JPH028390A - Lead dioxide electrode and production thereof - Google Patents

Abstract

PURPOSE:To obtain a PbO2 electrode having superior physical strength and exfoliation resistance by successively forming an electrically conductive and corrosion resistant underlayer, an intermediate layer of a specified corrosion resistant component which is less active than PbO2 and a PbO2 layer on the surface of a corrosion resistant metal substrate. CONSTITUTION:The surface of a substrate of an electrically conductive and corrosion resistant metal such as Ti, Ta or Nb is roughened and cleaned. An underlayer of a Pt family metal, the oxide thereof, MnO2 or SnO2 is formed on the surface of the substrate and an intermediate layer of a corrosion resistant component which is less active than PbO2, e.g., a metal selected among the groups IVA, IVB, VA, VB and VIB of the periodic table, the oxide, carbide, nitride or boride thereof, the oxide of Fe, Mn, Co or Al or a corrosion resistant org. material such as fluororesin is formed on the underlayer by baking, electrolysis, thermal spraying or other method. A PbO2 layer is then formed on the intermediate layer by electrolysis to produce a PbO2 electrode not causing cracking due to internal residual stress and having superior durability. This electrode is used as the anode in an electrolytic reaction or other process.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a lead dioxide electrode with excellent durability and a method for manufacturing the same.

(Prior art and its problems) A lead monoxide electrode is mainly used as an anode in electrolysis such as mirabilite electrolysis and organic matter electrolysis, which performs oxygen generation and anodic oxidation. The conventional manufacturing method for lead dioxide electrodes is to coat lead dioxide by electrolysis either directly on a substrate such as titanium or on a substrate formed with a base layer made of a platinum group metal or its oxide. Lead dioxide coated by this method has disadvantages such as residual internal stress, lack of physical strength, cranking, and poor adhesion to the substrate.Electrolytic method The internal stress remains due to
Due to the unavoidable electrodeposition stress during electrolysis, the electrode substrate is often not held perfectly flat but is held in a slightly distorted state. When removed from the device, the distortion is resolved and the substrate itself returns to its planar shape, but on the other hand, the lead dioxide layer itself that is densely coated on the substrate is strained, and internal stress remains in the lead dioxide layer. This is because you end up doing it.

In order to eliminate this drawback, for example, a corrosion-resistant substrate is coated with a base layer of platinum or palladium oxide, and an intermediate layer of α-lead dioxide is coated on the base layer, and then a base layer of β-lead dioxide is coated on the base layer. An electrode having a coating layer formed thereon has been proposed, and the lead oxide layer is substantially formed by an electrolytic method (Japanese Unexamined Patent Publications Nos. 63-57791 and 63-57792). According to this publication, when α-lead dioxide, which is the intermediate layer, is formed by electrolytic method, the α-lead dioxide has almost no internal strain but has poor conductivity, whereas when β-lead dioxide is formed by electrolytic method, Although β-lead dioxide has good conductivity, it has a large internal strain. The purpose of the invention described in the above-mentioned publication is to compensate for the drawbacks of the lead oxide layer by constructing it as described above.

However, when multiple layers with the same activity are formed, an electrolytic reaction accompanied by gas generation occurs in the inner catalyst layer, and the generated gas causes problems such as shortened lifespan due to distance between the outer catalyst layers, etc. Defects are likely to occur.

Furthermore, in the electrode described in the above-mentioned publication, the two types of lead dioxide are substantially formed by an electrolytic method, and the drawbacks of coating by the electrolytic method described above remain in the lead oxide layer.

(Objective of the Invention) The present invention eliminates the above-mentioned drawbacks, minimizes residual internal stress while partially using an electrolytic method, improves physical strength, and prevents peeling of the surface coating layer. The object of the present invention is to provide a lead dioxide electrode and a method for manufacturing the same.

(Means for Solving the Problems) The present invention firstly provides a corrosion-resistant metal substrate, a base layer formed on the metal base and made of a material having corrosion resistance and conductivity, and a base layer formed on the base layer. A lead dioxide electrode comprising: an intermediate layer made of a corrosion-resistant material that is more inert than lead oxide, and a lead dioxide coating layer formed on the intermediate layer;
A base layer made of a corrosion-resistant and electrically conductive substance is formed on a corrosion-resistant metal substrate, an intermediate layer made of a corrosion-resistant substance that is more inactive than lead dioxide is formed on the base layer, and an intermediate layer is further formed on the intermediate layer. A method of manufacturing a lead dioxide electrode comprising forming a lead dioxide coating layer.

