JP2818859B2 - Method for producing carbon-boride ceramic spherical composite - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention has a structure in which the surface is covered with graphite and the inside has fine carbon (graphite) and mainly boride ceramics dispersed in each other. The present invention relates to a method for producing a 2 mm spherical carbon-boride composite material.

[0002]

2. Description of the Related Art Composite materials comprising carbon and ceramics are used as materials having the characteristics of carbon such as heat resistance, chemical resistance, lubricity, etc. and the characteristics of ceramics such as heat resistance, oxidation resistance and high strength. I have. The method for producing this composite material is a method in which ceramic powder is ground and mixed with raw coke, which is a carbonaceous material having caking properties, molded and fired (Japanese Patent Publication No. 2-7907), and the ceramic powder is mixed with coke. And baking under pressure such as hot press
No. 1-27352). Recently, a method for manufacturing a composite material with excellent toughness in which plate-like or needle-like SiC is dispersed by mixing powder of silicon carbide (SiC) and boron carbide (B ₄ C) with raw coke, and firing after molding (Japanese Unexamined Patent Publication No. Hei 6
-87653). The composites obtained by these methods are all block-shaped and used as structural materials.

[0003] Since carbon and ceramics each have properties, it is considered that a functional material can be obtained by changing from a block shape to another form in order to exhibit these properties. And a boride ceramic powder are mixed, and the mixed powder is heat-treated at a temperature of 2400 ° C. or more to propose a spherical carbon-boride ceramic composite and a method for producing the same.
-71396).

[0004]

Generally, boride ceramics are one of high melting point compounds, and are produced by heating metals, oxides or carbides thereof, and boron compounds such as boron and boric acid at a high temperature. Therefore, it is an expensive material as compared with general-purpose ceramics such as oxide ceramics. The method for producing a spherical carbon-boride composite proposed in Japanese Patent Application No. 6-71396 previously uses this expensive boride ceramic as a raw material and requires a high-temperature heat treatment of 2400 ° C. or more. However, the produced spherical composite must be expensive.

[0005] In order to make the spherical carbon-boride complex, which is a new and expected functional material, one of the industrial materials, it is necessary to improve the production process and reduce the production cost as much as possible. It is an object of the present invention to improve this manufacturing process.

[0006]

As described above, boride ceramics are stable at high temperatures and hardly form carbides even in the presence of carbon. Carbides are similarly stable substances, but when boron and its compounds coexist,
It is well known that it becomes a boride. For example, heat treatment of a mixture of titanium carbide (TiC) and boron carbide (B ₄ C) produces titanium boride. On the other hand, it is well known that oxide ceramics are reduced in the presence of carbon and generate carbides under heat treatment conditions.

[0007] From these facts, boride ceramics can be produced by using oxides, boron and its compounds and carbon in the case of oxide ceramics, and carbides and boron and its compounds in the case of carbide ceramics as raw materials. Can easily be considered. However, when an oxide or a carbide ceramic is used as a raw material, a chemical reaction is involved, and it is not considered that a spherical carbon-boride ceramic composite is formed by the same mechanism as when a boride ceramic is used. In other words, the formation mechanism of the spherical composite in the case of boride ceramics has a eutectic point with carbon at a high temperature, and since this eutectic point is lower than the melting point of the boride itself, it melts from the part in contact with carbon, As the carbon dissolves, it becomes spherical due to surface tension. And it is thought that the carbon dissolved in the cooling process is deposited. Thus, this mechanism is a physical change that occurs between boride and carbon, and is not accompanied by a chemical reaction.

[0008] Then, when a condition search for spheroidization using oxide and carbide ceramics and a boron compound was conducted, a spherical carbon-boride ceramic composite having the same shape and structure as those of boride ceramics was searched. It is known that is formed at a lower temperature than that of boride ceramics, and the present invention has been accomplished.

Hereinafter, the method of the present invention will be described. As starting materials, powders of carbon and oxide or carbide ceramics and boron or a compound thereof are used. Carbon is carbon black, coke, their graphitized products, and natural graphite, and any of carbonaceous and graphitic can be used. These carbon powders preferably have a smaller particle size,
An average particle size of at least about 10 μm or less is used.

The oxide ceramic is made of zirconium oxide (Z
rO ₂ ), titanium oxide (TiO ₂ ), tantalum oxide (Ta ₂ O ₅ ), vanadium oxide (V ₂ O ₅ ), niobium oxide (Nb ₂ O ₅ ), molybdenum oxide (MoO ₂ ), and tungsten oxide (WO ₃ ), And carbide ceramics are titanium carbide (TiC), zirconium carbide (Zr
C), tantalum carbide (TaC), vanadium carbide (VC), niobium carbide (NbC), molybdenum carbide (MoC, Mo ₂ C), a tungsten carbide (WC) and hafnium carbide (HfC), these one or It is a mixture of two or more. Further, the boron compounds are boric acid, boron oxide and boron carbide. As these starting materials, use is made of fine powder having a particle diameter of about 50 μm or less, preferably an average particle diameter of 10 μm or less. Hafnium oxide as oxide ceramics and metallic boron as boron can also be used as raw materials,
These are all expensive.

A predetermined amount of carbon, oxide or carbide ceramics and a boron compound are sampled and mixed. The amount of each of the carbon, oxide or carbide ceramics and boron compound is important for forming a spherical body.
That is, the compounding amount of the boron compound with respect to the oxide or carbide ceramic is an amount corresponding to the boride generated by the reaction of the metal of the oxide or carbide ceramic with boron in the boron compound or an amount larger than that. Since there are many borides having different ratios of metal and boron, it is necessary to know the structure of the boride to be formed. In the case of the oxide or carbide ceramic used in the present invention,
Diborides except WO ₃ , WC, MoO ₂ , Mo ₂ C and MoC
In WO ₃ and WC, ditungsten pentaboride (W ₂ B ₅ )
MoO ₂ , Mo ₂ C and MoC produced molybdenum diboride (MoB ₂ ) and molybdenum monoboride (MoB). Thereby, the necessary amount of boron can be obtained by calculation. The amount required to convert all the oxides or carbides into borides by experiments was about 1.3 times the calculated value (theoretical amount). When the amount of boron is small, all oxides or carbides do not change into borides and coexist as carbides. When the amount of boron is excessive, boron carbide is generated. Therefore, by adjusting the amount of boron, a spherical body in which a boride and a carbide coexist can be produced.

On the other hand, the amounts of the oxide or carbide ceramic and the boron compound with respect to carbon cannot be simply determined. It is thought that the role of carbon is to provide (1) a reducing agent for oxide ceramics and boron compounds, (2) carbon as a component of spheroids, and (3) the generated boride to provide a space for spheroidization. Can be (1) can be calculated by determining the types and amounts of oxide ceramics and boron compounds, but (2) and (3) are unknown. Therefore, the carbon content needs to be determined experimentally.

In the case of oxide ceramics, when WO ₃ having the highest formula weight and specific gravity is used and heat treatment is performed while changing the mixing amount with carbon, the amount of WO ₃ is about 0.6 with respect to 1 part by weight of carbon.
It was found to be less than parts by weight. In other words, when the amount is less than this amount, the entire amount is a spherical composite, but when the amount is more than this, the spherical bodies are fused together, or the spherical diameter becomes large, so that the spherical body becomes greatly deformed, and the container used for the heat treatment is used. It adheres firmly in the molten state, and the yield of a sphere substantially close to a true sphere decreases. When the same treatment was performed using WC in the case of carbide ceramics, it was found that the amount of WC was about 2 parts by weight or less with respect to 1 part by weight of carbon. Above this amount, the amount of those firmly adhered in the molten state to the bottom of the vessel used for the heat treatment increased. However, the size of the spheres in the carbon did not change.

As described above, the amount that can be mixed with carbon is different between oxides and carbides, and carbides can be mixed in larger amounts. This is because the effect of carbon is different between oxides and carbides. In other words, oxides require carbon for reduction, while carbides generate carbon by converting them to borides, so that the generated spheres come into contact with each other, inhibiting the coalescence of the above (3). It can be said that. The carbon powder, oxide or carbide ceramic powder and boron compound are mixed well. Among the boron compounds, boric acid, boron oxide and sodium borate are water-soluble, so that they may be dissolved in a small amount of water and added to the carbon powder and the oxide or carbide ceramic powder and mixed.

