JP3838523B2 - Method for producing the composition - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for producing a composition containing a perovskite type compound.
[0002]
[Prior art]
In recent years, electronic devices have been remarkably reduced in size and performance. Correspondingly, the same applies to the ceramic electronic components constituting the electronic device, and various improvements of the ceramic manufacturing process have been studied for the purpose of miniaturization and high performance, but the limit has been almost reached. Therefore, there is a need to improve the material in order to obtain ceramics that are superior to the current situation.
[0003]
For example, as dielectric ceramics, uniform and spherical perovskite type compounds (hereinafter referred to as ABO ₃ type compounds) of 1 μm or less, preferably 0.5 μm or less have been studied. The ABO ₃ type compound having such a particle size has a high surface energy if the particle size is small, and if the particle size distribution is uniform and spherical, the packing during molding is improved, so that the sinterability is remarkably improved. A dense and strong ceramic can be obtained at a lower temperature. Furthermore, in order to realize a multilayer ceramic capacitor with a thin layer and multiple layers, a ceramic green sheet having a thickness of 10 μm or less is required, but in that case, it is 1 μm or less, preferably 0.5 μm or less. Therefore, a spherical ABO ₃ type compound is required.
[0004]
Conventionally, as a method for producing an ABO ₃ type compound such as barium titanate, barium carbonate and titanium oxide are reacted (calcined) at a high temperature of 1000 ° C. or higher to synthesize barium titanate, and mechanically pulverized and classified. A method (solid phase synthesis method) is known. On the other hand, metal alkoxide methods, hydroxide methods, hydrothermal synthesis methods, and the like are known as wet synthesis methods.
[0005]
[Problems to be solved by the invention]
However, in the case of the solid phase synthesis method, the calcined barium titanate is consolidated, so that it is difficult to obtain a fine state of 1 μm or less even if mechanical pulverization and classification are performed. Moreover, since the particle shape is in the form of crushed material, when it was molded into an arbitrary shape and sintered, it lacked sinterability. Furthermore, as described above, in order to realize a thin and multi-layered multilayer ceramic capacitor, it is necessary to form a ceramic green sheet having a thickness of 10 μm or less without any problem. When the barium titanate powder obtained by the above method was used, there was a problem that the green sheet density decreased or the thickness variation of the green sheet increased.
[0006]
As for the wet synthesis method, in the case of the metal alkoxide method, the raw materials are expensive and there is a problem in industrialization. On the other hand, regarding the hydroxide method, attention has been paid in that the raw materials are relatively inexpensive and the resulting powder has high sinterability.
[0007]
For example, in JP-A-60-90825, a method of heating titanic acid and barium hydroxide at a temperature below the boiling point in the presence of a large amount of water is used. In this case, titanic acid is adjusted in advance. Must. For example, when titanic acid is precipitated by neutralization of an aqueous solution of a titanium compound, since it is a colloid, there is a problem that washing and filtration are industrially difficult.
[0008]
JP-A-59-39726 discloses a method in which a water-soluble barium salt such as barium chloride or barium nitrate is dissolved in an aqueous solution of titanium salt, the pH is adjusted to 13 or more by adding an alkali, and heating is performed at a boiling point or lower. Has been proposed. However, since the barium titanate powder obtained by this method is too fine with a particle diameter of 0.02 to 0.03 μm, there is a problem that the density when molded is low and the shrinkage during sintering is large. Depending on the case, it may not be preferable.
[0009]
With regard to the hydrothermal synthesis method, in recent years, it has attracted particular attention as being able to obtain an optimum barium titanate powder that can withstand the thinning and multi-layering of multilayer ceramic capacitors.
[0010]
For example, in Japanese Patent Application Laid-Open No. 61-31345, a mixture of a group A element such as Ba and Sr and a hydroxide of a group B element such as Ti and Zr with a desired A / B ratio is hydrothermally reacted in an aqueous medium. Then, a method is proposed in which the group A element dissolved in the aqueous medium is made into a water-insoluble form, filtered, washed and dried. However, in this case, there is a problem that the amount of so-called insolubilizing agent that makes the group A element water-insoluble must be determined for each production lot. That is, in the hydrothermal reaction, since the reaction rate varies from production lot to production lot, the concentration of group A element ions dissolved in the filtrate is analyzed each time, and the amount of insolubilizing agent added is determined according to the value. It is necessary to decide.
[0011]
In JP-A-62-72525, any one compound of carbonate, chloride and nitrate such as barium is dissolved in an aqueous solution of titanium tetrachloride, and sodium hydroxide or potassium hydroxide is added. In addition, a method of heating in an autoclave has been proposed. However, as a result of detailed studies, it has been clarified that alkali metal impurities such as Na and K cannot be removed and remain, for example, about 800 to 1000 ppm in the synthesized barium titanate powder.
[0012]
The object of the present invention is uniform and spherical particles of 1 μm or less, preferably 0.5 μm or less, and the molar ratio of A site element to B site element is in the range of 1.000 ± 0.002, Another object of the present invention is to provide a production method capable of obtaining an ABO ₃ type compound having good crystallinity and extremely low impurities such as alkali metals.
