The ball-milling process involves both fracturing and welding of particles. Particles of ductile materials are very likely to attach to each other when entrapped between balls. Therefore, conventional milling methods fail to grind ductile materials into nanoparticles. However, using brittle particles together with the starting materials, one can fracture and highly activate ductile particles through planetary ball milling. During the milling process, brittle particles are easily fractured down, and their sharp edges chop the particles of the ductile materials incessantly into pieces until both ductile and brittle particles are nano-sized (a process which is unlikely, if not impossible, to accomplish by ball milling of ductile materials alone). In this chapter, the effects of ball milling of ductile materials (e.g., graphite, aluminum, and zinc) together with a brittle material (here, NaCl), for preparation of metal nanoparticles or metal oxide nanoparticles are investigated. A theoretical explanation of the mechanism is also presented based on the facts and practical measurements.
Part of the book: Abrasive Technology