JPH0221743B2 - - Google Patents
Info
- Publication number
- JPH0221743B2 JPH0221743B2 JP57234350A JP23435082A JPH0221743B2 JP H0221743 B2 JPH0221743 B2 JP H0221743B2 JP 57234350 A JP57234350 A JP 57234350A JP 23435082 A JP23435082 A JP 23435082A JP H0221743 B2 JPH0221743 B2 JP H0221743B2
- Authority
- JP
- Japan
- Prior art keywords
- pore diameter
- pores
- gas sensitive
- gas
- diameter
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 239000011148 porous material Substances 0.000 claims description 108
- 239000003054 catalyst Substances 0.000 claims description 21
- 230000004044 response Effects 0.000 description 16
- 239000000843 powder Substances 0.000 description 11
- 230000000694 effects Effects 0.000 description 9
- 239000002994 raw material Substances 0.000 description 9
- 230000035945 sensitivity Effects 0.000 description 8
- 238000002156 mixing Methods 0.000 description 7
- 239000002245 particle Substances 0.000 description 7
- 239000000919 ceramic Substances 0.000 description 6
- 239000004065 semiconductor Substances 0.000 description 5
- 229910010413 TiO 2 Inorganic materials 0.000 description 4
- 238000010304 firing Methods 0.000 description 4
- 238000000034 method Methods 0.000 description 4
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 4
- 238000001354 calcination Methods 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 238000000465 moulding Methods 0.000 description 3
- 230000004043 responsiveness Effects 0.000 description 3
- 229910006404 SnO 2 Inorganic materials 0.000 description 2
- 239000011247 coating layer Substances 0.000 description 2
- IVMYJDGYRUAWML-UHFFFAOYSA-N cobalt(II) oxide Inorganic materials [Co]=O IVMYJDGYRUAWML-UHFFFAOYSA-N 0.000 description 2
- 238000002485 combustion reaction Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 238000012856 packing Methods 0.000 description 2
- 239000011164 primary particle Substances 0.000 description 2
- XLOMVQKBTHCTTD-UHFFFAOYSA-N zinc oxide Inorganic materials [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 description 2
- 239000004372 Polyvinyl alcohol Substances 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- 239000000853 adhesive Substances 0.000 description 1
- 230000001070 adhesive effect Effects 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- -1 and among these Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000004568 cement Substances 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000008187 granular material Substances 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 239000012212 insulator Substances 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 1
- 229910052753 mercury Inorganic materials 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910000510 noble metal Inorganic materials 0.000 description 1
- 229910052763 palladium Inorganic materials 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 229920002451 polyvinyl alcohol Polymers 0.000 description 1
- 239000010970 precious metal Substances 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 238000010298 pulverizing process Methods 0.000 description 1
- 229910052703 rhodium Inorganic materials 0.000 description 1
- 239000011163 secondary particle Substances 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 229920003002 synthetic resin Polymers 0.000 description 1
- 239000000057 synthetic resin Substances 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
Description
本発明は応答が速く、耐久性に優れたガス感応
体素子に関するものである。
内燃機関あるいは各種燃焼機器等において排ガ
ス中のガス成分を検知するのに従来より多孔性酸
化物半導体セラミツクスを感応体素子とする各種
