Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Electrocaloric Properties of the Zr-Substituted Batio3 – Na0.5bi0.5tio3 Ceramics(2023) Akkaşoğlu, Oğuz; Adem, UmutThe aim of this study is to investigate electrocaloric properties and thermodynamic behaviour, obtaining high adiabatic temperature change (ΔT) values with a broad temperature span of zirconium doped barium titanate-sodium bismuth titanate by substitution of Zr into B-site (titanium). Ceramics are synthesized in a pellet form by solid-state reactions. Chemical composition was Ba0.7Na0.15Bi0.15TixZr1-xO3 (abbreviated as BT-NBT) where x= 0.00, 0.01, 0.02, 0.03, 0.035, 0.04 and 0.05. Phase analysis was conducted by X-ray diffraction method. Microstructural analysis and average grain size determination was performed by Scanning Electron Microscopy. To understand phase transitions and physical behaviours, dielectric measurements are performed. Ferroelectric properties are investigated by using temperature dependent polarization, strain and current-electric field relationships. Electrocaloric measurements are done by using temperature dependent polarization-electric field data. Maxwell relations are used to calculate temperature dependent electrocaloric temperature change, ΔT, and from this data, temperature span, Tspan, was calculated. It was observed even though Zr substitution into the Ti-site rapidly decreases the Curie temperature and introduces relaxor ferroelectric character to the samples. However, the 1st order like nature of the ferroelectric-paraelectric phase transition at the Curie temperature and, consequently significant ΔT is maintained even for 4 % Zr substituted sample close to room temperature. Temperature span, on the other hand, has a lower value compared to previous works related to barium titanate systems. Electrocaloric efficiency is comparable to other works on Pb-free sytems and these results showed that BT-NBT systems have promising features for electrocaloric cooling technologies.Master Thesis Synthesis of Drug Loaded Ph Sensitive Albumin Nanoparticles(2023) Argıtekin, Eda; Akdoğan, Yaşar; Adem, UmutSerum albumin-based nanoparticles (NPs) are commonly used for drug delivery due to their stability, biodegradability, ease of particle size control and no toxicity. In this study, bovine serum albumin (BSA) was functionalized with catechol-containing dopamine (D) to synthesize D-BSA NPs using pH responsive catechol-metal coordination bonds. Instead of using glutaraldehyde, V(III) ion was used as a cross-linker for synthesizing NPs. Catechol-V(III) coordination bonds provided pH responsive NPs due to their different stoichiometry of catechol-metal complexes (e.g. mono-, bis- or tris-) at different pH values. For the synthesis of D-BSA NPs, desolvation method was used with acetone as desolvating agent. Uniformly sized NPs were synthesized with an average of 294 nm with a PDI value of 0.15. Doxorubicin is loaded to NPs with a 15:1 DOX:D-BSA molar ratio. DOX encapsulation efficiency and drug loading capacity of D-BSA NPs were found to be 98% and 10%, respectively. Conversion to bis- and/or mono- catechol-V(III) complexes in acidic medium resulted in degradation of NPs and rapid release of the loaded doxorubicin (DOX). DOX releases reached to 51, 76 and 95% at pH values 7.4, 5.5 and 4.2, respectively at the end of 80 hours. Furthermore, the cytotoxic effects of prepared D-BSA NPs, in comparison to free DOX were studied with MCF-7 cells. Increasing D-BSA concentrations up to 0.2 mg/mL did not affect the cell viability, significantly. But, upon cell (MCF-7) uptake in vitro, DOX-loaded D-BSA NPs and free DOX reduced cell viability by 75% and 20% in 24 hours, respectively.Master Thesis Piezocatalytic and Piezoelectric Properties of P(vdf) and Its Copolymer/Terpolymer Films(01. Izmir Institute of Technology, 2023) Tengizdeniz, Ceren; Adem, Umut; Genç, AzizNowadays, the release of colored organic pollutants such as Rhodamin B dye, resulting from industrial activities endanger the people, animals, and plants. Many methods have developed to destroy these harmful pollutants. Piezocatalysis, a newly used environmentally friendly method, takes advantage of the piezoelectric effect, and uses mechanical vibration to produce active species on opposite surfaces of matter for degradation of dye. In this study, piezocatalytic and piezoelectric properties of P(VDF) based homopolymer, copolymer and terpolymers were investigated. With the addition of 2nd and 3rd monomer to the homopolymer, observation of change in piezoelectric and piezocatalytic properties and removal efficiency of pollution in water, were aimed. P(VDF) homopolymer, P(VDF-TrFE) copolymers with composition of 55/45 and 50/50 mol%, and P(VDF-TrFE-CTFE) terpolymer with 62/31/7 mol% were synthesized by solution casting method. It was