Physical and Chemical Processes in Melting of Potassium Oxide-Lead-Silica Glass

JSGT 1933 V17 T305-T319

A study has been made of the process of conversion into glass of a mixture containing potassium carbonate, lead oxide and silica, calculated to yield a glass of percentage composition SiO₂48, PbO 45·5, K₂O 6·5. The progress of reaction on heating at a series of temperatures up to 1200° was followed by the determination of the total loss of weight with time of the batch during heating, the determination of the gases evolved at different temperatures, chemical analysis of the products, and microscopic examination. The tests were applied to K₂CO₃ alone, to the binary mixtures K₂CO₃+ SiO₂, K₂CO₃+Pb₃O₄, Pb₃O₄+SiO₂, and finally to the mixture K₂CO₃+Pb₂O₄+SiO₂. The K₂CO₃employed contained approximately 15% of moisture. In the temperature range 100–300° there was no indication of any marked reaction other than the liberation of moisture, although even at 300° slight liberation of CO₂ occurred from the mixture K₂CO₃+SiO₂ and from the ternary mixture. Initial dissociation of the red lead appeared to occur at 500°, and was complete below 600°. The reaction K₂CO₃+SiO₂ proceeded at an increasing rate at temperatures above 500°, and very rapidly at 800°. Microscopic examination showed that even after chemical reaction was complete the product was very inhomogeneous, having refractive index varying from point to point. At 1000° and above the homogeneity substantially improved by reason of the solution both of lead oxide and silica. At 1200° the product was practically isotropic.

M. A. Besborodov, A. A. Appen, T. F. Korzukhina, E. P. Chodikel & G. A. Shinke