JP2018162202A - Method for producing bismuth ruthenate powder and bismuth ruthenate powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: In view of the problems of the prior art in the lead-free resistor composition, as a conductive material for thick film resistors, an average particle diameter and a crystallite diameter of approximately 20 nm or more and 100 nm or less are substantially the same. Provided is a method for producing a bismuth ruthenate powder having the obtained bismuth ruthenate powder. SOLUTION: A method for producing bismuth ruthenate powder, comprising mixing a ruthenium compound powder and a vitreous material powder containing 80% by mass or more of a bismuth oxide, and melting at 600 ° C. to 750 ° C. in an atmosphere containing oxygen. A first step of forming a heat-treated heat-treated product in which bismuth ruthenate particles are precipitated in a glassy material by heat treatment; and a second step of separating the bismuth-ruthenate particles by dissolving the molten heat-treated product with an acid. The manufacturing method of the bismuth ruthenate powder characterized by including. [Selection] Figure 1

Description

  The present invention relates to a method for producing bismuth ruthenate powder by obtaining bismuth ruthenate particles by melt heat treatment, and a bismuth ruthenate powder obtained by the production method.

  Thick film resistors are widely used in chip resistors, thick film hybrid ICs, resistor networks, and the like. As a method for producing the thick film resistor, usually, a paste in which conductive powder is uniformly dispersed is printed on a conductor circuit pattern or electrode formed on the surface of an insulating substrate, and this is fired. Is used.

The paste used for manufacturing the thick film resistor is manufactured such that conductive particles and glass binder such as glass frit are uniformly dispersed in an organic medium called a vehicle. Among these, the conductive particles play the most important role in determining the electrical characteristics of the thick film resistor, and fine powders of ruthenium oxide (RuO ₂ ) or lead ruthenate (Pb ₂ Ru ₂ O ₇ ) are widely used. Yes.
In general, ruthenium oxide is used as a conductor in a wide range from a low resistance value to a high resistance value, and in particular, in the high resistance region, lead ruthenate having a smaller variation in the resistance value with respect to the conductor concentration is often used.

By the way, a thick film resistor can be obtained by kneading conductive particles and glass particles in a paste, printing, and firing. After firing, the conductive particles form a conductive path along the grain boundary of the glass, and a resistance value is obtained.
Adjustment for obtaining the set resistance value is performed mainly by changing the mixing ratio of the conductive material and the glass frit.
Therefore, in order to form a conductive path and obtain good resistance characteristics, it is necessary to set the particle diameter of the conductive particles (average particle diameter by SEM observation or the like) to 100 nm or less. When the average particle diameter exceeds 100 nm, the conductive path is not sufficiently formed, and the resistance value becomes abnormally high, for example, the resistance characteristics cannot be sufficiently obtained.

  On the other hand, in recent years, there has been a demand for eliminating the use of toxic lead from electronic devices, so that lead-free conductive particles instead of lead ruthenate powder used as conductive particles for thick film resistors in the high resistance region have been developed. It is desired. In addition, in order to completely remove lead from the thick film resistor, it is necessary to exclude lead from the glass binder used at the same time. A conductive powder that can provide the properties is required.

As a solution to this problem, Patent Document 1 proposes a resistor paste using iridium oxide powder. However, iridium is expensive and an inexpensive ruthenium compound is required. Therefore, various ruthenium composite oxide powders for conductive powders represented by chemical formulas such as Bi ₂ Ru ₂ O ₇ , CaRuO ₃ , SrRuO ₃ , BaRuO ₃ , LaRuO ₃ have been proposed.

In addition, as a method for producing bismuth ruthenate powder, as disclosed in Patent Document 2 and Patent Document 3, RuO ₂ powder and Bi ₂ O ₃ powder are mixed and 650 ° C. to 950 in an air atmosphere. Examples thereof include a method of roasting at 0 ° C. and a method of co-precipitating a ruthenium salt and a bismuth salt disclosed in Patent Document 4 and baking the dried product at 700 ° C. to 900 ° C.

  However, in any of the methods, particle size coarsening exceeding the crystallite diameter of 100 nm is unavoidable due to the progress of abnormal grain growth and sintering aggregation between particles in the roasting step for reaction.

