(582b) Discrete Element Method Modeling of Preparation of Reactive Nanomaterials by Mechanical Milling

Reactive nanocomposite powders with different compositions were recently prepared by arrested reactive milling, a mechanical milling technique. Shaker and planetary mills were used for laboratory scale production. A discrete element method (DEM) model was used to characterize the material evolution in the mill by tracking a milling progress function, defined by the energy transferred from the milling media to the material under processing. It was observed that the milling tools interact differently in shaker and planetary mills and contribute to the refinement of the milled material in different ways. Specifically, head-on collisions between milling balls controlled the rate of powder refinement in the shaker mill, while rolling motion of the balls caused the powder refinement in the planetary mill. Both shaker and planetary mills are widely used in laboratory experiments; however, attritor mills are better suited for scaled-up production of new materials and thus an accurate description of the respective milling process is needed. In this work, a DEM model is developed and used to assess the powder processing in an attritor mill. Previously, milling effectiveness of attritor and shaker mills were compared to each other based on both laboratory experiments and simplified models. However, the results of such comparisons were inconsistent with experimental observations related to mechanical alloying. In this effort, the commercial EDEM software by DEM Solutions Inc. was used. A model 01HD attritor mill by Union Process was described in the code. Predictions were made for the mill operated with milling media comprising steel balls of different diameters. The influences of milling parameters, including number and dimensions of the milling balls, rate of impeller rotation, and the impeller's vertical position on the energy transfer from the milling media to the powder were investigated. In addition, the energy transfer in the attritor mill was directly compared to that predicted by the same DEM code for shaker and planetary mills. Results and their implications for design of larger scale production facilities for preparation of reactive nanocomposite materials will be discussed.