KR101572324B1 - Method for preventing corrosion of iron foil - Google Patents

Abstract

The present invention relates to a method for cleaning an iron body, Anodizing the workpiece by a constant current; Washing the iron oxide layer formed on the anodized iron foil with deionized water; And a step of heat treating the washed iron oxide layer in a nitrogen gas atmosphere. According to the method of the present invention, the corrosion potential of the iron foil work is moved in a positive direction through a simple continuous process to greatly reduce the corrosion and form an oxide layer in which defects, which are problems of the oxide film, are removed, .

Description

[0001] The present invention relates to a method for inhibiting corrosion of iron foil,

The present invention relates to a method for inhibiting the corrosion of iron foil on iron foil, and more particularly, to a method for inhibiting iron foil corrosion by electrochemically forming an oxide film on a foil foil to provide corrosion resistance against corrosion.

BACKGROUND ART [0002] In general, a technique for manufacturing an iron plate having a coating film composed of a metal is known as a method for protecting iron from corrosion. This technique is basically known as a barrier protective coating and an anode active protective coating. The barrier protective coating is in particular a protective coating consisting of aluminum, tin or chromium. To produce a barrier protective coating, an aluminum alloy, for example, is deposited on the steel strip by a process referred to as a so-called hot-dip coating process.

The most widely used anode active corrosion protection layer is zinc coated. In particular, the action of these zinc coatings is based on the fact that if the damage of the zinc layer on the steel is to the base layer of steel, the chemically less precious zinc can first be corroded to protect the base layer of steel.

The zinc coating includes a pure zinc coating, a zinc coating containing a low content of aluminum, a zinc coating (Galfan) containing an aluminum content of about 5%, and a zinc aluminum coating containing approximately half of zinc and aluminum.

The coatings are likewise plated using a hot dip method, in which the preheated steel strip is transported through a zinc bath or a zinc or zinc alloy bath. Plating layers, referred to as so-called galvannealed layers, represent a special case where hot-dip galvanization is used to deposit a zinc layer or zinc alloy layer on a base layer of steel, followed by annealing Step is carried out on the one hand to form a zinc / iron alloy layer, on the other hand, to cause a diffusion reaction between the zinc and iron of the steel substrate. This layer is considered to be an alloying hot-dip galvanized layer. However, when the corrosion of iron is prevented by the above-mentioned hot-dip coating method, there is a problem that the corrosion resistance is reduced according to the consumption time of unnecessary zinc and aluminum.

In order to solve the above problems, Korean Patent Laid-Open Publication No. 1998-0002298 has a main constitution in which a base steel sheet (1) and a 0.12 to 0.18 weight% A1, 99.88 to 99.82 weight% Zn alloy plated layer 2 made of hot-dip galvanized steel comprising a chromate layer 3 which is chromate treated on the alloy plating layer 2 and a flexible polyester coating layer 4, 5 which is formed on the chromate layer 3, The manufacturing method includes a step of plating the steel sheet through an alloy plating bath of 455-465 ° C made of 0.12-0.18 wt% A1 and 99.88-99.82 wt% Zn, adjusting the amount of plating coating by an air wiping method, (3) of 20 to 80 mg / m < 2 > by drying at 60-140 < 0 > C temperature condition applied with a thin film using the method described above, and after the rollable coating of the flexible polyester paint RTI ID = 0.0 > 241 C < / RTI & Lexus is a coating step and the embossing roll in block coat layer (PRA forehead and a top coat. 2F) The final reduction was initiated to melt the lower edge coated color steel sheet and a manufacturing method which comprises the reduction process in which patterns are formed.

However, when the anti-corrosive layer is formed by the above-described method, a chromium hydrochloride layer and a flexible polyester coating layer, which are chromate-treated again, are additionally formed after the alloy plating layer is formed in order to perform roll coating, There is a problem.

The present invention provides a corrosion inhibiting method capable of increasing the resistance to corrosion by forming a corrosion inhibiting layer on a brickwork through a simple electrochemical method.

