JPH0518929A - Electrode for measuring ph and its manufacture - Google Patents

Abstract

PURPOSE:To obtain an electrode for measuring pH and its measuring method which enables the entire electrode to be formed finely, is rigid and at the same time superb in chemical resistance, achieves an improved response over a wide pH range and a stable measurement for a long period of time. CONSTITUTION:An electrode for measuring pH is provided with a conductive support 1 and an iridium oxide sensitive film 3 which is formed on a surface of the conductive support 1 and preferably is provided with the conductive support 1, an insulation film 2 which is provided at one portion of the conductive support 1, and the iridium oxide sensitive film 3 which is formed while it is in contact with the conductive support 1 at a portion without any insulation film 2. The iridium oxide sensitive film 3 consists of an iridium oxide where a ratio of oxygen to iridium is 2.5-3.5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pH measuring electrode having a hydrogen ion-selective solid sensitive membrane used for measuring pH of a solution, and a method for producing the same.

[0002]

2. Description of the Related Art A pH measuring electrode having a hydrogen ion-selective solid sensitive membrane is used for measuring the pH of a solution, and a typical example thereof is a glass electrode having a glass sensitive membrane. Recently, ISFET electrodes have also been used in a certain range, and in a special solution such as a high temperature solution or a special application, a pH using a metal such as platinum or a metal oxide such as titanium oxide as a solid sensitive film is used. Measurement electrodes are used.

When actually measuring the pH of a solution, the above-mentioned pH measuring electrode is used as an indicator electrode, and this indicator electrode is placed in a measuring solution together with a reference electrode such as a sweet potato electrode or a silver-silver chloride electrode. Immerse, p of the measurement solution from the potential difference between both electrodes
The H value is determined.

However, ordinary glass electrodes are fragile and therefore troublesome to handle, and have poor chemical resistance, so that the usable solutions are limited. Also, pH meter and other pH
As the demand for miniaturization of measuring devices has increased, it has been difficult to miniaturize the glass electrode in terms of manufacturing technology, and thus there has been a problem that the glass electrode cannot cope with miniaturization of the pH measuring device.

On the other hand, in the conventional pH measuring electrode using a metal or a metal oxide as the solid sensitive film, the measurable pH range is extremely narrow depending on the type of the solid sensitive film to be used, and in the short term. There was a defect that stable measurement could not be performed between the two. Further, the ISFET electrode has drawbacks such as large drift, being affected by light, and requiring a special amplifier circuit.

[0006]

In view of the above-mentioned conventional circumstances, the present invention is capable of forming a fine electrode as a whole, is robust, has excellent chemical resistance, and has a measurable pH range. It is an object of the present invention to provide a pH measuring electrode that can obtain a wide and good response and can perform stable measurement for a long period of time, and to provide a manufacturing method thereof.

[0007]

In order to achieve the above object, the pH measuring electrode of the present invention comprises a conductive support and an iridium oxide sensitive film formed on the surface of the conductive support, In particular, a conductive support, an insulating film provided on a part of the surface of the conductive support, and an iridium oxide-sensitive film formed in contact with the conductive support at least on a part of the conductive support where there is no insulating film. And the iridium oxide-sensitive film has a ratio of oxygen (O) to iridium (Ir) of 2.5.
It is characterized by being composed of iridium oxide of up to 3.5.

In the pH measuring electrode of the present invention, an iridium oxide sensitive film is formed on the surface of a conductive support by a known thin film manufacturing technique such as a sputtering method, an ion beam deposition method, an ion plating method or a CVD method. Can be manufactured by That is, an iridium oxide sensitive film made of iridium oxide having an oxygen to iridium ratio of 2.5 to 3.5 is formed on at least a part of the surface of the conductive support in contact with the conductive support.

As another method of manufacturing a pH measuring electrode in which the portion other than the iridium oxide sensitive film is covered with an insulating film, an insulating film is first provided on the surface of the insulating film conductive support, and a part of this insulating film is formed. After the removal, at least the insulating film of the conductive support has a ratio of oxygen to iridium of 2.5 to
The method of forming an iridium oxide sensitive film composed of iridium oxide of 3.5 in contact with the conductive support, or after forming the iridium oxide sensitive film on the surface of the conductive support, iridium oxide on the surface of the conductive support is formed. There is a method of forming an insulating film on a portion where the sensitive film does not exist.

As the conductive support, a metal material such as aluminum, tantalum, platinum, titanium, iridium or the like is preferable. The shape of the conductive support is arbitrary, for example, a plate shape,
It may be rod-shaped or pipe-shaped. Further, the position where the iridium oxide sensitive film is provided is also arbitrary such as the tip or the side surface of the conductive support. The insulating film provided on the surface of the conductive support is preferably an oxide such as alumina, silicon dioxide or tantalum pentoxide, or a nitride such as silicon nitride.

[0011]

In the present invention, iridium oxide is used as the solid sensitive film of the pH measuring electrode. Since this iridium oxide sensitive film is formed on the surface of the conductive support by utilizing the known thin film manufacturing technique such as the sputtering method as described above, its shape and size can be freely determined. For example, since a fine iridium oxide sensitive film can be formed on the surface of a thin wire-shaped conductive support, it is possible to construct a pH measuring electrode which is extremely smaller than the conventional one.

When an iridium oxide sensitive film and an insulating film are formed on a conductive support, one of the concrete methods is shown in FIG.
As shown in FIG. 3, when a thin insulating film 2 is formed on the surface of the conductive support 1 in advance by a normal thin film manufacturing technique such as natural oxidation, anodic oxidation or vapor deposition, the iridium oxide sensitive film 3 is formed. Alternatively, there is a method in which a part of the insulating film 2 is removed and the iridium oxide sensitive film 3 is formed in contact with the conductive support 1 at the removed portion of the insulating film 2. As another method, there is also a method of first forming the iridium oxide sensitive film 3 on the surface of the conductive support 1 and then covering the exposed surface of the conductive support 1 with the insulating film 2.

The insulating film 2 formed in advance can be removed by various mechanical or chemical means. Particularly, the iridium oxide sensitive film 3 can be formed by an ion process such as a sputtering method or an ion beam evaporation method. By using, it is possible to remove a part of the insulating film 2 by atoms that collide at high speed, so that the removal of the insulating film 2 and the formation of the iridium oxide sensitive film 3 can be easily performed at the same time. It has the advantage that it can be processed.

The pH measuring electrode of the present invention manufactured as described above has the iridium oxide sensitive film 3 electrically connected to the conductive support 1 at a predetermined position of the conductive support 1 as shown in FIG. The surface of the conductive support 1 other than the portion provided with the iridium oxide sensitive film 3 is covered with the insulating film 2. As a typical usage of this pH measuring electrode, as shown in FIG. 2, for example, the opposite side of the conductive support 1 from the iridium oxide sensitive film 3 is fixed by a support tube 5 such as plastic or glass, and the potential difference is The lead wire 4 to the detector is connected to the conductive support 1 and led out through the inside of the support tube 5.

Even if an insulating film is not provided, at least a part of the iridium oxide sensitive film is exposed to form an electrode even if the exposed portion of the conductive support is completely covered with an insulating support tube or the like. It is possible to For example, as shown in FIG. 4, the iridium oxide sensitive film 3 is formed on the surface of the conductive support 1.
Is provided and the iridium oxide sensitive film 3 is directed outward and inserted into a support tube 5 made of an insulating material such as glass so that the conductive support 1 is not exposed, and the glass is melted and sealed, or an adhesive or the like is used. By sealing and fixing with, it is possible to cover the conductive support 1 and configure a pH measuring electrode.

When the ratio of oxygen (O) to iridium (Ir) is in the range of 2.5 to 3.5, the iridium oxide sensitive film of the present invention has a pH of 0 to 1 as a solid sensitive film of a pH measuring electrode.
It was found that a good linear response was obtained in the entire pH range of 4, the response speed was high at about 1 second, and there was no drift or hysteresis, and stable measurement was possible for a long period of time.

Therefore, the measurable pH range is much wider than that of a conventional pH measuring electrode using a solid sensitive film made of a metal such as platinum and a metal oxide such as titanium oxide, and stable measurement is possible. The possible period is also long. Further, compared with a normal glass electrode, since iridium oxide is used as a solid sensitive film, it is far more robust and less fragile than glass, and since it has excellent chemical resistance, there are almost no restrictions on the measurement solution. There are advantages.

