JPH0216270B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a composite sintered body of silicon carbide and silicon nitride, and more particularly, to a method for manufacturing a composite sintered body in which silicon carbide and silicon nitride are uniformly mixed and dispersed, and has high high-temperature strength and excellent thermal shock resistance. Recently, the use of ceramics for mechanical parts that can withstand use at high temperatures has been proposed, and various types of so-called engineering ceramics have been proposed. Many of them are based on non-oxide ceramics, particularly silicon carbide and silicon nitride. These silicon carbide ceramics and silicon nitride ceramics have excellent high-temperature strength, but do not have sufficient thermal shock resistance;
The latter has a contradictory characteristic in that it has excellent thermal shock resistance but is not so good in high temperature strength. The present inventors have discovered the present invention as a result of research into a method for obtaining a sintered body that overcomes the drawbacks of each of the above, has excellent high-temperature strength, and has sufficient thermal shock resistance. , an inorganic silicon compound containing a halogen, ammonia, and a carbonaceous substance in an amount smaller than the theoretical amount required to convert silicon nitride produced by the reaction between the two into silicon carbide in a non-oxidizing atmosphere. To the mixed powder of silicon carbide and silicon nitride obtained by the reaction, one or more selected from the group of metals of the periodic table, groups and group metals, and their acid additions and carbides is added as a sintering aid. The gist of the present invention is a method for producing a composite sintered body of silicon carbide and silicon nitride, which is characterized by mixing and sintering or hot pressing in a non-oxidizing atmosphere. In order to fully achieve the effects of the present invention, it is necessary that silicon carbide and silicon nitride are sufficiently and uniformly dispersed, and for this purpose, it is preferable that both silicon carbide and silicon nitride are ultrafine particles. . That is, the surface area of the mixed powder of silicon carbide and silicon nitride is at least 5 m ² /g, more preferably 10 m 2 /g or more.
It is preferable to set it to m ² /g or more. In addition to the above-mentioned effects, the use of such ultrafine particles also has the advantage that a sintering reaction is more likely to occur during subsequent sintering. Furthermore, the blending ratio of silicon carbide and silicon nitride in the mixed powder can be selected as desired depending on the required performance regarding high temperature strength and thermal shock resistance, but according to the experience of the present inventors, It is preferable that at least 5% by weight of one of silicon carbide and silicon nitride be present in the mixed powder. That is, if the amount of silicon carbide in the mixed powder is less than 5% by weight, the purpose of the presence of silicon carbide, which is to provide sufficient high-temperature strength, cannot be achieved, and if the amount of silicon nitride is less than 5% by weight, the thermal shock resistance is improved. This is because the purpose of making silicon nitride exist cannot be fully achieved. Here, examples of the halogen-containing inorganic silicon compound used as a raw material include SiCl ₄ ,
SiHCl ₃ , SiH ₃ Cl ₂ , SiH ₃ Cl, SiBr ₄ , SiHBr ₃ ,
SiH ₂ Br ₂ , SiH ₃ Br, SiI ₄ , SiHI ₃ , SiH ₂ I ₂ ,
SiH ₃ I, SiCl ₂ Br ₂ , SiCl ₂ I _2, etc. Some of these are gaseous at room temperature, but others are liquid or solid. For example, it is appropriate to gasify the mixture by suitable means such as indirect heating and then use it for the reaction. The amount of ammonia used in the reaction is suitably 0.1 to 6 in molar ratio to the halogen-containing inorganic silicon compound used as a raw material. If the amount of ammonia used is less than the above range, the reaction rate of the halogen-containing inorganic silicon compound is low and is not industrially practical, whereas if it exceeds the above range, solid ammonium halide will precipitate. Both are unfavorable as they are accompanied by difficulties in reaction operation. Among these ranges, the molar ratio is 0.5 to 5.
It is particularly preferable to employ the following, since the reaction can be carried out effectively and industrially advantageously. Next, carbonaceous substances include, for example, carbon itself such as amorphous carbon and graphite, as well as halogen-containing saturated or halogen-containing unsaturated hydrocarbons, or halogen-containing aromatic hydrocarbons, all of which have hydrogen relative to halogen atoms. One type or a mixture of two or more types can be used as appropriate. Among these carbonaceous materials, it is preferable to use carbon black, dichloroethylene, methyl chloride, methylene chloride, dichloroethane, trichloroethane, and vinyl chloride because the conversion rate to silicon carbide increases. The amount of these carbonaceous substances used is smaller than the theoretical amount required to convert silicon nitride produced by the reaction between a halogen-containing inorganic silicon compound and ammonia into silicon carbide. The specific amount used varies depending