JPH01207653A - Co sensor - Google Patents

Abstract

PURPOSE:To suppress the change of a sensor with age and the dependency thereof on temp. and humidity by adding a specific ratio of a sulfur compd. to SnO2. CONSTITUTION:A pair of coiled electrodes 4, 6 in common use as heaters are provided in a sintered body 8 of the SnO2 of the CO sensor 2 consisting of the SnO2 system. The change of the sensor 2 with age decreases if the sulfur compd. is added to the sintered body 8 at this time. This effect is obtd. from about 1mgr addition amt. per 1gr SnO2 in terms of SO4 and the upper limit of said amt. is confined to 60mgr. The dependency of the sensor 2 on temp. and humidity is suppressed by the addition of the sulfur. This effect is determined by the addition amt. of the same range. The sulfur compd. is, therefore, added to the sintered body 8 at 1-60mgr per 1gr SnO2 in terms of SO4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to improvement of a 5nOt-based CO sensor, and particularly to suppression of its change over time and temperature/humidity dependence.

[Prior art] Japanese Patent Publication No. 61-60.386 discloses that Z
It discloses adding r Ot or T i Oy and sulfate ions. This publication is based on Z r Ov and Ti
It is pointed out that e, suppresses the aging change of SnO, and sulfate ion increases the sensitivity to propane and methane.

However, this publication does not mention the detection characteristics for CO.

For metal oxide semiconductor CO sensors, the following is important:

(1) Suppressing changes in the sensor over time and increasing the reliability of detected values.

(2) Suppressing the temperature and humidity dependence of the sensor.

[Problem of the Invention] An object of the present invention is to suppress the change over time of a CO sensor and to suppress the dependence on temperature and humidity.

[Structure and operation of the invention] In this invention, a sulfur compound is added to Snow.

The amount added is 1 to 60 per SnO and Igr in SO4 terms.
mgr, more preferably 2 to 20 mgr.

, Adding sulfur compounds to Snow reduces the aging of the sensor. This effect is equivalent to l Br in SO4
It is expressed from the addition amount of about 1/grsno, l 2 mg
The maximum effect can be obtained at approximately r/grSnOt. SO4
When the amount added was further increased, the change over time increased again, and 60 mg
The upper limit is r/grsno.

Another effect of adding sulfur is that the temperature and humidity dependence of the sensor is suppressed. This effect also applies to Imgr/gr
It appears when the amount of sulfur added is approximately snot (in terms of SO4), and reaches its maximum when the amount of sulfur added is about 2 mgr/grsnOt. When the addition m is further increased, the temperature and humidity dependence worsens again, and the upper limit of the sulfur addition amount is 60 mgr/grS n in terms of SO4.
Ot.

These effects do not require the addition of ZrO or TiOz, and appear as the effects of the sulfur compound itself.

[Example] Preparation of sensor An aqueous solution of S nC+4 was neutralized with ammonia to form a stannic acid sol. After washing the sol with water, it was calcined in air at 800° C. for 1 hour and pulverized to obtain S n O material. 5 mgr/grSnug of Pd in terms of metal Pd was added to the obtained SnO as a Pd aqua regia solution.

After the addition, Snow was dried and fired in air at 700° C. for 1 hour to support Pd. Pd is PL, lr.

Any noble metal catalyst such as Rh, nuO2)ne, Au, etc. can be used, or it may not be added.

A preferable addition range is 1 to 50 mgr of noble metal catalyst per 1 SnSn0t. In addition to this,
V for suppressing changes over time (mainly exists in the form of v to
s), or F for suppressing temperature/humidity dependence may be added. The inventors found that 0.5-20 mgr vanadium per SO4 ion as V v Os suppressed the aging of CO secene, and 0.5-10 mgr per gr SnO.
It has been found that 0 mgr of fluorine suppresses the temperature and humidity dependence of the sensor.

After adding Pd, the 5n02 was ground again to form C with the shape shown in Figure 1.
It was set as O sensor 2. In the figure, 4 and 6 are a pair of coiled electrodes that also serve as heaters, and 8 is a sintered body of 5nO7. Incidentally, the sintering of SnO was performed at 850'C for 10 minutes in air. The sensor 2 after sintering was impregnated with dilute sulfuric acid and heat-treated at 600° C. for 30 minutes.

The amount of sulfur compound added was varied by varying the concentration of dilute sulfuric acid. The shape and structure of the sensor 2 are arbitrary.

The added sulfur compound exists primarily as SO4 ions. The addition form and addition timing of the sulfur compound are arbitrary; for example, it may be added in the form of a solution of 5nSO, (NH,)2SO4, or the like. Further, it may be added before sintering the sensor 2. In this case, for example, a sulfur compound is added together with Pd. In the following, all sulfur compounds are expressed as those converted to SO4.

Sensor characteristics The characteristics of sensor 2 are determined according to the HL method (Japanese Patent Publication No. 53-43.320
Evaluation was made using That is, one cycle consists of heating the sensor 2 to 300° C. for 60 seconds and then keeping it at 80° C. for 90 seconds, and this cycle is repeated. Then, CO is detected from the sensor output just before 90 seconds have elapsed on the low temperature side. The pattern of temperature change, that is, the temperature on the low temperature side and the high temperature side, the time of one cycle, etc., are arbitrary. Alternatively, instead of the HL method, CO may be detected by constantly maintaining the sensor 2 at a constant temperature (for example, about 50 to 250°C). In either case, changes over time and temperature/humidity dependence can be suppressed by adding a sulfur compound. In either case, the amount of sulfur added is the same.

