Kinetics of phase transformation and optical property of pink coral zirconia powders

Abstract

The kinetics of phase transformation and optical property of pink coral zircon powders have been studied. The ZrO2–SiO2–Fe2O3 precursor powders were synthesized using Zr(NO3)4⋅4H2O, Si(C2H5O)4 and Fe(NO3)3⋅9H2O as initial materials via the hot–wet routes. The kinetics of phase transformation of the ZrO2–SiO2–Fe2O3 precursor powders was characterized by thermo-gravimetric (TG)/differential scanning calorimeter (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM), nano-beam electron diffraction (NBED), and spectrophotometry. The crystallization temperatures of tetragonal zirconia (t-ZrO2) and zircon (ZrSiO4) of ZrO2–SiO2 precursor powders with 1mol% Fe2O3 were estimated to be approximately 1204K and 1496K, respectively, based on a DSC analysis conducted at a heating rate of 20K/min. The activation energies of t-ZrO2 formulation are 428.2, 403.2, and 399.9kJ/mol, respectively, for ZrO2–SiO2 precursor powders containing 1, 3, and 5mol% Fe2O3, respectively, whereas the activation energies of the Fe/ZrSiO4 formulation are 271.9, 261.9, and 257.7kJ/mol, respectively. The parameter of growth morphology (n) and index of crystallization (m) were approximated as 2.0 and 1.0, respectively, meaning that two-dimensional growth with plate-like morphology was the primary mechanism of ZrO2 crystallization from ZrO2–SiO2–Fe2O3 precursor powders. The XRD results show that when the precursor powders of ZrO2–SiO2–1mol% Fe2O3 and ZrO2–SiO2–5mol% Fe2O3 after calcination at 1323–1473K for 1h, the ZrO2 phase of the product powders was fully converted to zircon (ZrSiO4). On the other hand, no reflection peak of Fe2O3 appeared in the XRD patterns for the ZrO2–SiO2–Fe2O3 precursor powders after calcination at 1223–1473K for 1h. The dominant wavelength of the zircon increased from 591.4nm to 630.1nm when the precursor powders after calcination at 1473K for 1h.