JPS5827864B2 - Method for measuring the concentration of hydrogen ions and hydrofluoric acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for determining the concentration of hydrogen ions and hydrofluoric acid in a pickling bath.

Nitric acid HN for pickling of metals, mainly stainless steel
O3, hydrofluoric acid HF, and iron Fe, chromium Cr,
A bath containing metal ions such as nickel Ni is used.

HNO3 dissolves the metal under the metal oxide film and dissolves Fe, C
Metal ions such as r, Ni, etc. form complexes with fluoride, thereby further dissolving the metal.

At this time, HNO3 and HF are consumed as the pickling process progresses, so the functionality of the bath gradually deteriorates.

Therefore, it is important for bath management to quickly and accurately measure the concentrations of HNO3 and 2 among the components in the bath and to maintain these concentrations appropriately.

FIG. 1 shows a reference electrode and an electrode selectively sensitive to hydrogen ions in the measurement bath liquid (hereinafter referred to as a hydrogen ion selective electrode).

), or an electrode that is selectively sensitive to fluorine ions (hereinafter referred to as a fluorine ion-selective electrode) or a reference electrode.

) is a schematic diagram of a known device for measuring the potential difference between a reference electrode 2 and a hydrogen ion selective electrode 3 or a fluorine ion selective electrode 31 in a measurement solution 1 using a voltmeter 4. Measure with.

The reference electrode 2 consists of an electrode 5, an internal solution 6, and a diaphragm γ, and the hydrogen ion selective electrode 3 or the fluorine ion selective electrode 31 consists of an electrode 8, an internal solution 9, and a hydrogen ion sensitive membrane 10, or a fluorine ion sensitive membrane 10. The film 10 is constructed to withstand strong corrosive conditions in which highly concentrated hydrofluoric acid coexists.

Note that when measuring the potential difference between the hydrogen ion selective electrode and the fluorine ion selective electrode, the hydrogen ion selective electrode 3 and the fluorine ion selective electrode 31 described above are used, respectively.

The hydrogen ion concentration in the measurement solution is calculated based on the measured potential difference between the reference electrode and the hydrogen ion selective electrode (known calculation formula omitted), and the hydrofluoric acid concentration is
It is determined by calculation on the basis of the measured potential difference between the reference electrode and the hydrogen ion selective electrode, as well as the measured potential difference between the reference electrode or the hydrogen ion selective electrode and the fluorine ion selective electrode.

(Known calculation formula omitted) However, in the above conventional method, the measured value of the potential difference between the reference electrode and the hydrogen ion selective electrode is It varies depending on the HF concentration used.

Figure 2 shows the internal solution at 0. IN HCl, 1. O
The effect of changes in HF concentration on the potential difference was investigated for measurement solutions of HNO3 and 0 in N and HNO3 in IN.

According to this figure, the HF concentration is 0. From around IN, the potential increases as the concentration increases, and the tendency is 1, ON
It has further increased since then.

This means that the HF concentration in the bath is 1. It can be seen that when the value becomes ON or higher, the value appears to deviate greatly toward the upper and higher side.

According to research conducted by the present inventors, the composition of an actual pickling bath for stainless steel is H=0.1 to 3N.

HF=0.5~5N, Fe=ON30g/
l, NiO~5g/! ', Cr=O~10f
//l, while the measurement accuracy required for bath management is ±0.2 N.

Therefore, the measured values of hydrogen ion concentration and hydrofluoric acid concentration calculated based on the measured value of the potential difference between the reference electrode and the hydrogen ion selective electrode or the fluorine ion selective electrode by the above-mentioned conventional method are as follows: It is clear that this method has the drawback of not being able to satisfy the accuracy required for bath management.

The present invention eliminates the above-mentioned drawbacks and provides for the potential difference between the reference electrode and the hydrogen ion-selective electrode and between the reference electrode or the hydrogen ion-selective electrode and the fluoride ion-selective electrode in the measurement solution. In the concentration measurement method of measuring the potential difference and calculating the hydrogen ion concentration and the hydrofluoric acid concentration based on the measured value, nitric acid is added to the measurement solution to adjust the nitric acid concentration of the solution to 0.05 to 0. The method is characterized by measuring the potential difference between a reference electrode and an electrode selectively sensitive to hydrogen ions in the measurement solution after setting the pressure to 20 N.

Hereinafter, the present invention will be explained in detail with reference to examples.

Example I Using a commercially available reference electrode (manufactured by Orion, USA) and a strongly acidic cation exchange membrane type hydrogen ion selective electrode, mixed solutions of HNO3 and HF with various mixing ratios and nitric acid concentrations were measured. FIG. 3 shows the results of determining the potential difference between the two electrodes as a solution.

