic region / a long plateau stage / and a densification stage. Whereas, curves of loose powder sintered samples were similar to that of bulk alloy. Shearing failure in foam samples occurred as series of deformation bands formed in the direction normal to the applied load and cell collapsing occured in discrete bands. Average neck size of samples sintered in loose or compacted condition were found to be different even when they had the same porosity, and the strength was observed to change linearly with the square of neck size ratio. The relation between mechanical properties of the foam and its relative density, which is calculated considering the micro porous cell wall, was observed to obey power law. The proportionality constant and the exponent reflect the structure and properties of cell walls and edges and macro pore character.

Porous TiNi alloys (Ti-50.4 at. %Ni and Ti-50.6 at. %Ni) with porosities in the range 21%-81% were prepared successfully applying a new powder metallurgy fabrication route in which magnesium was used as space holder resulting in either single austenite phase or a mixture of austenite and martensite phases dictated by the composition of the starting prealloyed powders but entirely free from secondary brittle intermetallics, oxides, nitrides and carbonitrides. Magnesium vapor do not only prevents secondary phase formation and contamination but also provides higher temperature sintering opportunity preventing liquid phase formation at the eutectic temperature, 1118 &deg / C resulting from Ni enrichment due to oxidation. By two step sintering processing (holding the sample at 1100 &deg / C for 30 minutes and subsequently sintering at temperatures higher than the eutectic temperature, 1118 &deg / C) magnesium may allow sintering probably up to the melting point of TiNi. The processed alloys exhibited interconnected (partially or completely depending on porosity content) open macro-pores spherical in shape and irregular micro-pores in the cell walls resulting from incomplete sintering. It has been found that porosity content of the foams have no influence on the phase transformation temperatures while deformation and oxidation are severely influential. Porous TiNi alloys displayed excellent superelasticity and shape memory behavior. Space holder technique seems to be a promising method for production of porous TiNi alloys. Desired porosity level, pore shape and accordingly mechanical properties were found to be easily adjustable.

The aim of this study was to extract nickel and cobalt from the lateritic nickel ores of G&ouml / rdes region by hydrometallurgical methods under the optimum conditions. Limonitic and nontronitic types of G&ouml / rdes lateritic nickel ores were used during experiments. Agitative and column leaching experiments at atmospheric pressure were conducted with various parameters / these were duration, temperature and initial sulfuric acid concentration of leach solution. It was shown that in agitative leaching, under the optimum conditions that were determined as 24 hours of leaching at 95&deg / C with initial sulfuric acid concentration of 192.1 g/L for nontronite and 240.1 g/L for limonite, nickel and cobalt extractions were 96.0% and 63.4% for nontronite / 93.1% and 75.0% for limonite, respectively. Overall acid consumptions of ores were calculated as 669 kg H2SO4/ton dry ore for nontronitic type nickel ore and 714 kg H2SO4/ton dry ore for limonitic type nickel ore. Column leaching experiments also showed that nickel and cobalt could be extracted from both ore types by heap leaching. Nontronite type of laterite was found to be more suitable for column leaching by sulfuric acid. In column leaching, the calculated nickel and cobalt extractions were 83.9% and 55.2% for nontronite after 122 days of leaching with 100 g/L sulfuric acid concentration. Acid consumption of nontronite was found to be 462 kg H2SO4/ton dry ore.

The aim of this study is to produce Nb doped PZT thin films and then investigate the effects of Nb+5 ion on the structural, dielectric and ferroelectric properties. Niobium (Nb) doped lead zirconate titanate thin films (PNZT) were produced by solution deposition with nominal compositions, Pb(1-0.5x)(Zr0.53Ti0.47)1-xNbxO3 where x = 0.00 - 0.07. Single and multi-layered films were deposited onto (111)-Pt/Ti/SiO2/Si-(100) substrates by spin coating. PZT compositions near the morphotropic phase boundary (MPB) was chosen because excellent ferroelectric and dielectric properties were achieved in this area. The effects of sintering temperature, sintering time, variation of thickness in the films and change of niobium content were investigated with regard to phase development, microstructure, and ferroelectric and dielectric characteristics. The best results were obtained in double layered films (390 nm) which were sintered at 600 &deg / C for 1 h. Grain size of the films decreases with increasing Nb content except for 1 at % Nb doped films. The average grain size of 1 at % Nb doped thin films was calculated as 130 nm by using FESEM. Optimum doping level was found in 1 at % Nb doped films. For 1 at % Nb doped [Pb0.995(Zr0.53Ti0.47)0.99Nb0.01O3] films, remnant polarization (Pr) of 35.75 &amp / #956 / C/cm2 and coercive field (Ec) of 75.65 kV/cm have been obtained. The maximum dielectric constant was achieved in 1 at % Nb doped films which was 689. Tangent loss values were found between 2-4 % and these values were independent of Nb concentrations. Ferroelectric and dielectric properties were decreased at higher Nb doping levels because of the changes in the grain size, distortion of the crystal structure and pinning of the domains.