JP4588302B2 - Method for producing composite oxide particles and composite oxide particles - Google Patents

Description

The present invention relates to a method for producing composite oxide particles having a novel and unique particle shape, and composite oxide particles.
Specifically, the present invention relates to a method for producing composite oxide particles having a particle shape of a tubular shape and containing magnesium such as MgAl ₂ O ₄ , MgSiO ₃ , Mg ₂ TiO ₄ , or MgFe ₂ O _4, and composite oxide particles .

Technical background

As the composite oxide containing magnesium, MgAl ₂ O ₄ , MgSiO ₃ , Mg ₂ TiO ₄ , or MgFe ₂ O ₄ is used as an industrial material.
For example, MgAl ₂ O ₄ is used for refractories and sintering aids, Mg ₂ SiO ₄ is used for heat storage materials and insulating materials, and Mg ₂ TiO ₄ is used as dielectric materials for high-frequency capacitors and multilayer chip capacitors. .
In addition, (Mg, Mn) Fe ₂ O ₄ is a soft magnetic material for coils and magnetic cores, BaMg ₂ Fe ₁₆ O ₂₇ is a hard magnetic material for permanent magnets, and (Zr, Mg) O ₂ is ionic conductive. such as an oxygen sensor as sexual material, BaMgAl ₁₀ O _17: Eu ²⁺ is such as fluorescent materials, Pb-Zr-Nb-Mg-based composite oxide are used in such oscillators and resonators as a piezoelectric material.

Many studies have been made on complex oxides containing magnesium, and some of them focus on the particle shape and powder physical properties of the complex oxides.
In particular, the particle shape is a fibrous material obtained by fiberizing and heating a viscous material in which an aluminum salt and a magnesium compound prepared under the specific conditions of Patent Document 1 below are mixed. A magnesium aluminate fiber excellent in corrosion resistance and heat resistance characterized by the above, or an alloy powder having a specific composition of Patent Document 2 is ejected from a nozzle and obtained by firing in an oxygen atmosphere. Examples thereof include spherical composite metal oxide particles such as spinel and forsterite, wherein particles having a diameter of 85% by weight or more and the ratio of the short axis to the long axis of the particles are 1.0 to 1.3. .

There is another proposal, and in Patent Document 3, the thickness of the shell is obtained by spray burning a W / O type emulsion in which a metal salt is dissolved or suspended, and has a shell that defines a hollow chamber. Has been proposed hollow oxide powder particles such as spinel, characterized by having a diameter of 20 nm or less.
Further, in Patent Document 4, cordierite (Mg ₂ Al ₄ Si ₅ O ₁₈ ), which can be suitably used as an integrated circuit sealing material or a circuit board insulating material and has a spherical particle shape. A powder made of magnesium-containing oxide particles such as forsterite (Mg ₂ SiO ₄ ) has been proposed.

As a thing paying attention to powder physical properties, it has both a high specific surface area and an attrition resistance characterized by baking a mixture of an aluminum acid salt of Patent Document 5 and a basic alkaline earth metal-containing composition. A method for producing an aluminum-containing spinel composition such as MgAl ₂ O _4, and an average particle diameter of 3 to 20 μm and a specific surface area of 80 m ² / synthesized using the hydroxide raw material of Patent Document 6 and firing. MgAl ₂ O ₄ spinel powder characterized by being g or more.
In addition, in Patent Document 7, the BET specific surface area represented by the chemical formula Mg _1-X M ²⁺ _X O (M ²⁺ : Mn ²⁺ , Fe ²⁺ , Co ^2+, etc.) is 4 m ² / g or less. A magnesium oxide solid solution blended in a resin or rubber as a thermally conductive oxide has been proposed.

[Prior art documents]
JP-A-62-41318 JP-A-63-185803 JP 2000-203810 A JP 2003-2640 A Japanese Patent Publication No. 5-66889 JP 2001-48529 A Japanese Patent No. 2937602

As described above, various studies have been made on composite oxides containing magnesium, but the composite oxide has a new shape that can cope with higher performance, higher functionality, new function addition, and the like. There is a need for composite oxides containing magnesium.
In particular, in the case of inorganic particles such as metal oxides, the particle characteristics may change greatly by controlling the particle shape and particle diameter, etc., and by using a new shape, high performance, high functionality, and addition of new functions Can be expected.

The inventors of the present invention have been studying basic magnesium carbonate that can be used as one of raw materials for composite oxides containing magnesium, and have a novel and unique shape of tubular aggregated particles made of flaky fine crystals. Have been applied for patents (Japanese Patent Application Nos. 2002-179462 and 2002-220768).
Further, as a result of examining the modification of the tubular aggregated particles of basic magnesium carbonate, the present inventors have found that the tubular aggregated particles of basic magnesium carbonate coated with a metal oxide (Japanese Patent Application No. 2002-376709) and In addition, a fine particle-encapsulating composite tubular basic magnesium carbonate in which other fine particles are fixed inside a tubular aggregated particle of basic magnesium carbonate has been developed, and a patent application has already been filed for these (Japanese Patent Application No. 2003-136851).

Furthermore, as a result of intensive investigations on the production of oxide particles using the above-described basic aggregated tubular magnesium particles and modified products thereof, the present inventors have succeeded in development.
Therefore, the present invention should solve the problem of providing a method for producing composite oxide particles containing magnesium that exhibit a novel shape and that exhibit various excellent characteristics derived from this shape, and composite oxide particles. It is to be an issue.
That is, an object of the present invention is to provide a method for producing a composite oxide particle containing magnesium that exhibits a novel shape and exhibits various excellent characteristics derived from this shape, and a composite oxide particle. Is.

In order to solve the above-mentioned problems, the present invention provides a method for producing composite oxide particles containing magnesium having a novel and unique shape such as a tubular shape, and composite oxide particles.
The method for producing composite oxide particles having a tubular particle shape according to the present invention comprises, as a precursor, particles composed of tubular agglomerated particles composed of flaky fine crystals of basic magnesium carbonate and other components, and the precursor is used as a precursor. It is characterized by firing.
The tubular composite oxide particles of the present invention are oxides containing magnesium and other elements, and the particle shape thereof is tubular, and preferably has an outer diameter of 1 to 20 μm, an inner diameter of 0.5 to 5 μm, and a long length. 5 to 200 μm, and the length / outer diameter ratio is 2 to 50.

  The tubular composite oxide particles of the present invention can be produced by utilizing the basic magnesium carbonate of tubular aggregated particles composed of flaky fine crystals recently developed by the present inventors. Add one or more substances necessary for depositing a metal compound into the suspension, and coat the surface of the tubular aggregated particles of basic magnesium carbonate with a metal oxide, or in a suspension of the metal compound The basic magnesium carbonate is soaked or added in the process of synthesizing the basic magnesium carbonate so that the metal compound fine particles are encapsulated in the tubular aggregated particles of the basic magnesium carbonate, and then they are fired. Therefore, the manufacturing method is relatively simple.

The manufactured composite oxide particles are tubular and have a new and unique shape, preferably an outer diameter of 1 to 20 μm, an inner diameter of 0.5 to 5 μm, a length of 5 to 200 μm, and a length / outer The ratio of diameters is 2 to 50, and various excellent characteristics are manifested from this shape.
Specifically, since it is a porous particle derived from a tubular shape, it exhibits high adsorption and absorption characteristics, and the bulk density as a powder is low, so the weight of the product to be blended and sound insulation It is also effective in improving heat insulation performance.
Moreover, when utilizing as an oxide catalyst etc., the improvement of catalyst efficiency is anticipated by a high specific surface area. Furthermore, since the composite oxide particle is a composite in which magnesium and other elements are oxidized, it can be expected to exhibit characteristics derived from the presence of both elements different from the oxide of a single element.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the best mode for carrying out the present invention will be described in detail. However, the present invention is not limited thereby, but is specified by the description of the scope of claims. Not too long.
In the production method of the present invention, magnesium and other elements are obtained by firing a precursor composed of a tubular aggregated particle composed of flaky fine crystals of basic magnesium carbonate and other components, and firing the precursor. It is characterized by producing complex oxide particles having a tubular shape.

