Microspheres with Diverse Material Compositions Can be Prepared by Mechanical Milling

This study introduces a novel, simple, and scalable method of preparing spherical particles from a range of materials of potential interest in food, pharmaceuticals, energetics, and additive manufacturing. Spherical particles with dimensions in the range of ≈1–100 μm are prepared by mechanical milling of precursor materials in the presence of a blend of immiscible liquids. Microspheres of hard and ductile materials including metals (aluminum, titanium), metalloids (boron), oxides (of iron or silicon), organic compounds (melamine, sucrose), and composites (aluminum–boron, aluminum–titanium, aluminum–copper oxide, aluminum–iron oxide) were prepared. The proposed mechanism leading to the formation of spheres includes formation of a Pickering–Ramsden emulsion coexisting with a dense suspension of solids in the continuous phase. Milling continuously transfers energy to the multiphase mixture, destabilizing particles located on the liquid interface. This causes a net transport of solids from the continuous phase into the emulsion droplets where solids accumulate and form microspheres that can be recovered after milling. The process continues until the solid loading of the droplets exceeds a limit, or until the continuous phase suspension is depleted. Microspheres prepared by this method may be of interest as feedstock for additive manufacturing, for drug formulations, catalysts, membranes, and in various other technologies.