JP3007732B2 - Silicon nitride-mixed oxide sintered body and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a strength and by eliminating the pores and microcracks in the ceramic causing reduced reliability, silicon nitride having high strength and reliability (Si ₃ N ₄₎ based oxide relates sintered body of ceramics, in particular, tissue uniform Si ₃ N ₄ - method (Ln-Al-Si) oxide sintered body (although, Ln is a rare-earth elements and compounds thereof) making the same and We suggest about.

[0002]

2. Description of the Related Art In general, ceramic materials are promising as structural materials because of their high strength at high temperatures and excellent heat resistance, oxidation resistance and corrosion resistance. In particular, there is a great deal of interest in the application of such ceramics to structural materials used in a temperature range exceeding the usage limit of metals. Among these ceramics, Si ₃ N ₄ is one of the most promising structural materials that can be used at high temperatures because of its excellent heat resistance and oxidation resistance.

[0003] However, Si ₃ N ₄ is a material that is extremely difficult to be sintered, so that it is extremely difficult to obtain a dense sintered body without adding an auxiliary agent. For this reason, conventionally, Si ₃ N ₄ powder has been fired by adding Y ₂ O ₃ , CeO ₂ , AL ₂ O ₃ , AlN, MgO, etc. as a sintering aid. However, a Si ₃ N ₄ sintered body obtained by using a single or a combination of these oxides as a sintering aid has a high strength, but has a lower toughness than zirconia ceramics. As a result, Si ₃ N ₄ sintered body that has high strength at high temperature and excellent characteristics such as oxidation resistance is not reliable for use as a structural material because its toughness is still low. It was a material.

[0004] In contrast, as devised to increase the toughness of the Si ₃ N ₄ sintered body, by growing Si ₃ N ₄ crystal anisotropically, Si ₃ N ₄ sintered body strength and toughness Kawashima et al. (Ken Kawashima, Hiromi Okamoto,
Shuji Yamamoto, Akira Kitamura, Silicon Nitride Ceramics 2, Uchida Lao Tsuru, p. 135-146). In other words, by putting the formed body in a capsule and sintering while applying gas pressure, by growing the Si ₃ N ₄ crystal anisotropically,
Si ₃ N ₄ -Rare earth oxide- with Y ₂ O ₃ and AL ₂ O ₃ as sintering aids
A method for improving the toughness of an alumina-based composite sintered body has been proposed.

[0005]

However, since this method is a method of sintering while applying gas pressure using a capsule, there are few suitable materials for the capsule material, and the formed form is put in the capsule. Therefore, it is not possible to sinter a material having a complicated shape, and the manufacturing cost is increased. In addition, in the Si ₃ N ₄ sintered body synthesized by this method, the crystal grows anisotropically large, so there is a large defect inside the sintered body, and it breaks starting from that Therefore, the reliability as a material was lacking, and there was a problem in practical use.

The formation mechanism of this Si ₃ N ₄ -rare earth oxide-alumina sintered body is considered as follows. First, in a first stage of sintering under no pressure, an oxide solid solution or a compound of an oxide is generated from a rare earth oxide and alumina. Next, in a second stage, the Si ₃ N ₄ is dissolved and diffused in the oxide, and the Si ₃ N ₄ grains are grown and shrunk to form a dense sintered body.

However, in the second stage, Si ₃ N ₄
Flour occur simultaneously a chemical reaction when dissolved in an oxide, Si ₃
N ₄ reacts with alumina to decompose and generate gases such as CO and NO. As a result, defects such as voids and pores are generated in the sintered body, resulting in a disadvantage that the strength of the interface between Si ₃ N ₄ and the oxide is reduced.

[0008] The object of the present invention is to provide Si ₃ N ₄ and rare earth oxide
The reliability of Si ₃ N ₄ -Rare earth oxide-Alumina sintered body obtained by sintering alumina-based oxide with high strength and high toughness without defects such as voids and pores as described above And to propose a novel technique for an advantageous production method thereof.

[0009]

As a result of diligent research to achieve the above object, the present inventors have found that rare earth oxides
By mixing silica with alumina-based oxide, rare-earth oxide-alumina-silica-based powder and Si ₃ N ₄
And the mixture was fired. In such a mixture firing, the reaction between Si ₃ N ₄ and alumina is suppressed, so that
Since the generation of pores was reduced and the sintering of Si ₃ N ₄ and the oxide proceeded gently, it was found that a dense sintered body was easily obtained.

