Impact energy and reactive milling - A self propagating reaction

Analytical expressions and a semiempirical model were used to describe the reciprocating motion of a vibro-mill and the tridimensional vial course of a shaker mill. The results were substantiated experimentally. A piezoelectric transducer and a magnetic position sensor were concurrently employed to determine the impact frequency, to locate the impact time along the vial cycle and to find the vial velocity at impact. The impact energy intensity was found to be in good agreement with the calculated parameter, modelling and experimental approaches supporting each other satisfactorily. Data were employed to follow the mechanochemical dehalogenation process between hexachlorobenzene and calcium hydride. Beyond an impact energy threshold, self-propagating transformations were observed leading to an instantaneous degradation of the organocompound. Changes in the reaction yield suggest that different mechanisms become operative depending on the reactant composition. Milling runs performed at different impact energy regimes demonstrate that self-sustaining phenomena occur when a definite energy dose has been supplied to the reacting system, irrespective to the energy intensity of the impact.