Magnesium oxide for annealing separation agent, method for producing the same, and method for producing directional electromagnetic steel sheet using the same

Abstract

To provide magnesium oxide for an annealing separation agent in which variations in the concentration of trace elements in magnesium oxide are suppressed.SOLUTION: Magnesium oxide for an annealing separation agent contains boron. The boron content is 500 to 1500 ppm. The coefficient of variation of the concentration of boron is 0.50 or less. Therefore, variation in the concentration of boron in the magnesium oxide is suppressed.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to magnesium oxide for an annealing separator, a method for producing the same, and a method for producing a grain-oriented electrical steel sheet using the same.

Background Art

[0002] When producing a grain-oriented electrical steel sheet, magnesium oxide for an annealing separator is applied to the steel sheet. The amount of trace elements contained in the magnesium oxide affects the product characteristics of the completed grain-oriented electrical steel sheet. For example, Patent Document 1 discloses magnesium oxide for an annealing separator containing 400 to 1500 ppm of boron, 1 to 650 ppm of sodium, 500 ppm or less of chlorine, and 0.10 to 0.70 mass% of sulfur in terms of SO 3 conversion, and having a total molar ratio of chlorine and sulfur to the total moles of boron and sodium contained, (Cl + S) / (B + Na), of 0.50 to 0.80.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Patent Document 1 stipulates the content of trace elements in magnesium oxide for an annealing separator. However, Patent Document 1 does not describe the variation in the concentration of trace elements in magnesium oxide.

[0005] An object of the present invention is to provide magnesium oxide for an annealing separator in which the variation in the concentration of trace elements in magnesium oxide is suppressed, a method for producing the same, and a method for producing a grain-oriented electrical steel sheet using the same.

Means for Solving the Problems

[0006] The present invention includes the following respective disclosures.

[0007] (First Disclosure) The first disclosure is magnesium oxide for an annealing release agent. The magnesium oxide contains boron. The content of the boron is 500 to 1500 ppm. The coefficient of variation of the concentration of the boron is 0.50 or less.

[0008] (Second Disclosure) In the second disclosure, in the first disclosure, the magnesium oxide further contains sodium. The content of the sodium is 0.1 to 200 ppm. The coefficient of variation of the concentration of the sodium is 0.25 or less.

[0009] (Third Disclosure) In the third disclosure, in the first disclosure or the second disclosure, the magnesium oxide further contains at least one or more elements selected from Cl, Mn, Fe, and Cu.

[0010] (Fourth Disclosure) The fourth disclosure is a method for producing magnesium oxide for an annealing release agent. The method for producing the magnesium oxide includes a reaction step and a forming step. In the reaction step, while continuously supplying a magnesium hydroxide raw material containing boron and an alkali raw material to a reaction tank respectively, the magnesium hydroxide raw material and the alkali raw material are reacted in a state where turbulent flow occurs, and the upper layer slurry of the magnesium hydroxide formed by the reaction is continuously taken out from the reaction tank. In the forming step, the taken-out magnesium hydroxide is fired to form magnesium oxide. The magnesium oxide contains boron. The content of the boron is 500 to 1500 ppm. The coefficient of variation of the concentration of the boron is 0.50 or less.

[0011] (Fifth Disclosure) The fifth disclosure is a method for manufacturing a grain-oriented electrical steel sheet. The method for manufacturing the grain-oriented electrical steel sheet includes a coating step of applying a slurry containing magnesium oxide for an annealing separator to a decarburized annealed steel sheet, and an annealing step of annealing the steel sheet coated with the slurry. The magnesium oxide contains boron. The content of the boron is 500 to 1500 ppm. The coefficient of variation of the concentration of the boron is 0.50 or less.

Effects of the Invention

[0012] According to the present invention, it is possible to provide magnesium oxide for an annealing separator in which the variation in the concentration of trace elements in magnesium oxide is suppressed within a specific range, a method for manufacturing the same, and a method for manufacturing a grain-oriented electrical steel sheet using the same.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, preferred embodiments of magnesium oxide for an annealing separator, a method for manufacturing the same, and a method for manufacturing a grain-oriented electrical steel sheet using the same according to the present invention will be described.

[0014] [Magnesium Oxide for Annealing Separator] The magnesium oxide for an annealing separator of the present invention is a powder mainly composed of magnesium oxide, but may contain other trace elements. However, "containing" trace elements means containing the trace elements inside and / or outside the particles of magnesium oxide. The content of magnesium oxide in the annealing separator is at least 95% by mass or more, preferably 98% by mass or more. Therefore, the content of trace elements in the annealing separator is less than 5% by mass, preferably less than 2% by mass. Hereinafter, the magnesium oxide for an annealing separator will also be simply referred to as magnesium oxide.

