JPH11223584A - Derusting method for test piece to be analyzed - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a derusting method in which rust caused on the surface of a test piece as a steel material or a plated steel material can be removed quickly and precisely by a method wherein the test piece is immersed in a bath composed of an aqueous solution in which hydrochloric acid and hexamethylenetetramine at specific concentrations are contained. SOLUTION: A derusting method is a method in which rust caused on the surface of a test piece as a steel material or a plated steel material is removed in a process in which the rust is quantitatively analyzed. The test piece is immersed in a bath composed of an aqueous solution in which 5 to 25 wt.% of hydrochloric acid and 0.1 to 10 g/l of hexamethylenetetramine are contained and whose solution temperature is within a range of 20 to 70 deg.C. After the rust is dissolved and stripped in this manner, 0.1 to 5 wt.% of hydrogen peroxide is added to the bath. The hydrochloric acid has an action which dissolves iron rust, and the hexamethylenetetramine has an action which increases the removing property, especially the stripping property, of the rust. The hydrogen peroxide has an action which dissolves the rust which is stripped so as to be deposited inside a container. Thereby, the rust on the surface of the test piece can be removed completely in a short time while the erosion of substrate iron is being suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rust removing solution for removing rust of corrosion products generated on the surface of steel such as steel and plated steel, and is used for quantifying the rust. The present invention relates to a rust removing solution used for removing rust to improve the appearance of a steel material and capable of dramatically shortening the time required for removing the rust.

[0002]

2. Description of the Related Art As corrosion products formed on the surface of steel or plated steel, so-called rust is typical, and the rust is iron rust (so-called red rust) and zinc rust (so-called white rust). And represented by And zinc rust dissolves more easily than iron rust from the viewpoint of dissolving rust by the rust removing solution. In this specification, unless stated otherwise, the term "rust"
Shall include both iron rust and zinc rust. Especially when emphasizing iron rust, even when both rusts are included, "iron rust"
Is used. The term “removal” of rust is a term including both a case where rust is removed from a steel material or the like by a melting phenomenon and a case where rust is removed from a steel material or the like by a peeling phenomenon. Further, the “surface” of a test piece or the like refers to a flat portion, a curved portion,
It shall include all of the end face part and the edge part.

[0003] The use of the above-mentioned rust removing solution for removing rust includes (1) quantitative analysis of rust formed on a test piece in order to evaluate the corrosion resistance of a steel material, and (2) structure and exterior, etc. In order to reproduce the aesthetic appearance of the steel plate, it can be roughly classified into a case where rust generated on a steel material or a plated steel material in use is removed.

The present invention is directed to the use of the above item (1). When a plated steel sheet for building materials used in a house or the like is corroded, in order to accurately determine the weight of rust generated on the plated steel sheet, a test piece cut out from the corrosion-coated steel sheet or the like, It is desired that rust generated on the surface and the end face of a test piece, such as a steel plate, subjected to an exposure test be removed completely and completely without eroding the underlying steel (hereinafter referred to as ground iron). .

Conventionally, as a rust removing solution used for quantitatively evaluating the progress of the corrosion, for example, JIS Z2
371 Iron and steel specified in Appendix 1 are used. As a typical example, each of the following rust removing solutions and the method of using the same are briefly described.

As a method often used as a test method for evaluating the corrosion resistance of steel materials used in automobiles, distilled water is added to 50 g of sodium hydroxide and 200 g of granular zinc to make 1000 ml, and a test piece is added to this aqueous solution for 30 to 40 minutes for 80 minutes. Hold at ~ 90 ° C. The main point in evaluating the corrosion resistance of steel materials used in automobiles is mainly in measuring the corrosion depth. Thus, the corrosion products of the test piece are dissolved and removed (hereinafter referred to as Prior Art 1), and the depth of the corrosion hole is measured.

[0007] 3.5 g of hexamethylenetetramine is added to 500 ml of hydrochloric acid, and distilled water is added to make 1000 ml. The test piece is kept in this aqueous solution at 20 to 25 ° C for 10 minutes. This is a method of dissolving and removing corrosion products of a test piece (hereinafter referred to as prior art 2).

