Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
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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: 4Citation - Scopus: 4Effects of Catalyst Precursor Type and Preparation Conditions, and Solvent Type on Activity and Selectivity of Pt/Sio2 Catalyst in Citral Hydrogenation(Walter de Gruyter GmbH, 2011) Depboylu, Can Okan; Yılmaz, Selahattin; Akkurt, SedatIn this study, citral hydrogenation reaction in liquid phase over silica gel supported Pt catalysts was investigated. It was desired to hydrogenate carbonyl group selectively to produce valuable unsaturated alcohols, namely geraniol and nerol. Pt/SiO2 catalysts were prepared by impregnation method. The effects of parameters investigated in the present study included Pt precursor type (hexachloroplatinic acid (HCLPA), platinum II acetylacetonate (PAA)), catalyst activation temperature (350°C and 450°C), catalyst activation without calcination, catalyst washing with 0.1 M NaOH and solvent type (ethanol, 2-pentanol). The catalysts activities and selectivities were affected by the type of precursor and activation temperature. The maximum citral conversion (89.50 percent) was achieved at lower activation temperature (350°C) with PAA precursor based catalyst. It was observed that higher activation temperature provided lower citral conversion but higher selectivity to unsaturated alcohols; increasing the activation temperature to 450°C decreased citral conversion to 26.10 percent. But selectivity to unsaturated alcohols, geraniol and nerol, increased from 7.06 to 54.60 percent. Catalyst washing and 2-pentanol prevented acetal formation. Catalyst activation without calcination gave lower citral conversion (20.84 percent) and selectivity to unsaturated alcohols (30.00 percent). Copyright © 2011 The Berkeley Electronic Press. All rights reserved.Conference Object Kompozit Alüminyum Köpüklerin Hazırlanması ve Mekanik Özelliklerinin Belirlenmesi(2015) Güden, Mustafa; Elbir, Semih; Yılmaz, SelahattinPreslenmiş tabletlerin ısıtılması yöntemi ile hazırlanan kapalı hücreli SiC-parçacık takviyeli alüminyum kompozit köpüğün köpükleşme ve basma mekanik testi özellikleri belirlenmeye çalışılmıştır. Bu özellikler aynı yöntemle hazırlanan saf alüminyum köpüğün özellikleri ile karşılaştırılmıştır. Sonuçlar, SiC-parçacık takviyeli köpüklerde köpükleşmenin ve plato gerilmesinin daha yüksek olduğunu göstermiştir.Article Citation - WoS: 54Citation - Scopus: 62Sic-Particulate Aluminum Composite Foams Produced by Powder Compacts: Foaming and Compression Behavior(Springer Verlag, 2003) Elbir, Semih; Yılmaz, Selahattin; Toksoy, Ahmet Kaan; Güden, Mustafa; Hall, Ian W.The foaming behavior of SiC-particulate (8.6% by volume) aluminum composite powder compacts contained Titanium Hydride blowing agent was investigated by heating above the melting temperature (750°C) in a pre-heated furnace. Aluminum powder compacts were also prepared and foamed using similar compaction and foaming parameters in order to determine the effect of SiC-particulate addition on foaming and compression behavior. The linear expansions of the compacts at various furnace holding times were ex situ determined. Optical and scanning electron microscopy techniques were used to characterize prepared and deformed foams microstructures. The SiC-particulate addition was found to increase the linear expansion and reduce the extent of the liquid metal drainage and cell coarsening of the aluminum compacts. The composite foam samples also showed higher compressive stresses, but a more brittle behavior as compared with aluminum foams.Article Kapalı Hücreli Alüminyum Köpük Metallerin Üretim Metodları ve Mekanik Özellikleri(TMMOB Metalurji ve Malzeme Mühendisleri Odası, 1999) Elbir, Semih; Yılmaz, Selahattin; Güden, MustafaKapali hücreli alüminyum köpük metallerin üretim metodları, mikroyapisi, mekanik özellikleri ve uygulama alanları özetlenmiştir. Bu malzemelerin en önemli mekanik özelliklerinden birisi basma altında yüksek miktarda enerji emme kapasiteleridir. Fraunhofer Research Center tarafından toz metalurjisi ile üretilen değişik yoğunluktaki alüminyum köpük metallerine basma testleri yapılmıştır. Basma gerilmesi yoğunluğun artmasıyla yükselmiştir. Fakat enerji emme kapasiteleri yoğunluğun artması ile azalmıştır. Köpük metal hücre duvarlarının oksit tabakası ile kaplı olduğu gözlenmiştir.