Although the precursor used in the present invention is as described above, specifically, the following two forms (1) and (2) can be preferably used.
(1) The surface of tubular aggregated particles made of flaky fine crystals of basic magnesium carbonate is covered with a metal oxide.
(2) A fine particle of a metal compound is encapsulated inside a tubular aggregated particle made of flaky fine crystals of basic magnesium carbonate.

The precursor (1) can be obtained by preparing a tubular aggregated particle made of flaky fine crystals of basic magnesium carbonate and then subjecting it to a specific modification treatment.
The precursor of the above (2) is subjected to a specific modification treatment on the basic magnesium carbonate tubular agglomerated particles as in (1), or in the process of preparing the basic magnesium carbonate tubular agglomerated particles. Can be obtained.

Therefore, first, a method for preparing tubular aggregated particles made of flaky fine crystals of basic magnesium carbonate as a raw material for the composite oxide particles of the present invention will be described.
As a method for obtaining the tubular aggregated particles, the method of Japanese Patent Application No. 2002-179462 or Japanese Patent Application No. 2002-220768 filed by the present inventors is suitable.

  The manufacturing method of the former Japanese Patent Application No. 2002-179462 is a method in which a water-soluble magnesium salt and a water-soluble carbonate are mixed in an aqueous solution, the diameter is 0.5 to 10 μm, and the length is 25 to 55 ° C. A first step of producing 5-500 μm normal magnesium carbonate columnar particles, and a temperature of the suspension of normal magnesium carbonate columnar particles that is higher than the temperature at which normal magnesium carbonate was generated in the first step; Basic magnesium carbonate of tubular aggregated particles made of flaky fine crystals can be produced by the second step of heat treatment at a temperature of 35 to 80 ° C. and a pH of 9.5 to 11.5.

As the water-soluble magnesium salt used in the first step, various water-soluble magnesium salts can be used without particular limitation, and examples thereof include magnesium chloride, magnesium sulfate, magnesium nitrate, and magnesium acetate.
Water-soluble carbonates can also be used without particular limitation, and examples thereof include sodium carbonate, potassium carbonate, ammonium carbonate, etc., but strong alkali carbonates, specifically, sodium carbonate, potassium carbonate should be used. However, the tubular aggregated particles of basic magnesium carbonate can be prepared more efficiently, which is preferable.

In the first step, the water-soluble magnesium salt and the water-soluble carbonate as described above are reacted in an aqueous solution to precipitate the columnar particles of normal magnesium carbonate. Conditions in which water-soluble magnesium salt and water-soluble carbonate are mixed in the solution and magnesium ions and carbonate ions react, such as a method of adding a magnesium chloride aqueous solution to a solution and a method of adding ammonium carbonate to a magnesium sulfate aqueous solution If it is.
In the reaction at that time, it is preferable to stir the reaction solution in order to ensure the uniformity of the reaction.

About the shape of the normal magnesium carbonate produced | generated in a 1st step, it is desirable that it is columnar, the diameter is 0.5-10 micrometers, and length is 5-500 micrometers.
The reason is that it is assumed that a unique shape called a tube is formed when basic magnesium carbonate is generated from the surface of columnar particles of normal magnesium carbonate.
That is, it can be said that the shape of normal magnesium carbonate, which is an intermediate product, greatly affects the shape of basic magnesium carbonate, which is a final product.
Therefore, it is important to adjust the synthesis conditions of the normal magnesium carbonate in accordance with the shape of the basic basic magnesium carbonate, particularly the diameter and length, to obtain a proper shape of the normal magnesium carbonate.

Furthermore, in the case of normal magnesium carbonate having a shape other than the above, when the basic magnesium carbonate is generated in the second step, the time required for the generation becomes extremely long and the production efficiency is lowered, or the target tubular carbonate is formed. Particles may not be obtained.
As such, in order to produce columnar particles of normal magnesium carbonate that can obtain the tubular aggregated particles of basic magnesium carbonate efficiently in the second step in the target shape, The temperature at which the reactive magnesium salt reacts with the water-soluble carbonate is desirably 25 to 55 ° C, more desirably 28 to 50 ° C.

If the temperature at that time is less than 25 ° C., the production rate of magnesium carbonate as an intermediate product becomes extremely slow, and the production efficiency is lowered, which is not realistic. On the other hand, if the temperature exceeds 55 ° C., the desired shape of normal magnesium carbonate cannot be obtained, or the tubular aggregated particles of basic magnesium carbonate cannot be obtained in the subsequent second step.
The normal magnesium carbonate produced in the first step is a magnesium carbonate hydrate represented by the chemical formula MgCO ₃ .nH ₂ O, and is generally n = 3, but other than n = 3 Even if it is a thing, if it is a shape as mentioned above, it will not be restrict | limited.

If the shape of the normal magnesium carbonate produced in the first step is adjusted to control the shape of the basic magnesium carbonate tubular aggregated particles produced in the second step, the reaction conditions in the first step are appropriately controlled. By doing so, the shape of the normal magnesium carbonate can also be adjusted within the above-mentioned range.
For example, regarding the diameter of the columnar particles of normal magnesium carbonate, the columnar particles having a smaller diameter can be obtained by relatively increasing the temperature at which the normal magnesium carbonate is generated.
About pH, the one where the pH when the production | generation of normal magnesium carbonate is started in a 1st step is higher can produce | generate the columnar particle | grains of a normal magnesium carbonate with a smaller diameter.

  Thus, the suspension of columnar particles of normal magnesium carbonate having a diameter of 0.5 to 10 μm and a length of 5 to 500 μm obtained in the first step may be directly used for the second step. However, if you want to recover the anionic component of soluble magnesium salt or the cationic component of soluble carbonate dissolved as an impurity in the suspension, or if these impurities are contained in the basic magnesium carbonate that is the final product. If it is not desirable to remain, the liquid may be replaced with water or the like to remove impurities.

Subsequently, in the second step, the suspension of columnar particles of magnesium carbonate obtained in the first step is preferably 40 to 70 ° C., more preferably 45 to 65 ° C., and higher than the first step. To produce basic magnesium carbonate.
It is important that the heat treatment temperature in the second step is higher than the temperature at which normal magnesium carbonate is generated in the first step, and the temperature difference between the first step and the second step is preferably 2 to 2. It is good to set it as 35 degreeC, More desirably, it is 2-25 degreeC, More desirably, it is 2-20 degreeC.

Regarding this temperature difference, there is a more appropriate range depending on the temperature at which columnar particles of normal magnesium carbonate are generated in the first step and the pH when heat treating the normal magnesium carbonate in the second step.
For example, when the pH of the second step is 10.5, the temperature difference is 20-35 ° C. when the first step is 25-35 ° C., and the temperature difference is 35-45 ° C. when the first step is 35-45 ° C. When the temperature in the first step is 5 to 25 ° C. and the temperature in the first step is 45 to 55 ° C., the temperature difference is preferably 2 to 15 ° C.

If the temperature is lower than the first step or less than 40 ° C., the desired tubular aggregated particles of basic magnesium carbonate cannot be obtained, or the reaction time becomes extremely long and the production efficiency decreases, which is not realistic. .
When the temperature exceeds 70 ° C., the uniformity of the basic magnesium carbonate particles to be produced deteriorates, and the mixing of irregular to spherical aggregated particles becomes remarkable.
In the second step, as in the case of the first step, it is preferable to stir the reaction liquid in order to ensure the uniformity of the reaction.

Further, the pH of the normal magnesium carbonate suspension during the heat treatment is desirably 9.5 to 11.5, and more desirably 10.0 to 11.5.
That is, when the pH is less than 9.5, the rate of production of basic magnesium carbonate from normal magnesium carbonate is slowed, and not only the production efficiency is lowered, but also normal magnesium carbonate may remain in the final product. It is also from.
On the other hand, if the pH exceeds 11.5, the uniformity of the particles of the final product is impaired, and amorphous or spherical particles are likely to be mixed.

