Improvement of the Thermal Stability of Zircon by Formation of the Solid Solution of Cr in Zircon

In this paper, the effects of Cr2O3 additive on the thermal stability and zircon decomposition were investigated. The substitution of Cr at zircon lattice and the formation of solid solution were also discussed. Cr2O3 was added at up to 4 wt.% to zircon. The sintering of samples was carried out at the temperatures of 1450–1650°C for 3 h. The phase composition, physical properties, and microstructural changes for the sintered samples were characterized. Results of Rietveld refinement analysis showed that 1 wt.% of chromia retarded the decomposition of zircon (nearly 40%). Further addition of this additive slightly improved the thermal stability of zircon. Also, up to 2 wt.% of chromia additive decreased the porosity of zircon and suppressed the grain growth. However, 4 wt.% of chromia increased the porosity contents. XRD peaks of zircon shifted to higher angles by the addition of 2 wt.% of Cr2O3 and zircon lattice parameters were decreased, attributed to the formation of a solid solution. Energy dispersive spectroscopy analysis detected the presence of Cr at zircon grains. However, 4 wt.% (4.8 at.%) of Cr2O3 resulted in the formation of a secondary phase concluded that this amount of Cr2O3 is beyond the solubility limit of Cr in zircon.