JPH0629123B2 - Method for producing silicon ceramics - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for producing silicon ceramics, and more specifically, to a silicon ceramic material, that is, silicon nitride, silicon carbide or silicon nitride and silicon carbide using high molecular weight polysilazane as a raw material. The present invention relates to a method for producing a composite with.

[Technical Background of the Invention and Problems Thereof] Only four studies described below have been reported as studies on the production of silicon ceramics using silazane or polysilazane having a silicon-nitrogen-silicon bond as a starting material.

West German Patent No. 2,236,078 (1974) discloses a method in which dimethyldichlorosilane and ammonia are brought into contact with each other in a gas phase or a liquid phase to obtain a polysilazane oligomer, and then the polysilazane oligomer is heat-treated. Also, the Journal of Application Polymer Science
Replication Polymer Science), 27 , 3751 (1982), methyltrichlorosilane and methylamine are contacted to generate methyltrimethylaminosilane, which is heat treated at 520 ° C to obtain polycarbosilazane, and then at about 1,200 ° C. A method of heat treatment has been reported. However, it is difficult to obtain a high molecular weight silazane by any of these methods, and it is difficult to obtain a silicon ceramics in a high yield due to evaporation even in the heat treatment of polysilazane.

Furthermore, the Communication of American Ceramics Society (Commun. Of Amer. Ceram. Soc
(Ciety, C-13 (1983)) discloses a method of contacting dichlorosilane with ammonia to obtain polysilazane, and then heat treating it at 1,150 ° C. However, this method has a problem that the obtained polysilazane is poor in stability and is easily decomposed at room temperature in the presence of oxygen, and a part thereof is converted into siloxane.

Furthermore, as shown in JP-A-58-63725,
A method is disclosed in which chlorine-containing disilane is contacted with ammonia to obtain polysilazane, and heat treatment is performed to obtain silicon ceramics. According to this method, it is reported that polysilazane can be polymerized, but since chlorine-containing disilane as a raw material is used in a state of a mixture having different chlorine numbers, polysilazane having a certain property is obtained. It's difficult. Further, it has been reported that only β-silicon carbide can be obtained by heat-treating this polysilazane at 1600 ° C. Therefore, it is impossible to produce silicon nitride according to the purpose by this method.

[Object of the Invention] The present invention obtains a high molecular weight polysilazane using a halosilane having a silicon-hydrogen bond, which is a by-product during the synthesis of organohalosilanes and is relatively easily separated by distillation, as a starting material. Furthermore, it is an object of the present invention to manufacture silicon ceramics easily and in high yield using this polysilazane as a raw material.

[Summary of the Invention] As a result of repeated studies to achieve the above object, the present inventors have found that when a dihalosilane represented by the general formula RHSiX ₂ is used, the dihalosilane represented by the general formula R ₂ SiX ₂ is compared with the dihalosilane represented by the general formula R ₂ SiX _2. A high molecular weight silazane oligomer is obtained (in the above two formulas, R represents a monovalent hydrocarbon group having 1 to 6 carbon atoms, and X represents a halogen atom), and the obtained silazane oligomer is at room temperature. Although it is relatively stable, it was found that the polymer is easily polymerized by heating. Furthermore, they found that silicon ceramics can be obtained in good yield by heat-treating this polysilazane at a high temperature, and completed the present invention.

That is, in the present invention, in the method for producing silicon ceramics using polysilazane, as polysilazane, ammonia is brought into contact with a dihalosilane represented by the general formula: RHSiX ₂ (wherein R and X have the same meanings as described above). Then, by heating at 50 to 500 ° C. under an inert and anhydrous atmosphere, the molecular weight obtained by polymerizing is 10,000.
Using the above polysilazane,
It is characterized in that after the preliminary heat treatment in the temperature range of up to 1,000 ° C, the heat treatment is carried out at a temperature of 1200 ° C or higher in an inert atmosphere or vacuum.

That is, the first feature of the present invention is that, as polysilazane used as a raw material of silicon ceramics, ammonia and dihalosilane represented by the general formula: RHSiX ₂ (wherein R and X have the same meanings as described above). It is to use polysilazane obtained by a novel reaction of contacting.

