ömer güler | Firat University (original) (raw)

Papers by ömer güler

Handbook of Carbon Nanotubes, 2021

The intermetallic matrix composites (IMCs) of Ni3Al reinforced by SiC were fabricated by powder m... more The intermetallic matrix composites (IMCs) of Ni3Al reinforced by SiC were fabricated by powder metallurgical routes via solid state reaction of nickel and SiC particulates by volume combustion process. Pure nickel, aluminum and SiC powders were used as initial substances. The powders were mixed, and the compacts were combusted in an atmosphere controlled furnace. The synthesis of the SiC added Ni3Al was attempted to improve the nature of the Ni3Al composite. The initially added SiC particles were unstable and decomposed partially within the matrix during combustion, and the morphology of the IMCs changed upon the dissolution rate of SiC and combustion temperature. It was confirmed that the dissolution rate of SiC was effective on improvement of the hot working temperature of Ni3Al IMCs.

This study reports on the mechano-thermal synthesis of carbon - boron nitride nano structures fro... more This study reports on the mechano-thermal synthesis of carbon - boron nitride nano structures from elemental graphite and boron nitride powders. Initially, amorphous hybrid structure was obtained by high energy ball milling technique from hexagonal graphite and hexagonal boron nitride powders. X-ray spectra taken from ball milled samples indicated that the hexagonal graphite and boron nitride, composed of layers, was transformed into the amorphous hybrid for a milling time of 20 h by the way of high energy input. Subsequent isothermal annealing of milled hybrid powders was conducted at 1300 oC for 2 h in Ar gas. It was revealed via investigation of transmission electron microscopy that carbon - boron nitride hybrid nano structures were formed after annealing.

In this study, carbon nanotubes, which were produced by using chemical vapour deposition and mech... more In this study, carbon nanotubes, which were produced by using chemical vapour deposition and mechano-thermal methods, were combined with zinc oxide matrix at different ratios and the effects of the nanotubes on electrical and optical properties of zinc oxide were examined. It was observed that electrical conductivity of zinc oxide at room temperature increased with the increase in the reinforcement rate both in carbon nanotube reinforced samples produced by using chemical vapour deposition and those produced by using the mechano-thermal method. Carbon nanotube reinforced samples produced by using chemical vapour deposition yielded relatively better results for the same reinforcement rate.

Multi-walled carbon nanotubes (MWCNTs) are a highly effective adsorbent of methylene blue (MB), a... more Multi-walled carbon nanotubes (MWCNTs) are a highly effective adsorbent of methylene blue (MB), and they can be used to remove MB from aqueous solutions. In this study, we used MWCNTs that were synthesized by chemical vapor deposition method. The physicochemical properties of MWCNTs were characterized by Brunauer-Emmett-Teller (BET) surface area, surface functional group analysis by fourier transform infrared (FTIR) analysis, zero point charge (pHzpc), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The factors that affected the adsorption properties of MB onto MWCNTs were investigated, including initial pH, contact time, dosage, initial concentration, and temperature. The equilibrium adsorption data were analyzed using two common adsorption models, i.e. the Langmuir and Freundlich models. The results indicated that the Langmuir isotherm fits the experimental results well. The maximum adsorption capacity obtained from the equation of the Langmuir isotherm at 323 K was 95.30 mg/g, indicating that the MWCNTs adsorbed MB effectively. The kinetic study illustrated that the adsorption of MB onto MWCNTs fits the pseudo-second-order kinetic model. The thermodynamic parameters indicated that the adsorption of MB onto MWCNTs was a spontaneous, endothermic process.

The effect of the amount of carbon nanotubes on the electrical and optical properties of carbon n... more The effect of the amount of carbon nanotubes on the electrical and optical properties of carbon nanotube (CNT)-zinc oxide nanocomposites was investigated. In this study, carbon nanotubes were prepared by chemical vapor deposition in a fluidized reactor. The diameters and lengths of the carbon nanotubes that were synthesized were determined by high-resolution transmission electron microscopy to be 20–30 nm and a few micrometers, respectively. Then, CNTs were added to commercial zinc oxide powder to prepare the nanocomposite. The structural, optical, and electrical properties of the samples were characterized by various techniques, such as scanning electron microscopy (SEM), UV-vis absorption, and electrical transport measurements. The room temperature conductivity σ25 values of the undoped ZnO and ZnO doped with 0.1% CNTs, 0.2% CNTs, and 5% CNTs were found to be 6.55×10-5, 5.46×10-4, 1.23×10-3, and 2.83×10-2 S/cm, respectively. The optical band gaps of the composites were determined by the Kubelka-Munk theory based on the analysis of diffuse reflectance. The results that were obtained indicated that the electrical and optical properties of ZnO semiconductors can be improved by the incorporation of CNTs. However, the ZnO lost some of its distinctive properties when excess amounts of CNTs were used in the ZnO-CNT composites.

