Master Degree / Yüksek Lisans Tezleri
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Master Thesis Joining and Interfacial Properties of Aluminum/Glass Fiber Reinforced Polypropylene Sandwich Composites(Izmir Institute of Technology, 2009) Guruşçu, Aslı; Tanoğlu, MetinThe joining of separate components using a suitable technique is a critical step in the manufacture of composite structures. For good property performance of aluminum/glass fiber reinforced polypropylene (Al/GFPP) laminates, one of the most important problems is to obtain good adhesive bond strength.In the present study, Al/GFPP laminates have been manufactured with various surface pretreatment techniques. Adhesion at the composite/metal interface has been achieved by surface pretreatment of Al with amino based silane coupling agent, incorporation of polyolefin based adhesive film and modification with PP based film containing 20 wt. % a maleic anhydride modified polypropylene (PP-g-MA). The mechanical properties shear, peel and bending strength of the adhesively bonded Al/GFPP laminates were investigated to evaluate the effects of those various surface treatments. In addition, peel strengths of Al foam/GFPP laminates with various surface treatments were measured. The fracture surfaces have been examined by scanning electron microscope (SEM). Results showed that the adhesion of the laminated Al/GFPP systems were improved by treatment of aluminum surfaces with amino-based silane coupling agent. Based on peel and bending strength results, Al/GFPP laminates with incorporation of polyolefin based adhesive films exhibited significant increase on the adhesive behaviour. Modification of Al/GFPP interfaces with PP-g-MA layer leads to highest improvement on the adhesion properties.Master Thesis Development and Characterization of Pmma Based Porous Materials Used for High Pressure Casting of Sanitaryware Ceramics(Izmir Institute of Technology, 2004) Ergün, Yelda; Tanoğlu, MetinThe ceramic whiteware / sanitaryware industry is rapidly undergoing to implement high-pressure casting techniques for ceramic article production. In high pressure technique, porous materials with open cell microstructure that allow drainage of water from the ceramic suspension under applied pressure are needed. In addition, a relatively high mechanical performance of the porous structure is required to obtain a long service life from the material under the cycled high pressures. The polymethyl methacrylate (PMMA) based polymeric porous structures have become the most suitable type of materials for this purpose because of their short casting periods and high service lives. The superior service life and performance of these materials are closely related to their microstructure. In the present study, PMMA-based porous materials were produced by water-in-oil emulsion polymerization technique. The porous systems were produced with various compositions of the constituents in the emulsion and various filler sizes to investigate the effect of the constituents and the sizes on the microstructure of PMMA-based materials. The variations on the pore microstructure were related to the performance of the material. The pore morphology and porosity of the samples was investigated using optical and scanning electron microscopy techniques (SEM). Water permeability was measured using a custom made permeability apparatus. The mechanical properties such as compressive collapse stress and elastic modulus values were determined by performing mechanical compression tests. It was found that increasing water surfactant concentration increases the porosity, water permeability and decreases mechanical properties and reversely increasing the amount of monomer in the emulsion decreases the porosity, water permeability and increases the mechanical properties. Fracture toughness values of the materials were measured by using single edge notch three point bending (SENB) test method. Fracture toughness test results and fracture surface analysis show that materials are fractured in brittle manner. It was found that lower concentrations of water and higher concentrations of monomer result in thicker cell walls and improve the fracture toughness of the material. To investigate the residual mechanical properties, specimens were subjected to cyclic loadings. After cyclic loading, increase of elastic modulus with the percentage of 52 and decrease of collapse stress values were measured.Master Thesis Preparation and Characterization of Alumina Powders and Suspensions(01. Izmir Institute of Technology, 2000) Şakar, Aylin M.; Polat, HürriyetThis study involves the preparation of fine alumina powders derived from Bayer gibbsite and also aqueous alumina suspensions by using tri block copolymers. Preparation of alumina powders was performed by decomposition of gibbsite into transition alumina phase followed by controlled transformation to alpha phase. To increase transformation rate.. to a-alumina in transition phase hence influence the nucleation and growth rate of the solid-solid phase transformation ball milling and ultrasonication was applied. Gibbsite was thermally treated at 900°C to reach a transition form of alumina. In some cases a heat treatment at 350 °C was applied to create a network of submicroscopic cracks in the heated gibbsite that may help grinding. Ball milling and ultrasonic treatment before calcination at 1100, 1200 °C and 1450 °C followed these heat treatments. Characterizations of the powders were performed with XRD, FTIR, thermal analysis, density measurements and particle size determinations. According to the XRD patterns, complete transformation to alpha form occurred in powders previously heat treated at 900°C, mechanical treated and then cfllcined at 1200 °C in 8 hours and 1450 °C in 2 hours. Powders that were calcined at 1100 °C and 1200 °C in 1-2 hours contained considerable amount of kappa form together with alpha. The effect of the polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO/PPO/PEO) blockcopolymers on the dispersion behaviour of alumina powder suspensions in water were investigated at <1>.0.125,1.0,14 and 50 vol% solid loadings by rheological and turbidity measurements. To compare the effects of block copolymers with other type of dispersants, measurements of some other well known dispersants were also conducted at 10-7 to 10-3 M. The results indicated that type block copolymers with high EO percentage have a positive effect when they are used with ultrasonic treatment on the agglomerated alumina suspensions. But it was not able to create stable dispersions ll1 the absence of ultrasonic bath application. Turbidity measurements at <1>.0.5 wt% showed that some dispersants gave higher dispersion but the stability was reached after a time period. Ultrasonic treatment created stability but lowered the turbidity values.Master Thesis Tribological Behaviour of Polymer Nanocomposities Containing Tungsten Based Nanoparticles(Izmir Institute of Technology, 2007) Karal, Kazım; Tanoğlu, MetinThe use of nanostructured fillers in epoxy systems has a significant role on the development of thermosetting composites. Recent investigations on inorganic nanoparticles filled polymer composites reveal their significant potential in producing materials with low friction and/or high wear resistance. In the present study, epoxy nanocomposites and fiber reinforced polymer (FRP) composites were prepared with the addition of tungsten based nanostructured particles which are produced by mechanical alloying. The effects of the nanostructured additives on the tribological, mechanical and thermal properties of composite laminates and nanocomposites were investigated. Composite laminates with and without filler were manufactured by using hand lay-up technique and cured under compression. It was found that tungsten based particle loading has no significant effect on the flexural properties of the nanocomposites and the composite laminates, and the tensile properties of the nanocomposites. It was found that while the addition of 3 wt. % of nanoparticles increases the hardness values, it significantly improves the wear resistance of nanocomposites. Furthermore, the significant improvement on the wear resistance was observed with the addition of 3 wt. % W-SiC-C (24h mechanical milling) powder onto the surface of fiber reinforced epoxy. The worn surfaces were examined with scanning electron microscopy (SEM) and the results revealed that wear mechanisms are altered due to the presence of nanoparticles in the matrix. Differential scanning calorimetry (DSC) results showed that nanoparticles have no significant effect on glass transition temperatures (Tg) of nanocomposites. Incorporation of nanoparticles increased the thermo mechanical properties of nanocomposites and composite laminates; including the storage and loss modulus and Tg.Master Thesis Preparation and Characterization of Inorganic Membranes by Using Sol-Gel Techniques(01. Izmir Institute of Technology, 2000) Yelken, Gülnihal; Çiftçioğlu, MuhsinIn this research the preparation of ceramIC membranes for gas separation applications by using sol-gel techniques were investigated. The effects of water/alkoxide ratio, H+/alkoxide ratio on the catalysis of the hydrolysis-condensation reactions and the peptization process were investigated by using N2 adsorptiondesorption isotherms, thermogravimetric analysis and FfIR (Fourier Transform Infra Red). The performance and the potential use of these materials in gas separation applications depend mainly on the ability in controlling-designing the microstructurepore network in these materials.The alumina and silica sols were prepared by using aluminium isopropoxide and tetraethylorthosilicate. Sols with different H+/ AI+3 and H20 / AI+3 ratios were prepared.These peptized clear boehmite sols were used for the preparation of unsupported Ah03 membranes at 600°C. The similar ratios were varied for the preparation of clear silica sols and these sols were further dried and heat treated at 400 C.The thermogravimetric analjsis has shown that the weights of the unsupported membranes were stable at the above temperatures. The boehmite was observed to decompose to the y-Alz03 phase at about 425°C. The FfIR analysis have proved the formation of boehmite in the sols and all the organic solvent peaks disappeared upon heat treatment.The y-Alz03 membranes all displayed Type IV isothems typical of mesoporous materials. Hysteresis loops were present in all these isotherms and fast desorption took place in the 0.4-0.6 PlPo range. The BJH pore size distributions were sharp for all the samples.The desorption pore size distributions were found to become wider at an intermediate acid content membrane which also had the lowest BET surface area. The BET particle sizes of these membranes were estimated to be in the 70-100 A0 range.The throat and pore cavity sizes of monosize sphere packings for this particle size range were observed to be in close agreement with the experimentallly determined adsorptiondesorption pore sizes.The silica samples all displayed Type I isotherms with no hysteresis typical of microporous materials. The HK (Horvoath Kawazoe) pore sizes were in the 4-5 AO range. An effect of the water content of these acid-catalyzed sols on the pore size were also detected.Master Thesis Quasi-Static Crushing Behavior of Nomex Honeycomb Filled Thin-Walled Aluminum Tubes(Izmir Institute of Technology, 2008) Çakıroğlu, Cem; Güden, MustafaThe experimental and numerical studies presented in this thesis were focused on the experimental and numerical quasi-static crushing behavior of Nomexl1 honeycomb filled thin-walled aluminum tubes. Nomexl1 honeycombs having different cell sizes (3.2, 4.8 and 6.4 mm) and the same density (48 kg/m3) were used to fill thin walled aluminum tube, 25 mm in diameter and 0.29 mm in thickness. Compression tests were conducted at quasi-static the strain rates of 1.64 10-2, 6.56 10-3 and 3.28 10-3 s-1. The results showed that the honeycomb cell size had a strong effect on the crushing behavior. Decreasing cell size increased crushing loads and the specific absorbed energy values of empty tubes. The highest strengthening effect of filling was found in 3.2 mm cell size honeycomb filled tubes. Although no effects of 4.8 and 6.4 mm cellsize honeycomb filling on the deformation mode of tube was observed (mixed), 3.2 mm cell size honeycomb filling changed the deformation mode to mixed/concertina. The numerical model of empty tube, 6.4 mm cell size honeycomb and 6.4 mm cell size honeycomb filled tube were performed using LS-DYNATM and ANSYSTM finite element analysis programs. To acquire maximum computational efficiency, a mesh optimization was done. The effect of the honeycomb cell wall thickness was also investigated numerically and shown to have a strong effect on the crushing behavior of honeycomb. The experimental and numerical studies conducted showed that 3.2 mm cell size Nomex® honeycomb might become an alternative to aluminum foam filler in thin walled tubes as long as the tube crushing load was comparable with honeycomb crushing load.Master Thesis Development of Carbon Black-Layered Clay/Epoxy Nanocomposites(Izmir Institute of Technology, 2008) Pekşen Özer, Bahar Başak; Tanoğlu, Metin; Tanoğlu, MetinIn this study, a novel epoxy nanocomposite with electrical conductivity and having improved mechanical and thermal properties was synthesized. Carbon black/ epoxy composites and carbon black-layered clay/epoxy nanocomposites were prepared by mixing via 3-roll mill. The first type of the composite was produced to determine the percolation threshold concentration (Vc). The second type with constant carbon black concentration, slightly over Vc, was synthesized to investigate the influence of clay content on the thermal, mechanical, electrical and structural properties of nanocomposites. Carbon black used in the study was extra conductive filler with 30 nm spherical particles. Layered clay was Na+ Montmorillonite treated with ditallow dimethlyamine to assure better intercalation within the epoxy resin. Vc value was determined to be 0.2 vol% and 0.25 vol% carbon black was added together with varying clay contents to the epoxy system to produce nanocomposites. Only the nanocomposites with 0.5 vol. % clay loading showed electrical conductivity. However, the composites with higher clay loadings showed insulating behaviour due to hindrance of carbon black network by clay layers. According to the XRD results, nanocomposites exhibited some extent of exfoliation. It was found that tensile modulus values of the epoxy increased;however flexural modulus values remained constant, with increasing clay content.Elastic modulus of neat epoxy (3.7 GPa) was increased about 28 % with 0.5 vol% clay addition. Thermomechanical analysis results revealed that the storage modulus, glass transition temperature and initial degradation temperature of epoxy was slightly enhanced due to clay loading.Master Thesis Cation Exchange in Zeolites Structure Modification by Using a Microwave(Izmir Institute of Technology, 1999) Akdeniz, Yelda; Ülkü, SemraIn this research, characterization and modification of clinoptilolite minerals from different deposits have been studied to determine its utility for different Clinoptilolite minerals obtained from the source located in Western (FTIR) to determine the structural properties. The FTIR spectra of the samples showed the characteristic vibrations of the clinoptilolite framework. Thermal properties were determined using Differential Thermal Analyzer (DTA), Thermal Gravimetric Analyzer (TGA), and Differential Scanning Calorimetry (DSC). The analysis showed that the structure of the samples were stable up to 650 DC and due to the Fe203 present in the tuff, phase inversion was observed. Accelerated Surface Area and Porosimeter (ASAP 2010) used to determine the adsorptionrelated properties using N2 and Ar adsorption isotherms. The samples showed different adsorption behaviour toward each gas. The pore size distribution of clinoptilolite samples showed that they have mesaporous structure.The clinoptilolite was modified by ion exchange using 1N NaCI salt solution in waterbath, and in microwave maintained at 80 DC for 10 min, 60 min and 120 min. The efficiency of each method on ion exchange was compared. The Na+ amount in the zeolite was found to be 2.25 and 3.24 % by weight after 2 hours of exchange in waterbath and microwave, respectively. The results showed that microwave method used for modification was more efficient.Master Thesis The Preparation and Characterization of Hydroxyapatite Bioceramic Implant Material(Izmir Institute of Technology, 2000) Çiftçioğlu, Rukiye; Harsa, Hayriye ŞebnemThe use of hydroxyapatite (HA) powders and ceramIcs as a biomaterial was investigated in this work. A commercial HA powder was used for the preparation of HA ceramics and the adsorption of Bovine Serum Albumin (BSA) onto HA has been investigated.The powder and the sintered ceramics were characterized by TGA, DT A, Optical Microscopy, Microhardness Tester, XRD, and FTIR.The sintering studies have shown that it was possible to prepare porous ceramics above 800°C and dense ceramics at 1200-1250°C range.The HA powder lost about 5.5% by weight during heat treatment up to 1000DC and 80% of this weight loss is due to adsorbed water.The particle size of the powder was determined to be submicron whereas the grain sizes of the 1250°C sintered ceramic was in the 1-5 /l um range.A maximum Vickers Hardness of 585 Hv was determined for the 1250°C sintered 97.2% dense ceramic.XRD patterns of the powder and the 1250°C sintered ceramic were identical and almost phase pure. A small CaO peak was detected in the samples which was believed to be remnants of the powder preparation process.The adsorption of BSA onto HA has been studied as a function of time, protein concentration, pH, ionic strength, and HA solids loading. Adsorption experiments were also conducted with commercial alumina and zirconia ceramic powders. Uptake curves have shown that the adsorption process was almost completed in less than ten minutes Adsorption isotherms 'at different pH ( 4.5-7.4) have been obtained and analyzed using the Langmuir model. The Langmuir parameters qm ( maximum amount of protein adsorbed, mg BSA/g HA) and K' (affinity constant, mllmg BSA) have been calculated. qm decreased from 119 to 61.3 with the increase in pH from 4.7 to 7.4. A maximum of 46.1 for K' was determined at pH.5.6 and K' had the lowest value of 3.5 at pH.7.4. Electrostatic attractions were held responsible for the K' maximum at pH.5.6 since HA and BSA surfaces are oppositely charged. The presence of a considerably high amount of BSA adsorption on the HA surface at pH.4.7 where the protein should have close to zero net charge was attributed to hydrophobic effects. The amount of adsorption at equilibrium in the 4.5-5.8 pH range was determined to be twice of that in the 6-8 pH range. Almost 100% of the protein was recovered with a HA solids loading of 750 mg HA/50 ml solution at equilibrium for an initial BSA concentration of I mg BSA/ml solution.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.