JPH06118043A - Amine sensor - Google Patents

Abstract

PURPOSE:To provide a sensor highly sensitive to amine compound with low resistance value and high selectivity between hydrogen or ethanol and the amine compound by adding RuO2 or Au in a specified ratio to a mixture obtained by mixing WO3 to In2O3 in specified ratios. CONSTITUTION:In a sensor, at least one material of the group consisting of RuO2 and Au is added in the amount of 0.01-5wt.% to the total amount wt.% of WO3 and In2O3 to a mixture consisting of 95-30wt.% of WO3 and 5-70wt.% of In2O3. Preferably, WO3 is set to 90-50wt.%, In2O3 to 10-50wt.%, and the adding quantity of RuO2 or Au to 0.6-3wt.%. RuO2 or Au is added to WO3 to sharply increase amine sensitivity, and In2O3 is mixed to suppress a higher resistance of the sensor. The relative sensitivity between amine compounds and hydrogen or ethanol is improved to improve selectivity. In a gas sensor 2, for example, a metal oxide semiconductor film 6 in which RuO2 or Au is added to the mixture of WO3 and In2O3 is provided on an alumina base 4.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a sensor for amine compounds such as ammonia, trimethylamine and aniline.

[0002]

Amine compounds such as ammonia, trimethylamine, and aniline are one of the typical malodorous substances, and the odor is known as the rotten odor of fresh fish. Ammonia is a typical refrigerant and is also used in various plants. In the case of detecting an amine compound, interfering gases are generally hydrogen and ethanol, and hydrogen is a major interfering substance particularly when detecting leakage of ammonia as a refrigerant or leakage of ammonia from a plant or the like.

However, in general, a semiconductor gas sensor has a low amine sensitivity, and the selectivity between an amine compound and hydrogen or ethanol is not sufficient. The gas sensor in which RuO2 was added to WO3 showed high sensitivity to amine,
The resistance value was extremely high and it was difficult to put it into practical use.

[0004]

An object of the present invention is to provide an amine sensor which is highly sensitive to amine compounds such as ammonia, trimethylamine and aniline, has a low resistance value, and has high selectivity between hydrogen and ethanol and amine compounds. is there.

[0005]

DETAILED DESCRIPTION OF THE INVENTION The amine sensor of the present invention is disclosed in WO 3 95
To a mixture of ~ 30 wt% and In2O3 5-70 wt%,
If the total amount of WO3 and In2O3 is 100 wt%, R
At least one member of the group consisting of uO2 and Au.
It is characterized in that 01 to 5 wt% was added. Here, the mixing ratio of WO3 and In2O3 is preferably WO3 90
~ 50wt%, In2O3 10-50wt%, Ru
The addition amount of O2 or Au to the total amount of WO3 and In2O3 is more preferably 0.6 to 3 wt%. In this specification, the composition of the gas sensor is expressed in wt% and R
Unless otherwise specified, the total amount of WO3 and In2O3 is 100 wt% unless otherwise specified. The existing forms of WO3 and RuO2 used are complicated and may be partially reduced, but since most of them are WO3 and RuO2, they are treated as existing forms. It is considered that a part of Au used in the same manner exists as an oxide, but since most of it exists as a simple substance of Au, it is treated as existing in this form.

[0006]

The basic finding of the present invention is that the addition of RuO2 or Au to WO3 dramatically increases the amine sensitivity. However, along with this, the resistance value of the gas sensor increases abnormally, making it difficult to measure the resistance value. When WO3 is mixed with In2O3, it is possible to suppress the increase in the resistance of the sensor due to the addition of RuO2 or Au and keep the resistance value of the sensor within a practical range. In2O3
The second effect of the addition is to improve the relative sensitivity between the amine compound and hydrogen or ethanol, and to improve the selectivity to the amine compound. As a result, when RuO2 or Au is added to the mixture of WO3 and In2O3, an amine sensor having high resistance to amine compounds and low interference with hydrogen or ethanol can be obtained within a practical resistance range.

