MECHANICAL ALLOYING PROCESSES AND REACTIVE MILLING

The great flexibility of mechanically driven processes in designing functional materials has stimulated wide attention in the different side branches and research fields. Our current interest concerns both the inherent chemical properties of amorphous metal powders-in view of a possible exploitation in heterogeneous catalysis-as well as their chemical behaviors under reactive milling. Chemical effects were found to be responsible for changing the course of Mechanical Alloying processes (MA). Furthermore, deep structural characterizations of the powders under milling have revealed the subtle and sometimes unavoidable influence of gaseous contaminants from the reaction environment. These results were obtained from the use of complementary diffraction techniques and from the neutron diffraction analysis in particular. It is only natural to refer to these chemical aspects in terms of reactive milling and Mechanochemistry. Within this framework we focused on the active role of hydrogen, as a gaseous reagent or released in activated form from metal hydride lattices, to steer the end-products of MA and Mechanical Milling (MM) processes. On this basis, the possibility to run gaseous hydrogenation reactions under milling was also proven. For a better understanding of the underlying mechanism, MA and Mechanochemistry both require the proper definition of the main milling parameters. To this extent, an experimental method is briefly outlined for the direct evaluation of the collision frequency and energetical factors in ball milling processes.