KR20140098159A - Method for exfoliating coating layer of electrode for electrolysis - Google Patents

Abstract

The present invention relates to a coating layer containing an electrode material containing a noble metal and / or a metal oxide on the surface of an electrode substrate (electrode substrate) including valve metals or valve metal alloys such as titanium and tantalum And the titanium alloy or the substrate material of the electrode used for electrolysis containing an insoluble metal electrode having an insoluble metal electrode having an insoluble metal electrode having a specific surface area And / or a method for recovering and reusing a conductive substrate of a titanium or titanium alloy base. The removing method includes sequentially treating an insoluble metal electrode having a coating layer with an alkaline treatment process using a pseudo alkali aqueous solution, a heating and a firing process, and an acid treatment process, wherein the alkali treatment process comprises adding a thickener to the caustic alkali aqueous solution By using an alkali treatment liquid prepared by adding the alkali treatment liquid.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method of separating a coating layer of an electrolytic electrode,

The present invention relates to a coating layer containing an electrode material containing a noble metal and / or a metal oxide on the surface of an electrode substrate (electrode substrate) including valve metals or valve metal alloys such as titanium and tantalum And the titanium alloy or the substrate material of the electrode used for electrolysis containing an insoluble metal electrode having an insoluble metal electrode having an insoluble metal electrode having a specific surface area And / or a method for recovering and reusing a conductive substrate of a titanium or titanium alloy base.

However, when used for a certain period of time or more, this type of electrolytic electrode can not be used for a long period of time between electrode gasses including a valve metal such as titanium and tantalum or a valve metal alloy and a coating layer containing an electrode material containing noble metal and / Corrosion occurs at the interface, which forms a passive layer on the surface of the gas, which makes the reactivation process difficult. As a result, the surface of the substrate must be shaved until a new surface appears, or the electrode must be fabricated from a new electrode substrate.

Among the electrolytic electrodes, in the case of an electrode for generating oxygen, vacuum spattering is performed on the surface of an electrode base including a valve metal such as titanium and tantalum or a valve metal alloy, including ion plating, When an electrolytic electrode having an electrode coating layer containing iridium oxide coated on the surface of the thin film and a thin film of 0.5 to 3 占 퐉 containing metals such as tantalum and niobium formed by the electrode substrate and the coating layer is used, (For example, see Patent Document 1).

However, when such an oxygen generating electrode is applied to an electrolytic reaction to produce a copper foil, a chemical compound containing lead and antimony is attached to the surface of the electrolytic electrode as electrolytic electrolyte . In the electrolytic reaction, lead in the electrolytic solution adheres as lead oxide which is a good conductor, but antimony is adhered as a poor conductor, antimony oxide. On the other hand, conductive oxidized lead turns into non-conductive lead sulfate when electrolysis is stopped. Moreover, lead and antimony adhered on the surface of the electrode are separated from the surface of the electrolytic electrode during the start and stop of the electrolytic reaction and during the electrolytic reaction. As a result, the oxygen generating electrode has a non-uniform current distribution, resulting in poor quality of the copper foil thickness, and has a defect that can not be used continuously for a long time as an electrolytic electrode.

In this case, the deposits on the surface of the electrode including lead and antimony were removed with Scotch-Brite (registered trademark), an abrasive produced by Sumitomo 3M Limited, for reactivation of the electrode for electrolysis. Is scrapped off from the surface of the oxygen generating electrode used in the electrolytic reaction. However, when the oxygen generating electrode is continuously used for three months, it is difficult to reactivate the electrolytic electrode by the abrasive.

It is well known that an insoluble metal electrode having a coating of ruthenium oxide or iridium oxide on the surface of a conductive titanium substrate is widely used in industrial electrolysis typified by chlor-alkali electrolysis. The life span of these electrodes is extremely long, and they are often used for over 10 years. However, even if there is no deterioration of the electrode material, only deteriorated electrode material is formed between the coating layer and the substrate titanium due to the system problem or the non-conductive form within a relatively short period of time, Thereby inducing a failure.

