Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Rheological Characterization and Extrusion of Alumina Based Pastes for the Preparation of Tubular Ceramic Membrane Supports(Izmir Institute of Technology, 2016) Yılmaz, Kenan; Çiftçioğlu, MuhsinMembrane applications in the industry currentlyis dominated by polymeric membranes, however, in recent years the development of ceramic membranes gained significant attention because of their superior chemical/thermal stability and corrosion resistance. The separation capacities of ceramic membranes basically depend on the nature of the selective oxide layers formed on the inner surfaces of tubular ceramic supports. Ceramic tubular membrane supports were prepared from alumina pastes, with solid loadings as high as 55 vol. % and water was used as the major liquid phase. Boehmite along with hydroxypropyl cellulose ethers with different molecular weightswere used as binder materials. Glycerol was used as a lubricant in the paste formulations. Extrusion of alumina paste was conductedwith a ram extruder using capillary dies with a series of L/D ratios at different extrusion velocities and the data was analyzed by using Benbow and Bridgwater model. The rheological properties of various pastes were determined according to the 4 and 6-parameter models.The six parameter model was concluded to better represent the experimental data. The viscosities of the paste batches were also determined by using the model parameters o, 1, and exponent n. The pastes were determined to have a shear thinning behaviour Piston extruder was used for shaping of tubular ceramic supports and the pressure varied in the 20-90 bar range with paste composition and rheology. The tubular extruded supports were dried, debinded to burn out organic binders and sintered at 1525ºC for the formation of about 40% porous mechanically strong membrane supports.Master Thesis Preparation and Determination of Rheological Behavioour of Fine Strontium Titanate Powder Suspensions(Izmir Institute of Technology, 1999) Ünal, Uğur; Çiftçioğlu, MuhsinIn this project, strontium titanate powders were prepared by using solgel and Pechini methods. In sol-gel method, the powders were prepared by mixing the Ti02 sol and Sr(N03h solution. Precipitation was observed after the addition of Sr(N03)2 solution. Two powders were prepared by each method. In sol-gel method, acid:alcohol ratio was changed. In Pechini method, 50% of citric acid was substituted with polyacrylic acid. The characterization of the powders were performed by Fourier Transform Infrared Spectrophotometer (FTIR), Thermogravimetric Analyzer (TGA), Scanning Electron Microscope (SEM), X-Ray Diffraction and Optical Microscope. The calcination temperature of 650°C was chosen for sol-gel powder according to TGA data. XRD pattern showed that this temperature was not high enough to form complete SrTi03 phase, but no peaks related to nitrates or organic groups was observed in FTIR spectra. Sintering studies indicated that the agglomeration of sol-gel powder was very strong because the relative densities were very small. Pechini powders had weaker agglomerates and sintered to higher densities. The diameters of the Pechini powders were found as in the range of 0.2-0.5 um. The powders were dispersed in white oil and the rheological behaviour of these dispersions was studied by a rheometer. Several runs at different shear rates, and volume fractions were done. The suspensions without surfactant showed shear-thinning behavior, which indicates that the suspensions were flocculated. The addition of surfactant in certain amount produced stabilized suspenSIOns. The stabilized suspenSIOns showed Newtonian or Dilatant behaviour. The increase in the solids loading did not show significant change in the viscosity of stabilized suspension.Master Thesis Preparation and Characterization of Sterically and Electrostatically Stabilized Tio2 Suspensions(Izmir Institute of Technology, 1999) Uluçay, Ayhan; Çiftçioğlu, MuhsinThe aim of this study was the investigation of stable Ti02 powder suspenSIO formation in water. The water based paints are environmentally safe and expected to replace organic based solvents.Four different commercial titania pigment powders with different characteristics were used. Only a high molecular weight surfactant was used. Suspensions were prepared for four titania powders at 5,1O,and 20 % by volume solid content and the same suspensions were used in the investigation of the effects of the surfactant on the stability of suspensions. The surfactant was added in the range of 0.1 to 0.5 % by weight of pigment.Two characterization methods were used III the analysis: sedimentation and rheological characterization.It has been found that there are some stable pH ranges for the suspensions prepared by four Ti02 powders. In these ranges, it is expected to behave as dilatant - shear thickening and the sediment was densely packed. Three zones, sediment, falling and supernatant zones, were observed in disperse suspensions ..As a result of this, the pH ranges of these powders in water is observed visually. If it has rutile structure in powder C G (95% Ti02 content, 5% Ab03 coated), it works very well in basic mediums. Also rutile powder G (99% Ti02 content, uncoated), it is expected at pH.2 and basic mediums. The anatase powders ,E and F (both are 99% Ti02 content, uncoated), are stable in basic mediums. The F has wider stable zone than the powder E.The results of this work have shown that rutile alumina coated powder C suspensions were stable in basic media. Rutile powder G suspensions were stable at pH.2 and basic media. Anatase powders E and F were stable in basic media with powder F being stable in a wider pH range. The combined analysis of sedimentation -rheological behaviour of suspensions were found to be very helpful in understanding the suspension behaviours. Relatively high sediment packing densities in the 50-60% of theoretical titania density were obtained for some of the suspensions.Master Thesis Determination of the Particle Interactions -Rheology Suface Roughness Relationship for Dental Ceramics(Izmir Institute of Technology, 2007) Kes, Mürşide; Polat, HürriyetIn this study, relationship between particle interactions, rheology and surface roughness for dental ceramics was determined. For this purpose IPS Empress 2 veneer powder was chosen and characterized with XRD, SEM, EDS, Zeta Potential and Particle Size measurements.Particle interactions have been interpreted in the light of DLVO Theory for distilled water and electrolyte solutions at different concentrations (0.1, 0.25, 0.5, 0.75,1 M NaCl and CaCl2). The results indicated that interactions between particles change with electrolyte concentration and valency. Electrical Double Layer Thickness (Debye Length) compresses and Energy Barrier height decreases as electrolyte concentration and valency increase mean that there is agglomeration between particles. In order to understand the rheological properties of the system shear rate versus shear stress and shear rate versus viscosity graphs were interpreted for the same environmental conditions, distilled water and electrolyte solutions at different concentrations. It was obtained that at low electrolyte conditions particles formed agglomerates, however at high electrolyte conditions the system reached equilibrium where particles formed gel structures due to their non-Newtonian behaviour.The results obtained from rheological measurements were compared with the results obtained from AFM, profilometer and SEM measurements for the surfaces prepared with IPS Empress 2 veneer powder and it was concluded that in the presence of electrolytes (Na+ and Ca2+) surface roughness increased at low concentrations due to agglomeration of particles whereas surface roughness decreased at high concentrations most probably due to gelation in the system. Moreover, this situation was supported with contact angle measurements where contact angle mean values are high and ditributions are wide at low electrolyte concentrations while contact angle mean values are small and distributions are narrow at high concentrationsMaster Thesis Investigation of the Effects of Dissolved Oxygen Concentration, Aeration and Agitation on the Morphology and Rheology in Submerged Fungal Fermentation(Izmir Institute of Technology, 2007) Öncü, Şelale; Ünlütürk, SevcanThe effects of pH, agitation speed, dissolved oxygen tension (DOT) and aeration, significant in common fungal fermentations, on the production of polygalacturonase (PG) enzyme and their relation to morphology and broth rheology were investigated in a batch bioreactor using Aspergillus sojae which has no available literature report on the pectinase production. All four factors were effective on the response parameters under study. An uncontrolled pH increased biomass and PG activity by 27% and 38%, respectively compared to controlled pH (pH 6). pH did not significantly affect the broth rheology but created an impact on the pellet morphology. Similarly, the maximum biomass obtained at 500 rpm and at 30h was 3.27 and 3.67 times more than at 200 and 350 rpm, respectively. The maximum enzyme productivity of 0.149 U ml-1 h-1 was obtained at 200 rpm. Non . Newtonian and pseudoplastic broth rheology was observed at 500 rpm agitation speed. Furthermore, a DOT range of 30-50% was essential for maximum biomass formation, whereas only 10% DOT was required for maximum PG synthesis. Non . Newtonian shear thickening behavior (n>1.0) was depicted at DOT levels of 10% and 30%, whereas, non-Newtonian shear thinning behavior (n<1.0) was dominant at 50% DOT. When 2.5 l/min aeration experiment was investigated detaily; it was determined that at about 21st hour, polygalacturonase production approaches its maximum (1.49 U) and pellets are smaller, high in number. At 48th hour; polygalacturonase production declines to zero, biomass reaches its maximum and pellets are big (average pellet size is 1.94±0.58 mm) and fluffy with compact centers. At the end of fermentation (96.hour), fermentation medium is close to Newtonian. The overall fermentation duration (50-70h) was considerably shorter as opposed to common fungal fermentations revealing the economic feasibility of this particular process. As a result this study not only introduced a new strain with a potential of producing a highly commercially significant enzyme but also provided certain parameters significant in the design and mathematical modelling of fungal bioprocesses.Master Thesis Development of Liquid Armor Materials and Rheological Behavior of Shear Thickening Fluids (stfs)(Izmir Institute of Technology, 2011) Erdoğan, Taner; Tanoğlu, MetinColloidal dispersions have been extensively used in many industrial applications such as cosmetic, paint, cement, lubricant and ceramic. Shear thickening is non- Newtonian flow behavior often observed in concentrated colloidal dispersions as an increase in viscosity with increasing shear rate or applied stress. Shear thickening fluids (STFs) exhibit fluid and solid-like properties depending on the shear rate and thus can be used in a variety of applications. In the present study, STFs have been synthesized with various weight fractions of silica nanoparticles in polyethylene glycol (PEG)/ethyl alcohol by mechanical mixing method. The steady and dynamic rheological behavior of shear thickening fluids (STFs) was investigated with rheometer. STFs thermal properties were investigated through thermogravimetric analysis. STFs have been used to improve the performance of Kevlar woven fabrics for protective applications in ballistic and stab. STFs/Kevlar fabric composites have been prepared with different impregnation techniques to evaluate the effects of the STFs. The ballistic performance and stab resistance of STFs impregnated Kevlar fabrics were investigated. Rheological measurements revealed the shear thickening effect of silica nanoparticles/PEG systems depending on the shear rate. In dynamic experiments, the strain thickening behavior was found at critical combination of strain amplitude and frequency. The viscous G modulus values were found to be greater than the elastic Gï‚¢ modulus. The elastic Gï‚¢ and the viscous G modulus values were found to increase when the strain amplitude is kept constant and frequency is increased. The same strain thickening behavior was also found when the frequency was kept constant and the strain amplitude was increased. The puncture resistance of STFs/Kevlar fabric composites exhibited significant improvements as compared to the neat Kevlar targets. Based on the SEM results, STFs were uniformly impregnated over the entire surface on the Kevlar fabric and Kevlar fabrics completely coated with STFs. The ballistic test results revealed STF/Kevlar fabric composites have potential to obtain liquid armor materials.Master Thesis Investigation of the Rheological Behaviour of Nanosuspensions(Izmir Institute of Technology, 2011) Çelen, Öykü; Çiftçioğlu, MuhsinThe rheology of concentrated calcium carbonate, titania, silica, alumina and zirconia suspensions of submicron/nanosized particles in non-aqueous media was investigated. Calcium carbonate and silica particles were synthesized by carbonation route and Stöber method respectively while titania, alumina and zirconia powders were obtained commercially. Suspensions of the ball milled natural calcium carbonate powders were also prepared. The dispersion of these powders especially at high solids loadings was observed to be difficult. The viscosity of the 45 vol% suspensions of precipitated CaCO3 particles increased about 21 times at a shear rate of 400 sec-1 relative to its initial value indicating shear-thickening behaviour. The onset of shear thickening was at 20, 30 and 40 vol% for three different commercial titania powder suspensions. The onset of shear thickening was at lower solids volume contents and the increase in viscosity with shear rate was far less dramatic for the titania suspensions with polydispersed particle size distributions. The critical shear rate was 187 sec-1 for silica suspensions at 47 vol% with a discontinuous jump in viscosity. Rheological data at higher shear rates was not obtained due to the torque limitations of the rheometer. The critical shear rate of the polydispersed alumina powder suspensions were higher than their relatively monodispersed counterparts. The highest solids loading achieved in alumina based suspensions was 62 vol%. The dynamic shear rheology measurements showed that the solid part of the silica suspension was becoming more dominant over the liquid part as the solid content was increased. The volume fraction dependence of the high shear viscosity was fitted to a modified Krieger-Dougherty model for titania and silica suspensions. The fit of the rheological data to the Power law and to a modified version of Cross model were analysed.