In this study, carbon nanotubes were synthesized at temperatures of 500C and 800C by the fluidized-bed chemical vapor deposition method. The synthesized material was purified by using 3 M HCl at 75°C, 15 h. After synthesis and purification, the polyaniline-doped H_3BO_3 and BF_3 and composites were prepared by coagulation method. Transmission electron microscope and Fourier transform infrared spectroscopy were used to characterize the carbon nanotubes and their composites. Thermal stabilities were measured by thermogravimetry and differential scanning calorimetry instruments. The thermogravimetry and derivative thermogravimetry curves indicated that the thermal stability of polyaniline-doped H_3BO_3 and BF_3 increased with carbon nanotube doping. The electrical properties of carbon nanotubes and their composites were also determined. The obtained electrical conductivity values of the nanocomposites including the polyaniline-doped H_3BO_3 and BF_3 were typical for organic semiconductor materials. It can be evaluated that the electrical properties of the polyaniline based polymers can be controlled by carbon nanotube doping.
The objective of this work is to produce activated carbon from sugar beet molasses containing TiO₂ for CO₂ adsorption and reduction. Textural properties of activated carbons were obtained based on the adsorption-desorption isotherms of nitrogen at 77 K. The specific surface areas of activated carbons were calculated by the Brunauer-Emmett-Teller method. The volumes of micropores were obtained by density functional theory method. The adsorption isotherms of CO₂ were measured up to the pressure of 1 atm at a temperature of 40°C. The best activated carbon adsorbed 1.9 mmol/g of CO₂.
Hazelnut shell was used as a precursor in the production of activated carbon by chemical activation with H_3PO_4 since there is a huge volume of such a solid waste resulting from the hazelnut production in eastern Black Sea region of Turkey. Effects of final activation temperature, time and H_3PO_4 concentration used in the impregnation stage on the porous development were investigated. Activation at low temperature represented that micropores were developed first and then mesoporosity developed, enhanced up to 400C and then started to decrease due to possible shrinking of pores. The optimum temperature for hazelnut shell was found to be around 400C on the basis of total pore volume and the Brunauer-Emmett-Teller surface area. It was clearly demonstrated that H_3PO_4 concentration used in the impregnation stage was not only effective for development of surface area and pore volumes but also an effective tool for tailoring the pore structure and size distribution.
Two carbon nano-structured samples containing 5 and 20% of carbon nanocones in their volume were investigated. Using the Sieverts apparatus the hydrogen was loaded into the samples. The measurements of heat capacity in the temperature range from 100 K to 320 K and the positron lifetime measurements at the room temperature were performed for hydrogenated and non-hydrogenated carbon nanocones. The desorption of hydrogen at the temperature of 230 K is deduced from the heat capacity measurements. The detection of the positronium, the bound state of positron and electron, in the measured samples reveals the presence of open volume defects of ca. 0.198 ± 0.002 nm.
Cemented carbides are hard materials used in tough materials machining as well as in situations where other tools would wear away. These are one of the most successful composite engineering materials ever produced. The advantage of cemented carbides is that their structure and composition can be engineered to have properties tailored to specific applications and operations. These materials allow faster and more precise machining and will leave a better surface finish. Carbide tools can also withstand higher temperatures than standard high speed steel tools. Considering their application and known range of properties, main disadvantage of cemented carbides is appearance of their sudden fracture during machining process. This is caused by the low toughness at dynamic rates and overcoming this problem is yet to be researched further. In order to understand these limitations and provide suggestions for the improved design of the material, combined experimental and numerical analysis is currently being performed. Cohesive strength values numerically determined using Dugdale cohesive zone model are compared to flexural strength obtained experimentally. Reduction in flexural strength was then analysed and explained, relating it to the flaw size on the tensile surface of the specimen.
