Ngk Insulators, Inc.

Yuki Nakayama

Noriko Hirata

Taku Okamoto

Osamu Nakasone

Shota Kageyama

Yusuke Vincent Fujii

Kosuke Monna

Kei Kosaka

Takayuki Sakurai

Satoshi Nishikawa

Yusuke Watanabe

Takayuki Sekiya

Soichiro Yoshida

Shotarou Niizuma

Nobuhiko Mori

Shotaro Niizuma

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 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 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.

Provided is a method of suitably judging necessity of a recovering process carried out on a mixed-potential gas sensor based on an extent of reversible deterioration occurring in a sensing electrode. The method includes the steps of: (a) performing impedance measurement between a sensing electrode exposed to a measurement gas and a reference electrode exposed to a reference atmosphere, which are provided in the gas sensor; and (b) judging necessity of a recovering process based on electrode reaction resistance or a diagnosis parameter correlating with the electrode reaction resistance wherein the electrode reaction resistance and the diagnosis parameter are obtained based on a result of the impedance measurement. The two steps are intermittently or periodically repeated during use of the gas sensor, and it is judged that a recovering process is necessary when the judge parameter satisfies a predetermined threshold condition in the step (b).

Gas-sensor diagnosing method

Provided is a gas sensor which is capable of preferably sensing an ammonia gas, and has excellent durability. A mixed-potential gas sensor includes a sensor element composed of an oxygen-ion conductive solid electrolyte, and a heater provided inside the element. The sensor element includes on a surface thereof a sensing electrode formed of a cermet including Pt, Au and an oxygen-ion conductive solid electrolyte, and also includes a reference electrode formed of a cermet of Pt and an oxygen-ion conductive solid electrolyte, and a porous electrode protective layer whose porosity is 5 to 40% covering at least the sensing electrode. The Au abundance ratio in a surface of noble metal particles forming the sensing electrode is 0.4 or more. The concentration of an ammonia gas is determined on the basis of a potential difference occurring between the sensing electrode and the reference electrode when the sensor element is disposed in a measurement gas and heated to 400&#xb0; C. to 800&#xb0; C.

Ammonia gas sensor and method for measuring concentration of ammonia gas

A sensor element includes: a sensing cell including a sensing electrode and a reference electrode; an oxygen pump cell configured to pump out oxygen in an internal space when a predetermined voltage is applied between an inner side pump electrode formed facing to the internal space and an outer side pump electrode formed on an outer surface of the sensor element; and a heater capable of heating the sensing cell and the oxygen pump cell. The concentration of a target gas component in measurement gas is specified based on a sensor output generated at the sensing cell and a pump current at the oxygen pump cell while the heater heats the sensing cell to a temperature of 400&#xb0; C. to 600&#xb0; C. and heats the oxygen pump cell to a temperature of 580&#xb0; C. to 850&#xb0; C. determined in accordance with a diffusion resistance provided to the measurement gas by a gas introduction part.

A gas sensor with excellent detection sensitivity is provided. A sensing electrode, which is provided in a mixed-potential gas sensor for measuring a concentration of a predetermined gas component of a measurement gas to sense the predetermined gas component, is formed of a cermet of a noble metal and an oxygen-ion conductive solid electrolyte. The noble metal includes Pt and Au. A range of at least 1.5 nm from a surface of a noble metal particle included in the sensing electrode is a Au enriched region having a Au concentration of 10% or more.

Gas sensor and method for manufacturing gas sensor

A gas sensor capable of measuring a high concentration range is provided. A sensing electrode provided in a sensor element of a mixed-potential gas sensor for measuring the concentration of a predetermined component in a measurement gas is formed of a cermet including a noble metal and an oxygen-ion conductive solid electrolyte. The noble metal includes Pt and Au. A Au abundance ratio, which is an area ratio of a portion covered with Au to a portion at which Pt is exposed in a surface of noble metal particles forming the sensing electrode, is 0.1 or more and less than 0.3.

Gas sensor, method for producing conductive paste, and method for manufacturing gas sensor

A gas sensor includes a sensor element made of an oxygen-ion conductive solid electrolyte and is configured to determine a concentration of a measurement target gas component based on a sensitivity characteristic as a predetermined functional relation held between a sensor output and the concentration of the gas component. The sensor output is a potential difference generated between a sensing electrode of the sensor element heated to a predetermined sensor drive temperature and a reference electrode. At the reference electrode, Au is concentrated at a predetermined maldistribution degree on the surface of a noble metal particle. In the present invention, the sensitivity characteristic is calibrated so as to suit the maldistribution degree at the reference electrode, based on the value of a predetermined alternative maldistribution degree index acquired in a non-destructive manner by performing predetermined measurement while the sensor element is heated to the predetermined temperature.

Gas sensor calibration method

A gas sensor includes a sensor element made of an oxygen-ion conductive solid electrolyte, at least one electrode provided to the sensor element so as to contact a measurement gas, and a controller configured to control the gas sensor. The sensor element is heated, by a heater provided to the sensor element, at a temperature higher than an operating temperature set in advance for a predetermined time period at start of the gas sensor, and then the temperature of the sensor element is decreased to the operating temperature.

Method of reducing output degradation of gas sensor

A method of inspecting an electrode provided in a gas sensor element includes the steps of: producing, in advance, a calibration curve representing a relation between an Au maldistribution degree defined based on a ratio of an area of a portion at which Au is exposed on a noble metal particle surface and calculated from a result of XPS or AES analysis on an inspection target electrode, and a predetermined alternative maldistribution degree index correlated with the Au maldistribution degree and acquired in a non-destructive manner from the gas sensor element heated to a predetermined temperature; acquiring a value of the alternative maldistribution degree index for the inspection target electrode of the gas sensor element while the gas sensor element is heated to the predetermined temperature; and determining whether the Au maldistribution degree satisfies a predetermined standard based on the calibration curve and the acquired inspection value.

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Nagoya, Japan

Yuki Nakayama