JP7360572B1 - Magnesium oxide for annealing separator and grain-oriented electrical steel sheet - Google Patents

Abstract

An object of the present invention is to provide magnesium oxide for use as an annealing separator for obtaining grain-oriented electrical steel sheets with excellent coating properties. The present invention has a BET specific surface area of 12.0 m2/g or more and 30.0 m2/g or less, a pore mode diameter of 0.1 μm or more and less than 0.4 μm as determined by mercury intrusion pore distribution measurement, and This is a magnesium oxide for use as an annealing separator, and the mode volume of pores is 1.3 cm3/g or more.

Description

The present invention relates to magnesium oxide (MgO) for use as an annealing separator and grain-oriented electrical steel sheet.

Grain-oriented electrical steel sheets used in transformers and generators are generally made of silicon steel containing about 3% silicon (Si), which is hot-rolled, then cold-rolled to the final thickness, and then decarburized and annealed. , finished annealing, and manufactured. In decarburization annealing (primary recrystallization annealing), a SiO ₂ film is formed on the surface of the steel sheet, a slurry containing magnesium oxide for an annealing separation agent is applied to the surface, dried, wound into a coil shape, and then final annealed. By doing so, SiO ₂ and MgO react to form a forsterite (Mg ₂ SiO ₄ ) film on the surface of the steel plate. This forsterite coating serves to add tension to the surface of the steel sheet, reduce iron loss, improve magnetic properties, and provide insulation to the steel sheet.

This forsterite coating determines the product's appearance and electrical insulation, and also influences its market value. The film formation process affects the inhibitor decomposition behavior of the surface layer of the steel sheet, and ultimately the secondary recrystallization, and the quality of the film affects the quality of the magnetic properties of the product. Furthermore, the appearance of the coating influences the final appearance of the grain-oriented electrical steel sheet as a product. Therefore, the appearance of the coating has an impact on the product value and has a large effect on the product yield, and if the coating is non-uniform, the manufacturing yield of the product will be reduced. Therefore, improving the properties of such coatings plays an important role in the manufacturing technology of grain-oriented electrical steel sheets.

Conventionally, in order to improve the properties of grain-oriented electrical steel sheets, research has been conducted on magnesium oxide as an annealing separator, and various efforts have been made to improve quality. For example, B, CaO, SO ₃ , Various studies have been made on the powder characteristics of magnesium oxide for use as an annealing separator, such as the concentration of impurities such as Cl, citric acid activity (CAA), BET specific surface area, and particle size distribution. However, since magnesium oxide plays a very complex role in the manufacturing process of grain-oriented electrical steel sheets, it is unclear how changes in the powder properties of magnesium oxide affect the product properties of grain-oriented electrical steel sheets. , has not yet been completely elucidated.

Under these circumstances, magnesium oxide for use as an annealing separator has been proposed, focusing on the pores of magnesium oxide particles and controlling the pores. Patent Document 1 discloses a technique for improving the magnetic properties and coating properties of a grain-oriented electrical steel sheet by setting the distribution of _N2 gas adsorption isotherms and water vapor adsorption isotherms of magnesium oxide particles to a specific range. There is. Additionally, Patent Document 2 discloses a technique for improving the magnetic properties and coating properties of grain-oriented electrical steel sheets by controlling the pore volume of magnesium oxide particles within a specific range, as measured by a gas adsorption method. .

Japanese Patent Application Publication No. 10-088240 Japanese Patent Application Publication No. 10-046259

However, the techniques disclosed in Patent Documents 1 and 2 use gas adsorption methods to measure ultrafine pores ranging from 0.1 nm to several tens of nanometers, making it difficult to control during manufacturing and ensuring good results. It has not been easy to stably obtain an annealing separator that provides film properties.

For this reason, the above-mentioned conventional magnesium oxide for annealing separator cannot completely prevent the occurrence of film defects in grain-oriented electrical steel sheets, and grain-oriented electrical steel sheets with excellent film properties cannot be stably obtained. Therefore, it lacked reliability. That is, magnesium oxide for use as an annealing separator with sufficient performance has not yet been found.

Therefore, an object of the present invention is to provide magnesium oxide for use as an annealing separator for obtaining grain-oriented electrical steel sheets with excellent coating properties. Specifically, it is an object of the present invention to provide magnesium oxide for an annealing separator that can form a forsterite film with excellent film appearance and film adhesion on the surface of a steel plate. Another object of the present invention is to propose a method for manufacturing a grain-oriented electrical steel sheet using the above-mentioned magnesium oxide for an annealing separator.

