JPH0339988B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical field] The present invention involves igniting a new fine carbon-containing mixture containing silicon oxide, elemental carbon, and boron oxide to form a new composite carbide containing silicon carbide and boron carbide, and sintering this under specific conditions. This paper relates to a method for producing a new composite carbide sintered body. [Background Art] Silicon carbide sintered bodies obtained by sintering silicon carbide powder have significantly superior mechanical strength at high temperatures compared to conventional metal materials, so they are used in engines,
It is expected to be used in gas turbines, etc. However, in conventional manufacturing methods, the mechanical strength of the resulting silicon carbide sintered body depends on the physical properties and purity of the silicon carbide material 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 implementation. The above-mentioned sintered body is characterized in that the finer the silicon carbide powder that is its raw material, the easier it is to obtain a greater 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 is known 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 known as disclosed in Japanese Patent Application Laid-open No. 32035 and Japanese Patent Application Laid-open No. 148712/1984, and it is said that the higher the purity and fineness of the boron-based substance used for the addition, the greater the effect. In order to obtain such a silicon carbide sintered body to which a boron-based substance is added, conventionally, silicon carbide and elemental boron or a boron-based substance are mechanically pulverized and mixed using a ball mill or the like, and then a carbonaceous substance is added thereto. In addition, by heating once, elemental carbon is generated by thermal decomposition of the carbonaceous material to form a mixture of silicon carbide powder, boron-based material powder, and elemental carbon powder, and this is generally sintered. It was manufactured using a unique 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 it by However, this method is a batch method, and has problems such as a complicated work process when mixing and charging the raw materials and the contamination of impurities. In addition, the generated silicon carbide is extracted 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 using 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 produced by obtaining an ingot of boron carbide through a solid-phase reaction with boron oxide or elemental boron at a higher temperature than a carbonaceous material, and then crushing and dispersing this ingot. It's manufactured. Therefore, with conventional methods, it is difficult to obtain highly pure and fine particles similar to silicon carbide powder. 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 generally known, as the amount of oxides contained in silicon carbide increases during the sintering process,
Since the density of the obtained sintered body and the strength of the molded body are lowered, boron carbide is basically preferable as the boron-based substance to be added, as mentioned above, in terms of preventing oxides from being mixed in. Although there is a problem that it is easily oxidized because it is difficult to obtain a pure and fine material, the reality is that elemental boron is mainly used out of necessity. [Object of the Invention] The object of the present invention is to produce silicon that can be obtained without performing any mechanical grinding or mixing operations such as ball mills, which have many problems such as noise, abrasion, contamination of impurities, and generation of dust. A new carbon-containing mixture made of an extremely uniform mixture of fine particles of oxides, elemental carbon, and boron oxides is used as a raw material, and this new carbon-containing mixture produces a new composite with significantly superior mechanical strength and less variation in strength. An object of the present invention is to provide a method for manufacturing a carbide sintered body. Other objects of the invention will become apparent from the description below. [Disclosure of the Invention] As a result of thorough examination of the conventional losses, the present inventors have developed a conventional method for directly obtaining silicon carbide powder from a silicon compound, etc., as a method for obtaining a silicon carbide sintered body with excellent physical properties. A method different from the above is used, in which a novel carbon-containing mixture containing silicon oxide, elemental carbon and borate with sufficiently high uniformity and fine constituent particles is first produced, and this defined carbon-containing mixture is ignited. The inventors discovered that by sintering the obtained new composite carbide, a composite carbide sintered body with a high sintering speed and small variation in strength could be obtained, and the present invention was completed. That is, the present invention introduces a decomposable silicon compound, a decomposable carbon compound, and a decomposable boron compound into hot gas containing water vapor and decomposes them to produce silicon oxide,
A composite carbon mixture obtained by generating a mixed aerosol dispersoid containing aerosols of elemental carbon and boron oxide, and collecting the generated dispersoid, having a formula weight ratio of C/(Si+B)(g- atms/g-
