JPH03205363A - Sintered silicon nitride and production thereof - Google Patents

Abstract

PURPOSE:To obtain a sintered silicon nitride exhibiting high strength at high temperature comparable to the strength at normal temperature by forming a mixture of Si3N4 powder, rare-earth oxide powder and SiC powder and calcining the formed article in N2 atmosphere. CONSTITUTION:A raw material composed of Si3N4 powder, rare-earth oxide powder and SiC powder is mixed and formed to obtain a formed article. The article is calcined in N2 atmosphere to effect the essential crystallization of the integranular phase of Si3N4 particle during the temperature-lowering stage. The rare-earth oxide is preferably Y2O3, Yb2O3, etc., and its amount is preferably 2.7-10mol% [calculated as the ratio of (molar amount of rare-earth oxide)/(molar amount of rare-earth oxide + molar amount of Si3N4)]. The amount of SiC is preferably 0.1-11wt.% (in the outer percentage) based on the mixture of silicon nitride and rare-earth oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a high-temperature, high-strength silicon nitride sintered body and a method for manufacturing the same.

(Prior art) Conventionally, as a silicon nitride sintered body to which oxides of ■a-based elements including rare earth oxides are added, for example, Japanese Patent Publication No. 48-7486
In the publication, SisN+ of 85 mol% or more and II
[A method for producing a sintered body in which 15 mol% or less of at least one selected from the oxides of a-based elements is mixed, molded, and sintered in a non-oxidizing atmosphere is also disclosed in Japanese Patent Publication No. 4921091. At least 50wt%, Y203
or 50 wt% or less of at least one selected from oxides of La-based elements, and Aj22030. 01 ~2
A silicon nitride sintered body comprising 0 wt% is disclosed.

However, simply adding rare earth elements to silicon nitride does not produce a sintered body with high high-temperature strength, and addition of A6zOs promotes densification, but the grain boundary phase has a low softening point and significantly reduces high-temperature strength. There was a problem to resolve.

In order to solve this problem of high-temperature strength, the present applicant added a rare earth element in a predetermined composition or ratio in a predetermined ratio to SiaN4 powder, and identified the crystal phase of the sintered body in Japanese Patent Application Laid-open No. 63-100067. This paper discloses a technology that achieves high strength at high temperatures.

(Problems to be Solved by the Invention) The silicon nitride sintered body disclosed in JP-A-63-100067 can achieve high strength at a certain high temperature, but there is a problem that the strength is lower than that at room temperature. This is thought to be due to the fact that even after grain boundary crystallization, some amount of glass phase remains. Regarding this point, in order to reduce the amount of residual glass phase, when the total amount of oxygen contained in the silicon nitride raw material is converted to the amount of Si02, the amount ratio of the added rare earth oxide to SiO2 is increased and the amount of residual glass phase is reduced. There is a method that can be considered to create a structure that is difficult to form, but this method has the problem of making it difficult to make it dense.

Furthermore, if the ratio of the added rare earth oxide to Si02 is small, densification is achieved but the crystallization of the grain boundary phase does not progress sufficiently.

13. An object of the present invention is to solve the above-mentioned problems and provide a silicon nitride sintered body and a method for manufacturing the same, which can obtain high-temperature high strength almost equivalent to the strength at room temperature.

(Means for Solving the Problems) The silicon nitride sintered body of the present invention is a sintered body consisting essentially of Si31tl4, a rare earth element compound, and SiC,
S of the sintered body! It is characterized in that the grain boundary phase of the 3N4 grains consists essentially of a crystalline phase.

Further, the method for manufacturing a silicon nitride sintered body of the present invention includes SfaN+
After mixing and shaping raw materials consisting of powder, rare earth oxide powder, and SiC powder to obtain a compact, the compact is fired in an N2 atmosphere, and during the cooling process, Si3N and grain boundary phases of the particles are substantially removed. It is characterized by crystallization.

(Function) In the above structure, by adding SiC to Si3N4 powder containing a predetermined rare earth oxide and crystallizing it by sintering in a N2 atmosphere, the grain boundary phase of the Si3N4 particles is substantially eliminated. Baked 4 containing SiC as a crystalline phase? This is because it has been found that this silicon nitride sintered body has virtually no residual glass phase at the grain boundaries and can achieve high strength almost equivalent to room temperature strength even at high temperatures.

That is, the total amount of oxygen contained in the silicon nitride raw material is
In terms of (2), if a large amount of rare earth oxide is added to SiO2, it can be sufficiently densified by adding SiC,
Moreover, SiC promotes crystallization of grain boundaries.

