Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Synthesis of Carbon-Based Flexible Temperature-Controlled Semiconductive Composites(01. Izmir Institute of Technology, 2024) Gündüz, Esra Sıla; Polat, Mehmet; Polat, HürriyetGünümüzde, yarı iletken polimer matrisli kompozitler ve kullanım alanları araştırmacıların ilgisini çekmektedir. Ayarlanabilir sıcaklık profillerine sahip yarı iletken esnek polimer matrisli kompozitler, robotik, havacılık ve enerji sektörlerinde kullanım alanı bulmaktadır. Ancak karbon nanotüpler, grafen veya metal nanopartiküller gibi pahalı iletken fazlarlara duyulan ihtiyaç nedeniyle üretim maliyeti yüksektir. Bu çalışma, bu tür kompozitlerin üretimi için polidimetilsiloksan matrisinde karbon siyahı ve doğal grafit gibi ucuz iletken malzemelerin kullanılmasını amaçlamaktadır. Kompozitler 'Çözelti karıştırma' yöntemiyle (%10 ila %35 metanolde) hazırlandı ve dağılabilirlik, elektriksel iletkenlik, termal tepki ve mekanik ve morfolojik özellikler açısından test edildi. Bu substratların yüzeylerinin ıslanmayan, düşük enerjili yüzeyler (Fowke teorisine göre 26 J/m2) olduğu bulundu; bu nedenle parçacıklar daha yüksek konsantrasyonlarda (>%30) topaklanma eğilimliydiler. Aglomerasyonun olumsuz sonuçlarını ortadan kaldırmak için yüzey aktif madde ilavesi kullanıldı. Karbon içeriğinin ayarlanması iletkenliği 0 ile 10,79 S/m arasında modüle edilmesini sağlamıştır. 3,17 S/m iletkenliğe sahip tipik bir kompozit, 30 V yük altında 49,7°C yüzey sıcaklığı göstermiştir. PDMS ile karşılaştırıldığında kompozitlerin mekanik özellikler olumluydu; optimum iletkenliğe ve sıcaklık tepkisine sahip bir kompozit, çekme mukavemetinde %50'lik bir düşüşe rağmen elastik modülde %97,8 ve yırtılma mukavemetinde %197 artış gösterdi. Çalışma, istenen sıcaklık profillerine sahip yarı iletken esnek kompozitlerin üretiminde önemli ekonomik potansiyelin altını çiziyor.Master Thesis Co-ni Separation In Ix-sx Circuit(2023) Ceyhan, Ayşe Merve; Polat, MehmetEti Gübre stands out as the sole facility capable of reclaiming multiple metals from chalcopyrite flotation tails in Turkey. While the overall performance of the process has been deemed satisfactory, the cobalt and nickel products have yet to meet commodity standards. The objective of this project is to ascertain the feasibility of using a series of hydrometallurgical techniques, namely, solvent extraction and ion exchange resin technologies, for attaining premium-quality cobalt and nickel products from a compound comprising cobalt, nickel, and other assorted elements. Extracting cobalt and nickel selectively from impurities, reaching over 95% recovery in a solution containing various elements and steep concentration differences, presents a considerable challenge. Moreover, accomplishing this within an already operational process adds another layer of complexity, demanding alignment with the existing process's stability. The strategy involved selectively separating and refining cobalt and nickel from the sulfate solution through solvent extraction (SX) methods and employing the Ion Exchange (IX) method for further purification.Master Thesis Use of Snps With Controlled Size & Shape for Enhanced Surface Hydrophobicity & Hardness for Coil Coating Applications(01. Izmir Institute of Technology, 2023) Sulubaş, Şevval; Polat, Mehmet; Polat, HürriyetIncreasing the hardness of surface while improving hydrophobicity simultaneously has important implications in coating applications. The use of nano sized particles for this purpose is an interesting area of research. SNPs with mono and multi size distributions in a wide size range were successfully synthesized using the Stöber Method directly or after proper modifications such as utilizing seed particles as in Stöber growth solutions. The synthesized monosize and bi-modal silica particles were then employed in coating studies. The silica nanoparticles were added to a clear coat without pigments and fillers, followed by the introduction of a pigmented topcoat. The addition of 25% monosize silica nanoparticles led to a contact angle (CA) of 92°, while an equal amount of bi-modal silica particles increased the CA to 106°. Notably, the highest CA value of 116.7° was achieved with a 40% addition of bi-modal silica particles. When measured CA was converted to actual CA by incorporating the roughness parameter, the maximum effective CA was calculated as 140°. In terms of mechanical properties, loading monosize silica nanoparticles up to 35% resulted in a surface hardness of 2H. Further increasing the loading to 45% improved the surface hardness to 3H. While a 40% addition of monosize silica was necessary to achieve a pencil hardness of 3H, 20% addition of bi-modal sample was sufficient. The findings above demonstrate that addition of nanosized silica particles simultaneously improve hardness and surface hydrophobicity and that a