Method of making ruthenium electrodes for electrochemical sensor with solid electrolyte

IPC classes for russian patent Method of making ruthenium electrodes for electrochemical sensor with solid electrolyte (RU 2342652):

G01N27/406 -

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FIELD: chemistry.

SUBSTANCE: present invention pertains to the technology of making electrodes on a solid electrolyte from stabilised zirconium dioxide, and can be used for making electrochemical solid electrolyte sensors for concentration of oxygen in different oxygen-containing gases. The essence of the invention lies in that, to make a ruthenium electrode, ruthenium is deposited on a degreased and activated surface of a solid electrolyte, through recovery of ruthenium from an aqueous solution of rutheniumhexamine (II) chloride, containing 0.2-0.4 g/dm³ ruthenium per 1 cm² of the covered surface. Acidity of the solution is established by adding a solution of potassium hydroxide with concentration ranging from 0.36 g/l to 0.78 g/l to the reaction system. The process takes place at temperature of 170-210°C in an enclosed volume for 130-180 minutes.

EFFECT: reduced power input through lowering temperature, number of operations and duration of the process, as well as reduced temperature at which the electrode starts working.

3 cl, 1 tbl

The invention relates to the analysis of gases and analytical instrumentation, in particular to the technology of manufacturing electrodes on the solid electrolyte of stabilized Zirconia, and can be used in the manufacture of electrochemical solid electrolyte sensor of oxygen concentration in various oxygen-containing gases, such as flue gases of power plants, the exhaust gases of internal combustion engines, etc.

Actual when mass production and industrial use of electrochemical sensors is the technology of manufacturing electrodes of the oxygen sensors with solid electrolyte sensor element providing the required technical result, namely high operational reliability of the electrodes in the structure of the oxygen sensors, increase the electrochemical activity of the electrode (porosity, resistivity, adhesion, etc.), the temperature decrease of the electrode.

These requirements to the greatest extent meet the electrodes based on noble metals.

There are various ways of getting electrodes of the oxygen sensors on the solid electrolyte sensing element Zirconia: burn powder paste, sintering pastes, pyrolysis of complex compounds, electrochemical deposition, vacuum Abilene and others.

A known method of making electrodes for electrochemical solid electrolyte oxygen sensor method primechanie mechanical mixture of metal powder and ligaments to the surface of the substrate in a hydrogen atmosphere [Russia, author's certificate No. 1709655, CL 22F 7/04]. The process is carried out first in an atmosphere of hydrogen sulfide to the formation and subsequent melting of sulphides, and then in an atmosphere of hydrogen until full recovery.

This method of manufacturing electrodes does not provide for their operation in the composition of the oxygen sensor operational reliability and the necessary electrochemical activity of the electrodes.

In another known method [Russia, author's certificate No. 2149217, CL SS 24/04] carry out degreasing and cleaning the surface of the material, then it is applied mechanically particles of a substance selected from the group of metals, alloys, metal oxides, hydroxides or sulphides of metals, followed by heating up to 200-500°in a non-oxidizing atmosphere.

The proposed method is energy-consuming and does not allow to control the thickness of the resulting layer.

A method for manufacturing electrodes of the solid electrolyte sensor of oxygen concentration by the method of vacuum deposition [Russia, author's certificate No. 1473528, CL G01N 27/417. The measuring electrode is performed in a multilayer film made of platinum, and after application of each layer is measured electrical resistance of the electrode and the coating layer is terminated by reaching resistance values that do not exceed 1 Ohm. For each suitabilty metal layer, except the last, adsorb gas, inert with respect to the components of the analyzed medium and controlled mixture. The disadvantages of this method of manufacturing electrodes are increased energy consumption by spraying several layers of platinum and additional adsorption gas, high ohmic resistance of the electrodes.

Known methods of manufacturing electrodes of an electrochemical sensor with solid electrolyte closest to the present invention is a method of manufacturing electrodes [Russia, patent No. 2029946, CL G01N 27/417, 1995]. This method comprises applying to the solid electrolyte element of stabilized Zirconia paste of a mixture of powders of platinum and solid electrolyte, the subsequent burn-in paste having the following composition, wt.%: the solid electrolyte 4-80, platinum 10-86, carbon 10-50. The burn-in is carried out in a protective atmosphere at 1300-1650°C for 5 hours and then in an oxidizing atmosphere at 900-1400°C for 24 hours. The disadvantages of this method of manufacturing electrode are high energise the rata to maintain high temperatures for a long period of time, relatively high temperature threshold start working electrode 270°C.

The present invention is to reduce power consumption by lowering the temperature, the number of operations and time of the process, and reducing the temperature of the electrode.

The problem is solved due to the fact that in the method of manufacturing a ruthenium electrode electrochemical sensor with solid electrolyte, including the application of ruthenium, according to the invention, the ruthenium is applied on the pre-fat and an activated surface of the solid electrolyte by the recovery of ruthenium from aqueous chloride solution hexaammineruthenium (II)containing 0.2-0.4 g/DM³ruthenium on 1 cm²the coated surface. The process of applying lead in alkaline solution of potassium hydroxide with a concentration of from 0.36 to 0.78 g/l, at a temperature of 170-210°With, in a confined space, for 130-180 minutes the Coating is a metallic ruthenium (0) without impurities ruthenium in other oxidation States.

