JP2004143036A - Method for manufacturing lithium titanate minute sphere - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a lithium titanate minute sphere having remarkably high density of ≥80% T.D and free from the occurrence of crack on the surface of the sphere. <P>SOLUTION: This method for manufacturing lithium titanate minute sphere is performed by connecting a process for supplying fine powder or a minute sphere of lithium titanate (Li<SB>2</SB>TiO<SB>3</SB>) to a hydrogen peroxide solution of ≥60°C to dissolve ≥95% of lithium titanate, a process for dehydrating or deacidificating the dissolved liquid while keeping 60-80°C to obtain a lithium titanate concentrated liquid having Li<SB>2</SB>TiO<SB>3</SB>concentration of 15-30 mass%, a process for dropping the concentrated solution into acetone to obtain a wet gel sphere, a process for calcining the resultant wet gel sphere at 150-250°C after drying, and a process for heating the gel sphere obtained by the calcination to 700°C at a rate of 10-100 °C/hr and after heating from 700°C to the sintering temperature at a rate of 100-200 °C/hr, sintering at the prescribed sintering temperature. <P>COPYRIGHT: (C)2004,JPO

Description

【００２７】同表から明らかなように、Ｌｉ_２ＴｉＯ_３粉末中に種々の酸化物粉末を配合した場合には、Ｌｉ_２ＴｉＯ_３粉末単味の場合に比べて、高温特性の一層の向上を図ることができた。
【００２８】
【発明の効果】かくして、本発明によれば、密度が８０％Ｔ．Ｄ．以上と極めて高く、また微小球の表面にクラックの発生がないリチウムタイタネート微小球を、安定して得ることができる。
【図面の簡単な説明】
【図１】本発明に従うリチウムタイタネート微小球の製造方法の一例を示すフローチャートである。[0001]
The present invention relates to a method for producing lithium titanate (Li ₂ TiO ₃ ) microspheres, and more particularly to a method for producing lithium titanate microspheres suitable for recycling Li from used lithium titanate microspheres. It is about.
[0002]
2. Description of the Related Art In a nuclear fusion reactor, tritium, which hardly exists in nature, is propagated by reacting neutrons and Li as described below. As such a tritium breeding material, Li-containing ceramics, for example, Li ₂ O, LiAlO ₂ , Li ₂ TiO _{3 and the} like are used, and these are mainly used in the form of microspheres.
^{6 Li + 1 n → 4 He} + 3 T + 4.8 MeV ( exothermic)
As an example of a method for producing the above-described Li-containing ceramic microspheres, Patent Literature 1 discloses a technique for producing lithium titanate (Li ₂ TiO ₃ ) microspheres by an indirect wet method. In this method, lithium titanate powder as a raw material is dispersed in an aqueous solution of polyvinyl alcohol to form a dripping stock solution, and this dripping stock solution is dropped from a nozzle into acetone, gelled to form a wet gel sphere, dried, and then temporarily dried. After baking to remove the polyvinyl alcohol, sintering is performed to finally obtain lithium titanate microspheres.
In the above-mentioned Li-containing ceramics used as a tritium breeding material, since Li is a scarce resource, the used tritium breeding material, for example, from used lithium titanate microspheres to lithium titanate microspheres is used. It is desired that Li be recycled and Li be recycled.
From this viewpoint, when the method for producing lithium titanate microspheres disclosed in Patent Document 1 described above is applied to remanufacture lithium titanate microspheres from used lithium titanate microspheres, There was a problem as described.
That is, since the used lithium titanate microspheres cannot be used as a raw material, the used lithium titanate microspheres are converted into a solution, Li is recovered as Li ₂ CO ₃ powder, and then calcined with TiO ₂ powder. For example, it was necessary to disperse a single phase of Li ₂ TiO ₃ by reacting in a polyvinyl alcohol aqueous solution to obtain a dropping stock solution. For this reason, although lithium titanate microspheres having better properties can be obtained as compared with the conventional rolling granulation method or the like, the number of manufacturing steps is increased, resulting in a problem that the manufacturing cost is increased.
To solve this problem, Non-Patent Document 1 discloses an attempt to directly dissolve used lithium titanate microspheres to obtain microspheres. However, in this method, although lithium titanate microspheres are directly dissolved, a raw material powder is produced from the dissolved solution, and microspheres are obtained from the raw material powder produced by the same conventional rolling granulation method. Therefore, the number of manufacturing steps is large, and as a result, an increase in manufacturing cost cannot be avoided.