That is, the present invention relates to a mixed oxide of 99.9 to 90% by weight of Ln4Al2O9 or LnAlO3 (where Ln is a rare earth element or a compound thereof) and 0.1 to 10% by weight of silica; 95-5 wt% of silicon nitride Si3N4 over these mixtures;
And then heating the molded body in a non-oxidizing atmosphere at a temperature rising rate of 5 to 2000 ° C./min.
A method for producing a Si3N4- (Ln-Al-Si) oxide-based sintered body, characterized in that the firing is performed at a temperature in the range of 1500 to 1900C for 0.1 to 600 minutes, and the Si3N4- synthesized by the method.
(Ln-Al-Si) An oxide-based sintered body.

[0011]

In general, it is considered that silica added to other oxide ceramics has a low melting point of 1550 ° C., becomes a glassy state, and precipitates at grain boundaries, lowering high-temperature strength.
Therefore, this silica was rather one of the compounds that one did not want to add.

On the other hand, in the present invention, attention is paid to this silica, and sintering becomes possible when a mixture of Si ₃ N ₄ and (rare earth oxide-alumina-silica-based powder) is used. It does not precipitate at the grain boundaries to form glass, and furthermore, forms a solid solution in the rare earth oxide-alumina system or, if present in a solid solution amount or more, reacts with the rare earth oxide or alumina to form a silicate compound. Therefore, it was found that there was no problem of lowering the high-temperature strength.

According to the findings of the present inventors, the addition of this silica to other compounds effectively acts to obtain a dense sintered body, rather than the oxide portion of the sintered body. It is effective for improving the strength and toughness of the steel.

The minute amount of silica present on the surface of unoxidized Si ₃ N ₄ alone is insufficient to increase the strength and toughness of the oxide.

Next, the Si3N4- (Ln-Al-Si) oxide of the present invention contains 5 to 95% by weight of rare earth oxide powder and 94.9 to 4.
Mixed oxide consisting of 9 wt% and silica 0.1-10 wt%,
Ln4Al2O9 or LnAlO3 (where Ln is a rare earth element or a compound thereof); 99.9 to 90% by weight; and 5 to 95% by weight of a mixed oxide composed of 0.1 to 10% by weight of silica;
It is obtained by mixing 3N4 powder or Si3N4 whiskers, or 95 to 5 wt% of a mixture thereof, and firing.

Here, when the rare earth oxide powder is less than 5 wt%, the characteristics of the mixed oxide are deviated from those of alumina alone, and the sinterability with Si ₃ N ₄ is deteriorated. When the content of alumina is less than 4.9 wt%, the characteristics of the mixed oxide are almost deviated from those of the rare earth oxide alone, and Si ₃ N ₄
And the sinterability becomes worse.

On the other hand, when the content of the rare earth oxide exceeds 95% by weight, the properties of the oxide are no different from those of the rare earth oxide, and
If it exceeds 94.9 wt%, the properties of the oxide will not be different from those of alumina. Therefore, the rare earth oxide powder and alumina are limited to the above range.

If the addition amount of silica is less than 0.1 wt%, abnormal growth of crystal grains of the sintered body cannot be suppressed, so that the strength and toughness of the oxide portion of the sintered body are small, and Can not get. On the other hand, the amount of silica added is
If it exceeds 10 wt%, the effect of addition does not change, but silica, which is larger than the amount of solid solution, reacts with the rare earth oxide or alumina to form a silicate compound, which is rather undesirable.
Therefore, the amount of silica added is limited to the above range of 0.1 to 10% by weight.

Further, if the amount of the mixed oxide is less than 5 wt%, the sinterability with Si ₃ N ₄ is deteriorated, and a dense sintered body cannot be obtained. On the other hand, when the amount of Si ₃ N ₄ is less than 5 wt%,
That is, if the amount of the mixed oxide exceeds 95 wt%, a sintered body excellent in hardness and high-temperature strength, which are the effects of adding Si ₃ N ₄ , cannot be obtained. Therefore, the mixing ratio of the mixed oxide and Si ₃ N ₄ is limited as described above.

The rare earth oxide (Ln ₂ O ₃ ) includes
Sc ₂ O ₃ , Y ₂ O ₃ , La ₂ O ₃ , CeO ₂ , Pr ₂ O ₃ , Nd ₂ O ₃ , Sm ₂ O ₃ , Eu ₂ O ₃ ,
Gd ₂ O ₃ , Tb ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ O ₃ , Er ₂ O ₃ , Tm ₂ O ₃ , Yb ₂ O ₃ ,
Lu ₂ O ₃ is preferably used.

