Method for manufacturing alumina particle material

Abstract

To provide a novel manufacturing method for manufacturing an alumina particle material having a small particle size.SOLUTION: In order to prevent generated particles from agglomerating with each other even if a concentration is high when they are introduced into a high temperature oxidizing atmosphere, it is considered that raw material particles are dispersed in a liquid and are introduced into the high temperature oxidizing atmosphere as a dispersion. The method for producing an alumina particle material of the present invention includes steps of: dispersing a raw material particle material composed of metallic aluminum having a volume average particle size of 0.1 μm or more and 40 μm or less in a combustible liquid in a concentration of 1% or more and 75% or less based on a total mass to prepare a dispersant; and supplying the dispersant under a high temperature oxidizing atmosphere and firing the raw material particle material to manufacture an alumina particle material.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for manufacturing alumina particle materials.

Background Art

[0002] As methods for manufacturing alumina particle materials with a small particle size of about 30 nm to 300 nm, there are: (1) an aqueous wet synthesis method; (2) a method of charging a raw material particle material made of metallic aluminum into a high-temperature oxidation atmosphere, burning it, and then rapidly cooling it (VMC method); (3) a manufacturing method of forming spherical alumina particles in a flame containing aluminum chloride, oxygen, and a combustible gas (Patent Document 1); and (4) a method of evaporating a raw material containing aluminum and magnesium by thermal plasma in an oxygen atmosphere (Patent Document 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the manufacturing methods of alumina particle materials described in (1) to (4) have the following problems: (1) The material produced by aqueous wet synthesis is essentially boehmite and not alumina, and furthermore, the produced particles are amorphous, making it difficult to produce spherical particles with excellent dispersibility and fluidity. (2) The VMC method synthesizes coarse particles in addition to particles smaller than 300 nm. Therefore, it has not been possible to selectively obtain particles with small particle sizes such as 300 nm or smaller or 100 nm or smaller. (3) In the method, aluminum chloride is used as a raw material, making it difficult to remove residual chloride ions, making it difficult to use in applications with strict impurity requirements, such as electronic materials. (4) In the method, a large amount of energy is required to generate thermal plasma, while the amount of alumina particle material produced is not sufficient.

[0005] This invention was completed in view of the above circumstances, and aims to solve the problem of providing a novel manufacturing method for producing alumina particle material with small particle size. [Means for solving the problem]

[0006] As a result of diligent research, the inventors discovered that in the VMC method, by dispersing the raw material particle material in a flammable liquid and introducing it under a high-temperature oxidizing atmosphere, small-particle alumina material is preferentially produced. The reason why coarse particles are formed in the VMC method is presumed to be that the oxides, which have become liquid droplets at high temperatures due to the oxidation reaction of the metal, aggregate at high concentrations to form a single particle before solidifying upon cooling.

[0007] Therefore, in order to suppress the aggregation of the generated droplet-like oxides, the input concentration of the raw material particle material, which is made of aluminum, was diluted, which made it possible to reduce the particle size of the resulting alumina particle material. However, combustion was difficult to occur, that is, the oxidation reaction itself did not proceed easily, and unreacted material tended to remain. Furthermore, in order to allow the oxidation reaction to proceed easily even in a diluted state, the particle size of the raw material particle material was made fine within a predetermined particle size range, but due to poor feedability, combustion (oxidation reaction) did not proceed stably.

[0008] Therefore, in order to maintain the feedability of highly reactive fine powder raw material particles while allowing the oxidation reaction to proceed even in a dilute state, we conceived a method of dispersing the raw material particles in a flammable liquid and introducing it into a high-temperature oxidizing atmosphere, thereby solving the problem and completing the present invention.

[0009] In other words, the present invention, which solves the above problems, is a method for producing alumina particle material, comprising a dispersion preparation step of dispersing raw material particle material composed of metallic aluminum with a volume average particle size of 0.1 μm or more and 40 μm or less in a flammable liquid at a concentration of 1% or more and 75% or less based on the total mass, A process for manufacturing alumina particle material, comprising supplying the dispersion under a high-temperature oxidizing atmosphere and burning the raw material particle material, It holds.

