Lowering crystallization temperature of zircon by nanoheterogeneous sol-gel processing

The use of deliberate heterogeneity on the nanometre scale via the sol-gel technique was introduced by this laboratory in 1982. In this study the thermal behaviour of different zircon (ZrSiO₄)-composition precursors obtained via a sol-gel route and seeded with sols of zircon, rutile or thorite (α-ThSiO₄) have been studied. Both compositional diphasicity and isostructural seeding were found to lower the zircon crystallization or formation temperature. As anticipated from the "nucleation and epitaxial growth" mechanism model, rutile seed crystals, with a structure different from that of the equilibrium phase did not show any effect. An unexpected counter-effect was observed when the isostructural thorite seeds were used. These results suggest that crystallization temperatures in zircon can be lowered either by utilizing the heat of reaction in compositionally diphasic gels, or by nucleation and epitaxial growth in structurally diphasic gels.[/p]