のガスセンサーが知られている。この多孔性酸化
物半導体セラミツクスを用いたガス感応体素子
は、セラミツク粒間をガスが拡散する速度が応答
速度の律速で、その素子の応答特性が決まる。こ
の為、素子の厚みを薄くしてガス交換速度を速め
る工夫が開示された（特開昭55−63747号、特開
昭52−150696号）、しかし素子厚みを薄くすると、
内部の電極線を素子の中心にセツトすることは困
難であり、且つ機械強度も不足する。一方、半導
体セラミツクスの気孔径を大きくする方法もある
が、初期は優れた応答を示すが、耐久後の劣化が
大きく、又低温活性が良くない。又耐久劣化を防
ぐ為に、担持させる貴金属触媒量を多くすると、
素子の応答速度が逆に遅くなる欠点があつた。逆
に気孔径を小さくすると、低温活性は良いが、応
答が遅く、時には表面に排ガス中よりデポジツト
が沈着し、素子表面が目詰りし、応答が遅れる傾
向がある。この改良として素子の表面に被覆層を
付けることが知られている（実開昭55−53451号、
特開昭55−82045号、特開昭55−100164号）。しか
し、被覆層自体の気孔径を制御することはむつか
しく、又下地の素子との密着性を確保するには多
くの困難をともなう。本発明はこれらの従来の素
子の欠点を改良し、耐久性、応答性に優れ、製造
しやすいガス感応体素子を提供することを目的と
するものである。
かかる目的は、ガス成分によつて電気抵抗値の
変化するガス感応体と、それに設けられた電極対
を備えたガス感応体素子において、前記ガス感応
体は、主に大きな径の気孔が群をなしている大気
孔径部と、主に小さな径の気孔が群をなしている
小気孔径部とがブロツク状に分かれた状態で混在
して成り、前記大気孔径部は、この部分内の気孔
の径の平均値が0.3〜1.0μmの範囲内の値として形
成され、前記小気孔径部は、この部分内の気孔の
径の平均値が0.2〜0.4μmの範囲内の値として形成
され、前記小気孔径部の気孔の径の平均値に対す
る前記大気孔径部の気孔の径の平均値は、1.2以
上であることを特徴とするガス感応体素子によつ
て達成することができる。
以下に本発明を詳細に説明するに、本発明のガ
ス感応体素子はガス成分によつて電気抵抗値の変
化するガス感応体とそれらに設けられた１対の電
極とから成る。ガス感応体を構成する材料として
は、SnO2，ZnO，CoO，TiO2等の多孔性酸化物
半導体セラミツクスが適用でき、例えば第１図に
示す形状に成形されて使用される。第１図に示す
ガス感応体素子１の場合には電極としては白金線
２が用いられるが、ガス感応体の形状が異なる場
合、例えばハニカム形状又は積層体である場合に
は、面状の電極であつても良く、ガス感応体及び
電極の形状は本発明では問わない。
本発明はガス感応体中に主に大きな径の気孔が
群をなしている大気孔径部と、主に小さな径の気
孔が群をなしている小気孔径部とがブロツク状に
分かれた状態で混在しており、大気孔径部はその
内部の気孔の径の平均値（以下、単に気孔径と記
す）が、0.3〜1.0μmの範囲内の値に調整され、小
気孔径部はその内部の気孔径が、0.2〜0.4μmの範
囲内の値に調整されているものである。尚、本発
明では、気孔径は、水銀圧入式ポロシメーターで
測定される平均値をさす。
大気孔径部において、気孔径を0.3〜1.0μの範
囲内のいずれかの値に限定したのは、0.3μより小
さくするとガス交換性を促進させ、素子の応答性
を改善させる効果が失われ、1.0μより大きいと素
子の機械的強度が劣化するからである。大気孔径
部において、特に好ましい気孔径の範囲は0.5〜
0.8μである。
小気孔径部において、気孔径を0.2〜0.4μの範
囲内のいずれかの値に限定したのは、0.2μよりも
小さいとガスが分子拡散をする事が不可能となり
応答が極端に悪くなり、0.4μよりも大きくなると
素子の感ガス性、耐久性不足となるからである。
特に好ましい気孔径はその感応素子の使用用途に
よつて決められるべきである。気化器制御のエン
ジン制御システムではセンサーの応答より低温活
性が重視されるので小さめの気孔径が望ましく、
電子噴射制御の場合は応答を重視するので大きめ
の気孔径が望ましい。小気孔径部は上記の選択で
決められるが、これに対し、本発明の大気孔径部
の効果を発揮せしめるには、その気孔径の比は、
小気孔径部の気孔径に対して1.2倍以上であるこ
とが必要で、望ましくは1.5倍以上とするのが良
い。
小気孔径部と大気孔径部の最適混在比率は、
各々の気孔径に応じて最適比率を求めるのが適当
であるが、一般的には大気孔径部が10％以上あれ
ば効果があり、80％以上になると、むしろ大気孔
径部による欠点が目立つようになる。望ましくは
大気孔径部が30〜60体積％の範囲であると実用的
には多く使える。小気孔径部と大気孔径部の混在
の仕方は、小気孔径部と大気孔径部とは、ブロツ
ク状に分かれて存在するが、それぞれは偏在して
いるのではなく、第２図のように文字通り混然１
体となつている状態を指す。この状態になつてい
ることによつて、大気孔径部と小気孔径部のそれ
ぞれの効果が発現できる。
このようなガス感応体素子を製造するには、例
えば原料のSnO2，ZnO，CoO，TiO2等の粉末を
予め仮焼すると、仮焼温度が高い程粒子が大きく
なり、粒子間隔を大きくすることができるので、
種々の温度で仮焼した原料粉末を所望の量比で混
合し、成形してこのように原料粉末の仮焼温度に
よつて仮焼原料粉末の気孔径を制御し、そうして
制御することによつて種々の気孔径とした仮焼原
料粉末の調合割合や、仮焼原料粉末から成る成形
体の焼成温度を管理することによつて、大気孔径
部と小気孔径部とが存在し且つそれらの気孔径が
前記所定の要件を満たす本発明のガス感応体素子
を製造できる。
尚、仮焼原料粉末の混合時各粒子は１次粒のオ
ーダーまで粉砕されないように注意する必要があ
る。粉砕が進みすぎると２種の１次粒子同志が近
接し、互いに最密充填をとろうとし、適度な細孔
分布を得ることができない。逆に混合が不充分で
あると、粗孔粒と細孔粒はマクロ的にも不均質と
なり再現性のある結果を得ることができない。粉
末形成の場合、混合後、一旦加圧成形をし、それ
を再びほぐす事により再造粒してマクロ的には均
質、ミクロ的には不均質な広範囲な細孔分布を得
ることができる。
従つて２次粒子の大きさは、成形する素子の大
きさから比較し再現性のあるマクロ的均質性を与
える大きさから決められるべきであり、３×４×
１mm程度の素子の場合は10〜200μ程度が望まし
い。10μ以下の場合は、１次粒の最密充填を起こ
し易く、200μ以上の場合、素子の大きさからみ
てマクロ的に不均質になり易い。
上記の方法によらず原料粉末中に焼成中飛散す
る合成樹脂製の粉末を混合して同様に焼成しても
良い。当然のことながら本発明はこれらの製造方
法により限定されるものではない。
なお、セラミツク半導体の感ガス性は低温にな
ると低下するので、センサーにヒーターを組み入
れたり素子中に触媒を担持させ、感ガス性を高め
ることができる。触媒としては貴金属触媒が望ま
しく、中でもPt，Rh，Pdが優れた効果が得られ
る。自動車排ガスセンサーに触媒を適用すると
き、触媒は低温での感ガス性を高める事ができる
が、本発明素子では多量に使用すると素子の応答
を遅くすることが本発明者らの実験の結果判明し
た。この理由は触媒中に排ガス中の成分、特に
H2が固溶し、この拡散速度が素子の応答を律速
することによるものと考えられる。従つて、触媒
を大量に使用すると、低温での感ガス性、耐久変
動を良くする事は可能であるが、応答性自体は低
下するので、おのずとその適量が定まる。本発明
者は、触媒を素子中に均一に分散させず、感ガス
として有効な小気孔径の部分に多く添加する事に
より、応答性をそれほど低下させずに、感ガス
性、耐久変動を向上させる事を見い出した。触媒
添加量は個々の触媒特有の性質によつて各々最適
量は定まるが、Pt触媒の場合は、小気孔径部で
0.5〜20モル％、大気孔径部で５モル％以下が適
当である。このようにして製造されたガス感応体
