Combustible Gas In Air Research Articles

A New Pellistor-Like Gas Sensor Based on Micromachined CMOS Transistor

A new generation of thermal sensors based on a suspended thermal transistor MOS (TMOS), fabricated in the standard CMOS-SOI process, released by postetching, has been recently developed. One of the important features of TMOS is its high responsivity due to the transistor built-in amplification and subthreshold operation enabling a wide range of battery applications. This paper focuses on a new gas sensor, dubbed GMOS, based on the TMOS. The GMOS is a catalytic gas sensor (pellistor-like), and as such detects combustible gases in air. The CMOS-SOI technology combined with tungsten metallization enables operation at very high temperatures (450 °C was tested). The sensors and readout are processed with the same CMOS-SOI technology. Accordingly, the GMOS sensor, processed in low-cost CMOS-SOI technology, promises to become the widely accepted gas sensing approach for mobile applications, including wearables, smart homes, as well as smartphones.

Theoretical estimation of the lower flammability limit of fuel-air mixtures at elevated temperatures and pressures

We present an approach for predicting the lower flammability limits of combustible gas in air. The influence of initial pressure and temperature on lower flammability limit has been examined in this study. The lower flammability limits of methane, ethylene and propane in air are estimated numerically at the pressure from one to 100 bar and the temperature from ambient to 1200 K. It was found that the predicted LFLs of methane, ethylene and propane decrease slightly with the elevated pressure at the high temperature. The LFLs variation for methane-air mixture is 0.17, 0.18, 0.18 volume% with the initial pressure from one to 100 bar at the initial temperature of 800 K, 1000 K and 1200 K respectively, which is significantly higher than that at lower temperature. And the LFL of methane-air mixture at 1200 K and 100 bar reaches 1.03 volume% which is much lower than that at 1 bar and ambient temperature. On the other hand, the LFLs variation is 0.11–0.12 volume% for ethylene-air mixture and 0.06–0.07 volume% for propane-air mixture with the initial temperature from 800 K to 1200 K at the same range of pressure. The LFL values at high temperatures and pressures represent higher risk of explosion.

The Design of Air Quality Detecting Intelligent System

This paper proposes an intelligent system of detecting air quality based on SPCE061A. The system mainly detects the concentration of combustible gas in air through gas sensors. After a series of data analysis, air quality information will be presented on the LCD screen. At the same time, when the gas concentration exceeds a value, it can relive harm automatically and remote alarm. So that it can prevent the happening of the malignant accident.

Numerical research of heat and mass transfer at interaction of several hot particles with typical polymeric material

The results of numerical investigation of heat and mass transfer at polymeric material ignition by several small-size hot particles are presented. The developed mathematical model considers the thermal conduction in polymeric material and hot particles, thermal decomposition of condensed substance, diffusion and thermal convection of combustible gases in air. It has been determined that the joint effect of several local energy sources on the ignition delay time is absent when the distance between hot particles exceeds their characteristic size.

Solid electrolyte sensor as a detector for gas chromatographic determination of combustible contaminants in air

In this paper, it is demonstrated for the first time that a solid electrolyte sensor based on stabilized cubic zirconium dioxide can be used for the chromatographic detection of combustible gases in air with the use of air as a carrier gas. The current of oxygen ions that passes through the sensor serves as an analytical signal. It is possible to obtain either a positive or negative signal of a combustible gas, depending on the polarity of the potential applied to the sensor and physicochemical processes that occur at the surface of the electrodes. Using the flux of oxygen ions passing from external air into the flow of the carrier gas, combustible contaminants can be detected in the range 0.1–5 vol % by the heat of a catalytic oxidation reaction. With the reverse flux of oxygen ions, the same contaminants can be detected at a level of 0.01–0.1 vol % by means of competitive adsorption.

Sol-gel synthesis of sub-micron titanium-doped chromia powders for gas sensing

Cr1 − xTixO3+x/2, with x = 0.05,0.1 and 0.2, powders have been synthesised by an emulsion gelation route starting from aqueous chloride solutions. Gel particles were produced by de-anionisation of a water-in-oil emulsion using an immiscible organic amine solution. After calcination to produce the oxide, the powders were characterised in terms of particle size distribution, crystallinity, surface composition, particle shape, surface area, anion contamination and doping uniformity. By optimising the processing variables it has been possible to produce un-agglomerated, spherical, uniformly doped powders with a narrow particle size distribution. The mean particle size can be controlled within the range 0.3 to 3 microns and the particles are porous and nano-crystalline. The powders have been used to fabricate thick film sensor structures and show good response to combustible gases in air.