In this case, the internal solution of the hydrogen ion selective electrode is 0,9
N HNO3 and 0. A mixture of IN and HC' was used.

From FIG. 3, it can be seen that when the HNO3 concentration is 0.05 to 0.2ON, almost constant measured values can be obtained regardless of changes in the HF concentration.

According to the actual measurements, I (a solution of NO3 alone and a solution of HNO3
The potential difference between 4 and a solution containing 5 times the amount of HF was less than 1 mV.

A deviation of 1 mV is equivalent to 0.15N in terms of HNO3 concentration.
Since it is within the range, it is an acceptable value for bath management.

Example 2 Table 1 shows specific numerical values when the HNO3 concentration and the ■' concentration are changed.

Table 1 Relationship between HNO3 and HF concentration changes and potential differences
In this case, it can be seen that even if the HF concentration changes, the potential difference is within 1 mV, which is within an acceptable range for bath management.

Example 3 A sample solution was collected from a stainless steel pickling bath, and after adjusting the concentration of HNO3 to 0.12N by adding I(NO3) to the sample solution, the reference** electrode of Example 1 and hydrogen ions were added to the sample solution. Hydrogen ion concentration calculated based on these measured values by measuring the potential difference between the selective electrode and the hydrogen ion selective electrode and the fluorine ion selective electrode (manufactured by Orion, USA) Tables 2 and 3 show the measured values of hydrogen ion concentration and hydrofluoric acid concentration, which were separately determined by a precision chemical analysis method, and the hydrofluoric acid concentration (fixed value according to the present invention).

The measured values in Table 2 are 0.05N HNO3NO3 solution 1
00 self! These are the results of measurements after accurately measuring 2 ml of pickling solution for stainless steel, adding 300 ml of pickling solution, and thoroughly stirring.

If the hydrogen concentration (I (NO3 concentration)) is accurately determined, the HF concentration can also be determined accurately from the HF dissociation constant and Nernst's equation.

As is clear from Tables 2 and 3, it can be seen that the hydrogen ion concentration and hydrofluoric acid concentration can be determined with an accuracy within ±0.2N.

From the above, when accurately measuring the hydrogen ion concentration of the measurement solution, it is possible to measure it regardless of the HF concentration as long as the HNO3 concentration is adjusted to a range of 0.05 to 0.2 N. Now, in order to apply this to the measurement of an actual pickling bath for stainless steel, proceed as follows.

That is, the HNO3 concentration of the pickling bath for stainless steel is usually 0.
1-2. Since it is known as a result of chemical analysis that it is ON, in order to set this in the range of 0.05 to 0.20 N,
The solution may be diluted approximately 50 times with 0.05N HNO3, and the diluted solution may be measured using a reference electrode, a hydrogen ion selective electrode, and a fluorine ion selective electrode.

As described above, according to the method of the present invention, it is possible to accurately determine the hydrogen ion concentration and hydrofluoric acid concentration in a pickling bath in which a high concentration of HF coexists, and it is possible to perform highly accurate bath management.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a known device for measuring the potential difference between a reference electrode and a hydrogen ion selective electrode in a measurement solution, or between a reference electrode or a hydrogen ion selective electrode and a fluorine ion selective electrode. It is a diagram. Figure 2 shows the HF concentration in the measurement solution (horizontal axis) and the reference electrode.
The relationship with the potential difference (vertical axis) between hydrogen ion selective electrodes is shown. Figure 3 shows the relationship between the HNO3 concentration in the measurement solution (horizontal axis) and the potential difference between the reference electrode and the hydrogen ion selective electrode (vertical axis) using the mixing ratio of HNO3 and HF as a parameter. 1 is HNo3 alone, curve 2 is HNO3
:HF=3:1, curve 3 is HNO3:HF1:1, curve 4 is HNO3:HF=1:3, curve 5 is HNO3:
The case of HF=1:5 is shown.

Claims (1)

[Claims] 1 Potential difference between the reference electrode and an electrode selectively sensitive to hydrogen ions and hydrogen ions σ in the measurement solution
Concentration measurement that measures the potential difference between this selectively sensitive electrode or reference electrode and an electrode that selectively sensitive to fluorine ions, and calculates the hydrogen ion concentration and the hydrofluoric acid concentration based on the measured value. In the method, after adding nitric acid to the measurement solution to make the nitric acid concentration of the solution 0.05 to 0.20N, The concentration measuring method described above comprises measuring a potential difference.