The present invention will be explained in detail below.

The lead dioxide coated electrode and the manufacturing method thereof according to the present invention include:
A lead dioxide electrode is formed by forming a base layer on a corrosion-resistant metal substrate, and forming a lead dioxide coating layer on the base layer by an electrolytic method, between the base layer and the lead dioxide coating layer. Forming an intermediate layer made of a material with low activity, absorbing residual internal stress of the lead dioxide coating layer formed on the intermediate layer to eliminate reduction in durability, and shielding the electrolyte by the intermediate layer. This substantially prevents the electrolytic solution from coming into contact with a base layer having relatively high electrochemical activity and generating gas, and the generated gas causes cranking of the lead dioxide coating layer, thereby reducing the amount of the coating layer. It is characterized by preventing peeling. The lead dioxide electrode according to the present invention is suitably used as an electrode for electrode reactions involving oxygen generation, that is, as an anode for sulfuric acid bath electrolysis, water electrolysis, organic matter electrolysis, etc., but is not limited to these, and is used for other electrolysis. It can be used as an electrode for

The corrosion-resistant metal substrate used in the present invention is a conductive metal such as so-called valve metal such as titanium, tantalum, niobium, zirconium, etc., and various shapes such as plate, rod, lath, etc. can be used without limitation. be able to. The metal substrate is preferably pretreated to improve the adhesion of the underlayer, etc., which will be described later, and to remove impurities on the surface of the metal substrate, and the pretreatment includes blasting using sand or grid. There are surface roughening treatments and degreasing treatments such as immersion in trichlorethylene.

Next, a base layer made of a platinum group metal such as platinum, palladium, iridium, or ruthenium, an oxide thereof, manganese dioxide, lead dioxide, or the like is formed on the corrosion-resistant metal substrate. An underlayer made of manganese dioxide or lead dioxide is particularly desirable because it is inexpensive. The method for forming the underlayer is not particularly limited, but in the case of platinum group metals, electrolytic plating may be performed using the metal substrate as a cathode, or other electroless plating methods may be used. In the case of manganese or lead dioxide, a thermal decomposition method may be used in which a solution of a compound of the corresponding metal is applied and baked. Thermal spraying can be used for platinum group metals and platinum group metal oxides, but it is not appropriate to apply the thermal spraying method to manganese dioxide or lead dioxide because crystal transformation of manganese monoxide, etc. occurs at the thermal spraying temperature. . This base layer is an essential component for maintaining conductivity between the metal base and the intermediate layer, and if the base layer does not exist, there will be no insulation at the joint surface between the intermediate layer or lead dioxide coating layer and the metal base. An oxide film is likely to be formed, the conductivity gradually decreases, and the potential increases, which is an adverse effect.

Next, an intermediate layer is formed on the metal substrate on which the underlayer is formed. The intermediate layer is a metal or an oxide, carbide, nitride, or boride of a metal selected from Group 8 of Periodic Table IVA, IVB, VA, VB, or VIB, or iron;
Contains at least one of manganese, cobalt, aluminum oxides or corrosion-resistant organic compounds,
Any material can be used as long as it has an electrochemical activity not greater than that of lead dioxide and has sufficient corrosion resistance. Generally, the above metal oxides have corrosion resistance;
Although oxygen overvoltage is also high, it is suitable, but carbides, nitrides, or borides of these metals can also be used. Corrosion-resistant organic compounds such as fluororesin and polyethylene are also preferably used. In the intermediate layer, the electrolyte contacts the base layer with low overvoltage through the lead dioxide coating layer, which often has a bottle ball, and the base layer functions as an electrode catalyst to generate gas, and the generated gas causes lead dioxide to increase. It has the function of preventing thalassoking, etc. from occurring in the coating layer, and is preferably a non-porous layer, but even if it is porous, the mere presence of the intermediate layer will prevent the above-mentioned base layer from forming. gas generation can be significantly prevented.

