JPS61247956A - Analysis of antimony contained in galvanizing film - Google Patents

Abstract

PURPOSE:To determine quantitatively a trace amt. of antimony exactly at a high speed by preparing a test liquid in which the antimony is reduced to tervalency and subjecting the liquid to a voltammetric measurement. CONSTITUTION:An ascorbic acid is added to a reducing agent to a soln. obtd. by dissolving a galvanizing film from the base iron by a concd. nitric acid and the soln. is boiled to prepare the test liquid in which the amtimony is reduced to tervalency. The liquid is then subjected to the voltammetric measurement. The plating film is preferably dissolved by the concd. nitric acid while a dissolving vessel is cooled by icy water. The content of copper and bismuth is separately measured and the correction based on the measured result thereof is executed when the test liquid contains the copper and bismuth. the exact content of the antimony is thus determined.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) Antimony contained as an impurity in a zinc-based plating film is known to have an adverse effect on plating properties such as thermal peeling. Therefore, it is necessary to control the antimony content contained in the zinc-based plating film, but in order to do so, the content must be measured as a preliminary step.The present invention was developed to meet this need. The present invention relates to a method for easily and accurately determining trace amounts of antimony in galvanized coatings.

(Prior art and its problems) DPASV (differential pulse anodic stripping voltammetry) is a method suitable for analyzing trace metal ions in a solution.
There is voltammetry such as DPV (differential pulse voltammetry).

This method is an electrochemical analysis method that obtains information about ions in a test liquid from a potential-current curve at an electrode immersed in the test liquid. In this method, the influence of zinc can be eliminated by appropriately selecting the electrodeposition potential.

In order to apply this voltammetry to the determination of antimony in a galvanized coating, it is first necessary to dissolve only the galvanized coating from the plated steel sheet.

Hydrochloric acid solution containing antimony chloride (JISH0401
) and hydrochloric acid or sulfuric acid solutions containing organic inhibitors, but these are unsuitable for quantifying antimony in galvanized coatings. For example, when using a hydrochloric acid solution containing antimony chloride, the analytical component antimony is contained in the solution, so the analytical value will be high.
Furthermore, when hydrochloric acid or sulfuric acid is used, antimony becomes a hydride and volatilizes due to the hydrogen generated during zinc dissolution, resulting in low analytical values. It is also possible to use dilute nitric acid (JIS H1111), which is used for the analysis of tin, etc. However, since the end point of the reaction with dilute nitric acid is unclear, it dissolves not only the plating film but also the underlying steel plate, so if the base metal contains antimony, the analysis value will be high.

On the other hand, voltammetric measurements are greatly influenced by the valence of the analyte ions in the test solution. Looking at antimony, antimony comes in trivalent and pentavalent forms, and pentavalent antimony does not show a peak in voltammetry measurements unless it is in a special solution system.However, in a solution obtained by dissolving a galvanized film, Most of the antimony contained in it is in a pentavalent state. Therefore, it is necessary to reduce pentavalent antimony to trivalent antimony and perform quantitative determination in this reduced state. As a method for reducing antimony from pentavalent to trivalent, a method has been proposed in which antimony is reduced with sulfur dioxide in the presence of iodide ions (Analytica
Chimica Acta 146 (118
3) 131-89), l, rudder, this method is
It is not practical because it takes as long as 30 minutes to complete the reaction.

(Objective of the Invention) Therefore, an object of the present invention is to study the dissolution of a galvanized film and the reduction of pentavalent antimony, and to quickly and accurately quantify trace amounts of antimony by voltammetry.

(Structure of the Invention) In order to achieve the object, the present invention dissolves antimony by adding ascorbic acid as a reducing agent to a solution obtained by dissolving the galvanized coating from the steel base with concentrated nitric acid and boiling it. The method is characterized in that a test solution reduced to a value is prepared, and then voltammetry measurement is performed.

In this case, it is desirable to dissolve the plating film with concentrated nitric acid while cooling the dissolution container with ice water.Also, if the test solution contains copper or bismuth, separately measure the content of copper and bismuth. By making corrections based on the measurement results, accurate antimony content can be determined.

(Functions and Effects) When dissolving a plating film with concentrated nitric acid, when the dissolution reaction is completed and the surface of the base metal appears, a passive film is formed on the surface by the concentrated nitric acid. As a result, the dissolution reaction does not proceed any further, and the solution obtained by dissolving the plating film is not affected by the elution of the base metal.In this case, if the dissolution reaction is performed while cooling with ice water, the solution will be reduced due to the reaction heat. Temperature rise is suppressed, and elution of base iron is further prevented. The influence of this concentrated nitric acid on the volatilization of antimony and the elution of base iron is shown in Figures 1 and 2, respectively.

