Corrosion measuring device
阅读说明:本技术 腐蚀测量装置 (Corrosion measuring device ) 是由 Z·A·卡恩 H·纳齐尔 A·萨伊德 于 2018-11-21 设计创作,主要内容包括:用于检测物体(216)的涂层(250)的腐蚀的设备(200),该设备包括:导电的主体(202),其限定了用于容纳电解质(206)的腔(204),该主体(202)布置成在使用中与该物体(216)导电接触,并且布置成在使用中将电解质(206)与物体隔离;以及位于腔(204)内的第一电极(208),该第一电极(208)用于与恒电位仪(402)或恒电流仪电连接,并且被布置成在使用中与腔(204)中的电解质(206)电接触;其中,该主体(202)包括第一部分(222)和第二部分(224),该第二部分(224)能够相对于该第一部分(222)在缩回位置和延伸位置滑动地移动。(An apparatus (200) for detecting corrosion of a coating (250) of an object (216), the apparatus comprising: an electrically conductive body (202) defining a cavity (204) for containing an electrolyte (206), the body (202) being arranged to be in electrically conductive contact with the object (216) in use and arranged to isolate the electrolyte (206) from the object in use; and a first electrode (208) located within the cavity (204), the first electrode (208) for electrical connection with a potentiostat (402) or galvanostat and arranged to be in electrical contact with the electrolyte (206) in the cavity (204) in use; wherein the body (202) comprises a first portion (222) and a second portion (224), the second portion (224) being slidably movable relative to the first portion (222) in a retracted position and an extended position.)
1. An apparatus for sensing an electrochemical change in an object, the apparatus comprising:
a substantially electrically conductive body defining a cavity for containing an electrolyte, the body having a first surface arranged, in use, to be in electrically conductive contact with the object along substantially the entire length of the first surface and being physically arranged, in use, to isolate the electrolyte from the object; and
at least a first electrode located at least partially within the cavity, the first electrode for connection to a potentiostat or galvanostat and arranged to be in electrical contact with an electrolyte in the cavity in use;
wherein the conductive body comprises at least a first portion and a second portion slidably movable relative to the first portion from a first retracted position to a second extended position such that a length of the first surface is greater when the second portion is in the second position than when the second portion is in the first position.
2. The apparatus of claim 1, wherein the first and second portions are substantially tubular and arranged such that at least a first of the portions is radially within the other when the second portion is in the first position.
3. The apparatus of claim 1 or 2, wherein the body is arranged to hold electrolyte in substantially any orientation of the body.
4. The apparatus of claim 2 or 3, wherein each of the first and second portions comprises a substantially closed end distal to the other portion.
5. The apparatus of any of the preceding claims, wherein the apparatus further comprises an electrolyte contained by the chamber; a potentiostat or galvanostat electrically connected to the first electrode; and an electrical connector arranged to be electrically connected to the object.
6. Apparatus according to any one of claims 1 to 5, wherein the body comprises at least one magnet arranged, in use, to apply a magnetic force to the object, thereby attaching the body to the object.
7. The apparatus of claim 5, wherein the electrically conductive body is a permanent magnet.
8. A system for sensing an electrochemical change in an object, the system comprising:
the first device of any one of the preceding claims, wherein the first electrode is a counter electrode; and
the second device of any of the preceding claims, wherein the first electrode is a working electrode.
9. The apparatus of any one of claims 1 to 8, wherein the apparatus further comprises a substantially electrically conductive cover on at least a portion of the first surface, the substantially electrically conductive cover being arranged to conduct electricity between the first surface and an object in use.
10. Apparatus according to claim 9 when dependent on claim 2, wherein the cover is arranged on a second part of the second part which is not radially within the first part when the second part is in the first position.
11. The device of claim 9 or 10, wherein the cover is arranged to be in a first state when the second portion is in the first position and in a second state when the second portion is in the second position, wherein the second state is extended relative to the first state.
