Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
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Article Citation - WoS: 40Citation - Scopus: 38Anisotropic and Outstanding Mechanical, Thermal Conduction, Optical, and Piezoelectric Responses in a Novel Semiconducting Bcn Monolayer Confirmed by First-Principles and Machine Learning(Elsevier, 2022) Mortazavi, Bohayra; Fazel Shojaei; Yağmurcukardeş, Mehmet; Alexander Shapeev; Xiaoying ZhuangGraphene-like nanomembranes made of the neighboring elements of boron, carbon and nitrogen elements, are well-known of showing outstanding physical properties. Herein, with the aid of density functional theory (DFT) calculations, various atomic configurations of the graphene-like BCN nanosheets are investigated. DFT results reveal that depending on the atomic arrangement, the BCN monolayers may display semimetallic Dirac cone or semiconducting electronic nature. BCN nanosheets are also found to exhibit high piezoelectricity and carrier mobilities with considerable in-plane anisotropy, depending on the atomic arrangement. For the predicted most stable BCN monolayer, thermal and mechanical properties are explored using machine learning interatomic potentials. The room temperature tensile strength and lattice thermal conductivity of the most stable BCN monolayer are estimated to be orientation-dependent and remarkably high, over 78 GPa and 290 W/m.K, respectively. In addition, the thermal expansion coefficient of the monolayer BCN at room temperature is estimated to be −3.2 × 10−6 K−1, which is close to that of the graphene. The piezoelectric response of the herein proposed BCN lattice is also predicted to be close to that of the h-BN monolayer. Presented results highlight outstanding physics of the BCN nanosheets.Article Citation - WoS: 13Citation - Scopus: 15Effect of Silicon Nitride Coating Thickness on Silicon Wafer Substrates for Signal Enhancement in Laser-Induced Breakdown Spectroscopic Analysis of Liquids(Elsevier, 2022) Kaplan, Dilara; Yalçın, Şerife HanımIt has been shown by previous studies of our group that the use of nitride-coated silicon wafer surfaces as a sample loading substrate in dried-droplet LIBS analysis provided enhancement in plasma emission signal and better detection limits compared to uncoated or oxide-coated silicon wafer surfaces. To further investigate the effect of coating thickness for enhanced sensitivity in dried nano-droplet analysis of liquids, silicon-wafer substrates of different nitride coating thicknesses; 75, 300, 450, and 1000 nm, were comparatively studied. With 75 nm silicon nitride coating, the thin-film effect due to the anti-reflective behavior of the silicon nitride film is observed, and plasma emission signal is enhanced up to three times compared to 300 nm coated substrates. With coating thicknesses of 450 nm and 1000 nm, on the other hand, thermophysical and mechanical properties of the silicon nitride material, like thermal conductivity and hardness, become more dominant factors, leading to higher emission signals for all the elements studied. With 1000 nm coating thickness, enhancement factors of 4.8, 6.4, and 3.7 were obtained for the elements of Pb, Cu, and Cr, respectively. Optimization of the experimental LIBS parameters was conducted, calibration curves were constructed, and analytical figures of merits were determined. Sub-picogram amounts absolute detection limits; 0.7 pg Pb, 0.6 pg Cr, and 0.4 pg Cu, in 500 nanoliter droplets were obtained from the slopes of the calibration curves. The nitride-coated substrates' analytical performance was tested using certified reference solutions, standard water, and real water samples. The materials and the methodology developed can be used for waste-water monitoring of environmental samples by LIBS.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: 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: 39Citation - Scopus: 39Processing and Thermal Characterization of Polymer Derived Sicn(o) and Sioc Reticulated Foams(Elsevier, 2020) Santhosh, Balanand; Ionescu, Emanuel; Reitz, Emanuel; Albert, Barbara; Sorarù, Gian Domenico; Ahmetoğlu, Çekdar VakıfHighly porous polymer-derived SiCN(O) and SiOC ceramics with low thermal conductivity were developed by replicating polyurethane (PU) foams. The PU templates were impregnated with polysilazane or polysiloxane precursor, followed by pyrolysis at different temperatures (1200 °C - 1500 °C) yielding SiCN(O) or SiOC ceramic foams, respectively. The swelling and cross-linking behavior of the used precursors had a significant impact on the morphology of the prepared foams. The samples had bulk densities ranging from 0.03 g.cm-3 to 0.56 g.cm-3 and a total porosity in the range from 75 to 98 vol%. Fourier transform infrared (FT-IR), Raman spectroscopy, X-ray diffraction (XRD) were employed to follow the structural evolution together with morphological characterization by scanning electron microscopy (SEM). The obtained ceramics were thermally stable up to 1400 °C, and the linear thermal expansion coefficient values of the porous SiCN(O) and SiOC components in the temperature range from 30 to 850 °C were found to be ~1.72 x 10-6.K-1 and ~1.93 x 10-6.K-1, respectively. Thermal conductivity (?) as low as 0.03 W.m-1 K-1 was measured for the SiCN(O) and SiOC foams at room temperature (RT). The ? of the ceramic struts were also assessed by using the Gibson-Ashby model and estimated to be 2.1 W.m-1 K-1 for SiCN(O), and 1.8 W.m-1 K-1 for SiOC. © 2019 Elsevier Ltd and Techna Group S.r.l.Article Citation - WoS: 2Citation - Scopus: 2Tuning Thermal Transport in Graphene Via Combinations of Molecular Antiresonances(Elsevier Ltd., 2018) Sevim, Koray; Sevinçli, HaldunWe propose a method to engineer the phonon thermal transport properties of low dimensional systems. The method relies on introducing a predetermined combination of molecular adsorbates, which give rise to antiresonances at frequencies specific to the molecular species. Despite their dissimilar transmission spectra, thermal resistances due to individual molecules remain almost the same for all species. On the other hand, thermal resistance due to combinations of different species are not additive and show large differences depending on the species. Using a toy model, the physics underlying the violation of