JP7746764B2 - Method for manufacturing RTB based sintered magnet - Google Patents

Description

This application relates to a method for producing R-T-B based sintered magnets.

R-T-B based sintered magnets (R is a rare earth element that must contain at least one selected from the group consisting of Nd, Pr, and Ce; T is at least one transition metal element that must contain Fe; and _B is boron) are composed of a main phase of a compound having an _R2Fe14B crystal structure, a grain boundary phase located at the grain boundaries of this main phase, and a compound phase formed by the influence of trace additive elements and impurities. R-T-B based sintered magnets exhibit high remanence B _r (hereinafter sometimes simply referred to as "B _r ") and high coercivity H _cJ (hereinafter sometimes simply referred to as "H _cJ "), and are known as magnets with the highest performance among permanent magnets.

For this reason, R-T-B based sintered magnets are used in a variety of motors in the automotive sector, including electric vehicles (EVs, HVs, PHVs), renewable energy sectors such as wind power generation, home appliances, and industrial sectors. R-T-B based sintered magnets are an essential material for making these motors smaller, lighter, more efficient, and more energy-efficient (improving energy efficiency). Furthermore, R-T-B based sintered magnets are used in the drive motors of electric vehicles, and the replacement of internal combustion engine vehicles with electric vehicles contributes to preventing global warming by reducing greenhouse gases such as carbon dioxide (reducing fuel and exhaust gases). In this way, R-T-B based sintered magnets are making a significant contribution to the realization of a clean energy society.

Such an R-T-B based sintered magnet is manufactured, for example, through steps such as preparing an alloy powder, press-molding the alloy powder to produce a powder compact, and sintering the powder compact. The alloy powder is manufactured, for example, by the following method.
First, an alloy is produced from a molten metal of various raw materials by a method such as ingot casting or strip casting. The resulting alloy is then subjected to a pulverization process to obtain an alloy powder with a predetermined particle size distribution. This pulverization process typically includes a coarse pulverization process and a fine pulverization process. The former is carried out, for example, by utilizing the hydrogen embrittlement phenomenon, and the latter is carried out, for example, by using an airflow pulverizer (jet mill).

R-T-B based sintered magnets are required to have even higher performance and lower costs. Techniques for improving performance include, for example, refining the structure (refining the alloy powder) and reducing the oxygen content, while techniques for reducing costs include, for example, improving crushing efficiency. Patent Document 1 describes a method for improving crushing efficiency in which an alloy cast by strip casting is coarsely crushed to obtain alloy powder, to which a specific lubricant is added and mixed, and then crushed in a jet mill.

Japanese Patent Application Publication No. 9-17677

In recent years, efforts have been made to further refine alloy powders in order to improve performance, but this has led to problems with productivity due to the accompanying reduction in crushing efficiency. Therefore, there is a strong demand for improved crushing efficiency in fine crushing. An embodiment of the present disclosure provides a new method for producing R-T-B based sintered magnets that can improve crushing efficiency.

In a non-limiting exemplary embodiment, the method for producing an R-T-B based sintered magnet of the present disclosure includes the steps of adding at least one lubricant to a coarsely pulverized powder of an alloy for an R-T-B based sintered magnet (R is at least one rare earth element and must include at least one element selected from the group consisting of Nd, Pr, and Ce; T is at least one transition metal element and must include Fe; and B is boron) produced by a quenching method, mixing the resulting mixture, and pulverizing the mixture to obtain a fine powder; and producing a sintered body from the fine powder, wherein the lubricant includes an alkylamidoamine-type compound represented by the following formula (1):
(R ¹ )CONH(R ² )N(R ³ ) ₂ Formula (1)
( ^R1 is an alkyl chain having 17 to 21 carbon atoms, and ^R2 and ^R3 are each an alkyl chain having 1 to 4 carbon atoms.)
In one embodiment, the alloy for an RTB based sintered magnet is produced by strip casting.

In one embodiment, the alkylamidoamine compound is behenamidopropyldimethylamine.

In one embodiment, the amount of the lubricant added to the coarsely pulverized powder is 0.02% by mass or more and 0.3% by mass or less.

In one embodiment, the lubricant is dissolved in a solvent to prepare a solvent solution, and the solvent solution is added to and mixed with the coarsely pulverized powder.

