Solubility Of Helium Research Articles

Grain-boundary diffusion and solubility of helium in submicrocrystalline palladium

The diffusion and solubility of helium in palladium with a submicrocrystalline structure are investigated by thermal desorption of helium from He-saturated specimens at temperatures T = 293–508 K and saturation pressures P = 0.1–35 MPa. As the saturation pressure rises, the effective diffusion coefficient increases, exhibits a plateau, and then decreases to its initial value. Along with the four plateaus discovered earlier, the solubility versus saturation pressure dependence in the range 25.5–35.0 MPa demonstrates a fifth plateau, where the solubility is as high as (3.0 ± 0.4) × 1017 cm−3. It is shown that the helium diffuses along grain boundaries, at which clusters (traps) consisting of eight to ten vacancies are localized, and dissolves in these clusters. The high value of Ceff in the fifth plateau is explained by pairwise merging of adjacent vacancy clusters. From the Deff(P) dependences, the vacancy clusters concentration is estimated as C* = 2.32 × 1016 cm−3. Within the experimental error, this value coincides with that obtained from the solubility data. Calculations of the energy of helium-defect interaction in submicrocrystalline Pd that are made using the molecular dynamics method support the experimental results.

Inert gas solubility in binary germania–silica glasses

Helium and neon solubility have been measured in vitreous silica, vitreous germania, and in a series of binary GeO2–SiO2 glasses. Measurements were made over a broad temperature range using a saturation-outgassing method. The enthalpy of solution of these gases is smaller for vitreous germania than for vitreous silica. Inert gas solubility decreases rapidly as silica is initially replaced by germania in the network, with a more gradual decrease in solubility with continued reduction in silica content. Solubility measurements at varying pressures establish that inert gas solubility in vitreous germania obeys Henry’s Law up to 1atm of gas pressure, as has already been established for vitreous silica. Additional helium solubility and diffusivity measurements were made using the permeation method at temperatures below 300°C. Helium diffusivity also decreases as silica is replaced by germania, with an approximately linear dependence on composition. The activation energy for diffusion increases as the germania concentration increases. Results of this study are attributed to changes in interstice size and/or distribution as a function of glass composition and experimental temperature.

The influence of defects in the crystal structure on helium diffusion in quartz

The solubility and diffusion of helium in quartz crystals are investigated as functions of the distribution and density of structural defects. The types of defects in the crystals are identified and their distribution over growth sectors is determined by x-ray diffraction topography and phase radiography with a synchrotron radiation source. The effective solubility and effective diffusion coefficients for helium in quartz are estimated from the experimental data on the amount of helium extracted from samples with different contents of defects. It is revealed that the effective diffusion coefficient of helium depends on the number of dislocations.

Application of holographic interferometry for determining the solubility of gases in liquids

The effect of a gas dissolved in a liquid on the variation of the refractive index of the compressed mixture was studied. The compression process was monitored with the aid of a holographic interferometer. The sensitivity of this method allows the compressibility of water and the solubility of helium and nitrogen to be studied at pressures below 4 atm. A procedure for obtaining qualitative and quantitative data on the solubility of gases in liquids is proposed.

Mass-spectroscopic study of the diffusion and solubility of helium in submicrocrystalline palladium

By the method of helium thermal desorption from submicrocrystalline palladium presaturated in the gaseous phase, the diffusion coefficient Deff and solubility coefficient Ceff of helium are measured in the range P=0–3 MPa and T=293–508 K. The pressure dependence of Ceff flattens at high pressures. At low saturation pressures, the temperature dependences of the diffusion and solubility coefficients may be divided into (1) high-temperature (400–508 K) and (2) low-temperature (293–400 K) ranges described by the exponentials D1, 2=D0exp (−E1, 2D/kT) and C1, 2=C0exp (−E1, 2S/kT). The energies of diffusion activation are E2D=0.0036±0.0015 eV and E1D=0.33±0.03 eV, and the solution energies are E2S=−0.025±0.008 eV and E1S=0.086±0.008 eV in the low-and high-temperature ranges, respectively. Mechanisms behind the diffusion and solution of helium are discussed.

