JP2008031016A - Tantalum carbide powder, tantalum carbide-niobium composite powder and their production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide tantalum carbide powder and solid solution of tantalum carbide-niobium as raw material for composite material, each of which is composed of fine and uniform particles uniformly dispersed, also stoichiometrically sufficiently bonded with carbon and has a low oxygen content, and to provide their production methods. <P>SOLUTION: Each of the tantalum carbide powder and tantalum carbide-niobium composite powder has a primary particle average diameter of 0.10 to 0.40 μm measured by a specific surface area method (BET method), a secondary particle average diameter of 0.40 to 1.0 μm measured by an FSSS method, and also has (the primary particle average diameter/secondary particle average diameter) within the range of 0.21 to 0.40. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a tantalum carbide powder and a tantalum carbide-niobium carbide solid solution used as an additive for composite materials in the field of high-temperature materials and cutting tool materials. The present invention relates to a tantalum carbide powder having a low content, a solid solution of tantalum carbide-niobium, a manufacturing method thereof, and a composite material using the same.

  Tantalum carbide (TaC) powder and tantalum carbide-niobium carbide (NbC) solid solution ((Ta, Nb) C) are used as additives to suppress the growth of WC crystals that occur during the sintering of ultrafine cemented carbides. It is widely used as an additive for suppressing wear and improving heat resistance and oxidation resistance of cemented carbide tools and cermet tools for cutting metal materials and the like.

  Conventionally, the following techniques are mainly disclosed regarding the manufacturing method and characteristics of tantalum carbide powder.

  In Patent Document 1, the transition metal alkoxide is hydrolyzed in the vicinity of the conduction point of the transition metal oxide in an alcohol liquid in which carbon is suspended, and then dried, thereby uniformly dispersing the carbon particles therein. A method is disclosed in which an oxide gel is prepared, and the gel is heat-treated in a vacuum or in an inert gas to form granular carbides, and the granular carbides are loosened to produce carbide ultrafine powder.

Specifically, the tantalum carbide powder produced by the method disclosed in Patent Document 1 is ethyl in which 0.1 mol of tantalum ethoxide (Ta (C ₂ H ₅ O) ₅ ) is suspended in 0.35 mol of carbon powder. Hydrolysis is performed by adding ethyl alcohol containing 1 mol of water in alcohol, and after removing the alcohol, moisture is removed at 60 ° C. Furthermore, carbon is uniformly dispersed in the amorphous oxide, and the resulting gel is heat-treated in a vacuum at 1400 ° C. to obtain tantalum carbide. The tantalum carbide powder shown in FIG. 3 of Patent Document 1 by the same method has an average particle diameter of about 0.4 μm and a particle size distribution measurement result having a maximum particle diameter of about 5 μm and FIG. A line diffraction pattern is shown. However, Patent Document 1 does not show other detailed characteristics.

  Patent Document 2 includes at least selected from Group IVB transition metals (Ti, Zr, Hf), Group VB transition metals (V, Nb, Ta), and Group VIB transition metals (Cr, Mo, W) oxides. Rapid carbothermal reduction is achieved by subjecting a reactive particle mixture of one metal oxide and a carbon source to a heat treatment in a non-oxidizing atmosphere at a rate in the range of 100 K / second to 100,000,000 K / second. Disclosed is a production process that produces a precursor particle mixture that is then heat treated at a finishing temperature to obtain a finished product metal carbide. It has been shown that the reactive particle mixture of tantalum is subjected to heat treatment at reaction temperatures of 1750 ° C. and 1950 ° C. to obtain 0.3 μm tantalum carbide powders by the method disclosed in Patent Document 2, respectively. However, other detailed characteristics are not shown.

  Patent Document 3 discloses a method for producing a high-quality tantalum carbide with low oxygen and low free carbon with high yield. Specifically, in Patent Document 3, tantalum pentoxide and carbon are mixed, primary carbonization is performed in a hydrogen furnace, the amount of free carbon of the obtained carbide is measured, and then the amount of carbon is adjusted based on the measurement result In the method for producing tantalum carbide, which is added to the primary carbide and then subjected to secondary carbonization at a predetermined temperature in a vacuum carbonization furnace, the primary carbonization treatment temperature is 1400 to 1800 ° C., and the secondary carbonization treatment temperature is 1800 to 2000. It is shown to be in ° C. According to the method of Patent Document 3, a tantalum carbide powder having a total carbon content of 6.25% by mass, a free carbon content of 0.02% by mass and oxygen of 0.25% by mass is obtained. It is shown to be crushed to diameter.

  In order to improve the strength of cemented carbide, cermet, and other composite materials, uniform dispersion of additive elements is important.

  However, in the above prior art, tantalum carbide powder excellent in uniform dispersibility in the composite material, that is, the powder is less agglomerated, fine and uniform, and sufficiently stoichiometrically bonded to carbon. No tantalum carbide powder with a low oxygen content is provided. Similarly, a tantalum carbide-niobium composite powder with little agglomeration of powder, fine and uniform particles, and a low stoichiometrically sufficient amount of oxygen combined with carbon is not provided. Furthermore, it can be said that a manufacturing technique that can provide these powders at a low cost, that is, a manufacturing technique of a short process that can reduce the manufacturing cost is not provided.