Various electrode reactivation methods have been proposed to cope with this. When the electrode body is sufficiently thick and has a plate shape, the surface is worn by machining, removing the surface adherends with a blast or the like, removing the residue by machining, acid cleaning or alkali treatment, Water, and the like have been used alone or in combination thereof. When such processing is performed, titanium or titanium alloy, which is a gaseous substance, is likely to be reusable. However, the coating layer containing an expensive electrode material is small in amount, and processing materials such as machining or blasting, (By-products), the amount of the by-products can not be substantially recovered. In other words, attempts have been made to recover the electrode material and / or the electrode base material, and the possibility has been found, but in most cases, the recovery cost is high and it has not been practically done for economic reasons. In addition, although the gaseous titanium or the titanium alloy can be recovered in the same manner as in the case of chemically immersing in the alkali molten salt, the coating layer containing the electrode material is dissolved in the excessive molten salt and technically recovered, It is the current state that it is not done for economic reasons.

When it is considered that only the coating layer containing the electrode material is to be recovered, there is proposed a chemical peeling method after rolling treatment in which the mechanical peeling is promoted, or a method of quenching after heating at high temperature. Although the electrode material can be recovered by these methods, titanium can not be used as the gas as it is, and the gas must be redissolving to be reused as a raw material.

In recent years, due to an increase in the price of titanium and a shortage of supply of titanium, it has become difficult to obtain titanium or titanium alloy gas, and recovery from the titanium or titanium alloy gas is required for reuse. Further, the platinum group metal contained in the coating layer having the electrode material is a rare metal which is extremely expensive, and it is expected that the platinum group metal may be recovered together. However, in the conventional method with slight expectation, its recovery is impossible. For example, when the gas is sufficiently thick, surface grinding can be applied for recovery, but grinding is practically impossible when the thickness is 1 mm or less. Although it can be achieved, the gas can be thinned and lapped for satisfactory energization, and reuse as gas is extremely limited. Many recovery techniques have been proposed. The following patent documents are representative known technologies.

Patent Document 1 discloses a method for peeling a coating layer containing an electrode material by dissolving a surface of an electrode base with a corrosive acid to separate the coating and recovering the coating and the gas. However, since a stable and strong oxide is present between the electrode substrate and the coating, and chemical bonds often occur between the coating layer containing the electrode material and the gaseous metal, it is practically not easy to peel the coating.

Patent Document 2 shows a method of recovering a gas and a coating in such a manner that a highly concentrated alkali aqueous solution is coated on an electrode surface and then heated to dissolve a coating layer containing an electrode material in an aqueous alkaline solution. However, this method has problems such that considerable abrasion of titanium gas occurs simultaneously in the aqueous alkaline solution and the coating dissolves in the alkaline matrix, which makes recovery difficult.

Patent Document 3 and Patent Document 4 also disclose a method of physically and chemically peeling a coating layer containing an electrode material and then recovering a coating layer containing the electrode material. As a peeling method, Patent Documents 3 and 4 refer to acid etching or polishing of the gas, but these methods recover the coating through exhaustion of gas which may cause excessive wear to reuse the gas.

Patent Document 5 discloses a method of peeling the electrode material by corrosion of the titanium surface by acid treatment after physically weakening the adhesion between the coating layer containing the electrode material and titanium by performing rolling treatment on the used electrode . The method is also effective in simultaneously recovering the titanium gas and the coating layer containing the electrode material, but still titanium can not be recovered as needed for redissolution for recovery.

Patent Document 6 discloses a method of separating and recovering a coating and gaseous titanium by cutting an electrode into pieces and barrel polishing. Although the process is relatively simple and effective, the gas can not be recovered as it is.

Patent Document 7 discloses a process of (1) a step of covering a surface of an electrode with a caustic alkali aqueous solution as a pretreatment, (2) a step of maintaining it at 350 ° C to 450 ° C for 10 minutes to 60 minutes for reaction, and Hydrochloric acid, sulfuric acid, and nitric acid, or a mixture thereof. Even by this method, in view of the maintenance of the caustic alkali solution, the coating material can not be separated from the electrode substrate, and the electrode substrate can not be used for reuse. As described above, these conventional methods do not provide a method of simultaneously recovering the coating layer containing the electrode material and the gaseous metal. Therefore, it is practically not carried out simultaneously to recover the titanium or titanium alloy of the electrode base and the coating layer containing the electrode material.

