FI56859C - FOERFARANDE FOER FRAMSTAELLNING AV EN ELEKTROD FOER ANVAENDNING VID ELEKTROLYS - Google Patents

Description

FSSFH [»] (11) ANNOUNCEMENT cc QC Q

LJ K} UTLÄGCNI NOSSKRIFT 3000 Ό • 5SS C (45) Patent granted on 10 04 1930

Patent title T (51) Kv.lk. '/ Int.CI. * C 25 B 11/10 FINLAND — FINLAND (21) - ** · * "· **« «» ι 3l + i * 8 // 10 (22) Htkemltpllvi - Ameknlngtdig 22.12.70 ^ ^ (23) Alkuplivl — Glltl | h «tidt | 22.12.70 (41) Tullut JulklHksI - Bllvlt off * nt || j 23 * 06.71) * rrtltt.rUi.IHtu. ( 44) Ν «« Μ..ι ^ »| .Μ» Μ.ιω. »ρ, Λ_

Patent- 0 € h ragittaratyralaan 'An * ökan utit | d och uti.ikriftun publiund 31.12.79 (32) (33) (31) Pinned atuolkaut— Btflrd priorluc 22.12.69

England-England (GB) 62332/69 (71) Imperial Metal Industries (Kynoch) Limited, Kynoch Works, Witton,

Birmingham 6, England-England (GB) (72) Joseph Bernard Cotton, Sutton Coldfield, Warwickshire, Peter Charles Steele Hayfield, Castle Bromwich, Warwickshire, Ian Robert Scholes,

The present invention relates to a process for the preparation of an electrode, to the manufacture of an electrode for use in electrolysis - to a method for the manufacture of an electrode for use in electrolysis - to a method for the manufacture of an electrode for use in electrolysis for use in electrolysis, in which at least the surface of the electrode core consists of a film-forming metal such as titanium, tantalum, niobium, zirconium or their alloys, and in which an electrically conductive electrolyte-tolerant layer containing a metal belonging to the group of platinum metals or and wherein an additional layer of film-forming metal oxide is applied below and / or on top of this layer. Examples of such electrolytic methods are chlor-alkali metal electrolysis, persalt electrolysis, electroplating and cathodic protection.

It has already been proposed, e.g. British Patent Publication No. 925 ΟθΟ discloses a method of manufacturing an electrode comprising a titanium core portion and a porous coating thereon on a metal belonging to the platinum group, said titanium core being provided with a barrier layer by anodizing or oxidizing it before the coating is applied thereto. This patent discloses the advantages of such a method that it is not necessary to remove the oxide film inherent in titanium before coating it with a platinum group metal, to ensure that titanium is protected against corrosion by this barrier layer also with a platinum group metal. during coating, which may be relevant if this coating is damaged, that it is not necessary to remove the barrier layer before a new platinum group metal coating, and that it is easy to provide an adhesive platinum group metal coating.

Swedish Patent Publication No. 3 ^ 020 discloses a method for manufacturing an electrode in which the core of the electrode is titanium. One or more layers of film-forming oxides are formed on the surface of this electrode core by oxidation in air. However, these oxide layers are very dense. They can therefore only reach a limited thickness as a result of the oxygen always diffusing only more slowly and more slowly through the oxide layer. In addition, the oxide layer cannot properly absorb the subsequent precious metal layer.

The object of the invention is to show in what way the oxide layer can be made to the desired strength, while at the same time being able to absorb the subsequent precious metal layer.

The process according to the invention is characterized in that an additional film-forming layer of metal oxide is obtained by doping from a hot acidic solution containing cations of the film-forming metal. Experiments have shown that a film-forming metal oxide layer is thus formed, the strength of which is low enough to allow diffusion to occur easily. The oxide layer can therefore be made to the desired strength depending on how the subsequent noble metal layer is desired to be absorbed.

In addition, according to the invention, the oxide layer of the film-forming metal can be applied to said surface before the layer containing the metal belonging to the group of platinum metals or this oxide. The oxide layer thus binds a metal belonging to the group of Plati nametals to the core of the electrode.

