JP3793065B2 - Hydrocarbon sensor and manufacturing method thereof - Google Patents

Description

【００５６】
なお、表１中、Ａｕ_nＡｌ_mとは、ＡｕＡｌ₂以外のＡｕ−Ａｌ合金を意味する。
【００５７】
表１に示した（水素中の電流出力）／（空気中の電流出力）の比が大きいほど、炭化水素センサの電極の酸素ブロッキング性能が高いことを示す。また、表１に示した熱サイクル後の電流出力変化は、その値が小さいほど、熱サイクルの影響を受けにくく信頼性が高い炭化水素センサであることを示す。
【００５８】
表１から明らかなように、電極中の初期の単体Ａｌ（単体金属であるＡｌ）の含有率が７モル％以下の炭化水素センサは、熱サイクルの影響を受けにくく信頼性が高いことがわかった。電極中の単体Ａｌは、使用時の熱サイクルなどによって徐々に酸化されて酸化アルミニウム（Ａｌ₂Ｏ₃）となる場合がある。したがって、そのような状態を考慮すると、電極中の単体Ａｌの含有率をａモル％とし、電極中の酸化アルミニウムの含有率をｂモル％としたときに、ａ＋２ｂ≦７の関係を満たすような電極を用いることによって、熱サイクルの影響を受けにくく信頼性が高い炭化水素センサが得られる。
【００５９】
また、表１から、電極中のＡｕＡｌ₂の含有率が高いほど、酸素ブロッキング特性が良好であることがわかった。特に、電極が、ＡｕＡｌ₂と単体ＡｕとをＡｕＡｌ₂：Ａｕ＝Ｘ：１−Ｘ（ただし、０．６≦Ｘ）のモル比となるように含む場合には、酸素ブロッキング特性が非常に良好であった。
【００６０】
なお、実施例１では、基板としてＢａＺｒ_0.6Ｃｅ_0.2Ｇｄ_0.2Ｏ_{3- α}からなる基板を用いた場合について説明したが、ＢａＺｒ_0.4Ｃｅ_0.4Ｉｎ_0.2Ｏ_{3- α}からなる基板を用いても同様の結果が得られた。
【００６１】
（実施例２）
実施例２では、実施形態２で説明した炭化水素センサ２０を製造した一例について説明する。
【００６２】
まず、縦横１０ｍｍ×１０ｍｍで厚さ０．４５ｍｍのプロトン伝導体（ＢａＺｒ_0.6Ｃｅ_0.2Ｇｄ_0.2Ｏ_{3- α}焼結体）からなる基板（基板２１に相当）に、Ａｕ−Ａｌ系の電極（電極２２に相当）を焼き付けた試料を準備した。Ａｕ−Ａｌ系電極には、表１のＮｏ．２の組成を有する電極とＮｏ．４の組成を有する電極とを用いた。リード線には、耐熱性および耐食性の高い直径０．１５ｍｍのＰｔリード線（リード線２３ａおよび２３ｂに相当）を用いた。そして、リード線と電極とをさまざまな金属ペースト（導電性接着剤２４ａおよび２４ｂに相当）で焼成接着した。
【００６３】
このようにして得られた炭化水素センサについて、４．９×１０^-2Ｎ（５ｇｆ）の力でリード線を引っ張って、リード線と電極との接着強度を調べた。また、室温−８００℃のサイクルを１２０回行う熱サイクル試験を行ったのち、同様の方法でリード線と電極との接着強度を調べた。結果を表２に示す。
【００６４】
【表２】

【００６５】
なお、表２中、○は引っ張り試験で剥がれや断線が生じなかった場合を示し、×は引っ張り試験で剥がれや断線が生じた場合を示す。また、表２中、ＴＲ１４０、ＴＲ１２０６およびＭＨ２０１４は田中貴金属株式会社製の金属ペーストの品番であり、Ｎ−２７６４、Ａ−３３６０、Ｕ３４００、Ｕ３８２０およびＡ−３４４４はＮＥケムキャット製の金属ペーストの品番であり、９２０３Ｃはノリタケカンパニー製の金属ペーストの品番である。
【００６６】
表２から明らかなように、金属ペーストがＰｔおよびＡｕを含む場合、ならびに、金属ペーストがＡｕおよびＡｌを含む場合には、Ａｕ−Ａｌ系電極とリード線との接着強度が高いことがわかった。このように、実施形態２の炭化水素センサによれば、接触不良や断線がなく、信頼性が高い炭化水素センサが得られる。
【００６７】
なお、本発明の炭化水素センサは、ペーストの溶剤、バインダーなどの微量副成分や粒度、および焼成条件などについて、本実施例のものに限定されない。実施例２では、Ａｕ／Ａｌ、Ｐｔ／Ａｕの各々の成分を混合したものを２種類ずつ挙げたが、その混合比はどのような混合比でもよく、Ｐｔ：９９モル％／Ａｕ：１モル％の混合比でもよい。また、市販ペーストの組み合わせもどのような組み合わせでもよい。もちろん接着剤の構造、形状はどんなものでもよい。また、電極の組成や成分も、本実施例の例に限定されない。
【００６８】
（実施例３）
実施例３では、実施形態３で説明した製造方法で炭化水素センサを製造した一例について説明する。
【００６９】
まず、プロトン伝導体（ＢａＺｒ_0.6Ｃｅ_0.2Ｇｄ_0.2Ｏ_{3- α}焼結体）からなる基板（基板３１に相当）を用意し、この基板上にＡｕ粒子とＡｌ粒子とを含むペーストを塗布してペースト層（層３２に相当）を形成した。このとき、Ａｕペースト（田中貴金属株式会社：ＴＲ１２０６）とＡｌペースト（ノリタケカンパニー：９２０３Ｃ）とを、混合比を変えて混合することによって、Ａｕ粒子とＡｌ粒子とを含むペーストを調整した。このとき、ＡｕＡｌ₂を多く形成するため、ＡｕＡｌ₂の化学量論比の近傍となるような割合でＡｕペーストとＡｌペーストとを混合した。
【００７０】
その後、焼成条件を変化させて塗布したペーストを焼成（焼き付け）し、電極を形成した。このようにして得られた電極の組成を分析した。得られた結果を表３に示す。
