RU2745017C1 - Non-polarized comparison electrode - Google Patents

Abstract

FIELD: corrosion monitoring, electrochemistry.SUBSTANCE: invention relates to stationary non-polarizable long-term reference electrodes and is intended for corrosion monitoring systems and electrochemical protection of underground metal structures from corrosion. The non-polarizable reference electrode contains a non-conductive housing filled with an electrolyte from a saturated salt solution, in which a metal rod is partially immersed with a conductor connected to it from the outside in an insulator, as well as a bentonite mixture with a wetted separator and a body baffle separating the bentonite mixture and the electrolyte from a saturated salt solution, containing one or more through holes filled with ion-exchange material, at least one capillary rod is used as an ion-exchange material, which are microchannels filling the inner part of the tubular body, the lower end of the rod is in the electrolyte from a saturated salt solution, and the upper end is in bentonite mixture, moreover, a metal rod is also fixed in the partition.EFFECT: technical result is to reduce the overall dimensions while maintaining the increased reliability of the device in long-term operation.1 cl, 1 dwg

Description

The technical field to which the invention relates

The invention relates to stationary non-polarizable long-term reference electrodes and is intended for corrosion monitoring systems and electrochemical protection of underground metal structures from corrosion.

State of the art

There is a relatively wide range of devices for measuring the total and polarization potentials of underground pipelines and steel structures during corrosion monitoring. The most widespread are non-polarizable reference electrodes. The operation of such electrodes, as a rule, is based on a structure with a body made of a certain metal (copper, zinc, silver / silver chloride) immersed in a saturated solution of a salt of the same metal, separated from the external environment by a chemically inert housing with an ion-exchange membrane.

The known device (Patent RU No. 2296977, publ. 10.04.2007). consists of a non-conductive housing filled with an electrolyte containing distilled water, ethylene glycol and copper sulfate (CuSO4⋅5H2O). In the central part of the electrode body, a copper rod is fixed, electrically connected to a terminal by a copper conductor. To ensure ion exchange, while maintaining tightness, a sheet ion-exchange membrane with a thickness of 30-60 microns is used, pressed through a rubber sealing gasket with a perforated sleeve to the body. The device has a simple structure and low cost. The disadvantage of the known device is the low service life associated with the slow expiration of the saline solution from the electrolytic chamber through the porous bottom (polymer membrane) under the influence of gravity, the strong influence of the characteristics of the polymer membrane on the service life of the electrode,

the problem of osmotic pressure on the membrane.

Known long-acting silver-chlorine reference electrode (Patent Application RU 2012135512, published 02/27/2014), containing a case filled with electrolyte, which houses another reference electrode with a silver metal rod, equipped with an insulated wire led through the side wall of the case to the outside , a potential sensor located on the upper end surface of the housing, from which two insulated wires are led out from the inner surface through the side surface of the housing. In this case, the reference electrode has a plastic case with holes, a hollow capillary screw plug with a cover is screwed into the upper end surface of the case, the hollow screw plug has through capillaries filled with electrolyte, a rubber gasket and a ceramic washer are fixed between the screw plug cover and the potential sensor. the washer is impregnated with the electrolyte of the dielectric body and contacts the bottom end with the open surface of the potential sensor and the inner surface with through capillaries of the hollow capillary screw plug. The device helps to increase the service life of the internal silver chloride electrode, which is usually a laboratory control electrode such as EVL-1M1 or ESS-01. The claimed capillary is used only as an ionic conductor, the capillary effect associated with the rise of liquid upward along the capillary is not used in the known device. It should also be noted the disadvantage associated with the fact that it is difficult to ensure the tightness of this structure and, accordingly, the failure-free operation.

A device is known (Operation manual, passport "Copper sulfate reference electrode MSES.SC" Etalon "-1.0 according to TU 3435-005-09890805-2013", manufacturer "Soyuzkompelkt" LLC, Moscow, 02.02.2017, scanned copy in Appendix 1 ), in which the ion-exchange membrane is located in the upper part of the housing, which prevents the electrolyte from leaking out by gravity. The electrolytic chamber in this electrode is made in the form of a "U" -shaped tube. One part of this tube is filled with a gel electrolyte, into which a piece of tissue is immersed in contact with an ion exchange membrane located at the top of the electrode. The other part of the tube is filled with a liquid electrolyte solution with a metal (copper) rod immersed in it. Both parts of the tube are in contact with each other through a membrane located in the lowermost curved part. The "U" -shaped tube is housed in an outer cylindrical housing that has a cable entry. The advantages of the known device are the preservation of the electrolyte volume due to the prevention of leakage through the membrane, low weight, and the disadvantage of a low service life (maintaining the normalized potential) in mineralized operating environments - no more than 6 months.