[0010] Preferably, the volume-average particle size of the raw material particle material is 0.5 μm or more and 10 μm or less. Furthermore, preferably, the flammable liquid has a flash point of 10°C or higher, a heat of combustion of 5.0 kcal / g or higher, and a single-molecule oxygen content of 0.1 or more and 0.5 or less. Moreover, preferably, the dispersion has a concentration of the raw material particle material of 30% or more and 50% or less. [Effects of the Invention]

[0011] The present invention's method for producing alumina particle material, having the above configuration, allows for the preferential production of alumina particle material with small particle sizes, even when using the VMC method. [Brief explanation of the drawing]

[0012] [Figure 1] This is an SEM image of the alumina particle material prepared according to Test Example 5. [Modes for carrying out the invention]

[0013] The method for producing the alumina particle material of the present invention will be described in detail below based on the following embodiments. The method for producing the alumina particle material of this embodiment is a suitable method for producing alumina particle material with a volume-average particle size of 300 nm or less.

[0014] The method for producing the alumina particle material of this embodiment comprises a dispersion preparation step, an alumina particle material production step, and other steps selected as necessary.

[0015] The dispersion preparation process involves preparing a dispersion by dispersing raw material particulate material in a flammable liquid at a concentration of 1% or more and 75% or less based on the total mass. The raw material particulate material consists of metallic aluminum. Being composed of metallic aluminum means containing 50% or more by mass of metallic aluminum. Other materials such as metals other than aluminum may be included as separate, individual particulate materials in a mixture with the aluminum particulate material, or as alloys or intermetallic compounds within the same particulate material as aluminum. For example, silicon, magnesium, zirconium, and titanium may be included. When intended for use as a filler for electronic materials, the raw material particulate material preferably has a low Na content. For example, it is desirable to have a Na content of 1 ppm or less. Furthermore, it is preferable that the raw material particulate material has low U and Th content. For example, it is desirable to have a U and Th content of 5 ppb or less each.

[0016] The raw material particle is manufactured by atomizing the materials constituting the raw material particle by an appropriate method. Methods for atomization include pulverization and atomization. The raw material particle may also be surface-treated with silane compounds or silazane compounds.

[0017] The raw material particle material has a volume average particle diameter of 0.1 μm or more and 40 μm or less. The lower limit value of the volume average particle diameter is preferably 0.5 μm, 1 μm, 1.5 μm, or 2 μm, and the upper limit value is preferably 10 μm, 15 μm, 20 μm, or 30 μm. These lower limit values and upper limit values can be arbitrarily combined. When the particle diameter of the raw material particle material is increased, the particle diameter of the obtained alumina particle material tends to increase. Conversely, when the particle diameter of the raw material particle material is decreased, the particle diameter of the obtained alumina particle material tends to decrease.

[0018] The dispersion is obtained by dispersing the raw material particle material in a combustible liquid. The raw material particle material is dispersed at a concentration of 1% or more and 75% or less based on the mass of the entire dispersion. Examples of the lower limit value of the concentration of the raw material particle material include 5%, 10%, 15%, 20%, and 30%, and examples of the upper limit value include 40%, 45%, 50%, 60%, and 70%. These lower limit values and upper limit values can be arbitrarily combined. When the concentration of the raw material particle material is increased, the particle diameter of the obtained alumina particle material tends to increase. Conversely, when the concentration of the raw material particle material is decreased, the particle diameter of the obtained alumina particle material tends to decrease.

[0019] The method for dispersing the raw material particle material in the combustible liquid is not particularly limited, and the raw material particle material can be gradually added to the combustible liquid, or conversely, the combustible liquid can be gradually added to the raw material particle material, or both can be mixed at once. Further, when mixing, a stirrer, an ultrasonic generator, a high-pressure disperser, etc. can be used.

[0020] The combustible liquid may be composed of a single compound or a mixture of a plurality of compounds, and means a liquid that continues to burn when burned under the same oxidation atmosphere (the same concentration of oxide substances such as oxygen) as the high-temperature oxidation atmosphere described later. Therefore, in the case of a mixture of a plurality of compounds, one or more of the compounds constituting the combustible liquid may include those that cannot be said to be a combustible liquid alone.

[0021] The flammable liquid preferably has a flash point of 10 °C or higher, more preferably 30 °C or higher, from the perspective of the volatility of the dispersion. Further, the flammable liquid preferably has a combustion heat of 5.0 kcal / g or higher, more preferably 6.0 kcal / g or higher, from the perspective of promoting the oxidation reaction from the raw material particle material to the alumina particle material. Furthermore, from the perspective of achieving both the dispersion stability of the raw material particle material and the promotion of the oxidation reaction, the compound constituting the flammable liquid preferably has an oxygen atom content per molecule of 0.1 or more and 0.5 or less. Note that the "oxygen atom content per molecule" in this specification is the total value of the atomic weights of oxygen when the total molecular weight of the flammable liquid is taken as 1. Additionally, from the perspective of achieving both the dispersion stability of the raw material particle material, the feedability of the raw material particle material, and the promotion of the oxidation reaction, the concentration of the raw material particle material in the dispersion is preferably 30% or more and 50% or less.

