Diffusion Coefficient, Solubility, and Permeability for Helium in Glass

Abstract

A method is described for simultaneously measuring the diffusion coefficient, solubility, and permeability for a given gas in a single sample of solid material. The method utilizes solutions of the diffusion equation (for both plane and cylindrical geometry) which make it easily possible to calculate the diffusion parameters from data taken either in the period of steady-state gas flow or in the early part of the transient period. Using ultra-high vacuum techniques, it is possible to make the measurements with extremely small amounts of gas and without errors due to leaks or contamination in the gas handling system. Values for the diffusion parameters have been determined for helium in Pyrex glass (Corning 7740), and comparisons with previous measurements are made. Directly measured values of the diffusion coefficient are given for the first time. The diffusion coefficient and permeability both exhibit a temperature dependence of the form exp (−E/kT) both having the same activation energy (6.4×103 cal/mole) within the experimental error. The solubility exhibits little or no variation with temperature over the range 25°C to 300°C, and is in good agreement with the only previous measurement, carried out at 515°C.

Polynorbornenes with Oligodimethylsiloxanyl Substituents for Selectively Oxygen Permeable Membrane Material

“…Such increase in permeability coefficients is similar to that seen in the case of introduction of n-butyl or pentamethyldisiloxanyl groups at the p-position of polystyrene (20)(21)(22)(23)(24).4·5·9·10 In order to obtain a little more 290 insight into the mechanism of permeation, the permeability coefficient was divided into diffusion and solubility coefficients according to eq 3 as a first approximation although the Tg of the polymer is considerably higher than 25°C.…”

Improving the helium gas barrier properties of epoxy coatings through the incorporation of graphene nanoplatelets and the influence of preparation techniques

“…To determine the helium gas diffusion (D) coefficients and steady state flux (J0) of the graphene/epoxy nanocomposites the following one-dimensional variation of Fick's law of diffusion was applied with the appropriate boundary conditions [4,13,23,45,48]:…”

Permeability of Gases Through Filled and Unfilled Rubber Membranes

“…Therefore, the heats of solution are more negative in the filled rubbers. Interestingly, tH 5 for H 2 is much more negative than that for D 2 so that the difference in overall heat of solution between H2 and D 2 in unfilled rubber is not only wiped out, but also becomes positive for the filled rubbers. Consequently# the free volume increments could not be determined in the filled samples, but it is reasonable to assume that the free volume L13 is lowered in the filled rubber since the diffusion process is impeded beyond reasonable assumptions about a diminished cross section and increased tortuosity…”

“…In general, the solubility, S(rb+f), of a gas in a rubber-filler system may be resolved into three factors, first Srb, related to the solubility in the rubber, second, Sf, related to the gas adsorption by the filler and, third, 5 With rubber containing filler of say, 0.2 volume fraction, the solubility of the gas should, in this case, be 80% of that of the gum compound. For special mineral fillers such as whiting, aluminum oxide and barium sulfate and with the non-reinforcing carbon blacks, the experimentally determined solubilities by van Amerongen (3 0 ) are in fact only a little higher than this 80% value (see Table 15).…”