JP 2007-277040 A Japanese Patent Publication No.51-28353 JP 2007-208033 A JP-A-4-26519

  In view of the problems of the prior art in such a lead-free resistor composition, the present invention has an average particle diameter and crystallite diameter of approximately 20 nm or more and 100 nm or less as a conductive material for thick film resistors. The present invention provides a method for producing a bismuth ruthenate powder having a crystallite diameter and also provides a bismuth ruthenate powder obtained.

  The first invention of the present invention is a method for producing bismuth ruthenate powder, in which a ruthenium compound powder and a vitreous material powder containing bismuth oxide in an amount of 80% by mass or more are mixed and 600 ° C. in an atmosphere containing oxygen. A first step of forming a melt heat-treated product in which bismuth ruthenate particles are precipitated in a glassy material by melting and heat-treating at 750 ° C., and separating the bismuth ruthenate particles by dissolving the melt-heat treated product with an acid. The manufacturing method of the bismuth ruthenate powder characterized by including the 2nd process to do.

  According to a second aspect of the present invention, there is provided a method for producing bismuth ruthenate powder, wherein the vitreous substance powder in the first aspect is a bismuth glass frit having a softening point of 450 ° C. or lower.

  A third invention of the present invention is a method for producing a bismuth ruthenate powder, wherein the bismuth glass frit according to the second invention has a softening point of 300 ° C. or higher and 450 ° C. or lower.

  According to a fourth invention of the present invention, the ruthenium compound powder in the first to third inventions is an amorphous ruthenium oxide hydrate powder or a crystallite obtained from a peak of (110) plane in powder X-ray diffraction A method for producing a bismuth ruthenate powder, wherein the ruthenium oxide powder has a diameter of 20 nm or less.

  In the fifth aspect of the present invention, the half width determined from the peak of the (111) plane in powder X-ray diffraction is in the range of 0.16 to 0.48 °, and the crystallite diameter is 20 nm or more and 100 nm. It is a bismuth ruthenate powder characterized by the following.

  A sixth invention of the present invention is a bismuth ruthenate powder characterized in that an average particle size determined from an FE-SEM image of the bismuth ruthenate powder in the fifth invention is 20 nm or more and 100 nm or less.

  According to the present invention, there is provided a bismuth ruthenate powder having an average particle diameter and a crystallite diameter of approximately 20 nm or more and 100 nm or less, which can be used as a lead-free thick film resistor forming conductor. It can be obtained, greatly contributes to deleading of electronic equipment, and has an industrially significant effect.

2 is an FE-SEM image of bismuth ruthenate particles obtained in Example 1. FIG. 2 is an XRD diffractogram of bismuth ruthenate particles obtained in Example 1. FIG.

  In the method for producing bismuth ruthenate powder according to the present invention, a mixture of a ruthenium compound powder and a vitreous substance powder containing 80% by mass or more of a bismuth oxide is heated to 600 ° C. to 750 ° C. in an oxygen-containing atmosphere. A first step of forming a melt heat-treated product by melting and heat-treating bismuth ruthenate particles in the glass; and a second step of separating the ruthenium bismuth particles by dissolving the melt-treated heat product with an acid. It is characterized by that.

  The method for producing bismuth ruthenate powder according to the present invention is based on an oxide solid phase reaction represented by the following formula (1).

[First step]
First, the first step of depositing bismuth ruthenate as particles inside the glassy substance will be described.
That is, nucleation and growth of particles of bismuth ruthenate are allowed to proceed inside the molten glass by raising the glass to a temperature higher than the melting temperature. By this means, molten glass having a high viscosity of precipitated particles. By being protected within the material, sintering of the particles is suppressed, and a single crystal monodispersed powder is obtained.

(Formulation)
It is desirable to use amorphous ruthenium oxide hydrate powder or ruthenium oxide powder having a crystallite diameter of 20 nm or less as the ruthenium source.
Amorphous ruthenium oxide hydrate powder is obtained by adding an acid solution to an alkaline solution containing ruthenium ions to obtain a ruthenium hydroxide precipitate, which is washed with water, separated into solid and liquid, and dried. As a result, ruthenium oxide hydrate powder is formed.
The formed ruthenium oxide hydrate powder is confirmed to be amorphous with no diffraction peak observed from XRD diffraction, and amorphous ruthenium oxide hydrate powder is obtained.