In addition to preventing the electrolyte from contacting the underlying layer, the intermediate layer also acts as a cushion for the lead dioxide coating layer, which will be described later, and absorbs the internal stress remaining in the coating layer, thereby increasing the durability of the entire electrode. Contributes to improving sexual performance.

Although the method for forming the intermediate layer is not particularly limited, it is preferable that the baking method or thermal spraying method be used. The baking method mainly involves coating the base layer with a mixture of the components forming the intermediate layer and a binder, or a binder containing the components of the intermediate layer alone, and heating it to remove all or part of the binder. This is a method of removing the intermediate layer component and baking the intermediate layer component on the base layer. The binder in the main baking method is a relatively sticky substance that has the function of attaching to the base layer the intermediate layer components that do not adhere to the base layer by themselves at room temperature, such as silicon oxide and sodium oxide. Examples include water glass diluted with water, which is a mixture of organic substances, and organic polymer substances dissolved in a solvent. Note that some binders are only partially removed by baking, and as long as the remaining substance can be used as an intermediate layer component, the binder may be used alone as described above. The baking method includes, for example, applying a mixed slurry of diluted water glass and lead dioxide powder, which is an intermediate layer component, onto the base layer, heating and baking it, and then immersing it in warm water to harden the water glass. This is a method in which the sodium oxide component is eluted, leaving only silicon oxide, and an intermediate layer consisting of lead dioxide and silicon oxide is formed on the base layer. In addition, when an organic compound is used as a binder, the substance is decomposed into water, carbon dioxide, etc. and removed by baking.
Regarding boat fishing, regardless of whether a ceramic-based or organic-based binder is used, if a residual component remains after baking, the residual component must have properties that match the purpose of forming the intermediate layer. Must.

The upper limit of the heating temperature during baking is not particularly limited when the base layer is a platinum group metal or its oxide, but when baking at a high temperature when the base layer is manganese dioxide, crystal transformation of the manganese dioxide may occur. Baking is preferably carried out at a temperature of up to about 550° C., since this may lead to deterioration that may be caused by this, leading to a shortened service life.

On the other hand, in the thermal spraying method, a single powder or a mixed powder of intermediate layer components, such as a mixed powder of lead oxide, titanium oxide, and tin oxide, is thermally sprayed onto the base layer by a normal thermal spraying method.

When the thickness of the intermediate layer component is increased, the electrical resistance increases and the electrolytic voltage increases. Therefore, when used in normal electrolytic reactions, it is preferable to reduce the thickness of the intermediate layer as much as possible to suppress the increase in the electrolytic voltage. .

On the other hand, in certain electrolytic reactions, such as organic electrolytic reactions, the reaction may not occur unless a certain electrolytic voltage is reached. Therefore, when this electrode is used for such an electrolytic reaction, a desired voltage value can be obtained by adjusting the thickness of the intermediate layer. The voltage value can be adjusted by adjusting the thickness of the lead oxide coating layer, but this is difficult because the lead dioxide coating layer has high conductivity and even if the thickness is increased, it does not affect the electrolytic voltage much. Preferably, the voltage is adjusted by adjusting the thickness of the intermediate layer.

Next, a lead dioxide coating layer is formed on the intermediate layer by an appropriate method, preferably a conventional electrolytic method. When forming the lead dioxide coating layer by the electrolytic method, for example, the metal substrate and the titanium plate on which the underlayer is formed are used as an anode and a cathode, respectively, and lead nitrate is used as an electrolyte at a liquid temperature of 50 to 90°C and a current density. It is preferable to carry out at 0.5 to 5 A/dm".

There are two crystal forms of lead dioxide, α and β, and the crystal form of the lead dioxide coating layer formed by this electrolytic method is β type if the electrolytic reaction is carried out under acidic conditions, and α type if the electrolytic reaction is under alkaline conditions. Become.

The lead dioxide coating layer produced by this electrolytic method has distortion due to residual internal stress, which is a drawback of the electrolytic method, and the use of the electrolytic method itself is not preferable. However, if the lead dioxide coating layer is formed by other methods, Since the contact resistance between the intermediate layer and the lead dioxide coating layer becomes too large, leading to an increase in electrolytic voltage, it is preferable to use an electrolytic method in the present invention.

