JP2007240437A

JP2007240437A - Gas sensor

Info

Publication number: JP2007240437A
Application number: JP2006066138A
Authority: JP
Inventors: Hitoshi Nakamura; 仁中村
Original assignee: Komyo Rikagaku Kogyo KK
Current assignee: Komyo Rikagaku Kogyo KK
Priority date: 2006-03-10
Filing date: 2006-03-10
Publication date: 2007-09-20
Anticipated expiration: 2026-03-10
Also published as: JP4205725B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas sensor which is high in reliability of the measurement results and little affected by the density change of electrolyte or the vibration. <P>SOLUTION: The gas sensor 1 comprises the opposite pole 5, the comparison pole 6, and the operation pole 7, and at least between the comparison electrode 6 and the electrolyte, the anion-exchange membrane 15 is arranged. In the electrolyte, OH<SP>-</SP>passes through the anion-exchange membrane and arrives at the comparison electrode 6. The comparison electrode 6 is not directly contact with the electrolyte, and hardly affected even the density of the electrolyte is changed or the electrolyte flows. Consequently, this gas sensor 1 is reliable because it does't largely fluctuates even in the case elapsed long days after production or exposed under the vibration. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

本発明は各種ガスを検知するためのガスセンサに関するものである。 The present invention relates to a gas sensor for detecting various gases.

定電位電解式ガスセンサは、作用電極、対極、比較電極の３電極と電解液および容器とを有している。
作用電極、対極、比較電極の３電極はガス透過性の多孔質膜の内側に結合されており、いずれも電解液に接している。 The constant potential electrolytic gas sensor has three electrodes, a working electrode, a counter electrode, and a reference electrode, an electrolytic solution, and a container.
The three electrodes, the working electrode, the counter electrode, and the reference electrode, are bonded to the inside of the gas permeable porous membrane, and all are in contact with the electrolytic solution.

作用電極はガス透過性の多孔質膜に密着しており、試料ガスは多孔質膜を透過して作用電極に達して作用電極表面で酸化あるいは還元される。
この際に対極との間にガス濃度に応じた電流が流れ、ガス濃度測定が行われることになるが、あらかじめ基準となる比較電極に対して作用電極の電位を一定に保つことにより、特定のガスを選択的に、かつ安定に測定できるという特徴を持つ。 The working electrode is in close contact with the gas permeable porous membrane, and the sample gas passes through the porous membrane to reach the working electrode and is oxidized or reduced on the surface of the working electrode.
At this time, a current corresponding to the gas concentration flows between the counter electrode and the gas concentration measurement is performed. By keeping the potential of the working electrode constant with respect to the reference electrode serving as a reference in advance, a specific voltage is measured. It has the feature that gas can be measured selectively and stably.

定電位電解式ガスセンサは小型・軽量で、常温で作動し消費電力が小さいこと、および感度が高くｐｐｍレベルの識別が可能なため、各種毒性ガス（例えば一酸化炭素（ＣＯ）、硫化水素（Ｈ₂Ｓ）、アンモニア（ＮＨ₃）等）を対象とした許容濃度管理用の携帯用検知器、測定器用センサとして広く使用されている。
特開２００１−２０８７２３号公報 The potentiostatic gas sensor is small and light, operates at room temperature, consumes little power, and has high sensitivity and can be distinguished at the ppm level, so various toxic gases (for example, carbon monoxide (CO), hydrogen sulfide (H ₂ S), ammonia (NH ₃ ), etc.) are widely used as portable detectors and sensor devices for allowable concentration management.
JP 2001-208723 A

定電位電解式ガスセンサの電解液としては、一般的に硫酸水溶液（対象ガスがＣＯ、Ｈ₂Ｓ等の場合）あるいは塩化カルシウム（ＣａＣｌ₂）や塩化リチウム（ＬｉＣｌ）等の中性塩水溶液（対象ガスがＮＨ₃の場合）が使用されており、これらの水溶液は吸湿性を有するため、測定使用雰囲気中の湿度との平衡関係より液量・濃度が変化する。
電解液の液量・濃度が変化すると、センサのゼロ出力が変化し、また、センサに振動が加わって内部で電解液が流動すると、センサ出力が過渡的に大きく変動するという問題があった。 The electrolyte of a potentiostatic gas sensor is generally a sulfuric acid aqueous solution (when the target gas is CO, H ₂ S, etc.) or a neutral salt aqueous solution such as calcium chloride (CaCl ₂ ) or lithium chloride (LiCl) (target) When the gas is NH ₃ ), and these aqueous solutions are hygroscopic, the liquid amount and concentration change depending on the equilibrium relationship with the humidity in the measurement use atmosphere.
When the amount / concentration of the electrolytic solution changes, the zero output of the sensor changes, and when the vibration is applied to the sensor and the electrolytic solution flows inside, there is a problem that the sensor output varies greatly in a transient manner.

