Thermal Decomposition Of Acetylene Research Articles

Optical properties and structure of acetylene flame soot

Acetylene black is a special type of carbon black, obtained from the thermal decomposition of acetylene. Acetylene flames enable the investigation of the soot optical properties. A reliable knowledge of the optical properties of acetylene soot is necessary for interpreting the optical measurements in flames and the development of acetylene black applications in industry. However, a wide variation in the optical properties of soot is observed in different formation conditions. The main factors affecting soot formation in flames are fuel composition, equivalence ratio, and reaction time connected with the height above a burner. In this study, we measured the absolute value of the refractive index function of acetylene soot E(m,1064) at a wavelength of 1064 nm, as well as the ratio of the refractive index functions E(m,1064)/E(m,532) at laser wavelengths of 532 nm and 1064 nm in a premixed acetylene/air flame using laser-induced incandescence. The soot structure was studied using high-resolution electron microscopy. The obtained results showed that E(m,1064) increased from 0.19 to 0.53 and that the ratio of E(m,1064)/E(m,532) increased from 1.12 to 1.55 according to the height above a burner. These changes in the optical properties are attributed to differences in soot structure, such as different distances between graphene planes inside soot crystallites, which decreased from 0.43 to 0.36 nm as the height above the burner increased from 5 to 20 mm. It was concluded that the optical properties and structure of acetylene soot differ from those formed in other hydrocarbon flames.

On the Possibility of Promoting a Detonation Condensation Wave in Acetylene with Methane Additions

A numerical analysis of the recently discovered promoting of the growth of condensed carbon nanoparticles during the thermal decomposition of acetylene in the presence of methane additives has been performed. Calculations carried out using the modern kinetic mechanism, describing the growth of carbon nanoparticles during hydrocarbon pyrolysis and combustion, have confirmed a significant acceleration of the growth of polyaromatic hydrocarbons and nanoparticles, as well as temperature and pressure during shock wave pyrolysis of acetylene with the addition of 10% methane. The results indicate a possible decrease in threshold pressure and acceleration of the development of acetylene detonation in the presence of methane additions.

The morphological transformation of carbon materials from nanospheres to graphene nanoflakes by thermal plasma

Carbon materials are synthesized by the thermal decomposition of acetylene using a magnetically rotating arc under atmospheric pressure. The effects of hydrogen addition, gas injection position, acetylene concentration, and reaction temperature on the morphology of pyrolysis products are evaluated. Carbon spherical particles and graphene nanoflakes are also obtained. Results indicate that a large amount of hydrogen, a low carbon flow, and high temperatures can promote the morphological transformation of carbon materials from nanospheres to graphene nanoflakes. Combined with a gas–phase kinetic model and a simulation of computational fluid dynamics, the reaction zone with a critical temperature of 2500 K can be divided basically into nucleation and surface growth, which correspond to the temperature–rise zone and high–temperature maintenance zone, respectively. Essential factors affecting graphene formation may include the formation of sheet–like nuclei and continuous planar growth at the side active sites of the structure. A low collision frequency of precursors and the high temperatures favor the formation of sheets–like nuclei. Planar surface growth requires hydrogen to terminate dangling bonds at edges and a high temperature to induce growth without a curvature.

Chemical Vapor Deposition-Grown Nickel-Encapsulated N-Doped Carbon Nanotubes as a Highly Active Oxygen Reduction Reaction Catalyst without Direct Metal-Nitrogen Coordination.

Nickel-encapsulated nitrogen-doped carbon nanotubes (Ni–TiO2–NCNTs) are synthesized via chemical vapor deposition by thermal decomposition of acetylene with acetonitrile vapor at 700 °C on the Ni–TiO2 matrix. TiO2 is used as a dispersant medium for Ni nanoparticles, which assists in higher CNT growth at high temperatures. A reference catalyst is made by following the similar procedure without acetonitrile vapor, which is called a Ni–TiO2–CNT. Acid treatment of these two catalysts dissolved Ni on the surface of CNTs–NCNTs, producing catalysts with enhanced surface area and defects. The transmission electron microscopy–energy-dispersive X-ray spectra analysis of acid-treated version of the catalysts confirmed the presence of encapsulated Ni. Oxygen reduction reaction (ORR) activity of these catalysts was analyzed in 0.1 N KOH solution. Among these, the acid-treated Ni–TiO2–NCNT exhibited highest ORR onset potential of 0.88 V versus reversible hydrogen electrode and a current density of 3.7 mA cm–2 at 170 μg cm–2 of catalyst loading. The stability of the acid-treated Ni–TiO2–NCNT is proved by cyclic voltammetry and chronoamperometry measurements which are done for 800 cycles and 100 h, respectively. Primarily N doping of CNTs is the reason behind the improved ORR activity.

