KR900004064B1 - Process for production of magnesium oxide - Google Patents

Abstract

The process for producing magnesium oxide as anneal separating agent for directional electric steel plate, comprises the step of precipitating magnesium hydroxide by the reaction of seawater and calcium hydroxide, the step of cleaning magnesium hydroxide to include max. 0.1 wt.% total weight of K, Na and Cl and 0.5-3.0 wt.% other impurities, the step of crushing the dried magnesium hydroxide to under 3 micron meter average particle size, and the step of baking the crushed magnesium hydroxide at 950-1050 deg.C.

Description

Method for manufacturing MgO for oriented electrical steel sheet annealing separator

1 is a graph showing a change in the degree of CAA showing the activation ability of MgO with the firing time and temperature.

2 is a graph showing the degree of hydration according to the CAA diagram of MgO.

3 is a graph showing the cumulative sum of particle size distribution of Mg (OH) ₂ before firing and particle size distribution of MgO after firing

The present invention relates to a method for producing MgO for grain-oriented electrical steel sheet annealing separator that can be applied to the surface of the grain-oriented electrical steel sheet to form a glass coating layer having excellent insulation and magnetic properties. In general, in the production of grain-oriented electrical steel sheet, the annealing separator is coated with MgO suspension on the surface of the material after decarbonization annealing to prevent fusion between coils at high temperature annealing, and reacts with oxides (mainly FeO, SiO ₂ ) on the surface of the material. In order to form the glass film excellent in insulation, MgO is used normally as an annealing separator used here. MgO is produced by calcining ore such as dolomite or by precipitating Mg ions in seawater with alkali hydroxides such as Ca (OH) _2, and then washing, drying, crushing and calcining. Unlike the high density, inert refractory materials (usually called magnesia), which are manufactured from seawater, which are mostly made of seawater, MgO is used for low density and active MgO. This is because the formation of a refractory layer of (2MgO, SiO ₂ ) is required. In the annealing separator application process, MgO powder is mixed with water to make a suspension, and this is coated with rubber coat, and then the suspension attached to the surface of the material is dried to form an insulating film by high temperature annealing, so that the annealing separation MgO is suspended. It should be well adhered to the material because of its good point of view, and the film formed should be good for the main characteristics such as insulation, adhesion and magnetic properties of the material. Most commonly used MgO is high activity (citric acid activation, CAA is less than 100) and some low activity (CAA is more than 100) is used. When high activity is used, MgO is easily hydrated in the mixed solution coating process, and thus Mg (OH) ₂ However, the coating adhesion is good, but this hydration water is decomposed in the high temperature annealing process to prevent and block the film formation, resulting in unstable film formation. There is this.

The present inventors have studied the characteristics of MgO in order to solve this problem, and proposed the present invention based on the present invention. The present invention adjusts the application ability of the mixed liquid by adjusting the appropriate range of activating ability, content of component and particle size. The purpose of the present invention is to prepare MgO for annealing separator of a grain-oriented electrical steel sheet having excellent coating properties and good coating properties.

Hereinafter, the present invention will be described in detail.

In the present invention, Mg ions in seawater are reacted with alkali hydroxides such as Ca (OH) ₂ to precipitate Mg (OH ₂ ), and then washed, dried and calcined to produce MgO for grain-oriented electrical steel sheet annealing separator. , Precipitation and precipitation of Mg (OH) ₂ by reaction of seawater with Ca (OH) ₂ ; Mg (OH) comprising: a component of the sum of K, Na and Cl containing other than ₂ to less than 0.lwt% and by washing the Mg (OH) ₂ has a total of components such that 0.5-3.0wt% including other components; Drying the washed Mg (OH) ₂ : Crushing the dried Mg (OH) ₂ to 5% or less of the particles having a particle size of 50 μm or more and 5% or less of the particles having an average particle size of 3 μm or less and 3 μm or less of the average particle size. Step: and calcining the crushed Mg (OH) ₂ at a temperature of 950-1050 ℃ CAA also relates to a method for producing MgO for a grain-oriented electrical steel sheet annealing separator having a low activity of 250-450 seconds.

