JP3992214B2 - Rare earth element-containing barium titanate powder and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention, the insoluble properties of basic carbonates or oxides relates barium rare earth-containing titanate powder and a manufacturing method thereof contained in the surface of the rare earth elements.
[0002]
Conventional method
Barium titanate is widely used as a material for ceramic capacitors. When used in a ceramic capacitor, a rare earth element compound such as an oxide of a rare earth element is also added to the ceramic raw material powder. As a method for adding rare earth element oxides to barium titanate, it is common to use barium titanate powder and rare earth element oxide powder as a mixed powder using a mixing facility such as a ball mill. is there.
[0003]
In recent years, as the ceramic capacitor has been made thinner and smaller, more uniform mixing of barium titanate powder and rare earth element oxide powder has been demanded. Barium titanate powder has also been made finer, and accordingly, rare earth element oxide powder to be mixed has been required to have a smaller particle size. For sub-micron or larger particles that are normally distributed as fine particles of rare earth oxide oxides, the mixing with the barium titanate powder becomes non-uniform, resulting in uneven sintering, etc. In addition, sufficient characteristics are not appearing in ceramic capacitors that have been reduced in size.
[0004]
[Problems to be solved by the invention]
An object of the present invention is to obtain a powder in which barium titanate and a rare earth element compound are uniformly mixed even when viewed microscopically in order to solve the above-described conventional drawbacks.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, the present onset light rare earth element-containing barium titanate powder is an insoluble basic carbonates or oxides of at least one kind of rare earth element to barium titanate powder surface, the powder surface the concentration of the rare earth elements 50 wt% or more by XPS in, characterized by being free Yes.
Method for producing a rare earth element-containing barium titanate powder of the present invention, powdered barium titanium acid, a suspension containing a water-soluble salt and urea of rare earth elements of 70 ° C. or more, is heated to a temperature below the boiling point of the solution, after the surface of the barium titanate powder to precipitate an insoluble basic carbonates of rare earth elements, characterized in that it separated solid-liquid separation. Also, a suspension containing barium titanate powder, a rare earth element water-soluble salt and urea is heated to a temperature not lower than 70 ° C. and not higher than the boiling point of the solution, and the surface of the barium titanate powder is insoluble in the rare earth element carbonate. after precipitation of the solid-liquid separation, the obtained powder and wherein the sintered child at 600 ° C. or higher. Further, ammonia was added to a suspension containing barium titanate powder and a rare earth element water-soluble salt to precipitate a rare earth element hydroxide, followed by solid-liquid separation. characterized by tempering formed at a temperature.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The present inventor has alumina surface to precipitate basic carbonate of yttria, the method of making the yttria / alumina mixture particles, previously you are patent (JP-A 11-21124) further time, barium titanate It was confirmed that a rare earth element basic carbonate could be deposited on the surface of the particles, and the present invention was completed.
A slurry solution containing an aqueous solution of a water-soluble salt of a rare earth element, urea, and barium titanate powder is prepared. The slurry solution is heated to 70 ° C. or higher and lower than the boiling point of the solution while stirring. By heating, the urea is hydrolyzed to decompose into ammonia and carbon dioxide, insoluble of basic carbonate of the rare earth element is uniformly deposited on the barium titanate powder surface. An insoluble basic rare earth element-containing barium titanate powder carbonate are uniformly deposited in the rare earth element on the surface by the insoluble of the basic carbonate is a solid-liquid separation of the barium titanate powder deposited on the surface Can be obtained.
[0007]
Thus obtained surface-insoluble of basic carbonate of the rare earth element (hereinafter, simply referred to as an insoluble salt) a rare earth element-containing barium titanate powder was precipitated, the temperature of 600 ° C. or more, or in an oxidizing atmosphere in the air To obtain a rare earth element-containing barium titanate powder having a rare earth element oxide adhered to the surface of the barium titanate powder.
