JPS5822551B2 - Improved electrode manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention generally relates to a method of applying a coating material to an electrode support, generally a valve metal.

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; Complete reusability saves manufacturing costs and reduces air pollution caused by volatilization of tin compounds during the coating process.

More particularly, the invention provides that by using a tin compound in the form of a sulfate salt in a coating composition mixture,
This invention relates to a greatly improved method for producing electrodes having a support of valve metal, such as titanium, supporting an electrode coating composition comprising a tin component and a valve metal component, or both and a ruthenium component.

Electrochemical production methods are gaining importance in the chemical industry because they have greater ecological acceptability, allow for energy conservation, and can reduce product costs.

Therefore, significant research and development efforts have been devoted to electrochemical methods and their hardware.

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 a commercially possible range. Electrodes that can be manufactured with high quality control at a low cost.

Only a few materials, such as solder, 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, metal, nickel, lead, lead alloys, platinum or platinized titanium.

This type of electrode lacks dimensional stability, has a high cost of 1,
High wear rate, contamination of electrolyte, precipitation contamination of cathode,
Sensitivity to impurities or high overpotentials for the desired reaction limit applications.

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 electrodes that overcome many of the undesirable properties mentioned above and can still store energy with low overpotentials at higher current densities.

For example, platinum can be
It is known that it is an excellent material for use as an anode in the -inning process) and that it satisfies many of the criteria mentioned above.

However, platinum is expensive and has not yet been found to be industrially suitable to date.

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.

Half-electrolytic sliding potential. If it is high, the electrolyzer will consume more electrical energy, which is undesirable.

A disadvantage of lead alloy anodes is that the lead dissolves in the electrolyte and forms lead deposits on the cathode, which contaminates the desired resulting deposit.

Furthermore, PbO2 changes to Pb3O4, which has poor conductivity.

Oxygen can penetrate under this layer and peel off this film,
As a result, particles are generated and become 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, the cost per square foot of electrode surface area is $30.00.
00/m'), making it undesirable for industrial use.

Furthermore, it was proposed to electroplate platinum on the surface of titanium and apply other deposits of lead dioxide or manganese dioxide to this.

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 Contaminate products deposited on the positive cathode surface.

The current density of such anodes is therefore limited and the handling of such anodes must be done with great care.

Another improvement that has been 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 (77,
As long as the current density remains below 5 milliamps per square inch (155 milliamps per square inch (155 milliamps per square inch) Ffl), relatively low overvoltages will result, but as the current density increases to around 1 ampere per square inch (155 milliamps per square inch) Significant disadvantages occur at high current densities.

Nowadays, many coatings use titanium, ruthenium and soot dioxides, or tin and antimony oxides, on top of which manganese or lead oxides are used.
Hep coating is applied.

These coatings have shown substantial promise in reducing overvoltages in that area and increasing service life in corrosive conditions within electrolytic cells.

A major drawback of these materials is that substantial amounts of soot are volatilized when the coating is baked to the tin oxide, especially in the tin oxide application process.

The reason is that tin compounds, such as stannic chloride pentahydrate, convert to stannic hydroxide during baking 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
Because tin boils at around 14°C, and the transformation of tin compounds to their respective oxides occurs at much higher temperatures, most of these substances are lost to the atmosphere, resulting in Less than 50% of the tin material is utilized in the actual coating.

This creates severe problems in quality control when manufacturing large, large quantities of electrodes.

Reproducibility of coating compositions is rarely possible due to the volatilization of tin that occurs with conventional methods of applying coatings 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 soot in coating compositions has not been commercially successful because the volatility of soot creates reproducibility problems and increases contamination, which is currently subject to stringent standards. and the manufacturing cost of certain electrodes is increasing due to the loss of tin.

Accordingly, it is an object of the present invention to provide a method for producing electrode coating compositions having desirable quality control properties and manufacturing costs within commercially viable ranges.

