JP2733516B2 - Gas sensor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a gas sensor used for detecting an oxidizing gas or a reducing gas such as oxygen contained in an exhaust gas of an automobile or the like.

[Conventional technology]

In order to optimally control the air-fuel ratio of an internal combustion engine of an automobile or the like, a sensor that detects oxygen and unburned gas components in exhaust gas is used.For example, a concentration cell type oxygen sensor using stabilized zirconia as an electrolyte, An electric resistance sensor using a semiconductor made of a sintered body such as tin oxide or titanium oxide has been used. Among them, a perovskite oxide having a composition of SrSnO ₃ has an n-type semiconductor characteristic, and a lattice defect is generated corresponding to an oxygen partial pressure in an atmosphere. It is known that when the combustion exhaust gas is used as an atmosphere, the air-fuel ratio is particularly remarkable when the air-fuel ratio changes near the stoichiometric air-fuel ratio.

[Problems to be solved by the invention]

When a semiconductor having the composition of SrSnO ₃ as described above is used as a sensor for controlling the air-fuel ratio of an automobile, for example, the rate of change in electric resistance with respect to the change in the air-fuel ratio is
At 700-800 ° C., there is a disadvantage that it is large, but it becomes small as the temperature becomes low at 500-400 ° C., and when the air-fuel ratio changes from L to R rather than from rich (R) to lean (L). There is also a problem that the response speed is slow, and a control circuit and a correction circuit to be combined with such a sensor are complicated, so that there is a disadvantage that it is difficult to use.

Therefore, the present invention has improved sensitivity and response speed,
It is an object of the present invention to provide an easy-to-use gas sensor for controlling an air-fuel ratio in an automobile or the like.

[Means for solving the problem]

The sensor of the present invention which can achieve the above object has a general formula: Sr _(1-X) .Y _(X) .SnO _(3-d) where 0 <x ≦ 0.4, 0 <d <1. It is characterized by comprising using the perovskite type complex oxide which has.

The perovskite-type composite oxide for a gas sensor according to the present invention is an n-type semiconductor having a lattice defect based on oxygen deficiency, similarly to a conventionally known oxide semiconductor of this type. To construct a sensor using this, first, a high-purity strontium compound, a yttrium compound,
And a tin compound. As each of the starting compounds, an oxide or a compound which can be decomposed by heating to form an oxide may be used.

Each of such raw material compounds is blended so that the total amount of strontium and yttrium and the amount of tin are equimolar based on the content of each metal element, and further based on 1 mol of the total amount of strontium and yttrium. It is blended so that yttrium becomes 0.4 mol or less.

Such a raw material blend is a perovskite-type composite oxide by a usual method for producing this type of composite oxide, that is, by sufficiently mixing and pulverizing using a pulverizer, and firing it at 1000 to 1400 ° C. It can be.
The composite oxide thus obtained is formed into a fine powder using a pulverizer and then formed into a desired sensor chip shape using a press or the like. At this time, electrodes and the like may be embedded as necessary. . This molded body, for example, 1200 ~ 1400 ℃
And a gas sensor element is obtained by attaching electrode terminals as necessary.

〔Example〕

Strontium carbonate as a raw material containing strontium, yttrium oxide (III) as a raw material containing yttrium, and tin tin as a raw material containing tin dissolved in nitric acid to form a tin nitrate solution, and tin oxide (IV) obtained by heating the solution, After being sufficiently dried, the mixture was stoichiometrically weighed so as to have a molar ratio shown in Table 1, and this mixture was mixed and pulverized using a vibration mill. Next, the pulverized material was tableted, charged into an electric furnace, and fired in an air atmosphere at 1200 ° C. for 20 hours to obtain a composite oxide sintered body.

The obtained composite oxide sintered body was pulverized using a vibration mill into fine powder.
5kgf / cm ² by inserting into a 3mm x 3mm mold fixed at intervals
To produce a molded body having a thickness of 1 mm. Next, the formed body was fired in an electric furnace at 1350 ° C. for 2 hours to prepare a sensor element (FIG. 1). The oxygen deficiency of these oxides, that is, the value of d in the general formula, was about 0.05 to 0.3.

The No. 3 sensor element prepared in this manner was placed in a furnace at 700 ° C., and platinum electrodes were connected to the measurement terminals of the electric resistance measurement device, respectively, and a flammable gas and air set to a predetermined air-fuel ratio were set. Was passed through a catalyst tank heated to 350 ° C., and the exhaust gas burned by the catalyst was introduced into the furnace to measure the electric resistance value of the sensor element. Then, when the electric resistance value (r) was measured when the air-fuel ratio of the air-fuel mixture supplied to the catalyst tank was changed, it was confirmed that the change was as shown in FIG.

Next, for each of the created sensor elements, the change in the electric resistance value at 600 ° C. when the air-fuel ratio (λ) changes 10% above and below the stoichiometric air-fuel ratio (λ = 1), respectively, The sensitivity was calculated as shown in Table 1, and is shown in Table 1.

Further, for the sensor elements No. 1 and No. 3, the sensitivity was measured while changing the temperature of the atmosphere from 400 ° C. to 800 ° C., and the results shown in Table 2 were obtained.

In addition, for the sensor elements No. 1 and No. 3
While maintaining the temperature at 0 ° C or 800 ° C, the air-fuel ratio (λ) of the atmospheric exhaust gas was changed from 1.1 to 0.9 (→ R) and from 0.9 to 1.1 (→ R).
L), the response time (sec) required for the output to change between 10% and 90% at the time of rapid conversion was measured, and the results shown in Table 3 were obtained.

From these results, the sensor element of the present invention can
It can be understood that the concentration of the exhaust gas of the automobile engine can be detected with high sensitivity and high response speed in a wide temperature range as compared with the sensor element of SnO ₃ composition.

〔The invention's effect〕

The gas sensor of the present invention is constituted by using a perovskite-type composite oxide having a novel composition and has a high sensitivity and responds promptly regardless of the direction of the change in the air-fuel ratio. When the control circuit is used, there is no need for a complicated correction circuit in the control circuit, and control with a focus on the stoichiometric air-fuel ratio can be easily performed using a simple control circuit.

[Brief description of the drawings]

FIG. 1 is an external perspective view of an embodiment of the gas sensor of the present invention, and FIG. 2 is a graph showing an example of a change in electric resistance with respect to the air-fuel ratio.

Claims (2)

(57) [Claims] (1) A general formula: Sr _(1-X) .Y _(X) .SnO _{(3-d) wherein} a perovskite-type composite oxide having 0 <x ≦ 0.4 and 0 <d <1 is used. A gas sensor characterized in that: 2. A fine powder of a perovskite-type composite oxide having the following formula: Sr _(1-X) .Y _(X) .SnO _{(3-d) wherein} 0 <x ≦ 0.4,0 <d <1. Gas sensor with electrodes mounted on a sintered body.