JPS6330368A - Novel composite carbide - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a novel composite carbide obtained by igniting a novel carbon-containing mixture containing silicon oxide, elemental carbon, and boron oxide.

More specifically, the present invention relates to a novel composite carbide that can be sintered to suitably produce a novel composite carbide sintered body.

[Background technology]

The silicon carbide sintered body obtained by sintering silicon carbide powder is
Because it has significantly superior mechanical strength at high temperatures compared to conventional metal materials, it is expected to be used in engines, gas turbines, and other applications.

However, in conventional manufacturing methods, the mechanical strength of the resulting silicon carbide sintered body is due to the physical properties and purity of silicon carbide powder and its raw materials, silicon oxide such as silica sand, and elemental carbon such as coke. Excessive variation in the results is an obstacle to industrial application.

The above-mentioned sintered body has the property that the finer the silicon carbide powder that is its raw material, the easier it is to obtain a higher strength and the faster the sintering speed. Furthermore, the higher the purity of the raw material silicon carbide powder, the smaller the variation in the strength of the sintered body.

Furthermore, in the process of sintering silicon carbide powder, it was reported in Japanese Patent Publication No. 57-32035 that adding boron-based substances other than boron oxide, such as elemental boron and boron carbide, and elemental carbon have the effect of increasing the density of the sintered body. It is well known as disclosed in Japanese Patent Application Laid-Open No. 51-148712, etc., and it is said that the higher the purity and the finer the boron-based substance used for the addition, the greater the effect.

In order to obtain a silicon carbide sintered body to which such a boron-based substance is added, conventionally, silicon carbide and elemental boron or boron-based IFI materials are mechanically pulverized and mixed using a ball mill or the like, and then a carbonaceous substance is added thereto. A common method is to generate elemental carbon by thermal decomposition of the carbonaceous material by adding and heating it to form a mixture of silicon carbide powder, boron-based material powder, and elemental carbon powder, and then sintering this. It was a manufacturing method.

In this method, to produce silicon carbide, silicon dioxide, such as silica sand, and a carbonaceous material, such as coke, are pulverized and mixed, and the mixture is subjected to a solid-phase reaction at high temperatures in, for example, an Acheson-type direct current resistance furnace. A common method is to obtain

However, this method is a batch method, and there are problems such as a complicated work process when mixing and charging raw materials and contamination of impurities.

In addition, the generated silicon carbide is taken out as an ingot, so in order to obtain the fine powder required as a raw material for a sintered body, this ingot is crushed for a long time with a crusher such as a ball mill, and then only the fine particles are classified. Therefore, there are problems such as increased costs, complexity of the work process, and contamination of impurities during the work process.

Furthermore, regarding the boron-based substances added when obtaining a silicon carbide sintered body, boron oxide causes oxygen to be mixed into the sintered body, and is not effective in increasing the density of the sintered body, but on the contrary, it decreases the density. Therefore, it is inconvenient. Therefore, as the boron source, a boron-based substance other than boron oxide that does not contain oxygen is selected, but boron carbide is particularly preferred because it has excellent oxidation resistance, and elemental boron is next preferred.

However, boron carbide powder, like silicon carbide powder, is usually produced by obtaining an ingot of boron carbide through a solid-phase reaction between boron oxide or elemental boron and a carbonaceous material at a higher temperature, and then pulverizing and dispersing the ingot. Therefore, there is a problem in that it is difficult to obtain highly pure and fine particles similar to silicon carbide powder using conventional methods.

On the other hand, when elemental boron is used as a boron source, the finer the powder, the better, but the finer the powder, the greater the drawback that oxidation easily progresses even if it is left in the air. However, as is known from -11fi, as the amount of oxides contained in the sintering process of silicon carbide increases, the density of the obtained sintered body decreases and the strength of the molded body decreases. , the boron-based substance to be added is
As mentioned above, boron carbide is basically preferable in terms of preventing the contamination of oxides, but since it is difficult to obtain highly pure and fine particles, it has the problem of being easily oxidized, but it is unavoidable that elemental boron is mainly used. The reality is that there are.

