JPH09221308A - Nitrogen-containing silane compound - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably obtain silicon nitride ceramics high in strength, toughness, reliability and oxidation resistance with high reproducibility by using a specified nitrogen-containing silane compd. mainly comprising silicon diimide as a starting material. SOLUTION: The nitrogen-containing silane compd. having >=100nm average grain size, 1.4-1.9g/cm<3> true density, 0.045-0.090g/cm<3> bulk density, 600-1000m<2> /g specific surface area, 45.5-51.5wt.% nitrogen content, 44.5-51.5wt.% silicon content, <=3.5wt.% oxygen content, less than 0.25wt.% carbon content, <=180ppm halogen content and <=100ppm metallic impurity is used. This production method of ceramics is not restricted, but a solution of halogenated silane and an org. solvent is supplied to alloy to react to an org. solvent layer of a reaction system separated into two layers by a specific density difference between liquid ammonia and the org. solvent which does not dissolve into the ammonia and has larger specific density. Pressure is set to 0.54-13.6atm and reaction temp. is set to -45 to 36 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel nitrogen-containing silane compound, and in particular, it produces silicon nitride ceramics having particularly high strength and high toughness among silicon nitride ceramics used as structural ceramics. The present invention relates to a nitrogen-containing silane compound suitable as a starting material for

[0002]

2. Description of the Related Art Silicon nitride ceramics have excellent properties such as high strength, high toughness and high corrosion resistance, and are used in various fields as structural materials and mechanical parts used at temperatures of 1000 ° C. or lower. The application development of is progressing. In this silicon nitride sintering, Y ₂ O ₃ , Al ₂ O ₃ is usually used.
Since oxides such as 5 to 10% by weight are added for sintering, the mechanical properties of the obtained sintered body change depending on the sintering conditions. In order to prevent changes in mechanical properties due to such changes in sintering conditions and to produce silicon nitride ceramics capable of stably exhibiting excellent mechanical properties regardless of sintering conditions, Y ₂ O ₃ , Search for sintering aids such as MgO, Sc ₂ O ₃ and Cr ₂ N, NbB, TaSi ₂ , ZrS
In parallel with the study of dispersion of hard particles such as i _2, the production conditions of silicon nitride powder, which is a raw material for producing a sintered body, are also studied.

Conventionally, an imide decomposition method in which a silicon halide is reacted with ammonia has been known as a method for producing silicon nitride powder. The silicon nitride powder produced by this method is easily sinterable and excellent. It is said that it exhibits excellent sintered body performance. Therefore, as a result of detailed study of the relationship between the powder characteristics of the nitrogen-containing silane compound as the starting material for the imide decomposition method and the sinterability and sintered body characteristics of the obtained silicon nitride powder, it was found that nitrogen-containing silane compounds having specific powder characteristics It was found that, when a silane compound is used, by sintering the resulting silicon nitride powder under normal sintering conditions, silicon nitride ceramics having excellent mechanical properties can be stably manufactured with good reproducibility. It was

[0004]

It is an object of the present invention to provide a nitrogen-containing silane compound as a starting material for producing a silicon nitride powder capable of producing silicon nitride ceramics having excellent mechanical properties with good reproducibility and stability. It is in.

[0005]

The present invention has a true density of 1.
4 to 1.9 g / cm ³ , light load density of 0.045 to 0.0
90 g / cm ³ and a specific surface area of 600 to 100
The present invention relates to a nitrogen-containing silane compound mainly composed of silicon diimide having an oxygen content of 0 m ² / g, an oxygen content of 3.5% by weight or less, and a carbon content of less than 0.25% by weight. The nitrogen-containing silane compound of the present invention is mainly represented by the chemical formula Si
It is composed of silicon diimide represented by (NH) ₂ . The nitrogen content of the nitrogen-containing silane compound is 45.5 to 5
1.5 wt%, silicon content is 44.5-51.5 wt%.

