WO2023095871A1

WO2023095871A1 - Alumina powder and alumina slurry including same

Info

Publication number: WO2023095871A1
Application number: PCT/JP2022/043523
Authority: WO
Inventors: 哲平梶野; 寛岸田
Original assignee: 住友化学株式会社
Priority date: 2021-11-26
Filing date: 2022-11-25
Publication date: 2023-06-01
Also published as: CN117794862A; TW202332655A

Abstract

An alumina powder satisfying the following relationship (1). Relationship (1): Rsp/(total surface area of alumina powder)≤12.0 Rsp and the total surface area of alumina powder in relationship (1) are obtained respectively using the following equations (2) and (3). Equation (2): Rsp=(Rav-Rb)/Rb Rav is the inverse of a transverse relaxation time measured by examining, by pulse NMR spectroscopy, a volume X (ml) of an alumina slurry obtained by dispersing the alumina powder in a dispersion medium, and Rb is the inverse of a transverse relaxation time measured by examining, by pulse NMR spectroscopy, a volume X (ml) of the dispersion medium. Equation (3): Total surface area (m2) of alumina powder = (mass (g) of alumina powder in the volume X (ml))×(BET specific surface area (m2/g) of alumina)

Description

Alumina powder and alumina slurry containing the same

The present disclosure relates to alumina powder and alumina slurry containing the same, and more particularly to alumina powder suitable for polishing alumina slurry and polishing alumina slurry containing the same.

In the manufacturing process of semiconductor parts such as IC chips, multilayer wiring is formed by repeating the photolithography process and the CMP (Chemical Mechanical Polishing) process.

The CMP process is a technique for flattening the Si wafer surface after the photolithography process. A CMP slurry obtained by dispersing an abrasive (for example, ceramic powder) in a dispersion medium is commercially available. This CMP slurry is diluted with the dispersion medium and used in the CMP process.
At present, copper wiring is the mainstream of wiring in semiconductor components. Therefore, CMP slurry containing silica powder as an abrasive is mainly used.

In addition to silica powder, alumina powder is also known as a ceramic powder for polishing (for example, Patent Document 1). Patent Document 1 describes an alumina powder having an average particle size of about 5 μm or less, substantially free of coarse particles of 10 μm or more, and free of coarse agglomerated particles.

JP-A-8-12323

As the line width of the wiring becomes narrower (for example, the line width is 7 μm or less), the electrical resistance of the Cu wiring increases, so the use of ruthenium wiring or cobalt wiring is being studied instead of copper wiring. Ruthenium and cobalt are harder than copper and are difficult to polish with silica powder. Therefore, it is conceivable to use a CMP slurry containing alumina powder, which is harder than silica powder, as an abrasive.

However, conventional CMP slurries containing alumina powder (alumina slurries) have the problem that the alumina powder tends to aggregate and settle. Therefore, there is a demand for an alumina powder that does not easily aggregate and settle in an alumina slurry (that is, an alumina powder that has excellent dispersibility in an alumina slurry).
Patent Document 1 does not consider the dispersibility of the alumina powder in the alumina slurry.

An object of the present invention is to provide an alumina powder having excellent dispersibility in an alumina slurry, and an alumina slurry containing the alumina powder.

Aspect 1 of the present invention is
It is an alumina powder that satisfies the following formula (1).

Rsp/total surface area of alumina powder ≤ 12.0 (1)

Rsp and the total surface area of the alumina powder in formula (1) are obtained from the following formulas (2) and (3), respectively.
Rsp=(Rav−Rb)/Rb (2)
Rav is the reciprocal of the transverse relaxation time when pulse NMR measurement is performed on an alumina slurry of volume X (ml) in which alumina powder is dispersed in a dispersion medium,
Rb is the reciprocal of the transverse relaxation time when the dispersion medium of volume X (ml) is subjected to pulse NMR measurement.
Total surface area of alumina powder (m ² ) = (mass (g) of alumina powder in volume X (ml)) x BET specific surface area of alumina (m ² /g) (3)

Aspect 2 of the present invention is
Furthermore, it is an alumina powder according to aspect 1, which satisfies the following formula (4).

3.0 ≤ Rsp / total surface area of alumina powder (4)

Aspect 3 of the present invention is
3. The alumina powder according to aspect 1 or 2, having a lattice strain of 0.002 or less.

Aspect 4 of the present invention is
An alumina slurry comprising the alumina powder according to any one of aspects 1 to 3, a dispersant, and a dispersion medium.

According to the embodiments of the present invention, it is possible to provide alumina powder with excellent dispersibility in alumina slurry, and alumina slurry containing the alumina powder.

