Compositions: ceramic – Ceramic compositions – Refractory
Patent
1994-12-30
1996-09-24
Bell, Mark L.
Compositions: ceramic
Ceramic compositions
Refractory
501100, 501101, 501108, C04B 3503, C04B 3504, C04B 3552
Patent
active
055590640
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to chrome-free bricks, and in particular, to chrome-free bricks well suited for use as lining material lined on the inner surfaces of furnaces or vessels for steel-making, cement kilns and glass fusion furnaces, which are directly exposed to high temperatures.
BACKGROUND ART
Magnesia brick has been widely used as lining material because it has a high melting point and superior resistance to corrosion caused by a basic slag. Magnesia brick however is not resistant to structural spalling, and therefore there has been proposed magnesia-chrome brick in order to prevent the break-up caused by structural spalling. The major raw materials of magnesia-chrome brick are magnesia material and chromite. Magnesia-chrome brick is very resistant to corrosion and heat spalling in addition to structural spalling.
In recent years, it has been reported that the intake, inhalation or contact with large amounts of chrome causes a human body rhinitis, dermatitis, bronchitis etc. which are typical diseases caused by hexavalent chromium. Diseases caused by chrome(VI) are of a seriousness such that they have become an object of public concern. For these reasons, the waste of brick made from chromite or chromium oxides is difficult to dispose when considering environmental problems and therefore, there is a strong demand for the development of brick which does not contain chrome, that is, "chrome-free brick".
Thus, the prime object of this invention is to provide chrome-free brick which does not contain chrome and exhibits superior resistance to structural spalling, corrosion and heat spalling although it does not contain chrome.
DISCLOSURE OF THE INVENTION
After a number of experiments, we have found that the penetration of slag and molten steel can be prevented without increasing the densification of brick and, therefore the corrosion and structural spalling resistances of brick can be increased, by allowing adequate amounts of titania and alumina to be added in a composition which is mainly composed of a magnesia material and/or a magnesia-alumina spinel material and by adjusting pore diameter and reaction products by the reaction to be described later. With this fact, we have made the present invention.
Chrome-free bricks according to the invention are mainly made from a magnesia material and/or a magnesia-alumina spinel material and contain 1 to 10% by weight of titania and 1 to 15% by weight of alumina.
Titania TiO.sub.2 and alumina Al.sub.2 O.sub.3 are used mainly as matrix additives for accelerating reactions. The following are the basic reactions at high temperature, where a mixture of the matrix additives and a magnesia material and/or a magnesia-alumina spinel material is used, kneaded, molded and burned, and where they are used without the burning.
When titania TiO.sub.2 and alumina Al.sub.2 O.sub.3 are added to magnesia and the mixture is burned, the following reactions occur: ##STR1## As a result of the above reactions, the following product is formed. solution)
When titania TiO.sub.2 and alumina Al.sub.2 O.sub.3 are added to a magnesia-alumina spinel, the following reactions occur: ##STR2## As a result of the above reactions, a solid solution composed of MgO.Al.sub.2 O.sub.3 and 2MgO.TiO.sub.2 and a solid solution composed of Al.sub.2 O.sub.3.TiO.sub.2 and MgO.2TiO.sub.2 are formed.
The feature of the invention resides in the formation and presence of [MgO.Al.sub.2 O.sub.3 --2MgO.TiO.sub.2 ] s.s. which is the main reaction product formed in accordance with the above reaction. This main reaction product is formed on the surfaces of the particles of the magnesia material and magnesia-alumina spinel material which are the main raw materials working mainly as an aggregate, or produced in their matrix.
Hair cracks due to expansion and shrinkage occur at the boundary between the main reactive product and the particles of the aggregate, and besides, the main reactant product moves into the clearances formed between the aggregate particles, filling the clearances with the
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Okamoto Hisato
Osaki Hiroaki
Tsuchinari Akihiro
Yamamoto Tetsuo
Bell Mark L.
Harima Ceramic Co. Ltd.
Troilo Louis M.
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