JPH07109594A - Method for releasing gold or platinum-group coating metallic substrate and device therefor - Google Patents

Abstract

PURPOSE:To efficiently release a gold or platinum-group metal coating film without damaging a metallic substrate by anodization with its substrate coated with gold or platinum-group metal as the anode and a fluoride soln. as the electrolyte. CONSTITUTION:Anodization is carried out with a metallic substrate coated with gold or platinum-group metal as the anode and a fluoride soln. as the electrolyte. In this case, the concn. of the soln. is preferably controlled to 5-10mol% and the bath voltage to about 7-20V. Consequently, the electrolyte is infiltrated onto the substrate through the defective and consumed parts of the coating film and electrolyzed, and the coating film is delaminated by the oxygen generated at the interface. This releasing device 5 is constituted, for example, by forming the inner wall of the vessel main body 8 contg. an electrolyte 4 with a fluoride-resistant layer of PE, PP, PVC, 'Teflon(R)', etc., using stainless steel, graphite, Ti, Ta, etc., for the cathode 3 and connecting the cathode with the anode 2 through a power source 6.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to a method of stripping a coated metal from a metal substrate coated with a gold or platinum group metal.

[0002]

Gold and platinum group metals are chemically relatively stable metals. For example, platinum is usually used in a very thin coating of several μm in platinum plating of a titanium platinum electrode. Therefore, few attempts have been made to peel and recover platinum from the electrode. Therefore, there are almost no research reports or related patents published regarding the exfoliation of platinum.

Conventionally, as a method for peeling off such platinum plating, for example, industrially, (a) chemical peeling method using aqua regia and (b) mechanical peeling method using grinder or blast machine have been used. .

The chemical stripping method (a) is one in which a titanium platinum electrode is immersed in aqua regia to dissolve and recover platinum. Judging from the high chemical activity of titanium with respect to aqua regia,
It is impossible to suppress the dissolution of the titanium substrate. Also,
When recovering the dissolved platinum, a full-scale acid treatment facility is required, which causes high cost. Furthermore, in aqua regia,
Since the dissolution of the exposed titanium begins immediately after the coated platinum is dissolved and removed, the stripping conditions and the equipment must be strictly controlled in order to minimize the dissolution of the titanium substrate. Usually, in the dissolving process with aqua regia,
Since the part where the titanium substrate is exposed due to defects in the plating film such as pin holes of platinum plating, damage to the film during electrode use, etc. is dissolved intensively from the time of immersion,
On the surface of the titanium platinum electrode after the dissolution treatment, pit-shaped and groove-shaped dissolution marks at various stages are observed. In order to suppress this, a more delicate operation is required, and therefore, there are many points to be improved in the use of aqua regia in that strict control and adjustment of the peeling condition are required.

In the mechanical treatment method (b), polishing powder is collided with the surface of the titanium platinum electrode to mechanically remove the platinum plating film. However, even with this method, it is difficult to prevent the titanium substrate from being polished and removed together with platinum. Further, it is also very difficult to separate and collect the platinum removed by the polishing powder and the polishing powder. More specifically, since abrasive powder such as abrasive powder or blast powder of a grinder used for polishing removal is much harder than a platinum-plated coating or a titanium substrate, peeling removal is performed using such polishing powder. Then, the titanium substrate is also scraped off. Further, since the peeling powder obtained by peeling removal contains a mixture of polishing powder and peeled platinum powder, and the peeled platinum powder has various shapes, the platinum powder from the peeling powder can be removed. Is difficult to recover. Even if the mechanical treatment method is used, the titanium substrate after the exfoliation is considerably damaged as in the chemical treatment method. Therefore, there are almost no examples in which the titanium substrate is reused after the platinum plating film is removed.

Gold and platinum group metals are valuable resources, and their reuse is desired. The recovery and recycling of gold and platinum group metal coatings on metal substrates is important. In particular, gold without damaging the metal substrate as much as possible,
And a method of recovering a platinum group metal coating is desired.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art. Gold and platinum group metals coated on the surface of a metal substrate without damaging the metal substrate as much as possible. It is an object of the present invention to provide a method capable of efficiently peeling a coating film. Another object of the present invention is to provide an apparatus for efficiently performing such a peeling method.

[0008]

The method of the present invention uses a metal substrate whose surface is coated with gold or a platinum group metal as an anode,
It is characterized in that the gold or platinum group metal coated on the metal substrate is peeled off by performing an anodic electrolysis treatment in an electrolytic solution containing a fluoride solution as a main component. As the fluoride, HF, CrF ₃ , KF, NaF, NH ₄ F, H
F · NH ₄ F, NaF · HF, and other acidic fluorides can be used. Since the fluoride solution has an extremely strong chemical action, it does not have to have a high concentration and is usually used at a concentration of about 5 to 10 mol%. As the cathode used in the electrolytic treatment, stainless steel, graphite, titanium, tantalum, or the like can be used. An oxidizing agent, a surface active agent and the like can be added to the fluoride solution. Chromates and potassium manganate can be used as the oxidizing agent. The addition amount of the oxidizing agent is preferably 0.1 to 0.5 mol%. As the surface active agent, a nonionic active agent such as sorbit can be used.

The electrolysis voltage is preferably 7 to 20 V.
Is. If it is less than 7V, it takes too much time for peeling to be unpractical, and if it exceeds 20V, the reaction tends to occur too quickly to make it difficult to control the reaction. Examples of platinum group metals include platinum, ruthenium,
Examples include rhodium.

Further, in the peeling apparatus of the present invention, at least the inner wall of the electrolytic cell is made of a fluoride-resistant material, the electrolytic solution containing fluoride as a main component is housed in the electrolytic cell, and the electrolytic solution is immersed in the electrolytic solution. In the peeling device comprising the above-mentioned anode and cathode, and means for connecting these electrodes to flow an electric current,
A metal substrate whose surface is coated with gold or a platinum group metal is used as the anode. As the fluoride resistant material, polyethylene, polypropylene, vinyl chloride, Teflon, or the like can be used.

[0011]

In the method of the present invention, the oxygen generation reaction on the surface of the anode associated with electrolysis is utilized. That is, in the method of the present invention,
By electrolytic treatment, molecular oxygen is forcibly generated at the interface between the metal substrate and the gold or platinum group metal film, and the stress associated with the volume expansion of the molecular oxygen is used to cause delamination of the film. is there.

According to the method of the present invention, the fluoride-containing electrolytic solution first generates oxygen gas on the surface of the gold or platinum group metal coating. Next, this solution penetrates through defects such as pinholes and cracks of the gold or platinum group metal coating, cracks, or a consumable portion, and oxygen gas is generated. Defects such as pinholes and cracks usually exist as plating defects. Scratches, consumable parts, and the like are generated during use of the coated metal substrate industrially as a titanium platinum electrode, for example. When it is considered that there are no defects or consumable parts at all, the film can be appropriately scratched to the extent that the metal substrate is not damaged.

As the electrolytic treatment progresses, the electrolytic solution reaches the metal substrate due to these defects and the like, and actively generates oxygen gas at the interface between the coating and the metal substrate. Oxygen gas generated at the interface between the coating and the substrate in this manner pushes up the coating and separates it from the surface of the metal substrate. The area of the peeled film increases with electrolysis time. Since the peeled film is hard and brittle, when repeatedly contacted with the bubbles of oxygen gas, it may be separated in the form of flakes, strips or powders, and may float on the fluoride solution. The peeled gold or platinum group metal is not dissolved in the fluoride solution and can be visually confirmed. On the other hand, most of the metal substrate is dissolved in the fluoride solution. Therefore, the peeled film is
By using a simple method such as filtration, it is possible to separate the metal substrate without mixing. Thus, using the method of the present invention, a gold or platinum group metal coating can be easily recovered from a substrate coated with a gold or platinum group metal.

[0014]

EXAMPLES The present invention will be described in detail below with reference to examples. First, the peeling device commonly used in this embodiment will be described.

As shown in FIG. 1, the stripping device 5 includes an anode 2 made of a titanium platinum electrode to be electrolytically stripped in a container 1 containing an electrolytic solution 4 containing fluoride as a main component. , And the cathode 3 made of stainless steel is arranged. The cathode 3 is designed larger than the anode 2 in order to improve current efficiency. The container 1 includes an inner wall layer 7 made of Teflon having a fluoridation resistance and a container body 8 made of plastic. The anode 2 and the cathode 3 are connected by a connecting means 6 having a power source. When this power source is turned on, the electrolytic treatment of the anode 2 is started. The following solutions were prepared in advance in order to prepare the electrolytic solution contained in this peeling container. First, ammonium fluoride and ammonium hydrogen fluoride were used as fluoride salts to prepare a main liquid A and a main liquid B having the following concentrations. Main solution A NH ₄ F · HF aqueous solution 150 g / l Main solution B NH ₄ F aqueous solution 200 g / l Next, oxidizing agents A and B having the following concentrations were prepared as oxidizing agents. Oxidizing agent A CrO ₃ aqueous solution 20 g / l Oxidizing agent B KMnO ₄ aqueous solution 30 g / l Furthermore, commercially available sorbit (solid powder) was used as a surfactant. Surfactant sorbit solution 2g / l

As described above, in this stripping apparatus, since an electrolytic solution containing a high concentration of fluoride is used, sufficient ventilation measures and strict wastewater treatment equipment are required in the electrolytic stripping process. Further, the electrolytic treatment tank, the cathode material, the electrode connection terminal, the stirring device, and the ventilation device are made of a material that can withstand fluoride. The main liquid A or B and the oxidizing agent A or B of Examples 1 to 6 or more were appropriately mixed to prepare stripping solutions having 6 kinds of compositions of Examples 1 to 6 shown in Table 1 below.

Using these six types of stripping solutions, the equipment shown in FIG.
The anode for 60 minutes by changing the current density.
Electrolytic treatment was performed. Its current density and 30 minutes or 6
Table 2 shows the presence or absence of peeling after 0 minutes. Peeled off
Most of the membranes sink in the electrolytic solution and their size
Only those that were fine floated in the solution. Which coating
Was also easily recovered by filtration. Table 1 Composition of stripping solution Example Main solution A Main solution B Oxidizing solution A Oxidizing solution B Imprint (g) (g) (g) (g) 1 150 2 200 3 3 150 20 4 4 150 30 5 5 200 20 6 200 30 30 Note ) Target electrode: Titanium platinum electrode after platinum plating Peeling area: 20 cm²  Pre-treatment: None Peeling time: 30 to 60 minutes Peeling voltage: 8 to 9 V Post-treatment: Filtered and washed with water to recover platinum Table 2 Current density (A / dm² ) 25 30 35 40 45 50 55 Example 1 × × × ○ ○ ○ ◎ 2 × × × ○ ○ ○ ◎ 3 × ○ ○ ○ ◎ ◎ ◎ ◎ 4 × × ○ ○ ○ ◎ ◎ ◎ 5 × × ○ ○ ◎ ◎ ◎ ◎ 6 × × ○ ○ ○ ◎ ◎ Note) ◎: Peeling off within 30 minutes ○: Peeling off within 60 minutes ×: No peeling

The results shown in Table 2 show that 40 A / dm
² Good results have been obtained at the above current densities, but even at current densities lower than that, sufficient peeling can be achieved by increasing the treatment time.

Further, by increasing the concentration of the electrolytic solution, the stripping can be performed with a low current density and a short processing time. Therefore, in the method of the present invention, the current density is not particularly limited.

[0020]

As described above, according to the present invention,
The gold and platinum group metal coatings coated on the surface of the metal substrate can be efficiently removed from the metal substrate without damaging the metal substrate as much as possible. Further, the peeled film can be easily recovered by filtering the electrolytic solution.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of an apparatus of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Container, 2 ... Anode, 3 ... Cathode, 4 ... Electrolyte solution, 5 ... Stripping device, 6 ... Electrode connecting means, 7 ... Fluoride resistant layer, 8 ... Container body

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Yoshihiko Abe, 1-chome, Kita-ku, Kita-ku, Sapporo, Kita-ku, 11-1 chome, Hokkaido (72) Inventor, Hiroshi Sugimoto 13-chome, 12-chome, Nishi-ku, Sapporo, Hokkaido No. 15 Sapporo Electroplating Industry Co., Ltd.

Claims (2)

[Claims] 1. A gold substrate coated on a metal substrate, characterized in that a metal substrate whose surface is coated with gold or a platinum group metal is used as an anode, and a fluoride solution is used as an electrolytic solution to perform an anodic electrolytic treatment. Method of peeling platinum group metal. 2. An electrolytic cell having at least an inner wall made of a fluoride-resistant material, an electrolytic solution containing fluoride as a main component contained in the electrolytic cell, and an anode and a cathode immersed in the electrolytic solution. In a peeling device comprising means for connecting these electrodes and passing an electric current, a metal substrate whose surface is coated with gold or a platinum group metal is used as the anode, and an anodic electrolytic treatment is performed to form a metal substrate on the metal substrate. A peeling device for peeling the gold or platinum group metal coated on the surface.