JP2000044210A - Crucible for calcination of silicon nitride powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To mass-produce a crystalline powder consisting of isometric granular particles of a uniform grain size and having excellent packing characteristics with good productivity by providing a grating having a specified interval on the inside of a box-type crucible. SOLUTION: On the inside of the crucible a grating having 15 to 80 mm interval is provided. If the interval of the grating is smaller than 15 mm, the packing and discharging of the powder is difficult, which decreases not only the workability but the production efficiency. Moreover, the amt. of impurities mixed from the crucible wall to the calcined powder increases. Therefore, the grating with <15 mm interval is not preferable. If the interval is larger than 80 mm, uniform heating of the powder layer can not be obtd. The thickness of the grating is preferably 4 to 20 mm. If the thickness is smaller than 4 mm, the effect of the grating to absorb the heat generated in the powder layer is not enough obtd. and local heat generation is hardly prevented. If the thickness is larger than 20 mm, the packed amt. of the powder decreases to decrease the production efficiency. An amorphous silicon nitride powder and a nitrogen- contg. silane compd. are packed to the crucible and calcined in a nitrogen-contg. inert gas atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a firing crucible used for producing a large amount of easily sinterable silicon nitride powder suitable as a raw material for producing a silicon nitride sintered body useful as a high-temperature structural material. It is about.

[0002]

2. Description of the Related Art A method for producing a crystalline silicon nitride powder by firing an amorphous silicon nitride powder and / or a nitrogen-containing silane compound under an inert gas atmosphere or a reducing gas atmosphere is disclosed in US Pat. Already known.

[0003] In general, crystalline silicon nitride powder obtained by firing amorphous silicon nitride powder has disadvantages that needle-like crystals or columnar crystals are easily formed during crystallization, and the packing density is low. However, when this is used as a raw material for a sintered body, there is a problem that only a compact having a low bulk density can be obtained.

[0004] As a method of overcoming these disadvantages and producing crystalline silicon nitride powder composed of fine granular crystals,
For example, Japanese Patent Publication No. 61-11886 discloses that a nitrogen-containing silane compound having a powder bulk density of 0.1 g / cm ³ or more as silicon is heated at a rate of 15 ° C./° C. over a temperature range of 1350 to 1550 ° C. Control over 1 minute and 1550
There is disclosed a method for producing silicon nitride powder, wherein the method is heated to not less than 1 ° C. and less than 1700 ° C. According to the present invention, it is possible to produce a silicon nitride powder composed of only granular crystals that do not contain needle-like crystals. However,
As can be seen from the examples, this method is based on the results of a small-scale firing experiment, and when powder firing on a mass production scale is considered, there remains a problem to be solved. That is, when a large amount of amorphous silicon nitride powder is heated to around 1350 ° C., where crystallization of silicon nitride is considered to proceed, the temperature of the powder layer locally rises significantly due to generation of crystallization heat, and the temperature rises. The speed may be several tens to several thousand degrees Celsius / minute, which causes a problem that acicular crystals or columnar crystals are partially generated. In order to solve this problem, there is a means to secure a uniform heat by filling the powder layer into a thin dish-shaped baking container with a reduced thickness, but the workability and productivity are poor, and the baking process is difficult. However, there is a drawback that the cost increases.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a firing crucible suitable for mass-producing high-quality crystalline silicon nitride powder having a uniform particle shape and size. It is in.

[0006]

The present invention relates to a box-shaped crucible used for firing amorphous silicon nitride powder and / or nitrogen-containing silane compound into a crystalline silicon nitride powder in a firing furnace. Further, the present invention relates to a crucible for firing silicon nitride powder, wherein a lattice is provided at intervals of 15 to 80 mm inside.

The crucible of the present invention has a size of 15 to 80 mm inside.
Are provided at intervals of. The grid spacing is 15m
If it is smaller than m, it is difficult to fill and take out the powder, not only the workability is poor, but also the production efficiency is reduced. Also,
This is not preferable because the amount of impurities mixed into the fired powder from the crucible wall surface increases. For example, when a carbon crucible is used, the carbon content of the fired powder increases, which is not preferable. On the other hand, if it is wider than 80 mm, it is not preferable because it is not possible to secure uniform heat of the powder layer. The thickness of the grid is preferably 4 to 20 mm. If the thickness is less than 4 mm, the effect of absorbing the heat of the powder layer by the grid is small, and it becomes difficult to prevent local heat generation. On the other hand, if the thickness is more than 20 mm, the filling amount of the powder decreases, and the production efficiency decreases.

The size of the crucible is not particularly limited. However, in consideration of workability, it is usually preferable that each side and the height of the bottom face be in the range of 200 to 600 mm.
The height is preferably 600 mm or less in terms of soaking. As a material of the crucible, graphite, silicon carbide, silicon nitride, boron nitride, alumina, mullite, zirconia, or the like can be used.

