KR19990050169A - Method for improving the corrosion resistance of metal pellets - Google Patents

Abstract

The present invention relates to a method for improving corrosion resistance of metal pellets, and an object thereof is to provide a method for improving the corrosion resistance of metal pellets by coating metal pellets using an aqueous solution of SiO ₂ .

The present invention for achieving the abovementioned objects is how the metal pellets improve the corrosion resistance of the metal pellets, comprising a step of forming the SiO ₂ coating layer was dried and then 10 minutes at a deposition process on at least 3% SiO ₂ solution maintained at less than 140 ℃ As a matter of fact.

Description

Method for improving the corrosion resistance of metal pellets

The present invention relates to a method for improving the corrosion resistance of metal pellets, and more particularly, to a method for improving the corrosion resistance of metal pellets by forming a coating layer on the metal pellets.

Metallic iron pellets are produced by chemically reducing iron ore pellets at high temperatures using natural gas, etc., and are used as an alternative source of iron scrap in electric furnaces in steel mills. Currently, iron scrap is not only getting worse due to the trend of new mills in electric furnaces in steel mills, but also the price of iron scrap is increasing every year. As a result, the use of iron pellets, a source of iron, is gradually increasing.

Iron ore is generally produced and supplied mainly in the South American region, where low-cost electricity such as natural gas of iron ore is an underground resource. More than 95% of the metal iron pellets are used as scrap substitute raw materials and materials in the electric furnace factory. Especially when the metal iron pellets are used in the electric furnace plant, the chemical composition is uniform and accurately known. Not only the amount of unnecessary metal impurities is small, It has various advantages in preparation for iron scrap such as low noise generation and stable price.

However, since the iron pellets are produced by the high-temperature gas reaction, they exhibit very porous structural characteristics. Therefore, when the iron pellets are left in the air, the iron pellets absorb a considerable amount of water, and the reoxidation reaction and the corrosion reaction proceed. Oxidation and corrosion of these iron pellets are not a problem when they are supplied to steel mills located close to the iron pellet plant. However, as shown in the following formulas (1) and (2) As it progresses, it generates a large amount of heat and hydrogen gas, which implies the risk of fire.

3Fe + 2O ₂ ? Fe ₃ O ₄ + heat

3Fe + 4H ₂ O + heat → Fe ₃ O ₄ + 4H ₂

That is, metal iron is oxidized to oxide by contact with oxygen in the atmosphere and releases a large amount of heat. Because of the structural characteristics of porous iron pellets with poor thermal conductivity, the heat released is accumulated in the iron pellets. As the iron pellets absorb moisture in the atmosphere or are converted into oxides by contact with water or seawater, a large amount of hydrogen Gas. At this time, if there is a heat source, a fire occurs. If the metallization ratio (metal Fe / total Fe%) is lowered by the oxidation and corrosion reaction as well as the fire risk of the metal iron pellets, the recovery rate, productivity and cooling ability of the metal are lowered and the refractory consumption is increased A problem occurs.

Methods for minimizing the problems of the metal iron pellets include a method of reducing the reactivity of the metal iron pellets in the atmosphere by a passivation process and a method of monolithizing the metal iron pellets to minimize surface pores . Methods of passivating metal iron pellets include a natural aging method in which an optional oxide layer is formed on the surface of the pellet, an air contact method, and the like. However, the iron pellets produced by this method have a resistance effect against the oxidation reaction proceeded by air contact, but they do not show the corrosion resistance effect by water or sea water contact. On the other hand, the hot forming method for reducing the specific surface area of the metal iron pellets has a problem in that the iron pellets are produced by molding the metal iron pellets under high temperature and high pressure, although the effect of resistance to oxidation and corrosion is great.

Accordingly, the present inventors have conducted research and experiments to overcome the above problems, and have made the present invention based on the results. The present invention is based on the finding that the corrosion resistance of a metal pellet is improved by coating a metal pellet with an aqueous solution of SiO ₂ The present invention is directed to a method for improving the performance of a computer system.

The present invention for achieving the abovementioned objects is how the metal pellets improve the corrosion resistance of the metal pellets, comprising a step of forming the SiO ₂ coating layer was dried and then 10 minutes at a deposition process on at least 3% SiO ₂ solution maintained at less than 140 ℃ .

Hereinafter, the present invention will be described in detail.

In the present invention, the metal pellet is immersed in an aqueous solution of 3% or more of SiO ₂ for 10 minutes or more.

If the SiO ₂ concentration is less than 3%, the SiO ₂ layer can not be uniformly formed on the surface of the metal iron pellet. Therefore, the corrosion reaction progresses gradually with the elapse of time, and the metalization rate rapidly decreases.

In addition, even when the immersion time for immersion in an aqueous solution of SiO ₂ is 10 minutes or less, the corrosion resistance can not be improved due to the above-mentioned reasons.

The temperature of the solution when immersed in an aqueous solution of SiO ₂ is preferably less than 140 캜. In general, since the metal iron pellets have a property of self-burning at about 140 ° C., when the temperature is higher than the above temperature, the surface of the pellet starts to be slowly oxidized, thereby causing a decrease in the metallization rate.

The drying of the metal iron pellets after the immersion treatment can be carried out by a conventional method, but it is preferable to dry the iron iron pellets for 30 minutes or more at 100 ° C or more and less than 140 ° C. This is because the SiO ₂ components adsorbed on the pellet surface portion and the inner pores by the deposition form a strong bond with the pellets to form an SiO ₂ layer that prevents penetration of oxygen, water, seawater, etc. into the metal pellets from outside. .

The metal pellets treated according to the above conditions exhibit very stable characteristics against oxidation reaction by air contact as well as corrosion reaction by contact with water, seawater and the like.

Hereinafter, the present invention will be described in more detail by way of examples.

Example 1

(Examples 1 to 3)

The iron ore pellets were held in a hydrogen gas atmosphere at 950 DEG C for 5 hours to prepare iron metal pellets. A solution was prepared from tetraethyl orthosilicate (Si (OC ₂ H ₅ ) ₄ ) with SiO ₂ contents of 3%, 5% and 10%, respectively. Iron pellets were immersed in the solution at 25 ° C for 10 minutes Respectively. Then, the iron pellets were taken out of the solution, the excess solution was removed from the mesh vessel, and dried in a dryer maintained at 120 ° C for 1 hour to prepare a coated sample. To investigate the change of metal according to hwaryul after immersion for 10 minutes and the SiO ₂ content of 3% NaCl solution that is actually deposited on the samples made in the atmosphere when left to stand over time it is shown in Table 1 below.

(Comparative Examples 1 and 2)

Except that the substrate was immersed in a solution having a SiO ₂ content of 1% and 2%, and the results are shown in Table 1 below.

(Conventional Example 1)

The prepared metal pellets were aged in a nitrogen gas atmosphere containing about 5% of oxygen for 10 hours, and metallization rates were measured according to the elapsed time in the same manner as in the case of the above-described examples.

Reaction conditions The amount of deposited SiO ₂ Metallization rate due to aging (%) SiO ₂ concentration Deposition temperature Immersion time 2 days 4 days 10 days Honor One 3% 25 ℃ 10 minutes 0.42% 90.4 89.4 89.2 2 5% 25 ℃ 10 minutes 0.56% 90.8 90.4 90.0 3 10% 25 ℃ 10 minutes 1.15% 91.2 90.9 90.4 Comparative Example One One% 25 ℃ 10 minutes 0.12% 78 70 65 2 2% 25 ℃ 10 minutes 0.17% 84 80 73 Conventional example One Nitrogen gas atmosphere containing 5% oxygen - 10 hours _ 76.3 70.2 54.0

The iron pellets prepared by using the method of Inventive Examples (1 to 3) shown in Table 1, that is, using a solution containing 3% or more of SiO ₂ as a deposition medium and setting time for 10 minutes, were immersed in a 3% NaCl aqueous solution The change of the metallization ratio due to the standing after standing was only about 1% or less even after 10 days, indicating that the corrosion resistance was greatly improved.

However, when the SiO ₂ solution of 3% or less was used as the adherend as in the method of Comparative Examples (1) and (2), the metallization rate was remarkably decreased from the initial stage of the laying. In the case of Conventional Example 1, Only about 50% of the total amount was shown.

Example 2

(Examples 4 to 6)

The iron ore pellets were held in a hydrogen gas atmosphere at 950 DEG C for 5 hours to prepare iron metal pellets. A solution in which the content of SiO ₂ was 3% from tetraethyl orthosilicate (Si (OC ₂ H ₅ ) ₄ ) was prepared and heated to 50 ° C, 100 ° C and 130 ° C, Immersed, and maintained. Then, the iron pellets were taken out of the solution, the excess solution was removed from the mesh vessel, and dried in a dryer maintained at 120 ° C for 1 hour to prepare a coated sample. The results are shown in Table 2 below. [Table 2] < tb >< tb >< TABLE >

(Comparative Examples 3 to 6)

Except that iron pellets were immersed in a solution prepared by maintaining the temperature of the SiO ₂ solution at 140 ° C and 160 ° C for 1 minute and 5 minutes respectively at 50 ° C and 50 ° C, respectively, The results are shown in Table 2 below.

Reaction conditions Metallization rate due to aging (%) SiO ₂ concentration Deposition temperature Immersion time 2 days 4 days 10 days Honor 4 3% 50 ℃ 10 minutes 90.3 89.7 89.4 5 3% 100 ℃ 10 minutes 90.7 90.0 90.1 6 3% 130 ℃ 10 minutes 90.0 89.8 89.3 Comparative Example 3 3% 140 ° C 10 minutes 87.2 87.0 86.4 4 3% 160 ° C 10 minutes 86.4 86.2 85.4 5 3% 50 ℃ 1 minute 88.4 88.0 87.0 6 3% 50 ℃ 5 minutes 88.2 89.0 86.8

Further, even when the immersion treatment temperature is lower than 140 占 폚 as in the case of the inventive examples (4 to 6) shown in Table 2, it shows a high metallization rate after 10 days of aging. However, in the case of Comparative Examples (3 to 4) in which the immersion treatment temperature was 140 ° C or higher and Comparative Examples (5 to 6) in which the immersion treatment time was 10 minutes or less, the metallization rate was lowered at the beginning of aging, Thereafter, only a slight decrease was shown.

Therefore, from the above results, it is found that when SiO ₂ solution is used as a deposition medium, it is manufactured by using a SiO ₂ solution of 3% or more, a deposition treatment temperature of less than 140 ° C, and a deposition treatment time of 10 minutes or more, It can be confirmed that the reaction conditions are effective for improving the corrosion resistance.

As described above, according to the present invention, by treating with a SiO ₂ solution of 3% or more in order to improve the corrosion resistance of the metal pellets, it is possible to remarkably improve the resistance to corrosion caused by contact with water or sea water Effect.

Claims (3)

Wherein the metal pellet is immersed in an aqueous 3% or more SiO ₂ solution maintained at less than 140 캜 for 10 minutes or more and dried to form a SiO ₂ coating layer. The method according to claim 1, The aqueous solution of SiO ₂ The method of improving the corrosion resistance of metal, characterized in that the pellets prepared from tetraethyl ortho-silicate. The method according to claim 1, Wherein the drying is performed at a temperature of 100 ° C or more and less than 140 ° C for 30 minutes or more.