JP3668985B2 - Manufacturing method of ceramic powder - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for producing a ceramic powder comprising a perovskite type compound that is useful as a dielectric material for a multilayer ceramic capacitor.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, ceramic materials used for manufacturing electronic components have been improved in order to reduce the size and performance of the ceramic electronic components constituting the electronic device.
[0003]
As a dielectric ceramic material, a method for producing a ceramic powder made of a uniform and spherical perovskite compound having a particle size of 1 μm or less, preferably 0.5 μm or less has been studied. Ceramic powder with such a particle size has high surface energy due to its small particle size, and has a uniform particle size distribution and spherical shape, which improves the filling property during molding and significantly improves the sinterability. It can be expected to obtain a dense and strong ceramic at a lower temperature.
[0004]
Further, in order to realize the thinning and multi-layering of the dielectric layers of the multilayer ceramic capacitor, a ceramic green sheet having a thickness of 10 μm or less is required. For this reason, the grain size is preferably 1 μm or less. A uniform and spherical ceramic powder of 0.5 μm or less is desired.
[0005]
By the way, conventionally, a ceramic powder made of a perovskite type compound, for example, a barium titanate powder, has been synthesized by calcining barium carbonate and titanium oxide at a high temperature of 1000 ° C. or more and reacting them. Then, a method of pulverizing mechanically (solid phase synthesis method) is known.
[0006]
In addition, metal alkoxide methods, hydroxide methods, hydrothermal synthesis methods, and the like are known as wet synthesis methods.
[0007]
[Problems to be solved by the invention]
However, in the case of the solid phase synthesis method, the barium titanate after calcination is strongly agglomerated, so it was difficult to obtain fine particles having a particle diameter of 1 μm or less even by mechanical pulverization. Moreover, since the particle shape becomes a crushed material shape, when it is molded into an arbitrary shape and fired, it has a problem that it lacks sinterability. Further, as described above, in order to realize thinning and multi-layering of the dielectric layers of the multilayer ceramic capacitor, it is necessary to form a ceramic green sheet having a thickness of 10 μm or less. When the barium titanate powder obtained by the synthesis method is used, there is a problem that the density of the green sheet is reduced or the thickness variation of the green sheet is increased.
[0008]
On the other hand, the production of ceramic powder made of a perovskite type compound by a wet synthesis method, but in the case of the metal alkoxide method, the raw material was expensive and there was a problem in industrialization.
[0009]
Regarding the hydroxide method, attention has been paid in that the raw materials are relatively inexpensive and the resulting powder has high sinterability. For example, in Japanese Patent Application Laid-Open No. 59-39726, a water-soluble barium salt such as barium chloride or barium nitrate is dissolved in an aqueous solution of titanium salt, and an alkali is added to adjust the pH to 13 or higher. A method is disclosed. However, since the barium titanate powder obtained by this method has a particle diameter of 0.02 to 0.03 μm which is too fine, there is a problem that the density when molded is low and the shrinkage during sintering is large. Depending on the application, it may not be preferable.
[0010]
Japanese Patent Laid-Open No. 60-90825 discloses a method of heating titanic acid and barium hydroxide in the presence of a large amount of water at a temperature below the boiling point. A step of preparing in advance is necessary. At this time, for example, when titanic acid is precipitated by neutralization of an aqueous solution of a titanium compound, it becomes a colloidal shape, so that it is difficult to wash and filter industrially. Had.
[0011]
In recent years, the hydrothermal synthesis method has attracted particular attention because it can obtain an optimum barium titanate powder for thinning and multi-layering of multilayer ceramic capacitors. 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 subjected to a hydrothermal reaction in an aqueous medium. A method is disclosed in which the group A element dissolved in an 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. There was a need to decide.
[0012]
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 is disclosed. However, as a result of examining this method in detail, alkali metal impurities such as Na and K cannot be removed. For example, about 800 to 1000 ppm of Na or Ca remains in the synthesized barium titanate powder. It became clear to do.