The present invention relates to a method for cleaning and preparing iron foil; Anodizing the workpiece by a constant current; Washing the iron oxide layer formed on the anodized iron foil with deionized water; And a step of heat treating the washed iron oxide layer in a nitrogen gas atmosphere.

The step of washing the iron foil work may include washing the iron foil workpiece with a mixed solution of ethanol and acetone in an ultrasonic washing machine for 10 to 30 minutes.

Further, the step of performing the anodic oxidation may be characterized by performing anodic oxidation at a constant current of 500 to 1000 mA / cm < 2 >.

In addition, the step of anodizing the iron foil workpiece with a constant current may be characterized in that 25% (w / v) sodium hydroxide is added at a temperature of 23 to 27 ° C and anodic oxidation is carried out at a constant current.

The heat treatment may be performed at a heating rate of 2 ° C / min for 1 to 2 hours at a temperature of 500 to 600 ° C.

According to the method of the present invention, the corrosion potential of the iron foil work moves in a positive direction through a simple continuous process to greatly reduce corrosion and form an oxide layer in which defects, which are problems of the oxide film, are removed, .

1 is an FE-SEM image of the surface and cross-section of the iron oxide layer formed by heat treatment at different temperatures,
FIG. 2A is an XRD graph showing the crystallinity of the iron oxide layer formed by heat treatment once,
2B is a graph showing the corrosion potential of the iron oxide layer formed by heat treatment once,
3 is an FE-SEM image showing the surface and cross-section of an iron oxide layer produced by anodization,
FIG. 4 is a graph showing the XRD graph of the corrosion inhibitor produced by the corrosion inhibiting method according to an embodiment of the present invention,
FIG. 5 is a graph showing a Tafel plot of the Tafel behavior of an anodic oxidation annealed at a constant current of 1000 mA / cm 2, which is a corrosion inhibiting method according to an embodiment of the present invention,
FIG. 6 is a graph showing the Tappel's behavior according to the constant current of the iron plate manufactured by the method of the present invention,
FIG. 7 is an FE-SEM image of a steel plate manufactured by the corrosion inhibiting method according to an embodiment of the present invention,
FIG. 8 is a graph showing the Tappel's behavior of the annealing furnace manufactured by varying the heat treatment temperature in the corrosion inhibiting method according to one example of the present invention.

The present invention relates to a method for cleaning and preparing iron foil; Anodizing the workpiece by a constant current; Washing the iron oxide layer formed on the anodized iron foil with deionized water; And a step of heat treating the washed iron oxide layer in a nitrogen gas atmosphere.

Thermodynamically, corrosion is a spontaneous reaction due to the inherent nature of the metal and the tendency of the free energy value of Gibbs to change negatively. Examination of the standard potential sequence showing the corrosion tendency of various metals reveals that the negative standard electrode potential (V °) has the greatest correlation of metal oxidation. The standard potential of iron in the standard potential sequence is -0.440 V, which is more negative than nickel (Ni, -0.250 V), tin (Sn, -0.136 V), copper (Cu, 0.33 V) Value. Since iron is an essential metal in a variety of applications, the corrosion prevention method of iron is an important research task.

Electrochemical oxidation, commonly referred to as anodic oxidation, is a method that facilitates the formation of an oxide layer that can control the thickness of the metal surface while preventing corrosion. In the case of aluminum (Al), titanium (Ti), zirconium (Zr), magnesium (Mg), nickel (Ni) and zinc (Zn), a dense oxide film is dramatically enhanced by anode formation, It is an indispensable process for increasing the corrosion resistance in such metals.

Conversely, anodic oxidation of iron generally forms an oxide film that is either porous or non-protective, which is either dissolved in the electrolyte or is easily separated from the iron substrate. Therefore, many attempts to form anodic oxide films for corrosion inhibition have not been satisfactory.

A method of forming an iron oxide film by anodizing under sodium hydroxide (NaOH) has been disclosed. Recently, anodic oxidation in a hot sodium hydroxide solution has shown that a nanoporous oxide film containing magnetite is formed. The introduction of commercial corrosion inhibiting oils increased corrosion by a factor of hundreds.

