Chemical Engineering / Kimya Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/14
Browse
15 results
Search Results
Article Citation - WoS: 12Citation - Scopus: 12The Effect of Zn Substitution of Ca in Bipbsrcacuo Superconductors Sintered at 830°c(Springer Verlag, 2009) Kocabaş, Kemal; Şakiroğlu, Serpil; Çiftçioğlu, Muhsin; Ercan, İsmail; Epik, Hakan; Bilgili, ÖzlemThe effect of partial substitution of Ca by Zn in Bi 1.7Pb 0.3Sr 2Ca 2-x Zn x Cu 3O y at x=0.00, 0.05, 0.10, 0.15 and 0.20 levels on the electrical and structural properties was investigated in this work. The characterization of the ceramics prepared by the conventional solid-state reaction method were done by resistance-temperature measurements, XRD, SEM and density analysis. Low levels of Zn substitution of Ca caused significant changes in the properties of the ceramics. The low-T c superconducting properties were enhanced and the fraction of the low-T c (2212) phase were found to increase at x=0.15 level of Zn substitution at 830°C sintering temperature. Zero resistance was observed only in sample D with x=0.15 and the T c was determined as 92 K. The SEM micrographs and the density analysis have shown that this was the densest packed ceramic.Article Citation - WoS: 21Citation - Scopus: 32Separation of Whey Components by Using Ceramic Composite Membranes(Elsevier Ltd., 2006) Erdem, İlker; Çiftçioğlu, Muhsin; Harsa, Hayriye ŞebnemCeramic supports were prepared from alumina powder and dip-coated with zirconia sol. The ceramic composite membranes prepared were characterized with respect to their microstructure/pore structures. The supports were 40% porous of which 87% were open pores. The average particle size of the sol particles was 35 nm. The prepared membrane has good protein lactose separation properties with a relatively high protein content (PR ∼80%) and with relatively low lactose retention (LR ∼7%). The permeate flux value was around 40 l/m2h. These results indicate the possibility of the preparation of ceramic composite membranes for separation of whey components with higher yields.Article Citation - WoS: 44Citation - Scopus: 50Thermal Behaviour of a Zeolitic Tuff(Elsevier Ltd., 2007) Çağlar Duvarcı, Özlem; Akdeniz, Yelda; Özmıhçı Ömürlü, Filiz; Ülkü, Semra; Balköse, Devrim; Çiftçioğlu, MuhsinNatural zeolites undergo structural changes after heating which open their possible use in different fields, related to their chemical and physical properties, such as building stone, lightweight aggregate, ceramic foam, concrete bricks, tiles, porcelain stoneware and additive in puzzolonic cements. In this study, thermal behavior of zeolitic tuff quarried from Gördes-Manisa, region of Turkey was investigated. Zeolitic rocks were first reduced to 2 μm and pellets were prepared by dry-pressing. The pellets were heated for 30 min in the temperature range of 200-1200 °C. Heating the tuff up to 600 °C did not cause any structural change detectable by X-Ray powder diffraction (X-Ray), Fourier Transform Infrared Spectroscopy (FTIR) and thermal characterization methods with regard to the original sample, while further increase in the temperature caused structural breakdown of zeolitic tuff. The appearance of the broad low intensity peaks in X-Ray diffraction diagrams indicated most probably a partial transformation of crystal structure into an amorphous structure. The Scanning Electron Microscopy (SEM) micrographs showed that the crystals seen in the original rock sample were broken during grinding and pressing processes. The crystal structure disappeared above 1000 °C and the spherical pores was observed at 1200 °C. Chemical composition of the zeolitic tuff did not change significantly with respect to temperature. The highest density (2.28 g/cm3) and hardness (387 Hv) were obtained by sintering the pellets at 1000 °C for 30 min.Article Citation - WoS: 5Citation - Scopus: 7Alumina/Water Suspensions in the Presence of Peo-Ppo Triblock Copolymers(Elsevier Ltd., 2004) Şakar Deliormanlı, Aylin; 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 triblock copolymers. For this purpose alumina suspensions at various solids loadings were prepared using four different methods. These are: Method I: powder and water were stirred only; Method II: powder and water were stirred and ultrasonic treatment was applied; Method III: powder and water were stirred in the presence of block copolymers; Method IV: powder and water were stirred and ultrasonic treatment was applied in the presence of block copolymers. These suspensions were characterized by means of rheological measurements. Sedimentation and turbidity measurements were also conducted to support these results and to investigate the stability of these systems for longer times. Surface tension measurements were performed to investigate the adsorption behaviour of block copolymers onto alumina surface. It was found that the use of PEO-PPO-PEO type triblock copolymers improved the dispersion behaviour of aqueous alumina suspensions in the presence of ultrasonic treatment at low solids loadings. However their effect was not significant at high solids loadings and without ultrasonic treatment.