JPH1045464A - Beta"alumina ceramic material for sodium-sulfur secondary cell and cell using that - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve flexibility and mechanical strength by adding and mixing a source powder, water-soluble binder and specified plasticizer in water to prepare a slurry and then drying and granulating the slurry. SOLUTION: A source material powder, water-soluble binder and plasticizer of an emulsion of oxidized microwax having 30 to 60 carbon atoms by 0.05 to 2.0wt.% (expressed in terms of a solid content) are added and mixed to water to obtain a slurry. The obtd. slurry is dried and granulated to obtain β"alumina ceramic granules. The obtd. granules are sintered to obtain a β"alumina ceramic solid electrolyte having η0.4% porosity. By this method, the granules are uniformly broken by the pressure during forming so that intergranular faces are hardly produced and the crystalline forms can be maintained. Thereby, the obtd. sintered body of the solid electrolyte has a uniform crystal phase and uniform grain size and excellent mechanical strength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing granulated powder for producing a β ″ alumina ceramic sintered body. More particularly, the present invention relates to a β ″ suitable as a solid electrolyte for an electrochemical device such as a sodium-sulfur battery. Production method of granulated powder to be raw material powder of alumina ceramics sintered body and granulated powder,
Β-alumina ceramics made with the granulated powder, and sodium incorporating the β-alumina ceramics
The present invention relates to a sulfur secondary battery.

[0002]

2. Description of the Related Art As described in "Granulation Handbook" (published by Ohmsha, 1991), pages 742 to 743, the production of granulated powder of beta "alumina ceramics is carried out. In general, an organic solvent is used because Na, which is a main component of, is eluted in water or deteriorates by moisture absorption. However, Japanese Unexamined Patent Publication (Kokai) No. 6-2 discloses that water and an organic binder are added to raw material powder, wet-mixed, and dried and granulated.
No. 83199, Japanese Patent Publication No. 58-58
As known from Japanese Patent No. 44, a method of adding a polycarboxylic acid dispersant to stabilize a β ″ alumina slurry, mixing the raw material powder slurry, and drying and granulating is also a problem in the case of an organic solvent system. It has been proposed to reduce the risk of explosion or cost, and to avoid the effects of organic solvents on the human body.

[0003]

The former process described in the prior art involves the danger that the organic solvent may be ignited or burned by fire or static electricity, and that the suction may affect the human body. In order to avoid these problems, sufficient attention must be paid to facilities. Therefore, there is a problem that the equipment introduction cost becomes enormous. On the other hand, in the latter process, since the raw material powder is put into a mixing and crushing machine, and water and an organic binder are added and mixed and crushed, it is difficult to prevent deterioration of the β ″ alumina raw material powder which easily reacts with water. In the case of the process disclosed in Japanese Patent Publication No. 58-5844, a polycarboxylic acid dispersing agent is added in addition to water, so that the granulated powder is stable. However, no effect was observed in improving the flexibility, moldability, and strength of the sintered body of the granulated powder, and the addition of a plasticizer was disclosed in JP-A-63-40775.
However, due to the characteristics of the β ″ alumina ceramic raw material powder, the conventional plasticizers conventionally used, such as ethylene glycol and glycerin, did not provide a sufficient effect. My goal is,
After examining the characteristics of β ″ alumina ceramic raw material powder in detail, we found a granulation material and granulation method suitable for this powder,
It is to provide the technology.

[0004]

