JP6913996B2 - Manufacturing method of fine tungsten carbide powder - Google Patents

Description

INDUSTRIAL APPLICABILITY The present invention manufactures tungsten carbide powder containing fine-grained tungsten carbide (WC) powder as a raw material for its production in fields such as cutting tools and tungsten carbide-based cemented carbide used as abrasion-resistant tools for plastic machining of dies and the like. It's about the method.

Conventionally, for example, in a superhard material for a cutting tool using a tungsten carbide sintered body, it has been known that properties such as strength and hardness are improved by atomizing the tungsten carbide phase after sintering. Therefore, it is required to further reduce the size of the tungsten carbide powder as a raw material powder.
On the other hand, in the method for producing tungsten carbide powder, the raw materials used and the intermediate products produced in the intermediate process are atomized and activated, which may lead to ignition or ignition. Therefore, further atomization occurs. Therefore, it is required to provide a new manufacturing method of tungsten carbide powder with sufficient consideration for safety.

Various proposals have been made for the above-mentioned requirements for atomization as follows.
_{For example, in Patent Document 1, a carbon powder having a particle size of 1.0 μm or less is mixed with WO 3} powder having a particle size of 5 μm or less, the reduction step is omitted, a high temperature nitrogen gas atmosphere of 1250 to 1300 ° C., and It has been proposed that ultrafine WC powder having a particle size of 0.5 μm or less can be directly obtained through a pulverization step after carbonization treatment in a high temperature hydrogen gas atmosphere of 1400 to 1500 ° C.

Further, in Patent Document 2, high-purity ammonium metatungstate (AMT) or ammonium tungstate (AT) is used as the raw material powder instead of tungsten oxide powder, and high-purity carbon powder is added and mixed to form a slurry. By low-temperature drying, heat reduction treatment in a nitrogen atmosphere, addition of high-purity carbon powder, and carbonization treatment in a hydrogen atmosphere, an average of 0.5 μm or less is not required. It has been proposed to obtain fine-grained tungsten carbide powder having a particle size (Fisher-sub-sheave-sizer method (hereinafter referred to as "FSSS method") standard).

Further, in Patent Document 3, in the first heat treatment step, a mixture of ultrafine tungsten oxide and carbon powder is heated in an inert atmosphere and reduced until the _{intermediate products become W, W 2 C and WC.} After carbonization, the agglomeration and necking of the intermediate product are pulverized in the pulverization step, and the pulverized intermediate product is heated and carbonized in hydrogen in the next second heat treatment step to obtain nanoparticle size. After obtaining the tungsten carbide powder of, the powder is mechanically pulverized by a pulverizer ^{to have a BET specific surface area of 3.9 m 2} / g or more, and an average particle size of 100 nm or less in terms of the BET method. It has been proposed to produce ultrafine tungsten carbide powder having an increased specific surface area.

Further, in Patent Document 4, APT (ammonium paratungstate) is heated at 600 to 800 ° C. in the air to obtain tungsten trioxide as a raw material powder, and the tungsten trioxide powder and C powder are used as an organic solvent. After wet mixing using, a mixed powder containing tungsten powder and C powder is obtained by hydrogen reduction in a hydrogen atmosphere at 750 ° C. or lower, and then heated to 1000 ° C. or higher to obtain W powder in a hydrogen atmosphere. It has been proposed to react the C powder to produce a tungsten carbide powder having a size of 0.8 μm or less according to the FSSS method standard.

Japanese Patent No. 2617140 Japanese Patent No. 4023711 Japanese Patent No. 4647244 Japanese Patent No. 5443757

As mentioned above, although many proposals have been made for the method for producing fine-grained tungsten carbide powder, due consideration has been given to safety, for example, by utilizing an efficient low-temperature process while atomization is progressing. The current situation is that it has not.
Therefore, as described above, the present invention has been made in consideration of safety when producing ultrafine tungsten carbide powder, which is particularly atomized, in addition to the production of ordinary fine tungsten carbide powder. It is an object of the present invention to provide the manufacturing method of.