In order to adjust the pH to this range, the amount ratio of the water-soluble magnesium salt and the water-soluble carbonate in the first step may be adjusted, or an acidic substance or an alkaline substance may be added and adjusted in the second step. .
In the former case, the amount can be adjusted to the acidic side by increasing the amount of the water-soluble magnesium salt, and conversely to the alkaline side by increasing the amount of the water-soluble carbonate. In the latter case, hydrochloric acid, sulfuric acid, nitric acid or the like can be used as the acidic substance to be added, and sodium hydroxide, potassium hydroxide, aqueous ammonia or the like can be used as the alkaline substance.

In the second step, it is preferable to continue heating and stirring until the production of basic magnesium carbonate is completed. The termination of the production of basic magnesium carbonate can be determined by measuring the pH and conductivity of the suspension.
For example, regarding the pH, when the production of basic magnesium carbonate continues, the pH of the suspension gradually decreases, whereas when the production is completed, the pH remains almost constant. .

  The latter manufacturing method of Japanese Patent Application No. 2002-220768 includes a first step of preparing a magnesium hydrogen carbonate solution by introducing a carbon dioxide-containing gas into the magnesium hydroxide suspension, and the pH of the magnesium hydrogen carbonate solution is adjusted to pH 7. A second step of producing columnar particles of normal magnesium carbonate by adjusting to 5 to 11.0, and a suspension of the columnar particles of normal magnesium carbonate at a pH of 9.0 to 12.0 and a temperature of 30 to 75 ° C. A third step of producing basic magnesium carbonate by adjusting the temperature range after adjustment.

The first step is a step of preparing a magnesium hydrogen carbonate solution by introducing a carbon dioxide-containing gas into a magnesium hydroxide suspension, and the raw material magnesium hydroxide used here is particularly limited. In addition, magnesium hydroxide produced by the so-called seawater method, in which calcium hydroxide is precipitated by adding calcium hydroxide to seawater, can be used.
Further, there is no particular limitation on the carbon dioxide-containing gas, and carbon dioxide supplied from a cylinder or the like, diluted with air or the like, and those containing carbon dioxide such as combustion exhaust gas can be used.

In the first step, 90% or more of the magnesium hydroxide used as a raw material, preferably the total amount is preferably changed to magnesium hydrogen carbonate.
The reason for this is that when the amount of magnesium hydroxide not changed to magnesium hydrogen carbonate is large, the subsequent reaction in the second and third steps hinders the uniform reaction, and the final product of the basic magnesium carbonate tubular This is because the uniformity of the particle shape of the aggregated particles may deteriorate.

The change from magnesium hydroxide to magnesium hydrogen carbonate can be confirmed by measuring the pH and conductivity of the liquid.
For example, regarding the pH of the liquid, the magnesium hydroxide suspension before introducing the carbon dioxide-containing gas is about 9 to 11, whereas the total amount of magnesium hydroxide is changed to magnesium hydrogen carbonate. For example, the pH of the liquid becomes almost neutral.
In the first step, it is desirable to introduce the carbon dioxide-containing gas until the pH of the liquid is 8 or less, and it is more desirable to introduce until the pH is 7.5 or less.

There is no particular restriction on the liquid temperature when introducing the carbon dioxide-containing gas into the magnesium hydroxide suspension, but if the liquid temperature is too high, the solubility of magnesium hydrogen carbonate will decrease, and as a result, it will be prepared. Not only the amount of unreacted magnesium hydroxide remaining in the magnesium hydrogen carbonate solution increases, but also a phenomenon that magnesium hydrogen carbonate decomposes before the completion of the first step reaction is observed.
Therefore, when introducing the carbon dioxide-containing gas into the magnesium hydroxide suspension, it is desirable to maintain the liquid temperature at 35 ° C. or lower, and more desirably at 30 ° C. or lower.

  It is more preferable to remove the undissolved residue such as unreacted magnesium hydroxide and other impurities after introducing the carbon dioxide-containing gas into the magnesium hydroxide suspension. A basic magnesium carbonate solution with high purity and high uniformity of particles can be obtained in the subsequent third step.

In the subsequent second step, the magnesium hydrogen carbonate solution prepared in the first step is adjusted to pH 7.5 to 11.0 to produce columnar particles of normal magnesium carbonate. Also in this second step, it is preferable to stir the reaction solution in order to ensure the uniformity of the reaction as in the case of the first step.
In this second step, it is necessary to adjust the pH shifted to the neutral range in the first step to the alkali side. For this purpose, an appropriate amount of an alkaline substance is added to the magnesium hydrogen carbonate solution prepared in the first step. The pH is adjusted by adding.
Moreover, after adjustment, the pH needs to be in the range of 7.5 to 11.0.

In the second step, the pH needs to be adjusted as described above because if the pH is less than 7.5, tubular aggregated particles of basic magnesium carbonate cannot be obtained in the third step. is there.
On the contrary, when the pH exceeds 11.0, the normal magnesium carbonate becomes unstable, and basic magnesium carbonate is generated before the formation of normal magnesium carbonate is completed. Magnesium carbonate is generated, and not only the uniformity of the basic magnesium carbonate particles in the final product is remarkably deteriorated, but also the amount of alkaline substance used for pH adjustment is increased, which is economically good. Absent.

In order to produce the columnar particles of normal magnesium carbonate in the second step, the magnesium hydrogen carbonate solution prepared in the first step is adjusted to pH 7.5 to 11.0, and then the reaction is continued until the production of normal magnesium carbonate is completed. It is preferable to continue.
The completion of the production of normal magnesium carbonate can be confirmed by measuring the pH or conductivity of the liquid and observing that the value has stabilized.

Furthermore, about the temperature in that case, it is desirable to set it as 20-55 degreeC, and it is more desirable to set it as 30-55 degreeC.
When the temperature is lower than 20 ° C., in the third step later, in addition to the tubular aggregated particles of basic magnesium carbonate, amorphous aggregated particles are likely to be mixed.
Conversely, even in the case of a temperature exceeding 55 ° C., the uniformity of particles tends to deteriorate in the third step.

In the second step, the pH is adjusted as described above, preferably the temperature is adjusted as described above, and the reaction is continued until the formation of normal magnesium carbonate is completed, thereby generating columnar particles of normal magnesium carbonate. However, the columnar particles preferably have a diameter of 0.5 to 10 μm and a length of 5 to 500 μm.
In particular, when the diameter of the columnar particles is less than 0.5 μm or exceeds 10 μm, the tubular aggregated particles of basic magnesium carbonate targeted by the present invention may not be obtained in the subsequent third step.

In addition, the shape, particularly the diameter and length of the tubular aggregated particles of basic magnesium carbonate produced in the third step are affected by the diameter and length of the normal magnesium carbonate columnar particles produced in the second step. It is desirable to adjust the diameter and length of the normal magnesium carbonate produced in the second step according to the shape of the tubular aggregated particles of basic magnesium carbonate which is the production purpose.
In order to adjust the diameter and length of the columnar particles of normal magnesium carbonate, the pH and temperature for generating normal magnesium carbonate may be appropriately controlled in the second step.
For example, regarding the pH in the second step, within the above-mentioned range, columnar particles of normal magnesium carbonate having a small diameter can be obtained by setting the pH higher, and conversely by setting the pH to a lower value, Magnesium carbonate columnar particles can be obtained.

Further, regarding the temperature in the second step, columnar particles of normal magnesium carbonate having a small diameter can be obtained by setting the temperature to a higher temperature within the above-described range. Magnesium carbonate columnar particles can be obtained.
In addition, about the produced | generated columnar particle | grains of the normal magnesium carbonate, you may once filter and wash, the alkaline substance added at the 2nd step can be removed by doing so, and it contains in a product. This is preferable in that impurities can be further reduced.
In this manner, in the second step, columnar particles of normal magnesium carbonate are generated from the magnesium hydrogen carbonate solution.

