JPH0362667B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for producing ceramics using an organic silazane polymer as a ceramic precursor. Problems to be Solved by Conventional Technologies and Inventions Ceramics are attracting attention as materials with excellent heat resistance, wear resistance, and high-temperature strength, but it is extremely difficult to process ceramics because they are hard and brittle. It is. Therefore, when manufacturing ceramic products, there are two methods: first forming a fine powder of ceramic material into a desired shape using a method such as pressurization, and then sintering it, or melting an organic polymer as a ceramic precursor or using a solvent. dissolve,
A precursor method is employed in which the material is processed into a desired shape and then fired to become inorganic. The most important feature of the above precursor method is that it is possible to obtain ceramic products in shapes that are impossible with the sintering method using fine powder, and it is therefore possible to produce products with special shapes such as fibers or sheets. be. In this case, SiC and Si ₃ N ₄ , which are generally called ceramics, are heat resistant and SiC, respectively.
Si ₃ N ₄ has attracted wide attention due to its excellent properties at high temperatures, such as excellent thermal shock resistance and fracture toughness. SiC−Si ₃ by physical method
Various proposals have been made regarding methods for producing N ₄ -based ceramics and methods for producing organosilicon precursors thereof, but all of these proposals have had problems. That is, US Pat. No. 3,853,567 discloses that chlorosilanes and amines are reacted, and then
A method is disclosed in which SiC-Si ₃ N ₄ ceramics are obtained by heating to 800°C to obtain carbosilazane, spinning it, making it infusible, and firing at a high temperature of 800 to 2000°C. However, this method requires 520-650℃ to obtain carbosilazane.
This method requires high temperatures, making it extremely difficult as an industrial production method, and has drawbacks such as the low ceramicization yield of about 55% when carbosilazane is mineralized. In addition, in the examples of this US patent specification, only methyltrichlorosilane and dimethyldichlorosilane are described as chlorosilanes, and methylamine is described as an amine. U.S. Pat. No. 4,097,294 shows that various silicon-containing polymers are converted into ceramic materials by pyrolysis. However, only one example of silazane polymers has been disclosed, and the yield of ceramic formation is as low as 12% at maximum. Additionally, although this US patent specifies that it is possible to make ceramics into fibers and thin films, this is merely a suggestion of that possibility, and it is not intended to be a mere suggestion of the possibility of making ceramics into fibers or thin films. There is no mention of moldability or processability. JP-A No. 57-117532 discloses that the reaction between chlorodisilanes and disilazane
-139124 describes the reaction between chlorosilanes and disilazane, JP-A-58-63725 describes the reaction between chlorosilane and ammonia, and JP-A-60-135431 describes the reaction between trichlorosilane and disilazane. It has been shown that silazane polymers can be obtained by reaction with each other.
Furthermore, US Pat. No. 4,535,007 discloses that a metal halide is added to chlorosilanes and disilazane, and JP-A-60-208331 discloses that a metal halide is added to chlorodisilanes and disilazane. disclose the production of silazane polymers, respectively. It is said that all of the above silazane polymers can be made into ceramics by thermal decomposition. However, the ceramicization yield for all silazane polymers is 50 to 60%, which is a low yield. In addition, the above-mentioned publications do not describe in detail the moldability and processability of polymers, which are most important in the precursor method, as in the specification of .
In addition, even if there are examples of fiberized fibers, most of them do not mention the strength of the ceramicized fibers. There is a slight description of strength in JP-A-60-208331, but even in this case, only extremely low tensile strength of 53 Kg/mm ² or 63 Kg/mm ² was obtained. In Japanese Patent Application Laid-Open No. 60-226890,

Discloses a method for obtaining an ammonolysis product by reacting an organosilicon compound represented by the formula with ammonia, and then dehydrogenating and condensing this product with an alkali metal or alkaline earth metal hydride to obtain a silazane polymer. has been done. It is said that the properties of the polymer obtained by this method can be varied from oil-like to solid with no melting point depending on the degree of dehydrogenation condensation. However, when molding and processing a polymer from a molten state, for example when producing continuous fibers by melt spinning, it is necessary that the polymer has a constant degree of polymerization and is thermally stable.
