KR20090104088A - Cubic magnesium oxide powder and method for producing the same - Google Patents

Abstract

Disclosed is a magnesium oxide powder having a cubic shape and a large average particle diameter. Also disclosed is a method for producing such a magnesium oxide powder. Specifically disclosed is a magnesium oxide powder whose particles have a cubic shape when observed with a scanning electron microscope. This magnesium oxide powder has a 50% cumulative particle diameter (D50), as determined by a laser diffraction/scattering particle size distribution measuring method, of not less than 1.0 μm. This powder can be obtained by firing a magnesium oxide precursor in the presence of 0.5-30% by mass of a halide ion relative to the total mass of the precursor in a closed system.

Description

Cubic Magnesium Oxide Powder and Manufacturing Method Thereof {CUBIC MAGNESIUM OXIDE POWDER AND METHOD FOR PRODUCING THE SAME}

TECHNICAL FIELD This invention relates to a cube-shaped magnesium oxide powder and its manufacturing method.

Magnesium oxide is used for various additives, electronic parts, fluorescent material, target material, superconducting film base material, tunneling magnetoresistive (TMR) element as well as refractory material, It is used as a raw material for a protective film material for a plasma display panel (PDP) and a crystalline magnesium oxide layer for a plasma display panel (PDP), and attracts attention as an inorganic material having a very wide range of uses.

For example, magnesium oxide, which is a raw material for forming a crystal magnesium oxide layer for a plasma display panel (PDP), is a high-purity crystal powder in which the shape of primary particles is cubic, the grain size of each crystal is large, and the particle size distribution is further increased. Narrow, excellent crystal powder is desired.

As a manufacturing method of magnesium oxide powder, mainly the (1) gas phase method by oxidation of magnesium metal, (2) pyrolysis by baking precursors, such as magnesium hydroxide and magnesium carbonate, at the temperature more than pyrolysis temperature, The method and (3) the method of grind | pulverizing the lump obtained by the fusion method are known.

In the gas phase method, a high-purity cubic magnesium oxide powder can be obtained, but the particle diameter is less than 1 µm (see Patent Document 1 and Non-Patent Document 1). In addition, a large number of fine particles adhered to the crystal surface and the surface was not clean, and there was a problem in that the cubic particles and the non-cubic fine particles were mixed and not a monodisperse powder composed only of the cubic particles.

Magnesium oxide powder produced by more efficient pyrolysis method has a polygonal shape with rounded corners or corners of crystal grains, and thus it is difficult to obtain large particles. For this reason, carbon dioxide gas, water | moisture content, etc. in air | atmosphere are made to adsorb | suck, and this may hinder the performance of the characteristic inherent in magnesium oxide. Furthermore, in most cases, only particles having poor dispersibility due to agglomeration of the particles with each other were obtained.

In order to overcome the drawbacks in the above pyrolysis method, Patent Literature 2 discloses a method of mixing a chloride ion with a magnesium oxide precursor or magnesium oxide, followed by calcining, and mixing with an aqueous magnesium chloride solution and a basic precipitant solution and then filtering without washing. The firing method is described. In the examples of this document, the firing is described in an oxygen stream. The magnesium oxide crystals thus obtained are in the form of cubes but are only about 0.2 µm in particle size, and only particles are agglomerated with each other (Fig. 2 (A) of the document).

Patent Document 1: Japanese Patent Application Laid-Open No. Hei 1-282146

Patent Document 2: Japanese Patent Application Laid-Open No. 2006-36544

Non-Patent Literature 1: "Materials", Nov. 62, Vol. 36, No. 410, pp. 1157-1161

Challenge to be solved

In view of the above-mentioned phenomenon, an object of the present invention is to provide a magnesium oxide powder having a large particle size and a production method thereof.

Challenge solution

MEANS TO SOLVE THE PROBLEM As a result of carrying out various examinations in order to solve the said subject, when calcining a magnesium oxide precursor by a pyrolysis method and manufacturing magnesium oxide powder, this baking is carried out, and a specific amount of halide ion exists. In the state, it was also found that by performing in a closed system, unlike ordinary firing conditions, it was possible to produce magnesium oxide powder having a cube shape and a very large average particle diameter of 1 µm or more, which was impossible to obtain in the conventional manufacturing method. It led to the invention.