The dihalosilane used in the above reaction has the general formula RHSiX
₂ , the monovalent hydrocarbon group having 1 to 6 carbon atoms represented by R is an alkyl group such as methyl group, ethyl group, propyl group, butyl group or hexyl group; vinyl group And alkenyl groups such as allyl groups; phenyl groups and the like. A methyl group or a phenyl group is preferable from the viewpoint of ease of synthesis. X is a halogen atom such as fluorine, chlorine, bromine or iodine, but is generally a chlorine atom.

In producing the polysilazane, dihalosilanes having only the same R group may be used, or dihalosilanes having different R groups may be mixed and used at a predetermined ratio. The dihalosilane is generally obtained industrially by a direct method by-product, decomposition of chlorine-containing disilane with hydrochloric acid, Grignard reaction and the like.

The ammonia used in the present invention is preferably essentially anhydrous so as to prevent hydrolysis of the dihalosilane and hydrolysis of the resulting silazane oligomer. Essentially anhydrous here does not have to be an absolute anhydrous state,
This means that some water is acceptable.

The reaction proceeds at the same time when ammonia and dihalosilane come into contact with each other to form a polysilazane intermediate via an aminosilane compound. There is no limitation on the order of adding the raw materials, but since ammonia is in a gaseous state, a method of introducing ammonia to dihalosilane is generally used. In this case, 1 mol of dihalosilane is usually supplied with ammonia gas at a pressure of 1 atm at a temperature of about 70 to 100. As the reaction proceeds, the amount of ammonium chloride produced increases,
The viscosity of the reaction mixture is significantly increased. Therefore, it is desirable to add dihalosilane to a solvent having a low boiling point so that the reaction mixture is uniformly stirred. Examples of such a low boiling point solvent include pentane, heptane, hexane, benzene, toluene and the like. It is preferable that these solvents are essentially anhydrous for the reasons described above, and they are generally used after drying. When such a solvent is used, usually 100 to 1,000 parts by weight of the solvent is added to 100 parts by weight of dihalosilane.

Since the reaction proceeds simultaneously with the contact between ammonia and dihalosilane, the reaction can be carried out at room temperature. The reaction system may be heated to accelerate the reaction. Generally, when the reaction is carried out under normal pressure, it is heated to a temperature at which the low boiling point solvent refluxes. Furthermore, for the purpose of promoting the reaction, it may be carried out under a sealed condition. The reaction time is usually 0.
5 to 5 hours.

Although polysilazane is produced by the above reaction, the use of polysilazane having a molecular weight of 10,000 or more is a major feature of the present invention in order to obtain a desired ceramic in a high yield in the final heat treatment step. In order to increase the molecular weight of polysilazane as described above, it is necessary to heat-treat the polysilazane obtained by the above reaction in an inert and essentially anhydrous atmosphere. That is, heat treatment is performed by forming an atmosphere with, for example, commercially available dry nitrogen or dry argon. This heat treatment may be carried out by subjecting the reaction mixture containing polysilazane to the treatment as it is, or may be carried out by isolating polysilazane from the reaction mixture by a conventional method and subjecting it to the treatment. Isolation of polysilazane from the reaction mixture is carried out, for example, by filtering the by-produced ammonium salt and subjecting the filtrate to heat treatment or reduced pressure treatment to remove the low boiling point solvent and the volatile product. In the above reaction for polymerizing polysilazane, the degree of polymerization of polysilazane can be set by the heating temperature and time, and polysilazane having a degree of polymerization of hundreds of tens to tens of thousands or more can be arbitrarily obtained. The reaction is usually carried out in the temperature range of 50 to 500 ° C., preferably 150 to 350 ° C., but if it is lower than 50 ° C., the polymerization reaction does not easily occur, and if it exceeds 500 ° C., it becomes difficult to control the degree of polymerization. The reaction time is usually 0.2 to 10 hours.

