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Öğe Hardness and wear behaviours of al matrix composites and hybrid composites reinforced with B 4 C and SiC(Springer Nature, 2019-01-15) Çelik, Yahya Hışman; Kılıçkap, ErolThe conversion into the desired shape of the metal powders using Powder Metallurgy (PM) method enables economically mass productions. This case allows producing parts with complex and high dimensional accuracy with no machining. In this study the composites and hybrid composites with Al matrix were produced using PM method with different ratios B4C and SiC. Microhardness and wear experiments of the produced composites were investigated. Wear experiments were performed at a constant speed of 0.5 m/s, application loads of 5, 10 and 15 N and sliding distances of 250, 500, and 750 m. Then, SEM images of composites and hybrid composites were captured. The increase of the reinforcement ratio in the composites contributed to the increase of the hardness. The highest hardness value was computed as 58.7 HV from 16% B4C reinforced composite. In addition, the increase in the reinforcement ratio contributed to the increase of the wear resistance. The increase in the load and sliding distance also increased the wear. The minimum weight loss was calculated as 18 mg from 5 N load, 250 m sliding distance and 16% SiC reinforced composite.Öğe Analysis of spheroidized AISI 1050 steel in terms of cutting forces and surface quality(Slovenska Akademia Vied, 2016) Baday, Şehmus; Başak, Hüdayim; Güral, AhmetIn this study, the effects of microstructure differences obtained with the application of different spheroidizing heat treatment cycles on medium carbon steel on cutting forces and surface roughness values were investigated. For this purpose, a group of AISI 1050 materials was annealed at 700°C below Ac1 temperature for 720 min and cementite phases were spheroidized by the traditional method. Another group of materials was quenched after austenitization at 850°C for 15 min and then cementites were spheroidized in the ferrite matrix by over-tempering separately at 600°C for 15 and 60 min and at 700°C for 60 min. Machining of the samples was tested under dry cutting conditions in CNC turning center with SNMG 120408 cementite carbide cutting tool and proper PSBNR 2525M12 tool holder with 75-degree edge angle. Cutting forces of traditionally spheroidized samples were lower than the samples spheroidized after quenching. In addition, their cutting forces decreased due to the increase in the average sizes of spheroidal cementite. Minimum surface roughness value was obtained from the samples which were spheroidized at 600°C for 15 min after quenching. However, surface roughness rate of the sample increased as spheroidizing time increased.Öğe Morphological, structural and optical characteristics of graphene oxide layers and metal/interlayer/semiconductor photovoltaic diode application(National Institute of Research and Development for Optoelectronics, 2018) Güllü, Ömer; Çankaya, MuratThis work describes the optical, morphological and structural characterizations of graphene oxide (GO) layers grown by drop casting and annealing process. UV-vis optical measurement shows that the values of direct and indirect optical gap energy of the GO film are 3.89 eV and 3.21 eV, respectively. The graphene oxide (GO) layer has been placed in the metal/ interlayer /semiconductor (MIS) diodes (total 17 devices) on p-Si wafers. The graphene oxide diodes give a better barrier height enhancement as compared with the conventional diodes. The value of homogeneous barrier height for Al/GO/p-Si MIS junctions was extracted as 0.74 eV. The diodes were also investigated under 300 watt light illumination for photovoltaic applications. Additionally, interfacial properties of the MIS diode with GO interlayer were determined. It has been seen that the capacitance of the device changes as a function of gate voltage and signal frequency from the capacitance-frequency measurements. It has also been reported that the interfacial trap charges reduce the capacitance with increasing frequency values.