That is, the present invention is a cube-shaped magnesium oxide powder, characterized in that the particle shape observed by the scanning electron microscope is cubic, and the cumulative 50% particle size (D ₅₀ ) by laser diffraction scattering particle size distribution measurement is 1.0 μm or more. It is about. Here, the ratio (D ₉₀ / D ₁₀ ) of the cumulative 10% particle diameter (D ₁₀ ) and the cumulative 90% particle diameter (D ₉₀ ) by laser diffraction scattering particle size distribution measurement is preferably 10.0 or less, and BET (Brunauer, Emmett, Teller) It is preferable that the specific surface area is 5.0 m <2> / g or less. Moreover, it is preferable that purity is 99.9 mass% or more. It is preferable that the said cube-shaped magnesium oxide powder can be obtained by baking a magnesium oxide precursor in a closed system in the state which 0.5-30 mass% halide ion exists with respect to the said precursor whole quantity.

That is, the present invention relates to a cubic magnesium oxide particle, wherein the particle shape observed with a scanning electron microscope is cubic, and the length of one side of the cube is larger than 4.0 µm, and the cubic magnesium oxide particle is also present. It relates to a magnesium oxide powder comprising a.

Furthermore, the present invention relates to a method for producing a cubic magnesium oxide powder, wherein the magnesium oxide precursor is calcined in a closed system in a state where 0.5 to 30% by mass of halide ions is present relative to the total amount of the precursor. It is preferable that the magnesium oxide precursor is basic magnesium carbonate, magnesium hydroxide, or a mixture thereof.

effect

According to the present invention, magnesium oxide powder having a cube shape and a large average particle diameter can be obtained. Most preferably, according to the present invention, (1) cube shape is uniform, (2) average particle size is larger than 1 µm, (2) particle size is uniform, and (4) no particulates are included, and the cubic crystal The surface of is clean and smooth, and (5) each crystal grain is separated, and magnesium oxide powder which has the characteristic which is excellent in dispersibility can be manufactured.

Detailed Description of the Invention

The magnesium oxide powder of this invention is a cube shape of a primary particle. This shape can be confirmed by a scanning electron microscope. In addition, a "cuboid shape" does not refer to a rigid cube in a geometric sense, but refers to a shape that can be generally recognized as a cube by visually observing a micrograph as shown in FIGS. 1 to 5. Since the magnesium oxide powder of this invention isolate | separates each other without agglomerating a cube-shaped primary particle, it can have a property with favorable dispersibility.

The magnesium oxide powder of the present invention has a large average particle diameter and specifically satisfies 1.0 µm or more with a cumulative 50% particle size (D ₅₀ ) according to a laser diffraction scattering particle size distribution measurement. The cube-shaped magnesium oxide powder having an average particle diameter of such a great extent was first discovered by the present inventors. As the D ₅₀ is more preferably not less than 1.2㎛ or more preferred, and 1.5㎛. It is thought that it is possible to obtain a powder having a D ₅₀ of approximately 20 µm or less or 10 µm or less within the range of the production method according to the present invention. D ₅₀ is a median diameter and refers to a particle size (μm) corresponding to 50% by volume in a cumulative graph of particle size, and is a particle size in which the larger and smaller sizes are equal when the powder is divided into two particle sizes. .

Furthermore, regarding the fact that the primary particles are large and do not contain fine powder as a whole, the magnesium oxide powder of the present invention preferably has a specific surface area of 5.0 m 2 / g or less measured by the BET method, more preferably 4.0. M 2 / g or less, even more preferably 2.5 m 2 / g or less, particularly preferably 1.0 m 2 / g or less.

The magnesium oxide powder of the present invention is preferably provided with a cubic particle shape, and fine particles do not adhere to the cubic crystal surface, and the surface is clean and smooth. For this reason, the magnesium oxide powder of this invention has an even particle size. That is, it is preferable that the particle size distribution is narrow, and specifically, 10.0 at a ratio (D ₉₀ / D ₁₀ ) of the cumulative 10% particle diameter (D ₁₀ ) and the cumulative 90% particle diameter (D ₉₀ ) according to the laser diffraction scattering particle size distribution measurement. It is preferable to satisfy the following. More preferably, it is 6.0 or less, More preferably, it is 4.5 or less.

