Electrochemical cell, use of the electrochemical cell, and method for electrolytically contacting and electrochemically influencing a surface

Abstract

An electrochemical cell for electrolytically contacting and electrochemically inspecting surfaces which makes electrolytic contact with the surface through a body utilizing capillary action. The capillary force between surface and body utilizing capillary action prevents the electrolyte from escaping from the cell without the use of a sealing ring. The body utilizing capillary action allows the electrolyte to flow from an open porous container and wet the surface when the electrochemical cell contacts the surface. Escape of material from the open cell is prevented by the capillary action of the container and of the tip when the electrochemical cell is lifted from the surface. The electrochemical cell is independent of the force of gravity and enables measurements to be made on surfaces of any orientation. The electrochemical cell may be used to perform a multiplicity of electrochemical investigations and processes. The electrochemical cell may be moved over the surface continuously, thereby allowing electrochemical investigations or processes to be performed with lateral resolution. Due to the use of a maintenance-free reference electrode, the electrochemical cell may prefabricated commercially in complete form and stored for extended periods of time after closing.

Description

[0001] The invention relates to an electrochemical cell for electrolytically contacting and electrochemically inspecting surfaces according to the preamble of the first claim.[0002] The invention further relates to an application of the electrochemical cell according to the preamble of the independent method claim.[0003] The invention further relates to a method for electrolytically contacting and electrochemically modifying a surface according to the preamble of the independent method claim.PRIOR ART[0004] Essentially, there are two types of electrochemical cells which are used for electrochemically inspecting surfaces. With one cell, the surface to be examined is immersed in an electrolyte. The advantage here is that even rough or uneven surfaces may be electrochemically examined. The disadvantage is that only the surfaces of small components may be examined, since larger ones would require a large quantity of electrolyte. Selective examination of specific regions of a surface is ...

AI Technical Summary

Benefits of technology

[0011] The advantage of the invention is that the any escape of material from the electrochemical cell is prevented, with the use of a sealing ring, by the capillary action of the tip and of the container, and that the surface is wetted with a defined electrolyte simply by removing the cap and applying the tip. Since both the subsequent flow of the electrolyte to the surface and from the container to the tip is achieved exclusively by capillary action, the function of the electrochemical cell is completely independent of the effect of gravity. The result is that measurements can also be made on surfaces vertically oriented surfaces. In addition, it is easily possible to perform measurements in zero gravity. Since the container is open, atmospheric pressure also has no significant effect on the performance of measurements.

[0012] Since the cross-section of the tip is tapered toward the end and the container has maximum porosity, a large volume is available to conduct the electrolytic current in the container and in the tip. The ohmic voltage drop thus occurs only at the very end of the tip. As a result, any distortion of the measurement by the ohmic voltage drop can be minimized.

[0014] The use of a silver surface coated with silver chloride, or a silver surface, or a tungsten surface creates a very simple reference electrode which remains stable and completely maintenance-free for months at a time. There is no possibility of contamination of the electrolyte, such as occurs with most reference electrodes, by the saturated potassium chloride solution. The result is that the complete cell along with the electrolyte may be prefabricated. Operation is extremely simple and does not require a technician. No manipulation of the electrolyte is required. The entire procedure consists in the removal of the cap from the electrochemical cell and application to the examination surface. After use, the cap is replaced and the electrochemical cell is ready for the next use.

