METHOD FOR THE TREATMENT OF MAGNESIA-CARBON PRODUCTS

Abstract

The invention relates to a method for treating magnesia-carbon products.

Claims

1. A method for the treatment of magnesia-carbon products, comprising the following method steps: A. providing magnesia-carbon products comprising the following features: A.1 the magnesia-carbon products comprise magnesia and carbon; A.2 the magnesia-carbon products comprise proportions of Al.sub.4C.sub.3; B. providing water; C. providing a gas comprising the following features: C.1 the gas comprises carbon dioxide; C.2 the proportion of carbon dioxide in the gas is above the proportion of carbon dioxide in the air; D. providing a container that encloses a space; E. providing the magnesia carbon products in the space; F. subjecting the space to F.1 temperature; and F.2 pressure while providing the water and the gas in the space.

2. The method of claim 1, wherein the magnesia-carbon products are used magnesia-carbon products.

3. The method according to claim 1, wherein the magnesia-carbon products and the water are provided in the space in such proportions that in the space the molar ratio of water to Al.sub.4C.sub.3 is at least 8 to 1.

4. The method according to claim 1, wherein the gas and the water are provided in such proportions in the space that in the space the molar ratio of carbon dioxide to water is at least 1 to 1.

5. The method according to claim 1, wherein the space is subjected to temperature in the range of 100 to 320° C.

6. The method according to claim 1, wherein the space is subjected to pressure in the range of 0.1 to 6 MPa.

7. The method according to claim 1, wherein the gas is carbon dioxide gas.

8. The method according to claim 1, wherein the space enclosed by the container is sealed gas-tight after providing the magnesia-carbon products in the space.

9. The method according to claim 1, wherein the container is an autoclave.

10. The method according to claim 1, wherein the magnesia-carbon products comprise an Al.sub.4C.sub.3 content of at least 0.1% by mass, based on the total mass of the magnesia-carbon products.

11. The method according to claim 1, wherein the magnesia-carbon products comprise a proportion of MgO of at least 69% by mass, based on the total mass of the magnesia-carbon products.

12. The method according to claim 1, wherein the magnesia-carbon products comprise a carbon content of at least 1% by mass, based on the total mass of the magnesia-carbon products.

13. The method according to claim 1, wherein the space is subjected to temperature and pressure such that at least a portion of the Al.sub.4C.sub.3 decomposes during the subjection.

14. The method according to claim 13, wherein the decomposed Al.sub.4C.sub.3 reacts at least partially to form aluminum hydroxide.

15. The method according to claim 1, comprising the following further process steps: G. conveying the magnesia-carbon products from the room; H. mixing the magnesia-carbon products with one or more further substances to form a batch; and I. producing a refractory product from the batch.

Description

EXEMPLARY EMBODIMENT

[0066] A magnesia-carbon product in the form of a refractory magnesia-carbon brick was provided. To simulate the use of this magnesia-carbon brick in a steel industry aggregate, the magnesia-carbon brick was carbonized with an addition of 3% by mass of aluminum grit (based on 100% by mass of magnesia and carbon of the magnesia-carbon brick) as an antioxidant at 1,000° C. for 6 hours under a reducing atmosphere.

[0067] The magnesia-carbon product obtained thereafter was provided for carrying out the method of the invention. This magnesia-carbon product had the following chemical composition, which was determined by X-ray fluorescence analysis (XRF) according to DIN EN ISO 12677:2013-02: [0068] MgO: 92.6% by mass [0069] Al.sub.2O.sub.3: 5.0% by mass [0070] SiO.sub.2: 0.8% by mass [0071] CaO: 1.0% by mass [0072] Fe.sub.2O.sub.3: 0.6% by mass

[0073] In addition to these compounds, the loss on ignition was determined to be 8.8% by mass, based on the mass of the compounds without the loss on ignition.

[0074] In each case, the mass data given above are based on the total mass of the magnesia-carbon product.

[0075] The percentage of carbon was determined by means of a carbon analyzer of the type LECO CS-200/230 (trademark owner and manufacturer LECO Instrumente GmbH, Mönchengladach, Germany) according to the standard DIN EN ISO 15350:2010-08 with 8.2% by mass, based on the total mass of the magnesia-carbon product.