According to the invention, the film-forming metal oxide can be precipitated simply by at least one oxide layer of the film-forming metal being precipitated from solution by chemically decomposing the compound containing the film-forming metal.

In an alternative embodiment of the method, at least one oxide layer of the film-forming metal may be precipitated from solution by electrolysis.

For minor use, a solution formed by etching the electrode base can be used to deposit an oxide layer of the film-forming metal on a portion of the surface of the electrode base.

Finally, the method according to the invention may be characterized in that an electrically conductive, electrolyte-resistant layer containing a metal belonging to the platinum group or an oxide thereof is applied to said surface by preparing a paint mixture containing a compound of at least one metal belonging to the platinum group and coating part of the surface with this mixture, and that the paint mixture is finally heated to a temperature of 1 * 50-700 ° C in an oxygen-containing atmosphere.

A layer containing a metal belonging to the group of platinum metals or an oxide thereof can in a certain case be applied only on a part of the core of the electrode in order to fit an oxide layer of the film-forming metal thereon.

The areas of the surface on which the different layers are arranged can only partially overlap in a given case. The oxide layer of the film-forming metal is preferably the same metal as the metal of which the surface is composed.

It has not been expressly stated above that the layers in question are in many overlapping layers, but such a case is also within the scope of the invention. Thus, the method of the present invention also preferably comprises precipitating one or more layers, each of which contains a film-forming metal oxide from this solution, wherein at least one of the layers is deposited on a layer containing a platinum group metal or a platinum group metal oxide. For example, an electrode base having a film-forming metal surface may be provided with one or more layers containing platinum group metal or platinum group metal oxide, followed by one or more layers of film-forming metal oxide in solution, followed by one or more layers containing platinum group metal or oxide of such a film, followed by one or more layers of solution mixed with oxide of film-forming metal, etc. The oxide of this film-forming metal need not be the same in each layer, and the layers containing platinum group metal or oxide may be different from each other. for example, contains only metals, only oxides, or mixtures thereof, and various platinum group metals or mixtures thereof may be used.

Preferably, the oxide layer of the film-forming metal, or at least one of these layers, is precipitated from solution by chemically decomposing a compound in solution containing a film-forming metal. Alternatively, a single or at least 11,585,83 layers of well metal oxide are doped from solution by electrolysis.

This method of chemical decomposition can be illustrated by selecting titanium as an example, from which an aqueous solution containing a trivalent titanium ion is prepared. This is oxidized, for example, by bubbling air through the liquid to give titanium in the tetravalent state. Once the electrode base is immersed in the solution, the solution is heated close to its boiling point, causing the titanium to hydrolyze and titanium dioxide to precipitate on the titanium surface. Although not to be construed as limiting the invention, it is believed that the reactions that occur can be represented by the following simplified reaction equations: li ±

Ti + Uh20 -> Ti (OH) ^ + UH

followed by Ti (OH) ^ - ^ TiOg + 2H2O Using a 10% by weight sulfuric acid solution containing 0.1% by weight of tetravalent titanium, the weight gain of the titanium dioxide film is steady and 2 occurs at a rate of approximately 5 g / m / day. This rate can be varied by boiling the solution rapidly or by using the solution at a temperature slightly below its boiling point, but titanium dioxide should not be precipitated at too high a rate as a non-stick precipitate may form.

The maximum weight of this titanium dioxide film that can be usefully achieved is in the range of 20 to 30 g / m 2, after which a white, non-stick film is formed and flaking may occur.

When the desired weight of titanium dioxide is thus precipitated, this amount being more preferably in the range of 2.5 to 20 g / m, an associated precipitating layer of oxidized platinum group metal is applied thereon. In the case of ruthenium oxide, this method involves the use of a paint which is fired in air at 500 ° C for 20 minutes. The best possible paint composition is achieved by dissolving 60 g / l of RuCl 2 SHgO in a suitable alcohol saturated with ammonium chloride. This paint can be applied, for example, by using a brush so that the paint dries within a few minutes after application.

The electrolysis method can be applied in the case of titanium by preparing an aqueous solution containing a trivalent titanium ion, immersing the electrode core in a solution and coupling it as an anode to a cathode of a suitable substance, which is also placed in the solution. When the solution is close to its boiling point, a voltage of a typical value of 12 volts develops strongly on the electrode core frame of the 56,5859 adhesive coating. In this case, a coating rate of about 2 g / m / h can be achieved.

