Preparation of YVO4 powder from the Y2O3 + V2O5 + H2O system by a hydrolysed colloid reaction (HCR) technique

Prior to the formation of YVO₄ in the Y₂O₃ + V₂O₅ + H₂O system, two intermediate, partially hydrophobic, complex colloidal mixtures with metastable characteristics can be produced at room temperature and atmospheric pressure. The ball-milled system, having both hydrophobic and hydrophilic species, transforms into the stable yttrium orthovanadate phase due to intensive hydrolysis. At room temperature an orange mixture (possessing dispersed Y₂O₃ and 4Y₂O_3–P(OH)_p^p+·2VO₃^–, Y₂O_3–p(OH)_p^p+·6VO₃^–·xH₂O-like heteroaggregations) formed by 20 h mixing at pH ca. 4.0 transforms slowly, another red-brown heavily flocculated colloidal mixture (with dispersed Y₂O₃ and Y₂O_3–p(OH)_p^p+·V₁₀O₂₈^6–·yH₂O-like aggregation) formed by 70 h mixing at pH ca. 4.5 transforms rapidly into YVO₄ in water. During additional mixing of highly diluted red-brown mixtures this transformation can be completed at room temperature. At elevated temperatures (50–95 °C) the orange mixture precipitates into a red-brown decavanadate-type precipitatium which subsequently can also rapidly hydrolyse into an orthovanadate phase in the diluted aqueous systems. Both vanadium excess meta-and decavanadate-type aggregations exhibit amorphous character by X-ray diffraction.The semi-hydrophobic colloidal structure can modify the dissociation mechanism, which prevents the system from returning to the starting oxides, and gives a new HCR technique for YVO₄ preparation with a simple hydrolysis process at low temperatures and atmospheric pressure.