上記課題を解決するため、本発明は、筒状の容器本体と、前記容器本体の一端にそれぞれ配置された対極と比較電極と、前記容器本体の他端に配置された作用電極と、前記容器本体の内部に収容された電解液とを有し、前記対極と前記比較電極と前記作用電極とは、前記電解液中のイオンにより電気的に接続されたガスセンサであって、表面が前記比較電極と接触し、裏面が前記電解液と接触するイオン交換膜を有するガスセンサである。
本発明はガスセンサであって、前記イオン交換膜は、表面が前記対極と前記比較電極の両方に接触するガスセンサである。
本発明はガスセンサであって、容器本体内に含浸体が配置され、前記電解液は前記含浸体に含浸され、前記イオン交換膜は前記含浸体に含浸された前記電解液に接触するガスセンサである。
本発明はガスセンサであって、前記イオン交換膜は陰イオン交換膜であり、前記電解液は中性塩の水溶液であるガスセンサである。
本発明はガスセンサであって、前記中性塩は、塩化カルシウムと塩化リチウムのいずれか一方又は両方を含有するガスセンサである。
本発明はガスセンサであって、前記含浸体はＳｉＯ₂繊維で構成されたガスセンサである。 In order to solve the above-described problems, the present invention provides a cylindrical container body, a counter electrode and a reference electrode respectively disposed at one end of the container body, a working electrode disposed at the other end of the container body, and the container The counter electrode, the comparison electrode, and the working electrode are electrically connected by ions in the electrolyte solution, the surface of which is the comparison electrode And a gas sensor having an ion exchange membrane whose back surface is in contact with the electrolytic solution.
The present invention is a gas sensor, wherein the ion exchange membrane is a gas sensor whose surface is in contact with both the counter electrode and the comparison electrode.
The present invention is a gas sensor, wherein an impregnated body is disposed in a container body, the electrolytic solution is impregnated in the impregnated body, and the ion exchange membrane is in contact with the electrolytic solution impregnated in the impregnated body. .
The present invention is a gas sensor, wherein the ion exchange membrane is an anion exchange membrane, and the electrolyte is an aqueous solution of a neutral salt.
This invention is a gas sensor, Comprising: The said neutral salt is a gas sensor containing either one or both of calcium chloride and lithium chloride.
The present invention provides a gas sensor, the absorbing member is a gas sensor composed of SiO ₂ fibers.

本発明のガスセンサは電解液の濃度変化や、振動による影響が小さく、測定結果の信頼性が高い。 The gas sensor of the present invention is less affected by changes in the concentration of the electrolyte and vibrations, and the measurement results are highly reliable.

図１は、ガスセンサ１の内部構造を説明するための断面図である。
このガスセンサ１は全体形状が円柱状であり、円筒形状の容器本体３を有している。容器本体３の両端には、第一、第二の多孔質膜９ａ、９ｂがそれぞれ配置されており、第一、第二の蓋部１０ａ、１０ｂによって、パッキン４ａ、４ｂ、８ａ、８ｄを介して、容器本体３にそれぞれ固定されている。 FIG. 1 is a cross-sectional view for explaining the internal structure of the gas sensor 1.
The gas sensor 1 has a cylindrical shape as a whole and has a cylindrical container body 3. First and second porous membranes 9a and 9b are respectively arranged at both ends of the container body 3, and the first and second lid portions 10a and 10b respectively pass the packings 4a, 4b, 8a and 8d. Are respectively fixed to the container body 3.

第一、第二の多孔質膜９ａ、９ｂの片面は、容器本体３の内部にそれぞれ向けられており、第一の多孔質膜９ａの容器本体３内部側表面には、比較電極６と対極５が配置され、その間には隙間が形成されている。第二の多孔質膜９ｂの容器本体３内部側の面には、作用電極７が配置されている。 One side of each of the first and second porous membranes 9a and 9b is directed to the inside of the container main body 3, and the reference electrode 6 and the counter electrode are provided on the inside surface of the container main body 3 of the first porous membrane 9a. 5 are arranged, and a gap is formed between them. A working electrode 7 is disposed on the inner surface of the second porous membrane 9b on the container body 3 side.

第一の多孔質膜９ａ上には比較電極６の表面と対極５の表面を覆うようにフィルム状の陰イオン交換膜１５が取り付けられており、対極５と比較電極６との間の隙間は陰イオン交換膜１５と第一の多孔質膜９ａとで挟まれている。 A film-like anion exchange membrane 15 is attached on the first porous membrane 9a so as to cover the surface of the comparison electrode 6 and the surface of the counter electrode 5, and the gap between the counter electrode 5 and the comparison electrode 6 is It is sandwiched between the anion exchange membrane 15 and the first porous membrane 9a.

容器本体３の内部には、作用電極７の表面と、陰イオン交換膜１５の比較電極６上の部分の表面と対極５上の部分の表面とに接触した含浸体１６が配置されている。 An impregnated body 16 that contacts the surface of the working electrode 7, the surface of the portion of the anion exchange membrane 15 on the comparison electrode 6, and the surface of the portion of the counter electrode 5 is disposed inside the container body 3.

含浸体１６には電解液が含浸されている。陰イオン交換膜１５は陰イオンが通過可能なので、含浸体１６中の陰イオンにより、比較電極６と対極５と作用電極７は電気的に接続されている。 The impregnated body 16 is impregnated with an electrolytic solution. Since the anion exchange membrane 15 allows anion to pass therethrough, the reference electrode 6, the counter electrode 5, and the working electrode 7 are electrically connected by the anion in the impregnated body 16.

第一の蓋部１０ａには、空気孔１９が形成されている。空気孔１９の一端は大気に開放されており、他端は第一の多孔質膜９ａと接触し、第一の多孔質膜９ａ表面が空気孔１９内部に露出するようにされ、空気孔１９を通過した空気は第一の多孔質膜９ａ、更には対極５及び比較電極６を通過して、対極５及び比較電極６と、陰イオン交換膜１５の界面に到達する。 An air hole 19 is formed in the first lid portion 10a. One end of the air hole 19 is open to the atmosphere, and the other end is in contact with the first porous film 9a so that the surface of the first porous film 9a is exposed inside the air hole 19. The air that has passed through the first porous membrane 9 a passes through the counter electrode 5 and the comparison electrode 6, and reaches the interface between the counter electrode 5 and the comparison electrode 6 and the anion exchange membrane 15.

