Browsing by Author "Cengizler, H"

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    Failure of Welded Radiator Nipples Caused by Nonmetallic Inclusions
    Elkoca, O; Cengizler, H
    A splitting phenomenon in the weld zone of the radiator nipples was encountered after a threading operation. During the failure analysis, some oxide traces were macroscopically observed on the surfaces of unthreaded nipples. Subsequent scanning electron microscopy-x-ray spectrometer (SEM-EDS) examination through the surfaces of the unthreaded nipples and as-pickled steel sheet coupons that were used for nipple manufacturing revealed that the oxide traces were hot-rolling scale residuals. However, none of the traces of scale residuals were encountered on the cross sections of weld zone of unthreaded nipple samples. Contrarily, some cracks and inclusion residuals were observed through the interface between the protrusion and weld zone. EDS analysis and optical microscopy affirmed the presence of MnS-type inclusions. The same kind of inclusions was also observed when one of the unthreaded nipples was intentionally separated through the weld zone. In conclusion, the main cause for the failure was determined to be the adverse effect that the MnS inclusions in the steel had on the material ductility.
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    The effect of marble waste in the production of low-temperature porous material from alkali-activated fly ash
    Cengizler, H; Koç, M
    The production of low-cost open-pore ceramic materials from fly ash (FA) and marble waste (MW) was investigated. The effect of MW (5-40 wt.%) on the open porosity was determined. To reduce the sintering temperature and improve the properties of porous materials, the mixtures were activated with an alkali solution. Samples pressed from FA and FA+MW mixtures were sintered at low temperature (900 degrees C), but sufficient strength could not be obtained. However, when these mixtures were subjected to alkali activation, pressed and sintered at 900 degrees C, sufficient strength and porosity values were reached. The open porosity of the MW neat specimen was 12.70%, but it increased up to 39.91% at 40 wt.% MW, which was the highest ratio used in the literature. The main phase structure was nepheline at 0-20 wt.% MW, but gehlenite became the dominant phase at 40 wt. % MW. The compressive and flexural strength values of 40 wt.% MW added specimen was determined to be 12 and 5.35 MPa, respectively. The openpore ceramic of high MW ratio, produced by this new alternative route, has the potential for use in water purification membranes for macro filtration purposes.
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    SILICON AND MANGANESE PARTITION BETWEEN SLAG AND METAL PHASES AND THEIR ACTIVITIES PERTINENT TO FERROMANGANESE AND SILICOMANGANESE PRODUCTION
    Cengizler, H; Eric, RH
    Equilibrium between MnO-CaO-MgO-SiO2-Al2O3 slags and carbon saturated Mn-Si-Fe-C alloys was investigated under CO at 1500oC. Manganese and silicon activities were obtained by using the present data and the previously determined MnO and SiO2 activities of the slag. Quadratic multi-coefficient regression equations were developed for activity coefficients of manganese and silicon. The conclusions of this work are:(i)increase in the basicity and the CaO/Al2O3 ratios decreases the Mn distribution ratio,(ii)increase in the silica concentration and the MgO/CaO ratio increases the Mn distribution ratio, iii)carbon and manganese as well as carbon and silicon of the metal phase are inversely proportional,(iv)as Mn/Fe and Mn/Si ratio increases in the metal the carbon solubility increases,(v)decrease in the basicity increases the silicon content of the metal and (vi)increase in the silica content of the slag increases the silicon content of the metal and this effect is more pronounced at the higher Mn/Fe and Mn/Si ratios.
