JP6953157B2 - Fine Tungsten Carbide Powder - Google Patents

Description

The present invention is a nano-level grain used as a raw material for manufacturing a cutting tool, a tungsten carbide-based cemented carbide used as an abrasion-resistant tool for plastic working such as a mold, and also used as a catalyst for a fuel cell. It relates to a fine tungsten carbide (WC) powder having a diameter.

Conventionally, for example, in a cemented carbide 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 make the tungsten carbide powder as a raw material powder into fine particles.

In response to such a requirement, 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, and in nitrogen gas,} Subsequently, it has been proposed that ultrafine WC powder having a particle size of 0.5 μm or less can be directly obtained by heating in hydrogen gas and then pulverizing. Specifically, the particle size is 0 with a 150 mesh sieve. Ultrafine WC powder having an iron content of .22 μm and an iron content of 0.004% (40 ppm) has been obtained.

Further, in Patent Document 2, 1) ammonium metatungstate (AMT) or ammonium tungstate (AT) is used as a raw material powder, and carbon powder is added to an aqueous solution of AMT or AT, without requiring a pulverization step. Add and mix at a constant ratio of atomic ratio (C / W: 3 to 4) to the tungsten component of AT to form a slurry. 2) The slurry is dried at a low temperature of 350 ° C. or lower, and the carbon powder is used to dry the slurry. material powder by supporting, 3) the raw material powder in a nitrogen atmosphere, subjected to a reduction treatment at a temperature of from 900 to 1600 ° C., as a main component WC, becomes the remainder of W _{2 C} and metallic tungsten, containing no oxide A reduction reaction product is formed, and 4) then carbon powder is added to the reduction reaction product at a ratio of carbonizing to a WC of 1: 1 in atomic ratio with respect to the tungsten component in the reduction reaction product. -Mix and heat at 900 to 1600 ° C. in a hydrogen atmosphere to have an average particle size of 0.5 μm or less (Fisher-sub-sheave sizer method (hereinafter referred to as "FSSS method") standard). It has been proposed to obtain high-purity fine-grained tungsten carbide powder. Specifically, a tungsten carbide powder having an average particle size of 0.30 μm and a purity of 99.997% has been obtained.

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 a pulverization step, and the pulverized intermediate product is heat-carbonized in hydrogen in the next second heat treatment step to obtain nanoparticle size. By mechanically pulverizing with a pulverizer after obtaining the tungsten carbide powder of the ^{above, the carbonization of ultrafine particles having a BET specific surface area of 4.81 m 2} / g or more and an average particle size of 79 nm or less. It has been proposed to obtain tungsten powder.
Specifically, an ultrafine WC powder having a BET specific surface area of 5.73 m ² / g, an average particle size of 67 nm in terms of the BET method, and an iron content of 29 ppm was obtained. There is.

Further, in Patent Document 4, for example, tungsten trioxide obtained by heating APT (ammonium paratungstate) in the air at 600 to 800 ° C. is used as a raw material powder, and the tungsten trioxide powder and C powder are organically used. After wet mixing with a solvent, 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, and W in a hydrogen atmosphere. It has been proposed to react the powder with the C powder to obtain a tungsten carbide powder having a thickness of 0.8 μm or less according to the FSSS method standard.
Specifically, a fine particle WC powder having an average particle size of 0.6 μm and a total content of impurity elements including Si, Ca, and Fe of 200 ppm is obtained according to the FSSS method standard.

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

As described above, fine-grained tungsten carbide powder produced by various manufacturing methods and further, high-purity fine-grained tungsten carbide powder have been proposed, but they are even lighter than recent cutting tools and wear-resistant tools. There are strong demands for miniaturization, miniaturization, and thinning, and the shapes thereof are also diversified and complicated, and the cemented carbides constituting these are required to be further improved in strength and hardness.
Therefore, in the present invention, by studying the further atomization and purification of the tungsten carbide powder, the above-mentioned conventional fine-grained tungsten carbide powder, specifically, the BET specific surface area is 5.7 m ^{2 at the maximum.} At the / g level, that is, at the average particle size in terms of the BET method, the fine-grained tungsten carbide powder with a minimum level of 67 nm is further micronized, and in addition, further refinement is promoted, particularly high hardness and high density. It is an object of the present invention to provide a novel ultrafine tungsten carbide powder which is a raw material powder of a super hard alloy or a ceramics sintered body used in manufacturing a cutting tool and an abrasion resistant tool.

