Chemistry of inorganic compounds – Oxygen or compound thereof – Metal containing
Reexamination Certificate
1999-12-29
2002-03-05
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Oxygen or compound thereof
Metal containing
Reexamination Certificate
active
06352681
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for production of a barium titanate powder having a particle size of 1 &mgr;m or less and a crystallized Perovskite structure consisting of a spherical primary particle.
BACKGROUND ART
Barium titanate powders are widely used for dielectric materials for electronic parts such as PTC thermistors and piezoelectric devices, in particular, are suitable for substrates of multilayer ceramic capacitors. Multilayer ceramic capacitors are generally manufactured by alternately laminating a ceramic dielectric layer and an internal electrode layer, firmly pressing, and then sintering to integrate them. Barium titanate powder is slurried in a binder and is sintered to form a ceramic dielectric layer. Recently, in particular, the ceramic dielectric layer is made to be a thin laminate so as to meet the requirements of compact design and increased capacity. For such specifications, the ceramic dielectric layer must have good voltage tolerance characteristics, the barium titanate particles must not agglomerate in slurrying, and the capacity of the capacitor must be sufficiently ensured. To meet these requirements, the following characteristics are required in the barium titanate powder.
(1) The powder should consist of ultrafine particles having a uniform globular shape, and the particle size is preferably in the range of 0.05 to 0.5 &mgr;m, more preferably in the range of 0.05 to 0.3 &mgr;m, and the particle size distribution should be narrow.
(2) The powder should have good crystallinity, specifically having a Perovskite structure having a primary particle size ranging from 0.05 to 0.3 &mgr;m.
(3) The barium/titanium atomic ratio should particularly be close to 1.00, and particularly in the range of 0.99 to 1.01.
(4) The powder should have excellent dispersion characteristics when it is slurried or made into a pasted.
(5) The powder should have good sintering characteristics.
Until now, barium titanate powders have been produced by mixing titanium compounds and barium compounds, and then sintering them so as to cause a solid phase reaction. However, in such a production process, the above chemical compounds are made to react at high temperatures, and the particles of the obtained barium titanate powders become relatively large (for example, about 0.5 &mgr;m is the lower limit), the particle size distribution thereof is broad, and the shapes thereof are not uniform. Therefore, the dispersion characteristics of the barium titanate powder in the slurry is not so good. Such a broad range of particle size limits thinning of the ceramic dielectric layer. As a production process which can solve this problem, the liquid phase reaction method is known.
Various proposals have been made for this liquid phase reaction method. For example, Japanese Patent Publication No. 73695/93 discloses a production process in which titanium oxide hydrate, barium chloride and/or barium nitrate, and 2.1 to 5 moles of alkali metal hydroxide per 1 mole of the barium chloride and/or barium nitrate are reacted in 120 to 10000 moles of water per 1 mole of titanium at 60 to 110° C. Japanese Patent Publication No. 73696/93 discloses a production process in which titanium oxide hydrate, barium hydroxide, and alkali metal hydroxide are reacted in 120 to 10000 moles of water per 1 mole of titanium at 60 to 110° C. Japanese Patent Publication No. 39014/91 discloses a production process in which hydrolysis products of titanium compounds and water-soluble barium salts are reacted in strong alkali aqueous solutions. Japanese Patent Publication No. 649/94 discloses a production process in which a chloride of titanium or zirconium is hydrolyzed in an aqueous solution, then the aqueous solution is made alkali once so as to remove chlorine ions, and consecutively a water-soluble salt of barium, strontium, or calcium is added to the aqueous solution so as to react in strong alkali.
Japanese Patent Unexamined Publication No. 232923/95 discloses a production process in which a mixed aqueous solution of titanium compounds, such as titanium tetrachloride coexisting with barium salts is contacted with an alkali aqueous solution preheated at 70 to 100° C. so as to obtain approximately globular crystalline Perovskite structures.
However, in the production process in Japanese Patent Publication No. 73695/93, in addition to the long reaction time, the concentration control of the titanium oxide hydrate, control of barium/titanium atomic ratio, or control of the production process were difficult. In addition, the reaction progresses in the presence of large amounts of water of 120 to 10000 moles per 1 mole of titanium. The reaction progressing in such an extremely diluted system causes decreases in production efficiency, requires production facilities of large design, and large amounts of waste water to be treated. These problems are very similar in the production process of Japanese Patent Publication Nos. 73696/93 and 39014/91. The production process in Japanese Patent Publications No. 649/94 requires the process for restoring alkali conditions after hydrolyzing the chloride of titanium or zirconium in the aqueous solution, and the complicated processes and long periods for executing the process are required.
In particular, the solubility of the barium salt, such as barium chloride, is low in the acid phase. Therefore, in the production process in Japanese Patent Unexamined Publication No. 232923/5, the mixed acidic aqueous solution of the titanium compound and the barium salt is used for the starting material, and it is difficult to adjust the mixed aqueous solution. In particular, there is an upper limit to the concentration of the titanium compound and the barium salt in a mixed aqueous solution. In particular, when the mixed aqueous solution of titanium tetrachloride and barium chloride is prepared, the total concentration of the metal ion is limited to 1.2 moles per liter, and that the production efficiency is therefore limited. Furthermore, if the carbonate is contaminated in the starting material solution, control of the barium/titanium atomic ratio becomes difficult, and the carbonate is contaminated in the final product powder, decreasing the quality. This result in a problem in that the powder must be sintered to increase the dielectric constant.
In addition, although the barium titanate produced by the above conventional process is a fine particle, the dispersion characteristics in slurry is not so good. Therefore, the particles eventually agglomerate, *and thinning of the ceramic dielectric layer is difficult.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a production process for barium titanate powder which can satisfy the above requirements (1) to (5) by a remarkably simplified process, so as to solve the problems in production efficiency.
The inventors have conducted research for a production process which can achieve the above objects. As a result, they discovered that the target barium titanate powder can be produced at low temperature by a simple process in which a titanium compound and a barium compound are prepared in separate aqueous solutions of strong alkali and are instantaneously and continuously brought into contact with each other while being stirred. They also discovered that superior barium titanate powder can be obtained by contacting the titanium compound aqueous solution and the barium compound aqueous solution with each other while the titanium compound/barium compound molar ratio is controlled to be in the range of 0.8 to 1.2.
The present invention has been completed according to the above knowledge. The invention provides a process for production of a barium titanate powder by contacting an aqueous solution of titanium compound (referred to simply as “aqueous solution (I)” hereinafter) with an alkali aqueous solution of barium compound (referred to simply as “aqueous solution (II) hereinafter) while controlling the molar ratio of titanium compound barium compound to be within the range of 0.8 to 1.2 and stirring.
As tit
Horikawa Matsuhide
Kagohashi Wataru
Sakai Hideki
Bos Steven
Oliff & Berridg,e PLC
Toho Titanium Co., Ltd.
LandOfFree
Method for producing barium titanate powder does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for producing barium titanate powder, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for producing barium titanate powder will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2826981