The test pieces used in the above two methods are prepared by a corrosion acceleration test such as a salt spray test or an exposure test which is usually carried out under conditions determined in consideration of environmental conditions in practical use. Performed on corrosion test specimens.

[0009]

In order to evaluate the durability of a structure such as a plated steel material for a building material used in a house or the like, the corrosion loss per unit area (g / m ² ) of the used steel material is determined.
Is often used as an index. However, for example, in a steel house, there are many screwed portions and cut line portions of a plate, and accordingly, the inner surface and cut end surface of the screw hole are formed at many positions. FIG. 3 is a schematic perspective view for explaining rust generated on the inner surface of a screw hole, a cut end surface, or a flat surface of a steel material in a steel house. In the figure, 1 is a steel material, 2 is a screw, 3 is rust generated on the inner surface of the screw hole, 4 is rust generated on an end surface of the steel material, and 5 is rust generated on a flat portion of the steel material. Here, the corrosion of the screw inner surface impairs the screw tightening function, so that the strength of the structure is significantly reduced.

However, the weight of the rust 3 on the inner surface of the screw is smaller than the weight of the rust 5 on the flat portion, and it is difficult to determine the weight loss by the weight method. Therefore, the quantification method is IC
It must be performed by P analysis or the like. Since such an analysis method is employed, when removing the rust 3 on the inner surface of the screw with a rust removing solution, even a slight dissolution of the ground iron reduces the accuracy of the quantitative analysis value of the rust.

On the other hand, in the quantitative analysis of corrosion weight loss, even when a gravimetric method is applied or when a fine chemical method such as an ICP analysis is applied, it takes a very long time to dissolve rust formed on a test piece. Is not practical.

The problems of the prior arts 1 and 2 are as follows based on the above request. In the prior art 1, iron rust is considerably peeled off at a liquid temperature of about 70 ° C. However, brushing is required for complete peeling, and the efficiency is poor. Moreover,
The peeled iron rust does not dissolve in the rust removing solution. Also, the danger is high because of the high temperature alkaline solution.

According to Prior Art 2, the rust peeling time is reduced. However, the reduction of the peeling time is still insufficient. For example, according to an experiment conducted by the present inventors, it was not possible to remove rust generated in a storeroom even if the treatment was performed for 60 minutes or more.

Therefore, the problem to be solved by the present invention is that rust generated on a steel test piece or a plated steel test piece can be completely removed in a short time while suppressing erosion of the ground iron.
An object of the present invention is to find a rust removing method that can dissolve rust removed and precipitated by the rust removing solution in the solution in a short time. Thus, an object of the present invention is to provide a rust removing method capable of quickly and accurately removing rust generated on the surface of a test piece of steel or plated steel in quantitative analysis.

[0015]

Means for Solving the Problems The present inventors have intensively studied to solve the above-mentioned problems from the above-mentioned viewpoints.
As a result, the following items were found. Hydrogen peroxide has the effect of dissolving the rust generated on the surface of the steel test piece. It also has the effect of dissolving the rust that has been separated from the surface of the test piece by the rust removing solution and precipitated in the bath. However, it should be noted that hydrogen peroxide has the effect of dissolving ground iron. Hexamethylenetetramine has an effect of removing rust generated on the surface of a test piece or a steel material.

The present inventors have conceived that the above-mentioned problems can be solved by appropriately utilizing the functions and effects of the above-mentioned components and the above-mentioned items. The method for removing rust of an analytical test piece according to the present invention is a method for quantitatively analyzing the rust generated on the surface of a test piece of steel material and plated steel material. And 0.1 to 10 g / l of hexamethylenetetramine,
After immersing in a bath composed of an aqueous solution having a liquid temperature in the range of 20 to 70 ° C., and thus dissolving and peeling the rust,
It is characterized in that 0.1 to 5 wt.% Of hydrogen peroxide is added to the above bath.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the action and effect of the components in the rust removing solution in the rust removing method of the present invention and the reason for limiting the operating method as described above will be described.

