Specialized metallurgical processes – compositions for use therei – Compositions – Loose particulate mixture containing metal particles
Reexamination Certificate
2001-08-10
2003-11-25
Mai, Ngoclan (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Loose particulate mixture containing metal particles
C075S245000, C148S513000, C361S523000
Reexamination Certificate
active
06652619
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a niobium powder with a large capacitance per unit weight and good leakage current characteristics, a sintered body using the above-mentioned niobium powder, and a capacitor using the above-mentioned sintered body.
BACKGROUND ART
Capacitors for use in electronic apparatus such as portable telephones and personal computers are required to be small in size and large in capacitance. Of those capacitors, a tantalum capacitor is preferably used, because the capacitance is large, not in proportion to the size, and the tantalum capacitor also has good characteristics. The tantalum capacitor usually employs a sintered body of a tantalum powder as an anode. 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 having an increased surface area obtained by pulverizing the tantalum powder.
The increase in weight of the sintered body inevitably enlarges the shape, so that the requirement for a small-sized capacitor is not satisfied. On the other hand, when the tantalum powder is finely pulverized to increase the specific surface area, the pore size in the tantalum sintered body decreases, and the number of closed pores increases during the sintering step. The result is that the sintered body cannot be easily impregnated with a cathode agent in the subsequent step.
One approach to solve these problems is a capacitor using a sintered body of a powder material which has a greater dielectric constant than the tantalum powder. One powder material which has such a greater dielectric constant is a niobium powder.
Japanese Laid-Open Patent Application No. 55-157226 discloses a method for producing a sintered element for a capacitor. This method comprises the steps of subjecting a niobium powder ranging from an agglomerate to fine particles with a particle diameter of 2.0 &mgr;m or less to pressure molding and sintering, finely cutting the molded sintered body, connecting a lead portion to the finely cut particles of the sintered body, and thereafter sintering the connected body. However, the above-mentioned application does not describe the detailed characteristics of the obtained capacitor.
U.S. Pat. No. 4,084,965 discloses a capacitor using a sintered body of a niobium powder with a particle size of 5.1 &mgr;m obtained from a niobium ingot through hydrogenation and pulverizing. The capacitor disclosed has, however, a high leakage current value (hereinafter referred to as an LC value), and therefore the serviceability is poor.
As disclosed in Japanese Laid-Open Patent Application No. 10-242004, the LC value is improved by partially nitriding a niobium powder. However, when a capacitor having a large capacitance is produced using a sintered body of a niobium powder with a smaller particle diameter, the LC value of the obtained capacitor may become exceptionally high.
U.S. Pat. No. 6,051,044 discloses a niobium powder which has a particular BET specific surface area and contains nitrogen in a particular amount. A method for decreasing the leakage current is also disclosed. However, there is no disclosure nor suggestion concerning a niobium powder containing another element which can form an alloy with niobium. Furthermore, this patent does not disclose nor suggest the heat resistance necessary for capacitors in soldering and the like or stability of LC value against thermal history.
DISCLOSURE OF INVENTION
An object of the present invention is to provide a niobium powder capable of providing a capacitor having good heat resistance with a large capacitance per unit weight and a small leakage current value, a sintered body using the above-mentioned niobium powder, and a capacitor using the above-mentioned sintered body.
Through intense studies of the above-mentioned problems, the inventors of the present invention have found that a low LC value and good heat resistance can be maintained even in a capacitor provided with a large capacitance by decreasing the particle diameter of a niobium powder when at least one element selected from various elements which can form an alloy with niobium is added to niobium. The present invention has thus been accomplished. The term “alloy” in the present application includes a solid solution with the other alloy components. Namely, the present invention basically provides a niobium powder of the below (1) to (29), a sintered body of (30) to (31) obtained by sintering the niobium powders, a capacitor of (32) to (42), a process for producing niobium powders of (43) to (46), an electronic circuit of (47) and an electronic instrument of (48).
(1) A niobium powder for capacitors comprising at least one element selected from the group consisting of chromium, molybdenum, tungsten, boron, aluminum, gallium, indium, thallium, cerium, neodymium, titanium, rhenium, ruthenium, rhodium, palladium, silver, zinc, silicon, germanium, tin, phosphorus, arsenic, bismuth, rubidium, cesium, magnesium, strontium, barium, scandium, yttrium, lanthanum, praseodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, hafnium, vanadium, osmium, iridium, platinum, gold, cadmium, mercury, lead, selenium and tellurium.
(2) The niobium powder for capacitors as described in 1 above comprising at least one element selected from the group consisting of chromium, molybdenum and tungsten.
(3) The niobium powder for capacitors as described in 2 above, wherein said at least one element is tungsten.
(4) The niobium powder for capacitors as described in 2 above, wherein said at least one element is chromium and tungsten.
(5) The niobium powder for capacitors as described in 1 above comprising at least one element selected from the group consisting of boron, aluminum, gallium, indium and thallium.
(6) The niobium powder for capacitors as described in 5 above, wherein said at least one element is boron.
(7) The niobium powder for capacitors as described in 5 above, wherein said at least one element is aluminum.
(8) The niobium powder for capacitors as described in 1 above comprising at least one element selected from the group consisting of cerium, neodymium, titanium, rhenium, ruthenium, rhodium, palladium, silver, zinc, silicon, germanium, tin, phosphorus, arsenic and bismuth.
(9) The niobium powder for capacitors as described in 8 above comprising at least one element selected from the group consisting of rhenium, zinc, arsenic, phosphorus, germanium, tin and neodymium.
(10) The niobium powder for capacitors as described in 9 above, wherein said at least one element is rhenium.
(11) The niobium powder for capacitors as described in 9 above, wherein said at least one element is neodymium.
(12) The niobium powder for capacitors as described in 9 above, wherein said at least one element is zinc.
(13) The niobium powder for capacitors as described in 1 above comprising at least one element selected from the group consisting of rubidium, cesium, magnesium, strontium, barium, scandium, yttrium, lanthanum, praseodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, hafnium, vanadium, osmium, iridium, platinum, gold, cadmium, mercury, lead, selenium and tellurium.
(14) The niobium powder for capacitors as described in 13 above comprising at least one element selected from the group consisting of lanthanum, yttrium, erbium, ytterbium and lutetium.
(15) The niobium powder for capacitors as described in 14 above, wherein said at least one element is lanthanum.
(16) The niobium powder for capacitors as described in 14 above, wherein said at least one element is yttrium.
(17) The niobium powder as described in any one of 1 to 16 above, wherein said at least one element is contained in an amount of about 10 mol % or less in said niobium powder.
(18) The niobium powder as described in 17 above, wherein said at least one element is contained in an amount of about 0.01 to about 10 mol % in said niobium powder.
(19) The niobium powder as described in 18 above, wherein said at
Naito Kazumi
Omori Kazuhiro
Mai Ngoclan
Showa Denko K.K.
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