TWI432380B - Cube - like magnesia powder and its preparation method - Google Patents

Description

Cubic magnesia powder and preparation method thereof

The present invention relates to a cubic magnesium oxide powder and a process for the preparation thereof.

Magnesia, in addition to refractory, is also used as a tunnel for various additives or electronic components, as a raw material for phosphors, as a raw material for various targets, as a raw material for superconductor thin film substrates, and as a tunneling magnetoresistive element (TMR element). The barrier material, the protective film raw material for a color plasma display panel (PDP), or the raw material of the crystalline magnesium oxide layer for PDP, is an inorganic material having an extremely wide range of uses, and thus has attracted attention.

For example, magnesium oxide which is a raw material for forming a crystalline magnesium oxide layer for PDP is required to have a high-purity crystalline powder having a primary particle shape in a cubic shape, and each crystal has a large particle diameter, a narrow particle size distribution, and excellent dispersibility. Crystalline powder.

The method for producing magnesium oxide powder is mainly known as follows: (1) a gas phase method for oxidizing magnesium metal, and (2) a heat for firing a precursor such as magnesium hydroxide or magnesium carbonate at a temperature higher than a thermal decomposition temperature. The decomposition method, and (3) pulverizing the block obtained by the electrofusion method.

In the gas phase method, a high-purity cubic magnesium oxide powder can be obtained, but the particle diameter is only less than 1 μm (see Patent Document 1 and Non-Patent Document 1). Further, it also has a problem that a large amount of fine particles adhere to the crystal surface, causing a problem that the surface is not clean, or a mixture of cubic particles and non-cubic particles, and is not a monodisperse powder composed only of cubic particles.

The magnesium oxide powder produced by the more productive thermal decomposition method is a powder having a polygonal shape of a corner of a crystal particle or a rounded edge, and it is difficult to produce a large particle. Therefore, carbon dioxide, moisture, and the like in the atmosphere are adsorbed, which may hinder the original characteristics of the magnesium oxide. Further, most of the powders which are obtained by agglomerating particles and having poor dispersibility can be obtained.

In order to overcome the disadvantages of the above thermal decomposition method, Patent Document 2 describes two methods, that is, a method of firing a chloride ion after mixing it with a magnesium oxide precursor or magnesium oxide, and an aqueous solution of magnesium chloride and a base. After the precipitant solution is mixed, it is not washed, filtered, and then calcined. In the examples of this document, the above-described baking is carried out in an oxygen stream. The magnesium oxide crystals thus obtained have a cubic shape, but the particle diameter thereof is only about 0.2 μm, and only those in which particles are aggregated can be obtained (Fig. 2(A) of the document).

Patent Document 1: Japanese Patent Laid-Open No. 1-282146 Patent Document 2: Japanese Laid-Open Patent Publication No. 2006-36544

Non-Patent Document 1: "Materials", November, 62, Vol. 36, No. 410, p. 1157-1161

The present invention has been made in view of the above circumstances, and an object thereof is to provide a magnesium oxide powder having a cubic shape and a large average particle diameter, and a process for producing the same.

The present inventors have found that, in order to solve the above problems, various studies have been carried out, and it has been found that when a magnesium oxide precursor is fired by a thermal decomposition method to produce a magnesium oxide powder, in the presence of a specific amount of halide ions, The firing can be carried out in a closed system different from the general firing conditions, and a conventional system can be manufactured. The present invention is completed by a magnesium oxide powder having a cubic shape and having an average particle diameter of 1 μm or more.

That is, the present invention relates to a cubic magnesium oxide powder characterized in that the shape of a particle observed by a scanning electron microscope is a cubic shape and is measured by a laser diffraction scattering type particle size distribution. The cumulative 50% particle size (D ₅₀ ) is 1.0 μm or more. Here, the ratio of the cumulative 10% particle diameter (D ₁₀ ) to the cumulative 90% particle diameter (D ₉₀ ) measured by the laser diffraction scattering particle size distribution D ₉₀ /D ₁₀ is preferably 10.0 or less, and the BET specific surface area is preferable. It is preferably 5.0 m ² /g or less. Further, the purity is preferably 99.9% by mass or more. The cubic magnesium oxide powder is preferably obtained by firing a magnesium oxide precursor in the presence of a halide ion in an amount of 0.5 to 30% by mass based on the total amount of the precursor.