Japanese Patent Application Laid-Open No. 59-123730 Japanese Unexamined Patent Application Publication No. 2002-88494 Japanese Unexamined Patent Application Publication No. 2002-212650 Japanese Unexamined Patent Application Publication No. 2002-194581 Japanese Patent Application Laid-Open No. 2001-294948 Japanese Patent Application Laid-Open No. 2001-303141 Japanese Patent Application Laid-Open No. 2008-81837

The present invention relates to a method for manufacturing a thin film magnetic head comprising separating a coating layer containing a noble metal coated on its surface and / or an electrode material containing the noble metal oxide from a surface of an electrode base including a valve metal or a valve metal alloy including titanium and tantalum, The present invention is to provide a method of effectively recovering an electrode material by recovering an electrode gas including a valve metal or a valve metal alloy containing tantalum in a reusable state.

The present invention provides, as a first solution to the above problem, to provide a method of manufacturing a semiconductor device, which comprises depositing a noble metal and / or a noble metal on the surface of an electrode substrate including valve metals or valve metal alloys including titanium and tantalum, The surface of the insoluble metal electrode having the coating layer containing the electrode material including the metal oxide thereof is subjected to an alkali treatment process using a caustic alkali aqueous solution, Wherein the alkali treatment step is carried out by using an alkali treatment liquid prepared by adding a thickener to the aqueous alkali solution.

The present invention provides, as a second solution to solve the above problem, a method for peeling a coating layer from the surface of an electrode base, which comprises using a thickener containing a natural polysaccharide thickener.

The present invention, as a third solution to solve the above problem, is characterized by using a thickener comprising bio gum, guar gum derivative or cellulose derivative as the natural polysaccharide thickener A method for peeling a coating layer from an electrode base surface is provided.

The present invention provides, as a fourth solution for solving the above problems, a method for peeling a coating layer from the surface of an electrode base, characterized by using a thickening agent containing carboxymethyl cellulose as a thickening agent.

The present invention provides, as a fifth solution to solve the above problems, a method for peeling a coating layer from a surface of an electrode base, wherein a thickening agent containing xanthan gum is used as a thickening agent.

The present invention provides, as a sixth solution to solve the above problem, a method for peeling a coating layer from the surface of an electrode base, characterized in that an addition ratio of the thickening agent in the alkaline processing solution is 0.2 mass% or more and 1 mass% or less do.

According to a seventh solving means for solving the above problems, the present invention provides a method for peeling a coating layer from the surface of an electrode base, characterized in that an addition ratio of the thickening agent in the alkaline processing solution is 0.4 mass% to 1 mass% do.

According to the present invention, the electrode material can be effectively and efficiently separated from the electrode substrate. At this time, the electrode gas is not consumed more than necessary to protect itself, and the stabilized electrode material is not eluted by the molten salt treatment at the relatively low temperature condition and can be separated and recovered as a fragment or powder of the electrode material. In addition, the substrate metal or electrode material, which mainly contains titanium, hardly dissolves in acid, so consumption of acid used only for neutralization of the residual alkali can be minimized. The present invention is not limited to the electrode for generating oxygen, but can be applied to various electrolytic electrodes.

1 is a photograph showing the degree of peeling of one of the embodiments of the present invention.
2 is a photograph showing the degree of peeling of one of the embodiments of the present invention.
3 is a photograph showing the degree of peeling of one of the embodiments of the present invention.
4 is a photograph showing the degree of peeling of one of the embodiments of the present invention.
5 is a photograph showing the degree of peeling of one of the embodiments of the present invention.
6 is a photograph showing the degree of peeling of one of the embodiments of the present invention.

The present invention relates to a method for effectively peeling a noble metal and / or a coating layer containing an electrode material containing the noble metal oxide from a surface of an electrode base including a valve metal or a valve metal alloy including titanium and tantalum, The present invention relates to a method for separating and recovering an electrode material and an electrode material for recovering an electrode material. More particularly,

(1) a step of cleaning the surface,

(2) an alkali treatment step of treating the electrode coated surface with an alkali treatment liquid containing at least a pseudo alkali aqueous solution,

(3) a heating and firing step of promoting the reaction while maintaining the above-mentioned caustic alkali at a temperature near the melting point, and

(4) Acid treatment process immersed in acid

To an insoluble electrode.

