JPS5991358A - Nitrous gas sensor - Google Patents

Abstract

PURPOSE:To enable the continuous measurement of nitrous gas and to contrive to reduce cost, by combining an oxygen ion conductive solid electrolyte and a nitrous gas decomposition catalyst. CONSTITUTION:After porous platinum electrodes 2 are baked to both surfaces of a zirconia disc 1, platinum lead wires 3 are attached to said electrodes 2 and a nitrous gas decomposition catalyst 4 is subsequently baked to the single surface of the disc 1 to obtain a nitrous gas sensor. When a gaseous mixture is prepared by mixing gas containing oxygen in predetermined concn. and nitrous gas and flowed to the nitrous gas sensor, electromotive force is generated in the nitrous gas sensor by the difference of oxygen concn. The concn. of the nitrous gas in the gaseous mixture can be calculated from said electromotive force.

Description

[Detailed Description of the Invention] This invention is a new moon for measuring the concentration of laughing gas (nitrous oxide: N, 0) contained in anesthetic gas, etc.

This is related to a sensor. The 44ji sensor is desired to have excellent accuracy, response, and stability, as well as to be inexpensive.

As this type of conventional technology, an infrared laughing gas analyzer or gas chromatography is known.

However, both methods are expensive, and gas chromatography has the disadvantage of not being able to perform continuous measurements.

The object of the present invention is to eliminate the above-mentioned drawbacks and provide a laughing gas sensor that is capable of continuous measurement and is inexpensive.

Currently, anesthetic scum is used in many hospitals for the purpose of general anesthesia or sedation. This anesthetic gas is generally a gas containing laughing gas, but depending on the purpose and patient's condition, the concentration of laughing gas can be varied in the range of 10 to 30 vol. (mixed with oxygen or air). adjust)
Already used. The concentration of laughing gas in the anesthesia scum after mixing is:
It is possible to measure using an infrared laughing gas analyzer or gas chromatography, but the reality is that they are not used because they are expensive.

The inventors of the present invention have conducted extensive studies with the aim of developing an inexpensive laughing gas sensor that can be used for the above purposes. It was discovered that a laughing gas sensor that is inexpensive and has excellent performance can be obtained.

The advantages of the present invention will be specifically explained below with reference to Examples.

Example 1゜l) Preparation of laughing gas sensor (1) A zirconia disk stabilized with 8.0 mo1% ittria having a diameter of 6.4 mm and a thickness of 1.5 gates as shown in Fig. 1. After firing (=J) a porous hole I (platinum electrode (thickness: approx. 3 μm)) with an inner diameter of 4 on both sides of 1, the inner diameter was 0.
．． Attach the two platinum lead wires 3. Next, a laughing gas decomposition catalyst 4 is burned on one side of the zirconia disk to obtain a laughing gas sensor.The laughing gas decomposition catalyst is cobal oxide (Co3U, ) having a specific surface area of about 50TT?/g. Add an appropriate amount of silica sol to adjust the viscosity and form it into a sheet.
After drying at 120°0, it is fired in air for 500"0.2 hours. The obtained catalyst sheet is crushed and sized into 200-325 meshes, and an appropriate amount of silica sol is added to make it into a paste. .

Next, the paste was applied to one side of a zirconia disk to a thickness of about 0.3 mm, and then baked in air for 10 minutes (J, 2 hours) to obtain a laughing gas sensor (1).

2) Performance Evaluation Apparatus The performance of the laughing gas sensor (1) produced by the method described above was evaluated using the apparatus shown in FIG.

Silicone rubber was placed so that the laughing gas sensor 9 fixed to the alumina insulating tube 8 was placed in the center of the quartz reaction tube (center inner diameter 10 mm) inserted into the electric furnace 6 with the heater 5. Set tube 8 into tube 7 using stopper lO. The platinum lead wire 3 is coated with an inorganic adhesive 10 at the tip of the insulating tube 8.
Fixed and sealed by.

The measurement residue is laughing gas and air using a commercially available standard gas generator (
A honeycomb-shaped cordierite rectifying layer 12 is passed through the reaction tube 11 at a flow rate of 0.5 t/d. The gas is then introduced into the laughing gas sensor section and exhausted to the outside of the system through the reaction tube outlet 13. While monitoring the temperature of the sensor section 9 using the thermocouple 14, the generated electromotive force is measured using a commercially available digital
Measurement was performed using a multimeter 15.

The sensor electromotive force R'' (mV) in Table 1 is positive on the electrode side where the laughing gas molecule 91C catalyst is baked.From this, it can be seen that laughing gas (N20) is catalyzed on the electrode side where the fire decomposition catalyst is baked. Reaction (j゛1 produced by decomposition as in 11
! It is thought that this caused a difference in oxygen concentration between the two electrodes, and an electromotive force was generated between the two electrodes.