Preferably, a layer containing a platinum group metal or a platinum group metal oxide is applied by thermal decomposition of a particular paint coating. Typically, the paint coating is decomposed by burning it in a U50 ~ 700 ° C oven in an oxygen-containing gas for 5 minutes to 1 hour. This coating can later be heat treated in an oxygen-containing gas for up to 20 hours. If the coating contains ruthenium, the temperature may rise to as high as 700 ° C.

Typical exemplary embodiments of the present invention are explained in more detail below:

Example 1

An electrode core containing commercial grade titanium with low impurities and chemically removed from the surface is coated in this example without the use of chemical etching with a titanium oxide layer of 10 g / m 2. 15 g / m of oxidized ruthenium are placed on top of this layer.

The chemical precipitation of this titanium dioxide is carried out as follows. Commercial pure titanium is dissolved in heated 10% w / v 3+ sulfuric acid to give a purple / blue solution of a typical Ti solution. This solution is diluted to a concentration of 1 g of titanium per liter and the titanium ion is oxidized to tetravalent by bubbling air through this solution until the purple color disappears and the solution becomes colorless.

When this solution is close to its boiling point or at a slight boiling point, the core of the titanium electrode is immersed there in a vertical position until the precipitation of this titanium oxide has taken place. The length of the immersion time between 2k and 1 hour results in an amount of precipitation between 5 and 10 g / m At the end of this coating cycle, this electrode core was washed in water, lightly rubbed with a nylon brush to remove any loose coating, and then dried.

The oxidized ruthenium is obtained from a paint containing 60 g / l of RuCl 2 HgO dissolved in an alcohol saturated with ammonium chloride. This paint is applied on top of titanium using a nylon brush in several coats. Combustion is always carried out after two coats of coating, this treatment including circulating air at 500 ° C for 20 minutes.

The electrode of this Example 1 was subjected to an electrolytic experiment in which a coated edge of a plate having a size of 30 x 1 mm was located 2 mm above the free mercury surface. A saline solution having a concentration of 6 56859 of 22 g / l and a temperature of 70 ° C was passed between these electrodes and the test surface was made an anode compared to the mercury surface and an actual current density of Uo kiloampers / m was used. The electrolysis time at low cell voltage exceeded what could be obtained by placing the same amount of oxidized ruthenium on the etched titanium surface without first chemically placing a layer of titanium dioxide on it. This is a severe test due to the small gap and high current density of the anode and mercury.

Example 2

An electrode core which was commercially pure titanium, had a low impurity content, was heat treated in air, and had been chemically removed from the scale. After the surface of this electrode core was degreased using trichlorethylene vapor but without etching, two layers of oxidized ruthenium were applied to it and firing was carried out according to the same method as in Example 1. Ten g / m of titanium dioxide was placed on this surface using the method described in Example 1. To supplement this coating, U g / m of oxidized ruthenium was further applied by the method already used, placing it on top of the original two layers. Such a layered coating of the structure provided good properties in the electrolysis test when the test method described above in connection with Example 1 was used.

Example 3 In this example, a method very similar to Example 2 was used, except that the noble metal paint initially applied to the titanium consisted of a 70/30 platinum-iridium alloy. A single coat of "Hanovia IR1" paint was applied and dried in an oven at 250 ° C for 15 minutes followed by firing for 20 minutes at i + 50 ° C with all this in air.

2 10 g / m of titanium oxide was deposited on this layer using the sulfuric acid method 2 and finally U g / m of ruthenium metal as oxidized ruthenium, and good electrolytic properties were obtained with this coating.

The electrodes prepared according to Examples 1, 2 and 3 were found to have an overvoltage in the range of • · 2 current density in the range of 10 kiloampers / m chlorine, which is at least comparable to that of a titanium-core electrode coated with several layers of ruthenium oxide alone.

In carrying out the conversion cases of Examples 1, 2 and 3, film-forming metals other than titanium, for example niobium, tantalum and, if the chlorine environment is avoided, also zirconium, can be used as the electrode core.

