JPH082973A - Silicon nitride sintered compact and its production - Google Patents

Abstract

PURPOSE:To obtain a silicon nitride sintered compact of high denseness excellent in high-temperature characteristics even without the need for HP, HIP or GPS for the sintering process. CONSTITUTION:This silicon nitride sintered compact contains silicon, nitrogen, oxygen, two kinds of elements selected from group 3A elements, and one kind of element selected from group 3B elements. In this sintered compact, both the silicon and nitrogen have been converted into silicon nitride, and the other elements including the oxygen have been converted into the corresponding oxides. When the respective weights of the silicon nitride and these oxides are defined as (a), (b1), (b2), (c), the proportions for these compounds satisfy the following relationships: 6<=((b1)+(b2)+(c))/((a)+(b1)+(b2)+(c))<=12 and 1<=((b1)+(b2))/(c).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to ceramics suitable for structural members such as gas turbines and internal combustion engines, and more particularly to a silicon nitride sintered body excellent in oxidation resistance and mechanical strength at high temperature and a method for producing the same. is there.

[0002]

2. Description of the Related Art As disclosed in Japanese Patent Laid-Open No. Sho 60-191063, an oxide of a Group 3A element of the periodic table having an ionic radius smaller than 0.97 angstroms, and an ionic radius are mainly composed of silicon nitride. There is known a silicon nitride sintered body to which an oxide of a Group 4A element of the Periodic Table of elements having a value of greater than 0.97 Å and an oxide or a nitride of a Group 2A element of the Periodic Table are added. Further, as disclosed in Japanese Patent Application Laid-Open No. 63-248773, silicon nitride firing in which β-silicon nitride is added with an oxide of a group 3A element of the periodic table and an oxide of a group 4A element of the periodic table. The union is known.

However, in the conventional silicon nitride sintered body, the oxidation resistance and the mechanical characteristics vary depending on the composition ratio and the firing temperature, and the gas pressure firing method (GPS) and the hot isostatic pressure are used for the sintering. A dense product cannot be obtained unless the firing method (HIP) or hot press method (HP) is used.

[0004]

In view of the above-mentioned problems, the object of the present invention is to sinter the gas pressure firing method, the hot isostatic firing method,
It is an object of the present invention to provide a silicon nitride sintered body and a method for producing the same, which can obtain a dense one without using the hot press method.

[0005]

In order to achieve the above object, a silicon nitride sintered body according to the present invention comprises two kinds of elements selected from elements of Group 3A of the periodic table and elements of group 3B of the periodic table. It is characterized by containing one selected element.

More specifically, the silicon nitride sintered body according to the present invention is selected from silicon, nitrogen, oxygen, two kinds of elements selected from elements of Group 3A of the periodic table, and elements of group 3B of the periodic table. And one element selected from the group consisting of two elements selected from elements of Group 3A of the periodic table and one element selected from elements of group 3B of the periodic table. A and b are the weights when and are converted to oxides.
1, b2 and c, the composition ratio satisfies the following formula 6 ≦ (b1 + b2 + c) / (a + b1 + b2 + c) ≦ 12 and 1 ≦ (b1 + b2) / c.

[0007]

[Function] A silicon nitride raw material powder, an oxide powder of two elements selected from an element of Group 3A of the periodic table, an oxide powder of one element selected from an element of Group 3B of the periodic table, and By adding an oxide powder of one kind of element selected from Group 4B elements in Table 4, firing in a low-pressure nitrogen gas is performed to obtain a dense silicon nitride firing excellent in oxidation resistance and mechanical strength. The obtained product can be used for structural members such as gas turbines and internal combustion engines that require high temperature oxidation resistance and mechanical strength.

Where a clock character should be used for a number representing a group of the periodic table of elements, an arithmetic number will be used for convenience.

[0009]

EXAMPLES A silicon nitride sintered body according to the present invention was selected from silicon, nitrogen, oxygen, two kinds of elements selected from elements of Group 3A of the periodic table, and 1 selected from elements of group 3B of the periodic table. With seed elements. These elements are silicon nitride and 3A of the periodic table.
Two kinds of elemental oxides selected from group elements and periodic table 3
It has a composition with one kind of element oxide selected from the group B elements, and when the weight of each composition is a, b1, b2, c, the ratio of each composition is represented by the following formula. .