When this amorphous ruthenium oxide hydrate powder is roasted at a temperature of 350 ° C. to 400 ° C. for 15 minutes to 120 minutes in an air atmosphere, water is removed from the ruthenium oxide hydrate powder and ruthenium oxide (RuO oxide) is detected by X-ray diffraction. The peak of ₂ ) is confirmed.
When the crystallite diameter is calculated from the half width of the (110) plane of the X-ray diffraction of the obtained ruthenium oxide, it can be confirmed that the ruthenium oxide is a fine ruthenium oxide of 20 nm or less.

  In the method for producing bismuth ruthenate powder according to the present invention, ruthenium oxide having a crystallite diameter of 20 nm or less may be formed before the ruthenium source and the bismuth source react, and the ruthenium oxide having a crystallite diameter exceeding 20 nm. When the powder is used, the crystallite diameter of the obtained bismuth ruthenate powder tends to be larger than 100 nm.

As the bismuth source, a glassy material in which bismuth oxide (Bi ₂ O ₃ ) is blended by 80% by mass or more in terms of oxide is used.
Since it is a glassy substance, it is not necessary to provide a glass transition. It is desirable to use bismuth glass frit as an example of a glassy substance. By using the bismuth glass frit, it becomes glass melted by the below-described melting heat treatment, whereby the bismuth ruthenate particles can be precipitated, and further the growth of the particles can be suppressed.
This is because if the bismuth oxide (Bi ₂ O ₃ ) is less than 80% by mass, the reaction with the ruthenium source does not proceed in the melt heat treatment, and bismuth ruthenate does not precipitate.

As composition of bismuth glass frit, bismuth oxide (Bi ₂ O ₃ ) may be blended in an amount of 80% by mass or more, zinc oxide (ZnO ₂ ) 5 to 15% by mass, boron oxide (B ₂ O ₃ ) 5 to 5%. 15% by mass, silicon oxide (SiO ₂ ) and aluminum oxide (Al ₂ O ₃ ) can be contained.
With such a composition of bismuth glass frit, even if bismuth ruthenate particles are precipitated and bismuth atoms in the glass are consumed for precipitation of bismuth ruthenate particles, nitric acid or the like is used in the second step of the next step. Dissolve in acid.

The softening point of the bismuth glass frit is 450 ° C. or lower, desirably 300 ° C. to 450 ° C., more preferably 350 ° C. to 450 ° C.
If the softening point is higher than 450 ° C., the glass is not sufficiently softened and the precipitation reaction of bismuth ruthenate in the glass does not proceed sufficiently. In addition, a softening point is measured and evaluated by thermogravimetric / differential thermal analysis (TG-DTA) under conditions of a heating rate of 10 ° C./min in an air atmosphere.
In addition, when amorphous ruthenium oxide hydrate is used for the ruthenium source, the softening point of the glass is more preferably 350 ° C. to 450 ° C. in consideration of the removal of water when changing from amorphous ruthenium oxide to ruthenium oxide.

The bismuth glass frit is prepared by mixing the above-exemplified oxides with the above-mentioned mixing ratio, mechanically mixing them with a crusher or the like, and then putting them in a platinum crucible or the like and charging them into a firing furnace. After melting at 0 ° C. to obtain glass cullet, vitrification is performed by rapid cooling. The vitrified product is roughly pulverized with a crush mill or the like and finely pulverized with a ball mill or the like.
The 50% volume cumulative particle size of the particle size distribution meter using laser diffraction of glass frit is 10 μm or less, preferably 5 μm or less. When it is larger than 10 μm, it is difficult to be uniform when mixed with the ruthenium source, and the generated particles are easily segregated by the subsequent heat treatment.

(Melting heat treatment)
Ruthenium source amorphous ruthenium hydrate or ruthenium oxide powder and bismuth glass frit are mixed in a known manner. It can be made into a mixed powder using a mechanical dry mixing device such as a grinder. As a more uniform mixing method, the ruthenium compound may be added and mixed at the same time when pulverizing with a ball mill of bismuth glass.

  The mixing ratio of the amorphous ruthenium hydrate or ruthenium oxide powder and the bismuth glass frit is such that the glass frit is 70% by weight or more in terms of the dry powder ratio. When the glass frit is less than 70% by weight, the effect of suppressing the sintering of bismuth ruthenate particles by the glass becomes small, and the generation and coarsening of aggregated particles become remarkable.

The prepared mixture powder is put in, for example, an alumina crucible, charged in a firing furnace, and melt-heat treated at 600 ° C. to 750 ° C. in an atmosphere containing oxygen such as an air atmosphere.
The melt heat treatment holding time may be about 30 minutes to 2 hours, and may be set by taking the batch size into consideration and setting the end of the reaction of the product as a guide.
As the melting heat treatment temperature increases, the crystallite size of the bismuth ruthenate particles tends to increase. When the temperature is lower than 600 ° C., bismuth ruthenate is not sufficiently formed. When the temperature exceeds 750 ° C., the crystallite diameter becomes 100 nm or more.

[Second step]
The second step of taking out the bismuth ruthenate particles precipitated in the glassy substance will be described.

(Acid cleaning)
Remove the crucible from the firing furnace and cool. When the crucible and the water are rapidly cooled, the melt can be easily recovered from the crucible, for example, as glass cullet.
The recovered melt is dissolved in a dilute nitric acid aqueous solution having a concentration of 30% or less.
Solid-liquid separation by decantation, acid cleaning with dilute nitric acid aqueous solution to remove glass components.
Thereafter, filtration and washing are repeated a plurality of times to remove nitric acid, and the taken out particles are separated by filtration and dried to obtain a bismuth ruthenate powder having a crystallite diameter of 20 nm to 100 nm.

(Busmuth ruthenate powder)
The bismuth ruthenate powder obtained by the method for producing bismuth ruthenate powder according to the present invention, that is, the bismuth ruthenate powder according to the present invention has a chemical formula identified by powder X-ray diffraction of Bi ₂ Ru ₂ O ₇ and Bi ₂ Ru. _One phase of any of ₂ O _6.92 , Bi _1.9 Ru ₂ O _6.922 , Bi _1.87 Ru ₂ O _6.903 , Bi ₂ Ru ₂ O _7.3 , Bi ₃ Ru ₃ O ₁₁ Yes, the average particle diameter of each particle constituting the bismuth ruthenate powder determined from the FE-SEM image (field emission scanning electron microscope) is 20 nm or more and 100 nm or less, and the (111) plane in powder X-ray diffraction The half width determined from the peak is in the range of 0.16 to 0.48 °, and the crystallite diameter determined from the half width is 20 nm to 100 nm.
That is, the fact that the average particle diameter and the crystallite diameter obtained from the FE-SEM image are substantially equal means that the bismuth ruthenate powder is a single crystal.

By the way, in the conductive particles that play the role of forming a conductive path as a thick film resistor, it is necessary to control the average particle diameter by SEM observation or the like to 100 nm or less in order to obtain good electrical characteristics, and there is no variation. In order to obtain electrical characteristics, more uniform and monodispersed conductive particles are required.
When the average particle diameter exceeds 100 nm, the conductive path is not sufficiently formed, and the resistance value becomes abnormally high, for example, the resistance characteristics cannot be sufficiently obtained. When the particle diameter is finer than 20 nm, the resistance characteristic is good, but the powder activity due to the increase of the specific surface area becomes large, which may cause a problem in the viscosity stability of the paste. By using single crystal monodispersed particles of 20 to 100 nm, conductive particles excellent in dispersibility and stability can be obtained.

So far, the present invention has been described mainly on the method for producing bismuth ruthenate according to the present invention. Below, the effect of this invention is demonstrated by contrast with a prior art.
In the method for producing bismuth ruthenate disclosed in Patent Documents 2 and 3, it is necessary to add mechanical pulverization such as a ball mill or a bead mill in order to reduce the particle size to 100 nm or less. Impurities are inevitable due to wear. Further, mechanical pulverization damages the crystals of the bismuth ruthenate powder, resulting in polycrystalline bismuth ruthenate powder.

The method disclosed in Patent Document 4 is the same in that the coprecipitated powder is roasted, and the coprecipitated powder containing ruthenium and bismuth is likely to undergo particle growth in the roasting process, and coarse particles exceeding 1 μm are generated. There were problems such as easy to do. That is, with such a roasting method, it is difficult to obtain bismuth ruthenate particles having a uniform size as long as there is physical contact between the particles during firing.
Thus, according to the method for producing bismuth ruthenate according to the present invention, single crystal bismuth ruthenate powder having a crystallite diameter of 20 nm to 100 nm can be obtained.

