JPH0624834A - Composition for producing beta-alumina sintered compact - Google Patents

Abstract

PURPOSE:To provide a raw material composition capable of obtaining a dense a beta-alumina sintered compact excellent in Na ion conductivity by mixing zirconia powder, a Na compound, a stabilizer and Al powder at a specific weight ratio. CONSTITUTION:(A) 0.1-50wt.% zirconia powder, (B) 1-40wt.% Na compound (e.g. sodium carbonate), (C) 0.1-10wt.% stabilizer (e.g. Li carbonate) and (D) >=20wt.% Al powder are mixed, and the composition for producing the beta-alumina sintered compact is produced. Next the composition is molded any by performing a reactive sintering, the beta-alumina sintered compact is obtained. At the time of sintering, the Al powder is oxidized and further reacted with the Na compound and the stabilizer to obtain beta-alumina. At this time, Al is allowed to generate volume expansion. The volume expansion cancels partially the shrinkage due to the sintering and then the shrinkage ratio can be restrained at a lower ratio, thus the dimensional preeision of the sintered compact can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composition for producing a beta-alumina sintered body, which has excellent sodium ion conductivity and is used as a solid electrolyte for sodium-sulfur secondary batteries and alkali metal thermoelectric generators. A raw material composition for producing a sintered body suitable as a material.

[0002]

_2. Description of the Related Art β-Alumina is Na ₂ O.11Al ₂ O
₃ , β ″ -alumina is a compound having a theoretical composition of Na ₂ O · 5.33Al ₂ O _{3. In} the present invention, β-alumina, β ″ -alumina, or a mixture thereof is collectively referred to. It is called beta alumina.

Now, a material for a solid electrolyte of a sodium-sulfur secondary battery or an alkali metal thermoelectric power generator, which has been expected as a power source for a distributed power plant, a power source for an electric vehicle, or a power storage device for road leveling. As
A beta-alumina sintered body having excellent sodium ion conductivity has been investigated.

As a method for producing a sintered body of beta-alumina, there is a method of compacting and sintering powder consisting of beta-alumina alone. There is also a method of molding and sintering a mixture of α-alumina powder, a sodium compound (eg sodium carbonate etc.) and a stabilizer (eg lithium carbonate etc.). In this method, the process of synthesizing beta alumina by the reaction of α-alumina powder and a sodium compound and the process of sintering proceed simultaneously.

A method for obtaining a ceramic sintered body by mixing aluminum powder and alumina powder, molding the mixture, and reacting and sintering the mixture is disclosed in Japanese Patent Publication No. 3-502569. However, this publication does not disclose a reaction in which alumina reacts with a sodium compound to form beta alumina, nor does it disclose a composition for producing a beta-alumina sintered body containing a sodium compound.

[0006]

The beta-alumina sintered body suitable as a material for a solid electrolyte needs to be dense. However, beta-alumina is a material that is difficult to sinter, and it was difficult to sinter beta-alumina powder to produce a sintered body having a high density. To improve sinterability,
A method of synthesizing fine powder of beta alumina and using it for sintering has also been studied. However, since beta-alumina reacts with moisture in the air to cause deterioration and is particularly easy to decompose in fine powder, sufficient equipment for storage method and handling is required, and industrialization is difficult. It was

The method of molding and sintering a composition consisting of α-alumina powder, a sodium compound and a stabilizer has a problem that the reaction does not proceed sufficiently and α-alumina remains. Since α-alumina has no sodium ion conductivity, the conductivity decreases when it remains, and the produced sintered body was not always sufficiently suitable as a material for a solid electrolyte.

As described above, the technique for obtaining a beta-alumina sintered body suitable as a material for a solid electrolyte is not yet sufficient. Therefore, an object of the present invention is to provide a raw material composition for producing a beta alumina sintered body having excellent sodium ion conductivity and high density as a material for a solid electrolyte.

[0009]

In view of the above circumstances, the present inventors have made earnest studies on a raw material composition for producing a beta-alumina sintered body by reaction sintering using aluminum powder as a raw material. The present invention has been completed.

That is, the present invention comprises 0.1 to 50% by weight of zirconia powder, 1 to 40% by weight of sodium compound, 0.1 to 10% by weight of stabilizer, and 20% by weight or more of aluminum powder. A composition for producing a beta-alumina sintered body, and 0.1 to 50% by weight of zirconia powder,
Composition for producing beta-alumina sintered body, which comprises 0.1 to 60% by weight of alumina powder, 1 to 40% by weight of sodium compound, 0.1 to 10% by weight of stabilizer, and 10% by weight or more of aluminum powder. I will provide a.

The present invention will be described in detail below. Zirconia powder, sodium compound, stabilizer and aluminum powder are combined to make 100% by weight of the raw material composition, or zirconia powder, alumina powder, sodium compound, stabilizer and aluminum powder are combined to make 100% by weight. The raw material composition described above is mixed and pulverized by a pulverizer with a dispersion medium, and then this is dried to remove the dispersion medium to obtain a mixed powder. A beta-alumina sintered body is obtained by molding the mixed powder and performing reaction sintering.

The aluminum powder is oxidized by sintering in air, and further reacts with a sodium compound and a stabilizer for beta-alumina to become beta-alumina. At this time, aluminum causes volume expansion. This volume expansion partially cancels the contraction due to sintering, and the contraction rate can be suppressed to a low level. If the dimensional change is slight, the dimensional accuracy of the sintered body can be improved, and post-processing is not required, which is an extremely advantageous method industrially.

The aluminum powder used as a raw material is preferably fine particles having an average particle size of 300 μm or less in order to achieve uniform mixing. Further, it is necessary that the purity is high, and particularly, since silicon, iron and calcium reduce the sodium ion conductivity of the sintered body of beta-alumina, iron and silicon are preferably 1000 ppm or less, respectively.
More preferably, it is less than or equal to ppm. Calcium is 10ppm
Is preferable and 1 ppm or less is more preferable.

In the combination of zirconia powder, sodium compound, stabilizer and aluminum powder, the addition range of aluminum powder is 20 to 98.8% by weight. On the other hand, in the case of the combination of zirconia powder, alumina powder, sodium compound, stabilizer and aluminum powder, the addition range of aluminum powder is 10 to 98.7% by weight. In any case, when the addition amount of the aluminum powder becomes small, the addition amount of the sodium compound becomes relatively large, and the excess sodium remains as a compound containing aluminum such as NaAlO ₂ and the sodium ion conductivity of the sintered body is increased. It is not preferable because it lowers the property.

The shrinkage can be controlled by adding alumina powder to the raw material mixture. The alumina powder used here may be α-alumina, intermediate alumina such as γ-alumina, or a mixture thereof, but since the added alumina powder reacts with the sodium compound and the stabilizer, it changes to beta alumina. , With high purity,
A fine powder having an average particle size of 3 μm or less, which allows sodium and the stabilizer to easily diffuse into the alumina powder particles, is preferable.

When alumina powder is added, the amount added is in the range of 0.1 to 60% by weight. If the addition amount of the alumina powder is more than 60% by weight, the amount of the aluminum powder becomes small and the effect of reducing the shrinkage ratio may not be seen, and a part of the added alumina may become β-alumina or β ″ -alumina. However, intermediate alumina such as α-alumina or γ-alumina may remain in the sintered body as it is.If the amount of alumina powder added is less than 0.1% by weight, alumina should be added. The effect of controlling the shrinkage rate does not appear, but if the shrinkage rate is not controlled, alumina powder may not be added.

As the sodium compound, sodium salts such as sodium carbonate can be used. Also, N
Compounds containing aluminum such as aAlO ₂ may be used. However, sodium nitrate has a strong oxidizing property, which significantly accelerates the oxidation of aluminum powder during the mixing of the raw materials,
It is not preferable because it may cause an explosive oxidation reaction. The amount of sodium compound added is in the range of 1 to 40% by weight. If the content exceeds 40% by weight, the excess sodium becomes N
It remains as a compound containing aluminum such as aAlO ₂ and reduces the sodium ion conductivity of the sintered body.
If it is less than 1% by weight, the proportion of β ″ -alumina having relatively high sodium ion conductivity decreases and the proportion of β-alumina having relatively low sodium ion conductivity increases, or the sodium ion conductivity increases. Since α-alumina having no property is generated, the sodium ion conductivity of the sintered body is lowered.

As the stabilizer, salts containing metal ions such as magnesium, lithium, nickel, cobalt, copper, zinc and manganese can be used, but the present invention is not limited thereto. However, nitrate is not preferable for the same reason as sodium nitrate. The amount of stabilizer added is in the range of 0.1 to 10% by weight. 0.1
If the amount is less than wt%, α-alumina or γ-alumina remains in the sintered body to lower the sodium ion conductivity, which is not preferable. If the amount is too large, the excess stabilizer remaining in the sintered body lowers the sodium ion conductivity of the sintered body.
Below, 0.5 to 5% by weight is preferable, and 0.5 to 3% by weight is more preferable.

Although the mechanism of zirconia powder is not clear, it has the effect of promoting the oxidation of aluminum powder during firing. However, since zirconia does not have sodium ion conductivity, adding a large amount reduces the sodium ion conductivity of the sintered body. Therefore, the amount of zirconia added is in the range of 0.1 to 50% by weight. Preferably 1 to 25
% By weight. If the amount added is less than 0.1% by weight, the effect of promoting the oxidation of aluminum powder does not appear. 50% by weight
When it exceeds, the sodium ion conductivity of the sintered body is lowered, which is not preferable. The zirconia powder does not react with beta alumina, but contributes to the improvement of strength and fracture toughness by being dispersed as a second phase in the sintered body. The zirconia powder to be added may be either a monoclinic crystal or a tetragonal crystal and a cubic crystal stabilized by yttrium oxide, magnesium oxide, cerium oxide, etc., but in order to further enhance the effect of improving strength and fracture toughness, zirconia Is preferably dispersed in a tetragonal state.

The dispersion medium is not particularly limited, but it is desirable to use a non-aqueous organic solvent which is inert to aluminum, and for example, acetone, cyclohexane, mineral spirits, etc. can be used.

For mixing the raw material powders, it is desirable to use a mixing and crushing machine having a great crushing power, such as an attrition mill or a pal mill.

For drying, in order to remove the dispersion medium, the temperature and time may be appropriately determined according to the dispersion medium used.

As a method for producing the molded body, a dry press,
A method such as slip casting, tape casting or injection molding can be used. The molded body produced by the above method can be subjected to cold isotropic press (hereinafter abbreviated as CIP) treatment at a pressure of usually 45 to 900 MPa.

Sintering is preferably carried out in air in the temperature range of 1200 to 1600 ° C. for 5 minutes to 5 hours. 1
If the temperature is 200 ° C. or lower, the density of the obtained sintered body becomes low, which is not preferable. Abnormal grain growth occurs above 1600 ° C,
The mechanical strength is reduced and the life when used as a solid electrolyte is shortened.

When the relative density of the zirconia-containing beta-alumina sintered body is 85% or less, open pores remain, and liquid sodium sinters when used as a solid electrolyte of a sodium-sulfur secondary battery. It cannot be used because it penetrates the body.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto. The following method was used for the measurement. Density of sintered body: Archimedes method using ethanol. The theoretical density for calculating the relative density is 3.26 g / cm ³ for β-alumina and 3.29 g / c for β ″ -alumina.
The value of m ³ was used. Generation phase of sintered body: X-ray diffraction method (manufactured by Rigaku Corporation, model No. 2013). The formation ratios of α-alumina, β-alumina and β ″ -alumina are α (024) and β determined by X-ray diffraction measurement.
It was calculated from the ratio of the line intensities of the (0013) and β ″ (107) diffraction lines. Sodium ion conductivity of the sintered body: complex impedance plot method The specific resistance at 300 ° C. was measured.

[0027]

【Example】

Example 1 160.0 aluminum powder (manufactured by Toyo Aluminum Co., Ltd., purity 99.98%, average particle size 28.6 μm, analysis value by glow discharge mass spectrum is shown in Table 1)
g, sodium carbonate (Wako Pure Chemical Industries, Ltd., reagent special grade) 59.0 g, lithium carbonate (Wako Pure Chemical Industries, Ltd., reagent special grade) 6.9 g as a stabilizer, and yttrium oxide 3 mol% Zirconia powder (Sumitomo Chemical Co., Ltd., SYZ-3) solid-dissolved and stabilized is 60.0.
Attrition mill (Mitsui Miike Machining Machinery Co., Ltd., MA1SE, 2mmφ zirconia ball used) was added to 1200g of mineral spirits (Mineral Spirits A, manufactured by Nippon Oil Co., Ltd.). Then, they were mixed and pulverized for 6 hours. The mineral spirits were removed from the mixture by evaporation using a rotary evaporator. This powder is 4 × at a pressure of 20.4 MPa
A 5 × 20 mm shape was molded by a uniaxial press, and CIP was further performed at a pressure of 300 MPa to prepare a molded body. The compact density was 1.98 g / cm ³ . The compact was placed on a magnesia flat plate, covered with an alumina crucible, and sintered in air. After holding at 1200 ° C. for 1 hour, it was held at 1500 ° C. for 1 hour to perform sintering. The weight% of the used raw materials is shown in Table 2, and the measurement results of the density and the specific resistance of the obtained sintered body are shown in Table 3.