Furthermore, the present invention also relates to a cubic magnesium oxide particle characterized in that the shape of a particle observed by a scanning electron microscope is a cube shape, and the length of the side of the cube is larger than 4.0 μm, and also relates to a cube shape. Magnesium oxide powder of magnesium oxide particles.

Furthermore, the present invention relates to a method for producing a magnesium oxide powder, characterized in that a magnesium oxide precursor is fired in a closed system in the presence of a halide ion in an amount of 0.5 to 30% by mass based on the total amount of the precursor. to make. The magnesium oxide precursor is preferably basic magnesium carbonate, magnesium hydroxide, or a mixture of the foregoing.

According to the present invention, a magnesium oxide powder having a cubic shape and a large average particle diameter can be obtained. Under the best conditions, according to the present invention, magnesium oxide powder having the following characteristics can be produced, that is, (1) the particle shape is cubic, and (2) the average particle diameter Up to 1 μm or more, (3) the particle diameter is uniform, (4) no fine particles, the surface of the cubic crystal is clean and smooth, and (5) each crystal grain is separated, and the dispersibility is excellent.

The magnesium oxide powder of the present invention has a shape in which the primary particles have a cubic shape. This shape can be confirmed by a scanning electron microscope. In addition, "cube shape" does not refer to a cube having a strict geometric meaning, as shown in FIGS. 1 to 5, which means that a substantially cubic shape can be recognized by visually observing a microscope photograph. Since the cubic particles of the magnesium oxide powder of the present invention do not aggregate and separate from each other, they are excellent in dispersibility.

The magnesium oxide powder of the present invention is a powder having a large average particle diameter, specifically, a cumulative 50% particle diameter (D ₅₀ ) measured by a laser diffraction scattering particle size distribution of 1.0 μm or more. The cubic magnesium oxide powder having such a large average particle diameter was first discovered by the present inventors. The D ₅₀ is preferably 1.2 μm or more, more preferably 1.5 μm or more. Within the scope of the process of the present invention, a powder having a D _{50 of} approximately 20 μm or less, or 10 μm or less can be obtained. Further, D ₅₀ means a median diameter, which corresponds to a particle diameter (μm) of 50% by volume in the particle size accumulation table, and when the powder is divided into two groups by a certain particle diameter, the larger side is equal to the smaller side. Particle size.

Further, from the viewpoint that the primary particles as a whole are large and the fine powder is not contained, the specific surface area of the magnesium oxide powder of the present invention measured by the BET method is preferably 5.0 m ² /g or less. More preferably 4.0m ² / g or less, and still more preferably 2.5m ² / g or less, and particularly preferably 1.0m ² / g or less.

Preferably, the magnesium oxide powder of the present invention has a particle shape in a cubic shape, and the particles are not attached to the surface of the cubic crystal, and the surface is clean and smooth. Therefore, the magnesium oxide powder of the present invention has a uniform particle size, that is, a particle size distribution is preferred, and specifically, a cumulative 10% particle diameter (D ₁₀ ) and accumulation measured by a laser diffraction scattering particle size distribution. The ratio of 90% particle diameter (D ₉₀ ) D ₉₀ /D ₁₀ is preferably 10.0 or less. More preferably 6.0 or less, and even more preferably 4.5 or less.

The magnesium oxide powder of the present invention is a high-purity powder, and the purity is preferably 99.9% by mass or more, more preferably 99.99% by mass or more.

Next, a method for producing the magnesium oxide powder of the present invention will be described.

The manufacturing method of the present invention is based on a thermal decomposition method, and the present invention produces a magnesium oxide powder by subjecting a magnesium oxide precursor to 0.5 to 30% by mass of a halide ion relative to the total amount of the precursor. In the presence of a closed system, the firing is carried out. Thereby, a magnesium oxide powder having the above characteristics can be produced.

The magnesium oxide precursor is not particularly limited as long as it is a precursor used in a conventional thermal decomposition method, and examples thereof include magnesium hydroxide, basic magnesium carbonate, magnesium carbonate, and magnesium oxalate. Among them, magnesium hydroxide, basic magnesium carbonate, and the like are preferred because of the excellent properties of the obtained magnesium oxide powder.