【００７１】
【表３】

【００７２】
なお、表３中、Ｎｏ．４３の３％Ｈ₂とは、３ｖｏｌ％の水素を含んだ窒素雰囲気を意味する。
【００７３】
表３から明らかなように、Ａｕ粒子とＡｌ粒子とを含むペーストを焼成することによって、ＡｕとＡｌとを含む金属によって構成された電極を形成できた。また、ペーストを無酸素雰囲気下で焼成することによって、電極に含まれるＡｕＡｌ₂の含有率を高くすることができた。特に、上述のＡｕペースト（ＴＲ１２０６）およびＡｌペースト（９２０３Ｃ）を用いる場合、混合後のペーストが、Ａｕ粒子とＡｌ粒子とを、重量比でＹ：１−Ｙ（ただし、０．５４≦Ｙ≦０．６）の割合で含む場合には、ＡｕＡｌ₂の含有率を特に高くすることができた。
【００７４】
なお、表３の例では、ＡｕペーストとＡｌペーストを、ＡｕとＡｌとが７８：２２、６０：４０、５７：４３、５４：４６の重量比となるように混合し、８５０℃または９００℃で焼成する場合を示した。しかし、本発明は、上述したペーストの混合比や、焼成条件には限定されない。
【００７５】
次に、実施形態３で説明した製造方法について、特にリード線接続工程の条件を変えて炭化水素センサを製造した一例について説明する。
【００７６】
まず、表３のＮｏ．３６またはＮｏ．３８の条件で、プロトン伝導体（ＢａＺｒ_0.6Ｃｅ_0.2Ｇｄ_0.2Ｏ_{3- α}焼結体）からなる基板上に電極（カソード）を形成した。その後、Ｐｔからなるリード線と電極とを、導電性接着剤を用いて接続した。このとき、導電性接着剤と焼成条件とが異なる複数のサンプルを作製した。得られたサンプルについて、室温−８００℃のサイクルを１２０回行う熱サイクル試験を行った。各サンプルについて、熱サイクル前後におけるリード線と電極との接着強度を実施例２と同様の方法で評価した。評価結果を表４に示す。
【００７７】
【表４】

【００７８】
なお、表４中、Ｎｏ．４４およびＮｏ．４５では、電極の成分と、導電性接着剤に含まれる金属の成分とが等しい。
【００７９】
表４から明らかなように、無酸素雰囲気下で導電性接着剤の焼成を行うことによって、リード線と電極との初期および熱サイクル後の接着強度を高くすることができ、信頼性が高い炭化水素センサを製造できた。
【００８０】
実施例３では、ＢａＺｒ_0.6Ｃｅ_0.2Ｇｄ_0.2Ｏ_{3- α}からなる基板を用いた場合について説明したが、ＢａＺｒ_0.4Ｃｅ_0.42Ｉｎ_0.2Ｏ_{3- α}からなる基板を用いても同様の結果が得られた。
【００８１】
また、表４の例では、市販のペーストを用いてさまざまな雰囲気下で８５０℃で焼成してリード線と電極とを接続した。しかし、本発明は、上述した焼成温度や、ペーストの種類には限定されない。たとえば、焼成温度は、９００℃でもよい。また、表４の例では材料および混合比が異なる７種類の混合ペーストを用いたが、本発明は表４の例に限定されず、たとえば、Ｐｔ：９９モル％／Ａｕ：１モル％の混合比でもよい。また、電極はＡｕ−Ａｌ系の電極であれば実施例以外のものでもよい。
【００８２】
以上、本発明の実施の形態について例を挙げて説明したが、本発明は、上記実施の形態に限定されず本発明の技術的思想に基づき他の実施形態に適用することができる。
【００８３】
【発明の効果】
以上説明したように、本発明の第１の炭化水素センサによれば、酸素の影響を受けにくく、熱による特性劣化が生じにくい炭化水素センサが得られる。
【００８４】
また、本発明の第２の炭化水素センサによれば、電極の剥離やリード線の断線が生じにくく、信頼性が高い炭化水素センサが得られる。
【００８５】
また、本発明の炭化水素センサの第１の製造方法によれば、酸素の影響を受けにくい炭化水素センサを容易に製造できる。特に、電極を無酸素雰囲気中で形成することによって、酸素ブロッキング特性が特に高い炭化水素センサを製造できる。
【００８６】
また、本発明の炭化水素センサの第２の製造方法によれば、、酸素による影響を受けにくく、熱による特性劣化が生じにくく、さらにリード線と電極との接着強度が高い炭化水素センサを容易に製造できる。
【００８７】
本発明によって得られる炭化水素センサは、たとえば、３００℃から高温（たとえば８００℃）までの温度領域における炭化水素の検知および濃度測定に用いることができる。具体的には、住環境の炭化水素の検知、車のエンジンや、ストーブ、触媒燃焼機器の排ガス中の炭化水素の検知が可能であり、燃焼機関・機器の燃焼制御（リーンバーン）用として利用できる。
【図面の簡単な説明】
【図１】 本発明の炭化水素センサについて一例を示す（ａ）平面図および（ｂ）断面図である。
【図２】 本発明の炭化水素センサについて他の一例を示す（ａ）平面図および（ｂ）断面図である。
【図３】 本発明の炭化水素センサの製造方法について一例を示す工程断面図である。
【符号の説明】
１０、２０ 炭化水素センサ
１１、２１、３１ 基板
１２、２２、３３ 電極
１２ａ、２２ａ、３３ａ カソード
１２ｂ、２２ｂ、３３ｂ アノード
２３ａ、２３ｂ、３４ａ、３４ｂ リード線
２４ａ、２４ｂ、３５ａ、３５ｂ 導電性接着剤
３２、３２ａ、３２ｂ 層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hydrocarbon sensor and a method for manufacturing the same.
