JP3068658B2 - Heated gas sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating operation type gas sensor.

[0002]

2. Description of the Related Art In recent years, various heating-actuated gas sensors have been proposed and put into practical use. Above all, a limiting current type oxygen sensor using a solid electrolyte is composed of pure zirconia (ZrO ₂ ), yttria (Y ₂ O ₃ ), and magnesia (M
gO), calcia (CaO), and other divalent or trivalent metal oxides in a solid solution of about several mol% to hold fluorite-type cubic crystals at low temperatures. Possible, fast response speed, stable electromotive force, can be used in high temperature atmosphere, etc., to prevent oxygen deficiency accidents in closed rooms such as basements, oxygen concentration measurement in molten steel, engines and boilers, etc. This sensor is suitable for various purposes such as combustion management and pollution measurement.

As one example of this oxygen sensor, lead wires of sensor elements are respectively connected to the respective tips of four stem pins provided vertically on a ceramic stem such as alumina (Al ₂ O ₃ ). , The sensor element is covered with a porous ceramic cap having air permeability,
Some of the caps are bonded to the stem by amorphous glass.

[0004] The sensor element is usually made of a thin ionic conductor made of a solid electrolyte having ionic conductivity such as stabilized zirconia (eg, ZrO ₂ -8 mol% Y ₂ O ₃ ). It is configured to be held horizontally by lead wires.

As the lead wire, a Pt wire is mainly used from the viewpoints that it is hard to be oxidized in a measurement atmosphere and is stable, and that the mechanical strength does not decrease. As the amorphous glass, lead borosilicate glass or the like is mainly used. In addition, as a cap, Al which is extremely easy to handle in mass production and has excellent heat resistance is used.
₂ O ₃ , steatite ((Mg ₃ Si ₄ O ₁₀ (OH) ₂ ), etc. are preferably used. When it is not necessary to use an explosion-proof structure for the oxygen sensor, stainless steel may be used instead of the cap. There is also a case where a mesh cover made of steel is used.

[0006]

However, in the above-described oxygen sensor, since the operating temperature is as high as about 500 to 600 ° C. at the time of high temperature (at the time of heating), the following problems are included. . That is, the cap often contains a material that easily changes the operating atmosphere to an acidic atmosphere or a basic atmosphere, and there is a problem that the operating atmosphere tends to be a corrosive atmosphere for a Pt wire as a lead wire.

Also, amorphous glass or the like often contains PbO, and when this PbO-containing glass is used, the operating atmosphere becomes an atmosphere rich in PbO, which embrittles the Pt wire. There was also a problem. Considering the reliability of the lead wire in these atmospheres, particularly when heating (high temperature) and cooling (low temperature to room temperature) are repeatedly performed, the embrittlement of the Pt wire becomes remarkable, and the mechanical properties of the lead wire during operation are increased. There was a danger that the target strength was reduced and the lead wire was broken in some cases, and the oxygen sensor lost its function as a sensor.

The present invention has been made in view of the above circumstances, and repeatedly performs heating (high temperature) and cooling (low temperature to room temperature) in an acidic atmosphere, a basic atmosphere, an atmosphere rich in PbO, and the like. It is an object of the present invention to provide a heating-actuated gas sensor that does not become brittle or break even in a case and that can maintain good mechanical strength.

[0009]

In order to solve the above-mentioned problems, the present invention employs the following heat-actuated gas sensor. That is, a sensor element, a heater for heating the sensor element, and a plurality of lead wires joined to each of the sensor element and the heater, wherein the heater heats the sensor element, Operates , and the lead wire has a Pt of 70 to 95% by weight;
It is made of a platinum alloy containing 5 to 30% by weight of Rh . Further, 80 to 95% by weight of Pt, R
It is more preferable to use a platinum alloy containing 5 to 20% by weight of h.
preferable.

[0010]

According to the heating operation type gas sensor of the present invention, the material of the lead wire is 70 to 95% by weight of Pt and 5 to 30 weights of Rh.
% Of platinum alloy, acid atmosphere,
Even when heating (high temperature) and cooling (low temperature to room temperature) are repeatedly performed in a basic atmosphere, an atmosphere rich in PbO, or the like, there is no embrittlement or disconnection, and good mechanical strength is maintained.

[0011]

FIG. 1 is a schematic structural view showing an oxygen sensor 1 which is an embodiment of a heating-actuated gas sensor according to the present invention. In this oxygen sensor 1, lead wires 5 of a sensor element 4 are respectively connected to tip portions 3a of four stem pins 3, provided vertically to a stem 2, and the sensor element 4 has air permeability. Covered with a porous ceramic cap 6. The cap 6 is joined to the stem 2 by an amorphous glass 7.

The sensor element 4 includes an ionic conductor 11,
An electrode 12, an electrode protection layer 13, a void 14, a sealing layer 15,
It is schematically constituted by a heater 16 and four lead wires 5a to 5d.

The ionic conductor 11 is made of a thin solid electrolyte having ionic conductivity such as stabilized zirconia (for example, ZrO ₂ -8 mol% Y ₂ O ₃ ), and gas diffusion vertically penetrating the center thereof. A hole 11a is formed. The electrode 12 is a porous electrode made of Pt, and includes a cathode electrode 12a provided on the upper surface of the ionic conductor 11, and an anode electrode 12b provided on the lower surface.
The lead wire 5a is joined to the cathode electrode 12a, and the lead wire 5b is joined to the anode electrode 12b.

The electrode protective layer 13 is made of, for example, crystallized glass having a linear expansion coefficient similar to that of the ion conductor 11. The cathode electrode 12 a is formed on the upper surface of the ion conductor 11 above the cathode electrode 12 a. It is provided in a substantially hemispherical shape so as to cover the whole, and a gap portion 14 is formed between the electrode protection layer 13 and the ion conductor 11. The lower end 13 a of the electrode protection layer 13 is in close contact with the upper surface of the ionic conductor 11.

The sealing layer 15 is made of, for example, an airtight sealing glass. The sealing layer 15 is provided integrally and substantially hemispherically on the entire upper surface of the electrode protection layer 13. Is in close contact with the upper surface of the ionic conductor 11. The heater 16 is a heater for heating the ionic conductor 11 to a predetermined temperature, and is provided integrally on the upper surface of the sealing layer 15. A pair of lead wires 5c and 5d are joined to the heater 16.

As the lead wires 5a to 5d, platinum alloy wires containing Pt as a main component and Rh as a subcomponent in a range of 5 to 30 % by weight, particularly preferably in a range of 5 to 20% by weight are used. The platinum alloy wire is obtained by adding an impurity metal to the platinum alloy wire, for example, containing Pt as a main component and Rh as a subcomponent in a range of 5 to 30 % by weight, and containing Ru, Pd, Os, and Ir. At least one element selected from the group consisting of metals consisting of, Cu, Ag, and Au.
A platinum alloy wire contained in the range of 01 to 10.00% by weight may be used.

Table 1 shows an example of the composition ratio and characteristics of the platinum alloy wire.

[Table 1] These platinum alloy wires use conventional Pt in terms of tensile strength and hardness.
It turns out that it is superior to the line.

Here, a description will be given of experimental results of a heat cycle test performed for comparing and studying the lead wire 5 of the present invention and a conventional lead wire.

(Experimental Example 1) The results of the heat cycle test in an alkaline atmosphere are shown in Table 2.

[Table 2] Here, the sensor element 4 is set in an Al2O3 casing (consisting of a stem 2 and a cap 6 and the like), and sodium oxide (Na ₂ O) and potassium oxide (K ₂ O) using an amorphous glass containing. The conditions of the heat cycle test were as follows: one cycle was left at a high temperature of 450 ° C. for 5 minutes,
Leave at room temperature of 5 ° C. for 2 minutes and cycle up to 10
Repeated 000 times. The number of sensors used for the test was 20 each.

