Ratio Of Acetylene Research Articles

Direct detection of acetylene in air by continuous wave cavity ring-down spectroscopy

Diode laser-based continuous wave cavity ring-down spectroscopy (cw-CRDS) in the near-infrared region has been used to measure the mixing ratio of acetylene (C(2)H(2)) in ambient air. Detection lim ...

Selective growth of vertically aligned double- and single-walled carbon nanotubes on a substrate at590 °C

Vertically aligned double- and single-walled carbon nanotubes (DWNTs and SWNTs) were synthesized on asubstrate at 590 °C by hot-filament chemical vapor deposition. An optimized combination of iron andaluminum layers as the catalyst resulted in iron particles ranging from 1–5 nm floating in analuminum matrix after annealing. Selective synthesis of DWNTs and SWNTs from suchparticles was achieved by adjusting the dilution ratio of acetylene that was used as thesource gas. The yield of DWNTs among all CNTs was as high as 81%, while that ofSWNTs was almost 100%. The diameter distribution of DWNTs was narrow, with astandard deviation of about 12%.

Synthesis of Carbon Nanotubes by Swirled Floating Catalyst Chemical Vapour Deposition Method

A series of developments have been made in synthesizing Carbon Nanotubes (CNTs) by Catalytic Vapour Deposition (CVD) methods since its discovery as a possible route to the large scale and high quality production of CNTs. In this study, CNTs were synthesized continuously in a swirled floating catalytic chemical vapour deposition reactor using acetylene as carbon source, ferrocene as catalyst, with argon and hydrogen as carrier gases within the temperature range of 900-1050 degrees C. The effects of pyrolysis temperature, acetylene flow rate, hydrogen flow rate, and ratio of flow of acetylene to hydrogen on the rate of production of CNTs were investigated. The CNTs produced were purified with dilute nitric acid and the nature and quality of the CNTs were analysed by TEM, Raman spectrometer, EDX, and TGA. Results obtained revealed that a mixture of single and multi wall carbon nanotubes were produced continuously with a maximum yield rate of 0.31 g/min at 1000 degrees C and a flow ratio of acetylene to hydrogen of one to five.

Comparative studies on influence of acetylene to argon flow rate ratios on nano-scratch behavior of a-C:H films produced on steel substrates by plasma immersion ion implantation and deposition

Hydrogenated amorphous carbon (a-C:H) films were fabricated using mixed acetylene and argon plasmas with various flow rate ratios of acetylene to argon. The flow rate ratios ( F C 2H 2 to F Ar) have a large impact on the structure of the films. Enhanced film hardness and reduced sp 2 content were achieved at larger flow ratios attributable to the high ion flux and efficient etching by hydrogen. However, an excessively high flow rate leads to hydrogen loss from the structure, large stress during deposition, and potential deterioration in the film structure. The appropriate deposition rate is determined based on the scratch behavior of the film.

Influence of acetylene to argon flow rate ratios on structure and properties of hydrogenated amorphous carbon films produced on steel substrates by plasma immersion ion implantation and deposition

Hydrogenated amorphous carbon (a-C:H) films were fabricated using mixed acetylene and argon plasma with various flow rate ratios of acetylene to argon. Raman scattering and x-ray photoelectron spectroscopy show that changing the flow rate ratios (FC2H2 to FAr) has a large impact on the structure of the films. Enhanced film hardness and reduced surface roughness were achieved at higher ratios attributable to the high ion flux and efficient etching by hydrogen. However, the film surface exposed to atomic hydrogen at a higher C2H2 flow rate becomes rougher. The sp3 content and film hardness also reach saturation combined with a fissile surface due to the high stress.

Effect of negative self-bias voltage on microstructure and properties of DLC films deposited by RF glow discharge

Influence of system parameters such as RF power and discharge pressure on the negative self-bias voltage of substrate was systematically investigated by Oscilloscope with a high voltage probe. It is found that the self-bias voltages increase linearly with the square root of RF power, and decrease with the discharge pressure at both pure argon gas and gas mixture of argon and acetylene, and the self-bias voltages increase with the ratio of acetylene. Moreover, the hydrogenated amorphous carbon films were deposited by RF glow discharge at input RF power of 500 W and 700 W. The microstructure and mechanical properties of these a-C:H films were investigated via Raman spectroscopy and Nano-indentation technique. The I D/ I G ratio of a-C:H films deposited at 500 W (its value is 0.66) is lower than that of film deposited at 700 W (its value is 1.14). This implies that there is a higher fraction of sp 3 bonding in the film prepared at 500 W, and this trend is confirmed by the results of Nano-indentation test.

