JP7207082B2 - Magnesium oxide and its production method - Google Patents

Description

The present invention relates to magnesium oxide and its production method.

For example, as disclosed in Non-Patent Documents 1 and 2, a specific component is removed from an object to be treated such as industrial wastewater by a neutralization reaction or an adsorption reaction (hereinafter these may be collectively referred to simply as "reaction"). Magnesium oxide is attracting attention as a cleaning agent. Components removed by the cleaning agent include environmental contaminants including boron or fluorine. Hereinafter, the component to be removed by the cleaning agent is also referred to as the "reacted component".

Patent No. 5773695 Patent No. 5125258 WO2011/040593 Patent No. 5037066

Tomoya Nihei et al., "Generation Reaction of Layered Double Hydroxide Using MgO as Neutralizer and Application to Fluorine Wastewater Treatment Method", Journal of MMIJ vol. 129 (2013) p. 132-137 Tomohito Kameda, ``5RFb-1201 Development of treatment technology for boron and fluorine using magnesium compounds as adsorbents'' A. H. Chowdhury et al. , ''A facility synthesis of grainy rod-like porous MgO'' Materials Letters vol. 158 (2015) p. 190-193

By the way, the cleaning agent is required to have high reactivity with respect to reacted components. Here, the reactivity with respect to the reactant component is defined as the mass (or substance amount) of the reactant component with which, for example, a unit mass of the cleaning agent reacts per unit time. Low reactivity with the reactant requires a large amount of cleaning agent to treat the desired amount of reactant. As a result, the preparation cost of the cleaning agent (for example, the purchase cost of the cleaning agent, the manufacturing cost, etc.) is high. Furthermore, since a large amount of precipitate is generated by the reaction with the reacted component, the treatment cost of the precipitate is also high.

Furthermore, when the cleaning agent is solid (including powder), a high bulk density is also required. If the bulk density of the clarifier is low, the sediment produced by the reaction with the reacted component will be bulky, resulting in high costs for treating the sediment.

However, magnesium oxide has problems of low reactivity and low bulk density. Regarding magnesium oxide, various studies have been made as disclosed in Patent Documents 1 to 4, Non-Patent Document 3, etc. in addition to Non-Patent Documents 1 and 2 described above. However, no technology has been proposed to fundamentally improve the reactivity and bulk density of magnesium oxide.

Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to provide magnesium oxide having high reactivity and bulk density, and a method for producing the same.

One possible method for increasing the reactivity of magnesium oxide is to increase the specific surface area of magnesium oxide (that is, to make it porous). By increasing the specific surface area of magnesium oxide, the contact area with the component to be reacted per unit mass increases. Therefore, an improvement in reactivity can be expected. However, when magnesium oxide is made to have a high specific surface area, a large number of spaces are formed in the magnesium oxide, so the bulk density tends to be low.

Thus, increasing the specific surface area of magnesium oxide conflicts with increasing the bulk density. The present inventors have extensively studied the composition of magnesium oxide that simultaneously satisfies these two contradictory requirements.

As a result, the present inventors found that (1) the size of each magnesium oxide particle that constitutes magnesium oxide should be on the order of submicrons, and (2) the magnesium oxide particles should be a collection of fine crystallites of nano-order size. A study was made on the use of solid particles, that is, secondary particles. By setting the size of the magnesium oxide particles to submicron order, the bulk density of magnesium oxide can be increased. Furthermore, by forming the magnesium oxide particles into aggregates of fine crystallites of nano-order size, the specific surface area of the magnesium oxide particles themselves is increased. Thereby, the specific surface area of magnesium oxide, which is an aggregate of magnesium oxide particles, can be increased.

The present inventors have extensively studied a method for producing magnesium oxide having the above characteristic configuration, and found that the above characteristic configuration is obtained by subjecting basic magnesium carbonate pentahydrate to heat treatment in two stages with mutually different heating conditions. Succeeded in producing magnesium oxide. The present invention has been made based on such findings.

According to one aspect of the present invention, it contains substantially spherical magnesium oxide particles that are aggregates of crystallites with a crystallite diameter of 2 to 20 nm, and the magnesium oxide particles have a particle diameter of 80 to 800 nm. Magnesium oxide is provided.

