On the preparation of nanosized A1_2(WO_4)_3 by a precipitation method

摘要

Nanosized aluminum tungstate, A1_2(WO_4)_3, is prepared by a precipitation reaction between Na_2WO_4 and A1_2(WO_4)_3. The structure of the precipitated composition is determined by powder XRD analysis, IR and ~(27)Al MAS NMR spectroscopy. The thermal properties are examined by DSC, DTA and TG analyses combined with gas evolved analysis. Particle sizes and morphology are examined by TEM analysis. Precipitation reaction leads to the formation of an amorphous composition, which consists of dimer and trimer aluminum hydroxide species and WO_4~(2-) groups. Finely dispersed particles with dimensions of about 25 nm are formed. The precipitated composition is decomposed to amorphous A1_2(WO_4)_3 immediately after H_2O release. At 630 °C, amorphous Al_2(WO_4)_3 crystallizes in an orthorhombic modification of A1_2(WO_4)_3, the enthalpy of crystallization being 58 kJ/mol. The nanosized particles remain intact after the crystallization of amorphous A1_2(WO_4)_3. A significant particle growth take places when nanosized A1_2(WO_4)_3 is heated from 600 to 800 °C.