JPH02185990A - Ultrahigh purity copper and production thereof - Google Patents

Abstract

PURPOSE:To produce ultrahigh purity copper having a specified elongation and a specified hardness at ordinary temp. by using high purity copper as raw material to ge refined and carrying out primary electrolytic refining in a copper sulfate soln. acidified with sulfuric acid and secondary electrolytic refining in a copper nitrate soln. acidified with nitric acid. CONSTITUTION:High purity copper is electrolytically refined as the anode in a copper sulfate soln. acidified with sulfuric acid at <=100A/m<2> cathode and anode current densities to obtain primarily refined copper on a starting sheet as the cathode. This refined copper is electrolytically refined again as the anode in a copper nitrate soln. acidified with nitric acid at <=100A/m<2> cathode and anode current densities to obtain secondarily refined copper on a starting sheet as the cathode. This refined copper is ultrahigh purity copper having >=99.99999% (7N) purity, >=30% elongation and <=42 Vickers hardness at ordinary temp. The electrolytic solns. in the 1st and the 2nd stages are preferably kept at 30-50 deg.C. Ag and S can be remarkably removed by shifting the potential of each of the electrolytic solns. to an extremely low potential region.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to ultra-high purity copper with a purity of 99.99999% (7N) or more and a method for producing the same, and in particular to an elongation of 3.
The present invention relates to a steel material suitable for new uses such as IC bonding wire, which has properties close to gold, such as a Vickers hardness of 0% or more and a Vickers hardness of 42 or less.

[Prior art] Conventionally, methods for producing high-purity copper include repeating the sulfuric acid acidic copper sulfate electrolysis method, nitric acid acidic copper nitrate electrolysis method, or zone melting refining method several times, or refining using a combination of these methods. There were known ways to do it.

However, these conventional methods have a final purity of 5N~
It was known that 6N is the limit, and that the unavoidable impurities that are most difficult to remove in that case are mainly Ag and S.

[Problem to be solved by the invention] However, in recent years, in new fields such as electronics fields such as IC bonding wires and superconducting stabilizing materials, even Ag1 and S, which were previously allowed to be mixed in to a certain extent as unavoidable impurities, are being introduced. It has been desired to have an abundant supply of 7N grade ultra-high purity copper material that has been thoroughly removed. However, with conventional manufacturing techniques, it is difficult to achieve the above-mentioned purity, and some kind of solution has been desired.

[Means for Solving the Problems] As a result of intensive research in order to solve the problems, the present inventors have succeeded in extremely strictly controlling various conditions such as liquid temperature, liquid potential, and the type and amount of additives. Meanwhile, using high purity copper as a refining raw material as an anode and a sulfuric acid acidic copper sulfate solution as an electrolyte, refining electrolysis is performed at a cathode and anode current density of 100 A/m2 or less, and primary refined copper is deposited on a cathode seed plate. After obtaining the obtained copper, purification electrolysis is performed using the primary purified copper as the anode and the nitric acidic copper nitrate solution as the electrolyte at a cathode and anode current density of 100 A/rrr or less, and a second layer is formed on the cathode seed plate. We have discovered that it is possible to stably produce ultra-high purity copper of 99.99999% (7N) or higher by carefully carrying out a two-stage refining electrolysis process consisting of obtaining second refined copper. The present invention has been achieved. Furthermore, in the above electrolytic refining method, it was discovered that Ag and S could be removed extremely significantly by shifting the electrolytic solution potential during electrolysis to an extremely low potential region, and hydrogen gas was used as a medium to adjust the solution potential. or/and the presence of hydrazine or/and other reducing agents has been found to be very effective.

That is, the inventors of the present invention intentionally shifted the branch potential during electrolysis, preferably by using a reducing agent, to a low potential region that cannot normally be reached in the refining of copper by the conventional general electrolytic refining method. For example, in sulfuric acid acidic copper sulfate electrolysis, Ag can be removed more strongly, and conventional Ag
Even in nitric acid-acidic copper nitrate electrolysis, which was considered to be unsuitable for the removal of S, it was confirmed that Ag was removed even at the microscopic two-person g level, and S was completely removed.

That is, the present invention intentionally lowers the liquid potential by the above method, and more preferably by acting on the electrolytic bath with, for example, hydrogen gas or/and hydrazine or/and other applicable reducing agents. Purity of 99.99999% (7N) is achieved by electrolytically refining in a liquid potential range that normally does not exist.
The present invention provides a completely new copper electrolytic refining method that can produce the ultra-high purity copper described above. The product obtained by this method has an elongation at room temperature of 30% or more, a Vickers hardness of 42 or less, and a purity of 99.9999.
It is ultra-high purity copper characterized by having a content of 9% (7N) or more.

