RU38229U1 - ELECTROCHEMICAL SENSOR FOR DETERMINING OXYGEN CONCENTRATION IN LIQUIDS AND GAS MIXTURES - Google Patents

Description

An electrochemical sensor for determining the enditration of oxygen in liquids and

An electrochemical sensor for determining the concentration of oxygen in liquids and gas mixtures refers to control devices and can be used in any sector of the national economy.

Known electrochemical sensor for determining oxygen in liquids and gas mixtures, A. with. USSR No. 604403, operating according to the scheme with internal polarization of a galvanic pair: silver cathode (indicator electrode) - cadmium anode (auxiliary electrode) placed in the sensor housing 1.

The sensor is unstable, it is necessary to constantly monitor its calibration characteristics.

The closest in technical essence to the claimed device is an "Electrochemical sensor for determining the concentration of oxygen in liquids and gas mixtures according to A.S. USSR 296022 from 10.10.68, G 01 N 3/06, publ. 12.11.71, BI No. 8, containing a silver cathode (indicator electrode), a cadmium anode (auxiliary electrode) placed in the housing, the cadmium anode having the shape of a complex configuration, made by pressing cadmium chips, placed inside the contact of the indicator electrode, the sensor housing, followed by cathodic-anode activation in the housing and evacuation. The contact of the indicator electrode passes through the internal cavity of the sensor, adjoins the cadmium mass and is isolated from it by a fluoroplastic tube, which leads to the irrational use of a part of the volume of the internal cavity of the sensor and, in the case of violation of the fluoroplastic insulation when pressing the cadmium mass, can lead to short circuit of the anode and cathode. Pressing cadmium chips in the internal cavity of the sensor does not provide uniform density of the anode. This leads to a decrease in the term of stable operation of the sensor. Subsequent cathodic-anodic activation in the housing, with repeated change of reagents, reduces the quality of the working solution with the remnants of activating reagents, and accordingly, the accuracy of measurements and the time for obtaining reliable readings of such a sensor.

The objective of the proposed technical solution is to increase the period of stable operation of the electrochemical sensor for determining oxygen in liquids and gas mixtures and increase its reliability.

gas mixtures

MnKG01N3 / 06

the shell, the housing, the cathode and the anode housed in it, while the cathode contact passes inside the upper part of the housing, outside the anode location zone, before this zone it is led out of the sensor housing, and is located in the form of a single-layer winding on the sensor housing; the anode having a cylindrical shape is made by pressing a cadmium electrode mass outside the sensor housing, placed in the housing, followed by cathode-anode activation outside the shell.

In FIG. 1 is a drawing of an electrochemical sensor for determining oxygen in liquids and gas mixtures, where 1 is the sensor housing, 2 are slots for attaching the sensor to various research facilities, 3 is an indicator electrode (cathode), 4

-perforations for access of electrolyte from the inside of the sensor, 5 - anode, 6

-electric contact, 7 - a shell made of polystyrene, 8 - bandage, 9 - upper and lower bushings, 10 - plug, 11 - electrolyte.

Sensor housing 1 is made of glass-filled polyamide. In the upper part of the body there is a sleeve 9 and slots 2 for installing rubber sealing gaskets for mounting the sensor to various research installations. The indicator electrode 3 is made of chromium-nickel wire passing through the sleeve 9, which, not reaching the pressed cadmium electrode mass of the anode 5, is led out of the sensor housing 1, and is located in the form of a single-layer winding on the sensor housing 1, bypassing the anode 5 of the pressed cadmium electrode masses. An anode 5 of a cadmium electrode mass (chip) extruded outside the sensor housing is inserted into the inner part of the housing 1. The anode 5 from the pressed electrode mass is impregnated with an electrolyte (27% KOH solution) 11. The housing 1 is perforated with holes 4 for access of the electrolyte 11 from the inside of the sensor to the cathode 3 from the anode soaked with electrolyte 5. Electrical contact 6 made of chromium-nickel wire from the electrode mass the anode 5 is discharged through the sleeve 9. The indicator electrode 3 is coated externally with a semi-permeable shell 7 made of polyethylene 60-85 μm thick, which is attached at both ends to the housing 1 using a bandage 8 in the form of nylon filament windings. The lower part of the housing 1 is closed by a sleeve 9 and a plug 10, and the upper only by a sleeve 9.

Due to the fact that the indicator electrode (cathode) 3 passes through the sleeve 9, and, not reaching the anode location zone, is brought out to the sensor housing 1, where it is located in the form of a single-layer winding, the indicator electrode bypasses the anode from the electrode mass, the duration of the sensor increases and the danger of short circuiting disappears due to the destruction of the insulation between the anode and cathode.

Since the cadmium mass is pressed by the front of the sensor in 96% ethanol, a uniform mass density of the anode is achieved. This ensures a uniform porous structure of the anode of the oxygen sensor, which allows to increase the period of its stable operation.

The cathode and anode assembled in the sensor housing are prepared for final assembly by activation before being placed in a semipermeable shell.

The cathodic-anodic activation of the anode is carried out outside the sensor shell as follows. The sensor without a polyethylene sheath is placed in an electrolyte solution (27% KOH solution). Using an external electrode, which is spectrally pure graphite, the auxiliary electrode is polarized anodically for 10 min with a current density of 15 mA per 1 g of mass for the oxidation of the cadmium surface. Then the electrolyte is changed and an electrode with a current density of 20 mA per 1 g of mass is polarized cathodically for 15 minutes, during which the oxidized cadmium surface is restored and an active cadmium layer is formed. After that, the electrolyte is changed and the cathodic polarization is repeated. During cathodic polarization, the indicator electrode is connected to the auxiliary electrode and also polarized cathodically. After polarization is installed in a semipermeable shell, the working electrolyte is poured into the sensor, the remaining air bubbles are removed under vacuum, and the casing is closed with a stopper. The sensor is ready for operation.

The device works on the principle of a simple electrolytic (more precisely, polarographic) cell - the basis of a system sensitive to oxygen. When the cathode acquires a negative potential of a few tenths of a volt relative to the anode, the oxygen contained in the solution is restored at the cathode, causing a current that can be measured by the device.

Experimental studies of the inventive electrochemical sensor for determining oxygen in liquids and gas mixtures showed that, in comparison with a sensor of a similar purpose (prototype), the inventive device provides more reliable operation, as well as its service life is increased. For example, when using the described sensor in measuring instruments for the parameters of the aquatic environment (thermooximeters), the period of stable calibration parameters increased from 12 to 18 months.

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Claims (1)

An electrochemical sensor for determining the concentration of oxygen in liquids and gas mixtures, containing a semi-permeable shell, a housing, a cathode and anode placed in it, characterized in that the cathode contact passes inside the upper part of the housing, outside the anode location zone, in front of this zone it is led outside the sensor housing and is located in the form of a single-layer winding on the sensor housing, the anode having a cylindrical shape is made by pressing a cadmium electrode mass outside the sensor housing, placed in the housing followed by the cathode-anode th activation outside the shell.