JPS6027754B2 - Manufacturing method of metal anode for electrolytically producing manganese dioxide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The invention relates to a method for producing manganese dioxide by electrolysis, in which the substrate consists of a passivatable metal, the surface of which is covered at least in part with an active coating layer produced by precipitation of a noble metal. The present invention relates to the production of metal anodes, particularly titanium anodes.

The use of activated metal anodes in electrolytic processes is known.

In particular, titanium electrodes activated with noble metals are already used in chlor-alkali electrolysis. Laboratory scale 2
The use of such titanium anodes has also been investigated for the electrolytic production of manganese oxide. Metal anodes of this type, for example titanium anodes, have so far been produced by thermally decomposing noble metal salts on the surface of the metal used as the anode substrate in air at a temperature of about 550 qo.
Alternatively, precious metals were electrolytically deposited on this substrate to activate it.

Anodes activated in this manner have been demonstrated to be effective where gaseous or electrolyte lagoonal electrical products are generated. However, difficulties arise in the production of manganese dioxide, in which the product is deposited in solid form on the anode, as is known, and must be removed from the anode after the electrolysis has ended.

This is because the noble metal layer, which is not very tightly adhered, takes this opportunity to be at least partially peeled off from the substrate surface. As a result, after reinserting the anode into the electrolyte, it is no longer fully active, and after a short working time, the anode grows unevenly and the average terminal voltage increases, reducing the working terminal voltage. exceed in time. Long working times are particularly important for the economical use of precious metal plated anodes.

The object of the invention is to obtain a method for producing a metal anode activated with a noble metal, in which the activated noble metal layer resists even high mechanical loads.

Surprisingly, this purpose was achieved by coating the surface of the anode substrate with a noble metal, and then heating the anode substrate to 700-1100℃, especially 800-100℃.
This can be solved by phosphorous dulling at a temperature of zero.

Below 700° C. and above 1100° C., an active layer may optionally be produced on the anode substrate, but the reaction rates that occur in this case are unsuitable and the layers obtained in this way are not industrially satisfactory.

The noble metal is coated onto the substrate by cathodic deposition from its salt solution, or by treating the substrate with a salt solution of the noble metal followed by 65
Coated by heating to temperatures up to 0.000C and decomposing the noble metal salts. It is advantageous to prepare the anode under a noble gas atmosphere or under reduced pressure of less than 10-6 bar, in particular from 10-7 to 10-8 bar.

Argon is particularly suitable as the noble gas, and gold or platinum metals, such as platinum or ruthenium, are suitable as the noble metal. In order to improve the adhesion of the manganese dioxide, a metal plate is advantageously used as a substrate, which has a large number of holes spaced apart so that the manganese dioxide deposited on both sides of the plate can grow in unison.

Substrates in the form of expanded metal, double-nose plates or slotted plates (see FIGS. la, b and c) are proposed for this purpose. It is also possible to use molded bodies made of pressed and vacuum-phosphorized metal sponges. It is desirable to activate only the part of the anode that is immersed into the electrolyte with the noble metal.

Otherwise, the hydrogen generated during electrolysis will be absorbed by the noble metal layer above the bath, thereby prematurely arming and destroying the anode. Due to the inventive treatment of the anode, the noble metal atoms diffuse into the metal substrate, forming a noble metal-containing alloy of the respective metal on the anode surface.

This alloy layer essentially forms a component of the metal substrate so that the mechanical stress can no longer peel off the noble metal layer. X-ray metallography can detect intermetallic phases of Me=Pt, Ru or 1 and Ti as substrate metal, for example of the MeTi and MeTi3 type, on surfaces treated in this way. Suitable noble metals include gold and platinum; the latter can also be coated as a mixture. In addition to titanium, tantalum, zirconium and niobium are also suitable as substrate metals. The heat treatment must be carried out so that the diffusion process begins, but not so long as to cause most of the coated precious metal to diffuse deeply into the interior of the metal substrate.

In this case, there is a significant lack of noble metals on the surface, and such alloys have an electrochemical behavior that increasingly approaches that of the pure substrate metal. The amount of noble metal is at least 1-2 mole % in an anode surface layer that is at least 10-2 feet thick.

The optimal conditions for diffusion depend on the type of furnace used, the selected temperature,
It depends on the treatment time and the noble metal used and has to be determined empirically, for example by microsonde, as the case may be. It is advisable to pre-treat the anode surface before applying the noble metal layer, for example with fat-dissolving agents (alcohols, halogenated hydrocarbons, cleaning actives, etc.), optionally by sandblasting.

In addition to the shapes already mentioned, other processed forms of the substrate metal, such as tubes, combs, nets, etc., can be used as supports for the active noble metal layer according to the invention.

This is limited by the special requirements of cell formation. However, in addition to the slotted plate (see FIG. 1c), a design known as a double-nose plate (see FIG. 1b) has proved advantageous. It is important that good adhesion of the precipitate is ensured. The quality of the electrode is determined by the fact that electrolysis is carried out by this electrode and after a desired period of time the manganese dioxide deposited on it is separated from the electrode by mechanical means such as bending or generally by impact and used again for the same electrolysis. tested by

This process, called cycling, continues until the cell voltage during electrolysis exceeds a value that makes economical operation impossible.
or repeat until the manganese dioxide precipitation becomes so non-uniform as to preclude economical utilization of a given cell capacity.
The electrode of the present invention was tested under the following conditions: Electrolyte temperature Manganese concentration of 95q0 electrolyte 0.7 mol/Sulfuric acid concentration of electrolyte
0.7 mol/so current density Regarding the outer surface: 1. The external surface represents twice the geometrical dimension of the anode that immerses into the bath.

The effects of the manufacturing method according to the present invention are shown in the experimental results shown in FIGS. 2-4.