As a result, a high-temperature, high-strength silicon nitride sintered body having a crystalline grain boundary phase with an extremely small amount of glass phase can be obtained. The amount of rare earth oxide added is Sin. However, if SiC is not added in a small amount, densification can be achieved without adding SiC, but adding SiC promotes grain boundary crystallization, resulting in high-temperature, high-strength nitriding with a grain boundary phase with little glass phase. A silicon sintered body can be obtained.

Here, whether more or less rare earth oxide is added to rSiO2 is based on the amount of rare earth oxide added that provides the highest high temperature strength in the case of no SiC addition. The amount of rare earth oxide added that provides the highest high temperature and high strength without the addition of SiC varies depending on the =5-Si3N+ raw material used, and is not uniquely determined by the ratio of rare earth oxide to Sin2.

The amount of oxygen in the silicon nitride raw material is preferably 1 to 3% by weight. The amount of oxygen can be controlled by oxidizing the silicon nitride raw material. Alternatively, Sin2 powder may be added.

The total amount of rare earth oxides added is preferably 2.7 to 10 mol%. If the total amount added is less than 2.7 mol%, a liquid phase sufficient for densification cannot be obtained, and if it exceeds 10 mol%, S
This is because even if iC is added, densification tends to be difficult. Also Y203. As a rare earth oxide other than Yb203, Lu20a. Tm203, Er203, etc. can also be used as the same effective ingredient. The amount of rare earth elements in the sintered body remains the same as at the time of preparation. The mol% was calculated as (molar amount of rare earth oxide)/(molar amount of rare earth oxide + molar amount of Si3Na).

The amount of SiC added is preferably 0.1 to 11 wt% relative to the mixture of silicon nitride and rare earth oxide.

The external addition amount is 0.1. This is because if it is less than 11 wt%, sufficient densification effect 6 and crystallization promoting effect cannot be obtained, and if it exceeds 11 wt%, SiC may inhibit densification. More preferably, it is 0.5 to 7 wt%.

The amount of SiC in the sintered body may be slightly reduced compared to when it was prepared.

SiC can be used regardless of whether it is α type, β type, or non-quality.

In the method for manufacturing a silicon nitride sintered body of the present invention, first, a mixture of silicon nitride raw material powder, rare earth oxide, and SiC is prepared. Next, the obtained mixture is molded into a predetermined shape to obtain a certain shaped body. Thereafter, the obtained molded body was sintered at a temperature of 1700 to 210 in a normal pressure or pressurized N2 atmosphere depending on the sintering temperature.
By firing at a temperature of 0°C, preferably 1900 to 2000°C, and crystallizing during the temperature cooling process, the nitrided nitride of the present invention is substantially crystallized without remaining glass phase in the grain boundary phase of SjsN< grains. A silicon sintered body can be obtained.

(Example) An actual example will be explained below.

Purity 97% by weight, oxygen content 2.2% by weight, average particle size 0
．． 6 μm. ．． Silicon nitride raw material powder with a BET specific surface area of 17 po/g, a purity of 99.9% by weight, and an average particle size of 0.3-2.
5 μm additives listed in Table 1 and S with a purity of 99% by weight, an average particle size of 0.4 μm, and a BET specific surface area of 20 m/g.
Prepare iC in the proportions listed in Table 1, and use silicon nitride porcelain cobbles and a nylon resin container with an internal volume of 1.21 cm.
1 was added thereto, and the mixture was pulverized for 3 hours using a vibrating mill at a frequency of 1200 times/min. Thereafter, the water was evaporated and the powder was granulated to a particle size of 150 μm to obtain a powder for shaping. Next, a shaped body of 50 x 40 x 6 mm was produced by isostatic pressing at a pressure of 7 ton/cm2, and fired under the firing conditions listed in Table 1 to obtain silicon nitride sintered body No. 1 of the present invention. 1 to 27 were obtained. In addition, using the same raw materials, the additives and their blending ratios listed in Table 1 were prepared, and the mixture was crushed, granulated, and shaped in the same manner, and then baked under the baking conditions listed in Table 1 to obtain a comparative example. No. Sintered bodies of Nos. 28 to 31 were obtained. Note that Comparative Example No. 29. No. 30 was crystallized by reheating treatment.

The bulk density, grain boundary crystal phase, and four-point bending strength at room temperature and 1400° C. of these sintered bodies were measured.