Mechano-thermal method was used for synthesizing the carbon nanotubes (CNTs) in this study. In th... more Mechano-thermal method was used for synthesizing the carbon nanotubes (CNTs) in this study. In this method, graphite powders in the elemental form were firstly exposed to milling process in high-energy ball milling and then the milled powders were annealed at high temperatures. As a result of milling of the graphite, ultra-active disordered carbon structures were obtained. This structure serves as a carbon source for the formation of nanotubes during the annealing process. This study investigated the effect of the milling process. For this purpose, graphite powders were milled at different periods such as 5 and 150 h and then annealed at 1600 °C. The transmission electron microscopy and scanning electron microscopy examinations demonstrated that CNTs formed in samples milled both for 5 and 150 h. However, the difference in the milling time influenced the amount of CNTs, their size and the formation of other structures except from nanotubes.

In this study, carbon nanotubes at 0.05–1 wt-% ratios reinforced pure copper powder. Carbon nanot... more In this study, carbon nanotubes at 0.05–1 wt-% ratios reinforced pure copper powder. Carbon nanotubes (CNT) were used to reinforce the copper matrix, these materials were synthesized under laboratory conditions. Ultrasonic processes and ball-milling method were used to provide a homogenous dispersion during production of the Cu-CNT composite. The Cu-CNT composite powder was produced as bulk material and then, the thermal conductivity as well as the microhardness of the composite were measured. As a particular result, it turned out that the thermal conductivity and the hardness of the composite increased up to a specific ratio of the CNT reinforcement, while the reinforcement ratio exceeding this critical level provided an adverse effect.

n this study, graphite powder was exposed to two different stress types by using the same type of... more n this study, graphite powder was exposed to two different stress types by using the same type of mill in order to understand the formation of different carbon nanostructures. Two types of milling modes were selected as shock-type and shear-type stresses during the milling processes. Both shock-type and shear-type stresses were applied to the graphite powder. Then, milled powders were annealed at high temperatures for different times. The structural changes in the obtained samples were determined by XRD diffraction, SEM, FE-SEM and HR-TEM examinations. New carbon nanostructures were synthesised.

In this study, high-yield Boron Nitride Nanotubes (BNNT) were synthesized by using the high ener... more In this study, high-yield Boron Nitride Nanotubes (BNNT) were synthesized by using the high energy ball milling method. Hexagonal Boron Nitride (h-BN) powder was used as starting powder and the powders were subjected to milling process for different milling rotations and different milling periods in a planetary ball mill (Fritsch Pulverisette 7 Premium Line). The powders obtained after providing the milling process, were annealed inside a tube furnace under NH3+Ar atmosphere at 1300oC for a period of 2 hours. In conclusion, BNNT’s were produced by using this technique. The tubes produced have been examined by use of X-ray diffraction analysis (XRD), high resolution transmission electron microscopy (HR-TEM).

This study reports on the thermo-mechanical synthesis of carbon nano onions from elemental graphi... more This study reports on the thermo-mechanical synthesis of carbon nano onions from elemental graphite powders. Initially, amorphous carbon was obtained by high energy ball milling technique from graphite powders. X-ray spectra taken from ball milled samples indicated that the hexagonal graphite, composed of layers, was transformed into the amorphous carbon for a shorter milling time of 5 h by high energy input about 78 times of gravity. Subsequent isothermal annealing of milled graphite powders was conducted at 1400 °C for 4 h in Ar gas. It was revealed via investigation of transmission electron microscopy that carbon nano onions were formed after annealing.

In this study, carbon nanotubes were synthesized by chemical vapor deposition (CVD) process. In C... more In this study, carbon nanotubes were synthesized by chemical vapor deposition (CVD) process. In CVD process, milled iron powders were used as catalyst. Initially, iron powders were milled by high energy ball mill for 3h. Then, iron particles were homogeny distributed onto substrate and carbon nanotubes were obtained by CVD process inside tube reactor. Carbon nanotubes were investigated by HR-TEM to determine the effect of milled iron catalyst on nanotube formation.

In this study, carbon nanotubes were synthesized by mechano-thermal process from elemental graphi... more In this study, carbon nanotubes were synthesized by mechano-thermal process from elemental graphite powders. Initially,
high ultra-active amorphous carbon was obtained by short time milling process from graphite under inert atmosphere. Then,
isothermal annealing of milled graphite powders was conducted at 1600oC for 6 h in Ar gas. From the investigations of
Transmission electron microscopy and Scanning electron microscopy, it was revealed that bamboo and cylindrical
nanotubes were formed after isothermal annealing. In this study, nanotubes which have the diameters between 50 and 200
nm were produced at a short time ball milling process and a lower annealing temperature of 1600 oC although bamboo and
cylindrical nanotubes are reported to be produced after ball milling of graphite for 150 h and then annealing amorphous
graphite at least 1800 oC.

In this study, the electrical performance of ODS Cu-based contact materials produced by mechanica... more In this study, the electrical performance of ODS Cu-based contact materials produced by mechanical alloying (MA) was investigated. Cu-based powder mixtures that contain various oxides at different proportions were milled by the high energy planetary ball mill for 5 h. Mechanically alloyed powder mixtures containing ZnO, Al2O3 and Y2O3 at the ratios of 1, 2, 4 and 6 wt.% were pressed and sintered at 800 °C in vacuum environment. These compacts were then forged axially at the ratio of 75% at 650 °C so as to increase the density. At the first step, electrical conductivity experiments were applied to these samples to determine the best conductivity. Results showed that, reinforced Cu samples containing 4% oxides exhibited the best. At the second step, contact count experiments were made with these samples for determining contact performance for the counts of 3000, 6000 and 9000 turn on/off. The samples of 4 wt.% ZnO, 4 wt.% Al2O3, 4 wt.% Y2O3 reinforced Cu materials, respectively, exhibited both the best conductivity and the best contact performances.

Hard in situ synthesis of TiB2–Fe2B metal matrix composite (MMC) has been synthesised by volume c... more Hard in situ synthesis of TiB2–Fe2B metal matrix composite (MMC) has been synthesised by volume combustion synthesis (VCS) reactions of Fe–FeTi–FeB system. VCS samples were characterised by SEM, EDX, XRD and DTA. Results show that it is possible to synthesise in situ structured MMC samples (with TiB2 and Fe2B phases) by VCS. Metallographic investigations show that Fe2B and TiB2 are found dispersed throughout the metal matrix, and other borides are present in microlevel patches dispersed in a eutectic matrix. The Fe–TiB2 composites sintered at temperature of 1200°C consist of three different regions, i.e. α-Fe, TiB2 and Fe2B regions. The increase in sintering temperature to 1400°C leads to a hypereutectic microstructure of the Fe–B binary system having TiB2 grains uniformly distributed throughout the matrix. A semiliquid phase sintering occurred by increasing eutectic phase transformation temperatures to 1400°C, which increased the efficiency of VCS. On the other hand, increasing sintering time from 1 to 3 h decreased the volume fraction of α-Fe and increased the volume fraction TiB2 phase.

Multi-layer graphene were produced through synthesized expanded graphite (EG) liquid exfoliation ... more Multi-layer graphene were produced through synthesized expanded graphite (EG) liquid
exfoliation using organic solvent. Hexagonal graphite (HG) was used as starting material. HG
was mixed an acidic-mixture, dried, respectively after that subjected to thermal treatment. After
this process, EG was obtained. This obtained-EG was sonicated throughout 1 hour via an
ultrasonic homogenizer by blending an organic solvent. Samples were subjected to SEM, TEM,
FTIR, UV-vis-NIR spectroscopy investigations. After the investigations, it was shown that
nano-size graphene sheets were obtained.

The electrical and optical properties of carbon nanotubes hybrid zinc oxide (ZnO-CNTs) nanocompos... more The electrical and optical properties of carbon nanotubes hybrid zinc oxide (ZnO-CNTs) nanocomposites synthesized by ball mill technique have been investigated. The nanocomposites were prepared using zinc oxide (ZnO) powder and carbon nanotube (CNT) synthesized by catalytic thermal chemical vapor deposition (CVD). The diameters and lengths of the CNTs were respectively determined to be 20-30 nm and about 3-5 mm. DC conductivity measurements reveal that the nanocomposites are good conductive material. The room temperature DC electrical conductivity s dc of the un-doped ZnO and ZnO-CNT nanocomposites with 0.1% CNT, 0.5% CNT, and 1% CNT were found to be 6.55 £ 10 ¡5 , 5.46 £ 10 ¡4 , 1.49 £ 10 ¡3 , and 4.01 £ 10 ¡3 S/cm, respectively. This indicates that there is a remarkable improvement of the electrical conductivity as the CNTs' content increases. The optical band gaps of the composites were determined by Kubelka-Munk theory based on the analysis of diffuse reflectance. The band gap (E g ) values of the composites decreased with increasing CNT contents. The obtained results indicate that the electrical and optical properties of ZnO semiconductor can be improved by incorporation of CNT.

Handbook of Carbon Nanotubes, 2021