[Purpose of the invention]

The purpose of the present invention is to eliminate mechanical grinding methods such as ball mills, which have many problems such as noise, wear, contamination of impurities, and generation of dust.
By providing a new composite carbide obtained through a new carbon-containing mixture in which fine particles of silicon oxide, elemental carbon, and boron oxide are extremely uniformly mixed, which can be obtained without performing any mixing operation. be.

Another object of the present invention is to obtain a carbon-containing mixture consisting primarily of extremely fine particles of silicon carbide and boron carbide, which can be obtained by heating the novel carbon-containing mixture as described above or in a non-oxidizing atmosphere such as argon-helium. The object of the present invention is to provide a new composite carbide.

A further object of the present invention is to provide a new composite carbide that can be obtained by sintering this composite carbide made of silicon carbide and boron carbide to produce a new composite carbide sintered body.

Other objects of the invention will become apparent from the description below.

[Disclosure of the invention]

As a result of thorough consideration of the advantages and disadvantages of the above-mentioned conventional methods, the present inventors have found that
As a method for obtaining a silicon carbide sintered body with excellent physical properties, we use a method different from the conventional method of obtaining silicon carbide powder directly from silicon compounds, etc., that is, silicon oxidation with sufficiently high uniformity and fine constituent particles. If a new carbon-containing mixture containing solid carbon, elemental carbon, and boric oxide is first produced, and the novel composite carbide of the present invention obtained by heating this cash carbon mixture is sintered as a raw material, the sintering speed is high. It was discovered that a composite carbide sintered body with small variations in strength can be obtained, and the present invention was completed.

That is, in the present invention, a decomposable silicon compound, a decomposable carbon compound, and a decomposable boron compound are charged into a hot gas containing water vapor and decomposed to form aerosols of silicon oxide, elemental carbon, and boron oxide, respectively. A carbon-containing mixture obtained by generating a mixed aerosol dispersoid containing and collecting the generated dispersoid, the carbon-containing mixture having a formula weight ratio C/(Si+B) (g-a
carbon-containing mixture (tms/g-atms) of 3.5 or more (
Hereinafter, it will be abbreviated as "carbon-containing mixture in the present invention". ) is characterized by a novel composite carbide obtained by igniting it.

[Disclosure of the invention]

The present invention will be explained in detail below.

The carbon-containing mixture in the present invention refers to a mixture of silicon oxide, elemental carbon, and boron oxide obtained by charging and decomposing a decomposable silicon compound, a decomposable carbon compound, and a decomposable boron compound into a water vapor-containing gas. It is obtained by generating a mixed aerosol containing an aerosol of
atms/g-atms) is 3.5 or more.
It is characterized by

However, the carbon-containing mixture in the present invention is silicon oxide,
Fine particles of elemental carbon and boron oxide are mixed uniformly on the microscopic order, giving the appearance of a "mixed powder". A "mixture" is "a mixture of two or more substances that exist homogeneously as a whole and can be understood as a substance," so it truly satisfies the requirements for a "composition" as defined in the Industrial Examination Standards. should originally be called a "carbon-containing composition," but here, out of custom, the term "carbon-containing mixture" was used.

The mixed aerosol referred to in the present invention refers to a gas in which silicon oxide, elemental carbon, and boron oxide are mixed as fine solid dispersoids.The carbon-containing mixture in the present invention refers to This is a mixture containing silicon oxide, elemental carbon, and boron oxide obtained by collecting the above-mentioned solid matter that is a dispersoid in a mixed aerosol.

In the present invention, an aerosol of simple carbon can be easily obtained by charging a decomposable carbon compound into hot gas and decomposing it. On the other hand, silicon oxide or boron oxide aerosols can be thermally decomposed, oxidized, or hydrolyzed when a decomposable silicon compound such as silicon tetrachloride or a decomposable boron compound such as boron trichloride is introduced into a hot gas containing water vapor. It can be easily obtained by decomposition with etc. As can be easily understood, if a decomposable carbon compound, a decomposable silicon compound, and a decomposable boron compound are simultaneously charged into a hot gas containing water vapor, a mixed aerosol dispersion containing silicon oxide, elemental carbon, and boron oxide is immediately formed. You get quality.

