U.S. patent application number 14/006606 was filed with the patent office on 2014-03-20 for method for passivating tantalum metal surface and apparatus thereof.
This patent application is currently assigned to NINGXIA ORIENT TANTALUM INDUSTRY CO., LTD.. The applicant listed for this patent is Xuecheng Dong, Shiwu Hua, Yong Jin, Hui Li, Yuezhong Ma, Hongbo Qin, Xudong Xi, Shengfang Yang, Zhijun Yang, Qingsheng Zhang, Aiguo Zheng, Shiping Zheng. Invention is credited to Xuecheng Dong, Shiwu Hua, Yong Jin, Hui Li, Yuezhong Ma, Hongbo Qin, Xudong Xi, Shengfang Yang, Zhijun Yang, Qingsheng Zhang, Aiguo Zheng, Shiping Zheng.
Application Number | 20140076462 14/006606 |
Document ID | / |
Family ID | 46878597 |
Filed Date | 2014-03-20 |
United States Patent
Application |
20140076462 |
Kind Code |
A1 |
Zheng; Aiguo ; et
al. |
March 20, 2014 |
METHOD FOR PASSIVATING TANTALUM METAL SURFACE AND APPARATUS
THEREOF
Abstract
A method for passivating tantalum metal surface is provided, the
method comprises cooling tantalum metal to or below 32.degree. C.
and/or passivating tantalum metal surface by oxygen-containing gas
with a temperature of 0.degree. C. or below. Also provided is an
apparatus for passivating tantalum metal surface for applying the
method, comprising a heat treatment furnace, an argon
forced-cooling device and/or a device for cooling oxygen-containing
gas.
Inventors: |
Zheng; Aiguo; (Shizuishan
City, CN) ; Ma; Yuezhong; (Shizuishan City, CN)
; Zheng; Shiping; (Shizuishan City, CN) ; Dong;
Xuecheng; (Shizuishan City, CN) ; Qin; Hongbo;
(Shizuishan City, CN) ; Yang; Zhijun; (Shizuishan
City, CN) ; Hua; Shiwu; (Shizuishan City, CN)
; Li; Hui; (Shizuishan City, CN) ; Xi; Xudong;
(Shizuishan City, CN) ; Zhang; Qingsheng;
(Shizuishan City, CN) ; Yang; Shengfang;
(Shizuishan City, CN) ; Jin; Yong; (Shizuishan
City, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Zheng; Aiguo
Ma; Yuezhong
Zheng; Shiping
Dong; Xuecheng
Qin; Hongbo
Yang; Zhijun
Hua; Shiwu
Li; Hui
Xi; Xudong
Zhang; Qingsheng
Yang; Shengfang
Jin; Yong |
Shizuishan City
Shizuishan City
Shizuishan City
Shizuishan City
Shizuishan City
Shizuishan City
Shizuishan City
Shizuishan City
Shizuishan City
Shizuishan City
Shizuishan City
Shizuishan City |
|
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN |
|
|
Assignee: |
NINGXIA ORIENT TANTALUM INDUSTRY
CO., LTD.
Shizuishan City, Ningxia
CN
|
Family ID: |
46878597 |
Appl. No.: |
14/006606 |
Filed: |
March 23, 2011 |
PCT Filed: |
March 23, 2011 |
PCT NO: |
PCT/CN2011/000488 |
371 Date: |
December 4, 2013 |
Current U.S.
Class: |
148/281 ;
118/724 |
Current CPC
Class: |
C23C 8/12 20130101; C23C
8/02 20130101; C23C 8/10 20130101 |
Class at
Publication: |
148/281 ;
118/724 |
International
Class: |
C23C 8/10 20060101
C23C008/10 |
Claims
1. (canceled)
2. A method for passivating tantalum metal surface, characterized
in that it comprises following steps: a). providing tantalum metal
which has been subjected to heat treatment; b). lowering the
temperature of the tantalum metal to room temperature; c).
introducing an oxygen-containing gas at 0.degree. C. or below,
preferably 0.degree. C. to -40.degree. C., to passivate tantalum
metal surface; and d). optionally repeating the step c) once or
more.
3. A method for passivating tantalum metal surface, characterized
in that it comprises following steps: a). providing tantalum metal
which has been subjected to heat treatment; b). lowering the
temperature of the tantalum metal to 32.degree. C. or below,
preferably below 30.degree. C., and more preferably 10.degree.
C.-30.degree. C., by using cooled inert gases; c). introducing an
oxygen-containing gas at 0.degree. C. or below, and preferably
0.degree. C. to -40.degree. C. to passivate tantalum metal surface;
and d), optionally repeating the step c) once or more.
4. A method of passivating tantalum metal surface according to
claim 2, characterized in that the oxygen-containing gas is air, a
mixture gas of inert gas and oxygen, or a mixture gas of inert gas
and air.
5. A method of passivating tantalum metal surface according to
claim 2, characterized in that the oxygen-containing gas is air, a
mixture gas of inert gas and oxygen, or a mixture gas of inert gas
and air.
6. A method of passivating tantalum metal surface according to
claim 2, characterized in that the oxygen-containing gas is a
mixture gas of argon and air.
7. A method of passivating tantalum metal surface according to
claim 2, characterized in that the concentration of oxygen in the
oxygen-containing gas is 21 vol. % or below, preferably 5-20 vol.
%.
8. A method of passivating tantalum metal surface according to
claim 3, characterized in that said inert gas is argon.
9. An apparatus for carrying out the method of claim 1, the
apparatus comprising a heat treatment furnace, the heat treatment
furnace comprising: a hearth, a shell with a water-cooling jacket
constituting the hearth, an inlet for the oxygen-containing
passivation gas to enter the hearth, aeration pipelines, a heater
arranged within the hearth, and a heat treatment crucible for
accommodating tantalum metal to be treated; characterized in that
the apparatus further comprises a refrigeration system for an
oxygen-containing gas, the refrigeration system of an
oxygen-containing gas comprising: an inlet of an oxygen-containing
gas, which is used for receiving an oxygen-containing gas for
passivating tantalum metal; a heat exchange chamber, the
oxygen-containing gas is cooled in the heat exchange chamber by
means of heat exchange; and an outlet of an oxygen-containing gas,
the cooled oxygen-containing gas leaves the heat exchange chamber
from the outlet and enters the heat treatment furnace from the
upper part of the heat treatment furnace through thermal insulation
connection pipelines.
10. An apparatus for carrying out the method of claim 2, the
apparatus comprising a hearth, a shell with a water-cooling jacket
constituting the hearth, an inlet for oxygen-containing passivation
gas entering the hearth, an inlet for argon entering into the
hearth, an argon outlet positioned at upper part of the heat
treatment furnace, a heater arranged within the hearth, and a heat
treatment crucible for accommodating tantalum metal to be treated;
characterized in that the apparatus further comprises an argon
forced-cooling device and a refrigeration system of an
oxygen-containing gas, wherein the argon forced-cooling device
comprising: an inlet for argon to be cooled, the inlet for argon to
be cooled being connected to the argon outlet at the upper part of
the heat treatment furnace; a heat exchange chamber, the heat
exchange chamber receives argon at a high temperature from the heat
treatment furnace by means of the inlet for argon to be cooled and
cools it by heat exchange manner; an outlet of cooled argon, the
argon cooled in the heat exchange chamber being discharged from the
outlet of argon; a circulating pump, the circulating pump receives
the cooled argon from the outlet of cooled argon, and supplies the
cooled argon into the heat treatment furnace from the inlet for
argon at the lower part of the heat treatment furnace through
connection pipelines; and wherein the refrigeration system of an
oxygen-containing gas comprising: an inlet of an oxygen-containing
gas, which is used for receiving an oxygen-containing gas for
passivating tantalum metal; a heat exchange chamber, the
oxygen-containing gas is cooled in the heat exchange chamber by
means of heat exchange; and an outlet of an oxygen-containing gas,
the cooled oxygen-containing gas leaves the heat exchange chamber
from the outlet and enters into the heat treatment furnace from the
upper part of the heat treatment furnace through thermal insulation
connection pipelines.
11. An apparatus for passivating tantalum metal surface according
to claim 10, characterized in that the tantalum metal is cooled to
32.degree. C. or below, preferably 10.degree. C. to 30.degree. C.,
by means of the argon forced-cooling device.
12. An apparatus for passivating tantalum metal surface according
to claim 10, characterized in that the refrigeration system of an
oxygen-containing gas cools the oxygen-containing gas to provide an
oxygen-containing gas for passivation at a temperature of 0.degree.
C. or below, preferably -40.degree. C. to 0.degree. C.
13. An apparatus according to claim 11, characterized in that the
refrigeration, system of an oxygen-containing gas cools the
oxygen-containing gas to provide an oxygen-containing gas for
passivation at a temperature of 0oC or below, preferably -40oC to
0oC
Description
TECHNICAL FIELD
[0001] Present invention relates to the field of tantalum metal
production, and particularly to a method and apparatus for
producing tantalum powder or porous tantalum metal for electrolytic
capacitor.