If the precursor contains a large amount of impurities, the shape of the obtained magnesium oxide powder does not have a cubic shape, but tends to have a rounded polygonal shape, so that impurities of the precursor are preferably less. Specifically, the amount of impurities contained in the precursor is a total amount of impurities remaining when magnesium oxide is generated by a thermal decomposition method, and preferably 1.5% by mass or less, more preferably 0.01 or less, of the halide ion. Below mass%.

The firing is carried out in the presence of a halide ion. The halide ion may, for example, be a chloride ion, a fluoride ion, a bromide ion or an iodide ion, and a chloride ion is usually used. Specific examples of the compound containing a halide ion include hydrochloric acid, ammonium chloride, sodium chloride, potassium chloride, magnesium chloride, and the like.

The amount of halide ions present is in the range of 0.5 to 30% by mass based on the total amount of the magnesium oxide precursor. If the amount of the halide ion is too small, the effect of the present invention cannot be exhibited. On the other hand, if it is too large, the crystal of magnesium oxide is hard to grow. It is preferably in the range of 1.0 to 25% by mass, more preferably in the range of 10 to 25% by mass.

a compound containing a halide ion, which may be directly a magnesium oxide precursor, or an impurity derived from a magnesium oxide precursor, or a by-product produced by modulating a magnesium oxide precursor by a solution synthesis method, or a pair The magnesium oxide precursor may be additionally added, or may be, for example, hydrogen chloride as a gas in a gas atmosphere in a closed furnace. Further, the impurities contained in the magnesium oxide precursor or the by-products generated when the magnesium oxide is prepared may be sufficiently removed by washing or the like, and further added to the magnesium oxide precursor or the gas atmosphere.

The magnesium oxide precursor in the present invention is preferably obtained by solution synthesis.

When the magnesium oxide precursor is a mixture of basic magnesium carbonate and magnesium hydroxide, when the precursor is prepared by solution synthesis, for example, (1) mixing an aqueous solution of magnesium chloride with an aqueous solution of sodium hydroxide to obtain a magnesium hydroxide slurry, (2) partially carbonating one of the magnesium hydroxides in the slurry to produce an alkaline carbonate A slurry of magnesium and magnesium hydroxide, (3) filtering the slurry to obtain a mixture of basic magnesium carbonate and magnesium hydroxide. The mixture contains chloride ions of sodium chloride or by-product sodium chloride as a starting material.

In the above step (1), after the magnesium hydroxide slurry is obtained, it can be diluted with water, preferably the concentration of the slurry is adjusted to a range of 50 to 100 g/L, more preferably 60 to 90 g/L. . By lowering the concentration of the slurry, the viscosity of the slurry can be lowered to allow the carbonation reaction of the subsequent step (2) to proceed uniformly.

In the above step (2), a part of the magnesium hydroxide in the slurry is carbonated by blowing carbon dioxide gas into the slurry. The temperature of this carbonization reaction is preferably 40 to 80 °C. In this temperature range, conversion from magnesium hydroxide to basic magnesium carbonate can be rapidly carried out, and the reaction efficiency is good. Further, in this temperature range, a mixture of basic magnesium carbonate and magnesium hydroxide having a particle diameter excellent in filtration efficiency can be obtained.

The amount of carbon dioxide gas used in the carbonation reaction is such that a part of magnesium hydroxide in the magnesium hydroxide slurry is converted into basic magnesium carbonate to supply a mixture of basic magnesium carbonate and magnesium hydroxide. . The amount of carbon dioxide gas used is preferably from 0.2 to 2.0 mol equivalents per mol of magnesium hydroxide. Within this range, a mixture of basic magnesium carbonate and magnesium hydroxide excellent in filtration efficiency can be obtained with high efficiency.

In the above step (3), the slurry containing the basic magnesium carbonate and magnesium hydroxide obtained in the above step (2) is filtered to obtain a mixture of solid alkaline magnesium carbonate and magnesium hydroxide. Since the solid mixture contains chloride ions, it may be directly dried without washing, and then subjected to calcination described later, or The mixture may be washed with an appropriate amount of water to reduce the amount of chloride ions in the cake to an appropriate level, followed by drying and firing. When the washing is sufficiently performed, the content of the chloride ions is too low, and the effect of the present invention cannot be obtained. Therefore, it is necessary to control the degree of washing by the amount of washing water used, the washing time, and the like. However, it is also possible to sufficiently wash the chloride ions to completely remove the chloride ions, and then add a compound containing a halide ion.