The decomposable silicon compound that can be used in the present invention is represented by the general formula 5inXza*t (n is an integer from 1 to 4), where X is hydrogen, a halogen atom, an alkyl group, or an alkoxyl group, and the specific Typical silicon compounds include 5iC14, H5iC1t, 5iHa, 5fJi
, (CH2)n5i, (CHi)zsiclz, C
HzSiCli, SiF4.5i(OCJs)a, etc., and mixtures thereof do not cause any problem in the present invention.

The decomposable carbon compound used in the embodiments of the present invention is a vine-like compound that easily decomposes to produce elemental carbon (soot) when charged into hot gas, and it remains in the gas or liquid phase as it is. Those that can be easily turned into a liquid phase by raising the temperature can be suitably used.

For example, LPG, naphtha, gasoline, fuel oil, kerosene,
Petroleum products such as light oil, heavy oil, lubricating oil, and liquid paraffin; hydrocarbons such as methane, ethane, propane, butane, and pentane; methanol, ethanol, propatool,
Ethylene, acetylene, n-paraffin, butadiene,
Isoprene, isobutylene, benzene, toluene, xylene, cyclohexane, cyclohexene, dicyclopentadiene, ethylbenzene, styrene, cumene, pseudocumene, mesitylene, alkylbenzene, α-methylstyrene, dicyclododecatriene, diisobutylene, vinyl chloride, chlorobenzene, Petrochemical products such as C9 distillate mixture and ethylene bottom; tar products such as tar, hitch, taleosote oil, naphthalene, anthracene, carbazole, tar acid, phenol, cresol, xyresol, pyridine, picoline, and quinoline;
Preferable examples include oils and fats such as soybean oil, coconut oil, linseed oil, cottonseed oil, rapeseed oil, tung oil, castor oil, whale oil, beef tallow, squalane, oleic acid, and stearic acid, but of course they are not limited to these. do not have.

Since the purpose of the decomposable carbon compound used in the practice of the present invention is to supply carbon, for example, as described above,
A wide range of options are available. However, from the viewpoint of ease of handling and carbon yield, toluene, xylene, benzene, kerosene, light oil, heavy oil, C9 fraction mixture, ethylene bottom, etc. are preferred.

Decomposable boron compounds that can be used in the practice of the present invention include BF2, acts, BBrz, BHz, BJi,
Examples include BJJh, and mixtures thereof may also be used.

Note that inexpensive boric acid can also be used as the decomposable boron compound. In this case, you can replace boric acid with water or methanol,
It is convenient to dissolve the solution in a solvent such as ethanol and then introduce the solution into hot gas together with air, steam, etc. using a two-fluid atomization method.

When using boric acid as the boron compound, BCIs,
There is a problem that it is difficult to easily obtain a fine aerosol because it is difficult to oxidize compared to the above-mentioned decomposable boron compounds such as 8113, but according to the study of the present inventors, boric acid By adopting a method in which boric acid is dissolved in a solvent and then charged into a hot gas, boric acid becomes easily formed into a fine aerosol to a sufficient extent to achieve the object of the present invention. A more preferable aerosol can be obtained by using a two-fluid atomization method.

The decomposable silicon compound, decomposable carbon compound, or decomposable boron compound that can be used in the present invention can be easily converted into a gas phase or liquid phase as is or by heating, so it is necessary to eliminate specific impurities. If necessary, a highly pure mixture can be easily obtained by simple operations such as distillation, adsorption, and washing.

In addition, silicon oxide in the carbon-containing mixture in the present invention,
Of the proportion of elemental carbon and boron oxide! The l1 clause can be easily achieved by simply changing the amounts of the decomposable silicon compound, decomposable carbon, and decomposable boron compound, which are the raw materials injected into the hot gas from the nozzle, and adjusting their mutual ratios to the tA clause.

As a specific device for obtaining the carbon-containing mixture in the present invention, it is preferable to use a furnace.