It is another object of the present invention to provide a method of manufacturing an electrode coating composition that significantly reduces the volatilization of soot into the atmosphere, thus alleviating the airborne pollution problems associated with this manufacturing.

These and other objects of the present invention, as well as its advantages over the current and prior art, are achieved by the improvements described and claimed herein, as will be apparent from the following description.

The coating composition includes selecting a support, applying a coating material containing a tin sulfate compound and a valve metal or a ruthenium compound and a tin sulfate compound to at least a portion of the surface of the support, applying the coating material, and applying the coating material to the coating material. It has been found that it can be produced by a process consisting of drying the material and baking the coating material in an oxidizing atmosphere to bring the tin compound into its oxide form.

The valve metal in the present invention means aluminum, molybdenum, diopter, Kunkle, titanium, tungsten, zirconium, and alloys thereof, and does not include antimony.

An improved electrode for use in an electrolytic cell also includes a metal support and a coating material having a tin sulfate-containing compound applied onto the support and converted to an oxide form.
It has been found that a top coating selected from the group of manganese dioxide or lead dioxide can be made.

The tin sulfate-containing compounds are in forms or combinations that can be used simultaneously with tin sulfate, such as tin sulfate hydrate, sulfuric acid and tin sulfate, mild hydrochloric acid and tin sulfate, alcohol solution and tin sulfate, sulfuric acid solution and tin chloride, sulfuric acid solution. and tin chloride hydrate.

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 soot volatilization is currently a problem.

In the past, electrode coating compositions using soot 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 soot in the sulfate form.

This sulfate form of soot 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 include: Aluminum, molybdenum, niobium, quantal, titanium, tungsten, zirconium, nickel, steel, stainless steel and their alloys.

The preferred valve metal is titanium based on cost, availability, electrical and chemical properties.

There are a number of forms that titanium supports can take in the manufacture of electrodes, examples of which are tough sheet materials, expanded metal mesh materials with a high percentage of open area, and cold forming of titanium powder. It is a porous titanium with a density of 30 to 70% of pure titanium that can be produced by compression.

In the past, intermediate coatings have generally used stannic chloride pentahydrate as one of the materials in the mixture to be painted or applied to the substrate.

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 soot into the atmosphere at the temperatures at which these materials are baked into their respective oxides.

For this reason, semiconducting intermediate coatings can be formed in very few applications, whereas past methods require the application of material to be divided into several layers to obtain the desired range of resulting drop weights. went.

This semiconductive intermediate coating -H can be followed by a top coating of manganese dioxide or lead dioxide 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.

Single layer coating compositions containing titanium ruthenium and soot dioxide are further described in US Pat. No. 3,855,092, which is incorporated herein by reference.

The present invention will be further illustrated by the following reference examples and examples.

REFERENCE EXAMPLE 1 Antimony trichloride, ruthenium trichloride and various tin-containing compounds were added such that they all calculated into the final tin/ruthenium ratio analysis and gave a comparable initial tin/ruthenium ratio. A series of electrodes were made by coating a support metal, in this case titanium, with the solution containing the same amount.

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.

Since ruthenium compounds absorb some water and form hydrates, there is some inaccuracy in the calculation of the initial amount of ruthenium in this ratio, approximately by a factor of five.

After these various materials were applied to the support material, it was baked in an oxidizing atmosphere at a temperature of 475 DEG to 625 DEG C. for 5 to 10 minutes to convert each compound to its respective oxide.

This process was repeated several times to form layers of desired 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 final tin content in the coating material. The final tin/ruthenium ratio was determined by establishing the 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 soot on the order of 10:1, whereas when the compound used is stannic chloride pentahydrate reacted with sulfuric acid,
It can be seen that the soot loss is negligible.

In some cases, when using the sulfate form, the final ratio may even be higher than the initial ratio.

This is believed to be due to experimental error caused by the ruthenium compound containing water, which was probably lost to some extent during stripping.

Reference Example 2 A second experiment was conducted showing that substantially increased amounts of soot were retained in the coating.

