In alumina-rich spinel, Al3þ replacing Mg2þ ions on tetrahedral sites
with charge compensating cation vacancies on the octahedral sites accommodates
the excess alumina stoichiometry range in the crystal structure. Because
the ionic radius of Al3þ (0.050 nm) is also significantly smaller than that of
Mg2þ (0.065 nm), doping with excess Al3þ leads to the formation of vacant
cation sites, i.e., MA becomes cation deficient with a smaller unit cell volume.
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
In alumina-rich spinel, Al3þ replacing Mg2þ ions on tetrahedral siteswith charge compensating cation vacancies on the octahedral sites accommodatesthe excess alumina stoichiometry range in the crystal structure. Becausethe ionic radius of Al3þ (0.050 nm) is also significantly smaller than that ofMg2þ (0.065 nm), doping with excess Al3þ leads to the formation of vacantcation sites, i.e., MA becomes cation deficient with a smaller unit cell volume.Figure 3 (5) shows that the spinel lattice constant decreases with increasingmole number of alumina. If the lattice constant of spinel is known, thenusing Figure 3, the amount of excess alumina in an alumina-rich spinel canbe estimated. The cation vacancies formed in the alumina-rich spinel canaccommodate many different cations, conferring spinel-containing compositeswith some interesting properties. For example, due to the accommodation ofslag ions such as Fe2þ and Mn2þ by the spinel structure, spinel-containingrefractories show improved slag penetration resistance, which will be discussedin 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 vacantsites, i.e., doping with excess MgO leads to the formation of an anion-deficientstructure. In this case, the lattice constant increases slightly with increasingMgO content.Figure
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In alumina-rich spinel, Al3þ replacing Mg2þ ions on tetrahedral sites
with charge compensating cation vacancies on the octahedral sites accommodates
the excess alumina stoichiometry range in the crystal structure. Because
the ionic radius of Al3þ (0.050 nm) is also significantly smaller than that of
Mg2þ (0.065 nm), doping with excess Al3þ leads to the formation of vacant
cation sites, i.e., MA becomes cation deficient with a smaller unit cell volume.
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
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