The present inventors standardize the Rsp obtained by measuring the alumina slurry by pulse NMR with the total surface area of alumina, "Rsp / total surface area of alumina powder", as an indicator of the state of dispersion of alumina in the alumina slurry. I decided to Then, as a result of intensive study of the relationship between the index and the dispersion state of alumina, when "Rsp / total surface area of alumina powder" is 12.0 or less, the dispersion state of alumina in the alumina slurry is stable. It was found that agglomeration of alumina can be suppressed. Based on this knowledge, the present inventors completed an alumina powder excellent in dispersion stability in an alumina slurry and an alumina slurry using the same.

Alumina powder and alumina slurry will be explained.

[Embodiment 1: Alumina powder]
An alumina powder according to an embodiment of the present invention satisfies the following formula (1).

Rsp/total surface area of alumina powder ≤ 12.0 (1)

"Rsp" and "total surface area of alumina powder" in the formula are described in detail below.

(Rsp)
In order to obtain Rsp, first, an alumina slurry in which alumina powder is dispersed in a dispersion medium and a dispersion medium only (blank liquid) are each measured by pulse NMR to determine the relaxation time of ¹ H nuclei (pulse-excited magnetization is restored to the original value). Time to return to thermal equilibrium) is measured. Using the obtained measurement results, Rsp is calculated by the following equation (2).

Rsp=(Rav−Rb)/Rb (2)

Here, Rav is the reciprocal of the transverse relaxation time when an alumina slurry (for example, volume X (ml)) in which alumina powder is dispersed in a dispersion medium (for example, pure water) is subjected to pulse NMR measurement. Rb is the reciprocal of the transverse relaxation time when only the dispersion medium (eg, pure water) of the alumina slurry (eg, volume X (ml)) is subjected to pulse NMR measurement. In addition, the liquid which consists only of a dispersion medium may be called a "blank liquid." The blank liquid consists only of a dispersion medium, and usually has the same volume as the alumina slurry used in the pulse NMR measurement.

Rsp is an index relating to the mobility of the molecules of the dispersion medium (water molecules) adsorbed on the surface of the alumina powder. The alumina powder dispersed in the alumina slurry is dispersed in the alumina slurry with the molecules of the dispersion medium bound on its surface.
Here, when the number of molecules of the dispersion medium bound to the surface of the alumina powder increases, the transverse relaxation time (T2) shortens, resulting in an increase in the value of Rsp. Further, when the number of molecules of the dispersion medium bound to the surface of the alumina powder increases, the dispersed state in the dispersion medium is stabilized, thereby improving the dispersibility of the alumina powder.
For these reasons, the dispersibility of the alumina powder tends to improve as the value of Rsp increases.

It should be noted that when the concentration of alumina powder in the alumina slurry is high, the value of Rsp may become high even if the dispersibility is low. In order to correctly evaluate the dispersibility of alumina powder, the present inventors introduced an index in which the value of Rsp is normalized by the total surface area of alumina powder. This will be discussed later.

The pulse NMR measurement of the alumina slurry can be performed, for example, by a pulse NMR system particle interface characterization device "Magno Meter XRS" manufactured by Mageleka, Inc., USA. Measurement conditions are, for example, measurement frequency: 12 MHz, measurement nuclei: ¹ H NMR, measurement method: T2 (transverse relaxation time), sample amount: 0.3 ml, temperature 25°C.

(Total surface area of alumina powder)
The total surface area of the alumina powder (sometimes simply referred to as "total surface area" in the specification) is the total alumina powder contained in the amount X (ml) of the alumina slurry (for example, 0.3 ml) at the time of pulse NMR measurement. It is the total surface area and can be obtained by the following formula (3).

Total surface area of alumina powder (m ² ) = (mass (g) of alumina powder in alumina slurry X (ml)) x BET specific surface area of alumina powder (m ² /g) (3)

The BET specific surface area is determined by the one-point nitrogen adsorption method according to the method specified in JIS-Z-8830:2013 "Method for measuring specific surface area of powder (solid) by gas adsorption". As a specific surface area measuring device, for example, "Macsorb" manufactured by Mountec Co., Ltd. can be used.

The present inventors examined the dispersibility of alumina powder in alumina slurry based on this index. They have also found that an alumina powder having excellent dispersibility can be obtained when "Rsp/total surface area of alumina powder" is 12.0 or less. That is, the alumina powder according to the embodiment exhibits excellent dispersibility in alumina slurry by satisfying the following formula (1).

Rsp/total surface area of alumina powder ≤ 12.0 (1)

"Rsp/total surface area of alumina powder" is preferably 11.5 or less, more preferably 11.0 or less, and still more preferably 10.5 or less.

Furthermore, "Rsp/total surface area of alumina powder" is preferably 3.0 or more. That is, it is preferable to satisfy the following formula (4).