The mixture of the mixed carbon, oxide or carbide ceramic and boron is placed in a graphite container and heat-treated in an inert gas of helium or argon. The heat treatment temperature at this time is 2200 ° C. or more, but it depends on the type of oxide or carbide ceramic used as a raw material, and therefore it is necessary to experimentally determine each of them. This means that for each material, 22
This is performed by taking samples at intervals of 100 ° C. while raising the temperature to a temperature of 00 ° C. or higher, and observing a sediment obtained by fractionation of the specific gravity with a scanning electron microscope. As an example of the heat treatment temperature determined in this way, MoO ₂ , Mo
2200 ° C. for C, Mo ₂ C, V ₂ O ₅ and WC,
ZrO ₂ , ZrC, Ta ₂ O ₅ , WO ₃ and V ₂ O ₅ +
In the case of ZrO ₂ , 2300 ° C., Nb ₂ O ₅ , VC and T
2400 ° C. for iO ₂ + ZrO ₂ , 2500 ° C. for TiO ₂ , 2600 ° C. for TaC, TiC, N
The temperature is 2700 ° C. for bC and HfC. Note that if nitrogen gas is used as an inert gas as an atmosphere during the heat treatment, nitride ceramics may be generated, and thus cannot be used. Since the heat-treated product thus obtained is a mixture of spheres formed in carbon, it is necessary to separate the spheres by an appropriate method. Examples of the method include a method of dropping from an inclined plate, separation by a cyclone, and specific gravity fractionation.
Among them, the specific gravity fractionation method is the best. That is, put the heat-treated product in water containing a small amount of alcohol or a surfactant that wets carbon and spheres well as a specific gravity liquid, and disperse by stirring or the like,
After standing for a short time, remove the supernatant. A specific gravity solution is added to the sediment, and the same operation is performed. By repeating this operation, carbon having a low specific gravity is removed, and finally the sediment becomes only a spheroid.

The sphere obtained in this manner is a sphere close to a true sphere exhibiting a silver gray, and has a diameter of about 10 μm or more, and may have a diameter of 2 to 3 mm. The surface is a fine triangle, square,
It was a polygon covered by a hexagonal flat surface, and the element on this surface was carbon. Since the inside is a state in which carbon and carbide having a submicron size are mixed, the surface is covered with carbon, and the inside is a complex in which carbon and boride are mixed. It is considered that the formation mechanism of this composite is the same as that of the spherical carbon-boride ceramic composite proposed earlier. In other words, in the case of a spherical carbon-boride ceramic composite, by heat-treating a mixed powder of carbon and boride ceramics at a temperature of 2400 ° C. or higher, the boride in contact with carbon differs from the melting point of the boride. It was melted at a temperature, carbon was dissolved therein, and it became spherical due to surface tension, and carbon was precipitated during the cooling process. In the case of the present invention, since the raw material is an oxide or carbide ceramic, the difference is that this ceramic reacts with carbon to form a carbide during the heat treatment of the mixture with carbon and boron compounds. Comparing the melting points of oxide and carbide, the oxide is lower, so the oxide melts and spheroidizes, dissolves carbon in it, reacts with carbon to form carbide, and deposits carbon in the cooling process. Seem.

Hereinafter, the present invention will be described in more detail with reference to examples. In the following examples, oxides and carbide ceramics are represented by chemical formulas, a scanning electron microscope is abbreviated as SEM, a transmission electron microscope is abbreviated as TEM, and an X-ray microanalyzer is abbreviated as EPMA.

Example 1 In this example, the state of formation of a spherical body from carbon, oxide ceramics and boric acid was examined.

Carbon black (furnace black # 2300, manufactured by Mitsubishi Chemical Corporation, average particle size 15n)
m) 5 g of zirconium oxide (ZrO ₂ , cubic, average particle size 3
μm) and 2.5 g of boric acid (H ₃ BO ₃ ) were added and mixed well in a beaker. This was placed in a graphite crucible having an inner diameter of 25 mm and a height of 30 mm, heated in a argon stream in a Tamman furnace until each temperature reached 2000 to 3000 ° C., kept for 1 hour, and cooled. Put this in ethanol, disperse by ultrasonic vibration,
After allowing to stand for a short time, the supernatant was removed, and fresh ethanol was added to the precipitate, and the same operation as above was performed. When this operation was repeated 5 times, the supernatant liquid became almost colorless, and the precipitate was heated to 100 ° C. and dried.