100 parts by weight of a composite carbide obtained by igniting a carbon-containing mixture with an atms) of 3.5 or more is sintered together under conditions in which 0.2 to 2.0 parts by weight of a carbonaceous material coexists in terms of the amount of simple carbon. This paper focuses on a method for manufacturing a new composite carbide sintered body, in which the ratio of silicon to boron in the composite carbide sintered body is 0.15 to 4.5 by weight per 100 parts silicon. This is a summary. [Disclosure of the Invention] The present invention will be described 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 and collecting this aerosol dispersoid, with a formula weight ratio of C/(Si+B)(g-atms/g-
ATMS) is 3.5 or higher. However, the carbon-containing mixture in the present invention has fine particles of silicon oxide, elemental carbon, and boron oxide mixed uniformly on the microscopic order, giving the appearance of a "mixed powder." In addition, the term "mixture" here refers to "a mixture of two or more substances that exist homogeneously as a whole and are understood as a single substance", so it is exactly the same as the "mixture" mentioned in the Industrial Examination Standards. Originally, it should be called a "carbon-containing composition," but here, out of custom, the term "carbon-containing mixture" was used. The mixed aerosol as used in the present invention means 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 is a mixture containing silicon oxide, elemental carbon, and boron oxide obtained by collecting the above-mentioned solid matter as a dispersoid in the 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. Decomposable silicon compounds that can be used in the present invention are those represented by the general formula SinX _2o+2 (n is an integer from 1 to 4), where X is hydrogen, a halogen atom, an alkyl group or an alkoxyl group, Specific silicon compounds include SiCl ₄ , HSiCl ₃ , SiH ₄ ,
_{Si2H6 ,} ( _{CH3 ) 4Si} , ( _CH3 ) _{2SiCl2 , CH3SiCl3} ,
SiF ₄ , Si(OC ₂ H ₅ ) _4, 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 one that can easily decompose to produce elemental carbon (soot) when charged into hot gas, and can be used in a 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,
Petroleum products such as kerosene, light oil, heavy oil, lubricating oil, and liquid paraffin; hydrocarbons such as methane, ethane, propane, butane, and pentane; methanol, ethanol, propanol, ethylene, acetylene,
n-paraffin, butadiene, isoprene, isobutylene, benzene, toluene, xylene, cyclohexane, cyclohexene, dicyclopentadiene, ethylbenzene, styrene, kyumene, butoidcumene, mesitylene, alkylbenzene,
α-methylstyrene, dicyclododecatriene,
Diisobutylene, vinyl chloride, chlorobenzene,
Petrochemical products such as _C9 distillate mixtures and ethylene bottoms; tar products such as tar, hitch, creosote oil, naphthalene, anthracene, carbazole, tar acid, phenol, cresol, xyresol, pyridine, picoline, and quinoline; Preferred examples include, but are not limited to, oils and fats such as bean oil, coconut oil, linseed oil, cottonseed oil, rapeseed oil, tung oil, castor oil, whale oil, beef tallow, squalane, oleic acid, and stearic acid. . Since the purpose of the decomposable carbon compound used in carrying out the present invention is to supply carbon, a wide range of choices can be made for this purpose, for example as described above. However, due to ease of handling and carbon yield, toluene, xylene, benzene, kerosene, light oil, heavy oil, etc.
_C9 fraction mixtures, ethylene bottoms, etc. are preferred. Decomposable boron compounds that can be used in the practice of the present invention include BF ₃ , BCl ₃ , BBr ₃ , BH ₃ , B ₂ H ₆ ,
Examples include B ₃ N ₃ H ₆ , and mixtures thereof may also be used. Note that inexpensive boric acid can also be used as the decomposable boron compound. In this case, it is convenient to dissolve boric acid in water or a solvent such as methanol or ethanol, and then introduce the solution into hot gas together with air, steam, etc. by a two-fluid spraying method. When using boric acid as the boron compound,
There is a problem in that it is difficult to easily obtain a fine aerosol because boron is less easily oxidized than the above-mentioned decomposable boron compounds such as BCl ₃ and BH _3. However, according to the study of the present inventors, boric acid By adopting a method of dissolving boric acid in the above-mentioned solvent and then charging it into hot gas, boric acid can easily become a fine aerosol to a sufficient extent to achieve the object of the present invention,
Moreover, if this boric acid solution is charged by a two-fluid spraying method, a more preferable aerosol can be obtained. 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, the adjustment of the ratio of silicon oxide, elemental carbon, and boron oxide in the carbon-containing mixture in the present invention is based on the decomposable silicon compound, decomposable carbon, and decomposable boron compound, which are the raw materials injected into the hot gas from the nozzle. This can be easily accomplished by simply changing the amounts of and adjusting their ratios. As a specific device for obtaining the carbon-containing mixture in the present invention, it is preferable to use a furnace. This furnace includes a heating device, a decomposable silicon compound,