FIG. 2 shows the effect of a noble metal coating in the case of a ruthenium coating on an electrode made from pressed titanium sponge. Due to the vacuum heating in this case, it is emphasized that ruthenium dioxide, characterized by a blue-black color, as observed in industrially produced dimensionally stable titanium anodes for chlorine production, is not present at the temperatures applied. The electrode of the present invention is silvery white when platinum is used. Figure 2 shows the relationship between the amount of noble metal coated and the life of the electrode. The lifespan is approximately proportional to the amount of ruthenium (
According to the following example 2 containing various amounts of ruthenium). FIG. 3 shows the time course of the terminal voltage of an electrode coated with platinum by decomposition of hexachloroplatinic acid in air at 550 pm, in comparison with that of an electrode according to the invention on titanium expanded metal according to Example 3. show.

The effectiveness of different precious metals is of course different, and different coverages are required for comparable lifetimes.

This is illustrated in FIG. 4 for an electrode consisting of a double nose plate substrate with ruthenium and platinum coatings. The method of the invention will now be explained by way of example.

Example 1 Platinum-iridium (70-30) alloy 1 female/that coating A titanium plate with a thickness of 1.5 mm (slit hole plate ) Degrease, wash and sandplast using a known method.

Then apply with a brush a solution of the following composition: ratio 1 to 6
・Group 20 14 female ratio PtC〆6.4,
Chihito 20 341g concentrated hydrochloric acid
80 female ethanol
After 80 minutes, the electrode was dried at 120 qo,
Heat in a vacuum oven at 7-10-8 bar at 700 qo for 4 hours. The process of applying solution, drying and vacuum heating of the anode is performed in 5 steps.
Repeat several times. The total amount of precious metal applied is 1 female/female. The amount of precious metal is 11 mol% in the top layer of the anode layer with a thickness of 5.10-3. Example 2: A ruthenium-coated precipitated titanium sponge board is degreased and coated with a solution having the following composition.

RbiC So 3rd and 4th Days 20 14 Keys Concentrated Hydrochloric Acid 43 Female Worker Tanoh
The board is then dried at 120 qo, followed by heating at 55,000 for 45 minutes under a stream of air.

The coating and heat treatment were repeated three times. Next, 10-
Blunt at 900° C. for 4 hours in a vacuum of 7 bar. Example 1: Degrease and sandblast coated titanium expanded metal with platinum 1 female end, and wet it by soaking it in a solution with the following composition: QPtC E6/4
,9 days 20 22 concentrated hydrochloric acid
44 Hina Ethanol
445 g The expanded metal plate is then dried at 120° C. and heated in air at 550 qo for 3 minutes.

The steps of soaking, drying and heating in air are repeated two more times.
Next, expand the expanded metal at 800qo under argon for 5 minutes.
Time moth dulls. Example 4: Degrease the Akatsuki titanium plate manufactured from the platinum 2 female/that coated titanium sponge and immerse it in an electrolyte with the following composition: Day 2 PtC Night 6
20 Female Water 102Na2HP04
100 females (N days) 2HP04
20 female N ratio C
The temperature of the fifth thigh fin liquid was 68 qo, and the current density was 0. Mushi/d〆 (1.5V).

After 120 minutes, the plate was removed from the electrolyte, dried, and then
Heat to 100,000 hours.

[Brief explanation of drawings]

Figures 1A to 1C are diagrams showing three embodiments of the electrode substrate, and Figures 2 to 4 are graphs showing the relationship between working time and terminal voltage using the electrode of the present invention. Figure 3 shows the effect of the amount, Figure 3 shows the effect of Pt coating, and Figure 4 compares the effects of Ru and Pt coating. Figure la Figure lb Figure lc Figure 3 Figure 4 Figure N Ship

Claims (1)

[Scope of Claims] 1. A method for electrolytically producing manganese dioxide having a substrate made of a passivatable metal and an active coating layer formed by precipitation of a noble metal, covering at least a portion of the surface of the substrate. In the manufacturing method of metal anodes, especially titanium anodes, after coating the surface of the anode substrate with a noble metal, the anode substrate is
A method for producing a metal anode for electrolytically producing manganese dioxide oxide, which is characterized by annealing at a temperature of 1100°C. 2. The manufacturing method according to claim 1, wherein the noble metal is coated on the substrate from its salt solution by cathodic deposition. 3. The method of claim 1, wherein the substrate is coated with a noble metal by treating the substrate with a salt solution of the noble metal, followed by heating to a temperature of up to 650° C. to decompose the noble metal salt. 4. The manufacturing method according to any one of claims 1 to 3, wherein the anode is annealed at a temperature of 800 to 1000°C. 5. The manufacturing method according to any one of claims 1 to 4, wherein the annealing is performed under reduced pressure or in a rare gas atmosphere. 6. The method according to claim 5, wherein the anode is annealed at a pressure lower than 10-6 bar. 7. The method according to claim 6, wherein the anode is annealed at a pressure of 10^-^7 to 10^-^8 bar. 8. The manufacturing method according to any one of claims 1 to 7, wherein gold or platinum metal is used as the noble metal. 9. The manufacturing method according to claim 8, which uses platinum or ruthenium. 10. Any one of claims 1 to 9, in which a metal plate is used as a substrate, which has spaced holes that allow manganese dioxide deposited on the surface of the plate to grow in unison. The manufacturing method described in section. 11. The method according to claim 10, wherein the anode is used in the form of an expanded metal, slit plate or double nose plate. 12. The manufacturing method according to any one of claims 1 to 9, which uses a pressed and vacuum sintered metal sponge as the anode. 13 Any one of claims 1 to 12, in which the part of the anode that is immersed in the electrolyte is activated with a noble metal.
The manufacturing method described in section.