Argon Partial Pressure Research Articles

Distribution and significance of extraneous argon in UHP eclogite (Sulu terrain, China): insight from in situ 40Ar/ 39Ar UV-laser ablation analysis

In situ 40Ar/ 39Ar UV-laser ablation analyses of garnet, omphacite, epidote, phengite, barroisite and symplectite in a sample of UHP eclogite from Qinglongshan (Sulu terrain, China) reveal extremely heterogeneous argon isotopic ratios. Results from the 220–240 Ma eclogite indicate a significant and variable extraneous argon signature that is restricted to the early-formed phengite and epidote and later-formed barroisite. Individual, compositionally zoned, phengite grains record a large variation in 40Ar/ 39Ar dates (300–1100 Ma) that are positively correlated with celadonite content. These data are consistent with retrograde chemical exchange and argon isotopic repartitioning in response to decreasing partial pressures of argon during decompression. Consistent with the observation of atmospheric argon ratios in garnet, omphacite and symplectite these data support an interpretation that the extraneous Ar was incorporated early in the crystallization history of the eclogite, and not from a late infiltrating fluid. The ultimate source of the extraneous argon remains speculative, however on the basis of supporting stable oxygen and hydrogen isotope data from this locality, which support a closed isotopic system, it is inferred to have been inherited from the protolith of the UHP eclogite.

Microstructural investigations in Cf-SiC composites in as-sintered state and after creep experiments

The high interest in ceramic matrix composites during the last decade has led to a considerable number of studies devoted to their thermomechanical properties and damage processes. Despite their sensitivity to oxygen partial pressure, carbon fibres appear to possess higher stability and better mechanical properties if they are treated under protective atmospheres than other ceramic fibres (especially classical silicon carbide fibres). The aim of this investigation is to characterize at the nanoscale the main microstructural parameters of Cf-SiC composites provided by the SEP (Division of SNECMA, Bordeaux, France). This material was fabricated from a 2.5D preform made of high strength polyacrylonitrile (PAN)-based carbon fibres densified according to the chemical vapour infiltration process. A pyrocarbon (PyC) interphase was deposited on the fibre prior to the beta-SiC matrix infiltration. A careful high resolution electron microscopy (HREM) microstructural investigation focused on the fibre microstructure as well as on the different interfaces in the material: pyrocarbon/fibre and matrix/pyrocarbon interfaces. All these observations have been realized in longitudinal and transverse sections of the specimen. These observations are found in good agreement with Guigon's model for high strength ex-PAN carbon fibres. The PyC interphase texture was strongly anisotropic at the fibre/interphase and interphase/matrix interfaces over a mean thickness of 8-15 nm. Tensile creep tests were performed under partial pressure of argon between 1273 and 1673 K for stress levels ranging from 110 to 220 MPa. Scanning electron microscopy and high resolution electron microscopy were used to study the microstructural modifications inside the fibres and at the different interfaces. A discussion of the possible creep mechanisms based on the microstructural investigation and the creep results is presented.

Parameter optimisation of Ti-DLC coatings using statistically based methods

The influence of process parameters on the mechanical properties of magnetron-sputtered Ti-C:H films was investigated using fractional factorial experimental design. The parameters studied included substrate bias voltage, acetylene flow rate, and argon and nitrogen partial pressures. The results indicated that bias voltages in the range −20 to −60 V had little or no influence on the mechanical properties. The acetylene flow rate, which controlled the titanium content in the Ti-C:H layers, exhibited the most significant effect. An explanation based on the relationship between relative film thickness and critical applied loads is provided for the coating failure mechanisms.

Effect of partial pressure on the internal stress and the crystallographic structure of r.f. reactive sputtered Ti-N films

The influence of nitrogen partial pressure ( P N2) and argon partial pressure ( P Ar) on internal stress, crystallographic structure, and resistivity have been investigated for reactively sputtered Ti-N films in order to get some insight into the influence of deposition parameters. Ti-N films were deposited onto glass substrates by r.f. reactive magnetron sputtering using a plasma emission monitoring control system. The r.f. power applied was kept constant at 300 W during deposition, and the substrate temperature was room temperature. When P Ar is 0.4 Pa and P N2 is 1 × 10 −3 Pa or higher, films deposited become single phase of TiN, although preferential orientations of films change with P N2. Ti-N films deposited at a P N2 of 2–6 × 10 −3 Pa become a gold color, and the resistivity becomes minimum. The internal stress of deposited Ti-N films changes as a function of both argon and nitrogen partial pressure, and films deposited at a low P Ar tend to have high compressive stress. The internal stress is also related to preferred orientation of films. Films having the (001) preferential orientation show higher compressive stress than those having the (111) preferred orientation.

