FI58165B - ELEKTRODER FOER ELEKTROKEMISKA PROCESSER - Google Patents

Description

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Patent and Registration Office of the Court of First Instance of the United States of America »ki1ft * n publkvrrt 29-0Ö.Ö0 (32) (33) (31) Pyydatty Muolkaut —Begirt prlorket 26.10.73 11.02.7U England-England (GB) U989Ö / 73,

6175 / 7U

(71) Imperial Chemical Industries Limited, Imperial. Chemical House,

Millbank, London S.W.l, England-England (GB) (72) Bernard Hesketh, Frodsham, Cheshire, Christopher Pownall, Runcorn,

Cheshire, Nicholas William James Pumphrey, Runcorn, Cheshire, England-England (GB) (7U) Oy Kolster Ab (5U) Electrodes for electrochemical processes - Electrodes for electrochemical processors

The present invention relates to electrodes for electrochemical processes. In particular, the invention relates to electrodes comprising a support member of a film-forming metal or a film-forming alloy having an electrocatalytically active coating on it.

Our patent (UK patent 1 U02 UlU), also published as Belgian patent 788883, describes an electrode for electrochemical processes with good resistance to short-circuit damage, comprising a support member made of a film-forming metal or a film-forming alloy and an electrocatalytically active main on it. comprising an electrically conductive material of the matrix having electrocatalytic properties and a particulate or fibrous refractory material immersed in said matrix.

As suitable refractory materials for embedding in an electrically conductive matrix, glass, zirconia, alumina, quartz fibers (e.g. quartz wool), thorium dioxide, titanium dioxide and aluminosilicates are mentioned in said patent publication.

58165

We have now discovered special refractories which can advantageously be embedded in an electrically conductive matrix.

According to the present invention, for electrochemical processes, there is provided an electrode comprising a support member of a film-forming metal or a film-forming alloy and an electrocatalytically active coating on said support member comprising a matrix of an electrically conductive material having electrocatalytic properties and an abrasive not embedded in said matrix. or fibrous refractory. The present invention is characterized in that said refractory material contains particulate zirconium silicate.

By film-forming metal we mean one of the metals titanium, zirconium, niobium, tantalum or tungsten. By film-forming alloy we mean an alloy based on one of said film-forming metals and having similar anodic polarization properties to commercially pure film-forming metal.

The electrode support member is made of a film-forming metal titanium, zirconium, niobium, tantalum or tungsten, or a film-forming alloy. Preferably, the support member is made of titanium or a titanium-based alloy having similar anodic polarization properties to titanium. The electrode coating matrix may be formed of an electrically conductive material having electrocatalytic properties, i. which is active to transfer electrons from the electrolyte to the underlying film-forming metal or alloy of the electrode structure and which is resistant to anodic attack in an aqueous electrolyte containing chloride ions. For example, it may contain one or more platinum group metals, i. platinum, rhodium, iridium, ruthenium, osmium and palladium and / or oxides of one or more of these metals, rhenium, rhenium trioxide, magnetite, titanium nitride and borides, phosphides and silicides of platinum group metals. It may contain one or more of said platinum group metals and / or their oxides mixed with one or more base metals. "

Iin oxidine. Alternatively, it may contain one or more non-noble metal oxides alone or in admixture with one or more non-noble metal oxides and a non-noble metal dechlorination catalyst. Suitable base metal oxides include, for example, oxides of said film-forming metals, tin dioxide, germanium dioxide and oxides of antimony. Suitable dechlorination catalysts include difluorides of manganese, iron, cobalt, nickel and mixtures thereof, for example as described in UK Patent 1,277,033. Particularly suitable electrically conductive materials of the invention include platinum itself and materials based on ruthenium dioxide / titanium dioxide and ruthenium. - 58165 carbon dioxide / tin dioxide / titanium dioxide.