observed that the 2nd and 3rd monomer added to the homopolymer enhanced the piezoelectric properties and strain characteristics of the polymers. Maximum polarization and strain of terpolymer was observed as 11 µC/cm2 and 5.6 %, respectively. Due to the increase in piezoelectricity, a noticeable increase in piezocatalytic properties was observed. Terpolymer exhibited the highest and most efficient piezoelectric and piezocatalytic performance. P(VDF) homopolymer was reached 27% dye degradation efficiency. While copolymers with mol% 55/45 and 50/50, dye degradation efficiencies were 40% and 47%, respectively, terpolymer efficiency was 54%. From the dielectric measurements, within the transition region (49 mol% ≤ CVDF ≤ 55 mol%) of P(VDF-TrFE), both normal-ferroelectric and relaxor characteristics were observed. Terpolymer showed relaxor properties as expected.Master Thesis Comparison of Powder Synthesis Methods for the Production of Potassium Sodium Niobate (knn)(Izmir Institute of Technology, 2021) Pişkin, Cerem; Ahmetoğlu, Çekdar Vakıf; Adem, UmutAlkali niobate-based, i.e., potassium sodium niobate, KxNax-1NbO3 at x=0.5 (the composition at the morphotropic phase boundary (MPB)), based materials have been reported as promising lead-free piezoelectrics to be substituted with the most extensive lead-based, i.e., lead zirconate titanate (PZT) ones. In this thesis, KNN particles were obtained using three discrete powder synthesis routes: conventional solid-state reaction, hydrothermal synthesis, and sol-gel processing. The as-synthesized powders were characterized via several techniques to provide a comparative study and underline the difficulties upon KNN synthesis. In the conventional method, the phase pure K0.5Na0.5NbO3 powders were obtained at 850°C with 382 ∓ 68 nm particle size. Unfortunately, the process cannot be considered sustainable due to the high risk of non-perovskite impurity phase formations. Also, the results demonstrated that single phase KNN powder having the MPB composition could not be accomplished via a one-step hydrothermal reaction process because of the inevitable formation of the second NaNbO3 phase. Instead, post-heat treatment of biphasic (K-rich (x>0.5) KNN and NaNbO3) samples lead to induction of sodium incorporation into the crystal lattice, and eventually, phase-pure KNN particles with high proximity (x=0.58) to MPB were achieved. The KNN powder with the smallest particle size (145 nm) was obtained using the sol-gel method at 500°C. However, the samples showed carbonate impurities resulting from the reaction of unreacted alkali cations (K+ and/or Na+) with the ambient CO2. Hence, the KNN samples needed to be stored under inert atmosphere to ensure purity.Master Thesis Formation of Srtio3[tio2] Ceramic Composites at Low Temperatures(01. Izmir Institute of Technology, 2021) Karataş, Esin; Adem, Umut; Ahmetoğlu, Çekdar VakıfStrontium titanate ceramics are materials belonging to the perovskite material group with the formula ABO3. Strontium titanate ceramics have been a preferred material in many areas, such as the electroceramics industry, due to its high dielectric constant and high chemical stability and generally produced by manufacturing processes such as solid-state synthesis, hydrothermal method, and sol-gel. SrTiO3 ceramics have been produced in the literature with different temperatures, times, and starting materials. For ceramic products, a sintering step is required after the powder production step. Traditional sintering methods, which have been used for many years, are used to densify powders with high temperatures. Recently developed low-temperature densification methods enable the sintering process to be carried out at relatively lower temperatures. For this purpose, in this thesis, SrTiO3-TiO2 ceramic composites were produced at different reaction temperatures and times using the rHLPD method, which combines powder production and sintering steps in a single process. In the studies, the reaction temperature, time, and the effect of adding mineralizer to the prepared solution for the hydrothermal reaction on the final product were investigated. The aim of the thesis is to produce SrTiO3 from TiO2 green body using the rHLPD method. In addition, the production of SrTiO3-TiO2 ceramic composites with as high mole conversion and relative density values as possible was targeted with different parameters such as reaction temperature, reaction time, and addition of NaOH to the solution. As a result of the studies carried out with different parameters, SrTiO3-TiO2 ceramic composites with a final relative density value of approximately 81 % were produced. Consequently, in the XRD and Rietveld analysis, it was seen that the main phase was SrTiO3. In addition, there was a TiO2 phase in the structure. Finally, the SrCO3 phase was not detected