Conclusions
The spinel MgAl2O4 vaporizes considerably more slowly than magnesia, the process proceeding by the breakdown of the spinel into its component oxides, and the removal of MgO in the form of Mg+ and O2, the surface of the specimen being enriched in corundum. At high temperatures aluminate spinel shrinks noticeably.
The spinel MgCr2O4 begins to vaporize rapidly at 1500° by vaporization of Cr2O3 in the form Cr, CrO, and O2; at higher temperatures about 1600° MgO and Cr2O3 vaporize simultaneously. At higher temperatures chromite spinel had no noticeable shrinkage.
Tests on industrial refractories of magnesite and chrome-magnesite composition under jets burning propane-butane mixture showed that under these conditions vaporization of the material occurs. That of the magnesite refractory proceeds without noticeable change in chemical composition, the composition of the chrome-magnesite refractory is changed significantly, mainly by the vaporization of Cr2O3.
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Literature cited
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Translated from Ogneupory, No. 10, pp. 40–45, October, 1968.