Catalytic Combustion Type Gas Sensor Research Articles

High performance microheater-based catalytic hydrogen sensors fabricated on porous anodic alumina substrates

Catalytic combustion-type gas sensors are widely used in industry and everyday life for detecting flammable gases. However, high power consumption is one of the main drawbacks of the catalytic sensors. Replacing the platinum wire heating element with a thin-film microheater can significantly reduce power consumption, but maintaining high sensitivity and long-term stability of such devices is a challenge. Here we developed microheater-type catalytic hydrogen sensors based on porous anodic aluminium oxide served simultaneously as a substrate for platinum microheater and as a carrier for a catalyst. The fabricated sensors have a high sensitivity of 76 mV/vol% hydrogen. The deviation of the sensor response during continuous operation for 14 days is less than 4%. The relative humidity of the ambient atmosphere does not affect the sensor response. The fast sensor response time (0.4 s) makes it possible to use the pulsed power supply mode to reduce the power consumption to 3.2 mW without sacrificing the measurement accuracy. The performance of the developed catalytic hydrogen sensors promotes the high competitiveness in the market and the prospects for industrial applications.

Development of a Catalytic Combustion Type Gas Sensor with Low Power Consumption

Currently, gas leak alarms using AC power-supply are popular in Japan. However, there is pointed out, such as the hassle of installation property and power cord of the alarm, there was an increasing demand of the alarm of a battery drive system. The gas sensor of very low power consumption was required for realizing the battery operating system. Therefore, we focused on MEMS technology. The heating element occupying power most of for operating the sensor has been developed micro heater using a MEMS technology. The micro-heater has a rapid thermal response of several tens of milliseconds after the supply power. Furthermore, we developed a catalytic combustion type gas sensor reduced to 1/1000 of conventional power consumption by using the detection method of the intermittent operating. In general, miniaturization of the gas sensor would have a negative effect. Those effects were decreasing of the sensitivity / noise ratio and tending to susceptible to environmental factors. In this study, we report on improvement of the sensor for high sensitivity and high gas selectivity. The micro-heater was formed by sputtered platinum pattern on a silicon wafer. Formed platinum membrane was covered with a silicon nitride film. It is an air-bridge structure of the square of 90μm angle, suspended by etching the heater backside. The micro-heater has low power consumption because its thermal capacity is low. The catalytic combustion type micro-gas-sensor was prepared by sintering materials that Pd loaded γ-Al2O3 for a sensing element and only γ-Al2O3 for a reference element. The catalytic combustion type micro-sensor to give amplifies the potential difference generated both elements by a resistance change of the heater according to the catalytic combustion reaction of combustible gases. Measurements of gas sensitivity of the sensor which was heated to approximately 450°C， placed in a gas chamber, it was performed by injecting a test gas having a predetermined concentration. Response carve of the sensor when power was supplied to the micro-heater becomes detectable state at tens of milliseconds. Methane sensitivity was observed with good linearity. However, the hydrogen sensitivity was approximately three times the methane it, methane selectivity of the sensor was found to be low. Material of the reference element in order to improve this problem has been changed. The reference element materials have used γ-Al2O3 does not have catalytic combustion reaction with any combustible gases. The reference element material was to have sensitivity to miscellaneous gases such as hydrogen by changing from γ-Al2O3 in the Pt loaded γ-Al2O3. Miscellaneous gas sensitivity of each element cancelled each other, the selectivity of methane sensitivity was improved. As a result, the sensitivities of H2 / CH4 ratio have become possible to improve the methane selectivity to 1 times or less. The second improvement was to increase the methane gas sensitivity. By the small size of the device due to the low power consumption, the amount of catalyst could be applied would be very small. Further, since the planar structure, the detection target gas could react only one side of the catalyst, the sensitivity obtained by the combustion reaction was low. Therefore, we consider how to increase the gas contact point on the element. As a first method, it was optimize the amount of Pd supported on the catalyst. If the amount of Pd loaded ratio is substituted standard ratio for 1, the sensitivity of the methane was found to be a maximum value in the Pd ratio is 2. On the other hand, the specific surface area was decreased with an increase in the amount of Pd loaded in particular reduction of the specific surface area more than Pd ratio is 2 was significant. When the amount of Pd loaded increases gas contact points, gas sensitivity is improved to increase. However, the sensitivity is found to decrease by a metal agglomeration when Pd loaded content is too high may occur. As a second method, utilizing the characteristics of the sensor elements consists of an air-bridge, in order to encourage gas contact from the heater backside, some slit-shaped through-hole between the heater patterns. It becomes possible to wrap the catalyst heater backside by the structural modification. Then methane gas sensitivity of the sensor by gas contact point of the heater back side increases has been improved by 40% compared with the previous type. These improvements had the prospect of practical use of methane gas sensor of the catalytic combustion type with micro-heater using MEMS technology.

