Analysis of the geometric features of T-x-y diagrams with melt immiscibility for silicate systems

Abstract

Abstract Analysis of the geometric structure of phase diagrams for ternary systems with the two immiscible liquids has been carried out. T-x-y diagrams with the both types of the monotectic equilibriums (univariant and invariant ones) have been analyzed. Three-dimensional computer models of T-x-y diagrams for the four silicate systems with mono- and invariant equilibriums and different variants of the immiscibility surfaces location have been built. T-x-y diagram of the ZrO2-SiO2-Al2O3 system includes one immiscibility cupola, located in the ZrO2 crystallization field, which adjoins the ZrO2-SiO2 side. The 3D model of T-x-y diagram includes four invariant transformations: peritectic P: L+ZrO2+SiO2→R2, quasi-peritectic Q: L+ZrO2 →R1+R2, two eutectic E1: L→ZrO2+Al2O3+R1, E2: L→SiO2+R1+R2. Five surfaces of liquidus, which correspond to the beginning of primary crystallization of three initial components and two binary compounds R1=3Al2O3·2SiO2 and (congruently melting) and R2=ZrO2·SiO2 (decomposed without liquid) are formed in the system. T-x-y diagram TiO2-ZrO2-SiO2 is characterized by one eutectic E: L→TiO2+SiO2+ZrO2·TiO2 and one quasi-peritectic Q: L+ZrO2→SiO2+ZrO2·TiO2 transformations and includes two immiscibility surfaces from the sides of TiO2-SiO2 and ZrO2-SiO2 binary systems. FeO-SiO2-Fe2O3 system with common immiscibility cupola, that prolongs from the system FeO-SiO2 to the system SiO2-Fe2O3, is characterized by three invariant transformations of eutectic type, and one metatectic transformation V: B1 →L+B2+C, which corresponds to the transfer from high-temperature allotropy of silica (B1 - cristobalite) to the low-temperature one (B2 – tridymite). T-x-y diagram KAlSi2O6-Fe2SiO4-SiO2 has two immiscibility surfaces: one of them adjoins to the Fe2SiO4-SiO2 binary system and the second one is located on the Fe2SiO4 and tridymite liquidus surfaces, dividing the univariant curve on their boundary into two parts, and has three points of the maximum and three points of the minimum. Using of the computer models of T-x-y diagrams allows you to take into account different variants of the geometric structure of the investigated silicate systems.