In the above method, unless the polymerization is stopped midway, the polymer will become a solid with no melting point, and in order to obtain a meltable polymer, delicate control of reaction time, reaction temperature, amount of catalyst, amount of solvent, etc. is required. However, the adjustment is very difficult and there are problems with reproducibility. Furthermore, the polymer obtained by this method has disadvantages such as not being thermally stable and accompanied by the formation of gel-like substances.For these two reasons, the above method is not suitable as an industrial method for producing silazane polymers. do not have. In Japanese Patent Application Laid-Open No. 60-228489,

[Example 1]

Ammonolysis step [Methyldichlorosilane: Methyltricchlorosilane: Dimethyldichlorosilane = 75:15:10
(mol%)] After charging 850 ml of hexane into a dry four-necked flask (1) equipped with a stirrer, thermometer, NH ₃ inlet tube, and deep-cooled condenser, 43.1 g of methyldichlorosilane, 11.2 g of methyltrichlorosilane, 6.5 g of dimethyldichlorosilane was added and the mixture was cooled to -20°C. Excess gaseous ammonia was added to this solution at a rate of 12/Hr for 4 hours (total addition of NH ₃ 2.1
mole). The reaction mixture was warmed to room temperature while the condenser was replaced with an air-cooled condenser to allow unreacted _NH3 to escape. Next, by-produced ammonium chloride was removed from the reaction mixture in a dry box by filtration. The cake was further washed with 200 ml of hexane, and the hexane was stripped from the liquid under reduced pressure (60°C/1 mmHg). Residue (ammonolysis product)
Obtained 26 g of clear fluid liquid. Ammonolysis process [Methyldichlorosilane: methyltrichlorosilane: dimethyldichlorosilane = 65:25:10 (mol%)] 850 ml of hexane was charged into a four-necked flask (1) equipped with the same equipment as above, and 29.9 ml of methyl dichlorosilane was added to the 4-necked flask. g, methyltrichlorosilane 14.9
g, add 5.2 g of dimethyldichlorosilane, -20℃
It was cooled to Gaseous ammonia was added to this solution at a rate of 12/Hr for 4 hours. Thereafter, the same treatment as above was carried out to obtain 20 g of a transparent fluid liquid (ammonolysis product). Ammonolysis process [Methyldichlorosilane: Methyltrichlorosilane: Dimethyldichlorosilane = 65:20:15 (mol%)] Pour 1500ml of dehydrated hexane into No. 2 four-necked flask equipped with the same equipment as above, and add 59.8g of methyldichlorosilane. , 23.9 g of methyltrichlorosilane, and 15.5 g of dimethyldichlorosilane were added, and reacted with gaseous ammonia in the same manner. It was then treated in the same manner as above to obtain 42 g of a clear fluid liquid (ammonolysis product). Polymerization Step A 300 ml three-necked flask was equipped with a stirrer, a thermometer, and a dropping funnel, and 0.2 g (5 mmol) of potassium hydride and 125 ml of THF dehydrated with NaH were poured into the flask in a dry box. This flask was taken out of the dry box and connected to a nitrogen pipe. 10 g of the product obtained in the ammonolysis step was dissolved in 75 ml of THF from the dropping funnel at room temperature while stirring the mixture to disperse KH.
was added slowly over 15 minutes. Gas evolution was observed during this addition and stopped after 1 hour. Addition of 3 g of methyl iodide resulted in a white precipitate of KI. After stirring for another 30 minutes, most of the THF
The solvent was removed under reduced pressure and the remaining white slurry was
ml of hexane was added. Strain this mixture
When the hexane was removed from the liquid at 70° C. under reduced pressure (1 mmHg), 9.1 g of a viscous solid (silazane polymer) was obtained. This one has an intrinsic viscosity (benzene, 20℃) of 0.07,
It had a melting point of 90°C and was soluble in hexane, benzene, THF and other organic solvents. Also, from IR, NH at 3400cm ^-1 , C-H at 2980cm ^-1 , and C-H at 2150cm
Absorption of Si-H at ^-1 and SiCH ₃ at 1260 cm ^-1 were observed. Furthermore, the molecular weight was determined to be 1020 by benzene freezing point depression method. Polymerization process 10g of the ammonolysis product obtained in the ammonolysis process was added to THF in the same manner as in the polymerization process.
The reaction was carried out with 0.2 g of KH for 90 minutes. After gas generation stops
CH ₃ I was added and the same treatment was carried out. 9.3 g of a viscous solid (silazane polymer) was obtained, which had an intrinsic viscosity of 0.08 and a melting point of 120°C. Polymerization process 10g of the ammonolysis product obtained in the ammonolysis process was added to THF in the same manner as in the polymerization process.
The reaction was carried out with 0.2 g of KH for 90 minutes. After gas generation stops
CH ₃ I was added and the same treatment was carried out. 9.1 g of a viscous solid (silazane polymer) was obtained, which had an intrinsic viscosity of 0.07 and a melting point of 115°C. Fiberization process 30g of the silazane polymer obtained in the polymerization process was spun into fibers using a molhole spinning device (nozzle diameter 0.5mm).
Melt spinning was carried out at ℃. The spinning was very good even after 4 hours, and it was carried out at a winding speed of 400 m/min, and the obtained raw silk was further infusible treated with an electron beam at 120 Mrad. Then under slight tension and in a _N2 stream
It was baked at 1100°C for 30 minutes at a temperature increase rate of 100°C/Hr. The ceramic yield was 75%, and the obtained fibers had a fiber diameter of 6μ, a tensile strength of 250Kg/mm ² , and an elastic modulus of 25t/mm ²
This is the physical property. In addition, when the fiber composition was analyzed by elemental analysis, Si58.3%, C20.3%,
It was confirmed that the fiber was mainly composed of SiC-Si ₃ N ₄ consisting of 19.4% N and 2% O. Fiberization step 10 g of the silazane polymer obtained in the polymerization step was melt-spun at 160° C. using the same spinning device as in the fiberization step. The winding speed was 420 m/min, and the spinning was very good. Furthermore, the obtained raw silk was heated at 90 to 110℃ (5℃/Hr) in air under slight tension.
It was heated to make it infusible. Then under no tension
At 1200°C with a heating rate of 100°C/Hr in a _N2 stream
Bake for 30 minutes. The ceramic yield is 80%,
The obtained fiber has a fiber diameter of 8μ, a tensile strength of 200Kg/mm ² ,
The elastic modulus was 17t/ ^mm2 . Elemental analysis of the fiber composition revealed that Si56.2%, C19.2%, N15.4%, O9.2%
The fiber was mainly composed of SiC-Si ₃ N ₄ . Fiberization Step 20 g of the silazane polymer obtained in the polymerization step was melt-spun in a dry box at 150° C. at a winding speed of 450 m/min using the same spinning device as in the fiberization step. The spinning was good from beginning to end. The obtained raw silk was irradiated with 90 Mrad using an electron beam device in a vacuum to make it infusible. Thereafter, the obtained fibers were fired for 30 minutes at 1250° C. (100° C./Hr) in a N ₂ stream under tension. The ceramic yield was 77%. The fibers had a fiber diameter of 6μ, a tensile strength of 260Kg/mm ² , and an elastic modulus of 23t/mm ² . [Comparative example] Ammonolysis process After charging 850 ml of dehydrated hexane into a four-necked flask (1) equipped with a stirrer, thermometer, NH ₃ inlet tube, and deep cooling condenser, methyldichlorosilane was added.
Added 46g. Add 12% gaseous ammonia to this
The reaction was carried out at a rate of Hr for 3.5 hours. below,
A treatment similar to the ammonolysis step of the above example was carried out to obtain 20 g (85%) of a clear flowable liquid. Polymerization process KH0.2g and THF125 in a 300ml three-necked flask
ml was injected, the KH was dispersed by stirring, and a mixture of 75 ml of THF and 10 g of the previously obtained transparent fluid liquid was added dropwise from the dropping funnel over 15 minutes at room temperature.
To stop the reaction 30 minutes after completion of the dropwise addition.
2 g of CH ₃ I was added. Thereafter, the same treatment as in the polymerization step of the example was carried out to obtain 9.0 g of a viscous solid. This product had an intrinsic viscosity of 0.06 and a melting point of 75°C.
An attempt was made to control the temperature, amount of catalyst, and polymerization time to maintain a constant degree of polymerization in this system, but this resulted in a complete lack of reproducibility. Fiberization Step 8 g of the obtained silazane polymer was charged into a monohole (nozzle diameter: 0.5 mm) spinning device, melted at 110° C., and spun. Initially, the nozzle discharged well and spinning was possible, but after 30 minutes the nozzle no longer discharged. Although the temperature was gradually raised, the polymer did not discharge at all. After cooling, the polymer was taken out and its melting point was measured, and it was found that it did not melt even at 300°C and was also insoluble in the solvent. After irradiating the slightly spun raw silk with an electron beam at 90 Mrad, it was heated at 100°C in a _N2 stream.