素子１は、例えば第３図のように耐熱セメント等
の接着剤５によりアルミナ等の碍管６に接合さ
れ、該碍管６は主体金具７に取り付けられ、碍管
６の反対端より電極線２が外部に導出されて感ガ
スセンサーとされる。
以上、詳述したように本発明のガス感応体素子
は、主に大きな径の気孔が群をなしている大気孔
径部と、主に小さな径の気孔が群をなしている小
気孔径部とがブロツク状に分かれた状態で混在し
おり、大気孔径部は、この部分内の気孔径が0.3
〜1.0μmの範囲内の値とされ、小気孔径部は、こ
の部分内の気孔径が0.2〜0.4μmの範囲内の値とさ
れ、小気孔径部の気孔径に対する大気孔径部の気
孔径は、1.2以上である。そのため大気孔径部が
ガス交換性を促進させて素子の応答性を改善さ
せ、さらに素子表面に排ガス中より堆積物が沈着
した場合、表面の目詰りを防止させる。そして小
気孔径部は素子全体の機械的強度を保持する役割
を果たし、大気孔径部と小気孔径部とが程良く、
混在し組み合せられることにより本発明素子は応
答性と耐久性に優れたものとなるのである。しか
も大気孔径部に担持される触媒量を小気孔径部に
担持される触媒量よりも少なくすると、感ガス性
や耐久性を一層向上できる。
以下に本発明を実施例により更に詳細に説明す
るが、本発明はその要旨を越えない限り以下の実
施例により限定されるものではない。
実施例
比表面積３m2／ｇのTiO2を種々の温度で仮焼
し、気孔径の異なる次のＡ〜ＧまでのTiO2原料
粉末を得た。
次に挙げる第１表に、サンプル番号と仮焼温度
との関係を示す。第１表の右欄は、仮焼されたサ
ンプルＡないしＧを用い、次に記す条件によつて
成形、焼成を実施して作製した素子において、各
サンプルＡないしＧが示す気孔径の測定値を表す
ものである。
The present invention relates to a gas sensitive element with quick response and excellent durability. 2. Description of the Related Art Various gas sensors using porous oxide semiconductor ceramics as a sensitive element are conventionally known for detecting gas components in exhaust gas in internal combustion engines or various types of combustion equipment. In a gas sensitive element using this porous oxide semiconductor ceramic, the response rate is determined by the rate at which gas diffuses between ceramic particles, which determines the response characteristics of the element. For this reason, a method of increasing the gas exchange rate by reducing the thickness of the element has been disclosed (Japanese Patent Application Laid-Open Nos. 55-63747 and 1982-150696), but when the thickness of the element is reduced,
It is difficult to set the internal electrode wires at the center of the element, and the mechanical strength is also insufficient. On the other hand, there is also a method of increasing the pore size of semiconductor ceramics, but this method shows excellent initial response, but deteriorates significantly after durability and has poor low-temperature activity. In addition, in order to prevent durability deterioration, increasing the amount of precious metal catalyst supported,
On the contrary, there was a drawback that the response speed of the element was slow. On the other hand, if the pore size is made small, the low-temperature activity is good, but the response is slow, and sometimes deposits from the exhaust gas are deposited on the surface, which tends to clog the element surface and delay the response. It is known to improve this by adding a coating layer to the surface of the element (Utility Model Application No. 55-53451,
JP-A-55-82045, JP-A-55-100164). However, it is difficult to control the pore diameter of the coating layer itself, and there are many difficulties in ensuring adhesion to the underlying element. It is an object of the present invention to improve the shortcomings of these conventional elements and to provide a gas sensitive element which is excellent in durability and responsiveness and is easy to manufacture. This purpose is to provide a gas sensitive element that includes a gas sensitive body whose electrical resistance value changes depending on the gas component and a pair of electrodes provided thereon. The large pore size area is divided into blocks, and the large pore size area is divided into blocks, and the large pore size area is mainly composed of groups of small pores. The small pore diameter portion is formed with an average diameter of 0.3 to 1.0 μm, and the small pore diameter portion is formed with an average diameter of 0.2 to 0.4 μm. This