WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7150
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Conference Object Citation - Scopus: 2Preparation and Characterization of Hydroxyapatite/Calcium Phosphate Powders(Trans Tech Publications, 2004) Şimşek, Deniz; Çiftçioğlu, Rukiye; Harsa, ŞebnemThe preparation of calcium phosphate based powders through chemical precipitation in order to determine the optimum conditions for the preparation of stoichiometric, thermally stable hydroxyapatite (HA) powders was investigated in this work. The effects of parameters like pH, aging time, and heat treatment temperature on the phase structure and morphology of the powders were investigated by SEM and XRD.HA was prepared at a Ca/P ratio of 1.67. The precipitation pH had a profound influence on the morphology and crystallite size of the powders in the 4-11 pH range. Relatively large 5 mum prismatic particles were obtained at low pH whereas the powders were formed from agglomerates of nano sized particles at high pH. Powders had a HA dominant phase structure above a pH of 8. Phase pure HA powders were obtained with close to theoretical yields at pH = 10 and 11. The crystallite sizes of the powders varied from about 30 nm at 90degreesC to 50-90 mn at 1250degreesC with the smallest crystallite sizes obtained for pH 10 and 11 powders at 1250degreesC. The crystallite size increased significantly with aging temperature.Conference Object Citation - WoS: 2Citation - Scopus: 2Studies in the Utilization of Biobased Additives as Thermal Stabilizer for Plasticized Pvc(Trans Tech Publications, 2009) Okieimen, Felix Ebhodaghe; Egbuchunam, Theresa Obuajulu; Balköse, DevrimDivalent metal (barium, cadmium, calcium and zinc) soaps of rubber seed oil and their binary mixtures (BaJCd and CaJZn) and epoxidized rubber seed oil (4.5% epoxide content) and its admixtures with the single divalent metal soaps were evaluated as thermal stabilizer for dioctylphthalate plasticized PVC using changes in discolouration indices (yellowness index and UV absorption at 360nm) and initial rates of dehydrochlorination measured at 140 and 160°C. The results obtained showed that the divalent metal soaps were relatively effective in stabilizing the dioctylphthalate plasticized PVC against thermal degradation and that the binary soap mixtures enhanced the heat stabilizing effectiveness: marked reduction in the values of the discolouration indices; longer dehydrochiorination induction period and smaller values of rate constant of initial rate of dehydrochlorination. It was found that epoxidized rubber seed oil was less effective in comparison with the divalent metal soaps in stabilizing plasticized PVC against thermal degradation. These results show that the bio-based additives are compatible with dioctylphthalate plasticized PVC, stable to heat within the range of temperature used in the processing of plasticized PVC, inhibitlretard dehydrochlorination and reduce the extent of degradation.Conference Object Microstructure-Performance Relation in Pmma-Based Open-Cell Porous Materials for High Pressure Ceramic Sanitaryware Casting(Trans Tech Publications, 2004) Ergün, Yelda; Dirier, C.; Yılmaz, M.; Tokman, C.; Tanoğlu, MetinThe ceramic whiteware/sanitaryware industry is rapidly undergoing to implement high-pressure casting techniques for ceramic article production. In these techniques, materials with open pore microstructure that allows drainage of water under applied pressure are needed. The polymethyl methacrylate (PMMA) based polymeric porous materials have become the most suitable type of materials for this purpose because of their short casting periods and high service lives. However, the superior service life and performance of these materials are closely related to the microstructure. In the present study, the porous materials with various compositions of the constituents in the emulsion were produced to effect the microstructure of PMMA-based materials. The variations on the pore microstructure were interrelated to the performance of the material for high-pressure sanitaryware casting. The pore morphology and water permeability of the samples was measured using optical and SEM microscopy and permeability measurement techniques, respectively. The compressive collapse stress and modulus values were determined by performing compression testing. The results showed a significant interrelation between microstructure and the performance of the PMMA-based ceramic mould materials.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: 7Citation - Scopus: 7Investigation of the Pozzolanic Properties of Bricks Used in Horasan Mortars and Plasters in Historic Buildings(Trans Tech Publications, 2004) Böke, Hasan; Akkurt, Sedat; İpekoğlu, BaşakCrushed brick used in historic brick-lime mortars and plasters (Horasan) were characterized for understanding their properties to develop intervention mortars for conservation. Brick powders were separated from original mortars and plasters, and analyzed by XRD, SEM-EDS, TGA and pozzolanic activity (PA) measurements. The results showed that the microstructures of brick powders were not completely vitrified, and their XRD analysis failed to show the peaks for high temperature (T>900°C) phases. PA measurements of all brick powders showed an ample amount of artificial pozzolan property. Consequently, brick powders aimed for conservation of historic mortars must have high clay contents in addition to being low-fired (T<900°C) in order to produce maximum conversion into amorphous phase for ideal PA values.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.