U.S. patent application number 09/805274 was filed with the patent office on 2001-08-23 for apparatus for producing high-purity silver materials.
This patent application is currently assigned to DOWA MINING CO., LTD.. Invention is credited to Miura, Hiroshi, Ohgami, Takashi, Tayama, Kishio.
Application Number | 20010015113 09/805274 |
Document ID | / |
Family ID | 16099403 |
Filed Date | 2001-08-23 |
United States Patent
Application |
20010015113 |
Kind Code |
A1 |
Tayama, Kishio ; et
al. |
August 23, 2001 |
Apparatus for producing high-purity silver materials
Abstract
The novel apparatus for producing high-purity silver comprises
an electric furnace 1, an outer cylinder 3 contained in the furnace
in such a way that it can be evacuated with a vacuum pump 2, a feed
crucible 5 placed within the outer cylinder 3 and fixed onto an
aspiration table 9 provided in the center of a recovery mold 6, a
cooling trap 8 and a water-cooled flange 7 that are detachably
connected to the other parts including an inner cylinder 4 located
over the crucible 5. When a silver feed is heated within the
crucible at 3a specified temperature and pressure, the silver
evaporates and condenses on the ceiling of the inner cylinder to
yield silver particles, which are collected in the recovery mold;
gold, copper and other impurities having higher vapor pressures
than silver are left within the crucible whereas sulfur, sodium and
other impurities having higher vapor pressures are withdrawn by
means of the vacuum pump to be introduced into the cooling trap and
hereafter solidified. The recovered silver has a purity of at least
99.9999 wt %, with the total of impurities less than 1 ppm. This
high-purity silver is drawn into wires having sufficiently high
levels of purity to warrant their use in recording, acoustic or
image transmission applications.
Inventors: |
Tayama, Kishio; (Tokyo,
JP) ; Ohgami, Takashi; (Tokyo, JP) ; Miura,
Hiroshi; (Yokohama-shi, JP) |
Correspondence
Address: |
FRISHAUF, HOLTZ, GOODMAN, LANGER & CHICK, P.C.
25th Floor
767 Third Avenue
New York
NY
10017-2023
US
|
Assignee: |
DOWA MINING CO., LTD.
Tokyo
JP
|
Family ID: |
16099403 |
Appl. No.: |
09/805274 |
Filed: |
March 13, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09805274 |
Mar 13, 2001 |
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09256115 |
Feb 24, 1999 |
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6231637 |
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09256115 |
Feb 24, 1999 |
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08814112 |
Mar 10, 1997 |
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Current U.S.
Class: |
75/634 ; 266/208;
420/501 |
Current CPC
Class: |
C22B 9/04 20130101; Y02P
10/20 20151101; C22B 9/02 20130101; C22B 11/00 20130101; B22F
2998/10 20130101; Y02P 10/234 20151101; B22F 2998/10 20130101; B22F
9/12 20130101; B22F 5/12 20130101 |
Class at
Publication: |
75/634 ; 420/501;
266/208 |
International
Class: |
C21C 007/10; C22C
005/06; C22B 011/00; C22B 011/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 21, 1996 |
JP |
181362/1996 |
Claims
What is claimed is:
1. A high purity silver wire for use in recording, acoustic or
image transmission applications, which contains sulfur, iron,
copper, palladium, gold and lead in such amounts that none of them
will exceed 0.5 ppm as they are taken individually and wherein any
other impurities that can be measured in amounts not less than the
respective lower limits of detection add up to less than 1 ppm.
2. A high purity silver wire for use in recording, acoustic or
image transmission applications according to claim 1, which has a
purity of at least 99.9999 wt % with a total impurity content of
less than 1 ppm as measured by glow discharge mass spectrometric
analysis.
3. A high purity silver wire for use in recording, acoustic or
image transmission applications, said silver wire being produced by
drawing high-purity silver with a purity of at least 99.9999 wt %
that has a total impurity content of less than 1 ppm as measured by
glow discharge mass spectrometric analysis, said high-purity silver
being produced by using a special vacuum distillation refiner that
comprises an electric furnace, an outer cylinder contained in the
electric furnace in such a way that it can be evacuated with a
vacuum pump, a feed crucible placed within the outer cylinder and
fixed onto an aspiration table provided in the center of a recovery
mold, a cooling trap and a water-cooled flange that are detachably
connected to the other parts including an inner cylinder located
over the crucible.
4. A process for producing high-purity silver materials which
comprises placing a silver feed in a crucible located under an
inner cylinder contained in an outer cylinder which is placed in a
furnace; heating the silver feed within the crucible at a
temperature not lower than 1065.degree. C. and at a pressure not
higher than 0.1 Pa in such a manner that the silver may evaporate
and condense on the ceiling of the inner cylinder to yield silver
particles, which are collected in a recovery mold placed beneath
the crucible within the inner cylinder, with gold, copper and other
impurities having lower vapor pressures than silver being left
within the crucible whereas sulfur, sodium and the other impurities
having higher vapor pressures than silver are withdrawn by means of
a vacuum pump to be introduced into a cooling trap placed beneath
the recovery mold, said higher vapor pressure impurities being
solidified in said cooling trap.