in the structure.Master Thesis Experimental Analysis of Inkjet Printed Multi Metal Oxide Photoelectrodes for Water Splitting Applications(Izmir Institute of Technology, 2020) Tekneci, Gülsüm Efsun; Karabudak, Engin; Adem, UmutRecently, scientific research studies focus on renewable energy solutions as well as energy efficiency in managing the upcoming climate crisis which manifests itself in the form of global warming. However, the chaotic nature of renewable energy sources caused energy storage technologies to gain importance. In addition to battery technologies consisting of lithium and post-lithium ion, zinc-air, nickel-zinc and lead-acid; artificial photosynthesis products such as hydrogen and methanol also show superiority in transportation. Especially hydrogen fuel is in the leading position with gravimetric energy density of approximately 140 MJ/kg. In this study, the experimental procedure is conducted and analyzed to produce cost-effective multi-metal oxide catalysts at high speed and efficiency with a combinatorial approach using inkjet printing technology to obtain hydrogen by splitting water. Considering the abundancies in nature, especially nickel, cobalt, iron, manganese, copper and chromium salts were preferred to obtain oxide derivatives. Inkjet printing experiments were conducted with the printer provided by Sağlık İzleme Sistemleri A.Ş.. The precision of the printed layers was examined and compared with the literature values. In cases involving differences from the literature value, possible causes are emphasized and solutions are suggested. Problems in transition from single metal oxide printed layers to more complicated multi-metal oxide prints have been examined and solutions have been proposed. As a result, this experimental study is aimed to provide foresight for large-scale (photo)electrocatalyst production with the utilization of inkjet printing.Master Thesis Ferroelectric Ceramic Polymer Nanocomposites for Electrocaloric Cooling Applications(Izmir Institute of Technology, 2020) Tokkan, Melike; Adem, UmutIn this study, nanocomposites consisting of the polymer matrix and nanometer sized ceramic supporting phase were produced for electrocaloric cooling applications, which show potential as alternative refrigerant system. The aim of this study was to be able to estimate adiabatic temperature change (?T) of the composites by measuring saturated hysteresis loops for the composite materials that allow accurate calculation of the ?T using the indirect method based on Maxwell's relations. Ba0.94Ca0.06Ti0.925Sn0.075O3(BCST) composition ceramic was used as the supporting phase of the composite and P(VDF-TrFE)(55-45) co-polymer was chosen as the matrix. The ceramics were synthesized, as pellets by conventional solid-state method. Ferroelectric nanocomposites were manufactured by solution casting method by adding 5, 7.5, 10 volume percent of the ceramic powder, which was obtained by grinding the pellets by using ball milling. Phase analysis of all materials done using X-ray Diffraction method. Fourier Transform Infrared Spectroscopy was used to clearly understand the phase structure of polymer. Scanning electron microscopy was used for understand the distribution of ceramic particles in polymer matrix. Dielectric constant-dielectric loss and ferroelectric hysteresis loops were measured as a function of temperature for the electrical characterization of the materials. Adiabatic temperature change under electric field (?T) of the materials were calculated based on Maxwell's equations indirectly using the temperature dependent electrical polarization data. The dielectric constant and electrical polarization of the polymer matrix have increased with the addition of ceramic particles. The hysteresis loops of thebn pure polymer and composites were saturated, therefore the temperature change can be calculated accurately with the indirect method. Maximum ?T was calculated on the composite having 10vol% ceramic particles. (6.964K at 900 kV/cm).Master Thesis Manufacturing of Fire Resistant Porous Ca-Silicate Ceramics(Izmir Institute of Technology, 2019) Oğur, Ezgi; Ahmetoğlu, Çekdar Vakıf; Adem, UmutCalcium silicate hydrates are a group of materials belonging to the calcium silicate family. Calcium silicate hydrates are crucial materials in the building industry, especially for thermal insulation and fire-resistant applications. Tobermorite and xonotlite, calcium silicate hydrates, are the most popular materials in the literature due to their structural properties. These material are synthesized by hydrothermal processes. In some publications, several pre-treatments are applied to the starting materials before hydrothermal synthesis. In this thesis, the effects of these processes on different starting materials and how does changing the parameters