Figure 3 (5) shows that the spinel lattice constant decreases with increasing
mole number of alumina. If the lattice constant of spinel is known, then
using Figure 3, the amount of excess alumina in an alumina-rich spinel can
be estimated. The cation vacancies formed in the alumina-rich spinel can
accommodate many different cations, conferring spinel-containing composites
with some interesting properties. For example, due to the accommodation of
slag ions such as Fe2þ and Mn2þ by the spinel structure, spinel-containing
refractories show improved slag penetration resistance, which will be discussed
in detail in Section VI. In contrast to alumina-rich spinel, in MgO-rich spinel,
enlargement of the spinel unit cell occurs with the formation of oxygen vacant
sites, i.e., doping with excess MgO leads to the formation of an anion-deficient
structure. In this case, the lattice constant increases slightly with increasing
MgO content.
Figure