JP3572356B2 - Chlorine gas sensor - Google Patents

Description

なる反応が生じていることになる。
【００３４】
この場合、ネルンスト（Ｎｅｒｎｓｔ）の式は、

で表される。ここで、Ｅは起電力、Ｒは気体定数、ｎは（４）式で表される反応に寄与する電子数であり、（１）〜（３）式を参照することにより、この場合においては、ｎ＝２．０である。また、Ｆはファラデー定数であり、ａＡｌＣｌ_３などは、（４）式に出現する各化合物の活量である。
【００３５】
（Ａｌ_ＹＺｒ_１−Ｙ）_{４／（４−Ｙ）}Ｎｂ（ＰＯ_４）_３（Ｙ＝０．２）、ＺｒＰ_２Ｏ_７、ＮｂＰＯ_５、及びＮｂ_２Ｏ_５は固体であるから、それらの活量は１となり、加えてＡｌＣｌ_３は測定温度９００℃では安定であり、Ｏ_２濃度は常に２０体積％で一定であるため、ａＡｌＣｌ_３及びｐＯ_２は一定となる。このため、（５）式は簡略化され、
Ｅ＝Ｃ_２（定数）＋（ＲＴ／ｎＦ）ｌｎ（ｐＣｌ_２） （ｎ＝２．０） （６）
で表される。
【００３６】
（６）式から塩素ガス濃度の対数ｌｏｇ（ｐＣｌ_２）に対する起電力Ｅは、図３に示すような直線となるが、黒丸プロット及び白四角プロットで示される実測値は、この理論値と極めて近似した傾向を呈する。したがって、本実施例、すなわち本発明における塩素ガスセンサは、塩素ガス濃度と出力値である起電力とが実質的にネルンストの式に従うことが分かる。
【００３７】
以上、具体例を挙げながら発明の実施の形態に基づいて本発明を詳細に説明してきたが、本発明は上記内容に限定されるものではなく、本発明の範疇を逸脱しない限りにおいてあらゆる変形や変更が可能である。
【００３８】
【発明の効果】
以上説明したように、本発明によれば、難水溶性であるとともに、酸化・還元両雰囲気下でも極めて安定な固体電解質からなり、実際の環境下において実用可能な新規な塩素ガスセンサを得ることができる。したがって、塩素ガス検出器や環境保全用大気モニターなどの各種用途に使用することができる。
【図面の簡単な説明】
【図１】本発明の塩素ガスセンサの一例を示す構成図である。
【図２】本発明の塩素ガスセンサの応答曲線の一例を示すグラフである。
【図３】本発明の塩素ガスセンサの出力値（起電力値）と塩素ガス濃度との相関を示すグラフである。
【符号の説明】
１ 第１の固体電解質
２ 第２の固体電解質
３、４ 金ネット
５、６ 金線
１０ 塩素ガスセンサ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a chlorine gas sensor that can be used as a chlorine gas detector in a factory or the like.
[0002]
[Prior art]
Chlorine gas (Cl ₂ ) is one of the gases often used industrially. However, chlorine gas is toxic, and gas leaks from industrial equipment cause serious damage not only to humans but also to the environment. The best way to control the release of gas into the atmosphere is to find gas leak sites quickly and prevent further gas leaks. By installing chlorine gas sensors at various locations in each facility and constantly detecting the concentration of chlorine gas in the atmosphere, it is possible to quickly and accurately determine a gas leak site. For that purpose, a compact and inexpensive chlorine gas detector is indispensable.
[0003]
Conventionally, various chlorine gas sensors have been proposed. Particularly, a chlorine gas sensor using a solid electrolyte is extremely promising from the viewpoint of quick response and high selectivity.
[0004]
[Problems to be solved by the invention]
In recent years, SrCl ₂ , BaCl ₂ , PbCl ₂ , and the like have been proposed as solid electrolytes that can be suitably used as a chlorine gas sensor. However, SrCl ₂ and BaCl ₂ easily dissolve in water, and PbCl ₂ Also easily dissolves in warm water. Further, these solid electrolytes have insufficient durability in various atmospheres. Furthermore, Pb is toxic, and recently there is a tendency to avoid using such toxic substances from the viewpoint of environmental problems.
