JPH0449909B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for corroding metal coated with paint or lining material.

[Prior Art and Problems Therewith] It is widely known that the deterioration of coated metals applied with paint or lining materials due to corrosion varies depending on the corrosive environmental conditions. However, the rate of deterioration is generally extremely slow. Particularly in the case of metals coated with coatings or the like with excellent corrosion resistance, it is thought that it may not be possible to judge the quality of corrosion resistance with the naked eye until several decades have elapsed. Therefore, it is desired to establish a method for early predicting the corrosion resistance life of a coating film.

In this life prediction method, the current focus is on how to accelerate deterioration. Among these, the so-called electrolytic method, in which a DC voltage is applied to the coated metal, is attracting attention as a method of promoting corrosion reactions on the metal surface under the coating [e.g., Yamamoto et al.: Corrosion Prevention Technology]
35, 3 (1986)]. Alternatively, there is also the so-called coupling method, in which a coated metal and a bare zinc plate are coupled.

Now, using the above electrolytic method, if a DC voltage E of a certain magnitude is applied between the coated metal and the counter electrode (platinum, carbon, etc.) C (so-called between the terminals) via the corrosive liquid L, then The electrical circuit formed can be modeled by the equivalent circuit shown in FIG. Here, the metal W is coated with a paint or a lining material. The voltage E _w0 is the voltage caused by the electrode potential of the metal W, the resistance R _r is the non-ohmic polarization resistance near the surface under the metal coating that causes the overvoltage η, and R _f is the voltage caused by the electrode potential of the metal W. This is the electrical resistance of the applied paint or lining material itself, or the electrical resistance of laminated or deposited layers such as film defects. R ₀ is the electrical resistance of the corrosive liquid L. Further, the voltage E _c0 is the electrode potential of the counter electrode C, the resistance R _r ' is the polarization resistance near the surface of the counter electrode C that causes an overvoltage, and R _f ' is the electrical resistance near the surface of the counter electrode C.

The magnitude of the current I flowing through this closed circuit is expressed by the following formula.

I=(E−E _w0 −E _c0 )/(R _r +R _f +R ₀ +R _f ′+
R _r ′) ...(1) If the concentration of the electrolytic solution (corrosive solution) L is constant, the liquid resistance R ₀ will be almost constant. Furthermore, considering that the resistances R _f ′ and R _r ′ at the counter electrode C are small and can be substantially ignored, the above equation (1) becomes as follows.

I=(E-E _w0 −E _c0 )/(R _r +R _f +R ₀ )
...(1') However, in general, the electrical resistance R _f of a paint film coated with paint or lining material (hereinafter collectively referred to as a paint film) is determined by water absorption or dehydration of the paint film, or by water absorption or dehydration in the paint film. It does not always show a constant value due to the formation of water droplets or changes in the temperature of the corrosive environment. In addition, if there are defects such as scratches or pinholes in the paint film, corrosion reaction products of the metal under the paint film, so-called rust, will be deposited in these defective areas, and the electrical resistance R _f of this rust layer will also change. . Furthermore, when a coated metal is electrolyzed in seawater, more specifically, if the coated metal is electrolyzed in such a way that a reduction reaction occurs, deposits such as calcium ions present in seawater are deposited on the coated metal. .
The electrical resistance R _f of this deposited layer changes depending on the temperature of the seawater, the state of deposition, etc. In this way, the electrical resistance R _f changes as the properties of the coating film change and corrosion progresses.

In the constant potential method, which has been conventionally used for life prediction, a constant DC voltage is applied to allow the reaction to proceed. That is, even though the electrical resistance R _f of this coating film changes, electrolysis is carried out at a constant terminal voltage E. Therefore, even if a constant voltage E between the terminals is applied, the overvoltage η changes. The overvoltage η is a voltage required to cause a current to flow between the metal W and the counter electrode C, and changes depending on the current density and the like. If the overvoltage η changes during electrolysis, it does not mean that deterioration is caused by a constant corrosion force.

Also, a potentiostat, a so-called constant potential electrolysis device, is widely used, and the same can be said for electrolysis using this device. If this device is explained in Fig. 2, R _f ′, R _r ′, E _c0 applied to the counter electrode C
A reference electrode (a so-called reference electrode that exhibits a stable electrode potential in the corrosive liquid) is used to
is inserted into a solution and electrolyzed using a three-electrode system. However, in this case as well, although the metal W can be held (electrolyzed) with a constant potential difference when viewed from the reference electrode, the overvoltage η that governs the corrosion of the coated metal cannot be controlled to a constant level when R _f or E _c0 changes. It's not a thing.

