JPS6157571B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a combustible gas detection element containing indium oxide as a main active ingredient. Most of the combustible gas detection elements that have been put into practical use are made using n-type oxide semiconductors such as tin oxide (SnO ₂ ), zinc oxide (ZnO), or γ-ferric oxide (γ-Fe ₂ O ₃ ). It consisted of a sintered body as an active ingredient. This invention also provides n
The present invention aims to provide a novel and practical combustible gas detection element whose main active ingredient is indium oxide, which is a type oxide semiconductor. Indium oxide shows a change in resistance value sufficient to be used as an element when it comes into contact with flammable gas.
That is, it has sufficient gas sensitivity characteristics. but,
The sintered body has a very low element resistance value, so
If this is attempted to be used in a gas leak alarm, problems such as difficulty in circuit design will occur, which poses practical difficulties. Therefore, in order to increase the element resistance value to a practical range without reducing the excellent properties of indium oxide, the inventors considered the use of additives suitable for this, and detailed various additives. investigated. In the process, special oxides selected from among alkaline earth oxides, aluminum group oxides, transition metal oxides, carbon group oxides, platinum group oxides and rare earth oxides are formed. was found to be excellent as such an additive. Furthermore, in general, oxide semiconductors for gas detection are
When the combustible gas concentration increases to a certain extent, the rate of resistance change with respect to gas concentration change does not increase in proportion to the concentration and tends to reach saturation.
Indium oxide is no exception to this; moreover, in the case of indium oxide, saturation is already reached when the combustible gas is at a relatively low concentration, and the relationship between the change in element resistance and the concentration in the practical concentration range is poor. There is also the problem that it is not linear, that is, the concentration dependence of the element resistance (concentration separability) is somewhat small, but if the above-mentioned specially selected oxide is added as a subcomponent, this problem can also be solved. I understand that it will be resolved immediately. This invention was completed based on the above knowledge, and will be described in detail as follows. The combustible gas detection element according to the present invention is composed of indium oxide as its active ingredient, that is, the ingredient exhibiting gas detection ability. Indium oxide can be considered to normally exist in the element in the oxidized form of In ₂ O ₃ , but it can also exist in other oxidized forms, and the distinction between the oxidized forms does not matter. In this combustible gas detection element, the main components include alkaline earth oxides, aluminum group oxides, transition metal oxides, carbon group oxides, platinum group oxides, and rare earth metal oxides. The specially selected oxides below (in addition,
As described later, metallic platinum can also be a subcomponent, although it is not an oxide, so in this specification, metallic platinum is also included in this specially selected oxide). The above substances are added as subcomponents, and this is intended to solve the problem of the element resistance of indium oxide being too low and the problem of low concentration dependence (concentration separability). There is. In this invention, the following are specially selected subcomponents among the active ingredients. That is, magnesium oxide (MgO), calcium oxide (CaO), strontium oxide (SrO), and barium oxide (BaO) are selected as alkaline earth oxides, and aluminum oxide (Al ₂ O ₃ ) is selected as the aluminum group oxide. and gallium oxide are selected. Among these, gallium oxide can be considered to exist in devices in the oxidized form of Ga ₂ O ₃ , but it is also free to exist in other oxidized forms, and the distinction between the oxidized forms is not a problem. . Next, as the transition metal oxide, vanadium oxide, chromium oxide, iron oxide, manganese oxide, nickel oxide, hafnium oxide (HfO ₂ ), and tungsten oxide are selected. Among these, vanadium oxide is usually in the oxidized form of V ₂ O ₅ , and chromium oxide is usually in the oxidized form of Cr ₂ O ₃ .
Iron oxide is usually in the oxidized form α-Fe ₂ O ₃ , manganese oxide is usually in the oxidized form MnO ₂ , nickel oxide is usually in the oxidized form NiO, and tungsten oxide is usually in the oxidized form WO ₃ .
Although each may be considered to exist in the element, it is free to exist in oxidized forms other than these, and the distinction between the oxidized forms does not matter. Silicon oxide and germanium oxide are selected as carbon group oxides. Silicon oxide is usually in the oxidized form _SiO2 , and germanium oxide is commonly
Although it can be considered that each oxidized form of GeO ₂ exists in the element, it can also exist in other oxidized forms, and the distinction between the oxidized forms does not matter. Rare earth oxides include yttrium oxide (Y ₂ O ₃ ), scandium oxide (Sc ₂ O ₃ ), lanthanum oxide (La ₂ O ₃ ), cerium oxide, praseodymium oxide, samarium oxide (Sm ₂ O ₃ ), and gadolinium oxide. (Gd ₂ O ₃ ) is selected. Cerium oxide usually exists in the oxidized form of CeO ₂ and praseodymium oxide usually exists in the oxidized form of Pr ₂ O ₃ in the element, but they can also exist in other oxidized forms, The distinction between the oxidation forms does not matter. However, in this invention, just because the oxidation forms of commonly selected oxides are shown in the formulas above, it does not mean that these oxides have strictly stoichiometric compositions as shown in these formulas. It's not limited to things. That is, these oxides may also include those with non-stoichiometric compositions. Note that when producing a gas detection element, a component that functions as a binder or a component that functions simply as an extender may be added to the component that exhibits the ability to detect gas (gas detection ability). Even in such a case, the invention falls within the scope of the present invention as long as the component exhibiting gas detection ability consists of indium oxide and the above-mentioned specially selected oxide. In this specification, the combustible gas detection element according to the present invention is one in which the main active ingredient is indium oxide, and the subcomponent is one or more selected from the group consisting of the above-mentioned oxides. The reason why it is made up of the following is precisely the result of taking into consideration that, as mentioned above, when actually producing a gas detection element, components other than those exhibiting gas detection ability are often added. However, even though this has been stated, cases where the combustible gas detection element is composed only of the above-mentioned active ingredients are of course within the scope of the present invention, and are not intended to exclude such cases. . As the form of the combustible gas detection element according to the present invention, a form constituted by a sintered body is generally selected because good gas sensitivity can be easily obtained and stability over time is good. It is not limited to this, and may be formed into a thin film or a thick film, for example, and its form is free. In addition, the manufacturing raw materials, manufacturing methods, etc. are appropriately selected in consideration of the ease of obtaining the raw materials, cost, purpose of use, etc. The starting material for manufacturing is indium oxide when it is made into an element, and any type is not restricted as long as it is the above-mentioned specially selected oxide (the desired oxide itself may also be used). Further, it does not matter whether intermediate processing is added as necessary. Since this invention is configured as described above,
It is possible to provide a combustible gas detection element containing indium oxide as the main active ingredient, which has an appropriate element resistance value and sufficient gas sensitivity and concentration dependence. Next, examples will be described together with comparative examples. High purity In ₂ O ₃ powder (purity 99.99) manufactured by Yamanaka Chemical Industry Co., Ltd. is used as a raw material for indium oxide, the main component.
%), and oxide powder of high purity (99 to 99.99%) was used as the raw material for the oxide, which is a subcomponent. These raw materials were blended in proportions such that the element composition was as shown in the table below, and after thoroughly mixing with an Ishikawa-type crusher, a fixed amount of mixed powder (indium oxide single powder in Comparative Examples 1 to 3) was added. (20mg) was weighed and compression molded into a cylindrical element shape with a diameter of 2mmφ and a length of about 2mm with a platinum wire electrode embedded, and the firing temperature was
Gas sensitive bodies were produced by firing under the following firing conditions: 600°C, 800°C or 1000°C for 3 hours in air. A coiled heater was attached around each of the gas sensitive bodies obtained above, and the cap was further covered with a stainless steel wire mesh cap to serve as a gas detection section. The results of investigating the gas sensitivity characteristics of each element are shown in the table below, and all of the examples were superior to the comparative examples. The gas-sensitive characteristics were determined by applying a constant voltage to the coiled heater to maintain the temperature of the element at a constant 450°C, and then contacting the gas-sensitive element with air containing isobutane at concentrations of 0.1% and 0.3% by volume. The investigation was conducted by measuring the electrical resistance value of the material and determining its change.