Here, the crystallite diameter of the crystallite may be 4 to 15 nm.

Moreover, the particle diameter of the magnesium oxide particles may be 200 to 700 nm.

Also, the BET specific surface area calculated from the nitrogen adsorption isotherm may be 120 to 350 m ² /g.

According to another aspect of the present invention, there is provided a method for producing magnesium oxide, characterized by including the following steps (A) and (B).
(A) A step of heating basic magnesium carbonate pentahydrate to a first heating temperature at a temperature elevation rate of 10 to 100° C./min in the air or in an inert gas atmosphere to obtain magnesium carbonate.
The first heating temperature is 350 to 500 ° C. when heating basic magnesium carbonate pentahydrate in the atmosphere, and 350 to 500 ° C. when heating basic magnesium carbonate pentahydrate in an inert gas atmosphere. 550°C.
(B) A step of obtaining magnesium oxide by heating magnesium carbonate to 550 to 1100° C. under a reduced pressure atmosphere of 20 kPa or less.

Here, in step (A), basic magnesium carbonate pentahydrate may be heated under an inert gas atmosphere.

As explained above, the magnesium oxide according to the present invention has high reactivity and bulk density.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows schematic structure of the magnesium oxide which concerns on embodiment of this invention. 4 is an SEM photograph of magnesium oxide particles. It is an enlarged SEM photograph of magnesium oxide particles. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows the manufacturing process of magnesium oxide roughly.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the present specification and drawings, constituent elements having substantially the same functional configuration are denoted by the same reference numerals, thereby omitting redundant description.

<1. Composition of Magnesium Oxide>
(1-1. Composition of magnesium oxide)
First, the structure of magnesium oxide 10 according to the present embodiment will be described with reference to FIGS. 1 to 3. FIG. Magnesium oxide 10 is composed of a large number of magnesium oxide particles 11 .

The magnesium oxide particles 11 are aggregates (aggregates) of a large number of crystallites 12, that is, secondary particles. The magnesium oxide particles 11 are substantially spherical. SEM photographs of actually produced magnesium oxide 10 are shown in FIGS. Of course, the shape of magnesium oxide particles 11 is not limited to spherical.

As shown in FIGS. 2 and 3, the size of each magnesium oxide particle 11 is on the submicron order. Specifically, the particle diameter (sphere equivalent diameter) of the magnesium oxide particles 11 is 80 to 800 nm. In the following description, the particle size of the magnesium oxide particles 11 is also referred to as "secondary particle size of the magnesium oxide 10". Moreover, in this embodiment, the secondary particle size of the magnesium oxide 10 is a so-called average particle size. Specifically, the secondary particle size of the magnesium oxide 10 is defined as the median size of the particle size distribution measured by a laser diffraction/scattering particle size distribution analyzer or the like.

As described above, in the present embodiment, the size of the magnesium oxide particles 11 is extremely fine on the submicron order, so the bulk density of the magnesium oxide 10 can be increased. Furthermore, the dispersibility of the magnesium oxide 10 in an object to be treated such as industrial wastewater can be enhanced. Therefore, the magnesium oxide 10 can be quickly brought into contact with the reactant component, and as a result, the reactivity of the magnesium oxide 10 with respect to the reactant component can be enhanced. Furthermore, the specific surface area of magnesium oxide 10 can be increased. In this respect as well, the reactivity of the magnesium oxide 10 with respect to the components to be reacted can be enhanced.

If the secondary particle size of the magnesium oxide 10 is less than 80 nm, the bulk density is increased, but the handleability of the magnesium oxide 10 is reduced, resulting in reduced practicality. Therefore, it is necessary that the secondary particle size of the magnesium oxide 10 is 80 nm or more. When the secondary particle size of magnesium oxide 10 exceeds 800 nm, the bulk density is greatly reduced. From the viewpoint of the handleability and bulk density of the magnesium oxide 10, the secondary particle size of the magnesium oxide 10 preferably has a lower limit of 200 nm or more and an upper limit of 700 nm or less.

