New periclase-magnesium aluminate spinel refractories from sintered high-purity dead burned magnesite and new various presynthesized spinel-based compositions. II. Compositional variation between coexisting spinel, periclase, and Ca-silicate and Ca-aluminate phases in magnesia spinel refractories and in their spinel-based precursors

The chemistry and distribution of phases formed in a set of six laboratory-prepared magnesia-magnesium aluminate spinel ceramics and in three of their precursor spinel-based compositions, sintered at 1600°C and 1760°C respectively, are examined and compared. The evaluation of the results is the basis for the industry design of magnesia spinel refractories for new advanced applications. In each type of the materials, the spinel phases formed under their firing temperatures seem to have a strong preference for the normal structure. Cracked and noncracked domains in periclase crystals from spinel-based compositions is probably facilitated by differences in the thermal expansion coefficient of periclase crystals having domains differing in their Al2O3 contents. Periclase and spinel mixtures at lower temperatures (1600°C) involved reactions leading to the formation of different periclase s.s and spinel s.s, which depart clearly from equilibrium assemblages. Minor amounts of stoichiometric Ca-silicate and Ca-aluminate phases were formed in all materials.