JP2007261912A - Barium titanate powder and its manufacture process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing process of a barium titanate powder being reduced in the content of impurities. <P>SOLUTION: In the manufacturing process, the barium titanate powder is hydrothermally synthesized from a titanium compound and a barium compound. A titanium compound showing a pH of ≥6.6 and ≤10 is used for the titanium compound. The concentrations of the titanium compound and the barium compound are ≥1.0 mol/L respectively. The chlorine content of the titanium compound is ≤0.023 wt.%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a barium titanate powder having a low impurity content, and more particularly to a method for producing a barium titanate powder useful as a constituent material of an electronic component such as a multilayer ceramic capacitor.

  With the downsizing of electronic components, it is desired to reduce the size and increase the capacity of multilayer ceramic capacitors. In order to reduce the size and increase the capacity of the multilayer ceramic capacitor, it is necessary to reduce the thickness of the dielectric layer. As the dielectric thickness decreases, the barium titanate powder, which is a dielectric material, is being atomized.

  Examples of methods for producing barium titanate include a solid phase reaction method, a hydrothermal synthesis method, an oxalate method, and a sol-gel method. Among these methods, the liquid phase method is advantageous for producing fine barium titanate, and one of them is a hydrothermal synthesis method.

  The hydrothermal synthesis method is a method in which, for example, a water-soluble titanium salt (for example, titanium oxide) and a water-soluble barium salt (for example, barium hydroxide) are reacted in alkaline high-temperature and high-pressure water to obtain crystalline barium titanate powder. Yes (see Patent Document 1).

However, when conventional hydrothermal synthesis is performed under high temperature and high pressure, the impurity content increases. In particular, when synthesis is carried out at a temperature of 250 ° C. or higher, it has been confirmed that impurities are mixed in the barium titanate powder as contamination, depending on the material of the reaction vessel (for example, autoclave). This contamination by impurities adversely affects the electrical characteristics of the multilayer ceramic capacitor.
WO99 / 59919 (Japanese Patent Application No. 2000-549542)

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a production method for obtaining a barium titanate powder having a low impurity content, and a barium titanate powder obtained by the production method. It is to provide an electronic component such as a multilayer ceramic capacitor manufactured using the powder.

  When the present inventors produce barium titanate by a hydrothermal synthesis method, in the reaction between the titanium compound and the barium compound, the pH of the titanium compound, the chlorine content in the titanium compound, and / or the titanium compound and the barium compound It has been found that barium titanate with a low impurity content can be obtained by controlling the concentration of.

That is, according to the present invention,
A method for producing a barium titanate powder by a hydrothermal synthesis method using a titanium compound and a barium compound,
As the titanium compound, a titanium compound having a pH of 6.6 or more and 10 or less is used.

  Preferably, the concentration of chlorine impurities in the titanium compound is 0.023 wt% or less.

  Preferably, the concentration of the titanium compound and the barium compound is 1.0 mol / liter or more.

  Preferably, the titanium compound is titanium oxide.

Preferably, the water-soluble barium compound is barium hydroxide or barium hydroxide octahydrate.
According to the present invention, a barium titanate powder obtained by the above method is provided.

According to the present invention, an electronic component having a dielectric layer,
An electronic component is provided in which the dielectric layer is manufactured using the barium titanate powder described above.

  According to the present invention, there is provided a multilayer electronic component having an element body in which a plurality of internal electrode layers and dielectric layers are alternately stacked,

  A multilayer electronic component is provided in which the dielectric layer is manufactured using the barium titanate powder described above.

  In the method of the present invention, by using a titanium compound having a pH of 6.6 or more and 10 or less, the concentration of impurities contained in barium titanate can be effectively reduced. Further, in the method of the present invention, the concentration of impurities contained in barium titanate can be more effectively reduced by setting the concentration of chlorine impurities in the titanium compound to 0.023 wt% or less. Furthermore, in the method of the present invention, the concentration of impurities contained in barium titanate can be more effectively reduced by setting the concentrations of the titanium compound and barium compound to 1.0 mol / liter or more.