Therefore, the conventional early life prediction method is unreliable because the corrosion reaction does not occur under the application of a constant force, and the results of predicting the life of the coating depend on unknown factors. In order to accelerate the corrosion reaction by applying a constant force, it is necessary to keep the magnitude of the overvoltage η near the metal surface of the coated metal constant.

An object of the present invention is to provide a method and apparatus for deteriorating coated metals that keep overvoltage constant.

[Means for Solving the Problems] The coated metal deterioration method according to the present invention involves immersing a coated metal counter electrode coated with paint or lining material in a corrosive liquid, and applying a voltage between the coated metal and the counter electrode. In the coated metal deterioration method in which the coated metal is deteriorated by applying voltage, the value of the overvoltage required to proceed with the electrochemical reaction on the surface of the coated metal is set,
Among the resistances of the electric circuit between the coated metal and the counter electrode, the polarized resistance to which the above-mentioned overvoltage is applied due to an electrochemical reaction on the surface of the coated metal, and the coating film of the coated metal that is a resistance other than the above-mentioned polarized resistance. and the resistance of the corrosive liquid, and based on this measurement result, the voltage between the coated metal and the counter electrode is controlled so that the overvoltage becomes a set value.

The coated metal deterioration device according to the present invention applies a voltage between a sample electrode made of a coated metal coated with paint or a lining material, a counter electrode to the sample electrode, a reference electrode to the sample electrode, and a voltage between the sample electrode and the counter electrode. a potentiostat for applying a pulse voltage to the potentiostat; a pulse application means for setting a voltage so as to apply a pulse voltage to the potentiostat; , the voltage is set on the potentiostat so that almost no current flows between the coated metal and the counter electrode, and the measurement results are measured using the pulse polarization method. a calculation means for calculating a voltage value;
It is characterized by comprising applied voltage variable means for setting the voltage value calculated by the calculation means to the potentiostat.

[Function] In the coated metal deterioration method according to the present invention, the voltage between the coated metal and the counter electrode is changed to polarize so as to maintain the overvoltage at a set value, and corrosion is promoted with a constant deterioration force.

In the coated metal deterioration device according to the present invention, measurement can be performed using a pulse polarization method, and the overvoltage is maintained at a set value based on the measured value.

[Embodiments] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

In the deterioration device according to the present invention, electrolysis is performed using a three-electrode system. In the embodiments described below, a three-electrode coated metal deterioration device will be described, but if a counter electrode material with a stable potential is used and the area of the counter electrode is increased for electrolysis, it can serve as both the counter electrode and the reference electrode.
Therefore, the present invention can also be used for a bipolar coated metal deterioration device.

(a) Degradation method First, the deterioration method of the embodiment of the present invention will be explained. That is, as shown on the left side of Figure 1,
A metal W coated with a coating film, a counter electrode C, and a reference electrode R are immersed in a container 4 containing a corrosive liquid L.
Then, an appropriate voltage is applied between the covered electrode W and the counter electrode C so that the potential difference between the covered electrode W and the reference electrode R becomes E.

The equivalent circuit diagram of this container 4 is the same as that shown in FIG. This is a value that is automatically applied. As already explained with reference to Fig. 2, the voltage E _w0 is the voltage caused by the electrode potential of the metal W, and the resistance R _r is the non-ohmic polarization resistance near the surface under the metal coating that causes the overvoltage η. , and R _f is the electrical resistance of the paint or lining material itself applied to the metal W, or the electrical resistance of a rust layer or deposited layer such as a film defect. R ₀ is the electrical resistance of the corrosive liquid L between the reference electrode and the coated metal. Furthermore, the voltage E _c0 is the electrode potential of the counter electrode C, and the resistance R _r ' is the polarization resistance near the surface of the counter electrode C that causes overvoltage.
R _f ' is the electrical resistance near the surface of the counter electrode C. The potentiostat PO automatically sets E _c0 , R _r ′I,
R _f 'I is compensated, and the potential difference between the reference electrode R and the covering metal W is set to a set value E.