The mixed oxide and Si ₃ N ₄ powder or
In mixing with the Si ₃ N ₄ whisker, a usual machine used for mixing or kneading of powder can be used. This mixing may be either a dry method or a wet method. Particularly in the case of the wet method, mixing can be effectively performed by using a surfactant such as ethylamine or fish oil.

Next, the mixed raw material obtained as described above is dried once, and then formed into a predetermined shape. In this molding step, an organic polymer (polyethylene glycol, polyvinyl alcohol, etc.) is added as a molding aid to the above-mentioned mixed raw material, and molding can be carried out by applying a known molding technique in a usual manner.

Next, the production method of the present invention will be described.
In the method of the present invention, first, a mixture of Si ₃ N ₄ and a (Ln—Al—Si) mixed oxide is formed at a mixing ratio as described above. Next, the formed body is heated at a heating rate of 5 to 2000 ° C./min, and is subjected to a baking treatment at a temperature of 1500 to 1900 ° C. for 0.1 to 600 minutes to obtain a sintered body.

If the heating rate is lower than 5 ° C./min, a dense sintered body cannot be obtained, and it is impossible to raise the temperature faster than 2000 ° C./min. Is limited to the range.

If the sintering temperature is lower than 1500 ° C., a dense sintered body cannot be obtained due to insufficient sintering. On the other hand, if the sintering temperature is higher than 1900 ° C., Si ₃ N ₄ and alumina With the reaction, Si ₃ N ₄ is decomposed to form pores and is not densified. From this, the range of the appropriate firing temperature is 15
It is limited to the range of 00 to 1900 ° C.

Next, the calcination time is related to the calcination temperature, and it is preferable that the calcination temperature be long when the calcination temperature is low and short when the calcination temperature is high. No sintered body can be obtained, while the sintering effect hardly changes or the S
Since i ₃ N ₄ and alumina react with each other to form pores, the range is limited to 0.1 to 600 minutes.

It is to be noted that a non-oxidizing atmosphere (for example, an inert gas such as a nitrogen gas, an argon gas, or a helium gas) is preferable as an atmosphere for firing, since Si ₃ N ₄ is oxidized in an oxidizing atmosphere. Above all, the nitrogen gas atmosphere is good,
In a nitrogen high-pressure gas atmosphere, the decomposition of Si ₃ N ₄ can be suppressed, which is effective for synthesizing a dense sintered body at a high temperature.

The thus obtained Si ₃ N ₄ − of the present invention
The (Ln, Al, Si) oxide-based sintered body showed good sintering of Si ₃ N ₄ and oxide, and the toughness and strength of the oxide were remarkably improved as compared with the conventional one containing no silica. .

Next, the above-described technique for producing an oxide sintered body which is excellent in strength and toughness and can be used even at a high temperature by sintering an oxide containing silica and Si ₃ N ₄ is described above. This is particularly effective in the case of a rare earth oxide-alumina-silica-based sintered body containing a compound of Ln ₄ Al ₂ O ₉ or LnAlO ₃ as a main component. That is, a mixed powder 9 of a rare earth oxide and alumina having a composition of Ln ₄ Al ₂ O ₉ or LnAlO ₃
And 9.9～90Wt%, a mixed oxide 5 to 95 wt% of silica powder _{0.1 ~10wt%; Si 3 N 4} , or Si ₃ N ₄ whisker, or by mixing the mixture 95～5Wt% thereof,
The Si ₃ N ₄ -Ln ₄ Al ₂ O ₉ sintered body or SiC-LnAlO ₃ sintered body synthesized by the above-described method has a crystal grain size controlled to 30 μm or less. Was not produced and the strength and toughness were excellent.

The reason is that twins are not generated in the constituent particles in the sintered body, and a small number of twins are generated only with the progress of the cracks. It is considered that the energy of the strain can be absorbed by the movement of the twin plane, and the strength and toughness of the sintered body are increased. this is,
It is a mechanism of toughening that has not been known so far, and is a novel discovery of the inventors.

[0031]

【Example】

(Example 1) Si ₃ N ₄ powder in 130 ml of ethyl alcohol
60g, Y ₂ O ₃ powder 71.2g, Al ₂ O ₃ powder 16.1g and SiO ₂ powder
2.7 g of the mixed powder was added, 2 ml of diethylamine was further added, and the mixture was wet-mixed for 72 hours using a ball mill. After mixing is completed, the mixture is heated to 60 ° C. to evaporate the alcohol and
% Of an aqueous polyethylene glycol solution, and mixed by stirring, followed by drying. Thereafter, it was formed into a formed body having a size of 45 × 20 × 5 mm ³ . Next, the formed body is heated to 500 ° C. in air at a rate of 2 ° C./min.
It was calcined by holding for a time. Next, the calcined sample was heated at a rate of 50 ° C./min under a pressure of 9.8 kgf / cm ² of nitrogen gas.
The temperature was raised to 1650 ° C. and maintained at 1650 ° C. for 20 minutes to obtain a sintered body.

