PREPARATION AND PROPERTIES OF NONCRYSTALLINE ALKALI-METAL METATUNGSTATE HYDRATES

Three kinds of non-crystalline alkali metal metatungstate hydrates, M6H2W12Ot0, R H2O (M = Li+, Na+, K+), with different water contents were synthesized by an ion-exchange method, in which a H+-type ion-exchange resin was used, and a rapid dehydration method. The water content of synthesized products was controlled with freeze drying. Those products were characterized with X-ray diffraction, IR spectroscopy, and thermal analysis, and the electrical conductivity and the transport number were measured. Although X-ray diffraction showed that those were all non-crystalline, the existence of metatungstate anions with Keggin structure was confirmed by IR spectra. The electrical conductivity of the products depended on both the water content and the kind of alkali cation species. Their electrical conductivity was ca. 102 times larger than that of crystalline ones. The measurement of transport number indicated that the charge carrier was only protons. Thermal analysis showed that those products had no well-defined dehydration temperature in contrast to the crystalline alkali metal metatungstates. From these results, we concluded that non-crystalline alkali metal metatungstates had less restrained water molecules compared to crystalline ones, and were, therefore, good proton conductors. © 1990, The Chemical Society of Japan. All rights reserved.