Reactivity and microstructural evolution in the V-ZrSiO4 pigmenting system prepared from colloidal gels

In this paper is intended to examine the microstructural changes associated to the sequence of reaction in the formation of the zircon-vanadium blue pigment, prepared from mixtures of previosly obtained ZrO2 and V2O5 colloidal sols and tetraethylorthosilicate (TEOS). The reaction sequence followed by X-Ray diffraction (XRD), revealed the formation of a crystalline phase with the structure of tetragonal zirconia at the first step. The tetragonal to monoclinic phase transformation took place before the formation of the V+4-ZrSiO4, solid solution. The microstructures were observed by field emision scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDX). The formation of aggregates of tetragonal ZrO2 particles which were dispersed in an amorphous matrix of silica was firstly observed. The mechanism of zircon formation involved the reaction of amorphous silica with the zirconia particles previously transformed to the monoclinic form. The developed final microstructure of zircon phases consisted of well formed spherical aggegates up to 3 mu m in diameter.