Rearrangement Kinetics of the Liquid—Liquid Immiscible Microphases in Alkali Borosilicate Melts

Abstract

Probability calculations are presented which show the high degree of mutual intersection within a population of spheres grown from randomly placed nuclei. It is proposed that the observed networklike structures of the phases of certain liquid—liquid immiscible systems may be due to this statistical lumping. It is further proposed that interfaces of opposite curvature facilitated by this structure rather than polydispersisity give rise to transport phenomena resulting in observable rearrangements in these systems. Equations for a number of transport models are derived. Liquid—liquid phase separation was induced in alkali borosilicate melts by cooling below immiscibility temperature. Progressive stages of the geometric rearrangements within the microdisperse phases were arrested by undercooling. The kinetics of the decrease in interfacial area between the phases was studied by gas adsorption on the isolated silica-rich phase. It is found that interfacial area is proportional to the reciprocal of the square root of time. Comparison of this result with the rate equations derived for various simplified transport models suggests an interface-controlled bulk diffusion process. In spite of complications expected from the variety of possible temperature-dependent terms, the process was found to be Arrhenian, having an apparent activation energy of 40 kcal/mole. At present it cannot be decided which mechanism this value supports.