Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Conference Object Citation - WoS: 1Citation - Scopus: 1Microstructural Evolution During Homogenization Heat Treatment of Aa 6063 Alloy in Batch and Continuous Furnaces(Springer international Publishing Ag, 2024) Obali, Akin; Gokelma, Mertol; Urk, Deniz Kavrar; Dogan, Murat; Gokce, GokcenHomogenization heat treatment after casting is performed to eliminate the dendritic segregation and coarse eutectic intermetallic phases since they reduce the fracture toughness of aluminium alloys. By the homogenization treatment, ss-AlFeSi can be converted to more spherical alpha-AlFeSi particles. The ss -> a transition is crucial because the ss-AlFeSi particles cause a number of surface defects and limit the extrudability. Also, the rate of cooling in the homogenization furnace is one of the critical influencing factors on the size of the Mg2Si precipitates which affect the mechanical properties positively. In this study, billets of AA 6063 from the same cast were put through homogenization heat treatment by using batch-type and continuous furnaces. The solution, quenching, and aging heat treatment were applied to each sample. Microstructural characterization by SEM and the hardness test were conducted to understand the effects of the furnace type on the mechanical properties of aged AA 6063 aluminium.Article Citation - WoS: 37Citation - Scopus: 41Processing and Characterization of Geopolymer and Sintered Geopolymer Foams of Waste Glass Powders(Elsevier, 2021) Polat, Dilan; Güden, MustafaGeopolymer foams of fine and coarse waste glass (WG) powders were prepared using an activation solution of NaOH (8 M) and Na2SiO3. The effects of WG powder particle size, solid/liquid ratio (S/L = 1, 1.5, and 2) and Al foaming agent content (2-20 wt%) on the expansion and temperature behavior of the slurries were determined in-situ using a laser sensor and a thermocouple, respectively. The geopolymer foams processed using a coarse WG powder slurry, S/L = 2, and 2 wt% Al, were further sintered at 600, 700, 725, and 750 degrees C. The compression strengths and thermal conductivities of the geopolymer and sintered geopolymer foams were also determined. The slurry expansions continued until about a maximum, and the temperatures of the slurries increased to a maximum, 85-88 degrees C. At the maximum temperature, the slurry evaporation and the resultant increase in the S/L ratio limited the slurry expansion. Increasing the Al content decreased the final density of the foams (238-555 kg m-3), while the coarse powder slurries resulted in lower densities than the fine powder slurries. Three crystal phases, muscovite, sodium aluminum silicate hydrate, and thermonitrite, were determined in the geopolymer foams. The muscovite formation was noted to be favored at high S/L ratios. During sintering, the partial melting of glass particles started after about 700 degrees C, while sintering above this temperature decreased the final density of the foams. The reduced density above 700 degrees C was ascribed to the release of CO2 due to the decomposition of thermonitrite. Both the compressive strength and thermal conductivity of the geopolymer and sintered geopolymer foams increased with increasing foam density. The highest increase in the compressive strength and reduction in the density were seen in the geopolymer foams sintered at 750 degrees C.Article Citation - WoS: 1Citation - Scopus: 2Reactive Wetting of Metallic/Ceramic (al/Α-al2 O3 ) Systems: a Parallel Molecular Dynamics Simulation Study(TÜBİTAK - Türkiye Bilimsel ve Teknolojik Araştırma Kurumu, 2020) Aral, GürcanThe reactive wetting process of a flat solid alumina (?-Al2 O3) ceramic surface by metallic aluminum (Al) nanodroplets with different shapes (spherical, cylindrical, and layer) is studied using parallel molecular dynamics (MD) simulations based on a variable charge MD method, with focuses on heat transfer, mass transfer, and the structure of the reactive region at the Al/?-Al2 O3 interface. We find that the diffusion of oxygen (O) atoms from the substrate into the droplet leads to the formation of a continuous layer of reaction product at the interface. The diffusion length of oxygen atoms into the spherical Al droplet is found to be ~7.3 Å, and the number density of O atoms at the ~5 top layers of the substrate decreases substantially. As a result, the structural correlations near the reactive region differ considerably from those in the solid substrate. Heat generated by the exothermic reactions in the reactive region is transferred to both the substrate and the droplet. The heat transfer is found to be sensitive to droplet shape.