BACKGROUND ART
[0002] Tantalum metal is mainly used for manufacturing tantalum
electrolytic capacitors. However, the manufacturing process of
tantalum electrolytic capacitors usually comprises compacting
tantalum powder into a compact, sintering the compact in a vacuum
furnace into a porous body in which the particles are
interconnected, subjecting the porous agglomerate to anodic
oxidization in a suitable electrolyte to form homogeneous
interconnected dielectric oxide film on the surface of the porous
particles, i.e. form an anode, coating a cationic material on the
surface of the oxide film, and then packaging and forming the anode
and the cathode of an capacitor. The parameters used for evaluating
tantalum electrolytic capacitors mainly include capacitance, DC
(direct current leakage) and equivalent series resistance (ESR).
Development tendency in capacitors is to have high capacitance, low
leakage current and low equivalent series resistance (low tg.delta.
for anode). The amount of impurities in capacitor level tantalum
powder, which is the main feedstock of tantalum electrolytic
capacitors, particularly oxygen amount, has a great effect on the
leakage current. Low leakage current requires the tantalum powder
to have low oxygen content.
[0003] Generally, tantalum powders for electrolytic capacitors
should subject to heat treatment, for the purpose of purifying
tantalum powders on the one hand, and condensing tantalum
microparticles into porous particles on the other hand, so as to
improve the physical properties of tantalum powders, such as
flowability of tantalum powders, and thus improve the properties of
the electrolytic capacitors manufactured therefrom, such as the
capacitance, leakage current and equivalent series resistance (ESR)
of the capacitors. U.S. Pat. No. 3,473,915 discloses a heat
treatment of tantalum powders, comprising heat condensing 2-30
.mu.m of tantalum powders at 1200.degree. C.-1500.degree. C. under
inactive atmosphere to form multi-junction porous particles to
thereby obtain condensed tantalum powders. In recent several
decades, tantalum powder producers and capacitor manufactures have
conducted extensive studies on the heat treatment of tantalum
powders during the development of tantalum powders having high
specific surface area and small-type capacitors. The prior arts
concerning the agglomeration (condensation) heat treatment of
tantalum powders can be found in following patent documents: JP
2-34701, US5954856, WO99/61184, CN1197707A, CN1238251A,
CN1899730A.
[0004] Deoxidation heat treatment of tantalum powders generally
comprises mixing an appropriate amount of reducing agent including
alkaline metals or rare earth metals or hydrides thereof with
tantalum powders, subjecting to heat treatment at 700.degree.
C.-1100.degree. C. in vacuum or inert atmosphere to condense
tantalum powders and remove oxygen. The prior arts concerning the
deoxidation heat treatment of tantalum powders can be found in
following patent documents: U.S. Pat. No. 4,483,819, U.S. Pat. No.
4,537,641, CN1052070A, etc.
[0005] Since tantalum metal is a metal having strong affinity to
oxygen, tantalum and oxygen are chemically combined to form
Ta.sub.2O.sub.5, which is an exothermal reaction. If the surface of
tantalum powders has a layer of dense oxide film, tantalum can be
protected from being further oxidized. When such tantalum particles
covered by the dense oxide film are heated to a temperature above
300.degree. C., tantalum oxide film is cracked and destroyed, some
oxygen dissolves in tantalum substrate, and some oxygen is
dissipated or concentrated. Therefore, heated tantalum powders are
oxidized starting from the surface after being cooled and contacted
with oxygen-containing medium. The powders absorb new oxygen and
the oxygen content increases. If the rate of absorbing oxygen
cannot be effectively controlled, tantalum powders will
self-ignites. Hence, oxidization-controlled passivation technique
of tantalum powders has been developed. Said tantalum passivation
means that when the oxidization film of tantalum powders is
destroyed and in contact with oxygen-containing medium, the
supplying rate of oxygen is artificially controlled to control the
oxidization rate and temperature of tantalum powders under
controlled condition to thereby form passivated oxide film on the
surface of tantalum powders and avoid violent oxidization. Thus,
tantalum powders having high specific surface area (specific
surface area of above 0.1 m.sup.2/g) should subject to passivation
after heat treatment.
[0006] The tantalum metal surface passivation described in present
specification includes surface passivation of tantalum powders and
surface passivation of porous body formed by compacting tantalum
powders.
[0007] As electronic components are developed towards
miniaturization, tantalum microparticles having larger specific
surface area are required. As for tantalum powders having high
specific surface area, when the tantalum powder per unit volume
generated more heat energy during passivation, the temperature of
tantalum powder during passivation rises more rapidly. During the
passivation of tantalum powder after heat treatment, it was often
noticed that the temperature rises suddenly. This was due to the
fact that the tantalum powders began to oxidize violently, and the
aerating passivation must be stopped immediately. After the
temperature was lowered, aerating passivation was continued slowly.
After the passivation and discharge, it was found that there were
white tantalum oxide plaques on the surface of the tantalum
powders, and the tantalum powder having no white tantalum oxide
also had high oxygen content. If the passivation is not controlled
strictly, the tantalum powder may inflame, causing significant
loss. Hence, the passivation of tantalum powder becomes difficult
and key technique for developing tantalum powders with high
specific surface area.
[0008] Although the surface area of the porous compacts formed of
tantalum powders having high specific surface area, e.g. tantalum
compacts for manufacturing anodes of electrolytic capacitors, is
reduced after sintering, the surface of the porous agglomerate is
also oxidized and produces high temperature to make the porous
agglomerate contain excessive oxygen and the tantalum wires
brittle, or even cause violent oxidization of the porous tantalum
agglomerate. The tantalum anode manufactured with such porous
tantalum agglomerate has high leakage current. Thus, the porous
agglomerate formed of tantalum powders with high specific surface
area should subject to passivation treatment after sintering.
[0009] The prior arts including U.S. Pat. No. 6,927,967B2, U.S.
Pat. No. 6,432,161B1, U.S. Pat. No. 6,238,456B1, CN1919508A,
CN101404213A, U.S. Pat. No. 6,992,881B2, U.S. Pat. No. 7,485,256B2
and CN1899728A disclose the passivation of tantalum powders.
However, these prior arts involves introducing an oxygen-containing
gas at room temperature into a vacuum furnace subjected to heat
treatment and cooled to room temperature or higher temperature to
passivate tantalum powders. Such treatment and passivation consume
long period and cause violent oxidization of tantalum powders.
Chinese patent application CN101348891A discloses a method of
reducing oxygen by tantalum powder controlled passivation and
magnesium treatment, wherein the passivation treatment is carried
out using pure oxygen. This method is not suitable for the
passivation of tantalum powders with high specific surface area,
and the passivation treatment consumes a long period and has a low
yield.
[0010] Due to above problems in the prior art, a method and an
apparatus for producing tantalum powders with low oxygen content
and porous tantalum agglomerates are desired, and this method and
apparatus can avoid violent oxidization during the passivation of
tantalum metal surface.
SUMMARY OF THE INVENTION
[0011] In view of the problems existing in the prior art, an object
of present invention is to provide a method for passivating
tantalum metal surface, which can avoid the violent oxidization
during the passivation. Another object is to provide an apparatus
for carrying out the method for passivating tantalum metal
surface.
[0012] Present invention achieves above objects by providing a
method and apparatus for passivating tantalum metal surface. In
this method, the tantalum metal powders are subjected to heat
treatment and then cooled, and the passivation is carrier out using
oxygen-containing gases at lower temperature.
[0013] In particular, present invention provides following
technical solutions: [0014] (1) A method for passivating tantalum
metal surface, characterized in that it comprises following steps:
[0015] a). providing tantalum metal which has been subjected to
heat treatment; [0016] b). lowering the temperature of the tantalum
metal to 32.degree. C. or below, preferably to below 30.degree. C.,
and more preferably to 10.degree. C.-30.degree. C., by using cooled
inert gases; [0017] c). introducing an oxygen-containing gas to
passivate tantalum metal surface; [0018] d). optionally repeating
the step c) once or more, [0019] (2) A method for passivating
tantalum metal surface, characterized in that it comprises
following steps: [0020] a). providing tantalum metal which has been
subjected to heat treatment; [0021] b). lowering the temperature of
the tantalum metal to room temperature; [0022] c). introducing an
oxygen-containing gas at 0.degree. C. or below, preferably
0.degree. C. to -40.degree. C., to passivate tantalum metal
surface; and [0023] d). optionally repeating the step c) once or
more. [0024] (3) A method for passivating tantalum metal surface,
characterized in that it comprises following steps: [0025] a).
providing tantalum metal which has been subjected to heat
treatment; [0026] b). lowering the temperature of the tantalum
metal to 32.degree. C. or below, preferably below 30.degree. C.,
and more preferably 10.degree. C.-30.degree. C., by using cooled
inert gases; [0027] c). introducing an oxygen-containing gas at
0.degree. C. or below, and preferably 0.degree. C. to -40.degree.
C., to passivate tantalum metal surface; and [0028] d). optionally
repeating the step c) once or more. [0029] (4) A method of
passivating tantalum metal surface according to the technical
solution (1) or (2) or (3), characterized in that said
oxygen-containing gas is air, a mixture gas of inert gas and
oxygen, or a mixture gas of inert gas and air. [0030] (5) A method
of passivating tantalum metal surface according to the technical
solution (1) or (2) or (3), characterized in that said
oxygen-containing gas is a mixture gas of argon and air. [0031] (6)
A method of passivating tantalum metal surface according to the
technical solution (1) or (2) or (3), characterized in that the
concentration of oxygen in the oxygen-containing gas is 21 vol. %
or below, preferably 5-20 vol. %. [0032] (7) A method of
passivating tantalum metal surface according to the technical
solution (1) or (3), characterized in that said inert gas is argon.
[0033] (8) An apparatus for passivating tantalum metal surface
comprising a heat treatment furnace and an argon forced-cooling
device, wherein the heat treatment furnace includes: a hearth, a
shell with a water-cooling jacket constituting said hearth, an
inlet for oxygen-containing passivation gas entering the hearth, an
inlet for argon entering into the hearth, an argon outlet
positioned at upper part of the heat treatment furnace, a heater
arranged within the hearth, and a heat treatment crucible for
accommodating tantalum metal to be treated; the argon
forced-cooling device comprises a refrigerator, a heat exchange
chamber, an inlet for argon to be cooled, an outlet of cooled argon
and a circulating pump; [0034] wherein the inlet for argon to be
cooled is connected to the outlet of argon at the upper part of the
hearth of heat treatment furnace; during passivation treatment, the
argon with high temperature in the heat treatment furnace comes out
from the outlet of argon, passes through connection pipelines
cooled with cooling water at periphery, and enters into the heat
exchange chamber from one side of the heat exchange chamber; in the
heat exchange chamber, the argon entered is cooled, and then comes
out from the outlet of argon at the other side of the heat exchange
chamber and enters into a circulating pump, the cooled argon is
pressed out by the circulating pump, and introduced passing through
the connection pipelines into the heat treatment furnace from the
inlet for argon at the lower part of the heat treatment furnace to
reduce the tantalum metal to be passivated to a temperature of
32.degree. C. or below to be passivated by the oxygen-containing
gas. [0035] (9) An apparatus for passivating tantalum metal surface
comprising a heat treatment furnace and a refrigeration system for
oxygen-containing gases, wherein the heat treatment furnace
includes: a hearth, a shell with a water-cooling jacket
constituting said hearth, an inlet for the oxygen-containing gas
for passivation to enter the hearth, evacuation pipes, a heater
arranged within the hearth, and a heat treatment crucible for
accommodating tantalum metal to be treated; the refrigeration
system of oxygen-containing gases comprises: a refrigerator, a heat
exchange chamber, an inlet for oxygen-containing gases connected
with one side of the heat exchange chamber, an inlet for argon, and
an outlet for oxygen-containing gases connected with the other side
of the heat exchange chamber; [0036] wherein, during the
passivation treatment, the oxygen-containing gases and argon enter
from their corresponding inlets into the heat exchanger chamber and
are mixed, the mixed gases is cooled to a temperature below
0.degree. C. by heat exchanging with the medium pipe in the heat
exchange chamber, the cooled oxygen-containing gases comes out from
another outlet for oxygen-containing gases of the heat exchange
chamber, passes through thermal insulation pipelines and enters
into the heat treatment furnace from the upper part of the heat
treatment furnace for the passivation of tantalum metal to be
passivated. [0037] (10) An apparatus for passivating tantalum metal
surface comprising a heat treatment furnace, an argon
forced-cooling device, and a refrigeration system for
oxygen-containing gas, wherein the heat treatment furnace includes:
a hearth, a shell with a water-cooling jacket constituting said
hearth, an inlet for the oxygen-containing gas for passivation to
enter the hearth, an inlet for argon entering into the hearth, an
outlet of argon positioned at upper part of the heat treatment
furnace, a heater arranged within the hearth, and a heat treatment
crucible for accommodating tantalum metal to be treated; [0038] the
argon forced-cooling device comprises a refrigerator, a heat
exchange chamber, an inlet for argon to be cooled, an outlet for
cooled argon and a circulating pump; wherein the inlet for argon to
be cooled is connected with the outlet of argon at the upper part
of the hearth of heat treatment furnace, during passivation
treatment, the argon with high temperature in the heat treatment
furnace comes out from the outlet of argon, passes through
connection pipelines cooled with cooling water at periphery, and
enters into the heat exchange chamber from one side of the heat
exchange chamber; in the heat exchange chamber, the argon entered
is cooled, and then comes out from the outlet for argon at the
other side of the heat exchange chamber and enters into a
circulating pump, the cooled argon is pressed out by the
circulating pump, and introduced passing through the connection
pipelines into the heat treatment furnace from the inlet for argon
at the lower part of the heat treatment furnace to thereby reduce
the tantalum metal to be passivated to a temperature of 32.degree.
C. or below; and [0039] the refrigeration system of
oxygen-containing gases comprises a refrigerator, a heat exchange
chamber, an inlet for oxygen-containing gas connected with one end
of the heat exchange chamber, an inlet for argon, and an outlet for
oxygen-containing gas connected with another end of the heat
exchange chamber; during passivation treatment, the
oxygen-containing gases and argon enter from their corresponding
inlets into the heat exchanger chamber and are mixed, the mixed
gases is cooled to a temperature below 0.degree. C. by heat
exchanging with the medium pipe in the heat exchange chamber, the
cooled oxygen-containing gases comes out from the outlet at the
other side of the heat exchange chamber, passes through thermal
insulation pipelines and enters into the heat treatment furnace
from the upper part of the heat treatment furnace for the
passivation of tantalum metal to be passivated. [0040] (11) An
apparatus for passivating tantalum metal surface according to the
technical solution (8) or (10), characterized in that the tantalum
metal is cooled to 10.degree. C. to 30.degree. C. by means of the
argon forced-cooling device so as to be passivated by the
oxygen-containing gases. [0041] (12) An apparatus for passivating
tantalum metal surface according to the technical solution (9) or
(10), characterized in that the mixed gases are cooled to provide
an oxygen-containing gas for passivation of -40.degree. C. to
0.degree. C.
[0042] The advantages of the method for passivating tantalum metal
surface are safe, reliable and high yield, and the obtained
tantalum powders have low oxygen and hydrogen content, and the
anodes and tantalum electrolytic capacitors manufactured from the
tantalum powders exhibit good electric properties.
[0043] It should be understood that above general descriptions and
following detailed description in connection with drawings and the
detailed description of preferred examples are demonstrative
descriptions which are used for further explaining the claimed
invention, not for limiting the invention.
DESCRIPTION OF DRAWINGS
[0044] FIG. 1 is schematic diagram of an apparatus for passivating
tantalum metal surface in the prior art.
[0045] FIG. 2 shows an example of an apparatus for passivating
tantalum metal surface with an inert gas forced-cooling device
according to present invention.
[0046] FIG. 3 shows an example of an apparatus for passivating
tantalum metal surface with a refrigeration system of
oxygen-containing gas according to present invention.
[0047] FIG. 4 shows an example of an apparatus for passivating
tantalum metal surface with an inert gas forced-cooling device and
a refrigeration system of oxygen-containing gas according to
present invention.
[0048] FIG. 5 shows another schematic diagram of an apparatus for
passivating tantalum metal surface in the prior art.
[0049] FIG. 6 shows another example of an apparatus for passivating
tantalum metal surface with an inert gas forced-cooling device
according to present invention.
[0050] FIG. 7 shows another example of an apparatus for passivating
tantalum metal surface with a refrigeration system of
oxygen-containing gas according to present invention.
[0051] FIG. 8 shows another example of an apparatus for passivating
tantalum metal surface with an inert gas forced-cooling device and
a refrigeration system of oxygen-containing gas according to
present invention.
EMBODIMENTS
[0052] Present invention is further described hereinafter with
reference to the drawings and preferred examples:
[0053] In the specification, the unit ppm indicates "parts per
million" based on mass ratio, unless otherwise expressly
stated.
[0054] Present invention provides a method for passivating tantalum
metal surface. In the method of present invention, the tantalum
metal to be heat treated and passivated can be chemically reduced
tantalum powders which have not been heat treated, e.g. tantalum
powders prepared by reducing potassium tantalum fluoride with
sodium, an raw material powder obtained by hydrogenation and
grinding of tantalum ingots, and heat treated tantalum powders, and
porous tantalum agglomerates formed by compacting tantalum powders,
and so on. Before heat treatment, the tantalum powders are
preferably pelletized, particularly subjected to spheroidizing
granulation. During the granulation of tantalum powders, any
chemical substance benefiting to control the shrinkage rate of
tantalum powders at high temperature sintering and reducing surface
area loss at required ratio can be added as fire resistance agent,
such as a substance containing phosphor, nitrogen, boron, oxygen.
In the method of present invention, the tantalum powders can
subject to heat treatment by known techniques, for example, the
methods disclosed in CN1410209A, CN1238251A and CN1899730A, which
are incorporated herein by reference.
[0055] In the method of present invention, an inert gas
forced-cooling device can be used to cool heat treated tantalum
metal to a temperature below 32.degree. C. Said inert gas can be
argon, helium, xenon or a mixture thereof. However, in view of
cost, argon is preferably used to carry out forced-cooling.
[0056] According to the method of present invention, the particle
shape of tantalum powders to be heat treated is not limited; it can
be particulate, sheet, multiangular shape or any combination
thereof. The specific surface area of the tantalum powders is not
specifically required and can be 0.1 m.sup.2/g-10 m.sup.2/g,
preferably 0.2 m.sup.2/g-5 m.sup.2/g.