[0022] A dispersant may be added to the dispersion to improve and stabilize the dispersibility of the raw material particle material. The dispersant is not particularly limited, but it is preferable to employ an acidic dispersant that adsorbs to the basic sites on the surface of aluminum. Examples of the acidic dispersant include acidic dispersants of the polymer polycarboxylic acid type. The addition amount of the dispersant is not particularly limited, and examples of the lower limit values include 0.5%, 0.8%, and 1.0% based on the mass of the raw material particle material, and examples of the upper limit values include 2.5%, 2.0%, and 1.5%. These lower limit values and upper limit values can be arbitrarily combined.

[0023] The prepared dispersion is supplied under a high-temperature oxidation atmosphere to oxidize the raw material particle material to prepare the alumina particle material. The dispersion is preferably introduced into the high-temperature oxidation atmosphere in the state of fine droplets. For example, a sprayer can be used to atomize the dispersion. When atomizing with a sprayer, it can be directly sprayed into the high-temperature oxidation atmosphere or sprayed into some carrier gas and introduced into the high-temperature oxidation atmosphere in the state of the carrier gas containing the atomized dispersion.

[0024] In a high-temperature oxidizing atmosphere, an amount of oxidizing gas, such as oxygen, is supplied from the outside in sufficient quantities to adequately oxidize the supplied raw material particles. For example, the amount of oxidizing gas supplied into the high-temperature oxidizing atmosphere can be approximately 1 to 5 times the amount of oxygen theoretically required to oxidize the raw material particles. Examples of lower limits include 1.2 times, 1.5 times, 1.8 times, and 2.0 times, while examples of upper limits include 4.0 times, 3.5 times, and 3.0 times. These lower and upper limits can be combined arbitrarily.

[0025] In a high-temperature oxidizing atmosphere, non-reactive gases such as nitrogen and argon can be included in addition to oxidizing gases. By adjusting the amount of non-reactive gases, the concentration of dispersions and raw material particles in the high-temperature oxidizing atmosphere can be adjusted.

[0026] The concentration of the dispersion in a high-temperature oxidizing atmosphere is preferably within a predetermined range from the viewpoint of the stability of the oxidation reaction. For example, the dispersion is 13,000 mL / m³ in a high-temperature oxidizing atmosphere. 3 • From h to 40,000 mL / m 3 Supplying the material at a concentration of approximately 1 / h is preferable because it stabilizes the oxidation reaction and reduces the amount of unreacted aluminum contained in the alumina particle material.

[0027] The concentration of the raw material particle in a high-temperature oxidizing atmosphere is preferably within a predetermined range for reducing the particle size of the alumina particle material and ensuring the stability of the oxidation reaction. For example, the raw material particle material is present at 500 mL / m³ in a high-temperature oxidizing atmosphere. 3 From 18000 mL / m² 3 Supplying it at a certain concentration results in smaller synthesized particles, which is preferable.

[0028] A mixture of a non-reactive gas and an oxidizing gas can be supplied from the outside into a high-temperature oxidizing atmosphere. For example, air can be used as both the non-reactive gas and the oxidizing gas and supplied into a high-temperature oxidizing atmosphere. In this case, it is preferable to reduce the amount of moisture contained in the air.

[0029] A high-temperature oxidizing atmosphere can be formed by igniting a flame created by supplying a combustible gas, such as hydrocarbon gases like propane, hydrogen, or carbon-free gases like ammonia, along with a combustion-supporting gas, or by utilizing a high-temperature oxidizing atmosphere formed by igniting the dispersion itself.

[0030] It is preferable to use a reaction vessel such as a furnace as the apparatus for forming a high-temperature oxidizing atmosphere. In particular, it is preferable to have a configuration in which the dispersion is introduced from the top of the furnace and the manufactured alumina particle material is recovered from the bottom. In particular, it is preferable to form the high-temperature oxidizing atmosphere so as to surround the area in which the dispersion is introduced into the furnace, and it is even preferable to supply a sheath gas so as to surround the high-temperature oxidizing atmosphere.

[0031] In a high-temperature oxidizing atmosphere, the raw material particles burn to form alumina, and upon removal from the high-temperature oxidizing atmosphere, they are rapidly cooled to form alumina particle material. The obtained alumina particle material is recovered by conventional methods such as bag filters or cyclones. [Examples]

[0032] The method for producing the alumina particle material of the present invention will be described in detail below based on the following examples. The properties of the flammable liquid used in the examples are shown in Table 1.

