JP2788045B2 - Method for producing fine silicon nitride powder - Google Patents

Description

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, a method of producing a silicon nitride powder by heating a silica powder at 800 to 1600 ° C. in NH ₃ gas or a mixed gas of NH ₃ and C _m H _n (hydrocarbon). A powder obtained by mixing at least one of silicon nitride, silicon carbide, silicon oxynitride, and metal silicon as seed particles in an NH ₃ gas or a mixed gas of NH ₃ and C _m H _n (hydrocarbon) is used for 800 A method of producing silicon nitride powder by heat treatment at 1600 ° C. (for example,
-162516) is known.

[Problems to be solved by the invention]

In the method described above, the primary particle diameter of the generated silicon nitride powder is considerably large, 2 to 10 μm. For this reason, when sintering this silicon nitride powder, it is difficult to obtain a dense silicon nitride sintered body having low sinterability. In order to improve these points, when pulverizing silicon nitride powder using, for example, a rolling ball mill, a considerably long time of 100 to 200 hours is required. However, when such long-time pulverization is performed, enormous energy is consumed, and in some cases, problems such as contamination of impurities from the pulverization medium occur.

On the other hand, in the first method, if silicon nitride or the like added as seed particles is reduced to 0.5 μm or less, relatively fine silicon nitride powder having a primary particle diameter of 1 μm or less can be obtained. However, in this case, similarly, when the seed particles are pulverized using a rolling ball mill to make the particles fine, for example, a considerably long time of 50 to 150 hours is required, and the above-described problem occurs.

The present invention has been made to solve the above problems, and has as its object to provide a method capable of obtaining fine silicon nitride fine powder without performing long-time pulverization.

Measure the effect for Solving the Problems] manufacturing method of the fine silicon nitride fine powder of the present invention, a mixed gas of NH ₃ and C _m H _n the silica powder, the first step of heat treatment at 800 to 1400 ° C. And a second step of pulverizing the obtained product, and the obtained pulverized product in NH ₃ gas, or NH ₃ and C _m H _n ,
A third step of performing a heat treatment at 1200 to 1600 ° C. in a mixed gas of at least one of CO and an inert gas.

In the present invention, the first step is basically a reaction for generating Si ₃ N ₄ according to the following formula (a).

3SiO ₂ + 4NH ₃ → Si ₃ N ₄ + 6H ₂ O (a) In this first step, C _m H _n (hydrocarbon gas) is added because H ₂ O generated by the equation (a) is converted into (b) This is because the partial pressure of H ₂ O is reduced by performing the reaction according to the formula (1), and the reaction rate of the formula (a) is increased.

Although the process in which the reaction of the formula (a) proceeds and silicon nitride particles are generated has not been sufficiently elucidated,
According to the study of the present inventors, it is presumed that the following steps are followed. That is, first, particles that can be said to be very fine silicon nitride precursors of about 10 nm, which do not satisfy the perfect crystal structure and the stoichiometric ratio (hereinafter referred to as silicon nitride precursors), are generated. Individually assemble to form primary particles of silicon nitride having a nearly perfect crystal structure and stoichiometry. At this time, it is considered that the size of the primary particles is determined by the number of silicon nitride precursors to be assembled.

The heating temperature in the first step was set at 800 to 1400 ° C.
When the temperature is lower than 00 ° C., the reaction does not substantially proceed, and when the temperature exceeds 1400 ° C., substantially large primary particles having a particle size of 2 to 10 μm are immediately generated. This is because it will not be possible.

The mixing ratio of NH ₃ and C _m H _n in the first step is such that C _m H _{n is changed} to CH ₄
It is desirable that NH ₃ / CH ₄ = 0.5 to 2000, more preferably 1 to 1000, in terms of volume ratio in terms of volume.

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

For the pulverization in the second step, a commonly used pulverizer such as a rolling ball mill, a vibrating ball mill, a planetary mill, and a medium stirring mill can be used.

The crushing time is, for example, 5 to 10 hours when 4 kg of a ball having a diameter of 16 mm is charged together with 30 g of the material to be crushed into a ball mill having an inner diameter of 160 mm and an inner volume of 4.8. The pulverization time varies depending on the type and size of the pulverizer, but may be 10 hours or less, which is much shorter than in the past.

In the pulverization step, pulverization may be performed in the presence of a pulverization assistant. Si, Al, Zr, Y, M
g, Ti, Ce or La or nitrides, carbides, borides or oxides of these elements. Further, the amount of the grinding aid to be added is preferably 0.005 to 2 parts by weight based on 1 part by weight of the starting silica powder.
In the case where the pulverization assistant is thus coexisted, the primary particle diameter of silicon nitride finally obtained becomes small.

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

The heating temperature in the third step was set to 1200 to 1600 ° C.
If the temperature is lower than 1200 ° C., silicon nitride having a complete crystal structure and a stoichiometric ratio cannot be obtained. If the temperature is higher than 1600 ° C., the amount of fibrous silicon nitride increases. A more preferred heating temperature is 1400-1600 ° C.

In this third step, NH ₃ gas or N
H ₃ and C _m H _n, although a mixed gas of at least one of CO or inert gas is used, NH ₃ and C _m H _n, a mixed gas of at least one of CO or an inert gas When used, the content of NH ₃ is desirably 50% by volume or more. This is because when the content of NH ₃ is less than 50% by volume, the total amount of oxygen and the total amount of carbon in the generated silicon nitride powder increases, and fibrous silicon nitride is generated.

According to the method of the present invention, fine silicon nitride fine particles can be produced without using seed particles and in spite of the fact that the pulverization time can be greatly reduced as compared with the conventional method.

〔Example〕

 Hereinafter, embodiments of the present invention will be described.

Examples 1 to 6 and Comparative Examples 1 to 6 As a first step, 50 g of silica powder was filled in a silicon nitride container, and this container was inserted into a tubular furnace having an alumina core tube having an inner diameter of 100 mm. At the temperatures shown in the table, NH ₃ was supplied at a flow rate of 10 / min, and C ₃ H ₈ was supplied at a flow rate of 1 / min, and heated for 10 hours.

Next, as a second step, 30 g of the obtained product powder was
With 4 kg of 16 mm diameter ball, inner diameter 160 mm, inner volume 4.8
And then pulverized at 60 rpm for 10 hours. Note that this pulverizing step was not performed for Comparative Example 5.

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

The powder thus obtained was subjected to measurement of total oxygen content and total carbon content, identification of a crystal phase by X-ray diffraction, and observation and measurement of particle shape and primary particle diameter by SEM. Table 1 shows the results.

[Effects of the Invention] As described in detail above, according to the method of the present invention, fine silicon nitride fine powder can be obtained without adding seed particles and without performing long-time pulverization. As a result, the sinterability of the fine silicon nitride powder is improved, and a dense silicon nitride sintered body can be obtained. Therefore,
The industrial value of the method of the present invention is extremely large.

Claims (1)

(57) [Claims] 1. A mixed gas of a silica powder and NH ₃ and C _m H _n, 8
A first step of heat treatment at 00 to 1400 ° C., a second step of pulverizing the obtained product, and NH ₃
A heat treatment at 1200 to 1600 ° C. in a gas or in a mixed gas of NH ₃ and at least one of C _m H _n , CO or an inert gas. A method for producing silicon fine powder.