上述したように、陰イオンは陰イオン交換膜１５を通過可能だから、陰イオンは対極５及び比較電極６と、陰イオン交換膜１５との界面に到達する。
第二の蓋部１０ｂと第二の多孔質膜９ｂの間には通気室１３が形成されている。第二の蓋部１０ｂには、複数個のガス導入孔１８が形成されている。ガス導入孔１８の一端は、外部雰囲気に曝されており、他端は通気室１３に接続され、外部雰囲気に充満する気体がガス導入孔１８を通って通気室１３に導入され、第二の多孔質膜９ｂと接触するように構成されている。 As described above, since the anion can pass through the anion exchange membrane 15, the anion reaches the interface between the counter electrode 5 and the reference electrode 6 and the anion exchange membrane 15.
A ventilation chamber 13 is formed between the second lid portion 10b and the second porous film 9b. A plurality of gas introduction holes 18 are formed in the second lid portion 10b. One end of the gas introduction hole 18 is exposed to the external atmosphere, the other end is connected to the ventilation chamber 13, and a gas filling the external atmosphere is introduced into the ventilation chamber 13 through the gas introduction hole 18, and the second It is comprised so that it may contact with the porous membrane 9b.

ここでは、陰イオン交換膜１５の外周と、対極５及び比較電極６からなる電極部材の外周は、容器本体３の開口よりも大きくされており、蓋部１０ａと、パッキン４ａと、第一の多孔質膜９ａと、比較電極６と、対極５と、陰イオン交換膜１５は、ねじ１７によって容器本体３の開口に押圧して固定され、開口は陰イオン交換膜１５で閉塞されている。 Here, the outer periphery of the anion exchange membrane 15 and the outer periphery of the electrode member composed of the counter electrode 5 and the comparison electrode 6 are made larger than the opening of the container body 3, and the lid portion 10a, the packing 4a, the first electrode The porous membrane 9 a, the comparison electrode 6, the counter electrode 5, and the anion exchange membrane 15 are pressed and fixed to the opening of the container main body 3 with screws 17, and the opening is closed with the anion exchange membrane 15.

陰イオン交換膜１５の周囲と、比較電極６と対極５からなる電極部材の周囲はパッキン８ａによって気密に囲まれている。
対極５と比較電極６間の隙間の周囲は、対極５と、比較電極６と、パッキン８ａとで囲まれており、上述したように、この隙間の上下は陰イオン交換膜１５と第一の多孔質膜９ａとで挟まれている。 The periphery of the anion exchange membrane 15 and the periphery of the electrode member composed of the comparison electrode 6 and the counter electrode 5 are hermetically surrounded by the packing 8a.
The periphery of the gap between the counter electrode 5 and the comparison electrode 6 is surrounded by the counter electrode 5, the comparison electrode 6, and the packing 8a. As described above, the upper and lower sides of the gap are formed between the anion exchange membrane 15 and the first electrode. It is sandwiched between the porous membrane 9a.

後述するように、陰イオン交換膜１５は電解液を通さないから、この隙間にも電解液が浸入せず、上述したように比較電極６と対極５からなる電極部材の周囲は、パッキン８ａで囲まれているから、対極５と比較電極６の隙間に露出する側面と、電極部材周囲の側面には電解液が接触しない。従って、対極５と比較電極６には、電解液が直接接触しないようになっている。 As will be described later, since the anion exchange membrane 15 does not allow the electrolytic solution to pass therethrough, the electrolytic solution does not enter the gap. As described above, the periphery of the electrode member composed of the comparison electrode 6 and the counter electrode 5 is covered with the packing 8a. Since it is surrounded, the electrolytic solution does not contact the side surface exposed in the gap between the counter electrode 5 and the comparison electrode 6 and the side surface around the electrode member. Accordingly, the counter electrode 5 and the reference electrode 6 are not in direct contact with the electrolytic solution.

対極５と比較電極６の間の隙間の真裏位置には、第一の多孔質膜９ａを挟んで空気孔１９の一端が配置されており、空気孔１９を通過した空気は、直接その隙間に侵入せず、第一の多孔質膜９ａを通過してから隙間に導入される。 One end of an air hole 19 is disposed directly behind the gap between the counter electrode 5 and the reference electrode 6 with the first porous film 9a interposed therebetween, and the air that has passed through the air hole 19 directly enters the gap. It does not enter and is introduced into the gap after passing through the first porous membrane 9a.

ここでは、含浸体１６の作用電極７の表面に接触する部分と、陰イオン交換膜１５に接触する部分は、それぞれ外周が容器本体３の開口と略等しく、開口はそれぞれ含浸体１６で塞がれ、作用電極７表面の容器本体３の内部空間に位置する部分と、陰イオン交換膜１５表面の容器本体３の内部空間に位置する部分は含浸体１６で覆われている。 Here, the outer periphery of the part of the impregnated body 16 that contacts the surface of the working electrode 7 and the part of the impregnated body 16 that contacts the anion exchange membrane 15 are substantially equal to the opening of the container body 3, and the opening is closed by the impregnated body 16 In addition, a portion located in the inner space of the container body 3 on the surface of the working electrode 7 and a portion located in the inner space of the container body 3 on the surface of the anion exchange membrane 15 are covered with the impregnated body 16.

従って、容器本体３の内部空間には、各電極５〜７の表面も、電極５、６上の陰イオン交換膜１５の表面も露出せず、作用電極７表面と、電極５、６上の陰イオン交換膜１５表面のうち、作用電極７と陰イオン交換膜１５との間の空間内の電解液と接触可能な部分は、全て含浸体１６に含浸された電解液と接触した状態になっているから、後述するように電解液の量が増えて含浸体１６に含浸されきれなくなり、電解液が含浸体１６で囲まれた空間や、含浸体１６と容器本体３内壁で囲まれた空間に存在するようになっても（図２）、電極７や電極５、６上の陰イオン交換膜１５は、電解液との接触面積が変わらない。 Therefore, neither the surface of the electrodes 5 to 7 nor the surface of the anion exchange membrane 15 on the electrodes 5 and 6 is exposed in the internal space of the container body 3, and the surface of the working electrode 7 and the electrodes 5 and 6 are exposed. Of the surface of the anion exchange membrane 15, all the parts that can come into contact with the electrolytic solution in the space between the working electrode 7 and the anion exchange membrane 15 are in contact with the electrolytic solution impregnated in the impregnated body 16. Therefore, as will be described later, the amount of the electrolytic solution increases so that the impregnated body 16 cannot be completely impregnated, and the space surrounded by the impregnated body 16 or the space surrounded by the impregnated body 16 and the inner wall of the container body 3. (FIG. 2), the anion exchange membrane 15 on the electrode 7 and the electrodes 5 and 6 does not change the contact area with the electrolytic solution.