[0015] Magnesium oxide contains boron (B) as a trace element. When forming a forsterite film by the reaction of magnesium oxide for an annealing release agent with silicon dioxide on the surface of a steel sheet, boron has the effect of promoting the formation of the forsterite film. Also, when magnesium oxide is formed by firing magnesium hydroxide, when the holding temperature during firing is about 1200 to 1300 °C, boron has the effect of lowering the melting point of the substance to be fired.

[0016] The boron content in magnesium oxide is 500 to 1500 ppm. By magnesium oxide containing 500 ppm or more of boron, a forsterite film is sufficiently formed. By magnesium oxide containing 1500 ppm or less of boron, it is possible to suppress the formation of an excessive and uneven forsterite film. As the lower limit of the boron content, 700 ppm is preferable. As the upper limit of the boron content, 1200 ppm is preferable.

[0017] The coefficient of variation of the boron concentration in magnesium oxide is 0.50 or less from the viewpoint of suppressing the variation in the boron content in magnesium oxide for an annealing release agent. From the viewpoint of further suppressing the variation, the coefficient of variation is preferably 0.40 or less. However, the coefficient of variation is a coefficient corresponding to the variation in the boron concentration contained in individual magnesium oxide particles among a plurality of magnesium oxide particles in magnesium oxide. The method for obtaining the coefficient of variation will be described later.

[0018] According to the present invention, since the variation in the boron content, which is one of the trace elements in magnesium oxide for an annealing release agent, is suppressed, by uniformly applying magnesium oxide to a steel sheet, a predetermined amount of boron can be uniformly distributed on the steel sheet. Thereby, it is possible to suppress the occurrence of variations in the magnetic properties of the completed grain-oriented electrical steel sheet.

[0019] The particle size and shape of magnesium oxide particles are not particularly limited as long as the variation in the concentration of trace elements among particles can be reduced. Examples of the particle size include 0.02 to 5 μm. From the perspective of making it difficult for particles to aggregate in a slurry, the lower limit of the particle size is preferably 0.05 μm. From the perspective of uniformly dispersing particles in a slurry, the upper limit of the particle size is more preferably 1 μm. Examples of the planar shape of the particles include polygons, rectangles, polygonal shapes, ellipses, circles, irregular shapes, and combinations thereof.

[0020] The particle size distribution of magnesium oxide is not particularly limited as long as the variation in the concentration of trace elements among particles can be reduced. D10 is preferably 0.5 to 2.0 μm. D50 is preferably 1.5 to 4.0 μm. D90 is preferably 6.0 to 14 μm. The volume average diameter MV is, for example, 2.0 to 7.0 μm. By setting the particle size distribution within the above range, the aggregation of particles in the slurry can be suppressed while enhancing the dispersibility.

[0021] Magnesium oxide may contain other trace elements other than magnesium oxide and boron (B). Examples of such other trace elements include sodium (Na). When forming a forsterite coating using magnesium oxide containing sodium as a trace element, sodium has the effect of adjusting the formation rate of the forsterite coating.

[0022] The sodium content in magnesium oxide is preferably 0.1 to 200 ppm. When magnesium oxide contains 0.1 ppm or more of sodium, the formation rate of the forsterite coating can be increased. When magnesium oxide contains 200 ppm or less of sodium, the formation rate of the forsterite coating can be reduced and excessive formation can be suppressed. The lower limit of the sodium content is preferably 0.5 ppm. The upper limit of the sodium content is preferably 150 ppm.

[0023] The coefficient of variation of the sodium concentration in magnesium oxide is preferably 0.25 or less from the viewpoint of suppressing the variation in the sodium content in magnesium oxide for the annealing release agent. From the viewpoint of further suppressing the variation, the coefficient of variation is more preferably 0.20 or less. However, the coefficient of variation is a coefficient corresponding to the variation in the sodium concentration contained in individual magnesium oxide particles among a plurality of magnesium oxide particles in magnesium oxide. The method for obtaining the coefficient of variation will be described later.

[0024] Examples of other trace elements other than magnesium oxide and boron (B) include aluminum (Al). When forming a forsterite film using magnesium oxide containing aluminum as a trace element, aluminum has an effect of promoting the formation of the forsterite film.

[0025] The aluminum content in magnesium oxide is preferably 20 to 400 ppm. By containing 20 ppm or more of aluminum in magnesium oxide, a sufficient forsterite film can be formed. By containing 400 ppm or less of aluminum in magnesium oxide, it is possible to suppress the formation of an excessive forsterite film and the occurrence of unevenness. The lower limit of the aluminum content is preferably 25 ppm. The upper limit of the aluminum content is preferably 300 ppm.

[0026] The coefficient of variation of the aluminum concentration in magnesium oxide is preferably 0.40 or less from the viewpoint of suppressing the variation in the aluminum content in magnesium oxide for the annealing release agent. From the viewpoint of further suppressing the variation, the coefficient of variation is more preferably 0.30 or less. However, the coefficient of variation is a coefficient corresponding to the variation in the aluminum concentration contained in individual magnesium oxide particles among a plurality of magnesium oxide particles in magnesium oxide. The method for obtaining the coefficient of variation will be described later.