N, 0→N, -1-1/202・・・・・・・・・・
・・・・・・ +11 Now, dregs containing 1% oxygen concentration (if air is used as in this example, y=0
．． 209) and 1()OvO1% laughing gas are mixed to create a mixed gas (for example, anesthetic gas) with a laughing gas concentration of 00x vo1%, and it is assumed that the mixed gas is not flowed to the laughing gas sensor section. At this time, the oxygen concentration on the sensor electrode surface that is not coated with the laughing gas decomposition catalyst is the laughing gas decomposition reaction N, 0→N2+1/
If 20t does not progress at all, then 100y(1-x)
vo1% and IJru. The oxygen concentration at the sensor electrode surface coated with a laughing gas decomposition catalyst is determined by the mechanism described above, assuming that the laughing gas decomposition reaction proceeds completely in the catalyst layer and that no dilution occurs due to diffusion of the generated oxygen. Considering that the electromotive force Et (mV) of the laughing gas sensor is generated due to the oxygen concentration difference caused by , the following equation is established from the generally well-known Nernst equation.

y(]-x)+0.5y However, T is the sensor temperature (0K).

(In formula 21, oxygen concentration Y (X l 00 vat%) in diluent gas (air or oxygen in the case of anesthesia gas)
is known (if unknown, it can be determined in advance by some method), so using equation (2), the sensor current 'tw j]hi' can be used to calculate The fresh air concentration x (X100vo1%) can be determined.

The above is the operating principle of the laughing gas sensor according to the present invention.
In reality, the formula (2) does not hold true because the catalyst is not coated and the laughing gas decomposes on the sensor electrode surface, and dilution occurs due to the diffusion of C in the catalyst layer. I actually got it! The force H” (mV) (3)
Expressed as the formula, the H'F value test results show that for one thread number, most of the laughing gas concentration
1%) and can be regarded as a constant (however, it depends on the temperature).

ff”(rnV)=kEt(mV)=・・・−・・
・The results obtained in this example (first
Table) will be considered in more detail. Since air (Y = (1,209)) is used as the dilution residue, %(2
From Equation 1, next, transform Equation (4) into Equation (5), and calculate the newly introduced coefficient ff(X) with laughing gas # degree x(XIO(1vo
1%), the results shown in Table 2 are obtained.

H (mV) = α (X)・X・T・・・・・・・・・・
...(5) Table 2 From Table 2, the coefficient αt(X) is surprisingly dependent on the laughing gas concentration and sensor temperature over a wide range of laughing gas concentrations when air is used instead of the diluted scum. constant (~4.OX l
(You can see that it can be considered as 1″l. Next, (5) = αm
(x)・x@T ・・・・・・・・・・・・・・・(
6) However, α''(x): is α(x).

As mentioned above, for the actually measured electromotive force Em, since it depends on the sensor temperature, α''(X) differs from the display and hardly depends on the laughing gas concentration (α(x) (because it hardly depends on , and the above consideration (αfn(
x), zunawajik does not depend on X, but depends on temperature) can be paleoconfirmed.

Table 3 FIG. 3 shows the temperature dependence of αIr1(X) in the form of a ratio (-k) to α(X). In the figure, 45(1'0,550γ:, Fi50'Q, 75
0'Q, 850℃.

A line segment is drawn at the temperature condition of 95C)"C, which indicates the range of variation within the experimental conditions of the value at % temperature. On the lower temperature side from around 500°C, α
The reason why (X) is small is considered to be due to a decrease in the decomposition efficiency of laughing gas in the catalyst layer and a decrease in oxygen ion conductivity of the stabilized zirconia.

The reason why α1n(X) is smaller on the high temperature side than around 850° C. is considered to be because the decomposition of laughing gas on the sensor electrode surface or the rectifying layer on which the laughing gas decomposition catalyst is not baked cannot be ignored.

As mentioned above, if we find the sensor electromotive force Fr"ov relation to laughing gas 1tIj degree By measuring the 1 force Em of the 4-piece senna, it is possible to obtain 4 degrees x (X100 vol %) of laughing air.Also, when air is used as the dilution residue as shown in this example, the temperature If used under certain conditions, α''(X) can be considered to be almost a constant over a wide range of 4 degrees of laughing gas, so the constant α''(X) can be calculated from the sensor electromotive force for any laughing nitrogen concentration.
After that, you can also use equation (6).

Example 2 rI with a specific surface area of about 200 m'/g on one side of
A laughing gas sensor (2) was manufactured by baking nickel chloride.

2) Performance evaluation device A performance evaluation test was conducted under the same device conditions as in Example 1. However, in this case, the measurement was performed with 11V removed from the rectifying layer.