The magnesium oxide powder of this invention is high purity, As purity, 99.9 mass% or more is preferable, 99.99 mass% or more is more preferable.

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

Although the manufacturing method of this invention is based on the pyrolysis method, in this invention, magnesium oxide powder is performed by performing the process of baking a magnesium oxide precursor in a closed system in the presence of 0.5-30 mass% halide ion with respect to the said precursor whole quantity. To prepare. Thereby, magnesium oxide powder which has the various characteristics mentioned above can be manufactured.

The magnesium oxide precursor may be a precursor used by a conventional pyrolysis method, and is not particularly limited. Examples thereof include magnesium hydroxide, basic magnesium carbonate, magnesium carbonate and magnesium hydroxide. Among them, magnesium hydroxide, basic magnesium carbonate, and mixtures thereof are preferable because of excellent properties of the obtained magnesium oxide powder.

When the precursor contains a large amount of impurities, the obtained magnesium oxide powder does not have a cubic shape but tends to have a rounded polygonal shape, so that the impurity of the precursor is smaller. Specifically, the amount of impurities contained in the precursor is preferably 0.1% by mass or less, more preferably 0.01% by mass or less, of the total amount of impurities remaining when magnesium oxide is produced by the thermal decomposition method without the halide ions.

The firing is carried out in the presence of halide ions. The halide ions include chloride ions, fluoride ions, emulsified ions, and iodide ions, but chloride ions are usually used. Specific examples of the compound containing halide ions include hydrochloric acid, ammonium chloride, sodium chloride, potassium chloride, magnesium chloride, and the like.

As an amount of halide ions, it is the range of 0.5-30 mass% with respect to the magnesium oxide precursor whole quantity. If the amount of halide ions is too small, the effect of the present invention will not be achieved. On the contrary, if the amount of halide ions is too large, crystals of magnesium oxide become difficult to grow. Preferably it is 1.0-25 mass% range, More preferably, it is 10-25 mass% range.

The compound containing halide ions may be a magnesium oxide precursor itself, may be derived from impurities contained in the magnesium oxide precursor, may be a by-product produced when the magnesium oxide precursor is prepared by a solution synthesis method, and magnesium oxide The precursor may be added separately, or may be added to the gas atmosphere in a closed furnace as, for example, gaseous hydrogen chloride. In addition, impurities contained in the magnesium oxide precursor and by-products generated during the manufacture of magnesium oxide may be sufficiently removed by washing or the like, and then added to the magnesium oxide precursor or the gas atmosphere.

In the present invention, the magnesium oxide precursor is preferably one obtained by solution synthesis.

When the magnesium oxide precursor is a mixture of basic magnesium carbonate and magnesium hydroxide, in order to prepare the precursor by solution synthesis, for example, (1) an aqueous magnesium chloride solution and an aqueous sodium hydroxide solution are mixed to obtain a magnesium hydroxide slurry ( 2) Carbonate a portion of magnesium hydroxide in the slurry to obtain a slurry containing basic magnesium carbonate and magnesium hydroxide, and (3) filter the slurry to obtain a mixture of basic magnesium carbonate and magnesium hydroxide. This mixture contains chloride ions as either magnesium chloride as a starting material or sodium chloride as a by-product.

In the said process (1), after obtaining a magnesium hydroxide slurry, it is good to adjust the density | concentration of this slurry to 50-100 g / L range, More preferably, to 60-90 g / L range by diluting with water. This is to reduce the viscosity of the slurry by lowering the concentration of the slurry so that the carbonation reaction in the next step (2) proceeds uniformly.

In the said process (2), a part of magnesium hydroxide in a slurry is carbonated by blowing carbon dioxide gas into the said slurry. As for the temperature of this carbonation reaction, 40-80 degreeC is preferable. In this temperature range, the transition from magnesium hydroxide to basic magnesium carbonate is rapid, resulting in good reaction efficiency. Moreover, within this temperature range, a mixture of basic magnesium carbonate and magnesium hydroxide having a particle size with excellent filtration efficiency can be obtained.