The effect of In2O3 appears from about 5% by weight. For example, when 6% by weight of In2O3 is added to 94% by weight of WO3, the resistance value of the sensor can be reduced 10 times or more as compared with the case of not adding In2O3. Also In
Addition of 6 wt% of 2O3 can improve the selectivity of the amine compound for hydrogen and ethanol. In2O3
The effect of addition of 10 wt% or more is further increased, and WO3 90 to 50 wt% and I to 10 to 50 wt% are added.
It does not change much in the range where n2 O3 is added. WO3
When the amount of In2O3 exceeds 50 wt% with respect to 50 wt%, the ethanol sensitivity gradually increases. Then, in a system in which RuO2 or Au is added to plain In2O3 without using WO3, the ammonia sensitivity is low and the ethanol sensitivity is abnormally high, and the sensor is substantially an ethanol sensor.

From these facts, the weight ratio of WO3 and In2O3 is set to 95-30: 5-70, more preferably 90-50: 10-50.

Next, both RuO2 and Au enhance the amine sensitivity. Since the effects of RuO2 and Au are similar and the dependence on the addition amount is similar, the same addition amount range was used for RuO2 and Au in the present invention. The inventor examined various additives such as Pt, Pd and Re in addition to RuO2 and Au, but only RuO2 and Au were effective in improving the amine sensitivity. Comparing RuO2 and Au, RuO2 is generally more effective in improving the amine sensitivity. Next, the effect of addition of RuO2 or Au is 0.01 with the total weight of WO3 and In2O3 being 100 wt%.
It develops from about wt%, and the optimum value occurs in the range of about 0.6 to 3 wt%. For example, the total amount of In2O3 and WO3 is 1
When 0.02 wt% of RuO2 is added to 00 wt%, a remarkable sensitizing effect with respect to ammonia occurs, which becomes more remarkable when the added amount of RuO2 is 0.6 wt% or more. Further, even if the addition amount of RuO2 or Au is changed in the range of 0.6 to 3 wt%, the dependency on the addition amount is small. RuO
When the addition amount of 2 or Au exceeds 3 wt%, the resistance value of the sensor increases and the amine sensitivity gradually decreases. For example RuO
When the addition amount of 2 is 4 wt%, the ammonia sensitivity is Ru
This is almost equivalent to the case where the amount of O2 added is 0.02 wt%, and the resistance value is about 10 times that. If the added amount of RuO2 or Au exceeds 5 wt%, the resistance value of the sensor further increases and the amine sensitivity decreases. For example, WO3 75wt% to In2O3
A gas sensor in which 25 wt% is mixed and 10 wt% of RuO2 is added to the total amount of 100 wt% is
The ammonia sensitivity is practically zero. From this, R
The amount of uO2 or Au added is 0.01 to 5 wt%, preferably 0.6 to 3 wt%, based on the total weight of WO3 and In2O3 being 100 wt%.

The structure and shape of the sensor itself are arbitrary, and a thick film type gas sensor is shown in the embodiment, but not limited to this, for example, a thin film type gas sensor or a bulk type gas sensor may be used. Although the examples show that the amine sensor is detected while being kept at the optimum temperature for the amine compound, the method of using the sensor itself is arbitrary, for example, the sensor is periodically heat-cleaned at high temperature and the amine compound is detected at low temperature. You may do it. Also WO3, In2O3, RuO2, A
Ingredients other than u may be added additionally.

[0011]

EXAMPLE Commercially available WO3 (special grade reagent) was heat-treated in air at 500 ° C. for 2 hours, crushed with a ball mill, and the starting material WO3 was used.
It was 3. Similarly, the In (OH) 3 precipitate was dried, then heat-treated in air at 500 ° C. for 2 hours, and pulverized with a ball mill to obtain In2O3 as a starting material. WO3 and In2O3 are mixed in a predetermined ratio, Ru and Au are added in the form of an aqueous solution of ruthenium chloride or an aqueous solution of chloroauric acid, and after drying, the mixture is baked in air at 550 ° C. for 2 hours to remove RuO2 and Au. Was added. A mixture of WO3 and In2O3 added with RuO2 or Au was pulverized again by a ball mill, printed on an alumina substrate, and baked at 700 ° C for 30 minutes to obtain a gas sensor.

