Browsing by Author "Yerlikaya Z."

Now showing 1 - 11 of 11

Effect of polycondensation reaction conditions on the properties of thermotropic liquid-crystalline copolyester
(2008-08-01) Yikici M.; Yerlikaya Z.; Aksoy S.; Altinok H.
In this study a range of wholly aromatic copolyesters based on kink m-acetoxybenzoic acid (m-ABA) monomer (33mol%) and equimolar-linear p-acetoxybenzoic acid (p-ABA), hydroquinone diacetate (HQDA) and terephthalic acid (TPA) monomers (67mol%) have been synthesized by melt polycondensation reaction process at 280C and 260C for different time intervals. Characterization of copolyesters were performed by solution viscosity measurement, wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), hot-stage polarized light microscopy, proton-nuclear magnetic resonance analysis (1H-NMR). According to the results obtained, copolyesters showed thermotropic liquid crystalline behavior in an appropriate temperature range. The copolyesters were prepared in high yields. It was observed that the intrinsic viscosities of the copolyesters are increased regularly with increasing polymerization time and temperature. All the copolyesters were soluble in a trifluoroacetic acid/dichloromethane (30:70 v/v) except the copolyesters which were synthesized at 280C in 5h. According to the WAXD results; the degree of crystallinity of copolyesters were found to be between 5-15%. DSC and hot stage polarized light microscopy results showed that all the copolyesters are melt processable and a significant molecular interaction exist in a very broad temperature range (160C and 165C) in the nematic mesophase. The Tg values are increased with an increasing polycondensation reaction time and temperature and they were observed between 93-126C. Fibers prepared by a hand-spinning technique from the polymer melt exhibit well-developed fibrillar structure parallel to the fiber axis.
Effect of pressing conditions on some surface properties of HDF laminate parquets
(2016-01-01) Kara M.; Yerlikaya Z.; Ateş S.; Olgun Ç.
In this study, the effects of lamination conditions on some commercialhigh density fiberboard(HDF) panels surface quality characteristics, surface strength, impact resistance test(large diameter ball test), curing degree, scratch resistance, abrasion resistance are investigated. For this purpose, HDF panels are produced from mixture wood fibers(50% black pine and 50% beech wood) as 8.3 mm thickness. After panels sanded to 7.3 mm thickness, laminated at different pressures and times. Ithas been found thathigh pressure and short-term press time conditionshave significant effect on surface strength, impact resistance, and abrasion resistance values. The best surface quality measurements are obtained from A1 group, pressure 340 kg/m² and 13 s pressing time(average of surface strength value of this group is 1.83 N/mm2, impact resistance value is 25.25 N and abrasion resistance value is 3650 revolution), but the lowest value is B3 groups, 320 kg/m² pressure and pressing time of 18 s(average of surface strength of this group is 1.58 N/mm2, impact resistance value is 20 N and abrasion resistance value is 3200 revolutions). Besides production factors of HDF panels and laminating material properties, press operating conditionshave been found to be decisive factors in laminate parquet pressing process for high surface quality.
Effects of machining parameters on surface roughness and macro surface characteristics when the machining of Al-6082 T6 alloy using AWJT
(2017-01-01) Kartal F.; Yerlikaya Z.; Gökkaya H.
This study analyzes the effects of machining parameters on the surface roughness and macro surface characteristics when machining Al-6082 T6 alloy of ∅30 and 240 mm in size using abrasive water jet (AWJ) turning processes. The material removal tests were conducted using a computer numerical control (CNC) abrasive jet cutting machine for different parameters of nozzle feed rate (10, 15, 20 and 25 mm·min−1), abrasive flow rate (50, 150, 250 and 350 g·min−1), spindle speed (25, 50, 75 and 100 min−1) and standoff distance (2, 5, 8 and 11 mm). Pump pressure at 350 MPa, abrasive type of Garnet and size of 120 Mesh, and nozzle diameter of 0.75 mm are kept constant throughout the experiments. When macro surface characteristics were analyzed, it was found that increased spindle speed, decreased nozzle feed rate, increased abrasive flow rate and lower standoff distance resulted in smoother surfaces. According to the findings of this study, best results were obtained when spindle speed and abrasive flow rate were increased.
