ABSTRACT
The minerals in the group of “spinel” are double oxides that crystallize in the
cubic crystallographic system. They are generally indicated by the formula
AB2O4, where “A” is a divalent element such as Mg, Fe, Zn, Mn, Ni, Co, V,
and Cu, and “B” a trivalent element such as Al, Fe, and Cr with reciprocal dia-
dochal exchange. An enormous number of individual compounds (.200) and systems can justifiably be classified as spinels. Apart from those compounds clo-
sely related to the naturally occurring parent mineral spinel [i.e., magnesium-alu-
minate spinel, MgAl2O4 (MA)], there are many compounds that are structurally
related (with greater or lesser variations), and there are also a broad range of solid
solutions adhering to the same structure. Spinels associated with refractories sys-
tems include FeFe2O4, FeAl2O4, FeCr2O4, MgFe2O4, MgAl2O4, MgCr2O4, and
their solid solutions. Some of their properties are listed in Table 1 (1). Among
these spinels, MgAl2O4 and MgCr2O4 offer a good combination of physical
and chemical properties such as high refractoriness, high mechanical strength,
and high resistance to chemical attack, so they are consequently used to make
a variety of spinel-containing refractories. Although MgCr2O4-containing refrac-
tories are still being used in many areas, due to the carcinogenic nature of Cr6þ, they have been and are continuously being replaced by MgAl2O4-containing
refractories. Therefore, in this chapter, we emphasize the raw materials, proces-
sing, properties, and applications of MgAl2O4-containing refractories.