The above process is performed on the electrode on which the deposit or impurity on the surface is removed to minimize the corrosion of the gaseous material and the electrode material between the gaseous metal and the electrode material so that the interface is selectively corroded to separate and recover the gas, At the same time, the electrode material can be stably separated and recovered as a solid powder.

More particularly, the first step is to clean the surface by a method that can be suitably applied according to the deposit. For example, in the case of an electrode used for chlorine alkali electrolysis by an ion exchange membrane process, there is usually little adherence, so the surface is washed with water or immersed in a dilute hydrochloric acid solution for acid refinement. In the electrode used for manufacturing copper foil, the surface is frequently contaminated with a heavy metal compound such as lead sulfate and antimony oxide to perform acid refining. If necessary, these compounds can be removed by alkali washing with 10 to 30 mass% of an alkali salt, and then immersing them in a mineral acid solution. By combining these methods, a cleaner surface can be obtained.

Then, an alkali treatment step is carried out with an alkaline treatment solution of a caustic alkali aqueous solution. In the alkali treatment step, an alkali treatment liquid is applied onto at least the electrode coating surface. The caustic alkali used for the alkali treatment liquid is not particularly limited, but caustic soda is most preferable in terms of high reactivity and availability. Mixtures of caustic soda and caustic potassium may also be used. The actual reaction in the application of the alkali treatment liquid on the electrode surface is close to the molten salt reaction, and it is preferable to adhere at a high concentration. When the alkali treatment liquid is applied onto the surface of the electrode, since the viscosity of the alkali treatment liquid is low and flows relatively easily, it is not easy to stably adhere the applied alkali treatment liquid to the electrode surface. For this reason, in the alkali treatment step, it is necessary to stably maintain the alkali treatment liquid on the electrode surface. This application is performed, for example, in a region where the electrode material is present in a caustic soda aqueous solution of 50% by mass to 60% by mass. Further, for the same purpose, it is also possible to immerse at least the electrode coating surface in the alkaline processing solution having a similar definite concentration so that the surface thereof can adapt to the alkali. This application must be covered over the entire surface of the electrode and sufficiently imbibed. Generally, the electrode surface is water-repellent with respect to tentleness. The electrode surface is then blushed until its surface is adequately wetted or immersed in the solution for a period of time. However, in the case where only caustic alkali is applied, since the caustic alkali does not sufficiently adhere to the surface of the electrode to be treated, it is difficult to achieve the expected alkali treatment.

Therefore, in the present invention, a thickening agent is added to the above-mentioned caustic alkali aqueous solution to prepare an alkali treatment liquid. As the thickener, a thickener containing CMC or XAG is used.

In the present invention, the alkali treatment step is carried out using an alkali treatment liquid prepared by adding a thickening agent to the above-mentioned caustic alkali aqueous solution. As a result, adhesion of the caustic alkali on the coating layer is increased and the peeling effect is improved. In the present invention, the amount of the thickening agent used is adjusted to 0.2 mass% or more to increase the adhesion of the pseudo alkali on the coating layer, thereby inducing the enhanced peeling effect. In addition, it has been found that the peeling effect is completed by the amount of the thickener adjusted to 0.4 mass% or more. On the other hand, when the amount of the thickener used exceeds 1% by mass, gelation of the pseudo alkali immersion liquid proceeds and it becomes difficult to handle the pseudo alkali immersion liquid, so that the content is preferably 1% by mass or less. Furthermore, the amount of the thickener to be used is more preferably controlled to 0.5% by mass or less, whereby the gelation of the caustic alkali immersion liquid can be suppressed and its handling becomes easier.

As the thickening agent, those exhibiting a thickening effect in an alkali solution are used. As this type of thickening agent, it is preferable to contain a natural polysaccharide thickening agent. As natural polysaccharide thickener, bioglass, guar gum derivative, cellulose derivative and the like can be used. Of these thickeners, the following are particularly preferable.