次に、アンモニアガス（ＮＨ₃）を測定対象とするガスセンサ１について説明すると、含浸体１６には、予め塩化カルシウム（ＣａＣｌ₂）や塩化リチウム（ＬｉＣｌ）等の中性塩水溶液からなる電解液が含浸されている。 Next, the gas sensor 1 for measuring ammonia gas (NH ₃ ) will be described. The impregnated body 16 has an electrolytic solution made of a neutral salt aqueous solution such as calcium chloride (CaCl ₂ ) or lithium chloride (LiCl) in advance. Impregnated.

試料ガスが充満した雰囲気にガスセンサ１を配置し、拡散により試料ガスを各ガス導入孔１８から通気室１３内に導入させるか、試料ガスを少なくとも１個のガス導入孔１８から通気室１３内に導入し、通気室１３内を通し、他のガス導入孔１８から排出する。 The gas sensor 1 is disposed in an atmosphere filled with the sample gas, and the sample gas is introduced into the vent chamber 13 from each gas introduction hole 18 by diffusion, or the sample gas is introduced into the vent chamber 13 from at least one gas introduction hole 18. The gas is introduced, passes through the ventilation chamber 13, and is discharged from another gas introduction hole 18.

第一、第二の多孔質膜９ａ、９ｂは通気性を有しており、通気室１３に導入された試料ガスは第二の多孔質膜９ｂを透過し、作用電極７に到達する。作用電極７はガスを透過可能に構成され、試料ガスは作用電極７と電解液との界面に到達する。 The first and second porous membranes 9 a and 9 b have air permeability, and the sample gas introduced into the vent chamber 13 passes through the second porous membrane 9 b and reaches the working electrode 7. The working electrode 7 is configured to be permeable to gas, and the sample gas reaches the interface between the working electrode 7 and the electrolytic solution.

作用電極７と対極５と比較電極６にはそれぞれリードが接続されており、リードにより作用電極７を接地電位に接続し、ここでは、比較電極６と作用電極７との間の電圧が一定になるように、対極５の電位を制御する。 A lead is connected to each of the working electrode 7, the counter electrode 5, and the comparison electrode 6, and the working electrode 7 is connected to the ground potential by the lead. Here, the voltage between the comparison electrode 6 and the working electrode 7 is constant. Thus, the potential of the counter electrode 5 is controlled.

作用電極７と電解液との界面で、下記式（１）に示すアンモニアの酸化反応が進行し、電解液中のＯＨ^-が消費される。 At the interface between the working electrode 7 and the electrolytic solution, the oxidation reaction of ammonia shown in the following formula (1) proceeds, and OH ⁻ in the electrolytic solution is consumed.

ＮＨ₃ ＋３ＯＨ^- →１／２Ｎ₂＋３Ｈ₂Ｏ＋３ｅ^- ……（１）
上述したように、電解液中の陰イオンと空気中の酸素は、対極５と陰イオン交換膜１５の界面に到達するから、酸素と陰イオンは対極５と陰イオン交換膜１５との界面で反応し、下記式（２）に示す還元反応が進行され、電解液中にＯＨ^-が供給される。 NH ₃ + 3OH ⁻ → 1 / 2N ₂ + 3H ₂ O + 3e ⁻ (1)
As described above, since the anion in the electrolytic solution and the oxygen in the air reach the interface between the counter electrode 5 and the anion exchange membrane 15, the oxygen and the anion are at the interface between the counter electrode 5 and the anion exchange membrane 15. The reaction causes a reduction reaction represented by the following formula (2) to proceed, and OH ⁻ is supplied into the electrolytic solution.

３／４Ｏ₂＋３／２Ｈ₂Ｏ＋３ｅ^- →３ＯＨ^-……（２）
対極５を流れる電流は試料ガス中のアンモニアガス濃度に依存するので、対極５を流れる電流を測定すると、試料ガス中のアンモニアガス濃度が分かる。 3 / 4O ₂ + 3 / 2H ₂ O + 3e ⁻ → 3OH ⁻ (2)
Since the current flowing through the counter electrode 5 depends on the ammonia gas concentration in the sample gas, the ammonia gas concentration in the sample gas can be determined by measuring the current flowing through the counter electrode 5.

含浸体１６に含浸された電解液は、ガスセンサ１が試料ガスが充満した雰囲気に置かれた時には、ガス導入孔１８を介して試料ガスと接触し、ガスセンサ１が大気中で放置された時には、ガス導入孔１８を介して空気と接触する。 The electrolyte solution impregnated in the impregnated body 16 comes into contact with the sample gas through the gas introduction hole 18 when the gas sensor 1 is placed in an atmosphere filled with the sample gas, and when the gas sensor 1 is left in the atmosphere, It contacts with air through the gas introduction hole 18.