The furnace is equipped with a heating device, charging nozzles for decomposable silicon compounds, decomposable carbon compounds, and decomposable boron compounds, a hot gas charging duct, and a mixed aerosol discharge duct. . Further, as a heating device, there are combustion burners, energized heating elements, and the like, but combustion burners are preferable because they are simple and have high thermal efficiency.

FIG. 1 shows an example of a furnace used for this purpose.

In the present invention, there must be a space in the furnace at least 600°C or higher, preferably 700°C or higher, and more preferably 800°C or higher.At this temperature or higher, elemental carbon is released from the decomposable carbon compound, and water vapor is removed. Silicon oxide is obtained from decomposable silicon compounds and boron oxide is obtained from decomposable boron compounds as extremely fine particles in an atmosphere containing . Occur.

Note that such a high temperature is unnecessary because a temperature of 2000° C. or higher usually causes only heat loss. In addition, in addition to silicon oxide or boron oxide, even if elemental silicon or elemental boron, or even silicon halide or boron halide is interposed, the composite carbide sintering which is the final objective of the present invention can be achieved. There is no particular hindrance to obtaining a body.

The hot gas containing water vapor used in the present invention can also be obtained by injecting water vapor into hot gas obtained by an electric heating method, a high frequency heating method, or a discharge method. ethane, propane, etc.
Another method is to use air to combust a combustible material that generates water vapor by burning, such as hydrocarbons, which are raw materials, because hot gas containing water vapor can be obtained in the -step, which is simple in terms of equipment, and from the standpoint of thermal efficiency. It is also economical.

The decomposable silicon compound or decomposable boron compound used in the practice of the present invention is easily converted into a solid substance of elemental silicon or elemental boron through a thermal decomposition reaction in hot gas, and also undergoes oxidation of silicon through a hydrolysis reaction with water vapor. It changes to boron oxides or boron oxides. In addition, since the above reaction is extremely fast and is substantially completed in 0.01 to 0.1 seconds, a reaction time (residence time in the reaction zone) of 1 second is sufficient.

Therefore, under an atmosphere in which heat and water vapor coexist as in the present invention, it can be substantially ignored that the decomposable silicon compound or the decomposable boron compound evaporates out of the reaction system while remaining in a gaseous state.

The mixed aerosol dispersoid containing the silicon compound, elemental carbon, and boron oxide produced in this way is guided out of the furnace, and then the solids contained therein are collected using known methods such as bag filters, cyclones, and electric dust collectors. Although it is collected by a solid-liquid separation operation using a device, it is desirable to pre-cool it in order to reduce the heat load on the collection device.The pre-cooling method is as follows:
It is possible to employ means such as cooling the zone after the reaction or injecting water.

The carbon-containing mixture according to the present invention collected as described above can be collected using a high-frequency heating furnace, an energizing resistance furnace, a direct-fired tubular heating furnace, etc., and preferably argon, helium, nitrogen, hydrogen, -
1000-250 in a non-oxidizing atmosphere such as carbon oxide
By igniting to 0°C, preferably about 1200 to 2000°C, the composite carbide of the present invention, which is a homogeneous mixture of silicon carbide and boron carbide suitable as a raw material for a sintered body, can be obtained.

In the present invention, the purpose of the carbon-containing mixture is mainly to obtain the composite carbide of the present invention as described above. Therefore, the proportions of carbon, silicon, and boron in the fine powder of the carbon-containing mixture are -atm ratio, hereinafter the same)
/(Si+8) is required to be greater than 3.5. The reason for this is based on the inventors' experimental findings that the more carbon is contained in the mixture, the smaller the average particle diameter of the composite carbide obtained by heating the mixture becomes.

Although the exact reason cannot be made clear at present, the composite carbide of the present invention is produced by heating the carbon-containing mixture, and in this reaction process, composite carbide fine particles are produced and the particles grow. It is presumed that the presence of excess carbon has the effect of hindering the bonding between particles, resulting in a fine composite carbide with a small particle size.