[0002]
[Prior art]
Hydrocarbon sensors can detect hydrocarbon gas in the living environment, and can detect hydrocarbons in exhaust gas from automobile engines, heating stoves, and catalytic combustion equipment. What can be used for (burn) is known.
[0003]
As a sensor for measuring or detecting hydrocarbons, a hydrocarbon sensor including a thin substrate made of a proton conductor, which is a solid electrolyte, and two electrode layers made of platinum arranged on both sides of the substrate so as to face each other. Are known. In this hydrocarbon sensor, hydrocarbons in the atmosphere to be measured dissociate at the anode to generate protons. This proton moves through a substrate made of an electrolyte. The sensor detects this proton as a voltage or a current flowing between the electrodes.
[0004]
In order to use this hydrocarbon sensor in a combustion engine or combustion equipment, a proton conductor made of an oxide that can be used at room temperature or higher is required. In recent years, as a proton conductor made of an oxide, CaZr which is a calcium zirconium oxide is used._0.9In_0.1O_{3- α}(However, α represents oxygen deficiency. The same applies hereinafter.) Has been developed and is being applied to hydrocarbon sensors.
[0005]
However, the above-mentioned calcium-zirconium-based oxide has low proton conductivity (for example, about 5 × 10 5 at 600 ° C.^-FourS / cm). Therefore, the inventors have proposed a limiting current type (constant potential electrolysis type) hydrocarbon sensor using a barium cerium-based oxide exhibiting high proton conductivity (see Japanese Patent Laid-Open No. 10-300718). This sensor responded well to hydrocarbons, and was able to detect hydrocarbons on the order of several ppm to several percent almost linearly in the absence of oxygen.
[0006]
However, even in a sensor using a barium cerium oxide, when the hydrocarbon concentration is very small (for example, 10 ppm or less), the output of the sensor is affected by the oxygen concentration. This is because the barium cerium-based oxide has a property of conducting oxide ions, and the output of the sensor varies depending on oxygen taken in at the cathode. For this reason, the inventors have developed a sensor that uses a cathode mainly composed of metallic aluminum and prevents oxygen from entering at the cathode (see JP-A-11-337518). The effect of the cathode containing metallic aluminum was enormous, and even when oxygen of a constant concentration was mixed with the gas to be measured, the output did not increase at all.
[0007]
[Problems to be solved by the invention]
However, even with the above sensor, there is a problem that the ability to detect hydrocarbons decreases when the oxygen concentration is high. When purifying exhaust gas from an automobile engine with a catalyst, if the performance of the catalyst deteriorates, a high concentration hydrocarbon (HC) component and a high concentration oxygen will be contained in the exhaust gas. Therefore, the conventional sensor does not have sufficient characteristics as a sensor for detecting deterioration of the exhaust gas purification catalyst. In addition, when measuring hydrocarbons in exhaust gas, since the temperature change is severe, a sensor that is resistant to thermal cycling is required. In the case of a conventional sensor using an electrode containing Al, Al forms a non-conductor during the thermal cycle and deteriorates the characteristics.
[0008]
In order to solve the above problems, a first object of the present invention is to provide a hydrocarbon sensor that is not easily affected by oxygen and is less susceptible to deterioration of characteristics due to heat.
[0009]
The second object of the present invention is to provide a method for producing a hydrocarbon sensor that is not easily affected by oxygen.
[0010]
Further, in the conventional hydrocarbon sensor, Pt or Au has been used alone as a conductive adhesive between the electrode and the output lead wire. However, such a conventional hydrocarbon sensor has a problem in that electrode peeling or lead wire breakage easily occurs. In order to solve the above problems, a third object of the present invention is to provide a highly reliable hydrocarbon sensor.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, a first hydrocarbon sensor of the present invention is a hydrocarbon sensor comprising a substrate made of a solid electrolyte that conducts protons and a pair of electrodes formed on the surface of the substrate. At least one of the electrodes includes Au and Al, the content of simple Al (aluminum which is a simple metal) in the at least one electrode is a mol%, and the oxidation in the at least one electrode Aluminum (Al₂O_Three) Content is b mol%, a and b satisfy the relationship of a + 2b ≦ 7. According to the first hydrocarbon sensor, it is possible to obtain a hydrocarbon sensor that is not easily affected by oxygen and that is less susceptible to deterioration of characteristics due to heat.
[0012]
In the first hydrocarbon sensor, the at least one electrode is AuAl₂At least one metal selected from an alloy and simple substance Au (gold which is a simple metal) may be contained in a proportion of 50 mol% or more. That is, the at least one electrode is AuAl₂When both the alloy and the simple substance Au are included, they may be included so that the sum of both is 50 mol% or more. Metals having these compositions have a high melting point, and an electrode having high heat resistance can be obtained.
[0013]
In the first hydrocarbon sensor, the at least one electrode is AuAl₂And simple substance Au, AuAl₂: Au = X: 1-X (provided that the molar ratio is 0.6 ≦ X ≦ 1). According to this configuration, a hydrocarbon sensor including an electrode with particularly high oxygen blocking performance can be obtained.