[Function] In the present invention, the first step is primary purification by sulfuric acid acidic copper sulfate electrolysis, and the subsequent second step is secondary purification by nitric acidic copper nitrate electrolysis, and preferably in these electrolytic steps. This is an electrolytic refining method for copper characterized in that the electrolytic bath potential is intentionally controlled to an extremely low potential level. That is,
The refining process consists of two stages of electrolytic refining. If necessary, it is also possible to further improve the purity by subjecting the second refined copper to vacuum degassing treatment and then vacuum casting.

The following two routes for the discharge deposition of Ag onto the cathode in the electrolytic refining of copper can be broadly classified.

(2) Due to the increase in anode polarization pressure, some Ag is electrochemically eluted and deposited on the cathode.

■Spontaneous dissolution of Ag occurs from the anode slime, diffuses to the cathode, and is deposited by discharge.

In order to prevent the elution of Ag through the route (2) above, it is necessary to lower and maintain the anodic polarization pressure, which requires setting the anode current density low and adjusting the copper concentration of the electrolyte to the cathode electrodeposition state. It is important to keep it as low as possible without causing any problems. Furthermore, by lowering the copper concentration in the electrolyte, the anode slime can be easily separated from the anode dissolution surface, copper ions near the anode dissolution surface are diffused and anions are sufficiently replenished, and the anode polarization pressure is reduced. reduction is achieved.

In the method of the present invention, the copper concentration of the electrolyte in both the first and second steps is 30 g/! I or less, and the anode current density is 1.00 A/r at the end of electrolysis.
It is set with consideration given to not exceeding rl'.

Also, regarding both (1) and (2), setting the temperature of the electrolytic solution is an important factor. That is, setting a high temperature causes a decrease in the anodic polarization pressure, which is desirable for (2), but promotes spontaneous dissolution of Ag (2), and is thought to decrease the cathode polarization pressure, resulting in rough cathode electrodeposition.

Therefore, in the present invention, temperature selection was comprehensively judged from the viewpoints of anode and cathode polarization pressures, elution of slime, etc., and 30 to 50°C was determined to be the optimum temperature range. In the present invention, for example, sulfuric acid acidic copper sulfate electrolysis (
For example, Cu: 25g/D.

F, A, 160g/l, cathode and anode current density 90
In A/G), an anodic passivation phenomenon occurred at an electrolytic solution temperature of 20° C., and an increase in Ag in the recovered electrolytic copper was observed. On the other hand, in the high-temperature electrolytic test (60°C), the effect of gelatin as a smoothing agent weakened due to the decrease in cathodic polarization pressure.
Extremely rough cathode electrodeposition occurred, and local entrainment of the electrolyte was observed. Therefore, the electrolyte temperature in the method of the present invention needs to be higher than 20°C and lower than 60°C. Desirable liquid temperature is 30 to 50°C, more preferably 4°C.
It was confirmed that the temperature was 0±5°C.

On the other hand, a method in which free chlorine is allowed to coexist in electrolytic refining of copper for the purpose of removing Ag in an electrolytic solution is known.

In the first step of the method of the present invention, the amount of free chlorine added is 100 to 500 mg/I, compared to the conventional method where the amount of free chlorine added is 30 to BO + ng/I).
is used. A more preferable addition amount is 150 to 250
11g/l. The reason for increasing the amount added compared to the conventional one is that in addition to free chlorine, which contributes to the purpose of more actively removing Ag, the combination effect with gelatin causes a noticeable smoothing tendency in the cathode electrodeposition state. This is because it was discovered that the presence of free chlorine is necessary to improve the

Note that the second step is usually the final step of purification, so
For the purpose of preventing contamination, it is preferable to use a pure nitric acidic copper nitrate bath without adding any free chlorine. In the method of the present invention, sulfuric acid acidic copper sulfate electrolysis is adopted in the first step, and the electrolytic conditions are usually copper concentration 30 g/p or less, free sulfuric acid 160 to 180 g/Ω, temperature 30 to 50°C, and free chlorine. 100-500mg/l! , 30 to 80 g/gelatin can be electrodeposited copper. An example of more preferable electrolytic conditions is a copper concentration of 20 to 25 g/i) and a free sulfuric acid concentration of 170 g/i.
g/j), temperature 40±5℃, free chlorine 150-250
mg/N, and the cathode and anode current densities are 1-00A/N.
rd or less, preferably 50A/ or less.