[0007] In this regard, the present inventors have previously solved the above-mentioned problem by providing a solution adjusting step of obtaining a lithium titanate concentrated solution by converting a raw material lithium titanate powder into a solution and concentrating the solution. The lithium titanate concentrated solution obtained in the solution adjusting step is dropped into a gelling solvent to gel in the form of droplets, and then aged to obtain wet gel spheres. A solvent exchange is performed by immersing in a substitution solvent having a higher surface tension than the solvent to replace the gelling solvent with the substitution solvent in the pores of the wet gel sphere, and drying the wet gel sphere after the solvent exchange to form a gel. Producing a lithium titanate microsphere comprising: a gel sphere forming step of forming a sphere; and a microsphere firing step of firing the gel sphere obtained in the gel sphere forming step to obtain lithium titanate microspheres. We developed a method "disclosed in the patent document 2.
According to the above technology, lithium titanate microspheres having good properties can be obtained in a relatively simple manufacturing process, and the manufacturing cost can be advantageously reduced.
[0008]
[Patent Document 1]
JP-A-10-265222 [Patent Document 2]
JP 2001-278623 A [Non-Patent Document 1]
C. Alvani, S .; Casadio et. al. _{, "Reprocessing and PreparaTion of Li 2} TiO 3 Pebbles Through Li-Ti-Peroxocomplexes Wet GranulaTion Method", The Seventh InternaTional Workshop on CERAMIC BREEDER BLANKETINTERACTIONS, Petten, Netherlands, (1998)
[0009]
However, according to the technique disclosed in Patent Document 2, the density of the obtained lithium titanate microspheres is 50% T.P. D. The problem remained in the low places below. In addition, a problem remains in a place where cracks easily occur on the surface of the microsphere.
The present invention advantageously solves the above-mentioned problems, and has a microsphere density of 80% T.D. D. It is an object of the present invention to propose an advantageous method for producing lithium titanate microspheres which is extremely high and does not cause cracks on the microsphere surface.
In addition, the present invention does not require a solvent exchange step of replacing a gelling solvent with a substitution solvent as in the technique disclosed in Patent Document 2 mentioned above, and therefore, a lithium titer that can achieve more steps and cost savings An object of the present invention is to propose a method for producing nate microspheres.
That is, the gist of the present invention is as follows.
1. Supplying lithium titanate (Li ₂ TiO ₃ ) powder or microspheres to a hydrogen peroxide solution at 60 ° C. or higher to dissolve 95% or more thereof;
A step of maintaining the solution at 60 to 80 ° C. to obtain a lithium titanate concentrate having a Li ₂ TiO ₃ concentration of 15 to 30 mass% by dehydration, deoxidation, or the like;
Step of obtaining the wet gel spheres by dropping the concentrated solution into acetone,
A step of calcining the obtained wet gel spheres at a temperature of 150 to 250 ° C. after drying,
The gel balls obtained by calcining are heated up to 700 ° C. at a rate of 10 to 100 ° C./h, and from 700 ° C. to a sintering temperature at a rate of 100 to 200 ° C./h. A method for producing lithium titanate microspheres, which is a combination of steps of sintering at a sintering temperature.
2. _2. The lithium according to the above item 1, wherein an oxide powder as a high temperature property improving material is added to and mixed with lithium titanate (Li ₂ TiO ₃ ) powder or microsphere as a raw material in a range of 1 to 20 mol%. A method for producing titanate microspheres.
3. The oxide is TiO, Ti ₂ O ₃ , TiO ₂ , NbO, Nb ₂ O ₃ , NbO ₂ , Nb ₂ O ₅ , VO, V ₂ O ₃ , VO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , _{cr 2 O 3, MnO, Mn} 3 O 4, MoO 2, BeO, CaO, Li above 2, wherein a is _Gd 2 O 3, selected from among the ZrO ₂ and NiO one or two or more A method for producing titanate microspheres.
[0014]
DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described specifically.
FIG. 1 is a flowchart showing a process for producing the lithium titanate microspheres of the present invention.
As shown in the figure, the manufacturing process of the present invention is roughly divided into three steps of a solution adjusting step, a gel sphere forming step, and a microsphere firing step. Hereinafter, each step will be specifically described.