In an embodiment of the present invention, an alkali solution is introduced at room temperature to anodize the iron foil to form a non-porous iron oxide film. In order to remove the drawbacks of corrosion inhibition through a continuous heat treatment process, an amorphous structure Lt; / RTI >

The step of washing the iron foil work may include washing the iron foil workpiece with a mixed solution of ethanol and acetone in an ultrasonic washing machine for 10 to 30 minutes.

And washed with ethanol and acetone to completely remove foreign matters on the iron foil.

Further, the anodizing step may be characterized by performing anodization at a constant current of 500 to 1000 mA / cm < 2 >. As the current density increased, the thickness of the oxide film formed on the mandrel increased and the texture changed finely.

If it is outside the above range, an oxide film is not formed or many defects of an oxide film to be formed are generated, which is not suitable as a corrosion inhibiting method.

In addition, the step of anodizing the iron wire with a constant current may include the step of charging 25% w / v sodium hydroxide at a temperature of 23 to 27 ° C and anodizing the wire with a constant current.

An oxide film having a constant thickness was formed when anodic oxidation was performed under the above-mentioned temperature condition in an alkali solution.

The heat treatment may be performed at a heating rate of 2 ° C / min for 1 to 2 hours at a temperature of 500 to 600 ° C. The heat treatment may be performed in a nitrogen atmosphere.

Defects have been removed with the iron oxide film is formed on the crystalline DAN day via the heat treatment was changed to the generated by the anodic oxidation in the heat treatment process, hematite iron oxide film is magnetite _{(Fe 3 O 4) (Fe} 2 O 3). It is considered that the content of the magnetite is increased and the defects of the iron oxide layer are reduced, and that the amorphous structure is changed to crystalline.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the scope of the present invention is not limited to the following examples. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

< Example  1> Hill Oxide layer  formation

0.5 mm thick high purity iron (Goodfellow, England, 99.5%) was prepared as a substrate on which the iron oxide film was formed. Acetone and ethanol were added and washed in an ultrasonic cleaner for 10 minutes. Thereafter, anodic oxidation was performed using a two-electrode system in which platinum was used as a counter electrode and work electrode was used as a working electrode. A 25% (w / v) sodium hydroxide solution was used as the electrolyte and the temperature was adjusted to 25 ° C. Anodization was performed at constant current and current density was precisely controlled using a precision power supply (SourceMeter 2400, Keithley). After the anodic oxidation, it was washed again with deionized water.

The annealed sheet was heat-treated at 500 ° C. for 1 hour in a nitrogen (N ₂ ) atmosphere and then fired. Heat treatments were also performed at different temperatures for comparison.

< Experimental Example  1> Day Iron oxide membrane  Property Analysis

(FE-SEM) was obtained by field-emission scanning electron microscopy (S4300, Hitachi, Japan) in order to analyze the surface morphology of the hill surface after heat treatment. X-ray diffraction analysis was performed using an X-ray diffractometer (hereinafter referred to as "XRD") to measure the crystallinity of the iron oxide film.

All samples prepared for electrochemical corrosion test were carried in a 3.5% sodium chloride (NaCl) solution for 1 hour. The degree of corrosion was measured using potentiostat / galvanostat, AutoLab PGSTAT12, Eco Chemie). The composition of the three-phase electrode was platinum (Pt-mesh) as the anode, and Ag / AgCl 3M KCl as the reference electrode.

Potentiodynamic polarization was performed in a range of -1.5 V to 0 V with a potential scanning rate of 100 mV / s under 3.5% sodium chloride solution to measure the TAPELEL graph.

Electrochemical impedance spectroscopy (EIS) was performed by modulating the frequency range from 100 kHz to 100 mHz at a corrosion potential (E _corr ) of ± 10 mV.

1. Corrosion inhibition by heat treatment

 1 is an FE-SEM image of the surface and cross-section of an iron oxide layer formed by heat treatment at different temperatures. As expected, the thickness of the iron oxide layer increased with the heat treatment at higher temperatures.

