JPH0726927B2 - Odor detector - Google Patents

Description

The present invention relates to an odor detecting element.

[Conventional technology]

Conventionally, a three-point comparison odor bag method based on human sense of smell and a method of sampling the odor and analyzing it with a gas chromatograph have been used to detect the odor.

[Problems to be Solved by the Invention]

However, the former method is not only complicated in the evaluation procedure, but also difficult to make a correct evaluation and requires skill, while the latter method is large in size and difficult to carry, and in a short time in real time. It had the drawback of not being able to analyze.

An object of the present invention is to facilitate accurate evaluation in real time.

[Means for Solving the Problems]

The characteristic structure of the odor detecting element of the present invention is tin oxide (SnO ₂ )
A sintered semiconductor containing as a main component, a first component containing at least one kind of an oxide of an alkaline earth element, and Sc, Y, T
i, Zr, Hf, Th, Al, Ga, and a second component comprising at least one kind of oxide of a lanthanoid group element are carried, and its action and effect are as follows. is there.

[Work]

That is, the causes of the odor are generally alcohols, acetylene, hydrogen sulfide, methyl mercaptan, trimethylamine, styrene, esters, aldehydes, ketones,
Consists of volatile vapors such as carboxylic acids. Among them, the odor intensity acting on the receptor membrane of olfactory cells is stronger as the bond saturation in the molecule is lower, and the triple bond in the molecule is stronger than the double bond. It is strong and strong enough to have one or more unsaturated bonds. That is, it depends on the free valence in the molecule (extra binding capacity left for each constituent atom in the conjugated bond system of carbon), and further depends on the redox power of the molecule,
In the odor detecting element of the present invention, the semiconductor having the first component and the second component supported thereon has a structure as shown in Table 1, Table 2, Table 3 and FIG. First,
With the loading of the second component, the sensitivity becomes higher than that of a low-molecular-weight gas (H ₂ , CO, C ₄ H _10, etc.) that does not have an odor, and the selectivity for the odor molecules becomes higher. Moreover, looking at the initial response waveform to the odor of the sensing element, as shown in FIG. 3 (a), if the semiconductor is loaded with only CaO as the first component, ethanol 100 p
While the sensitivity to pm is not stable, as shown in FIG. 3 (b), when the semiconductor is loaded with CaO as the first component and LaO _3/2 as the second component, It shows stable output against 100ppm of ethanol from the beginning even if it does not pass, and can detect odor molecules in a short time.

Further, comparing FIG. 3 (a) and FIG. 3 (b), and comparing the sensitivities to 1000 ppm of hydrogen, compared with those carrying only the first component (FIG. 3 (a)). The one carrying the second component (FIG. 3 (b)) is
It can be seen that the output is stable at the beginning of energization (3rd
By comparing a in FIG. 3 (a) with b in FIG. 3 (b), it can be seen that b is flatter in a shorter time). Furthermore, comparing the sensitivities to 1000 ppm of hydrogen, the second component is supported (third component) as compared with the one in which only the first component is supported (FIG. 3 (a)).
It can be seen that the figure (b)) is suppressed to a very low level from the beginning of the energization. This means that, for example, in a portable detector, in many cases, the odor detecting element is guaranteed to be prompt and reliable and can be provided in an easy-to-use state in a situation where the detector is often used immediately after the start of energization.

Due to these facts, the basicity of the first component supported on the sintered semiconductor increases the reactivity of the tin oxide semiconductor with respect to the odor molecules, while suppressing the reactivity of the odorless molecules with the second component. It can be estimated that the output immediately after the start of energization can be stabilized. That is, it can be said that the first component and the second component were able to achieve stabilization of the initial output immediately after the start of energization while maintaining high selectivity for odor molecules.

[Advantages of the Invention] Therefore, since the odor detection element can perform accurate evaluation in a short time and can prevent misidentification as a low-molecular gas having no odor, the odor intensity can be easily learned in real time. Therefore, it can be easily used for evaluation of freshness and maturity of foods, and accurate evaluation of olfaction that has been conventionally performed by a doctor's intuition.

〔Example〕

 Next, an embodiment of the present invention will be described with reference to the drawings.

As shown in Fig. 1 (a), the main component is tin oxide (SnO ₂ ) formed by sintering a platinum (Pt) coil (1) embedded in the center into a spherical shape of approximately 0.4 mmφ. The semiconductor type odor detecting element (2) is provided, and the odor detecting element (2) is interposed on one side of the bridge circuit shown in FIG. 1 (b) to measure the output from the odor detecting element (2). A basic odor detection device is constructed by providing a voltmeter (V) for detecting odor molecules.

In the figure, R ₀ , R ₁ and R ₂ are resistors, and the temperature of the odor detecting element (2) is controlled by the bridge voltage from the power source (E).

The conductivity of the semiconductor made of tin oxide (SnO ₂ ) can be controlled by doping an appropriate amount of antimony (Sb ⁵⁺ ) or niobium (Nb ⁵⁺ ).