  Since the barium titanate powder obtained by the method of the present invention has a very low impurity concentration, a multilayer ceramic capacitor having a dielectric layer formed using the barium titanate powder has electrical characteristics such as a high temperature load life. Excellent.

  In addition, the barium titanate powder produced by the method of the present invention can be suitably used as a PTC thermistor, a pigment, etc. in addition to the dielectric layer of the capacitor.

Hereinafter, the present invention will be described based on embodiments shown in the drawings.
FIG. 1 is a schematic cross-sectional view of a multilayer ceramic capacitor according to an embodiment of the present invention.

  As shown in FIG. 1, a multilayer ceramic capacitor 1 as an example of an electronic component of the present invention has a capacitor element body 10 having a configuration in which interlayer dielectric layers 2 and internal electrode layers 3 are alternately stacked. A pair of external electrodes 4 are formed at both ends of the capacitor element body 10 so as to be electrically connected to the internal electrode layers 3 arranged alternately in the element body 10. The internal electrode layers 3 are laminated such that the side end faces are alternately exposed on the surfaces of the two opposite ends of the capacitor element body 10.

  The pair of external electrodes 4 are formed at both ends of the capacitor element body 10 and are connected to the exposed end surfaces of the alternately arranged internal electrode layers 3 to constitute a capacitor circuit.

  The shape of the capacitor element body 10 is not particularly limited, but is usually a rectangular parallelepiped shape. Also, there is no particular limitation on the size, and it may be an appropriate size according to the application. Usually, the length (0.6 to 5.6 mm) × width (0.3 to 5.0 mm) × height (0.3 to 1.9 mm).

  In the capacitor element body 10, outer dielectric layers 20 are disposed at both outer end portions in the stacking direction of the internal electrode layer 3 and the interlayer dielectric layer 2 to protect the inside of the element body 10.

  The composition of the interlayer dielectric layer 2 and the outer dielectric layer 20 is not particularly limited in the present invention, and is composed of, for example, the following dielectric ceramic composition.

  The dielectric ceramic composition of the present embodiment has, as a main component, barium titanate produced by a hydrothermal synthesis method described later. Subcomponents included in the dielectric ceramic composition together with the main component include Mn, Cr, Ca, Ba, Mg, V, W, Ta, Nb, and R (R is one or more of rare earth elements such as Y). Examples include oxides and one or more compounds that become oxides upon firing.

  The internal electrode layer 3 is preferably made of a base metal conductive material that substantially functions as an electrode. As the base metal used as the conductive material, Ni or Ni alloy is preferable.

  As the external electrode 4, at least one of Ni, Pd, Ag, Au, Cu, Pt, Rh, Ru, Ir, or an alloy thereof can be used. Usually, Cu, Cu alloy, Ni, Ni alloy, etc., Ag, Ag—Pd alloy, In—Ga alloy, etc. are used.

  In order to manufacture the multilayer ceramic capacitor 1 according to the present embodiment, for example, first, before firing, the interlayer dielectric layer 2 and the outer dielectric layer 20 shown in FIG. A dielectric layer paste that constitutes the outer dielectric layer, and an internal electrode layer paste that constitutes the pre-fired internal electrode layer for forming the internal electrode layer 3 shown in FIG. 1 after firing. prepare.

In this embodiment, barium titanate contained in the dielectric material in the dielectric layer paste is manufactured by a hydrothermal synthesis method. Specifically, it is as follows.
Method for producing barium titanate powder

  First, a titanium compound, a barium compound, and ion-exchanged water are prepared as starting materials.

As the titanium compound, one or more selected from halides, hydroxides, nitrates, sulfates, acetates, perchlorates, oxalates and alkoxides are used. Specific examples include titanium oxide, hydrous titanium oxide, titanium tetrachloride and hydrolysates thereof, or titanium oxide. Among these, titanium oxide fine particles are preferably used. The titanium oxide fine particles are not particularly limited, but are preferably anatase-type titanium oxide, rutile-type titanium oxide, or a mixture thereof. Preferably, the specific surface area of the titanium oxide fine particles is 35 m ² / g or more. That is, it is preferable that the titanium oxide fine particles have a small particle size. When the particle diameter of the titanium oxide fine particles is too large, the reaction tends to be insufficient.