[0014]
The second hydrocarbon sensor of the present invention is a hydrocarbon comprising a substrate made of a solid electrolyte that conducts protons, a pair of electrodes formed on the surface of the substrate, and lead wires connected to the electrodes. In the sensor, at least one of the pair of electrodes includes Au and Al, and the at least one electrode and the lead wire include a conductive adhesive including Pt and Au, or Al and Au. They are connected by a conductive adhesive. According to the second hydrocarbon sensor, a highly reliable hydrocarbon sensor can be obtained, which is less likely to cause electrode peeling or lead wire breakage.
[0015]
In the second hydrocarbon sensor, the at least one electrode and the lead wire are connected by a conductive adhesive containing Al and Au, and the component of the at least one electrode and the conductive adhesive are connected to each other. The component of the metal contained may be equal. According to this configuration, the electrode and the conductive adhesive are integrated to obtain stronger adhesive strength.
[0016]
The first method for producing a hydrocarbon sensor of the present invention is a method for producing a hydrocarbon sensor comprising a substrate made of a solid electrolyte that conducts protons, and an electrode formed on a surface of the substrate. The method includes forming the electrode including an alloy of Au and Al by applying and baking a paste including Au particles and Al particles thereon. According to the first manufacturing method, it is possible to easily manufacture a hydrocarbon sensor that is not easily affected by oxygen.
[0017]
In the first manufacturing method, the content of simple Al in the electrode immediately after firing may be 7 mol% or less. According to this configuration, it is possible to manufacture a hydrocarbon sensor that is unlikely to deteriorate in characteristics due to heat.
[0018]
In the first manufacturing method, the firing may be performed in an oxygen-free atmosphere. According to this configuration, a hydrocarbon sensor having particularly high oxygen blocking characteristics can be manufactured.
[0019]
In the first manufacturing method, the oxygen-free atmosphere may be an atmosphere made of at least one gas selected from nitrogen gas, argon gas, helium gas, and hydrogen gas.
[0020]
A second method for producing a hydrocarbon sensor according to the present invention includes a substrate made of a solid electrolyte that conducts protons, an electrode formed on a surface of the substrate, and a lead wire connected to the electrode. The method for manufacturing a hydrogen sensor includes a step of connecting the electrode and the lead wire with a conductive adhesive and firing in an oxygen-free atmosphere, wherein the electrode includes Au and Al. According to the second manufacturing method, it is possible to easily manufacture a hydrocarbon sensor that is not easily affected by oxygen, is not easily deteriorated in characteristics due to heat, and has high adhesive strength between the lead wire and the electrode.
[0021]
In the second manufacturing method, the conductive adhesive may be a conductive adhesive containing Pt and Au, or a conductive adhesive containing Al and Au. According to this configuration, it is possible to manufacture a hydrocarbon sensor having higher adhesion strength between the lead wire and the electrode.
[0022]
In the second manufacturing method, the oxygen-free atmosphere in the lead wire connecting step may be an atmosphere made of at least one gas selected from nitrogen gas, argon gas, helium gas, and hydrogen gas.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0024]
(Embodiment 1)
In the first embodiment, an example of the hydrocarbon sensor of the present invention will be described. FIG. 1A shows a plan view of the hydrocarbon sensor 10 according to the first embodiment, and FIG. 1B shows a cross-sectional view taken along line XX in FIG.
[0025]
Referring to FIGS. 1A and 1B, a hydrocarbon sensor 10 includes a substrate 11 made of a solid electrolyte that conducts protons, and a pair of electrodes 12 formed on the surface of the substrate 11. The hydrocarbon sensor 10 includes a lead wire connected to the electrode 12 as necessary. It is preferable to use what is demonstrated in the following Embodiment 2 for the conductive adhesive and lead wire at this time.
[0026]
The substrate 11 is made of a solid electrolyte that conducts at least protons. For example, BaCe_0.8Gd_0.2O_{3- α}And BaCe_0.8Y_0.2O_{3- α}Barium cerium oxide such as BaZr_0.8Y_0.2O_{3- α}Barium zirconium oxide or BaZr_0.6Ce_0.2Gd_0.2O_{3- α}And BaZr_0.4Ce_0.4In_0.2O_{3- α}A substrate made of a barium zirconium cerium-based oxide can be used. Here, α represents oxygen deficiency. α is a value such that the positive charge and the negative charge in the solid electrolyte are substantially equal. For example, BaCe_0.8Gd_0.2O_{3- α}In this case, since Ba is a divalent positive ion, Ce is a tetravalent positive ion, Gd is a trivalent positive ion, and oxygen is a divalent negative ion, α = 3- (2 + 0.8 * 4 + 0 .2 * 3) /2≈0.1.
[0027]
The pair of electrodes 12 includes a cathode 12a and an anode 12b. At least one electrode selected from the cathode 12a and the anode 12b (hereinafter also referred to as electrode A) includes Au and Al. In particular, the cathode 12a preferably contains Au and Al, that is, the electrode A.
[0028]
The electrode A preferably satisfies the relationship of a + 2b ≦ 7 when the content of simple Al (Al, which is a simple metal) in the electrode A is a mol% and the aluminum oxide in the electrode A is b mol%. Satisfies the relationship of a + 2b ≦ 5. The smaller the value of a + 2b, the better. The electrode A satisfying the relationship of a + 2b ≦ 7 is, for example, TR1206 (Au paste manufactured by Tanaka Kikinzoku Co., Ltd.) and 9203C (Al paste manufactured by Noritake Co.) at a weight ratio of 57:43 or 54:46. It can be formed by mixing and firing.