In order to solve the above problems, the present inventors have focused on the characteristics and manufacturing method of the fine tungsten carbide powder itself, reviewed the entire process until tungsten carbide is obtained from the raw material, and after giving due consideration to safety in particular, the present inventors. As a result of diligent research to obtain fine and uniform tungsten carbide powder, the following findings were obtained.
That is,
(A) In the method for producing tungsten carbide powder, first, in order to produce fine tungsten carbide powder, it is required to obtain fine particles of tungsten trioxide as the raw material powder. Production of this tungsten trioxide At present, tungsten trioxide is obtained by using, for example, ammonium paratungstate (hereinafter referred to as "APT") or the like as a starting material and baking it.
However, the calcination temperature of APT is generally in the range of 500 ° C. to 900 ° C. because calcination is insufficient at a temperature lower than 500 ° C., and the average particle size of the _{obtained tungsten trioxide (WO 3) powder.} The BET specific surface area was as large as 18 to 20 μm (FSSS method), and the BET specific surface area was at most 9.6 m ² / g even at 500 ° C., which is the maximum value.
In contrast, the present inventors have found that using the tungstate (WO 3 _· H 2 _O) as the starting material, the atmosphere or a nitrogen, an inert atmosphere such as Ar (hereinafter, referred to as "inert atmosphere".) When performing shaving, the shaving temperature can be expanded from 350 ° C to 900 ° C, and in particular, sufficient shaving can be performed even in the low temperature range of 500 ° C or less, so that the thermal efficiency and safety are improved. In addition to being extremely advantageous in terms of surface, _{the average particle size of the obtained tungsten trioxide (WO 3) powder is 3 to} 4 μm (further 0.22 μm after crushing) in the Fisher method, and APT is used as a raw material. The particle size is extremely small compared to that of the above-mentioned one, and it can be made finer by baking at low temperature. For example, when baking is performed at 350 ° C. under a nitrogen atmosphere, the BET specific surface area It has been found that fine tungsten trioxide (WO ₃ ) powder exceeding 34 m ^{2 / g can be obtained.}
(B) Next, in the method for producing fine tungsten carbide powder, various methods are known as methods for obtaining fine tungsten carbide from tungsten trioxide, and one of them is to reduce tungsten trioxide to metallic tungsten. A reduction / carbonization method is known, which comprises a reduction step of the above method and a carbonization step of carbonizing the obtained metallic tungsten and carbon by mixing and heating to obtain tungsten carbide.
In this reduction step, reduction is usually carried out at 600 to 800 ° C., _{and metallic tungsten is obtained through WO 3} → WO _2.9 → WO _2.72 → WO _2, and the particle size of the metallic tungsten obtained here is obtained. The BET specific surface area is 7 to 10 m ² / g as measured by the BET method, and the average particle size is 31 to 44 nm according to the BET method. By performing the reduction step at a temperature of 500 ° C. or lower ^{, β-fine particles having a BET specific surface area of 15 to 35 m 2} / g and an average particle size of 12 to 27 nm according to the BET method are finer than before. It has been found that W (W ₃ O) powder is obtained, and fine- _{grained tungsten carbide powder can be produced by mixing the fine β-W (W 3} O) powder with carbon powder and heating and carbonizing the powder.
(C) Further, the present inventors obtain an excellent fine-grained tungsten carbide powder by the reduction / carbonization method shown in (a) above, but the metal obtained in the reduction steps of _{WO 3} and WO _X. Tungsten carbide powder and β-W (W ₃ O) powder react with oxygen and easily ignite, and there is a safety risk in handling the powder. Since it was necessary to go through multiple troublesome processes of charging into the carbide furnace, a new manufacturing process including safety considerations was further examined.
That is, as a method for producing fine tungsten carbide from tungsten trioxide, tungsten trioxide powder and a predetermined amount of carbon powder are mixed and heated to reduce tungsten trioxide to metallic tungsten and tungsten carbide (WC, W ₂ C). ) Is known, but the present inventors have described the type of carbon powder to be added and the amount to be added to the amount of tungsten with respect to tungsten trioxide obtained from tungsten acid as a starting material. the reaction temperature, the conditions such as reaction time was changed, the reaction product obtained was confirmed by XRD, the reduction treatment at 500 ° C. or less, reduction to tungsten metal powder and β-W (W 3 _O) powder although the reaction proceeds, the carbide formation from resulting metal tungsten powder and β-W (W 3 _O) powder was newly discovered that not performed.
_{Therefore, the present inventors obtained fine β-W (W 3} O) from tungsten carbide by performing hydrogen reduction for a predetermined time at a temperature of 500 ° C. or lower in a hydrogen reduction furnace. By subsequently carrying out carbonization at 1000 ° C. or higher in a hydrogen atmosphere or an inert atmosphere in the same reduction furnace, fine tungsten carbide powder can be produced by a safer process without ignition or the like. By adjusting the treatment temperature and treatment time, ^{a nano-level tungsten carbide powder having a BET specific surface area of 6.41 m 2} / g or more and a BET method standard particle size of 60 nm or less after the carbonization step. Furthermore, a direct reduction / carbonization method has been established that can safely produce nano-level tungsten carbide powder having a BET specific surface area of 9.50 m ^{2 / g or more and a particle size of 40 nm or less based on the BET method.}