First, in a solution adjusting step, lithium titanate (Li ₂ TiO ₃ ) powder or microspheres are dissolved in a hydrogen peroxide solution. It is important to maintain the temperature of the hydrogen water at 60 ° C. or higher. This is because if the temperature of the hydrogen peroxide solution is lower than 60 ° C., the dissolution reaction of Li ₂ TiO ₃ becomes extremely slow, and the difference in the insoluble residue also increases.
In addition, it is preferable to perform this dissolution under stirring using a magnetic stirrer or the like. A stirring time of about 1 to 8 hours is sufficient, and 95% or more of the lithium titanate powder thus added can be dissolved.
Next, the solution is concentrated, and the concentration is performed by maintaining the solution at 60 to 80 ° C. That is, when the solution is maintained at 60 to 80 ° C., dehydration and deacidification proceed effectively, and concentration of the solution proceeds effectively.
And this _{concentration,} Li 2 TiO ₃ concentrations to obtain a 15～30Mass% lithium titanate concentrate.
Next, the concentrated solution is dropped into acetone using a nozzle or the like to obtain wet gel spheres. At this time, the size of the gel sphere can be appropriately changed by changing the nozzle diameter or the supply amount per drop.
If the droplet of the concentrated solution is dropped on acetone as it is, the droplet may be deformed while settling from the liquid surface to the bottom of the container. For example, if the droplet is deformed, a Teflon (registered trademark) slide may be used. It is preferable to obtain a spherical gel sphere by installing a guide having such an inclination on the bottom surface of the container from the liquid surface of acetone and using this inclination to roll or slide the droplet to the bottom surface.
Next, the obtained wet gel spheres are dried and calcined.
This drying is preferably performed in a temperature range of 70 to 150 ° C. for about 3 to 5 hours.
The calcination is performed in a temperature range of 150 to 250 ° C. for about 2 to 5 hours. In this calcination, the treatment may be performed at a constant temperature, but it is more advantageous to use a stepwise treatment in which the temperature is gradually increased.
Thus, spherical dry gel spheres are obtained.
Next, the obtained dried gel sphere is subjected to a sintering treatment.
In the firing treatment, it is important to control the rate of temperature rise from 700 ° C. to a range of 10 to 100 ° C./h and the rate of temperature rise from 700 ° C. to a sintering temperature to a range of 100 to 200 ° C./h. is there.
This is because if the heating rate up to 700 ° C. is less than 10 ° C./h, it takes too much time for sintering, while if it exceeds 100 ° C./h, cracks and the like occur due to residual gas release. If the rate of temperature increase from 700 ° C. to the sintering temperature is less than 100 ° C./h, sintering proceeds during the temperature increase, making it difficult to control the crystal grain size, while exceeding 200 ° C./h. This is because scattering of lithium or the like occurs.
Preferably, the sintering temperature is about 900 to 1400 ° C., and the sintering time is about 0.2 to 4 hours.
Further, in the present invention, an oxide powder as a heat resistance improving material is added to lithium titanate (Li ₂ TiO ₃ ) powder or microsphere as a raw material in a range of 1 to 20 mol%. Is advantageous.
Such _{oxides, TiO, Ti 2 O 3,} TiO 2, NbO, Nb 2 O 3, NbO 2, Nb 2 O 5, VO, V 2 O 3, VO 2, Y 2 O 3, Al 2 O 3 , Cr ₂ O ₃ , MnO, Mn ₃ O ₄ , MoO ₂ , BeO, CaO, Gd ₂ O ₃ , ZrO _2, and NiO are advantageously suitable. By adding and blending in the range of ２０20 mol%, the characteristics of the microspheres when used at a high temperature of about 900 to 1100 ° C. for a long time, that is, the high-temperature characteristics can be advantageously improved.
[0021]
Embodiments of the present invention will be described below. It goes without saying that the present invention is not limited only to this embodiment.
Example 1
First, in a solution adjusting step, 30 mass% of a hydrogen peroxide solution: 50 cm ³ was put into a beaker, and Li ₂ TiO ₃ powder as a raw material: 4 g was charged, followed by covering with a watch glass. This was placed in a water bath with a heater adjusted to 60 ° C. or higher, and dissolved while stirring using a magnetic stirrer. With stirring for 4 hours or more, Li ₂ TiO ₃ could be almost completely dissolved (95%).
After the dissolution, the solution was kept at about 60 ° C. to degas the impurity gas in the solution, and then the solution was cooled to room temperature. In addition, a precipitate was generated in the solution by this cooling.
