The synthesis of micro and nano WO3 powders under the sparks of plasma electrolytic oxidation of Al in a tungstate electrolyte

Plasma electrolytic oxidation (PEO) is commonly known as a coating technique. However, the present study shows that PEO of pure Al in 10 g l(-1) Na2WO4 center dot 2H(2)O leads to the synthesis of micro and nano sized powders of WO3. The as-synthesized WO3 powders have been characterized by SEM, TEM and photocatalytic tests. The plasma discharges during the PEO process have been investigated by real-time imaging and spectrographic method. The energetic features of the single discharge at different stages of PEO have been evaluated. It was suggested that the electrolyte species were directly decomposed into tungsten oxides within the discharge channels and then the oxides re-entered the electrolyte due to the lower melting and boiling points of WO3, and more importantly, its tendency of sublimation.