Materials Science and Engineering / Malzeme Bilimi ve Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4719
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Article Citation - Scopus: 3A Brief Overview on Geothermal Scaling(General Directorate of Mineral Research and Exploration (MTA), 2023) Isık, Tuğba; Baba, Alper; Chandrasekharam, Dornadula; Demir, Mustafa M.; Isık, Tuğba; Baba, Alper; Demir, Mustafa MuammerHot spring waters are rich in terms of minerals. Since there are dramatic changes in thermodynamic parameters in geothermal power plants, such as a decrease in temperature and pressure, severe precipitation occurs throughout the system components in an uncontrolled manner. There are three main chemistries in deposits: carbonates (mainly calcium carbonates), silicates (metal silicates), and sulphides (antimony sulphide-stibnite). Energy harvesting is remarkably reduced out of the insulating nature of the deposit. Various actions need to be taken to mitigate this undesirable issue of scaling in geothermal systems. Geothermal systems are in fact quite complex, and the composition of brine and, accordingly, the chemistry of the deposit are not identical. Therefore, each system should be studied individually, and a tailor-made remedy should be developed. In this overview, the types of deposits in terms of chemistry and the actions (pH modification or antiscalant dosing) that should be taken to reduce scaling are mentioned, and potential chemistries of antiscalants are given.Article Ferroelectricity of Ca9fe(po4)7 and Ca9mn(po4)7 Ceramics With Polar Whitlockite-Type Crystal Structure(Sivas Cumhuriyet Üniversitesi, 2020) Adem, UmutCa9Fe(PO4)7 is a member of the double phosphate family having polar whitlockite-type crystal structure. The phase transition from the room temperature polar R3c to the high temperature non-polar R c phase has been called a ferroelectric phase transition using complementary experiments such as temperature dependent second harmonic generation and dielectric constant measurements however no ferroelectric hysteresis measurement has been reported. In order to be able to call these polar materials ferroelectric, measurement of a saturated ferroelectric hysteresis loop is necessary to demonstrate that the electrical polarization of these materials is switchable. In order to realize this goal, we have synthesized Ca9Fe(PO4)7 as well as structurally identical Ca9Mn(PO4)7 using solid state synthesis. Crystal structure of the ceramics were confirmed using Rietveld refinement of the x-ray diffraction (XRD) patterns. Differential scanning calorimetry (DSC) measurements revealed phase transition temperatures of 848 and 860 K for Ca9Fe(PO4)7 and Ca9Mn(PO4)7, respectively. Our ferroelectric hysteresis measurements and current electric field loops (I-E) derived from the hysteresis loops showed that the loops cannot be saturated and the direction of the electrical polarization of both materials cannot be switched up to the largest applied electric field of 100 kV/cm. Possible origins of this behaviour are discussed.Article Citation - Scopus: 1Oxidizer Gases Effects on the Diameter-Controlled Synthesis of Carbon Nanotubes(MIM Research Group, 2021) İnce Yardımcı, Atike; Öğütlü, Ahmet Sabri; Öğütlü, DenizIn this study, the influence of the oxidizers on the synthesis of carbon nanotubes by C2H4 decomposition over Fe catalyst has been investigated. CO2, O2, and H2O have been used as oxidizers, and to control catalyst particle formation and their sizes in the pretreatment stage. The same oxidizers have also been used in the growth stage to maintain the catalyst particle size, remove amorphous carbon formation to keep catalyst particle active. The results of scanning electron microscopy indicated that the average diameters of nanotubes decreased from 13.4±1.2 nm to 6.2±0.5 nm and extremely dense nanotubes were obtained when we added a small amount of CO2. Adding O2 extremely decreased the areal carbon nanotube density while widens the diameter distribution. H2O addition resulted in larger average diameters and made the growth strongly pretreatment dependent. Within