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: 5Citation - Scopus: 6The Varying Densification Strain in a Multi-Layer Aluminum Corrugate Structure: Direct Impact Testing and Layer-Wise Numerical Modelling(Elsevier Ltd., 2017) Odacı, İsmet Kutlay; Güden, Mustafa; Kılıçaslan, Cenk; Taşdemirci, AlperAn aluminum (1050 H14) multi-layer corrugated structure composed of brazed 16 trapezoidal zig-zig fin layers was direct impact tested above the critical velocities for shock formation using a modified Split Hopkinson Pressure Bar. The experimentally measured stress-time histories of the cylindrical test samples in the direct impact tests were verified with the simulations implemented in the explicit finite element code of LS–DYNA. The quasi-static experimental and simulation deformation of the corrugated samples proceeded with the discrete, non-contiguous bands of crushed fin layers, while the dynamic crushing started from the proximal impact end and proceeded with a sequential and in-planar manner, showing shock type deformation characteristic. The experimental and numerical crushing stresses and the numerically determined densification strains of the fin layers increased with increasing impact velocity above the critical velocities. When the numerically determined densification strain at a specific velocity above the critical velocities was incorporated, the rigid-perfectly-plastic-locking idealized model resulted in peak stresses similar to the experimental and simulation mean crushing stresses. However, the model underestimated the experimental and simulation peak stresses below 200 m s−1. It was proposed, while the micro inertial effects were responsible for the increase of the crushing stresses at and below subcritical velocities, the shock deformation became dominant above the critical velocities.Article Citation - WoS: 21Citation - Scopus: 27Effect of High Aluminum Concentration in Water Resources on Human Health, Case Study: Biga Peninsula, Northwest Part of Turkey(Springer Verlag, 2010) Bakar, Coşkun; Özışık Karaman, Handan Işın; Baba, Alper; Şengünalp, FatmaWidespread and intense zones of silicified, propylitic, and argillic alteration exist as outcrop around the Biga Peninsula, NW Turkey. Most of the springs in the study area surface out from these altered volcanic rocks. The concentrations of aluminum (Al) in these springs ranged from 13.17 to 15.70 ppm in this region. These high levels of Al were found to exceed the maximum allowable limits (0.2 ppm) depicted in national and international standards of drinking water quality. Therefore, the effect of high Al in water resources on human health was evaluated in this research. A total of 273 people aged above 18 years and living in the Kirazli region (whose water supply is from springs emerging from these alteration zones) and in the Ciplak-Halileli region (whose water supply is provided from an alluvium aquifer) were selected as the research group. For this group, a questionnaire was completed that contained questions on descriptive characteristics of humans and a Mini-Mental State Examination (MMSE) was administered by the authors using the face-to-face interview technique. A neurological examination was then performed by the neurology specialist as a second-stage investigation. Finally, 10 ml of venous blood samples were obtained from these people as a third-stage analysis to determine the serum Al levels together with vitamin B12, folic acid, and thyroid-stimulating hormone parameters. The result typically revealed that the MMSE score was less in 31.9% and there was no statistically significant difference between the two regions. However, the result also showed that neuropathy in the history (including a careful past medical history) was significantly higher in the Kirazli region. © 2009 Springer Science+Business Media, LLC.Article Citation - WoS: 16Citation - Scopus: 19Application of Experimental Design on Determination of Aluminum Content in Saline Samples by Adsorptive Cathodic Stripping Voltammetry(TUBITAK, 2013) Yılmaz, Sinan; Öztürk, Betül; Özdemir, Durmuş; Eroğlu, Ahmet Emin; Ertaş, Fatma NilAdsorptive cathodic stripping voltammetric determination of aluminum at ng mL-1 levels in salt samples based on the metal complexation with Calcon (1-(2-hydroxynaphthylazo)-2 naphthol-4-sulfonic acid) and the subsequent adsorptive deposition onto a hanging mercury drop electrode was studied. Central composite design was used as a design method. Several