JP2001072481A - Production of anti-oxidant silicon carbide-silicon composite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high efficiency production process for an antioxidant SiC-Si composite material in low costs that develops excellent durability in the active oxidation area of a low oxygen concentration. SOLUTION: A nitridation promoter is added to the surface of a SiC formed body and allowed to coat the surface of the SiC formed body, and the SiC formed body is heat-treated, as it is allowed to contact with metallic silicon at a temperature higher than the melting point of metallic silicon in an nitrogen atmosphere to sinter SiC and the pores are impregnated and filled with fused Si, then cooled down. During these steps, fused Si is held at 1,000-1,400 deg.C for a prescribed time, to solidify the impregnated and filled Si melt and simultaneously nitride the Si on the surface layer. In a preferred embodiment, a Ca compound or Fe compound is used as a nitridation promoter, and the thickness of the Si3N4 layer formed on the surface layer is adjusted to >=1 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used as a member for a high-temperature heating furnace, for example, a baking furnace for heat-treating electronic parts and ceramic products, and various other members for high temperatures. The present invention relates to a method for efficiently and inexpensively producing an oxidation-resistant SiC-Si composite material exhibiting improved durability.

[0002]

2. Description of the Related Art A SiC sintered body has excellent material properties such as heat resistance, high-temperature strength, thermal shock resistance, abrasion resistance and corrosion resistance, and is useful as various structural members for high temperatures. Normally, a SiC sintered body is manufactured by a method of molding and firing using SiC powder as a raw material. However, since SiC has a strong covalent bond, sinterability is low, and pores are easily formed in the sintered body. It is difficult to obtain a dense sintered body. Then, S
A high-density SiC-Si composite material is filled with molten Si in the pores of the iC sintered body by impregnating with molten Si, and various structural members for high temperature, for example, a jig for a firing furnace, a sheath, and a shelf board It is used as a hanging rod, crucible, heat equalizing tube, etc.

[0003] In a SiC-Si composite material, Si in the surface layer is oxidized and converted into SiO ₂ in a high-temperature oxidizing atmosphere, and functions as an oxidation protective film for preventing diffusion and intrusion of oxygen. Have. However, in an active oxidation region having a low oxygen concentration, for example, an oxygen concentration of several percent or less, SiC and Si are oxidized to generate CO gas and SiO gas, and the generated SiO gas is used for heating an object to be heated or a furnace in a heating furnace. Reacts with parts, etc. to contaminate the product,
There are drawbacks such as lowering the yield and reducing the useful life of the member.

That is, the free Si exposed on the surface of the SiC—Si composite material is in a very active state, so that it reacts with a trace amount of oxygen to easily generate SiO gas. Therefore, for example, in a case where the firing furnace is closed, the atmosphere in the firing furnace easily becomes a state in which the oxygen concentration is low, and the SiO gas is easily generated.

In order to solve these difficulties, the applicant of the present invention has proposed that SiC is 70 to 90% by weight and Si is 30 to 90% by weight.
Oxidation resistance SiC-Si composite material, characterized in that the Si existing exposed to SiC-Si surface of the composite material composed of 10 wt% was converted into Si ₃ N _4, and, SiC as an aggregate A method for producing an oxidation-resistant SiC-Si composite material in which a SiC-Si composite material in which a body is melt-impregnated with Si is heat-treated at a temperature of 1400 to 2100 ° C in a nitrogen atmosphere has been proposed (Japanese Patent Application No. 10-96525). . According to this technology, SiC-
Owing to Si ₃ N ₄ formed on the surface of the Si composite material, generation of SiO gas can be effectively suppressed even in an oxidized region having a low oxygen concentration, and oxidation resistance can be improved.

However, when the SiC-Si composite material is heated to a temperature of 1410 ° C. or more when the SiC-Si composite material is heat-treated in a nitrogen atmosphere, the impregnated Si melts and liquefies, and a part of the Si flows out. In addition, when cooling, the volume expansion occurs during the solidification of the molten Si, so that Si is blown out from the composite material surface to generate voids, resulting in a decrease in material strength. In this way, the outflow and blowing of Si
When a void is formed in the surface layer of the C-Si composite material, the portion serves as a starting point to cause chipping (a phenomenon in which a part of the structure on the surface is repelled), thereby contaminating an object to be processed or reducing the material strength. Problems occur.

Accordingly, the present applicant has lowered the heat treatment temperature when forming Si ₃ N ₄ on the surface of the SiC—Si composite,
As a result of research on a method of efficiently nitriding at a temperature lower than the melting point of Si, at least,
SiC-S impregnated and filled with molten Si in pores of iC
i. A method for producing an oxidation-resistant SiC—Si composite material, comprising adding a Ca salt to a composite material and heat-treating the composite material under a nitrogen gas pressure of 1 to 10 kg / cm ² at a temperature of 1250 to 1400 ° C. No. 11-66304). According to this manufacturing method, the Si exposed on the surface is nitrided to form Si ₃ N
₄ is lower than the melting point of Si, the SiC-
It is possible to effectively prevent the generation of voids and a decrease in strength in the surface layer portion of the Si composite material.

[0008]

However, according to the method disclosed in Japanese Patent Application No. 11-66304, heat treatment for producing a SiC-Si composite material by melting and impregnating Si into a SiC molded body, Heat treatment for nitriding Si in the surface layer portion of the Si composite material to convert it into Si ₃ N ₄ and at least two heat treatment steps are required, thereby reducing production efficiency and increasing heat energy consumption, There are problems such as an increase in manufacturing costs.

The inventor of the present invention has made intensive studies to solve these problems, and as a result, after impregnating and filling a SiC molded body with a melted Si melt, a SiC-Si composite material was manufactured. It has been found that an oxidation-resistant SiC-Si composite material can be efficiently manufactured in substantially one heat treatment step by performing a nitridation reaction using a cooling process to convert Si in the surface layer into Si ₃ N _4. Was.

The present invention has been developed on the basis of the above findings, and its purpose is to be suitably used as various members for high temperatures, including members of a firing furnace for heat-treating electronic parts and ceramic products, and especially oxygen. Oxidation resistant SiC-Si that exhibits excellent durability in active oxidation regions with low concentrations
An object of the present invention is to provide a method for efficiently producing a composite material at a high efficiency and at a low cost.

[0011]

According to the present invention, there is provided a method for producing an oxidation-resistant SiC--Si composite material, comprising the steps of: adding a nitriding accelerator to a surface of a SiC compact; In the process of sintering the SiC while impregnating and filling the pores with the Si melt and then cooling it in a nitrogen gas atmosphere at a temperature equal to or higher than the melting point of the metal Si in a state of being in contact with the Si, The structure is characterized in that the Si melt impregnated and filled is kept at a temperature range of 1400 ° C. for a predetermined time to solidify and nitridate Si in the surface layer.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A SiC compact is kneaded by adding an organic binder such as methylcellulose or glycerin and water to SiC powder, molding the kneaded product into a desired shape by pressure molding or casting, and then heating. It is made by drying.

The SiC compact has a nitriding accelerator added and adhered to the surface thereof. The nitriding accelerator promotes the nitridation reaction of Si and functions to lower the reaction temperature for causing the reaction of 3Si + 2N ₂ → Si ₃ N _4.
e compound and the like are used. As the Ca compound, for example, water-soluble salts such as calcium chloride and calcium acetate are preferably used, but Ca salts such as calcium sulfate and calcium carbonate having low water solubility are also dispersed in water and used as an aqueous suspension. Can be. Similarly, chlorides, sulfates, and the like are used as the Fe compound, but iron oxide powder can also be used.

A method of adding a nitriding accelerator to the surface of the SiC molded body is to immerse or apply the SiC molded body in an aqueous solution or a suspension of a Ca compound or an Fe compound, and then apply heat and dry. Can be applied. Alternatively, the powders of these compounds can be directly applied to the surface of the SiC molded body by a method such as dusting or rubbing.
The SiC molded body preferably has a bulk specific gravity of about 2.2 to 2.8. If the bulk specific gravity is less than 2.2, the porosity increases, so that the amount of Si impregnated also increases, and SiC-Si
The creep resistance and wear resistance of the composite material decrease. On the other hand, if the bulk specific gravity exceeds 2.8, the number of pores remaining after the impregnation with the Si melt increases, which results in a decrease in the strength characteristics and oxidation resistance of the SiC-Si composite material.

[0015] The SiC molded body having the surface to which the nitriding accelerator has been added and deposited as described above is in a state where metal Si is in contact therewith.
For example, in a state in which the SiC molded body is covered with the metal Si powder, the SiC molded body is heated to a temperature equal to or higher than the melting point of metal Si (1410 ° C.) in a nitrogen gas atmosphere and heat-treated to sinter the SiC molded body. The pores are impregnated and filled with a Si melt. The Si melt impregnated and filled in this way
The C sintered body is cooled to a temperature below the melting point of metallic Si
By solidifying the melt, a SiC-Si composite material is produced.

According to the present invention, in the cooling step, by maintaining the cooling temperature at a predetermined temperature in a temperature range of 1000 to 1400 ° C. for a certain period of time, the Si present in the surface layer of the SiC—Si composite material is exposed. It is characterized in that it is converted into Si ₃ N ₄ by nitriding. In this case, S
By the action of the nitriding accelerator added to the surface of the iC compact, the nitriding reaction can smoothly proceed at a temperature lower than the melting point of metallic Si.

