JPH06305718A - Production of alpha-silicon nitride powder - Google Patents

Abstract

PURPOSE:To obtain alpha-silicon nitride powder capable of giving a silicon nitride sintered compact excellent in strength even at high temp. by sintering. CONSTITUTION:Ytterbium oxide preferably having <=1mum particle diameter is added to metallic silicon powder preferably having 3-6mum average particle diameter by 5-20 pts.wt. per 100 pts.wt. of the silicon powder and the silicon powder is nitrided preferably at 1,350-1,500 deg.C for 1-5hr in an atmosphere of gaseous nitrogen or a nitrogen-contg. nonoxidizing gas to produce the objective alpha-silicon nitride powder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an α-type silicon nitride powder capable of obtaining a sintered body having high strength even at high temperature.

[0002]

2. Description of the Related Art Conventionally, a silicon nitride powder sintered body obtained by sintering silicon nitride powder has been developed for various uses as a high temperature strength material. Various studies have been carried out in order to obtain a sintered body having high strength.

Here, as a raw material for a sintered body, a silicon nitride powder having a high α-conversion rate has been conventionally required, and a method of directly nitriding a metal silicon powder to obtain an α-type silicon nitride powder. There have been proposed various methods, and in particular, many methods have been proposed for increasing the α of silicon nitride by adding a metal or a metal compound to the metal silicon powder. For example, JP-A-54-15499 discloses metallic iron and iron compounds, JP-A-54-58700.
Palladium oxide in JP-A-54-120298.
Japanese Patent Laid-Open No. 59-92906 discloses a calcium compound.
Japanese Patent Laid-Open Publication No. 61-2590.
No. 6 discloses a method of adding vanadium and a vanadium compound, and JP-A-61-2560 proposes a method of adding manganese and a manganese compound when nitriding a metal silicon powder.

However, since the above-mentioned nitriding reaction is an exothermic reaction, α-type silicon nitride is likely to be transformed into high-temperature stable β-type silicon nitride, which limits the amount of metallic silicon powder that can be charged at the time of nitriding, resulting in mass productivity. There is a problem of being inferior.
In addition, depending on the additive added when nitriding the metal silicon powder, not only the strength at high temperature but also the strength at room temperature may be adversely affected. Therefore, the silicon nitride obtained by the above method It is generally practiced to pulverize the powder into fine powder and then subject the additive to a chemical treatment such as acid treatment to remove the additive.

On the other hand, when sintering a silicon nitride powder to obtain a sintered body, it is a general method to add a sintering aid such as various oxides to the silicon nitride powder and perform liquid phase sintering. However, the grain boundary phase component in the obtained sintered body structure depends on the above-mentioned sintering aid, and the lowering of the viscosity of the grain boundary phase component causes the lowering of the viscosity of the sintered body at high temperature. Depending on the type of sintering aid, a high temperature and high strength silicon nitride powder sintered body may not be obtained.

The present invention has been made in view of the above circumstances.
An object of the present invention is to provide a method for producing an α-type silicon nitride powder, which can obtain a silicon nitride sintered body having high strength even at a high temperature.

[0007]

Means and Actions for Solving the Problems As a result of intensive studies for achieving the above-mentioned object, the present inventor has found that preferably 100 parts by weight of metal silicon powder having an average particle diameter of 3 to 6 μm is preferably particles. Ytterbium oxide (Yb ₂ O ₃ ) having a diameter of 1 μm or less is added in an amount of 5 to 20 parts by weight, preferably 13 in a nitrogen gas or a non-oxidizing gas atmosphere containing nitrogen.
By nitriding the metal silicon powder at a temperature of 50 to 1500 ° C. for 1 to 5 hours, a highly α-type α-type silicon nitride powder can be produced, and the silicon nitride obtained from the silicon nitride powder can be produced. It has been found that the sintered body has excellent strength even at high temperatures.

That is, the present inventor has conducted various studies on a method for obtaining a highly alpha-converted silicon nitride powder. As a result, the metallic silicon powder is heated in a nitrogen gas or a non-oxidizing gas atmosphere containing nitrogen. In the normal nitriding method,
Surprisingly, when Yb ₂ O _{3 is} added among the rare earth oxides that have been widely used in the conventional sintering of silicon nitride powder as an additive for nitriding metallic silicon powder,
As described above, the inventors have found that highly α-converted silicon nitride powder can be obtained, and completed the present invention.

Here, it is considered that a columnar β-type silicon nitride powder, which has been conventionally produced when sintering a silicon nitride powder, is intricately entangled with the α-type silicon nitride powder to form a high-strength sintered body. Therefore, it is necessary to use α-type silicon nitride powder as a raw material for obtaining a high-strength silicon nitride sintered body. Also recently
In order to obtain a silicon nitride powder sintered body having high strength at high temperature, it is necessary that the composition of the grain boundary phase in the sintered body structure is capable of preventing a decrease in viscosity at high temperature. Various findings have been announced, and various sintering aids have been added when sintering the silicon nitride powder in order to make the components of the grain boundary phase as described above, Among them, the rare earth oxide itself has a high melting point, and the compound generated by the reaction with the silica layer (SiO ₂ ) existing on the surface of the silicon nitride powder particles that reacts during sintering also contributes to sintering. It is reported that, depending on the type of the agent, the compound has a high melting point, and thus it is possible to prevent the viscosity of the grain boundary phase from decreasing.