However, if this formula weight ratio is too large, the carbon compound will simply be lost; therefore, a value of about 3.5 to 20 is appropriate for the above formula weight ratio. In addition,
Cough formula volume ratio! As already mentioned, Section I1 can be easily accomplished by simply changing the amount of raw material injected from the nozzle of the furnace.

In the step of igniting the carbon-containing mixture of the present invention to obtain the composite carbide of the present invention, if oxygen exists in the heating atmosphere, the elemental carbon will burn and be removed. , heating under a non-oxidizing atmosphere such as hydrogen is preferred, however,
Normally, during the heat treatment step, silicon oxide or boron oxide and carbon react to form a composite carbide and at the same time carbon monoxide is formed, and the system naturally becomes a non-oxidizing atmosphere. It is not necessary to supply an inert gas such as into the system.

In this heat treatment step, it is preferable to heat the η carbon-containing mixture once after performing an operation of tightening, that is, increasing the bulk specific gravity, in order to obtain a fine composite carbide powder. If a carbon-containing mixture is heated in this state, a rod-shaped composite carbide with particles growing in one direction is likely to be produced, but if heated after tightening and increasing the bulk specific gravity, a spherical shape with uniform particle diameters can be produced. This is based on the experimental findings of the present inventors that the following can be obtained. In this case, the bulk specific gravity is at least 0.15 g/ec
It is preferable to perform tightening as described above, and such tightening operation can be easily carried out by compression, stirring type granulation, or the like.

The composite carbide of the present invention obtained by igniting the carbon-containing mixture is composed of extremely fine particles of silicon carbide, boron carbide, and elemental carbon.

Thus, a sintered composite carbide can be obtained by sintering the composite carbide of the present invention, but in that case, the weight ratio of boron to 100 silicon is in the range of 0.15 to 4.5. If the amount of boron is less than this, sintering will not occur, and if it exceeds this, abnormal grain growth will occur.
This is because a dense sintered body cannot be obtained.

In addition, in order to obtain a composite carbide sintered body by sintering the composite carbide of the present invention, it is necessary to sinter the composite carbide to a certain extent (composite carbide 1
The presence of carbon (on the order of 0.2 to 2.0 parts by weight per 00 parts by weight) is required. However, since the carbon content in the composite carbide of the present invention obtained by igniting the carbon-containing mixture of the present invention is usually in excess of the above ratio, it is necessary to It is preferable to partially remove the carbon of
This can be easily done by heating to about C. Specifically, this can be easily carried out by heating the composite carbide of the present invention in air or by placing it in a hot gas atmosphere containing oxygen, which is obtained by burning fuel with excess air. In addition,
A composite carbide whose residual carbon is removed by combustion or whose carbon content is adjusted by such means is also referred to as the composite carbide of the present invention.

Although it is of course possible to obtain a sintered body by burning a composite carbide with an adjusted carbon ratio by the method described above, a more desirable method is to obtain a sintered body by burning the composite carbide with an adjusted carbon ratio. The process involves substantially completely burning off the elemental carbon from the composite carbide, adding new elemental carbon to the composite carbide, and then sintering it.

The reason for this is 7. When the composite carbide of the present invention containing elemental carbon obtained by heating a carbon-containing mixture is placed in an oxygen-containing hot gas atmosphere, when viewed microscopically, the powder appears to be in contact with the hot gas. It is presumed that this is because only the elemental carbon in the portion where the sintered body is removed is burnt away more quickly, and the residual form of the elemental carbon is not necessarily uniform enough to obtain the desired sintered body.

When newly adding elemental carbon, a liquid hydrocarbon with a relatively high carbon content is mixed with the composite carbide powder obtained by burning off the elemental carbon as described above. By heating in a non-oxidizing atmosphere,
A method in which elemental carbon is produced in a composite carbide is preferably employed.

Suitable liquid hydrocarbons used for this purpose include, for example, an acetone solution of a phenol/formaldehyde condensate, an acetone solution of a resorcinol/formaldehyde condensate, glycerin, a benzene solution of coal tar pitch, etc. It is not limited to this.