  The problem of the conventional manufacturing method and the problem of the obtained powder property will be described in more detail.

  The reaction of obtaining a carbide by heat-treating a mixture of tantalum pentoxide and carbon or niobium pentoxide and carbon at a high temperature is a large endothermic reaction and a large amount of reaction as shown in the following thermochemical reaction formulas It proceeds with the generation of gas (CO).

  When trying to obtain fine tantalum carbide and tantalum carbide-niobium solid solutions with low oxygen content stoichiometrically bound to carbon by the common conventional methods found in the prior art, to cope with large endothermic reactions Heat treatment at a high temperature and primary carbonization in a non-oxidizing atmosphere to solve a large amount of reaction gas, followed by secondary carbonization in a vacuum atmosphere and heat treatment to the finishing temperature of the precursor, etc. Heat treatment is required.

  Therefore, there is a problem in terms of manufacturing cost that the amount of electric power and the number of manufacturing steps required for high temperature heat treatment increase.

  In addition, since the carbides obtained by these methods are processed at a high temperature, the primary particles are coarsened by the grain growth, and large secondary particles are formed by the necking or agglomeration of the primary particles in the course of the grain growth. There is a problem. The coarser primary particles and necking or large aggregated particles that are heat-treated at a higher temperature are less likely to be refined in the subsequent pulverization step. Further, it is difficult to pulverize uniformly, and impurities are likely to be mixed when pulverized strongly.

  When the above-mentioned coarse tantalum carbide powder and tantalum carbide-niobium composite powder are used as raw materials for cemented carbide and cermet composite materials, the dispersed and solid solution phase diameters of tantalum carbide and tantalum carbide-niobium solid solution become coarse and systematically. Will lack uniformity. In addition, there is a possibility that a tissue defect may occur due to contamination with impurities. That is, there is a problem that the strength of the composite material used as the application is lowered.

  Even if a fine mixture of fine oxides of tantalum or niobium and carbon is made and heat treatment is performed at a low temperature of 1400 ° C. or lower to obtain fine tantalum carbide or niobium carbide, sufficient reduction and carbonization reaction is achieved. Since it is not performed, there is a problem that the residual oxygen content increases. Oxygen remaining in the carbide powder causes a decarbonization reaction during the sintering process of cemented carbide, cermet, and tantalum carbide and composite materials in which a solid solution of tantalum carbide and niobium carbide is dispersed, generating a brittle phase that becomes a defect. Since pores are generated by the product gas of the decarbonization reaction, there is a problem that causes a decrease in strength of the sintered body.

JP-A-2-204319 JP-T-9-501391 JP 2000-44222 A

  Therefore, the first technical problem of the present invention is that bonded carbon, which is a finely divided fine particle that can be uniformly dispersed as a raw material of the composite material, has a sufficient stoichiometric bond with carbon, and has a low oxygen content. Tantalum carbide powder having 6.09 to 6.22 mass% and oxygen content of 0.39 mass% or less, and tantalum carbide having bonded carbon 6.19 to 10.95 mass% and oxygen content of 0.39 mass% or less It is to provide a solid solution of niobium.

  Further, the second technical problem of the present invention is a manufacturing method that does not require the two-stage heat treatment shown in the conventional method by appropriate selection, that is, an inexpensive tantalum carbide powder and tantalum carbide that require only one heat treatment. -It is providing the manufacturing method of the composite carbonization powder which consists of a niobium solid solution.

  As a result of repeating various experiments in order to solve the above problems, the present inventors have found a new heat treatment means for uniform reaction of reduction and carbonization, and have achieved the present invention.

  That is, the tantalum carbide powder of the present invention has an average primary particle size measured by the specific surface area method (BET method) of 0.10 to 0.40 μm and an average secondary particle size measured by the FSSS method of 0.40. And 1.0 (average primary particle diameter / secondary particle average diameter) is 0.21 to 0.40.

  In the tantalum carbide powder of the present invention, the total amount of carbon in the tantalum carbide powder is 6.13 to 6.33% by mass, free carbon is 0.15% by mass or less, and bonded carbon is 6.09 to 6.22. It is characterized by having a mass% and an oxygen content of 0.39 mass% or less.

  Moreover, the tantalum carbide-niobium composite powder of the present invention is a tantalum carbide-niobium composite powder further containing niobium in the tantalum carbide powder, and the niobium carbide is contained in a composition ratio of 0.50 to 99.5 mass%. It is characterized by becoming.

  Further, the tantalum carbide-niobium composite powder of the present invention is the tantalum carbide-niobium composite powder having an average primary particle size measured by a specific surface area method (BET method) of 0.10 to 0.40 μm and an FSSS method. The secondary particle average diameter measured in (1) is 0.40 to 1.0 μm, and (primary particle average particle diameter / secondary particle average diameter) is 0.21 to 0.40.

