JPS5931005B2 - Flammable gas detection element - 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 flammable gas detection elements that have been in practical use are
Tin oxide (SnO2), zinc oxide (ZnO), or γ-ferric monoxide (γ-Fe2O3), which are n-type oxide semiconductors,
) as an active ingredient.

The present invention aims to provide a novel and practical combustible gas detection element whose main active ingredient is indium oxide, which is also an n-type oxide semiconductor.

Indium oxide exhibits a sufficient change in resistance when it comes into contact with a combustible gas to be used as an element, that is, it has sufficient gas sensitivity characteristics.

However, since the element resistance value of the sintered body is very small, 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 destroying the poor characteristics of indium oxide, the inventors considered the use of additives suitable for this, and investigated various additives in detail. investigated.

In the process, we discovered that vanadium oxide, tungsten oxide or manganese oxide are excellent as such additives. Furthermore, in general, in oxide semiconductors for gas detection, when the concentration of combustible gas increases to a certain degree, the rate of change in resistance value with respect to change in gas concentration does not increase in proportion to the concentration and tends to reach saturation. Indium is no exception to this, and in the case of indium oxide,
If this alone is used, saturation will already be 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 will not be linear. ) is rather small, but it has been found that adding vanadium oxide, tungsten oxide, or manganese oxide can immediately solve these problems.

The present invention was completed based on the above findings, and includes a sintered body and a combustible material that detects the presence of combustible gas by detecting the electrical resistance of the sintered body. a sintered body in which the main component in the active component is indium oxide, the subcomponent is at least one of vanadium oxide, tungsten oxide, and manganese oxide; Ratio of components (however, when calculating the ratio, indium oxide is changed to In2O3,
Cnadium oxide becomes V2O5, tungsten oxide becomes W
The gist of the present invention is a combustible gas detection element characterized by having 5 to 40% by weight of O3 (converted to MnO2 for manganese oxide). Next, this invention will be explained in more detail. As described above, in the combustible gas detection element according to the present invention, the component showing the ability to detect gas (gas detection ability), that is, the main component in the active component is composed of indium oxide, and the subcomponent is is composed of at least one of vanadium oxide, tungsten oxide, and manganese oxide.
That is, in this invention, vanadium oxide, tungsten oxide, or manganese oxide is used as the above-mentioned additive, which solves the problem of the element resistance value of indium oxide being too low and the concentration dependence. We are trying to solve the problem of small size. In the device according to this invention, indium oxide is usually 1n203
Vanadium oxide usually exists in the oxidized form of V2O5, tungsten oxide usually exists in the oxidized form of WO3, and manganese oxide normally exists in the oxidized form of MnO2 in the element. Of course, the present invention also includes the presence of other oxidized forms having different valences, either alone or in combination.

It goes without saying that the oxidation form referred to herein includes those having non-stoichiometric compositions due to lattice defects and the like. However, in this specification, when considering the proportions of components constituting the element, all indium oxide is converted to In2O3, and all vanadium oxide is converted to 20.
5, all tungsten oxide is converted to WO3, and all manganese oxide is converted to MnO2. By the way, in order to be put to practical use as an element for constructing a gas leak alarm, the resistance value of the element must be within a certain range, and the rate of change in resistance value must also be maintained above a certain level. Of course.

Therefore, prior to completing this invention, the inventors investigated factors that affect the element resistance value and the rate of change in resistance value. As a result, it was found that the amount of subcomponents added was the most important factor. As a result of further experiments and research, the following findings were obtained. In other words, when the amount of the subcomponent added exceeds 40% by weight in the active ingredient, the property of indium oxide, which is excellent in gas sensitivity, does not work effectively and the performance of the element tends to decrease. If the amount added is less than 5% by weight, the effect of increasing the element resistance value cannot be expected to be significant, and the effect of addition is small in terms of gas sensitivity, concentration separation, etc. For this reason, in the present invention, the appropriate proportion of the subcomponent in the active ingredient is 5 to 40% by weight, and therefore indium oxide is the balance b, that is, 60 to 95% by weight.
It is said that it accounts for % by weight. However, when making a gas detection element, a component that functions as a binder or a component that functions simply as a filler may be added to the component that exhibits gas detection ability. Even in such a case, as long as the component exhibiting gas detection ability consists of indium oxide and at least one of vanadium oxide, tungsten oxide, and manganese oxide,
falling within the scope of this invention. In this specification, it is stated that the combustible gas detection element according to the present invention is composed of indium oxide as a main component and at least one of vanadium oxide, tungsten oxide, and manganese oxide as a subcomponent. This is precisely the result of considering that, as mentioned above, when actually producing a gas sensing element, components other than those exhibiting gas detection ability are often added.
However, even though this has been stated, it is not intended to exclude such cases, as cases where the flammable gas detection element is constituted only by the above-mentioned active ingredients are of course within the scope of the present invention. . 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 can be of any type as long as it is vanadium oxide, tungsten oxide, or manganese oxide, which is indium oxide when it becomes an element (the desired oxide itself may also be used), and as necessary. It does not matter whether the intermediate treatment is added to the starting material. Since the present invention is configured as described above, a combustible material containing indium oxide as the main active ingredient, which has an appropriate element resistance value and sufficient gas sensitivity and concentration dependence (concentration separability). A gas detection element can be provided.

Next, examples will be described together with comparative examples.

High purity 1n2 as a raw material for indium oxide, the main component
03 powder (purity 99.9%) is used as a raw material for vanadium oxide, tungsten oxide, and manganese oxide, which are subcomponents.
99%) of V2O5 powder, WO3 powder, and MnO2 powder were used.

These raw materials were blended in a proportion such that the element composition would be as shown in the table below, and after thoroughly mixing with a crusher, a fixed amount of mixed powder (indium oxide single powder in Comparative Examples 1 and 2) was added. (20mg) Weighed the platinum wire electrode embedded diameter 2
A gas-sensitive body (sintered body) is produced by compression molding it into a columnar element shape with mmφ and length of about 2n1rn, and firing it at a firing temperature of 600°C or 800°C, a firing time of 3 hours, and in air. I made it. A coiled heater was attached around each gas sensitive body obtained above, and the cap was further covered with a wire mesh cap made of stainless steel 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 sensitivity characteristics were determined by applying isobutane-containing air with an isobutane concentration of 0.1% by volume and 0.3% by volume while maintaining the temperature of the element at a constant 450°C by applying a constant voltage to the coiled heater. The study was conducted by measuring the electrical resistance value of the gas sensitive body and determining its change.

here, The gas sensitivity is expressed as In addition, the concentration separability is given by equation 2, each was requested.

In the formula, Rair is the resistance value RO of the element in air (dew point 13°C). l; resistance value RO of the element in isobutane-containing air with an isobutane concentration of 0.1% by volume (dew point 13°C); 3: Represents the resistance value of the element in isobutane-containing air (dew point: 13° C.) with an isobutane concentration of 0.3% by volume.

As is clear from the results shown in the table above, In
In the 2O3 single-component system, the element resistance is low and outside the practical range, but by adding at least one of V2O5, WO3, and MnO2 to In2O3, the element resistance increases and concentration separation in the practical concentration range is achieved. will improve.

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 subcomponent is at least one of vanadium oxide, tungsten oxide, and manganese oxide, and the proportion of the subcomponent in the active ingredient (however, when calculating this, indium oxide is , vanadium oxide is converted to V_2O_5, tungsten oxide is converted to WO_3, and manganese oxide is converted to MnO_2) in an amount of 5 to 40% by weight.