JPH0612355B2 - Metal surface contamination degree detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to the production process of copper or copper alloy, surface modification (sandblasting, pickling, etc.), or surface cleanliness of copper or copper alloy due to carbonaceous material, The present invention relates to a method for detecting the degree of contamination on a metal surface for determining the degree of contamination.

[Conventional technology]

To determine the degree of contamination of the material surface caused by the carbonaceous adhesion of copper or copper alloy material, after immersing the metal in nitric acid solution, wipe the surface with absorbent cotton, and determine the degree of blackening of cotton. ing. However, this method has not been put to practical use because of its low sensitivity and lack of quantitativeness.

[Problems to be solved by the invention]

By the way, as a cause of abnormal corrosion of copper or copper alloy pipes, which is often used as a heat exchanger for plants and cooling equipment, in fresh water and seawater, it was thought that carbon contamination of the material surface due to the manufacturing process was considered. , There is no suitable detection means,
As a countermeasure, some measures such as shaving the surface layer were taken.

However, there was no means to detect whether or not this treatment was appropriate.

That is, electron spectroscopy, electron microscopy, X-ray analysis and the like are of little use.

Therefore, an object of the present invention is to provide a method for detecting the degree of contamination of a metal surface, which can detect the degree of contamination sharply by a simple method.

[Means for solving problems]

In order to achieve the above object, the present invention uses the following method. That is, the counter electrode is arranged facing the metal to be inspected,
A reference electrode is provided between these to provide a potential difference between the metal to be inspected and a potential difference is provided between the metal to be inspected and the reference electrode, and these are immersed in a chromic acid solution to remove the metal to be inspected. By measuring the current flowing between the counter electrode and the counter electrode, from the measurement step of measuring the current in the electrolyte based on the chromic acid solution for the metal to be inspected, from the state of the current obtained from the measurement step And a determination step of determining the cleanliness or contamination of the metal to be inspected.

[Action]

In the present invention, an electrolytic solution that has an oxidizing action without damaging (not corroding) the metal material base and has an active reducing action on the carbonaceous surface is used. Chromic acid is used as an electrolytic solution satisfying this condition, and this chromic acid is used. The metal to be inspected is immersed in this chromic acid-based electrolyte, the metal is polarized in the solution, and the magnitude of the reducing current generated is measured to determine the cleanliness or contamination of the surface. . That is, the reduction reaction of (Cr6 valence) → (Cr3 valence) due to the reaction of HCrO ₄ ⁻ + 7H ⁺ + 3e → Cr ⁺⁺⁺ + 4H ₂ O is active in the carbonaceous material, and the degree of contamination or the degree of cleaning is based on the fact that an electric current easily flows. To inspect.

Therefore, according to the present invention, it is possible to provide a method for detecting the degree of contamination on a metal surface, which can determine the degree of contamination or the degree of cleaning sharply by a simple method.

〔Example〕

 First, the principle of the present invention will be described.

INDUSTRIAL APPLICABILITY The present invention does not damage the metal base material (does not corrode) and has an oxidizing action, and has a carbonaceous surface (the surface of carbon alone).
Then, a chromic acid solution, which is a solution having a vigorous reducing action, is used as the electrolytic solution. The metal to be inspected is immersed in this chromic acid-based electrolyte, and the metal is polarized in the solution.
The level of reduction current generated in the potential range of +0.6 to 0 V (based on silver / silver chloride electrode) is measured to determine the cleanliness degree or contamination degree of the surface.

That is, the equilibrium potential of the reduction reaction of chromic acid is theoretically expressed by the following equation.

HCrO ₄ ⁻ + 7H ⁺ + 3e → Cr ⁺⁺⁺ + 4H ₂ O (1) The silver-silver chloride standard E (in 3.3 MkCl) is E = 1.144-0. 1379PH + 0.0197 · log ([HCr
O ₄ ⁻ ] / [Cr ⁺⁺⁺ ]) The reduction potential changes depending on the concentration ratio of PH (pH) and [HCrO ₄ ⁻ ] / [Cr ⁺⁺⁺ ] of the liquid.

Varying from the equilibrium potential of the potential E _x in the direction of the less noble,
Depending on the potential chloride (E−E _x ) = ΔE, 3e of the first equation
A current corresponding to (electrical quantity) flows.

However, this current is different depending on the surface substance on which the reaction occurs, and, for example, platinum alone is inactive because no current flows even if the potential change ΔE is greatly changed. On the other hand, as shown in FIG. 4, in the simple substance of carbon, the current starts to flow from + 0.6V and a peak occurs at around + 0.4V, and the current decreases with the decrease of the potential. Very active. Thus, the reaction of the first equation (Cr
A reduction reaction of (hexavalent) → (trivalent Cr) is active in carbonaceous matter, and an electric current easily flows.

Therefore, if carbon adheres to the platinum surface, a current flows under the above-mentioned potential condition, so that the degree of contamination on the surface of the metal material to be inspected can be immediately known.

The potential generated by this current varies slightly depending on the concentration of chromic acid, the material used as the base, the degree of carbon deposition (distribution), the temperature, and the flow of the electrolyte, but the generated current in the potential range of +0.6 V to 0 V varies. If used, it is possible to cover most of the differences due to these various conditions, and it is possible to detect the degree of dirt on the surface of the inspected metal material.

