JPS6230125B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for producing silicon nitride powder, particularly α
The present invention relates to a method for producing silicon nitride powder having a high silicon nitride content.

Silicon nitride (hereinafter abbreviated as Si ₃ N ₄ ) has a sintered body that has excellent heat resistance, corrosion resistance, and wear resistance, as well as high hardness and light weight. Because of this, it is attracting attention as a new ceramic material, and is used in gas turbines,
It is expected to be used as cutting tools, high-temperature bearings, and mechanical sealing materials.

On the other hand, regarding this Si ₃ N ₄ , α
Both type Si ₃ N ₄ and β-type Si ₃ N ₄ exist, but for the various uses mentioned above, sintered bodies of raw material powder mainly composed of α-type Si ₃ N ₄ are required at room temperature or above 1000°C. Even at high temperatures, it exhibits better physical properties than sintered bodies obtained from powder materials mainly composed of β-type Si ₃ N ₄ , and α-type Si ₃ N ₄ is particularly suitable for cutting tool chips that require wear resistance. It is known that sintered bodies obtained from powders of

Therefore, _it is desired to produce and supply Si ₃ N ₄ powder with _a high content of α-type Si ₃ N ₄ .
In order to produce Si ₃ N ₄ , this reaction must be carried out at as low a temperature as possible; however, since this reaction is exothermic, it is necessary to cool the reaction system; Since it is a low-temperature reaction, it has the disadvantage that the reaction time is long, and therefore it is considered to be extremely difficult to produce Si ₃ N ₄ containing 90% or more of α-type Si ₃ N ₄ .

The present invention solves these disadvantages by using α-type Si ₃ N ₄
This relates to a method for producing Si ₃ N ₄ powder containing a high content of 50% or more of α-type silicon nitride and 50% or more of β-type silicon nitride obtained by the reaction between metallic silicon and nitrogen gas. This method is characterized by pulverizing silicon nitride containing 50% or less to an average particle size of 5 μm or less, and then classifying it and recovering the portion with a small particle size.

To explain this, the present inventors have investigated various methods of obtaining Si _{3 N 4 powder with a high content of α-type Si 3 N 4 ,} and have investigated the reaction system between metallic silicon and nitrogen gas. However, it is difficult to obtain Si ₃ N ₄ containing 90% or more of α-type Si ₃ N ₄ , so we decided to obtain it by physical means, and
Research on the separation method of Si ₃ N ₄ and β-type Si ₃ N ₄ revealed that when Si 3 N 4 produced by a chemical reaction between metallic silicon and nitrogen gas is crushed to about 5 μm, α-type Si ₃ N ₄ can be separated. In this reaction, Si ₃ N ₄ tends to develop as needle-like crystals, which are easily broken during the crushing operation. Therefore, when the thus-pulverized product is then classified, it is surprisingly possible to find small particles with a small particle size. It was discovered that the portion had a high content of α-type Si ₃ N ₄ , and the present invention was completed by further study on this.

Si ₃ N ₄ , which is used as the starting material in the method of the present invention, is said to be produced by the direct reaction of metallic silicon and nitrogen gas, which is a conventionally known method. If the content of α-type Si ₃ N ₄ is 50% or less, α-type Si 3 N 4 will remain even after the subsequent classification process.
This is required to contain at least 50% α-type Si ₃ N ₄ , as it becomes difficult to obtain a high content of Si ₃ N ₄ ;
The following β-type Si ₃ N ₄ and metal impurities such as Fe, Al, Ca etc.
The content may be 0.5% or less, Si 0.3% or less, and SiO ₂ 1.5% or less.

The Si ₃ N ₄ as the starting material may be pulverized using any known means, such as a jet mill, a ball mill, an attritor, a vibration mill, a crusher, etc., but this pulverization is insufficient. and alpha type
Since the effect of Si ₃ N ₄ being easily pulverized is no longer sufficient, it is necessary to pulverize it to about 5 μm. Also, this crushing
Si ₃ N ₄ powder may be pulverized to a submicron size of 5 μm or less, but if it is too fine, the separation efficiency of α-type and β-type by subsequent classification will be rather deteriorated, so this should be done in the range of 1 μm to 5 μm. It is recommended that the range be within the range of .