Synthesis of multi-walled carbon nanotube in a gas-solid fluidized bed

Multi-walled carbon nano-tubes (MWCNTs) were produced by acetylene decomposition on Fe-catalyst in a fluidized bed reactor (0.056 m-IDx1.0 m-high) with a sintered metal distributor (40 μm pore size). The Fe-catalysts were tested in decomposition of the different ratios of acetylene, hydrogen and nitrogen at the temperature range of 823–973 K. The physical properties of the carbon nano-tubes were determined by HR-TEM, SEM and Raman spectroscopy. The multi-walled carbon nano-tubes produced from the fluidized bed reactor are sub-aggregates and entangled with each other. The synthesized MWCNTs have outer diameters of a few tens of nanometers at 823–973 K. It has been found that the synthesized CNT agglomerates are in good condition with less amorphous carbon with the reaction time of 30 to 60 minutes from the analyses of Raman Spectra, SEM and TEM, The ratio (I D /I G ) of amorphous carbon (I D = 1,295 cm-1) and crystalline carbon (I G =1,590 cm-1) range from 1.15 to 1.49.

Parametric Study on Growth of Carbon Nanocoil by Catalytic Chemical Vapor Deposition

Carbon nanocoils (CNCs) were synthesized by the catalytic pyrolysis of acetylene over a mixture of Fe and SnO2 particles in a chemical vapor deposition (CVD) apparatus. The effects of reaction temperature, the composition of Fe and SnO2 in the catalyst, and the ratio of acetylene (C2H2) to helium (He) gas were examined. An optimum output was obtained when the Fe/SnO2 ratio was 2/1, the flow rates of C2H2 and He gases were 150 and 700 sccm, respectively, and the reaction temperature was 700°C. Under these conditions, the CNCs were of 80% purity, with average coil diameters of 750 nm, fiber diameters of 300 nm and pitches of approximately 750 nm. The CNC yield weighed up to 60 times that of the catalyst in 10 min.

Detonation forming of aluminium cylindrical cups experimental and theoretical modelling

In this study, cylindrical cups formation of aluminium alloy sheets using a gas detonation forming system (DIN 99.5 (Etial 5)) was investigated. This system was achieved by accepting the volume ratio of acetylene (C 2H 2)–oxygen (O 2) being equal, and double staged detonation forming apparatus was designed and manufactured. For this purpose, the complete filling up of the DSDT with reactant was controlled by a manometer and a flow-meter being operated by computer software. Shock speed and pressure values of the gas detonation being applied to the forming cups were recorded by a computer-controlled system. The amount of formability of aluminium cups in the cylindrical moulds was measured and analyzed. The theoretical model of the formed cups’ shape was realized and analyzed with the help of ‘the explicit dynamic analysis code’ module incorporated ANSYS/LS-DYNA computer software. The comparison of the experimental and theoretical results obtained from unit strain, thickness variation and volume of cups formability was carried out. Theoretical and experimental results showed approximately 80–90% similarities in formability of desired shape and inconsistencies between these two models were investigated to find out optimum formability of cups and ratio of reactant, based upon the above mentioned theoretical and experimental results.

Chemical composition of air masses transported from Asia to the U.S. West Coast during ITCT 2K2: Fossil fuel combustion versus biomass‐burning signatures

