Materials Science and Engineering / Malzeme Bilimi ve Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4719
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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: 6Citation - Scopus: 6The Expansion Behavior of Slurries Containing Recycled Glass Powder Carboxymethyl Cellulose, Lime and Aluminum Powder(Elsevier, 2020) Zeren, Doğuş; Şentürk, Ufuk; Güden, MustafaThe rheology and foaming/expansion of the slurries of a waste/recycled glass powder with 50, 55 and 60 wt% of solid (glass powder) were experimentally investigated. The glass powder slurries were foamed using aluminum powder as foaming agent (0.75 wt%) and calcium hydroxide as activator (1 wt%). Sodium carboxymethyl cellulose (CMC) was added to the slurries as a binder with the amounts between 0 and 4 wt%. The expansions of the slurries were measured in-situ using a laser sensor and reported as percent volume expansion. The CMC-addition increased the viscosities of the slurries, particularly the fine size powder slurries. The slurries with the relatively low-viscosity exhibited lower initial expansion rates compared to the slurries with the relatively high-viscosity. The maximum expansions of the slurries increased from 300 to 350%, when the viscosity increased to 5 Pa s and reached a steady value around 400% between 5 and 50 Pa s. The expansions of the slurries could not be achieved above 50 Pa s since they became too thick to be foamed. The foam samples made from the slurries with 55 and 60 wt% of solid and sintered at 700 and 750 degrees C for 30 min had the average densities between 355 and 530 kg m(-3) and the average compressive strengths between 0.2 and 0.5 MPa. Increasing sintering time to 60 min at 750 degrees C increased the average compressive strength from 0.5 to 1.5 MPa for the foam samples made from the slurry with 60 wt% of solid. These proved that both sintering temperature and time were effective in increasing the compressive strengths of the foamed structures. The thermal conductivities of the sintered foam samples with the densities of 355 and 504 kg m(-3) were measured 0.042 and 0.057 W m(-1) K-1, respectively. (C) 2019 Elsevier Ltd. All rights reserved.Article Citation - WoS: 17Citation - Scopus: 17Monitoring the Doping and Diffusion Characteristics of Mn Dopants in Cesium Lead Halide Perovskites(American Chemical Society, 2018) Güner, Tuğrul; Akbalı, Barış; Özcan, Mehmet; Topçu, Gökhan; Demir, Mustafa Muammer; Şahin, HasanCesium lead perovskites, in the form of CsPbX3 or Cs4PbX6, have been widely used for various optoelectronic applications due to their exceptionally good optical properties. In this study, the effect of Mn doping on the structural and optical properties of cesium lead halide perovskite crystals are investigated from both experimental and theoretical points of view. It is found that adding MnCl2 during the synthesis not only leads to a Mn-driven structural phase transition from Cs4PbBr6 to CsPbCl3 but also triggers the Br- to Cl- halide exchange. On the other hand, it is observed that, under UV illumination, the color of Mn-doped crystals changes from orange to blue in approximately 195 h. While the intensity of Mn-originated photoluminescence emission exponentially decays in time, the intensity of CsPbCl3-originated emission remains unchanged. In addition, diffusive motion of Mn ions results in both a growing population of MnO2 at the surface and transition of the host into a cesium-rich Cs4PbCl6 phase.Conference Object The Shape and Size Effect of the Diatom Frustule Addition on the Compression Behavior of an Epoxy(Trans Tech Publications, 2018) Zeren, Doğuş; Kesici, Kutsal; Sukatar, Atakan; Güden, MustafaThe effects of the Achnanthes Taeniata and the diatomaceous earth (diatomite) frustules addition on the compressive strength of an epoxy matrix were investigated experimentally. The Achnanthes Taeniata frustules having relatively high length/diameter aspect ratio (2-4) were isolated and cultured in laboratory. While the as-received commercial natural diatomite frustules were non-homogenous in shape and size. The filling epoxy matrix with ~6 wt% of commercial natural diatomite increased the compressive strength from 60 MPa to 67 MPa, while the Achnanthes Taeniata frustules addition increased to 79 MPa. The increased compressive strength and modulus of the the Achnanthes Taeniata frustules filled epoxy was attributed to the higher aspect ratio and relatively strong bonding with the epoxy matrix. The more effective load transfer from the matrix to the Achnanthes Taeniata frustules associated with the enhanced interface bonding was also proved microscopically. The frustules were observed to pull-out on the fracture surface of the Achnanthes Taeniata frustules filled epoxy.Article Citation - WoS: 8Citation - Scopus: 9The Increased Compression Strength of an Epoxy Resin With the Addition of Heat-Treated Natural Nano-Structured Diatom Frustules(SAGE Publications Inc., 2017) Zeren, Doğuş; Güden, MustafaNatural diatom frustules composing nanometer size