Methane gas sensors

Figure 7. Schematic diagram of the methane gas sensor. 1. Pump ...

PANI composites with oxides of rhodium, palladium, osmium, iridium, and platinum were rarely investigated, especially in the recent period. Fabrication of methane gas sensor by layer-by-layer self-assembly of PANI/ PdO ultra thin films consisting of a dense network of NFs (Figure 2.23 left) on quartz crystal microbalance was successfully performed by Xie et al. [240] (Figure 2.23 right). 

Wang Y, Tong MM, Zhang D, Gao Z (2011) Improving the performance of catalytic combustion type methane gas sensors using nanostructure elements doped with rare earth cocatalysts. Sensors 11 19-31... 

In context with methane detection during offshore oil drilling, another infrared fiber optic methane sensor was reported25. The detector comprises 3 main units a microcomputer-based signal processing and control unit, a nonconducting fiber optic gas sensor, and an optical fiber cable module. The system operates at an absorption line of methane where silica fibers have very low losses. 

The thermal conductivity of methane is about twice as high as that of any other flammable compound of natural gas. Sensors for determining the methane number use this effect, and the principle is already in use for gas engines [2], as their performance depends heavily on the methane number. 

The model analytes, which were used to show the sensor performance of the microsystems include carbon monoxide, CO, and methane, CH4. The sensor microsystems were designed for practical applications, such as environmental monitoring, industrial safety applications or household surveillance, which implies that oxygen and water vapors are present under normal operating conditions. In the following, a brief overview of the relevant gas sensor mechanisms focused on nano crystalline tin-oxide thick-film layers will be given. 

In this manner, a nearly universal and very nonselective detector is created that is a compromise between widespread response and high selectivity. For example, the photoionization detector (PID) can detect part-per-billion levels of benzene but cannot detect methane. Conversely, the flame ionization detector (FID) can detect part-per-billion levels of methane but does not detect chlorinated compounds like CCl very effectively. By combining the filament and electrochemical sensor, all of these chemicals can be detected but only at part-per-million levels and above. Because most chemical vapors have toxic exposure limits above 1 ppm (a few such as hydrazines have limits below 1 ppm), this sensitivity is adequate for the initial applications. Several cases of electrochemical sensors being used at the sub-part-per-million level have been reported (3, 16). The filament and electrochemical sensor form the basic gas sensor required for detecting a wide variety of chemicals in air, but with little or no selectivity. The next step is to use an array of such sensors in a variety of ways (modes) to obtain the information required to perform the qualitative analysis of an unknown airborne chemical. 

Chan K, Ito H, Inable H (1984) An optical fiber based gas sensor for remote adsorption measurement of low level methane gas in near infrared region. J Lightwave Technol 2 234—237... 

In principle, this sensor is also applicable to CO measurement in the gas phase for it was possible to keep the enzyme stable in a wet medium behind the gas-permeable membrane. In comparison with other biocat-alytic gas-sensing devices, e.g. those for methane (Karube et al., 1982a) or NH3 and NO2 (Hikuma et al., 1980b) the sensor was more compact and its response was substantially faster. This enzyme electrode therefore represents a promising approach to novel gas sensors. 

In contrast to equilibrium-based sensing such as described above, it is also possible to use the zeolite film as a membrane controlling molecular access to an appropriate transduction mechanism. In this case, Pd-doped semiconductor gas sensors were used as a fairly non-selective sensor platform. After coating these sensors with a thin film of MFI-type or LTA-type zeolites, they were examined with respect to gas phase sensing of different analytes such as methane, propane and ethanol, at different humidity levels (Fig. 14).[121] The response of a zeolite-coated sensor towards the paraffins was strongly reduced compared to the non-coatcd sensor device, thus resulting in an increase of the sensor selectivity towards ethanol. 

Semiconductor gas sensors for methane, propane, butane, ammonia, alcohol, hydrogen, CO, VOCs, etc. 

Madou MJ, Morrison SR (1989) Chemical sensing with solid state devices. Academic Press, San Diego, CA, London Mandayo GG, Castano E, Gracia FJ, Qrera A, Cornet A, Morante JR (2003) Strategies to enhance the carbon monoxide sensitivity of tin oxide thin films. Sens Actuators B Chem 95 90-96 Massok P, Loesch M, Bertrand D (1995) Comparison for the between two Figaro sensors (TGS 813 and TGS 842) for the detection of methane, in terms of selectivity and long-term stability. Sens Actuators B Chem 24-25 525-528 Matsuura Y, Takahata K (1991) Stabilization of SnO sintered gas sensors. Sens Actuators B Chem 5 205-209 Meixner H, Lampe U (1996) Metal oxide sensors. Sens Actuators B Chem 33 198-202... 

Massie C, Stewart G, McGregor G, Gilchrist JR (2006) Design of a portable optical sensor for methane gas detection. Sens Actuators B 113 830-836... 

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