Multiscale investigation of the creep behaviour of a 2.5D Cf-SiC composition

This paper deals with some results on the creep behaviour of a 2.5D Cf-SiC composite. This material fabricated by CVI was tested in tension under an argon partial pressure for temperatures ranging from 1273 to 1673 K and stresses between 110 and 220 MPa. Results regarding creep curves (strain-time) and strain rate-time curves tend to confirm the existence of a secondary stage. Damage-stress and damage-time curves are also presented. The limits of the Dorn′s formalism are evidenced as well as the occurrence of a damage process leading to a so-called damage-creep mechanism. In order to explain this macroscopic creep behaviour of the composite, investigations at the mesoscopic, microscopic and nanoscopic scales were necessary. Five modes of matrix microcracking are observed together with different pull-out features regarding the extracted fibre surface. The damage accumulation via matrix microcracking appears to be a time dependent mechanism. Two modes of interfacial sliding are evidenced: at 1473 K and 220 MPa, the pyrocarbon (PyC) interphase is fractured leading to debonding between carbon layers, while at 1673 K, there is a loss of anisotropy of the PyC layer close to the matrix and, thus, an interfacial sliding appearing as a viscous flow. To elucidate the role of the carbon fibres, a nanoscale study via HREM has been conducted. An increase of the mean diameters of the basic structural units (BSUs) and of the areas of local molecular orientation (LMOs) within the fibres has been observed when increasing temperature under 220 MPa. In fact, these changes do not contribute to the macroscopic strain. Therefore, this restructuration effect has been called “nanocreep” of the carbon fibre as it appears to have a negligible contribution to the macroscopic creep behaviour of the 2.5D Cf-SiC composite.

TiN reactive sputter deposition studied as a function of the pumping speed

TiN is an extremely important barrier material in present day integrated circuits. The most common deposition method is reactive sputter deposition from a titanium target in a argon –nitrogen gas mixture. In reactive sputter deposition of TiN a fraction of the nitrogen feed gas is incorporated in the film. This consumption might lead to non-uniform deposition for large wafersizes and/or low pumping speeds. For relatively low pumping speeds, or a large fraction of incorporated nitrogen, it was expected that the film uniformity over the wafer would deteriorate. TiN was deposited at fixed partial pressures of argon and nitrogen. The pumping speed was varied over one order of magnitude. Even at the lowest pumping speed tested, i.e. at 84% consumption of the supplied nitrogen, the uniformity did not deteriorate. The process proved to be insensitive to the pumping speed. We propose that the explanation of this insensitivity is due to the high reactivity of Ti atoms on the target to N atoms, while the chance for additional nitrogen atoms to be adsorbed at the nitrided target is very small. The target is operated in the poisoned mode which means that the target surface consists of TiN. Calculations showed that the number of N atoms striking the target is about 80 times larger than the flux of Ti atoms sputtered from the target. The sticking coefficient of N2 on Ti is high, therefore the chance for the target to recover its TiN surface after a nitrogen atom or a TiN fragment is sputtered off is high. On the other hand the sticking coefficient of nitrogen on TiN is very low. An increase in partial pressure of nitrogen will not result in extra ‘adsorbed nitrogen’ on the target. Therefore the ratio of titanium to nitrogen atoms removed from the target by the ion bombardment is insensitive to the partial pressure of the nitrogen and hence to the pumping speed.

