JP3007730B2 - Rare earth oxide-alumina sintered body and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth oxide-alumina sintered body and a method for producing the same, and more particularly, to reducing pores in ceramics which cause a reduction in strength and toughness and suppressing abnormal grain growth. Proposed a systematically dense rare earth oxide-alumina sintered body having high strength and toughness.

[0002]

2. Description of the Related Art Oxide ceramics have high strength at high temperatures and are excellent in heat resistance, oxidation resistance and corrosion resistance. Therefore, they must be used at least up to several hundred degrees of their melting point. Can be. Therefore, the melting point is 2000
Rare earth oxides (oxides of rare earth elements and mixtures thereof) and alumina exceeding 0 ° C. have been regarded as promising ceramic materials for high temperatures. In particular, even in the case of a mixed ceramic comprising these two types of oxides, the melting point is around 2000 ° C., which is considered to be effective as a so-called high-temperature material.

[0003] However, in general, in the case of oxide-mixed ceramics, when a mixture of oxides is fired to obtain a sintered body, the crystal grains cause abnormal growth, resulting in a large crystal grain size of 100 μm or more. There is a problem that pores are easily formed and are not easily densified. Moreover, the obtained sintered body had extremely low strength, toughness and hardness due to the abnormally grown crystal grains and the pores. For these reasons, to date, such sintered bodies of such oxide-mixed ceramics have not reached practical use.

[0004] In particular, compounds having a composition of rare earth oxides of Ln ₄ Al ₂ O ₉ and LnAlO ₃ are very brittle polycrystalline sintered bodies because they form twins by martensitic transformation during firing. There was a fatal drawback that you could only get it.

[0005]

As a method for suppressing abnormal grain growth of a polycrystalline sintered body of an oxide-mixed ceramic, a method of controlling a firing temperature and a firing time is conventionally effective. It was thought vaguely. However, rare earth oxide-alumina-based sintered bodies have not been put into practical use as ceramic materials because the suppression technology has not yet been established.

An object of the present invention is to establish the above-mentioned suppression technique that can be repeated, that is, to find out suitable conditions for a firing temperature and a firing time of a polycrystalline sintered body of an oxide mixed ceramic, Accordingly, it is an object to propose a rare earth oxide-alumina sintered body suitable for practical use, in which the crystal grain size of the sintered body is appropriately controlled, and which has excellent strength and toughness, and is suitable for practical use.

[0007]

Means for Solving the Problems As a result of earnest studies to realize the above-mentioned object, the inventors have found that when the crystal grain size of a mixture sintered body of a rare earth oxide and alumina is controlled to 30 μm or less, It has been found that desired strength and toughness desired for such a sintered body can be obtained. Therefore, when further research was conducted on the conditions for obtaining such a crystal grain size, the firing temperature was set to 1500 under a predetermined mixing ratio.
It has been found that it is effective to perform calcination at a temperature within the range of ℃ 1800 ° C. and a calcination time of 0.1 to 10 hours, and the present invention having the following gist configuration has been completed.

That is, the present invention relates to a rare earth oxide
A mixture of wt% and 95-5 wt% of alumina is formed, and then the mixture is heated at a heating rate of 1-200 ° C / min and kept at a temperature range of 1500-1800 ° C for 0.1-10 hours. A rare earth oxide characterized by being fired to obtain a sintered body containing Ln ₄ Al ₂ O ₉ or LnAlO ₃ as a main component.
A method for producing an alumina sintered body, and a rare earth oxide-alumina sintered body having a crystal grain size of 30 μm or less synthesized by the method.

[0009]

According to the findings of the inventors, the rare earth oxide-alumina sintered body has a particle diameter of 30 μm.
It is important to control below, and it has been found that such control of the crystal grain size can be achieved by devising firing conditions. Therefore, as a result of further research, it was found that the proper combination of the two and sintering at the appropriate firing temperature and appropriate firing time required pores and abnormal grain growth in the sintered body, which reduced the strength and toughness. The present inventors have found that the present invention is effective in preventing the above, and arrived at the present invention.

