Materials Science and Engineering / Malzeme Bilimi ve Mühendisliği
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Book Part Citation - Scopus: 1A Recycling Route of Plastics Via Electrospinning: From Daily Wastes To Functional Fibers(Walter de Gruyter GmbH, 2019) Isık, Tuğba; Horzum,N.; Demir, Mustafa MuammerSince large-scale plastic production has begun in the 1940s, plastics have been produced and used globally, bringing many advantages to modern life. The consumption of plastics has increased exponentially due to their low cost, chemical resistance, lightness, durability and ability to combine with other materials. However, plastic materials represent high tonnage in urban wastes, and it is known that these plastics discarded at the end of their useful life by filling the landfill sites. Electrospinning is a well-established and versatile technique for the fabrication of submicron fibers. In addition, it is a promising approach for the recycling of waste polymers without using complex methodologies. In this chapter, utilization of electrospinning approach for the recycling of daily wastes will be discussed. The literature about the daily wastes of both synthetic materials and natural/agricultural materials will be analyzed, and the applications of these materials will be given in detail. © 2019 Walter de Gruyter GmbH, Berlin/Boston. All rights reserved.Article Citation - WoS: 8Citation - Scopus: 10Impact of Simulated Inflammation and Food Breakdown on the Synergistic Interaction Between Corrosion and Wear on Titanium(Elsevier, 2024) Lima, A.R.; Pinto, A.M.P.; Toptan, F.; Alves, A.C.This paper investigates the impact of lactic acid and phosphoric acid additives in artificial saliva (AS), simulating inflammation and food breakdown, on the electrochemical and tribo-electrochemical behavior of titanium. The results showed that, unlike lactic acid, phosphoric acid significantly reduced corrosion resistance, mainly due to local damage and heterogeneities on the passive film. Non-additivated AS caused greater wear volume loss, with mechanical wear identified as the main mechanism. However, when additives were present, a synergistic interplay between corrosion and wear was observed. The study concludes that prolonged exposure to food breakdown could accelerate material degradation in titanium. © 2024 Elsevier LtdArticle Citation - WoS: 2The Effect of the Temperature of Heat Treatment Process and the Concentration and Duration of Acid Leaching on the Size and Crystallinity of Nano-Silica Powders Formed by the Dissociation of Natural Diatom Frustule(American Scientific Publishers, 2022) Ülker, Sevkan; Güden, MustafaThe present study focused on the processing of nano-silica powders in varying sizes and crystallinities through IP: 846247.10 On: Wed, 14 Dec 2022 07:29:25 heat treatment (900-1200 degrees C), hydrofluoric acid leaching (1-7 N), and ball milling (1 h, 500 rpm) of natural Copyright American Scentfic P blishers diatom frustules. The starting natural frustules were determined to be composed of amorphous silica (88%) Delivered by Ingenta and quartz. The partially ordered crystalline low-quartz and or precursor to low-cristobalite started to form at-900 degrees C. As the heat treatment temperature increased, the crystallinity of the frustules increased from 9.3% at 25 degrees C to 46% at 1200 degrees C. Applying a ball milling reduced the mean particle sizes of the as-received and heat-treated frustules from 15.6-13.7 mu m to 7.2-6.7 mu m, respectively. Acid leaching of the as-received and heat-treated frustules resulted in a further increase in the crystallinity. Furthermore, a ball milling applied after an acid leaching was very effective in reducing the particle size of the as-received and heat-treated frustules. The mean particle size of the acid-leached frustules decreased to 774-547 nm with a crystallinity varying between 12 and 48% after ball milling. A partially dissolved amorphous phase was observed in between crystalline silica grains after acid leaching, which resulted in a rapid fracture/separation of the frustules in ball milling.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 - WoS: 9Citation - Scopus: 7Understanding the Impact of Sri2 Additive on the Properties of Sn-Based Halide Perovskites(Elsevier, 2022) Yüce, Hürriyet; Perini, Carlo A. R.; Hidalgo, Juanita; Castro-Mendez, Andres-Felipe; Evans, Caria; Demir, Mustafa MuammerOrganic-inorganic halide perovskites have been identified as favorable candidates for the next generation of photovoltaics. Adding alkali metal halides to perovskite films has been shown to be a viable option to improve the perovskite film quality and to modulate their fundamental properties. In this work, we perform optical and electron-beam based characterizations of mixed Sn/Pb based perovskite films to investigate the effect of the addition of the alkaline metal halide SrI2. By analyzing structural (X-ray diffraction), morphological (Scanning Electron Microscopy), optical (photoluminescence), and chemical properties (X-ray photoelectron spectroscopy), we show a complex interplay of effects upon addition of Sr2+ into the perovskite solution. Low concentrations of Sr2+ increases lattice strain, which hints at incorporation of the additive into the perovskite lattice and improves the film optoelectronic properties. As the additive concentration increases beyond 0.5 mol %, microstrain decreases. At concentrations >0.5 mol %, Sr2+ induces significant reduction of the average domain size, which impacts both structural and optical properties of the perovskite film.Article Citation - WoS: 61Citation - Scopus: 64Electrospun Gelma Fibers and P(hema) Matrix Composite for Corneal Tissue Engineering(Elsevier Ltd., 2021) Arıca, Tuğçe A.; Güzelgülgen, Meltem; Yıldız, Ahu Arslan; Demir, Mustafa MuammerThe development of biocompatible and transparent three-dimensional materials is desirable for corneal tissue engineering. Inspired from the cornea structure, gelatin methacryloyl-poly(2-hydroxymethyl methacrylate) (GelMA-p(HEMA)) composite hydrogel was fabricated. GelMA fibers were produced via electrospinning and covered with a thin layer of p(HEMA) in the presence of N,N?-methylenebisacrylamide (MBA) as cross-linker by drop-casting. The structure of resulting GelMA-p(HEMA) composite was characterized by spectrophotometry, microscopy, and swelling studies. Biocompatibility and biological properties of the both p(HEMA) and GelMA-p(HEMA) composite have been investigated by 3D cell culture, red blood cell hemolysis, and protein adsorption studies (i.e., human serum albumin, human immunoglobulin and egg white lysozyme). The optical transmittance of the GelMA-p(HEMA) composite was found to be approximately 70% at 550 nm. The GelMA-p(HEMA) composite was biocompatible with tear fluid proteins and convenient for cell adhesion and growth. Thus, as prepared hydrogel composite may find extensive applications in future for the development of corneal tissue engineering as well as preparation of stroma of the corneal material. © 2020 Elsevier B.V.Book Citation - Scopus: 19Advanced Sensor and Detection Materials(John Wiley and Sons Inc., 2014) Tiwari, Ashutosh; Demir, Mustafa MuammerPresents a comprehensive and interdisciplinary review of the major cutting-edge technology research areas-especially those on new materials and methods as well as advanced structures and properties-for various sensor and detection devices. The development of sensors and detectors at macroscopic or nanometric scale is the driving force stimulating research in sensing materials and technology for accurate detection in solid, liquid, or gas phases; contact or non-contact configurations; or multiple sensing. The emphasis on reduced-scale detection techniques requires the use of new materials and methods. These techniques offer appealing perspectives given by spin crossover organic, inorganic, and composite materials that could be unique for sensor fabrication. The influence of the length, composition, and conformation structure of materials on their properties, and the possibility of adjusting sensing properties by doping or adding the side-groups, are indicative of the starting point of multifarious sensing. The role of intermolecular interactions, polymer and ordered phase formation, as well as behavior under pressure and magnetic and electric fields are also important facts for processing ultra-sensing materials. The 15 chapters written by senior researchers in Advanced Sensor and Detection Materials cover all these subjects and key features under three foci: 1) principals and perspectives, 2) new materials and methods, and 3) advanced structures and properties for various sensor devices. © 2014 Scrivener Publishing LLC. All rights reserved.Book Part Citation - WoS: 11Recent Progresses in Perovskite Solar Cells(Intech Europe, 2017) Demiç, Şerafettin; Özcivan, Ahmet Nuri; Can, Mustafa; Özbek, Cebrail; Karakaya, MervePerovskite solar cell (PSC) can be regarded as a continuation of dye sensitized solar cell (DSSC) in terms of the sensitization phenomena that occurred in the functioning molecules. In 2012, a breakthrough propose has been made for the sensitization of PSCs, in which a solid-state structure is offered as an equivalent sensitizer used in DSSC. The power conversion efficiency (PCE) of those solid-state cells reached about twofold of its initial value during the past several years. Immediately after, the researchers followed this propose worldwide. They have introduced an improved efficiency of as much as 20%, which was originally started from its initial value of 4%, just in 4 years. Thus, the new concept, solid perovskite molecules, has eliminated the need for the liquid electrolyte in DSSC while still carrying the advantages of organic solar cells (OSCs). Therefore, the distinctive material of PSC-the organometallic halide molecules (also known as OMH or organic-inorganic trihalides)-inclined an unexpected reputation for solar cell (SC) researches. Hence, it seems that we will witness a new age for solar conversion devices depending on the recent hopeful progresses on PSCs. The high rate of photovoltaic (PV) conversion capacity in PSC is generally expressed by the basic properties possessed by the organic-inorganic