Also, instead of hydrolyzing urea into ammonia and carbonic acid by heating as described above, titanic acid can also be obtained by adding ammonia to precipitate rare earth element hydroxide, followed by solid-liquid separation and firing. A rare earth element-containing barium titanate powder having a rare earth element oxide adhered to the barium powder surface can be obtained.
As the insoluble salt of the rare earth element is uniformly deposited directly on the surface of the barium titanate powder, the distribution state of the barium titanate and the rare earth element becomes uniform within the range of the particle diameter of the barium titanate powder. In the conventional powder mixing of barium titanate powder and rare earth element oxide powder, it was the limit that the powder particles were adjacently distributed even in the most advanced mixing state. It becomes possible to distribute microscopically and uniformly.
[0008]
As the particle diameter of the barium titanate powder, the fine distribution of Ti, Ba, and rare earth elements is defined by the particle diameter, so that an appropriate one is used according to the purpose. Specifically, an average particle size of about 0.1 to 2.0 microns is appropriate. The particle diameter is preferably as uniform as possible.
As the rare earth element, any element of a lanthanoid including yttrium can be used. As the water-soluble salt, a rare earth element mineral salt can be used. Examples of mineral acid salts include nitrates, chlorides, acetates and sulfates.
The concentration of each component when preparing as a mixed slurry is as follows.
The solid content concentration of the barium titanate powder needs to be such a concentration that the barium titanate powder can be easily stirred as a slurry in the reaction vessel.
[0009]
The concentration of the water-soluble salt of the rare earth element may be added by calculating the addition amount from the solid content concentration of the barium titanate powder in accordance with the target ratio of Ti, Ba, and rare earth element, but it is particularly used for capacitors. In this case, the water-soluble salt of the rare earth element is preferably used in an amount of 0.5 to 10 % by mass based on the solid content of barium titanate.
The concentration of urea is 3 times or more, preferably 12 to 20 times the molar concentration of the water-soluble salt of the rare earth element.
The temperature for heating the slurry solution is 70 ° C. or higher and the boiling point of the solution or lower, preferably 80 ° C. or higher, more preferably 90 ° C. or higher. If it is less than 70 degreeC, reaction will take time too much, and if it heats to a boiling point, stable reaction cannot be expected.
[0010]
By heating, urea is hydrolyzed into ammonia and carbonic acid, and reacts with rare earth element ions in the slurry solution to become an insoluble basic carbonate. Most of the precipitation reaction of the insoluble basic carbonate occurs on the surface of the barium titanate powder in the slurry, so that the surface of the barium titanate powder is coated with an insoluble salt of a rare earth element.
The time required for heating depends on the rare earth element ion concentration, the urea concentration, the heating temperature, etc. in the reaction vessel. For example, the rare earth element ion concentration is 0.05 mol / liter, and the urea concentration is 0.1. In the case of 75 mol / liter and a heating temperature of 95 ° C., about 60 minutes is sufficient.
[0011]
To confirm whether or not the precipitation reaction is complete, a part of the slurry is sampled and filtered from the reaction vessel, and alkali is added to the filtrate to confirm that the rare earth element hydroxide precipitate does not precipitate. be able to.
The rare earth element-containing barium titanate powder with the rare earth element insoluble salt deposited on the surface is solid-liquid separated using a Bifnel funnel, centrifuge, centrifugal settling machine, decanter, dryer, etc., and the resulting cake is dried. Thus, a rare earth element-containing barium titanate powder having a rare earth element insoluble salt attached to the surface is obtained.
Furthermore, the rare earth element-containing barium titanate powder having the rare earth element insoluble salt adhered to the surface thereof is baked at a temperature of 600 ° C. or higher, preferably 600 to 1400 ° C. in an oxidizing atmosphere for 30 minutes or longer. A rare earth element-containing barium titanate powder is obtained in which a rare earth element oxide is uniformly deposited on a barium acid powder.