上述した、塩化カルシウムや塩化リチウム等の中性塩の水溶液は吸湿性が高いので、試料ガスの水分含有量が高い場合や、ガスセンサ１を高湿度の環境に置いた場合には、電解液が試料ガス又は空気中の水分を吸収し、図２に示したように、電解液２２の量が増えて、電解液中の溶質の濃度が低下する。 Since the aqueous solution of neutral salt such as calcium chloride and lithium chloride described above has high hygroscopicity, when the moisture content of the sample gas is high or when the gas sensor 1 is placed in a high humidity environment, the electrolyte solution is Moisture in the sample gas or air is absorbed, and as shown in FIG. 2, the amount of the electrolytic solution 22 increases and the concentration of the solute in the electrolytic solution decreases.

逆に、試料ガスの水分含有量が低い場合や、ガスセンサ１を低湿度の環境に放置すると、電解液から水が蒸発して電解液の濃度が上昇する。このように、ガスセンサ１中の電解液の濃度及び量は、使用環境によって変動しやすい。 On the contrary, when the moisture content of the sample gas is low, or when the gas sensor 1 is left in a low humidity environment, water evaporates from the electrolytic solution and the concentration of the electrolytic solution increases. Thus, the concentration and amount of the electrolyte in the gas sensor 1 are likely to vary depending on the usage environment.

従来のガスセンサは、比較電極６が電解液と直接接触していたため、電解液の濃度が変動したり、振動によって電解液が含浸体１６中で流動すると、作用電極７と対極５との間に流れる電流値が大きく変動し、ガス濃度を示す出力信号が大きく変動した。
これに対し、本願のガスセンサ１は、陰イオン交換膜１５が設けられ、比較電極６が電解液に直接接触しないようになっている。 In the conventional gas sensor, since the comparison electrode 6 is in direct contact with the electrolytic solution, when the concentration of the electrolytic solution fluctuates or the electrolytic solution flows in the impregnated body 16 due to vibration, the working electrode 7 and the counter electrode 5 are interposed. The flowing current value fluctuated greatly, and the output signal indicating the gas concentration fluctuated greatly.
On the other hand, the gas sensor 1 of the present application is provided with the anion exchange membrane 15 so that the comparison electrode 6 is not in direct contact with the electrolytic solution.

陰イオン交換膜１５は外部のｐＨが変動しても、内部のｐＨが変動し難い性質（緩衝作用）を有しており、含浸体１６に含浸された電解液の濃度が変化してそのｐＨが大きく変動しても、陰イオン交換膜１５内部のｐＨの変動量は小さいから、比較電極６と陰イオン交換膜１５との界面ではｐＨは大きく変動しない。従って、電解液のｐＨ変動が上記式（２）の反応に与える影響が小さく、電解液の濃度が変化しても、ガス濃度を示す出力信号に影響が出難い。 The anion exchange membrane 15 has a property (buffer action) in which the internal pH does not easily change even if the external pH changes, and the concentration of the electrolyte solution impregnated in the impregnated body 16 changes to change the pH. However, the pH does not fluctuate greatly at the interface between the reference electrode 6 and the anion exchange membrane 15 because the amount of fluctuation of the pH inside the anion exchange membrane 15 is small. Therefore, the influence of the pH variation of the electrolytic solution on the reaction of the above formula (2) is small, and even if the concentration of the electrolytic solution changes, the output signal indicating the gas concentration is hardly affected.

しかも、比較電極６は含浸体１６中の電解液と直接接触しないから、電解液の液量が変化したり、ガスセンサ１に振動が加わることで、含浸体１６中で電解液が流動しても、その影響を受けない。 In addition, since the comparison electrode 6 does not directly contact the electrolyte solution in the impregnated body 16, even if the electrolyte solution flows in the impregnated body 16 by changing the amount of the electrolyte solution or applying vibration to the gas sensor 1. Not affected by it.

尚、含浸体１６は繊維や多孔質体等、内部に細孔を多数有するものが使用可能であり、一般に含浸体１６には通常ガラス繊維ろ紙が用いられるが、ここでは含浸体１６はＳｉＯ₂繊維ろ紙（純粋なＳｉＯ₂で構成されたろ紙）で構成されている。 The impregnated body 16 may be a fiber, a porous body, or the like having a large number of pores inside. Generally, a glass fiber filter paper is generally used as the impregnated body 16, but here the impregnated body 16 is made of SiO _2. It is made of fiber filter paper (filter paper made of pure SiO ₂ ).

ガラス繊維ろ紙はＮａやＫ等のアルカリ金属を含有しており、ガラス繊維ろ紙を用いた場合には電解液にアルカリ金属のイオンが溶出して電解液のｐＨがアルカリ側に変化するが、ＳｉＯ₂繊維ろ紙はＮａやＫ等のアルカリ金属を含有しておらず、ＳｉＯ₂繊維ろ紙を用いた場合には電解液のｐＨが変化しない。 Glass fiber filter paper contains alkali metals such as Na and K. When glass fiber filter paper is used, alkali metal ions are eluted into the electrolyte solution, and the pH of the electrolyte solution changes to the alkali side. ₂ fiber filter paper did not contain an alkali metal such as Na or K, pH of the electrolyte solution does not change in the case of using the SiO ₂ fiber filter paper.

従って、ＳｉＯ₂繊維ろ紙を含浸体に用いると電解液のｐＨが変化せず、ガスセンサ１の出力信号に影響を与えない。ＳｉＯ₂繊維ろ紙は、アルカリ金属の影響を受けやすい塩化カルシウムや塩化リチウム等の中性塩水溶液を電解液に用いた場合に特に有効である。 Therefore, when SiO ₂ fiber filter paper is used for the impregnated body, the pH of the electrolyte does not change, and the output signal of the gas sensor 1 is not affected. The SiO ₂ fiber filter paper is particularly effective when an aqueous neutral salt solution such as calcium chloride or lithium chloride, which is easily affected by alkali metals, is used as the electrolyte.

上記図１に示したガスセンサ１を実施例のガスセンサとし、下記に示す測定条件で「ゼロ出力変位」と「出力変動ピーク値」を測定した。尚、ここでは対極５と、比較電極６と、作用電極７はＰｔ電極であり、電解液は塩化リチウム（ＬｉＣｌ）水溶液であった。また、含浸体１６はＳｉＯ₂繊紙ろ紙（アルカリ分を含まない純粋なＳｉＯ₂の繊紙からなるろ紙）であった。 The gas sensor 1 shown in FIG. 1 was used as the gas sensor of the example, and “zero output displacement” and “output fluctuation peak value” were measured under the following measurement conditions. Here, the counter electrode 5, the reference electrode 6, and the working electrode 7 were Pt electrodes, and the electrolyte was a lithium chloride (LiCl) aqueous solution. Further, the impregnation member 16 was SiO ₂繊紙filter paper (filter paper made of pure SiO ₂繊紙free alkalinity).

〔ゼロ出力変位試験〕
４個のガスセンサ１について、試験前に予めゼロ出力（アンモニアを含有しない試料に対する出力）と、５０ｐｐｍのアンモニアに対する出力を測定し、出力信号とアンモニア濃度（ｐｐｍ）との関係を予め求めた。各ガスセンサ１を室温、相対湿度（ＲＨ）９２％の雰囲気下に３９日間放置した後、再度ゼロ出力を測定し、試験前のゼロ出力との差をアンモニア濃度に換算し、その値をゼロ出力変位とした。 [Zero output displacement test]
For the four gas sensors 1, the zero output (output for the sample not containing ammonia) and the output for 50 ppm of ammonia were measured in advance before the test, and the relationship between the output signal and the ammonia concentration (ppm) was determined in advance. After each gas sensor 1 is left in an atmosphere of room temperature and relative humidity (RH) 92% for 39 days, the zero output is measured again, the difference from the zero output before the test is converted into the ammonia concentration, and the value is output as zero. Displacement.

〔出力変動ピーク値試験〕
ガスセンサ１を振幅１０ｃｍ、２往復／秒で１０秒間振動させ、振動を加える前の出力に対する振動後の出力値の変化を調べたところ、振動直後に一旦出力信号の値が上がった後、徐徐にその値が低下した。このときのセンサ出力変化幅の最大値をアンモニア濃度に換算し、出力変動ピーク値とした。
出力変動ピークと、上記ゼロ出力変位とを下記表１に記載する。 [Output fluctuation peak value test]
The gas sensor 1 was vibrated for 10 seconds with an amplitude of 10 cm, 2 reciprocations / second, and the change in the output value after vibration was examined with respect to the output before the vibration was applied. Its value decreased. The maximum value of the sensor output change width at this time was converted into the ammonia concentration to obtain an output fluctuation peak value.
The output fluctuation peak and the zero output displacement are shown in Table 1 below.

陰イオン交換膜１５を設けず、対極５と比較電極６を直接電解液に接触させた以外は上記実施例のガスセンサと同じ構造のものを比較例１のガスセンサとした。 The gas sensor of Comparative Example 1 was the same as the gas sensor of the above example except that the anion exchange membrane 15 was not provided and the counter electrode 5 and the comparative electrode 6 were directly in contact with the electrolyte.

放置日数を３９日間から１８日間に変えた以外は、上記実施例と同じ条件で４個の比較例１のガスセンサについてゼロ出力変位を求めた。また、４個の比較例１のガスセンサについて、上記実施例と同じ条件で出力変動ピーク値を求めた。その結果を下記表２に記載する。 The zero output displacement was determined for the four gas sensors of Comparative Example 1 under the same conditions as in the above example except that the number of days left was changed from 39 days to 18 days. Further, for the four gas sensors of Comparative Example 1, output fluctuation peak values were obtained under the same conditions as in the above example. The results are listed in Table 2 below.

上記表１、２を比較すると明らかなように、陰イオン交換膜を設けた実施例のガスセンサ１は、比較例１のガスセンサに比べてゼロ出力変位の値が低く、出力変動ピーク値の値も低かった。このことから、陰イオン交換膜を比較電極６に設けることで、電解液の濃度変化による出力変位、及びガスセンサ１に振動が加えられた際の出力変動を抑制できることがわかる。 As is clear from the comparison of Tables 1 and 2 above, the gas sensor 1 of the example provided with the anion exchange membrane has a lower value of zero output displacement and a value of the output fluctuation peak value than the gas sensor of Comparative Example 1. It was low. From this, it can be seen that by providing the reference electrode 6 with the anion exchange membrane, it is possible to suppress the output displacement due to the concentration change of the electrolytic solution and the output fluctuation when the gas sensor 1 is vibrated.

次に、上記実施例のガスセンサ１を用いて下記に示す経時的出力変化試験を行った。
〔経時的出力変化試験〕
実施例のガスセンサ１を室温で放置した際の、アンモニアガス濃度が５０ｐｐｍの試料ガスに対するセンサ出力（μＡ）の経過時間に伴なう変化を測定した。 Next, using the gas sensor 1 of the above example, the temporal output change test shown below was performed.
[Time-dependent output change test]
When the gas sensor 1 of the example was allowed to stand at room temperature, the change with the elapsed time of the sensor output (μA) with respect to the sample gas having an ammonia gas concentration of 50 ppm was measured.

ＳｉＯ₂繊紙ろ紙に変え、含浸体１６として通常のガラス繊維ろ紙を使用した以外は、上記実施例と同じ構造のガスセンサを比較例２のガスセンサとした。尚、比較例２に用いたガラス繊維ろ紙は、酸化ホウ素を含むホウケイ酸ガラスであり、酸化ホウ素以外にもＮａやＫを含有する。
比較例２のガスセンサを用いて、上記「経時的出力変化試験」を行った。実施例と比較例２の「経時的出力変化試験」の結果を図３のグラフに示す。 A gas sensor having the same structure as that of the above example was used as the gas sensor of Comparative Example 2 except that a normal glass fiber filter paper was used as the impregnated body 16 instead of the SiO ₂ fiber filter paper. The glass fiber filter used in Comparative Example 2 is a borosilicate glass containing boron oxide, and contains Na and K in addition to boron oxide.
Using the gas sensor of Comparative Example 2, the “time-dependent output change test” was performed. The results of the “temporal output change test” of the example and the comparative example 2 are shown in the graph of FIG.

図３のグラフから明らかなように、実施例のガスセンサ１は製作後、日数が経過してもセンサ出力の値の変化が小さいが、比較例２のガスセンサは日数が経過かする程、センサ出力の値が大きく減少した。 As apparent from the graph of FIG. 3, the change in the sensor output value is small even after the number of days has elapsed after the manufacture of the gas sensor 1 of the example, but the gas output of the comparative example 2 has a sensor output as the number of days elapses. The value of decreased significantly.

また、実施例と比較例２のガスセンサで、オーバーシュート現象（出力が一旦上昇して最大値を示した後、その出力が徐徐に低下する現象）の有無を調べたところ、比較例２のガスセンサは製作後３５日を経過するとオーバーシュート現象が見られたが、実施例のガスセンサは製作後３５日を経過してもオーバーシュート現象が確認されなかった。
以上のことから、含浸体１６にＳｉＯ₂繊紙ろ紙を使用すれば、長期にわたって安定してガス濃度の測定が可能なことがわかる。 In addition, when the gas sensor of the example and the comparative example 2 was examined for the presence of an overshoot phenomenon (a phenomenon in which the output once increased and showed a maximum value and then the output gradually decreased), the gas sensor of the comparative example 2 In the gas sensor of Example, overshoot phenomenon was not confirmed even after 35 days after manufacture.
From the above, it can be seen that if SiO ₂ fiber filter paper is used for the impregnated body 16, the gas concentration can be measured stably over a long period of time.

以上は、容器本体３内部に含浸体１６が配置された場合について説明したが、本発明はこれに限定されるものではなく、図４に示したように、含浸体を設けず、容器本体３内部に電解液を配置してもよい。 The case where the impregnated body 16 is disposed inside the container main body 3 has been described above. However, the present invention is not limited to this, and as shown in FIG. An electrolytic solution may be disposed inside.

しかし、このガスセンサ５０は、振動が加わったり、電解液の液量が変動すると、対極５や比較電極６や作用電極７が電解液と接触する面積が変動し、測定が不安定になるので、ガスセンサ５０を持ち運んで使用したり、傾けて使用する必要がある場合には、含浸体を設けることが好ましい。
本願のガスセンサ１に用いる陰イオン交換膜１５は、電解液を通過させないが、陰イオン（ここではＯＨ^-）を通過させる膜である。 However, in this gas sensor 50, when vibration is applied or the amount of the electrolytic solution varies, the area where the counter electrode 5, the comparative electrode 6 and the working electrode 7 are in contact with the electrolytic solution varies, and the measurement becomes unstable. When it is necessary to carry and use the gas sensor 50, it is preferable to provide an impregnated body.
The anion exchange membrane 15 used in the gas sensor 1 of the present application is a membrane that does not allow electrolyte solution to pass but allows anion (here, OH ⁻ ) to pass therethrough.

イオン交換膜の種類は電解液の種類に応じて変更すべきものであり、上述したように、電解液が中性塩溶液の場合は陰イオン交換膜１５を使用するが、電解液が硫酸水溶液（測定対象がＣＯ、Ｈ₂Ｓ等）やりん酸水溶液等の酸性水溶液の場合には陽イオン交換膜を使用する。 The type of ion exchange membrane should be changed according to the type of electrolytic solution. As described above, when the electrolytic solution is a neutral salt solution, the anion exchange membrane 15 is used, but the electrolytic solution is an aqueous sulfuric acid solution ( A cation exchange membrane is used when the measurement target is an acidic aqueous solution such as CO or H ₂ S) or a phosphoric acid aqueous solution.

電解液として、硫酸水溶液よりも吸湿性の高い酸性水溶液を用いる場合には、電解液の濃度が変わりやすく、上述した不都合が起こりやすいので、陽イオン交換膜を用いることが特に有効である。
電解液２２は、上述した酸性水溶液や、中性塩水溶液が使用可能であるが、塩基性の電解液は空気中の二酸化炭素と反応してしまうため、望ましくない。 When an acidic aqueous solution having higher hygroscopicity than sulfuric acid aqueous solution is used as the electrolytic solution, the concentration of the electrolytic solution is likely to change and the above-mentioned disadvantages are likely to occur. Therefore, it is particularly effective to use a cation exchange membrane.
As the electrolytic solution 22, the above-described acidic aqueous solution or neutral salt aqueous solution can be used, but the basic electrolytic solution is not desirable because it reacts with carbon dioxide in the air.

以上は、表面が比較電極６と対極５に接触し、裏面が電解液と接触する陰イオン交換膜１５を設け、比較電極６と対極５に電解液を直接接触させない場合について説明したが、本発明はこれに限定されるものではない。 The above has described the case where the anion exchange membrane 15 having the front surface in contact with the reference electrode 6 and the counter electrode 5 and the back surface in contact with the electrolytic solution is provided and the electrolytic solution is not in direct contact with the comparative electrode 6 and the counter electrode 5. The invention is not limited to this.

