JPH02208211A - Production of fine silicon nitride powder - Google Patents

Abstract

PURPOSE:To obtain fine silicon nitride powder without carrying out pulverization for a long period by heat-treating silica powder in a mixed gas of NH3 and a hydrocarbon, pulverizing the heat-treated powder and further heat-treating the pulverization treatment product in a specific mixed gas. CONSTITUTION:Silica powder is heat-treated in a mixed gas of NH3 and a hydrocarbon at 800-1400 deg.C. The resultant product is then subjected to pulverization treatment. The obtained pulverization treatment product is further heat- treated in NH3 gas or a mixed gas of NH3 and at least one of the hydrocarbon, CO and an inert gas at 1200-1600 deg.C to afford the objective fine silicon nitride powder. The above-mentioned pulverization is carried out for 5-10hr if, e.g. 30g substance to be pulverized, together with 4kg balls having 16mm diameter, is charged into a ball mill having 160mm inside diameter and 4.8l internal volume. If the aforementioned heating temperature is <1200 deg.C, silicon nitride having the complete crystal structure and stoichiometric ratio is not obtained. If the temperature exceeds 1600 deg.C, contamination of fibrous silicon nitride is increased. Both cases are not preferred.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for producing fine silicon nitride powder.

[Conventional technology]

Conventionally, silicon nitride powder has been produced, for example, by the following method. That is, ■silica powder is mixed with NI(
3. A method for producing silicon nitride powder by heat treatment at 800 to 1600°C in a gas or a mixed gas of NH3 and COH (hydrocarbon). ■ Silicon nitride, silicon carbide, as seed particles in silica powder, A powder containing at least one of silicon oxynitride or silicon metal is mixed in NH, gas, or NH3 and Cff1.
800-1600℃ in mixed gas with H, (hydrocarbon)
A method of manufacturing silicon nitride powder by heat treatment with a method (for example, Japanese Patent Application Laid-Open No. 83162516) is known.

[Problem to be solved by the invention]

In the method (2) described above, the primary particle size of the silicon nitride powder produced is considerably large, ranging from 2 to 10 μm. For this reason, when this silicon nitride powder is sintered, the sinterability is low, making it difficult to obtain a dense silicon nitride sintered body. In order to improve these points, when the silicon nitride powder is pulverized using, for example, a transfer ball mill, it takes a long time of 100 to 200 hours. However, such long-term grinding consumes a huge amount of energy and, in some cases, causes problems such as contamination of impurities from the grinding media.

On the other hand, in method (2), if the silicon nitride etc. added as seed particles are made finer to 0.5- or less, the primary particle size is 1-
The following relatively fine silicon nitride powder can be obtained. However, in this case as well, when pulverizing the seed particles using a transfer ball mill, for example, to make the seed particles finer,
It takes a considerable amount of time, 50 to 150 hours, and the above-mentioned problems arise.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a method capable of obtaining fine silicon nitride powder without requiring long-term pulverization.

[Means and actions to solve the problem]

The method for producing fine silicon nitride powder of the present invention involves heating silica powder at 800 to 1400°C in a mixed gas of NH3 and C□H7.
a first step of heat-treating the obtained product; a second step of pulverizing the obtained product; and a second step of pulverizing the obtained product in NH3 gas.
or 1200 to 1600°C in a mixed gas of NH, and at least one of C□H4, CO, or an inert gas.
The present invention is characterized by comprising a third step of heat treatment.

In the present invention, the first step is basically a reaction in which 51 g of N4 is produced according to the following formula (a).

3 S i02 +4 NH3→S 13 H4+6H
20-(a) The reason for adding C□H, (hydrocarbon gas) in this first step is to add H20 produced by equation (a) to (
This is to lower the partial pressure of H20 and increase the reaction rate of formula (a) by reacting according to formula (b).

Although the process by which the reaction of formula (a) proceeds and silicon nitride particles are generated has not yet been fully elucidated, it is estimated that the following process follows according to the research conducted by the present inventors. be done. That is, first, very fine particles of about 10 nm that can be called silicon nitride precursors (hereinafter referred to as silicon nitride precursors) that do not satisfy a perfect crystal structure and stoichiometry are generated, and what are these particles? The particles collectively form primary particles of silicon nitride having a nearly perfect crystal structure and stoichiometry. At this time, it is thought that the size of the -order ion is determined by the number of silicon nitride precursors that aggregate.

The heating temperature in this first step was set at 800 to 1400°C because the reaction does not substantially proceed below 800°C.
This is because when the temperature exceeds 0°C, considerably large primary particles with a particle size of 2 to 1Oρ are immediately generated, and it becomes impossible to obtain fine silicon nitride powder even if the subsequent steps are carried out.

