Chemical Engineering / Kimya Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/14
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Article Citation - WoS: 2Citation - Scopus: 3A Phenomenological Kinetic Flotation Model: Distinct Time-Variant Floatability Distributions for the Pulp and Froth Materials(Elsevier, 2023) Polat, Mehmet; Polat, HürriyetA simple and easy-to-use phenomenological kinetic flotation model, strongly connected with the physics of the process, is proposed in this paper. The model explicitly contains the cell volume, aeration rate, volumetric holdup, mean bubble size, and particle density as input variables. It can be employed to characterize the floatability distributions of the particles in the pulp and the froth separately any time during the flotation process. Two new time-dependent kinetic parameters, the bubble loading factor & phi;(t) and the maximum cell mass transfer capacity Mmax(t) also appear in the model expression. & phi;(t) is a measure of the degree of crowding of the bubble surfaces and accounts for the deviations from the first-order rate equation. Mmax(t) describes the maximum amount of mass that can be transported to the froth phase by the bubble population in the cell. Screen fractionation of each froth product collected at different time intervals during a single kinetic flotation test is sufficient to generate the data required by the model for analysis. Application of the model to this data yields directly time-dependent functions for the floatability of the particles reporting to froth Kf(t) or remaining in the cell Kp(t) for each size fraction separately, without the need for any empirical parameters. The test of the model was carried out using published kinetic flotation data from the literature.Article Citation - WoS: 6Citation - Scopus: 7Designing Robust Xylan/Chitosan Composite Shells Around Drug-Loaded Msns: Stability in Upper Git and Degradation in the Colon Microbiota(Elsevier, 2023) Zeybek, Nüket; Büyükkileci, Ali Oğuz; Güleç, Şükrü; Polat, Mehmet; Polat, Hürriyetong residence times, near-neutral pH values, and release triggered by the enzymatic action of the resident microbiota offer unique opportunities for improved drug delivery in the colon. The fact that a delivery agent must also pass through the complete GI tract without degradation presents a challenge due to widely changing pH conditions. In this study, a promising colon-targeted drug delivery system was composed of a xylan/chitosan composite shell formed on curcumin-loaded mesoporous silica nanoparticles (MSNs). A novel synthesis approach was employed to facilitate precipitation of negatively charged xylan on negatively charged MSNs by concurrent chitosan polymerization. Curcumin-loaded xylan/chitosan-coated MSNs (C-MSNs) were determined to contain nearly 42% xylan by the inclusion of chitosan in a one-to-one ratio with xylan. The xylan/chitosan composite shell demonstrated excellent stability in the acidic upper GI tract. The hydrolysis of glycosidic bonds by resident microbiota was the triggering mechanism for xylan degradation and curcumin release in the colon. The presence of xylan has the further benefit of increasing the number of beneficial bacteria and improving short-chain fatty acid production for improved colon health.Article Citation - WoS: 22Citation - Scopus: 26Coal Fly Ash as a Potential Fixation Reagent for Radioactive Wastes(Elsevier Ltd., 2015) Lieberman, Roy Nir; Green, Uri; Segev, Giora; Polat, Mehmet; Mastai, Yitzhak; Cohen, HaimIsrael produces ∼1.3 Mt/year of fly ash (FA), a byproduct of its coal-fired power plants. Due to increasing environmental regulations, these imported coals are processed to reduce the sulfur concentration (∼0.6%). These processing methods result in a material that has an enriched alkali/alkali earth component with pozzolanic and basic properties (pH > 10.5). FAs are utilized worldwide, mainly as a cement additive for the construction industry. Recently, it was demonstrated that Class F FA can act as an excellent fixation reagent for acidic wastes from the phosphate or the oil regeneration industries. In the current work the potential utilization of Class F FAs as fixation reagents for low-activity radioactive waste from the nuclear industry was examined. Aqueous solutions containing radionuclide simulants: cesium (Cs+), strontium, (Sr2+), and cerium (Ce3+, Ce4+) were used as case studies with promising results. It is suggested that the primary fixation mechanism involves the aluminate/silicate anions at the FA surface. A novel experimental fixation approach utilizing the formation of carbonates is demonstrated and a new interaction mechanism is suggested based on the electrostatic interactions of the positively charged