Spontaneous Phase Changes during Rapid Cooling of Beryl Melts; their Detection and Characterization

Abstract

A FUSION-QUENCH sequence as a means to opening the very refractory cyclo-silicate mineral beryl, Be₃Al₂Si₆O₁₈, is the basis of a well-known extractive process¹ in beryllium metallurgy. Much of the fundamental chemistry involved has been obscured by uncertainties surrounding the constitution of beryl melts and the crystallization paths which they can follow during cooling at rates too swift to allow equilibrium to be attained. We have found non-equilibrium ordering processes, and their dependence on thermal conditions, to be of importance in determining the chemical reactivity of chilled beryl melts. The difficulty of systematically studying events occurring spontaneously during the course of rapid cooling has been overcome by a refinement to the technique ol high-temperature microscopy². In addition to being able to observe the melt directly, heat effects, accompanying phase generation during chilling, can be detected. A series of pseudo-liquidus temperatures associated with any crystallization can be defined, and any dependence that the ordering processes occurring in the melt may have on variation in the rate of cooling can be established.