RU2383660C1 - Method of fabrication of electrode for electrolysis of water solutions of alkali metal chlorides - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method of fabrication of electrode for electrolysis of water solutions of alkali metal chlorides consists in preliminary treatment of electrode titanium base surface, in application coating onto it, where coating consists of thermo-decomposed compounds of titanium, iridium and ruthenium; further the method consists in their succeeding thermal treatment in oxidising atmosphere and in producing electro-catalytic coating containing oxides of titanium, iridium and ruthenium; also surface of electro-catalytic coating is additionally treated with 20-25% water solution of hydrogen peroxide by means of sputtering it at amount of 80-140 g/m² and successively heat treated at temperature of 450-480°C.

EFFECT: raised resistance of electrode, increased service life.

5 cl, 4 tbl

Description

The invention relates to the field of electrochemical production, specifically to a process technology for the manufacture and regeneration of an oxide-metal electrode used as an anode in the electrolysis of alkali metal chloride solutions, for example, in the production of chlorine, caustic soda, sodium chlorate, hypochlorite.

A known electrode for electrochemical processes containing an electrically conductive base of titanium or tantalum, on which an active coating is applied, consisting of a metal oxide of a platinum group and a mixture of metal oxides containing oxide of titanium or tantalum and at least one oxide of an alloying metal selected from the group : tin, silver, chromium, lanthanum, aluminum, cobalt, antimony, molybdenum, nickel, iron, tungsten, vanadium, phosphorus, boron, beryllium, sodium, calcium, strontium, lead, copper, bismuth. The alloying metal oxide is taken in an amount of 0.1-50% by weight of titanium dioxide or tantalum pentoxide. The ratio of the content of the platinum group to the remaining metals of the oxide coating is 20: 100-85: 100. [US Patent No. 3948751]. The disadvantage of this electrode is the low resistance of the anode coating and high overvoltage on the cells.

A known electrode for the electrochemical production of chlorine and alkali, containing a valve metal base with an active coating deposited on it from a mixture of tin, ruthenium and titanium oxides, the ingredients are taken in the following ratio, mol%:

Ruthenium Dioxide - 15-30 Titanium dioxide - 25-55 Tin Dioxide - 30-60

The active coating of the electrode in its composition has a high tin content, which reduces its catalytic properties. [Patent SU No. 1468970].

A known electrode for electrochemical processes, containing a conductive substrate of a film-forming metal coated with it, consisting of an oxide or a mixture of noble metal oxides: platinum, iridium, rhodium, palladium, ruthenium, rhenium, osmium. The coating may additionally contain an oxide or a mixture of oxides of base metals: manganese, lead, chromium, cobalt of iron, titanium, tantalum, zirconium, as well as silicon in an amount of less than 50% by weight of the oxide or mixture of oxides of noble metals. [Patent SU No. 416925].

The disadvantage of this method of manufacturing an electrode is its low resistance.

A known electrode for the electrolysis of an aqueous solution of a metal halide containing an electrically conductive base from a valve metal with an active mass deposited on its surface containing iridium oxide, oxide of a valve metal and base metal oxide with the following ingredients, mol%:

Iridium oxide - 5-75 Valve metal oxide - 5-70 Tin Oxide - 20-70

The base of the electrode is made of titanium, tantalum, niobium, zirconium or their alloys. [SU patent No. 1056911]. The operation of such an electrode in a saline solution is associated with an increased solubility of iridium with its increased content, and an increased content of tin oxide impairs the electrocatalytic properties of the coating.

The closest to the invention in technical essence and the achieved result is an electrode for the electrolysis of aqueous solutions of alkali metal chlorides, containing a valve metal base coated with a mixture of titanium, iridium and ruthenium oxides. [Patent SU No. 1401072]. A disadvantage of the known electrode is the lack of resistance of the electrode.

The objective of the invention is to increase the resistance of the electrode.

The technical result, which is achieved by using the invention, is to increase the service life of the electrode.

The problem is solved by a method of manufacturing an electrode for the electrolysis of aqueous solutions of alkali metal chlorides, which includes pre-treatment of the surface of the titanium base of the electrode, coating it with thermally decomposable compounds of titanium, iridium and ruthenium, followed by heat treatment in an oxidizing atmosphere to obtain an electrocatalytic coating containing oxides titanium, iridium and ruthenium, namely its feature, which consists in the fact that the surface of the electrocatalytic coating ytiya further treated with 20-25% aqueous hydrogen peroxide solution by spraying it in an amount of 80-140 g / m ^2, followed by heat treatment at a temperature of 450-480 ° C.

