A MEMS-based microthermal analysis of explosive materials

• The paper describes a MEMS based sensor for explosive trace detection by micro-thermal analysis.
• The results of micro thermal analysis of explosive materials of different size and origin are shown and discussed.
• It is shown that the areas of the endotherms are larger than thus of the exotherms. The reasons are discussed.
• The MEMS sensor can be potentially applied to low cost, wide spread, man portable field detectors.

An upgraded microcalorimeter comprising a MEMS-based thermal conductivity vacuum gauge with a ∼1.3 mV/K thermopile sensor and a thin Si3Nx film heater was constructed. The improved features relative to a previous design are linear rise of the temperature with time and rapid heating of up to ∼500 °C/s. The device was used for thermal analysis of micrometer-size particles of the explosives TNT, RDX and PETN by measuring temperature changes while heating the film heater. The TNT thermogram features a single exotherm that is well separated from the endotherm. The area and position of the melting and decomposition peaks in the RDX thermogram are proportional to the particle mass. The observed heats of melting agree with known thermodynamic data. The observed heat of deflagration is less than 1% of the calculated value, because a large fraction of the heated sample was sputtered from the heater and most of the heat was lost to the surrounding. Monitoring the air temperature above the heater with an ultrathin thermocouple yielded identifiable thermograms in accord with the surface thermograms. Such contactless sensing above the heater can detect the decomposition of micrometer-size particles and offers potential for the development of an inexpensive, simple to use field explosive detector.