RU2165615C1 - METAL-OXIDE pH-ELECTRODE - Google Patents

Abstract

FIELD: measurement of pH-solutions. SUBSTANCE: sensitive element in metal-oxide pH-electrode is ion-sensitive outer surface of case manufactured of metal in the form of sleeve with metal rod- electric conductor placed in its internal space, in center along axial line, electrically connected to bottom base of sleeve with use of another metal or ion-conductive solution and insulated from its side internal surface. EFFECT: independence of potential of pH- electrode from agitation of liquid, stability in time, resistance to strong oxidizing agents, mechanical strength. 2 cl, 4 dwg

Description

1. The technical field
The invention relates to techniques for electrochemical analyzes, namely: electrodes for measuring the pH of solutions, and can be used in various fields of chemical technology.

2. The level of technology
Known electrodes: pH electrode / patent 1582106 / and a glass pH electrode / B. M. Kanter, A. V. Kuzakov, M. V. Kulakov, Potentiometric and titrometric instruments, ed. "Engineering", Moscow, 1970, p. 38 /.

 In the first case, the sensing element placed in the insulating tube is placed in a metal case.

 In the second case, the sensitive element / semi-element / is placed in an ion-conducting solution, placed in the inner container of the glass electrode.

 In this case, the selection of a useful signal, in the first case, millivolts is made from the outer surface of the sensitive element, and in the second case, millivolts from the inner surface of the glass sensitive element / membrane /.

As noted in the literature, these pH electrodes, having a fairly high degree of stability of the potential, can not always work in extremely difficult production conditions:
- the presence of sediments and suspensions with significant adhesive ability;
- the effect of instability of movement and mixing of the liquid;
- insufficiently strong design: over time, under the action of strong oxidizing agents, corrosion of the binding components of various parts of the pH electrode takes place;
- damage to the outer surface of the sensing element / half element / under the influence of fluorine ion.

 As a result, the reliability of the operation of pH electrodes decreases, from the point of view of the time factor of their continuous operation in solutions without forcibly restoring the functional dependence on measuring the pH of the medium / it requires either cleaning the outer surface of the sensitive element or replacing it with a new one /, which reduces the resource operation of the pH electrode.

 Closest to the claimed invention is a message placed in a literary source / Bates R., Determination of pH. Theory and Practice, ed. "Chemistry", Leningrad Branch, 1972, pp. 288-289 / about what you can do without an internal solution. Electrical contact with the inner surface of the glass membrane is carried out by filling the bulb with mercury or coating the inner surface with a thin layer of silver. Patents are published offering the use of metal and alloys for this purpose / P.A. Kryukov, A.A. Kryukov, ed. testimonial. 51509, June 31, 1937; H. Bender, O.J. Pyc, U.S. Patent 2117596, (May 17, 1938).

 Moreover, it is also noted that in one embodiment of the device for the glass electrode, its outer surface is covered with metal and the salt bridge is placed inside the pH electrode. Metal, thus, provides the necessary electrical contact with the glass and at the same time serves as electrical protection.

 However, as noted there, metal-coated electrodes are not as satisfactory as with the internal auxiliary semi-element, so they did not find wide application.

These features of the prototype are common with the claimed invention:
- the implementation of electrical contact with the inner surface of the glass membrane due to the bulb of mercury;
- coating the outer surface of the glass electrode with metal or alloy.

In this case, the aim of the invention is to obtain the required technical solution:
- independence of the potential of the pH electrode from mixing the liquid;
- stability of the potential of the pH electrode over time;
- independence of the potential of the pH electrode from the adhesive ability of impurities and suspensions in solution;
- resistance to strong oxidizing agents, including fluorine ion;
- mechanical strength:
- the possibility of the pH electrode in environments under high pressure;
- stability of the steepness of the pH electrode from the temperature drop of the liquid;
- the absence of a salt bridge in the internal cavity of the pH electrode;
allows you to significantly expand the arsenal of technical means of applying the invention for measuring pH in solutions of technological processes of chemical industries.

3. The invention
The invention is aimed at solving the problem of expanding the arsenal of technical means of using pH electrodes for measuring pH in solutions with potentiometric measurements.

 The technical result, the solution of this problem, lies in the implementation of this purpose.

 This technical result is achieved by the fact that the sensitive element is the ion-sensitive outer surface of the housing made of metal in the form of a glass, placed in its inner cavity in the center along an axial line, electrically connected to the bottom base of the glass using another metal or ion-conducting solution, a metal rod - electrical conductor.