In order to solve the above problems, the present inventors decided to conduct research focusing on the macropore (approximately 100 nm or more) region of magnesium oxide particles for annealing separator, which has not received attention until now. As a result of a detailed study using mercury intrusion pore distribution measurement, which is a method that can strictly evaluate pores, we found that among magnesium oxides, magnesium oxide with pore mode diameter and mode volume adjusted to a certain range. However, it has been discovered that magnesium oxide is more suitable for obtaining grain-oriented electrical steel sheets with excellent coating appearance and coating adhesion, and the present invention has been achieved.

That is, the gist of the present invention is that the BET specific surface area is 12.0 m ² /g or more and 30.0 m ² /g or less, and the mode diameter of the pores as measured by mercury intrusion pore distribution measurement is 0.1 μm or more and 0.1 μm or more. The magnesium oxide for annealing separator has a pore size of less than 4 μm and a mode volume of pores of 1.3 cm ³ /g or more.

Furthermore, the magnesium oxide for annealing separator of the present invention has a CAA40% of 50 seconds or more and 170 seconds or less, a Cl content of 500 ppm or less, and a volume-based cumulative 50% particle diameter (D ₅₀ ) of 0.5 μm or more. It is preferable that it is 7.0 μm or less. By setting CAA40%, Cl content, and _D50 within the specified ranges, magnesium oxide for annealing separation agent can form a forsterite film with excellent film appearance and film adhesion on the surface of the steel sheet. You can definitely get it.

Furthermore, the magnesium oxide for annealing separator of the present invention preferably has a total content of Zn, Zr, Ni, Co, and Mn of 200 ppm or more and 10,000 ppm or less, and preferably has a Zn content of 200 ppm or more and 10,000 ppm or less. More preferably, the Zn content is 200 ppm or more and 9000 ppm or less. By containing the above elements in a predetermined range, the mode volume of the pores of magnesium oxide can be adjusted, so the mode volume of the pores and the mode diameter of the pores can be more easily controlled within the predetermined range. becomes possible. Therefore, it is possible to obtain magnesium oxide for an annealing separating agent that can stably form a forsterite film with excellent film appearance and film adhesion on the surface of a steel plate.

Moreover, the gist of the present invention resides in an annealing separator containing the above-mentioned magnesium oxide for an annealing separator. By using the annealing separator of the present invention, grain-oriented electrical steel sheets with excellent magnetic properties and insulation properties can be manufactured.

Further, the gist of the present invention is to form a SiO ₂ film on the surface of a steel plate, and to form a forsterite film on the surface of the steel plate by applying the above-mentioned annealing separation agent to the surface of the SiO ₂ film and annealing. A method of manufacturing a grain-oriented electrical steel sheet, comprising: By the manufacturing method of the present invention, a grain-oriented electrical steel sheet with excellent magnetic properties and insulation properties can be manufactured.

According to the present invention, it is possible to provide magnesium oxide for use as an annealing separator for obtaining grain-oriented electrical steel sheets with excellent magnetic properties and insulation properties. Specifically, according to the present invention, it is possible to provide magnesium oxide for an annealing separator that can form a forsterite film with excellent film appearance and film adhesion on the surface of a steel plate.

The magnesium oxide for an annealing separator of the present invention has a BET specific surface area of 12.0 m ² /g or more and 30.0 m ² /g or less, and a pore mode diameter of 0.1 μm as measured by mercury intrusion pore distribution measurement. The diameter is at least 0.4 μm, and the mode volume of the pores is at least 1.3 cm ³ /g.

In the present invention, the mode diameter and mode volume of the pores of magnesium oxide for an annealing separator are measured by mercury porosimetry. In the present invention, by using the mercury intrusion method, it is possible to measure the mode diameter and mode volume of pores in the macropore (approximately 100 nm or more) region of magnesium oxide particles, making it possible to strictly control these. It has become.

