RU2228520C1 - Coulometric cell - Google Patents

Abstract

FIELD: analytical instrumentation, manufacture of hygrometers. SUBSTANCE: coulometric cell is made of two parts, working and testing, located in internal conduit of glass body, three platinum or rhodium wire helicoidal electrodes. One electrode is common and two others are positioned with working gap between turns of common electrode. Gap between electrodes in working part of cell is variable and lies within limits from 0.8 to 0.1 mm. Gap has maximal value at start of working part of cell and minimal value at its finish diminishing evenly or stepwise from maximum to minimum. EFFECT: prolonged service life of cell, raised upper limit of measurement of gas humidity. 2 dwg

Description

The present invention relates to the field of analytical instrumentation and can be used in coulometric hygrometers.

Known coulometric cell (AS No. 1357814, G 01 N 27/02), consisting of platinum helicoidal electrode wires located in the inner channel of the dielectric casing, a sorbent film covering the electrodes, and leads to the outer surface of the casing.

As the sorbent film, for example, a film of partially hydrated phosphoric anhydride P ₂ O _{5 is used} . To the electrodes, through the terminals on the outer surface of the housing, a DC voltage is applied.

The analyzed gas is passed through the internal channel of the housing from the working part. Two processes continuously occur in the cell: an almost complete absorption of moisture by a film of a hygroscopic substance with the formation of phosphoric acid and electrolysis of water into hydrogen and oxygen with the regeneration of phosphoric anhydride,

P ₂ O ₅ + H ₂ O → 2HPO ₃ ;

2HPO ₃ → H ₂ + 1 / 2O ₂ + P ₂ O ₅ .

At a constant gas flow rate according to the Faraday law, the magnitude of the electrolysis current is a measure of the moisture content of the gas, i.e. coulometric devices have a calculated scale provided that moisture is completely absorbed in the cell.

It is known that phosphoric anhydride is carried away by the analyzed gas over time. When moisture is absorbed, phosphoric anhydride is initially wetted and liquefied at the input site. During electrolysis, the formation of small bubbles filled with electrolysis products (oxygen and hydrogen) occurs. Bubbles burst with the formation of minute splashes of phosphoric anhydride, which are transferred by the analyzed gas to the next turns along the gas path. Previous turns of the electrodes of the working part of the cell are exposed from the sorbent film and cease to participate in electrolysis.

This front of active electrolysis moves from the beginning of the working part to the end and goes to the control part of the cell, in which the electrolysis current appears, which indicates a failure of the cell. Cell requires regeneration. And since the number of regenerations is limited due to corrosion of the electrodes and glass, the cell service life is also limited. In addition, the overload of the first turns of electrodes along the gas path limits the upper limit of moisture measurement.

The essence of the invention lies in the fact that the coulometric cell, consisting of two parts, working and control, located in the inner channel of the glass case, three wire platinum or rhodium helicoidal electrodes, one of the electrodes is common, and the other two electrodes are located between the turns of the common with a gap between the turns of the sorbent film covering the electrodes and the inner channel of the housing, and the conclusions, differs from the prototype in that in the proposed cell, the moisture absorbed by the sorbent more evenly distributed is divided along the length of the working part, due to which there are no large electrolysis overloads at the inlet section, and the upper limit of moisture measurement rises. This is achieved by the fact that the gap between the electrodes of the working part of the cell is variable and lies in the range from 0.8 to 0.1 mm. The gap has a maximum value at the beginning of the working part of the cell, a minimum value at the end of the working part, evenly or stepwise decreasing from maximum to minimum.

Figure 1 schematically shows a coulometric cell in which the gap between the electrodes of the working part is uniformly reduced from the maximum value a ₁ to the minimum a _n . Such a coulometric cell device is more preferable, because in it, moisture is more evenly distributed along the length of the working area. But it is technologically difficult to do.

Figure 2 schematically shows a coulometric cell in which the gap between the electrodes of the working part is stepwise reduced from the maximum value a ₁ to the minimum a ₂ . There can be two or more steps. Figure 2 shows two stages and each stage is approximately equal to half the working part. A stepped device is less preferred. But it is technologically more feasible.

Non-touching helicoidally wound platinum or rhodium electrodes 1, 2 and 3 are placed on the inner surface of the thick-walled glass tube 4 and partially recessed in it. The tube 4 is at the same time the cell body. The electrode 1 is common and is wound along a helicoidal line along the entire length of the cell. Between the turns of the common electrode along the helicoidal lines are the electrodes 2 and 3.

The section between the electrodes 1 and 2 makes up the working part of the cell, and the section between the electrodes 1 and 3 makes up the control part. A layer 5 of a hygroscopic substance is applied to the inside of the tube 4. The terminals 6, 7 and 8 of the electrodes 1, 2 and 3, respectively, are made of the same material as the electrodes, and are welded to the outer surface of the tube 4 in the form of spherical bodies.

As the gas flows in the direction of the arrow, moisture is absorbed by the film of absorbent material. Because the gap between the electrodes in the first turns of the working section is greater than in the subsequent ones, which means that the ohmic resistance is also greater with its subsequent decrease towards the end of the working section of the cell. Full electrolysis of moisture does not occur at the first turns of the electrode, as occurs in a known cell, but is distributed along the length of the working section.

With the correct selection of the gaps between the electrodes, it is possible to obtain a fairly uniform electrolysis of moisture along the length of the working section.

Due to this, the cell service life is increased and the upper limit for measuring moisture in gases increases.

With a stepwise distribution of the gap between the electrodes, it is also possible to reduce the electrolysis load on the electrodes and increase the limit of measuring moisture in gases by approximately as many times as the steps on the working section of the cell.

Claims (1)

Coulometric cell, consisting of two parts, working and control, located in the inner channel of the glass case, three platinum or rhodium wire helical electrodes, one of the electrodes is common, and the other two electrodes are located between the turns of the sorbent film covering the gap between the turns, electrodes and the inner channel of the housing, and conclusions, characterized in that the gap between the turns of the working part of the cell is variable and is 0.8-0.1 mm, while the maximum value for the gap has at the beginning of the working part of the cell, the minimum value is at the end, uniformly or stepwise decreasing from maximum to minimum.

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