Violet tungsten oxide powder may be applied for the production of thermal insulation masterbatch. Such masterbatch may be applied to producing thermal insulating film with the characteristics of high transparency, high heat insulation and excellent weather resistance so that it can be used in the heat insulation fields of construction and automotive.
The preparation of violet tungsten oxide is generally using ammonium paratungstate (APT) as raw material, and is reduced in an industrial rotary tube furnace under certain conditions, such as, the atmosphere of NH3, calcination, due to the decomposition of H2 by NH3, APT in a mild reducing atmosphere is calcined, stepwise decomposition, reduction to produce violet tungsten oxide. The general chemical reaction equation is as follows:
3[5(NH4)2O?12WO3?5H2O]=2W18O49+40H2O+35H2+15N22.2
Since the preparation process requires the introduction of NH3, it is necessary to know the effect of the amount of NH3 on the preparation of violet tungsten oxide. NH3 can decompose N2 and H2 at high temperature. The production of H2 causes APT to be calcined under mild reducing atmosphere, and gradually decomposes to form W18O49. Therefore, in order to ensure a reducing atmosphere in the furnace, a certain amount of NH3 must be supplied.
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