JP6929755B2 - Hafnium carbide powder for plasma electrodes, its manufacturing method, hafnium carbide sintered body and plasma electrode - Google Patents

Description

The present invention relates to a hafnium carbide powder for a plasma electrode, which is used as a raw material for a plasma electrode used in, for example, a plasma torch and suppresses contamination of carbon particles as an impurity, a method for producing the same, a hafnium carbide sintered body, and a plasma electrode.

Generally, a carbon thermal reduction method is known as a method for producing a powder of a compound such as hafnium carbide. This carbon thermal reduction method is a method in which a metal oxide powder and carbon black are heated to a high temperature in an inert gas atmosphere to carry out a reduction reaction.

For example, Patent Document 1 shows a method for producing an aluminum nitride powder using a carbon thermal reduction method. In this production method, aluminum nitride powder is produced by mixing aluminum oxide powder and carbon black and performing a reduction reaction at a temperature higher than 1600 ° C. This carbon thermal reduction method can produce aluminum nitride powder with high purity, small particle size, and stable performance by a simple production process.

When producing hafnium carbide powder based on such a carbon thermal reduction method, _{a mixed powder of hafnium oxide (HfO 2} ) and carbon black (C) is heated to a high temperature of about 2000 ° C. in an argon atmosphere. Hafnium carbide (HfC) powder is produced by performing the reduction reaction.

Japanese Unexamined Patent Publication No. 2016-164112

In the method for producing hafnium carbide powder by the conventional carbon thermal reduction method described above, since the reduction reaction is carried out at a high temperature of 2000 ° C., a carbon-made rutsubo is used at the time of heat treatment, and the periphery of the rutsubo is carbon as a heat insulating material. Covered with powder. Therefore, when the produced hafnium carbide powder is recovered from the rutsubo, it is inevitable that carbon particles of several μm to several tens of μm are mixed in the hafnium carbide powder. Therefore, the carbon particles mixed in the hafnium carbide powder become impurities, and the quality of the hafnium carbide powder deteriorates. As a result, there is a problem that the quality of the plasma electrode obtained from the sintered body of hafnium carbide powder is deteriorated and the life is shortened.

Therefore, an object of the present invention is a hafnium carbide powder for plasma electrodes, which can suppress the mixing of carbon particles as impurities and improve the quality of the hafnium carbide powder, a method for producing the same, and a hafnium carbide sintered body. And to provide plasma electrodes.

In order to achieve the above object, the hafnium carbide powder for the plasma electrode of the present invention is a hafnium carbide powder represented by the chemical formula HfC _x (where x = 0.5 to 1.0) and is an impurity. The content of carbon particles is 0.03% by mass or less.

According to the hafnium carbide powder for a plasma electrode of the present invention, it is possible to suppress the mixing of carbon particles as impurities and improve the quality of the hafnium carbide powder.

