JP7340928B2 - Alumina powder for sintering - Google Patents

Description

The present invention relates to alumina powder, and particularly to alumina powder for sintering.

Conventionally, alumina powder suitable for various uses has been provided. For example, Patent Document 1 describes an inorganic powder for thermal spraying that includes spherical alumina powder with an average particle size of 0.02 to 0.5 μm and ceramic powder (for example, alumina powder with an average particle size of 3 to 40 μm). .
Patent Document 1 states that when spherical alumina powder is adhered to the surface of ceramic powder and the adhesion rate is 30% or more, the fluidity of the inorganic powder can be significantly improved. In Patent Document 1, the inorganic powder is manufactured by mixing spherical alumina powder and ceramic powder in a mixer.

Japanese Patent Application Publication No. 2007-8730

Alumina powder for use in alumina sintered bodies is provided as a use different from Patent Document 1. When producing an alumina sintered body from alumina powder, first, the alumina powder is pressure-molded to form a molded body. An alumina sintered body can be manufactured by sintering the obtained molded body.

Sintering the molded body may reduce its dimensions. The reduction in size due to sintering is called sintering shrinkage, and it is desirable that such sintering shrinkage not occur. Therefore, the alumina powder is required to be resistant to sintering shrinkage (herein referred to as "good dimensional accuracy").
Further, the alumina powder is required to have moldability so that the molded product can maintain a desired shape during pressure molding.
Furthermore, the alumina powder is required to have sinterability such that the alumina particles in the alumina powder are sufficiently bonded when the molded body is sintered.

Alumina particles having a relatively large particle size (for example, alumina particles having an average particle size of 1 μm or more) have good dimensional accuracy, but do not have sufficient formability and sinterability.
On the other hand, alumina particles with a relatively small particle size (for example, alumina particles with an average particle size of less than 1 μm) have good formability and sinterability, but poor dimensional accuracy.
In order to solve these problems, dimensional accuracy, formability, and sinterability can be improved by using an alumina mixed powder in which alumina particles with a large particle size and alumina particles with a small particle size are diffused and mixed.

However, in addition to dimensional accuracy, formability, and sinterability, there is a need for an alumina powder that can yield a dense alumina sintered body. A sufficiently dense alumina sintered body cannot be obtained with the alumina mixed powder obtained by diffusion mixing.
Further, since the alumina powder of Patent Document 1 is used for thermal spraying, the characteristics required of the alumina powder for alumina sintered bodies have not been studied.

Therefore, an object of the present invention is to provide an alumina powder that can produce a dense alumina sintered body.

Aspect 1 of the present invention is
An alumina powder containing a plurality of alumina particles,
In the molded body obtained by pressure-molding the alumina powder at a pressure of 30 MPa, the total pore volume is 0.20 mL/g or less, and the cumulative pore volume of pores with a pore diameter of 1 μm or more is less than 10% of the total pore volume. This is an alumina powder.

Aspect 2 of the present invention is
5 to 95% by volume of alumina particles with a particle size of 1 μm or more and less than 100 μm,
The alumina powder according to Embodiment 1 contains 5 to 95% by volume of alumina particles having a particle size of 0.1 μm or more and less than 1 μm.

Aspect 3 of the present invention is
The alumina powder according to aspect 1 or 2, wherein the particle size distribution curve of the plurality of alumina particles shows at least one peak in each of a particle size range of less than 1 μm and a particle size range of 1 μm or more.

Aspect 4 of the present invention is
The alumina powder according to any one of aspects 1 to 3, wherein the content of organic matter is less than 1% by mass in terms of C amount.

The alumina powder of the present invention can produce a dense alumina sintered body.

FIG. 1 is a schematic diagram of alumina powder according to Embodiment 1. FIG. 2 is an example of a particle size distribution curve of alumina particles. FIG. 3 is a particle size distribution curve of alumina particles created in Examples and Comparative Examples. FIG. 4 is a graph of pore radius versus cumulative pore volume for molded body samples produced in Examples and Comparative Examples. FIG. 5 is a graph of firing temperature versus alumina sintered body density for alumina sintered body samples obtained by firing the molded body samples produced in Examples and Comparative Examples. FIG. 6 is a particle size distribution curve of alumina powder samples produced in Examples and Comparative Examples.

