JPH028391A - Lead dioxide electrode and production thereof - Google Patents

Abstract

PURPOSE:To obtain a PbO2 electrode having superior durability by forming a thermally sprayed layer contg. a specified metal oxide and an electrically nonconductive material on the surface of a corrosion resistant metal substrate and by forming a beta-PbO2 layer on the thermally sprayed layer. CONSTITUTION:The surface of a substrate of a corrosion resistant metal such as Ti, Nb, Ta or Zr having a plate, bar or expanded mesh shape is roughened and cleaned by degreasing. A thermally sprayed layer of a mixture of at least one kind of electrically conductive oxide having high oxygen overvoltage selected among PbO2, MnO2 and TiO2 with an electrically nonconductive material rendering low porosity to the layer, e.g., resin such as PE or epoxy resin or rubber is formed on the surface of the substrate. A coating layer of beta-PbO2 is then formed on the thermally sprayed layer by electrolysis, thermal spraying, baking or other method to produce a PbO2 electrode capable of effectively preventing the contact of the base metal with an electrolytic soln. and having superior durability.

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 dioxide electrode is mainly used as an anode for oxygen generation, anodic oxidation, etc. in mirabilite electrolysis, organic matter electrolysis, etc.

A conventional method for producing lead dioxide electrodes is to electrolytically coat lead dioxide either directly on a substrate such as titanium or on a substrate on which a base layer made of a platinum group metal or its oxide is formed. The base layer has the function of preventing the base from deteriorating due to contact with the electrolyte, but the components used in the base layer, particularly the platinum group metals and their oxides, have electrode activities that are higher than the lead dioxide. It is considerably higher than the lead dioxide that constitutes the coating layer, and in such electrodes, the components of the base layer also function as electrode active substances and electrolyze the electrolyte to generate gas between the base layer and the lead dioxide coating layer. let The generated gas has a disadvantage in that when it is released from the electrode surface into the electrolytic solution, it serves to separate the coating layer from the underlying layer, resulting in a shortened electrode life.

In order to solve this problem, it may be possible to select a component with lower activity than the lead dioxide as the base layer component, but it is essential that the base layer component is electrically conductive.
The activity of the base layer component that satisfies the above conditions is equivalent to or slightly inferior to the activity of the lead dioxide (for example, Japanese Patent Application Laid-open No. 1983-1982).
57791, JP-A-63-57792). Therefore, even if other base layer components are selected, gas generation in the base layer cannot be completely prevented, and the problem of peeling of the lead dioxide coating layer cannot be avoided.

Furthermore, the platinum group metals and their oxides are very expensive, and their use as an underlayer increases the cost of the electrode, making it uneconomical.

(Object of the Invention) The present invention provides a lead monoxide electrode and its lead monoxide electrode which solves the above-mentioned drawbacks by using a mixture of a normal electrode active material and a non-conductive material as a component of a sprayed layer that functions as a base layer. The purpose is to provide a manufacturing method.

(Means for Solving the Problems) The present invention first provides a corrosion-resistant metal substrate, at least one of lead dioxide, manganese dioxide, and titanium dioxide formed on the metal substrate, and a non-conductive substance. and a lead dioxide coating layer formed on the mixed sprayed layer, and secondly, a layer of lead dioxide, manganese oxide and titanium dioxide is coated on a corrosion-resistant metal substrate. Manufacturing a lead dioxide electrode comprising thermally spraying a mixed powder of at least one type of powder and a powder of a non-conductive substance to form a mixed sprayed layer, and forming a lead oxide coating layer on the mixed thermally sprayed layer. It's a method.

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 mixed sprayed layer of lead dioxide, etc. and a non-conductive substance is formed between the corrosion-resistant metal substrate and the lead dioxide coating layer, and the electrical resistance of the mixed sprayed layer is increased by the non-conductive substance. The oxygen overvoltage is increased to minimize gas generation in the mixed sprayed layer, effectively preventing peeling of the lead dioxide coating layer and significantly extending the life of the electrode. 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 can be used for other electrode reactions. It can be used as an electrode for electrolysis.