Full factorial design approach to carbon nanotubes synthesis by CVD method in argon environment

Whereas meeting product quantity and quality are prime intent in process optimization of materials manufacturing, the application of the more reliable full factorial experiment has not been well-explored in optimization studies of Carbon nanotubes (CNTs) synthesis. In this study, statistical full factorial design of experiment was explored in the parametric studies of CNTs synthesis via acetylene-chemical vapour deposition (CVD). Bimetallic (FeCo) catalyst supported on CaCO3 was employed for the synthesis of CNTs. The dependence of CNTs yield on the growth time (45/60 min), growth temperature (700/750 °C), acetylene flow rate (150/190 ml/min), and argon flow rate (230/290 ml/min) was investigated in the 24 factorial design of experiment. The growth temperature and acetylene flow rate were found to have the most significant effects on the yield of CNTs, and a maximum yield of 170% was obtained at growth conditions of 60 min, 700 °C, 190 ml/min acetylene flow rate, and 230 ml/min argon flow rate. Since acetylene undergoes polymerization or dissolution during non-catalyzed thermal decomposition, the significant effects of temperature and acetylene flow rate as illustrated by the factorial analysis suggests that the selective ability of the FeCo/CaCO3 catalyst towards CNTs growth in the thermal decomposition of acetylene in CVD was mainly thermodynamics-controlled. Characterization of CNTs samples synthesized at different conditions shows that highest-yield conditions do not guarantee best quality properties.

탄화수소연료의 열분해 Soot발생특성 분석에 관한 연구

Soot and harmful exhaust gas produced by liquid hydrocarbon fuel caused various environmental problems. In this study, soot characteristics produced by thermal decomposition of acetylene and diesel were analyzed, which are formed at different temperatures. These fuels were observed to produce particulate matters, and collected soot samples were observed by using TEM & SEM. These were found to be significantly different in structure and crystallinity.

High-strength carbon nanotube/carbon composite fibers via chemical vapor infiltration.

In this study, we have developed an efficient and scalable method for improving the mechanical properties of carbon nanotube (CNT) fibers. The mechanical properties of as-synthesized CNT fibers are primarily limited by their porous structures and the weak bonding between adjacent CNTs. These result in inefficient load transfer, leading to low tensile strength and modulus. In order to overcome these limitations, we have adopted chemical vapor infiltration (CVI) to efficiently fill the internal voids of the CNT fibers with carbon species which are thermally decomposed from gas phase hydrocarbon. Through the optimization of the processing time, temperature, and gas flow velocity, we have confirmed that carbon species formed by the thermal decomposition of acetylene (C2H2) gas successfully infiltrated into porous CNT fibers and densified them at relatively low temperatures (650-750 °C). As a result, after CVI processing of the as-synthesized CNT fibers under optimum conditions, the tensile strength and modulus increased from 0.6 GPa to 1.7 GPa and from 25 GPa to 127 GPa, respectively. The CVI technique, combined with the direct spinning of CNT fibers, can open up a route to the fast and scalable fabrication of high performance CNT/C composite fibers. In addition, the CVI technique is a platform technology that can be easily adapted into other nano-carbon based yarn-like fibers such as graphene fibers.

Synthesis of a Novel Structure Carbon Nanocoils and their Application in Photo Diode Devices

In this paper, the novel structure of carbon nanocoils were synthesized successfully by catalytic thermal decomposition of acetylene in CVD reactor under inert atmospheric pressure. Fe as a catalyst coated alumina beads used as substrate , both were placed inside a cylindrical shape stainless steel mesh SSC and located at the mid of CVD reactor. Preliminary study of application of prepared carbon nanocoil in synthesis of photodiode showed that the photodiode has a good rectification and the forward current obeys to tunneling-recombination model.