It is equipped with charging nozzles for decomposable carbon compounds and decomposable boron compounds, a hot gas charging duct, and a mixed aerosol discharge duct. In addition, combustion burners are used as heating devices,
There are electric heating elements, but combustion burners are preferable because they are simple and thermally efficient. FIG. 1 shows an example of a furnace used for this purpose. In the present invention, there must be a spatial region in the furnace at least 600°C or higher, preferably 700°C or higher, more preferably 800°C or higher. At temperatures above this temperature, decomposable carbon compounds produce elemental carbon, and in an atmosphere containing water vapor, decomposable silicon compounds produce silicon oxides, and decomposable boron compounds produce boron oxides as extremely fine particles. The result is a mixed aerosol state, which is a mixture of gases and these solids. Note that such a high temperature is unnecessary since a temperature of 2000° C. or higher usually only results in heat loss. Furthermore, even if elemental silicon or elemental boron, or even silicon halide or boron halide is present in addition to silicon oxide or boron oxide, the composite carbide sintered body, which is the final objective of the present invention, can be achieved. It's not a particular hindrance to getting it. 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. The method of burning combustible materials such as hydrogen, methane, ethane, propane, etc., or raw material hydrocarbons, which produce water vapor by combustion, with air can produce hot gas containing water vapor in one step, so the equipment is suitable. It is simple and economical in terms of thermal efficiency. 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 a hydrolysis reaction with water vapor. Therefore, it changes to silicon oxide or boron oxide. In addition, since the speed of the above reaction is extremely high and the reaction is substantially completed in 0.01 to 0.1 seconds, the reaction time (residence time in the reaction zone) is 1.
It is enough to take seconds. Therefore, under an atmosphere in which heat and water vapor coexist as in the present invention, it can be virtually 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 silicon compounds, elemental carbon, and boron oxides produced in this way is guided outside the furnace, and the solids contained therein are removed using known collection devices such as bag filters, cyclones, and electric dust collectors. It is collected by a solid-liquid separation operation using a solid-liquid separation operation, but it is desirable to pre-cool it in order to reduce the heat load on the collection device. As a method for pre-cooling, means such as cooling the zone after the reaction or injecting water can be adopted. The carbon-containing mixture according to the present invention collected as described above is preferably heated using a high-frequency heating furnace, an electric current resistance furnace, a direct-fired tubular heating furnace, etc. Under oxidizing atmosphere, 1000-2500℃ preferably 1200-2000℃
By heating to a certain degree, a composite carbide consisting of a uniform mixture of silicon carbide and boron carbide suitable as a raw material for a sintered body can be obtained. In the present invention, since the purpose of the carbon-containing mixture in the present invention is mainly to obtain a composite carbide as described above, the carbon in the fine powder of the carbon-containing mixture,
The ratio of silicon and boron is 3.5 as a formula weight ratio (ratio of g-atm. The same applies hereinafter) C/(Si+B)
It is required to be larger. The reason for this is based on the inventors' experimental findings that the more carbon is included in the mixture in excess, the smaller the average particle diameter of the composite carbide obtained by heating the mixture becomes. The exact reason for this is of course not clear at present, but the composite carbide is generated by heating the carbon-containing mixture, and during this reaction process, composite carbide fine particles are generated 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. As already mentioned, the formula weight ratio can be easily adjusted by simply changing the amount of raw material injected from the nozzle of the furnace. In the process of igniting a carbon-containing mixture to obtain a composite carbide in the present invention, if oxygen exists in the heating atmosphere, the elemental carbon will burn and be removed. It is preferable to heat under a non-oxidizing atmosphere. However, normally, in the heat treatment step, silicon oxide or boron oxide reacts with carbon, producing a composite carbide and at the same time carbon monoxide is produced, and the system naturally becomes a non-oxidizing atmosphere. In particular, it is not necessary to supply an inert gas such as argon into the system. In this heat treatment step, it is preferable to once tighten the carbon-containing mixture, that is, to increase the bulk specific gravity, and then heat it, in order to obtain a fine composite carbide powder. If a carbon-containing mixture is heated in a state where the bulk specific gravity is small, a rod-shaped composite carbide with particles growing in one direction is likely to be formed, but if the bulk specific gravity is increased by tightening and then heated, the particle size becomes uniform. This is based on the experimental findings of the present inventors that a uniform spherical shape can be obtained. In this case, the bulk specific gravity is at least