12. The apparatus of claim 11, wherein the covering is a mesh, folded material, or coil arranged to extend or compress, or both.
13. The apparatus of any preceding claim, wherein substantially all of the body is substantially electrically conductive.
14. The apparatus of any preceding claim, wherein the body comprises a first tube and a second tube in fluid communication with the cavity, the first tube being arranged for introducing electrolyte into the cavity, the second tube being arranged to allow air to escape from the cavity.
15. The apparatus of claim 14, wherein the first tube extends further into the lumen than the second tube.
Technical Field
The present invention relates to a device and a system for sensing electrochemical changes in an object. In an embodiment, it relates to an electrochemical cell device. In other embodiments, it relates to a system comprising the apparatus.
Background
It is often desirable to be able to accurately detect electrochemical changes in certain objects. Detecting electrochemical changes in the object may, for example, help determine maintenance requirements of the object. For example, if a significant electrochemical change is detected in the object, it may be determined that a protective coating needs to be applied or reapplied to the object, or that a portion of the object needs to be replaced. If no significant electrochemical change is detected in the object, it can be determined that maintenance is not required. Parts of various structures (e.g., pipelines, automobiles, aircraft, and oil drilling platforms) are subjected to electrochemical change testing to determine maintenance requirements.
Errors in the detection of electrochemical changes in an object can result in over-maintenance or under-maintenance. For example, in the event that a significant electrochemical change is falsely detected, a protective coating may be unnecessarily applied or reapplied to the object, or a portion of the object may be replaced, when the object has not actually undergone a significant electrochemical change. In the event that the measurement of the electrochemical change is not detected, although the object is actually undergoing such a change, even if appropriate maintenance is required, the appropriate maintenance may not be performed.
One method of detecting electrochemical changes in an object is by the Linear Polarization Resistance (LPR) technique.
Another method of detecting electrochemical changes in an object is by performing Electrochemical Impedance Spectroscopy (EIS). In EIS, an alternating potential is applied to an electrochemical cell and the response of the cell (its electrochemical impedance) is measured. The measured impedance, in particular its frequency dependence, can be analyzed to determine whether an electrochemical change has occurred in the object. Specific examples of using EIS will be described in the detailed description section below.
EIS can be performed on virtually any object or system that can be modeled by an equivalent circuit. For example, EIS may generally be performed on an object composed of a metal substrate with a protective coating. Standard devices for performing EIS on such objects consist of electrochemical cells and potentiostats or galvanoscopes. An electrochemical cell consists of an electrolyte, a reference electrode, a counter electrode and a working electrode. The object (consisting of the metal substrate and its coating) acts as the working electrode.
The reference and counter electrodes are placed in an electrolyte, which is typically a solution that closely resembles the actual application environment of the material being tested. The electrolyte, reference electrode and counter electrode were placed over the coated sample (working electrode). All electrodes are connected to a potentiostat or galvanostat, or to an instrument that can act as a potentiostat or galvanostat. Potentiostats apply a potential between a reference electrode and a working electrode and analyze the response of the system to determine the electrochemical state of the system and how that state changes over time. A galvanostat controls the current between the working electrode and the counter electrode and measures the potential difference between the reference electrode and the working electrode.
There are two broad classes of devices for performing EIS: open electrochemical cells and sealed electrochemical cells. Each having a reference electrode, a counter electrode and an electrolyte (and a working electrode in the form of the object to be measured in use) as described above. In open electrochemical cells, the electrolyte is brought into direct contact with the object to be measured. An example of such an open electrochemical cell is shown in fig. 1 (a). As can be seen from this figure, the body of the cell provides a wall to contain the electrolyte, but no base. Instead, the base is provided by the object to be tested so that the electrolyte is in contact with the object to be tested. In contrast, in a sealed electrochemical cell, the electrolyte is not in direct contact with the object to be tested; instead, the walls of the battery body separate the electrolyte from the object to be tested. Both open and sealed electrochemical cells (of known form) have disadvantages.