The measurement results in Table 4 are organized in the same manner as in Example 1, and the deviation of the sensor electromotive force from the theoretical value is calculated by α of α gate X) shown in equation (6).
FIG. 4 shows the ratio (=k) to t(X). Each line segment in FIG. 4 has the same meaning as in FIG. 3.

Example 3 1) Fabrication of laughing gas sensor (31) A laughing gas sensor (3) was produced in the same manner as in Example 1.

However, in this example, the catalyst was coated in the following manner. About 150rI? A commercially available spherical (5ψ) activated alumina extrusion having a specific surface area of 150 ~
After applying it to a thickness of 0.5 gourd on the sized 250 mesh, it was baked in air for 1'02 hours.Next, a coating containing 2 wt% platinum (pt) was applied. After soaking in an aqueous solution of platinic acid (11, PtCl, l), it was dried, and further subjected to a ring treatment for 5 + 111' (3 + 2 hours) in a hydrogen stream, resulting in Pt/A'2'J s
W! l! 11'l of coating was applied.

2) Performance evaluation device One performance evaluation test was conducted under the same device conditions as in Example 1. However, the rectifying layer is removed and the measurement waste is removed. A0.1° is x
, ot7- conditions.

The measurement results in Table 5 are summarized in the same manner as in Example 1, and the deviation of the sensor electromotive force from the theoretical value is expressed as the ratio (=k) of α1(X) to α(X) shown in equation (6). This is shown in FIG.

As can be seen by comparing FIGS. 3 to 5, laughing gas sensors (1) to (3) all have similar characteristics.

The differences in characteristics between 1) and (3) are thought to be due to differences in the type of ozone decomposition catalyst, the thickness of the catalyst layer, the pore structure of the catalyst layer, the presence or absence of a rectifying layer, etc. However, the difference is small.

In the above embodiments, the electrodes are formed by baking the paste, but for example, the electrodes are formed by baking the paste.
It may be formed by a sputtering method. Also,
The catalyst is coated on one electrode surface, but considering the function of the catalyst, it is not necessarily necessary to coat it directly; a plate-shaped catalyst may be pressed onto the electrode surface, or as shown in Figure 6. It is also clear that the catalyst 4 may not completely cover the electrode surface 2.

Furthermore, in the above embodiment, a pair of electrodes were provided on opposing surfaces of the oxygen ion conductor, but as shown in FIG. 7, oxygen ions! 7IT [(Two tubes 4 @ 2, 2 are installed at a distance from each other on the same 71-tatami surface of the body, and one tk pole of each is connected to a laughing gas decomposition catalyst 4.) It is clear that he also has the ability to sense laughing gas and has the ability to run on his own.

As described above in the examples, according to this method, porous noble metal electrodes and lead wires are attached to a disk-shaped stabilized zirconia art dealer; after CJ, laughing gas is placed on one electrode. By using an element with a convenient structure in which the decomposition catalyst 5 is coated, the concentration of laughing gas in the gas phase can be determined from the electromotive force generated by the difference in oxygen concentration IW between the two electrode surfaces, and this can achieve the desired goal. However, it is clear that similar effects can be obtained by using stabilized zirconia in the shape of a plate, cylinder, or test tube. It is also clear that similar effects can be obtained by using other oxygen ion conductive solid solutes, such as bismuth oxide (zOs) stabilized with erbium oxide (KvtOs), instead of stabilized zirconia. It is.

As the 't4M material, platinum shown in the examples is most preferred from the viewpoint of electrode oiliness and chemical stability, but rhodium, palladium, gold, silver, etc. can also be used.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of one embodiment of the present invention, Figure 2 is a cross-sectional view of the sensor performance i' high value device K, Figures 3 to 5 are line diagrams showing the results of deviation performance planning, and Figure 6. , fJ7 respectively show other embodiments of the present invention. 4. Laughing gas decomposition catalyst.

Claims (1)

[Claims] ]) Two electrodes are provided at a distance from each other on the surface of an oxygen ion-conducting solid electrolyte having a desired shape, and one electrode surface is immersed in a measuring gas using a laughing gas decomposition catalyst. A laughing gas sensor characterized by determining the concentration of laughing gas. 2. A laughing gas sensor according to claim 1, characterized in that electrodes are provided on different surfaces of the oxygen ion conductive solid electrolyte. 3) The sensor according to claim 1 or 2, characterized in that the oxygen ion conductive solid electrolyte is made of zirconia stabilized with any one of yttoria, calcia, or magnesia. Laughing gas sensor. 4) A laughing gas sensor according to any one of claims 1 to 3, characterized in that the electrode is made of a noble metal such as platinum, rhodium, palladium, silver, or gold. 5) In the sensor according to claim 3 -, 4
50-1000℃, more preferably 500-850'
Laughing gas sensor 1 is characterized by being used in the temperature range of 0.