FIG. 5 is a cross-sectional view schematically showing a manufacturing apparatus used in the first manufacturing method of hafnium carbide powder. FIG. 5 is a cross-sectional view schematically showing a manufacturing apparatus used for the first heat treatment in the second manufacturing method of hafnium carbide powder. FIG. 5 is a cross-sectional view schematically showing a manufacturing apparatus used for the second heat treatment in the second manufacturing method of hafnium carbide powder. (A) A schematic plan view showing a planetary ball mill for milling, (b) a cross-sectional view showing a pot containing balls and raw materials inside, and (c) showing balls and raw materials inside. A vertical sectional view showing a pot. (A) is a schematic perspective view showing a sintering mold used in a pulse energization pressure sintering apparatus, and (b) is an explanatory view showing a pulse energization pressure sintering apparatus. (A) is a schematic cross-sectional view showing a plasma cutting device (plasma cutting torch), and (b) is a cross-sectional view showing a plasma electrode. (A) is a graph showing the relationship between the arc time (min) and the electrode wear depth (mm) in the case where the milling treatment of Example 1 is not performed, and (b) is the case where the milling treatment of Example 1 is performed. The graph which shows the relationship between the arc time (min) and the electrode wear depth (mm). (A) is a graph showing the relationship between the arc time (min) and the electrode consumption mass (mg) when the milling treatment of Example 1 is not performed, and (b) is an arc when the milling treatment of Example 1 is performed. The graph which shows the relationship between time (min) and electrode consumption mass (mg). (A) is a graph showing the relationship between the arc time (min) and the electrode wear depth (mm) for Comparative Example 1, and (b) is the arc time (min) and the electrode wear mass (mg) for Comparative Example 1. A graph showing the relationship with. (A) is a graph showing the relationship between the arc time (min) and the electrode wear depth (mm) for Comparative Example 2, and (b) is the arc time (min) and the electrode wear mass (mg) for Comparative Example 2. A graph showing the relationship with.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
The hafnium carbide powder of the present embodiment is a powder for obtaining a plasma electrode, and is a hafnium carbide powder represented by the chemical formula HfC _x (where x = 0.5 to 1.0), and carbon as an impurity. The content of particles (free carbon) is 0.03% by mass or less. _{Hafnium carbide is obtained by reducing hafnium oxide (HfO 2} ) with carbon (C) based on the following reaction formula (1). In this case, when the carbon content (atomic weight) is 3 or more, the residual amount of carbon particles is large, while when the carbon content (atomic weight) is less than 2, unreduced hafnium oxide remains. The ratio of (atomic weight) is preferably 2 to 3.

HfO ₂ + 3C → HfC + 2CO ↑ ・ ・ ・ (1)
This hafnium carbide powder is for a plasma electrode, and the plasma electrode is prepared from a sintered body in which the hafnium carbide powder is sintered. Hafnium carbide powder should have few impurities and high purity, but carbon particles having a particle size of about 5 to 50 μm are contained as impurities in the manufacturing process. The content of the carbon particles is 0.03% by mass or less in the hafnium carbide powder. If the content of carbon particles exceeds 0.03% by mass, the quality of the hafnium carbide powder sintered body and the plasma electrode obtained from the sintered body will vary, and the durability of the plasma electrode will decrease, resulting in a reduced life. Becomes shorter.

The average particle size of the hafnium carbide powder is preferably 0.5 to 2 μm, more preferably 0.5 to 1 μm. When the average particle size is smaller than 0.5 μm, it is difficult to prepare such fine hafnium carbide powder, and the production process tends to be complicated or the production time tends to be long. On the other hand, when the average particle size is larger than 2 μm, the variation of the hafnium carbide powder particles becomes large and excessive particles are present, which makes it difficult to obtain a homogeneous sintered body.

Next, as a method for producing hafnium carbide powder for a plasma electrode, a first production method and a second production method will be described.
First, the first manufacturing method will be described.

As shown in FIG. 1, a carbon first crucible 12 is arranged in the high-frequency induction heating furnace 11, and the first crucible 12 is covered between the first crucible 12 and the inner surface of the high-frequency induction heating furnace 11. As described above, carbon (C) powder 13 as a heat insulating material is filled. On the upper wall of the first crucible 12, a supply pipe 14 into which argon gas as an inert gas is introduced and a discharge pipe 15 for discharging a gas such as carbon monoxide (CO) generated in the first crucible 12 are provided. Is connected.

A second crucible 17 made of silicon carbide (SiC) containing pellets 16 of a mixed powder of _{hafnium oxide (HfO 2} ) and carbon (C), which is a raw material, is arranged in the first crucible 12. A plurality of ventilation holes 18 for introducing argon gas and discharging gas such as carbon monoxide are opened on the side wall of the second crucible 17.

Then, in the first method for producing hafnium carbide powder, the pellet 16 is housed in the second crucible 17, and then the second crucible 17 is placed in the first crucible 12. Subsequently, when the argon gas is supplied from the supply pipe 14 into the first crucible 12, the argon gas is filled in the first crucible 12, and the argon gas further enters the second crucible 17 through the ventilation hole 18 to enter the second crucible 2. The inside of the crucible 17 is filled with argon gas.