The results are shown in Table 1. In Table 1, the bulk density of the sintered bodies was measured by the Archimedes method. In addition, in the table, values are shown as values relative to theoretical density. However, the theoretical density is
It was calculated from the blended powder composition and the density of the blend. The density of the formulation is S+3Na: 3.2 g/cm3, Y203: 5.
Og/cm3, Yb203:9.2g/cm", T
m203: 8.8g/crn", Lu203: 9.4g
/cm3, Er20s: 8.6g/cm3. SiC
:3. 2 g/cm3 was used. Four-point bending strength is JI
It was measured in accordance with SR-1601R Bending Strength Test Method for RAI Ceramics. The grain boundary crystal phase was determined from the results of X-ray diffraction using CuKa rays, and is indicated by J in Table 1.
is a crystal with a casvidin structure and is a JCPDS card 32-l.
Si3N.・4Y203・Sift
The crystallographic position of Y can be replaced by other rare earth elements.

H is apatite structure crystal JCPDS card 30-1
Si.462 is a representative example. N.・10Y203・9Si
It has the same type of diffraction line as Oz, and the crystallographic position of Y can be replaced by other rare earth elements. K is a crystal with a wollastonite structure and JC
2Y203 represented by PDS card 31-1462.
It has the same type of diffraction line as Si02 SisN4, and the crystallographic position of Y can be replaced by other rare earth elements. L is Re2
A crystal represented by SiOs (Re/10 rare earth elements) JCPDS card 2]. -1
．． 456.21-1458. 21-1461. 22
-992. It has the same type of diffraction line as any one of No. 36-1476. S is Re. Crystal represented by Si20y (Re: rare earth element) JCPDS card 20-1416
．． 21-1457. 21-1459. 21-14
60. 22-994. It has the same type of diffraction line as either 22-1103.

Note that the proportion of the grain boundary crystal phase listed in Table 1 is βSj3N+
The sum of the integrated intensities of the strongest peaks of each crystalline phase at grain boundaries, excluding grain boundaries, is the proportion of that total.

Moreover, the silicon nitride sintered body NO. A transmission electron micrograph of No. 4 is shown in FIG. In FIG. 1, particles denoted by A are β-Si3N. The region indicated by B is the grain boundary phase, and the particles indicated by C are SiC.

10 As is clear from Table 1, the present invention No. 1 with a large amount of rare earth oxide added and SiC added. Nos. 1 to 6 have a high relative density of 97% or more, high strength at high temperatures, and a small decrease in strength from room temperature. On the other hand, Comparative Example No. 1 without adding SiC. 28 is not sufficiently densified. As a result, S
It can be seen that the addition of iC is effective for densification.

When the amount of rare earth oxide added is not large, for example, in Nα8,12 of the present invention, the grain boundaries are mainly crystallized into the H phase by adding SiC, but the grain boundaries are crystallized by reheating without adding SiC. Comparative Example No. in which the field was crystallized. 29. 3
It has higher strength at higher temperatures than 0. The effect of the addition of SiC in this case is due to promotion of crystallization of grain boundaries rather than a densification effect, and is thought to be due to less residual glass.

(Effects of the Invention) As is clear from the above description, according to the silicon nitride sintered body and the manufacturing method thereof of the present invention, SiC is added to Si3N4 powder containing a predetermined rare earth oxide and By firing and crystallizing it, it is possible to obtain a sintered body containing SiC in which the grain boundary phase of SiaN4 particles is substantially the crystalline phase, and it is possible to obtain high-temperature high strength almost equivalent to the strength at room temperature. .

[Brief explanation of drawings]

FIG. 1 shows silicon nitride sintered body No. of the present invention. 4 is a transmission electron micrograph showing the crystal structure of No. 4. Engraving of drawings (no changes in content) Figure 1 C: SjC procedure document walk-through)

Claims (4)

[Claims] 1. A sintered body consisting essentially of Si_3N_4, a rare earth element compound, and SiC, the sintered body containing Si_3N_
A silicon nitride sintered body characterized in that the grain boundary phase of four grains consists essentially of a crystalline phase. 2. The silicon nitride sintered body according to claim 1, wherein the rare earth element is Y and/or Yb. 3. Si_3N_4 powder, rare earth oxide powder and Si
After mixing raw materials consisting of C powder and molding to obtain a molded body, the molded body is fired in an N_2 atmosphere, and Si_
A method for producing a silicon nitride sintered body, characterized by substantially crystallizing a grain boundary phase of 3N_4 particles. 4. The method for producing a silicon nitride sintered body according to claim 3, wherein the rare earth oxide powder consists of Y and/or Yb.