The electrode formed in this manner has good durability and is particularly useful as an electrode for oxygen-generating electrolysis.

(Examples) Examples of the present invention will be described below, but these examples do not limit the present invention.

The surface of a titanium expanded metal substrate measuring 50 mm in length, 150 mm in width, and 1 fi in thickness was roughened by sandblasting, and then the substrate was immersed in trichlorethylene to degrease the surface of the substrate. Approximately 50 g/j on the substrate surface
! (7) Apply IrCl4 aqueous solution with a brush and heat at 100°C.
After drying, heat treatment was performed at 600° C. for 10 minutes.

The amount of Ire2 supported in the underlayer thus formed was 2 to 3 g/M per apparent surface area of the substrate.

Next, a No. 3 water glass solution diluted to 30% was applied onto the base layer, dried at 100°C, and dried at 600°C for 1 hour.
Heat treatment was performed for 0 minutes. After repeating this coating-drying-heating process twice, it was immersed in warm water to remove the sodium oxide in the water glass to form an intermediate layer.

The thickness of the intermediate layer thus formed was 10 to 20 μm. Next, a lead dioxide coating layer was electrodeposited on the surface of the intermediate layer by a conventional electrolytic method. The electrolysis conditions were a titanium plate as the cathode and a concentration of 500 g/7 as the electrolyte. A lead nitrate aqueous solution was used, the liquid temperature was 75 to 80°C, the current density was 2 A/dm2, and the electrolysis time was 4 hours. The thickness of the lead dioxide coating layer thus formed was approximately 400 μm.

Example 2 Lead dioxide powder manufactured by Wako Pure Chemical Industries, Ltd. and 30 as a binder
A slurry prepared by mixing No. 3 water glass solution diluted to 1% by weight in a weight ratio of 1 = 2 was applied to the surface of the base layer of Exband Metal prepared in the same manner as in Example 1, and after drying at 100°C. , and was heat-treated at 400° C. for 10 minutes to form an intermediate layer. The thickness of the intermediate layer was 10 to 20 μm. Next, a lead dioxide coating layer was formed on the intermediate layer by the same electrolytic method as in Example 1 to obtain a lead dioxide electrode.

Example 3 Powders of lead dioxide, tin dioxide, titanium dioxide, and titanium metal were added to the surface of the base layer of expanded metal prepared in the same manner as in Example 1 at a ratio of 8:1:0.1:o.
, 3 in a weight ratio was thermally sprayed using a TERODYN 5YST E M3000 type gas spraying equipment manufactured by Nippon Utesoku Co., Ltd. to a thickness of about 10 to 20 μm.
The middle layer was obtained. Next, a lead dioxide coating layer was formed on the intermediate layer by an electrolytic method under the same conditions as in Example 1, to obtain a lead dioxide electrode.

A lead dioxide electrode was produced in the same manner as in Example 3, except that silicon oxide powder was used as the intermediate layer forming powder instead of the mixed powder in Example 3.

Example 5 Tetra-n-butoxytitanium Ti (0-n-C
4H7) was applied in an appropriate amount, dried, and then baked at 500° C. for 10 minutes. This resulted in a titanium dioxide intermediate layer having a thickness of about 10 to 20 μm. Next, a lead dioxide surface was formed on the intermediate layer by an electrolytic method under the same conditions as in Example 1, thereby forming a lead dioxide electrode.

Example 6 A solution containing 500 g/β of manganese nitrate was applied to the surface of the base layer of expanded metal prepared in the same manner as in Example 1, and heat treated at 350°C for 20 minutes to give a
A manganese dioxide intermediate layer having a thickness of 0 to 30 μm was formed. Next, a lead dioxide coating layer was formed on the intermediate layer by electrolysis under the same conditions as in Example 1 to obtain a lead dioxide electrode.

Example 7 Manganese sulfate 50g/j using an expanded metal having a base layer formed in the same manner as in Example 1 as an anode.
! and free sulfur #40g/j! Electrolysis was carried out at a current density of 50 A/- using an electrolytic solution containing the following: to form a manganese dioxide intermediate layer with a thickness of about 20 μm on the expanded metal base layer coating layer. The temperature of the electrolyte at this time was maintained at 80° C. or higher, and a graphite plate was used as the cathode. Next, a lead dioxide coating layer was formed on the intermediate layer under the same electrolytic conditions as in Example 1 to form a lead dioxide electrode.

