JP2003075394A - Detector for oxidizing-gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stable detector for oxidizing-gas of a long life quick in a response speed. SOLUTION: This oxidizing-gas detector for detecting the oxidizing-gas has the working electrode inside a detection vessel provided with a gas-permeable diaphragm, contains an electrolyte in which a supporting electrolyte containing a halide is dissolved in a liquid containing at least one kind selected from the group comprising ethylene glycol and propylene glycol, and detects the oxidizing gas by detecting a current flowing between the working electrode and the counter electrode under the condition where a potential of the working electrode is held at a prescribed potential.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrochemical detector for detecting an oxidizing gas, and more particularly to an electrochemical detector suitable for detecting chlorine, bromine, fluorine and the like. Detector. [0002] Various detection means are used for detecting oxidizing gases represented by chlorine, bromine and fluorine.
Among them, the diaphragm type electrochemical detection means proposed by the present inventors has a relatively simple structure, but high measurement accuracy,
It is used as a means for detecting a leaked gas in a manufacturing process of a semiconductor device handling chlorine, fluorine and the like. The oxidizing gas diaphragm type electrochemical detection means measures the current flowing when the oxidizing gas permeated through the diaphragm is introduced into the electrochemical cell containing the aqueous solvent electrolyte and the halogen reacts with the hydrogen generated by polarization. Is used to measure the concentration of halogen. As a diaphragm type detector, Japanese Patent Publication No. 60-72 is known.
No. 23 discloses an electrode disposed close to a gas-permeable membrane, and mainly employs a deliquescent material composed of bromide, iodide, or a mixture of any of lithium, calcium, and magnesium as an electrolyte. An oxidizing gas measurement electrode containing a component solution is described. By using a solution of deliquescent material, it is possible to keep the liquid in equilibrium with the moisture in the air at all times, and it is possible to operate for a long time without evaporating the electrolyte to dryness. It is said to have. When the oxidizing gas detecting means is used in a method for detecting a gas to be diffused, such a detecting means can be used without any problem. However, when the detecting means is used as a suction type, it is difficult to obtain a sufficient result by such a detecting means. For example, an oxidizing gas detecting means is often used for monitoring chlorine, fluorine and the like in exhaust gas of a dry scrubber or the like for treating exhaust gas in a semiconductor manufacturing process. In this case, it is necessary to measure the concentration of the oxidizing gas in a large amount of dry nitrogen flowing in the duct. However, since the detection operation is performed in an environment in which a large amount of dry gas flows in the duct, moisture is lost from the electrolyte layer between the diaphragm and the working electrode, and the electrolyte layer and the diaphragm dry and operate as detection means. There was a problem that it would not be. An object of the present invention is to provide an oxidizing gas detecting means capable of measuring an oxidizing gas with high reliability even in a detecting operation in a duct through which a large amount of dry gas flows. It is an object of the present invention to solve the problem caused by the evaporation of the electrolyte and extend the life of the detection device. SUMMARY OF THE INVENTION An object of the present invention is to provide a detector for an oxidizing gas, which has a working electrode in a detection tank provided with a gas-permeable diaphragm and contains a supporting electrolyte containing a halide. Containing an electrolytic solution dissolved in a liquid containing at least one selected from ethylene glycol and propylene glycol, and detecting the current flowing between the working electrode and the counter electrode while maintaining the working electrode at a predetermined potential. This can be solved by an oxidizing gas detector that detects an oxidizing gas. In the detection tank, the above-mentioned oxidizing gas detector having a working electrode and a counter electrode as well as a reference electrode is provided. The above-mentioned oxidizing gas detector is provided with a pressure adjusting film that allows gas to permeate in a gas phase part in a detection tank. The oxidizing gas detector wherein the potential of the working electrode is set to 0 to 0.5 V with respect to the potential of the counter electrode. The above oxidizing gas detector wherein the oxidizing gas is at least one selected from the group consisting of chlorine, fluorine and bromine. DETAILED DESCRIPTION OF THE INVENTION The present invention uses an electrolyte having a specific composition containing an electrolyte and a means for measuring potential and current as a detector for an oxidizing gas, so that a large amount of dry gas can be ventilated. It has been found that it is possible to provide a detector of an oxidizing gas which can be measured stably even in a restricted environment. That is, the oxidizing gas detector according to the present invention comprises, as an electrolytic solution, ethylene glycol and propylene glycol containing potassium iodide and potassium bromide in a detecting tank having a gas-permeable diaphragm. A non-aqueous solvent electrolyte is used, and the measurement can be performed without being affected by the humidity of the measurement environment. In particular, in the oxidizing gas detector of the present invention, it has been found that stable operation is possible because water is not mixed in the electrolytic solution. The present invention will be described below with reference to the drawings.