<Embodiment 1>
The alumina powder of the present invention is a powder used to produce an alumina sintered body, and contains a plurality of alumina particles. The alumina sintered body can be manufactured by press-molding alumina powder to form a molded body and sintering the formed molded body.

As a result of intensive studies, the present inventors found that in a molded body formed by pressure molding alumina powder at a pressure of 30 MPa, the total pore volume is 0.20 mL/g or less, and the cumulative pore volume of pores with a pore diameter of 1 μm or more. It has been discovered for the first time that if an alumina sintered body is manufactured using an alumina powder that satisfies the condition that pore volume is less than 10% of the total pore volume, an alumina sintered body that is denser than conventional ones can be obtained.
Note that the alumina powder that satisfies the above conditions is denser than conventional ones, not only for molded bodies press-formed at a pressure of 30 MPa, but also for molded bodies press-formed at other pressures (for example, 10 MPa to 1000 MPa). It was found that an alumina sintered body with excellent properties could be obtained.

The alumina powder capable of forming the above-mentioned molded body is obtained by mixing large-sized alumina particles and small-sized alumina particles while crushing them. Examples of such a method include a method of mixing large-sized alumina particles and small-sized alumina particles using a jet mill.

FIG. 1 is a schematic diagram of an alumina powder 10 of the present invention. In the two types of alumina particles mixed by the jet mill, the small-sized alumina particles 11 are bonded to the surfaces of the large-sized alumina particles 12 with sufficient strength. In this specification, particles in which the small-sized alumina particles 11 are bonded to the surfaces of the large-sized alumina particles 12 with sufficient strength are referred to as "alumina composite particles 13" in this specification. In this specification, "bonded with sufficient strength" means that small alumina particles fall off from large alumina particles during normal operations (for example, filling a mold for pressure forming). It is intended not to.
Note that when the alumina composite particles 13 are dispersed in an aqueous solution and subjected to ultrasonic vibration for 5 minutes or more at an ultrasonic intensity of 40 W, many of the alumina composite particles 13 have small-sized alumina particles 11 that become large particles. It falls off from the surface of the alumina particles 12 of the same diameter.

In Patent Document 1, large-sized alumina particles and small-sized alumina particles are diffused and mixed in a mixer (double cone blender). It is presumed that in such diffusion mixing, the large-sized alumina particles and the small-sized alumina particles are simply in contact with each other and are not bonded to each other.

A molded body for examining the characteristics of the alumina powder 10 of the present invention is prepared as follows.
Add 0.04 g of water (equivalent to 1% by mass of alumina powder 10) to 4 g of alumina powder 10 and mix (for example, put alumina powder and water into a bag such as a plastic bag, seal the bag, etc.) shake vigorously up and down to mix. The obtained mixture is loaded into a pellet molding mold (cylindrical shape with an inner diameter of 20 mm) and pressurized at 30 MPa for 30 seconds using a uniaxial press. This yields alumina powder pellets (diameter 20 mm, thickness 4-6 mm). This alumina powder pellet was dried at 120° C. for 4 hours to obtain a molded body for measuring characteristics.

Pore volume and pore radius are measured by mercury intrusion porosimetry (JIS R 1655:2003).
The cumulative amount of mercury that enters the pores is measured while increasing the pressure applied to mercury. Regarding the obtained measurement results, the pressure is converted to the pore radius, and the cumulative amount of penetration is converted to the cumulative pore volume. Then, using the converted values, a graph is created by plotting the cumulative pore volume for the range of pore radius from 100 μm to 0.0018 μm. From this graph, the total pore volume, the cumulative pore volume at a predetermined pore radius, etc. are read.

Here, the "total pore volume of pores with a pore radius of 0.0018 μm or more" (sometimes simply referred to as "total pore volume") refers to the total volume of pores with a pore radius of 0.0018 μm or more. On the graph, this corresponds to the cumulative pore volume at a pore radius of 0.0018 μm.
"Cumulative pore volume of pores with a pore radius of 1 μm or more" (sometimes simply referred to as "cumulative pore volume of 1 μm or more") refers to the total volume of pores with a pore radius of 1 μm or more. On the graph, it corresponds to the cumulative pore volume at a pore radius of 1 μm.
"The ratio of the cumulative pore volume of pores with a pore radius of 1 μm or more to the total pore volume" (sometimes simply referred to as "the ratio of pores with a pore radius of 1 μm or more") is calculated from the following formula (1). do.