The amount of carbon dioxide gas used in the carbonation reaction is an amount capable of converting a part of magnesium hydroxide in the magnesium hydroxide slurry into basic magnesium carbonate to provide a mixture of basic magnesium carbonate and magnesium hydroxide. It is preferable that the usage-amount of specific carbon dioxide gas is 0.2-2,0 mol equivalent with respect to 1 mol of magnesium hydroxides. Within this range, it is possible to efficiently obtain a mixture of basic magnesium carbonate and magnesium hydroxide having excellent filtration efficiency.

In the step (3), the slurry containing the basic magnesium carbonate and magnesium hydroxide obtained in the step (2) is filtered to obtain a mixture of basic magnesium carbonate and magnesium hydroxide as a solid. Since the solid mixture contains chloride ions, the solid mixture may be dried without washing as it is, and then calcined as described below. The mixture is washed with an appropriate amount of water to lower the amount of chloride ions in the cake to an appropriate level. You may dry and bake. If the washing is sufficiently performed, the content of chloride ions becomes so low that the effect of the present invention cannot be obtained. Therefore, the degree of cleaning needs to be controlled according to the amount of washing water used, the washing time, and the like. However, after the rinse is sufficiently removed to completely remove the chloride ions, a halide ion-containing compound may be added separately.

In the case where the magnesium carbonate precursor is magnesium hydroxide, in order to prepare the precursor by solution synthesis method, for example, (1) an aqueous magnesium chloride solution and an aqueous sodium hydroxide solution are mixed to obtain a magnesium hydroxide slurry, and (2) the slurry is filtered. Solid magnesium hydroxide is obtained. This solid contains chloride ions as magnesium chloride as a starting material or sodium chloride as a by-product.

After the magnesium hydroxide slurry is obtained in the step (1), the concentration of the slurry is preferably adjusted in the range of 50 to 100 g / L, more preferably in the range of 60 to 90 g / L by dilution with water, furthermore, It is preferable to grow the magnesium hydroxide particles in the slurry. Thereby, the filtration efficiency in a process (2) can be improved. Although it does not specifically limit as said aging condition, What is necessary is just to maintain a fixed time at high temperature in the state which stirred a slurry. As aging temperature, about 80-150 degreeC, for aging time, moisture-about several hours are good, for example.

In the step (2), the magnesium hydroxide slurry obtained in the step (1) is filtered to obtain solid magnesium hydroxide. Since this solid contains chloride ions, it may be treated as described above.

In the method for producing magnesium oxide by the thermal decomposition method of the present invention, it is necessary to perform firing of the magnesium oxide precursor in a closed system in the presence of halide ions. The closed system in the present invention refers to a system that is almost sealed so that gas present in the space for firing does not substantially flow out, and gas does not substantially flow from outside, and is opened under an atmosphere such as air and oxygen. This is different from the usual firing method performed by or by flowing these air streams. In the present invention, by calcining in a closed system, the halide ions do not scatter to the outside and remain in a baking chamber, and are sufficiently interposed in the process of growing crystals of magnesium oxide powder, thereby obtaining a cubic crystal powder having a very large average particle diameter. .

Firing in this closed system can be performed, for example, by using a sealed electric furnace that is substantially free of inflow and outflow of atmospheric gas, or by placing it in a crucible that can be sealed. As temperature at the time of baking, about 600 degreeC-1400 degreeC is good, and about 1200 degreeC is the most preferable. When the temperature at the time of baking is too high, the obtained crystal | crystallization may aggregate and a dispersibility may worsen. Although it also changes with temperature as baking time, it is about 1 to 10 hours normally. For example, when temperature is about 1200 degreeC, about 5 hours are suitable. In addition, the rate of temperature increase for firing is not particularly limited, but is preferably about 5 to 10 ° C / min.

Although the atmosphere at the time of this baking is not specifically limited, For example, air, oxygen, nitrogen, argon etc. are mentioned, The atmosphere and oxygen atmosphere are preferable so that the impurity contained in a precursor can be removed as oxidizing gas. .