Embodiments of the present disclosure provide a new method for producing R-T-B based sintered magnets that can improve crushing efficiency.

FIG. 1 is a diagram showing a schematic configuration example of an RTB based sintered magnet alloy crushing system 1000 according to this embodiment.

In the fine pulverization of R-T-B-based sintered magnets, Patent Document 1 proposes using a fine, homogeneous alloy obtained by strip casting and then adding a lubricant to the coarsely pulverized alloy powder, thereby improving pulverization efficiency, corrosion resistance, and magnetic properties. In this way, the combination of the refined alloy structure achieved by switching from the ingot method to the strip casting method and the lubricant's effects has resulted in improved pulverization efficiency, corrosion resistance, and magnetic properties. To achieve even higher magnetic properties, the mainstream method for pulverizing R-T-B-based sintered magnets is to use a high-purity inert gas (e.g., nitrogen, argon, helium, etc.) with a purity of 99.5% or higher as the pulverization gas. However, in conditions with little or no oxygen or moisture in the pulverization gas, significant aggregation of the pulverized powder particles and adhesion to the pulverizer interior occur. This reduces the probability of collisions between powder particles and impairs fluidity within the pulverization chamber, slowing the progress of pulverization and resulting in a significant decrease in pulverization efficiency. This phenomenon is difficult to resolve simply by increasing the amount of stearic acid added as a lubricant. Furthermore, if an attempt is made to resolve this issue by adding stearic acid alone, it would be necessary to add an excessive amount of stearic acid, which would result in an increase in the amount of residual C caused by the addition of stearic acid, which could have a negative impact on magnetic properties.

Based on these findings, the inventors conducted extensive research and found that milling efficiency can be significantly improved by adding a lubricant containing an alkylamidoamine-type compound represented by the following formula (1) (a lubricant containing a surfactant coupling agent) to coarsely milled powder before milling. This is thought to be because the formation of a lubricating surface with surfactant properties containing an alkylamidoamine-type compound on the surface of the powder particles during the milling process suppresses reaction of the powder particles with inert gases (e.g., nitrogen gas) and impurities in the gas (such as moisture and carbon dioxide), as well as suppressing aggregation between powder particles during milling, improving the probability of collisions between powder particles, and eliminating the use of the energy of the milling gas for breaking down aggregates and instead using it for milling more efficiently.
(R ¹ )CONH(R ² )N(R ³ ) ₂ Formula (1)
( ^R1 is an alkyl chain having 17 to 21 carbon atoms, and ^R2 and ^R3 are each an alkyl chain having 1 to 4 carbon atoms.)

<Method of manufacturing RTB based sintered magnet>
Hereinafter, an embodiment of a method for producing a sintered RTB based magnet according to the present disclosure will be described.

This disclosure relates to a method for producing an R-T-B based sintered magnet. Here, R is at least one rare earth element and must contain at least one element selected from the group consisting of Nd, Pr, and Ce, and T is at least one transition metal element and must contain Fe.

The method for producing this RTB based sintered magnet is as follows:
(1) adding at least one lubricant to a coarsely pulverized powder of an alloy for an RTB-based sintered magnet, mixing the mixture, and pulverizing the mixture to obtain a fine powder;
(2) preparing a sintered body of the fine powder.

First, the composition of a preferred RTB based sintered magnet is shown below.
R is a rare earth element and must contain at least one element selected from the group consisting of Nd, Pr, and Ce. Preferably, a combination of rare earth elements represented by Nd-Dy, Nd-Tb, Nd-Dy-Tb, Nd-Pr-Dy, Nd-Pr-Tb, Nd-Pr-Dy-Tb, Nd-Ce-Dy, Nd-Ce-Tb, Nd-Ce-Dy-Tb, Nd-Pr-Ce-Dy, Nd-Pr-Ce-Tb, or Nd-Pr-Ce-Dy-Tb is used.

Among the R elements, Dy and Tb are particularly effective in improving the coercive force _HcJ . In addition to the above elements, other rare earth elements such as La may also be contained. The R content of the R-T-B based sintered magnet is, for example, 27% by mass or more and 35% by mass or less. Preferably, the R content of the R-T-B based sintered magnet is 32% by mass or less (more preferably 27% by mass or more and 31% by mass or less, and even more preferably 29% by mass or more and 31% by mass or less). This allows for better magnetic properties to be obtained.