Percentage of pores of 1 μm or more = (cumulative pore volume of 1 μm or more) ÷ (total pore volume) × 100 (%) (1)

Most of the alumina composite particles 13 are dispersed in an aqueous solution and subjected to ultrasonic vibration at an ultrasonic intensity of 40 W for 5 minutes or more, thereby forming small-sized alumina particles 11 and large-sized alumina particles. It can be separated into 12 parts. When the particle sizes of the small-sized alumina particles 11 and the large-sized alumina particles 12 after separation were measured, the small-sized alumina particles 11 had a particle size of 0.1 μm or more and less than 1 μm; The alumina particles 12 preferably have a particle size of 1 μm or more and less than 100 μm. The particle size of the small-sized alumina particles 11 is more preferably 0.2 μm or more and less than 0.8 μm, particularly preferably 0.3 μm or more and less than 0.7 μm. The particle size of the large alumina particles 12 is more preferably 3 μm or more and less than 50 μm, particularly preferably 10 μm or more and less than 25 μm.

It is desirable that the alumina powder 10 contains appropriate amounts of each of the small-sized alumina particles 11 and the large-sized alumina particles 12. When a molded body is formed, the large-sized alumina particles 12 mainly have the function of forming the skeleton of the molded body, and the small-sized alumina particles 11 mainly function as large-sized alumina particles. It has the function of filling the gaps between 12 and reducing the size of the pores. In order to more effectively exhibit those functions, it is necessary to increase the content of the small-sized alumina particles 11 in the small-sized alumina particles 11 and the large-sized alumina particles 12 after separating the alumina composite particles 13. It is preferable that the content of the large alumina particles 12 be 5 to 95% by volume. The content of the small-sized alumina particles 11 is more preferably 8 to 70% by volume, particularly preferably 10 to 50% by volume. The content of large-sized alumina particles 12 is more preferably 30 to 92% by volume, particularly preferably 50 to 90% by volume.

Note that the alumina powder 10 may consist only of alumina composite particles 13 that include only small-sized alumina particles 11 and large-sized alumina particles 12, or in addition to the alumina composite particles 13, small-sized alumina particles A small amount of particles 11 and/or large-sized alumina particles 12 (particles that remain independent without being bonded to each other) may be included within a range that does not impair the effects of the present invention. Furthermore, in addition to the alumina composite particles 13 and the small-sized alumina particles 11 and/or the large-sized alumina particles 12, other alumina particles (for example, alumina particles with a particle size of 100 μm or more, and/or Alumina particles (less than 0.1 μm) may be included within a range that does not impair the effects of the present invention.

The particle size and content of the small-sized alumina particles 11 and the large-sized alumina particles 12 contained in the alumina powder 10 are changed by the ultrasonic vibration. After separating, it is measured by laser diffraction dispersion method. First, alumina powder 10 is dispersed in an aqueous solution, and ultrasonic vibration is applied at a vibration intensity of 40 W for 5 minutes or more. Thereby, almost all of the alumina composite particles 13 can be separated into large-sized alumina particles 12 and small-sized alumina particles 11. Thereafter, the particle sizes of the large-sized alumina particles 12 and the small-sized alumina particles 11 dispersed in the solution are measured by a laser diffraction dispersion method.

From the obtained measurement results, a particle size distribution curve (for example, FIG. 2) is created in which the frequency is plotted on the vertical axis and the particle size is plotted on the horizontal axis. In this particle size distribution curve, the peak position in the range of less than 1 μm is defined as the particle size of the small alumina particles 11, and the peak position in the range of 1 μm or more is defined as the particle size of the large alumina particles 12.