Development of a Catalytic Combustion Type Gas Sensor with Low Power Consumption

A catalytic combustion type methane gas sensor with super low power consumption using MEMS technology was developed for a battery drive type gas alarm. In this study, it is reported the actions of improvement for methane gas selectivity and sensitivity of the sensor from a viewpoint of the reliability satisfaction for practical use. As the method of improving gas selectivity, it was made to offset with constituting a reference element from a Platinum loaded catalyst. For the improvement of methane sensitivity, the amount of loaded Palladium was made to optimize in order to increase gas reactive sites on catalyst. And slit-shaped through-holes were formed on micro heater, as taking advantage of air bridge structure for promoting the gas contact from the heater backside. Methane sensitivity has improved drastically by these complex improvement effects.

半導体式ガスセンサおよび接触燃焼式ガスセンサ

半導体式ガスセンサおよび接触燃焼式ガスセンサ

Micromachined catalytic combustion type gas sensor for hydrogen detection

A catalytic combustion hydrogen sensor has been fabricated using the microelectromechanical system technology. The application of hafnium oxide thin films as the insulating layer has been deposited by electron beam evaporation. The semiconductor combustion catalyst tin oxide layer was prepared by chemical vapour deposition. It is a novel application of semiconductor material to a catalytic combustion gas sensor. The resistivity of hafnium dioxide thin film is about 3 × 1012 Ω cm at 900°C. Both the sensing elements and the reference elements could be connected in a suitable circuit such as a Wheatstone configuration with low power consumption. The catalytic combustion sensor shows high response to hydrogen at an operating voltage of 4 V and has a higher relative sensitivity and a good linearity for concentrations of hydrogen ranging from 0 to 4% in volume. Good consistency and high accuracy of the micromachined catalytic combustion gas sensor were achieved.

Research on Micro Twin-Bridges Catalytic Combustion Type Kerosene Gas Sensor Technology

Based on the principle of catalytic combustion type gas sensor, a kerosene gas sensor with micro twin-bridge structure is fabricated using silicon micromachining technology. A pair of platinum film resistor is fabricated by film processing, and its nominal resistance is 20Ω at 0°C. The nano-alumina catalytic carrier and noble metal catalyst are coated on the surface of sensitive resistance in order to form the sensitive bridge and compensating bridge. The monolithic integration of catalytic element and compensating element is achieved on the silicon micro twin-bridge for fabrication of kerosene sensor. The simulation result shows that once temperature of one bridge rises to 650K, the other bridge may increases about 10°C. The test on kerosene sensor by calibration device indicates that the sensor can detect the kerosene volume fraction ranging from 0 to 7000×10-6 and the sensor output property is linear.

Research on the Optical Fiber Gas Sensing System Based on the Gas Concentration Measurement

At present , the catalytic combustion type gas sensors is still used in our country which is the extensive use of underground coal mine gas detection instrument , this kind of sensor slow response, calibration cycle is short, and the apparatus for the selectivity of methane is poor. Thus it can be seen that develop a safe and reliable, selective, high sensitivity of gas concentration measurement system that for mine safety operation, the personal safety and environment protection has a very important social significance and economic significance. Optical fiber sensing monitoring system according to the gas absorption spectrum principle with double light path structure on the mine gas online monitoring the concentration of the gas, has avoid the explosion, dust and so on many special advantages.

Catalytic combustion type gas sensor

Catalytic combustion type gas sensor

Rapid evaluation of oxidation catalysis by gas sensor system: total oxidation, oxidative dehydrogenation, and selective oxidation over metal oxide catalysts

The rapid evaluation of catalysis is an indispensable technology for the success of combinatorial chemistry. A small-sized, less expensive, easily operating screening is desirable for parallel settings which dramatically shortens the evaluation time. Recent advances in gas sensors have enabled us to use them for the rapid evaluation of oxidation catalysis. Three typical catalytic oxidations over metal oxide catalysts were evaluated by gas sensor systems optimized for each catalytic system. The first one is the total oxidation of carbon monoxide in air. Five catalytic combustion-type gas sensors were used in a parallel reactor system to shorten the evaluation time. The second one is the oxidative dehydrogenation (ODH) of ethane over the mixed oxide of nickel and iron. The evaluation of the ODH catalysis was performed by a selective olefin sensor which determines the concentration of C 2H 4 in C 2H 6. The third one is the selective oxidation catalysis of propane over alkali modified Fe/SiO 2. The effluents including CO, CO 2, aldehydes and ketones in propane were analyzed by the CO, CO 2 and semiconductor-type gas sensors selective toward aldehydes and ketones. These evaluation results indicated that gas sensors have a good potential for the rapid evaluation of oxidation catalysts.

Flammable Gas Alarm Sensors

Recently, in this country, town gas and LPG have come into wide use as fuel, giving us clean energy in burning. These gases have, however, potential hazards that might cause explosion when they leak out accidentally or mistakenly. To cope with such the risk, gas sensors have been put into practical application and thusspread quickly. These are two kinds of practical gas sensors, semiconductor gas sensor and catalytic combustion type gas sensor. Although they are both working well at present, further improvement would be necessary because their gas sensing capabilities are required to be steady and stable in a long run even under severe environmental stresses, and they should not be supposed to make any wrong alarms. This paper is intended to report on analysis of the chemical mechanism of the interaction between the sensors and fuel gases, and also some physical property changes observed at the sensor surfaces, as acted upon by both the fuel gases and environmental stresses, such as temperature, humidity, miscellaneous gasses, and so on.