JPH01203952A - Electric conductivity meter - Google Patents

Abstract

PURPOSE:To provide an electric conductivity meter which is stable and is highly resistant to corrosion and to obtain a good linear relation between the conductivity between electrodes to be measured and an actual salt concn. by incorporating at least any one noble metal oxide among Pt, Ir, Os, Pd, Ru and Rh on the surface of the base bodies of the metallic electrodes. CONSTITUTION:At least one or two noble metal oxides are incorporated into the coating layer of a conductive metal oxide which coats the surface of electrode base bodies to be used for the electrodes. The coating layer which contains >=1 among the oxides of Ti, Ta, Nb, Zr, Hf, Al, Si, Sn, Sb, and Bi as the metal oxide except noble metals is equally satisfactory. for example, an electrode cell consisting of a pair of the electrodes 1, 1, an intermediate chamber spacer 2, and cell frames 3, 3 is formed. The electrodes formed by coating TiO2 doped with 30mol.% RuO2 on the surface of the Ti electrode base bodies to 10mum thickness are used. The electrical conductivity meter which is stable and is highly resistant to corrosion is thereby obtd. and the god linear relation between the conductivity between the electrodes to be measured and the actual salt concn. is thereby obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrical conductivity meter for continuously measuring the electrolyte concentration in an aqueous solution or suspension containing an electrolyte.

Electrical conductivity meters are useful for measuring the concentration of salts contained in solutions containing biochemical substances, foods, etc., and are particularly useful for measuring the concentration of salts contained in solutions containing biochemical substances, foods, etc. It is effective for measuring salt concentration in the desalination of biological substances by FA or the desalination of salt-containing liquids by electrodialysis or reverse osmosis membranes.

[Prior Art] Conventionally, as a method for continuously measuring the salt concentration in a salt-containing liquid, the electrical conductivity of the target liquid is measured using a pair of electrodes inserted into the target liquid, and this is calculated as the salt concentration. There are known methods of conversion. As materials for the electrodes used in this measurement, metals such as Fe, U, Pt, Au, and Heg, alloys such as stainless steel, platinum black-plated PT, or carbon have conventionally been used.

However, Fe, (:u, and stainless steel) have poor corrosion resistance and high impedance at the electrode interface, making it difficult to make accurate and stable measurements. The relationship between the reciprocal of the total impedance of the cell) and the actual salt concentration deviates significantly from the linear relationship, making it difficult to accurately calculate the salt concentration from the conductivity.

Further, when Pt, Au, and Ag are used as they are, the impedance at the electrode interface is large and a similar problem occurs. On the other hand, the properties of platinum black electrodes tend to change when kept in a dry state. Furthermore, Pt and 8U are expensive and unsuitable for use in inexpensive and simple equipment.

The problem with carbon electrodes is that they have poor mechanical strength.

[Problems to be Solved by the Invention] The purpose of the present invention is to be more stable and corrosion resistant than these conventional electrical conductivity meters, and to be able to reduce the difference between the measured conductivity between the electrodes and the actual salt concentration. The objective is to provide an electrical conductivity meter with good linear relationship.

[Means for Solving the Problems] The present inventors have proposed using a metal coated with a conductive metal oxide for the electrode of an electrical conductivity needle for continuously measuring the salt concentration in a salt-containing liquid. It was discovered that an electrical conductivity meter that is stable, has excellent corrosion resistance, and has a good linear relationship between the measured conductivity between the electrodes (the reciprocal of the total impedance of the electrode cell) and the actual salt concentration was discovered. The invention has been completed.

The electrical conductivity meter according to the present invention is characterized in that the metal electrode includes a noble metal oxide (hereinafter simply referred to as noble metal oxide) of at least one of Pt, Ir, Os, Pd, Ru, and Rh on its base surface, Or along with this, Pt, Ir
, Os, Pd, Ru, and Rh, which may contain a conductive metal oxide coating layer. This conductive metal oxide coating layer may further contain a conductive metal oxide other than the above-mentioned noble metal.

The present invention will be explained in detail below.

The electrical conductivity meter of the present invention is composed of an electrode (or a cell incorporating the electrode) and a circuit for measuring impedance. Here, at least two electrodes are required, and they are fixed to a carrier such as a cell at an appropriate interval.

A circuit for measuring impedance can usually consist of a power source (usually using alternating current) and a bridge circuit to apply an electric field to the electrode (References, Nippon Kagaku Lifeline, "New Experimental Chemistry Course 5") Maruzen (pp. 369-372), for example, without using a bridge circuit, connects a fixed resistor and an electrode cell in series, applies a constant voltage to this, and reduces the voltage drop that occurs in the electrode cell. May be measured.

The conductive metal oxide coating layer that coats the surface of the metal substrate used in the electrode in the present invention is formed as a layer of a noble metal oxide or a conductive metal oxide that may contain a noble metal as described above. Ru. As the above noble metal element, one or more of Ru, Os, Rh, Ir, Pd, and Pt is selected. In addition, the coating layer is made of metal oxides other than noble metals (Ti, Ta, Nb, Zr, ) If
, AjZ, Si, Sn, Sb, and Bi oxides. The noble metal oxide contained in the conductive metal oxide coating layer has a content ratio of noble metals other than the noble metal oxide or conductive metal oxides other than these noble metals of 95% by weight or less, preferably 90% by weight or less. , it is best to give it within a range of 80 weight zero or less. When the content ratio of the noble metal is more than 95% weight zero 4W, there are problems such as a decrease in the mechanical strength of the coating layer, a decrease in adhesive strength with the substrate, and an increase in cost.
Furthermore, if the content of conductive metal oxides other than noble metals exceeds 95 weight x 1y, there is a problem that the impedance of the electrode increases.

The layer thickness of the above-mentioned coating layer is usually about 0.1 to 20 μm,
Preferably, the thickness is about 0.5 to 10 μm.

The means for imparting conductivity is not particularly limited, but in general, a solid reaction using heat treatment or a method using a salt as a starting material and thermal decomposition of the salt can be used. Alternatively, as will be described below, it is also possible to adopt a method that allows the synthesis of the conductive oxide and the coating on the base metal at the same time.

Further, as the electrode base coated with the conductive metal oxide, any one of Ti, Ta, Nb, and Zr or a base alloy thereof can be used. Usually Ti is preferably used. The reason for this is that these metal materials are chemically stable and electrochemically stable against the DC or AC power waveform applied during conductivity measurement.
This is due to the ability to maintain good adhesive strength with conductive metal oxides.

Various techniques can be applied to coat the conductive metal oxide. For example, a method is to synthesize a conductive metal oxide in advance and turn it into a powder, then add a small amount of an appropriate inorganic or organic binder to form a paste, and then print and bake it on a base metal. As a salt, a method can be considered in which a mixed solution of the salt is applied onto the base metal, dried, and then a conductive oxide is simultaneously synthesized by thermal decomposition and coated on the base metal, and a method using PVD or CVD is also considered.

Table 1 shows the unipolar AC impedance measurements of various electrode materials.

Table 1 AC impedance of a single pole These are measurements at an AC frequency of 1 kHz, which is commonly used in conductivity measurements, and the effective area of the electrode is 2 cm.
Measured at 0°C. The impedance of a single pole is made up of a complex relationship consisting of the resistance of the electrode surface layer, the resistance of the electrode-solution interface, and the capacitance, and is generally treated as a vector on a complex plane. The magnitude of impedance corresponds to the absolute value of the length of this vector. As is clear from Table 1, the impedance of the electrode No. 3 having the conductive oxide coating applied to the present invention is extremely small. This is understood to be due to the fact that the electrical resistance of the conductive oxide layer is very low, and the electrochemical resistance present at the conductive oxide-solution/liquid interface is also very low.

In this way, the electrode coated with a conductive oxide has a very small impedance at the electrode interface, so even if it is used to measure the electrical conductivity of a liquid using the two-electrode method, its value as the reciprocal of the liquid resistance can be determined with sufficient accuracy. can.

Furthermore, the above electrode can also be used for measuring the electrical conductivity of a liquid by the four-electrode method (reference literature, Nippon Kagaku Kinsen, "New Experimental Chemistry Course 5" Maruzen pp. 367-376). In this case, if used as a current-carrying electrode or a probe electrode for potential difference measurement, it can be used stably against corrosive liquids such as strong acids.
It becomes possible to measure electrical conductivity.

The target liquid used for salt concentration measurement with the electrical conductivity meter of the present invention includes polysaccharides, amino acid derivatives, oligopeptides,
Solutions of proteins, nucleic acid-related substances, oxygen, biochemical substances including antibiotics, biological extracts from animals and plants, food additives, and liquid foods (juice, soup, milk, coffee, soy sauce, etc.) etc.

The electrical conductivity meter of the present invention is characterized in that the above-mentioned target liquid is
When desalting by diffusion dialysis, electrodialysis, gel filtration, etc., the salt concentration is continuously measured and its value (or relative value)
It can be used to display or further control the operation of the device based on it. In particular, if this electrical conductivity meter is used, the measured values are accurate and stable, so highly accurate control is possible, and it is inexpensive and economical because it does not use a large amount of expensive metals such as Pt.