chemical and instrumental parameters (pH, ligand concentration, deposition time, deposition potential, and complexing time) were involved in the experimental design. Analytical parameters such as repeatability, linearity, and accuracy were also investigated and the detection limit was found as 0.32 ng mL-1.Article Citation - WoS: 11Citation - Scopus: 15Effects of Humic Acid on Root Development and Nutrient Uptake of Vicia Faba L. (broad Bean) Seedlings Grown Under Aluminum Toxicity(Taylor and Francis Ltd., 2015) Büyükkeskin, Tamer; Akıncı, Şener; Eroğlu, Ahmet EminInteractions of humic acid with development and uptake by seedlings of Vicia faba L., (cv. Eresen 87) grown in conditions of aluminium toxicity have been investigated in pot experiments in a controlled greenhouse environment. The objective of the study was to investigate whether humic acid moderates aluminum toxicity. The seedlings were treated with solutions of aluminum chloride (AlCl3) prepared in Hoagland control nutrient solution (HO) and 50 and100 μM and humic acid + Hoagland (HA) solutions, respectively. The 50 and100 μM HA solutions increased root fresh (RFW) and dry (RDW) weights, where the RFW differed significantly from controls (HO) after statistical evaluation by NCSS (NCSS, Kaysville, Utah) with two-sample T-test range at the 5% level. The results of the current experiment suggested that humic acid had suppressed or counteracted the toxic effect of aluminum (Al3+) on both main and lateral root growth. Humic acid seems to block the effect of Al3+ on nutrient uptake, as tested by atomic absorption spectrophotometry (AAS) and flame photometery (FP). Al3+ content in the roots was significantly decreased by 219% in 50-μM HA and by 49% in 100-μM HA treatments respectively. Potassium (K+), sodium (Na+), and iron (Fe3+) were recorded as the other elements taken up in the greatest amounts among the tested nutrients, in addition to Al3+. Humic acid increased the contents of Na+, K+, manganese (Mn2+), and zinc (Zn2+) significantly in both concentrations of HA treatment compared to controls. The Fe3+ content in the roots decreased, in both treatments of HA, application by 252% and 32% respectively. The reduction in the former was significant.Article Citation - WoS: 32Citation - Scopus: 35Liquid Phase Transformation of ?-Pinene Over Beta Zeolites Containing Aluminium or Boron, Titanium and Vanadium as Lattice Ions(Elsevier Ltd., 2005) Gündüz, Gönül; Dimitrova, Raina D.; Yılmaz, Selahattin; Dimitrov, LjubomirBeta zeolites with different modules (SiO2/Al2 O3) and containing B, Ti or V in lattice positions were synthesised by different methods and tested as catalysts in liquid phase transformation of α-pinene at 100 °C in a batch reactor. It was established that the hydrogen forms of Beta samples with a SiO2/Al2O3 module of about 55-66 and containing both micro- and mesopores displayed high catalytic activity in liquid phase isomerization of α-pinene. Samples with boron, titanium or vanadium, as lattice ions possess insignificant catalytic activity.Article Citation - WoS: 104Citation - Scopus: 115An Exposure and Risk Assessment for Fluoride and Trace Metals in Black Tea(Elsevier Ltd., 2008) Sofuoğlu, Sait Cemil; Kavcar, PınarExposure and associated health risks for fluoride and trace metals in black tea were estimated. Fifty participants were randomly recruited to supply samples from the tea that they drink, and self-administer a questionnaire that inquired about personal characteristics and daily tea intake. Analyzed trace metals included aluminum, arsenic, barium, cadmium, cobalt, chromium, copper, manganese, nickel, strontium, and zinc. Fluoride and four metals (Al, Cr, Mn, Ni) were detected in all samples while barium was detected only in one sample. The remaining metals were detected in >60% of the samples. Fluoride and aluminum levels in instant tea bag samples were greater than in loose tea samples (p < 0.05) while the differences in elemental concentrations of loose and pot bag tea samples were not significant. Median and 90th percentile daily tea intake rates were estimated as 0.35 and 1.1 l/day, respectively. Neither fluoride nor aluminum levels in black tea were found to associate with considerable risks of fluorosis and Alzheimer's disease, respectively. However, carcinogenic risk levels for arsenic were high; R > 1.0 × 10-6 even at the median level. According to sensitivity analysis, daily tea intake was the most influencing variable to the risk except for arsenic for which the concentration distribution was of more importance.