In the third step, which is the last step following the second step, the suspension of columnar particles of magnesium carbonate obtained in the second step is subjected to pH 9.0 to 12.0 at a temperature of 30 to 75 ° C. To produce basic magnesium carbonate.
Also in the third step, as in the case of the first step and the second step, it is preferable to stir the reaction liquid in order to ensure the uniformity of the reaction.

About the temperature at the time of producing | generating basic magnesium carbonate in the 3rd step, it is necessary and important that it is 30-75 degreeC.
If the temperature is less than 30 ° C., the desired tubular basic magnesium carbonate cannot be obtained, or the reaction time becomes extremely long, resulting in a decrease in production efficiency, which is not realistic.
On the other hand, when the temperature exceeds 75 ° C., the uniformity of the basic magnesium carbonate particles to be produced deteriorates, and the mixing of irregular to spherical aggregated particles becomes remarkable.

About pH in this step, it is necessary to set it as 9.0-12.0. The reason is that if the pH is less than 9.0, not only the production rate of basic magnesium carbonate from the normal magnesium carbonate is slowed, but the production efficiency is lowered, and the normal magnesium carbonate remains in the final product. Because there is.
On the other hand, if the pH exceeds 12.0, the uniformity of the final product particles is impaired, and irregular or spherical particles are likely to be mixed.

Further, the pH in the third step is desirably higher than the pH at which the columnar particles of normal magnesium carbonate are generated in the second step, and more desirably 0.3 or more.
By doing so, it becomes possible to more efficiently produce the basic aggregated tubular particles of magnesium carbonate having high uniformity and various powder properties.
In order to adjust the pH within this range, an acidic substance or an alkaline substance may be added and adjusted in the third step.

In addition, it is desirable to adjust the temperature and pH in the third step according to the shape of the normal magnesium carbonate produced in the second step, particularly the diameter and length. Magnesium carbonate tubular aggregated particles can be obtained.
Specifically, when the diameter of the normal magnesium carbonate is small, the pH and temperature in the third step are preferably lower, and conversely, when the diameter of the normal magnesium carbonate is large, the pH and temperature in the third step are higher. Is preferred.

In the third step, it is preferable to continue stirring while maintaining the temperature in the above-described range until the production of basic magnesium carbonate is completed.
In that case, it is not necessary to maintain the temperature immediately after adjusting to the temperature of 30 to 75 ° C., and the temperature may vary within the temperature range, but it is preferable that the variation is as small as possible.
In addition, about completion | finish of the production | generation of the basic magnesium carbonate, it can confirm by measuring pH, electrical conductivity, etc. of suspension.
For example, with respect to pH, when the production of basic magnesium carbonate continues, the pH of the suspension decreases, whereas when the production is completed, the pH changes to be substantially constant.

By subjecting the tubular aggregated particles of basic magnesium carbonate thus prepared to a specific modification treatment, the precursor (1) or (2) used in the present invention can be obtained. it can.
The precursor in a form in which the surface of the tubular aggregated particles composed of the flaky fine crystals of basic magnesium carbonate shown in (1) is coated with a metal oxide is the Japanese Patent Application No. 2002-376709 for which the present inventors have already applied for a patent. It is preferable to prepare by this method.

In this method, one or more substances necessary for precipitating a metal oxide are added to a suspension of tubular aggregated particles of basic magnesium carbonate composed of flaky fine crystals. The outer surface and / or inner surface of the tubular aggregated particle is coated with a metal oxide.
The metal oxide referred to here includes not only pure oxides but also hydrated oxides such as hydrates and hydroxides.
In the surface treatment, the concentration of the prepared basic magnesium carbonate suspension may be adjusted as it is or appropriately, and the once-dried basic magnesium carbonate aggregated particles are dispersed in a solvent such as water. Suspensions may be used.

When the surface treatment is carried out in an aqueous system, either of the above methods may be used. However, when the surface treatment is carried out in an aqueous system other than an aqueous system, for example, the latter once dried is suspended in a solvent again. It is necessary to use a suspension.
The suspension concentration of the basic magnesium carbonate tubular aggregated particles may be appropriately adjusted in consideration of the amount of the surface-treated basic magnesium carbonate to be produced. If the concentration is too low, the surface obtained by one treatment Since the amount of the treated basic magnesium carbonate is small and the production efficiency is deteriorated, and when the concentration is too high, uniform surface treatment tends to be impossible. Therefore, the suspension concentration of the basic magnesium carbonate is desirably 5 to 50 g / It is preferable to set L.

By adding one or more substances necessary for precipitating the metal oxide to the suspension of the basic magnesium carbonate tubular aggregated particles, the surface of the basic magnesium carbonate tubular aggregated particles is added. Metal oxide is deposited.
As for the substance to be added to one or more kinds necessary for precipitating the metal oxide, it is appropriately selected according to the kind of metal oxide coated on the surface of the tubular aggregated particle of basic magnesium carbonate and the reaction for precipitating it. Just choose.

In particular, a method of depositing a metal oxide by a hydrolysis reaction is preferable. In this case, a substance that is hydrolyzed to precipitate a metal oxide by adding to a suspension of tubular aggregated particles of basic magnesium carbonate, Specifically, alkali salts such as sodium silicate and sodium aluminate, and organometallic compounds such as metal alkoxides can be used.
In the case of sodium silicate, silica is precipitated, in the case of sodium aluminate, alumina, and in the case of metal alkoxide, the metal oxide is precipitated.

In the case of a substance that does not hydrolyze just by adding it to a basic magnesium carbonate suspension, an alkaline substance or an acidic substance is added to the basic magnesium carbonate suspension to adjust to a pH range where hydrolysis reaction occurs. Or by adding a substance that promotes hydrolysis, the hydrolysis reaction can be caused to precipitate the metal oxide.
The important point in this precipitation reaction is that the metal oxide is deposited on the surface of the basic magnesium carbonate.
If the precipitation reaction takes place at a place other than the surface of the basic magnesium carbonate, the surface of the basic magnesium carbonate cannot be efficiently coated, and the product is composed of the basic aggregated tubular particles of magnesium carbonate and the metal oxide particles. It becomes just a mixture.

Accordingly, it is necessary to appropriately adjust the reaction conditions so that the metal oxide precipitates on the surface of the basic magnesium carbonate.
The reaction conditions vary depending on the type of metal oxide to be deposited and the type of reaction to deposit it, and cannot be uniquely defined. However, as a tendency, conditions that slow the precipitation reaction are preferable.
With regard to the precipitation of metal oxides by hydrolysis, if the addition rate of added alkali aluminate or alkali silicate is slowed, the precipitation reaction slows down, and if the temperature during the reaction is lowered, the precipitation reaction slows down. It is common.

What is necessary is just to adjust suitably according to the composition of the composite oxide particle which is the manufacturing objective of this invention as a metal oxide which precipitates by adding 1 type, or 2 or more types of substances, for example, silica, alumina, titania, for example. Manganese oxide, iron oxide, cobalt oxide, zinc oxide, zirconia, yttria, niobium oxide, rare earth oxide, and the like.
At this time, if the surface treatment is performed with silica, a magnesium-silicon composite oxide is obtained, a magnesium-aluminum composite oxide is obtained with alumina, and a magnesium-iron composite oxide is obtained with iron oxide.

  The reaction conditions are specifically described for the case where alumina is coated. An alkali aluminate such as sodium aluminate or potassium aluminate is added to an aqueous suspension of basic magnesium carbonate, and the alumina is reacted by hydrolysis reaction of the alkali aluminate. The method of precipitating on the surface of the basic magnesium carbonate tubular aggregated particles is the most convenient and desirable method because it allows the surface treatment of the basic magnesium carbonate to be effectively performed.

In this case, it is desirable that the suspension of the basic aggregated tubular magnesium carbonate particles has a concentration of 5 to 50 g / L.
When the amount is 5 g / L or less, the amount of the surface-treated basic magnesium carbonate obtained by one treatment is reduced and the production efficiency is deteriorated.
On the other hand, when the concentration exceeds 50 g / L, the viscosity of the suspension tends to be high and the alumina coating tends not to be uniform.