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    Production of ceramic glass foam of low thermal conductivity by a simple method entirely from fly ash
    Cengizler, H; Koç, M; San, O
    Ceramic glass foam/foams (CGF) from two different F-class fly ashes were produced via a well-known simple conventional sintering method using sodium silicate (Na2SiO3) as a foaming and fluxing agent. The research aimed to understand the effects of each fly ash, Na2SiO3 ratio, and sintering conditions on the properties and microstructure to produce a commercial CGF of low thermal conductivity. The chemical composition of fly ash from the thermal power plants of Tuncbilek and Seyitomer were quite similar but had different melting temperatures and microstructures. While the foam structure was successfully obtained at 1100 degrees C with 30 wt.% Na2SiO3 from Tuncbilek fly ash, a similar structure was obtained at 1150 degrees C from the Seyitomer fly ash. The effects of Na2SiO3 content and sintering temperature on the properties and microstructure of the CGF from the Tuncbilek fly ash of a lower melting point, in particular, were investigated systematically. The optimal sintering temperatures were determined to be 1200, 1150, and 1100 degrees C at the highest fly ash ratios of 90, 80 and 70 wt.%, respectively. The CGF were produced with 69.76-75.43% porosity, 0.55-0.69 gr/cm(3) bulk density, 3.2-5.35 MPa compressive strength and 0.10-0.21 W/(m K) of low thermal conductivity. XRD results showed that optimal CGF samples mainly contained spinel, quartz and hematite crystal phases and amorphous phase. In this research, a thermal insulation material was successfully produced using an industrial waste completely with a well-known simple method. It is thought that this will contribute beneficially to the environment and the economy.
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    Formcoke production from char fines of hard brown coals by air curing
    Cengizler, H; Kemal, M
    The purpose of the present study was to explore the technical feasibility of formcoke production from non-coking bright hard brown coals and pitch as a binder by air curing. The briquettes obtained from the chars of Soma coals carbonised at 500, 600, 700, 800 and 900(o)c with 12% pitch were air cured in a streaming gas containing 16% O-2 (air+N-2) for 120 min at 270(o)C and the formcoke strength was found to be 10-40% higher than that of raw briquettes. Under the prevailing conditions, the formcoke strength and the apparent specific gravity of the green and formcoke briquettes increased as the carbonisation temperature increased, reaching a maximum at the optimum carbonisation temperature of 800(o)C. M-40 and M-10 values and the compressive strength of SK800 formcokes were determined to be 92.3, 7.7% and 23.5 MPa respectively being similar to those of conventional cokes produced at coke ovens. The optimum curing conditions (pitch content, curing time and temperature) were determined using TK800 char. The optimum curing time for TK800 briquettes at 220(o)C was determined to be 90 min. The formcoke strength of TK800 briquettes subjected to a thermal treatment at 220(o)C was lower than that of the briquettes air cured at the same temperature. The optimum curing temperature for TK800 briquettes with 10% pitch and cured in a gas stream containing 16% O2 in terms of formcoke strength was determined to be 285(o)C. M40 and M10 values and the compressive strength of TK800 formcokes were determined to be 91, 8.1% and 19.6 MPa respectively. The experimental results reveal the advantages of the method because the formcokes produced possess suitable properties for various metallurgical processes and smokeless fuel consumption. The gas and tar obtained during the carbonisation of raw coal are the added benefits.
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    Tannery wastewater sediments produced by clinoptiolite/polyacrylamide-aided flocculation as a clay additive in brick making
    Köseoglu, K; Cengizler, H; Israil, LI; Polat, H
    Toxic tannery wastewater(s) (TWW) pose(s) a great risk to the environment. This study explores the potential of mitigating the harmful effects of TWW through sedimentation using clinoptiolite in the presence of various anionic, cationic and non-ionic flocculants with different molecular weights and charge densities followed by encapsulation in a brick structure for stability. Compressive strength (CS), size reduction after firing (SRAF), water absorption (WA) and colouring parameters of bricks were determined. X-Ray diffraction (XRD) and scanning electron microscopy (SEM)-energy dispersive X-ray (EDX) analyses were conducted on brick bodies. Kinetic leaching experiments were conducted for possible heavymetal release from the bricks. Bricks containing 10 wt% leather waste and 5 wt% clinoptiolite sintered at 800 degrees C instead of 920 degrees C possessed similar properties to the standard brick (SB).