When the magnesium oxide precursor is magnesium hydroxide, in order to prepare the precursor by solution synthesis, for example, (1) mixing an aqueous solution of magnesium chloride with an aqueous solution of sodium hydroxide to prepare a magnesium hydroxide slurry, and (2) filtering the slurry to A solid magnesium hydroxide is obtained. The solid contains chloride ions of sodium chloride or a by-product of sodium chloride as a starting material.

In the above step (1), after the magnesium hydroxide slurry is prepared, the concentration of the slurry is preferably adjusted to a range of 50 to 100 g/L, more preferably to 60 to 90 g/L, by dilution with water. The range, and preferably the growth of the magnesium hydroxide particles in the slurry by aging. Thereby, the filtration efficiency of the step (2) can be improved. The aging conditions are not particularly limited, and may be maintained at a high temperature for a predetermined period of time under stirring of the slurry. The aging temperature is, for example, about 80 to 150 ° C, and the aging time is about several minutes to several hours.

In the above step (2), the slurry of the magnesium hydroxide obtained in the above step (1) is filtered to obtain a solid magnesium hydroxide. Since the solid matter contains chloride ions, the solid matter can be treated in the above manner.

In the method for producing magnesium oxide by the thermal decomposition method of the present invention, it is necessary to carry out the burning of the magnesium oxide precursor in the presence of a halide ion and in a closed system. to make. The closed system of the present invention is a system that is substantially sealed so that the gas existing in the space for firing does not substantially flow out to the outside, and substantially does not flow from the outside, and is open to the atmosphere or oxygen. The general firing method is carried out under an ambient atmosphere or while flowing the gas streams. In the present invention, by baking in a closed system, the halide ions are not scattered to the outside, but remain in the container for firing to fully participate in the crystal growth process of the magnesium oxide powder, thereby obtaining an average particle diameter. Great cubic crystal powder.

The firing of the closed system can be carried out, for example, by using a closed electric furnace in which substantially no ambient atmosphere flows or flows in, or by placing a sealable gasket. The temperature during firing can be from about 600 ° C to about 1400 ° C, preferably around 1200 ° C. If the temperature at the time of baking is too high, the obtained crystal may be aggregated, and the dispersibility may be deteriorated. Although the firing time varies depending on the temperature, it is usually about 1 to 10 hours. For example, when the temperature is about 1200 ° C, it is preferably about 5 hours. Further, the speed at which the temperature is raised in order to perform baking is not particularly limited, but may be about 5 to 10 ° C / min.

The ambient atmosphere at the time of the calcination is not particularly limited, and examples thereof include air, oxygen, nitrogen, and argon. However, it is preferably an atmosphere or an oxygen atmosphere, whereby the impurities contained in the precursor can be made into an oxidizing gas. Remove.

Although the cubic magnesium oxide powder having a large average particle diameter is grown by firing under the above-described conditions, since it is baked in a sealed state, impurities such as a compound containing a halide ion cannot be sufficiently removed. Mix the powder after firing. In order to reduce the amount of the halide ion-containing compound to increase the purity of the magnesium oxide powder, the production method of the present invention, Preferably, after the primary firing of the closed system, the second firing is further performed in an open system.

The secondary firing may be carried out by a general open system, for example, in a gas atmosphere in which an ambient atmosphere flows, or an electric furnace under an oxygen flow in an atmospheric atmosphere. The temperature, the time, and the gas in the furnace at the time of the secondary firing are not particularly limited as long as impurities such as a compound containing a halide ion can be removed, but since the crystal growth is completed in one firing, the second time is completed. The firing time is relatively short.

According to the process of the present invention, cubic magnesium oxide particles having an extremely large particle diameter as shown in Fig. 4 can be obtained. When the cube-shaped particles were observed by a scanning electron microscope, the length of the cube side was more than 4.0 μm. Such cube-shaped particles that are both large and particle-free and have a clean and smooth surface have not been proposed so far. Within the scope of the process of the present invention, particles having a length of one side of the cube of 20 μm or less or 10 μm or less can be obtained. Magnesium oxide powders comprising such particles are also within the scope of the invention.