The suspension pH before addition of the alkali aluminate is preferably 7.0 to 9.5.
When the pH is less than 7.0, the precipitation rate of alumina from the alkali aluminate becomes too fast, and alumina particles are likely to be formed at places other than the surface of the tubular aggregated particles of basic magnesium carbonate.
Conversely, when the pH exceeds 9.5, there is a tendency that a uniform surface coating is not achieved.
Since the pH of the suspension of the basic magnesium carbonate tubular aggregated particles is usually about 10.5 to 12, it is desirable to adjust the pH to 7.0 to 9.5 by adding an appropriate amount of acid.

  In addition, if the suspension of basic magnesium carbonate immediately after preparation is used directly, the carbonic acid generated by the formation reaction of basic magnesium carbonate is dissolved in the suspension. Therefore, the pH is low due to the influence of carbonic acid. In general, the pH is in the range of 7.0 to 9.5. Therefore, it is desirable to use a suspension of basic magnesium carbonate immediately after preparation as it is because addition of an acid is unnecessary.

The alkali aluminate added to the aqueous suspension of basic aggregated tubular magnesium carbonate particles is desirably in the form of an aqueous solution with a concentration of 0.5 to 10 g / L.
If the concentration is lower than this range, the time required for precipitating a predetermined amount of alumina becomes longer and the production efficiency becomes worse.
Conversely, if the concentration exceeds 10 g / L, uniform surface coating tends to be impossible.

What is necessary is just to adjust suitably about the addition amount of an alkali aluminate according to the composition of the composite oxide particle which is the manufacturing objective of this invention.
For example, when it is desired to produce MgAl ₂ O ₄ as a composite oxide of magnesium and aluminum, the ratio of Mg to Al is 1: 2, and when Mg ₄ Al ₂ O ₇ is desired to be produced, Mg and Al The amount of alkali aluminate added is adjusted so that the Al ratio is 2: 1.
The rate at which the alkali aluminate solution is added to the suspension of basic magnesium carbonate may be adjusted as appropriate according to the amount of alkali aluminate added and the concentration of the solution, and preferably in the surface-treated basic magnesium carbonate. The addition rate of the alkali aluminate solution is preferably 0.2 to 10 g / min in terms of Al ₂ O ₃ with respect to 100 g of MgO.

The temperature of the suspension may be appropriately adjusted according to the amount of alkali aluminate added, the solution concentration, and the addition speed, and is preferably 25 to 70 ° C.
By setting it as this range, the surface coating state of alumina can be densified, and as a result, composite oxide particles can be obtained effectively.
In addition, after the addition of the alkali aluminate is completed, it is preferable to continue stirring until the precipitation of alumina from the alkali aluminate is completed.
When the precipitation of alumina continues, the pH of the suspension gradually rises, but when the precipitation is finished, the pH remains almost constant, so the completion of the precipitation is judged by observing the pH of the suspension. it can.

Next, a method for coating silica will be described.
In this method, an alkali silicate such as sodium silicate or potassium silicate is added to an aqueous suspension of basic magnesium carbonate, and silica is converted into the surface of the tubular aggregated particles of basic magnesium carbonate by hydrolysis reaction of the alkali silicate. Is the most convenient and desirable method because it allows the surface treatment of basic magnesium carbonate to be performed most simply and effectively.

In this case, the suspension of the basic magnesium carbonate tubular aggregated particles is desirably set to a concentration of 5 to 50 g / L.
When the amount is 5 g / L or less, the amount of the surface-treated basic magnesium carbonate obtained by one treatment is reduced and the production efficiency is deteriorated.
On the other hand, if the concentration exceeds 50 g / L, the viscosity of the suspension tends to be high and silica coating tends to be impossible.

The suspension pH before addition of the alkali silicate is desirably 7.5 to 10.5.
When the pH is less than 7.5, the deposition rate of silica from the alkali silicate becomes too fast, and silica particles are likely to be formed on the surface other than the surface of the tubular aggregated particles of basic magnesium carbonate.
Conversely, when the pH exceeds 10.5, there is a tendency that a uniform surface coating is not achieved.
Since the pH of the suspension of the basic magnesium carbonate tubular aggregated particles is usually about 10.5 to 12, the pH is adjusted to 7.5 to 10.5 by adding an appropriate amount of acid. Is desirable.

In addition, if a suspension of basic magnesium carbonate immediately after preparation is used directly, the carbonic acid generated by the formation reaction of basic magnesium carbonate is dissolved in the suspension as described above. Is usually in the range of pH 7.5 to 10.5 described above.
Therefore, it is desirable to use the basic magnesium carbonate suspension immediately after preparation as it is because the addition of an acid is unnecessary.

The alkali silicate added to the aqueous suspension of the basic magnesium carbonate tubular aggregated particles is desirably in the form of an aqueous solution and the concentration is 0.5 to 10 g / L.
If the concentration is lower than this range, the time required for precipitating a predetermined amount of silica becomes longer and the production efficiency becomes worse. Conversely, if the concentration exceeds 10 g / L, uniform surface coating tends to be impossible.

Further, the amount of addition may be appropriately adjusted according to the composition of the composite oxide particles which is the production object of the present invention.
For example, when it is desired to produce MgSiO ₃ as a composite oxide, Mg: Si is 1: 1, and when Mg ₂ SiO ₄ is desired, Mg: Si is 2: 1. What is necessary is just to adjust the addition amount of an acid alkali.

The addition rate of the alkali silicate aqueous solution may be appropriately adjusted according to the addition amount of the alkali silicate and the concentration of the solution. Desirably, the alkali silicate is used with respect to 100 g of MgO in the surface-treated basic magnesium carbonate. The addition rate of the solution is preferably 0.05 to 10 g / min in terms of SiO ₂ .
By setting it as this range, the surface coating state of silica can be densified, and as a result, composite oxide particles can be obtained more effectively.

The temperature of the aqueous suspension of the basic magnesium carbonate tubular aggregated particles may be appropriately adjusted according to the amount of alkali silicate added, the solution concentration, and the addition rate, and preferably 5 to 40 ° C. .
By setting it within this range, the surface coating state of silica can be densified, and as a result, the pH of the surface-treated basic magnesium carbonate can be effectively reduced to 9.5 or less. During the addition of the alkali silicate, it is preferable to stir the suspension in order to perform uniform surface coating.

After the addition of the alkali silicate is completed, the stirring is preferably continued until the precipitation of silica from the alkali silicate is completed.
If silica precipitation continues, the pH of the suspension will gradually increase, but the pH will remain almost constant once precipitation is complete, so the completion of precipitation is judged by measuring the pH of the suspension. it can.
The surface-treated basic magnesium carbonate thus obtained is in the form of a suspension, but in order to remove impurities produced as a by-product of the surface coating reaction, it is dehydrated and washed to remove impurities produced as a by-product. It is desirable to do.

The impurities produced as a by-product are, for example, sodium hydroxide by-produced by the hydrolysis reaction in alumina coating with sodium aluminate, and potassium hydroxide in silica coating with potassium silicate. Is dissolved in the suspension of the surface-treated basic magnesium carbonate produced.
For this reason, the amount of impurities in the prepared surface-treated basic magnesium carbonate may increase, and the value as a product may be reduced.
In this way, a precursor in a form in which the surface of the tubular aggregated particles composed of the flaky fine crystals of basic magnesium carbonate described in the above (1) is coated with the metal oxide can be prepared.

Next, a method for producing a precursor in a form in which fine particles of a metal compound are encapsulated in the tubular structure of the tubular aggregated particles of basic magnesium carbonate shown in the above (2) will be described.
The precursor is prepared by the method of Japanese Patent Application No. 2003-124883 already filed by the present inventors, specifically, by bringing tubular aggregated particles of basic magnesium carbonate and a liquid containing metal compound fine particles into contact with each other. be able to.

