Abstract
Hexagonal ammonium tungsten bronze (ATB, (NH4)xWO3) and tungsten trioxide obtained by the thermal decomposition from monoclinic ammonium paratungstate (APT) and tungstic acid were reduced in dry hydrogen. Monoclinic WO2.90, tetragonal WO2.90, monoclinic WO2, and cubic β-W (i.e. W3O) for intermediate were produced. The decomposition of β-W was investigated by DTA in argon atmosphere. The reduction process are as follows.
WO3(1)monoclinic WO2.90(2)monoclinic WO2(3)cubic W (α-W)
(4)(NH4)xWO3(5)tetragonal WO2.90(6)(7)cubic W3O (β-W) (8)
Reduction path of the WO3 that accompanied by heat evolution while thermal decomposition of APT is (1)(2)(3). Reduction of ATB of endothermic compound proceeds as (5)(6) and β-W form. The WO3 from tungstic acid of endothermic compound is reduced path as (4)(5) and β-W also form. The β-W decompose to WO2 and α-W accompanied with heat evolution with elevation of reduction temperature. It is conceivable that endothermic energy during thermal decomposition go down activation energy to produce tungsten metal.