The present invention has been made based on the above findings.
"(1) A method for producing fine tungsten carbide powder.
(A) A process for producing tungsten trioxide powder from raw materials,
(B) the mixing the tungsten trioxide powder and carbon powder, and a reducing step of heating the reduction under a hydrogen reducing atmosphere to produce a β-W (W 3 _O) powder,
(C) at the β-W (W 3 _O) under powder hydrogen reducing atmosphere or an inert atmosphere, and carbonization steps carbonized by the carbon residues exist, to produce a fine tungsten carbide powder,
Is a method for producing fine-grained tungsten carbide powder having
Wherein step (a), said raw material is a tungsten acid _(WO 3 · _H 2 O) was calcined under an air atmosphere or under an inert atmosphere at 500 ° C. from 350 ° C., to produce the tungsten trioxide powder It ’s a process,
Step (b), the tungsten trioxide powder under the hydrogen reducing atmosphere, and heated and reduced at 500 ° C. or less of the temperature is a step of producing the β-W (W 3 _O) powder,
Wherein step (c), the hydrogen reducing atmosphere or the inert atmosphere, Ri said _{β-W (W} 3 O) carbonization step Der powder performed at 1000 ° C. or higher,
Wherein (b) carbonizing step is the the reduction step is a step (c) step, Ru carried out in the same reducing furnace,
A method for producing fine tungsten carbide powder.
( 2 ) In the method for producing the fine tungsten carbide powder described in (1),
The fine-grained tungsten carbide powder is a ^{method for producing fine-grained tungsten carbide powder, characterized in that the BET specific surface area is 6.41 m 2} / g or more and the average particle size by the BET method is 60 nm or less.
( 3 ) In the method for producing fine-grained tungsten carbide powder according to (1) or (2).
The fine-grained tungsten carbide powder is a ^{method for producing fine-grained tungsten carbide powder, characterized in that the BET specific surface area is 9.50 m 2} / g or more and the average particle size by the BET method is 40 nm or less.
( 4 ) In the method for producing fine-grained tungsten carbide powder according to any one of (1) to ( 3).
The method for producing fine tungsten carbide powder, wherein the fine tungsten carbide powder has a purity of 99.9% or more, excluding oxygen and nitrogen which are gas components.
( 5 ) In the method for producing fine-grained tungsten carbide powder according to any one of (1) to ( 4).
The fine tungsten carbide powder, method for producing a fine tungsten carbide powder, wherein the Fe content is 100ppm or less. "
It has the characteristics of.

The present invention relates to a novel method for producing fine-grained tungsten carbide powder using a newly proposed direct reduction / carbonization method, as summarized below.

1. 1. Raw material powder <Type of raw material>
In particular, in the case of producing finer fine-grained tungsten carbide, it is required that the raw material tungsten trioxide and the tungsten powder and tungsten oxide obtained by the intermediate treatment are fine particles.
Tungsten trioxide can be produced by calcination or the like using various tungsten-containing compounds as starting materials, but since the particle size of tungsten trioxide obtained by the tungsten-containing compound as the starting material is different, as described above. As the starting material, tungstic acid, which has a fine particle size of tungsten trioxide after calcination and a large BET specific surface area, was used. Further, it is desirable to use fine carbon powder such as carbon black used as a carbonizing agent, and a carbon powder having a particle size of 1.0 μm or less is used.
<Purity of raw materials>
By using, for example, 99.9% by mass or more of high-purity carbon powder such as tungstic acid as a starting material or carbon black or activated carbon, 99.9% by mass or more, and further, 99.99% by mass or more. % Or higher purity tungsten carbide powder can be produced.

