DE2304380C3 - Electrodes with a Delafossit surface - Google Patents

Description

25th

30th

For numerous electrochemical? Reactions such as the electrolysis of brines, hydrochloric acid and Sulfates, electroplating, electrolytic mining, electrolytic manufacturing of metal powders, electrolytic cleaning, electrolytic pickling and electrochemical generation of electrical power Non-Consumable Anodes Are Required So far, graphite anodes have been used for such purposes especially for the electrolysis of brines and the electrolysis of hydrochloric acid. In younger For such processes, electrodes have been developed which have a suitable electrically conductive base or have a substrate and an electrocatalytic coating thereon. Typically such electrocatalytic coatings the metals of the platinum group, such as. B. platinum, osmium, iridium, ruthenium, Palladium and rhodium and their oxides.

From DE-OS 18 16 820 electrodes are known in which the electrocatalytic coating with a inorganic glaze is combined. The disadvantage is that it makes some of the active The electrode surface is blocked and the electrodes are less efficient.

DD-PS 77 963 describes electrodes with surfaces made of oxides of the platinum metal group. These surfaces have a low electrical conductivity and are not yet sufficient with the usual loads resistant to chemical attack. bo

The object of the present invention was to avoid the disadvantages of the known electrodes and to create an anode that has a low chlorine overvoltage and below even at high current densities Resists chemical attack for long periods of time in operating conditions.

It has now been found that a particularly suitable anode for carrying out electrochemical Reactions is obtained when using a delafossite surface applied to a suitable electrically conductive substrate or base are oxides of Delafossite high electrical conductivity from the stoichiometric formula

SUBSCRIPTION ₂

where in this formula A is platinum or palladium, B is typically chromium, cobalt or rhodium.

The present invention relates to an anode according to claim 1.

When used in electrolysis cells, the anodes have a chlorine overvoltage of up to 033 volts! a current density of 53.82 amps per dm ² .

Delafossite also include non-stoichiometric compounds that are compatible with the stoichiometric Delafossites are isostructural. A suitable electric conductive substrate is an electrically conductive substrate that is essentially not covered by the Electrolytes are attacked.

As already stated, the anodes according to the invention have a delafossite surface on one electrically conductive substrate The Delafossite have a unique crystal structure, that of the natural mineral's delafossite (CuFeO2) is similar. the small differences in the crystal structure being due to the slightly different radii of the ions are due.

Delafossite results in particularly satisfactory electrode materials because they combine high electrical conductivity, which is comparable to that of metals, with high resistance to chemical attack, which is comparable to that of refractory metal oxides. So is z. B. the electrical conductivity of compressed powders of platinum and palladium delafossite in the order of about 10 ³ to 10 * (ohm-centimeter) - '. Such platinum and palladium delafosites are also resistant to attack by strong acids, such as aqua regia at 70 ° C and also to nascent chlorine.

The Delafossite are a family of oxides made up of two or more metals, the oxide being a rhombohedral Has a structure with a hexagonal crystal habit similar to that of the mineral delafossite CuFeOj is similar. Delafossite can also be characterized by the fact that its crystals form a space group of 166 have a shocnflies group from Oj j.

a full standard symbol of Ri- (R, - 3, two over

m) and an international symbol of Ri _n , (R. Querstrich 3, m). Such oxides and their crystallography have been described repeatedly in the literature.

As a general rule, the Delafossite are further characterized by the fact that the A ions that correspond to the Copper in the mineral delafossite have an effective ionic radius equal to that of two oxygen coordinations corresponds to, d. h "that the effective ion radii range from 0.45 to 0.68 angstroms. In the case of platinum and Palladium delafossite, the Α-ions have effective ion radii in the range from 0.58 to 0.61 Angstroms. the B ions, which correspond to the iron ions in the mineral delafossite, have an ion radius that is one corresponds to oetahedral coordination, d. that is, the effective atomic radii range from about 0.50 to are approximately 1.05 angstrom units. The one used here

The term "effective ionic radius" closes the equivalent Expression "crystal ionic radius".

CT. Prewitt, RD Shannon and DB Rogers, Chemistry of Nobfe Metall Oxides, Inorganic Chemistry, Vol. 10 (1971), report that the synthetic platinum, cobalt delafossite (PiCoO ₂ ) has the crystallographic structure of the Delafossil type. Both the stoichiometric and the non-stoichiometric platinum Kobali Delafossite are particularly suitable for use in the electrodes according to the invention

The delafossite crystal structure and the relations between the platinum-cobalt-delafossite, the palladium-delafossite and the mineral-DeMossite (CuFeO2) explained in more detail by referring to the figures. The figures show the following:

F i g. 1 is a graph of the X-ray diffraction values found in the literature for the mineral Delafossii (CuFeG?) And the table I are reproduced;

F i g. Figure 2 is a graph of the X-ray diffraction values reported in the literature for platinum-cobalt-delafossite (PtCoO?) Are given and compiled in Table 2;

F i g. Figure 3 is a graph of the X-ray diffraction values reported in the literature for palladium-cobalt delafossite oxide (PdCoO?) Are given and compiled in Table 3;

F i g. Figure 4 is a graph of the X-ray diffraction values reported in the literature for palladium-chromium jo Delafossite (PdCrO?) And in Table 4 are compiled;

FIG. 5 is a graph of the X-ray diffraction values reported in the literature for palladium-rhodium-delafossite (PdRhO ₂ ) and summarized in Table 5.

The F i g. 1 to 5, which reproduce the values given in the literature and summarized in Tables 1 to 5, are plotted on the same scale as the abscissa and have a common -to ordinate. The abscissa indicates /// 0, the specified ratio of the intensity of the reflected beam to the incident beam. The ordinate d indicates the specified distance between the planes, calculated from the a ~> equation by Bragg, which will be explained in more detail later.

F i g. 1 was based on the values from Salier and Thompson. Phys. Rev., Volume 44. Page 644 (1935), reported in A.S.T.M. X-Ray Powder Diffraction File 12-752. and reproduced in Table 1, created · .. The > t> F i g. 2. 3. 4 and 5 were based on the values of R.D. Shannon et al .. Inorganic Chemistry, Volume 10. Seuen 713. 717 op cit .. and here in Tables 2. 3. 4 and 5 reproduced, created.

F i g. 6 is an X-ray diffraction of palladium-cobalt delal'ossii (PdCoO ₂ ) prepared for use as an electrode material in Example 1;

7 is an X-ray diffraction of platinum-cobalt delafossite (F'tojCooi0 ₂ ) prepared for use as an electrode material in Example 2;

8 is an X-ray diffraction of platinum-cobalt delafossite (PtojCoo.7JjO ₂ ) prepared for use as an electrode material in Example 3.

The crystallographic units of platinum and palladium delafossite give a unique family of b5 X-ray diffractions represented by peaks at "d" spacings from 5.9072 to 6.0229 angstroms, 2.9728 to i37 angstroms. a doublet with a spacing between peaks of 0.06-0.07 Angstroms with the; first peak at 2.4260 to 23609 Angstroms and the second peak of the doublet at 2.5884 to 2.5141 Angstroms, one peak at 2.1460 to 2.2643 Angstroms and another peak at 1.6483 to 1.7104 Angstroms are. For the mineral delafossite only values of 2 θ degrees in excess of about 30 ° are known, ie for d distances of less than 2.86 angstroms. The mineral delafossite (CuFeO?) Has the doublet at 2.58 and 2.508 angstroms and the peaks at 2.238 and 1.658 angstroms. The differences in the results of X-ray diffraction between the individual members of the delafossite family are due to the slightly different cation radii.

