Non-Isothermal Sublimation Kinetics of 2,4,6-Trinitrotoluene (TNT) Nanofilms.

Walid Hikal,Brandon Weeks

doi:10.3390/molecules24061163

Abstract

Non-isothermal sublimation kinetics of low-volatile materials is more favorable over isothermal data when time is a crucial factor to be considered, especially in the subject of detecting explosives. In this article, we report on the in-situ measurements of the sublimation activation energy for 2,4,6-trinitrotoluene (TNT) continuous nanofilms in air using rising-temperature UV-Vis absorbance spectroscopy at different heating rates. The TNT films were prepared by the spin coating deposition technique. For the first time, the most widely used procedure to determine sublimation rates using thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC) was followed in this work using UV-Vis absorbance spectroscopy. The sublimation kinetics were analyzed using three well-established calculating techniques. The non-isothermal based activation energy values using the Ozawa, Flynn–Wall, and Kissinger models were 105.9 ± 1.4 kJ mol−1, 102.1 ± 2.7 kJ mol−1, and 105.8 ± 1.6 kJ mol−1, respectively. The calculated activation energy agreed well with our previously reported isothermally-measured value for TNT nanofilms using UV-Vis absorbance spectroscopy. The results show that the well-established non-isothermal analytical techniques can be successfully applied at a nanoscale to determine sublimation kinetics using absorbance spectroscopy.

Highlights

Explosives detection keeps rising as a critical issue due to the global rise in terrorist activity and needs more intensive investigation
In this article we illustrate the successful use of UV-Vis absorbance spectroscopy in non-isothermal measurement of TNT sublimation kinetics, using different heating rates and three different famous calculation techniques
The values measured here are in very good agreement with the values determined by the most sensitive techniques used in measuring sublimation kinetics of TNT: Quartz crystal microbalance (QCM) and Knudsen effusion method 97 ± 7 and 103 kJ/mole, respectively [4,23]

Summary

Introduction

Explosives detection keeps rising as a critical issue due to the global rise in terrorist activity and needs more intensive investigation. In this article we illustrate the successful use of UV-Vis absorbance spectroscopy in non-isothermal measurement of TNT sublimation kinetics, using different heating rates and three different famous calculation techniques. No other techniques have been reported to measure the sublimation kinetics of secondary explosives non-isothermally due their low melting point (80 ◦ C for TNT). The common procedure used to determine sublimation kinetics non-isothermally in famous techniques uses different heating rates. This procedure is not suitable in these techniques for low volatile explosives such as TNT, 1,3,5-Trinitro-1,3,5-triazinane (RDX), and Pentaerythritol tetranitrate (PETN). We report the use of this procedure to non-isothermally determine the activation energy of TNT sublimation using absorbance spectroscopy

Experimental Section

Theory

Results and Discussion

Absorbance

Conclusions