Manipulation Of Lewis Acid-Base Complexation In The Zr-Centered Quaternary System For Monodisperse Spherical Zircons

Zircon (ZrSiO4) is a distinctive material widely investigated and applied for its superb physicochemical advantages. To date, great challenges remain in the synthesis of high-quality zircon powders for their stringent crystallization requirements at elevated temperature and inherent preferential growth along the [200] direction. Herein we, for the first time, present monodisperse spherical zircon (MSZ) powders synthesized via a facile onestep hydrothermolysis at 200 degrees C by rationally manipulating the Lewis acid-base complexation of zirconium with competitive ions (Lewis basic R ligands) in a Zr-OH-R-F quaternary system. Systematical investigations were revealed encircling the complexation of Zr4+ with the R ligands from various sources, which involve the adjusting acids (HR), Zr/Si reactants and halogen-containing mineralizers. Sufficient acidity from the adjusting acid and weak enough Zr-R affinity are confirmed as two paramount factors modulating the crystallization and growth of high-quality MSZ crystals, which undergo a unique metamorphic morphological transition from monolayered, to multilayered, to donut-shaped and ultimately to micrometer-sized spherical particles. The hydrothermal zircons are first confirmed as Zr-deficient (Zr/Si ratios <1.0) zirconium silicates as (ZrO4)(1-x)Si [(OH)(1-y)center dot R-y](4x), rather than the Si-deficient Zr(SiO4)(1-x)[(OH)center dot R](4x) as initially proposed and hitherto generally accepted. The MSZ powders exhibit fair thermal stability and terrific monodispersity even after calcination at 1100 degrees C, superior photoreflectance and much lower thermal conductivity (0.18-0.48 W m(-1) K-1) over non spherical zircons. The novel MSZ powders provide arresting prospects to extend the applications of zircon in many traditional and emerging fields.