The crystallites 12 forming the magnesium oxide particles 11 are fine particles of nano-order size. Specifically, the particle diameter of the crystallites 12, that is, the crystallite diameter (equivalent sphere diameter) is 2 to 20 nm.

The crystallite size is measured by the X-ray diffraction method. Specifically, a diffraction peak near 42 degrees is extracted from the X-ray diffraction pattern of magnesium oxide 10, and the crystallite size is calculated from the half width of this diffraction peak based on Scherrer's formula.

Furthermore, since the size of the crystallites 12 constituting the magnesium oxide particles 11 is nano-order, the specific surface area of the magnesium oxide 10 can be increased, and the reactivity with the reactant component can be increased.

The specific surface area of the magnesium oxide 10 can be increased as the crystallite size is smaller. However, when the crystallite size is less than 2 nm, aggregation of the magnesium oxide particles 11 progresses, and as a result, the secondary particle size of the magnesium oxide 10 exceeds 800 nm. From this point of view, the crystallite size should be 2 nm or more. If the crystallite size is too large, the specific surface area of the magnesium oxide 10 will decrease, and the reactivity with the reactant component will decrease. From this point of view, the crystallite diameter should be 20 nm or less. From the viewpoint of the secondary particle size and reactivity of the magnesium oxide particles 11, the lower limit of the crystallite size is preferably 4 nm or more. The upper limit of the crystallite size is preferably 15 nm or less, more preferably 10 nm or less.

Therefore, as an example of a preferable configuration of the magnesium oxide 10, there is a configuration in which the crystallite size is 4 to 10 nm and the secondary particle size of the magnesium oxide 10 is 200 to 700 nm. Of course, the structure of the magnesium oxide 10 is not limited to this structure.

(1-2. BET specific surface area)
In the present embodiment, both the secondary particle size and the crystallite size of the magnesium oxide 10 are small, so the specific surface area of the magnesium oxide 10 is large. Specifically, the BET specific surface area of magnesium oxide 10 is preferably 120 to 350 m ² /g. In this case, the magnesium oxide 10 has good handleability and high reactivity.

(1-3. Loose bulk density)
As described above, the bulk density of magnesium oxide 10 increases. Specifically, the loose bulk density is preferably 0.16 to 0.50 g/ml. In this case, the magnesium oxide 10 has good handleability, and also has high reactivity and dispersibility.

<2. Method for producing magnesium oxide>
Next, a method for producing magnesium oxide 10 will be described with reference to FIG. The method for producing magnesium oxide 10 includes the following steps (A) and (B).
(A) A step of heating basic magnesium carbonate pentahydrate to a first heating temperature at a temperature elevation rate of 10 to 100° C./min in the air or in an inert gas atmosphere to obtain magnesium carbonate.
The first heating temperature is 350 to 500 ° C. when heating basic magnesium carbonate pentahydrate in the atmosphere, and 350 to 500 ° C. when heating basic magnesium carbonate pentahydrate in an inert gas atmosphere. 550°C.
(B) A step of obtaining magnesium oxide 10 by heating magnesium carbonate 30 to 550 to 1100° C. under a reduced pressure atmosphere of 20 kPa or less.

In this embodiment, the basic magnesium carbonate pentahydrate 20 is subjected to two stages of heat treatment (steps (A) and (B)) under different heating conditions. In step (A), magnesium carbonate 30 is produced from basic magnesium carbonate pentahydrate 20, and magnesium oxide 10 is produced from magnesium carbonate 30 in step (B). That is, in the present embodiment, the basic magnesium carbonate pentahydrate 20 is not directly converted into magnesium oxide, but the magnesium carbonate 30 is once produced by dividing the heat treatment into two stages. Once the magnesium carbonate 30 is produced, it is very important for the production of the magnesium oxide 10 . Details will be described below.