can be achieved by a gas sensitive element characterized in that the average value of the diameter of the pores in the large pore diameter portion is 1.2 or more relative to the average value of the diameter of the pores in the small pore diameter portion. The present invention will be described in detail below. The gas sensitive element of the present invention comprises a gas sensitive body whose electrical resistance value changes depending on the gas component and a pair of electrodes provided thereon. Porous oxide semiconductor ceramics such as SnO 2 , ZnO, CoO, TiO 2 and the like can be used as the material constituting the gas sensitive body, and are used after being formed into the shape shown in FIG. 1, for example. In the case of the gas sensitive body element 1 shown in FIG. 1, a platinum wire 2 is used as the electrode, but if the gas sensitive body has a different shape, such as a honeycomb shape or a laminate, a planar electrode is used. The shapes of the gas sensitive body and the electrodes are not critical in the present invention. In the present invention, the gas sensitive body is divided into an atmospheric pore diameter area in which pores of large diameter form a group and a small pore diameter area in which pores of mainly small diameter form in a group. The average value of the diameter of the internal pores (hereinafter simply referred to as pore diameter) is adjusted to a value within the range of 0.3 to 1.0 μm in the large pore diameter part, and the average value of the diameter of the internal pores in the small pore diameter part is adjusted to a value within the range of 0.3 to 1.0 μm. The pore diameter is adjusted to a value within the range of 0.2 to 0.4 μm. In the present invention, the pore diameter refers to an average value measured with a mercury intrusion porosimeter. The reason why the pore diameter in the atmospheric pore diameter part was limited to a value within the range of 0.3 to 1.0μ is because if it is smaller than 0.3μ, the effect of promoting gas exchange and improving the response of the element will be lost. This is because if it is larger than 1.0μ, the mechanical strength of the element will deteriorate. In the atmospheric pore diameter part, a particularly preferable range of pore diameter is 0.5 to
It is 0.8μ. In the small pore diameter part, the pore diameter was limited to a value within the range of 0.2 to 0.4μ, because if it is smaller than 0.2μ, it will be impossible for gas to diffuse molecules, and the response will be extremely poor. , if it is larger than 0.4μ, the gas sensitivity and durability of the element will be insufficient.
The particularly preferred pore size should be determined by the intended use of the sensitive element. In a carburetor-controlled engine control system, low-temperature activity is more important than sensor response, so a smaller pore diameter is desirable.
In the case of electronic injection control, response is important, so a larger pore diameter is desirable. The small pore diameter portion is determined by the above selection, but in order to exhibit the effect of the large pore diameter portion of the present invention, the ratio of the pore diameters is as follows:
It is necessary that the pore diameter of the small pore diameter portion is 1.2 times or more, preferably 1.5 times or more. The optimal mixing ratio of the small pore diameter part and the large pore diameter part is
It is appropriate to find the optimal ratio according to each pore size, but generally speaking, if the atmospheric pore size accounts for 10% or more, it will be effective, and if it exceeds 80%, the drawbacks due to the atmospheric pore size will become more noticeable. become. Desirably, the atmospheric pore size ranges from 30 to 60% by volume for practical use. The way in which the small pore diameter part and the atmospheric pore diameter part coexist is that although the small pore diameter part and the atmospheric pore diameter part are separated into blocks, they are not unevenly distributed, but as shown in Figure 2. Literally confused 1
Refers to the state of becoming a body. By being in this state, the respective effects of the large pore diameter portion and the small pore diameter portion can be expressed. In order to manufacture such a gas sensitive element, for example, powders such as SnO 2 , ZnO, CoO, TiO 2 as raw materials are calcined in advance, and the higher the calcination temperature, the larger the particles and the larger the particle spacing. Because you can
The raw material powders calcined at various temperatures are mixed in a desired quantity ratio and molded, and the pore diameter of the calcined raw material powder is thus controlled by the calcining temperature of the raw material powder. By controlling the mixing ratio of the calcined raw material powder with various pore sizes and the firing temperature of the compact made of the calcined raw material powder, it is possible to create a molded body with large pore diameter portions and small pore diameter portions. The gas sensitive element of the present invention whose pore diameter satisfies the above-mentioned predetermined requirements can be manufactured. In addition, when mixing the calcined raw material powder, care must be taken not to crush each particle to the order of primary particles. If the pulverization progresses too much, the two types of primary particles will come close to each other and will try to form a close packing with each other, making it impossible to obtain an appropriate pore distribution. On the other hand, if the mixing is insufficient, the coarse pore particles and the pore particles become macroscopically non-uniform, making it impossible to obtain reproducible results. In the case of powder formation, it is possible to obtain a wide range of pore distribution that is macroscopically homogeneous and microscopically heterogeneous by once pressurizing after mixing and then loosening it again to re-granulate it. Therefore, the size of the secondary particles should be determined from the size that provides reproducible macro homogeneity when compared with the size of the element to be molded, and is 3 x 4 x
In the case of an element of about 1 mm, the thickness is preferably about 10 to 200 μ. If it is less than 10μ, close packing of primary grains tends to occur, and if it is more than 200μ, it tends to become macroscopically non-uniform considering the size of the element. Instead of using the above method, synthetic resin powder that is scattered during firing may be mixed into the raw material powder and fired in the same manner. Naturally, the present invention is not limited to these manufacturing methods. Note that the gas sensitivity of ceramic semiconductors decreases at low temperatures, so the gas sensitivity can be increased by incorporating a heater into the sensor or by supporting a catalyst in the element. Preferably, the catalyst is a noble metal catalyst, and among these, Pt, Rh, and Pd provide excellent effects. When a catalyst is applied to an automobile exhaust gas sensor, the catalyst can increase gas sensitivity at low temperatures, but the results of experiments conducted by the present inventors have revealed that using a large amount of the catalyst in the device of the present invention slows down the response of the device. did. The reason for this is that the catalyst contains components in the exhaust gas, especially
