Phase equilibrium studies in Si 2N 2O-containing systems: II. Phase relations in the Si 2N 2OAl 2O 3La 2O 3 and Si 2N 2OAl 2O 3CaO systems

Abstract

Sub-solidus phase relations have been studied in the Si 2N 2OAl 2O 3La 2O 3 and Si 2N 2OAl 2O 3CaO systems. The results show that no new compound is found in the Si 2N 2OAl 2O 3La 2O 3 system, but there exists a new compound CaO·Si 2N 2O and a continuous cubic solid solution between 3CaO·Si 2N 2O and 3CaO·Al 2O 3 in the Si 2N 2OAl 2O 3CaO system. In the Si 2N 2O-rich area of these two systems the excess Si 2N 2O reacts with La 2O 3 and CaO to form Si 3N 4, and either La 10(SiO 4) 6N 2 (H-phase) or CaSiO 3, respectively. Several quaternary compatibility regions occur in the Si 2N 2OAl 2O 3La 2O 3 system: HSi 3N 4La 2O 3·Si 2N 2OLa 2O 3·Al 2O 3 HSi 3N 4La 2O 3·Al 2O 3La 2O 3·11Al 2O 3 HSi 3N 4La 2O 3·11Al 2O 3Al 2O 3 HSi 3N 4Al 2O 3O′ss HSi 3N 4O′ssSi 2N 2O and in the Si 2N 2OAl 2O 3CaO system: Si 3N 4CaSiO 3CaO·Si 2N 2O3CaO·Al 2O 3 Si 3N 4CaSiO 33CaO·Al 2O 32CaO·Al 2O 3·SiO 2 Si 3N 4CaSiO 32CaO·Al 2O 3·SiO 2Al 2O 3 Si 3N 4CaSiO 3Al 2O 3O′ss Si 3N 4CaSiO 3O′ssSi 2N 2O From the results of this work, the sub-solidus phase diagrams of the Si 2N 2OAl 2O 3La 2O 3 and Si 2N 2O 3Al 2O 3 sytems are presented.