Boron carbide as a barium-free green light emitter and burn-rate modifier in pyrotechnics.

Although there has been significant interest in the develop ment of environmentally friendly pyrotechnics, the develop ment of cost effective barium free green light emitting pyro technic formulations has remained elusive. Many barium compounds are human health hazards, and recent work by Steinhauser has shown that barium ores as raw materials may contain radioactive radium. Recent papers by Klap tke have shown that copper(II) based high nitrogen content compounds can contribute to green light emission, but not all of these compounds combust to yield bright green light in pyrotechnic formulations. Many of these copper salts are difficult and expensive to synthesize, and they can be sensitive to impact, friction, and electrostatic discharge. The use of amorphous boron and potassium nitrate (BKNO3) is known to have green light emitting qualities owing to its formation of metastable boron oxide (BO2), but these mixtures often burn too rapidly to find practical use in long burning pyrotechnic applications. The Armament Research, Development, and Engineering Center (ARDEC) recently disclosed a series of formulations in which crystalline boron was used as an inert additive to extend the burn time of amorphous boron containing green light emitting pyrotechnics. However, the use of crystalline boron in pyrotechnics is an expensive solution toward the development of barium free green light emitting pyrotech nics, and a cheaper alternative was desired. A program was initiated by ARDEC to develop a cost effective barium free alternative to a US Army green light emitting pyrotechnic item, namely the M125A1 hand held signal (Table 1). As summarized in Table 1, barium nitrate served as the oxidizer, magnesium 30/50 (mesh size) was the main fuel source, and Laminac 4116/Lupersol was the binder system. The unique role of poly(vinyl chloride) (PVC) was its liberation of chlorine during the combustion process, which reacts with barium to yield metastable barium(I) chloride (BaCl), the species directly responsible for green light emission. Chlorine also reacted with incandescent magnesium oxide to produce the more volatile magnesium chloride species, further aiding in boosting the observed color purity of the pyrotechnic flame. To establish a relevant data point toward developing a cost effective barium free pyrotechnic, BKNO3 was chosen as the initial fuel/oxidizer system, with Epon 828/Epikure 3140 serving as the binder system (Table 2). Owing to the absence