Öğe The characteristic diode parameters in Ti/p-InP contacts prepared by DC sputtering and evaporation processes over a wide measurement temperature(World Scientific, 2017-06) Ejderha, Kadir; Asubay, Sezai; Yıldırım, Nezir; Güllü, Ömer; Türüt, Abdülmecit; Abay, BahattinThe titanium/p-indium phosphide (Ti/p-InP) Schottky diodes (SDs) have been prepared by thermal evaporation and DC magnetron sputtering deposition. Then, their current-voltage (I-V) characteristics have been measured in the sample temperature range of 100-400K with steps of 20K. The characteristic parameters of both Ti/p-InP SDs have been compared with each other. The barrier height (BH) values of 0.824 and 0.847 at 300K have been obtained for the sputtered and the evaporated SDs, respectively. This low BH value for the sputtered SD has been attributed to some defects introduced by the sputtered deposition technique over a limited depth in to the p-type substrate. The BH of the evaporated and sputtered diodes has decreased with the standard deviations of 58 and 64mV obeying to double-Gaussian distribution (GD) in 220-400K range, respectively, and it has seen a more sharper reduction for the BHs with the standard deviations of 93 and 106 mV in 100-220K range. The Richardson constant values of 89.72 and 53.24A(Kcm)-2 (in 220-400K range) for the evaporated and sputtered samples, respectively, were calculated from the modified ln(I0/T2)-q2σs2/2k2T2 vs (kT)-1 curves by GD of the BHs. The value 53.24A(Kcm)-2 for the sputtered sample in high temperatures range is almost the same as the known Richardson constant value of 60A(Kcm)-2 for p-type InP.Öğe Simultaneous electrochemical evaluation of ascorbic acid, epinephrine and uric acid at disposable pencil graphite electrode: Highly sensitive determination in pharmaceuticals and biological liquids by differential pulse voltammetry(Elsevier, 2018) Levent, Abdulkadir; Önal, GünayAim and Objective: As is known, AA, EP and UA can also coexist in biological fluids. Therefore, the determination of the levels of these compounds in biological fluids is extremely important both for the diagnosis and treatment of the related diseases. In the presence of many interfering substances in biological fluids such as blood and urine samples, it is very important that these compounds can be selectively analyzed. Materials and Methods: All electrochemical experiments were performed using an Autolab PGSTAT 128N potentiostat. Before beginning the electrochemical measurements, the PGE was activated. The electrochemical pretreatment of PG was exercised by anodically +1.40 V for 60 s. Then, measurements were performed with CV (-0.4 V to 1.2 V) and DPV (-0.2 V to 0.7 V) for single and simultaneous voltammetric behaviour of AA, EP, and UA in the electrochemical method. Results: The anodic peak potentials of AA and UA were observed at about +0.32 V and +0.62 V, respectively. On the other hand, for EP, while anodic peak potential was observed at about +0.53 V, in the reverse scan, cathodic peak potentials were observed at about +0.41 V and +0.007 V. The39 reduction peak observed at +0.3 V with the oxidation peak observed at +0.53 V are the reversible peaks. In the method developed for the electrochemical simultaneous determination of AA, EP and UA using PGE with DPV technique in BR buffer solution (pH 4.0), the anodic peak potentials are sufficiently separated from each other. Conclusion: A voltammetric method was developed for the simultaneous determination of AA, EP and UA with PGE for the first time. Here, the most important thing is that the simultaneous determination of AA, EP and UA was successfully achieved with that targeted voltammetric method which was sensitive, low-cost, practical and well-repeated; and that these were proven to be selectively applicable in pharmaceutical products and biological liquids.Öğe Separation, optimization, and quantification of cytokinins by a recently developed amide-embedded stationary phase(Taylor & Francis, 2017-07-06) Aral, Hayriye; Haşimi, Duygu; Aral, Tarık; Levent, Abdulkadir; Ziyadanoğulları, BerrinIn this study, some plant growth regulators known as cytokinins [kinetin (K), zeatin (Z), thidiazuron (TDZ), benzylaminopurine (BAP), and dimethylallylaminopurine (AAP)] were separated by HPLC using an amide-embedded mixed-mode stationary phase which was synthesized by Aral et al. in recent years. The effect of mobile phase content, mobile phase pH, buffer concentration, and temperature on separation process was studied. In addition, a quantitative determination of cytokinins from Salvia limbata extract was studied, and some validation parameters such as limit of detection (LOD), limit of quantification (LOQ), and relative standard deviation (RSD) were calculated as a range of 0.03–0.1, 0.1–0.26 mg/L, and 0.03–0.08, respectively.