It is preferable to tighten the concentration to 0.15 g/cc or more. 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, the composite carbide sintered body of the present invention can be obtained by sintering the composite carbide, but in that case, it is preferable that the weight ratio of boron to 100 silicon is in the range of 0.15 to 4.5. . This is because if the amount of boron is less than this, sintering will not occur, and if it exceeds this, abnormal grain growth will occur and a dense sintered body will not be obtained. Further, in order to obtain a composite carbide sintered body by sintering the composite carbide of the present invention, a certain amount of carbon (approximately 0.2 to 2.0 parts by weight per 100 parts by weight of the composite carbide) 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 remove some of the carbon. Basically, carbon can be easily removed by heating the composite carbide of the present invention to about 500 to 1000°C in the presence of oxygen. 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 obtained by burning fuel with excess air. Note that a composite carbide in which residual carbon is removed by combustion or the carbon content is adjusted by such means is also referred to as a composite carbide in 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 use the method described above to Once the elemental carbon is substantially completely removed from the composite carbide by sintering,
After newly adding elemental carbon to this, sintering is performed. The reason for this is that 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 the powder is viewed microscopically, the portions that are apparently in contact with the hot gas It is presumed that this is because only the elemental carbon of the sintered body is burned and removed 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 a composite carbide powder obtained by sintering and removing elemental carbon as described above. A method is preferably adopted in which elemental carbon is generated in a composite carbide by heating this in a non-oxidizing atmosphere. 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, and a benzene solution of coal tar pitch. 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 aqueous hydrofluoric acid solution to reduce the oxygen content to at least 0.5.
It is desirable that the amount be less than 1 part by weight from the viewpoint of strength and physical properties of the carbide sintered body or carbide molded body obtained by sintering and processing this. This washing 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 the elemental carbon is burned and removed from the composite carbide. (Effects 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. It is characterized by the fact that it undergoes thermal decomposition, oxidation, hydrolysis, etc., and from the stage where each molecule is generated, particles are grown while being mixed at the molecular level. Therefore, the resulting mixture of fine particles of silicon oxide, elemental carbon, and boron oxide is essentially uniform and much finer than that obtained by conventional mechanical mixing methods. Therefore, it has extremely superior quality in this respect. In addition, there are no problems with dust or noise when carrying out this method, and unlike the batch method, the mixture can be obtained continuously, so it is not a work that has been a problem with the conventional method of mechanically crushing ingots using the batch method. There are no problems such as the complexity of the process and the contamination of impurities due to wear of the crusher itself. The method for producing a composite carbide sintered body of the present invention uses a carbon-containing mixture having excellent physical properties as described above as a starting material and ignites it to produce a composite carbide sintered body having an extremely wide specific surface area and consisting of extremely small particles. Since the composite carbide is sintered, the sintering speed is fast and sintering is easy, and a dense sintered body can be obtained. In addition, at this time, if the ratio of carbon to silicon and boron in the carbon-containing mixture is made excessive, the resulting composite carbide powder will be even finer and a powder with a wider specific surface area will be easily obtained. This results in even better sinterability. Furthermore, since the composite carbide is mainly composed of silicon carbide and boron carbide, there is no need to separately synthesize and add and mix a boron-based material, especially silicon carbide, in the sintering step, and the elemental boron, which is easily oxidized, can be removed. There's no need to use it. [Preferred Mode for Carrying Out the Invention] The present invention will be specifically described below with reference to Examples. Note that % indicates weight %. Example 1 Using the furnace shown in Fig. 1 (diameter 300 mm, length 3 m), air was supplied from duct 2 and hydrogen was supplied as hot air fuel from combustion burner 3 at 80 Nm ³ /h and 12 Nm ^{3 /} h, respectively.