[0057] The deoxidization heat treatment of tantalum powders in
reductive atmosphere can be carried out by known techniques in the
art. Generally, a small amount of a reducing agent having an
affinity to oxygen greater than that of tantalum to oxygen can be
added in the tantalum powders, such as alkaline earth metals, rare
earth metals, and hydrides thereof; most commonly, a metal
magnesium powder of 0.5%-4% based on the weight of tantalum is
added to the tantalum powder.
[0058] FIG. 1 is a diagram of an apparatus 100 for passivating heat
treated tantalum metal surface in the prior art. The apparatus for
passivating heat treated tantalum metal surface comprises: a hearth
110, a shell 111 with a water cooling jacket having a water inlet
111-1 and a water outlet 111-2, the shell constitutes the hearth
110, and a vacuum pressure meter 112 communicated with the hearth
110, an inlet 120 of the oxygen-containing passivation gas entering
into the hearth 110, an inlet 140 of argon, evacuating pipelines
141, a heat insulation screen 130 arranged in the hearth, a heater
150 arranged in the heat insulation screen 130, a thermocouple 160
for measuring temperature, a heat treatment crucible 180, and a
tantalum powder 170 to be treated contained in the crucible
180.
[0059] FIG. 2 is a diagram of an apparatus for passivating tantalum
metal surface with an argon forced-cooling device according to
present invention. The apparatus for passivating tantalum metal
surface comprises: a hearth 210, a shell 211 with a water cooling
jacket having a water inlet 211-1 and a water outlet 211-2, the
shell constitutes the hearth 210, and a vacuum pressure meter 212
communicated with the hearth 210, an inlet 220 of oxygen-containing
gas for passivation, an inlet 240 of argon, evacuating pipelines
241, a heat insulation screen 230 arranged in the hearth 210, a
heater 250 arranged in the heat insulation screen 230, a
thermocouple 260 for measuring temperature, a heat treatment
crucible 280, and a tantalum powder 270 to be treated charged in
the crucible 280. The apparatus for passivating tantalum metal
surface further comprises a device 200A for forced-cooling argon;
the components in the device 200A for forced-cooling argon and the
functions thereof are as follows: an outlet 207 at the upper part
of the heat treatment furnace, the argon with high temperature in
the furnace comes out from the outlet 207 of argon, passes through
connection pipelines 208 cooled with cooling water at periphery,
and enters into the heat exchange chamber 201 from the inlet 202 of
argon at one side of the heat exchange chamber. In the heat
exchange chamber 201 there is a medium pipeline 204 cooled by a
refrigerator 200, the refrigerator 200 allows a cooling medium to
pass through the heat exchanger chamber 201; in the heat exchange
chamber 201, the argon entered is cooled, and then comes out from
the outlet 205 of argon at the other side of the heat exchange
chamber, passes through a pipeline 206 and enters into a
circulating pump 209, the cooled argon is pressed out by the
circulating pump 209, and introduced passing through the connection
pipelines into the heat treatment furnace from the inlet 240 of
argon at the lower part of the heat treatment furnace. (wherein the
cooling water at the periphery of pipeline 208 enters from 208-1 at
one side of the heat exchange chamber adjacent to the refrigerator
heat exchange chamber, and comes out from 208-2 adjacent to one
side of the heat treatment furnace, before the tantalum powder is
passivated, it is forcedly cooled by means of the argon
forced-cooling device to reduce the temperature of the tantalum
powder to 30.degree. C. or below, preferably to 10.degree.
C.-30.degree. C. to effectively control the oxidization of tantalum
powder and avoid the violent oxidization of tantalum powder. During
the forced-cooling with argon, the pressure of the system is
maintained between 0.09 MPa-0.11 MPa by supplying argon to the
circulating system or exhausting.
[0060] FIG. 3 shows an apparatus for passivating tantalum metal
surface with an oxygen-containing gas refrigerating system for
passivating tantalum metal surface. The apparatus for passivating
tantalum metal surface comprises: a hearth 310, a shell 311 with a
water cooling jacket having a water inlet 311-1 and a water outlet
311-2, the shell constitutes the hearth 310, and a vacuum pressure
meter 312 communicated with the hearth 310, an inlet 320 of
oxygen-containing gas for passivation at the upper part of the
hearth, an inlet 340 of argon, evacuating pipelines 341, a heat
insulation screen 330 arranged in the hearth, a heater 350 arranged
in the heat insulation screen 330, a thermocouple 360 for measuring
temperature, a heat treatment crucible 380, and a tantalum powder
370 to be treated contained in the crucible 380. The apparatus for
passivating tantalum metal surface further comprises a
refrigerating system 390A of oxygen-containing gas for passivation,
the refrigerating system 390A of oxygen-containing gas for
passivation comprising: a refrigerator 390, a heat exchange chamber
391, the medium cooled by the refrigerator passes through the heat
exchange chamber 391; the oxygen-containing gas and argon enter
from the inlet 392 and the inlet 393 of argon respectively into the
heat exchanger chamber 391 and are mixed, the mixed
oxygen-containing gas and the refrigeration medium pipe 394
connected with the refrigerator 390 undergo heat exchange, the
cooled oxygen-containing gas comes out from the outlet 395 at the
other side of the heat exchange chamber 391, passes through thermal
insulation pipelines 396 connecting the outlet 395 and the inlet
320 at the upper part of the heat treatment furnace and enters into
the hearth 310; in which there is a pressure meter 398 communicated
with the heat exchange chamber 391, a thermometer 397 is arranged
near the outlet 395 of oxygen-containing gases; and a water outlet
399 arranged at the bottom of the heat exchanger 391. When the
passivation of a batch of tantalum metal is completed, each
component in the heat exchanger is dried using hot air, the melted
water flows out from the water outlet 399. The oxygen-containing
gases is cooled to below 0.degree. C., preferably below -10.degree.
C., more preferably -10.degree. C. to -40.degree. C.
[0061] FIG. 4 is a schematic diagram of an apparatus for
passivating tantalum metal surface with an argon forced-cooling
device and a refrigeration system of oxygen-containing gas
according to present invention, comprising: a hearth 410, a shell
411 with a water cooling jacket having a water inlet 411-1 and a
water outlet 411-2, the shell constitutes the hearth 410, and a
vacuum pressure meter 412 communicated with the hearth 410, an
inlet 420 of oxygen-containing gas for passivation, an inlet 440 of
argon, evacuating pipelines 441, a heat insulation screen 430
arranged in the hearth, a heater 450 arranged in the heat
insulation screen 430, a thermocouple 460 for measuring
temperature, a heat treatment crucible 480, and a tantalum powder
470 to be treated contained in the crucible 480, characterized in
that the apparatus for passivating tantalum metal surface further
comprises: an argon forced-cooling device 400A and a refrigerating
system 490A of oxygen-containing gas, wherein the components in the
device 400A for forced-cooling argon and the functions thereof are
as follows: an argon outlet 407 at the upper part of the heat
treatment furnace, the argon with high temperature in the furnace
comes out from the outlet 407 of argon, passes through connection
pipelines 408 cooled with cooling water entering from 408-1 and
coming out from 408-2 at periphery, and enters into the heat
exchange chamber 401 from one side of the heat exchange chamber
401, in the heat exchange chamber 401 there is a medium pipeline
404 cooled by a refrigerator, in the heat exchange chamber 401, the
argon entered is cooled, and comes out from the outlet 405 of argon
at the other side of the heat exchange chamber 401, passes through
a pipeline 406 and enters into a circulating pump 409, the cooled
argon is pressed out by the circulating pump 409, and introduced
passing through the connection pipelines into the heat treatment
furnace 410 from the inlet 440 at the lower part of the heat
treatment furnace, the components in the refrigeration system 490A
of oxygen-containing gas and their functions are as follows: the
cooling medium is cooled by the refrigerator 490; the cooled medium
flows passing through the medium pipeline 494 into the heat
exchange chamber 491, in which there is a pressure meter 498
communicated with the heat exchange chamber 491; in the heat
exchange chamber 491, the oxygen-containing gas and argon enter
from their corresponding inlets 492 and 493 respectively into the
heat exchange chamber 491 and are mixed; the mixed
oxygen-containing gas is cooled by heat exchanging with the medium
pipeline 494 in the heat exchange chamber 491, the cooled
oxygen-containing gas comes out from another outlet 495 of the heat
exchange chamber 491, passes through thermal insulation pipelines
496 and enters into the heat treatment furnace 410 from the inlet
420 at the upper part of the heat treatment furnace, a thermometer
497 is arranged near the outlet of the oxygen-containing gas, the
thermometer being used for measuring the temperature of
oxygen-containing gas; a water outlet 499 is arranged at the bottom
of the heat exchange chamber 491. When the passivation of a batch
of tantalum metal is completed, each component in the heat
exchanger is dried using hot air, the melted water flows out from
the water outlet 499.
[0062] FIG. 5 is a schematic diagram of a prior apparatus for
passivating tantalum metal surface after the tantalum powder is
subjected to deoxidization heat treatment by external heating (not
shown), comprising: a deoxidization heat treatment reaction vessel
510, an upper cover 511, an argon inlet pipe 540 arranged on the
upper cover 511, an evacuating pipeline 541, a nitrogen inlet pipe
542, an inlet pipe 520 of oxygen-containing gas for passivation, a
vacuum pressure meter 512 for measuring the pressure in the
reaction vessel, a tantalum crucible 580 arranged in the reaction
vessel 510, a tantalum powder mixed with magnesium powder contained
in the crucible 580, a thermocouple 561, 562 and 563 for measuring
the temperature of upper part, middle part and lower part of the
reaction vessel, respectively, and a thermal insulation screen
assembly 530 located in the upper part of the crucible 580.