The present invention is based on such a principle, and one embodiment thereof will be described below with reference to the drawings.

The present invention relates to a method for detecting the degree of contamination by carbonaceous substances generated in the manufacturing process of copper or copper alloys, and does not include dirt due to dust, corrosion products, oil or the like.

FIG. 1 shows a flow sheet of an embodiment according to the present invention. In FIG. 1, 1 is a container, 2 is a chromic acid solution, 3
Is an electromagnetic stirrer, and 4 is a stirring blade.

The chromic acid solution 2 in the container 1 is agitated by the electromagnetic agitator 3 and the agitating blade 4 under constant conditions. A sample material 5, a counter electrode 6 such as a platinum plate, and a reference electrode 7 for measuring the electrode potential of the sample material 5 are immersed in the chromic acid solution 2.

Further, the test material 5 is connected to the lead wire 8a, the counter electrode 6 is connected to the lead wire 8b, and the reference electrode 7 is connected to the potentiostat 9 by the lead wire 8c.

In such a configuration, the potentiostat 9 changes the potential difference between the sample material 5 and the reference electrode 7 at a constant speed as shown in the second equation.

Et = E _N + vt (dE / dt) = v (2) Here, E _N is the natural potential of the sample material 5, Et is the potential of the sample material 5 at time t, and v is the potential scanning speed.

A current 10 flows from the potentiostat 9 through the lead wire 8b, the counter electrode 6, the chromic acid solution 2, the test material 5, the lead wire 8a, and the potentiostat 9 in response to this potential difference Et, and the current 10 at this time is the test material. 5 depends on the degree of activity with respect to chromate ion.

Fig. 2 shows the copper alloy test material I (manufactured by Company A), Fig. 3 shows the copper alloy test material II (manufactured by Company B), Fig. 4 shows the carbon material, and Fig. 5 shows the potential difference and current of the platinum material. It is a figure showing an example of a measurement result.

The copper alloy test material I in FIG. 2 and the copper alloy test material II in FIG. 3 show copper alloy materials having different manufacturing steps for comparison. That is, the copper alloy test material I shown in FIG.
The copper alloy test material II in the figure is free of contamination. Further, FIG. 8 shows a negative polarization curve of the copper alloy test material I similar to the copper alloy test material I after removing the carbon contamination. As can be seen, compared to FIG. 2, the current becomes smaller as a whole, and the distribution becomes flat in the high potential region, showing a curve that is completely different from that in the contaminated state.

That is, when the surface of the test material is contaminated with carbon or the like, the electric current based on the above formula 1 flows in the chromic acid solution. Therefore, the copper alloy test material I of FIG. 2 and the copper alloy test material of FIG. Trial material
The difference in II is considered to be due to the difference in surface cleanliness due to the difference in manufacturing process. For example, such a difference in surface cleanliness of the pipe occurs due to a defect in cleaning the lubricating oil when the copper pipe is drawn out in the manufacturing process and a defect in the purity of the inert gas in the annealing process. Conventionally, such a difference in cleanliness of the material to be inspected could not be measured, but according to the present invention, the difference in cleanliness can be clearly recognized as described above.

As is clear from FIGS. 2 to 5, the carbon material is extremely active in the reduction of chromic acid, and the peak value of the current makes it possible to detect sensitively whether the surface of the copper alloy is contaminated with the carbon material. Recognize.

The measurement conditions of FIGS. 2 to 5 are as follows.

． Electrolyte solution 0.1M chromic acid solution. Potential scanning speed 125 V / min A more specific description will be given. The present invention relates to a method for detecting the degree of contamination by carbonaceous matter, which is used for detecting the degree of contamination caused by carbonaceous matter that occurs in the manufacturing process of copper or copper alloy. And the present invention finds that the carbon electrode is extremely active in the reduction of chromate ions,
Using this phenomenon, we calculated the reduction current of copper or copper alloy material with carbonaceous material in a chromic acid solution, and obtained a very good correlation between the magnitude of the reduction current and the degree of surface contamination. I took advantage of this fact.

In the present invention, the magnitude of reduction current is measured according to the following procedure.

As shown in the configuration of FIG. 1, first, the container 1 is filled with the chromic acid solution 2. The sample material 5, the counter electrode 6, and the reference electrode 7 for measuring the potentials of the sample material 5 are immersed in the chromic acid solution 2.

In such a configuration, the potentiostat 9 is used to change the potential of the sample material 5 from the natural potential (the potential indicated by the metal immersed in the solution) to the negative direction, and at that time, the current flowing between the counter electrode 6 and the counter electrode 6 is changed. taking measurement. The relationship curve between the potential and the current is called a polarization curve, and the relationship curve when the potential is changed in the negative direction is called a negative polarization curve (FIGS. 2 to 5).

In the negative polarization curve of carbon alone in FIG. 4, +0.6
It can be seen that a reducing current of several tens of mA flows in the potential region of V to 0 V (with respect to the silver / silver chloride reference electrode).
Further, it can be seen that the reduction current also flows in the copper alloy test material I manufactured by Company A with severe carbon contamination shown in FIG.