affect the process are examined. Besides, the main objective of the thesis is to produce the xonotlite phase using recycling materials as economically as possible. Calcium silicate hydrates powders containing approximately 61 wt. % xonotlite was produced with using lime and recycled glass by hydrothermal synthesis method. The obtained product has a mainly fibrous morphology due to the main phase is xonotlite. According to phase analysis, tobermorite, scawtite, and the trace of calcite phases are also present in the general structure. The thermogravimetric analysis demonstrated that approximately 20% loss is observed up to 800˚C (at about that temperature transformation of the xonotlite to the wollastonite phase is occur.). The mass change remained constant between 800˚C and 1200˚C. Calcium silicate powder (obtained by thermal treatments from CSH) was also thermally analyzed and consequently remained stable up to 1200˚C, (the loss was approximately <1%).Master Thesis Obtaining and Characterization of Artificial Leather Using Different Types of Plasticizers(Izmir Institute of Technology, 2019) Akkuş Altındağ, İffet; Akdoğan, Yaşar; Adem, UmutArtificial leather is the material which has wide range of use in life from fashion garment, upholstery to technical applications such as defense industries. PVC artificial leather is preferred material by manufacturers because of its low cost and modification can be done easily by using true plasticizers which are fitting for purpose. In this study, number of six different plasticizers which are non-phthalate plasticizers; trioctyl trimelliate (TOTM), tributyl trimelliate (TBTM), dioctyl terephthalate (DOTP), tributyl citrate (TBC), dioctyl adipate (DOA) and dioctyl succinate (Plast BIO) were used for obtaining artificial leather. To characterize the properties of different kinds of plasticizer in artificial leather, mechanical tests including tensile and tear strengths, elongation at break, cold flexibility and effects of migrability tests were applied. Materials were formulated at three degrees of plasticizers ratios. Also, chemical changes during plasticization were observed using FTIR spectroscopy with ATR accessory, according to types and used levels of plasticizers. In conclusion, plasticizers showed different properties, i.e. material with TOTM plasticized had maximum tear and tensile strengths, while DOA and TBC including materials showed maximum elongation under same load. Considering cold flexibility of six plasticizers, DOA, BIO and TBC have more resistance to cold were obtained, respectively. In addition, migration studies showed that plasticizers including TOTM and TBTM have the least migration properties.Master Thesis Production and Characterization of Porous Ceramics for Aircraft Arresting Systems(Izmir Institute of Technology, 2019) Çapraz, Furkan; Ahmetoğlu, Çekdar Vakıf; Adem, UmutDespite developments in aviation, accidents still occur and lead to loss of lives. Technical or environmental factors may cause overrun accidents. In the case of aircraft that fail to stop along the runway distance during take-off or landing, such accidents are called overrun. Aircraft stopping systems (AAS) are passive safety systems used to prevent to take damage of passengers and aircraft during overrun. In the literature, foamed concrete was generally used as the AAS material. However, some studies have also been carried out on other materials that may be used as the AAS material. In present thesis, the aim was to produce porous calcium silicates instead of foamed concrete in AAS. The slip casting method was used to produce porous calcium silicate monoliths. The main components used in the manufacturing of porous wollastonite were xonotlite (as a matrix material), polymethyl methacrylate (as a sacrificial pore former, PMMA), polyvinyl alcohol (as a binder, PVA), Dolapix CE 64 (as a dispersing agent) and distilled water. Three different xonotlite ratios (8, 9 and 10% by volume) have been studied with four different xonotlite/ PMMA ratios (1, 0.82, 0.54 and 0.33 by volume). Also, specimens without PMMA were produced for each xonotlite ratio. The suspensions were stirred for 3 h at 750 rpm and then casted into the gypsum mold. The samples which were dried at room temperature (RT) were heat treated at 1000 oC. After production step microstructural, structural and mechanical analysis o the porous calcium silicates were carried out. Cold Crushing Strength (CCS) tests were performed out for determining mechanical properties. CCS values of the porous monolith parts ranged between 1376 kPa and 53.2 kPa depending on xonotlite/ PMMA ratios. In addition, the porosity values ranged from 93.38 to 87.82%. The resuts showed that some of these porous calcium silicate monoliths are suitable to use instead of foamed concrete as the AAS material.