  Moreover, the tantalum carbide-niobium composite powder of the present invention is the above-mentioned tantalum carbide-niobium composite powder, wherein the total carbon amount is 6.34 to 11.10% by mass, the free carbon is 0.15% or less, The carbon content is 6.19 to 10.95% by mass, and the oxygen content is 0.39% by mass or less.

  The method for producing a tantalum carbide powder according to the present invention is a method for producing any one of the above tantalum carbide powders, a mixing step of mixing a tantalum oxide powder and carbon black to obtain a mixed powder, and the mixed powder. A granulation step of obtaining a granulated powder using a granulator, and heat treatment of the granulated powder in a hydrogen or hydrogen-argon mixed atmosphere at 1450 to 1600 ° C. using a rotary furnace having a carbon rotating tube And a heat treatment step for obtaining a heat-treated product of tantalum carbide powder by reduction and carbonization reaction, and a crushing step for crushing the heat-treated product of tantalum carbide powder to obtain a fine powder.

  The method for producing a tantalum carbide-niobium composite powder according to the present invention is a method for producing any one of the above tantalum carbide-niobium composite powders, wherein tantalum oxide powder, carbon black and niobium oxide are mixed and mixed. 1450 to 1600 ° C. hydrogen using a mixing step to obtain a granulated powder using a granulator, and a granulated powder using a rotary furnace having a carbon rotating tube. Alternatively, a heat treatment step in which heat treatment is performed in a hydrogen-argon mixed atmosphere to obtain a heat treated product of the tantalum carbide-niobium composite powder by reduction and carbonization reaction, and the heat treated product of the tantalum carbide-niobium composite powder is crushed and fine powder And a crushing step for obtaining the above.

  According to the present invention, tantalum pentoxide powder, niobium pentoxide and carbon black are used as raw materials, and a uniform reaction can be caused by facilitating the supply of heat necessary for the reduction and carbonization reaction and the discharge of the reaction product gas. It is possible to provide a tantalum carbide powder and a tantalum carbide-niobium composite powder that are fine, uniform and excellent in dispersibility without aggregation, and methods for producing them.

  Further, according to the present invention, a tantalum carbide powder and a tantalum carbide-niobium composite powder with low oxygen and sufficient carbon bonding can be obtained at a temperature lower than that of the conventional general method and by only one heat treatment. Further, it is possible to provide a tantalum carbide powder and a tantalum carbide-niobium composite powder that can significantly reduce the manufacturing cost, and a method for manufacturing the same.

  In addition, when the tantalum carbide powder and tantalum carbide-niobium composite powder of the present invention are used in the field of cutting tools and high-temperature materials such as cemented carbide and ceramics, the size of the origin of bending fracture is compared with conventional tantalum carbide powder. And can contribute to the improvement of the bending strength.

  The present invention will be described more specifically.

  The present invention provides a tantalum carbide powder, a tantalum carbide-niobium composite powder using the same, and a method for producing them.

(I) First, the tantalum carbide powder of the present invention and the production method thereof will be described.

The tantalum carbide powder of the present invention has an average primary particle diameter _DT p measured by a specific surface area method (BET method) of 0.10 to 0.40 μm, and an average secondary particle diameter _DT measured by the FSSS method. s is 0.40 to 1.0 μm. _{Then, D T p / D T s} (1 average primary particle size / secondary particle average diameter) is 0.21 to 0.40. This tantalum carbide powder has a total carbon content of 6.13 to 6.33% by mass, free carbon of 0.15% by mass or less, bonded carbon of 6.09 to 6.22% by mass, and oxygen content of 0.39. It is below mass%.

  The method for producing the tantalum carbide powder of the present invention includes a mixing step of mixing a tantalum oxide powder and carbon black to obtain a mixed powder, a granulating step of obtaining the granulated powder from the mixed powder using a granulator, The granulated powder is heat-treated in a hydrogen or hydrogen-argon mixed atmosphere at 1450 to 1600 ° C. using a rotary furnace having a carbon rotating tube, and a heat-treated material of tantalum carbide powder is obtained by reduction and carbonization reaction. A heat treatment step, and a crushing step of crushing the heat treated material of the tantalum carbide powder to obtain a fine powder.

(I) Next, the reason why the particle size of the tantalum carbide powder of the present invention is limited to the above numerical range will be described.

(A) First, the average particle diameter will be described.

  Fine powder with an average primary particle size of less than 0.10 μm calculated from the value measured by the BET method can be obtained at a low heat treatment temperature, but residual oxygen increases due to unreacted, and this residual oxygen is the sintering process of the composite material. At this time, a reaction gas is generated and causes pores. On the other hand, a coarse powder exceeding 0.40 μm obtained at a high heat treatment temperature is strong in aggregation and necking, and is difficult to be pulverized, making uniform dispersion in cemented carbide, cermet and other composite materials difficult. The particle size was limited to 0.10 to 0.40 μm.