[0063] FIG. 6 is a schematic diagram of an apparatus for
passivating tantalum metal surface after the tantalum powder is
subjected to deoxidization heat treatment by external heating (not
shown) with an inert gas forced-cooling device according to present
invention, comprising: a deoxidization heat treatment reaction
vessel 610, an upper cover 611, an argon inlet pipe 640 arranged on
the upper cover 611 and extended into the lower part of the
reaction vessel 610, an evacuating pipeline 641, a nitrogen inlet
pipe 642, an inlet pipe 620 of oxygen-containing gas for
passivation, a vacuum pressure meter 612 for measuring the pressure
in the reaction vessel, a tantalum crucible 680 arranged in the
reaction vessel 610, a tantalum powder 670 mixed with magnesium
powder contained in the crucible 680, thermocouples 661, 662 and
663 for measuring the temperature of upper part, middle part and
lower part of the reaction vessel, respectively, and a thermal
insulation screen assembly 630 located in the upper part of the
crucible 680, characterized by further comprising an argon
forced-cooling device 600A, the device 600A for forced-cooling
argon comprising: an argon outlet 607 at the upper part of the
reaction vessel 610, the argon with high temperature in the furnace
comes out from the outlet 607 of argon, passes through connection
pipelines 608 cooled with cooling water entering from 608-1 and
coming out from 608-2 at periphery, and enters into the heat
exchange chamber 601 from one side of the heat exchange chamber
601, in the heat exchange chamber 601 there is a medium pipeline
604 cooled by a refrigerator, in the heat exchange chamber 601, the
argon entered is cooled and comes out from the outlet 605 of argon
at the other side of the heat exchange chamber 601, passes through
a pipeline 606 and enters into a circulating pump 609, the cooled
argon is pressed out by the circulating pump 609, and introduced
passing through the connection pipelines into the heat treatment
furnace 610 from the inlet 640 at the lower part of the heat
treatment furnace.
[0064] By forced-cooling with argon, the temperature of tantalum
powder is reduced to 30.degree. C. or below, preferably to
10.degree. C. to 20.degree. C., before the passivation of tantalum
powder.
[0065] FIG. 7 is a schematic diagram of an apparatus for
passivating tantalum metal surface after the tantalum powder is
subjected to deoxidization heat treatment by external heating (not
shown in the figure) with a refrigeration system of
oxygen-containing gas according to present invention, comprising: a
deoxidization heat treatment reaction vessel 710, an upper cover
711, an argon inlet pipe 740 arranged on the upper cover 711, an
evacuating pipeline 741, a nitrogen inlet pipe 742, an inlet pipe
720 of oxygen-containing gas for passivation, a vacuum pressure
meter 712 for measuring the pressure in the reaction vessel, a
tantalum crucible 780 arranged in the reaction vessel 710, a
tantalum powder 770 mixed with magnesium powder contained in the
crucible 780, thermocouples 761, 762 and 763 for measuring the
temperature of upper part, middle part and lower part of the
reaction vessel, respectively, and a thermal insulation screen
assembly 730 located in the upper part of the crucible 780,
characterized by further comprising a refrigeration system 790A of
oxygen-containing gas for passivation, the refrigeration system
790A of oxygen-containing gas comprising: a refrigerator 490 for
refrigerating cooling medium; the cooled medium flows passing
through the medium pipeline 794 into the heat exchange chamber 791,
in which there is a pressure meter 798 communicated with the heat
exchange chamber 791; in the heat exchange chamber 791, the
oxygen-containing gas and argon enter from their corresponding
inlets 792 and 793 into the heat exchange chamber 791 and are
mixed; the mixed oxygen-containing gas undergo heat exchange
reaction with the medium pipeline 794 in the heat exchange chamber
791, and thus is cooled, the cooled oxygen-containing gas comes out
from outlet 795 at the other side of the heat exchange chamber 791,
passes through thermal insulation pipelines 796 and enters into the
reaction vessel 710 from the inlet 720 at the upper part of the
reaction vessel, a thermometer 797 is arranged near the outlet of
the oxygen-containing gas, the thermometer being used for measuring
the temperature of oxygen-containing gas; a water outlet 799 is
arranged at the bottom of the heat exchange chamber 791.
[0066] When the passivation of a batch of tantalum metal is
completed, each component in the heat exchanger is dried using hot
air, the melted water flows out from the water outlet 799.
[0067] FIG. 8 is a schematic diagram of an apparatus for
passivating tantalum metal surface after the tantalum powder is
subjected to deoxidization heat treatment with an inert gas
forced-cooling device and a refrigeration system of
oxygen-containing gas according to present invention, comprising: a
deoxidization heat treatment reaction vessel 810, an upper cover
811, an argon inlet pipe 840 arranged on the upper cover 811 and
extended into the lower part of the reaction vessel 810, an
evacuating pipeline 841, a nitrogen inlet pipe 842, an inlet pipe
820 of oxygen-containing gas for passivation, a vacuum pressure
meter 812 for measuring the pressure in the reaction vessel, a
tantalum crucible 880 arranged in the reaction vessel 810, a
tantalum powder 870 mixed with magnesium powder contained in the
crucible 880, thermocouples 861, 862 and 863 for measuring the
temperature of upper part, middle part and lower part of the
reaction vessel, respectively, and a thermal insulation screen
assembly 830 located in the upper part of the crucible 880,
characterized by further comprising an argon forced-cooling device
800A and a refrigerating system 890A of oxygen-containing gas, the
components of the device 800A for forced-cooling argon and the
functions thereof are as follows: an argon outlet 807 arranged at
the upper part of the reaction vessel 810, the argon with high
temperature in the furnace comes out from the outlet 807 of argon,
passes through connection pipelines 808 cooled with cooling water
entering from 808-1 and coming out from 808-2 at periphery, and
enters into the heat exchange chamber 801 from one side of the heat
exchange chamber 801, in the heat exchange chamber 801 there is a
medium pipeline 804 cooled by a refrigerator, in the heat exchange
chamber 801, the argon entered is cooled and comes out from the
outlet 805 of argon at the other side of the heat exchange chamber
801, passes through a pipeline 806 and enters into a circulating
pump 809, the cooled argon is pressed out by the circulating pump
809 and introduced passing through the connection pipelines into
the heat treatment furnace 810 from the inlet 840 at the lower part
of the reaction vessel. The components in the refrigeration system
890A of oxygen-containing gas and functions thereof are as follows:
the cooling medium is cooled by the refrigerator 890; the cooled
medium flows passing through the medium pipeline 894 into the heat
exchange chamber 891, in which there is a pressure meter 898
communicated with the heat exchange chamber 891; in the heat
exchange chamber 891, the oxygen-containing gas and argon enter
from their corresponding inlets 892 and 893 into the heat exchange
chamber 891 and are mixed; the mixed oxygen-containing gas
undergoes heat exchange with the medium pipeline 894 in the heat
exchange chamber 891 and thereby is cooled, the cooled
oxygen-containing gas comes out from outlet 895 at the other side
of the heat exchange chamber 891, passes through thermal insulation
pipelines 896 and enters into the reaction vessel 810 from the
inlet 820 at the upper part of the reaction vessel, a thermometer
897 is arranged near the outlet of the oxygen-containing gas, the
thermometer being used for measuring the temperature of
oxygen-containing gas; a water outlet 899 is arranged at the bottom
of the heat exchange chamber 891.
[0068] When the passivation of a batch of tantalum metal is
completed, each component in the heat exchanger is dried using hot
air, the melted water flows out from the water outlet 899.
[0069] In present invention, charging tantalum powder into the heat
treatment furnace is not specially limited. However, in
consideration of heat homogeneity, nitridation and passivation
homogeneity and sufficiency, the thickness of tantalum powder is
preferably 60 mm or below, and more preferably 40-50 mm; For the
purpose of safety and higher yield, the tantalum powder is
preferably gently charged in a tantalum crucible and leveled.
Present invention usually employs circular or square crucible with
shallow depth, such as, tantalum crucible having
length.times.width.times.depth=about 350 mm.times.210 mm.times.75
mm.
[0070] The temperature of heat treatment and holding time of
tantalum powder is determined based on different types of tantalum
powders and requirements, generally holding for 30-90 minutes at a
temperature of 900.degree. C.-1400.degree. C. and a vacuum pressure
lower than 1.33.times.10.sup.-1 Pa.
[0071] The heat treated tantalum powder is optionally nitridated by
introducing nitrogen during cooling.
[0072] After subjecting to temperature holding at 900.degree.
C.-1400.degree. C., the tantalum powder is cooled in vacuum
furnace, and can be cooled by a shell with cooling water jacket,
the tantalum powder is cooled in vacuum to a temperature, e.g.
about 500.degree. C. or below, cooled with room temperature argon
to about 80.degree. C. or below, and then subjected to forcedly
circulation cooling with argon below room temperature so that the
tantalum powder is cooled to 30.degree. C. or below, preferably to
20.degree. C. or below, e.g. to 10.degree. C. to 20.degree. C., and
then subjected to passivation treatment by introducing an
oxygen-containing gas.
