JPS5827865B2 - Hydrogen ion and hydrofluoric acid concentration measuring device - Google Patents

Description

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

Nitric acid (HNO3) and hydrofluoric acid (HF) in the pickling bath
), as well as metal ions such as iron (Fe), chromium (Cr), and nickel (Ni), form complexes with fluorides when pickling metals and alloys, primarily stainless steel. , which further melts the metal or alloy.

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 HF among the components in the bath and to maintain these concentrations appropriately.

Conventionally, the HNO3 concentration, that is, the hydrogen ion concentration in the bath, and the hydrofluoric acid concentration have been measured using neutralization titration or wet chemical analysis using metal complexes. The disadvantages are that the error is large, the time required for analysis is long, and the management of the pickling bath is not practical.

The present invention eliminates such drawbacks, and as shown in FIG. 1, a reference electrode 2, a hydrogen ion selective electrode 3, a fluorine ion selective electrode 4 provided in a measurement solution 1,
a changeover switch 5 for measuring the potential difference between the hydrogen ion selective electrode and the reference electrode or between the hydrogen ion selective electrode and the fluorine ion selective electrode, and a potentiometer 7;
a regulator 6 for adjusting the gain of the potential difference between the hydrogen ion selective electrode and the fluorine ion selective electrode, a measured value of the potential difference between the hydrogen ion selective electrode and the reference electrode, and a hydrogen ion selective electrode and the fluorine ion selective electrode; It is comprised of a calculator 8 that calculates the concentrations of hydrogen ions and hydrofluoric acid based on the measured potential difference between the ion-selective electrodes, and a display 9 that displays the calculated values of the calculator.

In this specification, a hydrogen ion selective electrode refers to an electrode selectively sensitive to hydrogen ions, and a fluorine ion selective electrode refers to an electrode selectively sensitive to fluorine ions.

Next, the measurement principle of the device of the present invention will be described.

The potential difference EH+ between the hydrogen ion selective electrode and the reference electrode, and the potential difference EF between the fluorine ion selective electrode and the reference electrode
- is expressed as Nernst's equation as follows.

Here, EH+: Potential difference between the hydrogen ion selective electrode and the reference electrode BF-, Potential difference between the fluorine ion selective electrode and the reference electrode [H+]: Hydrogen ion concentration CF-): Fluorine ion concentration EoH+, EoF-2SH+ , SF-: Individual constants Further, the dissociation constant of hydrofluoric acid is expressed by the following formula.

Here, KHF "Dissociation constant (HF) of hydrofluoric acid: Concentration of hydrofluoric acid (1), (2), (3) From equations, potential difference between hydrogen ion selective electrode and hydrofluoric acid selective electrode. Beef l
(−EH” EF −) is SH+=SF−(−8H
F) When adjusting, it is shown as follows.

Therefore, (by equation 1, when EoH+ and SH+ are known, measuring BH+ will yield [H+], and by equation (4),
By measuring EoCell, SHF, and ECell, (HF) can be obtained.

Here, EoH+, SH+ are experimentally determined EH+-
EoF-2SF- can be obtained from the experimentally obtained E"-1ogCF:] relational line.

Theoretically, SF- should be the same as SH+, but since there is a slight difference due to the characteristics of the electrodes, in the device of the present invention, it is adjusted so that SF--SH+, and this value is defined as SHF.

EoCeIl is E determined as above.

, Eo, S, and the chemical constant KHF (
5) It is determined by the formula.

Next, a method for measuring hydrogen ion and hydrofluoric acid concentrations using the apparatus of the present invention will be explained.

Prior to the measurement, for the preparation, E.

It is necessary to obtain H+, SH+EoF- and SF-.

First of all, the problem with EoH+ and s”+ is the hydrogen ion concentration [
H+] is known, and the potential difference BH+ between the hydrogen ion selective electrode 3 and the reference electrode 2 is measured using various nitric acid solutions that differ in stages as measurement solutions, and the potential difference BH+ as shown in FIG. 2 is obtained.
−log [H”) is found.

And E as the EH+ value corresponding to log(H″-]-〇.

In addition to finding H+, SH+ is also found as the slope of the straight line.

E again. and S, the fluorine ion concentration [F
-] is known, and the potential difference EF- between the fluorine ion-selective electrode 4 and the reference electrode 2 is measured using various sodium fluoride solutions that differ stepwise as measurement liquids, and the third
Find the relationship line between EF--1ogCF-] in the figure.

and E as the EF-value corresponding to logCF )=0.