The target material using the MgO of the present invention is a oriented electrical steel sheet containing 2.8-3.2wt% Si and the crystal orientation is (110) [001], to prepare MgO as an annealing separator in the decarbonized annealing plate It includes techniques to use.

The most important factor in forming the glass film uniformly and densely is the ability of MgO itself to be activated, which is expressed as a CAA which indicates the rate of hydration by citric acid solution, and the degree of CAA depends on the firing conditions. In Figure 1 it can be seen that the effect of the calcination time is not significant, the calcination temperature is important, and as the calcination temperature is higher, the CAA degree increases to lose low activation, that is, the activation ability.

The well-known high-activity MgO has a high hydration rate and shows the activation degree of CAA and the degree of hydration at 30 ° C. for one hour in water. The smaller the degree of CAA, the greater the degree of hydration, and in particular, CAA is more than 250 seconds. Since there is little hydration ability, it satisfies the object of the present invention, and at 450 or more, the viscosity of the mixed suspension is so small that the adhesion to the material is poor and the film formation rate is too slow, making it difficult to apply in the production plant. It can be seen in Figure 1 that the optimum firing temperature, which can have a degree of 250-450 seconds, is 950-1050 ° C.

As can be seen in the examples below, in order to solve the deterioration of adhesion during the application of low activity MgO, seawater was used to investigate elements other than Mg inevitably contained in the production of MgO. K, Na, Cl, S, and B are the majority, and all of these components have been found to increase the viscosity of the mixed suspension to improve the coating workability, of which K, Na, Cl have an adverse effect on the glass film formation. However, it was confirmed that other components such as Ca and Si promoted the film formation to improve the magnetic properties of the product as well as the film properties such as insulation and adhesion.

Therefore, in the present invention, the content of other elements contained in Mg (OH) ₂ was limited to 0.5-3.0 wt%, and the sum of K, Na, and Cl in these other elements was limited to 0.1 wt% or less. The reason for limiting the content of other elements as described above is that when the other element content is 0.5wt% or less, it does not help to improve the coating workability, and when 3wt% or more, the forming film may become uneven. It is easy to manage the ingredients in the manufacturing process will be useful to lower the manufacturing cost.

In addition, the composition of the other components contained in Mg (OH) ₂ precipitated by the reaction of seawater with Ca (OH) ₂ to a range consistent with the present invention can be achieved by conventional seawater washing and pure water (clean water) cleaning. It can be described through Table 1 below.

TABLE 1

For impurities containing Mg (OH) ₂ , it is easily prepared in the range of the present invention by seawater washing and water purification, which are common methods, and as shown in Table 1, the sum of K, Na, and Cl is 0.1 wt%. It can be seen that after washing seawater, at about 3 or 4 times of water purification, 0.5-3wt% of other components can be only washed with seawater.

In the present invention, the present invention is not limited to the above-mentioned cleaning method, and any cleaning method may be used in the case of containing any other components as described above.

On the other hand, there coating operation to the improvement requires the particle size control of the use MgO Initial Mg (OH) ₂ and 950 ℃, 3 sigan shows a particle size of the fired MgO as the cumulative sum to a third the initial Mg (OH) ₂ Since the particle size of MgO decreases due to moisture volatilization and internal pore reduction by sintering, it is necessary to control the initial particle size of Mg (OH) ₂ .

In the examples described below, the particles of Mg (OH) ₂ are 3 μm or less, which are excellent in adhesion and subsequent film formation, and are excluded from the conditions of the present invention due to difficulty in managing work due to poor adhesion.

The application of the optimum annealing separator in combination with the factors for the improvement of the above-described determinants has been made possible by the preparation of specific MgO by the composition of Mg (OH) _2, the particle size management and the firing condition management.

Hereinafter, a description will be given through Examples.

Example 1

Mg (OH) ₂ prepared by the reaction of seawater with Ca (OH) ₂ is 0.02, and the sum of K: Na: Cl contained in Mg (OH) ₂ by ordinary seawater and water purification as shown in Table 1 is 0.02. It is -0.3wt%, and the total content of elements including other components is 1.75-l.77wt%, dried and crushed to make particles and average size 2μm, and calcined at 980 ℃ for 3 hours, and the CAA is 410 seconds. MgO was made.