[0076] Finally, the amount of Al.sub.4C.sub.3 in the magnesia-carbon product was first determined qualitatively by X-ray diffraction according to DIN EN 13925-2:2003-07 and then quantitatively determined by energy dispersive X-ray spectroscopy (EDX) according to the complementary standards ISO 16700:2016(E) and ISO 22309:2011(E) to be 1.9% by mass, again based on the total mass of the magnesia-carbon product.

[0077] The carbon product was introduced into the space of a commercial, industrial autoclave together with liquid water, and the chamber was then sealed gas-tight.

[0078] The space was then subjected with excess pressure of 3 MPa and a temperature of 200° C. Due to the temperature, the water introduced into the space formed a water vapor atmosphere in the space.

[0079] At the same time, a gas comprising carbon dioxide in the form of pure carbon dioxide gas was introduced into the space.

[0080] The water was introduced into the space (and was subsequently present in the space as water vapor in such a mass) equal to 3% of the mass of the magnesia-carbon product provided in the space. Thus, the molar ratio of water to Al.sub.4C.sub.3 in the space was slightly above 12:1.

[0081] Further, the carbon dioxide gas was introduced into the space in such a mass that the molar ratio of carbon dioxide to water in the space was 1:1.

[0082] This application of temperature and pressure to the space while providing carbon dioxide gas and water vapor was maintained for a period of 12 hours.

[0083] During this treatment of the magnesia-carbon product, the Al.sub.4C.sub.3 present in it was decomposed into aluminum hydroxide and CH.sub.4. At the same time, a conversion of MgO to brucite was suppressed.

[0084] After the magnesia-carbon product was treated in the space, it was conveyed out of the space and the amount of Al.sub.4C.sub.3 in the magnesia-carbon product was again determined by X-ray diffraction. Thereafter, no more Al.sub.4C.sub.3 could be detected in the magnesia-carbon product.

[0085] Furthermore, the amount of brucite in the magnesia-carbon product was determined by X-ray diffraction according to the standard DIN EN 13925-2:2003-07. According to this, the presence of brucite could not be detected.

[0086] The magnesia-carbon product conveyed out of the space was mixed with other materials in the form of magnesia and graphite to form a batch. In the batch, the proportion of magnesia-carbon products treated by the method of the invention was 30% by mass, based on the total mass of the batch. Subsequently, a refractory product in the form of a new magnesia-carbon product was produced from the batch. For this purpose, the batch was pressed into a magnesia-carbon brick and then annealed at a temperature of 200° C. for a period of 6 hours. The refractory product obtained thereafter in the form of the magnesia-carbon brick is shown in FIG. 1. It can be clearly seen that the magnesia-carbon brick as shown in FIG. 1 does not exhibit any cracks or spalling.

[0087] For comparison purposes, another magnesia-carbon brick was produced. This was produced in accordance with the magnesia-carbon brick (MgO—C brick) described above, but with the only difference that instead of the magnesia-carbon product treated in accordance with the exemplary embodiment, the untreated magnesia-carbon product provided for the exemplary embodiment was used for the production. The magnesia-carbon brick obtained thereafter is shown in FIG. 2. It can be clearly seen that this brick has considerable cracks, as a result of which the properties of the brick are considerably adversely affected.

[0088] FIG. 3 shows a highly schematized flow diagram of a further embodiment of the method according to the invention.

[0089] According to reference sign 1, a used magnesia carbon product was first removed from a steel ladle and, according to reference sign 2, provided for carrying out a method according to the invention. The magnesia carbon product provided according to 2 was then provided together with water 4 in the space enclosed by an autoclave 3, and the space was sealed gas-tight.

[0090] Furthermore, a gas 5 comprising carbon dioxide, the proportion of which was higher than the proportion of carbon dioxide in the air, was provided.

[0091] Subsequently, the space as subjected to temperature 6 and pressure 7. Furthermore, the gas 5 comprising carbon dioxide was introduced into the space at the same time.

[0092] After the magnesia carbon product 2 was appropriately treated in the space of the autoclave 3, it was conveyed out of the space of the autoclave 3 according to 8 and mixed with other substances 10 to form a batch 9. Finally, a new refractory product 11 was produced from the batch 9.