Cubic magnesium oxide powder having a large average particle diameter grows with firing under the above conditions, but since firing is carried out under sealing, impurities such as the halide ion-containing compound are not sufficiently removed and mixed into 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, in the production method of the present invention, it is preferable to perform a second firing in an open system after the primary firing in the above closed system.

This secondary firing may be performed in a normal open system, and may be performed, for example, in a gas furnace with a flow of atmospheric gas under an atmospheric atmosphere, an electric furnace under an oxygen gas stream, or the like. As the temperature, time, and gas in the furnace during the second firing, impurities such as halide ion-containing compounds may be removed. Although not particularly limited, crystal growth has already been completed in the primary firing, The time may be relatively short.

According to the production method of the present invention, it is possible to obtain cubic magnesium oxide particles having a very large particle diameter as shown in FIG. When observed with a scanning electron microscope, this cubic particle has the length of one side of a cube larger than 4.0 micrometers. Such large, fine particles, clean and smooth cubic particles have not been reported at all. Within the range of the manufacturing method which concerns on this invention, it is thought that it is possible to obtain particle | grains whose length of one side of a cube is 20 micrometers or less or 10 micrometers or less. Magnesium oxide powder containing this particle is also in the scope of the present invention.

Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these Examples.

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

(1) Scanning electron microscope (SEM) observation

The SEM composition image was taken using the scanning electron microscope (brand name: JSM-5410, JEOL make), and the particle shape observation and the length of one side of the magnesium oxide cube were measured.

(2) Laser diffraction scattering particle size distribution measurement

10% cumulative particle diameter (D ₁₀ ), 50% cumulative particle diameter (D ₅₀ ), 90% cumulative particle diameter (D ₉₀ ) using a laser diffraction scattering particle size distribution analyzer (trade name: HIRA, manufactured by Nigiso Corporation) ) Was measured.

(3) BET specific surface area measurement

The specific surface area was measured by the gas adsorption method using the specific surface area measuring apparatus (brand name: Macsorb1210, product made by Mountain Tech).

(4) measuring the purity of magnesium oxide

Magnesium oxide purity was computed as the value which subtracted the sum total of the impurity amount measured by 100 mass%.

(5) Determination of impurity content of magnesium oxide

The amount of impurities of magnesium oxide (Si, Al, Ca, Fe, V, Cr, Mn, Ni, Zn, B, Zr, Cu, Na, K, Cl) is an ICP luminescence analyzer (trade name: SPS-1700, Seiko) It was measured after dissolving the sample with acid using the instrument).

(6) halide amount measurement method of magnesium oxide precursor

The halide amount of the magnesium oxide precursor was measured by an ICP luminescence analyzer (trade name: SPS-1700, manufactured by Seiko Instruments).

Example 1

A magnesium hydroxide (Mg (OH) ₂ ) slurry was obtained by reacting an aqueous solution of magnesium chloride (MgCl ₂ ) with an aqueous solution of sodium hydroxide (NaOH). The magnesium hydroxide slurry was diluted with ion exchange water to a slurry concentration of 75 g / L, and 30 L of the diluted magnesium hydroxide slurry was blown with stirring at a speed of 100 to 150 rpm to adjust the temperature to 60 ° C. Next, a carbon dioxide gas having a CO ₂ concentration of 100% by volume was blown at a flow rate of 10 L / min for 3 hours (0.8 molar equivalents) while maintaining the temperature at 60 ° C to convert a portion into basic magnesium carbonate.

Subsequently, the cake obtained by filtering this slurry was washed with 20 L of ion-exchange water. Thereafter, the cake was dried in a dryer at 120 ° C. for 10 hours to obtain a precursor. X-ray diffraction analysis showed that the precursor was a mixture of magnesium hydroxide and basic magnesium carbonate (Formula: 4MgCO ₃ · MG (OH) ₂ · 8H ₂ O and 4MgCO ₃ · MG (OH) ₂ · 4H ₂ O). It was 3 mass% at the time of measuring the content of the chloride ion contained in the said precursor.

