The technology of alumina-silica refractories is traditionally explained using the
alumina (Al2O3)–silica (SiO2) phase equilibrium diagram (Figure 1). A phase diagram
is essentially a “map” of temperature versus composition showing “phases” or
discrete areas/volume elements of similar composition within a material at equilibrium
and at a given temperature. The idea is that certain compositions will
produce certain qualities of refractories. The diagram in Figure 1 shows composition
in mole percent and temperature in degrees Celsius. There are updated
representations of this system, but the essential facts remain the same.