Measurements made using open electrochemical cells may result in damage to the object being measured due to direct contact between the electrolyte and the object. Fig. 1(b) schematically illustrates this damage, and fig. 1(b) shows a schematic of the sample after testing with the open electrochemical cell shown in fig. 1 (a). Furthermore, open electrochemical cells can only be reliably used on substantially horizontal surfaces of objects. If the open electrochemical cell is secured to an angled surface, or a surface that faces substantially downward, of an object, electrolyte will leak from the cell. If the amount of electrolyte changes during the measurement due to electrolyte leakage, the resulting measurement will be unreliable.
The use of sealed electrochemical cells for measurements avoids the above disadvantages, but has its own disadvantages. For example, in existing sealed electrochemical cells, it is difficult to achieve good electrical contact between the cell body and the object to be measured. If there is an air gap between the battery body and the object to be measured, either the measurement cannot be made at all or the measurement will be inaccurate.
In order to improve electrical contact between the battery body and the object, the battery body may be fixed to the object using an adhesive. However, this leaves residual adhesive on the object after testing, which can promote undesirable electrochemical changes in the object. Furthermore, since the material properties of the adhesive do not generally match those of the object to be tested, this can lead to inaccuracies in the measurements made using such cells. Although such inaccuracies can be mathematically eliminated, such elimination is only approximate. Finally, since batteries containing electrolytes can be relatively heavy, they cannot be reliably secured to non-horizontal surfaces using adhesives because of the risk that they will fall off.
Open and sealed electrochemical cells also suffer from some disadvantages common to both types of cells.
First, to sense electrochemical changes in an object that has been coated with a protective non-conductive coating, some of the coating must be removed in order to make electrical contact with the object and thereby form a working electrode. This exposes a (usually small) area of the object to the environment and thus to further electrochemical changes, such as corrosion.
Second, while existing electrochemical cells for measuring electrochemical changes in an object may be used in laboratory applications, they may not be practical or even suitable for in situ measurements, particularly where the area to be analyzed is large. Conventional batteries, due to their small footprint, can typically only analyze a few centimeters of the object on which they are placed. This means that such conventional cells have limited use in large area analysis.
Although such sensors have a maximum theoretical sensing range of about 0.5m around the sensor, the accuracy of the sensing may decrease as the distance from the sensor increases. This may mean that a large number of sensors (or a large number of repeated measurements) are required to sense over a large area. There will also be "dead zones" between the sensed regions, since the sensed regions are approximately circular and therefore not subdivided.
To increase the sensing area using a smaller sensor, a conductive gel may be spread over the coating. Such gels, while relatively inert, attract salts or other corrosive particles and can act to stick them to surfaces even after the gel is wiped off. This may increase the electrochemical change in the object.
The use of larger sensors increases the area that can be tested, but larger sensors are not suitable for all applications. When it is desired to sense only a small area in a difficult to access location, a larger sensor may not be suitable because it may not fit in the available space. Even where the location is accessible, if only a relatively small area is of interest, the use of a larger sensor may result in a measurement that is processed for too long a time relative to a smaller sensor that may have been applied to the area of interest.
It is an aim of at least certain embodiments to address one or more of these issues.
Disclosure of Invention
[ first aspect ]
According to a first aspect of the present disclosure, there is provided an apparatus for sensing an electrochemical change in an object, the apparatus comprising: a substantially electrically conductive body defining a cavity for containing an electrolyte, the body being arranged in electrically conductive contact with the object in use and being physically arranged to isolate the electrolyte from the object in use; and at least a first electrode located at least partially within the cavity, the first electrode being for electrical connection with a potentiostat or galvanostat and being arranged, in use, to be in electrical contact with the electrolyte in the cavity; wherein the body comprises at least one magnet arranged to, in use, apply a magnetic force to the object, thereby attaching the body to the object.