3.0 ≤ Rsp / total surface area of alumina powder (4)

"Rsp/total surface area of alumina powder" is more preferably 4.0 or more, still more preferably 5.0 or more, and particularly preferably 6.0 or less. "Rsp/total surface area of alumina powder" may be 7.0 or more, or may be 8.0 or more.

The value of "Rsp/total surface area of alumina powder" can be set within the desired range by controlling the manufacturing conditions. For example, when producing alumina powder, use of seed crystals and high-speed rotary shearing stirring of seed crystal slurry and aluminum alkoxide can be mentioned. A chelated aluminum alkoxide may be used as the aluminum alkoxide.

(lattice strain)
The alumina powder preferably has a lattice strain of 0.002 or less. When the lattice strain is 0.002 or less, the particle surface is stable, and even fine alumina powder can be prevented from agglomerating in the dispersion medium. This can further improve the dispersibility of the alumina powder in the alumina slurry. The lattice strain is more preferably 0.001 or less, still more preferably 0.0005 or less, and particularly preferably 0.0003 or less.

The lattice strain can be set within the desired range by controlling the manufacturing conditions. For example, when producing alumina powder, use a method (aluminum alkoxide method, etc.) that can obtain high-purity alumina, and do not over-pulverize the alumina powder in the step of pulverizing it. When alumina powder is produced using the Bayer method, the purity of alumina is lowered, and lattice strain tends to increase.

　The lattice strain of alumina powder can be obtained by the following procedure by Rietveld analysis.

First, the alumina powder is subjected to X-ray diffraction measurement by the 2θ/θ method to obtain actual measurement data of the X-ray diffraction profile. Rietveld analysis is performed on the obtained data using a Rietveld analysis program (RIETAN-FP) with the crystal structure of alumina being α-alumina. α-alumina has a hexagonal crystal structure and a corundum structure of space group R-3c.

From the results of Rietveld analysis, for peaks derived from Kα with 2θ values of 40° to 80°, the 2θ value and integral width of each peak are obtained, and the crystallite size and lattice strain are evaluated by the Halder-Wagner method. . In the evaluation by the Halder-Wagner method, the 2θ value and the integral width of each peak are substituted into the following formula (5) (Halder-Wagner formula), the vertical axis is (β / tan θ) ² , and the horizontal axis is β Plot as /(tan θ sin θ). Next, the obtained plot is fitted with a straight line to determine the slope and intercept, and the crystallite size and lattice strain are determined from the slope and intercept values.

Halder-Wagner formula:
(β/tan θ) ² = (Kλ/D)×β/(tan θ sin θ)+16ε ² (5)

In formula (5), β is the integral width, θ is the diffraction angle when X-ray diffraction is measured by the 2θ/θ method, K is the Scherrer constant, λ is the X-ray wavelength, and D is the crystal. is the child size and ε is the lattice strain.
The Scherrer constant K is 4/3, and the X-ray wavelength λ is 1.50406 Å.
If the lattice strain ε is smaller than 1×10 ⁻⁴ , ε ² may become negative in fitting due to the effects of measurement and analysis errors. If ε ² becomes negative, the lattice strain ε is defined as “less than 1×10 ⁻⁴ ”.

The alumina powder preferably has an alumina purity of 99.9% or more, preferably 99.99% or more. Further, the alumina is preferably α-phase alumina (α-alumina), but may contain other alumina (for example, intermediate alumina such as β-alumina and γ-alumina). For example, when the alumina in the alumina powder is 100% by mass, 85% by mass or more is preferably α-alumina.
The alumina powder preferably has an average particle size of 40 nm to 200 nm.

An example of a manufacturing method capable of manufacturing the alumina powder of the present embodiment is shown.

A method for producing an alumina powder according to an embodiment includes:
preparing a seed crystal slurry in which seed crystals are dispersed;
mixing the seed crystal slurry and aluminum alkoxide to obtain an aluminum hydroxide slurry;
a step of drying and calcining the aluminum hydroxide slurry to obtain an alumina powder;
A step of pulverizing the obtained alumina powder is included.
A step of chelating the aluminum alkoxide may be included prior to the step of obtaining the aluminum hydroxide slurry.

I will explain each process in detail.

[1. Step of preparing seed crystal slurry]
After dispersing alumina particles (raw material of seed crystals) in water, wet pulverization is performed with a ball mill. After that, centrifugation is performed with a refrigerated centrifuge (for example, CR7N manufactured by Himac) to remove precipitates. Thus, a seed crystal slurry in which seed crystals are dispersed is obtained.

The seed crystal is preferably alpha alumina. By using seed crystals of α-alumina, the α-formation of alumina can be advanced by low-temperature firing in the later-described firing step.
The particle size of seed crystals is preferably small, and usually 0.01 μm to 0.2 μm is used.