[0013]
Therefore, an object of the present invention is uniform and spherical particles having a particle size of 0.5 μm or less, the molar ratio of A site element to B site element is in the range of 1.000 ± 0.002, It is an object of the present invention to provide a method for producing a ceramic powder made of a perovskite type compound that has high properties and is extremely low in impurities such as ants.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, a method for producing a ceramic powder according to the present invention includes a hydroxide or chloride of at least one element selected from the group consisting of Mg, Ca, Sr, Ba and Pb, and Ti, Zr. , Hf and Sn, a step of obtaining a slurry of a mixture of a hydroxide of at least one element selected from the group consisting of an alkaline aqueous solution and a hydrothermal reaction of the mixture slurry at at least two different temperatures to form a perovskite A type compound is obtained.
[0015]
[Action]
In the production of a ceramic powder composed of an ABO ₃ type perovskite type compound, the A-site element hydroxide or chloride and the B-site element hydroxide are hydrothermally heated at two different temperatures in the presence of OH ions. Ceramics with uniform and spherical particles with a particle size of 0.5 μm or less, high crystallinity without deviation in A / B molar ratio, and greatly reduced residual amount of alkali metal impurities. A powder is obtained.
[0016]
【Example】
Hereinafter, the Example is demonstrated about the manufacturing method of the ceramic powder of this invention.
(Example 1)
First, a mixture slurry was prepared. That is, 0.1 mol of Ti (OC ₃ H ₇ ) _{4 was} accurately weighed and put into a polytetrafluoroethylene beaker having an internal volume of about 400 cc together with about 30 cc of isopropyl alcohol. Next, while this solution was stirred with an ultradisperser, about 135 cc of an aqueous solution containing 0.6 mol of NaOH was added for hydrolysis. Thereafter, 0.1 mol of BaCl ₂ was added to obtain a mixture slurry.
[0017]
Next, the polytetrafluoroethylene beaker containing the mixture slurry was attached to an autoclave apparatus. Then, hydrothermal reaction was carried out for 1 hour while stirring at 150 rpm with a stirring rod made of polytetrafluoroethylene under the conditions of a temperature of 120 ° C. and a pressure of 4 kg / cm ² . Next, the temperature was raised to 200 ° C., and a hydrothermal reaction was carried out for 4 hours in the same manner as described above. After completion of the reaction, washing with water and filtration were repeated, followed by drying and crushing to obtain BaTiO ₃ powder.
[0018]
Next, crystal structure of the obtained BaTiO ₃ powder by X-ray diffraction (XRD) analysis, particle state by electron microscope (SEM) observation, Ba / Ti molar ratio by X-ray fluorescence analysis, atomic absorption analysis and ion chromatography The amount of impurities was confirmed by analysis. As a result, the obtained BaTiO ₃ powder has a cubic perovskite structure, and the particles are spherical with a particle size of 0.2 to 0.3 μm and have good dispersibility, and the Ba / Ti molar ratio is 1. There was almost no deviation from 0.001. Further, the amount of impurities in the BaTiO ₃ powder was as low as 140 ppm for Na and 20 ppm for Cl.
[0019]
On the other hand, for comparison, the same mixture slurry as the above example was hydrothermally reacted at 120 ° C. for 1 hour. As a result, the obtained BaTiO ₃ powder had a particle size of around 0.1 μm and a Ba / Ti molar ratio of 1.002, but the amount of Na as an impurity was very high at 1400 ppm.
[0020]
Similarly, for comparison, the same mixture slurry as in the above example was hydrothermally reacted at 200 ° C. for 4 hours. As a result, the amount of Na as an impurity was reduced to the same level as in the above examples, but the resulting BaTiO ₃ powder was not uniform in particle diameter and poor in dispersibility.
[0021]
(Example 2)
First, a mixture slurry was prepared. That is, 0.1 mol of Ti (OC ₃ H ₇ ) _{4 was} accurately weighed and introduced into a polytetrafluoroethylene beaker having an internal volume of about 400 cc together with about 30 cc of isopropyl alcohol. Next, while this solution was stirred with an ultradisperser, about 135 cc of an aqueous solution containing 0.6 mol of NaOH was added for hydrolysis. Thereafter, 0.1 mol of SrCl ₂ was added to obtain a mixture slurry.
[0022]
Next, this mixture slurry was subjected to a hydrothermal reaction in the same manner as in Example 1 to obtain SrTiO ₃ powder.
