JP4475587B2 - Nitrous oxide gas sensor - Google Patents
Nitrous oxide gas sensor Download PDFInfo
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- JP4475587B2 JP4475587B2 JP2005100930A JP2005100930A JP4475587B2 JP 4475587 B2 JP4475587 B2 JP 4475587B2 JP 2005100930 A JP2005100930 A JP 2005100930A JP 2005100930 A JP2005100930 A JP 2005100930A JP 4475587 B2 JP4475587 B2 JP 4475587B2
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Description
本発明は、大気中または特定の雰囲気下の亜酸化窒素ガス濃度を測定するガスセンサに関する。 The present invention relates to a gas sensor that measures the concentration of nitrous oxide gas in the air or in a specific atmosphere.
亜酸化窒素（Ｎ２Ｏ）はヒトの中枢神経に作用し、視覚、聴覚、触覚、痛覚などを抑制する働きがあるため、手術時の麻酔用ガスとして医療現場で広く用いられている。 Nitrous oxide (N 2 O) acts on the central nervous system of humans and suppresses visual, auditory, tactile, and painful sensations, and is therefore widely used in the medical field as an anesthetic gas during surgery.
一方、職業的に、数年にわたりＮ２Ｏに暴露された女性は自然流産率が高いことが報告されており、Ｎ２Ｏを取扱う職場では安全衛生面からその濃度を管理することが必要である。また、Ｎ２Ｏは二酸化炭素（ＣＯ２）の約３００倍の温室効果ガスであるため、漏洩などによる大気中への放出を抑制することも重要となっている。 On the other hand, women who have been exposed to N 2 O for several years have been reported to have a high rate of spontaneous abortion, and it is necessary to manage the concentration from the viewpoint of health and safety in workplaces that handle N 2 O. is there. In addition, since N 2 O is a greenhouse gas approximately 300 times as large as carbon dioxide (CO 2 ), it is also important to suppress release into the atmosphere due to leakage or the like.
これらの目的を達するために、Ｎ２Ｏセンサが用いられている。 In order to achieve these purposes, N 2 O sensors are used.
しかしながら、現在用いられているＮ２Ｏセンサの多くは高価な赤外線吸収方式（例えば特許文献１参照）であるため普及しておらず、また、ＣＯ２ガスの吸収特性はＮ２Ｏガスの特性と重なっているため、被測定ガス中のＣＯ２ガス濃度によりＮ２Ｏ濃度の測定値に誤差が生じるという問題がある。 However, many of the N 2 O sensors currently used are not widely used because they are expensive infrared absorption methods (see, for example, Patent Document 1), and the absorption characteristics of CO 2 gas are the characteristics of N 2 O gas. Therefore, there is a problem that an error occurs in the measured value of the N 2 O concentration due to the CO 2 gas concentration in the gas to be measured.
一方、特許文献２には、全固体型素子を用いた化学センサが提案されているが、金属酸化物電極のＮ２Ｏガス吸着による導電率変化を利用したものであり、高濃度域でガス感度が飽和する問題がある。また、特許文献３には、酸素イオン伝導性を有する固体電解質（酸化物イオン伝導体）を用いることが提案されているが、原理的に酸素分圧の影響を受けるため、同文献に示すように参照電極が必要で構造が複雑で高価になるという問題がある。
本発明が解決しようとする課題は、測定値へのＣＯ２濃度や酸素分圧の影響が小さく、かつ安価なＮ２Ｏガスセンサを提供することにある。 The problem to be solved by the present invention is to provide an inexpensive N 2 O gas sensor that is less affected by the CO 2 concentration and oxygen partial pressure on the measured value.
本発明のＮ２Ｏガスセンサは、陽イオン伝導体を電解質とし、電解質の少なくとも一面に亜酸化窒素分解触媒を電極層として有することを特徴とする。 The N 2 O gas sensor of the present invention is characterized by having a cation conductor as an electrolyte and having a nitrous oxide decomposition catalyst as an electrode layer on at least one surface of the electrolyte.
このＮ２Ｏガスセンサにおいては、Ｎ２Ｏガス濃度に応じて電解質と電極層との間に起電力を発生するため、この起電力を公知の方法により測定することにより、Ｎ２Ｏガス濃度を知ることができる。
In the N 2 O gas sensor, for generating an electromotive force between the electrolyte and electrode layers in accordance with the
そして、本発明では、電解質として陽イオン伝導体を使用することで、原理的に酸素分圧の影響を受け難く、特許文献３で示すような手段によらずとも精度の高いＮ２Ｏガスセンサが実現できる。 In the present invention, by using a cation conductor as an electrolyte, in principle, the N 2 O gas sensor is hardly affected by the partial pressure of oxygen and is not affected by the means shown in Patent Document 3. realizable.