As part of the Intercontinental Transport and Chemical Transformation experiment in 2002 (ITCT 2K2), a National Oceanic and Atmospheric Administration (NOAA) WP‐3D research aircraft was used to study the long‐range transport of Asian air masses toward the west coast of North America. During research flights on 5 and 17 May, strong enhancements of carbon monoxide (CO) and other species were observed in air masses that had been transported from Asia. The hydrocarbon composition of the air masses indicated that the highest CO levels were related to fossil fuel use. During the flights on 5 and 17 May and other days, the levels of several biomass‐burning indicators increased with altitude. This was true for acetonitrile (CH3CN), methyl chloride (CH3Cl), the ratio of acetylene (C2H2) to propane (C3H8), and, on May 5, the percentage of particles measured by the particle analysis by laser mass spectrometry (PALMS) instrument that were attributed to biomass burning based on their carbon and potassium content. An ensemble of back‐trajectories, calculated from the U.S. west coast over a range of latitudes and altitudes for the entire ITCT 2K2 period, showed that air masses from Southeast Asia and China were generally observed at higher altitudes than air from Japan and Korea. Emission inventories estimate the contribution of biomass burning to the total emissions to be low for Japan and Korea, higher for China, and the highest for Southeast Asia. Combined with the origin of the air masses versus altitude, this qualitatively explains the increase with altitude, averaged over the whole ITCT 2K2 period, of the different biomass‐burning indicators.

Estimating N2 fixation in two species of Alnus in interior Alaska using acetylene reduction and 15N2 uptake

:In interior Alaskan boreal forests two species of alder, Alnus tenuifolia and Alnus crispa, represent keystone species in floodplain and upland landscapes, respectively, due to the ability of these plants to form symbiotic associations with the nitrogen-fixing actinomycete, Frankia. It is believed that as much as 70% of the nitrogen (N) accumulated during the 200-y successional development of these forests is derived through atmospheric fixation by these species. Estimates of gross N inputs in these and many other ecosystems have traditionally utilized the acetylene reduction assay (ARA), which requires a conversion factor of the ratio of acetylene to N2 reduced by nitrogenase, the primary enzyme. Despite the fact that small variations in the reduction ratio can substantially influence estimates of N inputs, few studies have investigated how it varies spatially and temporally. The present study sought to 1) determine this conversion factor for both species of alder in situ by calibration of the ARA against a 15N2 uptake method we developed for field use and 2) determine whether the conversion factor varied with the successional stage in which the alders occurred. Averaged across all plants, the ratio of acetylene to N2 reduced was significantly greater in A. crispa. Significant differences in the value of the conversion factor were observed between early succession and later (mid and late) successional sites for both species. Such differences were also observed among replicate sites within and among stages. However, these stage and site differences may also be due to seasonal effects, which could not be controlled for with our design. Specific acetylene reductase activity (SARA) was only correlated with 15N2 uptake for early successional sites measured early in the growing season, when N2-fixation rates were lowest and the conversion factor was closest to the theoretical value of 4. A significant negative correlation was found between the conversion factor value and the rate of enzyme activity as determined by the 15N2 uptake method. Two hypotheses are proposed to explain this result: 1) that it is due to changes in the kinetic properties of nitrogenase at high levels of enzyme activity, resulting in an increased affinity of the enzyme for N2 relative to C2H2, and 2) that the concentration of C2H2 used in our ARA was insufficient to saturate nitrogenase.

Thermal spray coating of aluminum nitride utilizing the detonation spray technique

The main objective of this work is to examine the feasibility of depositing aluminum nitride (AlN) powders, synthesized using self-propagating high-temperature synthesis, on a mild steel substrate using the detonation spray coating technique. Thick coatings produced by utilizing the AlN powder were obtained at four different oxygen–acetylene ratios and analyzed for microstructure, microhardness, porosity, indentation fracture toughness, and phase distribution. The AlN powder particles were found to be undergoing oxidation during the deposition process. The interrelationship between the spray parameters and the extent of oxidation of AlN during the coating process was investigated. Tribological performance of the coatings was evaluated using a dry sand abrasion test and a pin-on-disc sliding wear test. The mechanical and tribological properties of the above four coatings were compared with pure alumina (Al2O3) coatings. The correlation between the structure of the coatings and their tribological performance was also established.

Maximum rates of N2 fixation and primary production are out of phase in a developing cyanobacterial bloom in the Baltic Sea

Although N2‐fixing cyanobacteria contribute significantly to oceanic sequestration of atmospheric CO2, little is known about how N2 fixation and carbon fixation (primary production) interact in natural populations of marine cyanobacteria. In a developing cyanobacterial bloom in the Baltic Sea, rates of N2 fixation (acetylene reduction) showed both diurnal and longer‐term fluctuations. The latter reflected fluctuations in the nitrogen status of the cyanobacterial population and could be correlated with variations in the ratio of acetylene reduced to 15N2 assimilated. The value of this ratio may provide useful information about the release of newly fixed nitrogen by a cyanobacterial population. However, although the diurnal fluctuations in N2 fixation broadly paralleled diurnal fluctuations in carbon fixation, the longer‐term fluctuations in these two processes were out of phase.