Non-conductive refractories are any particulate or fibrous materials that are chemically stable and resistant to melting at the temperatures used during coating manufacture (temperatures in the range of 1 * 00-500 ° C, for example), are resistant to electrochemical attack, are non- conductive and having electrical properties that during the manufacturing process in use in accordance with the present invention do not substantially change upon interaction with the electrocatalytically active substance used in the matrix. The term non-conductive usually refers to insulators having an electrical resistance at room temperature in the range of about 10 22 ... -5 10 ohm cm as opposed to good conductors with a resistance of about 10 ohm cm-29 and semiconductors with a resistance of about 10 - 10 ohm cm ("Introduction to

Solid State Physics ", C. Kittel Wiley and Sons, New York 1953). In this application, we mean that a refractory material is non-conductive relative to the electrically conductive material used in the matrix, and such refractories include those having a resistance greater than about 10 ohms. cm and preferably alu-10 22 to 10 to 10 ohm cm.

By "embedded" we mean coatings in which non-conductive refractory particles are bonded together with an electrically conductive material in the matrix.

The refractory material of the electrode coating according to the invention, zirconium silicate, is in particulate form. The zirconium silicate may be present as a naturally occurring zirconium or as a synthetic compound obtained, for example, by heating a mixture of the component oxides ZrO 2 and SiO 2 or by heating a mixture of the compounds which give the component oxides upon heating.

Zirconium silicate may be mixed with zirconia fibers (e.g. zirconia fibers prepared as described in our UK Patents 1 U25 93 ^, 1 Uh5 331, 1 335 618 and 1 360 197).

A non-fibrous, particulate refractory can be used in which the particle size varies over a wide range, for example from 0.05 to 200 microns, although the preferred size range is from 0.1 to 75 microns.

The refractory zirconia fibers used are preferably such that no dimension of a single fiber exceeds 1 mm.

The relative proportion of the particulate or fibrous refractory embedded in the coating matrix is preferably 5 to 95% by volume based on the total volume of the coating components as given below. In general, increasing the relative proportion of particulate or fibrous refractory results in a continuous improvement in the short-circuit resistance of the coating thus obtained, although even very small amounts of refractory (e.g., 5 ~ 25% by volume) have a beneficial effect on short-circuit resistance, especially if refractory is added.

581 65

it

The preferred relative proportion of refractory material is in the range of 20-90% by volume based on the total volume of the components in the coating.

Volume percentages for particulate or fibrous refractories are based on the volumes of coating components calculated from the known weights of the various coating materials and the specific gravity of these components (e.g., as given in Handbook of Chemistry and Physics, 53rd Edition, 1972-3, Chemical Rubber Company ). No attention has been paid to porosity when performing the calculations.

The electrodes of the invention can be fabricated by an incineration technique in which a metal and / or metal oxide coating is formed on a film-forming metal support member by depositing a layer of a paint composition containing thermally degradable compounds from each metal the paint layer by evaporating the liquid conveyor and then burning the paint layer by heating the coated support member to a suitable temperature of 250-800 ° C to decompose the metal components of the paint and form the desired coating. The refractory particles or fibers may be mixed with the above-mentioned paint composition before it is placed on the support member. Alternatively, the refractory particles or fibers may be added to the layer formed by the above-mentioned paint composition while it is still in a fluid state on the surface of the support member, after which the paint layer is dried by evaporating the liquid carrier and burned in a known manner.

The coated electrodes are preferably constructed by adding several layers of paint to the support member, each layer of paint being dried and fired before the next layer is added. Preferably, this same technique, namely by placing multiple layers of paint and drying and firing each layer used, is used in the manufacture of electrodes in accordance with the present invention using either of the methods described above.

Refractory particles or fibers may be present in each paint layer that are added to build the coating.

When the refractory material is in the form of fibers having an average (median) length of more than 50 microns and when the material is placed on the surface of the paint film after the paint is placed on the surface of the support member but still in a fluid state, it is preferable to add fibers only to the first or first to the paint layers, i.e. the subsequent paint layers are then placed on top of the previous ones without adding a refractory to the coating. When the refractory is in non-fibrous particulate form or in the form of very short fibers (median length less than 50 microns), it is preferred to incorporate the refractory prior to applying the paint to the support member and to include the refractory in all or final paint layers used to build the coating.

