JP3430479B2 - Anode for oxygen generation - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insoluble anode used in an electrolysis process involving generation of oxygen, mainly in electroplating zinc, tin or copper and surface treatment of stainless steel.

[0002]

2. Description of the Related Art Lead or a lead alloy is currently used as an anode for electrogalvanizing steel sheets. Lead is consumed relatively quickly, and the dissolved lead causes contamination of the plating solution and deterioration of the plating film. There's a problem. As an alternative anode, various insoluble anodes using a noble metal oxide as an electrode active substance have been proposed. However, in an electrode that is simply prepared by coating an electrode active substance and firing it in an oxygen atmosphere, the electrolytic solution permeates the electrode catalyst layer during electrolysis, and the oxygen generated on the substrate surface causes the electrode coating layer to be formed. An insulative passivation film is formed between the metal substrates, which causes a disadvantage that the function as an electrode is lost even if the remaining amount of the electrode active substance is sufficient. Therefore, considering the use of an expensive noble metal as the electrode active material, its economic efficiency is not good at all.

In order to solve this problem, Japanese Patent Laid-Open No. 2-2
It is proposed in Japanese Patent No. 82491 that an electrode formed by forming an intermediate layer of metal tantalum by a sputtering method or the like and further coating an electrode active substance is effective for preventing passivation of a substrate. Further, JP-A-2-247393 proposes an electrode in which an amorphous layer having no grain boundary is formed as an intermediate layer, and an example thereof is an electrode formed by depositing an amorphous layer of titanium, tantalum or the like by a sputtering method. ing. JP-A-53-9
In Japanese Patent No. 5180, there is proposed an electrode in which a titanium substrate is coated with a tungsten / tantalum mixed film by a method such as vapor deposition, ion plating, and cathode sputtering, and a rhodium thin film is vapor deposited. However, there is no disclosure of the kind of metal tantalum exemplified in the intermediate layer of these electrodes.

Japanese Patent Laid-Open No. 4-301062 proposes an electrode in which a titanium coating is formed on the valve metal by plasma spraying in order to improve the adhesion between the electrode base and the electrode active layer. Japanese Patent Application Laid-Open No. 56-112458 proposes an electrode in which ruthenium oxide is formed by a thermal decomposition method after plasma spraying tantalum on a titanium substrate. Japanese Patent Application Laid-Open No. 48-40676 discloses a coated electrode in which a metal such as titanium or tantalum, which has durability in an electrolytic environment, is spray-coated by a technique such as plasma spraying, and an electrode active substance is deposited on the metal. Is proposed.
However, since the plasma sprayed layer of the titanium or tantalum coating has a sparse structure, it is also recognized that the system having a high plating solution flow rate such as a zinc plating line lacks durability in long-term use. Further, in a galvanizing line or the like, in the case of single-sided plating or when the plating amounts on both sides are made different, a potential difference occurs between the upper and lower anodes, and the low potential side anode becomes a cathode. Since metal titanium and metal tantalum (α-tantalum) are easily embrittled by hydrogen, the electrode is deteriorated by the effect of hydrogen generated by cathodization during electrolysis.

[0005]

The object of the present invention is to prevent the deterioration of the electrode due to the passivation of the substrate and the negative polarization, which is a problem in the insoluble electrode for oxygen generation, which is mainly studied as the anode for electroplating. , To provide a long-life electrode.

[0006]

The present inventors have found that in an insoluble electrode for oxygen generation, an anode having a β-tantalum intermediate layer formed between a titanium substrate and an electrode active material coating layer by a sputtering method is α- Various electrodes of the tantalum intermediate layer type, such as an anode having an α-tantalum layer coated by ion plating, plasma spraying, or a sputtering method, as well as an electrode having an electrode active substance coated on the tantalum substrate itself, have more excellent functions. The present invention has been completed by finding that it has.