In addition, in the mixture obtained by adding elemental carbon to the composite carbide of the present invention, more than 1 part by weight of oxygen is contained in the form of silicon oxide and boron oxide based on 100 parts by weight of the composite carbide. There are cases. In such cases, remove the oxide by washing with a hydrofluoric acid solution to reduce the oxygen content (
It is desirable that both amounts be 0.5 parts by weight or less in terms of strength and physical properties of the carbide sintered body or carbide molded body obtained by sintering and processing this.

This cleaning step with an aqueous hydrofluoric acid solution can also be carried out before adding elemental carbon to the composite carbide, ie, in a step after burning and removing elemental carbon from the composite carbide.

〔Effect of the invention〕

As described above, in the present invention, in order to obtain a carbon-containing mixture of raw materials, a decomposable silicon compound, a decomposable carbon compound, and a decomposable boron compound are subjected to a chemical reaction in a hot gas containing water vapor, that is, thermal decomposition, oxidation, It is characterized by the fact that it is made to undergo hydrolysis, etc., and from the stage where each molecule is generated, particles are allowed to grow while remaining mixed on the order of molecules. Therefore, it is easier to obtain a mixture of fine particles of silicon oxide, elemental carbon, and boron oxide that are essentially uniform and much finer than those obtained by conventional mechanical mixing methods. In this respect, it has extremely superior quality. Also, in its implementation, dust,
There are no problems such as noise, and unlike the batch method, the mixture can be obtained continuously, which eliminates the complexity and pulverization of the work process, which was considered a hindrance in the conventional method of mechanically crushing ingots in the batch method. There is no problem of contamination with impurities due to wear of the machine itself.

The composite carbide of the present invention uses a carbon-containing mixture with excellent physical properties as described above as a starting material and is obtained by igniting it, so it has an extremely wide specific surface area and is a powder consisting of extremely small particles. be. Therefore, by sintering the composite carbide, the sintering speed is high, the sintering is easy, and a dense sintered body can be obtained.

Furthermore, if the ratio of carbon to silicon and boron in the carbon-containing mixture is made excessive, the powder of the composite carbide of the present invention becomes even finer and has a larger specific surface area.

Furthermore, since the composite carbide of the present invention mainly consists of silicon carbide and boron carbide, in the sintering step,
There is no need to separately synthesize and add and mix a boron-based material, especially silicon carbide, and there is no need to use elemental boron, which is easily oxidized.

[Preferred Mode for Carrying Out the Invention] The present invention will be specifically explained below with reference to Examples. Note that % indicates weight %.

Example 1 Using the furnace shown in Fig. 1 (diameter 300 mm, length 311), air was supplied from duct 2 and hydrogen was supplied as hot air fuel from combustion burner 3 at flow rates of 8 ON m'/h and 12 μm'/h, respectively. and 5iC1a as a decomposable silicon compound.
, a C9 fraction mixture as a decomposable carbon compound, and BCl3 as a degradable boron compound in a weight ratio of 1:1.
．． 9: Nozzle 4 mixed with 0.0077
It was then charged into the furnace at a flow rate of 14 kg/h. Inside the furnace is the first
The temperature was maintained at 1000-1100°C at position A in the figure. The aerosol generated in the furnace is extracted from duct 6,
After cooling, the mixture was collected using a bag filter to obtain 5.0 kg/h (dry weight) of the carbon-containing mixture of the present invention.

This mixture contains 15.8% silicon, 65.6% carbon, and 0.07% boron (the remainder is 18.4% bound oxygen, 0.1% carbon-attached hydrogen, and other 0.1% or less), weight ratio C/(Si+B) is 9.6
As a result of ESCA spectrum analysis, the bonding forms between silicon or boron and other elements include 5t-0 bond, B
Only -0 binding was observed. Also, the bulk specific gravity is 0.0961
/cc.

500 g of this carbon-containing mixture was placed in a cylindrical container, uniaxially compressed to a bulk specific gravity of 0.351/cc, then inserted into a graphite crucible, and heated in a high-frequency heating furnace in an argon cloud atmosphere for 170 g.
Ignite at 00°C for 2 hours, cool down to 750°C in air.
The mixture was heated to .degree. C. and the remaining elemental carbon was burned off to obtain 115 g of the composite carbide of the present invention.

