Yazar "Ozdemir, Orhan" seçeneğine göre listele

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    An investigation of the effect of clay type on coal flotation along with DLVO theoretical analyses
    (Taylor & Francis Inc, 2020) Gungoren, Can; Guven, Onur; Cinar, Mustafa; Ozdemir, Orhan
    Coals generally exist with clay minerals, which are very fine-sized minerals, and adversely affect the flotation of coal. For instance, they make the coal surface hydrophilic by coating coal surfaces and therefore, they inhibit bubble-particle attachment. Clay minerals can also cause over-consumption of reagents due to their high surface area. Additionally, clay minerals can transfer into the concentrate during the flotation process by entrainment because of their low weight and small particle size, and thus, increase pulp viscosity and changing froth stability. In this study, the influence of various clay minerals (kaolinite, illite, and bentonite) on the flotation behavior of coal sample was studied in detail by conventional flotation tests. In addition, the values obtained from flotation tests were correlated with theoretical energy barrier values established with classical DLVO theory based on zeta potential values of coal and clay samples measured at different pH values. According to the results of this study, no significant effect of clay minerals was observed on coal flotation. This was probably because of the high floatability of the coal used for this study. Both the results obtained from the experiments and theoretical analysis, DLVO calculations, showed that the type of clay mineral is the main indicator parameter for coal flotation.
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    Effect of blunging process on purification of halloysite ore from ferrous impurities by dry magnetic separation
    (Oficyna Wydawnicza Politechniki Wroclawskiej, 2024) Durgut, Emrah; Cinar, Mustafa; Boylu, Feridun; Ozdemir, Orhan
    The objective of this research is to study the effects of feed particle size, splitter angle, and washing process on Fe2O3 removal efficiency in the separation of ferrous impurities from halloysite ore by dry magnetic separation in order to increase the purity of halloysite sample after crushing and blunging processes separately. Firstly, after crushing ore in a jaw crusher and sizing to -2+1 mm, -1+0.5 mm, and -0.5+0.212 mm fractions, the sized materials were fed to REMS-type dry magnetic separator at a constant belt speed of 300 rpm with the splitter angles of 0, 15, 30 degrees separately. Maximum Fe2O3 removal efficiency (FRE) (97.1%) was obtained in the nonmagnetic product at -0.5+0.212 mm size fraction and 0 degrees splitter angle. The minimum Fe2O3 content (1.3%) was reached in the nonmagnetic product obtained in the experiment with the feed size of -2+1 mm and a splitter angle of 0 degrees. Secondly, dry magnetic separation was applied to the washed -2+0.212 mm size fraction after drying at room temperature to evaluate the coarse particle -sized halloysite ore that was gained by mechanical dispersion in the aqueous medium towards sodium hexametaphosphate (SHMP), while a significant part of the clay minerals went into fine size after the dispersion process. In the experiment performed with a 0 degrees splitter angle after washing, it was determined that halloysite concentrate of 0.4% Fe2O3 content could be obtained with 98.8% Fe2O3 removal efficiency. As a result of dry magnetic separation experiments, it was seen that Fe2O3 removal efficiency decreased as the splitter angle increased, while Fe2O3 content in magnetic and nonmagnetic products increased. It was determined that washing and cleaning of finesized minerals plastered on particle surfaces after mechanical dispersion and particle release of minerals with different magnetic properties increased the dry magnetic separation efficiency, and nonmagnetic products with very low Fe2O3 (0.4%) and high Al2O3 (31.9%) content was obtained. The blunging process in the presence of dispersant caused the dispersion of clay minerals and allowed to liberating of the ferrous minerals from the halloysite ore, hence the increase in the FRE for the magnetic separation.
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    Effect of Blunging/Dispersion Parameters on Separation of Halloysite Nanotubes from Gangue Minerals
    (Mdpi, 2022) Durgut, Emrah; Cinar, Mustafa; Terzi, Mert; Unver, Ilgin Kursun; Yildirim, Yildiz; Boylu, Feridun; Ozdemir, Orhan
    Clay minerals need to be dispersed with blungers before their utilization in the related industries due to their plastic properties, and size reduction is carried out in a wet medium. Clay minerals also contain impurities such as nonplastic materials in their structure. Mechanical dispersion parameters are important in the separation of clay group minerals (halloysite and kaolinite) from their typical non-clayey gangue minerals (quartz and goethite). In this study, the removal of impurities from halloysite ore obtained from Kizildam, Turkey, was examined in terms of mechanical dispersion parameters, namely, feed size, blunging time and speed, pulp concentration, pulp temperature, and the aging process. The effect of these parameters on halloysite dispersion was determined by particle size, chemical, and mineralogical analysis, and optical and scanning electron microscope images. The results obtained from the studies of the mechanical dispersing and particle size distribution of the products indicated that the optimum dispersion parameters were determined as -10 mm feed size, 8 h, and 1000 rpm blunging time, and speed, 35% pulp concentration at 25 degrees C pulp temperature. Under these optimum conditions, a 72.3% amount of -38 mu m clay product containing 35.6% of halloysite, 46.5% of kaolinite, 12.0% quartz, 1.9% goethite, 0.9% gibbsite, and 3.2% other minerals were obtained from the halloysite ore, having 30.5% of halloysite, 43.4% of kaolinite, 19.1% quartz, 2.9% goethite, 1.4% gibbsite, and 2.7% other minerals. In this study, it was understood that feed size, pulp concentration, blunging time, and speed were important parameters, while pulp temperature and the aging process had no significant effect on the mechanical dispersion of Kizildam halloysite. In addition, impurities such as quartz and iron-bearing minerals were separated from the ore by blunging and sieving.