According to the method for producing a rare earth oxide-alumina sintered body of the present invention, first, 5 to 95 wt% of rare earth oxide powder and 95 to 5 wt% of alumina powder are mixed.

Here, when the rare earth oxide powder is less than 5 wt%, the properties of the obtained rare earth oxide-alumina sintered body are deviated from those of the alumina sintered body alone, while the alumina is less than 5 wt%. In this case, the properties of the obtained rare earth oxide-alumina sintered body are biased to the properties of the rare earth oxide alone, so the range is limited to the above range.

The rare earth oxide (Ln ₂ O ₃ ) includes
For example, 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 and Lu ₂ O ₃ are preferably used.

In mixing the oxide powder, an ordinary machine used for mixing or kneading 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 continuously formed into a predetermined shape.
In this molding step, an organic polymer (polyethylene glycol, polyvinyl alcohol, or the like) is added as a molding aid to the above-mentioned mixed raw material, and molding can be performed by applying a commonly known molding technique.

Next, the green compact is heated at a heating rate of 1 to 200 ° C. and is sintered at a temperature of 1500 to 1800 ° C. for 0.1 to 10 hours to form a sintered body. If the firing temperature is lower than 1500 ° C., a dense sintered body cannot be obtained due to insufficient sintering, while if it is higher than 1800 ° C., abnormal growth of crystal grains is caused. From this, the range of the appropriate firing temperature is limited to the range of 1500 to 1800 ° C. Next, the sintering time is related to the sintering temperature, and it is preferable that the sintering temperature be long when the sintering temperature is low and short when the sintering temperature is high. On the other hand, if it exceeds 10 hours, abnormal growth of crystal grains is caused, so that the range is limited to 0.1 to 10 hours. If the heating rate is lower than 1 ° C./min, sintering takes too much time, which is not economical. If the heating rate is higher than 200 ° C./min, a dense sintered body cannot be obtained. Is limited to the range.

The firing is preferably performed in an oxidizing atmosphere, but may be performed in a non-oxidizing atmosphere (eg, nitrogen gas, argon gas, helium gas) or in a vacuum.

In the rare earth oxide-alumina sintered body obtained by applying such firing conditions, the crystal grain size of the constituent particles is controlled to 30 μm or less. As a result, it is possible to obtain a rare earth oxide-alumina sintered body having strength and toughness that could not be expected in the related art.

In general, when the crystal grain size of the constituent particles of the ceramics exceeds 50 μm, the strength is significantly reduced. Therefore, in order to obtain a ceramic material with high strength,
Must be 50 μm or less. Therefore, in the present invention, when the average particle size is 30 μm or less, the maximum particle size is 50 μm.
m, the average crystal grain size is controlled to 30 μm or less.

Next, the control of the crystal grain size by controlling the sintering conditions is performed by controlling Ln ₄ Al ₂ O which causes martensitic transformation during sintering.
_This is particularly effective in the case of a rare earth oxide-alumina sintered body containing a compound ₉ or LnAlO ₃ as a main component. That is, a mixture of a rare earth oxide having a composition of Ln ₄ Al ₂ O ₉ or LnAlO ₃ and alumina is fired by the above-described method of the present invention to synthesize Ln ₄ Al ₂ O ₉ or LnA.
A rare earth oxide-alumina sintered body containing lO ₃ as a main component is:
Since the crystal grain size was controlled to 30 μm or less, no brittleness was observed when the crystal grain size was 100 μm.

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. And the movement of the twin plane can also absorb the energy of the strain, so that the strength and toughness of the sintered body are considered to be increased. This is a previously unknown mechanism of toughening, and is a novel discovery of the inventors. Hereinafter, description will be made in accordance with embodiments.

