DE1467221B2 - Process for the production of an electrode suitable for chlor-alkali electrolysis - Google Patents

Description

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The invention relates to improvements in and to the titanium backing is too low. The received

Process for producing one for the chloralkali surface structures have when used as

Electrolysis suitable electrode, which consists of a titanium anode only a short life, z. B. only the

carrier with a surface made of platinum, and half the life of the anodes, which is up to 350

it is an improvement in the heated in the French 5,500 ⁰ C.

The invention described in U.S. Patent 1,263,876. When using the manufactured according to the invention

In this patent specification is, inter alia, an improvement in electrodes z. B. as anodes in mercury

drive to the production of a structure from a silver cell for the electrolysis of brine or brine

Titanium supports with a surface of one are generally found to be in any

Platinum metal described, in which on the titanium io current density above a minimum value is lower

carriers require a coating of a platinum-containing cell voltages as structures that according to

Applies preparation that produces a platinum compound in the aforementioned French patent

contains an organic carrier and were placed on heating.

at least 500 ° C a substantially platinum subject of the invention is now a process existing deposit forms, and the surface of the 15 ren for the production of a chlor-alkali electro-platinum metal produced by a plurality of Iy se suitable electrode, which from A titanium support arranges the above-mentioned deposits on top of each other, with a surface made of platinum, in which by pretreating the coating process with which the titanium support is first pretreated to remove the above-mentioned platinum-containing preparation and oxide skin and then several times a subsequent heating at least 500 ° C applies again a coating from a preparation that removes from one. Preferably, the support made of titanium in the case of a platinum compound and an organic solution was first pretreated using this process in order to obtain the medium, and the coating was converted into a platinum metal coating by heating the surface mainly consisting of an oxide, thereby removing the layer (oxide skin). It has now been found that the best super-oxidizing atmosphere is carried out at a temperature of surface structures of the aforementioned type for use at least 350 ° C. and less than 500 ° C., for use as electrodes for the chlor-alkali electrolysis, the oxidizing atmosphere in which the above-mentioned coating is heated in accordance with the process of the French patent to form the deposit consisting essentially of platinum, which is obtained when the coating of the platinum is obtained by preparation in an oxidizing atmosphere on a 30, is preferably air.
Heated temperature of at least 350 ° C and less than 500 ° C in this description and claims. _ the term "titanium" includes not only titanium itself. If the coating is in an oxidizing atom but also titanium alloys, the properties of which are at temperatures above the anodic polarization of 500 ° C for 5 minutes, e.g. B. heated to 600 ° C, it was found 35 are comparable. Examples of titanium alloys are that the anode used in mercury cells for the titanium-zirconium alloys containing up to 14 ° / ₀ zircon, electrolysis of brine at a given current density for alloys of titanium with up to 5 ° / ₀ of a platinum a period of 5 months due to a long metal, such as platinum, rhodium or iridium, and lesamen development of overvoltage higher voltages of titanium with niobium or tantalum, which requires up to voltages. Presumably, this is due to the fact that 40 10 ° / ₀ contain the alloying ingredient,
Preparations containing too much platinum during heating are e.g. B. in the time sintering and also in the titanium diffusion "Platinum Metals Review", October 1958, date. If you described the coating in oxidizing. Here it is indicated that Metallisierprä atmosphere heated even higher, z. B. at 800 ° C, prepared from solutions of the resin or sulfo, the titanium on the surface is so strongly oxidized, 45 resinate of the platinum in essential oils exist, in that the electrical contact between the platinum layer wide scope for decorating glassware and and titanium is bad and the material is used in glazed ceramics and that when it is used as an anode in mercury cells, only little burning at 550 to 800 ° C allows the essential oils to pass through. Fired and the resinates and sulforesinates decomposed. According to the invention, it was found that one becomes 50 and that a shining, improved surface coating of the aforementioned firmly adhering platinum coating remains on the objects. One type is obtained when the coating is made from the above-mentioned platinum-containing preparation, which is suitable for platinum-containing preparation in an oxidizing atmosphere - the process according to the invention is heated to a temperature of at least 350 ° C under the name »Hanovia Liquid Bright Platinum and heated to less than 500 ° C and sold the said 55 Grade 05-X «, which consists of an organic deposit, which consists essentially of platinum liquid carrier, which consists of about 7.5 weight samples. cent platinum in the form of a thermally decomposed platinum compound. Suitable preparations can also be prepared in an oxidizing atmosphere by heating a platinum compound to a temperature below 350 ° C for 15 minutes, which when heated to metallic platinum and volatile, the organic substance of the said preparation decomposes into a volatile product organic partially charred and not completely evaporated solvent dissolves and the solution with a ge and burned. The resulting deposit of platinum mix of a resin and terpin oil, acetate acetic acid and carbon adheres to the titanium substrates ethyl ester or an essential oil. A solution of platinum chloride can also be used badly, presumably because of the presence of carbon, for example, because the hydrochloric acid in ethyl alcohol or isopropanol is the heating temperature required to achieve the required to an equal volume of a 1: 1 mixture of the degree of sintering of the platinum particles give each other abietic acid and clove oil.