For the mineral delafossite (CuFeO? / Are in Table 1 and in Fig. 1 the values of the X-ray diffraction are given or shown graphically. The results of the X-ray diffraction on DelafossLen of platinum group metals are shown in Tables 2 through 5 and in Figs graphic representations of FIG. 2 to 5 reproduced. It is pointed out again that the Values for Tables 1 to 5 and the graphs 1 to 5 are taken from the literature. These figures are idealized and show family relationships and trends. From the F i g. 1 to 5 is no Fundamental tone and no randomness that normally occurs in x-ray examinations.

When observing and recording X-ray examinations, samples of the delafossite powder are subjected to X-rays from a copper target. The methods for such an investigation are in the chapter of the book by Klug and Alexander, X-Ray Diffraction Procedures, John Wiley & Sons. Inc, New York (1954), pages 235 to 318, in particular pages 270 to 318, and in N ewf i e 1 d, X-Ray Diffraction Methods, John Wiley & Sons, Inc., Nev- York (1966), Pages 177 to 207.

Like Klug and Alexander and also N e w f i e I d state, X-rays are emitted at a wavelength of 1.5405 angstroms! to a To hit the sample of the powder to be examined. The X-rays are diffracted by a sample. the Diffracted X-rays are particularly intense at certain angles (0), which leads to the formation of Peaks in the leaves of the diffractometer or of lines in diffraction photographs.

Diffraction values are obtained in the X-ray examination with the help of a diffractometer, the one has a direct reading in 2 Θ. The value (180 ° minus 2 Θ) is the angle between the incident ray and the reflected beam.

Table 1 shows the diffraction values from the X-ray analysis for the mineral delafossite (CuFeO ₂ ). Particularly noteworthy is the doublet at 2.58 and 2.508 Angstroms and the eaks at 2.233 and 1.658 Angstroms.

For the diffraction values of the X-ray examination of powdery delafessites of metals of the platinum group, some similarities can be established. First, a particularly strong peak can be observed at a value of "d" about 5.9072 to 6.0229. Then U »in FIG. 2 to 5 that a strong doublet occurs, the peaks being separated from one another by about 0.06 to about 0.07 Angstroms with larger separations of the peaks and larger differences in the intensities in delafessites of the platinum group with larger elementary

cells and closely spaced peaks and of nearly equal intensity for delafossite of the platinum group with a more compact unit cell.

For the platinum-cobalt delafossite (PtCoO ₂ ) the peaks of the doublet are at 2.4260 and 2.3609 angstroms. For palladium-cobalt delafossite (PdCoO ₂ ), the two peaks of the doublet are around 2.4272 and 2.3616 angstroms, whereas for palladium-chromium delafossite the two peaks are 2.5065 and 2.4375 angstroms and for palladium -Rhodium delafossite (PdRhOj) the two peaks are around 2.5884 and 2.5141 Angstroms. Also noteworthy is the increasing difference in intensity between the two members of the doublet as the delafossites progress from the more compact unit cells to those with the less compact unit cells. The first peak of the doublet corresponds to a distance between the levels of about 2.42 Angstroms (PtGjO ₂ ) to about 2.58 Angstroms (PdRhO ₂ ). whereas the second peak corresponds to a distance between the planes of about 2.36 Angstroms (PtCoO :) Μ to about 2.51 Angstroms (PdRhOj).

There is also a strong peak at about 2.1460 to about 2.2644 Angstroms. This peak is around 2.14 Angstroms for the more compact unit cell of platinum-cobalt delafossite, at a distance of 2.1448 angstroms for palladium-cobalt delafossite (PdCoO ₂ ), and at a distance of 2.2088 for palladium-chromium delafossite (PdCrO :) and at 2.26 Angstrom for the slightly more compact unit cell of platinum-rhodium-delafossite (PtRhO ₂ ).

Also of interest is a faint doublet in the range of 2.0185 and 1.9814 angstroms with intensities of 0.30 to 0.40 for the more compact platinum-cobalt delafossite. As the unit cell increases in size, this particular doublet becomes more spread out and less intense. For the only slightly less compact palladium-cobalt delafossite, the doublet occurs at "rf" intervals of 2.0165 and 1.9715 angstroms, with the weaker of the two members having an intensity of about 0.15. For the -to palladium-chromium-delafossite (PdCrO ₂ ) the weaker of the two members of the doublet has an intensity of about 0.02 and the doublet occurs at 2.0753 and 2.0089 angstroms, respectively. For the even less compact palladium-rhodium-delafossite (PdRhOj), the terms of the doublet occur at 2.1198 and 2.0038 angstroms. both having intensities less than 0.05.

For the more compact crystals of the delafossite of the platinum group, a peak exists at about 1.76 to 1.81 angstroms. For platinum-cobalt delafossite (PtCoOj), this peak is about 1.7655 and has an intensity of about 030. For palladium-cobalt delafossite, the peak is observed at a distance of the planes of about 1.7616 angstroms and has an intensity of about 030 For the slightly less compact palladium-chromium delafossite (PdCrO ₂ ), the peak occurs at about 1.8084 angstroms and has an intensity of less than 0.05.

Table 1

X-ray examination of a
Powder of copper-iron delafossite
(CuFeO ₂ )

1 / I ₀

2.508
2.238
2.083
1.902
1.658
1.512
1.434
1.336
1.295
1.253
1.184
1.119
1.108
1.040
0.984
0.965

100 25

Table 2

X-ray examination of platinum-cobalt-delafossite (PtCoO ₂ )

d 1 / I ₀

5.9450 2.9728 2.4260 2.3609 2.1460 2.0185 1.9814 1.7655 1.6483 1.4856 1.4415 1.4135 1.3751 1.3513 1.2764

90 100 70 90 70 30 40 30 60 20 40 30 15 10 30

Table 3

X-ray examination of a powder of palladium-cobalt-delafossite (PdCoO ₂ )

d /// n

2.86 2.58

35 18th 2.9072 2.9559 2.4272 2.36? 6th 2.1448 2.0165 1.9713 1.7616 1.6445 1.4788 1.4373 1.4149 1.3762 1.3474 1.2762

45 90 80 100 85 15 50 30 85 35 70 65 15 15 65

Table 4

X-ray examination of a
Palladium-Chromium-Delarossite (PdCrO ₂ ) powder

d l / lo

6.0229 20th l / lo 3.0137 65 5 2.5065 30th 90 2.4375 100 10 2.2088 40 100 2.0753 2 95 2.0089 10 5 , 8084 5 2 1.6864 30th 85 1, JU / ** C.
J 15th 1.4722 15th 70 1.4614 20th 85 1.3791 2 80 1.3151 15th 60 Table 5 X-ray examination of Pal ladium-rhodium-delafossite (PdRhO ₂ ) (I. 6.0209 3.0130 2.5884 2.5141 2.2644 2.1198 2.0088 1.7104 1.5071 1.4874 1.5106 1.3503 1.2945

Finally, with regard to the X-ray examinations, a peak of medium intensity at around 1.6453 to around 1.7104 Angstroms should be pointed out. This peak has an intensity of about 030 for palladium-chromium delafossite and of about 0.85 for palladium-cobalt-delafossite (PdCoO ₂ ) and palladium-rhodium delafossite (PdRhO ₂ ). It is 1.6453 Angstroms for platinum-cobalt-delafossite (PtCoO ₂ ). at about 1.6445 angstroms for palladium-cobalt delafossite, at about 1.6864 angstroms for palladium-chrome delafossite and at about 1.7104 angstroms for palladium-rhodium delafossii.

