Master Degree / Yüksek Lisans Tezleri

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

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Author: search.filters.author.Özdemir, EkremSubject: search.filters.subject.Crystallization

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Now showing 1 - 4 of 4
  • Master Thesis
    Effect of Ions on Particle Size and Morphology in Calcium Carbonate (caco3) Crystallization
    (01. Izmir Institute of Technology, 2021) Osman Adam Osman, Ahmed; Özdemir, Ekrem
    The particle sizes of calcium carbonate (CaCO3) produced by the chemical crystallization method were reported to be almost always larger than 3 µm. Our recent studies in our lab has shown that the nano-CaCO3 particles can be obtained when calcium hydroxide (Ca(OH)2) solution was used as a stabilizer. In this study, an experimental setup was developed to crystalize CaCO3 from sodium carbonate (Na2CO3) and calcium chloride (CaCl2) solutions in a plug flow reactor (PFR) with a retention time of 9 seconds and added into a stabilizing solution. The CaCO3 particles of about 30% of vaterite and 70% of calcite were produced with a size larger than 13 µm in the PFR tubular reactor. The influence of cations and anions on the particle size and morphology were investigated. The hydroxide form of sodium (Na+), potassium (K+), calcium (Ca++), ve barium (Ba++) were used as the stabilizer solution containing cations. Totally calcite particles at sizes larger than 2 μm were produced with homogenous size distribution in the presence of Na+ and K+ ions. Nano-calcite particles were produced in solution containing Ca++ ions. A new crystalline form, Barytocalcite (BaCa(CO3)2), and whitherite (BaCO3) particles were produced in solution containing Ba++ ions. The sodium form sulfate (SO4=), nitrate (NO3-), carbonate (CO3=) and bisphosphate (HPO4=) were used as the stabilizer solution containing anions. The size and morphology of vaterite and calcite particles were seen almost the same and did not change with the particles synthesized in the PFR tubular reactor in the presence of SO4=, NO3-, and CO3= ions. A different form of particles such as monetite (CaHPO4) and hydroxyapatite (Ca5(PO4)3OH) were synthesized in the presence of HPO4= ion in the stabilizer solution. These formations clearly indicated that the CaCO3 particles synthesized in the PFR tubular reactor were dissolved and recrystallized in the stabilization solutions. It was successfully demonstrated that the synthesis of CaCO3 in nano sizes with the chemical method was achieved and devised a novel technique for the continuous production of nano-CaCO3. It was demonstrated that nano-calcite particles of about 350 nm were produced by the chemical method not previously reported in the literature.
  • Master Thesis
    Synthesis of Needle-Like and Rod-Like Nano Baco3 Particles
    (Izmir Institute of Technology, 2016) Kahyaoğlu, Tuğçe Nefise; Özdemir, Ekrem
    Barium carbonate (BaCO3) has been widely used in soft and heavy industries such as ferrite magnets, solid oxide fuel cells, optical glass manufacturing, coatings, and polymeric composite materials as well as ceramic and brick industries. Using BaCO3 in nano sizes will improve some of the physical properties of materials such as tensile strength, opacity, and thermal resistance. Production of BaCO3 by chemical method requires extensive crystallization times and higher temperatures. Production of BaCO3 by carbonation method usually yields particles with some agglomeration. In a study, conducted by our group funded by The Scientific and Technological Research Council (TUBITAK), a method was developed to synthesize hollow nano Calcium Carbonate (CaCO3) particles. It was aimed to apply the developed method, which is unique in its kind, to produce nano BaCO3 particles in different morphologies. Parameters such as effect of barium hydroxide (Ba(OH)2) concentration, CO2 flow rate, length in reaction chamber, and stirring rate were studied. Conductivity and pH values of the solution were monitored during crystallization. Surface morphology and crystal structure of the produced BaCO3 particles were characterized by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD), respectively. It was shown that rod-like BaCO3 particles produced in nano sizes with almost homogeneous size distributions. The rod-like BaCO3 particles had a diameter from 100 to 400 nm and an aspect ratio of about from 3 to 10. The produced rod-like nano BaCO3 were all in orthorhombic phase of BaCO3 called as Witherite.
  • Master Thesis
    Production of Nano Caco3 in Bench Scale by Small Penetration Theory
    (Izmir Institute of Technology, 2013) Toprak, Görkem; Özdemir, Ekrem
    Calcium carbonate (CaCO3) has been used as filling material in various industries such as paint, paper, and polymeric materials. Using filling materials will enhance some of the physical properties of the composite material and decrease the product costs. Especially, the physical properties of the composite materials were enhanced significantly when the CaCO3 is used in nano sizes. CaCO3 can be produced from natural sources by crushing, grinding, and sieving processes, however, calcite obtained from the natural sources are usually in micron sizes and they are not in the desired quality and purity. Here, it was proposed that the dissolution rate of CO2 is the limiting step in CaCO3 crystallization and a small penetration method was developed for the limited dissolution of CO2 in the Ca(OH)2 solution. When Ca(OH)2 was added into the 10 mM CaCO3, zeta potential values of CaCO3 particles were increased from negative to positive value indicating that CaCO3 particles were stabilized in the presence of Ca(OH)2 solution. Rice-like CaCO3 particles were synthesized at the very early stage of crystallization. When crystallization progresses, the high energetic end sites started to dissolve, and the dissolution was progressed through the inside of the particles resulting in hollow calcite particles. BET surface area of hollow calcite particles was found to be 14.75 m2/g. Different parameters such as Ca(OH)2 flow rate, CO2 flow rate, Ca(OH)2 concentration, pipe diameter etc. were studied. Calcite particles in nano sizes, homogeneous size distribution, hollow shapes, and different morphologies were achieved to be produced.
  • Master Thesis
    Nano calcite (CaCO3) production in semi-batch bubble reactor
    (Izmir Institute of Technology, 2013) Ülkeryıldız, Eda; Özdemir, Ekrem
    Calcium carbonate (CaCO3) has been widely used as filling material in many industries due to its low cost and enhancement in some of the physical properties of the composite materials. The main purpose of this study was to produce CaCO3 particles by carbonation method in nano size, homogeneous size distribution and different morphologies. A semi-batch bubble reactor was designed in order to introduce carbon dioxide (CO2) into the Ca(OH)2 solution or its slurry with a controlled fashion. Different parameters such as stirring rate, Ca(OH)2 concentration, CO2 flow rate, and pulse CO2 injection were examined. Also, jet flow was applied in the stirred tank reactor to prevent particles from aggregation. Conductivity and pH values of solutions were monitored during crystallization. Zeta potential values and average particle size were measured instantly by dynamic light scattering (DLS). Particles produced were separated by centrifugation, dried at 105 oC in an oven for 1 day, and characterized by the Scanning Electron Microscopy (SEM) for their morphology, and X-Ray diffraction (XRD) for their crystal structures. On the basis of XRD analysis, the main crystal form of precipitated particles was calcite. According to SEM images, elongated chain-like, cubical, and rectangular particles were achieved to be produced with particle size of about 200 nm to 400 nm.