JPH04114908A - Silicon nitride powder - Google Patents

Abstract

PURPOSE:To obtain silicon nitride powder providing sintered powder having excellent strength by specifying alpha fraction ratio, BET specific surface area, average particle diameter and inner oxygen content. CONSTITUTION:This silicon nitride powder is powder having >=90% alpha fraction ratio, >=10m<2>/g BET specific surface area, <=0.8mum average particle diameter and >0.5wt.% inner oxygen content. In the powder, when the inner oxygen content is <0.5wt.%, strength of obtained sintered material is reduced, the purpose is not attained. When the alpha fraction ratio is <90%, problems with respect to strength are caused. When the BET specific surface area is <10m<2>/g and the average particle diameter exceeds 0.8mum, sintering properties are inferior.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to silicon nitride powder from which a sintered body having excellent strength can be obtained.

Silicon nitride sintered bodies obtained by sintering silicon nitride powder have been developed for various uses as high-temperature strength materials, and it is difficult to obtain sintered bodies with high strength. Various studies are being conducted for this purpose.

Here, it is known that the oxygen content of silicon nitride powder, which is the raw material for sintering, affects the strength of the obtained sintered body (Ceramics 17 (1982) No. 10), and high-strength sintered A silicon nitride powder whose oxygen content is adjusted in order to obtain solid bodies has also been proposed (Japanese Unexamined Patent Publication No. 1-313308).

However, even with such a sintered body of silicon nitride powder, the strength may be insufficient depending on the application, and even higher strength is desired.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a silicon nitride powder from which a sintered body having excellent strength can be obtained.

As a result of intensive studies to achieve the above objectives, the inventor has determined that the α fraction is 90% or more and the BET specific surface area is 10 m.
By controlling the internal oxygen content of silicon nitride powder with an average particle size of 0.8/IAl or less to less than 0.5% by weight, it is possible to obtain a sintered body with extremely high strength. I found that there is something I can do.

That is, it has been thought that the properties of silicon nitride sintered bodies, especially the strength, are influenced by the oxygen content in the raw material powder as described above, but the present inventors have determined the existence form of oxygen in this raw material powder. After conducting various studies, we found that controlling the internal oxygen content to less than 0.5% by weight is extremely effective in improving the strength of the sintered body, especially when the α fraction is 90% or more. In a silicon nitride powder with a BET specific surface area of 10 m/g or more and an average particle diameter o of 8/JJrl or less, the internal oxygen content is controlled to less than 0.5% by weight, and more preferably the external oxygen content is 0.5% by weight. % or less, it has been found that a silicon nitride sintered body with significantly increased strength can be obtained from this silicon nitride powder.

Therefore, the present invention has an α fraction of 90% or more, a BET specific surface area of 1
Provided is a silicon nitride powder having an average particle size of 0 rrr/g or more, an average particle size of 0.8 pIl or less, and an internal oxygen content of less than 0.5% by weight.

Here, controlling the internal oxygen content of silicon nitride powder is also disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 1-313308, but the proposal in this publication is to control the surface (external) oxygen content by 0.3. ~0.6% by weight, internal oxygen content 0.5~1
．． The content is 1% by weight.

However, as shown in the comparative example below, those with an internal oxygen content of 0.5% by weight or more are inferior in terms of sintered body strength compared to those with less internal oxygen, and the internal oxygen content of silicon nitride powder is It is a new finding by the present inventor that the strength of the sintered body can be increased by controlling the amount of oxygen to less than 0.5% by weight.

The present invention will be explained in more detail below.

The silicon nitride powder of the present invention has an α fraction of 90 as described above.
% or more, BET specific surface area is 10 m2/g or more, preferably 11-1.5 m/g, and average particle size is 0.8
less than 0.4%, preferably 0.4 to 6IJXl, with an internal oxygen content of less than 0.5% by weight, preferably 0.2% by weight
The external oxygen content is preferably less than 0.5% by weight, more preferably 0.5% by weight or less.

When the internal oxygen content exceeds 0.5% by weight, the strength of the obtained sintered body decreases, making it impossible to achieve the object of the present invention. In addition, if the α fraction is less than 90%, problems will occur in terms of strength, and the BET specific surface area will be less than 10 rn'
If it is less than /g, the sinterability will be poor,
Furthermore, if the average particle diameter exceeds 0.8 tones, the sinterability will be poor.

Here, the internal oxygen content and external oxygen content can be measured using an oxygen analyzer such as TC-436 manufactured by LECO Co., Ltd. by heating mode analysis. In other words, in heating mode analysis, many peaks appear during the heating process;
These peaks are roughly classified into tail type (peaks with a tail) and symmetric types (peaks with line symmetry) using the following determination method, and the internal oxygen content and external oxygen content are determined using the following formulas.

Wjn-W'×ss+5T Wout = W' -Win Win: Internal oxygen content Wout: External oxygen content W・2 total oxygen amount (internal oxygen quantum external oxygen amount) Ss:
Integral value of symmetrical peak S□: Integral value of tail-type peak Here, the total oxygen amount is measured by a non-dispersive infrared absorption method.