In addition, the titanium dioxide layers used can be replaced by layers of other film-forming metal oxides. It is not necessary to use the same film-forming metal as the oxide layer and the electrode core.

Thus, a layer of titanium dioxide can be fitted to the electrode core of tantalum.

τ S6859

In addition, the electrode core may either be formed of a film-forming metal on its own, or it may be provided with a core of a different metal, such as copper, in order to improve its electrical conductivity. Example U

A commercial grade titanium electrode core was etched using 10 wt / l. oxalic acid for 8 to 16 hours. This core was then charged with a positive voltage of 12 volts compared to the lead cathode and this core and cathode were immersed in 7 weight-5? to a sulfuric acid solution containing 5 g / l of titanium of 3+ (...... o.

Ti ions. This solution was heated and kept at 90 ° C. Layer 2 of titanium dioxide precipitated on the electrode core at a deposition rate of approximately 2 g / m / 2 hour. Thus, a coating having a thickness of 15 g / m 2 was prepared.

After coating, this electrode core was washed in water and dried. This titanium dioxide coating was found to be firmly adhered to its titanium substrate.

The electrode core was then electrically conductive coated by dissolving iridium chloride and ruthenium chloride in n-butyl alcohol to give a paint mixture which was applied in a plurality of layers to the electrode core on titanium dioxide, dried each layer and fired 2 layers at a time in air at 500 ° C for 20 minutes. This electrically conductive coating was found to be well adhered to titanium dioxide and consisted of a mixture of iridium metal or its oxide and ruthenium oxide in an amount of about 15 g / m 2. The ratio of metal contents of iridium to ruthenium was varied between 3: 1 »1: 1 and 1: 3 using different paint mixtures for different sample electrode cores. Satisfactory electrodes were always achieved. Example 5

The procedure of Example 1+ was repeated with the variation of using a paint mixture of ruthenium chloride alone dissolved in n-butyl alcohol. This paint mixture was also fired at 500 ° C for 20 minutes and sufficiently different layers were applied to give 15 g / m ruthenium oxide. The resulting electrode was thus found to have excellent resistance to losses when used as an anode in the electrolysis of brine in a mercury cell to produce chlorine.

Example 6

The procedure of Example 4 was repeated with the modification of using a paint mixture of platinum and iridium chlorides dissolved in n-butyl alcohol. This paint mixture was also fired at 500 ° C for 20 minutes and sufficient layers were applied to obtain a mixture of about 15 g / m platinum and iridium firmly adhered to the titanium dioxide coating. The electrodes prepared according to this example had excellent properties in the electrolysis of chlorine using a membrane cell.

Example 7

The procedure of Example 1+ was repeated with the variation of using a paint mixture of iridium chloride dissolved in n-butyl alcohol.

. ..... .. o. ........

This paint mixture was also fired in a 500 ° C oven for 20 minutes and sufficient layers were applied to give an amount of iridium metal of about 10 g / m 2 as a tightly adhering layer to this titanium dioxide. Whether iridium was present in its metallic or oxide form, or as a mixture of both, has not been determined. This electrode was very useful in the electrochemical preparation of sodium chlorate from saline solutions.

Example 8

The procedure of Example 7 was followed with the modification that the paint mixture also contained some tetra-n-butyl titanate. This produces an electrode, an electrode in which the top layer is a mixture of titanium and iridium oxides. The order of the paint mixture is arranged to give equal amounts by weight of titanium dioxide and iridium oxide, provided that this iridium is completely oxidized. This example can be modified by replacing iridium with ruthenium.

Example 9

The procedure of Example 1+ was repeated with the modification that the titanium electrode core was replaced with an electrode core that was tantalum. The titanium dioxide layer was applied to the tantalum base as described but this tantalum should be mechanically roughened instead of etched. The resulting electrode was thus found to have a high resistance to abrasion when used as an anode in the electrolytic production of chlorine in a mercury cell.

Example 10

The procedure of Example 9 was repeated, modified so that the electrically conductive coating applied to the titanium dioxide layer was as in Example 5.

This also gave a very satisfactory electrode.