The obtained sintered body was densely sintered, and almost no pores were observed. The bending strength of the sintered body is 1100 MPa, and the fracture toughness value K _IC = 16MP ·
m ^1/2 .

Example 2 In 90 ml of ethyl alcohol, 80 g of Si ₃ N ₄ powder, 17.01 g of Gd ₂ O ₃ powder, and 2.39 g of Al ₂ O ₃ powder
A mixed powder of 0.6 g of SiO ₂ powder and 1.5 g of diethylamine were added, and the mixture was wet-mixed for 72 hours using a ball mill. After completion of the mixing, the mixture was heated to 60 ° C. to evaporate the alcohol, and then stirred and mixed in a 5% aqueous polyethylene glycol solution, followed by drying. Then 45 × 20 ×
It was molded into a green compact having a size of 5 mm ³ . Next, the formed body was heated to 500 ° C. in air at a rate of 2 ° C./min, and calcined at 500 ° C. for 2 hours. Next, the calcined sample was heated to 80 ° C. under a pressure of 9.8 kgf / cm ² of nitrogen gas.
The temperature was raised to 1750 ° C. at a rate of 1 / min, and maintained at 1750 ° C. for 5 minutes to obtain a sintered body.

The obtained sintered body was densely sintered, and almost no pores were observed. The bending strength of the sintered body is 1200 MPa, and the fracture toughness value K _IC = 14MP ·
m ^1/2 .

[0035] ethyl alcohol (Example ₃₎ 90ml, Si 3 N ₄ powder 67.9g, Nd ₂ O ₃ powder 22.33g, Al ₂ O ₃ powder 6.77
It was charged with a mixed powder of g and SiO ₂ powder 3.0 g, further 1.5ml
Was added and wet-mixed for 72 hours using a ball mill. After completion of the mixing, the mixture was heated to 60 ° C. to evaporate the alcohol, and then stirred and mixed in a 5% aqueous polyethylene glycol solution, followed by drying. afterwards,
It was molded into a green form having a size of 45 × 20 × 5 mm ³ . next,
This formed form is heated in air at a rate of 2 ° C./min.
The temperature was raised to 500 ° C., and calcined at 500 ° C. for 2 hours.
This calcined sample was placed under a pressure of 5 kgf / cm ² of nitrogen gas.
The temperature was raised to 1800 ° C. at a rate of 50 ° C./min and maintained at 1800 ° C. for 2 minutes to obtain a sintered body.

The obtained sintered body was densely sintered, and almost no pores were observed. The bending strength of the sintered body is 1050MPa, and the fracture toughness value K _IC = 13MP ·
m ^1/2 .

Example 4 A mixed powder of 90 g of Si ₃ N ₄ powder, 7.0 g of Y ₂ O ₃ powder, 2.0 g of Al ₂ O ₃ powder and 3.0 g of SiO ₂ powder was placed in 90 ml of ethyl alcohol. Further, 1.5 ml of diethylamine was added and wet-mixed for 72 hours using a ball mill. After completion of the mixing, the mixture was heated to 60 ° C. to evaporate the alcohol, and then stirred and mixed in a 5% aqueous polyethylene glycol solution, followed by drying. Then 45x
It was molded into a green compact having a size of 20 × 5 mm ³ . Next, the formed product is heated in air at a rate of 2 ° C./min.
The temperature was raised to 500 ° C., and calcined at 500 ° C. for 2 hours. This calcined sample was subjected to 500 kg under a pressure of 30 kgf / cm ² of nitrogen gas.
The temperature was increased to 1800 ° C. at a rate of temperature increase of 1 ° C./min, and maintained at 1800 ° C. for 10 minutes to obtain a sintered body.

The obtained sintered body was densely sintered, and almost no pores were observed. The bending strength of the sintered body is 1100 MPa, and the fracture toughness value K _IC = 13MP ·
m ^1/2 .

