Temperature of the milling balls in shaker and planetary mills

The temperature increase of the milling balls in two laboratory mills, frequently used for mechanical alloying and mechanochemical experiments, was studied using direct calorimetric measurements. The ball temperature remains below 100 C in a SPEX 8000 shaker mill and it is cooler when flat-ended rather than round-ended vial is used, although the milling intensity, as measured by the mechanical dose rate, follows the opposite trend. Temperatures over 200 C are typical in planetary mills operating at similar milling intensities. It is suggested that the higher ball temperatures result from more oblique collisions and friction, while the lower temperature but higher intensity of the shaker mill with flat-ended vial is due to the larger proportion of frontal impacts.