JP5881205B2 - Gas sensor - Google Patents

Description

  The present invention relates to an improvement in a filter of a gas sensor.

  Zeolite is used as a gas sensor filter for detecting LPG and the like. This is because zeolite does not adsorb nonpolar hydrocarbons but adsorbs polar ethanol and the like. However, zeolite has an insufficient ability to remove poisoning substances such as silicone gas and sulfurous acid gas, and if exposed to a high concentration of poisoning gas, the characteristics of the gas sensor may be affected.

  Here is related prior art. Patent Document 1 (JP2006-349513A) discloses the use of zeolite, activated alumina, or the like for the filter of a metal oxide semiconductor gas sensor. Patent Document 2 (JP3568060B) discloses the use of activated clay, zeolite or the like for the filter of the gas sensor. However, it is not known to use a mixture of zeolite and activated alumina as a filter.

JP2006-349513A JP3568060B

  The subject of this invention is providing the gas sensor provided with the filter which does not adsorb | suck hydrocarbon etc. and has a high removal capability of silicone gas.

The gas sensor of the present invention includes a filter that removes interfering gas, a heater, and a metal oxide semiconductor for LPG detection. The gas sensor is provided separately from the filter, and is a gas to be detected in the gas processed by the filter. A gas sensor including a sensor main body for detecting LPG as a component is characterized in that the filter is a mixture of zeolite and activated alumina in a mass ratio of 9: 1 to 1: 4. Preferably, in addition to zeolite and activated alumina, neither a basic component nor an acidic component is added to the filter in order to increase the adsorption ability of acidic or basic polar gas.

The type of the sensor body is arbitrary, such as a sensor using a change in resistance value of a metal oxide semiconductor, an electrochemical type, or a contact combustion type. In the present invention, a metal oxide semiconductor is used. The gas to be detected is any hydrocarbon such as methane, LPG or the like, or hydrogen or CO. However, in the case of LPG, since a filter such as activated carbon cannot be used , LPG is detected in the present invention . LPG is suitable for detection with a sensor body using a metal oxide semiconductor or a contact combustion type sensor body. In particular, LPG has a long track record in detection using a metal oxide semiconductor . A semiconductor is used. The gas to be removed includes, for example, a gas that causes a false alarm such as ethanol, and poisonous substances such as silicone gas and sulfurous acid gas.

  2 to 7 show the effects of exposing a metal oxide semiconductor gas sensor to silicone gas. When zeolite is 20 to 90 mass% and activated alumina is 80 to 10 mass%, the influence of silicone gas is small. I understand that Table 1 shows the effect of exposing the metal oxide semiconductor gas sensor to sulfurous acid gas. When the active alumina content is 10% by mass or more in a mixture of zeolite and activated alumina, the influence of sulfurous acid gas is reduced. I understand that. Preferably, the ratio of zeolite to activated alumina is 90-30% by mass of zeolite and 10-70% by mass of activated alumina.

Sectional view of the gas sensor of the embodiment Characteristics chart of comparative example using 100% zeolite filter Example characteristics using 90% zeolite and 10% activated alumina filter Example characteristics using a filter of 80% zeolite and 20% activated alumina Example characteristics using a 60% zeolite 40% activated alumina filter Example characteristics using 30% zeolite-70% activated alumina filter Characteristics chart of comparative example using 100% activated alumina filter

  In the following, an optimum embodiment for carrying out the present invention will be shown.

  The gas sensor 2 of an Example and its characteristic are shown in FIGS. In FIG. 1, reference numeral 4 denotes an insulating base that supports the stem 6. A sensor main body 8 is provided with a metal oxide semiconductor film 10 and a film heater 12 on an insulating substrate, and is connected to the stem 6 by a lead wire 14. A metal or resin cover 16 includes a filter 18, and supports the upper and lower sides of the filter 18 with metal meshes 20 and 22 and supports the metal mesh 22 with a ring 24. Reference numeral 26 denotes a protrusion for supporting the ring 24.

  The structure of the gas sensor is arbitrary, for example, a MEMS gas sensor in which a metal oxide semiconductor film and a heater film are provided on an insulating film on a cavity of a silicon substrate, or a bead shape in which a heater and an electrode are embedded in a bead-shaped metal oxide semiconductor. A gas sensor or the like may be used. Further, instead of a metal oxide semiconductor gas sensor, a contact combustion gas sensor, an electrochemical gas sensor, or the like may be used.

  The filter 18 is composed of a mixture of 20 to 90% by mass of zeolite and 80 to 10% by mass of activated alumina. The zeolite is, for example, a zeolite having a high silica content and a high silicone gas adsorption ability, and is a mordenite type zeolite. The type of zeolite, such as Y-type zeolite, is arbitrary. The activated alumina is composed of γ alumina, amorphous alumina, or the like, and the type when γ alumina is further classified into γ, χ, etc. is arbitrary. Also, the filter 18 may be added with fine particles such as Pt and Au for decomposing adsorbed ethanol at room temperature, or a basic component or acidic component for enhancing the adsorption ability of acidic or basic polar gas. good.

  For example, the filter 18 is maintained at an ambient temperature, and removes poison gas such as silicone gas and sulfurous acid gas that poisons the sensor body 8 from gas introduced into the gas sensor 2 and interfering gas such as ethanol causing false alarm. The shape is arbitrary, such as a granular shape, a powder shape, and a plate shape. The mass of the filter 18 per sensor is, for example, about 10-150 mg, preferably about 20-100 mg.

With the structure of FIG. 1, a gas sensor 2 for LPG detection was produced. The metal oxide semiconductor film 10 is a SnO2 film having a thickness of 20 μm, and 1.5 mass% of Pd fine particles are supported with respect to 100 mass% of SnO2. The metal oxide semiconductor film 10 is heated to 430 ° C. by the heater 12 to detect LPG. The filter 18 has a total amount fixed at 60 mg, and a mordenide-type zeolite with a large granular silica content (cation type is H ⁺ , BET specific surface area 400 m ² / g, SiO ₂ and Al ₂ O ₃ molar ratio is 30) , The mixing ratio with granular activated alumina (BET specific surface area 270m ² / g, pore volume 0.38ml / g, weight loss when heated is 6.5% by mass, alumina content in solids is 99.7% by mass) changed.

  After measuring the initial characteristics of the gas sensor 2, as a durability test for silicone gas, put the gas sensor 2 in a tank containing 60 ppm total of D3, D4, and D5 cyclic siloxane at a total of 60 ppm. The sensor was taken out and the sensitivity to various gases was measured. The atmosphere in the tank was ventilated each time the sensor was taken out, and after ventilation, cyclic siloxanes of D3, D4, and D5 were injected at 20 ppm each for a total of 60 ppm. D3, D4, D5 3, 4 and 5 represent the number of silicon atoms in the silicone molecule, D3, D4 and D5 are low boiling point substances as silicone gas, and substances that easily become poisonous gas because they easily evaporate. It is.

  Measurements were made using three sensors for each filter composition, and the results of a 4-day durability test are shown in FIGS. In the figure, iB is isobutane, which indicates the alarm concentration when isobutane, propane, hydrogen, and methane are initially set to alarm at 1800 ppm. Ethanol sensitivity was measured in addition to the gas shown, but the alarm concentration was 10,000 ppm or higher for all filters. The data above and below the broken line in the figure indicate the maximum value and the minimum value of the alarm concentration.

  In the case of 100% by mass of zeolite, the hydrogen sensitivity increases on the second day of exposure, but in the case of 10-70% by mass of activated alumina, the sensitivity to gases such as hydrogen is stable. However, with 100% activated alumina, the durability to silicone gas again decreases. Accordingly, the zeolite content in the filter 18 is 20-90% by mass, and the activated alumina content is 80-10% by mass. The inventor changed the type of zeolite and changed the specific surface area of activated alumina, etc., but the high silicone content in the zeolite content range of 20-90% by mass and active alumina content in the range of 80-10% by mass. Durability to gas was obtained.

  As a poison gas other than the silicone gas, a test was performed in which an energized sensor was exposed to 200 ppm of sulfurous acid gas for 4 hours. The results are shown in Table 1. When the activated alumina content is 10% by mass or more, the influence of sulfurous acid gas is reduced. Table 1 shows the ratio of alarm concentrations before and after the endurance test. A change of about 10% is not a significant difference.

Table 1

Change ratio of zeolite and activity alarm concentration Mixing ratio of alumina (alarm concentration after endurance / alarm concentration before endurance)
(Mass%) iB Hydrogen Methane
100-0 0.6 0.5 0.6
90-10 1.0 0.9 1.1
80-20 1.1 1.0 1.1
60-40 1.0 1.0 1.0
30-70 1.1 1.1 1.0
0-100 1.1 1.0 1.1

  In order to evaluate the air permeability of the filter 18, when 4500 ppm of isobutane was injected into the tank containing the gas sensor 2, the response time until the output of the gas sensor 2 reached equivalent to 1800 ppm of isobutane was measured. The response time was about 15 seconds regardless of the activated alumina content.

  As described above, when the composition of the filter 18 is 90-20% by mass of zeolite and 10-80% by mass of activated alumina, the influence of silicone gas and sulfurous acid gas can be particularly reduced. Preferably, the ratio of zeolite to activated alumina is 90-30% by mass of zeolite and 10-70% by mass of activated alumina.

2 Gas sensor 4 Base 6 Stem 8 Sensor body 10 Metal oxide semiconductor film 12 Heater 14 Lead wire 16 Cover 18 Filter 20, 22 Wire mesh 24 Ring 26 Protrusion

Claims (2)

A filter to remove interfering gases ;
A gas sensor comprising a heater and a metal oxide semiconductor for LPG detection, provided separately from a filter, and a sensor main body for detecting LPG as a gas component to be detected in gas processed by the filter ,
The gas sensor according to claim 1, wherein the filter is a mixture of zeolite and activated alumina in a mass ratio of 9: 1 to 1: 4. 2. The gas sensor according to claim 1, wherein, in addition to zeolite and activated alumina, neither a basic component nor an acidic component is added to the filter in order to enhance the adsorption ability of acidic or basic polar gas. .