From the above results, the lead wire 5 of the present invention has no surface embrittlement and no breakage as compared with the conventional lead wire, and the mechanical strength such as tensile strength and hardness is remarkably improved. It is clear that there is.

Experimental Example 2 Table 3 shows the results of the heat cycle test in a PbO atmosphere.

[Table 3] Here, the sensor element 4 was set in a casing made of Al ₂ O ₃ , and a lead borate glass containing PbO was used for joining the cap 6 and the stem 2. The conditions of the heat cycle test and the number of sensors were the same as those in Experimental Example 1.

From the above results, it can be seen that the lead wire 5 of the present invention has no surface change and no breakage as compared with the conventional lead wire, and the mechanical strength such as tensile strength and hardness is remarkably improved. Is evident.

As described above, according to the above embodiment, the material of the lead wire 5 of the oxygen sensor 1 is a platinum alloy containing Pt as a main component and 5 to 30 % by weight of Rh as an auxiliary component. Even when heating (high temperature) and cooling (low temperature to room temperature) are repeatedly performed in an acidic atmosphere, a basic atmosphere, an atmosphere rich in PbO, or the like, the lead wire 5 can be prevented from being embrittled or broken, and the tensile strength can be reduced. Mechanical strength such as strength and hardness can be significantly improved. As described above, it is possible to provide an oxygen sensor capable of responding to high reliability, miniaturization, and the like.

The lead wire 5 can be applied to various sensors other than the above-described oxygen sensor. For example, heating activated carbon monoxide sensors and hydrocarbon sensors,
In a heat cleaning type humidity sensor or the like, similarly to the oxygen sensor, embrittlement and breakage of the lead wire can be prevented, and mechanical strength such as tensile strength and hardness can be significantly improved.

[0025]

As described above in detail, according to the heating-operated gas sensor of the present invention, the sensor element, the heater for heating the sensor element, and the plurality of the sensor elements and the heater which are joined to the heater, respectively. And a lead wire of
In the heating-actuated gas sensor, in which the heater operates the sensor element by heating the sensor element and measures the concentration of the surrounding gas, the lead wire is composed of platinum containing Pt as a main component and Rh as a subcomponent. Since it is made of an alloy, it can be heated (high temperature) and cooled (low temperature to low temperature) in an acidic atmosphere, a basic atmosphere, an atmosphere rich in PbO, or the like.
(Room temperature) can be prevented from becoming brittle and disconnected, and the mechanical strength such as tensile strength and hardness can be significantly improved. As described above, it is possible to provide a heating-actuated gas sensor that can cope with high reliability, miniaturization, and the like.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an oxygen sensor according to one embodiment of the present invention.

FIG. 2 is a front sectional view showing a sensor element of the oxygen sensor according to one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Oxygen sensor 2 Stem 3 Stem pin 4 Sensor element 5 Lead wire 6 Cap 7 Amorphous glass 11 Ion conductor 12 Electrode 13 Electrode protection layer 14 Void 15 Sealing layer 16 Heater

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-203266 (JP, A) JP-A-54-68695 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 27/41 G01N 27/12 G01N 25/20

Claims (2)

(57) [Claims] 1. A sensor element comprising: a sensor element; a heater for heating the sensor element; and a plurality of lead wires joined to the sensor element and the heater, wherein the heater heats the sensor element. In the heating-actuated gas sensor in which the sensor element operates and measures the concentration of the surrounding gas, the lead wire has a Pt of 70 to 95% by weight and a Rh of 5 to 5%.
A heating-actuated gas sensor comprising a platinum alloy containing 30% by weight . 2. The lead wire weighs 80 to 95 Pt.
%, A platinum alloy containing 5 to 20% by weight of Rh.
The heat-operated gas sensor according to claim 1, wherein
Sa.