2. Manufacturing conditions <Manufacturing of tungsten oxide powder by calcination>
Calcination of the tungsten acid used as a raw material for tungsten trioxide powder (WO 3 _· H 2 _O), as described above, thermal efficiency and safety aspects, or tungsten trioxide powder grain coarsening is suppressed by the low-temperature calcination It is preferably carried out in a temperature range of 350 ° C. to 500 ° C., and has a particle size of 3 to 4 μm (FSSS method standard) and a BET specific surface area ^{of more than 20 m 2} / g derived from tungstic acid. Tungsten oxide powder can be obtained. In particular, it can be atomized by low temperature or baking in an air atmosphere or an inert atmosphere, and at 350 ° C., a BET value of 30 m ² / g or more was obtained.
The tungsten trioxide powder using tungstic acid as a starting material can obtain particles having a high BET value by calcination, but agglomeration occurs. Therefore, by crushing with a jet mill or the like, fine particles of 300 nm or less without agglomeration can be obtained. Can be obtained.
As described above, in the present specification and claims, the inert atmosphere means an inert atmosphere such as nitrogen and Ar.

<Mixing of raw material powder>
(1) Mixing ratio of tungsten trioxide powder and carbon powder When the ratio (C / W) of the carbon content of the carbon powder to the W content in the tungsten trioxide powder is less than 1 in atomic ratio, it is oxidized in the reduction reaction product. On the other hand, if the atomic ratio exceeds 2, the ratio of WC in the reduction reaction product increases, and a large amount of free carbon after the reduction carbonization treatment remains. Therefore, the ratio is set to 1. It was set to ~ 2.
(2) Mixing method of raw material powder The mixing method of tungsten trioxide powder and carbon powder may be either a dry method or a wet method, and the dispersion medium when the wet method is used may be either an aqueous solution or an organic solvent. ..
As the organic solvent, lower alcohols such as methanol and ethanol, acetone, hexane and the like are generally used, but ethanol is preferable in consideration of drying property, environmental load and the like.

<Reduction of tungsten trioxide powder to β-W (W ₃ O) powder>
In this direct reduction / carbonization method, carbon powder is mixed with tungsten trioxide obtained from tungstic acid, and then in a treatment furnace, in a hydrogen reduction atmosphere, for example, in a hydrogen stream, the temperature is 500 ° C. or lower, for example, particularly. By holding at 450 to 500 ° C. for 2 hours or more, reduction from tungsten trioxide to fine β-W (W ₃ O) powder can be performed with carbon remaining, and the atmosphere (oxidation). By proceeding to the next step (carbonization treatment) without exposing it to the atmosphere), fine β-W (W ₃ O) powder can be produced extremely safely, even when some metallic tungsten is produced. It can also be handled.
It is not necessary to specify an upper limit for the hydrogen flow rate in the processing furnace, but if the flow rate is too small, the reduction reaction is not sufficient, and the precursor β-W (W ₃ O) is satisfactorily produced. Since there is no such thing, 10 liters / minute or more is desirable.

<Manufacturing of tungsten carbide powder by carbonizing β-W (W _{3 O) powder>}
In this direct reduction / carbonization method, the reduced fine β-W (W ₃ O) powder and the remaining carbon powder are subjected to different reduction furnaces or subsequently in the same reduction furnace under a hydrogen atmosphere or not. By undergoing a carbonization step in which the temperature is raised to 1000 ° C. or higher and held for 30 to 120 minutes in an active atmosphere, the BET specific surface area is 6.41 m ² / g or more, the particle size based on the BET method is 60 nm or less, and further. It was possible to produce nano-level tungsten carbide powder having a BET specific surface area of 9.50 m ² / g or more and a particle size of 40 nm or less based on the BET method.
The average particle size by the BET method is calculated from the specific surface area by regarding the particles as spheres, and can be obtained by the following formula.
Average particle size (nm) = {6 / (theoretical density (g / cm ³ ) x specific surface area (m ² / g))} x 1000
Where the theoretical density is
For tungsten carbide WC, 15.7 (g / cm ³ )
For metallic tungsten W, 19.3 (g / cm ³ )
For β-W (W ₃ O), 14.6 (g / cm ³ )
For tungsten trioxide WO ₃ , 7.16 (g / cm ³ ) was used.