The corrosion-resistant metal substrate used in the present invention is a conductive metal including valve metals such as titanium, quantal, niobium, and zirconium, and various shapes such as plate, rod, and expanded mesh shapes can be used without limitation. can do. The metal substrate is preferably pretreated in order to improve the adhesion of a mixed sprayed layer corresponding to a conventional base layer described later and to remove impurities on the surface of the metal substrate. There are surface roughening treatment by blasting using a grid, and degreasing treatment by immersion in a sodium hydroxide aqueous solution, trichlorethylene, etc.

Next, a sprayed layer made of a mixture of at least one selected from lead dioxide, manganese dioxide, and titanium dioxide and a non-conductive substance such as a resin is formed on the corrosion-resistant metal substrate. These thermal spray powders include single lead dioxide, single manganese dioxide, mixed powder of lead dioxide and manganese dioxide, mixed powder of lead dioxide and titanium dioxide, mixed powder of manganese dioxide and titanium oxide, and mixed powder of lead dioxide and manganese dioxide and titanium oxide. Therefore, it is not preferable to use titanium dioxide alone. It is preferable that the mixed sprayed layer contains lead dioxide, and the lead dioxide has good bonding properties with the lead dioxide coating layer, so that the mixed sprayed layer and the coating layer are bonded more completely, and the entire electrode is Contributes to longer lifespan.

The thermal spraying method may be a conventional method such as a gas spraying method or a plasma spraying method without any limitation, and the mixed thermal spraying layer is formed by this method. Thermal spraying conditions are appropriately determined depending on the coating composition, but if the non-conductive substance is a resin or the like and is likely to become brittle due to melting or the like at high temperatures, low-temperature thermal spraying is preferable. The components to be thermally sprayed are made into powder before thermal spraying, and the powder is thermally sprayed, as in the usual thermal spraying method. The thickness of the mixed thermal spray layer is 10
It is preferable to set it to 0 μm or less, and if it exceeds this, the overvoltage of the entire electrode becomes too large, which is generally not preferable. The mixing ratio of each component is 80 to 95% by weight of a powder of at least one component selected from lead dioxide, manganese oxide, and titanium dioxide, and 20 to 5% by weight of a non-conductive substance.
It is preferable to set it as % by weight, and when titanium dioxide is mixed with lead dioxide and/or manganese dioxide, the mixing ratio is preferably 30 to 5% by weight.

The non-conductive substance is a substance that can be mixed with the lead dioxide etc. to increase its overvoltage and is not deteriorated by the thermal spraying and does not deteriorate the lead dioxide etc., in other words, it is a substance that can form a thermal sprayed layer at a low thermal spraying temperature. The material is not particularly limited as long as it can be formed, and examples thereof include resins such as polyethylene, epoxy resin, and Bakelite, and rubbers. An example of a non-conductive material that causes a high spraying temperature is quartz glass, and at the spraying temperature of quartz glass, the lead dioxide and the like deteriorate, making it impossible to form the mixed sprayed layer with good performance.

As described above, when a mixed sprayed layer is formed on the metal substrate, for example, titanium constituting the metal substrate is heated during the thermal spraying and titanium dioxide is formed on its surface, and the titanium dioxide reacts with lead dioxide and manganese dioxide. A composite oxide is formed, and a corresponding single oxide or composite oxide is formed depending on the sprayed powder, resulting in a mixed sprayed layer consisting of a conductive oxide with a large oxygen overvoltage. The mixed sprayed layer has a sprayed surface with low adhesion to the metal substrate and low porosity by adding a non-conductive substance such as a resin.

Since the porosity is low, penetration of the electrolytic solution into the metal substrate is reliably prevented, and protection of the metal substrate can be achieved more effectively than conventional sprayed layers.

A coating layer of lead dioxide, particularly β-lead dioxide, is then formed on the mixed sprayed layer. The method of forming the coating layer is not particularly limited, and electrolytic methods, thermal spraying methods, baking methods, etc. can be employed, but it is optimal to perform the formation by electrolytic methods.