SiCl ₄ as a decomposable silicon compound, a C ₉ fraction mixture as a decomposable carbon compound, and BCl ₃ as a decomposable boron compound were mixed in advance at a weight ratio of 1:1.9:0.0077. The material was charged into the furnace through nozzle 4 at a flow rate of 14 kg/h. The inside of the furnace was maintained at a temperature of 1000 to 1100°C at position A in Figure 1. The aerosol generated in the furnace was extracted from the duct 6, and after cooling was collected by 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 and carbon by weight.
65.6%, boron 0.07% (the rest is 18.4% bonded oxygen, 0.1% hydrogen attached to carbon, 0.1% other)
(below), the formula weight ratio C/(Si+B) was 9.6.
As a result of ESCA spectrum analysis, the bonding forms between silicon or boron and other elements include Si-O bonds and B-
Only O bonds were observed. The bulk specific gravity of the carbon-containing mixture according to the present invention taken out from the bag filter was 0.096 g/cc.
Put 500g of this into a cylindrical container and uniaxially compress it to 0.35
After adjusting the bulk specific gravity to g/cc, it was inserted into a graphite crucible, heated at 1700°C for 2 hours in an argon atmosphere using a high-frequency heating furnace, cooled once, and heated to 750°C in air to form the remaining single substance. Carbon was removed by combustion to obtain 115 g of composite carbide according to the present invention. As a result of ESCA spectrum analysis of this material, Si−
The presence of C bonds and B--C bonds was confirmed, and it was found that the material 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 an needle crystal structure was confirmed, and the average particle size was 0.27μ according to electron microscope image analysis. It was observed that the particle shape was uniformly spherical. As a result of chemical analysis, the oxygen content of this substance is 1.6
It was %. Add this to 5 times the weight of HF aqueous solution (concentration
10%) for 5 hours, put the obtained 110 g of the dried product in container 1, add 300 c.c. of acetone solution in which 2.7 g of resorcinol formaldehyde condensate was dissolved, and mix for 10 hours at room temperature. Then, the container was immersed in a constant temperature water bath adjusted to 70°C, and the acetone was evaporated while kneading, and then heated at 600°C for 1 hour in a _N2 gas atmosphere to form the composite carbide of the present invention. A mixture of carbons was obtained. Its composition is 69.1% silicon, carbon
30.5%, boron 0.30%, oxygen 0.06% (other 0.1%)
(below), and elemental carbon was 0.89%. Next, put 100g of this mixture into a cylindrical container,
After uniaxial compression with a load of 0.5T/ ^cm2 , rubber press with a hydrostatic pressure of 2T/ ^cm2 , and further sintering at 2100℃ for 15 minutes in a nitrogen atmosphere of ^10-1 to 1mmHg to form a composite carbide. A sintered body was obtained. The density of this sintered body was measured to be 3.11 g/cc, which was a good value corresponding to 97% of the theoretical density of silicon carbide, 3.21 g/cc. Next, this sintered body was cut with a diamond cutter to make 30 test pieces, and JIS R-1601 ('81)
The bending strength was measured according to the following. There were two atmospheres for bending strength measurement: room temperature and nitrogen atmosphere at 1400℃.
Measurements were made using 3-point bending on 15 test pieces each. As a result, the average bending strength at room temperature was 46Kg/
mm ² and the standard deviation was 2.6 Kg/mm ² , and the average bending strength at 1400°C was 45 Kg/mm ² with a standard deviation of 2.5 Kg/mm ² . Comparative Example 1 A carbon-containing mixture containing silicon oxide and carbon was produced in exactly the same manner as in Example 1 except for using BCl ₃ in Example 1. This carbon-containing mixture was compressed in the same manner as in Example 1, heated using a high-frequency heating furnace, and the elemental carbon was further burned off to obtain 115 g of silicon carbide powder.
As a result of X-ray diffraction spectrum analysis of this powder, the crystal shape was cubic, and the average particle size was 0.25 μm as determined by electron microscope image analysis. This silicon carbide powder was prepared in the same manner as in Example 1.
Elemental boron powder with an average particle size of 4.0 μ was added to 110 g obtained by washing with an HF aqueous solution and drying so that the ratio of boron to silicon was 0.33 as in Example 1.
g, and additional carbon was added in exactly the same manner as in Example 1 to obtain 112 g of a mixture of silicon carbide, elemental boron, and carbon. Its composition is 69.1% silicon, 30.4% carbon, 0.30% boron, and 0.17% oxygen.
