Permeation of Gaseous Oxygen through Vitreous Silica

Abstract

THE permeation of gaseous oxygen through vitreous silica has been measured over the temperature-range 950°–1,080° C. in a permeation cell constructed with two portions separated by a thin-walled spherical bulb with a short neck. The bulb was 25 mm. outside diameter, and served as the membrane of vitreous silica ; its area was 18.9 cm.² and thickness 0.27 mm. The thickness was determined from electrical capacitance measurements. The silica was used as blown ; and no cleaning was done with hydrofluoric acid. The oxygen pressure, 300–800 mm. mercury, was applied to the convex side of the bulb. The low-pressure side led directly to a mass spectrometer with no leak intervening. The rate of permeation of gas was measured¹, in this case by the peak height of mass 32. It was assured that true permeation, and not merely degassing, was being measured by : (1) observing the slow rise of the oxygen peak after application of oxygen to the high-pressure side, (2) attainment of steady-state flow and then, (3) slow decay of the peak after the gas was removed from the high-pressure side.