Chemical Evaluation and Performance Characterization of Pentaerythritol Tetranitrate (PETN) under Melt Conditions

Abstract

Pentaerythritol tetranitrate (PETN) is a nitrate ester explosive commonly used in commercial detonators. Although its degradation properties have been studied extensively, very little information has been collected on its thermal stability in the molten state due to the fact that its melting point is only ∼20 °C below its onset of decomposition. Furthermore, studies that have been performed on PETN thermal degradation often do not fully characterize or quantify the decomposition products. In this study, we heat PETN to melt temperatures and identify thermal decomposition products, morphology changes, and mass loss by ultrahigh-pressure liquid chromatography coupled to quadrupole time of flight mass spectrometry, scanning electron microscopy, nuclear magnetic resonance spectroscopy, and differential scanning calorimetry. For the first time, we quantify several decomposition products using independently prepared standards and establish the resulting melting point depression after the first melt. We also estimate the amount of decomposition relative to sublimation that we measure through gas evolution and evaluate the performance behavior of the molten material in commercial detonator configurations.

Figure 1

DSC (mW/mg; black line) and mass loss (%; blue line) of PETN, with temperature (°C; red line) increased to 145 °C, followed by a second melt and resolidification (sample 1 in Table 1).

Figure 2

Endotherms overlaid from a representative sample in order to show melt hysteresis of PETN, where the first melt is indicated by a sharp endotherm and the second melt has a broad endotherm beginning as low as ∼125 °C.

Figure 3

SEM images, showing the heating cycle nomenclature.

Figure 4

UHPLC-QTOF analysis of PETN and heated PETN with the top 10 statistical differences that were found using Fisher ratio (F-ratio) analysis indicated.

Scheme 1. PETN Decomposition Products Observed in NMR and UHPLC-QTOF

Figure 5

NMR spectra of PETN after multiple heating cycles. The percentages show the molar ratio of each decomposition product, relative to the remaining amount of PETN in solution, taking the number of protons in each peak into account during integration of the peaks. The designation “s” refers to naturally occurring satellites on the PETN peak at the ∼1% level.

Scheme 2. Synthesis of PETriNal

Figure 6

Images of the RP-1 detonator during heating at melt temperatures, showing the unheated detonator (a), and partially melted PETN (b–e), during progression to full melt (f).

Figure 7

(a) Light output from luminous chemistry wave in a representative region of interest. Black line is taken during the nominal function of a representative control detonator at room temperature and red line from the detonator heated above the melting point, shown in (b). (b) (Top) Images of the RP-1 detonator during heated firing (molten PETN), overlaid with the original detonator; (bottom) images of a control detonator during firing, showing the sharp intense band of propagating light.