Specifically, the mode diameter and mode volume of the pores of the magnesium oxide particles are measured as follows. First, a cumulative pore volume curve showing the relationship between the pore diameter and cumulative pore volume of the magnesium oxide particles is obtained by measuring the pore distribution using mercury intrusion porosimetry. The horizontal axis of the cumulative pore volume curve is the pore diameter determined from the mercury intrusion pressure, and the vertical axis is the cumulative pore volume. The following formula (I) (Washburn's formula) is used to convert the mercury intrusion pressure to the pore diameter.
D=-(1/P)・4γ・cosΨ (I)
[Here, D: pore diameter (m), P: injection pressure of mercury (Pa), γ: surface tension of mercury (485 dyne cm ^-1 (0.485 Pa m)), Ψ: contact angle of mercury (130°=2.26893 rad). ]
Then, the obtained cumulative pore volume curve is converted into a log differential pore volume distribution curve. The log differential pore volume distribution curve is the value (dV/d (logD)) obtained by dividing the difference (dV) in each measurement section of the pore volume by the difference value d (logD) treated as the logarithm of the pore diameter. This is calculated and plotted against the average pore diameter of each section. From this log differential pore volume distribution curve, the maximum value of (dV/d(logD)) is obtained as the mode volume of the pore, and the pore diameter corresponding to the maximum value of (dV/d(logD)) is determined as the pore mode volume. Obtained as the mode diameter.

The magnesium oxide for an annealing separator of the present invention has a pore mode diameter of 0.1 μm or more and less than 0.4 μm, preferably 0.15 μm or more and less than 0.3 μm, as measured by mercury intrusion pore distribution measurement. Further, the magnesium oxide for an annealing separator of the present invention has a pore mode volume of 1.3 cm ³ /g or more, preferably 1.4 cm ³ /g or more, as measured by mercury intrusion pore distribution measurement. The upper limit of the mode volume is, for example, less than 2.5 cm ³ /g, preferably less than 2.3 cm ³ /g, and more preferably less than 2.0 cm ³ /g. Examples of the range of mode volume include 1.3 cm ³ /g or more and less than 2.5 cm ³ /g, preferably 1.3 cm ³ /g or more and less than 2.3 cm 3 /g, and 1.4 cm ³ /g or more and less than 2.3 ^{cm 3} /g. More preferably, it is less than .0 cm ³ /g.

Magnesium oxide, which has a pore mode diameter of 0.1 μm or more and less than 0.4 μm and a pore mode volume of 1.3 cm ³ /g or more as determined by mercury intrusion pore distribution measurement, is coated on the surface of the steel sheet. It is possible to form a forsterite film with excellent appearance and film adhesion. On the other hand, magnesium oxide, which has a pore mode diameter of 0.1 μm or more and less than 0.4 μm and a pore mode volume of less than 1.3 cm ³ /g as determined by mercury intrusion pore distribution measurement, is , it is not possible to form a forsterite film with excellent film appearance and film adhesion.

Although the detailed mechanism of how the mode diameter and mode volume of the pores of magnesium oxide particles affect the performance of magnesium oxide has not yet been clearly elucidated, the present inventors believe that ing. First, the pore diameter range of approximately 0.1 to 0.4 μm (that is, the mode diameter range of the pores of the present invention) determined by mercury intrusion pore distribution measurement is within the secondary particles where primary particles of magnesium oxide aggregate. It is thought that this corresponds to the diameter of the void. A large value of mode volume is considered to indicate that the distribution of pore diameters is narrow and uniform. Here, when using magnesium oxide for an annealing separator, it is suspended in water together with additives, etc., and made into a slurry to form an annealing separator. This is applied to a steel plate, dried, and then final annealing is performed. During slurry formation, magnesium oxide remains in water for a certain period of time, and some hydration progresses. Further, during annealing, the annealing separator releases moisture, CO ₂ , etc., and its volume decreases compared to when it was applied. At this time, the magnesium oxide for the annealing separator of the present invention has a mode volume of pores of 1.3 cm ³ /g or more, and it is thought that the voids in the secondary particles are aligned in a narrow range. The degree of loosening of secondary particle aggregation and progress of hydration in water becomes uniform over time. Therefore, uniformity during slurry application is maintained, and variations in the effect of volume reduction due to release of moisture, CO ₂ , etc. during annealing are also reduced. As a result, all the magnesium oxide particles in the annealing separator can uniformly contribute to the film forming reaction, so it is presumed that a uniform film is formed. In addition, if the mode diameter of the pore is too small, the aggregation of secondary particles will be strong, and if the mode diameter of the pore is too large, the gaps between the primary particles will be too large, so the pore diameter should be 0.1 μm or more and 0.4 μm. Should be in the range less than or equal to

In the magnesium oxide for annealing separator of the present invention, the mode diameter of the pores of magnesium oxide can be adjusted by known methods, such as controlling the firing temperature and time of magnesium hydroxide, crushing the magnesium oxide, and after crushing. Adjustments can also be made by measuring the mode diameter of the powder and pulverizing it multiple times, by pulverizing it using a pulverizer with a built-in classifier, and by measuring the mode diameter after pulverization and firing it multiple times.

