In theU.S. military,reactive materials (RM) are a new class of materials currently being investigated by theOffice of Naval Research and others as a means to increase thelethality of direct-hit or fragmentationwarheads. Reactive materials are similar toinsensitive high explosives, but are usuallythermite-likepyrotechnic compositions of two or more nonexplosive solid materials, which stay inert and do not react with each other until subjected to a sufficiently strong mechanical, electrical or laser stimulus, after which they undergo fast burning orexplosion with release of high amount ofchemical energy in addition to theirkinetic energy. Fragments or projectiles made of such materials have therefore greater damaging effect than inert ones, with expected lethality increase up to 500%.
The material classes under investigation arethermites,intermetallic compounds, metal-polymer mixtures (e.g.,magnesium/teflon/viton-like),metastable intermolecular composites (MIC), matrix materials, andhydrides.[1] These materials must be strong enough to act as structural components, be sufficiently stable to survive handling and launch, to penetrate a target, and sufficiently unstable to reliably ignite on impact.
The mixtures under investigation include one or more finely powdered (down tonanoparticle size)metalloids or metals likealuminium,magnesium,zirconium,titanium,tungsten,tantalum,uranium[2] orhafnium, with one or more oxidizers liketeflon or otherfluoropolymer, pressed orsintered or bonded by other method to a compact, high-density mass. To achieve a suitablereaction rate and insensitivity to impact, friction, andelectrostatic discharge, fuel particles have sizes usually between 1-250 μm.[3][4] A standard composition is aluminium-teflon (Al-PTFE).
Metals which can formintermetallic compounds by anexothermic reaction are another class of candidate materials. An example is alaminate of thin alternating layers ofaluminum andnickel, commercially available asNanoFoil.
The RM weapons under development include anactive protection system defensive grenade for intercepting incoming missiles or grenades and detonating them at a safe distance, and theBattleAxe warhead that covers a wide area with RM fragments with devastating results tosoft targets, while the unexploded fragments left behind have very low lethality versus conventionalcluster bomb remains.
Under research are materials with highmechanical strength, high density, highenergy density, and which can rapidly convert from a consolidated structural material to fine powder with large surface area, be dispersed and then ignited to produce a largethermobaric blast.[5]
Apalladium-cladaluminum wire, known under trademarkPyrofuze, is used as apyrotechnic initiator.
Reactive materials also have non-weapon uses. Thin layers of reactive materials, clad with asolder, are used forreactive bonding, e.g., in electronics, or forbrazing, such as incomposite armor plates.