(764f) Water Processed Nanothermite Inks for Direct Deposition On Low Energy Initiators

Pyrotechnic initiators
are used in a multitude of applications spanning from airbag inflation systems
to energetic detonators.  Specifically, semiconductor
bridge (SCB) initiators have seen increased use in recent years, particularly
in low energy devices.  Applications
requiring SCB's with dimensions of 80 μm or
smaller have sparked interest in the use of nano-sized
energetics due to increased interfacial contact area
between energetic particles and the bridge. 
Previous work in this area showed that nanothermites,
such as Al-Bi₂O₃, Al-MoO₃, etc., work well for
small initiators, but their application typically involves hazardous organic
solvents.  While water processing has
been suggested as an alternative to organic solvents, it has several drawbacks
including material degradation, dangerous heating due to reaction of nano-sized aluminum with water, and difficulties in
particle dispersion.  Currently, ammonium
dihydrogen phosphate (ADP) is used to inhibit
material degradation and subsequent reaction-induced heating in water processed
nanothermites. 
However, it was found that at the solids loading levels necessary for
syringe deposition of nanothermite mixtures, safe
processing was not possible with ADP.  This
work reports a methodology in which the use of a palmatic
acid coated nanoaluminum (L-ALEX) and an appropriate
dispersant overcomes the above issues. By processing these nanoenergetic
mixtures via a LabRAM Resodyn,
a high solids loaded ink (30% v/v) results that can be directly applied to the
bridge with no visible settling of reactants or cracks.  SCB ignition thresholds for these mixtures
were found to be comparable to mixtures in which the mixing medium was dimethylformamide
(DMF)
(35 mJ*m^-2 vs.
32 mJ*m^-2).  This new processing
technique allows for safer processing of sensitive nanoenergetics
at high viscosities and has been shown to deliver reliable performance at low
energy thresholds for SCB initiators.