The BET specific surface area of the seed crystal contributes to the crystallite size of the finally obtained alumina powder. The BET specific surface area of the seed crystal is preferably 20 m ² /g or more and 150 m ² /g or less, more preferably 35 m ² /g or more and 120 m ² /g or less.
The BET specific surface area is determined by the one-point nitrogen adsorption method according to the method specified in JIS-Z-8830:2013 "Method for measuring specific surface area of powder (solid) by gas adsorption".

The content of seed crystals in the seed crystal slurry is not particularly limited as long as the obtained seed crystal slurry has appropriate fluidity. For example, the seed crystal content in the seed crystal slurry is 10% by mass to 40% by mass.

[2. Step of Chelating Aluminum Alkoxide]
Optionally, a step of chelating the alumina alkoxide may be included. In this step, the aluminum alkoxide is chelated with a chelating agent. Due to chelation, bulky ligands are coordinated and become steric hindrance, so the condensation reaction of aluminum alkoxide that occurs during hydrolysis, which will be described later, is more effective than aluminum alkoxide that is not chelated. can be suppressed. By suppressing the condensation reaction, it becomes easier to obtain fine aluminum hydroxide particles.

As the aluminum alkoxide, for example, aluminum ethoxide, aluminum n-propoxide, aluminum isopropoxide, aluminum n-butoxide, aluminum sec-butoxide, aluminum t-butoxide and the like can be used.

As chelating agents, for example, ethyl acetoacetate, triethanolamine (TEA), and ethylenediamine (EDA) can be used.

[3. Step of mixing the seed crystal slurry and the (optionally chelated) aluminum alkoxide to obtain an aluminum hydroxide slurry]
The seed crystal slurry and (optionally chelated) aluminum alkoxide are continuously fed to an agitator for mixing. By subjecting this mixture to high-speed rotational shearing stirring with a stirrer, the water in the seed crystal slurry and the aluminum alkoxide undergo a hydrolysis reaction, resulting in a slurry containing aluminum hydroxide particles as a hydrolyzate (aluminum hydroxide slurry). is obtained.

The supply amounts of the seed crystal slurry and (optionally chelated) aluminum alkoxide are preferably controlled so that the seed crystal content in the mixture is appropriate. The preferred content of the seed crystals is the amount of the aluminum component in the seed crystals per 100 parts by mass of the total amount of the aluminum components in the mixture in terms of oxides of the metal components (aluminum alkoxide and the aluminum component contained in the seed crystals) in the mixture. is 1 part by mass or more, preferably 2 parts by mass or more, particularly preferably 4 parts by mass or more, and is 50 parts by mass or less, preferably 40 parts by mass or less, particularly preferably 30 parts by mass or less.

In addition, the supply amount of the seed crystal slurry and (optionally chelated) aluminum alkoxide is such that the compounding ratio of (water contained in the seed crystal slurry) / ((optionally chelated) aluminum alkoxide) is It is preferably controlled to be in the range of about 1.5 to about 6.0.

One of the features of this process is high-speed rotary shear stirring of the mixture. As used herein, "high-speed rotary shear stirring" means that the clearance between the turbine (rotor) and the stator (screen) is small (e.g., 2 mm or less) and the turbine (rotor) rotates at high speed (e.g., peripheral speed of about 1 m/ seconds to about 40 m/s), the stirring is performed by mechanical energy such as shear force, pressure fluctuation, cavitation, collision force, and potential core generated between the turbine (rotor) and stator (screen).

　T. Models such as K Homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.), Clearmix (manufactured by M Technic Co., Ltd.), Polytron Homogenizer, Megatron Homogenizer (KINEMATICA), and Supraton (manufactured by Tsukishima Kikai Co., Ltd.) can be mentioned.

In high-speed rotary shear stirring, the rotation speed of the turbine (rotor) is 3000 rpm to 21500 rpm, preferably 8000 rpm to 15000 rpm, for example 10000 rpm. When the rotational speed is within the above range, the two liquids of the water in the seed crystal slurry and the (optionally chelated) aluminum alkoxide can be sufficiently mixed, and the aluminum hydroxide in the produced aluminum hydroxide slurry can be aggregated. can be suppressed. As a result, an aluminum hydroxide slurry containing fine aluminum hydroxide particles is obtained. Also, the seed crystals can be uniformly dispersed in the aluminum hydroxide slurry.