It is preferable that at least one peak appears in the particle size distribution curve of the alumina particles in each of the particle size range of less than 1 μm and the particle size range of 1 μm or more. In other words, the alumina powder 10 has large particle size alumina particles 12 and small particle size alumina particles to the extent that peaks clearly appear in the particle size distribution curve in the particle size range of less than 1 μm and in the particle size range of 1 μm or more. 11. This means that the average particle size of the large alumina particles 12 and the average particle size of the small alumina particles 11 are sufficiently different, and that each alumina particle is contained in a sufficient amount. It means that. As a result, the alumina powder 10 has a function of forming the framework of the molded body by the large-sized alumina particles 12, and a function of reducing the pore size in the molded body by the small-sized alumina particles 11. can be demonstrated. The average particle size of the large alumina particles 12 is preferably 5 times or more the average particle size of the small alumina particles.

The content of the small-sized alumina particles 11 and the large-sized alumina particles 12 can be determined from separate particle size distribution curves.
From the particle size measurement results obtained by the laser diffraction dispersion method described above, a particle size distribution curve (for example, FIG. 3) is created in which the vertical axis is the volume-based cumulative distribution and the horizontal axis is the particle size. In this particle size distribution curve, (cumulative distribution value for particle size 1 μm) - (cumulative distribution value for particle size 0.1 μm) is the content of small particles, and (cumulative distribution value for particle size 100 μm) - (cumulative distribution value for particle size 1 μm) Cumulative distribution value) is taken as the content of large particle size.

It is preferable that the alumina powder 10 has a low content of organic matter. If organic matter is contained, when the molded body formed from the alumina powder 10 is fired, the organic matter is decomposed and CO ₂ is generated. The locations where the decomposed organic matter existed become pores in the alumina sintered body after firing.
Therefore, the content of organic matter is preferably less than 1% by mass in terms of C amount. Thereby, the pores inside the alumina sintered body can be reduced.

Note that "C amount conversion (carbon amount conversion)" means that the content of organic matter is expressed as the amount of C (carbon) after burning the organic matter. To measure the content of organic matter (in terms of C content), an NCH quantification device Sumigraph NCH-22F model (manufactured by Sumika Analysis Center) with oxygen circulation combustion and TCD detection method is used. As measurement conditions, carbon components are converted to CO ₂ at a reaction temperature of 850°C, reduced at a reduction temperature of 600°C, and then detected and quantified using a TCD gas chromatograph. At this time, separation is performed using a porous polymer packed column.

Next, a method for manufacturing alumina powder 10 will be explained.
The alumina powder 10 of the present invention includes first alumina particles having a specific surface area of 1.5 m ² /g or more and less than 15 m ² /g, and first alumina particles having a specific surface area of 0.01 m ² /g or more and less than 1.5 m ² /g. It can be manufactured by a method including a step of mixing the alumina particles of No. 2 while crushing them. Examples of such a method include a method including a step (mixing step) of mixing first alumina particles and second alumina particles using a jet mill.
An example of the mixing process will be explained below.

(1) Preparation of alumina particles First alumina particles having a specific surface area of 1.5 m ² /g or more and second alumina particles having a specific surface area of less than 1.5 m ² /g are prepared. The specific surface area of the first alumina particles is preferably 1.5 m ² /g or more and less than 15 m ² /g, more preferably 2 m ² /g or more and less than 10 m ² /g. The specific surface area of the second alumina particles is preferably 0.01 m ² /g or more and less than 1.5 m ² /g, more preferably 0.03 m ² /g or more and less than 1.0 m ² /g.
(2) Premixing The first alumina particles and the second alumina particles are placed in a bag, sealed, and shaken to premix the first alumina particles and the second alumina particles, Get a mixture. When premixing is performed, a portion of the first alumina particles adheres to the surface of the second alumina particles with a weak force.
The blending ratio of the first alumina particles and the second alumina particles to be introduced into the bag is preferably 20:80 to 80:20, more preferably 30:70 to 70:30 in terms of mass ratio. .
(3) Jet mill mixing Alumina powder 10 is obtained by jet mill mixing the mixture).
When mixed with a jet mill, the first alumina particles and the second alumina particles collide during mixing. At that time, the first alumina particles are crushed to become "small particle size alumina particles 11" in the alumina powder 10, and the second alumina particles are crushed to become "large particle size alumina particles 11" in the alumina powder 10. alumina particles 12''. Moreover, the small-sized alumina particles 11 become strongly bonded to the surfaces of the large-sized alumina particles 12.

