Substitution of Na, Fe and Si in tricalcium aluminate and the polymorphism of solid solutions

Abstract

The roles of (Na + Fe 3+) and (Na + Si) substituted in Ca 3Al 2O 6 have been determined by making approximately 200 experiments on 50 compositions. Pure oxide powders were heated at subliquidus temperatures until reaction was complete. High Na + Fe contents stabilize the pseudotetragonal phase to ambient temperatures. The extent of Si substitution at equilibrium is small; ca 0.5 to 2.0 wt %. While Na alone causes the unit cell to shrink from 15.2687 Å for pure Ca 3Al 2O 6 to ≈ 15.24 Å at 2.0 – 2.5% Na 2O, Na + Si substitution results in a further marked contraction to 15.19 Å at ≈ 2.5% Na 2O and ≈ 0.4% SiO 2.