In that state, the high frequency induction heating furnace 11 is operated to heat the inside of the high frequency induction heating furnace 11 to 1800 to 2000 ° C. By this heat treatment, a reduction / carbonization reaction of hafnium oxide occurs in the second rutsubo 17 according to the reaction formula (1), and hafnium carbide powder is produced.

At this time, the by-produced gas such as carbon monoxide (CO) gas is discharged from the vent hole 18 of the second crucible 17 to the outside from the discharge pipe 15 through the inside of the first crucible 12. After completion of the reaction, the second crucible 17 is taken out from the inside of the first crucible 12, and then the hafnium carbide powder is recovered from the inside of the second crucible 17.

Next, the particle size of the hafnium carbide powder can be adjusted by subjecting the obtained hafnium carbide powder to a milling treatment (crushing treatment). This milling process will be described.
As shown in FIG. 4 (a), the disk-shaped revolving body 21 constituting the planetary ball mill 20 for the milling process revolves in the counterclockwise direction shown by the arrow in FIG. 4 (a), for example. Four pots 22 forming a bottomed cylinder are arranged on the revolving body 21 at intervals of 90 degrees in the circumferential direction, and each pot 22 rotates in the clockwise direction shown by the arrow in FIG. 4A, for example. It has become. The revolution direction of the revolution body 21 and the rotation direction of the pot 22 can be arbitrarily set.

As shown in FIGS. 4 (b) and 4 (c), a plurality of balls 23 for crushing and the hafnium carbide powder 24 having different particle sizes are housed in the pot 22. Then, in that state, the revolving body 21 is revolved and each pot 22 is rotated. At this time, a strong centrifugal force is generated between the ball 23 and the hafnium carbide powder 24 due to the revolving motion and the rotating motion, and the collision energy of the ball 23 exerts a compressive force and a shearing force on the hafnium carbide powder 24, and the hafnium carbide powder 24 is crushed. It is refined and homogenized.

Next, a second method for producing hafnium carbide powder will be described. In this second manufacturing method, the first heat treatment by the first heat treatment device and the second heat treatment by the second heat treatment device are performed.

As shown in FIG. 2, a carbon third crucible 26 containing the pellet 16 is arranged in the high-frequency induction heating furnace 11 constituting the first heat treatment apparatus 25, and the third crucible 26 contains the pellet 16. Is connected to a supply pipe 14 into which an inert gas such as argon gas is injected and a discharge pipe 15 in which a gas such as carbon monoxide gas is discharged. A carbon powder 13 as a heat insulating material is filled between the third crucible 26 and the inner surface of the high frequency induction heating furnace 11 so as to cover the third crucible 26.

Then, with the pellet 16 accommodated in the third crucible 26, the inert gas is supplied from the supply pipe 14 into the third crucible 26 to fill it, and in that state, the high frequency induction heating furnace 11 is operated to operate the third crucible. The inside of the crucible 26 is heated to 1800 to 2000 ° C. to perform the first heat treatment. As a result, the reduction / carbonization reaction of hafnium oxide based on the reaction formula (1) is allowed to proceed to produce hafnium carbide powder 24.

As shown in FIG. 3, a silicon carbide fourth crucible 29 or a carbon fifth crucible 29 in which the pellet 16 is housed is contained in the vacuum vessel 30 of the vacuum heating furnace 28 constituting the second heat treatment apparatus 27. The crucible 33 is arranged. A vacuum suction pipe 31 is connected to the vacuum vessel 30, so that the inside of the vacuum vessel 30 is depressurized to a predetermined degree of vacuum. A heat insulating material 61 is arranged on the inner peripheral surface of the vacuum container 30, and a heater 62 is arranged in a space inside the vacuum container 30. A communication hole 32 is opened in the 4th crucible 29 or the 5th crucible 33 so that the inside of the 4th crucible 29 or the 5th crucible 33 can be set to the same degree of vacuum as the inside of the vacuum heating furnace 28.

Then, the third crucible 26 after the first heat treatment is taken out from the high frequency induction heating furnace 11, and the pellet 16 (hafnium carbide powder 24) is recovered from the third crucible 26. Here, the components of the pellet 16 (hafnium carbide powder 24) are analyzed, and if a large amount of unreacted hafnium oxide remains, carbon fine particles may be added.

The obtained pellet 16 is housed in the 4th crucible 29 or the 5th crucible 33, and the 4th crucible 29 or the 5th crucible 33 is placed in the vacuum heating furnace 28. Next, the air in the vacuum heating furnace 28 is sucked from the vacuum suction pipe 31 to set the inside of the vacuum heating furnace 28 to a predetermined degree of vacuum. At this time, the air in the 4th crucible 29 or the 5th crucible 33 is also sucked from the communication hole 32 of the 4th crucible 29 or the 5th crucible 33, and the inside of the 4th crucible 29 or the 5th crucible 33 is also in the vacuum heating furnace 28. It is set to the same degree of vacuum. In that state, the inside of the vacuum heating furnace 28 and the inside of the 4th crucible 29 or the 5th crucible 33 are heated to 1800 to 2000 ° C. to perform a second heat treatment, and the reduction / carbonization reaction of hafnium oxide is further promoted to carbonize. Reduces carbon particles in hafnium powder 24.

The obtained hafnium carbide powder 24 is subjected to a milling treatment in the same manner as in the first production method, and the hafnium carbide powder 24 is pulverized and homogenized.
Next, sintering of the hafnium carbide powder 24 will be described.

As shown in FIG. 5A, an upper punch 37 is fitted in the upper portion and a lower punch 38 is fitted in the lower portion in the inner space portion of the cylindrical die 36 constituting the sintering mold 35 (die). Is fitted, and a sample filling portion 39 is provided between the upper punch 37 and the lower punch 38. The sample filling portion 39 is filled with the milled hafnium carbide powder 24.

As shown in FIG. 5B, an upper electrode 43 is arranged on the upper punch 37 of the sintering mold 35 constituting the pulse energization pressure sintering apparatus 40 via a spacer 41, and a lower punch 38 is provided. A lower electrode 45 is arranged below the spacer 41 via a spacer 41. A pulse power supply 46 is connected between the upper electrode 43 and the lower electrode 45, and a pulse current is applied between the upper electrode 43 and the lower electrode 45. Then, as shown by the arrow in FIG. 5 (b), the upper electrode 43 and the lower electrode 45 are pressurized from above and below, and a pulse current is applied between the upper electrode 43 and the lower electrode 45 to carry the carbide. The hafnium powder 24 is heated and sintered by Joule heat to form a sintered body 47.

Next, the plasma electrode produced from the sintered body 47 of the hafnium carbide powder 24 will be described.
As shown in FIG. 6A, a substantially columnar plasma electrode 52 is attached to the tip of the plasma cutting torch 50, and an electrode tip 54 that emits a plasma arc 53 is fitted at the end. .. A plasma gas passage 55 for ejecting plasma gas is provided on the outer peripheral portion of the plasma electrode 52, and an assist gas passage 56 for ejecting an assist gas such as nitrogen gas is provided on the outer peripheral portion thereof.

As shown in FIG. 6B, a columnar mounting hole 57 is provided at the tip of the electrode body 52a constituting the plasma electrode 52, and the electrode tip 54 is fitted in the mounting hole 57. The electrode body 52a is manufactured by cutting a copper rod, and the electrode tip 54 is manufactured by electric discharge machining and grinding from a bulk body of a sintered body 47 of hafnium carbide powder 24. Then, the electrode tip 54 is fitted into the mounting hole 57 of the electrode body 52a and brazed, and then the portion protruding from the tip surface of the electrode body 52a is ground to form the plasma electrode 52.

