Chemical sensors ratio

Figure 7. Gas concentrations in engine exhaust at varying air-to-fuel ratio (A/F). Reproduced with permission from Ref. 6. Copyright 1984 Japan Association of Chemical Sensors.

The stoichiometry is therefore controlled by the composition of the guest mixture. The compounds are isostructural with respect to the location of the host molecules, and the guests lie in essentially the same sites and are partially disordered. This is an important result, in that the ratio of the guests can be controlled, and this phenomenon has implications for crystal engineering. Thus, the physical and chemical properties of such compounds can be governed, and this has significance in such fields as chemical sensors, optical and electronic properties of organic crystals, as well as their thermal stabilities and kinetics of desolvation. 

Chemical sensors are key in the transportation industry. Sensors are used to determine the fuel ratio, manage the optimum ratio, and measure the oil quality for pollution control. Chemical sensors monitor tailpipe emissions and catalytic converters. Additionally, sensors aid in chemical diagnostics of oil, transmission fluids, and other performance fluids. 

Chemical Sensors for Oxygen Detection and Air/Fuel Ratio Control... 

Another area of intense interest in conducting-polymer nanomaterials for chemical sensing is their combination with carbon nanostructures, most particularly carbon nanotubes, either single-walled (SWNT) or multiwaUed (MWNT). This again reflects the desire to combine the beneficial properties of both types of material to create new combinations with novel properties. CNTs empart high conductivity and high aspect ratios, which yield low percolation thresholds with nanodimensional stmctural order. This has led to their application as chemical sensors. However, CNT-based devices are difficult to fabricate, an issue which may be overcome by their dispersion in a conductive polymeric matrix. 

Metal oxides are among the most used active materials for conductometric chemical sensors. They have a wide variety of electrical properties spanning from insulator to quasi metallic behavior. The discovery of their sensing properties was made more than five decades ago, thereafter the interest of researchers was focused on nanostructured materials. These materials may give a greater modulation of the electrical properties for the interaction with the surrounding atmosphere thanks to the higher surface to volume ratio. 

The morphology of these nanostructures strongly depends on the technique selected for the preparation and on the operating conditions. Figures reports, as an example, some of the morphologies that may be achieved for tin and zinc oxide. The most important features of these nanowires for chemical sensors are their high surface to volume ratio and their single crystalline nature confirmed by transmission microscopy. 

---