Synergistic effects of CuO and CaF2 additives in facilitating low-temperature tricalcium silicate formation and stabilization

Abstract

This study investigates the effects of CuO, CaF₂, and their combination on phase formation in C₃S (alite) clinkers at different firing temperatures, aiming to reduce energy consumption in clinker production. Clinker samples with 0.1 wt.% CuO, 0.8 wt.% CaF₂, and a combination of 0.1 wt.% CuO and 0.8 wt.% CaF₂ were synthesized and fired at temperatures between 1200 °C and 1350 °C. The mineralogical composition of the clinkers was analyzed using X-ray diffraction patterns with Rietveld refinement technique. The results showed that alite formation was absent below 1350 °C in clinkers without additives. The addition of CuO promoted belite (C₂S) formation and reduced free lime content but did not significantly induce alite formation. In contrast, CaF₂ significantly enhanced alite formation, yielding monoclinic M₁ and M₃ polymorphs, with M₁ being the dominant phase. The addition of 0.8 wt.% CaF₂ accelerated alite phase content of 18.96 wt.% at 1200 °C, which further increased to 73.54 wt.% at 1350 °C. The combined addition of CuO and CaF₂ further improved alite formation at lower temperatures, with alite content higher than 50 wt.% at 1250 °C. These findings demonstrate that CuO and CaF₂ act synergistically to facilitate alite formation at reduced firing temperatures, providing a potential pathway for energy-efficient clinker production.