Chemical Engineering / Kimya Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/14
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Article Citation - WoS: 8Citation - Scopus: 7Cvd-Deposited Oxygen-Selective Fluorinated Siloxane Copolymers as Gas Diffusion Layers(American Chemical Society, 2022) Cihanoğlu, Gizem; Ebil, ÖzgençCopolymer thin films of 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4), 2-(perfluorohexylethylacrylate) (PFHEA), and 2-(perfluoroalkylethylmethacrylate) (PFEMA) were synthesized via initiated chemical vapor deposition (iCVD) as potential candidates for gas diffusion layers (GDLs) in gas diffusion electrodes (GDEs) for aqueous metal–air batteries. Thin-film GDLs exhibited an average water vapor transmission rate of 7.5 g m–2 day–1 and enhanced oxygen diffusion with oxygen permeabilities as high as 3.53 × 10–15 mol m m–2 s–1 Pa–1 (10.5 Barrer). The electrochemical performance of GDEs fabricated using commercial catalysts, current collectors, and synthesized GDLs was investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and potentiodynamic polarization measurements. The fabricated GDEs exhibited higher oxygen reduction current densities (228.2 mA cm–2) compared to commercial GDEs (132.7 mA cm–2). Copolymer GLDs exhibited an order of magnitude higher oxygen diffusion (39.5 × 10–8 cm2 s–1) in GDEs compared to commercial counterparts (1.84 × 10–8 cm2 s–1). Due to the high oxygen solubility of V4D4 and excellent hydrophobic behavior of PFHEA and PFEMA, their copolymers can effectively promote the diffusion of oxygen and restrict moisture intake, making them ideal materials for GDLs. Combining well-balanced properties of siloxane and fluorinated polymer chemistries, the iCVD process is an excellent low-cost method for the fabrication of GDLs for metal–air battery applications.Article Citation - WoS: 11Citation - Scopus: 13Sorption and Diffusion of Water Vapour on Edible Films(Springer Verlag, 2008) Berkün, Didem; Balköse, Devrim; Tıhmınlıoğlu, Funda; Alsoy Altınkaya, SacideTwo types of films consisting of sodium salt of carboxymethyl cellulose (NaCMC) and hydroxypropyl cellulose (HPC) as film forming materials and glycerin as plasticizer were prepared, characterized and their water vapour sorption properties were determined. The water sorption isotherms of the films were measured using a magnetic suspension balance. Results show that diffusion of water vapour in NaCMC based film is faster than that in HPC based films, due to the heterogeneous structure and larger pore dimensions of the NaCMC films.Article Citation - WoS: 12Citation - Scopus: 17Diffusion Mechanism of Water Vapour in a Zeolitic Tuff Rich in Clinoptilolite(Springer Verlag, 2008) Çakıcıoğlu Özkan, Seher Fehime; Ülkü, SemraThe adsorption kinetics of H2O in a clinoptilolite rich zeolitic tuff was experimentally investigated at 18°C. In the identification of the diffusion mechanism the isothermal adsorption model equation was used. It was found out that the intraparticle mass transfer becomes more dominant over the heat transfer with increase in particle size and the adsorptive dose pressure. Although initially intraparticle mass transfer was the controlling resistance later external heat transfer also contributes to the transfer mechanism.Article Citation - WoS: 5Citation - Scopus: 5Solvent Sorption in a Polymer-Solvent System - Importance of Swelling and Heat Effects(Elsevier Ltd., 2006) Alsoy Altınkaya, Sacide; Ramesh, Narayan; Duda, John LarrySorption experiments are often conducted in gravimetric sorption columns where several deviations from ideal conditions could potentially occur. For example, heat effects due to solvent sorption, errors introduced due to concentration dependent diffusion coefficients and swelling are unavoidable. In this study, we develop a model to study the importance of the combination of these effects in obtaining diffusion coefficients from sorption experiments. The model is used to explore a wide range of operating conditions and physical parameters.Article Citation - WoS: 2Citation - Scopus: 1Errors Associated With Swelling in the Analysis of Polymer-Solvent Diffusion Measurements(Elsevier Ltd., 2005) Alsoy Altınkaya, SacideSorption curves are generated from a mathematical model which includes the influence of the polymer swelling for unsteady-state sorption of a vapor or liquid by a polymer. To investigate the simultaneous effects of the specific volumes of the polymer-penetrant pair and the difference between the final and initial equilibrium concentrations on the sorption curves, statistical experimental design approach is used. Simulation results obtained from the numerical solution of model equations are utilized to estimate the error that would occur if one simply evaluates the diffusion coefficient using the traditional formulas derived from the analytical solution of the sorption equation. An empirical expression is developed that describes the effects of the difference between the final and initial equilibrium concentrations and the specific volumes of the polymer and the penetrant on the magnitude of error in diffusivity associated with the use of one of these traditional formulas so called the initial slope method. The predictive ability of the regression model is tested by performing additional simulations not used in the regression analysis.Article Citation - WoS: 26Citation - Scopus: 28Influence of Swelling and Diffusion-Induced Convection on Polymer Sorption Processes(John Wiley and Sons Inc., 2002) Alsoy Altınkaya, Sacide; Duda, John LarryUnsteady-state sorption of a vapor or liquid by a polymer is modeled to include the influence of the moving phase boundary associated with the polymer swelling and diffusion-induced convection. A formulation presented clearly elucidates the influence of these two effects on the overall sorption process. Numerical solutions of the model equations indicate the errors that can be induced when swelling or convection are neglected. For most polymer-solvent systems, the influence of the diffusion-induced convection associated with volume changes in mixing can be neglected in the analysis of sorption processes. In contrast, the correction for the moving boundary or swelling of the polymer phase can be quite significant, particularly when a large step change in solvent concentration is considered.Article Citation - WoS: 13Citation - Scopus: 15A Study of Adsorption of Water Vapour on Wool Under Static and Dynamic Conditions(Springer Verlag, 1998) Ülkü, Semra; Balköse, Devrim; Çağa, Tayfun; Özkan, Fehime; Ulutan, SevgiAdsorption of water vapour on wool provides not only textile comfort, but also convenience in transportation due to increase in its bulk density. The adsorption and desorption isotherms of water vapour for wool were determined by both volumetric technique using a Coulter Omnisorp 100CX instrument and gravimetric method employing a Cahn 2000 electronic microbalance. Adsorption isotherm fitting to B.E.T. model and hysteresis on desorption was observed. The average effective diffusion coefficient of water in wool was found to be 8.4 × 10-14 m2 s-1 at 25°C from gravimetric data. The effects of packing height and air velocity on the breakthrough curves were also investigated in the wool packed columns. For pseudo first order model, k values changing between 0.33 × 10-6 -69 × 10-6 s-1 was obtained for 2.2-6.4 cm s-1 air velocity and 0.05-0.20 m packing height ranges.