Since the thus obtained plating film solution dissolves only the plating film without causing any substantial change in the antimony content, the obtained measurement results are also accurate.

In addition, when ascorbic acid is used as a reducing agent to reduce pentavalent antimony to trivalent antimony, the reduction rate changes as shown in Figure 3 depending on the reaction temperature. Indicates the case when added to the test solution of the condition,
B indicates the same test solution at <60°C; C indicates the case where the test solution was boiled for 30 seconds after adding ascorbic acid.
In this way, the fact that a sufficient reducing effect can be obtained by boiling for only about 30 seconds brings about faster analysis work compared to the conventional method using sulfur dioxide.

Furthermore, in voltammetry measurements, if copper or bismuth is present in the test solution, they overlap with the antimony peak, causing errors. Therefore, by separately measuring the amounts of copper and bismuth and correcting the height at the antimony peak position based on the measurement results, accurate antimony content can be obtained. Note that, of course, if it is known in advance that there is no influence due to such impurities, there is no need to consider the correction.

(Example) Next, the characteristics of the present invention will be clarified through Examples.

First, a galvanized steel sheet sample (5 cm x 5 cas) was placed in a beaker, 30 μm of concentrated nitric acid was added, and the plating film was dissolved while cooling in ice water. Once the coating had dissolved, the reaction stopped and the sample was removed from the concentrated nitric acid solution.

Subsequently, (1+l) H2SO412 layer was added and white sulfuric acid fumes were slightly raised to remove HNO. This is because when HNOl is present when 7scorbic acid is added later, the reduction will not proceed properly.

After cooling, 8 g of Na0 and 300 m of H were added and the salts were dissolved by heating.Then, the mixture was transferred to a 100-layer volumetric flask and diluted to the marked line with water to obtain Solution A.

Next, 25 ran of liquid A was taken out, 17 g of NaC was added, and the mixture was heated and dissolved. Subsequently, 0.5 g of ascorbic acid was added to the mixture while it was still hot, and the mixture was boiled for about 30 seconds to reduce sb to trivalent. After cooling, 5011! ; The mixture was transferred to an L volumetric flask and diluted to the marked line with water to obtain Solution B.

A test solution was prepared as described above, and voltammetry measurements were performed.

In the first step, solution A was placed in a voltammetry measurement cell, and Cu and Bi were measured under the measurement conditions shown in Table 1.

In liquid A, the peaks of Cu and Bi are sufficiently far apart, so the amounts of Cu and Bi can be determined from the respective peak heights using a calibration curve prepared in advance. In addition,
Since sb is oxidized as pentavalent in liquid A,
It does not interfere with the measurement of Cu and Bi.

In the second step, the B solution was placed in a voltammetry measurement cell and measured under the measurement conditions shown in Table 2 to determine the height at the sb peak position. For this measurement.

Since the Cu and Bi peaks overlap, this amount was subtracted as follows. Cu of the sample in the first stage.

Since the amount of Bi is known, the amount of Cu and B prepared in advance is
From the relationship between the amount of i and the contribution of Cu and Bi at the Sb peak position, determine the contribution of Cu and Bi to the sb peak, and subtract this from the height of the sample at the sb peak position to obtain the true sb peak height. The results of the analysis of the synthesized sample thus obtained are shown in Table 3.As is clear from this table, when the method of the present invention is used, Analysis with good accuracy became possible.

[Brief explanation of the drawing]

Figure 1 shows the difference in antimony recovery rate depending on the type of acid, and Figure 2 shows the influence of nitric acid concentration on the elution of base iron.
FIG. 3 shows the relationship between the reduction rate of antimony by ascorbic acid and the reaction temperature. , ti Mouth 2 Illustrations 3 Illustrations

Claims (3)

[Claims] (1) Add ascorbic acid as a reducing agent to the solution obtained by dissolving the zinc-based plating film from the base iron with concentrated nitric acid, and boil it to prepare a test solution in which antimony is reduced to trivalent, and then perform voltammetry measurement. A method for analyzing antimony contained in a zinc-based plating film. (2) The method according to claim 1, wherein the plating film is dissolved with concentrated nitric acid while the dissolution container is cooled with ice water. (3) When copper and bismuth are present in the test solution, the method according to claim 1, in which the antimony content is determined by correcting copper and bismuth.