28
D. Gregurek et al.
Fig. 5 Magnesia-chromite
brick. Mineralogical
investigation. Example of
microstructural degeneration
due to high iron oxide
supply. Magnesia (MgO).
Formation of
magnesia-wuestite (mw)
Reduction/Red-Ox Phenomena
In the KIVCET furnace, Isasmelt
TM and in the short rotary furnace, under reducing
conditions, caused by low oxygen partial pressure or by the presence of metals, trivalent iron can be reduced to bivalent and further on to metallic iron. In the magnesiachromite brick, especially the original chromite and newly formed chromite precipitations are sensitive to reduction of iron oxide (Fig. 6). The decrease of the iron
valence results in a volume decrease and causes voids between the single grains. In
case of a subsequent oxidation, the original brick microstructure will not reform. A
frequent repetition of these reactions (Red-Ox) will result in a disintegrated brick
microstructure.
Fig. 6 Magnesia-chromite
brick. Mineralogical
investigation. Example of
highly reduced brick
microstructure. Partly
bondless, severely reduced
chromite (Cr)