  A fine powder having an average secondary particle diameter of less than 0.40 μm measured by the FSSS method can be obtained at a low heat treatment temperature, but there is a problem of pore generation at the same high oxygen as described above. In addition, coarse powder exceeding 1.0 μm obtained at a high heat treatment temperature is strong in aggregation and necking, and is difficult to be pulverized, making uniform dispersion in cemented carbide, cermet and other composite materials difficult. Was limited to 0.40 to 1.0 μm.

Powder with an average primary particle size / average secondary particle size of less than 0.21 can be obtained at a low heat treatment temperature. However, since the residual oxygen content is high, pores are generated due to reaction gas generation during the composite material sintering process. Cause. Further, when the carbonization condition exceeds 0.40, the carbide becomes coarse, and uniform dispersion becomes difficult in cemented carbide, cermet and other composite materials (average primary particle diameter / average secondary particle diameter) of 0.00. It was limited to 21 to 0.40.

(B) Next, the composition will be described.

  The stoichiometrically bound carbon of the tantalum carbide powder is 6.23% by mass, but the amount of carbon required to adjust the cemented carbide, cermet and other composite materials to an appropriate amount of carbon, that is, free carbon The amount of bonded carbon is limited to 0.19% by mass or less, the bound carbon amount is 6.09 to 6.22% by mass, which is close to the stoichiometrically bonded carbon, and the total carbon amount is limited to 6.13 to 6.33% by mass. . The reason is that when the total carbon content is 6.13 mass% or less, the raw material oxide is not sufficiently reduced, and the oxygen content increases. This is because it exceeds 15% by mass, making it difficult to adjust the carbon content of the composite material.

In addition, when the oxygen content exceeds 0.39 mass%, residual oxygen is reduced during the sintering process of the composite material, thereby generating CO or CO ₂ gas and forming pores due to this generated gas. In order to reduce the strength of the composite material, the content is limited to 0.39% by mass or less.

(C) Next, heat treatment will be described.

  In the method for producing tantalum carbide of the present invention, a mixture of tantalum oxide powder and carbon black is compression-molded into a granulated powder, and subjected to heat treatment using a rotary furnace having a carbon rotary tube as a reaction furnace. The reason is that the reaction proceeds with a large endotherm and a large amount of reaction gas (CO) as described above, so that the heat supply from the carbon rotating tube is sufficiently and uniform by constantly stirring in the rotary furnace. This is because the reaction product gas can be easily removed.

Further, when the heat treatment temperature is less than 1450 ° C., the reduction reaction becomes incomplete and residual oxygen increases, leading to pore formation due to generation of CO or CO ₂ gas in the sintering process of the composite material, while exceeding 1600 ° C. In this case, the primary and secondary particles of the generated carbide particles are coarse, and uniform dispersion in the composite material structure becomes difficult, and high strength cannot be obtained. For this reason, the heat processing temperature was limited to 1450-1600 degreeC.

(Ii) Next, the method for producing the tantalum carbide powder of the present invention will be specifically described.

(A) First, selection of a tantalum raw material that is a tantalum source will be described.

  It is desirable to use tantalum pentoxide powder as the tantalum source. The reason is that it is the most chemically stable and manufactured industrially. Furthermore, it is cheaper than other tantalum sources and is advantageous from the viewpoint of transportation and quality control. The tantalum pentoxide powder is desirably fine. The reason is that according to the heat treatment means of the present invention, the target powder particle size is obtained by utilizing the particle size of the raw material.

  In Examples described later, a tantalum pentoxide powder having an average primary particle size (= 6 ÷ (theoretical powder density) ÷ (BET value)) determined by the BET method is 0.15 to 0.21 μm. Using.

(B) Next, the selection of the carbon source will be described.

  As the carbon source used for reduction and carbonization, thermal black or acetylene black may be used, but fine carbon black is preferable because it is sufficiently close to the tantalum pentoxide powder to increase the reactivity. The primary particle diameter is preferably 1.0 μm or less.

(C) Next, the granulation step will be described.

  The mixed powder is preferably a granulated granulated powder, preferably having a particle diameter of 0.5 mm to 5 mm and having a uniform particle diameter. The thickener used in the granulation step may be any one that vaporizes in the heat treatment step or becomes a carbonaceous material, and examples thereof include paraffin, camphor, polyalcohol, and polyglycol. The solvent is preferably water or an alcohol solvent such as ethanol or isopropyl alcohol that can be easily dried at about 100 ° C.

(D) Next, the heat treatment process will be described.

  In general, heat treatment of a mixture of tantalum pentoxide and carbon black is performed by filling a carbon tray with this mixture and using a batch-type or pusher-type heating furnace. However, in the case of this method, there is a problem that heat treatment is high and heat is not easily transmitted because the material to be heat treated is powder particles. Further, as the filling thickness of the tray increases due to the endothermic reaction, heat is not easily transmitted to the central portion of the heat-treated material filled, and excessive heat energy must be applied to sufficiently heat-treat the central portion. In any of the above heat treatment methods, when the reaction is sufficiently performed up to the center of the filled material to be heat treated, the resulting carbide has a coarsely grained portion and a fine portion to which appropriate heat energy is applied. It will be.

