Energetic materials, especially those used as first-fire mixes, are susceptible to unintentional ESD initiation, which is not desired due to risk to person, property, or mission. However, ESD is difficult to eliminate in real-world situations because the amount of energy required to initiate an energetic material by ESD is usually several of orders of magnitude less than the amount of energy used to initiate the energetic material by other modes of initiation, such as heat, impact, or friction. It is also difficult to reduce the ESD sensitivity while maintaining desired modes of initiation and the desired performance of the energetic material. Accidental ESD initiation is problematic with thermite compositions, such as aluminum/copper oxide compositions, and intermetallic compositions, such as aluminum/nickel compositions. Thermite and intermetallic compositions are susceptible to accidental initiation by ESD since the fuels and oxidizers are usually in powder form. The addition of a fluoropolymer, such as VITON®, or alumina to the energetic material has also been tested. However, the exothermic reaction was affected and the ESD sensitivity was not greatly improved.
Energetic materials are also susceptible to unintentional ignition when exposed to heat, such as the heat produced by a fire. For instance, the energetic material may be unintentionally exposed to heat during storage or transportation, such as if a vehicle, vessel, building, or other containment including the energetic material catches fire. During a fire, the energetic material is exposed to a relatively low temperature for an extended period of time compared to the temperature and duration produced by the ignition of the energetic material, which may be on the order of seconds or milliseconds. The heating rate of the energetic material when exposed to a fire is also much slower than the heating rate of the energetic material when ignited. Nevertheless, the heat from the fire can be sufficient to ignite the energetic material, causing damage to nearby facilities and personnel. Furthermore, if the energetic material is contained in a confinement, such as in a case, the energetic material may react violently when heated, producing fragments (shrapnel) that cause damage to adjacent facilities and personnel. To reduce the sensitivity of the energetic material to unintentional ignition, the amount of the energetic material being stored or transported may be limited, or the energetic material may be carefully guarded during storage or transport.
A composite energetic material (CEM) is a class of energetic materials that includes fuel and oxidizer particles that are highly exothermic upon ignition. CEMs are also referred to in the art as thermites, reactive materials, and pyrotechnics. If the particle size of the components is on the nanoscale, then the CEMs may also be referred to as nanothermites, superthermites, metastable intermolecular composites, metastable interstitial composites, or metastable nanoenergetic composites. Since the reaction of CEMs is diffusion limited, the CEMs may be tailored toward specific applications by adjusting the compounds used as the fuel and oxidizer, unlike conventional explosive compositions whose reactivity is kinetically limited by the monomolecular crystal structure. To reduce the mechanical sensitivity of a manganese oxide/aluminum composition, carbon nanofibers have been filled with the manganese oxide. The manganese oxide and the aluminum are, thus, alleged to be separated from one another and the composition exhibited reduced mechanical sensitivity (friction sensitivity) compared to a manganese oxide/aluminum composition lacking the carbon nanofibers. The filled carbon nanofiber composition also had a decrease in ESD sensitivity compared to the manganese oxide/aluminum composition lacking the carbon nanofibers. The filled carbon nanofiber composition was also compared to a composition including manganese oxide and aluminum mixed with unfilled carbon nanofibers. The filled carbon nanofiber composition had an ESD sensitivity of 35 mJ while the unfilled carbon nanofiber composition had an ESD sensitivity of 1800 mJ.
As the use of CEMs increases, safety concerns relating to their ignition sensitivity and to their ESD sensitivity increase. To improve the safety of energetic materials, it would be desirable to reduce their potential for unintentional ignition and ESD sensitivity.