JPS6066148A - Corrosion rate deciding device - Google Patents

Abstract

PURPOSE:To eliminate automatically with a high accuracy a drift from a polarization potential value of a sample metallic piece, and to improve a corrosion rate analyzing accuracy by bringing a detecting polarization potential to a fast Fourier transformation and a reverse Fourier transformation. CONSTITUTION:A pulse charge from a pulse power source 11 is impressed to a sample metallic piece 1 immersed in a corrosion liquid 4 through a paired pole 3. Also, a polarization potential of the metallic piece 1 is detected based on a reference electrode 2 as a reference, and supplied to a fast Fourier transforming device 13 through a buffer amplifier 12. A frequency area signal which a time area signal change in the lapse of time in the polarization potential containing a parameter corresponding to a corrosion rate is converted by said device 13 is processed by a filter operating device 14, a DC component corresponding to a drift is eliminated automatically with a high accuracy, and thereafter, it is reconverted to the time area signal by a reverse Fourier transforming device 15. Accordingly, the drift is eliminated automatically with a high accuracy from a polarization potential value, and a corrosion rate analyzing accuracy is improved.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a corrosion rate determination device, and more specifically, the present invention relates to a corrosion rate determining device, and more specifically, a device that uses a sample metal piece as a working electrode to instantaneously apply an electric charge to this electrode and measure changes in the polarization potential of this electrode. [Technical background of the invention and its problems] In general, the reaction factors of corrosion reaction are polarization resistance Rp, g negative current density 1 corr, and terfur gradient βa, βC, which are related to corrosion rate. It is known that the following formula holds true.

Rp=, j/I...(1) V=(M/ZF)-Icorr-(3) In the above formula, η: polarization potential, E: Faraday current density,
M: atomic weight of sample metal, Z: valence number of eluted metal ions, F: Faraday constant number.

As is clear from the above equation, if the polarization resistance Rps and the terfour gradient βa and βC can be measured, it is possible to calculate the corrosion rate (2) and the corrosion current density Icorr. The inventor of the present application has already measured the polarization resistance Rp and the Terfur gradient βa and βC, and has determined the corrosion rate. 3, a capacitor 5 for supplying a known amount of electric charge to the sample metal piece 1 via the counter electrode 3, a power source 6 for supplying electric charge to this capacitor 5, a cell 4 for measuring corrosion rate equipped with a It is equipped with a relay 7 that instantaneously supplies electric charges to the sample metal piece 1 and a potentiometric recording device 8 that measures changes in the polarization potential of the sample metal piece 10 via a reference electrode 2.

In such a corrosion rate determination device, the polarization resistance Rp and the Terfur gradient βa are determined as follows.

βC can be calculated. When considering the polarization resistance, Rp, a charge is applied to the sample metal piece 1 under the condition that the absolute value of the polarization potential η, 1ηl<10 mV, and a curve of polarization value η versus waiting time is obtained. Under this condition, the following equations (4) and (5) hold true.

(-□) ... (4) 7 = 7 ... pOdRp yoQ = "ocd ... (5) η.: Polarization value Cd immediately after applying charge to the sample metal piece:
Differential capacitance Δq of the electric double layer of the sample metal piece: Charge density given to the electric double layer of the sample metal piece Since the above relationship holds, the polarization resistance Rp can be calculated from the curve and Δq.

In addition, when reducing the Terfur gradients βa and βC, 1η
1> A charge is applied to a sample metal piece under conditions of 50 to 60 mV to obtain a polarization value η-waiting time curve. Under this condition,
Equations 6 and 7 below hold true.

The above η- is the time t1 on the curve. t,,t,(t'1・1
/, ·t'3) polarization value η1. η3. η3(η′
1. η−1η3) υ Terfur gradients βa and βC can be set.

Already, if η- is a curve, if η>0, η1-η,
=η, -da, =Δη>0, and in the case of η less than 0, η', -η1=η'2-ηt=Δη'<0, and η1η2. η3 (η′□, η′2.η1)
and the corresponding tl + t2 + t3
(t'l + t'2 + t'3) can be used to determine the Terfel gradient.