T contains iron (including cases where T consists essentially of iron), and up to 50% by mass of this iron may be replaced with cobalt (Co) (including cases where T consists essentially of iron and cobalt). Co is effective in improving temperature characteristics and corrosion resistance, and the alloy powder may contain up to 10% by mass of Co. The content of T may account for the remainder of R and B, or R, B, and M, which will be described later.

The B content may also be any known content, with a preferred range being, for example, 0.85% by mass to 1.2% by mass. If it is less than 0.85% by mass, a high _HcJ may not be obtained, and if it exceeds 1.2% by mass, Br may decrease. The B content is more preferably 1.0% by mass or less, and even more preferably 0.98% by mass or less. Note that a portion of B can be substituted with C (carbon).

In addition to the above elements, an M element can be added to improve _HcJ . The M element is one or more elements selected from the group consisting of Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, In, Sn, Hf, Ta, and W. The total amount of M element added is preferably 5.0 mass% or less. This is because if it exceeds 5.0 mass%, Br may decrease. In addition, unavoidable impurities are also acceptable.

Furthermore, the average crystal grain size of the R ₂ T ₁₄ B phase, which is the main phase of the R-T-B based sintered magnet of the present disclosure, is preferably 2.0 μm or more and 7.0 μm or less, more preferably 3.0 μm or more and 5.0 μm or less, and even more preferably 3.0 μm or more and 4.0 μm or less. This allows for better magnetic properties to be obtained. The average crystal grain size can be determined, for example, by taking the number-average equivalent circle diameter of crystal grains (5,000 or more) evaluated by EBSD (Electron Backscatter Diffraction).
Next, a method for producing the RTB based sintered magnet of the present disclosure will be described.

<(1) Example of a process for obtaining a fine powder by adding at least one lubricant to a coarsely pulverized powder of an alloy for an RTB-based sintered magnet, mixing the mixture, and pulverizing the mixture>
The process of adding at least one lubricant to a coarsely pulverized powder of an alloy for an R-T-B based sintered magnet, mixing the resulting mixture, and pulverizing the mixture to obtain a fine powder includes the steps of preparing an alloy for an R-T-B based sintered magnet, coarsely pulverizing the alloy by, for example, a hydrogen pulverization method to obtain a coarsely pulverized powder, and supplying the coarsely pulverized powder to, for example, a jet mill device to pulverize the coarsely pulverized powder to obtain a fine powder.

Here is an example of a method for producing an alloy for an R-T-B based sintered magnet. An alloy ingot can be obtained by ingot casting, in which a metal or alloy previously prepared to have the composition described above is melted and poured into a mold. Alternatively, alloy flakes can be produced by a rapid cooling method, such as strip casting or centrifugal casting, in which the molten metal is brought into contact with a single roll, twin rolls, rotating disk, or rotating cylindrical mold, and rapidly cooled, to produce a solidified alloy that is thinner than the alloy produced by the ingot method.

In embodiments of the present disclosure, materials produced by either the ingot method or the quenching method can be used, but production by a quenching method such as strip casting is preferred. The thickness of quenched alloys produced by the quenching method is typically in the range of 0.03 mm to 1 mm and is plate-shaped. The molten alloy begins to solidify at the surface where it contacts the chill roll (the roll contact surface), and crystals grow columnarly from the roll contact surface in the thickness direction. Compared to alloys (ingot alloys) produced by conventional ingot casting (mold casting), quenched alloys are cooled in a shorter time, resulting in a finer structure and smaller crystal grain size. Because the R-rich phase is finely distributed within the grain boundaries, the quenching method provides excellent dispersibility of the R-rich phase. Therefore, fracture at the grain boundaries is more likely to occur when using hydrogen pulverization. Hydrogen pulverization of quenched alloys can reduce the size of the hydrogen pulverized powder (coarsely pulverized powder) to, for example, 1.0 mm or less. At least one lubricant is added to the coarsely pulverized powder obtained in this manner, and then the resulting powder is finely pulverized, for example, using a jet mill.

The pulverization system for performing fine pulverization according to the present disclosure will be described with reference to Figure 1. Figure 1 is a diagram schematically illustrating an example configuration of a pulverization system 1000 according to this embodiment. In this example, the R-T-B based sintered magnet alloy pulverization system 1000 includes a jet mill device 100, a cyclone collection device 200, and a bag filter device 300.