  Therefore, it is desirable to use a rotary furnace having a carbon rotary tube as the reaction furnace. The reason for this is that, as described above, since it proceeds with a large endotherm and a large amount of reaction gas (CO), heat can be uniformly and sufficiently supplied from the carbon rotating tube by constantly stirring. This is because the reaction product gas can be easily removed. The above-described reaction furnace can be achieved even if a fluidized bed furnace is used because uniform heat treatment and rapid discharge of the reaction gas are possible.

(E) Next, the crushing process will be described.

  The carbide was crushed using an impact pulverizer, a dry ball mill, or a jet mill. In the tantalum carbide powder of the present invention, the particles after the heat treatment are not firmly bonded, so that the granulated powder can be crushed without being strongly pulverized.

(II) Next, the tantalum carbide-niobium composite powder of the present invention will be described.

The tantalum carbide-niobium composite powder of the present invention is a tantalum carbide-niobium composite powder further containing niobium in the tantalum carbide powder, and the niobium carbide is contained in a composition ratio of 0.50 to 99.5 mass%. This tantalum carbide-niobium composite powder has an average primary particle diameter D _TN p measured by a specific surface area method (BET method) of 0.10 to 0.40 μm, and an average secondary particle diameter measured by the FSSS method. D _{TN s is} 0.40 to 1.0 μm. D _TN p / D _TN s (average primary particle diameter / average secondary particle diameter) is 0.21 to 0.40. This tantalum carbide-niobium composite powder has a total carbon content of 6.34 to 11.10% by mass, free carbon of 0.15% or less, bonded carbon of 6.19 to 10.95% by mass, and oxygen content of 0. .39% by mass or less.

  The method for producing the tantalum carbide-niobium composite powder of the present invention comprises a mixing step of mixing tantalum oxide powder, carbon black and niobium oxide to obtain a mixed powder, and granulating the mixed powder using a granulator. A granulating step for obtaining a powder, and the granulated powder is heat-treated in a hydrogen or hydrogen-argon mixed atmosphere at 1450 to 1600 ° C. using a rotary furnace having a carbon rotating tube, and carbonized by reduction and carbonization reaction. A heat treatment step for obtaining a heat-treated product of the tantalum-niobium composite powder, and a crushing step for crushing the heat-treated product of the tantalum carbide-niobium composite powder to obtain a fine powder.

(I) Next, the reason why the tantalum carbide-niobium composite powder of the present invention is limited to the above numerical range will be described.

(A) First, the composition will be described.

  For the tantalum carbide-niobium composite powder, the stoichiometrically bound carbon of niobium carbide is 11.45% by mass, and for the same reason as the tantalum carbide powder described above, the range of the carbon content and the oxygen content is changed between tantalum and niobium. It was limited to a suitable range according to the mixing ratio.

(B) Next, the particle size of the tantalum carbide-niobium composite powder will be described.

  Fine powder with an average primary particle size of less than 0.10 μm calculated from the value measured by the BET method can be obtained at a low heat treatment temperature, but residual oxygen increases due to unreacted, and this residual oxygen is the sintering process of the composite material. At this time, a reaction gas is generated and causes pores. On the other hand, a coarse powder exceeding 0.40 μm obtained at a high heat treatment temperature is strong in aggregation and necking, and is difficult to be pulverized, making uniform dispersion in cemented carbide, cermet and other composite materials difficult. The particle size was limited to 0.10 to 0.40 μm.

  A fine powder having an average secondary particle diameter of less than 0.40 μm measured by the FSSS method can be obtained at a low heat treatment temperature, but there is a problem of pore generation at the same high oxygen as described above. In addition, coarse powder exceeding 1.0 μm obtained at a high heat treatment temperature is strong in aggregation and necking, and is difficult to be pulverized, making uniform dispersion in cemented carbide, cermet and other composite materials difficult. Was limited to 0.40 to 1.0 μm.

  Powder with an average primary particle size / average secondary particle size of less than 0.21 can be obtained at a low heat treatment temperature. However, since the residual oxygen content is high, pores are generated due to reaction gas generation during the composite material sintering process. Cause. In addition, when the carbonization condition exceeds 0.40, the carbide becomes coarse, and it is difficult to uniformly disperse the cemented carbide, cermet and other composite materials, and (average primary particle diameter / average secondary particle diameter) is 0.21. Limited to ~ 0.40.

(C) The heat treatment will be described.

  In the method for producing a tantalum carbide-niobium composite powder of the present invention, a rotary furnace having a tantalum oxide powder and a mixture of niobium oxide and carbon black is granulated into a granulated powder, and a carbon rotary tube is used as a reaction furnace. Heat treatment. The reason is that the reaction proceeds with a large endotherm and a large amount of reaction gas (CO) as described above, so that the heat supply from the carbon rotating tube is sufficiently and uniform by constantly stirring in the rotary furnace. This is because the reaction product gas can be easily removed.