The obtained gas sensor is shown in FIG. In the figure, 2 is a gas sensor, 4 is an alumina substrate, and 6 is WO3.
Is a metal oxide semiconductor film obtained by adding RuO2 or Au to a mixture of In and O2, 8 is a heater film, 10 is a common electrode, 12 is a detection electrode, and 14 is a heater electrode. Electric power is supplied to the heater 8 from the common electrode 10 and the heater electrode 14, and the sensor 2
To the optimum temperature. In this state, the resistance value of the metal oxide semiconductor film 6 is measured using the common electrode 10 and the detection electrode 12.

After heating the obtained sensor to the optimum temperature for 2 weeks, the sensitivity to ammonia, hydrogen, ethanol, trimethylamine, aniline, etc. was measured. From the temperature dependence experiment of the sensor 2, when RuO2 was used, the optimum temperature was set to 380 ° C. as a temperature having high sensitivity to ammonia and excellent response characteristics. Next, when Au was used, the optimum temperature was 430 ° C., which was rather high, so the measurement was performed at this temperature.

FIGS. 1 and 2 show the characteristics of a sensor in which the weight ratio of WO3: In2O3 is 85:15 wt% and the addition amount of RuO2 is 1.36 wt% with respect to the total amount of WO3 and In2O3. FIG. 1 shows the resistance value in air, and FIG. 2 shows the sensitivity in 50 ppm of ammonia, 100 ppm of hydrogen, and 100 ppm of ethanol. In this specification, the sensitivity is defined as the ratio of the resistance value in gas and the resistance value in air. Unless otherwise specified, the concentration of gas is 50 ppm for ammonia, 100 ppm for hydrogen, and 100 ppm for ethanol. In addition to this, trimethylamine (TMA) and aniline are required to be detected at low concentrations, so the sensitivity to 10 ppm was measured.

3 and 4, WO3 75 wt%, In2
The characteristics of the amine sensor in which 1.2 wt% of RuO2 is added to a mixture of 25 wt% of O3 and 100 wt% of WO3 and In2O3 are shown. FIG. 3 shows the resistance value in air, and FIG. 4 shows the sensitivity to gas.

The resistance value of these sensors is 3 at the optimum temperature.
In the atmosphere of 80 ℃, inside and outside of 200KΩ, In2O3
The resistance value of FIG. 3 in which In2O3 is increased to 25 wt% is lower than that of 15 wt% in FIG.

Next, the sensitivity to ammonia, hydrogen, and ethanol changes as shown in FIGS. 2 and 4 in the range of 320 to 410 ° C., and 320 ° C. is the optimum temperature only from the point of distinguishing hydrogen and ammonia. However, since the response speed is low at 320 ° C., the sensor characteristics were measured with 380 ° C. as the optimum temperature.

The amount of RuO2 added to WO3 is 1.6 w
Table 1 shows the effect of In2O3 for the system with t%.

[0019]

[Table 1] Table 1 No. WO3 / In2O3 RuO2 / Rsair NH3 50ppm H2 100ppm EtOH 100ppm (wt%) (WO3 + In2O3) (KΩ) / Air / Air / Air 1 * 100: 0 0 360 0.85 0.48 0.15 2 * 100: 0 1.6 10,100 0.31 0.65 0.02 3 94: 6 1.50 850 0.25 0.58 0.03 4 85: 15 1.36 230 0.10 0.40 0.04 5 75: 25 1.20 170 0.09 0.40 0.045 6 60: 40 0.96 56 0.10 0.45 0.04 7 40: 60 0.64 25 0.10 0.51 0.02 8 * 0: 100 1.6 7 0.45 0.55 0.01 * is a comparative example, and the addition amount of RuO2 is WO3 and In2O.
The total amount of 3 is 100 wt% and is shown in wt% unit. Sensitivity is indicated by the ratio with the resistance value in the air, and the smaller this value, the higher the sensitivity.

As is clear from Sample 1 in Table 1, RuO
A system in which neither 2 nor In2O3 is added has low ammonia sensitivity and does not serve as an amine sensor. When RuO2 is added to this, the ammonia sensitivity remarkably increases, but the resistance value of the sensor increases several tens of times, and the resistance value in air reaches about 10 MΩ, which is not practical. When In2O3 is added to this, the resistance value of the sensor sharply decreases. For example, in the sample 3 containing 6% by weight of In2O3, the resistance value in air is reduced to 1/10 or less as compared with the sample 2 containing no In2O3. Therefore, the lower limit of the amount of In2O3 added is set to 5 wt%. In2
When the amount of O3 added is 15 wt%, the resistance value of the sensor is further lowered and the sensitivity of ammonia is further improved. From this, the amount of In2O3 added is preferably 10 wt% or more. The amount of In2O3 added in Samples 4 to 6 in Table 1 was 15
In the range of -40 wt%, the characteristics of the sensor are essentially unchanged. On the other hand, the amount of In2O3 added is 6
In Sample 7 with 0 wt%, the sensitivity to ethanol increases and the ammonia selectivity decreases. Therefore, In2
The amount of O3 added is preferably 10 to 50 wt%. As in Comparative Example of Sample 8 in Table 1, In2O3 was used without using WO3.
In the system in which RuO2 is added, the sensor is substantially an alcohol sensor. Therefore, the upper limit of the amount of In2O3 added is set to 70 wt%. Next, In2O3 not only lowers the resistance value of the sensor, but also further enhances the sensitivity of ammonia or reduces the sensitivity to ethanol, and as a result, improves the selectivity to amine compounds. However, this effect is
When the additive amount of is over 50 wt%, it gradually decreases. For example, in Sample 7 with In2O3 of 60 wt%, the sensitivity to ethanol is not different from that without In2O3, and only the aspect that the ammonia sensitivity is improved remains. become.

In Table 2, WO3 75 wt% and In2O3 2
The effect of the added amount of RuO2 on the 5 wt% system is shown.

[0022]

[Table 2] Table 2 No. WO3 / In2O3 RuO2 / Rsair NH3 50ppm H2 100ppm EtOH 100ppm (wt%) (WO3 + In2O3) (KΩ) / Air / Air / Air 11 * 75: 25 0 85 0.81 0.72 0.13 12 75 : 25 0.02 90 0.32 0.68 0.11 13 75: 35 0.10 100 0.25 0.55 0.09 14 75: 25 0.6 120 0.15 0.53 0.09 15 75: 25 1.20 170 0.09 0.40 0.045 16 75: 25 2.5 350 0.07 0.42 0.038 17 75: 25 4 780 0.35 0.56 0.10 18 * 75: 25 10 8,900 1.01 0.98 0.83 * indicates a comparative example, and the addition amount of RuO2 is WO3 and In2O.
The total amount of 3 is 100 wt% and is shown in wt% unit. Sensitivity is indicated by the ratio with the resistance value in the air, and the smaller this value, the higher the sensitivity.

The addition of RuO2 sharply increases the sensitivity to amine compounds such as ammonia. This effect is R
Although it occurs with the addition of 0.02 wt% uO2, 0.6 wt%
With the above addition, it becomes more remarkable. The amount of RuO2 added is 3
When it exceeds wt%, the ammonia sensitivity decreases conversely, and RuO
When 2 wt% of 2 is added, the sensitivity of the sensor to various gases is substantially lost. In addition, 10 wt% of RuO2
The% added sensor has an extremely high resistance value.

Table 3 shows the effect of adding Au to the mixture of WO3 and In2O3.

