032

Title:

Microspheres with any material composition can be prepared by mechanical milling

Discipline: Energetic materials

Presenter:

Mehnaz Mursalat

Abstract:

Powders with spherical particles with dimensions in the range of 10 – 100 µm are prepared by mechanical milling of precursor materials in the presence of a liquid process control agent comprising a blend of immiscible fluids (hexane and acetonitrile in this study). The proposed mechanism leading to formation of spheres includes formation of a Pickering-Ramsden emulsion in the milling vial coexisting with a high-density suspension of solid in a continuous phase. The complex mixture of phases is actively agitated during milling, resulting in destabilization of surfaces of emulsified droplets. However, instead of destroying such droplets, their instant repair occurs due to absorption of solid particles suspended in the continuous phase. Simultaneously, some particles get absorbed by droplets, leading eventually to formation of filled spherical particles that can be recovered after milling. Spheres with a broad range of compositions are prepared which include hard and ductile elements, metals, metalloids, oxides, organic compounds, and composites. The materials chosen for this study included aluminum, boron, melamine, sugar, iron(III) oxide, fumed silica, and composites of Al-B, Al-CuO and Al-Fe2O3. Interestingly, spheres were observed to form when specific liquid/liquid (for immiscible components) and solid/liquid ratios were used. The surface morphologies and particle sizes were characterized using scanning electron microscopy; specific surface areas and particle size distributions were also measured. Thermal analysis was used to assess the materials reactivity. Effect of process parameters, such as milling time on material properties, including size and surface area was established. Milling duration altered sizes and density (porosity) of formed spheres. A polymeric binder, dissolved in the emulsion droplets was introduced to some of the spheres to enhance their mechanical stability. Spheres of boron, Al-CuO and Al-B composites were found to exhibit attractive energetic characteristics. This novel technique of synthesizing spheres is simple, scalable and cost effective and the prepared spheres may be of interest as feedstock for additive manufacturing, for drug formulations, catalysts, membranes, and in various other technologies.

Author(s):

Mehnaz Mursalat, Daniel L. Hastings, Mirko Schoenitz, Edward L. Dreizin

Funding Acknowledgements:

US Defense Threat Reduction Agency (DTRA)