Analysis of gases evolved from heated coal, wood and PVC conveyor belt their effect on zinc oxide single‐crystal semiconductor gas sensors

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Abstract
An analysis, using gas chromatography and gas chromatography‐linked mass spectroscopy, of the major products evolved as a function of temperature from coal, wood and PVC conveyor belting is described. The effect of these products, both collectively and as individual species, on the electrical properties of zinc oxide gas sensors has been investigated: the conductance of the sensors was measured in air containing either the total products evolved from the heated materials or the individual products eluted from a gas chromatographic column. Thus, the products from the different materials which make up the total zinc oxide gas sensor response at different material temperatures were identified. For coal dust heated in air the sensors responded to aromatic hydrocarbons H2 and CO, which were evolved between 100° and 200°C. For coal heated in nitrogen the sensors responded to the aromatic hydrocarbons evolved between 100° and 170°C. For PVC conveyor belt heated in air, the low temperature response was to the low levels of HCl evolved below 200°C. Finally, for hardwood dust heated in air the sensors responded primarily to the acid vapour evolved between 170° and 200°C.