Effect of Accelerated Aging on Microstructure and Initiation of Vapor-Deposited PETN Films*

Pentaerythritol tetranitrate (PETN) is a commonly-used explosive, but one that is known to have issues with stability over long periods of time. In this work, we use vapor-deposited PETN films as a model system to demonstrate how the microstructure and growth to detonation under shock impact in a dense, fine-grained solid evolve following accelerated aging at elevated temperatures. Scanning electron microscope images of the top surface and fracture cross-section of the films are used to characterize the microstructure, while a high-throughput experimental setup that utilizes an array of laser-driven flyers to impact samples with photonic Doppler velocimetry diagnostics is employed to characterize the growth of reactions leading to detonation. One-dimensional hydrocode simulations were performed with reactions disabled to illustrate where the experimental data deviate from the predicted inert response. Significant grain coarsening was observed to occur within only a few hours at elevated temperatures, with only moderate additional coarsening over much longer time periods thereafter. Similarly, significant shifts in initiation threshold are observed early in the aging process, with minimal further changes later. Implications of these aging-related changes to microstructure and initiation will be discussed.