FIG. 1 shows the result of observing the shape of the sediment obtained by SEM. As can be seen in FIG. 2 (a), the sediment treated at 2000 and 2200 ° C. was an amorphous mass in which powder or fine particles were aggregated.
Are spherical particles having a diameter of about 10 μm to 1 mm which are close to true spheres, and when treated at 3000 ° C., spherical particles having the same size and shape were formed.

[0021]

FIG.

FIG. 2 is an enlarged view of the spherical body of FIG.
The EM photograph shows that the surface of the spherical body is polygonal. When the elemental composition of this surface was analyzed with the EDX attached to the SEM, carbon and a small amount of zirconium were detected.As a result of the line analysis, the plane portion of the polygon was carbon, and the zirconium Existed. Also,
As a result of powder X-ray diffraction, graphite and zirconium boride (ZrB ₂ )
And diffraction lines corresponding to zirconium carbide (ZrC).

[0023]

FIG. 2

A sphere is embedded in a resin, and the polished cross section is
The distributions of carbon, zirconium and boron were examined by EPMA. As a result, carbon, zirconium, and boron were detected at different positions, and zirconium and boron were detected at the same position. Each of them had a submicron size and was mixed with each other. Further, when the spherical body was pulverized and observed with a TEM, it was found to be irregular plate-like particles. When the elemental composition of the plate-like particles was analyzed by EDX attached to the TEM,
Carbon and zirconium were detected from separate plate-like particles, and the electron diffraction pattern of each plate-like particle became a spot, and the interplanar spacing determined therefrom corresponded to graphite, ZrB ₂ and ZrC.

From the above results, this spherical body is a spherical composite in which the surface is mainly covered with carbon and the inside is a mixture of small pieces of carbon and zirconium boride. Carbon and zirconium boride have excellent crystallinity. It turned out to be something.

As other oxide ceramics, titanium oxide (TiO ₂ , average particle diameter 1 μm), molybdenum oxide (MoO ₂ , average particle diameter 5 μm), tantalum oxide (Ta ₂ O ₅ , average particle diameter 7 μm)
m), niobium oxide (Nb ₂ O ₅ , average particle size 5 μm), tungsten oxide (WO ₃ , average particle size 3 μm), vanadium oxide (V
The same carbon black as above using ₂ O ₅ , average particle diameter 8 μm) and lanthanum oxide (La ₂ O ₃ , average particle diameter 6 μm)
2.5 g of each oxide ceramic and 2.5 g of boric acid for 5 g
Was added and mixed, the mixture was heated in the range of 2000 to 3000 ° C. every 100 ° C., and kept for 1 hour for heat treatment. Next, sediment was collected by specific gravity fractionation using ethanol as a specific gravity liquid, and the state of formation of spheroids was examined. The minimum temperature at which the spherical body was formed in this way was determined as the formation temperature, and the crystal phase was examined by X-ray diffraction, and is shown in Table 1. As a mixture of two kinds of oxide ceramics, a mixture of 1.25 g each of TiO ₂ and ZrO ₂ and V ₂ O
_When 2.5 g of boric acid was added to a mixture of 1.25 g of each of ₅ and ZrO ₂ , the same heat treatment was carried out. The obtained precipitate was examined, and the results are shown in Table 1.

Table 1 ────────────────────────────────── Experiment Oxide Formation Temperature Crystalline Theory of Boric Acid Quantity number (℃) (g) ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 1-1 TiO ₂ 2500 C, TiB ₂ , TiC 3.9 1-2 ZrO ₂ 2300 C, ZrB ₂ , ZrC 2.5 1-3 MoO ₂ 2200 C, MoB ₂ 2.4 1-4 Ta ₂ O ₅ 2300 C, TaB ₂ 1.4 1-5 Nb ₂ O ₅ 2400 C, NbB ₂ 2.3 1-6 WO ₃ 2300 C, W ₂ B ₅ 1.7 1-7 V ₂ O ₅ 2200 C, VB ₂ , V ₄ C ₃ 3.4 1-8 La ₂ O ₃ × 1-9 TiO ₂ + ZrO ₂ 2400 C, (Ti, Zr) B, TiC, ZrC 1-10 V ₂ O ₅ + ZrO ₂ 2300 C, VB ₂ , ZrB ₂ , ZrC ─────────────── ───────────────────

As can be seen from this table, the formation temperature is different except for the case of La ₂ O ₃ , but a spherical body was formed from any oxide, and the shape was similar to that of FIG. .
The crystal phases determined by X-ray diffraction were carbon (C) and respective borides, but in the case of TiO ₂ and V ₂ O ₅ , a small amount of titanium carbide and vanadium carbide were present.