Fixed symmetrical type (SS): From the apex 2 of peak 1 shown in Figure 1 to the middle part 4 of Ia3, which is lowered to the X-axis, draw a line parallel to the X-axis at the middle part 4. When the distances a and b from points 5 and 6 that intersect with peak 1 are measured by tL, that is, at the half value of peak 1 @c (a = a + b), a / b is 0.8≦ Peak 7 where a/b≦1.1 'I'/L' W (ST): Peak where 1.1<a/b at half-width C of peak 1 In addition, temperature increase mode analysis shown in Figure 2 In the chart, the symmetric and tail peaks are as shown.

Furthermore, it is preferable that the above-mentioned temperature increase mode analysis is carried out in the range of 0° C. to 2000° C. for about 0 to 300 seconds.

The above-mentioned silicon nitride powder is produced by controlling the oxygen content of the raw material silicon powder and the moisture content in the atmosphere in the normal direct nitriding method in which silicon metal powder is heated in a nitrogen gas atmosphere or a non-oxidizing gas atmosphere containing nitrogen. It can be manufactured by controlling. In this case, the particle size of the metal silicon powder is preferably 1 to 10 tones. Further, as the non-oxidizing gas atmosphere containing nitrogen, an atmosphere consisting of a mixed gas of hydrogen gas and nitrogen gas containing about 5 to 25% by volume of hydrogen gas is preferably used. Furthermore, the nitriding temperature is usually 120
The temperature is 0 to 1400°C, and the nitriding time is usually about 2 to 5 hours.

The silicon nitride powder of the present invention can be produced by using a metal silicon powder as the raw material having an oxygen content of 1% by weight or less in the above manufacturing method, and reducing the amount of moisture in the atmosphere to the metal silicon powder. It can be manufactured by con-I-rolling depending on the oxygen content. That is, when the oxygen content of the raw metal powder is 0.4 to 1% by weight, the water content is less than 11,000 pp, preferably 500 pp.
pm while the oxygen content is controlled to less than 0.4
If the water content is less than 1000-6000pp by weight
m, preferably 4000-5000 ppm, the internal oxygen content of the silicon nitride powder can be controlled to less than 0.5% by weight.

In this case, the internal oxygen content of the obtained silicon nitride powder can be adjusted by increasing or decreasing the moisture content in the atmosphere within the above range.

By sintering the silicon nitride powder of the present invention, a silicon nitride sintered body having excellent strength can be obtained.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[Examples 1 to 5. Comparative Examples 1 to 3] Metallic silicon powder having an oxygen content in the range of 0.1 to 0.4% by weight was passed through water with a mixed gas of N2 and N2 under a gas atmosphere containing 4.300 ppm of water. were heated and nitrided according to conventional methods at a maximum temperature of 1380'C,
Each of these was wet-pulverized and acid-treated with a mixed acid of HF and HNO3 to obtain silicon nitride powder.

α fraction, average particle size, BET of these silicon nitride powders
Specific surface area, internal oxygen content, and external oxygen content were measured. The results are shown in Table 1.

Here, the internal oxygen content of the silicon nitride powder in Table 1 was measured by the above-mentioned heating mode analysis method, and the external oxygen content was determined by Horiba E.
This is the value obtained by subtracting the above internal oxygen amount from the total oxygen amount measured by MGA2800.

Note that FIG. 2 shows a chart of temperature increase pattern analysis conducted on the silicon nitride powder of Example 1.

Next, 90 parts of the silicon nitride powder (parts by weight, the same applies hereinafter)
37 parts of Y2O and 2033 parts of Afi were added to each, wet-mixed in a ball mill, dried, formed into a mold at a pressure of 2t/cJ, and sintered at 1800°C for 1 hour to form a rod-shaped sintered body (
3x4n volumes) were obtained. The three-point bending strength of this sintered body at room temperature was measured based on JIS R-1601. The results are also listed in Table 1.

From the results shown in Table 1, it was confirmed that the sintered body obtained from the silicon nitride powder of the present invention had improved strength by -10=.

[Examples 6-8. Comparative Examples 4 and 5] Examples except that silicon nitride powder having the α fraction, average particle diameter, specific surface area, internal oxygen amount, and external oxygen amount shown in Table 2 was used, and the sintering time was 4 hours. A rod-shaped sintered body (diameter 3 mm x length 4 mm) was obtained under the same conditions as 1.
The three-point bending strength at a temperature of 'C is JIS R-1,60.
Measured based on 1. The results are also listed in Table 2.

It was confirmed that the obtained sintered body had high strength even at a high temperature of 1200°C.

[Brief explanation of drawings]

FIG. 1 is a graph for explaining a method for determining peaks in temperature-rising mode analysis, and FIG. 2 is a graph showing a chart obtained by temperature-raising mode analysis. Applicant Shin-Etsu Chemical Co., Ltd. Agent Patent Attorney Takashi Kojima From the results in Table 2, it is clear that the silicon nitride powder of the present invention is

Claims (1)

[Claims] 1. α fraction 90% or more, BET specific surface area 10^m2/g
As described above, the silicon nitride powder is characterized in that it has an average particle diameter of 0.8 μm or less and an internal oxygen content of less than 0.5% by weight. 2. Claim 1, wherein the external oxygen content is 0.5% by weight or less
Silicon nitride powder as described.