Particle Tracking in Horizontal Ball Milling

Ball milling is a material processing method that allows near room temperature process of elements in powder and permits to synthesize materials with peculiar properties otherwise difficult or impossible to obtain. Due to the repeated fractures and cold welding of the reactants particles, solid solutions, amorphous alloys and equilibrium nanostructured materials can be obtained. Products coming from mechanosynthesis process can be advantageously applied as high performance structural and functional materials. Different milling devices can be utilized for the powder processing: planetary mill, attritor, horizontal ball mill, 1D and 3D vibrating machines. The wide differentiation in configuration of the mills obstacles the development of a unified model on powder transformation kinetics in the milling process and then most of processing procedures are still developed by using a trial and error method. The focus of this paper is on a horizontal fixed vial ball mill; in this configuration a high speed rotor launches several tumbling against the vial wall. During hits, a quantity of energy is released to the trapped powder and the solid state reactions are promoted. To characterize the powder transformation process, knowledge of the kinematics of the balls system must be inferred. For this purpose an experimental setup based on digital image acquisition was constructed and the movement of balls inside the vial was filmed. Particle trace analysis methodology permitted to obtain balls trajectories, velocity vector field and total hit frequency. The kinetic energy of the impacting balls inside the vial was quantified, so that the energy released to the powder in a milling experiment can be estimated.