Next, the operation of the hafnium carbide powder 24 of the present embodiment and the method for producing the same will be described.
When the hafnium carbide powder 24 is produced, there are the above-mentioned first production method and the second production method. In the first manufacturing method, the second crucible 17 is arranged in the first crucible 12, and the hafnium carbide powder 24 is produced in the second crucible 17, so that the second crucible is sealed from the high frequency induction heating furnace 11. After taking out 17, the hafnium carbide powder 24 can be recovered from the second crucible 17. Therefore, it is not affected by the first crucible 12 made of carbon and the carbon powder 13 as a heat insulating material, and it is possible to avoid mixing of carbon particles in the hafnium carbide powder 24.

In the second manufacturing method, the first heat treatment, which is a conventional method, is performed in the third crucible 26 in the high-frequency induction heating furnace 11, and then the hafnium carbide powder 24 is taken out from the third crucible 26 to take out the fourth crucible. It is transferred into the 29 or the 5th crucible 33 and placed in the vacuum heating furnace 28 to perform the second heat treatment. Therefore, the carbon particles mixed in the hafnium carbide powder 24 in the first heat treatment are consumed by the reduction / carbonization reaction of hafnium oxide in the second heat treatment. As a result, the content of carbon particles in the hafnium carbide powder 24 is suppressed.

Therefore, the content of carbon particles as impurities in the hafnium carbide powder 24 is suppressed to 0.03% by mass or less. Therefore, the quality of the sintered body 47 sintered from the hafnium carbide powder 24 can be improved, and cracking due to carbon particles can be suppressed in the electrode chip 54 of the plasma electrode 52 produced from such the sintered body 47. And can extend its life.

The effects obtained by the above-described embodiment are summarized below.
(1) The hafnium carbide powder 24 for the plasma electrode 52 of this embodiment is a hafnium carbide powder represented by the chemical formula HfC _x (where x = 0.5 to 1.0), and carbon as an impurity. The particle content is 0.03% by mass or less.

Therefore, according to the hafnium carbide powder 24 of the embodiment, the mixing of carbon particles as impurities can be suppressed, and the quality of the hafnium carbide powder 24 can be improved.
(2) The average particle size of the hafnium carbide powder 24 is 0.5 to 2 μm. Therefore, the hafnium carbide powder 24 has fine particles, a narrow particle size distribution, is homogeneous, and a dense sintered body 47 can be obtained.

(3) In the first method for producing hafnium carbide powder, pellets 16 of a mixed powder of hafnium oxide and carbon are housed in a second crucible 17 made of silicon carbide, and the second crucible 17 is made of carbon first. It is placed in a crucible 12 and heated at 1800 to 2000 ° C. to produce hafnium carbide powder 24. Therefore, the hafnium carbide powder 24 can be generated in the second crucible 17 arranged in the first crucible 12, and the hafnium carbide powder 24 is recovered after the second crucible 17 is taken out from the first crucible 12. It is possible to prevent impurities from being mixed into the hafnium carbide powder 24.

(4) In the second method for producing the hafnium carbide powder 24, the pellet 16 is housed in a carbon third crucible 26 as a first heat treatment, and the third crucible 26 is housed in a high frequency induction heating furnace 11. In a state where the high-frequency induction heating furnace 11 is filled with carbon powder 13, an inert gas is supplied into the third crucible 26 to carry out a heating reaction at 1800 to 2000 ° C. The obtained hafnium carbide powder 24 is transferred to the 4th crucible 29 or the 5th crucible 33, and as a second heat treatment, the inside of the vacuum heating furnace 28 and the inside of the 4th crucible 29 or the 5th crucible 33 are evacuated to 1800 to 2000 ° C. Is heated to produce hafnium carbide powder 24.

Therefore, carbon particles, which are impurities in the hafnium carbide powder 24 obtained in the first heat treatment, can be reacted in the second heat treatment to reduce as much as possible.
(5) The produced hafnium carbide powder 24 is subjected to a milling treatment to adjust the particle size of the hafnium carbide powder 24. By this milling treatment, the hafnium carbide powder 24 can be refined and homogenized.