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    Effect of calcite and mica contents in nepheline syenite samples on the ceramic body sintering behaviours and surface roughness
    (Oficyna Wydawnicza Politechniki Wroclawskiej, 2022) Durgut, Emrah; Cinar, Mustafa; Ozdemir, Orhan
    In this study, the effects of calcite and mica contents in nepheline syenite (NS) samples beneficiated by high intensity dry magnetic separation and flotation methods on ceramic bodies were investigated in detail. The NS samples were, first, sintered to observe the physical and surface roughness properties, and characterized based on the change of NS samples such as color, shrinkage, water absorption, and surface roughness after the sintering process. L-a-b color and Ra, Rz, Rt values for the NS samples were determined. The decrease in calcite and mica contents affected the surface of sintered specimens positively by reducing roughness values. Additionally, the water absorption values were found to be directly proportional to Ra values for unglazed surfaces. In conclusion, calcite and mica minerals in NS samples negatively affected surface quality by forming pinholes due to dehydroxylation and outgassing reactions in the sintering process.
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    Effect of crystallinity and surface silanol groups on rheological properties of different sepiolites
    (Oficyna Wydawnicza Politechniki Wroclawskiej, 2022) Cinar, Mustafa; Guelgoenuel, Ilhan; Ozdemir, Orhan; Celik, Mehmet S.
    In this study, differences in the rheological properties of three different types of brown sepiolites (K1, K2, and K3) along with one beige (B) sepiolite with different physicochemical properties were explained based on their crystallinity and level of surface silanol groups. Towards this aim, SEM images, XRD and chemical analyses, cation exchange capacity (CEC), and water absorption tests were conducted along with surface area measurements and time-dependent pH profiles. The pH profiles at 3% by wt. revealed that each sepiolite sample attained the equilibrium at different times. These differences showed a parallel behavior with the degree of crystallinity. While sepiolite with better crystallinity (K1) was rather slow in reaching the equilibrium pH, the sepiolites with poor crystallinity (B and K3) reached their equilibrium pH more quickly. The rheological studies conducted with different sepiolites at 3% solids concentration exhibited time-dependent flow of the Bingham plastic model and thixotropic. Differences observed in the rheological behavior of sepiolites were found to correlate with the fiber size, CEC, surface area, and water absorption. The results further indicated that sepiolites with low crystallinity or high level of surface silanol groups (K3 and B sepiolites) show the best rheological properties.
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    Electroluminescence properties of a PIN structure made by nearly stoichiometric a-SiCx:H active layer
    (Pergamon-Elsevier Science Ltd, 2009) Sel, Kivanc; Akaoglu, Baris; Ozdemir, Orhan; Atilgan, Ismail
    a-SiCx:H PIN diode has been fabricated within a single pump-down process under the same deposition conditions used for doped and undoped PECVD grown thin films, whose optical and electrical properties are determined and compared with a-Si:H. Current-voltage characteristics of PIN diode are evaluated and concluded to be limited by tunnelling of holes at p-i interface into valence band tail states. Electroluminescence measurements revealed radiative monomolecular recombinations. Deconvolution of the luminescence spectra is utilized to analyse recombination mechanism to be dominated by the transitions between band tails and deep states, which are created by the large density of both silicon and carbon dangling bonds, probable in the stoichiometric a-SiCx:H film. Finally, a small luminescence peak around 1.9 eV would be an evidence of reduced probability of tail to tail transitions, than that of the transitions between tail and deep states. (C) 2008 Elsevier Ltd. All rights reserved.