In the second step, the electrolytic copper (primary refined copper) obtained in the first step is used as an anode, and electrolytic refining is usually performed in a nitric acidic copper nitrate bath having a pH of around 1.5. The conditions such as copper concentration, electrolyte temperature, and current density may be exactly the same as in the first step, but as described above, it is preferable not to add organic additives such as gelatin and free chlorine at all.

Next, the effect of the electrolyte potential will be described. In the present invention, by intentionally lowering the electrolyte potential to an extremely low potential region and performing electrolysis, the removal of Ag in the first step and the removal of Ag and S in the second step are extremely remarkable. I have discovered something. That is, for example, in the first step, the copper concentration is 25 g/Ω, the electrolyte temperature is 40° C., the free sulfuric acid is 160 g/i), and the free chlorine is 20 On.
+g/n, cathode and anode current density is 50A/i, anode Ag grade is 10ppm, S1M solution 0 solution potential is 85hV
(vs NHE), the Ag grade in the electrolytically recovered electrolytic copper was 0.20 ppm, but when the solution potential was intentionally lowered to GGOmV (vs NHE), the Ag grade decreased. It was 0.09 ppm.

In addition, in the second step, for example, the copper concentration is 25 g/I
I, electrolyte temperature 40°C, I) H-1,5, cathode and anode current density 50A/rr? , anode Ag quality is 0.13p
p.m.

Under the condition that the electrolyte potential is 840 mV (vs N HE ), the Ag grade in the electrolytically recovered electric shell is O, l0p.
The pI was 11, but due to the deliberate addition of a reducing agent, the pI was 5.
The Ag grade in the electrolytic copper recovered by electrolytic reduction to 1 button V (vsNHE) is 0. O was 3 ppm.

Regarding S, using an anode containing 2.5 ppm S,
Under the same electrolytic conditions as above, we investigated the S content in electrolytic copper electrolytically recovered under various solution potentials, and found that it was 85h+
S -0.05ppi in V (vs NHE), 7
Electrolysis at low liquid potential with S −0, O2 ppm at 80 + aV (vs NHE) and then intentionally introducing a reducing agent,
730mV.

At 670mV, 530cV (vs NHE),
The S grade in the recovered electrolytic copper was all 0.01 ppm or less.

The reason for this cannot necessarily be clearly explained, but the inventors of the present invention suggest the following. In other words, regarding Ag, the Ag that is in equilibrium with each liquid potential
When focusing on ion concentration, for example, the normal potential of 850
mV (vs N HE ) is 7.3 mol/II, while the intentionally adjusted liquid potential of 600 mV (vs N
HE) is 4.3X10'mol/Ω, which is about 10,
It is thought that there will be a difference of more than 1,000 times (data; A
t1as or Electrochemjeal Eq
ullbrla InAqueous 5oluti
on; by Marcel Pourbaix)
o This suppresses the spontaneous dissolution of Ag in the anode slime, and therefore it becomes possible to produce low-Ag electrolytic copper by setting the anode current density low, lowering the anodic polarization pressure, and suppressing the electrochemical dissolution of Ag. Seem. On the other hand, the current theory cannot necessarily explain the phenomenon in which the quality of S in the recovered electrolytic copper in the second step is significantly related to the solution potential of the electrolytic solution.

In the method of the present invention, electrolysis is preferably carried out in a region completely different from the solution potential region in ordinary electrolytic refining. For this purpose, intentional introduction of a reducing agent is extremely effective. The effect of the presence of a reducing agent is also supported by the fact that when a gas is used, inert gases such as argon gas and nitrogen gas have almost no effect, and the presence of hydrogen gas is necessary, even if it is in a trace amount. When using a hydride as a reducing agent, hydrazine is most effective from the viewpoint of prevention of contamination of the electrolytic bath and effectiveness. Hydrazine includes hydrazine hydrate, hydrazine hydrochloride, hydrazine sulfate, etc., but hydrazine hydrate is most suitable in order to avoid accumulation of chloride ions and sulfate radicals in the electrolytic bath.

After the secondary refined copper obtained by nitric acid acidic copper nitrate electrolysis is vacuum degassed as necessary, the tertiary refined copper obtained through the third step of vacuum casting is further improved in purity. It can be used as ultra-high purity copper.

The present invention will be explained in more detail below using examples.