Next, the temperature of the solution was adjusted to 60 ± 1 ° C., and the solution was concentrated with stirring until the Li ₂ TiO ₃ concentration became 23 mass%.
The concentrated solution was transferred to a mortar, and the precipitate precipitated in the solution was kneaded to refine the precipitate. Furthermore, ultrasonic vibration and fluidization deaeration were performed to obtain a dripping stock solution.
In the gel sphere forming step, as a dropping operation, a concentrated dropping stock solution was dropped into acetone at 20 ° C. The dropped droplets were allowed to stand for about 1 hour until completely solidified, and aged.
The gel balls after aging were transferred to an electric furnace and dried at 90 ° C. for 3 hours and at 110 ° C. for 1 hour to obtain dried gel balls.
Next, the dried gel spheres obtained as described above were calcined under the conditions of 170 ° C., 1 hour, 185 ° C., 1 hour, and 200 ° C., 0.5 hour.
Thereafter, the temperature is raised to 700 ° C. at a rate of 40 ° C./h, and then from 700 ° C. to a sintering temperature of 1200 ° C. at a rate of 170 ° C./h, followed by sintering at 1200 ° C. for 4 hours. , Li ₂ TiO ₃ microspheres were obtained.
The density of the Li ₂ TiO ₃ microspheres thus obtained is 85% T.D. D. High enough, and no cracks occurred on the surface of the microspheres.
Embodiment 2
The same treatment as in Example 1 was carried out except that the mixed powder in which the oxide powder was mixed in the Li ₂ TiO ₃ powder at various ratios shown in Table 1 as a raw material was used to convert the Li ₂ TiO ₃ microspheres. Obtained.
Table 1 also shows the results of examining the density of the Li ₂ TiO ₃ microspheres thus obtained, the presence or absence of cracks on the microsphere surface, and the high-temperature characteristics.
Here, the high temperature characteristics were evaluated as follows.
That is, the growth of the crystal grains at 100 ° C. for 100 hours was examined, and when the degree was 2 μm or less, ○ was evaluated when it was more than 2 μm and 5 μm or less, and Δ when it was more than 5 μm was evaluated. The degree of growth of the crystal grains of the microsphere was examined by scanning electron microscope observation.
[0026]
[Table 1]

As is apparent from the _table, when incorporated various oxides powder Li 2 TiO _{3 powder,} as compared to the case of Li 2 TiO ₃ powder plain, to further improve the high temperature properties I was able to plan.
[0028]
Thus, according to the present invention, the density is 80% T. D. Thus, lithium titanate microspheres which are extremely high and have no cracks on the surface of the microspheres can be stably obtained.
[Brief description of the drawings]
FIG. 1 is a flowchart showing an example of a method for producing lithium titanate microspheres according to the present invention.

Claims (3)

Supplying lithium titanate (Li ₂ TiO ₃ ) powder or microspheres to a hydrogen peroxide solution at 60 ° C. or higher to dissolve 95% or more thereof;
A step of maintaining the solution at 60 to 80 ° C. to obtain a lithium titanate concentrate having a Li ₂ TiO ₃ concentration of 15 to 30 mass% by dehydration, deoxidation, or the like;
Step of obtaining the wet gel spheres by dropping the above concentrated solution into acetone,
Calcining the obtained wet gel spheres at a temperature of 150 to 250 ° C. after drying,
The gel balls obtained by calcining are heated up to 700 ° C. at a rate of 10 to 100 ° C./h, and from 700 ° C. to a sintering temperature at a rate of 100 to 200 ° C./h. A method for producing lithium titanate microspheres, which is a combination of steps of sintering at a sintering temperature. Lithium titanate (Li 2 _{TiO 3)} in powder or microspheres as a raw material of claim 1, wherein the added mixed within a range powder oxide of 1 to 20 mol% as a high temperature properties enhancing material A method for producing lithium titanate microspheres. The oxide is TiO, Ti ₂ O ₃ , TiO ₂ , NbO, Nb ₂ O ₃ , NbO ₂ , Nb ₂ O ₅ , VO, V ₂ O ₃ , VO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , _{cr 2 O 3, MnO, Mn} 3 O 4, MoO 2, BeO, CaO, Gd 2 O 3, according to claim 2, characterized in that ZrO ₂ and selected one or more from among NiO A method for producing lithium titanate microspheres.

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