KR0158561B1 - Method of manufacturing thick-film for one-fired inflammability gas sensor - Google Patents

Abstract

The present invention is to use a metal oxide instead of a conventional metal catalyst, and to provide a thick film for a gas sensor excellent gas sensitivity only once firing without going through a double firing step, an object thereof.

In the present invention, the atomic composition is selected from Nb ₂ O ₅ : 1.0% and NiO: 1.0% or less as an oxide catalyst in a basic composition consisting of Mg (NO ₃ ) ₂ , 6H ₂ O: 1% or less and the balance SnO ₂ . The present invention relates to a thick film for high-sensitivity gas sensors, characterized in that one or two kinds are added.

Description

Manufacturing method of thick film for high sensitivity flammable gas sensor by one time firing

1 is a connection state diagram of a thick film specimen for a gas sensor for measuring the gas sensitivity.

2 is a schematic configuration diagram of a gas sensitivity measuring device for the specimen of FIG.

3 is a graph showing the gas sensitivity according to the temperature change for the present invention and the comparative material.

The present invention relates to a thick film for a gas sensor of the gas alarm for detecting a gas leak, and more particularly to a ceramic thick film for a high sensitivity gas sensor.

In general, there are many types of gas sensors for gas alarm, but in actual industry, ceramic semiconductor gas sensors that are easy to handle are mainly used.

The most important point in such a gas sensor is to provide high sensitivity, and in the past, a gas sensor in which a metal catalyst is added to SnO ₂ as a main component is mainly used to enhance the gas sensitivity of the gas sensor.

As a typical representative technique for a gas sensor material using a metal catalyst, a method using Pt (UK Patent No. 2249179. 1992.4.29), a method using Pd (Japanese Patent Laid-Open No. 4-218760, 1992.8. 10) and a method using Au (Japanese Patent Laid-Open No. 1-232247, 1989.9.18) and the like, but the above techniques have an advantage of improving gas sensitivity characteristics, but limiting the particles of the metal and double firing. There is a disadvantage to go through the process. In other words, the manufacturing method is to limit the particle size of the metal particles to 0.1㎛ sintered SnO ₂ as the main component at 900 ℃ or more, and then to coat the metal particles on the surface of the particle and then baked at about 600 ℃. In addition, there is a method of adding PdCl instead of metal particles (Japanese Patent Laid-Open Publication No. Hei 5-133923, May 28, 1993), but this method also has a disadvantage of undergoing a double firing process.

Accordingly, the present invention is intended to provide a method for producing a thick film for gas sensors having a high sensitivity to SnO ₂ as a main component, using a metal oxide instead of a conventional metal catalyst, and only one firing without a double firing step There is a purpose.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

In the present invention, the atomic composition is selected from Nb ₂ O ₅ : 1.0% and NiO: 1.0% or less as an oxide catalyst in a basic composition consisting of Mg (NO ₃ ) ₂ , 6H ₂ O: 1% or less and the balance SnO ₂ . It relates to a method for producing a thick film for high sensitivity gas sensor, characterized in that the firing once in the temperature range of 900-1400 after the addition of one or two species.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention uses SnO ₂ as a base material, and SnO ₂ exhibits excellent gas sensitivity characteristics by increasing conductivity when contacted with flammable gas.

As a sintering aid to the SnO ₂ or less Mg (NO _{3) 2,} to facilitate the sintering was added to 6H ₂ O, In this case the sintering aid is usually from 1.0 at% (hereinafter,% Abraham) with respect to the base SnO ₂ material Add.

The present invention can omit the secondary firing step for coating the conventional metal catalyst by adding a metal oxide to the basic SnO ₂ material and the sintering aid instead of the conventional metal catalyst. At this time, Nb ₂ O ₅ and NiO are used as the metal oxide, and the amount of addition thereof is preferably 1.0% or less of Nb ₂ O ₅ and NiO alone or in combination. If Nb ₂ O ₅ and NiO are added in an amount of 1.0% or more alone or two kinds are added together, a second phase is formed in the sintered structure, and thus electrical conductivity is inferior, making it unsuitable for use as a thick film for a gas sensor.

The thick film for the gas sensor, which has been prepared as described above, may be calcined by a conventional method and then manufactured by only one sintering heat treatment step. At this time, the sintering temperature is generally preferably carried out in the temperature range of 900 ~ 1400 ℃, because the sintering itself is insufficient when sintering at 900 ℃ or less, the starting material is melted if Because it becomes.

The manufactured thick film for a gas sensor is unlike the second phase is formed when using a conventional metal catalyst when observed by TEM, to form a partial solid solution by the surface oxide, it will have excellent sensitivity.

Hereinafter, the present invention will be described in detail through examples.

EXAMPLE

About 50 g of a starting material having a composition as shown in Table 1 was placed in a plastic barrel having a volume of 250 kPa, 50 kPa of distilled water as a mixed solvent, and 200 g of zirconia ball were ball milled for 12-14 hours. The ball milling slurry was dried in a drying oven for at least 5 hours, then heated to 500 ° C. at a rate of 5 ° C. per minute, held for 2 hours, calcined, and cooled at a rate of 10 ° C. per minute. The calcined powder was passed through a 200 mesh sieve while grinding with a mortar, and the passed powder was mixed with an organic binder in a weight ratio of 5: 3 and printed on a 96% alumina substrate using a 100 mesh screen. The printed pattern was dried at 150 ° C. for 24 hours, heated to 900 ° C. at a rate of 5 ° C. per minute, maintained for 2 hours, and then fired, and cooled at 10 ° C. per minute to prepare a thick film for a gas sensor.

In order to measure the gas sensitivity for the gas sensor thick film manufactured as described above, the thick film 11 to be measured is placed on the alumina substrate 12 as shown in FIG. 1, and the wires 14 are wound on both ends of the thick film 11. Apply the silver electrode 13 between the thick film 11 and the wire 14, and then measure the resistance of the thick film in the range of -5 to +5 volts using a two-terminal method using a measuring device as shown in FIG. It was.

The measuring apparatus of FIG. 2 includes a heating furnace 3 for generating heat of a tube 2 in which the specimen 1 of FIG. 1 is embedded, a gas mixer 7 for supplying a mixed gas into the tube 2, and air to the gas mixer. And flowmeters 6a and 6b for supply control of CO gas. It consists of a flow meter controller 6 for controlling these flow meters 6a and 6b, a voltage current meter 4 for measuring the resistance of the specimen 1 and a computer 5 for controlling them, and the gas sensitivity is dry. It is measured as the resistance in the air atmosphere divided by the resistance in the gas atmosphere.

At this time, the resistance was measured during cooling at intervals of about 30 ° C. at a temperature range of 150 to 300 ° C., and the resistance was measured three times at 20 minute intervals after maintaining the equilibrium while flowing dry air in the measurement temperature maintaining state.

After the resistance was measured in a dry atmosphere, the resistance was measured in the same manner as the resistance measurement in a dry atmosphere in a CO atmosphere of 5000ppm concentration.

As described above, the results of gas sensitivity of the specimen measured according to the temperature change are shown in FIG. 3.

As can be seen in FIG. 3, in the case of the comparative material without additives other than the sintering aids Mg (NO) and 6HO, the gas sensitivity was hardly exceeded 2.0, while in the case of the inventive material (A) containing NbO, the temperature was around 250 ° C. Sensitivity is up to 4.0, and in the case of the invention material (B) in which NiO is added instead of NbO, the gas sensitivity is improved to 5.0 or more, and in the case of the invention material (C) in which NbO and NiO are added together, the sensitivity is about 3 at 350 ° C or less. It can be seen that the sensitivity is maintained. Therefore, it can be seen that the invention material satisfying the condition range of the present invention maintains the gas sensitivity equal to or higher than the gas sensitivity of the conventional thick film for a gas sensor even after one firing.

As described above, the present invention has the effect of using a metal oxide instead of a conventional metal catalyst and providing a thick film for a gas sensor excellent in gas sensitivity even with a single firing without undergoing a double firing step.

Claims (1)

In the method for producing a thick film for combustible gas sensors, Nb ₂ O ₅ : 1.0% or less as an oxide catalyst in a basic composition consisting of Mg (NO ₃ ) ₂ , 6H ₂ O: 1% or less and the balance SnO ₂ in atomic%; and NiO: A method for producing a thick film for a highly sensitive flammable gas sensor by one firing, characterized in that the firing is carried out once at a temperature of 900-140 ° C. after adding one or two selected from 1.0% or less.