As a result of ESCA spectrum analysis of this product, the presence of 5i-C bonds and B-C bonds was confirmed, and it was found that it was composed of silicon carbide and boron carbide.

In addition, as a result of powder X-ray diffraction spectrum analysis, the presence of silicon carbide with a cubic crystal structure and boron carbide with a needle-edge crystal structure was confirmed, and the average particle diameter was 0.27μ according to electron microscope image analysis. It was observed that the particle shape was uniformly spherical.

Chemical analysis showed that the oxygen content of this product was 1.6%.

Examples 2 to 5 The same method as in Example 1 was carried out using methane, P1, and Rossene in addition to hydrogen as the hot air fuel, and using the silicon compounds, carbon compounds, and boron compounds shown in Table 1, respectively. A carbon-containing mixture of the present invention was obtained. Table 2 shows the composition of each of the obtained carbon-containing mixtures.

As a result of ESCA spectrum analysis of the carbon-containing mixture, only 5i-0 bonds and B-0 bonds were observed as bond forms between silicon or boron and other elements.

In Table 1, the same number indicating the position of the charging nozzle means that the charging nozzle was mixed in advance. For example, in Example 2, 5iCI4 and A heavy oil were mixed in advance and charged from nozzle 4. BF means that the material was charged into the furnace through the nozzle 5 at the same time.

Table 2 In addition, in Example 5, a solution obtained by mixing boric acid and ethanol in a weight ratio of 0.08:1 was injected into the nozzle 4.
It was then charged into the furnace. The charging method was a two-fluid spraying method using air, and the amount of air was 0.25 Nmff/h.

Each of the obtained carbon-containing mixtures was compressed, ignited, cooled and the remaining carbon was burned off in the same manner as in Reference Example 1 under the conditions shown in Table 3 to obtain the composite carbide of the present invention. .

Table 3 Results of ESCA spectrum analysis of the obtained composite carbide,
The existence of 5i-C1-C bond was confirmed. Furthermore, the average particle diameters determined by electron microscope image analysis were as shown in Table 3.

As a result of powder X-ray diffraction spectrum analysis, the presence of cubic silicon carbide and needle-edge boron carbide was confirmed in all of the composite carbide powders of the present invention.

Further, in Example 3, the presence of hexagonal silicon carbide was also determined, and the proportion thereof was estimated to be about 10 parts by weight per 100 parts by weight of cubic silicon carbide.

Reference Example 1 (Manufacturing Example of Sintered Body) The composite carbide of the present invention obtained in Example 1 was mixed with 5 times the weight of I(
110. obtained by soaking in F aqueous solution (concentration 10%) for 5 hours and then drying. 300 in which 2.7 g of resorcinol formaldehyde condensate was dissolved.
cc of acetone solution was added, mixed at room temperature for 10 hours, and the container was further immersed in a constant temperature water bath adjusted to 70 °C.
After acetone was removed by evaporation while kneading, this was heated at 600'C for 1 hour in a N2 gas atmosphere to obtain a mixture of composite carbide and additional carbon. Its composition is 69.1% silicon, 30.5% carbon, and 0.30 boron.
%, oxygen 0.06% (others 0.1% or less),
Elemental carbon was 0.89%.

Next, put 100g of this hot container into a cylindrical container and
After l-axis compression with a load of CD, rubber pressing was performed with a hydrostatic pressure of 2 T/cffl, and the composite carbide sintered body was further sintered at 2100°C for 115 minutes in a nitrogen atmosphere of 10 to 1 mmHH to obtain a composite carbide sintered body. Ta. The density of this sintered body was measured and found to be 3.11 g/cc, which was a good value corresponding to 97χ of the theoretical density of silicon carbide, 3.21 g/cc.

Next, this sintered body was cut with a diamond cutter, and
A test piece was prepared and tested according to JIS R-1601 ('81).
The 0-bending strength was measured in two different atmospheres: room temperature and nitrogen atmosphere at 1400°C, and each was measured by three-point bending using 15 test pieces.