According to the above-mentioned corrosion rate determination device, it is possible to obtain suitable data, but if the offset of the polarization potential is not accurately adjusted to zero before applying a charge when measuring the one-polarization potential, serious problems may occur during analysis. This becomes a cause of error.

This will be explained using model calculations.

Consider the 0-It parallel circuit shown in FIG. 2 as an equivalent circuit of the electrodes. Here, C corresponds to the electric double layer capacitance Cd, and R corresponds to the polarization resistance Rp.

100μF as C and IOKΩ as R, and η.

By substituting 10 mV as , the polarization potential η (mV) is expressed as
4), it can be expressed as υ equation (8).

η= 10xexp(-t/100xl(r'xlox
lO") = 10xexp (-t) . . . direct equation Conventionally, the straight line at 1 = = 0 of this straight line is the product of η, and the slope of the straight line is the product of pCd-RP, and these and the dimensions are given. The values of the electric charge Δq were used to calculate the values of cd, R, and p, respectively.

However, if an offset crab is superimposed on the polarization potential, as shown in Figure 4 (Figure 4 shows the case where 1 mV is superimposed as a turf set), when the polarization potential is converted into the number of sentences, the time 1 η in the winter when it is not the 1st section line. It takes 75 hours to calculate the product of Cd-Rp.

Therefore, in the past, the voltage and voltage Bt were read and zero-adjusted before charge application. Great care must be taken to make good measurements; in addition to being necessary, a slow tonnage of the potential) 75Z was difficult to measure with high accuracy.

[Purpose of the invention]

The present invention was made in view of the above-mentioned circumstances, and its purpose is to perform fast Fourier transform and inverse Fourier transform on the superimposed polarization potential of offset (1) to accurately offset the superimposed polarization potential by It is there if you remove it well.

[Summary of the invention]

The present invention includes a charge applying section that applies a predetermined amount of charge to a sample metal piece immersed in a corrosive liquid, and a time change in the polarization potential of this sample metal piece that is detected in an open circuit state, and this detection signal is Consists of a potential detection section that amplifies, a fast Fourier transform device that frequency-analyzes the output of this potential detection section, and an inverse Fourier transform device that performs inverse Fourier transform after removing the DC term from the output of this fast Fourier transform device. This is a counterfeiting speed determining device characterized in that:

In general, for any continuous function f(t) in the time domain, 7
- Complex function F (
goods) is the frequency F(1
)=fconi−f(t) (CO5ωt −j sstoneωt
) d t −(9) is a function in the domain, and its absolute value IF) 1 is called an amplitude term and Arg(F←)) is called a phase shift term.

Moreover, in a completely orthogonal function system, this Fourier transform transforms from the frequency domain function F w> back to the time domain function f (
It is also possible to reproduce t), and this transformation is called an inverse Fourier transformation.

Next, let us consider applying a filter in the frequency domain to an arbitrary continuous function f (z) in the time domain.

(This corresponds to, for example, using a low-pass filter to remove unnecessary high-frequency components from an audio signal.) If the filter function (weighting function) is ω(1), after filtering Continuous function 11 in the time domain of (
1) is expressed by the formula αQ. Here, ■ indicates a composure calculation. This compo-rich calculation is performed in the time domain as follows: y (t) = f (t) ■ ω (1)...0QIn order to obtain data at any one point in time, a large amount of data before and after that time is required. Therefore, it is extremely difficult to perform calculations over the entire time domain function f (t). Therefore, consider applying the above-mentioned Fourier transform to this filtering operation. This operation is performed using the formula a0: G(b)=F←)・WIJ)...0υ
It is indicated by. Here, Gri), Fi), and wu) are frequency domain functions obtained by performing Fourier transformation on f (O+ f (t), ω(1)) of 200, respectively. By applying the above-mentioned inverse Fourier transform to G←) obtained in
), the filter operation ends. By performing filter operations in the frequency domain in this way,
It becomes possible to set various filter functions that are impossible with filter operations in other time domains, which require only one calculation for each frequency as shown in Equation I.

Therefore, in the present invention, the time domain function f (t) is expressed as the formula (
Using the change over time of the polarization potential shown in 4), it is shown on the second side as a filter function W←).

