A study of thermodynamic stability of oxide phases in heating multicomponent ceramic binders

Abstract

A computer simulation of the thermodynamic stability of phases in firing ceramic silicate binders in the SiO₂-A1₂O₃-B₂O₃-K₂O-Na₂O system for abrasive tools based on grained normal electrocorundum is described. The thermodynamic data for the computation are chosen from the HSC 203 data base of the Outokumpu concern and TAPP of the E. S. Microwave Inc. It is established that when the binder (67.73% SiO₂,20.0% A1₂O₃,5.47% B₂O₃, 5.78% K₂O,2.84% Na₂O with CaO, MgO and Fe₂O₃ impurity oxides, the remainder TiO₂) is fired at 1250°C, the most stable phases bear potassium (KAlSi₃O₃ and KAlSi₂O₆), the amount of the sodium-bearing phases diminishes substantially after 900–1100°C with only the Na₂O · A1₂O₃ · 2SiO₂ phase remaining stable. This seems to explain the fact that the proportion of K₂O to Na₂O in feldspar pegmatites and ceramic binders for abrasion tools is regulated by standards.