Next, the precursor, which is a mixture of magnesium hydroxide and basic magnesium carbonate, was calcined by heating to a temperature of 6 ° C./min at a temperature of 6 ° C./min and kept at the same temperature for 5 hours in a closed electric furnace in an air atmosphere, where no atmospheric gas was introduced. Magnesium oxide powder was formed. Furthermore, this was refired for 1 hour at 1200 ° C. in a gas furnace where atmospheric gas was introduced into the atmosphere. The result of observing the obtained magnesium oxide powder with a scanning electron microscope (15,000 times) is shown in FIG. Almost all of the shapes of the crystals observed are cubic, and the particle shape is very even. In addition, univariate cubic crystal phase is from about 1㎛ before and after, it can be seen that D ₉₀ / D ₁₀ is a very narrow particle size distribution from which small. Unlike FIG. 9 described later, fine particles are not attached to the crystal surface, and the crystal surface is smooth and clean. Moreover, the individual cubic grains are well separated.

Example 2

A precursor, which was a mixture of basic magnesium carbonate and magnesium hydroxide, was obtained in the same procedure as in Example 1 except that the amount of ion-exchanged water used in the washing step was changed to 10 L, and magnesium oxide powder was also obtained. However, content of the chloride ion contained in the said precursor was 8 mass%. The result of observing the obtained magnesium oxide powder with a scanning electron microscope (15,000 times) is shown in FIG. Compared with Example 1, one side of the cubic crystal is about 1.5 µm large.

Example 3

Except not performing the washing process, the precursor which is a mixture of basic magnesium carbonate and magnesium hydroxide was obtained in the same procedure as Example 1, and magnesium oxide powder was also obtained. However, content of the chloride ion contained in the said precursor was 14 mass%. The result of observing the obtained magnesium oxide powder with a scanning electron microscope (15,000 times) is shown in FIG. Compared with Example 1, one side of the cubic crystal is about 2 µm in size.

Example 4

The basic magnesium carbonate and basic magnesium carbonate were used in the same procedure as in Example 1 except that the amount of ion-exchanged water used in the washing step was changed to 30 L and 6N hydrochloric acid was diluted by 10 times with ion-exchanged water and added to the cake before washing and washing. A precursor, which is a mixture of magnesium hydroxide, was obtained, and magnesium oxide powder was also obtained. However, content of the chloride ion contained in the said precursor was 20 mass%. The result of observing the obtained magnesium oxide powder with a scanning electron microscope (15,000 times) is shown in FIG. One side of the cubic crystal reaches about 4 mu m, and very large cubic magnesium oxide particles are formed.

Example 5

A magnesium hydroxide solution (MgCl ₂ ) was reacted with sodium hydroxide solution (NaOH) to obtain a magnesium hydroxide (Mg (OH) ₂ ) slurry. The magnesium hydroxide slurry was diluted with ion exchange water to a slurry concentration of 75 g / L, and 30 L of the diluted magnesium hydroxide slurry was maintained at 115 ° C. in an autoclave while stirring at a speed of 500 to 600 rpm and hydrothermally reacted for 1 hour. . Subsequently, the cake obtained by filtering this slurry was washed with 30 L of ion-exchange water. The cake was then dried in a dryer at 120 ° C. for 10 hours to obtain a precursor. At this point in time, the content of chloride ions contained in the precursor was measured. Next, the precursor was overheated to 1200 ° C. at a heating rate of 6 ° C./min and maintained at the same temperature for 5 hours in a closed electric furnace in which no atmospheric gas flowed in and out of the atmosphere, thereby producing magnesium oxide powder. Furthermore, this was refired for 1 hour at 1200 ° C. in a gas furnace containing an inflow and outflow of atmospheric gas under an atmospheric atmosphere. The result of observing the obtained magnesium oxide powder with a scanning electron microscope (15,000 times) is shown in FIG. Almost all of the shapes of the crystals observed are cubic, and the particles are very even. In addition, one side of the cubic phase crystal is about 0.5 mu m, and it can be seen that the particle size distribution is very narrow because D ₉₀ / D ₁₀ is small.

Comparative Example 1

The magnesium oxide powder was obtained in the same manner as in Example 1 except that the firing was carried out in a gas furnace with an inflow and outflow of atmospheric gas under an atmospheric atmosphere. The result of observing the obtained magnesium oxide powder with a scanning electron microscope (15,000 times) is shown in FIG. In the obtained magnesium oxide powder, crystals do not grow in a cubic form, the particle size is also small, and each particle is agglomerated.

