The glass transition of trinitrotoluene (TNT) by flash DSC

• The glass transition temperature of TNT has been determined using Flash DSC.
• TNT exhibits a dynamic fragility typical of small molecule liquids of m ≅ 62.
• Three regimes: vitrification, vitrification and cold crystallization, crystallization only.
• Activation energy Eg at Tg is 290 kJ/mol.

Flash differential scanning calorimetry has been used to determine the glass transition response of the rapidly crystallizing energetic material, TNT. After heating at 600 K/s, it was found that for cooling rates from 1000 K/s to 10 K/s the glass transition changes from 247.5 K to 239.3 K. The dynamic fragility index was determined to be m = 62 ± 6 and the activation energy determined from the range of cooling rates in which vitrification occurred was found to be 290 ± 16 kJ/mol. Crystallization was found to occur during cooling at rates below 0.3 K/s, whereas cold crystallization was found on subsequent heating after cooling between 10 K/s and 30 K/s. At cooling rates of 100 K/s and above, and for the same heating rate of 600 K/s investigated, the glass transition event was observed, but cold crystallization during heating did not occur. Hence, the crystallization behavior of the fully amorphous TNT upon heating depends on the cooling rate and vitrification path.

Flash DSC heating traces for TNT cooled at different rates. Three regimes of behavior evident: q >100 K/s only glass transition is observed. 10 K/s < q < 100 K/s, glass transition, cold crystallization and melting are observed. 0.1 K/s < q < 10 K/s, only melting is observed, no glass transition or cold crystallization are observed.Figure optionsDownload as PowerPoint slide