FIG. 1 is a diagram illustrating an oxidizing gas detector of the present invention. The oxidizing gas detector 1 of the present invention has a gas permeable membrane 3 that allows the oxidizing gas to pass through one end of a detecting tank 2, and an electrolytic solution 4 in the detecting tank 2. The gas permeable membrane 3 is attached to the detection tank 2 by an attachment member 5. As the gas-permeable film 3, a porous film made of a fluororesin that shows stable characteristics for an oxidizing gas for a long time can be used. Specifically, the average pore diameter is 0.1 μm or more.
It has a pore diameter of 5.0 μm and a film thickness of 0.05 mm to 0.1 mm.
A 3 mm polytetrafluoroethylene porous membrane is used. In addition, the working electrode 6 is arranged close to the gas permeable membrane 3, and a liquid film of an electrolytic solution is formed between the gas permeable membrane 3 and the working electrode 6. As the working electrode 6, an electrode having stable characteristics even when polarized in an electrolytic solution such as a gold or platinum electrode can be used. Further, in order to increase the contact area between the working electrode and the electrolytic solution, the working electrode may be formed with irregularities on the surface. As the working electrode, in addition to those using electrodes from the above-mentioned noble metal plate and the like, a gas permeable film in which the surface of the gas permeable film is coated with gold, platinum, etc. by a method such as vapor deposition and the working electrode are integrally formed. You may use something. A counter electrode 7 is provided in the electrolytic solution. As the counter electrode 7, any one can be used as long as it can stably exhibit a function as an electrode in an electrolytic solution. Specifically, metals such as platinum and silver can be mentioned. In particular, silver produces silver bromide and silver chloride on the surface by bromide ions and chloride ions in the electrolytic solution, and provides stable silver and silver bromide. Since it functions as an electrode and a silver / silver chloride electrode, it shows a stable potential as a counter electrode of a reaction contributed by halide ions, and thus is preferable. When a silver wire or the like is used as a silver electrode used as a counter electrode, silver halide precipitates on the surface during the aging of the oxidizing gas detector and acts as a silver / silver halide electrode. Silver may be used as an anode in an electrolytic solution in which halide ions are present to deposit silver halide on the surface.
The silver / silver halide electrode used as a counter electrode preferably has a large surface area so as not to be affected by a change in potential due to a current flowing at the time of detection. , A spiral shape or the like is preferable. The working electrode 6 is connected to one input terminal of the amplifier 9. Also, the other input terminal is connected to a stable variable voltage power supply 10 in which one electrode is connected to the counter electrode 7, thereby connecting the detection tank to the detector mounting means 11 through which the detection gas is passed. 7 is maintained at a predetermined value, and gas is detected.