Example 11

The procedure of Example 5 was repeated with the additional modification that the electrode core was sandblasted tantalum. A very useful electrode was also produced in this way.

This tantalum was then replaced with niobium, and the procedure of this example was repeated to produce another very useful electrode, although some difficulties were encountered in preventing the avoidable oxidation of niobium during the combustion of ruthenium chloride paint in air at 500 ° C.

9 56859 This procedure was repeated again using an etched zirconium electrode core. This produced thin layers of titanium dioxide which adhered to the zirconium support and served as a satisfactory base for the ruthenium oxide which precipitated from the paint mixture.

This procedure was repeated again with the modification that the electrode core was a titanium alloy containing 6 wt. aluminum. U-weight- # vanadium and the rest titanium. This also produced a satisfactory electrode.

In another variation, the titanium alloy just described was replaced with a 0.2 wt% palladium alloy. This also produced a satisfactory electrode.

Example 12

A commercially pure titanium electrode base was etched using 10% by weight or volume of oxalic acid for about 10 hours. This core was then provided with a positive voltage of 12 volts compared to the lead cathode and the core and cathode were immersed in 15, U weight /? to a solution of phosphoric acid containing U, 3 g / l of trivalent titanium ions. This solution is heated and maintained at 90 ° C

2 at about 7 hours. Thus, a 13.3 g / m titanium dioxide coating with good adhesion was developed for the electrode core.

This electrode base was then provided with an electrically conductive coating using the method of Example 5. When the resulting electrode was used in the electrolysis of brine in a mercury cell to produce chlorine, it was found to be as resistant as the electrode of Example 5.

Example 13

The procedure of Example 12 was repeated except that the solution containing trivalent titanium ions was first replaced by 10% by weight. with a solution of sulphamic acid containing 1 g / l of titanium. After 5 hours at 90 [deg.] C., 5 to 6 g / m @ 2 of highly tackifying titanium dioxide evolved. The resulting electrode was thus satisfactory.

This example was also repeated using 20% by weight of sulfamic acid containing 5 g / l of titanium. Within seven hours, a permanent coating of titanium dioxide of 3 g / m 2 was developed.

Example 1 ^

The procedure of Example 12 was repeated using a titanium-containing solution of 20% by weight or volume of oxalic acid as a solution containing 5 g / l of titanium. 3+. ......

which is Ti in its state. When a voltage of 12 volts prevailed between the electrode core and the lead cathode and the solution was at boiling temperature, a titanium dioxide coating developed in 2k per hour, which was strongly adhering to the electrode core and was present in an amount of about 35 g / m 2.

Example 15

The electrically pure titanium electrode core was etched using 10% by weight or volume of oxalic acid for about 8 hours. This core was then made electrically conductive on its surface using a paint mixture of ruthenium chloride dissolved in n-butyl alcohol. This paint was applied to the etched titanium surface in a series of different layers, whereby each layer was dried and always 2 layers at a time were fired at 500 ° C in air for 20 minutes. This is continued for 2 until the titanium surface has 10 g / m of ruthenium oxide.

A titanium dioxide coating was then applied to this coating by setting it as an anode at 7 wt. to a sulfuric acid solution containing 5 g / l of trivalent titanium. This electrode core was then exposed to a 2 volt positive voltage at 90 ° C compared to the lead cathode in solution. After 7 hours, a tightly adherent layer of 2 12 g / m 2 titanium dioxide had formed on the ruthenium oxide surface. The resulting electrode thus had excellent wear resistance when used in the electrolysis of brine in a mercury cell to produce chlorine.

Example 16

A commercially pure titanium electrode core was etched using a solution of 20% by weight or volume of oxalic acid at 80 ° C to 90 ° C. The duration of etching was 16 hours.

At the end of this etching period, the oxalic acid solution contained the required amount of about 5 g / L of titanium dissolved therein from this electrode core. If this solution does not contain enough titanium after sufficient etching, the adjustment can be performed by adding titanium powder or titanium oxalate to a titanium content of about 5 g / l. Without removing this electrode core from this solution, this core is connected as an anode to the lead cathode in this solution, the voltage applied to this anode is about 12 volts, and the solution is boiled. This causes a coating of titanium dioxide to precipitate on this etched electrode base and after 2 hours contains about 30 g / m of tightly adhering titanium dioxide.