Next, the electrode reaction of the iridium oxide sensitive film will be described. In an aqueous solution, iridium oxide and hydrogen ions maintain the equilibrium state shown in the following chemical formula 1, and the equilibrium potential at this time is represented by the following mathematical formula 1:

Embedded image 2IrO ₂ + 2H ⁺ + 2e ⁻ = Ir ₂ O ₃ + H ₂ O

[Equation 1] E (mV) = 681-59.1 pH (at 25 ° C.) That is, the asymmetric potential is different from that of the glass electrode, but the electromotive force per pH is shown by the Nernst equation, which is 59.
15 mV.

As described above, when the ratio of O to Ir in the iridium oxide sensitive film is out of the range of 2.5 to 3.5,
Good responsiveness of the pH measuring electrode cannot be obtained, and drift occurs, resulting in poor stability. For example, using a pH measuring electrode having an iridium oxide sensitive film as an indicator electrode and a silver-silver chloride electrode as a reference electrode, both electrodes are immersed in a standard solution of pH 6.86, and the potential difference between both electrodes is periodically measured. Change of Ir: O of iridium oxide sensitive film
Table 1 shows the relationship between the potential difference and the dipping time obtained for each ratio. The iridium oxide sensitive film has an Ir: O ratio of 1 :.
The thickness was changed to 2, 1: 3 and 1: 4, and the film thickness was set to 500Å.

[0020]

[Table 1] From the above Table 1, when the ratio of Ir: O is 1: 2 and 1: 4, the fluctuation of the potential difference is extremely large, whereas when the ratio is 1: 3, the stable potential difference is stable over a long period of time. It turns out that it can be obtained.

The thickness of the iridium oxide sensitive film is 400 to 1
The range of 0000Å is preferable, and the response speed becomes slower than this range, and drift is likely to occur, so that the stability tends to be lowered. A pH-measuring electrode having an iridium oxide sensitizing film with an Ir: O film thickness of 1: 3 was used as an indicator electrode, and a silver-silver chloride electrode was used as a reference electrode. Table 2 shows the results of periodical measurement of the potential difference between the two electrodes by immersing in.

[0022]

[Table 2] As a result of the above test, the film thickness of the iridium oxide sensitive film is 500Å
It was found that the response speed was fast at 10000 Å and 10000 Å, and the potential difference was stable for a long period of time, but the response speed was slow at 250 Å and 12000 Å, causing drift.

[0023]

Example 1 An electrode having the structure shown in FIGS. 1 and 2 was manufactured as the pH measuring electrode of the present invention. That is, an insulating film 2 of tantalum pentoxide having a thickness of 70Å was formed by natural oxidation on the entire surface of a conductive support 1 made of a tantalum wire having a diameter of 0.5 mm and a length of 2 cm. A 0.2 mm × 3 mm sensitive film forming part is left on the side surface near one end of the conductive support 1 covered with the insulating film 2 and the remaining part is masked, and placed in a film forming chamber of a sputtering apparatus, and an oxidizing atmosphere is set. An Ir target was sputtered therein at a voltage of 0.8 KV for 100 minutes. As a result, in the sensitive film forming portion exposed from the mask of the conductive support 1, the insulating film 2 on the surface is almost completely removed, and at the same time, the conductive support 1 is electrically connected and Ir: O is 1: 3. The iridium oxide sensitive film 3 was formed to a thickness of 1000Å.

Next, the insulating film 2 on the other end side of the conductive support 1
Was partially removed, and the lead wire 4 was connected to the exposed conductive support 1. After that, except for one end side including the iridium oxide sensitive film 3, the conductive support 1 and the lead wire 4 are solidified into a columnar shape so as to be wrapped with a support tube 5 made of PVC, and the iridium oxide sensitive film 3 is provided on one end side surface and An electrode for pH measurement having a lead wire 4 at the end was obtained.

The obtained pH measuring electrode is used as an indicator electrode,
When pH responsiveness was examined using a normal sweet potato electrode as a reference electrode, it was 59.9 mV per pH in the range of pH 0 to
A good linear response was obtained with a slope of. Further, as a result of alternately measuring the potential difference between the standard solutions of pH 1.68 and pH 12.00, good reproducibility was obtained as shown in Table 3.

