JPH02310397A - Apparatus for reducing loss of lead and lead alloy electrode in chromium electroplating bath - Google Patents

Abstract

PURPOSE: To suppress the dissolution and consumption of a lead-based anode into a plating liquid with a chrome plating device having the insoluble anode consisting of a lead or lead alloy by providing the anode with an auxiliary cathode via an auxiliary power source and passing a specific slight quantity of current between the anode and the auxiliary cathode.

CONSTITUTION: An object 3 to be plated as a cathode and the insoluble anode 1 consisting of the Pb or Pb-Sn alloy system are immersed in a plating cell 7 contg. the Cr plating liquid contg. CrO₃ and H₂SO₄ and are energized by a power source 4 for plating, by which a plating film of Cr is formed on the cathode 3. In such a case, the anode 1 is provided with the auxiliary cathode 2 as an anode protective circuit via a diode 6 by the auxiliary power source 5 and the low current of 0.01 to 0.3% of the plating current is passed under a voltage of 1.8 to 2.2 V thereto, by which the dissolution and consumption of the Pb of the anode 1 into the plating liquid is prevented.

COPYRIGHT: (C)1990,JPO

Description

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to the electroplating of chromium using lead or lead alloy anodes, and more particularly to chromium plating bath apparatus in which the weight loss of such lead anodes is substantially reduced. and on methods.

Description of the Prior Art Chromium plating baths using chromic acid solutions as the chromium source invariably use lead or lead alloy anodes. However, [The Electrochemistry of Lead]
f Lead) J, Turn (A, T, Kuhn),
Academic Press
) (1979), pp. 40'5-407, lead and lead alloy anodes are attacked by soluble species in chromic acid solutions (resulting in anode weight loss). This anodic dissolution proceeds at a considerable rate, the rate being proportional to the acidity of the solution. Therefore, it was necessary to find a corrosion-resistant alloy for this medium. For example, alloys containing 10% tin and 0.5% cobalt appear to exhibit good resistance.

co! Addition of 1 to 2 grams per liter (g/j) of + ions can also reduce anodic corrosion.

Although this anodic corrosion problem exists in both conventional hexavalent chromium plating baths and mixed catalytic chromium plating baths, it is important to note that high-energy, high-efficiency baths, such as U.S. Patent No. 4,588,48
This is particularly important in the so-called rHEEF-25J baths described in No. 1. rHEEFJ is manufactured by M&T Chemicals (
M&T Chemicals Inc.,+Rahway
, New Jersey) is a registered trademark. HEEF
The -25 bath contains chromic acid, sulfate and an alkyl sulfonic acid, preferably an unsubstituted alkyl sulfonic acid or a salt thereof for functional chromium precipitation, with a sulfur to carbon ratio of ≧173. Typical alkylsulfonic acids are methylsulfonic acid, ethylsulfonic acid, propylsulfonic acid, methanedisulfonic acid and 1,2-ethanedisulfonic acid.

Other hexavalent chromium plating baths are disclosed, for example, in U.S. Pat. No. 3,745, to Chess in et al.
No. 097 (issued July 1973, 10B); Ao
No. 3,654.101 (April 1972)
No. 4,450,050 (issued May 22, 1984) to Chessin et al.; and No. 4.472°249 (issued September 18, 1984) to Chessin et al. published). All such patents are assigned to the assignee of this invention.

SUMMARY OF THE INVENTION The present invention is an improved chromium plating system that substantially reduces the conversion of lead or lead alloy anodes used in the system to soluble species, wherein the potential on said anode is The system includes an anodic protection circuit that applies a scoring potential lower than that required for normal electroplating of chromium. The electroplating bath of the present invention can be prepared using conventional mixed catalysts or alkylsulfonic acid-containing (HE)
EF-25) Can be of chrome electroplating type.

In the 1s mode, an auxiliary cathode is provided near the anode and the desired voltage is imposed on the anode.

Description of the Preferred Embodiment During electroplating of chromium, the surface of the lead or lead alloy anode used therein is oxidized to a film of lead dioxide on the anode, which stabilizes the anode during the process.

However, when the current is stopped, i.e. during the non-plating period, this protective lead dioxide film is removed by the lead anode or by trivalent chromium in solution producing chromate ions.
can be reduced to seeds.

The lead (n) oxide can then react with chromate ions to form non-positive lead chromate. If the lead oxide and lead chromate materials are as adherent to the lead anode as the lead dioxide film, very little corrosion of the anode will occur. However, when these species flake off the anode and fall into the bath, the new ship anode surface is exposed and further corrosion can occur.

