Multitechnique approach to V–ZrSiO4 pigment characterization and synthesis optimization

The synthesis of blue-turquoise V–ZrSiO4 pigment from an aqueous solution of Na2O·2.5SiO2·5H2O (soluble glass) and the citrate complexes of zirconium and vanadium was investigated as a function of V2O5 contents, mineralizers (NaF and/or LiNO3) addition and thermal cycle. Blue V–ZrSiO4 was obtained without mineralizers addition for the (ZrO2)(SiO2)(V2O5)0.09 composition; QPA analysis shows that a thermal cycle 3 h long, Tmax = 800 °C, can lead to a 78.0 wt.% of ZrSiO4. The addition of mineralizers gave rise to 73.0 wt.% of ZrSiO4 for the (ZrO2)(SiO2)(NaF)0.16(V2O5)0.09(LiNO3)0.09 composition and a thermal cycle 2 h long, Tmax = 800 °C. LiNO3 can favour both ZrSiO4 formation and a fairly blue colour, up to LiNO3 = 0.09 moles; NaF seems effective on ZrSiO4 formation only when mixed with LiNO3 through the formation of LiF. HT-XRD analysis of this composition agrees with QPA results at the corresponding temperature; ZrSiO4 was present (64.0 wt.%) at 730 °C and good colour parameters were obtained.