Pulmonary blood flow measured by inspiratory inert gas concentration forcing oscillations

The aim of this study was to discover if the forced inspired inert gas sinewave technique could be used to measure pulmonary blood flow, using nitrous oxide as the indicator gas, following inotropic stimulation of the heart by dobutamine, in the presence of a constant alveolar ventilation. Cardiac output (range 1–4.5 L min −1) was measured in six dogs by thermodilution and by calculation from the sinusoidal expired partial pressures of argon and nitrous oxide using: (i) analytical equations and a conventional continuous ventilation three-compartment lung model, which did not include recirculation; and (ii) a digital simulation tidal ventilation lung model (Gavaghan and Hahn, 1996. Respir. Physiol. 106, 209–221) which was adapted to include nitrous oxide mixed-venous recirculation from a combined single viscera compartment. The continuous ventilation model calculations always underestimated thermodilution cardiac output, with the bias error increasing to almost −1 L min −1 at the longest forcing periods, 4–5 min. In contrast, the tidal ventilation model calculations were in close agreement to thermodilution cardiac output, with biases of −0.04 and −0.26 L min −1 at forcing periods of 2 and 3 min, respectively.

Sonoluminescence stability for gas saturations down to 0.01 Torr

Water solutions with very small argon partial pressures were investigated. The experiments were performed in a sealed cell. The argon was used in both a pure form and in mixtures with other gases. A regime of stable sonoluminescence was seen at lower driving pressures for argon partial pressures down to 0.01 Torr. Mie scattering, light pulse measurements, and visual observations over tens of thousands of cycles were used to determine if the bubble was stable. As the drive pressure was increased, the bubble moved into a slow time scale instability on the order of several seconds which sometimes caused break up. These experiments are discussed and compared to other published data involving gas mixtures at saturation levels up to 1 atm.

Simple method for the control of substrate ion fluxes using an unbalanced magnetron

Substrate ion fluxes from unbalanced magnetron sources are generally controlled by the use of additional magnetic fields. These methods are not always suitable for differentially controlling the ionic flux from multiple sources. We report here a simple method suitable for attaining such control that can be easily adapted to most unbalanced magnetron systems. The flux leakage from an unbalanced magnetron is controlled by the use of a mild steel keeper with a detachable mild steel annulus. The annulus redirects the unbalanced field lines through the keeper to the rear poles of the magnetron. The flux leakage is thus controlled by varying the thickness of the annulus. Ion saturation currents measured at the substrate, with and without a 0.9 mm thick mild steel annulus, were found to differ by a factor of approximately 3 at an argon partial pressure of 1 mTorr. Furthermore we demonstrate that the changes in ion current density are achieved without alteration to the magnetron operating parameters.

Investigation of the mechanisms of magnetron sputtering of aluminium with mixtures of argon and nitrogen in the partially reactive mode

Abstract This paper discusses the DC magnetron sputtering of aluminium targets with argon–nitrogen gas mixtures. To elucidate the mechanisms dominating the incorporation of nitrogen in the resulting AlN x films, the dependences of nitrogen consumption and fractional target coverage were investigated in the partially reactive mode. The experiments show that the nitrogen consumption is proportional both to the discharge current and to the ratio of nitrogen partial pressure to argon partial pressure. The target coverage is also linearly dependent on this ratio. These results can be interpreted as an effect of intermediate target ion plating: only the amount of nitrogen in the films which has been previously plated on the target surface is incorporated.

The spectroscopy of the plasma plume induced during laser welding of stainless steel and titanium

Results of spectroscopic measurements of laser-induced plasmas under welding conditions are presented and discussed. The metals welded were stainless steel and titanium. It is shown that the intensities of the atomic lines of metals give information on the peripheral region of the plasma plume. The plasma-plume parameters are found to be similar for these two metals. The ratios of intensities of the ionic and atomic lines of the metals give maximum temperatures of about 11 000 K. These temperatures are several thousand kelvins higher than the temperatures determined from the atomic lines. The plasma plumes over the keyhole consist of metal vapours diluted by argon used as the shielding gas. The electron densities determined from the Stark broadening of the argon lines are about . The average partial pressure of the metal vapours is found to be 0.2 atm, the argon partial pressure 0.6 atm and the remaining pressure is due to electrons. Equilibrium conditions have been examined and it has been found that the plasma is in local thermal equilibrium.