表面が比較電極６と接触し、裏面が電解液に接触する陰イオン交換膜１５を設けて、比較電極６だけが電解液に直接接触しないようにしてもよいし、表面が比較電極６と作用電極７に接触し、裏面が電解液に接触する陰イオン交換膜１５を設けて、比較電極６と作用電極７の両方が電解液に直接接触しないようにしてもよい。 An anion exchange membrane 15 whose front surface is in contact with the reference electrode 6 and whose rear surface is in contact with the electrolytic solution may be provided so that only the comparative electrode 6 is not in direct contact with the electrolytic solution. An anion exchange membrane 15 that is in contact with the electrode 7 and whose back surface is in contact with the electrolytic solution may be provided so that both the comparison electrode 6 and the working electrode 7 are not in direct contact with the electrolytic solution.

更に、図４の符号５０に示すガスセンサのように、表面が比較電極６と対極５に接触し、裏面が電解液２２に接触する陰イオン交換膜１５ａと、表面が作用電極７に接触し、裏面が電解液２２に接触する陰イオン交換膜１５ｂとを設け、比較電極６と対極５と作用電極７とが電解液に直接接触しないようにしてもよい。 Furthermore, like the gas sensor shown by the code | symbol 50 of FIG. 4, the surface contacts the comparison electrode 6 and the counter electrode 5, the back surface contacts the electrolyte solution 22, and the surface contacts the working electrode 7, An anion exchange membrane 15b whose back surface is in contact with the electrolytic solution 22 may be provided so that the comparison electrode 6, the counter electrode 5, and the working electrode 7 do not directly contact the electrolytic solution.

第一、第二の多孔質膜９ａ、９ｂはガス透過性を有するものであって、試料ガスと反応性が低いものであれば特に限定されるものではないが、例えば４フッ化エチレン樹脂（ＰＴＦＥ）製の多孔質樹脂膜を用いることができる。 The first and second porous membranes 9a and 9b are not particularly limited as long as they have gas permeability and are low in reactivity with the sample gas. For example, tetrafluoroethylene resin ( A porous resin film made of PTFE) can be used.

対極（Ｃ．Ｅ．）５、比較電極（Ｒ．Ｅ．）６、作用電極（Ｗ．Ｅ．）７の電極材料も特に限定されないが、耐腐食性の金属、具体的には白金（白金黒）や
金等の貴金属であり、ガス透過性の多孔質膜９ａ、９ｂに結合される。 The electrode materials of the counter electrode (C.E.) 5, the reference electrode (R.E.) 6, and the working electrode (W.E.) 7 are not particularly limited, but are corrosion-resistant metals, specifically platinum (platinum). Black) or a noble metal such as gold and bonded to the gas permeable porous membranes 9a and 9b.

電極材料は粉末を単独で、又は、４フッ化エチレン樹脂粉末等のバインダーと混合し、適当な溶剤に分散させ、多孔質膜９ａ、９ｂをろ紙として用い、減圧濾過によって直接多孔質膜９ａ、９ｂに付着させ(又は減圧濾過によって得たフィルムを多孔質膜９ａ、９ｂ上に転写し)、圧着して電極を形成することができる。 The electrode material is powder alone or mixed with a binder such as tetrafluoroethylene resin powder and dispersed in an appropriate solvent, and the porous membranes 9a and 9b are used as filter paper, and the porous membrane 9a directly by vacuum filtration. The electrode can be formed by adhering to 9b (or transferring the film obtained by filtration under reduced pressure onto the porous membranes 9a and 9b) and pressing.

また、これらの電極は、真空蒸着、スパッタリング、イオンプレーティング等の方法、または無電解めっきの方法で多孔質膜に密着形成してもよい。容器本体３の形状も円形筒状に限定されず、四角筒状であってもよい。 Further, these electrodes may be formed in close contact with the porous film by a method such as vacuum deposition, sputtering, ion plating, or electroless plating. The shape of the container body 3 is not limited to a circular cylinder, and may be a square cylinder.

本願のガスセンサの一例を説明する断面図Sectional drawing explaining an example of the gas sensor of this application 電解液の量が増えた状態を示す断面図Sectional view showing the state of increased amount of electrolyte センサ出力と経過日数との関係を示すグラフGraph showing the relationship between sensor output and elapsed days 本願のガスセンサの他の例を説明する断面図Sectional drawing explaining the other example of the gas sensor of this application

Explanation of symbols

１、５０……ガスセンサ３……容器本体５……対極６……比較電極７……作用電極１５、１５ａ、１５ｂ……イオン交換膜（陰イオン交換膜）１６……含浸体２２……電解液 DESCRIPTION OF SYMBOLS 1,50 ... Gas sensor 3 ... Container body 5 ... Counter electrode 6 ... Comparative electrode 7 ... Working electrode 15, 15a, 15b ... Ion exchange membrane (anion exchange membrane) 16 ... Impregnation body 22 ... Electrolysis liquid

Claims

A cylindrical container body;
A counter electrode and a reference electrode respectively disposed at one end of the container body;
A working electrode disposed at the other end of the container body;
An electrolyte contained in the container body,
The counter electrode, the comparison electrode, and the working electrode are gas sensors electrically connected by ions in the electrolyte solution,
A gas sensor having an ion exchange membrane having a surface in contact with the reference electrode and a back surface in contact with the electrolyte.

The gas sensor according to claim 1, wherein a surface of the ion exchange membrane is in contact with both the counter electrode and the reference electrode.

An impregnated body is disposed in the container body,
The electrolytic solution is impregnated in the impregnated body,
The gas sensor according to claim 1, wherein the ion exchange membrane is in contact with the electrolytic solution impregnated in the impregnated body.

The ion exchange membrane is an anion exchange membrane;
The gas sensor according to any one of claims 1 to 3, wherein the electrolytic solution is an aqueous solution of a neutral salt.

The gas sensor according to claim 4, wherein the neutral salt contains one or both of calcium chloride and lithium chloride.

The gas sensor according to claim 4 or 5, wherein the impregnated body is composed of SiO ₂ fiber.