In addition, a feature of the proposed method is that the heat treatment in an oxidizing atmosphere is carried out at a temperature of 370-480 ° C, and the surface treatment of the electrocatalytic coating with hydrogen peroxide and its subsequent heat treatment is carried out at least once. In addition, the electrocatalytic coating contains oxides of titanium, iridium and ruthenium in the following ratio of components (% wt.): Titanium oxide - 50-52, iridium oxide - 30-32, ruthenium oxide - 17-19. And in addition, the electrocatalytic coating additionally contains tin and cobalt oxides in the following ratio of components (% weight): titanium oxide - 48-51, iridium oxide - 28-31, ruthenium oxide - 16-18, tin oxide - 2-3, oxide cobalt - 0.5-1.5.

Example

A coating solution, a mixed solution of the following thermally degradable components: hexachloridiric acid, hydroxycotrichloridruthenium and titanium trichloride is applied to the titanium base of the electrode, previously shot-blasted, degreased and etched.

A coating solution is prepared from stock solutions:

An aqueous solution of ruthenium hydroxide trichloride (Ru (OH) Cl ₃ ) with a concentration of 120-180 g / l, an aqueous solution of titanium trichloride (TiCl ₃ ) 190-250 g / l and an aqueous solution of hexachloridiric acid with a concentration of 100-150 g / l.

A coating solution containing, in addition to the above components of the tin and cobalt compound, is prepared by dissolving the cobalt salt of 6-aqueous dichloride and the 5-aqueous tin tetrachloride salt therein.

The coating solution is applied to the working surface of the electrode by layer-by-layer spraying in an electrostatic field and with a flow rate of 33-44 ml / m ² per layer, which corresponds to 1.33-1.78 g / m ^{2 of the} main substance as a result of applying the active coating in an amount of 9- 12 layers.

After applying each layer, the electrode is subjected to drying with heated air for 5-10 minutes, and then heat treatment at a temperature of 370-400 ° C for the first 3-4 layers, and subsequent layers at a temperature of 400-480 ° C.

The multilayer deposition of the above coating solution on the surface of the electrode makes it possible to obtain electrodes with an electrocatalytic coating containing metal oxides in it: mixtures of titanium, iridium, and ruthenium oxides at a ratio (wt%): 50-52: 30-32: 17-19, respectively; and mixtures of oxides of titanium, iridium, ruthenium, tin and cobalt in the ratio,% weight: 48-51: 28-31: 16-18: 2-3: 0.5-1.5, respectively

Next, a 20-25% aqueous solution of hydrogen peroxide is sprayed in an amount of 80-140 g / m ² on the working surface of the electrode and heat treatment is carried out at a temperature of 450-480 ° C.

According to the above-described method of manufacturing an electrode with the application of an active coating, 6 samples with the same catalytic coating were made,% weight: TiO ₂ - 51; IrO ₂ - 31; RuO ₂ - 18.

Sample 1 after applying the catalytic coating by the above method was not treated with hydrogen peroxide, respectively, did not conduct additional heat treatment.

Sample 2 was treated with hydrogen peroxide once, followed by heat treatment.

Sample 3 was treated with hydrogen peroxide with appropriate heat treatment 2 times, 4 sample 3 times, 5 sample 4 times, 6 sample 5 times.

The resistance of the electrodes (samples) was evaluated by wear resistance (determination of weight loss) by the method of alternating polarity and amalgamation and by measuring the anode potential under conditions of chlorine electrolysis at various current densities. The values of the characteristics obtained as a result of the tests are shown in table 1.

The essence of the method of variable polarity and amalgamation is as follows: the test sample at a current density of 100,000 A / m ² in a solution of sodium chloride with a concentration of 300 g / l is subjected to alternating anodic and cathodic polarization for 40 minutes. Then the electrode is lowered for 30 s into a sodium amalgam with a concentration of 0.2% by weight. After these tests, the electrode is washed in distilled water, dried and weight loss is determined

The measurement of the potential of the anode is carried out under the conditions of chlorine electrolysis: the concentration of sodium chloride solution is 300 g / l, temperature 60 ° C, pH 3.5-4.0, current density 5000, 7500 and 10000 A / m ² .