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    Production of porous ceramic from clinoptilolite incorporating aluminum powder
    San, O; Koç, M; Cengizler, H
    In this study, production of porous ceramic from clinoptilolite incorporating aluminum powder at various sintering temperatures was investigated. The mixtures were sintered at 1150, 1200, 1250 and 1300 degrees C for 1 h in air atmosphere. SEM and XRD analyzes were conducted to observe the microstructural evolution and the phase composition, respectively. The DSC/TG analyzes of the clinoptilolite and aluminum powder mixture indicated that 1150 degrees C was a significant temperature at which oxidation of molten aluminum enhanced and the softening of the clinoptilolite began. The progress in oxidation of aluminum with increasing temperature led to corundum phase crystallization while the amount of cristobalite decreased. Aluminum distribution in the ceramic matrix began at 1200 degrees C but pore channels with very smooth surfaces were obtained at 1250 degrees C. At this temperature, the pores interconnected to each other had narrow pore size distribution (4-180 pm) with low friction coefficient of 0.64 resulting from enhanced corundum phase formation in the structure. Results showed that the porous ceramic sintered at 1250 degrees C with 32.8% apparent porosity and a pure water permeability of similar to 2050 L/ (m(2).hr.bar) promises great potential for use as a filtering media and/or support.
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    Cracking during cold forming process of rear brake component
    Elkoca, O; Cengizler, H
    The root cause for cracking of rear brake components occurred during cold forming process was investigated. Optical micrographs showed the abundance of extended inclusions with several rounded ones in the steel. SEM image revealed the fracture surface which contained many extended cavities formed by extended inclusions and dimples all indicating a ductile rupture. EDS analysis confirmed that the extended inclusions were MnS type while the rounded ones were formed as a result of Ca-treatment. The crack propagation along with inclusions was clearly observed on the polished planes and on the fracture surface. It was determined that MnS type inclusions were the root cause for the cracking phenomena. The abundance of extended MnS inclusions indicated insufficient inclusion modification through Ca-treatment and insufficient removal of these inclusions in failed steel. (C) 2007 Elsevier Ltd. All rights reserved.
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    Optimal Use of Calcined Boron Waste as a Flux in the Production of Low-Temperature-Sintered Floor Tiles
    Cengizler, H; Koç, M
    Abstarct-This study focused on the recycling and optimal use of colemanite waste (CW) in floor tile/tiles (FT) production. Experimental compositions were prepared with various concentrations of CW calcined at 800 degrees C and FT body. The sinterability at low temperatures (1000-1100 degrees C) and the effect of calcined CW on FT properties were investigated. The physical-mechanical properties of the tiles were characterized by linear shrinkage, water absorption and bending strength tests. The microstructure and the phase development of the tiles were determined by SEM-EDX and XRD, respectively. The optimal tile compositions in conformity with the related standards were obtained at 1050 degrees C (30 wt % CW) and 1100 degrees C (5 and 10 wt % CW). The tiles produced with high ratio CW (30 wt %-1050 degrees C) additions had 0.32% water absorption, 5.70% linear shrinkage, and 52.43 MPa bending strength values. The CW calcined at 800 degrees C was favourably used in FT production to lower the sintering temperature with a new possibility to recycle this waste and conserve natural resources.
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    Effect of calcination temperature on use of high-boron-content waste for low-temperature wall tile production
    Cengizler, H
    The effects of the calcination temperature on raw-colemanite-waste properties and calcined waste content on wall tile production were investigated. Waste containing 11.24% B2O3 calcined between 500 and 800 degrees C was added to wall tile granules in various ratios (0-100 wt.%) to produce a low-temperature-sintered wall tile by adding the maximum content of boron waste, as determined through optimal calcination. The low-temperature (850-1000 degrees C) sinterability of the samples and the effect of the calcined colemanite-waste content on the wall tile properties were investigated. The samples were characterised using X-ray fluorescence, X-ray powder diffraction, differential thermal analysis, thermogravimetric analysis, Fourier-transform infrared spectroscopy, scanning electron microscopy, and colourimetry. The waste calcined at 800 degrees C exhibited a substantially different phase distribution, bond structure, morphology, and colour. The wall tile produced using 40 wt.% colemanite waste calcined at 800 degrees C and subsequently sintered at 950 degrees C exhibited the optimal properties. The linear firing shrinkage, water absorption, and flexural strength of the optimised wall tile were 0.88%, 16.04%, and 36.07 MPa, respectively. The optimised wall tile exhibited major albite, quartz, and diopside phases and 64% higher strength. The sample calcined at 800 degrees C showed that high colemanite-waste content could be incorporated into ceramic bodies.
