JP2004325321A - Method of measuring amount of hexavalent chromium in chromate coating film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of measuring a hexavalent chromium amount contained in a coating film for anticorrosion treatment of a metal material such as chromate treatment, in a short time with highly efficient extraction. <P>SOLUTION: This method of measuring the hexavalent chromium amount contained in the chromate coating film has a crack forming process for forming a crack in the chromate coating film, an extraction process for immersing the crack-formed chromate coating film into an extraction liquid to extract hexavalent chromium, and a quantitative determination process for determining quantitatively the extracted hexavalent chromium. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for measuring the amount of hexavalent chromium contained in a metal material rust preventive film such as a chromate film used for automobiles and home electric appliances.
[0002]
[Prior art]
In Europe, the use of lead, mercury, cadmium and hexavalent chromium has been banned in principle by the "European Assembly and Ministerial Council Directive on End-of-Life Vehicles", which came into effect in October 2000 (hereinafter referred to as the EU End-of-Life Vehicle Directive). Was done.
[0003]
Hexavalent chromium in vehicles and the like is contained in chromate-treated films and dacro-treated films that are widely used as rust preventive treatments for various metal parts such as bolts and nuts. Chromate treatment is a treatment to form a chemical conversion film of chromic acid hydrate containing hexavalent chromium and trivalent chromium on galvanized plating. It suppresses the sacrificial corrosion of zinc due to the barrier effect and hexavalent if the coating is damaged. Chromium is reduced to trivalent chromium, and the self-healing property of regenerating the film can maintain high rust prevention performance. On the other hand, the dacro treatment is a coating treatment in which metallic zinc flakes are bound with a chromic anhydride binder containing hexavalent chromium and trivalent chromium.
[0004]
The EU End-of-Life Vehicle Directive stipulates that the application of hexavalent chromium in the rust-preventive film to a maximum of 2 g / unit is excluded, but does not specify quantitative analysis methods. It is presumed that the chromate film contains a mixture mainly composed of ZnCrO ₄ as hexavalent chromium and salts contained in a chromate liquid such as Cr (OH) ₃ .nH ₂ O as trivalent chromium as chromium compounds. You.
[0005]
Although there is X-ray photoelectron absorption analysis etc. as a direct analysis method of the hexavalent chromium content contained in the chromate film (see Patent Document 1, etc.), the analysis value represents the entire sample because of the outermost surface analysis. And that it is difficult to separate hexavalent and trivalent peaks.
[0006]
ISO 3613 specifies a method for analyzing chromium eluted from a chromate-treated film by a boiling method. However, this method is merely a method for investigating hexavalent chromium which may be released into the environment when the vehicle is scrapped. Therefore, the total amount of hexavalent chromium present in the chromate film cannot be measured by the ISO3613 method.
[0007]
The base of the chromate film is generally plated with aluminum or zinc, but these metals have a strong ionization tendency and generate hydrogen gas when exposed to acids or alkalis, so dissolve the chromate film and measure the amount of hexavalent chromium. It is difficult. This is because hexavalent chromium is reduced to trivalent chromium by the generated hydrogen gas. For this reason, an extraction method using a solvent is desirable in order to analyze hexavalent chromium in the coating. However, since the chromate-treated membrane has a dense structure and low permeability of the extraction solvent, the hexavalent chromium in the coating is low. It was extremely difficult to extract the total amount of.
[0008]
Thus, development of a highly reliable quantitative analysis method for hexavalent chromium contained in a chromate-treated film has been desired.
[0009]
[Patent Document 1]
JP-A-5-164710
[Problems to be solved by the invention]
An object of the present invention is to provide a method for extracting and measuring the amount of hexavalent chromium contained in a metal material anticorrosion treatment film such as chromate treatment in a short time and with high efficiency.
[0011]
[Means for Solving the Problems]
The present inventors have thought that prior to extracting hexavalent chromium from the chromate film, fine cracks are formed in the chromate film to increase the hexavalent chromium extraction area. That is, the method for measuring the amount of hexavalent chromium in the chromate film of the present invention comprises a crack forming step of forming a crack in the chromate film, and immersing the cracked chromate film in an extract to extract hexavalent chromium. It has an extraction step and a quantitative analysis step of quantifying the extracted hexavalent chromium.
[0012]
The crack forming step is preferably a step of forming a crack by applying a thermal shock to the chromate film by a thermal cycle. Here, the cooling / heating cycle is a cycle in which cooling at −180 ° C. or lower and heating at about room temperature are repeated, and the cooling is preferably cooling with liquid nitrogen.