また、本発明では、Ｎ２Ｏ測定値に対するＣＯ２の影響を小さくすることができる。これは、Ｎ２Ｏに対しては、電気化学的にＮ２Ｏ＋２ｅ-→Ｎ２＋Ｏ2-の反応が電極上で進行するが、ＣＯ２に対しては、同様な反応が起こりにくいためと考えられる。
In the present invention, it is possible to reduce the influence of CO 2 for
電解質となる陽イオン伝導体としては、ナトリウム超イオン伝導体、ナトリウムイオン伝導体、又はリチウムイオン伝導体を使用する。ナトリウム超イオン伝導体としては、Ｎａ（１＋ｘ）Ｚｒ２ＳｉｘＰ（３−ｘ）Ｏ１２（１≦ｘ≦３）が好ましく、ナトリウムイオン伝導体としては、Ｎａ−βアルミナ：Ｎａ２Ｏ・ｘＡｌ２Ｏ３（９≦ｘ≦１１）、又はＮａ−β”アルミナ：Ｎａ２Ｏ・ｘＡｌ２Ｏ３（４≦ｘ≦６）が好ましい。また、リチウムイオン伝導体としては、Ｌｉ（１＋ｘ）ＡｌｘＭ（２−ｘ）Ｐ３Ｏ１２（Ｍ＝Ｔｉ，Ｇａ；０≦ｘ≦１）が好ましい。一方、電極層となる亜酸化窒素分解触媒としては、スピネル型酸化物ＣｏＡｌ２Ｏ４ を使用する。 The cation conductor as the electrolyte, uses sodium super ionic conductor, sodium ion conductor, or a lithium ion conductor. As the sodium superionic conductor, Na (1 + x) Zr 2 Si x P (3-x) O 12 (1 ≦ x ≦ 3) is preferable, and as the sodium ion conductor, Na-β alumina: Na 2 O · xAl 2 O 3 (9 ≦ x ≦ 11) or Na-β ″ alumina: Na 2 O.xAl 2 O 3 (4 ≦ x ≦ 6) is preferable. As the lithium ion conductor, Li (1 + x) Al x M (2-x) P 3 O 12 (M = Ti, Ga; 0 ≦ x ≦ 1) is preferable, while the nitrous oxide decomposition catalyst serving as the electrode layer is a spinel oxide CoAl 2 O 4. Is used .
以上説明した本発明のＮ２Ｏガスセンサは、陽イオン伝導体の板を製作し、その上に亜酸化窒素分解触媒の金属酸化物電極層を形成するという簡単な方法で製造でき、出来上がったセンサの構成も簡単であるため、従来のＮ２Ｏガスセンサに比べて安価に提供できる。 The N 2 O gas sensor of the present invention described above can be manufactured by a simple method in which a cation conductor plate is manufactured and a metal oxide electrode layer of a nitrous oxide decomposition catalyst is formed thereon. Since this configuration is also simple, it can be provided at a lower cost than conventional N 2 O gas sensors.
以上のように本発明によれば、安価なＮ２Ｏガスセンサが実現可能であり、かつ測定値へのＣＯ２濃度の影響を小さくすることができる。 As described above, according to the present invention, an inexpensive N 2 O gas sensor can be realized, and the influence of the CO 2 concentration on the measurement value can be reduced.
以下、実施例に基づき本発明に係るセンサの実施の形態について説明する。ただし、本発明はこの実施例に限定されるものではない。 Embodiments of a sensor according to the present invention will be described below based on examples. However, the present invention is not limited to this embodiment.
図１は、本発明に係るセンサの構造を示す側面断面図である。同図に示すように、本発明に係るセンサは、陽イオン伝導体（実施例ではナトリウム超イオン伝導体）からなる電解質１の上に亜酸化窒素分解触媒（実施例ではスピネル型酸化物ＣｏＡｌ２Ｏ４）からなる電極層２を形成して構成されるものである。
FIG. 1 is a side sectional view showing a structure of a sensor according to the present invention. As shown in the figure, the sensor according to the present invention has a nitrous oxide decomposition catalyst (a spinel oxide CoAl 2 in the embodiment) on an electrolyte 1 made of a cation conductor (a sodium superionic conductor in the embodiment). The
まず、図１に示すような本発明に係るセンサの製造方法の一例を示す。 First, an example of a method for manufacturing a sensor according to the present invention as shown in FIG. 1 will be described.