Hyperpolarized Helium3 Encapsulated in Microbubbles: A New Class of Blood Pool MRI Contrast Agent

A novel blood pool agent, based on hyperpolarized helium3 (HP 3He), was investigated for tissue perfusion using MRI. The results are reported in this paper. Thanks to the considerable polarization value obtained by optical pumping process, HP 3He has already demonstrated a great potential for anatomical and functional lung ventilation studies (1,2). In order to benefit from this large polarization and NMR signal advantages, we have studied the feasibility of this new contrast agent for perfusion imaging. To overcome the problem of the low helium solubility in blood, methods based on helium transportation using carrier agents have been investigated (3). In our study, a phospholipid-based substrate has been developed for helium encapsulation. Injections of 3m-diameter microbubble solutions have been used for in vivo intravascular imaging. In this work, the lung parenchyma perfusion imaging (4) as well as imaging of the coronary arteries (5) and myocardium perfusion are investigated.

New Data on the Solubility of Inert Gases in Liquid Alkali Metals at High Temperature

The solubility of helium, neon, argon, krypton, and xenon in molten lithium, sodium, potassium, rubidium, and cesium is calculated in the ranges of temperature from 600 to 1500 K and pressure from 0.1 to 10 MPa. The calculated data are compared, in comparable ranges of the parameters of state, with the results of the experimental investigations available in the literature of the solubility of inert gases in liquid alkali metals.

Solubility of Gases in Vitreous Silica Described by a Distribution of Dissolution Energies

The solubility of gases in vitreous silica complies well with Henry's Law at low pressures. Deviations observed at high pressures have been explained by site saturation, i.e., the number of dissolved molecules approaches the number of available sites that are assumed to have all the same energy of solution. In the present study, the observed deviations from Henry's Law are explained by a gradual saturation of sites of increasing energy. Experimental data of the solubility of hydrogen, helium, and neon in vitreous silica can be described by a Gaussian distribution of dissolution energies and Fermi-Dirac statistics. The solubility of hydrogen in metallic glasses, as well as the solubility of small molecules in glassy polymers, has been interpreted, and now, glasses in vitreous silica fit into this general concept of small particles in amorphous matrices.

Vascular and perfusion imaging using encapsulated laser-polarized helium.

In this work, the use of hyperpolarized (HP) 3He for in vivo intravascular imaging on animal is reported. To overcome the problem of the low solubility of helium in blood, we propose an approach based on helium encapsulation in lipid-based carrier agents. The mean diameter of the 3He microbubbles, measured equal to 3.0+/-0.2 microm, makes it possible to conduct in vivo studies. In vitro spectroscopy yielded a longitudinal relaxation time T(1) equal to 90 s and an apparent transverse relaxation time T(2)(*) of 4.5 ms. Angiographic imaging (venous and cardiac cavity visualization), as well as lung perfusion imaging, were demonstrated in rats using intravenous injections of microbubble suspensions. Suitable signal and spatial resolution were achieved. The potential of this technique for lung perfusion assessment was assessed using an experimental animal embolism model. Lung perfusion defects and recovery towards a normal perfusion state were visualized. This study was completed with the demonstration of a new ventilation-perfusion lung exploration method based entirely on HP 3He.

Recovery of the Potential of Interaction between Helium Atoms and Fluorine Ions Using the Data on Interstitial Diffusion and Solubility of Helium in Fluorides of Alkaline-Earth Metals

The method is treated of determining “static” pair potentials of interaction between neutral gas atoms and ions, recovered by the interaction energies of particles located at fixed distances from one another, using data on the activation energy of diffusion and dissolution of gas in ionic crystals. The results of investigation of the diffusion and solubility of helium in fluorides of alkaline-earth metals at distances in the range from 0.175 to 0.275 nm are used to recover the interaction potential in the He–F–system, U[He–F– ] = (90 ± 15)exp{–(28.5 – 1.5)r} eV. A comparison is made with the experimental and theoretical data of other authors.

Investigation of the noble gas solubility in H 2O–CO 2 bearing silicate liquids at moderate pressure II: the extended ionic porosity (EIP) model

