JPH11295262A - Production of ion electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an ion electrode while decreasing resistance between a sensitive film and a lead wire and suppressing fluctuation. SOLUTION: In an apparatus for measuring the ion concentration of a solution to be measured based on the potential difference between a reference electrode and an ion electrode immersed in the solution, the ion electrode having an inner electrode 3 embedded in a glass sensitive film is produced by preheating the inner electrode 3, immersing the inner electrode 3 into molten glass 5, lifting up the inner electrode, solidifying the molten glass and sustaining a temperature (about 500 deg.C) not exceeding the softening point of the glass for a specified time (about 30 min).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an ion electrode used in an ion concentration measuring device such as a pH sensor, and more particularly, to an ion electrode with reduced internal resistance and improved responsiveness. And a method for producing the same.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram of a conventional pH sensor representing an ion concentration measuring device. In the figure, reference numeral 10 denotes an ion electrode whose electrode potential changes according to a change in ion concentration (activity) in the liquid to be measured, and reference numeral 20 denotes a reference electrode showing a constant potential.

In the ion electrode 10, 11 is 0.2 to
It is a glass thin film made of thin glass of 0.5 mm and is sensitive to H + ions. Reference numeral 12 denotes an internal solution composed of a buffer solution having a predetermined pH, potassium chloride or the like, and reference numeral 13 denotes an internal electrode composed of a silver / silver chloride or calomel electrode.

[0004] The ion concentration in the solution is obtained by measuring a potential difference E generated between both the ion electrode 10 and the reference electrode 20 with a potentiometer PT and converting it to pH. Assuming that the electrode potential of the ion electrode 10 is Eise and the electrode potential of the reference electrode 20 is Eref, the potential difference E generated between both electrodes is represented by the following equation. E = Eise−Eref = E0 + S · log ai

Here, ai is the activity of the ion to be measured by the ion electrode, E0 is a constant, and S is 2.303 (RT / Z
iF), when Zi = 1, the voltage is 0.05916 V at 25 ° C. Therefore, ai can be obtained by measuring the potential difference E.

However, as can be understood from the following equation, the ion concentration measuring apparatus having the above-described configuration performs measurement by changing the electrode potential difference Eise due to aging of the internal liquid in the ion electrode, for example, changes in pHi and Ci. This may cause an error. Eise = {2.303RT (pHi-pHs) / F} + (Cs
-Ci) where R is the gas constant, T is the absolute temperature, F Faraday constant, pHi is the pH of the internal solution, pHs is the pH of the measurement solution, C
i is a specific potential on the internal liquid side, and Cs is a specific potential on the measurement liquid side. The glass thin film of the ion electrode has a thickness of 0.2 to 0.1 mm.
There is a problem that it is thin and fragile at 5mm, requires skill to make, and is difficult to mass produce.

FIG. 6 shows a conventional ion concentration measuring apparatus which solves such a problem, in which a glass thin film of an ion electrode is directly formed on an internal electrode by sputtering or the like, or an internal electrode of the ion electrode is formed of molten glass. By immersing it inside, it is formed so as to be sealed in a glass thin film and eliminates the need for an internal liquid, eliminating measurement errors caused by the internal liquid, and being resistant to impact and easy to manufacture. The device has been realized.

[0008]

The ion electrode shown in FIG. 6 preheats an internal electrode (platinum) and melts the internal electrode (platinum) in the following composition and weight ratio (mol%) (about 140%).
0 ° C) glass “Lithium carbonate (Li2CO3) → 29.49 (mol%) Anhydrous cesium carbonate (Cs2CO3) → 1.69 (〃) Barium carbonate (BaCO3) → 2.30 (〃) Quartz sand (SiO2) → 57 0.81 (〃) Titanium oxide (TiO2) → 1.33 (〃) Tantalum oxide (Ta2O5) → 2.67 (〃) Niobium oxide (Nb2O5) → 0.11 (〃) Lanthanum oxide (La2O3) → 4.60 (〃) ”, the internal electrode was pulled up to solidify the glass, and then kept at about 420 ° C. for about 30 minutes for annealing.

However, when annealing is performed at the above temperature using glass having such a composition and weight ratio,
The resistance value between the sensitive film and the lead wire is high, and the zero point among the electromotive force characteristics varies depending on the individual solid, and the production reproducibility is poor (poor yield… If the variation is large, the adjustment range of the converter will be exceeded. ). Also,
The present invention has been made in order to improve the electromotive force characteristics of an ion electrode of such an ion concentration measuring device, and provides a method for manufacturing an ion electrode having a low resistance value between a sensitive film and a lead wire and having no variation. The purpose is to do.