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    Toxic Elements Leachability Tests on Light Weight Fly Ash Bricks
    Cengizler, H
    In Present work, a series of batch leach tests were carried out to investigate the leachability of some toxic elements contained in the light weight fly ash bricks. The primary aim of these tests was to rind out whether the light weight fly ash bricks were environmentally safe. The tests simulating the acid rain environment and natural rain water were conducted to gain insight regarding the behaviour of the elements during weathering. The light weight fly ash bricks were tested using the TCLP method and ASTM method A extraction to determine their toxicity levels.
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    An efficient process for recovery of fine coal from tailings of coal washing plants
    Çiçek, T; Cöcen, I; Engin, VT; Cengizler, H
    Gravity concentration of hard lignites using conventional jigs and heavy media separation equipment is prone to produce coal-rich fine tailings. This study aims to establish a fine coal recovery process of very high efficiency at reasonable capital investment and operational costs. The technical feasibility to upgrade the properties of the predeslimed fine refuse of a lignite washing plant with 35.9% ash content was investigated by employing gravity separation methods. The laboratory tests carried out with the combination of shaking table and Mozley multi-gravity separator (MGS) revealed that the clean coal with 18% ash content on dry basis could be obtained with 58.9% clean coal recovery by the shaking table stage and 4.1% clean coal recovery by MGS stage, totaling to the sum of 63.0% clean coal recovery from a predeslimed feed. The combustible recovery and the organic efficiency of the shaking table + MGS combination were 79.5% and 95.5%, respectively. Based on the results of the study, a flow sheet of a high-efficiency fine coal recovery process was proposed, which is also applicable to the coal refuse pond slurry of a lignite washing plant.
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    Activity of MnO in MnO-CaO-M9O-SiO2-Al2O3 Slags at 1500°C
    Cengizler, H; Eric, RH
    A thermodynamic study was made on the MnO-CaO-MgO-SiO2-Al2O3 slags that are typical of the production of ferromanganese in submerged arc furnaces. The Al2O3 content of the slags was kept constant at 5 per cent by mass. The activity-composition relationship in Pt-Mn binary alloys were re-determined for calibration purposes at 1300, 1400 and 1500 degrees C and po(2) values between 5.40 x 10(-6) and 4.54 x 10(-13) atm. A linear regression equation was derived to predict the activity coefficients of manganese, in Pt-Mn alloys at 1500 degrees C. The effect of concentration, basicity ratio and CaO-to-MgO ratio on MnO activities in above mentioned complex slags was investigated at 1500 degrees C and at two different po2 values of 4.76 x 10(-7) and 5.80 x 10(-8) atm. It was found that a(MnO) values increase with increasing MnO, and tend to increase with an increasing CaO-to-MgO ratio. The amnovalues also increase with increasing basicity ratio. The activity coefficient of MnO increases with an increase in its mole fraction in the slag. Quadratic multivariable regression model equations which represent the activity data successfully and which can be used to predict the MnO activities in the compositional range of this study were developed. The MnO activity data was interpreted in terms of a slag model which describes the thermodynamic properties of the slag successfully.
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    Technical and economical applicability study of centrifugal force gravity separator (MGS) to Kef chromite concentration plant
    Çiçek, T; Cöcen, I; Engin, VT; Cengizler, H; Sen, S
    The results of multigravity separator (MGS) upgrading tests on fine chromite gravity tailings using -100 and -100+150 mu m fractions of the initial sample (-1 mm) with 24.7% Cr2O3 grade were presented. The metal screen analysis revealed that 20.66% of the total Cr2O3 content was present in the -106 mu m size fraction. Under optimal operational conditions, a concentrate with 43.7% Cr2O3 content and 65.0% chromite yield for the size fraction of -100 mu m and a concentrate with 30.5% Cr2O3 and 83.3% yield for the size fraction of -100+150 mu m could be produced. Shaking table test results revealed that the coarse fraction of the tailings could not be enriched any further owing to the high concentration of interlocked particles. However, a saleable concentrate could be obtained by MGS when the coarse tailings were ground down to -100 mu m and used as the feed. The results of the study suggested that multigravity separation of the Kef tailings was technically feasible and economically viable. The payback time of two alternatives suggested for the utilisation of MGS in Kef concentrator was calculated to be <7 months.