[0005]
An object of the present invention is to provide a chlorine gas sensor which is made of a material having poor water solubility, can be used in various atmospheres, and can be put to practical use.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a first solid electrolyte capable of moving aluminum ions, magnesium ions, or rare earth ions, and a first solid electrolyte including a rare earth oxychloride provided adjacent to the first solid electrolyte. The present invention relates to a chlorine gas sensor comprising a solid electrolyte of No. 2 and detecting the concentration of chlorine gas without involving movement of oxygen ions .
[0007]
The present inventors show that, when a solid electrolyte is used for a sensor, they generally exhibit quick response and high selectivity. Therefore, the solid electrolyte constituting the chlorine gas sensor is a novel, slightly water-soluble alternative to the above SrCl ₂ or the like. Intensive studies were conducted to obtain a solid electrolyte. As a result, rare earth oxychloride (LnOCl: Ln represents a rare earth element) exhibits high water solubility, is extremely stable even in both oxidation and reduction atmospheres, and exhibits good mobility for chlorine ions. Was found.
[0008]
On the other hand, the present inventors move a magnesium ion, an aluminum ion, or a rare earth ion, have good ion mobility, show high water solubility, and are extremely stable under both oxidation and reduction atmospheres. We have successfully developed a solid electrolyte.
[0009]
When the rare earth oxychloride comes into contact with chlorine gas,
Cl ₂ + 2e ⁻ → 2Cl ⁻ (1)
According to the equilibrium equation, chloride ions are formed, and the chlorine ions can move in the rare earth oxychloride.
[0010]
In the solid electrolyte, for example, aluminum is
Al → 2 / 3Al ³⁺ + 2e ⁻ (2)
It exists in the form of aluminum ions according to the equilibrium equation: Therefore, by arranging the rare earth oxychloride and the solid electrolyte so as to be adjacent to each other, chlorine ions that have been moving in the rare earth oxychloride are:
2Cl ⁻ + 2 / 3Al ³⁺ → 2 / 3AlCl ₃ (3)
It reacts with aluminum ions according to the following reaction formula to produce aluminum chloride, and an electromotive force is generated according to the amount of the produced aluminum chloride.
[0011]
Since the amount of chlorine ions moving in the rare earth oxychloride is proportional to the detected chlorine gas amount, the electromotive force also shows a value according to the chlorine gas amount. Therefore, the first solid electrolyte and the second solid electrolyte containing the rare earth oxychloride are arranged adjacent to each other, and the solid electrolyte generated when the rare earth oxychloride comes into contact with chlorine gas is generated. By measuring the electric power, the detected chlorine gas amount can be quantified.
[0012]
In addition, since these solid electrolytes are poorly water-soluble and extremely stable under both oxidizing and reducing atmospheres, by arranging these solid electrolytes adjacent to each other, they can be practically used as chlorine gas detectors and the like. A chlorine gas sensor can be provided.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail based on embodiments of the invention.
FIG. 1 is a configuration diagram showing an example of the chlorine gas sensor of the present invention. The chlorine gas sensor 10 shown in FIG. 1 includes a first solid electrolyte 1 that can move aluminum ions, magnesium ions, or rare earth ions, and a first solid electrolyte 1 that is provided adjacent to the first solid electrolyte 1 and that contains a rare earth oxychloride. 2 solid electrolytes 2. The first solid electrolyte 1 and the second solid electrolyte 2 are bonded and fixed with an inorganic adhesive (not shown).
[0014]
Further, gold nets 3 and 4 are provided on the main surfaces of the first solid electrolyte 1 and the second solid electrolyte opposite to the adjacent main surfaces, respectively, and via the gold nets 3 and 4, , Are provided with gold wires 5 and 6, respectively.
[0015]
When the chlorine gas sensor 10 is disposed in a predetermined chlorine gas-containing atmosphere, the rare earth oxychloride constituting the second solid electrolyte 2 detects chlorine gas, and the chlorine in the rare earth oxychloride is detected as described above. The ions become mobile. The chlorine ions reach the first solid electrolyte 1, where they react with aluminum ions and the like constituting the solid electrolyte 1 as shown by the reaction formula (3).
[0016]
As described above, since the electromotive force is proportional to the amount of chlorine gas contacted by the second solid electrolyte 2, the amount of chlorine gas, that is, the chlorine gas sensor 10 is arranged by measuring the value of the electromotive force. The amount of chlorine gas in the set atmosphere can be determined.
