Investigation of gas-solid reactions realised by ball milling

The gas-solid reaction process was investigated by ball milling of elemental Ti powder under different atmospheres of H 2 , N 2 and NH 3 . The pressure variations of the milling atmosphere show that the hydriding and nitriding reactions occur during ball impacts at room temperature. Mechanical activation of the Ti powder using a pre-milling treatment under vacuum, upon subsequent exposure to gas, leads to a slight absorption of gas, but cannot promote gas-solid reactions. Gas-solid reactions can only be realised by ball impacts. This type of room temperature reaction process limits the grain growth of new phases and results in a nanocrystalline structure.