Since silicon diimide has a three-dimensional network structure of silicon atoms and nitrogen atoms, the true density of silicon diimide changes depending on the regularity of the Si--N bonds.
The nitrogen-containing silane compound of the present invention has a true density of 1.4 to 1.
9 g / cm ^3, preferably from 1.5~1.7g / cm ^3. When the true density is less than 1.4 g / cm ³ ,
When this is fired, crystallization shifts to the high temperature side, and needle-like crystals are easily generated. When the proportion of needle-like crystals increases, the strength characteristics of the obtained sintered body deteriorate, and the variation also increases, and the reliability of the sintered body deteriorates. Furthermore, the oxidation resistance of the sintered body also deteriorates, causing an increase in the amount of oxidation and a decrease in the strength after oxidation. Further, when the true density is higher than 1.9 g / cm ³ , the crystallization shifts to the low temperature side when firing, and angular and stable granular particles are generated. However, particles that are excessively stabilized have low sintering activity, and it is difficult to densify them when producing a sintered body, which is not preferable.

The light packaging density is 0.045 to 0.090.
g / cm ³ , preferably 0.055-0.085 g /
cm ³ . When the light packaging density is less than 0.045 g / cm ³ , the β fraction of the silicon nitride powder obtained by firing the powder decreases, and the powder agglomerates strongly. As a result, it becomes difficult to uniformly disperse the auxiliary agent when it is mixed with the sintering auxiliary agent by a wet ball mill or the like. Β of silicon nitride powder
There is an optimum value for the fraction, and an excessively low β fraction is not preferable. Also, as an effect of making it difficult to uniformly mix with the auxiliary agent,
There is a problem that the room temperature strength and the high temperature strength of the sintered body are reduced. Further, when the light packaging density is higher than 0.090 g / cm ³ , the β fraction of the silicon nitride powder obtained by firing this increases, and the agglomeration of the powder weakens, so that the powder easily breaks. Therefore, the auxiliary agent can be uniformly dispersed when it is mixed with the sintering auxiliary agent by a wet ball mill or the like.
However, this is not preferable because it causes a problem that the press density of the molded body decreases and the fracture toughness of the sintered body decreases.

[0008] The specific surface area is 600~1000m ² / g, preferably from of 700-800m ² / g. When the specific surface area is smaller than 600 m ² / g, the aggregation index of the powder obtained by firing the same increases, and the high temperature strength of the finally obtained sintered body decreases. Also, 1000 m ² / g
If it is larger than this, the α fraction of the silicon nitride powder is lowered and the sinterability is deteriorated, which is not preferable. The oxygen content is 3.5% by weight or less, preferably 2.5% by weight or less. When the oxygen content is more than 3.5% by weight, the sinterability of the obtained silicon nitride powder is good, but the high temperature strength of the obtained sintered body decreases. Further, since the amount of internal oxygen in the obtained silicon nitride powder is large, the strength of the obtained sintered body after oxidation is reduced. Furthermore, when a nitrogen-containing silane compound is produced, a carbon-containing substance (for example, toluene) is mixed as an impurity from a raw material or a reaction solvent, and its content is less than 0.25% by weight in terms of carbon.
It is preferably less than 0.10% by weight. When the carbon content is 0.25% by weight or more, the carbon content of the silicon nitride powder obtained by firing the nitrogen-containing silane compound is 0.10.
It is not preferable because the amount is more than the weight%, resulting in poor sinterability.

Further, the nitrogen-containing silane compound of the present invention is
It is desirable that the average particle size, the content of metal impurities, and the content of halogen be in the following ranges in order to achieve the intended purpose. The average particle size is preferably 100 nm or less.
If the average particle size is larger than 100 nm, needle crystals are likely to be formed when firing this. When the proportion of needle-like crystals increases, the strength characteristics of the obtained sintered body deteriorate, and the variation also increases, and the reliability of the sintered body deteriorates. Furthermore, the oxidation resistance of the sintered body also deteriorates, causing an increase in the amount of oxidation and a decrease in the strength after oxidation. Further, although the metal impurities remain in the fired powder as they are, the metal impurities serve as a source of destruction and destruction of the sintered body. Therefore, in order to produce a highly reliable sintered body, the metal impurities should be reduced. There must be. In the present invention, the metal impurity content is preferably 100 ppm or less. Metal impurity content is 100ppm
If the amount is larger than the above range, the strength of the obtained sintered body decreases.
Further, the composition of the grain boundary of the obtained sintered body is changed, and the segregation of impurities at the grain boundary occurs, so that the oxidation resistance of the sintered body is deteriorated, and the increase in the amount of oxidation and the decrease in the strength after oxidation occur. The halogen content is preferably 180 ppm or less. About half of the halogen contained in the nitrogen-containing silane compound remains in the calcined powder. The halogen contained in the silicon nitride powder collects in the grain boundary phase of the sintered body and has the effect of lowering the softening temperature of the grain boundary phase. Therefore, when the halogen content is more than 180 ppm, the high temperature strength of the finally obtained sintered body is lowered and the oxidation resistance is also deteriorated.

