Crystallization of belite–melilite clinker minerals in the presence of liquid phase

Crystallization of belite–melilite clinker minerals was studied from the view point of a high temperature equilibrium. Ca2SiO4–Ca2Al2SiO7 and Ca2SiO4–Ca2AlFeSiO7 clinkers were synthesized at 1330 °C–1650 °C. The constituent phases were determined by X-ray powder diffractometry and optical microscopy. Chemical compositions of the individual clinker minerals were determined using an electron probe microanalyzer.We established the two types of P2O5-bearing pseudobinary phase diagrams in the systems Ca2SiO4–Ca2Al2SiO7 at 1505 °C–1650 °C and Ca2SiO4–Ca2(Al,Fe)2SiO7 at 1330 °C–1550 °C. In the latter system, the liquid phase appeared at 1390 °C, which is approximately 150 °C lower than the temperature of liquid formation in the former system. The melilite phenocrysts larger than 50 μm were observed not only in the slowly cooled Ca2SiO4–Ca2(Al,Fe)2SiO7 clinker but also in commercial belite–melilite clinkers. These crystals would be nucleated and grown from a liquid phase which was formed at relatively low temperatures.