A Study of the Reaction Rates between Silica and Other Oxides at Various Temperatures. Part V. Theory of Reaction Rates in Binary and Ternary Mixtures
JSGT 1953 V37 T190-T212
If the reaction between silica and a metallic oxide or oxides produce a glass which remains as a layer surrounding the core of unaltered silica in each silica grain, the progress of the reaction between the silica and the metallic oxide or oxides can be derived. The formula is derived from the assumptions that the rate of reaction between silica and a metallic oxide or oxides depends upon: (1) the surface area of the silica, and (2) the thickness and nature of the glass layer formed due to interaction between silica and the metallic oxide or oxides. This relation is in good agreement with a number of the practical results obtained from measurements of the reaction rates in binary and ternary mixtures in Parts I, II and III. It may be expected, however, that many cases will arise in which the glass formed by the reaction is sufficiently fluid to flow away from the grains as rapidly as it is produced, so that a glassy layer of constant or zero thickness exists around each silica grain as the grain diminishes in size. This relation is in good agreement with a number of the results obtained in Parts I, II and III, particularly with those relating to mixtures containing high proportions of the alkalis and where the firing was carried out at comparatively high temperatures. Intermediate cases are also found and one is discussed in detail in the paper. The results have been applied to determine the temperature at which the reaction between silica. and the other oxides begins to develop rapidly; there is a marked increase in the rate of reaction between silica and other oxides when the temperature is higher than 850°. This can be attributed to the rapid disruption of the rings of SiO4 tetrahedra in the quartz crystals which, from the temperature of inversion to tridymite, is known to begin at a temperature of approximately 870°. This also enables the temperature to be determined at which the reaction rates first become detectable. By extrapolating, it can be shown that the reaction between silica 75% and soda 25% (added as sodium carbonate) starts at about 400°, which is in good agreement with practical results obtained by other investigators. It may be deduced from this result that at 400° a just detectable proportion of the SiO4 linkages are liable to become broken due to thermal vibration.
Abd-El-Moneim Abou-El-Azm