On the other hand, the copper alloy test material II manufactured by Company B without carbon pollution shown in FIG. 3 and the platinum simple substance shown in FIG.
The reduction current in the potential region of V to 0 V is extremely small, 1 mA or less. Therefore, by previously obtaining the relationship between the carbon contamination level and the reduction current, it is possible to evaluate the carbon contamination level from the measured reduction current level.

The impedance method can also be applied to the present invention. The impedance method in this case applies an AC voltage between the sample material 5 and the reference electrode 7, measures the AC current flowing at that time, and obtains the impedance (voltage / current). It is no different from the negative polarization curve measurement method.

Next, FIG. 6 shows that the copper alloy test material I shown in FIG. 2 is sand-plasted, but shows that the carbon material is not completely removed.

The one in FIG. 8 ground about 100 μm from the surface is the third
It can be confirmed that the contamination was completely removed, almost the same as in Fig. 5 and Fig. 5.

The magnitude of the reduction peak current of chromic acid depends on the chromic acid concentration,
Since it varies depending on the stirring state of the solution, the potential scanning speed, the temperature, etc.,
It is necessary to perform measurement under these constant conditions in terms of reproducibility and accuracy. Generally, as the carbon coverage is high, the chromic acid concentration is high, the stirring is vigorous, the potential scanning speed is high, and the temperature is high, the current peak value increases. This peak current can also be observed as a normal chromate ion diffusion current by adding sodium sulfate or the like.

FIG. 7 shows a flow chart of an embodiment of the present invention combined with a manufacturing process. As shown in the figure, in the middle of the pipe manufacturing line 11, for example, a pipe withdrawal 14 from a degreasing cleaning unit 12 or an annealing device (including an inert gas manufacturing device) unit 13,
14 'is carried out, and this is reduced by a combination of a cell 15 containing a chromic acid solution and a potentiometer 16 shown in FIG. 1 and a combination of a cell (standard cell) 17 containing a material with a clean surface and a potentiometer 18. The current is measured, and the difference or ratio between the outputs of the potentiometers 16 and 18 is taken by the comparison amplifier 19, and this value and a factor predicted in advance by the lubricating oil removal work and the annealing work process, for example,
Dirty wash oil, insufficient number of washes, the temperature ..., in for example methane reforming of inert gas produced CH 4 _{+ +} ^H 2 _O in (C /
The output 22 of the artificial intelligence (processing device 20, judgment standard 21) such as H ₂ O) ratio, catalyst aging, temperature defect, etc. is transmitted to the degreasing cleaning part 12 and the annealing device part 13 of the production line 11 to avoid irrationalities. I will fix it. Incidentally, once the value of the standard cell 17 is stored in the artificial intelligence side, the standard cell 17 and the potentiometer 18 may be removed thereafter.

Further, the method of the present invention is not limited to the copper alloy material as a measurement target, but is effective as a means for detecting carbon contamination of iron, copper, zinc, and other metals that are passivated by chromic acid.

As described above, the present invention does not damage the metal material substrate (does not corrode), has an oxidizing action, and has a reducing action active on the carbonaceous surface. And then polarize the metal in the solution to measure the reduction current generated in the potential range of +0.6 to 0 V (based on silver / silver chloride electrode) to measure the cleanliness or contamination of the surface. The judgment is made.

Carbon exhibits electrochemical behavior similar to white metal, and when it is present on a metal, it acts as an active point for the reduction reaction of an oxidant in a solution, for example, dissolved oxygen in seawater, and causes abnormal dissolution or corrosion of the metal. Promote to. INDUSTRIAL APPLICABILITY The present invention makes it possible to easily judge in a single time what has been almost impossible as a means for monitoring the metal material manufacturing process and judging the degree of surface finishing. And it can greatly contribute to the reduction of corrosion accidents in the product plant.

〔The invention's effect〕

As described above in detail, according to the present invention, it is possible to provide a method for detecting the degree of contamination of a metal surface, which can determine the degree of contamination sharply by a simple method.

[Brief description of drawings]

FIG. 1 is a flow chart showing an embodiment of the present invention.
FIGS. 6 to 8 show negative polarization curves of various materials, and FIG. 7 is a flow sheet showing an example of a tube manufacturing process to which the present invention is applied. 1 ... Container, 2 ... Chromic acid solution, 3 ... Magnetic stirrer,
4 ... Stirring blade, 5 ... Test material, 6 ... Counter electrode, 7 ... Reference electrode, 8a, 8c ... Lead wire, 9 ... Potentiostat.

Claims (1)

[Claims] 1. A counter electrode and a reference electrode, which are arranged facing each other to the metal to be inspected, and which are provided between them to provide a potential difference with the metal to be inspected. And a potential difference between them, and soaking them in a chromic acid solution, and measuring the current flowing between the metal to be inspected and the counter electrode, the metal to be inspected in an electrolyte solution based on a chromic acid solution. And a determination step of determining the cleanliness or contamination degree of the metal to be inspected from the state of the current obtained from the measurement step. .