[0012]
When the temperature is lower than 600 ° C., firing is insufficient, and an undecomposed rare earth element insoluble salt may remain in the rare earth element-containing barium titanate powder to which the rare earth element oxide is attached.
The barium titanate powder of the present invention thus obtained has an insoluble salt or oxide of rare earth elements attached to the surface, and the rare earth element concentration on the surface is XPS as shown in FIG. 4 to be described later. 50 % by mass or more of rare earth elements are attached at a high concentration.
Further, in the present invention, in addition to the above-described method, a rare earth element water-soluble salt is precipitated as a rare earth element hydroxide in the presence of ammonia on the surface of barium titanate, and calcined to produce barium titanate powder. It is good also as the powder which contained the oxide of rare earth elements on the surface.
[0013]
【Example】
Hereinafter, although an embodiment and a comparative example are given and an embodiment of the present invention is explained concretely, the present invention is not limited to this.
(Example)
100 g of barium titanate powder having an average particle size of about 1.0 micron and 0.05 mol of yttrium nitrate were mixed in pure water to make a total volume of 10 liters. Furthermore, 45 g of urea was added and dissolved, and the mixture was heated at about 95 ° C. for 60 minutes with stirring. After confirming that there was no rare earth element in the liquid phase, the slurry was filtered with a Bifnel funnel, and the filter cake was washed with pure water and then calcined at 700 ° C. for about 2 hours. The rare earth element-containing barium titanate powder to which the rare earth element oxide was adhered was observed with an electron microanalyzer and XPS. The electron microanalyzer showed that the rare earth element was present in the same distribution as the barium titanate powder particles. In XPS, it was observed that the rare earth element thinly covered the surface layer vicinity of the barium titanate powder particles as follows.
[0014]
1 to 3 show an analysis of rare earth element-containing barium titanate powder, in which rare earth element oxides are uniformly adhered, using an electron microanalyzer. 1 shows Ti, FIG. 2 shows Ba, and FIG. 3 shows Y in the same field of view. By comparing FIGS. 1-3, it can be seen that Ti, Ba, and Y constitute the same powder particles. For example, a large lump from the upper left to the lower right in FIGS. 1 to 3, a middle lump that rises to the right on the upper right side, an independent lump on the upper right side on the right side, and an upper right corner on the right side of the screen 3 vertical lumps are seen corresponding to each other, appearing white on the screen, the part without powder particles is slightly above the center of the left side and 1/3 from the bottom left side toward the center. It corresponds to the part extending downward, the lower left corner, one third from the lower center, the relatively wide part with the black part showing the particle in the upper center, a little above the lower right corner, etc. Seen.
FIG. 4 is a diagram in which the distribution state of Ti, Ba, and Y in the surface depth direction is verified by XPS for the same sample as FIGS. FIG. 4 clearly shows that Y is concentrated on the surface of the powder particles, and Ti and Ba are mainly present in the grains due to lack of the surface. The surface depth is represented by the sputtering speed of the control sample, SiO ₂ .
In addition, the SEM photograph of the rare earth element oxide containing barium titanate powder obtained in the Example is shown in FIG.
[0015]
(Comparative example)
100 g of barium titanate powder having an average particle size of about 1.0 micron, 5.645 g of yttrium oxide having an average particle size of about 0.3 micron, 100 g of pure water and a small amount of peptizer were mixed for 24 hours by a ball mill. When the slurry was dried, about 100 g of mixed powder was obtained. When the obtained mixed powder was observed with an electron beam microanalyzer, a difference in distribution was observed between barium titanate and yttrium oxide, and a state in which mixing was not uniform as compared with the examples was observed. Moreover, when it observed by XPS, it turned out that the yttrium oxide particle has not adhered to the barium titanate surface as follows.
