JPS58123446A - Gas detecting element - Google Patents

Abstract

PURPOSE:To provide a small size and high reliable gas detecting element which has a fast responsing speed and a high output voltage, by a method wherein the respective electrode materials being different in a type are applied to both surfaces of a specified sintered material, being used as an oxygen ion conductive material, and the sintered material and the electrode are covered with a porous protecting layer. CONSTITUTION:A raw material of a magnetic composition is oxides such as La2O3, WO3 and ZrO3 with a purity of not less than 99.8%, which are weighed so that they are brought to 0.4<=x<=1.0 by a chemical formula of La2(WxZr1-x)2)7, they are mixed by a ball mill for 46hr togetherwith pure water, the mixture is filtered and dried, and after it is temporarily burned at 1,200 deg.C for 2hr, it is repulverized by an attritor. A 5% alcohol liquid is then added to granulate it, the granulation is press-molded 10mm. in diameter and about 5mm. in length, and after the work is sintered at 1,200 deg.C for 1hr, it is cut to 0,5mm. in thickness. After a platinum electrode 2 is baked to one side of a sintered material 3, a silvere electrode 1 is baked to the opposite side thereof, and lead wires 4 and 4' are connected thereto. A glass paste is further coated as a porous protecting layer 6 to produce a baked glass detecting element at 500-700 deg.C. The element has a sufficiently fast answering speed to hydrogen, isobutane or the like, is excellent in returning property, is about linearly increased in a value of an electromotive force with the rise in gas concentration, and has an excellent selectivity to gas.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas sensing element that detects gas by generating an electromotive force depending on gas concentration.

As a gas sensing element using conventional solid electrolyte materials,
A solid electrolyte oxygen sensor using zirconia (Zrω→) stabilized with calcia (C.O) or ittria is well known. Electrodes 1 and 2 made of porous platinum layers are provided inside and outside the piezoelectric layer,
Moreover, it has a structure in which lead wires 4 and 4' are provided. The oxygen concentration is measured by placing a ZrOz pipe in the gas to be measured, and filling the inside of the pipe with a gas having a known oxygen partial pressure, such as air or pure oxygen gas.

At this time, the relationship a between the electromotive force generated between electrode 1 and electrode 2 and the oxygen partial pressure is given by the Nernst relational expression (1).

E=(RT/4F)Jsc(PO-RePot (“))
Q) Here, Pot0' and Pot"' are the partial pressures of oxygen in the gas in which electrode 1 and electrode 2 are placed, respectively.

Therefore, the oxygen concentration in the gas to be measured can be determined from the value of the electromotive force generated based on the difference in oxygen partial pressure inside and outside the solid electrolyte pipe.

An example of an oxygen concentration meter using this type of oxygen concentration battery is the measurement of oxygen concentration in automobile exhaust gas. The dye is 11 dissolved in molten steel! It is used for purposes such as quantity control.

However, the above-mentioned conventional solid electrolyte materials and gas sensing elements using the same have various drawbacks as follows.

That is, Calcia (C,0) or Ittria ('b
Stabilized zirconia pipes such as Om) cannot be obtained as dense porcelain pipes unless at a high temperature of 1400° C. or higher, and manufacturing is not easy. Furthermore, the adhesive surfaces of the electrodes 1 and 2 and the zirconia pipe 3 shown in FIG. Moreover, the zirconia pipe itself has the disadvantage of being susceptible to cracks and deterioration of its properties.

Furthermore, since it is necessary to supply a gas with a known oxygen concentration, such as air or oxygen, as a reference gas to one electrode portion, there is a drawback that the shape is large and it is difficult to miniaturize. Furthermore, since the temperature of the gas to be detected needs to be several hundred degrees, its applications are naturally limited.

In order to eliminate the above-mentioned drawbacks, an element having a structure as shown in FIG. 2 has been proposed. That is, electrodes 1 and 2 are formed by printing and baking Pi paste on both sides of a stabilized zirconia disc 30, and a catalyst layer 5 and an electrode lead wire 4 are further formed on one electrode. It is true that such a structure makes it easier to miniaturize the device. However, the time required for the output voltage to reach a certain value after gas introduction, that is, the response speed, was extremely slow, requiring a time of 5 minutes or more. There was also the problem that the output voltage decreased due to deterioration of the catalyst layer.

An object of the present invention is to eliminate these drawbacks and provide a gas sensing element that is small in size, has a fast response speed, has a large output voltage, and is highly reliable.

The gas loading/unloading element of the present invention is Lag (WxZrx -x)
It is represented by the chemical formula g Oy, and 0. +<χ41. o
For example, the porcelain composition shown in the range 2 is used.
As shown in the figure, electrode pastes of different types I1 are baked on the upper and lower surfaces of the sintered integral disk 3 having the above composition to form electrodes 1 and 2, and lead wires 4 are attached to the porous protective layer 6. The sintered body and electrode are coated with a nine-layer structure.

The following will be described in detail based on examples.
The oxides used as raw materials to produce the porcelain composition of rs-xho were lanthanum oxide (La2ha), tungsten oxide (CWog), and zirconium oxide (ZrO) with a purity of 99.816 or higher. La m these
(WxZt -IC) x=0.7 in snow Oy
Weigh out the predetermined amount of each, mix with pure water in a bowl for 46 hours, dry the mouth, and heat at 1200℃ for 2 hours.
After calcining for a period of time, it was re-pulverized using a Raikai machine.

Then, 5% polyvinyl alcohol solution was added, granulated, and press-molded to a diameter to f length of about 5W%.
After sintering at 0℃ for 1 hour, it was cut to a thickness of 0.5M1WL.
As shown in Figure 3, after baking a platinum electrode on one side, burn a straw electrode on the other side and connect lead wire 4.4'! −
Nine. Further, a glass paste was applied as a porous protective layer 6 and baked at 500°C to 700°C.

Suppression! Specifically, as shown in Fig. 4, the sample prepared in the above method is placed in a quartz pipe 7 wrapped around a heater 5, and the sample is heated to a temperature of 300°C to 400°C. Approximately 100 CC of gas with known concentration in the pipe for 1 minute
The voltage induced in the sample when flowing was measured.

The results are shown in FIGS. 5 to 7.

Figure 5 shows that a gas mixture of air and isobutane at 3000 ppm was poured into a quartz pipe heated to a sample temperature of 400°C, and the electromotive force induced in the sample was measured1.The induced voltage was , the steady value of 80 within 5 seconds
The response speed was sufficiently fast. It was found that the recovery performance after switching the gas to only air was also good, and the recovery took place within 1 minute, indicating that the performance was sufficient for practical use.

Figure 6 shows H2 (straight line 1) and isobutane (sea 04Ht).
*) This is the measured value of the electromotive force when the mixture ratio is applied to the air (straight line 2). The value of electromotive force increased almost linearly as the gas concentration increased. There are also differences in the values depending on the type of gas, indicating that selectivity to the gas can be obtained.

Normally, the concentration required for detection of flammable gas is 1/4 to 1/1 oo of the lower explosive limit. For isobutane this value ranges from approximately 100f/rn to 5000-
9. It can be concluded that for this level of isobutane concentration, the output voltage of the device of the present invention is likely to be approximately 50 mV or more, and thus has sufficient effectiveness.

In addition, as shown in FIG. 3, the is electrode and electrode 2 are made of the same electrode material f.
When #+ is used, the output voltage will be less than 10mV,
It did not show any effective characteristics as a gas detection element. Further, even when one electrode was made of baked silver and the other VC- was made of palladium, the most favorable characteristics were exhibited as in the case of platinum.

In other words, this means that element 4i) can be controlled depending on the combination of electrode materials selected.

Figure 7 shows that when the ratio of zirconium dioxide (ZrOs) and tungsten oxide (WOs) in the sintered body composition is changed in the gas detection element of the present invention, 1 t* of monoacid (C
o) 't3000pp) JJ inspection for air containing m9
! It shows the output voltage of the I element.

In practice, detection of an electromotive force value of 10 mV or less is increasingly difficult due to the circuit configuration. Therefore, it is desirable that the electromotive force be as large as possible, and a line of 50 mV or more is required. Therefore, hL-s (WxZrs-X)! is used in the present invention. In the ceramic composition indicated by 0ma, the range of the blending ratio X of tungsten oxide and zirconium oxide can be said to be desirably within the range of O, 1j).

The table below shows a temperature cycle test in which the gas sensing element of the present invention was placed in an electric furnace maintained at 500°C from room temperature, held for 5 minutes, then deposited at room temperature again and left for 20 minutes. The conventional element in the table, which shows the rate of change in output voltage after repeating up to 500 times, has the structure shown in Figure 2, and the material is zirconia (Zr) stabilized with calcia (CAO).
h) Produced using 9. Test results revealed that in conventional devices, the solid electrolyte and the electrodes, or between the electrodes and the catalyst layer, may become separated due to temperature cycles, or cracks may occur, resulting in a significant drop in output voltage. became. - The device according to Rikiki's invention exhibits stable characteristics with almost no decrease in output voltage. (9) The porous protective layer is effective for stabilizing device characteristics, and those without a protective layer have the same resistance to temperature cycles as conventional devices.

As described above, it is clear that the gas sensing element of the present invention is small, easy to sinter, resistant to temperature cycles, has sufficient stability, and exhibits practically useful performance in terms of response speed and output voltage. .

Furthermore, in this example, combinations of silver and platinum and silver and palladium are shown as electrode materials, but other combinations such as a mixture of nickel and saponified nickel are also possible.

[Brief explanation of the drawing]

Diagram 1 and Diagram 2 are diagrams showing the traditional gas vL Keiko Sakaki. %I, Figure 3 shows the fourth aspect of the gas detection element of the present invention, and the fourth figure is a diagram showing a custom-made foot measuring device of the gas discrepancy system of the present invention. Figure 5 and Figure 6 are the Hakamae diagrams of the gas detection elements of Mokuenshi 4. Figure 7 is the composition ratio and origin of 1 and 2 are the pipes of Shiranami Shiraku, 3 is the pipe of the Ichiza Shigetsu, and 4 is the lead. - 100 million, 3 is one fu - Chusei's green I [body, 4ba lead - 15 is]! 1! - No. 5 is a heater, and 7 is a quartz pipe. Floor 6 Kyoukai Koishi, l is Bo-kei Kome 1 Karizunao - 12 Figure 5 Figure 6 too too too tooo. Force°S5Jl 3 (pr-n) Fig. 7 Laz (WX Zr+-x )z (77υ
0.5 7
．． 0×

Claims (1)

[Claims] In a gas detection element in which electrodes are provided on both sides of a sintered body having oxygen ion conductivity and lead wires are attached to the skeleton electrodes, the sintered body contains La, (WxZrt-x
Using an oxygen ion conductor of >20t (tomo 0.41 A gas detection element characterized by being coated with a protective layer.