[0073] The oxygen-containing gas is a mixed gas consisting of argon
and oxygen, in consideration of economics, the oxygen-containing
gas is preferably a mixed gas consisting of air and argon.
According to present invention, the concentration of oxygen in the
oxygen-containing gas is 21 vol. % or below; the lower the
concentration of oxygen, the oxidation of tantalum can be
controlled more effectively. Since the specific heat of gas lower,
in consideration of effect, it is desirable that the concentration
of oxygen in the oxygen-containing gas is as low as possible.
However, in consideration of yield and economics, at the beginning
of passivation, preferably the content of oxygen in the
oxygen-containing gas is 5-15 vol. %.
[0074] As for tantalum powder having low specific surface area, it
is enough that the passivation is carried out once. As for tantalum
powder having high specific surface area, it is preferred that the
passivation is carried out twice or more. The first passivation is
carried out using a gas with low oxygen content, and then the
oxygen concentration of oxygen-containing gas is increased
gradually, the oxygen concentration is up to the oxygen
concentration in air, about 21 vol. %.
[0075] According to present invention, an oxygen-containing gas and
a dilution gas, e.g., argon, were introduced from their respective
inlets into the heat exchange chamber in a volume ratio calculated
by gas pressure, the gasses are mixed and underwent heat exchange
with the heat exchanger, the temperature of the discharged
oxygen-containing gas was measured at the outlet. The temperature
of the oxygen-containing gas described in present invention means
the temperature of discharged gas measured at the outlet.
[0076] When tantalum powder was passivated, the heat treatment
furnace was evacuated to about 200 Pa, and then the
oxygen-containing gas was continuously or discontinuously
introduced into the heat treatment furnace to make the final
pressure in the heat treatment furnace reach to about 0.1 MPa.
[0077] The heat treatment described herein means the heating course
of tantalum powder at a temperature of above 300.degree. C. in
vacuum or an inert atmosphere or reductive atmosphere, and includes
the sintering of porous tantalum compact, e.g., the sintering for
manufacturing anode of tantalum electrolytic capacitor, and a
device similar to heat treatment of tantalum powder can be
employed, e.g. a device as shown in FIG. 2-FIG. 4.
[0078] The oxygen content of tantalum powder disclosed herein was
determined by means of TC-436 oxygen nitrogen joint determinator;
the hydrogen content of tantalum powder was determined by means of
RH-404 hydrogen content determinator. The wet electronic property
data of tantalum powder disclosed herein were measured as follows:
the tantalum powder was compacted into a cylindrical compact with a
density of 4.5 g/cm.sup.3, a diameter of 3.0 mm and a height of
4.72 mm, in which 0.3 mm tantalum wire was embedded, each compact
containing about 150 mg of tantalum powder; the compact was
sintered at 1320.degree. C. for 10 minutes to form an agglomerate;
the agglomerate was placed in 0.1 mass % phosphoric acid at
80.degree. C., the voltage was raised to 30 V at a current density
of 60 mA/g and the voltage was kept for 120 minutes to form an
anode in which dielectric oxide film was covered on the surface of
tantalum particles; the leakage current of the anode was determined
in 0.1 mass % phosphoric acid at 25.degree. C., and the specific
electric capacity (specific capacity) and loss were determined in
20 mass % of sulfuric acid solution.
[0079] In order to further explain present invention, the preferred
embodiments of present invention are described as follows by
combining examples and drawings. However, it should be understood
that these descriptions are only further explanation of the
features and advantages of present invention, but not limitation to
the scope of the invention.
EXAMPLES
Example 1
[0080] A feedstock powder which was prepared by reducing potassium
tantalum fluoride with sodium is provided; the feedstock powder has
a specific surface area of 1.82 m.sup.2/g, a bulk density of 0.51
g/cm.sup.3, and oxygen content of 6200 ppm. The raw material
powder, was mixed with 120 ppm of phosphorus based on the weight of
the tantalum powder, spheroidizing granulated to obtain spherical
particles with a bulk density of 1.02 g/cm.sup.3. The spheroidizing
granulated tantalum powder was charged into a crucible, and the
crucible was placed in a tantalum powder heat treatment passivation
device as shown in FIG. 4, heated in vacuum below
1.33.times.10.sup.-1 Pa to 1200.degree. C. and held for 30 minutes,
and then the heating was stopped and the temperature was lowered to
200.degree. C.; argon was introduced to lower the temperature to
80.degree. C., the forced-cooling argon system 400A was actuated,
the argon with high temperature in the heat treatment furnace came
out from the outlet 407, passed through the pipeline 408 cooled
with cooling water, entered into the heat exchange chamber 401 from
the gas inlet 402 and underwent heat exchange with the
refrigerating medium pipe 404 connected with the refrigerator;
argon was cooled through heat exchange, the cooled argon came out
from the outlet 405, pumped by using a circulating pump 409 to pass
through the pipeline 406 and enter the heat treatment furnace from
the gas inlet 440 of the heat treatment furnace, constituting
circulation of argon. The circulated argon caused the crucible and
tantalum powder in the heat treatment furnace cooled, after the
cooling was carried out for about 2 hours, the temperature in the
furnace was lowered to 25.degree. C., and the tantalum powder was
passivated. The passivation process comprises evacuating the gas in
the furnace from the aeration pipeline 441 to a vacuum of about 200
Pa, the refrigeration system 490A of oxygen-containing gas was
actuated to make air and argon enter the heat exchange chamber 491
from 492 and 493 respectively according to following conditions,
mix and undergo heat exchange with 494, and then came out from the
outlet 495, passed through the thermal insulation pipeline 496, and
entered the hearth 410 from the inlet 420; first, the
oxygen-containing gas with an oxygen concentration of about 5 vol.
% (1 volume of air and 3 volume of argon were introduced by
pressure meter from the inlet 492 and the outlet 493 into the heat
exchange chamber 491) underwent heat exchange with the
refrigerating medium pipe 494 connected with the refrigerator and
thereby was cooled, the oxygen-containing gas at a temperature of
-10.degree. C. to -20.degree. C. came out from the outlet 495 of
oxygen-containing gas, passed through the thermal insulation pipe
496 and entered the heat treatment furnace from the gas inlet 420
at the upper part of the heat treatment furnace, the pressure was
increased in 8 stages and 3 hours from 200 Pa to OA MPa: (200
Pa-0.005 MPa)/30 minutes, (0.005 MPa-0.01 MPa)/30 minutes, (0.01
MPa-0.02 MPa)/20 minutes, (0.02 MPa-0.03 MPa)/20 minutes, (0.03
MPa-0.045 MPa)/20 minutes, (0.045M Pa-0.06 MPa)/20 minutes, (0.06
MPa-0.08 MPa)/20 minutes, (0.08 MPa-0.1 MPa)/20 minutes, total 3
hours; second, the oxygen-containing gas at -10.degree. C. to
-20.degree. C. with an oxygen concentration of about 10 vol. % (1
volume of air and 1 volume of argon were mixed) were increased from
200 Pa to 0.1 MPa in 3 hours according to the first aeration
procedure; third, the pressure was increased from 200 Pa to 0.1 MPa
in 3 hours using air at -10.degree. C. to -20.degree. C. according
to the same procedure as the first procedure; fourth, the pressure
was increased from 200 Pa to 0.1 MPa in 4 stages total 2 hours
using air at -10.degree. C. to -20.degree. C.: (200 Pa-0.01 MPa)/30
minutes, (0.01 MPa-0.03 MPa)/30 minutes, (0.03 MPa-0.06 MPa)/30
minutes, (0.06 MPa-0.10 MPa)/30 minutes. The four passivations were
carried out in total 11 hours. During the whole procedure, the
temperature in the furnace was firstly elevated gradually to
28.degree. C., then the temperature was gradually steady and varied
between 25.degree. C. and 28.degree. C., and finally the
temperature was lowered gradually to 25.degree. C. After
discharging, the tantalum powder was taken out, and no violent
oxidation phenomenon occurred. The heat treated tantalum powder was
passed through 80 mesh screening to obtain S-1h tantalum powder.
The oxygen and hydrogen contents of the tantalum powder were
analyzed, the results were shown in Table 1. 2 wt % Magnesium
powder based on the tantalum powder was blended to form a mixed
powder, the mixed powder was charged into the tantalum powder
deoxidization reaction vessel as shown in FIG. 6, held at
850.degree. C. for 3 hours to carry out deoxidization treatment,
the heating was stopped, and the temperature was lowered, and the
treated tantalum powder was nitridated at 280.degree. C., and then
forcedly cooled with argon, when the temperature of tantalum powder
was lowered to 15.degree. C., according to the passivation
procedure similar to the heat treatment as described above, an
oxygen-containing gas at 31.degree. C. was introduced, and
passivation was carried out in 4 times using an oxygen-containing
gas with an oxygen concentration of about 5 vol. %, 10 vol. %, 21
vol. % and 21 vol. %, the first 3 passivations were carried out for
3 hours each, and the last passivation was carried out for 2 hours,
total 11 hours. After discharging, the passivated tantalum powder
was pickled, washed with water, and dried to obtain S-1d tantalum
powder. The oxygen and hydrogen contents of the tantalum powder
were analyzed, the results were shown in Table 1. The electric
performance of the tantalum powder was determined, and the results
were shown in Table 2.