6 ≦ (b1 + b2 + c) / (a + b1 + b2 + c) ≦ 12 1 ≦ (b1 + b2) / c The silicon nitride sintered body according to the present invention is selected from silicon, nitrogen, oxygen, and a group 3A element of the periodic table. Two elements and one element selected from Group 3B elements of the periodic table, and these elements are silicon nitride and two kinds of element oxides selected from Group 3A elements of the periodic table. And Periodic Table 3B
An oxide of one element selected from the group of elements and Periodic Table 4
It has a composition with SiO ₂ , which is an oxide of a Group B element, and when the weight of each composition is a, b1, b2, c, d, the ratio of each composition is represented by the following formula.

6 ≦ (b1 + b2 + c + d) / (a + b1 + b2 + c + d) ≦ 12 1 ≦ (b1 + b2) / c 1 ≦ (b1 + b2 + c) / d More specifically, two kinds of element oxides selected from Group 3A elements of the periodic table are Y Oxide (Y ₂ O ₃ ) of Yb, Ho,
One oxide selected from Dy, Er and La (Yb _{2
O 3, Ho 2 O 3,} Dy 2 O 3, Er 2 O 3, La 2 O
1 of ₃ ). Two kinds of element oxides selected from Group 3A elements of the periodic table are silicon nitride and SiO ₂ during firing.
Reacts with to form a high melting point compound in the crystal grain boundaries of silicon nitride, and enhances the oxidation resistance at high temperatures. The amount of addition of two kinds of element oxides selected from the elements of Group 3A of the Periodic Table to silicon nitride is preferably 10 to 20%, and optimally about 12%. When the amount of addition of two kinds of element oxides selected from Group 3A elements of the Periodic Table to silicon nitride increases, oxidation resistance at high temperature improves but mechanical strength at high temperature decreases.
2 selected from Group 3A elements of the periodic table for silicon nitride
When the amount of the seed element oxide added is small, the degree of sintering is lowered and the oxidation resistance at high temperature is also lowered. Of the two kinds of element oxides selected from Group 3A elements of the periodic table, the addition amount of Y oxide is one kind of element oxide selected from Yb, Ho, Dy, Er and La. Less than quantity, the latter 50
% Is appropriate.

One kind of element oxide selected from the group 3B elements of the periodic table is, for example, an oxide of Al. Periodic table 3
Al ₂ O ₃ which is an oxide of a group B element and SiO ₂ which is an oxide of a group 4B element of the periodic table have an effect of removing excess oxygen contained in a sintered body, and have a bending strength at high temperature. Increase. The excess oxygen means an excess amount of oxygen that exceeds the amount of oxygen that can chemically bond with the metal element. The addition amount of one kind of element oxide selected from Group 3B elements of the periodic table is preferably 25 to 40%, and preferably 30 to 35% of the total addition amount of oxides of each element.
Is the best. If the amount of addition of one type of elemental oxide selected from Group 3B elements of the periodic table is large, the bending strength at low temperature is lowered. If the amount of addition of one type of elemental oxide selected from Group 3B elements of the Periodic Table is small, the bending strength at high temperature decreases.

In producing the silicon nitride sintered body of the present invention, the powder of silicon nitride and the powder of oxide of each element are mixed in a predetermined weight ratio and, if necessary, an appropriate binder is added. The mixture is mixed and molded into a desired molded body by a usual molding method (for example, a normal pressure firing method) at a pressure of 2000 kgf / cm ² , for example, and the pressure is 9 to 10 kgf / cm ² and the temperature is about 170.
Baking is performed in an atmosphere containing nitrogen gas at 0 ° C. or higher for about 6 hours. The firing method is not limited to the gas pressure firing method (GPS), the hot isostatic firing method (HIP), the hot press method (HP), or the like, and the atmospheric pressure firing method (LGPS) may be used.

The present invention will be described below based on examples.

Example 1A: Silicon nitride powder (Si ₃ N ₄ )
Is 88 wt% and Y ₂ which is an oxide of a Group 3A element of the periodic table.
4 wt% of O ₃ powder, 2 wt% of Ho ₂ O ₃ powder that is an oxide of a Group 3A element of the periodic table, and 4 wt% of Al ₂ O ₃ powder that is an oxide of a Group 3B element of the periodic table. 2 wt% of SiO ₂ powder, which is an oxide of Group 4B element of the table, is mixed,
These powders were designated as C.I. I. P. Pressure of 2000 kgf /
It was molded under cm ² , and the molded body was fired at a temperature of 1900 ° C. for 6 hours in an atmosphere containing nitrogen gas at a pressure of 9.3 kgf / cm ² to produce a silicon nitride sintered body.

The obtained silicon nitride sintered body was heated at a temperature of 1000
An oxidation test was carried out at 150 ° C. for 150 hours. The results of measuring the relative density before and after the oxidation test, the bending strength (JIS R1601 four-point bending), and the oxidized weight (high temperature oxidation resistance) are shown in FIGS.

Example 1B: 88% by weight of silicon nitride (Si ₃ N ₄ ) powder and Y ₂ which is an oxide of a group 3A element of the periodic table.
O ₃ powder and 4 wt%, and 2 wt% of _Yb 2 _{O 3} powder is an oxide of the Periodic Table 3A group elements, and 4 wt% of _Al 2 _{O 3} powder is an oxide of the Periodic Table 3B group elements, SiO ₂ powder, which is an oxide of a Group 4B element of the periodic table, is mixed with 2 wt%,
These powders were designated as C.I. I. P. Pressure of 2000 kgf /
It was molded under cm ² , and the molded body was fired at a temperature of 1900 ° C. for 6 hours in an atmosphere containing nitrogen gas at a pressure of 9.3 kgf / cm ² to produce a silicon nitride sintered body.

The obtained silicon nitride sintered body was heated at a temperature of 1000.
An oxidation test was carried out at 150 ° C. for 150 hours. The results of measuring the relative density, bending strength, and oxidized weight before and after the oxidation test are shown in FIGS. 1 and 2 together with Comparative Example 1 as in Example A.

As is clear from FIGS. 1 and 2, the silicon nitride sintered body according to the present invention has very high bending strength at room temperature and high bending strength at high temperature, and is used for structural members such as heat engines. It bears.

[0020]

As described above, the present invention includes silicon nitride and two kinds of element oxides selected from the elements of Group 3A of the periodic table,
It is characterized by containing an oxide of one kind of element selected from Group 3B elements of the periodic table, and has extremely high bending strength at room temperature and high temperature, and can be used for structural members such as heat engines. A silicon nitride sintered body is obtained.

The silicon nitride sintered body of the present invention can be manufactured by the normal pressure firing method, so that it is easy to manufacture and has little variation in products.
Manufacturing costs can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing characteristics of a silicon nitride sintered body according to the present invention in comparison with a conventional example.

FIG. 2 is a table showing test results of the silicon nitride sintered body together with a conventional example.

Claims (6)

[Claims] 1. A silicon nitride sintered body containing two kinds of elements selected from elements of Group 3A of the periodic table and one kind of element selected from elements of group 3B of the periodic table. . 2. Containing silicon, nitrogen, oxygen, two kinds of elements selected from elements of Group 3A of the periodic table, and one kind of element selected from elements of group 3B of the periodic table. The weight of each element when silicon is converted into silicon nitride, and two kinds of elements selected from elements of Group 3A of the periodic table and one kind of element selected from elements of group 3B of the periodic table are converted into oxides. Is defined as a, b1, b2, c, the composition ratio satisfies the following formula 6 ≦ (b1 + b2 + c) / (a + b1 + b2 + c) ≦ 12 and 1 ≦ (b1 + b2) / c. A silicon nitride sintered body. 3. The group 3A element of the periodic table is Y, Yb, H
The silicon nitride sintered body according to claim 1, wherein the silicon nitride sintered body is one selected from o, Dy, Er, and La, and the element of Group 3B of the periodic table is Al. 4. A powder of silicon nitride, a powder of oxides of two kinds of elements selected from elements of Group 3A of the periodic table, and a table 3B of the periodic table.
A method for producing a silicon nitride sintered body, which comprises mixing with a powder of an oxide of one kind of element selected from a group element and firing the mixture in a gas containing nitrogen. 5. Silicon, nitrogen, oxygen, two kinds of elements selected from Group 3A elements of the periodic table, and one kind of element selected from Group 3B elements of the periodic table, The elements are silicon nitride, two kinds of element oxides selected from Group 3A elements of the Periodic Table, one kind of element oxides selected from Group 3B elements of the Periodic Table, and SiO _{2 by} weight a , B1, b2
When c and d, the composition ratio satisfies 6 ≦ (b1 + b2 + c + d) / (a + b1 + b2 + c + d) ≦ 12, and 1 ≦ (b1 + b2) / c, 1 ≦ (b1 + b2 + c) / d. A molded body made from a proportion of powder is heated to 170 in a gas containing nitrogen.
Characterized by firing in a temperature range of 0 to 2000 ° C.,
A method for manufacturing a silicon nitride sintered body. 6. The group 3A element of the periodic table is Y, Yb, H
O, Dy, Er and La selected from the group consisting of 3B, and the element of Group 3B of the periodic table is Al.
5. The method for producing a silicon nitride sintered body according to item 5.