2A is an XRD graph showing the crystallinity of the iron oxide layer formed by a single heat treatment. Crystals were not formed at 300 ° C, whereas oxides containing a mixture of hematite and magnetite were formed at 400 ° C. The hematite peaks at 40.863 ° (113), 49.464 ° (024) and 54.074 ° (116) were increased after heat treatment at 500 ° C.

FIG. 2B is a graph showing the corrosion potential of the iron oxide layer formed by heat treatment once. The graph shows that the corrosion potential (E _corr ) did not change at all in terms of crystallinity and thickness, indicating that a single heat treatment does not help to inhibit iron corrosion. Interestingly, pure annealing at 600 ° C shows a slight increase in corrosion current when annealed once.

2. On anodic oxidation  Corrosion inhibition by

3 is an FE-SEM image showing the surface and cross-section of an iron oxide layer produced by anodic oxidation. The workpieces were prepared by anodizing at different current densities. Here, the thickness of the barrier type oxide film changes in accordance with introduction of a potentiostatic mode or a built-in constant current mode. 3, it can be seen that the thickness of the oxide film changes in proportion to the density of the introduced current. This is because the built-in potential is proportional to the density of the current to be introduced. Also, it was confirmed that the particle size was greatly increased when the current density was 1000 mA / cm 2, because a uniform electric field was applied to the oxide layer at 1000 mA / cm 2.

3. Anodic oxidation  And corrosion inhibition by heat treatment

 X-ray diffraction analysis of the oxide films prepared by different methods showed that the pure oxide film and amorphous formed by the anodic oxidation were amorphous so that the iron peak in the iron substrate of the two samples (Fe, JCPDS # 87-021) Only at 44.673 ° (110).

After heat treatment at 500 ℃, both samples changed from amorphous to crystalline containing magnetite and hematite.

The presence of magnetite was found at 24.150 ° (012), 33.162 ° (104), 35.630 ° (110), 40.863 ° (113), 49.464 ° (024) and 54.074 ° (116) (Fe ₂ O ₃ , JCPDS # 87-1165 ), While the presence of hematite was 30.077 ° (220), 35.426 ° (311), 37.058 ° (222), 43.054 ° (400), 53.412 ° (422) (Fe ₃ O ₄ , JCPDS # 89-0950).

FIG. 4 is an XRD graph of the aluminum foil manufactured by the corrosion inhibiting method according to an embodiment of the present invention. FIG. Referring to the drawings, the composition of magnetite and hematite did not change according to the change in the current density introduced, and was influenced by the change of conditions in the heat treatment process.

Generally, changes in magnetite and hematite are believed to be due to the reaction represented by the following formula.

   [Chemical Formula 1]

2Fe + 0 ₂ ? 2FeO

6FeO + O ₂ ? 2Fe ₃ O ₄

3 Fe (OH) ₂ ? Fe ₃ O ₄ + H ₂ + 2 H ₂ O

4Fe ₃ O ₄ + O ₂ ? 6Fe ₂ O ₃

FIG. 5 is a graph showing a Tafel plot of the Tafel behavior of an annealed and annealed anodic current at a constant current of 1000 mA / cm 2, which is a corrosion inhibiting method according to an embodiment of the present invention. Referring to the drawing, it can be seen that corrosion inhibition is enhanced when anodic oxidation and heat treatment are performed at a constant current of 1000 mA / cm 2. Compared with the other samples, it was confirmed that the iron oxide layer of the annealed and calcined anode had the lowest corrosion current and the most positive corrosion potential.

The iron oxide layer by a single anodic oxidation formed a thin layer of amorphous structure containing many of the weaknesses of the corrosive iron. This indicates that the firing process through heat treatment is essential to increase the corrosion resistance of the oxide layer.

FIG. 6 is a graph illustrating Tappel's behavior according to a constant current of a barbed wire manufactured by the method of the present invention. Referring to the figures, as expected, thick and dense iron oxide layers exhibited excellent resistance to corrosion.