The jet mill device 100 receives the material to be pulverized via a raw material input pipe 34 from a raw material tank (not shown) containing coarsely pulverized powder to which a lubricant has been added. The addition of lubricant will be described in detail later. The material to be pulverized is coarsely pulverized powder of an R-T-B based sintered magnet alloy with an average particle size of 10 μm or more and 500 μm or less.

The raw material input pipe 34 is equipped with multiple valves, which are opened and closed to maintain an appropriate internal pressure within the jet mill device 100. The material to be ground is introduced into the jet mill device 100 and is finely ground by collisions between the materials due to high-speed inert gas injection from the nozzle pipe 36, as well as collisions with collision plates installed to efficiently advance the grinding process.

R-T-B based sintered magnet alloy powder is active and easily oxidized. For this reason, it is preferable to use a dry (high-purity) inert gas with a dew point of -60°C or below, such as nitrogen, argon, or helium, as the gas used in the jet mill device 100, in order to avoid the risk of heat generation and fire and to reduce the oxygen content as an impurity, thereby improving the performance of the magnet.

The powder particles (fine powder) finely pulverized inside the jet mill apparatus 100 are carried by the ascending air current and guided from the upper outlet into the inlet pipe 20 of the cyclone collector 200. Insufficiently pulverized coarse particles are separated by a classifying rotor installed to classify the coarse particles, remaining inside the jet mill apparatus 100 for further crushing by collision. Classification of these coarse particles can be performed using a classifying rotor or by centrifugal separation using a swirling flow. Thus, the material to be crushed (coarsely crushed powder) introduced into the jet mill apparatus 100 is crushed into fine powder with an average particle size (median diameter: d50) of, for example, 2.0 μm to 6.0 μm before being transferred to the cyclone collector 200. The average particle size of the fine powder is preferably 2.0 μm to 6.0 μm, more preferably 2.5 μm to 4.5 μm, and even more preferably 2.5 μm to 3.5 μm. The final RTB-based sintered magnet can have even better magnetic properties.

The cyclone collector 200 is used to separate powder from the airflow carrying it. Specifically, coarsely pulverized powder of R-T-B-based sintered magnet alloy is pulverized in a jet mill at the upstream stage, and the fine powder produced by the pulverization is supplied to the cyclone collector 200 through the inlet pipe 20 along with the gas used in the pulverization. A mixture of inert gas (pulverization gas) and the pulverized fine powder forms a high-velocity airflow and is sent to the cyclone collector 200. The cyclone collector 200 is used to separate the pulverization gas from the fine powder. The fine powder separated from the pulverization gas is collected in the powder collector 50 via the outlet 40. The pulverization gas is supplied to the bag filter device 300 via the outlet pipe 30. The bag filter device 300 collects very small particles, and clean gas is released to the outside through the exhaust port 32. It is also possible to use only a bag filter for this solid-gas separation without using the cyclone collector 200, but this would have a significant impact on the environment and safety, such as the dispersion of fine powder into the atmosphere due to filter damage. A bag filter may also be used in combination to separate fine particles from the gas separated by the cyclone collector.

In the method for producing an R-T-B based sintered magnet of the present disclosure, at least one lubricant is added to and mixed with the coarsely pulverized powder, and then the resulting mixture is pulverized using the pulverization system described above to obtain a fine powder. A distinctive feature of the present disclosure is that the lubricant contains an alkylamidoamine-type compound represented by the following formula (1):
(R ¹ )CONH(R ² )N(R ³ ) ₂ Formula (1)
( ^R1 is an alkyl chain having 17 to 21 carbon atoms, and ^R2 and ^R3 are each an alkyl chain having 1 to 4 carbon atoms.)
This can improve the crushing efficiency.

The lubricant may contain small amounts of other known lubricating ingredients such as zinc stearate, but to more reliably achieve high milling efficiency, it is preferable that 50% by mass or more of the lubricant be an alkylamidoamine-type compound, more preferably 80% by mass or more of the lubricant be an alkylamidoamine-type compound, even more preferably 90% by mass or more of the lubricant be an alkylamidoamine-type compound, and most preferably the lubricant is an alkylamidoamine-type compound (excluding unavoidable impurities). Furthermore, the alkylamidoamine-type compound contained in the lubricant is preferably behenamidopropyldimethylamine, an alkylamidoamine-type compound that satisfies the above formula (1). This allows for more reliably improved milling efficiency.