Is measured as Further, a pressure adjusting film 15 is attached to a gas phase portion of the detection tank 2. As the pressure adjusting film 15, it is preferable to use a gas permeable film having higher gas permeability than the oxidizing gas permeable film 3. By providing the pressure adjusting film 15 in the gas phase, it becomes effective for pressure equilibrium. That is, when the gas phase portion of the detection tank communicates with the atmosphere, the distance between the oxidizing gas permeable film 3 and the working electrode 6 is kept constant by vaporization of the gas through the oxidizing gas permeable film and the sensitivity is deteriorated. Does not happen. The detector is connected to the detector mounting means 11 through which the detection gas is passed, and the detection of the gas is performed. Further, in the electrolytic solution 4, potassium bromide (KBr),
Ethylene glycol and propylene glycol are contained as a non-aqueous solvent together with a supporting electrolyte such as potassium chloride (KCl). By setting the potential of the working electrode to 0 to 0.5 V with respect to the potential of the counter electrode, measurement in a wide concentration range becomes possible. Further, since the electrolyte of the present invention comprises ethylene glycol and propylene glycol, even if a gas permeable membrane having a large pore diameter is used, the evaporation of the electrolyte can be suppressed. Therefore, the problem of drying the liquid film of the electrolytic solution near the working electrode is eliminated, and the working electrode potential can be kept constant. Furthermore, although ethylene glycol or propylene glycol is used as a non-aqueous solvent, the electrolytic solution of the present invention containing these, which contains a supporting electrolyte, has a sufficient electrochemical solution even when it does not contain water. You can get the output. Ethylene glycol is toxic to the human body, so care must be taken in handling it. However, propylene glycol is a substance that is highly safe for the human body, and it is preferable because it has a higher current when detecting an oxidizing gas than ethylene glycol. FIG. 2 is a diagram for explaining another embodiment of the present invention. The oxidizing gas detector 1 has a gas permeable membrane 3 for transmitting an acidic gas at one end of a detection tank 2, and an electrolyte 4 in the detection tank 2. Further, the gas permeable membrane 3 is attached to the detection tank 2 by an attachment member 5. Further, the working electrode 6 is arranged close to the gas permeable membrane 3, and a liquid film of an electrolytic solution is formed between the gas permeable membrane 3 and the working electrode 6. As the working electrode, an electrode formed of a noble metal plate or the like, or a gas permeable film obtained by coating a surface of a gas permeable film with gold, platinum, or the like by vapor deposition or the like and a working electrode integrally formed can be used. The electrolyte 4 includes a counter electrode 7 and a reference electrode 8.
Is arranged. The reference electrode 8 is connected to one input terminal of the high-input impedance amplifier 12, and the counter electrode 7 is connected to the output side thereof. The potential of the working electrode 6 is maintained at a constant potential with respect to the reference electrode 8. . Also, by connecting the stable variable voltage power supply 10 to one input terminal of the high input impedance amplifier 12, the potential of the counter electrode 7 can be set to a predetermined value. The working electrode 7 is connected to a current amplifier 13, and a current obtained by detecting an oxidizing gas in the detection tank is taken out as a detection output 14. Further, a pressure adjusting film 15 is attached to a gas phase portion of the detection tank 2. As the pressure adjusting film 15, it is preferable to use a gas permeable film having higher gas permeability than the oxidizing gas permeable film 3. By providing the pressure adjusting film 15 in the gas phase, it becomes effective for pressure equilibrium. That is, when the gas phase portion of the detection tank communicates with the atmosphere, the distance between the oxidizing gas permeable film 3 and the working electrode 6 is kept constant by vaporization of the gas through the oxidizing gas permeable film and the sensitivity is deteriorated. Does not happen. Then, the detector is coupled to the detector mounting means 11 through which the detection gas is passed, and the detection of the gas is performed. Since the oxidizing gas detector shown in FIG. 2 is provided with the reference electrode together with the working electrode and the counter electrode, the potential of the working electrode can be stably maintained, and when only the working electrode and the counter electrode are used. As a result, stable measurement can be performed in a wider potential range. The present invention will be described below with reference to examples. Example 1 A pore having a diameter of 0.1 μm and a thickness of 60 μm was formed in an opening having a diameter of 12 mm.
m with a porous membrane made of polytetrafluoroethylene (Fluorophore manufactured by Sumitomo Electric), equipped with gold and platinum electrodes as working electrodes, and an oxidizing gas detector with silver / silver chloride electrodes as counter electrodes. An electrolyte obtained by dissolving 18 g of potassium bromide and 5 g of potassium chloride in 1000 ml of ethylene glycol was injected to prepare an oxidizing gas detector. The voltage and current between the working electrode and the counter electrode in air having chlorine concentrations of 3 ppm and 1.2 ppm were measured by the obtained oxidizing gas detector. At the same time, the voltage and current in the case of only air were measured. The results are shown in FIG. Although it does not show a constant current value in a wide potential range, it can be sufficiently used for detection. Example 2 A pore having a diameter of 0.1 μm and a thickness of 60 mm was formed in an opening having a diameter of 12 mm.