Öğe Investigation of the effect of different variables on strength of adhesive joints(WILEY, 2014-10-01) Adin, Hamit; Deniz, Mehmet EminIn this article, the tensile strength of different adhesive bonded joints under a tensile load was analyzed numerically. The effects of certain parameters, including the bonding length and bonding ratio, were investigated. For this reason, the epoxy adhesive was used. Joints were prepared with aluminum materials. The stress analyses were employed using the Finite Element Method (FEM). ANSYS (v.14.0.1) FEM tool was utilized to investigate the stress distribution characteristics of aluminum lap joint under tensile loading. Numerical results were found to be quite reasonable. The numerical results show that the influences of variations are very notable when the equivalent stresses are between 18 MPa and 20 MPa. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Öğe HPLC separation of different groups of small polar compounds on a novel amide-embedded stationary phase(Elsevier, 2014-05-10) Aral, Hayriye; Aral, Tarık; Çelik, Kadir Serdar; Ziyadanoğulları, Berrin; Ziyadanoğulları, RecepRetention behaviors of an amide-embedded silica base stationary phase, which was recently developed by our group, were studied by using six different groups of small polar compounds including phenolic compounds, substituted anilines, chlorinated herbicides, Sudan dyes and some nucleotides and nucleosides in HPLC. The chromatographic behaviors of the prepared stationary phase for these analytes were compared with those of a commercially available reversed-phase column ACE C18 under same conditions. Among the six groups of analytes studied, the amide-silica stationary phase showed enhanced selectivity towards phenolic compounds, substituted anilines, Sudan dyes and herbicides under reversed-phase conditions and satisfactory selectivity towards nucleosides and nucleotides which could not be separated with ACE C18 column under HILIC conditions. Experimental data provided some evidence that functional groups on the stationary phases might have certain degrees of influence on selectivity possibly through secondary interactions with the model compounds. The retentions of the moderately polar compounds such as phenolic acids, anilines and herbicides on the stationary phase are higher than highly polar compounds such as nucleotides and nucleosides due to both the hydrophobic and hydrophilic interactions between the stationary phase and analytes. The quantitative determination of Sudan dyes (I, II, III, and IV) in red chilli peppers was performed. Many red chilli peppers were screened and three of them contained Sudans dyes.Öğe New inner product quasilinear spaces on interval numbers(Hindawi, 2016) Bozkurt, Hacer; Yılmaz, YılmazPrimarily we examine the new example of quasilinear spaces, namely, "IRn interval space." We obtain some new theorems and results related to this new quasilinear space. After giving some new notions of quasilinear dependence-independence and basis on quasilinear functional analysis, we obtain some results on IRn interval space related to these concepts. Secondly, we present Is,Ic0,Il∞, and Il2 quasilinear spaces and we research some algebraic properties of these spaces. We obtain some new results and provide an important contribution to the improvement of quasilinear functional analysis.Öğe Barrier enhancement of Al/n-InP Schottky diodes by graphene oxide thin layer(Scientific Publishers, 2019) Güllü, Ömer; Çankaya, Murat; Rajagopal Reddy, VarraIn the present work, the surface morphology, structural and optical features of graphene oxide (GO) films are investigated. The Al/GO/n-InP MIS diode is formed by depositing GO layer on n-InP wafer for the barrier enhancement. Interfacial properties of the MIS diode with GO interlayer are extracted from current–voltage (I–V) measurement. The simple diode parameters such as barrier height and ideality factor are extracted from I–V plots, and the values are compared with those of conventional Al/n-InP MS contact. The value of barrier height (BH) for the Al/GO/n-InP contact is found as 0.85 eV. The BH value of 0.85 eV of the Al/GO/n-InP MIS structure is as high as around 100% compared to the value of 0.43 eV of the Al/n-InP reference contacts. We have showed that the value of 0.85 eV is one of the highest values presented for reference contacts with an interlayer.