[0026]

[Table 3]

[0027]

Example 2 An electrode having the structure shown in FIG. 3 was manufactured as the pH measuring electrode of the present invention. That is, a lead wire 4 is connected to one surface of a conductive support 1 made of a platinum disk having a diameter of 2 mm and a thickness of 0.2 mm, and one side surface of the conductive support 1 is released at both ends having the same outer diameter. The supporting tube 5 made of the glass right cylindrical body was brought into contact with one end, and the one end was heated and sealed, and at the same time, the conductive support 1 was fixed to the supporting tube 5.

Next, the exposed conductive support 1 of platinum disk is washed with acid to remove the oxide film on the surface, and a sensitive film forming portion having a diameter of 1 mm is left at the center of the other surface. Other parts are masked, placed in a film forming chamber of a sputtering device, and electrically connected to the conductive support 1 by sputtering an Ir target in the same manner as in Example 1 to oxidize Ir: O at 1: 3. The iridium sensitive film 3 was formed to a thickness of 1000Å. Next, the iridium oxide sensitive film 3 is masked and the support tube 5
An insulating film 2 of tantalum pentoxide, alumina, or the like was formed to a thickness of 800Å by a sputtering method so as to cover the conductive support 1 protruding from the.

The obtained pH measuring electrode is used as an indicator electrode,
When pH responsiveness was examined using a normal sweet potato electrode as a reference electrode, it was 59.9 mV per pH in the range of pH 0 to
A good linear response was obtained with the gradient of and the reproducibility was also good.

[0030]

According to the present invention, by using an iridium oxide sensitive film as a hydrogen ion-selective solid sensitive film, it is robust and excellent in chemical resistance and has a pH of 0-14.
A good response with good reproducibility over the entire pH range of
It is possible to provide a pH measurement electrode having a high response speed of about 1 second and capable of stable measurement over a long period of time.

Further, the conductive support and the iridium oxide sensitive film formed on the surface thereof can be freely configured to have any shape and size, and the conductive support is not formed by the fine iridium oxide sensitive film. Since the lead wire can be derived from the body, it is possible to miniaturize the entire pH measuring electrode and to have a simple structure, and to meet the demand for miniaturization of pH meters and other pH measuring devices. It enables pH measurement in the special fields required.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a main part showing a specific example of a pH measuring electrode of the present invention.

FIG. 2 is a schematic cross-sectional view showing a specific example of the pH measuring electrode of the present invention.

FIG. 3 is a schematic cross-sectional view of a main part showing another specific example of the pH measuring electrode of the present invention.

FIG. 4 is a schematic cross-sectional view of a main part showing still another specific example of the pH measuring electrode of the present invention.

[Explanation of symbols]

1 Conductive support 2 insulating film 3 Iridium oxide sensitive film 4 lead wire 5 Support tube

Claims (5)

[Claims] 1. A conductive support and an iridium oxide sensitive film formed on the surface of the conductive support, wherein the iridium oxide sensitive film is composed of iridium oxide having an oxygen to iridium ratio of 2.5 to 3.5. Characteristic pH measuring electrode. 2. A conductive support, an insulating film provided on a part of the surface of the conductive support, and a conductive support formed in contact with the conductive support at least at a location where the insulating film does not exist. An electrode for pH measurement, comprising an iridium oxide sensitive film, wherein the iridium oxide sensitive film is made of iridium oxide having a ratio of oxygen to iridium of 2.5 to 3.5. 3. The iridium oxide sensitive film has a thickness of 400.
The electrode for pH measurement according to claim 1 or 2, wherein the electrode has a pH of -10000Å. 4. An insulating film is provided on the surface of a conductive support, a part of this insulating film is removed, and a portion of the conductive support where at least the insulating film is removed has a ratio of oxygen to iridium of 2.5 to 2.5. A method for producing a pH measuring electrode, which comprises forming an iridium oxide sensitive film made of iridium oxide of 3.5 in contact with a conductive support. 5. An iridium oxide sensitive film made of iridium oxide having an oxygen to iridium ratio of 2.5 to 3.5 is formed on at least a part of the surface of the conductive support in contact with the conductive support, and then the conductive support is formed. A method for producing a pH measuring electrode, which comprises forming an insulating film on a portion of the surface of the support where the iridium oxide sensitive film does not exist.