Investigation of surface roughness and MRR for engineering polymers with the abrasive water jet turning process
(2016-07-01) Kartal F.; Yerlikaya Z.
This study investigates the abrasive water jet turning (AWJT) process of commonly used plastics, such as polytetrafluoroethylene (PTFE), castamide, and polyamide (PA), in engineering. Machining parameters were used as follows: nozzle feed rate (10, 30, and 50 mm min−1), abrasive flow rate (50, 250, and 450 g min−1), and spindle speed (1 000, 2 000, and 3 000 min−1). The effects of the machining parameters on the average surface roughness and material removal rate were investigated. According to results, average surface roughness and material removal rate were affected by the nozzle feed rate by 87.15 % and 82.48 %, abrasive flow rate by 9.84 % and 13.49 %, and spindle speed by 1.09 % and 0.08 %, respectively. Optimization results that the nozzle feed rate should be 10 mm min−1, while the abrasive flow rate is 450 g/min and spindle speed is 3 000 min−1 in order to obtain the minimum surface roughness and maximum material removal rate.
Optimization of abrasive water jet turning parameters for machining of low density polyethylene material based on experimental design method
(2014-01-01) Kartal F.; Çetin M.H.; Gökkaya H.; Yerlikaya Z.
Studies to improve the machining of engineering materials have great importance for mechanical systems. Abrasive water-jet turning (AWJT) is a new and effective process for increasing machinability of engineering materials by providing temperature free cutting conditions, high surface quality and having no tool wear problem. In this study, AWJT of low density polyethylene (LDPE) material were investigated in terms of average surface roughness (ASR) and material removal rate (MRR) values and process parameters were optimized by experimental design method. The primary objectives of the study are to investigate AWJT process and system parameters to enhance machinability of LDPE material and to determine optimal processing parameters. Nozzle feed rate (5, 25 and 45 mm/min), abrasive flow rate (50, 200 and 350 g/min) and spindle speed (1000, 1500 and 2500 min^-1) were analyzed as process parameters. Taguchi L27 orthogonal full factorial design, optimization box and analysis of variance (Anova) were used for the experimentation and results analysis. Experimental results show that, AWJT process is more efficient in the machining of LPDE material than the conventional machining methods by increasing surface quality and MRR parameters. Minimum ASR and maximum MRR were obtained 1.67 lm and 14072.02 mm³/min respectively; at optimum parameters of 5 mm/min nozzle feed rate, 350 g/ min abrasive flow rate and 2500 min^-1 spindle speed. © Carl Hanser Verlag, Munich.
Synthesis and quantum chemical calculations 5-phenyl-1,3,4-dithiadiazole derivatives
(2016-01-01) Kandemirli F.; Sayiner G.; Yerlikaya Z.; Muglu H.; Gür M.
1-phenyl-1,3,4-thiadiazole derivatives were synthesized and characterization was carried out by the elemental analyses, 1H-NMR, IR spectroscopy were obtained by means of the DFT/6-311G(d,p) method were performed for the quantum chemical calculations.
Tensile test specimen preparing three different cutting method influence on the AA 6061-T6
(2014-01-01) Kartal F.; Gokkaya H.; Yerlikaya Z.; Polat R.
Aluminum 6061 (T6) material which is widely used in aviation and defense industries was treated with tensile test in this study. The samples for tensile test were manufactured using three production methods (namely, milling, CO2laser and abrasive water jet (AWJ). Following the tests sample surfaces were assessed for their surface roughness values. Samples which meet the TS EN ISO 6892-1 standard were assessed for their tensile strength, yield strength, percentage elongation and constriction. Among the test samples, sample prepared by milling proved to provide the best surface roughness value (1.32 μm). The highest tensile strength was obtained from the sample prepared using AWJ while the lowest was obtained from the sample prepared using laser cutting. Samples prepared using abrasive water jet showed 6.57 % difference in terms of tensile strength from samples prepared using milling.
The effect of practices based on argumentation-based inquiry approach on teacher candidates’ critical thinking
(2021-01-01) Sönmez E.; Kabataş Memiş E.; Yerlikaya Z.
