Synthesis of Tungsten Oxide Nanoparticles using a Hydrothermal Method at   Ambient Pressure
  Tungstite (WO3.H2O) nanoparticles were synthesized using a simple and inexpensive low temperature and low pressure hydrothermal method by adding hydrochloric acid to diluted sodium tungstate solutions (Na2WO4.2H2O) at temperatures below 5oC. A heat treatment at temperatures at or above 300oC resulted in a phase transformation to monoclinic WO3, while preserving the nanoparticles morphology. The products were characterized using powder x-ray diffraction, transmission electron microscopy (including electron energy-loss spectroscopy and electron diffraction) and x-ray photoelectron spectroscopy. 
Majid Ahmadi, Reza Younesi and Maxime J-F Guinel
cond-mat.mtrl-sci