(6) The sintered body 47 of the hafnium carbide powder 24 is obtained by heating and sintering the hafnium carbide powder 24 by the pulse energization pressure sintering apparatus 40. Therefore, the sintered body 47 can be obtained more easily than the hafnium carbide powder 24, and is homogeneous with few impurities based on the characteristics of the hafnium carbide powder 24.

(7) The plasma electrode 52 can be formed by the sintered body 47 of the hafnium carbide powder 24. Therefore, the plasma electrode 52 can exhibit stable quality and can extend its life.

Hereinafter, the embodiment will be described in more detail with reference to Examples and Comparative Examples.
(Example 1)
In this Example 1, the hafnium carbide powder 24 was produced by the above-mentioned first production method.

First, the hafnium oxide powder having an average particle size of 1 μm or less, which is the raw material of the hafnium carbide powder 24, and the carbon black powder having an average particle size of 0.1 μm or less are wet-mixed, dried, and then crushed to obtain the particle size of the aggregate. The pellet 16 had a diameter of 3 mm or less and was press-molded to prepare a columnar pellet 16 having a diameter of 75 mm.

The obtained pellet 16 was housed in the second crucible 17, and the second crucible 17 was placed in the first crucible 12. Then, with the argon gas supplied from the supply pipe 14 into the first crucible 12, the high frequency induction heating furnace 11 is operated to heat the inside of the second crucible 17 to 1800 to 2000 ° C. to reduce and carbonize hafnium oxide. To produce hafnium carbide powder 24. The average particle size of the obtained hafnium carbide powder 24 was 0.72 μm. The content of carbon particles, which are impurities in the hafnium carbide powder 24, was 0.01% by mass. The particle size of the carbon particles was 5 to 10 μm.

Next, the obtained hafnium carbide powder 24 was milled for 4 hours by a dry milling method using a planetary ball mill 20.
Subsequently, the hafnium carbide powder 24 after the milling treatment is heated to 1800 to 1900 ° C. under a pressure of 70 to 90 MPa with a pulse energization pressure sintering apparatus 40 and sintered, and a sintered body having a diameter of 30 mm and a length of 6 mm is obtained. 47 was prepared. The sintered body 47 was subjected to electric discharge machining to obtain an electrode tip 54 of a plasma electrode 52 having a diameter of 2 mm and a length of 6 mm. Using this electrode tip 54, the plasma electrode 52 was manufactured by performing operations such as silver brazing, cutting, and chamfering.

Regarding the obtained plasma electrode 52, the relationship between the arc time (min) of the plasma arc 53 and the electrode wear depth (mm) and the arc time (min) of the plasma arc 53 and the electrode wear mass (mg) under the condition of a current of 300 A. ), And are shown in FIGS. 7 and 8. 7 (a) and 8 (a) show the case where the hafnium carbide powder 24 is not milled, and FIGS. 7 (b) and 8 (b) show the case where the hafnium carbide powder 24 is milled. .. In addition, □, Δ and × in each figure represent the results of three samples with sintering conditions of 1850 ° C. and 80 MPa, and ○ marks represent cases where the sintering conditions are 1900 ° C. and 70 MPa.

As shown in FIGS. 7 and 8, the plasma electrode 52 obtained by using the hafnium carbide powder 24 of Example 1 has a long life regardless of the presence or absence of the milling treatment of the hafnium carbide powder 24. Shown. Furthermore, it was shown that the difference between the samples was smaller in the case where the milling treatment was performed than in the case where the milling treatment was not performed, and the samples were homogeneous.

(Comparative Example 1)
In Comparative Example 1, hafnium carbide powder 24 was produced by a conventional method. That is, the hafnium carbide powder 24 was produced by the first heat treatment in the second production method.