[0033] (Test Example 1) • Dispersion preparation process As the raw material particle material, a particle material made of aluminum with a volume-average particle size of 2.0 μm was used. When the raw material particle material was 100 parts by mass, 1 part by mass of Mariam AFB-1521 (manufactured by NOF Corporation) as an acidic dispersant was added and thoroughly stirred. Then, the raw material particle material was dispersed in a ratio of 1 part by mass to 99 parts by mass of propylene glycol monomethyl ether (PGM) as a flammable liquid to obtain the dispersion of Test Example 1.

[0034] Furthermore, when dispersions prepared using a basic dispersant (manufactured by NOF Corporation: high-molecular-weight amine compound: Esream AD-374M or Esream AD-3172M) instead of an acidic dispersant were evaluated using an optical microscope with a coverslip on a glass slide, aggregation was observed in the dispersion of Test Example 1, whereas aggregation was observed in the latter.

[0035] • Alumina particle material manufacturing process The obtained dispersion was supplied at a rate of 20 mL / min at an ejector pressure of 0.1 kPa and sprayed into a furnace that had a high-temperature oxidizing atmosphere inside to prepare alumina particulate material. The obtained alumina particulate material was separated using a cyclone.

[0036] ·evaluation The volume-average particle size of the obtained alumina particle material was measured using a laser diffraction particle size analyzer, and the specific surface area was measured using the BET method with nitrogen. The amount of unreacted aluminum was measured by suspending the alumina particle material in a pH 14 basic aqueous solution and quantifying the gas produced when unreacted aluminum was dissolved. The results are shown in Table 2.

[0037] The dispersion stability in Table 2 was evaluated by placing the dispersion in a transparent container, letting it stand for a predetermined time, and then checking whether a precipitate formed that could not be removed by its own weight even when the container was turned upside down. If no precipitate formed after 30 minutes of standing, the dispersion was judged to be able to exist stably for a long period of time and was marked with "○". Otherwise, the dispersion was judged to be unstable and would quickly separate by precipitation and was marked with "×".

[0038] The dispersion volatility in Table 2 was evaluated by placing the dispersion to a thickness of 5 mm in a drying dish and leaving it to stand for a predetermined time at 25°C. The evaluation was based on whether or not the flammable liquid evaporated and turned into a powder. If the dispersion did not turn into a powder even after standing for 30 minutes, it was judged that the dispersion volatility was low and handling such as feeding and storage was easy, and this was indicated with "○". Otherwise, it was judged that the above handling was difficult and this was indicated with "×".

[0039] (Examples 2-32 of the test) The flammable liquid, the volume-average particle size of the raw material particle material, and the concentration of the raw material particle material in the dispersion were changed to the combinations shown in Table 2 to prepare the dispersions for each test example. Alumina particle material was then manufactured using the same alumina particle material manufacturing process as in Test Example 1, and the volume-average particle size, specific surface area, and amount of unreacted aluminum were measured in the same manner as in Test Example 1.

[0040] (Comparative example) Alumina particle material was produced in the same manner by introducing raw material particles with a volume-average particle size of 2 μm directly into a high-temperature oxidizing atmosphere at a rate of 4 g / min using nitrogen gas as a carrier gas, with an ejector pressure of 0.1 kPa. The results of evaluating the obtained alumina particle material in the same manner as the test example are shown in Table 2.

[0041] [Table 1]

[0042] [Table 2]

[0043] As is clear from the table, in Test Examples 1-24 and 31, where alumina particle material was produced using a dispersion prepared in a flammable liquid at a concentration of more than 0.5% and less than 80%, it was found that the amount of unreacted aluminum in the produced alumina particle material was 2.0% or less, and that alumina particle material with a small particle size could be selectively produced.

[0044] Furthermore, it was found that increasing the concentration of the raw particle material in the flammable liquid slightly increased the particle size, suggesting that the particle size can be controlled in the region of 300 nm or less by adjusting the concentration.

[0045] In contrast, in Test Example 25, where the dispersion concentration was 0.5%, lower than in the other test examples, although the particle size was small, the amount of unreacted aluminum significantly exceeded 2.0%. From these results, it was inferred that in Test Examples 1 to 24, where the concentration of raw material particles in the dispersion was above a predetermined value, combustion (oxidation reaction) itself was more likely to occur because the reaction source raw material particles were sufficiently present.

[0046] Furthermore, in Test Example 26, where the dispersion concentration was 80%, the particle size exceeded 300 nm, and the amount of unreacted aluminum significantly exceeded 2.0%. From these results, it was inferred that in Test Examples 1-24, where the raw material particle material in the dispersion was less than 80%, aggregation of the raw material particle material in the dispersion was suppressed, thereby improving feed stability and allowing combustion (oxidation reaction) to occur stably.