[ Effect ]
The at least one magnet is arranged to apply a magnetic force to the object in use, thereby attaching the body to the object, allowing easy attachment and detachment of the battery to and from the object.
The at least one magnet also eliminates the need to attach the object to the object using glue. Thus, glue residues on the inspection surface are avoided. Furthermore, the at least one magnet also allows for an improved current flow between the at least first electrode and the object, since the glue may provide a resistance to this current flow.
The at least one magnet allows good contact of the body with the object without a significant air gap between the body and the object. This allows current to flow into and out of at least the first electrode through the cell body and the object without encountering significant resistance due to the presence of an air gap in the circuit.
The body is physically arranged to isolate, in use, the electrolyte from the object, thereby allowing the device to be used to sense the electrochemical state of the object without the electrolyte coming into contact with the object. This eliminates the risk of damage to the object being tested due to direct contact between the electrolyte and the object.
[ definitions ]
When used for sensing electrochemical changes in an object, the apparatus may be used to perform electrochemical impedance spectroscopy on the object. When used for sensing electrochemical changes in an object, the apparatus may be used to perform a linear polarization resistance method on the object. The expression "in use" may denote "when the device is used for sensing an electrochemical change in an object". Thus, the expression "in use" may denote "when performing electrochemical impedance spectroscopy on an object using the apparatus" or "when performing a linear polarization resistance method on an object using the apparatus". The substantially conductive body is arranged to prevent the electrolyte from contacting the object when physically arranged to isolate the electrolyte from the object. When, in use, placed in electrically conductive contact with an object, the body may be arranged in direct physical contact with the object. When, in use, placed in electrically conductive contact with an object, the body may be arranged to be in electrically conductive contact with the object through a substantially electrically conductive intermediary (e.g. a substantially electrically conductive cover as described in detail below).
In the case of being substantially conductive, the substantially conductive body is sufficiently conductive to conduct electricity between the first electrode and the object. In other words, the substantially conductive body is conductive. Substantially all of the body may be substantially electrically conductive. This means that the body can be applied to the object in a variety of orientations and still be in electrically conductive contact with the object. This also means that the body can be made of a single material. This may be more cost effective than using more than one material. Alternatively, only a portion of the body may be substantially electrically conductive. This means that a portion of the body that needs to be in electrically conductive contact with the object in order to perform sensing using the device may be formed from an electrically conductive material, while the rest of the body may be formed from another material. This may reduce the cost of the device, where the conductive material is much more expensive than the other materials used.
[ electrodes ]
The first electrode may be a counter electrode. In other words, the first electrode may be arranged to deliver, in use, electrical current to the electrolyte. The counter electrode may be in the form of a grid. The counter electrode may be a substantially electrochemically inert material. The counter electrode may be platinum or aluminum.
The device may further comprise a second electrode. The second electrode may be a reference electrode. In other words, the second electrode may be arranged for measuring the potential of the other electrode. The reference electrode may be a hydrogen electrode, a saturated calomel electrode, a copper sulfate-copper (II) electrode, a silver chloride electrode, or a palladium-hydrogen electrode.
The first electrode may be a working electrode.
[ Main body ]
The body may be aluminum. The host may be platinum. When the body is aluminum, the body has a relatively high electrical conductivity and is relatively electrochemically inert, while also being formed from a relatively inexpensive material. When the body is formed of platinum, the body has high conductivity and is electrochemically non-reactive. This means that the body is able to conduct current through the device to and/or from the object to be measured without itself undergoing an electrochemical change. The electrochemical change of the body may affect the measurement of the electrochemical change in the object, as this measurement will result in the electrochemical change of the cell body.
The body may have a first surface arranged, in use, to be in electrically conductive contact with an object along substantially the entire length of the first surface, and may comprise at least a first portion and a second portion slidably movable relative to the first portion from a first retracted position to a second extended position such that the length of the first surface is greater when the second portion is in the second position than when the second portion is in the first position.