bi-modal particle size distribution results in a superior performance compared to mono-modal particle size distribution.Master Thesis Synthesis and Characterization of Boron Composite Nanoparticles for Wear and Friction Reduction(Izmir Institute of Technology, 2019) Gökmen, Esin; Polat, MehmetSince most of the conventional lubricants reach their performance limits, new antiwear and extreme pressure (EP) additives are designed so that lubricants can minimize friction and wear when used in high temperature and pressure conditions. There is growing interest in the use of nanoparticles as an additive in lubricants. Due to its outstanding chemical properties, boron is frequently involved in the design of nanoparticles. Especially borate derivatives and hexagonal boron nitride (h-BN) have already taken their places in many lubricant formulations. The aim of this study was the production of silica-boron composite nanoparticles that can replace the phosphate-derived additives used in lubricant formulations and to provide the extreme pressure, antiwear and friction-regulating properties at the same time. For this purpose, the Stöber method that is used for silica production was modified to produce Si/Na-Borate nanoparticles. It was found that the synthesis of composite nanoparticles in desired size distribution and morphology as well as composite structures composed of Si and Na-Borate, was possible changing the amounts of ingredients and modes of addition. It was observed that the morphology and the chemical structure of these particles depend on the amount of Na-Borate (1, 3, and 5% w/w) and the addition type of Na-Borate (Direct, 500 �����L/min, 5�����L/min). Then composite nanoparticles were characterized using SEM, FTIR and ICP-MS and some tests were conducted to examine the structure of particles. The tribological performance of these particles tested using Four Ball Test method have shown that there is a significant improvement in the presence of these particles.Master Thesis Modification of Chemical and Morphological Properties of Lead-Acid Battery Negative Active Material(Izmir Institute of Technology, 2014) Kama, Burak Muhammet; Polat, MehmetLead-acid batteries which are indispensable equipment for motor vehicles are one of the most important electrochemical processes commercially thanks to their advantages, such as low cost and capability of providing high energy. The new generation cars which such as climates, smart screens, stronger engines etc., require the batteries which should have longer cycle life and higher cold-cranking ampere. In this study, the aims were elucidating the exact working mechanism of lead-acid battery negative active material and improving the commercial lead-acid battery for micro-hybrid vehicles. For this purpose, experimental studies were separated to three parts. First one is the characterizing of negative electrode raw materials, leady oxide, lignosulfonate, carbon, barium sulfate. Second one is determination of rheological properties of negative paste in different cases. Third one is the preparation of pastes and then performance testes (reserve capacity, cold-cranking ampere and cycle life) of negative plates prepared from the pastes characterized in second part. As a result of first part of studies, it was shown that the all of carbon materials and leady oxide suffer from agglomeration in lignosulfonate solutions prepared in different concentrations. In second part, the rheological properties of negative paste were determined in different preparation cases and shown that the amount of additives and preparation method has big effects. Finally, the negative plates were prepared with two methods, wet and dry mixing. After that the plates were formed and then electrical tests were performed. Consequently, a battery which has better properties, physically and chemically, was obtained. However, this improvement was not enough due to the dispersion problems of carbon samples tested in this study.Master Thesis An Investigation of Dye-Surfactant Intetactions in Aqueous Solutions for Elucidating the Mechanisms of Ultrafiltration(Izmir Institute of Technology, 2014) Olcay, Aybike Nil; Polat, Mehmet; Polat, HürriyetLow Molecular Weight Contaminants (LMWCs) in waters are serious environmental concern due to removal problems with classical techniques such as chemical coagulation, biological treatments and adsorption. LMWCs are usually copresent with surface active agents in contaminated waters. Though such advanced removal techniques as ultrafiltration and micelle enhanced ultrafiltration are said to perform better, no systematic study is present for elucidating how the contaminantsurfactants interactions affect removal efficiency. In this study, methylene blue (MB), a dye widely employed in textile, paper and chemical industries, was chosen as the model contaminant. Surfactants