Epitaxial growth of WO3-x needles on (10(1)over-bar-0) and (01(1)over-bar-0) WC surfaces produced by controlled oxidation with CO2

The controlled oxidation with CO2 of both high surface area (high S-g) and low surface area WC to form WO3-x needles, has been observed in situ, insid e a controlled environment transmission electron microscope (CETEM), and al so ex situ, in a standard flow reactor; the tungsten oxide needles, which c onsist mainly of distorted gamma-WO2.72, propagate in an epitaxial fashion from the (10 (1) over bar 0) and (01 10) surfaces of the parent WC crystals ; possible mechanisms for the formation of the needles are proposed.