In order to solve the above problems, the present inventors have focused on the characteristics and manufacturing method of the fine-grained tungsten carbide powder itself, reviewed the entire process until tungsten carbide is obtained from the raw material, and refined the fine-grained tungsten carbide powder, and further As a result of diligent research to obtain highly purified fine-grained tungsten carbide powder, the above-mentioned problems have been solved based on the following two findings (knowledge 1 and finding 2).

A. Findings 1
In order to solve the above problems, the present inventors have reviewed and prepared a conventional method for producing fine-grained tungsten carbide powder, for example, a conventional method for producing fine-grained tungsten carbide powder described in Patent Document 2. After the raw material powder was dried at a low temperature, a new _{reduction nitriding treatment was performed in an ammonia (NH 3} ) atmosphere prior to the subsequent reduction carbide treatment in a nitrogen atmosphere, and then an inert atmosphere such as nitrogen and Ar was performed. (Hereinafter, referred to as "inert atmosphere".) It has been found that a new finer tungsten carbide powder can be obtained by performing a reduction carbonization treatment under a hydrogen atmosphere and then a carbonization treatment under a hydrogen atmosphere. .. (Hereinafter referred to as "Knowledge 1")
That is, when the present inventors _{confirmed the reaction product after the reduction nitriding treatment in the ammonia (NH 3} ) atmosphere by the XRD spectrum, tungsten oxynitride (WON) was produced as the reduction nitriding reaction product. Moreover, the BET specific surface area of the produced tungsten oxynitride (WON) powder was ^{extremely high at 10 to 50 m 2} / g, and it was extremely fine.
Then, the formation of the fine particles of tungsten oxynitride (WON) promotes the atomization of the final product, tungsten carbide. _{Therefore, the reduction nitriding treatment temperature in an ammonia (NH 3} ) atmosphere is set to, for example, 600 to 800 ° C. As a result, the ratio of tungsten oxynitride (WON) to the reduction nitriding reaction product increases, and as the final product, the BET specific surface area is 6.41 m ² / g or more, and the average particle size in terms of the BET method is 60 nm or less. Furthermore, it has been found that a fine tungsten carbide powder having a BET specific surface area of 9.50 m ² / g or more and an average particle size of 40 nm or less in terms of the BET method can be obtained.
Further, at that time, it was found that by using a high-purity raw material, a high-purity fine-grained tungsten carbide powder having an Fe content of 30 ppm or less and further 20 ppm or less as an impurity can be obtained. It is a thing.
Here, the fine-grained tungsten carbide powder produced based on this finding 1 is hereinafter referred to as "fine-grained tungsten carbide powder A".
The reason why the tungsten carbide powder according to the present invention produced according to Finding 1 is extremely fine compared to the conventional fine tungsten carbide powder is first described in the reduction nitriding step in an _{ammonia (NH 3) atmosphere.} In addition to being able to produce extremely fine tungsten oxynitride as a precursor of tungsten carbide powder, in the subsequent steps, the reduction carbonization step in nitrogen and the carbonization step in hydrogen, the above-mentioned steps were taken. It is presumed that tungsten oxynitride has found a production condition in which reduction carbonization proceeds without grain growth.
The ultrafine tungsten carbide powder according to the present invention obtained in such a production process is at an ultrafine level that cannot be produced by a conventional production method.

B. Knowledge 2
Further, the present inventors obtained tungsten trioxide from the conventional, for example, ammonium paratungstate (APT) or the like described in Patent Document 4 or the like, and then reduced it to metallic tungsten. Regarding the method of producing fine-grained tungsten carbide by the reduction / carbonization method, which is to further mix and heat this with carbon to obtain tungsten carbide powder, we investigated a new production process based on new knowledge, and compared it with the conventional fine-grained tungsten carbide powder. , It was found that a new finer tungsten carbide powder can be obtained. (Hereinafter referred to as "Knowledge 2")

