JPS6138816B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to a method for manufacturing a gas sensing element whose main active ingredient is indium oxide. [Background Art] Most gas detection elements that have been put into practical use are made of n-type oxide semiconductors such as tin oxide (SnO ₂ ), zinc oxide (ZnO), or γ-ferric oxide (γ-ferric oxide).
It consisted of a sintered body containing Fe ₂ O ₃ ) as an active ingredient. This invention also provides n
A mixed powder containing indium oxide, which is a type oxide semiconductor, as the main active ingredient is sintered in the same way,
The present invention aims to provide a method for obtaining a gas sensing element. Like the tin oxide and zinc oxide, indium oxide exhibits a sufficient change in resistance as a gas detection element, that is, has sufficient gas sensitivity characteristics.
However, the individual sintered body has a very low element resistance, so if you try to use it for a gas leak alarm, problems such as circuit design will occur.
There are practical difficulties. Furthermore, in the case of indium oxide, saturation is already reached when the gas is at a relatively low concentration when used alone, and the relationship between the change in element resistance and the concentration in the practical concentration range is not linear; that is, the element resistance depends on the concentration. Another problem is that the sensitivity (concentration separation) is rather low, making it difficult to set the detection level. Another disadvantage of indium oxide is that it is susceptible to humidity, which can cause false alarms. [Purpose of the Invention] In view of the above problems, the present invention uses indium oxide as the main active ingredient, and also brings the element resistance to a practical range without destroying the excellent properties of indium oxide. It is an object of the present invention to provide a method for manufacturing a gas sensing element that has a high concentration separation property and is less susceptible to the influence of humidity. [Disclosure of the Invention] In order to achieve the above object, the inventors considered the use of additives and conducted detailed studies on various additives. In the process, they discovered that iron oxide is an excellent additive. That is, by using indium oxide as the main active ingredient and adding iron oxide as a subcomponent, they succeeded in making the product less susceptible to humidity. They also succeeded in increasing the element resistance value and increasing the concentration separation to some extent. However, since the element resistance value and concentration separability were still not fully satisfactory, the addition of a second subcomponent was considered. This invention was completed as a result. That is, in the present invention, when a starting material to be a metal oxide is fired to obtain a gas sensing element whose main active ingredient is indium oxide and whose subcomponent is iron oxide, nickel oxide is added as a second subcomponent. ,
At least one selected from the group consisting of vanadium oxide, chromium oxide, cobalt oxide, hafnium oxide, tungsten oxide, niobium oxide and manganese oxide is also blended, and the main component in the active ingredients, the first Subcomponent (iron oxide)
and the ratio of the second subcomponent (however, when calculating the ratio, indium oxide is converted to In ₂ O ₃ , iron oxide is converted to Fe ₂ O ₃ , nickel oxide is converted to NiO, vanadium oxide is converted to V ₂ O ₅ , chromium oxide becomes Cr ₂ O ₃ , cobalt oxide becomes Co ₃ O ₄ , hafnium oxide becomes HfO ₂ ,
Tungsten oxide to _WO3 , niobium oxide _{to Nb2O5}
and manganese oxide (respectively converted to MnO ₂ ) is 85 to 25% by weight of the main component, 5 to 40% by weight of the first subcomponent, and 10 to 35% by weight of the second subcomponent. The gist of this invention is a method for manufacturing a gas sensing element, which is characterized by adjusting the blending amount of starting materials for each metal oxide. Next, this invention will be explained in more detail. As described above, in the method for producing a gas detection element according to the present invention, the active ingredient in the obtained element, that is, the main ingredient in the ingredient showing the ability to detect gas (gas detection ability) is indium oxide. consists of the first
The starting material is adjusted so that the subcomponent of is composed of iron oxide. Further, as a second subcomponent, a starting material which is one or more selected from among the eight types of oxides such as the above-mentioned nickel oxide is added. It is. Each metal oxide constituting the active ingredient may take various oxidation forms due to different valences. The type does not matter. Regarding oxides that exist in multiple oxidation forms, in addition to cases in which one of the oxidation forms exists alone in the element, cases in which multiple types of oxidation forms exist in the element together. There is also. Note that the oxidation form referred to herein includes those having non-stoichiometric compositions due to lattice defects and the like. However, the main component is usually indium oxide.
In In ₂ O ₃ , the first subcomponent, iron oxide, is in the oxidized form of Fe ₂ O ₃ (the crystal type does not matter, but it is usually α-Fe ₂ O ₃ ), and the second subcomponent is Fe 2 O 3 . The component nickel oxide is NiO, vanadium oxide is V ₂ O ₅ ,
Chromium oxide is Cr ₂ O ₃ , cobalt oxide is Co ₃ O ₄ , hafnium oxide is HfO ₂ , tungsten oxide is
WO ₃ , niobium oxide is Nb ₂ O ₅ , manganese oxide is
It is in the oxidized form _MnO2 . Therefore, in this specification, when considering the proportions of components constituting an element, all oxides are converted into the oxidized form shown above. In the method for manufacturing a gas sensing element according to the present invention, it is important to select starting materials such that the proportions of the main component, first subcomponent, and second subcomponent fall within the following range. That is, the ratio of the first subcomponent to the total effective components in the sintered gas detection element is 5 to 40% by weight, and the ratio of the second subcomponent is 5% to 40% by weight.
10 to 35% by weight, with the main component being the remainder i.e.
It is important that it is between 85 and 25% by weight. This is because when the ratio of the first subcomponent or the second byproduct is outside the above range at the lower limit, the effect of addition is small, whereas when it is outside the upper limit, adverse effects occur. In addition, in this invention, in addition to the above-mentioned active ingredients, components that function as a binder or components that function as a mere filler may be added. Even in such cases, the active ingredients that are more than capable of gas detection are indium oxide, which is the main component, and primary
It falls within the scope of the present invention as long as it consists of iron oxide as a subcomponent and a second subcomponent selected from among the eight types mentioned above. In this specification, in the method for producing a gas sensing element according to the present invention, the main component in the active ingredient is indium oxide, the first subcomponent is iron oxide, and the second subcomponent is selected from the group consisting of the above eight types. The statement that it consists of at least one selected thing is precisely because
As mentioned above, this is a result of taking into consideration that components other than those exhibiting gas detection ability are often added when actually producing a gas detection element. However, even though this is stated above, it goes without saying that the scope of the present invention also falls within the scope of the present invention when a gas sensing element is manufactured by sintering only the above-mentioned effective ingredients.
It is not intended to exclude such cases. The starting materials for manufacturing can be indium oxide or iron oxide when used as a device, and any type can be used as long as it is selected from the eight types mentioned above (the desired oxidation (It may be the product itself) or may be an intermediate treatment added to the starting material if necessary. Next, examples will be described together with comparative examples. High-purity In ₂ O ₃ powder is used as the raw material for indium oxide, which is the main component, and each oxide is used as the raw material for iron oxide, the first subcomponent, and the oxides listed in the table below, which are the second subcomponent. High purity powder was used. These raw materials were blended in proportions such that the element composition was as shown in the table below, and after thoroughly mixing with a crusher, a fixed amount (20 mg) of mixed powder (Comparative Example 10 was indium oxide single powder) was weighed out. The gas sensitive body (sintered) was then compression molded into a cylindrical element shape with a diameter of 2 mmφ and a length of about 2 mm with platinum wire electrodes embedded therein, and fired in air for 3 hours. formed a body). A coiled heater was attached around each gas sensitive body obtained above, and the body 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-sensitive characteristics of each element are shown in the table below, and when the various gas-sensitive characteristics were judged comprehensively, all of the Examples were superior to the Comparative Examples. The gas sensitivity characteristics were determined by applying a constant voltage to the coiled heater to maintain the temperature of the element at a constant 450°C, while using purified air with an isobutane concentration of 0.1% by volume.
and 0.3% by volume of isobutane-containing air, respectively, and measure the electrical resistance value of the gas sensitive member.
The investigation was conducted by determining the change.

【table】

〔Effect of the invention〕

Since the present invention is configured as described above, the gas sensing element obtained thereby possesses the excellent characteristics of indium oxide, and methane,
Shows a sufficient change in resistance value when in contact with test gases such as propane, butane, and carbon monoxide. Moreover, it has an appropriate element resistance value, sufficient gas sensitivity and concentration dependence (concentration separability), and is not easily affected by humidity.

Claims (1)

[Claims] 1. In order to obtain a gas sensing element in which the main active ingredient is indium oxide and the subcomponent is iron oxide by firing the starting raw material that becomes the metal oxide, nickel oxide, vanadium oxide, and iron oxide are added as the second subcomponent. At least one selected from the group consisting of chromium, cobalt oxide, hafnium oxide, tungsten oxide, niobium oxide, and manganese oxide is also blended, and the main component and the first subcomponent ( (iron oxide) and the ratio of the second subcomponent (however, when calculating the ratio, indium oxide is converted to In ₂ O ₃ , iron oxide is converted to Fe ₂ O ₃ , nickel oxide is converted to NiO, vanadium oxide is converted to V ₂ O ₅ , chromium oxide to Cr ₂ O ₃ , cobalt oxide to Co ₃ O ₄ ,
Hafnium oxide becomes HfO ₂ , tungsten oxide becomes
(converted to WO ₃ , niobium oxide to Nb ₂ O ₅ , and manganese oxide to MnO ₂ ) are the main components.
85-25% by weight, 5-40% by weight of the first subcomponent, the second
A method for producing a gas sensing element, comprising adjusting the blending amount of the starting materials for each of the metal oxides so that the amount of the subcomponent is 10 to 35% by weight.