Oxidation with a gold electrode coated on one surface of a porous membrane made of polytetrafluoroethylene (Fluoropore manufactured by Sumitomo Electric) with a working electrode, a silver electrode as a counter electrode, and a reference electrode consisting of silver and silver chloride electrodes Potassium bromide 1 in gas detector
8 g, potassium chloride 5 g, ethylene glycol 100
An electrolyte solution obtained by dissolving the solution in 0 ml was injected to prepare an oxidizing gas detector. The current flowing between the working electrode and the voltage between the working electrode and the counter electrode in air having chlorine concentrations of 3 ppm and 1.2 ppm was measured by the obtained oxidizing gas detector. At the same time, the voltage and current in the case of only air were measured. The results are shown in FIG.
A constant current value is shown over a wide potential range, and stable measurement is possible. COMPARATIVE EXAMPLE 1 1 g of potassium iodide and a buffer 8 of pH 5 were used as electrolytes.
A oxidizing gas detector was prepared in the same manner as in Example 1 except that 500 ml of water and 500 ml of ethylene glycol were used, and the voltage and detection current of chlorine-containing air were measured in the same manner as in Example 1. , And the results are shown in FIG. Example 2 An electrolytic solution was prepared in which the mixing ratio of ethylene glycol and water was changed, and the detection current for air having a chlorine content of 3 ppm was measured. FIG. 6 shows the capacity ratio on the horizontal axis and the vertical axis on the vertical axis. The current indicated. Next, an electrolytic solution was prepared in which the mixing ratio of propylene glycol and water was changed, and the detection current for air having a chlorine content of 3 ppm was measured. FIG. 6 shows the capacity ratio on the horizontal axis and the vertical axis shows the detection current. . When only ethylene glycol or propylene glycol is used as the solvent, the same output can be obtained as when water is used as the solvent. In addition, as shown in the above Examples and Comparative Examples, a stable measurement with a large potential window is possible as compared with the case of using the electrolyte mixed with water. The oxidizing gas detector of the present invention uses a working electrode, a counter electrode, or a reference electrode, and a halogenated compound in a non-aqueous solvent comprising ethylene glycol or propylene glycol as an electrolyte. Since it contains potassium, it suppresses evaporation of the electrolyte solution, eliminates the problem of drying of the acidic gas permeable membrane near the working electrode, and detects oxidizing gas over a wide potential range quickly and accurately. It is possible to do.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram illustrating an oxidizing gas detector of the present invention. FIG. 2 is a diagram illustrating another embodiment of the present invention. FIG. 3 is a diagram illustrating a change in current with respect to a change in potential of a working electrode. FIG. 4 is a diagram illustrating a change in current with respect to a change in potential of a working electrode. FIG. 5 is a diagram showing a change in current with respect to a change in potential of a working electrode. FIG. 6 is a diagram illustrating the relationship between the mixing ratio of ethylene glycol and propylene glycol with water and the output current. [Explanation of Symbols] 1 ... Acid gas detector, 2 ... Detection tank, 3 ... Acid gas permeable membrane, 4 ... Electrolyte, 5 ... Mounting member, 6 ... Working electrode, 7 ...
Counter electrode, 8: reference electrode, 9: high input impedance amplifier, 10: variable voltage power supply, 11: detector mounting means, 12
... High input impedance amplifier, 13 ... Current amplifier, 1
4 ... Detection output, 15 ... Pressure adjustment film

Claims (1)

Claims: 1. An oxidizing gas detector, comprising a working electrode in a detection tank provided with a gas-permeable diaphragm, wherein a supporting electrolyte containing a halide is formed from ethylene glycol or propylene glycol. An oxidizing gas is detected by detecting a current flowing between the working electrode and the counter electrode while maintaining the potential of the working electrode at a predetermined potential, containing an electrolytic solution dissolved in a liquid containing at least one selected. An oxidizing gas detector, characterized in that: