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Öğe Azo dye-functionalized magnetic Fe3O4/polyacrylic acid nanoadsorbent for removal of lead (II) ions(Elsevier B.V., 2020) Sadak, Omer; Hackney, Robert; Sundramoorthy, Ashok K.; Yilmaz, Galip; Gunasekaran, SundaramWe report the fabrication of a nanoadsorbent for the removal of heavy metals. The nanoadsorbent is comprised of ferric oxide (Fe3O4) magnetic nanoparticles (MNPs) covalently conjugated with polyacrylic acid (PAA) and further functionalized with an azo dye (Congo red, CR) using carbodiimide. This Fe3O4 core and PAA-CR shell system (MNP/PAA-CR) exhibited binding affinity towards various cations (Pb2+, Fe2+, Fe3+, Cd2+, and Cu2+) at room temperature. Using MNP/PAA-CR we studied its heavy metal removal effectiveness and kinetics targeting Pb2+ under various reactions conditions including time and pH. The Pb2+ removal efficiency and adsorption capacity were maximal at pH 6.5 and 45 min of reaction time, and the Pb2+ adsorption kinetics better fit a pseudo second-order model than a first-order model. The adsorption of Pb2+ by MNP/PAA-CR was also investigated by the so-called Langmuir and Freundlich isotherms, and the Langmuir isotherm predicted a maximum absorption of 195.3 mg.g-1. Our results further indicated that MNP/PAA-CR is potentially reusable after desorption of the adsorbed metal with only small decline in adsorption ability over five consecutive cycles of regeneration. © 2020 Elsevier B.V.Öğe Conventional and Microcellular Injection Molding of a Highly Filled Polycarbonate Composite with Glass Fibers and Carbon Black(Mdpi, 2022) Yilmaz, Galip; Devahastin, Apichart; Lih-Sheng TurngConventional solid injection molding (CIM) and microcellular injection molding (MIM) of a highly filled polycarbonate (PC) composite with glass fibers and carbon black were performed for molding ASTM tensile test bars and a box-shape part with variable wall thickness. A scanning electron microscope (SEM) was used to examine the microstructure at the fractured surface of the tensile test bar samples. The fine and uniform cellular structure suggests that the PC composite is a suitable material for foaming applications. Standard tensile tests showed that, while the ultimate strength and elongation at break were lower for the foamed test bars at 4.0-11.4% weight reduction, their specific Young's modulus was comparable to that of their solid counterparts. A melt flow and transition model was proposed to explain the unique, irregular tiger-stripes exhibited on the surface of solid test bars. Increasing the supercritical fluid (SCF) dosage and weight reduction of foamed samples resulted in swirl marks on the part surface, making the tiger-stripes less noticeable. Finally, it was found that an injection pressure reduction of 25.8% could be achieved with MIM for molding a complex box-shaped part in a consistent and reliable fashion.Öğe A new approach for high-quality production of UHMWPE by applying powder vibration densification before sintering(Elsevier, 2023) Yilmaz, Galip; Uslu, EminDue to its extreme viscosity, UHMWPE powder requires elevated pressure and temperature settings to ensure a fully solid structure. But a gentle process is vital for reliability in certain applications, such as prosthetic liners. A unique type of large gap, not mentioned in the literature, has been observed to resist closing more than regular gaps due to the number of particles forming a shield against pressure. As a solution, a mechanical vibration treatment of the particles before heating was used to eliminate these particular large gaps. Optimum vibration parameters were found, and the samples' final solid density and mechanical properties increased. The particles' dimensions and coefficient of friction were measured, and their vibration-dependent characteristics were discussed. A custom-made microscope apparatus was used to observe the vibration-induced densification of the particles and the gaps resisting closing.Öğe Pelletizing ultra-high molecular weight polyethylene (UHMWPE) powders with a novel tapered die and addition of high density polyethylene (HDPE): Processing, morphology, and properties(Elsevier Sci Ltd, 2022) Yang, Huaguang; Yilmaz, Galip; Jiang, Jing; Xie, Jun; Langstraat, Thomas; Chu, Raymond; van Es, MartinThe extremely high molecular weight and molecular entanglement have rendered ultra-high molecular weight polyethylene (UHMWPE) superior properties. However, poor inter-particle diffusion makes it difficult to pelletize UHMWPE powders for easy processing/handling. A novel tapered die with air cooling was proposed to pelletize UHMWPE and a UHMWPE blend with 5 wt% high-density polyethylene (HDPE) for compression molding and material characterization. The tensile strength of samples prepared with the tapered die outperformed those by the regular die or from virgin powders. The addition of HDPE further improved the tensile strength. Fourier transform infrared spectroscopy (FTIR) revealed little chain scission and the lowest amount of oxidation from the tapered die. Intrinsic viscosity (IV) measurements confirmed the negligible chain scission and showed an increment in IV for the UHMWPE/HDPE blend. Multi-angle light scattering with size-exclusion chromatography (SEC-MALS) indicated no change in the UHMWPE molecular weight distribution, but some crosslinking in the blend. Polarized optical microscopy (POM) showed that the HDPE and extrusion led to a finer UHMWPE domain size and better fusion between UHMWPE and HDPE. The combined effect of enhanced molecular chain diffusion, improved consolidation, and lower oxidation using the tapered die led to 40% improvement of tensile strength for the UHMWPE/HDPE blend.