The method for producing the nitrogen-containing silane compound of the present invention is not particularly limited as long as the nitrogen-containing silane compound having the above-mentioned properties can be obtained. For example, as shown below, halogenated silane and liquid ammonia are used. Can be produced by reacting That is, liquid ammonia,
Liquid ammonia and an organic solvent that is slightly soluble and has a specific gravity larger than that of liquid ammonia are separated into two layers due to the difference in specific gravity.A mixed solution of a halogenated silane and the organic solvent is supplied to the lower organic solvent layer of the reaction system. By doing so, the halogenated silane reacts with the liquid ammonia. Then, the nitrogen-containing silane compound produced in the above reaction is washed with liquid ammonia to remove by-produced ammonium halide.

In the above reaction, the pressure is 0.54 to 1
A nitrogen-containing silane compound having a true density in the range of 1.4 to 1.9 g / cm ³ can be synthesized by setting 3.6 atm and the reaction temperature in the range of −45 to 36 ° C. Also, the pressure is 1.5 to 7.2 atm, and the reaction temperature is -25 to 1
By setting the temperature in the range of 5 ° C., the true density is 1.5 to 1.7.
It can be controlled within the range of g / cm ³ . Further, the light loading density of the nitrogen-containing silane compound is changed from 0.045 to 0.4.0 by changing the drying time and the stirring rotation speed when the generated nitrogen-containing silane compound is dried using a jacket type stirring tank or the like.
It can be controlled within the range of 090 g / cm ³ . Since the relationship between the drying condition and the light packaging density varies depending on the dryer used, the relational expression between the two may be examined in advance to set the condition appropriately.

Furthermore, the ratio (volume basis) of halogenated silane and liquid ammonia in the reaction is 0.030 to 0.
047, preferably by changing in the range of 0.035 to 0.041, the specific surface area 600 to 1000 m ²
/ G, preferably 700 to 800 m ² / g of a nitrogen-containing silane compound can be synthesized. In the initial stage of the reaction, liquid ammonia exists in a large excess,
Since ammonia is consumed as the reaction progresses, liquid ammonia is also continuously supplied to the reaction tank. Then, in a steady state, the volume ratio of the halogenated silane and the liquid ammonia supplied into the reaction tank is changed. In addition, the oxygen content of the nitrogen-containing silane compound is 3.5% by weight or less, preferably by reducing the water content in the liquid ammonia used when washing the nitrogen-containing silane compound obtained in the above reaction as much as possible. , 2.5 wt% or less. Specifically, the amount of water H (ppm) in liquid ammonia and the amount of cleaning liquid / the amount of nitrogen-containing silane compound W
The product (H × W) with (l / kg) is 31500 or less, preferably 22500 or less. Similarly, the content of the organic compound in the liquid ammonia used when cleaning the nitrogen-containing silane compound is 1500 ppm or less, preferably,
By setting it to 600 ppm or less, the carbon content of the nitrogen-containing silane compound is less than 0.25% by weight, and preferably,
It can be less than 0.10% by weight.

