KR0149200B1 - Manufacturing method of tin oxide-based semiconducting thick film for gas sensor - Google Patents

Abstract

The present invention relates to a method for producing a tin oxide-based semiconducting thick film for a gas sensor that can detect a leak of gas in advance, and by appropriately setting the raw material powder manufacturing process and the heat treatment process, a buffer film is not formed between the thick film and the substrate. The present invention provides a method of manufacturing a semiconducting thick film of a gas sensor which is not only cracked but also excellent in gas sensitivity.

The present invention is a gas comprising a tin oxide-based raw material powder manufacturing step, mixing the raw material powder and the organic binder to form a paste, applying the paste on a substrate, drying the coating layer and heat treatment step In the method for manufacturing a tin oxide-based semiconducting thick film for a sensor, the step of preparing the raw material powder is performed so that the ball is at least 1 times the powder weight, and the solvent is added at a weight ratio of 0.5 to 3.0 times the powder and the solvent to 6 to 6 After first ball milling for 24 hours, calcining at 400 to 600 ° C. for 0.5 to 3 hours, second ball milling in the same manner as the first ball milling conditions, and then pulverizing with a mortar to 100 to 250 mesh network Sieving to produce a raw powder; After the heat treatment step is dried, the coating layer is heated to a temperature range of 300 to 500 ° C. at a temperature rising rate of 2 ° C./min or less, and maintained at this temperature for 30 minutes or more, and then 850 to 1250 at a temperature rising rate of 10 ° C./min or less. It is a summary of the method for producing a tin oxide based semiconducting thick film for a gas sensor, which is heated to a temperature range of 占 폚 and held at this temperature for 10 minutes to 3 hours to sinter.

Description

Manufacturing method of tin oxide-based semiconducting thick film for gas sensor

1 is a surface photograph of a semiconducting thick film prepared by the present invention method and a method outside the present invention.

The present invention relates to a method for producing a tin oxide based semiconducting thick film for a gas sensor capable of detecting a leak of gas.

The most popular type of semiconductor gas sensor is a type of heating wire inside a semiconducting ceramic. That is, the heating wire is inserted into the semiconductor, and heat is generated by flowing a current through the heating wire, thereby raising the temperature of the semiconductor to about 200 to 300 ° C, which is easy to detect gas.

The characteristics of the recently released sensor are about 75 times higher than the conductivity when hydrogen is 200 ppm in air (Figaro TGS821) (hereinafter referred to as sensitivity). It is the device with the highest sensitivity.

However, the higher the sensitivity of the sensor, the better the alarm's function, so new materials are being created to increase the sensitivity.

In practice, the sensor's response is also proportional to the area of gas on the surface. Therefore, the sensitivity of the final sensor is sensitively dependent on the microstructure of the starting material.

On the other hand, when the ceramic thick film is applied on the order of 20 to 200 mu m, cracks are liable to occur during drying or heat treatment. In this case, the conductivity of the semiconductor material drops sharply, and it cannot function as a sensor element.

In order to prevent surface cracking, a method of forming a buffer film between a substrate and a thick film is generally proposed.

However, in this case, if only the mechanical properties are required, it does not matter much, but where chemical properties such as gas sensors are important, the sensitivity of the sensor is likely to be affected by the chemical action of the buffer membrane.

Therefore, there is a need for a method of coating a target semiconducting thick film on a substrate without applying any buffer film between the substrate and the semiconductor thick film.

The present inventors conducted research and experiments on the raw material powder of the tin oxide-based semiconducting thick film and the post-coating heat treatment process, and based on the results, the present invention proposes a raw material powder manufacturing process and a heat treatment process. It is an object of the present invention to provide a method for producing a tin oxide-based semiconducting thick film for a gas sensor which is excellent in gas sensitivity as well as no cracking without forming a buffer film between the thick film and the substrate.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The present invention provides a gas comprising a tin oxide-based raw material powder manufacturing step, a raw material powder and an organic binder are mixed to form a paste, a paste is applied onto a substrate, a drying step of a coating layer, and a heat treatment step. In the method for manufacturing a tin oxide-based semiconducting thick film for a sensor, the step of preparing the raw material powder is performed so that the ball is at least 1 times the powder weight, and the solvent is added at a weight ratio of 0.5 to 3.0 times the powder and the solvent to 6 to 6 After the first ball milling for 24 hours, calcining at 400 to 600 ℃ for 0.5 to 3 hours, the second ball milling in the same manner as the first ball milling conditions, and then pulverized by firing to 100 to 250 mesh mesh Sieving to produce a raw powder; After the heat treatment step is dried, the coating layer is heated to a temperature range of 300 to 500 ° C. at a temperature rising rate of 2 ° C./min or less, and maintained at this temperature for 30 minutes or more, and then 850 to 1250 at a temperature rising rate of 10 ° C./min or less. The present invention relates to a method for producing a tin oxide-based semiconducting thick film for a gas sensor, which is heated to a temperature range of 占 폚 and maintained at this temperature for 10 minutes to 3 hours.