[0016]
About the obtained mixed powder, according to FIG. 5 (figure by Ti), FIG. 6 (figure by Ba), and FIG. Although Ti and Ba indicate the same powder particles, Y constitutes separate powder particles, and it is known that there is a large unevenness in the distribution of Ti, Ba, and Y on the entire screen. . For example, the two black and white Ti and Ba (particle) portions shown in the upper right corner of FIGS. 5 and 6 are hardly noticeable in Y of FIG. 7, and the small particle portion of the upper right corner visible in FIG. 5 (Ti) and FIG. 6 (Ba) are almost white, and the black part having a complicated shape that occupies a large portion in the central part of FIGS. 5 and 6 is almost white in FIG.
In FIG. 10, the SEM photograph of the rare earth element oxide containing barium titanate powder obtained by the comparative example is shown.
[0017]
FIG. 8 is an observation result by XPS similar to the example of the obtained mixed powder. According to FIG. 8, in the sample made by powder mixing, Y, Ti, and Ba are clearly distributed to the vicinity of the surface as compared with FIG. 4, and Y adheres to the surface of the barium titanate particles. I understand that it is not.
[0018]
【The invention's effect】
According to the present invention, a rare earth element-containing barium titanate powder in which an insoluble salt or oxide of a rare earth element is uniformly attached to a barium titanate powder can be obtained in a simple process and economically. The value is extremely high.
[Brief description of the drawings]
FIG. 1 is a photograph showing the surface distribution state of titanium obtained by an electron beam microanalyzer of rare earth element-containing barium titanate powder obtained by uniformly attaching rare earth element oxide to barium titanate powder obtained in the examples. is there.
FIG. 2 is a photograph showing the surface distribution of the same barium in the same field of view as FIG.
3 is a photographic view showing the surface distribution state of the same yttrium in the same visual field as FIG. 1. FIG.
FIG. 4 is a distribution diagram in the depth direction of titanium, barium and yttrium by XPS of rare earth element-containing barium titanate powder obtained by uniformly attaching rare earth element oxides obtained in Examples to barium titanate powder.
FIG. 5 is a photograph showing the surface distribution of titanium by an electron beam microanalyzer of the mixed powder obtained in the comparative example.
6 is a photograph showing the surface distribution of the same barium in the same field of view as FIG.
7 is a photographic view showing a surface distribution state of the same yttrium in the same visual field as FIG. 5. FIG.
FIG. 8 is a distribution diagram in the depth direction of titanium, barium, and yttrium by XPS of the mixed powder obtained in the comparative example.
FIG. 9 is a SEM photograph of rare earth oxide-containing barium titanate powder obtained in Example.
FIG. 10 is a SEM photograph of rare earth oxide-containing barium titanate powder obtained in a comparative example.

Claims (4)

An insoluble basic carbonates or oxides of at least one kind of rare earth element to barium titanate powder surface, the concentration of the rare earth elements in the powder surface 50 mass% or more by XPS, and features that you have been free Yes rare earth element-containing barium titanate powder. Barium titanate powder, a suspension containing a water-soluble salt and urea of rare earth elements 70 ° C. or more, is heated to a temperature below the boiling point of the solution, insoluble of basic carbonate of the rare earth element on the surface of the barium titanate powder The method for producing a rare earth element-containing barium titanate powder according to claim 1, wherein the salt is precipitated and then separated into solid and liquid. Barium titanate powder, and heated in a water-soluble salt and temperature suspension of the boiling point of 70 ° C. or more solution comprising urea rare earth elements, basic insoluble of rare earth elements on the front surface of the powder of barium titanate powder The method for producing a rare earth element-containing barium titanate powder according to claim 1, wherein the carbonate is precipitated and then separated into solid and liquid, and the obtained cake is fired at a temperature of 600 ° C or higher. After adding ammonia to a suspension containing barium titanate powder and a water-soluble salt of rare earth elements to precipitate rare earth element hydroxides, solid-liquid separation is performed, and the resulting cake is heated at a temperature of 600 ° C. or higher. The method for producing a rare earth element-containing barium titanate powder according to claim 1, wherein the firing is performed.

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