[0013]
[Means for Solving the Problems]
That is, the gist of the production method of the composition according to the present invention is that (a) at least one salt selected from the group A elements consisting of Mg, Ca, Sr, Ba, and Pb, and Ti, Zr, A first step of obtaining a mixture slurry of at least one salt selected from the group B element consisting of Hf and Sn and water or an alkaline aqueous solution; (b) hydrothermal reaction of the mixture slurry for hydrothermal synthesis powder And (c) a third step in which a mixture of the hydrothermally synthesized powder obtained in the second step and an alkaline aqueous solution containing an alkaline earth metal is subjected to a hydrothermal reaction.
[0014]
In the third step, as the alkaline aqueous solution containing an alkaline earth metal , for example, a barium hydroxide aqueous solution having a pH adjusted between 7 and 10 is used.
[0015]
After adjusting the mixture slurry in the first step, a synthetic powder is obtained by hydrothermally treating the mixture slurry in the next second step. When this synthetic powder contains an alkali metal such as Li or Na, it is preferably washed. What is necessary is just to repeat arbitrarily the frequency | count of washing | cleaning until the amount of alkali metals can be reduced to a fixed amount. After that, it is filtered and dried to obtain a dry powder. This dry powder is brought into the next third step, mixed with an alkaline aqueous solution containing an alkaline earth metal , and this mixture is hydrothermally reacted. Here, alkali metal impurities including the ABO ₃ type compound can be further reduced.
[0016]
[Action]
According to the present invention, a powder obtained by hydrothermal synthesis further mixed with an alkaline aqueous solution containing an alkaline earth metal, the mixture has a step of hydrothermal reaction, wherein the ABO ₃ type compounds The amount of alkali metal impurities contained can be reduced. Since the ABO ₃ type compound thus obtained has a small particle size, a uniform particle size, and a spherical shape, the reactivity is good and the sintering temperature can be lowered. Further, since the pulverization process can be omitted, it is possible to prevent impurities from being mixed due to pulverization.
[0017]
【Example】
Example 1
0.1 mol of Ti (O—iC ₃ H ₇ ) ₄ and 30 ml of isopropyl alcohol (hereinafter referred to as IPA) are put into a polyfluorinated ethylene resin beaker. The solution is then hydrolyzed with 135 ml containing 0.6 mol NaOH aqueous solution while stirring with an ultradisperser. Then, 0.1 mol of BaCl ₂ .2H ₂ O is charged (first step).
[0018]
This mixture slurry was put into a polyfluorinated ethylene resin beaker and mounted on an autoclave apparatus. The temperature was 170 ° C. and the pressure was 16 kg / cm ² for 4 hours. Hydrothermal synthesis was performed using a resin stir bar while stirring at 150 rpm. The obtained precipitate was taken out, washed with water and filtered several times, and then dried and crushed to obtain a raw material powder (second step). The particle diameter of this powder was 0.2 to 0.3 μm, Ba / Ti ratio: 1.001, Na content: 1000 ppm, and Cl content: 20 ppm.
[0019]
Next, 20 g of the powder and 200 ml of an aqueous solution of barium hydroxide adjusted to pH = 10 are put into a polyfluorinated ethylene resin beaker as described above, and the beaker is placed in an autoclave apparatus. A hydrothermal treatment was performed while stirring at 150 rpm using a stirring rod made of a polyfluorinated ethylene resin for 4 hours under conditions of temperature: 200 ° C. and pressure: 15 kg / cm ² . After completion of the treatment, the raw material powder was obtained through filtration, drying and crushing (third step).
The particle diameter of this powder was 0.2 to 0.3 μm, Ba / Ti ratio: 0.999, Na content: 100 ppm, and Cl content: 20 ppm. FIG. 1 is an X-ray diffraction pattern of the composition obtained by this method, and shows that it has a cubic perovskite structure from the sharp peak of (110).
[0020]
If a little explanation is added about each process, in the 1st process, Ba and Ti are charged in the ratio of equimolar ratio, but a molar ratio shift occurs after the 2nd process hydrothermal synthesis. In order to prevent this, an OH concentration of at least 4 times, preferably 6 times or more the charged concentration of Ba and Ti is required.
[0021]
Next, after the second step, washing is performed, but washing is performed several times with an alkaline aqueous solution in order to prevent Ba loss. The alkaline pH is at least 9 or more. Note that the number of cleanings affects the reduction of impurities such as Na, K, and Cl. Although Cl can be almost completely removed by washing 2 to 3 times, alkali metal impurities such as Na and K, when reaching a certain concentration, are constant without being reduced no matter how many times they are washed thereafter. In this example, the amount of residual Na remained at 1000 ppm after the third and subsequent washings. This is presumed that alkali metal impurities such as Na are incorporated in the crystal lattice of barium titanate.