By using a function and performing a filter operation, we succeeded in removing only the offset DC component from the temporal change in the polarization potential.

By performing the filter operation as described above, an accurate constant force can be obtained by removing errors in offset and Oshi analysis.

[Embodiments of the invention]

Referring to FIG. 5, an embodiment of the corrosion rate first determination apparatus of the present invention is shown.

As shown in the figure, a constant electric quantity pulse power source 11 is connected to the counter electrode 3 and the sample metal piece 1. This pulse power source 11 applies a predetermined charge μf (μf) to the sample metal piece 1 via the counter electrode 3.
1 is provided with a DC constant voltage power supply 6, a canister 5, a relay 775, and the like if they fit as described above. In addition, the sample metal piece 1 and the reference electrode 2 detect the polarization potential of the surface of the sample metal piece 1 with the reference electrode 2 as a reference.
A buffer amplifier 12 (combined with an operational amplifier for amplifying this and achieving impedance matching between the measurement system and the downstream electronic circuit) is connected.

Connected to this output amplifier 12 is a fast Fourier transform device 13 that converts the time-domain 'IN' voltage change over time into a frequency-domain signal. Connected to the output of the fast Fourier transform device 13 are a filter calculation device 14 for removing DC terms from the frequency domain signal, an inverse Fourier transform device 15 for returning the filtered frequency domain signal to the time domain, and a potentiometer 8. has been done.

Next, using this apparatus, a charge was applied to the equivalent circuit shown in FIG. 2, and the subsequent change in polarization potential over time was measured.

When the equivalent circuit is used, it is necessary to intentionally disturb the operating point of the buffer amplifier 12 because it essentially does not generate a DC offset.
A mV offset is generated.

FIG. 6 shows the measurement results at the output end of the buffer amplifier 12, and FIG. 7 shows the measurement results at the output end of the inverse Fourier transform device 15.

Comparing both figures, it can be seen that by using the corrosion rate determination device according to the present invention, it is possible to completely eliminate the change in polarization potential over time caused by DC offset.
It can be seen that accurate measurements can be made.

〔Effect of the invention〕

According to the present invention, it is possible to completely automate the operation of removing DC off-sets, which conventionally required a great deal of labor and caused serious analysis errors when measuring corrosion rates using the coulostat method. In addition to achieving a significant improvement in analysis accuracy, this method also enables completely unmanned measurements, making a significant contribution to the technological advances required when applying the coulostat method as a corrosion monitoring method in actual plants.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the basic configuration of the corrosion rate determination device, Figure 2 is the equivalent circuit of the electrode used in conventional model calculations, and Figure 3 is the equivalent circuit of the electrode used in conventional model calculations. An explanatory diagram showing an example of calculating the change in polarization potential over time. Figure 4 is an explanatory diagram showing an example of calculation when an offset of 1 mV is superimposed under the same conditions as in Figure 3. Figure 5 is one configuration of the present invention. FIG. 6 is an explanatory diagram showing a measurement example of the equivalent circuit in FIG. 2 based on FIG. 5, and FIG. This is an explanatory diagram. l... Sample metal piece, 2... Reference electrode, 3... Counter electrode, 4... Corrosion rate measurement cell, 5... Capacitor,
6... Power source, 7... Relay, 8... Potential difference recording device, 11... Pulse power source, 12... Buffer γ amplifier, 13... Fast Fourier transform device, 14... Filter Arithmetic device, 15... inverse Fourier transform device. Agent Patent Attorney Kensuke Chika (and 1 other person) Figure 1 q Figure 3 Kenshu C3eC) Figure 5 Figure 6 Makifil (Sec)

Claims (1)

[Claims] A charge applying unit that applies a predetermined amount of charge to a metal sample immersed in a corrosive liquid, and a potential detection unit that detects time changes in the polarization potential of this metal sample in an open circuit state and amplifies this detection signal. A fast Fourier transform device that performs frequency analysis on the output of this potential detection section, and an inverse Fourier transform device that performs an inverse 7-lier transform after removing the direct current term from the output of this fast Fourier transform device. A corrosion rate determination device characterized by: