JPS5835951B2 - Manufacturing method of high-strength silicon nitride sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a high-strength silicon nitride heat exchanger whose main component is silicon nitride (5i3N4).

For more details, please refer to silicon nitride
The present invention relates to a method for manufacturing a sintered body having high strength by adding gallium oxide (Ga20s), gallium oxide (Ga20s), and aluminum oxide (A1203).

Sintered bodies mainly composed of S A3 N4 have attracted attention in recent years due to their heat resistance, high strength, and low coefficient of thermal expansion, and are used in automobile engine parts, gas turbine parts, cutting tools, etc. used in

And 5i3N, which has higher strength and density than before,
As a sintering aid for Y2O3-Al□03゜MgO, Al
□03-MgO type compounds have been tried.

However, even with the addition of these sintering aids, the strength of the sintered body was still insufficient.

By the way, as a result of intensive study on how to further increase the strength of the conventional product, the inventors of the present invention have developed B.
The present invention was completed based on the discovery that eO* Ga2O3 and A1□03 can be added in specific amounts as sintering aids.

That is, the object of the present invention is to provide a method for manufacturing a novel high-strength silicon nitride burner having two components of BeO and Ga2e3, or three components including Al2O3. ~99.9% by weight
, a sintering aid consisting of BeO, Ga2O3, and Al2O3 whose component ratios on a weight basis are in the range of 0
．． 1 to 50% by weight is added thereto and sintered at a temperature of 1300 to 1850°C.

In the following, the present invention will be described in detail.
It is necessary that N4 account for 50-99.9% by weight of the inorganic raw material.

There are three types of Si3N4: α type, β type, and amorphous type, and in the present invention, any type or a mixture thereof can be used.

In the present invention, as a sintering aid, two components of Be02Ga203 or three components including Al2O3 are used.

The proportion of these sintering aids in the inorganic raw material is 0.1
~50% by weight, and if it is less than this range, sintering becomes difficult.

The above three components in the sintering aid must satisfy the above formulas (1), (2) and (2).

However, if the 5t3N4 raw material contains Al 203 or Fe2O3 as an impurity, or if A
If an impurity that produces l2O3 or Fe2O3 is contained, an amount of Al2O3 corresponding to the amount of the impurity can be removed from the sintering aid.

In formula (1), the value of Ga2O3 is preferably 3.75eO to 8.24, more preferably 4.27 to 7
．． A value of 50 provides the best sinterability and therefore the highest strength.

In formula (2), the value of Al2O3 is preferably 2.04eO or less, more preferably 1.75 or less, increasing the strength of the sintered body.

■In the formula, the value of Al2O3 is less than 0.41Ga
2O3 is most preferred.

As Ga2O3, both α type and β type can be used,
As Al2O3, either the α type or the γ type can be used.

Also, the oxide BeO is added as a sintering aid. Ga2O3 and Al2O3 do not have to be these from the beginning,
Salts of beryllium, gallium, and aluminum, which become oxides of these during the sintering process, can also be used, and such cases are also included in the present invention.

In addition, BeO = Ga2O3 and Al2O3 are added as independent oxide raw materials, and are reacted in advance.
A double oxide solid solution having a JIJ umgallate crystal structure can also be used.

Also, for A1□03, instead of adding this as an ingredient, 5
It is also possible to use substances that are mixed in when t3N4, BeO, and Ga 20 s are crushed using an alumina pot mill or an alumina ball.

In order to produce the high-strength silicon nitride sintered body of the present invention from the above raw materials, first Si3N4 powder, BeO powder, Ga2O
3 powder and Al2O3 powder are selected in a predetermined composition ratio and mixed to prepare.

Next, a binder is added to this mixture as needed and pressed to obtain a predetermined molded body.

Thereafter, this molded body is placed in air or a weakly oxidizing atmosphere such as CO2 gas, or in a non-oxidizing atmosphere such as N2.
Sintering is carried out under pressure in gas or Ar gas at 1300 to 1850°C, preferably 1400 to 1800°C.

However, the ratio of sintering aid is BeO + Ga203 + A
I 20 g.

Value, o, 1゜SiN + BeO+ Ga2O3+
When Al2O34 is within the range of 0.50, pressurization is not necessarily required.

Pressure sintering is usually carried out using a graphite type O uniaxial hot press or a hot isostatic press.

The pressure is generally 100 to 400 kg/d for graphite molds, and 1000 to 2000 kVd for hot isostatic presses, although the higher the pressure, the better the results obtained.

By sintering in this manner, a novel silicon nitride sintered body containing an oxynitride solid solution phase of a BeGa2O, -BeAl204 solid solution having a beryllium gallate type crystal structure and Si3N4 is obtained.

The composition of the new sintered body is mostly 813N, which has shifted to the β type.
4 and the above-mentioned oxynitride solid solution phase, and contains almost no glass phase.

The novel high-strength nitrided silicon sintered body manufactured by the method of the present invention described above is superior to conventional nitrided silicon sintered bodies in terms of strength at temperatures below 1300°C.

