JPS5853734B2 - Kanenseigaskenchi Soshinoseizouhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a combustible gas sensing element, and its purpose is to provide a method for manufacturing a gas sensing element using gamma-type iron sesquioxide as a gas sensitive material. One object of the present invention is to provide a method for obtaining a gas sensitive material that is sensitive to gas and has stable electrical and mechanical properties.

Various types of combustible gas detection elements are known.

One of the most common is a metal oxide semiconductor that is used as a gas sensitive material, and this takes advantage of the property that this material changes its resistance value when it responds to flammable gas. It is.

This type of gas detection element basically has the same structure as thin film resistors and sintered body resistors, which are electronic circuit components, and therefore its manufacturing method is also similar to that of those resistors. The various manufacturing methods are similar.

For example, the gas sensitive body of a combustible gas detection element using stannic oxide, which is an N-type oxide semiconductor, is made by molding a mixture of stannic oxide powder and a suitable inorganic binder, and then firing it at a high temperature. Obtained by 1.

A so-called thick film type gas sensitive material can also be obtained by forming the mixture into a slurry, coating it once on a suitable insulating substrate, and then firing it.

In order to detect the resistance value of these gas sensing elements, one pair of electrodes is provided, and since it is advantageous to operate this type of gas sensing element at a higher temperature than room temperature, the area near the gas sensing element generates heat. The gas detection element is completed by providing a body.

The present invention relates to a method for manufacturing a gas sensing element using a sintered product of gamma-type iron sesquioxide (γ-Fe2O3), which is one of the N-type oxide semiconductors, as a gas sensitive material.

There are several problems that must be considered when producing a gas sensitive material by sintering γ-Fe203 powder as a raw material.

One of these is to find a manufacturing method that makes the surface area of the sintered material as uniform as possible in order to increase its sensitivity to gas.

This is natural since being sensitive to a gas is essentially a surface phenomenon of a solid.

However, increasing the surface area by one factor causes another new problem.

That is, such a gas sensitive material has high electrical resistance, low mechanical strength, and poor life characteristics.

Another problem is that γ-Fe2O3 is heated at a high temperature, which makes it extremely sensitive to α-type F.
Because of the property of e203f transition, the firing temperature cannot be set too high.

The temperature of this transition to the α-type is influenced by the production history, particle size, content of impurities, etc. of γ-Fe2O3, but is generally said to be 470°C to 850°C.

Therefore, in order to avoid the transition to .alpha.-Fe203, the firing temperature of the gas sensitive material must be selected to be lower than the transition temperature range, and the firing temperature of the iron oxide powder must be considerably lower.

Until now, no methods were known to solve the problems mentioned above, but as a result of extensive experimental studies, the inventors found that particularly selected organic compounds and γ-F
The above-mentioned (1'-Fe2
We have discovered that sintering can be performed at a temperature below the transition temperature to Q3, and that the other two problems mentioned above can also be solved, and we have now clearly developed a new manufacturing method for gas sensing elements.

That is, the present invention relates to the production of a combustible gas detection element using gamma-type iron sesquioxide (γ-Fe2O3) having a spinel crystal structure as a gas sensitive material. It is characterized in that it is kneaded to form a paste-like material and the paste-like material is sintered to produce a γ-Fe203 sintered product.

Here, the organic compound is any one of triethanolamine, jetanolamine, polyethylene glycol, chrycerin, bentanediol, and tetraethylenepentamine.

Next, the present invention will be explained in detail by giving examples.

Example 400 ml of an aqueous solution containing both 0.1 mol of ferrous chloride and 0.2 mol of ferric chloride is added dropwise into 500 ml of an alkaline aqueous solution containing 1.6 mol of caustic soda to form a precipitate.

This precipitate is hydrated magnetite.

This precipitate is thoroughly washed once with water by decanting, dried at 100°C, and ground in a mortar.

This magnetite powder was oxidized by heating at 350 DEG C. in air to obtain .gamma.-type iron sesquioxide (.gamma.-Fe2O3) powder.

This powder is thoroughly mixed with various organic compounds.

In this example, in order to obtain a so-called thick film type gas sensitive material, an amount of organic material sufficient to make the mixture into a paste was added.

The amount varies depending on the type of organic matter.

For example, γ-Fe2o3 powder 10. ? RF Koki, for triethanolamine, 1 ml is 6.5 ml, for polyethylene glycol, 1 ml is 1077111, for diethanolamine, 1 ml is 6, Oml, for glycerin, 1 ml is 7.7 ml, for bentanediol. and for tetraethylenepentamine, 1 is 5.2, respectively.
A paste with appropriate softness was obtained.

This paste was coated once on an alumina substrate on which a pair of comb-shaped gold electrodes had been provided in advance, and baked in air at 450 DEG C. for 2 hours to obtain a so-called thick film of .gamma.-Fe2O3.

Note that the gas detection element is made of this γ-Fe203 thick film with a thickness of 300 mm.
A heating element was installed on the other side of the alumina substrate so that the temperature could be heated to ~400°C.

The results of the characteristics of the gas sensing element thus obtained are shown in the table on page 7.

In this table, each characteristic is defined as follows.

a. Initial characteristics: characteristics at the time of creation.

Ra i r , 26 when the device is held at 350°C
℃.

Resistance value in air with relative humidity of 65%.

Rgas is the resistance value when the element is held at 350°C in air containing 0.2% isobutane at 25°C and 65% relative humidity.

b. Life characteristics; the values of Ra1r and Rga s after 5000 hours of holding the device at 350°C in air at 25°C and 65% relative humidity.

C. Degree of sintering of the gas sensitive body: At the time when the gas sensitive body was created, 3M Scotch Electrical Tape 456 was pasted on the surface of the sintered body, and when it was gently peeled off, it became 1 on the substrate. The amount of iron oxide is expressed as a percentage of the total amount of iron oxide.

From these results, it can be concluded that γFe2O3 sintered material made using triethanolamine, jetanolamine, polyethylene glycol, glycerin, bentanediol, and tetraethylenepentamine has excellent properties as a gas sensitive material. are doing.

As mentioned above, a gas sensitive material is made using γ-Fe203 powder doped with appropriate impurities for the purpose of changing the transition temperature to α-Fe203 and improving the stability as a gas sensitive material. It goes without saying that even in case 1, the organic compounds mentioned above in the present invention have exactly the same effect.

In addition, even when one noble metal is added to γ-F e203 powder for the purpose of improving the response speed as a gas sensitive material, the organic compound revealed in the present invention has the same effect. Motsu.

As is clear from the above explanation using examples, the present invention provides a method for easily producing a gas sensitive material having superior properties to those of γ-Fe2O3, and has great industrial benefits. It is something that brings.

Claims (1)

[Claims] 1. In a method for manufacturing a combustible gas detection element comprising a gamma-type iron sesquioxide sintered material whose resistance value changes in response to combustible gas when heated by a heating element, the gamma-type iron sesquioxide sintered material However, gamma-type iron sesquioxide powder with a spinel-type crystal structure, triethanolamine, jetanolamine, polyethylene glycol, chrycerin,
1. A method for producing a flammable gas detection element, comprising kneading one of bentanediol and tetraethylenepentamine to form a paste-like material, and firing the paste-like material.