[0029]
The electrode A is AuAl₂It is preferable that at least one metal selected from an alloy and simple substance Au is contained in a proportion of 50 mol% or more, and more preferably 75 mol% or more. AuAl₂Higher contents of the alloy and the simple substance Au are more preferable. In this case, the electrode A is AuAl₂And simple substance Au, AuAl₂: Au = X: 1-X (provided that the molar ratio is 0.6 ≦ X ≦ 1).
[0030]
When either the cathode 12a or the anode 12b is not the electrode A containing Au and Al, for example, an electrode made of Pt or an electrode made of Au can be used as the electrode.
[0031]
The electrode 12 can be formed using, for example, a method of applying and baking a metal paste, a solid phase method, a vapor phase film forming method such as sputtering or CVD, or a liquid phase film forming method such as plating.
[0032]
Since the hydrocarbon sensor 10 of Embodiment 1 includes the electrode A containing Au and Al, the performance of blocking oxygen with the electrode is high. Therefore, the hydrocarbon sensor 10 is not easily affected by oxygen. Moreover, since the hydrocarbon sensor 10 has a small amount of simple substance Al in the electrode A, the characteristic deterioration due to heat hardly occurs.
[0033]
(Embodiment 2)
Embodiment 2 demonstrates another example about the hydrocarbon sensor of this invention. FIG. 2A shows a plan view of the hydrocarbon sensor 20 according to the second embodiment, and FIG. 2B shows a cross-sectional view taken along line YY in FIG. 2A.
[0034]
2 (a) and 2 (b), a hydrocarbon sensor 20 according to Embodiment 2 includes a substrate 21 made of a solid electrolyte that conducts protons, and a pair of electrodes 22 (cathode 22a) formed on the substrate 21. And lead wires 23a and 23b connected to the cathode 22a and the anode 22b, respectively.
[0035]
As the substrate 21, a substrate similar to the substrate 11 of Embodiment 1 can be used.
[0036]
At least one electrode selected from the cathode 22a and the anode 22b (hereinafter sometimes referred to as an electrode B) contains Au and Al. Specifically, an electrode similar to the electrode A described in Embodiment 1 can be used. When either the cathode 22a or the anode 22b does not contain Au and Al, for example, an electrode made of Pt or an electrode made of Au can be used as the electrode.
[0037]
For the lead wire 23a and the lead wire 23b, for example, a lead wire made of a metal such as Pt, Au, or Ag can be used.
[0038]
The cathode 22a and the anode 22b are connected to the lead wire 23a and the lead wire 23b by conductive adhesives 24a and 24b, respectively.
[0039]
A metal paste can be used for the conductive adhesives 24a and 24b. Here, the metal paste is obtained by adding a binder, a resin, a solvent, or the like to particles made of metal as necessary (the same applies to the following metal paste). For example, polyvinyl alcohol (poly (vinyl alcohol): PVA) or polyvinyl chloride (PVC) can be used as the resin. For example, terpineol or butyl acetate can be used as the solvent.
[0040]
Of the conductive adhesives 24a and 24b, a conductive adhesive that connects the electrode B and the lead wire (hereinafter, also referred to as a conductive adhesive B) is a conductive adhesive containing Pt and Au, or A conductive adhesive containing Al and Au. Specifically, for example, a conductive adhesive containing Pt and Au as main components (including Pt and Au in a total amount of 50 mol% or more), and Al and Au as main components (Al and Au). Can be used in a total amount of 50 mol% or more). More specifically, for example, a metal paste containing Pt particles and Au particles or a metal paste containing Al particles and Au particles can be used. Here, when a conductive adhesive containing Al and Au is used as the conductive adhesive B, it is preferable that the component and composition of the electrode B and the component and composition of the metal contained in the conductive adhesive B are equal.
[0041]
In the hydrocarbon sensor 20 of the second embodiment, the conductive adhesive B that connects the electrode B containing Au and Al and the lead wire contains Pt and Au, or Al and Au. Therefore, according to the hydrocarbon sensor 20, as will be described in the following examples, a hydrocarbon sensor having high adhesion strength between the electrode and the lead wire and high reliability can be obtained.
[0042]
(Embodiment 3)
In Embodiment 3, an example of the method for producing a hydrocarbon sensor of the present invention will be described. The production method of the present invention is a method for producing a hydrocarbon sensor comprising a substrate made of a solid electrolyte that conducts protons, an electrode formed on the surface of the substrate, and a lead wire connected to the electrode. The manufacturing process of the manufacturing method of Embodiment 3 is shown in FIG.
[0043]
In this manufacturing method, first, as shown in FIG. 3A, two layers 32 (layer 32a and layer 32b) are formed by applying a paste to both surfaces (surfaces) of the substrate 31. As the substrate 31, a substrate similar to the substrate 11 described in Embodiment 1 can be used.
[0044]
At least one layer selected from the layer 32a and the layer 32b is formed of a paste containing Au particles and Al particles (hereinafter also referred to as paste C). When either the layer 32a or the layer 32b is not formed by a paste containing Au particles and Al particles, for example, it is formed by a paste containing only Au particles or a paste containing only Pt particles. These layers can be formed by, for example, a screen printing method. The thickness of these layers is, for example, about 10 μm.
[0045]
The paste C can be formed, for example, by mixing an Au paste containing Au particles and an Al paste containing Al particles.
[0046]
Thereafter, the substrate 31 on which the layers 32a and 32b are formed is baked to form a pair of electrodes 33 (a cathode 33a and an anode 33b) on the substrate 31, as shown in FIG. This firing step is preferably performed in an oxygen-free atmosphere. Examples of the oxygen-free atmosphere include an atmosphere composed of at least one gas selected from nitrogen gas, argon gas, helium gas, and hydrogen gas. At least one electrode selected from the cathode 33a and the anode 33b is an electrode containing Au and Al.
