Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 7Citation - Scopus: 7Contributory Roles of Concentration and Ph in Caco3 Growth Inhibition for Submicron Particles Synthesis With Additive Ca2+(Elsevier B.V., 2024) Majekodunmi,O.T.; Kilic,S.; Ozdemir,E.Excessive growth of CaCO3 precipitates is inhibited by additive Ca2+. Here, we report the influence of concentration and solution pH on the extent of growth inhibition. Equal volumes of equimolar CaCl2 and Na2CO3 solutions were mixed and continuously dispersed in Ca(OH)2 solution, where Ca2+ irreversibly adsorb on the precipitates. Compared to conditions where additive Ca2+ are absent, this method can produce more than 90% decrease in particle size. We observe the degree of growth inhibition increases as the concentration of additive Ca2+, relative to the volume of precipitates, increases. An unusual role of pH is also revealed: growth inhibition that leads to the synthesis of monodisperse submicron CaCO3 particles is only observed in high alkaline pH conditions. Additive Ca2+ adsorb on CaCO3 precipitates in pH conditions above the isoelectric point (pH ≈ 9), but their ability to limit CaCO3 growth diminishes when pH < 12. © 2024 Elsevier B.V.Article Citation - WoS: 1Citation - Scopus: 1Inhibition of Caco3 Growth and Synthesis of Submicron Particles by Preferential Adsorption of Additive Ca2+ Ions on Fresh Precipitates(Royal Society of Chemistry, 2022) Majekodunmi, Olukayode T.; Kılıç Özdemir, Sevgi; Özdemir, EkremThis study demonstrates a method to inhibit the growth of CaCO3 and synthesize submicron particles in a chemical precipitation process under ambient and high supersaturation conditions. Equimolar CaCl2 and Na2CO3 solutions were mixed in a model tubular reactor at a constant flow rate, and the precipitates were continuously dispersed in stirred 250 mL of 10 mM Ca(OH)2 solution. This approach resulted in the synthesis of colloidally stable submicron CaCO3 particles for a precipitant concentration ≤75 mM. Varying the precipitates’ retention time in the tubular reactor had no significant effects on the particle size and colloidal stability. Time-dependent changes in the mean size, crystal form, morphology and specific surface area of the synthesized particles were also studied. For a precipitant concentration of 75 mM, the particles were monodispersed and porous spindle-like scalenohedral crystals which gradually grew in all faces as more precipitates were fed into the Ca(OH)2 solution. The mean hydrodynamic size of the particles was ∼850 nm at the 8th minute. However, in the absence of additive Ca2+ ions, the particles obtained at the 8th minute were polydisperse mixtures of vaterite and rhombohedral calcite particles greater than 4 μm in size. The results show that free additive Ca2+ ions are irreversibly adsorbed onto the particles as the precipitates dissolve and recrystallize into smaller crystals upon reaching the Ca(OH)2 solution.Article Citation - Scopus: 1Synthesis of Stable Nano Calcite(Turkish Chemical Society, 2018) Kılıç, SevgiSynthesis of calcium carbonate (CaCO3) particles in the presence of a population of carbon dioxide (CO2) bubbles was investigated in the calcium hydroxide (Ca(OH)2) solution, which is a natural stabilizer for CaCO3. Possible chemical speciation reactions were presented for an inorganic synthesis of hollow nano-CaCO3 particles. In the progress of CaCO3 synthesis, some of the particles started to dissolve at their edges and turned into hollow nano-CaCO3 particles. Some of the pores closed at the end of crystallization as a result of dissolution-recrystallization mechanism. Hollow nano-CaCO3 particles with sizes of about 300 nm were synthesized with a narrow size distribution. It was concluded that the hollow nano-CaCO3 particles could be advantageous due to lower weights and higher surface areas.Article Citation - WoS: 23Citation - Scopus: 31Nano-Caco3 Synthesis by Jet Flow(Elsevier Ltd., 2017) Ülkeryıldız, Eda; Kılıç, Sevgi; Özdemir, EkremA new methodology was introduced to produce hollow nano calcite particles in homogenous size distribution without aggregation. The design consisted of a jet flow system in which the crystallization region was separated from the stabilization region. The newly produced nano CaCO3 particles of about 140 nm were removed from the crystallization region as quickly as possible into the stabilization region before aggregation or crystal growth. In the stages of crystallization, the particles started to dissolve from their edges which opened-up the pores inside the particles. At the late stages of crystallization, the open pores closed. These particles were stable in Ca(OH)2 solution and no aggregation was detected. Different particles with different morphologies can be produced by adjusting the stages in the crystallization.Article Citation - WoS: 48Citation - Scopus: 52Stability of Caco3 in Ca(oh)2 Solution(Elsevier Ltd., 2016) Kılıç, Sevgi; Toprak, Görkem; Özdemir, EkremThe effect of calcium hydroxide (Ca(OH)2) on the stability of calcium carbonate (CaCO3) particles was investigated with respect to the surface potential and particle size. Both CaCO3 and Ca(OH)2 were dissolved in ultrapure water at concentrations up to 100 mM. The solubility limits were about 18 mM for Ca(OH)2 and about 0.13 mM for CaCO3 at 23 °C in water. Dissolution of commercial CaCO3 in 10 mM of Ca(OH)2 solution and dissolution of Ca(OH)2 in 10 mM of CaCO3 slurry were also studied at similar conditions. Conductivity, pH, zeta