Development of tungsten oxide hydrate phases during precipitation, room temperature ripening and hydrothermal treatment

Morphology and structure transformation of tungstic acid hydrate, H(2)WO(4)(.)nH(2)O precipitates, have been studied in aqueous phase with various levels of residual [Na+ ]s at room temperature and at 120 degreesC in autoclave. Spindle-shaped morphology is characteristic for the washing product of the freshly prepared precipitates. Residual sodium is a persistent contaminant in (H2WO4H2O)-H-.. Sodium ion content in the solid phase has been found to control reaction route at hydrothermal treatment of tungstic acid hydrates. Morphological changes against [Na (+)]s content at 120 degreesC are significant. Rectangular crystallites of WO3 H2O, hexagonal platelets of WO(3)(.)1/3H(2)O or their mixture can develop from the precursor spindle-shaped (H2WO4H2O)-H-. particles with various [Na+](s) at 120degreesC. It is noteworthy that particles that ripened at room temperature display faces and axes seemingly corresponding to those of the crystallites developed in the hydrothermal process. (C) 2002 Elsevier Science B.V. All rights reserved.