[0047]
In this way, a hydrocarbon sensor can be manufactured. In addition, after the process of FIG.3 (b), as shown in FIG.3 (c), the lead wire connection which connects the electrodes 33a and 33b and the lead wires 34a and 34b with the conductive adhesives 35a and 35b, respectively. A process may be included. This lead wire connecting step is preferably performed by connecting the electrode 33 and the lead wire 34 with a conductive adhesive 35 and firing in an oxygen-free atmosphere. Examples of the oxygen-free atmosphere at this time include an atmosphere made of at least one gas selected from nitrogen gas, argon gas, helium gas, and hydrogen gas.
[0048]
As the conductive adhesive 35, a general metal paste can be used, but it is preferable to use the conductive adhesive B described in the second embodiment. Specifically, it is preferable to use a conductive adhesive containing Pt and Au or a conductive adhesive containing Al and Au.
[0049]
In the manufacturing method of Embodiment 3, an electrode containing Au and Al can be easily formed by using a paste containing Au particles and Al particles. Therefore, according to the manufacturing method of Embodiment 3, it is possible to easily manufacture a hydrocarbon sensor including an electrode with high oxygen blocking performance. In addition, in the manufacturing method of Embodiment 3, by forming a metal paste in an oxygen-free atmosphere to form an electrode, as described in the following examples, AuAl₂A hydrocarbon sensor having an electrode with a high content of oxygen and a particularly high oxygen blocking performance can be produced.
[0050]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. In addition, this invention is not limited to the conditions of a following example.
[0051]
(Example 1)
In Example 1, an example in which the hydrocarbon sensor 10 described in Embodiment 1 is manufactured will be described.
[0052]
First, Au paste and Al paste were mixed at various ratios, and this was printed on one surface of a substrate made of a proton conductor (corresponding to the substrate 11) and baked to form an electrode (corresponding to the cathode 12a). Firing was performed at 850 ° C. in a nitrogen atmosphere. At this time, the substrate has BaZr_0.6Ce_0.2Gd_0.2O_{3- α}A substrate consisting of In addition, TR1206 manufactured by Tanaka Kikinzoku Co., Ltd. was used as the Au paste, and 9203C manufactured by Noritake Company was used as the Al paste. In Example 1, 17 types of samples were prepared by changing the ratio of Au paste and Al paste in a weight ratio of 78:22, 75:25,..., 51:49.
[0053]
After forming the electrode, the composition of the formed electrode was quantitatively analyzed by X-ray diffraction. Further, a hydrocarbon sensor was fabricated by baking a Pt electrode as an anode. About this hydrocarbon sensor, the thermal cycle test which repeats temperature rising / falling temperature 120 times between room temperature-800 degreeC was done. And the IV characteristic of the hydrocarbon sensor before and behind a thermal cycle was measured in the electric furnace which can control atmosphere, and the change by a thermal cycle was calculated about the electric current value at the time of 1.0V. Further, for the hydrocarbon sensor before the thermal cycle, the IV characteristics were measured in hydrogen and in air (oxygen-containing atmosphere), and the ratio of current values when a voltage of 1.0 V was applied was calculated.
[0054]
Electrode composition obtained by the above composition and AuAl in the electrode₂Table 1 shows the / Au ratio, the ratio of current values in hydrogen and air, and the amount of change in current value before and after thermal cycling.
[0055]
[Table 1]

[0056]
In Table 1, Au_nAl_mIs AuAl₂Other than Au—Al alloy.
[0057]
The larger the ratio of (current output in hydrogen) / (current output in air) shown in Table 1, the higher the oxygen blocking performance of the electrode of the hydrocarbon sensor. Moreover, the current output change after the thermal cycle shown in Table 1 indicates that the smaller the value is, the more reliable the hydrocarbon sensor is, which is less affected by the thermal cycle.
[0058]
As is apparent from Table 1, it is understood that a hydrocarbon sensor having an initial content of elemental Al (Al, which is an elemental metal) in the electrode of 7 mol% or less is less susceptible to thermal cycles and has high reliability. It was. The simple substance Al in the electrode is gradually oxidized by the thermal cycle at the time of use, and aluminum oxide (Al₂O_Three). Therefore, in consideration of such a state, when the content of simple Al in the electrode is a mol% and the content of aluminum oxide in the electrode is b mol%, the relationship of a + 2b ≦ 7 is satisfied. By using the electrode, it is possible to obtain a hydrocarbon sensor that is hardly affected by the thermal cycle and has high reliability.
[0059]
Also, from Table 1, AuAl in the electrode₂It was found that the higher the content of, the better the oxygen blocking property. In particular, the electrode is AuAl₂And simple substance Au and AuAl₂: Au = X: 1-X (provided that the molar ratio of 0.6 ≦ X) was included, the oxygen blocking property was very good.
[0060]
In Example 1, the substrate is BaZr._0.6Ce_0.2Gd_0.2O_{3- α}Although the case where the board | substrate which consists of was used was demonstrated, BaZr_0.4Ce_0.4In_0.2O_{3- α}Similar results were obtained using a substrate comprising
[0061]
(Example 2)
In Example 2, an example in which the hydrocarbon sensor 20 described in Embodiment 2 is manufactured will be described.
[0062]
First, a proton conductor (BaZr) having a length and width of 10 mm × 10 mm and a thickness of 0.45 mm._0.6Ce_0.2Gd_0.2O_{3- α}A sample in which an Au—Al-based electrode (corresponding to the electrode 22) was baked on a substrate (corresponding to the substrate 21) made of a sintered body was prepared. For the Au—Al-based electrode, No. 1 in Table 1 was used. No. 2 and No. 2 electrode. An electrode having a composition of 4 was used. As the lead wire, a Pt lead wire (corresponding to the lead wires 23a and 23b) having a diameter of 0.15 mm having high heat resistance and corrosion resistance was used. Then, the lead wire and the electrode were baked and bonded with various metal pastes (corresponding to the conductive adhesives 24a and 24b).
