FI101427B - Procedure and measurement sensor for corrosion control - Google Patents

Description

1 101427

Method and measuring sensor for corrosion monitoring

The invention relates to a method for controlling corrosion, which method is set out in the preamble of appended claim 1. The invention also relates to a measuring sensor for carrying out the method, which sensor is shown in the preamble of the appended claim 6.

In environmental measurements, there is clearly a need to find an inexpensive method for monitoring the general state of the environment. Acceleration of corrosion is one of the characteristics of environmental degradation. It is also an indicator with immediate observable impact and great economic significance. To date, efforts have been made to monitor corrosion indirectly by measuring the concentration of corrosive substances in a controlled site. The effect of such substances is difficult to predict, and certainty about the existence of corrosion conditions is usually only obtained by visually observing the effect of corrosion on the object. Until now, there has been no method for real-time monitoring of corrosion conditions, which would provide information on the change of conditions in the corrosive direction at a sufficiently early stage, e.g. in industrial processes or sites where equipment may be affected by corrosion.

US-5327225 discloses a specially designed sensor based on fiber optics, with which e.g. corrosion by the SPR phenomenon 25. This possibility is shown in Example 5 of the publication with reference to Figure 12. However, the design of this sensor is only suitable for detecting one type of corrosion.

The present invention makes it possible to create a measurement method for simultaneously monitoring different corrosion phenomena, which is based on the corrosion phenomenon itself, is extremely sensitive, is able to detect corrosion: at a very early stage and is nevertheless inexpensive. The measuring sensor associated with the method is easy to construct from known components.

According to the invention, the corrosion monitoring method is characterized by what is set forth in the characterizing part of the appended claim 1, and the measuring sensor for monitoring the corrosive properties of the environment is characterized by what is set forth in the characterizing part of the appended claim 6. The method takes advantage of the surface-plasmon resonance (SPR) phenomenon, which changes under the influence of corrosive conditions on several metal films on the same substrate 5 placed side by side on the same substrate, each with its own detector. The corresponding measuring sensor may comprise an optically transparent, thin glass or plastic plate on the surface of which several separate, thin metal films have been vaporized. In addition, there may be other metal films on top of the metal film on the surface of the plate, i.e., the metal film may be a multilayer film, or dielectric films (e.g., a polymer film) to form a layered film structure. The structure of the well may resemble the structures in a controlled object, for example if the object has metal parts, the metal film may be the same metal, and if the object has plastic, lacquer or paint coatings, the dielectric layer on the metal film 15 may be the same plastic, lacquer or paint. material.

For other preferred embodiments of the invention, reference is made to the appended dependent claims and the following description.

20

The invention will be described in more detail below with reference to the accompanying drawings, in which Figure 1 shows the principle of SPR measurement, whereby Figure 1a) observes the so-called Kretschmann configuration, and Fig. 1b) shows a resonance curve, Fig. 2 shows a simulated SPR resonance curve, Fig. 3 is an example of a curve fitting, Fig. 4 shows a simple technical implementation of a sensor according to the invention, Fig. 5 shows different sensor options, Fig. 6 shows a circuit board integrated sensor implementation to be installed, and 3 101427 Figure 7 shows an optical probe as one of the sensor options.

Figure 1 illustrates the optical surface plasmon resonance technique used in the measurement. In the measurement of corrosion conditions, a measuring layer 1, which may be a layered structure comprising different films, is placed on a controlled object so that its surface is exposed to possible corrosive conditions. The well structure always has a metal well 2 with a thickness d of the order of tens of nanometers, e.g.