Furthermore, if the electrode is installed not in the target liquid reservoir but in a part of the piping through which the target liquid flows, it will not be affected by increases or decreases in the amount of liquid, so more stable measured values can be obtained.

[Examples] Next, the present invention will be explained with reference to Examples, but the present invention is not limited to the Examples.

Example 1 As shown in FIG. 1, an electrode cell consisting of a pair of electrodes 1.1, an intermediate chamber spacer 2, and cell frames 3, 3 was prepared. The electrode is TiO2 doped with 30n+ou of RuO2.
was coated on the surface of a Ti electrode base to a thickness of 10 μm.

Electrode preparation was performed as follows.

JISlf! as a base for electrodes! Select pure titanium and first pickle it in a 15% sulfuric acid aqueous solution at 80°C for 1 hour.
The substrate surface was activated.

A coating solution was prepared by dissolving predetermined amounts of titanium tetrachloride and ruthenium tetrachloride in a 10% aqueous hydrochloric acid solution, and was uniformly coated onto the substrate with a brush. After sufficiently drying at room temperature until there is no humidity, heat in an electric furnace in an air atmosphere at 450°C for 20
Thermal decomposition treatment was carried out under conditions of 1 minute. This coating, drying, and heat treatment operation was repeated 10 times to obtain a predetermined coating thickness. The composition of the coating layer made of the conductive metal oxide thus obtained was determined by X-ray analysis to be TiO
Confirm that the composition is 2,30mo℃ zero RuO2, and
The i/Ru atomic ratio was the same as the composition ratio of the coating solution. Moreover, the thickness of the coating layer was confirmed by a fracture cross-section inspection.

Figure 2 shows the shape of this electrode. Here, the thickness of the electrodes 1.1 is 1 am each, and the thickness of the intermediate chamber spacer 2 is 1.5 am.
mm, and the pore diameter of the channel 5 through which the target liquid flows, which is surrounded by the central portion of both, was 1 mm.

Several saline solutions with different concentrations were flowed through this cell at a flow rate of 40 m/7 min, and the electrical conductivity (reciprocal of the impedance of the entire cell) was measured using an impedance measuring circuit 4 equipped with a 1 k) lz AC power supply. The relationship between the electrical conductivity ratio of the IM thus obtained to the saline solution and the salt concentration is shown by curve A in FIG. This shows that there is a fairly good linear relationship between the two.

Example 2 After immersing the electrode part of the conductivity meter produced in Example 1 in IN hydrochloric acid for 24 hours, the same measurements as in Example 1 were performed, and the total impedance of the electrode cell was within ±1%. Reproduced with an error of

Comparative Example 1 An electrode cell was prepared in the same manner as in Example 1 except that the electrode material was 5LIS316, and the relationship between its electrical conductivity (reciprocal of the impedance of the entire cell) and salt concentration was determined. This result is shown by curve B in FIG. It can be seen that the curve is considerably larger and more convex than curve A.

Further, in the same manner as in Example 2, the impedance was measured by soaking the electrode portion in IN hydrochloric acid for 24 hours and then pouring saline solution, but it was completely unstable and measurement was impossible.

[Effects of the Invention] The present invention has made it possible to accurately measure the salt concentration in an aqueous solution of a biochemical substance or the like using a simple device. Therefore, it becomes possible to control the desalting process using a separation membrane or gel with high precision using a very inexpensive device.

[Brief explanation of the drawing]

FIG. 1 shows a schematic diagram of an electrode cell portion of an electrical conductivity meter according to an embodiment of the present invention, and FIG. (b) shows the shape of the electrode used for this. Figure 3 shows the results of measuring the electrical conductivity of saline water using the electrical conductivity meters of Example 1 and Comparative Example of the present invention.
The electrical conductivity ratio of M to saline is plotted against the salt concentration. 1... Electric 8i 2... Intermediate chamber spacer 3.
... Cell frame 4 ... Impedance measurement circuit 5 ... Channel salt concentration CM)

Claims (1)

[Claims] 1. The metal electrode has Pt, Ir, Os, Pt on its base surface.
d, contains at least one noble metal oxide of Ru and Rh, or together with Pt, Ir, Os, Pt.
An electrical conductivity meter for measuring electrolyte concentration in a solution, characterized by having a conductive metal oxide coating layer that may contain noble metals such as d, Ru, and Rh. 2 The conductive metal oxide coating layer containing the noble metal oxide is
Furthermore, Ti, Ta, Nb, Zr, Hf, Al, Si, Sn
2. The electrical conductivity meter according to claim 1, comprising at least one metal oxide selected from , Sb, and Bi. 3. The electrical conductivity meter according to claim 1, wherein the base of the metal electrode is made of Ti, Ta, Nb, Zr, or a base alloy thereof.