[0017]
The solid electrolyte capable of moving aluminum ions constituting the first solid electrolyte 1 is a composite having a composition of Al _{1 + X} Zr ₆ P ₉ O _{36 + 3 / 2X} + Zr ₂ O (PO ₄ ) ₂ or (Al _Y Zr _1-Y ) _{4 / (4-Y)} Nb (PO ₄ ) ₃ (0 < Y <1) which is a solid solution having a crystal structure of Nasicon type or β-iron sulfate type Is preferred.
[0018]
The composite is prepared by mixing powders having a composition of, for example, Al (OH) ₃ , ZrO (NO ₃ ) ₂ .2H ₂ O, and (NH ₄ ) ₂ HPO ₄ at a predetermined ratio, and baking as necessary. To obtain a mixed powder. The mixed powder is formed into a predetermined shape and size, and then fired under predetermined conditions. The solid solution is prepared by mixing powders having a composition of, for example, Al (OH) ₃ , ZrO (NO ₃ ) ₂ .2H ₂ O, Nb ₂ O _5, and (NH ₄ ) ₂ HPO ₄ at a predetermined ratio. The mixed powder is obtained by sintering to obtain a mixed powder. The mixed powder is formed into a predetermined shape and size, for example, a pellet, and then fired under predetermined conditions.
[0019]
Further, as a solid electrolyte capable of moving magnesium ions, a composite having a composition of Mg _{1 + X} Zr ₄ P ₆ O _{24 + X} + Zr ₂ O (PO ₄ ) ₂ or (Mg _Y Zr _1-Y ) _{2 / (2 -Y)} A solid solution having a composition of Nb (PO ₄ ) ₃ (0 < Y <1) and preferably having a Nasicon type or β-iron sulfate type crystal structure. Similarly, as a rare earth ion movable solid electrolyte, a composite having a composition of R _{1 + X} Zr ₆ P ₉ O _{36 + 3 / 2X} + Zr ₂ O (PO ₄ ) ₂ or (R _Y Zr _1-Y ) _{4 / (4-Y)} Nb (PO ₄ ) ₃ (0 < Y <1), which is a solid solution (R: rare earth ion) having a NASICON-type or β-iron sulfate-type crystal structure Is preferred.
[0020]
The composite is prepared by, for example, preparing a powder having a composition of MgHPO ₄ .3H ₂ O or R ₂ O ₃ (R: rare earth ion), ZrO (NO ₃ ) ₂ .2H ₂ O, and (NH ₄ ) ₂ HPO ₄ . The mixed powder is obtained by mixing at a ratio and firing if necessary, forming the mixed powder into a predetermined shape and size, and then firing under predetermined conditions. The solid solution, for example, MgHPO ₄ · 3H ₂ O or _R 2 _O 3 _(R: rare-earth _{ions), ZrO (NO 3) 2} · 2H 2 O, Nb 2 O 5 and _{(NH 4)} 2 HPO ₄ having a composition By mixing the powder at a predetermined ratio and firing if necessary, a mixed powder is obtained, and the mixed powder is formed into a predetermined shape and size, for example, a pellet, and then fired under predetermined conditions. Make it.
[0021]
Note that the NASICON-type crystal structure means a crystal structure that has a three-dimensional tunnel and is designed so that a specific ion species can easily move in the tunnel. The origin of the _{name, Na 1 + X Zr 2 P} 3-3X Si 3X O 12 (0 <X <3: NASICON) with sodium ions (Na ⁺⁾ as a movable ionic species is derived from. The β-iron sulfate type crystal structure has a similar structure to the NASICON type crystal structure, and also has a three-dimensional tunnel capable of easily moving a specific ion species.
[0022]
The rare earth oxychloride constituting the second solid electrolyte 2 preferably has a general formula of LnOCl (Ln: rare earth element). In particular, the rare earth oxychloride is preferably LaOCl in which the rare earth Ln is composed of La because of its high thermal stability. Such a rare earth oxychloride exhibits extremely good mobility with respect to chloride ions, and even when the amount of chlorine gas is extremely small, the chlorine gas is detected and the chlorine ions become movable. . Therefore, when configured as a chlorine gas sensor, it has excellent sensitivity.
[0023]
Preferably, the rare earth oxychloride contains calcium as a doping element. Thereby, the chlorine ion mobility of the rare earth oxychloride is further improved, and the sensitivity of the chlorine gas sensor can be further improved.
