Permeation of Gaseous Oxygen through Vitreous Silica

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.