on the mixing ratio of silicon nitride and silicon carbide to be obtained, but in order to achieve the purpose of the present invention, it is generally necessary to use a molar ratio of 0.05 to silicon in terms of carbon. It is appropriate to use about 0.95. These raw materials are then allowed to react in a non-oxidizing atmosphere. It is appropriate to adopt a reaction temperature of about 400 to 1700°C. If the reaction temperature is less than the above range, ammonia is not effectively utilized and the reaction rate of the halogen-containing silicon compound decreases, whereas if it exceeds the above range, grain growth of the final product becomes significant. So I don't like either of them. Further, it is appropriate to adopt a reaction time of 0.1 seconds to 5 hours. If the reaction time is less than the above range, the reaction will not substantially proceed, whereas if it exceeds the above range, the grain growth of the final product will become significant, which is not preferable. In the present invention, the raw materials used are usually mixed together at the same time, but if desired, a nitrogen compound of silicon is obtained in advance and the carbonaceous material is mixed with this, so that the reaction is carried out in two stages. It is also possible to Further, as the non-oxidizing atmosphere used in the present invention, it is appropriate to employ, for example, a gas flow of argon, helium, hydrogen, or the like. In an oxidizing atmosphere, silica, which is a sintering raw material and causes a decrease in high-temperature strength, will be mixed in, so care must be taken. Now, in order to obtain a sintered body using such a mixed powder, a suitable sintering aid is sufficiently uniformly dispersed in this mixed powder, and this is shaped and fired in a non-oxidizing atmosphere. Alternatively, a mixed powder in which a sintering aid is uniformly dispersed may be placed in a mold made of carbon or the like, and then hot pressed in a non-oxidizing atmosphere. Here, as the sintering aid, groups of the periodic table,
selected from group metals, elemental metals of groups, and oxides and oxides thereof. Among the above, one or more selected from magnesium oxide, boron, boron carbide, boron oxide, aluminum oxide, yttrium oxide, and carbon are preferred. When specifically using the sintering aid exemplified above, the type and amount may be selected depending on the blending ratio of silicon carbide and silicon nitride in the raw material powder, but the present invention According to the experience of researchers, when a large amount of silicon carbide is mixed in the raw material powder, boron,
It is preferable to use one selected from boron carbide, boron oxide, aluminum oxide, and carbon, and when the blending ratio of silicon nitride is large, it is preferable to use one selected from magnesium oxide, aluminum oxide, and yttrium oxide. In addition, when these sintering aids are added to the raw materials, they do not need to be the above-mentioned compounds; for example, salts containing metal elements of the above-mentioned compounds, such as halides, carbonates, nitrates, sulfates, and acetic acid. Of course, any salt, alcoholate, etc. that changes into the above-mentioned compound during sintering or hot pressing may be used. In addition, the sintering temperature and hot press temperature can be selected depending on the blending ratio of silicon carbide and silicon nitride in the raw materials, and the sintering temperature can be selected from 1700 to 2100℃, and the hot press temperature can be selected from 1600 to 2000℃. Good. Known non-oxidizing atmospheres such as nitrogen, argon, and hydrogen can be used. Examples 1 to 5 An externally heated flow-through reactor with a quartz reaction tube with an inner diameter of 36 mm and a length of 900 mm as the inner tube and an alumina tube with an inner diameter of 50 mm and a length of 1000 mm as the outer tube, and an externally heated flow-through reactor was installed at the bottom of the reaction tube. Silicon halide (carrier gas: N ₂ ), ammonia gas, and halogen-containing hydrocarbon (carrier gas: N ₂ ) are each introduced separately from the top of the reaction tube maintained at a predetermined temperature using a device consisting of a reaction product collector and a reaction product collector. A reaction was caused by blowing into the tube. The powdered product collected in the collector was transferred to a graphite crucible under a nitrogen atmosphere, and heat-treated in an electric furnace in an inert gas stream. The reaction conditions, heat treatment conditions, and analysis results of the obtained powder are as shown in Table 1. For Examples 1 to 3, this mixed powder was mixed with Al ₂ O ₃ as a sintering aid at an external ratio to the raw material.
Using 10% by weight, these were press-molded at room temperature to a pressure of 200 kg/cm ² and then sintered at 1975° C. for 5 hours in an Ar atmosphere. For Examples 4 and 5, 1% by weight of MgO was similarly used as a sintering aid, and after press molding, sintering was performed at 1750° C. for 5 hours in an N ₂ atmosphere. The physical properties of the sintered body are also listed in Table 1. In addition, the thermal shock resistance temperature in the table is a heating temperature that does not cause a decrease in strength when a heated sample is dropped into water.