A semi-theoretical model is proposed to predict partitioning of noble gases between any silicate liquid and a H 2O–CO 2 gas phase with noble gas as a minor component, in a large range of pressures (at least up to 300 MPa). The model is based on the relationship between the concentration of dissolved noble gas and ionic porosity of the melt, found by Carroll and Stolper [Geochim. Cosmochim. Acta 57 (1993) 5039–5051] for H 2O–CO 2 free melts. It evaluates the effect of dissolved H 2O and CO 2 on the melt ionic porosity and, consequently on Henry’s constants of noble gases. The fugacities of the noble gases in the H 2O–CO 2–noble gas mixtures are also considered in our equilibrium calculations of dissolved gas by using a modified Redlich–Kwong equation of state for the H 2O–CO 2–noble gas system. The formulated model (referred to as the extended ionic porosity model) clearly predicts a positive dependence of noble gas solubility on dissolved H 2O in melt, which becomes negligible when water concentration is higher than 3 wt%. Oppositely, noble gas solubility decreases as a consequence of increasing CO 2 in both basaltic and rhyolitic melts. The increase of noble gas solubility as a consequence of H 2O addition to the melt grows exponentially with the increase of the noble gas atomic size. As a result, although xenon solubility is much lower than the helium solubility in anhydrous melts, they become almost comparable at several percent of dissolved H 2O in the melt. On this basis, an exponential augmentation of the number of large free spaces in silicate liquid can be inferred in relation to increasing dissolved H 2O. Comparison between our predicted values and available experimental data [A. Paonita et al., Earth Planet. Sci. Lett. 181 (2000) 595–604] shows good agreement. At present, the EIP model is the unique tool which predicts how the main volatiles in magmatic systems affect the noble gas solubility in silicate melts, therefore it should be taken into account for future studies of noble gas fractionation in degassing natural magmas.

Investigation of the He solubility in H 2O–CO 2 bearing silicate liquids at moderate pressure: a new experimental method

We have designed the first available experimental method capable to investigate the solubility of inert gases in H 2O–CO 2 bearing silicate melts in a large range of pressures. The method overcomes the difficulties imposed by the physical state of volatiles at room conditions. Experiments were done by using an internally heated pressure vessel, where sealed capsules containing the sample are introduced. The peculiarity of the method consists in the capability of loading, in accurately known proportions (even lower than ppm), volatiles in a gaseous state at room conditions. Gas is loaded as a weighed amount of a gas-bearing glass, which was previously prepared by using the same gas as a pressure medium of a superliquidus experimental run. By analyzing the gas concentration in the prepared glass, the glass itself can be used as a gas source. We applied this method in order to investigate the helium solubility in silicate melts having dissolved volatile mixtures mostly composed of H 2O and CO 2, in a range of pressure suitable to provide useful information regarding pre-eruptive magma degassing. Our results indicate that helium solubility is strongly affected by the H 2O content in silicate liquid, displaying an increase by about a factor three as a consequence of the addition of 3 wt% H 2O to the melt. Taking into account the physical mechanism of He dissolution, the sites of the silicate melt structure, where noble gases can be accommodated, drastically increase by adding modest aliquots of H 2O. The influence of dissolved CO 2 on helium solubility is not certain, although few signs would suggest an opposite effect with respect to H 2O, at least in basalt melts. On the basis of the obtained results, we could reasonably expect that the helium behavior during the degassing of H 2O–CO 2 bearing magmas is sensibly different with respect to a H 2O–CO 2 free silicate liquid. Therefore, the effect of the major volatiles on noble gas solubility in magmas should be taken into account in the investigation of several geological processes, such as magma genesis, ascent and degassing, or mantle evolution.

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Mass spectrometric investigation of low-temperature diffusion and solubility of helium in lead fluoride crystals

Thermal desorption of helium from presaturated crystals was used for mass spectrometric investigations of the diffusion and solubility of helium in lead fluoride crystals in the temperature range 606–714K which precedes the transition of the crystal to the superionic state. The experimental apparatus and measurement method are described and mechanisms for the diffusion and solubility of helium in PbF2 are discussed.

Measurement and Correlation of Vapor−Liquid Equilibria for Asymmetric Mixtures of Helium and Polar Compounds

Phase compositions of vapor−liquid equilibrium (VLE) were measured for three binary asymmetric systems of helium with 1-hexanol, 1-octanol, or 1-decanol at temperatures from 353 to 453 K and pressures up to 10 MPa. The solubility of helium in 1-alkanols, as evidenced by the experimental results, is enhanced by increasing both pressure and temperature. Over the investigated conditions, the saturated gas-phase composition of the 1-alkanol component decreases with an increase of pressure at a constant temperature. Henry's constants of helium in 1-alkanols were determined from the isothermal VLE data. The new data were used to test various cubic equations of state and mixing rules.

Diffusion and solubility of helium in lead fluoride single crystals in the superionic transition region

Temperature curves of the diffusion coefficients and solubilities of helium in pure and holmium-doped lead fluoride crystals are obtained in the superionic phase-transition range. Possible mechanisms of the interaction of helium with ions are discussed, along with mechanisms of the solubility and diffusion of helium in a crystal.

