JPS5930791B2 - Electrode manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of applying coating materials to generally valve metal electrode supports.

In this method, the coating composition includes a tin compound, which is later converted to its oxide form to produce an electrode with significantly increased reproducibility of the manufacturing process, and this method makes it possible to make tin metal more Full utilization saves manufacturing costs and reduces air pollution caused by volatilization of tin compounds during the coating process. More particularly, the present invention provides a method of having a support of a valve metal, e.g. titanium, support an electrode coating composition having tin as one component by using a tin compound in the form of a sulfate in the coating composition mixture. Concerning a greatly improved method of manufacturing electrodes. The electrochemical manufacturing method is
It is gaining importance in the chemical industry due to its greater ecological acceptability, potential for energy conservation, and reduced product costs.

Therefore, significant research and development efforts are being devoted to electrochemical methods and their... -ware. One major element of the hardware is the electrode. The objective is to provide an electrode that: withstands the corrosive atmosphere in the electrolytic cell; has the lowest overvoltage for the desired electrochemical reaction; and within the commercially possible range. Electrodes that can be manufactured with high quality control at a low cost. It is amazing that only a few materials can effectively form electrodes, especially anodes. This is because most other materials are sensitive to the highly corrosive conditions that exist within the anode chamber of an electrolytic cell. These materials include graphite, nickel, lead, lead alloys, platinum or platinized titanium. This type of electrode lacks dimensional stability, is expensive, has a high wear rate, contaminates the electrolyte, precipitates contaminates the cathode, is sensitive to impurities, or has a high overpotential for the desired reaction. Applications are limited. Overpotential refers to a potential above the theoretical potential at which the desired reaction would occur at a constant current density. The history of electrodes has been filled with repeated attempts and proposals to overcome some of the problems associated with electrodes in electrolytic cells, none of which have been successful in optimizing the properties of electrodes for use in electrolytic cells.

The problem is to find an electrode that overcomes many of the undesirable properties mentioned above and can still sustain energy at higher current densities and store energy with low overpotentials. For example, platinum is an excellent material for use as an anode in electrowinning processes and is known to meet many of the aforementioned criteria. However, since platinum is expensive, it has not yet been found to be industrially suitable. Carbon and lead alloys have been used commercially, but carbon anodes wear quickly, significantly contaminate the electrolyte, increase electrical resistance, and increase semi-electrolytic sliding potential. When the semi-electrolytic sliding potential is high, the electrolytic cell consumes more electrical energy, so
Undesirable. A disadvantage of lead alloy anodes is that the lead dissolves in the electrolyte and forms a lead deposit on the cathode, which contaminates the desired resulting deposit. Also, PbO2
changes to Pb3O4, which has poor conductivity. Oxygen can penetrate beneath this layer and strip this film, resulting in particles forming and becoming trapped in the deposited copper on the cathode. This degrades the copper plating, which is highly undesirable. It has been proposed to apply platinum or other noble metals onto titanium supports to retain their attractive electrical properties and further reduce manufacturing costs.

However, even with limited use of precious metals such as platinum, B3O per square foot of electrode surface area. OO dollars (323.
00/Rrl'), making it undesirable for industrial use. Furthermore, it has been proposed to electroplate platinum on the surface of titanium, to which other deposits of lead dioxide or manganese dioxide can be applied. Electrodes with lead dioxide coatings have the disadvantage of relatively high oxygen overpotentials, and both types of coatings have high internal stresses when deposited electrolytically, are susceptible to flaking from the surface during industrial use, and are and contaminate products deposited on the cathode surface. Therefore, the current density of such anodes is limited and must be handled with great care. Another improvement attempted is to form a layer of manganese dioxide on the surface of the titanium support, which is relatively porous and consists of multiple layers of manganese dioxide to form an integral coating. ing. This has a current density of 0.5 amps/in2 (7
As long as the current density remains below 7.5 milliamps per square inch (155 milliamps per shoulder), the required overvoltage increases fairly rapidly and becomes higher. This results in considerable disadvantages in terms of current density. Recently, a number of coatings have been developed using titanium, ruthenium and tin dioxide,
Or tin and antimony oxides are used, on which a top coating of manganese or lead oxides is plated.

These coatings have shown substantial promise in reducing overvoltage in the area and increasing service life in the corrosive conditions within the electrolytic cell.
A major drawback of these materials is that substantial amounts of tin are volatilized when the coating is baked to the tin oxide, especially due to the method of applying the tin oxide. The reason is that tin compounds, such as stannic chloride pentahydrate, convert during baking to stannic hydroxide b1 and then to stannic oxide, which is desired for certain electrode coatings. When carrying out this method, much of the tin itself does not remain in the coating, but evaporates into the atmosphere. This occurs at least in part because stannic chloride boils at temperatures around 114°C,1 and because the transformation of tin compounds to their respective oxides occurs at much higher temperatures, these materials Most of the tin material is lost to the atmosphere, resulting in 50 (fl) of the tin material.
Only a smaller amount is used for the actual coating. This creates severe problems in quality control when manufacturing large, large quantities of electrodes. Reproducibility of coating compositions is almost impossible because of the volatilization of tin that occurs with the way conventional coatings are applied to support materials. Therefore, theoretical tin calculations alone can pose problems in calculating the possible service life of a given electrode. To date, the use of tin in coating compositions has not been commercially successful.
The reason is that the volatility of tin creates reproducibility problems, increases contamination, which is currently subject to strict standards, and increases the manufacturing cost of certain electrodes due to the loss of tin. It is therefore an object of the present invention to provide a method for manufacturing electrodes with desirable quality control characteristics and manufacturing costs within commercially viable ranges.

Another object of the present invention is to provide a process for making an electrode that significantly reduces the volatilization of tin into the atmosphere, thus alleviating the air pollution problems associated with its manufacture. These and other objects of the present invention, as well as advantages over the present and prior art, are achieved by the improvements described and claimed herein, as will be apparent from the following description. Ru.

The coating composition includes selecting a support, applying a coating material containing a tin sulfate compound to at least a portion of the surface of the support, and drying the coating material.
It has now been found that the coating material can be prepared by a process consisting of baking the coating material in an oxidizing atmosphere to convert the tin compound into its oxide form. The improved method of making electrode coating compositions of the present invention can be used to make any coating having as a substitute any tin compound for which tin volatilization is currently a problem.

In the past, electrode coating compositions using tin have utilized thermally decomposable compounds in the form of chlorides, which have low boiling points and therefore create volatilization problems. The present invention uses tin in the sulfate form, or chloride compounds and sulfuric acid which produce tin in the sulfate form.
This sulfate form of tin becomes the oxide form in the final electrode coating composition by a simple decomposition mechanism.
Tin volatilization during baking is drastically reduced. The support material used for such electrode coating compositions can be any electrically conductive metal with sufficient mechanical strength to serve as a support for the coating;
Typical examples of metals are aluminum, molybdenum, niobium, tantalum, titanium, tungsten, zirconium,
Nickel, steel, stainless steel and their alloys. The preferred valve metal is titanium based on cost, availability, electrical properties and chemical properties. There are a number of forms that titanium supports can take for electrode manufacture, examples being tough sheet materials, expanded metal mesh materials with a high percentage of open area, and cold forming of titanium powder. 30 to 70 of pure titanium that can be produced by compression
% porous titanium. One type of coating that can utilize the present invention is one in which a support material as described above is coated with a semiconducting intermediate coating of tin and antimony oxides.

These compositions are generally mixtures of tin dioxide and a small amount of antimony "dopant", with 1 dopant ranging from 0.1 to 1, calculated based on the combined weight of SnO2 and Sb2O3.
Present in an amount of 30% by weight. In most of these cases, the preferred amount of titanium trioxide is from 3 to 15% by weight. In the past, these intermediate coatings generally used stannic chloride pentahydrate as one of the materials in the mixture to be painted or applied to the support. The present invention uses a tin sulfate material or stannic chloride pentahydrate and sulfuric acid to obtain the tin sulfate form. Since this sulfate form has a simple decomposition mechanism at temperatures around 320°C, there is very little volatilization of tin into the atmosphere at the temperatures at which these materials are baked into their respective oxides. Therefore, the semiconductive intermediate coating can be formed with very few applications. A top coating of manganese dioxide or lead dioxide can be applied over this semiconductive intermediate coating to create an electrode with excellent current efficiency and service life.

To produce electrode coating compositions that can be used,
There are many other examples of electrode coating compositions that utilize tin compounds.

Prior to applying the tin sulfate-containing coating composition, the support material can be precoated with a number of other compositions.
The invention is further illustrated by the following examples.

Reference Example 1 Antimony trichloride, ruthenium trichloride and various tin-containing compounds are all combined into the final tin/
by coating the support metal, in this case titanium, with a solution containing an amount such as to give an initial tin/ruthenium ratio calculated and comparable to the analytical value of the ruthenium ratio. I made an electrode for this.