The average particle diameter of the nitrogen-containing silane compound is changed by controlling both the temperature of the reaction tank and the mixing ratio (volume ratio) of the halogenated silane supplied to the reaction tank and the organic solvent for dilution. be able to. In order to make the average particle diameter of the nitrogen-containing silane compound 100 nm or less, the mixing ratio should be 0.
It may be set to 08 or more. The metal impurities are mixed by the sliding wear and the contact wear of the stirring blades installed inside the reaction tank, the cleaning tank, the dryer, etc., and can be reduced by adjusting the equipment and improving the control accuracy. Specifically, the gap between the stirring blade and various metal parts (filter plate, container wall, etc.) should be 5 mm or more, preferably 10 mm or more, and the maximum peripheral speed at the tip of the rotary blade should be 5 m / s or less. By controlling, the amount of metal impurities can be reduced to 100 ppm or less. The halogen content varies depending on the amount of liquid ammonia used when washing and removing ammonium halide from the mixture of the nitrogen-containing silane compound obtained by the reaction and ammonium halide. Normally, liquid ammonia contains 40 l per 1 kg of nitrogen-containing silane compound.
By using above, the halogen content is 180pp
m or less. The halogen content can be reduced as much as possible by using a large amount of liquid ammonia, but excessive cleaning leads to cost increase and is not economical.

As the halogenated silane used in the above reaction
For SiF_Four, H_TwoSiF₆, HSiF_Three, H_ThreeSiF _Five, H_ThreeSiF, H_FiveSiF_Threeetc
Fluorinated silane, SiCl_Four, HSiCl_Three, H_TwoSiCl_Two, H_ThreeSuch as SiCl
Lorsilane, SiBr_Four, HSiBr_Three, H_TwoSiBr_Two, H_ThreeSiBr, etc.
Lomosilane and SiI_Four, HSiI _Three, H_TwoSiI_Two, H_ThreeYouth such as SiI
Silane silanes can be used. Also, RSiX_Three, R_TwoSiX
_Two, R_ThreeSiX (R is CH_Three, C_TwoH_Five, C_ThreeH₇An alkyl group such as
Halogen) and other halogenated alkylsilanes may also be used.
Can be.

As the organic solvent, those which are inert to liquid ammonia and halogenated silane, which do not dissolve in liquid ammonia at the reaction temperature and have a specific gravity larger than that of liquid ammonia are used. For example, n-
Specific examples thereof include aliphatic hydrocarbons having 5 to 7 hydrocarbons such as heptane, n-hexane, n-pentane and C-hexane, aromatic hydrocarbons such as benzene, toluene and xylene, and mixtures thereof.

By using the nitrogen-containing silane compound of the present invention as a starting material, it is possible to produce a silicon nitride powder capable of stably producing a silicon nitride ceramic having excellent mechanical properties with good reproducibility. First, a nitrogen-containing silane compound is calcined at a temperature in the range of 600 to 1200 ° C. in an atmosphere of an inert gas containing nitrogen or ammonia having an oxygen content of 5% or less to produce an amorphous silicon nitride powder.
At this time, the nitrogen-containing silane compound gradually decomposes from room temperature and particularly violently decomposes at 250 to 600 ° C. to generate ammonia. Examples of the inert gas containing nitrogen or ammonia include nitrogen or ammonia, or a mixed gas with argon, helium, or the like.

Next, the obtained amorphous silicon nitride powder is fired in an inert gas atmosphere containing nitrogen or ammonia to produce a crystalline silicon nitride powder. The firing temperature is 140
It is in the range of 0 to 1600 ° C. If the firing temperature is lower than 1400 ° C, crystallization of silicon nitride does not proceed sufficiently. Further, if the firing temperature exceeds 1600 ° C., crystalline silicon nitride powder composed of coarse crystals is likely to be generated, which is not preferable. Further, a rapid temperature increase is not preferable in order to make the particle shape uniform, and it is desirable to increase the temperature slowly in the range of 1150 to 1400 ° C. over 1.5 hours.

As the heating furnace used for heating the nitrogen-containing silane compound and the amorphous silicon nitride powder, a batch type electric furnace by a high frequency induction heating method or a resistance heating method, a pusher furnace, a rotary kiln furnace, a shaft kiln furnace, a flow furnace A chemical firing furnace or the like is used. Particularly, the continuous firing furnace is an effective means for efficiently dissipating the heat generated by the crystallization reaction of amorphous silicon nitride.

