RO126848A0 - Antioxidant additives for producing refractory products mgo-c and alo-c - Google Patents

Abstract

The invention relates to some antioxidant additives used for producing magnesia-carbon and alumina-carbon refractory products which form the refractory coating of furnaces, said additives comprising metals, oxides of said metals, metal carbides and carbon which, at high temperatures, form stable complex compounds of the type AlSiC, AlOC, AlOC, AlBC, AlZrC, non-volatile and non-hydratable, which protect the refractory coating of furnaces increasing the operating period thereof. According to the invention, in a first embodiment, the additives are carried out by homogenizing some micronic pulverous mixtures comprising the following parts by weight : up to 20% metal Al, 10 % metal Si or ferrosilicon, 20% alumina or corundum, 5% amorphous silica, 20% ZrOor refractory zirconium products, up to 10% silicon or boron carbide, 10 % silicon or aluminium nitride, respectively, 25% superaluminous refractory cement, 10 % carbon as petroleum coke, metallurgical coke, anthracite or graphite, and 10% phenol formaldehyde resins resins, and in a second embodiment, to the above-mentioned mixture there are also added 2...3% liquid phenolic resin, the mixture is pressed in the shape of bricks, that are thermally treated at a temperature within the range of 185...250°C and finally milled to a fineness of maximum 0.2...0.5 mm.

Description

ANTIOXIDANT ADDITIVES FOR THE MANUFACTURE OF MgO-C AND A1 ₂ O ₃ -C REFRACTORY PRODUCTS

The invention relates to the composition of antioxidant additives used in the manufacture of magnesium-carbon and alumino-carbon refractory products, in order to increase their performance in operation.

Magnesium-carbon and alumino (corundum) carbon refractory products have been widely used in the last 50 years due to their high resistance to corrosion, erosion and thermal shocks. However, these specific properties of these products decrease with the oxidation and reduction of the carbon (graphite) content.

To slow down the process of carbon oxidation, in industrial practice, in the manufacture of these refractory products, in the mixture of raw materials (magnesite, alumina, graphite, etc.) add small amounts of substances (additives) called "antioxidants".

Known additives used lately are metal powders of Al, Si, Mg and their alloys or metal carbides such as SiC or B4C. Also, some complex substances were experimented, such as aluminum oxycarbs previously synthesized at high temperatures in a neutral or reducing atmosphere, but in difficult and expensive conditions.

The disadvantages of these known antioxidant additives are also determined by the fact that on the one hand the respective metals (Al, Si, Mg and their alloys) during use at high temperatures, volatilize and create additional pores that decrease the resistance of these refractories, and on the other On the other hand, these metals form carbides of the AI4C / 3 type which, during cooling, react with the water vapor in the atmosphere and destroy the refractory lining.

Reactions can be as follows:

4A1 + 3C AI4C3 heaters (1)

A1 ₄ C ₃ + 15H ₂ O ..... cooling-fr 4A1 (OH) ₃ + 3CO + 9H ₂ (2)

The present invention removes the mentioned disadvantages, in that it uses as antioxidant additions mixtures of substances containing metals, oxides of the respective metals, metal carbides and carbon, these when heating the refractory liner during use form "in situ" stable complex compounds (type AI4S1C4 , AI4O4C, A1 ₂ OC, AUB4C7, AUZrC4)., Non-volatile, which do not hydrate on cooling in contact with water vapor.

The reactions that may occur in the "in situ" formation of stable antioxidant compounds are:

4A1 + 2A1 ₂ O ₃ + SiC + 6C ___ _k Al ₄ SiC ₄ + AI4O4C + 2CO (3)

4A1 + A1 ₂ O ₃ + SiC + 4C AI4S1C4 + A1 ₂ OC + 2CO (4)

8A1 + ZrO ₂ + SiC + 9C ___ ► Al ₄ SiC4 + Al ₄ ZrC ₄ + 2CO (5)

8A1 + B ₄ C + A1 ₂ O ₃ + 9C --- ► A1 ₂ OC + A1 ₈ B ₄ C ₇ + 2CO (6)

12A1 + 2B ₂ O ₃ + SiC + 16C --- ► Al ₄ SiC ₄ + A1 ₈ B ₄ C ₇ + 6CO (7)

/ îk_- 2 0 1 1 - 0 0 5 8 8

1 -06- 2911

Table no. 1 Composition of antioxidant additives · according to the invention.

- weight parts-

Raw material A B C D E F G H To the powder 1 1 1 - 1 1 2 2 Yes powder - - - - - 1 - - FeSi> 75Si powder - - - 1 - - - - Al2O3 1.5 2 - - 2 2 2 - SiO ₂ (fume silica) - - - 0.5 - - - - Chic 0.5 0.5 1 0.5 - - - 0.5 b ₄ c - - - - - 1 - ZrO ₂ (ZAC) - - - - - - 2 Si ₃ N ₄ - - - 1 1 - - A1N film - - - - - - - A ₂ C (HAC80) - 2.5 - - - - - Carbon (coke oil, graphite) - 0.7 0.7 0.5 - - 1 1 Solid phenolformaldehyde resin (PhFR) powder 0.5 0.5 - 0.5 0.5 0.5 - 0.5

In table no. 1 are presented some examples of antioxidant mixtures, which can be used in the manufacture of refractory products with carbon continuous, added as such in the composition of carbon bricks or after a previous pressing-tempering-granulation.

The mixtures, according to the invention, form "in situ" during the use of the liner, compounds of the type shown in reactions (3), (4), (5), (6) and (7) which are stable to oxidation, do not volatilize and does not form simple carbides according to reaction (1) which hydrate on cooling according to reaction (2).

The application of the invention has the following advantages:

• Does it allow the realization of magnesium-carbonic and alumino-carbonic products at superior quality parameters _? both after tempering and after heat treatment at 1000 ° C.

• Allows the realization of magnesium-carbon and alumino-carbon products, which have good resistance to successive heating / cooling without dehydration and disintegration.

• Allows the realization of magnesium-carbon and alumino-carbon products more resistant to oxidation and with higher performance in operation.

• Does it lead to savings _? both in manufacture and use _? these refractory products.

Claims (2)

CLAIMS: 1. The invention relates to the production of antioxidant additives! used in the manufacture of magnesium-carbon and alumino (corundum) -carbon refractory products, characterized in that they are made of micron powder mixtures composed of 0-2 parts of metallic aluminum, 0-1 parts of silicon metal or ferrosilicon, 0-2 parts of alumina or corundum, 0-0.5 parts amorphous silica, 0-2 parts zirconia or zirconia refractory products, 0.5-1 parts silicon carbide or boron, 0-1 parts silicon or aluminum nitrides, 0-2.5 parts superaluminous refractory cement, 0-1 parts carbon (petroleum coke, metallurgical coke, anthracite, graphite) and 0-1 parts phenolic formaldehyde resins and after homogenization are packaged properly and can be used as antioxidant]. Antioxidant additives of compositions according to Claim 1, characterized in that after dry mixing, 2-3% liquid phenolic resin is added, mixing is continued, pressed in the form of blocks (bricks), heat treated at 185-250 ° C, granulate and grind to a fineness of max. 0.2-0.5 mm, after which it is packaged and can be used as antioxidant additives !.