Studies in the Distribution of Temperature through Molten Glasses in a Tank Melting Furnace. Part IV. The Effect of Cobalt Oxide on the Temperature of Soda–Lime–Silica Glasses at Different Depths in a Laboratory Scale Furnace.
JSGT 1946 V30 T356-T363
The effect of cobalt oxide on the temperature distribution of molten soda–lime–silica glass was studied in a laboratory scale tank furnace. To the parent glass of percentage composition SiO2 73·5; Al2O3 1·0; CaO 9·0; Na2O 16·5, cobalt oxide was added in amounts varying from 0·0022 to 0·44 per cent., care being taken to maintain a constant concentration of iron oxide present in the glass as impurity. For the series of ten glasses obtained, the vertical temperature gradient at the centre of the mass of glass was determined. Up to about 0·025 per cent. cobalt oxide, a concentration bestowing a distinct coloration on the glass, the temperature gradients, varied from 7° to 12° per inch depth, these values being considerably lower than those found in amber or green glasses. Only when the amount of cobalt oxide exceeded 0·1 per cent., was there an appreciable increase in the temperature gradient. Similarly, a commercial cobalt· blue glass had a temperature gradient of 36° per inch as compared with 45° and 85° per inch for an amber and a dark-green glass, respectively. The investigation showed that the colour and transmission of cobalt-blue glasses at room temperature cannot be taken as an indication of their heat-transmitting properties in the molten state.
R. S. Allison, R. Halls & W. E. S. Turner