10 at 50 nm. The metal film is attached to one side of the optically transparent body 4. The optically transparent body 4 may consist of a transparent plate to be described later and a prism of the same material, with one side of which the plate is placed in contact using a suitable index 15 matching oil. The prism can be any suitable prism structure used in the SPR technique. Of course, the metal film can also be made directly on the surface of the prism, but the plate is easier to replace. Through the prism, a p-polarized light beam is directed through the sensor plate to the metal film 2 on its surface. The prism is dimensioned so that the light from the interface of the me-20 stable film 2 and the transparent body 4 is completely reflected back to the prism. At a given wavelength of light and the value of the incident angle Θ, the surface plasmon resonance is observed, whereby the reflected light disappears. In addition to the wavelength of light and the optical properties of the media, this resonance depends essentially on the thickness d of the metal film 2 and the dielectric constant (metal material). In this case, all the energy of light is transferred to an electromagnetic wave propagating in the plasma formed by free electrons in the metal. The so-called resonance phenomenon the eva-nescent electric field extends from a metal surface to only a few hundred to 30 nanometers. The Evanescent field sees a reaction in or in the immediate vicinity of the metal, such as ‘·’ surface oxidation or a change in the dielectric layer 3 on the metal film 2, because it represents a certain change in the refractive index. The changes in the well structure 35 of the measuring layer 1 are measurable from the reflected light, because the resonance (loss of light) shifts to another value of the incident angle. In this case, the changes can be monitored simply by measuring the changes in the reflected light. If the light reflected from the film is measured 101427 as a function of the angle of incidence of 4 light, the so-called SPR resonance curve (Figure 1b). The position of the curve changes and changes in its shape (resonance width, depth) occur if the structure of the metal film 2 or the dielectric layer 3 on it changes.

5

The surface plasmon resonance method is very sensitive and can detect nanometer-sized changes in thickness in the metal film or in the dielectric layer on top of it. Figure 2 shows a simulated gold well resonance curve in a liquid and the changes that occur when a dielectric material is deposited on the film. By fitting the resonance curve calculated from the theoretical model to the measured resonance curve, the thicknesses of different layers, the real and imaginary part of the dielectric constant (absorption coefficient) and the roughness of the interfaces between the layers can be calculated in layer structures consisting of several films. Figure 3 shows an example of a curve fitting.

As shown in Fig. 4, the sensor construction can be very simple, including a plastic prism coated with a metal film 2, which acts as an optically transparent body 4, an LED light source 5, a polarizer 20, and a photodiode acting as a detector 7. The detector receives light reflected through a metal foil (measuring beam M) and has an interface 8 to a recording device 9 for recording measurement data. By means of the reflecting surface 10 transmitting part of the light, the reference beam R passing from the light source 5 through the polarizer 6 is directed to the reference detector 11, 25 which has a connection 12 to the recording device. The power consumption of the power supply 13 can be made very small, because the measurement requires only one short pulse of light and the measurement can be done, for example, only once a day or a week. The dashed line in the figure illustrates the interface in the body 4, which is created by using a separate plate attached to a prism 30.

· ‘The method can also be easily used for continuous monitoring or alarm applications. It is possible to monitor and obtain real-time information about changes in the conditions of the monitored object. In such an application 35, the measuring layer 1 on the sensor is continuously measured. For example, if changes occur in the floor that exceed preset limits, an alarm is issued. Figure 4 shows a display device or alarm device 14, p. 101427, connected to the recording device 9, from which measurement results can be read or which gives an alarm with certain measurement results.

Figure 5 shows the structure of the sensor plate 5 to be attached as part of the transparent body 4. A thin metal film 2 is formed on the surface of the optically transparent thin glass or plastic plate 4a. It can also be seen that the same sensor may comprise several thin metal films 2 adjacent in the plane of the plate 4a (e.g. copper well, gold well, tinned copper well, steel film, etc.). In this case, the light propagating from the light source can be collimated I. paralleled by means of collimating optics, whereby the parallel rays hit the entire area of the plate. The prism structure under the plate 4a can then consist of one large prism or a series of small prisms. For example, when using the strip of Fig. 5a in which the films 2 are in succession in one direction, the corresponding prism structure may be located parallel (shown in broken lines) so that its cross section in a plane perpendicular to this direction is constant. When a plate with several rows of membranes 2 (Fig. 5c) is used, there may correspondingly be elongate prism structures parallel to the rows below it. Each membrane 2 has its own detector 20, i.e. in the case of Fig. 5a a row of detectors and in the case of Fig. 5c a 2-dimensional detector mat rice. In addition, the metal film on the surface of the plate may have one or more dielectric films 3 (e.g. a plastic film), whereby a layered structure according to Fig. 5b is formed.