Example

Hereinafter, the present invention will be described in further detail by way of examples, but the invention is not limited thereto.

In the following examples, various physical properties and the like were measured in the order shown below.

(1) Scanning electron microscope (SEM) observation method Using a scanning electron microscope (product name: JSM-5410, manufactured by JEOL), the SEM composition image was taken to observe the particle shape and measure the length of the cubic magnesium oxide side.

(2) Laser diffraction scattering particle size distribution measurement method using laser diffraction scattering type particle size distribution measuring device (product name: HIRA, Nikkiso) to measure cumulative 10% particle size (D ₁₀ ), cumulative 50 % particle size (D ₅₀ ), and cumulative 90% particle size (D ₉₀ ).

(3) BET specific surface area measurement method The specific surface area was measured by a gas adsorption method using a specific surface area measuring device (product name: Macsorb 1210, manufactured by Mounttech).

(4) Magnesium oxide purity measurement method The purity of the magnesium oxide is a value obtained by subtracting the total of the measured impurities from 100% by mass.

(5) Magnesium oxide mass measurement method The impurity amount of magnesium oxide (Si, Al, Ca, Fe, V, Cr, Mn, Ni, Zn, B, Zr, Cu, Na, K, Cl) is an ICP luminescence analyzer (product name: SPS-1700) The product was prepared by dissolving the sample in acid after Seiko Instruments.

(6) Method for measuring the amount of halide of magnesium oxide precursor The amount of the halide of the magnesium oxide precursor was measured by an ICP emission spectrometer (product name: SPS-1700, manufactured by Seiko Instruments).

Example 1

A sodium hydroxide (NaOH) aqueous solution was reacted with an aqueous solution of magnesium chloride (MgCl ₂ ) to prepare a magnesium hydroxide (Mg(OH) ₂ ) slurry. The magnesium hydroxide slurry was diluted with ion-exchanged water to a slurry concentration of 75 g/L, and 30 L of the diluted magnesium oxide slurry was stirred at a speed of 100 to 150 rpm, and water vapor was blown thereto to adjust the liquid temperature to 60 °C. Next, while maintaining the liquid temperature at 60 ° C, a carbon dioxide gas having a CO ₂ concentration of 100% by volume was blown into the lower portion of the tank for 3 hours (0.8 mol equivalent) to convert a portion into an alkaline carbonic acid at a flow rate of 10 L/min. magnesium.

Next, the slurry was filtered, and the obtained cake was washed with water at 20 L of ion-exchanged water. Thereafter, the cake was dried in a dryer at 120 ° C for 10 hours to obtain a precursor. As a result of X-ray diffraction analysis, the precursor is magnesium hydroxide and basic magnesium carbonate (chemical formula: 4MgCO ₃ .Mg(OH) ₂ .8H ₂ O and 4MgCO ₃ .Mg(OH) ₂ .4H ₂ O) a mixture. At this time, after measuring the chloride ion content contained in the above precursor, it was 3% by mass.

Next, the precursor of the mixture of the magnesium hydroxide and the basic magnesium carbonate is heated to 1200 ° C at a heating rate of 6 ° C / min under an atmospheric atmosphere in a closed electric furnace flowing out of the atmosphere without ambient atmosphere. The temperature was maintained for 5 hours, whereby firing was performed to form magnesium oxide powder. Further, in an atmosphere of an atmospheric atmosphere, the gas which flows into the gas in an ambient atmosphere flows out and re-fires at 1200 ° C for one hour. Fig. 1 shows the results of observation of the obtained magnesium oxide powder by a scanning electron microscope (15,000 times). The crystal shapes observed were almost all cube-shaped, and the particle shapes were extremely uniform. Further, one side of the cubic crystal is about 1 μm, and a powder having a very narrow particle size distribution is known from a small D ₉₀ /D ₁₀ . Unlike FIG. 9 described later, fine particles are not adhered to the crystal surface, and the crystal surface is smooth and clean. Further, each of the cubic crystal grains is sufficiently separated from each other.

