A study of refining Part 1: Measurements of the refining of a soda-lime-silica glass with and without refining agents
GT V01 1960 144-154
The data presented here refer to 60 g melts of glass of composition in weight %, 73.5 SiO2, 10.0 CaO, 16.5 Na2O, founded in platinum in an electric furnace at 1400 and 1450" C. There was no significant convection of the melt. Melts were made at 1400°C, containing all possible combinations of 0, 0.10 and 0.50% As2O3 with 0, 1.00 and 5.00% Nus0 supplied as sodium peroxide. Four of these combinations were investigated in detail at 1400" C and two at 1450" C. By counting the seed remaining in 30 g slabs cast from melts founded for different times it was possible to construct graphs showing the decrease of total number (N) of seed per cm3 with time. This relation was approximately, but not exactly, exponential. The refining agents affected the number of seed present at the beginning of refining as well as the rate of refining; because of this it was concluded that melting and refining could not be considered as two independent processes. Measurements of seed size distributions allowed the decrease of the number of seed per cm3 (n), of given diameter (x), with time to be plotted. Most of the data were well fitted by an exponential relation between n and t. The refining agents altered the shapes of the seed size distributions and the rates at which seed disappeared. Small seed disappeared more slowly in melts containing 0.50% As203 and 5.0% Nu20 as Nu202 than in melts containing 0.50% Asz03 and 1.0% Nu20 as Na202. This suggested that it was possible to supply too much oxygen for any given addition of Asz03. Raising the temperature had effects similar to some combinations of refining agents, affecting seed size distributions and rates of disappearance of seed.
Michael Cable
