JPS5926895B2 - A device for measuring the partial pressure of a given gas component in a monitored gas environment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to an improved apparatus for measuring the partial pressure of a given gas component in a monitored gas environment.

BACKGROUND OF THE INVENTION AND PRIOR ART Although a number of techniques and devices have been developed for monitoring partial pressures of gaseous components using both solid and liquid electrolytes, the practical usefulness of some of these devices remains unclear. The practical usefulness of the current-operated type, particularly of the current-operated type, is often limited due to sensitivity to gas flow rate changes and temperature changes, and due to deterioration of the electrode structure.

A typical example of an electrochemical cell operating in a diffusion-limited current mode of operation is the ``Polarographic Method for Determination of Oxygen Partial Pressure (Meth
odForPolarographyCMasure
mentOfOxygenPartialPressu
No. 3,691,023, issued September 12, 1972.

In this US patent, an oxygen ion conducting solid electrolyte electrochemical cell monitors the oxygen partial pressure of a gas. The current measured is a function of the oxygen diffusing through the pores of the electrode, thus reducing the oxygen present at the electrode/electrolyte interface, creating an electrochemical cell that operates in a diffusion-limited, heavy-flow mode of operation. A voltage of sufficient magnitude is applied across the electrodes of the battery to cause depletion. There is a linear relationship between the partial pressure and diffusion current of the gas component of interest, which is selected here as oxygen, and
The diffusion current can therefore be expressed as a direct indication of the oxygen partial pressure of the sample gas. A device constructed in accordance with the teachings of this US patent is designed such that in the presence of two high partial pressure sample gases, there is a gap between the electrodes to deplete the oxygen at the electrode/heavyweight interface to achieve diffusion-limited current mode operation. It is generally limited to monitoring relatively low gas partial pressures because the applied potential becomes unduly large. Furthermore, the operation of this prior art device is sensitive to variations in gas flow rate, changes in electrode structure, which change the diffusion properties of the electrodes. U.S. Patent No. 3,787,
No. 308 proposed the use of orifice plates to limit exposure of the electrochemical cell to a monitored environment and extend the useful range of oxygen-measuring electrochemical cell devices. The oxygen measurement device includes a pair of batteries connected to a bridge circuit for operation in the null mode of an electrochemical cell to measure the oxygen content of the environment. This arrangement is disadvantageous because it requires a standard gas source, is complex in construction, and expensive to manufacture. SUMMARY OF THE INVENTION With reference now to the accompanying drawings, a technique is disclosed herein that improves the practical utility of electrochemical cells that measure currents limited by gas diffusion.

namely, an adapter comprising an internal chamber and a battery forming part of one wall of the internal chamber such that the internal electrodes of the battery are exposed to the environment of the internal chamber and the external electrodes are exposed to another environment. An assembly is disclosed that includes a gas diffusion hole separate from the electrochemical cell and dimensioned to diffuse gas from an environment external to the adapter into the interior chamber. A potential is applied between the electrodes of an electrochemical cell to supply (pump) the gas to be monitored from an internal chamber, thereby creating a pressure gradient of the gas to be monitored in and out of the pore, and the gas species diffusing through the pore. develops a current that is directly proportional to the amount of. The potential applied between the electrodes of the cell needs only to be large enough to maintain a gas partial pressure gradient between the inside and outside of the gas diffusion hole to ensure gas diffusion to the internal electrodes. It is. In the partial pressure measuring device of the present invention, if a predetermined gas component is supplied by an electrochemical cell as described above, the diffusion rate of the gas species through the gas diffusion hole indicates the partial pressure of the gas species in the environment to be monitored. It is based on the observation that something is a thing. According to the technology disclosed in this specification, the gas diffusion holes in the housing or adapter in combination with the electrochemical cell are arranged as described above in which the size of the electrodes and the structure of the holes determine the gas diffusion capability of the gas measuring device. Unlike technology, it is a factor that determines gas diffusion properties.

Furthermore, since the electrode structure is no longer the critical factor determining gas diffusion, the porosity or structure of the electrodes on the operational life of the electrochemical cell does not significantly affect the operation of the improved cell of this invention.

Moreover, the device of the invention does not require a standard gas environment in contact with one electrode of the cell; the last monitored gas flow rate change in the gas environment is such that the change in flow rate is not transmitted through the gas diffusion holes. Therefore, it does not significantly affect the operation of the improved battery device according to the present invention.

Accordingly, it is a principal object of the present invention to provide an improved apparatus for measuring the partial pressure of a given gas component in a monitored gas environment.

The invention relates to an electrochemical cell comprising a first electrode and a second electrode placed in intimate contact with an electrolyte having a composition capable of conducting a predetermined gaseous component; a gas diffusion device having an aperture that allows a predetermined gas component in the environment to diffuse to contact a first electrode; and a measuring device connected to the first electrode and the second electrode. In an apparatus for measuring the partial pressure of a predetermined gas component in a gaseous environment, the electrochemical cell has a predetermined pressure through the pores sufficient to promote diffusion of the gas component through the pores. The apparatus is characterized in that it operates as a pumping means for establishing a partial pressure difference of gas components.