[0047] Furthermore, in Test Example 32, where water was used instead of the flammable liquid, the alumina particle material obtained showed an unreacted aluminum content significantly exceeding 2.0%. From this result, it was inferred that the oxidation reaction of the raw material particle material proceeds sufficiently when the flammable liquid is used.

[0048] In a comparative example (conventional VMC method) using dried raw material particles without dispersion, the alumina particle material obtained included both small and large particle materials in roughly equal proportions, indicating that selectively obtaining small particle materials is difficult.

[0049] Comparing the test examples 1-24 and 27-31 using flammable liquids, the following findings were obtained. First, comparing test examples 5, 19, 20, 22, and 27-31, which used a dispersion with a particle size of 2 μm and a dispersion concentration of 40% as the raw material particle material, it was found that test example 5, which used PGM as the flammable liquid, was preferable to the other test examples using flammable liquids in that it had the lowest amount of unreacted aluminum. This was thought to be because the oxygen atom content per molecule was between 0.1 and 0.5, resulting in high dispersibility of the raw material particle material and a stable oxidation reaction. In addition, the low volatility of the dispersion allowed for stable feeding without drying, which was also thought to have contributed to its ease of handling from a safety standpoint.

[0050] Furthermore, it was found that Test Example 28, which used octane as the flammable liquid, was able to synthesize smaller particle size alumina than Test Example 27, which used toluene as the flammable liquid. This was thought to be because the high oxygen atom content per molecule prevented aggregation in the flammable liquid, resulting in superior dispersibility, and thus the raw material particles could react in a dilute state.

[0051] In Test Example 29, which used MEK as the flammable liquid, it was found that alumina with smaller particle sizes could be synthesized compared to Test Example 27, which used toluene as the flammable liquid. Because MEK has a high oxygen atom content per molecule, it exhibited superior dispersibility without aggregation in the flammable liquid. This was thought to be because the raw material particles could react in a dilute state. However, due to its high volatility, the spray condition from the feed and sprayer was somewhat unstable due to the drying of the dispersion. This resulted in a higher amount of unreacted aluminum compared to the case with PGM under the same conditions (Test Example 5).

[0052] Furthermore, when comparing test examples 5, 19, 22, 24, 30, and 31, which differ only in the flammable liquid used (PGM, butanol, IPA, MIBK, methanol, ethanol), it was found that using flammable liquids with higher heat of combustion tended to result in less unreacted aluminum. This was thought to be because the self-heat of combustion stabilized the flame formation, thus assisting the oxidation reaction of the raw material particles.

[0053] Next, comparing Test Examples 12, 21, and 23, which used a dispersion with a particle size of 5 μm and a dispersion concentration of 40% as the raw material particle material, it was found that, similar to the case using the 2 μm raw material particle material described above, Test Example 5, which used PGM as the flammable liquid, was preferable to the other test examples using flammable liquids in that it contained less unreacted aluminum.

[0054] Furthermore, when the flammable liquid was PGM and the dispersion concentration was 40%, a comparison of test examples 15, 5, 12, 17, and 18, in which the particle size of the raw material particle material was varied to 0.1 μm, 2 μm, 5 μm, 10 μm, and 30 μm, revealed that the particle size of the alumina particle material tended to increase as the particle size of the raw material particle material increased. This suggests that the particle size of the alumina particle material can be controlled in the region of 300 nm or less by the particle size of the raw material particle material.

Claims

1. A method for producing an alumina particle material having a volume-average particle size of 300 nm or less, A dispersion preparation step involves preparing a dispersion in which raw material particle material composed of metallic aluminum with a volume average particle size of 0.1 μm or more and 40 μm or less is dispersed in a flammable liquid at a concentration of 1% or more and 75% or less based on the total mass. A process for manufacturing alumina particle material, comprising supplying the dispersion under a high-temperature oxidizing atmosphere and burning the raw material particle material, It has, The method for producing alumina particle material wherein the flammable liquid has a flash point of 10°C or higher, a heat of combustion of 6.0 kcal / g or higher, and a single-molecule oxygen content of 0.1 to 0.

5.

2. The method for producing an alumina particle material according to claim 1, wherein the volume-average particle size of the raw material particle material is 0.5 μm or more and 10 μm or less.

3. The method for producing an alumina particle material according to claim 1 or 2, wherein the dispersion has a concentration of 30% or more and 50% or less of the raw material particle material.

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