Ngk Insulators, Inc.

Shota Kageyama

Yuki Nakayama

Yusuke Vincent Fujii

Takayuki Sekiya

Kei Kosaka

Yusuke Watanabe

Naoya Saito

Tetsuya Ishikawa

Kazuhito Sakakibara

A gas sensor includes a sensor element and one or more hollow columnar dense bodies. The sensor element includes an element main body having a side surface, a porous layer and a water-penetration reduction portion that cover at least a front end-side part of the side surface. The water-penetration reduction portion disposed on the side surface so as to divide the porous layer or to be located closer to the rear end than the porous layer, an overlap length W that is the length of a continuous overlap between a range in which the water-penetration reduction portion is present in a longitudinal direction and a range in which inner peripheral surfaces of the one or more dense bodies are present in the longitudinal direction being 0.5 mm or more, and having a dense layer covers the side surface, the water-penetration reduction portion reduces the capillarity of water.

Gas sensor

A gas sensor element in which oxidation of electrodes and a heater occurring with continued use is suppressed is provided. The gas sensor element includes a plurality of solid electrolyte layers stacked one over another, and includes an electrochemical cell including a pair of electrodes and a portion of the plurality of solid electrolyte layers existing between the pair of electrodes; a heater part capable of heating the gas sensor element; and a gettering layer located between the plurality of solid electrolyte layers and between the plurality of solid electrolyte layers and each of the pair of electrodes, and gettering impurities in a metal component of the electrodes and the heater part during driving of the gas sensor element.

Gas sensor element

A sensor element includes element main body including side surfaces, a detection unit, connector electrodes disposed on the rear end-side part of the side surfaces, a porous layer that covers at least front end-side part of the side surface, the porous layer having a porosity of 10% or more, and a water-penetration reduction portion. The water-penetration reduction portion is disposed on the side surface so as to divide the porous layer or to be located closer to the rear end than the porous layer. The length L of the water-penetration reduction portion is 0.5 mm or more. The water-penetration reduction portion includes, among a dense layer covering the side surface and having a porosity of less than 10% and a gap region in which the porous layer is absent, at least the dense layer. The water-penetration reduction portion reduces the capillarity of water.

Sensor element and gas sensor

A gas sensor includes a sensor element and one or more hollow columnar dense bodies. The sensor element includes an element main body having a side surface, a porous layer and a water-penetration reduction portion that cover at least a front end-side part of the side surface. The water-penetration reduction portion disposed on the side surface so as to divide the porous layer an overlap length W that is the length of a continuous overlap between a range in which the water-penetration reduction portion is present in the longitudinal direction and a range in which inner peripheral surfaces of the one or more dense bodies are present in the longitudinal direction being 0.5 mm or more, the water-penetration reduction portion being a gap region in which the porous layer is absent, the water-penetration reduction portion reduces the capillarity of water.

A sensor element includes: a main pump cell constituted by an inner electrode provided to face a first inner space into which a measurement gas is introduced, an external electrode provided on an element surface, and a solid electrolyte therebetween; and a measurement pump cell constituted by a measurement electrode provided to face a second inner space communicated with the first inner space, an external electrode, and a solid electrolyte therebetween. A diffusion resistance from a gas inlet to the inner electrode is 200 to 1000 cm. For the first inner space and a unit electrode part of the inner electrode, a space length is 2.5 to 10 mm, a space thickness is 50 to 300 &#x3bc;m, an electrode length/the space length is 0.5 to 1.0, and an electrode width/the space width is 0.5 to 1.0.

A sensor element includes: a main pump cell constituted by an inner pump electrode facing the first inner space into which a measurement gas is introduced, an external pump electrode provided on an element surface, and a solid electrolyte located therebetween; a measurement electrode facing a second inner space communicating with the first inner space and functioning as a reduction catalyst for NOx; and a measurement pump cell constituted by the measurement electrode, the external pump electrode, and a solid electrolyte located therebetween. A diffusion resistance from the gas inlet to the inner pump electrode ranges from 200-1000 cm, a resistance of the main pump cell is equal to or smaller than 150&#x3a9;, a distance between the electrodes ranges from 0.1-0.6 mm, and the inner pump electrode which is a cermet made of an Au&#x2014;Pt alloy and ZrOhas an area ranging from 5-20 mm.

A sensor element includes: a first inner space into which a measurement gas is introduced from outside; a second inner space communicated with the first inner space; a main pump cell constituted by an inner pump electrode facing the first inner space, an external pump electrode on a surface of the sensor element, and a solid electrolyte located therebetween; a measurement electrode facing the second inner space and functioning as a reduction catalyst for NOx; and a measurement pump cell constituted by the measurement electrode, the external pump electrode, and a solid electrolyte located therebetween. The inner pump electrode is a cermet made of an Au&#x2014;Pt alloy containing Au ranging from 0.6 wt % to 1.4 wt % and ZrO, and has a thickness ranging from 5 &#x3bc;m to 30 &#x3bc;m, a porosity ranging from 5% to 40%, and an area ranging from 5 mmto 20 mm.

In a sensor element, a reference gas regulation pump cell pumps in oxygen to the periphery of a reference electrode in which a reference gas is introduced, by the flow of a control current Ipbetween the reference electrode and an outer pump electrode located in a region exposed to a measurement-object gas. An average current density of the reference electrode under the flow of the control current Ipis higher than 0 &#x3bc;A/mmand lower than 400 &#x3bc;A/mm. The average current density is preferably not higher than 170 &#x3bc;A/mm. An average value of the control current Ipis preferably higher than 1 &#x3bc;A. The outer pump electrode as a measurement-object gas side electrode of the reference gas regulation pump cell may be provided on an outer surface of a layered body (or more specifically, on a second solid electrolyte layer).

A sensor element mainly contains an oxygen ion conductive solid electrolyte. By applying, across a first electrode formed on a surface of an internal space into which a measurement gas is introduced from an outside and a second electrode formed on an external surface of the element, a predetermined voltage determined based on a potential difference between the first electrode and a reference electrode provided inside the element, oxygen in the internal space can be pumped out. In a case where pump reference processing is performed, a DC voltage having a maximum value of 1.4 to 2.0 V inclusive is applied across the reference and second electrodes for 10 to 1200 seconds inclusive in a state in which the reference and second electrodes are respectively electrically connected to negative and positive terminals of an external DC power supply, and an element temperature is set to 700 to 850&#xb0; C. inclusive.

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Nagoya, Japan

Shota Kageyama