JPS6138818B2 - - 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 resistance change, that is, has sufficient gas sensitivity characteristics as a gas sensing element.
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 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 Another problem is that the concentration dependence (concentration separability) is rather small, 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 increases the element resistance value to a practical range without destroying the excellent properties of indium oxide. High and
The object of the present invention is to provide a method for manufacturing a gas sensing element that has high concentration separation and is less susceptible to 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 and increasing its stability over time. They also succeeded in increasing the element resistance and concentration separation. However, since this product was not yet fully satisfactory in terms of concentration separation, the addition of a second subcomponent was considered. It has also been found that platinum, platinum oxide, palladium, and palladium oxide are effective as the second subcomponent. 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, the second subcomponent is platinum, At least one selected from the group consisting of platinum oxide, palladium, and palladium oxide is also blended, and the main component in the active ingredients, the first
(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 , platinum and platinum oxide are converted to PtO (and palladium and palladium oxide are each converted to PdO), 1 to 10% by weight of the total active ingredient is the second subcomponent, the remaining 95 to 50% by weight is the main component, and the remaining 5% by weight is the secondary component. ~50
The gist of the present invention is a method for manufacturing a gas sensing element, which is characterized in that the blending amount of the starting materials for each of the metal oxides is adjusted so that the weight percent becomes the first subcomponent. 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, one or two selected from the group consisting of platinum, platinum oxide, palladium, and palladium oxide.
The structure is such that a starting material that is more than a seed is added. The metals and metal oxides constituting the active ingredient may take various oxidation forms due to their different valences, but the types do 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 forms mentioned here include those with non-stoichiometric compositions due to lattice defects and the like. However, the main component is usually indium oxide.
In In ₂ O ₃ , iron oxide, which is the first subcomponent, is in the oxidized form Fe ₂ O ₃ (although it can be said that the crystal type does not matter, it is usually α-Fe ₂ O ₃ ), and the second subcomponent is Fe 2 O 3 . The two components, platinum oxide, are in the oxidized form PtO and palladium oxide is PdO. Therefore, in this specification, when considering the proportions of components constituting an element, all oxides are converted into the oxidized form shown above. Furthermore, when considering the proportions of platinum and palladium, these are also converted into PtO or PdO. 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, first, the second subcomponent accounts for 1 to 10% by weight of the total active ingredient. The balance, that is, 90 to 99% by weight of the total active ingredient is composed of the main component and the first subcomponent, but the first subcomponent accounts for 5 to 50% by weight of this balance, and the entire remainder, that is, this remainder. The main component accounts for 95 to 50% by weight. If the amount of iron oxide, which is the first subcomponent, is outside the above range at the lower limit, it is difficult to make it less susceptible to the influence of ambient humidity, and if it is outside the upper limit, the effect of adding the second subcomponent will not be apparent. If the amount of the second subcomponent added exceeds the above range at the lower limit, the sensitivity to gas will not be sufficiently improved, and conversely, if it deviates from the upper limit, the effect of the addition of the first subcomponent will not appear. 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 a case, the active ingredient that shows gas detection ability is indium oxide, which is the main ingredient, and the first
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 the above four types. In this specification, in the method for manufacturing 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 four types. The statement that it is made up of at least one kind of material 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. As a starting material for manufacturing, it can be indium oxide or iron oxide when it is made into a device, and any type can be used as long as it is selected from the four types mentioned above (the desired oxidation It may be platinum, palladium itself), or intermediate treatment added to the starting material if necessary. Next, examples will be described together with comparative examples. The raw material powders were blended in a proportion such that the element composition was as shown in the table below, and after thoroughly mixing with a pickler, a fixed amount (20 mg) of the mixed powder (comparative example 3 was an indium oxide single powder) was weighed out. 2mm in diameter with embedded platinum wire electrode (0.2mmφ in diameter, 15mm in length)
A gas-sensitive body (sintered body) is formed by compression molding into a cylindrical element shape with a diameter of approximately 2 mm and firing under the following conditions: firing temperature: 600°C or 800°C, firing time: 3 hours, in air. I made it. 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-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 and maintaining the temperature of the element at a constant 450°C, while using purified air with an isobutane concentration of 0.1% by volume.
The electrical resistance of the gas sensitive member was measured by contacting it with isobutane-containing air and methane-containing air with a methane concentration of 0.1% by volume, and the changes in the electrical resistance were determined.

【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 calcining the starting material to be a metal oxide, platinum, platinum oxide, palladium and At least one member selected from the group consisting of palladium oxide is also blended, and the proportions of the main component, the first subcomponent (iron oxide), and the second subcomponent in the active ingredients (however, In calculating this, indium oxide is converted to In ₂ O ₃ , and iron oxide is converted to In 2 O 3.
(converted to Fe ₂ O ₃ , platinum and platinum oxide to PtO, and palladium and palladium oxide to PdO), but 1 to 10% by weight of the total active ingredient is the second subcomponent, and the balance is 95% by weight. A method for manufacturing a gas sensing element, characterized in that the blending amount of the starting materials for each of the metal oxides is adjusted so that ~50% by weight is the main component and the remaining 5-50% by weight is the first subcomponent. .