5 58165

In the preferred electrodes of the present invention, the coating matrix contains at least one platinum group metal in elemental and / or oxide form and at least one film-forming metal oxide. Suitable thermally decomposable platinum group metal compounds for use in the above paint compositions for the preparation of these preferred electrodes include platinum group metal halides and haloic acid complexes, e.g. RuCl 2, RhCl 2, H 2 PtCl 2, H 2 IrCl 2 and organic compounds of platinum group metals, e.g. resinates of these metals and alcohol-oxides. Suitable thermally decomposable compounds from the film-forming metals include alkoxides, alkoxy halides in which halogen is chlorine, bromine or fluorine, and resinates of these metals. Most preferred, especially when the electrode support member to be coated is titanium or a titanium alloy, are alkyl orthotitanates, their partially condensed (hydrolyzed) derivatives, commonly referred to as alkyl polytitanates, and alkyl halothitanates containing halogen of chlorine, bromine or fluorine, especially from two to four carbon atoms.

The paint composition is prepared by dissolving or dispersing a thermally decomposable compound of at least one platinum group metal and a thermally decomposable compound of at least one film-forming metal in a liquid carrier, preferably a lower alkanol, e.g. an alkanol containing two to six carbon atoms per molecule. The refractory particles or fibers are suspended in this paint composition if they are to be added to the electrode support member at the same time as the paint film.

When the platinum group metal is completely or mainly in elemental form in the final coating matrix, a reducing agent, e.g., linalool, is included in the paint composition and the temperature at which each paint layer is fired is limited. o to a maximum of about C.

The coating of the final electrode very preferably consists of a mixture of platinum group metal oxide and film-forming metal oxide, containing 5-65 (preferably 25 ~ 50%) by weight of platinum group metal oxide in said matrix, together with a particulate or fibrous refractory material embedded in an amount 5 ~ 95% by volume based on the total volume of the coating components as defined above.

The most preferred electrodes of the invention for use as anodes in a mercury cathode cell comprise a support member of titanium or a titanium-based alloy and a coating containing 20-90% by volume of non-conductive, particulate or fibrous refractory oxide as defined above in a matrix , containing 50 to 75% by weight of titanium dioxide (preferably 65 to 70% by weight of titanium dioxide). However, according to a variant 6 58165 of this embodiment of the invention, up to 50% by weight of ruthenium dioxide and titanium dioxide in said matrix may be replaced by one or more of the following substances: tin dioxide, germanium dioxide and oxides of antimony, as described in our UK patent , having the following three-component mixture: 27 to 1% by weight of ruthenium dioxide, 26 to 50% by weight of titanium dioxide and 5% by weight of tin dioxide, together with 20 to 90% by volume of particulate or fibrous refractory material.

In another modification, the coatings may contain tin dioxide, germanium dioxide, and oxides of antimony, which may further include a dechlorination catalyst other than the noble metal or noble metal oxide described above. Preferred coatings of this type consist of a matrix of a three-component mixture of tin dioxide and antimony oxides (calculated as Sb 2 O 2) in a weight ratio of SnO 2 S 2 O 2 of 5: 1 to 100: 1, and 0.1 to 1.0% by weight of manganese difluoride, together with 20 to 90% by volume of a non-conductive particulate or fibrous refractory.

These modified coatings are preferably obtained by incorporating thermally decomposable compounds from one or more of the following substances: tin, germanium and antimony. Suitable thermally decomposable compounds of tin, germanium and antimony include alkoxides of these elements, their alkoxy halides with halogen or chlorine, and antimony halides.

It is to be understood that the relative proportions of thermally decomposable compounds of platinum group metals, film forming metal and / or tin and / or germanium and / or antimony in the paint composition to form the electrode coating matrix are adjusted to correspond to a chemically equivalent base in the desired matrix of these elements and / or their oxides.