Example 2 All the same raw materials as in Example 1 were used, and aluminum powder was 160.0 g and sodium carbonate was 59.0.
g, 6.9 g of lithium carbonate as a stabilizer, and 2 mol of zirconia powder containing 3 mol% of yttrium oxide as a solid solution.
Mineral Spirit 1
Add to 200 g, mix and grind as in Example 1,
A molded body was produced in the same manner as in Example 1. The molded body was sintered in the same manner as in Example 1. The weight% of the used raw materials is shown in Table 2, and the measurement results of the density and the specific resistance of the obtained sintered body are shown in Table 3.

Example 3 All the same raw materials as in Example 1 were used, and aluminum powder was 160.0 g and sodium carbonate was 59.0.
g, 6.9 g of lithium carbonate as a stabilizer, and 5 mol of zirconia powder in which 3 mol% of yttrium oxide was dissolved.
2g, a mixed composition consisting of mineral spirits 120
In 0 g, the mixture was mixed and pulverized in the same manner as in Example 1 to produce a molded body in the same manner as in Example 1. The molded body was sintered in the same manner as in Example 1. Table 2 shows the weight% of the raw materials used.
Table 3 shows the measurement results of the density and the specific resistance of the obtained sintered body.

Example 4 All the same raw materials as in Example 1 were used, 160.0 g of aluminum powder and 50.3 of sodium carbonate were used.
g, 6.2 g of lithium carbonate as a stabilizer and 5 mol of zirconia powder in which 3 mol% of yttrium oxide was dissolved.
Mineral Spirit 1
Add to 200 g, mix and grind as in Example 1,
A molded body was produced in the same manner as in Example 1. The molded body was sintered in the same manner as in Example 1. The weight% of the used raw materials is shown in Table 2, and the measurement results of the density and the specific resistance of the obtained sintered body are shown in Table 3.

Example 5 83.6 g of aluminum powder similar to that in Example 1, α-
Alumina powder (Sumitomo Chemical Co., Ltd., AL-440
B, average particle size 2.6 μm) 157.8 g, sodium carbonate 61.6 g similar to Example 1, lithium carbonate similar to Example 1 as a stabilizer 7.2 g, and yttrium oxide 3 mol% solid. A mixed composition consisting of 56.0 g of the same dissolved zirconia powder as in Example 1 was added to 1260 g of cyclohexane, mixed and pulverized in the same manner as in Example 1, and a molded body was produced in the same manner as in Example 1. did. The obtained molded body was sintered in the same manner as in Example 1. The weight% of the used raw materials is shown in Table 2, and the measurement results of the density and the specific resistance of the obtained sintered body are shown in Table 3.

Example 6 γ-alumina powder (manufactured by Sumitomo Chemical Co., Ltd., AKP-G01) in place of the α-alumina powder in Example 5
Using 5), a mixed powder was obtained in the same manner as in Example 5. A molded body was produced in the same manner as in Example 1. The molded body was sintered in the same manner as in Example 1. The weight% of the used raw materials is shown in Table 2, and the measurement results of the density and the specific resistance of the obtained sintered body are shown in Table 3.

Comparative Example 1 All the same raw materials as in Example 5 were used, 29.9 g of aluminum powder and 248.7 of α-alumina powder were used.
g, 59.5 g of sodium carbonate as a stabilizer, 6.9 g of lithium carbonate, and 56.0 g of zirconia powder in which 3 mol% of yttrium oxide was solid-solved and stabilized, and 1260 g of cyclohexane was added to the mixed composition. ,
Mixing and pulverization were performed in the same manner as in Example 1, and a molded body was produced in the same manner as in Example 1. The obtained molded body was sintered in the same manner as in Example 1. The weight% of the used raw materials is shown in Table 2, and the measurement results of the density and the specific resistance of the obtained sintered body are shown in Table 3.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

[Table 3]

[0037]

The beta-alumina sintered body obtained by using the composition of the present invention is dense and has good sodium ion conductivity, and is suitable for sodium-sulfur secondary batteries and alkali metal thermoelectric generators. Since it is suitable as a material for a solid electrolyte, it is extremely useful industrially.

Claims (2)

[Claims] 1. A zirconia powder in an amount of 0.1 to 50% by weight, a sodium compound in an amount of 1 to 40% by weight, and a stabilizer in an amount of 0.1 to 50% by weight.
A composition for producing a beta-alumina sintered body, which comprises 10% by weight and 20% by weight or more of aluminum powder. 2. Zirconia powder is 0.1 to 50% by weight, alumina powder is 0.1 to 60% by weight, sodium compound is 1 to 40% by weight, stabilizer is 0.1 to 10% by weight, aluminum powder. A composition for producing a beta-alumina sintered body, which comprises 10% by weight or more.