The proposed method is as follows.

stage 1 - degreasing the ceramic surface. The purpose of this operation is to remove from the surface of the solid electrolyte contamination. Degreasing is performed by boiling in 10%solution of Na₂CO₃within 20-40 min, followed the washing water.

stage 2 - activating the ceramic surface. Activating the surface of the solid electrolyte is necessary to obtain metal particles which are the nuclei of crystallization in the process of recovering ruthenium from aqueous solution of the complex salt. This stage allows you to get high-quality conductive metal layer is sufficiently thick in the subsequent single application of ruthenium. Activation is the surface treatment solution containing ions of the metal of the activator Pd²⁺and metal ions sensitizer Sn²⁺[Nikolaev, Y., Starlings CYP, Frolov V.V. metal coating by a chemical method. - M., engineering, 1983, p. 22] In this solution during subsequent processing solution "accelerator" (25% solution hydrohloride ammonium (NH₄)HF₂) proceeds recovery of palladium:

Pd²⁺+Sn²⁺→Pd⁰+Sn⁴⁺

The equilibrium reaction is shifted towards the formation of products due to the poor solubility of fluorides tetravalent tin in hydrohloride ammonium. In order to remove the reaction products from metallic palladium ceramics washed in running water. The solution is to activate contains, g/DM³: 0,8-1,0 PdCl₂; 40-45 SnCl₂; 140-150 KCl; 160-200 cm³/DM³concentrated HCl. The process and the cultivated includes the following operations: processing solution is activated; rinse in running water; processing solution accelerator; rinse in running water.

stage 3 - applying the metal layer of ruthenium. The solid electrolyte is prepared by the above described method, are placed in a Teflon autoclave with an aqueous solution of chloride hexaammineruthenium (II)containing 0.2-0.4 g/DM³ruthenium on 1 cm²the coated surface. the pH of the solution sets introduction into the reaction system solution of potassium hydroxide concentration of from 0.36 g/l to 0.78 g/l Solution of vacuum within 20-40 min and saturated with nitrogen to remove molecular oxygen, after which the autoclave is pressurized. The process is conducted in an autoclave at a temperature of 170-210°for 130-180 minutes under stirring, and then the autoclave is cooled and opened. The surface of the solid electrolyte with metal ruthenium, washed with distilled water. Removing oxygen from the system is a prerequisite for obtaining high-quality coatings, as in his presence when thermolysis along with metallic ruthenium is formed of poorly soluble compounds of ruthenium variable composition. The interval duration, the process temperature and the concentration of potassium hydroxide in solution conditions are almost full recovery of ruthenium from the solution. The criterion for assessing the quality of the coating is the th appearance. The coating should be smooth, light-gray to dark-gray, with a metallic sheen. The proposed method does not require additional recovery operations, because the floor is metal and does not contain ruthenium in other oxidation States.

Thus, the method of manufacturing electrodes by the method of pressure recovery examinate ruthenium (II) allows to reduce the energy consumption of the process by reducing the temperature to 170-210°and time to 130-180 min compared with 900-1650°and 29 h, respectively, the closest analogue. In addition, the proposed method has a simple instrument design, technologically advanced and environmentally friendly.

Obtained as described above, the electrode has a brilliant light gray coating. The thickness of the obtained film was 5-7 μm. Tests of electrochemical sensors in a laboratory setup. Determined EMF sensor when the feed speed of technical nitrogen 10-60 l/h in the temperature range 100-600°C. the Lower temperature threshold for operation of the electrode made of the proposed method, 150°compared with 270°With the closest analogue. Therefore, the main objective of the invention is to reduce the temperature of the sensor is reached.

Below are examples of the implementation of the Britania "Method of manufacturing a ruthenium electrode electrochemical sensor with solid electrolyte. The surface preparation method was previously developed and in all examples the same.

150

Examples of implementation of the invention "Method of manufacturing a ruthenium electrode electrochemical sensor with solid electrolyte".
No.	The mode of deposition of the ruthenium	Coverage
The composition of the solution	Process temperature, °	The process time min
Content in the solution of ruthenium g/DM³on 1 cm²surface	KOHN, g/l
1.	0,4	0,36	210	180	Floor dark-grey spots, non-shiny
2.	0,3	0,36	190	150	Floor grey smooth with a metallic Shine
3.	0,2	0,36	170	130	Floor light gray smooth with a metallic Shine
4.	0,4	0,56	210	180	Floor dark-grey spots, non-shiny
5.	0,3	0,56	190	The floor is dark gray with metallic luster
6.	0,2	0,56	170	130	Floor grey smooth with a metallic Shine
7.	0,4	0,78	210	150	Floor dark-grey spots, non-shiny
8.	0,3	0,78	190	150	Floor light gray smooth with a metallic Shine
9.	0,2	0,78	170	130	Floor light gray smooth with a metallic Shine
10	0,4	0,36	190	130	Floor gray smooth, non-shiny
11	0,3	0,56	210	150	Floor grey smooth with a metallic Shine
12	0,2	0,78	210	150	Floor grey smooth with a metallic Shine
13	0,4	0,36	190	150	Floor grey smooth with a metallic Shine
14	0,3	0,56	170	130	Floor light gray smooth with a metallic Shine
15	0,2	0,78	190	180	Floor light gray smooth with a metallic Shine

1. A method of manufacturing a ruthenium electrode electrochemical sensor with solid electrolyte of stabilized Zirconia, including the application of ruthenium, characterized in that the ruthenium is applied on the pre-fat and an activated surface of the solid electrolyte by the recovery of ruthenium from aqueous chloride solution hexaammineruthenium (II)containing 0.2-0.4 g/DM³ruthenium on 1 cm²cover the surface.

2. The method according to claim 1, characterized in that the process of applying lead in alkaline solution of potassium hydroxide with a concentration of from 0.36 to 0.78 g/l at a temperature of 170-210°in a confined space within 130-180 minutes

3. The method according to claim 1, characterized in that the coating is a metallic ruthenium (0) without impurities ruthenium in other oxidation States.