The closest in technical essence (prototype) is the device (Operation Manual "Copper sulfate non-polarizable reference electrode ENES-4M according to TU 3435-016-73892839-2010", manufactured by LLC ZNGA Anod, published on 05/17/2017, scanned copy in Appendix 1), consisting of an electrolytic chamber filled with electrolyte, a bentonite chamber filled with a bentonite mixture, fastened with a nut, a metal (copper) rod connected by a conductor (cable) with a tip, a bentonite chamber in the body of which there is a hole with an ion-exchange membrane glued in (pressed) around the perimeter from a sheet of porous polymer material, a rubber sealing gasket that serves to ensure the tightness of the compartments, an external ceramic separator located in the upper part of the electrode and separating the volume of the bentonite chamber from the external environment. The bentonite mixture serves as an effective trap for chloride ions penetrating from the external environment, and is also a kind of water seal, having the ability to swell and thicken in the volume provided to it when exposed to moisture from the external environment. Thus, the chamber with a liquid electrolyte solution is protected from the external environment not only by a membrane, but also by a chamber with a bentonite filler.

In addition, an important feature of the prototype is the immersion of the conical bentonite chamber into the electrolytic chamber to a certain depth, which is approximately 1/3 of the total depth of the electrolytic chamber. This solution makes it possible to give the bentonite chamber an additional function of a conductor of moisture and electrolyte ions from the depth of the electrolytic chamber to the upper part of the electrode, where the ions come into contact with the operating environment, the soil.

The advantage of the known device is that it excludes leakage of electrolyte over time, under the influence of gravity since the ion exchange membrane is moved to the top of the electrode, which has a positive effect on durability and reliability.

One of the disadvantages of the prototype, which includes both a membrane and an additional bentonite chamber, is the presence of irrational solutions. First, due to the immersion of the bentonite chamber inside the electrolytic chamber, the copper rod was transferred to the opposite lower part of the electrode, and therefore the cable supplied to the electrode from above bends around the electrode body along the lateral generatrix and joins the rod in the lower part, which requires additional cable consumption. Secondly, an irrational solution is the need to use a large volume of bentonite to achieve communication of the electrolyte with the external environment in the case of some quite possible tilt of the electrode when burying and installing in the ground. Third, an irrational solution in the prototype, which is present in most other known devices, is the use of polymer membranes and ceramic separators necessary for separating the bentonite and electrolytic chambers, as well as for separating these chambers from the external environment of the electrode while maintaining ion exchange through them, since the cost of such materials from specialized well-known manufacturers is usually high.

Another disadvantage of the prototype is the large overall volume, which requires drilling large-diameter wells for the installation for operation. For example, due to some functional overload of the bentonite chamber, its volume is large enough and occupies about 1/3 of the volume of the electrolytic chamber.

Disclosure of invention

The objective of the invention is a more rational use of materials, a decrease in cost, an increase in compactness, while maintaining an increased service life and reliability of the electrode.

The technical result of the invention is to reduce the overall dimensions while maintaining the increased reliability of the device in long-term operation.

The technical result is achieved due to the fact that in a non-polarizable reference electrode containing a non-conductive housing 1 filled with an electrolyte from a saturated salt solution 2, into which a metal rod 3 is partially immersed with a conductor 4 connected to it from the outside in an insulator 5, as well as a bentonite mixture 6 with with a wetted separator 7 and, a body baffle 8 separating the bentonite mixture 6 and the electrolyte from a saturated salt solution 2, containing one or more through holes filled with ion-exchange material, characterized in that at least one capillary rod 9 is used as an ion-exchange material, which is a microchannel filling the inner part of the tubular body, the lower end of the rod is in the electrolyte from a saturated salt solution, and the upper end is in the bentonite mixture 6, and the metal rod 3 is also fixed in the body partition 8.

Brief Description of Drawings

The invention is illustrated by the drawing in FIG. 1, where a schematic diagram of a non-polarizable reference electrode is given: 1 - non-conductive housing, 2 - electrolyte from a saturated salt solution, 3 - metal rod, 4 - conductor, 5 - insulator, 6 - bentonite mixture, 7 - wetted separator, 8 - body baffle , 9 - capillary rod.

Implementation of the invention

The non-conductive body 1 is made of a durable chemically inert material, for example, a composite plastic. The electrolyte from the saturated salt solution 2 is poured into the lower cavity of the non-conductive body 1, onto which the baffle 8 is then hermetically fitted, which is part of the non-conductive body 1. The metal rod 3 pressed into the body baffle 8 is immersed in one part into the electrolyte from the saturated salt solution 2, and the other part remains outside for connecting the conductor 4. The connection point and bare metal sections are protected by a sealed insulator 5. The body baffle 8 also contains pressed capillary rods 9, which are a system of microchannels filling the tubular body. The lower end of the capillary rods 9 is immersed in the electrolyte from a saturated salt solution 2, and the upper end is brought out into the bentonite mixture 6, thus, the capillary rods 9 replace the ion-exchange membrane, which is, as is known, a wettable porous body in the form of a sheet or film. In this case, the microchannels of the rods are an alternative to the pores of the membrane. The cavities for the bentonite mixture 6 are located on the body partition 8. Since the capillary rods 9 have a diameter significantly less than the area of the working surface of the sheet ion-exchange membrane in the prototype, the proposed electrode does not require a large volume of the bentonite chamber. Bentonite mixture 6 should be localized around the end of the capillary rod 9. Bentonite mixture 6 in dry form usually contains 25-95% bentonite powder, 5-25% activator salt. The composition may contain other components that serve to increase the viscosity of the mixture and sorption of toxic ions. The bentonite powder itself serves not only as a sorbent of toxic ions, but also as a water seal, having the property to expand and seal all joints and cavities with an excess of moisture, and vice versa, to shrink in dry soil. The wetted separator 7 is located in the upper part of the device, has a developed surface, serves to fix the volume of the bentonite mixture 6 and improve the contact of this mixture with the operating environment.

As you know, the height of the liquid column (the height of the liquid rise above the surface) with the capillary effect is described by Yurin's law:

h = 2 σ cos β / ρ g r,

where σ is the surface tension of liquid-air, β is the contact angle, ρ is the density of the liquid, g is the acceleration of gravity, r is the radius of the capillary.

In the proposed non-polarizable reference electrode, by selecting r and H - the distance between the surface of the electrolyte from a saturated salt solution 2 and the upper end of the capillary rod 9, the required standardized characteristics of the electrode are adjusted, for example, the transition resistance, and also minimizes the electrolyte output through the upper end of the rod, since the force of the capillary and sorption effect F _{K is} directed oppositely to the force of gravity F _T acting on the electrolyte.

It is possible to control the capillary effect in the proposed device not only constructively, but also prescription, by adjusting the parameters of the electrolyte from a saturated salt solution σ and ρ, by introducing substances into the recipe for its preparation that do not affect the electrode's own potential, but with parameters σ and ρ different from water, for example ethylene glycol.

The immersion of the capillary rods 9 in an electrolyte from a saturated salt solution 2 to a certain depth, selected empirically, is necessary to achieve stable contact in the event of an unintentional tilt of the electrode when installed in the ground.

Claims (1)

A non-polarizable reference electrode containing a non-conductive housing filled with an electrolyte from a saturated salt solution, in which a metal rod is partially immersed with a conductor connected to it from the outside in an insulator, as well as a bentonite mixture with a wetted separator and a body baffle separating the bentonite mixture and electrolyte from saturated salt solution containing one or more through holes filled with ion-exchange material, characterized in that at least one capillary rod is used as the ion-exchange material, which are microchannels filling the inner part of the tubular body, while the lower end of the rod is in the electrolyte from a saturated salt solution, and the upper one is in a bentonite mixture, and a metal rod is also fixed in the partition.

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