KR100919226B1 - Electro-chemical process for evaluating thickness of metal plated-layer - Google Patents

Abstract

The present invention is to determine the state of peeling the thickness of the surface coating layer when applying the weight loss method used to measure the thickness of the coating layer coated on the surface in order to prevent the corrosion of the base metal by using the corrosion equilibrium potential transition method of the electrochemical method It relates to an electrochemical method for metal plating layer thickness evaluation.

Description

Electro-chemical process for evaluating thickness of metal plated-layer

The present invention can simply dissolve the coating layer completely in a solution by using the open-circuit corrosion potential method, which is an electrochemical method, in minimizing the dissolution of the metal when measuring the thickness of the coating layer coated on the surface to prevent corrosion of the metal. The present invention relates to an electrochemical method for evaluating the thickness of a metal plating layer to determine a time period.

The most commonly used method for measuring the thickness of the plating layer is the weight loss method. This is a method of measuring the thickness of the plating using the density (d) and the test area (S) of the plating material by measuring the difference between the weight (W1) after plating and the weight (W2) after peeling the plating layer. Here, the plating layer thickness T is calculated as [(W1-W2) * d / S]. But conventionally

Iv) clean and dry the foreign matter on the specimen with alcohol or a suitable solvent,

Ii) chemically and electrically dissolving the coating in a suitable solution;

Iii) After completion of dissolution, the surface is washed with alcohol / distilled water and dried.

Here, in addition to the coating on the plated layer in step ii), there is a possibility that the weight loss due to dissolution of the base material used as the base (base) may occur, thereby causing a measurement error. In addition, in order to accurately measure a number of times, by applying an experimental design method and the like to determine the optimum peeling time through surface observation and component analysis, it takes a lot of time.

As described above, in order to determine the weight (W2) after peeling the plating layer, it takes a long time to find the time that the specimen is completely peeled by immersing the specimen in the plating layer dissolution solution. There are many difficulties.

Accordingly, the present invention measures the change in the open circuit potential voltage according to the plating layer peeling solution immersion time using a potentiostat to determine the time for which the constant open circuit corrosion voltage is measured with time. The purpose of the present invention is to set the time to be completely peeled off from the peeling solution, and to determine the time for the complete separation of the plating layer when applying the weight loss method by using an electrochemical method, thereby preventing corrosion of the metal using the same.

In the present invention, in order to determine the plating layer removal time using a plating layer removal solution to minimize the metal dissolution time when measuring the thickness of the coating layer coated on the surface to prevent corrosion of the base metal,

In the electrochemical method for the evaluation of the thickness of the plating layer, using the open-circuit corrosion potential method, the time to reach the steady state of the open-circuit corrosion potential value at which the coating layer on the base metal surface is completely dissolved is determined as an appropriate plating layer removal solution immersion time. Invention.

Here, the plating layer removal time to be determined means the minimum immersion time.

By determining the complete removal time of the plating solution when applying the weight loss method according to the present invention using an electrochemical method, as described above, the plating layer can quickly determine the complete removal time of the peeling solution. In addition, the accuracy of the measurement can be improved compared to the visual inspection method using the naked eye and microscope.

Figure 1: Schematic diagram of reactions that can occur when the plated metal is immersed in the stripping solution

FIG. 2: Schematic diagram of various types of corrosion potentials that may occur when the plated metal interface is peeled off (where t ₀ : minimum time for peeling of the plated layer)

3: Conceptual view of the operation of the simulation device for the determination of the electrochemical peeling time

4: Schematic diagram of capillary tip device with fine holes formed at the end

5: A state explanatory diagram when an analytical specimen is loaded into the plating-side peeling vessel of FIG. 3.

1 schematically illustrates a reaction that may occur when a plated metal is immersed in a plating stripping solution. Here, when the base metal (M ₂ ) and the plating layer (M ₁ ) formed on the surface of the material metal (M ₂ ) are immersed in the plating stripping solution, an ionization reaction occurs when a metal ion is present in the plating stripping solution, and the metal is converted into a metal ion. The electron emission reaction occurs accordingly.

The dissolution reaction of the plated metal (M ₁ ) at the metal interface

M ₁ → M ₁ ^{n +} + ne ⁻ to dissolve the metal compound at the interface.

The dissolution reaction of the metal compound at the interface

When the intermetallic compound is generated at the M ₁ / M ₂ interface, for example, a metal compound is generated at the interface of Fe ₅ Zn ₂₁ , FeZn ₇ , FeZn _13, and the like during Fe-Zn hot dip plating. Therefore, the reaction in such a case is collectively called an intermetallic compound dissolution reaction.

Dissolution reaction of base metal (M ₂ )

M ₂ → M ₂ ^{m +} + me ^-The base metal dissolution reaction proceeds. Where n and m are oxidized singers that appear upon ionization of the metal.

When the immersion in the plating stripping solution as shown in Figure 1, the plating layer is first peeled off and surface changes begin to occur. Subsequently, dissolution reaction of the plating layer occurs at the interface, thereby forming an electrochemical potential thereto. As peeling of the plating layer proceeds, this electrochemical equilibrium potential undergoes a change as shown in FIG. 2.