In the present invention, β-tantalum is added on a conductive metal substrate made of titanium metal or its alloy.
A β-ta layer is obtained by depositing a thin film intermediate layer of metal tantalum containing 0% or more by a sputtering method, and further forming an electrode active substance coating layer containing a platinum group metal oxide on the surface thereof .
With a thin film intermediate layer of metallic tantalum containing 50% or more of tantalum.
Is an excellent oxygen generating anode shade polarizable you.

Titanium or its alloy is used for the conductive electrode substrate in the present invention, and titanium metal or Ti-Ta, T is used.
Titanium-based alloys such as i-Ta-Nb and Ti-Pd are suitable. The substrate may have any desired shape such as plate, perforated plate, rod or net.

Next, β-tanta forming the intermediate layer of the electrode of the present invention
Metal tantalum thin film containing 50% or more of
Thin film or coating)
It is formed. High frequency sputtering for sputtering
Both DC and DC bipolar sputtering are possible.
More preferred is netron sputtering. β-
It is desirable that the thickness of the tantalum thin film be 1 to 5 μm.
Yes. If it is less than 1 μm, it does not adhere sufficiently, and if it exceeds 5 μm.
However, there are problems such as difficulty in sputtering processing.
Specifically, in an argon gas atmosphere, 1 × 10^-2Torr
High frequency discharge in the following high vacuum. At this time, the substrate temperature
Is 400 ° C or below, and the residual gas should be sufficiently removed.
Need to Continue this sputtering for more than a certain time
As a result, a β-tantalum film of 1 μm or more is formed on the substrate.
It is formed. Also, the total pressure is 1 x 10 ^-2Torr's Argo
Partial pressure is 1 × 10 in the atmosphere^-FiveBe below Torr
Nitrogen gas or oxygen gas is supplied to the
By continuing for a fixed time or more, β- of 1 μm or more on the substrate
A tantalum coating is formed. The substrate temperature at this time is 50
It is preferably 0 ° C or lower. The partial pressure of nitrogen gas or oxygen gas is 1
× 10^-FiveAbove Torr, several percent or more of α-tan in the film
Tar is mixed. 1 x 10^-FourMore than Torr
At partial pressure, nitrides or oxides are formed.
Argon gas atmosphere for DC bipolar sputtering
Bottom 1 × 10^-2Substrate temperature in high vacuum below Torr
Is maintained at about 300 ° C or lower,
An internal coating can be formed.

Next, an electrode active layer (catalyst layer) containing an electrochemically active platinum group metal oxide is provided on the surface of the intermediate layer having no electrode activity in this way. Platinum group metal oxides or mixed oxides of these with valve metals such as titanium and tantalum are suitable as electrode active substances suitable for electrodes associated with oxygen generation. The weight ratio of the platinum group metal to the valve metal in the mixed oxide is preferably 10 to 97% by weight of the platinum group metal and 3 to 90% by weight of the valve metal. Further, it is preferable to coat the platinum group metal so that the content of the platinum group metal in the mixed oxide is 1 to 300 g / m ² . Typical examples are iridium-tantalum mixed oxide, iridium-titanium mixed oxide, iridium-ruthenium mixed oxide, iridium-ruthenium-titanium mixed oxide, ruthenium-titanium mixed oxide, ruthenium-tantalum mixed oxide. Is mentioned. Particularly preferred is 70 to 95% by weight of iridium oxide in terms of metal, and 5% tantalum oxide in terms of metal.
This is the case of 30% by weight of the mixed oxide, and the case of coating the mixed oxide so that the amount of iridium is ² to 200 g / m ² .

Thus, as the coating layer of the electrode active substance, the conventionally used thermal decomposition method, electrochemical oxidation method, powder sintering method and the like can be applied, but the thermal decomposition method is preferable. That is, these metal salt solutions are applied and dried several times, and finally heat-treated at a temperature of 350 to 550 ° C. In this way, the electrode of the present invention having the intermediate layer of the β-tantalum thin film can be obtained.

[0012]

The crystal structure of β-tantalum forming the intermediate layer of the electrode of the present invention is tetragonal, and is superior in corrosion resistance and electrical characteristics to body-centered cubic α-tantalum. That is, it was confirmed that the β-tantalum intermediate layer type insoluble electrode was more stable than the α-tantalum intermediate layer type insoluble electrode which had been deteriorated due to long-term operation or electrode short circuit. When α and β-type tantalum are mixed, it was revealed that the durability against negative polarization is remarkably excellent when the β-tantalum content in the intermediate layer is 50% or more. In addition, the crystal form of metal tantalum is generally α-type such as ingot, and it is difficult to form β-tantalum by a method other than the sputtering method. The content rate of β-tantalum used here is calculated from the area ratio of the diffraction peak of β-tantalum (002) and the diffraction peak of α-tantalum (110) in the X-ray diffraction analysis.

[0013]

EXAMPLES The present invention will be described in detail with reference to Examples and Comparative Examples. Example 1 A commercially available titanium plate having a size of 50 mm × 10 mm × 1.5 mmt was degreased by ultrasonic cleaning in acetone. next,
Approximately 10 at 4 kgf / cm ² using # 30 alundum
Both sides of the titanium were blasted for minutes. The titanium plate was washed in running water for a whole day and night and dried, and used as an electrode substrate. This titanium plate was attached to a high frequency magnetron sputtering device. At this time, diameter 100 mm x 3
The mmt tantalum target and the substrate were arranged at a distance of 40 mm, and the chamber internal pressure was set to 1 × 10 ⁻⁶ Torr or less. Argon gas is blown into the chamber, 1 × 1
After setting to 0 ^-2 Torr, high frequency sputtering at 13.56 MHz was continued for about 60 minutes. At this time, the high frequency input power is 200 W (0.3 kV) and the substrate temperature is 170 ° C.
Met. By this operation, a tantalum film having a thickness of about 2 μm and a thickness of about 30 g per 1 m ² was formed. The surface of the obtained coating film was analyzed by X-ray diffraction (XRD). as a result,
A β-tantalum diffraction pattern was observed. An electrode coating liquid having the following liquid composition was prepared and applied to the electrode substrate thus prepared. TaCl ₅ 0.32 g H ₂ IrCl ₆ · 6H ₂ O 1.00 g 35% HCl 1.0 ml n-CH ₃ (CH ₂ ) ₃ OH 10.0 ml This was dried at 120 ° C. for 10 minutes and then kept at 500 ° C. It baked in the electric furnace for 20 minutes. This coating operation of the electrode active material was repeated 10 times to prepare an electrode having 30 g-Ir / m ² of iridium oxide as the active material (the weight composition ratio of the catalyst layer was Ir / Ta = 7/3). The tip of the catalyst coating layer of this electrode was cut out to 10 × 10 mm, and the other portion was sealed and used as the anode for life test. An electrolytic life acceleration test of the electrode thus manufactured was performed. The bath conditions are 70 ° C., 100 g / dm ³ Na _{2 at} pH 1.2.
SO ₄ solution. A zirconium plate was used as the cathode.
The electrolysis method is constant current electrolysis, and the current density is 300 A / d.
It was set to m ² . Five or more electrodes having the same specifications were prepared, and the average of the times when the cell voltage increased by 5 V as compared with the electrolysis start voltage of these electrodes was defined as the electrode life. As a result of fluorescent X-ray analysis of the electrode after the test, the amount of residual catalyst was about 14 g-Ir / m ² and the catalyst consumption rate was 2.80 mg-Ir / m ² hr. Table 1 shows the electrode life and the catalyst utilization rate. The catalyst utilization rate was expressed as the ratio of the amount of catalyst decrease at the end of electrode life to the initial amount of catalyst.