E=E _w0 +R _r I+R _f IR ₀ I ……(2) Therefore, η=R _r I=E−(R _f +R ₀ )I−E _w0 ……(3) The features of this embodiment are as follows. Even if E _w0 , R _r , R _f , _and R ₀ change, the overvoltage η (=R _r
Set value E (=E _w0 +R _r I+R _f
The objective is to degrade the coating metal W while correcting I+R ₀ I). That is, the magnitude of the polarization resistance R _r and the magnitude of the resistance other than the polarization resistance (R _f + R ₀ ) are detected, and the overvoltage η applied to the polarization resistance R _r is made constant according to the ratio of the two. E is changed. In order to apply η with a constant magnitude, always know the voltage drop due to R _r and R _f + R ₀ and the value of E _w0 , and change the magnitude of E according to the amount of change in these values. Must be.

Next, concrete numerical values will be given and explained. Now, assume that the overvoltage η is maintained at 0.005V and electrolysis is performed to progress deterioration. The polarization resistance R _r and other resistances R _f and R ₀ are measured at predetermined intervals. Initially R _r =
If 10kΩ, R _f = 50kΩ, R ₀ = 0.2kΩ, then
R _r / (R _f + R ₀ ) = 10/50.2 = 1/5.02,
Each voltage applied to R _r and R _f +R ₀ is 1×
0.005V and 5.02×0.005V, i.e. 0.005V and
Just set it to 0.0251V. Therefore, the set value E of the potential difference between the reference voltage R and the coating metal W may be set to a value shifted from E _w0 by 0.0301V=(0.005+0.0251)V. Then, after a predetermined period of time has elapsed,
If only the electrical resistance R _f of the coating film changes due to water absorption and decreases to 30 kΩ, then R _r / (R _f +
R ₀ )=10/30.2=1/3.02, and the reference electrode R
The set value E of the potential difference between and the coating metal W is:
It is sufficient to change the value to a value shifted by 0.0201V=(0.005+0.0151)V from E _w0 . Furthermore, after a predetermined period of time has elapsed, for example, as the adhesion between the paint film and the metal deteriorates,
Suppose that paint film blisters occur, R _r decreases, and it is detected as 1kΩ. R _f is 30kΩ,
If R _p is 0.2 kΩ and electrolysis is continued, R _r /
(R _f + R _p ) = 1/(30 + 0.2) = 1/30.2, so the magnitude of the set value E of the potential difference between the reference electrode R and the coating metal W is _0.0156V (= 0.005
+0.0151) You can change it to a value shifted by V.

The present invention thus detects the polarization resistance R _r and the resistances R _f and R ₀ other than the polarization resistance, and detects the polarization resistance R _r
The coating metal is deteriorated by varying the applied voltage to maintain the overvoltage η applied to a predetermined value. However, the resistance of corrosive liquid
If the amount of change in R ₀ is small, or
If the magnitude of R ₀ is negligibly small compared to R _f , it is sufficient to detect R _f and R _r . Also, R _f and
The sum of R ₀ and R _r may be detected.

Furthermore, as explained using the above numbers,
(R _f + R ₀ ) is sufficiently small compared to R _r , and the overvoltage η
Metals for which (R _f +R ₀ )I can be ignored, that is, metals in which there is no coating film on the metal surface or where there is no deposited rust film on the defective portion of the coating film are outside the scope of the present invention. In this case, there is no need to use the present invention, and the measurement can be performed using a conventionally known potentiostat or the like.

(b) Resistance measurement method Methods for determining polarization resistance R _r and resistance other than polarization resistance R _f +R ₀ (hereinafter abbreviated as R _f ) include:
Known methods include pulse polarization and sweep polarization. In this example, it was determined by the pulse polarization method. This is because R _f and R _r are determined by short-time polarization. As explained later, R _f and
During the time when R _r is to be detected, the overvoltage η applied to R _r cannot be maintained at a predetermined level. For example, in the pulse polarization method, the value of the original applied voltage E is temporarily changed to the value of the natural electrode potential.
Since it is necessary to set E _w0 and to superimpose only the pulse applied voltage V, the overvoltage η is changed in principle. On the other hand, in the sweep polarization method as well, the overvoltage η is changed during the sweep by the applied voltage V. The pulse polarization method can be performed in a much shorter time than the sweep polarization method. Therefore, in order to minimize the risk that the test system will change due to the voltage V applied to determine R _f and R _r , it is advantageous to use the pulse polarization method. In addition, measurements using the pulse polarization method are performed at appropriate intervals, and each time,
Calculate R _f and R _r , and if a change is observed in R _f and R _r , change the magnitude of E so that the overvoltage η can be kept constant according to the magnitude of R _f and R _r . Bye.