(2-1. Step (A))
In step (A), first, basic magnesium carbonate pentahydrate 20 shown in FIG. 4 is prepared. Basic magnesium carbonate pentahydrate ₂₀ has a structure represented by the molecular formula of Mg ₅ (CO ₃ ) ₄ (OH) 2.5H ₂ O, and is prepared from urea, magnesium acetate tetrahydrate, and water as raw materials. It can be obtained by hydrothermal synthesis. An example is as follows. That is, urea, magnesium acetate tetrahydrate, and water are mixed at a ratio (mass ratio) of 1:5:16. Then, the mixed liquid is put into a high-pressure container and heated at 180° C. for 5 hours. That is, so-called hydrothermal synthesis is performed. Thus, basic magnesium carbonate pentahydrate 20 is produced. Basic magnesium carbonate pentahydrate 20 often has an elongated shape. The method for producing basic magnesium carbonate pentahydrate 20 is not limited to this example. That is, the method for producing basic magnesium carbonate pentahydrate 20 is not limited.

Next, the basic magnesium carbonate pentahydrate 20 is heated to the first heating temperature at a temperature elevation rate of 10 to 100° C./min in the air or in an inert gas atmosphere. As a result, water is decomposed and removed from the basic magnesium carbonate pentahydrate 20 to produce magnesium carbonate 30 .

Here, the magnesium carbonate 30 is an aggregate of many magnesium carbonate particles 31 . The particle size of magnesium carbonate 30 (that is, the particle size of magnesium carbonate particles 31 ) is equivalent to the secondary particle size of magnesium oxide 10 . In addition, the particle diameter of the magnesium carbonate 30 is a so-called sphere-equivalent diameter. Also, the particle size of the magnesium carbonate 30 is defined as the median size of the particle size distribution measured by a laser diffraction/scattering particle size distribution analyzer or the like.

Therefore, by adjusting the particle size of the magnesium carbonate 30, the secondary particle size of the magnesium oxide 10 can be adjusted. The particle size of the magnesium carbonate 30 varies depending on the decomposition rate when water is decomposed from the basic magnesium carbonate pentahydrate 20 , that is, the temperature rise rate of the basic magnesium carbonate pentahydrate 20 . In the present embodiment and examples described later, the temperature of the substance to be heated substantially means the ambient temperature (for example, the temperature in the furnace in which the substance to be heated is installed).

The heating rate in step (A) is 10 to 100° C./min. If the temperature rise rate is less than 10° C./min, the particle size of the magnesium carbonate 30 and, in turn, the secondary particle size of the magnesium oxide 10 become excessively large, possibly exceeding the aforementioned 800 nm. If the heating rate exceeds 100° C./min, the secondary particle size of the magnesium oxide 10 becomes very small, possibly falling below 80 nm.

The first heating temperature in step (A) varies depending on the atmosphere. Specifically, the first heating temperature is 350 to 500 ° C. when basic magnesium carbonate pentahydrate is heated in the atmosphere, and basic magnesium carbonate pentahydrate is heated in an inert gas atmosphere. If so, it will be 350 to 550°C. Thereby, water can be decomposed and removed from the basic magnesium carbonate pentahydrate 20 . If the heating temperature is lower than the lower limit of the first heating temperature (that is, 350° C.), the decomposition of the basic magnesium carbonate pentahydrate 20 does not proceed sufficiently, and magnesium carbonate with a small particle size cannot be obtained. may not be possible. If the heating temperature exceeds the upper limit of the first heating temperature (that is, 500° C. or 550° C.), the crystallites 12 of the magnesium oxide 10 may become coarse. That is, when the heating temperature exceeds the upper limit value of the first heating temperature, carbon dioxide may be further separated from the magnesium carbonate produced in step (A), and magnesium oxide 10 may be produced. In this case, the heating is substantially performed in one step. This is the same as the conventional manufacturing method of magnesium oxide 10, and as a result, crystallites 12 of magnesium oxide 10 are coarsened.

The heating in step (A) is performed in the air or in an inert gas atmosphere. Although the reason is not clear, by heating in such an atmosphere, the crystallite size of the magnesium oxide 10 can be reduced, and the specific surface area of the magnesium oxide 10 can be increased. Heating in step (A) is preferably carried out under an inert atmosphere. In this case, the crystallite size of magnesium oxide 10 can be made smaller more easily. It is preferable to flow the gas that constitutes the atmosphere. In addition, when the heating in step (A) is performed in an oxidizing gas (that is, a gas that causes or assists combustion of other substances more than air (atmosphere) by supplying oxygen) atmosphere, oxidation The crystallite diameter of magnesium 10 increases and the specific surface area decreases.

