What is behind ‘tungsten blue oxides’?

Abstract

According to the proposed quantitative chemical and X-ray analyses, the composition of the ‘tungsten blue oxides’ (TBO) investigated varies over a very broad spectrum, depending on the temperature, atmosphere, and speed and also on the actual manufacturing process of the ammonium paratungstate tetrahydrate (APT·4H 2O) reduction. In addition to crystalline compounds {hexagonal tunsten bronze (HTB), WO 3, W 20O 58, and W 18O 49} the industrially produced TBO contains 30–55% of X-ray-amorphous fraction. APT·4H 2O changes in a stream of dry hydrogen at 130°C into the phase APT·∼2H 2O, observed for the first time. The intermediate X-ray-amorphous phases ranging from 250 to 350°C are the starting pool not only for HTB but also for the crystalline tungsten oxides. The HTB-containing TBO powders display a considerable potassium incorporation via the cation exchange of H + being replaced by K +. The solid-state high-resolution 1H NMR investigation of TBO allows a distinction to be made between different proton-containing species.