  As the barium compound, one or more selected from halides, hydroxides, nitrates, sulfates, acetates, perchlorates, oxalates and alkoxides are used. Preferably used. The water-soluble barium compound is not particularly limited, and examples thereof include barium hydroxide, barium hydroxide octahydrate, barium acetate, and barium chloride. Among these, barium hydroxide or barium hydroxide octahydrate is exemplified. Is preferably used.

  In addition, you may add alkaline compounds, such as amines, such as sodium hydroxide, ammonia, potassium hydroxide, and tetramethylammonium hydroxide, as needed.

  In the present embodiment, these compounds may be prepared in advance in the form of powder, aqueous solution or suspension.

  Next, each of these compounds is put into a reaction kettle such as a pressure vessel, and a hydrothermal reaction is performed to obtain a reaction product. The material of the pressure vessel can withstand high temperature and pressure, and is made of, for example, SUS316 or HC-276.

  SUS316 has Fe as a main component, and other components include C ≦ 0.08%, Si ≦ 1.00%, Si ≦ 1.00%, Mn ≦ 2.00%, P ≦ 0.045%, S ≦ 0.030%, 10.00% ≦ Ni ≦ 14.00%, 16.00% ≦ Cr ≦ 18.00%, 2.00% ≦ Mo ≦ 3.00%.

  The main component of HC-276 is Ni. As other components, 14.5 ≦% Cr ≦ 16.5%, 15.0 ≦% Mo ≦ 17.0%, 3.0% ≦ W ≦ 4. 5%, 4.0% ≦ Fe ≦ 7.0%, C ≦ 0.02%, Si ≦ 1.0%, Co ≦ 2.5%.

  When each compound is put into a reaction vessel such as a pressure vessel, the titanium compound and the barium compound are charged so as to have a predetermined Ba / Ti ratio. Preferably, the barium compound is added in the number of moles equal to or greater than the number of moles of the titanium compound. When the number of moles of the titanium compound is A and the number of moles of the barium compound is B, B / A is preferably 1 to 2. In this case, it is preferable to remove the excess barium compound obtained together with the barium titanate powder. More preferably, the barium compound is added in a substantially equimolar amount with respect to the number of moles of the titanium compound. In this case, it is not necessary to remove excess barium compound.

  In the present embodiment, a titanium compound having a pH of 6.6 or more and 10 or less, preferably a pH of 7.0 to 9.0 is used as the titanium compound used for hydrothermal synthesis. Moreover, in the present embodiment, a titanium compound in which the concentration of chlorine impurities in the titanium compound is preferably 0.023 wt% or less, more preferably 0.010 wt% or less is used. Further, in the hydrothermal synthesis, the concentration of the titanium compound and barium compound is preferably set to 1.0 mol / liter or more, more preferably 2.0 mol / liter or more.

  In addition, when adding each compound, for example, ion exchange water or the like may be added together in a predetermined amount.

  The hydrothermal reaction is usually performed in an aqueous alkaline solution having a high hydrogen ion concentration (pH), preferably 11 or more.

  The hydrothermal reaction temperature is preferably 80 ° C. or higher, more preferably 150 ° C. or higher, because it is necessary to increase the reaction rate. From the viewpoint of preventing an increase in the pressure of the solution, the upper limit of the reaction temperature is preferably about 500 ° C. In this embodiment, a reaction temperature of 200 ° C. to 300 ° C. is preferable.

  The hydrothermal reaction time is not particularly limited, but is preferably 30 minutes or more, more preferably 60 minutes or more. Since it is uneconomical if it is too long, the upper limit of the reaction time is preferably about 360 minutes.

  The hydrothermal reaction is preferably performed in an atmosphere in which no carbon dioxide exists. When the hydrothermal reaction is performed in an atmosphere in which carbon dioxide is present, there may be a disadvantage that a barium carbonate phase is generated.