The mode volume of the pores can be adjusted by various methods, such as adjusting the secondary particle size of the precursor magnesium hydroxide, adjusting the firing conditions of the precursor magnesium hydroxide, adding metal elements, and adjusting the magnesium oxide precursor. There are several methods such as pulverization, pulverization multiple times by measuring the mode volume after pulverization, pulverization using a pulverizer with a built-in classifier, or adjusting the mode volume by mixing multiple magnesium oxide powders. , but not limited to. For example, adjustment can be made by adding Zn, Zr, Ni, Co, and Mn as metal elements in a predetermined range to magnesium oxide for an annealing separator and firing the mixture. Typically, a certain amount of Zn, Zr , Ni, Co, and Mn can be adjusted to increase the mode volume. Among them, by preferably using Zn, the modal volume can be stably adjusted, and typically by adding a certain amount of Zn, the modal volume can be adjusted to increase.

Further, the total content of Zn is preferably 200 ppm to 10,000 ppm. Preferably it is 250 ppm to 9500 ppm, more preferably 300 ppm to 9000 ppm. If the total content is less than 200 ppm or more than 10,000 ppm, magnesium oxide with a pore mode volume of 1.3 cm ³ /g or more cannot be obtained. The contents of Zn, Zr, Ni, Co, and Mn can be controlled by a known method, for example, by a method for controlling the amount of trace amounts of content, which will be described later. The above Zn, Zr, Ni, Co and Mn may be added to the magnesium oxide precursor for annealing separator in the form of their oxides, hydroxides, chlorides, sulfides, carbonates, sulfates, etc. I can do it. In particular, when adding Zn, it is preferable to use zinc chloride and/or zinc oxide. Note that ppm in the specification means mass ppm unless otherwise specified.

The BET specific surface area of the magnesium oxide of the present invention is 12.0 m ² /g or more and 30.0 m ² /g or less. When the BET specific surface area of magnesium oxide is less than 12.0 m ² /g, the primary particle size of magnesium oxide becomes coarse, the reactivity of the magnesium oxide particles deteriorates, the forsterite film formation rate decreases, and the oxidation Because magnesium particles are coarse, residues tend to remain when removed with acid. When the BET specific surface area of magnesium oxide is larger than 30.0 m ² /g, the primary particle size of magnesium oxide becomes small and the reactivity of the magnesium oxide particles becomes too fast, making it difficult to form a uniform forsterite film. Therefore, in the present invention, the BET specific surface area is 12.0 m ² /g or more and 30.0 m ² /g or less, preferably 12.0 m ² /g or more and 23.0 m ² /g or less.

CAA uses a solid-liquid phase reaction to empirically simulate the reactivity of the solid-solid phase reaction between silicon dioxide and magnesium oxide that occurs on the surface of an actual electrical steel sheet. This is to measure the reactivity of magnesium particles. If the CAA40% of magnesium oxide is greater than 170 seconds, the reactivity of the magnesium oxide particles will be poor and the forsterite film formation rate will be slow, so a sufficient film will not be formed and the iron loss and magnetic flux density of the grain-oriented electrical steel sheet will decrease. characteristics tend to deteriorate. On the other hand, if the CAA40% of magnesium oxide is less than 50 seconds, the reactivity of the magnesium oxide particles becomes too fast, making it impossible to form a uniform forsterite coating, resulting in poor coating appearance and coating adhesion on grain-oriented electrical steel sheets. There is a tendency to That is, when 40% CAA is used for less than 50 seconds, the amount of hydration becomes too large, while when it exceeds 170 seconds, the reactivity is too low and good film properties tend not to be obtained. Therefore, in the present invention, CAA40% is, for example, 50 seconds or more and 170 seconds or less, preferably in the range of 50 to 150 seconds, more preferably in the range of 60 to 130 seconds.

The volume-based cumulative 50% particle diameter (D ₅₀ ) is preferably 0.5 μm or more and 7.0 μm or less. When the volume-based cumulative 50% particle diameter (D ₅₀ ) is smaller than 0.5 μm, the activity is high and the aggregation becomes large, making it difficult to handle and forming a good film. When the volume-based cumulative 50% particle diameter (D ₅₀ ) exceeds 7.0 μm, the primary particle diameter of magnesium oxide becomes coarse, the reactivity of the magnesium oxide particles worsens, and the rate of forsterite film formation slows down. , it becomes difficult to form a sufficient film. More preferably, _D50 is 0.7 μm or more and 6.0 μm or less, and even more preferably 1.0 μm or more and 5.0 μm or less.