[0027] Magnesium oxide may contain various trace elements known to contribute to the promotion of film formation, improvement of film properties, and / or improvement of magnetic properties in grain-oriented electrical steel sheets. Such trace elements include, for example, at least one or more elements selected from chlorine (Cl), copper (Cu), phosphorus (P), iron (Fe), manganese (Mn), titanium (Ti), and calcium (Ca), or compounds thereof. For example, chlorine is an element that promotes the formation of a forsterite film. Copper is an element that improves the film properties and magnetic properties of grain-oriented electrical steel sheets. Phosphorus is an element that promotes the formation of a forsterite film.

[0028] [Method for producing magnesium oxide for annealing separator] The method for producing magnesium oxide is not particularly limited as long as it can produce magnesium oxide with the above configuration, particularly with little variation in the concentration of trace elements. Examples of such production methods include the following three methods. The first method is a method in which a raw material of a target trace element is added to a magnesium hydroxide raw material, an alkali raw material is continuously reacted with the magnesium hydroxide raw material to synthesize magnesium hydroxide, and the magnesium hydroxide is fired to obtain magnesium oxide. The second method is a method in which magnesium hydroxide is synthesized by a batch reaction in which a raw material of a target trace element and a magnesium hydroxide raw material are simultaneously added to an alkali raw material, and the magnesium hydroxide is fired to obtain magnesium oxide. The third method is a method in which a powder of a raw material of a target trace element and a powder of magnesium hydroxide are mixed and fired to obtain magnesium oxide. Further, when the magnesium hydroxide raw material contains an excessive amount of trace elements, a chelating agent suitable for the trace element may be added to the magnesium hydroxide raw material.

[0029] However, examples of the magnesium hydroxide raw material include water-soluble magnesium salts or hydrates thereof, and specifically, magnesium chloride hexahydrate, magnesium chloride dihydrate, and anhydrous magnesium chloride are preferable. In addition, seawater, irrigation water, or bittern may be used as the magnesium hydroxide raw material.

[0030] The raw materials for the target trace elements, that is, the target trace element raw materials, include, for example, the trace elements themselves and compounds of trace elements. Examples of the compounds of trace elements include acids, bases and their salts containing trace elements, oxides, chlorides, nitrates, sulfates, carbonates, and phosphates of trace elements. When the trace element is boron, examples of the boron compounds as boron raw materials include boric acid, alkali metal borate salts, ammonium borate salts, alkali metal metaborate salts, and boron oxide. Examples of the alkali metal borate salts include magnesium borate, calcium borate, and sodium borate. When the trace element is sodium, examples of the sodium compounds as sodium raw materials include sodium chloride, sodium nitrate, sodium phosphate, sodium sulfate, and sodium borate. When the trace element is aluminum, examples of the aluminum compounds as aluminum raw materials include aluminum chloride, aluminum nitrate, aluminum phosphate, aluminum sulfate, aluminum borate, and aluminum oxide.

[0031] Examples of the alkali raw materials include calcium hydroxide, sodium hydroxide, potassium hydroxide, and ammonia. When calcining magnesium hydroxide, examples of the calcination atmosphere include air and nitrogen.

[0032] The chelating agent is not particularly limited as long as it can form a chelate complex with the target trace element raw material. When the trace element is boron, an example of the chelating agent is 1,2-ethanediol. When the trace element is aluminum, an example of the chelating agent is triethanolamine.

[0033] In the first method, for example, first, a target trace element raw material and a magnesium hydroxide raw material are added to deionized water to form an aqueous solution containing the target trace element raw material and the magnesium hydroxide raw material, that is, an aqueous solution of the magnesium hydroxide raw material. On the other hand, an alkali raw material is added to deionized water to form an aqueous solution containing the alkali raw material, that is, an aqueous solution of the alkali raw material. Next, the aqueous solution of the magnesium hydroxide raw material and the aqueous solution of the alkali raw material are continuously poured into the reaction tank at predetermined flow rates respectively. Then, in the reaction tank, the magnesium hydroxide raw material added with the target trace element raw material and the alkali raw material are reacted while generating turbulent flow by stirring, and the upper slurry of magnesium hydroxide formed by the reaction is continuously taken out from the reaction tank (reaction step). At this time, the aqueous solution of the magnesium hydroxide raw material and the aqueous solution of the alkali raw material are poured into the reaction tank at a flow rate such that the ratio of Mg to OH is approximately 1:2. "Approximately" means that the error in the flow rate is in the range of ±50%. At that time, if necessary, the inside of the reaction tank is maintained at a predetermined pressure and a predetermined temperature. In this way, by continuously reacting the magnesium hydroxide raw material added with the target trace element raw material and the alkali raw material in a state where turbulent flow is generated, magnesium hydroxide added with the target trace element is synthesized. If necessary, washing, filtration, and drying are performed. Then, the magnesium hydroxide added with the trace element is calcined at a predetermined temperature to obtain magnesium oxide added with the trace element (formation step).