5. The process according to claim 4, wherein said silver feed
within the crucible is heated at a temperature in the range of
1200-1350.degree. C. and at a pressure in the range of 0.02 Pa or
less.
6. The process according to claim 4, wherein said recovery mold is
made in the shape of a mold which is to be used in a step
subsequent to the purifying process.
7. An apparatus for producing high-purity silver materials which
comprises an electric furnace, and outer cylinder contained in the
electric furnace in such a way that it can be evacuated with a
vacuum pump, a feed crucible placed within the outer cylinder and
fixed onto an aspiration table provided in the center of a recovery
mold, a cooling trap and a water-cooled flange that are detachably
connected to the other parts including an inner cylinder located
over the crucible.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to silver wires for use in video
display apparatus such as VTR or TV or in audio equipment.
[0002] Conductors conventionally used in recording, acoustic or
image transmission applications are made of annealed copper wires,
which are produced by cold working oxygen-free or tough pitch
copper with a purity of about 99.9 wt % followed by annealing, or
copper wires prepared by plating such annealed copper wires.
[0003] With copper wires having purities on the order of 99.9 wt %,
signals cannot be transmitted correctly without phase differences
and, as a result, only blurred images or unsharp sounds are
produced. To solve these problems, high-purity copper wires
produced by working raw materials having purities of at least
99.999 wt % have recently been introduced into the market.
[0004] Similar effects are exhibited by silver wires that are
produced by a process which comprises solidifying silver with a
purity of at least 99.95 wt % in one longitudinal direction to
yield an ingot, drawing it by either cold or warm working and
further working the wire under conditions that will not cause
recrystallization. This process is described in Unexamined
Published Japanese Patent Application No.163505/1986 under the
title of "A Process for Producing Conductors for Use in Video
Display Apparatus or Audio Equipment". However, the demand of the
market has solely been for high-purity copper wires.
[0005] Thus, in the metal purifying technology, 6N and 7N copper
materials have successfully been developed (purities of at least
99.9999 wt % will hereunder be designated as "6N" and purities of
at least 99.99999 wt % as "7N"); on the other hand, practically
feasible methods of purifying silver materials are yet to be
developed and no silver wires of high purity have been produced
that can be tested for their performance to thereby obtain data
that compare with high-purity copper wires.
SUMMARY OF THE INVENTION
[0006] An object, therefore, of the invention is to establish a
process for producing high-purity silver materials by novel means
and thereafter work them into wires, thereby providing high-purity
silver wires suitable for use in recording, acoustic or image
transmission applications.
[0007] The present inventors conducted intensive studies with a
view to attaining the stated object and found that by using a
special vacuum distillation refiner, high-purity silver with a
purity of at least 99.9999 wt % could be obtained that had a total
impurity content of less than 1 ppm as measured by glow discharge
mass spectrometric analysis. When high-purity silver wires drawn
from this raw material were assembled into video display apparatus
or audio equipment, there could be produced images or sounds that
were sharper than those obtained with the conventional high-purity
copper wires. The present invention has been accomplished on the
basis of this finding.
[0008] Thus, the stated object of the invention can be attained by
a high-purity silver wire for use in recording, acoustic or image
transmission applications, which contains sulfur, iron, copper,
palladium, gold and lead in such amounts that none of them will
exceed 0.5 ppm as they are taken individually and wherein any other
impurities that can be measured in amount not less than the
respective lower limits of detection add up to less than 1 ppm.
BRIEF DESCRIPTION OF THE DRAWING
[0009] FIG. 1 is a vertical section showing schematically an
apparatus for producing the high-purity silver of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0010] An exemplary apparatus for producing high-purity silver for
use in the present invention is shown schematically in FIG. 1. An
electric furnace 1 contains an outer quartz cylinder 3 which is
adapted to be capable of being evacuated with a vacuum pump 2. The
outer cylinder 3 contains a feed crucible 5, a recovery mold 6, a
cooling trap 8 and a water-cooled flange 7 that are connected
together in a detachable manner, and an inner quartz cylinder 4 is
mounted over the feed crucible.
[0011] A suitable amount of silver feed (with a purity of about
99.99 wt %) is charged into the crucible 5 and heated in the
electric furnace at a temperature of at least 1065.degree. C.,
preferably between 1200 and 1350.degree. C. , with the degree of
vacuum being controlled at 0.1 Pa or below, preferably 0.02 Pa or
below; as a result, the silver feed in the crucible evaporates and
condenses on the ceiling of the inner quartz cylinder to yield
purified silver particles, which drop between the crucible 5 and
the inner quartz cylinder 4 and thereafter fall into the recovery
mold 6 which is connected to the bottom of the crucible.
[0012] While the silver feed contains various kinds of impurities,
those which have lower vapor pressures than silver such as gold,
copper, palladium and iron will remain in the crucible 5 whereas
those having higher vapor pressures such as sulfur, sodium, calcium
and lead will not condense but remain in a gaseous form that is
withdrawn by means of the vacuum pump 2 to be introduced into the
cooling trap 8 via a suction hole in the bottom of the crucible;
thereafter, those impurity gases are cooled to solidify by the
action of the water-cooled flange 7.
