Argon-acetylene Mixtures Research Articles

Tribological properties of CrAlSiC coatings fabricated under various conditions for generating carbon plasma

There were investigated tribological properties of CrAlSiC coatings deposited by two techniques. In both techniques a plasma source of a cathode-arc discharge with Cr-Al-Si composite target served the source of Cr, Al, and Si atoms during coating deposition. A plasma source of a pulsed cathode-arc discharge with graphite cathode and a gas discharge device to generate a non-self-sustained discharge in argon-acetylene mixture have been used for generating carbon plasma in first and second techniques, correspondingly. First coating has a low coefficient of friction. Under frictional action, coating wears out uniformity without chipping. Second coating is less resistant to frictional action.

Substantially Improved Na-Ion Storage Capability by Nanostructured Organic-Inorganic Polyaniline-TiO2 Composite Electrodes.

Developing sodium (Na)-ion batteries is highly appealing because they offer the potential to be made from raw materials, which hold the promise to be less expensive, less toxic, and at the same time more abundant compared to state-of-the-art lithium (Li)-ion batteries. In this work, the Na-ion storage capability of nanostructured organic–inorganic polyaniline (PANI) titanium dioxide (TiO2) composite electrodes is studied. Self-organized, carbon-coated, and oxygen-deficient anatase TiO2–x-C nanotubes (NTs) are fabricated by a facile one-step anodic oxidation process followed by annealing at high temperatures in an argon–acetylene mixture. Subsequent electropolymerization of a thin film of PANI results in the fabrication of highly conductive and well-ordered, nanostructured organic–inorganic polyaniline-TiO2 composite electrodes. As a result, the PANI-coated TiO2–x-C NT composite electrodes exhibit higher Na storage capacities, significantly better capacity retention, advanced rate capability, and better Coulombic efficiencies compared to PANI-coated Ti metal and uncoated TiO2–x-C NTs for all current rates (C-rates) investigated.

Characterization of magnetically confined low-pressure plasmas produced by an electromagnetic field in argon-acetylene mixtures

Dust particles formation was investigated in magnetically confined low-pressure plasma produced in argon-acetylene mixtures. The plasma characteristics were measured in order to identify the species involved in the dust particles formation. Their dependence on the operating conditions including magnetic field intensity, acetylene fraction in the gas mixture and operating pressure was examined. In contrast with noble gases, in the presence of acetylene, the electron temperature increases with the magnetic field intensity, indicating additional charged particles losses in the plasma. Indeed, in these conditions, larger hydrocarbon ions are produced leading to the formation of dust particles in the plasma volume. The observed dependence of positive ion mass distribution and density and relative negative ion density on the operating parameters suggests that the dust particles are formed through different pathways, where negative and positive ions are both involved in the nucleation.

Long-term spatio-temporal evolution of the dust distribution in dusty argon rf plasmas

The 3D dust distribution in dense dust clouds confined in argon rf plasmas is measured by a computed tomography (CT) technique based on the extinction of visible light. On the one hand, clouds of micron-sized particles were created by injecting standardized plastic particles into the plasma. On the other hand, sub-micron sized dust with well-defined properties is grown in situ in an argon acetylene mixture. Once created, both kinds of dust clouds decay in the course of minutes to hours. This decay is monitored by CT measurements. It is revealed that micro-dust clouds feature a drastic change of the dust distribution due to a size reduction of the dust. Dust clouds of sub-micron particles, in contrast, show a strong variation of the overall dust density while the relative dust distribution remains nearly unchanged. The evolution of the overall dust density is subject to two effects: the loss of particles due to an imperfect confinement and the reduction of the dust size via etching.

Synthesis of amorphous hydrogenated carbon thin films by magnetized radio-frequency discharge in argon–acetylene mixture at very low gas pressure

This paper presents a characterization study of carbon thin films grown on crystalline silicon substrates using a magnetized high-frequency discharge in argon–acetylene mixture at very low pressure. Thin films with different morphological structure are obtained. Depending on the gas pressure, acetylene percentage and process time, it is possible to categorize the surface film morphology into three categories: smooth, cracked or microstructured. Moreover, when applying external magnetic field, it has been observed that depending on the substrate direction (perpendicular or parallel) to the reactor axis, it is possible to obtain different film morphologies. For specific conditions, energetic argon ions are formed which lead to film surface damaging and to their inclusion when they impinge the film surface. Chemical pathways and most likely isomers that contribute to the growth are also identified and discussed. Synthesizing materials in such low pressure conditions is of particular interest for better understanding the complex phenomena taking place in the plasma such as instabilities induced by particles and infra-red spectra of carbonaceous interstellar dust.