The obtained silicon nitride powder is mixed in the same manner as in the case of the conventional silicon nitride powder, for example, by mixing it with a sintering aid such as aluminum oxide, yttrium oxide or magnesium oxide, and molding the mixture into a predetermined shape. Then, the silicon nitride ceramics (sintered body) can be manufactured by sintering. The molding pressure is 0.5 to 5 ton / c
It may be about m ² and the above sintering conditions are the sintering temperature 1
500 to 2000 ° C, atmospheric pressure 0.5 to 100 atm,
The sintering time may be about 1 to 10 hours.

The silicon nitride ceramics (sintered body) produced by using this silicon nitride powder has not only high strength, high toughness and high Weibull coefficient but also high oxidation resistance as compared with conventional ones. Since it is also excellent, it is particularly suitable as a raw material for manufacturing silicon nitride ceramics used as structural materials for heat engines such as turbo rotors, valves, and diesel engine auxiliary combustion chambers used at temperatures of 1400 ° C. or lower and machine parts. It is a thing.

[0021]

EXAMPLES Examples of the present invention will be given below together with comparative examples.
The present invention will be described in more detail. Examples 1 to 14 and Comparative Examples 1 to 8 [Production of Nitrogen-Containing Silane Compound] Under the temperature and pressure shown in [Table 1], the air in the vertical reactor having a diameter of 30 cm and a height of 45 cm was replaced with nitrogen gas. After that, liquid ammonia and toluene were charged. In the reaction tank, it was separated into liquid ammonia in the upper layer and toluene in the lower layer. A solution of silicon tetrachloride and toluene prepared in the proportions shown in [Table 1] was supplied to the lower layer which was slowly stirred through a conduit.
With the supply of the toluene solution, a white reaction product was deposited near the interface between the upper and lower layers. After the reaction was completed, the reaction solution was transferred to a filtration tank, the product was filtered off, and washed with liquid ammonia,
A nitrogen-containing silane compound mainly composed of silicon diimide was obtained.

In the above reaction, the true density was controlled by changing the reaction temperature. Further, the light load density was controlled by changing the drying time and the stirring rotation speed when the generated nitrogen-containing silane compound was dried with heating steam using a jacket type stirring tank (with a 45-degree inclined two-blade paddle). As for the drying time, since the temperature starts to rise when the solvent is completely blown out, the time when the temperature of the powder layer starts to rise is set as the end point of the drying. The specific surface area was controlled by changing the ratio (volume basis) of silicon tetrachloride and liquid ammonia during the reaction. In the initial stage of the reaction, liquid ammonia is present in a large excess, but since ammonia is consumed as the reaction proceeds, liquid ammonia is also continuously supplied to the reaction tank.
Then, nitrogen-containing silane compounds having various specific surface areas were synthesized by changing the volume ratio of silicon tetrachloride and liquid ammonia supplied into the reaction tank in the steady state within the range shown in [Table 1].

The oxygen content was controlled by changing the amount of water in the liquid ammonia used when washing the produced nitrogen-containing silane compound within the range shown in [Table 1]. Similarly, the carbon content was controlled by changing the toluene content in the liquid ammonia used when cleaning the nitrogen-containing silane compound within the range shown in [Table 1]. The average particle size was controlled by changing the temperature of the reaction tank and the volume ratio of silicon tetrachloride and toluene supplied to the reaction tank within the range shown in [Table 1].
The chlorine content was controlled by changing the amount of liquid ammonia used when cleaning the nitrogen-containing silane compound within the range shown in [Table 1]. The metallic impurities changed depending on the adjustment state of the stirring blade.

[0024]

[Table 1]

The powder characteristics of the obtained nitrogen-containing silane compound are shown in Table 2. The true density of the nitrogen-containing silane compound was measured by using dehydrated xylene as a liquid medium and immersing it in xylene using a pycnometer. During the measurement, defoaming was sufficiently performed. (Implementation according to JIS H1902) The light packaging density was measured according to JIS K5101 using a commercially available 100 ml graduated cylinder as a filling container. The average particle size was determined by observing the nitrogen-containing silane compound with a transmission electron microscope and measuring the particle size distribution on a micrograph to determine the average particle size of the primary particles. As for the specific surface area, Shimazu-Micromeritics Flowsorb 2300 type is used.
The BET single point method was used for measurement. The oxygen content was measured by an inert gas melting-infrared absorption method using a TC-136 oxygen / nitrogen simultaneous analyzer manufactured by LECO. The carbon content was measured by the combustion-thermal conductivity method using a LECO WR-12 type carbon analyzer.

[0026]

[Table 2]

[Production of Silicon Nitride Powder] The produced nitrogen-containing silane compound was thermally decomposed at 1000 ° C. in a nitrogen atmosphere containing 0.5% of oxygen to obtain an amorphous silicon nitride powder. Then, the obtained amorphous silicon nitride powder is subjected to a grinding treatment with a vibration mill, and then with an electric furnace in a nitrogen atmosphere for 1 minute.
The temperature was raised to 1550 ° C. at a heating rate of 00 ° C./h and kept at the same temperature for 1 hour to obtain an off-white silicon nitride powder. Observation of the obtained silicon nitride powder with a scanning electron microscope showed only equiaxed granular particles of 0.05 to 0.5 μm.

Test Example of Use Using the silicon nitride powders obtained in Examples 1 to 14 and Comparative Examples 1 to 8, sintered bodies were manufactured by the following manufacturing methods. [Production of Sintered Body] 6 wt% Yb ₂ O _{3 in} silicon nitride powder,
After adding 1.5 wt% of Al ₂ O ₃ and 0.5 wt% of HfO ₂ and wet-mixing with a ball mill, ² ton / cm ²
A rubber press molding was performed under the pressure of 1 to produce a molded body. This molded body was filled in a silicon nitride crucible and placed in an electric furnace for 1
In a nitrogen atmosphere at atmospheric pressure, the temperature is raised at a heating rate of 200 ° C./h,
It hold | maintained at 1770 degreeC for 4 hours, and the silicon nitride sintered compact was obtained. The ultimate density, bending strength and fracture toughness of the obtained sintered body are shown in [Table 3]. The bulk density of the sintered body was measured by the Archimedes method, the bending strength was measured by a four-point bending test according to JIS R 1601, and the fracture toughness value was measured by a SEPB method according to JIS R 1607. In addition, from the obtained sintered body,
A test piece having a predetermined shape was cut out, and the surface was ground and polished to be smooth. Put this test piece in a box-type electric furnace,
The weight increase after heat treatment at 1300 ° C. for 100 hours under air flow was measured. The value obtained by dividing the weight increase of the sample by its outer surface area was taken as the oxidation weight gain (g / m ² ). Further, the four-point bending strength at room temperature of the anti-deposition test piece subjected to the oxidation treatment under the same conditions was measured to determine the strength after oxidation.

[0029]

[Table 3]

[0030]

By using the nitrogen-containing silane compound of the present invention as a starting material, high strength, high toughness, high reliability,
It is possible to manufacture a silicon nitride powder capable of stably manufacturing a silicon nitride ceramic having high oxidation resistance with good reproducibility.

Claims (4)

[Claims] 1. A true density of 1.4 to 1.9 g / cm ³ , a light loading density of 0.045 to 0.090 g / cm ³ , a specific surface area of 600 to 1000 m ² / g, and an oxygen content of A nitrogen-containing silane compound mainly composed of silicon diimide having a carbon content of 3.5% by weight or less and a carbon content of less than 0.25% by weight. 2. The nitrogen-containing silane compound according to claim 1, which has a true density of 1.5 to 1.7 g / cm ³ and a light loading density of 0.055 to 0.085 g / cm ³ . 3. The nitrogen-containing silane compound according to claim 1, which has a specific surface area of 700 to 800 m ² / g, an oxygen content of 2.5% by weight or less, and a carbon content of less than 0.10% by weight. 4. The average particle size is 100 nm or less, the metal impurity content is 100 ppm or less, and the halogen content is 180 p.
The nitrogen-containing silane compound according to claim 1, which has a pm or less.