Characterization of explosives traces by the Nanocalorimetry

Abstract

Thermal characterization of energetic materials is often a non-trivial task. Experiments on such materials employing differential scanning calorimetry (DSC) have been mainly performed using special high-pressure crucibles, in which the pressure uncontrollably changes during the measurement. Conducting constant pressure experiments would allow addressing the decomposition reaction kinetics in a more quantitative way. In addition, the explosives detection requires sensing much smaller amounts of samples than those used in the DSC measurements. Explosives in the state of traces typically provide the sample sizes in the nano-gram to pico-gram range. The present work has been carried out with the Nanocalorimeter ( www.nanotlab.com), which can safely measure nano-gram-size samples. The Nanocalorimeter is operational in both DC and AC modes. In the DC mode, the device can perform heating ramps at ultra-fast heating rates (10 3–10 6 K/s) that are up to 1 million times faster than the conventional DSC. In the AC mode, which is analogous to the Modulated-DSC, the interval of the temperature modulation frequencies is also unmatched: the upper frequency bound reaches 3.0–10.0 kHz. Similar to the experimental setups described in the literature, the Nanocalorimeter employs a commercial gas sensor with integrated heating elements and thermocouples. In this work, a series of energetic materials of practical interest such as hexogen (cyclotrimethylenetrinitramine) and pentrite are characterized for the first time using ultra-fast heatings. The samples have been deposited on the sensor membrane using either micro-manipulation or spin-coating. Coupling of the Nanocalorimeter to a fast CCD camera was found quite useful to simultaneously visualize the processes occurring on a micro-second time-scale.