The time for maintaining the temperature of the basic magnesium carbonate pentahydrate 20 at the above heating temperature, that is, the heating time, may be adjusted so that the desired magnesium oxide 10 is obtained. As an example, the heating time may be about 30 minutes to 1 hour.

(2-2. Step (B))
In step (B), magnesium carbonate is heated to 550 to 1100° C. under a reduced pressure atmosphere of 20 kPa or less. As a result, magnesium oxide 10 is generated by decomposing carbon dioxide from magnesium carbonate, and the decomposed carbon dioxide is quickly removed from magnesium oxide 10 . Thereby, magnesium oxide 10 having a small crystallite size can be produced.

When the pressure reduction in step (B) is insufficient (that is, when the pressure exceeds 20 kPa. The same applies when performing under a pressurized atmosphere), the decomposition reaction of magnesium carbonate and the regeneration of magnesium oxide 10 and carbon dioxide during heating. A binding reaction occurs reversibly. In this process, the activity of the crystallites 12 of the magnesium oxide 10 increases, and the fusion between the crystallites 12 progresses. As a result, the crystallite size of the magnesium oxide 10 becomes coarse. The lower limit of the pressure during decompression is not particularly limited, but may be 5 kPa or more.

If the heating temperature is less than 550° C., the decomposition reaction of magnesium carbonate does not proceed sufficiently, and magnesium oxide cannot be obtained. If the heating temperature exceeds 1100° C., the crystallites 12 of the magnesium oxide 10 become coarse. The heating temperature is preferably 850° C. or lower. This is because the crystallite diameter can be made smaller.

The time for maintaining the temperature of magnesium carbonate at the above heating temperature, ie, the heating time, may be adjusted so that the desired magnesium oxide 10 is obtained. As an example, the heating time may be about 30 minutes to 1 hour.

As described above, the secondary particle size of magnesium oxide 10 obtained in step (B) is equivalent to the particle size of magnesium carbonate 30 obtained in step (A). If the step (A) is omitted and only the step (B) is performed, that is, if the basic magnesium carbonate pentahydrate is subjected to the heat treatment of the step (B), the crystallite diameter of the magnesium oxide 10 can be reduced, but the secondary particle size cannot be reduced.

As described above, in the method for producing the magnesium oxide 10 according to the present embodiment, the heat treatment is performed in two stages. Thereby, the magnesium oxide 10 having a small secondary particle size and a small crystallite size can be produced.

<1. Measurement method of each parameter>
Next, an example of this embodiment will be described. First, the method of measuring each parameter will be described.

(1-1. Crystallite size of magnesium oxide)
The crystallite size of magnesium oxide was measured using an X-ray diffractometer (SmartLab manufactured by Rigaku Corporation). Specifically, the measurement result of the X-ray diffraction device was converted into an X-ray diffraction pattern using analysis software. Next, a diffraction peak near 42 degrees was extracted from the X-ray diffraction pattern of magnesium oxide, and the crystallite size was calculated from the half width of this diffraction peak based on Scherrer's formula.

(1-2. BET specific surface area of magnesium oxide)
Nitrogen gas adsorption measurement was performed using BELSORPmini manufactured by Microtrac Bell to obtain a nitrogen adsorption isotherm. The measurement temperature was 77K. Nitrogen adsorption isotherms were measured over a range of relative pressures from 0 to 0.995. Next, the nitrogen adsorption isotherm was analyzed by the BET method using analysis software attached to BELSORPmini, and the BET specific surface area was calculated.

(1-3. Loose bulk density of magnesium oxide)
The loose bulk density of magnesium oxide was measured using a powder tester (PT-N manufactured by Hosokawa Micron Co., Ltd.). Specifically, a cup with an internal volume of 100 cm ³ was set in the device, and a sieve with an opening of 710 μm was set thereon. Then, 300 g of magnesium oxide was put on the sieve, and while vibrating the sieve, the magnesium oxide was dropped into the cup until the magnesium oxide overflowed the cup excessively. Next, a heaping portion of magnesium oxide filled in the cup was scraped off with a blade, and the mass of magnesium oxide was measured. Then, the loose bulk density was calculated by dividing the mass of magnesium oxide by the internal volume of the cup. The loose bulk density was measured three times and the arithmetic mean value was recorded.