As shown in FIG. 2, the pellet 16 of the first embodiment is housed in a carbon third crucible 26, the third crucible 26 is arranged in a high frequency induction heating furnace 11, and the third crucible 26 and the high frequency induction are arranged. A carbon powder 13 was filled between the inner surface of the heating furnace 11 and the inner surface of the heating furnace 11 as a heat insulating material. Next, the high-frequency induction heating furnace 11 was operated to heat the inside of the third rutsubo 26 to 1800 to 2000 ° C., and the hafnium carbide powder 24 was obtained by the reduction / carbonization reaction of hafnium oxide.

The average particle size of the obtained hafnium carbide powder 24 was 0.71 μm. The content of carbon particles, which are impurities in the hafnium carbide powder 24, was 0.06% by mass. The particle size of the carbon particles covered a wide range of 5 to 50 μm.

Next, the hafnium carbide powder 24 was milled by a dry milling method using a planetary ball mill 20 in the same manner as in Example 1. Further, the hafnium carbide powder 24 was heated and sintered by the pulse energization pressure sintering apparatus 40 in the same manner as in Example 1 to obtain a sintered body 47 having a columnar shape having a diameter of 30 mm. The sintered body 47 was subjected to electric discharge machining to obtain an electrode chip 54, and a plasma electrode 52 was manufactured.

Regarding the obtained plasma electrode 52, the relationship between the arc time (min) of the plasma arc 53 and the electrode wear depth (mm) and the arc time (min) of the plasma arc 53 and the electrode wear mass (mg) under the condition of a current of 150 A. ), And are shown in FIGS. 9 (a) and 9 (b). The □, Δ, ○ and × marks in each figure indicate the results of four samples under the same conditions.

As shown in FIGS. 9 (a) and 9 (b), the plasma electrode 52 obtained by using the hafnium carbide powder 24 of Comparative Example 1 has a current of 150 A, which is half that of Example 1. Nevertheless, the arc time is 180 to 300 min, the consumption depth and the consumption mass increase sharply, and the life is obviously short.

(Example 2)
In this Example 2, the hafnium carbide powder 24 was produced by the second production method described above. The pellet 16 used as a raw material for the hafnium carbide powder 24 was prepared in the same manner as in Example 1.

As shown in FIG. 2, the pellet 16 is housed in a carbon third crucible 26, the third crucible 26 is arranged in the high frequency induction heating furnace 11, and the third crucible 26 and the inner surface of the high frequency induction heating furnace 11 are arranged. Carbon powder 13 was filled between the two as a heat insulating material. Next, the high-frequency induction heating furnace 11 was operated to heat the inside of the third rutsubo 26 to 1800 to 2000 ° C. to perform the first heat treatment, and the hafnium carbide powder 24 was obtained by the reduction / carbonization reaction of hafnium oxide.

Next, as shown in FIG. 3, the third crucible 26 was taken out from the high frequency induction heating furnace 11, and the hafnium carbide powder 24 in the third crucible 26 was loaded into the fourth crucible 29 made of silicon carbide. Subsequently, after arranging the fourth crucible 29 in the vacuum heating furnace 28, the inside of the vacuum heating furnace 28 was heated to 1800 to 2000 ° C. under a vacuum of about 10 Pa to perform the second heat treatment. By this second heat treatment, a hafnium carbide powder 24 was obtained in which the reduction / carbonization reaction of hafnium oxide was promoted and carbon particles as residual impurities were reduced.

The average particle size of the hafnium carbide powder 24 thus obtained was 1.19 μm. The content of carbon particles, which are impurities in the hafnium carbide powder 24, was 0.02% by mass. The particle size of the carbon particles was 5 to 10 μm.

(Example 3)
In Example 3, the same as in Example 2 except that the hafnium carbide powder 24 in the third crucible 26 was loaded into the carbon fifth crucible 33 and the second heat treatment was performed. Hafnium carbide powder 24 was prepared.

