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What are the phases?
The following phases are important in high temperature processing to design the refractory for a given requirement
a. Slag: It is a mixture of mostly molten oxides and sulphides , in some processes phosphate is also a constituent of slag. Oxides are either acidic such as silica, fireclay or basic like MgO, MgO-C,alumina, FeO.
Among sulphides CaS, MnS, FeS, PbS etc, are prominent phases. The slag is molten and its temperature in different processing lay within the range
b. Liquid metal: In metal extraction from ores, metal is extracted in the liquid stage. Composition of metal, and its temperature are important. For example in iron and steel industry, hot metal is a mixture of iron, carbon, silicon, manganese and phosphorus. The temperature varies in between  to  In copper-making the temperatures are within the range  . Molten aluminum is produced at  and likewise other non ferrous metals.
c. Matte: it is a high temperature molten phase and consists of a mixture of molten sulphides like Cu2S, FeS, Ni3S2 etc. The temperatures vary within the range 1100°C to 1250°C.
d. Gases: Several different types of gases like CO, CO2, N2 H2O (vapor), argon, O2 are used at high temperatures in several unit processes like roasting, calcination, smelting, refining, converting etc.The temperatures may vary in between 600oC to1500°C. The gases like CO2, H2O, and O2 are oxidizing, wheras the gases like CO, and H2 are reducing. N2 and argon are inert.
e. Speisses are molten solutions of arsenides, or arsenides and antimonides when the materials being treated contain large quantities of As and Sb.
f. Drossses are heterogeneous products skimmed or driven form the surface of molten metal during refining. They are mixtures of precipitated solid and liquid compounds with substantial proportion of mechanically trapped molten metal.
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