1) Bio Sword: XAG

2) guar gum derivative: guar gum

3) Cellulose derivatives: CMC

4) Others: carrageenan, pectin

Normally, it is kept at room temperature for 10 to 30 minutes after application and then dried at a temperature of 60 to 200 ° C. By this operation, most of the water in the caustic alkali is evaporated, and the caustic alkali anhydride is precipitated on the surface. The drying time is not particularly limited, but is preferably about 10 minutes to 30 minutes. However, the drying process is not essential. If the alkali solution is uniformly maintained on the electrode surface, the drying step may be omitted, and the subsequent heat treatment step will perform the same function.

Further, this is heat-treated at a temperature slightly higher than the melting point of the caustic alkali. That is, since caustic soda has a melting point of about 330 ° C, it is preferably about 350 to 450 ° C. At this temperature, the reaction is carried out for 10 minutes to 1 hour, usually 30 minutes. Although the reaction mechanism is not clear, it is possible to subsequently separate the electrode material by reacting with the acid. It is then considered that alkali ions in the pseudo alkali react with the electrode material, the oxide between the electrode material and the gas, and the surface of the gaseous titanium to become alkali complex. Moreover, in view of the fact that the elution of the electrode material or titanium gas is very small, the reaction between the electrode material and the oxide between the gases tends to occur selectively. After this treatment, the electrode is left to cool. Such cooling can be performed in a furnace, but from the viewpoint of efficiency, it is preferable to perform cooling in the atmosphere outside the furnace. Of course, it is also possible to carry out the following inorganic acid immersion treatment without cooling, in which case care must be taken for splashing of the acid.

Next, the alkaline-treated electrode is immersed in an inorganic acid such as nitric acid, hydrochloric acid or sulfuric acid. The concentration of the inorganic acid is not particularly limited, but a dilute acid of about 10 to 20 mass% is usually preferred. The temperature of the inorganic acid is not particularly limited, but it is preferable to raise the temperature to accelerate the reaction, and it is preferably 40 ° C or more. By such an immersion treatment, the alkali metal titanate is dissolved in the acid, and at the same time, the electrode material is separated and separated from the gaseous metal containing titanium or titanium alloy. At this time, peeling can be promoted by stirring the acid solution or brushing the electrode surface for better liquid contact. Normally, it can be sufficiently separated in one treatment cycle, but it can be completely separated by repeating 2 to 3 cycles from alkali application to heating and firing if necessary. Here, since the electrode material itself is stabilized by heating, it can be recovered as a precipitate without being dissolved in almost acid. As a result, the titanium metal or the titanium alloy, which is a gaseous metal, is hardly consumed, and the electrode material can be recovered as an oxide solid.

The acid used may be an inorganic acid such as hydrochloric acid, nitric acid, sulfuric acid or a mixed acid thereof. However, from the viewpoint of the solubility of the dissolution product, nitric acid or hydrochloric acid is preferable. In the case of sulfuric acid, care must be taken because titanium in the electrode material or electrode material slightly soluble in repeated use may cause precipitation as titanium sulfate. However, this is not a problem in particular. However, it is clear that if precipitation occurs, separation with the electrode material becomes troublesome, so it is preferable to carry out the work while appropriately removing such precipitate.

The oxide solids, which are separate electrode materials, can be recovered under normal conditions. For example, by hydrogen reduction, the platinum group metal component in the electrode material is reduced by hydrogen reduction and metallized for recovery. When the component is ruthenium, it is vaporized as RuO ₄ by thermal oxidation in hypochlorous acid, and is recovered as ruthenium acid chloride in such a manner that it is captured in hydrochloric acid. When the component is iridium, it is converted into chlorine gas and chlorinated iridium salt together with alkali chloride, and then the alkali is separated and the iridium component is recovered as iridium chloride or iridium chloride. In other cases, it may be recovered by dissolving in aqua regia. It is also possible to recover it by electrolysis. At this time, since titanium oxide or tantalum oxide, which is the same electrode material, is not reduced to hydrogen, it does not chlorinate or dissolve, so it can be completely separated from the platinum group metal. A part of the electrode material may dissolve in the acid. In this case, ammonia is added to the used acid to neutralize it, so that the ammonium salt of the platinum group metal is precipitated and separated by filtration. This may be recovered separately from the initial oxide precipitation, but it may be recovered by precipitation filtration with the oxide precipitate after the ammonia treatment.