(1-4. Secondary particle size of magnesium oxide)
The secondary particle size distribution of magnesium oxide was measured using a laser diffraction/scattering particle size distribution analyzer (MT3300EX II manufactured by Microtrac Bell). Water was used as the solvent, and the rotation speed of the centrifugal field was 3000 rpm. Then, the median diameter was measured using analysis software dedicated to the apparatus, and this median diameter was taken as the secondary particle diameter (average particle diameter) of magnesium oxide.

(1-6. Particle size of magnesium carbonate)
The particle size distribution of magnesium carbonate was measured using a laser diffraction/scattering particle size distribution analyzer (MT3300EX II manufactured by Microtrac Bell). Water was used as the solvent, and the rotation speed of the centrifugal field was 3000 rpm. Then, the median diameter was measured using analysis software dedicated to the apparatus, and this median diameter was taken as the particle diameter (average particle diameter) of magnesium carbonate.

<2. Preparation of magnesium oxide>
(2-1. Production of basic magnesium carbonate pentahydrate (Examples 1 to 10, Comparative Examples 1 to 7))
Urea (manufactured by Wako Pure Chemical Industries, Ltd., special grade), magnesium acetate tetrahydrate (manufactured by Kanto Chemical Co., Ltd., deer special grade) and water are mixed at a ratio (mass ratio) of 1: 5: 16, and the mixture is placed in a high-pressure container. I put it in Then, the high-pressure vessel was set in an electric furnace and heated at 180° C. for 5 hours.

After the internal temperature of the electric furnace has cooled to 40 ° C. or less, the high pressure vessel is taken out, the contents of the high pressure vessel are filtered, and the collected material is vacuum dried at 50 ° C. for 5 hours to obtain basic magnesium carbonate 5 water. I got Japanese food.

(2-2. Preparation of magnesium oxide (Examples 1 to 9, Comparative Examples 1 to 4))
(2-2-1. Step (A))
3 g of basic magnesium carbonate pentahydrate was weighed and put into a quartz sample tube. Next, the sample tube was set in an electric furnace, and the temperature inside the electric furnace was raised to the first heating temperature listed in Table 1 under an argon gas flow of 150 ml/min at the first heating rate listed in Table 1. heated up. The atmosphere in the electric furnace is shown in Table 1 as the first heating atmosphere. Then, the temperature in the electric furnace was maintained at the heating temperature for 30 minutes. Then, after the inside of the furnace cooled down to room temperature, the magnesium carbonate in the sample tube was recovered.

(2-2-2. Step (B))
Then, 0.5 g of the recovered magnesium carbonate was put into the sample tube. Then, the sample tube was set in an electric furnace. The atmosphere in the electric furnace was air. Then, the pressure inside the electric furnace was reduced from the atmospheric pressure to the second heating atmosphere shown in Table 1. Then, the temperature in the electric furnace was raised to the second heating temperature shown in Table 1 at a heating rate of 10°C/min. Then, the temperature in the electric furnace was maintained at the heating temperature for 30 minutes. Then, after the inside of the furnace cooled down to room temperature, the magnesium oxide in the sample tube was recovered.

(2-3. Preparation of magnesium oxide (Example 10, Comparative Example 5))
The oxidation according to Example 10 or Comparative Example 5 was performed in the same manner as in 2-2 above, except that the atmosphere (first heating atmosphere) in step (A) was a pure air (atmosphere) flow of 150 ml/min. Magnesium was produced.

(2-4. Preparation of magnesium oxide (Comparative Example 6))
Comparative Example 6 was obtained by performing the same step as 2-2 above except that the atmosphere (second heating atmosphere) of step (B) was an argon gas flow of 150 ml / min (that is, the pressure was not reduced). Magnesium oxide was produced.