2 is a schematic diagram for predicting each of the various types of corrosion potential changes that may occur. That is, FIG. 2 is a schematic diagram of an equilibrium corrosion potential graph with time estimated to occur when a plating layer peeling reaction occurs in a plating layer. That is, the present invention is to determine the time to reach the steady state of the open-circuit corrosion potential value, which is completely peeled off the coating layer of the base metal surface by using the open-circuit corrosion potential method as described above as an appropriate plating layer removal solution immersion time Let's make a point.

As can be seen in Figure 2, after a predetermined time (t ₀ ), the plating layer is completely peeled off and the solution reacts with the base metal, whereby a constant open circuit corrosion voltage is observed. This is because the base metal reacts uniformly with the plating peeling solution to generate the base metal dissolution reaction. Therefore, when the base metal dissolution reaction occurs, it is possible to determine the elapsed time (t ₀ ) until then, thereby determining the complete peeling time of the plating layer in the plating layer peeling solution without a separate experimental plan. That is, each t ₀ time in the predicted graph assumed in FIG. 2 is determined as the minimum time for peeling the plating layer.

When the embodiments of the present invention are listed, they can be classified into the following four types.

In determining the plated layer removal time using the plated layer removal solution, the time at which the open circuit corrosion potential value reaches a steady state is determined as the appropriate plated layer removal solution immersion time.

Iii) a method for determining the Zn plating removal time when fabricating a standard specimen used for measuring Zn thickness in Zn hot-dip plating used for automotive inner / exterior materials as an example to which the method can be applied;

Ii) As another example to which the method can be applied, a method for determining Al plating removal time when fabricating a standard specimen used for measuring Al thickness of Al plated steel sheet used as an exhaust pipe material for automobiles;

Iii) As another example to which the method can be applied, the Pb-Sn plating thickness removal time is used to prepare a standard specimen for measuring Pb-Sn plating thickness in a Pb-Sn plated steel sheet used as a fuel tank material. How to determine;

Iii) The method is also an electrochemical method for the evaluation of plating thickness, which is applicable to the method of determining the removal time when removing various metals from the surface after conversion coating.

In this context, conversion coating is a type of metal surface treatment, and refers to a coating layer coated to protect a metal surface. This includes chromate treatment / phosphate treatment.

Figure 3 is a schematic diagram of the present simulation device for determining the electrochemical peeling time. Here, to evaluate the thickness of the plating layer

In the first step, the specimen is mounted on a holder or holder.

In the second step, the plating stripping solution is placed in a container.

In the third step, platinum Pt is used as a counter electrode, and the platinum electrode is mounted on a cell.

In the fourth step, an SCE electrode is mainly used as an electrode, and is mounted as another electrode.

In the fifth step, the equilibrium corrosion potential over time is measured in a potentiostat, and data processing and recording is performed on a computer.

As shown briefly in FIG. 3, the distance a between the analysis specimen and the SCE electrode is important. This is because when the distance between the specimen and the SCE electrode is long, the voltage drop caused by the solution occurs between the specimen and the SCE electrode.

Therefore, two devices are essential for realizing the present invention. One of them is to prevent the voltage drop caused by the resistance of the solution, and a capillary tip device designed for this purpose is essential, and the other is to prevent the distortion of the signal by infiltrating the plating peeling solution into the specimen device. A device for this is also essential.

4 shows a tip having a minute hole at the lower end to minimize the voltage drop caused by the solution as described above, and has a constant angle to minimize the voltage drop caused by the solution. It can be made.

FIG. 5 is an explanatory diagram for explaining a state when an analysis specimen is loaded into the plating layer peeling vessel of FIG. 3. FIG.

In the figure above, it is important to make room for the whole specimen to be pulled up. If not, it is cumbersome because additional work such as wiring is required.

In order to prevent infiltration of the solution, the outside of the device is provided with rubber packing (packing), and the material of the outside and the screw is preferably made of Teflon-based resin having strong chemical resistance.

Claims (3)

In determining the plating layer removal time by using the plating layer removal solution to minimize the metal dissolution time when measuring the thickness of the coating layer coated on the surface to prevent corrosion of the base metal, An electrochemical method for evaluating the thickness of a plated layer characterized in that by using the open-circuit corrosion potential method, the time to reach the steady state of the open-circuit corrosion potential value at which the coating layer on the base metal surface is completely dissolved is determined as an appropriate plating layer removal solution immersion time. The method of claim 1, (Iii) The method is used to determine the Zn plating removal time when manufacturing standard specimens for measuring Zn thickness in Zn hot-dip plating used as automotive inner / exterior materials. (Ii) The method is used to determine the Al plating removal time when manufacturing a standard specimen used for measuring Al thickness of Al-coated steel sheet used as an exhaust pipe material for automobiles. (Iii) The method also determines the Pb-Sn plating thickness removal time when manufacturing standard specimens used to measure Pb-Sn plating thickness in Pb-Sn plated steel sheets used as fuel tank materials. (Iii) the above method or in determining the removal time after conversion coating of various metals on the surface. Electrochemical method for evaluating plated layer thickness that is applicable. The plating layer according to claim 1, wherein an elapsed time (t ₀ ) until a constant open circuit corrosion voltage is observed as the plating layer is completely peeled off and the peeling solution reacts with the base material is determined as a minimum time for the plating layer to be peeled off completely. Electrochemical Method for Thickness Evaluation.