Example 2 An electrode having an intermediate layer of a β-tantalum thin film was prepared in exactly the same manner as in Example 1 except that the composition of the electrode coating liquid was changed to the following. TaCl ₅ 0.18 g H ₂ IrCl ₆ · 6H ₂ O 1.00 g 35% HCl 1.0 ml n-CH ₃ (CH ₂ ) ₃ OH 10.0 ml The results of the same electrode life acceleration test as in Example 1 were performed. Table 1
Shown in.

Example 3 An electrode having an intermediate layer of β-tantalum thin film was prepared in exactly the same manner as in Example 1 except that the composition of the electrode coating liquid was changed to the following. TaCl ₅ 0.08 g H ₂ IrCl ₆ · 6H ₂ O 1.00 g 35% HCl 1.0 ml n-CH ₃ (CH ₂ ) ₃ OH 10.0 ml The results of the same electrode life acceleration test as in Example 1 were performed. Table 1
Shown in.

Example 4 An electrode was prepared in the same manner as in Example 1 except that high frequency sputtering was continued for about 35 minutes, and an intermediate layer of β-tantalum thin film having a thickness of about 1 μm and a thickness of about 16 g per 1 m ² was formed. The same electrolytic life acceleration test was performed. The results are shown in Table 1.

Example 5 An electrode was prepared in exactly the same manner as in Example 1 except that high frequency sputtering was continued for about 150 minutes, and an intermediate layer of β-tantalum thin film having a thickness of about 5 μm and a thickness of about 5 μm per 1 m ² was formed. The same electrode life acceleration test was performed. The results are shown in Table 1. In Examples 1 to 5 above, β / was determined by X-ray diffraction measurement.
(Α + β) was 65%.

Comparative Example 1 A titanium plate treated in the same manner as in Example 1 was prepared. Tantalum sputtering was performed in the same manner as in Example 1 except that this titanium plate was placed 20 mm from the target. As a result of measuring the XRD of the obtained coating, α
-A tantalum diffraction pattern was observed. An electrode coating solution having the same composition as in Example 1 was prepared on this surface, and 30 g-Ir
/ M ^{2 was} applied to prepare an electrode. The same electrolytic life acceleration test as in Example 1 was performed, and as a result of the fluorescent X-ray analysis of the electrode after the test, the residual catalyst amount was about 20 g-Ir / m ² , and the catalyst consumption rate was 2.67 mg-Ir / m ^2. It became hr. Table 1 shows the electrode life and the catalyst utilization rate.

Comparative Example 2 A titanium plate treated in the same manner as in Example 1 was prepared. Next, a tantalum wire having a wire diameter of 1.2 mm was used for thermal spraying with an arc sprayer to obtain a tantalum sprayed layer (intermediate layer) having a thickness of 50 μm. As a result of measuring the XRD of this coating, a diffraction pattern of α-tantalum was recognized. 30 g-Ir / m ^{2 of the} same electrode coating liquid as in Example 1 was applied to this electrode substrate,
An electrode for comparison was prepared. The results of the same electrolytic life acceleration test as in Example 1 are shown in Table 1.

Comparative Example 3 A titanium plate that had been subjected to the same treatment as in Example 1 was prepared. Next
In addition, a tantalum wire with a wire diameter of 1.2 mm is used for decompression plasma.
50 nm thick tantalum sprayed layer (intermediate layer)
Got As a result of measuring the XRD of this coating, α-tanta
The diffraction pattern of Le was observed. Example of this electrode substrate
30 g-Ir / m of the same electrode coating liquid as 1 ²Apply and compare
The electrode for was produced. Electrolytic life acceleration test similar to that of Example 1
The results of the tests are shown in Table 1. In Comparative Examples 1 to 3 above
In X-ray diffraction measurement, the diffraction peak of α-tantalum alone
Was observed.

Comparative Example 4 A titanium plate treated in the same manner as in Example 1 was prepared, and 30 g of an electrode coating liquid having the same liquid composition as in Example 1 was directly applied to the surface of the titanium plate.
An electrode coated with -Ir / m ² was prepared. The results of the same electrolytic life acceleration test as in Example 1 are shown in Table 1.

Example 6 An electrode similar to that of Example 1 was prepared and a polarity reversal test was conducted. The bath conditions were 50 ° C. and 100 g / dm ³ Na ₂ SO ₄ aqueous solution having a pH of 1.2. A platinum plate was used as the counter electrode. The electrolysis method was set to a current density of 200 A / dm ² and 2
The measurement was performed by applying a reverse current of 20 A / dm ² every 0 minutes for 5 minutes. The electrode life was defined as the time when the cell voltage during positive energization increased by 5 V compared to the starting voltage. This polarity reversal test was conducted to examine the durability of the electrode against negative polarization, and the results are shown in Table 2.

Comparative Examples 5 to 8 The same electrodes as those of Comparative Examples 1 to 4 were prepared and the same polarity reversal test as in Example 6 was conducted. The results are shown in Table 2.

[0024]

[Table 1]

[0025]

[Table 2]

As is clear from the results of the above Examples and Comparative Examples (Table 1 and Table 2), each Example using β-tantalum as an intermediate layer is a Comparative Example in which an α-tantalum intermediate layer is provided by a sputtering method. The electrode life is about twice as long as that of No. 1, especially about 5 times as long as the polarity reversal test. Further, even when compared with an electrode having an α-tantalum intermediate layer formed by a thermal spraying method or a low pressure plasma method, the electrode life is similar to the above although the film thickness of these electrodes is much larger. Have a difference.

Experimental Examples 1 to 6 (however, Experimental Examples 1 to 4 correspond to Example 7 and Experimental Examples 5 and 6 correspond to Comparative Example 9) The electrodes of the following Experimental Examples 1 to 6 were prepared and the same as Example 6. The polarity reversal test was performed. The results are shown in Table 3. Experimental Example 1 A titanium plate treated in the same manner as in Example 1 was prepared. This titanium plate is placed 40 mm from the target,
The pressure inside the chamber was set to 1 × 10 ⁻⁶ Torr or less. Nitrogen gas with a partial pressure of 1.0 × 10 ⁻⁵ Torr was blown into the chamber, and then argon gas was blown into the chamber to adjust the pressure inside the chamber to 1 × 10 ⁻² Torr. Next, high-frequency input power of 200 W (0.3 kV) and high-temperature sputtering of 13.56 MHz were continued for about 90 minutes under conditions of a substrate temperature of 400 ° C. This operation 1 m ² per about 50 g, the thickness of 3μm
A tantalum coating of X on the surface of the obtained film
It was analyzed by the line diffraction method. As a result, α-tantalum is about 17
The presence of about 83% of β-tantalum containing 0.1% was confirmed. A catalyst layer was formed on the thus-prepared electrode substrate by the same method as in Example 1.

Experimental Example 2 A titanium plate treated in the same manner as in Example 1 was prepared. This titanium plate is placed 20 mm from the target,
The partial pressure of nitrogen gas in the chamber is 1.75 × 10 ^-5 To
In the same manner as in Experimental Example 1 except that rr was used, high-frequency sputtering was continued for about 150 minutes at a high-frequency input power of 200 W (0.3 kV) and a substrate temperature of 400 ° C. With this operation, about 80 g per 1 m ² and thickness about 5
A μm tantalum coating was formed. The surface of the obtained coating film was analyzed by the X-ray diffraction method. As a result, the presence of about 52% of β-tantalum including about 48% of α-tantalum was recognized. A catalyst layer was formed on the thus prepared electrode substrate by the same method as in Example 2. Experimental Example 3 The composition and amount of the catalyst layer were the same as in Example 3, and Experimental Example 2
An electrode having an intermediate layer of β-tantalum thin film similar to that was prepared.