Comparative Examples 1 and 2 An electrode with the intermediate layer removed from the lead dioxide electrode of Example 1 (Comparative Example 1), and an electrode with the intermediate layer and base layer removed (Comparative Example 2)
was produced under the same conditions as in Example 1.

A total of nine electrodes of Example 1 to Comparative Example 2 were each used as an anode,
Free sulfuric acid 150g/j! When an accelerated durability electrolysis test was conducted at a high current density of 10,000 A/rl using an electrolytic solution containing 60° C., the results shown in Table 1 were obtained. As can be seen from this table, the electrode without a base layer or intermediate layer (Comparative Example 2) becomes passivated within a day, and the electrode without an intermediate layer (Comparative Example 2) becomes passivated within a day. 1) maintained a certain lifespan, but the lead dioxide coating layer gradually cracked due to oxygen bubbles generated from the platinum group underlayer, which has a low oxygen generation overvoltage, through small pinholes in the lead oxide coating layer. It is presumed that the electrodes finally collapsed and became passivated.On the other hand, the electrodes of each example all had sufficient durability of 1000 hours or more.

(Effects of the Invention) The lead dioxide electrode and the manufacturing method thereof according to the present invention provide an electrode in which a lead dioxide coating layer is formed on a corrosion-resistant metal substrate by an electrolytic method via a base layer, and an intermediate layer is formed between the base layer and the coating layer. It is characterized by the fact that it was formed.

Therefore, the intermediate layer existing inside the outermost lead dioxide coating layer prevents the electrolyte from coming into contact with the base layer with low overvoltage and generating gas in the base layer, and the gas causes the lead dioxide coating layer to This prevents cranking from occurring and shortening the electrode life. In addition, the lead dioxide coating layer formed by the electrolytic method is dense and internal stress remains, making it easy for cranking to occur. However, in the lead dioxide electrode according to the present invention, the intermediate layer is The lead coating layer acts as a cushion to absorb the residual internal stress, effectively preventing the occurrence of cranking or the like due to the internal stress.

Therefore, the lead dioxide electrode according to the present invention has dramatically increased durability compared to conventional lead dioxide electrodes without an intermediate layer, and enables stable operation over a long period of time.

Claims (7)

[Claims] (1) a corrosion-resistant metal base, a base layer formed on the metal base and made of a material having corrosion resistance and conductivity, and an intermediate layer formed on the base layer and made of a corrosion-resistant substance that is more inert than lead dioxide; and a lead dioxide coating layer formed on the intermediate layer. (2) The intermediate layer is a metal selected from Groups IVA, IVB, VA, VB, or VIB of the periodic table, or an oxide, carbide, nitride, or boride of a metal, or iron, manganese,
The lead dioxide electrode according to claim 1, which contains at least one of cobalt, aluminum oxides, or corrosion-resistant organic compounds. (3) Forming a base layer made of a corrosion-resistant and conductive substance on a corrosion-resistant metal substrate, forming an intermediate layer made of a corrosion-resistant substance that is more inactive than lead dioxide on the base layer, and further forming an intermediate layer on the intermediate layer. A method of manufacturing a lead dioxide electrode comprising forming a lead dioxide coating layer on the electrode. (4) The method for producing a lead dioxide electrode according to claim 3, wherein the binder containing the intermediate layer component or a mixture of the intermediate layer component and the binder is coated on the base layer and heat-treated to form the intermediate layer. . (5) The method for producing a lead dioxide electrode according to claim 3, wherein the intermediate layer is formed by applying a solution containing a thermally decomposable salt of the intermediate layer metal component onto the base layer and heat-treating the solution. (6) The method for manufacturing a lead dioxide electrode according to claim 3, wherein the intermediate layer is formed by depositing the intermediate layer component on the base layer by thermal spraying. (7) The method for producing a lead dioxide electrode according to claim 3, wherein the intermediate layer is formed by electrolysis from an electrolytic bath containing ions of the intermediate layer metal component.