Manufacture of improved fused cast refractory

Abstract

Basic fused cast refractory with principal crystal phases of periclase and magnesium-spinel is made by adding nonfused oxidic inorganic grog particles to molten mass of the refractory as it is cast into a mold cavity, thereby resulting in increased modulus of rupture at temperature in the range of about 1340.degree.-1500.degree. C. and avoidance of shell formation. Molten mass has a composition consisting essentially (by weight) of 45-78% MgO, 0-30% Cr.sub.2 O.sub.3, 0-35% Al.sub.2 O.sub.3, 0-17% FeO + Fe.sub.2 O.sub.3, at least 82% MgO + Cr.sub.2 O.sub.3 + Al.sub.2 O.sub.3 + FeO + Fe.sub.2 O.sub.3, 1-8% SiO.sub.2, 0-2% CaO + BaO + SrO.sub.2, 0-10% TiO.sub.2 and 0-3% fluorine. Nonfused particles have a loss on ignition at 1000.degree. C. of less than about 0.5% by weight and an aggregate SiO.sub.2 content at least about equal to the SiO.sub.2 content of the molten mass forming the cast refractory. Grog particles are of a size (e.g., within the range of particles passing about 25 mm. sieve openings and retained by about 0.5 mm sieve openings) and in an amount (e.g., about 2.5 to 70% by weight of the cast refractory) sufficient to effect at least partial melting of and penetration into the particles by and resolidification with the cast molten mass so as to form a continuous coherent crystal structure throughout the solidified cast mass wherein discrete grog particles and remnants thereof (if any exist) are not optically identifiable.