Further, when the heat treatment temperature is less than 1450 ° C., the reduction reaction becomes incomplete and residual oxygen increases, leading to pore formation due to generation of CO or CO ₂ gas in the sintering process of the composite material, while exceeding 1600 ° C. In this case, the primary and secondary particles of the generated carbide particles are coarse, and uniform dispersion in the composite material structure becomes difficult, and high strength cannot be obtained. For this reason, the heat processing temperature was limited to 1450-1600 degreeC.

(Ii) Next, the method for producing the tantalum carbide-niobium composite powder of the present invention will be described more specifically.

(A) First, selection of a tantalum source that is a tantalum source and a niobium source that is a niobium source will be described.

  As the tantalum source and niobium source, it is desirable to use tantalum pentoxide powder and niobium pentoxide powder, respectively. The reason is that it is the most chemically stable and manufactured industrially. Furthermore, it is cheaper than other tantalum sources and niobium sources, and is advantageous from the viewpoint of transportation and quality control. The tantalum pentoxide powder and niobium pentoxide powder are preferably fine particles. The reason is that according to the heat treatment means of the present invention, the target powder particle size is obtained by utilizing the particle size of the raw material. In Examples to be described in detail later, pentoxide having an average primary particle size (= 6 ÷ (theoretical powder density) ÷ (BET value)) obtained by the BET method of 0.15 to 0.21 μm. Tantalum powder and niobium pentoxide powder were used.

(B) Next, the selection of the carbon source will be described.

  As a carbon source used for reduction and carbonization, thermal black or acetylene black may be used, but fine carbon black is preferable because it is sufficiently close to tantalum pentoxide powder or niobium pentoxide powder to increase reactivity. The primary particle diameter is preferably 1.0 μm or less.

(C) Next, the granulation step will be described.

  The mixed powder is preferably a granulated granulated powder, preferably having a particle diameter of 0.5 mm to 5 mm and having a uniform particle diameter. The thickener used in the granulation step may be any material that vaporizes in the heat treatment step or becomes a carbon-based material, and examples thereof include paraffin, camphor, polyalcohol, and polyglycol. The solvent is preferably water or an alcohol solvent such as ethanol or isopropyl alcohol that can be easily dried at about 100 ° C.

(D) Next, the heat treatment process will be described.

  In general, heat treatment of a mixture of tantalum pentoxide, niobium pentoxide and carbon black is performed by filling a carbon tray with this mixture and using a batch type or pusher type heating furnace. However, in the case of this method, there is a problem that heat treatment is high and heat is not easily transmitted because the material to be heat treated is powder particles. Further, as the filling thickness of the tray increases due to endothermic reaction, heat is not easily transmitted uniformly to the central portion of the filled material to be heat-treated, and excessive heat energy must be applied to sufficiently heat-treat the central portion. . In any of the above heat treatment methods, when the reaction is sufficiently performed up to the center of the filled material to be heat treated, the resulting carbide has a coarsely grained portion and a fine portion to which appropriate heat energy is applied. It will be.

  Therefore, it is desirable to use a rotary furnace having a carbon rotary tube as the reaction furnace. The reason for this is that, as described above, since it proceeds with a large endotherm and a large amount of reaction gas (CO), heat can be uniformly and sufficiently supplied from the carbon rotating tube by constantly stirring. This is because the reaction product gas can be easily removed. The above-described reaction furnace can be achieved even if a fluidized bed furnace is used because uniform heating and rapid discharge of the reaction gas are possible.

(E) Next, the crushing process will be described.

  The carbide was crushed using an impact pulverizer, a dry ball mill, or a jet mill.

  In the tantalum carbide-niobium composite powder of the present invention, the particles after the heat treatment are not firmly bonded, so that the granulated powder can be crushed without being strongly pulverized.

  Examples of the present invention will be described below, but the present invention is of course not limited to the examples.

(Production of tantalum carbide powder and tantalum carbide-niobium composite powder)
Tantalum pentoxide powder having an average primary particle size range of 0.15 to 0.21 μm and carbon black having an average particle size of 0.5 μm as defined above, and an average primary particle size range of 0.15 to 0.001. Predetermined amounts of 21 μm niobium pentoxide and carbon black having an average particle size of 0.5 μm were prepared so as to have NbC mass% and carbon amount shown in Examples 1 to 8 in Table 1 and Table 2 below, respectively. And mixed.

  Next, after adding 1% by mass of paraffin as a carbon-based thickener and 1% by mass of isopropyl alcohol as a solvent to each of these mixed powders and stirring, extrusion granulation A granulated granulated powder having a diameter of 3 mm was prepared using a machine. Here, the amount of the solvent added was adjusted to an amount capable of maintaining the shape of the granular granulated powder after extrusion granulation. The solvent added during granulation was removed by drying at 100 ° C.

  Next, these granulated powders were heat-treated at a heat treatment temperature, holding time, and atmosphere described in Tables 1 and 2 using a rotary furnace having a carbon rotating tube. The holding time is a time for passing through a predetermined temperature region of the rotary furnace, and was adjusted by the number of rotations of the carbon rotary tube.