[0021]

【Example】

(Example 1) in an alcohol solution of 50 ml Ho ₂ O ₃ powder 66g and the Al ₂ O
9 g of the _three powders were added, 1 ml of diethylamine was further added, and the mixture was wet-mixed using a ball mill for 48 hours. After mixing, heat to 60 ° C. to evaporate the alcohol, then
Mix in 5% polyethylene glycol aqueous solution,
This was dried. Thereafter, it was formed into a formed form having a size of 45 × 20 × 4 mm ³ . The resulting form is then placed in air for 2 hours.
The temperature was raised to 500 ° C. at a rate of 500 ° C./min, and calcined at 500 ° C. for 1 hour. The calcined sample was heated to 1650 ° C. in air at a rate of 10 ° C./min, and kept at 1650 ° C. for 4 hours to obtain a sintered body.

The average crystal grain size of the obtained sintered body is 3 μm
Met. Further, the bending strength of the sintered body was 600 MPa, and the fracture toughness value K _IC was 7 MP · m ^1/2 .

Example 2 Nd ₂ O in 100 ml of alcohol
₃ Put the flour 115g and Al ₂ O ₃ powder 35 g, further added diethylamine 2 ml, 72 hours a wet mixed using a ball mill. After the mixing was completed, the mixture was heated to 60 ° C. to evaporate the alcohol, and then mixed in a 5% aqueous polyethylene glycol solution and dried. Then 45 × 20 × 4
It was formed into green product of the magnitude of mm ^3. Next, the green compact was heated to 500 ° C. in air at a rate of 1.5 ° C./min, and calcined at 500 ° C. for 1 hour. The calcined sample was heated to 1550 ° C. in air at a rate of 10 ° C./min,
It was kept at 1550 ° C. for 2 hours to obtain a NdAlO ₃ sintered body.

The average crystal grain size of the obtained sintered body is 3 μm
Met. Further, the bending strength of the sintered body was 550 MPa, and the fracture toughness value K _IC was 7 MP · m ^1/2 .

Example 3 Er ₂ O ₃ in 70 ml of alcohol
88.2 g of the powder and 11.8 g of the Al ₂ O ₃ powder were added, and 1 ml of diethylamine was further added, followed by wet mixing using a ball mill for 72 hours. After the mixing was completed, the mixture was heated to 60 ° C. to evaporate the alcohol, and then mixed in a 5% aqueous polyethylene glycol solution and dried. Then 45 × 20 × 4
It was formed into green product of the magnitude of mm ^3. Next, the green compact was heated to 500 ° C. in air at a rate of 2 ° C./min, and calcined at 500 ° C. for 2 hours. The calcined sample was heated to 1530 ° C. in air at a rate of 15 ° C./min,
It was kept at 1530 ° C. for 5 hours to obtain a sintered body.

The average crystal grain size of the obtained sintered body is 5 μm
It was below. Further, the bending strength of the sintered body was 600 MPa, and the fracture toughness value K _IC was 8 MP · m ^1/2 .

Example 4 Tm ₂ O ₃ in 70 ml of alcohol
88.3 g of the powder and 11.7 g of Al ₂ O ₃ powder were added, and 1 ml of diethylamine was further added, followed by wet mixing using a ball mill for 72 hours. After the mixing was completed, the mixture was heated to 60 ° C. to evaporate the alcohol, and then mixed in a 5% aqueous polyethylene glycol solution and dried. Then 45 × 20 × 4
It was formed into green product of the magnitude of mm ^3. Next, the formed body was heated to 1600 ° C. in air at a rate of 2 ° C./min, and kept at 1600 ° C. for 2 hours to obtain a sintered body.

The average crystal grain size of the obtained sintered body is 5 μm
Met. Further, the bending strength of the sintered body was 550 MPa, and the fracture toughness value K _IC was 7 MP · m ^1/2 .

