HIGH-ENERGY MILLING OF WO3 OXIDES - AMORPHIZATION AND REACTION WITH CS2CO3

Three WO3 oxides with ReO3-, pyrochlore-, and hexagonal-type structure s have been studied in nonreactive and reactive grinding conditions by high-energy ball milling. In nonreactive grinding conditions, pyrochl ore- and hexagonal-type WO3 oxides amorphize by collapse of the oxide structure. Monoclinic WO3 cannot be amorphized in these experimental c onditions: the effect of high-energy ball milling is to decrease the c rystallite size to a limit value. In reactive grinding conditions WO3 + Cs2CO3 mixtures lead to the formation of a lacunar cubic pyrochlore- type cesium tungstate. The reaction kinetics are strongly influenced b y the WO3 oxide structure and its behavior in nonreactive grinding. Th e mechanochemical reactivity is higher for monoclinic WO3 and seems to depend on the presence of intercrystallite boundaries rather than on the amorphous oxide phase. (C) 1994 Academic Press, Inc.