Inkjet Printing of Metallic Initiators
This study explored the development of various printed metallic initiators. The purpose was to create an initiator that could easily be integrated with a printed energetic material, specifically, a liquid suspension of nanothermite. Printing the initiator allowed for precise control and easy manipulation of the geometry. Thus, the geometry could be custom made for various applications. Bridge wire initiators were first investigated due to their presence in current initiation systems. A bridge wire is a thin wire that a high electrical current is sent through. The current causes the bridge wire to heat and can ignite an energetic material, if it reaches the material's critical ignition temperature. If the current heats the bridge wire faster than it can expand in response, the bridge wire will break and the resulting shock can ignite the energetic material. Bridge wires of various length were tested to determine how the length affects the breakage time. In addition, the bridge wires were tested under various voltages (between 7.5 V and 13.75 V). It was found that increasing the voltage decreased the break time. Finally, a nanothermite [nano-aluminum and nano-bismuth (III) oxide] was pipetted on to the bridge wires. Ignition of the energetic material from the breaking of the wire was achieved, but it proved unreliable due to various factors including, but not limited to, print quality. The bridge wires were subsequently tested as a part of a circuit with a wireless trigger. The bridge wires were able to break through the energetic material at 15 V, but did not ignite the nanothermite [nano-aluminum and nano-copper (II) oxide]. This indicates that the bridge wire did not heat enough to ignite the nanothermite or that the shock produced from breaking the wire was not enough to ignite the material. Further investigation into the effect of the length of the bridge wire on ignition and the use of different nanothermites will be conducted in future work. To explore alternative geometries, spark gap initiators of various sizes were also printed. A spark gap was created by printing two conducting electrodes close enough to each other to allow an electric spark to jump between them. The breakdown voltage for the spark gaps varied, but reliable spark over occurred under 5 kV and 50 μA. The ability to create a printed initiator integrated with printed energetic material was also demonstrated. Printed nanothermite [nano-aluminum and nano-copper (II) oxide] was placed in the center of a spark gap, covering both electrodes. The spark gaps required a much higher voltage to achieve ignition of the energetic material than the bridge wires, but for the utilized geometry, they achieved a significantly higher reliability. For ignition, 5 kV proved sufficient but the current required was 75 μA. Overall, the successful printing of metallic initiators was demonstrated. Bridge wire and spark gap initiator geometries were created and tested. The ignition of energetic material for the different initiator types was demonstrated.
Rhoads, Purdue University.
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