Table 1 Characteristics Samples one 2 3 four 5 6 The potential of the anode under conditions of electrolysis in a NaCl solution at a current density, A / m ² 5000 1,375 1,350 1,345 1,330 1,330 1,330 7500 1,390 1,375 1,355 1,340 1,340 1,340 10,000 1,415 1,390 1,370 1,350 1,350 1,350 Weight loss of electrocatalytic coating, determined by the method of alternating polarity at a current density of 10,000 A / m ² and amalgamation in a NaOH solution, mg / cm ² 0.45 0.25 0.15 0.09 0.09 0.09

In addition, another 12 samples were made. The composition of the active coating of the manufactured samples corresponds to the specified data in table 2.

table 2 Samples TiO ₂ (% weight) IrO ₂ % weight RuO ₂ % weight SnO ₂ % weight CoO ₂ % weight 1 and 1 * (prototype) 51.1 30.7 18.2 - - 2 and 2 * 52.0 29.0 15.0 4.0 0 3 and 3 * 50,0 30.5 17.0 2.0 0.5 4 and 4 * 49.5 29.5 17.5 2.5 1,0 5 and 5 * 51.0 28.0 19.0 0 2.0 6 and 6 * 45.0 27.0 15.0 7.0 5,0 Samples 1, 2, 3, 4, 5, 6 after applying the active coating were not subjected to treatment with an aqueous solution of hydrogen peroxide. Samples 1 *, 2 *, 3 * 4 *, 5 *, 6 * were treated with a solution of hydrogen peroxide in one layer and performed additional heat treatment.

The resistance of the electrodes (samples) was evaluated by wear resistance (to determine the weight loss) by the method of alternating polarity and amalgamation and by measuring the anode potential under conditions of chlorine electrolysis at different current densities. The values of the characteristics obtained as a result of the tests are shown in tables 3 and 4.

Table 3 Samples Characteristics one 2 3 four 5 6 The potential of the anode under conditions of electrolysis in a NaCl solution at a current density, A / m ² 5000 1,375 1,395 1,380 1,375 1,400 1,395 7500 1,395 1,410 1,395 1,395 1,415 1,410 10,000 1,410 1,425 1,415 1,410 1,420 1,425 Weight loss of electrocatalytic coating, determined by the method of alternating polarity at a current density of 10,000 A / m ² and amalgamation in a NaOH solution, mg / cm ² 0.45 0.48 0.42 0.42 0.50 0.52

Table 4 Characteristics Samples one* 2 * 3 * four* 5* 6 * The potential of the anode under conditions of electrolysis in a NaCl solution at a current density, A / m ² 5000 1,365 1,390 1,370 1,360 1,385 1,390 7500 1,380 1,395 1,380 1,370 1,390 1,395 10,000 1,390 1.41 1,395 1,385 1,400 1,405 Weight loss of electrocatalytic coating, determined by the method of alternating polarity at a current density of 10,000 A / m ² and amalgamation in a NaOH solution 0.25 0.32 0.25 0.23 0.35 0.39

As can be seen from the results of Table 1, a three-fold treatment of the electrode surface with hydrogen peroxide followed by additional heat treatment improves the electrocatalytic properties of the anode coating and, as a result, the performance of the electrode, subsequent processing does not significantly change the quality of the coating.

The authors of the claimed technical solution conducted additional studies by known methods, as a result of which it was found that the surface treatment of the anode after applying the electrocatalytic coating with hydrogen peroxide followed by heat treatment contributes to the compaction of the electrocatalytic layer and eliminates microcracks, porosity and friability of the coating.

The advantage of the proposed method for manufacturing the electrode is to improve the quality characteristics of the electrode: increasing the wear resistance of the electrocatalytic coating and reducing the anode potential. Increasing the wear resistance of the electrode coating allows you to increase the life of the electrodes up to 24 months.

Claims (5)

1. A method of manufacturing an electrode for the electrolysis of aqueous solutions of alkali metal chlorides, including pre-treating the surface of the titanium base of the electrode, coating it with thermally decomposable compounds of titanium, iridium and ruthenium, followed by heat treatment in an oxidizing atmosphere to obtain an electrocatalytic coating containing titanium oxides, iridium and ruthenium, characterized in that the surface of the electrocatalytic coating is additionally treated with a 20-25% aqueous solution of water peroxide kind by spraying it in an amount of 80-140 g / m ² followed by heat treatment at a temperature of 450-480 ° C. 2. A method of manufacturing an electrode according to claim 1, characterized in that the heat treatment in an oxidizing atmosphere is carried out at a temperature of 370-480 ° C. 3. The method of manufacturing the electrode according to claim 1, characterized in that the surface treatment of the electrocatalytic coating with hydrogen peroxide and its subsequent heat treatment of the electrode is carried out at least once. 4. The method of manufacturing the electrode according to claim 1, characterized in that the electrocatalytic coating contains oxides of titanium, iridium and ruthenium in the following ratio of components: titanium oxide 50-52 wt.%; iridium oxide 30-32 wt.%; ruthenium oxide 17-19 wt.%. 5. The method of manufacturing the electrode according to claim 1, characterized in that the electrocatalytic coating further comprises tin and cobalt oxides in the following ratio of components, wt.%: Titanium oxide 48-51, iridium oxide 28-31, ruthenium oxide 16-18, oxide tin 2-3, cobalt oxide 0.5-1.5.