Diameter control of carbon nanotubes using argon–acetylene mixture and their application as IR sensor

Multi-walled carbon nanotubes (CNTs) were grown via pyrolytic chemical vapor deposition technique and explored for their infrared sensing behavior. CNT synthesis was carried out over cobalt zinc ferrite [Formula: see text] catalyst nanoparticles under different gas flow conditions to control outside diameter of the nanotubes. It was found that a progressive decrease in the carbon precursor gas (acetylene in this case) from 5:1 to 9:1 (v/v) causes reduction of average CNT diameter from 85 nm to 635 nm. Growth conditions involving higher temperatures yield nanotubes/nanofibers with outer diameter of [Formula: see text][Formula: see text]500 nm, presumably due to surface aggregation of nanoparticles or increased flux of carbonaceous species at the catalyst surface or both. Current–voltage characteristics of the nanotubes depending on the CNT diameter, revealed linear or nonlinear behavior. When incorporated as sensing layer, the sensitivity of [Formula: see text][Formula: see text]5.3 was noticed with response time of [Formula: see text][Formula: see text]4.1 s. It is believed that IR sensing characteristics of such CNT-based detectors can be further enhanced through post-synthesis purification and chemical functionalization treatments.

Spectroscopic study of hydrogen Balmer line shapes in a hollow cathode glow discharge in NH3 and Ar/NH3, Ar/CH4 and Ar/C2H2 mixtures

The results of Doppler spectroscopy of hydrogen Balmer lines emitted from a stainless steel (SS) and copper (Cu) hollow cathode (HC) low-pressure glow discharge in ammonia, as well as in argon-ammonia, argon-methane and argon-acetylene mixtures are reported. The earlier results of electron beam interactions with NH3, CH4 and C2H2 were used for analysis of Balmer line shapes in HC glow discharge.

Doppler spectroscopy of hydrogen Balmer lines in a hollow cathode glow discharge in argon–methane and argon–acetylene mixture

The results of Doppler spectroscopy of hydrogen Balmer lines emitted from a stainless steel (SS) and copper (Cu) hollow cathode (HC) low-pressure glow discharge in argon–methane and argon–acetylene mixtures are reported. The role of dissociative excitation and dissociative ionization and excitation of hydrocarbon molecules in Balmer line shape formation is studied and discussed in relation to earlier electron beam interaction experiments with CH4 and C2H2. Experimental results of excessive Doppler broadening (EDB) of Balmer lines are reported also.

Mechanical properties of copper/carbon nanocomposite films formed by microwave plasma assisted deposition techniques from argon–methane and argon–acetylene gas mixtures

Nanostructured copper/amorphous hydrogenated carbon (a-C:H) composite films have been deposited on silicon substrates by a hybrid technique combining microwave plasma-enhanced chemical vapor deposition and sputter-deposition processes from argon–methane and argon–acetylene mixtures of various compositions. The size of crystallites, ratio between sp 2 and sp 3 types of carbon bonds, hardness, friction coefficient, and wear resistance of composite films were investigated as functions of the carbon content in the films expressed by the atom number ratio C/(C + Cu). The size of crystallites decreased down to 2 nm in films having high carbon contents (60%, C/(C + Cu)). Composite films formed from Ar–C 2H 2 mixtures with a carbon content of 78% (C/(C + Cu)) exhibited relatively high hardness (6.1 GPa) and very high elastic recovery upon unloading (90%). However, the wear resistance of hard Cu/a-C:H films was very low ((5.7 ± 0.6) × 10 −6 mm 3/Nm). During the friction tests, a very low resistance to crack formation and cross-sectional propagation was observed. Cu/a-C:H films formed from Ar–CH 4 mixtures and containing 75% of carbon (C/(C + Cu)) possessed low friction coefficients (0.02–0.04) and volume wear coefficients ((0.11 ± 0.02) × 10 −6 mm 3/Nm). The intensity Raman peak ratio I D/ I G (0.71) proved to be much lower for the films having a low value of volume wear coefficient. This is the result of the presence of nanosized carbon clusters in the polymer-like matrix and copper crystallites that provides very low shear stresses during friction tests and forms nanosized wear debris.