The electrolytic method uses, for example, a metal substrate on which the underlayer is formed, a titanium plate, etc. as an anode and a cathode, respectively, and lead nitrate as an electrolytic solution at a liquid temperature of 50 to 90°C and a current density of 0.5 to 5 A/d.
It is preferable to carry out in m2. 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 will be the β type if the electrolytic reaction is carried out under acidic conditions, and the α type if the electrolytic reaction is under alkaline conditions. From the viewpoint of adhesion to the mixed thermal sprayed layer, it is preferable to use the β type.

On the other hand, in the thermal spraying method, lead dioxide powder is thermally sprayed onto the mixed thermal spraying layer by a normal thermal spraying method.

When the baking method is used, a mixture of a lead compound and a binder is coated on the mixed sprayed layer, and all or part of the binder is removed by heating to form a lead dioxide coating layer on the mixed sprayed layer. This is a method of burning. The binder in the main baking method is a relatively sticky substance that has the function of adhering to the mixed thermal spraying layer lead compounds that do not adhere to the mixed thermal spraying layer alone 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 if the remaining substances cannot be used as a coating layer component, they cannot be used as the binder of the present invention.

The baking method involves, for example, applying a mixed slurry of the diluted water glass and lead dioxide powder onto the base layer, heating and baking it, and then immersing it in hot water to elute the sodium oxide content in the fixed water glass. In this method, a mixed sprayed layer consisting of lead dioxide and a small amount of silicon oxide is formed on the mixed sprayed layer, leaving only silicon oxide. When an organic compound is used as a binder, the substance is generally decomposed into water, carbon dioxide, etc. and removed by baking, and this is a preferred method because other residual components are not mixed into the mixed sprayed layer.

The upper limit of the heating temperature during the baking is preferably carried out at a temperature of up to about 550°C, in order to prevent the deterioration of manganese dioxide, etc. in the mixed sprayed layer, which is sometimes thought to be caused by crystal transformation. .

In the electrode formed in this way, since the components of the mixed sprayed layer have a higher overvoltage than the lead dioxide of the coating layer, electrolytic reactions hardly occur on the mixed sprayed layer, preventing the coating layer from peeling off due to generated gas. Therefore, it has good durability and is particularly useful as an electrode for oxygen-generating electrolysis.

Further, the mixed sprayed layer of the electrode according to the present invention is formed of metal powder such as lead dioxide and non-conductive material powder such as resin,
While ordinary metal spraying forms a sprayed layer with high porosity, the present invention makes it possible to fill the voids with the non-conductive material powder to form a dense mixed sprayed layer. Therefore, it is not necessarily necessary to form an underlayer of expensive platinum group metals or their oxides as in the past, and it is possible to provide an electrode that is less expensive and has the same performance.

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

Example 1 Plate thickness 1. The surface of ON's expanded band mesh made of titanium was sandblasted, then degreased in a 200 g/J aqueous sodium hydroxide solution for 2 hours, washed with water, and the base of the expanded mesh was coated with β-dioxide produced by an electrolytic method. 95% by weight of lead powder (-100~325 mesh powder) and polyethylene powder (-50~325 mesh powder)
The mixed powder with 5% by weight was gas sprayed using gas spraying equipment (Terodyne System 3000, Nippon Utesoku Co., Ltd.) to form a mixed sprayed layer with a thickness of 10 to 50 μm.

Next, using the substrate as an anode and the titanium plate as a cathode, using an aqueous lead nitrate solution (saturated solution at 80°C) as an electrolyte, and stirring the solution with a magnetic stirrer, it was heated at a temperature of 80°C for 2 hours.
Electrolyzed for 2 hours at a current density of A/dm2 to a thickness of approximately 250 μm.
An electrode having a β-lead dioxide coating layer was obtained.

The β-
An electrode with a lead dioxide coating layer was obtained.

1 Hunger 1 Manganese dioxide powder (-1
A lead dioxide-coated electrode was obtained in the same manner as in Example 1, except that a mixed sprayed layer was formed using a mixed powder of 90% by weight of 00-325 Mesophyll powder and 10% by weight of polyethylene powder.