Preferred Embodiments of the Invention The invention will become more readily apparent from the following description of the embodiments, taken in conjunction with the accompanying drawings.

The invention disclosed herein is directly applicable to any and all gas monitoring electrochemical cells, regardless of cell composition.

Although the embodiment selectively illustrated in FIG. 1 to describe the invention is an embodiment for a solid electrolyte electrochemical cell, the inventive technique disclosed herein can be applied to the gas components of interest, namely oxygen, sodium, It is clearly applicable to liquid and polymeric electrolytes used in devices for monitoring chlorine, hydrogen, etc. The present invention is not concerned with a charged chemical cell per se, but rather with the use of an adapter or housing having gas diffusion holes in which a differential pressure of a given gas component is established, and the use of an adapter or housing for establishing such a differential pressure. Concerning the use of batteries as a supply means. Referring to FIG. 1, the above-mentioned U.S. Pat. No. 3,691,0
23 is a schematic representation of a gas monitoring assembly 10 comprising an electrochemical cell 20 consisting of a solid electrolyte 24, an inner electrode 22 and an outer electrode 26 sealed within the walls of a gas diffusion adapter 30; This is explained by:

The gas diffusion adapter 30 allows gas diffusing through the gas diffusion holes 32 to enter the interior chamber 34 from the monitored gas environment G;
It includes a gas diffusion hole 32 sized to limit contact with the internal electrode 22 . The electrolyte material is selected based on the electrochemically active gas species to be monitored. If oxygen is the gas in question to be monitored, then the electrolyte is chosen from a substance that supports the movement of oxygen; if sodium is the gas species in question to be monitored, a sodium-conducting electrolyte is chosen, etc. It is. The structure of the internal electrode 22 is porous to facilitate selection of the gas species to be monitored.

Platinum is a conventional electrode composition. As mentioned above, the electrolyte composition is selected to support conduction of the gas species to be monitored. Specifically, the embodiment selected to illustrate the invention consists of an oxygen ion-conducting solid electrolyte that exhibits significant oxygen ion conductivity and minimal electronic conductivity and that is suitable for use in any of a number of solid electrolyte oxygen cells. It corresponds to two structures and compositions. As mentioned above, the choice of electrochemical cell material depends on the gas species in question to be monitored. For example, in sodium ion monitoring applications, the electrochemical cell 20 of FIG. 1 can be replaced by a cell containing an electrolyte exhibiting significant sodium ion conductivity, such as beta-alumina. Similarly, electrochemical Kameike compositions can be varied to include a number of polymeric, solid or liquid electrolytes suitable for monitoring the gas species to be monitored. In the embodiment of FIG. 1, external electrode 26 may be exposed to a monitored gas environment G or other environment including air.

It is clear that a stable standard gas environment in contact with the external electrode 26 is not required. Diffusion of gas from the monitored gas environment G into the interior chamber 34 through the gas diffusion holes 32 transfers oxygen, the gas species of interest to be monitored, present in the interior chamber 34 to the electrolyte 24. This is accomplished by establishing a pressure gradient through the gas diffusion holes 32 by applying a DC voltage from the power source 40 between the inner electrode 22 and the outer electrode 26 with a polarity directed to be transported through the gas to the outer electrode 26 .

This causes the diffusion of oxygen from the monitored gas environment G through the gas diffusion holes 32 into the interior chamber 34 . Internal electrode 22
The dimensions of the gas diffusion hole 32 are sufficient to ensure that the gas diffusion through the gas diffusion hole 32 is never equal to or greater than the gas diffusion capacity of the inner electrode 22 compared to the size of the gas diffusion hole 32. It has a large area. In other words, the gas diffusion limiting factor in the gas measurement assembly 10 is the size of the gas diffusion holes 32, not the size of the internal electrodes 22. In this arrangement, it is the diffusion of gas through the gas diffusion holes 32 that determines the movement of charge through the electrolyte 24 and the current resulting from the gas diffusion monitored by the current measurement circuit 42. It should be noted that the battery 20 does not function as a gas component measuring device, but rather as a device for performing charge transport operations. This is in contrast to the diffusion-limited mode described in the above-mentioned U.S. patent, where the gas transport capacity of the internal electrode 22 determines the transfer of charge through the electrolyte and thus the magnitude of the measured current. It is. The other major difference between prior art operation and the concept shown in FIGS. 1 and 4 is the strict regulation of the DC potential applied between the electrodes of an electrochemical cell.

As mentioned above, the potential applied to prior art devices necessary to establish diffusion-limited current mode operation is of sufficient magnitude to deplete the oxygen present at the electrode-electrolyte interface. and must be stable enough to maintain this state. Since the prior art device is exposed to an environment corresponding to the monitored gaseous environment G, Kameike's operation involves applying an applied potential that depletes the gas component of interest to be monitored from the sensitive electrode/Kameike interface. Depends on ability. The operation of such devices is such that conventional electrochemical cell construction establishes diffusion-limited current operation of cells directly exposed to gases containing relatively high partial pressures of the gaseous component to be monitored. Since they cannot withstand the magnitude of the required potential, they are limited to relatively low partial pressures. In the embodiment of FIG. 1, it is not the internal electrode 22, but rather the size of the gas diffusion holes 32 that establishes the diffusion-limited current mode of operation.

