JPS5849820B2 - oxygen gas sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel oxygen gas sensor, and more specifically, to an oxygen gas sensor using a porcelain composition whose electrical resistance responds sensitively to changes in oxygen concentration at high temperatures. It is something.

Until now, electrical resistance materials whose characteristics change with oxygen concentration include Z n 0 1S n 0 2 and V 20 , which have been made into semiconductors from room temperature to around 400°C.
Oxides such as s, LaNi03, Lico02, B
Complex oxides such as aFe120,g are known, and
Solid electrolytes such as stabilized zirconia are known as electrolytes that change at high temperatures up to around 00°C.

However, among these electrical resistance materials, semiconductor oxides and composite oxides have a linear resistance change with respect to oxygen concentration, making it difficult to obtain a sharp response. This has the disadvantage that measurement errors inevitably increase.

On the other hand, solid electrolytes such as stabilized zirconia are susceptible to electrode deterioration and partial volatilization of material components when used at high temperatures, and are susceptible to electron conduction in low oxygen partial pressure regions. This method has the disadvantage of causing large measurement errors.

Therefore, in this type of technical field, there has been a great demand for an oxygen gas sensor element that can provide a nonlinear and sensitive response to changes in resistance value with respect to oxygen concentration and can stably maintain its characteristics over a long period of time.

As a result of extensive research in order to meet these demands, the present inventors have discovered a ceramic composition having a basic composition consisting of a specific range of molar ratios of a specific metal oxide and an oxide of Mo. We have found scales that are compatible with this, and have come up with the present invention.

That is, the present invention provides (4) Mg, Ca, Sr and Ba.
At least one metal oxide selected from
B) consists of an oxide of Mo or a part of it is replaced with an oxide of Cr, and the molar ratio of (4) and (B) is 5:4
to 5:9 or even (
C) A ceramic composition containing at least one metal oxide selected from Fe, Mn, Co, Ni, and Si in an amount not exceeding 10 moles based on component (4) is used as an electrical resistor. The present invention provides an oxygen gas sensor characterized in that the oxygen concentration can be detected by the change in electrical resistance value under a high temperature atmosphere.

In the present invention, Mg, Ca as the component (4)
, Sr, and Ba in combination with an oxide of Mo or a part thereof replaced with an oxide of Cr as the component (B). However, with any other combination, it is not possible to obtain a ceramic composition that exhibits nonlinearity in electrical resistance characteristics.

In addition, the molar ratio of component (4) and component (B) must be in the range of 5:4 to 5:9; if this is smaller than the above range, it will become chemically unstable. , if it becomes larger than this range, non-linear characteristics will be lost.

Furthermore, in component (B), a part of the Mo oxide is replaced with Cr.
When using a substituted Cr oxide, it is preferable that the amount of Cr oxide does not exceed 20 moles more than the amount of Mo oxide.

If this amount exceeds 20 moles, the nonlinear characteristics will not be sufficiently exhibited.

In the present invention, in addition to the basic composition consisting of component (4) and component (B) described above, Fe and Mn are used as a third component.
, Co, Ni, and Si in an amount not exceeding 10 molar range based on component (4), further improving its stability. be able to.

If this amount exceeds the above range, the stability tends to decrease, which is not preferable.

The porcelain composition used in the present invention includes, for example, component (4) and (
B) Components or substances that can be converted into these components by calcination, such as carbonates of the corresponding metals, and the powder of the third component, if desired, are thoroughly dried and mixed in a predetermined molar ratio, and heated at about 1200°C. It can be manufactured by calcining, then embedding and molding two metal wires that will become electrodes, and then sintering at about 1300°C.

The porcelain composition thus obtained has the general formula (where A is at least one metal selected from Mg, Ca, Sr, and Ba, and B is Mo or a combination of Mo and Cr; x:y is a ratio between 5:4 and 1:2, Z
is the number of oxygen atoms that saturates the valences of A and B).