Effect of Helium in Helium Headspace Carbon Dioxide Cylinders on Packed-Column Supercritical Fluid Chromatography

Supercritical fluid chromatography of PAHs was performed with pure carbon dioxide and helium headspace carbon dioxide at various cylinder fill levels. The retention times of the PAHs increased when helium headspace carbon dioxide was used as a carrier fluid relative to pure carbon dioxide. The increased retention times were affected by the level of the liquid phase present in the helium headspace carbon dioxide cylinder. As more liquid phase was removed from the cylinder, the effect of helium on the solvating power of CO(2) was reduced because the relative amount of helium dissolved in the liquid phase decreased. Furthermore, the effect of helium headspace carbon dioxide was investigated with methanol-modified carbon dioxide mobile phases for the analysis of steroids. We observed that the relative solubility of helium in carbon dioxide resulted in longer retention times when compared to pure carbon dioxide as the liquid level of carbon dioxide decreased.

Calculation of helium solubilities using Henry's constants from cubic equations of state with generalized correlations for the interaction parameters

Abstract A previously developed generalized correlation of the binary temperature-dependent interaction parameter in the Soave-Redlich-Kwong (SRK) and Peng-Robinson (PR) equation of state for low boiling helium mixtures (Schulze, 1993) is extrapolated to calculate Henry's constants. The calculated solubilities of helium are in good agreement with experimental data for non-polar and polar solvents, except for solvents with hydrogen bonds. For this group (water, alcohols) a new generalization is given. The results are compared with other methods of calculating helium solubilities.

Solubility of helium in methanol + water, ethanol + water, 1-propanol + water, and 2-propanol + water solutions at 25 .degree.C

The solubility of helium was measured in four aqueous alcohol solutions (methanol+water, ethanol+water, 1-propanol+water, and 2-propanol+water systems) over the full range of composition at 25 o C and 101.925 kPa. Both the excess quantity referring to the Ostwald coefficient and that referring to the excess volume show similar minima as a function of the volume fraction of alcohol

Experimental measurements of 3He and 4He mobility in olivine and clinopyroxene at magmatic temperatures

In-vacuo heating of 0.5 –0.7 mm olivine and clinopyroxene grains separated from Hawaiian ultramafic xenoliths leads to complete He loss within hours to days for temperatures of 700–1400°C. Diffusivities calculated from the observed release rates assuming spherical grains and initially homogeneous He distributions define Arrhenius relations with activation energies of 420 ± 20 and 290 ± 40 Kj/mol and log 10 D 0 of +5.1 ± .7 and +2.1 ± 1.2 cm 2/s in olivine and pyroxene, respectively. Values at 1350°C are 5.3 × 10 −9 cm 2/s in olivine and 10 times faster in pyroxene (4.7 × 10 −8 cm 2/s). These values include small corrections for grain size variations and, in the case of olivine, about 15% prior diffusive He loss. However, an important factor that has not been considered in previous studies of this type, is that the xenolith He resides predominantly within CO 2 rich fluid inclusions. Theoretical description of He loss in such a case demonstrates that the diffusivities calculated using the standard approach actually represent the product of the true volume diffusivity ( D) and the helium solubility, as represented by the distribution coefficient K Dv (defined by C crystal C fluid ). Although He solubility in crystals is not well determined, estimates based on the CO 2 concentrations in these samples suggest that it is very low ( K Dv of 3 × 10 −4 for pyroxene and 6 × 10 −6 for olivine; which also implies low crystal-melt distribution coefficients of .05 and .001). The resultant corrected diffusion rates are significantly faster than those obtained by the standard approach (~ 10 −4 cm 2/s at 1350°C and are thus higher than basaltic melt values). The most reasonable interpretation of this result is that He release is enhanced by internal grain fractures, including the planar healed cracks along which most fluid inclusions are arrayed. This treatment illustrates the difficulties involved in extrapolating laboratory He release measurements to nature, in particular the strong influence of mineral defects. The diffusivities reported here probably represent upper limits for mantle He transport or magmaphenocryst He exchange. As such, they imply that He transport over kilometer length scales in the mantle is dominated by convection rather than diffusion, and that phenocrysts in extrusive rocks will retain most of their pre-eruption helium contents. In combination with the observation that 3He diffuses only marginally faster than 4He (4 ± 4% faster in pyroxene and 9 ± 4% faster in olivine) this implies that significant isotopic fractionation of residual helium contents is unlikely to occur.