[0034] In the second method, for example, first, the target trace element raw material and the magnesium hydroxide raw material are added to deionized water to form an aqueous solution containing the target trace element raw material and the magnesium hydroxide raw material, that is, an aqueous solution of the magnesium hydroxide raw material. On the other hand, the alkali raw material is added to deionized water to form an aqueous solution containing the alkali raw material, that is, an aqueous solution of the alkali raw material. Next, the aqueous solution of the alkali raw material is poured into the aqueous solution of the magnesium hydroxide raw material in the reaction tank at a predetermined flow rate, and in the reaction tank, the magnesium hydroxide raw material added with the target trace element and the alkali raw material are reacted in a state where turbulent flow is generated by stirring (reaction step). At that time, if necessary, the inside of the reaction tank is maintained at a predetermined pressure and a predetermined temperature. In this way, by reacting the magnesium hydroxide raw material added with the target trace element with the alkali raw material little by little in a state where turbulent flow is generated, magnesium hydroxide added with the target trace element is synthesized. If necessary, washing, filtration, and drying are performed. Then, the magnesium hydroxide added with the trace element is calcined at a predetermined temperature to obtain magnesium oxide added with the trace element (forming step).

[0035] In the third method, for example, first, the magnesium hydroxide raw material is added to deionized water to form an aqueous solution containing the magnesium hydroxide raw material, that is, an aqueous solution of the magnesium hydroxide raw material (without trace elements). On the other hand, the alkali raw material is added to deionized water to form an aqueous solution containing the alkali raw material, that is, an aqueous solution of the alkali raw material. Next, the aqueous solution of the alkali raw material is poured into the aqueous solution of the magnesium hydroxide raw material (without trace elements) in the reaction tank at a predetermined flow rate, and in the reaction tank, the magnesium hydroxide raw material and the alkali raw material are reacted. At that time, while stirring if necessary, the inside of the reaction tank is maintained at a predetermined pressure and a predetermined temperature. In this way, by reacting the magnesium hydroxide raw material and the alkali raw material, magnesium hydroxide not containing trace elements is synthesized (reaction step). The powder of the magnesium hydroxide having no such trace element is mixed with the powder of the target trace element raw material. Then, the magnesium hydroxide mixed with the target trace element raw material is calcined at a predetermined temperature to obtain magnesium oxide added with the trace element (forming step).

[0036] As an example of another manufacturing method, for instance, there is a method that uses magnesium oxide obtained by firing mineral magnesite. In this manufacturing method, first, magnesium oxide obtained from mineral magnesite is hydrated to obtain magnesium hydroxide powder. Subsequently, the third method described above is carried out using the magnesium hydroxide powder to obtain magnesium oxide.

[0037] Here, the meanings of the terms related to the firing of a magnesium hydroxide sample used in this specification are as follows. "Heating-up time" means the time from room temperature to reach the target maximum temperature when firing the sample. "Holding temperature" means the target maximum temperature when firing the sample, also referred to as the firing temperature. "Holding time" means the time to maintain the holding temperature when firing the sample. "Cooling-down time" means the time from the holding temperature to reach room temperature after the holding time has elapsed when firing the sample. Note that cooling includes not only active cooling using a cooling means but also gentle cooling such as natural cooling.

[0038] <Firing conditions> Magnesium oxide can be controlled by adjusting the final firing conditions for obtaining magnesium oxide and the trace elements contained in the precursor subjected to the final firing. The firing conditions include the heating-up time, the holding temperature, the holding time, and the cooling-down time.

[0039] As conditions for obtaining magnesium oxide, for example, the heating-up time is preferably from 0.5 hour to 3 hours, more preferably from 1 hour to 2 hours. The holding temperature is preferably from 600 °C to 1300 °C, more preferably from 700 °C to 1200 °C. The holding time is preferably from 0.1 hour to 15 hours, more preferably from 0.2 hour to 13 hours. The cooling-down time is preferably from 0.1 hour to 6 hours, more preferably from 0.2 hour to 5 hours.

[0040] If the heating time, holding time, and cooling time are shorter than the above ranges, the firing of magnesium hydroxide may not be completed, or the reactivity of magnesium oxide may be too high during the formation of the forsterite film, making it difficult to form forsterite uniformly. On the other hand, if the heating time, holding time, and cooling time are longer than the above ranges, the reactivity of magnesium oxide becomes too low, making it difficult to form forsterite.

[0041] Boron contained in magnesium oxide has the effect of lowering the melting point of the substance to be fired when the holding temperature during firing is about 1200 - 1300°C. The content of boron contained in magnesium oxide is preferably 0.05 - 0.15% by mass. When magnesium oxide having a boron content within such a numerical range is used as an annealing separator, the properties of the forsterite film can be improved, and the magnetic properties and insulation properties of the grain-oriented electrical steel sheet can be made good.

[0042] The content of sodium contained in magnesium oxide is preferably 0.1 - 200 ppm. When magnesium oxide having a sodium content within such a numerical range is used as an annealing separator, the properties of the forsterite film can be improved, and the magnetic properties and insulation properties of the grain-oriented electrical steel sheet can be made good.

[0043] <Firing atmosphere> The atmosphere during firing may be nitrogen or air. It is only necessary that heat is evenly applied to the substance to be fired. The substance to be fired may be uniformly stirred during firing. Examples of the apparatus for performing such firing include a rotary kiln.

[0044] <Control of the content of trace elements in magnesium oxide> The content of trace elements in magnesium oxide can be controlled as follows. First, measure the content of trace elements in the raw materials for manufacturing magnesium oxide. Then, based on the results, add or remove trace elements in the raw materials or intermediate products so that the content of trace elements in magnesium oxide reaches the desired content. Examples of raw materials include magnesium raw materials, mineral magnesite, and alkalis reacted with magnesium raw materials. Examples of intermediate products include magnesium hydroxide.

[0045] The method of adding trace elements is not particularly limited. For example, a method of mixing a compound containing the trace element to be restricted into the raw materials or intermediate products can be mentioned. The mixing method can be either wet or dry. Note that the intermediate products include the above-mentioned precursors.

[0046] The method of removing trace elements is not particularly limited. Examples of such methods include a method of washing the raw materials or intermediate products, and a method of adding a chelating agent to the target trace element. A specific example of washing is water washing.

[0047] After mixing intermediate products with different compositions to adjust the excess or deficiency of trace elements, final firing can be performed to obtain magnesium oxide with the content of trace elements reaching the desired content. Or, magnesium oxide after final firing with different compositions can be mixed to adjust the excess or deficiency of trace elements to obtain magnesium oxide with the content of trace elements reaching the desired content.

[0048] In the manufacturing process of magnesium oxide, various additives known to have the function of improving film properties and magnetic properties may be effectively added. Examples of such additives include copper (Cu), phosphorus (P), aluminum (Al), manganese (Mn), titanium (Ti), calcium (Ca), and their compounds.

[0049] <Control of the particle size distribution (D10, D50, D90, MV) of magnesium oxide> The particle size distribution of magnesium oxide can be controlled by the following method. One method is to adjust at least one of the reaction temperature, reaction rate, and stirring conditions when synthesizing magnesium hydroxide by reacting a magnesium raw material and an alkali raw material. Another method is to grind the precursor before the final firing. Another method is to control the firing conditions of magnesium hydroxide. Another method is to refire or grind the magnesium oxide after the final firing.

[0050] Under the above conditions, magnesium oxide for an annealing separating agent is manufactured. Since this magnesium oxide has the above-described predetermined configuration, variations in the content of trace elements in the magnesium oxide can be suppressed.

[0051] [Method for manufacturing a grain-oriented electrical steel sheet using magnesium oxide for an annealing separating agent] Next, a method for manufacturing a grain-oriented electrical steel sheet using the magnesium oxide for an annealing separating agent described above will be explained. The manufacturing method includes a coating step of applying a slurry containing the above-described magnesium oxide to a decarburized and annealed steel sheet, and a high-temperature annealing step of annealing the steel sheet coated with magnesium oxide.

[0052] <Coating step> The above-described magnesium oxide is uniformly dispersed in a liquid to form a slurry containing magnesium oxide. The liquid is, for example, water. At this time, the slurry is formed at a low temperature such as 5°C so that the magnesium oxide does not hydrate.

[0053] The concentration of magnesium oxide is, for example, 5 to 30% by mass. The lower limit of the concentration of magnesium oxide is preferably 7% by mass from the viewpoint of facilitating uniform coating of the slurry on the steel sheet. The upper limit of the concentration of the annealing separating agent is preferably 25% by mass from the viewpoint of making the viscosity of the slurry easy to coat.

[0054] The viscosity of the slurry at 5°C is, for example, 2.2 to 5.2 mPa·s. The lower limit of the viscosity of the slurry at 5°C is preferably 2.6 mPa·s from the viewpoint of ensuring a sufficient coating amount. The upper limit of the viscosity of the slurry at 5°C is preferably 4.6 mPa·s from the viewpoint of facilitating the coating of the slurry.