In addition to finding F, SF- is also found as the slope of the straight line.

Comparing SH+ and SF- thus obtained, 51-i+
= SF - (-8HF), the gain of the potential difference between the hydrogen ion selective electrode 3 and the fluorine ion selective electrode 4 is adjusted by the regulator 6, and the adjustment value SH
F and E determined from the above experiment.

From H+ and EoF-, E is obtained from formula (5).

Find ce l l. Next, the above E.

Preparation for measurement is completed by storing the values of H+, SH+, EoCell, SHF, and KHF, and equations (1) and (6) in the calculator 8.

A measurement solution is charged into the apparatus of the present invention prepared for measurement as described above, and the selector switch 5 is first set to the reference electrode side, and the potential difference EH between the reference electrode 2 and the hydrogen ion selective electrode 3 is
+ is measured by the potentiometer 7 and output to the arithmetic unit 8.

The arithmetic unit 8 converts the above E to A, 'I), and
The converted value and E stored in advance.

Using the values of H+ and SH+ and equation (1), the hydrogen ion concentration [
H+], and the calculated value is displayed on the display 9.

Next, the changeover switch 5 is set to the fluorine electrode side, and the potential difference Bcell between the fluorine ion selective electrode 4 and the hydrogen ion selective electrode 3 is measured by the potentiometer 7 and output to the arithmetic unit 8.

The arithmetic unit 8 performs A/D conversion on the Ecell, and also converts the converted value and the E cell stored in advance.

The hydrofluoric acid concentration [HF] is calculated using the cellSHF value and equation (6), and the calculated value is displayed on the display 9.

Next, the results of measuring hydrogen ion and hydrofluoric acid concentrations using the apparatus of the present invention will be shown in Examples.

Example 1 The concentrations of hydrogen ions and hydrofluoric acid in various measurement solutions taken from a stainless steel pickling bath were determined using the device of the present invention and the precision chemical analysis method, and the results of comparing the measured values of both are shown in Table 1 and Table 1. It is shown in Table 2.

As is clear from Tables 1 and 2, it can be seen that the hydrogen ion concentration and hydrofluoric acid concentration can be determined with an accuracy within ±0.2N.

In addition, when using the chemical analysis method, it took 10 minutes to measure the hydrogen ion concentration and 40 minutes to measure the hydrofluoric acid concentration, whereas when using the device of the present invention, it took 10 minutes to measure the hydrogen ion concentration and hydrofluoric acid concentration. could be measured simultaneously within 1 minute.

As described above, according to the apparatus of the present invention, the concentrations of hydrogen ions and hydrofluoric acid in an acid bath can be measured quickly and accurately, and highly accurate bath management can be performed.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the apparatus of the present invention, where 1 is a measurement solution, 2 is a reference electrode, 3 is a hydrogen ion selective electrode, 4 is a fluorine ion selective electrode, 5 is a changeover switch, 6 is a regulator, and 7 is a A potentiometer, 8 a computing unit, and 9 a display. FIG. 2 is a straight line showing the relationship between the logarithmic value of the hydrogen ion concentration [H+] and the potential difference BH+ between the hydrogen ion selective electrode and the reference electrode. Figure 3 shows the logarithm of the fluorine ion concentration CF-) and the potential difference E between the hydrogen ion selective electrode and the fluorine ion selective electrode.
This is the relationship straight line between F-.

Claims (1)

[Claims] 1. A reference electrode, a hydrogen ion selective electrode and a fluorine ion selective electrode provided in the measurement solution, and a reference electrode connected to the hydrogen ion selective electrode and the fluorine ion selective electrode to determine the gain of the potential difference between these electrodes. A regulator for adjusting, a contact connected to the fluorine ion selective electrode through the regulator, a contact directly connected to the reference electrode, and a common contact for individually selecting and setting these two contacts. a changeover switch having a changeover switch connected to a common contact of the changeover switch and connected to a hydrogen ion selective electrode via the regulator, and operating the changeover switch to change the potential difference between the hydrogen ion selective electrode and the reference electrode. A potentiometer that measures the potential difference between the ion selective electrode and the fluorine ion selective electrode, and a calculator that is connected to the potentiometer and calculates the hydrogen ion concentration and hydrofluoric acid concentration based on the output of the potentiometer. and a display device connected to the computing device and displaying the hydrogen ion concentration and the hydrofluoric acid concentration as well as the output of the computing device. Acid concentration measuring device.