Example 5 La ₂ O ₃ in 70 ml of alcohol
76.2 g of the powder and 23.8 g of the Al ₂ O ₃ powder were added, and 1 ml of diethylamine was further added, followed by wet mixing using a ball mill for 72 hours. After the mixing was completed, the mixture was heated to 60 ° C. to evaporate the alcohol, and then mixed in a 5% aqueous polyethylene glycol solution and dried. Then 45 × 20 × 4
It was formed into green product of the magnitude of mm ^3. Next, the green compact was heated to 500 ° C. in air at a rate of 2 ° C./min, and calcined at 500 ° C. for 2 hours. The calcined sample was heated to 1650 ° C. in air at a rate of 5 ° C./min.
It was kept at 1650 ° C. for 2 hours to obtain a sintered body.

The average crystal grain size of the obtained sintered body is 4 μm
Met. The bending strength of the sintered body was 600 MPa, and the fracture toughness value K _IC was 6 MP · m ^1/2 .

Example 6 Yb ₂ O ₃ in 80 ml of alcohol
88.5 g of the powder and 11.5 g of the Al ₂ O ₃ powder were added, and 1 ml of diethylamine was further added, followed by wet mixing using a ball mill for 72 hours. After the mixing was completed, the mixture was heated to 60 ° C. to evaporate the alcohol, and then mixed in a 5% aqueous polyethylene glycol solution and dried. Then 45 × 20 × 4
It was formed into green product of the magnitude of mm ^3. Next, the green compact was heated to 500 ° C. in air at a rate of 2 ° C./min, and calcined at 500 ° C. for 2 hours. The calcined sample was heated to 1600 ° C. at a rate of 10 ° C./min in air,
It was kept at 1600 ° C. for 2 hours to obtain a sintered body.

The average crystal grain size of the obtained sintered body is 3 μm
Met. Further, the bending strength of the sintered body was 650 MPa, and the fracture toughness value K _{IC was} 6.5 MP · m ^1/2 .

Thus, the rare earth oxide-alumina sintered body obtained by the method of the present invention 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, the fracture toughness value is about twice that of alumina or mullite.

[0034]

As described above, according to the present invention, by controlling the crystal grain size of the sintered body to 30 μm or less, formation of pores is prevented, and a dense and high strength and toughness can be obtained. A uniform rare earth oxide-alumina sintered body can be easily obtained. Therefore, a rare earth oxide-alumina sintered body that has not been conventionally put to practical use as a ceramic material can be put to practical use.

Therefore, according to the present invention, the engine parts,
Gas turbine blades, parts for gas turbines, parts for corrosive equipment, parts for crucibles, parts for ball mills, heat exchangers and refractory materials for high temperature furnaces, refractory materials for high altitude flying objects, combustion tubes, die casting parts, insulating materials, fusion reactors Materials, reactor materials, solar furnace 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, sports Supplies, pumps, nozzles, magnetic heads, rollers, guides, bearings, ferrules, and other items that can be effectively used in a wide range of fields can be provided.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C04B 35/50 C04B 35/10

Claims (2)

(57) [Claims] 1. A rare earth oxide of 5 to 95% by weight and alumina of 95 to 95% by weight.
Ln ₄ Al ₂ O ₉ or LnA obtained by firing 5 wt%
lO ₃ (where Ln is a rare earth element and a mixture thereof)
The a sintered body composed mainly, rare earth oxide, characterized in that the crystal grain size of the sintered body is 30μm or less - alumina sintered body. 2. A mixture of a rare earth oxide and alumina is formed, and then the mixture is heated at a rate of 1 to 200 ° C./min and kept in a temperature range of 1500 to 1800 ° C. for 0.1 to 10 hours. And sintering , Ln ₄ Al ₂ O ₉ or LnAlO ₃
(However, Ln is a rare earth element and a mixture thereof)
A method for producing a rare earth oxide-alumina sintered body, which comprises producing a sintered body as a component.