Slaking-resistant calcia refractory

A slaking-resistant calcia refractory which is a brick fired to a predetermined shape, consisting essentially of (a) 2% by weight or less of silicon dioxide, (b) aluminum oxide (Al.sub.2 O.sub.3) and magnesium oxide (MgO) of the amount defined in the graph of FIG. 5 as within the region enclosed by the lines connecting point A (2.5 wt% Al.sub.2 O.sub.3 and 0 wt% MgO), point B (1.5 wt% Al.sub.2 O.sub.3 and 1.5 wt% MgO), point C (1.5 wt% Al.sub.2 O.sub.3 and 8.5 wt % MgO) and point D (10 wt% Al.sub.2 O.sub.3 and 0 wt% MgO), (c) 0.9% by weight or less of iron oxide, and (d) a predominant amount of calcium oxide.

A slaking-resistant calcia refractory consisting essentially of, as a fired mixture, (a) 0.7-2% by weight of silicon dioxide, (b) aluminum oxide (Al.sub.2 O.sub.3) and magnesium oxide (MgO) of the amount defined in the graph of FIG. 5 as within the region enclosed by the lines connecting point E (3 wt% Al.sub.2 O.sub.3 and 0 wt% MgO), point F (2 wt% Al.sub.2 O.sub.3 and 3 wt% MgO), point G (2 wt% Al.sub.2 O.sub.3 and 8 wt% MgO) and point D (10 wt% Al.sub.2 O.sub.3 and 0 wt% MgO), (c) 0.4% by weight or less of iron oxide, and (d) a predominant amount of calcium oxide.

A slaking-resistant calcia refractory consisting essentially of, as a fired mixture, (a) 2% by weight or less of silicon dioxide, (b) aluminum oxide (Al.sub.2 O.sub.3) and magnesium oxide (MgO) of the amount defined in the graph of FIG. 5 as within the region enclosed by the lines connecting point A (2.5 wt% Al.sub.2 O.sub.3 and 0 wt% MgO), point B (1.5 wt% Al.sub.2 O.sub.3 and 1.5 wt% MgO), point C (1.5 wt% Al.sub.2 O.sub.3 and 8.5 wt% MgO) and point D (10 wt% Al.sub.2 O.sub.3 and 0 wt% MgO), (c) 0.9% by weight or less of iron oxide, (d) 0.03-0.2% by weight of boron oxide, and (e) a predominant amount of calcium oxide.

A slaking-resistant calcia refractory which is a brick fired to a predetermined shape, consisting essentially of (a) 2% by weight of silicon dioxide, (b) aluminum oxide (Al.sub.2 O.sub.3) and magnesium oxide (MgO) of the amount defined in the graph of FIG. 5 as a within the region enclosed by the lines connecting point A (2.5 wt% Al.sub.2 O.sub.3 and 0 wt% MgO), point B (1.5 wt% Al.sub.2 O.sub.3 and 1.5 wt% MgO), point C (1.5 wt% Al.sub.2 O.sub.3 and 8.5 wt% MgO) and point D (10 wt% Al.sub.2 O.sub.3 and 0 wt% MgO), (c) 0.3-0.9% by weight of iron oxide, (d) 0.03-0.2% by weight of boron oxide, and (e) a predominant amount of calcium oxide.