The temperature at which the nitriding reaction is carried out is from 1000 to 1400
The reason for setting the temperature to ° C. is that if the processing temperature exceeds 1400 ° C., the solidified impregnated and filled Si melt is not sufficiently solidified, and the upper surface of the converted Si ₃ N ₄ is again covered with the Si melt. If the temperature is lower than 1000 ° C., the nitriding reaction of Si does not proceed sufficiently.

In this case, the thickness of the Si ₃ N ₄ formed on the surface layer of the SiC—Si composite material is 1 μm or more in order to provide excellent oxidation resistance in the active oxidation region where the oxygen concentration is low. It is preferable to form it. Si
The thickness of ₃ N _4, at the time of cooling under a nitrogen gas atmosphere, temperature holding for the nitriding reaction, and by controlling the time for holding can be adjusted to a predetermined thickness .

As described above, the present invention impregnates and fills a SiC molded body with a melted metal Si melt heated and melted to form SiC-S
In manufacturing the i-composite, a nitriding reaction is performed by performing a heat treatment in a nitrogen gas atmosphere by utilizing the cooling process, and the Si exposed on the surface layer portion of the SiC-Si composite is converted to Si.
_Since it is converted into ₃ N ₄ , an oxidation-resistant SiC—Si composite material can be efficiently manufactured in substantially one heat treatment step.

Therefore, according to the present invention, it is preferably used as various members for high temperatures, including members for a baking furnace for heat-treating electronic parts and ceramic products, and has excellent durability especially in an active oxidation region having a low oxygen concentration. It is possible to efficiently produce an oxidation-resistant SiC-Si composite material exhibiting high efficiency at high efficiency and at low cost.

[0021]

EXAMPLES Examples of the present invention will be specifically described below in comparison with comparative examples.

Examples 1-3, Comparative Examples 1-2 Methyl cellulose and water were added to SiC powder having an average particle diameter of 50 μm and kneaded. The kneaded product was put into a mold, pressed and molded at a temperature of 120 ° C. After drying, a SiC molded body having a bulk specific gravity of 2.5 was produced. This SiC molded body was immersed in a 5 wt% aqueous solution of calcium chloride using calcium chloride as a nitriding accelerator, and then heated and dried at a temperature of 120 ° C., and calcium chloride was added to the entire surface of the SiC molded body. did.

Metallic Si is laid on the SiC compact and heated to a temperature of 2000 ° C. in a nitrogen gas atmosphere to melt the metal Si, thereby sintering the SiC compact and forming pores generated during sintering. Was impregnated and filled with a melt of metallic Si. Then, while cooling in a nitrogen gas atmosphere, impregnation,
The filled Si melt was solidified, and in this cooling process, a nitriding reaction was caused by changing the holding temperature and time, and the surface layer Si was nitrided and converted to Si ₃ N ₄ .
By this way, the single heat treatment, the surface layer portion Si ₃ N
₄ is formed, SiC is 80 wt%, Si is produced aspect 300 mm, the SiC-Si composite sheath shape of height 100mm consisting 20 wt% of the composition.

Example 4 A SiC-Si composite material was produced in the same manner as in Example 1, except that iron oxide powder was used instead of calcium chloride as a nitriding accelerator and the iron oxide powder was directly rubbed into a SiC compact. did.

COMPARATIVE EXAMPLE 3 In the cooling process, Examples 1 to 3 were repeated except that the temperature was kept at a specific temperature for a certain period of time and immediately cooled to room temperature.
A SiC-Si composite material was manufactured by the same method as in the above.

Reference Example Si was obtained by the same method as that of Japanese Patent Application No. 11-66304.
A C-Si composite was produced. That is, the average particle diameter is 50
Methyl cellulose and water were added to the μm SiC powder and kneaded, and the kneaded product was put into a mold, pressed and heated and dried at a temperature of 120 ° C. to produce a SiC molded body having a bulk specific gravity of 2.5. Metal Si is spread over the SiC compact, heated to a temperature of 2000 ° C. in argon gas to melt the metal Si, and the SiC compact is sintered and the pores generated during sintering are filled with metal Si. The melt was impregnated and filled. Then, the mixture is cooled to solidify the Si melt.
A pod-shaped SiC-Si composite material having a composition of wt% and Si of 20 wt% and a length and width of 300 mm and a height of 100 mm was prepared. The SiC-Si composite material was immersed in an aqueous calcium chloride solution (concentration: 5 wt%), taken out, heated and dried at 120 ° C., and then heat-treated at 1350 ° C. for 3 hours in a nitrogen gas atmosphere. Thus, the surface Si is changed to S
The i ₃ N SiC-Si composites was converted to ₄ were prepared.