Example 2

In addition to changing the amount of ion exchange water used in the water washing step to 10L Further, in the same manner as in Example 1, a precursor of a mixture of basic magnesium carbonate and magnesium hydroxide was obtained, and a magnesium oxide powder was obtained. The content of the chloride ion contained in the precursor is 8% by mass. Fig. 2 shows the results of observing the obtained magnesium oxide powder by a scanning electron microscope (15,000 times). When compared with Example 1, one side of the cubic crystal is enlarged to about 1.5 μm.

Example 3

A precursor of a mixture of basic magnesium carbonate and magnesium hydroxide was prepared in the same order as in Example 1 except that the water washing step was not carried out, and a magnesium oxide powder was obtained. The content of the chloride ion contained in the precursor is 14% by mass. Fig. 3 shows the results of observing the obtained magnesium oxide powder by a scanning electron microscope (15,000 times). When compared with Example 1, one side of the cubic crystal is enlarged to about 2 μm.

Example 4

The same procedure as in Example 1 was carried out except that the amount of ion-exchanged water used in the water washing step was changed to 30 L, and 6N hydrochloric acid was diluted to about 10 times with ion-exchanged water, and then added to the cake after washing with water and before drying. A precursor of a mixture of basic carbonic acid and magnesium hydroxide was prepared, and a magnesium oxide powder was obtained. The content of the chloride ion contained in the precursor is 20% by mass. Fig. 4 shows the results of observing the obtained magnesium oxide powder by a scanning electron microscope (15,000 times). One side of the cubic crystal reaches about 4 μm, forming extremely large cubic magnesium oxide particles.

Example 5

A sodium hydroxide (NaOH) solution was reacted with a magnesium chloride (MgCl ₂ ) solution to prepare a magnesium hydroxide (Mg(OH) ₂ ) slurry. The magnesium hydroxide slurry was diluted with ion-exchanged water to a slurry concentration of 75 g/L, and 30 L of the diluted magnesium oxide slurry was stirred at a speed of 500 to 600 rpm while maintaining the liquid temperature at 115 ° C in an autoclave for 1 hour. Hydrothermal reaction. Next, the slurry was filtered, and the obtained cake was washed with water at 30 L of ion-exchanged water. Thereafter, the cake was dried in a dryer at 120 ° C for 10 hours to obtain a precursor. At this time, the chloride ion content contained in the above precursor was measured and found to be 1% by mass. Next, in a closed-type electric furnace in which an ambient atmosphere gas flows out in an atmospheric atmosphere, the precursor is heated to 1200 ° C at a heating rate of 6 ° C / min, and maintained at the same temperature for 5 hours, thereby being fired. Magnesium oxide powder. Further, in a gas atmosphere in which an ambient gas flows out, it is re-fired at 1200 ° C for 1 hour in an atmospheric atmosphere. Fig. 5 shows the results of observing the obtained magnesium oxide powder by a scanning electron microscope (15,000 times). The crystal shapes observed were all substantially cubic, and the particle shapes were extremely uniform. Further, one side of the cubic crystal is about 0.5 μm, and a small particle size distribution range is known from the small D ₉₀ /D ₁₀ .

Comparative example 1

Magnesium oxide powder was obtained in the same manner as in Example 1 except that the atmosphere was gas-fired in a gas atmosphere in which the ambient gas was flowed out. Fig. 6 shows the results of observing the obtained magnesium oxide powder by a scanning electron microscope (15,000 times). The obtained magnesium oxide powder does not grow into a cubic shape, and the particle diameter is also small and the particles are aggregated.

Comparative example 2

A precursor of a mixture of basic magnesium carbonate and magnesium hydroxide was prepared in the same order as in Example 1 except that the amount of ion-exchanged water used in the water washing step was changed to 50 L, and a magnesium oxide powder was obtained. The content of the chloride ion contained in the precursor is 0.1% by mass. Fig. 7 shows the results of observing the obtained magnesium oxide powder by a scanning electron microscope (15,000 times). The obtained magnesium oxide powder does not grow into a cubic shape, and the particle diameter is also small and the particles are aggregated.

