Bulk detection of explosives and development of customized metal oxide semiconductor gas sensors for the identification of energetic materials

Abstract

Based on previous work, a setup allowing discrimination between energetic and non-energetic materials was developed. In order to cover novel materials not yet included in databases, a library free approach was chosen. The evaluation of explosion hazards for solid and liquid samples in the lowest milligram range was carried out by relying on the response of the substances towards thermal activation rather than on their chemical nature. The reaction was monitored by a combination of metal oxide semiconductor (MOX) gas sensors, photodiodes and a pressure sensor. Utilization of ambient air as a carrier gas and indirect control over sample weight by the geometry of the heater allow uncomplicated handling under real working conditions. In the first phase readily available physical and chemical sensors were applied. The rate of correct assignments was 99.8% with no false negatives and only 1 false positive out of 475 experiments. The possibility of library free operation was also confirmed by an additional series of experiments on materials not used for training the system. In the second phase the readily available MOX gas sensors were replaced by custom designed ones, which allowed single substances and classes of energetic materials by means to be discriminated by means of principal component analysis (PCA).