[0024]
In Figure 1, the first solid electrolyte 1 has a thickness of usually 0.3Mm～1.2Mm, its surface area has a size of 50 mm ² 100 mm ^2. In addition, the shape can be set to any shape as required, such as a disk shape or a rectangular flat plate shape. Similarly, the second solid electrolyte 2 has a thickness of usually 0.3Mm～1.2Mm, its surface area has a size of 50 mm ² 100 mm ^2. In addition, the shape can be formed into an arbitrary shape according to the shape of the solid electrolyte 1.
[0025]
【Example】
Hereinafter, the present invention will be described based on specific examples. In this embodiment, a chlorine gas sensor 10 as shown in FIG. 1 was manufactured.
[0026]
(Production of chlorine gas sensor)
_{First, Al (OH) 3, ZrO} (NO 3) 2 · 2H 2 O, the powder of _Nb 2 _{O 5} and _{(NH 4)} 2 HPO ₄ having a composition, the molar ratio of 8: 32: 19: the 114 After heating at 1000 ° C. for 12 hours, pellets were formed, and calcined by heating at 1200 ° C. for 12 hours under flowing dry air. The obtained fired body sample is pulverized in an agate mortar, then pelletized, and fired at 1300 ° C. for 12 hours in a stream of dry air to obtain (Al _Y Zr _1-Y ) _{4 / (4-Y)} Nb (PO _{) 4} ) A disk-shaped first solid electrolyte 1 made of a solid solution having a composition of ₃ (Y = 0.2) was obtained. The thickness of the first solid electrolyte 1 was 0.6 mm, and the size of the surface area was 95 mm ² .
[0027]
Next, the LaOCl powder and the CaCO ₃ powder were mixed at a molar ratio such that La: Ca = 9: 1, and heated at 900 ° C. for 6 hours under a flow of dry air to obtain a Ca-doped rare earth oxychloride. LaOCl was obtained, and a disk-shaped second solid electrolyte 2 was obtained. The thickness of the second solid electrolyte 2 was 0.6 mm, and the size of the surface area was 95 mm ² .
[0028]
Next, the first solid electrolyte 1 and the second solid electrolyte 2 obtained as described above were bonded together using an unillustrated adhesive such as Sumiceram (registered trademark) . Thereafter, a gold net 3, a gold wire 5, a gold net 4, and a gold wire 6 are provided on the upper surface of the first solid electrolyte 1 and the lower surface of the second solid electrolyte 2, and a chlorine gas sensor 10 as shown in FIG. Completed.
[0029]
(Evaluation of chlorine gas sensor)
FIG. 2 is a graph showing a response curve of the chlorine gas sensor 10 obtained as described above, and FIG. 3 is a graph showing a correlation between an output value (electromotive force) of the chlorine gas sensor 10 and a chlorine gas concentration. . Note that the output value is an electromotive force value between the gold wires 5 and 6. As the chlorine gas, a 1% chlorine gas diluted with a nitrogen gas was used, and this was further diluted with an oxygen gas and a nitrogen gas so that the chlorine gas concentration was 2,000 to 8,000 ppm. The total flow rate was set at 100 ml / min, and the oxygen concentration was controlled to be 20% by volume.
[0030]
FIG. 2 shows that when the chlorine gas concentration is changed with time, the electromotive force between the gold wires 5 and 6 also changes following the change in the chlorine gas concentration. Further, the response speed defined by 90% of the output change is also within several minutes, and it can be seen that good response is exhibited.
[0031]
FIG. 3 shows the correlation between the output value of the chlorine gas sensor 10 at 900 ° C. and the chlorine gas concentration, and shows a slight difference between the concentration increase (solid circle plot) and the concentration decrease (white square plot). However, it can be seen that the logarithmic concentration of chlorine gas and the electromotive force value, which is the output value, approximately correspond to one to one and are in a proportional relationship.
[0032]
From the above, it can be seen that the chlorine gas sensor obtained in this example can be used as a practical sensor.
[0033]
On the other hand, in the present embodiment, the first solid electrolyte is a solid solution having a composition of (Al _Y Zr _1-Y ) _{4 / (4-Y)} Nb (PO ₄ ) ₃ (Y = 0.2) having aluminum ion mobility. It is composed of Therefore, by referring to the above-described equations (1) to (3), the first solid electrolyte and the second solid electrolyte as a whole

That is, a certain reaction has occurred.