The precipitate obtained by the heat treatment at 2000 ° C. was a powder or an aggregate of fine particles, but boride was formed in any oxide. It can be said that it is a boride. La ₂ O ₃
In the case of, even when heat-treated at 3000 ° C., a spherical body is not generated, and it is an aggregate of fine particles, and its crystal phase does not match any of the X-ray diffraction lines of oxides, borides and carbides, and is identified I couldn't do that. Therefore, Experiment Nos. 1-8 are reference examples.

As described above, in the case of ZrO ₂ , TiO ₂ and V ₂ O ₅ , carbides are formed in addition to the respective borides, and the spherical bodies are composed of carbon (graphite), borides and carbides. Met. It is considered that the carbide was generated because the amount of boron necessary for converting the oxide into boride was insufficient, so that 2.5 g of the oxide was converted into the boride described in the crystal phase column in Table 1. The required amount of boric acid was determined by calculation, and the value was described as a theoretical amount in the right column of Table 1. ZrO ₂ had the same amount, but TiO ₂ and V ₂ O ₅ had less. Therefore, 5 g of carbon black, 2.5 g of ZrO ₂ , TiO ₂ and V ₂ O ₅
The mixture was mixed while changing the amount of boric acid, and heat-treated at 2600 ° C. for 1 hour. This was fractionated with ethanol to obtain a spherical body.
The crystal phase of the sphere was examined by X-ray diffraction, and the results are shown in Table 2.

Table 2 ───────────────────────────── Experiment Oxide Boric acid content Theoretical amount vs. crystal phase number (g)割 合 2-1 ZrO ₂ 3.0 1.20 ZrB ₂ , ZrC 2-2 〃 3.5 1.40 ZrB ₂ 2-3 TiO ₂ 5.0 1.29 TiB ₂ , TiC 2-4 〃 5.25 1.35 TiB ₂ 2-5 〃 5.5 1.42 TiB ₂ 2-6 V ₂ O ₅ 4.0 1.18 VB ₂ , V ₄ C ₃ 2-7 〃 4.5 1.32 VB ₂ ─────────────────────────────

From these results, it can be seen that the amount of boric acid required to convert all the oxides to boride is about 1.3 times the theoretical amount.

Example 2 In this example, the state of formation of a spherical body when boron carbide (B ₄ C) was used as a boron compound for carbon black and oxide ceramics was examined.

The same carbon black as in Example 1 was used as carbon, and TiO ₂ and WO ₃ with the smallest formula weight in Table 1 were used as oxide ceramics. B ₄ C used had an average particle diameter of 4 μm. After adding and mixing the amounts of TiO ₂ or WO ₃ and B ₄ C shown in Table 3 to 5 g of carbon black, the mixture was placed in a graphite crucible and heat-treated at 2600 ° C. for 1 hour in an argon stream with a Tamman furnace. In the same manner as in Example 1, a sediment was obtained by a specific gravity fractionation method using ethanol as a specific gravity liquid. The shape of the sediment was observed by SEM, and the crystal phase was examined by X-ray diffraction. The results are shown in Table 3.

Table 3 ──────────────────────────── Experiment Oxide B ₄ C amount Shape Crystal phase No. Type Amount (g) ( g) ━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 2-1 TiO ₂ 2.5 1.0 Spherical C, TiB ₂ , TiC 2-2 〃 2.5 1.5 〃 C, TiB ₂ 2-3 〃 3.0 1.5 〃 C, TiB ₂ 2-4 〃 3.5 1.5 Lumped C, TiB ₂ 2-5 WO ₃ 2.5 0.8 Sphere C, W ₂ B ₅ 2-6 〃 3.0 0.8 〃 C, W ₂ B ₅ 2-7 〃 3.5 0.8 Lump C, W ₂ B ₅ 2-8 〃 2.5 2.5 Spherical C, W ₂ B ₅ ───────────────── ───────────

From these results, even in the case of B ₄ C, the oxide was converted to a boride to form a sphere. The shape of the sphere was similar to FIGS. Further, when the amount of the oxide relative to the carbon black was increased, the graphite crucible became a rounded mass at the bottom, and powdered carbon black remained thereon, with a small amount of spheres present therein. What constitutes this lump is mainly the quantitative ratio of carbon black and oxide, and it can be said that the ratio is at least 0.6 part by weight. Therefore, Experiment Nos. 2-4 and 2-7 are reference examples.