[0055] The slurry is continuously applied to the decarburized annealed steel sheet using a roll coating device or a spray device. However, the slurry is applied at a low temperature such as 5°C so that magnesium oxide does not hydrate. At this time, since magnesium oxide having the above configuration is used, by uniformly applying the slurry containing the magnesium oxide on the steel sheet, variations in the content of trace elements in the applied slurry can be suppressed. Thereafter, the applied slurry is dried at a temperature of, for example, about 300 to 500°C.

[0056] <High-temperature annealing process> The steel sheet coated with the above-described slurry, and thus the steel sheet coated with magnesium oxide, is annealed. Examples of the annealing conditions include 1000 to 1200°C and 10 to 20 hours. Thereby, a forsterite film is formed on the surface of the steel sheet, and thereafter, a grain-oriented electrical steel sheet using the above-described annealing release agent is formed by performing a known predetermined treatment as necessary.

[0057] In the method for manufacturing a grain-oriented electrical steel sheet of the present invention, since it has the above-described predetermined configuration, by uniformly applying magnesium oxide on the steel sheet, a forsterite film with suppressed variations in the content of trace elements can be formed on the steel sheet. Thereby, a grain-oriented electrical steel sheet with improved magnetic properties can be obtained.

[0058] Note that the magnesium oxide for the annealing release agent of the present invention, its manufacturing method, and the method for manufacturing a grain-oriented electrical steel sheet using the same are not limited to the above-described embodiments and the examples described later, and can be appropriately combined, substituted, or changed within the scope not departing from the object and gist of the present invention.

[0059] <Measurement Method and Test Method> The various measurement methods and test methods are as follows.

[0060] 1. Concentration of trace elements, its average value, standard deviation, and coefficient of variation The concentration of trace elements, its average value, standard deviation, and coefficient of variation were determined by the following methods. (1) Magnesium oxide (powder) to be measured was prepared. (2) The magnesium oxide was formed into pellets with a length of 4 mm and a width of 4 mm to obtain samples. (3) The samples were set in a D-SIMS (Dynamic Secondary Ion Mass Spectrometry) PHI ADEPT-1010 manufactured by ULVAC-PHI, Inc. Then, under the condition that the primary acceleration voltage was 5.0 kV, the concentration of trace elements at 250 measurement points in the depth direction from the surface of the sample to a depth of about 5 μm was measured. (4) Based on the concentrations of trace elements at the 250 measured points, the average value (μ) and standard deviation (σ) of the concentrations of trace elements were determined. (5) The coefficient of variation was calculated as the standard deviation (σ) / average value (μ). Note that the concentration of trace elements at each measurement point of D-SIMS does not necessarily mean the concentration of trace elements in each individual particle. The measurement points exist every 5 μm / 250 = 0.02 μm, and the measurement interval is generally smaller than the particle size of magnesium oxide. Therefore, the concentration of trace elements at each measurement point can approximate the concentration of trace elements in more detail than each individual particle.

[0061] 2. Content of trace elements The content of trace elements was also determined by the following method. 0.5 g of the sample to be measured was dissolved in 5 ml of 30% HNO 3 solution, and then diluted to 100 ml with ultrapure water to obtain a test solution. The test solution was measured by the calibration curve method using an emission spectroscopic analyzer SPS3520-DD (manufactured by Hitachi High-Technologies Corporation) to obtain the content of trace elements.

[0062] 3. Particle size distribution The particle size distribution was measured using a particle size distribution measuring device MT3300EXII (manufactured by Microtrac Bell Corporation). First, the inside of the particle size distribution measuring device was filled with ethanol and the solvent was circulated. An appropriate amount of the sample to be measured was added thereto and it was confirmed that it was within the appropriate range. Thereafter, the solvent containing the sample was circulated for 1 minute and then the particle size distribution was measured. The measurement time was set to 30 seconds.

Example

[0063] The present invention will be further described below by way of examples and comparative examples. However, the present invention is not limited to these examples and comparative examples.

[0064] (1) Regarding the sample The samples of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 were produced as follows.

[0065] [Example 1] 386 g of magnesium chloride hexahydrate, 0.80 g of boric acid and 3.0 g of sodium chloride were dissolved in deionized water to obtain 1.9 L of an aqueous solution. This aqueous solution and 1.7 L of a 2 mol / L aqueous sodium hydroxide solution were each poured into a container with an overflow volume of 220 mL at normal pressure and 25°C and continuously reacted to obtain a magnesium hydroxide slurry. During the reaction, a screw propeller with a diameter of 2.5 cm was used and stirring was carried out at a rotational speed of 450 rpm. Next, the temperature of the aqueous solution was set to 45°C and heat treatment was carried out for 5.0 hours under stirring conditions of 350 rpm. Further, the magnesium hydroxide slurry that had been subjected to the above treatment was filtered to obtain a cake. The obtained cake was washed twice with 25 times the weight of pure water based on the solid content and dried at 105°C for 12 hours to obtain magnesium hydroxide. This magnesium hydroxide was calcined at 900°C for 1 hour to obtain magnesium oxide. The particle size distribution of this magnesium oxide was such that D10 was 1.0 μm, D50 was 2.9 μm, D90 was 10 μm, and the volume average diameter MV was 5.0 μm.

[0066] [Example 2] 386 g of magnesium chloride hexahydrate, 0.75 g of boric acid, and 2.5 g of sodium chloride were dissolved in deionized water to obtain 1.9 L of an aqueous solution. At normal pressure and 25 °C, 1.7 L of a 2 mol / L aqueous sodium hydroxide solution was added dropwise to this aqueous solution at a rate of 100 mL / min to obtain a magnesium hydroxide slurry. During the reaction, a screw propeller with a diameter of 2.5 cm was used, and stirring was carried out at a rotational speed of 600 rpm. Next, the temperature of the aqueous solution was set to 40 °C, and heat treatment was carried out for 5.0 hours under stirring conditions of 400 rpm. Further, the treated magnesium hydroxide slurry was filtered to obtain a cake. The obtained cake was washed twice with 25 times the weight of pure water based on the solid content, and dried at 105 °C for 12 hours to obtain magnesium hydroxide. This magnesium hydroxide was calcined at 900 °C for 1 hour to obtain magnesium oxide. The particle size distribution of this magnesium oxide was D10 = 1.1 μm, D50 = 3.2 μm, D90 = 12 μm, and the volume average diameter MV = 5.3 μm.

[0067] [Comparative Example 1] 386 g of magnesium chloride hexahydrate, 0.50 g of boric acid, and 3.0 g of sodium chloride were dissolved in deionized water to obtain 1.9 L of an aqueous solution. At normal pressure and 25 °C, 1.7 L of a 2 mol / L aqueous sodium hydroxide solution was added dropwise to this aqueous solution at a rate of 170 mL / min to obtain a magnesium hydroxide slurry. During the reaction, a screw propeller with a diameter of 2.5 cm was used, and stirring was carried out at a rotational speed of 450 rpm. Next, the temperature of the aqueous solution was set to 40 °C, and heat treatment was carried out for 5.0 hours under stirring conditions of 400 rpm. Further, the treated magnesium hydroxide slurry was filtered to obtain a cake. The obtained cake was washed twice with 25 times the weight of pure water based on the solid content, and dried at 105 °C for 12 hours to obtain magnesium hydroxide. This magnesium hydroxide was calcined at 850 °C for 1 hour to obtain magnesium oxide. The particle size distribution of this magnesium oxide was D10 = 0.9 μm, D50 = 2.6 μm, D90 = 9.8 μm, and the volume average diameter MV = 5.0 μm.

[0068] [Comparative Example 2] 386 g of magnesium chloride hexahydrate was dissolved in deionized water to obtain 1.9 L of an aqueous solution. This aqueous solution and 1.7 L of a 2 mol / L aqueous sodium hydroxide solution were each poured into a container with an overflow capacity of 220 mL at normal pressure and 25 °C and reacted continuously to obtain a magnesium hydroxide slurry. During the reaction, a screw propeller with a diameter of 2.5 cm was used and stirring was carried out at a rotational speed of 400 rpm. Next, the temperature of the aqueous solution was set to 40 °C and heat treatment was carried out for 5.0 hours under stirring conditions of 350 rpm. Further, the magnesium hydroxide slurry subjected to the above treatment was filtered to obtain a cake. The obtained cake was washed twice with 25 times the weight of pure water based on the solid content, and dried at 105 °C for 12 hours to obtain magnesium hydroxide. Boric acid and sodium chloride as reagents were mixed with this magnesium hydroxide and calcined at 950 °C for 1 hour to obtain magnesium oxide. The particle size distribution of this magnesium oxide was such that D10 was 1.3 μm, D50 was 3.4 μm, D90 was 11 μm, and the volume average diameter MV was 5.5 μm.

[0069] (2) Regarding the evaluation items For the magnesium oxides of Example 1, Example 2, Comparative Example 1, and Comparative Example 2, the average value, standard deviation, and coefficient of variation of the concentration of trace elements, as well as the content of trace elements, were evaluated.

[0070] (3) Regarding the evaluation results (a) Example 1 The average value μ of the concentration of boron (B), which is a trace element, was 3.12×10 20 atoms / cm 3 The standard deviation σ of the boron concentration was 0.484×10 20 atoms / cm 3 Thus, the coefficient of variation σ / μ of the boron concentration was 0.155, which was 0.50 or less. The boron content was 1078 ppm, which was within the range of 500 to 1500 ppm.

[0071] The average value μ of the concentration of sodium (Na), which is a trace element, was 13.0×10 17 atoms / cm 3It was. The standard deviation σ of the sodium concentration was 7.79×10 16 atoms / cm 3 It was. Therefore, the coefficient of variation σ / μ of the sodium concentration was 0.0598, which was 0.25 or less. The sodium content was 22 ppm, which was within the range of 0.1 to 200 ppm.

