Diffusion of Oxygen from Contracting Bubbles in Molten Glass

Some experimental measurements on the rate of contraction of oxygen bubbles in molten glass were compared with an equation for the diffusion‐ controlled contraction of a sphere. This comparison showed that the equation was valid until about 80% of the oxygen had diffused from the bubbles, so that the diffusion coefficient of the oxygen in the molten glass could be calculated from the experimental measurements. These values of the diffusion coefficient were higher than one would expect from the Stokes‐Einstein equation for diffusion in liquids. Thus it was concluded that some short‐circuiting mechanism such as diffusion in channels in the glass was operative. It also appeared that the oxygen diffused in the glass as atoms, rather than as molecules. From contraction measurements on glasses with different fining agents it was concluded that the mechanism of fining by such agents as antimony and arsenic oxides was not discharge of oxygen gas as had been generally supposed but was reduction of the concentration of oxygen in the glass, which caused the oxygen in the bubbles to diffuse into the glass more rapidly.