Tungsten Oxide Crystalline Form Affects Tungsten Carbide Property

Under certain conditions the six-phase tungsten oxide（h-WO₃）can exist in stable form. When annealing temperature exceeds 400℃, it can turns into monoclinic system（γ-WO₃）. Nano tungsten oxide applied in electric and optical field is different from tungsten oxide bulk. The main differences are phase transition temperature drops evidently, so sometimes orthorhombic tungsten oxide（β-WO₃）appears and is stable under room temperature.

Chemical stoichiometric number of tungsten oxide seems simple, its phase transition and structure change is complex. The ideal tungsten oxide is octahedron, W⁶⁺  exists in the center part of it. O₂ as anion distribute in the other eight edges. Actually, W⁶⁺  often deviates from the center part, the whole structure turns into tetragonal crystal（α-WO₃）, temperature range is T>740℃. For orthorhombic system, 740℃>T>330℃; monoclinic system: 330℃>T>17℃ and triclinic system: 17℃>T>-43℃.

Below are SEM graphs of tungsten oxide, testing equipments are: ICP-AES Spectrograph, X-ray Powder Diffractometer, TSM-6360 LV scanning electron microscope, MICROPLUS laser diffraction particle size analyzer.

In a word, tungsten oxide has various crystalline forms, its transition can affect its property, tungsten oxide crystalline form can largely affects tungsten carbide property. Due to this factor, tungsten oxide can be applied in many fields because of its multi-properties.