Interlayer water molecules of vandium pentaoxide hydrate. Part 1.—Phase equilibrium with water vapour at a relative pressure higher than 0.005

Abstract

The reversibility of the sorption of H₂O molecules into vandium pentaoxide hydrate (V₂O₅·nH₂O) has been examined. The phases 1 and 2, having interlayer distances c= 0.89 and 1.12 nm, respectively, which appeared when the as-grown sample was heated up to 200 °C, were reproducibly hydrated to phase 3 (c= 1.47 nm) under saturated H₂O vapour at 25 ° C. Phase 2 was reversible converted to phase 3 over a relative H₂O vapour pressure of 0.5 by sorption of H₂O molecules. The determination of the isoteric heat of sorption suggested the presence of at least two composite phases i the ‘phase 3’, as determined by X.r.d., with similar interlayer distances, but differeing in H₂O content (n= 1.5–2.7 and > 2.7).