[0013] In the present invention, the recovery mold already assumes
the shape of the mold which is to be used in a step subsequent to
the purifying process; hence, there is no need to recast the
purified silver as in the prior art and less contaminated
high-purity silver can be produced by a simple process having no
distinction between purifying and casting stages.
[0014] Then, with the temperature in the recovery mold maintained
at 1300.degree. C. , the silver is hot- and cold-worked into a wire
(1.5 mm.sup..phi.) under ordinary conditions. Analysis with a glow
discharge mass spectrometer revealed that none of the sulfur, iron,
copper, palladium, gold and lead contents was more than 0.5 ppm
whereas other impurities such as sodium, silicon, potassium,
calcium, chromium and nickel, of which the detection limits on the
glow discharge mass spectrometer were each 0.1 ppm and below, were
present in a total amount of less than 1 ppm.
[0015] The following example is provided for the purpose of further
illustrating the present invention but is in no way to be taken as
limiting.
EXAMPLE
[0016] FIG. 1 is a vertical section showing schematically the
apparatus for producing the high-purity silver of the invention and
reference will be made to this Figure in the following
description.
[0017] First, 100 g of electrolytic silver with a purity of 99.99
wt % was charged into a feed crucible 5, which was fixed onto an
aspiration table 9 installed in the center of a recovery mold 6.
The assembly was then set up in an electric furnace 1 as shown in
FIG. 1.
[0018] The feed crucible 5 and the recovery mold 6 were enclosed
with an outer cylinder 3 and an inner cylinder 4 both of which were
made of quartz. A vacuum pump 2 would cause the air within the
inner cylinder 4 to be withdrawn through a hole (not shown) in the
upper part of the aspiration table 9 until a vacuum was drawn into
the inner cylinder 4.
[0019] After the feed crucible 5 was set up in the electric furnace
1, the vacuum pump 2 was operated to lower the pressure in the
inner cylinder 4 down to 0.01 Pa. Upon 5-min purification at a
furnace temperature of 1300.degree. C., the silver in the feed
evaporated and contacted the ceiling of the inner cylinder 4 over
the feed crucible 5, whereupon it began condensing slowly to form
particles, which dropped into the recovery mold 6 provided beneath
the feed crucible 5.
[0020] Impurities in the feed that had higher vapor pressures than
silver remained gaseous and were aspirated by means of the vacuum
pump to pass through the holes in the upper part of the aspiration
table and thereafter solidified on the cooling trap. Analysis
showed that the solidified product was chiefly composed of
substances of high vapor pressure such as sulfur, sodium, calcium
and lead. The metal left in the feed crucible was also analyzed,
revealing that it was chiefly composed of substances of low vapor
pressure such as gold, copper, palladium and iron.
[0021] In the next step, the purified silver in the recovery mold 6
was drawn into a silver wire (11 mm.sup..phi.) as it was cooled by
passage through a withdrawing port (not shown) provided on a
lateral side of the mold. The thus prepared raw material was hot-
and cold- drawn under ordinary conditions into a thinner silver
wire having a diameter of 1.5 mm. The silver wire was then analyzed
for the concentration of impurities by means of a glow discharge
mass spectrometer and the results are shown in Table 1.
[0022] The high-purity silver wire was further drawn to a diameter
of 0.1-0.3 mm. A plurality of such wires were prepared, braided
together and extrusion coated with a resin (PVC) insulator.
Alternatively, individual wires were coated with the same
insulator. Such wires were processed into speaker cords and audio
pin cords, each of the latter being fitted with a plug on both
ends; the cords were connected to a stereophonic system for sound
reproduction. For comparison, commercial 4N and 6N copper wires
were processed into the same cords and connected to the
stereophonic system. The sound reproduced with the high-purity
silver wires of the present invention had very high levels of
reverberation at high pitch, provided a very good sound field
effect, offered very good localization and was characterized by
salient tone colors.
1TABLE 1 Impurity levels, ppm Na Si S K Ca Cr Fe Ni Cu Pd Au Pb
Example 1 <0.01 <0.01 0.05 <0.01 <0.01 <0.01 0.04
<0.01 0.01 <0.01 <0.1 <0.01
[0023] The high-purity silver wires of the invention were also
compared with the conventional products in terms of image quality.
The results are shown in Table 2; very sharp images were produced
with the invention wires.
2 TABLE 2 Image sharpness Acoustic quality Invention Very sharp
Very high reverberation Ag wire of treble level and good woofing of
bass level 4N Cu wire Less sharp Acceptable 6N Cu wire Moderate
Very high reverberation of treble level
[0024] As described above, the present inventions for the first
time succeeded in establishing a practically feasible process for
the production of very high-purity silver (>99.9999 wt %) and
the high-purity silver wire of the invention can be easily prepared
by drawing the very-high purity silver produced by that process.
Using the thus prepared silver wire one can realize further
improvements in acoustic and image characteristics.
* * * * *