25

The sensor according to the invention is placed in a controlled state so that the gaseous substances causing corrosion of the metal in the air as well as moisture come into contact with the metal films or other coatings on the surface of the plate. Air and its impurities (eg

30 SO2, ΝΟχ, water vapor) cause corrosion of metals and physical and / or chemical changes in dielectric layers.

•

The surface plasmon resonance method is a very sensitive method and can detect nanometer-scale thickness changes in the metal film 35 or on the dielectric layer 3 thereon. The method is therefore very suitable if it is desired to detect corrosion as early as possible or to detect changes in ambient conditions. However, the method can also be applied in such a way that it indicates when the corrosion has reached a certain limit. This can be done with a thicker metal film 2, the corrosion of which to a certain resonance-specific thickness triggers an alarm.

5

In order to control the effect of the substances in the medium on the metal, all metals with a negative dielectric constant (SPR metal) and which change under the influence of a corrosive substance are considered. Ho-10 pea, copper and aluminum are particularly suitable because they provide a very thin film. Iron may also be an issue. In addition to pure metals, suitable alloys containing SPR metals can also be used.

The SPR method has significant advantages over other methods for measuring the state of the environment. The SPR method directly measures corrosion from controlled materials. For example, the measurement of certain gaseous pollutants does not yet tell us anything about the corrosive conditions, but in addition to them, temperature and humidity should be measured and the probability of corrosion deduced from them.

20 SPR sensor is cheap. Its cost in its simple form is only a few tens of marks, and its implementation is comparable to the fire alarms in use. The equipment needed to measure gases is expensive and requires maintenance and calibration.

25

The sensor part can be integrated into a very small size. In principle, the whole device with its sensors and electronic components can be obtained in the size class of a standard 7-foot IC circuit as shown in Figure 6, including light source 5, optical parts and detector 7. In such an implementation, device 30 could be on a directly monitored cabinet or electronic circuit board. the connections (power to the LED light source and signal from the detector) can be arranged via the connection pins. The light can also be connected to and brought from the prism using optical fibers as shown in Figure 7. In this case, the measuring head 14, 35 itself, which is connected to the part 15 comprising the light source and the detector by means of a connecting cable 16, can be made very small and made to fit even in cramped spaces (e.g. inside motors). As a fully optical structure, it is not sensitive to electrical interference.

7 101427

The effect of corrosive properties on thin well structures can be studied in many different ways. An optically transparent body comprising a measuring layer 1 or a part thereof, such as a sensor plate, can be exposed to the environment by exposing it for a certain time, for example so that gaseous substances in air and moisture come into contact with metal films or dielectric coatings on the plate. Air and its impurities (eg SO2, ΝΟχ) cause corrosion of metals and physical and / or chemical changes in the dielectric layer. The dielectric layer can also act as a filter so that it releases only a certain or certain impurities to the surface of the metal where corrosion occurs.

In addition to the gaseous medium, the optically transparent body or part thereof comprising the measuring layer 1, such as a sensor plate, can also be placed in a liquid medium such as tap water, wastewater or process liquid, whereby the corrosive substances affect the metal layers or dielectric layers in the sensor or sensor plate. The invention can be used by contacting the measuring layer 20 with a controlled medium whose information on the actual effect of the substances is desired.

Also, the light sources do not need to be in constant optical contact with the metal foil. The measuring layers with their substrates can be taken to the objects to be examined or placed on different sides of the object to be measured without optical coupling. Prior to exposure, all membranes are examined. The properties of the metal films and / or other layers (e.g., thickness, dielectric constant, surface roughness) are measured by the SPR method, and the data obtained are stored. After exposure, the properties of the membranes are re-measured and compared to the values measured before exposure. Based on the values, it is possible to find out how the membranes have changed. It is seen, for example, whether the film is corroded (change in thickness and / or surface roughness), whether an additional layer has formed (e.g. an oxide layer, such as on an aluminum surface), or whether any layer has disappeared. Based on this, information is obtained as to how different metals and layer structures have reacted. For example, comparing the changes in the measurement layers located at different sites reveals relative differences related to the quality of the environment (amount of corrosive substances).