Example 2
[0081] The feedstock tantalum powder, as employed in Example 1, was
charged in the tantalum powder heat treatment furnace with an argon
forced-cooling device as shown in FIG. 2, and subjected to heat
treatment according to the same conditions in Example 1, when the
temperature of tantalum powder was lowered to about 200.degree. C.,
argon was introduced, and the forced-cooling argon system 200A was
actuated, the argon with high temperature in the heat treatment
furnace came out from the outlet 207 at the upper part of the
furnace, passed through water cooled pipeline 208, entered into the
heat exchange chamber 201 from the gas inlet 202 and underwent heat
exchange with the refrigerating medium pipe 204 connected with the
refrigerator 200; argon was cooled through heat exchange, the
cooled argon came out from the outlet 205, passed through pipeline
206, pumped by using a circulating pump 209 to enter the heat
treatment furnace 210 from the gas inlet 240 of the heat treatment
furnace, constituting circulation of argon; the circulated argon
caused the crucible and tantalum powder in the heat treatment
furnace cooled, after the cooling was carried out for about 4
hours, the crucible and tantalum powder were forcedly cooled argon
to a temperature of 10.degree. C., and the tantalum powder was
passivated. The heat treatment furnace was evacuated to about 200
Pa; first, the oxygen-containing gas at 32.degree. C. with an
oxygen concentration of about 5 vol. % was increased in 8 stages
and 4 hours from 200 Pa to 0.1 MPa: (200 Pa-0.005 MPa)/30 minutes,
(0.005 MPa-0.01 MPa)/30 minutes, (0.01 MPa-0.02 MPa)/30 minutes,
(0.02 MPa-0.03 MPa)/30 minutes, (0.03 MPa-0.045 MPa)/30 minutes,
(0.045 MPa-0.06 MPa)/30 minutes, (0.06 MPa-0.08 MPa)/30 minutes,
(0.08 MPa-0.1 MPa)/30 minutes; second, the oxygen-containing gas at
32.degree. C. with an oxygen concentration of about 10 vol. % was
increased from 200 Pa to 0.1 MPa in 4 hours according to the first
aeration procedure; third, the pressure was increased from 200 Pa
to 0.1 MPa in 4 hours using air at 32.degree. C. according to the
same procedure as the first procedure; fourth, the
oxygen-containing gas was increased from 200 Pa to 0.1 MPa in 4
stages total 2 hours using air at 32.degree. C.: (200 Pa-0.01
MPa)/30 minutes, (0.01 MPa-0.03 MPa)/30 minutes, (0.03 MPa-0.06
MPa)/30 minutes, (0.06 MPa-0.10 MPa)/30 minutes. The four
passivations were carried out in total 14 hours. During the whole
procedure, the temperature in the furnace was firstly elevated
gradually to 33.degree. C., then the temperature was gradually
steady and varied between 28.degree. C. and 32.degree. C. After
discharging, the tantalum powder was taken out, no violent
oxidation phenomenon occurred. The heat treated tantalum powder was
passed through 80 mesh screening to obtain S-2h tantalum powder.
The oxygen and hydrogen contents of the tantalum powder were
analyzed, the results were shown in Table 1, 2 wt % Magnesium
powder based on the tantalum powder was blended in the S-2h
tantalum powder to form a mixed powder, the mixed powder was
charged into the tantalum powder deoxidization reaction vessel as
shown in FIG. 7, held at 850.degree. C. for 3 hours to carry out
deoxidization treatment, the heating was stopped, and the
temperature was lowered, and the treated tantalum powder was
nitridated at 280.degree. C., and then the temperature of the
tantalum powder in the reaction vessel was lowered to 31.degree.
C., an oxygen-containing gas at -10.degree. C. to -40.degree. C.
was introduced in 4 times, according to the passivation procedure
similar to the heat treatment as described above, and the tantalum
powder was passivated using an oxygen-containing gas with an oxygen
concentration of about 5 vol. %, 10 vol. %, 21 vol. % and 21 vol.
%, the first 3 passivations were carried out for 3 hours each, and
the last passivation was carried out for 2 hours, total 11 hours.
After discharging, the passivated tantalum powder was pickled,
washed with water, and dried to obtain S-2d tantalum powder. The
oxygen and hydrogen contents of the tantalum powder were analyzed,
the results were shown in Table 1. The electric performance of the
tantalum powder was determined, and the results were shown in Table
2.
Example 3
[0082] The heat treatment device shown in FIG. 3 was used, and the
same tantalum powder as in Example 1 was subjected to heat
treatment under the same condition as described in Example 1. After
the heat treatment, the shell was cooled with water to lower the
temperature, and argon was introduced for 12 hours to lower the
temperature to 30.degree. C., and the tantalum powder was
passivated. The passivation process comprises: evacuating the argon
in the furnace to about 200 Pa, the refrigeration system 390A of
oxygen-containing gas was actuated to make air and argon enter into
the heat exchange chamber 391 respectively from 392 and 393
according to following conditions, mix and undergo heat exchange
with 394, and then came out from the outlet 395, passed through the
thermal insulation pipeline 396, and entered the hearth 310 from
the inlet 320; first, the oxygen-containing gas with an oxygen
concentration of about 5 vol. % was cooled to -20.degree. C. to
-40.degree. C. and increased in stages from 200 Pa to 0.1 MPa: (200
Pa-0.005 MPa)/30 minutes, (0.005 MPa-0.01 MPa)/30 minutes, (0.01
MPa-0.02 MPa)/30 minutes, (0.02 MPa-0.03 MPa)/30 minutes, (0.03
MPa-0.045 MPa)/30 minutes, (0.045 MPa-0.06 MPa)/30 minutes, (0.06
MPa-0.08 MPa)/30 minutes, (0.08 MPa-0.1 MPa)/30 minutes, total 4
hours; second, the oxygen-containing gas at -20.degree. C. to
-40.degree. C. with an oxygen concentration of about 10 vol. % was
increased from 200 Pa to 0.1 MPa in 4 hours according to the first
aeration procedure; third, the pressure was increased from 200 Pa
to 0.1 MPa in 4 hours using air at -20.degree. C. to -40.degree. C.
according to the same procedure as the first procedure; fourth, the
pressure was increased from 200 Pa to 0.1 MPa in 4 stages using air
at -20.degree. C. to -40.degree. C.: (200 Pa-0.01 MPa)/30 minutes,
(0.01 MPa-0.03 MPa)/30 minutes, (0.03 MPa-0.06 MPa)/30 minutes,
(0.06 MPa-0.10 MPa)/30 minutes. The four passivations were carried
out in total 14 hours. The temperature in the furnace was firstly
elevated gradually to 35.degree. C., then the temperature was
gradually steady and varied between 32.degree. C. and 35.degree. C.
After discharging, the tantalum powder was taken out, no violent
oxidation phenomenon occurred. The heat treated tantalum powder was
passed through 80 mesh screening to obtain S-3h tantalum powder.
The oxygen and hydrogen contents of the tantalum powder were
analyzed, the results were shown in Table 1. 2 wt % magnesium
powder based on the tantalum powder was blended in the tantalum
powder S-3h to form a mixed powder, the mixed powder was charged
into the tantalum powder deoxidization reaction vessel as shown in
FIG. 8, held at 850.degree. C. for 3 hours to carry out
deoxidization treatment, the heating was stopped, and the
temperature was lowered, and the treated tantalum powder was
nitridated at 280.degree. C., and then forcedly cooled with argon,
when the temperature of tantalum powder was lowered to 15.degree.
C., an oxygen-containing gas at -10.degree. C. to -40.degree. C.
was introduced in 4 times, according to the passivation procedure
similar to the heat treatment as described above, the tantalum
powder was passivated with an oxygen-containing gas with an oxygen
concentration of about 5 vol. %, 10 vol. %, 21 vol. % and 21 vol.
%, the first 3 passivations were carried out for 3 hours each, and
the last passivation was carried out for 2 hours, total 11 hours.
After discharging, the passivated tantalum powder was pickled,
washed with water, and dried to obtain S-3d tantalum powder. The
oxygen and hydrogen contents of the tantalum powder were analyzed,
the results were shown in Table 1. The electric performance of the
tantalum powder was determined, and the results were shown in Table
2.
Comparative Example 1
[0083] The same tantalum powder as in Example 1 was employed, and
the heat treatment was carried out at same temperature, after
heating was stopped, the temperature was lowered to 200.degree. C.
in vacuum, and argon was introduced to cool for 12 hours, when the
temperature was lowered to 32.degree. C., the passivation was
begun; the passivation process comprises: evacuating the argon in
the furnace to about 200 Pa, first, air at 31.degree. C. was
introduced into the heat treatment furnace in 8 stages to increase
the pressure in the furnace from 200 Pa to 0.1 MPa: (200 Pa-0.005
MPa)/120 minutes, (0.005 MPa-0.01 MPa)/60 minutes, (0.01 MPa-0.02
MPa)/60 minutes, (0.02 MPa-0.03 MPa)/60 minutes, (0.03 MPa-0.045
MPa)30 minutes, (0.045 MPa-0.06 MPa)/30 minutes, (0.06 MPa-0.08
MPa)/30 minutes, (0.08 MPa-0.1 MPa)/30 minutes, total 7 hours,
wherein the temperature elevated suddenly for 6 times during the
aeration, the highest temperature was up to 60.degree. C.; when it
was found that the temperature elevated suddenly, the aeration was
stopped immediately; and after the temperature was lowered to about
32.degree. C., the aeration in the furnace was carried out again.
