Specialized metallurgical processes – compositions for use therei – Compositions – Loose particulate mixture containing metal particles
Reexamination Certificate
2002-06-20
2004-08-24
Mai, Ngoclan T. (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Loose particulate mixture containing metal particles
C075S354000, C241S015000, C241S016000
Reexamination Certificate
active
06780218
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for producing a niobium powder for capacitors. The present invention also relates to a niobium powder for capacitors, which is reduced in the oxygen content in niobium and thereby can provide a capacitor having a large capacitance per unit mass and good leakage current characteristics; a sintered body using the powder; and a capacitor using the sintered body.
The niobium for capacitors means a material mainly comprising niobium and usable for the production of capacitors.
BACKGROUND ART
Capacitors for use in electronic instruments such as cellular phone 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 mass of the sintered body or to use a sintered body increased in the surface area by pulverizing the tantalum powder.
The method of increasing the mass of the sintered body necessarily involves enlargement of the capacitor shape and cannot satisfy the requirement for downsizing. In the method of pulverizing tantalum powder to increase the surface area, the pore size of the tantalum sintered body decreases and closed pores increase, as a result, impregnation of the cathode agent in the later step becomes difficult. As one of means for solving these problems, a capacitor using a sintered body of a material having a dielectric constant larger than that of tantalum is being studied. The material having a larger dielectric constant includes niobium and a niobium alloy.
With respect to the method for producing a niobium powder for capacitors, JP-A-55-157226 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) discloses a method for producing a sintered element for capacitors by molding agglomerated powder into niobium powder having a particle size of 2.0 &mgr;m or less and sintering the niobium powder. However, details on the properties of the capacitor are not described in this patent publication.
U.S. Pat. No. 4,084,965 discloses a capacitor using a sintered body of niobium powder of 5.1 &mgr;m obtained by hydrogenating and grinding a niobium ingot. However, the capacitor disclosed is large in the leakage current (hereinafter sometimes simply referred to as “LC”) and the practicability thereof is low.
JP-A-10-242004 discloses a technique of partially nitriding niobium powder and thereby improving the LC value. However, when a high-capacitance capacitor is produced by using a niobium sintered body of niobium powder having a fine particle size, a capacitor having a peculiarly large LC value appears in some cases.
DISCLOSURE OF THE INVENTION
The present inventors have found that the dispersion of LC value is ascribable to oxygen contained in a niobium powder for capacitors and, for example, when a niobium powder for capacitors, having a low oxygen content obtained by grinding a niobium hydride or a niobium hydride alloy at a low temperature is used, the LC characteristics can be improved. The present invention has been accomplished based on this finding. More specifically, the present invention is composed of the following matters.
(1) A process for producing a niobium powder for capacitors, comprising a step of grinding a niobium hydride or a niobium hydride alloy in the presence of a dispersion medium, wherein the grinding temperature is from −200 to 30° C.
(2) The process for producing a niobium powder for capacitors as described in 1 above, which comprises a step of dehydrogenating the niobium hydride powder or niobium hydride alloy powder at a temperature of 100 to 1,000° C. after the grinding.
(3) The process for producing a niobium powder for capacitors as described in 1 or 2 above, wherein the grinding temperature does not elevate during the grinding.
(4) The process for producing a niobium powder for capacitors as described in any one of 1 to 3 above, wherein the dispersion medium is at least one member selected from the group consisting of water, an organic solvent and a liquefied gas.
(5) A niobium powder for capacitors, obtained by the production process described in any one of 1 to 4 above.
(6) The niobium powder for capacitors as described in 5 above, wherein the average particle size of the niobium powder for capacitors is from 0.01 to 10 &mgr;m.
(7) The niobium powder for capacitors as described in 5 or 6 above, wherein the BET specific surface area of the niobium powder for capacitors is from 0.5 to 40 m
2
/g.
(8) The niobium powder for capacitors as described in any one of 5 to 7 above, wherein the bulk density of the niobium powder for capacitors is from 0.5 to 4 g/ml.
(9) The niobium powder for capacitors as described in any one of 5 to 8 above, wherein the pore size peak of the niobium powder for capacitors is from 0.01 to 7 &mgr;m.
(10) The niobium powder for capacitors as described in any one of 5 to 9 above, wherein the oxygen content of the niobium powder for capacitors is 2.5 mass % or less.
(11) The niobium powder for capacitors as described in any one of 5 to 10 above, wherein the niobium powder for capacitors further comprises at least one element selected from the group consisting of boron, nitrogen, carbon and sulfur.
(12) A niobium granulated product for capacitors, having an average particle size of 10 to 500 &mgr;m, which is obtained by granulating the niobium powder for capacitors described in any one of 5 to 11 above.
(13) The niobium granulated product for capacitors as described in 12 above, wherein the BET specific surface area of the niobium granulated product for capacitors is from 0.5 to 40 m
2
/g.
(14) The niobium granulated product for capacitors as described in 12 or 13 above, wherein the pore size peak of the niobium granulated product for capacitors is within the range from 0.01 to 500 &mgr;m.
(15) The niobium granulated product for capacitors as described in any one of 12 to 14 above, wherein the bulk density of the niobium granulated product for capacitors is from 0.05 to 4 g/ml.
(16) The niobium granulated product for capacitors as described in any one of 12 to 15 above, wherein the oxygen concentration of the niobium granulated product for capacitors is 3 mass % or less.
(17) A sintered body obtained by sintering the niobium powder for capacitors described in any one of 5 to 11 above and/or the niobium granulated product for capacitors described in any one of 12 to 16 above.
(18) A capacitor comprising the sintered body described in 17 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.
(19) The capacitor as described in 18 above, wherein the dielectric material is mainly composed of niobium oxide.
MODE FOR CARRYING OUT THE INVENTION
The practical embodiment of the present invention is described below.
It is a known technique that a niobium ingot is hydrogenated and ground using an appropriate grinder in the presence of an appropriate dispersion medium (see, U.S. Pat. No. 4,084,965). However, when a niobium powder for capacitors is produced by this method, the capacitor using the niobium powder suffers from high LC value and large dispersion of LC value and lacks in reliability. This is considered ascribable to the fact that oxygen present in the dispersion medium reacts with or adsorbs to niobium hydride due to heat generated during grinding and at the manufacture of a sintered body, niobium oxide is produced by the crystallization and adversely affects particularly the LC. Accordingly, for improving the LC characteristics, it is important to suppress the oxygen amount in the niobium hydride powder. In order to suppress the oxygen amount in the niobium hydride powder, for example, a method of preventing the elevation of temperature during grinding may be used. This applies als
Kawasaki Toshiya
Naito Kazumi
Omori Kazuhiro
Tsumita Yasuo
Wada Kouichi
Mai Ngoclan T.
Showa Denko Kabushiki Kaisha
Sughrue & Mion, PLLC
LandOfFree
Production process for niobium 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 Production process for niobium powder, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Production process for niobium powder will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3293248