The aim of the investigations was a modification of DTO, a commercial activated carbon (AC), to improve CO₂ adsorption capacity. The adsorption of CO₂ up to 40 bar at 40°C temperature was investigated. The volumetric method was applied for CO₂ adsorption isotherm measurements. The starting material - DTO - was modified using chemical activation (KOH, ZnCl₂, K₂CO₃). The textural parameters of all the ACs were determined by nitrogen adsorption at the liquid nitrogen temperature of -196°C on Quadrasorb SI. Results showed that the AC modified with KOH had the highest S_{BET}, V_{tot}, V_{mic} values of 2063 m²/g, 1.13 cm³/g, and 0.67 cm³/g, respectively. ACs with a wider pore size distribution (from micropores to mesopores) were obtained. The maximum CO₂ adsorption was equal to 14.44 mmol/g for DTO/KOH - modified carbon whereas 8.07 mmol/g of CO₂ was adsorbed at DTO. The CO₂ adsorption capacities of the ACs were found to be closely correlated with the BET surface areas of the materials tested. The experimental data was fitted to the Freundlich, Langmuir, Sips and Toth equations to determine the model isotherm. The Sips model was found to be the best for fitting the adsorption of CO₂.
Aim of this research is to obtain effective, molasses based activated carbon, which would adsorb big amounts of CO₂. Molasses was mixed with KOH. Weight ratio of dry materials was 1:1 (AC1, AC3) and 1:2 (only AC2). Homogeneous mixture was obtained. Material was left for 3 h at 25°C. Drying lasted for 12 h at 200°C, and the material was grounded. The mixture was pyrolysed at 750°C, under constant flow (18 dm³/min) of nitrogen. The material was grounded again. Then, powder was washed with water, until filtrate was neutral, which took about 5 dm³ of water. AC3 was washed with 1 dm³ of water. After drying, materials were soaked in HCl (0.1 mol/dm³) for 19 h, and washed with water, until filtrate was neutral. CO₂ adsorption was performed under high pressure up to 40 atm, at 40°C. Specific surface area (according to the Brunauer-Emmett-Teller equation) was calculated for AC1, AC2 and AC3 and it is respectively 1985, 1967, and 2026 m²/g, micropore volume - 0.714, 0.707, and 0.728 cm³/g and it was between 75% and 89% of total pore volume. The excess uptake at 40 atm pressure was as follows: AC1 - 14.02 mmol/g, AC2 - 12.75 mmol/g, and AC3 - 15.79 mmol/g.
Amorphous carbon electrodes were deposited using atmospheric pressure plasma torch from the mixture of argon and acetylene gases on the stainless steel substrates. The ratio of Ar/C_2H_2 was in the range of 15-55. The deposited coatings were immersed in low pressure oxygen plasma for 1 min. Scanning electron microscopy images show that when Ar/C_2H_2 ratio increases from 15 to 55, the electrodes surface roughness decreases. The Raman scattering spectroscopy results indicated that the I_{D}/I_{G} ratio decreases from 2.04 to 1.35. It was observed that with the increase of Ar/C_2H_2 ratio from 15 to 55, the capacity of supercapacitor increases from 16 mF to 36 mF. The electric capacity of capacitors has increased up to 7 times after their exposure in oxygen plasma.
H.C. Starck HS Grade boron carbide (B₄C) powders with multi-walled carbon nanotube (CNT) were sintered by Spark Plasma Sintering (SPS) method in a vacuum atmosphere to obtain highly dense and fine grained final ceramic products. Powder mixtures were densified by SPS at 1650 and 1725°C using 40 MPa pressure for 5 min. The effects of heating rate, spark plasma sintering temperature and CNT additive on density, hardness, fracture toughness and microstructures of B₄C-CNT samples are investigated. Density measurements were carried out using Archimedes method. Hardness and fracture toughness were examined by Vickers indentation technique. Scanning Electron Microscope (SEM) was used to observe microstructural investigation.