Hereinafter, the present invention will be described in more detail by way of examples and comparative examples of the present invention, but the present invention is not limited to these examples. In addition, it is as follows about the measuring method of the FE-SEM average particle diameter used by the Example and the comparative example, the specific surface area, a structure | tissue, and crystallinity, and the calculation method of a crystallite diameter.

(1) Measurement of average particle size of bismuth ruthenate powder:
The particle shape was observed using a Hitachi SEM S-4800 FE-SEM apparatus, and 100 particles were randomly measured from a field of view of 100,000 times to obtain an FE-SEM average particle diameter.
(2) Specific surface area:
Specific surface area was determined by the BET single point method using a Macsorb HM Model-1208 manufactured by Mounteh. The degassing conditions were a temperature of 200 ° C. and a duration of 30 minutes.
(3) Identification of the structure of the roasted product:
X-ray diffraction apparatus Identification was performed using an X'Pert-Pro (PANallytical) apparatus.
(4) Crystallinity (half width):
X-ray diffractometer The peak half-value width of the ruthenium oxide (110) plane and the (111) plane of bismuth ruthenate was determined using an X'Pert-Pro (PANallytical) apparatus.
(5) Crystallite diameter:
Based on the half-width of the diffraction line obtained in (4) above, the crystallite diameter of the (111) plane was calculated using Scherrer's equation. For the calculation, crystalline Si powder was used as a standard sample.

The ruthenium compounds used in the examples and comparative examples of the present invention are shown in Table 1.
“R-1” is a dried amorphous ruthenium oxide hydrate obtained by dissolving metal ruthenium powder in a sodium hypochlorite solution and a potassium hydroxide solution and adding nitric acid.
“R-2” is a ruthenium oxide powder obtained by baking the above “R-1” at 400 ° C.
“R-3” is a ruthenium oxide powder obtained by baking the above “R-1” at 850 ° C.
When the crystallite diameter was confirmed on the XRD explanation (110) plane, “R-1” was amorphous, “R-2” was 15 nm, and “R-3” was 22 nm.

Table 2 shows the compositions of the bismuth-containing glass frit used in Examples and Comparative Examples of the present invention.
The compositions from “G-1” to “G-5” and the glass softening point are shown.

  10% by weight of ruthenium compound powder and 90% by weight of glass frit containing bismuth are weighed, mixed for 2 hours using a crusher q1, put into an alumina crucible, and heated at a roasting temperature shown in Table 3 in a firing furnace. The melt heat treatment was carried out for a period of time, then removed from the furnace, put into water and quenched. The roasting atmosphere is air.

The recovered melt was dissolved in glass with a 20% aqueous nitric acid solution.
Solid-liquid separation by decantation, acid washing with 5% nitric acid aqueous solution and filtration, and washing with warm water were repeated a predetermined number of times to separate the powder by filtration. This was dried at 110 ° C. to obtain a powder.
Thereafter, the above characteristics were evaluated, and the results are shown in Table 3, FIG. 1 and FIG.
1 and 2 show an FE-SEM image (FIG. 1) and XRD diffraction results (FIG. 2) of bismuth ruthenate particles obtained in Example 1. FIG.
Hereinafter, the results obtained by changing the implementation conditions from Example 1 will be described.

A sample material according to Example 2 was obtained and evaluated under the same conditions as in Example 1 except that the glass frit was changed to “G-2”.
The results are summarized in Table 3.

A test material according to Example 3 was obtained and evaluated under the same conditions as in Example 1 except that the ruthenium compound was changed to “R-2”.
The results are summarized in Table 3.

A test material according to Example 4 was obtained and evaluated under the same conditions as in Example 1 except that the roasting temperature was changed to “600 ° C.”.
The results are summarized in Table 3.

A test material according to Example 5 was obtained and evaluated under the same conditions as in Example 1 except that the roasting temperature was changed to “650 ° C.”.
The results are summarized in Table 3.

A test material according to Example 6 was obtained and evaluated under the same conditions as in Example 1 except that the roasting temperature was changed to “750 ° C.”.
The results are summarized in Table 3.

(Comparative Example 1)
A sample material according to Comparative Example 1 was obtained and evaluated under the same conditions as in Example 1 except that the glass frit was changed to “G-3”.
The results are summarized in Table 3.

