Nano Tungsten Trioxide Preparation by Sol-Gel Method

Nano tungsten trioxide powder is an important industrial raw material, which can be used to prepare nano-tungsten powder and nano-tungsten carbide powder. In addition, nano WO₃ has a strong ability to absorb electromagnetic waves. It can be used as a good absorbent material in the utilization of solar energy and an important invisible material in the military.

At present, the common methods of preparing WO₃ include solid phase method, sol-gel method, chemical precipitation method, microemulsion method and hydrothermal synthesis method. Among them, the sol-gel process has the advantages of simple process, little environmental pollution, little corrosion to equipment, and relatively low production cost. The main preparation processes include:

(1) Preparation of raw materials:
Ammonia water (14mol/L) and deionized water are mixed to form the required ammonia water solution at a ratio of 1:1.

(2) Preparation of sol:
Tungstic acid 4.9972g (0.02mol) was dissolved in 72 ml ammonia aqueous solution. Citric acid (16.832g), whose molar ratio of tungstic acid was 4:1, was added to the dissolved tungstic acid solution. A transparent yellowish sol was obtained by stirring in a magnetic heated agitator at 85 ℃ for 8-12 hours in a water bath.

(3) Gel drying process:
The prepared gel was dried in the infrared oven and the brown expanded gel was obtained.

(4) Tungsten trioxide powder was obtained by calcination.
The Yellow nanometer tungsten trioxide powder was obtained from the gel in corundum crucible and fired at a temperature of 650 degrees in a box type oven for about two hours. The obtained nanoparticles are spherical, with a particle size ranging from 40 to 60 nm and uniform distribution.

Firstly, ammonia water (NH₃·H₂O) reacts with tungstic acid (H2WO4) to form (NH₄)₂WO₄, then citric acid is added to ionize H+, reacting with (NH₄)₂WO₄ to form H₂WO₄ slowly. At the same time, citric acid and ionized NH₄⁺, forming a macromolecule framework, separating tungstic acid molecules, and finally burning to form WO₃ with nanometer size. The whole process has no stringent requirements on PH value, ion concentration, simple and easy to control, non-toxic gases and non-corrosive substances, no pollution to the environment, no harm to equipment.

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