DE2100652A1 - Electrode for chlor-alkali electrolysis and process for its manufacture - Google Patents

Description

METALLGESELLSCHAFT Frankfurt (M), January 7, 1971

Aktiengesellschaft DrOz / MMü (Frankfurt / Main

House no. 6603 M.

Electrode for chlor-alkali electrolysis ^ and process for its manufacture-

The invention relates to an electrode, in particular anode, for the chlor-alkali electrolysis with graphite as Framework body, as well as a process for the production of this electrode

It is known that simple graphite anodes have a high overvoltage in the chlor-alkali electrolysis, are not sufficiently corrosion-resistant and also not dimensionally stable. With increasing corrosion and wear the voltage and thus the power consumption continue to rise, so that the electrode is often readjusted and eventually needs to be renewed.

Therefore there has been no lack of attempts to improve the technical disadvantages of graphite, be it that one by coating the graphite with a wide variety of Substances tried to increase its chemical stability, or else by applying kata "ytiech active substances wanted to reduce the overvoltage of chlorine and graphite.

In order to improve the chemical stability of graphite, it has been proposed to treat graphite with fluorine (French patent 1 506 442), an impregnation with certain ketones (US patent 30 46 216) with Oelen (USSR patent specification 201 341, Czech Fatentechrift

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100 959), with drying oils (French patent specification 1 335 152), with pitch (French patent 1 541 750) or with synthetic resin (Belgian patent 634 242, Belgian patent 708 888, British Patent specification 10 74 042), or low-melting alloys such as lead and bismuth (British Patent 11 36 808) to apply.

To reduce the overvoltage of the chlorine, it has been proposed to combine graphite with titanium (Dutch Offenlegungsschrift 66 05 125) or to be coated with titanium, zirconium or tantalum and the metal layer through a Activate platinum metal. (German Auslegeschrift 1 286 513, British Patent 10 69 403, French Patent 15 16 524X

I have another path taken by technology in replacing graphite with suitable metals, especially titanium. In British patent specification 941 177 and in French patent specification 14 19 603, an electrode has been proposed which has a base body made of titanium, the surface coating with a platinum metal or a platinum-metal alloy is activated.

A large number of publications deal with the production of effective activation layers for the base metal consisting of titanium or titanium, tantalum, zirconium or niobium (British patent specification 964 631, British patent specification 974 57O ₁ British patent specification 984 973, British patent specification 11 36 869, Dutch laid-open specification 64 02 931, Dutch laid-open specification 66 06 302, US patent specification 30 55 811, German published specification 1,467,221).

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Further suggestions for coating the titanium base metal consist of the application of oxide coatings made of titanium dioxide or tantalum pentoxide, which are made semiconducting (German Offenlegungsschrift 18 14 576, South African patent specification 6 307 482)

of alloys of molybdenum or tungsten with iron, cobalt or nickel (British patent specification 1 004 580)

of ruthenium dioxide (British Patent 11 68 558).

The two-layer structure also takes up a lot of space the framework electrode, which is predominantly made of titanium. It consists of precious metal and a porous, protective coating of the base metal (French patent 1 502 587) made of precious metal and titanium dioxide (Dutch patent specification 99 396)

made of precious metal and silicon dioxide (Dutch Offenlegungsschrift 66 12 095)

from layers applied to the electrolyte, with suitable electrol3 * additives water glass, zirconium oxychloride, Aluminum chloride, gallium chloride and boric acid can be (Dutch laid-open specification 66 12 096, German Offenlegungsschrift 1 567 925),

from platinum and iron, which is then oxidized (US Pat. No. 3,103,484).

It is also known to replace activated titanium electrodes with those made from

Nickel or nickel alloys, rhodium or iridium, each of which can be platinized (British patent specification 1 026 115)

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or by those made of niobium, tantalum, tungsten, zirconium, which are activated with rhodium, iridium, palladium or platinum (French patent 1 393 835, French patent 1 208 618)

by one made of a perforated metallic carrier electrode, which forms a porous layer of a metal, such as nickel, cobalt, iron, with a metal dispersion in the pores (French patent 1 157).

From the German Auslegeschrift 1 421 047 an anode made of a titanium alloy is known, which are coated with a thin layer of titanium nitride by heating in a nitrogen or ammonia atmosphere is to give the anode protection against aggressive media and to improve its conductivity.