The present invention relates to a method for producing fine tungsten carbide powder, which is a safe ultrafine tungsten carbide powder that does not ignite without omitting the reduction step of the fine tungsten powder by the newly proposed direct reduction / carbonization method. It is extremely useful because it has found a method for producing powder.
Further, in the present invention, it is possible to produce fine-grained tungsten carbide powder having various particle sizes from the micron or submicron order to the nano level, and in particular, a sintered body produced using nano-level tungsten carbide powder. Has excellent hardness and is extremely useful in the manufacture of cutting tools and the like.

Next, the method for producing the fine tungsten carbide powder according to the present invention will be specifically described with reference to Examples.

Table 1 shows the production conditions in the baking step, the reduction step, the carbonization step when the tungsten carbide powder was manufactured by the direct reduction / carbonization method according to the present invention, the characteristics of the starting raw material powder, and each step. tungsten trioxide powder, a metal tungsten _{powder, β-W (W 3 O} ) powder, and show those characteristic values of tungsten carbide powder after carbonization measured and organized.

In Examples 1 to 6 of the present invention, which are examples of the present invention, tungstic acid having a purity of 99.9% by mass is calcined at 350 ° C. to 500 ° C. in an air atmosphere or a nitrogen atmosphere to have a particle size of 3 to 3. Tungsten trioxide powder derived from tungstic acid ^{having a BET specific surface area of more than 20 m 2} / g at 4 μm (FSSS method standard) could be obtained.
Next, the reaction product obtained by mixing this tungsten trioxide powder with carbon black having a particle size of 0.1 μm or less and a purity of 99.9% by mass and performing reduction in a hydrogen atmosphere of 500 ° C. or less is obtained as X. was confirmed by -ray diffraction (XRD) method, it was confirmed that beta-W which has a cubic crystal structure (W 3 _O) a fine mixed powder of carbon black is obtained.
Further, the obtained mixed powder of fine β-W (W ₃ O) and carbon black is heated at 1000 ° C. or higher in a hydrogen-reducing atmosphere and carbonized to obtain a BET specific surface area of 6.41 m. ^It was possible to produce a fine-grained tungsten carbide powder having an average particle size of 2 / g or more and an average particle size of 60 nm or less by the BET method, and further, a high-purity fine-grained tungsten carbide powder having a Fe content of 30 ppm or less.
Incidentally, BET specific surface area in Table 1 β-W (W 3 _O) is, β-W (W 3 _O) is, and atomized in a state of being mixed with fine powder of carbon, be measured directly by itself Therefore, the value when only tungsten oxide, which does not contain fine carbon powder, is reduced and produced as a raw material is described.

On the other hand, in Comparative Example 1, since the reduction temperature in the reduction step was 600 ° C., which exceeded the reduction temperature range of the present invention, β-W (W ₃ O) was not generated as a constituent phase. The BET specific surface area of the tungsten carbide powder obtained through the carbonization step was 5.70 m ² / g, and the average particle size in terms of the BET method was 67 nm, so that the atomized tungsten carbide powder could not be obtained.
Further, in Comparative Example 2, although β-W (W ₃ O) powder was produced in the reduction step, the carbonization temperature in the carbonization step was low, so that tungsten carbide (WC) was not sufficiently produced, and W ₂ As a result of C remaining, the desired tungsten carbide (WC) powder could not be obtained.
Further, in Conventional Example 1, tungsten trioxide powder is used as a raw material, mixed with acetylene black, reduced in nitrogen at 1100 ° C., and then carbonized in hydrogen at 1100 ° C. to obtain tungsten carbide powder. However, due to the high reduction temperature _{, the formation of β-W (W 3} O) powder could not be confirmed by XRD, and the tungsten carbide powder obtained in the carbonization step had a BET specific surface area. 5.38 m ² / g, the average particle size in terms of BET method was 71 nm, and a satisfactory fine-grained tungsten carbide powder could not be obtained.