  The hydrothermal reaction is preferably performed at a high pressure of 1.0 atm or higher, more preferably 4.5 atm or higher.

  Next, the obtained reaction product (slurry) is dried to obtain barium titanate powder. Drying can be performed by a conventionally known method.

  In addition, after drying the obtained reaction material once in air | atmosphere, you may wash | clean in weak acid solutions, such as acetic acid aqueous solution. By doing so, only excess barium (barium carbonate) can be removed.

  The barium titanate thus produced by the hydrothermal synthesis method has a certain spherical shape, the particle diameter calculated from the reciprocal of the specific surface area is preferably 40 to 140 nm, the particle size distribution is narrow, and the crystal The property is also good. Further, the atomic ratio of Ba / Ti is very close to 1.00 to 0.998 to 1.002. Furthermore, the dispersibility when slurryed is extremely high. Therefore, it is suitable as a main component material contained in the dielectric material in the dielectric layer paste.

Moreover, the barium titanate manufactured by the hydrothermal synthesis method of the present embodiment can reduce impurities such as Cr ₂ O ₃ , MnO, Fe ₂ O ₃ , NiO, and MoO ₃ . Therefore, when a capacitor is produced using the barium titanate powder obtained by the method of this embodiment, the capacitance and reliability can be improved, and a high-capacity and high-reliability product can be obtained. There is expected.

  In the present embodiment, the dielectric layer paste having the dielectric material containing barium titanate obtained as described above and the internal electrode layer paste are used, and the pre-fired dielectric layer and the pre-fired internal electrode A green chip in which the layers are laminated is manufactured. The green chip is subjected to a binder removal process, a firing process, and an annealing process performed as necessary, to obtain the capacitor element body 10 shown in FIG. 1, and the external electrode 4 is formed on the element body 10. Thus, the multilayer ceramic capacitor 1 is manufactured.

  Since the multilayer ceramic capacitor 1 of the present embodiment is manufactured using the barium titanate powder of the present invention, it has a high capacity and high reliability.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to such embodiment at all, Of course, in the range which does not deviate from the summary of this invention, it can implement in various aspects. .

Next, the present invention will be described in more detail by giving more specific examples of the embodiment of the present invention. However, the present invention is not limited to only these examples.
Samples 1-7

  Barium hydroxide and titanium oxide having the pH and chlorine content shown in Table 1 were dissolved in 250 ml of ion-exchanged water (pH: 7.0 to 8.0, water temperature 25 ° C.), and barium hydroxide and titanium oxide were dissolved. Was placed in a reaction vessel made of stainless steel SUS316, and hydrothermal synthesis was performed at 280 ° C. for 1 hour.

  The pH of titanium oxide is 10 g of titanium oxide charged into 300 ml of ion exchange water (pH 7.0 to 8.0, measured at a water temperature of 25 ° C.) under the conditions of a solution temperature of 25 ° C. and a stirring speed of 100 rpm. Therefore, it measured using Yokogawa Electric Corporation make type | model number PH82-21-J.

The solution after the reaction was dried with a dryer at 130 ° C. for 12 hours and pulverized in an agate mortar.
The composition analysis of the obtained barium titanate powder was performed with a fluorescent X-ray analyzer (Rigaku ZSX-100e). Table 1 shows the impurity content contained in barium titanate. Moreover, the specific surface area of the obtained barium titanate was measured by multisorb (Yuasa Ionics), and the average particle diameter of the barium titanate powder was calculated from the reciprocal of the specific surface area. The average particle diameter of the obtained barium titanate powder is shown in Table 1.

Samples 11-17

Barium titanate powder was produced and evaluated in the same manner as in Samples 1 to 7 except that the concentrations of titanium oxide and barium hydroxide were 0.6 mol / liter. The results are shown in Table 1.
Samples 21-24

  Barium titanate was used in the same manner as Samples 1 to 7 except that titanium oxide having a chlorine content of 0.010 wt% at pH 7 was used and the concentrations of titanium oxide and barium hydroxide were changed as shown in Table 2. A powder was produced and evaluated in the same manner. The results are shown in Table 2.