Comparative Example 2

A precursor, which was a mixture of basic magnesium carbonate and magnesium hydroxide, was obtained in the same procedure as in Example 1 except that the amount of ion-exchanged water used in the washing step was changed to 50 L, and magnesium oxide powder was also obtained. However, content of the chloride ion contained in the said precursor was 0.1 mass%. The result of observing the obtained magnesium oxide powder with a scanning electron microscope (15,000 times) is shown in FIG. In the obtained magnesium oxide powder, crystals are not grown in a cubic form, the particle size is also small, and each particle is agglomerated.

Comparative Example 3

As a precursor of magnesium oxide, magnesium hydroxide (Tateho Chemical Co., Ltd. product, purity 99 mass%, primary particle diameter 0.3-0.5 micrometer, specific surface area 30-40 m <2> / g) containing about 1 mass% of impurities was used. The content of chlorine was 0.5 mass%. Next, the magnesium hydroxide was calcined by superheating to 1200 ° C. at a heating rate of 6 ° C./min at a temperature of 6 ° C./min in a closed electric furnace in which no atmospheric gas flowed in and out of the atmosphere, and then calcining to produce magnesium oxide powder. Furthermore, this was refired for 1 hour at 1200 ° C. in a gas furnace containing an inflow and outflow of atmospheric gas in an atmosphere. The result of observing the obtained magnesium oxide powder with a scanning electron microscope (15,000 times) is shown in FIG. In the case where the obtained magnesium oxide contains about 1% by mass of impurities and the MgO purity is low, the crystal form of particle growth occurring is not a cube.

Comparative Example 4

The result of observing the magnesium oxide powder produced by the commercial vapor phase method with the scanning electron microscope (15,000 times) is shown in FIG. It contains a cubic crystal, but at the same time a large amount of fine particulate crystals are attached to the surface can not be said to be clean.

Comparative Example 5

The result of observing the commercially available magnesium oxide powder with the scanning electron microscope (15,000 times) is shown in FIG. The crystal is not cubic, the particle size is also small, and each particle is agglomerated.

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

TABLE 1

TABLE 2

The cubic magnesium oxide powder of the present invention includes additives, fillers, raw materials for electronic parts, pharmaceuticals, reagents in laboratories, various target materials, superconducting thin film base material, tunnel barrier material for TMR elements, protective film material for PDP, and PDP. It is useful as a raw material for a crystalline magnesium oxide layer.

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

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.

4 is an electron micrograph of the magnesium oxide powder obtained in Example 4.

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

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

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

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

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

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

Claims (9)

A cubic magnesium oxide powder, characterized in that the particle shape observed in a scanning electron microscope is a cubical shape, and the cumulative 50% particle size (D ₅₀ ) by laser diffraction scattering particle size distribution measurement is 1.0 µm or more. The cubic phase according to claim 1, wherein the ratio (D ₉₀ / D ₁₀ ) of the cumulative 10% particle diameter (D ₁₀ ) and the cumulative 90% particle diameter (D ₉₀ ) by laser diffraction scattering particle size distribution is 10.0 or less. Magnesium oxide powder. The cubic magnesium oxide powder according to claim 1 or 2, wherein the BET specific surface area is 5.0 m 2 / g or less. Magnesium oxide purity is 99.9 mass% or more, The cube-shaped magnesium oxide powder of Claim 1 or 2 characterized by the above-mentioned. The cubic magnesium oxide powder according to claim 1 or 2, which is obtained by firing a magnesium oxide precursor in a closed system in a state where 0.5 to 30% by mass of halide ions are present relative to the total amount of the precursor. A cubic magnesium oxide particle, characterized in that the particle shape measured by a scanning electron microscope is cubic, and the length of one side of the cube is larger than 4.0 µm. Magnesium oxide powder containing the cubic magnesium oxide particle of Claim 6.  A magnesium oxide precursor is calcined in a closed system in a state where 0.5 to 30% by mass of halide ions are present with respect to the total amount of the precursor. The method for producing a cubic magnesium oxide powder according to claim 8, wherein the magnesium oxide precursor is basic magnesium carbonate, magnesium hydroxide, or a mixture thereof.

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