Specialized metallurgical processes – compositions for use therei – Compositions – Loose particulate mixture containing metal particles
Reexamination Certificate
2002-07-26
2004-06-29
Mai, Ngoclan (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Loose particulate mixture containing metal particles
C075S245000, C361S321100, C361S523000
Reexamination Certificate
active
06755884
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a niobium powder from which a capacitor capable of maintaining the performance for a long period of time and having good reliability can be produced, and also relates to a niobium sintered body and a capacitor using the sintered body.
BACKGROUND ART
Capacitors for use in electronic instruments such as potable telephone and personal computer are demanded to have a small size and a large capacitance. Among these capacitors, a tantalum capacitor is preferred because of its large capacitance for the size and good performance. In this tantalum capacitor, a sintered body of tantalum powder is generally used for the anode moiety. In order to increase the capacitance of the tantalum capacitor, it is necessary to increase the weight of the sintered body or to use a sintered body increased in the surface area by pulverizing the tantalum powder.
The former method of increasing the weight of the sintered body necessarily involves enlargement of the capacitor shape and cannot satisfy the requirement for downsizing. On the other hand, in the latter method of pulverizing tantalum powder to increase the surface area, the pore size of the tantalum sintered body decreases or closed pores increase at the stage of sintering and therefore, impregnation of the cathode agent in the later process becomes difficult. As one of means for solving these problems, a capacitor using a sintered body of powder of a material having a dielectric constant larger than that of tantalum is being studied. The material having a larger dielectric constant includes niobium.
However, niobium has a large affinity for oxygen as compared with tantalum and therefore, is readily oxidized. This tendency is more outstanding as the niobium is in the form of powder and the specific surface area thereof is larger. Furthermore, the oxidation reaction more readily proceeds as the temperature in the environment is higher. In the manufacture of a sintered body from a niobium powder, a molded article of niobium powder is usually sintered under heating in a vacuum and in this process, a reaction with oxygen in an air takes place in some cases at the time of taking out the sintered body from the heating furnace to allow a large amount of oxygen to adhere to the surface. If the amount of oxygen adhered is large, the shape of the sintered body deviates from the designed value in an extreme case. If a capacitor is manufactured from such a sintered body and subjected to an accelerated test at a high temperature, the capacitor performance is sometimes greatly deteriorated and not satisfied in view of reliability.
As for a technology related to the present invention, a capacitor using a partially reduced niobium oxide (NbO
n
, n=0.7 to 1.1, oxygen content: 11 to 16% by mass) obtained by heat-treating diniobium pentoxide (Nb
2
O
5
) in the presence of hydrogen, which has a large capacitance and excellent leakage current characteristics, has been proposed (see, WO 00/15555). However, when a capacitor is manufactured using a niobium oxide obtained in a test by the present inventors and subjected to an accelerated test at a high temperature, the capacitor performance is deteriorated and not satisfied.
DISCLOSURE OF INVENTION
As a result of extensive investigations to solve the above-described problems, the present inventors have found that when a niobium powder obtained by granulating a powder having an oxygen content previously adjusted to a specific range is used as the starting material niobium powder of a niobium sintered body, a capacitor reduced in the deterioration in an accelerated test at a high temperature and having high reliability can be obtained. The present invention has been accomplished based on this finding.
More specifically, the object of the present invention is to provide a niobium powder for capacitors, a sintered body thereof and a capacitor using the sintered body, which are described below.
1. A niobium powder for capacitors, having an average particle size of from 10 to 500 &mgr;m, which is a granulated powder having an oxygen content of 3 to 9% by mass.
2. The niobium powder for capacitors as described in 1 above, wherein the specific surface area is from 0.2 to 15 m
2
/g.
3. The niobium powder for capacitors as described in 1 or 2 above, which is partially nitrided.
4. The niobium powder for capacitors as described in 3 above, wherein the nitrided amount is 10~100,000 ppm by mass.
5. A sintered body using the niobium powder for capacitors described in any one of 1 to 4 above.
6. The sintered body as described in 5 above, wherein the specific surface area is from 0.2 to 5 m
2
/g.
7. A capacitor fabricated from the sintered body described in 5 or 6 above as one part electrode, a dielectric material formed on the surface of the sintered body, and another part electrode provided on the dielectric material.
8. The capacitor as described in 7 above, wherein the dielectric material is mainly composed of a niobium oxide.
9. The capacitor as described in 8 above, wherein the niobium oxide is formed by electrolytic oxidation.
10. The capacitor as described in any one of 7 to 9 above, wherein the another part electrode is at least one material selected from an electrolytic solution, an organic semiconductor or an inorganic semiconductor.
11. The capacitor as described in 10 above, wherein the another part electrode is composed of an organic semiconductor and the organic semiconductor is at least one organic semiconductor selected from the group consisting of an organic semiconductor comprising a benzopyrroline tetramer and chloranile, an organic semiconductor mainly comprising tetrathiotetracene, an organic semiconductor mainly comprising tetracyanoquinodimethane, and an organic semiconductor mainly comprising an electrically conducting polymer obtained by doping a dopant into a polymer comprising two or more repeating units represented by the following formula (1) or (2):
(wherein R
1
to R
4
, which may be the same or different, each represents a hydrogen atom, an alkyl group having from 1 to 6 carbon atoms or an alkoxy group having from 1 to 6 carbon atoms, X represents an oxygen atom, a sulfur atom or a nitrogen atom, R
5
is present only when X is a nitrogen atom and represents hydrogen or an alkyl group having from 1 to 6 carbon atoms, and each of the pairs R
1
and R
2
, and R
3
and R
4
may combine with each other to form a ring).
12. The capacitor as described in 11 above, wherein the organic semiconductor is at least one member selected from polypyrrole, polythiophene polyaniline and substitution derivatives thereof.
DETAILED DESCRIPTION OF INVENTION
The niobium powder for capacitors of the present invention is obtained by granulating a primary particle powder (hereinafter simply referred to as “primary powder”) of niobium into an appropriate size.
The primary powder can be granulated by a conventionally known method. Examples of the method include a method where powder particles are left standing at a high temperature of 500 to 2,000° C. in a vacuum and then wet or dry cracked, a method where powder particles are mixed with an appropriate binder such as acrylic resin or polyvinyl alcohol and then cracked, and a method where powder particles are mixed with an appropriate compound such as acrylic resin, camphor, phosphoric acid or boric acid, left standing at a high temperature in a vacuum and then wet or dry cracked. The particle size of the granulated powder can be freely controlled by the degree of granulation and cracking, however, a granulated powder having an average particle size of 10 to 500 &mgr;m is usually used. The granulated powder may be classified after the granulation and the cracking. After the granulation, the granulated powder may also be mixed with an appropriate amount of non-granulated powder.
The niobium powder for capacitors of the present invention is preliminarily adjusted to have an oxygen content of 3 to 9% by mass.
As described above, when a niobium powder is sintered and molded and then the sintered body is taken out into an air, an
Nagato Nobuyuki
Naito Kazumi
Mai Ngoclan
Showa Denko K.K.
LandOfFree
Niobium powder for capacitor, sintered body thereof and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Niobium powder for capacitor, sintered body thereof and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Niobium powder for capacitor, sintered body thereof and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3364234