JPS58189546A - Manufacture of detecting element of gaseous alcohol - Google Patents

Abstract

PURPOSE:To obtain a highly sensitive alcohol detecting element, by incorporating each oxide of Cr, Mg, Zr components and satisfying a prescribed equation in terms of the mol ratio of Zr component and also, calcining so that the average value of half-value width of specific two faces X-ray diffraction of the oxides is requlated to a specific range. CONSTITUTION:The titled element contains the oxides of Cr, Mg, Cr and each oxide is permissible to exist independently or mixedly in various oxidation forms according to the valency and in case when the mol ratio is expressed in Mc, Mm, Mz expressed in terms of each CrO3, MgO, ZrO2 the molar fraction MZ is shown by equation in figure and moreover, the oxides are so regulated that the average value of half-value width of each specific two faces of Cr, Zr oxides is in a specific range, and the average value of the half-value width of X-ray diffraction of 2, 0, 0 and 2, 2, 2 faces of magnesium oxide is 0.30-0.50 deg.. A pair of platinum electrodes is embedded in a mixture of said three oxides and high pressure molding is carried out. Then, a molded product is calcined in the range of 1,000-1,400 deg.C and the detecting element highly sensitive and stable only for gaseous alcohol is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an alcohol gas detection element, particularly a chromium oxide based alcohol gas detection element.

More specifically, the present invention relates to an alcohol gas detection element that exhibits a significant change in resistance in the presence of a trace amount of alcohol gas contained in the atmosphere, and provides an element that is highly sensitive to alcohol gas.

Background of the Invention Generally 5n02, ZnO, Fe2O3, In2O3
.

~v03. It is known that a metal oxide semiconductor such as CeO2 exhibits a sensitive resistance change when heated to a high temperature and comes into contact with a fuel gas such as hydrogen gas, methane gas, or butane gas. Utilizing this property, gas leak detectors have been created that are equipped with a circuit that detects resistance changes caused by contact with fuel gas of a certain concentration or higher using a voltage difference signal. Although it contributes to prevention,
The above-mentioned metal oxides have a property of showing resistance changes even in the case of ethanol gas generated from the seasoning used for textiles, so detection reliability is poor, and practical problems caused by detection errors remain unresolved. there were.

Brief Summary of the Invention The purpose of the present invention is to provide an alcohol gas detection element with excellent selectivity for alcohol, which exhibits a significant resistance change at low concentrations of ethanol gas contained in the atmosphere. The chromium component contains chromium oxide, the magnesium component contains magnesium oxide, the zirconium component contains zirconium oxide, and the molar ratio of the chromium component is Mcl, the molar ratio of the magnesium component is M+n, and the zirconium component Letting the molar ratio of 11 be Mx, the molar fraction of 11 satisfies the relationship (M m + M c ) 2 + '' with an M value of -001 to 05, and the above magnesium oxide is 2.0.0 and 2.0. 2. A method for manufacturing an alcohol gas sensing element, which comprises firing a mixture of metal oxides whose half value in two X-ray diffraction curves is ()30° to 050° at 1000 to 1400°C. This is what we provide.

In the present invention, the metal oxide mixture is constituted by containing a chromium component, a magnesium component, and a zirconium component as active ingredients. The chromium component includes chromium oxide, the magnesium component includes 7gnesium oxide, and the zirconium component includes zirconium oxide, and these oxides do not mean that they can be mixed alone to form a mixture; and chromium oxide in the form of magnesium chromate produced during the calcination step, mixed with zirconium oxide. The magnesium and chromium components may partially or entirely contain magnesium chromate produced by mutual reaction as described above. Furthermore, a portion may exist in the form of an element, or may take the form of a compound other than an oxide.

When the oxide takes the form of an oxide, the oxide also includes cases where the oxide takes the oxidized form of cypress because its constituent elements have multiple types of valences. These oxides that exist in several oxidized forms include not only cases in which one of the saponified forms exists alone, but also cases in which a plurality of oxidized forms of IiI class exist together. Note that the saponification form referred to here includes those having non-stoichiometric compositions due to lattice defects and the like.

For the above chromium component, magnesium component, and zirconium component, the molar ratio of each component is Mc.

When Mm, Mx M-tomi -1=0. (It~o5 (To M+”c) 2+Mz The mole fraction in the relational expression must be satisfied.

In this case, when handling magnesium chromate, calculations are made assuming that magnesium oxide and chromium oxide are contained in equimolar amounts.

Furthermore, the average value of the half value of the X-ray diffraction of the 2,0.0 and 2.2.2 planes of the magnesium oxide contained in the magnesium component must be 0.3o to o,so'.

That is, if one of the above conditions is not satisfied, there will be problems in terms of performance both as a compensating element and as an alcohol gas element used alone. To explain more specifically, for example, a known gas detection element made of Kinho oxide, which exhibits a resistance change when it comes into contact with notane gas, methane gas, and water-based gases that make up fuel gas, has similar resistance to alcohol gases other than the above gases. When used as a detection element to detect gas thinning of fuel gas to indicate changes,
! The resistance changes depending on the concentration of alcohol gas generated during the process, leading to #4 radiation. So this [M
The alcohol gas detection element used as a compensating collector to avoid the change in resistance with respect to alcohol gas, so-called alcohol gas sensitivity, is greater than the above-mentioned fuel gas detection element, and the resistance value changes with respect to alcohol gas and fuel gas. This is because there must be a large difference. In other words, an alcohol gas detection element that satisfies this condition can be obtained from a mixture of metal oxides having the above composition.

In addition, the detection ability of an alcohol gas element used alone is not much different from the changing resistance value of gases other than alcohol gas, and if they are in close proximity, detection errors may occur, resulting in poor reliability. Therefore, there must be a large difference in resistance value compared to the resistance value for gases other than alcohol gas, and if this difference in resistance value is large, the selectivity for alcohol gas must be reasonable, and this condition is satisfied. The alcohol gas detection element is obtained from a mixture of metal oxides having the composition as described above.

Regarding the chromium-depleted component, the 7O oxide contained in this component is effective in further improving alcohol sensitivity and selectivity under specific conditions.

In other words, the chromium oxide contained in the chromium component is 1°0.4
and 1.0.10m X-ray diffraction half-value average value is 010
~o, ao'', an alcohol gas detection element with excellent alcohol sensitivity and selectivity can be obtained compared to a case where no restriction is imposed on the chromium component.

Furthermore, the above-mentioned toxic performance of the alcohol gas detection element obtained from the mixture of metal oxides made by adding the above-mentioned conditions to the magnesium component and the chromium component is achieved under the specific conditions of the zirconium component contained in the above-mentioned mixture. Let's get even better. In other words, when the average half value of 1.1.1 and a, o, oIi[l of zirconium oxide contained in the zirconium component is 0.15 to 0.50°, the alcohol gas sensitivity and selectivity are further improved. An excellent alcohol gas detection element can be obtained.

A mixture of L period composition can be obtained by mixing in anhydrous or hydrogenated conditions. 91t1i when mixing under hydrogenation
It is appropriate to add water in a proportion of 3 to 25 CC based on the total Iji filter 12 of I4 oxide. This mixing may be done in the presence of a binder, such as polyvinyl alcohol or cellulose, which is gasified by calcination. This case is effective in that it is possible to obtain an alcohol gas sensing element with a stable shape in which the bonding force between the metal oxides is uniform.

The mixture obtained by mixing under hydrogenation is dried to form a powder.

This mixture is filled into a mold and then shaped.

Paired electrodes such as platinum wires are embedded in the mixture filled in the mold and molded. Molding is done under high pressure.

This pressure is the pressure that solidifies into a certain shape, and is 1 t/cj ~
3t/d is appropriate.

When molding is performed at a pressure lower than It/f, the alcohol gas sensitivity is low, and when it exceeds 3 [/d, a similar tendency is exhibited. To give an example of the shape of the molded product, a cylinder with a diameter of 2 cm and a height of 3 cm is used.