That is,
(A) In the method for producing a tungsten carbide powder, first, in order to produce a fine tungsten carbide powder, it is required to obtain a fine particle powder of tungsten trioxide as a raw material powder thereof. Production of this tungsten trioxide At present, tungsten trioxide is obtained by using, for example, 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 if the temperature is 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 standard ), and the BET specific surface area was ^{at most 9.6 m 2} / g even at 500 ° C., which is the maximum value of the calcination temperature.
In contrast, the present inventors have found that using the tungstate (WO 3 _· H 2 _O) as a starting material, or an air atmosphere, in an inert atmosphere, in the case of performing the calcination, the calcination temperature of 350 It can be expanded from ℃ to 900 ℃, and it can be sufficiently calcinated even in the low temperature range of 500 ℃ or less, which is extremely advantageous in terms of thermal efficiency and the obtained tungsten trioxide (WO ₃ ). The average particle size of the powder is 3 to 4 μm according to the FSSS method standard , which is extremely small compared to the one using APT as a raw material, and moreover, it can be made finer as it is calcinated at low temperature, for example, in a nitrogen atmosphere. When calcination is performed at 350 ° C, fine tungsten trioxide (WO ₃ ) with an average particle size of 3 to 4 μm (0.22 μm after crushing) and a BET specific surface area ^{of more than 34 m 2 / g.} ) Found that powder 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, it is usually reduced at 600 to 800 ° C. _{to obtain metallic tungsten through WO 3} → WO _2.9 → WO _2.72 → WO _2, and the particle size of the metallic tungsten obtained here is. As measured by the BET method, the BET specific surface area is 7 to 10 m ² / g, and the average particle size is 31 to 44 nm according to the BET method, whereas the present inventors have reduced this tungsten trioxide. By performing the step at a temperature of 500 ° C. or lower ^{, β-W of 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 standard is finer than before. (W ₃ O) was obtained, and it was found that fine tungsten carbide powder can be produced by mixing such fine β-W (W _{3 O) with carbon powder and heating and carbonizing the powder.}

(C) Next, the present inventors obtained the 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 powder and β-W (W 3 _O) flour, easily reacts with oxygen firing, since there is a risk in the safety in the powder handling, mixing with carbon powder in an inert gas atmosphere, extraction, Since it was necessary to go through multiple troublesome processes of charging into a carbonization 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. After that, by performing carbide in a different reduction furnace or subsequently in the same reduction furnace in a hydrogen atmosphere or an inert atmosphere at 1000 ° C. or higher, a safer process without ignition or the like is performed. By adjusting the treatment temperature and the treatment time, the BET specific surface area is 6.41 m ² / g or more, which is the average based on the BET method, by adjusting the treatment temperature and the treatment time. We have found that it is possible to produce nano-level tungsten carbide powder having a particle size of 60 nm or less, and further, nano-level tungsten carbide powder having a BET specific surface area of 9.50 m ² / g or more and an average particle size of 40 nm or less based on the BET method. rice field.
Further, at that time, it has been found that by using a high-purity raw material, a high-purity fine-grained tungsten carbide powder having a Fe content of 30 ppm or less contained as an impurity can be obtained.
Here, the novel fine-grained tungsten carbide powder produced based on Knowledge 2 is hereinafter referred to as "fine-grained tungsten carbide powder B".
The reason why the obtained tungsten carbide powder in the present invention produced according to Knowledge 2 is extremely fine compared to the conventional fine tungsten carbide powder is that the raw material powder is extremely fine tungsten trioxide (WO ₃ ). _{In addition to obtaining powder and using it, fine β-W (W 3} O), which is a precursor of tungsten carbide powder, is produced in the hydrogen reduction step, and production without grain growth is also carried out in the subsequent steps. It is presumed that this was due to the discovery of the conditions.
The ultrafine tungsten carbide powder according to the present invention obtained in such a production process is at an ultrafine level that cannot be produced by a conventional production method.

As described above, the present invention has been made based on the above-mentioned findings 1 and 2.
(1) A fine-grained tungsten carbide powder having a BET specific surface area of 8.67 m ² / g or more and 12.05 m ² / g or less, and an average particle size of 32 nm or more and 44 nm or less by the BET method.
(2) BET specific surface area, 9.50m ² / g or more, 12.05m ² / g or less, an average particle diameter of 32nm or more by a BET method, fine tungsten carbide powder, characterized in that at 40nm or less.
(3) The fine-grained tungsten carbide powder according to ( 1 ) or ( 2 ) above, wherein the Fe content is 30 ppm or less.
(4) The fine-grained tungsten carbide powder for a cemented carbide material according to any one of ( 1 ) to ( 3 ) above. "
It has the characteristics of.
In particular, the fine-grained tungsten carbide powder according to the present invention produced according to Findings 1 and 2 is an intermediate product of extremely fine particles as a precursor of the tungsten carbide powder in the manufacturing process. Alternatively, by newly generating β-W (W ₃ O), a novel nano-level ultrafine tungsten carbide powder, which could not be achieved by the conventional method, is provided, and the conventional fine particles are provided. It is possible to provide a sintered product having higher strength, higher hardness, higher density, and excellent folding resistance than a sintering tool using tungsten carbide powder.

