Hollow metallic microspheres produced by spark erosion

Hollow spherical particles of Ni, CoFe, the ferromagnetic shape memory alloy ${\mathrm{Ni}}_{49}{\mathrm{Mn}}_{30}{\mathrm{Ga}}_{21}$ , and the giant magnetostrictive alloy ${\mathrm{Fe}}_{83}{\mathrm{Ga}}_{17}$ , with diameters up to several tens of microns were produced by spark erosion, using liquid nitrogen as the dielectric liquid. In contrast, the particles were primarily solid when the dielectric liquid was argon. The wall thicknesses of the hollow particles depended on the elemental composition. Different models are considered to account for the formation of the spark-eroded hollow spheres, and some of the potential benefits to be derived from their use are described.