potential, and average particle sizes were measured for each solution. The morphological characteristics of the particles were analyzed by the SEM images. It was found that the zeta potential of CaCO3 particles was greater than + 30 mV when they were placed in the Ca(OH)2 solution compared to a zeta potential value of - 10 mV in water. It was concluded that the Ca(OH)2 solution is a stabilizer for the CaCO3 particles.Article Citation - WoS: 20Citation - Scopus: 23Rice-Like Hollow Nano-Caco3 Synthesis(Elsevier Ltd., 2016) Ülkeryıldız, Eda; Kılıç, Sevgi; Özdemir, EkremWe have shown that Ca(OH)2 solution is a natural stabilizer for CaCO3 particles. We designed a CO2 bubbling crystallization reactor to produce nano-CaCO3 particles in homogenous size distribution without aggregation. In the experimental set-up, the crystallization region was separated from the stabilization region. The produced nanoparticles were removed from the crystallization region into the stabilization region before aggregation or crystal growth. It was shown that rice-like hollow nano-CaCO3 particles in about 250 nm in size were produced with almost monodispersed size distribution. The particles started to dissolve through their edges as CO2 bubbles were injected, which opened-up the pores inside the particles. At the late stages of crystallization, the open pores were closed as a result of dissolution-recrystallization of the newly synthesized CaCO3 particles. These particles were stable in Ca(OH)2 solution and no aggregation was detected. The present methodology can be used in drug encapsulation into inorganic CaCO3 particles for cancer treatment with some modifications.Article Citation - WoS: 14Citation - Scopus: 15Effect of Carbonic Anhydrase on Caco3 Crystallization in Alkaline Solution(American Chemical Society, 2016) Molva, Murat; Kılıç, Sevgi; Özdemir, EkremThe effect of bovine carbonic anhydrase (CA) on calcium carbonate (CaCO3) crystallization was investigated. A new method was developed to estimate the biocatalytic activity of CA in alkaline solution. The CA was immobilized within polyurethane (PU) foam, and compared its biocatalytic activity with the free-CA and bare-PU foam. A minireactor was created in a calcium hydroxide (Ca(OH)2) solution in order to control the CO2 transfer rate, and reproducible results were obtained. It was found that the free-CA lost its activity in less than 6 min at pH 12.5 in alkaline Ca(OH)2 solution. The CaCO3 crystallization rates for the immobilized-CA were found to be a U-shape, relatively lower at lower immobilized-CA amounts compared to those for the free-CA and bare-PU foam and higher when the amount of immobilized-CA increased. It was concluded that a higher immobilized-CA amount is required to accelerate the CaCO3 crystallization rates in Ca(OH)2 solution.Article Citation - WoS: 64Citation - Scopus: 70Mechanical and Morphological Properties of Recycled High-Density Polyethylene, Filled With Calcium Carbonate and Fly Ash(John Wiley and Sons Inc., 2006) Atikler, Ulaş; Başalp, Dildare; Tıhmınlıoğlu, FundaIn this study, mechanical and morphological properties of composites made up of recycled high-density polyethylene (HDPE) filled with calcium carbonate and fly ash (FA) were studied. Interfacial interactions were modified to improve the filler compatibility and mechanical properties of the composites by surface treatment of the FA filler with 3-amino propyl triethoxy silane. The composites were prepared by using a Thermo Haake Rheomixer. Effect of filler loading and treatment of FA with silane coupling agent on mechanical and morphological properties were investigated and it was found that silane treatment indicated significant improvements on the mechanical properties of the HDPE-FA composites. The improvement with silane treatment of FA was also confirmed by applying the Pukanszky model. Scanning electron microscopy on the fracture surface of composites had given direct evidence of better interfacial adhesion via silane treatment.Article Citation - WoS: 35Citation - Scopus: 45Types of the Scaling in Hyper Saline Geothermal System in Northwest Turkey(Elsevier Ltd., 2014) Demir, Mustafa Muammer; Baba, Alper; Atilla, Vedat; İnanlı, MustafaTuzla is an active geothermal area located in northwestern Turkey, 80km south of the city of Canakkale and 5km from the Aegean Coast. The geothermal brine from this area, which is dominated by NaCl, has a typical temperature of 173°C. Rapid withdrawal of fluid to ambient surface conditions during sampling causes precipitation of various compounds known as scaling. Scaling is one of the important problems in Tuzla geothermal system that reduces the efficiency of the geothermal power plant and causes economical loss. The aim of this study was to determine the type of scaling as a first step towards preventing its formation. The scales formed in the geothermal system were divided into two groups according to location: the ones that formed in downhole and the ones that accumulated along the surface pipeline. Both scales were examined in terms of their elemental composition, structure and morphology using XRF, XRD, and SEM, respectively. The former was found to be mainly composed of PbS (Galena) and CaCO3 (aragonite or calcite). In contrast, the latter was heterogeneous in nature and consisted of mainly saponite like amorphous structure along with submicrometer-sized amorphous silica particles, layered double magnesium and iron hydroxide, and NaCl.