Although the development based on activated titanium or tantalum electrodes is particularly remarkable The well-known electrolysis processes and electrodes still adhere to technical advances significant disadvantages.

If the known electrodes based on titanium or tantalum without the use of graphite as a framework electrode are produced, they are expensive, often not very stable and not short-circuit proof In addition, the vast majority of electrodes based on titanium or tantalum have the disadvantage in common: that the activation layer under the conditions of Electrolysis is not sufficiently adhesive · A reactivation within certain and mostly short time intervals is essential if the intended purpose of low power consumption is to be maintained,

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The invention is based on the object of avoiding the known disadvantages and an electrode for alkali electrolysis to create, which is dimensionally stable, short-circuit-proof and highly conductive and the separation of chlorine with the lowest possible overvoltage possible. This object is achieved by using an electrode, in particular Anode, for the chlor-alkali electrolysis with graphite as the framework body according to the invention of the framework body a surface coating made of hard material and of at least one metal and / or metal oxide Has platinum group, which is used to fix an electrically porous and under / electrolysis conditions chemically resistant oxide coating.

The surface coating of the frame body may be made of a mixture of hard material and are made at least one metal and / or metal oxide of the platinum group, it may However, ^a ^ ei layers may be formed, the lowermost layer of hard material and

the upper layer made of a metal and / or metallic

oxide of the platinum group.

Titanium carbide, but in particular titanium nitride, are preferably suitable as the hard material.

Platinum group metal oxide is a particularly suitable one Part of the coating.

A coating of silicon dioxide is preferably used to fix the primarily applied surface coating, Titanium dioxide, zirconium dioxide, niobium pentoxide or tantalum deoxid

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- ο -

The production of the electrode is done in the way that the framework body made of graphite with a coating of hard material and at least one metal and / or Metal oxide of the platinum group provided and then the coating with an electrically porous and under the electrolysis conditions chemically resistant oxide coating is fixed.

The framework body can preferably be coated in three ways

1) Hard material and at least one metal and / or metal oxide of the platinum group are applied in a mixture together by plasma spraying '

2) Primarily the hard material is applied by plasma spraying and the at least one metal and / or metal oxide of the platinum group is produced from a suspension or solution by impregnation and subsequent tempering at an elevated temperature, which is expediently in the range of 300-600 ^° C

3) Primarily the hard material is applied by plasma spraying and the at least one metal and / or metal oxide the platinum group is deposited from the gas phase on the hard metal layer.

To produce the coating, the hard material is preferably titanium carbide, but in particular titanium nitride and the hard material At least one metal and / or metal oxide of the platinum group Metal oxide of the platinum group is particularly suitable

In an expedient embodiment of the method, the coating used for fixing is provided by hydrolytic cleavage of chlorides of the elements silicon, titanium, zirconium, niobium or tantalum and volatilization of the solvent.

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The "advantage achieved with the invention" exist in particular in that the electrode has both good durability and dimensional stability and a cheap one exhibits electrical behavior. As a result of the excellent conductivity properties of the hard materials and Activation by metal and / or metal oxide of the platinum group is the overvoltage of the chlorine on one economic interesting value decreased. The electrode is very short-circuit proof. An erosion of the The platinum metal or platinum metal oxide layer is a consequence of the external sealing of the electrode Oxide layer prevented. The invention makes it possible to use graphite, which is of interest for economic reasons to be used as a base material for production.

The invention is explained in more detail using the following examples:

Example 1:

A graphite block with the dimensions 40 × 40 × 15 mm is coated on one side by plasma spraying with titanium nitride in such a way that the layer thickness is between 0.1 and 0.3 mm. After washing with alcohol and subsequent drying, the titanium nitride layer is painted with a solution of 1 g of RuCl, in 5 ml of butanol and 2 g of linseed oil in such a way that about 15 g of ruthenium are applied ^{per m 2.} This paint is baked for 15 minutes at 400 ^° C. in a hydrogen or luminous gas atmosphere, a mixture of ruthenium metal and ruthenium oxide being formed. This layer is in turn coated with a solution of 5 g of TiCl ^ in 20 ml of butanol and also baked at 400 ° C. for 15 minutes in the specified atmosphere.

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Example 2:

A graphite block is coated with titanium nitride as described. The titanium nitride layer is then homogeneously coated with ruthenium metal applied via the gas phase. For this purpose, the graphite block is heated ^{to temperatures above 300 °} C. by induction heating under a vacuum or a protective gas atmosphere. As a volatile ruthenium compound, the diaromatic metal complex of ruthenium (II) or (0) is evaporated with benzene or hexamethylbenzene. The complex is thermally decomposed on the heated surface of the titanium nitride and metallic ruthenium is deposited. This layer is protected by an electrically porous SiO ₂ layer, which is produced by applying a mixture of 5 g of SiCl ^ in 20 ml of butanol and then firing at 400 ° C.

Example 3:

The described titanium nitride coated graphite body is coated with a Pailadiunwlridiumresinat solution and then baked at 400 ⁰ C. Thereafter, the coating of 15 g / m formed is protected with a porous layer of tantalum pentoxide which an alcoholic tantalum pentachloride solution is prepared on the nitride layer and subsequent heat treatment at 400 ⁰ C within 15 minutes by brushing.

Example 4;

A graphite block is coated with a mixture of titanium nitride and ruthenium oxide (390 by plasma spraying. The resulting ruthenium metal oxide mixture is thereby

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concentrated on the surface of the titanium nitride layer and then through a porous zirconium oxide layer, by applying an alcoholic ZrCl ^ solution and subsequent annealing at 400 ° C is protected.

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Claims (13)

- ίο - claims SSSSS = S = SS = SS = SS = SS = S = S = Ss 1) electrode, particularly an anode, for chlor-alkali electrolysis with graphite as a scaffold body, characterized in that the frame body has a superficial B _e coating of hard material and having at least one metal and / or metal oxide of the platinum group, the electrically porous for fixing a and under the Electrolysis conditions chemically resistant oxide coating, ' ¹ 2) Electrode according to claim 1, characterized in that the surface coating of the framework consists of a mixture of hard material and at least one metal and / or metal oxide of the platinum group. 3) The electrode according to claim 1, characterized in that the surface coating of the _T frame body made of hard material and at least one metal and / or metal oxide of the platinum group of two virtually separate layers with hard material is as a base layer. 4) Electrode according to claim 1, 2 or 3, characterized in that the hard material or titanium carbide, in particular titanium nitride, consists. 5) The electrode according to one or more of claims 1-4, characterized in _t that metal oxide of the platinum group component is the coating. 6) Electrode according to one or more of claims 1-5 » characterized in that the fixing is used - 11 - 209830/0811 Oxide coating consists of SiO ₂ , TiO ₂ , ZrO ₂ , Nb ₂ O ₅ or O ₅ . 7) A method for producing the Bektrode with graphite as the skeleton body according to claim 1, characterized in that the frame body is provided with a coating of hard material and at least one metal and / or metal oxide of the platinum group and electrically porous coating with a chemically under the electrolysis conditions resistant oxide coating is fixed. 8) The method according to claim 7, characterized GEK hen characterized in that the coating of hard material or hard material fund least eiS ^m metal and / or metal oxide of the platinum group metal is applied by plasma spraying. \ 9) A method according to claim 7, characterized g ekennzeich net that for the · formation of the coating of the hard material by plasma spraying and the at least one metal and / or metal oxide of the platinum group metal from a suspension or solution by impregnation and subsequent heat treatment at elevated temperature, preferably in the range from 300 - 600 ° C is applied to the hard material layer. 10) Method according to claim 7, characterized in that, to produce the coating, the hard material is applied by plasma spraying and the at least one metal and / or metal oxide of the platinum group is deposited from the gas phase on the hard metal layer. - 12 209830/0881 11) Method according to one or more of claims 7-10, characterized in that _t is a titanium carbide hard material, in particular titanium nitride, is applied. 12) The method according to one or more of claims 7 - zei chnet _f that metallic oxide is applied 10, labeled in characterized as at least one metal and / or metal oxide of the platinum group. 13) Method according to claim 7, characterized in that the coating serving for fixing is produced by hydrolytic cleavage of chlorides of the elements Si, Ti, Zr, Nb or Ta and volatilization of the solvent. 209830/0881