The effects of environment and internal oxygen on fatigue crack propagation in ti-6al-4v

The role of environmental and internal oxygen on fatigue crack propagation is assessed for the titanium alloy Ti-6Al-4V at laboratory temperature. Growth rates for part through corner cracks are demonstrated to be highly dependent on the amount of oxygen present. Compared to data for conventional plate material at atmospheric conditions, tests conducted under a vacuum of 10 −6 torr illustrate a marked reduction in the rates of growth for the facet dominated phase at low values of ΔK. Intermediate vacuum levels and partial pressures of argon or hydrogen lead to growth rates that are similar to or slightly lower than the conventional atmospheric baseline. Significant growth rate accelerations are observed, however, for 6/4 material containing internal oxygen concentrations in excess of the standard 1700–2300 ppm. This acceleration is enhanced by the application of a high load ratio, R = 0.5. The implications with respect to current ideas on environmental interactions are discussed.

Plasma conditions for the deposition of wear-resistant carbon-coatings

The properties of sputter and microwave-ECR plasmas have been investigated with a plasma emission monitor (PEM) in the range between 280 and 820 run with various resolutions. Additional Langmuir probe measurements of the sputter plasma were performed to determine the spatial variation of electron density and temperature. Using helium as an additional measuring gas, the electron temperature has been determined by comparing the intensities of an argon and a helium emission line. The concentration of atomic hydrogen and CH radicals can be determined by actinometry. A comparison between the two types of plasmas shows similar electron temperature dependencies on the plasma power, the argon partial pressure and the acetylene partial pressure. The electron temperatures determined from PEM and Langmuir probe measurements correlate very well. When the microwave ECR plasma is used at the same time as the sputter plasma the electron temperature in the sputter plasma is reduced because of the charged particle current flowing out of the ECR plasma. The electron temperature in the ECR plasma varies only slightly when the sputter plasma is switched on but the concentration of atomic hydrogen increases because of the additional conversion of the acetylene on the target surface.

Influence of the deposition parameters on boron nitride growth mechanisms in a hollow cathode arc evaporation device

Boron nitride (BN) layers were deposited in a hollow cathode arc evaporation device (HCAED). The cubic-BN (c-BN) content was determined by Fourier transform infrared spectroscopy. The film thickness was deduced by reflectance measurements in the visible range. The c-BN content and growth rates were measured in dependence on substrate temperature, substrate bias voltage, nitrogen and argon partial pressures and substrate materials (Si, Al, high-speed steel). Calculated flux rates of neutrals and ions to the substrate are used to derive sticking coefficients of boron. On silicon we could identify parameter ranges were nearly pure c-BN layers were deposited. Film thickness of 1.5 μm could be reached on silicon without peeling off.

Characterization of an argon-hydrogen microwave discharge used as an atomic hydrogen source. Effect of hydrogen dilution on the atomic hydrogen production

This work is devoted to the study of an argon-hydrogen microwave plasma used as an atomic hydrogen source. Our attention has focused on the effect of the hydrogen dilution in argon on atomic hydrogen production. Diagnostics are performed either in the discharge or in the post-discharge using emission spectroscopy (actinometry) and mass spectrometry. The agreement between actinometry and mass spectrometry diagnostics proves that actinometry on the Ha(656.3 nm) and Hβ(486.1 nm) hydrogen Balmer lines can be used to measure the relative atomic hydrogen density within the microwave discharge. Results show that the atomic hydrogen density is maximum for a gas mixture corresponding to the partial pressure ratioP H 2/P Ar range between 1.5 and 2. The variation of atomic hydrogen density can be explained by a change of the dominant reactive mechanisms. At a low hydrogen partial pressure the dominant processes are the charge transfers with recombinations between Ar+ and H2 which lead to ArH+ and H 2 + ion formation. Both ions are dissociated in dissociative electron attachment processes. At a low argon partial pressure the electron temperature and the electron density decrease with increasing partial pressure ratio. The dominant mechanisms become direct reactions between charged particles (e, H+, H 2 + , and H 3 + ) or excited species H(n=2) with H2 producing H atoms.

Study of the growth mechanisms of chromium nitride films deposited by vacuum ARC evaporation

Chromium nitride films have been deposited using the vacuum arc evaporation technique. The influence of the main deposition parameters (nitrogen pressure p N 2 , substrate temperature T s, substrate bias voltage V s and argon partial pressure p Ar) on the structural and mechanical properties of the coatings has been investigated. It has been found that the nitrogen pressure determines the phase composition in the layers, while T s, V s and p Ar have more direct effects on the texture of the films. The mechanical properties which depend on the composition but also on the structure and the morphology of the coatings, exhibit a strong dependence on all the deposition parameters.