[0018] Hydrochloric acid has an action of dissolving iron rust, but when its concentration is 5 wt.% Or less, its dissolving ability is reduced. On the other hand, if the hydrochloric acid concentration exceeds 25 wt.%, The hydrochloric acid is liberated, so that it is difficult to control it. Therefore, it is desirable that the concentration of hydrochloric acid in the rust removing solution be in the range of 5 to 25 wt.%.

Hexamethylenetetramine has an effect of enhancing rust removal, particularly peelability. FIG. 1 is a graph showing a comparison of weight loss of steel due to dissolution and erosion of ground iron by various components having a rust peeling action. As described above, hexamethylenetetramine is effective as an additive component to the rust removing solution at the time of quantitative analysis of a small amount of rust on a test piece because it exhibits an effect on rust peeling and does not dissolve and erode the metal. . Further, FIG. 2 shows the effect of suppressing the dissolution of base iron when an inhibitor (corrosion inhibitor) is added to hexamethylenetetramine.

When the amount of hexamethylenetetramine added is 0.
In the case of 1 g / l or less, rust only dissolves from the rust surface, but if added more, rust comes to separate from the rust-ground iron interface, and rust can be removed in a short time. . However, when hexamethylenetetramine is added in an amount of more than 10 g / l, the effect is saturated when the concentration of hydrochloric acid is high. Therefore, adding more expensive hexamethylenetetramine in a larger amount increases the cost.

Therefore, it is desirable to limit the amount of hexamethylenetetramine to be added within the range of 0.1 to 10 g / l.

Hydrogen peroxide has an effect of dissolving rust on the surface of a test piece or a steel material, an effect of dissolving rust that has been separated by a rust removing solution and settled in a container, and further has an effect of dissolving ground iron. Also have. Therefore, in order to remove rust quickly, its effect is great if it is added, but care must be taken since the base iron is dissolved at the same time. That is, in a rust removing solution for a steel test piece or a plated steel test piece on the premise of micro analysis of rust generation, hydrogen peroxide must not be contained in the step of removing rust from the test piece. However, it is desirable to add hydrogen peroxide to the rust removing solution containing rust that has been once removed from the test piece and settled in the container, so that the precipitated rust is quickly dissolved.

On the other hand, when removing rust from a steel material or the like performed for aesthetic restoration, an appropriate amount of hydrogen peroxide is added in order to increase the rust removal rate by utilizing the rust dissolving action of hydrogen peroxide. Is desirable.

If the amount of added hydrogen peroxide is less than 0.1 wt.%, The effect of dissolving the rust formed on the surface and the effect of dissolving the precipitated rust cannot be sufficiently exhibited. On the other hand, the addition amount is 5w
If the content exceeds t.%, dissolved oxygen increases due to foaming, and the analysis accuracy decreases.

Therefore, the concentration of hydrogen peroxide added is 0.1
It is desirably within the range of ~ 5 wt.%.

The inhibitor (corrosion inhibitor) is added to a rust removing solution for quantitatively analyzing the rust of a test piece in the present invention, as is generally used in the rust removal of a steel test piece. Metal dissolution should be suppressed. The type and amount of the inhibitor may be determined according to a conventional method.

Next, the reasons for limiting the rust removing operation method will be described. The test piece is immersed in the bath while maintaining the temperature of the rust removing solution within the range of 20 to 70 ° C. If the liquid temperature is lower than 20 ° C., the rust removal rate from the surface of the test piece becomes slow, and the processing time becomes long, which is not practical. On the other hand, if the liquid temperature is higher than 70 ° C., there is a possibility that erosion of the ground iron occurs, which is not desirable.

Therefore, it is desirable to keep the liquid temperature during rust removal within the range of 20 to 70 ° C.

