JPH01100291A - Chromium plating method - Google Patents

Abstract

PURPOSE:To carry out stable, high quality Cr plating by using lead-based electrodes and noble metal electrodes in combination in a tervalent Cr preparation tank and regulating the ratio between the working area of the former electrodes and that of the latter electrodes. CONSTITUTION:One or more kinds of lead-based electrodes 5 selected among lead, lead alloy and lead dioxide electrodes are placed in a tervalent Cr preparation tank 2 and noble metal electrodes 3 each having a coat contg. a Pt family metal or the oxide thereof are placed in a plating tank 1. The ratio between the working area of the electrodes 5 and that of the electrodes 3 is regulated to 1:1-1:10. The electrodes 5, 3 may be arranged in the same tank. Thus, stable, high quality Cr plating can be carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a chromium electroplating method, and particularly to a chromium plating method using two or more types of plating electrodes.

(Conventional technology) Platinum, iron, lead,
Electrodes made of lead alloys or lead dioxide are known. Among the electrodes mentioned above, platinum is expensive, iron elutes in relatively large amounts into the plating solution and contaminates the coating bath, and lead is soft (flexible). (For these reasons, lead alloy or lead dioxide electrodes are now commonly used. In particular, lead alloys or lead dioxide electrodes are commonly used on conductive substrates such as titanium through interlayers of platinum group metals and their oxides. Lead-coated electrodes are widely used in the plating industry because they have less electrolytic wear and less sludge formation than lead alloys.

However, these lead alloy electrodes or lead dioxide electrodes are heavy and have poor workability when replacing the electrodes.They also consume a lot of power because they exhibit a high polarization potential in a chromium plating bath. However, lead chromate, which is the main component of the sludge produced, has drawbacks such as the need to safely dispose of lead chromate as a waste liquid due to pollution regulations.

On the other hand, noble metal electrodes, in which the surface of a conductive metal substrate such as titanium is coated with one or more platinum group metals such as platinum, iridium, and rhodium, and one or more of their oxides, are coated with lead alloys and dioxide in a chromium plating bath. It is known that it exhibits an extremely low polarization potential compared to lead-based electrodes such as lead. However, this electrode has a low ability to oxidize trivalent chromium to hexavalent chromium and cannot perform continuous chromium plating. For this reason, chromium plating methods using this electrode as the main material have not been carried out, and it is only used as an auxiliary plating electrode for passing plating current to a portion of the object to be plated that has slight throwing problems.

(Problem to be Solved by the Invention) When electrodepositing chromium, it is possible to contain a small amount of trivalent chromium in the chromium plating bath in a pool of catalytic species such as chromic acid, sulfuric acid, and heptadide. It is important to adjust the concentration of trivalent chromium in order to achieve good quality plating. When plating is carried out in a chromium plating bath, trivalent chromium is produced at the cathode, which is oxidized at the anode to become hexavalent chromium, that is, chromic acid. This reduction and oxidation effect varies depending on the electrode material used, and trivalent chromium reaches equilibrium at a certain concentration. As mentioned above, the noble metal electrode has little ability to oxidize trivalent chromium, and if plating continues, the trivalent chromium concentration in the bath will increase, resulting in poor plating. Furthermore, since lead-based electrodes have a high oxygen overvoltage (and excellent oxidation ability), if plating is continued, the concentration of hexavalent chromium will increase and the concentration of trivalent chromium will decrease too much, making it impossible to perform high-quality plating.

Under these circumstances, a method that solves the above problems, consumes less electricity, generates less sludge, and provides stable chromium plating for a long period of time without frequently adjusting the trivalent chromium concentration. development was desired.

(Means for Solving the Problems) As a result of intensive study, the inventors of the present invention used a lead-based electrode and a noble metal electrode in combination, kept the ratio of the electrode action areas of both electrodes within a certain range, and improved the characteristics of both electrodes. The present inventors have discovered that the above-mentioned problems can be solved by effectively utilizing the present invention.

That is, the present invention provides an electrode active area ratio of one or more lead-based electrodes selected from lead, lead alloys, and lead dioxide electrodes to a noble metal electrode coated with platinum group metals and/or their oxides of 1:1. This is a chromium plating method in which plating is performed using a lead-based electrode and a noble metal electrode in combination with a ratio of 1 to 1:10.

The noble metal electrode used in the present invention is, for example,
Examples of electrodes for water electrolysis and electrowinning of metals as disclosed in Japanese Patent No. 54555 include thermal decomposition and electrolysis of platinum group metals such as platinum, iridium, rhodium, and one or more of their oxides. This is a so-called insoluble electrode for oxygen generation obtained by coating a titanium, tantalum, niobium, silconium, or alloy substrate thereof by a method such as plating, plasma spraying, or sintering. These noble metal electrodes may be used alone or in combination of two or more.

In addition, as a lead-based electrode, for example,
57 and Japanese Patent Publication No. 58-31396, a valve metal substrate made of titanium or the like is thinly coated with platinum, iridium, or other platinum group metals, and one or more of their oxides by a thermal decomposition method. For example, an intermediate layer is provided, and a lead dioxide electrode electrodeposited thereon from a lead nitrate bath or a lead monoxide bath can be mentioned. Also silver, calcium,
Oxygen generating electrodes used in electrolytic refining of metals, such as lead alloy electrodes or lead electrodes containing several percent of one or more of tin, antimony, etc., are used. These lead-based electrodes may be used alone or in combination of two or more.

As the chromium plating bath used in the present invention, a Sargent bath, a heptafluoride bath containing ammonium heptadide, silicate heptafluoride, or borate heptafluoride, a boric acid bath, or the like can be used.

Next, one embodiment of the present invention will be described with reference to the drawings.

In Fig. 1, when a current flows from the noble metal electrode (3) provided in the plating bath (1) to the object to be plated (8), trivalent chromium in the plating bath increases, but the plating solution is transferred to the piping (9).
) is sent to the trivalent chromium adjustment tank (2), where it is oxidized by a lead-based electrode (5) between it and the cathode (4). The plating solution, which has been oxidized and has a reduced trivalent chromium concentration, is passed through a filter (7) by a circulation pump (6) to a pipe (9').
It returns to the plating tank (1) through the In this case, the trivalent chromium concentration in the bath is controlled to an appropriate concentration of 1 to 7 g/l as trivalent chromium ions by means of an electric current passing through the lead-based electrode (5). The cathode (4) provided in the trivalent chromium adjustment tank (2) may be made of iron, stainless steel, titanium,
Lead, aluminum, etc. are used, and if chromium metal adheres during adjustment electrolysis, scrape it off as appropriate before use.

In Figure 1, the lead-based electrode is installed separately in the trivalent chromium adjustment tank (2) and the precious metal electrode is installed in the plating tank (1), but the picture electrodes are mixed and installed in the same tank and plated. You can also do this. In this case, it is desirable that the types of electrodes used are uniform and that they are evenly distributed and attached. In addition, the plating tank is made deep so that lead chromate sludge, which is generated due to consumption of the lead-based electrode, is deposited at the bottom of the plating tank.

The electrode action area ratio of the present invention is, for example, in FIG.
The geometric area under the surface of the plating liquid that is subjected to electrolysis and facing the cathode (4) of the lead-based electrode (5) provided in the trivalent chromium adjustment tank (2), and the plating area in the plating tank (1). It means the ratio of the geometric area of a noble metal electrode that is under the liquid level and is used for plating while facing the object to be plated, and does not include the electrode surface on the opposite side of the surface facing the object to be plated. Therefore, in the case of Figure 1,
Assuming that the dimensions of each electrode plate are the same, the electrode active area ratio of the lead-based electrode and the noble metal electrode is 1:4.

(Example) Next, the present invention will be specifically explained based on examples.

Examples 1 to 7, Comparative Examples 1 to 3 The dimensions of the electrodes were unified to medium 50 ml x length 200 ml 11, and the electrode action area ratio was controlled by changing the number of lead-based electrodes and noble metal electrodes used. Using a Sargent bath containing 250 g/l of chromic anhydride and 2.5 g/l of sulfuric acid, the bath temperature was set to 40°C in the same bath, and the current was applied according to the area ratio of each electrode using two DC power supplies. Then, chromium plating was performed on a copper plate measuring 60+I1m x 150mm in length, and the quality of the plating was visually determined. The results are shown in Table 1.

In Table 1, pb is a commercially available lead electrode with a purity of 99.5%,
Pb-8n represents a lead alloy electrode containing 7% by weight of tin. P
b O2 was made by spot welding a 24-mesh titanium wire mesh with a wire diameter of 0.4 mm onto a sandblasted titanium plate to make an anode base, degreasing this base with trichlene, and etching it with 3% 7th acid. , after applying an ethanol solution of chloroiridic acid with a brush, at 450°C in the atmosphere.
The heat treatment for 30 minutes was repeated three times to form an intermediate layer, and the anode current density was increased in an electrodeposition solution consisting of 250 g/l of lead nitrate and 25 g/l of copper nitrate, using this substrate as an anode and a stainless steel plate as a cathode. 2.5A/dm2, liquid temperature 60℃,
This represents a lead dioxide electrode manufactured by electrodeposition for 12 hours under pH 4.0 conditions. For noble metal electrodes, a titanium plate is steam-degreased with trichlene, etched with hot oxalic acid to roughen the surface, and a solution prepared by dissolving the chloride of the platinum group metal in Improper Tool is brushed onto the base. inside s
o o 'c, manufactured by a pyrolysis method in which scratching consisting of firing treatment for 1 hour is repeated 10 times. I
rO2/Ti is iridium dioxide (IrO2RuC)
2”rio2/Ti is a mixture of iridium dioxide, ruthenium dioxide and titanium dioxide, PtI
r0z represents an electrode coated with platinum and iridium dioxide, respectively, on a titanium substrate.

Example 8 Middle 1. A Sargent bath containing 230 g/l of chromic anhydride, 700 ppm of 7 ions, and 2.0 g/l of sulfuric acid was placed in a chromium plating tank with a length of 2.5 m and a depth of 1.5 + Il. Using 4 lead electrodes and 20 IrO2/Ti electrodes, 2 lead dioxide electrodes and 2 IrO2/Ti electrodes were placed on the left and right sides of the plating bath.
A total of 12 Ti electrodes (10 each) were attached to the same bus bar on the left and right sides. A crescent (aluminum sash lock) was passed continuously on the center line between the electrodes, and a plating current of 270OA was applied.
Table 2 shows the results of automatic continuous plating at a bath temperature of 40°C.

Comparative Example 4 Lead-tin alloy (tin content near weight%) without using noble metal current
) Table 2 shows the results of plating performed in the same manner as in Example 8, except that only 24 electrodes were used.

(Effects of the invention) By using a lead-based electrode and a noble metal electrode in combination and regulating the ratio of the electrode active area of the picture electrode, it is possible to use a noble metal electrode as the main electrode for chrome plating, which has not been done in the past. As a result, it is now possible to stably produce high-quality chromium plating without frequently adjusting the trivalent chromium concentration. By using noble metal electrodes, power consumption can be greatly reduced, and since the use of lead-based electrodes can be reduced (or eliminated), sludge treatment costs are almost eliminated.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating an embodiment of the chrome plating method of the present invention. 1. Plating tank 2. Trivalent chromium adjustment tank 3. Precious metal electrode 4. Cathode 5. Lead-based electrode Patent applicant Nippon Carlit Co., Ltd. No. 10 5 4 'J Procedural Amendment October 1988 2s Day

Claims (1)

[Claims] The electrode active area ratio of one or more lead-based electrodes selected from lead, lead alloys, and lead dioxide electrodes and a noble metal electrode coated with platinum group metals and/or their oxides is 1:1 to 1.
:10, a chromium plating method characterized by plating using a lead-based electrode and a noble metal electrode in combination.