JPS58123448A - Gas detecting element - Google Patents

Abstract

PURPOSE:To provide a small size and high reliable gas detecting element which has a fast answering speed and a high output voltage, by a method wherein electrode materials being different in a type are applied to both sides of a sintered material with a specified composition, being used as an oxygen ion conductive material, and the sintered material and the electrode are covered with a porous protecting layer. CONSTITUTION:An oxide of a raw material of a magnetic composition is Y2O3, WO3 and ZrO2 with a purity of not less than 99.8%, which are respectively weighed so that they are brought to 0<=x<=0.8 by a chemical formula of Y2(W1-xZrx)O6, they are mixed by a ball mill for 46hr togetherwith pure water, the mixture is filtered and dried, and after the mixture is temporarily burned at 1,200 deg.C for 2hr, it is repulverized by an attritor. A 5% polyvinyl 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 1 is baked to one side of a sintered material 3, a silver electrode 2 is baked to the opposite side thereof, a lead wire 4 is connected thereto, and a glass paste is applied as a porous protecting layer 6 and is baked at 500-700 deg.C to produce a glass detecting element. The element has a fast answering speed to hydrogen, isobutane, or the like is also excellent in a returning property, is approximately linearly increased in a value of an electromotive force with the increase in gas concentration, and also has an excellent selectivity to gas.

Description

[Detailed description of the invention] The present invention relates to a gas detection element that detects gas.

As a conventional gas detection element using a solid electrolyte material, a solid electrolyte oxygen sensor using 9-zirconia (ZrO) stabilized with calcia (CaO) or yttrium (Y-Os) is well known. As shown in Fig. IJIL1, this is a structure in which electric currents @l and l@2 are applied by a porous platinum layer to the inside and outside of a pipe 3 made of a solid electrolyte, and a lead ll4t is provided. - To measure oxygen concentration, a zirconia pipe is placed in the gas to be measured, and the inside of the pipe is filled with a gas of known oxygen partial pressure, such as air or line oxygen gas.

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

1 = CRT/4F) I n (Pot”'/
Pop'''% (1) where PO, (1) and 2 cans (1
) is the partial pressure of oxygen in the gas in which electrodes 1 and 2 are placed, respectively.

Therefore, the oxygen Sat 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. The one-degree needle is used for purposes such as measuring the oxygen concentration in automatic military exhaust gas or controlling the amount of dissolved oxygen in molten steel.

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

That is, Calcia (Cab) or Ittoria (y, o
, ) zirconia pipe stabilized by force as
Unless the temperature is 1400° C. or higher, a magnetic layer pipe with several layers cannot be obtained, and manufacturing is not easy. Furthermore, the electrodes 1 and 2 shown in FIG. 1 have the disadvantage that they are prone to scratches and deterioration of characteristics.

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 of the electrodes, it also has the disadvantage of being large in size and difficult to miniaturize. Furthermore, since the temperature of the gas to be detected needs to be several hundred degrees, its use is naturally limited.

In order to eliminate the above-mentioned drawbacks, an element having a structure as shown in FIG. 2 has been proposed. In other words, an electrode l formed by printing and baking Pt paste on the front and back of a stabilized zirconia disc 30.
and an electrode 2, and furthermore, a catalyst layer 5 and an electrode lead ls4 are provided on one of the electrodes. It is true that the nickel-like structure facilitates miniaturization of the device.

However, the time it takes for the output voltage to reach a certain value after gas introduction, that is, the response speed, is extremely slow and requires 5 minutes or more. In addition, there was also the problem that the output voltage decreased due to deterioration of the catalyst layer.The purpose of the present invention is to eliminate these drawbacks and to provide a highly reliable gas detection element that is small in dust, has a fast response speed, has a large output voltage, and is highly reliable. is intended to provide. :' 1 The gas detection element of the present invention is Y snow (W+ -x Z rx
) Using a porcelain composition expressed by the chemical formula 0 and in the range of 0≦X≦αS, for example, as shown in Fig. By baking different electrode pastes of
2, a lead wire 4 is attached, and the sintered body and electrode are further covered with a porous protective layer 6.

The following will be described in detail based on examples.

The oxide used as a raw material in the ninth stage of producing the magnetic composition Y, (W, + x Z rx )O- has a purity of 99
．． 8- or higher yttrium oxide (y*os), tungsten oxide (WOs) and zirconium oxide (ZrOt
), these are Y* (W+ −x Z rx )
A predetermined amount of each was weighed to give X-〇, 4 in O-, mixed with pure water in a ball mill for 46 hours, dried, calcined for 2 hours at 1200c, and re-pulverized in a Raikai machine. . After that, 5% polyvinyl alcohol solution was added and granulated, press-formed to a diameter of 10 cm and a length of approximately 51111 cm, sintered at 1200°C for 1 hour, and then cut to a thickness of 0.5 cm, as shown in Figure 3. After baking a platinum electrode on one side, a silver electrode was baked on the opposite side. Lead wires were attached to form the porous protective layer 6, and glass paste was applied and baked at 500°C to 700°C.

Measurement Ka As shown in Fig. 4, a quartz pipe 7 with a heater 5 wrapped around it is heated so that the sample temperature reaches 300 to 400 degrees Celsius, the sample prepared in the previous method is placed, and the temperature of Kl in the quartz pipe is 1 degree. The voltage induced in the sample was measured when a known gas was heated at about 10100 C for 1 minute.