resistance summation rule is investigated. It is demonstrated that equivalent resistance of two scatterers having the same resistances can be close to the sum of the constituents or ∼ 70% of it depending on the relative positions of the antiresonances. The relative positions of the antiresonances determine the net change in transmission, therefore the equivalent resistance. Since the entire spectrum is involved in phonon spectrum changes in different parts of the spectrum become important. Performing extensive first-principles based computations, we show that these distinctive attributes of phonon transport can be useful to tailor the thermal transport through low dimensional materials, especially for thermoelectric and thermal management applications.Article Citation - WoS: 126Citation - Scopus: 138Thermal Performance Optimization of Hollow Clay Bricks Made Up of Paper Waste(Elsevier Ltd., 2014) Sütçü, Mücahit; Del Coz Diaz, Juan Jose; Alvarez Rabanal, Felipe Pedro; Gençel, Osman; Akkurt, SedatIn this paper, the thermal behavior of hollow clay bricks made up of paper waste has been studied and their thermal performance has been optimized. On the one hand, both strength and thermal properties of different paper waste concentrations have been obtained by means of laboratory tests. Thermal conductivity of the microporous brick materials with additives produced in this study reduced from 0.68 W/m K to 0.39 W/m K compared with that of the sample without additives. On the other hand, the finite element method (FEM) has been applied to the nonlinear numerical thermal analysis of three different hollow bricks, including radiation and convection phenomena inside holes. Next, using the design of experiments (DOE) over the FEM models, several parameters such as the material conductivity, the convection and radiation properties and the mean brick temperature have been studied. In general, the thermal resistance is a nonlinear function that depends on the geometry of the recesses, the material properties and the temperature distribution. In all analyzed cases, minimizing the material thermal conductivity of bricks and decreasing the recesses surface radiation emissivity caused a lower thermal transmittance in the brick. Finally, the most important conclusions and the main findings of this research are exposed.Article Citation - WoS: 33Citation - Scopus: 35Thermal Dispersion in Porous Media - a Review on the Experimental Studies for Packed Beds(American Society of Mechanical Engineers, 2013) Özgümüş, Türküler; Mobedi, Moghtada; Özkol, Ünver; Nakayama, AkiraThermal dispersion is an important topic in the convective heat transfer in porous media. In order to determine the heat transfer in a packed bed, the effective thermal conductivity including both stagnant and dispersion thermal conductivities should be known. Several theoretical and experimental studies have been performed on the determination of the effective thermal conductivity. The aim of this study is to review the experimental studies done on the determination of the effective thermal conductivity of the packed beds. In this study, firstly brief information on the definition of the thermal dispersion is presented and then the reported experimental studies on the determination of the effective thermal conductivity are summarized and compared. The reported experimental methods are classified into three groups: (1) heat addition/removal at the lateral boundaries, (2) heat addition at the inlet/ outlet boundary, (3) heat addition inside the bed. For each performed study, the experimental details, methods, obtained results, and suggested correlations for the determination of the effective thermal conductivity are presented. The similarities and differences between experimental methods and reported studies are shown by tables. Comparison of the correlations for the effective thermal conductivity is made by using figures and the results of the studies are discussed. Copyright © 2013 by ASME.Article Citation - WoS: 61Citation - Scopus: 74Production of Anorthite Refractory Insulating Firebrick From Mixtures of Clay and Recycled Paper Waste With Sawdust Addition(Elsevier Ltd., 2012) Sütçü, Mücahit; Akkurt, Sedat; Bayram, Alican; Uluca, UluçProduction of porous anorthite refractory insulating firebricks from mixtures of two different clays (K244 clay and fireclay), recycled paper processing waste and sawdust addition are investigated. Suitability of alkali-containing-clay, low-alkali fireclay, pore-making paper waste and sawdust in the products was evaluated. Prepared slurry mixtures were shaped, dried and fired. Highly porous anorthite ceramics from the mixtures with up to 30% sawdust addition were successfully produced. Physical properties such as bulk density, apparent porosity, percent linear change were investigated as well as the mechanical strengths and thermal conductivity values of the samples. Thermal conductivities of the samples produced from fireclay and recycled paper waste decreased from 0.25 W/mK (1.12 g/cm 3) to 0.13 W/mK (0.64 g/cm 3) with decreasing density. Samples were stable at high temperatures up to 1100 °C, and their cold strength was sufficiently high. The porous anorthite ceramics produced in this study can be used for insulation in high temperature applications. © 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.Article Citation - WoS: 61Citation - Scopus: 66The Use of Metal Piece Additives To Enhance Heat Transfer Rate Through an Unconsolidated Adsorbent Bed(Elsevier Ltd., 2010) Demir, Hasan; Mobedi, Moghtada; Ülkü, SemraThe effects of metal piece additives on effective thermal conductivity and diffusivity of an unconsolidated adsorbent bed in which adsorbent is silica gel were investigated. The metal piece additives were copper, brass, aluminum and stainless steel with two different sizes as 1.0-2.8 mm and 2.8-4.75 mm. The effective thermal conductivity and diffusivity of the mixed bed were predicted by comparison of the experimental results with the solution of dimensionless heat conduction equation for the bed. The performed experiments showed that the addition 15wt% of aluminum pieces with sizes between 1.0 and 2.8 mm enhances the effective thermal diffusivity and conductivity of a pure silica gel bed by 157% and 242%, respectively. © 2010 Elsevier Ltd and IIR.