The amount of lubricant added to the coarsely pulverized powder is preferably 0.02% by mass or more and 0.3% by mass or less. By adding 0.02% by mass or more and 0.3% by mass or less of lubricant to the coarsely pulverized powder, it is possible to improve pulverization efficiency while suppressing an increase in the amount of C (carbon) in the fine powder after pulverization, and to suppress a decrease in the magnetic properties of the final R-T-B based sintered magnet. More preferably, the amount of lubricant added to the coarsely pulverized powder is 0.02% by mass or more and 0.15% by mass or less.

Preferably, the lubricant is dissolved in a solvent to prepare a solvent liquid containing the lubricant, which is then added to and mixed with the coarsely pulverized powder. This further improves pulverization efficiency. The solvent liquid consists of the lubricant and a liquid component that dissolves the lubricant. Examples of dissolving solvents (liquid components) include xylene, alcohol, and isoparaffin. Fatty acid esters may also be used as solvents. A low boiling point poses safety issues, including handling, such as ignition, while a high boiling point can cause insufficient evaporation or increase residual carbon, affecting magnetic properties. Therefore, a solvent with a boiling point or initial boiling point of 60 to 200°C is preferred. The amount of the solvent liquid added to the coarsely pulverized powder is preferably 0.05% by mass or more but 1.50% by mass or less. The liquid component is preferably added in an amount between 3 and 7 times the amount of the lubricant. After addition and mixing, the mixture can be pulverized immediately. To remove the liquid component, it can be easily evaporated by leaving it in an inert gas such as nitrogen, argon, or helium. Because alkylamidoamine-type compounds are often granular or waxy, it is difficult to add them evenly and homogeneously to coarsely pulverized powder. Therefore, as disclosed herein, by melting or gelling a lubricant consisting of an alkylamidoamine-type compound in a solvent beforehand, it becomes easier to add it evenly and homogeneously to the coarsely pulverized powder. Furthermore, using a solvent containing a lubricating component such as a fatty acid ester can also improve milling efficiency.

<(2) Example of a process for producing a sintered body of fine powder>
In a preferred embodiment, the step of producing a sintered body of the fine powder includes the steps of producing a powder compact from the fine powder by pressing in a magnetic field, and sintering the powder compact.

A process of producing a powder compact from the fine powder by pressing in a magnetic field. In terms of suppressing oxidation, it is preferable to form the powder compact by pressing in an inert gas atmosphere or by wet pressing. The pressing can be performed using a known pressing device. The compact is then sintered to obtain a sintered body.

Sintering the powder compact The compact is preferably sintered at a temperature between 1000°C and 1150°C under a pressure of 0.13 Pa ( ^10-3 Torr) or less, more preferably 0.07 Pa (5.0 x ^10-4 Torr) or less. To prevent oxidation during sintering, residual gas in the atmosphere can be replaced with an inert gas such as helium or argon. The resulting sintered body is preferably subjected to heat treatment, which can improve its magnetic properties. Known conditions for the heat treatment, such as the heat treatment temperature and time, can be used. The rare earth sintered magnet body thus obtained is then subjected to grinding and polishing, surface treatment, and magnetization, as necessary, to produce the final rare earth sintered magnet.

In a preferred embodiment, the method for producing an R-T-B based sintered magnet disclosed herein further includes a diffusion step in which a heavy rare earth element RH (RH is at least one of Tb, Dy, and Ho) is diffused from the surface of the sintered body to its interior. Diffusing the heavy rare earth element RH from the surface to the interior of the sintered body can efficiently increase the coercive force.

The present disclosure will be explained in more detail using examples, but the present disclosure is not limited thereto.

Example 1
An alloy for an R-T-B based sintered magnet was produced by strip casting, so that the composition of the R-T-B based sintered magnet was 22.7% by mass of Nd, 7.5% by mass of Pr, 0.07% by mass of Tb, 0.95% by mass of B, 2.0% by mass of Co, 0.4% by mass of Al, 0.1% by mass of Cu, 0.3% by mass of Ga, 0.5% by mass of Zr, and the remainder being Fe. The resulting alloy was coarsely pulverized by hydrogen pulverization to obtain a coarsely pulverized powder. The average particle size of the coarsely pulverized powder was measured. The average particle size was in the range of 200 μm to 400 μm.