Hereinafter, the present invention will be described in more detail.
A. Fine Tungsten Carbide Powder A
A-1. Raw material powder <Type of raw material>
Raw material powders include tungsten-containing compounds that are usually used as raw materials in the production of tungsten carbide powders such as ammonium metatungstate (AMT), ammonium tungstate (AT), ammonium paratungstate (APT), tungstic acid, and tungsten trioxide. Powder can be used.
Further, as the carbon powder, carbon powder which is usually used as a raw material when producing a tungsten carbide powder such as carbon black or activated carbon can be used.
<Purity of raw materials>
High-purity tungsten carbide powder can be produced by setting the purity of the tungsten-containing compound and carbon powder used as raw materials to 99.9% by mass or more, or 99.99% by mass or more.
A-2. Mixing of raw material powder <Mixing ratio of tungsten-containing compound powder and carbon powder>
When the ratio of the carbon content (C / W) of the carbon powder to the W content in the tungsten-containing compound powder is less than 1, the oxide remains in the reduction reaction product, while the atomic ratio exceeds 2. As a result, the ratio of carbon in the reduction reaction product increases, and a large amount of free carbon after the reduction carbonization treatment may remain. Therefore, the ratio was set to 1 to 2.
<Mixing method of raw material powder>
The mixing method of the tungsten-containing compound powder and the 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.
A-3. Drying temperature The tungsten-containing compound powder and carbon powder mixed by the wet method are dried at a low temperature to become a raw material powder in which the carbon powder carries the tungsten-containing compound.
When this drying temperature exceeds 350 ° C., a decomposition reaction of the tungsten-containing compound occurs, and the coarsening of the tungsten compound produced after the decomposition causes the reduction reaction product produced in the heat reduction treatment in the next step to become finer. Since it may be difficult, the drying temperature was set to 350 ° C. or lower.

A-4. Reduction nitriding temperature in ammonia (NH ₃ ) atmosphere The raw material powder obtained by mixing tungsten-containing compound powder and carbon powder is reduced nitriding in ammonia (NH ₃ ) atmosphere in the reduction nitriding step, and X-ray. A reduction nitriding reaction product containing a mixture of tungsten oxynitriding (WON) powder, which is a precursor of fine-grained tungsten carbide powder having a cubic crystal structure, and carbon powder is produced by a diffraction method.
If the reduction nitriding temperature in the ammonia (NH ₃ ) atmosphere is less than 600 ° C., the reduction reaction and the nitriding reaction are not sufficiently performed, so that the precursor tungsten oxynitride (WON) is not satisfactorily produced. , The unreacted tungsten compound may cause grain growth and coarse particle formation in the reduction carbonization reaction in the next step, and if the temperature exceeds 800 ° C., the reduction reaction with ammonia proceeds and the W powder produced. The reduction nitriding temperature was set to 600 ° C. to 800 ° C. because there is a possibility that grain growth may occur.
Reducing nitriding in an ammonia (NH _{3 ) atmosphere can be performed, for example, by introducing an ammonia (NH 3} ) air stream into a reducting nitriding apparatus in which the raw material powder is arranged and heating it to a predetermined temperature. It is not necessary to specify an upper limit for the flow rate _{of ammonia (NH 3} ) into the reduction nitriding apparatus.
However, if the flow rate is too small, the reduction reaction and the nitriding reaction are not sufficient, the precursor tungsten oxynitride (WON) is not satisfactorily produced, and the unreacted tungsten compound is used in the reduction carbonization reaction in the next step. The flow rate is preferably 10 liters / minute or more because it may cause grain growth and coarse particles. For the same reason, unreacted tungsten compounds are not produced, and the treatment time is long. It is desirable that the particles do not grow or become coarse particles for about 1 to 2 hours.
In the above, from the viewpoint of dispersibility of the carbon powder, the tungsten-containing compound powder and the carbon powder are mixed at an initial stage, and then the reduction nitriding treatment is performed in an ammonia atmosphere to produce fine tungsten carbide powder. However, the tungsten-containing compound powder may be subjected to a reduction nitride treatment first, and the resulting fine tungsten oxynitride (WON) powder may be mixed with the carbon powder, followed by reduction carbonization treatment and carbonization treatment. Fine tungsten carbide powder can be produced.

A-5. Reducing carbonization temperature the reduction nitriding reaction product in an inert atmosphere, in a reducing carbonization step, nitrogen is reduced carbonized in an inert atmosphere such as Ar, tungsten carbide (WC) as a main component, the remainder W ₂ C It is composed of metal tungsten and carbon powder, and produces a reduced carbonization reaction product which is substantially free of oxides and oxynitrides.
If the reduction carbonization temperature in the inert atmosphere is less than 1000 ° C., the reduction reaction and the carbonization reaction do not proceed sufficiently, and the reduction to metallic tungsten may not be sufficiently performed. The reduction carbonization temperature was set to 1000 ° C. or higher.
Reduction carbonization in an inert atmosphere can be performed, for example, by replacing the gas introduced into the apparatus with a nitrogen stream. Regarding the nitrogen flow rate into the device at that time, if the flow rate is too small, the unreacted tungsten compound may cause grain growth and coarse particle formation in the carbonization reaction in the next step, so 10 liters / minute. That's all.
Further, if the treatment time is too short, the unreacted tungsten compound may cause grain growth or coarse particle formation in the carbonization reaction in the next step, and if it is too long, grain growth or coarse particle formation proceeds. It is desirable to use about 1 to 2 hours because fine tungsten carbide particles may not be obtained.
Although the upper limit of the reduction carbonization temperature is not particularly specified, the carbonization treatment at a high temperature causes the WC particles to grow and become coarse particles, and fine tungsten carbide particles cannot be obtained. Therefore, the temperature is 1300 ° C. or lower. preferable.

A-6. Carbonization Temperature in Hydrogen Atmosphere The carbonization reaction product is carbonized in a hydrogen atmosphere in the carbonization step to produce fine tungsten carbide powder.
For carbonizing temperature in a hydrogen atmosphere is less than 1000 ° C., the carbonization reaction does not proceed sufficiently, there is a possibility that carbide is not sufficiently performed in the tungsten carbide of the metal tungsten and W _{2 C} (WC), hydrogen The carbonization temperature in the atmosphere is 1000 ° C. or higher.
The upper limit of the carbonization temperature is preferably 1300 ° C. or lower so that coarse particles do not proceed due to grain growth of WC particles.
If the treatment time is too short, unreacted tungsten compounds may remain, and if it is too long, grain growth and coarse particle formation may proceed, and fine tungsten carbide particles may not be obtained. Therefore, 1 to 2 hours. Degree is desirable.

A-7. Tungsten Carbide Powder The specific surface area of the obtained tungsten carbide powder was measured by the gas adsorption method and shown as the BET specific surface area. The average particle size of the tungsten carbide powder is shown as the average particle size based on the BET method calculated from the BET specific surface area.
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
Here, the theoretical density is 15.7 (g / cm ³ ) for tungsten carbide WC and 12.1 (g / cm ³ ) for tungsten oxynitride (WON).

B. Fine Tungsten Carbide Powder B
B-1. Raw material powder <Type of raw material>
In order to produce ultrafine 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.

B-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) is and thermal efficiency and safety aspects, characteristics such as tungsten trioxide powder of grain coarsening is suppressed by the low-temperature calcination Therefore, it is preferable to carry out in a temperature range of 350 ° C. to 500 ° C., and obtain a tungsten trioxide-derived tungsten trioxide powder having ^{a particle size of 3 to 4 μm (FSSS method standard) and a BET specific surface area of more than 20 m 2 / g.} be able to. In particular, it can be atomized by low temperature or baking in an atmospheric atmosphere or an inert atmosphere, and at 350 ° C., a BET value of 30 m ² / g or more was obtained. In particular, it could be atomized by low temperature or baking in an air atmosphere or a nitrogen 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.

<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) raw material powder mixing method tungsten trioxide powder and mixed how carbon powder may be any of how the dry method and a wet method, the dispersion medium in the case of using a wet method, an aqueous solution, any organic solvent But it may be.
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, after mixing carbon powder with tungsten trioxide obtained from tungstic acid, in a treatment furnace, in a hydrogen reduction atmosphere, for example, in a hydrogen stream, at 500 ° C. or lower, for example, in particular, by holding for 2 hours or more at 450 to 500 ° C., the reduction to the three fine tungsten oxide of β-W (W 3 _O) powder, without reacting with carbon in a state of being left carbon Since it is possible to proceed to the next step (carbonization treatment) without exposing it to the atmosphere (oxidizing atmosphere), it is extremely safe to produce fine-grained β-, even when some metallic tungsten is produced. W (W ₃ O) powder can be produced and 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 hydrogen atmosphere or inactivity in different reduction furnaces or subsequently in the same reduction furnace. 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 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. , A 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 could be produced.
As described in paragraph 0020 to A-7, 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
Here, the theoretical density is 15.7 (g / cm ³ ) for tungsten carbide WC, 14.6 (g / cm ³ ) for β-W (W _{3 O), and tungsten trioxide (g / cm 3).} For WO ₃ ), 7.16 (g / cm ³ ) was used, and for metallic tungsten, 19.3 (g / cm ³ ) was used.