This is thought to be due to the fact that H 2 is dissolved in solid solution and its diffusion rate determines the response of the element. Therefore, if a large amount of catalyst is used, it is possible to improve gas sensitivity at low temperatures and durability fluctuations, but the responsiveness itself decreases, so the appropriate amount is determined naturally. The inventor of the present invention improved gas sensitivity and durability fluctuations without significantly reducing response by adding a large amount of catalyst to small pore diameter areas that are effective as gas sensitivity, rather than uniformly dispersing the catalyst throughout the element. I found something to do. The optimum amount of catalyst added depends on the characteristics of each individual catalyst, but in the case of Pt catalysts, it is
Appropriately it is 0.5 to 20 mol%, and 5 mol% or less in the atmospheric pore diameter area. The gas sensitive element 1 manufactured in this manner is bonded to an insulator tube 6 made of alumina or the like using an adhesive 5 such as heat-resistant cement, for example, as shown in FIG. The electrode wire 2 is led out from the opposite end of the electrode 6 to form a gas-sensitive sensor. As described above in detail, the gas sensitive element of the present invention has an atmospheric pore diameter section where pores of mainly large diameter form a group, and a small pore diameter section where pores of mainly small diameter form a group. The air pores are mixed and divided into blocks, and the pore diameter in this part is 0.3.
The value is within the range of ~1.0 μm, and the pore diameter within this portion of the small pore diameter portion is defined as a value within the range of 0.2 to 0.4 μm. is greater than or equal to 1.2. Therefore, the atmospheric pore diameter portion promotes gas exchange and improves the response of the element, and furthermore prevents clogging of the surface when deposits from the exhaust gas are deposited on the element surface. The small pore diameter part plays the role of maintaining the mechanical strength of the entire element, and the large pore diameter part and the small pore diameter part are well balanced.
By mixing and combining them, the device of the present invention has excellent responsiveness and durability. Furthermore, by making the amount of catalyst supported in the large pore diameter portion smaller than the amount of catalyst supported in the small pore diameter portion, gas sensitivity and durability can be further improved. EXAMPLES The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. Example TiO 2 having a specific surface area of 3 m 2 /g was calcined at various temperatures to obtain the following TiO 2 raw powders A to G having different pore diameters. Table 1 below shows the relationship between sample numbers and calcination temperatures. The right column of Table 1 shows the measured values of the pore diameters of each sample A to G in the elements produced by molding and firing the calcined samples A to G under the following conditions. It represents.