As the nitrogen-containing silane compound to be fired in the crucible of the present invention, silicon diimide, silicon tetraamide, silicon nitrogenimide, silicon chlorimide and the like are used. These are known methods, for example, a method of reacting silicon halide such as silicon tetrachloride, silicon tetrabromide and silicon tetraiodide with ammonia in the gas phase, and reacting the liquid silicon halide with liquid ammonia. It is manufactured by a method. In addition, as the amorphous silicon nitride powder, a known method, for example, the nitrogen-containing silane compound in a nitrogen or ammonia gas atmosphere 600-120.
Heat decomposition at a temperature in the range of 0 ° C., silicon tetrachloride,
Those produced by a method in which a silicon halide such as silicon tetrabromide or silicon tetraiodide is reacted with ammonia at a high temperature are used. The average particle diameter of the amorphous silicon nitride powder and the nitrogen-containing silane compound is usually 0.005 to
It is 0.05 μm.

The above-mentioned amorphous silicon nitride powder and / or nitrogen-containing silane compound is filled in a crucible of the present invention and fired in a nitrogen-containing inert gas or nitrogen-containing reducing gas atmosphere to form crystalline silicon nitride. A powder is obtained. Examples of the nitrogen-containing inert gas include nitrogen or a mixed gas of nitrogen, argon, and helium. Examples of the nitrogen-containing reducing gas include ammonia, hydrazine, and the like that release nitrogen gas by thermal decomposition at a high temperature, or a mixed gas of nitrogen, hydrogen, carbon monoxide, and the like.

In the calcination, it is preferable that the temperature is raised slowly by controlling the rate of temperature rise in the entire temperature range of 1200 to 1400 ° C. to 10 ° C./min or less in the temperature rising process. Such a slow temperature rise is an effective means for reducing the surface energy due to the grain growth of amorphous silicon nitride, securing the generation density of crystal nuclei, and suppressing the grain growth in the early stage of crystallization. When the holding temperature is lower than 1200 ° C., such an effect is not recognized. Conversely, when the holding temperature is higher than 1400 ° C., a rapid crystallization reaction proceeds, and the crystalline silicon nitride powder produced It is difficult to control the powder characteristics (particle shape, particle diameter, crystal phase, etc.) of the powder. The rate of temperature rise in the entire temperature range of 1200 to 1400 ° C. is 10 ° C./min or less. Heating rate is 10 ℃
When the temperature exceeds 1 / min, rapid crystallization occurs when the temperature is raised to 1400 ° C. or higher, and the temperature rise due to heat of crystallization is several hundred ° C. at the maximum.
As soon as the α-type silicon nitride powder comprising the desired fine crystals is obtained, it becomes impossible to obtain. In addition, in particular, 1200 to 13
If the holding time at 00 ° C. is too long, the crystal growth proceeds under the condition that nucleation is slightly suppressed, so that the shape of the generated granular crystal becomes a polyhedral shape, but the particle size is rather large. The powder having a small specific surface area.

After the temperature of the object to be fired is increased under the above-mentioned heating conditions to increase the crystallinity to 40% or more, the temperature may be increased to a higher temperature, for example, to 1700 ° C. There are no restrictions. If the final firing temperature is 1500 ° C,
It is desirable to maintain the same temperature for 15 to 60 minutes to complete the crystallization. Also, the final firing temperature is 1700 ° C.
If it exceeds, not only coarse crystals grow but also decomposition of the produced crystalline silicon nitride powder starts, which is not preferable.

As the firing furnace used for heating the amorphous silicon nitride powder and / or the nitrogen-containing silane compound, for example, a batch firing furnace using a high-frequency induction heating method or a resistance heating method, a pusher furnace, or the like can be used. .

[0014]

EXAMPLES Examples of the present invention will be described below together with comparative examples.
The present invention will be described in more detail. The oxygen content of the crystalline silicon nitride powder was measured by the LECO method. The degree of crystallinity was determined by the ceramic industry association, Vol. 93, No. 4, (1985), 3
According to the hydrolysis test described on pages 94 to 397, the α-type crystal content was calculated according to the X-ray diffraction method described on pages 777 to 780 of Ceramic Bulletin Vol. 56, No. 9, (1977). Surface area is BET by nitrogen gas adsorption
It was measured by the one-point method. The particle morphology of the powder was observed with a scanning electron microscope, and the presence ratio of particles having an aspect ratio of 2.5 or more was determined by area fraction by image analysis.
Further, according to the constant weight method described in JIS R-1628,
The tap density was measured. For the measurement of the press molding density, a tableting mold having a diameter of 13 mm was used. A mold was filled with 1 g of the powder, and a molding pressure of ² ton / cm ² was applied to produce a disc-shaped pellet. The external dimensions (diameter and thickness) and weight of the molded body were measured, and the bulk density was calculated. further,
By laser scattering diffraction method, measure the particle size distribution of the powder,
Median diameter, weight ratio of particles of 2 μm or more and 0.1
The weight ratio of particles having a size of 5 μm or less was determined.

