JPH0244026A - Production of superfine particles of crystalline barium titanate - Google Patents

Abstract

PURPOSE:To reduce a particle size of a product and a cost of production by adding titanium tetraalkoxide to barium hydroxide suspended in alcohol, carrying out hydrolysis and aging the resulting suspension at room temp. for a specified time. CONSTITUTION:Titanium tetraalkoxide is added to barium hydroxide suspended in alcohol at room temp. in about 1 molar ratio of barium hydroxide to titanium tetraalkoxide and hydrolysis is carried out by adding high purity water enough for the hydrolysis. The resulting suspension is aged at room temp. for >=3hr. Since all the reactions can be allowed to proceed at ordinary temp., an average particle size of the product is reduced to <=0.05mum. Since a low-cost silver electrode is used, the cost of production is reduced.

Description

Detailed Description of the Invention (JT4 Field of Industrial Benefits) The present invention applies to crystalline barium titanate, which has particularly strong industrial requirements among barium titanates that are widely used mainly in capacitors in the electronics field. The present invention relates to a method for producing ultrafine particles.

(Prior Art) Examples of conventionally known industrial methods for producing barium titanate are as follows.

(() A production method using titanium oxide and barium carbonate as raw materials and a high-temperature solid phase reaction) A method using a metal alkoxide obtained by reacting barium and titanium with alcohol as a starting material and hydrolyzing the solution (special 1977 ■ Method of reacting titanium isopropoxide and barium hydroxide in an aqueous potassium hydroxide solution using barium hydroxide ~ I4 (J
.

Amer-Chem, Soc, 77, fi194 (19
55)) φ) Barium hydroxide and titania at 100℃ or higher
A method of reacting at a temperature of 48 hours or more (Unexamined Japanese Patent Application Publication No. 1983 (1987) (F1 issue left in the prior art)) In the method of (1) above, the particle size of the barium titanate obtained is several 7 tm or more, there are many impurities, and the particle size is very small. It is difficult to maintain a constant barium ratio, and it has the disadvantage that it cannot be said to be practically satisfactory in the current electronics field, which requires a high level of performance.

The above-mentioned ■ has been proposed as a solution to this problem, but 1
In this case, there are problems in handling and high costs due to the use of expensive metallic barium or metallic titanium, and there remain issues that need to be resolved as a practical industrial technology.

In addition, as a method for producing barium titanate using barium hydroxide as a starting material, the above-mentioned (2) and! , 4) has been proposed, but the former (■) requires the coexistence of an alkali metal, the generated particle size is as large as 1 to 5 gm, and it is difficult to obtain crystalline barium titanate. There are problems such as requiring a temperature of 80"C or more, and the latter (■) requires an extremely long reaction at a temperature of 100"C or more, as is clear from the claims. However, there were still three issues that needed to be revised in terms of practical industrial technology.

Furthermore, barium titanate, which has been commonly used in the past,
When used as an M-layer capacitor, the particle size is several ILm.
Due to its large size, a high sintering temperature of about 1300° C. is required, and therefore expensive palladium is required as an internal electrode, resulting in a significant cost increase.

(Means for Solving the Problems) The present inventors have arrived at the present invention as a result of intensive research in order to solve the problems remaining in the prior art, and propose it to the public.

That is, the feature of the present invention is that titanium tetraalkoxide is added to barium hydroxide suspended in alcohol at room temperature, and then water is added to hydrolyze it. ′
The present invention provides a method for producing crystalline barium titanate ultrafine particles, which is characterized in that ultrafine particles having an average primary particle diameter of 0.05 μm or less are obtained by ripening for F or more.

The barium hydroxide used in the present invention can be either hydrous or anhydrous. In addition, barium hydroxide and titanium tetraalkoxide can be used as appropriate commercially available products, but are not particularly limited as long as they do not adversely affect the properties of the crystalline barium titanate ultrafine particles produced. However, it is preferable to select and use one with as high a purity as possible.

As the alcohol used in the present invention, methanol, ethanol, propatool, butanol, etc. can be used, but alcohols other than those marked with # may be used as long as they do not have an adverse effect on the crystalline barium titanate ultrafine particles produced. It is also possible to select and use them as appropriate. However, considering the purity of the crystalline barium titanate ultrafine particles produced, it is preferable to use alcohols with as few impurities as possible.

The water used in the present invention is purified to the highest possible purity by degassing by bubbling nitrogen, argon, etc. into ion-exchanged water, or by J-distillation in a nitrogen or argon atmosphere. It is preferable to use

The alcohol used in Book 1] is not particularly limited as long as it can form a suspended liquid of barium hydroxide.

Further, the quantitative ratio of barium hydroxide and titanium tetraalkoxide needs to be changed depending on the characteristics of the crystalline barium titanate ultrafine particles to be produced, but usually the molar ratio is only slightly changed around 1.

The amount of water used on the moon is not particularly limited as long as it is enough to complete the hydrolysis reaction.

Aging in the present invention is carried out at room temperature for 3 hours or more,
Room temperature in this case means that experimental operations are performed without adding special means such as heating or cooling, and is usually 10 to 3
It means a range of about 0°C.

(Effects of the Invention) The crystalline barium titanate a fine particles obtained by the present invention have an average primary particle diameter of 0.05 fiLm or less 1 usually about 0.05 fiLm or less. Since the barium titanate layer is in the distribution range of 1 to 0.02 μm, when used in a planted layer capacitor, the barium titanate layer can be made extremely thin, making it possible to reduce the thickness of the capacitor body and increase its capacity. becomes possible. Furthermore, by lowering the sintering temperature and by using less expensive silver or an alloy of silver and palladium instead of palladium as the internal electrode, a significant cost reduction can be achieved.

(Examples and Comparative Examples) The present invention will now be explained in more detail with reference to Examples and Comparative Examples.

￥Example 1゜Ba(OH)2 was placed at room temperature under N2 atmosphere in a round bottom flask with an internal capacity of 500 and equipped with a stirrer, which was sufficiently purged with N2 gas.
・07.9g of 8L (Ba: 0.025mou) and 100JI of ethanol were charged and suspended under stirring, and 47.1g of 1(0-iGtH+) (Ti:
Add 0.025+++oJ1).

Next, a mixture of 50 ml of wood that had been sufficiently de-CO2-treated by bubbling with N2 gas and 50 mM of ethanol was added dropwise at room temperature under a N2 atmosphere over a period of 2 hours, and aged for 5 hours. I got something. From X-ray diffraction of the product, crystallinity B
It was confirmed that aT i03 was generated.

Note that the generated particles are y! with an electron m* mirror. As I guessed,
The particle size was approximately 0.01 JL m as a primary particle.

Example 2゜Aging If! ? The experiment was conducted in the same manner as in Example 1 except that the time period was 10 hours. The formation of crystalline BaT io3 was confirmed by X-ray diffraction of the obtained product, and microscopic observation of the product revealed that the particle size of the primary particles was 0. It was Ollum.

Comparative Example 1° An experiment was conducted in the same manner as in Example 1, except that the aging time was 2 hours. From X-ray diffraction of the obtained product, no formation of nine-base Ba7i03 was confirmed.

Claims (1)

[Claims] (1) By adding titanium tetraalkoxide to barium hydroxide suspended in alcohol at room temperature, then hydrolyzing it by adding water, and then aging for 3 hours or more while maintaining the same temperature. A method for producing crystalline barium titanate ultrafine particles, characterized in that ultrafine particles having an average primary particle diameter of 0.05 μm or less are obtained.