perovskite crystal, such as better optical properties and well diffused charges along huge distances during the charge transport. In addition, a low temperature processing is applicable during its production. Moreover, the perovskite layer provides a tunable band gap. Therefore, depending on better developments on designed molecules, PSC may gain extreme performances compared to the other competitors, such as OSC or DSSC devices. This chapter starts with a general discussion on the need for an affordable clean energy conversion device that is urgent for the future of humanity, due to publicly well-known global warming issue. In Section 2, basic properties of PSC are mentioned together with their structure and working principles. Section 3 continues with an overview on organometallic perovskite molecules after a brief introductory history is presented. The absorption and band gap properties are also discussed. Since most perovskite materials need a hole transporting material (HTMs) within the PSC, the kinds of HTMs that are designed for PSCs are described in Section 3. The rendering of long-term stabilization has special importance for PSCs since the instability issue remained idle in spite of those recent increased efficiency values attained by various research groups. Therefore, the stability issues are discussed in a separate part in Section 4. We finally close the chapter discussing the challenges and opportunities relying on the chapter content. We note that the recent investigations on PSCs have special importance for its large-scale realization in order to make them ready for the photovoltaic industry of the future. Hence, there are various announced meetings focusing on its mass production due to the unexpected sharp rise of the perovskite efficiency in the last 6 years. Hence, all the new cutting-edge scientific findings are also dealt with commercialization issues now, in order to attain the desired low cost fabrication, including the yield of high purity and the formation of smooth films during the continual manufacture of perovskite layers.Conference Object Development of Graphene Nanoplatelets Reinforced Aluminium Matrix Nanocomposites by a Combination of Semi-Solid Stirring and Ultrasonic Treatment(European Conference on Composite Materials, 2016) Kandemir, Sinan; Aydoğan, YücelGraphene Nanoplatelets (GNPs) consisting of graphene layers with a thickness less than 100 nm have recently emerged as a promising reinforcement type owing to their excellent physical and mechanical properties to improve mechanical properties of alloys beyond ceramic nanoparticles. Although there are numerous studies on GNPs reinforced polymer matrix composites in the literature, the number of studies related to the incorporation of GNPs in metal matrices is limited. It is a challenging task to incorporate and uniformly distribute GNPs into liquid metals due to their poor wettability and large surface-to-volume ratio. The purpose of this study is to effectively disperse GNPs into liquid aluminium. 0.5 wt.% GNPs with an average thickness of 50-100 nm and size of 5 ?m were first incorporated into A360 aluminium alloy under semi-solid stirring, and then the composite was ultrasonically treated in fully liquid state. The microstructural investigation of the nanocomposites by optical and scanning electron microscopy may suggest that relatively uniform distribution and effective deagglomeration of GNPs in the matrix were achieved. The hardness of the GNPs reinforced nanocomposites increased in comparison with that of semi-solid stirred and ultrasonically processed A360 alloy without reinforcement, indicating the potential of GNPs for strengthening metals. © 2016, European Conference on Composite Materials, ECCM. All rights reserved.Book Part Future Applications of Artificially-Synthesized Organic Molecules Containing Transition-Metal Atoms(Elsevier, 2018) Mayda, Selma; Kandemir, Zafer; Bulut, NejatArtificially-synthesized organic molecules which contain transition-metal atoms offer new possibilities for applications in the electronics, pharmaceutical, and chemical industries. Hence, developing an understanding of the electronic properties of this kind of organic molecules is important. With this purpose, here we study the electronic properties of metalloproteins, metalloenzymes, and Ru-based dye molecules as examples for this kind of organic molecules. In particular, we perform combined Hartree-Fock (HF) and quantum Monte Carlo (HF+QMC) calculations, as well as combined density functional theory (DFT) and QMC (DFT+QMC) calculations to study the electronic properties of these molecules. Our results show that new electronic states named as impurity bound states (IBS) form in metalloproteins, metalloenzymes, and Ru-based dye molecules. We show that the electron occupancy of IBS is critically important in determining the low-energy electronic properties of these molecules. In this respect, the IBS may play a central role in developing new applications based on artificially-synthesized organic molecules containing transition-metal atoms. © 2018 Elsevier Inc. All rights reserved.