The chemical nature of the Delafossite will now be discussed again. The delafossite are oxides or oxy compounds of two or more metals and are generally as follows formula

SUBSCRIPTION ₂

When considering this formula, it must be taken into account that non-stoichiometric compounds which have defects in their structures can also be used according to the invention. Such non-stoichiometric delafosites with errors in their structure have the formula A _x BZ) ₂ , where either χ or y or both are less than 1 and can be, for example, about 0.070 to 1.00. Such delafosites can also be used to good effect in the invention.

The metal ion represented by A in the formula can be any monovalent metal ion with an effective ionic radius of about 0.45 Angstrom units to about 0.68 Angstrom units. Such monovalent ions are palladium (Pd ⁺ ) with an effective ionic radius of about 0.59 angstroms and platinum (Pt ⁺ ) with an effective ionic radius of about 0.60 angstroms. Two or more such monovalent cations can also exist in the same delafossite crystal. The preferred delafosites are those in which the monovalent cation has an effective ionic radius of about 0.58 to 0.61 angstroms, such as e.g. B. Palladium (+ 1) and platinum (+ 1).

The cation represented by B in the formula is most commonly chromium, cobalt and rhodium. Are you typically a trivalent cation with an effective ionic radius of about 0.50 Angstroms to about 1.05 angstroms and mostly about 0.50 angstroms to about 0.89 angstroms. The preferred trivalent cations are those with an effective ionic radius from about 0.50 to about 0.70 angstroms, such as e.g. B.

Cobalt (Co ³ +) with an effective ionic radius of about 0.52 Angstroms, chromium (Cr ³ +) with an effective ionic radius of 0.62 Angstroms and rhodium (Rh ³ +) with an effective ionic radius of about 0.70 Angstroms.

The platinum delafosites include the stoichiometric oxygen compounds of platinum and cobalt with the delafossite structure (PtCoO ₂ ) and also the non-stoichiometric oxygen compounds of platinum and cobalt with the delafossite structure. Such

J5 non-stoichiometric Delafossite have the formula

Pt ₁ Co ₁ O ₂

where η has a value between 0.5 and 0.8.

As additional components in the Delafossi

ten, especially in the platinum delafossites, small ones Amounts of other metal ions occur, such as. B.

Ions of scandium, titanium, vanadium, chromium, manganese. 4j iron, cobalt or nickel. If so, the Delafossit following formula:

Pt, Co, M0 ₂

where χ is about 0.70 to 1.00 / about 0.70 to 1.00 and ζ is less than 0.11. Typically, ζ is about 0.004 to about 0.11. and M is Sc, Ti, V, Cr. Mn, Fe, Co or Ni.

The platinum-cobalt delafossite, which is an electrode surface particularly useful in accordance with this invention has the formula

"Pt, Co, O ₁

I - π I - "I

in which η has a value from about 0.50 to about 0.8.
bo palladium delafossite, which is particularly suitable as an electrode surface, corresponds to the formula

PdMO ₂

where M is cobail, chromium, rhodium, or a mixture thereof. Examples of very particularly suitable palladium delafossites are palladium-cobalt delafossite (PdCoO ₂ ), palladium-chromium delafossite (PdCrO ₂ ), and palladium-rhodium delafossite (PdRhO ₂ ).

The anodes of the invention in most cases provide an electrically conductive substrate or base member with a delafossite surface. In such an embodiment of the invention, the delafossite in FIG direct contact with the base member and the electrolyte

In addition, the platinum and palladium delafossite can be used to generate an electrical to form a conductive coating on the electrically conductive base or substrate, the delafossite surface to a further outer coating of a suitable electrocatalytic material, e.g. B. a spinel owns how this z. B. in US-PS 37 11 382 disclosed is. Instead of the spinel, a perovskite or a perovskite bronze can be used, such as this z. Am the previous DE-OS 22 10 065 is disclosed. Alternatively, as an outer coating over the Delafossit coating other electrocatalytic materials can be used, such as ruthenates, ruthenides, Rhodite, Rhodate.

It is also possible to have a porous layer between the delafossite surface and the electrolyte a substantially non-reactive material such as titanium dioxide, vanadium oxide, tantalum oxide. Tungsten oxide, Arrange niobium oxide, hafnium oxide, zirconium oxide, silicon dioxide. Such outer coatings will mechanical resistance of the Delafossit surface even further improved. In addition, the porous outer coatings provide a large surface area for catalytic reactions of those formed on the electrode Products or raw materials. These outer oxide coatings are preferably formed "in situ", as this will be explained in more detail later.

Different fabrics can be mixed with the Delafossit materials. So you can z. B. conductive Materials such as Perowskiie, Perowskii-Bfönzen, metals the platinum group, platinum group oxides and mixed carbides, nitrides, oxides and borides, the are resistant to the electrolyte, use in a mixture with the Delafossit. Such Materials can be present to give better conductivity or reactivity. Alternative materials are the oxides of titanium, tantalum, niobium, hafnium, tungsten, aluminum, vanadium, silicon and other film-forming metals. These additives also improve the shelf life of the Delafossite. To bind the delafossite particles to the substrate, any oxide can be used that is "in situ" are formed during manufacture of the surface and which are substantially opposite to that Electrolytes are not reactive.

The anodes with a Delafossit coating according to the invention also include an electrode which consists entirely of delafossite, but such electrodes are usually used for economic reasons Not used. Therefore, anodes according to the invention which have a delafossite surface are preferred or coating on a suitable electrically conductive substrate. The delafossite surface can only be 8 angstroms thick. For practical reasons, however, a Delafossit surface is used worked that has a thickness or thickness of at least 1.52 microns, with thicknesses of at least 3.81 to 5.08 microns are preferred. The deiafossi surfaces but need not be stronger than about 635 to 7.62 Micron. A delafossite coating thicker than 7.62 microns, e.g. 2032, can be used Microns without incurring any detrimental effects

Effects can be observed, but no further benefit becomes so strong through use Coatings achieved.

A "suitable electrically conductive substrate or base" means a substrate with a electrical resistivity within the economic limits meant with this substrate also still essentially non-reactive with the electrolyte and the products of electrolysis should be. In the electrolysis of brines, for. B. does not use a suitable electrically conductive substrate Solutions of sodium hydroxide or sodium chloride react, and also do not react with nascent chlorine to be attacked.

Suitable electrically conductive substrates are, for. 3. Rectifier valve metals. The rectifier metals are those metals that form an oxide film under anodic conditions. To the judges belong e.g. B. titanium, tantalum, niobium, hafnium, tungsten. Aluminum, zirconium, vanadium and their alloys. In In most cases, for economic reasons, titanium or titanium alloys are used as the substrate for the base member of the electrodes used in this invention. However, other materials can also be used can be used, such as graphite or carbon. One can also laminate a rectifier metal with a use less expensive metal, such as iron or steel, with a delafosate coating on the rectifier metal.

Alternatively, titanium hydride or another electrically conductive, anodically stable hydride can be used as electrically conductive substrate can be used in the electrode of this invention. Such a hydride can be the sole component of the substrate or it can be in the form of a flat structure on the other material

n:

auiticgcii.

Alternatively, the hydride can be a hydride surface of a metal, e.g. B. a titanium substrate min one Titanium hydride layer between the metallic substrate and the delafossite surface.

In a preferred embodiment of the invention, a layer of an electrically conductive material, which has a better conductivity than the delafossite and is resistant to the electrolyte, is arranged between the delafossite and the substrate. Such an intermediate layer may be formed from a platinum group metal such as e.g. B. of metallic ruthenium, rhodium, palladium, osmium, iridium, platinum or their alloys. Particularly suitable alloys for this purpose are, for. B. platinum-palladium alloys, especially those containing about 3 to about 15 wt .-% platinum, also platinum-iridium alloys, especially those containing about 2 to about 50 wt .-% iridium. Alternatively, such an intermediate layer may be an oxide of a platinum group metal such as e.g. B. ruthenium oxide (RuO ₂ ), rhodium _{oxide (Rh 2} O ₃ ), palladium oxide (PdO ₂ ), osmium oxide (OsO ₂ ), iridium oxide (Ir ₂ O ₃ ). Platinum oxide (PtO ₂ ) or mixtures thereof. Such mixtures can include mixtures of platinum oxide and palladium oxide containing from about 3 to about 15 weight percent platinum oxide or platinum oxide and iridium oxide mixtures containing from about 2 to about 50 weight percent iridium oxide. In connection with the metals of the platinum group or their oxides, oxides of other metals can also be used, such as the oxides of titanium, zirconium, hafnium, vanadium, niobium, tantalum, tungsten and aluminum. When such conflicts

schenschicii'.en are present, they will normally be from about 0.51 to about 3.05 microns thick, with thicknesses from about 1.52 to 3.05 microns being preferred. The intermediate layers can, however, also be thinner and, for example, only have a thickness of 0.13 microns if they are applied evenly so that they result in a pore-free coating. It is also possible to use thicker intermediate layers, but this is not associated with any significant advantage. If, in the case of an anode with a delafossite surface on a substrate, the substrate reacts with the delafossite to form an electrically insulating barrier after prolonged use at high current densities, a layer of a less reactive material that is more resistant to the electrolyte can be placed between the substrate and the delafossite the substrate. Less reactive materials are understood to mean materials that do not form an electrically insulating barrier or that do not help to form such a barrier when placed between the delafossite and the substrate. Such less reactive materials can be the noble metals already mentioned or their oxides. Alternatively, when less reactive materials, platinum-cobalt Delafossit (Picoo _2), palladium-chromium DelafoGsit (PdCrO ₂₎ or palladium-rhodium Delafossit (PdRhO ₂₎ are used to form an intermediate layer between a palladium-cobalt Delafossit (PdCoO ₂ ) coating and a titanium substrate. When such interlayers are used, they typically have a thickness of 0.51 to 3.05 microns with thicknesses of 1.52 to 3.05 microns being preferred. If the intermediate layers are applied evenly and are pore-free, they can also be thinner, e.g. B. 0.13 microns thick. Thicker coatings are also possible. The anodes with Delafossit surfaces according to the invention can be used for any electrochemical process with a non-consumable electrode. By "non-consumable" is meant that the electrode is not dissolved by the electrolyte and is not redeposited on the opposite electrode. The electrodes according to the invention can, for. B. be used for the electrolysis of brines, sulfates, hydrochloric acid, phosphates. Alternatively, the electrodes are useful in processes in which cations are deposited on a cathode, such as e.g. B. in the electrolytic extraction of metals, electrolytic refining. Electroplating. Electrophoresis, electrolytic cleaning and electrolytic pickling. From appropriate solutions can copper, nickel. Iron, manganese, brass, bronze. Cadmium. Gold, indium, silver, tin. Zinc, cobalt, chromium and similar metals can be electroplated onto cathodes. Alternatively, metal powder can be prepared by depositing cationic release on a suitable cathode using the anodes of this invention. The electrodes according to the invention can also be used for the electrolytic cleaning of aqueous solutions, of sodium phosphate, sodium carbonate. Furthermore, the electrolytic pickling of suitable materials, which are cathodic with respect to the anodes according to the invention, can be used to oxidize organic compounds electrolytically. So you can z. B. carry out the electrolytic oxidation of propylene to propylene oxide or ProDvlenelvcol with the electrodes according to this invention. In addition, metal structures such as hulls can be cathodically protected using the anodes of this invention.
In addition, the anode of this invention can be used in fuel cells. When using the electrode with the delafossite coating in fuel cells, these electrodes will be permeable to the flow of the electrolyte. Such an electrolyte permeability can be achieved by an electrically conductive

ίο porous substrate with a deposited on it Delafossitmateria! can be achieved or by a dispersion of Delafossite particles in a suitable inert medium or by other methods known in the art.

The anodes according to the invention can be made by synthesizing the Delafossil and subsequently on it a suitable electrically conductive substrate or carrier. Delafossite can be removed by oxidation at low temperatures and high pressures, like

z. B. by a hydrothermal reaction. They can also be oxidized high temperatures and high pressures due to solid reactions and due to oxidation at low Temperatures and low pressures in an oxidizing flux. Alternatively it is possible to delafossite at low pressure and low temperatures in an anion exchange reaction to manufacture.

Delafossite useful in the present invention can e.g. B. by the methods which are described in the following references: RD Shannon et al., Chemistry of Noble Metal Oxides, 1. Syntheses and Properties of ABO ₂ Delafossite Compounds, Inorganic Chemistry, Volume 10, page 713 (1971) ; U.S. Patent 3,498,931; U.S. Patent 35 14 414 and U.S. Patent 34 14 371.

Hydrothermal syntheses of Delafossite are carried out at relatively low temperature under oxidizing conditions carried out. The hydrothermal method can

4u z. B. be used for the production of platinum-cobalt delafossites, the copper delafossite and the silver delafossite. The method requires the .'Erwärmung of two oxides in water in a sealed inert tube, such as. B. a platinum or gold tube (at high pressure, z. B. about 3000 atmospheres and a temperature of about 500 to 700 ⁰ C for about 24 hours).

The platinum, palladium delafossite can be at relative low pressures and low temperatures are produced in a reaction by an exchange characterized by ions and the formation of a solid or molten salt as a by-product is. This method uses the halide of platinum, palladium and the oxide of the second metal reacted to form delafossite and a halide of the second metal. Alternatively, it can Halide or the metal and the halide of the first metal and a lithium oxide compound of the second metal (such as lithium chromate, lithium cobaltate or lithium rhodate) to form delafossite and Lithium halide are implemented.

The anion exchange reaction is carried out in an evacuated sealed silica tube at a temperature of about 500 to about 800 ⁰ C.

The halide salts obtained as a by-product are passed through after the delafossite is formed Expenses, e.g. B. with water, removed If metallic platinum or palladium remains or if the chloride

of the precious metal remains, these residues become by leaching with a suitable solvent such as hydrobromic acid or aqua regia, removed.

Delafossite can also be made by diffusing finely powdered mixed oxides at high temperatures. The platinum and palladium delafossite require a temperature above 700 ^° C. and a pressure of about 3000 atmospheres in order to obtain the delafossite through a reaction in the solid state.

The delafossite produced by one of these methods can either be used as such for an electrode can be used or preferably serve as a surface or coating of an electrode made of a suitable base or substrate material.

Typically, the electrically conductive base or substrate material is a rectifier metal such as titanium. A Such a substrate can be in the form of a flat, plate-like structure or it can also be the In the form of a perforated plate or an expanded latticework. Alternatively, it can be in the form of fine wires, rods or other shapes are present, such shapes allowing the outflow of the gases formed from the volume between the anode and the cathode into spaces behind the anode.