The odor detecting element (2) contains 0.25 to 20 mol.% Of the first component composed of at least one kind of oxides of alkaline earth elements.
And Sc, Y, Ti, Zr, Hf, Th, Al, Ga, and 0.25 to 20 mol.% Of the second component consisting of at least one kind of oxides of the lanthanoid group element as a sintered tin oxide semiconductor. The supported odor (however, the mixing ratio of the first component to the second component is 90% or less), and the odor detecting element (2) thereof is as shown in Table 1, Table 2 and Table 3. It is highly sensitive to gases that cause odors, low in odorless low-molecular gases (H ₂ , CO, C ₄ H _10, etc.), and highly selective to odors. Further, as shown in FIGS. 3 (a) and 3 (b), when both the first component and the second component are mixed and carried together rather than the first component alone, the responsiveness and sensitivity are stable. And the H ₂ (10
The output (sensitivity) for 0 ppm) is also kept low.

In particular, CaO-LaO is a typical example of the first and second components.
_{For the 3/2} system, as shown in Table 2 above, ethanol (1
The maximum sensitivity is near the mixture of CaO and LaO _3/2 in an equimolar ratio. At the same time, the sensitivity ratio (selection of hydrogen (H ₂ ), carbon monoxide (CD), isobutane (C ₄ H ₁₀ ) etc. It can be seen that sex) is also maximized.

FIG. 2 is a logarithmic scale graph showing that the sensor sensitivity (ΔV) can be expressed as a power of the gas concentration C (ppm).

Therefore, the odor is stronger when the degree of saturation is lower in the molecule that causes it, stronger with triple bonds than with double bonds, and stronger with one or more unsaturated bonds, depending on the free valence. In addition, it is said that the odor detection element (2) has a lower sensitivity in the change of its sensitivity as the molecule has a lower degree of unsaturation.

Molecules with triple bonds are more sensitive than those with double bonds.

Organic gas having O, N, S, etc. in the molecule has high sensitivity.

It is generally sensitive to reducing gases. As can be seen from the characteristics such as the above, it corresponds to the strength of the odor molecule and can accurately measure the strength of the odor.

Next, a method for producing the odor detecting element (2) will be described.

(I) A tin oxide (SnO ₂ ) semiconductor paste obtained by doping with antimony (Sb ⁺⁵ ) to obtain an appropriate conductivity is applied to a platinum (Pt) coil (1) to form a spherical shape of about 0.4 mmφ. Then, after drying, a predetermined current is applied to the platinum coil (1) to heat it, and the tin oxide powder is sintered at a predetermined temperature, for example, about 650 ° C. for 1 hour.

Although the external shape remains the same as that shown in FIG. 1 due to sintering, it is microscopically porous.

(Ii) For tin oxide semiconductor, at least one of alkaline earth element (Be, Mg, Ca, Sr, Ba) nitrate as a first component, and Sc, Y, Ti, Zr, Hf, Th as a second component. , Al, Ga
And, an aqueous solution in which at least one of a lanthanoid element (La, Ce, Pr, Tb, Yb, etc.) nitrate and a chloride of Ti (titanium trichloride) is mixed, after impregnation, and dried in the same manner as above, By energizing the platinum coil (1), it is thermally decomposed in air at about 600 ° C. by utilizing Joule heat generation, and finally supported as an oxide.

The odor detecting element (2) obtained by the above manufacturing method is incorporated in the well-known bridge circuit of FIG. 1 (b).

In addition, the sensor temperature is approximately due to Joule heat generation of the coil (1).
It is set at 400 ° C and controlled by the bridge voltage (E).

[Another embodiment]

As a method for supporting the first component and the second component on the sintered tin oxide (SnO ₂ ) semiconductor, in addition to the above-mentioned impregnation method, a usual supporting method such as an electrophoresis method, or other supporting method is adopted. Is also good.

It is suitable for the odor detecting element to adjust the content rates of the first component and the second component carried by the odor detecting element (2) to 0.25 to 20 mol.%, Respectively. In other words, 0.25mo each
When it is less than 1%, the selectivity for odor gas molecules decreases, and when it is more than 20%, the detection output for various gases decreases.

[Brief description of drawings]

The drawings show an embodiment of the present invention. Fig. 1 (a) is a schematic sectional view of an odor detecting element, Fig. 1 (b) is an electric circuit diagram of an odor detecting device, and Figs. 2 and 3 (a). , (B) are change graphs.

Claims (3)

[Claims] 1. A sintered semiconductor containing tin oxide (SnO ₂ ) as a main component, a first component containing at least one kind of oxide of an alkaline earth element, and Sc, Y, Ti, Zr, Hf, Th. , Al, Ga, and a second component comprising at least one kind of oxide of a lanthanoid group element, and an odor detecting element. 2. The odor detecting element according to claim 1, wherein the first component and the second component are carried on the sintered semiconductor in a mixed state. 3. The contents of the first component and the second component are respectively 0.25 to 20 mol.% With respect to tin oxide.
Alternatively, the odor detection element described in 2.