Thrust 1: Explosives Characterization

The Homeland Security establishment was surprised and alarmed by the emergence of tri-acetone tri-peroxide (TATP) as a nitrogen-free explosive threat necessitating new restrictions on liquids in airplane carry-on luggage. It is not clear how many other new improvised explosives can be devised. The objective of F1 is to evaluate performance of energetic materials related to Homeland Security efforts. We will use the expertise of faculty members from Chemistry, Chemical Engineering and Mining Engineering to determine key criteria of these materials. Building on a core expertise of energetic materials programs, we expect to create new technologies to generate a superior understanding of explosives relevant to DHS. A strong knowledge-based experimental and theoretical program exists and will be extended and results will be disseminated through literature and presentations. Through this research program, the team will train future scientists and engineers in high explosives science and technology.

The primary difference between a high explosive and any material that undergoes a chemical decomposition process is the rate at which the decomposition occurs. The rate at which the decomposition occurs within a material is not simply an intrinsic property of the explosive such as the chemical composition. The decomposition rate is determined by a number of factors including the particle characteristics of the explosive, the magnitude and duration of the stimulus that triggered the chemical reactions, and the confinement of the explosive. For high explosives, the rate and amount of energy released is normally sufficient to establish a self-sustaining shock known as detonation. A detonation wave is a pressure discontinuity that moves through a material faster than the speed of sound in the material, typically in the 2-12 km/s range.

Materials which undergo slower decomposition (up to 400 m/s) are usually referred to as low explosives and do not detonate under normal conditions. Gunpowder is the most common low explosive that has been used to make improvised explosive devices. Although not normally considered explosives, powders will detonate when confined in pressure and volume.

Explosives of interest can be broken down to three primary categories:

1. Organic explosives such as RDX, HMX, PETN, and TATB are commonly used commercially for blasting and in the military. These explosives are made of C, H, N, and O elements, and usually contain a nitrate functional group. The explosive is commonly referred to as mono-energetic since both the fuel and oxidizer are contained within a single molecule. Another common organic explosive is acetone peroxide which does not contain a nitrate group, making detection difficult since the nitrate group is a primary signal for many sensors.


2. Explosive salts such as ammonium perchlorate, sodium azide and ammonium nitrate are commonly used for industrial applications and in rocket propellants. Specifically, ammonium nitrates are also used widely as a fertilizer, thus they are readily available for large and small scale uses.


3. New materials, which are seeing wider use in explosive devices, are thermite compounds. Thermites most often use two metals; one acts as an oxidizer (molybdenum oxide) and a second metal as a fuel (aluminum). Newer thermites based on aluminum and Teflon are of particular concern since the energy released can be incredibly high with fluorine transfer instead of oxygen. Although not normally considered high explosives, thermites have a higher energy density than organic high explosives and reaction rates approaching a detonation. A major concern with thermites is that the heat generated from these materials is capable of melting metals such as the skin of an aircraft or building girders.

The physical and chemical properties of these composite explosives are quite different, both intrinsically (e.g. chemical bonding, reactivity, energetic characteristics, shock sensitivity, etc.) and extrinsically (e.g. density, voids, grain structures, defects, etc.). Yet, the detailed knowledge of these intrinsic and extrinsic properties is critical to characterize explosive materials, as well as to develop appropriate detection and mitigation methods.

>F1-A Vapor/Liquid Equilibria & Phase Behavior of H₂O₂

>F1-A2 Investigation of Chemical & Phase Stabilities of Potential IEDs

>F1-B Nanomaterials for Enhanced Detection of Explosives and Mitigation of Explosive Events