Hydraulically-bonded monolithic refractories containing a calcium oxide-free binder comprised of a hydratable alumina source and magnesium oxide

A hydraulically-bonded monolithic refractory, the refractory comprising:

• (a) from about 30% to about 80% by weight refractory aggregate selected from the group consisting of alumina, spinel, magnesia, bauxite, carbon, zircon, zirconia, chromia, mullite, andalusite, sillimanite, fireclay, fused silica, silicon carbide, zirconia-mullite, and combinations thereof, wherein substantially all of the refractory aggregate has a particle size greater than 200 mesh;
• (b) from about 1% to about 30% by weigh refractory fines selected from the group consisting alumina, spinel, bauxite, carbon, zircon, zirconia, chromia, mullite, andalusite, sillimanite, fireclay, fused silica, silicon carbide, zirconia-mullite, and combinations thereof, wherein substantially all of the refractory fines have a particle size of less than 200 mesh and wherein the refractory fines are other than dead-burned magnesium oxide fines;
• (c) from about 2% to about 10% by weight hydratable alumina binder wherein the hydratable alumina binder is a hydraulically setting reactive alumina free of calcium oxide;
• (d) from about 1% to about 30% by weight dead-bummed magnesium oxide fines;
• (e) up to about 0.25% by weight dispersant selected from the group consisting of sodium polyacrylate polymer, naphthalene sulfonic acid-containing polymer, and combinations thereof;
• (f) up to about 0.20% by weight set retarder selected from the group consisting of citric acid, sodium citrate, acid set retarders, and combinations thereof;
• and
• (g) up to about 0.30% by weight organic fibers selected from the group consisting of polypropylene, polyester, vinyl acetate, and combinations thereof.

A hydraulically-bonded monolithic refractory, the refractory resulting from the mixture of:

• (a) from about 30% to about 80% by weight refractory aggregate selected from the group consisting of alumina, spinel, magnesia, bauxite, carbon, zircon, zirconia, chromia, mullite, andalusite, sillimanite, fireclay, fused silica, silicon carbide, zirconia-mullite, and combinations thereof, wherein substantially all of the refractory aggregate has a particle size greater than 200 mesh;
• (b) from about 1% to about 30% by weight refractory fines selected from the group consisting alumina, spinel, bauxite, carbon, zircon, zirconia, chromia, mullite, andalusite, sillimanite, fireclay, fused silica, silicon carbide, zirconia-mullite, and combinations thereof, wherein substantially all of the refractory fines have a particle size of less than 200 mesh and wherein the refractory fines are other than dead-burned magnesium oxide fines;
• (c) from about 2% to about 10% by weight hydratable alumina binder wherein the hydratable alumina binder is a hydraulically setting reactive alumina free of calcium oxide;
• (d) from about 1% to about 30% by weight dead-burned magnesium oxide fines;
• (e) up to about 0.25% by weight dispersant selected from the group consisting of sodium polyacrylate polymer, naphthalene sulfonic acid-based polymer, and combinations thereof;
• (f) up to about 0.20% by weight set retarder selected from the group consisting of citric acid, sodium citrate, acid set retarders, and combinations thereof;
• and
• (g) up to about 0.30% by weight organic fibers selected from the group consisting of polypropylene, polyester, vinyl acetate, and combinations thereof.

A hydraulically-bonded monolithic refractory made by the process comprising the steps of:

• (a) mixing from about 30% to about 80% by weight reactory aggregate wherein substantially all of the refractory aggregate has a particle size of greater than 200 mesh, from about 1% to about 30% by weight refractory fines wherein substantially all of the refractory fines have a particle size of less than 200 mesh other than magnesium oxide fines, from about 2% to about 10% by weight hydratable alumina binder wherein said hydratable alumina binder is free of calcium oxide, and from about 1% to about 30% by weight magnesium oxide fines for about 3 to 7 minutes to form a dry monolithic refractory composition;
• (b) mixing the dry monolithic refractory composition with about 4% to about 8% by weight water for about 3 to 10 minutes to form a flowable monolithic refractory castable composition;
• (c) subjecting the flowable monolithic refractory castable composition to forming to form the refractory;
• (d) curing the refractory at temperatures ranging from 10.degree. C. to 38.degree. C. for about 4 to 24 hours;
• and
• (e) drying the refractory at temperatures ranging from 100.degree. C. to 816.degree. C. until substantially all the water is removed from the refractory.