JPS6035310B2 - magnesia carbon brick - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to magnesia carbon bricks, particularly 17
The purpose is to suppress deterioration in durability due to reduction and volatilization of magnesia that occurs when magnesia carbon bricks are used under conditions of 0,000 or more.

Magnesia carbon bricks are widely used as linings for electric furnaces, converters, metallurgical furnaces, special smelting furnaces, etc., and are difficult to penetrate with slag and do not cause structural spalling, or are excellent in thermal spalling. Due to these excellent properties, it has superior durability compared to conventional maguro bricks and dolomite bricks.

However, it is natural that the conditions for its use are limited to an atmosphere in which the oxidation of carbon, which is the main component, is small. Even when used under such conditions, damage to magnesia-carbon bricks is limited by carbon oxidation. Therefore, conventional technologies related to magnesia carbon bricks are mostly limited to manufacturing methods that include binders to suppress carbon oxidation, such as binders for finely manufacturing bricks, or antioxidant materials. Ta. However, the present inventors have a converter with an average tapping temperature of about 170,000 or higher, and when magnesia carbon bricks are used in the pool part of the converter, which has the highest temperature, the durability is low. Therefore, after examining the cause of damage to magnesia carbon bricks in detail and investigating the cause of carbon oxidation, we found that magnesia oxidizes carbon, especially at high temperatures of about 17,000°C or higher, that is, carbon is oxidized by the oxygen of magnesia. This is a major cause, and making magnesia/carbon bricks more granular and adding antioxidants is effective against oxidation of carbon due to the intrusion of oxygen from the outside, but It was also found that it was ineffective. It is well known that magnesia and carbon react at high temperatures, and the following reaction formula has been considered: Mg○1C→Mg+Co For example, the Refractory Technology Association's " Refractories” (32-Madara 6, 1980)
It is said that magnesia clinker has a small amount of &03, making it difficult to react, and that magnesia clinker having a low Ca◯/S02 ratio promotes the reaction.

However, the range of the Ca○/Si02 ratio and Mg○ content is not explained at all, and the most important form of existence of Ca○ is not described. ．． Also, “refractories” (2
7-1242, 1975) describes that the addition of a small amount of calcium oxide suppresses the volatilization of magnesia regarding the solid solution of calcium oxide in magnesia in air. However, in this case, high purity Mg○ in an oxidizing atmosphere
It is only a description of the simple evaporation phenomenon of Ca○ interdissolution of -Ca○ system and Mg○, and there is no mention at all of the decomposition of Mg0 in a reducing atmosphere. Furthermore, it is already well known that such a reaction occurs inside pitch-magnesia dolomite-based refractories.

For example, when these refractories are used, the carbon derived from the pickle reduces Mg0, and the ring-formed Mg vapor reoxidizes on the surface of use, forming a dense layer of Mg0. Since this layer has excellent corrosion resistance against slag, the effect of pitch is described as improving the durability of bricks as a result. However, in this case, the carbon content is 2 to 3%, and since it is dispersed in the pores of the brick, the carbon does not oxidize and cause serious defects in the brick structure, whereas magnesia carbon bricks are unfired. Since it is a brick, and carbon itself constitutes the connective tissue of the brick, oxidation of carbon is the main cause of damage to magnesia carbon bricks, as mentioned above. The present inventors have focused on the fact that the coexistence stability of magnesia and carbon, slag resistance, and heat resistance are important factors in selecting a magnesia clinker for the durability of magnesia-carbon bricks, and from this point of view, various As a result of investigation, it was found that it is desirable to use magnesia containing Ca○ or ZrO2 as a magnesia clinker having excellent properties such as satisfactory coexistence with carbon, and based on this, the present invention was completed. It is.

The gist is that the Ca○/Si02 ratio is between 2 and 10.
Contains 1.5% to 4% by weight of aggregated magnesia with Ca0, or/and 21.5% to 4% solid solution of Z with a Zr02/Si02 ratio of 2 to 10, and carbon. Magnesia is characterized by
It provides carbon bricks.

First, magnesia that satisfies the objectives of the present invention, such as coexistence stability with carbon, has Mg○ of 93% by weight or more, Ca○ content of 2% by weight or more, and furthermore, Ca0 constitutes silicate between elliclase grains. The coexistence stability with carbon, that is, the effect of suppressing reduction and evaporation is low only in the free Ca◯ state, and it is preferable that the carbon content is at least 1.5% by weight or more, and that it is hard to form in Veryclase.

Also, in the case of Z2 content, if Mg0 is 93% by weight or more, Zr
02/Si02 ratio is 2.0 or more, and 2 of Z is at least 1
．． Preferably, it is hardened to 5% by weight Vericlase. Here, the reason why the composition of magnesia is limited to the above range will be explained. First, when o Mg0 reaches 93% by weight, the slag resistance, which is a characteristic of magnesia, decreases.

o When Ca○/Si02 is less than 2, the silicate produced between veryclase grains is a low-melting substance such as monticerite or melwinite, and the hot strength is low and the slag resistance is poor.

In addition, the stability in a reducing atmosphere is poor compared to this a0.Si02 and 3Ca○.Si02. If Ca◯/Si02 exceeds 0, some free Ca◯ will be present, which will cause difficult handling problems such as hydration, which is not preferable. Zr02 is Ca
It has the same effect as ○, and the Zr02/Si02 ratio is also C.
The same restrictions apply as for a○/Si02. o Ca○ or Zr02 has a solubility limit in Mg○ of about 4% by weight, but the reduction and evaporation suppressing effect is not much different at 3.5% by weight or more, so the most preferable amount is 2.0 to 3%. .5% by weight
It is.

Note that when the amount of solid solution is less than 1.5% by weight, the effect of suppressing reduction and evaporation is small. The coexistence stability of magnesia and carbon in the present invention, that is, the mechanism for suppressing the reduction and evaporation of magnesia, has not been clearly elucidated, but it is believed that the solid solution of Ca○ in beryclase causes resistance under reduction of beryclase. At the same time, it is assumed that the unsolidified Ca0 is due to the synergistic effect of a protective layer formed between silicates, especially Xa0.Si02, ao.Sj02, ao.Sj02, or glass of this system, between the berclace grains.

The magnesia of the present invention has the greatest reduction and evaporation suppressing effect when magnesia containing 1.5% by weight or more of Ca○ or Z2 is used as a solid solution in the magnesia part of the Bone brick, but ordinary Ca○ or Zr02 can be replaced with less than 1.5% by weight of hardened magnesia. Practically effective results can be obtained when the amount is less than 5% by weight of the magnesia portion. Of course Ca○Gokou Magnesia and Z
The r○2 solid solution magnesia can be used either in combination or alone. The carbon used in the present invention includes natural graphite, artificial graphite, electrode layers, petroleum coke, carbon black, etc. Among them, natural scaly graphite is particularly preferred.

In the brick of the present invention, the ratio of magnesia to carbon depends on the type and use of magnesia, but magnesia is 9%
It is preferable that the carbon content be 5 to 65% by weight, and the carbon content be 5 to 35% by weight.

This is because if the carbon content is less than 5% by weight, the carbon-containing brick cannot fully exhibit its property of being difficult to get wet with slag, and if it is more than 35% by weight, it is difficult to obtain a sufficient packing density for manufacturing the bricks, resulting in poor durability. This is because the In addition, in the present invention, these magnesia and carbon are the main components of the brick, but it is desirable that they contain at least 9% by weight or more in the brick, and a small amount of silicon,
aluminum, ferrosilicon, silicon carbide, phosphate,
There is no problem in adding a sintering agent such as a silicate or an antioxidant.

In the present invention, a binder such as tar pitch or resin that generates carbon when heated is added to a mixture of magnesia and carbon whose particle size has been adjusted to form a slurry.

This mixture is molded and then heated and treated in a conventional manner to be used as unfired bricks. In use, if a metal case is required, it is covered by simultaneous molding with metal during molding. It may also be used as fired bricks fired in a reducing atmosphere. The present invention will be further explained below based on Examples.

Example Particle Size Various magnesia and flaky graphite powders shown in Table 1 were blended as a binder and phenol resin was added, heat-kneaded, molded at a molding pressure of 1500 k9/m, and then heat treated at 200 CO for 2 hours to obtain each sample. .

Table 2 shows the weight loss rate and porosity after firing these samples for 1,800,004 hours in a reducing atmosphere. Invention No. 1, No. 2, No. Sample No. 3 had a lower weight loss rate and lower apparent porosity than the comparative product, and was able to suppress reduction and evaporation.

Invention No. 2 was used on the converter trunnion side at an average tapping temperature of 171,000, and the amount of damage caused by conventional magnesia carbon bricks was 0.6 to 0.7 rails/charge, while the amount of damage was 0.4 to 0.5 walls/charge. /Charge and a remarkable effect was seen.

Table 1 Note 1) Shows the amount of solid solution of Ca○ or Zr02 (the amount of solid solution was calculated from the change in the lattice constant of X-rays).

Note 2) The weight loss after reduction heating at 1800°C was due to the reduction of Mg○, and was taken as an indicator of the level of reduction. The measurement was performed by embedding magnesia in carbon breeze, heating it, and calculating from the change in weight of magnesia after heating. Table 2

Claims (1)

[Claims] 1 CaO with a CaO/SiO_2 ratio of 2 to 10
．． Magnesia characterized by containing magnesia in a solid solution of 5% to 4% by weight or/and magnesia in a solid solution of 1.5% to 4% by weight of ZrO_2 having a ZrO_2/SiO_2 ratio of 2 to 10, and carbon.・Carbon brick.