The results are shown in Figure 5.

In FIG. 5, 3000 ppNA of isobutane was mixed in air and poured into a quartz pipe heated to a sample temperature of 400 CK, at which time the electromotive force induced in the sample was measured.

The induced voltage line reached the steady-state value of 80- within 5 seconds, showing a sufficiently fast response speed.The recovery performance after switching the gas to only air was also poor and returned within 1 minute, which was sufficient. This is a performance that can be put to practical use.

Figure 6 shows H, (straight #11) and isobutane (i-CmH
+・) (Line 2) is the measured value of electromotive force when changing the mixing ratio to air. The value of the electromotive force increases almost linearly as the gas concentration increases. The value also differs depending on the type of gas, indicating that selectivity can be obtained for the gas. Normally, the concentration required for detection of flammable gas is below the lower explosive limit of '/4 to l/1oo. It is said that In the case of imbutane, this value is approximately 1100
ppm to 5000ppm, and for this level of isobutane concentration, the device of the present invention is 50mVl! It can be concluded that there is an output voltage of more than J[, and that there is sufficient effectiveness.

Furthermore, if the same electrode material is used for electrode 1 and electrode 2 shown in Fig. 3, the Ktj output voltage will be 1 mV or less, and it will not exhibit effective characteristics as a gas detection element. In this case, even when the other electrode was made of palladium, it showed the best characteristics, similar to platinum.

In other words, this means that the device characteristics can be controlled by the combination of selected electrode materials.

Figure 7 shows carbon monoxide (CO) when the ratio of zirconium dioxide (ZrO) and tungsten oxide (WOs) in the sintered body composition is changed in the gas detection element of the present invention.
It shows the output voltage of the gas detection element for air containing 3000p.

In practice, a method for detecting an electromotive force value of 10 mV or less is more difficult due to the circuit configuration. Therefore, it is desirable that the electromotive force be as large as possible, and 50 mV or more is required. Y* (W+ −x Z x ) used in the present invention as a friend
In the ceramic composition represented by Cb, the range of the blending ratio X of zirconium oxide and tungsten oxide is 0≦X≦0.8
is desirable.

In addition, the table shown below shows how the gas sensing element of the present invention is measured from room temperature to
The rate of change in output voltage after a temperature cycle test was repeated up to 500 times, in which the tube was placed in an electric furnace held at 500° C., held for 5 minutes, taken out to room temperature, and left for 20 minutes.

The conventional element in the table has a critical structure as shown in FIG. 2, and was manufactured using zirconia (ZrO) stabilized with calcia (Cab). Test results revealed that in conventional devices, the solid electrolyte and the electrodes or between the electrodes and the catalyst layer separated due to temperature cycles), and cracks occurred, resulting in a significant drop in output voltage. - The device according to the invention exhibits stable characteristics with almost no decrease in output voltage.

In addition, a porous protective layer is effective for stabilizing device characteristics, and those without a protective layer are very hot! The degree of S for Nycle was also the same as that of the conventional element.

It has been found that in the gas sensing element of the present invention, containing a small amount of yttrium oxide in the porous protective layer has the effect of increasing the adhesive strength between the protective layer and the solid electrolyte.As described above, the gas sensing element of the present invention It is clear that the sensing element is small, easy to sinter, resistant to temperature cycles, has sufficient stability, and exhibits practically useful performance in both response speed and output voltage.

9-9 In this example, combinations of silver and platinum and silver and palladium are shown as electrode materials, but other combinations can be used, such as using a mixture of nickel and nickel oxide as one electrode and using silver or nickel oxide as the other electrode material. Expanded platinum gold 10-Q1 Surrounding listener rl explanation The first and second mistakes are the structure of DE rice's waste detection element /l<
'(J-Fig.

FIG. 3 is a diagram showing the structure of the scum detection element of this example.

Condolence 41 is a set-up that provides the timeliness of the light detection element in the heather.
Kuzu diagram 0 → 5 evil, Figure 6 Wisdom, this example's waste detection element's waiting ratio 0, 弔 7- is the 4-element example's waste intelligence system child basket 1 fu 1 Prf
9 - Figure 0.41 - (l, 2 is for self-reflection, 3 is for dedication.)
No, 4,4-ba lead.

In Figure 2 IC, 1, 24 mausuji - sorry, 3 is the arm storage of Ichifusaki λ, 4 and 4 are the leads, 5 is the catalyst layer d)
ni-) 0 porridge 3.4 evil - koote 1.2 is 1 regret, 3 is solid - is 1 linden eye, 4.4 is 1 what do, ha 0 hole Teiho IJ51
1wf, 5+, +t:, -no, 7 is Ishidai Paig.

Condolence 1) 1 meeting ko-,,)v"(lij water Atko Ai-=f
Φ Note *w, 2nd figure 1st figure 2 figure 3 figure 4 figure 5 figure 8 line jFIIl'1 (4i) force°゛su JL degree (PPfn)

Claims (1)

[Claims] In a gas detection element formed by providing electrodes on both sides of a sintered body having oxygen ion conductivity and further attaching the electric lead wire, Yt(W+-xZrx)O is used as the sintered body.
a (0≦×≦Q, 8) An oxygen ion conductor is used, and different types of electrode materials are applied to both sides of the sintered body to protect the iron sintered body and the electrodes in a porous manner. A gas detection element characterized by being coated with a layer.