A study of refining - Part 3 : The function of arsenious oxide during melting and refining

GT V02 1961 151-158

By using chromium as an indicator of oxygen saturation it was shown that all melts were undersaturated with oxygen and that the function of arsenic at founding temperatures was to absorb oxygen. Refining was aided by oxygen diffusing out of seed into the glass. For oxygen to accelerate refining in this way it was necessary to postulate that most seed were quite rich in oxygen at the beginning of refining. Evidence supporting this conclusion was found in the literature. From analyses of the arsenic present in melts as As5+ and the results from the melts containing clzromium it was possible to estimate the oxygen solubility conferred on a glass by adding arsenic to the batch. The oxygen solubility was large compared with that of nzost other gases. Some simple experiments were made to show that refining agents had an effect on the course of the melting reactions but a much more detailed investigation is needed to determine how seed rich in oxygen are formed. It is concluded that during melting, coalescence played an important part in removing bubbles but beyond the batch-free time seed were removed by dissolving and rising to the surface of the melt. The first of these two processes was the more important. 

Michael Cable,* Department of Glass Technology, University of Sheffield