Electrochemical Capacitors Fabricated Using Porous Silicon

Electrochemical capacitors based on porous silicon nanostructures were prepared and studied. Capacitors are favored over batteries for certain applications because they can provide higher power, albeit at lower energy densities, and do not degrade significantly over many thousands of charging cycles. These properties are a direct result of the fact that capacitors do not rely on chemical reactions to store energy. In this work, measurements from the porous silicon capacitors reveal that high capacitance can be achieved contrary to previously reported early studies [1, 2]. The devices were fabricated using silicon process methods with the potential to be incorporated into integrated circuits.Porous silicon nanostructures having extremely high surface-to-volume ratios with channel sizes 20 nm to 100 nm were combined with an ionic electrolyte to create an electrochemical capacitor. Unpassivated silicon structures, however are not stable over a long period of time due to unwanted oxidation/reduction reactions with the electrolyte, resulting in rapidly decreasing capacitance over repeated charge-discharge cycles. Our work has focused on optimizing the porous silicon nanostructure (i.e. surface area, pore morphology, etc.) and passivating the surfaces. For use as an electrochemical capacitor, surface coatings such as atomic layer deposition (ALD) titanium nitride (TiN) or carbon (e.g. graphene) [3,4] were found necessary for long-term stability. Recently published work by one of our coauthors [5] has confirmed that coating the porous silicon with graphene-like carbon can reduce these unwanted chemical reactions, greatly increasing the device’s lifetime and maximum operating voltage.The total surface area needs to be high to obtain large capacitance, so the aspect ratio of the pores needs to be high making it difficult to coat the surfaces. Also, the high aspect ratios can lead to high effective series resistance (ESR) because of the long path that ionic charge carriers have to traverse. Two different deposition techniques were developed to stabilize the silicon surface of high aspect ratio structures: conductive coatings using ALD and thermal carbonization using gas phase treatments in a furnace [6]. Results from these structures and coatings are described.[1] S. E. Rowlands, R. J. Latham, & W. S. Schlindwein, “Supercapacitor devices using porous silicon electrodes”, Ionics 5, 144–149 (1999).[2] S. Desplobain, G. Gautier, J. Semai, L. Ventura and M. Roy, "Investigations on porous silicon as electrode material in electrochemical capacitors", Phys. Stat. Sol. (c), 4, 2180, 2007.[3] D.S. Gardner, Z. Chen, W. Jin, S.B. Clendenning, E.C. Hannah, T.V. Aldridge, J.L. Gustafson, U.S. Patent Appl. 20130273261, filed Sept. 30, 2011.[4] D. S. Gardner, W. Jin, Z. Chen, C.W. Holzwarth, C.L. Pint, B.K. Moon, and J.L. Gustafson, U.S. Patent Appl. 20140078644, filed Sept. 17, 2012.[5] L. Oakes, A. Westover, J. W. Mares, S. Chatterjee, W. R. Erwin, R. Bardhan, S. M. Weiss, and C. L. Pint, “Surface engineered porous silicon for stable, high performance electrochemical supercapacitors”, Nature Scientific Reports, 3 , 3020, Oct. 2013.[6] J. Salonen, M. Bjorkqvist, E. Laine, L. Niinisto, “Stabilization of porous silicon surface by thermal decomposition of acetylene”, Appl. Surface Science, 225, 389–394 (2004)..

Electron Microscopy Study of Y-Shaped Carbon Fibers with Different Morphologies

A series of techniques, including field emission scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, and energy dispersive X-ray spectroscopy were employed to investigate three types of Y-shaped carbon fibers that were synthesized by the thermal decomposition of acetylene using an atmospheric pressure catalytic chemical vapor deposition process and copper tartrate as a catalyst precursor. On the basis of electron microscopy analysis, we propose that the simultaneous growth of three pieces of carbon fibers on the same copper catalyst particle results in the formation of Y-shaped carbon fibers. When several copper catalyst particles became positioned in a stratified arrangement, other types of Y-shaped carbon fibers were obtained. Our study indicates that the morphology of various Y-shaped carbon fibers can be controlled by tailoring the configuration of the copper catalyst particles used to generate them.

Synthesis of nano-carbon (nanotubes, nanofibres, graphene) materials

In the present study, we report the synthesis of carbon nanotubes (CNTs) using a new natural precursor: castor oil. The CNTs were synthesized by spray pyrolysis of castor oil-ferrocene solution at 850°C under an Ar atmosphere. We also report the synthesis of carbon nitrogen (C-N) nanotubes using castor oil-ferrocene-ammonia precursor. The as-grown CNTs and C-N nanotubes were characterized through scanning and transmission electron microscopic techniques. Graphitic nanofibres (GNFs) were synthesized by thermal decomposition of acetylene (C2H2) gas using Ni catalyst at 600°C. As-grown GNFs reveal both planar and helical morphology. We have investigated the structural and electrical properties of multi-walled CNTs (MWNTs)-polymer (polyacrylamide (PAM)) composites. The MWNTs-PAM composites were prepared using as purified, with ball milling and functionalized MWNTs by solution cast technique and characterized through SEM. A comparative study has been made on the electrical property of these MWNTs-PAM composites with different MWNTs loadings. It is shown that the ball milling and functionalization of MWNTs improves the dispersion of MWNTs into the polymer matrix. Enhanced electrical conductivity was observed for the MWNTs-PAM composites. Graphene samples were prepared by thermal exfoliation of graphite oxide. XRD analysis confirms the formation of graphene.