Samples 31-34

  Except for changing the synthesis temperature as shown in Table 3, barium titanate powder was produced and evaluated in the same manner as in Samples 21 to 24. The results are shown in Table 3.

Samples 41-44

Barium titanate powder was produced and evaluated in the same manner as Samples 31 to 34 except that the concentrations of titanium oxide and barium hydroxide were changed to 0.6 mol / liter. The results are shown in Table 3.
Samples 51-54

Barium titanate powder was produced and evaluated in the same manner as Samples 41 to 44 except that titanium oxide having a pH of 4 and a chlorine content of 0.065 wt% was used. The results are shown in Table 3.
Samples 61-64

Samples 1 to 17 except that the reaction vessel was changed to Hastelloy HC-276, the synthesis temperature was 290 ° C., the concentrations of barium hydroxide and titanium oxide, and the chlorine content of titanium oxide were as shown in Table 4. In the same manner, barium titanate powder was produced and evaluated in the same manner. The results are shown in Table 4.
Samples 71-74

  The reaction vessel was changed to Hastelloy HC-276, the barium hydroxide concentration and the titanium oxide concentration were changed to 1.0 mol / liter, and the synthesis temperature was changed as shown in Table 4 in the same manner as in Samples 1 to 17. A barium titanate powder was produced and evaluated in the same manner. The results are shown in Table 4.

Evaluation

  As shown in Table 1, it can be confirmed that the impurity concentration of barium titanate can be lowered when the pH of titanium oxide is 6.6 or more and 10 or less, preferably 7.0 to 9.0. It was. Further, it was confirmed that the impurity concentration of barium titanate can be reduced when the chlorine content of titanium oxide is preferably 0.023 wt% or less, more preferably 0.010 wt% or less.

  As shown in Table 2, in the hydrothermal synthesis, the concentration of the titanium compound and the barium compound is preferably set to 1.0 mol / liter or more, more preferably 2.0 mol / liter or more, so that It was confirmed that the impurity concentration can be reduced.

  As shown in Table 3, when the synthesis temperature is particularly high, when the pH of titanium oxide is 7.0, and when the concentration of titanium oxide and barium hydroxide is 1.0 mol / liter or more, It was confirmed that the impurity concentration of barium titanate can be reduced.

  As shown in Table 4, it was confirmed that even in a reaction vessel made of HC-276 that is not made of stainless steel SUS316, the same effect as that of a reaction vessel made of stainless steel SUS316 can be obtained.

FIG. 1 is a schematic cross-sectional view of a multilayer ceramic capacitor according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Multilayer ceramic capacitor 10 ... Capacitor element main body 2 ... Interlayer dielectric layer 20 ... Outer dielectric layer 3 ... Internal electrode layer 4 ... External electrode

Claims (8)

A method for producing a barium titanate powder by a hydrothermal synthesis method using a titanium compound and a barium compound,
A method for producing a barium titanate powder, wherein a titanium compound having a pH of 6.6 or more and 10 or less is used as the titanium compound.   2. The method for producing barium titanate powder according to claim 1, wherein the concentration of chlorine impurities in the titanium compound is 0.023 wt% or less.   The manufacturing method of the barium titanate powder of Claim 1 or 2 which sets the density | concentration of the said titanium compound and the said barium compound to 1.0 mol / liter or more. The method for producing a barium titanate powder according to any one of claims 1 to 3, wherein the titanium compound is titanium oxide. The method for producing a barium titanate powder according to any one of claims 1 to 4, wherein the water-soluble barium compound is barium hydroxide or barium hydroxide octahydrate. Barium titanate powder obtained by the method according to claim 1. An electronic component having a dielectric layer,
The said dielectric material layer is manufactured using the barium titanate powder of Claim 6, The electronic component characterized by the above-mentioned. A multilayer electronic component having an element body in which a plurality of internal electrode layers and dielectric layers are alternately laminated,
A multilayer electronic component, wherein the dielectric layer is manufactured using the barium titanate powder according to claim 6 or 7.

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