A new method using a catalytic sensor for the identification and concentration measurement of combustible gases

The present state-of-the-art in gas detection does not allow the precise titration of a combustible gas in air with a single catalytic sensor, because the signal also depends on parameters other than the oxidation of the gas. This is why catalytic transducers always consist of both a detector and a compensating element. We present here a process that permits the avoidance of the compensating element, and, moreover, allows the identification of the combustible gas and the recognition of high concentrations of some gases.

Conduction—concentration relationship in chemoresistive thick-film SnO 2 gas sensors

The steady-state conductance G of thick-film SnO 2 chemoresistive gas sensor is measured for different CO concentrations c in air, in the 0–300 ppm range, at 0 and 100% relative humidity. The conductances G 0 at 0 and G at 120 ppm CO in normal air are measured as a function of time in non-steady-state conditions, during the first two hours of stabilization, after keeping the sensors unheated (out of operation) for seven days. The time dependence of the conductance at sudden changes of the CO concentration between c=0 and c ≠ 0 in normal air is also measured. Experimental results indicate that the ratio ( G 2− G 0 2)/ G 0 depends almost linearly on c down to very low values (about 1 ppm); it is fairly independent of humidity in the steady state, and of time during the stabilization stage. This can offer a possibility for using SnO 2 sensors not only for the detection, but also for the quantitative measurement, of small concentrations of a combustible gas in air.

Analysis of combustible gases in air with calorimetric gas sensors based on semiconducting BaTiO 3 ceramics

This paper presents a novel method to analyse a mixture of combustible gases in air by using electrically self-heated ceramic PTC resistors of semiconducting BaTiO 3 as microcalorimeters. The temperature dependence of the heat of a heterogeneous catalytic oxidation exhibits a transition state from the kinetic to the diffusion-controlled region at a certain temperature, which is characteristic for the combustible gas and the catalyst used. This characteristic temperature dependence of the heat of reaction can be used to identify one combustible gas in air. Moreover, the variation of the temperature dependence with the composition of a mixture of two combustible gases in air offers the possibility of determining the particular concentrations of the two gases by using PTC-microcalorimeters in an isothermal mode of operation.

Tin dioxide gas sensors. Part 1.—Aspects of the surface chemistry revealed by electrical conductance variations

Detailed measurements are reported of the dependence of the conductance of porous, sintered pellets of tin dioxide, on temperature, moisture and oxygen partial pressure. Comparison is made with the behaviour of thin layers prepared by radio-frequency sputtering. The effect of introducing a non-equilibrium mixture of a combustible gas in air, on the conductance and conductance activation energy is described. The theoretical basis for current interpretations of the behaviour of this material is reviewed. The results are discussed using a model in which the conductance of the porous pellets is controlled by different sorts of intergrain contact, represented as necks, necks depleted of conduction electrons, and Schottky barriers. The results are best rationalised by postulating that the conductance is in fact controlled by Schottky barriers separating domains or agglomerates, each comprising a rather large number of crystallites. The effects of temperature, moisture, oxygen partial pressure and combustible gases are discussed in terms of their effect on the Schottky barrier height by way of altrations in the area density, charge and occupancy of surface states (chemisorbed oxygen species). The existence of a surface state level located ≳ 1.1 eV below the conduction band edge is deduced. Adsorbed water strongly affects both the conductance and the response to combustible gases. Loss of water from the surface over the temperature range 280–450 °C results in a sigmoidal conductance-temperature relationship in moist air. The effect is to lower the resistance at temperatures below this range to no more than one-tenth of the values observed for dried pellets. A surface transformation O2–↔ OH– is inferred. In dried air, with dried pellets, inflexions in the conductance-temperature behaviour at temperatures below 230 °C are tentatively attributed to the effect of O2–↔ O–↔ O–2 surface transformations. The onset of a conductance response to the presence of a combustible gas coincides with the onset of a surface-catalysed combustion. At higher temperatures an effect of combustible gases is to lower the conductance activation energy for the porous pellets, but not for the sputtered layers. The effect of moisture on the response to CO was to extend the response to lower temperature; on dried pellets in dried air the response disappeared abruptly when the temperature fell below 350 °C.