Solid State Synthesis of Willemite, Zn2SiO4: Role of Precursors

Abstract

Three precursors of equivalent oxide composition 2ZnO.SiO2, namely, (i) a colloidal gel prepared from zinc nitrate tetra+hexahydrate (partially crystallized) and a colloidal silica sol, (ii) a colloidal gel (amorphous) prepared from zinc chloride n-hydrate and the same colloidal silica sol, and (iii) a mechanical mixture of quartz and ZnO, have been used for examining their relative reactivities in the formation of willemite, Zn2SiO4. The samples were heat-treated at temperatures in the range 1000°C–1400°C and for soaking periods of less than 1 hr to 80 hours. X-ray analyses showed the nitrate-derived gel to be the most reactive, followed by the chloride-derived gel; the crystalline oxide mixture showed sluggish reaction. Attempts have been made to explain this difference in reactivity in terms of the thermal behaviour of the precursors below 1000°C.