(458m) Thermal Behavior of CL-20 at Ultra-High Heating and Cooling Rates Using Flash DSC

First synthesized in the late 1980s, Hexanitrohexaazaisowurzitane (CL-20) has been an energetic material of significant interest due to its exceptionally high molecular density. Conventional differential scanning calorimetry (DSC) has been used extensively in past literature to characterize the thermal transition behaviors of CL-20’s various polymorphs. However, the conventional DSC work cannot determine the melting temperature for CL-20 due to thermal degradation prior to melting due to the relatively slow heating of the DSC (≤ 200 K min^-1; ≤ 3.3 K s^-1). In the current work, a Flash DSC was used to characterize the thermal behavior of CL-20 using ultra-high rates of heating and cooling. In Flash DSC, thermal rates can be as high as 40,000 K s^-1 (2,400,000 K min^-1) for heating and 4,000 K s^-1 (240,000 K min^-1) for cooling. The chip calorimeter uses a sample mass on the order of 10-1000 ng, as compared to a few milligrams in conventional DSC. Here, the thermal behavior of CL-20 was determined using heating rates up to 1000 K s^-1 (60,000 K min^-1) and allowed for several experimental repetitions reaching temperatures up to 300 °C, which is well above the typical point of decomposition of CL-20. At high heating rates, little to no sample degradation was observed. Preliminary results suggest the appearance of a melting peak just beyond 200 °C (473 K). As was previously demonstrated for TNT using the same technique [1], the goal is to produce an amorphous glass by quenching a melt at a fast enough rate to avoid crystallization. We aim to similarly investigate the thermal behavior of different material compounds with CL-20 (e.g. HMX, polyvinyl acetate) in the form of co-crystals and spray-dried material, some of which have been shown to form amorphous structures [2].

[1] N. Shamim, Y.P. Koh, S.L. Simon, and G.B. McKenna, "The glass transition of trinitrotoluene (TNT) by flash DSC," Thermochimica Acta, 620, 36-39 (2015).

[2] V. Stepanov, R. B. Patel, R. Mudryy, and H. Qiu, “Investigation of Nitramine-Based Amorphous Energetics,” Propellants Explos. Pyrotech. 41, 142-147 (2016).