Synthesis of hydrogen tungsten bronzes H xWO 3 by reactive mechanical milling of hexagonal WO 3

Abstract

Recently, we have reported the formation of hydrogen tungsten bronzes by reactive mechanical milling monoclinic tungsten (VI) oxide under hydrogen atmosphere. In this work we report the milling of hexagonal WO 3 under H 2 atmosphere. Our main results are the structural transformation of the hexagonal oxide to the high temperature polymorph of WO 3 with orthorhombic structure, and the formation of different hydrogen tungsten bronzes at distinct milling times. The bronzes seem to be formed from the orthorhombic oxide, and compared with the bronzes obtained by milling monoclinic WO 3 are rather unstable after short exposure to air. The materials are characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and total hydrogen content determination.