When the body is arranged as just described, it may be "telescopic". This will be discussed further below with respect to the third aspect.
[ magnet ]
The at least one magnet arranged to, in use, apply a magnetic force to the object and thereby attach the body to the object may be a permanent magnet. The at least one magnet may be samarium cobalt. Samarium cobalt magnets are lightweight, small in size, strong, highly corrosion resistant, and can be used at high temperatures and in harsh operating conditions.
The at least one magnet may be a substantially electrically conductive body. That is, the conductive body may be a permanent magnet.
The apparatus may further comprise an electrolyte contained by the chamber; a potentiostat or galvanostat electrically connected to the first electrode; and an electrical connector arranged to be electrically connected to the object. This arrangement provides a complete device that can be used by simply applying the body to the object and connecting the electrical connector to the object without further modification or addition to sense the electrochemical change in the object.
[ second aspect ]
According to a second aspect of the present disclosure, there is provided a system for sensing an electrochemical change in an object, the system comprising: the first device according to the first aspect, wherein the at least first electrode comprises a counter electrode; the second device according to the first aspect, wherein the at least first electrode comprises a working electrode.
[ Effect ]
By providing the second device according to the first aspect, an object in which an electrochemical change is to be sensed can be made into the working electrode without the need to connect an electrical connector directly to the object. Thus, in applications where the object has a protective coating, there is no need to remove a piece of the coating in order to test the object under the non-conductive coating.
[ third aspect ]
According to a third aspect of the present disclosure, there is provided an apparatus for sensing an electrochemical change in an object, the apparatus comprising: a substantially electrically conductive body defining a cavity for containing an electrolyte, the body having a first surface arranged, in use, to be in electrically conductive contact with an object substantially along the entire length of the first surface, and being physically arranged, in use, to isolate the electrolyte from the object; and at least a first electrode located at least partially within the cavity, the first electrode for connection to a potentiostat or galvanostat and arranged to be in electrical contact with the electrolyte in the cavity in use; wherein the conductive body comprises at least a first portion and a second portion, the second portion being slidably movable relative to the first portion from a first retracted position to a second extended position such that the length of the first surface is greater when the second portion is in the second position than when the second portion is in the first position.
[ Effect ]
The body may be "stretchable" in that the substantially electrically conductive body comprises at least a first portion and a second portion, the second portion being slidably movable relative to the first portion from a first retracted position to a second extended position, such that the length of the first surface is greater when the second portion is in the second position than when the second portion is in the first position. That is, the body may be extended by sliding the first portion or the second portion or both portions relative to each other such that the second portion is in the second extended position. This increases the length of the first surface that is arranged to make electrically conductive contact with the object in use (with respect to the second portion when in the first position). This, in turn, increases the surface area of the body in electrically conductive contact with the object. This means that the device can be made relatively portable and adapted to sense electrochemical changes of objects in relatively small objects or difficult to access areas when the second part is in the first position, while allowing analysis of larger surfaces when the second part is in the second position. This makes the device more versatile than a device with a fixed size. Thus, it may not be necessary to use, for example, a conductive gel to increase the surface area that can be analyzed with the device. Instead, it may simply be extended.
[ sealing ]
The body may be arranged to hold the electrolyte in substantially any orientation of the body. The first and second portions (first second portions) may be substantially tubular and may be arranged such that at least the first portion (first portion) of one of the portions is radially within the other portion when the second portion is in the first position. The first and second portions may be arranged such that when the second portion is in the first position, a larger part of one of the portions is radially located within the other portion than when the second portion is in the second position. Each of the first and second portions may include an end that is distal from the other portion and closed. For example, the distal ends may be arranged to not allow liquid to pass through them.
When arranged to hold the electrolyte in substantially any orientation, this configuration allows the body to be attached to the surface in substantially any orientation without the electrolyte escaping from the body. As described above, if the electrolyte escapes during the measurement, the measurement result is adversely affected. This sealing design may work in conjunction with the use of magnets in the device, as these features together allow the device to be attached in any orientation (even upside down) so that it can be attached to structures such as ceilings and challenging geometries.
[ conductive coating ]
The device may further comprise a substantially electrically conductive cover on at least a portion of the first surface, the substantially electrically conductive cover being arranged to conduct electricity between the first surface and the object in use. The cover may be arranged on a second portion of the second part when the second part has at least a first portion located radially in the first part (when the second part is in the first position), the second portion not being radially within the first part when the second part is in the first position. The cover may be arranged to move from a first state when the second part is in the first position to a second state when the second part is in the second position, wherein the second state extends relative to the first state.
In this way, the cover extends and retracts with corresponding movement of the second portion and thereby allows the conductive contact between the second portion and the object to be measured to be maintained irrespective of the position of the first portion. If there is no cover, when the first and second portions are substantially tubular, and the second portion has a first portion that is radially within the first portion when the second portion is in the first position, and a second portion of the second portion that is not radially within the first portion when the second portion is in the first position, the second portion will not be in conductive contact with the surface if the body is applied to the planar surface. This may allow the entire body to be in electrically conductive contact with the object to be measured, or at least to increase the contact area relative to an arrangement in which no covering is present.
The cover may be a mesh arranged to extend and/or compress. The cover may be a folded material arranged to extend and/or compress. The cover may be a coil arranged to extend and/or compress. Each of these arrangements allows the covering to be moved from a first state when the second portion is in the first position to a second state when the second portion is in the second position, wherein the second state is extended relative to the first state.
The substantially conductive cover may have a conductivity at least equal to a conductivity of the substantially conductive body.
The substantially electrically conductive covering may extend radially around the second portion. This allows the device to be used in any radial orientation while maintaining electrical contact between the second portion and the object to which the body is applied.
[ tube ]
The body may include a first tube and a second tube in fluid communication with the cavity. The first tube may be arranged for introducing an electrolyte into the cavity. The second tube may be arranged to allow air to escape from the cavity. The first tube may extend further into the lumen than the second tube. This allows the body to be completely filled with electrolyte and thereby prevents air pockets within the cavity which could adversely affect measurements made using the apparatus.
[ magnet ]
The body may comprise at least one magnet arranged, in use, to apply a magnetic force to the object, thereby attaching the body to the object. As discussed above with respect to the first aspect, this allows the body to be attached to the object without the use of glue. The at least one magnet may be arranged on a radially inner surface of the second part when the second part has at least a first portion located radially in the first part when the second part is in the first position.
Optional features of each aspect are also optional features of each other aspect, and a person skilled in the art may infer a change in term if necessary, where it is meaningful to infer a change in term.
Drawings
Specific embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which:
fig. 1(a) shows a schematic of an open electrochemical cell;
FIG. 1(b) shows a portion of an object after EIS has been performed on the object using an open electrochemical cell;
fig. 2 shows a first example of an apparatus for sensing an electrochemical change in an object, the apparatus being in the form of a two-electrode electrochemical cell device and being shown in its extended state;
fig. 3 shows the two-electrode electrochemical cell device in its retracted state;
figure 4 shows a two-electrode electrochemical cell device connected to a galvanostat, for use in its extended state;
FIG. 5 shows a working electrode of an electrochemical cell device;
FIG. 6 shows a system for sensing an electrochemical change in an object in the form of a two electrochemical cell device arrangement; and is
Figure 7 shows a single electrode electrochemical cell device with a combined counter and reference electrode.