A lubricant was added to the coarsely pulverized powder under the conditions shown in Table 1. The lubricants used were A: an alkylamidoamine-type compound (specifically, behenamidopropyldimethylamine), and B: zinc stearate. No. 1 in Table 1 uses zinc stearate as the lubricant, and the amount of lubricant added to the coarsely pulverized powder is 0.04% by mass. Nos. 2, 4, and 5 are examples in which the type or amount of lubricant added was changed. Additionally, Nos. 3, 6, and 7 in Table 1 were examples in which the lubricant was dissolved in a solvent to prepare a solvent solution containing the lubricant, and this solvent solution was then added and mixed with the coarsely pulverized powder. Isoparaffin was used as the liquid solvent component. No. 3 in Table 1 uses behenamidopropyldimethylamine as the lubricant, and the lubricant was dissolved in isoparaffin to create a solvent solution containing the lubricant. The amount of the solvent solution added to the coarsely pulverized powder was 0.24% by mass (0.04% by mass of lubricant, 0.2% by mass of the liquid component of the solvent). Nos. 6 and 7 are also examples in which a lubricant was dissolved in a solvent.

The coarsely pulverized powder to which a lubricant had been added under the conditions shown in Table 1 was fed into the jet mill device 100 shown in Figure 1 and pulverized to obtain a fine powder. In this example, nitrogen gas was used as the inert gas. The average particle size (median diameter: d50) and pulverization efficiency of the resulting finely pulverized powder are shown in Table 1.

As shown in Table 1, when comparing samples with the same lubricant content (Nos. 1 to 3, 4 to 6), the present invention examples, which satisfy the conditions of this disclosure, achieve higher milling efficiency than the comparative examples. Furthermore, the present invention examples (Nos. 3 and 6), in which the lubricant was dissolved in a solvent to prepare a solvent solution containing the lubricant and then added to the coarsely pulverized powder, achieve higher milling efficiency. Furthermore, No. 7, which has a lubricant content of 0.15% by mass, achieves high milling efficiency, but the difference in milling efficiency is small compared to No. 6. Increasing the amount of lubricant increases the carbon content in the fine powder after milling, which may result in a deterioration in the magnetic properties of the final R-T-B based sintered magnet. Therefore, from the perspective of magnetic properties, it is better to reduce the amount of lubricant added. Therefore, the amount of lubricant added to the coarsely pulverized powder is preferably 0.02% by mass or more and 0.3% by mass or less, and more preferably 0.02% by mass or more and 0.15% by mass or less.

100: Jet mill device, 200: Cyclone collection device, 300: Bag filter device

Claims (5)

a step of adding at least one lubricant to a coarsely pulverized powder of an R-T-B based sintered magnet alloy (R is at least one rare earth element and must include at least one element selected from the group consisting of Nd, Pr, and Ce; T is at least one transition metal element and must include Fe; and B is boron) produced by a quenching method, mixing the mixture, and pulverizing the mixture to obtain a fine powder;
and preparing a sintered body of the fine powder,
The lubricant contains an alkylamidoamine compound represented by the following formula (1):
A method for producing an RTB based sintered magnet.
(R1)CONH(R2)N(R3)2 Formula (1)
(R1 is an alkyl chain having 17 to 21 carbon atoms, and R2 and R3 are each an alkyl chain having 1 to 4 carbon atoms.) 2. The method for producing an RTB based sintered magnet according to claim 1, wherein the alloy for an RTB based sintered magnet is produced by a strip casting method. 3. The method for producing a sintered RTB based magnet according to claim 1, wherein the alkylamidoamine compound is behenamidopropyldimethylamine. 4. The method for producing a sintered RTB based magnet according to claim 1, wherein the amount of the lubricant added to the coarsely pulverized powder is 0.02% by mass or more and 0.3% by mass or less. 5. The method for producing an RTB based sintered magnet according to claim 1 , wherein the lubricant is dissolved in a solvent to prepare a solvent liquid, and the solvent liquid is added to and mixed with the coarsely pulverized powder.