Experimental Study of Unequilibrated Silica Transfer from Liquid Water to the Vapor Phase

Abstract

Experiments were carried out in hermetically sealed platinum capsules, with water saturated with silica with respect to quartz at 300°C in the lower parts of the electric furnaces, where the temperature slightly increases upward at 0.15°C/cm. Our earlier studies (Alekseyev and Medvedeva, 2017) have shown that these exactly experimental parameters are favorable for silica transfer from the liquid to vapor phase. The statistically processed experimental results show that the molal silica concentration in the liquid phase (m) exponentially decreases with time. This dependence and the fact that the newly produced opal occurs on the capsule walls above the meniscus are consistent with the distillation model. The scatter of the experimental m values turned out to be caused not by differences in the temperature gradient in different wells of the electric furnaces but by the natural roughness of the inner walls of the capsules, which differed from one capsule to another and could even change with time in any given capsule. In the capsules with roughness artificially made on their walls, m decreased much more rapidly, and not only in the bottom but also in the upper parts of the electric furnaces, where temperature decreased upward (–0.08°C/cm). This may suggest that the discovered phenomenon is spread in nature more widely than surmised previously, because this phenomenon does not strongly depend on the direction of the temperature gradient, and voids in natural rocks usually have rough walls.