The surface of carbon monolith (CM) was chemically treated in order to obtain antibacterial filters with silver deposit for water treatment. The chemical treatment involved submerging the as-received CM in HNO_{3}, KOH and H_{2}O_{2} solution. The specific surface area was examined by N_{2} adsorption. Silver deposition at the surface of CM samples was performed using cheap and simple procedure of immersing CM samples in aqueous solution of AgNO_{3}. Temperature programmed desorption method has been used in order to investigate the nature and thermal stability of surface oxygen groups before and after silver deposition. The composition and crystalinity of silver deposits have been examined by X-ray diffraction. Chemical treatment does not cause any drastic changes of CM specific surface area, but increases a total amount of surface oxides. Amount of deposited silver is several times higher for all chemically treated samples. The results show that increasing the amount of CO yielding groups on CM surface leads to increased amount of Ag deposit and decreases its crystallite sizes
Quantum mechanical properties of the graphene are, as a rule, treated within the Hilbert space formalism. However a different approach is possible using the geometric algebra, where quantum mechanics is done in a real space rather than in the abstract Hilbert space. In this article the geometric algebra is applied to a simple quantum system, a single valley of monolayer graphene, to show the advantages and drawbacks of geometric algebra over the Hilbert space approach. In particular, 3D and 2D Euclidean space algebras Cl_{3, 0} and Cl_{2, 0} are applied to analyze relativistic properties of the graphene. It is shown that only three-dimensional Cl_{3, 0} rather than two-dimensional Cl_{2, 0} algebra is compatible with a relativistic flatland.
The layers were prepared by ion beam assisted deposition of iridium and platinum onto AVCarb® Carbon Fiber Paper P50 electrocatalyst supports for the production of diffusion layers of the membrane-electrode assemblies of low temperature fuel cells with polymer electrolyte membrane. Formation of the layers in the ion beam assisted deposition mode, by means of the deposition of metal and mixing of precipitating layer with the substrate by the accelerated (U=10 kV) ions of the same metal, was performed. In this process neutral fraction of metal vapour and ionized plasma of vacuum pulsed electric arc discharge were used. The investigations of morphology and composition of layers were carried out by the scanning electron microscopy, energy dispersive X-ray microanalysis, wave dispersive X-ray fluorescence analysis, and the Rutherford backscattering spectrometry methods. It was established that the obtained catalytic layers contain atoms of the deposited metals and substrate material as well as impurity oxygen atoms. The surfaces contain also metal inclusions of several micrometer size which arise from the precipitation of deposited metal droplets from the arc discharge of an ion source. The content of iridium and platinum atoms in the layers is ≈2×10¹⁶ cm¯²; the concentration of the deposited metals equals about several atomic percent.
We present a symmetry analysis of allowed infrared and Raman modes in graphene and highly oriented pyrolytic graphite. Surface structure for highly oriented pyrolytic graphite is examined using atomic force microscopy. As experimental tools, we used infrared spectroscopic ellipsometry in order to investigate the pseudodielectric function of highly oriented pyrolytic graphite in the mid-infrared range (500-7000 cm^{-1}) and Raman spectroscopy to investigate the influence of layers number decrease. As a result, we propose a method for an experimental verification of graphene.
The samples of thin film (d ≈ 40 nm) tetrahedral amorphous carbon (ta-C), deposited by the filtered cathodic vacuum arc have been implanted with N⁺ at a fluence of 3×10¹⁴ cm¯² and ion energy E=20 keV. The induced structural modification of the implanted material results in a considerable change of its optical properties, best manifested by a significant shift of the optical absorption edge to lower photon energies as obtained from optical transmission measurements. This shift is accompanied by a considerable increase of the absorption coefficient (photodarkening effect) in the measured wavelength range (350÷2500 nm). These effects could be attributed to both the additional defect introduction and the increased graphitization, as confirmed by the X-ray photoelectron spectroscopy measurements. The optical contrast thus obtained (between implanted and unimplanted film materials) could be made use of in the area of high-density optical data storage using the focused ion beams.
The properties of carbon nanotubes can be dramatically altered by the presence of defects. In this work we address the properties of two different kinds of defective nanotubes: junctions of achiral tubes with topological defects and partially unzipped carbon nanotubes. In particular, we begin by focussing on the interface states in carbon nanotube junctions between achiral tubes. We show that their number and energies can be derived by applying the Born-von Karman boundary condition to an interface between armchair- and zigzag-terminated semi-infinite graphene layers. We show that these interface states, which were thought to be due to the presence of topological defects, are in fact related to the graphene zigzag edge states. Secondly, we study partially unzipped carbon nanotubes, which can be considered as the junction of a carbon nanotube and a graphene nanoribbon, which has edge features giving rise to novel properties. Carbon nanoribbons act as transparent contacts for nanotubes and viceversa, yielding a high conductance. At certain energies, nanoribbons behave as valley filters for carbon nanotubes; this holds considering electron-electron interaction effects. Furthermore, the application of a magnetic field turns the system conducting, with a 100% magnetoresistance. These novel structures may open a way for new carbon-based devices.
Amorphous carbon and NiO/carbon composites were used as an electrode material for supercapacitors. The investigations were performed to evaluate the influence of the Ar/C_2H_2 ratio on the capacitance values of carbon and NiO/carbon electrodes. The surface morphology of the carbon electrodes changes from snowflake-like to columnar with the increase of the Ar/C_2H_2 ratio. The Raman scattering spectroscopy results demonstrated that the I_{D}/I_{G} ratio decreases from 1.33 to 0.91 with the increase of the Ar/C_2H_2 ratio. It indicates the decrease of the sp^2 bonded carbon in the coatings. The specific capacitance of the carbon electrodes increases with the increase of the Ar/C_2H_2 ratio. The NiO/carbon electrodes show capacitance values 10 times larger as those of carbon electrodes. The largest specific capacitance of 27.7 F/g was obtained for NiO/carbon electrode, when carbon coating was deposited under Ar/C_2H_2=27.
In this study a carbon and NiO/carbon electrodes were prepared and investigated. The surface roughness increases with the increase of the torch power. The addition of the NiO changes the surface structure from a snowflake-like to a mesh-like. It was demonstrated that the addition of the nickel oxide to amorphous carbon increases the specific capacitance of composite electrode. However, the NiO/carbon electrodes have a lower breakdown voltage values and longer charge-discharge cycles.
We investigated the magnetic behavior of charcoal composite with incorporated magnetite and silver ions. The magnetization curve measured at 282 K showed saturation magnetization of 8 emu/g. By benefiting from a mechanical process, the magnetic activated carbon, supporting silver ions (MCAG), acts as a magnetic filter uptaking the bacteria. This idea was confirmed by the DGGE analysis in which the bacterial DNA was detectable in the sediment after the treatment.
In this study, mechanical behavior of epoxy composite reinforced by unidirectional and woven fiber is investigated experimentally. In the preparation of composite samples woven shaped glass, aramid and carbon fibers and unidirectional shaped glass and carbon fibers were used. Tension, compression and shear tests were carried out to determine mechanical properties of composites. It is seen from the test results, that unidirectional carbon fiber shows better performance than the glass fiber. Mechanical properties of 0°-oriented unidirectional fiber are better than those of 90°-oriented unidirectional fiber. Mechanical properties of aramid-fiber-reinforced composite are higher than those of glass and carbon fiber, when the woven types of fibers are considered.
Thermo-optical properties of hydrogenated amorphous carbon nitride layers (a-C:N:H) deposited on crystalline silicon by plasma assisted chemical vapour deposition were studied. The layers were characterized by the Fourier transform infrared spectroscopy and their chemical composition, i.e. [N]/[C] ratio, was determined by energy dispersive X-ray technique. The optic measurements were made by spectroscopic ellipsometer Wollam M2000 equipped with a heated vacuum chamber. The measurements of ellipsometric angles were carried out during heating the sample from room temperature to 300°C. Refractive index, extinction coefficient and the layer thicknesses were calculated by fitting the model of the layer to the ellipsometric data. The results confirm that at about 23°C the layer properties are changed. The measured thermo-optical parameters, dn/dT and dk/dT, show abrupt change from negative to positive values which can be explained by structure graphitization. Simultaneously, the bandgap decreases from 2.5 to 0.7 eV and the layer thickness drops to about 50% of the initial value.
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