[0023]
Thereafter, the properties and the like of the obtained SrTiO ₃ powder were confirmed in the same manner as in Example 1. As a result, the obtained SrTiO ₃ powder has a cubic perovskite structure, the particles have a spherical shape with a particle size of 0.1 to 0.2 μm and good dispersibility, and the Sr / Ti molar ratio is 0. There was almost no deviation from 999. Moreover, the amount of impurities in the SrTiO ₃ powder was as low as 160 ppm for Na and 20 ppm for Cl.
[0024]
(Example 3)
First, a mixture slurry was prepared. That is, 0.1 mol of Ti (OC ₃ H ₇ ) ₄ was accurately weighed and introduced into a polytetrafluoroethylene beaker having an internal volume of about 400 cc together with about 30 cc of isopropyl alcohol. Next, while this solution was stirred with an ultradisperser, about 135 cc of an aqueous solution containing 0.6 mol of NaOH was added for hydrolysis. Thereafter, 0.1 mol of Sr (OH) ₂ was added to obtain a mixture slurry.
[0025]
Next, this mixture slurry was subjected to a hydrothermal reaction in the same manner as in Example 1 to obtain SrTiO ₃ powder.
[0026]
Thereafter, the properties and the like of the obtained SrTiO ₃ powder were confirmed in the same manner as in Example 1. As a result, the obtained SrTiO ₃ powder has a cubic perovskite structure, and the particles are spherical with a particle size of 0.1 to 0.2 μm and have good dispersibility, and the Sr / Ti molar ratio is 1 There was almost no deviation from 0.001. Moreover, the amount of impurities in the SrTiO ₃ powder was as low as 150 ppm for Na and 20 ppm for Cl.
[0027]
As described above, in the production of the ceramic powder composed of the ABO ₃ type perovskite type compound, the hydroxide or chloride of the A site element and the hydroxide of the B site element are produced in the presence of OH ions. Hydrothermal reaction at 120 ° C. for 1 hour at 200 ° C., followed by further hydrothermal reaction at 200 ° C. for 4 hours to greatly increase the residual Na content from 1400 ppm to 140-160 ppm. Could be reduced.
[0028]
In this production method, the OH concentration in the mixture slurry is at least 4 times, preferably 6 times or more of the charged concentrations of A and B, in order to prevent the A / B molar ratio shift after the hydrothermal reaction. is necessary. In the above embodiment, 0.6 mol of NaOH, which is 6 times the amount of 0.1 mol of A and B, is added.
[0029]
In the above embodiment has been described manufacturing method of the BaTiO ₃ powder and SrTiO ₃ powder, the present invention is not limited only thereto. That is, the general formula ABO ₃ (where A is at least one selected from the group consisting of Mg, Ca, Sr, Ba and Pb, and B is at least one selected from the group consisting of Ti, Zr, Hf and Sn) ), For example, CaTiO ₃ , (Ba, Ca) TiO ₃ , BaZrO ₃ , Ba (Ti, Zr) O ₃ , (Ba, Ca) (Ti, Zr) O ₃ , PbTiO ₃ , Similar effects can be obtained in the production of Ba (Ti, Sn) O ₃ , Ba (Ti, Hf) O _{3, and the} like.
[0030]
【The invention's effect】
As is apparent from the above description, the method for producing a ceramic powder of the present invention comprises a hydroxide or chloride of an A site element and a hydroxide of a B site element in an ABO ₃ type perovskite compound. Hydrothermal reaction is carried out at two different temperatures in the presence of ions.
[0031]
Accordingly, the particles are uniform and spherical particles of 0.5 μm or less, the molar ratio of the A site element to the B site element is in the range of 1.000 ± 0.002, the crystallinity is high, and the ant pottery metal Thus, a ceramic powder made of a perovskite type compound with very little impurities such as can be obtained.
[0032]
Therefore, by using this ceramic powder, it is possible to manufacture a monolithic ceramic capacitor having a thinner and multi-layered structure.

Claims (1)

Hydroxide or chloride of at least one element selected from the group consisting of Mg, Ca, Sr, Ba and Pb and hydroxylation of at least one element selected from the group consisting of Ti, Zr, Hf and Sn A process for obtaining a mixture slurry of a product and an alkaline aqueous solution, and a hydrothermal reaction of the mixture slurry at at least two different temperatures to obtain a perovskite type compound.