[0063]
About the hydrocarbon sensor obtained in this way, 4.9 × 10^-2The lead wire was pulled with a force of N (5 gf) to examine the adhesive strength between the lead wire and the electrode. Further, after conducting a thermal cycle test in which a cycle of room temperature to 800 ° C. was performed 120 times, the adhesion strength between the lead wire and the electrode was examined by the same method. The results are shown in Table 2.
[0064]
[Table 2]

[0065]
In Table 2, ○ indicates a case where peeling or disconnection did not occur in the tensile test, and × indicates a case where peeling or disconnection occurred in the tensile test. In Table 2, TR140, TR1206, and MH2014 are part numbers of metal paste manufactured by Tanaka Kikinzoku Co., Ltd., and N-2864, A-3360, U3400, U3820, and A-3444 are part numbers of metal paste made by NE Chemcat. Yes, 9203C is the product number of the metal paste manufactured by Noritake Company.
[0066]
As is clear from Table 2, it was found that when the metal paste contains Pt and Au, and when the metal paste contains Au and Al, the adhesive strength between the Au—Al-based electrode and the lead wire is high. . Thus, according to the hydrocarbon sensor of the second embodiment, a highly reliable hydrocarbon sensor without contact failure or disconnection can be obtained.
[0067]
In addition, the hydrocarbon sensor of the present invention is not limited to the one of this embodiment with respect to trace minor components such as paste solvent, binder, particle size, and firing conditions. In Example 2, two types of materials in which the respective components of Au / Al and Pt / Au were mixed were listed. The mixing ratio may be any mixing ratio, and Pt: 99 mol% / Au: 1 mol. % Mixing ratio may be used. Further, any combination of commercially available pastes may be used. Of course, the adhesive may have any structure and shape. Further, the composition and components of the electrode are not limited to the example of this embodiment.
[0068]
(Example 3)
In Example 3, an example in which a hydrocarbon sensor is manufactured by the manufacturing method described in Embodiment 3 will be described.
[0069]
First, proton conductor (BaZr_0.6Ce_0.2Gd_0.2O_{3- α}A substrate made of a sintered body (corresponding to the substrate 31) was prepared, and a paste containing Au particles and Al particles was applied on the substrate to form a paste layer (corresponding to the layer 32). At this time, a paste containing Au particles and Al particles was prepared by mixing Au paste (Tanaka Kikinzoku Co., Ltd .: TR1206) and Al paste (Noritake Company: 9203C) at different mixing ratios. At this time, AuAl₂To form a large amount of AuAl₂The Au paste and the Al paste were mixed at a ratio so as to be close to the stoichiometric ratio.
[0070]
Thereafter, the paste applied by changing the firing conditions was fired (baked) to form an electrode. The composition of the electrode thus obtained was analyzed. The obtained results are shown in Table 3.
[0071]
[Table 3]

[0072]
In Table 3, No. 43% 3% H₂Means a nitrogen atmosphere containing 3 vol% hydrogen.
[0073]
As is apparent from Table 3, an electrode composed of a metal containing Au and Al could be formed by firing a paste containing Au particles and Al particles. In addition, by baking the paste in an oxygen-free atmosphere, AuAl contained in the electrode₂The content of can be increased. In particular, when the above-described Au paste (TR1206) and Al paste (9203C) are used, the paste after mixing contains Au particles and Al particles in a weight ratio of Y: 1-Y (where 0.54 ≦ Y ≦ 0.6Al) if included at a rate of 0.6)₂The content of can be increased particularly.
[0074]
In the example of Table 3, Au paste and Al paste are mixed so that the weight ratio of Au and Al is 78:22, 60:40, 57:43, 54:46, and is 850 ° C. or 900 ° C. The case of firing with was shown. However, the present invention is not limited to the paste mixing ratio and firing conditions described above.
[0075]
Next, the manufacturing method described in the third embodiment will be described with respect to an example in which a hydrocarbon sensor is manufactured by changing the conditions of the lead wire connecting process.
[0076]
First, in Table 3, No. 36 or no. Under the condition of 38, the proton conductor (BaZr_0.6Ce_0.2Gd_0.2O_{3- α}An electrode (cathode) was formed on a substrate made of a sintered body. Thereafter, the lead wire made of Pt and the electrode were connected using a conductive adhesive. At this time, a plurality of samples having different conductive adhesives and firing conditions were produced. About the obtained sample, the thermal cycle test which performs a cycle of room temperature-800 degreeC 120 times was done. For each sample, the adhesive strength between the lead wire and the electrode before and after the thermal cycle was evaluated by the same method as in Example 2. The evaluation results are shown in Table 4.
[0077]
[Table 4]

[0078]
In Table 4, No. 44 and no. In 45, the electrode component is equal to the metal component contained in the conductive adhesive.
[0079]
As can be seen from Table 4, by firing the conductive adhesive in an oxygen-free atmosphere, the initial strength between the lead wire and the electrode and after the thermal cycle can be increased, and carbonization is highly reliable. A hydrogen sensor could be manufactured.
[0080]
In Example 3, BaZr_0.6Ce_0.2Gd_0.2O_{3- α}Although the case where the board | substrate which consists of was used was demonstrated, BaZr_0.4Ce_0.42In_0.2O_{3- α}Similar results were obtained using a substrate comprising
[0081]
Moreover, in the example of Table 4, it baked at 850 degreeC by various atmosphere using the commercially available paste, and the lead wire and the electrode were connected. However, the present invention is not limited to the above-described firing temperature and paste type. For example, the firing temperature may be 900 ° C. In the example of Table 4, seven types of mixed pastes having different materials and mixing ratios were used. However, the present invention is not limited to the example of Table 4, for example, Pt: 99 mol% / Au: 1 mol% It may be a ratio. Further, the electrode may be other than the embodiment as long as it is an Au—Al based electrode.