When a titanium member is used as a substrate material, that titanium member can be used for its use as a Prepare the electrode by degreasing and then an etch is carried out. Degreasing can be done by any known method, e.g. More colorful Use of detergents, abrasives or organic degreasing agents. Then the degreased titanium substrate can be etched with hydrofluoric acid, hydrochloric acid, or similar materials. The etching is used to remove the naturally occurring oxide film and through it to replace a thin film of hydride.

The delafossite can be applied to the etched titanium surface in various ways. So can one z. B. a slurry of delafossite in a solvent such as ethanol, butanol, benzyl alcohol, Manufacture phenol, benzene, cumene. Such a slurry can be applied to the titanium surface, e.g. B. Apply with a paintbrush or a brush. After each spread, heat is applied to decompose or volatilize the solvent. The slurry can additionally contain finely divided materials, such as Silicon, titanium, zirconium, hafnium. Vanadium, niobium, tantalum, molybdenum, tungsten or other materials used in the Are capable of "in situ" during the process of evaporation or decomposition of the solvent To form oxide. As a rule, a chloride is used as such a finely divided material, such as e.g. B. Titanium trichloride.

Alternatively, a slurry can be made from delafossite, a metal, an organic one Solvents such as ethanol, butanol, benzyl alcohol, phenol, benzene, cumene, polyene and one Silicon dioxide compound or a metal compound, which is soluble or dispersible in the organic solvent, such as. B. a resinate. Such a one Slurry can be brushed onto the titanium using e.g. B. about 4 to about 8 spreads used and warmed after each spread to break down or volatilize the organics. Alternatively, for the application of the Delafossits on the substrate but also other methods can be used, such as joining by pressing or cathodic electrophoresis.

In the above procedures for the top pull of the titanium substrate with the delafossite, the Use of a titanium or a silicon compound indicated, but such compounds are for * Function of the electrode is not required. The oxidation products of such compounds as

to z. B. titanium dioxide or silicon dioxide, however, confer Alternatively, the delafossite surface can provide additional physical strength and durability Oxides of zirconium, hafnium, vanadium, niobium, tantalum, molybdenum or tungsten on the surface of the dei Electrode can be manufactured "in situ" in order to improve the resistance and durability of the electrode surface.

The invention is explained in more detail in the following examples

example 1

One is made of a titanium substrate, a cover made of a palladium-cobalt-Delafossil (PdCoO ₂ ) and one between the titanium and the Delafossit inlaid layer of metallic platinum existing electrode.

The Delafossit is made from 2.6642 g of palladium chloride (PdCl ₂ ) and 2.2482 g of cobalt oxide in such a way that the chloride and the oxide are thoroughly ground in a 2 hour evacuated sucked quartz tube of an outer diameter of 10 mm, filling a length of 12.7 cm and heated therein for 1 hour at 110 ⁰ C, followed by closing the quartz tube is then heated the sealed quartz tube at 85O ⁰ C, keeping it 15th Minutes at this temperature, the temperature is then allowed to ^{drop to 700 °} C. and heating is continued at this temperature for 65 hours. The resulting product is scraped off the quartz wall, it is ground thoroughly, and it is washed twice at 25 ° C. with 200 ml Water, then with acetone and dry it. You get 2.4 g of a gray metallic product with a particle size in the range from 0.03 to 03 and from 1 to 7 Micron.

This powder is examined by X-ray diffraction

in a Philips diffractometer. For the X-ray tube a voltage of 35 kilovolts and a current of 15 milliamps are used, one for the detector Voltage of 1265 volts. The radiation from a copper target is used and a divergence is used aperture of 1 °, a beam aperture of 0.1524 mm and a diffusion aperture of Γ. The detector is allowed to rotate with a time constant of 2 seconds at 2Θ - 2 ' per minute and the test specimen at 2Θ - Γ per minute. The following table (6) and in FIG. 6 measured values shown.

Table 6

5.925 4,572 3.448 2.957 2.566 2,440 2.362

40 5 5

90

10

60

100

continuation

2.252
2.148
1.759
1.646
1,480
1.438
1.415
1,350
1.325
1.277
1.273

40

10

50

10

20th

30th

20th
After an electrolysis period of 816 hours, it has a voltage of 3.92 volts and a chlorine overvoltage of 033 volts

Example 2

An electrode is produced from a titanium substrate and the Delafossite PtOiCoOiO _{2 as a coating layer.}
The delafossite is exhibited by an anion exchange

ίο platinum chloride, cobalt oxide (CoO) and cobalt oxide (Co ₃ O ₄ ). The cobalt oxides are used in the form of a mixture consisting of 03048 g Co ₃ O ₄ and 0.1274 g CoO. They are in the form of a powder with a grain size of less than 325 mesh. They pounds in a mortar to even greater size, the powder mixture you are in a quartz tube of einem.5 "-ßeren diameter of 10 mm and a length of 10! 6 cm, this sucks evacuated, it closes, it heated to 700 ⁰ C and keeps it at this temperature for 25 hours. Man

A titanium strip 14.6 cm long is washed. a width of 9.5 mm and a thickness of 3.175 mm with one under the trademark »Comet« 20 receives one from a black fuiver and hot water commercially available household cleaning crystals containing abrasives. One grinds this up agent, rinsing it in distilled water, dipping it into material, filling it into another quartz tube, sucking it 3 one minute in 1% hydrofluoric acid and places it

⁰ C

then in 12 η hydrochloric acid at 27 ° ^{C. for 23 hours}

A solution of 10 g of a platinum resinate of the Engelhard "0-5X" type, calculated as metal, containing 7.5% by weight of platinum is prepared in 9 g of toluene and this solution is applied in three layers to the etched tiran strip. In each case after application of the first two layers of heating the strip at a rate of 50 ⁰ C in 5 minutes at 500 ⁰ C and hold it for 10 minutes at this temperature. After application of the third layer by heating the strip at a rate of 50 ° C in 5 minutes at a temperature of 550 ⁰ C. In this temperature is maintained it for 10 minutes.

It is made from 0.5 g of the palladium-Kobali delafossite (PdCoOr). 1 g of one by adding 3.4 g Table 7

Titanium chloride (TiCIi) made into 20 g of ethanol

4.5 wt .-% titanium solution and 1.0 g of ethanol a 4u d

Mud and carries six coats from it

a brush on the titanium strips as described on. After each coating, the strip is heated to 100 ° C. and held at this temperature for 30 minutes. After the last coat has been applied, the strip is heated in vacuo at one speed from 100 ° C in 10 minutes to 400 ° C, after which it is 40 Holds at this temperature for minutes.

After applying the last layer, test the electrode in a beaker chlorate cell. As in Chloratzellc, a 500 ml beaker is used which contains a saturated saline solution and in which the platinum-coated titanium cathode is through a Teflon spacer at a distance of 9.5 mm from the anode Electrolysis at a current density of 53.82 amperes per dm ² and a cell voltage of 3.5 volts. At a current density of 53.82 amperes per dm ² , the cell has a chlorine overvoltage of 0.08 volts.

The anode is placed in a laboratory chlorodiaphoboragma cell. The cell has an iron net cathode which is at a distance of 9.5 mm from the anode and separated from it by asbestos paper. The electrolysis of a saline solution containing 315 g of NaCl per liter is carried out at a current density of 53.82 amperes per dm ² and one Temperature of about 9O ⁰ C through. The cell has a voltage of 3.64 volts and a chlorine overvoltage of 0.08 volts After hours evacuated at the beginning, it was heated to 710 ⁰ C, keeping it for 18 hours at this temperature and then for another 15 hours at a temperature between 700 and 710 ⁰ C, cools the quartz tube and removes the material from it. You crush it in a mortar, put it in a 150 ml beaker and add 100 ml of water. The sludge obtained is filtered through a sintered glass filter funnel at 25 ° C. The insoluble residue is washed twice with 25 ml of water and then with acetone. A gray-black solid is obtained which, as described in Example 1, is examined by X-ray scattering. An X-ray diagram is obtained with the values shown in Table 7 and FIG. 7 measured values shown.