When the thus obtained alumina powder 10 is pressure-molded into a molded body at a pressure of 30 MPa, the total pore volume is 0.20 mL/g or less, and the cumulative pore volume of pores with a pore diameter of 1 μm or more is Molded bodies with less than 10% of the total pore volume can be obtained.

Note that the alumina particles include, in addition to the first alumina particles and the second alumina particles, other alumina particles (for example, alumina particles with a particle size of 100 μm or more and/or alumina particles with a particle size of less than 0.1 μm). May include. Other alumina particles (referred to as "third alumina particles") are preferably mixed with the first alumina particles and the second alumina particles in a jet mill. For example, in "(1) Preparation of alumina particles", not only the first alumina particles and the second alumina particles but also the third alumina particles are prepared, and in "(2) Premixing", the third alumina particles are prepared. The particles are premixed in a bag with the first alumina particles and the second alumina particles to obtain a mixture of the first alumina particles, the second alumina particles and the third alumina particles. In "(3) jet mill mixing", the alumina powder 10 can be obtained by mixing the obtained mixture with a jet mill.

(1) Production of alumina powder sample The production conditions of the alumina powder used in Examples 1 and 2 and Comparative Examples 1 to 4 are described below. Table 1 also lists the blending ratios and mixing methods of the first alumina particles and second alumina particles in Examples 1 to 2 and Comparative Examples 1 to 4. In the column of mixing method in Table 1, "JM mixing" means that mixing was performed using a jet mill pulverizer, and "-" means that no mixing was performed.

α-alumina seed particles with an average particle size of 0.25 μm are mixed with high-purity aluminum hydroxide obtained by the hydrolysis method of aluminum alkoxide, and by firing in a hydrogen chloride atmosphere, a specific surface area of 4.8 m ² is obtained. /g of first alumina particles were obtained. High purity aluminum hydroxide obtained by an aluminum alkoxide hydrolysis method was calcined in a hydrogen chloride atmosphere to obtain second alumina particles with a specific surface area of 0.2 m ² /g. The first alumina particles and the second alumina particles were blended at a mass ratio of 20:80, put into a plastic bag, and after the plastic bag was sealed, they were shaken strongly up and down to diffuse and mix. Thereafter, the alumina powder sample P1 of Example 1 was prepared by mixing while pulverizing with a jet mill pulverizer (horizontal jet mill pulverizer PJM-280SP manufactured by Japan Pneumatic Industries Co., Ltd.).

(Example 2)
Example 2 is the same as Example 1 except for the mixing ratio of the first alumina particles and the second alumina particles.
The first alumina particles and the second alumina particles were blended at a mass ratio of 30:70 and put into a plastic bag, and after the plastic bag was sealed, they were strongly shaken up and down to diffuse and mix. Thereafter, the resulting mixture was mixed while being ground with a jet mill (horizontal jet mill PJM-280SP manufactured by Japan Pneumatic Industries Co., Ltd.) to prepare alumina powder sample P2 of Example 2.

(Comparative example 1)
The first alumina particles and the second alumina particles were each separately pulverized using a jet mill pulverizer (horizontal jet mill pulverizer PJM-380SP manufactured by Japan Pneumatic Industries Co., Ltd.). The first alumina particles and second alumina particles after pulverization were mixed at a mass ratio of 20:80, put into a plastic bag, and after sealing the plastic bag, they were shaken strongly up and down to diffuse and mix, and then compared. Alumina powder sample P3 of Example 1 was prepared.

(Comparative example 2)
Comparative Example 2 is the same as Comparative Example 1 except for the mixing ratio of the first alumina particles and the second alumina particles after pulverization.
The first alumina particles and the second alumina particles were each separately pulverized using a jet mill pulverizer (horizontal jet mill pulverizer PJM-380SP manufactured by Japan Pneumatic Industries Co., Ltd.). The first alumina particles and the second alumina particles after pulverization were mixed at a mass ratio of 30:70, put into a plastic bag, and after sealing the plastic bag, they were strongly shaken up and down to diffuse and mix. Alumina powder sample P4 of Example 1 was prepared.