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So far, preparations containing platinum have been used with the equivalent of 2 to

spoken, but this expression is of course contained 9 parts by weight of platinum. There are also

Lich not limited to preparations that allow platinum as lower platinum contents, but are then allowed

Contains only precious metal. Certain commercial paints required many.

Preparations contain smaller amounts of other metals. The platinum group remaining after firing, especially rhodium and / or coating, is finely distributed and has a light gray matt or iridium. Such preparations can be easy according to the appearance. In operation as an anode, the coating looks like the aforementioned methods are made by very dark gray or black. Presumably you are small amounts of easily decomposable rhodium - it is this degree of distribution of the platinum coating that adds one or iridium salts to the platinum salt. The expression io more satisfactory work of the "platinum metal" manufactured according to the invention therefore also includes platinum, the electrodes provided e.g. B. a small amount of rhodium and / or iridium de-silver cell allowed as anodes in a mercury for the electrolysis of brine,
holds. One such example is an alloy of 70 ° / ₀ The preparation containing platinum is based on the gePlatinum and 30 ° / ₀ Iridium. It was found that the optimum temperature 15 titanium surface, from which the oxide skin was removed, for heating the platinum coatings is applied, since an even better adhering platinum preparation is then obtained in an oxidizing atmosphere for coating. This is particularly useful when the production of anode coatings that work at the low- each anode in each cell of a number of alkalists cell voltage for long periods of time, amalgam cathode cells have a surface area that is to some extent of the type of 20 used according to the invention The method made depends on the preparation containing platinum. For example, since in such a row any of the cells resulting from "Hanovia Liquid Bright Pia- coatings can be put out of service by connecting their tinum Grade 05-X" the most suitable structures to the anode with their cathode while being used as a Anodes in the electrolysis of salt - the rest of the series leaves in operation. With this volumetric liquor, if it were taken to 400 to 500 ° C, preferably 25, hydrogen from the anode is instantaneously heated to 475 ° C, while a preparation made of Ig platinum is discharged. It has been found that these electrodes can withstand hydrochloric acid, 10 ml of ethanol, and the same amount of sudden cathodic polarization produced by a 1: 1 mixture of clove oil and.

Abietic acid gives the most suitable constructions when prepared by the process of the invention one the coating to 350 to 500 ° C, preferably 30 electrodes can be designed so that they as 400 ° C heated. The optimal heating temperature for improved anodes for electrolytic cells A special preparation containing platinum can produce chlorine and alkali hydroxide by electrolyte simple attempt can easily be determined. trolysis of aqueous alkali chloride solutions used The first coating can be made of a platinum containing, e.g. B. as an anode structure of the in Preparation can be applied directly to the surface of the 35 described in British patent specification 911425 Titanium carrier can be applied, which initially type or as the anode of the British patent for removing the oxide skin, for example according to the type described in 885 817 or as impermeable partition described in British patent specification 758 013, which is made with an anodic surface process, has been pretreated. Coating on one side of a platinum metal, if necessary one can see the titanium support also 40, in a multiple cell according to the British ■ pretreatment to separate the oxide skin and here- patent specification 845 043.

to electrolytically apply a layer of platinum before The examples below illustrate the Herman the first plating of a platinum containing position and the operation of such electrodes as anodes Applies preparation. in mercury cells and diaphragm cells for the production of chlorine and caustic soda according to an embodiment of the invention 45. Since the titans become the supports, which are to be provided with a platinum coating, in the form of stretched or rolled titanium parts degreased the surface of the titanium support, then sheet metal, of which the actual surface 4 days with analytically pure concentrated hydrochloric acid was not exactly known, the loading of the etched, allowed to dry, then with a platinum ent- titanium surface with the platinum metal and holding the cells Painted preparation, the platinum chlorine current density, based on the total geometric hydrofluoric acid, ethanol, clove oil and abietic acid area of the anode, calculated, and for the more convenient Contains in the aforementioned proportions, this was measured as the area of the associated whereupon the obtained coating z. B. taken by cell cathode which are essentially planar Infrared radiation dries and then was in the air.

burns in an oven at 375 to 475 ^° C. for 10 minutes. 55: Painting, drying and baking then becomes Example 1
repeated as often as necessary to obtain a platinum coating of the desired thickness. For a comparison, given the current example, one can apply five to fifteen coatings of the cell voltage of a mercury cell, the preparation containing the platinum, and dry and bake an electroplated platinum coating for every 60 anode. on a stretched titanium sheet, with cells-The number of coatings required to achieve the desired voltages of mercury cells of the same thickness as the platinum layer depends on measurements carried out, which contained a structure of the platinum content of the preparations and the thickness of each which were heated as an anode Coatings from an applied coating. For a given preparation containing platinum on a stretched type of preparation, the maximum usable titanium sheet contained, and the coatings for platinum content, depends mainly on the viscosity of the gel of each anode at a certain temperature in the mixture. Preferably platinum-containing ones are richly fired between 475 and 550 ° C.

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An anode was made by adding 100 g. The extent of loss of platinum from the after

Platinum per square meter, calculated on the cells produced using the method according to the invention

cathode surface, on a stretched titanium sheet gal- stretched titanium sheet when used as an anode in

vanisch applied, the degreased, 4 days with an analytical mercury cell in the electrolysis of brine

pure concentrated hydrochloric acid and then it was of the same order of magnitude as that

was drying. expanded titanium coated galvanically with platinum

A number of anodes were also made, sheet metal used as the anode in a mercury cell

by serving in a similar manner to de-electrolysis of brine. The loss was about

greased, etched and dried similar titanium - 1 g of platinum per ton of chlorine, which is different from the one at 4 kA / m ²

sheet each ten coatings of a commercial io operated mercury cell was produced.
Platinum-containing preparation made from platinum resinate in

an essential oil (clove oil), which is the equi-B ice ρ ie 1 2
containing about 8 percent by weight platinum,

and every coating burned in the open air. A preparation containing platinum with about 3

A 15 percent by weight platinum was obtained on each stretched titanium sheet.

Deposition of platinum put in an amount of 60 g / m ² :

Cathode area. Each of the superimposed 5 g of abietic acid was mixed with 5 g of eugenol

trains was fired at the same temperature. mixes, ^{heated to 150 0} C and cooled. One received

For each coated titanium sample, a different one became a light brown syrup. 1 g platinum chlorohydrogen

Stoving temperatures in the range from 475 to 55O ⁰ C 20 acid were in 2 ml of anhydrous ethyl alcohol

used. dissolved and mixed with the syrup. '

It was brine with a content of 23 weight two prepared according to Example 1 and pretreated

percent sodium chloride using one of the delte stretched titanium sheets were each with four-

produced anodes in each mercury cell with ten coatings of the aforementioned platinum preparation

6O ⁰ C electrolyzed. The relationship between current-25 provided. Each coating was air at 35O ⁰ G

density and voltage of the mercury cell for current - on one titanium sample and at 500 ° C on the other

densities above 2 kA / m ² are fired through the straight sample. ^; ■ '

Equation Each coated titanium sheet was used as an anode and

y - a Λ-hr indirectly after its manufacture in a mercury

30 test cell used. The determination of the cells, expressed in which V is the cell voltage, A of the voltage for a range of current densities showed the section on the voltage axis which is extrapolating the straight line backwards below 2 kA / m ^{2 by the following properties at current densities} . The platinum deposition was approximately hold, C the current density (kA / m ² ) and b the 30 g / m ² , calculated on the cell cathode area.
Slope of the curve is. 35

For the mercury cell with the electroplated platinum on the carrier made of stretched Titanium sheet as the anode was found to be by plotting the voltage against the current density

V = 3.48 + 0.20 C. j _ec j _e ( _these anodes were then placed in a diaphragm - for the mercury cells that put the platinum coating test cell, the chlorine and sodium hydroxide solution produced from the heated platinum-containing preparation and in a current density of 6 kA / m ² the support of expanded titanium sheet containing as an anode with a brine concentration of 18 weight percent, the amount was 45 NaCl was run at 7O ⁰ C during application of the stresses. established the versus current density that on by continu- loss Platinum from the anode W during 26 hours of operation for 23 weeks at one point was 0.16 g / t of chlorine generated.
Current density of 4 kA / m ²