Ethylene selectivity variation in acetylene hydrogenation reactor with the hydrogen/acetylene ratio at the reactor inlet

Variation in the selectivity of ethylene produced by acetylene hydrogenation in an integral reactor was analyzed as a function of the hydrogen/acetylene ratio in the reaction stream at the reactor inlet. The analyses were made for two sample catalysts, which showed different dependence of the ethylene selectivity on the reactant composition. Even a small mismatch between the hydrogen/acetylene ratio at the reactor inlet and the ratio for converted reactants caused a large change in the ethylene selectivity along the reactor position, particularly when the conversion was high. The results of this study indicate two important factors to be considered in the design and operation of acetylene hydrogenation process: the hydrogen/acetylene ratio in the reactor inlet should be controlled close to the ratio for converted reactants; and catalysts showing high ethylene selectivity over a wide range of the hydrogen/ acetylene ratio are required for the design of a highly selective hydrogenation process.

Deposition mechanisms and properties of oxygenated carbon nitride films from rf discharges of acetylene, nitrogen, oxygen and argon mixtures

Oxygen-containing carbon nitride films were deposited in rf discharges of C 2H 2, N 2, O 2 and Ar mixtures. Actinometric optical emission spectroscopy was used to determine relative concentrations of the species H, O, CH, CN and CO in the discharge as a function of the proportion of oxygen in the feed, using Ar as an actinometer. The Ar emission intensity decreases as the proportion of O 2 in the feed increases, indicating that O 2 has a `cooling effect' on the discharge. The variations in the concentrations of CH and CN species, two possible precursors of film formation, showed different behaviors. The concentration of CH increases monotonically as the proportion of O 2 in the feed is increased, but the concentration of CN shows a maximum at an oxygen to acetylene ratio of about 0.15, which coincides with the maximum film deposition rate. This strongly suggests that the CN species is the main precursor of film formation. Infrared reflection spectroscopy revealed the presence of CN, CH, NH and CO functionalities in the deposited films. The presence of such species and their relationship to deposition via gas-phase and surface reactions are outlined. The optical properties of the films were investigated using transmission and reflection ultraviolet–visible spectroscopy. At increasing proportions of oxygen in the gas feed, the refractive index decreases while the optical gap increases. Free radicals were investigated using electron paramagnetic resonance. Unpaired spin concentrations of the order of 10 20 cm −3 were measured in the films a short time after deposition. These large spin concentrations are common in films prepared by plasma-enhanced chemical-vapor deposition (PECVD) but decrease at relatively high rates with time. Possible mechanisms accounting for the high spin concentrations and for the disappearance of the free radicals are discussed.

Diamond deposition in low-pressure acetylene flames: in situ temperature and species concentration measurements by laser diagnostics and molecular beam mass spectrometry

Diamond deposition in a flat, premixed acetylene–oxygen–argon flame at 50 mbar was investigated to characterize the reactive gas phase in the vicinity of the substrate. For this, flames with and without a substrate present were analyzed as a function of stoichiometry; also, the distance between the substrate and the burner was varied. Optimal conditions for the deposition of diamond films were found for oxygen–acetylene ratios of 1.3 and 1.4 and at distances between substrate and burner of 8, 9, and 10 mm. The flame structure in this region was investigated. In particular, gas temperature and OH radical concentrations were measured by laser-induced fluorescence (LIF). Furthermore, hydrogen atoms were monitored using three-photon excitation and subsequent fluorescence detection. Molecular beam mass spectrometry was employed to obtain an overview of stable species and hydrocarbon intermediates. The results provide a substantial experimental basis for comparison with theoretical models and are consistent with earlier observations, which stress the importance of H and CH 3 for the diamond deposition process. In addition, the observations indicate the participation of hydrocarbon species with more than 2 carbon atoms, e.g., C 3H 3, C 4H 3, and C x H 2 with x = 4, 6, or 8, in the gas-phase reactions controlling the deposition of diamond; an active role for these species in diamond chemical vapor deposition (CVD) has not been discussed before. As a first interpretation, diamond formation seems to be controlled by a counterbalance between OH and hydrocarbon intermediates at a position in the flame where sufficient H-atoms and CH 3 radicals are present to support diamond film growth.

TRACE A trajectory intercomparison: 2. Isentropic and kinematic methods

Kinematic and isentropic trajectories are compared quantitatively during a single 5‐day period (October 13–18, 1992) when several flights for the Transport and Atmospheric Chemistry Near the Equator‐Atlantic (TRACE A) experiment were conducted off the west coast of Africa. European Centre for Medium‐Range Weather Forecasts (ECMWF) data are used to compute the 5‐day backward trajectories arriving at locations over the South Atlantic Ocean and nearby parts of South America and southern Africa. Two versions of kinematic trajectories are examined. One version employs vertical motions supplied with the ECMWF data. These trajectories often differ greatly from those based on the isentropic assumption. The kinematic trajectories usually undergo considerably greater vertical displacements than their isentropic counterparts; however, most diabatic rates are consistent with those of synoptic‐scale systems. Ratios of acetylene to carbon monoxide are related to backward trajectories at various locations along a TRACE A flight. A second version of kinematic trajectories employs vertical motions diagnosed from ECMWF horizontal wind components using the continuity equation. These vertical motions are stronger than those supplied with the ECMWF data, causing many of the trajectories to have larger vertical displacements and considerably different paths than the original kinematic versions. Many of these kinematic trajectories undergo diabatic rates that exceed generally accepted values on the synoptic scale. This occurs, in part, because the diagnosed vertical motions are inconsistent with the ECMWF data. The research indicates that the kinematic procedure yields realistic 5‐day backward trajectories when the three‐dimensional wind data are available from a numerical model or other dynamically consistent data set such as provided by ECMWF.

Generation of carbon aerosols by fragmentation of acetylene in a laser-induced plasma

One of the possible ways to generate carbon aerosols in the sub-micrometer range is the fragmentation of carbon-rich gases. In our case, the fragmentation is caused by the generation of a laser-induced plasma in an acetylene/argon atmosphere. The particles are subsequently generated by homogeneous nucleation. With this technique it is possible to build an aerosol generator with an output of more than 0.8 g h −1 of elemental carbon aerosol. The maximum of the size distribution of the generated particles varies in the range of 80–400 nm, when the ratio of acetylene to argon is increased from 0.1 to 1.5. The size distribution and the morphological structure of the carbon particles is very similar to real combustion aerosols. One of the applications of this aerosol generator could thus be the simulation of combustion aerosols, e. g. for testing diesel engine soot filters.

Diamond thin films synthesized by a multinozzle oxy-acetylene chemical vapour deposition method

Diamond thin films were fabricated using a custom-made multinozzle oxy-acetylene flame apparatus. These films were characterized by scanning electron microscopy, X-ray diffraction and Raman spectroscopy. Experimental results show that this multinozzle combustion flame technique can produce high quality diamond films, as judged by Raman spectroscopy, with relatively large deposition areas. The surface morphology, crystal structure and optical properties of these films are found to be greatly affected by processing parameters, such as substrate temperature, gas ratio of acetylene to oxygen, and the configuration of the multinozzle. Compared with the single-nozzle oxy-acetylene flame technique, this multinozzle method has greater potential for obtaining large-area diamond film coatings. However, more engineering design and investigation are needed. The uniformity of these films and the relationship between the deposition conditions and their properties are discussed.

Crystal growth and gas ratio effect of diamond films synthesized by oxyacetylene flames

The crystal growth mechanism and the gas mixture ratio effect of diamond films synthesized using the oxyacetylene combustion flame technique have been investigated using scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The experimental results show that the gas mixture ratio of acetylene to oxygen has a great influence on the surface microstructure and the formation of diamond films. We report here new observations of two-dimensional step growth mechanism on (110) surfaces of these diamond films. Such layered steps cannot be explained by the periodic-bond-chain theory, and a possible crystal growth mechanism is proposed.