Effect of cooling rate and Na 2O content on the character of the interstitial materials in portland cement clinker

Abstract

Both the chemical and phase compositions of the crystalline interstitial phases in clinker vary significantly depending on the cooling rate and Na 2O content of clinker. In slowly cooled clinker the calcium aluminoferrite phase is definitely lower in amount and Al 2O 3/Fe 2O 3 ratio than in rapidly cooled clinker. The coexistence of Na 2O encourages this change. With slow cooling, SiO 2 and MgO in the ferrite phase decrease in content with an increase in the ratio of SiO 2 to MgO due to the precipitation of periclase. In the calcium aluminate phase MgO decreases as well; but SiO 2, in the coexistence with Na 2O, remains high even on slow cooling because of the coupled ion exchange Ca 2++Al 3+→Na ++Si 4+, which causes the crystal system to change from cubic to orthorhombic.