  The obtained carbide was pulverized at a rotational speed of 4000 rpm using a Fuji Paudal impact crusher atomizer KIIW-2 type. The characteristics of the powder obtained by pulverization are shown in Tables 1 and 2 below.

  Next, the same raw material powder as in the example is prepared, predetermined amounts are prepared so as to be NbC mass% and carbon amount shown in Comparative Examples 9 to 12 in Table 2 below, and mixed by the same means as in the example. A granulated powder was prepared. In Comparative Examples 9 to 11, heat treatment was performed at a temperature exceeding the upper and lower limits of the examples shown in Table 1 in order to determine the temperature range of the reduction / carbonization reaction.

In Comparative Example 12, a Tamman pusher using a graphite tube heater was used in order to confirm the heat treatment conditions for obtaining the total carbon, free carbon, bonded carbon, and oxygen content close to those of the Examples.

  Tables 1 and 2 above show the preparation conditions of the tantalum carbide powder and the tantalum carbide-niobium powder and the characteristics of the carbide powder obtained thereby. As can be seen from the experimental results shown in Tables 1 and 2 above, in Comparative Examples 9 and 10 having a heat treatment temperature of 1450 ° C. or lower, fine particles were obtained, but the reduction reaction was not completed, so the oxygen of the raw material oxide Minutes remain. In particular, Comparative Example 1 subjected to heat treatment at 1400 ° C. was in the middle of the reduction reaction, in an unreacted state in which a large amount of carbon to be consumed for reduction remained, and too much free carbon could not be analyzed. Further, in the production method of Comparative Example 10 in which heat treatment was performed at 1430 ° C., the boundary heat treatment temperature for obtaining good tantalum carbide at this temperature is bound carbon, oxygen, and (average primary particle diameter / 2) It was found from the value of the average particle size).

  The primary particle diameter and the secondary particle diameter of the carbide obtained with increasing temperature increased. The carbide whose oxygen has been reduced to a good level as a raw material for cemented carbide, cermet and other composite materials is obtained at 1450 ° C. in Example 1, and the bonded carbon obtained by subtracting free carbon from the total carbon is also at a good level close to the theoretical value. Reached.

  In Example 3 subjected to heat treatment at 1600 ° C., grains were grown to a grain size at the boundary where uniform dispersion was possible in cemented carbide, cermet and other composite materials.

  In Comparative Examples 11 and 12, the heat treatment temperatures of the conventional production methods of tantalum carbide powder and tantalum carbide-niobium composite powder were additionally tested. The tantalum carbide powder obtained in this additional test had primary and secondary particle sizes equivalent to those commercially available.

  The results obtained by observing the tantalum carbide powders of Example 1 and Comparative Example 12 with a scanning electron microscope at a magnification of 6,000 times are shown in FIGS. 1 and 2, respectively. In Comparative Example 12, the grains grew and strong necking and aggregation were observed with coarse particles, whereas the particles of the tantalum carbide powder of Example 1 were observed as fine and easy to aggregate.

Therefore, it was found from Comparative Example 12 that the product of the present invention cannot be obtained even when the heat treatment temperature is increased and the holding time is increased.

(Characteristic comparison of ultrafine cemented carbide)
Using the tantalum carbide and tantalum carbide-niobium composite powders obtained in Examples 1 to 8 and Comparative Examples 10 to 12, 0.5 μm WC—0.80 mass% Cr—1.7 mass% (Ta, Nb) C An ultrafine cemented carbide of −6.5 mass% Co was produced by the following method, and the dispersion state at the powder stage before sintering and the characteristics of the cemented carbide after sintering were compared. The production conditions for the examples and comparative examples were the same.

  The above composition was wet mixed in ethanol using an attritor, and the solvent was heated at 90 ° C. and dried.

  The dispersion state of Ta in the dried mixed powder was investigated using an energy dispersive X-ray detector. The investigation sample was the powder of Example 1 and Comparative Example 11. The Ta dispersion state of Example 1 is shown in the photograph of FIG. 3, and the Ta dispersion state of Comparative Example 11 is shown in the photograph of FIG. White and large spots in FIGS. 3 and 4 indicate the tantalum carbide powder. Compared with Comparative Example 11, it was observed that Example 1 was finely and uniformly dispersed with white portion of Ta. The measuring instrument is a field emission scanning electron microscope manufactured by Hitachi, Ltd. and an energy dispersive X-ray detector EMAX manufactured by Horiba, Ltd.

  Next, the dried mixed powder was molded at a press pressure of 98 MPa, and further HIP molded at 1350 ° C., 1.013 MPa for 1 hour. This was sintered in a vacuum atmosphere at 1430 ° C. to obtain a cemented carbide.

The properties of the obtained cemented carbide were evaluated by a hardness test and a bending test according to JIS H5501 and a porosity according to ISO 4505. This characteristic evaluation is shown in Table 3 below. Table 3 below shows the characteristics of the ultrafine cemented carbide obtained using the tantalum carbide powder and the tantalum carbide-niobium powder.