It was baked at 1100°C for 30 minutes at a heating rate of Hr. The ceramic yield was 58%, and the obtained fibers had a fiber diameter of 7μ, a tensile strength of 50Kg/mm ² , and an elastic modulus of 5t/mm ² , which were low physical properties. [Example 2] 20 parts by weight of the organic silazane polymer obtained in the polymerization step of Example 1, 80 parts by weight of silicon carbide powder, and 100 parts by weight of hexane were mixed, dispersed and kneaded, and then the hexane was evaporated. The obtained mixed powder was pressure molded at a molding pressure of 1 t/mm ² to obtain a compacted powder compact on a sheet with a diameter of 25 mm and a thickness of 10 mm. Next, this compacted compact was heated from room temperature to 150°C at a temperature increase rate of 2°C/min, and held at 150°C for 1 hour to be infusible.
The temperature was raised from room temperature to 1200°C at a temperature increase rate of 100°C/Hr in an argon stream, and after holding at this temperature for 1 hour, the furnace was cooled. The obtained ceramic molded body had a density of 2.2 g/cm ³ and a bending strength of 12 Kg/mm ² . [Example 3] Organic silazane 20 obtained in the polymerization process of Example 1
Parts by weight, 70 parts by weight of silicon nitride fine powder (average particle size 1 μm), 15 parts by weight of silicon carbide whiskers, and 30 parts by weight of xylene were placed in a ball mill and mixed for 8 hours. After mixing, the xylene was removed under reduced pressure, and the powder was cooled and ground into a fine powder. This powder was placed in a mold, leveled uniformly, and pressure-molded at a pressure of 1.5 t/cm ² , and then the molded product was taken out from the mold to obtain a sheet-like molded product with a thickness of 1 mm. Next, this sheet was heated in air from room temperature to 150°C at a heating rate of 2°C/min, and held at 150°C for 1 hour to perform an infusibility treatment. Furthermore, the temperature of the infusible sheet was raised to 1200°C at a heating rate of 200°C/Hr in a nitrogen atmosphere.
After holding this temperature for 1 hour, the furnace was cooled. The obtained ceramic sheet has a thickness of 0.95 mm and a density of 2.2
g/cm ³ and had flexibility. [Example 4] 3% by weight of boron and 15% by weight of the organic silazane polymer obtained in the polymerization process of Example 1 were added to β-carbon silicon powder with an average particle size of 0.5 μm, and a mixture of Silicon carbide fibers with a length of 5 cm and a thickness of 10 to 15 μm are uniformly oriented in one direction, and the fiber content is
After layering them alternately to a volume of 40%, they were molded using a mold press at a pressure of 0.4t/mm ² . This molded body was heated from room temperature to 150°C at a heating rate of 2°C/min, and held at 150°C for 1 hour to make it infusible.
The mixture was heated to 1600°C at a temperature increase rate of 240°C/Hr under a nitrogen stream, and then held at 1400°C for 1 hour to obtain inorganic fiber reinforced composite ceramics. This material had a bending strength of 40 Kg/mm ² at room temperature and had high physical properties.

Claims (1)

[Claims] 1 A mixture of methyldichlorosilane, methyltrichlorosilane and dimethyldichlorosilane is reacted with ammonia to obtain an ammonolysis product, and this ammonolysis product is polymerized using a basic catalyst capable of deprotonation. 1. A method for producing ceramics, which comprises: obtaining an organic silazane polymer, then melting and molding the organic silazane polymer, making it infusible, and then firing it to obtain ceramics. 2 The mixing ratio of methyldichlorosilane, methyltrichlorosilane, and dimethyldichlorosilane is 55~
80 mol%: 10 to 30 mol%: 5 to 25 mol%. The manufacturing method according to claim 1. 3. The manufacturing method according to claim 1 or 2, wherein the organic silazane polymer has a melting point of 60 to 200°C. 4. Any one of claims 1 to 3, wherein the organic silazane polymer is melted and molded and then heated in air to 50 to 150°C to make it infusible.
The manufacturing method described in section. 5. Claims 1 to 3, in which the organic silazane polymer is melted and molded and then irradiated with an electron beam at a dose of 50 to 200 Mrad in vacuum or _N2 gas to make it infusible. The manufacturing method according to any one of Items. 6. The manufacturing method according to any one of claims 1 to 5, wherein the forming step is a spinning step, and the ceramic fiber is obtained by spinning a molten organic silazane polymer. 7. The manufacturing method according to any one of claims 1 to 6, wherein the firing temperature is 700 to 2000°C. 8. The manufacturing method according to any one of claims 1 to 7, wherein the firing atmosphere is in a vacuum or in a gas selected from inert gas, N ₂ gas, H ₂ gas, and NH ₃ gas. .