【table】

[Table] Examples 6 to 10 Using the same reaction apparatus as in Example 1, silicon tetrachloride (carrier gas: N ₂ ) and ammonia gas were blown into the upper part of the reaction tube from separate introduction tubes to cause a reaction. However, the reaction temperature is 1000℃, the reaction time is 2.5 seconds,
The SiCl ₄ concentration was 9% by volume, and the NH ₃ /SiCl ₄ =1.3.
The powdered intermediate product collected in the collector and carbon black (particle size: about 25 mμ) were mixed in a nitrogen gas atmosphere, then transferred to a graphite crucible and heat-treated at 1550° C. for 2 hours in a hydrogen stream. Table 2 shows the processing conditions and the analysis results of the obtained powder. Using this mixed powder, in Examples 6 and 7, B and C were used as sintering aids at an external ratio of 1% by weight to the raw material, and after hot press molding,
Sintering was performed at 1975°C for 5 hours in an Ar atmosphere. or,
For Examples 8, 9, and 10, as a sintering aid
Similarly, 1% by weight of MgO was used, and after press molding at room temperature to 200 kg/cm ² , sintering was performed at 1750° C. in an N ₂ atmosphere for 5 hours. The physical properties of the sintered body are also listed in Table 2. Examples 11 to 15 The same reaction as in Example 1 was carried out, and the powdered intermediate product collected in the collector was dispersed in a methylene chloride solution of polyvinyl chloride under a nitrogen gas atmosphere, and then chlorinated. The solid material obtained by evaporating methylene was placed in a graphite crucible at 400°C under a hydrogen atmosphere.
After heat treatment for 1 hour, the temperature was raised to 1550°C and heat treatment was performed for 2 hours. Table 2 shows the processing conditions and the analysis results of the obtained powder. Using this mixed powder, sintered bodies were obtained according to Example 1 for Examples 11 and 12, and according to Example 4 for Examples 13, 14, and 15. The physical properties of the sintered body are also listed in Table 2.

[Table] Comparative Examples 1 to 2 Silicon carbide powder and silicon nitride powder with a purity of 99% were used as raw materials, and Table 3 was added to each of the above raw material powders.
Add the specified amount of the sintering aid shown in and mill it in a ball mill for 24 hours.
Uniform mixing was carried out while also serving as time pulverization. Next, the obtained mixed powder was sintered under the conditions listed in Table 3. The properties of the obtained sintered body are also listed in Table 3.

【table】

Claims (1)

[Scope of Claims] 1. An inorganic silicon compound containing a halogen, ammonia, and a carbonaceous material in an amount smaller than the theoretical amount required to convert silicon nitride produced by the reaction of the two into silicon carbide, As a sintering aid for a mixed powder of silicon carbide and silicon nitride obtained by reacting in a non-oxidizing atmosphere, 1 selected from metal carriers of groups, groups and groups of the periodic table, and acid additions and carbides thereof. A method for producing a composite sintered body of silicon carbide and silicon nitride, which comprises adding and mixing one or more species and sintering or hot-pressing the mixture in a non-oxidizing atmosphere. 2. The method for producing a composite sintered body of silicon carbide and silicon nitride according to claim 1, wherein the mixed powder contains at least 5% by weight of either silicon carbide or silicon nitride. 3. The method for producing a composite of silicon carbide and silicon nitride according to claim 2, wherein the mixed powder has a non-surface area of 5 m ² /g or more. 4. The composite of silicon carbide and silicon nitride according to claim 1, wherein the sintering aid is one or more selected from magnesium oxide, boron, boron carbide, boron oxide, aluminum oxide, yttrium oxide, and carbon. How the body is made.