  As shown in Table 3 above, it was confirmed that a high bending strength was obtained when the finest tantalum carbide powder of Example 1 was used. Further, when observing the fracture starting point of the specimens fractured in the bending tests of Examples 1 to 8, the solid solution tantalum phase appearing at the fracture starting point becomes smaller as the finer tantalum carbide powder is used, contributing to higher strength. I was able to confirm. Further, it was confirmed that the porosity was A02 and there was no pore and the powder was sintered satisfactorily.

  In Comparative Example 10, the pore porosity, which is considered to be caused by oxygen in tantalum carbide, was inferior to A04, and the bending strength was significantly reduced. In Comparative Examples 11 and 12, the solid solution tantalum phase appearing at the fracture starting point was large, and the strength could not be improved.

  Based on the above results, when the tantalum carbide powder and the tantalum carbide-niobium composite powder according to the present invention are used as a raw material of a composite material produced by powder metallurgy, fine particles can be uniformly dispersed, so that the strength of the composite material is improved. It became clear that it contributed to.

  In addition, the application example to the above-mentioned ultrafine cemented carbide does not limit the application of the present invention, and can be widely applied to powder metallurgy using tantalum carbide powder and tantalum carbide-niobium composite powder as raw materials.

  The tantalum carbide powder and tantalum carbide-niobium composite powder according to the present invention are applied to high-temperature materials such as cemented carbide or cermet and additives for composite materials in the field of cutting tool materials.

It is a scanning electron micrograph (6,000 times) which shows the particle size of the tantalum carbide powder of Example 1 of this invention. It is a scanning electron micrograph (6,000 times) which shows the particle size of the tantalum carbide powder of the comparative example 12 obtained on the conventional conditions. It is a photograph which shows the Ta distribution image by the magnification of 1,100 by the X-ray detector of the attritor mixed powder using the tantalum carbide powder by Example 1 of this invention. It is a photograph which shows the Ta distribution image in the magnification of 1,100 times by the X-ray detector of the attritor mixed powder using the tantalum carbide powder of the comparative example 12.

Claims (7)

  The primary particle average particle diameter measured by the specific surface area method (BET method) is 0.10 to 0.40 μm, the secondary particle average particle diameter measured by the FSSS method is 0.40 to 1.0 μm, and (1 A tantalum carbide powder having a secondary particle average particle size / secondary particle average particle size in the range of 0.21 to 0.40.   2. The tantalum carbide powder according to claim 1, wherein the total amount of carbon contained in the tantalum carbide powder is 6.13-6.33 mass%, free carbon is 0.15 mass% or less, and bonded carbon is 6.09- A tantalum carbide powder having a mass of 6.22% by mass and an oxygen content of 0.39% by mass or less.   A tantalum carbide-niobium composite powder further comprising niobium in the tantalum carbide powder according to claim 1, wherein the composition contains 0.50 to 99.5 mass% of niobium carbide. Composite powder.   In the tantalum carbide-niobium composite powder according to claim 3, the average primary particle diameter measured by a specific surface area method (BET method) is 0.10 to 0.40 µm, and the average secondary particle diameter measured by the FSSS method. Is 0.40 to 1.0 μm, and (average primary particle diameter / secondary particle average diameter) is 0.21 to 0.40.   5. The tantalum carbide-niobium composite powder according to claim 3, wherein the total carbon amount is 6.34 to 11.10 mass%, the free carbon is 0.15 mass% or less, and the combined carbon is 6.19 to 10.95. A tantalum carbide-niobium composite powder having a mass% and an oxygen content of 0.39 mass% or less. A method for producing a tantalum carbide powder according to claim 1 or 2, wherein the tantalum oxide powder and carbon black are mixed to obtain a mixed powder;
A granulation step of obtaining a granulated powder from the mixed powder using a granulator;
The granulated powder is heat-treated in a hydrogen or hydrogen-argon mixed atmosphere at 1450 to 1600 ° C. using a rotary furnace having a carbon rotating tube, and a heat-treated material of tantalum carbide powder is obtained by reduction and carbonization reaction. A heat treatment step;
And a pulverizing step of pulverizing the heat-treated material of the tantalum carbide powder to obtain a fine powder. A method for producing a tantalum carbide-niobium composite powder according to claims 3 to 5, wherein a tantalum oxide powder, carbon black and niobium oxide powder are mixed to obtain a mixed powder;
A granulation step of obtaining a granulated powder from the mixed powder using a granulator;
The granulated powder is heat-treated in a hydrogen or hydrogen-argon mixed atmosphere at 1450 to 1600 ° C. using a rotary furnace having a carbon rotating tube, and the tantalum carbide-niobium composite powder is heat-treated by reduction and carbonization reaction. A heat treatment step for obtaining a product,
A method for producing a tantalum carbide-niobium composite powder, comprising: crushing the heat-treated material of the tantalum carbide-niobium composite powder to obtain a fine powder.