This composite oxide maintains the following equilibrium state with other composite oxides.

When the Gibbs phase law is applied to this system, the degree of freedom becomes l, and when the temperature is fixed, the equilibrium oxygen partial pressure is always determined.

Furthermore, similar results can be obtained by adding a third component within the above-mentioned range.

As described above, the ceramic composition used in the present invention has the characteristic that the electrical resistivity changes significantly and rapidly in a non-linear manner with the equilibrium oxygen partial pressure as the boundary.

That is, at least 108 o in a high oxygen partial pressure range.
A material with an insulating property of hmα level or higher is
In the oxygen partial pressure range below the equilibrium oxygen partial pressure, 1
The metal conductivity changes to about 0'ohm-α or less.

By utilizing this large difference in electrical resistivity values before and after the equilibrium oxygen partial pressure, that is, nonlinearity, it is possible to accurately measure a constant oxygen partial pressure.

In this case, the difference in electrical specific resistance values can be adjusted to some extent by changing the ceramic composition as desired.

All of the porcelain compositions used in the present invention are extremely stable at high temperatures of around 100°C, and even after long-term use,
A part of the material components do not evaporate, and the electrode can be directly embedded in the edge of the material and fired, and then used as an integrated product. This has the advantage that electrode deterioration does not occur.

Therefore, it is a convenient material for long-term use at high temperatures of around 100°C.

As mentioned above, in the ceramic composition used in the present invention, the material itself does not change over time, and the influence of electrodes and other factors is small, and the large non-linear change in electrical resistivity with respect to oxygen concentration can be ignored. Therefore, it can be suitably used as a fixed point for correcting the oxygen partial pressure of a highly accurate high-temperature oxygen concentration sensor, or an oxide, composite oxide, or solid electrolyte oxygen sensor that changes over time.

Next, the present invention will be explained in more detail with reference to Examples.

Example Component (4) metal oxide powder, component (B) metal oxide powder, and optionally added third component metal oxide powder were mixed in the molar ratio shown in the following table, and polyvinyl alcohol was added as a binder. Add 5 weight φ to form a lump, about 1200
Calcinate for 30 minutes at ℃.

Next, this calcined material is crushed, and the diameter is 81ILN1 and the length is 101mm.
It is molded into a cylindrical shape of ItN, and a 0.0.
Electric resistors having various basic compositions were manufactured by embedding platinum wires with a diameter of 8 mm and sintering them at about 1300° C. for 30 minutes.

The electrical resistor obtained in this way was held at 1000'C for 30 minutes, the oxygen partial pressure was gradually lowered from normal pressure, and during this period, a current of 6 cm DC was continuously passed through, and the change in resistance was measured. did.

Then, the oxygen partial pressure when there is a sudden non-linear change from a high resistance value to a low resistance value was determined.

This operation was repeated five times to confirm that the same results were obtained, and the values are shown in the following table.

Although this value was repeatedly measured over a period of one year, no change over time was observed.

From this, it was found that this electrical resistor could be suitably used as an oxygen gas sensor element.

Claims (1)

[Scope of Claims] 1 (A) at least one metal oxide selected from Mg, Ca, Sr, and Ba; and (B)
A porcelain assembly consisting of an oxide of Mo or a part of which is replaced with an oxide of Cr, in which the molar ratio of (4) and (odor) is in the range of 5:4 to 5:9, is 2 (A) M g + C at S r and Ba.
At least one metal oxide selected from
B) an oxide of Mo or a part thereof replaced with an oxide of Cr; and (C) at least one oxide of a metal selected from Fe, Mn, Co, Ni and Si. and the molar ratio of (4) and (B) is 5=4 to 5:
Using a porcelain composition as an electric resistor in which (C) does not exceed 10 molar range based on the precept (4),
An oxygen gas sensor characterized by being able to detect oxygen concentration based on changes in electrical resistance in a high-temperature atmosphere.