Example 5 10 g of Si ₃ N ₄ powder, 78.9 g of Ho ₂ O ₃ powder, and 10.65 g of Al ₂ O ₃ powder in 90 ml of ethyl alcohol
And charged with a mixed powder of SiO ₂ powder 0.45 g, further added diethylamine 1.5 ml, 72 hours a wet mixed using a ball mill. After completion of the mixing, the mixture was heated to 60 ° C. to evaporate the alcohol, and then stirred and mixed in a 5% aqueous polyethylene glycol solution, followed by drying. Then 45
A green compact having a size of × 20 × 5 mm ³ was formed. Next, the formed product is heated in air at a rate of 2 ° C./min.
The temperature was raised to 0 ° C., and the temperature was maintained at 500 ° C. for 2 hours for calcination. Next, the calcined sample was heated to 1680 ° C. in nitrogen gas at a rate of 50 ° C./min, and kept at 1680 ° C. for 20 minutes to obtain a sintered body.

The obtained sintered body was densely sintered, and almost no pores were observed. The bending strength of the sintered body was 1050MPa, and the fracture toughness value K _IC = 14MP ·
m ^1/2 .

Example 6 50 g of Si ₃ N ₄ powder, 42.36 g of Er ₂ O ₃ powder and 5.64 g of Al ₂ O ₃ powder in 90 ml of ethyl alcohol
A mixed powder of 2.0 g of SiO ₂ powder and 2.0 g of SiO ₂ powder were added, and 1.5 ml of diethylamine was further added, followed by wet mixing using a ball mill for 72 hours. After completion of the mixing, the mixture was heated to 60 ° C. to evaporate the alcohol, and then stirred and mixed in a 5% aqueous polyethylene glycol solution, followed by drying. Then 45
It was molded into a green compact having a size of × 20 × 5 mm ³ . Next, the formed product is heated in air at a rate of 2 ° C./min.
The temperature was raised to 0 ° C., and the temperature was maintained at 500 ° C. for 2 hours for calcination. Next, this calcined sample is heated at a rate of 80 ° C./min in air.
The temperature was raised to 1800 ° C. and maintained at 1800 ° C. for 10 minutes to obtain a sintered body.

The obtained sintered body was densely sintered, and almost no pores were observed. The bending strength of the sintered body was 1100 MPa, and the fracture toughness value K _IC = 15MP ·
m ^1/2 .

The Si ₃ N ₄ thus obtained by the method of the present invention
-(Ln, Al, Si) oxide-based sintered body is dense and free of pores,
It is composed of particles having an average crystal grain size of 30 μm or less. Moreover, the sintered body of the present invention has sufficient strength and fracture toughness for practical use. In particular, regarding the fracture toughness value, about 3% of the conventional Si ₃ N ₄ sintered body or its composite material.
It has twice the value, and also has a value that is at least 50% greater in strength.

[0044]

As described above, according to the present invention, the rare earth oxide-alumina-silica mixed oxide and Si ₃ N ₄ are fired to control the crystal grain size of the sintered body to 30 μm or less. In addition, by preventing the formation of pores, it is possible to achieve both high toughness of oxide sintered body and excellent properties of high temperature strength of Si ₃ N _{4. 3} N ₄ −
(Ln, Al, Si) oxide-based sintered bodies can be easily obtained.

Therefore, according to the present invention, the engine parts,
Gas turbine blades, parts for gas turbines, parts for corrosion-resistant equipment, parts for crucibles, parts for ball mills, heat exchangers for high-temperature furnaces, heat-resistant materials, heat-resistant materials for high-altitude flying objects, combustion pipes, parts for die casting,
Insulation materials, fusion reactor materials, nuclear reactor materials, solar reactor materials,
Tools, heat shielding materials, electronic circuit substrates, sealing materials, fittings and valve parts, biomaterials such as artificial bones and artificial roots, dielectric materials, blades and cutter blades, sporting goods, pumps, nozzles, magnetic heads, rollers, Guides, bearings, ferrules, and other materials that can be effectively used in a wide range of fields can be provided.

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Claims (2)

(57) [Claims] Claims 1. A silicon nitride having a content of 95 to 5 wt% and Ln4Al2O9
Or LnAlO3 (where Ln is a rare earth element and
Et compounds) 99.9～90Wt% and silica 0.1 10 wt mixed oxide 5 to 95 wt% consisting percent, silicon nitride formed of a sintered body of - mixed oxide-based sintered body. 2. 95-5 wt% of silicon nitride and Ln4Al2O9
Or LnAlO3 (where Ln is a rare earth element and
Compounds of 99.9 to 90 wt% and a mixed oxide of 0.1 to 10 wt% of silica and 5 to 95 wt% are mixed, and then the obtained mixture molded body is heated to 5 to 2000 ° C. in a non-oxidizing atmosphere. / Min at a heating rate of 1500 to 1900
A method for producing a silicon nitride-mixed oxide-based sintered body, characterized in that the firing is carried out while maintaining the temperature in a temperature range of 0.1 to 600 minutes.