Pure Sulfur Hexafluoride Research Articles

Measurements of the ( p, ρ, T) relation of ethylene, ethane, and sulphur hexafluoride in the temperature range from 235 K to 520 K at pressures up to 30 MPa using an accurate single-sinker densimeter

Comprehensive ( p, ρ, T) measurements on pure ethylene (83 values), pure ethane (168 values), and pure sulphur hexafluoride (220 values) have been carried out in the homogeneous gas and liquid phases for temperatures from 235 K to 520 K at pressures up to 30 MPa. The measurements were performed by means of an accurate single-sinker densimeter based on the Archimedes’ buoyancy principle. The total uncertainty of the measurements in density ρ was estimated to be ±(0.02 to 0.025)%. The measurements have been compared with results of other experimentalists and with values calculated from current equations of state.

Measurement and correlation of the (p, ρ, T) relation of sulphur hexafluoride (SF 6). I. The homogeneous gas and liquid region in the temperature range from 225 K to 340 K at pressures up to 12 MPa

Comprehensive ( p, ρ, T) measurements on pure sulphur hexafluoride have been carried out in the single-phase region (609 values) and along the entire (vapour + liquid) coexistence curve (95 values). The results reported in this first paper cover the homogeneous gas and liquid region in the temperature range from 225 K to 340 K at pressures up to 12 MPa. The total uncertainty of the measurements in density is ⩽±(0.015 to 0.023) per cent with the exception of the critical region for temperatures from 316 K to 324 K ( Tc= 318.723 K) at densities between 450kg · m−3and 1000kg · m−3( ρc= 742.26 kg·m−3), where the total uncertainty in pressure is⩽±(0.007 to 0.011) per cent. Values for the second and third virial coefficients have been determined from the measurements in the homogeneous gas region of sulphur hexafluoride. The experimental results have been compared with the results of other workers.

Measurement and correlation of the ( p, ρ, T) relation of sulphur hexafluoride (SF 6). II. Saturated-liquid and saturated-vapour densities and vapour pressures along the entire coexistence curve

Comprehensive and accurate measurements of the saturated-liquid and saturated-vapour densities together with the vapour pressure of pure sulphur hexafluoride were carried out from the temperature T= 224 K (triple-point temperature Tt= 223.555 K) to 0.033 K below the critical temperature ( Tc= 318.723 K). Typical values of the total uncertainties of the measurements are: ⩽±0.01 percent for the vapour pressures,⩽±0.015 percent for the saturated-liquid densities, and⩽±0.016 percent for the saturated-vapour densities. The values for the critical density and the critical pressure ( ρc= 742.26 kg · m−3, pc= 3.7550 MPa) and the isothermal compressibilities in the critical region close to the phase boundary have also been determined from these measurements. Comparisons with experimental results of previous workers are presented. Using the new values of this work, new correlation equations for the vapour pressure, the saturated-liquid density, and the saturated-vapour density have been established.

Air sampling at the chest and ear as representative of the breathing zone.

Tracer gas concentrations were measured on a 60%-sized mannequin holding a pure sulfur hexafluoride source in its hands at waist height while it stood in a wind tunnel. Samplers were placed at the mannequin's mouth, in front of the ear, and at three chest locations at lapel level. Simultaneous 15-min time-weighted average samples were taken by drawing air into different sampling bags with sampling pumps. For the factorial study design, test conditions included cross-draft velocities of 10, 22, 47, and 80 ft/min; three mannequin orientations (facing to, side to, and back to cross-draft), and rotating speed through an 80 degrees arc (fast, slow, and no movement). Each study condition was tested twice. Concentrations at all sampling locations when the mannequin faced to the front and side were less than a tenth of the levels measured at the nose (Cnose) when the mannequin faced downstream. Higher velocities significantly increased concentration at the Back orientation and generally reduced it at the Side and Facing orientations. Concentrations at the nose were different from concentrations at other sites. For 34 of 36 samples the mean chest concentration (Cchest,) was higher than the Cnose (geometric mean three times higher). The ratio of ear (Cear) and Cnose varied with orientation. At the Back orientation, Cear, was lower than Cnose, whereas Cear was higher than Cnose at the Side and Facing to flow orientations. Velocity affected the ratios of concentrations. At the Back orientation, the chest sampler provided lower overestimates of Cnose, at higher velocities than at lower values. Mannequin movement, done only at the Back orientation, proved important only for the ear location. Results showed significant and substantial differences between concentrations at the nose and lapel. However, these findings should be interpreted with caution because a very dense tracer gas and an unheated, nonbreathing mannequin were used. In more realistic conditions, the findings probably would show far smaller differences in concentrations at different sampling sites.

Heat of Adsorption of Pure Sulfur Hexafluoride on Micro-Mesoporous Adsorbents

The isotherms and the isosteric heats of adsorption of pure SF6 were measured on two microporous zeolites (NaX and Silicalite), one mesoporous alumina, and two activated carbons (BPL and PCB) at 305 K. The adsorption isotherms were Type I by Brunauer classification. The PCB carbon adsorbed SF6 most strongly and the alumina adsorbed SF6 most weakly. The adsorption of SF6 on the other three materials were comparable in the low pressure region despite their drastic differences in the physicochemical properties. The heat of adsorption of SF6 on the silicalite and the alumina remained practically constant over a large range of coverage. The heat of adsorption of SF6 increased with increasing adsorbate loading on the NaX zeolite in the high coverage region. The heat of adsorption of SF6 on the activated carbons decreased with increasing adsorbate loading before leveling off in the high coverage region.

HISTOPATHOLOGIC ABNORMALITIES IN RABBIT RETINA AFTER INTRAVITREOUS INJECTION OF EXPANSIVE GASES AND AIR

Purpose: To evaluate histopathologic retinal changes in rabbit eyes after injection of pure perfluoropropane (C3F8) gas, pure sulfur hexafluoride (SF6) gas, or air into the vitreous cavity. Methods: Air, C3F8 gas, or SF6 gas (0.4 mL each) were injected into rabbit vitreous cavities. Two, 4, and 6 weeks later, light and electron microscopic examinations were conducted, and the immunohistochemical localization of glutamate in the retina was studied. Noninjected eyes served as controls. Results: At all time points, thinning or disappearance of the outer plexiform layer in the superior retina in eyes that received C3F8 gas was found; the inferior retina was the same as in controls. In eyes that received SF6 gas or air, light and electron microscopy showed that the superior and inferior retina were the same as in controls at all time points. Immunohistochemical examination showed abnormal glutamate distribution of the superior retina in eyes injected with C3F8 gas, SF6 gas, or air. However, glutamate distribution was the same as in controls in the inferior retina in eyes injected with C3F8 gas, SF6 gas, or air. Conclusions: Retinal tamponade using intraocular gases induces histopathologic retinal changes in the superior retina of the rabbit eye, where the gases are in continuous contact with the eye.

Histopathologic abnormalities in rabbit retina after intravitreous injection of expansive gases and air.

To evaluate histopathologic retinal changes in rabbit eyes after injection of pure perfluoropropane (C3F8) gas, pure sulfur hexafluoride (SF6) gas, or air into the vitreous cavity. Air, C3F8 gas, or SF6 gas (0.4 mL each) were injected into rabbit vitreous cavities. Two, 4, and 6 weeks later, light and electron microscopic examinations were conducted, and the immunohistochemical localization of glutamate in the retina was studied. Noninjected eyes served as controls. At all time points, thinning or disappearance of the outer plexiform layer in the superior retina in eyes that received C3F8 gas was found; the inferior retina was the same as in controls. In eyes that received SF6 gas or air, light and electron microscopy showed that the superior and inferior retina were the same as in controls at all time points. Immunohistochemical examination showed abnormal glutamate distribution of the superior retina in eyes injected with C3F8 gas, SF6 gas, or air. However, glutamate distribution was the same as in controls in the inferior retina in eyes injected with C3F8 gas, SF6 gas, or air. Retinal tamponade using intraocular gases induces histopathologic retinal changes in the superior retina of the rabbit eye, where the gases are in continuous contact with the eye.

Process and equipment simulation of dry silicon etching in the absence of ion bombardment

The dependence of the etch rate uniformity across the wafer on the reactor design and various process parameters was investigated for the reactive ion etching (RIE) of silicon using pure sulphur hexafluoride (SF 6). The experiments were carried out in two different single wafer reactors without ion bombardment to determine the chemical component of the etch rate. The influence of pressure, gas flow, rf power, and loading on the radial course of the etch rate was measured and compared with the respective results of numerical simulation. The commercially available PHOENICS-CVD simulation tool was used for the solution of the fluid dynamic transport equations after some adaptations for its application to etching. A simple chemical model is proposed for the description of gas phase and surface plasma reactions, respectively. The values of the reaction rate parameters were fitted from the experimental data. The simulation represents the main experimental trends and can be applied to process and equipment optimization.

The Nearly Classical Behavior of a Pure Fluid on the Critical Isochore Very Near the Critical Point Under the Influence of Gravity

Comprehensive measurements of the isothermal compressibility along the critical isochore in the critical region of pure sulfur hexafluoride (SF6) and pure carbon dioxide (CO2) were carried out. All measurements were performed with a multicell apparatus, especially designed for pρT measurements in the critical region. The height of the measuring cells was either 30 or 11 mm. Independent of the cell height, we found for both fluids nearly “classical” values for the critical exponent γ in the limiting approach to the critical point. However, at a certain distance from the critical point {(T − T c) ≈ 90 mK or τ ≈ 2.82 × 10−4 for SF6 and (T − T c) ≈ 55 mK or τ ≈ 1.81 × 10−4 for CO2}, we observed a transition to values of the critical exponents which nearly meet the predictions of the renormalization-group theory. Since in the fitting range (T − T c ≥ 1 mK) the correlation length (ξ ≤ 0.5 μm) is very much smaller than the geometrical dimensions of the measuring cells, we conclude that the reason for the different behavior is an explicit gravity effect governing the inner critical region. The two different loci of the transition points for sulfur hexafluoride and carbon dioxide can be attributed to the different gravity impact on the fluid corresponding to the different critical densities of the two substances.

High pressure investigations of positive ion/molecule reactions in pure sulfur hexafluoride and in a mixture of sulfur hexafluoride and argon

The results of investigations of positive ion/molecule reactions in pure sulfur hexafluoride and in a mixture of sulfur hexafluoride with argon are presented. The essential purpose of this paper is to examine the mechanisms by which positive ions are formed in SF 6 and in mixtures of SF 6 and argon. Relative values of the ion currents have been determind as a function of gas pressure in the ion source, and of the concentration of SF 6 in the gaseous mixture with argon. Measurements were performed by use of a mass spectrometer with a high pressure ion source constructed by the authors. The reaction rate constant for SF 5 + ions in pure sulfur hexafluoride was determined.

Measurements of the (pressure, density, temperature) relation of sulphur hexafluoride (SF 6) in the homogeneous region at temperatures from 321.15 K to 333.15 K and at pressures up to 8 MPa and on the coexistence curve at temperatures from 288.15 K to 315.15 K

This paper presents accurate (p, ρ, T) measurements on pure sulphur hexafluoride (SF6) on four supercritical isotherms (321.15 K, 323.15 K, 328.15 K, and 333.15 K) at pressures from 0.5 MPa to 8 MPa. The measurements have been carried out to determine reference values for a new apparatus specially developed for (p, ρ, T) measurements in the immediate vicinity of the critical point. The total uncertainty of the measurements is

Bipolar Ion and Electron Diffusion Charging of Aerosol Particles in high purity argon and nitrogen

AbstractThe bipolar diffusion charging process is studied theoretically for aerosol particles in high purity argon and nitrogen. The Fuchs theory is extended by the incorporation of the free electron charging of the aerosol particles. The ion parameters for positive and negative ions are assumed to be identical. The influence of the free electrons explains the differences between the mean mobility and mean mass of negative and positive ions. The ratio of the electron number concentration to the number concentration of negative ions is used to fit the curves, calculated by the extended model, to the experimentally determined bipolar charge distribution in argon and nitrogen. The extended Fuchs model was found to be rather insensitive to variations in the mobility and mass compared with the model with four different ion parameters. Further experimental studies of the bipolar charge distribution in a gas mixture of pure nitrogen and sulfur hexafluoride, SF6, indicate the importance of the free electrons in the bipolar diffusion charging process.

Vapour—liquid equilibrium in the sulphur hexafluoride — n-pentane system at high pressure

Vapour pressure of pure sulphur hexafluoride was measured in the temperature range from 290 K to the critical point. Measurements of binary vapour—liquid equilibrium data were carried out isothermally at temperatures 313.15 K, 323.15 K, and 333.15 K and pressures from 2 MPA up to near the critical pressure (4 MPa maximum). A part of the vapour—liquid critical line was determined for mole fraction of sulphur hexafluoride higher than 0.7, which means the temperature range from 319 to 340 K and the pressure range from 3.7 to 4.2 MPa.

The Application of SF6 in the Geochemical Research

For mass spectrometric measurements of δ31S, pure sulphur hexafluoride was prepared quantitatively from different mineral sulphides by the reaction with elemental fluorine under pressure. The results of δ31S measurements on SF6 samples were confirmed by comparison of δ31S values with the classical method leading to SO2. Numerous mass spectrometric measurements of SF6 and SO2 with regard to the experimental conditions of the synthesis, the influence of background, memory effect, and adsorption were made. The measurements of small isotopic variations of sulphur with SF6 has advantages in comparison to the SO2 technique. The method described can be successfully used for routine work.