The mixing ratio of NH and C□H in the first step is Cm
H, is converted to CH4 and the volume ratio is N H3' / CH
4-0.5 to 2000, more preferably 1 to 1000.

In the present invention, the second pulverizing step is a step for physically separating the silicon nitride precursor to suppress coarsening of the primary particles of silicon nitride.

For the second step of pulverization, commonly used pulverizers such as a transfer ball mill, a vibrating ball mill, a planetary mill, and a media stirring mill can be used.

The grinding time is, for example, 5 to 10 hours when 4 kg of balls with a diameter of 16 mm are charged together with 30 g of the material to be ground into a ball mill with an inner diameter of 160 mm and an internal volume of 4.8 g.

Although the grinding time varies depending on the type and size of the grinder, it may be 10 hours or less in any case, which is much shorter than conventional methods.

In addition, at the time of a pulverization process, pulverization may be performed in the presence of a pulverization aid. As grinding aids, 5i1A, Q SZ
r s Y s M g ST t SCe or La.

Alternatively, nitrides, carbides, borides, or oxides of these elements can be mentioned. The amount of grinding aid added is 0.00 parts by weight of silica powder as the starting material.
The amount is preferably 5 to 2 parts by weight. When a grinding aid is present in this way, the primary particle diameter of silicon nitride finally obtained becomes smaller.

In the present invention, the third step is a step of forming primary particles of silicon nitride having an almost perfect crystal structure and stoichiometric ratio by aggregating silicon nitride precursors.

The reason why the heating temperature in this third step was set to 1200 to 16009C is that silicon nitride with a perfect crystal structure and stoichiometric ratio cannot be obtained below 200°C, and fibrous silicon nitride cannot be obtained when it exceeds 1600°C. This is because the amount of contamination increases. A more preferable heating temperature is 1400 to 1600°C.

In this third step, NH, gas, or a mixed gas of NH, and at least one of C, , CO, or an inert gas is used as the atmospheric gas, but NH3
When using a mixed gas of at least one of Cff, H, Co, or an inert gas, the content of NH3 is desirably 50% by volume or more. This is NH3
This is because if the content is less than 50% by volume, the total amount of oxygen and total carbon in the produced silicon nitride powder will increase, or fibrous silicon nitride will be produced.

According to the method of the present invention, fine silicon nitride particles can be produced without using seed particles and while the grinding time can be significantly shortened compared to the conventional method.

〔Example〕

The present invention will be explained in detail below.

Examples 1 to 6 and Comparative Examples 1 to 6 In the first step, 50 g of silica powder was filled into a silicon nitride container, and this container was inserted into a tube furnace having an alumina furnace core tube with an inner diameter of 100 mm. At the temperature shown in the table, NH, at a flow rate of 10Ω/min, C3Hs at 1
Each was supplied at a flow rate of Ω/min and heated for 10 hours.

Next, as a second step, 30 g of the obtained product powder was
With a ball 4 kg with a diameter of 16 mm, an inner diameter LGO
The mixture was placed in a silicon nitride pot with an mr of 6 and an internal volume of 4.8Ω, and pulverized at 80 rpm for 10 hours. Note that in Comparative Example 5, this pulverization step was not performed.

Next, in the third step, the obtained pulverized product is heated in the atmosphere shown in Table 1, at the temperature shown in the table, for the time shown in the table, using the same container and tube furnace as in the first step. As a result, silicon nitride fine powder was obtained.

Regarding the powder thus obtained, the total oxygen content and total carbon content were measured, the crystal phase was identified by X-ray diffraction, and the particle shape and carbon particle diameter were observed and measured by SEM. These results are shown in Table 1.

[Effect of the invention] As detailed above, according to the non-inventive method n, 1, -, fine silicon nitride fine powder can be produced without adding species I particles and without carrying out long-term pulverization. Obtainable. As a result, the sinterability of the silicon nitride cumulative powder becomes good, and a dense silicon nitride sintered body can be obtained. Therefore, the value of 71〉5 Invention Method 4) is extremely large.

Claims (1)

[Claims] Silica powder in a mixed gas of NH_3 and C_mH_n,
The first step is heat treatment at 800 to 1400°C, the second step is pulverization of the obtained product, and the pulverized product is pulverized in NH_3 gas or NH_3 and C_mH_n,C.
A method for producing fine silicon nitride powder, comprising a third step of heat treatment at 1200 to 1600° C. in a mixed gas with at least one of O or an inert gas.