Master Degree / Yüksek Lisans Tezleri
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Master Thesis Preparation and Characterization of Whisker and Particulate Sic-Ai2 O3 Ceramic Composites(Izmir Institute of Technology, 1999) Ünver, Özlem Ebru; Çiftçioğlu, MuhsinThis work involves the preparation and the characterization of SiC particulate-Alz03 and SiC whisker- Alz03 ceramic composites. A new technique was used in order to increase the density of composite. Fine Alz03 and SiC whiskers and particulates were used as a matrix and secondary phase, respectively. Whiskers and particulate were coated with Al-S04-OH precursor by precipitation using urea. In this method, it was important to keep the alumina hydrate in the noncrystalline state at 5.5>pH>8.6. The alumina- hydrate compound was separated from SiC whiskers and particulates when the reaction was continued at high pH (pH>8.7) causing the crystallization of alumina precursor. Alumina hydrate coated SiC whiskers and particulate were used as the starting material for the preparation of SiCw/p reinforced Alz03. Die pressing was used as the most appropriate and cheapest consolidation technique of composite materials. Upon sintering Al-S04OH on the SiC transformed into Alz03 by providing empty spaces for matrix densification in the proposed technique ( shrink- fit idea). Green bodies with SiC whisker and particulate contents in the range of 10 to 40 vol.% were sintered at 14500C for 2h under atmospheric conditions. The densities of sintered composites were measured by using Archimedes method. The density of composites containing 10%, 20%, 30% and 40 vol.% coated SiC particulate and whisker composites changed from 81% to 70% of theoretical density and from 79% to 75% of theoretical density, respectively. The density of coated composites were -22% greater than that of the uncoated composites .The thermal behavior of Al-S04-OH on the SiC was characterized by using TGA, DTA. TGA curves showed that materials are hydrated and dehydroxylization was observed between -700 and 800°C. TGA and DTA curves indicated that desulfurization then occurred at about -950°C. Chemical characterization of the coated SiC whiskers and particulates were obtained by using FTIR spectrometer.The hardness of these composites were measured by usmg Vickers Microhardness Testing Device. Vickers microhardness of the 20vol.% and 30vol.% coated SiCp ,and 20vol.% and 40 vol.% SiCw-Alz03 composites were measured as 10.71, 12.94, 10.89 and 5,96 GPa, respectively and compared with the mechanical properties of the composites manufactured by the conventional methods.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 Preparation and Characterization of Polymer-Zeolite Composite Membranes(01. Izmir Institute of Technology, 1999) Ebil, Özgenç; Çiftçioğlu, MuhsinThis thesis is on the investigation of polymer-zeolite composite membranes for gas separation and the effects of a number of parameters such as solvent and zeolite type, zeolite content, polymer/solvent ratio and preparation temperature on the microstructure of the final membrane. Although there is an increasing interest in polymeric composite membranes, most of the previous work concentrated on the synthesis and performance measurements of new membrane materials rather than the effects of different methods and parameters on processmg.In this study polymer-zeolite composite membranes were prepared by a phase inversion technique. Polysulfone, natural zeolite and synthetic zeolite 13X were used as polymer and second phases respectively. Dichloromethane and dimethylformamide were used as solvents. Four experimental sets of membranes containing the same polymer but different solvents and zeolites with increasing zeolite loadings were prepared and characterized by thermo gravimetric analysis, infrared spectroscopy, optical microscopy and scanning electron microscopy.It has been found that the types of the solvent and zeolite directly affect the final microstructure of the membranes. Solvent removal rate and distribution of zeolite particles are important and have strong effects on the mechanical performance of the membranes.Membranes prepared by using synthetic zeolite 13X and dichloromethane were determined to be the best zeolite distributions in the microstructure by optical microscopy and thermogravimetric analysis. Uniform and mechanically strong membranes with 20-60 % synthetic zeolite contents were prepared. Mechanically weak and relatively nonuniform membranes were prepared by using natural zeolite clinoptilolite. The incorporation of an ultrasonic treatment of the zeolite dispersion most likely contributed in the successful deagglomeration of the second phase in the polymer matrix.Master Thesis The Preparation Characterization and Sintering of Nanocrystalline Ceramics(01. Izmir Institute of Technology, 1999) Çağlar, Özlem; Çiftçioğlu, MuhsinNanocrystalline Titania was prepared by a chemical synthesis technique commonly known as sol-gel method. In the sol gel method, Titanium (IV) Isopropoxide was mixed with Isopropanol and Nitric Acid solution in predetermined ratios. A rapid hydrolysis reaction occurs between Titanium (IV) Isopropoxide and water in the Nitric Acid solution resulting in the formation of Titan oxide (Titania). The sols were clear sols and then gelled without any change in its clarity.Nanocrystalline Titania were tried to prepare by two different techniques in this work. The first technique involved the drying of the gel and subsequent sintering of the dried gel. A number of organic additives (oxalic acid, acetic acid, polyacrylic acid and stearic acid) were mixed into the sol before gelation in order to control drying (drying control chemical addives-DCCAs). Powders was prepared from sols and gels by several processes and a solid form was obtained by dry pressing and subsequently sintered in second technique. Oxalic acid was the most efficient DCCA among the others.The dried gels and powder compacts were sintered at 650, 700, 750, 800, and 850C. The sintering behaviors of them were examined. Relative densities of the dried gels were between 79-99% depending on the sintering temperature. The green body density of the pellets were varied between 41-52%. Their relative densities after sintering were varied between 55-83% depending on the sintering temperature. The pellets were pressed at different pressures to observe the pressure effect on the densification. Increase in pressure improve the densification behavior. The best route for the nanocrystalline powder preparation was the Route 4. This powder had smaller size of agglomerate most probably the agglomerates were broken during the ultrasonic radiation.The pore size analyses showed the pore structure of the gel. The pore size of the gels are about 35 nm. FTIR Spectra gave the crystal structure of the sols gels and powders. As a result, the sintering behavior of the dried gels is better than the powder compacts. The pellets can be densified to higher densities by appropriate forming technique. Although, the dried gels have significantly high densities, the shape and the weight of the gels can not be controlled.