JP3566553B2 - Method for producing tantalum carbide - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to the production of tantalum carbide used for improving the quality and performance of carbide cutting tool materials such as cutting tools, inserts, cutters, drills and dies.
[0002]
[Prior art]
As a raw material for producing tantalum carbide, metal tantalum powder has been used before, but tantalum oxide is currently used because metal tantalum powder is relatively expensive.
[0003]
The method of producing tantalum carbide is as shown in FIG. 1. First, tantalum oxide and carbon are mixed by a ball mill, and the mixture is formed into small briquettes by pressing. Next, this is put into a carbonization furnace and heated to 1400 to 1800 ° C., and tantalum carbide is formed by the following reaction formula (1).
Ta ₂ O ₅ + 7C → 2TaC + 5CO (1)
There are two methods for this carbonization, a hydrogen furnace method of carbonizing in a hydrogen atmosphere and a vacuum furnace method of performing vacuum.
[0004]
In the hydrogen furnace used in the hydrogen furnace method, as shown in FIG. 2, a molybdenum wire is wound around an alumina furnace tube, and an electric current is passed through the tube to heat the tube. The core tube is housed in an air-tight iron case, and alumina powder is filled around the core tube as a heat insulator. The raw materials are put into a carbon boat, sequentially inserted from one side, and extruded from the other side. The flow of hydrogen is discharged from the inlet in the opposite direction to the flow of the boat.
[0005]
On the other hand, in the vacuum furnace used in the vacuum furnace method, as shown in FIG. 3, a raw material is put into a graphite crucible, a high-frequency current is passed through a coil outside the crucible, and the crucible is heated by an induced current flowing on the surface of the crucible. The vacuum furnace is connected to a vacuum pump, and discharges generated gas while maintaining the atmosphere in a vacuum.
[0006]
The obtained tantalum carbide is coarsely crushed by a crusher and further crushed by a ball mill to obtain fine tantalum carbide.
[0007]
There are the following problems in the production of the above-mentioned conventional tantalum carbide. That is, in the hydrogen furnace method, carbonization is insufficient on a mass production scale, and a large amount of oxygen and free carbon remain in tantalum carbide. Further, in the carbonization reaction, CO gas is generated as shown in the above reaction formula (1), and when a vacuum furnace is used, Ta ₂ O _{5 as} a powder raw material is blown up, which makes the operation difficult and the production yield is poor. Become.
[0008]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for producing high-quality tantalum carbide having low oxygen and low free carbon with good yield.
[0009]
[Means for Solving the Problems]
The present inventors produce tantalum carbide by utilizing the features of the hydrogen furnace method in which carbonization is insufficient but no gas is blown up and the vacuum furnace method in which carbonization is sufficient but gas is blown up. The present invention was achieved by performing primary carbonization by a hydrogen furnace method and performing secondary carbonization by a vacuum furnace method.
[0010]
The present invention has the following features.
(1) Mix tantalum oxide and carbon, perform primary carbonization at a predetermined temperature in a hydrogen furnace, measure the amount of oxygen and free carbon in the obtained carbide, and then adjust the amount of carbon based on the measurement results. A method for producing tantalum carbide by adding carbon to primary carbides and then performing carbonization twice at a predetermined temperature in a vacuum carbonization furnace.
(2) The method for producing tantalum carbide according to the above (1), wherein the treatment temperature for primary carbonization is 1400 to 1800 ° C, and the treatment temperature for secondary carbonization is 1800 to 2000 ° C.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
The tantalum carbide according to the method of the present invention is produced through weighing, mixing, primary carbonization, blending, secondary carbonization, coarse pulverization, fine pulverization, and sieving.
In the weighing step, Ta ₂ O ₅ and C, which are raw materials, are each weighed by a predetermined amount by a platform weigher or the like.
In the mixing step, the weighed Ta ₂ O ₅ and C are mixed by a vertical mixer or the like so as to be uniformly mixed.
[0012]
In the primary carbonization step, the mixed raw materials are charged into a boat and charged into a hydrogen furnace in a hydrogen atmosphere at regular intervals as shown in FIG. A constant flow rate of hydrogen gas is blown into the hydrogen furnace from the outlet at the other end of the board loading port, and is maintained in a hydrogen reducing atmosphere. In the furnace, Ta ₂ O ₅ and C react in a temperature range of 1400 to 1800 ° C. to perform primary carbonization. When the heating temperature is lower than 1400 ° C., primary carbonization becomes insufficient, and the amount of free carbon and oxygen in tantalum carbide increases. Further, it is difficult for the furnace temperature to exceed 1800 ° C. in view of the structure and the material of the furnace.
[0013]
In the blending step, tantalum carbide after primary carbonization is stirred and mixed with a Hensel mixer or the like in order to average the quality of each board. A sample of the agitated mixture is taken and the free carbon and oxygen content are analyzed and measured. When the amount of carbon required for the reaction is insufficient, carbon is supplementarily added and stirred and mixed.