Experimental Example 4 The composition and amount of the catalyst layer were the same as in Example 4, and Experimental Example 2 was used.
An electrode with an intermediate layer of β-tantalum thin film similar to
did. Experimental example 5 A titanium plate that had been subjected to the same treatment as in Example 1 was prepared. This
Place the titanium plate of 20 mm from the target,
The partial pressure of nitrogen gas in the chamber is 1.9 × 10 ^-FiveTor
High-frequency input power in the same manner as in Experimental Example 1 except that r was used.
1 at 200 W (0.3 kV) and substrate temperature of 400 ° C
High-frequency sputtering at 3.56 MHz continued for about 60 minutes
I got it. 1m by this operation²Approximately 30 g, thickness of approximately 2 μm
A tantalum coating of X on the surface of the obtained film
It was analyzed by the line diffraction method. As a result, α-tantalum about 62
The presence of about 38% of β-tantalum containing 0.1% was confirmed. This
The electrode substrate manufactured in the same manner as in Example 1
Then, a catalyst layer was prepared.

Experimental Example 6 The composition and amount of the catalyst layer were the same as in Example 3, and Experimental Example 5
An electrode having an intermediate layer of β-tantalum thin film similar to that was prepared.

[0031]

[Table 3]

Next, a life test of an electrode having a thin film intermediate layer containing 50% or more of β-tantalum was conducted. Examples 8, 9 The thickness of the intermediate layer of the β-tantalum thin film is 2 μm and 1 μm.
Other than the above, a thin film intermediate layer was formed by the same method as in Experimental Example 1, and then a catalyst layer was formed by the same method as in Example 2 and Example 3 to obtain Example 8 and Example 9, respectively. The results of the same electrode life acceleration test as in Example 1 are shown in Table 4.

[0033]

[Table 4]

From the above, an electrode having a tantalum thin film intermediate layer containing β-tantalum in an amount of 50% or more is resistant to cathodization by polarity reversal, particularly β-tantalum in an amount of 80% or more and an iridium oxide-tantalum oxide mixed oxide catalyst layer. It was found that when the composition of iridium oxide is 80 to 95% in terms of metal and the tantalum oxide is 20 to 5% in terms of metal, the electrode life is greatly extended.

[0035]

In the oxygen generating anode according to the present invention,
The intermediate layer formed by sputtering β-tantalum prevents electrolytic oxidation of titanium forming the substrate, and has strong corrosion resistance and electrolytic oxidation resistance of itself and good conductivity. In addition, the results of the polarity reversal test also confirm that it is very effective for making this electrode a cathode. Further, the electrode active layer obtained by thermally decomposing the intermediate layer has good adhesion to the intermediate layer, has a large catalytic activity for oxygen generation, and is excellent in corrosion resistance to a sulfuric acid solution like the intermediate layer. The above effects are particularly remarkable as compared with an anode having an intermediate layer formed by sputtering α-tantalum.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Ryuichi Otokawa               2-7-1, Mukonosato, Amagasaki City, Hyogo Prefecture               304                (56) References JP-A-6-306669 (JP, A)                 JP-A-5-230682 (JP, A)

Claims (3)

(57) [Claims] 1. A thin film intermediate layer of metallic tantalum containing 50% or more of β-tantalum is deposited on a conductive metallic substrate made of metallic titanium or its alloy by a sputtering method, and a platinum group metal oxide is further deposited on the surface thereof. 50% or more of β-tantalum formed by forming an electrode active substance coating layer containing
An oxygen generating anode having a thin film intermediate layer of metallic tantalum contained above and excellent in negative polarization resistance. 2. A metal tantalum thin film intermediate layer having a thickness of 1 to
The anode for oxygen generation according to claim 1, which has a thickness of 5 μm. 3. Iridium oxide as the electrode active substance is 70 to 95% by weight in terms of metal, and tantalum oxide is 5 to 5% in terms of metal.
The oxygen generating anode according to claim 1 or 2, which is a mixed oxide composed of 30% by weight.