(2-5. Preparation of magnesium oxide (Comparative Example 7))
Magnesium oxide according to Comparative Example 7 was produced by performing the same steps as in 2-2 above, except that the atmosphere (first heating atmosphere) in step (A) was a reduced pressure atmosphere of 10 kPa.

(2-6. Preparation of magnesium oxide (Comparative Examples 8 and 9))
The same process as in 2-2 above was performed except that the raw material of magnesium oxide was light basic magnesium carbonate (Comparative Example 8) or heavy basic magnesium carbonate (Comparative Example 9) (both manufactured by Wako Pure Chemical Industries, Ltd.). Magnesium oxide according to Comparative Example 8 or Comparative Example 9 was produced by carrying out.

(2-7. Commercially available magnesium oxide (Comparative Examples 10 and 11))
As commercially available magnesium oxide, Starmag R manufactured by Kojima Chemical Co., Ltd. (Comparative Example 10) and #500 manufactured by Tateho Chemical Industry Co., Ltd. (Comparative Example 11) were prepared. Table 1 summarizes the production conditions (synthesis conditions) of the above-described examples and comparative examples.

<3. Evaluation of physical properties of magnesium oxide>
The crystallite size, secondary particle size, BET specific surface area, and loose bulk density of magnesium oxide according to each example and comparative example were measured according to the above-described method for measuring each parameter. Table 2 summarizes the results.

<4. Reactivity Evaluation of Magnesium Oxide>
In order to evaluate the reactivity of magnesium oxide, the reaction time required for neutralization of the acidic solution was investigated. Specifically, polyaluminum chloride containing 10% by mass of Al ₂ O ₃ (manufactured by Taimei Chemical Industry Co., Ltd.) was added to water to prepare an Al(III) solution having an Al(III) concentration of 100 mg/L. Then, 0.060 g of magnesium oxide was added to the Al(III) solution while stirring 300 mL of the Al(III) solution adjusted to 22° C. with a stirrer. Then, the pH change over time of the Al(III) solution was measured using a glass electrode pH meter (D50 manufactured by HORIBA). The time from the addition of magnesium oxide to the Al(III) solution until the pH exceeded 8 was then recorded as the reaction time. The reactivity of magnesium oxide was then evaluated based on the reaction time. Specifically, the reactivity of magnesium oxide was evaluated based on the following criteria. Table 2 summarizes the evaluation results.

[pass rank]
S: Those whose reaction time is within 30 minutes.
A: Those whose reaction time is within 45 minutes.
B: Those whose reaction time is within 60 minutes.
[Fail Rank]
C: Not reaching pass rank B. That is, the reaction time exceeds 60 minutes.

As is clear from Tables 1 and 2, the particle size of magnesium carbonate is equivalent to the secondary particle size of magnesium oxide. Therefore, it can be seen that the secondary particle size of magnesium oxide can be adjusted by adjusting the particle size of magnesium carbonate. Furthermore, in Examples 1 to 10 in which the crystallite size and secondary particle size of magnesium oxide satisfy the requirements of the present embodiment, excellent reactivity evaluation results were obtained. Specifically, results of B rank or higher were obtained in all cases. Furthermore, the bulk densities of Examples 1 to 10 all met the requirements of this embodiment and maintained a high level. In particular, in Examples 1 to 6, the crystallite diameter was 4 to 10 nm and the BET specific surface area was 120 to 350 m ² /g, which were values within the preferable ranges, so the reactivity was ranked S. On the other hand, in Examples 7 and 8, the reactivity was A rank. In Examples 7 and 8, the crystallite size exceeded 10 nm and the BET specific surface area was out of the preferred range (less than 120 m ² /g), so it is considered that the reactivity was ranked A.

The reason why the BET specific surface area was less than 120 m ² /g in Example 7 is considered to be that the second heating temperature is higher than in Examples 1-6. As a result, it is considered that the crystallite size of magnesium oxide increased and the BET specific surface area became smaller than 120 m ² /g. The reason why the BET specific surface area was smaller than 120 m ² /g in Example 8 is considered to be that the degree of pressure reduction of the second heating atmosphere is lower than in Examples 1-6. As a result, it is considered that the crystallite size of magnesium oxide increased and the BET specific surface area became smaller than 120 m ² /g.