Öğe Solidification analysis for variable thickness aluminum castings: simulation and chill design insights(Iop Publishing Ltd, 2023) Yilmaz, Galip; Colak, Murat; Uslu, EminManufacturing high-quality casting parts with complex geometries requires high engineering skill and precision. One essential quality concern is isolated hot spots within the castings, often in thick sections. Each hot spot must be consistently fed or mitigated through directional solidification techniques. The impact of various mold sands and the geometry of chill parts on solidification direction was investigated using specialized casting and general-purpose simulation programs. A parametric optimization method was employed to analyze directional solidification to adjust the geometry of the chill parts. The results indicate that employing diverse mold sands to enhance cooling in the thick sections was a viable strategy for achieving directional solidification in parts where the feeding pathway is obstructed due to changes in cross-section. Furthermore, the study revealed that intricate details in the chill part's geometry are not critical; however, a minimum volume (or weight) was necessary for adequate directional solidification. Lastly, an easily applicable mathematical model has been developed to determine the required volume of chill parts to ensure successful directional solidification.Öğe Tek ve çift katmanlı yapay damar konfigürasyonlarının Holzapfel-Gasser-Ogden hiperelastik modeli ile mekanik uyumluluk analizi(2022) Yilmaz, Galip; Uslu, EmınYaygınlaşan kalp-damar hastalıkları, yapay damarların önemini artırmıştır. Üretim şartları gereği farklı tasarımlar içeren bu damarların, doğal bir mekanik davranış göstermesi gerekmektedir. Üretim öncesi ihtiyaç duyulan analizlerin yapılması için karmaşık ve hiperelastik bir özellik gösteren damar mekaniğini modelleyen birçok çalışma bulunmaktadır. Bunlar arasından yaygın kullanımı olan Holzapfel-Gasser-Ogden (HGO) hiperelastik modeli bu çalışmada kullanılmıştır. Bu çalışma kapsamında bir simülasyon ortamı HGO modeliyle hazırlanmış ve literatürdeki verilerle doğruluğu teyit edilmiştir. İlk numune iki katmanlı tipik bir yapıda oluşturulmuştur. Sonraki numunelerde üretimde karşılaşılan farklı yöntemlere dayanan katman konfigürasyonları denenmiştir. İkinci numune için dış katmanın normalden çok ince bir yapıda tasarlandığı durum incelenmiştir. Az bir uyumsuzluk olmasına rağmen kalınlığı azalan dış katmanın damarın mekanik özellikleri üzerinde güçlü bir etkisinin olmadığı gözlemlenmiştir. Üçüncü tip numunede ise dış katmanın geometrik ve malzeme özellikleri bakımından iç katman olarak tasarlandığı bir durum denenmiştir. Mekanik özelliklerinin karmaşık ve uyumsuz olduğu gözlemlenmiştir. Son numune olarak, tek katmanlı bir yapı tasarlanmıştır. Bir miktar uyumsuzluk gösterse de bu numune sadelik açısından avantajlı bulunmuştur. Ayrıca ikinci ve üçüncü numunelerin malzeme parametreleri değişimiyle uyum analizi yapılmıştır. Üçüncü numunenin aksine ikinci numune için dış katman içindeki liflerin malzeme özelliklerinin ayarlanmasıyla kolayca referans numunesinin özelliklerinin yakalanabileceği gösterilmiştir.Öğe Thermal, rheological, and mechanical characterization of compression and injection molded ultra-high molecular weight polyethylene, high density polyethylene, and their blends(Wiley, 2023) Yang, Huaguang; Yilmaz, Galip; Jiang, Jing; Langstraat, Thomas; Chu, Raymond; van Es, Martin; Garg, PriyaTensile and impact test samples of ultra-high molecular weight polyethylene (UHMWPE), high-density polyethylene (HDPE), and their blends at various UHMWPE/HDPE weight ratios were prepared via compression molding and injection molding for thermal, rheological, and mechanical characterization. A twin-screw extruder with either a tapered die with air-cooling or a regular die was used to compound and extrude the materials prior to pelletization and molding. To the best of our knowledge, there has been no publication on pelletizing neat UHMWPE using a regular extruder. The differential scanning calorimetry analysis suggested the occurrence of re-crystallization and co-crystallization for all the blends. The rheology test confirmed that all the blends exhibited a solid-like behavior and the degree of compatibility increased with increasing HDPE content in the blends. A strong synergistic effect was observed the blends possessed a higher tensile and impact strength than their neat UHMWPE and HDPE counterparts. The compression molded (95/5) UHMWPE/HDPE samples extruded using the tapered die yielded the highest tensile strength (50.1 MPa), which was about 40% higher than that of the neat UHMWPE samples. The best composition of these blends for compression and injection molded parts is 10% HD and 50% HD, respectively.