The Si ₃ N ₄ powder thus pulverized is then subjected to a classification process, which can be done by either air sieving or water elutriation. In the case of elutriation, a known hydraulic classifier may be used. In this classification process, the Si ₃ N ₄ powder is
Since the Si ₃ N 4 is crushed to a size of less than 1 μm, it is sufficient to separate it into, for example, those of 1 μm or more and those smaller than 1 μm, which means that α-type Si 3 N ₄ is easier to crush than β-type Si ₃ N ₄ . α-type in the part less than 1 μm from
The amount of Si ₃ N ₄ increases, and the particles with small particle size obtained by classification are α-type Si ₃ N _4.
According to this, if a relatively high content, for example 80%, is used as a starting material, it will contain α-type Si ₃ N ₄ at a high content of up to 90%. The industrial advantage is that Si 3 N 4 containing Si ₃ N ₄ powder can be easily obtained.

Next, examples of the present invention will be given.

Example 1 70% α-type Si ₃ N ₄ made by the reaction of metallic silicon and nitrogen gas with an average particle size of 325 mesh,
Using a jet mill, 10 kg of commercially available Si ₃ N ₄ powder containing 30% of β-type Si ₃ N ₄ was milled at a raw material supply rate of 3 kg/
hour, air volume ^2.0m3 /min, pusher nozzle 7kg/
cm ² , grinding nozzle at 5 to 6 kg/cm ² to give an average particle size of 5 μm, and elutriate this pulverized product with a hydraulic classifier to reduce the average particle size to 1 μm.
When I collected 5 kg of Si 3 N ₄ , I found that it was Si ₃ N 4 containing 85% α-type Si ₃ N ₄ by X-ray diffraction _{. N4}
It was powdery.

In addition, 5 kg of the Si ₃ N ₄ powder containing 85% α-type Si ₃ N ₄ obtained here was classified into those with an average particle size of 0.8 μm or more and those with an average particle size of 0.8 μm or less, and the When we investigated the content of α-type Si ₃ N ₄ in the
Those with a diameter of m or more contained 84%, and those with a diameter of 0.8 μm or less contained 87% of α-type Si ₃ N ₄ .

Example 2 92% α-type Si 3 N 4 and β-type Si ₃ N ₄ made by reaction of metal silicon and nitrogen gas with an average particle diameter of 7 μm
Si ₃ N ₄ powder containing 8% Si ₃ N ₄ was charged into a vibratory mill filled with 80% media of 3/8 inch diameter, vibration frequency 1000 cpm, vibration width 10 mm, n-hexane wet method, amount of powder supplied. It was pulverized under the processing conditions of 1 kg/hour and 1 hour of pulverization to obtain Si ₃ N ₄ powder with an average particle size of 4.5 μm.

Next, this powder was divided into those with an average particle size of 1 μm or more and those with an average particle size of 1 μm or less using a wind sieve classifier, and the particles with an average particle size of 1 μm or less accounted for ₄₀ % by weight. When the content of ₄ was examined by X-ray diffraction, it was found to contain 98% α-type Si ₃ N ₄ .

Comparative Example The same sample as in Example 1 was used, except that the feed rate to the jet mill was changed to 5 kg/hour.
When this was pulverized under the same conditions as above, Si ₃ N ₄ powder with an average particle size of 13 μm was obtained.

Then, when this was sent to a wind sieve device and recovered using a cyclone and back filter, 80% of it was
was collected using a cyclone, and the average particle size of these collected powders was 15 μm for the cyclone collected powder and 3 μm for the back filter collected powder.
The content of Si ₃ N ₄ remained unchanged at 70% in the cyclone-recovered powder, and only slightly increased to 72% in the back-filter recovered powder.

Claims (1)

[Claims] 1 α obtained from the reaction of metallic silicon and nitrogen gas
50% or more type silicon nitride, 50% β type silicon nitride
Silicon nitride powder with increased content of α-type silicon nitride, characterized by pulverizing the silicon nitride containing the following to an average particle size of 5 μm or less, classifying it, and recovering the small particle size part. manufacturing method.