Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1999-11-09
2001-07-03
Beck, Shrive (Department: 1762)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C501S137000
Reexamination Certificate
active
06254991
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for preparing ceramic powder and, more particularly, to a process for preparing ceramic powder in a core-shell structure.
2. Description of the Related Art
As ceramic electronic parts have recently been developed so as to make their sizes smaller and smaller and to make their quality higher and higher, a variety of materials have also been developed so as to catch up with such development. Under such technical background, ceramic powder having a core-shell structure is now being highlighted as a material for ceramic electronic parts.
Such ceramic powder having a core-shell structure is configured in such a manner that it comprises a highly crystalline core portion and a shell portion formed on and around the core portion and composed of a different composition material. The such ceramic powder can smooth temperature features of a ceramic condenser when it is used as a dielectric material.
The ceramic powder with such a core-shell structure can be produced, for instance, by admixing ceramic powder with an additive and firing the resulting mixture at a high temperature to thereby subject it to solid phase reaction to allow the additive to be formed on and around surfaces of the ceramic powder
Further, it is favorable if ceramic powder having a core-shell structure could be produced from highly crystalline ceramic powder because such a highly crystalline ceramic powder has good electrical features such as dielectric constant and so on. The highly crystalline ceramic powder, however, has the drawbacks that it Is so low in reactivity that a considerably high temperature is required to cause an occurrence of solid phase reaction, resulting to a rise in manufacturing cost.
On the other hand, a low-crystalline ceramic powder can produce ceramic powder with a core-shell structure because it can readily be subjected to solid phase reaction by firing It at a lower temperature. Such a low-crystalline ceramic powder, however, presents the drawbacks that ceramic electronic parts prepared therefrom may result in poor electrical and mechanical characteristics.
SUMMARY OF THE INVENTION
Therefore, the present invention has the object to provide a process for preparing ceramic powder with a core-shell structure having good electrical and mechanical features by firing ceramic powder at a lower temperature.
In order to achieve the object, the present invention provides a process for preparing ceramic powder, which comprises the step of dissolving a crystalline ceramic powder in water so as to leave a core portion of the ceramic powder while heating; the step of depositing a component of the ceramic powder dissolved in the water on and around surfaces of the core portion thereof as a deposited material from the water by gradually cooling the ceramic powder and the water obtained in the step of dissolving; and the step of firing a mixture of the ceramic powder obtained in the step of depositing with an additive at a high temperature to subject the deposited material and the additive to solid phase reaction to form a shell portion on and around the core portion of the ceramic powder.
Other objects, features and advantages of the present invention will become apparent in the course of the description which follows.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The process in accordance with the present invention can provide ceramic powder having a core-shell structure by dissolving a crystalline ceramic powder in water so as to leave a core portion of the ceramic powder while heating; depositing a component of the ceramic powder dissolved In the water on and around surfaces of the core portion thereof as a deposited material from the water by gradually cooling the ceramic powder and the water obtained in the step of dissolving; and firing a mixture of the ceramic powder obtained in the step of depositing with an additive at a high temperature to subject the deposited material and the additive to solid phase reaction to form a shell portion on and around the core portion of the ceramic powder.
The ceramic powder to used for the present invention may include, for example, barium titanate powder, barium titanate zirconate powder, lead titanate zirconate powder or lead titanate powder, although the ceramic powder to be used for the present invention is not restricted to those specifically stated above.
As the crystalline ceramic powder to be used for the present invention, there may be preferably mentioned, for example, one synthesized by hydrothermal method. It is to be noted herein, however, that the crystalline ceramic powder is not restricted to the one as stated above and any other ceramic powder produced by different methods may also be used as long as it is crystalline.
In accordance with the process of the present Invention, It is preferred that the ceramic powder and water are heated at temperature ranging from approximately 80° C. to 120° C. In this case, a speed of dissolving the ceramic powder in water can be facilitated by heating the ceramic powder and water under elevated pressure. It is to be noted herein that the duration of heating the ceramic powder can exert the effect upon the thickness of the shell portion of the ceramic powder. When the ceramic powder is heated for a longer time, on the one hand, the shell portion can be made thicker. When the ceramic powder is heated for a shorter time, on the other, the thickness of the shell portion may become thinner.
It is further preferred that the mixture of the ceramic powder with water is gradually cooled at the rate of approximately 2° C. to 20° C. per hour. If the speed of gradually cooling the mixture at the rate of lower than 2° C., on the one hand, it will take a too long time to cool the mixture. If the mixture is cooled at the rate of greater than 20° C., on the other, the component of the ceramic powder dissolved in the water may not be deposited on and around surfaces of the core portion thereof as the deposited material to a sufficient extent. It is to be noted herein that, as the deposited material has a hydroxyl group, a water content or voids resulting from pores, the reactivity of the deposited material with the additive is considered to be high.
Further, the additive to be used for the present invention may preferably include, for example, Nb2O5, Co3O4, MnO2, Ta2O5 or VO5, although the additive is not restricted to those stated hereinabove and any other additive can also be used as long as it can achieve the effects sought to be attained by the present invention.
REFERENCES:
patent: 3490927 (1970-01-01), Kahn et al.
patent: 4487755 (1984-12-01), Arendt
patent: 4627966 (1986-12-01), Micheli
patent: 4654075 (1987-03-01), Cipollini
patent: 4749664 (1988-06-01), Ross et al.
patent: 5055434 (1991-10-01), Thometzek et al.
patent: 5468427 (1995-11-01), Stangle et al.
Zumdahl, Steven S., “Chemistry”, D.C. Heath and Company, Lexington, MA, pp. 484-486, 1989.
Chazono Hirokazu
Kono Yasuhisa
Mizuno Yoichi
Saito Kenji
Beck Shrive
Snider Ronald R.
Snider & Associates
Strain Paul D.
Taiyo Yuden Co. Ltd.
LandOfFree
Prepared ceramic 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 Prepared ceramic powder, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Prepared ceramic powder will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2474216