101427 8 In this context, the words "corrosion" and "corrosive" are to be understood broadly and refer to any permanent change in the structure of the measuring layer 1 caused by substances in the monitored medium, most commonly corrosion and / or oxidation due to reaction of the substances with the measuring layer material. The materials of the measuring layer do not have specific binding sites formed specifically on the surface, but are ordinary structural materials forming chemically uniform layers, and differ in this respect from immunological assays, which aim to detect the presence of a specific component in a well-defined sample by specific biological binding.

It is quite possible that certain corrosive substances can also be identified and even quantified from chemical changes in well structures. A suitable method, such as fuzzy logic, character recognition, or a neural network-type learning algorithm, can be used to analyze changes in membranes.

Claims (12)

A method for corrosion monitoring, which continuously or at certain intervals measures a quantity dependent on corrosion conditions with a meter placed on a controlled object, the measurement being performed using surface plasmon resonance (SPR) by measuring the corrosion conditions on the metal film (2). effect of the change caused by the metal membrane (2) on the surface plasmon resonance phenomenon of the light reflected, characterized in that the method uses several adjacent metal films (2) on the same substrate, from which the reflected light is received by a separate detector for each film. Method according to Claim 1, characterized in that a metal is used as the metal film (2) on which a dielectric layer is formed under the influence of the controlled corrosion conditions, the formation of this layer being detected by a change in the surface plasmon resonance phenomenon. Method according to Claim 1, characterized in that the metal film (2) used is a metal which undergoes thinning and / or a change in surface roughness under the influence of controlled corrosion conditions, these surface changes being detected by a change in the surface plasmon resonance phenomenon. 25 Method according to Claim 1, characterized in that the metal film (2) is coated with a dielectric layer (3) which undergoes physical and / or chemical changes as a result of controlled corrosion conditions, these layer changes being detected by a change in the surface plasmon resonance phenomenon. Method according to Claim 1, characterized in that the metal film (2) is coated with a dielectric layer (3) which emits impurities under controlled corrosion conditions to the surface of the metal film (2) acting as a filter, the changes in the metal film (2) caused by these impurities being detected. through a change in the surface plasmon resonance phenomenon. 10 101427 A measuring sensor for corrosion monitoring arranged to mow continuously or at certain intervals a quantity depending on the corrosion conditions, the sensor comprising a measuring layer (1) comprising a metal film (2) which is susceptible to corrosion conditions and in which a change due to corrosive conditions is expected , an optical source (5) of the optically transparent body (4) to which the measuring layer is attached is directed from the side of the optically transparent body (4) toward the metal film (2), the light source wavelength, light angle and quality of the measuring layer being selected so that the metal film (2) surface light resonance phenomenon occurs in light reflected through at least some of the conditions expected in the application of the measuring sensor, a detector (7) arranged to receive light reflected through a metal film, and a detector (20) from the detector (9) for recording the measurement results of the detector, characterized in that the sensor has several adjacent metal foils (2) on the same substrate, each with its own detector. 25 Measuring sensor according to Claim 6, characterized in that the measuring layer consists of a bare metal film (2). Measuring sensor according to Claim 6, characterized in that the measuring layer (1) comprises a metal film (2) and a dielectric layer (3) arranged on it. Measuring sensor according to one of the preceding claims 6 to 8, characterized in that the measuring layer (1) is fixed to the surface of the optically transparent plate (4a) which can be fastened on the opposite side to form an optically transparent body (4) assembled on the second optically transparent body. 11 101427 9 101427 Measuring sensor according to one of Claims 6 to 8, characterized in that it is integrated in a component with connection legs which is arranged on a circuit board. 5 Measuring sensor according to one of Claims 6 to 8, characterized in that the measuring layer (1) and the optically transparent body (4) are arranged at a measuring head (14) which communicates with the light source and the detector via an optical fiber connecting cable (16). 12 101427