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: 2Citation - Scopus: 2Investigation of the Permeability of Pure Gases in Sol-Gel Derived Al 2o 3 Membrane(Trans Tech Publications, 2004) Topuz, Berna; Çiftçioğlu, Muhsin; Özkan, FehimeThe preparation, characterization and pure gas permeation of sol-gel derived alumina membranes were investigated in this work. The effects of acid concentration/type and water content on the particle size in the sols and pore size distributions of the unsupported membrane were investigated by N 2 adsorption/desorption isotherms and Dynamic Light Scattering. Increasing the H +/Al 3+ mole ratio from 0.1 to 0.25 caused the hydrodynamic sol particle size and BJH pore size to decrease from 65 to 30 nm and 3.6 to 2.9 nm, respectively. The pore size increased from 2.8 nm to 3 nm upon increasing the calcination temperature from 500 to 600°C. Unsupported membranes were heat treated in the 200 to 1200 °C range for the characterization of the phase structure. Pinhole and crack free alumina membranes about 3 μm (2-layer) in thickness was observed from the SEM pictures with insignificant infiltration. The CO 2 permeability through the double layer γ-Al 2O 3 membrane calcined at 600 °C was 2.25*10 -7 mol/m 2.s.Pa, and had a slight pressure dependence indicating Knudsen Diffusion and Laminar Flow being the effective transport mechanisms. Upon the calcination of a similar 2-layer alumina membrane at 500°C, the CO 2 permeability decreased to 1.51 *10 -8 mol/m 2.s.Pa. without pressure dependence.Conference Object Citation - WoS: 5Citation - Scopus: 5Preparation of Ceramic Composite Membranes for Protein Separation(Trans Tech Publications, 2004) Erdem, İlker; Çiftçioğlu, Muhsin; Harsa, Hayriye ŞebnemCeramic supports were prepared from fine alumina and zirconia powders by dry-pressing and slip-casting. These supports were heat treated in the 1100° - 1200°C temperature range and dip-coated with ceramic sols prepared from alkoxides by using sol-gel methods. The average sol particle sizes were measured as 3-7 nm for zirconia and 30-40 nm for alumina by laser scattering technique. The optimum heat treatment temperature range was determined as 500°-600°C for dip-coated membranes by using TGA (thermo gravimetric analysis) results. The microstructure of the ceramic composite membranes was investigated by SEM (Scanning electron microscope). The clean water permeability (CWP) of the membranes was tested by using deionized water in a filtration set-up. Separation experiments were performed with bovine serum albumin (BSA, Stokes diameter: 7 nm) solution and whey to determine the protein separation capacity of the composite membranes. The CWP of the dry pressed alumina supports heat treated at 1100°C was found to be higher than the permeability of the slip-casted zirconia supports heat treated at 1200°C. The protein retention of the slip-casted zirconia support was determined as 60% by using UV-Vis spectrophotometer (Abs. at 280nm). A protein retention value of 96% was achieved for whey after the modification of the support with dip-coating. The permeate flux was 40 L/m2hour for dry-pressed alumina support dip-coated with zirconia sol calcined at 500°C.Conference Object Effect of Peo/Ppo Type Triblock Copolymers on Dispersion Behaviour of Aqueous Alumina Suspensions(Trans Tech Publications, 2001) Şakar, Aylin M.; Polat, Hürriyet; Çiftçioğlu, MuhsinThe aim of this study was to investigate the stability and dispersion behaviour of aqueous alumina suspensions in the presence of polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO/PPO/PEO) type block copolymers. The influence of water soluble triblock copolymers with molecular weight ranging from 2900 to 12600 g/mole were tested at Φ = 0.125, 1, 10, 20 vol % solid loading alumina suspensions by rheological, turbidity, sedimentation and surface tension measurements. The results indicate that an alternative dispersant for alumina suspensions is the PEO/PPO triblock copolymers. Their stabilisation mechanism was attributed to the depletion stabilisation. Rheological measurements indicated that these block copolymers (at high EO percentages) coupled with ultrasonic treatment have a positive effect on the dispersion of the agglomerated alumina suspensions. It was not possible to create stable dispersions in the absence of ultrasonic bath treatment. Turbidity measurements at Φ = 0.025, 0.125 vol % showed that, alumina suspensions with PEO/PPO added were stable and have higher turbidity values than block copolymer free suspensions.Conference Object Citation - WoS: 5Citation - Scopus: 5Preparation and Microstuructural Development of Nanocrystalline Titania and Alumina(Trans Tech Publications, 2004) Çağlar Duvarcı, Özlem; Çiftçioğlu, Muhsin; Güden, Mustafa; Arıkut, G.The preparation of nanocrystalline titania and alumina was investigated by sol-gel methods using titanium isopropoxide, boehmite and aluminum isopropoxide. Various drying control chemical additives like oxalic acid, acetic acid and polyacrylic acid were used for modifying the drying behaviour and shrinkage of the gels. The sintered densities of the ceramics prepared by sol-gel processing and the dried gels were in the 79-99% of theoretical density for rutile. The green and sintered densities of the pellets prepared by uniaxial pressing of powders derived from sols, gels and precipitation techniques for titania were in the 40-52% and 55-83% respectively. The titania ceramics were observed to experience anatase-rutile phase transformation upon heat treatment at 650oC. The grain size of the sintered ceramics at 650oC was determined to be about 26 nm. Grain size of titania increased to 213 nm. at 850oC. The mechanical properties of these nanocrystalline ceramics were investigated by using microhardness testing.