More specifically, the precursor (2) includes a suspension containing the metal compound fine particles, preferably a suspension subjected to a dispersion treatment by mechanical dispersion treatment or ultrasonic irradiation, and a basic carbonate. It can be prepared by mixing powder or slurry of magnesium agglomerated particles of magnesium, stirring the mixture so as to be uniform, and drying.
The metal compound fine particles used here can be appropriately selected according to the composition of the composite oxide which is the production object of the present invention.

  For example, fine particles of oxide such as silica, alumina, titanium oxide, iron oxide, zinc oxide, zirconia, manganese dioxide and other metal oxides, hydroxides such as aluminum hydroxide, barium hydroxide, yttrium hydroxide, Calcium carbonate, strontium carbonate, barium carbonate, yttrium carbonate, zinc carbonate, copper carbonate, manganese carbonate, zirconyl carbonate, cadmium carbonate, cobalt carbonate, cerium carbonate, nickel carbonate, carbonate fine particles, calcium fluoride, aluminum fluoride, chloride Fine halide particles such as silver can be used.

  Furthermore, sulfide fine particles such as zinc sulfide, cadmium sulfide, silver sulfide, iron sulfide, copper sulfide, calcium titanate, magnesium titanate, strontium titanate, barium titanate, lead titanate, nickel cobaltate, lanthanum manganate, Double oxide fine particles such as magnesium aluminate, aluminum silicate, lithium tantalate, lithium niobate and ferrite, fine metal particles such as gold, silver, platinum and palladium, and fine mineral particles such as smectite, sericite, zeolite, cristobalite and apatite Various fine particles can also be used.

In this precursor preparation treatment operation, it is desirable that the suspension containing the metal compound fine particles is sufficiently permeated into the tubular aggregated particles of basic magnesium carbonate, and the pressure is reduced by a vacuum pump or an aspirator. It is preferable to deaerate the inside of the tubular structure of basic magnesium carbonate.
By doing so, many metal compound fine particles can be uniformly encapsulated inside the tubular aggregated particles of basic magnesium carbonate, and as a result, a composite oxide can be obtained efficiently in subsequent firing, and composite Variations in the composition of the oxide particles can be reduced.
In this way, the precursor having the form shown in the above (2) can be obtained.

In addition, the precursor of the form (2) described above is not limited to the method of Japanese Patent Application No. 2003-136851 already filed by the present inventors, specifically, in the process of preparing the tubular aggregated particles of basic magnesium carbonate. It can also be obtained by adding fine particles of a metal compound.
The method of Japanese Patent Application No. 2003-136851 refers to the process of forming basic magnesium carbonate tubular aggregated particles as described above by adding one or more fine particles by addition or the like, thereby A precursor in a form in which fine particles of a metal compound are encapsulated inside tubular aggregated particles is prepared.

The fine particles to be included may be appropriately selected according to the composition of the composite oxide particles of the present invention as in the case of the method of Japanese Patent Application No. 2003-124883, and those exemplified in the method can be used similarly. .
These fine particles to be encapsulated are added to the inside of the tubular aggregated particles made of flaky fine recrystallization of basic magnesium carbonate by adding them in the process of producing the tubular aggregated particles made of flaky fine recrystallization of basic magnesium carbonate. A precursor in a form in which fine particles are encapsulated can be obtained.

The addition timing of the fine particles may be in the process of generating basic magnesium carbonate as described above, that is, before the generation of basic magnesium carbonate is completed.
As described above, the mixing timing is preferably before the start of the production of basic magnesium carbonate from the intermediate product of normal magnesium carbonate, more preferably before the start of production of normal magnesium carbonate. Good.
By setting it as such a mixing time, the mixed fine particle can be more efficiently compounded inside the tubular aggregated particles of basic magnesium carbonate.

The amount of the fine particles to be mixed is not particularly limited and can be appropriately adjusted according to the composition of the composite oxide particles of the present invention.
The form of the fine particles upon mixing may be in the form of a powder or in the form of a suspension dispersed in an appropriate solvent.
In particular, it is preferable from the viewpoint of reaction efficiency at the time of subsequent firing that the fine particles are dispersed inside the tubular aggregated particles of basic magnesium carbonate.

In such a case, the suspension is preferably added in the form of a suspension. Preferably, a suspension in which fine particles are sufficiently dispersed by mechanical dispersion treatment, ultrasonic irradiation treatment or use of a dispersant is preferably used. Good.
Of course, in the case of a liquid material such as a fine particle sol, it can be added as it is or in an appropriately diluted state.
As described above, in the production process of the basic magnesium carbonate tubular aggregated particles, the fine particles are fixed inside the basic magnesium carbonate tubular aggregated particles by mixing one kind or two or more kinds of fine particles by addition or the like. The precursor of the finished form can be prepared.

The precursor (1) or (2) of the composite oxide particle of the present invention can be prepared by the method as described above.
Moreover, the form which these (1) or (2) overlapped may be sufficient.
For example, alumina particles are encapsulated inside the basic magnesium carbonate tubular aggregated particles surface-coated with silica, or barium oxide particles are encapsulated inside the basic magnesium carbonate tubular aggregated particles surface-coated with iron oxide. Can be used. Incidentally, by using these as precursors, a magnesium-silicon-aluminum composite oxide and a magnesium-iron-barium composite oxide can be obtained, respectively.

The composite oxide fine particles of the present invention can be produced by firing the precursor prepared by the above-described method.
Regarding the firing conditions, the basic magnesium carbonate constituting the precursor reacts with the metal oxide coated on the surface or the metal compound fine particles encapsulated in the tubular structure to produce the composite oxidation intended for production. It is necessary to make it a condition for producing a product.

The firing conditions will be described with a specific example. A tubular aggregated particle of basic magnesium carbonate whose surface is coated with alumina is used as a precursor, and a tubular particle of spinel (MgAl ₂ O ₄ ) is used as a composite oxide. In the case of manufacturing, it is desirable to bake at a temperature of 850 ° C. or higher.
Furthermore, in order to produce tubular aggregated particles of forsterite (Mg ₂ SiO ₄ ) as a composite oxide using basic magnesium carbonate tubular aggregated particles encapsulated in a tubular aggregated particle as a precursor, 700 ° C. or higher It is preferable to bake at a temperature of.

Moreover, the form of the composite oxide tubular particles can be changed by adjusting the firing temperature.
When fired at a temperature near the lower limit of the production temperature of the composite oxide to be produced, the wall of the tubular particle becomes relatively porous, whereas the wall with a relatively smooth surface increases as the temperature is increased. There is a tendency to become tubular particles with parts.
Note that if the firing temperature becomes too high and the temperature is close to or higher than the melting point of the composite oxide, the tubular particles tend to cause fusion or the tubular structure cannot be maintained. It is preferable to avoid firing at temperatures near or above.

As a firing method, various heating furnaces and firing furnaces that can ensure the formation temperature of the composite oxide are applicable, and there are no particular restrictions. With respect to the firing atmosphere, the production efficiency can be improved by adjusting to an atmosphere in which a composite oxide intended for production is easily generated.
The composite oxide particles of the present invention obtained as described above are oxides containing magnesium and other elements, and the particle shape is tubular.

The elements other than magnesium contained in the composite oxide can be appropriately selected according to the application and use form of the composite oxide particles of the present invention.
In particular, aluminum, silicon, titanium, manganese, iron, zinc, strontium, barium, zirconium, niobium, and lead are suitable for efficiently obtaining a complex oxide with magnesium, and the resulting complex oxide with magnesium Thus, composite oxide particles having characteristics such as heat resistance, dielectric properties, piezoelectricity, and soft magnetism can be obtained.

And the oxide containing 1 type, or 2 or more types of elements selected from the said elements etc. and magnesium is composite oxide of this invention.
For example, magnesium aluminate such as spinel (MgAl ₂ O ₄ ) which is a composite oxide of magnesium and aluminum, forsterite (Mg ₂ SiO ₄ ) and steatite (MgSiO ₃ ) which are composite oxides of magnesium and silicon And magnesium titanate such as Mg ₂ TiO ₄ and MgTiO ₃ which are composite oxides of magnesium and titanium.