【table】

【table】

[Table] Here, the gas sensitivity is expressed by the formula R _air −R ₀ . ₁ /R _air ×100, and the concentration separation is expressed by the formula R ₀ . ₁ /R ₀ . ₃ , respectively. In the formula, R _air is the resistance value of the element in air (dew point 13°C) R _0.1 ; the resistance value of the element in air containing isobutane (dew point 13°C) with an isobutane concentration _{of 1000} ppm R _0.3 ; Each represents the resistance value of the element in isobutane-containing air with an isobutane concentration of 3000 ppm (dew point 13°C). As is clear from the results shown in the table above, by adding a specially selected oxide to indium oxide, the resistance value of the device is reliably increased. Furthermore, depending on the type of additives or their combination, not only the concentration dependence but also the gas sensitivity can be improved. The High Pressure Gas Safety Association's "Liquefied Petroleum Gas Leak Alarm Certification Regulations for General Consumers, etc." stipulates that an alarm should be issued at a gas concentration of 1000 to 3000 ppm. It can be said that the performance is sufficient to pass the test.

Claims (1)

[Claims] 1 A combustible gas detection element that detects the presence of a combustible gas by detecting a sintered body and the electrical resistance of this sintered body, the element comprising a The component is indium oxide, and the subcomponents are magnesium oxide, calcium oxide, strontium oxide, barium oxide, aluminum oxide, gallium oxide, vanadium oxide, chromium oxide, iron oxide, manganese oxide, nickel oxide, hafnium oxide, tungsten oxide, oxide. A flammable gas comprising one or more selected from the group consisting of silicon, germanium oxide, yttrium oxide, scandium oxide, lanthanum oxide, cerium oxide, praseodymium oxide, samarium oxide, and gadolinium oxide. Sensing element.