Effects of the speed ratio on the efficiency of planetary mills

The ignition time (t_ig) of the mechanically induced self-sustaining reaction (MSR) process involving the formation of TiB₂ from Ti/2B elemental mixtures was used to study the influence of the ratio (k = -ω /ω ) between the rotational speed of the supporting disc (ω ) and vials (ω ) on the milling efficiency of a Pulverisette 4 planetary mill. The variation of the inverse of the ignition time (1/t_ig), which is directly related to the milling power provided by the planetary mill, with the process conditions has shown that it is not possible to find a single k value as optimal independently of the experimental conditions used (ω and the ball-to-powder ratio, BPR). Moreover, it was observed that the lowest milling efficiency (longer t_ig values) was found for k = 1, which is the usual value employed in routine laboratory works. The best efficiencies were found for the larger k values (2.5 or 3). At lower ω _d, the shortest t_ig was obtained for k = 2.5 and at higher ω _d for k = 3, independently of BPR.