Studies of the system CaO-SiO2-Al2O3-MgO in relation to the stability of blastfurnace slag

Phase equilibria in the 5% magnesia plane of the quaternary system CaO-SiO₂-Al₂O₃-MgO and in the high lime region of one of the bounding ternary systems, namely CaO-Al₂O₃-SiO₂, have been investigated by high temperature microscopy and X-ray analysis and substantial new data is presented. This study is one of a series designed to determine the extent of dicalcium silicate formation in the system CaO-SiO₂-Al₂O₃-MgO which accounts for over 95% of the composition of blastfurnace slag. Phase diagrams are presented based on an examination of approximately 150 synthetic compositions. The results are relevant to the stability of blastfurnace slag. The mineralogical information assembled will be of use also however in the wider application of industrial by-products some of which contain compounds occurring in the system lime-silica-alumina-magnesia. The results are also relevant to cement chemistry and to the study of igneous rocks.