In the embodiment according to the present invention, the best resistance to corrosion was exhibited when anodic oxidation and heat treatment were performed at a constant current of 1000 mA / cm 2 at the highest current density. As the constant current of anodic oxidation was increased, the thickness of the iron oxide layer increased. After the defects of the iron oxide layer were removed by heat treatment, it was judged that a thick and dense layer was formed, and as a result, it was confirmed to have excellent corrosion resistance.

Also, as the size of crystal grains formed at a high current density increases, it is considered to have a reduced crystal boundary area, and in this case, it is judged that the potential to corrode iron is lowered.

The electrochemical analysis (EIS) results show that the radius of the semicircle is indirectly indicative of the resistance to charge transfer, and with reference to the Tappel graph, one heat treatment of the annealed work forms the smallest semicircle, Speeded up. Therefore, it seems that corrosion is easier than pure annealing. The anodized and iron oxide layer showed the largest semicircle, showing the slowest charge transfer on the surface.

FIG. 7 is an FE-SEM image of a steel plate manufactured by the corrosion inhibiting method according to an embodiment of the present invention.

The optimum temperature was found by successively heating the anodized iron oxide layer at a constant current of 1000 mA / cm 2 at different temperatures. FIG. 8 shows that when the annealing temperature was increased, the intensity of the peak The thickness of the iron oxide layer increased by an increased amount. The average thickness of the iron oxide layer heat treated by anodic oxidation was found to be thicker than the thickness of the iron oxide layer baked by one heat treatment.

However, it was confirmed that cracks were formed in the iron oxide layer when heat treatment was performed at 600 ° C. or higher.

FIG. 8 is a graph showing the Tappel's behavior of the annealing furnace manufactured by varying the heat treatment temperature in the corrosion inhibiting method according to one example of the present invention.

It is confirmed that the temperature is the optimum temperature for increasing the corrosion resistance in case of 500 ° C heat treatment. Although there is an advantage in forming magnetite when heat treatment is performed at a temperature higher than the above temperature, there is a problem in that it does not increase the corrosion resistance and generates cracks in the process of forming a thick iron oxide layer.

In the present invention, the iron oxide film formed on iron foil has an increased corrosion resistance through anodic oxidation or continuous firing process and a combination thereof. This method can be regarded as a kind of electrochemical treatment.

Although the iron oxide film having a thickness of 2 탆 or more can be formed only by one-time anodic oxidation, corrosion resistance is reduced due to irregularity of the iron oxide film and a plurality of defects. In addition, the corrosion resistance of the iron oxide film is not increased by a single heat treatment.

Conversely, the combination of anodic oxidation and continuous calcination moves the corrosion potential in the positive direction on the Tafel plot, indicating increased corrosion resistance.

On the other hand, the formation of thick oxide during the anodic oxidation is thought to be related to the more positive shift of the corrosion potential after the heat treatment. Electrochemical impedance spectroscopy confirmed that the slowest charge transfer was observed in the oxide film produced by anodizing and calcining. From the viewpoint of maximum displacement of corrosion potential (E _coor ), which is the intersection point of _Tappel extrapolation in the _Tappel graph, the optimum heat treatment temperature after the anodic oxidation was 500 ℃.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. will be. It is therefore intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

Claims (5)

Washing and preparing the barbed work;
Adding 25% (w / v) sodium hydroxide at a temperature of 23 to 27 ° C and anodizing at a constant current of 500 to 1000 mA / cm 2;
Washing the iron oxide layer formed on the anodized iron foil with deionized water; And
The washed iron oxide layer was heat-treated at 500 to 600 ° C for 1 to 2 hours at a heating rate of 2 ° C / min under a nitrogen gas atmosphere to convert the iron oxide layer from hematite (Fe ₂ O ₃ ) to magnetite (Fe ₃ O ₄ ) Comprising the steps of: The method according to claim 1,
The step of cleaning the bar work includes:
The method for inhibiting corrosion of iron alloy according to any one of claims 1 to 9, wherein the iron corpuscle is put into a mixed solution of ethanol and acetone and is then washed in an ultrasonic washing machine for 10 to 30 minutes. delete delete delete

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