In addition to the aforementioned zinc (Zn), zirconium (Zr), nickel (Ni), cobalt (Co), and manganese (Mn), the magnesium oxide of the present invention can also contain, for example, calcium (Ca), silicon (Si), aluminum ( It can contain trace amounts of substances such as Al), iron (Fe), phosphorus (P), boron (B), sulfur (S), fluorine (F), and chlorine (Cl).

When the magnesium oxide of the present invention contains calcium (Ca), the content of calcium is preferably 0.2 to 2.0% by mass in terms of CaO. When the magnesium oxide of the present invention contains silicon (Si), the silicon content is preferably 0.05 to 0.5% by mass. When the magnesium oxide of the present invention contains aluminum (Al), the content of aluminum is preferably 0.01 to 0.5% by mass. When the magnesium oxide of the present invention contains iron (Fe), the iron content is preferably 0.01 to 0.5% by mass. When the magnesium oxide of the present invention contains phosphorus (P), the content of phosphorus is preferably 0.01 to 0.15% by mass in terms of P ₂ O ₃ . When the magnesium oxide of the present invention contains boron (B), the boron content is preferably 0.04 to 0.15% by mass. When the magnesium oxide of the present invention contains sulfur (S), the sulfur content is preferably 0.01 to 1.5% by mass in terms of SO ₃ . When the magnesium oxide of the present invention contains fluorine (F), the content of fluorine is preferably 0.05% by mass or less. When the magnesium oxide of the present invention contains chlorine (Cl), the content of chlorine is preferably 500 ppm or less, more preferably 400 ppm or less, and even more preferably 300 ppm or less.

The magnesium oxide of the present invention may have a total pore area of 5 m ² /g or more and less than 30 m ² /g, for example, as determined by mercury intrusion pore distribution measurement; The average pore diameter may be 0.2 μm or more and less than 3.0 μm. In the present invention, the total pore area is the sum of pore areas calculated from measurement data assuming that the pores are cylindrical. For the total pore area and average pore diameter, values measured at an injection pressure of up to 59,950.54 psia are used. In addition, the total pore area and average pore diameter of magnesium oxide can be adjusted by known methods, such as controlling the firing temperature and time of magnesium hydroxide, and further adjusting the total pore area and average pore diameter after pulverization. Adjustment can also be made by measuring and firing multiple times.

In the present invention, a known method can be used for producing magnesium oxide. For example, using magnesium chloride as a raw material, calcium hydroxide is added in the form of a slurry to this aqueous solution and reacted to form magnesium hydroxide. Next, this magnesium hydroxide is filtered, washed with water, dried, and then fired in a heating furnace to form magnesium oxide, which can be pulverized to a desired particle size to produce it.

Further, instead of calcium hydroxide, an alkaline compound having a hydroxyl group such as sodium hydroxide or potassium hydroxide can also be used. In addition, magnesium oxide is produced by the Aman process in which an aqueous solution containing magnesium chloride such as seawater, irrigation water, bittern, etc. is introduced into a reactor and magnesium oxide and hydrochloric acid are directly produced at 1773 to 2273 K. Magnesium oxide can be produced by grinding to a particle size of .

Furthermore, magnesium oxide can also be produced by hydrating magnesium oxide obtained by sintering the mineral magnesite, sintering the obtained magnesium hydroxide, and pulverizing it to a desired particle size.

The amount of trace inclusions in MgO can be controlled by known methods. As a method for controlling the amount of trace contents in MgO, for example, during the manufacturing process of the crude product or by controlling the obtained crude product so that the amount of trace content in MgO is within a predetermined range. This can be done by controlling the amount of trace amounts of content before the final firing. Control during the manufacturing process of crude products can be carried out, for example, by analyzing the amount of trace amounts contained in raw materials, and based on the results, using wet or dry methods to control the amount of trace contents to be controlled at a predetermined amount. It can be controlled by adding or removing by wet method. Addition of trace amounts of substances can be carried out, for example, by mixing the elements to be added and drying the mixture. In addition, trace amounts of inclusions can be removed, for example, by physically cleaning the excess inclusions with a wet method or by chemically separating them. Chemical separation can be accomplished, for example, by forming a soluble hydrate and separating it by dissolving, filtering, and washing, or by forming an insoluble compound and precipitating it, and separating it by adsorbing the precipitate. This can be done by The amount of trace elements contained in the crude product before final calcination can be controlled by, for example, combining and mixing crude products with different compositions, so that the amount of trace elements is kept within a predetermined range. The shortage can be adjusted and controlled by final firing. Furthermore, in order to control the amount of trace elements, in each case after producing the crude product MgO and analyzing the MgO obtained, the above procedure is followed depending on the individual results regarding the amount of trace elements. can be repeated and combined.

