JPS5810646A - Relative concentration measuring device for solution - Google Patents

Abstract

PURPOSE:To make it possible to measure a wide range of solution concentration by seeking relative difference of potentials of the solutions that constitute a pair of half batteries. CONSTITUTION:A solution B to be inspected is poured into a measurement tank 10, and a measurement electrode A is immersed in this solution B to form a half battery on one side. Further, a reference solution B' is filled in a reference tank 20, and a reference electrode A' is immersed in the reference solution B' to form a half battery on the other side. This reference tank 20 is immersed in the solution B to be inspected, and the potential difference between the two half batteries is measured with a potential measurement device D. This potential difference is generated in accordance with the temperature difference between the reference solution B' and the solution to be inspected.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring relative concentration in which a difference in concentration of a solution is detected as a difference in potential.

Conventionally, concentrated acid or alkali solutions have been used in surface treatment processes such as etching and plating, and how well these solutions are managed is a major factor that influences product yield and quality.

Therefore, measuring the concentration of the surface treatment liquid is an important task.
Various methods are used, such as p, PH measurement, specific gravity measurement, and conductivity measurement.

However, in the PH measurement method, the measurable solution concentration range is preferably 1N or less, and considering practical accuracy, it must be said that 0.1N or less is practical. Therefore, at the surface treatment work site,
Applying the pH measurement method to a concentrated solution of 10N or 12 to 36N is not a good method because of large measurement errors.

Furthermore, although the specific gravity measurement method does not have the above-mentioned difficulties, it takes time to measure. Therefore, there are problems in measuring the constantly changing concentration of a solution, such as poor workability and time lag.

Furthermore, both of the above two methods are methods for determining the absolute value of the solution concentration, and when the reed, acid, or alkaline solution is a mixture of multiple solutions or contains many impurities, Difficult or impossible to measure.

The present invention provides a method for measuring relative solution concentration, which is different from the above-mentioned absolute value measuring method.

Therefore, the present invention can be particularly effective in measuring concentrated solutions, such as acid or alkaline solutions and ionic solutions.

Further, according to the present invention, a concentration difference can be detected even if the solution is not pure, but is mixed with many other types of solutions, or contains impurities.

In addition, the present invention can be said to be a measuring method that can satisfactorily and quickly accomplish its purpose, even in the measurement of solutions whose concentration changes continuously, such as in etching or plating operations.

Before explaining the present invention, the terms used in the explanation and the potential generated in the solution will be explained.

As shown in Figure 1, when the electrodes (8) and (4) are immersed in the electrolyte solution (2) in the tank (1),
If they are the same kind of metal, the potential difference (Ea) between these electrodes is zero.

However, if the electrodes (8) and (4) are different metals, Ea=
An electrode potential difference of α (α is a numerical value in mV) is generated.

In addition, when the electrodes (8) and (4) are separated by a diaphragm (5) and different types of solutions or solutions of the same type but with different concentrations are placed on each side, a liquid valve potential or a concentration potential is generated. This is well known.

A device in which an electrode is inserted into this solution to generate a potential is called a half-cell, and the one shown in the first diagram constitutes a pair of half-cells by a diaphragm.

Further, there is an "aqueous solution reference electrode" as a means similar to the present invention. This is used to determine the activity and concentration of dissolved ionic species, including pH.
A silver-silver chloride electrode, a calomel electrode, a mercury-mercuric oxide electrode, and the like are known.

However, both are difficult to manufacture and handle;
In addition, the potential display is extremely unstable, and it is only an experimental method and has not been accepted as a practical method.

For example, a hydrogen electrode cannot be used if a substance that would be adsorbed to a platinum electrode is present in the solution. Furthermore, even if a mercury-mercuric oxide electrode is used, it cannot be used in a solution containing ions that form a strong complex with Hg.

The present invention solves the problems of conventional measurement methods by simply determining the relative potential difference between solutions constituting a pair of half-cells without determining the absolute value. This made measurement possible.

The present invention will be explained in detail below with reference to FIGS. 2 and 3.

Figure 2 shows a measurement tank, in which a sample solution to be measured is placed, and the measurement electrode (A) is immersed in this solution. , one half-cell is configured.

2) is a reference tank, and an isolation membrane (q) is attached to the bottom of this tank, and the inside of the tank is filled with a reference solution.
The relationship between B) and those in the test liquid will be explained later.

The reference liquid (iK is the reference electrode (AJ) is immersed in it, and this reference tank is the test liquid (uniformly immersed, forming the other half cell). In order to measure the potential difference, a potential measuring device (D), which is a means of potential measurement, is connected to the amphibious battery.

A case will be described in which, for example, the acid concentration of an etching bath is measured using the measuring means configured as described above.

A solution of a desired concentration, which is first extracted from the etching bath, is placed in a reference tank as a reference solution.

The test solution (Bl) is a solution that is taken out from the etching bath every predetermined period of time after starting the etching process. , the capacity of the solution deteriorates.

In this case, many potential change factors, such as the reference solution (disease) and the test solution (metal ions eluted between the eyes, a mixture of impurity acid solutions, etc.), will act relatively on the electrode, and the difference will correspond to the concentration difference between the solutions. Only the potential difference can be detected by a potential measuring device (mouth).

Moreover, this potential difference is proportional and can be detected as a function of concentration ratio.

Therefore, in the case of the above etching bath, by measuring the concentration difference at the limit of use in advance, it is possible to accurately determine when to replace the etching solution by looking at the results of detecting changes in concentration over time. can.

Although the above is a case of a mixed solution used in an etching bath, the method of the present invention can be similarly used to measure the concentration ratio of solutions containing acids, alkalis, and ions. .

In particular, in the method of the present invention, since it is a relative ratio between the reference solution and the test solution, it is possible to more accurately measure the concentration difference even in concentrated solutions such as strong acid or strong alkaline solutions. be.

Furthermore, if the concentration of the test liquid is measured by an absolute measurement method and the change in concentration is further measured by the method of the present invention, the method of the present invention can also be used to perform an absolute value measurement method. It becomes possible.

A feature of the present invention is that the reference electrode described above does not need to be used as the measurement electrode, and solid electrodes, such as metals suitable for the solution such as titanium, tantalum, and molybdenum, and metal oxides thereof can be used. .

The reference electrode used is of the same quality as the measurement electrode.

The separation membrane can be selected depending on the properties of the solution, such as a fluorocarbon membrane or a porous polymer membrane.

Figure 3 shows how the measuring electrode (A) is connected to the measuring solution (T).
and selectively permeable membrane (F) to form a half cell, reference liquid volume)
Also uses a selectively permeable membrane (b).

If you distribute the measurement solution (E11 reference solution (Bl) in the order of increasing concentration, the potential difference (Eb) will be very sharp, so depending on the solution, choose this measurement method. Just do it like this.

As explained above in detail, according to the method of the present invention,
Relative concentrations can be measured relatively easily over a wide range of solutions, such as concentrated acid or alkali solutions, solutions from etching baths or plating baths, solutions containing other impurities, and mixtures of various solutions.

Furthermore, it has great advantages such as the ability to incorporate signals appearing as potentials into various work processes as a process control device by processing them with electrical devices.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a longitudinal cross-sectional view for explaining the structure of a half-cell, FIG. 2 is a vertical cross-sectional view showing one embodiment of the present invention, and FIG. 3 is a longitudinal cross-sectional view showing another embodiment of the present invention. A longitudinal cross-sectional view showing an example of a tank for measuring zero
Reference tank■) Measuring electrode tank (A) Measuring electrode (5) Reference electrode (B) Test liquid (equalized reference liquid (q-bound)) Isolation membrane (D Potential measuring device (Measurement solution Figure 1)

Claims (1)

[Claims] A solution to be measured and an electrode immersed in this solution form one half cell; a reference solution having the same composition as the solution to be measured and a different concentration; Relative concentration measurement of a solution, which consists of an electrode immersed in a solution, bringing this reference solution into contact with the above solution via a diaphragm material to form the other half cell, and detecting the potential difference generated between these two cells. Method.