Microstructural Evolution from Praseodymium‐Containing Zircon Gels to Prx‐ZrSiO4 Solid Solutions

Abstract

Structural evolution and coupled microstructural transformations occurred on annealing mineralizer‐free Pr‐containing ZrSiO4 gels up to final praseodymium‐doped zircon yellow pigments are reported. Gels with nominal compositions Prx‐ZrSiO4, 0 ≤ x ≤ 0.125, were prepared from mixtures of zirconium and silicon alkoxides and praseodymium acetylacetonate. Crystallization pathway and microstructural changes of thermally treated dried gels were followed by infrared spectroscopy, X‐ray diffraction, field emission scanning and transmission electron microscopies, respectively.Results indicated that the crystallization pathway through the whole process of final Prx‐ZrSiO4 solid solutions formation displayed three well‐defined steps. The crystallization of tetragonal Pr‐containing ZrO2 nanocrystals occurred first, followed by their phase transformation to the monoclinic form. The last step was the reaction between the monoclinic Pr‐zirconia and the amorphous silica and its kinetics was dependent on the amount of the nominal praseodymium content.The microstructure before the Pr‐zircon formation consisted of an arrangement of tetragonal‐ or monoclinic Pr‐containing ZrO2 particles coated by an amorphous silica layer, with sizes lower than 100 nm and between 200 and 400 nm, respectively. The final Prx‐ZrSiO4 solid solution products were particles sized in the range between 200 nm and 1 μm. Microstructural changes revealed that the whole formation process to final Prx‐ZrSiO4 non‐aggregated particles was led by the synthetic procedure used for the preparation of gel precursors.