The BET specific surface area, CAA40%, and _D50 of magnesium oxide can be adjusted by a known method, for example, by the following method. That is, by adjusting the reaction temperature and the concentration of the alkali source during the manufacturing process of magnesium hydroxide, the primary particle size and secondary particle size of magnesium hydroxide can be controlled, and the BET specific surface area, CAA40%, and D ₅₀ can be adjusted. Further, the BET specific surface area, CAA40%, and _D50 of magnesium oxide can also be adjusted by controlling the firing temperature and time of magnesium hydroxide with a controlled particle size. Further, as a method for adjusting the BET specific surface area, CAA40%, and _D50 , the BET specific surface area, CAA40%, and _D50 can be measured after pulverization, and the results can be adjusted by performing firing multiple times. Furthermore, the fired magnesium oxide can be processed into jaw crushers, gyratory crushers, cone crushers, impact crushers, roll crushers, cutter mills, stamp mills, ring mills, roller mills, jet mills, hammer mills, pin mills, rotary mills, vibrating mills, The BET specific surface area, CAA40%, and _D50 of magnesium oxide after pulverization can also be adjusted by pulverizing it using a pulverizer such as a planetary mill or a ball mill. Further, as a method for adjusting the BET specific surface area, CAA40%, and _D50 , the BET specific surface area, CAA40%, and _D50 can be measured after pulverization, and the pulverization is performed multiple times. Furthermore, the BET specific surface area, CAA40%, and _D50 of magnesium oxide can also be adjusted using a pulverizer equipped with a classifier. Furthermore, the BET specific surface area, CAA40%, and _D50 can also be adjusted by combining and mixing a plurality of magnesium oxide powders.

The grain-oriented electrical steel sheet of the present invention can be manufactured, for example, by the following method. Grain-oriented electrical steel sheets are produced by hot rolling a silicon steel slab containing 2.5 to 4.5% Si, followed by pickling and cold rolling, or by cold rolling twice with intermediate annealing in between. Adjust to the specified thickness. Next, the cold-rolled coil is subjected to recrystallization annealing, which also serves as decarburization, in a wet hydrogen atmosphere at 923 to 1173 K, and at this time, an oxide film containing silica (SiO ₂ ) as the main component is formed on the steel plate surface. . An annealing separator containing magnesium oxide for an annealing separator of the present invention is uniformly dispersed in water to obtain a water slurry, and the water slurry is continuously applied onto the steel plate using roll coating or spraying, Dry at approximately 573K. The thus treated steel plate coil is subjected to final finish annealing at, for example, 1473K for 20 hours to form a forsterite coating (Mg ₂ SiO ₄ ) on the steel plate surface. The forsterite coating is an insulating coating and can impart tension to the surface of the steel sheet, thereby improving the iron loss value of the grain-oriented electrical steel sheet.

The present invention will be explained in detail with reference to the following examples, but these examples are not intended to limit the present invention in any way.

<Measurement method/test method>
(1) Method for measuring the content of metal elements After completely dissolving the sample to be measured in acid, diluting it with ultrapure water, using an ICP emission spectrometer (PS3520 VDD, manufactured by Hitachi High-Tech Science Corporation), The content of metal elements was measured.

(2) Method for measuring the content of chlorine (Cl) After dissolving the measurement sample in nitric acid, diluting it with ultrapure water and measuring the mass using a spectrophotometer (UV-2550 manufactured by Shimadzu Corporation), The chlorine (Cl) concentration in the sample was calculated.

(3) Method for measuring BET specific surface area BET specific surface area was measured by gas adsorption method (BET method) using a specific surface area measuring device (trade name: Macsorb, manufactured by Mountech Co., Ltd.).

(4) Method for measuring volume-based cumulative 50% particle diameter (D ₅₀ ) Disperse the sample to be measured in methanol, and use a laser diffraction scattering particle size distribution analyzer (MT3300EX-II manufactured by LEEDS & NORTHRUP) to measure the sample size. The volume-based cumulative 50% particle diameter (D ₅₀ ) was measured. At that time, the particles were dispersed for 180 seconds using ultrasonic waves with an output of 40 W.