[0022]
It has been found that this reduction of residual Na can be solved by performing a rehydrothermal treatment in the third step. This is a very new fact that could not be expected at all from the known examples. The higher the temperature as rehydrothermal treatment conditions, the better. However, when using a polyfluorinated ethylene resin beaker, 200 ° C. or lower is desirable. The reaction time is sufficient for 4 hours.
[0023]
In addition, the solution at the time of rehydrothermal treatment needs to be alkaline in order to prevent Ba loss. As what imparts alkalinity, aqueous solutions containing alkaline metals such as aqueous ammonia, sodium hydroxide solution and potassium hydroxide solution, and aqueous solutions containing alkaline earth metals such as barium hydroxide solution are conceivable.
[0024]
Among these, ammonia water is not preferable because ammonia is volatilized under hydrothermal treatment conditions, and Ba loss occurs due to a decrease in pH, and the volatilized ammonia reacts with a polyfluorinated ethylene resin beaker. In addition, an aqueous solution containing an alkali metal such as a sodium hydroxide solution cannot be used because it is one of the purposes to remove the alkali metal from the composition obtained in the present invention.
[0025]
Accordingly, an aqueous solution containing an alkaline earth metal such as a barium hydroxide solution is preferable. In particular, a barium hydroxide solution is preferable, and the pH at that time is preferably set to 7 to 10, preferably 9 to 10. When the pH exceeds 10, the Ba / Ti ratio of the finally obtained powder shifts to a higher Ba side, and if the pH is 9 or less, Ba loss occurs in hydrothermal treatment conditions.
[0026]
(Example 2)
0.1 mol of Ti (O—iC ₃ H ₇ ) ₄ and 30 ml of IPA are placed in a beaker made of a polyfluorinated ethylene resin, and stirred with an ultradisperser, 0.6 mol of NaOH. Hydrolysis is carried out with 135 ml of an aqueous solution containing. Then, 0.1 mol of SrCl ₂ is added (first step).
[0027]
A polyfluorinated ethylene resin beaker containing this mixture slurry was mounted on an autoclave apparatus, and the polyfluorinated ethylene resin was subjected to a temperature of 170 ° C. and a pressure of 16 kg / cm ² for 4 hours. Hydrothermal treatment was performed while stirring at 150 rpm using a stirrer bar. The obtained precipitate was taken out, washed with water and filtered several times, and then dried and crushed to obtain a raw material powder (second step). The particle diameter of this powder was 0.1 to 0.2 μm, Sr / Ti ratio: 1.002, Na content: 900 ppm, and Cl content: 10 ppm.
[0028]
Next, 20 g of the above powder and 200 ml of an aqueous barium hydroxide solution adjusted to pH = 10 were placed in a polyfluorinated ethylene resin beaker, and this beaker was attached to an autoclave device. Hydrothermal treatment was performed for 4 hours under the conditions of temperature: 200 ° C. and pressure: 15 kg / cm ² while stirring at 150 rpm using a stirring rod made of polyfluorinated ethylene resin. After completion of the treatment, the raw material powder was obtained through filtration, drying and crushing (third step).
[0029]
As a result of observation with an electron microscope, the particle diameter and particle shape of this powder were 0.1 to 0.2 μm and spherical, Sr / Ti ratio: 0.998, Na content: 80 ppm, Cl content: 10 ppm. It was. From the results of X-ray diffraction, strontium titanate having a cubic perovskite structure was generated.
[0030]
As described above, regarding the examples, the barium titanate (BaTiO ₃ ) powder and the strontium titanate (SrTiO ₃ ) powder have been described. For example, CaTiO ₃ , (Ba, Ca) TiO ₃ , Ba (Ti, Zr) Of course, powders such as O ₃ , (Ba, Ca) (Ti, Zr) O _{3 and the} like can be produced by the same method.
[0031]
【The invention's effect】
The ABO ₃ type powder produced according to the present invention has a particle size of 0.1 to 0.3 μm and a spherical shape, and an A / B ratio in the range of 1.000 ± 0.002. In addition, it has good crystallinity and contains very few alkali metal impurities. The ABO ₃ type powder having these characteristics can cope with high functionality and high reliability in addition to thin and multi-layered multilayer ceramic capacitors.
[Brief description of the drawings]
1 is an X-ray diffraction pattern of barium titanate produced according to Example 1. FIG.

Claims (2)

(A) at least one salt selected from group A elements consisting of Mg, Ca, Sr, Ba, and Pb; and at least one salt selected from group B elements consisting of Ti, Zr, Hf, and Sn; A first step for obtaining a mixture slurry with water or an aqueous alkaline solution, (b) a second step for hydrothermally reacting the mixture slurry to obtain a hydrothermal synthetic powder, and (c) hydrothermal power obtained in the second step. A third step of hydrothermally reacting a mixture of a synthetic powder and an alkaline aqueous solution containing an alkaline earth metal, and a method for producing a composition containing a perovskite type compound. The method for producing a composition according to claim 1, wherein, in the third step, an aqueous barium hydroxide solution having a pH adjusted between 7 and 10 is used as the alkaline aqueous solution containing an alkaline earth metal .

Images