Next, two methods for determining R _f and R _r will be explained.

First, the pulse polarization method used in this example will be explained. Assume now that the electrical equivalent circuit of the coated metal is the circuit shown in FIG. The difference from the circuit shown in FIG. 2 is that the electric double layer capacitance C _d1 of the metal surface is taken into consideration. When the overvoltage η is small and R _r is a constant value, when the voltage pulse V shown in the upper part of FIG. 4 is applied across the circuit of FIG. It changes like the curve shown at the bottom of the figure.

The curve for 0≦t≦t ^* and the curve for t≧t ^* can be expressed by the following equations, respectively.

I=V[1/R _f +R _r +R _r /R _f (R _f +R _r ) exp (−R _f +R _r /C _d1 R _f R _r t)] …(4) I=(I ^* −V /R _f ) exp[-R _f +R _r /C _d1 R _f R _r (t-t ^* )] ...(5) Here, t ^* and I ^* are the time when the voltage pulse V is interrupted and its This is the previous current value.

Equations (4) and (5) are derived as follows. First, the derivation of equation (4) will be explained. As shown in Figure 3, the voltage drop in the entire circuit is expressed as V,
Denote the voltage drop across R _f by V ₁ , the voltage drop across R _r by V ₂ , the current across the circuit by I,
The current flowing through C _d1 is denoted by I ₁ , and the current flowing through R _r is denoted by I ₂ . At this time, the following relational expression (4-1)
~(4-5) holds true.

V = V ₁ + V ₂ ... (4-1) I = I ₁ + I ₂ ... (4-2) I = V ₁ /R _f ... (4-3) I ₁ = C _d1・(dV ₂ / dt) ...(4-4) I ₂ = V ₂ /R _r ...(4-5) Equation (4-2), Equation (4-4) and (4-5)
From the formula, the following formula holds true.

I=C _d1 (dV ₂ /dt)+V ₂ /R _r (4-6) Furthermore, the following equation holds from equations (4-1) and (4-3).

I=(V-V ₂ )/R _f ...(4-7) Since the right sides of equations (4-6) and (4-7) are equal, C _d1 (dV ₂ /dt)+V ₂ /R _r =(V-V ₂ )/R _f (4-8) This equation can be rearranged to become the following equation.

(-(R _f ^-1 +R _r ^-1 )・V ₂ +V/R _f ) ^-1 × (dV ₂ /dt) = C _d1 ^-1 ...(4-9) For simplicity, -(R _f ^{- 1} +R _r ^-1 )=A V/R _f =B C _d1 =C, the following equation is obtained.

(A・V ₂ +B) ^-1 (dV ₂ /dt)=C ^-1 Integrating this equation yields the following equation.

(1/A)1n(A·V ₂ +B)=t/C+X Here, the integral constant X is determined by the initial conditions of t=0 and V ₂ =0.

(1/A)1nB=X Therefore, the following formula is obtained.

(1/A)1n{(A・V ₂ +B)/B} =t/C...(4-10) By transforming this equation, (AV ₂ +B)/B=exp{(A/ C) t}V ₂ =B/A{ex
p(A/C・t)−1}……(4-11) Substituting equation (4-11) into equation (4-7) and rearranging, I=(V+B/A)/R _f − (B/A)exp{(A/C)t}/R _f ...(4-12) Here, B/A=-R _r V/(R _f +R _r ) A/C=-(R _r +R _f )/C _d1 R _f R _r , so the following formula is obtained.

I = (V - R _r V / (R _f + R _r )) / R _f + (R _r V / (R _f + R _r )) / R _f × exp {- (R _r + R _f ) / C
_d1 R _f R _r )t} By rearranging this equation, equation (4) is obtained.

I=V[1/R _f +R _r +R _r /R _f (R _f +R _r ) exp (−R _f +R _r /C _d1 R _f R _r t)] ...(4) Next, equation (5) The derivation of is explained. In this case, since the voltage pulse is cut off, the following equation holds true instead of equation (4-1).