(Comparative Example 2)
A test material according to Comparative Example 2 was obtained and evaluated under the same conditions as in Example 1 except that the glass frit was changed to “G-4”.
The results are summarized in Table 3.

(Comparative Example 3)
A test material according to Comparative Example 3 was obtained and evaluated under the same conditions as in Example 1 except that the glass frit was changed to “G-5”.
The results are summarized in Table 3.

(Comparative Example 4)
A test material according to Comparative Example 4 was obtained and evaluated under the same conditions as in Example 1 except that the ruthenium compound was changed to “R-3”.
The results are summarized in Table 3.

(Comparative Example 5)
A test material according to Comparative Example 5 was obtained and evaluated under the same conditions as in Example 1 except that the roasting temperature was changed to a low temperature of “550 ° C.”.
The results are summarized in Table 3.

(Comparative Example 6)
A test material according to Comparative Example 6 was obtained and evaluated under the same conditions as in Example 1 except that the roasting temperature was changed to a high temperature of “800 ° C.”.
The results are summarized in Table 3.

  As is clear from Tables 1 to 3, the ruthenium powder according to the present invention has the following effects.

1) Selection of bismuth-containing glass Examples 1-2 and Comparative Examples 1-3 show the effects of the composition and softening point of bismuth-containing glass.
In the glass frits “G-1” and “G-2” used in Examples 1 and 2, the production of bismuth ruthenate was confirmed, but the glass frit “G-3” used in Comparative Examples 1 to 3, In “G-4” and “G-5”, RuO ₂ was identified from the XRD diffraction of the recovered powder after acid washing, and the production of bismuth ruthenate was not confirmed.

2) Selection of ruthenium compound Examples 1, 3 and Comparative Example 4 show the effect of changing the ruthenium compound.
In Examples 1 and 3, bismuth ruthenate having a crystallite diameter in the range of 20 to 100 nm was produced, but in Comparative Example 4, as a result of using a ruthenium oxide crystallite diameter exceeding 20 nm, the particle size was As a result, the crystallite diameter exceeded 100 nm.

3) Influence of melt heat treatment temperature Examples 1, 4 to 6 and Comparative Examples 5 to 6 show the influence of the melt heat treatment temperature.
As shown in Comparative Example 5, when the roasting temperature, which is the melting heat treatment temperature, was 550 ° C., the formation of bismuth ruthenate was not confirmed, and unreacted ruthenium oxide was confirmed.
On the other hand, as shown in Comparative Example 6, when the roasting temperature exceeded 700 ° C., the particle growth of bismuth ruthenate was rapidly promoted, the crystallite size increased to 329 nm, and the average particle size became coarser to about 1 μm.

Claims (6)

A method for producing bismuth ruthenate powder,
Ruthenium compound powder and glassy material powder containing 80% by mass or more of bismuth oxide are mixed, and heat treatment is performed at 600 ° C. to 750 ° C. in an atmosphere containing oxygen to precipitate bismuth ruthenate particles in the glassy material. A first step of forming a molten heat-treated product,
A second step of dissolving the melt heat-treated product with an acid to separate bismuth ruthenate particles;
The manufacturing method of the bismuth ruthenate powder characterized by including.   The method for producing a bismuth ruthenate powder according to claim 1, wherein the vitreous substance powder is a bismuth glass frit having a softening point of 450 ° C or lower.   The method for producing bismuth ruthenate powder according to claim 2, wherein the bismuth glass frit has a softening point of 300 ° C or higher and 450 ° C or lower.   The ruthenium compound powder is an amorphous ruthenium oxide hydrate powder or a ruthenium oxide powder having a crystallite diameter of 20 nm or less determined from a peak of (110) plane in powder X-ray diffraction. Item 4. The method for producing bismuth ruthenate powder according to any one of Items 1 to 3.   Ruthenium having a half width determined from a peak of (111) plane in powder X-ray diffraction in a range of 0.16 to 0.48 ° and a crystallite diameter of 20 nm or more and 100 nm or less Bismuth acid powder.   6. The bismuth ruthenate powder according to claim 5, wherein an average particle size obtained from an FE-SEM image of the bismuth ruthenate powder is 20 nm or more and 100 nm or less.