The hydrolysis of aluminum alkoxide can be performed using a continuous reactor. A continuous tank type, a continuous pipeline type, or the like can be applied as the continuous reactor. In the tank continuous type, the seed crystal slurry and (optionally chelated) aluminum alkoxide are continuously fed into a tank equipped with a high-speed rotational shear stirrer, and the same amount of liquid as the fed liquid is continuously fed. In this method, aluminum alkoxide is hydrolyzed (and aluminum hydroxide particles are produced) while discharging it effectively. In the pipeline continuous type, a seed crystal slurry and (optionally chelated) aluminum alkoxide are continuously fed to a high-speed rotational shear mixer incorporated in the line. According to these continuous reactors, compared to batch reactors, the productivity is extremely high and the conditions for producing aluminum hydroxide particles are uniformed, so water with a uniform particle size distribution and no coarse agglomerated particles can be obtained. An aluminum hydroxide slurry containing aluminum oxide is obtained.

[4. Step of drying and calcining the aluminum hydroxide slurry to obtain an alumina powder]
An alumina powder is obtained by drying the aluminum hydroxide slurry by a known method and firing the obtained aluminum hydroxide in a firing furnace.
Firing is generally carried out at 800° C. or higher, preferably 900° C. or higher, and generally 1000° C. or lower, preferably 980° C. or lower, more preferably 960° C. or lower. If it exceeds 1000° C., it is difficult to obtain fine alumina powder. If the temperature is less than 800° C., the α-phase content in the alumina powder tends to be low.

Firing may be performed in the atmosphere or in an inert gas such as nitrogen gas or argon gas, and it is effective to perform firing while maintaining a high water vapor partial pressure in the atmosphere. . In particular, when the step of chelating aluminum alkoxide is not included, the α-phase can be obtained at a low firing temperature by firing in an atmosphere with a high water vapor partial pressure (that is, an atmosphere with a high dew point). When the step of chelating aluminum alkoxide is included, the α-phase can be obtained in an atmosphere with a low water vapor partial pressure (that is, an atmosphere with a low dew point) and a low firing temperature.

Firing can be performed in a conventional tubular electric furnace, box electric furnace, tunnel furnace, far infrared furnace, microwave heating furnace, shaft furnace, reverberatory furnace, rotary furnace, roller hearth furnace, gas (LNG, LPG) furnace, etc. It can be carried out using a firing furnace. Firing may be performed batchwise or continuously. In addition, it may be carried out in a stationary manner or in a fluidized manner.

As a method for controlling the dew point during firing, for example, when an electric furnace using electric energy as a heat source or a tubular furnace is used as the firing furnace, a method of spraying water into the dry air introduced into the furnace, or A method of introducing steam into the furnace is effective. When a gas combustion furnace is used as the firing furnace, it is effective to introduce moisture generated by burning fuel such as gas or petroleum into the furnace, and it is more effective to additionally introduce steam. .

The dew point is obtained from a conversion table using the amount of water vapor, or from a formula using the water vapor pressure. The water vapor pressure and the water vapor amount (absolute humidity) can be obtained from the saturated water vapor pressure or the saturated water vapor amount and the relative humidity, respectively. The saturated water vapor pressure can be calculated from the Tetens formula.

When the step of chelating the aluminum alkoxide is not included, the dew point in the furnace is preferably controlled to 30 ° C. or higher, more preferably 40 ° C. or higher, and the dew point is 50 ° C. or higher. It is particularly preferable to control the temperature to be 0° C. or higher.

[5. Step of pulverizing the obtained alumina powder]
The alumina powder obtained is pulverized. A medium pulverizer such as a vibration mill, a ball mill, and a jet mill can be used for pulverizing the alumina powder. Further, the alumina powder after pulverization may be classified.

[Embodiment 2: Alumina slurry]
An alumina slurry according to an embodiment of the present invention includes the alumina powder according to Embodiment 1, a dispersant, and a dispersion medium.

Dispersants include pH adjusters such as acids or alkalis, condensed phosphoric acid or condensed phosphates, polystyrene sulfonates, polycarboxylic acid-type polymer compounds, polyacrylic acid-type polymer compounds, polyoxyethylene sorbitan fatty acid esters, polyoxy Ethylene sorbitol fatty acid ester and the like can be mentioned.

Surfactants include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants. Examples of anionic surfactants include ammonium polycarboxylate.

Viscosity modifiers include water-soluble cellulose ethers, polysaccharides, polyhydric alcohols and their derivatives, water-soluble polymer compounds, water-soluble oxides and their salts with thickening action, and biopolymers.

Although the dispersion medium is not particularly limited, for example, organic solvents such as water, ethanol, acetone, and NMP can be used.

The mixing ratio of the alumina powder, the dispersant and the dispersion medium can contain other components as necessary as long as the object of the present invention is not impaired. Other components include, for example, dispersants, surfactants, viscosity modifiers, and the like. When these other components are used, their content is usually in the range of 0.01 to 10% by weight with respect to the total weight of the abrasive grains. Alumina powder can be included at 0.5 to 70% by weight of the slurry.