The present invention provides a conventional ultrafine tungsten carbide powder, particularly an ultrafine tungsten carbide powder that is finer than the fine particle tungsten carbide powder known for a conventional cemented carbide material. Sintered bodies and cutting tools manufactured using the ultrafine tungsten carbide powder are extremely useful because they are more excellent in properties such as strength and hardness.

Next, the ultrafine tungsten carbide powder according to the present invention will be specifically described with reference to Examples.

Table 1 shows Examples 1 to 11 of the present invention, which are examples of the fine-grained tungsten carbide powder A produced based on Finding 1, as Example 1 (however, Examples 1 to 3, 6 to 8 and 10 of the present invention). ~ 11 are described as examples of the present invention, but are reference examples. The same shall apply hereinafter), and are also known as raw materials for hard materials in the above-mentioned prior art documents. An ultrafine tungsten carbide powder produced by a conventional method, which is an ultrafine tungsten carbide powder, is shown as Conventional Example 1.
Specifically, Table 1 shows the types of W-containing compound raw materials used as raw materials, the FSSS average particle size (μm), and the types of carbon raw material powders for Examples 1 to 11 of the present invention and Conventional Example 1. The BET value (m ² / g), the atomic ratio of C / W, and the mixing method of the W-containing compound raw material and the carbon raw material powder are shown.
In addition, in the reduction carbonization step, the reduction carbonization temperature, the treatment time, the atmospheric gas and its flow rate, the type of the production phase of the reduction carbonization reaction product, the BET value (m ² / g), N%, O%, C. %, The reduction temperature, the treatment time, the atmospheric gas and the flow rate in the reduction carbonization step, the type and BET value (m ² / g) of the production phase of the reduction carbonization reaction product, and the treatment temperature in the carbonization step. The treatment time, the atmospheric gas, and the characteristic values (BET specific surface area, BET equivalent particle diameter, carbon content, Fe content) of the obtained tungsten carbide powder are shown.
As shown in Table 1, in Examples 1 to 11 of the present invention, AMT, APT, tungsten trioxide, and tungstic acid are prepared as raw materials for the tungsten-containing compound, and the average particle size of the carbon raw material powder is 0.1 μm. The following carbon black or activated carbon is prepared, and in wet mixing, pure water, ethanol or methanol is used as a solvent and mixed with a stirrer or a mixing device such as an attritor to form a slurry, which is dried at a low temperature at 350 ° C. Was carried out to obtain a raw material powder. Further, in the dry mixing, the same mixing device was used in the dry mixing to obtain a raw material powder.

Next, the raw material powder is _{subjected to reduction nitriding in an ammonia (NH 3} ) atmosphere at a temperature of 600 to 800 ° C., a part of the reduction nitriding reaction product is taken out, and an XRD (X-ray diffraction) method is used. As a result, it was confirmed that in all of the examples of the present invention, tungsten oxynitride (WON) having a cubic crystal structure was produced.
Regarding the BET specific surface area of tungsten oxynitride (WON), since tungsten oxynitride (WON) is atomized in a state of being mixed with carbon fine powder, tungsten oxynitride (WON) in a state where carbon fine powder is removed ) Only as the BET specific surface area.

Next, using a nitrogen atmosphere as the inert atmosphere, the reduction nitride reaction product was held at 1000 ° C. or higher in a nitrogen atmosphere for a predetermined time, and a part of the reduction carbonization reaction product obtained by reduction and carbonization was taken out. was confirmed by the XRD (X-ray diffraction) method, any one of the examples of the present invention, mainly of tungsten carbide (WC), the remainder consisted of W _{2 C} and tungsten metal.

Next, the reduced carbonization reaction product was held in a hydrogen atmosphere at 1000 ° C. or higher for a predetermined time, carbonized, and the obtained carbonization reaction product was confirmed by X-ray diffraction. All of the carbonization reaction products were tungsten carbide (WC).
Further, the BET specific surface areas obtained by the BET method all had 6.41 m ² / g or more, and the average particle size in terms of BET was 60 nm or less, and nano-level tungsten carbide was obtained.