The tungsten carbide powders obtained as Examples 1 to 6 of the present invention and Comparative Example 1 are crushed with a cemented carbide ball mill, and then pressed and sintered with a hot press to prepare a WC sintered body. did. A WC sintered body was obtained by filling a mold with crushed powder, raising the temperature to 1800 ° C. while pressurizing at 30 MPa, and holding for 30 minutes.
Table 2 shows the measured density, Vickers hardness, and bending resistance of the obtained WC sintered body.
The Vickers hardness, bending force, and sintered body density, which are the characteristic values of the WC sintered body produced using the tungsten carbide powder of Comparative Example 1, are Vickers hardness 1850 kgf / mm ² and bending force 170 kgf, respectively. While / mm ² and the sintered body density were 98.7%, the WC sintered body produced using the fine-grained tungsten carbide powder according to Examples 1 to 6 of the present invention had fine particles of tungsten carbide as a raw material. All of them have excellent characteristics of high hardness and high density, with Vickers hardness (Hv) of 2300 kgf / mm ² or more, bending force of 170 kgf / mm ² or more, and sintering density of 99.5% or more. It had.

The method for producing fine-grained tungsten carbide powder according to the present invention provides a method for safely producing fine-grained tungsten carbide powder, and is extremely useful.
Further, in the production method according to the present invention, it is possible to produce a tungsten carbide powder having a large BET specific surface area and a small particle size in terms of the BET method, and sintering produced using the obtained fine tungsten carbide powder. Since the body has a high hardness, it is extremely useful for manufacturing cutting tools and abrasion-resistant tools for plastic machining such as dies.

Claims (5)

A method for producing fine tungsten carbide powder.
(A) A process for producing tungsten trioxide powder from raw materials,
(B) the mixing the tungsten trioxide powder and carbon powder, and a reducing step of heating the reduction under a hydrogen reducing atmosphere to produce a β-W (W 3 _O) powder,
(C) at the β-W (W 3 _O) under powder hydrogen reducing atmosphere or an inert atmosphere, and carbonization steps carbonized by the carbon residues exist, to produce a fine tungsten carbide powder,
Is a method for producing fine-grained tungsten carbide powder having
Wherein step (a), said raw material is a tungsten acid _(WO 3 · _H 2 O) was calcined under an air atmosphere or under an inert atmosphere at 500 ° C. from 350 ° C., to produce the tungsten trioxide powder It ’s a process,
Step (b), the tungsten trioxide powder under the hydrogen reducing atmosphere, and heated and reduced at 500 ° C. or less of the temperature is a step of producing the β-W (W 3 _O) powder,
Wherein step (c), the hydrogen reducing atmosphere or the inert atmosphere, Ri said _{β-W (W} 3 O) carbonization step Der powder performed at 1000 ° C. or higher,
Wherein (b) carbonizing step is the the reduction step is a step (c) step, Ru carried out in the same reducing furnace,
A method for producing fine tungsten carbide powder. In the method for producing fine tungsten carbide powder according to claim 1,
The fine-grained tungsten carbide powder is a ^{method for producing fine-grained tungsten carbide powder, characterized in that the BET specific surface area is 6.41 m 2} / g or more and the average particle size by the BET method is 60 nm or less. In the method for producing a fine tungsten carbide powder according to claim 1 or 2.
The fine-grained tungsten carbide powder is a ^{method for producing fine-grained tungsten carbide powder, characterized in that the BET specific surface area is 9.50 m 2} / g or more and the average particle size by the BET method is 40 nm or less. In the method for producing fine-grained tungsten carbide powder according to any one of claims 1 to 3.
The method for producing fine tungsten carbide powder, wherein the fine tungsten carbide powder has a purity of 99.9% or more, excluding oxygen and nitrogen which are gas components. In the method for producing fine-grained tungsten carbide powder according to any one of claims 1 to 4.
The fine tungsten carbide powder, method for producing a fine tungsten carbide powder, wherein the Fe content is 100ppm or less.