Therefore, this sintered body is suitable as a material for structures where stress concentration such as impact and fatigue is a problem.

The reason for this is that the double oxide solid solution in the BeGa 204-BeAl 204 system, which has a BeIJ IJ um gallate crystal structure, has a similar crystal structure and lattice constant to β-type Si3N4, so during the sintering process, this solid solution
This is thought to be because it easily reacts with sN4 to form an oxynitride solid solution, resulting in a sintered body with a uniform composition and structure without forming a foreign crystal phase or glass phase between particles. .

In addition, the thermal expansion coefficient of Be-IJ-IJ um gallate solid solution is approximately 3X10'/'C in both the a-axis direction and the C-axis direction, which is very close to the thermal expansion coefficient of β-type Si3N4. It is believed that a sintered body having a low coefficient of thermal expansion of the entire sintered body including the interfacial phase, high resistance to thermal shock, and high strength at high temperatures can be obtained.

Furthermore, impurities such as Al2O3 and Fe2O3, which caused strength reduction in conventional sintered bodies, are incorporated into the beryllium gallate-type BeGaO-BeA12044 solid solution, resulting in a sintered body with a uniform structure. This is also considered to be one of the reasons for the improvement in strength.

The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to the following Examples unless the gist of the invention is exceeded.

Example 1 α type 9 with a purity of 99% and an average particle size (50% diameter) of 0.7 μm
90% by weight of silicon nitride powder consisting of 0% and 10% β-type, and 1.3% by weight of 99.9% pure Beam oxide.
, 7.8% by weight of gallium oxide with a purity of 99.99% and 0.9% by weight of aluminum oxide with a purity of 99.9% were added and mixed by pulverization for 100 hours in a vibrating mill using an alumina pot and an alumina ball. Shaped into a disc shape with a thickness of about 1 ONM and heated at a temperature of 1750°C in nitrogen gas.
, and pressure sintered for 30 minutes at a pressure of 300 kgAd.

The obtained sintered body is 3X3X251! After processing into a square bar marked *, a bending test was conducted to measure the bending strength.

Table 1 shows the constituent substances identified based on transverse refraction intensity values and X-ray diffraction.

Example 2 90% by weight of the same silicon nitride powder as used in Example 1
, IJ IJ oxide 1.5% by weight, Gallium oxide 6
．． Trichlorotrifluoroethane was added to 5% by weight of aluminum oxide and 20% by weight of aluminum oxide, and the mixture was wet-milled for 2001* hours using an alumina pot and an alumina ball.

This powder mixture was pressure sintered under the same conditions as in Example 1, and the same bending test as in Example 1 was conducted.

The results are shown in Table I. Example 3 Purity 99.9%, average particle size 0.35 μ door, α type 85%,
95% by weight of silicon nitride powder consisting of 15% β-type (to which 0.9% by weight of the aluminum oxide used in Example 1 and 4.1% by weight of gallium oxide were added, and an alumina pot and an alumina ball were added. Wet pulverization was carried out by adding ethanol.

The pulverization method was to dry the powder after 200 hours of pulverization in a vibrating mill, form it into an α shape in the same manner as in Example 1, and then pressure sinter it in argon gas at a temperature of 1700° C. and a pressure of 200 kg/ai for 30 minutes.

This sintered body was processed into the same dimensions as in Example 1, and the bending strength was measured.

The results are shown in Table 1.

Example 4 Purity 99.9%, average particle size 3.5μ, α type 30%, β
0.8% by weight and 5.2% by weight of the aluminum oxide and gallium oxide used in Example 1 were added to 94% by weight of silicon nitride powder consisting of 70% mold, and an alumina pot and an alumina ball were prepared. Dry pulverization was carried out for 100 hours.

This mixed powder was molded into a disk having the same dimensions as in Example 1, and then pressure sintered in nitrogen gas at a temperature of 1700°C and a pressure of 250/9/d for 60 minutes.

This sintered body was processed into a rectangular column having the same dimensions as in Example 1, and a bending test was conducted.

Table 1 shows the bending strength and the constituent substances in the sample.

As can be seen from Table 1, Examples 1 to 4 according to the present invention exhibit very large bending strengths of 98 to 118#/- at room temperature, but this is due to the BeOtGa2 added as an additive.
O3t Al2O3 and alumina pot mill and alumina balls (Al2O mixed in during the grinding process)
3 reacts during the sintering process to form a BeGa204 solid solution phase with the same crystal structure as β-Si3N4 at the grain boundaries, and this solid solution phase and /! This is thought to be because a solid solution was also formed between the 5L-8L3N4 particles and the particles were strongly bonded.

Claims (1)

[Claims] I Sia N450 to 99.9% by weight, BeO
, Ga2O3 and A1□03, and add 0.1 to 50% by weight of a sintering aid whose component ratio on a weight basis is in the range of 13
A method for producing a high-strength silicon nitride sintered body, characterized by sintering at a temperature of 00 to 1850°C.