Cell performance of polymer electrolyte fuel cell with urchin-like carbon supports

Urchin-like structured carbon comprising carbon nanotubes grown on Fe catalyst-seeded mesoporous carbon have shown promising results as catalyst supports for use in direct methanol fuel cells (DMFCs) and proton exchange membrane fuel cells (PEMFCs). The Fe catalyst is prepared on the mesoporous carbon by immersion process followed by a high temperature reduction. The growth of carbon nanotubes then progress, for a predetermined time, through the thermal decomposition of acetylene at 800°C. The resulting structure, comprising intimately connected mesoporous carbon and carbon nanotubes, is shown to offer performance advantages as a catalytic support for DMFCs and PEMFCs. When the hot-pressing pressure is fixed 20kgcm−2 to fabricate a membrane electrode assembly (MEA) with urchin-like carbon supports, the CNT growth time is found to be 60min for a highest maximum power density in both DMFCs and PEMFCs. The maximum power densities are 43 and 79% higher than those with purely mesoporous carbon in DMFCs and PEMFCs, respectively. In a direct comparison with commercial E-TEK catalyst, the urchin-like catalyst shows higher maximum power densities, in DMFC and PEMFC, by approximately 17 and 31%, respectively.

Low-temperature synthesis of carbon nanofibers by decomposition of acetylene with a catalyst derived from cupric nitrate

Abstract Carbon nanofibers have been synthesized by the thermal decomposition of acetylene with a copper nanocatalyst derived from cupric nitrate trihydrate at a low temperature of 260 °C. The resultant carbon nanofibers were characterized using transmission electron microscopy and X-ray power diffraction. The copper nanoparticles changed from initial irregular shapes to regular shapes during the growth of nanofibers. The copper nanoparticle size has a considerable effect on the morphology of carbon nanofibers. Helical carbon nanofibers with a symmetric growth mode were grown on copper nanoparticles with a grain size less than 50 nm. When the catalyst particle size was in the range of 50–200 nm, straight carbon nanofibers were obtained dominantly.

Studies on synthesis and hydrogenation behaviour of graphitic nanofibres prepared through palladium catalyst assisted thermal cracking of acetylene

The nano-variants of carbon including graphitic nanofibres (GNF) have recently been considered to be exotic (light weight, high storage capacity) hydrogen storage materials. In the present paper, we report growth of aligned bundles of GNF. The length and width of cross-section of the bundles is ∼50 and ∼25 μm, respectively. The length of individual GNF is ∼50 μm and diameter ∼0.25 μm. The GNFs have been synthesized through thermal decomposition of acetylene using palladium (Pd) sheets as catalyst. This represents a new form of catalyst. The GNFs bundles grown by the present method are easier to hydrogenate. They adsorb hydrogen at a lower pressure of ∼80 atm as against ∼120 atm for the GNF grown in the earlier studies. The storage capacity obtained in the present investigation is ∼17 wt.%. Electron microscopic investigations reveal that as against the as grown GNF, the hydrogenated version embodies microstructures exhibiting fragmentation of graphitic layer bundles. The reasons for the growth of GNF in the form of aligned bundles, the ease of hydrogenation and relevance of GNF fragmentation after hydrogenation have been outlined.

Template‐based synthesis of carbon nanofibres and their field emission characteristics

AbstractA synthesis technique based on an anodic aluminium oxide (AAO) template was developed to synthesize carbon nanofibres via thermal decomposition of acetylene using nickel as a catalyst. The structure and morphology of the nanofibres were studied with scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. It was found that most of the carbon nanofibres have a diameter of 150 nm, similar to that of the template nanopores. Also, they have novel shapes. Their electron field emission property was measured and a threshold field of 6.6 MV m−1 was observed. Copyright © 2004 John Wiley & Sons, Ltd.

Characteristics of Carbon Nanotube with Synthetic Conditions in Catalytic Chemical Vapor Depositon

Carbon nanotubes were synthesized at various conditions using Ni-catalytic thermal chemical vapor deposition method and their characteristic properties were investigated by SEM, TEM and Raman spectroscopy. Carbon nanotubes were formed on very fine Ni-catalytic particles. The carbon nanotubes synthesized by thermal decomposition of acetylene at <TEX>$700^{\circ}C$</TEX> had a coiled shape, while those synthesized at <TEX>$850^{\circ}C$</TEX> showed a curved and Y-shape having a bamboo-like morphology. It was found that the carbon nanotube was also made on the fine Ni-catalytic particles formed on the surface of 100~400nm sized large ones after pretreatment with <TEX>$NH_3$</TEX>.ber composites show the high dielectric constant and large conduction loss which is increased with anisotropy of fiber arrangement. It is, therefore, proposed that the glass and carbon fiber composites can be used as the impedance transformer (surface layer) and microwave reflector, respectively. By inserting the foam core or honeycomb core (which can be treated as an air layer) between glass and carbon fiber composites, microwave absorption above 10 dB (90% absorbance) in 4-12 GHz can be obtained. The proposed fiber composites laminates with sandwitch structure have high potential as lightweight and high strength microwave absorbers.

Growth of carbon nanotubes and nanofibres in porous anodic alumina film

By acetylene pyrolysis at 650 and 550°C, carbon nanotubes were synthesized successfully in porous alumina templates anodized in sulfuric and/or oxalic acid solution. For templates anodized in oxalic acid followed by boiling in distilled water, thermal decomposition of acetylene at 650°C in the pores results in the formation of carbon nanofibres. For templates anodized in sulfuric acid, only carbon nanotubes were formed, even if boiling in water was adopted to process it. This indicates that the modifications of the catalytic effects in acetylene pyrolysis by boiling in water are different for these two types of templates. All the carbon nanotubes and nanofibres have similar lattice structures under HRTEM examination. No carbon nanotubes or nanofibres can be formed when the chemical vapour deposition temperature decreases to 500°C.

Thermal decomposition of acetylene on Pt(1 1 1) studied by scanning tunneling microscopy

The adsorption and the thermal decomposition processes of C 2H 2 on Pt(1 1 1) have been investigated by the use of scanning tunneling microscopy. For a high C 2H 2 coverage, a (2×2) structure is observed locally after the C 2H 2-covered Pt(1 1 1) surface is heated to 120 K. By heating to 220 K, the sample surface is covered with the (2×2) structure separated with brighter lines. After heating up to 370 K, (2×2) domains related to ethylidyne species appear with larger and brighter protrusions. For a low C 2H 2 coverage, adsorbates are located randomly and no ordered islands are observed after heating to 120 K. In contrast, heating to 220 K leads to the formation of (2×2) islands. This indicates that the adsorbate–adsorbate interaction in the (2×2) structure observed by 120 K heating is different from that in the (2×2) structure observed by 220 K heating; the former is repulsive, but the latter attractive. Therefore, it is suggested that different surface species are formed by the decomposition of C 2H 2 at 220 K. The detail of the decomposition processes of C 2H 2 and the relation between the adsorbate–adsorbate interaction and the surface species are discussed. The results are also reported measured by heating up to higher temperatures above 400 K.

A structure model and growth mechanism for novel carbon nanotubes

The growth of carbon nanotubes from catalytic thermal decomposition of acetylene on fine iron particles has been studied. Electron microscopic images of the carbon nanotubes “as formed” and after annealing treatment are presented. Besides the ordinary carbon nanotubes which have been reported (S. Iijima, Nature, 354 (1991) 56), we have found, at first time, two other new kinds of carbon nanotubes: one is straight or curved nanotube with many irregular multi-layered diaphragms in the hollow core, in particular, the fringes of the wall of the tubes are not parallel to the axis of the tube; another one has many regular diaphragms (bamboo-like) which keep almost constant distance with each other. A model that postulates two steps growth of nanotubes from catalyst particles is proposed to explain the microstructure of the novel carbon nanotubes.

Elastic deformation of a carbon nanotube adsorbed on a stepped surface

Carbon nanotubes prepared by thermal decomposition of acetylene on cobalt catalysts were investigated by scanning tunnelling microscopy (STM). One of the STM images revealed a nanotube with a diameter ca 1 nm getting over atomic steps on the (HOPG) graphite substrate on which the samples were deposited. The deformation and the stresses in this nanotube were evaluated from continuous-medium elasticity, using 12-6 CC pair potentials to describe the interaction with the substrate. A good agreement was found between the computed shape of the deformed nanotube and that revealed by the STM. The calculations also indicated that the stresses only slowly increased with increasing step height and, for that reason, a nanotube adsorbed on a surface can get over sharp steps a few nanometres high without breaking. This result attests to the high flexibility of the carbon nanotube.