The condensation zone of glass furnace regenerators is prone to attack. Although
the temperature in this zone is not particularly high (800 _ 10008C), the refractories
are exposed to an extremely corrosive environment. The main corrosive
agents in this zone include Na2O, SO3, and Na2SO4, which are introduced
through the waste gases used. Al2O3–SiO2 system refractories, e.g., high alumina
and mullite-based refractories, are not suitable for application in this zone, since
they react rapidly with alkalis to form low-melting phases. Magnesia or dolomite
refractories are also not suitable, because MgO and CaO can react easily with
SO3 gas to form low-melting MgSO4 and CaSO4, respectively. MA is most suitable
in glass checkers because of its excellent resistance to these corrosive agents.
Industrial trials showed that pure fused spinel bricks can achieve 10 years’ service
life (24) and pure spinel bricks (spinel-bonded spinel) should be ideal in
such an application. These bricks are, however, expensive and have poor thermal
shock resistance so that MgO-spinel bricks have been tried. As mentioned earlier,
the thermal expansion mismatch between MgO and MA can lead to improved
thermal shock resistance. However, due to MgO’s lower resistance to corrosive
soda- and sulphate-containing compounds, especially SO3 gas, MgO–MA bricks
for such application need careful design. One strategy is using MgO as aggregates
rather than as fines in the matrix; another is using enough spinel that the MgO
clinkers are completely covered by spinel. Use of MgO-rich spinel to introduce
MgO is effective because of the higher coverage of MgO by spinel. Table 5 lists