The oxidation resistance of the SiC-Si composite thus manufactured was evaluated by the following method.
The results obtained are shown in Table 1 in comparison with the production conditions.
The SiC—Si composite material was placed in a heating furnace, and heated to 1300 ° C. for 1 hour in a nitrogen gas atmosphere containing 2 vol% of oxygen, and the surface state was visually observed. The operation of placing the SiC-Si composite material in a heating furnace, heating it to a temperature of 1250 ° C. in a nitrogen gas atmosphere containing 1 vol% of oxygen, holding it for 1 hour, and then allowing it to cool to room temperature is repeated. The surface condition was visually observed, and the number of repetitions until an abnormality occurred was measured.

[0028]

[Table 1] (Table note) * 1; Presence or absence of immersion treatment in calcium chloride aqueous solution (concentration 5 wt%) * 2; Presence or absence of treatment of iron oxide powder * 3; * 4: A: 500 times or more, B: about 50 times, C: about 2-3 times. * 5: Heat treatment conditions when a SiC-Si composite material is prepared, immersed in an aqueous solution of calcium chloride (concentration: 5 wt%), and then heated in a nitrogen gas atmosphere to cause a nitriding reaction.

From the results shown in Table 1, the SiC-Si composite materials of Examples 1 to 4 manufactured according to the manufacturing conditions specified in the present invention are the same as those of Comparative Examples 1 to 3 lacking any of the manufacturing conditions.
It is recognized that the oxidation resistance in the active oxidation region where the oxygen concentration is low is superior to that of the C-Si composite material. That is, in the comparative example 1 in which the holding temperature at which the nitridation reaction is performed during the cooling process is high, the solidification of the impregnated and filled Si melt is insufficient, so that the upper surface of the Si ₃ N ₄ converted by the nitridation reaction is again covered with the Si melt. And the oxidation resistance is lowered. On the other hand, in Comparative Example 2 where the holding temperature is low, the oxidation resistance is lowered because the nitridation reaction of Si does not proceed sufficiently, and in Comparative Example 3 where the nitridation reaction hardly occurs, the oxidation resistance is naturally low. .

Then, a heat treatment for producing a SiC—Si composite material by melting and impregnating Si into the SiC compact,
Heat treatment for nitriding and converting Si in the surface layer portion of the Si-Si composite material to Si ₃ N ₄ , and S of the reference example in which the heat treatment was performed twice.
It can be seen that the oxidation resistance is not inferior to that of the iC-Si composite material, and that the manufacturing process is simplified and the heat energy consumption is reduced. The formed Si ₃
In Example 3, where the thickness of N ₄ is small, it is recognized that the oxidation resistance tends to be slightly lowered.

[0031]

As described above, the oxidation-resistant SiC of the present invention is used.
According to the method for producing a Si composite material, a SiC molded body is impregnated and filled with a Si melt that has been heated and melted to produce a SiC—Si composite material, and then a nitriding reaction is performed by utilizing the cooling process to form a surface layer. By converting part of Si to Si ₃ N ₄ ,
Efficiently oxidation-resistant SiC—substantially in one heat treatment step
A Si composite can be manufactured. The heat treatment is S
Since the heat treatment is performed at a temperature equal to or lower than the melting point of i, the generation of voids in the surface layer portion of the SiC-Si composite material due to the outflow or blowing of Si during heat treatment is prevented, the oxidation resistance is excellent, and the durability is excellent particularly in the active oxidation region where the oxygen concentration is low. SiC-
It is possible to efficiently produce a Si composite material at high efficiency and at low cost. Therefore, oxidation-resistant SiC-Si, which is preferably used as various members for high temperatures, including members of a baking furnace for heat-treating electronic components and ceramic products, etc.
It is extremely useful as a method for producing a composite material.

Claims (3)

[Claims] 1. A method comprising: adding a nitriding accelerator to the surface of a SiC molded body; applying a heat treatment at a temperature equal to or higher than the melting point of the metal Si in a nitrogen gas atmosphere in a state of contact with the metal Si;
While sintering, impregnating and filling the pores with a Si melt, and then cooling,
A method for producing an oxidation-resistant SiC-Si composite material, comprising holding a Si melt impregnated and filled while maintaining a temperature range of ° C for a predetermined time and nitriding Si in a surface layer portion. 2. The method for producing an oxidation-resistant SiC—Si composite according to claim 1, wherein the nitriding accelerator is a Ca compound or an Fe compound. 3. Si ₃ formed by nitriding Si on the surface layer
3. The method for producing an oxidation-resistant SiC-Si composite according to claim 1, wherein the thickness of N ₄ is 1 μm or more.