As described above, conventionally, when a silicon nitride powder is sintered, a sintering aid such as a rare earth oxide is added to improve the high temperature and high strength of the sintered body obtained by sintering the silicon nitride powder. In contrast to this, in the present invention, on the other hand, highly nitrided silicon nitride powder is obtained by adding ytterbium oxide among rare earth oxides when nitriding the metal silicon powder. Although this ytterbium oxide itself has a low melting point, it is considered that it contributes to the low temperature reaction when nitriding the metal silicon powder, and therefore a highly α-type α-type silicon nitride powder can be obtained.

The present invention will be described in more detail below. In the method for producing α-type silicon nitride powder of the present invention, ytterbium oxide (Yb) is added to 100 parts by weight of metallic silicon powder.
₂ O ₃ ) is added in an amount of 5 to 20 parts by weight, and the metal silicon powder is nitrided in a nitrogen gas or a non-oxidizing gas atmosphere containing nitrogen.

Here, it is preferable that the raw material metal silicon powder has an average particle diameter of 3 to 6 μm, particularly 4 to 5 μm.

The ytterbium oxide (Yb ₂ O ₃ ) added to the metallic silicon powder preferably has a purity of 99.9% or more in consideration of the physical properties of the sintered body after nitriding. Therefore, the average particle size is preferably 1 μm or less.

The amount of ytterbium oxide added is 5 to 20 parts with respect to 100 parts (parts by weight, the same hereinafter) of metallic silicon powder, but it is particularly preferably 5 to 10 parts. If the amount added is less than 5 parts, it is difficult to obtain highly α-type silicon nitride powder, and if it exceeds 20 parts, the grain boundary phase of the sintered body obtained by sintering the obtained silicon nitride powder is high in temperature. Since the viscosity is lowered, it adversely affects the high temperature and high strength of the obtained sintered body.

The gas for nitriding the metal silicon powder is nitrogen or a non-oxidizing gas containing nitrogen.
Examples of the non-oxidizing gas containing nitrogen include a mixed gas of hydrogen gas and nitrogen gas, particularly a mixed gas of nitrogen gas containing hydrogen gas in an amount of about 0 to 25% by volume and ammonia gas.

Further, when the metal silicon powder is nitrided in the gas atmosphere, the nitriding temperature is 1350 to 1500 ° C.
Then, the nitriding time can be set to about 1 to 5 hours.

After the completion of nitriding, the silicon nitride powder may be pulverized by a method such as a wet stirring medium method, if necessary. In addition,
The obtained silicon nitride powder can be used as it is as a raw material for a silicon nitride sintered body without chemical treatment such as acid treatment.

The silicon nitride powder obtained in the present invention can be made into a silicon nitride sintered body by a conventional method. However, since this silicon nitride powder is highly α-converted, it can be sintered to obtain It is possible to obtain a silicon nitride sintered body which is excellent in strength even at high temperature, because the structure of the sintered body at high temperature, especially the viscosity reduction in the grain boundary phase, is prevented.

[0019]

EXAMPLES The present invention will be specifically described below by showing Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[Examples 1 to 3 and Comparative Examples 1 to 10] 26.7 mol (7) of metal silicon powder having an average particle diameter of 4 to 5 μm.
50 g) was added with the rare earth oxides shown in Table 1 in the amount equivalent to the cations shown in Table 1 and charged on a silicon nitride tray so that the height of the charging layer was constant, and this was mixed with N ₂ and H _2. In a gas atmosphere, heating and nitriding were performed at a maximum temperature of 1400 ° C. for 2 hours according to a conventional method to obtain silicon nitride powder.

Here, the alpha conversion of the silicon nitride powder is measured by an X-ray diffractometer (Geiger flex, RAD-II).
A) is measured under the following measurement conditions, and α is calculated by the following formula.
The rate of conversion was calculated. Targate: Cu Filter: Ni Voltage: 30 kV Current: 15 mA Count, scale: 4000 c / s Time constant: 0.5 sec Scan speed: 2 degrees / min Chart speed: 2 cm / min Divergence slit: 1 degree Receiving slit: 0.3 mm Scatter slit: 1 degree Viewing angle: 28-37 degrees

[0022]

[Equation 1]

[0023]

[Table 1]

[0024]

According to the manufacturing method of the present invention, the α-type silicon nitride powder can be easily and reliably manufactured, and the silicon nitride powder manufactured by the manufacturing method of the present invention can be sintered. Thereby, a silicon nitride sintered body having excellent strength even at high temperature can be obtained.

Claims (1)

[Claims] 1. The present invention is characterized in that 5 to 20 parts by weight of ytterbium oxide is added to 100 parts by weight of metal silicon powder, and the metal silicon powder is nitrided in a nitrogen gas or a non-oxidizing gas atmosphere containing nitrogen. Method for producing α-type silicon nitride powder.