This l■11 β was prepared in the same manner as in Example 1 except that the thermal spray layer was formed using only manganese dioxide powder as the powder for the thermal spray layer.
- An electrode with a lead dioxide coating layer was obtained.

Example 3 β-lead dioxide powder 47.5% as mixed powder for mixed thermal spray layer
A lead dioxide-coated electrode was obtained in the same manner as in Example 1, except that a mixed sprayed layer was formed using a mixed powder of 47.5% by weight of titanium dioxide powder and 5% by weight of polyethylene powder.

↓ Except for the fact that the mixed thermal sprayed layer was formed using a mixed powder of 67% by weight of β-lead dioxide powder, 28% by weight of titanium dioxide powder, and 5% by weight of polyethylene powder as the mixed powder for the mixed thermal sprayed layer. A lead dioxide coated electrode was obtained in the same manner as in Example 1.

Comparative Example 3 β-Lead dioxide was formed in the same manner as in Example 1, except that the base layer was formed using a mixed powder of 70% by weight of β-lead dioxide powder and 30% by weight of titanium dioxide powder as the powder for the thermal spray layer. An electrode having a coating layer was obtained.

Big Flag ■] Lead dioxide was prepared in the same manner as in Example 1, except that the mixed sprayed layer was formed using a mixed powder of 90% by weight of manganese dioxide powder and 10% by weight of epoxy resin powder as the mixed powder for the mixed thermally sprayed layer. A coated electrode was obtained.

Comparative Example 4 An electrode having a β-lead dioxide coating layer was obtained in the same manner as in Example 1, except that the sprayed layer was formed using platinum oxide powder alone as the powder for the sprayed layer.

A total of nine lead dioxide coated electrodes of Examples 1 to 5 and Comparative Examples 1 to 4 were used as anodes in a 200 g/l sulfuric acid aqueous solution at 50°C, and an accelerated electrolytic test was conducted at a current density of 100 A/dm2. . The results are shown in Table 1.

In the electrodes of Examples 1 to 5, no peeling or weight loss was observed even when the electrodes were used for 1000 hours or more, and stable electrolysis could be performed. Each electrode in the comparative example achieved β in a short time.
- Peeling occurred on the entire surface between the lead dioxide layer and the sprayed layer.

Table 1 (Effects of the Invention) The lead dioxide electrode according to the present invention comprises a corrosion-resistant metal base, a mixed sprayed layer containing a non-conductive substance formed on the metal base, and a carbon dioxide formed on the mixed sprayed layer. A lead coating layer is included.

The non-conductive substance such as resin in the mixed sprayed layer has a function of making the overvoltage of the mixed sprayed layer higher than the overvoltage of the lead dioxide coating layer. Therefore, the electrolytic reaction occurs selectively on the lead dioxide coating layer, and hardly occurs on the mixed sprayed layer. Therefore, no gas is generated on the mixed sprayed layer, and the lead dioxide coating layer does not peel off due to the generated gas.

Furthermore, although the mixed sprayed layer is formed by a thermal spraying method, the particles of the non-conductive substance fill the gaps between the particles of lead dioxide, etc., thereby lowering the porosity. This effectively prevents contact with the metal substrate, which is the original function of the mixed sprayed layer, and makes the protection of the metal substrate more reliable, dramatically increasing durability and enabling stable operation over a long period of time. .

Further, in the present invention, it is not necessary to use platinum group metals, the raw material cost is low, and a lead dioxide electrode with good performance can be manufactured at low cost.

Claims (2)

[Claims] (1) a corrosion-resistant metal base; a mixed sprayed layer formed on the metal base and containing at least one of lead dioxide, manganese dioxide, and titanium dioxide; and a non-conductive substance; and a mixed sprayed layer formed on the mixed sprayed layer. A lead dioxide electrode comprising a lead dioxide coating layer. (2) spraying a mixed powder of at least one powder of lead dioxide, manganese dioxide, and titanium dioxide and a powder of a non-conductive substance onto a corrosion-resistant metal substrate to form a mixed sprayed layer;
A method for manufacturing a lead dioxide electrode, comprising forming a lead dioxide coating layer on the mixed sprayed layer.