Detailed Description
With reference to fig. 2, an example of an apparatus for sensing an electrochemical change in an object will now be described. In this example, the apparatus is a two-electrode
The two-electrode
The cavity 204 also has a
In other examples, the
By using
The
The housing 202 of the
The
The magnetic flux density of the
The thickness of the
The inner
The
The
Referring now to fig. 7, an example of an alternative apparatus for sensing an electrochemical change in an object will now be described. In this example, the apparatus is a single electrode
The
Referring now to fig. 4, an apparatus for sensing an electrochemical change in an object will now be described. In this example, the setup is used to measure the condition of the coated metal substrate 226. The device consists of the
A single electrochemical cell arrangement may be used to perform EIS. EI S is particularly useful for analyzing the condition of coatings that have been applied to conductive substrates (e.g., conductive metals). For example, EIS can be used to analyze non-conductive polymer coatings used to protect conductive substrates from, for example, corrosion.
A single electrochemical cell arrangement is provided for measuring the corrosion rate of the substrate 226. In this example, the substrate 226 has a coating 250 applied thereto. To assemble the individual electrochemical cell devices together, the electrochemical cell device chamber 204 is filled with electricity via inlet tube 252A solute 206. Air escapes through the
Before or after the
Magnets within the
During non-destructive measurements,
The single electrochemical cell arrangement 400 can also be used for nondestructive corrosion measurements of metal coatings, bare metals, and alloys by the Linear Polarization Resistance (LPR) method.
The dual
The counter electrode cell device in this example is a two-electrochemical cell device shown in fig. 2. A working electrode cell apparatus 500 is shown in fig. 5. The
The working electrode battery device contains a working electrode connected to a WE battery cable 504 (fig. 5), and also contains a metal mesh 506 within the chamber. When both
The dual battery device arrangement may be used to perform EIS to measure the condition of the coating 250 to which the
whereinoIs the vacuum permittivity (about 8.854 · 10)-12F·m-1),rIs the relative permittivity (dielectric constant) of the coating, a is the surface area of the coating in square meters, and d is the thickness of the coating in meters.
Thick high quality coatings have very low capacitance C due to their very low relative dielectric constant (4 to 8)c. In contrast, degraded coatings have a high capacitance C due to their higher dielectric constant (50-80)c. Water has a dielectric constant of 80. Thus, if the degraded coating absorbs water, its dielectric constant may be in the range of 50-80.
The dual
The impedance of the coated substrate 226 is measured by applying a small sinusoidal signal between the
where ω is called the "frequency" and α is an index, equal to 1 for a capacitor. A measurement batch is typically made up of multiple frequency sweeps while monitoring the response of the system.
The study using the
The impedance response of the system during potential scanning is typically linear. The response depends on the potential range. Very small values may produce poor signal-to-noise ratios, resulting in noisy data. Very large values can result in impedance response non-linearity. For most electrochemical systems, the normal range is 1-30 mV. In this example, 20mV is used. The user can verify the linear response by performing the same experiment over different potential ranges.
The measurement time is a function of the frequency range. A very small frequency results in a longer measurement time. For time-varying systems, such as the formation of corrosion films, maintaining a small frequency range ensures minimal variation of the system during data collection. Electrochemical impedance measurements may, for example, start at a frequency of about 1kHz and may last up to 1MHz, which may take up to 2 minutes. For coatings that do not require degradation at high frequencies, the measurement can start at a frequency of 0.001Hz or even lower. To obtain high quality measurements, each experiment can be performed over a large frequency range, for example from 0.001Hz to 1 MHz.
The data of the measured impedance can be matched to an equivalent circuit. Each component of the circuit represents a physical behavior in the system. For example, the resistor represents the resistance provided by the electrolyte 206, while the capacitor represents the capacitance of the coating 250. As the coating 250 degrades, the equivalent circuit expands due to the start-up of the new process. Matching of the equivalent circuit helps to understand the physical process of degradation of the coating 250.
The extendable nature of the
Thus, the above description discloses devices and systems for sensing electrochemical changes in an object, and ways of effecting these devices and systems.
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