This study was conducted to examine the effects of practices based on the Argumentation-Based Enquiry (ABI) approach on the critical thinking of science teacher candidates in a course named the General Chemistry Laboratory course. The General Chemistry Laboratory course was taught through the ABI approach for 12 weeks, and 94 teacher candidates from three different classes participated in the study. We collected data using the Critical Thinking Test, administered at the beginning and the end of the study, and by conducting semi-structured interviews with 18 students conducted at the end of the study. The results showed that the teacher candidates who went through the ABI process experienced significant improvements in their critical thinking with regard to both skills and tendencies. In semi-structured interviews, prospective teachers stated that the stages within the ABI approach allowed them to think critically and supported the development of critical thinking.
Thermal and morphological properties of thermotropic liquid-crystalline copolyesters containing poly(ethylene terephthalate), 4-hydroxyphenylacetic acid and main-chain rigid aromatic units
(2010-06-01) Babacan V.; Aksoy S.; Yerlikaya Z.; Altinok H.
Thermotropic liquid-crystalline polymers (TLCPs) have aroused considerable interest due to their attractive properties as highperformance materials. Significant research attention has been devoted to investigating the relationship among monomer structures, syntheses and end-use properties of TLCPs. The study reported here concerns the preparation, characterization and melt spinning of novel copolyesters containing two different flexible units together with two different aromatic units in the polymer chains. A range of copolyesters based on p-hydroxybenzoic acid (p-HBA), m-hydroxybenzoic acid, p-hydroxyphenylacetic acid and poly(ethylene terephthalate) were synthesized. The liquid crystallinity, thermal properties and degrees of crystallinity of these copolyesters were investigated using hot-stage polarized light microscopy, differential scanning calorimetry, thermogravimetry and wide-angle X-ray diffraction. Copolyester fibres were characterized using scanning electron microscopy. The copolyesters were melt-processable, thermally stable and could be processed above their melting temperatures without degradation. The degree of crystal structure was found to depend upon the content of p-HBA. The fibres prepared showed that polymer chains had a well-developed fibrillar structure. Novel TLCPs containing flexible units in the main chain were synthesized and characterized. Copolyesters containing p-HBA units ranging from 55 to 70 mol% exhibited phase-separated liquid-crystalline morphology, appropriate melting temperatures and high thermal stability for melt processing. © 2010 Society of Chemical Industry.
Thermal properties and crystallinity of thermotropic liquid crystalline copolyesters prepared from poly(ethylene terephtalate) (PET) and rigid aromatic units
(2007-04-01) Tan A.; Altinok H.; Yerlikaya Z.; Aksoy S.
A series of copolyesters were synthesized by melt-polycondensation reaction of poly(ethylene terephtalate) (PET) with various proportions of equimolar compositions of p-acetoxybenzoic acid (p-ABA), hydroquinone diacetate (HQDA) and terephtalic acid (TPA). Viscosity, liquid crystallinity, thermal properties, degree of crystallinity and thermal stabilitiy of these copolyesters were investigated by Ubbelohde viscometer, hot-stage polarized light microscopy (PLM), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and thermogravimetric analysis (TGA), respectively. On the basis of viscosity measurement, it was observed that intrinsic viscosity values of the copolyesters are increased regularly with increasing amounts of aromatic units (p-ABA, HQDA and TPA) in the polymer chain. Thermotropic liquid crystalline behavior was observed in the copolyesters containing over 50mol% of rigid p-ABA/HQDA/TPA aromatic units. DSC analysis of the anisotropic copolyesters revealed broad and weak endotherms associated with the nematic phases, and the melting temperatures were found to be in the processable region. As the mol% of PET in the polymer chain increased, the specific enthalpies of fusion and the degree of crystallinity of the copolyesters were also increased regularly.
Urinary Neutrophil Gelatinase-Associated Lipocalin, Cystatin C and Clusterin as Biomarkers for Acute Kidney Injury in Cattle with Tropical Theileriosis
(2023-01-01) Tumer K.C.; Dincer P.F.P.; Babacan S.; Yerlikaya Z.