On the other hand, in the conventional example 1, the tungsten carbide powder produced in the conventional example 1 is BET because the fine particles of tungsten oxynitride (WON) are not obtained as an intermediate product without undergoing the reduction nitriding step. The specific surface area was as ^{small as 3.20 m 2} / g, the BET-equivalent particle size was 119 nm, and the particle size was on the order of submicron.

Further, Table 2 shows that the tungsten carbide powders obtained in Examples 1 to 11 of the present invention and Conventional Example 1 were used and obtained by hot press sintering under the conditions of 1800 ° C. and a pressing force of 30 MPa. The hardness, bending force and density of the sintered body are shown. The WC sintered bodies produced using the tungsten carbide powders of Examples 1 to 11 of the present invention all have a Vickers hardness of 2100 kg / mm ² or more, a bending force of 120 kg / mm ² or more, and a density of 98.1%. As described above, the hardness, the bending resistance, and the density are far superior to those of the conventional product, Conventional Example 1.

Table 3 shows Examples 21 to 26 of the present invention, which are examples of the fine-grained tungsten carbide powder B produced based on Finding 2, as Example 2, and together, as Comparative Example, Tungsten Carbide Powder. In the production method according to the example of the present invention, Comparative Example 21 and Comparative Example 22 obtained by changing some production conditions are shown, and further described as a conventional example of tungsten carbide powder in the prior art document. Among them, Conventional Example 2 which is an ultrafine tungsten carbide powder known as a raw material for a hard material is shown.
Comparative Example 21 is outside the reduction temperature range in the reduction step with respect to the example of the present invention, and has a specific surface area equivalent to that of Conventional Example 2 which is a conventional ultrafine tungsten carbide powder, and is converted by the BET method. It has a particle size.
Further, Comparative Example 22 is out of the carbonization temperature range in the carbonization step with respect to the example of the present invention.
Then, in Table 3, specifically, with respect to Examples 21 to 26 of the present invention and Comparative Examples 21 and 22, the baking step and the reduction step when the tungsten carbide powder was produced by the direct reduction / carbonization method. manufacturing conditions in the carbonization step, and tungsten trioxide powder generated in characteristics and each step of the starting material _{powder, β-W (W 3 O} ) powder, tungsten carbide powder after carbonization, and a characteristic value of the metal tungsten powder The measured and arranged items are shown, and in Conventional Example 2, the production conditions in each step of the conventional method, the characteristic values of the raw material powder, and the characteristic values of the obtained tungsten carbide powder are shown.

In Examples 21 to 26 of the present invention, which are examples of the present invention, in the calcination step, tungstic acid having a purity of 99.9% by mass is used as a raw material powder at 350 ° C. to 500 ° C. in an air atmosphere or a nitrogen atmosphere. By baking, a tungstic acid-derived tungsten trioxide powder having a particle size of 3 to 4 μm (FSSS method standard) and a BET specific surface area ^{of more than 20 m 2 / g was obtained.}

Next, in the mixing step, the tungsten trioxide powder and carbon black having a particle size of 0.1 μm or less and a purity of 99.9% by mass are mixed, and then in the reduction step, at 500 ° C. or lower under a hydrogen atmosphere. reduction was carried out, the reaction product obtained was confirmed by XRD (X-ray diffraction) method, cubic beta-W having a crystal structure of the crystal (W 3 _O) a fine mixed powder of carbon black is obtained I confirmed that.
Further, in the carbonization step, the obtained mixed powder of fine particles β-W (W ₃ O) and carbon black is heated to 1000 ° C. or higher in a hydrogen reduction atmosphere and carbonized to obtain a BET specific surface area. A high-purity fine-grained tungsten carbide powder having a diameter of 6.41 m ² / g or more, an average particle size of 60 nm or less by the BET method, and an Fe content of 30 ppm or less could be obtained.
The fine-grained tungsten carbide powder according to the present invention obtained here is a fine-grained tungsten carbide powder conventionally known as a raw material for hard materials, that is, has a BET specific surface area of 5.38 m ² / g and is averaged by the BET method. The fine particle tungsten carbide powder of Conventional Example 2 having a particle size of 71 nm has been further atomized.
In Conventional Example 2, 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. but is intended to produce a high reduction temperature in the reduction step, also different atmosphere, was not confirmed for the generation of β-W (W 3 _O) powder at XRD.

Further, Comparative Example 21 is consistent with Examples 21 to 26 of the present invention in terms of the purity of the raw material and the calcination conditions, but the reduction temperature in the reduction step is 600 ° C., which exceeds the reduction temperature range of the present invention. As a constituent phase, β-W (W ₃ O) is not generated, the BET specific surface area of the tungsten carbide powder obtained through the carbonization step is 5.70 m ² / g, and the average particle size in terms of the BET method is 67 nm. Yes, the particle size was almost the same as that of the tungsten carbide powder of Conventional Example 2 in terms of BET.
In Comparative Example 22, starting material purity and calcination conditions, in the reduction conditions in the reduction step, consistent with the present invention examples 21 to 26, further, although the β-W (W 3 _O) powder is generated Since the carbonization temperature in the carbonization step was low, the formation of tungsten carbide (WC) was not sufficient, _{and as a result of W 2} C remaining, the desired tungsten carbide (WC) powder could not be obtained.
Regarding the BET specific surface area of β-W (W ₃ O) in Table 3, β-W (W ₃ O) is atomized in a state of being mixed with carbon fine powder, and it should be measured directly by itself. Therefore, the value when only _{β-W (W 3} O), which does not contain fine carbon powder, is reduced and produced as a raw material is described.

Next, the fine-grained tungsten carbide powders obtained as Examples 21 to 26 of the present invention and Comparative Example 21 were crushed with a cemented carbide ball mill, then the crushed powder was filled in a mold and hot-pressed. While pressurizing at 30 MPa, the temperature was raised to 1800 ° C. and held for 30 minutes to perform sintering, and a WC sintered body was obtained.
Table 4 shows the measured hardness, density and resistance to folding force of the WC sintered bodies obtained in Examples 21 to 26 of the present invention and Comparative Example 21.
WC sintered body produced using the ultra fine tungsten carbide powder obtained in the present invention example 21 to 26 are all, Vickers hardness 2300 kg / mm ² or more, transverse rupture strength 170 kg / mm ² or more, the density It was a tungsten carbide sintered body having excellent properties of 99.5% or more, high hardness, high density, and high folding resistance. On the other hand, the tungsten carbide sintered body produced by using the tungsten carbide powder of Comparative Example 21 has a Vickers hardness of 1850 kg / mm ² , a bending force of 130 kg / mm ² , and a density of 98.7%. Compared with the tungsten carbide sintered bodies obtained in Examples 21 to 26 of the present invention, the hardness, the bending force, and the density were all significantly inferior.
The points are that the WC sintered body produced by using the ultrafine tungsten carbide powders obtained in Examples 21 to 26 of the present invention, the BET specific surface area equivalent to that of the tungsten powder of Comparative Example 21, and the BET specific surface area. It is presumed that the same is true in comparison with the WC sintered body produced by using the tungsten carbide powder of Conventional Example 2 having the average particle size converted by the BET method.

According to the present invention, in the process of producing a tungsten carbide powder, fine particles of tungsten oxynitride (WON) or β-W (W), which have not been conventionally obtained as an intermediate product of fine particles or a precursor of tungsten carbide powder, can be obtained. _{Ultra-fine tungsten carbide powder obtained by producing 3} O) and passing through them. For example, it has ^{a high BET specific surface area of 6.41 m 2} / g or more, and is an average grain converted by the BET method. A conventional method in which nano-level ultrafine tungsten carbide powder having a diameter of 60 nm or less, a ^{high BET specific surface area of 9.50 m 2} / g or more, and an average particle size in terms of the BET method of 40 nm or less. It provides a novel nano-level ultrafine tungsten carbide powder that could not be obtained.
Moreover, the sintered body produced by using the ultrafine tungsten carbide powder according to the present invention has higher strength, higher hardness and higher density than the conventional sintered body using the fine particle tungsten carbide powder. It is extremely useful as a cutting tool and an abrasion resistant tool for plastic working such as dies.

Claims (4)

A fine tungsten carbide powder having a BET specific surface area of 8.67 m ² / g or more and 12.05 m ² / g or less, and an average particle size of 32 nm or more and 44 nm or less by the BET method. BET specific surface area, 9.50m ² / g or more, 12.05m ² / g or less, an average particle diameter of 32nm or more by a BET method, fine tungsten carbide powder, characterized in that at 40nm or less. The fine-grained tungsten carbide powder according to claim 1 or 2, wherein the Fe content is 30 ppm or less. The fine tungsten carbide powder for a cemented carbide material according to any one of claims 1 to 3.