% (others 0.1% or less), and elemental carbon is 0.90
It was %. 100g of this mixture was prepared in exactly the same manner as in Example 1,
After molding, it was heated to obtain a sintered body. The density of this sintered body was measured and was 3.00 g/cc.
This corresponds to 93% of the theoretical density of silicon carbide. Next, using this sintered body, 30 test pieces were cut out in exactly the same manner as in Example 1, and a three-point bending strength test was performed. As a result, the average bending strength at room temperature was 40 kg/
mm ² and the standard deviation was 3.5 Kg/mm ² , and the average bending strength at 1400°C was 38 Kg/mm ² with a standard deviation of 3.8 Kg/mm ² . Examples 2 to 5 In addition to hydrogen, methane and propane were used as the fuel for hot air, and the silicon compounds, carbon compounds, and boron compounds shown in Table 1 were used.
1

A carbon-containing mixture of the present invention was obtained in the same manner as in [Table]. The composition of each of the obtained carbon-containing mixtures of the present invention is shown in Table 2.
Shown below.

[Table] Results of BSCA spectrum analysis of carbon-containing mixture,
Only Si-O bonds and B-O 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 materials were mixed in advance and charged. For example, in Example 2, SiCl ₄
This means that a mixture of A and A heavy oil was charged into the furnace through nozzle 4, and at the same time, BF ₃ was charged into the furnace through nozzle 5. In Example 5, a solution prepared by mixing boric acid and ethanol at a weight ratio of 0.08:1 was charged into the furnace through the nozzle 4. The charging method is a two-fluid spray method using air, and the amount of air is 0.25N.
m ³ /h. Each of the obtained carbon-containing mixtures was compressed, ignited, once cooled, and the remaining carbon was burned off in the same manner as in Example 1 under the conditions shown in Table 3 to obtain the composite carbide of the present invention.

【table】

[Table] As a result of ESCA spectrum analysis of the obtained composite carbide, the presence of Si-C and B-C bonds was confirmed.
Furthermore, the average particle diameters determined by image analysis using an electron microscope were as shown in Table 3. As a result of powder X-ray diffraction spectrum analysis, the presence of cubic silicon carbide and needle-shaped boron carbide was confirmed in all of the composite carbide powders of the present invention. In Example 3, the presence of hexagonal silicon carbide was also confirmed, and the proportion thereof was estimated to be about 10 parts by weight per 100 parts by weight of cubic silicon carbide. To 110 g of each of these composite carbide powders obtained by washing and filtering with an HF aqueous solution in the same manner as in Example 1,
Add 300 c.c. of acetone solution in which the amounts of resorcinol formaldehyde condensates shown in Table 4 were dissolved, and add additional carbon in exactly the same manner as in Example 1 to obtain a mixture of composite carbide and carbon. Ta.
The composition of each was as shown in Table 4. A mixture of these composite carbides and carbon was molded in exactly the same manner as in Example 1, and then sintered together at 2100° C. for 15 minutes to obtain each composite carbide sintered body. Respectively

The density of the sintered body in [Table] is based on the theoretical density of silicon carbide,
The values were as shown in Table 4. Next, 30 test pieces were cut out from these sintered bodies in exactly the same manner as in Example 1, and a three-point bending strength test was conducted. The results are shown in Table 4. From Examples 1 to 5 and Comparative Example 1, 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 does not contain boron oxide. It can be seen that compared to the sintered body obtained using the carbon-containing mixture as a starting material, the sintered body has a higher density, greater strength, and less variation.

[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 are shown.

Claims (1)

[Claims] 1. A decomposable silicon compound, a decomposable carbon compound, and a decomposable boron compound are charged into hot gas containing water vapor and decomposed to produce silicon oxide, elemental carbon, and boron oxide, respectively. A carbon-containing mixture obtained by generating a mixed aerosol dispersoid containing an aerosol of Composite carbide obtained by igniting the above carbon-containing mixture 100
0.2 to 0.2 to part by weight of carbonaceous material in terms of simple carbon equivalent
A new method for producing a composite carbide sintered body characterized by sintering it in one piece under conditions in which 2.0 parts by weight coexist. 2. The method for producing a new composite carbide sintered body according to claim 1, wherein the weight ratio of boron to 100 silicon is 0.15 to 4.5.