Therefore, the magnitude of the DC pressure developed by the power source 40 is intended to maintain a partial pressure gradient across the gas diffusion hole 32 to ensure diffusion of gas from the monitored gas environment G into the interior chamber 34. Selected for bamboo. The fact that the size of the gas diffusion holes 32 determines the diffusion-limiting properties of the gas monitoring assembly 10 makes it possible to select the design of the electrochemical cell 20 and to make the operation of the electrochemical cell 20 substantially independent of temperature changes. Freely select the voltage level. Referring to Figure 2, this figure shows measured battery current versus a given operating temperature.
Oxygen at applied voltage and gas diffusion hole diameter? Several sets of curves showing the relationship are shown.

In the figure, curve 1 is 1000'C, l volt (7), gas diffusion hole area 0.1m7i1 curve 2 is 1000'C, 1V
, 0.85md1 curve 3 is 1000℃, 1V, 2.26
m7i1 curve 4 is 1000℃, 1V, 2.26miIL
1 curve 5 is 700℃, 1V, 2,26mi1 curve 6 is 7
00℃, 1V, 2.26md1 curve 7 is 700℃, 1V
, 2.26m7i1 curve 8 is 1000℃, 0.6V, 2
．． Measured current value (milliampere) and oxygen at 26m7i, respectively? This is a diagram plotting the relationship between curve 5
, 6, 7, and 8 represent transition points in the mode of operation of the cell from the diffusion mode established by the gas diffusion holes 32 represented by the straight portions of their curves. On the other hand, in the portion of the curve after the inflection point, the current is limited by the diffusion characteristics of the tube pole disclosed in the above-mentioned US patent. The linear portions of curves 3 and 5, corresponding to the same gas mixture, applied voltage and gas diffusion holes, but with different ambient temperatures, coincide exactly, thus demonstrating the relative insensitivity of the gas monitoring assembly 10 to temperature changes. Please note that A typical curve of gas diffusion hole size versus cell sensitivity is shown in FIG. The selection of the hole sizes shown in FIG. 3 for the gas diffusion holes 32 ensures a wide range of gas partial pressure responses for the gas monitoring assembly 10, and the selection of the dimensions of the gas diffusion holes 32 is optimized as shown in FIG. This can be achieved by using curves of the type described. Since the external electrode 26 in the embodiment of FIG. 1 is exposed to the monitored gas environment G, clearly indicating that there is no need for a stable gas standard environment, the gas monitoring assembly at the flange F of FIG. In the embodiment of body 10, inner electrode 22 is exposed to gas from a monitored gas environment G diffusing through gas diffusion holes 32, while outer electrode 26 is exposed to gas from a monitored gas environment G flowing through pipe P. isolated from G.

Although most practical implementations of this invention will use a gas adapter with one gas diffusion hole, modifications may be made to install more than one gas diffusion hole if operational requirements dictate. It is clear that it can be used.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional explanatory diagram of an embodiment of the present invention, FIGS. 2 and 3 are graphs explaining the operation of the present invention representatively shown in FIG. 1, and FIG. FIG. 2 is a schematic explanatory diagram of another embodiment of the present invention shown in FIG. In the diagram: 10... Gas monitoring assembly, 20...
・Battery, 22...Internal electrode, 24...
Solid electrolyte, 26... External electrode, 30...
...Gas diffusion adapter, 32...Gas diffusion hole,
34...Inner chamber, 40...Power supply, 42
...Ammeter, G...Monitored gas environment, F...Flange, P...Pipe.

Claims (1)

Claims: 1. An electrochemical cell comprising a first electrode and a second electrode placed in intimate contact with an electrolyte having a composition capable of carrying a predetermined gaseous component, exposed to a monitored gaseous environment. a gas diffusion device having holes through which said predetermined gas component diffuses into contact with a first electrode; and a measuring device connected to said first electrode and said second electrode. In an apparatus for measuring the partial pressure of a gaseous component, the electrochemical cell establishes a partial pressure difference in the gaseous component across the aperture sufficient to promote diffusion of the gaseous component through the aperture. said measuring device is intended to measure the resulting current which is a measure of the rate of diffusion of said gaseous component as an indication of the partial pressure of said gaseous component in said monitored environment. An apparatus for measuring the partial pressure of a predetermined gas component in a monitored gas environment. 2. The size of the pores is sufficient compared to the size of the first electrode such that the diffusion of gas through the pores is not equal to or exceeds the gas diffusion capacity of the first electrode. 2. The device of claim 1, wherein the device is small. 3. The predetermined gas component is oxygen, and the electrochemical cell exhibits oxygen ion conductivity. An apparatus according to claim 1. 4. A gas diffusion device and an electrochemical cell are combined to form a gas generator enclosure with an internal chamber, the electrochemical cell being installed on one wall of said enclosure and supplying a predetermined gas component from the internal chamber. 2. The apparatus of claim 1, wherein a differential pressure of a predetermined gas component is established across the hole.