Coating processes – Heat decomposition of applied coating or base material
Patent
1992-03-02
1993-10-12
Bell, Janyce
Coating processes
Heat decomposition of applied coating or base material
427379, B03D 302
Patent
active
052523578
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a process for the manufacture of a porous and rigid insulating refractory material capable of working in contact with a molten ferrous metal, especially as a casting for steel. It also relates to the rigid insulating porous refractory material thus obtained.
It is well known to employ refractory materials in contact with a molten metal, especially when casting steel. It is important that this material should be capable of withstanding temperatures of more than 1000.degree. C., especially from 1400.degree. to 1600.degree. C. (in the case of steel) without damage, deterioration or corrosion.
In practice, brick or concrete are essentially employed, such materials being dense and massive. Now, it is known that these materials are not well suited for use in continuous casting processes, because of their low thermal insulating nature. This results in great difficulty in controlling heat losses and hence maintaining the metal temperature, which is essential in continuous casting processes in order to obtain a uniform metallurgical quality.
Insulating composite ceramic materials are known, which are employed essentially for minimizing the heat losses from an enclosure such as a furnace, due to their very low thermal conductivity. Unfortunately, these products, while indeed being refractory and insulating, are easily wetted and penetrated by the molten steel. The metal not only ruins the insulating nature by entering the pores of the material, but also tends to corrode the ceramic by being oxidized in contact with the ceramic.
PRIOR ART
In document FR-A-1,438,091 it has been proposed to improve the whiteness of porcelain by impregnating it, especially under vacuum, with zirconia acetate, and then drying it and firing it. During the firing the zirconia is fixed by silicate bonds, and this imparts an improved whiteness to the ceramic.
In document U.S. Pat. No. 4,568,652 it has been proposed to decrease the harmful effects of the impurities contained in refractory bauxites with a low content of alumina (42 to 70%) and of low porosity (porosity lower than 20%), by impregnating them with a solution containing at most ten percent (10%) of a metal capable of forming a refractory oxide, such as chromium, iron, calcium, molybdenum, zirconium, for example under vacuum, and then, after drying at 110.degree. C., by heating the impregnated material at least to 1450.degree. C. The oxides formed then react with the impurities to increase the refractoriness of the base material and to decrease the external wettability by glass or slags.
The invention mitigates these disadvantages. It is aimed at a process for preparing an insulating and rigid porous refractory material which is not wetted, nor penetrated or corroded by liquid steel, and is easy to use and suitable in particular for a utilization in the various continuous or pressure casting processes for molten ferrous metal, especially by making it possible to control the rates of cooling of the metal.
DESCRIPTION OF THE INVENTION
The process of the present invention for the manufacture of a rigid insulating refractory material capable of working in contact with a molten ferrous metal, in which: solution of a zirconium salt; porosity of between 85 and 95%; 800.degree. and 900.degree. C. for two to six hours, so that the walls of the pores of the base ceramic material are covered with a fine protective layer of zirconia.
In other words, the invention consists in immersing a highly porous refractory ceramic material in a solution of zirconium salts and then, after drying, in pyrolyzing this solution so as to convert this zirconium salt into zirconium oxide and thus to form a fine oxide layer which covers the walls of the pores (or of the fibers) of the base ceramic material, which nevertheless remains highly porous, rigid and refractory.
It would not have been expected that the deposition of a fine layer of zirconia by the pyrolysis of a zirconium salt on the walls of the pores of a ceramic material avoids the wettability of this mate
REFERENCES:
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patent: 3925575 (1975-12-01), Church et al.
patent: 3944683 (1976-03-01), Church et al.
patent: 4568652 (1986-02-01), Petty, Jr.
Chemical Abstracts, vol. 93, No. 26, Dec., 1980.
Journal of the Ceramic Society of Japan, vol. 98, No. 1, 1990, "Surface Modification of Mullite by Partial Infiltration of Zirconia".
Journal of the Ceramic Society of Japan, vol. 98, 1990, "Effect of HIP Treatment on the Fracture Strength of Reaction-Sintered SiC".
Bell Janyce
Produits Cellulosiques Isolants-Procelis
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