Alumina slurries are prepared by mixing abrasive grains (and optional ingredients) in a dispersion medium to uniformly disperse them. The mixing method is not particularly limited, and examples thereof include a stirring mixing method using an ultrasonic disperser, a homogenizer, etc., and a pulverizing mixing method using a wet mill or the like.
The mixing method can be performed by a conventionally known mixing method, and the mixing order is arbitrary. Alternatively, three or more components may be premixed and then the remaining components mixed, or all may be mixed at once.

Since the alumina slurry of Embodiment 2 uses the alumina powder of Embodiment 1, the alumina powder in the alumina slurry has good dispersibility and is less prone to agglomeration.

The alumina powder according to Embodiment 1 and the alumina slurry according to Embodiment 2 are used, for example, in a silicon wafer CMP process, a substrate planarization CMP process on which a fine pattern is formed, an insulating film CMP process, a metal film CMP process, and It is used in the CMP process of difficult-to-work substrates (sapphire, SiC, GaN, Ga ₂ O ₃ , diamond).

In the examples, nine types (No. 1 to 9) of alumina powder samples were prepared.
First, sample no. A method for preparing alumina powder No. 1 will be described, and then sample No. 1 will be described. 2 to 9, the preparation method of the alumina powder is explained.

1. Sample no. Preparation of alumina powder in 1 [Preparation of seed crystal (α-alumina) slurry]
After dispersing alumina particles (raw material of seed crystals) in water, wet pulverization was performed with a ball mill. After that, centrifugation was performed for 30 minutes at 4000 rpm in a cooling centrifuge (manufactured by Himac: CR7N) to remove precipitates. As a result, a seed crystal slurry in which seed crystals were dispersed was obtained.
Also, the BET specific surface area of the seed crystals in the obtained seed crystal slurry was measured. First, the moisture in the seed crystal slurry is evaporated to obtain seed crystals, and the nitrogen adsorption method is performed according to the method specified in JIS-Z-8830:2013 “Method for measuring specific surface area of powder (solid) by gas adsorption”. The BET specific surface area was obtained by the method. Table 1 shows the measurement results of the BET specific surface area of the seed crystal.

[Preparation of chelated aluminum isopropoxide]
Aluminum isopropoxide was chelated to prepare chelated aluminum isopropoxide (indicated as "Yes" in "Presence or absence of chelation" in Table 1).
By mixing aluminum isopropoxide and ethyl acetoacetate (chelating agent) at a molar ratio of 100:3, 3 mol % chelated aluminum isopropoxide was obtained.

[Production of fine α-alumina powder]
The chelated aluminum isopropoxide and the seed crystal slurry were hydrolyzed by mixing with a precision emulsifying disperser Clearmix CLM-2.2S (manufactured by M Technic Co., Ltd.) at a rotation speed of 10000 rpm. An aluminum hydroxide slurry was thus obtained.
The compounding ratio of the chelated aluminum isopropoxide and the seed crystal slurry is such that the ratio of (water contained in the seed crystal slurry)/(chelated aluminum isopropoxide) is 2.7/1 (molar ratio). decided to When blended at such a compounding ratio, the aluminum hydroxide slurry contains, in terms of metal component oxide, 100 parts by mass of the total amount of chelated aluminum isopropoxide and the aluminum component contained in the seed crystal. 10 parts by mass of the aluminum component contained in the The content (parts by mass) of each aluminum component was obtained by calculation on the assumption that all of the aluminum isopropoxide used was converted to alumina.

The obtained aluminum hydroxide slurry was dried at 150° C. to obtain aluminum hydroxide particles, which were placed in an alumina crucible and fired in a box type electric furnace. The sintering conditions were such that the temperature was raised to the sintering temperature (975° C.) shown in Table 1 at a rate of temperature increase of 200° C./hour, and the sintering temperature was maintained for 4 hours. By firing, an α-alumina powder was obtained.
This α-alumina powder was further pulverized with a ball mill to obtain fine-grained α-alumina powder.

2. Sample no. Preparation of alumina powder of No. 2 Sample No. The method was the same as the method for preparing alumina powder in No. 1, but the following points were changed.
・In the aluminum hydroxide slurry, 5.6 parts by mass of the aluminum component contained in the seed crystal per 100 parts by mass of the total amount of the chelated aluminum isopropoxide and the aluminum component contained in the seed crystal, in terms of the oxide of the metal component. The compounding amount of the seed crystal was changed so that

3. Sample no. Preparation of 3 Alumina Powder To high-purity aluminum hydroxide produced by the alkoxide method, a Si source was added using a dish-type granulator, and the mixture was fired in a box-type electric furnace. As for the firing conditions, the temperature was raised to the firing temperature (1200° C.) shown in Table 1 at a heating rate of 200° C./hour, and the firing temperature was maintained for 4 hours to obtain high-purity alumina. This high-purity alumina was pulverized with a vibration mill to obtain fine-grained high-purity alumina powder.
As shown in Table 1, no seed crystals were used.