[0014]
In the secondary carbonization step, the crucible is filled with tantalum carbide that has undergone the blending step, and is charged into a vacuum carbonization furnace as shown in FIG. The inside of the furnace is maintained in a vacuum state, maintained at a temperature of 1800 ° C. to 2000 ° C., and subjected to secondary carbonization to reduce free carbon and oxygen remaining in the primary carbonization step. If the furnace temperature is lower than 1800 ° C., the carbonization is insufficient and the effect of reducing free carbon and oxygen is weak. If the temperature is higher than 2000 ° C., the tantalum carbide powder starts to condense, and energy is wasted.
[0015]
In the coarse grinding step, the tantalum carbide after the secondary carbonization is taken out from the crucible, and the lump of tantalum carbide is coarsely ground by a jaw crusher or the like into a size acceptable in the subsequent fine grinding step.
In the fine pulverizing step, the coarsely pulverized tantalum carbide is charged into a ball mill or the like so as to have a desired particle size and finely pulverized.
In the sieving step, finely pulverized tantalum carbide is supplied to a vibrating sieve or the like, and those having a desired particle size or more are separated and removed.
[0016]
【Example】
Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples.
Example 1
After weighing 138 Kg of Ta ₂ O _{5 and} 26 Kg of C on a platform scale, stirring and mixing the mixture with a vertical mixer for 5 minutes, filling the mixture into a carbon board (2 Kg / piece), and using a resistance heating type hydrogen at a rate of 2 pieces per 3 hours. The mixture was supplied to a furnace and kept at a temperature of 1650 ° C. for 14 hours to perform primary carbonization.
[0017]
The analysis values of the primary carbonized product were T-C 6.4%, F-C 0.3%, and O 0.8%. The amount of carbon deficiency was calculated from the analysis value, 120 g of carbon was added to 120 kg of primary carbide, and the mixture was stirred and mixed with a Hensel mixer. The prepared product was filled in a carbon crucible (100 kg / piece), and a high-frequency induction heating vacuum furnace was used. Was charged.
Hold in a furnace at 1950 ° C. for 5 hours, take out the crucible after cooling, coarsely pulverize the tantalum carbide taken out of the crucible to 2 cm or less with a show crusher, and then fill 500 kg × 600 L stainless steel filled with 230 kg of iron balls of 20φ to 50φ. 100 kg was charged into a ball mill and pulverized for 20 hours.
Thereafter, the resultant was sieved with a 150-mesh vibrating sieve to obtain 118 kg of a product of 150 mesh or less.
[0018]
The product yield was 98%. The product quality of tantalum carbide is T-C 6.25%, F-C 0.02%, and O 0.25%, and the quality (FC <0.2 %, O <0.3%).
[0019]
Comparative Example 1
After weighing 138 Kg of Ta ₂ O _{5 and} 26 Kg of C, the mixture was stirred and mixed with a vertical mixer, filled into a carbon board (2 Kg / piece), and carbonized at 1650 ° C. for 28 hours in a hydrogen furnace in a hydrogen atmosphere to obtain. The tantalum carbide was pulverized with a ball mill and sieved with a 150 mesh vibrating sieve to obtain 120 kg of a tantalum carbide product.
[0020]
The product yield was 98%, and the product quality was 0.25% for FC and 0.55% for O, deviating from the quality standards required for materials for carbide tools.
[0021]
Comparative Example 2
After weighing 138 kg of Ta ₂ O _{5 and} 26 kg of C ₂ , the mixture was stirred and mixed with a vertical mixer, filled in a carbon crucible (100 kg / piece), and carbonized at 1950 ° C. for 15 hours in a vacuum carbon furnace.
After the carbonization was completed, the crucible was taken out of the furnace, but a part of the tantalum carbide flowed out of the crucible and scattered into the furnace and the vacuum pump system.
Tantalum carbide was taken out of the crucible, coarsely pulverized with a jaw crusher, finely pulverized with a ball mill, and sieved with a 150 mesh vibrating sieve to obtain 105 kg of a product.
[0022]
The product quality is 0.2% of FC and 0.4% of O. The oxygen value exceeds the quality standard required for the material for carbide tools, and the product yield is as poor as 90%. Was.
[0023]
【The invention's effect】
According to the present invention, since the primary carbonization by the hydrogen furnace method and the secondary carbonization by the vacuum furnace method are performed, high-quality tantalum carbide having low oxygen and low free carbon can be produced with high yield.
[Brief description of the drawings]
FIG. 1 is a manufacturing process diagram of a conventional tantalum carbide.
FIG. 2 is a diagram illustrating the structure of a hydrogen furnace.
FIG. 3 is a diagram illustrating the structure of a vacuum carbonization furnace.
FIG. 4 is a manufacturing process diagram of tantalum carbide according to the method of the present invention.

Claims (2)

Mix tantalum oxide and carbon, perform primary carbonization at a predetermined temperature in a hydrogen furnace, measure the amount of oxygen and free carbon in the obtained carbide, and then adjust the amount of carbon based on the measurement results to adjust the primary carbide. A method for producing tantalum carbide, characterized in that carbon is added to the mixture and carbonization is performed twice at a predetermined temperature in a vacuum carbonization furnace. The method for producing tantalum carbide according to claim 1, wherein the treatment temperature of the primary carbonization is 1400 to 1800C and the treatment temperature of the secondary carbonization is 1800 to 2000C.

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