Next, the present invention will be described concretely with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

Example

The surface of the titanium plate was subjected to dry blasting treatment with iron grit (# 120 size), and then subjected to an acid cleaning treatment in an aqueous 20 mass% sulfuric acid solution (90 deg. C) for 10 minutes, Was carried out. The cleaned electrode substrate was set in an arc ion plating apparatus, and sputtering coating of a pure titanium material was performed. The coating conditions are as follows.

Target: Titanium disc (water-cooled back surface)

Vacuum degree: 3.0 × 10 ^-1 Torr (Ar gas substitution introduced)

Cloth Power: 25V-150A

Substrate temperature: 150 占 폚 (at sputtering)

Time: 35 minutes

Coating thickness: 2 micrometers

When X-ray diffraction was performed after the sputtering coating, a sharp crystalline peak belonging to the bulk of the substrate and a broad pattern attributable to the sputtering coating were observed, and it was found that the coating was amorphous.

Next, the iridium tetrachloride and the contaminated tantalum were dissolved in 35 mass% hydrochloric acid to prepare a coating solution. The sputtering-coated substrate was brushed and dried, and then dried in an air circulating electric furnace (550 DEG C for 20 minutes) Followed by pyrolytic coating to form an electrode coating layer made of a solid solution of iridium oxide and tantalum oxide. The coating thickness of the brush coating was set so that the coating thickness of the brush coating was approximately 1.0 g / m ² in terms of iridium metal. The application and baking operations were repeated 12 times. An empty product of the electrolytic electrode thus produced was cut into a size of 30 mm x 30 mm to prepare a sample (hereinafter referred to as " present sample ").

◇ Preparation of alkali treatment liquid containing thickener

XAG and CMC were selected as thickeners, and a state in which 1 mass% of each of them was dissolved in pure water was observed, and a preferable concentration range was observed.

As a result, it was judged that the use of 1.0 weight% or less of the thickener was preferable. The reason for this is that if it exceeds 1.0% by mass, XAG becomes turbid and becomes gelled when it is left standing, and stirring becomes difficult, and CMC is colorless and transparent and slightly thickened, , Both of which were determined to be the optimum concentration of not more than 1.0% by mass.

After a predetermined amount of the above thickener was dissolved in pure water in an amount of 1.0% by mass or less, NaOH-KOH was dissolved to 50% by mass. Thereafter, the concentration was adjusted to the following concentration to prepare an alkali treating solution containing a thickener.

A) 0.2% by mass XAG-added alkali treatment liquid

B) 0.5% by mass XAG-added alkali treatment liquid

C) 0.1% by mass CMC-added alkali treatment liquid

D) 0.2 mass% CMC-added alkali treatment liquid

E) 0.4% by mass CMC-added alkali treatment liquid

F) 0.5% by mass CMC-added alkali treatment liquid

The 0.2% by mass XAG-added alkali treatment solution of the condition A) was prepared in the following manner. First, 0.2 g of XAG was dissolved in 49.8 g of water to prepare a 0.4 mass% XAG aqueous solution. Next, 25 g of NaOH and 25 g of KOH were dissolved in 0.4 mass% of XAG aqueous solution to prepare an alkali treatment solution comprising 100 g of a 50 mass% NaOH-KOH aqueous solution containing 0.2 mass% of XAG. The XMC-added alkali treatment solution of the condition B) and the CMC-added alkali treatment solution of the conditions C), D), E) and F) were also prepared in this manner.

◇ Separation process

This sample was immersed in the alkali treatment solution containing the thickener, and then put into the crucible with the coated side of the present sample facing downward.

Thereafter, after baking at 360 DEG C for 30 minutes, this sample was treated with hydrochloric acid to peel off the coating.

The peeling step was performed twice to confirm the reproducibility.