the parameters tried for catalyst pretreatment and CNT growth processes, CO2 seemed the best choice for a weak oxidizing assistant. The strong dependency of the average diameter on pretreatment conditions indicated that pretreatment is a very important step in deciding the final diameters and their distribution.Article Citation - WoS: 11Citation - Scopus: 13Effect of Cnt Incorporation on Pan/Ppy Nanofibers Synthesized by Electrospinning Method(TÜBİTAK, 2020) İnce Yardımcı, Atike; Tanoğlu, Metin; Yılmaz, Selahattin; Selamet, YusufIn this study, carbon nanotubes (CNTs) added polyacrylonitrile/polypyrrole (PAN/PPy) electrospun nanofibers were produced. Average diameters of the nanofibers were measured as 268 and 153 nm for 10 and 25 wt% of PPy contents, respectively. A relatively higher strain to failure values (23.3%) were observed for the low PPy content. When as-grown CNTs (1 and 4 wt%) were added into the PAN/PPy blends, disordered nanofibers were observed to form within the microstructure. To improve the interfacial properties of CNTs/PAN/PPy composites, CNTs were functionalized with H2SO4/HNO3/HCl solution. The functionalized CNTs were well dispersed within the nanofibers and aligned along the direction of nanofibers. Therefore, beads formation on nanofibers decreased. The impedance of the nanofibers was found to decrease with the PPy content and CNT addition. These nanofibers had a great potential to be used as an electrochemical actuator or a tissue engineering scaffold.Article Citation - WoS: 8Citation - Scopus: 13Anticorrosion Coating for Magnesium Alloys: Electrospun Superhydrophobic Polystyrene/Sio2 Composite Fibers(TUBITAK, 2018) Horzum Polat, Nesrin; Kap, Özlem; Farzaneh, AmirSuperhydrophobic nanocomposite coatings for magnesium surfaces with remarkable corrosion resistance were fabricated by electrospinning in the presence of fluorosilane-functionalized silica (SiO2) nanoparticles. The effects of surface-modified silica (mod-SiO2) nanoparticles on the superhydrophobicity and corrosion resistance of polystyrene (PS)/mod-SiO2 fiber coatings were evaluated. The incorporation of the SiO2 nanoparticles endows PS fibers with rough surfaces exhibiting a water contact angle (WCA) of 165◦. The surface wettability, corrosion resistance, and their relation to the inorganic content in the PS fibers and the contact angle of the composite coatings were explored. Analysis of the corrosion results confirmed that the PS/mod-SiO2 coating protected the Mg surface from corrosion. In addition, PS fibers containing mod-SiO2 nanoparticles showed improved hydrophobicity, and excellent corrosion resistance was achieved with PS fibers containing 4 wt% SiO2 nanoparticles.Article Citation - WoS: 12Citation - Scopus: 15Morphological and Molecular Identification of Pennate Diatoms Isolated From Urla, Izmir, Coast of the Aegean Sea(TUBITAK, 2013) Kesici, Kutsal; Tüney, İnci; Sukatar, Atakan; Zeren, Doğuş; Güden, MustafaDiatoms represent an important class of aquatic phototrophs. They are not only one of the major contributors to global carbon fixation, but also play a key role in the biogeochemical cycling of silica. Molecular identification methods based on conserved DNA sequences, such as ITS (Internal Transcribed Spacer) have revolutionized our knowledge and understanding of conventional taxonomy. In this study, we aimed to compare the conventional identification methods with molecular identification methods. To do so, we isolated four diatom samples from Coast of Urla and characterized them using light microscopy (LM) and scanning electron microscopy (SEM) according to morphological features. Then, we amplified ITS regions using conventional polymerase chain reaction (PCR), sequenced the PCR products and analyzed the sequences using bioinformatic tools. Bioinformatic analysis indicated that the isolated species had high sequence similarity to Pseudo-nitzschia sp., Achnanthes sp., Amphora sp. and Cylindrotheca sp. We believe that molecular identification methods enable rapid and more reliable identification of diatom species and are crucial for monitoring harmful algal blooms.