GB2244810A - Electrochemical test cell for use on surfaces. - Google Patents

Abstract

The cell comprises a cell body which is generally closed but has an aperture 11 in a generally flat face 10 of the body, an electrolyte 13 distributed in a solid or semi-solid absorbent medium, for example gelatine, located within the cell body and exposed at the aperture, an electrode 7 extending from the electrolyte outwardly through the cell body for connection of an electrical lead, and means, for example an adhesive medium 14 for removably attaching the generally flat face to a surface under test. The cell body may be formed of two parts 3, 4 preferably of polyethylene, which snap-fit together. The cell may be used for measurement on exposed metal surfaces of structures such as bridges and oil rigs. <IMAGE>

Description

Test Cell.

The present invention is a cell suitable for use in carrying out electrochemical analyses.

In numerous situations it is necessary to carry out electrochemical tests on exposed surfaces of materials in situ at their place of use. Fbr example, it may be necessary regularly to monitor the condition of exposed metal structures such as bridges, oil rigs and the like, so that any deterioration may be detected at an early stage. Electrochemical tests require the construction of an electrochemical cell in which the metal under test fonts one of the electrodes and therefore such testing of metals in situ requires a cell to be constructed upon the exposed metal surface.Typical existing procedures involve gluing a glass tube to the surface under test, filling the tube with electrolyte and then inserting into the electrolyte a reference electrode and a counter electrode. Clearly this procedure is cumbersome and, because it is also time consuming, it is an unnecessarily expensive operation. However electrochemical tests of this type are reliable and informative and there is therefore a need for a more convenient method or apparatus for carrying out such tests.

It is an object of the present invention to provide an Improved electrochemical cell, whereby analyses of this type may be carried out more conveniently and quickly than using the method described above.

The e improved cell according to the invention oamprises a cell body which is generally closed but has an aperture in a generally flat face thereof, an electrolyte distributed in a solid or semi-solid absorbent medium located within the cell body and exposed at said aperture, an electrode extending from contact with said electrolyte outwardly through said cell body for connection of an electrical lead to the exposed part of said electrode, and means for removably attaching said generally flat face to a surface under test.

As will became apparent, the improved cell of the present invention may be made compact and easily portable and may be used conveniently and quickly by attaching it to the surface of the material under test, attaching the necessary electrical connections and carrying out the desired electrochemical test by a conventional procedure.

The cell body may conveniently be formed in two or more parts to nake the introduction of the electrolyte an easy operation and also to simplify its production and assembly. Thus it may comprise two moulded parts of a suitable non-conductive material, for example a synthetic polymeric material such as polyethylene. The two parts may be designed to be snap-fitted together after the electrolyte has been introduced, or may be secured together by plastics welding or by means of an adhesive.

The body or one of its parts may be moulded around the electrode or alternatively the body may be assembled around the electrode.

The cell body must have at least one generally flat face, since that face is placed in sealing engagement with the metal under test, but in other respects the body may have a wide variety of shapes, for example cubic, cylindrical or hemispherical. Thus the shape and dimensions of the cell body may be adapted to the shape and/or dimensions of the location in which it is to be used. In one preferred form, the cell body is a squat cylinder, preferably formed in two parts.

In the generally flat face of the cell body is an aperture by which the electrolyte is exposed in use. The aperture may be any desired shape, for example circular, elliptical, rectangular or in the form of an elongated slit Preferably the aperture is placed symmetrically in the generally flat cell face, for example centrally relative to a circular face.

The size of the cell body is not itself critical and its size may therefore be determined by convenience in handling. Good experimental results have been obtained with a cylindrical cell less than 1 an deep and about 4 to 5 an in diameter.

The electrolyte employed for incorporation in the cell is chosen according to the rature of the proposed electrochemical test. Thus the electrolyte may be an inorganic acid or any other compound conventionally used for this purpose. Such materials are well-known in the electrochemical art. In the cell according to the invention, however, the electrolyte is distributed in a solid or semi-solid absorbent medium. ror example, the medium may be a resilient permeable solid such as a sponge or a natural or synthetic permeable rubber or expanded plastics material. As one alternative, the medium in which the electrolyte is distributed may be a gel, for example gelatine, or some other jelly-like material.

The material under test, which in use is in contact with the electrolyte at the aperture, forms the first or working electrode and a second electrode is incorporated in the cell structure. This second electrode performs the two functions of both counter electrode by which the voltage across the cell is generated and also reference electrode which measures the cell potential. Preferably the area of this second electrode which is exposed to contact with the electrolyte is greater than, and more preferably at least twice, the area of the aperture in the generally flat face of the cell body.The electrode extends through the cell body from that part of the electrode which is in contact with the electrolyte to an exposed outer part by means of which it may be connected in the electrical circuit by which the cell potential is measured.

In use, the generally flat face of the cell is removably attached to the surface of the material under test. An appropriate adhesive medium is provided for this purpose.

In one form of the invention, the adhesive medium is a double-sided self-adhesive tape; such a tape may serve the additional purpose of sealing the aperture in the cell body until the cell is to be used, thereby preventing dehydration of the electrolyte during storage.

Conveniently, the whole cell assembly is sealed in a water-tight pack until required for use, to provide further protection against dehydration of the electrolyte while stored.

The invention will now be further described with reference to the accompanying drawings, which illustrate, by way of example only, one preferred embodiment of the electrochemical test cell according to the present invention and wherein: Fig. 1 is a sectional view of the cell; and Fig. 2 is a corresponding view of the cell in its position of use.

The body of the illustrated cell is formed in two parts 3, 4, which are moulded in polyethylene and are a snap-fit together by virtue of an annular rib 5 in the lid part 3 engaging a corresponding annular groove 6 in the part 4. The two body parts may be further secured together by adhesive. A lead electrode 7, which takes the form of a disc 8 with an upstanding contact boss 9, is secured in the part 3 and extends as shown through that part.

The lower face 10 of the body part 4 is generally flat in its unstressed state, as shown in Fig. 1, but has a circular aperture 11 therein, which is defined by a sharp circumferential edge 12 which stands proud of the face 10.

The interior of the cell is filled with an electrolyte 13 which is distributed in a gelatine medium. The aperture 11 is sealed, until the cell is to be used for test purposes, with a double-faced self-adhesive tape 14.

Preferably the whole cell assembly is supplied and stored in a sealed water-tight pack, from which it is removed when a test is to be carried out. The whole assembly is sufficiently cheap and simple in construction for it to be discarded after the test.

When the test is to be carried out upon a fixed workpiece 15 (Fig. 2) or on a test sample, the tape 14 is drawn back to expose the aperture 11 but is used to secure the cell to the workpiece as shown. Because the edge 12 stands proud of the adjacent surface of the cell, the body part 4 is deflected inwardly in the region of the aperture and the electrolyte 13 is thereby forced into intimate contact with the workpiece 15 within the area of the aperture 11. When an electrical circuit is now connected between the boss 9 and the workpiece, the area of the workpiece facing the aperture 11 acts as the working electrode and the electrode 7 functions as both counter electrode and reference electrode for monitoring the cell potential.

In one typical use of the illustrated test cell, the electrolyte 13 was a mixture of sulphuric acid and potassium thiocyanate, distributed in a gelatine medium.

The cell was used to carry out an electrochemical test, the so-called potentiokinetic reactivation or PKR test, on a welded austenitic stainless steel joint to measure its degree of sensitisation to weld decay.

Claims (15)

ClAIMS

1. An electrochanical test cell comprising a cell body which is generally closed but has an aperture in a generally flat face thereof, an electrolyte distributed in a solid or semi-solid absorbent medium located within the cell body and exposed at said aperture, an electrode extending from contact with said electrolyte outwardly through said cell body for connection of an electrical lead to the exposed part of said electrode, and means for removably attaching said generally flat face to a surface under test.

2. A test cell as claimed in claim 1, wherein the cell body is formed in two or more parts.

3. A test cell as claimed in claim 2, wherein the parts of the cell body are a snaps it together.

4. A test cell as claimed in any of the preceding claims, wherein the cell body is of polythene.

5. A test cell as claimed in any of the preceding claims, wherein the cell body or a part thereof is moulded around the electrode.

6. A test cell as claimed in any of the preceding claims, wherein the cell body is a squat cylinder.

7. A test cell as claimed in any of the preceding claims, wherein the aperture is placed symnetrically in the generally flat face of the cell body.

8. A test cell as claimed m any of the preceding claims, wherein the absorbent medium is a resilient permeable solid.

9. A test cell as claimed in any of claims 1 to 7, wherein the absorbent medium is a gel.

10. A test cell as claimed in any of the preceding claims, wherein the area of the electrode exposed to contact with the electrolyte is greater than the area of the aperture.

11. A test cell as claimed in claim 10, wherein said area of the electrode is at least twice the area of the aperture.

12. A test cell as claimed in any of the preceding claims, wherein the means for removably attaching the generally flat face of the cell body to a surface under -test comprises an adhesive medium.

13. A test cell as claimed in claim 12, wherein said adhesive medium is a double-sided adhesive tape.

14. A test cell substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

15. An electrochemical test cell as claimed in any of the preceding claims, sealed in a water-tight pack.