[0072] (b) Example 2 The average value μ of the concentration of boron (B), a trace element, was 3.59×10 20 atoms / cm 3 It was. The standard deviation σ of the boron concentration was 1.39×10 20 atoms / cm 3 It was. Therefore, the coefficient of variation σ / μ of the boron concentration was 0.386, which was 0.50 or less. The boron content was 980 ppm, which was within the range of 500 to 1500 ppm.

[0073] The average value μ of the concentration of sodium (Na), a trace element, was 9.92×10 17 atoms / cm 3 It was. The standard deviation σ of the sodium concentration was 19.0×10 16 atoms / cm 3 It was. Therefore, the coefficient of variation σ / μ of the sodium concentration was 0.191, which was 0.25 or less. The sodium content was 8 ppm, which was within the range of 0.1 to 200 ppm.

[0074] (c) Comparative Example 1 The average value μ of the concentration of boron (B), a trace element, was 1.46×10 20 atoms / cm 3 It was. The standard deviation σ of the boron concentration was 0.276×10 20 atoms / cm 3 It was. Therefore, the coefficient of variation σ / μ of the boron concentration was 0.190, which was 0.50 or less. The boron content was 650 ppm, which was within the range of 500 to 1500 ppm.

[0075] The average value μ of the concentration of sodium (Na), a trace element, was 25.2×10 17 atoms / cm 3 The standard deviation σ of the concentration of sodium was 67.0×10 16 atoms / cm 3 Therefore, the coefficient of variation σ / μ of the concentration of sodium was 0.266, exceeding 0.25. The sodium content was 19 ppm, within the range of 0.1 - 200 ppm.

[0076] (d) Comparative Example 2 The average value μ of the concentration of boron (B), a trace element, was 0.303×10 20 atoms / cm 3 The standard deviation σ of the concentration of boron was 0.288×10 20 atoms / cm 3 Therefore, the coefficient of variation σ / μ of the concentration of boron was 0.951, exceeding 0.50. The boron content was 540 ppm, within the range of 500 - 1500 ppm.

[0077] The average value μ of the concentration of sodium (Na), a trace element, was 2.30×10 17 atoms / cm 3 The standard deviation σ of the concentration of sodium was 3.99×10 16 atoms / cm 3 Therefore, the coefficient of variation σ / μ of the concentration of sodium was 0.173, being 0.25 or less. The sodium content was 26 ppm, within the range of 0.1 - 200 ppm.

[0078] The results of (a) - (d) above were summarized in Table 1.

Table 1

[0079] As can be seen from the above data, the magnesium oxide for the annealing separating agent of the present invention has the content of trace elements within a predetermined numerical range, and the variation in its content is suppressed. Therefore, by uniformly applying the magnesium oxide for the annealing separating agent onto the steel sheet, the trace elements can be uniformly distributed on the steel sheet. Thereby, a forsterite coating having good coating properties can be obtained. Accordingly, the magnetic properties of the grain-oriented electrical steel sheet manufactured using the magnesium oxide for the annealing separating agent can be improved.

Claims

1. The boron content is 500 to 1500 ppm, and the coefficient of variation of the concentration of the boron is 0.50 or less, magnesium oxide for annealing release agent.

2. further containing sodium, the sodium content is 0.1 to 200 ppm, and the coefficient of variation of the concentration of the sodium is 0.25 or less, magnesium oxide for annealing release agent according to Claim 1.

3. further containing at least one element selected from Cl, Mn, Fe, and Cu, magnesium oxide for annealing release agent according to Claim 1 or Claim 2.

4. A method for producing magnesium oxide for annealing release agent, comprising: a reaction step of continuously supplying a magnesium hydroxide raw material containing boron and an alkali raw material to a reaction tank, reacting the magnesium hydroxide raw material and the alkali raw material while a turbulent flow is generated, and continuously taking out an upper slurry of magnesium hydroxide formed by the reaction from the reaction tank; a forming step of firing the taken-out magnesium hydroxide to form magnesium oxide; and the boron content in the magnesium hydroxide is 500 to 1500 ppm, the coefficient of variation of the concentration of the boron in the magnesium hydroxide is 0.50 or less, A method for producing magnesium oxide for annealing release agent.

5. A method for producing a grain-oriented electrical steel sheet, comprising: a coating step of coating a slurry containing magnesium oxide for annealing release agent on a decarburized annealed steel sheet; an annealing step of annealing the steel sheet coated with the slurry; and the magnesium oxide contains boron, the boron content is 500 to 1500 ppm, the coefficient of variation of the concentration of the boron is 0.50 or less, A method for producing a grain-oriented electrical steel sheet.

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