The next feature of the present invention is to find a new application in which the polysilazane obtained by the above reaction can be used as a raw material for producing silicon ceramics. That is, in the present invention, finally, the polysilazane obtained by the above reaction for further polymerizing the polysilazane obtained by the catalytic reaction of ammonia and dihalosilane is used as it is, or after purification, at 1,200 ° C. or higher. It is heat-treated at a temperature. This heat treatment is performed under an inert atmosphere such as nitrogen gas or argon gas or in vacuum in order to prevent the oxidation reaction of polysilazane. The heating temperature is 1,20
The temperature range is 0 ° C or higher, preferably 1,300 to 1,800 ° C. If the temperature is lower than 1,200 ° C., it is not possible to obtain crystalline silicon ceramics, and it is not preferable to raise the temperature too high from the viewpoint of economy and prevention of sublimation of the generated ceramics. The heating time is usually 0.1 to 30 hours.
In addition, in order to prevent damage to the heating furnace due to the gas by-produced during the heat treatment of polysilazane, before the treatment at 1,200 ° C or higher, the polysilazane is preliminarily heat-treated in the temperature range of 500 to 1,000 ° C for 0.1 to 10 hours, By-products are removed.

In the above reaction, one kind or two or more kinds of polysilazanes can be optionally used. When polysilazane having a hydrocarbon group having a small number of carbon atoms as an organic group (for example, obtained by reacting dihalosilane in which R is a lower alkyl group with ammonia) is used as a raw material, silicon nitride is mainly obtained, while When polysilazane having a phenyl group as an organic group (obtained by reacting dihalosilane in which R is a phenyl group with ammonia) is used as a raw material, silicon carbide is mainly obtained. Further, by blending both polysilazanes in an appropriate ratio, it is possible to obtain a silicon ceramic composite in which silicon nitride and silicon carbide are mixed in a desired ratio.

[Effects of the Invention] According to the present invention, silicon ceramics can be easily obtained in high yield. Furthermore, by appropriately selecting an organic group that binds to a silicon atom of a starting material, dihalosilane, or a direct material, polysilazane, silicon ceramics composed of silicon nitride or silicon carbide, or silicon mixed with silicon nitride and silicon carbide. A ceramic composite is obtained. Further, by appropriately using two or more kinds of raw materials having different organic groups, the mixing ratio of silicon nitride and silicon carbide in the silicon ceramic composite can be freely adjusted. Therefore, the present invention is industrially very useful as a method for producing silicon ceramics.

[Examples of the Invention] Example 1 Production of Polysilazane Methyldichlorosilane was placed in a pressure resistant reaction vessel equipped with a stirrer.
100 parts by weight of CH ₃ HSiCl ₂ and n-hexane as low boiling point solvent
440 parts by weight were charged. After that, dry ammonia was blown into the pressure-resistant reaction vessel through a gas inlet. At the same time when the ammonia was blown in, the pressure rose and the reaction temperature rose.
Ammonia gas was gradually introduced so as to adjust the reaction temperature to 80 ° C. or lower, and after 30 minutes, heat generation due to the reaction and decrease in ammonia gas pressure were no longer observed. The supply amount of ammonia gas was 50 parts by weight. Then the introduction of ammonia gas was stopped, and after stirring for another 30 minutes,
The reaction product was taken out of the pressure resistant reactor. Thereafter, the ammonium salt was filtered off, and the obtained liquid was distilled under reduced pressure to remove low-boiling products and n-hexane to obtain 35.8 parts by weight of a relatively viscous polysilazane oligomer.

Next, 30 parts by weight of this polysilazane oligomer was placed again in the pressure-resistant reaction vessel, nitrogen gas substitution was performed, and then heat treatment was performed under various heating conditions. After completion of the heat treatment, when cooled to room temperature, decomposition gas was generated and residual pressure was observed. When the decomposed gas was released and the decomposed product was removed, a white to transparent polysilazane resin was obtained. The results are shown in Table 1. In addition, polysilazane NO.
No. 4 was a resinous solid, which was insoluble in a solvent such as acetone or n-hexane, and thus the molecular weight could not be measured. Since it is insoluble in a solvent such as -hexane, it has a larger molecular weight than polysilazane NO.3, which is a tar-like and solvent (acetone, n-hexane, etc.) soluble semi-solid.

Production of Silicon Ceramics Polysilazanes No. 1 to No. 4 in Table 1 were put into a silicon nitride crucible and heated at 750 ° C. for 1 hour while introducing nitrogen gas to obtain a black solid substance.