[0010]

In order to achieve the above object, according to the present invention, there is provided a fuel cell system comprising a reference electrode and an ion electrode which are immersed in a solution to be measured. 1. An ion concentration measuring device for measuring an ion concentration in the solution to be measured based on a potential difference, wherein the internal electrode is embedded in a sensitive film of glass. Preheat internal electrodes. Step 2. The internal electrode is immersed in molten glass. Step 3. Pull up the internal electrode. Step 4. After the molten glass is solidified, the glass is kept at a high temperature (about 500 ° C.) which does not exceed the softening temperature of the glass for a certain time (about 3 ° C.).
0 min) hold. It is characterized by being manufactured by a manufacturing method including a process. In claim 2, the molten glass is lithium carbonate (Li2CO3) → 33.00 (mol%) anhydrous cesium carbonate (Cs2CO3) → 1.08 (〃) barium carbonate (BaCO3) → 1.00 (〃) quartz Sand (SiO2) → 57.81 (〃) Titanium oxide (TiO2) → 1.33 (〃) Tantalum oxide (Ta2O5) → 2.67 (〃) Niobium oxide (Nb2O5) → 0.11 (〃) Lanthanum oxide ( La 2 O 3) → 3.00 (〃) and a compounding ratio (mol%).

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. The ion electrode of the present invention is apparently the same as the conventional ion electrode shown in FIG. 6, and differs from the conventional ion electrode in the manufacturing method and the composition of glass as a sensitive film.

First, a manufacturing process of an ion electrode will be described with reference to FIGS. In FIG. 1 (a), a lead wire 2 having a diameter of about 0.4 mm is provided through a closed bottom of a lead glass tube 1 having an outer diameter of about 8 mm and an inner diameter of about 6 mm in an airtight manner. An internal electrode (diameter 3) is placed at a position about 1 to 2 mm away from the bottom of the tube 1.
Pt) 3 having a thickness of about 0.1 mm and a thickness of about 0.1 mm is fixed.

A molten glass 5 is placed in a container 4, and the tip of a lead glass tube 1 to which an internal electrode 3 is fixed is immersed in the molten glass 5. Before the immersion, the lead glass tube 1 is heated to about 200 ° C., and the temperature of the molten glass 5 is heated to about 1400 ° C. FIG. 1B shows a state in which the lead glass tube 1 is immersed in the molten glass 5 for 1 to 2 seconds and pulled up.
Adheres in a state of being wrapped around.

FIG. 1C shows a mold 6 into which the lead glass tube 1 shown in FIG. 1B is inserted.
By inserting the lead glass tube 1 into a hole slightly larger than the outer diameter of the lead glass tube and having a depth of about 5 mm, as shown in FIG.
Is formed. In this state, the thickness of the sensitive glass 5a from the surface of the internal electrode 3 is 0.1 to
It is about 1 mm. It is desirable that the thickness of the sensitive glass 5a be constant in terms of the performance of the product.

Next, the ion electrode 1a is annealed while being maintained at a high temperature of about 500 ° C. which does not exceed the softening temperature of the glass for about 30 minutes. The difference from the conventional example is that the annealing temperature of the sensitive glass 5a is changed from the conventional 420 ° C. to 500 ° C. Here, the following composition and mixing ratio (mol%) of the molten glass 5 are used.

Lithium carbonate (Li 2 CO 3) → 33.00 (mol%) Anhydrous cesium carbonate (Cs 2 CO 3) → 1.08 (〃) Barium carbonate (BaCO 3) → 1.00 (〃) Quartz sand (SiO 2) → 57.81 (〃) Titanium oxide (TiO2) → 1.33 (〃) Tantalum oxide (Ta2O5) → 2.67 (〃) Niobium oxide (Nb2O5) → 0.11 (〃) Lanthanum oxide (La2O3) → 3.00 (〃) )

Although the composition of the sensitive glass in the present invention is the same as that of the conventional glass, the present invention uses lithium carbonate (LiC).
The compounding ratio (mol%) of O3) was changed from the conventional 29.49 to 33.0.
0 and the blending ratio of anhydrous cesium carbonate (Cs2CO3) (mol
%) From 1.69 to 1.08, barium carbonate (BaCO3)
Is from 2.3 to 1.00, and the mixing ratio (mol%) of lanthanum oxide (La2O3) is from 4.6 to 3.00.

FIG. 2 shows a comparison between the resistance values of a conventional sensitive glass prepared at the composition and the annealing temperature and those of the present invention prepared at the composition and the annealing temperature. Electrode (pt thickness 0.1m
(using an outer diameter of 3 mm and 4 mm)), and the resistance was measured based on the method of measuring the resistance of a pH electrode according to JIS (data is the average value of five prepared electrodes). As can be seen from the figure, the resistance value is significantly different between the case where only the sensitive glass is used and the case where pt is interposed between the sensitive glass and the contact value between the glass and pt is dominant in the resistance value.

Further, the resistance value of the conventional composition when only the sensitive glass is used and the resistance value of the composition of the present invention are 185 → 19.5.
(MΩ), 27 when a 3 mm outer diameter pt is interposed
The resistance value is reduced by about one digit from 00 to 342 (MΩ), and it can be seen that the resistance is reduced.