0=V ₁ +V ₂ ...(5-1) From equations (5-1) and (4-2), I=-V ₂ /R _f ...(5-2) Equation (4-2), (4-4) formula, (4-5) formula,
From formula (5-2), -V ₂ /R _f -V ₂ /R _r =C _d1 (dV ₂ /dt) ... (5-3) Here, for simplicity, 1/R _f -1/R _r =D C _d1 =F, then DV ₂ =F(dV ₂ /dt)...(5-4) Integrating this equation, (D/F)t=1nV ₂ +X...(5-5) Here, when the voltage pulse is interrupted at t ^* (t=
t ^* ), V=0, but since the capacitor C _d1 is charged, a voltage of V ₂ =V ₂ ^* is generated. Therefore ^, (D/F) _t ^* = 1nV ₂ ^{* +} X 1nV ₂ + (D/F)t ^* -1nV ₂ ^* If we rearrange this, (D/F) (t-t ^* ) = 1n (V ₂ /V ₂ ) ^* V ₂ = V
₂ ^* exp{(D/F)(t-t ^* )}...(5-6) Substituting equation (5-2) into equation (5-6), I=-(V ₂ ^* /R _f ) exp {(D/F) (t-t ^* )} ...(5-7) By the way, V ₂ ^* /R _f is the current value I ^* when V = V and t = t ^* , and ( From equations 4-1 and 4-3, we have the following relationship.

I ^* = V / R _f - _{V 2} ^* / R _f ... (5-8) From equations (5-7) and (5-8), I = (I ^{* -} V / R _f ) exp {(D /F) (t-t ^* )} Here, if D and F are returned to their original variables, equation (5) is obtained.

I=(I ^* −V/R _f ) exp[−R _f +R _r /C _d1 R _f R _r (t−t ^* )] …(5) Above, equations (4) and (5) are The derivation was explained.

Dividing both sides of equations (4) and (5) obtained in this way by V, we get I/V=1/R _f +R _r +R _r /R _f (R _f +R _r )exp (-R _f +R _r /C _d1・R _f・R _r t) ……(6) I/V=(I ^* /V−1/R _f )exp[−R _f +R _r /C _d1・R _f
・R _r (t-t ^* )] ...(7) The I/V value becomes a function only of the time t, which is unrelated to the magnitude of the voltage pulse V. Therefore, by setting R _f +R _r /C _d1・R _f・R _r =1/X...(8) 1/R _f −I ^* /V=Y...(9), the nature of both sides of equation (7) Taking the logarithm, it can be rewritten as the following formula.

1n (-I/V) = 1nY-1/X (t-t ^* ) ...(10) Therefore, from the slope of the graph of 1n (-I/V) and (t-t ^* ), Each value is determined (I ^* and t ^* are determined from FIG. 4).

Therefore, the values of R _f and R _r can be calculated.

By substituting the measured value I ^* , set value V, and analyzed value Y into equation (9), the coating film resistance R _f is obtained.

R _f = (Y + I ^* / V) ^-1 ... (11) Also, assuming that I = I ^* when t = t ^* in equation (4) or (6), and substituting equation (8), I ^* /V=1/R _f +R _r +R _r /R _f (R _f +R _r ) exp (-t ^* /X) (I ^* /V)・R _f・(R _f +R _r ) =R _f +R _r exp(-t ^* /X) Therefore, the following formula is obtained.

R _r = [1/R _f・1−exp(−t ^* /X)/1−(I ^* /V)R
_f −1/R _f ] ^-1 ...(12) From this, the polarization resistance R _r can be found from the analytical value X, calculated value R _f , measured value I ^* , set value V, and t ^* .

Furthermore, by substituting R _f and R _r into equation (8), the capacitance C _d1
is required.

However, the polarization resistance R _r is a constant value only when the overvoltage η is small. If voltage dependence is recognized in the curve of I/V and time t when the voltage pulse V is set to a larger value in sequence, it means that the overvoltage η has changed and a corrosion reaction of the coated metal has been detected.

Next, the sweep polarization method will be explained.

If the coating resistance R _f of the coated metal is large, the relationship between potential and current (polarization curve) during sweep polarization will appear to be an "approximately linear relationship" and the polarization of electrochemically reactive components near the coated metal surface will increase. The behavior is included on this "approximately linear relationship" curve. Therefore, the potential corresponding to the total resistance component at the initial stage of the sweep is calculated from the total electrolytic current I.
By constantly subtracting the (E)-current (I) relationship, an electrochemically related minute current (Δi)-potential E curve can be obtained. Then, R _f and R _r can be calculated from Δi as follows.