In this case, a known amount of solution mixture according to Reference Example 1 using various tin-containing compounds is calcined in a crucible,
The residue was analyzed by atomic absorption.

The firing temperature and cycle were the same as in Example ①.

The results of this experiment are reported in Table 1 below as the percentage of certain elements remaining in the coating material after such firing.

From Table 1, it can be seen that the soot retention rate is significantly higher when using the sulfate form of soot than when using the previously used chloride form of soot.

Reference Example 3 Evaluating the half-electrolytic sliding potential and service life of an electrode in comparison with an electrode that uses a large amount of a tin compound in the chloride form to produce an amount equal to the amount of soot in the coating of the compound in the sulfate form. In order to do this, we created a series of electrodes.

It was found that 25.1 g of stannic chloride pentahydrate produced approximately the same amount of soot as a mixture containing 5.48 g 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.

Additionally, when these two materials are coated on titanium with the same amount of ruthenium (g/sq ft), the resulting electrodes have approximately the same half-electrolytic sliding potential as reported in Table ■ below. It was found to give a long service life.

It can therefore be seen that approximately five times the amount of soot in the chloride form is required relative to the amount of soot in the sulfate form to produce an equal service life from the resulting electrode.

This means that significantly lower amounts of the tin compound in sulfate form can be used, thus saving net manufacturing costs for a given electrode lifetime.

As can be seen from Table 3, the reproducibility of tin compounds in sulfate form is much higher than that of tin compounds in chloride form, making it very easy to manufacture electrodes on a large scale.

Also, the use of the sulfate form results in significantly less soot volatilization into the atmosphere, thereby eliminating the pollution problems associated with the prior art.

Example 1 A conductive sample was prepared by etching a titanium sheet in a 50150 solution of hydrochloric acid and water, followed by 30 ml of butyl alcohol, 9.79 ml of 5nC14.5F 20.
coated with an electrode coating composition containing 2 ml orthobutyl titanate and 6 ml sulfuric acid to a thickness of three coats;
This was followed by baking at a temperature of 600°C in an oxidizing atmosphere.

Next, the obtained electrode sample was used as an anode at a rate of 150g/
One test was carried out in an electrolytic bath containing 50°C of sulfuric acid at a temperature of 50°C and the current density listed in Table 1, and the unit electrode potential of oxygen in both cases with and without resistance as shown in Table Obtained.

Example 2 1.192,9 ruthenium chloride, 5.74 g tin chloride, 5.581 nl butyl ticunate, 7.6 rn
Electrode samples were prepared by coating the titanium mesh substrate material with a solution containing 1 ml of sulfuric acid, and 11.22 ml of butanol.

The electrode sample was then heated at a temperature of 450° C. for 7 minutes.

This procedure was repeated ten more times to obtain the final coating.

The resulting electrode was tested in a conventional mercury electrolyzer in which chlorine and caustic soda are produced using a sulfur chloride electrolyte.

At a given current density, the electrode exhibited an average potential 0.04 volts lower than the corresponding DSA type electrode.

Thus, as is apparent from the foregoing description of the preferred embodiments, the compositions described herein achieve the objectives of the present invention and are suitable for use in the manufacture of electrode coating compositions and in electrodes used in electrolytic cells for electrochemical production. Solved the problem.

Claims (1)

[Scope of Claims] 1. Select a support, apply a coating material containing a tin sulfate compound and a valve metal compound to at least a portion of the surface of the support, and dry the coating material,
and baking the coating material in an oxidizing atmosphere to convert the tin compound and the valve metal compound into their oxide forms. 2. Select a support, apply a coating material containing a tin sulfate compound, a valve metal compound, and a ruthenium compound to at least a portion of the surface of the support, dry the coating material, and place the coating material in an oxidizing atmosphere. A method for producing an electrode, comprising baking the tin compound, the valve metal compound, and the ruthenium compound in the form of their oxides. 3. The method according to claim 1 or 2, wherein the valve metal compound is a titanium compound.