Additional solubilization reactions can occur if an alkyl sulfonic acid such as methanesulfonic acid is present in the bath;
Lead(II) oxide forms the directly soluble species. These reactions occur quickly during the non-plating period; when the plating current is applied, the lead(II) oxide on the anode can be oxidized back to lead dioxide(It/), and the corrosion is very severe. Very little will happen. It is known that lead(n) species that are not in electrical contact with the anode cannot be reoxidized and are therefore lost from the anode.

In the present invention, the formation of lead(II) species is retarded by anodic protection during non-plating periods, thereby retarding anodic solubilization corrosion and anodic weight loss. Anodic protection is achieved in the chromium galvanic plating system of the present invention by having an auxiliary or dummy cathode placed near the anode and applying a predetermined low voltage and low current between the cathode and the anode. Ru.

This voltage is lower than the electrode potential between the anode and the substrate cathode, which would otherwise result in electroplating of chromium. In this way an anode or oxidation potential is maintained around the beneficial lead(IV) dioxide film on the anode, preventing its reduction to lead(■) species.

In the course of studying the parameters of the present invention, it was unexpectedly found that anodic protection can be obtained by applying a voltage lower than the plating voltage to the anode. For example, a potential of about 1.8 to about 2.2 pol l-(V) at a current of about 0.01 to about 0.3% of the normal chromium electroplating current will cause solubilization corrosion of lead and lead alloy anodes. It was recognized that it is useful for reducing Furthermore, the protective current can be applied both while the bath is running and while the plating current is turned off, for example overnight.

Referring now to the drawings, a conventional electroplating system including a plating anode l is shown. The auxiliary circuit of the present invention is anode 1
It can be seen to include an auxiliary cathode 2, which can be a chromium-plated rod, placed close to the auxiliary power source 5 and connected in series thereto through an auxiliary power source 5. A rectifier or diode 6 can be included in the auxiliary circuit to keep it on during electroplating. Dummy electrodes and plated rectifiers can be used in combination as well.

In operation, a lower anodic protection voltage than the normal plating potential, about 2.8 cm, is applied between the auxiliary cathode and the anode. Generally a potential of at least about 2V is 0.02% of the plating current
Applicable below. For example, a voltage of 2,000 volts for 1500 ampere-hours is measured by reducing the Pb-7%S
HEEF-25 provides a 10-20% improvement in anodic corrosion and less than 1% of the plating current compared to plating at 1500 amps at 5 V with no auxiliary protection circuit.
35~ for anodic corrosion (lump '$i, amount) in chrome plating bath
resulting in a 55% reduction.

The presence of a diode in the auxiliary circuit prevents current flow to the auxiliary cathode during the plating cycle. The following examples demonstrate the effectiveness of the invention.

Example 1 Using the anodic protection circuit of FIG. 1, the auxiliary power source was kept on even when no plating was present. The diode is about 0.5
It was a 3 ampere (amp) 50 peak reverse voltage epoxy type with a voltage drop of V. The power supply was approximately 0.5 V higher than the voltage on the voltmeter shown as ■ in the figure.

Plating low ripple rectifier [Hyulet Paracard (
Hewlett-Packard) 6268B, 40V
, 30 amp) and an auxiliary circuit (Hewlett Packardo 200B, 20 V, 1.5 amp).

The auxiliary voltage was controlled at 2.0 and 2.15 μ in two separate experiments. Each test lasted 1500 amp hours, and the anode was weighed four times after the plating cycle during the experiment. A thin brown film was scraped off the electrode before weighing. During the day, plating was cycled on and off every 30 minutes. Plating, heating and stirring were done overnight. Chromic acid was supplemented during the test. HEEF-25 plating solution (chromic acid 250 grams per liter (g/l) and methylsulfonic acid 3.5 g
/l and sulfate ion 2.5g/1. ) was prepared at the beginning of each experiment and the solution was divided into two 4 liter beakers. The anode is 15 centimeters (cm) x 7.5c
mX1cmPb7%Sn, 12.7CIIX in solution
It was 7.5 cm x 1 cm. Approximately 225- of the anodes were in solution. The cathode was a 0.95 cs diameter drill rod. The auxiliary cathode was a chrome-plated rod and was not cleaned or replaced during the test. The results are shown in Tables 1 and 2.

Table 1 0.02% of plating current, 2.0 volt-ampere-hour Anode mass, g Mass loss, g
Corrosion and Control Test Control Test Percent 0
1144.1 1142.8 -- --
--572 1134.6 1135.1
9.5 7.7 18.9B96 1128.
1 1129.4 16.0 13.4 12
．． 31477 1115.6 1118.0 28.5
24.8 11.4 Table 2 0.1% of plating current, 2.15 volt-amp hour Anode mass, g Mass loss, g Corrosion and control Test Control Test Percent 0
1107.0 1109.2 -- --
--508 1098.8 1103.9
8.2 5.3 351014 1088
．． 5 1098.0 18.5 11.2 4316
88 r076, o 1092.4 31.0
16.8 55Table 1 is 2. Ov, 0 Table 2 shows that with anodic protection below 0.02% of the plating current, the test anode corroded ~20% less lO than the control anode.
15 V, 0.1% of the plating current or less showed that the test anodes corroded 35-55% less than the control anodes, thus anodes with protection were found to be up to about 100% of those used without protection. It is known that the amount of lumps decreased. In the remeasurement, the control anode corroded at the same rate within 1%.

Having described the preferred embodiments of this invention, those skilled in the art will appreciate that this invention is not limited thereto and that various modifications and changes can be made without departing from its spirit and scope. Dew.

[Brief explanation of drawings]

The drawing is a schematic representation of a chromium electroplating system according to the invention. 1... Plating anode, 2... Auxiliary cathode, 5... Auxiliary power supply. Procedural amendment IF (formal patent office director Yoshi 1) Moon Tsuyoshi 1, Indication of the case 1999 Patent Application No. 221400 3, Person making the amendment Relationship with the case Applicant 4, Agent 1 "j"t' ``・ iL[Year] Procedural Amendment Written January 1989 Yoshi, Commissioner of the Japan Patent Office 1) Takeshi Moon 1, Indication of the case 1999 Patent Application No. 221400 3, Relationship with the person making the amendment Case Applicant 4 , Agent 5, date of amendment order (1) “The result is...” on page 11, lines 16-17 of the specification.
- Shown. ” is corrected as follows: “The results are shown in Table 1, Table 2, and Figure 2.” (2)
Insert the following text after page 13, line 14 of the specification. 4. Brief Description of the Drawings Figure 1 is a schematic diagram of a chromium electroplating system according to the present invention. FIG. 2 shows the results of Example 1. 1... Plating anode, 2... Auxiliary cathode, 5...
...Auxiliary power supply. (3) Supplement Figures 1 and 2.

Claims (15)

[Claims] (1) A chromium electroplating apparatus having an anode and a cathode and a device for applying an electroplating potential and current to an article, the apparatus comprising means for reducing solubilization corrosion of a lead or lead alloy anode therein, the anode Apparatus comprising an anodic protection circuit for applying a protection potential thereon which is lower than the potential required for normal electroplating of chromium on said anode. (2) The chromium electroplating apparatus of claim (1), wherein the potential is applied at a low current. (3) The chromium electroplating apparatus according to claim (1), wherein the anodic protection circuit applies a protection potential during non-plating periods. 4. The chromium electroplating apparatus of claim 1, wherein the potential is about 1.8 to about 2.2 volts. 5. The chromium electroplating apparatus of claim 4, wherein the potential is about 2.0 to about 2.15 volts. (6) Low current is about 0.01 to about 0.3 of the electroplating current
%. The chromium electroplating apparatus according to claim 2. 7. The chromium electroplating apparatus of claim 6, wherein the low current is about 0.02 percent of the electroplating current. 8. The chromium electroplating apparatus of claim 1, wherein the anodic protection circuit includes a device for applying a protection potential during non-electroplating periods. (9) Claim (8) wherein the anode protection circuit includes a diode.
The described chrome electroplating equipment. (10) Claim (1) wherein the anode protection circuit is an auxiliary circuit.
Chromium electroplating equipment as described, (11) The chromium electroplating apparatus of claim (1), wherein the anodic protection circuit includes an auxiliary cathode and a plating power source operating at low voltage and current. (12) the voltage is about 2.0 to about 2.15 volts;
The chromium electroplating apparatus according to claim (11). 13. The chromium electroplating apparatus of claim 11, wherein the current is about 0.02 percent of the electroplating current. (14) Claim (14) wherein the anode protection circuit further includes a rectifier.
11) The chromium electroplating apparatus described above. (15) The chromium electroplating apparatus according to claim (14), wherein the rectifier includes a diode.