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 - Scopus: 1Microstructural Characterization of Industrial Chromite and Spinel Cement Kiln Refractories With Emphasis on the Iron-Rich Rims(Trans Tech Publications, 2004) Mercanköşk, Y.; Akkurt, Sedat; Çiftçioğlu, MuhsinMagnesia-chromite (MgO + MgO·Cr2O3) and magnesia-spinel (MgO + MgO·Al2O3) refractory bricks that are used in the high temperature zones of rotary cement kilns are investigated for their microstructural characteristics. Their microstructures are important because the size, shape and distribution of periclase grains, chromites and the quality of their bonding phases significantly affect their service performances. The purpose of this study was to characterize the microstructures of industrial brick samples to develop a protocol to compare different products e.g. for evaluation as replacement bricks. In some of the chromite containing bricks iron-rich rims were observed, while a domestic brick with similar chemistry had no such feature. These iron-rich rims were examined using SEM-EDS. It was found that the counter-diffusion of Fe+3 and Cr+3 were responsible for their formation. Exsolved chrome-spinel was widely observed in the microstructures of chromite bricks. Magnesia-spinel bricks were found to contain low melting calcium aluminates as bond phases in the microstructure, posing a threat to service performance. Portmortem microanalysis of industrially used bricks revealed alkali attack in addition to creep as main destruction mechanisms for brick. Traces of elements like Mo, S and alkalies were observed and thought to originate from the use of waste derived fuels.Conference Object Citation - WoS: 8Citation - Scopus: 12Mechanical Properties of Hydroxyapatite Composites Reinforced With Hydroxyapatite Whiskers(Trans Tech Publications, 2004) Şimşek, Deniz; Çiftçioğlu, Rukiye; Güden, Mustafa; Çiftçioğlu, Muhsin; Harsa, Hayriye ŞebnemSintering and mechanical behavior of pure and hydroxyapatite (HA) whisker reinforced HA composites were investigated in this work. Pure and composite samples were prepared by using a commercial powder and whiskers prepared by molten salt synthesis. The dry-pressed samples were sintered in the 800 and 1300°C range. The effect of whisker-addition on the mechanical properties of HA was investigated through compression and hardness testing. Compressive strength and fracture strain were observed to increase by the addition of whiskers.Conference Object Citation - WoS: 10Citation - Scopus: 13Preparation and Characterization of Polylactide-Hydroxyapatite Biocomposites(Trans Tech Publications, 2004) Gültekin, Naz; Tıhmınlıoğlu, Funda; Çiftçioğlu, Rukiye; Çiftçioğlu, Muhsin; Harsa, Hayriye ŞebnemIn the present study, the preparation and characterization of polylactide-Hydroxyapatite(HA) composite films for biomedical applications have been studied. The effects of number of parameters such as polymer type, HA loading, surface modification and its concentration on the mechanical and microstructural properties of the composites were investigated. Poly-L-Lactide and 96/4 Poly(L-Lactide co D-Lactide) copolymer-HA composites containing 10-40 wt% HA particles have been prepared by solvent casting technique. The HA powder was synthesized by precipitation technique. Interfacial interactions between HA and polylactide polymer were modified to improve filler compatibility and mechanical properties of the composites by surface treatment of the HA with two different silane coupling agents; 3-aminopropyltriemoxysilane (AMPTES) and 3-mercaptopropyltrimethoxysilane (MPTMS) at three different concentrations(0.5-2 wt%). Silane treatment indicated improvements in the mechanical properties of the composites compared to the untreated HA loaded polylactide composites. Tensile test results showed that the maximum improvement in the mechanical properties of the composites was obtained for PLA composites containing 1 wt% aminofunctional silane treated HA and 0.5-wt% mercaptopropyltrimethoxy silane treated HA for PDLA composites. Scanning electron microscopy studies also revealed better dispersion of silane treated HA particles in the polymer matrix.Conference Object Citation - WoS: 8Citation - Scopus: 8Low Temperature Synthesis of Spinel Powders by Mechanical Grinding(Trans Tech Publications, 2004) Yalamaç, Emre; Akkurt, Sedat; Çiftçioğlu, MuhsinLow temperature synthesis of spinel powder via intense mechanical grinding was performed. A dramatic decrease in the synthesis temperatures of ground powders was achieved. We were able to produce partially crystallized spinel at room temperature via a 110 minute grinding. Characterization of the synthesized powders was performed using SEM, XRD and DTA. Each stage of synthesis was analyzed using these techniques. Mixtures of Mg(OH)2 and Al(OH) 3 were used for synthesis. Temperatures as low as 800°C were able to produce bumps in the XRD patterns of ground powders at the 2θ angles for spinel crystals.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.