【表】
第１表の各原料に種々の量の触媒として白金ブ
ラツクを添加混合しポリビニルアルコール２重量
％を添加後、＃200〜325メツシユの粒子に造粒
し、各造粒物を適当な割合混合し、素子成形に供
した。成形は、所定の金型中に0.3φPt線を挿入
し、素子の電極用に使用した。素子形状は第１図
に示す形状でおよその寸法は2.5×3.7×1.0mmにし
た。
成形した素子は電気炉中1200℃１時間焼成し、
焼成後第３図のように組み立て、測定に供した。
測定は素子１を第４図のように接続し市販の2000
c.c.三元触媒車にてのEFIフイードバツク制御をさ
せ、無負荷2000r.p.m.での制御周波数Hzを測定し
た。ここで応答の良いセンサーほど高い制御性即
ち大きなHzを得ることができる。ついでアイドリ
ングに戻し、排ガス温が低下すると共にセンサー
の活性が低下し、フイードバツク停止直前の排ガ
ス温を読みとり、初期活性温度とした。この温度
が低いセンサーほど低温での作動性の良い即ち低
温活性が良いと判断できる。素子の耐久は、ガス
センサーを2000c.c.Ｅ／Ｇの排気管中に取り付けア
イドリング〜全開を25分間隔で繰り返す熱サイク
ルにて500時間耐久後、上記特性を確認した。こ
の時排ガス温度は350〜800℃で変化した。大小気
孔径部混在比、素子特性を第２表に示す。
制御周波数は、1.2Hz以上、排ガス温度は、245
℃以下であるならば、良い結果だと言える。[Table] Various amounts of platinum black as a catalyst were added and mixed to each raw material in Table 1, 2% by weight of polyvinyl alcohol was added, and the mixture was granulated into particles of #200 to 325 mesh. The proportions were mixed and used for element molding. For molding, a 0.3φPt wire was inserted into a predetermined mold and used for the electrode of the device. The element shape was as shown in Figure 1, with approximate dimensions of 2.5 x 3.7 x 1.0 mm. The molded element was fired at 1200℃ for 1 hour in an electric furnace.
After firing, it was assembled as shown in Figure 3 and subjected to measurement.
For measurement, connect element 1 as shown in Figure 4 and use a commercially available 2000
EFI feedback control was performed on a CC three-way catalyst vehicle, and the control frequency Hz was measured at 2000 rpm with no load. Here, the better the response of the sensor, the higher the controllability, that is, the higher the Hz. Then, the engine was returned to idling, and as the exhaust gas temperature decreased, the activity of the sensor decreased, and the exhaust gas temperature immediately before the feedback stopped was read, and was taken as the initial activation temperature. It can be determined that the lower the temperature of the sensor, the better its operability at low temperatures, that is, the better its low-temperature activity. Regarding the durability of the element, the above characteristics were confirmed after a gas sensor was installed in the exhaust pipe of a 2000 c.c. At this time, the exhaust gas temperature varied from 350 to 800°C. Table 2 shows the mixing ratio of large and small pore diameter parts and the device characteristics. Control frequency is 1.2Hz or higher, exhaust gas temperature is 245
If it is below ℃, it can be said to be a good result.
【表】【table】
【表】
大気孔径部の気孔径
＊気孔径比＝[Table] Pore diameter of atmospheric pore diameter section *Pore diameter ratio=
Claims (1)
感応体と、それに設けられた電極対を備えたガス
感応体素子において、 前記ガス感応体は、主に大きな径の気孔が群を
なしている大気孔径部と、主に小さな径の気孔が
群をなしている小気孔径部とがブロツク状に分か
れた状態で混在して成り、 前記大気孔径部は、この部分内の気孔の径の平
均値が0.3〜1.0μmの範囲内の値として形成され、 前記小気孔径部は、この部分内の気孔の径の平
均値が0.2〜0.4μmの範囲内の値として形成され、 前記小気孔径部の気孔の径の平均値に対する前
記大気孔径部の気孔の径の平均値は、1.2以上で
あることを特徴とするガス感応体素子。 ２ 前記大気孔径部が前記ガス感応体の30〜60体
積％占める特許請求の範囲第１項記載のガス感応
体素子。 ３ ガス成分によつて電気抵抗値の変化するガス
感応体と、それに設けられた電極対を備えたガス
感応体素子において、 前記ガス感応体は、主に大きな径の気孔が群を
なしている大気孔径部と、主に小さな径の気孔が
群をなしている小気孔径部とがブロツク状に分か
れた状態で混在して成り、 前記大気孔径部は、この部分内の気孔の径の平
均値が0.3〜1.0μmの範囲内の値として形成され、 前記小気孔径部は、この部分内の気孔の径の平
均値が0.2〜0.4μmの範囲内の値として形成され、 前記小気孔径部の気孔の径の平均値に対する前
記大気孔径部の気孔の径の平均値は、1.2以上で
あり、 しかも前記大気孔径部に担持されている触媒量
が前記小気孔径部に担持されている触媒量よりも
