Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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Subject: search.filters.subject.Porous materials

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Now showing 1 - 4 of 4
  • Master Thesis
    Numerical and Experimental Investigations on the Zeta Potential of Different Size Mesoporous Silica Nanoparticles With Different Porous Properties
    (Izmir Institute of Technology, 2020) Yakın, Fetiye Esin; Barışık, Murat
    Mesoporous silica nanoparticles (MSN) are utilized by many applications due to their high surface to volume ratio, tunable pore size, low toxicology, and colloidal stability. These properties make silica nanoparticles good candidates for targeted drug delivery applications. Targeted drug delivery steps include cellular internalization, endosomal escape, and cargo release to the selective tissue. The geometric properties of MSN such as particle size, pore size, and porosity, as well as surface chemistry and resulting surface charge density determine the MSN behavior in these steps. This study examines the influence of particle size, pore size, and porosity of an MSN to its surface zeta potential. We performed both numerical and experimental investigations. The zeta potential of various MSNs at different salt concentrations was calculated by solving the Poisson-Nernst-Planck equation with active surface charge boundary conditions considering surface chemistry. We validated our multi-ion model through experiments. Results indicate that zeta potential exhibits a strong dependence on particle size, pore size, and porosity. By increasing porosity and/or pore size, the absolute average zeta potential decreased up to 25% from the theoretical predictions. Second, zeta potentials of silica particles at different sizes and surface areas were experimentally measured at different salt concentrations. Particles were systematically characterized by measuring particle size using Dynamic Light Scattering (DLS), analyzing chemical properties using Fourier-transform infrared spectroscopy (FTIR), measuring surface area using Brunauer– Emmett–Teller (BET) analysis, and imaging using Scanning Electron Microscopy (SEM). A well-dispersed solution in colloidal stability was obtained by systematically tuning corresponding parameters. The absolute average zeta potential was found to increase with a decrease in particle size, while zeta potential was found to decrease with a decrease in surface area at a constant particle diameter, similar to numerical calculations.
  • Master Thesis
    Modelling of Pore Formation in Porous Materials
    (Izmir Institute of Technology, 2017) Ülker, Sevkan; Güden, Mustafa; Akdoğan, Yaşar
    The purpose of this thesis is to model the expansion behavior of aqueous slurries. Foamed or cellular material made using such method is known, especially in the concrete industry. What appears to be lacking in the literature is the knowledge of pore formation and pore growth in inorganic particles based on aqueous slurry systems that result in the formation of cellular structures. The motivation of this study is to provide a scientific view in identifying and explaining the critical parameters that govern the pore growth and expansion of such slurry based systems. Bubble growth and pore formation are also studied experimentally. Experimental results are used to compare with the empirical study conducted by Kanehira at al. (Kanehira, et al., 2013), and mathematical modeling of pore formation plotted with Wolfram Mathematica software. Experimental procedure consists of three types of aluminum and calcium ratios which provide information about bubble growth and pore formation. These types are 50% aluminum – 50% calcium hydroxide (50/50), 70% aluminum – 30% calcium hydroxide (70/30), and 80% aluminum – 20% calcium hydroxide (80/20). According to the results of studies, mathematical modeling system consists of the pressure difference between the inside and outside of a spherical bubble as the driving force for defining growth. While aluminum ratio increases, bubble growth rate decreases due to release of hydrogen gases which affect bubble expansion phenomenon. In the experimental and mathematical modeling, 50/50 ratio has maximum bubble growth rate compared to 70/30 and 80/20 ratios. The results of experimental and mathematical modeling suggest that viscosity is a very significant parameter which controls the bubble growth rate.
  • 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, Metin
    The 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
    Designing and Manufacturing of Porous Spinal Cages Using Ti6a14v Foamed Metal
    (Izmir Institute of Technology, 2009) Dizlek, Mustafa Eren; Güden, Mustafa
    Open cell Ti6Al4V foams with varying porosities (50, 60 and 70%) were prepared at sintering temperatures between 1200 and 1350 °C using ammonium bicarbonate particles (315 - 500 .m) as space holder. Two different biomedical grade commercial, gas atomized spherical Ti6Al4V powders were used to prepare foams. Powder 1 was in size range of between 45 - 150 .m and Powder 2 in size range of between 30 - 90 .m. The foams were sintered under argon atmosphere in a tightly enclosed tube furnace. The resulting cellular structure of the foams showed bimodal pore size distribution, comprising macro pores (300 - 500 .m) and micro pores (1 - 30 .m). Compression tests of foam samples have shown that increasing sintering temperature or decreasing porosity increased the elastic modulus, yield and compressive strength and failure strain. The improvement in the mechanical properties of foams prepared using smaller size Ti6Al4V powder with bimodal particle distribution were attributed to the increased number of sintering necks and contact areas between the particles. The foam prepared with optimum porosity, pore size and mechanical properties for bone in-growth was further used to produce prototype porous spinal cages which are widely used in spinal surgery for vertebrae fixation. The geometries and size of the prototype spinal cages were determined through the measurements taken from human vertebrae. The foams for spinal cage preparation were first prepared in the form of plates and then core-drilled using water jet based on the design geometrical parameters determined for each vertebra segment.