Molded silicon carbide bodies

Details Molded silicon carbide bodies Molded silicon carbide bodies

1996-11-08

1998-11-17

Group, Karl

Compositions: ceramic

Ceramic compositions

Carbide or oxycarbide containing

501 80, 501 82, 501 89, 501 92, 501 965, C04B 35565

Patent

active

058376313

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a carbon-bound molded SiC body with granular SiC, secondarily formed SiC, and a process for the production of the molded SiC body.
Refractory molded SiC bodies with a bonding matrix comprising SiAlON are used in blast furnace shafts and are found to be suitable against corrosive and abrasive stress. (Gie.beta.ereitechnik 1993 No. 5, page 163, left column, paragraph 4). But such molded bodies have an unsatisfactory resistance to thermal shock.
Furthermore, molded SiC bodies with a bonding phase comprising silicon nitride are not sufficiently resistant to temperature changes in the region of the lower shaft, belly or waist of the blast furnace. For use in blast furnaces, molded bodies on the basis of carbon have too low a resistance against abrasion.
According to DE-OS 22 32 719 for the shaft of blast furnaces are known molded SiC bodies with an SiC bond formed through the reaction of silicon with carbon during the burning. But these molded bodies are not sufficiently resistant against thermal shock and the attack of alkali compounds.
In EP 0 128 165 are disclosed mixtures of carbon-containing materials, refractory grains, such as silicon carbide, refractory oxides, silicon metal and coking carbon-containing bonding agents for the production of refractory bricks which are provided for lining blast furnaces (claim 1, 4, 9, 11). Through the burning, carried out at relatively low temperatures, molded bodies are obtained which have a bonding phase, generated from the carbon-containing bonding means, comprising carbon and silicon, to which in particular advantageous properties, such as low porosity, high strength, erosion resistance and oxidation resistance are traced back. But these molded bodies do not have sufficient resistance against abrasion and attack by alkalies and pig iron.


SUMMARY OF THE INVENTION

The task according to the invention is seen in a molded SiC body which has high mechanical strength and abrasion resistance, alkali resistance and pig iron resistance and oxidation resistance, i.e. a markedly lower furnace loss. The molded SiC body should further have improved resistance to thermal shock.
The solution of the task resides in a molded SiC body and a process for the production and the use of molded SiC body as described below.
That is, the present invention is directed to a molded SiC body comprising secondarily formed SiC, free carbon and an oxygen-containing silicon compound, and having an appropriate porosity and pore distribution.


BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 show the structure of molded SiC bodies of the present invention.


DETAILED DESCRIPTION OF THE INVENTION

The molded SiC body of the present invention comprises secondarily formed SiC, 3-33 percent by weight free carbon, and 0.1-10 percent by weight of an oxygen-containing silicon compound, and has a porosity of 8-23 percent by volume, preferably 14-23 percent by volume, and a pore distribution with a fraction of the pores having a mean pore diameter greater than 1 .mu.m, of less than 3 percent by volume.
Preferably, the molded SiC body contains 2-8 percent by weight of oxygen-containing silicon compound, and has a porosity of 17-20 percent by volume, and a pore distribution with a fraction of the pores having a mean pore diameter greater than 1 .mu.m, of less than 2 percent by volume; or contains 0.1-5 percent by weight of oxygen-containing silicon compound, and has a porosity of 8-17 percent by volume, and a pore distribution with a fraction of the pores having a mean pore diameter of greater than 1 .mu.m, of less than 3 percent by volume.
The oxygen-containing silicon compound preferably comprises SiO.sub.2, and may further comprise silicon oxygenitride.
The invention also provides a process for the production of the molded SiC body, which process comprises providing a mixture comprising 40-80 percent by weight of SiC in a grain size of maximally 3 mm, preferably maximally 2.5 mm, 5-40 percent by weight of a carbon carrier, in a grain size of maximally 0.

REFERENCES:
patent: 4272062 (1981-06-01), Fuziwara et al.
patent: 5135893 (1992-08-01), Dohi et al.
patent: 5212123 (1993-05-01), Schoennahl
patent: 5441799 (1995-08-01), Owens et al.

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