Example 1] First step 4N electrolytic copper from mine A (grade: -13ppm Ag).

Electrolytic refining was carried out in a sulfuric acid acidic copper sulfate solution under the following conditions using S = 7 ppm) as an anode.

Copper concentration 25g/D Free sulfuric acid 170g/l Free chlorine 200mg/N Gelatin 45z/electrodeposited copper solution Temperature 40°C Cathode current density 35A/a Anode current density 35A/rrr (At the end of electrolysis) To adjust the potential of the bath liquid, use pure hydrogen gas, which is blown directly into the liquid through a glass pole filter, to approximately 860 mV.
(vs NHE). In addition, since the liquid potential showed an increasing tendency during the electrolysis, hydrogen gas was blown in from time to time to stabilize it. The quality of the obtained electrolytic copper was Ag-0, O8ppm, S-2,7
It was ppm.

Second Step Using the electrolytic copper obtained in the first step as an anode, electrolytic refining was performed in a nitric acidic copper nitrate solution under the following conditions.

Copper concentration 25z/(1 pH 1,5 Temperature 40°C Cathode current density 35A/A anode current density 35A/rr? (At the end of electrolysis) Solution potential 530mV (vs NHE) Note that the adjustment of the electrolytic bath solution potential is performed using hydrogen The same procedure as in the first step was carried out using gas, and special grade braided hydrazine hydrate was also used during the electrolysis.

Table 1 shows the quality of the electrolytic copper obtained.

Note that the analysis was performed using a glow discharge mass spectrometer.

Table 1 Second process recovered electrolytic copper grade (unit: ppl Na <0.01 K <0.01 Mg <0.01 Afl<0.01 Si<0.01 s <o, ot Fe<0.01 Ni <0.01 Cr <0.01 As <0.01 Sb<0.02 Bl<O, old Ag O, 01 Pb <0.01 Zn <0.02 Cd <0.02 At the same time, the same electrolytic copper When the quality was confirmed using a spark source mass spectrometer, nothing other than Ag could be detected.Therefore, the only impurity evaluated and detected by both mass spectrometers was Ag, and its value was 0. .0
ip+)m.

From these results, it is understood that the purity of the steel obtained by the method of the present invention is in the ultra-high purity range of 99.99999% (7N) or higher.

Incidentally, the electrolytic copper obtained in the second step was heated using a graphite crucible.
The dissolution treatment was carried out at 1150°C for 2 hours under a vacuum of X 10-'torr. Next, sample pieces for each characteristic value allJ were prepared from this ingot and heated at 500°C in an Ar atmosphere.
The sample was annealed for 1 hour and then subjected to measurement. For comparison, the measurement results for commercially available oxygen-free copper (4N) are also listed at the same time.

Tensile strength (kg/mj) Elongation (%) Vickers hardness (llv) 15.6 22.1 46.2 75.2 40.6 55.0 [Effects of the invention] As described above, by the method of the present invention, It has become possible to obtain ultra-high purity copper of 99.99999% (7N) or higher by a simple method, which could not be obtained by other methods.

These ultra-high-purity copper materials are mainly used for IC bonding wires, laser mirrors, stabilizers for oxide superconductors, and high-performance acoustic cables, which cannot be made from conventional 4N copper or oxygen-free copper. It has a wide range of applications in new fields as an alternative to metal materials for making previously used items.

It should be noted that those skilled in the art will easily understand that there are various other reducing agents that can be used in the method of the present invention in addition to those disclosed herein, and therefore,
Any modifications are possible, and methods carried out by using such reducing agents are naturally within the scope of the present invention.

Claims (29)

[Claims] (1) Elongation at room temperature is 30% or more, Vickers hardness is 42 or less, and purity is 99.99999% (7N
) or higher. (2) (A) Purification electrolysis is performed using high-purity copper as a refining raw material as an anode and a sulfuric acid acidic copper sulfate solution as an electrolyte at a cathode and anode current density of 100 A/m^2 or less. A first step of obtaining primary refined copper; and (b) Refining electrolysis using the primary refined copper as an anode and a nitric acidic copper nitrate solution as an electrolyte at a cathode and anode current density of 100 A/m^2 or less. a second step of obtaining second refined copper on a cathode seed plate; (3) The method according to claim 2, characterized in that the temperature of the purifying electrolytic solution in the first step and the second step is 30 to 50°C. (4) The method according to claim 3, characterized in that the liquid temperature is 40±5°C. (5) 100 to 500 in the electrolytic bath in the first step
5. Process according to claim 2, characterized in that mg/l of free chlorine is added and gelatin is used as organic additive. (6) The method according to any one of claims 2 to 4, characterized in that the potential of the electrolyte in the first step and the second step is adjusted to 800 mV (vsNHE) or less using a reducing agent. (7) The reducing agent is any one selected from the group consisting of hydrogen gas, hydrazine, sodium borohydride, formaldehyde, oxalic acid, and glucose, or a combination of two or more selected arbitrarily. The method described in 6. (8) The method according to claim 5, wherein the potential of the electrolytic solution in the first step is adjusted to 800 mV (vsNHE) or less using a reducing agent. (9) A claim in which the reducing agent is any one selected from the group consisting of hydrogen gas, hydrazine, sodium borohydride, formaldehyde, oxalic acid, and glucose, or a combination of two or more selected arbitrarily. 8. The method described in 8. (10) The primary refined copper has a purity of 99.99999% (
The method according to any one of claims 2 to 4, wherein the ultra-high purity copper is 7N) or higher. (11) The primary refined copper has a purity of 99.99999% (
6. The method according to claim 5, wherein the ultra-high purity copper is 7N) or higher. (12) The primary refined copper has a purity of 99.99999% (
7. The method according to claim 6, wherein the ultra-high purity copper is 7N) or higher. (13) The primary refined copper has a purity of 99.99999% (
8. The method according to claim 7, wherein the ultra-high purity copper is 7N) or higher. (14) The primary refined copper has a purity of 99.99999% (
9. The method according to claim 8, wherein the ultra-high purity copper is 7N) or higher. (15) The primary refined copper has a purity of 99.99999% (
10. The method according to claim 9, wherein the ultra-high purity copper is 7N) or higher. (16) (a) High-purity copper as a refining raw material is used as an anode,
A first step of obtaining primary purified copper on a cathode seed plate by carrying out purification electrolysis using a sulfuric acid acidic copper sulfate solution as an electrolyte at cathode and anode current densities of 100 A/m^2 or less; (b) the above-mentioned first step; A second step of obtaining primary purified copper on a cathode seed plate by performing purification electrolysis at a cathode and anode current density of 100 A/m^2 or less using purified copper as an anode and a nitric acidic copper nitrate solution as an electrolyte; and (c) a third step of vacuum degassing the second refined copper and then vacuum casting to obtain tertiary refined copper; . (17) Claim 16, characterized in that the temperature of the purified electrolytic solution in the first step and the second step is 30 to 50°C.
Method described. (18) The method according to claim 17, characterized in that the liquid temperature is 40±5°C. (19) 100 to 50% in the electrolytic bath in the first step
Claims 16 to 18 characterized in that 0 mg/l of free chlorine is added and gelatin is used as an organic additive.
The method described in any of the above. (20) The method according to any one of claims 16 to 18, characterized in that the potential of the electrolyte in the first step and the second step is adjusted to 800 mV (vsNHE) or less using a reducing agent. (21) A claim in which the reducing agent is any one selected from the group consisting of hydrogen gas, hydrazine, sodium borohydride, formaldehyde, oxalic acid, and glucose, or a combination of two or more selected arbitrarily. 20. The method described in 20. (22) The method according to claim 19, characterized in that the potential of the electrolytic solution in the first step is adjusted to 800 mV (vsNHE) or less using a reducing agent. (23) A claim in which the reducing agent is any one selected from the group consisting of hydrogen gas, hydrazine, sodium borohydride, formaldehyde, oxalic acid, and glucose, or a combination of two or more selected arbitrarily. 22. The method described in 22. (24) The tertiary refined copper has a purity of 99.99999% (
The method according to any one of claims 16 to 18, wherein the ultra-high purity copper is 7N) or higher. (25) The tertiary refined copper has a purity of 99.99999% (
20. The method according to claim 19, wherein the ultra-high purity copper is 7N) or higher. (26) The tertiary refined copper has a purity of 99.99999% (
21. The method according to claim 20, wherein the ultra-high purity copper is 7N) or higher. (27) The tertiary refined copper has a purity of 99.99999% (
22. The method according to claim 21, wherein the ultra-high purity copper is 7N) or higher. (28) The tertiary refined copper has a purity of 99.99999% (
23. The method according to claim 22, wherein the ultra-high purity copper is 7N) or higher. (29) The tertiary refined copper has a purity of 99.99999% (
24. The method according to claim 23, wherein the ultra-high purity copper is 7N) or higher.