In Examples 9 and 10, the reactivity was ranked B. In Examples 9 and 10, the crystallite size exceeded 15 nm, and the BET specific surface area was even smaller. The reason why the BET specific surface area became small in Example 9 is considered to be that the second heating temperature is higher than that in Example 7. As a result, it is considered that the crystallite diameter increased and the BET specific surface area became smaller than 120 m ² /g. The reason why the BET specific surface area was less than 120 m ² /g in Example 10 is considered to be that the atmosphere in the step (A) was air. As a result, it is considered that the crystallite diameter increased and the BET specific surface area became smaller than 120 m ² /g.

On the other hand, in Comparative Examples 1 to 11, which do not satisfy the requirements of the present embodiment, the reactivity was ranked C. Specifically, in Comparative Example 1, since the first heating temperature exceeded 550° C., the crystallite diameter exceeded 20 nm. In Comparative Example 2, the crystallite diameter exceeds 20 nm because the degree of pressure reduction in the second heating atmosphere is low. In Comparative Example 3, the secondary particle size exceeds 800 nm because the first heating rate is too low. In Comparative Example 4, since the second heating temperature exceeds 1100° C., the crystallite size exceeds 20 nm. In Comparative Example 5, since the first heating atmosphere is atmospheric flow and the first heating temperature exceeds 500° C., the crystallite diameter exceeds 20 nm. In Comparative Example 6, the crystallite diameter exceeded 20 nm because the second heating atmosphere was not a reduced-pressure atmosphere. In Comparative Example 7, the secondary particle size exceeds 800 nm because the first heating atmosphere is neither air nor inert gas atmosphere. In Comparative Examples 8 and 9, since the starting material is not basic magnesium carbonate pentahydrate, the secondary particle size exceeds 800 nm. Comparative Examples 10 and 11 are commercially available magnesium oxide, and the secondary particle size exceeds 800 nm.

Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention belongs can conceive of various modifications or modifications within the scope of the technical idea described in the claims. It is understood that these also naturally belong to the technical scope of the present invention.

For example, in the above embodiment, the magnesium oxide 10 is composed only of the magnesium oxide particles 11 that satisfy the requirements of the present embodiment, but other types of magnesium oxide may be mixed. The amount of other types of magnesium oxide to be mixed may be adjusted according to the properties required of the magnesium oxide as a whole.

10 magnesium oxide 11 magnesium oxide particles 12 crystallites 20 basic magnesium carbonate pentahydrate 30 magnesium carbonate 31 magnesium carbonate particles

Claims (6)

Contains approximately spherical magnesium oxide particles that are aggregates of crystallites with a crystallite diameter of 2 to 20 nm,
Magnesium oxide, wherein the magnesium oxide particles have a particle size of 80 to 800 nm. 2. The magnesium oxide according to claim 1, wherein said crystallite has a crystallite diameter of 4 to 15 nm. 3. The magnesium oxide according to claim 1, wherein the magnesium oxide particles have a particle size of 200 to 700 nm. Magnesium oxide according to any one of claims 1 to 3, characterized in that the BET specific surface area calculated from the nitrogen adsorption isotherm is 120 to 350 m ² /g. A method for producing magnesium oxide, comprising the following steps (A) and (B).
(A) A step of heating basic magnesium carbonate pentahydrate to a first heating temperature at a temperature elevation rate of 10 to 100° C./min in the air or in an inert gas atmosphere to obtain magnesium carbonate.
The first heating temperature is 350 to 500 ° C. when the basic magnesium carbonate pentahydrate is heated in the atmosphere, and when the basic magnesium carbonate pentahydrate is heated in an inert gas atmosphere. , 350 to 550°C.
(B) A step of obtaining the magnesium oxide by heating the magnesium carbonate to 550 to 1100° C. under a reduced pressure atmosphere of 20 kPa or less. 6. The method for producing magnesium oxide according to claim 5, wherein in the step (A), the basic magnesium carbonate pentahydrate is heated under an inert gas atmosphere.

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