NNNS Chemistry blog
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Fun with boron
21 May 2011 - Pyrotechnics
Sabatini et al. of the Pyrotechnics Technology and Prototyping Division of the US army report a novel way to produce the green light used in fireworks and signals (DOI). The new light is still green but also environmentally friendly. In a traditional formulation you mix barium nitrate, magnesium metal (fuel), a polyester resin (binder) and PVC. Combustion of PVC produces chlorine and then green-burning barium(I) chloride.
This formulation suffers from two disadvantages according to Sabatini: the barium source used may be radioactive and PVC combustion triggers Polychlorinated biphenyl formation. The solution: replace BaCl by the equally metastable green-light emitter boron oxide BO2 which forms by reaction of potassium nitrate and elemental boron Together with a epoxy/polysamide binder this pyrotechnic formulation burns just as green except that it burns too fast. For formulation number three therefore boron carbide was added and in formulation 4 even replaced the elemental boron component. If the US army wasn't green enough already it just got a little bit greener.