silica particles were heat-treated at temperatures between 600 and 1200℃ for 2 h and used as filler/reinforcing agent (15 wt%) in an epoxy resin. The opal structure of as-received natural diatom frustules was transformed into cristobalite after the heat-treatment above 900℃. The epoxy resin test samples reinforced with heat-treated and as-received frustules and neat epoxy test samples were compression tested at the quasi-static strain rate of 7 × 10−3 s−1. The results showed that the inclusion of the frustules heat-treated at 1000℃ increased the compressive yield strength of the resin by 50%, while the addition of the diatom frustules heat-treated above and below 1000℃ and the as-received frustules increased the strength by ∼25% and 16%, respectively. The heat treatment above 1000℃ decreased the surface area of the frustules from 8.23 m2 g−1 to 3.46 m2 g−1. The cristobalite grains of the frustules heat-treated at 1000℃ was smaller than 100 nm, while the grain size increased to ∼500 nm at 1200℃. The increased compressive stresses of the resin at the specific heat treatment temperature (1000℃) were ascribed to nano size crystalline cristobalite grains. The relatively lower compressive stresses of the epoxy resin filled with frustules heat-treated above 1000℃ were attributed to the micro-cracking of the frustules that might be resulted from higher density of the cristobalite than that of the opal and accompanying reduction of the surface area and the surface pore sizes that might impair the resin-frustule interlocking and intrusion.Article Citation - WoS: 22Citation - Scopus: 28Mechanical Interlocking Between Porous Electrospun Polystyrene Fibers and an Epoxy Matrix(American Chemical Society, 2014) Demir, Mustafa Muammer; Horzum, Nesrin; Taşdemirci, Alper; Turan, Ali Kıvanç; Güden, MustafaAn epoxy matrix filled with nonwoven mats of porous polystyrene (PS) fibers processed by an electrospinning was compression tested at quasi-static (1 × 10–3 s–1) and high strain (315 s–1) rates. The electrospun PS fibers with a diameter between 6 and 9 μm, accommodated spherical pores on the surface with the sizes ranging from 0.1 to 0.2 μm. The filling epoxy matrix with 0.2 wt % PS fibers increased the compressive elastic modulus and compressive strength over those of neat epoxy resin. The microscopic observations indicated that the surface pores facilitated the resin intrusions into the fiber, enhancing the interlocking between resin and fibers, and increased the deformation energy expenditure of the polymer matrix.Article Citation - WoS: 60Citation - Scopus: 70Foam Glass Processing Using a Polishing Glass Powder Residue(Elsevier Ltd., 2013) Attila, Yiğit; Güden, Mustafa; Taşdemirci, AlperThe foaming behavior of a powder residue/waste of a soda-lime window glass polishing facility was investigated at the temperatures between 700 and 950 °C. The results showed that the foaming of the glass powder started at a characteristic temperature between 670 and 680 °C. The maximum volume expansions of the glass powder and the density of the foams varied between 600% and 750% and 0.206 and 0.378 g cm−3, respectively. The expansion of the studied glass powder residue resulted from the decomposition of the organic compounds on the surfaces of the glass powder particles, derived from an oil-based coolant used in the polishing. The collapse stress of the foams ranged between ∼1 and 4 MPa and the thermal conductivity between 0.048 and 0.079 W K−1 m−1. Both the collapse stress and thermal conductivity increased with increasing the foam density. The foams showed the characteristics of the compression deformation of the open cell brittle foams, which was attributed to the relatively thick cell edges.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.Article Citation - WoS: 10Citation - Scopus: 10Open Cell Lead Foams: Processing, Microstructure, and Mechanical Properties(Springer Verlag, 2012) Savacı, Umut; Yılmaz, Sinan; Güden, MustafaOpen cell lead foams with the porosities between 48 and 74 % were prepared by means of powder metallurgical and casting routes, using ammonium bicarbonate particles, silica beads, and sodium chloride salt particles as space holder. The resulting foam samples structure closely resembled open cell foam structure: each cell had few interconnections with neighboring cells. Small-sized lead (II) fluoride precipitates were microscopically observed in the interior of cells in the foam samples prepared using silica beads as space holder, resulting from the reaction between silica and hydrofluoric acid in the space holder dissolution step. The compression stress–strain curve of foam samples prepared by powder metallurgical route showed brittle deformation behavior following the initial elastic deformation region, while the foam samples prepared by casting route showed characteristic foam deformation behavior: cell edge crushing on the bent cell walls, and cell wall tearing. The collapse stresses, densification strains, and elastic moduli of the prepared foams were further fitted with scaling relations.