4. Sample no. 4 Preparation of Alumina Powder Aluminum hydroxide prepared by the Bayer method was calcined to prepare an alumina powder having a BET specific surface area of about 4 m ² /g. The obtained alumina powder was pulverized with a ball mill for 4 hours to obtain fine alumina powder having a BET specific surface area of about 5 m ² /g.
As shown in Table 1, no seed crystals were used.

3. Sample no. Preparation of alumina powder of No. 5 Sample No. The method was the same as the method for preparing alumina powder in No. 1, but the following points were changed.
・No seed crystals were used.
・The firing temperature was 1120°C.

6. Sample no. Preparation of alumina powder of sample No. 6. 2, except that the following points were changed.
- Aluminum isopropoxide was used without being chelated (indicated as "none" in "presence or absence of chelation" in Table 1).
・A gas furnace was used for the firing furnace. The firing temperature was 965°C.

7. Sample no. Preparation of alumina powder of sample no. 6 was the same as the method for preparing alumina powder, but the following points were changed.
・In the aluminum hydroxide slurry, the aluminum component contained in the seed crystal is 10 parts by mass per 100 parts by mass of the total amount of aluminum isopropoxide and the aluminum component contained in the seed crystal, in terms of the oxide of the metal component. , the compounding amount of seed crystals was changed.

8. Sample no. Preparation of alumina powder of sample No. 8. 6, but with the following changes.
・In the aluminum hydroxide slurry, the aluminum component contained in the seed crystal is 15 parts by mass per 100 parts by mass of the total amount of aluminum isopropoxide and the aluminum component contained in the seed crystal, in terms of the oxide of the metal component. , the compounding amount of seed crystals was changed.

9. Sample no. Preparation of alumina powder of sample No. 9. 6 was the same as the method for preparing alumina powder, but the following points were changed.
In the aluminum hydroxide slurry, the aluminum component contained in the seed crystal is 20 parts by mass per 100 parts by mass of the total amount of aluminum isopropoxide and the aluminum component contained in the seed crystal, in terms of the oxide of the metal component. , the compounding amount of seed crystals was changed.

[Pulse NMR measurement]
The resulting fine α-alumina powder was mixed with a dispersion medium (pure water) to prepare a 10% by mass mixed liquid. Using an ultrasonic homogenizer "Advanced SONIFIER" manufactured by Emerson Japan Co., Ltd., ultrasonic waves were applied to the mixture for 7 minutes to disperse the alumina powder in the dispersion medium to obtain an alumina slurry. The transverse relaxation time (T2) of this alumina slurry was measured with a pulse NMR system particle interface characterization device "Magno Meter XRS" manufactured by Mageleka, Inc., USA. Measurement conditions were measurement frequency: 12 MHz, measurement nucleus: 1H NMR, measurement method: T2, sample amount: 0.3 ml, and temperature of 25°C. The transverse relaxation time (T2) of the blank solution was also measured under the same measurement conditions using pure water. The reciprocal of the horizontal relaxation time (T2) of the alumina slurry was Rav, and the reciprocal of the horizontal relaxation time (T2) of the blank liquid was Rb.

Rsp=(Rav−Rb)/Rb (2)

[BET specific surface area]
The BET specific surface area of fine-grained α-alumina powder was measured. As a specific surface area measuring device, using "Macsorb" manufactured by Mountec Co., Ltd., according to the method specified in JIS-Z-8830: 2013 "Method for measuring specific surface area of powder (solid) by gas adsorption", Nitrogen adsorption method. The BET specific surface area was determined by the one-point method.

The total surface area (m ² ) of the alumina powder was calculated by multiplying the mass (g) of the alumina powder contained in 0.3 ml of the alumina slurry having a concentration of 10% by mass by the BET specific surface area (m ² /g) of the alumina powder. (See equation (3)' below).

Total surface area of alumina powder (m ² ) = (mass (g) of alumina powder in 0.3 (ml) of alumina slurry) x BET specific surface area of alumina (m ² /g) (3)'

From the obtained Rsp and the total surface area of the alumina powder, the value of the left side of the following formula (1) was obtained.

Rsp/total surface area of alumina powder ≤ 12.0 (1)

[Lattice strain]
The lattice strain of the alumina powder was obtained by the method described above.
X-ray diffraction measurement was performed on the fine-grained α-alumina powder by the 2θ/θ method to obtain actual measurement data of the X-ray diffraction profile. For the X-ray diffraction measurement, D8 ADVANCE manufactured by Bruker was used, CuKα rays were used as the X-ray source, and the voltage was 40 kV and the current was 40 mA during the measurement. Scanning was performed by a continuous measurement method in the range of 2θ from 5 to 80°, the scanning speed was 5 s, and the step width was 0.020°. From the results of analyzing the XRD diffraction profile by the Rietveld method using RIETAN-FP v2.63, for peaks with 2θ values from 40° to 80°, the 2θ value and the integral width of each peak are obtained, Crystallite size and lattice strain were evaluated by the Halder-Wagner method described above.

If the lattice strain ε is smaller than 1×10 ⁻⁴ , ε ² may become negative in fitting due to the effects of measurement and analysis errors. When ε ² became negative, the lattice strain ε was defined as “less than 1×10 ⁻⁴ ”.

[Dispersibility evaluation]
Using the alumina slurry (10% by mass) used for the pulse NMR measurement, the dispersibility (presence or absence of agglomeration) of the fine α-alumina powder in the alumina slurry was confirmed.
The particle size distribution of the fine α-alumina powder in the alumina slurry was measured by laser diffraction using a laser particle size distribution measuring device [Nikkiso Co., Ltd. “Microtrac”], and the cumulative percentage of the particle diameter equivalent to 95% on a mass basis. D95 was determined. For the measurement, a small amount of alumina slurry was added to a 0.2% by weight aqueous solution of sodium hexametaphosphate, and ultrasonic waves were applied to disperse the fine α-alumina powder in the aqueous solution. Also, the refractive index of the alumina particles was set to 1.76.

Tables 2 and 3 show the measurement results and calculation results for each sample. In addition, in Table 2, the underlined numerical values indicate that they are out of the scope of the embodiment of the present invention.

　Sample No. Since the alumina powders of 1 to 2 and 6 to 9 were prepared under the production conditions described in the embodiment, "Rsp/total surface area of alumina powder" was within the range defined in the embodiment of the present invention. In the alumina slurry using the alumina powder, the D95 of the alumina powder after ultrasonic dispersion was sufficiently small. From this, it was confirmed that the dispersibility of the alumina powder was good.

On the other hand, sample No. The alumina powder of No. 3 had a low rotational speed during production and no seed crystal slurry was added. Therefore, the obtained alumina powder had poor crystallinity, and easily aggregated when made into an alumina slurry. As a result, "Rsp/total surface area of alumina powder" was outside the scope of the embodiments of the present invention.

　Sample No. The alumina powder of No. 4 was obtained by pulverizing alumina produced by the Bayer method, and the purity of alumina was low. Therefore, the obtained alumina powder had poor crystallinity, and easily aggregated when made into an alumina slurry. As a result, "Rsp/total surface area of alumina powder" was outside the scope of the embodiments of the present invention.

　Sample No. In the alumina slurries using the alumina powders of Nos. 3 and 4, the D95 of the alumina powder after ultrasonic dispersion was large. From this, it was confirmed that the dispersibility of the alumina powder was poor and at least part of the alumina powder was agglomerated in the alumina slurry.

　Sample No. 5 was an alumina powder prepared without adding seed crystals. Therefore, D95 is sample no. Although smaller than samples No. 3 and 4, sample no. Larger than 1 and 2.

This application is accompanied by a priority claim based on a Japanese patent application, Japanese Patent Application No. 2021-192365, which has a filing date of November 26, 2021. Japanese Patent Application No. 2021-192365 is incorporated herein by reference.

Claims

Alumina powder satisfying the following formula (1).

Rsp/total surface area of alumina powder ≤ 12.0 (1)

Rsp and the total surface area of the alumina powder in formula (1) are obtained from the following formulas (2) and (3), respectively.

Rsp=(Rav−Rb)/Rb (2)

Rav is the reciprocal of the transverse relaxation time when pulse NMR measurement is performed on an alumina slurry of volume X (ml) in which alumina powder is dispersed in a dispersion medium,
Rb is the reciprocal of the transverse relaxation time when the dispersion medium of volume X (ml) is subjected to pulse NMR measurement.

Total surface area of alumina powder (m 2 ) = (mass (g) of alumina powder in volume X (ml)) x BET specific surface area of alumina (m 2 /g) (3)
2. The alumina powder according to claim 1, further satisfying the following formula (4).

3.0 ≤ Rsp / total surface area of alumina powder (4)
The alumina powder according to claim 1, which has a lattice strain of 0.002 or less.
An alumina slurry containing the alumina powder according to any one of claims 1 to 3, a dispersant, and a dispersion medium.