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

In order to manufacture a tin oxide-based semiconducting thick film according to the present invention, first, a tin oxide-based powder which is a starting material should be prepared. The manufacturing process is as follows.

That is, the ball is put at least 1 times the powder weight, and the solvent is added so that the weight ratio of the powder and the solvent is 1: 0.5 to 3.0 times, followed by the first ball milling for 6 to 24 hours, and then 0.5 to 3 at 400 to 600 ° C. After calcining for a period of time, the second ball milling in the same manner as the first ball milling conditions, and then pulverized with a mortar and sieved to 100 ~ 250mesh mesh to prepare a raw powder.

When the ball is put at 1.0 times or less of the powder weight during the first and second ball milling, it is difficult to obtain a powder having a uniform particle size since the grinding effect is small, so the amount of the ball should be 1.0 times or more of the powder weight. It is 1.0-4 times.

In the first and second ball milling, the amount of the solvent added is preferably 0.5 to 3.0 times the weight of the powder. The reason is that when the amount of the solvent is too small, the effect of dispersing the powder is insufficient. This is because the grinding effect is small, the drying time is long, and the composition of the powder becomes non-uniform. Distilled water, alcohol, acetone etc. are mentioned as said solvent.

In addition, it is preferable to limit the first and second ball milling times to 6 to 24 hours, because the ball milling effect is insufficient when the ball milling time is 6 hours or less, and when it is 24 hours or more, impurities due to ball wear This is because mixing occurs.

The size of the net sieve sifted after the final grinding is preferably 100 to 250 mesh, because if it is 100 mesh or less, agglomerates are generated to provide a starting point of cracking during sintering, and if it is 250 mesh or more, the yield is low.

Next, the powder prepared as described above is mixed with an organic binder in a conventional manner to prepare a paste, and then applied to a substrate and dried.

At this time, it is preferable to perform drying at normal temperature for about 24 hours.

Next, the temperature is heated to a temperature range of 300 to 500 ° C. at a temperature rising rate of 2 ° C./min or less and maintained at this temperature for 30 minutes or more, and then to a temperature range of 850 to 1250 ° C. at a temperature rising rate of 10 ° C./min or less. The mixture is kept at this temperature for 10 minutes to 3 hours and sintered.

When the temperature increase rate up to the temperature range of 300 to 500 ° C. is 2 ° C./min or more, tensile stress occurs on the surface due to rapid shrinkage, and cracks occur in the film, and the temperature increase rate is 2 ° C./min or less. It should be limited to, more preferably the temperature increase rate is 1 ℃ / min or less.

The above-mentioned holding at the temperature range of 300 to 500 ° C. is for removing the organic binder. If the holding time is 30 minutes or less, the organic binder is not sufficiently removed, and thus the holding time is 30 minutes or more, and the preferable holding time is 30 minutes. It is -5 hours.

If the holding temperature is too low, the organic binder is not sufficiently removed. If the holding temperature is too high, sintering occurs between particles, and holes are formed on the surface of the coating film by the organic binder gas.

When the temperature increase rate to 850-1250 degreeC which is a sintering temperature is 10 degreeC / min or more, there exists a possibility that a crack may generate | occur | produce in a film, It is preferable to limit the said temperature rising rate to 10 degrees C / min or less. More preferable temperature increase rate is about 5 degrees C / min or less.

By treating the starting powder as described above, a tin oxide-based semiconducting thick film for gas sensors having excellent gas sensitivity is produced.

Hereinafter, the present invention will be described in more detail with reference to Examples.