少ないことを特徴とするガス感応体素子。[Scope of Claims] 1. A gas sensitive element comprising a gas sensitive body whose electrical resistance value changes depending on gas components and an electrode pair provided thereon, wherein the gas sensitive body mainly has large-diameter pores. The atmospheric pore diameter section, in which the pores are grouped together, and the small pore diameter section, in which the pores mainly have a small diameter, form a group, are mixed together in a block-like divided state. The small pore diameter portion is formed so that the average value of the pore diameter within this portion is within the range of 0.2 to 0.4 μm. A gas sensitive element, wherein the average value of the diameter of the pores in the large pore diameter portion is 1.2 or more relative to the average value of the diameter of the pores in the small pore diameter portion. 2. The gas sensitive element according to claim 1, wherein the large pore diameter portion occupies 30 to 60% by volume of the gas sensitive body. 3. In a gas sensitive element comprising a gas sensitive body whose electrical resistance value changes depending on the gas component and an electrode pair provided thereon, the gas sensitive body mainly has pores with large diameters arranged in groups. The atmospheric pore diameter area and the small pore diameter area, in which pores of mainly small diameter form a group, are mixed together in a block-like state, and the atmospheric pore diameter area is the average diameter of the pores within this area. The small pore diameter portion is formed as a value within the range of 0.3 to 1.0 μm, and the small pore diameter portion is formed such that the average value of the diameter of the pores within this portion is within the range of 0.2 to 0.4 μm. The average value of the diameter of the pores in the large pore diameter part is 1.2 or more with respect to the average value of the diameter of the pores in the large pore diameter part, and the amount of catalyst supported in the large pore diameter part is supported in the small pore diameter part. A gas sensitive element characterized in that the amount of the catalyst is less than that of the catalyst.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP23435082A JPS59119253A (en) | 1982-12-25 | 1982-12-25 | Gas sensitive element |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP23435082A JPS59119253A (en) | 1982-12-25 | 1982-12-25 | Gas sensitive element |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS59119253A JPS59119253A (en) | 1984-07-10 |
| JPH0221743B2 true JPH0221743B2 (en) | 1990-05-16 |
Family
ID=16969615
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP23435082A Granted JPS59119253A (en) | 1982-12-25 | 1982-12-25 | Gas sensitive element |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS59119253A (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4659295B2 (en) * | 2001-08-27 | 2011-03-30 | ウチヤ・サーモスタット株式会社 | Metal oxide semiconductor gas sensor |
| JP4641832B2 (en) * | 2005-03-15 | 2011-03-02 | 富士電機システムズ株式会社 | Thin film gas sensor |
| JP4870938B2 (en) * | 2005-03-30 | 2012-02-08 | 新コスモス電機株式会社 | Manufacturing method of semiconductor gas detection element |
| US8079256B2 (en) | 2006-02-22 | 2011-12-20 | Testo Ag | Gas sensor and method for its production |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5796501A (en) * | 1980-12-09 | 1982-06-15 | Ngk Spark Plug Co | Moisture sensitive resistance element |
| JPS59159062A (en) * | 1983-03-01 | 1984-09-08 | Sumitomo Alum Smelt Co Ltd | Manufacture of humidity sensitive body for humidity element |
-
1982
- 1982-12-25 JP JP23435082A patent/JPS59119253A/en active Granted
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5796501A (en) * | 1980-12-09 | 1982-06-15 | Ngk Spark Plug Co | Moisture sensitive resistance element |
| JPS59159062A (en) * | 1983-03-01 | 1984-09-08 | Sumitomo Alum Smelt Co Ltd | Manufacture of humidity sensitive body for humidity element |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS59119253A (en) | 1984-07-10 |
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