(5) Method for measuring 40% CAA Put 100 mL of 0.4N citric acid solution and an appropriate amount (2 mL) of 1% phenolphthalein solution as an indicator into a 200 mL beaker, adjust the liquid temperature to 303 K, and use a magnetic stirrer. 40% final reaction equivalent of magnesium oxide (2.0 g) was added to the citric acid solution while stirring at 700 rpm using a The time required for this to occur was measured.

(6) Method for measuring mode diameter and mode volume “Autopore IV9510 (trade name)” (manufactured by Micromeritics) was used as a mercury intrusion type pore distribution measuring device. As the mercury, a special grade mercury reagent having a purity of 99.5 mass% or more and a density of 13.5335×10 ³ kg/m ³ was used. The measurement cell used was a powder sample cell with an internal cell volume of 5×10 ⁻⁶ m ³ and a stem volume of 0.39×10 ⁻⁶ m ³ . Each magnesium oxide powder serving as a measurement sample was accurately weighed within a mass range of 0.10×10 ^-3 to 0.13×10 ^-3 kg, and filled into a measurement cell (the measurement sample should be pre-opened). The particle size was made uniform using a standard sieve of 355×10 ⁻⁶ m). After this measurement cell was attached to the apparatus, the inside of the cell was maintained at a reduced pressure of 50 μHg (6.67 Pa) or less for 20 minutes. Next, the measurement cell was filled with mercury until the pressure reached 1.5 psia (10342 Pa). Thereafter, mercury was injected at a pressure ranging from 2 psia (13,790 Pa) to 60,000 psia (413.7 MPa), and the pore distribution was measured. The mode diameter and mode volume were calculated from the obtained pore distribution.

In addition, in order to convert the injection pressure of mercury into a pore diameter, the following formula (I) (Washburn's formula) is used.
D=-(1/P)・4γ・cosΨ (I)
here,
D: pore diameter (m),
P: Injection pressure of mercury (Pa),
γ: Surface tension of mercury (485 dyne cm ^-1 (0.485 Pa m)),
Ψ: Contact angle of mercury (130°=2.26893 rad).

(7) Preparation of steel plate for test As a test sample steel, a silicon steel slab for grain-oriented electrical steel plate was hot-rolled and cold-rolled to a final plate thickness of 0.28 mm by a known method, and then A steel plate decarburized and annealed in a humid atmosphere of 25% nitrogen and 75% hydrogen was used. The composition of the steel plate before decarburization annealing is, in mass%, C: 0.01%, Si: 3.29%, Mn: 0.09%, Al: 0.03%, S: 0.07%, N. :0.0053%, the remainder being unavoidable impurities and Fe. Magnesium oxide was applied onto this steel plate to form a forsterite film, and the properties of the film were investigated.

Specifically, the magnesium oxide of the present invention or the magnesium oxide of the comparative example was made into a slurry and applied to a steel plate so that the weight after drying was 14 g/ ^m2 , and after drying, it was heated at 1473K for 20.0 hours. Final annealing was performed. After finishing the final annealing, the steel plate was cooled, washed with water, acid-washed with an aqueous hydrochloric acid solution, washed with water again, and dried to form a forsterite film on the steel plate.

(8) Evaluation of the appearance of the forsterite film The appearance of the forsterite film was judged from the appearance of the film after cleaning. In other words, ◎ indicates that the gray forsterite coating is uniformly thick, ○ indicates that the coating is uniform but slightly thin, and ○ indicates that the coating is uneven and thin, but the underlying steel plate is exposed. If there is no part where the coating is coated, or if the coating is uneven and very thin, and there is a part where the underlying steel plate is clearly exposed, it is rated as ×.

(9) Evaluation of adhesion of forsterite film The adhesion of forsterite film was judged from the state of the film. In other words, if the film is uniformly formed and there are no peeled areas, or if the film is slightly uneven but there are no peeled areas, ○, and if the film is uneven and there are pinhole-like peeled areas. The case where the film was peeled off or the film was non-uniform and there was a clear peeling area was rated as ×.

<Example 1>
Calcium hydroxide slurry was added to bittern containing magnesium ions at a concentration of 2.0 mol/L so that the magnesium hydroxide concentration after reaction was 1.2 mol/L to obtain a mixed solution. The mixture was stirred at 600 rpm and reacted at 323 K for 7.0 hours. Thereafter, it was filtered using a filter press, washed with water, and dried to obtain magnesium hydroxide. Zinc chloride (manufactured by Kanto Kagaku, special grade reagent) was mixed with this magnesium hydroxide so that the Zn content in the magnesium oxide after firing was 720 ppm, and the mixture was fired in a rotary kiln at 1173K for 0.5 hours and then ground. Magnesium oxide powder of Example 1 was obtained. Note that the firing was performed under conditions such that the CAA of magnesium oxide was 40% in the range of 70 to 90 seconds.

<Example 2>
Magnesium oxide powder was obtained in the same manner as in Example 1, except that zinc chloride (special grade reagent) was mixed so that the Zn content in the magnesium oxide after firing was 2250 ppm.

<Example 3>
Magnesium oxide powder was obtained in the same manner as in Example 1, except that zinc chloride (special grade reagent) was mixed so that the Zn content in the magnesium oxide after firing was 4300 ppm.

<Example 4>
Calcium hydroxide slurry was added to bittern containing magnesium ions at a concentration of 2.0 mol/L so that the magnesium hydroxide concentration after reaction was 1.2 mol/L to obtain a mixed solution. Zinc chloride (manufactured by Kanto Kagaku, reagent special grade) was mixed with this mixed solution so that the Zn content in the magnesium oxide after firing was 8800 ppm, and then the mixed solution was reacted at 323 K for 7.0 hours while stirring at 600 rpm. , and then filtered with a filter press, washed with water, and dried to obtain magnesium hydroxide. This magnesium hydroxide was fired in a rotary kiln at 1173K for 0.5 hours and then pulverized to obtain magnesium oxide powder of Example 4. Note that the firing was performed under conditions such that the CAA of magnesium oxide was 40% in the range of 70 to 95 seconds.

<Example 5>
Magnesium oxide powder was prepared in the same manner as in Example 4, except that zinc oxide (manufactured by Wako Pure Chemical Industries, Ltd., reagent special grade) was mixed in place of zinc chloride so that the Zn content in the magnesium oxide after firing was 5250 ppm. Obtained.

<Comparative example 1>
Magnesium oxide powder was obtained in the same manner as in Example 1, except that zinc chloride (special grade reagent) was not mixed.

Regarding the obtained magnesium oxide powders of Examples 1 to 5 and Comparative Example 1, the contained components etc. were measured as described above, and grain-oriented electrical steel sheets obtained using these magnesium oxide powders were evaluated. . The results are shown in Table 1. Note that the contents of metal elements other than those shown in the table were at normal impurity levels.

As ^is clear from Table 1, magnesium oxide ( It was revealed that the forsterite coatings formed using Examples 1 to 5) were excellent in (a) the appearance of the coating and (b) the adhesion of the coating. On the other hand, a forsterite coating formed using magnesium oxide (Comparative Example 1) with a pore mode volume of less than 1.3 cm ³ /g as measured by mercury intrusion pore distribution measurement has (a) appearance of the coating, ( b) Both the adhesion of the film was poor.

From the above, it has become clear that a grain-oriented electrical steel sheet having an excellent forsterite coating can be produced using the magnesium oxide for an annealing separator of the present invention.

According to the present invention, it is possible to provide magnesium oxide for an annealing separator that can provide grain-oriented electrical steel sheets with excellent film properties.

Claims (6)

The BET specific surface area is 12.0 m ² /g or more and 30.0 m ² /g or less, the pore mode diameter measured by mercury intrusion pore distribution measurement is 0.1 μm or more and less than 0.4 μm, and the pore Magnesium oxide for an annealing separator having a mode volume of 1.3 cm ³ /g or more. According to claim 1, the CAA40% is 50 seconds or more and 170 seconds or less, the Cl content is 500 ppm or less, and the volume-based cumulative 50% particle diameter (D ₅₀ ) is 0.5 μm or more and 7.0 μm or less. Magnesium oxide for annealing separator. The magnesium oxide for an annealing separator according to claim 1 or 2, wherein the total content of Zn, Zr, Ni, Co, and Mn is 200 ppm or more and 10,000 ppm or less. The magnesium oxide for an annealing separator according to claim 1 or 2, wherein the content of Zn is 200 ppm or more and 10,000 ppm or less. An annealing separator comprising the magnesium oxide for an annealing separator according to claim 1 or 2 . forming a SiO ₂ film on the surface of the steel plate;
A method for manufacturing a grain-oriented electrical steel sheet, comprising the step of forming a forsterite film on the surface of the steel sheet by applying the annealing separator according to claim 5 to the surface of the SiO ₂ film and annealing.