Comparative Example In this comparative example, for comparison with the results of Examples 1 and 2, the state of formation of a spherical body by heat treatment of carbon and boride ceramics was examined, and the lowest temperature at which the spherical body was formed (forming temperature) It is what was asked.

As carbon, the same carbon black as in Example 1 was used, and boride ceramics were titanium boride (TiB ₂ ,
Average particle diameter 5μm), zirconium boride (ZrB ₂ , average particle diameter 1.5μm), tantalum boride (TaB ₂ , average particle diameter 4μ)
m), molybdenum boride (Mo ₂ B ₅ , average particle size 4 μm), niobium boride (NbB ₂ , average particle size 3 μm), vanadium boride (VB ₂ , average particle size 4 μm), tungsten boride (W
B, average particle diameter 3 μm) and lanthanum boride (LaB ₆ , average particle diameter 5 μm) were used.

5 g of boride ceramic powder was added to 5 g of carbon black and mixed. This was placed in a graphite crucible, and heated in a stream of argon at a temperature range of 2000 to 3000 ° C. every 100 ° C., and kept for 1 hour for heat treatment. A precipitate was obtained from the heat-treated product by a specific gravity fractionation method using ethanol as a specific gravity liquid.

The sediment was observed for its shape by SEM, and the lowest temperature (formation temperature) at which a spherical body was formed was obtained. Further, the crystal phase of the spherical body was examined by a powder X-ray diffraction method, and the results are shown in Table 4.

Table 4 ─────────────────────────── Experiment No. Boride formation temperature (° C.) Crystal phase ━━━━━━━ ━━━━━━━━━━━━━━━━━━━━ R-1 TiB ₂ 2700 C, TiB ₂ R-2 ZrB ₂ 2500 C, ZrB ₂ R-3 TaB ₂ 2600 C, TaB ₂ R-4 Mo ₂ B ₅ 2400 C, MoB ₂ R-5 NbB ₂ 2700 C, NbB ₂ R-6 VB ₂ 2500 C, VB ₂ R-7 WB 2600 C, WB R-8 LaB ₆ 2400 C, LaB ₆ ───────────────────────────

The shape of the formed spheres is the same as that of FIGS. 1b and 2 for any of the borides. The surface is covered with a polygon, and the elemental analysis by EDX shows carbon (C). A small amount of each boride metal was detected at the contacting part. The inside has a structure in which submicron flake-like carbon and boride are mixed due to the distribution of carbon, metal and boron by EPMA. Electron diffraction image of flake-like carbon and boride by TEM and powder X of spherical body From the X-ray diffraction line, both carbon and boride were excellent in crystallinity.

Comparing the results of Table 3 with the results of Example 1 (Table 1) and Example 2 (Table 3), the temperature at which spheroids are formed in any boride except for LaB ₆ Is higher. In other words, it has been known that when oxides and carbide ceramics and boric acid are used as starting materials, a spherical body is formed at a lower temperature. Although the case of LaB ₆ was generated spheroids so be heat-treated to 3000 ° C. from La ₂ O ₃ and boric acid spheroids did not produce, in order to produce the carbon -LaB ₆ spherical composite is It can be said that there is no other method than LaB ₆ as a starting material. The shape and structure of the sphere were the same regardless of the starting material.

Example 3 In this example, the state of formation of spheres from carbon, carbide ceramics and boric acid was examined.

As carbon, the same carbon black as in Example 1 was used. Carbide ceramics include titanium carbide (TiC, average particle size 8 μm), zirconium carbide (ZrC, average particle size 5
μm), molybdenum carbide (MoC, Mo ₂ C, average particle diameter 6μ)
m), tantalum carbide (TaC, average particle diameter 5 μm), niobium carbide (NbC, average particle diameter 6 μm), vanadium carbide (VC, average particle diameter 4 μm), tungsten carbide (WC, average particle diameter 3
μm), and hafnium carbide (HfC, average particle size 5 μm)
Further, a 1: 1 (weight ratio) mixture of TiC and ZrC and a 1: 1 (weight ratio) mixture of ZrC and WC were used.