[0025]

[Table 3] Table 3 No. WO3 / In2O3 Au / Rsair NH3 50ppm H2 100ppm EtOH 100ppm (wt%) (WO3 + In2O3) (KΩ) / Air / Air / Air 21 85: 15 1.36 180 0.15 0.45 0.03 22 75: 25 1.20 120 0.12 0.43 0.04 23 40: 60 0.64 15 0.13 0.56 0.03 24 * 0: 100 1.6 51 0.57 0.58 0.01 25 75: 25 0.1 60 0.32 0.65 0.09 26 75: 25 0.6 80 0.18 0.63 0.08 27 75: 25 2.5 260 0.15 0.53 0.11 28 * 75: 25 10 7,300 0.98 1.01 0.95 * indicates a comparative example, and the addition amount of Au is WO3 and In2O3.
The total amount of the above is set to 100% by weight and shown in wt% unit. Sensitivity is indicated by the ratio with the resistance value in the air, and the smaller this value, the higher the sensitivity.

The measured temperature in Table 3 is 430 ° C., and Au is R
Like uO2, it improves the sensitivity to amine compounds such as ammonia. As with RuO2, the amount of Au added is 0.01-
5 wt% is preferable, and more preferably 0.6 to 3 wt%
And For example, in the comparative sample 28 containing 10 wt% Au, the resistance value in air is as high as about 7 MΩ, and the sensitivity to ammonia is lost. Next, even in the system using Au, the mixing ratio of WO3 and In2O3 is 95 to 30: 5 to 7
0 wt%, more preferably 90 to 50:10 to 50 wt
%, Which is not shown in Table 3, but In
The resistance value of the sensor was extremely high in a system without 2O3 added, which was not practical. Further, as shown in the sample 24 of the comparative example in Table 3, in the system in which Au is added to In2O3 without using WO3, the sensor is substantially an ethanol sensor.

Table 4 shows the sensitivity of trimethylamine and aniline to a sensor in which the weight ratio of WO3 to In2O3 is 75:25 wt% and 1.2 wt% of RuO2 or Au is added.

[0028]

[Table 4] Table 4 No. WO3 / In2O3 RuO2 Au TMA 10ppm Aniline 10ppm (wt%) (wt%) (wt%) / Air / Air 31 75:25 1.20 0 0.25 0.32 32 * 75:25 0 1.20 0.28 0.29 * Indicates a comparative example, and the addition amounts of RuO2 and Au are WO3 and I
The total amount of n2O3 is 100 wt% and is shown in wt%. Sensitivity is indicated by the ratio with the resistance value in the air, and the smaller this value, the higher the sensitivity.

The sensitivity to trimethylamine and aniline is
Similar to the sensitivity to ammonia, a sensor with high sensitivity to trimethylamine and aniline was obtained by increasing the ammonia sensitivity.

[0030]

Industrial Applicability According to the present invention, an amine sensor having a resistance value within a practical range, high sensitivity to amine compounds, and small interference with hydrogen, ethanol, etc. can be obtained.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a resistance value of an amine sensor of an example in air.

FIG. 2 is a characteristic diagram showing the sensitivity of the amine sensor of Example to hydrogen, ammonia, and ethanol.

FIG. 3 is a characteristic diagram showing the resistance value of the amine sensor of the example in air.

FIG. 4 is a characteristic diagram showing the sensitivity of the amine sensor of Example to hydrogen, ammonia, and ethanol.

FIG. 5 is a sectional view of an amine sensor of an example.

[Explanation of symbols]

 2 amine sensor 4 alumina substrate 6 metal oxide semiconductor film 8 heater 10 common electrode 12 detection electrode 14 heater electrode

Claims (2)

[Claims] 1. WO3 95-30 wt% and In2O3 5
To 70 wt% of the mixture, 0.01 to 5 wt% of at least one member of the group consisting of RuO2 and Au was added, with the total amount of WO3 and In2O3 being 100 wt%.
Amine sensor. 2. The weight ratio of WO3 and In2O3 is 90-.
The amine according to claim 1, wherein the content is 50:10 to 50 wt% and the amount of addition of at least one member of the group consisting of RuO2 and Au to the total amount of WO3 and In2O3 is 0.6 to 3 wt%. Sensor.