Mechanical properties of nanostructured copper-hydrogenated amorphous carbon composite films studied by nanoindentation

Nanostructured copper/amorphous hydrogenated carbon (a-C:H) composite films approximately 500 nm in thickness have been deposited on silicon substrates by an hybrid technique combining a microwave plasma-enhanced chemical vapor deposition (PECVD) process with a sputter-deposition process from argon–acetylene mixtures and copper target. In these films, the a-C:H phase would act as a tough matrix while reinforcing nanocrystallites of copper are imbedded in the amorphous matrix. The mechanical behavior of nanocomposite films under point loading conditions was studied by nanoindentation using a Berkovich indenter. The transition from deposition of soft polymer-like to ion-hardened polymer-like a-C:H films was observed with increasing concentration of acetylene in the gas phase. The hardness of the Cu/a-C:H composite films is higher by a factor of two than that of pure a-C:H films deposited under similar conditions. The increase in hardness is probably related to the strengthening effect of copper nanocrystallites dispersed in the amorphous carbon matrix.

Mechanical properties of nanostructured copper-hydrogenated amorphous carbon composite films studied by nanoindentation

Nanostructured copper/amorphous hydrogenated carbon (a-C:H) composite films approximately 500 nm in thickness have been deposited on silicon substrates by an hybrid technique combining a microwave plasma-enhanced chemical vapor deposition (PECVD) process with a sputter-deposition process from argon–acetylene mixtures and copper target. In these films, the a-C:H phase would act as a tough matrix while reinforcing nanocrystallites of copper are imbedded in the amorphous matrix. The mechanical behavior of nanocomposite films under point loading conditions was studied by nanoindentation using a Berkovich indenter. The transition from deposition of soft polymer-like to ion-hardened polymer-like a-C:H films was observed with increasing concentration of acetylene in the gas phase. The hardness of the Cu/a-C:H composite films is higher by a factor of two than that of pure a-C:H films deposited under similar conditions. The increase in hardness is probably related to the strengthening effect of copper nanocrystallites dispersed in the amorphous carbon matrix.

Characterization and Tribological Properties of Nanostructured Copper/Carbon Composite Films Prepared by Microwave Plasma-Assisted Dual Deposition Processes

ABSTRACTNanocrystalline copper/hydrogenated amorphous carbon films have been deposited on Si substrates at the floating potential using a distributed electron cyclotron resonance microwave plasma reactor. In this deposition technique, the microwave plasma-enhanced chemical vapor deposition process of carbon from argon-methane or argon-acetylene mixtures of various compositions was associated with the sputter deposition of copper from a copper target. The total pressure was fixed at 0.13 Pa. For deposition, the substrates mounted on a water-cooled substrate holder were maintained at ambient temperature. The composition of films determined by Rutherford backscattering spectroscopy, energy recoil detection analyses and nuclear reaction analyses was investigated as a function of the gas phase composition. The structure of films was identified by X-ray diffraction (XRD) techniques and the size of copper crystallites incorporated in the amorphous carbon matrix was deduced from XRD data. The magnitude of residual stresses developed in these films was calculated from the radius of curvature of film/substrate samples determined by profilometry. The residual stress values were found to be nearly independent on the composition of films and deposition parameters.

Electron-Diffraction Evidence for Threefold Coordination in Amorphous Hydrogenated Carbon Films

An electron-diffraction analysis is presented of the structure of amorphous hydrogenated carbon prepared from a dc magnetron glow discharge in argon-acetylene mixtures. On the basis of the evidence provided by the reduced intensity function, the atomic radial distribution function, and a reconstruction of the reduced intensity function based on a graphite layer model, it is concluded that such films exhibit a threefold coordinated structure with only slight correlation in the positions of two-dimensional layers.

Pulsed Mass Spectrometric Study of Associative Ionization in Argon—Nitric Oxide and Argon—Acetylene Mixtures

Pulsed mass spectrometric studies of ArNO+ and ArC 2H 2 + ions formed by associative ionization show that even at very short times after excitation by 22−eV electrons, the predominant excited reactants are argon atoms in metastable states. Products of the specific reaction rates and the cross section for excitation into the triplet states of argon have been measured. From these results an estimate of 3 × 10 −17 cm 2 for the excitation cross section is made.

Maximization of argon-hydrocarbon Penning mixtures

Townsend's primary and secondary ionization coefficients have been measured in 0·003, 0·03, 0·3 and 3% of n-pentane, ethylene and acetylene mixed in argon for a total pressure in the range 0·5 to 500 torr and for a uniform field gap up to 1 cm. For n-pentane, a concentration of 15% was also employed. A marked Penning effect is again observed and is greatest in about 0·1% of acetylene in argon; the enhancement of Townsend's primary ionization coefficient in this mixture exceeds that previously observed in the classical rare gas mixtures. As usual, the hydrocarbons are observed to be efficient quenching agents, acetylene in this respect being the less efficient. At an optimum concentration of 0·03% for all the mixtures the sparking voltage is lowered considerably below that for pure argon, the lowering being the most - and amounting to a factor somewhat greater than 4 - in argon-acetylene mixtures.