After using the manufactured sensor 2 for two weeks (age measurement), evaluation of its characteristics was started. All results are shown as the average value of the sensor for each apl, and changes over time were evaluated based on behavior for 50 days after the end of the two-week aging period. In addition, the temperature and humidity dependence ranges from -10°C dew condensation to 50°C relative humidity 60°C.
The evaluation was performed in a high temperature and high humidity atmosphere of 10%.

Figure 2 shows the effect of sulfur on aging. Sensor 2, which had been aged for two weeks after manufacture, was used continuously for 50 days,
The resistance value in CC01O0pp was measured. Based on the sensor resistance (Rstd) immediately after aging, changes in the sensor resistance (Rs) are evaluated.

The resistance value was measured at 20°C1. ) 160% atmosphere. The sensor resistance increases slightly for the first 20 days, and then shifts to a stable period. When SO4 is not added, the sensor resistance gradually decreases and is not stable.

With the addition of 3 mgr/grS no of SO, the cent→cent resistance is quite stable. 6mgr/gr
With the addition of S not, the resistance to weight loss on the 20th day was 117L1.
ri is stable. With the addition of 12 mgr/grsno*, the resistance value stabilizes at a value near the initial value. On the other hand 36
When mgr/grS nOt is added, high resistance is observed in the stable period. The inventors performed similar measurements by changing the temperature change pattern of the sensor, but the same effects were obtained in both cases.

From these facts, SnO, Igr is converted into S O,
It is necessary to add 1 to 60 mgr of sulfur compound per
More preferably 2-20 mgrs, still more preferably 5-20 mgrs
Addition of 20 mgr is required.

The inventor repeatedly used sensor 2 for one day and left it for one day.
Changes were measured over 5 days. Also, after the first 10 days of use,
It was left for 40 days and changes in characteristics were evaluated. Table 1 shows the results of repeated use and storage, and Table 2 shows the results of storage for 40 days.

The measurement method is the same as in the case of FIG.

Table 1 Repeated use and storage * Amount of SO4 added Change in detected concentration (Co I Oop
pm standard) (mgr/grS no?) I O
Sun/Month 40th day 55th day 90
75 70G 95 85
85* A sensor that has been aged for 2 weeks was used for 55 days in a re-operation mode of 1 day of use and 1 day of leaving.The sensor resistance (Rs) to CC01O0I)p was recorded after 2 weeks of aging, and this C that gives the same resistance value as
Displays O concentration as detected concentration.

Table 240 days of storage* SO, amount added Change in detected concentration (CO10Q pp
mWtf4) (mgr/grsno2) IO day month 50th day 55th day 90 8
0 70* 40 after continuous use of sensor 2 for 10 days
The test piece was left for 1 day and then used continuously for 5 days.Other measurement conditions were the same as in Table 1.

The addition of SO4 did not cause any significant difference in the sensitivity or response speed of sensor 2 to various gases. Another effect of SO4 is that it suppresses the temperature and humidity dependence of the sensor 2. In Figure 3,
The temperature and humidity dependence of sensor 2 in CC01O0pp is shown. The sensor resistance at 20°C and 65% relative humidity is the standard value (Rs
td) and the ratio with the resistance value (Rs) under each temperature and humidity condition was determined. Note that the measurement was performed after aging for 2a.

In this measurement, temperature-humidity dependence and humidity dependence were handled together, but even if the ambient temperature or humidity is increased, the resistance of the sensor 2 decreases. Humidity dependence is generally greater than temperature dependence.

As is clear from the figure, the temperature and humidity dependence of the sensor 2 is reduced by adding SO4. As for the addition effect, the optimum value was obtained at l2mgr/grsnOt, as in the case of changes over time.
When the addition amount is increased to 36 mgr/grsnot, the temperature/humidity dependence increases again. and 3 mgr/grsnot
The temperature and humidity dependence is improved even with the amount added.

In addition, in the above-mentioned example, the results under specific usage conditions were explained for a sensor to which a specific noble metal catalyst was added. However, the effect of suppressing the temporal change and temperature/humidity dependence of sulfur compounds on the 5nOa-based CO sensor generally occurs regardless of the noble metal catalyst or usage conditions, and is not limited to the examples.

[Effects of the Invention] In the present invention, the aging change and temperature and 9 degree dependence of the 51102 series CO sensor are suppressed.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the Co sensor of the example, Figure 2, Figure 3.
Each figure is a characteristic diagram of an example. In the figure, 2 Co sensors and 8 Snow sintered bodies.

Claims (3)

[Claims] (1) In the SnO_2-based CO sensor, the SnO_2 contains SnO_21gr in terms of SO_4.
A CO sensor characterized in that 1 to 60 mgr of sulfur compound is added per CO sensor. (2) In the CO sensor according to claim 1, the amount of the sulfur compound added is SnO_21g in terms of SO_4.
CO, characterized in that it is 2 to 20 mgr per r.
sensor. (3) The CO sensor according to claim 1, wherein the sulfur is present as sulfate ions.