F ₁₇₅₀ = 3.20+ 0.20 C, _5o example

^ SOO- = 3.25 +0.20 C, _a preparation containing pi _{atm was made as follows-}

F ₅₂₅ O - 3.30 + 0.20 C, dimensions manufactured:

* 55o ° - 3.40 + 0.20 C. 2g abietic acid were mixed with 2g eugenol

Thus, z. B. mixes at a stoving temperature. This solution was mixed with a solution of

for the platinum-containing preparation of 475, 500, 525 55 1.216 g of platinum hydrochloric acid in 1.5 ml of ethanol

and 550 ⁰ C an advantage of 0.28, 0.23, 0.18 or offset. The resulting mixture was too viscous and

0.08 volts at all current densities above 2 kA / m ² was half its before use

in a structure produced according to the invention, diluted against volume of eugenol. The platinum content was

about 5 percent by weight over an anode of the electroplated platinum.

on a carrier made of expanded titanium sheet. 60 Two stretched titanium sheets made according to Example 1

It is also seen that anodes which had been degreased by firing, etched and dried were

of the applied platinum-containing preparation with thirteen coatings of the aforementioned

Temperatures of 475 and 500 ° C were produced, provided platinum preparations. Every coating was on

an advantage at lower working voltages for the air at 35O ⁰ C on the one titanium sample and at

have longer periods of time than those burned in by 65 475 ⁰ C on the other. During the exam

Heat treatment of the applied platinum containing as anodes in mercury test cells according to the case

Tending preparation at temperatures above 500 ° C game 2, the samples showed the following properties

were manufactured. . at current densities of more than 2 kA / m ² . The platinum

anode Firing temperature,
⁰ C Cell voltage W. 350 3.19 + 0.20 C

Deposition was about 30 g / m ² , calculated on the cell cathode area.

anode Firing temperature,
⁰ C Cell voltage Y
Z 350
475 3.24 + 0.20 C
3.11 + 0.20 C

Each of these anodes was then operated in diaphragm test cells according to Example 2. The extent the loss of platinum from anode Y during the first 26 weeks was 0.1 g / t produced Chlorine. The platinum loss from the anode Z over 24 weeks was approximately 0.2 g / t chlorine generated.

Example 4

Nine anodes for a mercury test cell suitable for large-scale operations for the electrolysis of brine were produced by applying twenty coatings of the commercial platinum preparation described in Example 1 to expanded titanium sheet which had been degreased, etched and dried according to Example 1, and each coating to the Baked in air at 475 ° C. The total platinum deposition on each surface of the titanium sheet was 40 g / m ² .

Brine containing 23 percent by weight of sodium chloride was electrolyzed continuously for 9 months at an average temperature of 60 ° C. in the cell at current densities between 2.9 and 5.4 kA / m ² , calculated on the cell cathode area. The average overvoltage for the nine anodes was initially 0.060 volts and increased to a value of only 0.067 volts by the end of the nine months. The total loss of platinum, measured by a radioactive layer thickness gauge, was 0.36 g / t chlorine produced.

Example 5

On a support made of expanded titanium sheet, which has been degreased, etched and dried according to Example 1 a platinum-iridium alloy containing 70% platinum and Contained 30% iridium by applying 32 coatings of a preparation to the pretreated sheet metal, which contained platinum resinate in rosemary oil and iridium resinate in clove oil, and on paint consistency with a solution of rosin in clove oil and cyclohexanone was diluted and 4.2 percent by weight Contained platinum and 1.8 percent by weight iridium.

ίο Each coating was ^{dried at 250 0} C and then baked in the air at 450 ^{0 C.} The total deposition of the alloy on the titanium surface was 30 g / m ² .
The structure was produced as an anode in a mercury About cell for the electrolysis of brine with a content of 23 weight percent sodium chloride at 70 ⁰ C and a current density of 6 kA / m ^{2 was} used. After 6 weeks of operation, the anode overvoltage was 0.113 volts.

Claims (3)

Patent claims: 1. Process for the production of an electrode suitable for chloralkali electrolysis, the consists of a titanium support with a surface made of platinum, in which the titanium support initially pretreated to remove the oxide skin and then a coating several times from a preparation that consists of a platinum compound and an organic solvent and converts the coating into a platinum metal coating by heating, characterized in that, that the heating in an oxidizing atmosphere at a temperature of at least 35O ° C and less than 500 ° C. 2. The method according to claim 1, characterized in that a preparation is used which contains an equivalent of 2 to 9% platinum. 3. Modification of the method according to claim 1 and 2, characterized in that the first Platinum coating is applied by electroplating. 009 540/336