2.5 g of carbide ceramics and 2.5 g of boric acid were added to 5 g of carbon black, and mixed well in a beaker.
A range of 3000 ° C. was heated in units of 100 ° C., and each temperature was maintained for 1 hour for heat treatment. The precipitate was obtained by a specific gravity fractionation method using ethanol as a specific gravity liquid. The lowest temperature at which a spherical body was formed by observing the shape of this sediment by SEM (generation temperature)
And the crystal phase was examined by X-ray diffraction. Table 5 summarizes the obtained results.

Table 5 ────────────────────────── Experiment No. Carbide Formation temperature Crystal phase Boric acid (° C) (° C) Theoretical amount ( g) ━━━━━━━━━━━━━━━━━━━━━━━━━━ 4-1 TiC 2700 C, TiB ₂ , TiC 5.15 4-2 ZrC 2300 C, ZrB ₂ , ZrC 3.00 4-3 TaC 2600 C, TaB 2 1.60 4-4 Mo 2 C 2200 C, MoB 2, MoB (2.88) 4-5 MoC 2200 C, MoB 2 2.88 4-6 NbC 2700 C, NbB 2, NbC 2.95 4-7 WC 2200 C, W ₂ B ₅ 1.98 4-8 VC 2400 C, VB ₂ , V ₄ C ₃ 4.93 4-9 HfC 2700 C, HfB ₂ 1.63 ───────────── ─────────────

In the case of any of the carbides, spherical bodies were formed by heat treatment at 2700 ° C. or higher. However, spherical bodies were formed at the lowest temperature in Mo ₂ C, MoC and WC, and the temperature was 2200 ° C. Was. The temperature at which the spheres are formed is not necessarily the same as that of the oxides shown in Table 1, but the tendency is the same, and the formation mechanism is considered to be the same.
That is, the heat-treated product at 2000 ° C. was an aggregate of fine particles in any of the carbides.
Since the boride has already been generated as in the case of the oxide of the above, it is considered that when the spherical body is formed, it is a boride and a carbide. Table 1 shows that carbides are present.
This is the case where there was not a sufficient amount of boron to become the boride described in the column of the crystal phase. In the case of Experiment No. 4-4, the generated borides were MoB ₂ and MoB, and the quantitative ratio was unknown. Therefore, the theoretical amount of boric acid was calculated as MoB ₂ .

The shape of the spherical body thus produced was the same as in FIG. 2, and no particular difference was observed. Also, the structure is EPMA
As a result of examination by TEM, the surface was covered with graphite, and the inside had a structure in which carbon (graphite) and boride having a submicron size were present, and in the case where carbide was present in the crystal phase, carbide was mixed. This structure was similar to that of the oxide of Example 1.

Example 4 In this example, the amount of boric acid required for converting all of the spherical carbide to boride was determined.

The carbon was carbon black as in Example 1, and the carbide was ZrC, each weighing 2.5 g. To these, 3.5, 3.8, 4.0 and 4.5 g of boric acid were added and mixed well in a beaker. This was placed in a graphite crucible, heated to 2600 ° C. in an argon stream, and held for 60 minutes for heat treatment. This treated product was fractionated with ethanol to obtain a sediment. When the shape of the sediment was observed by SEM, it was found that all of the sediment was a spherical body close to a true sphere. The crystal phase was examined by X-ray diffraction, and the results are shown in Table 6.

Table 6 ────────────────────────────── Experiment No. Amount of boric acid Crystalline phase (g) ratio to stoichiometric amount ━ ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 5-1 3.5 1.17 C, ZrB ₂ , ZrC 5-2 3.8 1.27 C, ZrB ₂ , ZrC (trace) 5-3 4.0 1.35 C, ZrB ₂ 5-4 4.5 1.50 C, ZrB ₂ ──────────────────────────── ──

From these results, it was found that the amount of boric acid for converting the total amount of ZrC to ZrB ₂ was about 1.3 times the theoretical amount.

Example 5 In this example, the amounts of carbon and carbide necessary for forming a spherical body were determined.

