The research group comprising Mr. Arjun V.S. Kidavu (SRF), Prof. Anil Kumar Chaudhary of DAE-CoE (ACRHEM), School of Physics, University of Hyderabad (UoH), and Dr. P.K. Soni, Scientist H and Associate Director, TBRL, Chandigarh have jointly investigated and verified the thermal decomposition mechanisms of RDX and TNT using QCL laser based pulsed Photoacoustic pyro-analyzer (indigenously designed). In the path-breaking research, the team has experimentally verified the Reactive Force Field model reported by Strachan et al. for premium RDX explosives and identified the different types of by-product gases in various temperature ranges using an indigenously designed photoacoustic (PA)thermal analyzer system. The study provides significant information about RDX and TNT explosive molecules’ exothermic energy release mechanisms under controlled conditions. That is an important aspect of their use as Rocket /missile fuel and storage under different. The team have identified NO2, N2O4 (dinitrogen tetroside), HCN, HNO2, and CH2O as byproduct gases from RDX whereas TNT releases HNO2 and CH2O along with NO2-N2O4 mixture.

The percentages of HCN, CH2O, and HNO2 for RDX are 19%, 26 %, and 12% of the NO2-N2O4 mixture, whereas TNT releases HNO2 and CH2O of 9% and 28%, respectively of NO2-N2O4 mixture.

 

 

 

 

 

 

 

In the second part, they have further modified the optical configuration of the used PA thermal analyzer sensor and converted it into a multi-pass geometry mode which helped us to detect these explosives from the soil samples collected from different locations of the defense test range using the same model i.e. based on their release by-product gaseous component. The detection limit of these gases lies between 65- 164 ppbv range.

The reported work opens a new channel of investigation and acts as an alarm in newly synthesized molecules and their impact on the environment and health of the users and inhabitants. Some of the released gases such as HCN, HNO2, NO2, HCHO have an adverse effect on the health of the users.

This work has been published (online) in the peer-reviewed journal Measurement. https:https://doi.org/10.1016/j.measurement.2025.116791

The authors express their sincere thanks to the DRDO, Ministry of Defence, Govt. of India for funding for developing an experimental facility under ACRHEM (DIA-CoE) Phase-III, University of Hyderabad and special thanks are due to the Director of DIA CoE (ACRHEM), School of Physics for all types of support.

Abstract

The identification of different types of by-product gases released during the thermal decomposition process of pure explosives like 1,3,5-trinitro-1,3,5-triazine (RDX) and trinitrotoluene (TNT), and their presence in soil samples collected from the defense range is reported. The Reactive Force Field model reported by Strachan et al. is experimentally verified for understanding the decomposition mechanism of RDX1 in terms of by-product gases such as NO2, N2O4 (dinitrogen tetroside), HCN, HNO2, and CH2O. The detected percentages of HCN, CH2O and HNO2 for RDX are 19 %, 26 % and 12 % of NO2-N2O4 mixture, whereas TNT releases HNO2 and CH2O are 9 % and 28 %, respectively of NO2-N2O4 mixture. A stainless-steel photoacoustic cell in single and multi-pass geometry was used. A Quantum Cascade Laser tunable between 5.3 to 7.3 µm range at 50 ns pulse duration was used. The detection limit of these gases lies between 65––164 ppbv range.