Second, air at 31.degree. C. was introduced into the heat treatment
furnace in 8 stages to increase the pressure in the furnace from
200 Pa to 0.1 MPa: (200 Pa-0.005 MPa)/60 minutes, (0.005 MPa-0.01
MPa)/60 minutes, (0.01 MPa-0.02 MPa)/60 minutes, (0.02 MPa-0.03
MPa)/60 minutes, (0.03 MPa-0.045 MPa)30 minutes, (0.045 MPa-0.06
MPa)/30 minutes, (0.06 MPa-0.08 MPa)/30 minutes, (0.08 MPa-0.1
MPa)/30 minutes, total 6 hours; wherein the temperature elevated
suddenly once to 50.degree. C. The third operation is the same as
the second operation, air at 31.degree. C. was introduced into the
heat treatment furnace, and the passivation was carried out for 6
hours. Fourth, the pressure was increased from 200 Pa to 0.1 MPa in
4 stages using air at 31.degree. C.: (200 Pa-0.01 MPa)/30 minutes,
(0.01 MPa-0.03 MPa)/30 minutes, (0.03 MPa-0.06 MPa)/30 minutes,
(0.06 MPa-0.10 MPa)/30 minute, total 2 hours. The four passivations
were carried out in total 21 hours. After the passivation, the
tantalum powder was taken out, and generated heat seriously. The
heat treated tantalum powder was passed through 80 mesh screening
to obtain E-1h tantalum powder. The oxygen and hydrogen contents of
the tantalum powder were analyzed, the results were shown in Table
1. 2 wt % magnesium powder based on the tantalum powder was blended
to form a mixed powder, the mixed powder was charged into the
tantalum powder deoxidization reaction vessel as shown in FIG. 5,
held at 850.degree. C. for 3 hours to carry out deoxidization
treatment, the heating was stopped, and the temperature was
lowered, and the treated tantalum powder was nitridated at
280.degree. C., according to the passivation procedure similar to
the heat treatment as described above, when the temperature was
lowered to 31.degree. C., air at 31.degree. C. was introduced in 4
times to carry out passivation. The first 3 passivations were
carried out in 8 stages for 5 hours each, and the fourth
passivation was carried out in 4 stages for 2 hours, total 17
hours. The passivated tantalum powder was pickled, washed with
water, and dried to obtain E-1d tantalum powder. The oxygen and
hydrogen contents of the tantalum powder were analyzed, the results
were shown in Table 1. The electric performance of the tantalum
powder was determined, and the results were shown in Table 2.
TABLE-US-00001 TABLE 1 the oxygen and hydrogen contents of the
tantalum powder tantalum powder No. O H S-1h 10600 70 S-1d 3800 140
S-2h 11300 78 S-2d 4100 140 S-3h 11600 60 S-3d 4000 130 E-1h 16500
180 E-1d 5800 200
TABLE-US-00002 TABLE 2 Measurement results of electric performance
of tantalum powder tantalum powder Leakage current Specific
capacity Loss No. nA/g .mu.F v/g (tg .delta.) % S-1d 58 85860 30.5
S-2d 59 85800 31.1 S-3d 59 84900 32.8 E-1d 126 85000 45.2
[0084] As seen from the results of Tables 1 and 2, the method of
present invention has the advantages of short production period,
and the tantalum powder prepared has low oxygen and hydrogen
contents, and low leakage current.
Example 4
[0085] The tantalum powder S-1d in Example 1, after deoxidization
heat treatment, was compacted into a cylindrical compact with a
density of 4.5 g/cm.sup.3, a diameter of 3.0 mm and a height of
4.72 mm, in which 0.3 mm tantalum wire was embedded, each compact
contained about 150 mg of tantalum powder; in a device as shown in
FIG. 4, the compact was sintered at 1320.degree. C. for 10 minutes
to form a tantalum agglomerate, and then heating was stopped, the
temperature was lowered to 200.degree. C., argon was introduced,
and the forced-cooling argon system 400A was actuated, the cooling
was carried out for about 3 hours to lower the temperature in the
furnace to 20.degree. C., and the tantalum agglomerate was
passivated. The passivation process comprises: evacuating the argon
in the furnace to a vacuum of about 200 Pa; first, an
oxygen-containing gas at -10.degree. C. to -40.degree. C. in a
concentration of about 10 vol. % was introduced into the heat
treatment furnace in 5 stages and 3 hours to increase the pressure
in the furnace from 200 Pa to 0.1 MPa: (200 Pa-0.01 MPa)/40
minutes, (0.01 MPa-0.03 MPa)/40 minutes, (0.03 MPa-0.05 MPa)/40
minutes, (0.05 MPa-0.07 MPa)/30 minutes, (0.07 MPa-0.1 MPa)/30
minutes. Second, air at -10.degree. C. to -40.degree. C. was
introduced into the heat treatment furnace in 4 stages and 2 hours
to increase the pressure in the furnace from 200 Pa to 0.1 MPa:
(200 Pa-0.01 MPa)/30 minutes, (0.01 MPa-0.03 MPa)/30 minutes, (0.03
MPa-0.06 MPa)/30 minutes, (0.06 MPa-0.10 MPa)/30 minutes. The two
passivations were carried out in total 5 hours. During the whole
procedure, the temperature in the furnace was firstly elevated
gradually to 32.degree. C., then the temperature was gradually
steady and varied between 29.degree. C. and 31.degree. C., and
finally the temperature was lowered gradually to 29.degree. C.
After discharging, the tantalum powder was taken out, and a
tantalum agglomerate S-4 was obtained. The oxygen and hydrogen
contents of the tantalum agglomerate were analyzed, the results
were shown in Table 3. The agglomerate was placed in 0.1 mass %
phosphoric acid at 80.degree. C., the voltage was raised at current
density of 60 mA/g to 30 V and maintained constant pressure for 120
minutes to form a tantalum anode S-4a; the leakage current of the
anode was determined in 0.1 mass % phosphoric acid at 25.degree.
C., and the specific electric capacity (specific capacity) and loss
were determined in 20 mass % of sulfuric acid solution, the results
were shown in Table 4.
Comparative Example 2
[0086] The same tantalum powder as in Example 4 was compacted into
same tantalum compact, and sintered under same condition, the
temperature was lowered to 200.degree. C., argon was introduced to
cool for about 6 hours to lower the temperature in the furnace to
33.degree. C., and tantalum agglomerate was passivated. The
passivation process comprises: evacuating the argon in the furnace
to a vacuum of about 200 Pa, first, air at 32.degree. C. was
introduced into the heat treatment furnace in 6 stages and 4.5
hours to increase the pressure in the furnace from 200 Pa to 0.1
MPa: (200 Pa-0.005 MPa)/60 minutes, (0.005 MPa-0.01 MPa)/30
minutes, (0.01 MPa-0.02 MPa)/30 minutes, (0.02 MPa-0.03 MPa)/30
minutes, (0.03 MPa-0.05 MPa)30 minutes, (0.05 MPa-0.06 MPa)/30
minutes, (0.06 MPa-0.08 MPa)/30 minutes, (0.08 MPa-0.1 MPa)/30
minutes. Second, air at 32.degree. C. was introduced into the heat
treatment furnace in 4 stages and 2 hours to increase the pressure
in the furnace from 200 Pa to 0.1 MPa: (200 Pa-0.01 MPa)/30
minutes, (0.01 MPa-0.03 MPa)/30 minutes, (0.03 MPa-0.06 MPa)/30
minutes, (0.06 MPa-0.10 MPa)/30 minutes. The two passivations were
carried out in total 6.5 hours. During the whole procedure, the
temperature in the furnace was firstly elevated gradually to
41.degree. C., After discharging, the tantalum agglomerate was
taken out to obtain tantalum agglomerate E-2s. The oxygen and
hydrogen contents of the tantalum agglomerate were analyzed, the
results were shown in Table 3. The agglomerate was formed to an
anode E-2a under the same condition as described in Example 3. The
electric performance of the agglomerate was determined, and the
results were shown in Table 4.
TABLE-US-00003 TABLE 3 the oxygen and hydrogen contents of the
tantalum agglomerate tantalum agglomerate No. O H S-4 5200 30 E-2
6500 70
TABLE-US-00004 TABLE 4 Measurement results of electric performance
of tantalum agglomerate tantalum powder Leakage current Specific
capacity Loss No. nA/g .mu.F v/g (tg .delta.) % S-4 48 85800 30.1
E-2 93 84000 44.8
[0087] It was seen from above description that the heat treatment
of tantalum powder by the inventive method is safe and reliable,
has high yield, and tantalum powder does not burn, and the tantalum
powder prepared has low oxygen and hydrogen contents, and the anode
prepared from the tantalum powder has low leakage current and good
electric performance.
[0088] In the above description, although the description is mainly
directed to tantalum powder, a person skilled in the art can
envisage that present invention is also suitable for other active
metal powders, such as niobium powder.
* * * * *