Next, to explain the firing that is applied to this molded product, the firing is performed at a temperature of 1000 to 1400°C, preferably 1270 to 1370°C.
°C is appropriate. Baking U: 2 The height of the temperature affects the height of the alcohol sensitivity. In other words, the man degree is 1400
When the temperature exceeds 1000°C, the alcohol gas sensitivity decreases, and there is no alcohol detection function as a compensating element for the bonito material gas detection sensor used as a pair, and the same tendency occurs even in the temperature range below 1000''C. If the firing temperature is limited to 1,270 to 1,370°C within such a temperature range, an alcohol gas detection element with excellent alcohol gas sensitivity and selectivity can be obtained.A firing time of 2 to 4 hours is sufficient. be.

The alcohol gas sensing element obtained through such firing conditions has porous properties.

As described above, the alcohol gas sensing element according to the present invention, which is obtained by firing a mixture of metal oxides, has high sensitivity to alcohol gas, has a large difference in resistance value compared to other gases, and detects alcohol residue. It is useful as a compensation element for exclusion and as a stand-alone element for detecting alcohol gas.

Examples of the present invention will be described below, and the results of measuring the alcohol gas sensitivity and selectivity of the obtained devices will be listed. The devices of each example and the corresponding comparison were manufactured under the following conditions.

Magnesium oxide as a magnesium component, chromium oxide as a chromium component, and zirconium oxide as a zirconium component were mixed in the indicated ratios under anhydrous conditions to obtain a mixture of gold llI4 oxides. Here, X of 2thI for each component
The average value in line diffraction was as indicated. Weighed 15 mF from this mixture, filled it into a mold, embedded a pair of platinum wire electrodes, and molded it at a pressure of 2 t/d to form a cylindrical molded product with a diameter of 2 x height of 3 lbs. Obtained. Various firing conditions were used, especially the firing temperature.

The set firing m was as indicated.

The alcohol gas sensitivity was determined using the formula below.

Hair -io, 1 □-~× 100 aIr Here, Ra1r is the resistance value in air without alcohol gas, io, l are the resistance values in air containing 0.1 volume of alcohol gas, and the element This value is when the temperature is set to 450°C.

Regarding selectivity, ethanol gas, isobutanemethane,
The resistance value in air containing 0.1% by volume of hydrogen was measured, and the resistance value was changed due to contact with ethanol gas, whereas the resistance value was changed due to contact with inbutane, methane, and hydrogen. Evaluation was made by comparing the resistance values. Note that the resistance value of each element is the value after heating to 450°C.

Incidentally, when examining the alcohol gas sensitivity and selectivity of the devices according to the above Examples and Comparative Examples, in Examples 1 to 15, the mole fraction of zirconium oxide was 001 to 05, and the mole fraction of zirconium oxide was 0.001 to 0.05, which was 0.5% in the half value of magnesium oxide. The average value of is 0.
30~050°, firing conditions 1000~140°
It is clear that when the temperature is set at 0° C., an alcohol gas detection element with excellent alcohol gas sensitivity and selectivity can be obtained.

Claims (1)

[Claims] ill Consists of a chromium component, a magnesium component, and a zirconium component, the chromium component includes chromium oxide, the magnesium component includes magnesium oxide, the zirconium component includes zirconium oxide, and the molar ratio of the chromium component is Mc , where the molar ratio of the magnesium component is Mm and the molar ratio of the zirconium component is Mx, the molar fraction of Mx satisfies the following, and the magnesium oxide is 2.0. O and 2,
2, the average value in half value of X-ray diffraction of 2do is 0.30
A mixture of metal oxides that is ~0.50'
Negativity of an alcohol gas detection element characterized by firing at 1400°C. (Claim 1) characterized in that the average half value of X-ray diffraction of 21 oxide 1.0.4 and 1.0.10 is 010 to 0.30°. The manufacturing method of the alcohol gas detection element described above. (31 zirconium oxide is 1.1.1 and 3.0°0
h] (D X-ray diffraction) half value rl+ average value is 0.1
The method for producing an alcohol gas detection element according to claim 1 or 2, characterized in that the tube has a diameter of 5 to 0.50'. (4) The method for manufacturing an alcohol gas sensing element according to any one of items 1 to 3, wherein the firing temperature condition is 1270 to 1370°C.