FIG. 3 shows a production method of the present invention, and FIG. 4 shows an experimental example in which three kinds of liquids having different pHs were measured using four ion electrodes each having a pt outer diameter of 3 mm according to a conventional example. ing. In the figure, the horizontal axis is pH, and the vertical axis is output value (voltage). As is apparent from these figures, when the ion electrode manufactured by the manufacturing method of the present invention is used, individual variations are reduced.

Although there is no theoretical elucidation on the reduction of the resistance of the ion electrode and the reduction of the variation due to the composition and the annealing temperature, generally, in the glass composition of the present invention, anhydrous cesium carbonate (Cs2CO3) , Barium carbonate (BaCO3) and lanthanum oxide (La2O3) are known to have no effect on the change in the resistance value, and lithium carbonate (LiCO3) is known to affect the change in the resistance value. Therefore, it was predicted that the resistance value would be reduced by changing these numerical values. Further, it is presumed that by increasing the annealing temperature, the affinity between pt and glass was improved and the contact resistance was reduced.

It is to be noted that the above description of the present invention has been presented by way of illustration and example only of a particular preferred embodiment. Thus, it will be apparent to one skilled in the art that the present invention may be modified or modified in many ways without departing from its essentials. For example, the annealing temperature can be changed by several percent, and the glass composition can be changed without affecting the performance as an ion electrode as long as it is within several percent of the indicated numerical value.

[0023]

As described in detail above, the ion concentration measuring apparatus of the present invention performs annealing of the ion electrode glass at a high temperature (about 500 ° C.) which does not exceed the softening temperature for a certain time (about 30 minutes). ) By holding and optimizing the composition of the glass, it became possible to manufacture an ion electrode having low resistance and no manufacturing variation. As a result, noise during measurement is small,
The responsiveness is improved, and a circuit with a high input impedance on the converter side is not required, and the constraints on the design conditions can be relaxed. In addition, productivity was improved because manufacturing variability was improved.

[Brief description of the drawings]

FIG. 1 is a view showing a manufacturing process of an ion electrode of the present invention.

FIG. 2 is a diagram comparing resistance values of a conventional sensitive glass and a sensitive glass of the present invention.

FIG. 3 is a diagram showing the relationship between pH and output of an ion electrode manufactured by the manufacturing method of the present invention.

FIG. 4 shows p of an ion electrode manufactured by a conventional manufacturing method.
It is a figure which shows the relationship between H and an output.

FIG. 5 is a configuration diagram of a conventional pH sensor representing an ion concentration measuring device.

FIG. 6 is a configuration diagram of a pH sensor showing another conventional ion concentration measuring device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lead glass tube 2 Lead wire 3 Internal electrode (platinum) 4 Container 5 Molten glass 5a Sensitive glass 6 type

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Taku Kanemi 29-3 Takatsudocho, Midori-ku, Chiba 611 Sunvere Chiba 611 (72) Inventor Takashi Kitamoto 2-9-132 Nakamachi, Musashino City, Tokyo Yokogawa Electric Corporation (72) Inventor Takeshi Ueda 2-9-132 Nakamachi, Musashino-shi, Tokyo Yokogawa Electric Corporation (72) Inventor Hideo Takeuchi 2-9-132 Nakamachi, Musashino-shi, Tokyo Yokogawa Electric Corporation ( 72) Inventor Tokuji Nishida 2-9-132 Nakamachi, Musashino City, Tokyo Inside Yokogawa Electric Corporation

Claims (4)

[Claims] 1. An ion concentration measuring apparatus for measuring an ion concentration in a solution to be measured by a potential difference generated between the reference electrode and the ion electrode immersed in the solution to be measured. Wherein the ion electrode is embedded in a glass sensitive film, wherein the ion electrode is manufactured by a manufacturing method including the following steps. Step 1. Preheat internal electrodes. Step 2. The internal electrode is immersed in molten glass. Step 3. Pull up the internal electrode. Step 4. After the molten glass is solidified, the glass is kept at a high temperature (about 500 ° C.) which does not exceed the softening temperature of the glass for a certain time (about 3 ° C.).
0 min) hold. 2. The method according to claim 1, wherein the sensitive film of glass has the following composition and blending ratio (mol%). Lithium carbonate (Li2CO3) → 33.00 (mol%) Anhydrous cesium carbonate (Cs2CO3) → 1.08 (〃) Barium carbonate (BaCO3) → 1.00 (〃) Quartz sand (SiO2) → 57.81 (〃) Titanium oxide (TiO2) → 1.33 (〃) Tantalum oxide (Ta2O5) → 2.67 (〃) Niobium oxide (Nb2O5) → 0.11 (〃) Lanthanum oxide (La2O3) → 3.00 (〃) 3. The method according to claim 1, wherein said sensitive film has a thickness of about 0.1 to 1.0 mm. 4. The method for manufacturing an ion electrode according to claim 1, wherein a resistance value including a contact resistance between said sensitive film and an internal electrode is set to 500 MΩ or less.