Comparative example 3

Magnesium hydroxide (manufactured by Tateho Chemical Industries Co., Ltd., purity 99% by mass, primary particle diameter 0.3 to 0.5 μm, specific surface area 30 to 40 m ² /g) containing about 1% by mass of impurities was used as a precursor of magnesium oxide. Things. The chlorine content was 0.5% by mass. Next, in a closed atmosphere furnace in which an ambient atmosphere gas flows out, the magnesium hydroxide is heated to 1200 ° C at a heating rate of 6 ° C / min, and maintained at the same temperature for 5 hours, thereby being fired. , producing magnesium oxide powder. Further, in an atmosphere of an atmospheric atmosphere, the gas which flows into the gas in an ambient atmosphere flows out and re-fires at 1200 ° C for one hour. Fig. 8 shows the results of observing the obtained magnesium oxide powder by a scanning electron microscope (15,000 times). When the impurities are contained in an amount of about 1% by mass and the purity of MgO is low, the obtained magnesium oxide grows in particles, but the crystal shape is not cubic.

Comparative example 4

Fig. 9 shows the results of observation of a commercially available gas phase magnesia powder by a scanning electron microscope (15,000 times). Although it contains cubes The body crystallizes, but at the same time a large amount of fine particulate crystals adhere to the surface, and the surface is not clean.

Comparative Example 5

Fig. 10 shows the results of observing a commercially available magnesium oxide powder by a scanning electron microscope (15,000 times). The crystals are not cubic, and the particle size is also small and the particles are aggregated.

Tables 1 and 2 show the measurement results of the physical property values and the impurity amounts of the magnesium oxide powders of Examples 1 to 5 and Comparative Examples 1 to 5.

The cubic magnesium oxide powder of the present invention is used as an additive, a filler, a raw material for electronic parts, a pharmaceutical, a reagent for a laboratory, various target materials, a raw material for a superconductor film base film, a tunnel barrier material for a TMR element, A protective film raw material for PDP, a crystalline magnesium oxide layer raw material for PDP, and the like.

Figure 1 is an electron micrograph of the magnesium oxide powder obtained in Example 1.

Figure 2 is an electron micrograph of the magnesium oxide powder obtained in Example 2.

Figure 3 is an electron micrograph of the magnesium oxide powder obtained in Example 3.

Figure 4 is an electron micrograph of the magnesium oxide powder prepared in Example 4. sheet.

Figure 5 is an electron micrograph of the magnesium oxide powder obtained in Example 5.

Fig. 6 is an electron micrograph of the magnesium oxide powder obtained in Comparative Example 1.

Fig. 7 is an electron micrograph of the magnesium oxide powder obtained in Comparative Example 2.

Fig. 8 is an electron micrograph of the magnesium oxide powder of Comparative Example 3.

Fig. 9 is an electron micrograph of the magnesium oxide powder of Comparative Example 4.

Fig. 10 is an electron micrograph of the magnesium oxide powder of Comparative Example 5.

Claims (4)

a cubic magnesium oxide powder having a cubic shape as observed by a scanning electron microscope, and a cumulative 50% particle diameter (D ₅₀ ) measured by a laser diffraction scattering particle size distribution of 1.0 μm or more, in a laser The ratio of the cumulative 10% particle diameter (D ₁₀ ) to the cumulative 90% particle diameter (D ₉₀ ) measured by the diffraction scattering particle size distribution is D ₉₀ /D ₁₀ of 10.0 or less, and the magnesium oxide purity is 99.9% by mass or more. The cubic magnesium oxide powder according to claim 1, wherein the BET specific surface area is 5.0 m ² /g or less. The cubic magnesium oxide powder according to claim 1 or 2, wherein the magnesium oxide precursor is in the presence of 0.5 to 20% by mass of chloride ions relative to the total amount of the precursor, at 600 to 1400 ° C. After 1 to 10 hours, after firing in a closed system, and then performing the second firing in an open system, the magnesium oxide precursor is alkaline magnesium carbonate, magnesium hydroxide, or a mixture thereof. . A method for producing a magnesium oxide powder, wherein the magnesium oxide precursor is fired in a closed system at a temperature of from 600 to 1400 ° C for 1 to 10 hours in the presence of 0.5 to 20 mass % of chloride ions relative to the total amount of the precursor After the formation, the second firing is performed in the open system to obtain a magnesium oxide powder having a magnesium oxide purity of 99.9% by mass or more, wherein the magnesium oxide precursor is alkaline magnesium carbonate, magnesium hydroxide, or a mixture thereof. .