[0034]
In this case, the Nernst equation is:

It is represented by Here, E is an electromotive force, R is a gas constant, n is the number of electrons contributing to the reaction represented by the equation (4), and by referring to the equations (1) to (3), in this case, , N = 2.0. F is a Faraday constant, and aAlCl _{3 and the} like are activities of each compound appearing in the equation (4).
[0035]
_{(Al Y Zr 1-Y)} 4 / (4-Y) Nb (PO 4) 3 (Y = 0.2), ZrP 2 O 7, NbPO 5, and _Nb 2 _{O 5} is from a solid, their The activity becomes 1, and in addition, since AlCl ₃ is stable at a measurement temperature of 900 ° C. and the O ₂ concentration is always constant at 20% by volume, aAlCl ₃ and pO ₂ are constant. Therefore, equation (5) is simplified,
E = C ₂ (constant) + (RT / nF) ln (pCl ₂ ) (n = 2.0) (6)
It is represented by
[0036]
From the equation (6), the electromotive force E with respect to the logarithm of the chlorine gas concentration log (pCl ₂ ) is a straight line as shown in FIG. 3, but the measured values shown by the black circle plot and the white square plot are extremely different from this theoretical value. It shows an approximate tendency. Therefore, in the present embodiment, that is, in the chlorine gas sensor of the present invention, the chlorine gas concentration and the electromotive force as the output value substantially follow the Nernst equation.
[0037]
As described above, the present invention has been described in detail based on the embodiments of the present invention with specific examples. However, the present invention is not limited to the above contents, and any modifications or changes may be made without departing from the scope of the present invention. Changes are possible.
[0038]
【The invention's effect】
As described above, according to the present invention, it is possible to obtain a novel chlorine gas sensor which is hardly water-soluble and is made of a solid electrolyte which is extremely stable even in both oxidation and reduction atmospheres, and which can be used in an actual environment. it can. Therefore, it can be used for various applications such as a chlorine gas detector and an air monitor for environmental protection.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an example of a chlorine gas sensor of the present invention.
FIG. 2 is a graph showing an example of a response curve of the chlorine gas sensor of the present invention.
FIG. 3 is a graph showing a correlation between an output value (electromotive force value) of a chlorine gas sensor of the present invention and a chlorine gas concentration.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 1st solid electrolyte 2 2nd solid electrolyte 3, 4 Gold net 5, 6 Gold wire 10 Chlorine gas sensor

Claims (6)

A first solid electrolyte that can move aluminum ions, magnesium ions, or rare earth ions; and a second solid electrolyte containing a rare earth oxychloride provided adjacent to the first solid electrolyte , A chlorine gas sensor characterized by detecting the concentration of chlorine gas without moving . The first solid electrolyte capable of moving aluminum ions is a composite having a composition of Al _{1 + X} Zr ₆ P ₉ O _{36 + 3 / 2X} + Zr ₂ O (PO ₄ ) ₂ or (Al _Y Zr _1-Y ) _{4 / (4-Y)} Nb (PO ₄ ) ₃ (0 < Y <1), which is a solid solution composed of a compound having a Nasicon type or β-iron sulfate type crystal structure, The chlorine gas sensor according to claim 1. The first solid electrolyte capable of moving magnesium ions is a composite having a composition of Mg _{1 + X} Zr ₄ P ₆ O _{24 + X} + Zr ₂ O (PO ₄ ) ₂ or (Mg _Y Zr _1-Y ) _{2 / (2-Y)} Nb (PO ₄ ) ₃ (0 < Y <1), which is a solid solution having a crystal structure of Nasicon type or β-iron sulfate type. 2. The chlorine gas sensor according to 1. The first solid electrolyte that moves rare earth ions is a composite having a composition of R _{1 + X} Zr ₆ P ₉ O _{36 + 3 / 2X} + Zr ₂ O (PO ₄ ) ₂ or (R _Y Zr _1-Y ) _{4 / (4-Y)} Nb (PO ₄ ) ₃ (0 < Y <1), a solid solution (R: rare earth ion) composed of a compound having a Nasicon type or β-iron sulfate type crystal structure The chlorine gas sensor according to claim 1, wherein: The chlorine gas sensor according to claim 1, wherein the second solid electrolyte contains calcium. The chlorine gas sensor according to any one of claims 1 to 5, wherein the sensor output regarding the chlorine concentration is expressed as an electromotive force substantially according to the Nernst equation.

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