Among the carbides shown in Table 4, WC having the highest formula weight and specific gravity was used, and B ₄ C was used as the boron compound.

WC is 5, 6, 8, 10, 12 and 14 g with respect to 5 g of the same carbon black as in Example 1, and the amount of WC is 1.4 times the theoretical amount required to convert the total amount of WC to W ₂ B ₅ . B ₄ C, i.e. 1.
26, 1.51, 2.02, 2.52, 3.02 and 3.52 g were added and mixed. Put this in a graphite crucible and in an argon stream,
Heat treatment was performed at 2600 ° C. for 1 hour. Then, the heat-treated product and the state of the crucible after removing the heat-treated product were examined. As a result, when the WC amount was 10 g or less, one to three spheres were fixed to the bottom of the crucible, but when the WC amount was 12 g or more, the amount increased rapidly, and almost at the entire bottom part, and at 14 g, the bottom part became small. And it was also stuck to the wall. When the amount of the WC adhered to the crucible increases, the yield of the spheres naturally decreases. Therefore, it was found that the amount of WC was 10 g or less, which hardly adhered to the bottom.

The heat-treated product recovered from the crucible was subjected to specific gravity fractionation with ethanol, and the precipitate obtained was observed by SEM.
, Regardless of the amount of the particles, the size was almost the same as 10 to 20 μm, and no particularly large one was observed.
The crystal phase examined by the X-ray diffraction method was W ₂
It was B _5.

[0058]

According to the present invention, by mixing a boron compound such as boric acid and an oxide or carbide ceramic, which is less expensive than boride ceramics, with carbon powder and subjecting the mixture to heat treatment, spherical carbon can be formed at a lower temperature than in the case of boride ceramics. A boride ceramic composite is produced.

[Brief description of the drawings]

FIG. 1 is a scanning electron micrograph of a product obtained by mixing and heat-treating carbon, zirconium oxide, and boric acid of Example 1.
(A) Heat treatment temperature 2000 ° C, (b) 2300 ° C. (50x magnification)

FIG. 2 is an enlarged scanning electron micrograph of a product obtained by mixing carbon, zirconium oxide, and boric acid of Example 1 and heat-treating the mixture at 2300 ° C. (1000x magnification)

Continuation of the front page (56) References JP-A-7-257920 (JP, A) JP-A-60-118671 (JP, A) JP-A-2-38365 (JP, A) Special table 57-501377 (JP, A) , A) (58) Field surveyed (Int. Cl. ⁶ , DB name) C04B 35/52 C04B 35/58 105

Claims (4)

(57) [Claims] 1. An oxide ceramic of not more than 0.6 parts by weight and a boron compound of not less than 1.3 times the amount of boron necessary for converting oxide ceramics to boride ceramics per part by weight of carbon. A method for producing a carbon-boride ceramic spherical composite, comprising mixing and heat-treating at a temperature of 2200 ° C. or higher and a temperature at which a spherical body can be formed. 2. Carbon is carbon black having an average particle diameter of 10 μm or less, coke and its heat-treated product or natural graphite, and oxide ceramics has an average particle diameter of 10 μm.
m or less of molybdenum oxide, titanium oxide, tantalum oxide,
The method for producing a carbon-boride ceramic spherical composite according to claim 1, wherein zirconium oxide, vanadium oxide, niobium oxide, and tungsten oxide are used, and the boron compound is boric acid, boron oxide, and boron carbide. 3. A mixture of a carbide ceramic of not more than 2 parts by weight and a boron compound of not less than 1.3 times the amount of boron necessary for converting the carbide ceramic into boride ceramics per 1 part by weight of carbon, A method for producing a carbon-boride ceramics spherical composite, wherein the heat treatment is performed at a temperature of at least ℃ and a temperature at which a sphere can be formed. 4. Carbon is carbon black, coke and its heat-treated product or natural graphite having an average particle size of 10 μm or less, and carbide ceramics has an average particle size of 10 μm.
m or less of molybdenum carbide, titanium carbide, tantalum carbide,
The method for producing a carbon-boride ceramic spherical composite according to claim 3, wherein zirconium carbide, vanadium carbide, niobium carbide, tungsten carbide and hafnium carbide, and the boron compound is boric acid, boron oxide and boron carbide. .