本発明に用いるナトリウム超イオン伝導体の原料としてケイ酸エチル（（Ｃ２Ｈ５）４ＳｉＯ４）、ケイ酸ナトリウム９水和物（Ｎａ２ＳｉＯ３・９Ｈ２Ｏ）、リン酸二水素アンモニウム（（ＮＨ４）Ｈ３ＰＯ４）およびオキシ硝酸ジルコニウム２水和物（ＺｒＯ（ＮＯ３）２・２Ｈ２Ｏ）を用いた。これらを混合して２時間攪拌し、７５℃に加温して水分を蒸発させ、得られた残渣物を１２０℃で一晩置いて乾燥させた。このようにして得られた固形物を７５０℃で１時間焼結し、その後４時間粉砕して粉末を得た。 As a raw material of the sodium superionic conductor used in the present invention, ethyl silicate ((C 2 H 5 ) 4 SiO 4 ), sodium silicate nonahydrate (Na 2 SiO 3 .9H 2 O), ammonium dihydrogen phosphate ( (NH 4 ) H 3 PO 4 ) and zirconium oxynitrate dihydrate (ZrO (NO 3 ) 2 .2H 2 O) were used. These were mixed and stirred for 2 hours, warmed to 75 ° C. to evaporate the water, and the resulting residue was left at 120 ° C. overnight to dry. The solid material thus obtained was sintered at 750 ° C. for 1 hour and then pulverized for 4 hours to obtain a powder.
この粉末を５２０ＭＰａでプレスし、１０００℃で６時間焼成して、ナトリウム超イオン伝導体Ｎａ３Ｚｒ２Ｓｉ２ＰＯ１２の板を得た。 This powder was pressed at 520 MPa and fired at 1000 ° C. for 6 hours to obtain a plate of sodium superionic conductor Na 3 Zr 2 Si 2 PO 12 .
次に、エチレングリコールに硝酸コバルト、硝酸アルミニウムおよびクエン酸を混合した液を、上記方法により製作したナトリウム超イオン伝導体の板の上に毎分４０００回転のスピンコート法により塗布する。その後、１２０℃で１０時間乾燥させ、次いで５５０℃で２時間仮焼して、ナトリウム超イオン伝導体Ｎａ３Ｚｒ２Ｓｉ２ＰＯ１２の板片面にスピネル型酸化物ＣｏＡｌ２Ｏ４の薄膜を有するセンサを得た。 Next, a solution obtained by mixing ethylene glycol with cobalt nitrate, aluminum nitrate and citric acid is applied onto the sodium superionic conductor plate produced by the above method by a spin coating method at 4000 rpm. Then, it is dried at 120 ° C. for 10 hours, and then calcined at 550 ° C. for 2 hours to have a thin film of spinel oxide CoAl 2 O 4 on one surface of the sodium superionic conductor Na 3 Zr 2 Si 2 PO 12. I got a sensor.
このセンサは、Ｎ２Ｏガス濃度に応じて電解質１と電極層２との間に起電力を発生するため、この起電力を公知の方法により測定することにより、Ｎ２Ｏガス濃度を知ることができる。
This sensor, for generating an electromotive force between the electrolyte 1 and the
実施例では、図２に示すように、上記方法で得られたセンサの電極層２に金メッシュを設置して試験電極３とし、参照極４として電解質１に白金黒および白金メッシュを設置し、測定装置とした。
In the example, as shown in FIG. 2, a gold mesh is installed on the
上記測定装置の試験電極３に被検知ガスとして微量のＮ２Ｏ又はＣＯ２を含む窒素（Ｎ２）ガスを、参照極４には空気をそれぞれ供給し、被検知ガスの種類および濃度を変化させて電極電位（４００℃における試験電極と参照極の電位差ΔＥ（ｍＶ））を測定した。 Nitrogen (N 2 ) gas containing a very small amount of N 2 O or CO 2 is supplied to the test electrode 3 of the measuring device, and air is supplied to the reference electrode 4 to change the type and concentration of the detected gas. The electrode potential (potential difference ΔE (mV) between the test electrode and the reference electrode at 400 ° C.) was measured.
その結果を表１に示す。
表１から、本発明のセンサの電極電位はＮ２Ｏ濃度に依存するが、ＣＯ２濃度の影響は小さいことがわかる。 From Table 1, it can be seen that the electrode potential of the sensor of the present invention depends on the N 2 O concentration, but the influence of the CO 2 concentration is small.
本発明のセンサを用いれば、高性能のＮ２Ｏ濃度測定装置を安価に製造することができ、環境中のＮ２Ｏ濃度を測定するため等に利用可能である。 By using the sensor of the present invention, a high-performance N 2 O concentration measuring device can be manufactured at low cost and can be used for measuring the N 2 O concentration in the environment.
１ 電解質
２ 電極層
３ 試験電極
４ 参照電極
1
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