(Comparative example 3)
Only the second alumina particles were pulverized with a jet mill pulverizer (horizontal jet mill pulverizer PJM-380SP manufactured by Japan Pneumatic Industries Co., Ltd.) to prepare alumina powder sample P5 of Comparative Example 3. That is, in Comparative Example 3, the first alumina particles were not blended or mixed.

(Comparative example 4)
Only the first alumina particles were pulverized with a jet mill pulverizer (horizontal jet mill pulverizer PJM-380SP manufactured by Japan Pneumatic Industries Co., Ltd.) to prepare alumina powder sample P6 of Comparative Example 3. That is, in Comparative Example 4, the second alumina particles were not blended or mixed.

（２）アルミナ粉末試料の粒度分布測定
アルミナ粉末試料Ｐ１～Ｐ６について、粒度分布を測定した。
粒度分布測定は、レーザ粒度分布測定装置〔マイクロトラック・ベル（株）製「マイクロトラックＭＴ３３００ＥＸII」〕を用いて行った。測定するアルミナ粉末を０．２質量％のヘキサメタ燐酸ソーダ水溶液（以下「分散液」とも称する）に少量添加し、装置内蔵の超音波に４０Ｗで５分間かけて、アルミナ粒子を分散させた。なお、アルミナの屈折率は１．７６とした。

(2) Measurement of particle size distribution of alumina powder samples Particle size distribution was measured for alumina powder samples P1 to P6.
The particle size distribution measurement was performed using a laser particle size distribution measuring device [Microtrac MT3300EXII, manufactured by Microtrac Bell Co., Ltd.]. A small amount of the alumina powder to be measured was added to a 0.2% by mass sodium hexametaphosphate aqueous solution (hereinafter also referred to as "dispersion"), and the alumina particles were dispersed by applying ultrasonic waves built into the device at 40 W for 5 minutes. Note that the refractive index of alumina was 1.76.

Alumina powder samples P1 and P2 of Examples 1 and 2 contained alumina composite particles 13 (particles in which small-sized alumina particles 11 and large-sized alumina particles 12 were combined). The alumina composite particles 13 did not separate even after adding the dispersion liquid, but were separated into small-sized alumina particles 11 and large-sized alumina particles 12 by performing ultrasonic dispersion.
In the alumina powder samples P3 and P4 of Comparative Examples 1 and 2, the small-sized alumina particles 11 and the large-sized alumina particles 12 were in contact with each other. When the dispersion liquid was added, the particles in contact with each other in alumina powders P3 and P4 were easily separated into small-sized alumina particles 11 and large-sized alumina particles 12.
Alumina powder sample P5 of Comparative Example 3 consisted only of large-sized alumina particles 12. Since the particles were only in contact with each other, they were easily separated when the dispersion was added.
Alumina powder sample P6 of Comparative Example 4 consisted only of alumina particles 11 of small particle size. Since the particles were only in contact with each other, they were easily separated when the dispersion was added.

In the particle size distribution obtained by laser diffraction method, with frequency on the vertical axis and particle size on the horizontal axis, the peak position in the range of less than 1 μm, the particle size of small particles, and the peak position in the range of 1 μm or more, The particle size was taken as the large particle size. The particle size distribution curve shown in Figure 3 is a particle size distribution obtained by laser diffraction, with the vertical axis representing the volume-based cumulative distribution and the horizontal axis representing the particle size. Cumulative distribution value) - (cumulative distribution value for particle size 0.1 μm) is the content (volume %) of small particle size, and (cumulative distribution value for particle size 100 μm) - (cumulative distribution value for particle size 1 μm) is large. It was defined as the particle size content (volume %).

(3) Preparation of molded sample for measurement In order to examine the characteristics of alumina powder samples P1 to P6, molded samples for measurement were prepared.
Separate 4g of each alumina powder sample, add 0.04g of water (equivalent to 1% by mass of the alumina powder sample), put it in a plastic bag, seal the bag, and shake it vigorously up and down to spread it. mixed. The obtained mixture is loaded into a pellet molding mold (cylindrical shape with an inner diameter of 20 mm) and pressurized at 30 MPa for 30 seconds using a uniaxial press. This yields alumina powder pellets (diameter 20 mm, thickness 4-6 mm). This alumina powder pellet was dried at 120° C. for 4 hours to obtain a molded sample for measurement.

(4) Pore distribution measurement of molded body sample After drying the molded body sample at 120° C. for 4 hours, it was measured by mercury intrusion method (JIS R 1655:2003) using Autopore IV9520 (manufactured by Micromeritics). Measurements were carried out in the range of pore radius from 100 μm to 0.0018 μm. Based on the measurement results, a graph was plotted with the horizontal axis representing the pore radius and the vertical axis representing the cumulative pore volume. The plotted graph is shown in FIG.
The cumulative pore volume at a pore radius of 1 μm (cumulative pore volume of pores with a pore radius of 1 μm or more) was defined as “cumulative pore volume (A) of 1 μm or more”.
The cumulative pore volume at 0.0018 μm (total pore volume of pores with a pore radius of 0.0018 μm or more) was defined as “total pore volume (B)”.
The "ratio of pores with a pore radius of 1 μm or more (A/B×100)" (ratio of pores with a pore radius of 1 μm or more) was calculated from the following formula (1).

Percentage of pores of 1 μm or more = (cumulative pore volume of 1 μm or more) ÷ (total pore volume) × 100 (%) (1)

For the molded body samples C1 to C6 molded from each of the alumina powder samples P1 to P6, the cumulative pore volume (A) of 1 μm or more, the total pore volume (B), and the ratio of pores of 1 μm or more (A/ B×100) measurement results are listed in Table 2.

(5) Measurement of bulk density of alumina sintered bodies Six molded body samples C1 to C6 molded from each of the alumina powder samples P1 to P6 were prepared, and the bulk density of the molded bodies and alumina sintered bodies was measured. It was measured.
Five of the six molded body samples prepared for each molded body sample C1 to C6 were fired at different firing temperatures (1100°C, 1200°C, 1300°C, 1400°C, and 1500°C). After raising the temperature to the firing temperature at a heating rate of 200° C./hour, the firing temperature was maintained for 5 hours to obtain an alumina sintered body sample.
One of the six molded body samples was a molded body sample before firing.

The bulk density was measured for the alumina sintered body sample and the molded body sample before firing.
The bulk density of the alumina sintered sample was measured by the Archimedes method (JIS R 1634:1998).
The bulk density of the molded body sample before firing was calculated as follows. First, the mass of the molded sample was measured using an electronic balance. Next, the thickness and diameter of the molded sample were measured with calipers, and the volume was calculated. The bulk density of the molded body sample before firing was determined by dividing the mass by the volume.

Table 3 and FIG. 5 show the bulk densities of the molded body sample and the alumina sintered body sample before firing.
If the bulk density of the compact before firing is high (that is, the particles are tightly packed at the time of forming the compact), it will be difficult to shrink after sintering. In this example, a sample having a bulk density of 2.50 g/cm ³ or more before firing was considered to be acceptable.
Further, in order for the alumina sintered body to have sufficient strength, the bulk density of the alumina sintered body must be high to some extent. In this example, an alumina sintered sample sintered at 1500° C. whose bulk density was 2.80 g/cm ^{3 or} more was considered to be acceptable.

(6) Measurement of particle size distribution curve of alumina particles The alumina powders of Examples 1 and 2 and Comparative Examples 1 and 2 were measured using a laser particle size distribution measuring device [Microtrack: MT-3300, manufactured by Nikkiso Co., Ltd.]. , the particle size distribution was measured by laser diffraction method. The particle size distribution curve is shown in FIG.

Examples 1-2 and Comparative Examples 1-4 are discussed below.
Alumina powder sample P1 of Example 1 and alumina powder sample P2 of Example 2 were manufactured by mixing first alumina particles and second alumina particles by jet mill mixing. Therefore, the molded body sample C1 obtained by pressure molding the obtained alumina powder sample P1 at a pressure of 30 MPa and the molded body sample C2 obtained by pressure molding the alumina powder sample P2 at a pressure of 30 MPa both have a total pore volume of 0. The cumulative pore volume of pores with a pore diameter of 1 μm or more was less than 10% of the total pore volume.
When molded body sample C1 and molded body sample C2 were sintered, alumina sintered body samples with high bulk density were obtained. Thus, it was found that by using alumina powder sample P1 of Example 1 or alumina powder sample P2 of Example 2, a dense alumina sintered body could be manufactured.