This indicates the amount of tin volatilization that occurs in each case. The initial tin/ruthenium ratio was determined from the weight of starting material in the coating solution. Because ruthenium compounds absorb some water to form hydrates, there is some inaccuracy in calculating the initial amount of ruthenium due to this ratio, approximately 5 (Ff). After applying these various materials to a support material, this is heated to 475-625% in an oxidizing atmosphere.
Each compound was converted to its respective oxide by baking at a temperature of 10°C for 5-10 minutes. This process was repeated several times to create the desired amount of weight gain. The amount of coating material had no observed effect on the resulting tin/ruthenium ratio. Therefore, any convenient weight of coating material could be used. Once this has been achieved, the catalyst layer is stripped from the titanium support with a molten salt, which is then dissolved in water to precipitate the metal, and the resulting solution is analyzed by atomic absorption to determine the carbon content of the coating material. The final tin/ruthenium ratio was determined by establishing the final tin/ruthenium ratio. These ratios and the tin compounds used are reported in Table 1 below. When using stannic chloride pentahydrate, there is a volatilization loss of tin on the order of 10:1, whereas when the compound used is stannic chloride pentahydrate reacted with sulfuric acid, the loss of tin It turns out that the loss is negligible.

In some cases, when the sulfate form is used, the final ratio may even be higher than the initial ratio. This is believed to be due to experimental error caused by the fact that the ruthenium compound contains water, which is probably lost to some extent during stripping. Reference Example 2 A second experiment was conducted showing that substantially increased amounts of tin were retained in the coating.

In this case, a known amount of a melt mixture according to Reference Example 1 using various tin-containing compounds is calcined in a crucible,
Phantom residues were analyzed by atomic absorption. The firing temperature and cycle were the same as in Reference Example 1. The results of this experiment, as a percentage of a constant element remaining in the coating material after such firing, are reported in the table below, from which it can be seen that the use of sulfate form of tin compares to the use of previously used chloride form of tin. In comparison, it can be seen that the retention rate of tin is significantly higher. Comparative example
1. To evaluate the semi-electrolytic sliding potential and service life of the electrode in comparison with electrodes that use large amounts of tin compounds in the chloride form to produce an amount equal to the amount of tin in the coating of the compound in the sulfate form. , created a series of electrodes.

It was found that 25.1 t of stannic chloride pentahydrate yielded approximately the same amount of tin as a mixture containing 5.48 y of stannic chloride pentahydrate reacted with sulfuric acid.

It can be seen that in this case, approximately five times as much tin compound is required if the sulfate form is not used in the coating. Also,
When these two materials are coated on titanium with the same amount of ruthenium (t/sq ft), the resulting electrodes have approximately the same half-electrolytic sliding potential and service life as reported in Table I below. I found out that it gives It can therefore be seen that approximately five times the amount of tin in chloride form is required relative to the amount of tin in sulfate form to produce an equal service life from the resulting electrode. This means that a much smaller amount of the tin compound in sulfate form can be used, thus saving significant manufacturing costs for a given electrode service life. As can be seen from Table 1, the reproducibility of the sulfate form of the tin compound is much higher than that of the chloride form of the tin compound, making it very easy to manufacture the electrode on a large scale. Also, the use of the sulfate form results in significantly less volatilization of tin into the atmosphere, thereby eliminating the contamination problems associated with the prior art. Example 1 A test electrode was prepared by coating a titanium mesh substrate material with a solution containing antimony trichloride and tin sulfate.

After applying the coating solution to the substrate material, the coating was baked in an oxidizing atmosphere at a temperature ranging from 475 DEG to 600 DEG C. for 5 to 10 minutes to convert the compounds to their respective oxides. This process was repeated several times to obtain layers with the desired weight gain. Then, as shown in the table below, in order to find out the unit electrode potential of oxygen both with and without resistance, at a temperature of 50°C,
The electrode samples were tested in 507 sulfuric acid electrolyte.

Next, as shown in the table below, in order to know the unit electrode potential of chlorine, about 4 d of hydrochloric acid added and 30
The same electrode was tested in an electrolytic solution containing 0 t/t of sodium chloride.

Claims (1)

[Claims] 1. Select a support, apply a coating material containing a tin sulfate compound and an antimony compound to the surface of at least a portion of the support, and dry the coating material,
A method for producing an electrode, characterized in that it is baked in an oxidizing atmosphere, thereby converting the tin and antimony compounds into their respective oxide forms. 2. Select a support, apply a coating material containing a tin sulfate compound and an antimony compound to the surface of at least a portion of the support, and dry the coating material,
forming a first coating by baking in an oxidizing atmosphere, thereby converting the tin compound and the antimony compound to their respective oxide forms; and then depositing the manganese compound and the lead on the first coating. applying a top coating material selected from the group consisting of compounds, drying the top coating material and baking in an oxidizing atmosphere, thereby converting the manganese compound and the lead compound to their respective oxide forms; A method of manufacturing an electrode, characterized by: