Portal de Periódicos da CAPES

Lead‐free Primary Explosives

2014; Wiley; Volume: 39; Issue: 1 Linguagem: Inglês

10.1002/prep.201480132

1521-4087

Thomas M. Klapötke, Neha Mehta,

Forensic Fingerprint Detection Methods

Primary explosives are substances which – unlike secondary explosives – show a very rapid transition from combustion (or deflagration) to detonation (fast deflagration to detonation transition, DDT) and are considerably more sensitive towards heat, impact, electrostatic or friction than secondary explosives. Primary explosives generate a shock-wave which makes transfer of the detonation to a less sensitive secondary explosive possible. They are therefore used as initiators (e.g. in detonators, primers, blasting cap, etc.) for secondary booster charges, main charges or propellants. Already in the early days of the commercial production of explosives, Alfred Nobel replaced mercury fulminate (MF, ONCHgCNO) – which he had introduced into blasting caps – with the primary explosives lead azide (LA) and lead styphnate (LS), which were safer to handle. The latter one is less powerful than LA but easier to initiate. However, the long-term use of LA and LS has caused considerable lead contamination in military training grounds. One has to consider here that >95% of all shooting, missile launches and explosions within the military or police force are done exclusively for training purposes in "friendly" areas. Lead azide (LA) and lead styphnate (LS) are two widely used materials responsible for dangerously high levels of lead found at some firing ranges. Clean-up of heavy metal waste is extremely costly and this money could be better spent improving the defense capability of our forces. In 2006, a SERDP report focused on environmentally benign primary explosives used in stab detonators. A recent article published on December 4th 2012 in the Washington Post entitled "Defense Dept. Standards On Lead Exposure Faulted" stated: A report released Monday afternoon has found "overwhelming evidence" that 30-year-old federal standards governing lead exposure at Department of Defense firing ranges and other sites are inadequate to protect workers from ailments associated with high blood lead levels, including problems with the nervous system, kidney, heart and reproductive system. Also in Europe, the European Chemicals Agency (ECHA) has put LA on the Candidate List of Substances of Very High Concern for Authorization which has been published in accordance with Article 59(10) of the REACH Regulation. The main reason here is the toxicity for reproduction system. An additional problem with the use of LA is also the danger of obsolescence, i.e. the danger of LA becoming obsolete. For many years LA was not produced in the US and the LA which is being currently used in the end items has been obtained from stockpile material which had and is deteriorating more and more during the years of storage. This problem has meanwhile been overcome by the production of dextrinated LA (DLA) and special purpose LA (SPLA). The latter one is essentially identical to RD1333 LA by Chemring Inc. Another issue with lead is that it forms copper azide in presence/contact with copper or copper alloys which can be very sensitive and cause fatal accidents during handling and storage. Its service life might be shortened due to ready hydrolysis in the presence of moisture and carbon dioxide. The above mentioned and other related findings and concerns have stimulated world-wide activities in the search for replacements for LA and LS that are heavy-metal free. The "problem" in finding suitable replacements, especially for LA, is that apart from the toxicity of lead and compatibility with copper, it is difficult to meet the performance. LA has the desirable sensitivities (impact ca. 2–4 J, friction<1 N) for a primary explosive, has a high thermal stability (Tdec=315°), is hydrolytically stable, shows a good redox stability, is essentially insoluble in water and is not light-sensitive, all properties which guarantee a long shelf life and longevity. At the moment, the most promising replacements for LA and LS are copper(I) 5-nitrotetrazolate (DBX-1) and potassium 5,7-dinitro-[2,1,3]-benzoxadiazol-4-olate 3-oxide (KDNP), which were both developed by John Fronabarger and Mike Williams at Pacific Scientific Energetic Materials Co. (PSEMC). The chemical and physical properties of DBX-1 and KDNP have been extensively investigated and it appears that DBX-1 (easily prepared from sodium 5-nitrotetrazolate, NaNT) is a suitable drop-in replacement for lead azide in a variety of ordnance applications whereas KDNP may be a suitable replacement for lead styphnate. For example, ARDEC could show that in-house produced DBX-1 is suitable as a drop-in replacement for LA and lead based stab mix (NOL-130) for use in M55 stab detonators. There are, of course, other potential materials which are currently being investigated for use as possible LA replacements. One compound is potassium dinitraminobistetrazolate (K2DNBT), which has recently been synthesized at LMU.1 Molecular structures of DBX-1 (left), KDNP (center) and K2DNBT (right). Future research and more extended testing needs show whether the above mentioned LA and LS replacements will live up to their expectation but it can be stated for sure that the time of lead-containing primary explosives such as LA and LS is coming to its end. Prof. Dr. Thomas M. Klapötke Chemist, Department of Chemistry, Energetic Materials Research Ludwig Maximilian University Munich, Germany Neha Mehta Chemical Engineer, SME – Primary explosives and Detonators Explosives Development Branch US Army, RDECOM-ARDEC, USA This work was performed supported by ARDEC (contract W911NF-12-1-0467) and LMU.