Preparation and characterization of nanothermite inks for direct deposition on initiation devices

Robert R Nellums, Purdue University

Abstract

Nanothermites show promise as a replacement for energetic materials in many devices but their use has been limited by high sensitivity during processing, hazardous processing solvents, and time consuming deposition. Incorporating processing and deposition into a single step, especially if no organic solvents were used, could allow nanothermites to be applied in a wider range of applications. First, this work reports on the performance and mixing quality of nanothermites prepared in a LabRAM resonant mixer at high solids loadings as compared to traditional ultrasonic mixing. Specifically, the aluminum-bismuth (III) oxide (Al/Bi2O3) system processed in N,N-dimethylformamide (DMF) was investigated. It was found that the performance and quality of mixing were correlated to the volumetric solids loading during processing; increasing volumetric solids loading decreases separation of particles, leading to more intimate mixing. The measured performance of this system processed in DMF at 30 vol.% was similar to traditionally sonicated mixtures in hexanes, uses significantly less solvent, results in a higher density final material, and can be scaled. Second, this work investigates the replacement of the processing solvent DMF with water. Processing safety was characterized by measurement of thermal rise during mixing, stability at elevated temperature, and electrostatic discharge (ESD) sensitivity. Mixture performance was characterized via semi-conductor bridge (SCB) ignition threshold, Parr cell ignition delay and Parr cell pressurization rate. It was found that nanothermites processed in water performed similarly to nanothermites processed in DMF, although secondary interactions between aluminum and water caused heating that could be dangerous in scaled nanothermite batches. This secondary interaction was eliminated by coating both metal and metal oxide with an organic acid. In addition, processing in water at a solids loading of 30 vol.% resulted in a high performance ink that was deposited into SCB initiators, resulting in a 25% reduction in the all fire threshold over traditional energetics. This work incorporates both water processing and resonant mixing with the preparation of nanoenergetics. This method uses an environmentally friendly mixing medium, can result in a higher density final material, and allows one-step mixing and deposition without a significant decrease in performance when compared to traditionally prepared nanothermites.

Degree

M.S.M.E.

Advisors

Son, Purdue University.

Subject Area

Mechanical engineering|Nanotechnology|Energy|Materials science

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