JPH02225306A - Production of easily sinterable silicon nitride powder - Google Patents

Abstract

PURPOSE:To obtain easily sinterable silicon nitride powder utilized for high- temperature structural material such as gas turbine part material exhibiting strength at high temperature by adding oxide of silicon to silicon nitride powder, mixing and heat-treating. CONSTITUTION:Fine powder (preferably >=10m<2>/g specific surface area) of oxide of silicon such as aerosil or white carbon is added to silicon nitride powder and heat-treated in non-oxidizing atmosphere such nitrogen or argon at 1500-1800 deg.C for 3-15 hour to obtain easily sinterable silicon nitride powder. Adding amount of fine powder of oxide of silicon is usually <=6wt.%. Sintered material of the aimed silicon nitride powder has >=800MPa bending strength at 1200 deg.C.

Description

[Detailed description of the invention] [Field of application of the material] Mainly, as an h-temperature structural material, it is used as a turbine member,
This invention relates to a method for producing silicon nitride powder wood that is easily sinterable and exhibits high-temperature strength, and is used for nozzles, receivers, etc.

(Prior technology) Methods for producing wood made from silica nitride powder include (1) direct nitriding based on metal nitride, (2) sled force reduction nitriding, and (3) halocarbonized yarn method. The powder produced by the method of these IL et al.
・There are big differences in bending strength, such as the sinterability of powder and the properties of furnace bonding after sintering, depending on rope, acidity, particle size, specific surface area, and IWI size.

In general, (the powder produced by method 11 is easily sinterable but has low high-temperature bending strength; the powder produced by method (2) is difficult to sinter but has high high-temperature bending strength; The powder obtained by method (3) is said to exhibit intermediate performance.

In particular, the silicon nitride powder produced by method (1) suffers more strain from pulverization on the surface of the powder than the other two methods, so by releasing all of that strain energy, Efforts are being made to impart these characteristics to objects.

One example is '#f Box No. 88011/1983.

This prior art uses silicon nitride powder between 1,400 and 1.9
After heat treatment at a temperature of 00°C, the oxygen contained in silicon nitride is removed. In addition to removing the oxygen as 1-8iO, some of the oxygen is solidified on the surface of the silicon nitride powder, and by adding 6% of the oxygen to the sintering aid, the grain boundary phase in the sintering chamber is removed.
? I: It is a technique that reduces the strength of Karasunoshima Island.

However, since this method utilizes mass transfer on the surface of the silicon nitride-based object of starting yA'I#+,
The problem is that starting materials are naturally limited, ie, fine powder or high oxygen content is required.

Therefore, the modification of the powder was limited, and one example of the results was the use of only a hot press, which left a problem in that the powder characteristics could not be fully grasped.

[Static listening that the invention attempts to solve]

The inventors of the present invention have carefully studied methods for improving powder and the binding of improved powder, keeping in mind the above assembling meeting in Japanese Patent Application Laid-open No. 53-88011. Mix fine silicon oxide powder with silicon nitride powder to saturation, and heat at 1,500 to 1,800℃ at 1 atmosphere of non-oxidizing temperature.
The present invention was completed by developing a powder that can be used for pressureless sintering after heat treatment at a temperature of .

[Means for resolving division issues]

That is, in the present invention, silicon oxide fine powder (il-added and mixed with silicon nitride powder, 1.500%
This is a method for producing easily sinterable silicon nitride powder, which is heat treated at a temperature of ~1,800°C.

Hereinafter, to explain the present invention further, in the present invention, the reason why the silicon oxide powder is fully exposed is that if the oxygen in the silicon nitride powder is biased towards the fine powder, the surface modification of the silicon nitride powder is only caused by the fine powder. The coarse grain example, which is considered to be low in oxygen, is based on the possibility that powder of about 5 to 10 μm may be left behind after modification. That is, in the present invention,! *The attempt is made to completely eliminate this interpolation by adding silicon oxide fine powder and causing it to react with the surface of the silicon nitride powder.

The amount of silicon oxide to be added is determined by considering the following objectives and the oxygen content of the raw material silicon nitride powder, but it is usually 6]LIL.
’% or less. That is, one of the purposes is to improve the powder with #I sinterability, and the other purpose is to reduce oxygen and rearrange the fine powders. The former uses silicon oxide fine powder at 23! It is intended to improve the wettability of the powder surface by applying heat only to within L% and performing heat treatment at a relatively low temperature, for example, about 1600°C. On the other hand, the latter is aimed at the technical contents of Japanese Patent Application No. 63-2773+50, and involves heat treatment at a high temperature of, for example, about 1750°C, adding as much silicon oxide fine powder as possible,
The purpose is to actively react, deoxidize, and reduce the amount of fine powder by not only reducing the acid content but also rearranging the fine powder. It is sufficient that the heat treatment is about 6 to 15 hours, depending on the temperature.

As mentioned above, the particle size of the silicon oxide is preferably small because it is intended to actively react with the surface of the silicon nitride powder. It is desirable that the weight of
It is convenient that it is a fine powder of 7 or more. Specific examples of such fine silicon oxide powder include Aeroshell, White Carbon, and the like.

Regarding the heat treatment atmosphere, the purpose is to create a low-acid atmosphere, so the atmosphere is non-oxidizing, for example, a family tree.

An atmosphere of argon, hydrogen, ammonia, etc. is suitable.

Further, the heat treatment temperature is usually 1,500 to 800°C. If the temperature is less than 1.500°C, the reaction between the silicon oxide fine powder and the silicon nitride powder, that is, the mass transfer, will not occur sufficiently, so that the powder cannot be modified. On the other hand, i, s
When the temperature exceeds 00°C, sublimation transition and partial decomposition of silicon nitride itself occur.

An example of this is that the disadvantages of wood, such as its high content of oxygen, have been modified into silicon nitride wood powder, which is easily sinterable and exhibits high temperature strength, by actively adding silicon oxide fine powder. The basic idea of the present invention is based on the reactions shown in the following formulas (11 and 21).

(X-813N4 + 8102-p2SL2ON2
(12Bi2ON2-pβ-8i3N4
+ 5ill (2) [Examples] Examples and comparative examples will be described below (the present invention will be specifically explained).

Examples 1-11. Ratio @ Examples 1 to 4 Commercially available silicon nitride powder 1001 area to specific surface area 50
5i02 of m2/fi was added and mixed in the proportions shown in Table 1. This mixed powder was placed in a carbon crucible and heated under the heat treatment conditions shown in Table 1 to produce silicon nitride powder.

Table 1 shows the properties of the obtained silicon nitride powder.

Next, Y2O3 (s+L average particle size 1.μrn), A1
203 (average particle diameter 1.4 μm), νgo (average particle diameter 1.2 μm) and )vjgo-AJ203 (average particle diameter 1.2 μrn) were mixed inside the VC at various ratios as shown in Table 2. ,1,1-t! Add J chloroethane and wet mix in a ball mill for 4 hours. After drying,
After molding with a mold into a 6×10×6011 Im shape at a molding pressure of 0 to η-2, CIP molding was performed at a molding pressure of 2700 to 9/F2. These cedar bodies were placed in a carbon crucible.
, 2 was fired in a gas atmosphere under the conditions shown in No. 2 to produce a sintered body. ), the intensity was increased.The results are shown in Figure 6.

The measured values shown in Tables 1 and 6 were determined by the following method.

(1 [Oxygen (lk!%): TC-13 manufactured by LECO
Using a Type 6 0/N simultaneous analyzer.

(2) Specific surface area (m”/&): Based on the Cantersorb Jr. BET 1 point method manufactured by Yuasa Ionics.

(3) α fraction (%): Based on X-type diffraction of Rigaku wo Kisha's Gai-Fusix)'IAD-It B type.

(4) Relative density (%): Based on the Archimethes method.

(5; Strength of the song (MPa): Based on Autograph A, 0-2000 A type, manufactured by Rotsu Seisakusho.

〔Effect of the invention〕

The silicon nitride powder produced according to the present invention has a low temperature bending strength of 890 MPa or more. This is due to the control of the powder characteristics related to the generation and growth of β-columnar crystals in the sintered body.

Watch applicant Denki Kagaku Kogyo Co., Ltd.

Claims (1)

[Claims] 1. Add and mix silicon oxide fine powder to silicon nitride powder,
A method for producing easily sinterable silicon nitride powder, comprising heat treatment at a temperature of 1,500 to 1,800°C in a non-oxidizing atmosphere.