[0015] Since any escape of material from the electrochemical cell is prevented by the capillary action of the tip even without the tip's contacting the surface, the electrochemical cell is extremely simple to manipulate. It may, for example, be held in the user's hand and applied to the highly curved surface of any large component (computer chip, automobile, pipeline, etc.). Since the interface of the tip is only at a single point, or the tip conforms elastically to the surface, any type of curved surface geometries may be examined. When a sealing ring is used, the surface must allow for a circular interface of the sealing ring, a fact which results in certain requirements in terms of flatness or surface radius. The surface of the component is wetted locally with electrolyte, thus allowing electrochemical investigations of local resolution. This type of simple operation was previously impossible using conventional electrochemical cells for large components with complex geometries and vertically oriented surfaces. With the invention, for example, the quality of a welding seam on a pipeline may be easily inspected without having to cut out the welding seam, grinding it flat, and inserting it into a classic cell. Thanks to the invention, it is therefore possible to conduct electrochemical investigations in a standardized routine fashion as a nondestructive test method in quality assurance, research, etc. Since no measures related to sealing, such as sealing rings, are required, the tip may be moved continuously along the surface, thereby allowing for simple electrochemical inspection of large surfaces with local resolution. Multiple sequential spot measurements are also easily performed. The electrochemical cell may be employed for a multiplicity of electrochemical investigations and processes. After completion of the electrochemical modification, the electrochemical cell is simply lifted from the surface and closed. When lifted, any escape of material from the cell is prevented by the capillary action of the tip. The electrochemical cell may be stored for long periods in a closed condition and used at any time without any preparatory efforts. This means a great savings in time when conducting electrochemical measurements. In addition, the electrochemical cell may be commercially prefabricated complete and ready to use, thus enabling its use in a standardized routine manner.

[0016] During prolonged measurements, the electrolyte is able to evaporate at the tip, thus leading to an increase in concentration. This may be prevented by surrounding the tip by a jacket. A high level of humidity is quickly established within the jacket which prevents any further evaporation. As a result, prolonged measurements may be performed with the electrochemical cell. The jacket may also be provided with additional functions. It may, for example, be composed of a conductive material, thereby creating an electromagnetic shield for the cell or the conductive contact with the surface. By additionally utilizing a spring, the jacket may also be used to ensure a constant application pressure. This feature enhances the reproducibility of measurements and the useful life of the tip.

[0017] Due to its porous structure, the tip prevents any convection of the electrolyte. For processes which are controlled by mass transfer, such convection produces poor reproducibility and prevents meaningful findings. In the tip, the subsequent transfer of the initial constituents for the electrochemical reactions is controlled almost exclusively by diffusion. This means that reproducible results are obtained. Use of the invention enables characterization of the mass transfer processes to be significantly improved.

Problems solved by technology

The disadvantage is that only the surfaces of small components may be examined, since larger ones would require a large quantity of electrolyte.

This method allows specific areas of the surface to be chosen selectively; however, the surface must be flat, and the size of the examined component is usually also restricted.

A significant problem with this type of cell is the gap created between the sealing ring and the surface.

In this gap, electrochemical inspection is possible only to a limited degree.

In addition, this gap is the site in which crevice corrosion tends to occur.

The sealing ring therefore results in undesirably uneven performance.

However, since a microscope is used here to apply the capillary, here as well the size of the examined component is limited.

The fabrication and handling of capillaries is also expensive and ill-suited for industrial use.

In addition, the problem of the sealing ring remains unsolved.

The result is that the saturated potassium chloride solution is able to remain in contact with the electrolyte, and any diffusion between the two bodies is limited.

Over time, however, the potassium chloride will escape from the reference electrode and contaminate the electrolyte.

This occurrence is especially undesirable during corrosion investigations since chlorides are extremely aggressive.

This preparation of the cell requires considerable care since even very small air bubbles may prevent contact between the reference electrode and electrolyte.

Faulty measurements, or even destruction of the examined surface, may result from this.

The closed cell also entails problems with atmospheric pressure since the electrolyte is forced back through the porous wall in response to fluctuations in pressure, or is drawn out of the cell.

If the cell is open, however, gravity causes the electrolyte to escape, unless extremely fine pores are used to prevent this.

However, the fine pores cause an ohmic voltage drop which affects the measurement.

It is not possible, or is possible only with great difficulty, to apply cells used previously to vertically oriented surfaces.

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