Now, assuming that the natural electrode potential is E _wp , the electrode potential is E, the electrolytic current is I, the coating resistance is R _f , and the polarization resistance is R _r , the relationship between E and I in the polarization resistance region is E-E _wp = I (R _f + R _r )≡I・R ...(13) If R _f is constant and is outside the polarization resistance range, R _r changes (represented by R _r ^* ), and E and I
The relationship can be expressed as E-E _wp = I (R _f + R _r ^* ) ... (14). FIG. 5 conceptually represents the relationship between equations (13) and (14). Here, the solid line is the actually measured I-
This shows the relationship between E. The slope (initial slope) of this curve at the origin can be expressed by equation (13). On the other hand, the actual voltage E for a certain current I can be expressed by equation (14). Therefore, the difference ΔE in E at a point where the current is the same is as follows from equations (13) and (14): ΔE=I(R _r −R _r ^* ) (15). From Figure 5, the relationship between △E and △i is
Since Δi/ΔE is equal to the initial slope, it can be expressed as ΔE=△i(R _f +R _r )=△i・R _t ……(16), and from equations (15) and (16), △i=1/R _t・I(R _r −R _r ^* ) ...(17). By the way, the Terfel equation (η=a+b
logI), R _r ^* is expressed by the following formula.

R _r ^* = η / I = (a + b logI) / I ... (18) If this formula can be applied to the coated metal, substituting formula (18) into formula (17) and rearranging, (△i / I) R _t =R _r −(a+b logI/I)
...(19) becomes. The second term on the right side of equation (19) approaches zero as I increases. Since Δi, I, and R _t are measured values, the polarization resistance R _r can be estimated from the intercept of the asymptote of the relationship between (Δi/I) R _t and I. Also
The coating resistance R _f can be found from R _f = R _t − R _r .

(c) Deterioration device Next, a deterioration device that embodies the deterioration method described above will be explained.

FIG. 1 shows the basic configuration of the deterioration device. As explained above, the coating metal W, the reference electrode R, and the counter electrode C are immersed in the corrosive liquid L in the container 4. The coated metal W is grounded through an electrical conductor (hereinafter referred to as a conductor) 1, and the reference electrode R and counter electrode C are connected to the potentiometer PO through conductors 2 and 3, respectively. A pulse application means Ep and an applied voltage variable means Ev are connected to the potentiostat PO through conductive wires 5 and 6.
PO current change and potential change are polarization resistance R _r and coating film resistance R _f (below, coating metal W and reference electrode R
It refers to the total resistance between Rr and _Rr . Specifically, the value of R _f +R ₀ ) is input to means (hereinafter referred to as calculation means) CL through a conductor 7. On the other hand, the preset overvoltage η is calculated from the overvoltage setting means H by the calculation means CL.
The size is input through the conductor 8. In addition, the calculation means CL calculates the ratio of the coating resistance R _f and the polarization resistance R _r , and from this ratio, the applied voltage variable means Ev
so that the magnitude of the output voltage can be controlled.
It is connected to applied voltage variable means Ev via a conducting wire 9. Further, display means REC is connected to the conductor 10 so that current, potential, overvoltage η, coating resistance R _f , polarization resistance R _r or elapsed time can be displayed.
is tangent to the calculation means CL. On the other hand, the potentiostat PO is grounded through a conductor 11. However, if the container 4 is a river or the sea, for example,
If this conductor 11 is grounded, measurement will not be possible, so the potentiostat PO is made floating with respect to grounding.

The coated metal W may be coated with a paint or lining material by any conventional method such as spraying, dipping, rolling or electrodeposition. Furthermore, the type of metal is not limited.

The reference electrode R only needs to have its own electrode potential stable in the corrosive solution used, and may be a commonly used electrode such as a calomel electrode or a silver-silver chloride electrode.

The counter electrode C may be made of the same material as the metal W to be coated, or may be a carbon plate or rod. The preferred material for the counter electrode is an inert material.
Examples include platinum and gold, but are not particularly limited. However, when the amount of corrosive liquid is small, it is desirable to use an inert counter electrode such as platinum.

A commonly used potentiostat (potential electrolysis device) is sufficient, but
If the coating film is free of defects and R _f is large, the input impedance of this potentiostat PO is 100 times or more greater than the sum of the film resistance R _f and polarization resistance R _r in the corrosive liquid. This is desirable.

The pulse application means Ep is a potentiostat.
In order to electrolyze (so-called polarization) the coated metal with a pulsed voltage of a certain magnitude using PO, it is a generator of pulsed voltage that overlaps pulsed voltages of a certain magnitude.

