HU207180B - Reference electrod for the cathodic protection of the metallic constructions - Google Patents

Abstract

A Mo/MoO3 electrode, partly covered in a synthetic material, with an uninsulated active part. The reference electrode is protected by a concrete cover made of Portland cement, fine sand and lime and is kept in water before the use.

Description

The present invention provides a reference electrode for cathodic protection of metallic structures using a Mo / MoO ₃ second-order electrode without the use of an electrolyte, which results in a small, independent, weather-independent measurement.

The steel material of both reinforced and reinforced concrete structures installed in the ground and outdoors is necessarily subjected to corrosion. Known and effective methods for reducing corrosion damage are cathodic protection with internal and external power. The principle of this method of protection is that the metal to be protected against corrosion is cathodically polarized by means of a protective anode or by connecting an external power source, and its electrode potential is shifted by some 100 mV, ie a cathodic current density of 5 to 500 mA.m ² set up permanently. The prerequisite for the effectiveness of the protection is the proper polarization of the metallic structure to be protected, which is verified by measuring or knowing the electromotive force of a galvanic cell formed from a reliable reference electrode and the metallic material to be protected.

It is known in the literature and practice to use Cu ²⁺ / Cu so-called first-order electrodes or Ag / AgCl and Hg / Hg ₂ Cl ₂ second-order electrodes for reference electrodes.

U. S. Patent No. 191524 discloses a high-load copper / copper sulphate electrode having a ceramic body encased in a saturated copper / copper sulphate outer filling mass, an embedded ceramic insert, and an internal filling mass, an electrode metal therein. The filling compounds are sealed with sealing plates and sealed by a barrier layer. An electrode is connected to the electrode via a metal connector. The ceramic body and the ceramic insert have a copper / hexacyano ferrate (II) semi-permeable membrane. The inner and outer filling mass comprises from 30 to 60% by weight of amorphous silica, and from 100 to 120 cm ^{3 of} glycerol per kg of dry matter and from 20 to 25 g of gypsum.

Also described is a system consisting of Cu / saturated CuSO ₄ solution: Endre Makáry-Dr. Endre Vámos, Chapter 10 of the book entitled 'Corrosion protection of underground metal structures', entitled 'Determining and measuring the potential of metal structures in soil'.

Cu-CuSO ₄ and Zn-ZnSO ₄ half-cells are reported in the Measurement of Polarized Potentials in Concrete Bridge Decks. Fromm HJ (Rés. Dev. Div., Ontario Minist. Transp. Commun., Downsview. ON Can.) Transp. Gap. Rec. 1978, 672, 23-8 (Eng), disclosing that carbon rods and Cu-CuSO ₄ and Zn-ZnSO ₄ semicells were tested and found to be the most reliable, most accurate carbon rods. Cells containing metal salts gave variable results.

DE 30063 350 discloses an external electrode arrangement for measuring the potential between a working electrode and a reference electrode. The inside of the electrode in the container is just a Teflon inner housing with an electrolyte (eg KC1) in the lower hollow space containing diatomaceous earth, asbestos or ZrO ₂ . This inner housing or electrolyte is connected by a tube of diatomaceous earth insulating material to the interior of the outer housing formed outside the container, which also contains electrolyte. Into this electrolyte-filled space extends an electrode having a helix-shaped silver wire with an AgCl coating. The electrode can be attached to the container with a threaded extension.

This reference electrode is suitable for controlling high temperature (275 ° C) and high pressure (68.6-75.5 bar) containers.

The disadvantages of these reference electrodes are their complicated design - special containers made of glass, ceramics, their electrolytes requiring dangerous, regular treatment, etc. - on the other hand, because of their difficult and often impracticable incorporation, e.g. They result from their ability to be embedded in concrete and their narrow applicability temperature range. Because of all these difficulties, these reference electrodes cannot provide a durable galvanic cell that is capable of continuous operation even at high temperatures for many years.

It is an object of the present invention to provide a reference electrode which can be incorporated into concrete, closed and open tanks, even pressurized, without requiring any subsequent treatment, at the same time as the structure, or in a simple manner, particularly steel reinforced concrete, Development of a reference electrode with high mechanical tolerance, reliably stable over a wide range of conditions, for the control of external, internal cathodic protection of pipelines and tanks for continuous measurement over years and for corrosion testing.

The present invention relates to a reference electrode for cathodic protection of metallic structures having an electrode terminal attached to an electrode. The electrode is formed of a Mo / MoO ₃ rod to which a binder is attached to the electrode outlet, the electrode outlet and a portion of the electrode being electrically insulated with a tube and tube-filled insulating layer, and the electrode is 0.05-0.2 wt% Mo / Mo0 ₃ powder mixture containing concrete.

The structure of the reference electrode according to the invention is illustrated in Figure 1.

In the construction of the electrode, a metal capable of producing a second kind of electrode is used. Molybdenum is most suitable for this purpose. For an electrode (1) formed of a suitable size Mo / MoO ₃ rod or other piece (eg strip), [MoO ₃ layer (2) is located on the surface of the Mo rod] by chemical or electrochemical bonding (3), welding, metal shrinking or otherwise there is a fixed (4) electrode outlet. To insulate the joint, a portion of the electrode (1) or electrode (4) outlet is surrounded by the plastic tube (5). Inside the plastic pipe (5), the gap is filled by the filling insulating layer (6), sealing the joint. The uninsulated active part (7) of the electrode (1), the plastic pipe (5) and a part (8) of the uninsulated end (8) of the electrode outlet (4) are surrounded by a porous ceramic concrete cover (9).

HU 207 180 Β

This reference electrode is implemented as follows. It is known from electrochemistry that many metals and their poorly water-soluble oxides - in our case Mo and oxide -

MoO ₃ + 3 H ₂ O + 6e '; = 5t Mo + 6 OH ~ produces an electrode potential which is reliably constant under certain conditions - given temperature and pH. Therefore, to achieve a reliable stable electrode potential, a suitable layer (2) of MoO ₃ (5) to 15 µm thick must be formed on the surface of the Mo rod. By chemical and / or electrochemical means, the shielded electrode lead (4) is fixed to the electrode (1) (rod, plate, etc.) by means of metallic contact (soldering, welding, spot welding). This metallic connection is insulated from the surrounding area by an electrically insulating plastic tube (5), and the gap is sealed with silicone rubber or epoxy resin or other insulating material. The electrode thus assembled is conveniently placed in a mold and poured with concrete. When embedding the electrode (1) in the concrete, considering that the concrete sheath is also an integral part of the electrode, proceed as follows. From Portland cement 500 and 0 0.2 mm grit sand blends to 200 grade concrete, 0.05-0.2% by weight of MoO ₃ the powder mixture and the electrode head inserted into the mold with the homogenized plastic mixture. For the preparation of the concrete, an aqueous solution saturated with Ca (OH) ₂ is used so that the concrete is ca. Within one month of setting, the electrode potential should stabilize within a shorter period of time. Preferably, the concrete is allowed to cure in a solution saturated with Ca (OH) _{2 for} 3 to 4 weeks and then stored in the same solution until use or incorporation into the structure. Verify the functionality of the finished electrode when connected to known reference electrodes in a galvanic cell by measuring the resulting electromotive force.

A large number of studies show that when coupled with a saturated mesh electrode to a galvanic cell using room temperature saturated Ca (OH) ₂ as the electrolyte, the electromotive force-time diagram shown in Figure 2 is obtained during the concrete setting time. As can be seen, the electromotive force stabilized at 610630 mV at 25 ° C within 1 month of completion of the concrete bonding process, after which it remained unchanged for months. Considering the standard electrode potential of the saturated quartz electrode is 242 mV - the electrode potential of the Mo / MoO ₃ electrode prepared under the above conditions at -380 ± 10 mV in saturated Ca (OH) ₂ solution.

The advantageous property of the reference electrode according to the invention, as compared to the previous ones, is that it does not contain any toxic material and therefore it can be used advantageously where the Cu / CuSO ₄ , Hg / Hg ₂ Cl ₂ electrodes are not (e.g. ).

Claims (2)

A reference electrode for cathodic protection of metallic structures, which is provided with an electrode terminal attached to an electrode, characterized in that the electrode (1) is formed of a Mo / MoO ₃ piece to which an electrode terminal (4) is fixed with a binder (3). ) and a portion of the electrode (1) is surrounded by an electrically insulating tube (5) and an insulating layer (6) that fills the tube (5) and the concrete (0.05-0.2% by weight Mo / MoO ₃ powder mixture). (9) is wrapped. A reference electrode according to claim 1, characterized in that the electrode is rod-shaped.