[0082]
Although the embodiments of the present invention have been described above by way of examples, the present invention is not limited to the above-described embodiments, and can be applied to other embodiments based on the technical idea of the present invention.
[0083]
【The invention's effect】
As described above, according to the first hydrocarbon sensor of the present invention, it is possible to obtain a hydrocarbon sensor that is not easily affected by oxygen and is less susceptible to deterioration of characteristics due to heat.
[0084]
Moreover, according to the 2nd hydrocarbon sensor of this invention, peeling of an electrode or disconnection of a lead wire does not arise easily, and a highly reliable hydrocarbon sensor is obtained.
[0085]
In addition, according to the first method for producing a hydrocarbon sensor of the present invention, a hydrocarbon sensor that is hardly affected by oxygen can be easily produced. In particular, by forming the electrode in an oxygen-free atmosphere, a hydrocarbon sensor with particularly high oxygen blocking characteristics can be manufactured.
[0086]
In addition, according to the second method for producing a hydrocarbon sensor of the present invention, a hydrocarbon sensor which is not easily affected by oxygen, hardly deteriorates in characteristics due to heat, and has high adhesion strength between a lead wire and an electrode can be easily obtained. Can be manufactured.
[0087]
The hydrocarbon sensor obtained by the present invention can be used for detection and concentration measurement of hydrocarbons in a temperature range from 300 ° C. to high temperature (for example, 800 ° C.), for example. Specifically, it can detect hydrocarbons in the living environment and can detect hydrocarbons in exhaust gas from car engines, stoves, and catalytic combustion equipment, and is used for combustion control (lean burn) of combustion engines and equipment. it can.
[Brief description of the drawings]
FIG. 1A is a plan view and FIG. 1B is a sectional view showing an example of a hydrocarbon sensor of the present invention.
2A is a plan view and FIG. 2B is a cross-sectional view showing another example of the hydrocarbon sensor of the present invention. FIG.
FIG. 3 is a process cross-sectional view illustrating an example of a method for producing a hydrocarbon sensor of the present invention.
[Explanation of symbols]
10, 20 Hydrocarbon sensor
11, 21, 31 Substrate
12, 22, 33 electrodes
12a, 22a, 33a Cathode
12b, 22b, 33b Anode
23a, 23b, 34a, 34b Lead wire
24a, 24b, 35a, 35b conductive adhesive
32, 32a, 32b layers

Claims (12)

In a hydrocarbon sensor comprising a substrate made of a solid electrolyte that conducts protons, and a pair of electrodes formed on the surface of the substrate,
At least one of the pair of electrodes includes Au and Al;
When the content of simple Al in the at least one electrode is a mol% and the content of aluminum oxide in the at least one electrode is b mol%, a and b have a relationship of a + 2b ≦ 7 A hydrocarbon sensor characterized by satisfying _2. The hydrocarbon sensor according to claim 1, wherein the at least one electrode includes at least one metal selected from AuAl ₂ alloy and elemental Au at a ratio of 50 mol% or more. Wherein at least one electrode, the AuAl ₂ and single _{Au, AuAl 2: Au = X} : 1-X ( provided that, 0.6 ≦ X ≦ 1) according to claim 2 containing as a molar ratio of Hydrocarbon sensor. In a hydrocarbon sensor comprising a substrate made of a solid electrolyte that conducts protons, a pair of electrodes formed on the surface of the substrate, and lead wires connected to the electrodes,
At least one of the pair of electrodes includes Au and Al;
The hydrocarbon sensor, wherein the at least one electrode and the lead wire are connected by a conductive adhesive containing Pt and Au or a conductive adhesive containing Al and Au. The at least one electrode and the lead wire are connected by a conductive adhesive containing Al and Au;
The hydrocarbon sensor according to claim 4, wherein a component of the at least one electrode is equal to a component of a metal contained in the conductive adhesive. In a method of manufacturing a hydrocarbon sensor comprising a substrate made of a solid electrolyte that conducts protons, and an electrode formed on the surface of the substrate,
A method for producing a hydrocarbon sensor, comprising: forming the electrode containing an alloy of Au and Al by applying and baking a paste containing Au particles and Al particles on the substrate. The method for producing a hydrocarbon sensor according to claim 6, wherein the content of simple Al in the electrode immediately after firing is 7 mol% or less. The method for producing a hydrocarbon sensor according to claim 6 or 7, wherein the firing is performed in an oxygen-free atmosphere. The method for producing a hydrocarbon sensor according to claim 8, wherein the oxygen-free atmosphere is an atmosphere made of at least one gas selected from nitrogen gas, argon gas, helium gas, and hydrogen gas. In a method for producing a hydrocarbon sensor comprising a substrate made of a solid electrolyte that conducts protons, an electrode formed on the surface of the substrate, and a lead wire connected to the electrode,
Connecting the electrode and the lead wire with a conductive adhesive and firing in an oxygen-free atmosphere,
A method for producing a hydrocarbon sensor, wherein the electrode contains Au and Al. The method for manufacturing a hydrocarbon sensor according to claim 10, wherein the conductive adhesive is a conductive adhesive containing Pt and Au, or a conductive adhesive containing Al and Au. The method for producing a hydrocarbon sensor according to claim 10 or 11, wherein the oxygen-free atmosphere is an atmosphere made of at least one gas selected from nitrogen gas, argon gas, helium gas, and hydrogen gas.

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