The MgO was mixed with MgO: H ₂ O = 12: 88, stirred with a stirrer to form a dispersion completely, and then coated, and dried at 600 ° C., followed by annealing at 1200 ° C. and H ₂ for 20 hours to obtain a glassy insulating coating.

TABLE 2

At this time, the film properties and magnetic properties of the liquid mixture after high temperature annealing were measured, and the results are shown in Table 3 below.

Here, in particular, the adhesion amount is the weight g / ㎡ after drying, the insulation is Franklin insulation value Amp. According to ASTM A715-15, the adhesion is 180 mm bend the minimum diameter without film peeling, magnetic properties W17 measured by a single plate measuring instrument Iron loss of / 50 and magnetic flux density of B10.

TABLE 3

As shown in Table 3, when the amount of K, Na, Cl is increased, the viscosity and adhesion increase to improve workability, but the insulation and adhesion deteriorate, and spots and stains appear on the appearance, which requires management to 0.1% or less. And it can be seen that the management of less than 0.1% of the scope of the present invention can produce a grain-oriented electrical steel sheet having excellent liquid properties and good film properties.

Example 2

The amount of K, Na, Cl of Mg (OH) ₂ prepared in the same manner as in Example 1 was adjusted to 0.08%, and the total content was adjusted to 0.2-3.5% including other components. MgO was prepared, with a CAA of 390 seconds.

This and the same specimen as in Example 1 after the same treatment, the liquid properties, coating properties and magnetic properties were investigated, and the results are shown in Table 4 below.

TABLE 4

As shown in Table 4, when the content of the element is increased, the viscosity and adhesion amount is increased, the workability is improved, the insulation and adhesion is good, and in particular, the magnetic properties of magnetic flux density and iron loss are improved, which enables the production of excellent quality products. When added more than 3% workability is good but the film properties are deteriorated and excluded from the scope of the invention.

Example 3

The total content of Mg (OH) ₂ prepared by the reaction of seawater with Ca (OH) ₂ is 1.53-1.55%, and Mg (OH) ₂ having a particle size of 1.6 μm after drying and crushing is 700-1200 MgO of 80-800 seconds was prepared by changing the temperature to ℃, and the change of various properties after the treatment was the same as in Example 1, and the results are shown in Table 5 below.

TABLE 5

As shown in Table 5, as the CAA degree increases and the activity is lost, the workability is deteriorated due to the decrease in viscosity and adhesion, but the film quality characteristics such as insulation and adhesion are extremely excellent, and the film formation rate is slowed over 600 seconds. This improvement is not possible and it can be seen that between 250 and 450 seconds, optimum film properties are possible.

Example 4

Mg (OH) ₂ of Example 3 was dried and crushed to adjust the particle size to 0.5-22.0 μm, and then calcined at l000 ° C. for 3 hours to prepare MgO having a CAA degree of 400 seconds, and then subjected to high temperature annealing by treating under the conditions of Example 1. The various characteristics are shown in Table 6.

TABLE 6

Claims (1)

In the method of producing MgO for an aromatic steel sheet annealing separator by reacting Mg ions in seawater with alkali hydroxides such as Ca (OH) ₂ to precipitate Mg (OH) _2, and then washing, drying and firing. Precipitating and precipitating Mg (OH) ₂ by reaction with Ca (OH) ₂ : The sum of K, Na and Cl among the components other than Mg (OH) ₂ is 0.1wt% or less and includes other components. Washing Mg (OH) ₂ to 0.5-3.0 wt% of the total ingredients: crushing the dried Mg (OH) ₂ so that the average particle size is 3 μm or less while the particles having a particle size of 5 μm or more are 5% or less: and Method for producing MgO for grain-oriented electrical steel sheet annealing separator comprising the step of calcining the crushed Mg (OH) ₂ at a temperature of 950-1050 ℃ MCAO also low activity 250-450 seconds.

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