Pulsed laser deposition of high-Tc superconducting YBa2Cu3Ox thin films in Ar/O2 atmosphere

Electrical and structural properties of superconducting YBa2Cu3Ox thin films, obtained with pulsed laser deposition in an Ar/O2 mixture at different oxygen partial pressures and constant total pressure, were studied. NdGaO3 (110) and LaAlO3 (001) substrates were used. The crystal quality of the films was found to correlate to the contents of inclusions with the axis oriented normal to the substrate plane. The increase of argon partial pressure resulted in decrease of particle density on the film surface to less than 106 cm−2, accompanied by an increase of a-oriented phase content and a rapid fall of the critical temperature from 91 K to 80 K

Behaviour of TiAlN coatings for tools applied in the thermoplastic moulding of inorganic glasses

Metal nitride coatings are of particular interest for the improvement of the service behaviour of tools for the thermoplastic moulding of optical components to be formed from inorganic glasses. Major problems in this application concern the wear of the coatings due to interactions with the hot glass and particularly the damage by stresses induced in the coatings by temperature varying from room temperature to the service temperature ranging up to 800 K and even higher. In the present study coatings of the TiAlN system were deposited on steel, fused silica and silicon substrates in reactive sputtering processes by variation of the process parameters such as total pressure, substrate temperature, discharge power and distance between target and substrate. The film composition was systematically varied by applying different argon and nitrogen partial pressures during the deposition. The paper describes the effects of the deposition parameters and film composition on the residual stresses and the service behaviour of coatings. The coatings were investigated by optical and mechanical methods. By appropriate selection of the deposition parameters the film properties and the service behaviour of forming tools could be improved. Results on the service behaviour are discussed on the basis of glass-forming experiments at high temperatures. According to the achieved results the nitrogen content y in TiAlN coatings was increased from y=0.75 to y=2.2 and the compressive film stress from 400 to 1500 MPa by increasing the number of collisions of sputtered TiAl species with nitrogen n N 2 between 0.2 and 1.2 in d.c. triode sputtering at 0.05 Pa total gas pressure. In r.f. magnetron sputtering at 1.3 Pa lower stresses between +200 and −200 MPa but nitrogen contents in the same ranges as in the d.c. process were obtained if the collision number n N 2 was maintained in the same range. Coatings with moderate compressive stresses and high nitrogen content showed the best behaviour in glass-forming experiments at high temperatures.

Formation of argon clusters by homogeneous nucleation in supersonic shock tube flow

The formation of argon clusters by homogeneous nucleation of pure argon diluted in helium was investigated in the supersonic outflow of a shock tube, where the clusters were detected by laser light scattering from the particles in supersaturated states. The thermodynamic states for the onset of homogeneous nucleation varied between 48 and 85 K with corresponding argon partial pressures in the range 2–850 Torr. Values of adiabatic supercooling with respect to the argon phase equilibrium ranged between 3 and 10 K. The experiments are in agreement with previous investigations in subsonic shock tube and supersonic Ludwieg tube expansions but disagree with previous investigations in steady supersonic nozzle expansions. It is possible to explain qualitatively the observed differences in argon nucleation behavior on the basis of a thermodynamic and kinetic concept independent of the basic assumptions of existing nucleation theories.

The influence of microstructure on X-ray-induced degradation of dark conductivity of a-Si:H layers

X-ray-induced degradation of dark conductivity at 293 K characterized by the relation between the values before and after the exposure S was investigated in magnetron-sputtered a-Si:H layers. A variation in the incorporation of hydrogen in these layers described by the relation of the integrals of the IR absorption peaks at 2000 cm-1 and 2090 cm-1 was carried out by a deposition of the layers at various substrate temperatures and argon partial pressures. We found a direct correlation between the hydrogenated void fraction R and the degradation factor S and an influence of the initial dangling bond density measured with the constant-photocurrent method (CPM) on the degradation factor. Some mechanisms of defect generation are discussed as sources of the X-ray-induced degradation behaviour of the dark conductivity.