[0013]
Further, as a method of forming a crack in the chromate film, a method of giving a mechanical impact to the chromate film may be used.
[0014]
Further, in the hexavalent chromium extraction step, the cracked chromate film is immersed in pure water at 100 ° C. for 30 minutes or more to extract hexavalent chromium, and the quantitative analysis step is performed by diphenylcarbazide absorption spectrophotometry. It is desirable.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
According to the present invention, countless fine cracks are generated in a chromate film integrally formed on a substrate, thereby enabling quantitative analysis of all hexavalent chromium contained in a chromate-treated film.
[0016]
In applying the method of the present invention, the substrate for the chromate treatment is not particularly limited, and examples thereof include parts such as a thin steel plate-like bolt and nuts used for automobiles and home electric appliances. can do. As the base metal, iron, aluminum, or the like can be suitably used, and their surfaces may be plated. As the type of plating, zinc-based plating is widely used, and examples thereof include electrogalvanizing and hot-dip galvanizing.
[0017]
The chromating method is not particularly limited. The present invention can be applied to a treated film formed by any method such as a reactive chromate treatment, a coating chromate treatment, and an electrolytic chromate treatment. In particular, the method of the present invention can be suitably applied to a film formed by a coating type chromate treatment. This is because the coating film often contains a high fraction of hexavalent chromium in the coating type chromate treatment.
[0018]
The crack forming step of forming a crack in the chromate film according to the present invention can be performed by applying a thermal shock to the chromate film in which quenching and rapid heating are repeated within a temperature difference of 200 ° C. or more. Here, it is desirable to repeatedly apply quenching and rapid heating in the range of extremely low temperature of -180 ° C or less and high temperature of about room temperature. The extremely low temperature of −180 ° C. or lower can be obtained by using, for example, liquid nitrogen (boiling point: about −196 ° C., the same applies hereinafter), liquid oxygen (−183 ° C.), or liquid helium (−270 ° C.). it can. Note that the extremely low temperature of -180 ° C or lower is that a large number of fine cracks are difficult to be formed in a thermal cycle between a low temperature of less than -180 ° C and room temperature, so that all hexavalent chromium cannot be extracted, or it is extremely long. It is not suitable because it requires an extraction time.
[0019]
FIG. 1 shows a surface observation photograph of the chromate-treated film subjected to the cooling / heating cycle of 5 times between the liquid nitrogen temperature and the room temperature. FIG. 1 shows an SEM image by a scanning electron microscope. FIG. 2 shows a normal chromate film surface before crack formation observed in the same manner as in FIG. The white dotted line in FIG. 1 is a crack generated by the cold heat treatment, indicating that the crack is concave with respect to the black chromate film surface. This crack is a series of extremely fine point-like holes (20 to 300 nm in diameter), and makes the surface area of the chromate-treated film extremely large with respect to the extract. The thickness of the chromate film was 1 μm, and the depth of the crack was 0.5 to 1 μm.
[0020]
In addition, it is conceivable to apply a thermal shock by heating the chromate film to a high temperature of several hundred degrees Celsius and rapidly cooling such as water cooling.However, in such a method of heating the chromate film, the distribution in the chromate film is heated. It is not suitable because hexavalent chromium cannot be extracted with distilled water or an aqueous solution of NaCl or the like, due to the separation of water and the progress of cross-linking.
[0021]
It is desirable to extract hexavalent chromium by immersing the cracked chromate film in pure water such as distilled water at 100 ° C. for 30 minutes or more. As the extract, a 1 to 10% aqueous NaCl solution, a 1 to 10% KCl aqueous solution, or the like can be used. However, in consideration of the quantitative analysis of hexavalent chromium thereafter, it is desirable to use pure water such as distilled water or ion-exchanged water. The higher the extraction temperature, the greater the effect. Further, the extraction time is desirably 30 minutes or more as shown in FIG.
[0022]
The quantitative analysis of the extracted hexavalent chromium may be performed by a known method. For example, diphenylcarbazide is added to an eluate of hexavalent chromium to form a complex, the absorbance of the complex is measured, and the concentration is calculated to determine the concentration. (VI) ”) is a suitable method for quantifying an extremely small amount of hexavalent chromium, such as hexavalent chromium, in the chromate film because the quantification range is 2 to 50 μg.
[0023]
As a method of forming a crack in the chromate film, a mechanical impact force can be applied. For example, a chromate-treated plate sandwiched between protective plates made of wood or resin is hit with a tool such as a hammer, or an iron ball or the like is dropped from a certain height to deform the chromate-treated plate to form a chromate film. Fine cracks may be formed.
[0024]
In addition, the dacro-treated film mainly applied as a rust preventive treatment for bolts, nuts, brake rotors, etc. is also contained in the film by forming fine cracks on the film surface in the same manner as the chromate-treated film. Thus, the entire amount of hexavalent chromium can be extracted in a short period of time, so that highly accurate quantitative analysis can be performed.
[0025]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
(Test material)
The base material is a cold-rolled steel plate (SPCC), the surface of which has been subjected to a zinc plating treatment with a thickness of 10 μm (thickness 1 mm, 50 mm × 50 mm), and a mixed solution of hexavalent chromium and trivalent chromium (Nihon Parkerizing Co., Ltd. ) Manufactured at 40 ° C. for 30 seconds. Excess treatment liquid was removed by tilting the test material. Furthermore, after immersion, it was dried in an electric oven set at 70 ° C. for 2 minutes. The thickness of the obtained chromate film was 1 μm.
(Crack formation method 1)
The test material was immersed in liquid nitrogen contained in a metal container for about 1 minute, cooled to liquid nitrogen temperature, and rapidly taken out to room temperature. This cooling / heating operation was repeated 3 to 5 times, and fine cracks were formed in the treated film by thermal shock (Sample 1). FIG. 1 shows the state of crack generation.
(Extraction process)
Sample 1 on which the above crack formation operation was performed and Sample 2 having no crack for comparison were each immersed in 100 mL of distilled water at 100 ° C. for 30 minutes to extract hexavalent chromium.
(Quantitative analysis)
After allowing each of the obtained hexavalent chromium extracts to cool, distilled water was added to make the volume to 200 mL, and quantitative analysis of hexavalent chromium was performed by the officially-specified diphenylcarbazide absorptiometry.
[0026]
In Sample 1, which had been subjected to the crack forming operation of the present invention, a quantitative value of hexavalent chromium of 2.8 μg / cm ² was obtained. On the other hand, in Sample ² which was not subjected to the crack forming operation, it was 0.13 μg / cm ² . Here, the area is the surface area of the chromate treatment. Sample 1 subjected to the crack forming operation was able to obtain a quantitative value of hexavalent chromium approximately 20 times higher than that of Sample 2 not subjected to the crack forming operation.
(Verification of the accuracy of hexavalent chromium)
A verification test was performed to confirm the accuracy of the quantitative value of hexavalent chromium according to the method of the present invention, that is, that no unextracted hexavalent chromium remains in the extracted chromate film.
1) Verification test 1
Extraction of hexavalent chromium, which was immersed in 100 mL of distilled water at 100 ° C. for 30 minutes, was repeated six times for the same sample to perform a total of 3 hours of extraction. Each extract was quantitatively analyzed in the same manner as described above, and the presence or absence of hexavalent chromium remaining in the sample was confirmed. FIG. 2 shows the results. As shown by the square in FIG. 2, the amount of hexavalent chromium after 30 minutes of extraction was 3.0 μg / cm 2. However, hexavalent chromium was not observed in the extract after further extraction for 30 minutes (total 60 minutes). Similarly, hexavalent chromium was not recognized in each of the extracted liquids for a total time of 90 minutes, 120 minutes, 150 minutes, and 180 minutes. The value of ◆ (2.9 μg / cm 2), which is the result of the first 30 minutes of extraction, is the result of the reproduction test.
2) Verification test 2
After immersion in 100 mL of distilled water at 100 ° C. for 30 minutes to extract hexavalent chromium, the surface of the chromate film was subjected to X-ray photoelectron spectroscopy (XPS) capable of qualifying hexavalent chromium (PHI5701M, manufactured by I-Bac Phi, Inc.). ) To confirm the presence or absence of hexavalent chromium. This is a qualitative analysis in a range of 800 μm in diameter of the film surface. FIG. 4 shows the obtained XPS spectrum. For comparison, the XPS spectrum of the chromate film surface before extraction is shown in FIG. In FIG. 5, 1 is the spectrum of trivalent Cr2P3 / 2, 2 is the spectrum of trivalent Cr2P1 / 2, 3 is the spectrum of hexavalent Cr2P3 / 2, and 4 is the spectrum of hexavalent Cr2P1 / 2. Here, the 2P3 / 2 peak positions of trivalent chromium and hexavalent chromium have binding energies of 577.2 eV and 579.6 eV, respectively. In FIG. 5, point A in spectra 1 and 2 indicates the presence of trivalent chromium, and point B in spectra 3 and 4 indicates the presence of hexavalent chromium. However, in FIG. 4, although the presence of trivalent chromium is recognized at point A in spectra 1 and 2, the presence of hexavalent chromium is not recognized because the relative intensities of spectra 3 and 4 are extremely weak. Therefore, it was confirmed that unextracted hexavalent chromium did not remain in the chromate film of Sample 1 after extraction.
(Crack formation method 2)
A mechanical force was applied to the chromate-treated test material to form cracks in the chromate-treated film. At this time, the test material was sandwiched from both sides with a protective thin plate (here, an acrylic resin plate with a thickness of 1 mm was used) so as not to scratch the treated film, and the test material was given an impact with a hammer on a rubber mat. Was deformed to obtain a sample 3.
[0027]
Extraction of Sample 3 was repeated in the same manner as in Verification Test 1, and each extract was subjected to quantitative analysis. FIG. 6 shows the results. As in the verification test 1, the amount of hexavalent chromium after 30 minutes of extraction was 3.1 μg / cm 2, but no hexavalent chromium was found in the extract after further extraction for 30 minutes (total of 60 minutes). . The value of ◆ (2.8 μg / cm ² ), which is the result of the first 30 minutes of extraction, is the result of the reproduction test.
[0028]
【The invention's effect】
According to the method for measuring hexavalent chromium in a chromate film of the present invention, the total amount of hexavalent chromium in a chromate film can be analyzed quickly and accurately. Therefore, it is expected that the quality control of the chromate-treated steel material can be appropriately performed, and at the same time, it greatly contributes to the research and development relating to hexavalent chromium such as a chromate treatment method.
[Brief description of the drawings]
FIG. 1 is a scanning electron micrograph showing cracks on the surface of a chromate film formed by applying a thermal shock according to the present invention.
FIG. 2 is a scanning electron microscope observation photograph showing a chromate film surface before a crack is formed.
FIG. 3 is a diagram showing a relationship between the number of times of hexavalent chromium extraction of a chromate film having a crack formed by thermal shock and the amount of hexavalent chromium in an extract.
FIG. 4 is a view showing an XPS spectrum of a chromate film after extraction of hexavalent chromium from a chromate film having a crack formed by thermal shock.
FIG. 5 is a view showing an XPS spectrum of a chromate film before extraction of hexavalent chromium from a chromate film in which a crack is formed by a thermal shock.
FIG. 6 is a diagram showing the relationship between the number of times of hexavalent chromium extraction of a chromate film having a crack formed by mechanical impact and the amount of hexavalent chromium in the extract.
[Explanation of symbols]
1: trivalent Cr2P3 / 2 spectrum 2: trivalent Cr2P1 / 2 spectrum 3: hexavalent Cr2P3 / 2 spectrum 4: hexavalent Cr2P1 / 2 spectrum

Claims (7)

In a method for measuring the amount of hexavalent chromium in a chromate film integrally formed on a substrate,
A crack forming step of forming a crack in the chromate film;
An extraction step of immersing the cracked chromate film in an extract to extract hexavalent chromium;
A quantitative analysis step of quantifying the extracted hexavalent chromium,
A method for measuring the amount of hexavalent chromium in a chromate film, comprising: The method for measuring the amount of hexavalent chromium in a chromate film according to claim 1, wherein the crack forming step is a step of forming a crack by applying a thermal shock to the chromate film by a thermal cycle. The method for measuring the amount of hexavalent chromium in a chromate film according to claim 2, wherein the cooling / heating cycle repeats cooling at −180 ° C. or less and heating at about room temperature. The method for measuring the amount of hexavalent chromium in a chromate film according to claim 3, wherein the cooling is cooling with liquid nitrogen. The method for measuring the amount of hexavalent chromium in a chromate film according to claim 1, wherein the crack forming step is a step of forming a crack by applying a mechanical impact to the chromate film. The method for measuring the amount of hexavalent chromium in a chromate film according to any one of claims 1 to 5, wherein the extraction step is a step of immersing the cracked chromate film in pure water at 100 ° C for 30 minutes or more. The method for measuring the amount of hexavalent chromium in a chromate film according to any one of claims 1 to 6, wherein the quantitative analysis step of hexavalent chromium is a diphenylcarbazide absorption spectrophotometry.

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