Magnesia-spinel refractory and method of producing the same

Compositions: ceramic – Ceramic compositions – Refractory

Reexamination Certificate

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Reexamination Certificate

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06239051

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnesia-spinel refractory having improved corrosion resistance and slag penetration resistance and used for a high-temperature metallurgical furnace, a cement rotary kiln, and the like for steel refining, nonferrous metallurgy, etc.
2. Description of the Related Art
A conventional magnesia ultra-high-temperature refractory is disclosed, which comprises a fused magnesia clinker as an aggregate, and a spinel solid solution phase containing an alumina component in an amount of 5 to 40% by weight relative to the entire matrix (refer to, for example, Japanese Patent Unexamined Patent Publication No. 4-55360). Japanese Unexamined Patent Publication No. 5-117019 discloses that magnesia-chrome or magnesia-spinel basic refractory bricks (a type of ceramics) are mainly used for a high-temperature metallurgical furnace, a cement rotary kiln, or the like for steel refining, nonferrous metallurgy, etc, and the magnesia-spinel refractory bricks are generally produced by mixing two raw materials, i.e., 50 to 90% by weight of magnesia (MgO) clinker and 10 to 50% by weight of spinel (MgO.Al
2
O
3
) clinker.
However, in molding and burning a mixture of magnesia clinker powder and spinel clinker powder, the spinel phase is not sufficiently produced in the crystal grain boundaries of periclase crystals, which are magnesia crystals, and thus a magnesia-spinel refractory having a high density and a strong structure cannot be obtained. Furthermore, since a mixture containing magnesia clinker and spinel clinker a- powders each containing coarse particles (particle diameter of about 1 to 3 mm), medium particles (particle diameter of about 250 &mgr;m to 1 mm) and fine particles (particle diameter of 250 &mgr;m or less) is molded and burned, the apparent porosity of the resultant refractory is about 10% or more, thereby failing to obtain a dense structure. Therefore, the refractory has problems in that it is easily corroded with melted slag and melted cement, or easily worn by structural spalling and abrasion.
SUMMARY OF THE INVENTION
The inventors carried out various studies about the above problems of magnesia-spinel refractories used for a high-temperature metallurgical furnace, a cement rotary kiln, and the like for steel refining, nonferrous metallurgy, etc. As a result, it was found that at least a portion of raw materials comprises granulated powder granulated by a spray dryer method, and a hydrostatic pressing method is used as molding means to improve spalling resistance and significantly improve corrosion resistance and slag penetration resistance, leading to the achievement of the present invention. Accordingly, it is an object of the present invention to provide a magnesia-spinel refractory in which the corrosion resistance and slag penetration resistance are significantly improved.
The object of the present invention is achieved by the following construction.
A magnesia-spinel refractory comprises a burned product of alumina and magnesia, which has a crystal structure composed of periclase having closed pores and spinel comprising a MgO.Al
2
O
3
component, wherein the periclase crystal grain boundaries have a spinel phase, and periclase and spinel form a dense and strong combined structure.
A magnesia-spinel refractory is obtained by mixing magnesia granulated powder and alumina powder, molding the resultant mixture, and then burning the molded product to form a dense and strong combined structure of periclase and spinel.
A magnesia-spinel refractory is obtained by mixing alumina granulated powder and magnesia powder, molding the resultant mixture, and then burning the molded product to form a dense and strong combined structure of periclase and spinel.
In the magnesia-spinel refractory, an alumina granulated powder is used in place of the alumina powder.
A magnesia-spinel refractory is obtained by mixing magnesia powder and alumina powder, granulating the resultant mixture, molding the granulated powder, and then burning the molded product to form a dense and strong combined structure of periclase and spinel.
A magnesia-spinel refractory is obtained by mixing magnesia granulated powder having a particle diameter of 10 to 150 &mgr;m and alumina powder having a particle size of 0.1 to 5 &mgr;m, molding the resultant mixture, and then burning the molded product to form a dense and strong combined structure of periclase and spinel.
A magnesia-spinel refractory is obtained by mixing alumina granulated powder having a particle diameter of 10 to 150 &mgr;m and magnesia powder having a particle size of 0.1 to 5 &mgr;m, molding the resultant mixture, and then burning the molded product to form a dense and strong combined structure of periclase and spinel.
In the magnesia-spinel refractory, an alumina granulated powder having a particle diameter of 10 to 150 &mgr;m is used in place of the alumina powder.
A magnesia powder for forming the magnesia granulated powder or an alumina powder for forming the alumina granulated powder has a particle diameter of 0.1 to 5 &mgr;m.
A magnesia-spinel refractory is obtained by mixing magnesia powder having a particle diameter of 0.1 to 5 &mgr;m and alumina powder having a particle diameter of 0.1 to 5 &mgr;m, granulating the resultant mixture, molding the granulated powder having a particle diameter of 10 to 150 &mgr;m, and then burning the molded product to form a dense and strong combined structure of periclase and spinel.
The granulated powder is obtained by a spray dryer method.
A hydrostatic pressing method is used as molding means.
A magnesia-spinel protecting tube comprises a burned product obtained from a mixture of magnesia and alumina.
A magnesia-spinel crucible comprises a burned product obtained from a mixture of magnesia and alumina.
The magnesia-spinel refractory is used for copper smelting and converting furnaces.
The protecting tube or crucible is used for slag of copper smelting and converting furnaces.
A method of producing a magnesia-spinel refractory comprises granulating each of a magnesia fine powder and alumina fine powder by using a spray dryer method, producing a mixture of magnesia powder and alumina granulated powder, a mixture of alumina powder and magnesia granulated powder, a granulated powder obtained by mixing a magnesia powder and alumina powder, or a granulated powder obtained by mixing a magnesia granulated powder and alumina granulated powder, molding any of the mixtures by a hydrostatic pressing method, and then burning the molded product.
The magnesia-spinel refractory of the present invention comprises a burned product of alumina and magnesia, which has a crystal structure composed of periclase having closed pores and spinel comprising a MgO.Al
2
O
3
component, wherein the periclase crystal grain boundaries have a spinel phase, and periclase and spinel form a dense and strong combined structure. Therefore, spalling resistance is improved, and corrosion resistance and slag penetration resistance are significantly improved. Also, in the magnesia-spinel refractory obtained by mixing magnesia granulated powder and alumina powder, mixing alumina granulated powder and magnesia powder, or mixing magnesia granulated powder and alumina granulated powder, molding the resultant mixture, and then burning the molded product to form a dense and strong combined structure of periclase and spinel, spalling resistance is improved, and corrosion resistance and slag penetration resistance are significantly improved. The magnesia-spinel refractory has a dense and strong combined structure of periclase and spinel, which is obtained by mixing a magnesia powder and alumina powder, granulating the resultant mixture, molding the granulated powder, and then burning the molded product. Therefore, the corrosion resistance and slag penetration resistance are improved. Furthermore, the spray dryer method is used as the method of forming the granulated powders, thereby improving the spalling resistance and significantly improving the corrosion resistance and slag pe

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