Although the electrodes of the present invention are particularly preferably used as anodes in mercury cathode cells in the electrolysis of alkali metal chloride solutions, they can also be used in other electrochemical processes, including other electrolytic processes, electrocatalysis such as fuel cells, electrosynthesis and cathodic shielding.

The invention is further illustrated by the following examples:

Example 1 3 g of ruthenium trichloride, produced by Johnson Matthey Chemicals Limited and containing 1 * 0% by weight of ruthenium, was dissolved in 18.75 g of n-pentanol. To this solution were added 12 g of tetra-n-butyl orthotitanate and 1.5 g of "Zircosil 5" zirconium silicate, an average particle size of 1.25 microns, manufactured by Associated Lead Manufacturers Limited ("Zircosil" is a registered trademark of τ 58165). This weight composition was chosen to give the final coating a volume composition of approximately $ 53 ZrSiO 2 and 47 # titanium and ruthenium dioxides. The paint was mixed very thoroughly and placed by spraying on a pre-etched experimental titanium anode section comprising 6 parallel sheets, each 110 mm long x 6 mm high x 1 mm thick. The upper edges of the leaves were attached at one end to a 3 nm thick titanium current inlet and at the other end to a corner piece of 2 mm thick titanium so that the leaves were rigidly supported to remain parallel in parallel.

After one coat of paint was added to the titanium anode portion, the paint was dried at 180 ° C and then fired in air at 450 ° C to convert the paint to ruthenium and titanium oxides. After cooling, a second layer of paint was added, dried and burned. This was repeated until a sufficient number of paint layers had been added. The total amount of oxides plus silicon "" silicon silicate after firing was equivalent to 75 g of coating per square meter of projection of the anode area.

A similar experimental titanium anode part was coated in the same way but this time leaving "Zircosil 3" out of the paint. In normal electrolysis, both anodes passed the same current under identical conditions in terms of temperature, saline strength, cell voltage, and so on. However, when immersed in a mercury cathode to a depth of 4 mm, the sample containing “Zircosil 5” in the coating passed only 260 Å, while the sample coated with ruthenium and titanium oxides alone took a short-circuit current of more than 1000 A.

The current taken by the sample coated with "Zircosil 3" in the matrix of mixed ruthenium and titanium oxides can be calculated to be due solely to electrolysis in a thin saline film surrounding the leaves; therefore, no short-circuit current actually results from direct electronic contact between the anode and the mercury amalgam roof.

Example 2 26.7 g of "Hanovia 05X" liquid clear paint manufactured by Engelhard Industries Limited was thinned to 13 »? g of dilution essence. To this solution was added 4.5 S "Zircosil 5". The paint was thoroughly mixed and painted on an etched titanium anode part similar to Example 1.

In this case, the sample was dried at 180 ° C and then fired at 430 ° C after each painting to produce a coating comprising a matrix of electrocatalytic active platinum metal in which an inorganic refractory was dispersed as an additive. The final total coating was equivalent to 36 g (platinum plus ZrSiO 2) of coating per square meter of anode projection surface. This coating corresponded to a volume composition of approximately 9% platinum and 9% zirconium silicate (ZrSiOr). Thus, the coated titanium strips had a low excess potential for .2 chlorine evolution (80 mV at 10 kA / ra) and only passes through a current of 2 kA immersed in lj · mm depth of flowing mercury at a voltage of h, 2 V. A similar coating made of "Hanovia 05X" paint, but this time without the addition of "Zircosil 5", allowed a strong current (greater than 100 A / cm) to flow as soon as the anode sample touched a mercury surface.

Example 3

The paint was mixed as in Example 1 except that 9 g of "Zir-cosil F" was added instead of the i +, 5 "Zircosil 5" added in Example 1. "Zircosil F" is a zirconium silicate with an average particle size of 25 microns manufactured by Associated Lead Manufacturers limited. This weight composition corresponds to a volume composition of the final coating of about 31% titanium and ruthenium oxides plus 69% ZrSiO 2.

The paint was placed on the substrate in the same manner as in Example 1 to obtain an equally satisfactory coating in terms of the current in the short-circuit space.

Example 1+

A paint was prepared with 3 g of ruthenium trichloride (containing Ho by weight of Ru), 18.75 g of n-pentanol, 12 g of tetra n-butyl orthotitanate, 3 g of "Zircosil 5" and 2 g of "Saffil" (fiber containing zirconia, diameter 2 microns, average length 20 microns, prepared as described in UK patent applications 12088/72, 36693/72 and 29909/70) to give a coating of 19% ZrOg) 35% ZrSiO 2 and U6% RuO 2 / TiO ^. A number of coatings of this paint were placed on the test anode of Example 1. In normal electrolysis, this anode sample passed through the same current as the anode sample containing Zircosil 5 as described in Example 1. When immersed in mercury, this sample passed a low - short - circuit current like the sample containing Zircosil 5. To further illustrate the short-circuit resistance of these coatings, the contact resistance between mercury and the anode surface was measured under standard conditions for coatings comprising (1) ruthenium and titanium oxides alone, (2) the coating contained ruthenium and titanium oxides and Zircosil 5, as in Example 1, as in Example 1. the coating described in this example.

2

The contact resistors were 0.011 ohm cm, 2 2 0.11 ohm cm and 1.96 ohm cm, respectively. The higher the contact resistance between the mercury and the anode surface, the lower the short-circuit current.

Example 5

A paint was prepared with 3 g of ruthenium trichloride and 12 g of tetra n-butyl orthotitanate in 23 g of n-pentanol and 0.214 g of Zircosil 3 * was added thereto. A number of coatings of this paint were applied to the titanium anode part as in Example 1. This paint composition was formed to 3% by volume of zirconium silicate particles in a matrix formed by 93% by volume of ruthenium and titanium dioxide. A strip of this coated portion was immersed to a depth of 4 mm in a static mercury pond under 21.3 wt% NaCl brine and a voltage of 3 x 5 V was applied. The total current was 1.12 A per cm of titanium anode strip length. The second anode part was also coated with a similar paint composition except that in this case Zircosil 3? this portion passed a 2.9 A strip length per cm under identical experimental conditions.

Example £

An alternative method of making non-barrier resistant coatings is to incorporate the particulate refractory material only into the outer layers of the coating. The two anode sheet portions were coated as described in Example 1 but omitting the refractory additive, i. with ruthenium and Λ titanium oxides only. The total amount was $ 2 g / m. Two and three paint coatings containing 3 g of ruthenium trichloride, 12 g of tetra n-butyl orthotitanate, 4 g of Zircosil F and 23 g of n-pentanol were then added, dried and fired as described in the previous examples. This procedure gave coatings that contained approximately 12 and 17 volume percent zirconium silicate as a whole. When ae was subjected to the experiment described in Example 6, these anode samples passed currents of 1.41 Å and 1.06 Å per cm of length of titanium strip.

Example γ

A paint was prepared with 3 g of ruthenium trichloride, 12 g of tetra n-butyl orthotitanate in 30 g of n-pentanol, and 77.4 g of "Zircosil F" was added thereto. A number of coatings of this paint were placed on the anode plate section and fired as in Example 1. This paint composition was calculated to give a coating containing 93% by volume of "Zircosil F" and 3% by volume of 10,581 65% ruthenium and titanium oxides. This sample was tested in a mercury test cell by immersion in a mercury stream flowing at a surface velocity of 30 cm / s. With a 3 mm immersion and an effective voltage of h, 2 V, the current was 133 A. Under similar experimental conditions, a sample coated as above, but without zirconium silicate, passed currents greater than 1000 A.

Example 8

A paint was prepared with 3 g of ruthenium trichloride, 12 g of tetra n-butyl orthotitanate in 25 g of n-pentanol. To this was added 9 g of "Zircosil 200". This is a zirconium silicate powder that is somewhat coarser than "Zircosil F": when "Zircosil F" is ground to pass through a British standard sieve with an orifice size of 75 microns. This paint was applied as multiple coatings to the titanium anode portion as shown in Example 1. The paint composition was formed to give a coating containing 69% by volume of zirconium silicate and 31% by volume of ruthenium and titanium dioxide. A strip of anode portion was immersed to a depth of H mm in a static mercury pond in an experiment similar to that described in Example 6. The current was 0.88 Å per cm of titanium strip when the current in the coating without added zirconium silicate was 2.9 Å per cm of band.

Example 9

A coating containing oxides of antimony and tin and manganese fluoride was prepared and placed on the etched titanium anode portion according to the following procedure.

18 g of antimony trioxide was boiled in concentrated nitric acid until the evolution of nitrogen oxides ceased. 8U g of metallic tin was dissolved in concentrated sulfuric acid with heating, and the precipitated tin dioxide formed was thoroughly mixed with antimony oxide and heated for some time in concentrated nitric acid. The precipitated mixture was washed free of acid and air dried at 200 ° C. To the dried mixed oxides was added 3% by weight of manganese difluoride. The resulting mixture was compressed into pellets (100 lb / in ^) and fired in an air oven at 800 ° C for 2 h. After firing, the mixture was crushed and the particle size was reduced to less than 60 microns. It was then re-compressed into beads and fired as above for 2 h at 1000 ° C. The resulting material was crushed and the particle size was reduced to less than 5 microns in a ball mill by grinding.

A solution of the compound as an alkoxide was prepared by refluxing a mixture of 15 g of stannous chloride and 55 g of n-amyl alcohol for 2 h. 2.13 g of antimony trichloride was dissolved in the resulting solution.

A composition suitable for coating the electrode body was prepared by suspending 0.17 g of the fluorine dioxide described above and 0.67 g of Zircosil 5 in 3.6 g of an antimony trichloride alkoxytin solution. This coating composition was applied to a strip of titanium which had been immersed overnight in a hot acid solution to etch the surface and which was then washed and dried. The paint coating was dried in an oven at 80 ° C and heated in an oven at air temperature at 50 ° C for 15 min. to substantially convert the coating to form oxides of antimony and tin and manganese trifluoride into a matrix embedded with a zirconium silicate moiety. The entire coating operation and the final heating in air at i + 50 ° C were repeated three times to increase the thickness of the coating. The coating contained about 59% by volume of zirconium silicate H1 in a volume percentage of SnOg / Sbg / ^ / MnFg (weight ratios of 85%, 1H% and 1%, respectively).

A portion of this coated strip was then tested for its short-circuit resistance (resistance) in mercury amalgam as described in Example 6. At an effective voltage of 3.5 V under 21.5 wt% NaCl brine, the total current was 0.20 A for the titanium crystal. length per cm.

Claims (7)

12 5 8165 Pat ent ive suction: An electrode for electrochemical processes comprising a support member of a film-forming metal or a film-forming alloy and an electrocatalytically active coating thereon comprising a matrix of electrically conductive material and a non-conductive particle embedded in said matrix of a material having electrocatalytic properties that said refractory material contains particulate zirconium silicate. Electrode according to Claim 1, characterized in that the refractory material consists of a mixture of particulate zirconium silicate and zirconia fibers. Electrode according to Claim 1 or 2, characterized in that the size of the zirconium silicate particles is in the range from 0.05 to 200 microns. Electrode according to Claim 2 or 3, characterized in that no dimension of the zirconia fibers exceeds 1 mm. Electrode according to one of Claims 1 to U, characterized in that the relative proportion of refractory material embedded in the coating matrix is 5 to 95% by volume, based on the total volume of the coating components. Electrode according to Claim 5, characterized in that the relative proportion of refractory material is in the range from 20 to 90% by volume. Electrode according to one of Claims 1 to 6, characterized in that the support element is made of titanium or a titanium-based alloy having similar anodic polarization properties to titanium. ö. Electrode according to one of Claims 1 to 7, characterized in that the matrix consists of at least one platinum group metal and / or one platinum group metal oxide, optionally in admixture with at least one base metal oxide.