◇ Separation Result

Table 1 shows the state of the used alkali treatment solution and the adhesion state.

The treatment liquid state is,

○: Easy to adjust and stable.

&Amp; cir &: Not satisfactory (see comment for the reason of DELTA)

Respectively.

The adhered amount of the treatment liquid was represented by the ratio when the case where the thickening agent was not used was regarded as 1.

The condition of the alkali treatment liquid and the attachment condition Content of thickener The state of the treatment liquid Conditions for attaching the treatment liquid comment A) 0.2 mass% XAG ○ 1.5 B) 0.5 mass% XAG △ 3 The solution is left to gel. C) 0.1% by mass CMC ○ One Slightly thick D) 0.2 mass% CMC ○ 2 E) 0.4 mass% CMC ○ 2 F) 0.5% by mass CMC △ 3 Gelling may occur during alkaline addition G) No thickener ○ One

When the amount of the thickener added was 0.2 mass% or more, the amount of the immersion liquid adhered was improved compared with the conventional method in which the thickener was not used, and the effect of the thickener was confirmed. Further, in the case of 0.1 mass% CMC of C), the adhered amount of the treatment liquid was 1, and an increase in the adhered amount was not observed.

A, B, D, E, and F, in which the adhesion amount was improved, and the conventional alkali treatment liquid G (Comparative Example) in which the thickening agent was not used, were checked for the degree of peeling. The results of the degree of peeling were as shown in Table 2.

The degree of peeling in Table 2,

X: The coating is not peeled off and mostly remains.

○: Only a small amount remained

◎: Completely peeled off

Respectively.

Evaluation result of degree of peeling Content of thickener Degree of peeling Photo of drawing A) 0.2 mass% XAG ○ 1 B) 0.5 mass% XAG ◎ 2 D) 0.2 mass% CMC ○ 3 E) 0.4 mass% x CMC ◎ See FIG. F) 0.5 mass% x CMC ◎ 5 G) No thickener × 6

From the above results, the degree of peeling was improved in all the samples of A, B, D, E, and F in which the adhesion amount was improved, and the effect of the thickening agent was confirmed. On the other hand, in the conventional alkali treatment solution which did not use the thickener of G), the coating remained substantially without peeling.

Particularly, in the case of B, E and F, the coating was completely peeled off and reproducibility was observed. E was the best condition.

From the above results, it can be seen that the peeling effect can be improved by setting the amount of the thickening agent to be 0.2 mass% or more, and further, by setting the amount of the thickening agent to 0.4 mass% or more, I have found that there is.

Industrial availability

The present invention, which can be recovered and reused without deforming the noble metal and / or the noble metal oxide and the electrode base belonging to the expensive and rare metal surface covering layer from the insoluble metal electrode using the electrode base mainly composed of titanium, .

Claims (7)

An insoluble metal having a coating layer containing an electrode material containing a noble metal and / or a metal oxide on the surface of an electrode substrate (electrode substrate) including valve metals or valve metal alloys including titanium and tantalum The surface of the electrode is sequentially treated with an alkali treatment process using a caustic alkaline aqueous solution, a heat firing process, and an acid treatment process, wherein the alkali treatment process comprises adding a thickener to the caustic alkali aqueous solution, ). The method for peeling a coating layer from an electrode base surface. The method according to claim 1,
A method for peeling a coating layer from an electrode base surface characterized by using a thickener containing a natural polysaccharide thickener. 3. The method of claim 2,
Wherein a thickener comprising bio gum, guar gum derivative or cellulose derivative is used as said natural polysaccharide thickening agent. 4. The method according to any one of claims 1 to 3,
Wherein a thickening agent comprising carboxymethyl cellulose is used as a thickening agent. 4. The method according to any one of claims 1 to 3,
And a thickening agent containing xanthan gum is used as a thickening agent. 6. The method according to any one of claims 1 to 5,
Wherein the proportion of the thickening agent in the alkali treatment liquid is 0.2 mass% or more and 1 mass% or less. 6. The method according to any one of claims 1 to 5,
Wherein the proportion of the thickening agent in the alkali treatment liquid is 0.4% by mass or more and 1% by mass or less.

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