Alumina powder sample P3 of Comparative Example 1 and alumina powder sample P4 of Comparative Example 2 were manufactured by mixing first alumina particles and second alumina particles by diffusion mixing. Therefore, molded body sample C3 obtained by pressure molding the obtained alumina powder sample P3 at a pressure of 30 MPa and molded body sample C4 obtained by pressure molding the alumina powder sample P4 at a pressure of 30 MPa both have pores with a radius of 1 μm or more. There were many pores, and the condition that "the cumulative pore volume of pores with a pore diameter of 1 μm or more is less than 10% of the total pore volume" was not satisfied. As a result, when molded body sample C3 and molded body sample C4 were sintered, alumina sintered body samples with low bulk density were obtained.

Alumina powder sample P5 of Comparative Example 3 contained only the second alumina particles and did not contain the first alumina particles. Molded body sample C5 obtained by pressure molding alumina powder sample P5 at a pressure of 30 MPa had many pores with a pore radius of 1 μm or more and a large total pore amount. Therefore, neither the condition that "the total pore volume is 0.20 mL/g or less" nor the condition that "the cumulative pore volume of pores with a pore diameter of 1 μm or more is less than 10% of the total pore volume" were satisfied.

Alumina powder sample P5 of Comparative Example 4 contained only the first alumina particles and did not contain the second alumina particles. Molded body sample C5 obtained by pressure molding alumina powder sample P6 at a pressure of 30 MPa had a large total pore amount. Therefore, the condition of "total pore volume of 0.20 mL/g or less" was not satisfied.

Regarding the particle size distribution curve shown in FIG. 6, in each of the alumina powders of Examples 1 and 2 and Comparative Examples 1 and 2, there is at least one particle in each of the particle size range of less than 1 μm and the particle size range of 1 μm or more. peak was confirmed.

In this way, the total pore volume of the molded product pressure-molded at a pressure of 30 MPa is 0.20 mL/g or less, and the cumulative pore volume of pores with a pore diameter of 1 μm or more is less than 10% of the total pore volume. By using alumina powder that satisfies the conditions, a dense alumina sintered body can be manufactured.

10 Alumina powder 11 Small-sized alumina particles 12 Large-sized alumina particles 13 Alumina composite particles

Claims (6)

An alumina powder containing a plurality of alumina particles,
The plurality of alumina particles include alumina composite particles,
The alumina particles after separating the alumina composite particles are:
5 to 95% by volume of alumina particles with a particle size of 1 μm or more and less than 100 μm,
Contains 5 to 95% by volume of alumina particles with a particle size of 0.1 μm or more and less than 1 μm,
The alumina powder includes first alumina particles having a specific surface area of 1.5 m ² /g or more and less than 15 m ² /g, and second alumina particles having a specific surface area of 0.01 m ² /g or more and less than 1.5 m ² /g. It is made by mixing particles with a mass ratio of 20:80 to 30:70,
In the molded body obtained by pressure-molding the alumina powder at a pressure of 30 MPa, the total pore volume is 0.20 mL/g or less, and the cumulative pore volume of pores with a pore diameter of 1 μm or more is less than 10% of the total pore volume. Alumina powder. The alumina powder according to claim 1, wherein the molded body obtained by pressure molding the alumina powder at a pressure of 30 MPa has a total pore volume of less than 0.157 mL/g. The alumina powder according to claim 1 or 2, wherein the molded body obtained by pressure molding the alumina powder at a pressure of 30 MPa has a total pore volume of 0.130 to 0.133 mL/g. The alumina particles after separating the alumina composite particles are:
50 to 90% by volume of alumina particles with a particle size of 1 μm or more and less than 100 μm,
Contains 10 to 50% by volume of alumina particles with a particle size of 0.1 μm or more and less than 1 μm,
Alumina powder according to any one of claims 1 to 3. The particle size distribution curve of the alumina particles after separation shows at least one peak in each of the particle size range of less than 1 μm and the particle size range of 1 μm or more, according to any one of claims 1 to 4. Alumina powder. The alumina powder according to any one of claims 1 to 5, wherein the content of organic matter is less than 1% by mass in terms of C content.

Images