SUMMARY OF THE INVENTION The present invention relates to a process for producing granulated β ″ alumina ceramics, comprising adding water to β ″ alumina raw material powder, wet-mixing the slurry, preparing a slurry, and drying and granulating the slurry. In addition to water added as a solvent and a water-soluble binder (binder), a plasticizer composed of a wax emulsion is added as an essential component, and the mixture is wet-mixed. It is known that a plasticizer is added in a method for producing granulated powder as a ceramic raw material. However, in the present invention, an unstable β ″ alumina slurry in a water slurry is kept stable, and In order to satisfy the properties of the granular powder, a remarkable effect of using a wax emulsion as a plasticizer has been found.In the present invention, the amount of the binder is desirably the minimum necessary to ensure the strength of the molded product, 5% by weight in terms of solid content
The following is desirable. In this case, the plasticizer is desirably 0.05 to 2.0% by weight in terms of solid content. When the solid content of the plasticizer is 0.05 or less, the effect of the plasticizer is insufficient, and when the compact is manufactured by pressing the granulated powder, the granulated powder is hardened because the granulated powder is hard. Gap remains. This results in pores when sintered. On the other hand, when 2.0% by weight or more is added, gaps in the granulated powder are eliminated, but after the plasticizer is decomposed and removed, many voids remain in the molded body. Therefore, it is important to keep the amount of the plasticizer component to be finally decomposed and removed to the minimum necessary amount, which is the upper limit. Since the granulated powder obtained by the production method of the present invention is a wax emulsion of a plasticizer, the wax emulsion penetrates and coats the raw material powder particles during slurry preparation or dry granulation, thereby promoting the flexibility of the particles. You. In addition, the plasticizer is water-dispersible and does not impair stability such as dispersion, sedimentation and viscosity of the slurry due to its unique properties. The function of the plasticizer is to relieve pressure concentration in the vicinity of the particle joint when pressurized, and to maintain and improve the homogeneity and denseness of the molded product by the dispersion.

Therefore, in a sintered body manufactured using the granulated powder obtained by the manufacturing method of the present invention, the granulated powder is uniformly broken by pressurization during molding, and the generation of grain boundaries is extremely small. The number of pores in the sintered body is smaller than that of the sintered body created by the manufacturing method, the crystal grains and the size of the crystal grains are uniform,
Since the ionic conductivity is low and the mechanical strength is high, it is suitable as a solid electrolyte such as a sodium-sulfur battery or a sodium thermoelectric conversion battery.

In the present invention, as a result of studying a plasticizer,
It became clear that the addition of a plasticizer was indispensable, and it was found that an emulsion of oxidized microwax having 30 to 60 carbon atoms was particularly effective for β ″ alumina ceramic raw material powder. If the number of carbon atoms in the oxidized microwax emulsion is less than 30, a sufficient plasticizing effect cannot be obtained, and if it is more than 60, it is difficult to emulsify.

In this case, a remarkable effect was observed in combination with a nonionic polymer type water-soluble binder, particularly, polyvinyl alcohol (PVA). The nonionic polymer type binder is particularly good because there is no thickening or gelling of the binder due to the elution of the alkali component in β ″ alumina. The technology of the present invention reduces pores remaining in the sintered body. In addition, since the mechanical strength can be increased, the thickness of the ceramic sintered body can be reduced, and the effect that the device can be reduced in size and weight can be expected.

When an organic solvent is used, there are problems such as explosion and organic solvent poisoning due to its extremely high flammability. However, when water is used, there is no danger of ignition or poisoning, but β ″
There was a problem that alumina decomposed, deteriorated or gelled.

[0009] Further, due to both the rigidity of the organic binder and the properties of the treatment method, the particle surface of the granulated powder is covered with the binder film, and the granulated powder is hardened. Soft processing is required to obtain fine particles. On the other hand, in the granulated powder for producing a β ″ alumina ceramic sintered body according to the present invention, a wax, particularly a plasticizer composed of an oxidized microwax emulsion, is added to the slurry preparation, and this plasticizer is used to increase the binder content. The resulting granulated powder has flexibility to cover the molecular chains and the raw material powder particles, can be uniformly broken at the time of molding, and has very few grain boundaries. Has a small number of voids, the crystal grains and the size of the crystal grains are uniform, the ionic conductivity and the mechanical strength are high, and the uniform microstructure of the sintered body prevents deformation and cracks. A β ″ alumina ceramic sintered body having a structure in which distortion and residual stress are easily generated like a ceramic hemispherical bottom tube can be easily obtained.

Hereinafter, the present invention will be described by way of examples. The embodiments described below show typical examples to which the present invention is applied, and the present invention is not limited to the embodiments shown here. The composition of β ″ alumina ceramics is not limited to the examples.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

Example 1 The amount of pores having an average diameter of 5 μm or more remaining in a sintered body and influenced by the amount of a plasticizer added during slurry preparation was examined. The composition of the raw material powder is about 8.6% by weight of Na ₂ O, about 0.7% by weight of Li ₂ O, and the remainder is Al ₂ O ₃ .
As a comparative example, a slurry prepared by adding an alcohol as a solvent and polyvinyl butyral (PVB) as a binder at the time of preparing a slurry and a slurry prepared by adding water but using no plasticizer as a solvent were used. The result is shown in FIG. The binder was constant at 3% by weight in terms of solid content. When a granulated powder obtained by adding a plasticizer at the time of preparing the slurry and drying and granulating is used, pores of 5 μm or more remaining in the sintered body are reduced to about 0% by adding the plasticizer in the range of 0.05 to 2.0% by weight. .2%, the lowest. Observation with a microscope revealed that there were few residual pores, that the size of the crystal grains in the sintered body of this example did not exceed 10 μm, and that the shapes were uniform.

Example 2 The amount of the pores having an average diameter of 5 μm or more remaining in the sintered body and influenced by the amount of the binder added during the preparation of the slurry was examined. The binder is polyvinyl alcohol (PVA). As the plasticizer, an oxidized microwax emulsion having about 40 carbon atoms was converted to a solid content and kept constant at 1.0% by weight. If the number of carbon atoms in the oxidized microwax emulsion is less than 30, the effect as a plasticizer is insufficient. The composition of the raw material powder is Na ₂ O
Is about 8.6% by weight, Li ₂ O is about 0.7% by weight, and the balance is A
l ₂ O ₃ . As a comparative example, a product prepared using water as a solvent and adding a polycarboxylic acid dispersant but not adding a plasticizer was used. The result is shown in FIG.
In the case of using a granulated powder obtained by adding a plasticizer at the time of slurry preparation and drying and granulating, the amount of pores having an average diameter of 5 μm or more remaining in the sintered body is about 50% as compared with the sintered body prepared by the conventional method. Reduce. Further, since the plasticizer also has a binder function, mechanical strength can be ensured even when the amount of the binder added is reduced. It was found that the rigidity of the binder was reduced by the effect of the plasticizer.

(Example 3) The stability of the slurry viscosity, sedimentation, etc. exerted by the water-soluble binder added during the preparation of the slurry was examined. As a nonionic polymer type binder, polyethylene oxide having a molecular weight of about 300,000 or polyvinyl alcohol (PVA) having a molecular weight of about 25,000
Was used to prepare a slurry. On the other hand, a slurry was prepared using polyacrylic acid ammonium having a molecular weight of about 250,000 as an anionic polymer type binder. The total amount of the plasticizer comprising the binder and the oxidized microwax emulsion having about 40 carbon atoms was constant at 2.15% by weight in terms of solids. Incidentally, the composition of the raw material powder is Na ₂ O of about 8.6 wt%, Li ₂ O of about 0.7 wt%, the rest is Al ₂
O ₃ . When polyethylene oxide or polyvinyl alcohol, which is a nonionic polymer type binder, is used, a stable slurry is obtained and can be supplied to the dry granulation step. In particular, when polyvinyl alcohol is used, the stability is excellent. On the other hand, when ammonium polyacrylate, which is an anionic polymer type binder, was used, the slurry became a gel, and a stable slurry was not obtained. Therefore, it was found that the combined use with the anionic polymer type binder was impossible.

Example 4 The formability of granulated powder exerted by a plasticizer added during slurry preparation was examined. The binder is polyvinyl alcohol (PVA) and the plasticizer is oxidized microwax emulsion with about 40 carbon atoms, polyethylene glycol, paraffin wax emulsion with about 30 carbon atoms, and glycerin. The total amount was constant at 2.15% by weight in terms of solid content. The composition of the raw material powder is about 8.6% by weight of Na ₂ O, about 0.7% by weight of Li ₂ O, and the remainder is Al ₂ O ₃ . When the surface of the molded body was observed with a microscope, many gaps of granulated powder particles were observed on the surface of the molded body to which polyethylene glycol or glycerin was added, whereas the surface of the molded body to which paraffin wax emulsion was added was observed. The surface has reduced gaps.
Furthermore, the surface of the molded body to which the oxidized microwax emulsion was added showed a more prominent tendency, and almost no gaps between the granulated powder particles were observed. It was found that a soft granulated powder can be produced by adding the oxidized microwax emulsion.

Example 5 A solid electrolyte tube prepared by using the granulated powder of the present invention was incorporated in a sodium-sulfur battery as shown in a schematic sectional view of FIG. 3, and a charge / discharge test was performed. Although a current of 100 Ah / cm ^{2 was applied to} each battery, no breakage of the solid electrolyte tube or a decrease in battery characteristics was observed, and the solid electrolyte tube prepared using the granulated powder of the present invention had excellent performance. I understood that.

[0016]

According to the present invention, there is provided a method for producing a dry granulated powder by adding water, a binder, a dispersant and the like to β ″ alumina raw material powder, wherein the raw material powder is mixed with water, a nonionic polymer type water-soluble binder, A wax emulsion is added as a plasticizer as an essential component in addition to a dispersant and an antifoaming agent, and the granulated powder is dried and granulated. For this reason, raw material powder particles are coated during dry granulation, and β ″ alumina granulated powder becomes flexible particles.
The sintered body produced by using the granulated powder has a conventional manufacturing method because the granulated powder is uniformly broken by the pressure during molding, and the generation of grain boundaries is extremely small and the crystal form is maintained. As compared with the sintered body prepared in the above, the size of the crystal phase and the crystal grains in the sintered body are uniform, and the mechanical strength is increased, so that it is industrially useful.

[Brief description of the drawings]

FIG. 1 is a view showing the effect of the plasticizer of the present invention.

FIG. 2 is a view showing the effect of reducing the binder by the plasticizer of the present invention.

FIG. 3 is a sectional view showing the overall structure of a sodium-sulfur battery to which the present invention is applied.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Solid electrolyte tube, 2 ... Positive electrode container, 3 ... Negative electrode container, 4 ...
Ceramic insulating ring, 5 ... sulfur, 6 ... sodium.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shigeru Sakaguchi 3-1-1, Sachimachi, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd. Hitachi Plant

Claims (8)

[Claims] 1. A method for producing a granulated powder for producing a β ″ alumina ceramic sintered body, wherein when water is added to a raw material powder to prepare a slurry, a wax emulsion is added as an essential component as a water-soluble binder and a plasticizer. A method for producing granulated β ″ alumina ceramics, comprising mixing and drying and granulating the obtained slurry. 2. The method according to claim 1, wherein the water-soluble binder is a nonionic polymer type binder. 3. The method according to claim 1, wherein the water-soluble binder is polyvinyl alcohol. 4. The granulated powder of β ″ alumina ceramics according to claim 1, wherein the wax emulsion added in claim 1, 2 or 3 is an oxidized microwax emulsion having 30 to 60 carbon atoms. Manufacturing method. 5. The β ″ alumina ceramic material according to claim 1, wherein the amount of the solid content of the plasticizer added in claim 1, 2, 3, or 4 is 0.05 to 2.0% by weight. A method for producing granular powder. 6. Granulated β ″ alumina ceramics powder prepared by the method according to claim 1, 2, 3, 4 or 5. 7. Sintering using the granulated powder prepared by the method described in claim 1, 2, 3, 4, 5 or 6, wherein the porosity of the sintered body is 0.4% or less. Characteristic β ″ alumina ceramic solid electrolyte. 8. A sodium-sulfur secondary battery using the solid electrolyte comprising the β ″ alumina ceramic according to claim 7.