oxidation of nitrogen-containing compounds, nitration has been a successful approach to the synthesis of new generations of more effective explosives. The oxygen in the nitrate group (NO3) provides the oxidant for the carbon and hydrogen. A compound called RDX is widely used in Navy warheads. A compound designated as HMX is about 10 percent more energy dense and has been superseding RDX when safe applications can be found. There are indications that HMX may be nearing the upper limit of energy density that can be made safe from inadvertent explosion, i.e., made safely “insensitive.” The Navy has had unfortunate accidents that have led to the policy that all new explosives must be proved safe. A new and promising explosive, CL-20, is now in the process of being certified as insensitive.
There are other families of chemicals that are not based on the nitration of organic compounds. Perchlorates (ClO4−), for instance, are also high explosives, and their balance of energy density and sensitivity can be favorable. ONR has supported research and development on perchlorates, and some formulations are in use.
Undersea explosives intended to destroy the hulls of ships and submarines often include aluminum in order to produce a large bubble, the dynamics of which in turn can place a large stress on the metal structure under attack. The advantage of using aluminum is partially lost by the passivation of the surface of the aluminum particle in the explosive by an inert layer of Al2O3, which leaves unreacted aluminum under the surface layer. To overcome this defect, ONR has an S&T program to replace some nitro- or nitrate groups with NF2. Doing so enhances the energy release, since the fluorine tends to undermine the Al2O3 and increases the activity of the aluminum by causing it to react more completely.