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    Evaluation of Different Dispersants on the Dispersion/Sedimentation Behavior of Halloysite, Kaolinite, and Quartz Suspensions in the Enrichment of Halloysite Ore by Mechanical Dispersion
    (Mdpi, 2022) Durgut, Emrah; Cinar, Mustafa; Terzi, Mert; Unver, Ilgin Kursun; Yildirim, Yildiz; Ozdemir, Orhan
    In this study, the dispersion properties of pure halloysite, kaolinite, and quartz minerals in halloysite ore were determined in the absence and presence of dispersants (sodium silicate, STPP, SHMP). First of all, the samples were characterized by chemical, mineralogical, BET, FTIR, and TEM analyses. Afterward, the physico-chemical properties of these minerals were investigated by zeta potential measurements and dispersion/sedimentation experiments in the absence and presence of the dispersants. The zeta potential measurements showed that the surface charges of all minerals changed from negative to positive as the PH changed from basic to acidic. The presence of dispersants at natural pHs indicated that the mineral surface charges tended to become more negative as the concentration increased in the zeta potential measurements. SHMP showed the most effect on the zeta potential. In the dispersion/sedimentation experiments, settling was slowed down with the use of dispersants. Finally, the dispersion properties of halloysite ore in the presence of dispersants were explored using mechanical dispersion and pulp viscosity experiments based on the amount of material passing to <38 mu m size and the chemical changes in the materials. As a result of the mechanical dispersion tests carried out in the presence of dispersants (sodium silicate, STPP, SHMP), 71.3% of the material with 30.8% Al2O3 and 50.5% SiO2 content passed to <38 mu m size without using dispersant, and 73.2% of <38 mu m sized material with 35.5% Al2O3 and 46.1% SiO2 content was gained in the use of 7.5 kg/ton SHMP, which was determined as the optimum within the scope of the study. In conclusion, dispersant use enhanced the mechanical dispersion effect for plastic clay mineral separation from hard minerals in an aqueous medium.
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    Improved flotation of heat treated lignite with saline solutions containing mono and multivalent ions
    (Oficyna Wydawnicza Politechniki Wroclawskiej, 2018) Ozdemir, Orhan; Ersoy, Omer F.; Guven, Onur; Turgut, Hatice; Cinar, Mustafa; Celik, Mehmet S.
    Flotation of lignites is inherently difficult. However, pre-heat treatment of coal is also known to make coal surfaces more hydrophobic possibly through removal of water entrapped in the structure of coal. In this context, the objective of this study was, therefore, to determine changes in the hydrophobicity of some lignites under moderately controlled heat treatment, and correlate the flotation response of lignites in different salt solutions of NaCl, KCl, CaCl2, and MgCl2 without using any reagent. The results of flotation tests suggested that, under the present test conditions, it was possible to float thermally pre-treated lignite samples of partially hydrophobic character in salt solutions in the absence of collector and frother. In addition, the effect of heat treatment on hydrophobicity, and in turn flotation was explained by a theoretical model based on extended DLVO interactions to quantify the effects of both heat treatment and salt concentration on bubble-particle interactions. The results of theoretical modeling suggested that the removal of hydrogen containing groups from coal surfaces significantly contributed to the electrical double layer and hydrophobic forces that governed the magnitude of energetic barrier and also the extent of bubble-particle attachment.
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    Study of minority carrier injection phenomenon on Schottky and plasma deposited p-n junction diodes
    (Elsevier Sci Ltd, 2009) Ozdemir, Orhan; Sel, Kivanc
    Both temperature dependent ac capacitance (C) together with ac conductance (G) under various frequencies (omega) and dc current (I) measurements as functions of bias (V) were employed to investigate majority as well as minority carrier injection phenomenon on chromium-p-type crystalline silicon (Cr/p-cryst. Si/ohmic contact) Schottky and aluminum/plasma deposited n-type hydrogenated amorphous silicon/p-c-Si (Al/n-aSi:H/p-c-Si/ohmic contact) p-n structures. Ambipolar transport process was eventual for both diodes and behaved differently according to the mentioned techniques: for a well defined forward bias interval, there was an increase in capacitance towards maximum that interpreted as majority carrier injection from the back electrode. On the other side, minority carrier injection from front electrode begun when the bias went beyond the critical voltage (i.e., built-in voltage) that corresponded to the peak position and caused sharp decrease in measured capacitance, leading to observation of a hump in C-V measurement. Moreover, shape and peak position of the hump were frequency/temperature dependent. Remarkably, in the bias range where capacitance pronounced, space charge limited current (SCLC) was discerned as enrolled carrier flow mechanism according to I-V measurement, confirming further majority carrier injection. In addition, both dc conductivity and ac conductance followed the same dependence with bias voltage in forward direction. On the other side, reverse current seemed proportional to square root of reverse bias, implying generation current in the depletion region. These experimental identifications convinced us of the existence of conductivity modulation issue for the structures at hand. (C) 2009 Elsevier Ltd. All rights reserved.