As a result, the average particle size of the obtained hafnium carbide powder 24 was 1.02 μm. The content of carbon particles, which are impurities in the hafnium carbide powder 24, was 0.02% by mass. The particle size of the carbon particles was 5 to 10 μm.

(Comparative Example 2)
In Comparative Example 2, regarding the conventionally used metal hafnium electrode, the relationship between the arc time (min) of the plasma arc 53 and the electrode consumption depth (mm) and the arc time of the plasma arc 53 (the arc time of the plasma arc 53) under the condition of a current of 300 A. The relationship between min) and the electrode consumption mass (mg) was determined and shown in FIGS. 10 (a) and 10 (b). In each figure, □ indicates the result of sample 1, and × indicates the result of sample 2.

As shown in FIGS. 10 (a) and 10 (b), in the metal hafnium electrode of Comparative Example 2, when the current is 300 A, the consumption depth and the consumption mass tend to suddenly increase at an arc time of 150 min. It is clear that the life is shorter than that of Example 1.

It is also possible to modify the embodiment as follows to embody it.
-As the milling process, a processing method using a vibrating ball mill, a wet ball mill, or the like can also be adopted.

-Instead of the high frequency induction heating, a heating method such as microwave heating or energization heating may be adopted.
-The material of the 4th crucible 29 or the 5th crucible 33 may be changed to ceramics such as alumina, magnesia, and zirconia.

11 ... High frequency induction heating furnace, 12 ... 1st crucible, 17 ... 2nd crucible, 20 ... Planetary ball mill, 24 ... Hafnium carbide powder, 25 ... 1st heat treatment device, 26 ... 3rd crucible, 27 ... 2nd Heat treatment device, 28 ... Vacuum heating furnace, 29 ... 4th crucible, 33 ... 5th crucible, 52 ... Plasma electrode.

Claims (7)

Formula HfC _x (where, x = 0.5 to 1.0) a powder of hafnium carbide represented by state, and are content 0.03 wt% carbon particles as an impurity, said carbon particles hafnium carbide powders for range der Ru plasma electrode particle size of the 5 to 10 [mu] m. The hafnium carbide powder for a plasma electrode according to claim 1, wherein the hafnium carbide powder has an average particle size of 0.5 to 2 μm. Formula HfC _x (where, x = 0.5 to 1.0) is represented by, in the manufacturing method of the hafnium carbide powder for the plasma electrodes content of carbon particles as a non neat is less than 0.03 wt% There,
A mixed powder of hafnium oxide and carbon is housed in a silicon carbide crucible, and the crucible is placed in a carbon crucible and heat-treated at 1800 to 2000 ° C. for a plasma electrode for producing hafnium carbide powder. A method for producing hafnium carbide powder. Formula HfC _x (where, x = 0.5 to 1.0) is represented by, in the manufacturing method of the hafnium carbide powder for the plasma electrodes content of carbon particles as a non neat is less than 0.03 wt% There,
A mixed powder of hafnium oxide and carbon is housed in a carbon crucible, the crucible is placed in a high-frequency induction heating furnace, and the high-frequency induction heating furnace is filled with carbon powder so as to cover the crucible. An inert gas is supplied into the crucible and the first heat treatment is performed at 1800 to 2000 ° C. to obtain a hafnium carbide powder, and then the hafnium carbide powder in the crucible is transferred to a silicon carbide or carbon crucible. A method for producing a silicon carbide hafnium powder for a plasma electrode, wherein the crucible is placed in a vacuum heating furnace and a second heat treatment is performed at 1800 to 2000 ° C. in a vacuum state to generate a carbide hafnium powder. The method for producing a hafnium carbide powder for a plasma electrode according to claim 3 or 4, wherein the produced hafnium carbide powder is subjected to a milling treatment to adjust the particle size of the hafnium carbide powder. A hafnium carbide sintered body for a plasma electrode in which the hafnium carbide powder according to claim 1 or 2 is sintered. A plasma electrode composed of a hafnium carbide sintered body for the plasma electrode according to claim 6.

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