After the rust of the test piece is completely dissolved and peeled off with an aqueous solution containing a predetermined concentration of hydrochloric acid and hexamethylenetetramine, a predetermined amount of hydrogen peroxide must be added to the bath. This is because hydrogen peroxide not only dissolves rust precipitated in the bath, but also dissolves the ground iron of the test piece. When the amount of rust generation is quantitatively analyzed by a gravimetric method, the amount of rust generation of the test piece is overestimated. In addition, when ICP analysis is performed when the amount of rust generated is very small and the gravimetric method cannot be used, the iron content of ground iron in addition to the iron contained in rust is added, and the analysis accuracy is reduced. I do. In particular, the rust generated on the end face of the test piece (Fig. 3
(In the case of rust corresponding to reference numeral 4) is very small in many cases, and accurate rust can be removed even in the quantitative analysis of such a small amount of rust.

[0030]

Next, the present invention will be further described with reference to examples. 0.5mm thick, 50mm wide, 100mm long Z
Test specimens were prepared by exposing 27 hot-dip galvanized steel sheets outdoors for 3 months. On the other hand, a rust removing solution composed of an aqueous solution containing hydrochloric acid and hexamethylenetetramine shown in Table 1 was prepared in a beaker having a predetermined capacity, and S was used as an inhibitor.
H-cut (manufactured by Aiko Chemical) was added in an amount of 0.1 wt.%.

The rust-removing solution thus prepared was heated to various temperatures shown in Table 1, and the exposed test piece was immersed in the solution and kept at that temperature for 5 minutes to remove a small amount of rust on the surface of the test piece. It was dissolved and peeled off.

Next, 0.2 wt.% Of hydrogen peroxide was added and adjusted in each of the above baths, and kept at 70 ° C. for 2 minutes.
Rust that had precipitated in the bath was dissolved. The iron in the solution thus obtained was quantitatively analyzed by an ICP analyzer. The end face of the test piece after rust removal was observed with an optical microscope, and the following evaluation was performed. For comparison, a test was also performed using a conventional rust removing solution. ：: Rust was completely removed. Δ: The remaining amount of rust on the test piece is less than 10%. ×: The residual amount of rust on the test piece is 10% or more.

From the above test results, all the rust removing solutions within the scope of the present invention, Examples 1 to 8, showed good rust removing results. In contrast, none of Comparative Examples 1 to 6 and the conventional rust removing solutions, which are rust removing solutions outside the scope of the present invention, provided satisfactory rust removing results. Note that no erosion of the base of the test piece was observed in any of the examples, comparative examples, and conventional examples.

[0034]

[Table 1]

[0035]

As described above, according to the present invention,
When accurately and quantitatively analyzing the rust of the test piece obtained in the rust generation acceleration test etc. performed when evaluating the corrosion resistance of steel materials,
It is possible to provide a method for removing rust on an analytical test piece, which can completely remove rust on the test piece surface in a short time while suppressing erosion of the ground iron. Thus, the present invention can provide an industrially useful effect.

[Brief description of the drawings]

FIG. 1 is a graph comparing the amount of dissolved and eroded ground iron by various components having a rust peeling action.

FIG. 2 is a graph showing the effect of inhibiting the dissolution of ground iron when an inhibitor (corrosion inhibitor) is added to hexamethylenetetramine.

FIG. 3 is a schematic perspective view illustrating rust generated at each location of a steel material used for a steel house.

[Explanation of symbols]

 Reference Signs List 1 steel material 2 screw 3 rust generated on inner surface of screw hole 4 rust generated on end surface of steel material 5 rust generated on flat surface of steel material

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Yoshiharu Ouchi 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd.

Claims (1)

[Claims] 1. A method for removing rust in a step of quantitatively analyzing rust formed on the surface of a test piece of steel material and plated steel material, the test piece comprising: hydrochloric acid: 5 to 25 wt.%, And hexamethylenetetramine: After being immersed in a bath containing an aqueous solution containing 0.1 to 10 g / l and having a liquid temperature in the range of 20 to 70 ° C., the rust is dissolved and peeled off, A method for removing rust on an analytical test piece, comprising adding 0.1 to 5 wt.% Of hydrogen.