The Flow of Glass

JSGT 1949 V33 T138-T163

The expression η/T=Ae^B/T(1+Ce^D/T)has been derived for the viscosity of glass as a function of temperature assuming that the flow of glass is controlled by the Si–O–Si bonds and that flow can occur when an oxygen atom has two positions available to it. The factor in brackets arises from the change of atomic configuration with temperature. In atomic arrangement the structure of water is very similar to that of fused silica, and as first check on the theory, it was shown that the above expression can be fitted very accurately to the observed values of viscosity of water as a function of temperature. Moreover, the experimental values of A and B were found to be in close accord with those predicted. The trend of the values of the constants when Na₂O is added to SiO₂ was discussed qualitatively on the basis of published data on soda–silica glasses. In every case the qualitative predictions were confirmed, and again the magnitudes of A and B were of the right order. It is emphasised, however, that from the point of view of checking theoretical predictions the available data are scanty, and the agreements obtained do no more than indicate that the theory is not incompatible with the observations. A series of viscosity–temperature measurements at many temperatures over the largest possible range of viscosities on a few soda–silica glasses spread over the range 10–50% soda would enable a more critical evaluation of the theory to be made.

R. W. Douglas