Then, this solid was heated at 1,600 ° C. for 1 hour to obtain a solid having a gray appearance. The obtained solid is harder than that produced from polysilazane having a small molecular weight. This solid was analyzed by X-ray diffraction, and the production ratio of various components in silicon ceramics was calculated by the gravimetric method from the calibration curve of a known sample. The results obtained are shown in Table 2. In Table 2 and the following, the yield is obtained by contacting ammonia with a dihalosilane represented by the general formula: RHSiX ₂ (wherein R and X have the same meanings as described above), and the subsequent reaction (ie, 50 in an inert, anhydrous atmosphere
Molecular weight of 10,000 by heating at ~ 500 ° C
It is the ratio of the weight of the obtained silicon ceramics to the weight of the polysilazane used in the above-mentioned polymerization reaction) (expressed in%).

Example 2 A gray silicon ceramic solid was obtained in the same manner as in Example 1 except that the heating temperature of the black solid was 1,700 ° C. The production ratios and yields of various components are shown in Table 3.

Example 3 Preparation of polysilazane Phenyldichlorosilane C ₆ H ₅ HSiCl ₂ as dihalosilane
Reaction was carried out with ammonia gas in the same manner as in Example 1 except that 100 parts by weight was used. Although the reaction temperature rose to a maximum of 81 ° C, the temperature dropped after 40 minutes and the pressure drop of ammonia gas also decreased. The supply amount of ammonia gas was 40 parts by weight. Then, 1 hour after the start of the reaction, the introduction of ammonia gas was stopped, and the stirring was continued for another 30 minutes. After completion of the reaction, ammonium salt was filtered off, and n-hexane was removed under reduced pressure to obtain 36 parts by weight of viscous polysilazane oligomer.

Next, 36 parts by weight of this polysilazane oligomer was added to Example 1
When heat treatment was carried out at a temperature of 300 ° C. for 2 hours in the same manner as above, 34 parts by weight of solid polysilazane resin was obtained in addition to a small amount of liquid. Since the solid polysilazane resin is insoluble in solvents such as acetone and n-hexane, the molecular weight could not be measured.

However, 36 parts of the viscous polysilazane oligomer obtained by the silazaneization reaction in this Example was treated with 1 part at 300 ° C.
After heat treatment for a period of time, 34 parts of a tar-like, acetone-soluble polysilazane resin was obtained together with a small amount of a liquid material. When the molecular weight of this polysilazane resin was measured, it was 180,000. Therefore, since the solid polysilazane resin of Example 3 is a resinous solid and insoluble in acetone, comparison with the polysilazane resin which is a tar-like, semi-solid soluble in acetone, , Having a molecular weight above 180,000.

Production of Silicon Ceramics The polysilazane obtained by the above reaction was heated in the same manner as in Example 1 to obtain silicon ceramics. The obtained ceramics consisted of β-SiC with very small amount of β-Si ₃ N ₄ , and the yield was 23%.

Example 4 The polysilazane resin of No. 4 in Table 1 and the polysilazane resin obtained in Example 3 were pulverized into powders, mixed at various ratios, and then heated in the same manner as in Example 1. By doing so, the silicon ceramics shown in Table 4 were obtained.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Niwata 133 Nishishinmachi, Ota-shi, Gunma Toshiba Silicon Corporation (72) Inventor Shunichiro Tanaka, 8 Shinsita-cho, Isogo-ku, Yokohama, Kanagawa Yokohama Metal Factory (56) References JP-A-49-69717 (JP, A) JP-A-60-226890 (JP, A)

Claims (2)

[Claims] 1. A method for producing silicon ceramics using polysilazane, wherein the polysilazane is ammonia and the general formula: RHSiX ₂ (wherein R represents a monovalent hydrocarbon group having 1 to 6 carbon atoms,
X represents a halogen atom) and then heated at 50 to 500 ° C. under an inert and anhydrous atmosphere to obtain a polymer having a molecular weight of 10,
000 or more polysilazane is used, and the polysilazane is 5
A method for producing a silicon ceramics, which comprises performing a preliminary heat treatment in a temperature range of 00 to 1,000 ° C. and then performing a heat treatment at a temperature of 1200 ° C. or higher in an inert atmosphere or a vacuum. 2. The heat treatment temperature of polysilazane is 1,300.
The method for producing silicon ceramics according to claim 1, wherein the temperature is 1800C.