NO.sub.x sensor for exhaust gas, and process for producing the same
AssigneeHonda Giken Kogyo Kabushiki Kaisha
InventorsMasaaki Nanaumi, Hiroshi Takeshita, Norihiro Ohta, Noriko Ohta, Yoshikazu Fujisawa, Yoichi Asano, Yoshiaki Takagi
Life of this patent
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Abstract
An NO.sub.x sensor is produced by sintering a plurality of columnar crystals of .beta.-type Nb.sub.2 O.sub.5. The average value M of aspect ratios b/a (wherein a represents a width and b represents a length) in the columnar crystals is set in a range of 2.11<M.ltoreq.5. The NO.sub.x sensor has a high sensitivity to NO.sub.x via an enhancement attained by control of crystal type and structure.
Claims15
An NO.sub.x sensor for an exhaust gas, which is made by sintering a plurality of columnar crystals of .beta.-type Nb.sub.2 O.sub.5, an average value M of aspect ratios b/a (wherein a represents a width, and b represents a length) in the columnar crystals being in a range of 2.11<M.ltoreq.5.
A process for producing an NO.sub.x sensor for an exhaust gas, comprising the steps of
- subjecting a powder comprised of an aggregate of .alpha.-type Nb.sub.2 O.sub.5 particles to a first heating treatment at a heating temperature T.sub.3 set in a range of 600.degree. C..ltoreq.T.sub.3 .ltoreq.890.degree. C., thereby producing the coalescence of the plurality of .alpha.-type Nb.sub.2 O.sub.5 particles to produce a plurality of larger particles of .alpha.-type Nb.sub.2 O.sub.5 ;
- and
- subjecting the powder resulting from said first heating treatment to a second heating treatment at a heating temperature T.sub.4 set in a range of 950.degree. C..ltoreq.T.sub.4 .ltoreq.1,200.degree. C., thereby producing the transformation of the .alpha.-type Nb.sub.2 O.sub.5 into .beta.-type Nb.sub.2 O.sub.5 and the coalescence of the larger particles to grow a plurality of columnar crystals of .beta.-type Nb.sub.2 O.sub.5, and sintering the columnar crystals.
An NO.sub.x sensor for an exhaust gas, comprising, a substrates having a pair of electrodes for measuring resistance, a film formed of a plurality of columnar crystals of .beta.-type Nb.sub.2 O.sub.5 on said substrate and covering said electrodes, said columnar crystals having an average value M of aspect ratios b/a, wherein a represents a width and b represents a length, in a range of 2.11<M.ltoreq.5.
A process for producing an NO.sub.x sensor for an exhaust gas, comprising the steps of:
- printing a paste of .alpha.-type Nb.sub.2 O.sub.5 particles and a binder solution on a substrate having a pair of electrodes;
- subjecting the paste and substrate to a primary heating treatment in a range of 100.degree. C. to 200.degree. C.;
- subjecting the paste and substrate to a secondary heating treatment in a range of 370.degree. C. to 470.degree. C.;
- subjecting a powder of an aggregate of .alpha.-type Nb.sub.2 O.sub.5 particles remaining from the paste after the primary and secondary heating treatments to a third heating treatment at a heating temperature in a range of 600.degree. C. to 890.degree. C., thereby producing a coalescence of the plurality of .alpha.-type Nb.sub.2 O.sub.5 particles to produce a plurality of larger particles of .alpha.-type Nb.sub.2 O.sub.5 ;
- and
- subjecting the powder resulting from said third heating treatment to a fourth heating treatment at a heating temperature in a range of 950.degree. C. to 1,200.degree. C., thereby producing a transformation of the .alpha.-type Nb.sub.2 O.sub.5 into .beta.-type Nb.sub.2 O.sub.5 and the coalescence of the larger particles to grow a plurality of columnar crystals of .beta.-type Nb.sub.2 O.sub.5, and sintering the columnar crystals.
A process for producing an NO.sub.x sensor for an exhaust gas, comprising the steps of sintering a plurality of columnar crystals of .beta.-type Nb.sub.2 O.sub.5 to have an average value M of aspect ratios b/a, wherein a represents a width and b represents a length, in the columnar crystals in a range of 2.11<M.ltoreq.5.
Dependencies are inferred from the claim text.