Diffusion Coefficients, Solubilities, and Permeabilities for He, Ne, H2, and N2 in Vycor Glass

Abstract

The permeability of a Vycor filter (680 cm2 area and 0.25 mm thick) is given for helium at six temperatures ranging from 299°K to 723°K, for neon and hydrogen at 673°K and 723°K, and for nitrogen at 673°K. The observed values and their temperature dependences are in good agreement with corresponding values for fused quartz reported elsewhere. Values of the diffusion coefficient of these gases in Vycor also were obtained experimentally, enabling calculation of their solubilities. Helium appears to deviate from activated diffusion in Vycor somewhere between 100° and 26°C. Its permeation velocity and diffusion coefficient at 26°C are larger than expected for activated diffusion, while its solubility at 26°C is one‐half its value at 100°C. These changes suggest that some structure sensitive diffusion process begins to dominate the activated or solution process at these lower temperatures. Helium flow rates through the filter as high as 2100 mm Hg (0°C)×cc/hr at a filter temperature of 450°C and a pressure difference of 35 cm Hg (0°C) were observed. On the basis of observed permeation rates for the above gases, it is estimated that the filtered helium has an impurity content of less than 1/50th of its unfiltered value.