There may be two or more elements other than magnesium. For example, cordierite (Mg ₂ Al ₄ Si ₅ O ₁₈ ) which is a composite oxide of magnesium, aluminum and silicon, magnesium, barium and iron The composite oxide particles of the present invention also include BaMg ₂ Fe ₁₆ O ₂₇ , which is a composite oxide, and BaMgAl ₁₀ O ₁₇ : Eu ²⁺ doped with europium using a composite oxide of magnesium, barium, and aluminum.

It is a feature of the present invention that the composite oxide described above is a particle having a novel and unique shape such as a tubular shape.
As for the shape of the tubular particles, it is desirable that the outer diameter is 1 to 20 μm, the inner diameter is 0.5 to 5 μm, the length is 5 to 200 μm, and the length / outer diameter ratio is 2 to 50.
Furthermore, in the pore distribution measured by the mercury intrusion method, the ratio is the ratio of the pore volume (A) having a pore diameter of 0.01 to 100 μm and the pore volume (B) having a pore diameter of 0.5 to 5 μm ( More preferably, B / A) is 0.45 to 0.85.
By setting the particle size and the pore distribution in such a manner, the characteristics derived from the particle shape called tubular can be improved.

The detailed form of the tubular particles is as follows.
That is, the tubular particles are aggregates of finer particles, and the shape and particle size of the fine particles can be adjusted by the type of composite oxide, the manufacturing conditions described above, and the like.
For example, when spinel (MgAl ₂ O ₄ ) is selected as the type of composite oxide, the fine particles are granular or short columnar particles of several nm to several μm. In the case of forsterite (Mg ₂ SiO ₄ ), the fine particles constituting the tubular particles are granular particles having a slight roundness of several tens nm to several μm.

The shape and particle size of the fine particles constituting the tubular particles often affect the characteristics of the composite oxide particles of the present invention.
In the case of an aggregate of relatively large particles, the irregularities on the surface of the tubular particles are reduced. Conversely, in the case of small particles, there are many irregularities and the surface becomes porous.
Therefore, it is preferable to appropriately adjust the production conditions and the like according to the use and usage form of the composite oxide particles of the present invention.
As for the aspect in which the fine particles are gathered in a tubular shape, the precise point is not clear, but the fine particles are welded or fixed together or gathered by some physicochemical bonding force to maintain the tubular shape. I guess that there is.

In addition to the characteristics of the composite particles, the composite oxide particles of the present invention having such a form have various excellent features derived from the unique shape of a tube.
For example, since it is a porous particle derived from a tubular shape, it exhibits high adsorption and absorption characteristics, and the bulk density as a powder is reduced, so the weight of the product to be blended, sound insulation, heat insulation It is also effective in improving.
Moreover, when utilizing as an oxide catalyst etc., the improvement of catalyst efficiency is anticipated by a high specific surface area.

[Examples and Comparative Examples]
Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these examples, and is specified by the scope of claims. Needless to say.

[Preparation of tubular aggregate particles of basic magnesium carbonate]
7. A carbon dioxide-containing gas composed of 25 vol% carbon dioxide and 75 vol% air is added to 2.0 L of a magnesium hydroxide suspension (30 g / L) while stirring at a temperature of 20 ° C. After introducing at a rate of 0 L / min for 30 minutes, the insoluble residue was removed to prepare a magnesium hydrogen carbonate solution (pH 7.3) (first step).

Following this step, an appropriate amount of aqueous sodium hydroxide solution is added to the magnesium hydrogen carbonate solution to adjust the pH of the solution to 9.0, and the temperature of the solution is raised to 35 ° C. by heating. While maintaining the temperature, the mixture was stirred for 60 minutes to prepare a suspension of normal magnesium carbonate (second step).
When this normal magnesium carbonate was observed by SEM, it was a columnar particle having a diameter of 1 to 3 μm and a length of 20 to 50 μm.

Subsequently, an appropriate amount of aqueous sodium hydroxide solution is added to the suspension of columnar particles of magnesium carbonate to adjust the pH of the solution to 10.5, and the temperature of the solution is increased to 50 ° C. by heating. While maintaining the same temperature, the mixture was stirred for 120 minutes to prepare basic magnesium carbonate (third step).
When this basic magnesium carbonate was observed with an SEM, the inner diameter was 1-2 μm, the outer diameter was 2-3 μm, and the length was made of flaky fine crystals having a thickness of 0.01-0.05 μm and a diameter of 0.2-1 μm. They were 5-30 μm tubular aggregated particles.

[Precursor preparation]
While maintaining and stirring the suspension of the tubular aggregated particles of basic magnesium carbonate prepared above (concentration 30 g / L) at a temperature of 20 ° C., a reagent sodium silicate solution (manufactured by Kanto Chemical Co., Ltd., deer grade 1) 200 mL of a solution obtained by diluting SiO ₂ content 35% by weight with ion-exchanged water was added at a rate of 5 mL / min with a tube pump, and stirring was continued for 15 minutes after the addition was completed (basic magnesium carbonate). The amount of sodium silicate added is 20.5 g in terms of SiO _{2 with} respect to 100 g of MgO weight in the inside).

Thereafter, the product suspension was separated by filtration, washed with 10 L of water, washed with 1 L of methyl alcohol, and dried at 105 ° C. to obtain surface-treated basic magnesium carbonate.
When the product was observed with an SEM, the flaky fine crystals forming the tubular aggregated particles of basic magnesium carbonate were covered with a smooth film of silica, and the entire surface of the flaky fine crystals of basic magnesium carbonate was completely covered. It was covered.

[Production of composite oxide particles]
The precursor (tubular aggregated particles of basic magnesium carbonate whose surface was coated with silica) obtained above was calcined at 800 ° C. for 2 hours in a muffle furnace.
When the product was analyzed by powder X-ray diffraction, it was confirmed to be forsterite (Mg ₂ SiO ₄ ).
Moreover, when observed by SEM, they were tubular particles having an inner diameter of 1 to 2 μm, an outer shape of 2 to 3 μm, and a length of 5 to 30 μm.

[Preparation of basic magnesium carbonate and precursor]
While maintaining and stirring 2.0 L of magnesium hydroxide suspension (30 g / L) at 20 ° C., a carbon dioxide-containing gas composed of 25 vol% carbon dioxide and 75 vol% air was added to the suspension. After introducing at a rate of 0 L / min for 30 minutes, the insoluble residue was filtered off to prepare a magnesium hydrogen carbonate solution (pH 7.3).
Thereafter, an appropriate amount of aqueous sodium hydroxide solution was added to the magnesium hydrogen carbonate solution to adjust the pH of the solution to 9.5.

Subsequently, a suspension obtained by ultrasonically dispersing 10 g of rutile type titanium oxide (CR-60 manufactured by Ishihara Sangyo Co., Ltd., surface treatment product of alumina) in 200 mL of ion-exchanged water was added to this liquid, and the liquid temperature was increased by heating. Was raised to 35 ° C. and stirred for 60 minutes while maintaining the same temperature to prepare a suspension of normal magnesium carbonate.
When this normal magnesium carbonate was observed with a scanning electron microscope (SEM), it was a columnar particle having a diameter of 1 to 2 μm and a length of 20 to 50 μm, and titanium oxide particles having a particle diameter of 0.21 μm adhered to the surface. It was in a state.

Subsequently, an appropriate amount of aqueous sodium hydroxide solution was added to the suspension of magnesium carbonate to adjust the pH of the solution to 10.5, and the temperature was raised to 45 ° C. by heating. The precursor was obtained by stirring for 180 minutes while maintaining.
When this precursor was observed with a transmission electron microscope (TEM) and SEM, the particle diameter was 0 inside the tubular aggregated particles of basic magnesium carbonate having an inner diameter of 1-2 μm, an outer diameter of 2-3 μm, and a length of 5-30 μm. It was confirmed that 2 μm titanium oxide particles were included.