fine precipitates with the negatively charged FA surface. © 2015 Elsevier Ltd. All rights reserved.Article Citation - WoS: 5Citation - Scopus: 5Determination of Electrostatic Potential Distribution by Atomic Force Microscopy (afm) on Model Silica and Alumina Surfaces in Aqueous Electrolyte Solutions(Elsevier Ltd., 2014) Yelken Özek, Gülnihal; Polat, MehmetAFM was employed as a physicochemical probe to determine the electrostatic potential distribution quantitatively on selected ideal oxide surfaces (quartz 0 0 0 1 and sapphire 0 0 0 1) in aqueous media. The force of interaction between a silicon nitride tip and the oxide surface was measured at a given point under well-defined solution conditions. Relevant theories were used to isolate the electrostatic component from the total force of interaction which was then employed to estimate the surface potential at that point. Repeating the procedure on selected locations generated a potential map of the surface. Comparison of these potentials with those obtained from independent electrokinetic measurements confirmed the validity of the approach. © 2014 Elsevier B.V. All rights reserved.Article Citation - WoS: 57Citation - Scopus: 69Leaching Behavior of Selected Trace Elements in Coal Fly Ash Samples From Yenikoy Coal-Fired Power Plants(Elsevier Ltd., 2012) Akar, Gül; Polat, Mehmet; Galecki, Greg; Üner, İpekoğluShort-term leaching test results of alkaline fly ash from Yenikoy coal-fired power plant were reported in this paper. ASTM D-3987-85 and TCLP-1311 test methods were applied to determine leaching behavior of selected elements namely, Fe, Ca, Cu, Co, Cd, Mn, Ni, Pb Zn, and Cr (VI) at different particle size fractions and test conditions. Chemical, mineralogical and morphological characterizations of ash samples were also performed using chemical, XRD and SEM-EDS analysis methods. The results showed that CaO dominates in the Yenikoy fly ash sample which directly affects the mobility of trace elements by determining the pH of the leaching medium. Higher mobility values of Cd, Co Cu, Pb, Ni and Zn elements were observed for TCLP-1311 procedure. The concentration of these elements in leachates showed a tendency to increase by decreasing particle size. Overall results suggested that the amount of the selected elements in the final leachates of both tests was lower than the limit values of landfill regulations except Cr (VI).Article Citation - WoS: 15Citation - Scopus: 12Solubility and Aging of Lead Magnesium Niobate in Water(Elsevier Ltd., 2009) Şakar-Deliormanlı, Aylin; Çelik, Erdal; Polat, MehmetLead magnesium niobate (PMN) is an important relaxor ferroelectric material commonly employed in multilayer capacitor and actuator manufacturing owing to its high dielectric constant and superior electrostrictive properties. However, stability of this material in water is not very well known and there is need for a detailed investigation. In this research, solubility of lead magnesium niobate powders in water was determined as a function of solids concentration. The obtained results showed that the amount of cation leaching from the PMN surface depends on the pH value of the suspension and the solids concentration. The Pb2+ and Mg2+ ion dissolution was very high especially in the acidic pH range. Nevertheless, neither the dissolution mechanism nor the effects of dissolved ions on the stability were the same for those ions. The study provides new aspects on the solubility of perovskite materials which possess more than one soluble cation in their structure.Article Citation - WoS: 7Citation - Scopus: 9Preparation of the Pb(mg1/3nb2 Films by Aqueous Tape Casting(Elsevier Ltd., 2009) Şakar-Deliormanlı, Aylin; Çelik, Erdal; Polat, MehmetLead magnesium niobate (PMN) is a relaxor ferroelectric material. Because of its high dielectric constant and superior electrostrictive properties it is commonly used in the manufacture of multilayer electronic devices which is typically produced by tape casting. However, preparation of PMN slurry formulations to use in aqueous tape casting process is not investigated in detail yet. Therefore, in this study aqueous PMN formulations were developed for tape casting and its relation with the final properties of PMN films were investigated. The slurries were prepared using poly(acrylic acid)-based comb polymer as the dispersant, nonionic acrylic latex as the binder and the hydroxypropyl methyl cellulose as the wetting agent. The results showed that it is possible to prepare flexible, crack-free PMN films using highly concentrated suspensions without using any plasticizer. The study gives guidelines for the aqueous tape casting of PMN and can be adapted to processing of other multi-component metal oxides.Article Citation - WoS: 23Citation - Scopus: 24Analytical Solution of Poisson-Boltzmann Equation for Interacting Plates of Arbitrary Potentials and Same Sign(Elsevier Ltd., 2010) Polat, Mehmet; Polat, HürriyetEfficient calculation of electrostatic interactions in colloidal systems is becoming more important with the advent of such probing techniques as atomic force microscopy. Such practice requires solving the nonlinear Poisson-Boltzmann equation (PBE). Unfortunately, explicit analytical solutions are available only for the weakly charged surfaces. Analysis of arbitrarily charged surfaces is possible only through cumbersome numerical computations. A compact analytical solution of the one-dimensional PBE is presented for two plates interacting in symmetrical electrolytes. The plates can have arbitrary surface potentials at infinite separation as long they have the same sign. Such a condition covers a majority of the colloidal systems encountered. The solution leads to a simple relationship which permits determination of surface potentials, surface charge densities, and electrostatic pressures as a function of plate separation H for different charging scenarios. An analytical expression is also presented for the potential profile between the plates for a given separation. Comparison of these potential profiles with those obtained by numerical analysis shows the validity of the proposed solution. © 2009 Elsevier Inc. All rights reserved.Article Citation - WoS: 29Citation - Scopus: 38Encapsulating Fly Ash and Acidic Process Waste Water in Brick Structure(Elsevier Ltd., 2010) Köseoğlu, K.; Polat, Mehmet; Polat, HürriyetFly ash contains metals such as cadmium, iron, lead, aluminum and zinc in its structure in appreciable amounts. These metals can leach out into surface and ground waters if fly ash is not properly disposed of. A similar problem also exists for acidic process waste waters discharged by numerous industries. The purpose of this study was to utilize such wastes as additives in the production of construction quality bricks for the purpose of waste elimination. The bricks produced were subjected to flexural strength and water retention capacity tests along with heavy metal leaching experiments in order to determine the applicability of the procedure and the best possible recipes. This paper summarizes the results obtained in these tests along with the possible mechanisms involved in stabilizing the two wastes in the brick structure. © 2009 Elsevier B.V. All rights reserved.Article Citation - WoS: 10Citation - Scopus: 10Determination of the Particle Interactions, Rheology and the Surface Roughness Relationship for Dental Restorative Ceramics(Elsevier Ltd., 2009) Kes, Mürşide; Polat, Hürriyet; Keleşoğlu, Serkan; Polat, Mehmet; Aksoy, GökhanThe effect of inter-particle interactions on the slurry properties and the final surface roughness of the dental ceramic restoratives was investigated. A commercial dental ceramic powder, IPS Empress 2 veneer, was used as the raw material. The magnitudes of the particle-particle interactions were computed by the DLVO theory for the ceramic slurries of different electrolyte solutions (0.1 M, 0.25 M, 0.5 M, 0.75 M, 1 M NaCl and CaCl2). As expected, the energies of particle-particle interactions were influenced significantly by the presence of electrolytes. These computations demonstrated that addition of electrolytes leads to a progressive depression of the repulsive double layer forces. The absence of these forces should inevitably lead to agglomeration caused by the ever-present van der Waals forces. The rheological measurements carried out using the slurries with same solution properties supported the findings of the DLVO computations. It was found that dental ceramic slurries showed a Newtonian behavior in the absence of electrolytes, which is indicative of little or no agglomeration in the slurry. On the other hand, the same slurries displayed a non-Newtonian, shear thinning behavior in the presence of electrolytes which can be attributed to agglomeration or gelation. Roughness of the ceramic surfaces produced from these slurries was studied by SEM analysis and profilometer measurements. Contact angle studies were also carried out on the same surfaces. It was observed that the surface became rougher initially with electrolyte addition to a maximum, most probably due to formation of isolated agglomerates due to a reduction of the repulsive double layer forces. After reaching a maximum, surface roughness decreased to a much lower value with further increase in electrolyte concentration. This was most probably caused by the formation of a relatively homogeneous, gel-like structure within the extensively agglomerated slurry due to a complete collapse of the double layer.