selected were anionic sodium dodecyl sulfate (SDS), cationic hexadecyltrimethyl ammonium bromide (CTAB) and non-ionic ethoxylated octylphenol (TX-100). Surface tension, size, charge and contact angle measurements were conducted to investigate dye-surfactant interactions. Cellulose nitrate filters were employed to determine the effect of these interactions in filtration efficiency. It was found that significant amount of MB was removed from solution since it attached on the negatively charged cellulose nitrate filter. Though presence of surfactants generally decreased MB removal efficiency, MB-SDS interaction created large-loose aggregates at low SDS concentrations which cannot pass the filter paper. The MB-CTAB/TX-100 interactions created positively charged MB-surfactant pairs which can attach to the filter surface causing a decrease in the removal. At concentrations above Critical Micelle Concentration (CMC), the efficiency of MB removal is low due to the formation of surfactant-micelles that are smaller than the pores of the filter. Detailed size distribution experiments suggest that MB molecules are within the micelles structure, not in the core as believed in literature and do not increase the size of the micelle.Master Thesis Determining Charge Distribution of Metal Oxide Surfaces With Afm Using Colloid Probe Technique(Izmir Institute of Technology, 2012) Güler, Ayşe; Polat, MehmetColloidal systems of micron-sized particles dispersed in a solvent are widely encountered in numerous industries. Homogeneity, dispersibility, rheology and forming characteristics of these systems depend solely on particles-particle interactions which in turn are determined by Van der Waals (vdW) and Electrical Double Layer (EDL) forces. The vdW forces are not affected by system chemistry. However, the EDL forces, which arise from the charging of on solid surfaces in a solvent, vary significantly with solution chemistry. So, manipulation of electrical forces is used widely in industrial applications to manipulate colloidal systems. Colloidal particles in solution carry a distribution of positive, negative and neutral charges depending on solution chemistry. Electrophoretic potential mesurements or colloidal titration methods yield only an average charge for the whole population, not the charge distribution on each particle surface. The streaming potential techniques also provide an average charge on the surface. Currently, there is no accepted technique to determine the charge distribution on solid surfaces. This work aims at using Atomic Force Microscopy (AFM) as a charge probe to achieve exactly this. The work improves on a recent study (Yelken, 2010) which used commercial SiN4 cantilevers to determine the charge distribution on quartz and sapphire surfaces by replacing SiN4 cantilevers with custom-made colloid probes of desired material (quartz in this case) to probe the surface. The current work which improves the flexibility and resolution of the method was tested with two quartz andMaster Thesis Synthesis of Silica Nano Particles With Custom-Made Morphology for Controlled Drug Delivery(Izmir Institute of Technology, 2012) Siretli, Çağrı; Polat, MehmetThe purpose was to have nanosized particles with low energy perimeters which function as non-reacting transporters for targeted delivery along with high energy sites inside the pores to achieve controlled release of specialized chemicals. Surfactants were used in combination with both base and acid catalyzed methods to achive desired structural properties and the characterization studies such as SEM, TEM, FTIR, BET surface area, pore size, size and zeta potential measurements were conducted. The effect of surfactants on mesoporous silica production changed depending on the type of methods. In the case of base catalysed method in alcohol, formation of stabilized emulsions with different sizes and their effect on the size and shape of silica particles was proposed. The effect of surfactants was attributed to their effect on a) the emulsification process and b) silica-silica and silica-surfactant interactions involved. In the case of base catalysed silica production in water, however, surfactant micelles were used as templates to produce pores. The effect of surfactant type and concentration was attributed to their effect on the CMC, micelle shape and size. Rod-like (~400 nm) at high and spherical (~200 nm) particles at low concentrations were synthesized. Here the surface area of ~1000 m2/g and average pore size of ~3 nm were obtained. Carbonization of these materials were performed to obtain nanosized silica particles with low energy perimeters successfully. Acid catalysed silica production in water was similar. Rod-like (600-800 nm) and cubic (800-1000 nm) nanoparticles were produced. These particles exhibited lower surface area of ~700 m2/g and larger pore size of ~5 nm.