[Production of composite oxide particles]
The precursor obtained above (tubular aggregated particles of basic magnesium carbonate in which titanium oxide fine particles were encapsulated) was calcined at 800 ° C. for 2 hours in a muffle furnace.
When the product was analyzed by powder X-ray diffraction, it was confirmed to be Mg ₂ TiO ₄ . Moreover, when observed by SEM, they were tubular particles having an inner diameter of 1 to 2 μm, an outer shape of 2 to 3 μm, and a length of 5 to 30 μm.

[Preparation of tubular aggregate particles of basic magnesium carbonate]
While stirring 2.0 L of magnesium hydroxide suspension (30 g / L) while maintaining the temperature at 20 ° C., a carbon dioxide-containing gas composed of 25 vol% carbon dioxide and 75 vol% air was added thereto. After introducing at a rate of 0.0 L / min for 30 minutes, the insoluble residue was removed to prepare a magnesium hydrogen carbonate solution (pH 7.3) (first step).

Following this step, an appropriate amount of aqueous sodium hydroxide solution is added to the magnesium hydrogen carbonate solution to adjust the pH of the solution to 8.0, and the temperature of the solution is raised to 35 ° C. by heating. While maintaining the temperature, the mixture was stirred for 60 minutes to prepare a suspension of normal magnesium carbonate (second step).
When this normal magnesium carbonate was observed by SEM, it was a columnar particle having a diameter of 5 to 10 μm and a length of 30 to 100 μm.

Subsequently, an appropriate amount of an aqueous sodium hydroxide solution is added to the suspension of columnar particles of magnesium carbonate to adjust the pH of the solution to 10.5, and the temperature is raised to 55 ° C. by heating. While maintaining the same temperature, the mixture was stirred for 120 minutes to prepare basic magnesium carbonate (third step).
When this basic magnesium carbonate was observed with an SEM, the inner diameter was 2 to 5 μm, the outer diameter was 5 to 10 μm, and the length was 20 to 20 μm, which was composed of flaky fine crystals having a thickness of 0.02 to 0.1 μm and a diameter of 1 to 2 μm. It was 50 μm tubular aggregated particles.

[Precursor preparation]
While maintaining 2.0 C of the suspension (concentration 20 g / L) of the tubular aggregated particles of basic magnesium carbonate prepared as described above while stirring the temperature at 30 ° C., the reagent sodium aluminate solution (manufactured by Kanto Chemical Co., Ltd., Deer first grade, Al ₂ O ₃ content 35 wt%) solution (concentration 40 g / L) 1.0 L was added at a rate of 5 mL / min with a tube pump, and stirring was continued for 15 minutes after completion of the addition (sodium aluminate Is 82 g in terms of Al ₂ O _{3 with} respect to 100 g of MgO in basic magnesium carbonate).

Thereafter, the product suspension was separated by filtration, washed with 10 L of water, washed with 1 L of methyl alcohol, and then dried at 105 ° C. to obtain an alumina surface-treated basic magnesium carbonate.
When the product was observed with an SEM, the flaky fine crystals forming the tubular aggregated particles of basic magnesium carbonate were covered with an alumina fine particle film, and the entire surface of the flaky fine crystals of basic magnesium carbonate was completely covered. It was covered.

[Production of composite oxide particles]
The precursor obtained above (tubular aggregated particles of basic magnesium carbonate whose surface was coated with alumina) was calcined at 1000 ° C. for 2 hours in a muffle furnace.
When the product was analyzed by powder X-ray diffraction, spinel (MgAl ₂ O ₄ ) was confirmed.
Moreover, when observed by SEM, they were tubular particles having an inner diameter of 2 to 5 μm, an outer shape of 5 to 12 μm, and a length of 20 to 50 μm.

[Preparation of tubular aggregate particles and precursors of basic magnesium carbonate]
While stirring 2.0 L of magnesium hydroxide suspension (30 g / L) while maintaining the temperature at 20 ° C., a carbon dioxide-containing gas composed of 25 vol% carbon dioxide and 75 vol% air was added thereto. After introducing at a rate of 0.0 L / min for 30 minutes, the insoluble residue was removed to prepare a magnesium hydrogen carbonate solution (pH 7.3) (first step).

Following this step, a suspension of 60 g of magnetite (average particle size 0.3 μm) ultrasonically dispersed in 500 mL of ion-exchanged water is added to the magnesium hydrogen carbonate solution, and then an appropriate amount of aqueous sodium hydroxide solution is added. The pH of the solution is adjusted to 8.0, and the temperature of the solution is raised to 35 ° C. by heating, followed by stirring for 60 minutes while maintaining the same temperature to prepare a suspension of normal magnesium carbonate. (Second step).
When this magnesium carbonate was observed by SEM, it was confirmed that the particles were columnar particles having a diameter of 5 to 10 μm and a length of 30 to 100 μm, and magnetite particles were adhered to the surface.

Subsequently, an appropriate amount of aqueous sodium hydroxide solution is added to the suspension of magnesium carbonate columnar particles to which magnetite particles are adhered to adjust the pH of the solution to 10.5, and the temperature of the solution is heated to 60 ° C. And then stirred for 120 minutes while maintaining the same temperature to prepare basic magnesium carbonate (third step).
When this basic magnesium carbonate was observed with an SEM, the inner diameter was 2 to 5 μm, the outer diameter was 5 to 10 μm, and the length was 20 to 20 μm, which was composed of flaky fine crystals having a thickness of 0.02 to 0.1 μm and a diameter of 1 to 2 μm. It was 50 μm tubular aggregated particles, and it was confirmed that magnetite particles were fixed inside.

[Production of composite oxide particles]
The precursor obtained above (tubular aggregated particles of basic magnesium carbonate in which magnetite particles were encapsulated) was calcined at 1000 ° C. for 2 hours in a muffle furnace. When the product was analyzed by powder X-ray diffraction, magnesium-iron composite oxide (MgFe ₂ O ₄ ) was confirmed.
Moreover, when observed by SEM, they were tubular particles having an inner diameter of 2 to 5 μm, an outer shape of 5 to 12 μm, and a length of 20 to 50 μm.

[Comparative Example 1]
50 g of industrial basic magnesium carbonate (amorphous) and 25 g of silica gel were mixed and ground in a ball mill and then calcined at 800 ° C. for 2 hours in a muffle furnace.
When the product was analyzed by powder X-ray diffraction, it was confirmed to be forsterite (Mg ₂ SiO ₄ ).
Moreover, when observed by SEM, it was an irregular-shaped particle | grain with a diameter of 5-10 micrometers.

₂ is a scanning electron microscope (SEM) photograph showing the particle shape of composite oxide particles (forsterite, Mg ₂ SiO ₄ ) obtained in Example 1. FIG.

Claims (6)

Containing magnesium and other metal elements, characterized in that the precursor is composed of tubular aggregated particles made of flaky fine crystals of basic magnesium carbonate and other metal compounds, and the precursor is fired. A method for producing composite oxide particles that are oxides that have a tubular shape. The method for producing composite oxide particles according to claim 1, wherein the precursor is obtained by covering the surface of tubular aggregated particles made of flaky fine crystals of basic magnesium carbonate with another metal oxide. 2. The method for producing composite oxide particles according to claim 1, wherein the precursor is one in which particles of another metal compound are encapsulated in tubular aggregated particles made of flaky fine crystals of basic magnesium carbonate. It is an oxide containing magnesium and other metal elements, the particle shape is tubular, the outer diameter is 1 to 20 μm, the inner diameter is 0.5 to 5 μm, the length is 5 to 200 μm, and the ratio of length / outer diameter Tubular composite oxide particles characterized by having 2 to 50. In the pore distribution measured by mercury porosimetry, the ratio (B / A) of the pore volume (A) having a pore diameter of 0.01 to 100 μm and the pore volume (B) having a pore diameter of 0.5 to 5 μm The tubular composite oxide particles according to claim 4 , wherein is from 0.45 to 0.85. The composite according to claim 4 or 5 , wherein the other metal element is one or more selected from aluminum, silicon, titanium, manganese, iron, zinc, strontium, barium, zirconium, niobium, and lead. Oxide particles.

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