I / k

5,901
3.292
2.968
2,428
2,364
2.146
2.077
2.020
1,979
1.764
1.648
1,549
1.445
1.441
1.414
1.374
1,350
1.321
1.277

90 10 100 30 70 40

5 10 80 10 40

60 20 10

5 10

S 10

A titanium strip 14.6 cm long, 9.5 mm wide and 3.175 mm thick is cleaned with the household cleaning agent "Comet", etched for 5 minutes in a 2 percent by volume hydrofluoric acid solution and then for 22 hours at 27 ° C 1 ⁿ n hydrochloric acid.

A sludge is produced from 0.25 g of the above-described platinum-cobalt delafossite (PUwComCH 0.5 g of a 4.2% by weight solution of titanium chloride (TiCb) in ethanol and 0.5 g of ethanol and is carried along with it heating a brush five top coatings on the titanium strip on. After each of the upper trains 1 to 4 to the strip to 100 ⁰ C, keeping it for 30 minutes. After the application of the final top coating by heating the strip in a vacuum tube then to 500 ° C It is kept at this temperature for 30 minutes as well.

The electrode is first tested in a beaker cell. A 40OmI beaker is used as the beaker cell. This contains the anode to be tested and a platinum-coated titanium cathode, 9.5 mm away from it through a Teflon spacer. A saturated saline solution is used as the electrolyte, which contains 315 g of saline per liter. After 18 hours, the electrode shows a voltage of 3.15 volts with a current density of 26.91 amps per dm ² and a voltage of 3.8 volts with a current density of 53.82 amps per dm ² . At a current density of 53.82 amperes per dm ² , the voltage against a calomel electrode is 1.12 volts and the chlorine overvoltage is 0.06 volts.

The electrode is then placed in a laboratory chlorine diaphragm cell. The cell contains an iron mesh cathode which is located at a distance of 9.5 mm from the anode and is kept separated from it by asbestos paper. At a current density of 53 "2 amps per dm ^J and a temperature of the electrolyte of 90" C \ hat '\ e cell at the beginning of a voltage of 338 volts -jnd a chlorine overvoltage of 0.06 volts. After a Betriel of 104 days the cell has a voltage of 3.70 volts and a chlorine overvoltage of 0.08 volts.

Example 3

An electrode is made from a titanium substrate and the Delafossite Pt <wCoo.73j0 ₂ as a coating layer.

The platinum-cobalt delafossite is produced by the anion exchange process in such a way that 5,322 g of platinum chloride (PtCl ₂ ) are added. Crush 13622 g of cobalt oxide (CojOO and 0.882 g of cobalt oxide (CoO) by grinding to a grain size of less than 325 meshes). Pour the mixture into a quartz tube with an outer diameter of 12 mm and a length of 12.7 cm, tube 2 sucks evacuated hours at 25 ° C and 16 hours at 125 ° C and then closes. After heating the powder tube containing at 70o ⁰ C, it holds 70 hours at this temperature, it cools then rapidly to room temperature, after which it Its contents consist of a gray metallic solid, solid blue crystals and a green solid. The total product is comminuted by grinding to a particle size of less than 325 mesh, the comminuted product is filled into a second quartz tube with an outer diameter of 12 mm and a length of 12.7 cm _(μ sucks the tube 1 hour at 25 ° C and 3 hours at 135 ° C deflated, it closes, it is heated to 700 ⁰ C, keeping it at this temperature for 47 hours. Hiernac h you cool it down to room temperature and open it. It contains blue and green crystals on its cooled end and also a gray metallic solid. The gray metallic solid is comminuted to a grain size of less than 325 meshes, washed twice at 25 ° C. with 25 ml of distilled water each time, then twice with acetone and dried at 70 ° C. The powder is then kept under vacuum at 25 ° C. for 16 hours. The light gray crystalline metallic substance obtained is examined by X-ray spectroscopy in the manner described in Example 1. The X-ray diagram is shown in Fig. 8. Apart from only minor differences, it is essentially identical to the X-ray diagram _{known from the Delafossit PtO 1 SCo 0} JO _{2 literature.}

The titanium strip is etched as described in Example 1 and carried on it from a sludge composed of 0.25 g of platinum-cobalt delafossite, 0.50 g of a titanium resinate solution calculated as the metal containing 4.2% by weight of titanium, 0, 19 g of toluene and 0.06 g of phenol consists of five coating layers. Heating the layers 1 to 4 at a rate of 5O ⁰ C in 10 minutes to 425 ° C, and the fifth layer is also at a rate of 50 ° C in 10 minutes to 500 ⁰ C All of the layers is maintained for 10 minutes at their respective maximum temperature .

The electrode obtained is tested in the manner described in Example 1 in a beaker chlorine cell. At a current density of 53.82 amps per dm ² and a temperature of the electrolyte of 6O ⁰ C, the cell has a chlorine overvoltage of 0.07 volts, and against a calomel electrode, an electrode voltage of 1,125VoIt

The anode is then placed in a laboratory chlorine diaphragm cell of the type described in Example 1 and the electrolysis is also carried out as described in Example 1 at a current density of 53.82 amperes per dm ² . The cell initially has a voltage of 3.65 volts and a chlorine overvoltage of 0.07 volts. After 744 hours of electrolysis, the cell has a voltage of 3.85 volts and a chlorine overvoltage of 0.28 volts.

Example *.

An electrode is produced from a titanium substrate and the palladium-rhodium delafossite (PdRhO _{2) as a coating layer.} The Delafossit is made from lithium rhodanate (LiRhO ₂ ) using the anion exchange process. metallic palladium and palladium chloride (PdCl ₂ ). The lithium rhodanate (LiRhO ₂ ) is obtained from rhodium _{oxide (Rh 2} Os) and lithium carbonate (Li ₂ COj). Rhodium oxide (Rh ₂ O j) is obtained when one of rhodium chloride (RhCl ₃ · 3 H ₂ O) was heated for 42 hours at 790 ⁰ C in an air stream. To produce lithium rhodate, the rhodium oxide is ground and 1.0367 g of it is mixed with 03660 g of lithium carbonate (Li ₂ COj). is the powder mixture in a Alundum shell, it is heated to 1040 ⁰ C, keeping it for 66 hours at this temperature, the product obtained is comminuted to a Could size of less than 325 mesh and checks röntgenspektroskopisch. The X-ray diagram obtained is essentially identical to the X-ray diagram known from the literature on lithium manganate (LiMnO _2).

Adjust the delafossite on the way forth diiß to 1.0817 g Lithiumrhodanat (LiRhO _2), 0.4068 g of metallic palladium and 0.6672 g of palladium chloride (PdCl ₂₎ are mixed, crushed the mixture by milling the powder in a quartz tube of an outer diameter of 9 mm and a length of 12.7 cm, the tube is vacuumed for 1 hour at 25 ° C and 3 hours at 110 ° C, the tube then closes, heated to 790 ° C and 75 hours at this Temperature.

J9

The product obtained is ground, placed in a second quartz tube with an outer diameter of 9 mm and a length of 12.7 cm, the tube is vacuumed, heated to 180 ^° C., kept at this temperature for 18 hours, and closed , heats it to 775 ° C and holds it at that temperature for 48 hours. The product obtained is washed four times with distilled water and once with acetone.

