Cryomilling and Characterization of Metal/ceramic Powders

Al/Fe2O3 thermite powders were prepared by cryomilling at liquid nitrogen temperature. The cryogenic temperature will restrain the mechanochemical reaction between alumina and iron oxide, leading to high reactivitive nanoscale powders. The size distribution of the powders was analyzed using laser particle size analyzer, and cryomilling was proved to be an effective method to prepare ultrafine powders. The differential scanning calorimetry (DSC) analysis indicated that the cryomilled powders get more fully-reacted, a larger proportion of solid-solid reaction and more heat release in the solid-liquid reaction, comparing with the powders milled at room temperaure. Furthermore, the reaction kinetics of Al-Fe2O3 system is analyzed by a model-free Starink method. The activation energy for solid-solid reaction of 2Al-Fe2O3 thermite mixture cryomilled for 40 min is determined as 250 kJ/mol. The alternating gradient magnetometer (AGM) analysis shows that long time milling evoked the thermit reaction between Al and Fe2O3, leading to the increase in saturation magnetization (M-s) and remanent magnetization (M-r).