The calculation means CL is for calculating the magnitude of R _f and the magnitude of R _r.It grasps the values of R _f and R _r , and uses these values to calculate the applied voltage E in Fig. 2. This determines the variable amount.

The overvoltage setting means H is for setting the overvoltage η to a certain level in advance, and is designed to maintain η at the preset level even if R _r and R _f change.

The applied voltage variable means Ev is the above calculation means.
The magnitude of the applied voltage E (Fig. 2) is varied based on CL.

The display means REC is a recorder or a printer, and displays the above E, R _f , R _r , i,
It displays and records η, etc.

Now, assuming that the potential of the metal W seen from the reference electrode R (the natural electrode potential E _wp (vs.R) of W itself is -1V (vs.R), first, the applied voltage variable means Ev changes the potential to +
Apply 1V and make the current between C and W almost zero.
In other words, W is electrolyzed near its own natural electrode potential. Next, pulse application means
At Ep, voltage pulse V is applied as shown in FIG. 4 above, and coating film resistance R _f and polarization resistance R _r are determined by calculation means CL from equations (4) to (12). And now,
If the overvoltage η is set to 0.005V and electrolytically maintained (the W pole itself is cathodically polarized), the overvoltage setting means H is set to 0.005V. And R _r
10kΩ, and R _f is 50kΩ (for example, in the case of seawater, the relationship R _f ≫ R ₀ holds true, and _{R 0 can} be almost ignored), as described earlier in the calculation means CL. If calculated as follows, the applied voltage will be +
It becomes 0.006V. Therefore, +0.006V may be added so that the magnitude of the applied voltage variable means Ev becomes +1.006V.

Then, after a certain period of time, R _f
and find R _r . In other words, once the electrolysis is interrupted,
Repeat the above operation to measure the potential of the metal W seen from the reference electrode R, and if it is -1.2V, first apply +1.2V by the applied voltage variable means Ev,
The current between -W is set to almost zero and electrolysis is carried out near the natural electrode potential of W itself, and then the pulse application means
A voltage pulse V is applied by Ep, the values of R _f and R _r are determined, and if there is a change in the magnitude of the ratio of R _f and R _r , the magnitude of the applied voltage is set in advance by the applied voltage variable means Ev. What is necessary is to change the overvoltage η so that the overvoltage η becomes the same. In this way, each time
While measuring the values of R _f and R _r , the applied voltage E is varied so that it becomes a constant overvoltage η. Each time, each value is displayed or recorded on the display means REC.

FIG. 6 shows a specific example of the deterioration device. container 4
a counter electrode C, a reference electrode R and a coated metal W
is installed, and a corrosive liquid L is contained in the container 4. The reference electrode R is tangential to the input (1) of the differential amplifier DA of the potentiostat PO, and the counter electrode C is
Its output (3) is connected via an ammeter. Further, the metal W is grounded, and the reference electrode R is also grounded via a voltmeter. On the other hand, the other input (2) of the differential amplifier DA of the potentiostat PO is connected to the switch SW1 and the power supply for varying the applied voltage.
It is grounded via Ev and switch SW2 or via pulse application means Ep. Also,
The outputs of the voltmeter and ammeter are input to the calculation means CL, and the overvoltage set value of the overvoltage setting means H is also input to the calculation means CL. Further, the output of the calculation means CL is connected to the display means REC and the servo motor M.
changes the magnitude of the power supply of the applied voltage variable means Ev.

If switch SW1 is now on side (a),
The output (3) of the differential amplifier DA of the potentiostat PO is zero, and only the magnitude of the voltmeter is input to the input (1) of the potentiostat PO. That is, only the natural electrode potential (versus the reference electrode R) E _wp of the metal W is measured.
Then, it is input to the calculation means CL as the output of the voltmeter, and the magnitude of this potential difference, that is, E _wp
The reciprocal of this magnitude is adjusted by the servo motor M to the power source for varying the applied voltage, and the magnitude of this power source is set to (-E _wp ). Next, when switch SW1 is set to side (b), the potential difference between the input of differential amplifier DA, that is, terminals 1 and 2, is
The voltage becomes approximately 0V, the output (3) of the differential amplifier DA becomes approximately zero, and the output of the ammeter also becomes approximately zero (that is, W is electrolyzed near the natural electrode potential).
Next, the switch SW2 is switched to (d) sum, the pulse application means Ep is activated, and a pulse voltage (rectangular wave) is applied for a short time. That is, input (1) of D and
(2), this pulse voltage is applied between C-
As soon as a pulse voltage is applied across W, the changes shown in FIG. 4 will appear on the voltmeter and ammeter. Then, based on this change, R _r and R _f are calculated by the calculation means CL according to formulas (4) to (12). Furthermore,
Based on the overvoltage value η (=R _r I) set by the overvoltage setting means H and the already measured value of E _wp , the distance between the reference electrode R and the covering metal W is determined according to formula (2). The potential difference E that should be generated can be calculated.
The value of this potential difference E is input as -E from the power source for varying the applied voltage via the servo motor M to the operational amplifier DA through the terminal 2. and,
The above method may be repeated at certain time intervals. In addition, the calculation is performed digitally by a so-called microcomputer via the analog/digital converter of the calculation means CL,
The servo motor M may be automatically controlled using this result via a digital/analog converter.