EXAMPLE 1 Silicon diimide obtained by reacting silicon tetrachloride with liquid ammonia was thermally decomposed at 1000 ° C. to obtain an amorphous nitride having a specific surface area of 320 m ² / g and an oxygen content of 0.8 wt%. A silicon powder was obtained. Next, after the obtained amorphous silicon nitride powder was ground by a vibration mill, a carbon crucible shown in FIG. 1 (inner size: W380 mm × D380 mm × H)
5.5 kg of amorphous silicon nitride powder was filled into a 380 mm, 7 grids, 40.5 mm grid spacing, and 8 mm grid thickness) and set in a batch type electric furnace.

Next, the inside of the electric furnace was evacuated to a vacuum of 0.1 torr or less, nitrogen gas was introduced, and heating was started under a flow of nitrogen gas. The temperature was raised from room temperature to 1200 ° C. in 2 hours, kept at the same temperature for 1 hour, and then heated to 1400 ° C. at a rate of 100 ° C./hr. Further, the temperature was raised to 1500 ° C. at a rate of 250 ° C./hr and maintained at the same temperature for 1 hour.
The furnace was allowed to cool to obtain 5.2 kg of crystalline silicon nitride powder.
Table 2 shows characteristic values of the obtained silicon nitride powder such as crystallinity, α phase content, particle shape, specific surface area, tap density, press molding density, and particle size distribution. FIG. 2 shows a scanning electron micrograph of the obtained powder.

Examples 2 to 5 The same amorphous silicon nitride powder as used in Example 1 was ground by a vibrating mill and filled in a carbon crucible having a lattice spacing shown in Table 1. And fired in a batch type electric furnace. Table 2 shows characteristic values of the obtained silicon nitride powder such as crystallinity, α phase content, particle shape, specific surface area, tap density, press molding density, and particle size distribution.

Comparative Example 1 6.4 kg of the same amorphous silicon nitride powder as used in Example 1 was ground by a vibration mill, and then crucible made of carbon (inner size: W380 mm × D380 mm × H38).
(0 mm, no grid)) and set in a batch type electric furnace.

Then, 6.1 kg of crystalline silicon nitride powder was obtained in the same manner as in Example 1. Table 2 shows characteristic values of the obtained silicon nitride powder, such as crystallinity, α phase content, particle shape, specific surface area, tap density, press molding density, and particle size distribution.
Shown in FIG. 3 shows a scanning electron micrograph of the obtained powder.

Comparative Examples 2 and 3 The same amorphous silicon nitride powder as used in Example 1 was ground by a vibrating mill and then filled in a carbon crucible having a lattice spacing shown in Table 1. Was set in a batch type electric furnace.

Next, firing was performed in the same manner as in Example 1. In Comparative Example 2, 3.3 kg of crystalline silicon nitride powder was obtained, and in Comparative Example 3, 5.4 kg of crystalline silicon nitride powder was obtained. In the case of Comparative Example 2, not only the workability of filling and unloading the powder was poor, but also the powder filling amount per crucible was greatly reduced, the production efficiency was deteriorated, and a desired amount of crystalline nitride was obtained. Silicon powder could not be obtained. Table 2 shows characteristic values of the obtained silicon nitride powder such as crystallinity, α phase content, particle shape, specific surface area, tap density, press molding density, and particle size distribution.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

By using the crucible of the present invention, a large amount of crystalline silicon nitride powder composed of equiaxed granular particles having a uniform particle size and having excellent filling characteristics can be produced with high productivity.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of the crucible of the present invention.

FIG. 2 is a scanning electron microscope photograph instead of a drawing showing the particle structure of the crystalline silicon nitride powder obtained in Example 1 of the present invention.

FIG. 3 is a scanning electron microscope photograph instead of a drawing showing the particle structure of the crystalline silicon nitride powder obtained in Comparative Example 1 of the present invention.

Claims (2)

[Claims] An amorphous silicon nitride powder and / or an amorphous silicon nitride powder in a firing furnace.
Alternatively, a box-shaped crucible used for firing a nitrogen-containing silane compound into crystalline silicon nitride powder, wherein 1
A crucible for firing silicon nitride powder, wherein a lattice is provided at intervals of 5 to 80 mm. 2. The crucible for firing silicon nitride powder according to claim 1, wherein the thickness of the lattice is 4 to 20 mm.