 It serves as another metal, for a strong electrical connection with the surface of the inner cavity of the glass and a metal rod - an electric conductor, another contact metal made of a "soft" metal material: solder-mixture of lead and tin. This contact is carried out by heating in the internal cavity of the body made of metal in the form of a glass, a small amount of solder to form its liquid / molten / state and, after placing a metal rod in the molten solder - an electrical conductor, allow it to cool to its original physical state. In this case, reliable electrical contact of the type of adhesion between metal products is ensured.

 Another contact material can be an ion-conducting solution, the electrical conductivity of which should be preserved over time from the influence of its heating unchanged for a long time.

As practice shows, based on literature data / cm. A.G. Kuhlman, General Chemistry, M., 1961, p. 193, Fig. XII-2 /, the most applicable for this case is an ion-conducting solution prepared on the basis of the use of sodium chloride / NaCl / - sodium chloride, for which the solubility, which affects the degree of conductivity of the ion current from a change in the temperature of the solution up to 100 ^o C, is negligible. This property of sodium chloride is also useful in that it decreases from the influence of temperature the corrosion process of metal destruction of both the body made of metal in the form of a glass and the metal rod - an electrical conductor.

 Figure 1 shows the proposed metal oxide pH electrode.

The metal oxide pH electrode contains:
1 - metal rod - electrical conductor;
2 - insulating gasket;
3 - an insulating sealant;
4 - a metal cup - a sensitive element;
5 - insulating gasket;
6 - metal type "solder": a mixture of lead and tin or an ion-conducting solution.

 The operation of the metal oxide pH electrode is based on electrostatic induction, when it is placed in the test solution arising on its outer ion-sensitive surface of the body due to the redox reaction, the electric potential on the surface of the inner cavity of the bottom base of the glass 4. In this case, the measurement of this induced electric potential is carried out using a metal rod - an electrical conductor isolated from its lateral inner surface of the insulator onnymi pads 2, 3 and 5 are electrically connected to the base bottom cup 4 or other metal 6 6 ionically conductive solution.

WORK OF METAL OXIDE pH ELECTRODE
Metal oxide pH electrode works as follows. When a metal oxide pH electrode is placed in the test solution, an electric potential arises on its outer ion-sensitive surface of the housing due to the redox reaction, the charge of which is fully induced on the surface of the inner cavity of the bottom base of the glass of reverse polarity / cm. lit. K. Krug, Fundamentals of Electrical Engineering, ed. 4th, M., 1935, pp. 92-93 /. This effect is quite visible when disconnecting a metal rod - an electrical conductor - from the surface of the internal cavity of the bottom base.

 Moreover, if a metal rod is attached to the surface of the inner cavity of the bottom base, a positive effect arises: the metal rod becomes a conductor of electric charges of the electrode potential of the outer ion-sensitive surface of the metal oxide pH electrode of the same polarity, which occurred due to the disappearance / disappearance / electric field inside its body.

 The same thing happens with the direct use of an ion-conducting solution, just like a metal rod - part of it, as a contact material. In this case, the ion-conducting solution provides not only a reliable electrical contact, but also acts as an additional resistor in the measurement circuit.

Figure 2 shows a graph of the functional dependence of the EMF of the metal oxide pH electrode on the pH of the solution according to laboratory measurements:
pH of the solution 9.5, 0.75
E, mV-EMF of metal oxide pH electrode -240, +230
θ $\genfrac{}{}{0ex}{}{\text{0}}{\text{C}}$ - solution temperature 23.6, 23.6
In FIG. Figures 3 and 4 show daily diagrams of the operation of glass and metal oxide pH electrodes, respectively, under production conditions of the sulfuric acid production process.

 From these diagrams it can be seen that the invention has a high degree of operational efficiency with practical accuracy in measuring the pH of the solution-acid obtained in the acid shop of the Krasnokamsk pulp and paper mill in the Perm region.

Claims (3)

 1. A metal oxide pH electrode comprising a housing, a metal rod - an electrical conductor, insulating gaskets, an insulating sealant and contact material, characterized in that the sensitive element is the ion-sensitive outer surface of the housing, made of metal in the form of a glass, placed in its inner cavity in the center along the center line, electrically connected to the bottom base of the glass using another metal or ion-conducting solution, isolated from its lateral inner surface metal rod - an electrical conductor.  2. The metal oxide pH electrode according to claim 1, characterized in that the contact material is a soft metal - solder is a mixture of lead and tin.  3. The metal oxide pH electrode according to claim 1, characterized in that the contact material is an ion-conducting solution.

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