ABSTRACT
A magnesia refractory is defined by the American Society for Testing and
Materials (ASTM) as “a dead-burned refractory material consisting predominantly
of crystalline magnesium oxide” (1). Furthermore, ASTM defines “dead-burned”
as “the state of a basic refractory material resulting from a heat treatment that
yields a product resistant to atmospheric hydration or recombination with carbon
dioxide” (2). The chemical formula for magnesium oxide is MgO. However, no
dead-burned magnesium oxide contains 100 wt.% MgO. Chemical assays of any
such refractory raw material show some level (generally less than 30 wt. % total)
of silica, lime, iron oxide, alumina, and boron oxide, that, mineralogically, occur
(1) in triple-point pockets and films between the MgO crystallites in the dead-
burned magnesium oxide material as, for example, various calcium silicates,
calcium magnesium silicates, calcium boron silicates, and calcium aluminates;
(2) as lime and iron oxide solid-solutions in the magnesia crystallites; and (3)
sometimes, as magnesioferrite exsolution intergrowths, within the magnesium
oxide crystallites themselves.