The timing of applying a voltage pulse, measuring the polarization resistance R _r and coating resistance R _f , and correcting the overvoltage η is determined by R _r or R _f or
The more easily both R _r and R _f are susceptible to change, that is, the faster the so-called deterioration occurs, the more frequently the treatment needs to be performed. Conversely, the smaller the change, the lower the R _r and R _f due to pulse voltage application.
The time interval for the measurement of is long and good. Also,
If the rate of decline of R _r is greater than the rate of decline of R _f , then
The applied voltage increases with time, and conversely R _r
If the rate of decrease in is less than the rate of decrease in R _f , then
The applied voltage decreases over time.

[Effects of the Invention] The overvoltage can be maintained at a predetermined value and the coated metal can be deteriorated. Therefore, prediction of the life of the coated metal becomes more reliable.

[Brief explanation of the drawing]

FIG. 1 is a basic configuration diagram of the deterioration device. Second
The figure shows a model circuit during electrolysis in a deterioration device. FIG. 3 is a diagram of an example of an electrical equivalent circuit of coated metal. FIG. 4 is a graph showing the response to application of a potential pulse to the coated metal. Figure 5 shows
FIG. 2 is a conceptual diagram of a voltage curve during sweep polarization of a coated metal. FIG. 6 is a block diagram of an example of a deterioration device. W...Covered metal, C...Counter electrode, R...Reference electrode, L...Corrosion liquid, PO...Potentiost.
Ep...pulse application means, Ev...applied voltage variable means, H...overvoltage setting means, CL...calculation means,
REC...Display means.

Claims (1)

[Scope of Claims] 1. A coating in which a coated metal coated with paint or a lining material and a counter electrode are immersed in a corrosive liquid, and a voltage is applied between the coated metal and the counter electrode to deteriorate the coated metal. In the metal deterioration method, the value of the overvoltage required to advance the electrochemical reaction on the surface of the coated metal is set, and the resistance of the electric circuit between the coated metal and the counter electrode is set.
The sum of the polarization resistance to which the above-mentioned overvoltage is applied due to an electrochemical reaction on the surface of the coated metal, the resistance of the coating film of the coated metal, which is a resistance other than the above-mentioned polarization resistance, and the resistance of the corrosive liquid is measured. , A coated metal deterioration method characterized by controlling the voltage between the coated metal and the counter electrode so that the overvoltage becomes a set value based on this measurement result. 2. The coated metal deterioration method as set forth in claim 1, wherein the measurement and control described above are performed at predetermined intervals. 3. The coated metal deterioration method described in claim 1 is characterized in that the above-mentioned resistance measurement is performed by a pulse polarization method in a state where almost no current flows between the coated metal and the counter electrode. Coated metal deterioration method. 4. A sample electrode made of a coated metal coated with paint or lining material, a counter electrode for the sample electrode, a reference electrode for the sample electrode, a potentiostat that applies a voltage between the sample electrode and the counter electrode, and a potentiostat. a pulse applying means for setting a voltage so as to apply a pulse voltage to a pulse voltage, an overvoltage setting means for setting a value of overvoltage required to proceed with an electrochemical reaction on the surface of the coated metal, and a voltage between the coated metal and the counter electrode. Calculating means for calculating the voltage value necessary to apply the above-mentioned overvoltage setting value based on the measurement result measured by the pulse polarization method by setting the voltage on the potentiostat so that almost no current flows; 1. A coated metal deterioration device comprising applied voltage variable means for setting a voltage value calculated by the calculation means to a potentiostat.