EXAMPLE

The starting composition was to add 1 at% of magnesium as a sintering aid and palladium as a catalyst to tin oxide. About 50 g of the material was placed in a plastic container having a volume of 250 cc, 50 cc of distilled water as a mixed solvent and 200 g of zirconia balls were ball milled for 14 to 16 hours. After the ball milling slurry was dried in a drying oven for 5 hours or more, the temperature was raised to 500 degrees Celsius at a rate of 5 degrees per minute, held for 2 hours, and calcined, and then cooled at a rate of 10 degrees per minute. For comparison, the calcined powder was again ball milled to the same conditions as above and dried. After calcination, the ball milled and non-milled ones were ground well by induction prior to particle size analysis and passed through a sieve with a density of 200 mesh.

Particle size analysis of the powders prepared as described above was performed, and the results are shown in Table 1 below.

Particle size analysis is performed by dispersing the sample powder with ultrasonic waves, and analyzing the result by ultrasonic wave once again after the particle size analysis, and repeating the results up to four times.

As shown in Table 1, it can be seen that the ball milling powder (invention powder) after calcination is much finer than the ball milling powder (comparative powder) after calcination.

The comparative powder and the inventive powder prepared as described above were mixed with an organic binder (organic binder No. 24 of ESL No. 24) and 1: 1 to prepare a paste, and then applied onto an alumina substrate.

Then, dried at room temperature for 24 hours.

Next, it heated to 350 degreeC at the temperature increase rate of 1 degree-C / min and 5 degree-C / min, hold | maintained at this temperature for 5 hours, and then heated to 900 degreeC at the temperature increase rate of 5 degree-C / min and 20 degree-C / min, After maintaining at this temperature for 2 hours, a semiconductive thick film was prepared by cooling at a cooling rate of 10 ° C / min. Hydrogen gas sensitivity for the semiconducting thick film prepared as described above was measured and the results are shown in Table 2 below.

Hydrogen gas sensitivity of Table 2 is measured as follows.

In order to measure the electrical resistance of the semiconducting sintered body, the specimen was placed in a 300 ° C electric furnace to connect power to both ends, and an ammeter was connected in series to measure the current. First, flow air, and then continue to measure the current while flowing 200ppm of hydrogen in the air, and record how many times the current is when the hydrogen is mixed with 200ppm of the air This was measured as a sensitivity to 200ppm hydrogen.

In addition, the surface photographs of the comparative material 5 and the inventive material in Table 2 were observed and the results are shown in FIG. In FIG. 1 (a), the comparative material 5 is shown, and (b) shows invention material.

As shown in Table 2, the powder (invented powder) prepared according to the present invention is heat-treated according to the present invention (invented material) is a powder outside the present invention and or heat-treated under conditions outside the present invention. It can be seen that the sensitivity of hydrogen gas is very excellent compared to ash (1-7)].

In addition, as shown in FIG. 1, in the case of the invention material, no crack was observed, whereas in the case of the comparative material 5, it was found that the crack was observed.

As described above, the present invention is the ball milling after the calcination in the production of the starting powder, the intermediate value of the particle size is reduced, thereby improving the sensitivity to the gas, as well as breaking the electricity supply path in the drying and heat treatment process By preventing surface cracks, a semiconductive thick film without cracks is formed without forming a buffer film between the semiconductor thick film and the substrate, thereby eliminating the buffer film applying process, and preventing a decrease in gas sensitivity due to chemical intervention of the buffer film. It works.

Claims (1)

Oxidation for gas sensor comprising the tin oxide raw material powder manufacturing step, mixing the raw material powder and the organic binder to make a paste, applying the paste on the substrate, drying the coating layer and heat treatment step In the method for preparing a tin semiconducting thick film, the step of preparing the raw material powder is carried out so that the balls are at least 1 times the powder weight, and the solvent is added so that the weight ratio of the powder and the solvent is 1: 0.5 to 3.0 times for 6 to 24 hours. After the first ball milling, calcining at 400 to 600 ° C. for 0.5 to 3 hours, followed by the second ball milling in the same manner as the above first ball milling conditions, and finally pulverizing with a mortar to sift to 100 to 250 mesh network to feed powder Is configured to produce; After the heat treatment step is dried, the coating layer is heated to a temperature range of 300 to 500 ° C. at a temperature rising rate of 2 ° C./min or less and maintained at this temperature for 30 minutes or more, and then 850 to a temperature rising rate of 10 ° C./min or less. A method for producing a tin oxide-based semiconducting thick film for a gas sensor, which is configured to be heated to a temperature section of 1250 ° C. and maintained at this temperature for 10 minutes to 3 hours.