Liquidus Relationships on 10% MgO Plane of the System Lime‐Magnesia‐Alumina‐Silica

The system CaO‐MgO‐Al 2 O 3 ‐SiO 2 is well known for its importance in many fields of ceramic technology, especially in the field of industrial refractories. The present study, although providing additional data on the liquid phases in basic refractory materials, was undertaken primarily to determine the composition‐melting‐ point behavior of iron blast‐furnace slags. About 95% of the composition of blast‐furnace slags generally can be expressed in terms of CaO, MgO, Al 2 O 3 , and SO 2 , the additional constituents being FeO, MnO, and S. The MgO content of these slags depends on the type of “stone” used as a flux, which may be essentially pure limestone, dolomitic limestone, or a mixture of limestone and dolomite as determined by economic factors related to sources of raw materials. The amount of MgO usually varies between 2 and 10% in the final slag, and it is often important to know the effect on the melting point of a substitution of MgO for CaO. In the present study one hundred and two glass compositions were prepared for liquidus and in some cases secondary‐phase temperature determinations by the quenching method. The investigation was confined chiefly to the central part of the plane adjacent to the lime‐silica‐magnesia face of the tetrahedron. Primary fields of s'lica, diopside, anorthite, pseudowollastonite, cordierite, melilite, spinel, mullite, merwinite, dicalcium silicate, periclase, and corundum were encountered in the course of the work. Liquidus temperatures ranged from a minimum of 1230°C. at the diopside‐anorthite‐tridymite intersection to a maximum of about 1650°C. in the dicalcium silicate field, which was the upper safe limit for the equipment. Petrographic and X‐ray diffraction methods were used to identify phases.