As a result, the average bending strength at room temperature was 46g7mm.
The standard deviation is 2.6 g/■-g, the average bending strength at 1400 "C is 45 Kg/am" and the standard deviation is 2.5.
Kg/mm"Reference Examples 2 to 5 (Example of Production of Sintered Body) The composite carbide powders of the present invention obtained in Examples 2 to 5 were washed and filtered with an HF aqueous solution in the same manner as in Reference Example 1, respectively. To each of the obtained 110g, resorcinol in the amount shown in Table 4 was added.
300 cc of an acetone solution in which a formaldehyde condensate was dissolved was added, and additional carbon was added in exactly the same manner as in Reference Example 1 to obtain a mixture of composite carbide and carbon. The respective compositions were as shown in Table 4.

A mixture of these composite carbides and carbon was molded in exactly the same manner as in Reference Example 1, and then sintered together at 2100°C for 15 minutes to obtain each composite carbide sintered body. The density of each sintered body was as shown in Table 4 with respect to the theoretical density of silicon carbide.

Next, from these sintered bodies, 30
The test pieces were cut out and subjected to a three-point bending strength test, and the results are shown in Table 4.

Comparative Reference Example 1 A carbon-containing mixture containing silicon oxide and carbon was produced in the same manner as in Example 1 except for the use of BCh in Table 4.

Using this carbon-containing mixture, it was compressed in the same manner as in Example 1, heated using a high-frequency heating furnace, and further burnt off the elemental carbon to obtain 115 g of silicon carbide powder. As a result, the crystal shape was cubic, and the average particle diameter was 0.25 μm as determined by image analysis using an electron microscope.

110 g of this silicon carbide powder was washed with an HF aqueous solution and dried in the same manner as in Reference Example 1, and the average particle size was 4.0.
Add 0.33g of elemental boron powder of μ so that the ratio of boron to silicon matches Reference Example 1, and add additional carbon in exactly the same manner as Reference Example 1 to combine silicon carbide, elemental boron, and carbon. 112 g of mixture was obtained. Its composition is 69.1% silicon, 30.4% carbon, 0.30% boron, 0.17% oxygen (others less than 0.1%), and elemental carbon is 0.90χ. Ta.

100 g of this mixture was molded and heated in exactly the same manner as in Reference Example 1 to obtain a sintered body.

The density of this sintered body was measured.3. OOg/cc, which corresponds to 93% of the theoretical density of silicon carbide.

Next, using this sintered body, reference example 1 and all (30
A test piece was cut out and a three-point bending strength test was performed, and the average bending strength at room temperature was 40Kg/ff1I11!
The standard deviation is 3.5Kg/IIIm", and the average bending strength at 1400°C is 38Kg/mm" with a standard deviation of 3.
It was 1Kg/steel 2.

From a comparison between Example 1 and Reference Example 1 and Comparative Reference Example 1, it was found that the composite carbide sintered body obtained using the carbon-containing mixture of the present invention containing silicon oxide, elemental carbon, and boron oxide as a starting material was It can be seen that the sintered body has a higher density, greater strength, and less variation than a sintered body obtained using a carbon-containing mixture as a starting material.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one example of a furnace used in carrying out the present invention. In the figure, 1: furnace material 2: duct 3: combustion burner 4: nozzle 5: nozzle 6: duct is shown. Patent distributor Mitsui Toatsu Chemical Co., Ltd. Figure 1

Claims (2)

[Claims] (1) A decomposable silicon compound in hot gas containing water vapor,
A decomposable carbon compound and a decomposable boron compound are charged and decomposed to generate a mixed aerosol dispersoid containing aerosols of silicon oxide, elemental carbon, and boron oxide, and the generated dispersoid is collected. A carbon-containing mixture obtained by
A novel composite carbide obtained by igniting a carbon-containing mixture having -atms) of 3.5 or more. (2) The composite carbide according to claim 1, wherein the weight ratio of boron to 100 parts of silicon is 0.15 to 4.5.