This method combines the etching of a titanium surface with the method of placing a coating of titanium dioxide and can be converted using sulfuric acid and hydrochloric acid as etching solutions.

This electrode is then provided with an electrically conductive coating consisting of a mixture of iridium and ruthenium oxide as described in Example b.

One of the major advantages of the electrodes of this invention is the excellent durability of this coating. This is always important, but it is critically important in chlor-alkali electrolysis using a mercury cathode.

56859 The electrodes of the present invention tolerate contact with mercury and mercury amalgam very satisfactorily. Without limiting the present invention in any way to the description, it is believed that this resistance is due to the film-forming metal oxide of this layer or layers and its application method to obtain such a layer or layers having a highly protective property and also providing excellent adhesion and excellent electrochemical properties.

The two main methods of the present invention disclosed involve the chemical doping of a film-forming metal oxide from its solution s as a first method and the electrolysis of a film-forming metal solution as a second method. When comparing these, it is obvious that the latter method provides electrodes with a longer lifetime in electrolysis and resistance to immersion in mercury and mercury amalgam, and will withstand caliber times more immersion than the electrodes of the first method. Production is also facilitated when this oxide is doped only at the positive voltage electrode core and at a higher deposition rate. Thus, it is preferred to deposit the oxide of the film-forming metal by electrolysis of a solution containing this metal.

Another advantage achieved when placing a titanium oxide layer on top of titanium by the methods of this invention has a higher anodic scattering stress in chloride solutions than that achieved with uncoated titanium. This is a remarkable property for anodes used in chlorine cells at high temperatures. The results thus obtained are shown in the table below.

table 1

Anodic scattering voltage for commercial grade titanium in 22% brine at 80 ° C 2 (Using a constant current density of 30 mA / cm)

Manufacturing method Decomposition voltage

Reference substance, heat-treated and 8.1 descaled 8.2 Heat-treated and descaled 7.9 + film formation 8 hours +) 19.3 19.0 Heat-treated and descaled 19.2 tu + film formation 17 hours +) 18, 5 18.5 18.2 Heat treated and descaled + film formation 2k hours +) 1 + 6 36 50 56859 +) film formation in quietly boiling 10% sulfuric acid containing 0.1 wt-Ji tetravalent titanium.

This advantage can be exploited with maximum efficiency by fitting a layer of titanium dioxide not only to the specific part of the surface of the electrode core where electrical conductivity is required but also to the rest of this surface.

The present invention also includes an electrode for use in electrolytic methods if it is manufactured by the method of the present invention.

Claims (6)

13 56859 1. A method of manufacturing an electrode for use in electrolysis, wherein at least the surface of the electrode core consists of a film-forming metal such as titanium, tantalum, niobium, zirconium or alloys thereof, and an electrically conductive electrolyte layer containing platinum metal or an oxide thereof, and in which an additional layer of film-forming metal oxide is arranged below and / or on top of this layer, characterized in that an additional layer of film-forming metal oxide is obtained by doping from a hot acidic solution containing film-forming metal cations. A method according to claim 1, characterized in that the oxide layer of the film-forming metal is placed before the layer containing the metal belonging to the group of platinum metals or this oxide. Process according to Claim 1 or 2, characterized in that the at least one oxide layer of the film-forming metal is precipitated from solution by chemically decomposing the compound containing the film-forming metal. Method according to Claims 1 to 3, characterized in that at least one oxide layer of the film-forming metal is precipitated from solution by electrolysis. Method according to Claims 1 to k, characterized in that a solution formed by etching the electrode base is used to deposit a layer of oxide-forming metal oxide on a part of the surface of the electrode base. Method according to one of the preceding claims, characterized in that the electrically conductive, electrolyte-tolerant layer containing a metal belonging to the platinum group or an oxide thereof is applied by preparing a paint mixture containing a compound of at least one metal belonging to the platinum group and coating at least a part of the surface with this mixture, and that the paint mixture is finally heated to a temperature of '450-700 ° C in an oxygen-containing atmosphere.