A titanium strip 143 cm long, 9.5 mm wide and 3.175 mm thick is cleaned and etched as described in Example 1 and four layers of a sludge made from 0.2 g of palladium-rhodium delafossite (FdRhO ₂ ) are painted on it, 0.4 g of a titanium resinate containing 4.2% by weight of titanium, 0.05 g of phenol and 0.15 g of toluene, with a brush. After each of the coatings 1 to 3, the strip is heated at a rate of 50 ^° C. in 10 minutes to 450 ^° C., whereupon it is kept at this temperature for 10 minutes. After the last layer has been applied, it is heated, likewise at one rate from 50 ^° C. in 10 minutes, to 500 ^° C. at this temperature, the strip is kept for 10 minutes.

The electrode produced in this way is tested as an anode as described in a beaker chlorate cell. At a current density of 53.82 amperes per dm ² and a temperature of the electrolyte of 60 ° C., the electrode has a chlorine overvoltage of 0.07 volts.

The anode is placed in a laboratory chlorine diaphragm cell of the type described in Example 1 and the electrolysis is carried out as described in Example 1 at a current density of 53.82 amperes per dm ² . At the beginning the cell has a voltage of 3.69 volts and a chlorine overvoltage of 0.07 volts. After 1320 hours of electrolysis, the cell has a voltage of 3.71 volts and a chlorine overvoltage of 0.15 volts.

Example 5

An electrode is made from a titanium substrate and the palladium-chromium delafossite (PdCrO ₂ ) as a coating! Delafossit is made from palladium metal, palladium chloride and lithium chromate using the anion exchange process. Lithium chromate is obtained by reacting lithium carbonate (Li ₂ CO ₃ ) with chromium oxide (Cr ₂ O ₃ ). For this purpose, a mixture of 3.6945 g of lithium carbonate (Li ₂ CO ₃ ) and 7.6010 g of chromium oxide (Cr ₂ O ₃ ) is ground. is the powder in an alundum crucible and heated up, it in 4 hours at 33O ⁰ C and 12 hours at 93O ⁰ C. The product obtained is grind it thereafter heated to 93O ⁰ C. 23 Stunde.i grind it again and heated it -23 hours 1040 ⁰ C. it grinds the dark green product obtained and analyzed, as described in example 1, röntgenspektroskopisch. According to its X-ray diagram, it has the same crystal form as LiM _n O ₂ .

A powder with a particle size of less than 325 mesh is prepared from 1.8190 g of lithium chromate (LiCrO ₂ ), 1.0670 g of palladium metal and 1.7761 g of palladium chloride (PdCl ₂ ) by grinding, and the powder mixture is placed in a quartz tube with an outer diameter of 10 mm and a length of 12.7 cm. vacuum the tube evacuated for 16 hours at 130 ° C, seal it, heat it to 800 ° C for 46 hours and cool it. It grinds the product obtained, it is filled into a second quartz tube of CUSTOMER UNIT, mm outer diameter of 10 and a length of 12.7 cm, the quartz tube sucks 5 hours at 130 ° C air empty, closes it, and heated in 64 hours 800 ⁰ C, which means that it is heated to 800 ° C for a total of 110 hours

The product obtained is ground to a grain size of less than 325 meshes, and it is washed 25 ° C with distilled water, then washes it twice more with acetone at 25 ° C and dries it.

A titanium strip measuring 14.6 cm in length, 9.5 mm in width and one in width is cleaned and etched Thickness, of 3.175 mm in the manner described in Example 1.

A solution of 10 g of a platinum resinate of the Engelhard "0-5X" type, calculated as metal, containing 7.5% by weight of platinum, is prepared in 9 g of toluene, so that the solution is 3.9% by weight of platinum, calculated as metal contains and applies four coatings to the titanium strip from this solution. Heating the strip in each case after the application of the coatings 1 to 3 at a rate of 50 ⁰ C in 5 minutes at 400 "X, and after the application of vierter.-coating, with a Geschwind ^ z.eit of 50 ⁰ C in 10 Minutes, to 50O ⁰ C and keeps it every fai minutes at the respective maximum temperature.

0.2 g of the palladium-chromium delafossite (PdCrO ₂ ), 0.4 g of 4.2% by weight of titanium, calculated as the metal, are made. containing titanium resinate, 0.05 g of phenol and 0.15 g of toluene and applies four layers of coating to the titanium strip with a brush. Heating the electrode in each case after the application of the coatings 1 to 3 at a rate of 50 ⁰ C in 10 minutes at 45O ⁰ C and after application of the last coating, also at a rate of 50 ⁰ C in 10 minutes, to 500 ⁰ C and keeps it in any case for 10 minutes at the respective maximum temperature.

The electrode is then tested as an anode in a beaker chlorate cell as described in Example 1. At a current density of 53.82 amps per dm ² , the anode has 0.05 volts.

Example 6

A further layer is exhibited with a titanium substrate with a layer of platinum applied to it the platinum Kobak Delafossil (PlojiCoojjO;) and one this layer covering the layer of porous titanium dioxide produced an electrode.

The platinum-cobalt delafossite is produced by the reaction of platinum chloride (PtCl ₂ ) with cobalt (II + IIIJ oxide (Co ₃ O ₄ ) and cobalt (II) oxide (CoO), so that 7.9842 g of platinum chloride (PtCl ₂ ), 3.6123 g of cobalt (II + III) oxide (Co ₃ O ₄ ) and 1.124 g of cobalt (II) oxide (CoO) are crushed in a mortar to a powder with a grain size of less than 325 mesh and misciit, the powder is filled into a quartz tube with an outer diameter of 10 mm and a length of 12.7 cm and ^{heated in a vacuum to 130 °} C. for 18 hours, after which the tube is closed.

Heating the sealed quartz tube 46 hours 700 ⁰ C, nir> mt, the resulting product from the quartz tube out, it grinds, there are in a second Quarzröhf of an outer diameter of 10 mm and a length of 12.7 cm, heating the tube in a vacuum for 8 hours 130 ⁰ C, closes it, and then heated in 64 hours 700 ° C.

The resulting product is taken out of the tube, washed five times at 25 ° C with distilled Water, then twice at 25 ° C with acetone, dries air it at 70 ° C, pound it in a mortar to a grain size of less than 325

Mesh and shred it further by making it a Treated for one hour in a commercial hammer mill with a hammer made of boron carbide.

After examination with an electron microscope, the material obtained has grain sizes im Range between 0.02 and 7.5 microns. The grain size distribution lies within two different size ranges. The main grain sizes are between 0.02 and 0.3 microns and between 1.5 and 6.0 microns. In the range of fine particles the mean grain size is 0.1 micron, in the range of larger particles it is 2.5 microns.

A 14.6 cm long, 9.5 mm wide and 3.175 mm thick titanium strip is cleaned and etched, as described in Example 1, and eight layers of 0.25 g of the Dclafossite PtosCooaO: 0.12 g titanium tetrachloride are painted on it (TiCU) in butanol, 0.75 g butanoi and 0.15 g phenol on existing sludge. Heating the strip after each coating at a rate of 5O ⁰ C in 5 minutes at 425 ° C. :O

A sludge is then prepared from titanium tetrachloride (TiCU) in butanol which, calculated as metal, contains 2.25% by weight of titanium, and this sludge is spread in four layers on the deiafossite surface of the titanium strip. Heating the strip in each case after the application of the coatings 1 to 3 20 minutes 110 ⁰ C and then After the application of the last coating one 20 minutes heating it to 11O ⁰ C. IC minutes at 425 ⁰ C. ind 15 minutes 500 ⁰ C.

The electrode produced in this way consists of jo of a titanium substrate as a base, a coating layer made of platinum-cobalt-delafossite and one of these covering outer layer of titanium dioxide. Place the electrode in a beaker chlorate cell as a Anode one. At a current density of 53.82 amperes per j; dm · hai the anöuc eifie tension VOiI 1,175 Vöii gcgcil a calomel electrode and a chlorine overvoltage of 0.12 volts.

Example 7

40

A titanium substrate is used as the base, a coating of platinum-cobalt-delafossite Pto.gCoo.8O2 and an outer layer of titanium dioxide applied thereon to produce an electrode.

A titanium strip 14.6 cm long, 9.5 mm wide and 3.175 mm thick is cleaned in the manner described in Example 1, and is carried out from a sludge of 0.5 g of the platinum-cobalt delafossite produced according to Example 6 (Pto. eCoo.8O2). 0.25 g titanium tetrachloride (TiCU). 0.75 g butanol and 0.15 g of phenol and heated six coatings on the strip after each coating first for 30 minutes 110 ⁰ C and then 15 minutes 400 ° C

A solution of titanium tetrachloride in butanol containing 2.1% by weight of titanium based on the metal is prepared and four coatings are applied from this solution to the deiafossite surface of the electrode. After each of the coatings 1 to 3, the electrode is heated first to RO ⁰ C for 20 minutes and then to 425 ° C for 10 minutes. After the fourth coating, it is first heated to 110 ° C for 20 minutes and then to 50 ° C for 15 minutes

The electrode consisting of the titanium substrate, a coating of the platinum-kobaite-delafossite and an outer coating of porous titanium dioxide is tested as described in Example 1 as an anode in a beaker-chlorate cell. At a current density of 53.82 amperes per dm ² , the anode has a voltage of 1.160 volts against a calomel electrode and a chlorine overvoltage of 0.10 volts.

The anode is placed in a laboratory chlorine diaphragm cell of the type described in Example 1 and the electrolysis according to Example I is carried out at a current density of 53.82 amperes per dm ² . The cell initially has a voltage of 374 volts and a chlorine overvoltage of 0.10 volts. After 74 days of electrolysis, the cell has a voltage of 3.94 volts and a chlorine overvoltage of 0.17 volts.

Example 8

A titanium substrate is used as a base, a coating made of platinum-cobalt-delafossite (Pto.eCoo.8O2) and a layer of ruthenium dioxide sandwiched between the substrate and the delafossite coating (RuO2) made an electrode.

A titanium strip 14.6 cm long, 9.5 mm wide and 3.175 mm thick is degreased, cleaned and etched in the manner described in Example 1 and five layers of 1.5 g of ruthenium trichloride (RuCl ₃ 3 H ₂ O) in sludge containing 9 g of ethanol. Dry the strip of any of the first four coatings 10 minutes in air and then heated it at air supply 10 minutes 30O ⁰ C. drying the final coating initially ebenfafli; 10 minutes in the air, but then heats it to 450 ⁰ C for 45 minutes with a supply of air.

From 0.5 g of the platinum-cobalt delafossite (PtojCooÄ) according to Example 6, 1.0 g of a solution of titanium tetrachloride (TiCU) in butanol, 0.2 g of phenol and containing 4.2% by weight of titanium, calculated as the metal, is made a drop of nonylphenoxypolyoxyäthylenäthanol produces a sludge and applies it to six coatings on the strip. After each coating, the strip is first heated for 20 minutes, to !! 0 ⁰ C and then. 15 minutes at 400 "C.

The strip is then coated with a layer of a solution of titanium tetrachloride (TiCU) in butanol, calculated as metal, containing 2.1% by weight of titanium and heated first to HO ⁰ C for 20 minutes and then to 500 ^{0 C for 15 minutes} The electrode obtained by this process has a uniform gray appearance.

The electrode is tested in the manner described in Example 1 as an anode in a beaker chlorate cell. At a current density of 53.82 amperes per dm ² , the anode has a voltage of 1.147 volts against a calomel electrode and a chlorine overvoltage of 0.09 volts.

The electrode is then inserted as an anode in a laboratory chlorine diaphragm cell of the type described in Example 1 and the electrolysis is carried out as described in Example t at a current density of 53.82 amperes per dm ² . The cell initially has a voltage of 3.60 volts and a chlorine overvoltage of 0.09 volts. After 936 hours of electrolysis, the cell has a voltage of 3.72 volts and a chlorine overvoltage of 0.07 volts.

Example 9

It is made with a titanium substrate as a base, a coating of palladium-cobalt delafossite (PdCoOi) and a layer of ruthenium dioxide inserted between the substrate and the delafossite coating (R11O2) an electrode.

You degrease, clean and etch a 14.6 cm long, 9.5 mm wide and 3.175 mm thick titanium strips

in the manner described in Example 1 and then with a brush four layers of a _{sludge containing 1.5 g of ruthenium trichloride (RuCl 3} · 3 HjO) in 9 g of ethanol are applied. Dry the strip of any of the first three coatings 10 minutes in air up <i then heating it in an air-open furnace to a temperature of 300 ⁰ C, holding it at the one 10 minutes, also dries the strip after the fourth coating 10 minutes in air, then heated in an air but it open oven at 450 ⁰ C and holding it for 45 minutes at this temperature.

From 0.2 g of the palladium-cobalt delafossite (PdCoO ₂ ) according to Example 1, 0.4 g of a titanium resinate containing 4.2% by weight of titanium, 0.15 g of toluene and 0.05 g are prepared Phenol produced a sludge and applied it to the titanium strip in six coatings. After each of the first five coatings by heating the strip at a rate of 5O ⁰ C in 5 minutes at 425 ⁰ C. After the last coating is heated to the strip at a rate of 50 ° C in

5 minutes to a temperature of 500 ^° C., at which it is kept for 15 minutes.

The electrode consisting of a titanium substrate, a coating of palladium-cobalt delafossite and a ruthenium dioxide layer interposed between the substrate and the delafossite coating is inserted as an anode in a beaker chlorate cell according to Example 1. At a current density of 53.82 amperes per dm ² , the anode has a voltage of 1.141 full against a calomel electrode and a chlorine overvoltage of 0.08 volts.

The anode is placed in a chlorine diaphragm cell of the dimensions customary in the laboratory and carried out the electrolysis according to Example 1 at a current density of 53.82 amperes per dm? by. The cell is on Beginning with a voltage of 3.48 volts and a chlorine overvoltage of 0.08 volts. After a period of Electrolysis of 576 hours has one cell Voltage of 3.49 volts and a chlorine overvoltage of 0.07 volts.

For this purpose 4 sheets of drawings

Claims (3)

Patent claims: 1. Anode for electrochemical processes with an electrically conductive carrier made of a rectifier metal or graphite with a top layer thereon, characterized in that that the top layer consists essentially of platinum-cobalt-delafossite, palladium-cobalt-delafossite, Palladium-Chromium-Delafossite or Consists of palladium-rhodium-delafossite Z anode according to claim 1, characterized by one between the carrier and the delafossite surface located intermediate layer, which essentially consists of ruthenium, rhodium, palladium, platinum, Osmium, iridium or their alloys or ruthenium oxide, rhodium oxide, palladium oxide, Platinum oxide osmium oxide, iridium oxide or mixtures thereof »? stands 3. Anode according to claims 1 or 2, characterized in that the carrier consists of titanium